Titan condenser manual
Contents
1. Titan 26 Condenser manual Version 1 0 6 Some frequently asked questions 1 I have changed the FEG settings What should be re aligned Only the full gun alignment should be performed Please note that it is not needed to re align the condenser 2 In TEM a beam shift is observed when going parallel to condensing mode and vice versa Should the condenser be re aligned First it should be checked that the C2 aperture is well aligned in C3 off mode and that the gun shift is well aligned When this does not help the condenser alignment should be re aligned 3 select TEM for parallel illumination but whatever do with the Intensity knob the illumination is always spreading You are using spot 1 The Titan beam current is limited to 150 nA At spot 1 it is potentially possible to get more than 150 nA at the specimen with parallel illumination Therefore the software forbids this mode Try spot number 2 or 3 4 can illuminate 50 um parallel with spot 4 but not with spot 3 What is happening The Titan beam current is limited to 150 nA When you are using spot 2 and 50 um parallelly illuminated area it is potentially possible to get more than 150 nA at the specimen Therefore the software forbids this combination 5 want to illuminate 100 nm homogeneously but the intensity is varying by 30 over the field of view Probably you are using the 100 um or 150 um C2 aperture and looking at the effect of the spherical aberration2. SKK paralle 00000000000000000000000000 23 Version 1 0 parallel 00000000000000000000000000 parallel 00000000000000000000000000 DER AV B 0000 h condensin p 90000000000 900000000000 D I IL condensing 00000000000000000000000000 Specimen illumination in TEM mode The apparent C2 aperture is indicated by the blue edges When C2 C3 is zoomed the size Daper of the apparent C2 aperture changes and the size D of the parallelly illuminated area is varied When the user selects an area outside the range of parallel illumination the beam switches to spreading mode or condensing mode and the non isoplanatism angle 8 becomes non Zero The sketch above shows that both in spreading and in condensing mode the non isoplanatism angle depends linearly on the size of illuminated area B Daper D 2h The next graph shows the non isoplanatism for four settings When the 150 um C2 aperture is replaced by the 50 um C2 aperture the non isoplanatism and the diameter of illuminated area reduce by a factor of three Of course the current density does not change but the total current reduces by a factor of nine Titan 24 Condenser manual Version 1 0 100mrad 5 3 a a Y 10mrad a O 1mrad Om C2r mier oprobe 0 1mrad AF Fiano E robe gt 150un re nanoprobe A Song C2 microprobe 150um C2 microprobe 1nm 10nm 100nm 1um 10um 100um illuminated area 10urad Non isoplanatism as a f
3. Titan 14 Condenser manual Version 1 0 3 4 3 Convergence zoom y g y A lt aa MS Be a C2 2 opere Changing the position of the intermediate image between C2 and C3 changes the convergence angle in Probe mode b Zs Changing the position of the intermediate image between C2 and C3 changes the diameter of the beam at the C3 lens and through this the convergence of the beam at the specimen in Probe mode see figure on previous page The user can vary the position continuously The software takes care that C2 and C3 are simultaneously changed such that the probe remains focused The intermediate image between C2 and C3 does not necessarily have to be a real image It is also possible to use C2 and C3 as a zoom system with a virtual intermediate image Then the beam is zoomed between C2 and C3 from diverging to converging The zoom range with a real intermediate image is much larger than the the zoom range with a virtual intermediate image Therefore the first option is called large range mode and the latter option is called the normal range mode Titan Condenser manual TS Q WP Y N eee Vy d SO HE ae Ts ill 15 Version 1 0 fr ie Left in the large range a real intermediate image exists between C2 and C3 Right in the normal range the image between C2 and C3 is only virtual The
4. C2 lens contributes very little to the spherical aberration at the probe in the normal range because the C2 lens is almost off it contributes less than 0 02mm In the large range the contribution is considerably larger especially at small angles where it can add up to 0 3mm to the total spherical aberration of the objective lens Therefore the normal range is the preferred mode for normal applications like STEM and EDX The large range can be used for special applications like LACBED large angle convergent beam electron diffraction Titan 16 Condenser manual Version 1 0 3 5 Fine tuning C3 In Probe mode the beam is focused on the specimen by fine tuning the C3 lens In TEM mode the beam is focused on the front focal plane of the upper objective lens by fine tuning the C3 lens The sketch below illustrates how the position of the focus of the beam in front of the upper objective lens is related to the parallellity of the beam at the sample and to the position of the focus of the beam at the back focal plane of the lower objective lens gt Ny ZI NNUAL BELAY OM PO EL EE IR V Za PG TIN V V A converging or diverging beam at the sample can be tuned to a parallel beam by varying the height of the source image in front of the objective lenses This height of the source image directly relates to the height of the diffraction pattern after the objective lenses Titan 17 Conden
