OpenAFM - Atomic Force Microscope


Thank you for kind words, I am happy you interested in AFM project.

I must admit I don’t follow what you mean by ‘large area AFM’.

The project has delays since I want to make shareable. It’s not enough to show some outdated schematic. I want it to be just like openFlexture, everyone could do it. For this I need to make it PCBs instead of breadboard. This transition taking much time but it important step.

The best place to see progress is still Hackaday, I sure there will be lots of progress soon.

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Cool project! I’m a bit late to the party. I did my PhD on AFM and STM, including building an STM from scratch and making custom AFM sensors, so I’d be happy to contribute some ideas.

First thoughts are:

  • I like the scanning mechanism with the piezo disks
  • I agree that the tuning fork is easier to fabricate and align than playing with a laser deflection system and silicone tips. The one issue you may have is they tend to be much stiffer. The cool thing is if you use conducting expoxy to attach the tip to the end, you can do combined STM/AFM. (STM electronics are much easier, and sometimes it is nice to start in STM, find something and then AFM it). Make sure the non-used tine of the fork is glued to a base, otherwise the mismatched modes of the two tines will eat all of your Q. (This is often called qPlus).
  • How are you exciting the tuning fork? Normally we shake with an external oscillator, so you could try by driving your piezo disks, but as the natural frequency of the frame that holds the tip will be much lower than the tuning fork, you may struggle to transmit signal. If this happens, it might be worth adding an excitation peizo under the tuning fork.
  • Have you considered Platinum-Iridium wire for the tip. It isn’t too expensive. At least for the very fine wire you need. You prepare with wire cutters at a very acute angle. Cut 80% of the way through and then pull apart to stretch and snap the very end. At lease for ambient STM the oxide on tungsten was always a problem, for AFM this shouldn’t be an issue, but I have never enjoyed Tungsten etching. It may actually be a bad idea for AFM though, as AFM is more sensitive to microscopic structure around the tip, than STM that really only uses the last atom.
  • On the topic of tip etching. You don’t want the etch to go the whole way through, you really want it to stop etching and the gravity to take over. If you attach a weight to the wire then this helps. It also makes it easy to pick up what falls off, giving you two tips (lots of debate in pubs as been had on weather the top or the bottom tip is the best!). Also it is worth monitoring the current during the etch process, once you work out what the current is where the tip snaps, if you can make a system that monitors the current (or manually watch it) until it almost reaches this current, then switch off the etching. The thought is if you get to very close to the breaking point with the etch, and then leave it for a couple of hours, gravity should take over and stretch it into a really nice tip*

Anyway, cool project. Sorry if I am just repeating things you already know, or have already covered in your notes. I had a skim, but I struggle to read in dark mode, and so I’ll have to copy it out to somewhere and give it a read on another day.

Cool project, thanks for sharing

  • As an aside we once put some really good STM tips and some awful ones (based on how they had imaged) into an SEM to look at the structure. The supposedly platinum-iridium tips with the pulling method actually create a crazy mess at the end, but if something atomically sharp and pointy is sticking out then great! For the Tungsten ones, one of the “bad” tips looked perfect, one of the good ones was actually curled up at the very end. Again this was pure STM, not combined AFM/STM so I don’t know how these ones would have performed with AFM.

First thank you for being interested in this project, it’s encourage me to go on. I’ve read and re-read you post. There is a lot of new information, thank you for sharing.

You are not late to the party, you got there right on time :wink:
Regarding quartz fork, I used AD9833 to generate frequency. It can provide frequency in 0.1Hz resolution

By the way, you said you built STM from scratch which electronics components you haved used to stabilize voltage?

I suppose on that side we cheated on the controller side as we used a commercial controller! We built the mechanics up from “scratch” using a combination of off the shelf components, custom machined parts and parts that were pre-machined from a previous design.

But I don’t think you will need anything better than a DC power supply, the voltages aren’t super tiny so need far less care than the tunnelling current. If the DC power supply is switch mode it may want a few smoothing capacitors on the output. Your I-V converter circuit should make a good virtual ground on for the tip (or sample depending on which one you bias).

The key bit of the electronics you need to get right to make sure your signal is not just noise is the tunnelling current (I-to-V) pre-amp which should be as close to the tunnelling junction as physically possible. The main thing is to get a decent op-amp, preferably one in a metal can. Rather than putting it on a circuit board you can solder large surface mount resistors (and capacitors for smoothing between the power rails) directly to the legs and then mount it directly behind either tip or sample.