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Nanostructured silicon carbon films composed of silicon nanocrystallites embedded in hydrogenated amorphous silicon carbon matrix have been deposited by plasma enhanced chemical vapour deposition technique using silane and methane gas mixture highly diluted in hydrogen. The structural and optical properties of the films have been investigated by X-ray diffraction, Raman, Fourier transform infrared, ultra violet-visible-near infrared and photoluminescence spectroscopies while the composition of the films has been obtained from nuclear techniques. The study has demonstrated that the structure of the films evolves from microcrystalline to nanocrystalline phase with the increase in radio frequency (rf) power. Further, it is shown that with increasing the rf power the size of silicon nanocrystallites decreases while the optical gap increases and a blueshift of visible room temperature photoluminescence peak can be observed. (c) 2012 Elsevier B.V. All rights reserved.

The effect of the rf power on the structural and electrical properties of nanostructured silicon carbon films deposited by Plasma Enhanced Chemical Vapour Deposition system, using silane and methane gas mixture highly diluted in hydrogen, has been investigated. The structural and electrical properties are found to depend strongly on rf power. The increase of the rf power decreases the size of the silicon crystallites as well as the crystalline fraction and increases the carbon content in the films. The study not only indicates the correlation between crystalline fraction and the electrical conductivity but also reveals the presence of nanocrystallites in the films deposited at high rf power.

Nanostructured silicon carbon films composed of silicon nanocrystallites embedded in the amorphous silicon carbon matrix are prepared by a rf-PECVD system at 250 °C from silane and methane gas mixture highly diluted in hydrogen onto 7059 Corning glass and p-layer deposited on tin oxide substrates by varying rf power from 25 to 65 W. The structural and compositional properties of the films have been investigated. The study demonstrates that rf power controls the crystalline fraction as well as the silicon crystallite size and that p-layer/tin oxide structure enhances the nucleation of silicon grains as compared to Corning glass (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanostructured silicon carbon thin films, composed of Si nanocrystallites embedded in hydrogenated amorphous silicon carbon matrix, have been prepared by varying rf power in ultra high vacuum plasma enhanced chemical vapour deposition system using silane and methane gas mixtures diluted in hydrogen. In this paper we have studied the compositional, structural and electrical properties of these films as a function of rf power. It is shown that with increasing rf power the atomic densities of carbon and hydrogen increase while the atomic density of silicon decreases, resulting in a reduction in the mass density. Further, it is demonstrated that carbon is incorporated into amorphous matrix and it is mainly bonded to silicon. The study has also revealed that the crystalline volume fraction decreases with increase in rf power and that the films deposited with low rf power have a size distribution of large and small crystallites while the films deposited with relatively high power have only small crystallites. Finally, the enhanced transport properties of the nanostructured silicon carbon films, as compared to amorphous counterpart, have been attributed to the presence of Si nanocrystallites.

Hydrogenated amorphous silicon carbon alloy films of different carbon content were prepared by Plasma Enhanced Chemical Vapor Deposition using silane and methane with helium dilution and were characterized to study their opto-electronic, structural and defective properties. A linear correlation between micro structural disorder and overall disorder has been demonstrated. Further, it has been shown that the increase in the intrinsic disorder leads to an increase in the defect density while the increase in voids results in the decrease in the mass density for the studied films.