5. Two important drawbacks of non isoplanatism are the local variation of defocus in HR TEM and the local variation of magnification when the specimen is tilted This section discusses these effects the limits that they pose on the non isoplanatism and typical values of non isoplanatism in the Titan condenser system 4 2 1 Focus variation in HRTEM The next figure sketches a specimen illuminated by a diverging beam Outer parts of the illuminated area on the specimen are imaged by outer parts of the objective lens The spherical aberration of the objective lens causes that the focusing strength increases at the outer parts of the objective Therefore the outer parts of the illuminated area on the specimen are more strongly focused than the inner parts This causes a defocus which varies over the field of view Titan 20 Condenser manual Version 1 0 objective lens 5 ii focus L defocus al a C The image focus depends on the position on the specimen because the diverging illumination uses different parts of the aberrated objective lens This effect can be described with the wave aberration function y 9 1 4 Cs X g 1 2 Af AQ with g the spatial frequency C the spherical aberration the electron wave length Af the defocus and the dots denote all other aberrations A beam tilt B at the specimen corresponds to a shift of spatial frequency t B A This causes a phase shift 27 x gtt x g 2rt Cs 1 g
6. area is changed with the Intensity knob on the left hand control pad The illumination is parallel when the illuminated area is within the range indicated to the right of the TEM button The area and range are directly proportional to the size of the C2 aperture For example when the C2 aperture is changed from 50 um to 100 um the area and range are doubled When the illuminated area is smaller than the minimum of the range of parallel illumination then the illumination system automatically switches to condensing mode In this mode the beam is slightly converging towards the sample When the illuminated area is larger than the maximum of the range of parallel illumination then the illumination system automatically switches to spreading mode In this mode the beam slightly diverges towards the sample Beam Settings Semranale 10 0 mrad 4 Range 6 5 14 1 mrad Free Ctrl Spot number 3 Probe Select Probe if you want to have a focused probe on the sample for example for STEM EDX EELS or CBED The semi convergence angle of the probe is indicated on the right of this button The focus of the probe is controlled with the Intensity knob on the left hand control pad except when the microscope is in STEM mode then it is usually controlled with the Focus knob on the right hand control panel Titan 4 Condenser manual Version 1 0 The default semi convergence of 10 mrad is optimum for most Titans without Probe Cs
7. combination of diverging illumination and changing specimen height causes a local variation of magnification We derive an upper limit on the divergence or convergence as follows 0 2 pixels 1024 pixels 3mm objective lens 2 4mm back focal plane A converging illumination causes a change of magnification when the specimen is lowered Titan 22 Condenser manual Version 1 0 Consider an experiment with a camera of 2048 by 2048 pixels a tilt which lowers the specimen at most by Az 3 um and suppose the maximum acceptable image shift is 0 2 pixels Thus the user maximally allows that after lowering by Az 3 um a feature on the edge of the camera shifts from 1024 pixels from the center to 1023 8 pixels from the center Now we consider an extreme lowering Az 5120 3 um 15 mm The feature on the edge of the camera will shift 5120 0 2 pixels 1024 pixels that is to the center of the camera All other features will also shift to the center of the camera This simply means that in this example the source is imaged 15 mm below the original specimen position It shows that in order to match the requirement of maximal 0 2pixels shift the source must be imaged at least 15 mm away from the specimen For an image of say 0 5 um radius this corresponds to a non isoplanatism of B 0 5 um 15 mm 0 03 mrad 4 2 3 Non isoplanatism in parallel mode Normally the parallel mode is tuned such that the diffraction pattern is exact
