We compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of the structure of these materials. For the full range of carbon-hydrogen alloys, including so-called ‘‘amorphous diamond,’’ hydrogenated ‘‘diamondlike’’ carbon, and plasma-polymers, a simple parametrization of the Raman spectrum in the usual 1000 cm−1 to 2000 cm−1 range can be used as a reliable predictor of hydrogenation and other properties (e.g., optical gap, hardness). Raman features in the 200 cm−1 to 1000 cm−1 range, a spectral region not usually reported for carbon films, may also be used as an indicator of hydrogenation. These growth method independent correlations greatly enhance the utility of Raman spectroscopy as a non-destructive characterization and process control tool.

We present coherent-potential-approximation (CPA) calculations and firstand second-order Raman spectra for diamonds with varying concentrations of ' C and ' C. The calculations are based on the valence-force model of Tubino, Piseri, and Zerbi [J. Chem. Phys. 56, 1022(1972]. Contrary to previous claims, we find that this model does not give a sharp peak in the density of states (DOS) near the Raman mode. Alternative dispersion curves that do give such a peak are discussed. Raman results are reported for high-quality, single-crystal synthetic diamonds with isotopic compositions ranging from nearly pure ' C to nearly pure ' C. A measurable deviation in the Raman frequency away from a simple M (" virtual-crystal" ) dependence and an observable broadening of the firstand second-order spectra are qualitatively consistent with CPA predictions for the effects of isotopic disorder. Quantitative agreement between theory and experiment is achieved only if the reference DOS contains the abovementioned peak. This supports the interpretation of the controversial second-order Raman peak in naturally abundant diamond (1.1 at. % "C) at 2667 cm ' as a DOS effect. At all compositions, the effects of isotopic disorder are relatively weak because of the small mass difference between ' C and ' C. For 1.1 at. % ' C, the maximum broadening predicted in the CPA is less than 1 cm ', nearly two orders of magnitude smaller than a previous estimate. For the lowest-frequency modes most relevant to the thermal conductivity, the CPA scattering rate reduces to the usual co dependence first derived by Klemens for phonon-isotope scattering. Using Callaway's theory, we show that this term can easily account for the recently observed 50% enhancement in room-temperature thermal conductivity upon elimination of ' C impurities, provided that sufficient normal scattering also occurs.

Carbon bonding environments (measured by nuclear magnetic resonance spectroscopy) and compressive stress in plasma-deposited hydrogenated diamond-like carbon (DLC) films have been examined systematically as a function of substrate bias voltage. These results are related in terms of random network theory to show that hard DLC formed in an intermediate voltage range (100–400 V) consists of small graphitic clusters linked in a random network which is stiffened by a high density of quaternary carbon.

Electrocatalytic hydrogenation offers a carbon and energy efficient strategy for upgrading pyrolytic bio-oil with renewable electricity in biomass processing depots.

We use simple arguments to fix the range of density of randomly distributed defects over which 1T electrons in a graphic sheet are strongly localized, but the underlying two-dimensional carbon network remains connected. This "defeated graphite" construct leads to simple structural models of both hydrogenated and unhydrogenated amorphous "diamondlike" carbon, which reproduce many important properties of those materials.