Amine-boranes such as pyridine- or piperazine-borane can be converted into infusible polymers by thermal crosslinking at temperatures up to 420°C. Further rise of the temperature up to 1050° C in argon results in transformation of the polymers into black residues. Microstructural (TEM/EELS, ESCA) and chemical investigations indicate the presence of single phase boron carbide nitrides which exhibit a graphite-like, turbostratic structure with a homogeneous distribution of the elements B, N, and C. Subsequent annealing at 2200° C in argon gives rise to crystallization of the pyrolytic material generating the thermodynamically stable phases BN, C, and B4C.

The semiconducting properties of the X-ray amorphous boron carbide nitride synthesized at 1050°C depend on the B/N/C-ratio which can be influenced a) by the type of amine-borane-precursor and b) by the applied atmosphere (Ar or NH3) during pyrolysis.

The amine-boranes can be converted into boron carbide nitride- and BN-monoliths at 1050°C under argon or reactive gas (NH3), respectively. The monoliths are transformed into composites with 91% rel. density containing BN, C, and B4C when heated up to 2200° C.

The aluminum imine complexes [RCH=NAlR'2]2 undergo thermal condensation polymerization to yield alazane [poly(alkylaminoalane)] polymers. The aluminum imine complexes are prepared in quantitative yield by reduction of nitriles, such as acetonitrile and benzonitrile, with alkylaluminum hydride reagents. These alazane polymers are thermoplastic, soluble in aprotic solvents, and display low moisture and oxygen sensitivity. The alazanes convert to aluminum nitride ceramics in non-oxidizing atmospheres above 500°C.

The emergence of aluminum nitride ceramics in electronic and structural applications has been largely due to the increased availability of high quality powders. Much of the process development has been concentrated in capturing markets within the electronics industry, mainly high thermal conductivity substrates. The thermal conductivity of A1N substrates is strongly dependent on oxygen chemistry and sintering parameters. A key source of oxygen is AlN powder impurities. In this study, powders with differing oxygen contents were formulated with various Y2O3 levels. The results indicate that the distribution of sintered oxygen is strongly correlated with the relative concentration of the powder's lattice and surface oxygen. Under the sintering parameters of the analysis, optimal thermal conductivities were achieved when Y4Al2O9 was present as the grain boundary phase. As predicted, the powders with the lowest lattice oxygen concentrations exhibited the highest thermal conductivities. Hence, depending upon the surface oxygen content, different yttria levels were required for optimal thermal conductivities, i.e., higher surface oxygen contents required higher sintering additive levels than did low surface oxygen powders.

An electrochemical method for the preparation of high purity metal nitride ceramic precursors is described. Constant current electrolysis of an electrolyte solution containing NH3 and NH4Br at an Al electrode yields a solid mixture consisting of Al(NH3)6Br3 and [Al(NH2)(NH)]n after evaporation of excess NH3. Calcination of this mixture above 800 C in flowing NH3 results in sublimation of Al(NH3)6Br3 and conversion of the ceramic polymer precursor, [Al(NH2)(NH)]n, to pure, high surface area AlN. Here we discuss some electrochemical aspects of the polymer precursor synthesis, precursor processing parameters, and materials characterization of the AlN powder before and after sintering.

The electrochemical preparation of polymeric precursors and the subsequent formation of non-oxide powders, ceramics and coatings is described. The metals were anodically dissolved in an electrolyte consisting of a primary organic amine, acetonitrile as a solvent, and a tetraalkylammonium salt. This procedure led to the formation of polymeric precursor solutions. Removal of the excess organic compounds resulted in the formation of polymeric amorphous solids. Pyrolysis was carried out at temperatures in the range of 750 to 1100°C. In an atmosphere of ammonia, metal nitrides were formed, while calcination under nitrogen or argon led to carbonitrides or to carbides, depending on temperature and the metal used. Up to now, this route has been applied to Al, Ti, Zr, Cr, Ta, Mg, Ca and Y, and it is suppossed, that this route is applicable to the formation of many metal carbides and nearly all metal nitrides relevant for materials science.