8. corrector The semi convergence angle can be varied in the Tune flap out The range of convergence angles is indicated on the right of the Probe button The semi convergence and range are directly proportional to the size of the C2 aperture For example when then the C2 aperture is changed from 50 um to 100 um the semi convergence angle and range are doubled Free Ctrl Select Free Ctrl if you want to illuminate the sample in a way that is not covered by the two basic modes TEM and Probe When the Free control mode is selected the Free Ctrl flap out automatically opens This flap out contains several more options for adjusting the illumination Reset beam Press Reset Beam to set the user shift normally set with the left hand trackball and user defocus to zero This helps to find the beam when it is lost Spot number The beam current is controlled with the Spot number setting Spot number 1 has the highest beam current and spot number 11 has the lowest beam current With each step the beam current reduces by about a factor of two With a monochromator further spot numbers are available in filtered mode These spots are selected in the Tune flap out Flap out The flap out button leads to the Tune and Free Ctrl tabs of the Beam Settings Control Panel 2 2 Beam Settings Tune The Beam Settings Tune Control Panel in TEM mode MF Fine focus back focal plane T HMF Convergence angle klonochromator spot number f lt 11
9. mode further spot numbers than 11 up to 17 can be selected When these spots are to be used the C3 aperture is used as the beam defining aperture instead of C2 and the C2 lens acts optically as an additional C1 lens The normal C2 function focusing defocusing the beam is switched to C3 2 3 Beam Settings Free Ctrl Free Ctrl Mode Minicondenser f TEM O Microprobe ea Nanoprobe The Beam Settings Free Ctrl Control Panel Probe ED off Angle range f Normal C3 off Large T HMF Fine focus back focal plane MEF Convergence angle The Free Control flap out automatically opens when the Free Control mode is selected in the Beam Settings control panel When the user switches from TEM or Probe to Free Control mode the illumination does not change The main difference is that several additional options become available Titan 6 Condenser manual Version 1 0 When the user switches back from Free Control to TEM or Probe mode the illumination is set back to fit within the restricted range of options available in these two main modes Mode The mode option controls how the C2 and C3 lens are set The TEM and Probe modes correspond to the TEM and Probe modes in the main Beam Settings control panel In the modes C2 off or C3 off the second or third condenser lens is set to zero and the condenser column behaves as a two condenser system very much comparable to the Tecnai and CM microscopes Normally the C2 off and C
10. of the C1 lens Try a smaller C2 aperture 6 In Probe mode the beam cannot be focused to a probe The specimen should be at eucentric height Press Reset beam If this does not help please do the Condenser alignment The Probe focus was okay but changed gun lens or extraction voltage or high tension and now the focus is off Probably the height of the image in front of the condenser has changed Do the Gun alignment Gun XO focus and stigmate 8 In TEM mode when I decrease the size of the illuminated area the beam moves away And the movement is even faster for small areas The condenser deflector is not well aligned Please do the condenser zoom alignment Alignments gt Condenser gt Condenser zoom 9 want to illuminate 20 nm with a beam as parallel as possible Should use TEM mode with condensing beam or should use Probe mode in the microprobe setting With the 50 um C2 aperture the convergence angle in condensing TEM mode is about 0 5 mrad The convergence angle in Probe mode with microprobe setting is variable between 0 5 mrad and 8 8 mrad in the large angle range At 0 5 mrad those two settings are optically the same The only difference is that TEM and Probe use separate sets of beam shift and beam tilt 10 I can not find the beam Can there be something wrong with the condenser alignment Press Reset Beam If the beam is still not visible switch the illumination to Free Ctrl and C3 of
11. 3 off modes will be seldom used They may be helpful to circumvent problems when the condenser lenses have become misaligned for some reason In the C2 off mode the Intensity knob controls the C3 strength and the C3 aperture must be used to limit the beam In the C3 off mode the Intensity knob controls the C2 strength and the C2 aperture must be used to limit the beam Minicondenser Normally the TEM illumination uses the Microprobe setting minicondenser lens on and Probe illumination uses the Nanoprobe setting minicondenser lens off In Microprobe the illuminated area and probe size are five times larger than in Nanoprobe The convergence angle in Microprobe is five times smaller than in Nanoprobe Angle range The angle range option is only available in Probe mode When the user switches from normal range to large range the C2 and C3 lenses get strongly excited and an additional intermediate image of the source is created between the C2 and C3 lens This gives optically more flexibility resulting in a larger range of convergence angles This mode is especially suited for LACBED large angle convergent beam electron diffraction However the strong excitation of the C2 and C3 lenses also gives more spherical aberration especially at small convergence angles where it can contribute up to 0 3 mm to the total spherical aberration of the objective lens Therefore in order to obtain a very low convergence angle in probe mode it is better n
