Deposition of mechanically hard amorphous carbon nitride films from decomposition of BrCN. Effects of substrate cooling and pulsed rf-bias voltage

Mechanically hard amorphous carbon nitride films were formed by applying a combination of radio frequency (RF) bias voltage to the substrate and the chemical vapor deposition process using the decomposition reaction of BrCN with the microwave discharge flow of Ar. Cooling water was circulated inside the substrate stage. The maximum hardness was (17 ± 1) GPa for the film prepared under the negative RF bias voltage, −V_RF, of 30 V. This hardness was nearly twice that of the film prepared without cooling, suggesting that substrate cooling was effective for suppressing the relaxation of the internal stress of the film due to the temperature rise during the application of the RF bias voltage. Under the continuous operation of the RF bias voltage, films cannot be formed for −V_RF > 40 V because of the sputtering by the bombardment of energetic Ar⁺. Then, the RF bias voltage was applied with a pulsed operation. By using this operation films were prepared in the range of −V_RF = 40-100 V. The hardness, (36 ± 10) GPa, was obtained for the film obtained under the conditions of −V_RF = 100 V, the pulse period of 1000 s, and the pulse-on time of 800 s. The observed hardness scattered largely for the different observation points within this film; a single observation point in that film showed the maximum hardness of 46 GPa. According to the IR spectra of the films, the three-dimensional C-N network structure was developed.     

Growth and properties of microcrystalline germanium–carbide alloys grown using electron cyclotron resonance plasma processing

We report on the growth and properties of a new material, microcrystalline (Ge, C), which has potentially important optical, electrical and structural properties. The material was grown using a remote, low pressure electron cyclotron resosnance (ECR) plasma process on glass, stainless steel and c-Si substrates. The growth was done with hydrogen dilution and ion bombardment at temperatures of 350–400°C. We discovered that the optical absorption curve parallels that of c-Ge, with increased bandgaps as C is incorporated. We obtained up to 2% C incorporation, which increased the gap to 1.1 eV. At comparable bandgaps, the absorption coefficient of the (Ge, C) material is much larger than that of c-Si. Raman and X-ray measurements detected microcrystalline structure, and a dependence of grain size on the substrate used. The lattice constant contracted with C incorporation, approximately obeying Vegard’s law. Both undoped and n-doped materials were grown.     

Correlation between interfacial structure and c-axis-orientation of LiNbO3 films grown on Si and SiO2 by electron cyclotron resonance plasma sputtering

Thin films of crystalline lithium niobate (LN) grown on Si(1 0 0) and SiO₂ substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600 °C on the Si(1 0 0) surface produced columnar domains of LiNbO₃ with well-oriented c-axes, i.e., normal to the surface. When the SiO₂ substrate was similarly exposed to plasma at temperatures above 500 °C, however, increased diffusion of Li and Nb atoms into the SiO₂ film was seen and this led to an LN–SiO₂ alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material.     

Transmission electron microscopy and Rutherford backscattering spectrometry studies of Ag2Te films formed from Ag‐Te thin film couples

Formation of Ag₂Te thin films from room temperature (300 K) solid state reaction of Ag and Te thin film couples is investigated. Rutherford Backscattering Spectrometry (RBS) studies confirmed the complete miscibility of the couples and the stoichiometry of the resulting Ag₂Te. Structural analysis by Transmission Electron Microscopy (TEM) showed a fine‐grained structure with monoclinic and orthorhombic phases. Annealing at high temperatures resulted in the growth of giant crystallites with monoclinic phase at random sites. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical, and electrical properties of electron beam evaporated CdSe thin films

CdSe films have been deposited on glass substrates at different substrate temperatures between room temperature and 300 °C. The films exhibited hexagonal structure with preferential orientation in the (002) direction. The crystallinity improved and the grain size increased with temperature. Band gap values are found decreasing from about 1.92 eV to 1.77 eV with increase of the substrate temperature. It is observed that the resistivity decreases continuously with temperature. Laser Raman studies show the presence of 2 LO and 3 LO peaks at 416 cm^‐1 and 625 cm^‐1respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric function of amorphous silicon films,its oxidation and voids,studied by electron spectroscopy