We repon on the syntheses, structural and thermoanalytical studies of two titanium complexes CpTiCl2N(SiMe3)2 and FTi[N(Sime3)2]3 and one vanadium complex V(NEt2)4. CpTiCl2N(SiMe3)2 has been used in a hot wall CVD reactor as a precursor to titanium nitride. Thin films of typically 1 XPS in thickness have been deposited at 600°C on glass, silicon and tool steel. XPS analyses of the deposits show titanium carbonitride to be formed. The new FTi[N(Sime3)2]3 complex can also be used as a precursor to titanium nitride. V(NEt2>4 led at 500°C to the deposition of vanadium carbonitride characterized by XPS analysis. Films tended to contain excess free carbon.

The reactions of TiCl4 with [(CH3)3Si]2NH have been examined under several reaction conditions. One of the reaction products, (CH3)3Si(H)NTiCl3, can be crystallized in 60% yield on reacting TiCl4 with TiCl4 with [(CH3)3Si]2NH in a 1:1 molar ratio in dichloromethane at -78°C. [(CH3)3Si(H)NTi(Cl2)(NH)]2TiCl2 is the primary product on increasing the amount of TiCl4 with [(CH3)3Si]2NH to two equivalents. (CH3)3Si(H)NTiCl3 and [(CH3)3Si(H)NTi(Cl2)(NH)]2TiCl2 form titanium nitride on pyrolysis at 600°C in an ammonia atmosphere.

Transition metal carbide precursors have been made in the past by the reaction of alkoxides with polymeric materials to form gels and resins. A new route to transition metal carbide precursors has been developed using alkoxides polymerized with dicarboxylic acids. (Dicarboxylic acid precursors have the advantage of precipitating as powders that can be removed from solvents by filtration and that are not very air sensitive.) Precursors were pyrolyzed under inert or reducing conditions to form metal carbides.

The choice of ligand(s) determined the carbon content after pyrolysis. Unsaturated ligands tended to increase carbon content. Materials from oils to fine powders were produced by varying the stereochemistry of the ligands. The morphology of the pyrolyzed product mimicked that of the precipitated powder. Pyrolysis was typically carried out under Ar/H2 at 1200–1600°C. X-ray diffraction (XRD) was used to follow the incorporation of carbon into the lattice.

Ti(NPri2)4 has been synthesized and used as a precursor for aminolysis andpolymerization by reaction with isopropylamine. The resultant dark red solution was utilized for dip coating of silicon substrates. Firing of these coatings in N2 or Ar produced dense and crack-free titanium carbonitride coatings.

The nitridation process of a polytitanocarbosilane, leading to the formation of a Si-Ti-N-O ceramics, has been investigated mainly by means of X-ray photoelectron spectroscopy (XPS). Ti2p spectra collected on samples fired at various stages of the transformation process clearly shown that Ti-N bonds of TiOxNy mixed units start to form at 500 °C. By increasing the firing temperature, the Ti2p peak shifts toward values typical of titanium nitride ceramics, so indicating the progressive nitrogen enrichment of the mixed units up to the formation of a TiN phase.

We have examined methods for controlling the morphology and microstructure of ceramic particles produced by spray pyrolysis. A variety of materials were examined including SrTiO3and BaTiO3 and the oxides of Al, Mg, Zn, Pd, V, Mo, and Bi. The morphology of the particles was influenced by using colloidal precursors in combination with molecular precursors for particle generation. Slow drying rates obtained by using high relative humidities and controlled axial temperature gradients did not influence particle morphology for the systems and conditions studied. The microstructure of Al2O3, V2O5, and PdO particles was controlled by varying the temperature to provide nanocrystalline or single-crystal particles. Evaporation and condensation of volatile species such as MoO3 and V2O5 dramatically modified particle microstructure and morphology.

Structural and thermal results concerning four barium tetramethylheptane-dionates, Ba(thd)2(H2)(CH3OH)3.CH3OH, amorphous Ba(thd)2, [Ba(thd)2]4, and Ba(thd)2(H2O)2(CH3OH)2, a methoxo bridged dimer of copper tetramethylheptane-dionate, [Cu(μ-OCH3)(thd)]2, and two yttrium tetramethylheptanedionates are presented and discussed.

Films of YBa2CU3O7-δ have been grown on 1” LaAlO3 by OMVPE utilizing M(tmhd)n (M = Ba, Cu: n = 2; M = Y: n = 3; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) as the source materials in a cold wall, vertical rotating disk reactor. The resultant films were characterized by SEM, XRD, Tc, Jc, and surface profilometry measurements. Relative to laser ablated thin films, the surface morphology was determined to be virtually featureless. In-situ depositions at substrate temperatures of <700°C, employing nitrous oxide as the oxidizing reagent, produced annular irregularities in the electronic properties of these films. The highest quality was observed near the film's center, with a marked decay evident toward the exterior 7 mm perimeter of the coated wafer.

