David Cockayne Centre for Electron Microscopy.

Transcription

1 David Cockayne Centre for Electron Microscopy. Depart of Materials, University of Oxford JEOL JEM-2100 TEM USER GUIDE November 2014 JLH / NPY 1

2 Contents Control panels...4 Tracker Ball...7 Aperture controls....8 Computer control windows...9 Vacuum system diagram. 10 Using the Initial checks Filling the ACD with liquid nitrogen Switching on High Voltage (HT)..15 Switching on electron beam...15 Gun alignment...16 Condenser alignment..16 Condenser astigmatism.16 Objective Lens Reference Voltage 16 Spot Size Condenser aperture selection...17 Alpha angles what they mean Illumination system alignment...18 Specimen airlock.19 Removing specimen from airlock...20 Loading specimen into airlock...21 Specimen holders Aligning Voltage Centre...29 Electron diffraction..30 At the end of your session. 31 Heating the ACD back to room temperature..32 2

3 The JEM 2100 has the following specification: High-tilt polepiece with +/- 40 o tilt available Objective lens spherical aberration coefficient C s = 1.4 mm. Point resolution: 0.25 nm. Lattice resolution better than 0.2 nm. Magnification range ,200,000 X Low mag range: 50 6,000 X Diffraction camera length: mm. STEM facility Oxford Instruments XEDX system Gatan Orius CCD camera 3

4 The JEM 2100 is a sophisticated instrument with a wide range of capabilities. This basic guide will help you to get started with TEM and as you progress, you will then move on to more advanced techniques, including STEM and EDX. It operates at up to 200 kilovolts, the usual settings being 200 or 80 kv. It is controlled by a combination of computer commands via a mouse, and two control panels with buttons and knobs. Note that many of the functions can be operated by either the computer or the control panels. NOT used in this microscope Left hand control panel The buttons: [BEAM] used to switch on the filament [Room Lamp] not used Probe Control selects the mode of operation TEM is for normal imaging & diffraction; EDS has a small probe with high beam current for 4

5 EDX analyses via a stationary probe; NBD has small, (approximately) parallel probe for nanobeam-diffraction; CBD has a very high convergence angle for convergent beam diffraction. Alpha selector is used to optimise parallel illumination, depending on mag range. Spot Size controls the size of a focussed beam on the specimen. DEF/STIG Buttons: Turn on or off the various deflector coils, also condenser & objective stigmators. DEF/STIG knobs on both right and left-hand panels control the DEF/STIG functions as chosen above. As such these are termed multifunction knobs. SHIFT (both panels) knobs (again multi-function knobs) move the beam sideways in X- or Y- directions (BEAM SHIFT). If for example GUN is selected then they become GUN SHIFT. [NTRL] cancels whatever has been input into the selected DEF/STIG coils and returns the chosen DEF/STIG deflector to the engineers basic alignment. NOTE: the aperture controls on this particular instrument are manual, and not operated from this panel. CRS: these increase the power of the linked control by 10X 5

6 Right hand control panel [Z] - up and down adjusts height of specimen. [IMAGE WOBB X & Y] - gives a split image to help set height/focus the specimen [HT WOBB] varies high voltage to assist correction of the HT centre alignment. [F1 to F6] function knobs. Useful ones are F1 to lift viewing screen and F4 for gun alignment. [MAG 1] normal TEM range of magnifications. [MAG 2] sets mag at 40,000X for alignment. MAG/CAM L knob - sets magnification. In diffraction mode, adjusts camera length. 6

7 [Low MAG] very low mag range useful for locating specimen. Note that the objective lens is OFF in this mode and will become thermally unstable, causing specimen drift if left in this mode. Use sparingly. [SA MAG] sets image mode for accurate electron diffraction. [SA DIFF] switches to electron diffraction. [STD FOCUS] sets objective lens strength to optimum value. DIFF FOCUS focusses electron diffraction pattern. OBJ FOCUS focusses the image. Coarse & fine controls, with extracoarse (16X) button. NOTE: The microscope does not use film, so the exposure panel is not used. Tracker Ball controls The specimen X-Y shift is driven by a tracker ball, or by X- and Y- buttons. The FINE control button is not used on the

