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A two-step process consisting of an initial nucleation stage with hydrogen followed by a growth stage without hydrogen is used to examine the role of hydrogen in ultrananocrystalline diamond deposition in Ar-rich microwave plasmas. An addition of 5% of [H.sub.2] to Ar-rich/C[H.sub.4] in the initial stage increases the nucleation density (up to [10.sup.9] [cm.sup.-2]) and the mean grain size (around 10 nm), accompanied by some improvement of crystallinity. However, an addition of [H.sub.2] above 10% suppresses nucleation by the etching of nucleation sites. The introduction of hydrogen atoms promotes the termination and stabilization of diamond grain surfaces toward [sp.sup.3] configuration, which are responsible for enhancing nucleation and crystallization. In contrast, Ar promotes renucleation by increasing the production of [C.sub.2] radicals in the plasma, which causes the degradation of the stabilization on the growing surfaces. Index Terms--Chemical vapor deposition (CVD), hydrogen, microwave plasma, nanocrystalline diamond, nucleation, optical emission, surface.

The lowest threshold energy of ion bombardment for cubic boron nitride (cBN) film deposition, which is prepared on positively biased Si (100) substrates from boron trifluoride gas in the high-density source region of inductively coupled plasma with mean ion impact energies from 45 down to a few eV or less, is presented. The findings have shown the existence of a way to deposit cBN films through quasistatic chemical processes under ultralow-energy ion impact.

Axial distributions of plasma parameters towards a positively biased substrate in an electron cyclotron resonance (ECR) plasma are measured as a function of substrate dc bias and pressure. It is observed that the pretreatment with low ion impact energy of around 10 eV produced a clean and smooth surface with minimal structural damage by high flux ion irradiation.

Research is presented concerning the control of the ion-to-adatom flux ration through the insertion of a grid mesh as a dual-bias into the front of a substrate. The deposition of crystalline materials is discussed.

A new study uses vacuum ultraviolet absorption spectroscopy to measure the decay rate of C atom density in inductively coupled plasmas.

A quadrupole mass spectrometer is used to study the precursor species of fluorocarbon film growth at the reactor wall irradiated by an electron cyclotron resonance C4F8 plasma. The study shows that the fluxes of CFx radicals and positive ions incident upon the wall are shown to be comparable with the net condensed carbon flux derived from the growth rate and in contrast, the trends in the amount of polymeric neutrals are not well correlated to the growth rate.

Diamond growth at pressures under 20m Torr was analyzed by employing inductively coupled plasma (ICP) enhanced chemical vapor deposition. ICP is favored for diamond growth because it offers high electron density of even at pressures under 100m Torr. Plasma diagnostics were conducted using Langmuir probe techniques optical emission spectroscopy. To control the incident ion energy, deposits were obtained employing positive substrate bias. The results are discussed.

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]

Cubic boron nitride (c‐BN) has an ultrahardness and a large bandgap energy like diamond. In the last 30 years, most of the attention has been directed towards the mechanical and electronic applications of c‐BN, while its biological potential has been overlooked. The authors report in vitro biocompatibility of high‐quality c‐BN films prepared by plasma‐enhanced chemical vapor deposition using the chemistry of fluorine. c‐BN films become superhydrophilic when chemical‐treated in hydrogen and nitrogen plasmas with or without the impact of low‐energy ions due to a marked increase in polar part of the surface free energy by removal of the fluorine atoms terminating c‐BN surfaces. Satisfactory proliferation and differentiation of osteoblastic cells comparable with a control sample and a superhydrophilic nanocrystalline diamond film, and the formation of mineral deposits by biomineralization are confirmed on the superhydrophilic c‐BN films with negative values of zeta potential. The results demonstrate a high potential of c‐BN as a noncytotoxic ultrahard coating material for biological and biomedical applications. [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]

Nitrogen-incorporated carbon nanowalls are prepared by microwave plasma-enhanced chemical vapor deposition using acetylene and methane. n-type conduction in the nanowalls is confirmed by Hall- and Seebeck-effect measurements. We show that increasing the amount of C2 radicals by adding Ar enables catalyst-free growth of nanowalls at a high rate up to about 1 μm/min and reduces the deposition temperature (TD) down to around 650 °C. A substrate pretreatment using diamond powder results in a composite of nanowalls and nanocrystalline diamond films, suggesting that the nanowall growth is limited by gas-phase conditions rather than surface conditions. The low conductivity nanowalls for low TD exhibit thermal activation in the Arrhenius plot, indicative of semiconducting conduction, while the high conductivity nanowalls for high TD are almost temperature independent, indicative of quasimetallic conduction. The high conductivity is attributed to a global increase in the sp2 cluster size and crystallinity, which is responsible for increasing delocalization of defect states associated with π bonding and, hence, quasimetallic character. [ABSTRACT FROM AUTHOR]