Nanostructured films composed of silicon crystallites dispersed in an hydrogenated amorphous silicon carbon matrix have been deposited by plasma enhanced chemical vapour deposition from silane-methane mixtures diluted in hydrogen by varying the rf power. Compositional, structural, optical and photoconductivity properties of the films have been investigated. The increase in rf power in the 40-80 W range enhances the incorporation of carbon and hydrogen in the amorphous matrix and decreases the volume fraction and size of the silicon crystallites leading to an enlargement of the optical band gap from 2.07 to 2.20 eV. Steady state photoconductivity measurements, performed under monochromatic radiations in the visible range, have demonstrated the occurrence of monomolecular recombination kinetics in the samples under illumination and that the mobility-lifetime product of the free electrons as a function of the optical gap decreases from 1.9 × 10–7 to 2.5 × 10–9 cm2V–1 as in the case of device quality films deposited by silane-methane mixtures diluted in hydrogen. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanostructured silicon carbon films, composed of silicon nanocrystals embedded in hydrogenated amorphous silicon carbon matrix, have been prepared by plasma enhanced chemical vapor deposition technique using silane and methane gas mixture diluted in hydrogen. The composition, structure and surface morphology of the films have been investigated by nuclear techniques, Raman, Fourier transform infrared spectroscopy and atomic force microscopy. The study has demonstrated that the nanostructured silicon carbon films can be deposited at low temperature (250 °C) by varying rf power and the crystallinity degree of silicon is quite uniform along the growth direction. Further, it has established that with increase in rf power crystalline volume fraction decreases while carbon content increases in the films (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Coins are important archaeological objects that can provide valuable information regarding coin minting methodology and provenance as well as politics and economics of the time. Punch-marked coins are the oldest known numismatics used in ancient India. 23 Indian punch-marked silver coins were analysed, for the first time, by using multi-elemental non-destructive energy dispersive X-ray fluorescence (EDXRF) technique. Our study reveals that silver, copper, iron, gold and lead are the significant constituents of the Indian punch marked silver coins, with minor/trace of elements like Ti, Cr, Co, Ni, As and Y also seems to indicate the fragmentation as well as the impoverishment of the power for the regimes that had produced the studied coins.

Silicon rich hydrogenated amorphous silicon-carbon alloy films were deposited by plasma enhanced chemical vapour deposition in low power regime from silane methane mixtures diluted in helium by varying the methane fraction between 0.4 and 0.8. Films with carbon content ranging from 0.06 to 0.28 were obtained with a deposition rate of about 0.1 nm/s. The influence of carbon incorporation on the optical properties as well as disorder and defect density of the films has been investigated. The increase in carbon content leads to a decrease of the refractive index and an increase of the optical gap and disorder in the films. The defect density also increases with increasing carbon content, however lower values than those of films deposited by undiluted silane methane mixtures have been obtained for a carbon content greater than 0.1. Finally, the enhancement of carbon content causes the shift of peak position as well as the increase in the intensity and the width of the photoluminescence spectra. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogenated amorphous silicon carbon alloy (a-SiC : H) films of various composition were prepared by the rf glow discharge decomposition of acetylene and silane as well as ethylene and silane and were also annealed for various annealing temperatures. Careful and detailed IR absorption and the optical bandgap (E opt ) measurements were undertaken for a-SiC : H films of different composition (x) and annealing temperatures (T a ). Interesting variation of E opt with x and T a have been observed. Our study demonstrates, for the first time, that the models involving alloying or/and ordering break down and the proposed quantum well model based on heterogeneity is found to be the only model capable of explaining the observed variation of E opt . This, consequently, may have considerable implications.

Hydrogenated amorphous silicon carbon films of different carbon content deposited by plasma enhanced chemical vapour deposition on Corning glass and crystalline silicon substrates have been irradiated by an excimer (KrF) laser. The properties of these samples were investigated by X-ray diffraction, field emission scanning electron microscopy and Fourier transform infrared spectroscopy before and after laser treatment, in order to understand the role of the carbon content as well as the substrate in the structural modifications. It has been demonstrated that the changes induced in the films by the laser treatment are independent of the substrate but depend on the carbon content which facilitates the crystallization process.

The optical properties of the hydrogenated amorphous silicon carbon alloy films, prepared by plasma enhanced chemical vapor deposition technique from silane and methane gas mixture diluted in helium, have been investigated using variable angle spectroscopic ellipsometry in the photon energy range from 0.73 to 4.59 eV. Tauc-Lorentz model has been employed for the analysis of the optical spectra and it has been demonstrated that the model parameters are correlated with the carbon content as well as to the structural properties of the studied films.

