Low-temperature deformation behaviour of polycrystalline copper

Low-temperature plastic flow in copper was investigated by studying its tensile and creep deformation characteristics. The dependence of the flow stress on temperature and strain rate was used to evaluate the thermal activation energy while the activation area was derived from the change-in-stress creep experiments. A value of 0.6 eV was obtained for the total obstacle energy both in electrolytic and commerical copper. The activation areas in copper of three selected purities fell in the range 1200 to 100 b². A forest intersection mechanism seems to control the temperature dependent part of the flow stress. The increase in the athermal component of the flow stress with impurity content in copper is attributed to a change in the dislocation density. The investigation also revealed that thermal activation of some attractive junctions also takes place during low-temperature creep. The model of attractive junction formation on a stress decrement during creep, yields a value of 45±10 ergs cm⁻² for the stacking fault energy in copper.     

Properties of polycrystalline silicon films prepared from fluorinated precursors

Polycrystalline silicon films have been prepared at low temperature on glass substrate from fluorinated precursors by PECVD technique varying the hydrogen dilution and gas flow rate. Undoped film with dark-conductivity 1.05×10⁻² S cm⁻¹ has been obtained. For n-type poly-Si film the highest conductivity achieved is 2.8 S cm⁻¹. Grain size observed from SEM varies from 4 to 6 μm for undoped and 2 to 3 μm for phosphorous doped films. The main crystalline peak is 〈111〉 whereas the crystallite size calculated from XRD is 350 Å. The optical absorptions and hydrogen contents in the films deposited under different conditions have been studied. Growth kinetics are dominated by the precursors SiF_nH_m (m+n≤3) and concentrations of F and H on the growth surface.     

Orientation analysis of polycrystalline silicon

An analysis of the crystallographic orientation of Wacker “Silso” polycrystalline silicon is reported. It is observed that many grains are penetrated perpendicular to the sample surface by equally oriented lattice planes. No connection could be found between grain size and grain orientation. 50% of adjacent grains in the center of the plate and 16% of adjacent grains in the edge region of the plate share common lattice planes which traverse the grain boundaries undisturbed.     

Bioactivity of polycrystalline silicon layers

After oxygen, silicon is the second most abundant element in the environment and is present as an impurity in most materials. The widespread occurrence of siliceous biominerals as structural elements in lower plants and animals suggests that Si plays a role in the production and maintenance of connective tissue in higher organisms. It has been shown that the presence of Si is necessary in bones, cartilage and in the formation of connective tissue, as well as in some important metabolic processes. In this work, polycrystalline silicon layers are tested in terms of bioactivity, i.e., their ability to induce hydroxyapatite formation from simulated body fluid. Hydroxyapatite is a biologically compatible material with chemical similarity to the inorganic part of bones and teeth. Polycrystalline silicon layers are obtained by aluminum induced crystallization of Al and amorphous Si thin films deposited sequentially on glass substrates by radio-frequency magnetron sputtering and subsequently annealed in different atmospheres. The hydroxyapatite formation is induced by applying a method of laser-liquid-solid interaction. The method consists of irradiating the samples with laser light while immersed in a solution that is supersaturated with respect to Ca and P. As a result, heterogeneous porous sponge-like carbonate-containing hydroxyapatite is grown on the polysilicon surfaces. Crystals that are spherical in shape, containing Ca, P and O, Na, Cl, Mg, Al, Si and S, as well as well-faceted NaCl crystals are embedded in the hydroxyapatite layer. Enhancement of the hydroxyapatite growth and increased crystallinity is observed due to the applied laser-liquid-solid interaction.     

Multiscale modeling of polycrystalline silicon

Polycrystalline solid is composed of randomly distributed grains and grain boundaries. The size of grains is usually in the nano/micro-scale. In this paper, the general micromorphic theory, as well as a specialized micromorphic theory for covalent and ionic crystals, is introduced. A statistical model for polycrystalline material is adopted. Each grain is modeled as crystallized solid by micromorphic theory, while the grain boundaries are modeled as in its amorphous phase by classical continuum theory. Size-dependent material properties of silicon are investigated. Finite element analysis of thermomechanical coupling phenomenon in polycrystalline silicon is performed and numerical results are presented and discussed.     

Preparation of trichlorosilane from hydrogenation of silicon tetrachloride in thermal plasma

A new method of producing trichlorosilane by hydrogenation of silicon tetrachloride with assistance of DC charged thermo-plasma was proposed. We have studied the dependence of degree of disassociation and ionization of hydrogen on temperature, as well as the function of heat capacity, via which the optimal volume and H₂: SiCl₄ molar ratio were confirmed. A DC power of 50 kW was equipped and the highest yield of trichlorosilane was above 70%, with an average yield about 60% and minimum unit energy expenditure about 3.2 kWh/kg for SiHCl₃. This process is possible to be industrialized.     

