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Monte Carlo simulations of the CO₂/NaCl(001) and CH₃Br/LiF(001) systems

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Monte Carlo simulations of the CO₂/NaCl(001) and CH₃Br/LiF(001) systems

Hu, Wei (1997) Monte Carlo simulations of the CO₂/NaCl(001) and CH₃Br/LiF(001) systems. Masters thesis, Concordia University.

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Abstract

Metropolis Monte Carlo simulations were used to examine the stable structures, phase coexistence and mechanism of nucleation and growth of films of CO$\sb2$ molecules adsorbed on the (001) surface of NaCl. This was done for submonolayer, monolayer, and multilayer coverages. The results show that the monolayer has two stable structures, a (2 x 1) herringbone structure and a (1 x 1) structure while the bilayer system has three stable structures: the (2 x 1), the (1 x 1) and the c(2 x 2). The trilayer system adopts a c(2 x 2) structure owing to the instability of the (2 x 1) structure. Multilayers most likely grow in the Stranski-Krastanov fashion whereby multilayer islands on top of a monolayer adopt a bulk-like crystalline structure $\{c$(2 x 2)$\}.$ At low coverages the CO$\sb2$ molecules behave like a 2D gas which aggregates into low density islands but finds it hard to nucleate the denser 2D solid phase directly, even in the presence of a surface step. This suggests that the adsorption of CO$\sb2$ molecules on the low density islands nucleates the 2D solid phase. The 2D gas-solid phase coexistence was found to obey the (2D) van der Waals equation of state. The critical coverage $\Theta\sb{c}$ and temperature T$\sb{\rm c}$ were found to be 0.162 and 142.9K respectively, close to the theoretical values of $\Theta\sb{c}$ = 1/6 and $T\sb{c}=151.2$K. For the CH$\sb3$Br/LiF(001) system, submonolayer and monolayer coverages were examined. The results show that for low coverages the molecules are tilted by 60$\sp\circ$ from surface normal while at monolayer coverage a stable (2 x 1) herringbone structure was found with a molecular tilt of 39.2$\sp\circ$ in agreement with experiment. An alternative incommensurate monolayer structure was found where the molecules are antiferroelectrically ordered perpendicular to the surface.

Divisions:Concordia University > Faculty of Arts and Science > Physics
Item Type:Thesis (Masters)
Authors:Hu, Wei
Pagination:xv, 104 leaves : ill. ; 29 cm.
Institution:Concordia University
Degree Name:Theses (M.Sc.)
Program:Dept. of Physics
Date:1997
Thesis Supervisor(s):Jack, David B
ID Code:188
Deposited By:Concordia University Libraries
Deposited On:27 Aug 2009 13:10
Last Modified:08 Dec 2010 10:13
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