Hydrogenated amorphous silicon carbon films of different carbon content were deposited by plasma enhanced chemical vapour deposition at low substrate temperature (200 °C) and were subjected to excimer laser annealing. X-ray diffraction spectra and field emission scanning electron microscopy images demonstrate that carbon content plays an important role in facilitating the crystallization process induced by the excimer laser treatment (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High Velocity Oxy-Fuel (HVOF) thermal sprayed coatingmade from Tungsten Carbide (WC) isconsidered as one of the most durable materials as wear resistance for industrial applications at room temperature. WC coating offers high wear resistance due to its high hardness and tough matrix imparts. The coating properties strongly depend on thermal spray processing parameters, surface preparation and surface finish. In this investigation, the effect of variousHVOF process parameters was studied on WC coating properties. The WC-12%Co coating was produced on Copper substrate. Prior to coating, theCopper substrate surface was prepared by grit blasting. WC-12%Co coatings were deposited on Coppersubstrates with varying process parameters such as Oxygen gas pressure, Air pressure, and spraying distance. Microstructure of coating was examined using Scanning Electron Microscope (SEM) and characterization of phasespresentin the coating was examined by X-Ray Diffraction (XRD). Microhardness of all coatingswas measured by VickerMicrohardness tester. At low Oxygen Pressure(10.00 bar), high Air pressure (7bar) and short nozzle to substrate distance of 170mm, best coating adhesion and porosity less structure isachieved on Coppersubstrate.

Kβ-to-Kα X-ray intensity ratios of Ti, Cr, Fe and Co in pure metals and in Cr0.26Fe0.74, Cr0.80Co0.20 and Ti0.80Cr0.20 alloys have been measured following excitation by 59.54 keV γ-rays from a 7400 MBq (200 mCi) 241 Am point-source. The valence electronic structure of Ti, Cr, Fe and Co in the samples have been evaluated by the comparison of the measured Kβ-to-Kα intensity ratios with the results of multiconfiguration Dirac–Fock calculations performed for various electronic configurations of these metals. The 3d-electron populations obtained for pure metallic Ti, Cr, Fe and Co agree well with the results of band structure calculations of Papaconstantopoulos (Handbook of band structure of elemental solids, Plenum Press, New York, 1986). Our analysis indicates significant increase of 3d-electron population of Ti, Cr and Fe in the alloys with respect to the pure metals, except for Cr in Cr0.26Fe0.74 where the absolute 3d-electron population of Cr is found to be slightly less as compared to that of pure Cr. It has been found that to reliably explain the observed changes in the valence electronic structure of Ti, Cr, Fe and Co in their alloys it is necessary to take into account the rearrangement of electrons between 3d and (4s,4p) states of individual metal atoms, while the transfer of 3d electrons from one element to the other element can be neglected.

Kβ-to-Kα X-ray intensity ratios of Fe and Ni in pure metals and in FexNi1−x alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a 241Am point source, to understand as to why the properties of permalloy Fe0.2Ni0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe0.2Ni0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties.

The variation of opto electronic parameters like the optical band-gap (Tauc gap E opt and the isoabsorption gap E 04 ), and structural parameters like the Tauc slope parameter B , of the hydrogenated amorphous silicon carbon alloy films prepared by r.f. glow discharge decomposition of silane and acetylene as well as silane and ethylene, are discussed for various compositions and also for different annealing temperatures. We observe, for the first time, an interesting new correlation between ( E 04 − E opt ) and the Tauc slope parameter B of amorphous semiconductors.

Silicon oxynitride films of various compositions have been prepared by the glow discharge decomposition of silane (SiH 4 ) and nitrous oxide (N 2 O). The refractive index of the films has been measured using ellipsometry, while the composition of the films has been determined using Rutherford backscattering (RBS) and elastic backscattering (EBS) techniques. This study has demonstrated that the measurement of composition using EBS technique is distinctly superior to RBS technique, particularly for the films like silicon oxynitride containing multicomponent light elements in low concentration.

