Michael Alan Tamor

Atomic constraint in hydrogenated ‘‘diamond‐like’’ carbon

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.

Correlation of the optical gaps and Raman spectra of hydrogenated amorphous carbon films

The Raman and infrared absorption spectra, optical gaps, and electron spin densities of amorphous carbon films deposited from hydrocarbon plasmas have been systematically studied as a function of deposition conditions and Raman probe wavelength. Although all other probes are consistent with a monotonic increase in intermediate‐range order with substrate bias voltage Vb, the optical gap decreases with increasing Vb (consistent with increasing graphitic domain size) only up to the onset of sputtering, where the gap sharply increases. We propose a simple structural model for a‐C:H which is consistent with these results and requires no sp3 bonding.

Amorphous hydrogenated carbon films for tribological applications. I. Development of moisture insensitive films having reduced compressive stress

Abstract Although earlier investigations on the tribological behaviour of amcrphous hydrogenated carbon (AHC) films in sliding contact with steel showed encouraging results, four open issues were identified. They were: (a) dependence of friction and wear on humidity (i.e., the friction coefficient and the wear increased with humidity), (b) limitations on film thickness (i.e., films greater than 2 μm thick delaminated due to large compressive stress), (c) deposition of films on substrates other than silicon and (d) lubricant compatibility (i.e., formation of lubricant-derived antiwear films on AHC film surfaces). Steps were taken to address some of these open issues by incorporating silicon in AHC films. Friction and wear tests were conducted on AHC films containing various amounts of silicon. Incorporation of silicon in AHC films rendered the friction coefficients and the wear of a steel counterface insensitive to moisture. Silicon incorporation in AHC films also significantly reduced compressive stress. This allowed deposition of 10 μm thick films. These effects were achieved without any compromise with the friction coefficient and the film wear if the amount of silicon in the film was kept within a certain concentration range. In addition, silicon-containing AHC films were thermally more stable than silicon-free films. Experiments conducted with two lubricants resulted in significantly lower wear of the silicon-free AHC films than that obtained for unlubricated sliding. Similar friction coefficients were obtained for AHC film/steel and steel/steel combinations in lubricated sliding.

Pendant benzene in hydrogenated diamond‐like carbon

We show that nearly all of the infrared absorption associated with sp2 coordination in diamond‐like carbon deposited from benzene plasma is due to pendant (mono‐substituted) benzene. Because these pendant groups have little effect on the optical and mechanical properties of the film, which are determined by the connected covalent network to which they attach, they obscure the connection between those properties and the sp3 /sp2 bonding ratio in diamond‐like carbon.

Amorphous hydrogenated carbon films for tribological applications II. Films deposited on aluminium alloys and steel

Abstract This paper describes the methods for the deposition of AHC films on aluminium alloys (2024, 7075 and an additional Al-Si alloy) and AISI 4340 steel. Both unmodified and silicon modified AHC films were deposited. AHC films could be deposited on aluminium alloys without any interlayer. The deposition of AHC films on steel required an interlayer which could be aluminium, silicon or chromium. Thin films (1–2 μm) deposited on aluminium alloys and steel influenced durability of films and friction coefficients in contact with steel. These were believed to be due to plastic deformation of substrates. Deposition of a thicker coating system (interlayer + AHC) reduced friction coefficients and also improved film durability. The durability of films deposited on steel substrates was evaluated under both unlubricated and lubricated conditions for 5.5 million cycles under 4.4 N load and up to 2.5 m/s sliding speed. Although there was wear, the films survived 5.5 million test cycles under unlubricated sliding, but in the presence of two lubricants, the film wear was very small and could not be measured. It was observed that the wear of the steel counterface in contact with silicon-containing AHC films could be higher than that against an uncoated steel in the presence of certain lubricants.

Solid state NMR study of carbon bonding in amorphous hydrogenated carbon films

Carbon bonding environments in hydrogenated amorphous carbon films (a-C:H) deposited from an rf-biased methane plasma onto various substrates have been quantified by application of solid state13C NMR. A family of films were prepared by systematically varying the substrate bias voltage. Quantitative data on carbon chemistry in these films is required for modeling the impact of structure on mechanical and optical properties. A variety of NMR acquisition pulse sequences have been investigated to determine the conditions under which quantitative13C NMR data can be acquired in this system. The results indicate that data acquisition from this material requires different protocols than for the study of polymeric hydrocarbon films. With proper experimental design, NMR is an excellent technique for structural studies of these materials.

Relationship of Processing Conditions to Growth Rate and Quality of Diamond Grown by Chemical Vapor Deposition

Diamond quality is strongly coupled to growth rate. Incorporation of nondiamond (sp 2 ) carbon and morphological instabilities both increase with increasing growth rates. The intersection of twins with the growth surface produces re-entrant corners that enhance growth in the plane of the twin. Morphology and the development of texture both depend on substrate temperature and methane concentration and hence on growth rate. Experimental evidence and modeling results that relate growth rates and quality to controllable process parameters are reviewed.

Impact of gasoline and natural gas prices on capacity planning for automakers and electricity generators under GHG emission constraints

Both automakers and electricity generators are facing increasingly more stringent greenhouse gas (GHG) emission targets. With the introduction of plug-in hybrid and electric vehicles, the transportation and electricity generation sectors become connected. This provides an opportunity for both sectors to work jointly to achieve cost efficient reduction of CO2 emissions. Due to the low cost and low carbon content of natural gas (NG), NG enabled vehicles are drawing increasing attention. With GHG targets rapidly decreasing, how to judiciously choose among plug-in hybrid vehicles, electric vehicles, NG-enabled vehicles, and gasoline vehicles to save societal cost is worth serious consideration. On the other hand, gasoline and NG prices play an important role in this decision-making process. In order to estimate the impact of gasoline and NG prices and quantify the benefit of the collaboration between automakers and electricity generators, an optimization model is developed to evaluate the total societal cost and CO2 emissions for both sectors. Various scenario analyses are conducted to understand the cost and capacity planning differences when gasoline and NG prices vary while the two sectors can work jointly or independently to meet the CO2 emission constraints. These results help us understand the impact of gasoline and NG prices in achieving GHG reduction targets for the two major sectors of CO2 emissions in the United States.Copyright