Brian R. Stoner

Textured diamond growth on (100) β‐SiC via microwave plasma chemical vapor deposition

Textured diamond films have been deposited on β‐SiC via microwave plasma chemical vapor deposition preceded by an in situ bias pretreatment that enhances nucleation. Approximately 50% of the initial diamond nuclei appear to be aligned with the C(001) planes parallel to the SiC(001), and C[110] directions parallel to the SiC[110] within 3°. The diamond was characterized by Raman spectroscopy and scanning electron microscopy.

Charge Transfer Equilibria Between Diamond and an Aqueous Oxygen Electrochemical Redox Couple

Undoped, high-quality diamond is, under almost all circumstances, one of the best insulators known. However, diamond covered with chemically bound hydrogen shows a pronounced conductivity when exposed to air. This conductivity arises from positive-charge carriers (holes) and is confined to a narrow near-surface region. Although several explanations have been proposed, none has received wide acceptance, and the mechanism remains controversial. Here, we report the interactions of hydrogen-terminated, macroscopic diamonds and diamond powders with aqueous solutions of controlled pH and oxygen concentration. We show that electrons transfer between the diamond and an electrochemical reduction/oxidation couple involving oxygen. This charge transfer is responsible for the surface conductivity and also influences contact angles and zeta potentials. The effect is not confined to diamond and may play a previously unrecognized role in other disparate systems.

Textured growth of diamond on silicon via in situ carburization and bias‐enhanced nucleation

Ordered diamond films have been deposited on single‐crystal silicon substrates via an in situ carburization followed by bias‐enhanced nucleation. Textured diamond films with greater than 50% of the grains oriented D(100)//Si(100) and D〈110〉//Si〈110〉 were grown in both a horizontal and vertical microwave plasma chemical vapor deposition reactor. Separate diamond films from each of the two reactors were analyzed both by scanning electron microscopy and Raman spectroscopy. The in situ carburization is speculated to form an epitaxial SiC conversion layer, thus providing an economical alternative to obtaining epitaxial diamond films on single‐crystal SiC.

Adhesion/cementation to zirconia and other non-silicate ceramics: Where are we now?

Non-silicate ceramics, especially zirconia, have become a topic of great interest in the field of prosthetic and implant dentistry. A clinical problem with use of zirconia-based components is the difficulty in achieving suitable adhesion with intended synthetic substrates or natural tissues. Traditional adhesive techniques used with silica-based ceramics do not work effectively with zirconia. Currently, several technologies are being utilized clinically to address this problem, and other approaches are under investigation. Most focus on surface modification of the inert surfaces of high strength ceramics. The ability to chemically functionalize the surface of zirconia appears to be critical in achieving adhesive bonding. This review will focus on currently available approaches as well as new advanced technologies to address this problem.

Deposition of aligned bamboo-like carbon nanotubes via microwave plasma enhanced chemical vapor deposition

Aligned multiwall carbon nanotubes have been grown on silicon substrates by microwave plasma enhanced chemical vapor deposition using methane/ammonia mixtures. Scanning electron microscopy shows that the nanotubes are well aligned with high aspect ratio and growth direction normal to the substrate. Transmission electron microscopy reveals that the majority phase has a bamboo-like structure. Data are also presented showing process variable effects on the size and microstructure of the aligned nanotubes, giving insight into possible nucleation and growth mechanisms for the process.

Highly oriented, textured diamond films on silicon via bias-enhanced nucleation and textured growth

Highly oriented diamond films were grown on single-crystal silicon substrates. Textured films were first nucleated by a two-step process that involved the conversion of the silicon surface to an epitaxial SiC layer, followed by bias-enhanced nucleation. The nucleation stage, which produced a partially oriented diamond film, was immediately followed by a (100) textured growth process, thus resulting in a film surface where approximately 100% of the grains are epitaxially oriented relative to the silicon substrate. The diamond films were characterized by both SEM and Raman spectroscopy. Structural defects in the film are discussed in the context of their potential effect on the electrical characteristics of the resulting film.

Application of carbon nanotubes as electrodes in gas discharge tubes

turn-on fields. Recent experiments have reported turn-on electric fields in the range of 1.5‐3 V/mm. 3‐5 The nanotubes emitters, especially the SWNTs, are capable of producing stable electron emission with a current density exceeding 4 A/cm 2 ~Ref. 5! which make them attractive cold-cathode materials for microvacuum electronic applications. Assynthesized SWNTs are in the form of either free-standing mat or powder, unsuitable for device applications. We have processed the raw materials to uniform films by a spray method. 6 Adhesion between the substrates and the films is enhanced by introducing either a carbon-dissolving or a carbide-forming metal interlayer. In this letter, we report the effects of carbon nanotube coating on the performance of the gas discharge tubes. The direct current ~dc! breakdown voltages of GDTs fabricated using SWNT-coated electrodes were measured and compared with commercial GDTs. A significant reduction in the breakdown voltage and voltage fluctuation ~over 1000 surges! was observed for the nanotubebased GDTs as compared to typical commercial devices.

Epitaxial nucleation of diamond on β-SiC via bias-enhanced microwave plasma chemical vapor deposition

Abstract Diamond has been successfully nucleated on mirror finish single-crystal β-SiC films via bias-enhanced microwave plasma chemical vapor deposition. Initial scanning electron microscopy indicated that approximately 50% of the diamond grains were oriented relative to the SiC substrate. Further, high resolution cross-sectional transmission electron microscopy (TEM) and electron diffraction confirmed that the diamond was in epitaxial alignment with the silicon carbide, with the D(100)//SiC(100) and D〈110〉//SiC〈110〉. The high resolution TEM also revealed an approximate 5° tilt about 〈110〉 towards 〈110〉. This tilting is believed to be the result of the high density of misfit dislocations at the interface. Speculations on the role of biasing in the promotion of epitaxial diamond nucleation on a foreign substrate are also discussed.

Electron emission from diamond coated silicon field emitters

Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias‐enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.

Oriented nucleation and growth of diamond films on β‐SiC and Si

Oriented diamond nuclei prepared by bias‐enhanced microwave plasma chemical vapor deposition on β‐SiC and Si were characterized by x‐ray texture diffractometry. In both cases, x‐ray pole figures reveal an epitaxial relation between the orientation of diamond nuclei and the substrate. However, the angular spread of the nuclei orientation is rather large, amounting to 9°–13° (FWHM) in both polar and azimuthal directions. When growing thick diamond films on top of these already oriented diamond nuclei, the evolution of the orientational order depends critically on the growth conditions. In the case of 〈100〉 oriented nuclei, growth conditions which favor the formation of a 〈100〉 fiber texture can even improve the degree of orientational order, whereas other growth conditions result in a deterioration of the epitaxial relationship.