ULTIMATE COMPUTING - Quantum Consciousness Studies

196 NanoTechnology
Figure 10.4: Schematic of STM from Tunneling Microscope Corporation (Doug
Smith). T = tip, S = sample stage, PZT = piezoceramic tube, CAM = coarse adjust
micrometer, FAM = fine adjust micrometer, LRS = lever reduction system. By
Conrad Schneiker (Schneiker, 1986).
The scanning speed in Mode I is determined by the response of the servo
system. Modes II and III are faster since the tip maintains only a constant average
height above the surface. The scanning speed in these modes is determined by the
response of the preamplifier only. Mode IV measures the joint density of states
which, for a small tip, is a map of the local distribution of electron states of the
substrate. For this mode, one “dithers” the tip-to-substrate bias voltage with a
small alternating current signal and monitors i/v. Using this mode, Smith and
Quate (1986) have done spatially resolved tunneling spectroscopy and observed
charge density waves. STM can thus be used to identify the elements comprising
specific atoms and to monitor molecular dynamics (Figure 10.5).