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density (Ed) and the annealing temperature were varied from 123 to 242 mJ/cm2 and from 250 to 1200 °C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for Ed ≥ 188 mJ/cm2, while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200 °C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.

Nanostructured films composed of silicon crystallites embedded in a hydrogenated amorphous silicon carbon matrix have been deposited by plasma enhanced chemical vapour deposition from silane-methane mixtures diluted in hydrogen varying the rf power. Structural, optical and photoconductivity properties of the films have been investigated. The increase in rf power in the 40-80 W range enhances the incorporation of carbon in the amorphous matrix and decreases the fraction and size of the silicon crystallites leading to an enlargement of the optical band gap from 2.07 to 2.20 eV. Steady state spectral photoconductivity measurements have been performed under monochromatic radiations in the 460-1050 nm range. It has been demonstrated that monomolecular recombination kinetics occurs in the samples under illumination and the deterioration of the phototransport properties, with increasing the rf power, are correlated to the reduction of the mobility lifetime product of the free electrons. However, the mobility lifetime product as a function of the optical band gap shows high values as in the case of device quality films deposited by silane-methane mixtures diluted in hydrogen.

In addition to the increase in the optical band gap (Eopt) with hydrogenation, interesting variation of Eopt results with the increase in the carbon content (x) and also annealing temperature (Ta) in the hydrogenated amorphous silicon carbon alloy films (a-Si1−xCx:H). Eopt increases with x, reaches a maximum and then decreases with the further increase in x while Eopt initially decreases with Ta and then increases with the further increase in Ta. The present study demonstrates that the models based on alloying or/and ordering fail to explain both the variation of Eopt with x as well as Ta, and the proposed model, which is an extension of the Brodsky quantum well model (Solid State Commun. 36 (1980) 55) to hydrogenated amorphous silicon carbon alloys. However, it is the only model capable of explaining the experimental results, a fact which may have considerable implications.

Silicon-rich, nearly stoichiometric and nitrogen-rich silicon nitride films have been prepared by the glow-discharge decomposition of silane and ammonia with nitrogen dilution, with and without ammonia plasma pre-treatment of the silicon substrate. A considerable improvement in the silicon nitride/silicon interface, as evident from the large reduction in the minimum interface state density (Dit)min, due to ammonia plasma pretreatment is observed.

In order to study the role of aluminum and gold as the gate electrode material, we have deposited silicon nitride films onto p-type silicon substrates via r.f. glow-discharge deposition and have fabricated metal-insulator-semiconductor (MIS) devices on these films using aluminum or gold as the top electrode material. Considerable penetration of aluminum gate material into our silicon nitride films is observed. The resulting decrease of the effective thickness of the MIS devices have led to tunneling in these films. However, no appreciable penetration of gold gate material is observed. Our study demonstrates clearly that gold is superior to aluminum as the gate electrode material in MIS devices for being suitable even when poor quality silicon nitride films are used as insulator in MIS devices.

Current conduction mechanisms have been studied for three representative films, namely, silicon-rich, nearly stoichiometric and nitrogen-rich silicon nitride films, prepared by rf glow-discharge decomposition of silane and ammonia with nitrogen dilution. Ohmic conduction has been observed for all the films at low electric fields. The dominance of Poole–Frenkel conduction at intermediate fields and Fowler–Nordheim conduction at high fields has been observed both for the nitrogen-rich and the nearly stoichiometric films. However, for the silicon-rich films, the Poole–Frenkel conduction mechanism dominates both for the intermediate as well as the higher fields. This study indicates that the silicon-rich films have the highest density of traps and the nitrogen-rich films have the lowest, which may be ascribed to the effect of nitrogen dilution.

Hydrogenated amorphous silicon carbon alloy films of different carbon compositions were prepared by plasma enhanced chemical vapor deposition system using silane and methane with helium dilution and were characterized by structural and optical techniques to understand the microstructural and overall disorder in amorphous semiconductors. The study demonstrates that the increase of the microstructural disorder results in an increase in the overall disorder and the local defect density induced by carbon incorporation seems to dominate the overall defect structure of the network.

