F
Fred Bloggs
- Jan 1, 1970
- 0
Tony said:
Okay- well I'll throw in my 10lbs of confusion over just exactly what
he's doing. This is STP or Scanning Tunneling Potentiometry which is a
variant on ST-Microscopy used to acquire "new insight into the local
electronic transport properties on the nanometer scale." The
conventional STM works by servoing a z-axis piezo positioner so as to
maintain a constant tip-sample tunneling current- which then ensures the
tip-sample separation, d, is a constant- and this gives incredibly high
resolution of a surface topography on the pico-meter scale through
measurement of z-axis variation. The tip-sample bias is also maintained
during this scan . A second variation is to vary this bias and acquire
the small perturbations in tip tunneling current to infer certain things
like "electronic density of states" and a bunch of other atomic
characteristics. So the thing looks like this:
View in a fixed-width font such as Courier.
STP acquires surface topography and potential distribution
of current flow through sample....
precise determination of
atomic topography dimension z
as tip scans x-y dimensions
feedback piezo positioner
tunneling CCS regulating I constant
+-----------+ tip
+----+ I tip--> |-----+ maintains constant d
| +-----------+ | between tip and sample
| |
| | I ~ exp(-Kappa x d)
| | tip
| | Kappa= decay constant
| z | function electron state energy
| | y TIP levels
| | / ^
| | / | Itip also =I ( Vtip-sample)
| +-----x d tip
| | <--on order several atomic diams
| v
| +---------------------+ <-----
| | | Isample
| +---| S A M P L E |----------+
| | | | |
| | +---------------------+ |
| | <------V (Isample)--- |
| | x |
| | |
| | |
| | ADJ SAMPLE |
| | BIAS FOR Isample |
| | _ |
| | | /| |
| +-------------| |/ ------------------+
| | /| |
| | / |
| | |
| | |
| +----------/\/\/\/\/\/\--------------+
| /|\
| | set reference for V(x)
| | |
+---------||------------+
| |
| Vtip,bias
---
/// tip bias voltage applied through resistor bridge
bridge adjusted for zero local potential between
tip and sample - then variation of Itip vs V (Isample)
x,y
can be acquired.
