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Jeffrey Roberts, Principal Investigator

A Theoretical Study of Diamond Growth Mechanisms and Morphology

The reactions and mechanisms believed to be important in the process of chemical vapor deposition (CVD) diamond growth are being investigated. This project is gaining a better understanding of how the underlying reactions contribute to the appearance of 111 or 100 faceted diamond. The methods used to study this process include ab initio electronic structure calculations and kinetic simulations. Electronic structure methods are used to calculate the energetics for growth reactions. Clusters of carbon atoms are used as models for the diamond surface. Comparisons can be made between reactions that occur within different structural environments. Differences in reaction rates may suggest the cause for the observed morphologies. A kinetic model of CVD diamond growth that simulates the dependence of 100 and 111 surface growth rates upon experimental parameters, such as surface termperature and gas-phase concentrations, has been developed. The model is being further developed to include 111 surface growth and more extensive simulations are being run. This model differs from previous diamond growth simulations due to the inclusion of H-atom and CH2 migration reactions that are believed to be important for predicting 111 versus 100 film growth. Rate parameters, found either from the literature or determined from ab initio calculations, for 69 possible reactions in the growth process have been used. It is hoped that this research will yield predictions for morphology and a molecular level description of its origins.

A kinetic Monte Carlo method has been designed to simulate the growth of diamond from small precursors. Specifically, the model is used to examine the competition of 11-surface growth versus 100-surface growth. Previously, the nature of this growth has been examined as a function of gas-phase radical concentration and temperature. Improvements are being made to the model so that it more accurately and completely reflects the complexity of possible surface reactions. These improvements are based on ab initio calculations that have been done to elucidate reaction energetics. Further simulations are being performed to more accurately model the growth process and film morphology. The simulations encompass a wider range of growth conditions, simulating the growth process within a hot-filament and thermal plasma growth environment. From these simulations, the dependence of film microstructure on growth conditions then will be determined.

This information is available in alternative formats upon request by individuals with disabilities. Please send email to alt-format@msi.umn.edu or call 612-624-0528.

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