Ankara : The Department of Physics and the Institute of Engineering and Science of Bilkent University, 1994.Thesis (Master's) -- Bilkent University, 1994.Includes bibliographical references leaves 64-69.Nanoscale modification of matter has been the subject of interest. Recently,
several experimental studies have demonstrated that by using a scanning
tunneling microscope one can translate atoms on metal surfaces to a desired
position. Furthermore, it has been shown that an atom between surface and
tip can be transferred reversibly which results in bistable conductance. The
controlled dynamics of adsorbed species has opened a new field of research.
This thesis work provides a theoretical investigation of the controlled lateral and
perpendicular motion of an inert gas atom (Xe) on metal surfaces.
The lateral motion of Xe on the Ni(llO) and P t(lll) surfaces is manipulated
by a W tip. The interaction energy of the physisorbed atom with the tip and
metal surface is described by an empirical potential. Using molecular statics
the energy surfaces are calculated and the adsorbtion sites are determined. By
using the molecular dynamics calculations, the variation in the coordinates of the
adsorbate Xe with the tip moving at a given height are obtained. Three different
modes of Xe translation are distinguished depending on the height of the tip.
These are i) carriage on the tip, ii) pushing and, iii) pulling modes. The range of the tip height where one of these modes occur is strongly depended on the
relaxation of electrodes and the geometry of the tip.
Controlled and reversible transfer of atoms between the metal surface and
the tip is studied by the transfer of Xe between two flat P t(lll) surfaces.
Physisorption of Xe on the P t(lll) surface is studied by an empirical potential
including short and long-range interactions and yielding correct account of several
experimental data. Effective charge on Xe and the dipole moment constructed
therefrom are calculated as a function of the Xe-surface separation. The potential
energy curve of Xe between two P t(lll) surfaces and quantum states of Xe therein
are calculated as a function of the applied voltage and separation between two
P t (lll) surfaces. Within this model, various mechanisms, such as tunneling of
Xe, dipole excitation and resonant tunneling, electromigration contributing to
the transfer of Xe are examined. The transfer rate of Xe is then calculated for
different mechanisms. Its dependence on the bias voltage is explored. The overall
behavior of the total transfer rate is not a power law. While at low bias voltages
thermal assisted atom tunneling is effective, the dipole excitation and resonant
tunneling becomes dominant at high bias voltages.Buldum, AlperM.S