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FEI XL40 Environmental Scanning Electron Microscope[edit]

The NC/VP Materials Characterization Facility is home to the only environmental scanning electron microscope on campus. The instrument is capable of operating in low or high vacuum modes, includes EDAX EDS, EBSD and both high (1,000 C) and low temperature stages. The large chamber accommodates a variety of specimens and the low vacuum environment can be operated with water vapor or another gas depending upon the requirements of the characterization to be performed.

Special note[edit]

Since the ESEM is a large-chamber instrument, there is significant potential for running samples, sample mounts, ancillary stage components or anything else on the stage into a detector and breaking something. Take your time while loading samples on the stage and pushing the door shut and watch that nothing is struck. Always return tilt to 0 and increase working distance (or distance from pole piece to sample) to 20 mm or more while venting and before opening the chamber. Switch to the CCD chamber camera prior to decreasing working distance, tilting the stage or moving to the periphery of very large samples. Keep in mind that nothing is inexpensive when it comes to electron microscopy - the back scatter detector is easily broken by running a sample into it and costs $4,300 to replace.

Abbreviations[edit]

  • ESEM - Environmental Scanning Electron Microscope
  • SE - Secondary Electron
  • BSE - Back Scatter Electron
  • SED - Secondary Electron Detector
  • BSED - Back Scatter Electron Detector
  • GSED - Gaseous Secondary Electron Detector
  • GAD - Gas Amplification Detector
  • EDS - Energy Dispersive X-Ray Spectroscopy
  • EDAX - trade name of the company that manufactured the EDS system installed on the ESEM
  • EDAM - Energy Data Acquisition Module, the EDAX box that contains the interface cards for EDS spectra collection and external microscope control
  • MC - Microscope Control
  • HT - High Temperature, generally associated with the high temperature stage
  • LT - Low Temperature, generally associated with the low temperature stage

Operating Procedure[edit]

Prior to turning on beam[edit]

The MC software incorporates auto saturation and auto bias control which is not used in this lab as these controls tend to drastically shorten the life of the filament. Prior to turning on the beam, ensure that these controls are disabled by performing the following.

  1. If the MC software is not running, start it by double clicking on the Microscope control shortcut on the desktop of the MC control PC.
  2. The MC software will prompt you to home the stage if system power has been recycled. Do not home the stage as that will be performed later.
  3. Maximize the Beam window and click the Set Gun button. The Set Gun dialog will open.
  4. Uncheck the Autobias and AutoSaturation selections.
  5. Set GunBias-position to 1.
  6. Click the OK button.

Sample Exchange[edit]

  1. In the BEAM dialog box in the microscope control to ensure that the accelerating voltage is off.
  2. Select the CCD CHAMBER CAMERA button(video camera icon) in the microscope control
  3. In the STAGE dialog box and set the Z-position to 20mm
    NOTE: The Z height MUST be at least 20mm when opening or closing the chamber.
  4. Observe the condition of the chamber and ensure that neither the stage nor the specimen will strike the pole piece when opening or closing the chamber door.
    • If in question, increase the value of the stage Z-position until everything will clear the pole piece.
  5. Expand the VACUUM dialog box in the microscope control, select the VENT button to begin venting the sample chamber.
  6. Open the main valve of the N2 Tank.
  7. Venting the chamber may take over 5 minutes. After a few minutes have passed very gently pull on the chamber door, while watching the CCD camera display, and slowly open the sample chamber to rest at the end of the track.
  8. Close the main valve on the N2 tank after opening the chamber door.
  9. Remove any existing sample and secure the new sample to the stage.
    • Also ensure that there is nothing on the bottom of the chamber. (screws, bits of paper, etc.)
  10. Slowly close the sample chamber door while observing the CCD camera display to ensure the stage/sample does not collide with anything.
    • If a collision looks likely, STOP then increase the stage Z-position before completely closing the door.
  11. Expand the VACUUM dialog box, hold the sample door closed and click PUMP. Release the chamber door once the pump starts.
  12. Wait for the vacuum to indicate “VACUUM OK” under the VACUUM menu of the microscope control.

