EDS
-Table of Contents
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- 1. SEM - - -
- 2. EDX - - -
- 3. Stellite Composition -
- 4. SEM SOP - - -
1. SEM
--Honestly, a really good introduction to SEM -
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- Concepts - - -
- Basic Operations - -
- Specific to Tescan Vega - -
1.1. Detectors
--The detection system may contain a set of detectors designed for detecting various signals resulting from electron beam interaction with the sample surface. The microscope is always delivered with the SE detector -
-1.1.1. SE detector
--The detector works in high vacuum only. -Secondary electrons enhance topographic contrast contrary to material contrast of back-scattered electrons. The secondary electron (SE) detector is a basic standard detector always present in the microscope. -The SE detector is of an Everhart-Thornley type. The grid on the front part of the detector has positive potential. This attracts and accelerates the low-energy secondary electrons arising on the specimen surface and focuses them onto the scintillator. The light flashes, which result from the impingement of the electrons on the scintillator, are transferred through the light guide to the photo-multiplier outside the chamber of the microscope. -
-1.1.2. BSE detector
--The detector works in high and low vacuum. -Back-scattered electrons (BSE) enhance material contrast of the sample. The BSE detector is of the scintillation type. An annular (YAG) mono-crystal scintillator with a conductive surface is placed in the optical axis directly under the lower pole extension of the objective. The high energy back-scattered electrons impinge the scintillator without any additional acceleration and excite the scintillator atoms that emit visible radiation photons successively. The photons are carried, by means of the light guide, through the side outlet of the scintillator to the cathode of the photo-multiplier. They are then processed in the same way as the signal coming from the secondary electrons. -The BSE detector is manufactured in an R-BSE (Retractable BSE) version. This modification allows the retraction of the detector from under the pole piece position if the detector is not used. This enables the specimens to be moved as close as possible to the objective when viewed by other detectors. -
-1.2. Considerations for Optimal SEM Imaging Results
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- Beam Settings
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- Voltage -Is specimen conductive (high) or non-conductive (low)? -Beam-sensitive (low) or not? -From what depth do you want signal to emerge, and which signal? - -
- Current -Is specimen conductive (high) or non-conductive (low)? Beam-sensitive (low) or not? -Optimize signal (high) vs. resolution (low), choose small aperture (imaging) or large (x-ray). - -
-Working Distance -If not constrained by geometry of application, optimize resolution (low) vs. depth of field (high); -signal may decrease at too long or too short W; when in doubt, operate at eucentric height. -
- --EDX should be done with a working distance of 15 mm -
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- -Detector Settings -
- --Detector Type: -
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- SE (topographic contrast, some Z) -
- BSE (atomic #, aka Z) -
- EDS/WDS (elemental composition). -
-Using detector Bias, you can switch between different modes, please do not do so. Take one picture SE and one picture BSE. One might argue that the acquisition process for both are the same, but do it anyway, it makes life so much easier when you’re trying to plot it on a report. -
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- Alignments
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- Basic Technique: -After gun tilt, iteratively adjust focus, astigmatism, lens alignment based on visual cues. -
- 1st Approximation (Focus/Stig): -Use reduced area window w/longest dwell time that gives near-live refresh rate. -
- Perfected: -Make comparisons using “alignment rectangle” in full frame or reduced window (integrate 1 frame). -
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- - Scan Settings
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- Brightness & Contrast: -Optimize using Videoscope at dwell/pixel capture settings. -(try in full frame or line scan). - -
-Live (single frame) vs. frame & line averaging/integration -Frame averaging spreads out dose to mitigate charging artifacts, by averaging out the effects of a sudden flash. However, it does not overcome the general effects of charging and should be seen as a last ditch effort. -
- --Note: This is unusual for thermal spray coatings and anything conductive. -
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-- Scan Orientation: -Change scan rotation to scan perpendicular vs. parallel to features; -evaluate scan artifacts (is there image compression/stretching due to beam drift?) and mitigate charging artifacts. -
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2. EDX
