Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy Page: 4 of 24
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1.2 Semiconductor Surface Structures
The use of new techniques to create new surface structures is providing new insights
into physics at the surfaces. Recently, Salling and Lagally observed the dimerized structure in
the second layer after removing dimers in the first layer by means of a voltage-pulsed STM tip
. Our preliminary results  show that the second layer structure is altered from that of
the thermally annealed surface and is similar to the bulk-terminated structure after removal of
part of the first layer by laser irradiation. These data may suggest that the structure of the
second layer of the Si(100) surfaces depends upon the process by which the atoms in the first
layer are removed.
For many years there have been many theoretical efforts to reveal the atomic structure
- __ of the underlying layer as dimers are removed from the Si(100)-2x1 surfaces. Pandey
predicted that upon removal of surface dimers, the atoms beneath the vacancies would bond
together to form new dimers . Contrary to Pandey's prediction, Roberts and Needs'
calculations show an energy cost to re-bond after dimer removal . But neither of these
results provide support for a bulk-terminated structure of the layer beneath surface vacancies.
The static structures of Si(100) surfaces are expected to be influenced by the existence
of adsorbates and/or vacancies. It is well known that the 2x1 reconstruction characteristic of
the clean surface is changed by adsorption of impurities such as H2  and H20 . This
relaxation is a result of extraction of electrons from the dimer bonds by the impurity which
saturates the surface dangling bonds. The Si(100) surface can also form 2x6, 4x8, 4x4, and
1x5 reconstructions with Sn atoms present on the surface, depending on Sn coverage , 2x2
for In presence , 2x3 for Ag coverage , and 4x4 for boron [13J.
Experiments were carried out in an ultra-high vacuum (UHV) chamber, equipped with
STM (Omicron) and coupled with a pulsed Nd:YAG laser. Most images were acquired in the
constant current mode using tunneling currents of 0.2-0.6 nA and sample bias between -1.5
and -3.0 V. The scan rate was typically 500 ps per point with image resolutions of 400 points
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Xu, Jun; Overbury, S.H. & Wendelken, J.F. Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy, article, July 1, 1995; Tennessee. (digital.library.unt.edu/ark:/67531/metadc667171/m1/4/: accessed February 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.