Initiate Beam and Train Z-Position[edit]

  1. Expand the BEAM dialog and select the desired accelerating voltage.
  2. Check that autobias and autosat are OFF
  3. Activate the beam by clicking the ACCELERATING VOLTAGE button.
    • Upon activating the beam, a dialog box will pop up asking you to confirm the Z-position. DO NOT click “Okay” yet.
  4. Use the DETECTORS tab to change to SE mode
  5. Navigate to find your sample and focus using the coarse and/or fine FOCUS knobs.
    • Lower magnification is better
  6. Click “OKAY” on the dialog box and note that the working distance (WD) in the data bar matched the Z-position under the STAGE menu
NOTE: If preforming EDS Analysis or working with BSE signal, adjust the Z-position to 10mm within the STAGE menu AFTER clicking "okay” in the dialog box. Otherwise adjust Z-position to suit needs.
IMPORTANT! : ALWAYS watch the Chamber Camera when making any adjustments to the Z-position!
IMPORTANT! : DO NOT WORK AT Z-POSITIONS LESS THAN 10mm!

Saturating the Filament (Should only be done when necessary)[edit]

NOTE: THE FILAMENT CURRENT IS GENERALLY SET TO AN APPROPRIATE VALUE AND INFREQUENTLY REQUIRES ADJUSTMENT

  1. Expand the BEAM dialog and deselect the FILAMENT LIMIT button
  2. Check the CROSSOVER box in order to view the filament image
  3. Adjust the BRIGHTNESS knob until the black background just changes to gray
  4. Adjust the CONTRAST knob until the bright “football” starts to saturate.
  5. Adjust the filament by clicking the arrows at the ends of the slider until the football is uniformly bright and clearly elliptical in shape.
    • A crescent shaped football indicates the filament current is too low.
    • A large very dense football indicates the filament is too high- reduce the contrast and readjust the filament current
  6. Select the FILAMENT LIMIT button to save the filament current setting
  7. Center the “football” over the cross-hair by clicking and dragging the mouse inside the GUN TILT reticle in the BEAM dialog
  8. Uncheck CROSSOVER in the BEAM dialog.

Capturing Images[edit]

  1. Locate a feature on the sample and focus using the coarse/fine FOCUS knobs.
  2. Increase magnification farther than the desired magnification for the image and focus as much as possible using the fine FOCUS knob only.
  3. Click on the SELECTED AREA in the toolbar (to the right of the CCD camera icon). This box will allow for a smaller live area for easier focusing.
    • If the box does appear on the image screen--move the mouse pointer to the center of the box and click to drag it to and area with a fair amount of features to focus on.
    • If the box does NOT appear on the image screen—click and drag diagonally on the image screen, after you stop clicking the SELECTED AREA should appear over the area you just selected. If the area you have selected does not have any or enough features to focus on, click in the center of the box and drag it to an area that does.
  4. Use the STIGMATOR knobs to finely focus on the sample. (only use at magnifications greater than 5k)
    • Depending on your magnification, a perfect focus may not be possible. This should be done to the best focus possible that eliminates all stretching.
  5. After focusing as much as possible, click on the SELECTED AREA icon again to remove it from the screen.
  6. Reduce the magnification to desired zoom.
  7. Fine Tuning the image before capturing
    • Use the BRIGHTNESS and CONTRAST knobs to adjust the values.
    • Waveform-(icon in the upper left hand corner (looks like a sine wave)). When adjusting the brightness, this will adjust the baseline of the graph, adjusting the contrast will adjust the amplitude. The graph should be roughly between the two lines, but depending on the sample may not be.
    • Scan Speed-This will slow down the scan and can be used to see the differences in the adjustments being made to the brightness and contrast. A slower scan speed may be necessary when capturing images at a higher magnification, but not always. This is up to the users’ discretion.
    • Ruler-(icon located directly under the “Scan” tab-looks like two crossed rulers) This can be used to measure the size of features or distance between them. NOTE: the ruler measurements, or any rulers saved to the screen on the image WILL NOT be saved when you save the image
  8. Click on the IN/OUT tab that will bring up a drop down menu.
  9. Click on IMAGE and a dialog box will pop up about saving the image.
  10. Enter the name you would like to save the image and make sure to save it in the correct folder
    • The system uses the 8.3 filenaming system. This means the name of the file cannot contain spaces or special characters and can only be 8 characters long.
    • If saving multiple images of the same sample, and you are comfortable with having the same name for each, click on the SAVE TIFF button in the upper right hand corner and the image will be saved. The file names will be incremented, e.g. gabbro01, gabbro02, etc.

EDS[edit]

NOTE: Make sure the sample is at a working distance of 10mm for best results. Always watch the Chamber Camera display when adjusting the Z-position.

