Study on stability of hydrogenated amorphous silicon films

Hydrogenated amorphous silicon （a-Si：H） films with high and same order of magnitude photosensitivity （-10^5） but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content （CH） as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si：H films. We used hydrogen elimination model to explain our experimental results.

Semi-quantitative study on the Staebler-Wronski effect of hydrogenated amorphous silicon films prepared with HW-ECR-CVD system

The method of numerical simulation is used to fit the relationship between the photoconductivity in films and the illumination time. The generation and process rule of kinds of different charged defect states during illumination are revealed. It is found surprisingly that the initial photoconductivity determines directly the total account of photoconductivity degradation of sample.

Smooth Surface Morphology of Hydrogenated Amorphous Silicon Film Prepared by Plasma Enhanced Chemical Vapor Deposition

Influence of the parameters of plasma enhanced chemical vapor deposition （PECVD） on the surface morphology of hydrogenated amorphous silicon （α-Si：H） film was investigated. The root-mean-square （RMS） roughness of the film was measured by atomic force microscope （AFM） and the relevant results were analyzed using the surface smoothing mechanism of film deposition. It is shown that an α-Si：H film with smooth surface morphology can be obtained by increasing the PH3/N2 gas flow rate for 10% in a high frequency （HF） mode. For high power, however, the surface morphology of the film will deteriorate when the Sill4 gas flow rate increases. Furthermore, optimized parameters of PECVD for growing the film with smooth surface were obtained to be Sill4：25 sccm （standard cubic centimeters per minute）, At： 275 sccm, 10%PH3/N2：2 sccm, HF power： 15 W, pressure： 0.9 Torr and temperature： 350℃. In addition, for in thick fihn deposition on silicon substrate, a N20 and NH3 preprocessing method is proposed to suppress the formation of gas bubbles.

Achieving Negatively Charged Pt Single Atoms on Amorphous Ni(OH)_(2)Nanosheets with Promoted Hydrogen Absorption in Hydrogen Evolution

Single-atom(SA)catalysts with nearly 100%atom utilization have been widely employed in electrolysis for decades,due to the outperforming catalytic activity and selectivity.However,most of the reported SA catalysts are fixed through the strong bonding between the dispersed single metallic atoms with nonmetallic atoms of the substrates,which greatly limits the controllable regulation of electrocatalytic activity of SA catalysts.In this work,Pt-Ni bonded Pt SA catalyst with adjustable electronic states was successfully constructed through a controllable electrochemical reduction on the coordination unsaturated amorphous Ni(OH)_(2)nanosheet arrays.Based on the X-ray absorption fine structure analysis and first-principles calculations,Pt SA was bonded with Ni sites of amorphous Ni(OH)_(2),rather than conventional O sites,resulting in negatively charged Pt^(δ-).In situ Raman spectroscopy revealed that the changed configuration and electronic states greatly enhanced absorbability for activated hydrogen atoms,which were the essential intermediate for alkaline hydrogen evolution reaction.The hydrogen spillover process was revealed from amorphous Ni(OH)_(2)that effectively cleave the H-O-H bond of H_(2)O and produce H atom to the Pt SA sites,leading to a low overpotential of 48 mV in alkaline electrolyte at-1000 mA cm^(-2)mg^(-1)_(Pt),evidently better than commercial Pt/C catalysts.This work provided new strategy for the control-lable modulation of the local structure of SA catalysts and the systematic regulation of the electronic states.

Amorphous Iridium Oxide-Integrated Anode Electrodes with Ultrahigh Material Utilization for Hydrogen Production at Industrial Current Densities

Herein,ionomer-free amorphous iridium oxide(IrO_(x))thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells(PEMECs)via low-cost,environmentally friendly,and easily scalable electrodeposition at room temperature.Combined with a Nafion 117 membrane,the IrO_(x)-integrated electrode with an ultralow loading of 0.075 mg cm^(-2)delivers a high cell efficiency of about 90%,achieving more than 96%catalyst savings and 42-fold higher catalyst utilization compared to commercial catalyst-coated membrane(2 mg cm^(-2)).Additionally,the IrO_(x)electrode demonstrates superior performance,higher catalyst utilization and significantly simplified fabrication with easy scalability compared with the most previously reported anodes.Notably,the remarkable performance could be mainly due to the amorphous phase property,sufficient Ir^(3+)content,and rich surface hydroxide groups in catalysts.Overall,due to the high activity,high cell efficiency,an economical,greatly simplified and easily scalable fabrication process,and ultrahigh material utilization,the IrO_(x)electrode shows great potential to be applied in industry and accelerates the commercialization of PEMECs and renewable energy evolution.