8 NOTE: in this orientation, the up/down, left/right arrows correspond to the image orientation on the viewing screen. B A C Aperture Controls The Condenser, Objective and Selected Area apertures are all controlled as shown above. Knob A is used to insert/withdraw an aperture, B is used to move it in or out a small distance, and C moves it sideways. The white circles on A indicate which aperture is in position (when white spot is aligned with black dot). Do NOT wind B too far anti-clockwise or it will detach completely! 8

9 Hard X-ray aperture This single aperture is used for minimising background X-rays in EDX spectra. It is very difficult to align, so don t attempt it yourself. If not visible when inserted, ask for help! The menu screen provides access to the main control systems through additional screens. HT is used to switch on high voltage and electron beam. SPC indicates specimen coordinates. Can be used to memorise and recall specimen positions. 9

10 Status Monitor indicates which systems are running useful if a major fault occurs. VAC schematic diagram of vacuum system, indicating pumps, valves and vacuum gauges. 10

11 Green lights - open valves. Orange lights Pirani gauges: PiG1- column vacuum PiG2 gun vacuum PiG3 camera chamber PiG4 specimen airlock PiG5 rotary pump Pink light Penning Gauge PEG1 (column) RP rotary pump DP - diffusion pump SIP ion pump PEG1 window indicates vacuum status Status windows indicate vacuum readings in various gauges 11

12 Operation panel for main (standard) system. Note that most of these are duplicated by buttons & knobs on the two consoles Operation panel [Stage] controls minimum steps sizes for X/Y specimen shift & tilt [NTRL] sets stage coordinates to zero. NOTE: Super Fine control is not used. NOTE: [Aperture] is not used. 12

13 Alignment panel for routine alignments. Under normal circumstances you will not need to Save and Load alignment files. Please do not do this unless you have discussed this in advance with EM Facility staff 13

14 USING THE JEOL JEM-2100 At the start of your session, carry out the following initial checks The microscope should be found in the following standard conditions: Filament OFF High Voltage set at 200 kv and OFF (unless a previous user the same day leaves it on for the next user) MAG at 500,000X Stage coordinates all at zero (neutral) Specimen OUT and non-tilt holder (without the end piece) IN the column Objective and Selector apertures OUT Orius camera OUT EDX & STEM detectors OUT Check that PEG1 Status in VAC diagram is at READY. If it is not READY go for help. Check the log sheet for any messages from previous users 14

15 FILL COLD TRAP RESERVOIR WITH LIQUID N 2 Obtain LN 2 from the cupboard and remember i) to use protective eyewear & gloves, and ii) lock the door afterwards. Get the code for padlock from one of the EM facility staff following safety training from them. 1. Make sure covers are on the TEM window and binoculars. LN 2 splashes on glass will crack it (VERY expensive!) 2. Insert funnel into the dewar neck 3. Carefully pour LN 2 to fill dewar (use goggles) and insert filler cap 4. After ~15 mins. refill tank it will then remain cold for several hours. SWITCH ON HIGH VOLTAGE (HT) In main control window check that the HT indicator: HT status is Ready Select operating voltage in High Voltage Control window using up/down buttons. Normally used at either 200 or 80 kv. Use 0.5 kv steps. If you are the first user of the day, you must first set the HT to 180 kv then increase the HT slowly to 200kV as per training instructions. Click HT [ON] button. Setting the accelerating voltage appears. No other windows can be accessed while HT is running up. HT icon in main control widow turns green when HT is on. Dark current (beam current without electron emission) should read around 41 µa for 80 kv, and 101 for 200 kv. SWITCH ON ELECTRON BEAM Remember: the beam will not switch on unless the specimen holder is in position and high voltage is on. In High Voltage Control window, click Filament ON, or press the [Beam Switch] button on left panel. Filament will gradually come on. Check emission current should be ~5 6 µa greater than dark current. If this is not the case and you are unsure ask for help. 15

