University of Minnesota Characterization Facility - X-ray Facility

Rocking Curves and ω-2θ Coupled Scans on Panalytical X-Pert with the Hybrid Optic

The following instructions are meant to be a guide, but many of the scan parameters may change based on your samples and experience. Please report any problems immediately to Linda Sauer (Room 14, 625-0076, lksauer@umn.edu). If you have any questions, please ask. The optics are delicate, please do not bump. If the x-rays are off, NEVER attempt to turn them back on.

Hardware Setup 1. The system must be setup with the x-ray tube using the line source. The hybrid

monochromator must be mounted on the incident beam side. Make sure the beam attenuator cable is plugged into the hybrid. If these conditions are not met, STOP and contact Linda.

2. The ½ degree divergence slit must be inserted in the hybrid and the manual attenuators must

NOT be in the hybrid. If the sample is less than 25 mm an appropriate beam mask should be inserted. The beam mask is necessary for alignment purposes, but can be removed during the regular scans if peaks between 37 and 45 degrees are not of interest. Broad peaks from the Al substrate holder will be present at ~38 and 44.25 degrees if a small sample is measured without the beam mask. An alternative is to mount a glass slide on the sample holder using a SMALL piece of double stick tape and then taping the sample to the glass slide. The beam mask will still be necessary for alignment, but the glass slide will eliminate the Al peaks. Please be careful removing the glass slide when you are finished as the slides may break.

3. The rocking curve (RC) + triple axis mount must be attached on the diffracted beam side

with Detector 1 attached to the triple axis position and Detector 2 attached to the rocking

curve position. If this condition is not met, STOP and contact the qualified personnel. A variety of slits found in the tray inside the enclosure (on the right) can be inserted in front of the RC detector to improve resolution.

Note: The following are the definitions of the angles in the software – ω – angle between incident x-rays and sample surface 2θ – angle between incident x-rays and detector ψ – sample tilt φ – in-plane sample rotation x,y – in-plane displacement of sample z – vertical displacement of sample

φ

2θ ω

ψ

User Setup 4. Log onto the computer: User: Charfac code # (for example 2310); Password; Domain:

CharFac. 5. Open the Data Collector program. 6. Enter your user name (created during training, please write down) and password. 7. Select Instrument/Connect in the Data Collector. The Go On Line box will appear. 8. Select High Resolution as the Configuration and RC as the Beam Path. Then press the OK

button. 9. A message dialog box will appear. Any line with a yellow triangle tells what the software is

assuming. Press the OK button. If a red stop sign appears, you cannot continue, please find an x-ray staff member for assistance.

10. If you previously had set sample offsets, a dialog may appear asking if you want to apply

these offsets. Yes keeps the sample offsets, No clears them. Unless you were the last person to use the machine, it is a very good idea to clear the offsets.

Optics Setup

11. Selected the Incident Beam Optics tab and double click on one of the items. The PreFIX

Module should be selected to be the Hybrid. The ½ degree slit should be selected in the Divergence Slit tab. The Beam Attenuator should have a Usage of Do Not Switch and the Activated box should be checked. The correct Mask (Inc. Mask Fixed 5,10,15,20 mm (MPD/MRD))should be selected in the Mask tab.

12. Select the Diffracted Beam Optics tab and double click on one of the items. For the rocking

curve detector, the PreFix Module should be selected to be the Triple Axis(Rocking Curve Optics). Select the correct Receiving Slit. Make sure the Detector is mini prop large window 2 and the Wavelength is K alpha 1.

13. If you will be using the triple axis detector, right mouse click on Triple Axis in the Diffracted

Beam Optics window tab and select Activate. The PreFix Module should be selected to be the Triple Axis(Monochromator 3 Bounce). Make sure the Detector is mini prop large window 1 and the Wavelength is K alpha 1.

14. Select the Instrument Settings tab, double click an item, select the X-ray tab, and set the

Generator to 45 kV and 40 mA.

Sample Mounting 15. Select the Instrument Settings tab, double click an item, select the Position tab, set Psi to 0

degrees, and set Z to 0 mm. Press the Apply button to move the stage. 16. Remove the sample holder by rotating until it releases. 17. Mount the sample as flat as possible on the stage with double sided tape or spring clips for

large wafer samples. 18. Replace the sample holder.