Kβ-to-Kα X-ray intensity ratios of Fe and Ni in pure metals and in FexNi1−x alloys for different compositions x (x=0.20, 0.50, 0.58) have been measured following excitation by 59.54 keV γ-rays from a 200 mCi 241Am point-source. For certain alloy compositions the Kβ-to-Kα intensity ratios of Fe and Ni differ considerably from those obtained for the pure metals. The 3d electron populations of Fe and Ni have been estimated by comparing the measured Kβ-to-Kα ratios with the results of multi-configuration Dirac–Fock (MCDF) calculations. Our results for the 3d electron populations of solid iron and nickel agree reasonably well with the earlier results of band structure calculations. In the case of alloys significant changes in the 3d electron population of Fe and Ni are observed for certain alloy compositions. These changes can be explained by assuming rearrangement of electrons between 3d and (4s,4p) valence band states of the individual metal atoms. For the alloy composition x=0.2 the change in the 3d electron population of Ni is the largest and has the opposite direction than in the case of other two alloy compositions. The totally different valence electronic structure of Fe0.2Ni0.8 alloy seems to explain the special magnetic properties of this alloy.

A novel oxidation process for silicon nitride films of various compositions have been undertaken utilizing nitrous oxide (N 2 O) plasma. Careful studies using elastic backscattering (EBS) technique to determine the composition and capacitance–voltage ( C – V ) measurements to determine the insulator charge density ( Q o ) and the interface state density ( D it ) have been made on the films before and after N 2 O plasma oxidation. The incorporation of oxygen into the silicon nitride films of various compositions due to the N 2 O plasma treatment is confirmed. The insulator charge density ( Q o ) as well as the minimum interface state density ( D it ) min are observed to be more for the N 2 O oxidized samples compared with the corresponding virgin samples.

The influence of carbon content on the crystallization process has been investigated for the excimer laser annealed hydrogenated amorphous silicon carbon alloy films deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, using silane methane gas mixture diluted in helium, as well as for the hydrogenated microcrystalline silicon carbon alloy films prepared by PECVD from silane methane gas mixture highly diluted in hydrogen, for comparison. The study demonstrates clearly that the increase in the carbon content prevents the crystallization process in the hydrogen diluted samples while the crystallization process is enhanced in the laser annealing of amorphous samples because of the increase in the absorbed laser energy density that occurs for the amorphous films with the higher carbon content. This, in turn, facilitates the crystallization for the laser annealed samples with higher carbon content, resulting in the formation of SiC crystallites along with Si crystallites. (C) 2007 Elsevier B.V. All rights reserved.

Kβ-to-Kα X-ray intensity ratios of Ti, V, Cr, and Co in pure metals and their disilicide compounds have been measured following excitation by 59.54 keV γ-rays from a 200 mCi 241Am point-source. The Kβ-to-Kα intensity ratios of all these metals in the disilicide compounds are found to be less than the corresponding ratios for pure metals. Comparison of the measured Kβ-to-Kα intensity ratios for the disilicides and pure metals with the multiconfiguration Dirac–Fock calculations indicates increase of the 3d electron populations of Ti, V, Cr, and Co in the disilicides from their pure metal values suggesting the rearrangement of electrons between 3d and 4s states of the individual metal atom. This rearrangement is found to be opposite to that observed in our previously reported work on NiSi2 and CuSi2.

Hydrogenated amorphous silicon–carbon alloy films were prepared by the glow discharge decomposition of silane and ethylene. The real and imaginary parts of the dielectric constants ϵ 1 and ϵ 2 of the film were determined at room temperature for the photon energies between 1.38 and 4.86 eV for the as-deposited ( T s =250 °C) as well as for subsequent anneals at different temperatures up to 1200 °C. The optical bandgap ( E opt ) was determined from the Tauc's relation while the characteristic optical parameters such as the dispersion energy ( E d ), average excitation energy ( E o ), plasmon energy ( ℏ w p ) and the valence electron density ( n v ) were obtained from the Wemple–DiDomenico model. We observe an interesting correlation between E opt and n v which seems to indicate the coupling of the valence and conduction band through single-particle excitation. © 1997 Elsevier Science S.A. All rights reserved.

