In order to make course scans at higher distances possible, a high bias voltage is needed. Based on the data available in this article:

https://web.archive.org/web/20030508182417/http://www.nanoworld.org/museum/young2.pdf

200 volts should allow field emission scanning in a vacuum. I plan to operate in atmosphere, or possibly in mineral oil as described here:

https://www.sciencedirect.com/science/article/abs/pii/092442479087067S

Spice shows the high voltage power supply working fairly well running off the +/- 15v supply rails.

One of the advantages of using a charge pump for the high voltage is the lower cost compared to other voltage boosters, but also much lower current spikes which would interfere with the ability to take accurate low current measurements.

PCB design coming soon!