Troubleshooting STM (scanning tunneling microscopy)?

[quarky2001]

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.

 

[eljose79]

Hi there,

It sounds like you are experiencing some difficulties with scanning probe microscopy, specifically with obtaining images of different surfaces. It's great that you are making your own probe tips, as this can often lead to higher quality and more precise measurements.

From your description, it seems like you have a good understanding of the basic principles of scanning probe microscopy and are properly setting up your instrument. However, there are a few potential factors that could be causing your current issues.

First, it's important to make sure that your probe is properly aligned and calibrated before attempting to scan. If the tip is not aligned correctly, it may not be able to accurately scan the surface and produce an image. Additionally, the tip should be checked for any contamination or damage that could affect its performance.

Another factor to consider is the quality of your sample preparation. It's possible that the surfaces you are trying to image are not smooth enough for the probe to accurately scan. Make sure to properly clean and prepare your samples before attempting to image them.

Additionally, the tip-sample distance and the probe voltage can also affect the quality of your images. It's possible that your tip is too far from the sample or that the voltage is not optimal for the specific surface you are trying to image. You may need to adjust these parameters to obtain better results.

Lastly, it's always a good idea to consult with other researchers or experts in the field for additional insights and troubleshooting tips. They may have encountered similar issues and can offer valuable advice.

I hope this helps and good luck with your scanning probe microscopy experiments!