E-STM Operating Instructions
Contents
1. then __4eeeach and repeat the seps in chapter Start measurement Cutting a new tip After a crash the tip with the sample or when scan lines start reproducing badly and consequently the image deteriorates you should proceed as fol lows Remove the magnifying cover from the scan head 41 PROBLEMS AND SOLUTIONS 42 Retract the sample holder first by using gaan then Remove the sample holder by hand Pull the tip out from under the tip holders carefully using a pair of sharp tweezers Carefully follow the instructions in chapter Preparing and installing the tip Repeat procedures in chapter M easuring graphite Z Offset does not change automatically In the default configuration of the easyScan E Line software the item in menu O ptions gt Auto Adjust Z O ffset is activated If the numeric value of Z O ffset in the Scan Panel does not alter slightly during scan Check that the option is activated T hescan lineisat oneof thelimits of thez range ncrease the value of Z Range Possibly the tip is at one of the limit positions of the z piezo Use Withdraw th en Approach TECHNICAL DATA Technical Data T he specifications given here are typical values of the N anosurf products T he exact specifications vary somewhat from instrument to instrument and are stored on the installation CD and can be found in the Calibration dialog see Software Re2. Please check that the mains voltage corresponds to that of the power sup ply 3 M akesurethat your mains connection is protected against excess voltage UN PACKING AND INSTALLATION HARDWARE INSTALLATION Choose a steady table where you can work undisturbed To ensurethe fault less operation of the STM it has to be kept away from vibrations heat emission and air current y m Casy Scan ir Put the STM scan head 2 onto the vibration isolation platform 6 Fix the scan head cable under the strain relief clip Connect the STM scan head to the easyScan E SPM electronics 1 Make sure your computer is turned off T hen connect the control elec tronics to a free serial port or RS232 or COM Port on your computer with the RS232 cable 4 If you are using the USB adapter for easyScan electronics DO NOT connect it now Connect the power supply 3 to the E SPM electronics and plugin the mains cable 5 Finally turn on the power supply Now the E SPM electronics and the microscope are connected and the LED on theE SPM electronics flashes SOFTWARE INSTALLATION UN PACKING AND INSTALLATION Software installation System requirements T he System requirements for the easyScan E Line software ae e PC with a Pentium 133 M H z processor or higher e afreeCO M Port or USB port e Windows 95 or higher 8 MB RAM or more 16 MB recommended e graphics adapter with 800 x 60
3. J If not you can Remove the sample and sample holder and pack up all parts The tip can be left in the scanner 35 First MEASUREMENTS FINISH MEASURING Store the sample holder in its container and check that the silica is still blue see chapter maintenance By storing the instrument in the suitcase it is protected from dust Simulta neously the rubber feet of the vibration isolation platform should be re lieved The damping capability may decrease with time 36 MAINTENANCE Maintenance To ensure the fault free operation of the microscope the following instruc tions for maintenance have to be followed Scan head It is very important to prevent the sample holder and the open part of the scanner from becoming dirty or damp e The sample holder is made of magnetic steel therefore it suffers from corrosion in ahumid environment To reduce corrosion and increase life expectancy the sample holder must be stored in its container together with the moisture absorbing silica container The container is waterproof but not airtight T he silica contains a blue indicator which turns pink when saturated It can be regenerated by heat ing the silica container 100 C for at least two hours until it turns completely blue again e f you touch the metal part of the sample holder or it does not move freely clean it with a soft cloth if necessary moistened with alcohol During cleaning move the cloth along the sample hold
4. i N ow your computer is communicating with the control electronics to ini tialise the system T his process is repeated every time the control electronics is turned off and on again W hen download is completed the electronic s red LEDschange from flashing to constantly shining the LED on thescan head shines orange and some control panels appear see figure M ain pro gram window N ow the system is ready to use FiRST MEASUREMENTS APPROACHING THE TIP Nanosurf easyScan E Line ioj xj File Panels Tools Options Window NM ZG Appr Scan Feed Spec View Datal Tooll Resut TD w 4 Rg H gt A view Panel xl Start Finish Up Down Zoom Full Move spec Photo DataType ForwardScan zl Apply Input ZOutput DI Delete ZOutput 0 128 128 Plane Topview LineMath Plane zl New ForwardScan ForwardScan Display TopView zl Visible Data Range Range 43 606nm E Full Difset 0 392nm a Optimize DI gt Feedback Panel x SetPoint 1 001nA E Apply P Gain D E Default l Gain fi3 E GapVoltage om E DI Position x Steps 0 Zero Z Range 200 000nm e TimeLine 0 200s Slope 0 00 5j Apply i SeanRange 200 00nm G Z Dffset 0 00nm Y Slope 0 00 5j t withdraw Rotation 0 0 5j x Dffset 0 00nm Measure Forward zl Se Approach Samples 128 a Y Dffset 0 00nm ScanDir Continous DE Simulation Default _E 5TM ezv Default_E STM ezs Uncal_E STM ezh E STM E