16 GUN ALIGNMENT Set spot size in TEM mode to 2 and alpha 3 (left panel) Set Mag to 40,000X Bring beam to screen centre (Shift X & Y) Engage [GUNA] (F4 on right console) or GUN in the DEF Select menu in Alignment Panel window. Optimise brightness by X & Y DEF/STIG knobs (L & R panels). The current density readout in pa/cm 2 will help you with this. Cancel F4 or GUN to memorise settings. CONDENSER ALIGNMENT: Set MAG to 40,000X and focus beam (Brightness knob) Set Spot size 1 Click DEF Select GUN in Alignment Panel window and centre beam with SHIFT X & Y Set Spot size 5 and focus beam. Engage [BRIGHT TILT] switch (right panel) or click DEF Select CLA in Alignment panel. Then centre beam with SHIFT X & Y. Repeat process until both spot 1 and 5 remain centred. Spot 2 is normally used for TEM a combination of good brightness and beam coherence. CONDENSER ASTIMATISM CORRECTION Focus and centre beam using BRIGHTNESS & SHIFT controls. Expand beam on either side of focus. If beam becomes elliptical or severely elongated correct it using either [COND STIG] (rt panel) or in Alignment panel click CL STIG, and use DEF/STIG knobs (both panels) to make spread beam circular. Cancel COND STIG or CL STIG. SETTING OBJECTIVE LENS REFERENCE CURRENT Because the vertical position of the specimen in the objective lens is critically important, the lens must first be set to its optimum current, and 16

17 the specimen is then raised or lowered into the correct plane. Set MAG at 40,000X. Press [STD FOCUS] switch (Right panel). This now sets the Objective Lens to its optimum voltage/current. SPOT SIZE Choose an appropriate spot size. Spot 1 or 2 will be suitable for most TEM work CONDENSER APERTURE Choose the appropriate aperture #1: (largest) 200 µm for maximum brightness, but low coherence. #2: 70 m, use this for routine TEM work. #3: 50 µm for better coherence, better for HREM, but less bright. #4: 10µm use this for small-probe work, but very dim, and may cause contamination. Centre the aperture in the usual way, Recheck gun tilt and adjust if necessary. ALPHA ANGLE The illumination system consists of three condenser lenses and a condenser mini-lens. The system allows you to select an optimum beam convergence setting for various magnification ranges: with the correct alpha setting you can have a (approximately) parallel beam onto your specimen. Choose an appropriate alpha setting for your work. It also provides a very wide degree of control over small-probe conditions, see below. In TEM mode there are 3 alpha settings available. In the small probe modes there are up to 9 alpha settings available. Alpha 3 is good for lower magnification ranges, i.e. up to 100,000X, (or 2,500X into the GIF) (This will give a "parallel" beam of 2.5 m diameter on specimen. i.e. 10cm on screen at 40,000X) Alpha 2 is good for medium magnification ranges, i.e. from to 100,000X 400,000X. Alpha 1 is suitable for high magnification, i.e. above 400,000X. (This gives a "parallel" beam of 0.5 m diameter on specimen. ~ 2cm on screen at 400,000X) If you have a wrong alpha setting you will find strong distortion in the illumination, particularly near the edges of the beam. 17

