Micro-Raman spectroscopy and x-ray diffraction measurements have been used to identify the presence of hexagonal diamond polytypes in chemical vapor deposited diamond films. The presence of additional reflections, in addition to the normal cubic diamond reflections in the diffraction spectra and bands at 1306 and 1193 cm−1 in the Raman spectra, are attributed to the presence of diamond 6H polytype. The presence of the 1324 cm−1 band in addition to the main diamond peak in the expanded spectra is attributed to regions with hexagonal symmetry, thus supporting the presence of hexagonal diamond polytypes. The compressive strain in diamond layers on the Si substrate is believed to create regions of hexagonal symmetry and vice versa.
Current–voltage (I–V) measurements are performed on a B-doped polycrystalline diamond film chemically vapor deposited on commercially available 170-μm-thick undoped and polished polycrystalline diamond. Four-probe resistivity measurements in the temperature range of 7–200 °C, potential profile measurements across a few grains in the current range of 10−6–10−4 A, and two-probe I–V measurements within a single grain and across an individual grain boundary show that: (i) current flow is nonuniform and is affected by current level, (ii) potential barriers exist at the grain boundaries, and (iii) the probe contacts are Ohmic when the probes are placed on rough microstructures. Based on the grain size distribution, a simple model that distinguishes between conduction paths made of large grains and small grains is used to interpret these results.
Analog MOS circuits are becoming increasingly sophisticated in terms of checking and correcting themselves. Self-correcting, self-compensating, or s e v calibrating techniques have been employed in Analog-todigital (A.D) converters to eliminate errors cuased by oflset and low frequency noise, and to cancel error effect and nonlinearities. For real-time applications, howcver, it is rather dificult to achieve validation of the converted data in the presence of faulty switching element(s). In this paper, fault effects and test generation of a current-mode MD converter are addressed. Results show that the converter achieves full testability with two test currents. In addition, an A/a converter with concurrent error detection capability is proposed. The converter detects all transient faults.
A novel experimental method has been developed and applied to measure the thermal conductivity of a thin (5.6 μm thick) boron-doped diamond film produced by a hot filament CVD process. Thermal fields were created by Joule heating in a 3-mm-diam, free-standing diamond diaphragm; infrared imaging thermography was used to quantify these fields. Parameter estimation was applied to determine the thermal conductivity of the film using more than 100 temperatures in each property determination. The experimental design chosen was selected on the basis of an analysis which maximized the sensitivity for the determination of thermal conductivity while minimizing the uncertainty in the estimation of this property. Parameters such as characteristic length, film resistivity, and thickness were chosen from the model to reduce convective effects, obtain the desired temperature rise, and minimize the uncertainty in the estimation of the thermal conductivity. Preliminary results for the thermal conductivity were obtained using the method of least squares to minimize the error between the measured temperatures recorded by the infrared temperature acquisition system and the calculated temperatures determined by the optimal radial heat flow model. A single doped film was energized at three power levels in five experiments. The thermal conductivity was determined to be 240±11 W/m K. The measured standard deviation of the mean matched the estimated uncertainty closely and the relative contributions to the experimental uncertainty have been quantified.
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