Web page links:
Field Emission Electron Microscope
Field Emission
Microscope
Quantum Mechanics
Quantum Mechanical Tunneling
Tunneling
Web page description:
The Field Emission Electron Microscope (FEEM) demonstrates quantum
mechanical tunneling of electrons. The microscope was invented by Erwin
Muller in 1936 [E. W. Muller. Z. Phys. 102, 734 (1936)]. The
magnification of a typical FEEM is approximately 500,000X. Its resolution
is about 20 Angstroms.
A FEEM tube consists of a cathode, in the form a sharply pointed metal
wire placed several centimeters in front of a transparent anode that has
been coated with a phosphor (Willemite). A barium "getter" keeps the
pressure in the FEEM tube below 1E-15 Pascal. As a high voltage is
applied between the cathode and the anode a very high electric field is
created at the cathode surface. When the field reaches a few volts per
nanometer the width of the energy barrier for electrons in the metal
approaches their de Broglie wavelength and tunneling through the barrier
becomes possible. Tunneling electrons emerge from the barrier as free
particles and accelerate to the anode where the phosphor coating
fluoresces and makes each electron impact visible. The image that appears
on the phosphor reflects the variation in the work function of the
cathode surface.