--Energy-dispersive X-ray spectroscopy (EDS, EDX, or XEDS), sometimes called energy dispersive X-ray analysis (EDXA) or energy dispersive X-ray microanalysis (EDXMA), is an analytical technique used for the elemental analysis or chemical characterization of a sample. The EDS analysis can be used to determine the elemental composition of individual points or to map out the lateral distribution of elements from the imaged area. -
- - --The energy dispersive spectroscopy (EDS) technique is mostly used for qualitative analysis of materials but is capable of providing semi-quantitative results as well. Typically, SEM instrumentation is equipped with an EDS system to allow for the chemical analysis of features being observed in SEM monitor. Simultaneous SEM and EDS analysis is advantageous in failure analysis cases where spot analysis becomes extremely crucial in arriving at a valid conclusion. Signals produced in an SEM/EDS system includes secondary and backscattered electrons that are used in image forming for morphological analysis as well as X-rays that are used for identification and quantification of chemicals present at detectable concentrations. The detection limit in EDS depends on sample surface conditions, smoother the surface the lower the detection limit. EDS can detect major and minor elements with concentrations higher than 10 wt% (major) and minor concentrations (concentrations between 1 and 10 wt%). The detection limit for bulk materials is 0.1 wt% therefore EDS cannot detect trace elements (concentrations below 0.01 wt%) [1]. -
- --Tutorial on using the AZtecLive software -Introduction to Energy Dispersive Spectroscopy (EDS) -
- --EDS Mapping displays the X-ray data as individual elemental images for different energy ranges. Mapping gives a quick understanding of the scanned area. Unlike Point Analysis, it shows the elements distribution across the scanned area. -
- - --Construct Maps -
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- Map -
- TruMap -Performs deconvolution to separate the images -
- QuantMap -
-Image Scan Size - 1024 -Dwell Time 10 um -Input Signal [ ] SE [ ] BSE -AutoLock On -
- --Fixed Duration -Energy Range 20 kEV -Number of channels 2048 -Process Time 2 -Pixel Dwell Time us 50 -Frame Live Time 10 -
- - - --Would suggest Line Spectra to show the change in composition from the top surface to the -
- - --Change the colors by selecting AutoLayer to really bring out the image -
- - - --Great PDF with EDS specific Periodic Table. Need to eventually make our own using https://tikz.net/periodic-table/ -
-2.1. Displaying Outset
--Use outset graphs in EDX in order to show the change in composition -
- - -3. Stellite Composition
-| - | Stellite | -- | Co | -Cr | -W | -Mo | -C | -Fe | -Ni | -Si | -Mn | -
|---|---|---|---|---|---|---|---|---|---|---|---|
| Blend A | -A1 | -(Stellite 6 (HS6)) | -Bal. | -29.50 | -4.60 | -0.22 | -1.09 | -2.09 | -2.45 | -1.32 | -0.27 | -
| - | A3 | -(50% HS6 + 50% HS20) | -Bal. | -30.68 | -10.45 | -0.25 | -1.72 | -2.30 | -2.37 | -1.16 | -0.27 | -
| - | A5 | -(Stellite 20 (HS20)) | -Bal. | -31.85 | -16.30 | -0.27 | -2.35 | -2.50 | -2.28 | -1.00 | -0.26 | -
| Blend B | -B1 | -(Stellite 1 (HS1)) | -Bal. | -31.70 | -12.70 | -0.29 | -2.47 | -2.30 | -2.38 | -1.06 | -0.26 | -
| - | B2 | -(75% HS1 + 25% HS12) | -Bal. | -31.19 | -11.56 | -0.27 | -2.23 | -2.24 | -2.30 | -1.02 | -0.26 | -
| - | B3 | -(50% HS1 + 50% HS12) | -Bal. | -30.68 | -10.43 | -0.25 | -1.98 | -2.19 | -2.21 | -0.99 | -0.27 | -
| - | B4 | -(25% HS1 + 75% HS12) | -Bal. | -30.16 | -9.29 | -0.22 | -1.74 | -2.13 | -2.13 | -0.95 | -0.27 | -
| - | B5 | -(Stellite 12 (HS12)) | -Bal. | -29.65 | -8.15 | -0.20 | -1.49 | -2.07 | -2.04 | -0.91 | -0.27 | -
| Blend C | -C1 | -(Stellite 4 (HS4)) | -Bal. | -31.00 | -14.40 | -0.12 | -0.67 | -2.16 | -1.82 | -1.04 | -0.26 | -
| - | C2 | -(75% HS4 + 25% HS190) | -Bal. | -30.06 | -14.40 | -0.14 | -1.31 | -2.15 | -2.07 | -1.03 | -0.27 | -
| - | C3 | -(50% HS4 + 50% HS190) | -Bal. | -29.13 | -14.40 | -0.16 | -1.94 | -2.13 | -2.32 | -1.02 | -0.29 | -
| - | C4 | -(25% HS4 + 75% HS190) | -Bal. | -28.19 | -14.40 | -0.18 | -2.58 | -2.12 | -2.56 | -1.01 | -0.30 | -
| - | C5 | -(Stellite 190 (HS190)) | -Bal. | -27.25 | -14.40 | -0.20 | -3.21 | -2.10 | -2.81 | -1.00 | -0.31 | -
| - | - | Co | -Cr | -W | -Mo | -C | -Fe | -Ni | -Si | -Mn | -
|---|---|---|---|---|---|---|---|---|---|---|
| Stellite 6 | -HS6 | -Bal. | -29.50 | -4.60 | -0.22 | -1.09 | -2.09 | -2.45 | -1.32 | -0.27 | -
| Stellite 20 | -HS20 | -Bal. | -31.85 | -16.30 | -0.27 | -2.35 | -2.50 | -2.28 | -1.00 | -0.26 | -
| Stellite 1 | -HS1 | -Bal. | -31.70 | -12.70 | -0.29 | -2.47 | -2.30 | -2.38 | -1.06 | -0.26 | -
| Stellite 12 | -HS12 | -Bal. | -29.65 | -8.15 | -0.20 | -1.49 | -2.07 | -2.04 | -0.91 | -0.27 | -
| Stellite 4 | -HS4 | -Bal. | -31.00 | -14.40 | -0.12 | -0.67 | -2.16 | -1.82 | -1.04 | -0.26 | -
| Stellite 190 | -HS190 | -Bal. | -27.25 | -14.40 | -0.20 | -3.21 | -2.10 | -2.81 | -1.00 | -0.31 | -
| - | Stellite 6 | -Stellite 20 | -
|---|---|---|
| A1 | -100 | -0 | -
| A3 | -50 | -50 | -
| A5 | -0 | -100 | -
| - | Stellite 1 | -Stellite 12 | -