The energy loss spectra of extremely pure and of oxidized amorphous silicon films were measured with 30 keV electrons in the energy loss range 2–25 eV with a resolution of 0.1 eV. The Si films were prepared by electron beam evaporation at a pressure below 10^?9 Torr during the evaporation process. The influence of contact to the atmosphere and to water on the energy loss spectrum was also investigated. The energy loss spectra can be described well by means of the dielectric theory extended to a multilayer system. The results of the measurements lead to the conclusion that the density of voids in the pure a-Si films deposited at room temperature is less than 5% of the bulk. This should be true as long as the effect of the voids can be described by a dielectric function.     

Structural,optical, electrical and luminescence properties of electron beam evaporated CdSe:In films

CdSe:In films were prepared by electron beam evaporation technique using CdSe and In₂Se₃ (purity ∼99.9%) pellets. The crystal structure of the films with and without Indium, measured by X‐ray diffraction (XRD), showed a typical wurtzite structure, higher Indium doping shifts the peak angle to higher side along with the broadening of the peaks. X‐ray photoelectron spectroscopy (XPS) studies indicated binding energies corresponding to 54 eV (Se3d_5/2), 444 eV (In 3d_5/2), 411 eV (Cd 3d_3/2), (Cd 3d_5/2). Atomic force microscope (AFM) studies indicated a uniform surface.The grain size decreases with increase of In doping. A decrease in the band gap was observed with increase of dopant concentration. Resistivity of the films is in the range of 10^‐3 Ωcm. Carrier density was in the range of 10²¹ cm^‐3 for the films. The photolumineasenec spectra (PL) spectra indicated three peaks. The peak intensity decreases as the Indium concentration increases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of high-temperature annealing on electron spin resonance in SiOx films prepared by R. F. sputtering system

Electron spin resonance (ESR) spectra are investigated in order to analyze paramagnetic defects in amorphous SiO_x films with 0.8 ≤ x ≤ 1.87 prepared by a co-sputtering of Si-wafer chips and a SiO₂ disk target. Effects of the thermal annealing at 900 °C and 1100 °C on the ESR spectra are also investigated. Four types of silicon dangling bond centers with forms of •Si ≡ Si_3 − nO_n (n = 0, 1, 2 or 3) are assumed in order to simulate the ESR spectra. The random bonding model appears to describe the network structure of the films with x ~ 2, that is, near the stochiometric composition of SiO₂. It is suggested that the structural fluctuation around silicon dangling bonds is larger in the sputtered SiO_x films used in the present work in comparison with those prepared by plasma-enhanced chemical vapor deposition.     

The electron paramagnetic resonance and optical spectra of copper and vanadium in phosphate glasses

In the present work the results of the systematic study of the EPR spectra of Cu²⁺ and V⁴⁺ ions in binary phosphate glasses are discussed. A comparison of the behaviour of the EPR spectra of two kinds of ions in the same glassy matrix allows one to determine more accurately the location of each kind of ions in this matrix. This paper deals mainly with the phosphate glasses ROP₂O₅ containing divalent modificators (R = Ca, Sr, Ba, Mg, Zn, Pb). The optical spectra were recorded on a SP-8 spectrophotometer in the range 300–1000 nm. The EPR spectra were recorded at room temperature on the EPR-3 spectrometer made in the USSR and operating in the X-band.     

Structural,optical and photoconductive properties of electron beam evaporated CdSxSe1‐x films

CdS_xSe_1‐x films were deposited by the electron beam evaporation technique on glass substrates at different temperatures in the range 30 – 300 °C using the laboratory synthesized powders of different composition. The films exhibited hexagonal structure and the lattice parameters shifted from CdSe to CdS side as the composition changed from CdSe to CdS side. The bandgap of the films increased from 1.68 to 2.41 eV as the concentration of CdS increased. The root‐mean‐roughness (RMS) values are 3.4, 2.6, 1.2 and 0.6 nm as the composition of the films shifted towards CdS side. The conductivity varies from 30 Ωcm^‐1 to 480 Ωcm^‐1 as the ‘x’ value increases from 0 to 1. The films exhibited photosensitivity. The PL spectrum shifts towards lower energies with decreasing x, due to the decrease of the fundamental gap with Se composition. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XPS characterization of corrosion films formed on the crystalline, amorphous and nanocrystalline states of the alloy Ti60Ni40

