Hot filament chemical vapour deposition of diamond ultramicroelectrodes

The hot filament chemical vapour deposition of boron-doped diamond was optimised for the fabrication of diamond ultramicroelectrodes. Applications of ultramicroelectrodes require thin, conformal and non-porous diamond coatings, which display electrochemical properties similar to those associated with good quality doped diamond electrodes. The growth conditions to attain these goals are elucidated. The influence of the use of nanodiamond ultrasonic seeding prior to growth, in order to promote nucleation, and varying the negative electrical bias and methane concentration during growth, to control the growth chemistry, are explored. Although Raman spectroscopy shows a deterioration of diamond phase quality with increased negative bias voltage during growth, cyclic voltammetry indicates an improved electrochemical performance due to decreased porosity at reduced grain size under moderate bias voltage. At even higher bias voltage, the electrochemical properties deteriorate due to aggregation of sp(2) hybridised carbon at grain boundaries. By combining efficient nucleation methods and appropriate methane concentrations and electrical bias during growth, small grain polycrystalline diamond coatings can be obtained, which show optimal electrochemical properties most suitable for ultramicroelectrode applications.     

Phase composition of thin silicon carbonitride films obtained by plazma endanced chemical vapour deposition using organosilicon compounds

Journal of Structural Chemistry - High-temperature silicon carbonitride films are synthesized by plasma decomposition of gas mixtures of 1,1,1,3,3,3-hexamethyldisilazane (HMDS) (the synonym used by...     

Textured fluorine-doped tin dioxide films formed by chemical vapour deposition

The use of an aerosol delivery system enabled fluorine-doped tin dioxide films to be formed from monobutyltin trichloride methanolic solutions at 350-550 °C with enhanced functional properties compared with commercial standards. It was noted that small aerosol droplets (0.3 μm) gave films with better figures of merit than larger aerosol droplets (45 μm) or use of a similar precursor set using atmospheric pressure chemical vapour deposition (CVD) conditions. Control over the surface texturing and physical properties of the thin films were investigated by variation in the deposition temperature and dopant concentration. Optimum deposition conditions for low-emissivity coatings were found to be at a substrate temperature of about 450 °C with a dopant concentration of 1.6 atm% (30 mol% F:Sn in solution), which resulted in films with a low visible light haze value (1.74%), a high charge-carrier mobility (25 cm(2) V s(-1)) and a high charge-carrier density (5.7×10(20) cm(-3)) resulting in a high transmittance across the visible (≈80%), a high reflectance in the IR (80% at 2500 nm) and plasma-edge onset at 1400 nm. Optimum deposition conditions for coatings with applications as top electrodes in thin film photovoltaics were found to be a substrate temperature of about 500 °C with a dopant concentration of 2.2 atm% (30 mol% F:Sn in solution), which resulted in films with a low sheet resistance (3 Ω sq(-1)), high charge-carrier density (6.4×10(20) cm(-3)), a plasma edge onset of 1440 nm and the films also showed pyramidal surface texturing on the micrometer scale which corresponded to a high visible light haze value (8%) for light scattering and trapping within thin film photovoltaic devices.     

UV laser-induced photolysis of 1,3-disilacyclobutane in oxygen for chemical vapour deposition of nano-sized polyoxocarbosilane films

The multi-pulse ArF laser irradiation into gaseous 1,3-disilacyclobutane–O₂ mixture in excess of buffer gas occurs as non-explosive chemical vapour deposition of solid methylsilicone films, whereas the single-pulse irradiation into the gaseous mixture in the absence of buffer gas results in explosive chemical vapour deposition of solid nano-structured polyoxocarbosilanes poor in hydrogen.     

Titanium arsenide films from the atmospheric pressure chemical vapour deposition of tetrakisdimethylamidotitanium and tert-butylarsine

Thin films of titanium arsenide have been deposited from the atmospheric pressure chemical vapour deposition (APCVD) of [Ti(NMe(2))(4)] and (t)BuAsH(2) at substrate temperatures between 350-550 °C. Highly reflective, silver coloured films were obtained which showed borderline metallic-semiconductor resistivities. The titanium arsenide films were analyzed by scanning electron microscopy (SEM), Raman spectroscopy, wavelength dispersive analysis of X-rays (WDX), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The films showed variable titanium to arsenic ratios but at substrate temperatures of 500 and 550 °C films with a 1 : 1 ratio of Ti : As, consistent with the composition TiAs, were deposited. Powder XRD showed that all of the films were crystalline and consistent with the formation of TiAs. Both nitrogen and carbon contamination of the films were negligible.     