5. to 50nm in order to con centrate the measurement to this range ZPiezoControl 0 128 128 Raw LineView 2PiezoControl 0 128 128 Raw LineView ForwardScan ForwardScan 168nm 25nm 74 8nm ZPiezoControl 99 2nm ZPiezoControl nm Axis 499nm Diminishing Z Rang amplifies the sgnal in Z direction 2 Limit the scan range click the TopV iew D isplay to make sure that it is active its titlebar is the same colour as the main bar 26 ACHIEVING ATOMIC RESOLUTION First MEASUREMENTS click Zeom The mouse pointer becomes a cross and the Tool Info Panel opens look for a flat region similar grey values in TopView and makea square there with the mouse pointer The size of the square is dis played in the Tool Info Panel Output 0 128 128 Plain TopVview Arm GE Hin a i r ON pgg HEH a CH P Release the mouse button when the squares size is about 30 50nm Confirm your selection by double clicking on the display using the left mouse button C onsequently the selection is enlarged to the whole display size You can abort the zoom function by clicking with the right mouse button UJ Atomic arrangements can normally be made out at a ScanR ange of about 4 nm and at a Z Range of about 1 5 nm Enter these values in Scan Panel one after the other Play with these values they can be reduced even further Between cha
6. TopView ForwardScan E h ZOut put 1 56nm rm X Axis 3 91mm f thescan linesin LineView areunstableand theimagein the TopV lew iS not sharp ZOutput 0 128 128 Raw LineView ForwardScan ZOutput 0 128 128 Plain TopView For war dScan 12 Drm ZOut put ZOutput 25mm 2 Don The graphite surface In a good top view image of graphite you will see a pattern consisting of white grey and black spots It looks like a three dimensional image of balls lying next to each other but be careful these are not the single atoms To Interpret the image correctly you must first be aware that bright spots show high points and dark spots low ones except in LineM ath D erive In the lattice model of graphite one can see that there are two different positions of the carbon atoms in the graphite crystal lattice One with a neighbouring atom in the plane below grey and one without a neighbour in the lattice below white Asa consequence the electrical conductivity of the graphite surface varies locally slightly so that the atoms without neigh bours appear higher than the others MEASURING GOLD First MEASUREMENTS ees 0 14nm Graphite surface left measurement right lattice moda T his also causes the lattice constant between the bright hills to have the higher than normal value of 0 25nm Measuring Gold It is more difficult to obtain good images of a gold Atomic str
7. c have been cleaned with ethanol Touch the Pt Ir wire 8 e with these tools only hold the end of the wire firmly with the pliers and cut a piece off approxi mately 5mm long Still holding this piece of wire with the pliers place the cutters at the free end as obliquely as possible See picture below Close the cutters until you can feel the wire then pull in the direction shown below T hetip needsto betorn off rather than cleanly cut through in order to get the required sharp tip write pulling and cutting S direction half round pliers wire cutter PREPARING FOR MEASUREMENT PREPARING AND INSTALLING THE STM TIP Important e Never touch the tip end with anything e T he golden tip holders in the open part of the scan head are very delicate and not to be twisted or lifted too high Hold the wire with the tweezers behind the freshly cut tip Insert it carefully under the golden tip holder clamp in the scan head without twisting them see figure mounting the tip 1 Hold the tip wire under a slight angle and move it over the groove against the first clamp so that the end of the wire is under the clamp figure a 2 Lower the wire so that it lifts the first clamp 3 Push the wire in until it touches the second clamp d Lift the wire a E a M ounting the tip PREPARING THE SAMPLE PREPARING FOR MEASUREMENT 5 Push the end of the wire below the second clamp figure b 6 Lower t
8. o o 3 a l i O H X Approaching the tip To start measuring the sample must be very close to the tip to enable a tunneling current to flow Approaching the sample without touching the tip is a delicate operation carried out in three steps The LED on the scan head tells you about the distance between the tip and the sample LED orange z piezo fully extended toward the sample the distance is too big not tunneling current can be detected LED red Z piezo fully retracted T hetip touched or crashed into the sample the tunneling current is too high LED green Z piezo within the measuring range tunneling cur rent should be flowing 1 Coarse approach by hand Push the sample holder figure components 8 f carefully to within Imm distance of the tip 20 APPROACHING THE TIP FIRST MEASUREMENTS If necessary try turning the sample holder around its axis so that the tip points towards a mirror like area of the sample Put the magnifying cover 7 over the scan head without touching the sample holder place the magnifier so that you can see the mirror image of the tip in the sample T he cover reduces air flow around the scan head and reduces thermal drift in measurements at atomic scale 2 Fine approach by piezo motor Open the Panels menu in the easyScan E Line program window Select the Approach Panel Watch the distance between tip and sample with help o