X-ray photoelectron spectroscopy investigations were carried out on the crystalline, amorphous and nanocrystalline states of the alloy Ti₆₀Ni₄₀ after corrosion test in 1 M HNO₃ aqueous medium using potentiodynamic polarization method. Polarization plots revealed that the nanocrystalline state is more corrosion resistant than the amorphous and crystalline states of the alloy Ti₆₀Ni₄₀. The XPS characterization of the oxide film formed after corrosion tests revealed that a multiple phase oxide film is formed on the crystalline and amorphous specimens of the alloy Ti₆₀Ni₄₀ consisting of Ti²⁺, Ti³⁺ and Ti⁴⁺ species along with some unoxidized Ti in metallic form (Ti⁰) in the case of crystalline specimen whereas the oxide film formed on nanocrystalline specimen consists of only Ti²⁺ and Ti⁴⁺ species. The high corrosion resistance of nanocrystalline state is attributed to the presence of fewer oxide species in the oxide film than that of the amorphous and crystalline states of the alloy Ti₆₀Ni₄₀.     

Photoinduced electron transfer and surface plasmon resonance in materials consisting of pyrene fluorophore and Au nanorods immobilized on MCM-48 surface

Mesoporous silica of the MCM-48 type as a support for fluorophore molecules was functionalized with 3-aminopropyl and 3-thiolopropyl groups. Then, molecules consisting of a fluorophore pyrene group and receptor fragments with donor N and O atoms were covalently attached by grafting of carboxyl groups to amino groups on a mesoporous silica surface. Additionally, Au nanorods were attached to thiol groups on the same surface. The vicinity of Au nanorods in a material with pyrene derivatives covalently grafted on the functionalized MCM-48 silica enhanced fluorescence of the composite material due to the surface plasmon resonance effect. The fluorescence emission of the prepared recognition material is quenched specifically owing to the photoinduced electron transfer effect after coordination reactions with Cu(II) ions. Moreover, the material exhibits selectivity for Cu(II) cations in aqueous solutions in presence of such metal ions as: alkali, alkaline earth, transition and heavy metals. During UV irradiation the studied material undergoes slowly photochemical degradation as a potential recognition element.     

The interpretation of the electric and optical properties of a-Si:H films produced by rf glow discharge through dark conductivity,photoconductivity and pulse controlled capacitance-voltage measurements

This paper deals with the interpretation of transport properties of amorphous silicon hydrogenated films (a-Si:H) through dark conductivity, photoconductivity and pulse controlled capacitance-voltage measurements. a-Si:H films were produced by rf glow discharge coupled either inductively or capacitively to a 3% SiH₄/Ar mixture at different crossed electromagnetic static fields. The data concerned with the dark activation energy, photoactivation energy, variation of the density of localized states and photosensitivity, (σ_ph/σ_d)_25°C, of a-Si:H films can account for their optoelectronic properties which are strongly dependent on the deposition parameters. We also observed that crossed electromagnetic static fields applied during film formation influences hydrogen incorporation in a different manner than previously proposed.     

Determination of the size and phase composition of silver nanoparticles in a gel film of bacterial cellulose by small-angle X-ray scattering,electron diffraction,and electron microscopy

The nanoscale structural features in a composite (gel film of Acetobacter Xylinum cellulose with adsorbed silver nanoparticles, stabilized by N-polyvinylpyrrolidone) have been investigated by small-angle X-ray scattering. The size distributions of inhomogeneities in the porous structure of the cellulose matrix and the size distributions of silver nanoparticles in the composite have been determined. It is shown that the sizes of synthesized nanoparticles correlate with the sizes of inhomogeneities in the gel film. Particles of larger size (with radii up to 100 nm) have also been found. Electron microscopy of thin cross sections of a dried composite layer showed that large particles are located on the cellulose layer surface. Electron diffraction revealed a crystal structure of silver nanoparticles in the composite.     

