I've recently started trying to use this technique, but I've had some difficulties I can't figure out how to overcome. We make our own probe tips from a very small length of 30 gauge wire, and they seem to be of decent quality. We've tried to image a layer of graphite, a gold surface, and what appears to be a very smooth surface deposition of carbon nanotubes. We've been able to get the approach right, i.e. a tunneling current flows without the probe touching the sample, but as soon as we begin scanning the current stops, and no image of the surface is produced. We haven't had many problems with 'crashing' the tip into the sample at all. I can think of a number of things that might be causing our problems, but I have a hunch that some are a lot more likely than others - and it would take some experience to know what the most likely factor is. We're using a probe voltage of 0.050 mV, and the approach is stopped once we get a tunneling current of 1.00 mA. We should have excellent vibration isolation; the microscope is sitting on a granite slab, on small foam blocks, on an optics table. The microscope we're using is the Nanosurf easyScan, if it helps. Does anyone have some insight they offer regarding the most likely problem areas? I have trouble contemplating where they might lie.