|---|---|---|
| B1 | -100 | -0 | -
| B2 | -75 | -25 | -
| B3 | -50 | -50 | -
| B4 | -25 | -75 | -
| B5 | -0 | -100 | -
| - | Stellite 4 | -Stellite 190 | -
| C1 | -100 | -0 | -
| C2 | -75 | -25 | -
| C3 | -50 | -50 | -
| C4 | -25 | -75 | -
| C5 | -0 | -100 | -
4. SEM SOP
-4.1. Stopping the Microscope
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- Switch off the high voltage by clicking on the HV button in the Electron Beam panel. -
- Remove your samples from the microscope. -
- Pump the microscope. -
- Close the program (use Exit from the File menu) select the Switch off (the microscope) and exit (the application) option. -
- Wait until the VegaTC program closes itself. The microscope configuration will be automatically saved on the hard drive. -
- Shut down OS Windows in the usual way. -
- Turn the main switch to the left (OFF position). -
4.2. Loading of the sample
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- Use only one gloved hand when handling samples and holders -
- Avoid letting the sample holder or any part of the sample exchange rod touch non-clean surfaces which may be contaminated with hand-oil -
- Never “blow on” or exhale on samples to dry them, use the IR lamp instead -
- Always make sure all screws are tight and that you always have a sure grip -
- Always ask if you have a question -
4.3. Images at Low Magnification
--There are four factory presets for the accelerating voltage (5 kV, 10 kV, 20 kV, 30 kV), one -for each HV index. The user does not need to make any further adjustments by switching -among them and using magnification up to 4000x. -
- --Click on the PUMP button in the Vacuum panel to start the pumping procedure -(Figure 2). It usually takes around 3 minutes to reach vacuum ready - status which -means that the microscope is ready to use. If there is a need to exchange the -specimen, follow the instructions in chapter 8.2. -
- - - --20240310-112336_screenshot.png -
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-In the SEM Detectors & Mixer panel select the appropriate detector from the list box -(Figure 3). We recommend using the SE or BSE detector. When the BSE detector is -used, make sure that the detector is not retracted! See chapter 6 for detailed infor- -mation -
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-20240310-112616_screenshot.png -
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- Select the accelerating voltage (30 kV recommended) using the combo box in the -
-Electron Beam panel (Figure 5). -
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- Clicking on the HV button in the Electron Beam panel turns the high voltage on and -
-starts the heating of the tungsten filament (see Figure 5). -
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- Right-click in the SEM Scanning window to open the menu and select the Minimum -
-Magnification function (Figure 6) -
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-20240310-112723_screenshot.png -
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-7 Select RESOLUTION mode (click on the Scan Mode function in the Info Panel (see -Figure 10) and select RESOLUTION or use the Continual Wide Field option – switches -automatically between WIDE FIELD and RESOLUTION mode and vice versa when -increasing or decreasing magnification) -
- --Focus the image by clicking on the WD icon in the Toolbar and turning the -Trackball from left to right (or vice versa). Alternatively use the Auto WD function for -focusing (see Figure 6). Double-clicking (left mouse button) in the SEM Scanning -window opens the Focus window. To remove the Focus window double-click -anywhere in the SEM Scanning window. -
- - --To select beam intensity (BI 10 recommended), first left-click on the BI icon -on the Toolbar and then use the arrows in the Pad panel (Figure 8). -
- - - --20240310-113043_screenshot.png -
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- To select the sample position in the Stage Control panel, click on the appropriate -
-number button on the carousel (Figure 9) or use the manual knobs in the case of the -SB microscope type. -
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- Placing the cursor over the SEM Scanning window and clicking the mouse wheel -
-moves that area on the stage into the centre of the image. See chapter 7.2 for other -mouse actions. -
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- To magnify the image click on the Magnification icon on the Toolbar and turn -
-the Trackball from left to right. -
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- Once the area of interest is magnified and focused as desired, right-click on the -
-Speed icon on the Toolbar and select the appropriate scanning speed. -
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- Clicking on the Acquire button in the Info Panel (Figure 10) or on the icon -
-on the Toolbar saves the image. Fill in the note, sign and description field -if necessary. Choose a folder in which to store the image. To change the parameters -of the image use the Image Parameters function in the main SEM menu -
