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SUMMARY:From vacuum tunnelling to quantum transport: Recent developments a
 nd new opportunities in Scanning Tunnelling Microscopy - Stefan Tautz\, Fo
 rschungszentrum Juelich
DTSTART:20100317T111500Z
DTEND:20100317T121500Z
UID:TALK22843@talks.cam.ac.uk
CONTACT:Michael Sutherland
DESCRIPTION:The invention of scanning tunnelling microscopy (STM) a quarte
 r of a century ago has revolutionized the study of physical and chemical s
 urface properties. In a standard STM experiment electrons tunnel from a sh
 arp metal tip through vacuum into the specimen surface and thus make its l
 ocal electronic density of states experimentally accessible. This informat
 ion can be used for Angström-scale imaging and spectroscopy.\n\nIn the pr
 esent talk I will focus on experiments with a low-temperature scanning tun
 nelling microscope (STM) in which the vacuum gap between tip and sample is
  eliminated. Correspondingly\, simple vacuum tunnelling through the STM ju
 nction gives way to more complex regimes of electron transport. This provi
 des opportunities for new and fascinating experiments. Two examples will b
 e discussed in detail.\n\nIn a first group of experiments\, the vacuum gap
  is eliminated by reducing the tip-surface distance up to the point when c
 ontact between tip and surface is\nestablished. If\, e.g.\, the tip approa
 ches a surface-adsorbed molecule\, a well-defined chemical bond between th
 e tip apex and the molecule may be formed. This technique allows precise m
 easurements of electron transport through molecules [1].\n\nIn a second gr
 oup of experiments\, the vacuum gap is eliminated by a condensed gas that 
 fills the space between tip and surface.  In the presence of this gas\n(e.
 g. molecular hydrogen) the STM generates a totally new image contrast whic
 h visualizes the geometric structure of the specimen (as revealed by its t
 otal\nelectron density) instead of its local electronic structure (as reve
 aled by the local density of states in the vicinity of the Fermi level) wh
 ich is commonly\nmeasured in STM [2\,3].\n\n[1] Nanotechnology 19\, 065401
  (2008)\n[2] New Journal of Physics 10\, 053012 (2008)\n[3] cond-mat arXiv
 :0910.5825\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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