Si Radicals Research Articles

Synthesis of MeBICAAC Supported Si(III) Radicals and a Silylone via Reduction Route From MeBICAAC-Si(IV) Precursors.

Past one decade has witnessed a tremendous growth in the field of carbene stabilized low-valent silicon compounds unravelling very exciting properties of these molecules. Herein, we have employed a bicyclic (alkyl)(amino)carbene, (MeBICAAC) to explore the low-valent chemistry of silicon. The reduction of bicyclic (alkyl)(amino)carbene-SiCl4 complex, [(MeBICAAC)SiCl4] (1) with KC8 afforded low-valent Si complexes, including Si(III) radical [(MeBICAAC)SiCl3] (2) and a complex with silicon center in a formal zero-valent state, [(MeBICAAC)2Si] (3). Similarly, the reduction of in-situ generated MeBICAAC adduct of Me2SiCl2 with one equivalent of KC8 led to the formation of [(MeBICAAC)SiMe2Cl] (4) complex having an unpaired electron. These complexes have been characterized by IR, UV-Vis., NMR, HRMS, EPR and their solid-state structures were also elucidated by single crystal X-ray crystallography. Further, DFT calculations revealed the lower energy singlet state for complexes 1, 3 and doublet state for complexes 2, 4.

Silicon Radical-Induced CH4 Dissociation for Uniform Graphene Coating on Silica Surface.

Due to the manufacturability of highly well-defined structures and wide-range versatility in its microstructure, SiO2 is an attractive template for synthesizing graphene frameworks with the desired pore structure. However, its intrinsic inertness constrains the graphene formation via methane chemical vapor deposition. This work overcomes this challenge by successfully achieving uniform graphene coating on a trimethylsilyl-modified SiO2 (denote TMS-MPS). Remarkably, the onset temperature for graphene growth dropped to 720°C for the TMS-MPS, as compared to the 885°C of the pristine SiO2. This is found to be mainly from the Si radicals formed from the decomposition of the surface TMS groups. Both experimental and computational results suggest a strong catalytic effect of the Si radicals on the CH4 dissociation. The surface engineering of SiO2 templates facilitates the synthesis of high-quality graphene sheets. As a result, the graphene-coated SiO2 composite exhibits a high electrical conductivity of 0.25Scm-1. Moreover, the removal of the TMP-MPS template has released a graphene framework that replicates the parental TMS-MPS template on both micro- and nano- scales. This study provides tremendous insights into graphene growth chemistries as well as establishes a promising methodology for synthesizing graphene-based materials with pre-designed microstructures and porosity.

Reactive Force Field Molecular Dynamics Study of the Effects of Gaseous Species on the Composition and Crystallinity of Silicon–Germanium Thin Films

We simulated the growth of a silicon–germanium (SiGe) film using reactive force field molecular dynamics (ReaxFF MD) in combinations of SiH3, SiH2, GeH3, and GeH2 radicals to evaluate the effects of gaseous species on thin-film composition and crystallinity and to understand the growth mechanisms. The film compositions could be estimated in these combinations because of the linear increase in the Ge content of the films. The average crystallinity grown by SiH3 was higher than that by SiH2 radicals. The crystallinity of the film grown by SiH3 radicals tends to be drastically decreased by GeH2 radicals. The growth mechanisms for XH3 and XH2 (X = Si or Ge) radicals were compared. XH3 radicals abstracted surface H atoms, and then more XH3 radicals chemisorbed onto the formed dangling bonds, resulting in film growth through a two-step reaction known as the Eley–Rideal-type (ER-type) mechanism. The ER-type mechanism grows the film with a low hydrogen content and high crystallinity. In contrast, XH2 radicals displayed not only the ER-type mechanism but also a one-step reaction, the H-capturing mechanism, which incorporates surface H atoms into the gaseous species. The H-capturing mechanism results in film growth with high hydrogen content and low crystallinity. The growth mechanisms are influenced by high/low H-coverage. The surface H atoms thermally move around the bonded atoms and give their kinetic energy to the diffusing gaseous species. Excess surface H atoms promote desorption. Our results from the ReaxFF MD suggested experimental settings and conditions that would enable the growth of high-quality films. Our results also suggested that SiH3 and GeH3 radicals should be mainly generated in the gas phase for high-quality SiGe film growth.