Second generation barium MOCVD precursors have been investigated for the growth of high quality superconducting and ferroelectric thin films. Novel barium β-diketonate polyether adducts have been synthesized and characterized by X-ray crystallography, 1H and 13c nmr spectroscopies, elemental analysis, melting and sublimation points. Metalorganic chemical vapor deposition experiments have been performed using this new class of barium β-diketonate polyether adducts. The as-deposited barium films were characterized by scanning electron microscopy and energy dispersive x-ray spectroscopy. These results were correlated with reaction intermediates observed by FT-IR in temperature programmed oxidation of barium bis(2,2,6,6-tetramethyl-3,5-heptanedionate) on magnesium oxide. Conditions under which the barium source reagents proceed to BaO, BaCo3 or BaF2 were elucidated.

Two organosilicon molecules tetraethysilane (TESi) and tetravinylsilane (TVSi) were used to prepare thin films of silicon carbide by chemical vapor deposition (C. V. D.). In each of the molecule, the ratio C/Si = 8, the only difference between TESi and TVSi is the structure of the radicals ethyl (.CH2-CH3) and vinyl (.CH=CH2). This feature induces different thermal behavior and leads to the formation of different materials depending on the nature of the carrier gas He or H2· The decomposition gases are correlated with the material deposited which is investigated by I.R. and Raman spectroscopy. The structure of the starting molecule influences the mechanisms of decomposition and consequently the structure of the material obtained.

The stability of a liquid emanating from a nozzle is profoundly affected by an electric field. This electric-field induced instability is used here to form ceramic precursor powders having well-controlled particle-size distribution and morphology. Moreover, a hybrid boundary element/finite element method is used to determine the shapes and stability of a drop hanging from a nozzle. The efficiency of two different electrode configurations is considered: in one configuration, the nozzle is attached to the top plate of a parallel-plate capacitor and in the other, the nozzle is surrounded by a concentric cylindrical electrode. The computational results show that such pendant drops lose stability at turning points with respect to field strength. The experimental and computational results reported here are of importance not only in the development of electrodispersion apparatus, but in fields as diverse as capillarity and separations.

Gas phase synthesis of titania from titanium tetrachloride (Ticl4) oxidation in the presence of dopants (SiCl4 and POCl3) was systematically investigated in an aerosol reactor as a function of temperature (1300–1700 K) and dopant concentration (0–15 mole % of TiCl4). The particle morphology was dramatically altered in the presence of dopants from polyhedral to spherical. Energy dispersive analysis indicated that the powders were homogeneous and that the dopants were not segregated at the surface or at the grain boundaries. Lattice parameter measurements from X-ray diffraction indicated that the dopant oxide was present in solid solution in titania. While titania synthesized in the absence of dopants was ∼80% anatase, the introduction of Si4+ and P5+ resulted in greater than 98 % anatase. The effects of foreign ions on titania phase composition, aggregate size and gas phase coalescence are explained by the creation of oxygen vacancies and reduction/enhancement of the titania sintering rates.

Metal-Organic Chemical Vapor Deposition (MOCVD) is a versatile technique for the deposition of thin films of metals, semiconductors and ceramics. Commonly used hot wall flow-reactor designs suffer from a number of limitations. Chemical processes occurring in these reactors typically include a combination of homogeneous (gas-phase) and heterogeneous (gas-surface) reactions. These complex conditions are difficult to model and are poorly understood. In addition, flow reactors use large quantities of expensive precursor materials and are not well suited to the formation of abrupt interfaces. We report here a novel MOCVD technique which addresses these problems and enables a more thorough mechanistic understanding of the heterogeneous decomposition pathways of metal-organic compounds. This technique, the low-pressure pulsed gas method, has been demonstrated to provide high deposition rates with excellent control over film thickness. The deposition conditions effectively eliminate homogeneous processes allowing surface-mediated reactions to dominate. This decoupling of gas-phase chemistry from film deposition allows a better understanding of reaction mechanisms and provides better control over film growth. Both single metal oxides and binary oxide systems have been investigated on a variety of substrate materials. Effects of precursor chemistry, substrate surface, temperature and pressure on film composition and morphology will be discussed.