9. 0 resolution and 16 bit colours high color or better resolution of 1024 x 768 recommended The Nanosurf USB Adapter for easyScan option must be acquired to use the USB port Installation Procedure Turn on your computer and start W indows Do not run any other program while installing the scan software If you are using the U SB Adapter for easyScan Install it first according to the instructions included with the adapter Insert the backup copy of your E LineCD Windows NT 2000 XP Make sure you have administrator privileges before installing the soft ware All operating systems Start the setup exe program on theCD T he following screen will now appear UN PACKING AND INSTALLATION SOFTWARE INSTALLATION WB easyScan E Line Yo C e nanoSurf v2 0 0 Welcome xj Message pa This program will install the E easyScan E Line Programm onto your computer Disk space needed 3280 kB i Don t Install Help Select the button Install to install the data acquisition program easy Scan on your computer Setup will ask for the directory in which the program files are to be copied Target Directory x Message OK BS Please enter the directory where the easyScan E Line files should be copied into SEH To accept the default click OK Help C Program Files N anosurf easyScan E Line Browse Put them in the proposed direct
10. F IMAGES First MEASUREMENTS Snapshots of images W hen you are satisfied with your image and would like to keep It you can take a snapshot and save it for later During the measurement you can select Photo in the ScanPanel After having completed the actual frame a copy of the measured Image is taken and displayed in a separate window behind the ScanPane If you would like to take the snapshot of the view as it appears during the measurement without waiting to finish the frame stop the scanning us ing step and generate a copy of the view using Protal After finishing the measurements you can store the photographs of your measurements in a storage medium eg your PC s hard drive see section Finish measuring STM Measurement modes T he surface can be scanned in two different ways in the Constant current CC and Constant height CH mode In the CC mode default setting the tunneling current is kept constant by the feedback loop and the movements of the tip by the z piezo are re corded This height profile is displayed in a LineView and the topo graphic image is displayed as a grey scale coded TopView T hetunneling current is not only dependent on the real topography but also on the local density of the electrons T his fact has to be considered when analysing the recorded images the images are always superimposed and the electronic structure of the surface In CH m
11. Yet Operating Instructions easyScan E STM Veson 2 0 TEXT amp Layout KARIN Hoot R Sum PIETER VAN SCHENDEL ENGLISH Vicky CONNOLLY NANOSURF AND THE NANOSURF LOGO ARE TRADEMARKS OF NANOSURF AG REGISTERED AND OR OTHERWISE PROTECTED IN VARIOUS COUNTRIES June 2003 sy NanosurF AG SWITZERLAND Prop BT00655 R 0 2 Table of Contents Introduction What is STM ssesccscensctthccdactennaidesaiadandadeieeeebaacnsadeecdncsseacnces Scanning with the EGIM Un packing and Installation Unpacking the instrument cccccecsesseeeeeeeeeeeeeeeeeeeeans Hardware Installation ccccececcececececececeeaeeecececenaeenens Software installation EE System requirements Installation Procedure Simulated microscope Preparing for Measurement Preparing and installing the STM mp Preparing the sample ccccceseeeccesseeeeeceeeeeeeseeeeeessaaees Installing the sample cccccseceeeceeseeeceseeseeeeeeeseeeeseees First Measurements Starting the MICFOSCOPE cccccececeseeeeeeceeeeeeseeeeeeeeeeeees Approaching the Up hice nara e cen oriri anria aiis 1 Coarse approach by hand 2 Fine approach by piezo motor 3 Automatic approach Start measurement ceeeeeeceececeeeeeeeseeeeeeeeeeeeeeeeeeeeeeaas Adjusting the sample s tilt coordinates ceeseeeee Achieving atomic resolution cccccseeeeeecsseeeeeseeeeeeeens Snapshots Of IMAGES sece
12. an active numerical input can be entered using the key board T he entered value must be confirmed by pressing the Enter or Return key or by clicking with the mouse pointer T heselection of a drop down menu eg 100 can be changed using the mouse T he selected value must be confirmed by pressing the Enter or Return key or by clicking with the mouse pointer 3 Automatic approach Click L rman in the Approach Panel 22 START MEASUREMENT First MEASUREMENTS Approach Panel Ei Position Steps withdraw Approach gt T he sample holder is now moved towards the tip with the help of the piezo motor until thetunneling current entered under SetPoint is detected N ow the distance between sample and tip is controlled by the feedback loop If the approach was successful the LED on the scan head changes from or ange to green and the message box Approach done appears Click the O K button N ow the set tunneling current is flowing between tip and sample When the LED changes to red instead of green the sample has crashed into the tip and the tip has to be cut again See chapter Problems and Solutions Start measurement W hen the tunnding current defined by SetPoint is flowing between tip and sample LED green you can start measuring Click eu in the Scan Panel to maximize the range of the scan Start measuring by clicking s
13. ccecccceeeeeeeseeeeeseeeeeeeeeeeeeaeees STM Measurement modes nnnnnsnnenonnnnnnnnnnennsnnnnnnnnnnnne Judging the quality of the images oo0nnnnnnnnnnnnnnnnenennnnn The graphite Surface c cccccccssseeeeceeseeeeceeeeeeseeesseeeees Measuring Gold cc cccccccceccseeseeeeseeceeeeeeseeseeeeeeeeeeeeeeeeees Pell Pls mMmeasSUrNG RE Turning off and storing the instrument Maintenance Scan head Scan electronics Problems and Solutions Technical Data 4 EE 4 INTRODUCTION Wuar is STM Introduction This manual gives instructions on how to set up and use your N anosurf easyScan E STM system Theaim isto help people who don t have a good knowledge of physics to get pictures of atomic resolution easily T his intro duction chapter gives some general information on the scanning tunneling microscopy technique and its implementation in the easyScan STM The next chapter Un packing and Installation should be read when installing your easyScan system The chapters Preparing for M easuranent and First M easurenents should be read by all users as they contain useful instructions for your everyday measurements The other chapters give more informa tion for advanced users T hose who need a more detailed description of the functions of the easyScan software should refer to the Software Reference manual What is STM Microscopy is one of the most exciting scientific techniques The insight into small dim
