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Locating position of STM tip

J

jmc

Jan 1, 1970
0
What methods and what sort of resoloution can I get from trying to locate
the position of an STM tip?
jmc
 
S

Sir Charles W. Shults III

Jan 1, 1970
0
STMs are driven by piezo linear elements in most cases, and the drive
voltage and any error feedback are used to locate the tip. Also, as the piezo
element acts like a capacitor, it will store a charge that is proportional to
its extension. Thermal noise can be a real problem, because even the energy of
room temperature molecules can add up to a significant error signal. Cooling is
the best way to get rid of this.
The largest sources of noise are a) thermal noise in the piezo elements
themselves, b) the amplifiers that drive the piezo elements, and c) vibration in
the room that the STM is being used in.
The resolution in an STM can be sub-angstrom with proper noise control and
very stable power supplies for the driver amplifiers.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
 
W

Winfield Hill

Jan 1, 1970
0
jmc wrote...
What methods and what sort of resoloution can I get from
trying to locate the position of an STM tip?

This is a common problem with two-tip STMs. With repeated
scans over a region with tip B you can identify the place
tip A was before, to a fraction of an atomic distance under
good circumstances. Using a capacitance-position sensor I
designed (and described with circuits here on s.e.d.), we
can locate a second tip to within 10nm, which means it's in
range for the scanning described above and can be further
located to a fraction of an atomic distance, e.g. 0.02nm.

Of course, these are all relative measurements.

Thanks,
- Win

whill_at_picovolt-dot-com
 
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