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1. 25 4 20 4 Intensity a u I i Wait dy Lu ji 5 l li 200 300 400 500 600 700 800 900 Raman shift cm Figure 24 Dampened spectra compared to a spectrum previously collected at 3 C The signal apparently decreases when the temperature of the SERS substrate is increased which can be seen in figure 25 At 25 C the ambient temperature the signal seemed to have disappeared implying that the SERS substrate is fully regenerated 30 UMEA UNIVERSITY 2014 06 12 Department of Physics Increasing the temperature of the SERS substrate after cooling 5 Isoflurane 35F T T T T I I T 3 10 degrees centigrade 3 degrees centigrade 30 25 degrees centigrade H d 50 degrees centigrade 25 4 20 J Intensity a u a a T uit H ZA Al Luni 5 200 300 400 500 600 700 800 900 Raman shift cm Figure 25 Regeneration of the SERS surface The intensities are adjusted to enhance visualization Kinetics Time mapping The time mapping shows that it is possible to monitor the kinetics of the substance binding to or being released from the substrate The result of the mapping can be seen in figure 26 The signal was calculated as the area of the 365 cm peak The signal increases rapidly rising im
2. Arduino 2014 Online Available http arduino cc en Main arduinoBoardUno Accessed 06 03 2014 Pololu Robotics amp Electronics Online Available http www pololu com picture view 0J116 Accessed 24 04 2014 Pololu Electronics amp Robotics 2005 Online Available http www pololu com file 0J59 smc05a_guide pdf Accessed 06 03 2014 B Beauregard Arduino Playground PID Library 2014 Online Available http playground arduino cc Code PIDLibrary Accessed 06 03 2014 Drugs com 11 2013 Online Available http www drugs com pro isoflurane html Accessed 11 04 2014 Benrr101 Wikipedia The Free Encyclopedia 25 09 2010 Online Available http upload wikimedia org wikipedia commons a a6 Isoflurane svg Accessed 19 05 2014 R S Golightly W E Doering and M J Natan Surface Enhanced Raman Spectroscopy and Homeland Security A Perfect Match ACS Nano p 2859 2009 TE Technology Inc 2010 Online Available http www tetech com FAQ Technical Information html 9 Accessed 07 03 2014 National Instruments 2014 Online Available 36 UMEA UNIVERSITY 2014 06 12 Department of Physics http sine ni com nips cds view p lang sv nid 201986 Accessed 06 03 2014 44 Elfa Distrelec 2014 Online Available https www elfa se elfa3 se_sv elfa init do item 10 389 19 amp toc 0 amp q arduino uno Accessed 06 03 2014 45 National Instruments 2014
3. M Barr Barr group 07 11 2007 Online Available http www barrgroup com Embedded Systems How To PWM Pulse Width Modulation Accessed 06 03 2014 Princeton University Online Available https www princeton edu achaney tmve wiki100k docs Pulse width_modulation html Accessed 06 03 2014 Tellurex 2011 Online Available http www tellurex com technology peltier faq php Accessed 06 03 2014 M J Nagy and S J Roman The effect of pulse width modulation PWM on the reliability of thermoelectric modules in Thermoelectrics 1999 Eighteenth International Conference on Baltimore MD USA 1999 Control Tutorials for Matlab and Simulink Online Available http ctms engin umich edu CTMS index php example Introduction amp section ControlPID Accessed 24 04 2014 OMEGA Engineering Inc Online Available http www omega com temperature Z pdf z115 117 pdf Accessed 24 04 2014 Wikipedia 28 02 2014 Online Available http en wikipedia org wiki Ziegler E2 80 93Nichols_method Accessed 06 03 2014 D M J Willis Proportional Integral Derivative Control 1999 Wikipedia 03 03 2014 Online Available http en wikipedia org wiki PID_control Derivative_term Accessed 06 03 2014 S M Dr Yeffry Handoko Putra UNIKOM Indonesian Computer University Online Available http elib unikom ac id files disk1 389 jbptunikompp gdl yeffryhand 19448 13 bab13 pdf Accessed 24
4. Online Available http sine ni com nips cds view p lang sv nid 201986 Accessed 06 03 2014 46 Conax Buffalo Technologies Online Available http www conaxtechnologies com tech newpdf WireSize pdf Accessed 24 04 2014 37 UMEA UNIVERSITY Department of Physics 7 Appendix Appendix A Source Code 2014 06 12 PROGRAMKOD FOR TEMPERATURKONTROLL AV MATCELL Arduino Uno med Pololu SMCO5a Low Voltage Dual Serial Motor Controller och PID kontroll Sp nningsregulator LM1084 3 3V N tadapter 5V 3A Peltierkylare TE Technology VT 31 1 0 1 3 och termistor Omega 44004 F ljande PID bibliotek implementeras i koden Arduino PID Library PID_v1 Beauregard 2014 Brett Beauregard lt br3ttb gmail com gt Obs Funktionerna for styrning av och kommunikation med SMCO5A kortet r inspirerade av f ljande lank http www psurobotics org wiki index php title Pololu_Dual_Serial_Motor_Controller SMCO5A Pololu Dual Serial Motor Controller Jeremy Bridon lt jbridon psu edu gt Anthony Cascone lt acascone psu edu gt MPORTERA BIBLIOTEK Htinclude lt SoftwareSerial h gt Mjukvaruseriekomm bibliotek include lt PID_v1 h gt PID kontrollbibliotek include lt math h gt Matematikbibliotek SKAPA DEFINIERA KONSTANTER OCH VARIABLER define rxPin 6 Definierar Recieve ing ngen for mjukvaruserieport f r drivkretsen define txPin 7 Definierar Transmit
5. so called Kelvin measurements 9 Thermistors Another kind of resistance thermometer is the thermistor A thermistor is basically a resistor whose resistance varies with temperature and usually consists of metal oxides As opposed to platinum resistance thermometers a thermistor s resistance usually decreases with increasing temperature 3 UMEA UNIVERSITY 2014 06 12 Department of Physics This is called negative temperature coefficient NTC Note though that there are also PTC thermistors 5 p 56 The resistance of the thermistor is often several orders of magnitude larger than that of copper lead wires and therefore the thermistor does normally not require three or four terminal measurement as the platinum RTDs do if high accuracy is required As with the RTDs thermistors measure absolute temperature However they generally have a more narrow working range compared to RTD or thermocouple sensors 10 Most thermistors have a maximum working temperature range of 55 to 114 C or thereabout and work best in within approximately 50 C of the ambient temperature however there are thermistors capable of handling slightly larger temperature ranges 11 The temperature is for NTC thermistors calculated approximately from the resistance of the thermistor through the Steinhart Hart equation equation 2 below 5 p 57 lee 3 Tw a bInR c In R 2 T K is the temperature in Kelvin R is the resistance of the thermistor and
6. unsigned char buffer 4 Start byte och ID byte buffer 0 0x80 Startbyte buffer 1 0x00 Drivkrets ID unsigned char index 0 Peltierindex vilka utg ngar pa drivkortet ska anv ndas if peltierIndex gt 0 peltierIndex lt 0 index 2 Lagg till riktning och skapa byte 3 i protokollet if GoCool buffer 2 0x00 index Bitwise OR else buffer 2 0x01 index Bitwise OR Energifl de till Peltierelement unsigned char targetpower 0 if power gt 128 targetpower 127 else if power lt 0 targetpower 0 else targetpower unsigned char power buffer 3 targetpower Skicka paketet till drivkrets Kommunicera buffer 4 Skriv till drivkretsen via den virtuella serieporten void Kommunicera unsigned char buffer int bufferCount for int i 0 i lt bufferCount i drivkretsSerial write byte buffer i Appendix B Introductory SERS Experiment using BPE Experimental As an introduction to SERS measurements a test was made to measure the response from BPE trans 1 2 Pyridyl 2 4 pyridyl ethylene on a Klarite substrate at different concentrations 200 nM 500 nM 1 uM 5 uM 10 uM 100 uM 500 uM and 1mM The Raman instrument setup was a Horiba Jobin Yvon LabRam 800 HR confocal Raman microscope with LabSpec 5 software equipped with an Andor Newton back illuminated EMC CDD and a 785 nm Sacher Lasertechnik Tiger diode laser A 5x lens was used in backscatter geometry
7. 04 2014 S Jiang Surface Enhanced Raman Scattering Spectroscopy Term Paper for Physics 598 OS p 3 2007 R F Aroca Plasmon enhanced spectroscopy Phys Chem Chem Phys Vol 15 p 5355 2013 M Fleischmann P Hendra and A McQuillan Raman Spectra of Pyridine Adsorbed ona Silver Electrode Chem Phys Lett 163 6 1974 35 UMEA UNIVERSITY 2014 06 12 Department of Physics 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 K Kneipp Y Wang H Kneipp L Perelman I Itzkan R Dasari and e al Single molecule detection using surface enhanced Raman scattering SERS Phys Rev Lett vol 78 1997 R P Van Duyne B Sharma R R Frontiera A l Henry and E Ringe SERS Materials applications and the future Materials Today No 1 2 pp 16 25 2012 W Grant and G Dent Modern Raman Spectroscopy 2005 G McNay D Eustace and W E Smith Surface Enhanced Raman Scattering SERS and Surface Enhanced Resonance Raman Scattering SERRS A Review of Applications Applied Spectroscopy Vol 65 No 8 pp 826 830 2011 R Aroca Surface Enhanced Vibrational Spectroscopy 2007 Linkam Scientific Instruments 2010 Online Available http www linkam co uk ts1500 gallery Accessed 11 03 2014 Engineering Toolbox Online Available http www engineeringtoolbox com thermal conductivity d_429 html Accessed 12 03 2014
8. 1 5 K 0 5 for cooling i e ambient temperature and below and K 1 K 0 3 for heating i e above ambient worked in this case The set point can be changed by the user when the program is running This is done by sending the desired target temperature e g 45 or 5 50 for 45 C or 5 50 C respectively on the Arduino hardware serial port by using for example the Arduino IDE s built in serial monitor The program senses when a message is sent on the serial port and converts the incoming temperature to a 10bit value and stores it in the set point variable of the PID controller The output of the PID controller is by default a 8bit value integer value O 255 to be compatible with the PWM pins of the Arduino board and thus needs to be rescaled to fit the output range of the SMCOBA Le O 127 and the corresponding voltage is applied to the Peltier cooler using the method described under the H bridge Controller header 21 UMEA UNIVERSITY 2014 06 12 Department of Physics Note that the set point should be ramped in an appropriate way e g 5 C or 10 C steps in order not to damage the Peltier cooler or other equipment by thermal shock as the system has rapid response and can cover large temperature differences in short time period 4 1 3 System Overview An overview of the temperature regulation system can be seen in figure 14 16 Figure 15 The regulation system box with fan cooled lid attached 22 UMEA UNIVE
9. In 1997 one was even able to perform single molecule detection by SERS 28 2 7 Surface Enhanced Raman Spectroscopy SERS If the molecules of interest are brought in close contact to a metal nanostructured surface with certain properties a large amplification often million fold of the Raman signal can be achieved The enhancement factor can be as high as 10 10 for certain substrates 29 30 p 113 The enhancement effect is generally attributed to two mechanisms the electromagnetic enhancement and the chemical enhancement The electromagnetic mechanism is considered to be the main contributor to the enhancement factor 31 30 p 116 The electromagnetic enhancement comes from the laser excitation of local surface plasmon resonances LSPRs i e confined collective electron oscillations of the free electron cloud in the nanostructured surface The adsorbed analyte molecules experience an intense electric field which is created by the LSPR 30 pp 117 118 Only oscillations that are perpendicular to the surface contributes to scattering so SERS substrate surfaces are often roughened to provide nanoscale features on the surface as oscillations in flat surfaces occur in the surface plane 30 p 117 Small gaps in the nanostructure where the resulting electromagnetic field is very strong are called hotspots and have been shown sensitive enough to enable single molecule detection 32 p 90 This means that SERS substrates
10. The SMCO5A is meant to control the output of up to two DC motors by 600 Hz PWM in 6bit precision i e 128 steps or O 127 in forward or reverse direction by using an H bridge It can handle a O 7 V operating voltage and be controlled by a 3 5 5 V logic voltage Output currents of up to 5 A can be handled if one of the two outputs are used or 10 A if the outputs are paralleled Note that one has to reconfigure the motor controller to use the parallel mode and in this case the standard mode was used 36 Figure 10 below is showing the SMCO5A controller 15 UMEA UNIVERSITY 2014 06 12 Department of Physics Figure 10 Pololu SMCO5A Low Voltage Dual Serial Motor Controller The SMCO5A board is communicating via serial communication so a software serial port is set up between the Arduino board and the motor controller board to avoid interference between the motor controller s communication with the Arduino board and the Arduino boards communication with the computer on the hardware serial port UART The SMCO5A automatically detects baud rate rates of 1200 19200 baud can be used The SMCOSA uses a protocol in the following format table 2 below 37 Table 2 Pololu SMCO5A command protocol format Byte 1 Byte 2 Byte3 Byte 4 etc Start byte 0x80 Device type 0x00 Data byte 1 Data byte 2 etc When a start byte 128 0x80 in hexadecimal notation is sent on the serial port the serial device devi
