Chemical vapor deposited boron carbide : growth by a vapor-liquid-solid process

Detailed analytical electron microscope (AEM) studies of yellow whiskers produced by chemical vapor deposition (CVD)1 show that two basic types of whiskers are produced at low temperatures (between 1200°C and 1400°C) and low boron to carbon gas ratios. Both whisker types show planar microstructures such as twin planes and stacking faults oriented parallel to, or at a rhombohedral angle to, the growth direction. For both whisker types, the presence of droplet-like terminations containing both Si and Ni indicate that the growth process during CVD is via a vapor-liquid-solid (VLS) mechanism.

High-temperature growth of graphene films on copper foils by ethanol chemical vapour deposition

Chemical vapor deposition (CVD) is widely utilized to synthesize graphene with controlled properties for many applications, especially when continuous films over large areas are required. Although hydrocarbons such as methane are quite efficient precursors for CVD at high temperature (∼1000 °C), finding less explosive and safer carbon sources is considered beneficial for the transition to large-scale production. In this work, we investigated the CVD growth of graphene using ethanol, which is a harmless and readily processable carbon feedstock that is expected to provide favorable kinetics. We tested a wide range of synthesis conditions (i.e., temperature, time, gas ratios), and on the basis of systematic analysis by Raman spectroscopy, we identified the optimal parameters for producing highly crystalline graphene with different numbers of layers. Our results demonstrate the importance of high temperature (1070 °C) for ethanol CVD and emphasize the significant effects that hydrogen and water vapor, coming from the thermal decomposition of ethanol, have on the crystal quality of the synthesized graphene.

Control and diagnostics of inductively coupled plasmas for chemical vapour deposition of nanocomposite carbon nitride-based films

Control and diagnostics of low-frequency (∼ 500 kHz) inductively coupled plasmas for chemical vapor deposition (CVD) of nano-composite carbon nitride-based films is reported. Relation between the discharge control parameters, plasma electron energy distribution/probability functions (EEDF/EEPF), and elemental composition in the deposited C-N based thin films is investigated. Langmuir probe technique is employed to monitor the plasma density and potential, effective electron temperature, and EEDFs/EEPFs in Ar + N2 + CH4 discharges. It is revealed that varying RF power and gas composition/pressure one can engineer the EEDFs/EEPFs to enhance the desired plasma-chemical gas-phase reactions thus controlling the film chemical structure. Auxiliary diagnostic tools for study of the RF power deposition, plasma composition, stability, and optical emission are discussed as well.

Large low-frequency resistance noise in chemical vapor deposited graphene

We report a detailed investigation of resistance noise in single layer graphene films on Si/SiO2 substrates obtained by chemical vapor deposition (CVD) on copper foils. We find that noise in these systems to be rather large, and when expressed in the form of phenomenological Hooge equation, it corresponds to Hooge parameter as large as 0.1-0.5. We also find the variation in the noise magnitude with the gate voltage (or carrier density) and temperature to be surprisingly weak, which is also unlike the behavior of noise in other forms of graphene, in particular those from exfoliation. (C) 2010 American Institute of Physics. doi:10.1063/1.3493655]

Metal-organic chemical vapor-deposited cobalt oxide films as negative electrodes for thin film Li-ion battery

In this study, thin films of cobalt oxide (Co3O4) have been grown by the metal-organic chemical vapor deposition (MOCVD) technique on stainless steel substrate at two preferred temperatures (450 degrees C and 500 degrees C), using cobalt acetylacetonate dihydrate as precursor. Spherical as well as columnar microstructures of Co3O4 have been observed under controlled growth conditions. Further investigations reveal these films are phase-pure, well crystallized and carbon-free. High-resolution TEM analysis confirms that each columnar structure is a continuous stack of minute crystals. Comparative study between these Co3O4 films grown at 450 degrees C and 500 degrees C has been carried out for their application as negative electrodes in Li-ion batteries. Our method of electrode fabrication leads to a coating of active material directly on current collector without any use of external additives. A high specific capacity of 1168 micro Ah cm(-2) mu m(-1) has been measured reproducibly for the film deposited at 500 degrees C with columnar morphology. Further, high rate capability is observed when cycled at different current densities. The Co3O4 electrode with columnar structure has a specific capacity 38% higher than the electrode with spherical microstructure (grown at 450 degrees C). Impedance measurements on the Co3O4 electrode grown at 500 degrees C also carried out to study the kinetics of the electrode process. (C) 2014 Published by Elsevier B.V.