Electrical and structural characteristics of oxides grown from polycrystalline silicon

A comparative study of dielectric properties of polysilicon oxide with silicon dioxide, grown on single crystal silicon, shows that the former is more conducting due to the presence of asperites at polysilicon/SiO₂ interface. This paper also reports attempts made to improve the electrical properties of polysilicon oxide by investigating the effects of oxidation temperature, polysilicon deposition temperature and doping on current field characteristics of polyoxide. Higher doping and higher oxidation temperature yield smoother interface with higher breakdown voltages and lower leakage currents. Surface morphology of polyoxide under different process conditions is also studied.     

Mitigation of the vapor hazard from silicon tetrachloride using water-based foams

The list of volatile hazardous chemicals contains a significant number of inorganic chlorides. Most react exothermically with water releasing a toxic,In a co-operate program, MSA and Wah Chang have investigated the potential of aqueous foam to mitigate the vapor hazard of one water reactive chloride,The tests conducted were successful in markedly reducing the vapor hazard from the spill. Foam blankets reduced the chloride concentrations in the air     

Low-temperature preparation of flexible a-Si:H solar cells with hydrogenated nanocrystalline silicon p layer

In this paper we report on flexible a-Si:H solar cells prepared on polyethylene naphthalate (PEN) substrates using p-type hydrogenated nanocrystalline silicon thin films (p-nc-Si:H) as the window layer. The p-nc-Si:H films were prepared at low temperature (150 °C) using trimethylboron (TMB) as a dopant gas. The influence of the silane concentration (SC) on the electrical and structural properties of ultra-thin p-nc-Si:H as well as the performance of solar cells on PEN was investigated. The results show that the crystalline fraction and conductivity of p-nc-Si:H thin films diminished, while the deposition rate and RMS roughness of films increased, when the SC increases from 0.53% to 0.8%. For the a-Si:H solar cells on PEN with the non-textured electrodes, the best efficiency of 6.3% was achieved with the p-nc-Si:H thin films deposited at SC = 0.67%.     

Low-temperature diffusion in polycrystalline Pd-Ag thin film system

Mutual diffusion in a polycrystalline Pd-Ag thin film system with an average grain size of 0.1 μm was studied in the temperature interval from 373 to 523 K. The effective diffusion coefficient D was determined by the X-ray diffraction technique in a region with a palladium content of 90–95%. The experimental D values are one to two orders of magnitude greater than the average coefficients of diffusion by grain boundaries in the same temperature interval.     

Deformation and recrystallization of polycrystalline silicon

A systematic study of recrystallization of hot-deformed single and polycrystalline silicon has been carried out. New grains were formed by nucleation and growth at temperatures between 1280 and 1410° C and the final grain size was a function only of the degree of deformation. For polycrystalline chemical vapour deposition (CVD)-grown silicon hot deformed at temperatures between 1 100 and 1310° C it was established that the largest grains (of the order of a few millimetres) can be grown after about 5% deformation. At this low strain the rates of nucleation and growth were low and consequently the time needed to complete recrystallization was rather long (20 h). Below 4% deformation no recrystallization occurred (critical degree of deformation is 4%). For both single and polycrystalline silicon grain growth after primary recrystallization was limited. This was due to the low mobility of high-angle grain boundaries in covalently bonded materials.     

Synthesis and oxidation of luminescent silicon nanocrystals from silicon tetrachloride by very high frequency nonthermal plasma

Silicon nanocrystals have recently attracted significant attention for applications in electronics, optoelectronics, and biological imaging due to their size-dependent optical and electronic properties. Here a method for synthesizing luminescent silicon nanocrystals from silicon tetrachloride with a nonthermal plasma is described. Silicon nanocrystals with mean diameters of 3-15 nm are synthesized and have a narrow size distribution with the standard deviation being less than 20% of the mean size. Control over crystallinity is achieved for plasma pressures of 1-12 Torr and hydrogen gas concentrations of 5-70% through adjustment of the plasma power. The size of nanocrystals, and resulting optical properties, is mainly dependent on the gas residence time in the plasma region. Additionally the surface of the nanocrystals is covered by both hydrogen and chlorine. Oxidation of the nanocrystals, which is found to follow the Cabrera-Mott mechanism under ambient conditions, is significantly faster than hydrogen terminated silicon due to partial termination of the nanocrystal surface by chlorine.     

