Camebax Microprobe Operating Manual - A Work in Progress

IF YOU FEEL UNCERTAIN ABOUT PERFORMING ANY OF THE PROCEDURES DESCRIBED BELOW -- SEEK HELP.

TOPICS

Introduction

The following conventions are used throughout this write up: (1) labels on the scanning console are given in bold; (2) items entered on or done with the Mac IIvx that serves as a terminal for the MICRO computer are shown in underlined; and (3) items entered on the MICRO keyboard are given in square brackets [ ].

Optical Microscope

The sample may be viewed in either reflected or transmitted light, which are selected using the toggle switch to the right of the oculars. The middle position of the switch is off.

There is only one magnification available: 400x. Each tick mark on the reticule corresponds to 1 µm.

Stage Automation

Probe Start-up

  1. Fill the liquid N2 dewar. If the day is either Monday or Friday, fill the dewar and record this fact in the log book.
  2. Turn on the Mac G3 and MAC IIvx. Press the arrow key in the upper right corner of each keyboard.
  3. Check the spectrometer and stage positions. The spectrometers should be located at approximately 600 and the stage at X=100, Y=100. If the spectrometer positions are incorrect, seek help. If the stage X and Y positions are incorrect, they can be adjusted by disengaging the motors by pulling out the clutch knobs and moved. Be sure to reengage the clutches when you are finished. Press [INIT] twice on the MICRO keyboard.
  4. Check the vacuum is adequate. The VACUUM CONTROL second. vac. light should be on. If not, check whether the gate value is open, If the gate value is closed, open it using the switch labeled VANNE SECONDAIRE in the back of the scanning console. The gate valve's closed position is marked. The gate valve, which is located behind the electron column, will open (it is a noisy process). Wait until the VACUUM CONTROL second. vac. light comes on, before proceeding.
  5. Turn on the high voltage. Turn the VOLTAGE coarse knob. Each click will be accompanied by a grinding noise as the bias resistors are changed. Position 5 corresponds to 15 keV.
  6. Start the control program. Double-click the MBX 1.41b alias icon.
  7. Move the stage to a fluorescent material. Benitoite (BENI), scheelite (SCHE), or willemite (WILL) are good choices. Click: Standard (Stage Control window), enter the standard abbreviation, then click Move. After the stage is done moving, check the focus.
  8. Saturate the filament. Do not exceed the previous saturation value recorded in the logbook
    1. Turn the range on the ABSORBED CURRENT display to 10-7.
    2. Depress the button below the filament temperature knob.
    3. Increase the filament temperature potentiometer gradually while watching the ABSORBED CURRENT meter. The absorbed current will increase and then stop increasing as it reaches a plateau. The filament is "saturated" at the leading edge of this plateau. If the specimen current drops off after reaching a peak, the electron gun needs aligning. Use the horizontal knobs on the side of the gun housing to maximize the current, then resaturate the filament.
  9. Check the column alignment.
    1. Look at the flourescent spot in the optical microscope.
    2. Turn the LENS 3 coarse potentiometer both ways to increase and decrease the size of the spot. The fluorescent area should expand and contract symmetrically from a point when you adjust the potentiometer up and down.
    3. If it does not, the column needs aligning. Adjust the position of the whole column by using the black knobs halfway up the electron column. Recheck the fluorescent area while adjusting the LENS 3 coarse potentiometer. Repeat the process until the expansion/contraction is symmetrical.
  10. Align the optical microscope. Adjust the two slanting knobs at the base of the electron column so that the spot is under the crosshairs when viewed using the eyepieces.
  11. Verify the spectrometer positions. Move to andradite (ANDR). Focus. Adjust the absorbed current to about 25 nA using the LENS 1 control potentiometer. Click: Functions > Spectrometer Controls > Verify to perform the verification. Repeat until all values are between 3 and negative 3.