11. To control the DC Peltier cooler using the Arduino platform the Peltier cooler module had to be interfaced to the Arduino board The Arduino Uno has 14 digital I O pins Six of the Arduino Uno board s digital pins 6 are marked PWM These can simulate analog DC signals using so called pulse width modulation PWM using the command analogWrite By choosing duty cycle of the PWM from O 100 represented in 8bit precision as an integer value of O 255 the average voltage can be controlled between 0 5 V This would have been a simple and convenient way of controlling the Peltier cooler but the Peltier device however requires more power than the Arduino board is capable of supplying The Arduino Uno board can only deliver currents up to the milliamp region This means that the energy to the cooler must be generated by an external source The Arduino board is then used to control the energy flow from the external power source through the cooler by using an external controller circuit e g a DC motor driver circuit as the same principle can be applied to Peltier coolers 6 0 1023 10bit precision The voltage range is O 3 3 V since 3 3 V is used as analog reference voltage in this setup note that the analog reference must be set to external in the program code using the analogReference EXTERNAL command when an external reference voltage is used or else the Arduino board can get damaged Pin 3 5 6 9 10 and 11 14 UMEA UNIVE
12. University of Cambridge 31 08 2009 Online Available http www msm cam ac uk utc thermocouple pages ThermocouplesOperatingPrinciples ht ml Accessed 06 03 2014 Pico Technology Online Available http www picotech com applications pt100 html Accessed 06 03 2014 WIKA Instruments Online Available http www wika us upload Download TB TE Thermal Response Times en us 26172 pdf Accessed 03 06 2014 Measurement Specialties 07 08 2013 Online Available http precisionsensors meas spec com pdfs rtd pdf Accessed 06 03 2014 Enercorp Instruments Ltd 2008 Online Available http www enercorp com temp Thermistors_comparision html Accessed 06 03 2014 Wavelength Electronics Online Available http www teamwavelength com info thermistors php Accessed 29 04 2014 TEC Microsystems 2013 Online Available http www tec microsystems com EN Intro_Thermoelectric_Coolers_files Thermoelectric 20Coolers 20B asics pdf Accessed 24 04 2014 TE Technology Inc 26 02 2007 Online Available http www tetech com docs tem_ thermoelectric_module mounting procedure pdf Accessed 19 03 2014 34 UMEA UNIVERSITY 2014 06 12 Department of Physics 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Active Cool Ltd 2014 Online Available http www activecool com technotes thermoelectric html Accessed 06 03 2014
13. approximately 0 7 Q 46 11 UMEA UNIVERSITY 2014 06 12 Department of Physics for the application However this was still a compromise because by using a common thermistor the maximum working temperature of the sensor would have to be lower than the desired 200 C The following conclusions could then be made e Thermistor was the most appropriate sensors under the given circumstances e Temperature measurement on both the substrate surface and the surrounding gas in the stage would not be possible simultaneously e Thermistors usually cannot handle 200 C which meant that maximum temperature of the SERS substrate will have to be less than maximum working temperature of the thermistor to avoid damage to the temperature sensor The model 44004 nonlinear thermistor element Omega Engineering Ltd has a working temperature span of 80 to 150 C a tolerance of 0 2 C and reasonably fast response time relatively low cost relative small size and can be used with two terminal connection This made it a suitable sensor for this application under the given circumstances 3 3 Installing Peltier module and Thermistor in the stage The thermoelectric cooling approach was chosen since it is capable of both cooling and heating that Peltier elements can be made small and only require two lead wires for both cooling and heating A suitable Peltier module was the VT 31 1 0 1 3 Peltier Module TE Technology Inc with an operating temperature ra
14. below Note that at 80 C the target temperature was changed before the temperature had stabilized Also note that the system is under damped up to about 60 C and is over damped above that temperature This means that above room temperature and up to about 60 C there is some overshoot and above 60 C there is little or no overshoot This is a compromise between being able to reach high temperatures and keeping the overshot as low as possible 24 UMEA UNIVERSITY 2014 06 12 Department of Physics 110 g f 90 weg 85 80 j 70 es i 60 ke 55 45 Se i q i 25 20 Figure 18 Temperature C vs time s plot from a test run of the heating of the temperature control cell The stability test showed that the temperature is kept within 0 22 C of the set point during the test with a standard deviation of 0 04 which is well within the 0 5 C stability requirement The temperature is not showing any signs of drift from the set point over time Table 5 below shows temperature readings from the thermistor and from a K type thermocouple placed on the surface of the Peltier module just next to the thermistor The temperature readings agree fairly well One has to consider that the K type thermocouple has considerably less accuracy than the 44004 thermistor element which is used in the cell 0 5 of reading 1 C for the thermocouple compared to 0 2 C for the ther
15. gt 120 Output 0 Sluta v rma om temperaturen verstiger 120 grader Detta f r att skydda temperatursensorn och peltierelementet if Setpoint gt 510 SetPeltier 0 128 Output Kylning else SetPeltier O 128 Output Varmning NEDAN F LJER DEFINITIONER AV FUNKTIONER FOR STYRNING AV DRIVKRETS Initiering av drivkretsen void startDrivkrets ngangs Utgangskonfiguration pinMode rxPin INPUT pinMode txPin OUTPUT pinMode resetPin OUTPUT drivkretsSerial begin 9600 P b rja seriekommunikation drivkrets delay 50 Vanta X millisekunder digitalWrite resetPin LOW Stang drivkretsen delay 10 Vanta X millisekunder digitalWrite resetPin HIGH Sla pa drivkretsen delay 100 Vanta X millisekunder for uppstart Funktion for att valja effekt och riktning void SetPeltier int peltierIndex int power Begr nsa till 0 255 if power lt 0 power 0 else if power gt 255 power 255 Konvertera till riktning boolean Cool if power gt 128 Cool true Kyl power 128 Power Power 128 else Cool false Varm 2014 06 12 UMEA UNIVERSITY 2014 06 12 Department of Physics power 127 power Skicka vidare till grundfunktionen av SetPeltier se nedan SetPeltier peltierindex power Cool Grundfunktion SetPeltier void SetPeltier int peltierlndex int power boolean GoCool Skapa paketbuffer
16. melting of the solders in the module Since a Peltier cooler has no moving parts is being capable of both cooling and heating and it can be made small it is suitable for controlling the temperature of the cell 2 4 Pulse Width Modulation PWM PWM is a method of generating a makeshift analog signal by digital means If a device is not capable of generating true analog signals one can simulate an analog signal by using short digital pulses If the pulses are short enough and the frequency is high enough the controlled device will experience the pulses as a continuous signal 15 The percentage of time that the voltage is on is called the duty cycle and determines the energy flow through the device If the duty cycle is 70 i e the voltage is on 70 of the time the device experiences 70 of full energy flow 16 The principle is illustrated in figure 4 below where the duty cycle is varying with time Voltage Pulse Average Time Figure 4 Illustration of pulse width modulation PWM showing the pulses blue with the area below marked in grey and the resulting average voltage red Using PWM with a Peltier cooler keeps power dissipation in the controller to a lower level than it would if a true analog continuous signal was applied 17 PWM will however cause rapid thermal cycling i e rapid thermal contraction and expansion in the Peltier cooler which potentially can cause degradation to the device over
17. must be able to support LSPRs and consist of plasmonic material such as gold Au or silver Ag which are the most commonly used substrate materials since they UMEA UNIVERSITY 2014 06 12 Department of Physics have plasmon frequencies in the visible region of the optical spectrum that is overlapping well with commonly used laser excitation wavelengths for Raman spectroscopy 29 For some applications colloidal metal nanoparticles may be better suited than solid surfaces 31 The chemical enhancement comes from the formation of charge transfer CT complexes which are formed when the analyzed molecules chemisorbs onto the metal surface The CT complexes can lead to change in polarizability of the molecules and thus increasing the Raman cross section 30 p 120 3 Method and Equipment 3 1 Linkam TS1500 Stage The Linkam TS1500 is a microscopy stage intended for controlling the temperature of samples from ambient up to 1 500 C at heating rates up to 200 C min The stage body has connections for water cooling and gas connections to the interior of the cell The stage is equipped with a heating cup with a heating element and a type S thermocouple for temperature sensing There are two contact leads for the heating filament and thermocouple connector leads for the thermocouple There are quartz windows both in the lid and below the heating cup 33 Figure 5 below shows the TS1500 stage with the lid attached Figure 5 TS1500 stage with l
18. of the thermistor by 1 C is usually referred to as the dissipation constant of the thermistor in datasheets If it has a dissipation constant of for example 4 mW C then the dissipated power will heat the thermistor by 2 3 10 mw 0 575 107 C 4mW C Such a small error is often well inside the sensor tolerance and is thus negligible However if the excitation current is larger say 1 mA then the same thermistor will be heated by 0 575 C This means care has to be taken not to feed the thermistor a too large excitation current to keep the measurement as accurate as possible 2 3 Thermoelectric Coolers Peltier modules A device capable of both cooling and heating is the thermoelectric cooler TEC which is also known as Peltier cooler or module The Peltier cooler consists of series of pairs of two different semiconductor materials with different Fermi levels that form p n junctions The p and n semiconductors are placed thermally in parallel and are connected by a conducting material in one end When a voltage is applied to the free ends of the semiconductors heat will be transported from one side of the Peltier module to the other due to the Peltier effect which is closely related to the Seebeck effect The flow of heat due to the Peltier effect Qpe is given by equation 10 12 Qpe IA Mp I 10 Ma and Mg are the Peltier coefficients of material A and B respectively is the current By reversing th
19. stress on the substrate and other equipment is avoided The round bead shape geometry of the Omega 44004 thermistor element is not optimal for the cell By decreasing the temperature sensor size and or using a flat sensor specifically designed for surface temperature measurements one could increase the thermal contact between the temperature sensor and the substrate surface and thereby increase the reliability of the temperature values from the sensor Note however that this does not increase the accuracy of the sensor The ideal would be finding a way to have four wire sensor connection not using the thermocouple connector which is the present case and a platinum RTD with small size and short response time since platinum RTDs have better long term stability and have rather linear response in the temperature range of the application Since the Pt 100 sensors are almost linear in the temperature range for this application one could perhaps replace the thermistor with a Pt 100 sensor and connect it with the thermocouple connector Then one can compensate for the added resistance at one temperature in the software and due to the approximate linearity of the Pt 100 it would probably work well through the temperature range One must bear in mind that the substance to be analyzed can interact with the cooler sensor and or thermal compound which was the case in the acetone test etcetera which affect performance of the temperature control system and