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiNx) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin film; deposited both oil a bare Si substrate and oil a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain modu i and prestresses of SiNx thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 +/- 19 GPa and 178 +/- 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 +/- 26 Gila and 194 +/- 34 MPa, respectively. However, the fracture strength values of SiNx films grown on the two substrates are quite different, i.e., 1.53 +/- 0.33 Gila and 3.08 +/- 0.79 GPa for the bare Si substrate a A the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, Surface, and volume of the specimens and fitted with the Weibull distribution function. For SiNx thin film produced oil the bare Si Substrate, the Volume integration gave a significantly better agreement between data and model, implying that the volume flaws re the dominant fracture origin. For SiNx thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the Volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiNx layer during SiO2 removal. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

MnSb/porous silicon hybrid structure prepared by physical vapor deposition

MnSb/porous silicon hybrid structure was prepared by physical vapor deposition technique. The structure and surface morphology of the MnSb films were analyzed by X-ray diffraction and scanning electron microscope, respectively. The magnetic hysteresis loops were obtained by an alternative gradient magnetometer. Based on the measurements, only MnSb phase was found and the surface morphology was rough and island-like. MnSb thin films show ferromagnetism at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

Stacking faults in SiCf/SiC composite obtained by chemical vapor reaction process

SiC fiber-reinforced SiC matrix composite (SiCf/SiC) is one of the leading candidates in ceramic materials for engineering applications due to its unique combination of properties such as high thermal conductivity, high resistance to corrosion and working conditions. Fiber-reinforced composites are materials which exhibit a significant improvement in properties like ductility in comparison to the monolithic SiC ceramic. The SiCf/SiC composite was obtained from a C/C composite precursor using convertion reaction under high temperature and controlled atmosphere. In this work, SiC phase presented the stacking faults in the structure, being not possible to calculate the unit cell size, symmetry and bond lengths but it seem equal card number 29-1129 of JCPDS.

Optical properties of boron-doped Si nanowires

Raman scattering and photoluminescence (PL) of boron-doped silicon nanowires have been investigated. Raman spectra showed a band at 480 cm(-1), indicating that the crystallinity of the nanowires was suppressed by boron doping. PL taken from B-doped SiNWS at room temperature exhibited three distinct emission peaks at 1.34, 1.42. and 1.47 eV and the PL intensity was much stronger than that of undoped SiNWS. The increased PL intensity should be very profitable for nano-optoelectronics. (C) 2004 Elsevier B.V. All rights reserved.

Microstructure characterization of transition films from amorphous to nanocrocrystalline silicon

Hydrogenated silicon (Si:H) films near the threshold of crystallinity were prepared by very high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) using a wide range of hydrogen dilution R-H = [H-2]/[SiH4] values of 2-100. The effects of H dilution R-H on the structural properties of the films were investigated using micro-Raman scattering and Fourier transform infrared (FTIR) absorption spectroscopy. The obtained Raman spectra show that the H dilution leads to improvements in the short-range order and the medium-range order of the amorphous network and then to the morphological transition from amorphous to crystalline states. The onset of this transition locates between R-H = 30 and 40 in our case, and with further increasing R-H from 40 to 100, the nanocrystalline volume fraction increases from similar to23% to 43%, and correspondingly the crystallite size enlarges from similar to2.8 to 4.4 nm. The FTIR spectra exhibit that with R-H increasing, the relative intensities of both the SiH stretching mode component at 2100 cm(-1) and wagging mode component at 620 cm(-1) increase in the same manner. We assert that these variations in IR spectra should be associated with the formation of paracrystalline structures in the low H dilution films and nanocrystalline structures in the high H dilution films. (C) 2003 Elsevier Science B.V. All rights reserved.

