LabAdviser/314/Microscopy 314-307/Technique/Holo/Off-axis ATEM: Difference between revisions
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== Notes/Tips == | |||
* For obtaining electron holograms from the region of interest, tilt the sample appropriately so that the diffraction contrast within the region of interest i.e. black areas are at a minimum <br/><br/> | |||
* Avoid Fresnel fringe in the camera’s field of view, so center the biprism wire accordingly <br/><br/> | |||
* In case of a core-shell structure, go to a high enough biprism voltage so that you can see the edges of the core sharp. <br/><br/> | |||
* While obtaining electron holograms from the sample you must be away from the membrane edges; you should have only the feature of interest in the holographic field of view <br/><br/> | |||
* The fringes in the object and reference holograms must be sharp, if they aren’t sharp reacquire them <br/><br/> | |||
* In obtaining reference holograms be sure to keep away from all parts of the sample; you should have only vacuum in the reference holograms. <br/><br/> | |||
* In the object holograms, put the sample at focus using the focus knob; the object edges will be sharp when it is at focus. If there is a hole near the object of interest then it will be sharp when in focus. You can use the edges of the hole for the correction of objective lens astigmatism. The fringe contrast around the holde should be homogeneous. <br/><br/> | |||
* The width of the feature of interest should be smaller than the fringe width of the biprism. <br/><br/> | |||
* The holographic FOV should be at the center of the image field-of-view <br/><br/> | |||
* Obtain many, say, 5-10 sets of the reference and object holograms for each condition <br/><br/> | |||
* Do the rotation centering before adjusting objective focus <br/><br/> | |||
* Remember that in Lorentz mode we can’t get a diffraction pattern <br/><br/> | |||
* You should aim to have 4-5 steps per fringe in the reference and object holograms. <br/><br/> | |||
* For analyzing the holograms while the experiment is running, in Digital Micrograph, go to | |||
*: Holo3 → Reconstruct → Reconstruct with ref, OR | |||
*: Holo3 → Reconstruct → Reconstruc. (reconstruct using just one image) OR | |||
*: Holo3 → Reconstruct → Reconstruct with ++, press space bar and adjust the mask size with the up and down arrow keys, press space bar and this will give you the phase image <br/><br/> | |||
* Go to a high enough biprism voltage to have fine enough fringes that will lead to non-overlapping central and side bands in the FFT <br/><br/> | |||
* Make sure that the fringes contrast across the imaging FOV is uniform. <br/><br/> | |||
* If in the imaging FOV of the reference fringes, you see some black areas then try spreading the beam. If you see some disturbance (e.g. curving) in the fringes of the reference it could be due to either nearness of the sample or some charged contaminants on the birism. So to get rid of it, move the sample away and/or move to a different part of the biprism my moving along its length. <br/><br/> | |||
* When obtaining CBED patterns ensure that you can clearly see features in the central disk <br/><br/> | |||
* If during your experiment involving electron holography, you see that the visibility of fringes has gone low, then for increasing the visibility of the fringes you can decrease the exposure time, decrease the biprism voltage, reduce the magnification, play with track ball and the intensity knob to get the beam to uniformly illuminate the region of interest. | |||