14. de the following precautions must be taken to keen equipment dust and grease free e N ever touch ether the wire for tips figure components 8 e the sample 8 g nor the open part of the STM scan head 2 with your fingers e Only touch the sample holder 8 f at the black plastic end Unpacking the instrument Before unpacking the instrument suitcase check for the following items Components T he easyScan DFM systen HARDWARE INSTALLATION UN PACKING AND INSTALLATION 0O N OU BR WN kW easyScan E SPM electronics STM scan head Power supply LPS 1 RS232 cable between computer and control electronics Mains cable Vibration isolation platform Magnifying cover with 10x magnifier Tool set containing a wire cutter k half round pliers pointed tweez ers d rounded tweezers e 30 cm Pt Ir 0 25mm wire for tips fz sample holder sample set HOPG graphite gold thin film three empty Sample supports easyScan E Line CD containing the easyScan E Line software this manual software reference manual atest sheet and a sheet with the calibration information aCase for storing and transporting the instrument Additionally the following material is needed that is not included with the contents of delivery A computer that meets the requirements described in the section Software Installation e Solvent to clean the tools eg ethanol acetone Hardware Installation Important
15. direction viewed from top SCANNING WITH THE E STM INTRODUCTION Datatypes 2 Views 2 ZOuUtputO 256 256 Raw Lineview ZOutput 0 256 256 Plane Topyview ForwardScan ForwardScan Scan images of graphite as views from the sde and the top The sample can also be scanned in a second mode When the feedback loop is lowed down very much P Gain 0 Gain 2 the tip scans at a fixed distance from the sample constant height mode T his time the vari ations in the tunneling current are measured and drawn line by line on the computer screen H owever thismodeonly works when thesampleis atomi cally flat because the tip would otherwise crash in to the sample What is so special about the Nanosurf easyScan E STM TheE STM was designed to allow people without training as a physicist to do experiments in the world of atoms Its design is compact simple and comfortable to operate With the E STM it is possible to do any STM experiment which can be carried out in air The special sample approach system allows simple handling of samples and tips whilst at the same time providing maximum stability of the tip sample distance All functions can be carried out using acomputer and the E Line software UN PACKING AND INSTALLATION UNPACKING THE INSTRUMENT Un packing and Installation T his chapter describes the installation of the N anosurf easyScan E ST M Important To enable measurements of atomic resolution to be ma
16. ed when e g the upward scan is very different to the downward scan showing two differently distorted lattices Consquent upward and downward scan howing thermal drift Thermal drift is very clearly perceptible on an atomic scale Variations of 1 10 C already cause variations in the length of e g the sample holder steel of several nanometers To decrease thermal drift keep the measurement running for some time to let the system stabilize up to about one hour 30 JUDGING THE QUALITY OF THE IMAGES FIRST MEASUREMENTS If during a good measurement the image quality diminished dramati cally the tip has most probably picked up some particles or you are near a step in the surface ZOutput 0 128 128 Plain TopVview ForwardScan ae See Problems and solutions mage quality suddenly deteriorates In the following cases the tip has to be replaced i e cut freshly in order to establish a stable tunneling contact and high image quality e f images in top view consist of only of uncorrelated lines ZOutput 0 128 128 Raw LineView ForwardScan Forwardscan ES 25nm gege ZOut put 25nm nm rea Arm ZOutput 0 128 128 Plain LineView ForwardScan pe el a J CH wN 1 56nm 31 First MEASUREMENTS THE GRAPHITE SURFACE 32 e f each image looks different Datatypes 1 Views 2 ZOutput 0 128 128 Raw LineView ZOutput 0 128 128 Plain
17. ensions has led to a new understanding of the structure of materials and forms of life W ith the help of the scanning tunneling microscope ST M it is possible to look into the fascinating world of the atoms T his completely new micros copy technique works without focusing elements and features atomic reso lution laterally and vertically T he Scanning Tunneling M icroscope was developed by Gerd Binnig and Heinrich Rohrer in the early 80 s at the IBM research laboratory in Ruschlikon Switzerland For this revolutionary innovation Binnig and Rohrer were awarded the N obe prize in Physics in 1986 In the STM a small sharp conducting tip is scanned across the samples Surface so close that the so called tunneling current can flow With the help of that current thetip surface distance can be controlled very precisely T herefore an enormous resolution is achieved so that the atomic arrange ment of metallic surfaces can be probed SCANNING WITH THE E STM INTRODUCTION To be able to get such excellent pictures of atomic resolution is almost in credible considering that the size of the atom in relation to thetip isthat of a golf ball to a mountain Scanning with the E STM In the E ST M two tiny springs clamp a platinum iridium tip onto a plat form which can be moved In three dimensions using piezo crystal transla tors that are driven with sub nanometer precision Sampleholder Backwardscan SSS Forwardsca
