Forums
Bruker Media
Community Media
Bruker AFM Probes
SPM Digest
Application Notes
NanoTheater
Website
中文
Brochures & Datasheets
Publications
Probes Catalog
Events
Manuals & Documentation
Presentations
Guide to AFM Modes
News
Journal Club
Webinars & Video
Nanovations
Other
Hi everyone. I'm using a Bruker/Veeco Caliber SPM with an MLCT chip (laser on the 'B' cantilever with a nominal stiffness of 0.02 N/m) to perform regular raster scans of a sputtered moly coating.
1. Having initially centered the laser on the PSD array, I notice that as my tip approaches the surface during auto-engage, the vertical deflection jumps to positive values (indicating an upward 'deflection' in the typical sense as against, say, something that might be caused by the adhesive force), often by a few hundred millivolts in the vertical direction (the lateral position does not deflect too much prior to engagement). Am I correct in assuming that this is due to aerodynamic drag? Is there any way I could reduce/eliminate this shift, whatever may be causing it?
2. Suppose I raster scan a surface at 3.5V set point voltage; when I disengage the probe, I often notice that the 'free-air' vertical position of the laser on the PSD array is no longer zero (or the near-zero value I adjusted it to prior to engaging). The drift in the vertical position of the laser is sometimes as great as 5-6V. Again, I do not notice appreciable changes in the lateral direction. What could be causing this?
Both these issues are worrisome to me because uncertainty about the zero-voltage prior to engaging or drift post-scanning both create large uncertainties for me in the in-scan normal force, which in turn affect repeatability of my data. I would appreciate any suggestions anyone might have on this.
Thanks!
Harman.
Harman,
The MLCT Bs are quite soft and thus quite sensitive. Change of the signal over time could simply be the lever bending due to thermal heating by the feedback laser beam. If you really need to know the loading of your lever I would suggest that after approach you simply retract the tip a few micron, measure the signal (= 0 load) adjust your mirror if necessary and then note the difference to your setpoint. The setpoint doe not have to be "zero" as the signals are relative. You can simply retract the piezo by clicking on the "feedback off/on" toggle button and typing in a negative offset in microns from your actual position.
Best, Stefan
Thanks Stefan, and apologies for the late reply. Mirror adjustment is what I've been doing all along, but I wasn't entirely sure if it's the best way around the problem.
Best,
Great. Yes, the "setpoint" in contact mode is a relative measure in relation to the "baseline" just before your tip contacts the surface. If your baseline shifts during the approach you may want to use the mirror (ors setpoint) to correct.
Glad it works now.
Stefan