HKL Flamenco EBSD Data Acquisition Flow

Transcription

1 HKL Flamenco EBSD Data Acquisition Flow Basic steps for automatic data acquisition (e.g. orientation mapping) This is basic routine for the new operator. Feel free to experiment with different settings as you gain experience to optimize your system for your samples and SEM! I. Mount Sample A. Cover all insulating mounting material with aluminum foil, carbon tape or conductive paint B. Ensure good, conductive contact is made between sample surface and holder/stage. Suggestion: C or Ag paint or metal tape lead C. If interested in highly precise absolute crystallographic orientations with respect to the sample surface or fiduciary marks within ~1 degree, mount Si chip on surface and ensure as flat as possible II. Set Up EBSP Acquisition A. Load sample into SEM B. Tilt the sample to 70 C. If the sample is insulating and session is on a LV SEM, pump down to Pa D. Turn the beam on E. Focus on sample surface at a working distance (WD) that matches a calibration file (Flamenco: Calibration Load) F. If desired, align fiduciary with stage X or Y G. Insert the Nordlys detector 1. Use the insertion distance indicated on the calibration file you ve chosen 2. Monitor the detector position on chamber scope, if equipped, to ensure it does not hit the sample Page 1 of 13

2 III. Collect/Apply Background Correction A. Select an appropriate area of the specimen B. Set the microscope scan at TV or fast-scan rate C. Open Flamenco: 1. Go to Setup Mode 2. Work with both the Frozen SEM image and Live EBSP pages visible so you can position the beam while viewing the resulting EBSP D. Set the SEM magnification as high as appropriate to the sample without producing discernible Kikuchi bands (Live EBSP page). Background collection on a single crystal, must be performed at a very low magnification, but be sure that the magnification is high enough so that the SEM field of view is filled by the sample E. Ensure that the SEM conditions are entered into the SEM parameters area in Flamenco F. On the Live EBSP page s Property Control Panel 1. Select the desired level of binning using the control on the property control panel. General guidelines for binning: Binning None 2 x 2 Suggested Use High resolution EBSPs for posters and publications Regular EBSD analyses where accuracy is more important than extreme speed e.g. manual phase identification 4 x 4 Regular EBSD analyses (e.g. routine grain size & texture analyses) 8 x 8 High speed analyses where a slight loss in accuracy is not important (e.g. large area texture analyses on strongly diffracting cubic materials such as metals or non-silicate oxides)) 8 x 8 superfast Ultra high speed analyses (see 8x8) HKL Channel 5 Flamenco Data Acquisition Flow Page 2 of 13

3 2. Adjust the Gain level (using the camera controls). Generally use Low gain for 8X8 and higher binning levels High gain for 4X4 and lower binning levels Note that high gain can increase noise, so for accurate phase discrimination, it may be better to use low gain 3. Ensure that the In-Software Image Enhancement (Background Correction) is switched off 4. Adjust the Timing per frame (exposure time, in milliseconds) until the signal in the Live EBSP window is suitable Timing too low (or probe current too low): insufficient signal in the image (too dark) Timing too high (or probe current too high): image over-saturated, forming a white area Timing too low Timing acceptable Timing too high 5. Collect the background (using the Collect Background button on the side of the Live EBSP page). The static background collection progress will be displayed in a message: 6. After the background collection is finished, the In-Software Image Enhancement checkbox is automatically activated HKL Channel 5 Flamenco Data Acquisition Flow Page 3 of 13

4 Ensure that both Static and Dynamic Background Correction are activated Ensure that the mode is set to Divide IV. Check Pattern Quality A. Go to Imaging mode ; collect an SEM image B. Return to Setup Mode 1. On the Frozen SEM image, activate spot mode by clicking near the center of the image. 2. Ensure that Dynamic Stretch (under the section marked simply Enhancement in the Live EBSP Property Control Panel) is deactivated 3. Use the Adjust Scale button to set the brightness/contrast of the Live EBSP. 4. The Lo and Hi sliders located just under the Dynamic Stretch control can be tweaked to further adjust the brightness/contrast of the Live EBSP HKL Channel 5 Flamenco Data Acquisition Flow Page 4 of 13

