Nanoprobe Scanning Quick Reference
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Chamber overview
The Nanoprobe Instrument (NPI) consists of a Focusing Optics Module which holds a Fresnel zone plate that is integrated with a central beam stop. This optic focuses through a differentially adjustable Order Sorting Aperture (OSA) matched to the beam stop so that the primary unfocused beam is blocked either by the central stop or the OSA permitting only primary focus (first order) beam downstream of the aperture- this OSA stage is also mounted on the FOM allowing the combination to be moved simultaneously. The combination of these two elements focuses the beam onto the Sample Module that provides translational and rotational control of the sample position. Laser interferometry is used to track the X/Y position of both the optic and sample stages relative to a common reference frame, allowing the user to scan the fine position of the optic differentially locked in to the sample position which continuously corrects uncontrolled positional drift over the scan.
Coarse scanning
Coarse or overview scanning of fields of view 50um-1mm is typically done using the Sample Y motion and Atto Z (or whichever linear motion axis is most coplanar with the sample surface as mounted) - while the zone plate is left stationary in the "optic in" position. These scans result in an up/down flip relative to a top-down optical image as shown.
Notes:
i) Sample Y / Atto Z motions cannot be stepped less than 0.5um, for finer steps than that you will need to lock the hybrid motion and use fine scanning.
ii) Sample X motions (under the rotation stage) are disabled as this will move the center of rotation relative to the beam axis
iii) Coarse scanning Focus X / Focus Y is possible but should be avoided as this will move the optic out of the beam footprint, off the center of rotation, and out of focus simultaneously.
Fine scanning
After a coarse position is chosen, fine scanning is typically used to make maps of field of view 200nm-20um. This scans the focusing optic module (Fresnel zone plate optic plus order sorting aperture) relative to the sample position differentially using piezo positioners locked in to the interferometric signal (smallest typical step ~5nm). When scanned from negative to positive there is a left/right flip relative to a top down optical view of the sample and the X direction is effectively compressed by the sample theta angle as shown.
Notes:
i) The X range should be kept to less than 30um to stay within the depth of focus at typical Bragg angles.
ii) The X/Y fine positioners are called "Hybrid nanopositioners" as if a call for motion is made that is out of the finite range of the piezos (~10um piezoY / 20um piezoX) then the piezo motion is ramped to the center of its range, a coarse motion is activated to place the new range center on the target position and then the piezo feedback loop is re-engaged to maintain position. This is done automatically but if the user would like to avoid stitching they should unlock the hybrid motion and manually drive to the desired scan center using Focus X/ Focus Y, and then keep the scans < 10um in width.
iii) The hybrid approach gives a continuous fine scanning range of up to 5mm for these positioners, however they will move out of focus and off the center of rotation with X movements > ~30um and will move the optic entirely out of the synchrotron beam footprint with movements>250um
iv) Movements of Sample theta and Atto X/Z are made inside the interferometric reference frame and so will result in motions of the sample without a change in hybrid X / hybrid Y readback value. Movements of Sample Y will be measured by the Hybrid Y readback value (as if the sample stage was drifting) and so typically the user will need to lock in at the NEW readback value coordinates after movement of Sample Y or it will effectively un-do the movement and might move the optic out of the beam
Focusing
Image for focusing here
