Investigation of surface treatment effect of catalyst on the lifetime for Cat-CVD method

In case of amorphous silicon (a-Si) film deposition by catalytic chemical vapor deposition (Cat-CVD) method, a metal catalyzing wire is converted to silicide and this silicidation causes shortening lifetime of the catalyzing wire. In the present work, the effect of surface carbonization of catalyzing wire against silicide formation is investigated to obtain long-life catalyzer. Characteristics of a-Si film deposited by carbonized tungsten (W) catalyzer are also investigated. Silicide layer thickness formed on carbonized catalyzing wires after 60 min a-Si film deposition decreases to half of that on uncarbonized wires. Device quality a-Si films having defect density less than 4 × 10¹⁵ cm^?3 are obtained by using carbonized W, indicating that surface carbonization of W catalyzer is effective process for industrial application of Cat-CVD method.     

Role of halogen in low-temperature growth of polycrystalline thin films by reactive thermal CVD

Low-temperature growth of polycrystalline silicon by reactive thermal CVD, in which a set of reactive gasses are selected to promote film growth and/or crystallization at low-temperatures in thermal CVD, was studied with disilane and halogens such as fluorine and chlorine. High quality polycrystalline Si films were grown on glass substrates in Si₂H₆–F₂ system at 450 °C, while polycrystalline films were hardly deposited when Si₂H₆–Cl₂ system was adapted in the similar condition. We examined the major factors that govern the crystal growth at low-temperature by comparing the experimental results from these two systems. We suggest that the chemical processes on the growing surface in which Si-network is formed while the terminators are eliminated play a significant role for nucleation and growth in the low-temperature deposition by reactive thermal CVD.     

Growth of pure ZnO thin films prepared by chemical spray pyrolysis on silicon

Structural, morphological, optical and electrical properties of ZnO thin films prepared by chemical spray pyrolysis from zinc acetate (Zn(CH₃COO)₂ 2H₂O) aqueous solutions, on polished Si(1 0 0), and fused silica substrates for optical characterization, have been studied in terms of deposition time and substrate temperature. The growth of the films present three regimes depending on the substrate temperature, with increasing, constant and decreasing growth rates at lower, middle, and higher-temperature ranges, respectively. Growth rate higher than 15 nm min⁻¹ can be achieved at T_s=543 K. ZnO film morphological and electrical properties have been related to these growth regimes. The films have been characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy.     

Influence of Ar/C2H2 ratio on the structure of hydrogenated carbon films

The amorphous hydrogenated carbon films (a-C:H) were obtained on Si (1 1 1) wafers by plasma jet chemical vapor deposition (PJCVD). a-C:H coatings have been prepared at 1000 Pa in argon/acetylene mixture. The Ar/C₂H₂ gas volume ratio varied from 1:1 to 8:1. It was demonstrated that by varying the Ar/C₂H₂ ratio the composition, growth rate of the coatings, and consequently the structure of the film, can be controlled. The growth rate and surface porosity of coatings deposited at Ar/C₂H₂ = 8:1 ratio decrease slightly with an increase in the distance between the plasma torch nozzle and substrate from 0.04 to 0.095 m. The transmittance of the coatings in the IR region of 2.5–25 μm slightly increases, while the absorption peaks at 2850–2960 cm^?1 related with sp³ CH_2–3 modes remain unchanged with an increase in the distance. The Raman spectroscopy indicated that the a-C:H coating formed at the Ar/C₂H₂ = 8:1 and 0.06 m has the highest sp³ C–C fraction. The proposed PJCVD technique allows to achieve the growth rates up to 300 nm/s.     