Aeolian driven silicate comminution unlikely to be responsible for the rapid loss of martian methane

Seasonally varying levels of methane have been measured at parts per billion by volume levels in the lower Martian atmosphere. The source of this methane is not understood, but equally intriguing is its rapid loss, which is higher than the current chemical or photochemical decomposition models suggest. This implies an unknown but efficient sink mechanism. Earlier investigations reported the formation of Si• during the comminution of borosilicate glass and quartz that permitted the uptake of methane. This led to the speculation that an analogous aeolian driven comminution of Si-rich minerals on Mars could similarly sequestrate atmospheric methane. However, borosilicate glass is an artificial material and crystalline quartz is not common on the surface of Mars. To investigate whether this mechanism could take place on materials that were more representative of those on Mars, we comminuted a set of Mars analogue silicate rocks/minerals (basalt, obsidian, feldspar, pyroxene, zeolite, opal) in the presence of 13C-labeled methane. Solid-state Nuclear Magnetic Resonance (NMR) analysis of borosilicate glass and quartz indicated silicon carbide bond formation and this observation was supported by attenuated total reflectance-Fourier transform infra-red spectroscopy and X-ray photoelectron spectroscopy. However, silicon carbide bonds and methane sequestration were not detected in our set of Mars analogue samples. We hypothesise that electron donation by redox-active elements within the analogue materials, such as Fe, may have suppressed Si-methyl bond formation during comminution. Aeolian driven Si radical formation appears unlikely to be responsible for the rapid loss of methane in the Martian atmosphere, and thus the methane sink mechanism(s) require further investigation.

Pulmonary Toxicity of Nine Sand Dusts Generated at Hydraulic Fracturing Sites in Comparison to Respirable Crystalline Silica

The levels of respirable crystalline silica (RCS) at gas wells employing hydraulic fracturing (fracking) sites have been reported to exceed regulatory standards. Inhalation of RCS in work places may cause silicosis and other diseases in workers. While the effects of inhalation of RCS in humans and animal models has been well‐characterized, the pulmonary hazards to worker associated with RCS inhaled at fracking sites has not been investigated. In this study, nine fracking sand dusts(FSDs) collected by vacuum dust controls from different fracking sites in the US were compared to MIN‐U‐SIL 5® (MIN) with respect to particle size, mineral composition, Si radicals and pulmonary toxicity. Chemical analysis revealed that total mineral content of the FSDs other than Si ranged widely from 9.9 g/kg to 32.5 g/kg when compared to 1.4 g/kg for MIN. This heterogeneity was confirmed by energy‐dispersive X‐ray spectroscopy (EDS). Hydrodynamic particle diameter of neat FSDs using dynamic light scattering (DLS) indicated non‐concordant, mono‐ orbi‐modal spectral distributions of particle sizes; the spectrum for MIN was mono‐modal. Electron paramagnetic resonance (EPR) analysis indicated the presence of the Si radical in MIN but not in neat FSDs. After incubating the FSDs in water the Si radical was revealed in some samples, indicating occlusion of the radical in neat FSDs. To examine pulmonary toxicity, rats were intratracheally instilled with a single dose of FSD or MIN (159 or 500 μg/rat), or vehicle. Thirty days later, bronchoalveolar lavage (BAL) was performed to assess the development of pulmonary inflammatory responses: changes in lactate dehydrogenase (LDH) and differential cell counts. This time point has been shown previously to be one at which pre‐silicotic responses to MIN are observed. As expected, MIN elicited a dose‐dependent increase in LDH levels, total BAL cells, and total alveolar macrophages, polymorphonuclear lymphocytes and eosinophils. As a group, the FSDs did not elicit these responses. These findings indicate that, in many respects, the chemical and biophysical characteristics, and the biological effects of the FSDs and MIN after intratracheal instillation, have distinct differences.Support or Funding InformationNIOSH 6927ZLDC

Thermal Stability of Organic Monolayers Grafted to Si(111): Insights from ReaxFF Reactive Molecular Dynamics Simulations.

