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Hello,
is there anyone having an idea of maximum resolution in Force volume (capacities to distinguish between two different adhesion point). As i remember, I've read somethings around 100 nm in a Veeco notes, could you confirm this and on what are based this values? Are people having an own experience on this subject?
Thanks for your answer
Guillaume
Guillaume,
Often the lateral resolution of force volume is simply limited by the lower pixel resolution that is typically used. Typically we use 64x64 or 128x128 grids instead of say 512x512 or higher for normal imaging. In this case your best resolution would simply be the scan size divided by the number of pixels. It's just not practical to use higher pixel densities since you need to perform a force curve at each point. The alternative is to use smaller scan sizes, which will reduce the spacing between pixels. Then you might reach a point where the resolution is limited by the indentation contact area or, in the limit of no indentation, by the tip sharpness.
A powerful way to get similar data at much higher resolution is our new PeakForce QNM mode (www.veeco.com/peakforceqnm). In this case the force curves are collected at a much higher rate, so we routinely capture images of material modulus, adhesion, etc. at normal image resolutions. An additional benefit is that the curves are automatically analyzed to yield quantitative values for these common material properties.
Regards,
-Ben
Dear Guillaume,
IF you are referring to the theoretical resolution of this technique, I would say that it's influenced by a large number of factors (tip radius, applied force, deformation of the sample, treatment of the tip spring to mind). However, AFAIK, no-one has done any systematic studies to try to find out the ultimate resolution. However, in principle, at least in vacuum, you can do some kinds of spectroscopy over individual atoms (see the one from Nature in 2007), so in more "normal" conditions, we can expect the possible resolution to be limited by sample movement/thermal noise on the probe, if you can take account of the other factors mentioned above...
Pete.
Ben and Pete have covered the situation pretty well, but here is a summary. To get the ultimate resolution you should:
1. Set the scan size and number of pixels so that they do not limit the resolution
2. Minimize the interaction region by using a sharp probe (small end radius) and small sample deformation (by using the smallest peak/trigger force possible).
As Ben notes, PeakForce QNM has a significant advantage when it comes to item 1 since it is much faster and allows more pixels in the image. Additionally PeakForce QNM can help with item 2 since it allows the peak force to be minimized to a greater extent than with force volume. It does this by removing any parasitic deflection that is not related to the interaction from each curve prior to determining the peak force that occurs during the contact part of the curve. Using this technique it is possible to image while measured forces are zero or even slightly less than zero if the tip-sample interaction has some attractive part. I've seen examples on liquid crystals with a feature pitch of <2nm in the adhesion channel.
sorry, I'm talking about lateral resolution off course
Dear Ben, Pete, and Bede,
thanks for your response
I'm aware about scan size, number of pixels, tip shape and size, and trigger force. Actually, we are working in liquid on living cell with biofunctionnalized tips (therefore PeakForce tapping isn't possible since limited ramp size, ramp speed,...) (for a recent example here) and I notice that we never succed to have a better resolution than 50-70 nm in FV mode. Parallel, I read in the PeakForce tapping brochure that lateral resolution in FV mode is around 100nm which in agreement with my own experiment. Plus, in the veeco manual, they talk about hardware and software limitations about lateral resolution in FV. I was just wondering what are these limitations apart ration scan size/pixels, tips shape and size (which isn't the problem here) and how veeco determines the 100 nm for the brochure (apart for the commercial point of view). I was also wondering wheter others people have an experiment on the subject, especially on living cells or with biofunctionalized tips. Finally, is there a way to increase the resolution in such case ?
Thanks again