The Schottky barrier height of Ti on p-type Si1–xGex/Si and Si have been investigated-in the temperature range 110–250 K using the current voltage technique. Rutherford Backscattering Spectroscopy ...

Punch-marked coins are the oldest known numismatic objects used in ancient India. Seven punch-marked silver coins were analysed by using the non-destructive multi-elemental PIXE technique. A 3 MeV proton beam from a pelletron accelerator was used for irradiation of these samples to obtain the spectral data and GUPIX software was employed to derive the elemental concentrations. The results reveals that silver, copper, gold and lead are significant constituents of the punch-marked silver coins and there are also traces of elements such as Ti, Cr, Mn, Fe, Co, Ni, As and Y, which seems to imply that PIXE can be used effectively for the non-destructive quantitative analysis of ancient coins. Copyright © 2004 John Wiley & Sons, Ltd.

A hydrogenated amorphous silicon-carbon (a-Si0.76C0.24:H) film has been prepared via the glow discharge decomposition of SiH4 and C2H4. The optical constants of this alloy film have been determined as a function of annealing temperature Ta for photon energies between 1.5 and 4.75 eV. The refractive index n and its imaginary part k show small but significant variation with annealing temperature. The optical energy gap Eopt also exhibits interesting variation with annealing temperature, decreasing with increasing annealing temperature up to Ta = 650°C and then increasing above this temperature. Further, Eopt is found to be correlated with the inverse of the full width at half-maximum of the SiC and the SiO IR stretch absorption mode, which seems to indicate that the changes in Eopt are structural in origin and that phonon order correlates well with electronic order.

Silicon nitride films of varying composition have been deposited with nitrogen dilution onto p-type silicon substrates at 250 °C by plasma enhanced chemical vapor deposition technique. Careful and detailed capacitance–voltage (C–V) measurements have been undertaken in the metal-insulator-semiconductor configuration. Silicon-rich films are found to exhibit large symmetric hysteresis loops in the C–V curve while the nitrogen-rich films display much smaller asymmetric hysteresis loops. Furthermore, the minimum interface state density is observed to decrease with the increase in nitrogen to silicon ratio. In this study we have observed that the concentration of both electron as well as hole traps are much lower for the nitrogen-rich films.

A hydrogenated amorphous SiC alloy film (a-Si1−xCx:H with x = 0.29) was prepared by glow discharge decomposition of a silane and ethylene gas mixture. A careful and detailed investigation of the IR absorption was undertaken in the range from 400 to 4000 cm−1 for both the as-deposited (Ts = 250°C) and annealed (up to 1200°C) film. In addition to the changes in the local bonding brought about by annealing, the study demonstrates clearly that there is a structural change from amorphous to microcrystalline at Ta = 800°C and then to a crystalline phase at Ta = 1200°C.

$K\ensuremath{\beta}\ensuremath{-}\mathrm{to}\ensuremath{-}K\ensuremath{\alpha}$ x-ray intensity ratios have been measured for all the $3d$ transition metals from titanium to copper, and the valence electronic structures of these metals have been determined by comparing the measured $K\ensuremath{\beta}\ensuremath{-}\mathrm{to}\ensuremath{-}K\ensuremath{\alpha}$ x-ray intensity ratios with the results of our multiconfiguration Dirac-Fock calculation. Our experimentally determined valence electronic structures for all the metals except V, Cr, and Mn are found to agree reasonably well with the results of augmented plane-wave (APW) band structure calculations. Our results for the valence electronic structure of V and Mn are found to be closer to the free atom values whereas the valence electronic structure of Cr is found to lie in between the valence electronic structure predicted by Compton profile studies and the one given by APW band structure calculations. The electron occupancies of $3d$ and $(4s,4p)$ states of V, Mn, and Cu are similar to free atom occupancies whereas for the other metals we find rearrangement of electrons between $3d$ and $(4s,4p)$ states of the metal with the transfer of electrons from $3d$ to $(4s,4p)$ states for Cr and from $(4s,4p)$ to $3d$ states in the case of Ti, Fe, Co, and Ni.

