'Watching' Atoms Move on Atomic Length and Time Scales with Helium Spin Echo
by John Ellis from SMF
Existence and Imaging of Atoms
60BC, Lucretius, brownian motion
Inferred by chemists, Dalton
Strongly rejected by physics establishment till Perrin
Imaging atoms: STEM
Imaging COlumns of atoms, TEM
Watching atoms move? - a Holy Grail
quantify using pair correlation funciton
Spin Echo Technique
Hexapole Polarizer for a
beam
why surfaces
- use in chemical engineering
- thermally activated motion
Analytical Diffusion Signitures
Modelling Motion at Surfaces: Na adatoms on a Cu(100) Surface
Modelling with 2d Langevin Equation
use the idea of that random impulse
MOdelling: validity?
But Langevin assumes 'white' noise, and real noise has a frequency cut-off, simulation suggests that the region of interest is white
Light Molecule Quantum Ballistic Motion
- UNactivated (Brownian) benzene
Benzene/graphite: simple model of nano motor
Rate theory
- The rate of a thermally activated process?
- work out the pre-exponential factor.
'Fiction' and Transition State Theory
- Problems:
- low frictions: rollercoasters from distant wells
- at high frictions atoms may recross barrier
Band structures
- energy
Use bandstructures for transition state calculation
- band width -> group velocity -> transition rate