20. therefore one should investigate if this is the case prior to tests Additionally by reducing the volume of the cell interior one could reduce the time it takes for the gas to fill the cell as well as directing the flow over the SERS substrate surface 6 Acknowledgements The author would like to gratefully acknowledge the supervisor Dr Per Ola Andersson and co supervisor Christian Lejon for their support throughout the project The author also wants to acknowledge Per Ake Gradmark for his counsel and help in electronics and soldering and Goran Palmskog for advice and assistance in the isoflurane experiment conducted in this project 33 UMEA UNIVERSITY 2014 06 12 Department of Physics References 1 2 3 4 5 6 7 8 9 10 11 12 13 Linkam Scientific Instruments 2010 Online Available http www linkam co uk ts1500 spec Accessed 07 03 2014 A S P Chang Detection of volatile organic compounds by surface enhanced Raman scattering Online Available http proceedings spiedigitallibrary org Accessed 06 03 2014 R S Golightly W E Doering and M J Natan Surface Enhanced Raman Spectroscopy and Homeland Security A Perfect Match ACS Nano Vol 3 No 10 pp 2859 2864 2009 FOI 2014 Online Available http www foi se en foi About FOI Accessed 06 03 2014 D Bj rkl f Givarteknik for m tning i processer Almqvist Wiksell 1991
21. utg ngen for mjukvaruserieport f r drivkretsen define resetPin 8 Definierar Reset utg ngen f r drivkretsen define inputPin AO Definierar temperatursensoringang double temperature Temperaturv rde Celsius double Rt Termistormotst nd double E_Uab E Uab double logRt log Rt const double RO 2252 3 Fixt referensmotst nd i sp nningsdelare float Rep RO F renkling int i Raknevariabel int antalprov 10 Antal prov att ta medel av int provvektor 10 Vektor array for prov for medelv rde double Setpoint Input Output Variabler double Tsp 25 Default maltemperatur double TspK Maltemperatur i Kelvin double Rsp Motstand vid maltemperatur float alpha Alphavarde float beta Betavarde float b3c Forenkling Termistorspecifika konstanter till Steinhart Harts ekvation Thermistor element 44004 Omega Engineering Ltd const float a 0 001468 const float b 0 0002383 const float c 0 0000001007 Tuning parametrar f r PID loop Kylning float Kp 1 5 Proportional gain f r kylning anv nd 1 5 float Ki 0 5 Integral gain f r kylning anv nd 0 5 float Kd 0 Derivative gain f r kylning anv nd O V rmning float hKp 1 Proportional gain f r v rmning anv nd 1 float hKi 0 3 Integral gain f r v rmning anv nd 0 3 float hKd 0 Derivative gain f r v rmning anv nd O UMEA UNIVERSITY Department of Physics Ska
22. valve was closed The condensation of the isoflurane thus seems to affect the cooling at least when the vaporizer was set to 5 since this phenomenon was not observed for the lower concentrations or at 3 C ambient temperature 23 5 C 25 C or at 50 C However the temperature rise does not seem to have affected the signal to any significant extent since the three spectra are practically identical Spectra mean for the three concentrations at 3 and 10 C are found in figures 22 and 23 respectively Only two of the three collected spectra of 3 isoflurane at 3 C were used since the third contained a broad peak between ca 680 780 cm centered at about 720 cm which was not visible in the first two spectra This peak could for example be due to stray light e g lighting entering the cell or dust Note that with the temperature set to 10 C figure 23 the signal is practically identical with the exception of the three peaks at 629 639 and 652 cm with the vaporizer set to 3 and 5 which indicates that the SERS substrate is saturated at 3 at this temperature 28 UMEA UNIVERSITY 2014 06 12 Department of Physics 3 degrees centigrade 35 IR I I I I I I 1 isoflurane mean of three spectra 3 isoflurane mean of two spectra 30 5 isoflurane mean of three spectra H 25 4 20 4 3 5 2 15H 4 N E o 10 4 H i I a 5 Y I A
23. would explain that the sensor was indicating 5 C as minimum temperature The temperature could also have been lower than 22 C when the sensor was reading 22 C and higher than 45 C when the sensor was reading 45 CH The cooling system is set to cooling for temperatures less than 25 C and heating above 45 C vii UMEA UNIVERSITY 2014 06 12 Department of Physics Figure C1 shows SERS spectra collected at ambient temperature 22 C and at a lower temperature sensor reading 5 C Acetone 140 F T T 7 22 degrees centigrade 5 degrees centigrade 120 4 100 al 80 3 3 2 60 4 0 E E 404 20 20 ji L L i i i L 200 400 600 800 1000 1200 1400 1600 1800 Raman shift cm Figure C 1 Spectra collected at 22 C blue and 5 C red for comparison Plots of analyses at 5 C and at 22 C after cooling can be found in figure C2 below The 790 cm peak was chosen since it was the dominating one of the acetone peaks Equilibrium is reached after approximately 20 minutes plots after 2 4 8 10 12 and 18 minutes are not shown The signal decreases when the Klarite SERS substrate is heated to 22 C the sensor was reading 22 C It is decreasing slower than expected which is probably due to the poor thermal connection between the temperature sensor and SERS substrate which means that the temperature of the s
24. 2 Department of Physics m Mean value 0 55 5 0 50 4 0 45 4 x 3 0 40 4 SS Ps 0 364 5 E 0307 SE 0251 I EEN 4 HS 0 204 i S E 0 15 LA Oo oe iert 9s leet I Si 0104 P ev 1 A S 0054 A oe RN RN 1E 7 1E 6 1E 5 1E 4 1E 3 0 01 Concentration M Figure B 2 Mean value of mapping of each concentration Error bars show standard deviation The horizontal axis has logarithmic scale Figure B3 below shows the result of the kinetic measurements of four concentrations as an example The fluctuations in signal made it difficult to establish when equilibrium was reached It seems that equilibrium was reached within the 20 minute time period for all concentrations except 10 uM and 1 mM where the signal curve had not leveled out However as a few minutes went by between the kinetic study and the mapping was started equilibrium was probably reached before the mapping was started for these concentrations as well 1 1 E 1 0 we SE 0 9 D Qo 7 a _ ee ES 0 8 A e e S 3 ee A S s 0 7 f ES ow amp 8 06 d WT e Za 5 S ei a 200nM Normalized sE 9 e 500nM Normalized ZS SZ 04 vo A 5uM Normalized 0 f e 500uM Normalized v E ki Time minutes Figure B 3 Kinetic analysis at four concentrations vi UMEA UNIVERSITY 2014 06 12 Department of Physics Appendix C Introductory SERS Experiment using Acetone Experimental To investigate if the temperature co
25. A Od Gel di li O Wi KMA dh vie ni OM Pay d dt hit Sy A wi oi i Ai ALO oMi A Wier d Er d d D ent Wh L li 200 300 400 500 600 700 800 900 Raman shift cm Figure 22 Spectra mean of the three concentrations with the temperature set to 3 C 10 degrees centigrade 35F 7 T I T T 1 isoflurane mean of three spectra 3 isoflurane mean of three spectra 30 5 isoflurane mean of three spectra H 25 4 Intensity a u 5 200 300 400 500 600 700 800 900 Raman shift cm Figure 23 Spectra mean of the three concentrations with the temperature set to 10 C When the substrate was heated the gain of the detector was by mistake not reset to the previous value used before the time mapping acquisitions This means that the signal and noise are amplified in the three spectra collected at 3 25 and 50 C when the substrate was heated However when 29 UMEA UNIVERSITY 2014 06 12 Department of Physics a damping factor of 0 05 i e damped 20 times is used on the spectra collected after the gain had been changed and plotted together with the 3 C spectrum collected before the gain was changed see figure 24 the spectra look rather similar 35 Increasing the temperature of the SERS substrate after cooling 5 Isoflurane e I I I I I I I ci 3 degrees centigrade previous 3 degrees centigrade 30 25 degrees centigrade H 50 degrees centigrade
26. PTC Features of the RTD include high stability approximate linearity interchangeability and accuracy The relationship between temperature and resistance in the platinum filament is given by the Callendar Van Dusen equation equation 1 below R T R 0 1 A T B T T 100 C T3 1 Tis the temperature in C R 0 is the nominal resistance at 0 C The A B and C are constants that are derived from experimentally determined parameters An example of an RTD is the Pt 100 sensor The platinum filament in the Pt 100 sensor has a resistance of 100 Ohms at O C RTDs such as the Pt 100 have fairly linear resistance dependence to temperature 7 Response times for RTD sensors are usually longer than for thermocouples or thermistors e g 10 s versus 0 5 s respectively 8 To measure temperature with a RTD one must supply it with a constant measuring current This current will have the effect that the sensor will heat up Therefore measuring currents must be kept low in order to avoid substantial errors due to self heating of the sensor See the Thermistors section below for further information about self heating As resistance thermometers relates the filament resistance to temperature and the resistance of a platinum filament is relatively close to the resistance of the lead wires resistance in the lead wires will affect the temperature measurement This problem is usually circumvented by using three or four wire measurement connections
27. RSITY 2014 06 12 Department of Physics External Power Supply and Voltage Regulator An external AC to DC adapter is used to power the Peltier cooler The adaptor Nordic Power model 04151A 050300 is supplying 5 V and 3 A which means that the voltage must be regulated down to a proper level for the Peltier cooler since the VT 31 1 0 1 3 has a maximum input voltage of 3 8 V This was done by using a voltage regulator in this case a fixed 3 3 V output LM1084 National Semiconductor The regulator was connected similarly to as shown in figure 9 3 3V Fixed output voltage regulator 1 GROUND 2 OUTPUT 3 INPUT LM1084 3 3V Regulated output Power supply positive terminal gt 4 75V C 10uF Tantalum capacitor Figure 9 LM1084 3 3V fixed output voltage regulator The decoupling capacitors are used for stability reasons in this case 10 uF tantalum electrolyte capacitors are selected The 3 3 V 3 A output from the voltage regulator is in the neighborhood of 85 of the maximum rating of the Peltier module which seemed appropriate as the Peltier module would never be overloaded in voltage or current Note that the voltage regulator becomes hot when high currents are passed through it and therefore a heat sink was mounted on the TO 220 casing to help heat dissipation H Bridge Controller A Low Voltage Dual Serial Motor Controller SMCO5A Pololu Corporation was used to control the power output to the Peltier module
28. RSITY 2014 06 12 Department of Physics Microcontroller Ve SS a nd v Analog reference Serialcontrol Reset Analog input voltage input Digital pin Digital pin Serial interface not used oo O SMCOSA Voltage regulator Power supply 8 6 7 oo P ye Not used Capacitor Reference resistor 22520 Thermistor Peltier cooler Figure 16 Overview of the data acquisition and instrument control system The user is selecting a target temperature set point by sending the desired temperature on the hardware serial port to the microcontroller the default set point is 25 C The program running on the microcontroller is recognizing when a temperature value is sent on the serial port and stores the value into a variable The temperature is then converted into a 10bit precision value O 1023 which is corresponding to the value that would be read on the analog input pin when the temperature sensor is at that temperature This value is then used as set point for the PID controller The program then measures the temperature by the method described in the temperature measurement section of the report This temperature is thereafter sent via the serial port to the computer so the user can read the temperature and the elapsed time since the program started The program then decides if the PID controller should be in direct or reverse mode cooling or heating depending if the set point temperature is ab