We used the ReaxFF reactive molecular dynamics simulations to investigate the chemical mechanisms and kinetics of thermal decomposition processes of silicon surfaces grafted with different organic molecules via Si-C bonds at atomistic level. In this work, we considered the Si(111) surface grafted with n-alkyl (ethyl, propyl, pentyl, and decyl) layers in 50% coverage and, Si-CH3, Si-CCCH3 and Si-CHCHCH3 layers in full coverage. Si radicals primarily formed by the homolytic cleavage of Si-C bonds play a key role in the dehydrogenation processes that lead to the decomposition of the monolayers. Contrary to commonly proposed mechanisms that only involve a single Si atom center, we found that the main decomposition pathways require two Si lattice atoms to proceed. The ability of surface silyl radicals to dehydrogenate the organic molecules depends on the flexibility of the carbon backbones of the organic molecules as well as on the C-H bond strength. The dehydrogenation of n-alkyl chains mainly involves the H atoms of the β-carbon (leading to 1-alkene desorption). However, as the surface coverage decreases, the flexibility of the alkyl chains allows for the dehydrogenation of any methylene group and even the terminal methyl group of the long decyl layer. On the contrary, the rigid carbon backbone of the Si-CCCH3 and Si-CHCHCH3 moieties hinders the dehydrogenation of the terminal methyl group, which confers these layers a higher thermal stability. For all layers, the surface ends up mostly hydrogenated as Si-C bonds break and new Si-H bonds are formed during the dehydrogenation reactions.

Nanoscale Silicon as a Catalyst for Graphene Growth: Mechanistic Insight from in Situ Raman Spectroscopy

Nanoscale carbons are typically synthesized by thermal decomposition of a hydrocarbon at the surface of a metal catalyst. Whereas the use of silicon as an alternative to metal catalysts could unlock new techniques to seamlessly couple carbon nanostructures and semiconductor materials, stable carbide formation renders bulk silicon incapable of the precipitation and growth of graphitic structures. Here, we provide evidence supported by comprehensive in situ Raman experiments that indicates nanoscale grains of silicon in porous silicon (PSi) scaffolds act as catalysts for hydrocarbon decomposition and growth of few-layered graphene at temperatures as low as 700 K. Self-limiting growth kinetics of graphene with activation energies measured between 0.32–0.37 eV elucidates the formation of highly reactive surface-bound Si radicals that aid in the decomposition of hydrocarbons. Nucleation and growth of graphitic layers on PSi exhibits striking similarity to catalytic growth on nickel surfaces, involving temperat...

Spatially resolved flame zone classification of a flame spray nanoparticle synthesis process by combining different optical techniques

Flame spray synthesis of silica nanoparticles is characterized by a set of complementary optical techniques. By means of laser-sheet based Mie scattering imaging, 2D-chemiluminescence imaging and coherent anti-Stokes Raman spectroscopy (CARS) local information on spatial droplet distribution, combustion zone, nucleation zone and temperature in the flame could be obtained. In addition, the outcomes from optical metrology are validated by thermophoretic sampling at different flame heights and the synthesized powders were analyzed by N2 gas sorption. By comparing these results the flame can be quantitatively classified into three distinct zones: (i) the droplet zone where precursor atomization and evaporation take place, (ii) the nucleation zone indicated by SiO⁎/Si⁎ radicals as a preliminary species before SiO2 particle formation and (iii) the sintering zone characterized by the highest temperatures in flame. In addition the spatial spreading of the nucleation zone as a function of precursor concentration is investigated. Theoretical calculations and experimental results show an extended nucleation regime for the lowest precursor concentration compared to higher concentrations. Although this study is performed with hexamethyldisiloxane (HMDS) precursor to synthesize silica nanoparticles as a model system, dimensionless analysis shows that the results, concerning the spray formation, can be transferred to the synthesis of other materials as well.

Remarkable enhancement of pyrolytic carbon deposition on ordered mesoporous silicas by their trimethylsilylation

We propose a novel and simple method to uniformly deposit a thin carbon layer on the pore walls in mesoporous silica (MPS) by the chemical vapor deposition (CVD) at as low a temperature as 600°C. Four types of MPSs (FSM16, SBA15, TMPS16 and MCM41) were trimethylsilylated and then the silylated MPSs were subjected to the CVD using acetylene. Thanks to the silylation, pyrolytic carbon deposition was significantly enhanced, although only little carbon deposition occurred on the non-silylated MPSs. It is found from the analyses of the former three types of MPSs that the carbon was deposited solely on the mesopore surface as a very thin layer and thereby the carbon-coated MPSs still keep a high surface area and a large pore volume with their mesopore structures intact. The decomposition of the trimethylsilyl groups during the CVD resulted in the formation of Si radicals on the silica surface and their catalysis can explain the observed uniform carbon coating, i.e., the radicals catalyze the trimerization of acetylene to form benzene and induce the carbonization on the silica surface. This mechanism allows the carbonization to occur only on the silica surface and the uniform carbon deposition was achieved as a result.

