132 research outputs found
Adsorbate-induced substrate relaxation and the adsorbate-adsorbate interaction
We formulate the theory of the perturbation caused by an adsorbate upon the
substrate lattice in terms of a local modification of the interatomic potential
energy around the adsorption site, which leads to the relaxation of substrate
atoms. We apply the approach to CO chemisorption on close-packed metal
surfaces, and show that the adsorbate-adsorbate interaction and a variety of
other properties can be well described by a simple model.Comment: 4 pages, 2 eps figures, RevTex, submitted to PR
Diorama Art – A Potential Medium For Museum Educationm
The study recognizes the traditional role diorama plays as an effective medium for museum education and employed both descriptive and experimental methods to produce a diorama to popularize it for the Ghanaian populace. It explored the use of non-traditional modelling material (corn shucks and cobs) in the preparation of diorama. The results of the study indicate that corn shucks and cobs which have less use in our environment as raw materials can be used as modelling medium to produce sculpture. As such other unconventional materials could be explored for modelling in order to open more avenues to sculptors. Besides, diorama could be a minimuseum, a potent tool to keep proper records, document valuable cultural and historic information to inspire and educate the public; as well as a way of building museums on school campuses to expand classroom teaching and learning.Keywords: Diorama, Museum, Education, Aperture, Assemblage
Many Body Theory of Charge Transfer in Hyperthermal Atomic Scattering
We use the Newns-Anderson Hamiltonian to describe many-body electronic
processes that occur when hyperthermal alkali atoms scatter off metallic
surfaces. Following Brako and Newns, we expand the electronic many-body
wavefunction in the number of particle-hole pairs (we keep terms up to and
including a single particle-hole pair). We extend their earlier work by
including level crossings, excited neutrals and negative ions. The full set of
equations of motion are integrated numerically, without further approximations,
to obtain the many-body amplitudes as a function of time. The velocity and
work-function dependence of final state quantities such as the distribution of
ion charges and excited atomic occupancies are compared with experiment. In
particular, experiments that scatter alkali ions off clean Cu(001) surfaces in
the energy range 5 to 1600 eV constrain the theory quantitatively. The
neutralization probability of Na ions shows a minimum at intermediate
velocity in agreement with the theory. This behavior contrasts with that of
K, which shows ... (7 figures, not included. Figure requests:
[email protected])Comment: 43 pages, plain TeX, BUP-JBM-
The mechanism of caesium intercalation of graphene
Properties of many layered materials, including copper- and iron-based
superconductors, topological insulators, graphite and epitaxial graphene can be
manipulated by inclusion of different atomic and molecular species between the
layers via a process known as intercalation. For example, intercalation in
graphite can lead to superconductivity and is crucial in the working cycle of
modern batteries and supercapacitors. Intercalation involves complex diffusion
processes along and across the layers, but the microscopic mechanisms and
dynamics of these processes are not well understood. Here we report on a novel
mechanism for intercalation and entrapment of alkali-atoms under epitaxial
graphene. We find that the intercalation is adjusted by the van der Waals
interaction, with the dynamics governed by defects anchored to graphene
wrinkles. Our findings are relevant for the future design and application of
graphene-based nano-structures. Similar mechanisms can also play a role for
intercalation of layered materials.Comment: 8 pages, 7 figures in published form, supplementary information
availabl
Room Temperature Kondo effect in atom-surface scattering: dynamical 1/N approach
The Kondo effect may be observable in some atom-surface scattering
experiments, in particular, those involving alkaline-earth atoms. By combining
Keldysh techniques with the NCA approximation to solve the time-dependent
Newns-Anderson Hamiltonian in the infinite-U limit, Shao, Nordlander and
Langreth found an anomalously strong surface-temperature dependence of the
outgoing charge state fractions. Here we employ the dynamical 1/N expansion
with finite Coulomb interaction U to provide a more realistic description of
the scattering process. We test the accuracy of the 1/N expansion in the
spinless N = 1 case against the exact independent-particle solution. We then
compare results obtained in the infinite-U limit with the NCA approximation and
recover qualitative features found previously. Finally, we analyze the
realistic situation of Ca atoms with U = 5.8 eV scattered off Cu(001) surfaces.
Although the presence of the doubly-ionized Ca species can change the absolute
scattered positive Ca yields, the temperature dependence is qualitatively the
same as that found in the infinite-U limit. One of the main difficulties that
experimentalists face in attempting to detect this effect is that the atomic
velocity must be kept small enough to reduce possible kinematic smearing of the
metal's Fermi surface.Comment: 15 pages, 10 Postscript figures; references and typos correcte
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