29. UMEA UNIVERSITY 2014 06 12 Department of Physics Development of a Temperature Controlled Cell for Surface Enhanced Raman Spectroscopy for in situ Detection of Gases Master s Thesis Project in Engineering Physics 30hp 2014 06 12 Andr Appelblad Supervisor Per Ola Andersson FOI Swedish Defence Research Agency Division of CBRN Defence and Security Cementv gen 20 901 82 Umea Sweden Poand foi se Co Supervisor Christian Lejon FOI Swedish Defence Research Agency Division of CBRN Defence and Security Cementv gen 20 901 82 Umea Sweden Christian lejon foi se Examiner Magnus Andersson Umea University Department of Physics magnus andersson physics umu se UMEA UNIVERSITY 2014 06 12 Department of Physics UMEA UNIVERSITY 2014 06 12 Department of Physics Abstract Sammanfattning English This work describes a master s thesis in engineering physics at Umea University carried out during the spring semester of 2014 In the thesis the student has constructed and tested a temperature controlled cell for cooling heating of surface enhanced Raman spectroscopy SERS substrates for rapid detection of volatile substances The thesis was carried out at the Swedish Defence Research Agency FOI in Umea Sweden A Linkam Scientific Instruments TS1500 cell was equipped with a Peltier element for cooling heating and a thermistor temperature sensor A control system was constructed based on an Arduino Uno microcontroller board an
30. a b and c are constants specific to the thermistor found experimentally and often given in the datasheet of the sensor A thermistor is a passive device and therefore as in the case with RTDs it requires a constant excitation current for temperature measurements to be made One can use a current source to generate the excitation current and measure either the resistance of the thermistor directly with an Ohm meter or alternatively measure the voltage across the thermistor see the circuit diagram in figure 1 below and calculate the resistance from that voltage Figure 1 Circuit diagram for a simple thermistor measurement setup using a current source to generate measurement current If the voltage between node A and B called Ung is measured then the resistance of the thermistor Rx in equation 3 is then calculated using Ohm s law U R 3 Then the temperature in C is calculated approximately by subtracting the absolute zero approx 273 15 C in the Celsius scale from the Steinhart Hart equation which uses Kelvin resulting in equation 4 1 a b In R c In Rx TCC 273 15 4 UMEA UNIVERSITY 2014 06 12 Department of Physics Instead of using a current source to provide the excitation current one can alternatively use a voltage source and a fix reference resistance Ro connected in series with the thermistor as a voltage divider circuit Such a circuit is illustrated in the circuit diagram in figure 2 b
31. ae enee 21 A 1 3 Sg nee EE ER 4 2 TEST E 24 4 2 1 Results of Temperature Control System Test 24 4 2 2 Results of Test Using ISOf Urane cccoconocooooncnncnononononnnnnnnnnonanononnnnnnnnnnnnnenonnnnnnnnnnnnnennnnnnncnnnn 26 E ecllet UD le IT ER 6 Acknowledgements cccccccssessssececececeesessnaececeescesseuaeseseesesesesauaeeeeeesseseeseuaeseeeessessesaaaeeeeeessessesenaees 33 UMEA UNIVERSITY 2014 06 12 Department of Physics RETEPENCES ive ge EES EE 34 TARP DOM CIN EE i Appendix A Source RE i Appendix B Introductory SERS Experiment using DPE iv A NO iv Results and DISCUSSION cti ii v Appendix C Introductory SERS Experiment using ACetonNe s sssssesrereresseseersrersrssserrnrsrrs son nr rr er sr sann nn an vii Eet EC vii Results and DISCUSSION ek dee eee ode hee vii UMEA UNIVERSITY 2014 06 12 Department of Physics 1 Introduction The aim of this master s thesis project in engineering physics is to investigate and modify a Linkam TS1500 temperature control microscopy stage 1 for in situ studies of gas adsorption on gold substrates aimed for surface enhanced Raman spectroscopy SERS Molecular vibrational spectra of volatile substances in a controlled environment are probed with a Raman microspectroscopy system If the SERS substrate is cooled gas surrounding the substrate can be condensed onto the SERS surface The cooling step thus increases the number of analyte molecules in close contact to the subst
32. and the confocal hole was set to 500um The grating used in the experiment was a 600 gr mm blazed at NIR wavelengths Due to etalon effects in the detector all spectra were corrected according to NIST Standard Reference Material 2241 using 10s acquisitions and 75 cycles The experimental procedure follows roughly the same experimental procedure as in Jason A Guicheteau Mikella E Hankus Steven D Christesen Augustus W Fountain Ill Paul M Pellegrino Erik D Emmons Ashish Tripathi Phillip Wilcox Darren Emge Standard method for UMEA UNIVERSITY 2014 06 12 Department of Physics characterizing SERS substrates Proceedings of SPIE Vol 8373 837320 p1 8 Downloaded on 20140306 from http proceedings spiedigitallibrary org After warming up the 785 nm diode laser output was stable and the Raman microscope was calibrated against the 520 7 cm peak of Si The Klarite SERS substrate was first placed in a clean Petri dish and analyzed dry using a 5x lens and 10 s acquisition time Then spectroscopic grade ethanol was added to the Petri dish and the substrate was observed to see if the ethanol was causing any visible change to the substrate surface If no changes in the surface were observed the substrate was then placed in the lowest concentration solution and was then analyzed every 2 minutes for a 20 minute time period as a kinetic study to see that the spectral response had stabilized before the next step After the 20 minutes of the ki
33. ature sensor had to be connected to computer software through some form of hardware Preferably the same software and hardware would be able to display the temperature and control the Peltier device in the stage There are various ways of accomplishing this however the method presented below was chosen in this project 3 4 1 Data Acquisition and Instrument Control Platform Arduino The Arduino platform is an open source electronics prototyping platform with both hardware and software available The Arduino platform is capable of acquiring data from sensors and controlling instruments The microcontroller board is programmed in the Arduino programming language which is based on Wiring The software Arduino Integrated Development Environment IDE is available for Windows Mac OS and Linux and is free of charge It is used for uploading programs to the microcontroller board and also has a serial monitor in which one can view the data being sent to the serial port and one can also send commands to the serial port The most common Arduino microcontroller board is the Arduino Uno R3 and it was chosen for this project 35 3 4 2 Data Acquisition The Arduino Uno R3 has six analog inputs which measure voltage with 10 bit precision There is no Ohm meter on the Arduino Uno board and the voltage divider setup described in section 2 2 2 was used since there is no current source on the Arduino Uno board To minimize the effects of noise on the temperature mea
34. ces knows that a command is to be issued and listens to see if the command is meant for it them determined by the device type byte it should be 0 0x00 in hexadecimal notation for SMCO5A If the command is meant for the device in question it reads the following data byte s and executes the command To set the output and direction a four byte packet of the following format refer to table 3 is sent on the software serial port to the SMCOSA Table 3 Packet for setting output level and direction for SMCO5A Byte 1 Byte 2 Byte 3 Byte 4 Start byte 0x80 Device type 0x00 Output ID and Output level 0x00 direction 0x00 or Ox7F i e O 127 0x01 i e O or 1 The output ID is specifying which of the two outputs 0 or 1 the command should be executed on and the direction 1 for forward or O for backward specifies the direction of the current through the device Note that the SMCO5A s interface protocol is compatible with other Pololu devices and thus multiple devices can be controlled by the serial line Note that all SMCO5A devices on the serial line respond to output IDs O and 1 Therefore other output IDs e g 2 and 3 refer to the user s manual for other configurations than the default configuration must be used to control specific outputs on 16 UMEA UNIVERSITY 2014 06 12 Department of Physics specific controllers if multiple controllers are used Since only one SMCOSA board and only one out
35. cess a brief overview Raman scattering is inelastic scattering of light by molecules The incident photon can excite the molecule into a virtual state from which the electron can either fall back into the same vibrational state that it was excited from i e elastic Rayleigh scattering or it can fall into another vibrational state in which the emitted photon has either lost energy to the molecule which is called Stokes scattering or gained energy from the molecule anti Stokes scattering 25 The so called fingerprint region approx 600 1800 cm of the Raman spectra provides information specific to the molecule and chemical groups This enables identification of species by matching spectral data against libraries of spectra from known molecules The Raman cross section is usually small much less sensitive than the related IR absorption of vibration spectroscopy and about 10 incident photons may be required for a single photon to be Raman scattered 26 Fluorescence is a competing photon emission process First the molecule is excited to a higher electronic state by absorbing light where after it relaxes back into the ground state by emitting a photon Typically this appears as broad background signals blurring the in this case sought Raman spectra Luckily for trace analysis scientists discovered already in 1974 that Raman scattering from molecules adsorbed on nanostructured silver electrodes enhanced the Raman signal 27
36. compact portable and easy to use and that small amounts of substances can be detected 3 Surface Enhanced Raman Spectroscopy SERS is a versatile non destructive detection method capable of fulfilling these needs as it offers rapid and accurate means to identify trace amount of harmful substances with little or no need for sample preparation High reproducibility SERS substrates are today commonly fabricated and few are commercially available e g Klarite substrates Renishaw Diagnostics Ltd and many of these are showing good sensitivity together with high reproducibility Due to its attributes SERS has potential to be used in homeland security applications 3 The Swedish Defense Research Agency abbreviated FOI after the Swedish name Totalf rsvarets forskningsinstitut is an assignment funded governmental research institute under the Ministry of Defense F rsvarsdepartementet which focuses on research analysis and development of technology Examples of research areas include detection of and protection against harmful substances such as CBRNE substances Main clients are the Swedish Armed Forces F rsvarsmakten and the Swedish Defense Material Administration F rsvarets Materiellverk but FOI also carries out research for civilian clients 4 Prior to this master s thesis a pilot study was carried out at FOI where semi volatile substances in gas phase were detected using SERS All tested substances were easier to detect af
37. d a pulse width modulated PWM H bridge motor driver to control the Peltier element using a proportional integral PI control algorithm The temperature controlled cell was able to regulate the temperature of a SERS substrate within 15 to 110 C and maintain the temperature over prolonged periods at 0 22 C of the set point temperature Gas phase of 2 chloro 2 difluoromethoxy 1 1 1 trifluoro ethane isoflurane was flowed through the cell and SERS spectra were collected at different temperatures and concentrations This test showed that the signal is increased when the substrate is cooled and reversibly decreased when the substrate was heated Keywords temperature control Raman scattering surface enhanced Raman spectroscopy SERS SERS substrate volatile substances Peltier module thermistor PWM H bridge PI D control Svenska Detta dokument beskriver ett examensarbete for civilingenj rsexamen i teknisk fysik vid Umea Universitet som utf rts under v rterminen 2014 examensarbetet har en kyl v rmecell f r temperaturkontroll av substratytor f r ytforstarkt ramanspektroskopi SERS f r snabb detektion av farliga flyktiga mnen konstruerats och testats Arbetet utf rdes vid Totalf rsvarets forskningsinstitut FOI i Ume Sverige Utg ngspunkten var ett Linkam Scientific Instruments TS1500 mikroskopsteg vilket utrustades med ett Peltierelement f r kylning varmning och en termistor f r temperatur vervakning Ett styrsyste
