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Document Type |
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Article In Conference |
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Document Title |
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A Monte Carlo Study of Dimer Adsorption with Different Orientation in Adlayer on Homogeneous Surfaces A Monte Carlo Study of Dimer Adsorption with Different Orientation in Adlayer on Homogeneous Surfaces |
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Subject |
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كيمياء |
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Document Language |
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English |
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Abstract |
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Adsorption with multisite occupancy is an important topic of surface science
because of its key role in a broad range of industrial processes such as heterogeneous
catalysis, microelectronics and nanotechnology. In the last few years, special attention
is paid for investigations of ordering phenomena in adsorbed monolayer with multisite
occupancy [1,2]. However, there is one more problem, at least. Namely, when one
considers adsorption of the molecules having no spherical symmetry it is necessary to
take into account possibility of the different orientation of the molecules in adlayer. In
the case of dimer-like adsorbed molecules each one can occupy one or two sites.
Particularly, in the case of adsorption of unsaturated organic molecules on
semiconductor surfaces and on the surfaces of some metals and its oxides, adsorbed
molecules can occupy one or two (or more) sites [3,4,5]. Thus, the aim of this work is
study of dimer adsorption on homogeneous surfaces with its different orientation in
adlayer.
To describe the adsorption of orientable dimer-like molecules we use the general
lattice gas model. We consider the adsorption homonuclear dimers on square,
triangular and honeycomb lattices. The dimers can occupy one or two sites on the
surface. To take into account own size of the molecules and its chemical structure we
involve infinity strong repulsive interactions between nearest-neighbor particles. The
adsorption process is simulated through a grand canonical ensemble Monte Carlo
method. The model parameters are chemical potential , temperature T and Δ -
difference between the adsorption heat on two sites and on one site.
We have calculated a set of isotherms for different values of Δ for all types of
lattices. As Δ increases, two well-defined steps corresponding to ordered phases
appear at coverage θ1=0,55(5) and θ2=0,5 – for honeycomb lattice; θ1=0,5 and θ2=0,5
– for square lattice; θ1=0,4 and θ2=0,33(3) – for triangular lattice. In the case of
honeycomb and triangular lattices, the dependence of coverage on chemical potential
has nonmonotonous behavior at sufficiently higher value of Δ, it means that with
increasing of pressure in gas phase the coverage of the surface diminishes. This
phenomenon is explained by specific character of ordered structures on each type of
lattice. |
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Conference Name |
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Tenth International Symposium on Heterogeneous Catalysis |
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Duration |
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From : 22/8/1429 AH - To : 26/8/1429 AH
From : 23/8/2008 AD - To : 27/8/2008 AD |
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Publishing Year |
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1429 AH
2008 AD |
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Article Type |
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Article |
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Added Date |
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Tuesday, February 17, 2009 |
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