Room Temperature Growth of Hydrogenated Amorphous Silicon Films by Dielectric Barrier Discharge Enhanced CVD

Hydrogenated amorphous silicon （a-Si： H） films were deposited on Si （100） and glass substrates by dielectric barrier discharge enhanced chemical vapour deposition （DBD-CVD） in （SiH4＋H2） atmosphere at room temperature. Results of the thickness measurement, SEM （scanning electron microscope）, Raman, and FTIR （Fourier transform infrared spectroscopy） show that with the increase in the applied peak voltage, the deposition rate and network order of the films increase, and the hydrogen bonding configurations mainly in di-hydrogen （Si-H2） and poly hydrogen （SiH2）n are introduced into the films. The UV-visible transmission spectra show that with the decrease in SiH4/ （SiHn＋H2） the thin films＇ band gap shifts from 1.92 eV to 2.17 eV. These experimental results are in agreement with the theoretic analysis of the DBD discharge. The deposition of a-Si： H films by the DBD-CVD method as reported here for the first time is attractive because it allows fast deposition of a-Si： H films on large-area low-melting-point substrates and requires only a low cost of production without additional heating or pumping equipment.

Characteristics of Disorder and Defect in Hydrogenated Amorphous Silicon Nitride Thin Films Containing Silicon Nanograins

The hydrogenated amorphous silicon nitride （SiNx） thin films embedded with nano-structural silicon were prepared and the micro- structures at the interface of silicon nano-grains/SiNx were identified by the optical absorption and Raman scattering measurements. Characterized by the exponential tail of optical absorption and the band-width of the Raman scattering TO mode, the disorder in the interface region increases with the gas flow ratio increasing. Besides, as reflected by the sub-gap absorption coefficients, the density of interface defect states decreases, which can be attributed to the structural mismatch in the interface region and also the changes of hydrogen content in the deposited films. Additional annealing treatment results in a significant increase of defects and degree of disorder, for which the hydrogen out-diffusion in the annealing process would be responsible.

Positive Magnetoresistance in Hydrogenated Amorphous Alloys Silicon Nickel a-Si_1-yNiy:H at Very Low Temperature with Magnetic Field

We present results of an experimental study of magnetoresistance phenomenon in an amorphous silicon-nickel alloys a-Si1-yNiy:H:H (where y = 0.23) on the insulating side of the metal-insulator transition (MIT) in presence of magnetic field up to 4.5 T and at very low temperature. The electrical resistivity is found to follow the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T -1/2. This behaviour indicates the existence of the Coulomb gap (CG) near the Fermi level.

Variable Range Hopping in Hydrogenated Amorphous Silicon-Nickel Alloys

On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on the electrical transport in amorphous silicon-nickel alloys a-Si1-yNiy:H exhibits that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2. This behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature TC, we obtained the Mott Variable Range Hopping regime with T-1/4, indicating that the DOS becomes almost constant in the vicinity of the Fermi level. The critical temperature TC decreases with nickel content in the alloys.

Effect of Additives on the Sintering of Amorphous Nano-sized Silicon Nitride Powders

Amorphous nano-sized silicon nitride powders were sintered by liquid phase sintering. The influences of the additives of Y2O3 and Al2O3 prepared by two different ways, the polyacrylamide gel method and the precipitation method, were investigated. The grain sizes of the additives prepared by the first method were finer than those of prepared by the latter method. When sintered at the same temperature, 1700 ℃, the average grain size of the silicon nitride is 0.3 um for the sample with the former additives, which is much finer than the one with the latter additives. The density of additives prepared by precipitation method is clearly lower than those of prepared by polyacrylamide gel method.