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-20240310-113251_screenshot.png -
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- Clicking on the icon opens the dialogue for saving the actual adjustment of the -
-microscope. It is possible to restore the saved adjustment of the microscope later. -
-4.4. Images at High Magnification
--The best resolution is achieved at the highest accelerating voltage (30 kV) of the primary -electrons. -
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- Insert an appropriate sample for high magnification images (e.g. tin on carbon -
-sample, Figure 18). -
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- Select the fourth HV index using the combo box in the Electron Beam panel (20 kV - -
-30 kV) and turn on the high voltage. -
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- Focus the image in RESOLUTION mode (click on the Scan Mode function in the Info -
-Panel and select RESOLUTION or use the Continual Wide Field option). -Note: Use the Degauss column function by means of the icon before changing WD&Z or WD. The image should remain in focus. -
- --Check the spot size, which is determined by the BI value. Right-click in the SEM -Scanning window to select the optimum BI value – Auto BI OptiMag. -
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- For the best resolution, it is necessary to work at a short working distance (WD). The -
-optimum WD is about 5 mm for the SE detector (in the case that the BSE is not -mounted underneath the objective lens). For BSE images the optimum WD is about -8.5 mm. To change the working distance together with Z-axis, without defocusing -the image, use the WD&Z function in the Stage Control panel (Figure 15). -
- --WARNING: Moving the manipulator with the specimen can cause it to collide with other inner -components of the microscope and can cause damage to the microscope. Control the -movements of the manipulator by video camera imaging (open the Chamber View by clicking -on the -icon). The manipulator’s movement can be stopped by clicking on the Stop -button in the Stage Control panel (see Figure 15). -
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-Gradually magnify and focus the image to achieve 10kx magnification. In the case -that the image is moving during focusing, it is necessary to check the centering -of the objective. Select the Manual Column Centering function using the combo box -in the Electron Beam panel after clicking on the Adjustment >>> button (Figure 16). -The Manual Centering Wizard window will appear (Figure 17). Clicking on the WOB -button opens the Focus window in the SEM Scanning window. Click on the Next>> -button to obtain the next instructions. The function of the centering has two adjust- -able values. To be sure just one value is changing, hold down the F12 key to change -only X movement at the Trackball, and the F11 key to change only Y movement. -
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- Each time that the image is too dark or light it is necessary to use the Auto Signal -
-function (see Figure 6 or use the icon ). To set the contrast and brightness -manually, click on the icon and use the Trackball. -
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-At higher magnifications (>10kx) it is necessary to check if astigmatism (Figure 18 -(a), (b)) is precisely corrected (Figure 18 (c)). To correct astigmatism click on the -Stigmator function in the Info Panel (Figure 19). For precise correction use the Focus -window (in the SEM Scanning window) and the F11 and F12 keys in the same way -as in point 6. -
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- Select the appropriate scanning speed and save the image. -
- Clicking on the icon opens the dialog for saving the current adjustment of the -
-microscope. It is possible to restore the saved adjustment of the microscope later. -
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4.5. Specimen Exchange
--The specimen should somehow be fixed or glued to the specimen stub before it is inserted into the chamber. It is possible to use 12.5 mm specimen stubs or any other specimen holders, delivered as microscope accessories (see chapter 9.7). -If the specimen is examined in high vacuum mode, it must be conductive or must be made conductive using one of the methods described in the technical information. The conductive surface of the specimen must be conductive contacted to the stub. -Non-conductive samples can be investigated in low vacuum mode. -Instructions: -
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- Vent the microscope by using the VENT button in the Vacuum panel. Wait until the pressure is at atmospheric level. -
- Set the tilt of the specimen stage to zero. -
- Open the chamber door by gently pulling it. -
- The automatic positions set up in the Stage Control panel can be used, which are intended for specimen position exchange. To select the sample position click on the appropriate number button on the carousel. At this time the button background is red to indicate the specimen exchange mode. -