12. Af Ag which reduces to 2r t 2 9 Cs 1 when we use Scherzer focus Af C 1 and the point resolution limit g 1 0 61 C 1 We demand this phase shift to be less than 1 4 which implies for a Titan 300 SuperTwin C 1 3mm 1 97pm that B t lt 0 3 mrad A typical HRTEM image spans an area of 100 nm diameter The beam tilt due to diverging or converging illumination is less than 0 3 mrad when the source image is at least 100 nm 0 3 mrad 3 mm away from the specimen t At Scherzer focus the limit on the beam tilt B will be stricter for higher spatial frequencies However frequencies far beyond the point resolution limit are usually imaged at a focus for which the contrast transfer function sin x 9 is more or less stationary around those frequencies This happens to be the same condition for which the effect of a beam tilt x g t x 9 is minimal so also for higher frequencies it is reasonable to estimate B lt 0 3mrad Titan 21 Condenser manual Version 1 0 4 2 2 Magnification variation Tomography requires a large series of images taken at different specimen tilt angles For good 3D reconstruction it is important that the magnification changes minimally between the images and minimally within an image The figure below shows how a diverging beam in combination with a specimen tilt causes magnification change non parallel illumination less magnification more magnification The
13. Nanoprobe By default the TEM illumination uses the Microprobe setting Press Nanoprobe to switch the TEM illumination to the Nanoprobe setting this switches the minicondenser lens off The minimum and maximum area that can be illuminated with a parallel beam in Nanoprobe are five times smaller than in Microprobe However when the illuminated area is outside the range of parallel illumination so when the illumination system has switched to condensing mode or spreading mode then the beam converges or diverges five times stronger in Nanoprobe than in Microprobe Therefore it is advised not to use Nanoprobe in combination with condensing mode or spreading mode Titan 5 Condenser manual Version 1 0 Auto Zoom When Auto Zoom is on the size of the illuminated area automatically scales with the magnification Fine Focus Back focal Plane Select MF Y Fine Focus Back Focal Plane to fine tune the position of the diffraction pattern at the objective aperture When selected the Multifunction Y knob controls the position of the diffraction plane In normal use this needs seldom to be changed The Beam Settings Tune Control Panel in Probe mode IT HMF Fine focus back focal plane T MF Convergence angle Monochromator spot number 16 Convergence angle When MF Y Convergence angle is selected the semi convergence angle of the probe can be varied with the Multifunction Y knob Monochromator spot number When the monochromator is in Filtered
14. Titan 1 Condenser manual Version 1 0 Titan Condenser manual Table of Contents TL MOTEN ae 2 ES NNN 3 o 3 22 Beam SUING S TUE Ree 4 23 Beam SAMSTEMT 5 gt ONS 7 TEMPO eee 7 32 MICIOPrODe NANODIODG nori A E 8 OG EE D EE ds 9 34 der 9 JAN SONNE 11 942 AEA ZOOM MAA AAA AA 12 SA o ENE ION 14 5 FETT NRS 16 30 TIWo condaenser lens TON TG 17 4 Fundamentals of parallel illumination ooccocccoccconnconcconnconncncnoncnonncnnncnoncnnnnonnnornnonocanonnnnnnnns 18 21 CONCIENCIA o ia 18 EZ NorSOPENENS MN 19 F21 FOCUS VANSON MN ARTEN Luer nede 19 4 2 2 Magnification variatio serseri aa E E AEE EEE EE Eaa 21 4 2 3 Non isoplanatism in parallel mode oocoocconcocnconiccnnoniocnconconoconnonoonncononnnnnnnononnnnannnnnnanenoss 22 4 2 4 Non isoplanatism in spreading and condensing Mode ooccocccnccncccncccncnnncnnnconocnnncnnnnconcnonncanonos 22 5 Hysteresis and NOMMAlIZAllOMN isinai A a a a a al 25 6 Some frequently asked QUESTIONS sissien aa A Ea Ea a ae aieiaa TR 26 Titan 2 Condenser manual Version 1 0 1 Introduction This is the user manual for the condenser system of Titan with software version 1 0 or higher Users who do not like reading manuals only need to read Section 2 1 That section discusses how to set the basic modes of the condenser Sections 2 2 and 2 3 discuss how to make modifications to these settings Chapter 3 has been written for users who like to know t
15. f This switches off the C3 lens and makes the system much less sensitive to missing alignments or misalignments If the beam is still not visible the problem is probably not caused by the condenser Titan 21 Condenser manual Version 1 0 11 The beam control panel can show the size of the illuminated area and can show the covergence angle Why doesn t it show the probe size The probe size depends on too many parameters lt depends not only on the condenser setting but also on how well the stigmators have been tuned on the defocus of the probe on the C2 aperture size and alignment on the gun lens setting on the extraction voltage and on the high tension
