Scaling laws for diamond chemical-vapor deposition. I. Diamond surface chemistry

A simplified model of the gas-surface chemistry occurring during chemical-vapor deposition of diamond thin films is presented. The model results in simple scaling relations, useful for process scale-up and optimization, for growth rate and defect density in terms of the local chemical environment at the substrate. A simple two-parameter expression for growth rate is obtained, which with suitable parameter choices reproduces the results of more detailed mechanisms and experiment over two orders of magnitude in growth rate. The defect formation model suggests that the achievable growth rate at specified defect density scales approximately quadratically with the atomic hydrogen concentration at the substrate

Cylindrical claw clamp has quick release feature

Claw clamp grasps cylindrical shapes by pressing its jaws around the object. The clamp is released by retraction of a release pin which extends beyond the clamp handle on both sides for better purchase

Diamond growth in a novel low pressure flame

Diamond growth using a new low-pressure combustion technique is reported. A large-area hydrogen/oxygen flame is used as the source of atomic hydrogen. Methane diluted in hydrogen is injected into the flame near a heated silicon substrate, on which diamond crystallites nucleate and grow. This technique is potentially capable of large-area film growth, since atomic hydrogen can be generated uniformly over arbitrarily large areas

Temperature dependence of species concentrations near the substrate during diamond chemical vapor deposition

Measurements have been made of the temperature dependence of CH3, CH4, and C2H2 very near the substrate during filament-assisted diamond growth. CH3 was detected using (2+1) resonance-enhanced multiphoton ionization (REMPI), and CH4 and C2H2 concentrations were measured using sampling mass spectrometry. A strong dependence of the CH3 REMPI signal on substrate temperature was observed, which at low temperatures may be characterized as having an activation energy of approximately 4±1 kcal/mole. Methane and acetylene, on the other hand, are relatively independent of substrate temperature. These results are most likely due to recombination of methyl to methane or ethane in the cool gas layer near the substrate or on the surface at low substrate temperatures

Magnetoplasmadynamic (MPD) accelerator assisted synthesis of diamond

The use of a magnetoplasmadynamic (MPD) accelerator for diamond synthesis is investigated. The acceleration process in an MPD device is reviewed and results presented for a test in which a low power (15 kW) MPD accelerator was used as the gas activation source for diamond deposition. A hydrogen–argon mixture was used in the discharge with externally injected methane as the carbon precursor. Results, including SEM images, Raman and x-ray diffraction spectra are presented for a 3.3 µm thick film deposited over a 100 min period. The Raman spectra include a broad background and shift in the diamond peak, indicative of contamination and stresses in the deposited film. Potential scaling benefits of the MPD accelerator as well as some of the drawbacks associated with methane injection and sample contamination underscored by the experiments are identified and discussed

Numerical modeling of the filament-assisted diamond growth environment

A numerical model of the filament-assisted diamond growth environment has been developed and used to calculate temperature, velocity, and species concentration profiles, accounting both for transport and detailed chemical kinetics. The computed hydrocarbon concentrations agree well with previously measured values, when allowance is made for 3D effects not included in our model. Upper-bound, diffusion-limited film growth rates for various assumed growth species have been computed, and it has been found no hydrocarbon species other than CH3, C2H2, or CH4 can account for measured diamond growth rates. The effect of thermal diffusion on H-atom profiles has been examined, and found to be only 10%. Although the environment is far from thermodynamic equilibrium, several reactions are close to partial equilibrium throughout the region from the filament to the substrate. It is also shown that homogeneous H-atom recombination is too slow to explain the experimentally observed decrease in the concentration of H with increasing initial methane concentration

Non Linear Modeling of Mixed Ionic Electronic Conductors

A nonlinear model for the study of Mixed Ionic Electronic Conductors (MIEC) is presented in this paper. The model is time dependent and takes into account electrical carriers motion, the electrical behavior of the MIEC-metal interface and the kinetics of the chemistry occurring at the MIEC surface. By applying a small potential input complex impedances are computed

Dynamics from diffraction

A model-independent approach for the extraction of detailed lattice dynamical information from neutron powder diffraction data is described. The technique is based on a statistical analysis of atomistic configurations generated using reverse Monte Carlo structural refinement. Phonon dispersion curves extracted in this way are shown to reproduce many of the important features found in those determined independently using neutron triple-axis spectroscopy. The extent to which diffraction data are sensitive to lattice dynamics is explored in a range of materials. The prospect that such detailed dynamical information might be accessible using comparatively facile experiments such as neutron powder diffraction is incredibly valuable when studying systems for which established spectroscopic methods are prohibitive or inappropriate