38. e current the cold and hot sides are switched turning the cooler into a heater See figure 3 below Heat is 2 released Hot side Heat sink Conducting material Insulator Cold side Heat is absorbed Figure 3 Illustration of a Peltier cooler Note that the heat released will not be due to the Peltier effect alone there will also be Joule heating which is independent of current direction due to the electrical resistance of the conducting materials and lead wires Although the cooling side and heating side can be switched by reversing the UMEA UNIVERSITY 2014 06 12 Department of Physics current the side of the Peltier module on which the lead wires are attached is often referred to as the hot side This is because the Joule heating of the copper wires will heat the side that they are attached to making it less effective for cooling than the other side Therefore if the Peltier module is to be used for cooling then the hot side should be connected to the heat sink 13 Peltier coolers can only maintain a limited temperature difference usually less than 70 C between the cool side and the hot side and as the Peltier module moves heat from one side to the other the heat released at the hot side must be properly dissipated in order for the cooling to work and the other way around when used as a heater 14 Therefore a heat sink should be connected to the hot side or else the Peltier cooler can overheat resulting in
39. e still having a large contact area to the stage body The Peltier cooler was then mounted on the thermally conducting plate according to figure 6 using thermally conducting epoxy adhesive This kind of adhesive forms a strong bond with high thermal conductivity between the cooler and the metal plate which replaces mechanical mounting e g screw mounting which would be impractical in this case A thin layer of thermally conducting 2 stated values are valid for a hot side temperature of 27 C 12 UMEA UNIVERSITY 2014 06 12 Department of Physics grease compound was then added between the plates and the stage body to fill out any unevenness and increase thermal conduction Figure 6 Peltier module mounted on thermal conducting plate profile view The temperature sensor was then installed into the cell and held in place on the Peltier module or substrate chip by a metal bracket clad in electrical insulator holding the thermistor lead wires down see figure 7 below and a small portion of thermally conducting grease was applied to the sensor to increase thermal conduction between the substrate and the sensor Figure 7 A metal bracket profile view to hold the thermistor down on the substrate surface or Peltier module surface The black portion is covered by insulator 3 4 Data Acquisition amp Instrument Control As a computer was to be used to monitor and control the temperature in the stage the signal from the temper
40. elow Figure 2 Circuit diagram for thermistor measurement using a voltage divider setup If the voltage between terminals A and B Un is measured the thermistor resistance can be calculated using the following method Uap is given by the standard voltage divider relation equation 5 below which is due to that Ro and R are connected in series and therefore the current through Ro R is the same as the current through R Rx Ry Ro 5 Uap This can be rewritten as equation 6 Rx Ro Uap RxE 6 Gathering the terms containing R results in equation 7 below R E Uap RoE 7 Solving for R yields equation 8 _ Uap Rx E Uap Ro 8 The thermistor resistance R can then be inserted into the Steinhart Hart equation Le equation 2 as in the previous case to obtain the temperature Self Heating of the Thermistor The excitation current passing through the thermistor element will cause Joule heating i e resistive heating in the thermistor The dissipated power follows Joule s first law i e equation 9 Q 2 R 9 Where Q is power is current and R is resistance For example if an excitation current of 10 UA is applied to a thermistor with a nominal resistance of 2 252 Q at 25 C the power dissipated is as follows according to equation 9 10 1076A 2 2520 2 3 1077W 2 3 10 mWw UMEA UNIVERSITY 2014 06 12 Department of Physics The power in mW that will raise the temperature
41. es three spectra were collected The vaporizer was then set to 0 isoflurane i e pure instrument air 19 UMEA UNIVERSITY 2014 06 12 Department of Physics The temperature was then set to 13 C and was allowed to stabilize The grating was set to 600 cm A time mapping was prepared i e a kinetic analysis in which the signal is monitored while the analyte is binding to or being released from the surface The software was set to collect spectra with 2 s acquisition every other second during a minute for a total of 31 spectra At the same time as the mapping was started the vaporizer was set to 5 and was allowed to be open for 5 s before the valve was closed After the time mapping had been completed a gain of 160 was then applied to the sensor and a similar time mapping was performed with the new sensor setting The total mapping time was then changed to 2 minutes still 2 s acquisitions every other second At the same time as the mapping was started the vaporizer was set to 5 isoflurane and after one minute the valve was closed When the third time mapping was completed the software was set to collect 4 s acquisitions every 5 s during three minutes At the same time the mapping was started the vaporizer was set to 5 and the valve was kept open for one minute before it was closed When the time mappings had been completed the acquisition settings were returned to 20 s acquisitions and 2 cycles The vaporizer was then set to 5
42. han thermocouples or thermistors which could prove to be a problem As mentioned earlier a thermocouple measures a temperature difference between the measurement end and the reference end which requires cold junction compensation This is a potential problem with thermocouples for temperature measurement in the stage because the reference temperature has to be known and preferably constant in order to get accurate temperature readings from the thermocouple This would require an ice bath to keep the reference end at a stable temperature of 0 C and the ice bath require maintenance lest the ice will melt The thermocouple connector in the stage is an S type connector 0 1600 C and thus not suitable for the 20 to 200 C temperature range and in addition to the thermocouple s low nominal accuracy this could lead to an inaccurate temperature measurement 10 The stage as it was supplied is designed to be connected to a Linkam controller unit with a contact plug connecting the controller unit to the two heater leads and the two leads of the thermocouple connector in the stage If more leads or wires than the stage is prepared for are to be used then one has to physically modify the stage body connection setup adding more leads and such changes could potentially be irreversible As the stage is expensive it was decided that this kind of modification should be avoided as far as possible leaving two leads available for the cooler heater positi
43. he target set point can be changed as the program runs effectively making it a dual stage controller i e controlling cooling or heating depending on what the set point is In this case the output to be controlled is the supplied voltage to the Peltier cooler represented by a 6bit value The process variable also called input is in this case the 10bit value integer value 0 1023 reading of the 17 UMEA UNIVERSITY 2014 06 12 Department of Physics temperature sensor and the set point is a 10bit value representing the desired target temperature of the substrate surface The controller was in this case tuned manually by a variant of the Ziegler Nichols method described earlier in section 2 2 4 of this document The gain constants Kp K and Kg were set to zero and K was then increased until the temperature started to oscillate around the set point meaning that the critical gain was achieved Thereafter gain constants were set to the Pl controller values of table 1 Pl control was used since the system is relatively fast responding and derivative control could therefore easily cause instability Regulation System Casing The electronic components of the regulation system were soldered onto an Arduino prototyping shield which fits directly onto the Arduino Uno R3 microcontroller board The Arduino microcontroller board with the shield attached was then mounted in a plastic box which was equipped with a cooling fan to increase heat dissipatio
44. he vaporizer had been set to 5 at 23 5 C The spectra collected when the temperature was set to 3 C and the vaporizer set to 5 clearly display isoflurane peaks Figure 21 below shows the three spectra collected when the temperature was set to 10 C and the vaporizer set to 5 isoflurane The signal had increased significantly compared to the spectra collected at 3 C Apparently by lowering the temperature the amount of analyte molecules in close proximity to the substrate surface is increasing whereupon a signal enhancement is seen Note that the three spectra are practically identical which supports reproducibility 27 UMEA UNIVERSITY 2014 06 12 Department of Physics Isoflurane 5 10 degrees centigrade I a T I i Spectrum 1 Spectrum 2 Spectrum 3 H bo 2 E E lk V Vd VW il AA d My j i d i M i i AN Ub Im Ig Min d j wy Jaf d V Wu Mk Niska NN hal WW UM cl du Wd NI Vgl A M 3 l l l I l l 200 300 400 500 600 700 800 900 Raman shift cm 7 Figure 21 Three spectra temperature set to 10 C and vaporizer set to 5 At the highest concentration with the vaporizer set to 5 the temperature started to climb from 10 up to 5 C for the first spectrum and 2 5 C for the second and third spectra The temperature returned to the preset temperature quickly after the isoflurane
45. id attached The depth between the bottom of the stage interior and the lower surface of the 1 mm thick quartz window in the lid is approx 15 1 mm with the heating cup removed The cooler heater setup SERS substrate and temperature sensor all need to fit in that space and still leave enough room to allow gas to flow over the substrate surface 3 2 Choosing Temperature Sensor Comparison between Thermocouples platinum RTDs and Thermistors Regarding the temperature sensor the key concerns are e Temperature range approximately 20 to 200 C e Response time as short as possible e Accuracy 0 5 C e Two wire sensor connection using the existing thermocouple connector leads e Sensor size as small as possible 10 UMEA UNIVERSITY 2014 06 12 Department of Physics The platinum RTD devices such as Pt 100 sensors generally have better accuracy tolerance than thermocouples or thermistors and measure absolute temperature as opposed to the differential temperature measured by thermocouples As the cooling heating device in the stage is being controlled by computer software relying on the temperature measured by the sensor the response time of the sensor must be kept to a minimum so the lag in the control system is as small as possible Otherwise the control system would set the cooling heating according to obsolete temperature values and the system would be ineffective The platinum RTD sensors usually have longer response times t
46. isoflurane the monitor being off scale above 5 The temperature was set to 3 C and was allowed to stabilize A spectrum was collected after two minutes The temperature was then set to 25 C and was allowed to stabilize before a spectrum was collected Then the temperature was set to 50 C and a spectrum was collected after the temperature had stabilized To ensure that the right substance is detected a normal Raman spectrum of liquid phase isoflurane was collected for comparison using a handheld Raman spectroscopy instrument First Defender RMX Thermo Fischer Scientific measuring directly in the storage bottle 20 UMEA UNIVERSITY 2014 06 12 Department of Physics 4 Results amp Discussion 4 1 System Description 4 1 1 The Modified Stage The modified stage can be seen in figure 13 below Figure 13 Top down view of the interior of the modified stage Note that the black thermistor bead is submerged in a drop of white thermal compound The SERS substrate is inserted between the thermistor bead and the Peltier module surface when SERS measurements are to be made 4 1 2 PID Control The target temperature should be reached in a reasonable amount of time however it should not overshoot the target temperature since the analyte could for example be unintentionally released from the substrate surface This meant that a compromise between fast response low or no overshoot and high stability was desired Values of K