$K\ensuremath{\beta}\ensuremath{-}\mathrm{t}\mathrm{o}\ensuremath{-}K\ensuremath{\alpha}$ x-ray intensity ratios of Fe and Ni in pure metals and in ${\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}$ alloys $(x=0.20,$ 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV $\ensuremath{\gamma}$ rays from a 200 mCi ${}^{241}\mathrm{Am}$ point source to understand why the properties of the ${\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x} (x=0.2)$ alloy are distinct from other alloy compositions. The valence electronic structure of Fe and Ni in the samples has been evaluated by comparing the measured $K\ensuremath{\beta}\ensuremath{-}\mathrm{t}\mathrm{o}\ensuremath{-}K\ensuremath{\alpha}$ intensity ratios with the results of multiconfiguration Dirac-Fock calculations. Significant changes in the $3d$ electron population (with respect to the pure metal) are observed for Fe and Ni for certain alloy compositions. These changes can be explained by assuming rearrangement of electrons between $3d$ and $(4s,4p)$ band states of the individual metal atoms. It has been found that the valence electronic structure of the ${\mathrm{Fe}}_{0.2}{\mathrm{Ni}}_{0.8}$ alloy is totally different from the other two alloys, which perhaps is connected to the special magnetic properties of this alloy.

Different classes of interesting materials (such as protocrystalline, microcrystalline and nanocrystalline) have been grown under conditions very near to those for the microcrystalline phase. In spite of the importance of these materials, a clear picture regarding their phase transitions is missing. A smooth transition from the microcrystalline to the nanocrystalline silicon phase, distinctly different from an abrupt order-disorder phase transition, has been demonstrated, for the first time, in hydrogenated silicon-carbon alloy films, prepared from a silane-methane gas mixture highly diluted in hydrogen, by varying the rf power in a plasma enhanced chemical vapour deposition system. The study has also provided the signature of medium range order in hydrogenated silicon-carbon alloy films.

The nanocrystalline silicon embedded in amorphous silicon carbide matrix was prepared by varying rf power in high vacuum plasma enhanced chemical vapor deposition system using silane methane gas mixture highly diluted in hydrogen. In this paper, we have studied the evolution of the structural, optical, and electrical properties of this material as a function of rf power. We have observed visible photoluminescence at room temperature and also have discussed the role played by the Si nanocrystallites and the amorphous silicon carbide matrix. The decrease of the nanocrystalline size, responsible for quantum confinement effect, facilitated by the amorphous silicon carbide matrix, is shown to be the primary cause for the increase in the PL intensity, blueshift of the PL peak position, decrease of the PL width (full width at half maximum) as well as the increase of the optical band gap and the decrease of the dark conductivity.

Relative $K$ x-ray intensities of $Mn$ in $Mn$, $MnO_{2}$, $LaMnO_{3}$ and $La_{0.7}B_{0.3}MnO_{3}$ ($B$ = $Ca$, $Sr$, and $Ce$) systems have been measured following excitation by 59.54 keV $\gamma$-rays from a 200 mCi $^{241}$Am point-source. The measured results for the compounds deviate significantly from the results of pure $Mn$. Comparison of the experimental data with the multiconfiguration Dirac-Fock (MCDF) effective atomic model calculations indicates reasonable agreement with the predictions of ionic model for the doped {manganites except} that the electron doped $La_{0.7}Ce_{0.3}MnO_{3}$ and hole doped $La_{0.7}Ca_{0.3}MnO_{3}$ compounds show some small deviations. The results of $MnO_{2}$ and $LaMnO_{3}$ deviate considerably from the predictions of the ionic model. Our measured $K\beta/K\alpha$ ratio of $Mn$ in $La_{0.7}Ca_{0.3}MnO_{3}$ cannot be explained as a linear superposition of $K\beta/K\alpha$ ratios of $Mn$ for the end members which is in contrast to the recent proposal by Tyson et al. from their $Mn$ $K\beta$ spectra., Comment: 14 pages, 4 figures. to appear in NIM-B.Please send an e-mail for figures