Stacking faults in lizardites 1T from electron diffraction data and modeling of diffraction effects

Stacking faults in lizardites 1T (polytype group A) have been studied by analyzing the oblique-texture electron diffraction patterns in combination with a numerical simulation of diffraction patterns. The simulation of diffraction profiles was performed for finite (10-layer) sequences using the statistical Markov model in the quasi-homogeneous approximation. Diffraction criteria are revealed, which indicate the presence of defects in lizardite 1T; these defects are related to the change in the layer orientation by 180° and displacements of adjacent layers by a/3. It is shown that in the case of the statistical distribution of defects, along with pairs of adjacent layers with layer packing features typical of polytype groups D and B, there are also sequences of layers 1T(A), correspondingly rotated by 180° or displaced by a/3 and 2a/3 with respect to the layers in the 1T matrix. The data obtained give deeper insight into the variations in layer packing in lizardites 1T.     

Local bonding of hydrogen in a-Si:H,a-Ge:H and a-Si,Ge:H alloy films

This paper reviews the local bonding of hydrogen (and deuterium) in a-Si:H(D), a-Ge:H(D) and a-Si, Ge:H(D) alloy films. We specify the types of atomic environments that have been identified through vibrational spectroscopy, primarily infrared (IR) absorption. We emphasize local modes and discuss the atomic motions that are responsible for the various spectral features. We discuss correlations between the occurrence of specific local bonding groups, e.g., polysilane and polygermane configurations, and the deposition techniques and parameters, including the substrate temperature (T_s), the gas mixtures and the RF power into a glow discharge, etc. We include a discussion of the theoretical approaches that have been used to treat vibrational modes in these materials. We emphasize the approximations that are valid because of the relatively light mass of the hydrogen and deuterium atoms compared with those of the silicon and germanium atoms. Finally we highlight the effects of neighboring alloy or impurity atoms on the frequencies of hydrogen vibrations in a-Si:H, and point out the differences between oxygen atom incorporation in a-Si and a-Ge alloys.     

Estimating accuracy of 17O NMR measurements in oxide glasses: Constraints and evidence from crystalline and glassy calcium and barium silicates

The use of ¹⁷O nuclear magnetic resonance (NMR) spectroscopy to measure site populations in silicate and aluminosilicate glasses has provided insights and challenges to conventional models of glass structure. In order to better understand the level of accuracy and precision achievable, we have synthesized crystalline barium metasilicate (BaSiO₃), barium orthosilicate (Ba₂SiO₄), tricalcium silicate (Ca₃SiO₅), a barium silicate glass ((BaO)_0.45(SiO₂)_0.55), and a calcium silicate glass ((CaO)_0.56(SiO₂)_0.44), and report ¹⁷O NMR spectra for all of these. After correcting the observed intensities for quadrupolar effects, we measure an NBO content of 66.7% ± 0.6% for the BaSiO₃, compared to the known value of 66.7%. Applying the same techniques for the glasses gives an NBO content of 58.8% ± 0.8% (vs. the expected 55.5% ± 1.4% from stoichiometry) for the barium silicate and 76.9% ± 1.2% (vs. 78.6% ± 1.4%) for the calcium silicate. Within our uncertainties, we find no evidence for deviation from conventional models of glass structure for the glasses studied here. We also see no NMR signal (detection limit of about 0.5%) at the expected position for “free” oxide ions (bonded only to Ca^2 +), as newly constrained by our data for crystalline Ca₃SiO₅, which contains this species.     

Growth,structure and properties of thin monocrystalline InSb films grown by recrystallization in a narrow gap

The results of investigation of recrystallization kinetics of (≦ 500 Å) InSb films are described with the aid of a laser refractometer. The thermodynamic process characteristic considered to the gap thickness and substrate material are investigated. It was revealed that the method of producing a protective SiO_x coating greatly affects the electric properties of InSb films.