The chemical bonding and morphology of chemical vapor deposited (CVD) diamond films exposed to thermal (∼0.04 eV) and hyperthermal (5 and 7.5 eV) atomic oxygen (AO) were studied by using high resolution electron energy loss spectroscopy (HREELS), atomic force microscopy, and theoretical simulations. Although exposure to thermal AO caused subtle changes to the surface morphology, hyperthermal AO resulted in selective etching of the diamond facets: (100) facets remained essentially unaffected, whereas (111)-oriented and other facets were severely etched. HREELS reveals that hydrogen is removed from the diamond surfaces during both thermal and hyperthermal AO exposures. By using isotopic labeling in the CVD growth procedure, it is observed that exposure to ambient conditions after the AO exposure leads to adsorption of adventitious hydrocarbons on the surface. The high background in the HREEL spectrum of samples exposed to hyperthermal AO suggests the presence of a graphitic layer. Simulations of the interaction between hyperthermal AO and (100) and (111) diamond surfaces were conducted by using direct dynamics based on density-functional-based tight binding methods, in an attempt to elucidate relevant reaction mechanisms. They suggest mechanisms for the partial graphitization of the (111) surface and for etching of this surface by way of CO2 desorption. Such damaged graphitic layers have been previously shown to erode easily when exposed to a hyperthermal AO beam. The simulations also suggest that the (100) surface, fully covered with ketones, is inert to carbon removal upon exposure to hyperthermal oxygen atoms, which scatter inelastically from this surface without reaction. The simulations suggest that a nearly full ketone coverage is the steady-state configuration for a (100) diamond surface exposed to AO.

No abstract

Investigation of oxygen-related defects and the electrical properties of atomic layer deposited HfO 2 films using electron energy-loss spectroscopy High resolution electron energy loss spectroscopy study of Fomblin Z-tetraol thin filmsa) A combined scanning tunneling microscopy and electron energy loss spectroscopy study on the formation of thin, well-ordered β-Ga 2 O 3 films on CoGa (001) Diamond surface oxidation by atomic oxygen, annealing up to ϳ700°C, and in situ exposure to thermally activated hydrogen were studied by high resolution electron energy loss spectroscopy ͑HREELS͒. After atomic oxygen ͑AO͒ exposure, HREELS revealed peaks associated with CH x groups, carbonyl, ether, and peroxide-type species and strong quenching of the diamond optical phonon and its overtones. Upon annealing of the oxidized surfaces, the diamond optical phonon overtones at 300 and 450 meV emerge and carbonyl and peroxide species gradually desorb. The diamond surface was not completely regenerated after annealing to ϳ700°C and in situ exposure to thermally activated hydrogen, probably due to the irreversible deterioration of the surface by AO.

The present work studies the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament ͑HF͒, microwave ͑MW͒, and direct current glow discharge ͑dc GD͒ chemical vapor deposition ͑CVD͒. The size of diamond grains which constitute the films varies in the following way: hundreds of nanometers in the case of HF CVD ͑"submicron size," ϳ300 nm͒, tens of nanometers in the case of MW CVD ͑3-30 nm͒, and a few nanometers in the case of dc GD CVD ͑"ultrananocrystalline diamond," ϳ5 nm͒. Raman spectroscopy, secondary ion mass spectroscopy, and high resolution electron energy loss spectroscopy ͑HR-EELS͒ were applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating that most likely, hydrogen is bonded and trapped in grain boundaries as well as on the internal grain surfaces. Raman and HR-EELS analyses show that at least part of this hydrogen is bonded to sp 2 -and sp 3 -hybridized carbon, thus giving rise to typical C u H vibration modes. Both vibrational spectroscopies show the increase of ͑sp 2 ͒-C u H mode intensity in transition from submicron to ultrananocrystalline grain size. The impact of diamond grain size on the shape of the Raman and HR-EELS hydrogenated diamond spectra is reported and discussed.

Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy

In situ studies of low energy nitrogen species incorporated into diamond films are significant as they could lead to a better understanding of bonding configuration and defects formation of the modified surface. In this report, we investigate the interaction of radio frequency (RF) nitrogen plasma onto a polycrystalline diamond surface at different temperatures (RT, 250, 500, and 750 8C). The influence of RF nitridation temperature on the bonding configuration, thermal stability, and concentrations of incorporated species were systematically investigated by in situ X-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy (HREELS). Our results showed that local bonding configurations were influenced by the temperature of the RF nitridation process. The amount of nitrogen incorporated into the diamond surface decreased as the nitridation process temperature increases. RF nitridation performed at 750 8C showed the absence of reorganization in the local bonding configurations upon annealing to 1000 8C and their thermal stability was also found to be better. HREELS results displayed partial retrieval of the characteristic optical phonon overtone of diamond, after annealing to 500 8C, which indicates that the RF nitridation process was successful in incorporating nitrogen into diamond surface without inducing a graphitic near surface region.

No abstract

No abstract