Photoluminesfcence of Er-doped SiO2 films containing Si nanocrystals and Er

Correlations between Si nanocrystal (nc-Si) related photoluminescence (PL), Er3+ emission and nonradiative defects in the Er-doped SiO2 films containing nc-Si (SRSO) are studied. Upon 514.5 nm laser excitation the erbium-doped SRSO samples exhibit PL peaks at around 0.8 and 1.54 mum, which can be assigned to the electron-hole recombination in nc-Si and the intra-4f transition in Er3+, respectively. With increasing Er3+ content in the films, Er3+ emission becomes intense while the PL at 0.8 mum decreases, suggesting a strong coupling of nc-Si and Er 31 ions. Hydrogen plasma treatment for the samples improve the PL intensities of the 0.8 and 1.54 mum bands, indicating H passivation for the nonradiative defects existing in the samples. Further-more, from the effect of hydrogen treatment for the samples, we observe variation of the number of nonradiative defects with annealing temperatures. (C) 2003 Elsevier Science B.V. All rights reserved.

Silicon nanowires grown on a pre-annealed Si substrate

Polycrystalline Si nanowires (poly SiNWS) were successfully synthesized by plasma-enhanced chemical vapor deposition (PECVD) at 440degreesC using silane as the Si source and Au as the catalyst. The diameters of Si nanowires range from 15 to 100nm. The growth process indicates that to fabricate SiNWS by PECVD, pre-annealing at high temperature is necessary. A few interesting nanowires with Au nanoclusters uniformly distributed in the body of the wire were also produced by this technique. (C) 2002 Elsevier Science B.V. All rights reserved.

Comprehensive analysis of microtwins in the 3C-SiC films on Si(001) substrates

Microtwins in the 3C-SiC films grown on Si(0 0 1) by atmosphere pressure chemical vapor deposition (APCVD) were investigated in detail using X-ray four-circle diffractometry. The Phi scan shows that 3C-SiC films can grow on Si substrates epitaxially and epitaxial relationship is revealed as (0 0 1)(3C) (SiC)parallel to (0 0 1)(Si),[1 1 1](3C-SiC)parallel to [1 1 1](Si). Other diffraction peaks at about 15.8 degrees in x emerged in the pole figures of the (I 1 1) 3C-SiC. We performed the pole figure of (1 0 (1) over bar 0)h-SiC and the reciprocal space mapping from the (1 1 1) reciprocal lattice point of base SiC to the (0 0 2) point of microtwin for the first time, indicating that the diffraction peaks at 15.8 degrees in x result from not hexagonal SiC but microtwins of 3C-SiC, and twin inclusions are estimated to be around 1%. (C) 2001 Published by Elsevier Science B.V.

Photoluminescence and Raman scattering correlated study of boron-doped silicon nanowires

Boron-doped (B-doped) silicon nanowires (SiNWS) have been prepared and characterized by Raman scattering and photoluminescence (PL). B-doped SiNWS were grown by plasma enhanced chemical vapor deposition (PECVD), using diborane (B2H6) as the dopant gas. Raman spectra show a band at 480cm(-1),which is attributed to amorphous silicon. Photoluminescence at room temperature exhibits three distinct emission peaks at 1.34ev, 1.42ev, 1.47ev. Possible reason for these is suggested.

Self-organization and dynamics of nanoparticles in chemically active plasmas for low-temperature deposition of silicon and carbon-based nanostructured films

Self-organization and dynamic processes of nano/micron-sized solid particles grown in low-temperature chemically active plasmas as well as the associated physico-chemical processes are reviewed. Three specific reactive plasma chemistries, namely, of silane (SiH4), acetylene (C 2H2), and octafluorocyclobutane (c-C4F 8) RF plasma discharges for plasma enhanced chemical vapor deposition of amorphous hydrogenated silicon, hydrogenated and fluorinated carbon films, are considered. It is shown that the particle growth mechanisms and specific self-organization processes in the complex reactive plasma systems are related to the chemical organization and size of the nanoparticles. Correlation between the nanoparticle origin and self-organization in the ionized gas phase and improved thin film properties is reported. Self-organization and dynamic phenomena in relevant reactive plasma environments are studied for equivalent model systems comprising inert buffer gas and mono-dispersed organic particulate powders. Growth kinetics and dynamic properties of the plasma-assembled nanoparticles can be critical for the process quality in microelectronics as well as a number of other industrial applications including production of fine metal or ceramic powders, nanoparticle-unit thin film deposition, nanostructuring of substrates, nucleating agents in polymer and plastics synthesis, drug delivery systems, inorganic additives for sunscreens and UV-absorbers, and several others. Several unique properties of the chemically active plasma-nanoparticle systems are discussed as well.