18 ILLUMINATION SYSTEM ALIGNMENT Beam position on specimen is controlled by 2 sets of deflector coils which are used to define beam position and tilt. These adjustments (beam tilt purity) are to make sure the beam doesn t tilt when it is shifted, and doesn t shift when tilted. Adjusting TILT X and Y so beam spot doesn t shift when beam is tilted (ESSENTIAL) Set MAG to 40,000 and focus beam to small spot, centred on screen. Engage [BRIGHT TILT] on left panel, or click DEF Select CLA in Alignment panel. Click Compensator Tilt in Alignment panel Click Wobbler Tilt X button in Alignment panel - spot splits into 2 in X direction. Make split spot into one using DEF/STIG X knob. If spot is also split in Y direction click Compensator Angle in Alignment panel, and correct using DEF/STIG X knob. Cancel Compensator Angle. Cancel Wobbler Tilt X button in Alignment panel. If beam is off-centre, engage [BRIGHT TILT] (left panel) and centre with Shift knobs Repeat process for TILT Y Adjusting SHIFT X & Y so beam doesn t tilt when shifted (OPTIONAL) Set up diffraction [SA DIFF] (right panel) and turn brightness knob fully clockwise Adust DIFF FOCUS knob to produce a caustic spot (image) on screen. Click Compensator Shift in Alignment panel Click Wobbler Shift X caustic spot splits into 2 parts Unify split spot by DEF/STIG knob X If spot also splits in Y direction click Compensator Angle in Alignment panel and unify with DEF/STIG knob X. Cancel Compensator Angle Cancel Wobbler Shift X Repeat process for Y- 18

19 Reminder notes on SPECIMEN EXCHANGE Please be very careful when loading & unloading specimens. Take your time and ask for help if unsure A B Specimen Airlock Follow these steps carefully Turn off the beam (if not already off) by either pressing the BEAM button on the left hand control panel or selecting the FILAMENT button in the HT window. Wait until beam if fully off. The HT can stay turned on. Reset the sample holder to its neutral position by double clicking on the Stage Neutral button in the top right hand corner of the left 19

20 monitor (black square with white letters). Wait until X, Y & Z values all are at zero &4 For removal of double-tilt holders, disconnect Y-tilt cable from airlock [B]. 1. Gently pull the holder out until it stops. Do this steadily and without placing any lateral or vertical pressure on the holder. 2. Now rotate the holder ~80 degrees ANTICLOCKWISE. DO NOT pull on the holder while rotating it. 3. Gently slide the holder out (~ 1 cm) until it stops. 4. Carefully rotate the holder the final ~10 degrees anticlockwise. Again DO NOT pull on the holder, as this will let air into the column 5. Switch the airlock switch to AIR and turn on gas line. Wait for the pressure airlock to reach air pressure/ SPECIMEN vacuum display will change to AIR and vacuum level will rise. After ~30s the airlock will be at atmospheric pressure. 6. Carefully remove holder from the airlock 7. Switch off gas line. 6 20

21 See pages for detailed instructions on loading different specimen holders. Before putting the specimen holder into the airlock: Check that the O-rings are clean and free of fluff or dirt. If fibres are found on an O-ring, carefully remove them with a cocktail stick. Do NOT use tweezers! Also, check the brown ceramic ring for dirt or grease any dirt or grease will cause specimen drift. And remember do NOT touch any part of a specimen holder beyond the O-rings with bare skin ALWAYS use neoprene or plastic gloves provided. Do not wipe the O-ring with a tissue or any other material. It has a thin coating of special high-vacuum grease already, so do not add any more &5 3 Wait for green light 1 1. Insert the holder with the small guide pin positioned in the airlock guide slot at 9 o clock [A]. Guide the holder gently into the column until it comes to a stop. Push the end of the holder gently to ensure a good seal and then release it. It should remain in position. If 21