Characteristics of Silicon Nanoparticles Depending on H2 Gas Flow During Nanoparticle Synthesis via CO2 Laser Pyrolysis

Silicon nanoparticle is a promising material for electronic devices, photovoltaics, and biological applications. Here, we synthesize silicon nanoparticles via <TEX>$CO_2$</TEX> laser pyrolysis and study the hydrogen flow effects on the characteristics of silicon nanoparticles using high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and UV-Vis-NIR spectrophotometry. In <TEX>$CO_2$</TEX> laser pyrolysis, used to synthesize the silicon nanoparticles, the wavelength of the <TEX>$CO_2$</TEX> laser matches the absorption cross section of silane. Silane absorbs the <TEX>$CO_2$</TEX> laser energy at a wavelength of <TEX>$10.6{\mu}m$</TEX>. Therefore, the laser excites silane, dissociating it to Si radical. Finally, nucleation and growth of the Si radicals generates various silicon nanoparticle. In addition, researchers can introduce hydrogen gas into silane to control the characteristics of silicon nanoparticles. Changing the hydrogen flow rate affects the nanoparticle size and crystallinity of silicon nanoparticles. Specifically, a high hydrogen flow rate produces small silicon nanoparticles and induces low crystallinity. We attribute these characteristics to the low density of the Si precursor, high hydrogen passivation probability on the surface of the silicon nanoparticles, and low reaction temperature during the synthesis.

Silylboranes as New Sources of Silyl Radicals for Chain‐Transfer Reactions

Various silylboranes, which were outfitted with a catecholborane moiety at one end and a (Me(3)Si)(3)Si moiety at the other end of a carbon chain, were prepared through the hydroboration of the corresponding unsaturated silanes. The C-centered radical species generated from these silylboranes efficiently cyclized to provide, through a 5-exo intramolecular homolytic substitution at the silicon center, the corresponding silacycle and a Me(3)Si radical that was subsequently trapped by sulfonyl acceptors. These cyclizations proceeded at unprecedented rates, due, in part, to a strong gem-dialkyl effect that was attributable to the presence of bulky substituents on a quaternary center located on the chain. In parallel, we designed arylsilylboranes that produced silyl radicals through a 1,5-hydrogen transfer. Such silyl radicals may be valuable radical chain carriers, for instance, in oximation reactions of alkyl halides. Finally, computational studies allowed calculation of activation barriers of the homolytic substitution step and additionally illustrated that the overall reaction mechanism involved a transition state in which the attacking carbon center, the central silicon atom, and the Me(3)Si leaving group were collinear.

Mimicking the Silicon Surface: Reactivity of Silyl Radical Cations toward Nucleophiles

Radical cations of selected low molecular-weight silicon model compounds were obtained by photoinduced electron transfer. These radical cations react readily with a variety of nucleophiles, regularly used in monolayer fabrication onto hydrogen-terminated silicon. From time-resolved kinetics, it was concluded that the reactions proceed via a bimolecular nucleophilic attack to the radical cation. A secondary kinetic isotope effect indicated that the central Si-H bond is not cleaved in the rate-determining step. Apart from substitution products, also hydrosilylation products were identified in the product mixtures. Observation of the substitution products, combined with the kinetic data, point to an bimolecular reaction mechanism involving Si-Si bond cleavage. The products of this nucleophilic substitution can initiate radical chain reactions leading to hydrosilylation products, which can independently also be initiated by dissociation of the radical cations. Application of these data to the attachment of organic monolayers onto hydrogen-terminated Si surfaces via hydrosilylation leads to the conclusion that the delocalized Si radical cation (a surface-localized hole) can initiate the hydrosilylation chain reaction at the Si surface. Comparison to monolayer experiments shows that this reaction only plays a significant role in the initiation, and not in the propagation steps of Si-C bond making monolayer formation.

