Doctoral Dissertations

Date of Award

8-1999

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Charles S. Feigerle

Committee Members

Frederick A. Grimm, Robert N. Compton, Ronald M. Magid, Thomas A. Callcott

Abstract

The vibrational structure and phonon character of hydrogen terminated and hydrogen free polycrystalline chemical vapor deposited (CVD) diamond was investigated using high resolution electron energy loss spectroscopy (HREELS). The experiments were conducted at a variety of incident energies: 8.8 eV, 6.0 eV, 3.2 eV, and 1.5 eV. HREELS of polycrystalline CVD diamond reveals a strong band at 2900 cm-1 with two maxima and a broad shoulder on the energy loss tail. The two maxima represent monohydride stretches on {111} and {100} crystal facets, while the broad shoulder is attributed to olefinic stretches associated with defects on {111} surfaces. Three strong phonon features were observed at 400 cm-1, 700 cm-1, and 1100 cm-1. The 1100 cm-1 band is difficult to resolve from the C-H bending mode at 1200 cm-1 unless the sample is first desorbed or the incident energy lowered below 6.0 eV. It was found that the 400 cm-1 band continued to increase in intensity as the beam energy was lowered. No compelling evidence of energy dependent dispersion was observed for any of the phonon bands.

The chemistry of chlorine interacting with CVD diamond films and natural C(100) diamond was also investigated. The reaction of the CVD surface with atomic chlorine removes all monohydride vibrational structure except that associated with {111} defects, whose intensity remains unchanged. Only a small feature near 800 cm-1 is evident as a possible C-Cl stretch. Auger spectroscopy and secondary ion mass spectrometry (SIMS) confirm the presence of chemisorbed chlorine on both C(100) and CVD diamond. Auger spectroscopy reveals a strong preference for chlorine addition to {100} facets, but the only detectable chlorine containing species as noted by SIMS is C2H4Cl+ for both C(100) and CVD diamond. It is suggested that chlorine primarily adsorbs to {100} surfaces by substituting for surface hydrogen, whereas sp2 hydrogen terminated defects near 3000 cm-1 appear to be unreactive to chlorine substitution.

Water has been implicated as important in low temperature growth of CVD diamond with oxygen addition. Water has also been reported to react dissociatively with diamond (100) single crystal and diamond powder to produce hydroxyl, ether, and carbonyl surface groups. The reactivity of water with hydrogen free CVD diamond was investigated using high resolution electron energy loss spectroscopy and Auger electron spectroscopy. No evidence was found for a dissociative reaction. In an effort to increase the functionality of diamond toward water addition, the CVD samples were first reacted with atomic chlorine. Again no evidence was noted of water dissociation on diamond. The chlorine terminated diamond surface was also reacted with molecular methanol, and once again no evidence of hydroxyl termination was observed. The temperature dependence of the C1 Auger signal was compared with the results of water and methanol addition. It was observed that any chlorine loss could be explained by simple thermal desorption rather than a chemical interaction between the C1 terminated diamond surface and dose gas.

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