Topics

8.1. Introduction

8.2. Optical Microscope

8.3. Probe Start-up

8.4. Sample Change

8.5. Performing Analyses

8.6. Storing Line Traverses

8.7. Acquiring BSE Images

8.8. Using the EDS System

8.9. Acquiring X-ray Dot Maps

8.10. Probe Shutdown

8.1. 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 [ ].

8.2. 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.

8.3. 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.
• Turn the range on the ABSORBED CURRENT display to 3 x 10^-8.
• Depress the button below the filament temperature knob.
• 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.
• Look at the fluorescent spot in the optical microscope.
• 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.
• 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 coarse potentiometer. Click: Functions > Spectrometer Controls > Verify to perform the verification. Repeat until all values are between 3 and negative 3.

8.4. Sample Change

1. Turn off the filament. Turn the filament temperature potentiometer to zero.
2. Switch to the airlock vacuum gauge. Turn the VACUUM GAUGES knob to PRIMARY GAUGES: air lock.
3. 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.
4. 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.
5. Open the sample chamber door. Hold the sample changer knob back while opening the sample chamber door. Turn the handle forward, up, then left.
6. 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.
7. Close the sample chamber door. Hold the sample changer knob back while closing the sample chamber door. Turn the handle forward, down, then right.
8. Vent the sample changer. Press the AIRLOCK air inlet button on the VACUUM CONTROL panel. The changer will vent and can be removed.
9. Remove the sample changer. Remove the sample changer and replace the airlock cover plate.
10. Turn off the airlock system. Press the AIRLOCK off button on the VACUUM CONTROL panel.
11. Switch to the secondary vacuum gauge. Turn the VACUUM GAUGES knob to SECONDARY GAUGE.

1. Go to point storage. Select memory in the Stage Controls window and select Store:Line.
2. Enter the line information.
• Enter a line number. You may enter a new line number or overwrite an existing line by using its number.
• Enter a descriptive optional label for the line.
• Click ADD.
3. Pick the endpoints. Two windows will open with instructive information.
• Move to the start point of your intended traverse using the joystick.
• Hit [BCKL] twice to be sure that the slop has been taken out of the stage gears.
• If the position shifts as a result of this, reposition and repeat with [BCKL] until the point does not move.
• Press [ADJU] twice to accept the starting point's position.
• 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.
• Enter the number of points in the traverse.
• Click OK.
5. Load the points file.
• Select memory in the Stage Controls window and select Files:Load.
• Click on the desired line and then click ADD. Information about the line will be displayed.
• Click OK. TheAuto Points File will now diplay the individual points.
• Click DONE.
• 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.

8.7. Acquiring BSE Images

8.8. Using the EDS System

1. On the MAC-G3, click on the button labeled DTSA_PPC to start the program that operates the EDS system. The EDS system is sensitive to light and can only operated with the optical microscope lights turned off.
2. Calibrate the energy spectrum by doing the following:

• Acquire a spectrum of the ANDR standard by pressing Option-Apple-A.
• Click the CALIBRATE button in the lower left. This will bring up a menu with a yellow background.
• Click the button labeled Si-Fe.
• Be sure that the option to “Use Calibration Data” is selected and click OK.

3. Set the preset (counting) time.

•  Select Acquire>Hardware Setup>DTSA_SpectralEngine from the menu.
•  A window labeled “Acquisition Setup” will open and you can select your counting time using the “Acquire Live Time” box. For our purposes 30 seconds is probably plenty long.
•  Click OK to exit.

4. Acquire a spectrum by pushing Option-Apple-A.  The spectrum will collect for 30 seconds.
5. You can identify the characteristic peaks of the spectrum by two methods. You may either: (1) Use the ¬ and ® keys to move the spectral-line markers to lower and higher atomic numbers, or (2) enter the atomic symbol of an element of interest on the keyboard. For example, entering “fe” to display the iron lines. The markers show the theoretical locations of the spectral lines for Fe. On the right side of the spectrum are three markers (two superimposed that show the positions of Fe-Ka1 and Fe-Ka2 and a short on showing Fe-Kb. On the left side of the spectrum are markers showing the many iron L lines.
6. You can determine the energy of any point on the spectrum by putting the cursor on the point of interest. The channel number and energy appear in the yellow boxes at the upper left of the display.
7. You can allow the program to try label the peaks by clicking the Peak ID button at the lower left to open a new window. Click the Auto Peak Label button to identify the peaks. The program is not particularly good at finding and identifying peaks, but this is sometimes useful. You can do this as the spectrum acquires and may want to click several times as the peaks become better defined.

8.9. Acquiring X-ray Dot Maps

8.10. Probe Shutdown

1. Turn off the filament. Turn the filament temperature potentiometer to zero.
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.