H.J. Doerr

The relationship between the spatially resolved field emission characteristics and the raman spectra of a nanocrystalline diamond cold cathode

Spatially resolved electron field emission measurements from a nanocrystalline diamond film grown by plasma‐enhanced chemical transport deposition have been obtained using a scanning probe apparatus with micrometer resolution. Macroscopic regions with a high emission site density, and turn‐on fields below 3 V/μm, comprised approximately 1/2 of the total sample area. The emitting and the nonemitting regions of the specimen are differentiated distinctly by Raman spectra and subtly by morphologies. Both areas are largely sp3‐bonded, but only the nonemitting regions exhibit a sharp line at 1332 cm−1, a well‐known signature of diamond in larger crystallites.

Structure and property relationships in microlaminate Ni-Cu and Fe-Cu condensates☆

Abstract Microlaminate metal matrix composites offer considerable potential as high strength high toughness materials with isotropic properties in the plane of the sheet. In this paper we deal with the preparation of Fe-Cu and Ni-Cu microlaminate composites by electron beam evaporation from two sources and alternating deposition onto a rotating substrate. The thickness of the laminae was varied by changing the evaporation rates of the metals and the speed of rotation of the substrate. The deposits were characterized by optical microscopy, scanning electron microscopy and electron microprobe analysis to study the thicknesses of the laminae and interdiffusion of elements between the layers. X-ray diffraction was used to study the composition of the laminates. The microhardness and tensile strength at room and high temperatures of the laminates were studied and correlated with the thicknesses of the laminae and the microstructure. The results showed very marked increases in strength and hardness as the size of the laminae decreased below about 2 μm. Superplastic behavior was observed at a certain thickness of the laminae, strain rate and temperature.

Preparation and properties of cubic boron nitride coatings

Cubic boron nitride (CBN) has attracted a great deal of interest in recent years for its unique mechanical and optical properties. Many physical as well as chemical vapor deposition processes have been explored to synthesize CBN coatings. These techniques, however, suffer limitations owing to the requirements of high substrate temperature and/or the necessity of using toxic starting materials. We have developed a new technique where CBN films can be prepared by evaporating boric acid in NH3 plasma. CBN films have been deposited at substrate temperatures as low as 450°C. Structure and optical and electrical characteristics of the films clearly demonstrate the simple cubic phase in the coatings. These results are presented in this paper.

Electron emission characterization of diamond thin films grown from a solid carbon source

Diamond films of various morphologies and compositions have been deposited on silicon substrates by a plasma-enhanced chemical transport (PECT) process from a solid carbon source. Electron emission efficiency of these diamond films is related to their morphology and composition. The electric field required to excite emission in a boron-doped polycrystalline diamond film ranged between 20 to 50 MV m−1. In an undoped conducting nanocrystalline diamond composite film, the field was as low as 5–11 MV m−1. The cold field electron emission of these films is confirmed from the Fowler-Nordhelm plots of the data. Enhancement of electron emission by band-bending and by the nanocrystalline microstructure are discussed. New diamond emitters made of nanocrystalline boron-doped diamond composite are proposed.

Structure-property relationships in microlaminate TiC/TiB2 condensates

Abstract This is the fourth of the series of papers on microlaminate materials prepared by evaporation techniques. The first two papers dealt with Cu/Ni, Cu/Fe, Ti/Ni and Cr/Cu microlaminate condensates, which are metal/metal systems, and the third dealt with the metal/ceramic system Ni/TiC. In this paper we present the results of our investigations on structure-property relationships in the ceramic/ceramic microlaminate composite TiC/TiB 2 . The composites were prepared at the Paton Electric Welding Institute and studied at the University of California, Los Angeles. The thickness of the composite sheet was 0.25–0.30 mm and the lamina thickness was varied in the range of 0.15–5μm. The microstructure and phases present were studied by microscopic and diffraction techniques whereas bend tests were used to study the mechanical properties.