The preferential orientation of the directionally solidified Si–TaSi2 eutectic in situ composite

The Si–TaSi₂ eutectic in situ composite is a favorable field emission material due to relatively low work function, good electron conductivity, and three-dimensional array of Schottky junctions grown in the composite spontaneously. The preferential orientation during directional solidification is determined by the growth anisotropy. In order to obtain the preferential direction of the steady-state crystal growth, the transmission electron microscopy (TEM) is used for analysis. It is found that the preferential orientation of the Si-TaSi₂ eutectic in situ composite prepared by Czochralski (CZ) technique is [3 3¯ 2¯] Si∥[0 0 0 1] TaSi₂, (2 2 0)Si∥(2 2¯ 0 0) TaSi₂. Whereas the preferential orientation of the Si–TaSi₂ eutectic in situ composite prepared by electron beam floating zone melting (EBFZM) technique is [0 1¯ 1¯ ]] Si∥[0 0 0 1] TaSi₂,(0 1¯ 1) Si∥(0 1¯ 1 1)TaSi₂. The preferential directions of the Si-TaSi₂ eutectic in situ composites prepared by two kinds of crystal growth techniques are distinctly different from each other, which results from different solid–liquid interface temperatures on account of the different crystal growth conditions, e.g. different solidification rate, different temperature gradient, different solid–liquid interface curvature and different kinetic undercooling.     

Electrical properties of liquid 3d transition metal–Si alloys

The electrical resistivity, R, and the thermoelectric power, S, have been measured for liquid transition metal–Si alloys (TM_cSi_1−c, TM = Ni, Fe, Mn), and liquid Cr_0.1Si_0.9 and Co_0.1Si_0.9 alloys as a function of temperature. The electrical resistivity increases rapidly with the addition of Fe, Mn and Cr to liquid Si and the liquid Mn_cSi_1−c alloys with 1 ⩾ c ⩾ 0.6 have an electrical resistivity of approximately 200 μΩ cm. The composition dependence of the electrical resistivity for liquid Fe_cSi_1−c and Ni_cSi_1−c systems exhibits a maximum at the composition c = 0.5 and c = 0.6, respectively. Liquid TM–Si alloys have a negative value of thermoelectric power over the wide composition range. The variation of R and S by the addition of Fe, Co and Ni solutes to liquid Si is in good agreement with that estimated from the 3d resonant scattering theory. The composition dependence of R and S of liquid Ni–Si can be qualitatively explained by the extended Ziman’s formula.     

Self-aggregated Si quantum dots in amorphous Si-rich SiC

Amorphous silicon quantum dots (Si-QDs) self-aggregated in silicon-rich silicon carbide are synthesized by growing with plasma-enhanced chemical vapor deposition on (100)-oriented Si substrate. Under the environment of Argon (Ar)-diluted Silane (SiH₄) and pure methane (CH₄), the substrate temperature and RF power are set as 350 °C and 120 W, respectively, to provide the Si-rich SiC with changing fluence ratio (R = [CH₄ ]/[SiH₄] + [CH₄]). By tuning the fluence ratio from 50% to 70%, the composition ratio x of Si-rich Si_1 ? xC_x film is varied from 0.27 to 0.34 as characterized by X-ray photoelectron spectroscopy (XPS), which reveals the component of Si_2p decreasing from 66.3 to 59.5%, and the component of C_1s increasing from 23.9% to 31% to confirm the formation of Si-rich SiC matrix. Annealing of the SiC sample from 650 °C to 1050 °C at 200 °C increment for 30 min induces the very tiny shift on the wavenumber of the crystalline Si (c-Si) related peak due to the precipitation of Si-QDs within the SiC matrix, and the Raman scattering spectra indicate a broadened Raman peak ranging from 410 to 520 cm^? 1 related to the amorphous Si accompanied with the significant enhancement for SiC bond related peak at 980 cm^? 1. From the high resolution transmission electron microscopy images, the critical temperature for Si-QD precipitation is found to be 850 °C. The self-assembly of the crystallized Si-QDs with the size of 3 ± 0.5 nm and the volume density of (3 ± 1) × 10¹⁸ (#/cm³) in Si-rich SiC film with R = 70% are observed after annealing at higher temperature.     

