Gold sample images, automated coarse approach, and progress on new hardware

A project log for Scanning Tunneling Microscope

A low-cost STM achieving atomic resolution with a piezo buzzer scanner

dan-berardDan Berard 04/19/2016 at 01:320 Comments

It's been a while since I've posted any updates, so here are a bunch of images taken with the microscope. I added an automated coarse approach mechanism some time ago using the very cheap 28BYJ-48 stepper motor. By driving the rear fine-pitch screw of the STM with this motor, which takes 2048 full steps/rev, I get a tip-sample step size of about ~6 nm. This (ideally) results in a crash-free approach, and much better quality images. You can read more about it on my blog:

Still no luck getting atomic resolution on gold, which I believe is due to some combination of acoustic noise/vibrations and DAC glitches, which are actually quite large and cannot be completely filtered out. You can see the "noise" in some of the images below. More on this later...

I'm also testing out a new PCB, which is very similar to the previous one but has the power supply, Teensy, and analog stuff integrated onto one board. I'm also working on a higher performance version, with better DACs, HV amplifiers, an FPGA, and hardware for tuning-fork AFM!

Here's a picture of the microscope with coarse approach motor:

A gold surface with a mirror finish looks quite rough at the nanoscale: (I really need to find some other samples to image...)

A smaller scan of the same area, shown as a 3D surface to emphasize the edges of the atomic planes:

Smaller scan of the same area:An attempt at imaging beta-mercaptoethanol (BME) bound to gold. The surface clearly looks modified (covered with a layer (or several) of BME molecules). I tried to take smaller scans to image the molecules, but the coating seemed to be swept away by the tip... maybe a crash? Going to have to try this again... :Zooming in on the above surface, most of the BME has disappeared.

Here are some more, zooming in on a gold surface:

1000 nm:

600 nm:

300 nm:

100 nm: