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Phys 460 Lecture 25

( pdf version - 6 slides/page )
Wed, November 29, 2006
Lecturer: Richard Martin 		No new homework today

Reading:
Kittel, Ch. 18, p 523-527

Surfaces – Tunneling - STM
Outline

  1. From previous lectures:
    • Part I: Crystal Structures, Diffraction, Reciprocal Lattice, Crystal binding
      Phonons, Dispersion curves, Thermal properties
    • Part II: Free electron gas, Energy bands for electrons in crystals Ekn, gaps, metals vs. insulators, semiconductors
    • Part III:
      • Semiconductor devices - inhomogeneous semiconductors - heterostructures
      • Semiconductor nanostructures
      • Metals - brief overview - electron gas ideas generalized to real metals
      • Superconductivity
      • Magnetism
  2. Surfaces
    1. Termination of a crystal makes a two-dimensional periodic surface
      • Perfect crystal - perfect 2D periodicity
      • Real crystals - planes with terraces, steps, .....
      • Example of GaAs
    2. Tunneling in quantum mechanics
      • Particles can tunnel through barrier
      • Exponential decay where E < V
      • Simple formulas that can be solved exactly for constant V
      • Example of a barrier of height V0
    3. STM
      • Electrons tunnel through space between tip and sample
      • Extreme sensitivity of tunneling current tas a function of the distance from tip to sample
      • Dominated by a single atom on tip - an atom that just happens to be on the tip
      • Atomic scale resolution even though the whole tip is much larger
    4. Examples
      • GaAs, Mn atoms on GaAs
      • Adatoms on Cu show ability to move adatoms around, electron waves, ....
      • GaN surface that illustrate growth, ….
    5. Atomic Force Microscope - AFM
      • Atomically sharp tip
      • Detect forces by very sensitive detection of displacement of cantilever
      • Works on insulators
      • Article in Physics Today, December, 2006
Email clarification questions and corrections to rmartin@uiuc.edu
Email questions on solving problems to xin2@.uiuc.edu