16. f the condenser column The first setting is the TEM mode in which the beam on the specimen is parallel Here the C3 lens images the source on the front focal plane of the upper objective lens The second setting is the probe mode mainly intended for STEM and for EDX or EELS analysis Here the C3 lens forms a beam which enters the upper objective lens roughly parallel 3 2 Microprobe Nanoprobe The specimen is in the middle of the magnetic field of the objective lens and therefore the objective lens acts on the beam below the specimen as well as on the beam just above the specimen These two actions are usually called the upper objective lens and the lower objective lens The upper objective lens is essential for STEM but the upper objective lens makes it difficult to get good TEM illumination especially for very large areas and for very small areas this is explained in more detail in Section 4 2 4 In order to improve the TEM illumination of very large areas and of very small areas a minicondenser lens is added just in front of the upper objective lens When this lens is switched on it compensates largely the upper objective lens This is sketched in the figure below EMS Trey NYT Pr CUNT FA IN o IMA W e A PG Ny Ui i E a The two basic settings of the condenser column in microprobe Left parallel illumination for TEM Right probe illumination for analysis or STEM Titan 9 Condenser man
17. he optics of the condenser It sketches the beam paths for all modes and how the paths change when the beam parameters are varied Chapter 4 provides background information on parallel illumination Parallel illumination is characterized by its coherence and by its amount of remaining convergence or divergence The chapter discusses how these vary with the different condenser modes This chapter can help the advanced user to optimize his illumination Chapter Error Reference source not found lists the alignment procedures This chapter is intended as a reference When the microscope is properly aligned the user will not need much of this section Chapter 6 gives answers to some frequently asked questions It is worthwhile to read this chapter because it touches some issues which could not be placed in a natural way in the other chapters Note Alignments are not covered in this manual Pelase refer to the seperate align pdf file Titan 3 Condenser manual Version 1 0 2 Titan User Interface 2 1 Beam Settings Beam settings Eb lurmination Parallel Area 4 96 um Range parallel 0 86 32 0 pm The Beam Settings Control Panel Free Ctrl The illumination on the microscope is controlled through the Beam Settings control panel and its flap outs Reset beam Spot number 3 v TEM Select this mode if you want to do normal TEM imaging The size of the illuminated area is indicated to the right of this button The illuminated
18. ion of the intermediate image between C2 and C3 changes the illuminated area in ZN TEM mode AZ 7N zs FRE When the user selects an area that is smaller than the smallest area that can be illuminated with a parallel beam the system switches to condensing mode In the condensing mode the source is no longer focused in the front focal plane of the upper objective lens but instead above thus making the beam convergent towards the sample When a zero sized area is selected the beam is simply focused as a probe on the sample This is sketched in the figure below When the user selects an area which is larger than the largest area that can be illuminated with a parallel beam the system switches to spreading mode In the spreading mode the source is no longer focused in the front focal plane of the upper objective lens but instead below thus making the beam divergent towards the sample This is also sketched in the figure below Titan Condenser manual spreading parallel parallel arallel parallel condensing condensing 13 Version 1 0 Specimen illumination in TEM mode The apparent C2 aperture is indicated by the blue edges When C2 C3 is zoomed the apparent C2 aperture changes size and the size of the parallelly illuminated area is varied When the user selects an area outside the range of parallel illumination the beam switches to Spreading mode or condensing mode
19. ition of the intermediate source image between C1 and C2 and the position of the intermediate source image between C2 and C3 Titan 10 Condenser manual Version 1 0 It is common to use the name zoom system for two neighboring lenses with an image in between that can be moved up and down without changing the position of the image in front of the first lens or that of the image after the second lens The Titan condenser system is a double zoom sysem with a C1 C2 zoom and a C2 C3 zoom The C1 C2 zoom is called the spot number and determines the beam current The C2 C3 zoom controls the beam diameter in TEM and the probe convergence in STEM This is summarized in the following table TEM STEM changing position varies beam current varies beam current between C1 and C2 changing position varies illuminated area varies convergence angle between C2 and C3 Condenser manual A SY PP DIS AZ ves lt q Se NY y VAR AE 424 WW de vi u ni eS a Titan 12 Condenser manual Version 1 0 Changing the position of the intermediate image between C1 and C2 changes the beam current not the illuminated area or convergence angle 3 4 2 Area zoom Changing the position of the intermediate image between C2 and C3 changes the diameter of the beam at the C3 lens and through this the size of the illuminated area in TEM The software takes care that C2 viv a ER We Changing the posit
