Thaddeus A. Roppel

Selective and low temperature synthesis of polycrystalline diamond

Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.

An interdisciplinary laboratory sequence in electrical and computer engineering: curriculum design and assessment results

In the fall quarter of 1997, the Auburn University Electrical Engineering Department (USA) implemented a new, interdisciplinary core laboratory sequence. This new laboratory sequence was one outcome of a complete curriculum revision based on four years of work by the departmental Curriculum Study Committee. This paper presents the laboratory curriculum design, and the results of a multi-part assessment conducted beginning one year after implementation. Many students are initially surprised by the level of challenge provided in the first laboratory course, but readily accommodate as they progress through the sequence. A multifaceted assessment strategy has evolved which uses end-of-term student evaluations, retrospective student evaluations, student oral interviews, and faculty interviews. The assessment information is used to improve the laboratories through modification of the laboratory manuals, better instructions to graduate teaching assistants, modifications of experiments, and a purposeful effort to keep all faculty informed of laboratory course content so they can build upon the laboratory experience in classroom teaching. The overall result of the new laboratory experience is that students have a more integrated approach to design and a much better understanding of the hardware, software and instrumentation used in electrical engineering practice. In addition, students who complete the sequence have better oral and written communication skills, and are more confident in approaching job interviews and initial job challenges.

Rank extraction in tin-oxide sensor arrays

Abstract It is shown that data pre-processing by rank-order filtering can significantly improve the odor discrimination capability of an array of chemical sensors, while simultaneously reducing the amount of data to be processed. This work is a first example in feature extraction from tin-oxide sensors that both reduces the size of the data set and simultaneously improves the discrimination performance of the array. This work is aimed toward the design of remote sensor modules where bandwidth reduction and improved accuracy are both essential to system performance. The effectiveness of extracting rank from a 30-element array of tin-oxide sensors is presented. Results are extrapolated to other arrays of chemical sensors whose specificities and response characteristics overlap. Methods for processing data and extracting rank-related features from arrays of tin-oxide sensors are comparatively analyzed. Processing parameters studied include those related to temporal filtering and window-averaging, pre-scaling (to remove baseline), sample acquisition time, and the number of ranks used in rank-order filtering of the data during the transient and steady state response. Cluster analysis, including principal component analysis (PCA) and a novel method described herein, is used to determine which of these processing techniques are most effective. Artificial neural networks, specifically multi-layer perceptrons and radial basis function networks, are used to further investigate the ability to discriminate odors on the basis of the extracted features. The analysis is performed for an array of 30 tin-oxide sensors applied to detecting a sampling of breath alcohol mixtures (beer, wine, vodka) and common interferents (acetone, formaldehyde, isopropyl). Ammonia is included as a contrast substance. For the set of seven odorants studied, it is found that using rank-order filtering with 10 or more ranks improves odor recognition rate by a multi-layer perceptron neural network from 92% to 95%. If one odor (vodka) is removed from the study set, the recognition rate for the remaining odors improves from 95% (with no rank-order filtering) to 99%. Simultaneously, the dimensions of the data set for each odor are reduced from 30 sensors×18,000 time steps (12 bit samples) to N integer values, where N is the number of ranks used in the rank-order filtering.

Neural networks and simulation: Modeling for applications

Artificial neural networks simulate biologi cal processes in an intriguing manner. Ideas gleaned from the study of neurophysiology and animal behavior have become realizable in recent years. The advent of computers capable of rapidly executing massively parallel and distributed processes has allowed ideas from diverse fields to be merged and tested. The resulting neural networks, simulated in software and/or hardware, provide an adaptable, robust modeling tool useful to simulationists in all disciplines.

Fabrication of Microchannels in Synthetic Polycrystalline Diamond Thin Films for Heat Sinking Applications

2,817,048 12/1957 Thuermel et al. .................. 317/234 3,142,595 7/1964 Wentorf, Jr....... 148/171 3,628, 106 12/1971 Frank et al. ... ... 357/55 3,678,995 7/1972 Collard .......... 165/85 3,840,451 10/1974 Golyanov . ... 204/92 3,872,496 3/1975 Potter ... ... 357/8 3,922,775 12/1975 Potter............ ... 29/589 3,925,078 12/1975 Kroger et al. . ... 96/36.2 3,973,320 8/1976 Greco ............ ... 29/578 3,974,514 8/1976 Kressel et al. ... ... 357/17 4,069,463 1/1978 McGroddy et al. ............... 33/94.5

Characterization of polycrystalline diamond thin films grown on various substrates

Abstract Polycrystalline diamond thin films have been selectively grown on various substrates such as silicon, silicon nitride, silicon dioxide, alumina, molybdenum, and boron nitride. This has been achieved by selectively damaging the substrate by an ultrasonic agitation process using diamond particles (typical size approximately 90 μm) in methanol. Microwave plasma-assisted chemical vapor deposition is used to grow diamond thin films using a gas mixture of hydrogen and methane. The films were analyzed for morphology by scanning electron microscopy, chemical nature by Raman spectroscopy, and adhesion strength by z -axis pull stud testing. Films grown on boron nitride were characterized by X-ray diffraction.

Characterization of Synthetic Diamond Thin Films

High‐pressure, microwave plasma‐assisted chemical vapor deposition is employed to deposit diamond thin films, using a gas mixture of methane and hydrogen on single‐crystal silicon substrates. The deposition rate is approximately 1 micron/h. As‐deposited diamond thin films on a silicon substrate and free‐standing diamond thin films are analyzed by scanning electron microscopy, Raman spectroscopy, and x‐ray diffraction. Thermal stability of free‐standing diamond thin films is studied in oxygen and argon ambient, separately, using thermogravimetric analysis. It is found that these films maintain integrity in oxygen up to 676°C.

High‐temperature superconductor opening switch

A jitter‐free, repetitive opening switch made of YBa2Cu3O7−x high‐temperature superconductor is demonstrated. The switch conducts electrical current at no loss when it is superconducting. A pulse or pulse train of magnetic field on the order of 100 G causes the transition of the switch from the superconducting state to the resistive normal state and forces current to flow through a load resistor that is connected in parallel with the switch. Repetitive operation of this switch at rep rates higher than 1 kHz has been demonstrated.

Thin film diamond microstructures

Abstract Patterned synthetic polycrystalline diamond films have been prepared by selective deposition, by selective abrasion, and by etching in atomic oxygen or air at reduced pressure. Patterned films are further processed to yield microstructures by anisotropic silicon etching. In this paper, techniques for selective deposition and microstructure fabrication are briefly reviewed, and a flow sensor and an accelerometer are described as potential applications.

Neural networks and PCA for determining region of interest in sensory data preprocessing

Principal component analysis (PCA) and artificial neural networks are used to investigate electronic gas sensor responses for various alcohol chemicals. PCA is used to identify and visualize the best features to use for classification as well as for detecting outliers. A regular feed forward back propagation neural network (FBP) was used for the actual classification due to the fact that FBP determines better the non-linear borders of the various region of interest involved in the classification. Furthermore, we consider the tradeoff between classification speed and accuracy.