5 Adjusting the sliders varies the brightness and contrast levels. The Adjust Scale button automatically adjusts these settings tolerable values, but many times a better result is achieved by using the sliders. Setting the slider values closer together gives more contrast in the EBSP, while setting them farther apart reduces the contrast 5. Click around the sample while viewing the EBSP image in Live EBSP. If EBSPs are poor quality, likely causes include poor surface condition, highly strained or amorphous sample, too thick coating, or not enough probe current to overcome scattering in LV mode V. Check Calibration A. Ensure that a calibration file with conditions closest to WD, detector position conditions is loaded (Flamenco: Calibration Load) B. Load the correct match unit into the Match Units dialogue C. Place the beam near center of Frozen SEM image, on a good quality EBSP (click near the center of the image; to exactly center the beam in the image, use the Center Image button on the left-hand side of the Frozen SEM window D. In the Live EBSP property control, set the #Frames Noise Reduction (frame averaging) to 7 or 8 E. Go to Flamenco s Cycle Control Panel to Snap EBSP F. Go to Flamenco s Band Detection Page (still in Setup Mode) 1. First, set appropriate settings for Band Detection In the Detect Bands Property Control Panel Detect Band Edges if the edges are clearly defined Set Min/Max number of bands to be automatically detected to 4/5 or 5/6 for cubic materials; 7/8 for lower symmetry phases HKL Channel 5 Flamenco Data Acquisition Flow Page 5 of 13

6 Set Hough resolution to 50 or 60 for cubic materials; 80 or 90 for lower symmetry phases 2. Go to Flamenco s Cycle Control Panel to Detect Bands 3. Visually verify that all detected bands are correct; delete and manually redraw bands as necessary Click the Remove All Bands button to remove all bands Highlight a band in the list and click the Remove Band button to remove a single band To mark the edges of a Kikuchi band: Click on the edge of the band and drag to the other end. Then, click the right mouse button and keep it down a parallel line will appear. Move the mouse until the line is over the other edge of the Kikuchi band. To mark the center of a Kikuchi band: Click on the center of the band and drag to the other end. HKL Channel 5 Flamenco Data Acquisition Flow Page 6 of 13

7 G. Go to Flamenco s Cycle Control Panel to Index the EBSP 1. If solution visually looks close, or in the ballpark, proceed to step VI 2. If solution is clearly completely wrong: ensure match unit is correct (or go to Si or other known) ensure the detector distance and/or WD match the calibration file exactly VI. Improve Calibration A. In the Band Detection window, ensure bands are perfectly detected, otherwise remove and manually redraw 1. Try to cover as much of the diffraction space as possible 2. Do not over-concentrate on any one crystallographic zone B. Refine the calibration 1. Activate the Calibration/Refine dialogue box using the Calibration/Refine button, or go to Calibration Projection Parameters HKL Channel 5 Flamenco Data Acquisition Flow Page 7 of 13

8 2. Tick all three checkboxes to the left (V/H Ratio, Pattern Center, and Detector Distance) in the Calibration/Refine dialogue 3. Click the Refine button several times until the MAD stabilizes C. Only accept refinement ( OK button) if the simulated pattern visually matches the actual EBSP perfectly, and the MAD is less than 0.7. If poor: 1. Check detected bands 2. Ensure that you know the phase you re actually examining 3. Ensure that the initial index is truly in the ballpark 4. Try another pattern D. Check calibration on several patterns throughout the field of view 1. Either (A) click on a new area in the Frozen SEM image or use Position Beam in the Cycle Control Panel, select the beam control button on the Frozen SEM Image and click in the image to select a new area; snap the EBSP ; detect bands then Index 2. Patterns that look indexable should be indexing well 3. If not, check the automatic band detection, and that the match unit list includes all the phases you expect VII. Check Indexing Under Conditions Used for Automatic Mapping HKL Channel 5 Flamenco Data Acquisition Flow Page 8 of 13