18. er in the axial direction do not move it around its circumference 37 MAINTENANCE e Clean the sample holder guide bars see picture above the surfaces of the piezo motor and the tip holder with a cotton swab if necessary lightly moistened with alcohol ensure the tip is renoved when doing this Scan electronics Clean the cabinet and the controls with a soft cloth lightly moistened with a mild detergent solution Do not use any abrasive pad or solvent like alco hol or benzine 38 PROBLEMS AND SOLUTIONS Problems and Solutions No connection to microscope easySCan communication Error x IN No connection to microscope Check power supply and seral cable connection Start Simulation Config COM Patt T his error message appears when the scanning software is waiting for an answer from scan electronics T his can have various reasons e T he microscope is not connected If you wish to perform a simulated measurement select _StattSimuiation O therwise check the connection and select maen e T he easyScan SPM electronics is not connected to the power supply check that the power LED s on the electronics are on check the connection e T he easyScan SPM electronics is not connected to the computer check the connection e T he wrong CO M port has been selected during software installation Use LenfiacoM Pott and select the correct CO M port in the dialog COM Port Configurati
19. f the magnifier N ow click Jin the Approach Panel to move the sample towards the tip to a distance of a fraction of a millimetre You should only just be able to see the gap between the tip and its mirror image the sample T he smallest visible gap depends somewhat on the obser vation angle of the magnifier Approach Panel x Position Steps Withdraws Approach gt 21 FIRST MEASUREMENTS APPROACHING THE TIP Open the Feedback Panel in the menu Panels Feedback Panel Ei SetPoint Dome f Pasin j2 El Defaut l Gain Dm H GapVoltage num RS gt Ensure that the following parameters are set correctly e the SetPoint tunneling current on approx 1 00nA e the GapVoltage tip sample voltage on 0 05V e the P Gain on 12 and the l Gain on 13 feedback loop param eters W hen you have to change the instrument settings in any panel you can use any of the following methods to change them e Activate any input by clicking in it with the mouse pointer or by select ing it with the Tab key e T he value of an activated input can be increased and decreased using the up and down arrow keys on the keyboard T he new value is automati cally used after one second e The value of a numerical input can also be Increased and decreased by clicking the arrow buttons with the mouse pointer T he new value is automatically applied after one second e The value of
20. ference Scan ranges and resolution M aximum XY Scan range tyo 0 5um 1 um optional Maximum Z range 200 nm D rive resolution Z 0 003 nm D rive resolution XY 0 015 nm gap voltage 10V in 5mV steps Set point current 100nA in 25pA steps sample size max 10mm diameter T he exact values are dependent on the calibration of the piezo elements D rive resolution is calculated by dividing the scan range over 16 bits easyScan electronics M ax scan speed 1800 data points per second feedback loop bandwidth 3 kHz Additional User ADC Input O ption available 43 TECHNICAL DATA yoeoiddy 7 je E 2 JOP OH diL peay ues NLS 3 Hvara 9 abeyon dey sare FRO 8 21 p ds yoeoiddy NVH WOU Adoosos9edS yoeoiddy yoeqp 4 Z cecsSy ueoS Ado SIXW Z A X lt t lt Cova a94 91607 gen Boud wojsn Liz 1z oa S HG 0 JeuueyD SOIUOIINBIF dS GUTT ueoSAsee Od SOH 44
21. he Z Range to 12nm or less Evaluate your measurements in the same way as you did with the graphite images Zoom measure save etc FINISH MEASURING First MEASUREMENTS Finish measuring To stop a measurement click st By clicking wiw 1 and then clicking _ Jin Approach Panel you can retract the sample holder to a safe and visible distance from the tip Close all panels in order to see the saved snapshots Activate the snapshot that you would like to save by clicking onto the image Select the menu File gt Save as Select the name and the folder you would like to store the image in T hese stored images and all the corresponding data can be opened with the easyScan E Line software viewed analysed and printed any time see also Software Reference Turning off and storing the instrument Exit the easyScan E Line program after having stored all desired images If you leave the program without saving some data the program asks if you really do not want to save them SE d AN Save changes to ezDatal No Cancel If however you would liketo save some images use leave the program with pe Disconnect the power supply from the mains supply If you perform measurements regularly leave the instrument with the cover over the scanner to protect it against dust If you do not operate the instrument for several weeks you should put it back into the instrument suitcase
