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Role of chamber pressure on crystallinity and composition of silicon films using silane and methane as precursors in hot-wire chemical vapour deposition technique
摘要： Hot-wire chemical vapour deposition is a versatile technique to deposit a-Si:H and nc-Si films at higher deposition rate (~5-10 ?/sec) as compared to Plasma enhanced chemical vapour deposition (1-2 ?/sec). We report the deposition of highly crystalline Si films at very high deposition rate (≥ 40?/sec) by adding methane to silane during thermal/catalytic decomposition. A series of films were deposited by varying the chamber pressure between 10-100 Pa at a substrate temperature of 300 °C and filament temperature 2000 °C. The hydrogen diluted silane (10% silane in hydrogen) and pure methane were used as precursors and gas flow rate ratio was kept constant at 10. Films prepared at lower pressure (≤ 20 Pa) were more crystalline and do not contain any trace of carbon atoms. Bandgap was found to increase from 1.24-1.63 eV when pressure was increased. It was observed that chamber pressure plays a key role in determining the crystallinity, disorder and composition of these films. Addition of methane to hydrogen diluted silane increased deposition rate and crystallinity of Si films at low pressure (≤ 20 Pa). Above 20 Pa pressure, carbon atoms signature was obtained. SiC films were obtained when pressure was > 100 Pa.
关键词： Deposition rate,Si films,Crystallinity,Hot-wire chemical vapour deposition
更新于2025-11-21 11:01:37
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Epitaxial growth and electrical performance of graphene/3Ca??SiC films by laser CVD
摘要： High electrical conductivity graphene/epitaxial-3CeSiC (G/epi-3CeSiC) composite films have the potential to the applications such as micro-electro-mechanical systems, distributed Bragg reflectors, solar cells, and photocatalysis in harsh environments. In this study, G/epi-3CeSiC composite films were prepared through laser chemical vapor deposition (LCVD) using hexametyldisilane (HMDS) as a safe single precursor. The electrical conductivity (s) of the composite films reached 2.23 (cid:1) 104 S/m, which is 2.2 times of the highest s reported for G/epi-3CeSiC composite. The deposition rate (Rdep) of the composite film with the highest s is 8.2 times of that of the G/epi-3CeSiC with the highest s ever reported. s of the pure epitaxial 3CeSiC film is only 81.2 S/m, which is the lowest value reported to date of 3CeSiC prepared through CVD using HMDS as a single precursor. Elimination of carbon is beneficial for increasing the breakdown field intensity and decreasing the leakage current of heterojunction when epitaxial 3CeSiC is used as semiconductor material.
关键词： Electrical conductivity,Deposition rate,Laser CVD,Graphene/SiC film,Epitaxial
更新于2025-09-23 15:19:57
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Numerical modelling of heat transfer, mass transport and microstructure formation in a high deposition rate laser directed energy deposition process
摘要： In laser directed energy deposition (L-DED) processes, by applying a converged powder stream, relatively high laser power and larger laser spot, the powder utilisation efficiency and processing speed can be increased. There is, however, lack of mathematical models for L-DED. In this paper, a three-dimensional numerical model is established to study the mass transport and heat transfer in the melt pools in high deposition rate (HDR) L-DED of 316L stainless steel. The Volume of Fluid (VOF) method is employed to track the melt pool free surfaces, and enthalpy-porosity method is used to model the solid-liquid phase change. A discrete powder source model is developed by considering the non-uniform powder feed rate distribution. Results show that this model can well predict the deposited track dimensions (width, height and dilution depth). Different from conventional L-DED processes, the impact of higher mass addition on the melt pool fluid flow and temperature distribution is significant. In the regions where filler powder is injected, a downward mass flow is observed, and the temperature is slightly reduced. With the extracted temperature distribution and geometry at the solidification front, the solidification conditions are also calculated, as well as the primary dendrite arm spacing (PDAS) of the solidified tracks. Due to the high laser energy input, the temperature gradient is lower, and coarser microstructures are formed compared with conventional L-DED. The simulated results are in good agreement with experimental results.
关键词： Heat transfer,High deposition rate laser directed energy deposition,Mass transport,Primary dendrite arm spacing
更新于2025-09-19 17:13:59
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Influence of adaptive slice thickness and retained heat effect on laser metal deposited thin-walled freeform structures
摘要： Light-weight, thin-walled freeform structures of aerospace materials can be realized through Additive Manufacturing process like powder- and wire-based Laser Metal Deposition (LMD) technique. Repeatability, in the context of deposited clad geometry and achieved microstructure hinders the wide-spread industrialization of high deposition rate LMD process, which is influenced by numerous intrinsic and extrinsic process parameters. In this paper, the influences of adaptive slice thickness and retained heat effect on build geometry and microstructure have been investigated. Experiments carried out with a powder-fed LMD system to build Ti-6Al-4V freeform structures have been examined for geometrical accuracy and microstructure analysis.
关键词： Layer-to-layer control,High deposition rate,Adaptive slice thickness,Retained heat effect,Laser Metal Deposition
更新于2025-09-12 10:27:22
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Numerical analysis for optimization of the sidewall conditions in a capacitively coupled plasma deposition reactor
摘要： Capacitively coupled plasma (CCP) is mainly being used in the semiconductor industry for plasma-enhanced chemical vapor deposition of uniform thin films. Because a discharge volume in the standard configuration of a CCP reactor is surrounded not only with electrode surfaces but also with a sidewall, the sidewall conditions affect the deposition rate profiles noticeably. By toggling the boundary condition from a grounded conductor to dielectrics with the variations of the relative permittivity and the thickness, we compare the spatial profiles for the species densities, ionization rate, power absorption, and particle fluxes in a SiH4/He CCP. Through the SiH4/He CCP fluid model, it is found that a thick and low-permittivity insulator achieves the most uniform plasma density distribution in the interelectrode region and, consequently, the best uniformity in the deposition rate profile of an a-Si:H film. As a validation, experimental results are compared with fluid modeling results, and they match well. For additional validation, a particle-in-cell simulation of pure Ar discharge is also performed. Although simulation conditions are totally different from those of the SiH4/He fluid model, it consistently demonstrates that the dielectric sidewall brings about more uniform distributions of the plasma parameters than the grounded sidewall.
关键词： deposition rate,SiH4/He CCP,PECVD,Capacitively coupled plasma,plasma uniformity
更新于2025-09-12 10:27:22
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Effects of Laser Irradiation on a Copper Electrodeposition Process and Coating Quality
摘要： In this study, a hybrid pulsed laser and electrochemical processing technique was used to deposit a copper coating on a stainless steel substrate. The laser irradiation mechanism in the electrodeposition process was studied by detecting the mechanical and thermal effects. The electrodeposition samples were irradiated by lasers with varying single-pulsed energies and compared. The grains of the coating were observed with a scanning electron microscope (SEM), and the tensile strength and ductility were measured using a UTM4000 series electronic universal testing machine. The results showed that the deposition rate may be increased, and the coating quality may be improved by laser irradiation with the proper single-pulsed energy. This is due to an increase in the conductivity and diffusion coefficient of the solution, arising from an increase in the solution temperature and the local stirring induced by plasma bubbles. The grain size and growth direction of the dendrite are also affected by laser irradiation.
关键词： Electrodeposition,Deposition rate,Plasma shockwave,Coating quality,Pulsed laser
更新于2025-09-04 15:30:14