47. kly interact with gold surfaces but shown possible to detect using the temperature control of the SERS substrate The choice of cooler heater temperature sensor and thermally conductive adhesive etc implies that the working temperature range is narrower than the originally desired 20 C to 200 C Instead it ranges approximately from 15 C to 110 C if the temperature of the water reservoir of the water cooling system is at room temperature 23 C as it was in the tests conducted in the project Due to the properties of the Peltier device one way to expand the temperature range would be to use a temperature controlled water reservoir for the water cooling system In that way one would be able to lower the temperature of the circulating water and thereby achieving a lower temperature of the cold side of the Peltier element Conversely heating the circulating water would yield higher temperatures however the temperature limits of individual components must be taken into consideration since they could be damaged To simplify for the user it would be convenient to have an automated set point or controller output ramp function in which the set point or controller output can be changed at a suitable rate preferably chosen by the user In the present case the user makes a manual set point ramp by 32 UMEA UNIVERSITY 2014 06 12 Department of Physics selecting target temperatures in reasonable steps and in this way undue thermal
48. l K K Ka P 0 5K Pl 0 45K Ko Tu 1 2 PD 0 8K K T 8 PID 0 60K 2K Ty K T 8 Other examples of tuning methods include the Cohen Coon Open Loop Method and of course manually adjusting the gain constants to give an appropriate controller output Generally if the system has a too low proportional gain it will be over damped slow to respond and may even not reach the desired set point e a steady state error droop If it has a too high proportional gain it will start to oscillate periodically around the set point A too small integral gain will not be able to compensate for any steady state error droop but a too large integral gain can cause instability The derivative gain is rarely used in real world applications as it can cause instability if the signal has noise or if the set point or process variable is changed suddenly 23 24 UMEA UNIVERSITY 2014 06 12 Department of Physics The integral term takes all errors up until the present into account and therefore if the system starts off far from the set point the initial error values will be large and the integral term will subsequently grow quickly This can cause excess overshoot until the opposite direction errors have decreased the integral term This phenomenon is called integral windup and can be overcome by for example not using the integral term until the process variable is within a certain range of the set point 2 6 Raman scattering pro
49. m baserat p ett Arduino Uno mikrostyrenhetskort konstruerades med ett motordrivkort H brygga vilket anv nder pulsbreddsmodulering PWM f r att reglera sp nningen till Peltierelementet utifr n en Pl regulator Den f rdiga cellen klarade att reglera temperaturen p ett SERS substrat i ett temperaturspann p ungef r 15 till 110 C med en temperaturstabilitet p 0 22 C av m ltemperaturen Cellen testades sedan p flyktiga mnen f r att visa dess funktion Difluorometyl 2 2 2 trifluoro 1 kloroetyleter isofluran i gasfas med instrumentluft som b rargas fl dades genom cellen och SERS spektra erh lls vid olika koncentrationer och temperaturer Vid samtliga koncentrationer visades att l gre temperatur ger kad signalstyrka N r ytan sedan v rmdes upp sj nk signalen reversibelt tillbaka till ursprungsv rdet Nyckelord temperaturkontroll ytf rst rkt ramanspektroskopi SERS flyktiga mnen Peltierelement thermistor PWM H brygga PI D regulator UMEA UNIVERSITY 2014 06 12 Department of Physics UMEA UNIVERSITY 2014 06 12 Department of Physics Table of Contents L INNE OC UCI N ass eege lected stance Agee cece ae EA 1 Eege e EE 2 21 Project Backgrounders senide aeee aaee A KROAT Aa EEE AE eE EA REEERE 2 2 2 Temperature MEasUreme Mtiini en a dis 2 22 1 TINE HMO COUP UE 2 2 2 2 Resistance Thermometers Platinum Resistance Thermometers amp Thermistors 3 2 3 Thermoelectric Coolers Peltier mod
50. mediately from the first spectrum begins to level out after 20 s and decreases after the vaporizer were set to 0 O indicated by the red vertical line in figure 26 Notice the sudden drop after about 140 s This drop could also be seen for the 243 cm peak as well as for the 416 cm peak In hindsight a better baseline could be attained by letting the kinetic mapping to go on a longer time without flowing isoflurane 31 UMEA UNIVERSITY 2014 06 12 Department of Physics 5 Isoflurane area of 365cm peak 1 1 T T T 1 T 1 T Peak area a u Isoflurane valve closed 0 9 4 Peak area a u o o S CO T T 1 E o T L K ys 4 0 4 H 03 i L L i L f L L 0 20 40 60 80 100 120 140 160 180 Time s Figure 26 Area of the 365 cm peak vs time plot The data is from the 4 time mapping The red vertical line is indicating when the isoflurane vaporizer was set to 0 5 Conclusion The described tests show that the temperature control cell is working well by cooling and thereby condensing analyte substances onto the SERS substrate volatile substances can be detected easily in situ By increasing the temperature of the SERS substrate the volatile analyte is released and the SERS substrate is fully regenerated It can also be concluded by the results of this project that reproducible SERS measurements are possible Isoflurane is just an example of many volatile substances that wea
51. mistor and it would have been better to use a platinum RTD as reference but as no platinum RTD was available at the time the thermocouple would have to suffice The size of the thermistor sensor is larger than the size of the measurement junction of the thermocouple The round geometry bead shape of the thermistor requires that thermal compound is used to increase the thermal contact between the thermistor and the SERS substrate or Peltier module surface Both of these reasons probably contributes to that the thermistor reads less extreme values than the thermocouple 25 UMEA UNIVERSITY 2014 06 12 Department of Physics Table 5 Thermistor temperature readings and K type thermocouple temperature readings for verification Thermistor Thermocouple temperature C temperature C 10 0 12 0 0 0 0 8 10 0 9 4 22 7 22 4 30 0 30 2 50 0 51 4 70 0 72 3 4 2 2 Results of Test Using Isoflurane In this section the results of the SERS experiment using the temperature control cell to detect isoflurane are presented and discussed A normal Raman spectrum of isoflurane in liquid phase and a SERS spectrum of isoflurane 5 concentration collected at 10 C is shown in figure 19 with wavenumbers of significant peaks noted The liquid phase spectrum was collected using a handheld Raman instrument measuring directly in the isoflurane storage bottle Isoflurane Gas phase SERS 365 Liquid pha
52. n from the H bridge controller and the voltage regulator and connections for power supply temperature sensor and Peltier module 3 5 Tests of the Temperature Control Cell 3 5 1 Temperature Control System Test Experimental Procedure A test of the cooling of the temperature control system was made by starting at ambient temperature 23 C and selecting 20 C as target temperature After the temperature had stabilized the target temperature was set to 15 C and temperature was allowed to stabilize This procedure was repeated for 5 C steps down to 15 C and up again to ambient temperature A similar test was then made for the heating of the temperature control system which as mentioned earlier has another set of PID gain factors As in the previous case the test was started at ambient temperature The target temperature was then set to 30 C and the temperature was allowed to stabilize at the target temperature The target temperature was then set to 50 80 110 100 80 60 40 30 C and then ambient temperature The temperature was allowed to stabilize at each target temperature To test the stability of the temperature regulation the cold side of the Peltier cooler was kept at 15 C for approximately 15 minutes and the temperature was observed A K type thermocouple was used as a reference thermometer and the temperature of the Peltier module surface was measured at number of temperatures and the thermocouple and thermistor value
53. nd after four minutes a spectrum was collected More spectra were collected every second minute until equilibrium has been reached Then the target temperature was set to 5 C and after the temperature had stabilized spectra were collected every second minute until equilibrium is reached The temperature was then set to 10 C and spectra were collected every second minute for 6 minutes The target temperature was then again set to 22 C and the temperature was allowed to stabilize Spectra were then collected every second minute for 8 minutes so one could observe that the signal is decreasing Then the target temperature was set to 45 C and a few spectra were collected after the temperature had stabilized to ensure that the acetone signal has disappeared Results and Discussion It seemed impossible to cool the substrate lower than 5 C during the test which was surprising It was also surprising that the signal had increased significantly between ambient temperature and 5 C it was expected to require lower temperatures than 5 C However after the test was completed it was observed that the thermal compound between the thermistor and the surface had been destroyed by the acetone causing a poor thermal connection between the sensor and the surface This probably means that the substrate surface was at a considerably lower temperature than 5 C perhaps as low as 15 C since it was impossible to decrease the temperature any further This
54. nd the optical density filter was changed to yield a power delivered at the surface of 20 mW Three spectra were collected in succession to show that the spectra are reproducible The vaporizer was then set to pure instrument air i e 0 isoflurane to clean the surface and after two minutes a spectrum was collected to ensure that the isoflurane signal had disappeared The vaporizer was then set to 3 the monitor showing approximately 5 and two minutes were allowed to pass to let the cell be completely filled with the gas before three spectra were collected in succession The vaporizer was again set to 0 isoflurane and after two minutes a spectrum was collected to ensure that the isoflurane signal had disappeared The laser was then focused on another nearby spot on the substrate surface to avoid laser damage on the SERS substrate Another spectrum was collected at this new spot The vaporizer was then set to 1 isoflurane the monitor showing approximately 2 5 probably because the vaporizer is intended for enflurane and after two minutes three spectra were collected in succession The temperature was then set to 10 C and was allowed to stabilize before three spectra were collected The vaporizer was then set to 3 isoflurane the monitor showing approximately 5 and after two minutes had been allowed to pass three spectra were collected The vaporizer was then set to 5 the monitor being off scale at above 5 and after two minut
55. netic study a few minutes passed as the Raman instrument was adjusted for duoscan i e sweeping mode A mapping was then made by analyzing at 5 spots sweeping a 50 x 50 um rectangle at each spot on an array over the substrate taking two spectra at each spot for averaging The substrate was then placed in the next concentration and the procedure is repeated for every concentration The signal was then calculated as the ratio of the area of the 1200 cm BPE peak and the area of the 880 cm ethanol peak from the mapping The data was plotted as the signal as a function of concentration Results and Discussion All concentrations were covered for the Klarite substrate Figure B1 below shows a spectrum for the 500 uM concentration as an example The ratio of the area of the 1200 cm BPE peak and the 880 cm ethanol peak from the mappings for the different concentrations is plotted in figure B2 with error bars showing the standard deviation Notice the large standard deviations due to large variations in signal between the mapping spots on the substrate BPE in ethanol I 70F T T 500uM 3rd spot of map 50 4 40b 4 30 4 Intensity a u i Walt ht hi F 0 L i ji 200 400 600 800 1000 1200 1400 1600 1800 Raman shift cm o Figure B 1 A SERS spectrum for 500 M BPE Ethanol using a Klarite substrate UMEA UNIVERSITY 2014 06 1
56. ng float average for i 0 i lt antalprov i provwvektor i analogRead inputPin delay 20 Ta medelv rde av l sta sensorvarden average 0 for i 0 i lt antalprov i average provwvektor i average antalprov Satt Input variabeln till detta medelvarde Input average Rakna ut temperaturvarde fran matt varde E_Uab 1023 average Rt RO average E_Uab logRt log Rt log naturliga logaritmen In X i Arduino Steinhart Harts ekvation temperature 1 a b logRt c logRt logRt logRt 273 15 float Time millis Millisekunder sedan programmet startades float Timeseconds Time 1000 Konvertera till sekunder Skriv tid sedan start och temperatur till serieporten Serial print Timeseconds Serial print Serial print temperature Serial print n 2014 06 12 UMEA UNIVERSITY Department of Physics delay 50 if Setpoint lt 510 Om maltemperaturen verstiger ca 25 grader stall om PID kontrollern f r varmning peltierPID SetControllerDirection REVERSE peltierPID SetTunings hKp hKi hKd else Annars stall in PID kontrollern f r kylning peltierPID SetControllerDirection DIRECT peltierPID SetTunings Kp Ki Kd delay 10 K r PID algoritm P PI eller PID beroende pa hur konstanterna valts peltierPID Compute delay 50 Output map Output O 255 0 127 Skala om till 6bit if temperature