20. ly in the plane of the objective aperture However the back focal plane of the objective lens is not exactly in the plane of the objective aperture Due to changing magnetic saturation it can vary with the high tension between 0 2 mm above and 0 5 mm below the objective aperture the precise values depend on the type of objective lens This range of 0 2 mm to 0 5 mm goes well with the non isoplanatism limits derived in Sections 4 2 1 and 4 2 2 which are a minimum distance between source image and specimen of 3 mm for HRTEM and 15 mm for tomography As shown in the sketch in Section 4 2 2 15mm distance means that the diffraction pattern must not be more than 0 6 mm above or below the back focal plane for 3 mm focal distance This is satisfied in all cases 4 2 4 Non isoplanatism in spreading and condensing mode The range of parallel illumination in TEM is limited by the strengths of the condenser lenses When the user selects an area which is larger than the largest area that can be illuminated with a parallel beam then the system switches to the spreading mode in which the beam is diverging towards the specimen When the user selects an area which is smaller than the smallest area that can be illuminated with a parallel beam then the system switches to the condensing mode in which the beam converges towards the specimen Titan Condenser manual spfeading 00000000000000000000000 arallel 000999000000000000000000000
21. mination However in this example the source image is not in the front focal plane of the objective lens and the angle varies with the specimen position This variation is called non isoplanatism 4 1 Coherence The coherence angle can be tuned by changing the magnification from the source to the source image in the front focal plane of the upper objective lens A higher gun lens or a higher spot number gives a smaller source image and a better coherence However it also gives less beam current This balance between coherence and beam current is described by the law of conservation of brightness I B naf 1 4 D Vee where beam current on the specimen B brightness of the FEG typically between 5 10 and 2 10 A mf sr V a half coherence angle D diameter of the illuminated area on the specimen Viel V 1 V Vo the relativized high tension Vo 2MelectronC 1022kV The next graph shows how depends on D and a for B 10 A m sr V Titan 19 Condenser manual Version 1 0 100mrad angle 10mrad 0 1mrad 10urad 1 rad i ee AO HS K EE REN ea Fer 0 1nm 1nm 10nm dum 10um 100um 1lluminated area Beam current as a function of illuminated area and coherence angle for a FEG operated at brightness B 10 A m sr V The beam current at the sample can not exceed 150 nA The software forbids and disables modes which potentially can give a beam current larger than 150 nA 4 2 Non isoplanatism
22. ot to switch to the large angle range but instead to switch to Microprobe setting Fine Focus Back focal Plane Select MF Y Fine Focus Back Focal Plane to fine tune the position of the diffraction pattern at the objective aperture When selected the Multifunction Y knob controls the position of the diffraction plane In normal use this needs seldom to be changed Convergence angle When MF Y Convergence angle is selected the semi convergence angle of the probe can be varied with the Multifunction Y knob Titan T Condenser manual Version 1 0 3 Optics The Titan microscope has six lenses in the illuminating system namely the gun lens the first condenser lens C1 the second condenser lens C2 the third condenser lens C3 the minicondenser lens MC and objective lens Obj The main function of these lenses is summarized in the following table Function Name Lens Beam current Probe size gun lens gun lens spot number C1 C2 zoom Beam width Beam convergence Aera Semi angle C2 C3 zoom Parallel beam focused beam TEM Probe C3 Compensate upper objective lens Microprobe Nanoprobe minicondenser Probe forming upper objective lens 3 1 TEM Probe f Ny TTI LL Zs AS Y TEM Probe The two basic settings of the condenser column in nanoprobe Left parallel illumination for TEM Right probe illumination for analysis or STEM Titan 8 Condenser manual Version 1 0 The figure above shows the two basic settings o
