Scanning Tunneling Microscopy (STM)
Based on quantum tunneling, STM images surfaces with atomic resolution using an electrically biased probe. This probe is brought in close proximity to a surface, and a bias voltage is applied, establishing a tunneling current. Holding the current constant, the tip is then rastered across the surface to obtain topography information.
Figure 1 shows a UHV STM image of a single-walled carbon nanotube on a hydrogen-passivated silicon (100) surface. Figure 2 is a UHV STM image of a UHV-cleaved III-V compound semiconductor modulation doped (MODFET) structure. The different layers from left to right are GaAs, AlGaAs, InGaAs, and semi-insulating GaAs.