Spectroscopic study of the decomposition process of tetramethylsilane in the N2–H2 and N2–Ar low pressure plasma

The optical emission spectroscopy has been used to study the decomposition process of tetramethylsilane in a low pressure plasma. The Si(CH₃)₄–N₂–H₂ and Si(CH₃)₄–N₂–Ar reactive mixtures, which are used for the deposition of SiCN layers, have been studied here. High energy active species were identified in the plasma phase and the electron excitation, vibrational and rotational temperatures as well as electron number density were determined for various compositions of the reactive mixtures. The electron excitation temperature (Si I, Ar I, H) was found to be higher than the vibrational temperatures (CN, N₂, N₂⁺) and considerably higher than the N₂⁺ rotational temperature, as the results of nonequilibrium state of plasma generated. It was observed that introduction of tetramethylsilane as well as growth of hydrogen percentage led to lowering of the electron density and the rotational temperature. Optical actinometry was applied to study the Si(CH₃)₄–N₂–H₂ reactive mixture.     

Fundamental Interactions of Molecules (Na2, Na3) with Intense Femtosecond Laser Pulses

The real-time dynamics of multiphoton ionization and fragmentation of molecules Na₂ and Na₃ has been studied in molecular beam experiments employing ion and electron spectroscopy together with femtosecond pump-probe techniques. Experiments with Na₂ and Na₃ reveal unexpected features of the dynamics of the absorption of several photons as seen in the one- and three-dimensional vibrational wave packet motion in different potential surfaces and in high laser fields: In Na₂ a second major resonance-enhanced multiphoton ionization (REMPI) process is observed, involving the excitation of two electrons and subsequent electronic autoionization. The possibility of controlling a reaction by controlling the duration of propagation of a wave packet on an electronically-excited surface is demonstrated. In high laser fields, the contributions from direct photoionization and from the second REMPI process to the total ion yield change, due to different populations in the electronic states participating in the multiphoton ionization (MPI) processes. In addition, a vibrational wave packet motion in the electronic ground state is induced through stimulated emission pumping by the pump laser. The 4¹Σ⁺_g shelf state of Na₂ is given as an example for performing frequency spectroscopy of high-lying electronic states in the time domain. Pure wave packet effects, such as the spreading and the revival of a vibrational wave packet, are investigated. The three-dimensional wave packet motion in the Na₃ reflects the normal modes in the X and B states, and shows in addition the pseudorotational motion in the B state in real time.     

Synthesis of tellurium containing syndiotactic polymethyl methacrylate using diphenyl ditelluride as a novel initiator

The synthesis of syndiotactic polymethyl methacrylate containing tellurium by using diphenyl ditelluride in the dioxan at (60 ± 0.1)°C for 2 h has been carried out. The presence of tellurium in the polymer has been confirmed qualitatively as well as by induced coupled plasma mass spectroscopy (ICP‐MS). The electron spin resonance spectrum shows the presence of T?Ph, and value of gyromagnetic constant g has been calculated as 2.2203. The T_g of the polymer, measured by DSC, is 105°C. The syndiotactic nature has been confirmed by FTIR and NMR spectroscopy and DSC. The system follows ideal kinetics with activation energy 66 kJ mol^?1. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1017–1022, 2006     

Influences of low-temperature ambient pressure N2 plasma and flame treatments on polypropylene surfaces

Using various techniques, such as Sum-Frequency Generation (SFG) vibrational spectroscopy, Attenuated Total Reflection Infrared Spectroscopy (ATR-IR), Raman scattering, and Scanning Transmission Electron Microscopy (STEM), this study investigated the influences of N₂ plasma and flame treatments on polypropylene surfaces. The results of the first two techniques suggest that the functional groups introduced by the treatments had not been exposed to the air side of the outermost surfaces of the polypropylenes but had been distributed from the surfaces to the bulk regions. Regarding the surface morphology after each treatment, Raman scattering and STEM measurements revealed that the treatments had induced the formation of amorphous regions on the surfaces. On the other hand, the number of functional groups introduced by N₂ plasma irradiation was more than that introduced by burning flame. Unlike the flame treatment, the N₂ plasma treatment created roughness on the polypropylene surfaces.     