Influence of the deposition parameters on the transition region of hydrogenated silicon films growth

Hydrogenated microcrystalline and amorphous silicon thin films were prepared by very high frequency plasmaenhanced chemical vapour deposition （VHF PECVD） by using a mixture of silane and hydrogen as source gas. The influence of deposition parameters on the transition region of hydrogenated silicon films growth was investigated by varying the silane concentration （SC）, plasma power （Pw）, working pressure （P）, and substrate temperature （Ts）. Results suggest that SC and Ts are the most critical factors that affect the film structure transition from microcrystalline to amorphous phase. A narrow region in the range of SC and Ts, in which the rapid phase transition takes place, was identified. It was found that at lower P or higher Pw, the transition region is shifted to larger SC. In addition, the dark conductivity and photoconductivity decrease with SC and show sharp changes in the transition region. It proposed that the transition process and the transition region are determined by the competition between the etching effect of atomic hydrogen and the growth of amorphous phase.

Fabrication of Fine-Grained Si_3N_4-Si_2N_2O Composites by Sintering Amorphous Nano-sized Silicon Nitride Powders

Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering （ LPS ）. The Si2 N2O phase was generated by an in-situ reaction 2 Si3 N4 （ s ） ＋ 1.5 02 （ g ） = 3 Si2 N2O （ s ） ＋ N2 （ g ） . The content of Si2 N2 O phase up to 60% in the volume was obtained at a sintering temperature of 1 650℃ and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1 700 ℃. The sintering procedure contains a complex crystallization and a phase transition ： amorphous silicon nitride→equiaxial α- Si3 N4→ equiaxial β- Si3 N4→ rod- like Si2 N2O→ needle- like β- Si3N4 . Small round-shaped β→ Si3 N4 particles were entrapped in the Si2 N2O grains and a high density of staking faults was situated in the middle of Si2 N2O grains at a sintering temperature of 1 650 ℃. The toughness inereased from 3.5 MPa·m^1/2 at 1 600 ℃ to 7.2 MPa· m^1/2 at 1 800 ℃ . The hardness was as high as 21.5 GPa （Vickers） at 1 600 ℃ .

Nanoporous SiO_x coated amorphous silicon anode material with robust mechanical behavior for high-performance rechargeable Li-ion batteries

Silicon is a promising anode material for rechargeable Li-ion battery (LIB) due to its high energy density and relatively low operating voltage. However, silicon based electrodes suffer from rapid capacity degradation during electrochemical cycling. The capacity decay is predominantly caused by (i) cracking due to large volume variations during lithium insertion/extraction and (ii) surface degradation due to excessive solid electrolyte interface (SEI) formation. In this work, we demonstrate that coating of a-Si thin film with a Li-active, nanoporous SiOx layer can result in exceptional electrochemical performance in Li-ion battery. The SiOx layer provides improved cracking resistance to the thin film and prevent the active material loss due to excessive SEI formation, benefiting the electrode cycling stability. Half-cell experiments using this anode material show an initial reversible capacity of 2173 mAh g^-1 with an excellent coulombic efficiency of 90.9%. Furthermore, the electrode shows remarkable capacity retention of ~97% after 100 cycles at C/2 charging rate. The proposed anode architecture is free from Liinactive binders and conductive additives and provides mechanical stability during the charge/discharge process.

Growth characteristics of amorphous-layer-free nanocrystalline silicon films fabricated by very high frequency PECVD at 250 ℃

Amorphous-layer-free nanocrystalline silicon films were prepared by a very high frequency plasma enhanced chem-ical vapor deposition （PECVD） technique using hydrogen-diluted Sill4 at 250 ℃. The dependence of the crystallinity of the film on the hydrogen dilution ratio and the film thickness was investigated. Raman spectra show that the thickness of the initial amorphous incubation layer on silicon oxide gradually decreases with increasing hydrogen dilution ratio. High-resolution transmission electron microscopy reveals that the initial amorphous incubation layer can be completely eliminated at a hydrogen dilution ratio of 98%, which is lower than that needed for the growth of amorphous-layer-free nanocrystalline silicon using an excitation frequency of 13.56 MHz. More studies on the microstructure evolution of the initial amorphous incubation layer with hydrogen dilution ratios were performed using Fourier-transform infrared spectroscopy. It is suggested that the high hydrogen dilution, as well as the higher plasma excitation frequency, plays an important role in the formation of amorphous-layer-free nanocrystalline silicon films.

