Other measurement needs

10. Other measurement needs#

10.1. SEAD#

Todo

10.2. Raster#

Todo

  • Single ROI area scans. A map of sorts.

  • explain INI file, plotting, dossier

10.3. XRF spectra#

Todo

  • %xrf

  • XRF as a metadata measurement

10.4. Glancing angle stage#

The glancing angle stage allows you to automate the alignment and measurement of up to 8 sample, optionally spinning the samples to suppress diffraction peaks from crystalline substrates.

This is not intended as a standing wave experiment. The angle chosen for the incident beam relative to the sample is usually large compared to the critical angle.

Rather, the purpose of this instrument is to spread the beam out over the surface of the sample by placing the sample at a shallow angle to the incident beam. This significantly increases the number of atoms contributing to the measurement, thus increasing the signal going to the fluorescence detector.

Here are all the commands related to the operation of the glancing angle stage.

RE(ga.to(N))

Rotate to sample N (N is an integer between 1 and 8). All spinners are halted and spinner N is started, unless ga.spin is False.

RE(ga.auto_align(angle))

Run the automated alignment procedure (Section 11.6) to align the sample at the specified angle (in degrees) relative the flat position.

The automated alignment procedure should always start when the stage is flat or approximately flat relative to the incoming beam. If you just aligned another sample, you should do either

RE(ga.flatten())

or

RE(mvr(xafs_pitch, -angle))

where angle is the argument to the previous ga.auto_align()) command or the angle to moved to if doing the alignment by hand.

RE(ga.flatten())

For a sample that has been aligned by the automated alignment procedure, return the sample to the position of flat and parallel to the beam.

ga.spin

This is True if the sample should be spinning during measurement. So

ga.spin = True

or

ga.spin = False
ga.orientation

This is a string, either parallel or perpendicular depending on the orientation of the sample stage. This orientation is referring to the relative orientation of the surface of the spinning sample and the electric vector of the incident beam. So

ga.orientation = 'parallel'

or

ga.orientation = 'perpendicular'
ga.on(N)

Turn on spinner N, where N is an integer between 1 and 8

ga.off(N)

Turn off spinner N, where N is an integer between 1 and 8

ga.alloff()

Turn off all spinners.

Once a sample is aligned and placed at the correct angle, you need to set the detector position to optimize the fluorescence signal. Here are the relevant commands:

%xrf

Measure an display a fluorescence spectrum. You want the total count rate (the OCR column in the table printed to the screen) to be around 200,000 counts on each of the 7 channels. Not the sum of channel! Each channel can be as high as 200,000 counts.

RE(mv(xafs_detx, YYY))

Move the detector to a new position, YYY, where that indicates a floating point number, typically something between 10 and 205. When you move the detector to a new position, always remeasure the XRF spectrum with %xrf.

The fully retracted position is 205. The closest position is usually set as a software limit when the experiment is being set up.

10.5. Linkam stage#

Here are the main commands for interacting with the linkam stage.

linkam.on()

Turn the heater on, enable temperature feedback.

linkam.off()

Turn the heater off, disable temperature feedback.

linkam.temperature()

Return the current temperature of the stage.

linkam.status()

Write a nicely formatted status summary to the screen.

RE(mv(linkam, TEMP))

Change linkam temparature with a progress bar printed on screen.

RE(mv(busy, TIME))

Wait for an equilibrium time with a progress bar printed on screen/

Note that the controls are not complete. When using the linkam stage as an LN2 cryostat, you need to manually turn the pump on and off using the CSS screen.

Future tech

Implement something using linkam.lnp_speed to control the pump.

Other parts of the beamline manual related to the Linkam stage:

10.6. Lakeshore controller and Displex#

Here are the main commands for interacting with the linkam stage.

lakeshore.on()

Turn the heater on, enable temperature feedback.

lakeshore.off()

Turn the heater off, disable temperature feedback.

lakeshore.readback.get()

Return the current temperature of the stage.

lakeshore.setpoint.get()

Return the current setpoint of the stage.

lakeshore.status()

Write a nicely formatted status summary to the screen.

lakeshore.to(TEMP)

Move to the indicated temperature with a progress bar that will count down the approximate time required to make this change. This works much more reliably in the heating direction than in the cooling direction.

lakeshore.units(UNIT)

Switch between C and K units on the CSS screen.

lakeshore.level(POWER_LEVEL)

Switch the four heater output levels. low means that 100 mA will be available for the heater. medium is 300 mA. high is 1 amp. Any other string will be interpreted as turning the heater off. high is almost always the correct choice.

Other parts of the beamline manual related to the Lakeshore controller and the Displex cryostat:

  • See Section 11.5 for details about Lakeshore automation using a spreadsheet.

  • See Figure G.2 to see how to set the hoisting straps for lifting the cryostat onto the xafs_y stage.

10.7. Wafers#

There is some functionality specifically for measuring films grown on large, round wafers. The basic experiment involves measuring XAS of 1 or more edges from selected positions on a film. BMM has sample holders specifically designed for holding standard size silica or crystalline wafers.

Most such experiments involve reliable motion to specific locations on the film. This usually starts with finding the center of the wafer and indexing locations relative to the center.

The method for finding the center involves finding the X,Y coordinates of three points around the periphery of the wafer, then using geometry to find the center of the circle intersecting those three points.

RE(wafer.edge())

With the focused beam in the vicinity of a point on the edge of the wafer, make a scan in xafs_x, plotting the signal on It, to find the X,Y coordinates of a point in the edge. This method will execute the linescan (Section 8), fit a lineshape to the measurement, then move to the position of the wafer’s edge. This must be repeated three times on three widely spaced points.

wafer.push()

After finding a point using RE(wafer.edge()), push the current X,Y coordinates to a list. After three measurements of the wafer edge, this list will contain the three X,Y coordinates of edge points.

wafer.points

The list containing the three edge points.

wafer.find_center()

Compute the wafer center from the contents of wafer.points.

RE(wafer.goto.center())

Move the xafs_x and xafs_y stages to the center position.

wafer.center

The center position of the wafer.

wafer.clear()

Clear the contents of wafer.points in order to start over.


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