57. nge of 40 to 200 C and a reasonable maximum power of 8 4 W The maximum input voltage is 3 8 V and the maximum current draw is 3 6 A The maximum temperature difference between hot side and cold side is 69 CH The TS1500 stage body is water cooled the water is at room temperature and the heat from the hot side of the Peltier cooler must thus be transported from the hot side of the cooler to the stage body for dissipation Since there is a window located in the bottom of the stage indicated in blue in figure 6 some sort of plate of a thermally conducting material preferably of copper or another thermally conducting material would thus have to be connecting the hot side of the Peltier cooler to the actively cooled stage body The plate could not be made too thick as this would decrease the free space above the cooler and thus decrease the space above the substrate in which the gas must be able to flow The stage has a 0 5 mm deep circular recess of 40mm diameter in the bottom so it is 0 5 mm deeper in the center than at the edge as shown in figure 6 A 0 5 mm thick aluminum plate of 40 mm diameter and a 1 0 mm thick aluminum plate of 64mm diameter with a cutout for the connection leads put together as shown in grey in figure 6 were used in this case Aluminum does not have as high thermal conduction as copper 205 vs 401 WK 34 but it is still a decent thermal conductor These plates only take up 1 5mm of the overall depth of the cell whil
58. ntrol cell is working as planned a test was made using a not so harmful volatile substance Acetone was chosen as analyte substance as it is volatile and commonly available and a Klarite SERS substrate was used The substrate was placed on top of the Peltier element i e between the thermistor and the Peltier element The Raman instrument setup was a Horiba Jobin Yvon LabRam 800 HR confocal Raman microscope with LabSpec 5 software equipped with an Andor Newton back illuminated EMC CDD and a 785 nm Sacher Lasertechnik Tiger diode laser A 5x lens was used in backscatter geometry and the confocal hole was set to 500um The grating used in the experiment was a 600 gr mm blazed at NIR wavelengths Due to etalon effects in the detector all spectra were corrected according to NIST Standard Reference Material 2241 Nitrogen gas N is used as carrier gas and the N gas is bubbled through a liquid phase of the Acetone to generate the analyte gas The gas was then led to the temperature control cell where the SERS substrate had been placed on the Peltier cooler After warming up the 785 nm diode laser output was stable and the Raman microscope was calibrated against the 520 7 cm peak of Si First the temperature was set to ambient room temperature in this case 22 C and a flow of 20 min min of clean N gas i e no acetone was applied A spectrum is collected after the cell had been completely filled with N gt Then the acetone was introduced a
59. ove or below the ambient temperature room temperature defined as 25 C in the program The PID controller then computes the appropriate output and the program sends the corresponding command on a software serial port to the H bridge controller which in turn sets the voltage supplied to the Peltier cooler at the corresponding level and direction The loop then starts again and the set point is kept at the last set value until a new set point is sent on the serial port The source code for the Arduino sketch kylcell ino can be found in Appendix C 23 UMEA UNIVERSITY 2014 06 12 Department of Physics 4 2 Test Results 4 2 1 Results of Temperature Control System Test Figure 17 shows the result from a test run of the cooling of the temperature control cell The system is almost exactly critically damped with virtually no overshoot and the temperature response is rapid 25 24 23 2 20 G 19 18 17 16 13 12 1 i a Dee 9 189 so 100 150 200 250 300 350 400 aso soo 50 600 650 700 750 800 Ze AA Ebook um oam 11 12 13 i 14 15 16 17 18 Figure 17 Temperature C vs time s plot from a test run of the cooling of the temperature control cell The results from the corresponding test of the heating of the temperature control cell are found in figure 18
60. pa PID loop med namnet peltierPID PID peltierPID amp lnput amp Output amp Setpoint Kp Ki Kd DIRECT Skapa mjukvaruserieport Rx Tx kommunikationsut ingangar SoftwareSerial drivkretsSerial rxPin txPin KONFIGURERINGSDEL k rs en gang void setup Serial begin 9600 Starta seriekommunikation delay 50 VIKTIGT F ljande kodrad m ste finnas om extern referenssp nning anv nds Annars kortsluts den interna referenssp nningen med den externa vilket kan skada arduinokortet analogReference EXTERNAL startDrivkrets Starta kommunikation och styrprotokoll f r drivkretsen peltierPID SetMode AUTOMATIC L ge f r PID kontrollern AUTOMATIC p S tt ing ngsl ge f r temperatursensoring ngen pinMode inputPin INPUT HUVUDLOOP k rs om och om igen void loop Las malvardestemperatur vid inmatning if Serial available gt OK Tsp Serial parseFloat TspK Tsp 273 15 Konvertera till Kelvin alpha a 1 TspK c Alfavarde b3c b 3 c F renkling beta sqrt b3c b3c b3c alpha alpha 4 Betavarde Rsp exp pow beta 0 5 alpha 1 0 3 0 pow beta 0 5 alpha 1 0 3 0 Motstand vid m ltemperatur Rsp_RO Rsp RO Forenkling Rakna om till v rde motsv spanning i sp nningsdelare 0 1023 och satt Setpoint variabeln till detta varde Setpoint 1023 Rsp_RO 1 Rsp_RO L s antalprov sensorv rden 0 1023 med liten f rdr jni
61. put is used Output 0 in this application this byte will be Ox00 for backward or Ox01 for forward Sending the example packet in table 4 below on the software serial port will issue the command forward direction at output level 78 to the SMCO5A controller hexadecimal representation of 78 is Ox4E Table 4 An example packet issuing the command Forward direction at output level 78 Byte 1 Byte 2 Byte 3 Byte 4 0x80 0x00 0x01 Ox4E The SMCO5A controller was connected according to figure 11 below Note that Power supply in figure 11 refers to the regulated output of the voltage regulator Since only one Peltier cooler is used pin 6 and 7 on the SMCO5A board are not connected Serial port interface pins t used Power supply V no 4 Ground Gnd Logic supply 5V O Serial control input SMCOSA Reset Device 1 positive output Device 1 negative output Device 0 negative output Device 0 positive output Power supply WWI DOR WNK Not used Serial control pin Peltier element Microcontroller board Figure 11 SMCOSA setup with Arduino microcontroller PID Control There is a free PID library available for the Arduino platform 38 This PID controller is a single stage controller either for heating or cooling However the direction of the controller which decides if the output should be increased or decreased if the process variable is above or below t
62. puter instead of using separate controller units in order to simplify operation The temperature controlled cell should also be able to accept vibration and gas flow sensing devices preferably also controllable by the computer interface To introduce the student in Raman spectroscopy and particularly to SERS an experiment was conducted in which Klarite substrates were submerged in BPE ethanol solutions and spectra were collected as functions of concentration and time Another introductory SERS experiment was conducted using the resulting modified stage in which gas phase acetone was flowed through the temperature controlled cell and spectra were collected as a function of temperature and time These experiments are summarized in Appendix B and C of this document The temperature controlled cell is then used with a SERS Raman instrument setup for gas phase detection of volatile substances in order to demonstrate that it works properly UMEA UNIVERSITY 2014 06 12 Department of Physics 2 Background 2 1 Project Background Society today has an increasing demand for fast and accurate methods for detection and identification of harmful substances such as chemical biological radiological nuclear and explosive CBRNE substances for defense and homeland security applications as well as in industry medical applications and other civilian applications 2 It is often demanded that the detection method can be used in the field and that devices are
63. rate surface leading to increased signal strength i e the gases will be detected more easily Conversely if the temperature of the substrate surface is increased volatile analyte molecules will desorb from the surface and evaporate leading to regeneration of the SERS substrate Thus the stage must have means to cool and thereby condense gases of interest onto a substrate surface as SERS requires close proximity between the analyte substance and the substrate surface In order to release the condensed analyte gas the stage must also be able to heat and thereby regenerate the substrate surface Accordingly the contractor wishes that the temperature of the SERS substrate to be contained within the stage must be monitored and regulated without interfering with the detection method It was also of interest to measure the temperature of the gas surrounding the SERS substrate in the cell for comparison with the substrate temperature The stage must accept commercially available SERS substrates named Klarite as well as other substrates so flexibility in that respect is of key concern The temperature of the SERS substrate should be possible to regulate within a temperature span of desirably 20 to 200 C or as close to this as possible primarily to allow condensation and evaporation of analytes of interest A temperature stability of 0 5 C is desired The regulation and monitoring of the temperature in the cell is preferred to be managed via com
64. s of equation 11 i e PID control or use parts of it e g Pl or PD control depending on the needs of the specific process For simple setups it might even be enough to use only the proportional term P When the error e t gets to zero the output of the P controller is zero This means that there will be a steady state error known as droop between the process variable and the desired set point By additionally using the integral term i e Pl control it will take care of the steady state error and help the process variable reach the set point The derivative term can be added i e PID control to decrease settling time and thus increasing stability 20 The process of determining the gain constants of the controller is called tuning There are several methods of PID tuning and some PID controllers even have built in automatic tuning to determine the gain constants An example of a tuning algorithm is the Ziegler Nichols Closed Loop Method In the Ziegler Nichols method the controller is first set to use only the proportional term Le K and Ka are set to zero and K is increased until constant amplitude oscillations of the process variable are obtained That gain is called the ultimate gain K which together with the period of the oscillations Tu are used to determine the gain constants Kp K and Ka according to table 1 below 21 22 Table 1 Gain constants for Ziegler Nichols tuning 21 Type of Contro
65. s were noted 3 5 2 Test using Isoflurane Experimental Procedure Isoflurane 2 chloro 2 difluoromethoxy 1 1 1 trifluoro ethane see figure 12 below is an anesthetic substance in the form of a colorless liquid with pungent odor It is used as an inhalation anesthetic by vaporizing the liquid As anesthetic substances can be harmful or even fatal if handled in the wrong way it should only be handled by persons with adequate knowledge and training in anesthetics 39 Figure 12 Isoflurane molecule 40 18 UMEA UNIVERSITY 2014 06 12 Department of Physics The Raman instrument setup was a Horiba Jobin Yvon LabRam 800 HR confocal Raman microscope equipped with an Andor Newton back illuminated EMC CDD and a 785 nm Sacher Lasertechnik Tiger diode laser LabSpec 5 software was used to operate the system and for data acquisition A 5x lens was used in backscatter geometry and the confocal hole was set to 500um The grating used in the experiment was a 600 gr mm blazed at NIR wavelengths Due to etalon effects in the detector all spectra were corrected according to NIST Standard Reference Material 2241 using 20 s acquisitions and 20 cycles on the reference The gas was generated using an Ohmeda Enfluratec 5 enflurane anesthetic vaporizer note that this vaporizer is meant for use with enflurane which means that the vaporizer used in this experiment was not calibrated for isoflurane with instrument air as carrier gas A Br hl amp Kjaer anesthe