Surface plasmon enhanced photoluminescence in amorphous silicon carbide films by adjusting Ag island film sizes

Ag island films with different sizes are deposited on hydrogenated amorphous silicon carbide （a-SiC：H） films, and the influences of Ag island films on the optical properties of the tx-SiC：H films are investigated. Atomic force microscope images show that Ag nanoislands are formed after Ag coating, and the size of the Ag islands increases with increasing Ag deposition time. The extinction spectra indicate that two resonance absorption peaks which correspond to out-of-plane and in-plane surface plasmon modes of the Ag island films are obtained, and the resonance peak shifts toward longer wavelength with increasing Ag island size. The photoluminescence （PL） enhancement or quenching depends on the size of Ag islands, and PL enhancement by 1.6 times on the main PL band is obtained when the sputtering time is 10 min. Analyses show that the influence of surface plasmons on the PL of a-SiC：H is determined by the competition between the scattering and absorption of Ag islands, and PL enhancement is obtained when scattering is the main interaction between the Ag islands and incident light.

Preparation and Characterization of Amorphous Silicon Oxide Nanowires

Large-scale amorphous silicon nanowires (SiNWs) with a diameter about 100 nm and a length of dozens of micrometers on silicon wafers were synthesized by thermal evaporation of silicon monoxide (SiO). Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show that the silicon nanowires are smooth. Selected area electron diffraction (SAED) shows that the silicon nanowires are amorphous and en-ergy-dispersive X-ray spectroscopy (EDS) indicates that the nanowires have the composition of Si and O elements in an atomic ratio of 1:2,their composition approximates that of SiO2. SiO is considered to be used as a Si sources to produce SiNWs. We conclude that the growth mechanism is closely related to the defect structure and silicon monoxide followed by growth through an oxide-assisted vapor-solid reaction.

Solid-phase Crystallization of Amorphous Silicon Films by Rapid Thermal Annealing

The morphous silicon films prepared by PECVD at substrate temperatures of 30℃ have been crystallized by rapid thermal annealing method, the budget of time-temperature in the annealing process is 600℃ for 120s, 850℃ for 120s, and 950℃ for 120s. The results indicate the crystallization at 850℃ and 950℃ are better as shown in micro-Raman scattering and scanning electronic microscope.

Open-circuit voltage analysis of p-i-n type amorphous silicon solar cells deposited at low temperature

This paper identifies the contributions of p-a-SiC：H layers and i-a-Si：H layers to the open circuit voltage of p-i-n type a-Si：H solar cells deposited at a low temperature of 125℃. We find that poor quality p-a-SiC：H films under regular conditions lead to a restriction of open circuit voltage although the band gap of the i-layer varies widely. A significant improvement in open circuit voltage has been obtained by using high quality p-~SiC：H films optimized at the ＂low-power regime＂ under low silane flow rates and high hydrogen dilution conditions.

The study of amorphous incubation layers during the growth of microcrystalline silicon films under different deposition conditions

The structural un-uniformity of microcrystalline silicon, thin film, amorphous incubation layerc-Si：H films prepared using very high frequency plasma-enhanced chemical vapour deposition method has been investigated by Raman spectroscopy, spectroscopic ellipsometer and atomic force mi- croscopy. It was found that the formation of amorphous incubation layer was caused by the back diffusion of SiH4 and the amorphous induction of glass surface during the initial ignition process, and growth of the incubation layer can be suppressed and uniform μc-Si：H phase is generated by the application of delayed initial SiH4 density and silane profiling methods.

Research on the optimum hydrogenated silicon thin films for application in solar cells

Hydrogenated silicon （Si：H） thin films for application in solar ceils were deposited by using very high frequency plasma enhanced chemical vapour deposition （VHF PECVD） at a substrate temperature of about 170 ℃, The electrical, structural, and optical properties of the films were investigated. The deposited films were then applied as i-layers for p-i-n single junction solar cells. The current-voltage （I - V） characteristics of the cells were measured before and after the light soaking. The results suggest that the films deposited near the transition region have an optimum properties for application in solar cells. The cell with an i-layer prepared near the transition region shows the best stable performance.