Homogeneous nucleation of diamond powder is reported. The experiments were performed in a low-pressure microwave-plasma reactor. The deposits were collected downstream of the reaction zone and subjected to wet oxidation to remove nondiamond carbons. The residues were analyzed by optical and electron microscopy, electron diffraction, and Raman spectroscopy. A variety of hydrocarbons diluted in argon, hydrogen, or oxygen gas mixtures were tested. In most cases only nondiamond materials, like graphite and carbyne, were obtained. Homogeneous nucleation of diamond was clearly observed in dichloromethane- and trichloroethylene-oxygen mixtures. The particles formed had crystalline shapes, mostly hexagonal. The largest particles were about 0.2 μm, although most of the particles were on the order of 50 nm in diameter. The powder was identified to be a mixture of polytypes of diamond.

The effects of heteroatom addition on the nucleation of solid carbon in a low-pressure plasma reactor were investigated. Silane or diborane were added to acetylene mixed in hydrogen or argon. Oxygen was added to some of the diborane containing gas mixtures. Silane containing mixtures resulted in powder comprised of weakly bonded amorphous hydrogenated carbon-silicon material. The addition of diborane resulted in substantial production of diamond particles, 5 to 450 nm in diameter, under the conditions that show no diamond formation without diborane present. The observed yield of the oxidation-resistant powder produced in boron-containing mixtures reached 1.3 mg/h with the linear growth rates of diamond particles on the order of 102–104 μm/h. Implication of these results to interstellar dust formation is discussed.

Using molecular-dynamics studies and static potential-energy minimization, we have resolved the mechanisms by which n-alkanes (ethane through n-decane) diffuse on a model Pt(111) surface in the low-coverage limit of a single adsorbed molecule. Our simulations reproduce all of the experimental trends seen for the adsorption and diffusion of C3–C6 on Pt(111) and Ru(001). The short alkanes (C2–C8) behave as rigid rods and their motion involves coupled translation and rotation in the surface plane. For this series, there is a linear increase of the diffusion barrier with the molecular chain length. We have analyzed the compliance of the motion of the assumptions of a nearest-neighbor hopping model. Although hopping motion can be observed for all of the molecules at sufficiently low temperatures, the hopping involves a significant fraction of long jumps. As the temperature increases, the adsorption becomes virtually delocalized. Despite the extensive deviations of the motion from the assumptions of a nearest-neighbor hopping model, the static diffusion-energy barriers, arising from the minimum-energy path for hops between nearest-neighbor binding sites, agree well with those obtained from the tracer-diffusion coefficients for butane, hexane, and octane. For these molecules, multiple-site hops and long flights appear to influence the values of the preexponential factors, which are too large. Neither the diffusion barrier nor the preexponential factor for ethane agrees well with theoretical estimates. We attribute these discrepancies to the smallness of the static diffusion barrier and/or the existence of unique dynamical behavior for this molecule. Due to the increased difficulty of in-plane rotation and increased mismatch between the geometries of the molecule and the surface, the diffusion barrier for n-decane drops below that for n-hexane. The characteristic mechanism of motion for n-decane involves significant C–C–C bond-angle bending.

decreased in intervals of 0.1 (to log Kb,s = -2.O), and the new steady-state current was evaluated a t each Kb,s, using the steady-state concentration profile evolved a t the previous value of Kbs as the initial condition. With this computational procedure, it was possible to generate working curves comprising 51 points in under 20 CPU minutes on a VAX 6410 mainframe computer.For simulations of the finite substrate problem, the radial coordinate in the diffusion equation (eq 3) was left untransformed over the region R = 0 to the larger of the edge of the substrate or electrode, Le., to R = h or a. Beyond this limit, the radial coordinate was transformed with an exponential function similar to that in eqn A2 in ref 1 1 I These changes required some modifications of the computational algorithm, but these should be self-evident on the basis of our earlier work." The number of grid points employed in the 2 direction for these calculations depended upon the normalized tipsubstrate separation, varying from 100 (log L = -1.2) to 200 (log L = 0.3). In the radial direction, the density and distribution of grid points depended upon the magnitude of h. For h 5 0.4, calculations employed 100 points over the substrate (and thus a total of 100/h points over the electrode). For 0.5 I h I 1, 250 points were utilized over the electrode, and for larger values of h, between 150 and 250 points were employed. Beyond the edge of the electrode (or substrate), between 100 and 200 points were necessary to give the desired level of accuracy. Registry No. Ru(NH3)P,The energetics of several possible diamond (1 00) surface growth reactions was investigated by a semiempirical quantum chemical method. These reactions included thermal and radical-driven dehydrogenation, hydrogen atom migration, and diamond growth by the addition of methyl, acetylene, carbon monoxide, and carbon atoms. Some of the major findings are as follows: the calculated potential energy barrier for H2 elimination from a (loo)-( 1 X 1) diamond dihydride forming a (2x1) surface dimer is in good agreement with experiment; diamond growth by CH3 addition on a dihydrogenated (lOO)-(lXl) surface encounters a large potential energy barrier, yet the barrier is lower for the addition of CH3 to a triplet surface diradical or to a monohydride dimer surface radical; CO addition reactions have substantial potential energy barriers; the energetics for the addition of C atoms onto a diamond (loo)-( 1 X 1) surface is very favorable; and the growth of diamond by the addition of C,H2 on a (100) surface is feasible and should be the energetically preferred channel for the growth on surface ledges and kinks.

In this paper, the correlation between the electrochromic performance and the surface morphology of the tungsten trioxide (WO 3 ) thin films sputtered by dc reactive magnetron sputtering with widely varying target-substrate distances was investigated. It is found that the optical density change (∆OD) of films is strongly affected by the target-substrate distance. The coloration efficiency (CE) at 633 nm was also found to be sensitive to the target-substrate distance, with 16 cm 2 /C of film sputtered at 6 cm and 50 cm 2 /C at 18 cm. X-ray diffraction showed that the crystal structure of films was amorphous. By using atomic force microscope to identify the surface porosity of the sputtered WO 3 films, we found that the film at longer target-substrate distance was rough, porous, and having a cone-shaped columns morphology, thus offering a good electrochromic performance for opto-switching applications.