Re:What are “actual pictures” of atoms actually pictures of?
by Animats on Sunday June 26, 2016 @01:59AM
(#11979588)
That's a good point. A very high gain DC amplifier with low noise would have been hard then. A STM needs to sense about 1na at 0.1V, which means a series resistance of about 100 megohms. Vacuum tube voltmeters of the 1940s and 1950s era were getting close, with about 10 megohms input resistance.[1] Sensing 0.1V through 100 megohms with tubes doesn't seem out of reach.
High RF gains are easier to get than DC gains; you can filter out everything but the frequency of interest and reduce noise. That's basically how radios amplify weak signals. But I don't think you can run an STM on RF.
High RF gains are easier to get than DC gains; you can filter out everything but the frequency of interest and reduce noise. That's basically how radios amplify weak signals. But I don't think you can run an STM on RF.
[1] http://www.tubebooks.org/Books/rider_VTVM.pdf