X-ray absorption spectroscopy based investigation of local structure in yttria stabilized zirconia nanoparticles generated by laser evaporation method: Effect of pulsed vs CW mode of laser operation

Two order higher ionic conductivity was reported by us (J. Khare et al., Ceram. Int. 40 (2014) 14677) in pellet made from yttria stabilized zirconia nanoparticles grown under pulsed mode in comparison with pellets made from yttria stabilized zirconia nanoparticles grown under CW mode of CO₂ laser based vaporization method. To understand possible cause of difference in conductivity, the local structure around Zr⁺⁴ ion and Y⁺³ ion has been investigated using X-ray absorption fine structure spectroscopy. The local structure around Zr has been found to depend on the mode of laser vaporization for nanoparticles generation. In case of pulsed mode of vaporization method the charge compensating oxygen vacancies created by the substitution of Y are preferentially forming dipole type defect configuration leading to high ionic conductivity. While formation of immobile tripole type defects are responsible for low ionic conductivity in pellets made from nanoparticles generated under CW mode of laser vaporization.     

Prospects for detecting metal–adsorbate vibrations by sum‐frequency spectroscopy

Sum‐frequency spectroscopy (SFS) was used in an attempt to detect the platinum–carbon vibration of CO adsorbed on Pt(111). The international free‐electron laser FELIX at the FOM Institute, Rijnhuizen, provided the required tunable far‐infrared (19–23 μm) source, while complementary measurements in the C–O stretch region (4.7–5.1 μm) were performed at the University of Oxford with a conventional nanosecond laser system. Ordered Pt(111) surfaces were prepared by the H₂/O₂ flame annealing approach and CO monolayers were produced by exposure of the Pt crystal to gaseous CO in a flow reactor. The monolayers were characterized by sum‐frequency (SF) measurements of the v _C-O vibrational frequency. The CO adsorbed primarily in the terminal (atop) configuration, with a v _C-O frequency of around 2078 cm⁻¹. In the far‐IR region, the non‐resonant background from the Pt substrate could readily be detected by SFS, but there was no evidence for the v _Pt-CO mode. Direct laser‐induced desorption and thermal desorption of CO are unlikely under the experimental conditions. It is therefore probable that the intrinsic cross‐section of the Pt–CO mode is too low for easy detection by SFS. The implications for the use of SFS to detect metal–adsorbate vibrational modes are discussed in light of these findings. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electric field gradient tensor in positions of rare-earth metals in RBa2Cu3O7 lattices

The parameters of the electric field gradient tensor (EFG) created in rare-earth metal (REM) sites of RBa₂Cu₃O₇ lattices (R = Nd, Sm, Gd, Dy, Y, Ho, Er, Tm) by crystal lattice ions have been determined by the method of emission Mössbauer spectroscopy on ⁶⁷Ga(⁶⁷Zn) and ¹⁵⁵Eu(¹⁵⁵Gd) isotopes. The EFG tensor has been calculated for REM sites in the approximation of the point charge model. It was shown that the agreement between the experimental and calculated parameters of the EFG tensor can be achieved if the holes are preferably localized in the chain oxygen sublattice.     

Excitation energy-dependent nature of Raman scattering spectrum in GaInNAs/GaAs quantum well structures

The excitation energy-dependent nature of Raman scattering spectrum, vibration, electronic or both, has been studied using different excitation sources on as-grown and annealed n- and p-type modulation-doped Ga_1 − xIn_xN_yAs_1 − y/GaAs quantum well structures. The samples were grown by molecular beam technique with different N concentrations (y = 0%, 0.9%, 1.2%, 1.7%) at the same In concentration of 32%. Micro-Raman measurements have been carried out using 532 and 758 nm lines of diode lasers, and the 1064 nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the 785 and 1064 nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the 532 nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of 532 nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. The results exhibited that the nature of the Raman scattering spectrum is strongly excitation energy-dependent, and with suitable excitation energy, electronic and/or vibrational transitions can be investigated.     