Perhydridosilicone films produced by IR laser‐induced chemical vapour deposition from disiloxane

Solid perhydridosilicone films have been produced by transversely excited atmospheric (TEA) and continuous‐wave CO₂ laser‐induced gas‐phase decompositions of H₃SiOSiH₃ controlled by elimination and polymerization of transient silanone H₂SiO and affording silane and hydrogen as side products. The decomposition mechanism is supported by evidence of scavenged intermediates and minor volatile products. The films are characterized by FT infrared and x‐ray photoelectron spectroscopy and by scanning electron microscopy and shown to undergo facile oxidation of the topmost layers in air and chemical changes upon argon ion sputtering. Copyright © 2000 John Wiley & Sons, Ltd.     

Adsorption and surface diffusion of silicon growth species in silicon carbide chemical vapour deposition processes studied by quantum-chemical computations

The effect chlorine addition to the gas mixture has on the surface chemistry in the chemical vapour deposition (CVD) process for silicon carbide (SiC) epitaxial layers is studied by quantum-chemical calculations of the adsorption and diffusion of SiH₂ and SiCl₂ on the (000-1) 4H–SiC surface. SiH₂ was found to bind more strongly to the surface than SiCl₂ by approximately 100 kJ mol^?1 and to have a 50 kJ mol^?1 lower energy barrier for diffusion on the fully hydrogen-terminated surface. On a bare SiC surface, without hydrogen termination, the SiCl₂ molecule has a somewhat lower energy barrier for diffusion. SiCl₂ is found to require a higher activation energy for desorption once chemisorbed, compared to the SiH₂ molecule. Gibbs free energy calculations also indicate that the SiC surface may not be fully hydrogen terminated at CVD conditions since missing neighbouring pair of surface hydrogens is found to be a likely type of defect on a hydrogen-terminated SiC surface.     

Aerosol assisted chemical vapour deposition of tungsten oxide films from polyoxotungstate precursors: active photocatalysts

Aerosol assisted chemical vapour deposition of polyoxotungstate precursors [n-Bu4N]2[W6O19] and [n-Bu4N]4H3[PW11O39] produces films of WO(3 - x) and WO3 on glass substrates; the WO3 films show significant photocatalytic decomposition of a test organic pollutant--stearic acid--when irradiated with either 254 or 365 nm radiation.     

Simultaneous growth of diamond and nanostructured graphite thin films by hot-filament chemical vapor deposition

Diamond and graphite films on silicon wafer were simultaneously synthesized at 850 °C without any additional catalyst. The synthesis was achieved in hot-filament chemical vapor deposition reactor by changing distance among filaments in traditional gas mixture. The inter-wire distance for diamond and graphite deposition was kept 5 and 15 mm, whereas kept constant from the substrate. The Raman spectroscopic analyses show that film deposited at 5 mm is good quality diamond and at 15 mm is nanostructured graphite and respective growths confirm by scanning auger electron microscopy. The scanning electron microscope results exhibit that black soot graphite is composed of needle-like nanostructures, whereas diamond with pyramidal featured structure. Transformation of diamond into graphite mainly attributes lacking in atomic hydrogen. The present study develops new trend in the field of carbon based coatings, where single substrate incorporate dual application can be utilized.     

IR laser‐induced decomposition of disiloxane for chemical vapour deposition of poly(hydridosiloxane) films

Continuous‐wave CO₂‐laser‐induced gas‐phase decomposition of H₃SiOSiH₃, dominated by elimination and polymerization of transient silanone H₂SiO and yielding silane and hydrogen as side‐products, represents a convenient process for chemical vapour deposition of poly(hydridosiloxane) films. Copyright © 1999 John Wiley & Sons, Ltd.     

