Ge(001) before and after gold evaporation and annealing
Kernel of the 4-probe microscope (left), crushed tip on Si surface (middle), two STM tips over gold structures on Ge(001) surface

SPM

Scanning Probe Microscopy is a method allowing for imaging certain structural properties of surfaces in scales from hundreds of micrometers down to atomic scale. There is a large number of kinds of SPMs (STM, AFM, DFM etc), however the main idea remains the same.

The most important part of a SPM is a sharp tip scanned on/over the surface and probing surface properties. The radius curvature of a tip apex is usually of the order of tens of nanometers. However, there are always some atomic-size protrusions present on the tip apex surface. Those protrusions form 'nanotips' and give the chance of probing the surface properties by few-atom probes. The tip is scanned precisely by a system typically based on piezo-electric elements.
 
    There are numerous versions of SPM:
  • STM (scanning tunnelling microscope) - the first SPM invented in early eighties. The inventors (Rohrer, Gerber) were rewarded the Nobel Prize in 1986. In the STM method a tunnelling current flowing between a conductive tip and a conductive surface is measured. Essentially, STM depicts density of electron states. (see....)
  • STM was also developed to investigate magnetic structures by evaporating magnetic materials onto a tip apex. Due to such a modification tunnelling electrons can be detected with respect of their spin polarization. On spin-polarized STM (SP-STM) you can read more in (....)
  • AFM (atomic force microscope) - is the technique invented in order to avoid the main restriction concerning STM - requirement of the sample conductivity.
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