No abstract

Diamond films exhibiting contiguous epitaxial crystallites (~3 -4 /mm) have been grown on single crystal (100) silicon by 2.45 GHz microwave plasma deposition. The diamond films were deposited by a three-step process. In the initial stage the silicon wafer was pretreated for 3 h in a 1.8% methane in hydrogen plasma at low pressure. The subsequent nucleation stage was performed, under identical processing conditions, except that a dc bias of -340 V was applied for 25 min. During this period the current increased from 38 mA at the start to 102 mA at the end of the bias. The final growth stage was performed, with an earthed substrate, utilizing a carbon monoxide/methane/hydrogen gas mixture whose composition is conducive to uniformly faceted (100) diamond growth. Scanning electron micrographs showed that a large fraction of the (100) faces of the diamond crystallites are aligned with the (100) plane of the underlying silicon lattice with the crystallite edges parallel to the (110) direction. Raman scattering was used to confirm this finding by measuring the angular dependence of the Raman backscattering intensity at 1332 cm" 1 using plane polarized excitation of individual crystallites within the diamond films.

The reaction of nitrogen with liquid lithium containing dissolved barium which follows a solutionprecipitation mechanism has been studied. Initially, nitrogen dissolves in the liquid metal to form an homogeneous solution; t h e reaction is first order with respect to nitrogen with an activation energy of 33.6 k J mol-l. Subsequently, it reacts to form a precipitate of Li,N; the Li,N crystallisation face is dependent on the barium content of the solution, nitrogen solubility rising with increasing barium content. The ternary nitride, LiBaN, is only formed on cooling the solution; there is no evidence for Ba,N or Ba,N, formation. This behaviour contrasts with that in the corresponding Na-M-N (M = Sr or Ba) systems where the solubility is directly proportional to the alkaline-earth metal content of the solution and the precipitating phase is the alkaline-earth metal subnitride, M,N ( M = Sr or Ba). Analysis of the crystallisation fields of Li, Li,Ba, LiBaN and Li,N indicated they are separated by monovariant curves which fall from the binary eutectics (Li-Ba, x,, = 0.1 05 and 416 K; Li-N, degenerate at 453.5 K, Li,N-LiBaN, unknown) through a quasi-peritectic equilibrium involving liquid, lithium, Li,Ba and LiBaN (372 K) to a ternary eutectic point based on liquid, lithium, Li,N and LiBaN (368 K).

The deposition of gold bearing tracks, by the argon ion laser photolysis at 257 nm of RAuI-PR3, R,R = C2H5, CH3, is reported, Deposits were obtained on optically polished fused quartz and (100) n-type single crystal silicon with a thermally grown oxide layer (3000 A). Tracks were deposited at a range of scan speeds from 0 to 200 pm s-l and characterized by scanning electron microscopy (SEM), laser ionization mass analysis (LIMA), and scanning profilometry.Electrical resistivities as low as 4.51 pQ cm, within a factor of 3 of the value for bulk gold (2.44 p& cm), were measured for tracks deposited a t 40 mW and a scanning speed of 7.5 pm s-l. However, the electrical conductivity of the deposits is highly sensitive to the structure of the organogold precursor. Mass spectral data obtained by LIMA indicate that the incorporation of the precursor and/or various photolysis byproducts into the deposit is related to the volatility of the ligand. Contamination is observed in tracks deposited from compounds containing the heavier ligand. Also, the electrical resistivities are correspondingly higher. Although isothermal annealing above 100 "C removes fragments containing the ligand, the resulting electrical conductivities are not improved.

Diamond films were selectively nucleated and grown on single crystal (100) silicon by microwave plasma assisted chemical vapor deposition with submicron spatial resolution. A thermal silicon dioxide layer on the wafers was patterned by standard photolithography. Nucleation was performed by applying a dc bias of 2250 to 2350 V in a hydrogen-methane plasma. Lifting off the oxide layer by HF etching prior to growth delineated the nucleation pattern which was replicated by the diamond film after growth. The growth of polycrystalline diamond was performed in a hydrogen-carbon monoxide-methane mixture selected to facilitate (100) texturing. Individual faceted crystallites were grown on a square matrix of sites, with a pitch of 3 mm, by controlling the nucleation densities within the windows exposing the prenucleated silicon. However, the orientation of the crystallites was randomly aligned with respect to the (100) silicon lattice within the micron scale windows employed in this study.3128