Lifetime of dominant radicals for the deposition of a-Si:H from SiH4 and Si2H6 glow discharges

Deposition kinetics of a-Si:H from Si₂H₆ as well as SiH₄ glow discharge has been investigated using a triode reactor with a variable electrode-substrate distance. The results of deposition rate and OES (optical emission spectroscopy) indicate that dominant radicals as a film precursor are different between SiH₄ and Si₂H₆ plasma and the radical in Si₂H₆ has a much shorter lifetime than that in SiH₄.     

Undoped amorphous SiNx: H alloy semiconductors: Dependence of electronic properties on composition

The electrical and optical properties of a-SiN_x:H thin films prepared by rf growth-discharge in SiH₄N₂H₂ without B or P doping have been measured for 0 < x ? 0.6. It is observed that the activation energy for extended-state electron conduction as well as the optical gap are unaffected by N content for x ? 0.4. The electron mobility in extended states is improved by as much as a factor of 10 by the N incorporation. There is a rapid conversion from the tetrahedral network to a Si₃N₄ network as x increases above ≈ 0.4.     

Mechanisms of the growth of nanocrystalline Si:H films deposited by PECVD

Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited using plasma-enhanced chemical vapor deposition from a SiF₄/SiH₄/H₂ gas mixtures. Properties were examined of nc-Si:H films produced by decreasing the deposition temperature (T_d) under two different hydrogen dilution ([H₂]) conditions. For these films, the X-ray diffraction, the Raman scattering, the Fourier transform infrared absorption and the stress were investigated. Our results show that the decrease in T_d has significant effects in the decrease of the average grain size (〈δ〉), the crystalline volume fraction (ρ) values, and an increase in the density of SiH-related bonds (N_SiH) values. On the contrary, increases in [H₂] decreased the 〈δ〉 and the N_SiH, while the ρ were increased. Our experiments also confirmed that the increase in ρ corresponds with the decrease in N_SiH. In view of these results, it may be concluded that the use of both low T_d and high [H₂] conditions might lead to growth of nc-Si:H films with small grains and high crystallinity. In this context, the surface processes (such as diffusion and etching) for the growth of nc-Si:H films were extensively discussed in this current work.     

Properties of a-Si : H : F deposited in SiF4/SiH4/Ar Gas mixtures by a glow-discharge technique

Films of silicon-hydrogen-fluorine alloys (a-Si : H : F) were prepared by capacitive coupling rf glow discharge in an SiF₄/SiH₄/Ar gas mixture. Up to 4% fluorine can be incorporated in films prepared with a gas mixture of SiF₄/(SiF₄ + SiH₄) = 0.72. The hydrogen concentration decreases as fluorine concentration increases but there is still more hydrogen than fluorine in films with the highest density of fluorine, which is in sharp contrast to the best films produced by the Madan and co-workers. Both dark conductivity and photoconductivity decrease as fluorine increases, though improvement of doping efficiency was observed in films with moderate concentrations of fluorine. The influence of hydrogen is more important than the influence of fluorine in the present silicon-hydrogen-fluorine alloys.     

Synthesis, Crystal Structure and Properties of the Binuclear Complex [Sm2(C10H9N2O4)2(C10H8N2O4)2(H2O)4]

Abstract  A novel binuclear Smarium (III) complex with N-(2-propionic acid)-salicyloyl hydrazone (C₁₀H₁₀N₂O₄, H₃L) was prepared and characterized. The crystal structure of [Sm₂(H₂L)₂(HL)₂(H₂O)₄] (1) was determined by X-ray single crystal diffractometry. 1 crystallizes in the monoclinic systerm, space group P2(1)/c, with a = 0.10229(2), c = 31.549(7), b = 0.70599(15) nm, and Z = 4. In the structure, Sm(III) is nine-coordinated by carboxyl O and acyl O atoms and imido N atoms of two ligands (H₂L and HL forms) and O atoms from two water molecules. H₂L and HL act as tridentate ligands which form two stable five-numbered chelating rings sharing one edge in the keto form for each ligand, and the carboxyl groups of two ligands were coordinated via bidentated bridging form. The coordination polyhedron around Sm (III) was described as a monocapped square antiprism. The inter- and intramolecular hydrogen bonds resulted in a three-dimensional network and provided extra stability for the structure. The complex was researched the interaction with calf thymus DNA by electronic absorption titration and emission titration. The results show that the complex is bound to calf thymus DNA mainly by intercalation .The complex also shows good fluorescence property. Index Abstract  The title compound, [Sm₂(H₂L)₂(HL)₂(H₂O)₄] was synthesized by the treatment of N-(2-propionic acid)-salicyloyl hydrazone (C₁₀H₁₀N₂O₄, H₃L) and Sm(NO₃) · 4H₂O and its crystal structure determined. Single crystal X-ray diffraction analysis reveals that Sm (III) is nine-coordinated by carboxyl O and acyl O atoms and imido N atoms of two ligands (H₂L and HL forms) and O atoms from two water molecules. The carboxyl groups of two ligands were coordinated via bidentated bridging form. The coordination polyhedron around Sm (III) was described as a monocapped square antiprism. The inter- and intramolecular hydrogen bonds resulted in a three-dimensional network and provided extra stability for the structure.      

