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1.
From TEM, XRD and Raman measurements, we compare the crystallization kinetics when HWCVD and PECVD a-Si:H films, containing different initial film hydrogen contents (CH), are crystallized by annealing at 600 °C. For the HWCVD films, the nucleation rate increases, and the incubation time and the full width at half maximum (FWHM) of the XRD (111) peak decrease with decreasing film CH. However, the crystallization kinetics of HWCVD and PECVD films of similar initial film CH are quite different, suggesting that other factors beside the initial film hydrogen content affect the crystallization process. Even though the bonded hydrogen evolves very early from the film during annealing, we suggest that the initial spatial distribution of hydrogen plays a critical role in the crystallization kinetics, and we propose a preliminary model to describe this process. 相似文献
2.
We have applied real time spectroscopic ellipsometry and secondary ion mass spectrometry to study the growth of amorphous silicon by hot-wire chemical vapor deposition. Differences in temperature and hydrogen content affect the optical properties of the film. These effects provide valuable insight into the growth process. We have compared a-Si:H films grown at two different temperatures to better understand these effects. Our studies reveal the presence of a distinct 100–200-thick layer at the top of the growing film. The properties of this layer are primarily determined by the ambient conditions in the growth chamber and appear relatively independent of substrate temperature. In contrast, the properties of the bulk of the film are strongly influenced by substrate temperature. These results imply that differences in film properties associated with substrate temperature are the result of subsurface reconstruction and diffusion processes. 相似文献
3.
A. Harv Mahan Phil A. ParillaHelio Moutinho Bobby ToMatthew S. Dabney David S. Ginley 《Thin solid films》2011,519(14):4455-4458
A determination of the steady state nucleation rate rn in thermally annealed a-Si:H has typically been performed using TEM, where the increase in grain density with isothermal sample anneal time can be directly observed for samples with small crystalline volume fractions. Using the classical model of crystallite nucleation and grain growth, this paper presents an alternative technique for determining rn using in situ XRD measurements of the crystallization time and EBSD measurements of the final grain size, the latter in fully annealed samples. HWCVD a-Si:H samples containing different as-grown film H contents CH have been examined by both techniques, and the agreement between these techniques is excellent. Rn is seen to decrease with increasing as-grown film CH. Differences in the values of rn are suggested as being due to variations in the transition rate per atom at the amorphous/crystalline interface. 相似文献
4.
Hydrogenated amorphous silicon (a-Si:H) films were prepared by changing substrate temperature of plasma-enhanced chemical vapor deposition to induce different contents of monohydride and polyhydride bonds, which were then crystallized into polysilicon (poly-Si) films by rapid energy transfer annealing. Fourier transform infrared and transmission spectra show that the formation of numerous polyhydride bonds increases the hydrogen content and reduces the refractive index of a-Si:H films. The rise in the concentration of polyhydride bonds in as-deposited a-Si:H films can result in the increase of ultraviolet reflectance, small peak shift, and change in full width at half maximum of Raman scattering and X-ray diffraction peaks of the obtained poly-Si films after annealing. These results demonstrate that high-concentration polyhydride bonds can promote the rapid crystallization of a-Si:H and obtain high-crystallinity poly-Si films. Transmission electron microscopy identifies that the poly-Si films have the typical dendrite-like grain structure. 相似文献
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6.
Hydrogenated amorphous silicon carbon (a-SiC:H) films were deposited using pure SiH4 and C2H2 without hydrogen dilution by hot wire chemical vapor deposition (HWCVD) technique. The photoluminescence, optical, and structural properties of these films were systematically studied as a function of substrate temperature (Ts). a-SiC:H films deposited at lower substrate temperature (Ts) show degradation in their structural, optical and network properties. The hydrogen content (CH) in the films was found to be increased with decrease of Ts studied. Photoluminescence spectra shift to higher energy and less FWHM at high Ts. Raman spectroscopic analysis showed that structural disorder increases with decrease in the Ts. 相似文献
7.
In order to understand material properties in a better way, it is always desirable to come up with new variables that might be related to the film properties. The B-parameter is such a variable, which relates to the quality of a-SiC:H films both in terms of electronic and optical properties. B (scaling factor) is essentially the slope of the straight-line part of the (E)1/2–E (Tauc plot). Due to dependence on a large number of parameters and no detailed research, many previous authors have surmised that B has an ambiguous correlation with carbon content. We have made an attempt to establish the relation between the B-parameter as a quality-indicating factor of a-SiC:H films in both carbon- and silicon-rich material. For this we studied a-SiC:H films deposited by the HWCVD method with broad deposition parameters of substrate temperature (Ts), filament temperature (TF) and C2H2 fraction. Our results indicate that the B-parameter varies considerably with process conditions such as TF, total gas pressure and carbon content. An attempt is made to correlate the B-parameter with an opto-electronic parameter, such as the mobility edge, which has relevance to the device-quality aspects of a-SiC:H films prepared by HWCVD. 相似文献
8.
