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Heterojunctions of p-type cubic boron nitride (cBN) and n-type silicon with sp2-bonded BN (sp2BN) interlayers are fabricated under low-energy ion impact by plasma-enhanced chemical vapor deposition, and their rectification properties are studied at temperatures up to 573 K. The rectification ratio is increased up to the order of 105 at room temperature by optimizing the thickness of the sp2BN interlayer and the cBN fraction for suppressing the reverse leakage current. A highly rectifying p-type cBN/thick sp2BN/n-type silicon junction diode shows irreversible rectification properties mainly characterized by a marked decrease in reverse current by an order of magnitude in an initial temperature ramp/down cycle. This irreversible behavior is much more reduced by conducting the cycle twice or more. The temperature-dependent properties confirm an overall increase in effective barrier heights for carrier injection and conduction by biasing at high temperatures, which consequently increases the thermal stability of the diode performance. [ABSTRACT FROM AUTHOR]

Field emission performance of boron nitride (BN) island films is studied in terms of cubic phase evolution in plasma-enhanced chemical vapor deposition. Fine-grained island films with large surface roughness can be grown for initial sp2-bonded BN and subsequent cubic BN (cBN) phases by using low-energy (∼20 eV) ion bombardment. Ultraviolet photoelectron spectroscopy reveals that the electron affinity is as low as 0.3 eV for both sp2-bonded BN and cBN phases. The evolution of cBN islands reduces the turn-on field down to around 9 V/μm and increases the current density up to 10-4 A/cm2. The emission is facilitated by the larger field enhancement due to the larger roughness and the higher conduction of cBN islands. The potential barrier height is estimated to be about 3.4 eV for emission from the Fermi level, while it is only about 0.3 eV for “conduction band emission.” [ABSTRACT FROM AUTHOR]

Methyl radicals (CH[sub 3]) and positive ionic species in a low-pressure inductively coupled plasma under diamond-depositing conditions have been detected by using a quadrupole mass spectrometer. Absolute calibration of the fluxes of CH[sub 3] and ionic species was made by the threshold ionization technique and Langmuir probe measurement, respectively. The CH[sub 3] density increased by two to three times with a small addition of carbon monoxide to a methane-hydrogen plasma and was on the order of 10[sup 11] - 10[sup 12] cm[sup -3]. As the pressure decreased from 60 to 10 mTorr, the ion-to-CH[sub 3] flux ratio increased from 0.2 to 4.3, accompanied by an increase in the fraction of light ions such as H[sub x][sup +] (x = 1-3). The average ion energy in the ion energy distribution at a grounded electrode was compared with the sheath potential and the discrepancy was found to be 0.5-2 eV depending on pressure and ion mass. The results were used to describe the specific surface process dominated by energetic (∼ several eV) ions rather than thermal neutrals. [ABSTRACT FROM AUTHOR]

Metal-insulator-metal capacitor structures using thick hexagonal and cubic boron nitride (hBN and cBN) films as dielectrics are produced by plasma jet-enhanced chemical vapor deposition, and their electrical transport and capacitance characteristics are studied in a temperature range of 298 to 473 K. The resistivity of the cBN film is of the order of 107 Ω cm at 298 K, which is lower than that of the hBN film by two orders of magnitude, while it becomes the same order as the hBN film above ∼423 K. The dominant current transport mechanism at high fields (≥1 × 104 V cm−1) is described by the Frenkel-Poole emission and thermionic emission models for the hBN and cBN films, respectively. The capacitance of the hBN film remains stable for a change in alternating-current frequency and temperature, while that of the cBN film has variations of at most 18%. The dissipation factor as a measure of energy loss is satisfactorily low (≤5%) for both films. The origin of leakage current and capacitance variation is attributed to a high defect density in the film and a transition interlayer between the substrate and the film, respectively. This suggests that cBN films with higher crystallinity, stoichiometry, and phase purity are potentially applicable for dielectrics like hBN films. [ABSTRACT FROM AUTHOR]

Plasma deposition of cubic boron nitride (cBN) films under low-energy (a few eV to ~ 40 eV) ion impact with the chemistry of fluorine is studied in terms of ion energy, ion flux, and ion to boron flux ratio onto the substrate. The ion energy and the ion to boron flux ratio are determined from the sheath potential and the ratio of incident ion flux to net deposited boron flux, respectively. For negative substrate biases where a mixture of turbostratic and amorphous BN phases only or no deposit is formed, both the ion energy and the ion to boron flux ratio are high. For positive substrate biases where cBN phase is formed, the ion energy and the ion to boron flux ratio are in the range of a few eV to 35 eV and 100 to 130, respectively. The results indicate that the impact of positive ions with high ion to boron flux ratios makes a substantial contribution to the formation of cBN phase, while that of negative ions and electrons makes only a minor contribution. [ABSTRACT FROM AUTHOR]