9 A. Typical band detection and Hough Resolution settings (note that these band detection settings are starting points when you re setting up your analysis. You may find that your samples do best with slightly different settings). 1. Cubic materials: Reflectors (under Match Units dialogue ) = Bands, min/max = 4/5 or 5/6 Hough resolution = Non-cubic materials: Reflectors = 75+ Bands, min/max = 5/6 or 7/8 Hough resolution = Mixture of phases with different crystal symmetries: Use settings optimized for the lowest symmetry phase B. Change # Frames Noise Reduction (frame averaging) back down to 1-3, a setting you might use to keep mapping speed high. Unless excessive, do not worry about noise as the Hough transform can deal with it C. Click around image, checking proper indexing as with Step V 1. If poor, try increasing the frame averaging in steps and checking indexing 2. If still poor, reload calibration and repeat steps V and VI D. Evaluate Performance on Small Test Map 1. Go to Automatic Mode 2. Set up a small beam job over several grains Click the button New Job on the Job List Dialogue Box HKL Channel 5 Flamenco Data Acquisition Flow Page 9 of 13

10 The New Job dialogue box will appear. To design a simple Orientation Map utilizing beam scanning only, choose New Map In the Frozen SEM Property Control Panel, enter a step size appropriate for the specimen s grain size HKL Channel 5 Flamenco Data Acquisition Flow Page 10 of 13

11 Click Maximize # points or use the blue box (which can be repositioned and/or expanded/contracted) to select the area to be mapped Add to Job List using Add Job to List button on Job List dialogue box 3. Ensure that the Solution and Band Detection pages are undocked so that you can see them at the same time 4. Patterns that look indexable should index well. Use breakpoint (a breakpoint is a stage in the indexing cycle at which Flamenco will pause until you tell it to proceed) in the Cycle Control next to Index step and evaluate the performance pattern by pattern. Evaluate visually and by ensuring the MAD is less than 1.3 Undock the Automatic Mode Cycle Control and drag it to a reasonable place on the screen by clicking on it and dragging while HKL Channel 5 Flamenco Data Acquisition Flow Page 11 of 13

12 continuing to hold the mouse button. When the Cycle Control window is free floating, the position in the Cycle Control will be shown by the green arrow, along with the time (in milliseconds) for each process to be performed. At the bottom of the window, the indexing result, the number of points saved and the last saved point are shown To set a breakpoint at the Index step, simply click on the small blue dot to the right of Index in the cycle. The Index stage will be highlighted in red, and acquisition will stop at Index during every subsequent cycle. To proceed again, press the Run button. 5. If good, indexable-looking patterns are not being indexed, Check band detection performance and settings If indexing looks good but orientation or phase is wrong, adjust the number of bands detected (increase) and/or the number of reflectors (increase) to improve discrimination If indexing is still sub-optimal, try increasing the frame averaging by one step 6. If performance looks good after adjustments, evaluate cycle time (length of time needed to move beam to position, snap EBSP, detect bands, and index) Restart job: Job Restart current job When the job starts, immediately minimize Flamenco to save processor overhead time HKL Channel 5 Flamenco Data Acquisition Flow Page 12 of 13

13 After ~1-2 minutes, bring Flamenco up again and check cycle time in Job List window Enter this value in Beam Scan Time Estimation in Tools Options Now, the time estimate in the Job List window will be realistic VIII. Design Automatic Job A. If you have limited time to run the map, using the cycle time you found to calculate the number of points you can acquire in the session time you have available B. If a specific area of coverage is most important, calculate the resultant step size 1. (area) / (total points) = step size 2. You may need to use beam stitching to cover the desired area C. If the map resolution (=step size) is most important, calculate the area available 1. (total points) * (step size) = length of side of (square) area D. Enter job(s) in Job List and check estimated times IX. Run! A. Note that you can look at the job in post-processing during acquisition. If anything appears to be wrong, pause the job, make an adjustment, unpause and verify that there s an improvement. If there is, you may want to restart the job (Job Restart Current Job) HKL Channel 5 Flamenco Data Acquisition Flow Page 13 of 13