  1. Open the INCA program on the desktop to the left of the main microscope computer.
  2. Select Full Acquisition Mode
  3. On the bottom left of the full INCA window there will be 4 selections, Click on ANALYZER
  4. Follow the flow chart in the Navigator tab
    a) PROJECT- Put in any notes or comments about the project being worked on
    ● Project Title, Owner, Customer Notes, Project Notes, Searchable Keywords
    b) SAMPLE-Allows for the creation of a new sample and provides the input details of the sample.
    ● Sample Name, I.D., Notes, Type, Polish, and the Sample coating, thickness, material, and density
    ● To create a new Sample, click on the Thumb Tack Icon to the left of the sample window.
    c) MICROSCOPE SETUP- Provides the opportunity to adjust the microscope conditions to best suit your sample
    Process Time: This is the length of the time spent reducing noise from the X-ray signal coming from the ED detector during processing. A greater process time will result in better peak separation.
    ● Greater process time = Slower Data acquisition
    ● Low process times are suitable for X-ray maps or qualitative chemical analysis
    ● Large process times are desirable for high resolution quantitative chemical analysis.
    ● It is recommended that the user begin with a larger process time in order to ensure that no details of the spectra are missed. High noise levels could cause neighboring peaks to overlap. If all peaks are well separated, the process time may be lowered.
    Acquisition Rate: This value changes with adjustments to the Process Time and Dead Time. It may fluctuate, if the fluctuation is large (e.g. 9.45 then 12.29) try adjusting the spot size by an increment of 0.1 or zooming in on the specimen
    Dead Time: This is the percentage of time during which the detector is inactive. This value should be around 20%.
    ● This will be affected by the process time. Choose the process time first and then adjust by changing the SPOT SIZE in the BEAM Dialog. (clicking on the arrow will adjust by 0.1, clicking inside the bar will adjust by 1.0)
    d) QUANT OPTIMIZATION-This is only necessary if quantitative measurements are desired and should only be performed once every session or every two hours.
    Quant optimization is taking a quick reading of the sample and adjusting the data according to the selected element. It is making a comparison of intensity of a peak from a known material, which can then make more accurate intensity measurements of unknowns.
    ● Select an element from the top drop down list that you know is in the composition of the sample. Start the optimization by clicking on the green circle on icon in the right corner. This can take a few minutes to finish. After the acquisition is complete, click the MEASURE button below the graph to set the new settings.
    e) ACQUIRE SPECTRUM- Click on the green circle button to begin acquiring the spectrum
    ● To create a new spectrum, click on the icon to the left of the Site of Interest drop down menu
    f) CONFIRM ELEMENTS-Use this section to add or remove Elements from the spectrum. The INCA Program will automatically ID some of the elements present in the sample but it may not be correct all the time. So it is always a good idea to have a rough guess of what the sample should contain.
    g) QUANT SETUP- Option to choose which elements are used for quantitative analysis and how the data is processed
    Processing Options:
    All Elements
    Element by Difference: Determines the weight percent of an element by assuming all the other elements have been accurately analyzed. Subtracts the analyzed total weight percent from 100% in order to calculate the remaining element.
    Element by Stoichiometry: Use this option if you want the concentration of one of the elements to be calculated assuming that is bound by predefined stoichiometry to all the other analyzable elements
    Element List:
    Current Spectrum: Quantifies the elements selected elements in Confirm Elements
    Fixed List: Manually input a set list of elements for Quantitative Analysis
    Combined: Quantifies all elements within a site of interest
    NOTE: Make sure to click SAVE after editing any options
    h) QUANT- This will quantify the results after the spectra has finished. There are a variety of tabs on the bottom of the window. Summary Results gives a quick overview of the Quantitative results of the elements chosen in the Quant Setup.
    To save the data, navigate to the ALL SPECTRA tab, make sure the spectra is checked and click on the icon on the upper right corner with the arrow pointing to the right. A dialog will pop up to edit the data to be saved. Check the options that apply to the project. Click OKAY and save to the correct folder. Click CLOSE after the file has been saved

Mapping[edit]

