J. W. Glesener

Investigation of the temperature dependence of the field emission current of polycrystalline diamond films

This letter reports on the measurement of the field emission current dependence of doped polycrystalline diamond (PCD) films on temperature. The motivation for this type of measurement was to assess the thermal stability of PCD field emitters and gain some insight into a possible emission mechanism. Between room temperature and 300 °C, for a fixed electric field, the emission current from B doped films was found to remain constant. Heavily doped nitrogen films were also examined and the emission current was found to increase exponentially with an activation energy of 0.16 eV.

Fabrication of a high surface area boron-doped diamond coated metal mesh for electrochemical applications

An electrode for electrochemical uses is made of a conductive metal mesh coated with boron-doped diamond. The electrode may be used in electrochemical reactions either as a cathode or as an anode, or can be used with an alternating current.

Growth of fcc Fe films on diamond

The epitaxial growth of fcc iron films on the (001) face of diamond has been achieved. The films were studied by reflection high‐energy electron diffraction and angle‐resolved Auger electron diffraction. The studies show that 4–5 atomic layers of Fe on C(100) form a continuous film. The films as deposited at room temperature are disordered, and after a high‐temperature anneal have a fcc structure at room temperature.

Chemical vapor deposition diamond nucleation induced by sp2 carbon on unscratched silicon

Chemical vapor deposition (CVD) diamond nucleation is enhanced on most substrates by scratching with diamond grit prior to growth. The damage induced by such scratching makes this an unsuitable technique for many applications, and sheds little light on fundamental nucleation mechanisms, since the bulk of the crystals on such substrates probably grow homoepitaxially on diamond fragments embedded in the substrate during scratching. In this paper, we describe recent results in which unscratched silicon substrates overlaid with carbon fibers undergo very rapid and heavy CVD diamond nucleation when exposed to CVD diamond growth conditions. Exposure of such fiber-treated substrates to high temperature in an ultrahigh vacuum induces the formation of etch pits and trails of particulate debris which are extremely efficient diamond nucleators. Both the pits and the debris are carbon rich, and thus satisfy two criteria for “spontaneous”, i.e. non-epitaxial growth; (1) carbon saturation of the substrate surface, and (2) the presence of high-energy edge sites. The specific relationships between these characteristics and CVD diamond nucleation are discussed.

Diamond tubes and fibers

Abstract Diamond-coated fibers, diamond tubes, and diamond fibers were produced using a hot-filament-assisted chemical vapor deposition process. Diamond coatings were deposited on prepared fiber substrates of silicon carbide, copper, tungsten, and copper-coated graphite. Diamond tubes were produced in situ as a result of the removal of the substrate by atomic hydrogen or after deposition by dissolving the substrate using a chemical etch. Diamond fibers in the shape of a half-cylinder were produced by masking a portion of the substrate fiber and removing the diamond after deposition. The diamond tubes and fibers that have been produced are typically 2–3 cm in length and are self-supporting structures.

Hole capture in boron‐doped diamond

A carrier capture model based on the work of Lax [Phys. Rev. 119, 1502 (1960)] and Gibb et al. [Philos. Mag. 36, 1021 (1977)] is applied to diamond. This model accounts for the lower activation energy for boron in diamond measured using deep level transient spectroscopy (DLTS) techniques. The model assumes that when a carrier in the valence band is captured by an impurity, it occupies the highest energy acceptor excited state and then is quickly funneled to the lowest excited acceptor level. At the lowest energy excited acceptor level the trapped hole either thermalizes back to the valence band or reaches the ground state of the impurity via a ‘‘slow’’ multiphonon decay. Using this kinetic picture, previously reported DLTS results are shown to be consistent with the energy parameters for the boron acceptor level. These results will be of interest to researchers simulating the device properties of diamond and are an indication of the influence of the acceptor spectrum on the electrical properties of boron‐...

Photoinduced current transient spectroscopy of boron doped diamond

A Schottky device fabricated on a natural type 2b diamond was characterized using photoinduced current transient spectroscopy (PICTS). A trapping level, presumed to be due to boron, with an activation energy of 0.29 eV was found from PICTS. Resistance measurements on the same device produced an activation energy of 0.38 eV. The two methods, while being described by the same exponential temperature dependence, have prefactors with different physical origins. Since the activation energy measured by PICTS is proportional to σeffe−E/kT, the difference in the measured values could be attributed to a temperature dependence in the ‘‘effective’’ hole capture cross‐section σeff. This report also demonstrates the potential of PICTS in identifying an electrically active trap in a sample whose high series resistance renders it difficult to characterize using capacitance based methods.

Electrochemical behavior of diamond-reinforced composites

A diamond-reinforced 1100 aluminum matrix composite (DRC) containing 15% by volume of 30 μm diamond particles was fabricated using standard powder metallurgy techniques at 600 °C. A temperature higher than that required solely for composite consolidation was selected to investigate whether carbide formation occurred. Scanning electron micrographs and Raman spectroscopy showed no detectable amount of carbide formation. Electrochemical testing showed that the pitting potential of the composite was the same as that of the pure matrix material, which also indicates that either carbides did not form or the amount formed was so small as not to alter the breakdown potential of the DRC.

Admittance spectroscopy of boron doped diamond

The boron acceptor level in diamond was investigated using admittance spectroscopy. The conductance of a flame grown sample was measured between 125 and 200 K at five frequencies between 0.1 and 5.0 kHz using a 16.0 mV ac signal applied across a Schottky diode at zero dc bias. The admittance spectroscopy technique yielded a deep impurity level of 0.33 eV. From the same set of data, a hole capture cross section of 2×10−12 cm2 was also measured. The cross section reported here is assumed to be caused by ionized boron acceptors.

Electron beam modification of the Schottky diode characteristics of diamond

Electron beam irradiation from a scanning electron microscope has been shown to improve the rectification characteristics of a boron doped diamond sample, as evidenced by measurement of a lowered reverse current in Al Schottky diodes. The sample processing procedure consisted of cleaning in heated CrO3/H2SO4 and NH4OH/H2O2 mixtures, exposure to an electron beam, a post‐exposure cleaning in NH4OH/H2O2, and metallization. Since published information on the effect of CrO3/H2SO4 and NH4OH/H2O2 mixtures on the diamond surface is lacking, we hypothesize that the exposure of the diamond surface to an electron beam releases hydrogen from the surface, while the post‐irradiation clean in boiling NH4OH/H2O2 may oxygenate the diamond surface. This result is consistent with previous work which demonstrated that annealing in hydrogen and oxygen ambients affected the surface resistance of diamond. These results indicate a high surface resistance is necessary to form good Schottky junctions in diamond.