22 using a double-tilt holder, you should hang the Y-cable anticlockwise over the holder body, to prevent twisting the holder Try not to put any sideways or up/down pressure on the holder. Note: Do NOT rotate the specimen holder at this time. 2. Set the airlock switch to PUMP. The orange lamp lights up, indicating that the airlock is pumping. The SPECIMEN vacuum level will begin to drop from 252μAmps. 3. Wait until the green light on the goniometer is lit and the SPECIMEN vacuum indicates VAC READY or the Specimen/PIG4 (Vacuum Window) value is 78μAmps. 4. To insert holder into the column - rotate the holder clockwise until it stops after ~ 10 degrees. 5. The holder will then move in by ~1cm. 6. Rotate the holder clockwise by a further ~80 degrees. The column vacuum will now pull it inwards so do not let go! Gently allow the sample holder to slide in until it reaches a stop. Finally, gently pull holder out a few mm and then return it back into position. This releases any strain on the O-rings. If using a double-tilt holder, now insert the plug into [B]. Now select the correct holder in the Control window (top right-hand corner). This tells the microscope which holder is in use. Switch on electron beam. Find an image of your specimen, and bring it into approximate focus using Z-up or Z-down buttons (right panel). X- or Y- image wobblers (right panel) can be helpful. 22

23 There are three holders available: You must observe the following rules when you use any of them. 1. You must ALWAYS wear plastic gloves when touching specimen holders. 2. After you load your specimen, check both O-rings carefully. and gently remove any dust or dirt particles. 3. Use a lint-free tissue (red and white box) (NOT an ordinary tissue!) to remove any grease from the brown ceramic ring at the end of the specimen rod. This surface connects the rod to the goniometer and if it is in any way greasy or dirty, there will be bad specimen drift. Single-tilt holder. 30 degrees of tilt around the rod axis. Robust and easy to use. Berryllium double-tilt holder. This is the most delicate (and most expensive!) holder, so please handle it carefully. The Be surrounding the sample gives clean, low-background EDX spectra with suitable specimens. This holder must NEVER be used for any magnetic specimens. The small tabs which hold the specimen are in turn held by small screws. Use the correct size of screwdriver, and do NOT overtighten these screws, as this will damage the gimbal (replacement cost: 7K). Strong double-tilt holder. Not available for general use see Sergio Lozano-Perez if you need to use this one. This is built from titanium, and MUST be used if your specimen is magnetic (e.g. steel). Specimens are held in position by a small screw. These screws are VERY expensive (~ 500 each), so be very careful not to lose one. The tilting gimbal pivots on two very small sapphire bearings, which are also very expensive (~ 1,000). You MUST ALWAYS use the correct support pillar when loading specimens. This supports the gimbal and prevents any excessive strain on the bearings. Do NOT over-tighten the retaining screw. 23

24 SINGLE-TILT HOLDER A Bronze clip B Specimen mounting plate Note: the bronze clip has a slot which fits under screw A; screw B acts as a pivot. ALWAYS use the mounting jig as shown here. Make sure the mounting plate is secure and straight in the holder rod after loading your specimen. DON T touch the mounting jig with bare fingers, or you will transfer grease to it. 24

25 LOW BACKGROUND Beryllium DOUBLE-TILT HOLDER Bronze clip Retaining screws Be cover plate Bronze clip Low background holder correctly positioned on mounting jig 25

26 NOTES: 1. This holder is very fragile! 2. The specimen loading side is the bottom side. The other side is the one that faces the X-ray detector. Make sure your specimen grid has the carbon side down when loading your specimen. 3. ALWAYS use the mounting jig to support the gimbal. 4. Place the mounting jig in position in the platform and lower the gimbal very gently onto the mounting jig. Tighten the perspex screw to keep the holder steady. 5. The sequence is: specimen, then the Be spacer ring, then finally the Be cover plate. 6. Use the Be spacer ring on top of your specimen if it is too thin. 6. DO NOT undo the retaining screws completely just enough to release the bronze clips from the locating pins. 7. DO NOT over-tighten the retaining screws. NOTE: the gimbal, spacer and cover plate are made of Be. This is very TOXIC. Handle these with great care! Using the holder: 1. X & Y tilt angles are limited to +/- 30 o with this holder. 2. When using this holder select Beryllium double-tilt holder in the Controller menu. 26

