The promise of new applications continues to drive research on ceramic precursor and sol-gel routes to materials preparation. These routes offer flexibility in the fabrication of materials in forms such as films, coatings, fibers, foams, and powders, etc. Our interest in ceramic precursors stems from their potential in the low cost fabrication of films. Such films can be employed in a variety of new automotive applications. In this article, we summarize our efforts to prepare soluble ceramic precursors and their conversion to group IV metal nitrides. A comparison of some properties of electrically conducting titanium nitride films prepared by dipcoat-fire cycle and low pressure CVD is presented. We also describe the fabrication of indium tin oxide films by a sol-gel process. These films are candidates in the low cost fabrication of electrically heatable catalyst devices.

Nanocrystalline diamond thin films have been produced by microwave plasma-enhanced chemical vapor deposition (MPECVD) using C60/Ar/H2 or CH4/Ar/H2 plasmas. Films grown with H2 concentration ≤ 20% are nanocrystalline, with atomically abrupt grain boundaries and without observable graphitic or amorphous carbon phases. The growth and morphology of these films are controlled via a high nucleation rate resulting from low hydrogen concentration in the plasma. Initial growth is in the form of diamond, which is the thermodynamic equilibrium phase for grains < 5 nm in diameter. Once formed, the diamond phase persists for grains up to at least 15–20 nm in diameter. The renucleation rate in the near-absence of atomic hydrogen is very high (∼1010 cm2sec−1), limiting the average grain size to a nearly constant value as the film thickness increases, although the average grain size increases as hydrogen is added to the plasma. For hydrogen concentrations less than ∼20%, the growth species is believed to be the carbon dimer, C2, rather than the CH3* growth species associated with diamond film growth at higher hydrogen concentrations. For very thin films grown from the C60 precursor, the threshold field (2 to ∼60 volts/micron) for cold cathode electron emission depends on the electrical conductivity and on the surface topography, which in turn depends on the hydrogen concentration in the plasma. A model of electron emission, based on quantum well effects at the grain boundaries is presented. This model predicts promotion of the electrons at the grain boundary to the conduction band of diamond for a grain boundary width ∼3–4 Å, a value within the range observed by TEM.

Thin film phosphors for field emission displays show the potential to overcome the life-limiting problems that traditional powders face because of their high surface areas. By depositing a fully dense thin film, the surface area can be dramatically reduced, while the electrical and thermal conductivity is increased. Metal organic chemical vapor deposition offers the ability to deposit high quality, dense films that are crystalline-as-deposited and at temperatures low enough to allow for inexpensive glass. Deposition has been produced from mixtures of Y(tmhd)3, TEOS, Tb(tmhd)3, and O2 using a liquid delivery system. Coatings were shown to be composed of Y, Si, and Tb by x-ray fluorescence, but x-ray diffraction did not show any crystallinity. Excitation using radioluminescence produced a peak in the visible green at approximately 540 nm, indicative of the excitation of Tb3+. The morphology of the deposition was smooth, with surface features on the order of one micron and below. Some limited microcracking was also observed in the morphology because of the thermal expansion mismatch.

High-density TiN (>098% of theoretical) has been prepared by hot pressing TiN powder with 2–4 wt.% Li2CO3 at temperatures between 1150–1550°C and pressures of ≈40–50 MPa. The Li2CO3 served as a fugitive sintering aid, enabling attainment of high density at low temperatures without adversely affecting the inherently good properties. Variation in processing variables and TiN powder characteristics resulted in material with various porosities. Measurement of mechanical properties such as flexural strength and fracture toughness showed that the high-density material has mechanical properties that are superior to those of several oxide ceramics. We have also quantified the effects of porosity on mechanical properties. In addition, adhesion and chemical stability tests were used to investigate graphite coated with TiN by chemical vapor deposition (CVD). Pin-pull tests were used to determine coating adhesion and failure stresses were analyzed by Weibull statistics. All pin-pull tests resulted in fracture of the graphite substrate, rather than separation at the TiN/graphite interface. The data showed a good fit to the two-parameter Weibull expression, with a failure strength of 16.4 MPa and Weibull modulus of 9.3. Both the high-density TiN and the TiN coating on the graphite were exposed to a corrosive molten salt CaCl2-7 wt.% CaO and a liquid metal alloy (Zn-10 wt.% Mg) at 800°C for 168 h to determine chemical interactions. No reaction was detected by scanning electron microscopy (SEM) or energy-dispersive X-ray (EDX) analysis. Thus, graphite coated with TiN by CVD combines the thermodynamic stability of TiN when exposed to reactive molten metals and salts, with the excellent machinability of graphite, and hence is promising for use in container vessels for pyrochemical processing of certain rare-earth and nuclear metals, where chemical inertness and good matching of thermal expansion coefficients are required.

