Introduction to scanning tunneling Microscope

Introduction to scanning tunneling Microscope (STM)Chien-Chang Chen(Nai-Chang Yehs group)

Image from an STMIron atoms on the surface of Cu(111)Image from an STMSTM schematic

"ScanningTunnelingMicroscope schematic" by Michael Schmid - Michael Schmid, TU Wien; adapted from the IAP/TU Wien STM Gallery. Licensed under Creative Commons Attribution-Share Alike 2.0-at via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:ScanningTunnelingMicroscope_schematic.png#mediaviewer/File:ScanningTunnelingMicroscope_schematic.png

Theory of STM: tunneling effect

Tunneling currentVideo: tunneling effect

thanks to http://www.toutestquantique.frTunneling current with bias

A little more approximationWhat STM can really detectSTM detect the electronic state, not the atom itself. We can detect different electronic state or even bonding by applying different voltage

The operation of STMConstant current modeuse the feedback to maintain the tip at constant density of state position. If the material is the same, this can be seen as constant distance from the sample. Thus we can get the topography image of the sample surfaceConstant height modedisable the feedback and let tip move in the constant height. The scan in this mode can be much faster, but can only be done in the flat surface to avoid the crash of the tip

PositioningThe STM tip position was controlled by several piezoelectrical componentFor the ease of use, it usually includes coarse positioner and fine positioner (tube scanner with tip)

ConclusionSTM and (AFM) make seeing atom and manipulate the atom not a dream at all.We can control and play the single atom. Someone even draw a movie by atomsSTM gives us the direct and extremely localized information about electronic density of state for the materials. Even the spin can be measured by the spin-polarized STM. STM is suitable to study the material with non-empty density of state, that is metal, semiconductorWith AFM, even the insulator can be studied directly