Checking the zero position of the detector 19. The zero position of the detector will shift slightly based on whether the triple axis optics are

used or if the rocking curve slits are used for the measurement. The most accurate measurements are made if the zero position of the detector is correctly determined. Insert the desired slit for the rocking curve detector or activate the triple axis setting that will be used for the measurement.

20. Select the Instrument Settings tab, double click an item, select the Position tab, set 2Theta to

0 degrees, Offset to 0 degrees, Omega to 0 degrees, set Z to 0 mm, and press OK. 21. Go to the Measure menu and select Manual Scan. 22. Select 2theta for the Scan axis, Continuous for the Scan Mode, 2 deg for the Range,

0.005 deg for the Step Size, 0.1 sec for the Time Per Step, and press Start. 23. After the scan is finished, right mouse click on the graph and select Peak Mode. 24. To accept the location of the peak, press the Move To button and then select OK. To select

a different position of the peak, press Cancel, right mouse click on the graph, and select Move Mode. Move the cursor until the intensity is the maximum. This will move the goniometer to this position.

25. Once the correct position of the detector is found, click on the Tools menu and select Sample

Offsets. Set the current 2theta position to 0 and select OK. 26. This correction should be performed for maximum accuracy of the 2theta peak position if

slits or detector (rocking curve vs. triple axis) are changed. If you are only performing rocking curves, this adjustment is unnecessary.

Setting the correct sample height 27. The correct sample height must now be found in one of two ways. One method uses a

micrometer which pushes against the sample surface, while the other method bisects the direct incident beam to determine the correct sample height. While the first method is satisfactory for bulk samples, it should be avoided for thin film samples due to possible damage of the thin layers by the micrometer. The second method works for both bulk and thin film samples and is highly recommended for delicate thin film samples.

a. Mount the micrometer on the stage and close the enclosure doors. b. Move the z position of the sample stage until the micrometer reads 1.0. (The small inner

dial will read 1 and the large outer dial should point to the 0 at the top of the micrometer.) c. Remove the micrometer and close the doors.

OR

a. Set 2Theta to 0 degrees, Offset to 0 degrees, Omega to 0 degrees, set Z to 8 mm, and press OK.

b. Go to the Measure menu and select Manual Scan. c. Select Z for the Scan Axis, Continuous for the Scan Mode, 4 mm for the Range, 0.01 mm

for the Step Size, 0.1 sec for the Time Per Step, and press Start. d. After the scan is finished, right mouse click on the graph and select Move Mode. e. Move the cursor until the intensity is ½ the maximum. This will move the goniometer to

this position. f. Return to the Manual Scan window, select Omega for the Scan Axis, 4 degrees for the

Range, 0.01 degrees for the Step Size, 0.1 sec for the Time Per Step, and press Start. g. Use the Move Mode again to select the maximum intensity. h. Repeat steps c. to g. until the values do not change. The Ranges and Step Sizes can be

made smaller once the approximate correct values are determined in the first scans. i. Once the optimum values are found, click on the Tools menu and select Sample Offsets.

Set the current Omega position to 0 and select OK. The omega will be further optimized on a peak, but this gives an initial correction.

Peak Optimization

28. If the lattice parameters and angles for this material are known and it will be studied often

this information can be stored in the system. Once this information is stored the reciprocal space interface can be used to drive the goniometer to specific reflections. To input this information continue with step 29. If it is unknown or already entered go to step 33.

29. Select Customise/Options and make sure the radio button in front of Single Crystal mode is

checked. Close this window. 30. Select Customise/Unit cells and then press the insert button. 31. Enter all the requested information for the unit cell. The primary and secondary hkl are the

growth vector and a wafer flat vector respectively. (If no wafer flat is present any vector perpendicular to the growth vector is sufficient.) The hkl values must be entered as integers with spaces between them.

32. After entering the all the information press the OK button and notice the new cell added to

the list. Then press the OK button. 33. If the scan will be performed in triple axis mode, it is still much easier to initially find the

peak in rocking curve mode and then switch to triple axis for the final alignment. To switch between the modes, right mouse click on Triple Axis or Rocking Curve in the Diffracted Beam Optics window tab and select Activate.

34. Before a scan is collected for an extended measuring time, preliminary scans are usually

done to optimize the peak(s) of interest. This can be done either using manual measurements, or automatically by creating an optimization program. The manual method will be outlined here.