Surface doping of TiO2 powders via a gas–melt reaction using thermal plasma as an excitation source

Surface doping is an effective method to engineer and functionalize powder materials without modulating the internal crystal structure. This study proposed a facile technique for surface doping via a gas–melt reaction using thermal plasma as an excitation source. Doping molten titania (TiO₂) particles with La was preliminarily explored owing to the broad photocatalytic applications of TiO₂. Scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscope, diffuse reflectance spectroscopy, photoluminescence spectroscopy and Fourier transform infrared spectroscopy were adopted to characterize the morphology, phase composite, chemical state, fine structure, and optical property of the doped TiO₂ powder, respectively. Results indicated that molten TiO₂ doped with La solidified into spherical particles under the effect of surface tension. No modification of the internal crystal structure was indicated in the XRD patterns, except that the diffraction peak of rutile TiO₂ (110) shifted to low angles after surface doping with La. The obtained TiO₂ powder exhibited sensitivity to sunlight and near-infrared light, and a La/Ti atomic ratio of 19.4% was achieved. The diffusivity D_i of La in molten TiO₂ ranged from 10⁻⁸ m²/s to 10⁻⁷ m²/s, as determined from the gas–melt reaction.     

Vibrational studies of microcrystalline diamond and diamond-like carbon by high resolution electron energy loss spectroscopy

High resolution electron energy loss spectroscopy (HREELS) has been applied to investigate the vibrational states of microcrystalline diamond and diamond-like carbon (DLC) films prepared in a low pressure inductively coupled plasma. The CO additive to a CH₄/H₂ plasma exhibits different phonon density of states. Without CO additive, the HREELS spectrum shows a faint peak at ∼1500 cm⁻¹ due to CC stretching vibration of sp² bonds, indicating that the sample is mainly composed of DLC. On the other hand, the HREELS profiles show a peak at ∼1100 cm⁻¹ assigned to CC stretching vibration of sp³ sites with CO additive. The intensity of the peak becomes strong and a shoulder centered at ∼700 cm⁻¹ corresponding to the bending vibration of sp³ bonded carbons appears with increasing CO additive. It consequently implies that the CO additive brings about the decrease of the fraction of sp² bonded carbons in the resultant films, and it is qualitatively in agreement with the previous characterizations by Raman spectroscopy, transmission electron microscopy, and reflection high energy electron diffraction.     

Improved ionic conductivity in NdGdZr2O7: Influence of Sc3+ substitution

Aliovalent Sc³⁺ doped pyrochlores NdGdZr_2?xSc_xO_7?δ (0.0 ≤ x ≤ 0.15) have been prepared by gel-combustion method followed by high temperature sintering. Detailed structural characterization of these compounds has been carried out using X-ray diffraction and Raman spectroscopy, which together have established the retention of pyrochlore structure of these compositions till x = 0.15 Sc³⁺ incorporation. Both X-ray diffraction and Raman results have also indicated the presence of local lattice distortion with net cell contraction upon Sc³⁺ incorporation in these solid solutions. Micro structural studies have revealed highly dense end products with uniform grain distribution and homogeneous compositions at grain size level. Ionic conductivity characterization of system been carried out from 473 to 573 K. A significant improvement in the total ionic conductivity of this series has been observed which has been explained in terms of additional oxygen vacancies created upon Sc³⁺ incorporation and enhanced lattice disorder.     

Characterisation of a coordinated imidazole as a structural model for superoxide dismutase

The copper complex [Cu(HL)](ClO₄)₂·2H₂O, where HL is N-[2-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethyl]–N-(benzimidazol-2-yl)methanimine, has been prepared and characterised by X-ray crystallography and solution absorption spectroscopy. Deprotonation of the benzimidazole moiety in this complex has been investigated by electronic spectroscopy. The results show a definite shift in λ_max for [Cu(HL)]²⁺, at 632–818 nm for the deprotonated [CuL]⁺, in acetonitrile. This complex has been synthesised as a structural homologue to half of the enzyme Cu–Zn superoxide dismutase (SOD) which contains a bridged imidazolate moiety between the two Cu and Zn metal ions.     

Improvement of structural and superconducting properties of Bi-2212 textured rods by substituting sodium

In this paper, the physical and superconducting properties of Bi₂Sr₂Ca_1−xNa_xCu₂O_8+δ with x=0.0, 0.05, 0.075, 0.1, and 0.20 textured superconducting fiber rods prepared by a laser floating zone (LFZ) technique were studied. The effects of Na⁺¹ substitution for Ca²⁺ have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transport measurements, dc-magnetization, magnetic hysteresis and magnetic critical current density. The powder XRD patterns of samples have indicated that Bi-2212 phase is the major one, independently of Na content. The best critical temperature, T_C, has been found as 93.3 K from M–T data for the sample with 0.075 Na substitution. The maximum magnetic J_C value has been calculated as 1.35×10⁵ A/cm² at 10 K for the 0.10 Na sample. The maximum transport critical current density has directly been measured as 1.3×10³ A/cm² at 77 K for the 0.05Na sample.     