Fabrication and optimization of single-junction nc-Si:H n–i–p solar cells using Si:H phase diagram concepts developed by real time spectroscopic ellipsometry

In this study, we have developed and applied deposition phase diagrams in the plane of the bulk layer thickness d_b and the H₂-dilution ratio R = [H₂]/[Si₂H₆] for Si:H materials deposited by 70 MHz VHF PECVD from [H₂] + [Si₂H₆] mixed gases on c-Si/(native-oxide)/n-layer substrates. To establish the phase diagrams, series of Si:H depositions having different R values over the range of 60–150 were measured in real time using a rotating-compensator multichannel ellipsometer. Using phase diagram concepts for guidance, we have fabricated high efficiency single-junction nc-Si:H n–i–p solar cells with ～3 Å/s intrinsic layers using the VHF PECVD process. We have found that the nc-Si:H solar cells with the best performance are obtained by incorporating i-layers deposited in the single-phase nanocrystalline silicon regime near the transition boundary to mixed-phase (a + nc)-Si:H. Applying insights from real time spectroscopic ellipsometry moreover, we have investigated in detail the effects of the phase of the underlying n-layer on the phase evolution of the overdeposited Si:H i-layer and on the overall device performance. With the strategy developed here, a stabilized efficiency of η = 9.46% (V_oc = 0.516 V, J_sc = 24.65 mA/cm², FF = 0.744) has been achieved for nc-Si:H solar cells (0.25 cm² in active area) fabricated with an i-layer deposition rate of ～2.2 Å/s.     

Deposition of microcrystalline silicon films at ultrafast rate by using a new microwave induced plasma source

Synthesis of microcrystalline silicon (μc-Si) film at an ultrafast deposition rate over 100 nm/s is achieved from SiH₄ + He by using a high density microwave plasma source even without employing H₂ dilution and substrate heating techniques. Systematic deposition studies show that high SiH₄ flow rate and working pressure increase film deposition rate while high He flow rate decreases the rate. On the other hand, crystallinity of deposited Si film decreases with increasing SiH₄ or He flow rate and working pressure. Enhancements of gas phase and surface reactions during film deposition process are responsible for the achievement of high deposition rate and high film crystallinity.     

About diffusion mechanism in silica liquid under pressure

We perform a molecular dynamic simulation to study the diffusion mechanism in silica liquid under pressure up to 25 GPa and at temperature of 3000 K. We find that total O―Si―O angle distribution can be expressed by a simple relation between partial O―Si―O angle distribution and fractions of units SiO_x. Specifically, we demonstrate that these liquids consist of identical units SiO₄, SiO₅ and SiO₆ and have common partial O―Si―O angle distribution. We also show that each particle undergoes a series of stages where the particle locates in unchanged unit SiO_x, x = 3, 4, … 7 or OSi_y, y = 1, 2, 3, 4. The diffusivity strongly depends on the rate of transitions Si^ξ → Si^ξ ± 1 and O^ζ → O^ζ ± 1 which is significantly different between low- and high-pressure samples. For low-pressure sample the transitions Si⁴ → Si⁵, Si⁵ → Si⁴, O² → O³ and O³ → O² are dominant, meanwhile for high-pressure sample there are transitions Si^ξ → Si^ξ ± 1 with ξ = 4, 5, 6 and O^ζ → O^ζ ± 1 with ζ = 2, 3, 4. This finding may be common for diffusion in all network-forming liquids. The simulation also reveals the spatially heterogeneous dynamics in low-pressure liquid where a large cluster of immobile particle exists for the time that a number of particles move over several inter-particle distances.     

Improved method for preparation of anhydrous silica by microwave irradiation with spectroscopic characterization and toxicity assay

Amorphous anhydrous silica SiO_{2 (mw)} (99.99%) is successfully synthesized through microwave irradiation technique and time of reaction is reduced up to 1 h. The dehydration phase study of Si–water, Si–OH, Si–O–Si networking, elemental analysis and surface morphology was carried out by FTIR, FTNIR, SEM and EDAX spectroscopic techniques. The broad absorption stretching and bending of Si–OH and H₂O at 3695.38–2832.96 cm^? 1, 1638 cm^? 1 and 1191.20–1017.14 cm^? 1 completely disappeared and appearance of new bands at 946.93 and 797.63 cm^? 1 confirmed the amorphous anhydrous silica with Si–O–Si networking. The SEM images of SiO_{2 (mwc)} described the smooth and fine particle texture and confirmed 99.99% Si–O–Si networking of anhydrous silica. The 99.99% purity was verified by EDAX spectra which exhibited sharp signals only for oxygen and silicon. Toxicity against Monomorium minimum and Tribolium castaneum with 100% mortality and LT₅₀ 91 min and 7.5 h respectively is being reported. It can be used for long storage of grains in the future.     