35. In Instrument Settings tab, double click on an item, select the Position tab, and select the

substrate material in the unit cell field. (If unit cell information was not entered, enter the 2theta value for the peak of interest in the 2theta field and 0 in the Offset field and press the OK button. Then, continue with step 36.)

36. Enter the plane of interest in the HKL field. This will set all the angles to the theoretical

values for this reflection. Then press the OK button. 37. Select Measure/Manual Scan from the main menu. 38. Select omega in the Scan Axis field, enter 0.01 in the Step Size field, 6 in the Range field, and

0.1 in the Time Per Step field. 39. If a peak is not found execute the following scan: phi as the Scan Axis field, enter 0.1 in the

Step Size field, 200 in the Range field, and 0.1 in the Time Per Step field. Once a peak is found continue with step 40.

40. After the measurement is completed press the right mouse button and select Move Mode. 41. Press and hold the left mouse button until the cursor is placed over the center of gravity of

the peak. If more than one peak is present choose the narrowest, most intense peak. This will move the goniometer to the selected position.

42. Back in the Manual Scan window, enter the follow parameters: psi in the Scan Axis field,

enter 0.05 in the Step Size field, 8 in the Range field, and 0.1 in the Time Per Step field. Then, press the Start button. (This is in the case of a symmetric reflection. If an asymmetric reflection is being studied enter phi for the Scan Axis and leave all the other scan parameters as suggested here.)

43. After the measurement is completed press the right mouse button and select Move mode. 44. Press and hold the left mouse button until the cursor is placed over the center of gravity of

the peak. If two peaks occur select the lowest intensity point between the two peaks. 45. If the final scan will be performed in triple axis mode, activate the triple axis mode.

46. Back in the Manual Scan window, enter the following parameters: omega in the Scan Axis

field, enter 0.002 in the Step Size field, 1 in the Range field, and 0.1 in the Time Per Step field. Press the Start button.

47. If the omega peak position has not changed since the first omega scan executed in step 36

continue with step 45. (The peak is in the same position if the center of gravity of the current peak on the screen is located at the omega position of the instrument at the completion of the measurement.) If the omega peak position has changed return to step 40.

48. If the intensity is lower than expected, the position of the detector can be changed. Back in

the Manual Scan window, enter the follow parameters: 2theta in the Scan Axis field, enter 0.01 in the Step Size field, 2 in the Range field, and 0.1 in the Time Per Step field. Press the Start button.

49. After the measurement is completed press the right mouse button and select Move mode. 50. Press and hold the left mouse button until the cursor is placed over the center of gravity of

the peak. If more than one peak is present choose the narrowest, most intense peak. This will move the goniometer to the selected position.

51. Once you are satisfied with the alignment, close the manual scan windows. 52. Back in the control window select the Incident Beam Optics tab. Double click on an item

related to the beam attenuator. Change the Usage field to Switch at preset intensity, set the Activate Level to 500,000, and the Deactivate Level to 400,000.

Measurement Program

53. Select File/New Program/Relative scan for a rocking curve and Relative scan or Absolute

Scan for a coupled scan. A relative scan is centered on the current position of the goniometer. An absolute scan scans a specific range of angles and is often used for coupled scans.

54. Enter proper range of measurement, step size and time per step. 55. Make sure that the desired Rocking Curve or Triple Axis setting is selected as the Secondary

Beam Path. 56. The Scan Axis should be omega for a rocking curve and 2theta-omega for a coupled scan

(omega-2theta is also a coupled scan but scans twice as far for the same selected degree range).

57. The Scan Mode is always continuous. 58. The Time Per Step should be in the range of 0.5 – 5.0. 59. Select File/Save as and enter a name for the program and then press the OK button. Close

this window.

Running the Measurement

60. Select Measure/Program/Relative scan or Absolute Scan depending on which type of

program was created above. 61. Enter the program name chosen in step 59 if it does not already appear. Enter a data set

name and sample identification. Do not modify any of the angular fields, the HKL field or the Unit cell field. Press the Start button.

When Done

62. Make sure the attenuator is set to Switch at Preset Intensity or Do Not Switch Activated. 63. Power the x-rays down to 40 kv and 10 ma. 64. Close the program, transfer your data (files are not backed up), and log off the computer.

Files can be viewed with the Data Viewer program and converted to ascii text files if desired. Please leave the work area clean.