Gary L. Doll

Corrosion resistant PEM fuel cell

The present invention contemplates a PEM fuel cell having electrical contact elements (including bipolar plates/septums) comprising a titanium nitride coated light weight metal (e.g., Al or Ti) core, having a passivating, protective metal layer intermediate the core and the titanium nitride. The protective layer forms a barrier to further oxidation/corrosion when exposed to the fuel cells operating environment. Stainless steels rich in CR, Ni, and Mo are particularly effective protective interlayers.

Observation of a negative electron affinity for boron nitride

This study reports UV‐photoemission (UPS) measurements made on boron nitride crystals and thin films. The materials examined are commercial grade c‐BN powder and thin films of BN deposited with ion beam assisted e‐beam evaporation and laser ablation. The thin film samples examined exhibited varying amounts of sp3 (cubic) and sp2 (hexagonal, amorphous) bonding as determined by FTIR measurements. The UPS measurements displayed the spectral distribution of the low energy photoemitted electrons and the total energy width of the spectra. These characteristics can be related to the electron affinity. The measurements on several of the BN powder and thin film samples revealed features in the emission spectra which are indicative of a negative electron affinity (NEA) surface.

Physical properties of vapor-grown carbon fibers

Abstract Vapor-grown carbon fibers (VGCF) are produced by depositing a layer of pyrocarbon from the vapor phase on a catalytically grown carbon filament. This morphology determines many properties of the fiber, since the filament is more graphitic than the pyrocarbon. In this paper we compare VGCF produced by a continuous process with those grown on a substrate. Fibers having thicker pyrocarbon layers are less graphitic as measured by X-ray diffractometry, electron diffraction and Raman spectroscopy. The bulk density of the fibers, near 2.03 g/cm3, is relatively high for carbon fibers; it decreases slightly as the pyrocarbon thickness increases. The surface area of the fibers determined by N2 adsorption is not larger than the calculated geometric area, indicating that the surface is relatively smooth and free of pores. Each of these measurements indicates that fibers produced by a continuous process are comparable to those grown on substrates, with respect to graphitization and surface properties.

Ion-assisted pulsed laser deposition of cubic BN films on Si (001) substrates

We report on oriented and adherent cubic BN films grown on (001) faces of silicon using the method of ion-assisted pulsed laser deposition. The structure of the films is cubic zinc-blende with a lattice constant of 3.62 A, as determined by infrared absorption and transmission electron microscopy. The films were found to be polycrystalline, and oriented with the cubic BN [110] axis parallel to the Si [001] direction.

Structural characterization of preferentially oriented cubic BN films grown on Si (001) substrates

Abstract Thin cubic boron nitride films have been deposited on (001) faces of silicon substrates using ion-assisted pulsed laser deposition. Infrared transmittance spectra of the films showed strong absorption at 1080 cm -1 , indicating sp 3 bonding of cubic symmetry of the deposited film. Cross-sectional and plan-view transmission electron microscopy showed the structure of the films to be cubic zinc-blende with a lattice constant of 0.362 nm. The films were found to be adherent and preferentially oriented with the cubic BN [110] axis parallel to the Si [001] direction.

Optical and electronic properties of nitrogen-implanted diamond-like carbon films

Optical and electrical measurements on nitrogen ion-implanted diamond-like carbon films are presented. Raman scattering measurements, which probe the crystallinity of the film surface, indicate that nitrogen implantation reduces the finite crystallographic order in the pristine carbon films. The absence of molecular vibrations in the infrared absorption spectra of the films argues against a polymeric structure of the ion-implanted films. Spectroscopic ellipsometry experiments determine the change in the optical constants of the carbon film due to nitrogen implantation. Electrical de conductivity measurements are interpreted within the framework of a schematic density of states picture of graphitic τ-electrons in an amorphous carbon system. Taken collectively, the optical and electrical measurements suggest that nitrogen implantation increases the density of localized states within the 1.5 eV bandgap of the quasi-amorphous carbon film, thereby reducing the bandgap and increasing the conductivity of the nitrogen-implanted films.

Electronic and atomic structure of metastable phases of boron nitride using core-level photoabsorption

Soft x‐ray core‐level photoabsorption has been measured from three forms of boron nitride, namely the hexagonal (hBN), cubic (cBN), and incoherent (iBN) phases. The B 1s and N 1s photoabsorption spectra of the hBN sample show evidence of both σ*‐ and π*‐empty states, indicative of sp2 bonding, while the cBN absorption spectra exhibits only sp3 bonding in absorption features characteristic of the zincblende structure. The incoherent phase of BN in the form of a thin film on a Si substrate possesses σ* and π* states similar to hBN. The B 1s π* absorption features of the iBN film show an angular dependence which suggests that the microstructure consists of hexagonal‐phase layer planes oriented normal to the BN/Si interface.

A gas phase chemical etchant for boron nitride films

We have demonstrated that boron nitride films deposited on silicon and tantalum can be etched in a hot filament environment with an input gas composition of 1% methane in hydrogen. Etching experiments were carried out at around 800 K on a tantalum foil and at somewhat higher temperatures on silicon substrates. If the etchant is atomic hydrogen or methyl radical, then we estimate etching efficiencies (atoms etched per collision) of ∼10−5 or 10−4 for these species, respectively.

Ellipsometric study of boron nitride thin-film growth on Si(100)

Variable angle spectroscopic ellipsometry over the photon energy (E) range 1.5≤E≤5.5 eV has been used to study the structure and optical properties of thin (<400 A) laser‐deposited boron nitride films grown on Si(100). The data are interpreted to indicate that initially the film grows next to the substrate in the cubic phase, followed by a reasonably sharp transition after 50–100 A of film growth to an amorphous phase.

New developments in the growth of epitaxial cubic boron nitride and diamond films on silicon

Abstract We report on the first successful growth of oriented crystalline diamond on the (001) surface of cBN/Si substrates using the method of pulsed laser deposition. X-ray diffraction measurements indicate that the diamond layer is 200A˚thick with a lattice constant of 3.56A˚. In addition, new X-ray diffraction measurements performed on boron nitride films deposited by pulsed excimer laser deposition are presented. The X-ray data, taken with both a molybdenum rotating anode source and synchrotron radiation, indicate that the epitaxial cBN films are≤200 A˚thick. The structures of metastable films (cBN and diamond) are very sensitive to growth conditions: we present evidence that an epitaxial-crystalline to incoherent phase transition occurs when the thickness of the films exceeds a critical value (∼ 200 A˚for our present growth conditions).