The optical properties of the hydrogenated amorphous silicon carbon alloy films, prepared by plasma enhanced chemical vapor deposition technique from silane and methane gas mixture diluted in helium, have been investigated using variable angle spectroscopic ellipsometry in the photon energy range from 0.73 to 4.59 eV. Tauc–Lorentz model has been employed for the analysis of the optical spectra and it has been demonstrated that the model parameters are correlated with the carbon content as well as to the structural properties of the studied films.

The real and imaginary parts n and k of the index of refraction of a carbon‐rich hydrogenated amorphous silicon‐carbon alloy film (a‐Si1−xCx:H, x∼0.87) have been determined for photon energies between 1.5 and 4.75 eV from measurements of reflectance R and transmittance T. The optical energy gap parameter Eopt has been determined from the energy dependence of e2=2nk, the imaginary part of the dielectric constant. Depending on assumptions involving the energy dependencies of valence‐ and conduction‐band densities of states and optical matrix elements, values of Eopt ranging from 1.65 to 2.5 eV have been obtained for the as‐deposited film (Td=250 °C). Independently of such assumptions, Eopt is observed to decrease to zero as the film is annealed. These results are consistent with enhanced tetrahedral coordination and demonstrate improved thermal stability for this silicon‐carbon alloy film as compared to an hydrogenated amorphous carbon film. The density of the film increased from 1.51 to 1.88 g/cm3 with ann...

The optical constants (\~n=n+ik, ${\ensuremath{\epsilon}}_{1}$=${n}^{2}$-${k}^{2}$, ${\ensuremath{\epsilon}}_{2}$=2nk) of a series of amorphous hydrogenated silicon-carbon alloy films (a-${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{C}}_{\mathrm{x}}$:H) have been determined for photon energies between 1.5 and 4.75 eV. These films have been prepared via the rf glow-discharge decomposition of ${\mathrm{SiH}}_{4}$ and ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$. The index of refraction n at 1.5 eV increases smoothly from n=1.67 for a-C:H (x=1) to n=3.18 for a-Si:H (x=0), while the optical energy gap ${E}_{\mathrm{opt}}$ reaches a maximum value of 2.68 eV for a carbon fraction of x=0.68. The films in this alloy series are proposed to be macroscopically homogeneous, while having a heterogeneous microstructure. Their optical response has been modeled, via the Bruggemann effective-medium approximation (EMA), as arising from three amorphous components: polymeric (a-${\mathrm{CH}}_{\mathrm{m}}$, m\ensuremath{\sim}2), graphitic (a-C), and tetrahedral (a-Si:C:H), and a void component. A Si- and C-centered tetrahedron model developed in the preceding paper has been used to predict the optical response of the amorphous tetrahedral component as a function of its composition. This EMA approach based on four components in the films gives a good description of the observed dependences of ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ on composition and provides a convincing demonstration that the appearance of the amorphous graphitic component in the films limits the attainable value of ${E}_{\mathrm{opt}}$ in this alloy series as the carbon content increases. In addition, the model provides strong evidence that complete chemical ordering with homogeneous dispersion exists within the amorphous tetrahedral (a-Si:C:H) component across the entire alloy series.

An amorphous hydrogenated silicon carbon alloy film (a Si1 x Cx :H with x = 0.29) was prepared by glow discharge decomposition of a silane and ethylene gas mixture. A careful and detailed investigation of the infrared absorption was undertaken in the range 400 to 4000 cm1 for both the as deposited (T =250°C) and annealed (up to 1200°C) film. This study demonstrates clearly that there is a structural change from amorphous to microcrystalline at T =8000C and then to crystalline phase at T a=1200° C.