Raman and IR absorption spectroscopic studies on α, β, and amorphous Si3N4

Vibrational excitations of α- and β-Si₃N₄ were studied by Raman and infrared absorption spectroscopies. Group theory was employed to interpret the observed spectra of crystalline α- and β-Si₃N₄. Both Raman and IR spectra of amorphous Si₃N₄ exhibit two broad peaks centered at about 400 and 900 cm^?1. Amorphous Si₃N₄ was found to be of the non-molecular, random-network type.     

Glass formation through hydrolysis of Si(OC2H5)4 with NH4OH and HCl solution

Monolithic silica glass was obtained by heating the gels prepared by hydrolyzing Si(OC₂H₅)₄ with NH₄OH and HCl solution. The effect of the condition of hydrolysis of Si(OC₂H₅)₄ on glass formation was examined by measuring the bulk density, the infrared spectra and the thermal shrinkage of the gel on heating. The gel prepared by hydrolysis with NH₄OH solution consisted of numerous spherical particles, the bulk density being about 0.8. This gel abruptly shrank at about 1050°C, being converted to the pore free material similar to fused silica. The conversion of the gel to glass followed the sintering model in which the viscous flow controlled the sintering process. The viscosity and the activation energy for viscous flow were calculated on the basis of the Frenkel equation. On the other hand, the spherical particles were not observed in the gel prepared by hydrolysis with HCl solution. The bulk density of the gel was about 1.8. This gel was converted to glass at about 700°C, which was lower than the temperature of glass formation for the gel obtained by hydrolysis with NH₄OH solution.     

Synthesis and crystal structures of two copper(I) π-complexes with 1-allyloxybenzotriazole of CuBr?C6H4N3(OC3H5) and 2CuCl?C6H4N3(OC3H5) compositions

Both compounds of CuBr⋅C₆H₄N₃(OC₃H₅) (sp. gr. P1, a = 7.633(1) Å, b = 9.987(1) Å, c = 14.898(2) Å, α = 104.75(1)^∘, β = 94.76(1)^∘, γ = 106.90(1)^∘) (I) and 2CuCl⋅C₆H₄N₃(OC₃H₅) (sp. gr. Cc, a = 11.2483(4) Å, b = 16.7076(6) Å, c = 7.2948(3) Å, β = 118.612(2)^∘) (II) composition were prepared by alternating-current electrochemical synthesis. In I due to a bridging function of organic moieties 16-membered cycles appear which are combined into ribbons {Cu₂Br₂[(C₆H₄N₃(OC₃H₅)]₂}_n. Each of two crystallographically independent copper atom possesses a trigonal-pyramidal arrangement with different degree of tetrahedral distortion. Distinctive numbers of hydrogen bonds around Br1 and Br2 atoms cause rather appreciable distinctions in copper–olefinic bond interaction effectiveness for each metal atom. In II Cu₂Cl₂ rhombs are joined to infinite chains oriented along [010] direction. Each ligand molecule is also coordinated through the C=C—bond of the allylic group to copper atom of one inorganic chain and through the nitrogen atom to a metal atom belonging to another copper-halide chain. Cu1 atoms is tetrahedrally surrounded by three chlorine atoms and nitrogen one, whereas a trigonal-planar arrangement of Cu2 atom is formed by two halogen atoms and slightly disordered olefinic group.     

Structure characterization of CVD amorphous Si3N4 by pulsed neutron total scattering

The structure factor S(Q) of chemically vapor-deposited (CVD) amorphous Si₃N₄ has been measured by pulsed neutron diffraction over the range of the scattering vector Q from 1–330 nm^?1. The oscillatory behavior in the S(Q) persists up to Q = 300 nm^?1 and there is appreciable small angle scattering intensity. The SiN bond length is l_SiN = 0.1729 nm, and its coordination numbers n_SiN and n_NSi are 3.70 and 2.78 respectively. The bond angles around a Si and a N atom are found to be 109.8 and 121°. Analysis of the small angle scattering intensity shows the existence of voids with an average diameter of about 1 nm and a volume fraction of about 4%, which may stabilize the amorphous structure of Si₃N₄ having rigid covalent bonds due to relaxing the strain energy accumulated in the matrix.     