Sol-gel derived YMnO3 films have been prepared on platinized Si wafers. Crystallization took place at firing temperatures above about 750C. The crystallized films were very conductive. YMnO3 films exhibited a dielectric constant of 23, a remanent polarization of 1.0 μC/cm2 and a coercive field of 12 kV/cm, all measured at -33C The FE loop was lossy and elliptical at room temperature but became more distinct at lower measuring temperatures or at higher measuring frequencies.

Thin epitaxial films of (La1-x,Prx)0.7Ca0.3MnO3 (x=0,0.25,0.5,0.75,l) were grown on LaA1O3, SrTiO3 and ZrO2(Y2O3) by aerosol MOCVD at 750°C Variation of x greatly influences the electrical properties of material by changing of the tolerance factor t. The tensile strain in the films on perovskite substrates produces the effect on the maximum resistivity temperature Tp comparable with the effect of chemical pressure nearby critical value of t ∼ 0.91. By variation of x the colossal magnetoresistance in very low magnetic fields was achieved in the thin films: an applied field of 0.3 T was enough for 32 times decrease of the resistivity of (La0.35,Pr0.35)Ca0.3MnO3 film on LaA1O3 at 155 K. The charge ordering starting in (La1-x,Prx)0.7Ca0.3MnO3 at 160–210 K leads to the switching from Arrhenius law (lggρ ∼ T1 ) to Mott law (lgρ ∼ T1/4) of resistivity. Large-angle boundaries dominating the structure of the films on ZrO2(Y2O3) increase the resistivity both above and below Tp.

As-deposited and derivatized WO3-X films of various stoichiometry were examined in a “nonlinear interface” configuration. The optical properties of the films at 632 nm were modulated using 850 nm and 488 nm CW lasers either separately or simultaneously, Some films were modified by electrochemical reduction. Purely photoinduced changes were interpreted in the context of photoinduced chemistry involving water and/or oxygen exchange with the ambient atmosphere. Both reversible and irreversible changes were observed. Applications as either all-optical switches or logic devices are discussed.

In making multi-level interconnects, a via layer is generally made of a dielectric layer grown on a TiN/AlSiCu/TiN metal stack. The via contact hole to the lower level metal is first etched after metal patterning and intermetal oxide deposition, then the resist mask for via etch is stripped in an oxygen plasma at high temperature before filling the via with tungsten or aluminum. However, during the resist stripping process, the titanium nitride (TiN) is exposed to oxygen radicals and becomes oxidized. This oxidized surface leads to high via resistance and may cause yield loss and poor adhesion of the subsequently deposited metal. Thus, the oxide layer must be removed completely before filling the via hole.

Utilizing a modern asher and combining microwave downstream plasma and low damage RIE we have successfully developed an integral process to strip the resist and to remove any oxidized TiN film. This process also gives clean vias that are free of polymer residues from the etching process.

Samples were characterized using Auger electron spectroscopy (AES), scanning electron microscopy (SEM), ellipsometry and via resistance measurements. The AES depth profile measurements and ellipsometry show clearly that a titanium oxide has grown onto TiN during the oxygen downstream ashing and is completely removed when adding the RIE step. The electrical measurements show that the resistance of vias cleaned with this two step process in a single tool is comparable to that of vias cleaned with Ar sputtering using a separate tool after the oxygen ashing process.

ZnO has high piezoelectric coupling coefficient and acoustic velocity; therefore, it is an attractive material candidate for high frequency and low loss filters. Piezoelectric ZnO thin film based RF devices offer the advantages such as low power consumption, circuit miniaturization and cost reduction through integration with main stream MMIC technology. We report CVD growth of epitaxial ZnO thin films on R-sapphire substrates. X-ray diffraction techniques have been used to study the crystallinity and orientation of the films, as well as the epitaxial relationship between the films and the substrate. High-resolution cross-sectional TEM reveals the atomically sharp interface structure. As grown ZnO films exhibit dominant n-type conductivity due to the oxygen vacancies. Excellent piezoelectricity has been achieved through a multi-step Li diffusion under oxygen ambient. Surface Acoustic Wave (SAW) filters with 10-micron wavelength have been fabricated. Low insertion loss and high piezoelectric coupling coefficient have been observed.