27 STRONG DOUBLE-TILT HOLDER Retaining screw ALWAYS use the mounting jig as shown above, and always use the special tool to tighten the retaining screw. 27

28 NOTES FOR USING STRONG DOUBLE-TILT HOLDER: 1. The specimen should be located 150 m up from the base of the recess in the gimbal. Use spacer rings as shown, with specimen facing UPWARDS. Spacer arrangement for a standard Cu grid Spacer arrangement for a 100 m thick specimen Spacer arrangement for a 150 m thick specimen. 28

29 ALIGNING THE VOLTAGE AXIS This step assumes that the other alignments described have already been carried out. This is the optimum alignment axis for high resolution. Set MAG to 100,000X or greater and focus image. Spread beam to fill screen. Engage [Bright Tilt] and [HT Wobb] (left & right panels) or Click Wobbler HT, and DEF Select CLA in Alignment panel Image will expand and contract around a point. Bring this point to the screen centre by DEF/STIG X & Y knobs. Cancel [HT Wobbler] or Wobbler HT 29

30 ELECTRON DIFRACTION: note that several different modes are available: Selected Area (SAED) in normal TEM mode, where diffraction area is limited by selector aperture Nano-beam (NBD) & Convergent Bam (CBD) special modes where very small beam diameters are used to define diffracting area. SELECTED AREA DIFFRACTION Select [SA MAG] (right panel) and set at desired value. Move object of interest to screen centre Insert selector aperture and focus edge of aperture. Note effective aperture diameters: µm, corresponds to ~ 1600 nm at specimen µm, corresponds to ~ 800 nm at specimen µm, corresponds to ~ 350 nm at specimen µm, corresponds to ~ 180 nm at specimen Press [SA DIFF], and select appropriate camera length using MAG/CAM L knob Reduce brightness by turning Brightness knob anticlockwise Use DIFF FOCUS knob to adjust sharpness of diffraction spots Bring central spot to screen centre with [PLA] button (left console) and DEF/STIG knobs. Cancel [PLA] Beam stopper can be inserted to cover central bright spot. If you are tilting the specimen, you can track any lateral movement by defocussing the diffraction pattern the selected area then appears in the central spot. In this way you can see both the image and its diffraction pattern simultaneously. 30

31 At the end of your session: Check the booking schedule to see if someone will be using the next session. If so, leave high voltage switched ON and the cold trap filled. Filament OFF High Voltage set at 200 kv and OFF unless someone else is using the microscope after your session. MAG at 500,000X Stage coordinates at zero (neutral) Covers on window & binoculars Double-tilt specimen holder OUT and non-tilt holder (without the end piece) IN the column. Make sure you remove your specimen from the holder you were using. Objective and Selector apertures OUT Orius camera OUT EDX & STEM detectors OUT All holders (apart from the non-tilt rod) must be in their plastic sleeves and in their boxes with the lids securely fastened. Specimen loading desk left tidy. Transfer all your data to the Z-drive Leave all PCs ON If no-one is using the next session, heat the cold trap (Anti-Contamination-Device) to return it to room temperature (see p. 30). Sign and fill in the log sheet, indicating which techniques you have used, and any problems. Also, report any problems to em-faults. 31

32 Returning the ACD to room temperature If the ACD is allowed to warm up when the LN 2 is depleted it will release organic vapour into the column and into the vacuum pumps which will degrade their performance. The following procedure is used to bring the ACD up to room temperature in a controlled manner, protecting the vacuum system. 1. Put covers on window and binoculars 2. Remove cap from reservoir 3. Goggles on! 4. Insert ACD heater into dewar, engage the plug into the 2-pin socket 5. Select TEM Controller - Maintenance window ACD & Bake 6. In Bake Out/ACD window select ACD Heat and click On button. This closes valves in the vacuum system and turns off the ion pump. The system is on a timer and will switch off in ~ 20 minutes. Note that you cannot pump out the airlock during this time, so make sure the specimen holder is in position before doing this operation. 32