Robert Hendry

Demonstration of a method to fabricate a large-area diamond single crystal

A multi-step process to fabricate a diamond single crystal that is larger than the original, natural, commercially-obtained crystals is described. Starting with 3.0 mm × 3.0 mm × 0.25 mm, natural, type Ia C(100) crystals that have had their edges oriented to (010) and (001), we have successfully bonded two to a Si substrate in close proximity to each other. Subsequent diamond homoepitaxy using plasma-enhanced chemical vapor deposition of up to

DC-DC converter suitable for thermoelectric generator

75 μm thickness has enabled epitaxial overgrowth to join the two diamonds. The topography was excellent, and microRaman spectroscopy indicated only a 0.6 cm−1 line broadening (crystal degradation) at the joint. The creation of etch pits (via oxidizing flame) on the joined diamond surface indicated a higher defect density at the joint, but this more-defective region was constrained to within the dimensions of the original gap between the diamond crystals. These results indicate that this process of epitaxial joining of diamond single crystals has the potential to be scaled up to larger area in order to fabricate a diamond single crystal of desired area and reasonable crystal perfection.

Two-dimensional model of a large area, inductively coupled, rectangular plasma source for chemical vapor deposition

With recent advancements in thermoelectric material performance, thermoelectric generators have become a viable alternative for power generation using small temperature differentials with benefits that can not be found in other energy conversion methods. The power generated by a thermoelectric generator, using a small /spl Delta/T, is characterized by a relatively high current (-/spl sim/5 A), but a relatively low voltage (<0.3 V), which is often not suited for many practical applications. In order to make use of the thermoelectric generated power in applications requiring a higher voltage, a DC-DC step up converter that can handle low input voltage is needed. Commercial available DC step up converters require an input voltage of at least 0.7 volts, which is the minimal voltage required for operating a bipolar junction switch. Several novel approaches for low input voltage DC-DC converter concepts have been studied and proved to be feasible. Their operations are based on some unconventional methods achieving DC to AC conversion for low input voltage. In one solid state approach, a normally-on transistor and a tunnel diode were utilized to achieve low voltage oscillation. A conversion concept was also developed which is based on an electromagnetic actuated mechanical switch. Operating principles and measured performance of these approaches will be reported.

Enhancement of Diamond Nucleation by Graphite Fibers Local to Substrate Surfaces in H2 - CH4 rf Discharges.

A novel design for an inductively coupled, rectangular plasma source is described. The design encompasses several key issues of large area thin film growth by chemical vapor deposition: structural integrity, electrostatic screening, substrate temperature control and maximal growth surface. A test reactor has been utilized to grow diamond films over /spl sim/1800 cm/sup 2/ at 13 MHz and /spl sim/1 torr pressure with 45 kW coupled power. The design is readily scalable to larger areas. To analyze the axial plasma uniformity, a two-dimensional (2-D) simulation model is presented. The electromagnetic coupling, nonequilibrium plasma chemistry and multispecies diffusion are self-consistently treated. In this 2-D approach, the slotted Faraday screen behaves as a diamagnetic medium in transmitting the magnetic field. Results are compared with experimental data for the hydrogen plasma extent, electron and gas temperatures. Neutral gas thermal conduction and hydrogen recombination dominate the energy deposition to the wall and in turn govern the plasma length. A tradeoff between quality and growth area is predicted for the reactor as the pressure is decreased.

Formation of diamond films from low pressure radio frequency induction discharges

Abstract A method has been discovered for enhancing diamond nucleation without using any mechanical treatment to the surface. We have observed that the presence of graphite fibers tangential to a substrate surface greatly enhances the nucleation of diamond crystals immediately underneath the fiber. Diamond growth has been observed along lines and in small clusters replicating the graphite fiber pattern following exposures of unscratched silicon, nickel, and fused quartz substrates to 2% CH 4 in H 2 rf-discharges.

Remote plasma enhanced CVD method and apparatus for growing an epitaxial semiconductor layer

Abstract Diamond films have been deposited in a low pressure, radio frequency (r.f.) induction plasma-assisted chemical vapor deposition system. The r.f.-induction system confines the plasma at the low pressures of operation 0.010–10.00 Torr to permit efficient dissociation of the reactant gases. A variety of chemical systems have been used to deposit diamond, including traditional H 2 -CH 4 discharges containing 0.5–2.0% CH 4 ; H 2 -CF 4 discharges containing 4–16% CF 4 , and water vapor discharges containing high concentrations of alcohol and/or acetic acid vapors. No molecular hydrogen is admitted to the growth chamber for the water-based processes. The water vapor becomes the functional equivalent of the molecular hydrogen used in more traditional H 2 -CH 4 discharges. The success of the low pressure r.f.-induction plasma for diamond growth from the wide variety of chemical systems is predicated on the generation of a high electron density plasma. Parent gaseous molecules are converted into appropriate high temperature stable products such as H, H 2 , CO, and C 2 H 2 as they traverse the plasma. Quadrupole mass spectroscopy has been used to study the conversion of the water-alcohol vapors to H 2 , CO, and C 2 H 2 as they pass through the r.f. plasma, 99% of the CH 4 O is converted into H 2 , H 2 O, and C 2 H 2 . These studies show plasma conversion of H 2 O into molecular H 2 . The excess oxygen is rapidly converted into CO through interactions of the O, presumably with solid carbon sources. Optical emission from both the water-based discharges and the molecular hydrogen-based discharges shows the propensity for atomic hydrogen generation from these low pressure r.f.-induction discharges.