High-Rate Deposition of Amorphous Silicon Films by Microwave-Excited High-Density Plasma

In this study, the deposition of amorphous silicon (a-Si) thin films using a microwave-excited high-density plasma system is described. We investigate the effects of plasma excitation gas species (argon or helium), total gas pressure, silane (SiH4) flow rate, and substrate stage temperature, estimating the resultant films from cross-sectional morphology, photoconductivity, and dark conductivity measured without light-induced degradation. It is confirmed that high-quality a-Si films (photosensitivity= 1.29 ×106) can be formed in the plasma excitation gas helium at a pressure of 13.3 Pa by relatively high rate (1.1 nm/s) deposition. At the same time, we measure the plasma emission derived from various radicals such as Si and SiH radicals in order to discuss the mechanism of radical generation in the plasma. The result of the measurement implies that when argon is used as plasma excitation gas, metastable states of argon markedly dissociate silane, which produces low-quality a-Si films. On the other hand, it seems that electrons dissociate silane mainly, which produces high-quality a-Si films, in helium.

Hot-wire chemical vapor deposition of epitaxial film crystal silicon for photovoltaics

We have demonstrated that hot-wire chemical vapor deposition (HWCVD) is an excellent technique to produce high-quality epitaxial silicon at high rates, at substrate temperatures from 620 to 800 °C. Fast, scalable, inexpensive epitaxy of high-quality crystalline Si (c-Si) in this temperature range is a key element in creating cost-competitive film Si PV devices on crystalline seed layers on inexpensive substrates such as display glass and metal foil. We have improved both the quality and rate of our HWCVD Si epitaxy in this display-glass-compatible T range. We understand factors critical to high-quality epitaxial growth and obtain dislocation densities down to 6 × 10 4 cm −2 by techniques that reduce the surface oxygen contamination at the moment growth is initiated. We have also developed and validated a model of the HWCVD silicon growth rate, based on fundamentals of reaction chemistry and ideal gas physics. This model enables us to predict growth rates and calculate the sticking coefficient of the Si radicals contributing to film formation between 300 and 800 °C. We obtain efficiencies up to 6.7% with a 2.5-micron absorber layer grown on heavily-doped ‘dead’ Si wafers although these cells still lack hydrogenation and light trapping. Open-circuit voltages up to 0.57 V are obtained on 2-μm cells. Efficient film crystal silicon photovoltaics will require dislocation spacing more than 6 times the cell thickness, or else effective H passivation of the dislocations.

Intermediate Gas Phase of CH4/[Si(CH3)2O]5 Plasma and Its Effect on Structure of SiCOH Film

This paper investigated the radical behaviour of the plasma of a mixture of methane (CH4) and decamethylcyclopentasiloxane (DMCPS) by optical emission spectroscopy. The plasma was generated by electron cyclotron resonance (ECR) discharge and was used for depositing porous SiCOH low dielectric-constant film. In the ECR discharge plasma, CH, H, H2, C2, Si, O and SiO radicals were obtained. The CH, H and C2 radicals were from the dissociation of CH4, while the SiO, Si and O radicals from the dissociation of the Si-O chain. CHx radicals absorbed in the film were thermally unstable and could be removed by annealing. The dissociation of the Si-O chain led to an increase in a ratio of the Si-Ocage to Si-Onetwork. The removed of CHx radicals and the increased Si-Ocage to Si-Onetwork ratio were beneficial for reducing the film density and dielectric constant.

Effect of NH 3 flow rate on growth, structure and luminescence of amorphous silicon nitride films by electron cyclotron resonance plasma

In this paper, hydrogenated amorphous silicon nitride (a-SiN x :H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effect of NH 3 flow rate R on the deposition rate, structure and luminescence were studied using various techniques such as optical emission spectroscopy, Fourier Transform Infrared absorption (FTIR), X-ray photoelectron spectroscopy (XPS) and fluoro-spectroscopy, respectively. Optical emission behavior of SiH 4 + NH 3 plasma shows that atomic Si radical concentration determines the film deposition rate. Structural transition of a-SiN x film from Si-rich one to near-stoichiometric/N-rich one with R was revealed by FTIR and the two phase separation of a-Si and a-Si 3N 4 was also convinced in Si-rich SiN x films by XPS. Either photo- or electroluminescence for all the SiN x films with R > 3 sccm shows a strong light emission in visible light wavelength range. As R < 6 sccm, recombination of electrons and holes in a-Si quantum dots is the main mechanism of photo/electroluminescence for Si-rich SiN x films, however, for photoluminescence, gap states' luminescence is also in competition; as R > 6 sccm, light emission of the SiN x film originates from defect states in its band gap.