22. he approach with a new tip If the approach fails again reduce Steosize further Save the best Steosize value using menu File gt Parameters gt Save 40 PROBLEMS AND SOLUTIONS Image quality suddenly deteriorates e When a scan line suddenly starts reproducing badly the tip may have picked up some particles or it is scanning close to a deformity in the sample s surface Continue measuring for a while 4 5 images eventually the tip loses the picked up material again Increase the scan range and zoom into a new flat area You can try to induce changes at the tip s end W hile measuring in crease the gap voltage in the Feedback Panel to 2V then reduce it to the old value again You can also induce changes of the tip s end by increasing the tunnel ing current to 20nA for ashort time then reducing it to its old value again Retract the sample using waa then perform anew approach If no Improvement can be seen after going through these procedures you have to prepare a new tip Did the scan linein the LineV lew suddenly disappear and the LED on the scanner turns orange the tip has lost contact U se Speech in the Approach Panel then repeat the steps in chap ter Start measurement e If the LED flashes green orange while measuring then the tip is losing contact from time to time and the tunneling contact is very unstable Click L wira in the Approach Panel
23. he wire so that it lifts the second clamp 7 Push the wire below the second clamp figure c T hefreshly cut tip should be well held under the clamps and reach about 2 3mm beyond the tip holder T he tip is now installed Preparing the sample TheSTM can only examine electrically conductive materials N evertheless the choice of material is rather small because the surface of the sample must not oxidise betotally clean and mirror liketo obtain useful results Because of this some of the samples need special preparation Gold thin film Cleaning the sample is neither possible nor necessary N ever touch the sam ple with your fingers or put it upside down anywhere this will only make it unusable faster Graphite T he surface of the graphite sample should be cleaned every few months D ueto the layered structure of graphite this can easily be done using apiece of adhesive tape see pictures below Put the sample on the table using the pair of tweezers Stick a piece of adhesive tape gently to the graphite and then pull it off again T he topmost layer of the sample should stick to the tape PREPARING FOR MEASUREMENT INSTALLING THE SAMPLE Remove any loose flakes with the pair of tweezers T he graphite sample is now ready for use and may not be touched with the fingers Installing the sample Important Always store the sample holder in its package in order to prevent corrosion see chapter M aintenance Unpack
24. line X Slope in the LineView middle line of the LineView Tan An i view i with ration 0o Tilt Samples and measurement orientation before tilt adjustment ADJUSTING THE SAMPLE S TILT COORDINATES First MEASUREMENTS T his slope depends on the fast scan direction and therefore on the rotation of the measurement as shown in figure Tilt position A and B It isdesirable that the measurement plane is parallel to the sample plane because this makes it easier to see smaller details in the measurement and because the z feedback loop can function more accurately in this case T herefore the sample plane should be made parallel to the sample plane by properly setting the values of X Slope and Y Slope You can align the measurement plane with the sample plane using the fol lowing procedure Alter the value of X Slope using the arrow buttons until the x axis of the scan line lies parallel to the x axis of the sample You can measure the slope in the LineV iew using the angle tool see Software Reference Enter the value 90 in the Rotation input to scan along the y direction of the scanner i e the sample s tilt as shown in the schematics view B If the input for Rotation is not visible you can make it visible by clicking zi TT j x stop Finish Up Down Zoom Full Move Spec Phato Datatypes 1 Views 2 ZOutput O 1 28 128 Raw LineView ZOutput 0 1 28 128 Raw To
25. n INTRODUCTION SCANNING WITH THE E STM T he sample to be examined approaches the tip within a distance of 1 nano meter Inm 1 1 000 000 000 m Classical physics would prohibit the appearance of electrons in the small gap between a tip and a sample but if a sharp tip and a conducting surface are put under a low voltage U 0 1V a very small tunneling current 1nA may nevertheless flow between tip and sample T his tunneling current is due to a quantum physics effect The strength of the tunneling current depends exponentially on the dis tance between the tip and the sample usually referred to as z distance This extreme dependence on the z distance makes it possible to measure the tip sample movement very precisely O ne of the three piezo crystals the Z piezo can now be used in a feedback loop that keeps the tunneling cur rent constant by appropriately changing the z distance To obtain an image of the sample the tip is scanned using the x and y piezo crystals T he feedback loop will now let the tip follow the structure of the sample s surface A height image can now be made by recording the position of the z feedback loop as a function of the x y piezo position T his landscape or topography of the atomic surfaceisthen drawn on thecom puter screen line by line const T he feedback loop maintains a constant tunnding current bewen thetip and the sample during motion in the x direction by changing the z
26. nges always al low the computer to scan the picture a couple of times before con tinuing Pay attention that the height of the signal in the LineView window does not exceed the window height If this happens the z R ange is set too small and should be increased Consider that one nanometer is the diameter of between four and eight atoms 27 First MEASUREMENTS ACHIEVING ATOMIC RESOLUTION 4 Some parts of the scan head react to the slightest temperature changes As thesethermal movements influence the measurements on the nanometer scale the sample has to be scanned as fast as possible Set the Time Line in the ScanPanel to 0 06s for atomic resolution x DataType Forward can sl Input ZOutput sl Delete LineM ath AEDE New Display Topiea M Visible Data Range Range oe um S Eull Offset 0 020um H Optimize gt View Pang If the contrast in the Top View window is too large or too small open the View Panel see figure and select Heime in the Visible Input Range section You can also set the contrast manually using Range and Offset See Software Reference Section View Pand for more information Datatypes 2 Views 2 ZOutput 0 256 256 Raw LineView ZOutput 0 256 256 Plane Topview ForwardScan ForwardScan E F gt gt Nex a O N E E bai CH Onm xis Good images of a successful measurement 28 SNAPSHOTS O