Plasma etching of As2S3 films for optical waveguides

Chalcogenide glasses are good candidate materials for ultra-fast non-linear optic devices. In this work, we present the photolithographic process and the plasma etching of arsenic tri-sulphide (As₂S₃) film. The films were deposited on thermally oxidized silicon substrates by ultra-fast pulsed laser deposition. To protect As₂S₃ film from photo-resist developer, thin resist layer ∼100-200 nm was remained on the UV exposed area by controlling resist development time. After removing the protective layer in oxygen plasma, As₂S₃ waveguides were patterned in inductively coupled plasma reactive ion etching (ICP-RIE) system using CF₄-O₂ gas mixture. We investigated the etch rate and the etch selectivity to photo-resist of As₂S₃ as a function of bias power, induction power, operating pressure, and gas flow rate ratio of CF₄ and O₂. The film is mainly etched by the chemical reaction with fluorine radicals. The content of oxygen in the plasma determines the etched sidewall profiles and nearly vertical profile was obtained at high oxygen content plasma.     

Synthesis and structure of (NH4)4[(DMF)2Mo8O26]· 2CH3CH2OH·2H2O (DMF= N , N -dimethylformamide)

A new organic-inorganic hybrid γ-octamolybdate complex, (NH₄)₄[(C₃H₇NO)₂Mo₈O₂₆]·2CH₃CH₂OH·2H₂O was synthesized from the mixture of ethanol, DMF, 4-aminobenzoic acid, (NH₄)₆Mo₇O₂₄·4H₂O, HCl and H₂O. The structure was determined by X-ray crystallography. It crystallizes in monoclinic P2₁/n space group with the crystal cell parameters of a = 8.8825(4), b = 21.1608(10), c = 11.1343(6) ?, β = 104.7720(10)°, V = 2023.64(17) ?³ and Z = 2. The crystal X-ray analysis shows that two DMF molecules are bound to γ-octamolybdate anion. The molecular structure is stabilized by the complex hydrogen bonding.     

Large grain μc-Si:H films deposited at low temperature: Growth process and electronic properties

We have studied structural and electronic properties of μc-Si:H films deposited from SiH₄ + H₂ and SiH₄ + H₂ + Ar gas mixtures. The use of Ar containing gas mixtures for depositions allows us to increase deposition rate by a factor of two and to obtain films with an important fraction of large grains in comparison with SiH₄ + H₂ gas mixtures. Electronic properties of fully crystallized films become more intrinsic with the increase of large grain fraction. Deposition of highly p- and n-doped μc-Si:H layers from the dopant/SiH₄ + H₂ gas mixture at a temperature of 175 °C is possible without any remarkable changes in crystallinity in comparison with undoped films deposited with the same discharge conditions.     

Effect of N2/CH4 flow ratio on microstructure and composition of hydrogenated carbon nitride films prepared by a dual DC-RF plasma system

Hydrogenated carbon nitride (a-CN:H) films were deposited on n-type (1 0 0) silicon substrates making use of direct current radio frequency plasma enhanced chemical vapor deposition (DC-RF-PECVD), using a gas mixture of CH₄ and N₂ as the source gas in range of N₂/CH₄ flow ratio from 1/3 to 3/1 (sccm). The deposition rate, composition and bonding structure of the a-CN:H films were characterized by means of X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectrometry (FTIR). The mechanical properties of the deposited films were evaluated using nano-indentation test. It was found that the parameter for the DC-RF-PECVD process had significant effects on the growth rate, structure and properties of the deposited films. The deposition rate of the films decreased clearly, while the N/C ratio in the films increased with increasing N₂/CH₄ flow ratio. CN radicals were remarkably formed in the deposited films at different N₂/CH₄ flow ratio, and their contents are related to the nitrogen concentrations in the deposited films. Moreover, the hardness and Young’s modulus of the a-CN:H films sharply increased at first with increasing N₂/CH₄ flow ratio, then dramatically decreased with further increase of the N₂/CH₄ flow ratio, and the a-CN:H film deposited at 1/1 had the maximum hardness and Young’s modulus. In addition, the structural transformation from sp³-like to sp²-like carbon-nitrogen network in the deposited films also was revealed.     

Chemical durability of lead silicate glass in HNO3, HCl and H2SO4 aqueous acid solutions

Acid dissolution of silicate glasses with different lead contents was rigorously investigated. Aqueous solutions containing 0.5, 1, and 2 N HNO₃, HCl and H₂SO₄ were used to measure the durability of the glass probes. Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Inductively Coupled Plasma (ICP), X-ray Diffraction (XRD) and weight loss analyses were used to evaluate the morphological/compositional changes of the probes, the ash deposit, and the aqueous solutions produced due to the dissolution of the glass specimens. Empirical results showed that any increase in the lead content of the probes deteriorated the durability of the glasses by accelerating the hydrolysis of the silica network. ZrO₂ and TiO₂ additions had inverse effect and improved the chemical durability and the practical life-time of the lead glasses.     