Spatial distribution of SiCl n ( n =0–2) in SiCl 4 plasma measured by mass spectroscopy

For a better understanding of the deposition mechanism of thin films in SiCl4 source gas, we have measured the spatial distributions of SiCln (n=0–2) radicals in SiCl4 radio frequency glow discharge plasma utilizing a mass spectrometer equipped with a movable gas sampling apparatus. The experimental results demonstrate that the relative densities of SiCln (n=0–2) radicals have peak values at the position of 10 mm above the powered electrode along the axial direction; the relative densities of the Si and SiCln (n=1, 2) radicals have peak values at the positions of 27 mm and 7 mm away from the axis along the radial direction, respectively. Generally speaking, in the whole SiCl4 plasma bulk region, the relative density of Si is one order of magnitude higher than that of SiCl, and the relative density of SiCl is several times higher than that of SiCl2. This reveals that Si and SiCl may be the primary growth precursors in forming thin films.

Topology-symmetry analysis of the mixed frameworks in the structures of phosphates, germanates, gallates, and silicates based on fundamental building blocks

A topology-symmetry analysis is performed for a number of phosphate, silicate, and germanate (gallate) structures. The fundamental structural unit of these structures is an {M(TO4)6} block consisting of the central octahedron sharing vertices with six tetrahedra. It is shown that, in the germanate, silicate, and gallate structures, the blocks are joined either through common vertices of the terminal tetrahedra or through additional Ge, Si, or Ga tetrahedra attached to the terminal tetrahedra with the formation of three-membered and six-membered rings or chains depending on the symmetry operations relating the blocks, i.e., with the formation of Ge, Si, or Ga tetrahedral radical anions. In the phosphate structures, the blocks are joined together only by sharing terminal tetrahedra in the neighboring blocks. This is caused by the higher charge of the P5+ central cation in the tetrahedron and by electrostatic interactions.

Detecting free radicals during the hot wire chemical vapor deposition of amorphous silicon carbide films using single-source precursors

A vacuum ultraviolet single photon ionization technique has been used to probe gas-phase species important in the hot wire chemical vapor deposition (HW-CVD) of amorphous silicon carbide(a-SiC:H) films using different single-source precursors. This study focuses on monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and 1,1-dimethyl-1-silacyclobutane, and the reactions of these precursors on tungsten and rhenium filaments between 1000 and 1950°C. Silane is also considered for comparison. Si radicals are found to be major products of hot wire decomposition for all the organosilicon precursors; CH3 is also observed. C and H radicals are expected to be produced as well but are not detected at the ionization energy used in these experiments. Within the series of methylsilanes, the reaction rate on the filament is found to decrease with increasing number of methyl groups on the precursor. We propose a model in which Si–H bonds are cleaved with lower activation barriers than Si–CH3 bonds as the molecule adsorbs onto the hot metal surface. 1,1-dimethyl-1-silacyclobutane produces Si with a lower apparent activation energy than the other molecules. Coverage-dependent reaction pathways are proposed to play a role in the temperature profile of CH3 generation. Infrared spectra of films deposited by HW-CVD show that the film composition and growth rate for the different precursors correlate with the hot wire chemistry studied by single photon ionization.

Prediction of radio frequency power effect on silicon nitride deposition using a genetic algorithm based neural network

Deposition rate of silicon nitride films was modelled using a neural network in conjunction with Box—Wilson experimental design. The films were deposited by a plasma enhanced chemical vapour deposition system. A neural network model was constructed and tested with 33 and 12 experiments respectively. Model prediction performance was significantly improved by applying genetic algorithm to training factor optimisation. To qualitatively estimate deposition mechanisms with the parameters, several plots were generated from the model and emphasis was placed on the investigation of the radio frequency power effect on the deposition rate under various plasma conditions. An increase in the deposition rate with increasing power was ascribed to more Si deposition near the reaction surface. The SiH4 effect was the most complex depending on the powers. In contrast, the power effect was insensitive to the variations in N2 flow rate. The power effect at high pressure was attributed to increased concentration of Si radicals in the gas phase. A comparison with a refractive index model facilitated to infer deposition mechanisms.