A Conversation for Make Yourself a Scanning Tunnelling Microscope

STM in air? and more..

Post 1

Limey Tank

Now please correct me if I'm wrong, but all the STMs I've ever seen operate in ultrahigh vacuum, and generally, once the sample is loaded there is a long wait for all the atoms to dissappear into the pumps.

Also all the STMs I've seen cost over €150,000 and need lots of filters and Fourier transform stuff etc. You also cannot get atomic resolution by using such a large tip as a 1mm wire cut at a 45 angle (although I've never tried it...smiley - smiley).

The tips are usually made of Tungsten and are only a couple of atoms wide at the end. The tips are sharpened by whacking up the voltage and some of the "spare" atoms fly off leaving a nice sharp needle.

Coating things in silver is a much simpler process than getting a STM scam IMOHO. A vacuum chamber and a power supply with a filament will produce nice enough films for practical use.

Also the voltage used depends on the bandgap of the material under examination. A voltage must be used in order to increase the probability of the electron leaping the potential well between the needle and sample. The larger the voltage the larger the probability. Then it's simply a matter of measuring the current on the order of femtoamps or picoamps, and using this information in a feedback loop to control the needle height.

The final image is then a graph of needle height v needle displacement in x-y direction (this is known as constant current mode)

i might be wrong, but it's never happened before smiley - smiley

Key: Complain about this post

STM in air? and more..

Write an Entry

"The Hitchhiker's Guide to the Galaxy is a wholly remarkable book. It has been compiled and recompiled many times and under many different editorships. It contains contributions from countless numbers of travellers and researchers."

Write an entry
Read more