CO2-laser-induced chemical vapour deposition of polycrystalline silicon from silane

Silicon dots have been deposited on silicon-coated quartz substrates by continuous wave CO₂-laser-induced decomposition of silane. The deposited material was determined by micro Raman scattering to be polycrystalline silicon. The height of the silicon dots was measured as a function of output laser power and irradiation time. The growth rate of silicon dots having a gaussian profile was found to be proportional to silane pressure and laser power. The laser power required for silicon melting (1683 K) was measured under specific experimental conditions. The substrate temperature could be calculated for any laser power assuming a linear temperature dependence on this power. The growth rate of silicon dots was found to be proportional to the substrate temperature. The growth kinetics of silicon dots may be limited by the number of collisions between “cold” silane molecules and the heated zone of substrates. A reaction mechanism based on this assumption is proposed in this paper.     

Study on volatilization rate of silicon in multicrystalline silicon preparation from metallurgical grade silicon

The quantity of silicon lost during evaporation is greater than theoretical expectation during the purification of metallurgical grade silicon by vacuum evaporation. In this paper, silicon volatilization rates were measured for evaporation times of 30, 45 and 60 min at 1723, 1773 and 1823 K, respectively. Results indicate that volatilization rates determined in our experiments are one or two orders of magnitude greater than those from theoretical calculation. The equation for theoretical calculation was revised (ω = (2.23-6.30)× 10⁻¹ p_pa(M/T)^1/2) using silicon evaporation coefficient of 8.5-24. The details of the experimental set-up were found to be important and the mass of silicon evaporated in particular was found to be related to the water-cooling system. The carbon/graphite inserts also and the presence of trace amounts of oxygen in the vacuum furnace could reduce the content of silicon in gaseous phase and support the evaporation of silicon. It was found under certain conditions that there are two principal stages involved: 1) Formation of vapor-liquid equilibrium, 2) Maintenance of the established vapor-liquid equilibrium during the silicon evaporation process. It was found that silicon process losses can be reduced by shortening the time of the first stage.     

Thin film polycrystalline silicon nanowire biosensors

Polysilicon nanowire biosensors have been fabricated using a top-down process and were used to determine the binding constant of two inflammatory biomarkers. A very low cost nanofabrication process was developed, based on simple and mature photolithography, thin film technology, and plasma etching, enabling an easy route to mass manufacture. Antibody-functionalized nanowire sensors were used to detect the proteins interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-α) over a wide range of concentrations, demonstrating excellent sensitivity and selectivity, exemplified by a detection sensitivity of 10 fM in the presence of a 100,000-fold excess of a nontarget protein. Nanowire titration curves gave antibody-antigen dissociation constants in good agreement with low-salt enzyme-linked immunosorbent assays (ELISAs). This fabrication process produces high-quality nanowires that are suitable for low-cost mass production, providing a realistic route to the realization of disposable nanoelectronic point-of-care (PoC) devices.     

Memory switching in polycrystalline silicon films

Non-volatile memory switching has been observed in polycrystalline silicon layers produced by chemical vapor deposition. Evidence for filamentary conduction is found for devices which are in their low impedance state. Devices have been cycled through high and low impedance states up to a maximum of 2x10⁴ times. Exposure to transient ionizing electron radiation caused the devices to switch to their low impedance state.     

Emission properties of polycrystalline diamond-coated silicon emitters

The electron emission characteristics of the polycrystalline diamond-coated silicon-field emission array (DSFEA) are studied and compared with that of the bare Si-field emission array (SFEA). For the DSFEA, a linear ohmic and a Fowler–Nordheim (FN) emission are observed at the low and high anode voltage regions, respectively. Potential electron emission model of the DSFEA is discussed. The threshold voltage for DSFEA is about 235 V, and the maximum emission current of 0.23 mA is obtained at anode voltage of 500 V. From the FN plot, the calculated effective work function of the DSFEA is 0.2115 eV. The low threshold voltage and high emission current of DSFEA are attributed to the low effective work function of emitter.     

Resistivity and photoconductivity of plasma-sprayed polycrystalline silicon

Polycrystalline silicon layers of area 8 cm² and thickness t ranging from 100 μm to 2 mm were prepared on alumina substrates by plasma spraying silicon powder. For t > 500 μm, these layers could be detached from the substrate. The conductivity could be made n or p type by in situ doping. The microstructure, impurity content and resistivity as a function of both phosphorus and boron doping concentrations were studied. The effect of heat treatment on the resistivity, Hall mobility and the photoconductivity is reported. The data are explained qualitatively on the basis of existing models of the transport behaviour of polycrystalline silicon.