Atomic diffusion of boron and other constituents in amorphous Si–B–C–N

The self-diffusion of boron is studied between 1550 and 1700 °C in polymer-derived amorphous solids of composition Si₃BC_4.3N₂. Ion implanted stable ¹⁰B isotopes are used as tracers and secondary ion mass spectrometry for depth profiling. The experimentally determined diffusivities obey an Arrhenius behavior with a high activation enthalpy of ΔH = (7.3 ± 1.3) eV and a high pre-exponential factor of D₀ = 1.6 m²/s. The results are discussed in relation to the diffusivities of the other constituents (Si, C, N) and possible diffusion mechanism are suggested.     

Microstructure and field emission properties of the Si–TaSi2 eutectic in situ composites by electron beam floating zone melting technique

The directionally solidified Si–TaSi₂ eutectic in situ composites, which have highly aligned and uniformly distributed TaSi₂ fibers embedded in the Si continuous matrix, are obtained by electron beam floating zone melting (EBFZM) technique at the solidification rate range 0.3–9.0 mm/min. The preferential orientation of the Si–TaSi₂ eutectic is also studied by selected area electron diffraction (SAED), which is [0 1¯ 1¯]Si∥[0 0 0 1]TaSi₂ and (0 1¯ 1)Si∥(0 1¯ 1 1)TaSi₂. Moreover, field emission properties of the Si–TaSi₂ eutectic in situ composites are investigated by transparent anode imaging technology. Approximately straight F–N curves show that this material has excellent field emission properties.     

Corrosion behavior of Fe-based ferromagnetic (Fe,Ni)–B–Si–Nb bulk glassy alloys in aqueous electrolytes

Fe-based ferromagnetic [(Fe_1?xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ (x = 0, 0.2 and 0.4) bulk glassy alloys (BGAs) with a diameter of 2 mm were prepared by copper mold casting. The corrosion behavior of glassy alloy rods obtained was investigated in 0.5 M NaCl, 0.5 M NaOH and 0.5 M H₂SO₄ aqueous electrolytes, respectively, using weight loss and electrochemical polarization measurements. It was found that the corrosion rates significantly decrease with an increase in Ni content in all examined solutions. The Ni-containing BGAs are spontaneously passivated with wide passive regions and low passive current densities in NaCl and NaOH solutions, but exhibit the active–passive–transpassive behavior in H₂SO₄ solution. The partial substitution of Ni for Fe results in a considerable improvement on the corrosion resistance of [(Fe_1?xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ BGAs, because of the structural and chemical homogeneousness of the amorphous phase and the effect of Ni on promoting the formation of a passive film. Besides their high glass-forming ability (GFA), excellent soft-magnetic properties and good mechanical performance, which have been reported before, these FeNi-based BGAs also feature rather high corrosion resistance.     

High-yield synthesis of semiconductive type-II Si clathrates with low Na content

To develop an efficient synthesis of type-II Si clathrates with low Na content (Na_xSi₁₃₆: x = 0–24), various conditions for annealing the Zintl phase NaSi were examined. The addition of a pre-annealing process under vacuum at 250 °C following the preparation of NaSi resulted in a decrease in the Na content of type-II Si clathrates from 4 to 2 when the pre-annealing duration ranged from 0 to 60 h, while the volume fraction of type-II Si clathrate crystals in the synthesized specimens (type-II/(type-I + type-II + d-Si)) deduced by powder X-ray diffraction and Rietveld analysis was maintained at approximately 85%. These preparation techniques that enable the high-yield synthesis of semiconductive type-II Si clathrates open opportunities for the application of these substances to semiconductor devices.     