27. ode the scanning tip does not follow the samples corrugation This time the strength of the tunneling current is measured This can be achieved by turning the feedback loop off But then no thermal drifts in Z direction can be compensated for and tip crashes can not always be avoided T his problem can be avoided by setting the feedback parameters to very low values 1 or 2 so that the feedback loop can follow theslow movements caused by thermal drift of the sample T hese are very small compared to the sample s corrugations To measurein CH mode 29 FIRST MEASUREMENTS JUDGING THE QUALITY OF THE IMAGES set P Gain to 0 and l Gain to 2 In Feedback Panel apply these new values by using La to visualize the current information choose Current as input in the View Panel Notice that Z Range is now called InputRange and the corresponding axis is labelled nA instead of nm when displaying a TopView image use in ViewPanel Visible Input Range Hemze in order to enhance the images contrast Judging the quality of the images From the quality of the measured images the quality of the tip and conse quently that of the tunneling contact can be observed A good tunneling contact is necessary for high quality images of atomic resolution e f temperature variations are present they cause so called thermal drift Consequently the images are stretched T his effect can be observ
28. on i xX easvS can Electronics connection COM Port mAg e T hescan electronics is performing a task which lasts an unforeseen length of time causing a time out Using Windows NT this can happen when the system is occupied with itself and blocks the serial port 2 Use Try again 39 PROBLEMS AND SOLUTIONS e T he electronics is damaged Contact your dealer Sample holder moves too slowly stops sometimes If the fine approach using and tr is affected Clean the sample holder guide bars and the surfaces of the approach motor following the procedure described in chapter M aintenance Approach is too slow stops sometimes Clean the sample holder guide bars and the surfaces following the proce dure described in chapter M aintenance Let the parts dry sufficiently If cleaning was no improvement open the Approach Range extended configuration using zl Increase the value of Stepsize and click ae N ow the motor moves the sample holder with larger steps during automatic approach Save the new value for Stepsize using menu File gt Parameters gt Save Tip often crashes into sample during Approach In this case the motor moves the sample holder with too bigger steps to wards the tip Open the Approach Panel s extended configuration using zl Decrease the value Stepsize in Automatic M oveC onfiguration by about 10 and click _ Aree Repeat t
29. ope You can start the easyScan software without having the microscope con nected to your computer We recommend using this simulation to explore the easyScan system measurements and software off line W hen the simulate microscope mode is started the following dialog box appears easyScan communication error x Ku No connection to microscope Check power supply and serial cable connection Start Simulation Config COM Pott i By clicking Start Simulation a simulation of the microscope is started This imitates most of the functions of the real microscope T he sample is replaced by a mathematical description of a surface You can now follow the instructions in the chapter First measurenents To explore the system in the Simulate M icroscope mode with the micro scope connected activate it in the menu O ptions SOFTWARE INSTALLATION PREPARING AND INSTALLING THE STM TIP PREPARING FOR MEASUREMENT Preparing for Measurement Preparing and installing the STM tip The STM tip is prepared and installed by you This is the most difficult part of your preparations It usually needs patience and some practise to get the first good tip O nly an accurately cut tip enables optimal measurements T herefore cutting and installing snould be carried out with great care First ensure that the cutting part of the wire cutters figure components 8 a the half round pliers 8 b and the pointed tweezers 8
30. ory unless the Program Files directory has a different name in your language of the W indows operating system Afterwards setup will ask for the start menu entry or program group in which easyScan is to be placed SOFTWARE INSTALLATION UN PACKING AND INSTALLATION Start Menu Entry x Message K BS Please enter a name for the start menu entry bs To accept the default click OK to hold the icons for easyScan E Line Cancel easyScan E Line sl Accept the proposed name by clicking O K or type another name T he installation setup will now ask for the COM Port Serial Port Selection xi Select the serial port where the easyScan Electronics is plugged into COM Part Select the serial port to which you have connected the E SPM electronics See section hardware ingallation figure components 1 T he setup program will start copying files onto your hard disk After successful installation you will get this confirmation Installation Completed x Message BS easyScan E Line has been installed successfully but we need to restart Windows for the changes to take effect i Stay here Help Important The E Line software CD delivered with the instrument contains calibra tion information specific to your instrument therefore you should there fore always keep a backup copy of the CD delivered with the instrument UN PACKING AND INSTALLATION Simulated microsc