66. se normal Raman 0 8 243 242 882 882 Intensity a u L l i i J J 200 300 400 500 600 700 800 900 Raman shift cm H Figure 19 Comparison between Raman spectrum of isoflurane in liquid phase and SERS spectrum of isoflurane in gas phase Note that the spectra are normalized The similarity between the spectra in figure 19 is striking it is indeed isoflurane that is detected Although additional peaks e g at 629 639 and 652 cm are showing up all significant peaks are seen in the SERS measurement and it is conclusive that isoflurane vapor is in situ monitored by SERS 26 UMEA UNIVERSITY 2014 06 12 Department of Physics The origins of the extra peaks are not further investigated but one should bear in mind that a SERS spectrum does not necessarily overlap a spectrum originating from normal Raman scattered photons The background spectrum collected at ambient temperature before any gas flow was applied is presented in figure 20 Klarite no gas flow 35 T T T 23 degrees centigrade 30 4 257 J 20 4 15H 4 Intensity a u 10 4 pta ar 200 300 400 500 600 700 800 900 Raman shift cm Figure 20 Background spectrum of the Klarite substrate at ambient temperature without any gas applied Temperature Study and Regeneration of the Substrate No peaks were detected after t
67. surement the 3 3 V pin was used as analog reference voltage instead of the standard 5 V that comes directly from the computer USB Additionally a series of several measurements are taken with a short delay and the average value is then calculated to further reduce effects of noise on the temperature measurement The setup is shown in figure 8 below 13 UMEA UNIVERSITY 2014 06 12 Department of Physics 3 3V 2252 Ohm Reference Arduino Resistor analog input 2252 Ohm Thermistor Gnd Figure 8 Voltage divider thermistor setup with Arduino The temperature sensor setup was connected to an analog input on the microcontroller board and by using the command analogRead an integer value 6 is returned which represents the voltage 4 on the analog input pin The returned value is related to the corresponding voltage as given below Voltage Value 12 The temperature measured by the thermistor is calculated by the method described in section 2 2 2 of this document The temperature together with the time passed since the program started can then be regularly sent to the serial port The serial monitor in the Arduino IDE cannot save the data so an external program will have to be used if the data is to be saved it is possible to manually copy paste the data from the Arduino IDE serial monitor into a text file The text file can then be opened with Microsoft Excel or similar software for data processing 3 4 3 Instrument Control
68. t of Physics will arise due to the Seebeck effect The voltage difference is related to the temperature difference between the two junctions and tables are used for translating the voltage into temperature 5 p 34 Thermocouples have rapid response and can operate over large temperature ranges Type K thermocouples i e Chromel Alumel thermocouples are the most common and have an operating temperature span of 200 to 1 350 C and an accuracy of about 1 5 C The thermocouple is a differential measurement sensor it measures the temperature at the measurement junction compared to the temperature at the reference junction This means that a thermocouple measurement setup will require a stable reference temperature i e cold junction compensation in order to give accurate temperature readings 6 2 2 2 Resistance Thermometers Platinum Resistance Thermometers amp Thermistors A resistance thermometer is a sensor in which the resistance varies with temperature The temperature of the object can thus be related to the resistance of the sensor filament The most common types of resistance thermometers are described below Platinum Resistance Thermometers A common type of resistance thermometer is the platinum resistance temperature detector RTD which is also known as platinum resistance thermometer PRT Platinum has the characteristic that its resistance increases with increasing temperature so called positive temperature coefficient
69. ter cooling the SERS substrate which indicates that temperature control is desired for gas phase detection with SERS Another result was that the SERS substrate could often be regenerated by increasing the temperature to a certain level The resulting modified stage can be used in future research for a variety of applications of gas phase detection with a range of SERS substrates and analyte substances as well as other applications where temperature control is needed This makes the project relevant as a master s thesis 2 2 Temperature Measurement To measure the temperature of the substrate surface in the TS1500 stage a suitable technique must be chosen Contact thermometry in which the temperature sensor is in contact with the surface seems to be an adequate choice instead of non contact thermometry There are several types of temperature sensors and examples of widely used sensors are thermocouples and resistance thermometers such as thermistors and platinum resistance temperature detectors 2 2 1 Thermocouple A thermocouple consists of two different conducting metal wires with atoms at different Fermi levels which are joined together in one end the so called hot measurement junction and to copper wires in the other end the so called cold reference junction s When the measurement junction is at another temperature then the reference end of the thermocouple a voltage difference 2 UMEA UNIVERSITY 2014 06 12 Departmen
70. tic gas monitor type 1304 was used to monitor the gas After warming up the 785 nm diode laser the output power was stable and the Raman microscope was Calibrated against the 520 7 cm peak of Si Then a fresh SERS substrate Klarite was placed in the temperature cell on top of the Peltier element i e between the thermistor bead and the Peltier element The cell was closed and connected to a water cooling system water at ambient temperature ca 23 5 C and to the gas feeding system The temperature control system was set to maintain the substrate at ambient temperature 23 5 C An optical density filter was used to reduce the illumination power on the sample surface and subsequently about 8 mW was focused on the SERS substrate A spectrum was collected before any gas flow was generated A flow of 1 L min of instrument air which was used as carrier gas was applied and the gas system was checked for leakage using leakage detection spray As no leakage was detected a concentration of 5 isoflurane was applied the vaporizer was set to 5 but the monitor went off scale above 5 so the actual concentration was unknown but above 5 A few spectra were collected to determine appropriate acquisition time and number of cycles The temperature was then set to 3 C and was allowed to stabilize at that temperature An additional couple of test spectra were collected and the appropriate acquisition settings were determined to 20 s and 2 cycles a
71. time Low PWM frequencies will introduce larger temperature variations and higher PWM frequencies instead cause more rapid thermal cycling so there is no obvious ideal frequency for the PWM signal A study 18 shows that the level of degradation is rather constant between different frequencies and is overall small and thus not a serious reliability concern A PWM frequency preferably in the low kHz range should be used to avoid substantial temperature variations 17 UMEA UNIVERSITY 2014 06 12 Department of Physics 2 5 Proportional Integral Derivative PID Control PID control is a common way of controlling a process to reach and maintain a set point for example maintaining temperature in a closed environment The PID algorithm is based on a control equation see equation 11 which governs the output u t to the process based on the error e t between a process variable and a set point u t P 1 D Kye t Ki fy etdde Ka feet 11 Kp Ki and Kg are gain constants that determine the contribution from each part of the equation e t is the error function i e the difference between the current measured value of the process variable and the desired set point The proportional term P of the equation takes the current error into account The integral term I takes all errors up to the present into account The derivative term D estimates the future errors by the rate of change of the error function 19 One can use all three term
72. ubstrate was probably below 22 C viii UMEA UNIVERSITY 2014 06 12 Department of Physics Acetone 790 1 cm peak 5 degrees centigrade T T T T 1 0 minutes 6 minutes 120 14 minutes H 20 minutes Ad minutes Intensity a u 740 760 780 800 820 840 Raman shift cm Figure C 2 Analyses at 5 C Figure C3 below shows a spectrum collected at 5 C and after the SERS substrate has been heated to 45 C for comparison It can be seen that the acetone has been released from the substrate surface i e the characteristic acetone peaks are no longer visible perhaps with the exception of the 790 cm peak which can still be discerned Acetone 140 T T T 7 5 degrees centigrade 45 degrees centigrade 120 4 100 4 80 4 3 Ss 2 60 4 oa E o 20 1 H L L 1 1 200 400 600 800 1000 1200 1400 1600 1800 Raman shift cm 71 Figure C 3 Spectra at 5 C and at 45 C Although the temperature readings are not to be trusted due to the thermal contact problem it is clear that the cooling increases signal strength significantly and that heating releases the volatile substance from the SERS substrate which is showing that the temperature control cell is working as planned UMEA UNIVERSITY 2014 06 12 Department of Physics
73. ules 6 2 4 Pulse Width Modulation PWM smnsssrsrsssrrrrssrrrrsserressrresserrrrrrr ense r rn sar KR RAR RR REAR RR BARR RR REAR RR REAR RR Ra nn enn 7 2 5 Proportional Integral Derivative PID Control 8 2 6 Raman scattering process a brief OVervieW sssesssrerrssssesrsreressnserrsreres rn sens rr renar sr sr Ar ARR Banan nr en nn 9 2 7 Surface Enhanced Raman Spectroscopy SERS sccccccsssscccssssececeesececseaeeecsesaececsesaeeeeseaeeeeseaaes 9 3 Method and Equipment smssseessssesrerrrssseserrerrsesrorrrrsr er rs sans rs r rr kr s RAR RR RR RR RR RR KR KR RR RR KKR KR RR RR RR RK KR KR RR RR RASK KR KR Rn 10 IL Wie Eu TS1500 EE 10 3 2 Choosing Temperature Sensor Comparison between Thermocouples platinum RTDs and UA le 10 3 3 Installing Peltier module and Thermistor in the stage 12 3 4 Data Acquisition amp Instrument Control 13 3 4 1 Data Acquisition and Instrument Control Platform Arduino ccconcccoconncnnnnnonononnnnnnnnnnnannnos 13 3 4 2 Data ACQUISITION vicio ada 13 3 43 InStrument Contro lisissa n a e a ae ti 14 3 5 Tests of the Temperature Control Cell 18 3 5 1 Temperature Control System Test Experimental Procedure ccccccccccessssssssteeeeeeesessees 18 3 5 2 Test using Isoflurane Experimental Procedure rr rr rn nn r rr rr rr rasen nr 18 4 Results amp DISCUSSION 2 so0s0skassosrisennsnesnsnssdidrr nr rr SRS rs FRA stR aaa nene nen 21 4 1 System Description 21 4 1 1 The Modified Ee 21 EE Go al
74. ve and negative terminal and the thermocouple connector for the temperature sensor This had the consequence that four terminal temperature measurement was not an option As another consequence measuring the temperature of both the substrate surface and the surrounding gas inside the stage at the same time would be impossible without modifying the stage body with more contact leads As the temperature of the SERS substrate is prioritized measurement of the gas temperature would thus have to be made outside the stage in the feed The platinum RTD probably would not be the best choice of sensor in this case because of four terminal requirement for accuracy and slow response time Due to the resistance of the thermistor usually being several orders of magnitude higher than the resistance of copper lead wires the thermistor does not need four terminal measurements as platinum sensors do The resistance of the thermistor is also significantly higher than the resistance of the thermocouple connector in the stage This meant that the thermistor could be connected using the thermocouple connector without affecting the temperature measurements to a large extent As only two wire connection was possible accuracy and response time is important and differential measurements were unpractical in this case a thermistor seemed to be the most appropriate choice 1 Assuming a 6 feet long 18 AWG S type thermocouple connector wire the added resistance would be

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