Influence of TiO2 film on photo-catalytic property of enamels

Ti(OC₄H₉)₄–C₂H₅OH–H₂O was used as matrix solution of titanium dioxide (TiO₂) film. Through sol–gel process, enamels were coated with TiO₂ film. Using methyl-orange as the simulative pollutant solution of photo-catalytic efficiency, we studied photo-catalytic activities of the enamels with and without TiO₂ film. Crystal structure and microstructure of the TiO₂ film were analyzed by means of scanning electron microscope (SEM) and X-ray diffract meter (XRD). Results showed that the photo-catalytic efficiency was greatly improved by the TiO₂ film coated on the enamel surface, and crystal of the TiO₂ film was anatase with imperfect crystal structure at the baking temperature of 450 °C. The TiO₂ film consisted of a lot of very small particles (0.01–0.05 μm and/or 10–50 nano), those particles had very small size and very large surface dimension as well as very high chemical activity, which made TiO₂ film have excellent photo-catalytic degradation.     

Influence of nickel content on the electrochemical behavior of Finemet type amorphous and nanocrystalline alloys

The aim of this work has been the systematic study of the influence of partial substitution of Fe by Ni in the Ni_xFe_73.5−xSi_13.5B₉Nb₃Cu₁ alloy within the range 0 ⩽ x ⩽ 10% atom (x = 0, 2, 4, 6, 8, 10) on electrochemical behavior, corrosion rate and the structural changes in amorphous and nanocrystalline alloys. The amorphous nature of the alloys was confirmed by X-ray diffraction and the chemical compositions were determined by ICP. The glass transition and kinetic crystallization of amorphous alloys were studied by DSC. The technique of XPS was used for evaluating the chemical states of elements present in native oxide films. The electrochemical behavior of amorphous and nanocrystalline alloys have been investigated in 0.5 M KOH using cyclic voltammetry. The experimental results show that the formation of different nanocrystalline phases is not excessively transformed by the addition of small amount of nickel and the electrochemical behavior is improved as nickel content increased.     

Nanostructural and optical features of amorphous AlxSi0.45−xO0.55 (0 ⩽ x ⩽ 0.05) thin films prepared by RF-magnetron sputter techniques

The nanostructural, chemical, and optical features of Al_xSi_0.45−xO_0.55 (0 ⩽ x ⩽ 0.05) thin films were investigated in terms of Al concentration and post-deposition annealing conditions; the films were prepared by co-sputtering a Si main target and Al-chips, and the annealing was carried out at temperatures of 400–1100 °C. The a-Si_0.45O_0.55 films prepared without Al-chips and annealed at 800 °C contain ∼3.5 nm-sized Si nanocrystallites. The photoluminescence (PL) intensity as well as the volume fraction of Si nanocrystallites increased with increasing the concentration of Al to a certain level. In particular, the intensity of the PL spectra of the Al_0.025Si_0.425O_0.550 films which were annealed at 800 °C increased significantly at wavelengths of ∼580 nm. It is highly likely that the observed increase in the PL intensity is caused by the raise in the total volume of the ∼3.5 nm-sized nanocrystallites in the films. The addition of Al as well as the post-deposition annealing allow adjustment and control of the nanostructural and light-emission features of the a-SiO_x films.     

Magnetic properties of liquid 3d transition metal–Si alloys

The magnetic susceptibility has been measured for liquid transition metal–Si alloys (TM_1−cSi_c, TM = Ni, Co, Fe, Mn) as a function of temperature. The magnetic susceptibilities of liquid Ni_1−cSi_c with c ⩾ 0.3, liquid Co_1−cSi_c with c ⩾ 0.4 and liquid Fe_1−cSi_c with c ⩾ 0.6 were found to be almost independent of temperature, which suggests that the Ni, Co and Fe ions on the Si side are in the non-magnetic state. Liquid Ni_1−cSi_c with c ⩽ 0.2, liquid Co_1−cSi_c with c ⩽ 0.3 and liquid Fe_1−cSi_c with c ⩽ 0.5 show the Curie–Weiss behavior with a reasonable value of effective Bohr magnetic number. Liquid Mn_1−cSi_c with c ⩽ 0.2 and c ⩾ 0.6 were found to be in their non-magnetic state. However, the Curie–Weiss behavior was observed for liquid Mn_1−cSi_c with c = 0.3, 0.4 and 0.5. The magnetic susceptibility of their liquid alloys in the non-magnetic state has been studied by using Anderson model. The density of 3d states at the Fermi level can be estimated from the data of magnetic susceptibility.