Boron nitride thin films on sapphire substrates were investigated for their tribological and optoelectronic applications. A gridless end Hall gun source and an electron cyclotron resonance (ECR) source were used for nitrogen species delivery while pure boron was evaporated at a rate of 0.2 Å/s. The surface stability of these thin films was investigated by high temperature annealing. Atomic force microscopy (AFM), friction force microscopy (FFM), and Knoop microhardness measurements were performed on the materials in order to assess their merits as tribological coatings. Finally, BN thin films were subjected to laser transient photoconductivity (TPC) experiments to determine both their optical laser damage threshold as well as their photoconductivity characteristics. For both single-pulse shot and multiple-pulse irradiation regimes, preliminary tests showed the higher the ion beam current used during growth (70–150 mA), the higher the optical damage threshold. The lower damage threshold was typical of BN films grown using an ECR plasma source and was measured to be in the range of ∼50 MW/cm2. Optical damage of films grown at ion beam currents above 100 mA was not observed at laser intensities up to few hundreds MW/cm2. A multiphoton excitation technique was utilized to obtain PC signals from this wide band gap material and preliminary results show that unusual PC voltage amplitudes as high as 0.5 V were observed.

Reasonably sized crystals of aluminum and gallium nitrides can be grown in supercritical ammonia using chloride and amide as the mineralizer. Best growth was achieved at 380°C in ammonia at 40,000 psi (270 MPa). Under these conditions crystals as large as 0.4 mm could be grown over several days. Attempts to optimize the identity and concentration of the mineralizer, and the acidity of the solution, led to several new products including A1F3(NH3)2.

Careless claims by scientists are often expanded further by journalists and grossly distort the scientific “truths” passed on to the public and policy maker. Recently, such overclaims have invaded the field of materials synthesis.

The real first principles of materials synthesis, based on the work of V.M. Goldschmidt (and Linus Pauling), have proved to be, and continue to be, very successful. By combining such principles with Edison's methodology of careful observation, precise experimentation and rapid feedback, thousands of new (inorganic) phases have been, and continue to be made (since 1948, several hundred from our own laboratory), producing dozens of useful, widely commercialized materials.

In contrast, in spite of seventy years of trying, the so-called “first principles” calculations (from the quantum mechanics of cores and electrons) have utterly failed to actually predict and synthesize a single new material or add anything to the deep and reliable insights of well known chemical theories. It is clear that what students and researchers in contemporary materials synthesis need most is a thorough grounding in crystal chemistry and phase equilibria (including metastable equilibria).

The history of the “C3N4” failure, as a harder than diamond candidate, is prototypical of the”calculating” approach to synthesis. It is contrasted with short summaries on four recent real advances into completely new processes for diamond synthesis.

We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectrocopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.

YBa2Cu3O7-x superconducting thin films have been prepared by a new material preparation method, namely pulsed thermal decomposition of ultrasonic-misted nitrate solution. The prepared films have been studied by using powder X-ray diffraction method, scanning electron microscopy and Rutherford backscattering spectrometry. The results obtained indicate (1) that by local heating of the substrate with an infrared lamp, c-axis oriented YBa2Cu3O7-x films can be deposited without segregation of impurity phases, (2) that a high decomposition temperature is necessary to increase flatness of thin YBa2Cu3O7-x films although a sufficient margin temperature is required to obtain impurity-phase-free films, and (3) that the efficiency of the process increases if the adhesion is large between the deposited film and the substrate.

A new methodology was developed to stabilized zirconia films at room temperature. The zirconium oxide films were prepared electrochemically by anodic oxidation of metallic zirconium at constant curcent density. X-ray diffraction (XRD) revealed the partial stabilization of the cubic phase in the ZrO2 films obtained in the presence of calcium. On the other hand, the films obtained in H3PO4 presented monoclinic phase. Scanning electron microscopy (SEM) showed that the oxide films obtained in calcium medium were porous, while the films obtained in H3PO4 were compact. X-ray photoelectron spectroscopy (XPS) identified ZrO2 and the intercalation of Na, N, P and CaO, as well as adventitious carbon. Using depth profiling, we observed that the concentrations of ZrO2, P and CaO increased with sputtering time.

