Nanoscience & Microscopies SEM, AFM & STM. Block Diagram of E-beam. SEM Picts. SEM Picts. Dendritic Growth. Ostrinium Nubilialis. Miami Research Results. STM. Scanning tunneling microscope. Outside the Barrier. Wavefunction extends outside of well edge for a finite square well.
SEM, AFM & STM
Wavefunction extends outside of well edge
for a finite square well
into space between finite wells
Two finite wells at close approachcan look like a barrier to the electrons!
The surface of alloys may differ in several respects from the corresponding bulk
structure. The surface may also exhibit a chemical order different from the one in
the bulk of the material. This influences processes such as gas adsorption and
catalysis, since adsorbed molecules often prefer a certain chemical environment
of substrate atoms.
It all started with an (111) oriented surface of
a PtNi alloy (bulk composition 25% Pt,
75% Ni; surface approx. 50% of each).
We found that we can distinguish between
Pt and Ni atoms on this surface with the STM!Since Pt and Ni are about 50% of the surface
atoms each, the brighter species is Ni.
The white blobs in the image are impurities
of unknown nature.
Science, 280, 1715 (1998).
Single molecule chemical reactions
Science News, 158, 215 (2000).Use of STM
"after" pictures of typical regions of a material
to see how it changes during a phase transition.
This is now see on an atomic scale.
As the lead atoms in this 20 x 13 nanometer
region are warmed from 40 to 136 Kelvin,
they switch from the corrugated to the flat
arrangement at the transition temperature
of 86 Kelvin .
Vienna University of Technology
Let’s also look at:
Electron micrograph of two 100 µm long V-shaped cantilevers
(by Jean-Paul Revel, Caltech; cantilevers from Park Scientific
Instruments, Sunnyvale, CA).
Low and High Gain
Low gain – “drag” tip across sample see deflection which is OK for relatively flat surfaces
High gain – tries to push down on sample to maintain a particular height which is OK for more bumpy surfaces, but not for soft surfaces
- Tapping mode
Good for local surface distortions to measure friction and spring forces on surfaces
Requires a frequency modulation technique which is good for biological samples- repulsive forces from surfaceAFM Modes
Nanotechnology, 13 659 (2002).
Used for fabrication, chemical and biological studies
A definite “force” in the nanoworld !STM & AFM