23. p of current density by a factor of sixteen Titan 25 Condenser manual Version 1 0 5 Hysteresis and normalization The condenser system requires a high excitation above 1T of the C3 lens when a small area is parallelly illuminated in TEM When the condenser switches afterwards to a setting with a lower C3 excitation remanent magnetic fields of typically 1 uT can give a slight deflection in the C3 lens The user can notice this as a hysteresis in the beam position of up to a few hunderd nanometers and a hysteresis in the beam tilt They are highest for TEM illumination in combination with an area of which the size has been reduced in condensing mode past the probe focus to negative diameter Then C3 can be excited up to 100 The simplest way to handle this is to press Normalize condenser to restore the beam to its normalized position This position usually reproduces better than 10 nm The user can choose to automize this condenser normalization In the Normalization control panel click on Illumination State then select Condenser The condenser will be automatically normalized when the illumination is untouched for 0 5 s after a change of the illumination Mormalizations Condition description STEM imaging lt gt diffraction STEM LM lt gt HM STEM spotsize TEM lt gt EFTEM TEM lt 3 Probe The Normalization Control Panel TEM camera length change Hormalizatons Condenser Projector i Objective
24. ser manual Version 1 0 3 6 Two condenser lens mode The user can switch off the C2 C3 zoom system by selecting the C2 off or C3 off mode This can be helpful when the C2 C3 zoom is not aligned or misaligned The condenser then behaves as a two condenser system similar to a Tecnai or a CM microscope The beam is generally no longer parallel as bit AN E 1 FE a Y AU IT amp ore m n a __ E In the C3 off mode the condenser behaves as a two condenser column The beam changes from converging to parallel to diverging when the illuminated area is increased Titan 18 Condenser manual Version 1 0 4 Fundamentals of parallel illumination The next figure sketches a non ideal TEM illumination source image focal plane Objective lens O a E i la BEN la PP Non ideal TEM illumination with half coherence angle a and non isoplanatism f The illumination differs from ideal parallel illumination in two aspects e The half coherence angle a is not zero The finite size of the cross over in the front focal plane of the objective lens introduces a spread of beam tilts with which the beam hits a single point on the specimen e The non isoplanatism is not zero Ideally the source image should be in the front focal plane of the objective lens so that the angle 2 with which the beam hits the specimen does not vary with the position on the specimen this gives parallel illu
25. ual Version 1 0 In TEM mode the parallelly illuminated area is five times larger when the minicondenser lens is on than when it is off Similarly in Probe mode the convergence angles are five times smaller when the minicondenser lens is on than when it is off Also in Probe mode the focused probe is larger when the minicondenser lens is on than when it is off For these reasons the setting with minicondenser lens on is called microprobe setting and the setting with minicondenser lens off is called nanoprobe setting TEM mode normally uses the microprobe setting and Probe mode normally uses the nanoprobe setting 3 3 Gun lens The gun lens is an electrostatic lens positioned directly behind the field emitter and extractor The user can choose eight settings for this lens called gun lens 1 to 8 The figure below sketches the rays for three gun lens settings Increasing gun lens leads to increased demagnification of the source and to decreased current in the beam Increasing the gun lens by 1 leads to a reduction of the beam current by approximately 35 El I NS As as Ly gunlens 1 gunlens 5 gunlens 8 3 4 Condenser zoom The image distance of C3 is normally fixed and its value depends on the mode used TEM Probe microprobe nanoprobe LM The gun lens determines the position of the object of C1 Two parameters remain to define the precise state of the condenser column These are the pos
26. unction of illuminated area for microprobe blue curves and nanoprobe pink curves for a Titan 300 SuperTwin The non isoplanatism is the average tilt of the illumination at the edge of the illuminated area relative to the average tilt of the illumination at the center of the illuminated area For each setting parallel illumination is possible in the range indicated by the double arrows The non isoplanatism is zero in these ranges Microprobe is the preferred setting for HR TEM since it gives smaller non isoplanatism in spreading and condensing mode the reason for this is that in microprobe the minicondenser lens partly compensates the upper objective lens thus creating a considerably larger distance h between specimen and apparent C2 aperture The non isoplanatism is below 0 5 mrad with the 50 um C2 aperture which roughly agrees with the limit of 0 3 mrad derived in Section 4 2 1 For tomography the parallel mode is clearly to be preferred over the condensing or spreading mode The graph shows that one can use microprobe for areas between 1 um and 40 um and nanoprobe for areas between 0 2 um and 8 um Since the default mode is microprobe in TEM the tomography user should take care to switch to nanoprobe for areas between 0 2 um and 1 um Of course in the converging mode any sub area can be illuminated with four times smaller non isoplanatism by increasing the diameter of the total illuminated area four times but this goes with a dro
Download Pdf Manuals
Related Search