Thin films of hydrogenated silicon are prepared by varying the filament temperature (TF) (1600-1900 °C) at a deposition rate of 8-12 Å/s without using any hydrogen dilution. While the films deposited at low TF are amorphous in nature, those deposited at higher TF (≥ 1800 °C) contain nanocrystallites embedded in the amorphous network. The optical band gap (E04) of the films (~ 1.89-1.99 eV) is slightly higher compared to the regular films, which is attributed to the improved short and medium range order as well as the presence of low density amorphous tissues in the grain boundary regions. The films show improved stability under long term light exposure due to more ordered structure and presence of hydrogen mostly as strong Si-H bonds. 相似文献
9.
Hydrogen amorphous silicon carbon (a-SiC:H) film deposited by the Hot Wire Chemical Vapor Deposition (HWCVD) technique on silicon substrates were soaked in simulated body fluid (SBF). Characterization of the film with different soaking durations in SBF was carried out by Fourier Transform Infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. It was found that the relative amounts of carbon in the a-SiC:H film surface decreases with increase in soaking period. XPS results showed the adsorption of Ca and Mg on the a-SiC:H surface. This indicates the formation of negatively charged surface possibly due to formation of silanol groups or dissolution of carbon to SBF confirming the bioactivity of the material. Contact angle decreased from 74° to 65° during 30 days of soaking in the body fluid. Present study is an attempt to observe the interaction of a-SiC:H film prepared by HWCVD technique with the body environment for its future suitability as artificial heart valve and stent coating materials. 相似文献
10.
Fracture of single crystal nanolaminated thin films has been investigated through in situ straining of cross-sectional samples of Cu/Ni nanolaminates grown on Cu (001) single crystal substrates. The earlest stages of deformation exhibits a confined layer slip mechanism. With continued straining, unstable fracture occurs creating a mixed-mode crack that propagates across the nanolaminate, roughly perpendicular to the interfaces. Eventually, stable crack growth with intense plastic deformation ahead of the crack tip occurs over many bilayers in the direction of crack growth. Simultaneously, plasticity was seen to spread only 1 or 2 bilayer distances normal to the crack, creating an extremely localized plastic zone. Transmission electron microscopic (TEM) examination after the test did not reveal the presence of dislocations in the crack wake, except where severe crack deflection was observed. By comparison, the plastic zone size in the substrate was greater by several of orders of magnitude. 相似文献
11.
《Materials Letters》1987,6(3):89-91
a-Si:H films deposited from various silane-containing gas mixtures have been studied regarding their porosity. Micropore densities of 2.O × 102cm-2, 5.0 × 104cm-2 and 5.0 × 104cm-2 were determined for a-Si:H:C1, a-Si:H(H2) and a-Si:H(Ar) films, respectively. It is suggested that these values correlate with the structural properties of the films, so that a-Si:H:Cl films seem to be the most uniform on the microstructural scale. 相似文献
12.
A series of hydrogenated amorphous silicon films have been deposited using plasma enhanced chemical vapour deposition (PECVD)
and hot-wire chemical vapour deposition (HWCVD) techniques. The total concentration of bonded hydrogen in the films was varied
between 3% and 18% as determined by hydrogen effusion measurements. Fourier transform infra-red (FTIR) spectra of the PECVD
and HWCVD samples exhibit strong absorption peaks that correspond to Si–H bend and stretch modes, and Si–H2 stretch modes. A quantitative fit of the FTIR peak areas to the hydrogen effusion concentrations reveals that there is reasonable
agreement between the required proportionality constants in PECVD and HWCVD material for the Si–H bend and stretch modes.
The uncertainty error for the FTIR proportionality constants is consistently greater for the HWCVD data set, however, which
may indicate that the effective dynamical charge of the Si–H dipoles is perturbed in the HWCVD material by bonded impurities
that are sourced from the tungsten wire. 相似文献
13.
Hot-wire chemical vapor deposition (HWCVD) and plasma-enhanced chemical vapor deposition (PECVD) of Si thin films show different growth kinetic processes. According to the fractal analysis, the root-mean-square surface roughness δ and the film thickness d have the relation of δ ∼ dβ, where β is the dynamic scaling exponent related to the film growth mechanism. It was found that β is 0.44 for Si films prepared by HWCVD and 0.24 by PECVD. The former refers to a stochastic deposition while the latter corresponds to the finite diffusion of the radicals. Monte Carlo simulations indicate that the sticking process of growth radicals play an important role in determining the morphology of Si films. 相似文献
14.
