Synthesis of tin-incorporated nanocomposite diamond like carbon films by plasma enhanced chemical vapor deposition and their characterizationNitrogen-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 C 2 radicals by adding Ar enables catalyst-free growth of nanowalls at a high rate up to about 1 m / min and reduces the deposition temperature ͑T D ͒ 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 T D exhibit thermal activation in the Arrhenius plot, indicative of semiconducting conduction, while the high conductivity nanowalls for high T D are almost temperature independent, indicative of quasimetallic conduction. The high conductivity is attributed to a global increase in the sp 2 cluster size and crystallinity, which is responsible for increasing delocalization of defect states associated with bonding and, hence, quasimetallic character.

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.

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Highly conductive, nitrogen-incorporated nanocrystalline diamond films with quasimetallic character emit electrons at low turn-on fields (∼3 V μm−1). These films exhibit stronger delocalization of carriers, indicative of smaller energy separation between the defect bands in the band gap. We show that the emission level derived from the measured emission characteristic and electron affinity shifts upward (up to a few eV) with increasing the film conductivity, thereby decreasing the effective potential barrier height for the emission. This is attributed to higher probabilities of electron injection into upper defect levels during the transport process, originating from internal band bending and increasing band continuity.

A route to high-purity nanocrystalline diamond films from C2 dimers and related mechanisms have been investigated by enhancing C2 growth chemistry in Ar-rich microwave plasmas. Efficient C2 production by direct dissociation from acetylene causes the micro- to nanocrystal transition with a low threshold Ar concentration of ∼70% and produces films of ∼20nm grains with a distinct visible-Raman peak of diamond. C2 grows nanodiamond on diamond surfaces but rarely initiates nucleation on foreign surfaces. The phase purity can be improved by increasing the dominance of nanodiamond growth from C2 over nondiamond growth from CHx(x=0–3) and large radicals.

Production and extinction processes of polymeric neutral species (CmFn;m⩾2) in electron cyclotron resonance C4F8 and CF4 plasmas have been studied by using a quadrupole mass spectrometer (QMS) employing low-energy electron attachment technique. This technique allows the detection of electronegative CmFn species as negative ions by scanning the attaching electron energy in the QMS typically in the range of 0–10 eV. In addition to the most abundant F− and CF3− signals resulting from dissociative attachment to various fluorocarbon species, pronounced attachment resonances of negative ions corresponding to the series of CmF2m±1− such as C3F7−, C4F9−, and C5F9− were primarily observed especially at low microwave powers and high pressures. The C4F8 plasma contained a large amount of polymeric species and a high fraction of reactive F-stripped species as compared to the CF4 plasma, providing evidence of a high potential of gas phase and surface polymerization in a low F/C ratio plasma. The amount and composition of polymeric species were examined by varying gas residence time and diluted hydrogen or argon concentration. At 20 mTorr, the overall amount of polymeric species was suppressed by enhanced gas flow with decreasing residence time, while a fraction of F-stripped species was increased. The amount of polymeric species was also suppressed with increasing diluted hydrogen, and the different behavior in the two plasmas was interpreted as the result of interactions between H atoms and polymeric species. The results provide insights into the kinetics and chemical activity of polymeric species in a high-density plasma as a practical etching source.

Articles you may be interested inSynthesis of cubic boron nitride films on Si tips via chemical vapor deposition and the field emission properties J. Vac. Sci. Technol. B 32, 02B102 (2014); 10.1116/1.4843075Quantitative study of ion bombardment induced phase transformation of cubic boron nitride by reflective electron energy-loss spectroscopy Ion implantation effects on the structure and nanomechanical properties of vapor deposited cubic boron nitride films J.The lowest threshold energy of ion bombardment for cubic boron nitride ͑cBN͒ film deposition is presented. cBN films are prepared on positively biased Si ͑100͒ substrates from boron trifluoride ͑BF 3 ͒ gas in the high-density source region of an inductively coupled plasma with mean ion impact energies from 45 down to a few eV or less. The great decrease in the threshold ion energy is mainly attributed to specific chemical effects of fluorine as well as high ion-to-boron flux ratios. The results show evidence for the existence of a way to deposit cBN films through quasistatic chemical processes under ultralow-energy ion impact.

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