Microstructure and hardness of Ti(C, N) coatings on steel prepared by the activated reactive evaporation technique

Abstract In view of the potential demand for wear-resistant coatings deposited at low substrate temperatures for applications in the cutting tool industry, titanium carbonitride films were prepared by the activated reactive evaporation technique on high speed steel substrates. Titanium was evaporated in C2H2N2 plasmas of various compositions ranging from pure C2H2 to pure N2, i.e. in C2H2 with 0, 30, 50, 70 and 100 vol.% N2. Knoop hardness values (at 50 gf load) were obtained both on top and in the cross section of each deposit and ranged from 2200 to about 5900, reflecting the variations in chemical composition and microstructure of the films. X-ray diffraction, transmission electron microscopy and scanning transmission electron microscopy analyses were performed to reveal those microstructural features of importance to the coating properties, i.e. phase composition, grain morphology and defect distribution (in particular, void and crack formations).

Diamond coatings from a solid carbon source

Abstract A plasma-enhanced chemical transport process was developed to deposit diamond films from a solid carbon source in a subatmospheric pressure hydrogen environment (106–400 mbar (80–300 Torr)). The process uses inexpensive simple equipment. The diamond films were examined by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. High quality diamond films were grown at 1 ωm h−1 deposition rate in static and dynamic flow systems. The effect of various surface coatings on diamond nucleation on a silicon substrate was investigated. The nucleation density on bare silicon was 4×106 cm−2. A high nucleation density up to 109 cm−2 was found on a fullerence-enriched carbon-coated silicon substrate. Diamond film morphology variations with deposition conditions were studied.

Deposition of tin-doped indium oxide films by a modified reactive magnetron sputtering process

Abstract It has been difficult to deposit high quality indium tin oxide (ITO) films onto large area polymeric substrates that cannot be heated (over 40–50 °C) during deposition or subjected to post-deposition annealing. We have developed a modified process based on reactive magnetron sputtering of a metallic indium tin alloy target to deposit good quality ITO films with deposition rates as high as 4A s-1 at a target-substrate distance of 10 in. Films with sheet resistance less than 10 Ω/□ and integrated visible transmission greater than 85% have been deposited using this process onto 12 in 12 × 12 in polymeric substrates at ambient temperature. A detailed description of the above process with an emphasis on obtaining control over the properties and reproducibility of good quality ITO films using this technique is presented in this paper.

Structure-property relationships in Cr/Cu and Ti/Ni microlaminate composites

Abstract Cr/Cu and Ti/Ni microlaminate composites were deposited as full density sheets from two electron beam evaporation sources. The deposits were characterized by X-ray diffraction, optical microscopy and scanning electron microscopy. Microhardness and tensile properties were measured at room and elevated temperatures as a function of lamina thickness. The strength increased markedly in the range of lamina thickness below 10 μm. The specimens showed brittle behavior at room temperature but exhibited some ductility in elevated temperature tests.

Effects of activated reactive evaporation process parameters on the microhardness of polycrystalline silicon carbide thin films

Polycrystalline s-SiC is expected to be an excellent material for thin film temperature sensors for the measurement of the surface temperature of gas turbine engine components operated at high temperatures (up to 1500°C). In this paper, Vickers and Knoop indentation microhardness tests were carried out on the silicon carbide films grown on Si(100) substrates by the activated reactive evaporation (ARE) process to measure one of the important mechanical properties, i.e. hardness of the films. The results of these tests are presented as a function of the ARE process parameters, such as C2H2 pressure PC2H2, substrate temperature Tsub, ARE electrode voltage VARE for the generation of d.c. glow discharge and substrate bias Vsub. It was found that the hardness of the films is very much dependent on these process parameters. A Vickers hardness value of 3680 kgf mm−2 (36.1 GPa) at 25 gf load (0.25 N) and a Knoop hardness value of 2060 kgf mm−2 (20.2 GPa) at 100 gf load (0.98 N) are obtained for polycrystalline s-SiC films (C-to-Si ratio, 1.17) prepared under the following deposition conditions: C2H2 pressure, 3 mTorr (0.4 Pa); substrate temperature, 700°C; ARE electrode voltage, +150 V; substrate bias, −50 V. Microhardness variation of the s-SiC films with applied load on the indenter was also studied. It was found that the hardness of the films decreases with increasing load, which is believed to be due to indentation size and substrate hardness effects.