Structural and electrical conduction properties of nitrogen-doped nanocrystalline diamond films are studied as a function of deposition temperature (TD) in a microwave Ar-rich/CH4 plasma with 30%N2 addition. Hall- and Seebeck-effect measurements confirm n-type conduction for TD above 1100 K. For TD from 1100 and 1220 K, the electron concentration increases up to 1020 cm-3 and the electron mobility is in the range of 4–8 cm2 V-1 s-1. For TD above 1250 K, the mobility decreases to ∼1 cm2 V-1 s-1. Low conductivity films deposited at low TD exhibit semiconductorlike thermal activation in the Arrhenius plots, while high conductivity films deposited at high TD are almost temperature independent, indicative of quasimetallic conduction. The nitrogen concentration in the films is about 0.3 at. %, independent of TD. As TD is increased, the sp2 content and order increase. This is responsible for the appearance of midgap states, their delocalization, and the larger distance between diamond grains. The high conductivity at high TD is due to the amount and crystallinity of sp2 carbon, rather than the nitrogen concentration. [ABSTRACT FROM AUTHOR]

A low-input capacitance emissive probe heated by a CO[SUB2] laser has been used to investigate frequency-modulated electric potentials in a radio-frequency (rf) glow discharge plasma. An excellent time-response ability of our probe system to a sharp potential change was confirmed by potential measurements with applying a step function voltage to the plasma. The electric field distribution as the first derivative of the potential distribution obtained by the probe method was compared with that by the laser optogalvanic spectroscopy to ensure the reliability of the measurements in the sheath region. The probe method was applied to directly monitor a temporal variation of axial potential and electric field distributions between two parallel-plate electrodes in a rf argon plasma. The formation of ion sheath regions on both electrode surfaces was confirmed at any phase in a rf cycle. The results were consistent with a one-dimensional model for potential and electric field distributions in the sheath region. [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]

A simple low-pressure condition at 80 mTorr has been employed to study the kinetics and role of C, O, and OH in diamond growth by using inductively coupled CO/CH[sub 4]/H[sub 2] and O[sub 2]/CH[sub 4]/H[sub 2] plasmas. Vacuum ultraviolet absorption spectroscopy (VUVAS) and actinometric optical emission spectroscopy (OES) were used to examine the densities of ground-state C atoms and emissive species such as OH, C[sub 2], and O, respectively. Diamond films consisting of nanocrystallites with sizes as small as 20 nm were obtained on positively biased Si substrates only when CH[sub 4] was fed. Both diamond and nondiamond growth were enhanced with increasing CO for a fixed CH[sub 4] concentration of 5%, while diamond growth was suppressed with increasing O[sub 2]. Comprehensive discussion along with the VUVAS and OES results suggested that the C atoms resulting mainly from CO by electron impact dissociation had a close relation with the formation of C[sub 2] or still larger species as the precursors to nondiamond phase, while the OH radicals resulting predominantly by loss reactions of the byproduct O atoms with H[sub 2] and CH[sub 4] were highly responsible for the enhanced diamond growth. A large amount of O atoms from O[sub 2] was shown to affect the initial nucleation stage seriously. The results support the growth chemistry of diamond from H-hybridized carbon radicals fragmented from CH[sub 4] rather than from H-stripped carbon radicals. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The properties of nitrogen-doped nanodiamond films are analyzed as a function of deposition temperature ([T.sub.D]). The studies have shown that the high conductivity at high [T.sub.D] is because of the amount and crystallinity of [sp.sup.2] carbon, rather than the nitrogen concentration.

Plasma diagnostics and kinetic rate analysis for radicals is used for studying the role of neutral radicals and charged ions in a low pressure limit diamond chemical vapor deposition in CO-CH(sub 4)-H(sub 2) plasmas, which are coupled inductively. The results show radical fluxes limit the nucleation and modify the dynamic effects of energetic ions.

A low-input capacitance emissive probe heated by a CO2 laser is used to investigate frequency-modulated electric potentials in a radio-frequency (rf) glow discharge plasma. The results were found consistent with a one-dimensional model for potential and electric field distribution in the sheath region.

The ion-to-CH3 flux ratio, ion energy and ionic composition in a low-pressure inductively coupled plasma (ICP) is examined by mass spectrometry with absolute calibration techniques. The specific surface process which is dominated by energetic ions is discussed.