Growth and shape control of orthorhombic Fe5(PO4)4(OH)3·2H2O single crystalline dendrites

Orthorhombic Fe₅(PO₄)₄(OH)₃·2H₂O single crystalline dendritic nanostructures have been synthesized by a facile and reproducible hydrothermal method without the aid of any surfactants. The influences of synthetic parameters, such as reaction time, temperature, the amount of H₂O₂ solution, pH values, and types of iron precursors, on the crystal structures and morphologies of the resulting products have been investigated. The formation process of Fe₅(PO₄)₄(OH)₃·2H₂O dendritic nanostructures is time dependent: amorphous FePO₄·nH₂O nanoparticles are formed firstly, and then Fe₅(PO₄)₄(OH)₃·2H₂O dendrites are assembled via a crystallization-orientation attachment process, accompanying a color change from yellow to green. The shapes and sizes of Fe₅(PO₄)₄(OH)₃·2H₂O products can be controlled by adjusting the amount of H₂O₂ solution, pH values, and types of iron precursors in the reaction system.     

A new dabco templated metal sulfate, (C6H14N2)[Mn (H2O)6](SO4)2. Chemical preparation, hydrogen-bonded structure and thermal decomposition

The crystal structure of manganese sulfate templated by 1,4-diaza-bicyclo[2.2.2]octane (abbreviated dabco), (C₆H₁₄N₂)[Mn(H₂O)₆](SO₄)₂, was investigated using single crystal X-ray diffraction data. It crystallises in the monoclinic system (space group P2₁/c) with the following unit-cell parameters: a = 12.1392(2) ?, b = 12.3117(2) ?, c = 12.2765(2) ?, β = 104.607(1)°, V = 1775.47(5) ?³ and Z = 4. The structure has been solved using direct methods and refined by least-squares analysis [R ₁ = 0.0381, wR ₂ = 0.1082]. The crystal structure of the title compound is built from isolated [Mn(H₂O)₆]²⁺ octahedral cations, 1,4-diaza-bicyclo[2.2.2]octandiium cations (C₆H₁₄N₂)²⁺ and sulfate anions (SO₄)²⁻ connected by a three-dimensional hydrogen-bond network. The thermal decomposition of the precursor, studied by thermogravimetry and temperature-dependent X-ray powder diffraction, proceeds through four stages giving rise to the mixture of Mn₂O₃and Mn₃O₄. Supplementary Material CCDC 620298 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.     

Problems of Surface Morphology and Layer Deposition during Plasma Etching Processes (II) Si-etching in CF4-, CF4/O2-and CF4/H2 Plasmas

The plasma etching of Si in CF₄-, CF₄/O₂-and CF₄/H₂ plasmas was investigated in dependence on the etching gas, the plasma conditions (pressure, power density) and etching time in different reactors. A roughening of the surface and the formation of a “semi-amorphous” surface layer with a power-like morphology was detected by TEM-and RHEED methods. It is supposed that the surface layer has a fundamental consequence as an intermediate state in the etching mechanism.     

Chemical durability of Na2OCaOSiO2 glasses in acid solutions

The resistance of Na₂OCaOSiO₂ glasses to acid solutions has been studied. The compositions studied were Na₂O · 4SiO₂, Na₂O · x CaO · (4?x) SiO₂ and a common electrode glass containing 22.63Na₂O and 5.58 CaO, mol%. The reaction was made at 40°C for about 3 h in 1N solutions of HCl, HNO₃ and H₂SO₄. Powdered glass samples were used and the reaction was followed by analyzing the solution for soda, lime and silica.The extraction rates of each constituent were measured. The effect of acid concentration was also studied for each glass using 10^?3–10N solutions of the three acids for a fixed time. The quantity of calcium extracted increased slowly at first with increasing calcium content in the glass, but rapidly when the lime content exceeded ≈10 mol%. Above this concentration, both calcium and sodium appears to pass into solution in the same proportion in which they are present in the glass. The extraction rate was found to depend on the type and concentration of the acid used, being least in H₂SO₄ and much higher and almost equal in both HCl and HNO₃.An attempt was made to correlate the results of decomposition of the soda-lime-silica glasses to their membrane potentials in acidic solutions.     

A new hydro-fluorinated amorphous silicon produced by using intermediate species SiF2

Intermediate species SiF₂, mixed with H₂, is used instead of SiF₄ as the material gas for a hydro-fluorinated amorphous silicon (a-Si:F:H). The deposition rate can be easily increased up to about 20 Å/sec without apparent degradation of photo-conductive property by using intermediate species, and also, Si-F or Si-H single bond configuration becomes dominant although there apparently exist Si-H₂ or Si-F₂ higher order bonds in the film produced by using SiF₄.     

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.