A transparent SiO2 thin film was grown with Xe2* excimer lamp and NF3, O2 mixed gases at room temperature. Unlike the conventional methods such as atomic layer epitaxy (ALE) at low temperature, this method requires only a few minutes for deposition without changing material gases. A Si substrate was placed in a reaction chamber, which was filled with NF3 and O2 gases. The gases were exposed to the Xe2* excimer lamp light, and SiF4 and NO2 were produced by photochemical reaction. The SiF4 was adsorbed on the substrate; which reacted with NO2 in gas ambient and was oxidized to form SiO2. The molecular layer was produced per reaction, and by voluntarily repeated reaction, the transparent SiO2 thin film was grown. As a result, the SiO2 film thickness of about 2200 Å was achieved for 15 minutes at room temperature. By annealing the formed SiO2 film, the surface current density of the formed SiO2 decreased; the higher the annealing temperature became, the more the surface density decreased.

A single-crystalline 3C-SiC is very difficult to etch compared with a polycrystalline SiC. Thus, a photochemical pattern etching of the SiC was demonstrated by using Xe2* excimer lamp and ArF or KrF excimer laser. To promote the surface reaction, a Xe2* excimer lamp was employed to produce many radicals on the sample surface; simultaneously, ArF or KrF laser light irradiated the surface via a circuit pattern to dissociate the Si-C bonds. The Si and C reacted with the F and N radicals photo-dissociated from NF3 gas to form SiF4, CFn and CN, which diffused in the reaction cell. As a result, the single-crystalline 3C-SiC was photo-chemically etched effectively. With the NF3 gas of 200Torr, the Xe2* excimer lamp of 7mW/cm2, and the KrF excimer laser of 650mJ/cm2, 20Hz and 10,000shots, the etch depth of 700 Å was successfully achieved.

We have measured the dependence of the strength of Raman activity of polycrystalline m-WO3 on spot size at constant laser power density. These data are compared to surface area scaling measurements obtained using scanning tunneling microscopy. We argue that the spatial distribution of scattering centers is the complement of the spatial distribution of crystallographic shear (CS) structures on or near the oxide surface. Our results are consistent with there being an essentially uniform spatial distribution of scattering sites which implies the spatial distribution of defect sites is also uniform. At the laser power density involved and at the defect densities studied, we found no evidence suggesting a large amount of cooperativity in the formation of CS structures. These results suggest a qualitative description of the structure of common oxide surfaces in agreement with a basic assumption of the JMAK theory of first order phase transformations.

Increased rate of material removal and a high degree of surface finish during the polishing of diamond is desirable not only in the technology of gem diamond processing, but also for the tribological, optical, electronic and thermal management applications of chemical vapor deposited (CVD) diamond films. Conventional mechanical abrasion techniques, though with comparatively larger material removal rates, have limitations to the surface finish attainable due to the inherent nature of the material removal process - predominantly micro-chipping. Chemical etching of diamond, on the other hand is understood to involve atom by atom material removal preferentially from defect sites, but with lower overall material removal rates. It has been realized that a combination of these two processes, leading to chemi-mechanical polishing, may therefore provide better overall results, in terms of material removal and surface finish.

In recent work on chemi-mechanical polishing of diamond, KNO3 - an oxidizing agent shown to be a dislocation etchant for diamond by Tolansky and Patel in the 1950s - has been employed. Dislocation etchants usually lead to the formation of block patterns on diamond surfaces under the usual etching conditions because of the normal and tangential etch rates (Vn and Vt) of comparable magnitude. KNO3 therefore would impose a limitation on the degree of surface finish attainable when used for chemi-mechanical polishing. However, if a chemical etchant and conditions for which Vn ≪ Vt could be established for diamond surfaces, better chemical polishing effects may be achieved. Experimental investigations in this direction have provided encouraging results and some aspects of the new results are presented.

The electrodeposition of nickel/silicon carbide (Ni/SiC) composite films formed from modified Watt's bath solutions under potentiostatic conditions on steel substrates was investigated. The effects of deposition potential, pH, variable concentration of SiC in suspension, and additives, such as coumarin and EDTA, on the nickel nucleation and growth transients, as well as on the composition and morphology of Ni/SiC films are described. Improved Vickers microhardness and corrosion resistance of these composite films were found in comparison to those of particle-free deposits.