Kiyoshi Okada Yoshikazu Kameshima Chengala D. Madhusoodana Rathindra N. Das 《Science and Technology of Advanced Materials》2013,14(4):479-484
Zeolite thin films were prepared on cordierite (Mg2Al4Si5O18) honeycomb substrates by in situ crystallization using soft hydrothermal conditions. The synthesized zeolite films (zeolite A and ZSM-5) were characterized by XRD, FTIR, SEM, NH3-TPD, and Ns2 and propane gas adsorption. Zeolite-A films were prepared by dip-coating on a cordierite substrate in a precursor of molar composition of Na2O:Al2O3: SiO2: H2O = 4:1:2:100 and heating in an autoclave at 80 °C for 6–10 h. The resultant zeolite-A films consisted of cubic crystals about 2–3 μm in size, achieving a thickness of 20 μm after re-coating. ZSM-5 films were similarly formed using a microporous silica precursor obtained by selective leaching of metakaolinite with tetrapropylammonium hydroxide (TPAOH) as the templating agent. The molar composition of the precursor was NaOH:microporous silica:TPAOH:H2O = 1:10:1:200. The dipped substrate covered with the wet precursor gel was heated in an autoclave at 150 °C for 24 h. The resultant films were composed of short prismatic <1 μm crystals achieving thickness of several to 10 μm after re-coating. The microstructure and porous properties of the ZSM-5 films were found to change according to the chemical composition and surface treatment of the cordierite substrates. The presence of a SiO2-rich interfacial layer between the substrate and zeolite film increased the amount of zeolite formed and the physical adsorption but decreased the solid acidity and amount of chemisorption. 相似文献
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16.
Jinlong Du Zaoming Wu Yanxiang Liang Xingjun Wang Peipei Wang 《Science and Technology of Advanced Materials》2018,19(1):212-220
The mechanism of radiation-induced detwinning is different from that of deformation detwinning as the former is dominated by supersaturated radiation-induced defects while the latter is usually triggered by global stress. In situ Kr ion irradiation was performed to study the detwinning mechanism of nanotwinned Cu films with various twin thicknesses. Two types of incoherent twin boundaries (ITBs), so-called fixed ITBs and free ITBs, are characterized based on their structural features, and the difference in their migration behavior is investigated. It is observed that detwinning during radiation is attributed to the frequent migration of free ITBs, while the migration of fixed ITBs is absent. Statistics shows that the migration distance of free ITBs is thickness and dose dependent. Potential migration mechanisms are discussed. 相似文献
17.
多晶硅薄膜的铝诱导晶化法制备及其晶粒的择优取向特性 总被引:1,自引:0,他引:1
采用铝诱导非晶硅薄膜晶化技术制备了多晶硅薄膜,并研究了多晶硅的成核和生长特性。非晶硅薄膜采用等离子体增强化学气相沉积法制备,其表面沉积铝薄膜后经不同温度的氮氛围退火处理。结果表明,退火后的硅薄膜层与铝层发生置换,所生长的多晶硅颗粒的平均尺寸约为150nm。X射线衍射分析结果揭示,薄膜的晶向显著依赖于退火温度,较低温度下,铝诱导晶化速率较慢,薄膜的优化晶向与非晶硅薄膜中团簇的初始原子排列趋势紧密相关。而较高温度下,铝诱导晶化促使多晶硅(111)择优成核及随后的固相生长。 相似文献
18.
A novel approach was developed to obtain uniformly dispersed nanostructured carbon reinforcement in aluminum matrix composite powders. This process involves in situ synthesis of carbon nanoflakes (CNFs) with thickness of 30-50 nm on the surface of aluminum powders through Friedel-Crafts alkylation of benzene under its supercritical conditions, at 300 °C and 5.7 MPa with benzene and C2Cl6 as carbon sources, and AlCl3 as catalyst. In this process, all the reactants and catalyst are in gaseous state, which play an important role in inducing homogeneous reaction and dispersion of the CNFs. Meanwhile, Al powders play an important role in inducing the morphology of the CNFs by providing the heterogeneous nucleation sites. 相似文献
19.
We report a synchrotron X-ray absorption spectroscopy study of the average neighborhood of Si near the transition from a-Si:H to μc-Si on wedge-shaped samples prepared by hot-wire CVD in a chamber using a movable shutter. The thickness of the wedge varies from 30 to 160 nm. Nucleation of μc-Si occurs at a critical thickness of approximately 100 nm. X-Ray absorption was measured at the Si K-edge (1.84 keV) by total electron photoemission yield. The absorption oscillations in the EXAFS region are very similar to all along the wedge. Analysis indicates an average tetrahedral first neighbor shell with radial disorder decreasing with crystallization. In the near-edge (XANES) region multiple scattering effects appear at the onset of crystallinity. Unlike single crystal silicon, these effects involve only double scattering within the first neighbor shell, indicating an ill-formed second shell in μc-Si. 相似文献
20.
Microcrystalline silicon solar cells deposited by VHF-PECVD with or without HWCVD grown p/i interface buffer layer were investigated. We studied long-term stability under storage in ambient atmosphere and performed light soaking experiments. Cells with i-layers covering a wide range of crystalline volume fractions were studied. All cells were stable or degraded slightly after storage for 2 years in air, regardless of crystalline volume fraction or presence of p/i buffer interface. Upon light soaking all cells show efficiency degradation to more or less extent depending on crystal volume fraction of the i-layer and the presence of the buffer layer: the solar cell with high crystal volume fraction are nearly stable, cells with high amorphous volume fraction degrade by up to 20%. The solar cell with HWCVD buffer layer shows better stability in the high efficiency range of relative efficiency degradation typically less than 10% after 1000 h AM 1.5 light soaking. The efficiency degradation is mainly caused by Voc and FF deterioration while Jsc is almost stable. 相似文献