Atomistic study of xenon crystal growth via low-temperature atom beam deposition

Abstract

We studied theoretically the deposition of Xe atoms on a sapphire substrate and the subsequent growth of ordered Xe phases via the low-temperature atom beam deposition method. This chemical synthesis method ͓D. Fischer and M. Jansen, J. Am. Chem. Soc. 41, 1755 ͑2002͔͒ is particularly suitable for synthesizing metastable solid compounds. The modeling procedure consisted of several steps, where we used empirical potentials to model the interactions within the substrate, the Xe-Xe interactions in the gas phase and the solid, and the interactions between the Xe atoms and the substrate. In a first step, we established that under the experimental conditions, no Xe clusters formed in the gas phase, and thus the deposition could be described by the adsorption of single Xe atoms on the substrate at low temperatures. Next, we simulated the Xe deposition process and we studied the growth mode depending on various synthesis parameters such as the deposition rate and the temperature of the substrate. Finally, the deposited Xe layers were tempered and the structure of the resulting compound was analyzed. We studied the establishment of locally ordered regions as a function of time, both during the deposition and the tempering. We observed that the final configuration was always crystalline, although defects such as stacking faults and dislocations were likely to form. The occurrence of different growth modes and the formation of defects were explained by studying diffusion and adsorption processes on the surface of both the substrate and the depositing phase.

Atomistic Modeling of the Low-Temperature Atom-Beam Deposition of Magnesium Fluoride

“…Figure ). This is in contrast to the previous study on Xe, where the temperature was fluctuating around the average values over the deposited layers during the deposition process itself. This temperature distribution in the MgF 2 deposit is most likely the result of the fast deposition rates that had to be used in the simulation because of time considerations, together with the large amount of heat released when the atoms and molecules are adsorbed at the surface.…”

“…However, many aspects of this synthesis are still unresolved, especially the genesis and structure of the amorphous deposit and the nucleation and growth processes involved in the formation of crystalline phase(s). In earlier work, we analyzed the deposition and growth of xenon films via the LT-ABD method. However, the processes involved in the synthesis of ionic compounds are expected to be considerably more complex, requiring further study.…”

Ab initio and empirical energy landscapes of (MgF2)nclusters (n = 3, 4)

“…17,[24][25][26][27][28] In earlier work, we have modelled the LT-ABD synthesis of Xenon on a sapphire substrate, taking all the steps of the synthesis route into account, ranging from the description of the gas phase over the deposition to the annealing of the deposited Xe-film. 29 In that work, the gas phase was particularly simple insofar as no stable Xe clusters were formed under synthesis conditions, and thus the deposition could be modeled by slowly condensing a low-density monatomic Xe-gas onto the substrate.…”

Molecular dynamics analysis of the crystallization of an overcooled aluminum melt

“…For example, a method for determining the energy barrier in crystal nucleation was considered in [7]. A study of crystal growth on a substrate was reported in [8]. Differences in the crys tallization mechanism for highly and moderately over cooled liquids were analyzed in [9].…”