LabAdviser/314/Microscopy 314-307/Postprocessing/Lattice fringes: Difference between revisions
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'''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php/LabAdviser/314/Microscopy_314-307/Postprocessing/Lattice_fringes click here]''' | '''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php/LabAdviser/314/Microscopy_314-307/Postprocessing/Lattice_fringes click here]''' | ||
(''content by Jakob Birkedal Wagner, March 2020'') | (''content by Jakob Birkedal Wagner @DTU Nanolab, March 2020'') | ||
[[Category:314]] | [[index.php?title=Category:314]] | ||
[[Category:314-Microscopy]] | [[index.php?title=Category:314-Microscopy]] | ||
= Analysis of lattice fringe images (HRTEM) using Digital Micrograph = | = Analysis of lattice fringe images (HRTEM) using Digital Micrograph = | ||
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At times, it is easier to measure lattice space distances using Fast Fourier Transforms (FFTs). With the image of interest as active press Ctrl F in order to get an FFT of the image (see below): | At times, it is easier to measure lattice space distances using Fast Fourier Transforms (FFTs). With the image of interest as active press Ctrl F in order to get an FFT of the image (see below): | ||
[[File:Lattice-fringes_reciprocal_1.png|600px|thumb| | [[File:Lattice-fringes_reciprocal_1.png|600px|thumb|left|Fig. 3:FFT of HRTEM image.]]<br clear="all" /> | ||
The complex FFT is by default shown as the logarithm of the modulus. The FFT is calibrated so it is possible to measure the lattice space distances directly by measuring the distance between the dominant Fourier components. | The complex FFT is by default shown as the logarithm of the modulus. The FFT is calibrated so it is possible to measure the lattice space distances directly by measuring the distance between the dominant Fourier components. | ||
[[File:Lattice-fringes_reciprocal_2.png|500px|thumb| | [[File:Lattice-fringes_reciprocal_2.png|500px|thumb|left|Fig. 4:Measure in FFT.]]<br clear="all" /> | ||
Here the distance between the Fourier components representing the same lattice space distance as analyzed above measured. The distance is d*=5.59 nm-1, which can be coverted by taking the reciprocal value: d=2/d*=2/5.59nm-1=3.58Å (here 2 reciprocal lattice space distances are measured, hence the ‘2’ in the calculation. The slight difference is due to the precision in the measurements and that the FFT here measures an average value over the image, while the direct space methods in this case is more local. | Here the distance between the Fourier components representing the same lattice space distance as analyzed above measured. The distance is d*=5.59 nm-1, which can be coverted by taking the reciprocal value: d=2/d*=2/5.59nm-1=3.58Å (here 2 reciprocal lattice space distances are measured, hence the ‘2’ in the calculation. The slight difference is due to the precision in the measurements and that the FFT here measures an average value over the image, while the direct space methods in this case is more local. | ||
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In order to get FFTs from smaller parts of the acquired micrograph, you have to define a region of interest (ROI) before you calculate the FFT: | In order to get FFTs from smaller parts of the acquired micrograph, you have to define a region of interest (ROI) before you calculate the FFT: | ||
[[File:Lattice-fringes_reciprocal_3.png|600px|thumb| | [[File:Lattice-fringes_reciprocal_3.png|600px|thumb|left|Fig. 5:ROI tool.]]<br clear="all" /> | ||
‘Right click’ on your image and choose the ‘Rectangle ROI’ tool (a). Mark the region of interest while holding down the ‘shift’ key. This way the ROI is restricted to a square making the FFT analysis more intuitive. After you have marked the ROI choose ‘Live FFT’ from the drop down menu (b). Now the outline of the ROI should become red. | ‘Right click’ on your image and choose the ‘Rectangle ROI’ tool (a). Mark the region of interest while holding down the ‘shift’ key. This way the ROI is restricted to a square making the FFT analysis more intuitive. After you have marked the ROI choose ‘Live FFT’ from the drop down menu (b). Now the outline of the ROI should become red. | ||
Now it is possible to move the ROI around the micrograph while following the FFT ‘live’: | Now it is possible to move the ROI around the micrograph while following the FFT ‘live’: | ||
[[File:Lattice-fringes_reciprocal_4.png|600px|thumb| | [[File:Lattice-fringes_reciprocal_4.png|600px|thumb|left|Fig. 6:ROI and live FFT (amorphous).]]<br clear="all" /> | ||
[[File:Lattice-fringes_reciprocal_5.png|600px|thumb| | [[File:Lattice-fringes_reciprocal_5.png|600px|thumb|left|Fig. 7:ROI and live FFT (crystaline).]]<br clear="all" /> | ||