This extended Poole-Frenkel model includes the effects of compensation. The relative densities of donor and acceptor sites control the slope of the log J vs E1/2 plots. With only one type of site present, the slope equals that expected for Schottky emission [slope= (e3/πεε0)1/2/2kT]. When sites of the opposite type compensate, the slope doubles. The degree of compensation must be known to determine the barrier heights separating the emission site from the band edge. Data from metal-silicon nitride-metal devices are consistent with this model with emission occurring from impurity sites approximately 2.0 eV from the conduction band edge.

Given a wavelet w and a noisy trace t + s * w + n, an approximation ŝ of the spike train s can be obtained using the [Formula: see text] norm. This extraction has the advantage of preserving isolated spikes in s. On some types of data the spike train ŝ can represent s as a sparse series of spikes, which may be sampled at a rate higher than the sample rate of the data trace t. The extracted spike train ŝ may be qualitatively much different than those commonly extracted using the [Formula: see text] norm. The [Formula: see text] norm can also be used to extract a wavelet ŵ from a trace t when a spike train s is known. This wavelet extraction can be constrained to give a smooth wavelet which integrates to zero and goes to zero at the ends. Given a trace t and an initial approximation for either s or w, it is possible to alternately extract spike trains and wavelets to improve the representation of trace t. Although special algorithms have been developed to solve [Formula: see text] problems, all of the calculations can be performed using a general linear programming system. Proper weighting procedures allow these methods to be used on ungained data.

Pyrolytic carbon (PyC) is widely used in manufacturing commercial artificial heart valve disks (HVD). Although PyC is commonly used in HVD, it is not the best material for this application since its blood compatibility is not ideal for prolonged clinical use. As a result thrombosis often occurs and the patients are required to take anti-coagulation drugs on a regular basis in order to minimize the formation of thrombosis. However, anti-coagulation therapy gives rise to some detrimental side effects in patients. Therefore, it is extremely urgent that newer and more technically advanced materials with better surface and bulk properties are developed. In this paper, we report the mechanical properties of PyC-HVD, i.e. strength, wear resistance and coefficient of friction. The strength of the material was assessed using Brinell indentation tests. Furthermore, wear resistance and coefficient of friction values were obtained from pin-on-disk testing. The micro-structural properties of PyC were characterized using XRD, Raman spectroscopy and SEM analysis. Also in this paper we report the preparation of freestanding nanocrystalline diamond films (FSND) using the time-modulated chemical vapour deposition (TMCVD) process. Furthermore, the sol-gel technique was used to uniformly coat PyC-HVD with dense, nanocrystalline-titanium oxide (nc-TiO2) coatings. The as-grown nc-TiO2 coatings were characterized for microstructure using SEM and XRD analysis.

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Thin film silicon nitride deposited from the reaction of silane and ammonia exhibits reproducible current characteristics at high fields less than breakdown. Conduction behavior with thickness is similar for films from 60 to 1600A on quartz and silicon substrates. A large temperature dependence, a linear variation of In ! with V 1/2, and no electrode dependence indicate thermal emission from the bulk as the dominant injection mechanism at room temperature.Insulating films conduct a small current before destructive breakdown occurs. The characteristics of this current indicate the reproducibility of the films and help design devices with regard to leakage and breakdown. This paper reports results of a study of the conduction properties of silicon nitride films deposited from the reaction of silane and ammonia. Figure 1 shows the system used for depositing the films. Table I describes the deposition cycle. Film DepositionThe Matheson Company furnishes the semiconductor-grade silane and ammonia. The hydrogen is commercial grade. The quartz reaction chamber with vertical flow uses a resistive-heated graphite substrate holder. After flowing over the heated substrate, the excess gases are burned and vented via a hood. A chromel-alumel thermocouple measures the temperature of the top of the substrate.Substrates are metal-coated quartz and polished silicon. Metals used for the base contact are Mo, Ni, and Pt. The silicon is 0.01 ohm-cm p-type mechanically polished with a 10-sec etch in 48% HF just before placing in the reaction chamber. Vapor degreasing in trichloroethylene cleans the metals. An electron gun at a pressure of 10 -9 Torr evaporates the molybdenum. All other metals are evaporated from tungsten filaments at a pressure of 10 -6 Torr. After film deposition the top electrode of A1 or Au is evaporated through a metal mask at 10 -6 Tort.A break in the film growth-rate curve shown in Fig. 2 occurs at an ammonia to silane ratio of 7: 1. Bean (1) and others attribute this break to the film becoming silicon rich. Deposition temperature is approximately 700~ for all films. An x-ray diffractometer reveals no structure of the films which are transparent and apparently amorphous. Thickness DeterminationThe thickness determination used capacitance measurements and the color of the interference fringes. A value of 2.0 for the index of refraction (1, 2) in the color determination seemed appropriate. The dielectric constant was determined as 5.5 from a series of devices as shown in Fig. 3. The error in thickness from color determination averages out with the several thicknesses and devices used. This value of dielectric constant was used to determine thickness of the very thin films. The capacitance readings are stable to 5 significant figures on metal-nitride-metal devices with zero bias. Conduction PropertiesFigures 4 and 5 show the conducting properties for a series of MIM and MIS devices with thicknesses ranging from 1600 to 60A. Curve (a) is from a film on a molybdenum-coated quartz substrate. The rest are from films o...