31. pView ForwardScan FornwardScan Z Blange 50 000nm E Time Line 0 160s G Slope 2 00 E ScanRange 500 00nm Z Diffset 30 98nm eI Y Slope A BU E Rotation 0 0 E Offset 0 00nm SG Measure Forward DI Meas Te ChO 1 Samples 128 E Y Dttset 0 00nm E ScanDir Continous D C Chi 2 Scan pand after adjusting the dopes 25 First MEASUREMENTS ACHIEVING ATOMIC RESOLUTION If the scan line is not horizontal alter the value for Y slope until the y axis of the scan lies parallel to the y axis of the sample Reset the Rotation to 0 The LineView shows the X slope again T he value of the Z O ffset varies slightly during measurement T his is cor rect because the option Auto Adjust Z O ffset in the menu O ptions should be active Achieving atomic resolution You prepared your measurement so that the scan line in the centre of the LineV lew is reproducing stably Now the scan range has to be reduced and the measured signals amplified in order to observe the atomic struc ture Reminder M easurements on the nanometer scale are very sensitive D irect light fast movements causing air flow and temperature variations near the scan head can influence and disturb the measurement It is best to let a promising measurement run for some time to let it stabilize thermally T he following settings apply to measurements on graphite 1 Reduce the value of Z Range in ScanPanel
32. tat in the Scan Panel If the preparation of tip and sample and the approach were successful images of the measurement will show alinein the LineV iew figure gart ing picture left and aplanein the TopV iew Watch the displays for awhile until the TopV iew image has been drawn about three times A nervous line in the LineV iew indicates a bad tunneling contact figure garting picture right Usually this is caused by the tip being too blunt or instable T his means that you should stop measuring and cut a new tip Click ze and follow the instructions of the chapter Problems and Solu tions 23 First MEASUREMENTS ADJUSTING THE SAMPLE S TILT COORDINATES 24 ZOutput 0 128 128 Raw LineView ZOutput 0 128 128 Raw LineView ForwardScan ForwardScan 168mm 14mm ZOut put ZOut put 1 8nm 188nm Anm Kx 499nm Anm Kx 496nm Starting picture left a good LineView right a nervous LineView If the line in the LineV iew is calm and reproduces consistently you can continue with the next section Adjusting the sample s tilt coordinates Ideally the plane of the measurement and the sample s surface should liein the x y plane of the scanner But mostly the sample plane is tilted with respect to that ideal plane In this case the sample cross section in the x measurement direction as shown in the LineView window has a certain slope Y Slope WT scan
33. the sample holder figure components 8 f touching only its black plastic handle Put the prepared sample onto the magnetic end of the sample holder using a pair of tweezers See below Place the sample holder carefully in the scan head so that it doesn t touch the tip see above Put the sample holder down on to the guide bars first and release it gently on to the approach motore support STARTING THE MICROSCOPE First MEASUREMENTS First Measurements All the preparations are now done TheSTM isassembled the software and a tip are installed and the graphite sample is ready In this chapter step by step instructions are given on how to operate the microscope and get your first pictures M ore detailed explanations of the software and the system are given in the software reference Important Never touch the sample s surface or the tip Good results depend strongly on the accuracy of the preparation of the tip and the sample Thetip must never comein direct contact with the sample T his damages the end of the tip and it has to be cut again Starting the microscope Check if the power supply figure components 3 is connected to the AC mains power and turn It on Thered LED of the E SPM electronics 1 flashes Start the data acquisition easyScan E Line software on your computer The main program window and a message box appear Process window E Downloading firmware to easyScan Electronics
34. uctures are difficult to observe because the electrons on the surface are much more homogeneously distributed unlike graphite But with sometraining the mono atomic gold steps can be observed d nanosurfteasyscan aul 69646 ezd Datatypes 1 Views 2 ZOutput 0 256 256 Plain Linevie Output 0 256 256 Plain TopVview 33 Eer MEASUREMENTS MEASURING GOLD 34 D ueto the fact that the gold sample cannot be cleaned by smplemeansit is possible that with time contaminants may prevent you obtaining good re Sults Tip Before you do any experiments with the gold sample it is necessary to prac tise on the graphite sample You should also test the quality of your tip using the graphite sample Proceed as you did with the graphite sample preparation amp slope com pensation but there are two exceptions to note select a gap voltage between 0 3 0 5V x Feedback Panel x SetPoint Dome f P Gain Di H Default l Gain e E GapVoltage num RS gt increase the value of parameter TimeLine to 0 3sin the Scan Panel If you do not get stably reoroduced scan lines you should look for another clean measuring spot First try with geen followed by rean If that does not change much retract the sample holder and rotate it a little by hand Repeat the approach If the image reproduces stably decrease the Z Range to 50nm and select a ScanR ange between 200 and 300nm N ow decrease t
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