Performing Analyses

  1. Choose your analytical setup. Enter Apple-L and select the desired procedure from the "Analytical Procedures" subdirectory.
  2. Search the Standard Intensities Library. Choose the option that does a search for any more recent records (calibrations) for the the current setup. Click OK.
  3. Set the beam current for analysis. Use the LENS 1 coarse potentiometer to set the beam current to the desired value. For most analyses this will be 10 nA.
  4. Specify output file. Enter an output file name. It's a good idea to identify the sample in the file name.
  5. Record run information in the log book. Write your name, the date, the time, the KV used, the filament temperature value, the beam current, the spot size, and the column vacuum.
  6. Check the standards. Check that the K-ratios for the standards are within 1% of 1.000. If not, recalibrate:
  7. Enter Apple R and select the element(s) and standard(s) to recalibrate. The MICRO will move to the appropriate standard automatically.
    1. Position and focus the standard carefully, then hit [ ADJU ].
    2. You must repeat this three times, after which, the computer will report the results.
    3. Accept the calibration if the Sigma Ratio is less than 2.0.
  8. Check secondary standard(s). Move to a standard similar to your unknowns (if possible) and perform an analysis to check the calibration. If any major elements are off by more than 2% (relative), you may wish to recalibrate the standard (see above).
  9. Perform analyses. Click the "Use previous backgrounds" box after performing the first analysis on an unknown. You may wish to unclick this box the first time you go to a new material; however, backgrounds should be pretty similar for all materials if selected correctly.

Storing Analysis Lines

  1. Go to point storage. Select memory in the Stage Controls window and select Store:Line.
  2. Enter the line information.
    1. Enter a line number. You may enter a new line number or overwrite an existing line by using its number.
    2. Enter a descriptive optional label for the line. This will appear in the description space on the printed output.
    3. Click ADD.
  3. Pick the endpoints. Two windows will open with instructive information.
    1. Move to the start point of your intended traverse using the joystick.
    2. Hit [BCKL] twice to be sure that the slop has been taken out of the stage gears.
    3. If the position shifts as a result of this, reposition and repeat with [BCKL] until the point does not move.
    4. Press [ADJU] twice to accept the starting point's position.
    5. Repeat the process for the ending point of the line.
  4. Select the number of points. After selecting the ending point, the computer will report the length of the line you have selected in microns.
    1. Enter the number of points in the traverse.
    2. Click OK.
  5. Load the points file.
    1. Select memory in the Stage Controls window and select Files:Load.
    2. Click on the desired line and then click ADD. Information about the line will be displayed.
    3. Click OK. The Auto Points File will now diplay the individual points.
    4. Click DONE.
    5. Specify a name for the autopoints file and click SAVE.
  6. Use the autopoints file. Click on the "Start using auto point file" box, then click Start.
  7. Select the auto points file. Click Load. The stage will move to the first point and begin the analytical traverse.

Probe Shutdown

  1. Turn off the filament. Turn the filament temperature potentiometer to zero. Push the button below the dial.
  2. Turn off the high voltage. Slowly turn the VOLTAGE coarse to zero. This will be accompanied by a grinding sound as the bias resistors change.
  3. Turn off the reflected/transmitted light. Flip the toggle switch to the center position.
  4. Put the MICRO to sleep. Press [ BYE ] twice. The spectrometers will move to 600 and the stage X and Y position will move to 100. Press [ DEL ] to blank the MICRO screen.
  5. Close the gate valve. Flip the VANNE SECONDAIRE switch in the back of the scanning rack to the closed position.
  6. Turn off the computers. Click: Special > Shut Down to turn off the G3 and MAC IIvx.

Sample Change

  1. Turn off the filament. Turn the filament temperature potentiometer to zero. Push the button below the dial.
  2. Move the stage to the sample change position (X=7000, Y=41500).
  3. Switch to the airlock vacuum guage. Turn the VACUUM GAUGES knob to PRIMARY GAUGES: air lock.
  4. Attach the sample changer. Remove the airlock cover plate and attach the sample change unit by hanging it from the two pins at the top.
  5. Pump down the sample changer. Press the AIRLOCK pump down button on the VACUUM CONTROL panel. The changer will pump out. Proceed when the vacuum is less than 2 Torr.
  6. Open the sample chamber door. Hold the sample changer knob back while opening the sample chamber door. Turn the handle forward, up, then left.
  7. Insert/remove the sample. Gently push in the sample changer rod until it seats. Rotate and withdraw it, levaing/capturing the sample. Be sure to pull the rod all the way out.
  8. Close the sample chamber door. Hold the sample changer knob back while closing the sample chamber door. Turn the handle forward, down, then right.
  9. Vent the sample changer. Press the AIRLOCK air inlet button on the VACUUM CONTROL panel. The changer will vent and can be removed.
  10. Remove the sample changer. Remove the sample changer and replace the airlock cover plate.
  11. Turn off the airlock system. Press the AIRLOCK off button on the VACUUM CONTROL panel.
  12. Switch to the secondary vacuum guage. Turn the VACUUM GAUGES knob to SECONDARY GAUGE.