Shaoqi Peng

Characteristics of carbon nitride films prepared by magnetic filtered plasma stream

Carbon nitride films have been formed using a magnetic field filtered plasma stream deposition system. The electrical, optical and mechanical properties of these films deposited at different N2 partial pressures have been studied. Infrared spectra exhibit characteristic bands of carbon nitrogen bonds at 2200, 1500, 1350 cm−1, showing that the C and N atoms are chemically bonded in the films. X-ray photoelectron spectroscopy has been employed to measure the atomic ratio of N to C in the films. By deconvolution of the XPS spectra, it was identified that the films consist of three phases, namely, β-C3N4, CNx and ta-C. The relative fractions of these phases in the films were also determined. The optical band gap obtained from optical absorption spectra varies from 3.85 to 4.51 eV depending on the N2 partial pressure. The measured value of Vickers hardness Hv is between 4000 and 7000 kg/mm2. The effect of N2 partial pressure on the properties of these films is also discussed.

Effects of nitrogen on the structure and properties of highly tetrahedral amorphous carbon films

Nitrogen-containing tetrahedral amorphous carbon films (ta-C) have been prepared using a magnetic field filtered plasma stream deposition method. The plasma stream was first formed by sputtering of a graphite target in nitrogen-argon atmospheres. The partial pressure of nitrogen, , was in the range 0-7 Pa at total pressure of deposition Pa. The optical and electrical properties of samples were studied using x-ray photoelectron spectroscopy (XPS), Fourier transform infrared absorption spectroscopy (FTIR), UV-visible optical absorption spectroscopy and measurements of electrical conductivity in the temperature range 300-500 K. The incorporation of small amounts of nitrogen will result in an increase in electrical conductivity, a slight drop of the band gap and an increase in band-tail absorption. These suggest that incorporation of a small amount of nitrogen into ta-C films will induce graphitization of bonding. For samples deposited at Pa, nitrogenation of films is very pronounced. The actual nitrogen content in films in terms of atomic percentage can be as much as 47%. The films have a wide band gap of 4.05 eV and an extremely low electrical conductivity. These suggest that a carbon nitride film is formed. The configurations of N atoms in the ta-C network are identified and discussed.

Optical and electrical characteristics of amorphous diamond films

Abstract Amorphous diamond (a-D) films have been formed by magnetic field filtered carbon ion deposition. The optical and electrical characteristics of these films as a function of the substrate bias voltage V b have been studied using optical absorption spectroscopy and electrical measurements. The results show that a-D films with high sp 3 fractions were formed when the substrate bias voltage V b was in the range −10 V to −50 V. The optical band gap of such a-D films was found to be larger than 3 eV. It is shown that optical absorption spectroscopy is a simple method to compare qualitatively the sp 3 fractions in carbon films. The mechanisms of transport in these films are also studied and discussed.

Structural, morphological and optical properties of C60 cluster thin films produced by thermal evaporation under argon gas

C60 cluster thin films were obtained by thermal evaporation under argon atmosphere. The surface morphology, optical absorption characteristics and structure of these films have been investigated. The ultraviolet-visible optical absorption spectrum of this C60 film is obviously different from that of the film obtained under vacuum conditions. The position and intensity of absorption peaks of the films grown in argon are modified compared with the film grown in vacuum. The bandgap energy changes from 2.02?eV to 2.24?eV. IR analyses show no evidence of chemical change. The x-ray diffraction pattern reveals the existence of a mixture of face-centred cubic and hexagonal close-packed phases. The collisions of C60 molecules and buffer gas molecules are discussed. We also found the surface particles of these C60 cluster films are larger and sharper than those of C60 films prepared in vacuum by the observation of atomic force microscopy (AFM). This may be advantageous for using C60 for electron field emission.

Effects of fluorine implantation into a-C:H thin films

Abstract Fluorine implantation into r.f. glow discharge hydrogenated amorphous carbon (a-C:H) has been performed and the properties of the implanted a-C:H films as functions of the implanted fluorine concentration C F have been studied using optical absorption, electrical and electron spin resonance (ESR) measurements. When C F is below 10 19 cm −3 , the optical gap E opt does not change significantly with C F . However, for higher C F values E opt decreases rapidly with increasing C F from 1.53 eV at C F = 1 × 10 19 cm −3 to about 1 eV at C F = 1 × 10 21 cm −3 . It is found that effective doping of the a-C:H films has been achieved when C F exceeds about 10 20 cm −3 . The conductivity activation energy E a drops significantly from 1.28 eV for the unimplanted and unannealed sample to 0.2 eV for the implanted and annealed sample with C F = 3 × 10 21 cm −3 . An increase of more than 10 orders of magnitude in σ RT has been observed between samples with sufficiently high C F values and unimplanted samples. In addition to a large main resonance due to carbon dangling bonds of g value g 1 = 2.0027 ± 0.0002, hyperfine splitting (HFS) has been induced by the implanted F atoms in the ESR spectra measured in the dark at the X band position at room temperature. However, these HFS signals exhibit a peculiar C F dependence and do not show up in some intermediate C F value range. For C F higher than about 10 20 cm −3 the large main resonance is also found to be composed of one big lorentzian component and one small gaussian component. While all the HFS signals annealed out at 200°C, the small gaussian component persisted even after annealing at 250°C.