Plasma deposition techniques of nanocrystalline and microcrystalline diamond and related mechanisms at pressures below 0.1 torr are reviewed. The mechanism of nucleation and growth of diamond in low-pressure conditions is discussed theoretically and experimentally along with the role of radicals and ions in two different ion-energy ranges. For ion impact energies below 20–30 eV, diamond deposition occurs on a surface. The growth process is limited by the substrate temperature and the flux of hydrogen radicals when the ion energy is reduced enough to several eV as shown by a kinetic rate analysis for radical species. The nucleation process is limited mainly by the degree of carbon saturation and, hence, the flux of carbon-containing species. For ion impact energies above 20–30 eV, diamond deposition occurs beneath a surface. Renucleation hinders the growth and diamond nanocrystals are embedded in an amorphous carbon matrix. The nucleation process depends strongly upon the ion energy, ion-to-depositing flux ratio, and substrate temperature as shown by the film density increment based on the subplantation model. [ABSTRACT FROM PUBLISHER]

Abstract: We report the feasibility of glass press molds using high-quality, thick cubic boron nitride (cBN) films prepared in a plasma jet by chemical vapor deposition. A press test using a cBN film for an optical glass is carried out at a high temperature (≥650°C), above the glass transition temperature. Surface morphology, chemical composition, and optical transparency of the glass after a press test are examined by atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersion X-ray spectroscopy, and ultraviolet-visible-near-infrared (UV-VIS-near-IR) and IR spectroscopy. The B and N concentrations at the top several nanometers of the glass increase by several at.% after a press test. This is attributed to diffusion of B and N from the film into the glass. The UV-VIS-near-IR transparency of the glass in a short wavelength range (≤900nm) decreases by several % due to light scattering at the roughened glass surface. In contrast, the IR transparency of the glass remains constant despite an increase in the surface roughness. [ABSTRACT FROM AUTHOR]

Nanostructured composite films consisting of almost vertically aligned graphene layers, so-called “carbon nanowalls” (CNWs), and nanocrystalline diamond films are prepared by plasma-enhanced chemical vapor deposition. The space between the walls for the composite films is widened compared to simple CNWs by interception of in-plane continuity of the wall structures. The nucleation density of diamond is responsible for the spacing and arrangement of the walls. Field emission measurements show that the composite films have lower turn-on fields (∼1 V/μm) and larger field enhancement factors (∼4000) than simple CNWs. The results indicate that electric field screening between neighboring walls is well suppressed. [ABSTRACT FROM AUTHOR]

Field emission performance of materials with mixed sp2/sp3 phases often depends upon the phase composition at the surface. In this study, the emission performance of high-quality cubic boron nitride (cBN) films is studied in terms of phase purity. Thick cBN films consisting of micron-sized grains are prepared from boron trifluoride gas by chemical vapor deposition in a plasma jet and an inductively coupled plasma. Both the bulk and surface phase purities as well as crystallinities of cBN evaluated by visible and ultraviolet Raman spectroscopy, glancing-angle x-ray diffraction, and x-ray photoelectron spectroscopy are the highest when the film is deposited in a plasma jet under an optimized condition. The emission turn-on field decreases with increasing the phase purity, down to around 5 V/μm for the highest cBN purity, due to the larger field enhancement, while it is higher than 14 V/μm without cBN (sp2-bonded hexagonal BN only). The results indicate that the total field enhancement for the high phase purity film is governed by the internal field amplification related to the surface coverage of more conductive cBN, rather than the external one related to the surface topology or roughness. [ABSTRACT FROM AUTHOR]

Sp2-bonded boron nitride (BN) films are deposited on Ni and Si substrates with mean ion impact energies between a few eV and around 100 eV by surface-wave plasma enhanced chemical vapor deposition and their electrical insulation characteristics are examined for temperatures up to 300 °C. The overall crystallinity and order of sp2 structure in the films increase with decreasing ion energy, while the mass density becomes as high as sintered hexagonal BN only when the ion energy is above ∼50 eV. For a given temperature, the electrical resistivity of the films measured for metal-BN-metal structures increases with decreasing ion energy, and hence increasing crystallinity and order of sp2 structure, almost independent of mass density. A decrease in resistivity with temperature is small below 150 °C, then becomes large above 150 °C with a drastic increase in apparent activation energy for carriers, which is attributed to generation and transport of the carriers that get over higher barrier heights associated with stronger ion impact. [ABSTRACT FROM AUTHOR]

Abstract: A pulse-modulated direct-current methane plasma is used to deposit amorphous hydrogenated carbon (a-C:H) films on Si and polymethyl methacrylate (PMMA) substrates. The structure and mechanical properties of the films are examined by applying a negative pulse bias voltage of 0.5 to 3kV to the substrate at a pulse bias period of 100 to 200μs. The deposition rate on both Si and PMMA increases with increasing the net input power, independent of the pulse period. The Raman spectra demonstrate that the films on Si are diamond-like carbon (DLC), while those on PMMA are polymer-like or soft amorphous carbon because of higher crystallinity of the sp2 phase and lower nanoscale hardness. The residual compressive stress of the films on PMMA is constantly low ranging from 0 to 2GPa due exclusively to high flexibility of PMMA, which causes the easy relief of the stress and thus the density decrease in the films. [Copyright &y& Elsevier]