Preparation of glutamine films on silicon substrates

Amino acids and polypeptides thin films, pure or attached to polymers, present large application as sensors and biosensors. The interactions between such films and the supports, their sensorial properties, as well as the development of techniques to produce thin regular films, are still challenges in the area. In this work, we present the preparation of L ‐glutamine thin films on silicon substrates, the factors that determine amino acid/silicon substrate interaction, and the morphology of the films. For this purpose, a 2⁴ factorial design is used, taking into account the effects of the solvent system, the glutamine concentration, the temperature, as well as the pretreatment of the substrate surface. The contact angles between a drop of glutamine solution and the silicon substrate were taken for the preliminary evaluation of the affinity between the amino acid and the substrate. The results have shown six promising experimental combinations with oxidized silicon as substrate to improve the solution/substrate interaction. Three of these promising conditions involved aqueous solution of L ‐glutamine and three alkalis solution. The obtained films were characterized by scanning electron microscopy (SEM), Rutherford backscattering (RBS), and Fourier transform infrared (FTIR) spectroscopy. The selected experimental conditions permitted to prepare a variety of films with L ‐glutamine, like small crystals, lamellas, needles, and smoothed regular films. The systems prepared in presence of alkalis solution yielded regular and smooth films. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of silicon nanowires on mesophase carbon microbead substrates by chemical vapor deposition

Silicon nanowires (SiNWs) have been fabricated by chemical vapor deposition at ambient pressure using SiCl(4) as a silicon source and mesophase carbon microbead powder as a substrate without any templates and/or metal catalysts. The SiNWs have a crystalline core with a very thin amorphous SiO(x) sheath. The obtained SiNWs are homogeneous with average diameters below 50 nm and lengths up to micrometers. Temperature and time effects on the growth of SiNWs were systematically studied. Higher reaction temperatures and longer reaction times resulted in larger diameters and higher yields of SiNWs. SiNWs with a better crystallinity can be obtained at higher temperatures and longer reaction times. The obtained SiNWs were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.     

Novel monomeric barium complexes as volatile precursors for chemical vapour deposition

A new range of barium complexes with single encapsulating ligands have been prepared for use in chemical vapour deposition (CVD). A novel pathway providing an unprecedented sequence of barium carbamates is reported. New dianionic bis β-ketoesterates and their barium, strontium and calcium derivatives were synthesised. High resolution mass spectrometry showed some barium derivatives to be monomeric, and preliminary testing indicated some volatility in these species. Calcium and strontium complexes were found to have nuclearities that varied according to their ionic radii relative to the chain length of the encapsulating ligand.     

Chemical vapour deposition on silicon: In situ surface studies

The decomposition of Fe(CO)₅ to produce Fe films on Si(100) has been examined in situ using Auger electron spectroscopy. Processes occurring during pyrolytic, UV photolytic and electron beam deposition are determined. The nature of the surface films produced by these different methods is compared and contrasted.     

Synthesis and characterisation of tungsten(VI) oxo-salicylate complexes for use in the chemical vapour deposition of self-cleaning films

Tungsten(VI) oxo-salicylate complexes were prepared in moderate yield (47 to 63%) by the reactions of WOCl4 and two equivalents of either 3-methylsalicylic acid (MesaliH2) or 3,5-di-isopropylsalicylic acid (di-i-PrsaliH2). Performing the reaction in refluxing toluene afforded the two analogous ditungsten complexes 1, [{WO(Mesali)(MesaliH)}2(mu-O)], and 2, [{WO(di-i-Prsali)(di-i-PrsaliH)}2(mu-O)], however in refluxing hexane the mononuclear tungsten complex , [WO(di-i-Prsali)(di-i-PrsaliH)Cl], was isolated. The single crystal X-ray study of revealed a pseudo-octahedral geometry around the tungsten centres. Aerosol assisted chemical vapour deposition of or afforded brown tungsten trioxide thin films. These films were converted to yellow fully oxidised WO3 on annealing in air at 550 degrees C for 30 minutes. The yellow WO3 films demonstrate preferred orientation on the substrate and show interesting functional properties-photo induced hydrophilicity and photocatalytic activity.     

Imaging SIMS for the investigation of substrate surfaces for CVD diamond deposition

The influence of substrate surface preparation on diamond nucleation is a major topic in the investigation of CVD-diamond deposition. The substrate, polishing material, its grain size, and the resulting surface roughness all influence diamond nucleation. Diamond can nucleate at scratches or residues of the polishing process which are providing nucleation sites. In this paper the surface of molybdenum and substrates polished with SiC and diamond powder was studied by imaging (2- and 3-dimensional) secondary ion mass spectrometry. The distribution and grain size of polishing residues (SiC, diamond) were determined and the reaction of diamond with the substrate during heating to deposition temperature was investigated. In this case a laterally inhomogeneous system of carbon containing species had to be characterized. Therefore compound-specific secondary ion mass spectrometry had to be performed. The results suggested that diamond residues on molybdenum substrates are partly dissolved during the heat treatment. The measurements indicate that a fraction of the diamond residues is still present after heat treatment and can provide nucleation sites for diamond deposition.