  1. Open the INCA program on the desktop to the left of the main microscope computer.
  2. Select Full Acquisition Mode
  3. On the bottom left of the full INCA window there will be 4 selections, Click on MAPPING
  4. Follow the flow chart in the Navigator Tab
    a) PROJECT- Put in any notes or comments about the project being worked on
    ● Project Title, Owner, Customer Notes, Project Notes, Searchable Keywords
    b) SAMPLE-Allows for the creation of a new sample and provides the input details of the sample.
    ● Sample Name, I.D., Notes, Type, Polish, and the Sample coating, thickness, material, and density:
    ● To create a new Sample, click on the Thumb Tack Icon to the left of the sample window.
    c) MICROSCOPE SETUP- Provides the opportunity to adjust the microscope conditions to best suit your sample
    Process Time: This is the length of the time spent reducing noise from the X-ray signal coming from the ED detector during processing. A greater process time will result in better peak separation.
    ● Greater process time = Slower Data acquisition
    ● Low process times are suitable for X-ray maps or qualitative chemical analysis
    ● Large process times are desirable for high resolution quantitative chemical analysis
    ● It is recommended that the user begin with a larger process time in order to ensure that no details of the spectra are missed. High noise levels could cause neighboring peaks to overlap. If all peaks are well separated, the process time may be lowered.
    Acquisition Rate: Take note of this value because it will be used in the Smartmap Setup. This value changes with adjustments to the Process Time and Dead Time. It may fluctuate, if the fluctuation is large (e.g. 9.45 then 12.29) try adjusting the spot size by an increment of 0.1 or zooming in on the specimen.
    Dead Time: This is the percentage of time during which the detector is inactive. This value should be around 20%.
    ● This will be affected by the process time. Choose the process time first and then adjust by changing the SPOT SIZE in the BEAM Dialog
    d) IMAGE SETUP-Options to edit for the Site of Interest Image.
    Image Resolution: The higher the resolution the longer it takes to get the image
    Speed: Should always be set to fast
    Data: Should be set to 8-Bit
    Frames: Increasing can improve the quality of the image but 1 frame is all that is necessary.
    e) SITE OF INTEREST- Click on the green circle button to obtain your site of interest.
    ● To create a new Site of Interest, click on the icon to the left of the Site of Interest drop down menu
    f) SMARTMAP SETUP-Options to edit the Smart Maps
    Map or Linescan Resolution: Increasing the resolution will significantly increase the time per frame of the Maps. The resolution cannot be greater than the resolution used for the Site of Interest.
    Conditions: These values do not need to be changed
    Acquisition Time:
    Frames: The number of frames that will overlap to produce the maps. The more frames the longer the map will take to complete. Only 1 frame is necessary.
    Map Dwell: This is the dwell time on a particular point. This number should be adjusted to optimize the COUNTS from the SMARTMAP. A good map should produce total counts in the hundreds of thousands.
    • To calculate an estimate of what the Map Dwell should be:
    1. Multiply the height and width of your selected resolution
    2. Divide by the Acquisition Rate from the microscope set up. (This should be in thousands. The bar is reading 8.56 it is actually 8,560)
    3. Multiply by 1000
    Example:
    Resolution: 256x192 Acquisition Rate: ~10,000
    [(256)(192)] = 4.9 → (4.9)(1000)=4900 10,000
    • 4900 would be the rough value of what the Map Dwell should be set to.
    • This value can always be adjusted if seeing the counts on the Smartmap are too high or too low.
    g) SMARTMAP- Click on the green circle icon to begin acquiring the map.
    h) ELEMENT SETUP-Use the given periodic table to select the elements to have maps of. The element text will turn yellow when selected. Double click to remove an element.
    i) ELEMENT MAPS-Shows the individual maps of various elements. Some maps will automatically pop up but they can be removed if not needed from the element setup.
    To save maps WITH the scale bar- right click on the map and then on export. Make sure to have the correct file path and edit the file name. Then click OKAY.
    To save maps WITHOUT the scale bar- Switch to the data tab and right click on the map you wish to save. Click export → TIFF. Navigate to the correct folder, name the file and save

Shutdown[edit]

  1. Decrease magnification from your sample using the MAGNIFICATION knob.
  2. In the BEAM dialog box in the microscope control and turn off the beam by clicking the ACCELERATING VOLTAGE button.
  3. Switch to the Chamber Camera.
  4. Expand the STAGE dialog and set the Z-position to 20mm to ensure that no collisions will happen.
    • If you feel that there will be a collision, increase the Z-position.
  5. In the VACUUM dialog and click the VENT button to vent the chamber.
  6. Turn on the main valve on the N2 Tank.
  7. Venting the chamber may take over 5 minutes. After a few minutes have passed very gently pull on the chamber door, while watching the CCD Camera, and slowly open the sample chamber to rest at the end of the track.
    • If a collision looks likely while opening the door, STOP then increase the Z-position before continuing opening the door.
  8. Close the main valve on the N2 tank after opening the chamber door.
  9. Remove the sample from the stage.
  10. Slowly close the sample chamber door while observing the CCD camera display to ensure the stage does not collide with anything.
  11. Expand the VACUUM dialog box, hold the sample door closed and click PUMP. Release the chamber door once the pump starts.