ESR splitting induced by ion implanted fluorine in amorphous silicon

Splitting in ESR signals measured in the dark at room temperature has been observed in fluorine implanted a-Si:H samples. Before implantation, the ESR spectra of the original samples show one resonance with g=2.005 as usual. After fluorine implantation, the ESR signals can be decomposed into two well characterized components: one with g=2.006 and ΔHpp=8.4G and the other with g=2.003 and ΔHpp=6.5G. It is observed that the spin density Ns of the g=2.006 resonance increases markedly after implantation but is essentially independent on the implanted F concentration CF, but Ns of the g=2.003 resonance increases rapidly with CF especially in the range from 1×1020 to 1×1021cm−3. After annealing, while there is only slight reduction in Ns of the g=2.003 resonance, there is significant reduction in Ns of the g=2.006 resonance and Ns falls rapidly with CF to unresolvable level for the high F dose cases. Possible origins of these resonances are discussed.

Morphology and characteristics of C60 thin films grown in argon atmosphere by thermal evaporation

The surface morphology, structure, and optical absorption characteristics of C60 thin films grown in argon atmosphere by thermal evaporation have been studied. X-ray diffraction studies reveal a mixture phase of face-centered-cubic and hexagonal-close-packed phases for this film. Infrared analyses show no evidence of chemical change. The observations of atomic force microscopy of C60 thin films grown in argon atmosphere found that surface particles are larger and sharper than that grown in vacuum, thus C60 thin films grown in argon atmosphere may be advantageous to using C60 for electron field emission. Ultraviolet-visible optical absorption spectrum of this film in the range of wavelength from 200 to 600 nm is very different than that of the film obtained under vacuum conditions. The position and intensity of absorption peaks are obviously changed compared to vacuum C60 thin film. The band gap energy of this film also changes from 2.02 to 2.24 eV compared to the film prepared under vacuum.The surface morphology, structure, and optical absorption characteristics of C60 thin films grown in argon atmosphere by thermal evaporation have been studied. X-ray diffraction studies reveal a mixture phase of face-centered-cubic and hexagonal-close-packed phases for this film. Infrared analyses show no evidence of chemical change. The observations of atomic force microscopy of C60 thin films grown in argon atmosphere found that surface particles are larger and sharper than that grown in vacuum, thus C60 thin films grown in argon atmosphere may be advantageous to using C60 for electron field emission. Ultraviolet-visible optical absorption spectrum of this film in the range of wavelength from 200 to 600 nm is very different than that of the film obtained under vacuum conditions. The position and intensity of absorption peaks are obviously changed compared to vacuum C60 thin film. The band gap energy of this film also changes from 2.02 to 2.24 eV compared to the film prepared under vacuum.

Depletion Fraction of Silane and Dominant Neutral Radical in RF Glow Discharge in Silane

A quadripole mass spectrometer was installed on the line of a PCVD system to measure the depletion fraction of silane and the monosilicon radicals in the discharges. The paper presents a method of measuring the depletion fraction of silane when setting the mass spectrometer at the high ionization voltage. The experimental results were compared and accordant with those reported before [1,2,3].

Internal photoemission transient current temperature spectroscopy — a new method for determination of the gao state distribution in a-Si:H

Abstract An internal photoemission transient current temperature spectroscopy (IPETCTS) has been demonstrated as a new method for the determination of the density of gap state distribution (GDOS) in a-Si:H. By using this method we have succeed in determinating the GDOS in undoped GD a-Si:H and SP a-Si:H films over a wide energy range.

Characterization of Carbon Nitride Films Prepared by Magnetic Filtered Plasma Deposition

Carbon nitride films prepared by magnetic filtered plasma deposition were characterized using Fourier transform infrared (FTIR) absorption and X-ray photoelectron spectroscopy (XPS). Characteristic bands corresponding to C-N, C=N, C=N, and C=C bonds were observed in FTIR spectra. It was found that the XPS C 1s and N 1s signals could be deconvoluted into three and two gaussian peaks, respectively. A plausible suggestion on the assignments of the XPS peaks to C 3 N 4 , CN x and ta-C phases was discussed. The relative abundance of the various CN bonds, the relative abundance of the various bonding components from XPS results, and their dependence on the nitrogen partial pressure P N during deposition were analyzed. Assuming the assignments of the XPS peaks to the various phases, the XPS results suggested that there would be an optimal P N that would favor the growth of the C 3 N 4 phase. The electrical conductivity, the optical band gap and the Vickers hardness of these films were measured and the effects of P N on these properties were studied.