Vanadyl formate VO(HCOO)2·H2O as a precursor for preparing nanoscale vanadium sesquioxide V2O3

Vanadyl formate monohydrate VO(HCOO)₂·H₂O has been synthesized by a facile two-stage method. The chemical and structural identity of the synthesized compound has been confirmed by X-ray diffraction, thermogravimetry, vibrational and absorption spectroscopy. It was established that during heating in water and ethylene glycol, VO(HCOO)₂·H₂O leads to vanadyl hydroxide VO(OH)₂ and vanadyl glycolate VO(OCH₂CH₂O) being formed. When heated in air or in helium at 300 °C and higher, VO(HCOO)₂·H₂O transforms into vanadium pentoxide or sesquioxide, respectively. VO(HCOO)₂·H₂O was used as a precursor for the synthesis of nanoscale vanadium sesquioxide (with an average particle size of 50 nm), which is stable under the normal conditions and is characterized by a lower metal-insulator transition temperature than the microsized (bulk) compound. The effect of transition temperature reduction for nanoscale vanadium sesquioxide agrees with the lower value of its unit cell volume (V = 296.74 Å³) as compared with that for bulk V₂O₃ (297.7 Å³). The main factor affecting the V₂O₃ particle size is the annealing temperature of precursor in inert atmosphere.     

Enhanced adhesion of polypyrrole/PW12O hybrid coatings on polyester fabrics

Polyester fabrics have been treated with plasma to increase polypyrrole/PW₁₂O₄₀^3‐ (hybrid material) adhesion to its surface. With the plasma treatment, the roughness of the fibers increases as it has been observed by means of atomic force microscopy (AFM). Polar functional groups are also created on the surface of polyester fabrics as X‐ray photoelectron spectroscopy (XPS) measurements have shown. These polar groups contribute to the adhesion of polypyrrole to the fibers. Coatings obtained on plasma treated fabrics were more resistant to washing and rubbing fastness tests. The use of an inorganic counter ion (PW₁₂O) that contains an element with a high atomic number (W) helps to locate zones where the coating is missed; this is achieved by means of micrographs obtained by backscattered electrons (BSE). The electrical resistance of the fabrics was also measured by electrochemical impedance spectroscopy (EIS), obtaining also better results with the plasma treated fabrics. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Resonant Raman studies of tetrahedral amorphous carbon films

Resonant Raman scattering has been used to study the tetrahedral amorphous carbon films deposited by the filtered cathodic vacuum arc technique. The excitation wavelengths were 244, 488, 514 and 633 nm, corresponding to photon energies of 5.08, 2.54, 2.41 and 1.96 eV, respectively. In the visible Raman spectra only vibrational modes of sp²-bonded carbon (G and D peaks) are observed, while a wide peak (called the T peak) can be observed at approximately 1100 cm⁻¹ by UV-Raman spectra which is associated with the vibrational mode of sp³-bonded carbon. Both the position and the width of the G peak decrease almost linearly with increasing excitation wavelength, which is interpreted in terms of the selective ππ* resonant Raman scattering of sp²-bonded carbon clusters with various sizes. The G peak position in the UV-Raman spectra, the T peak position and the intensity ratios of I_D/I_G and I_T/I_G all exhibit maximum or minimum values at the carbon ion energy of 100 eV. The changes of these spectral parameters are discussed and correlated with the sp³ fraction of carbon atoms in the films.     

Laser synthesis and luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

A laser melting method has been developed for the synthesis of highly luminescent, long-lasting SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors. The high temperature achieved in high-power density CO₂ laser irradiation of mixtures of SrCO₃, Al₂O₃, Eu₂O₃, and Dy₂O₃ enabled the one-step, fast synthesis of these phosphors in air at atmospheric pressure. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy characterization studies reveal that the produced materials consist of monoclinic SrAl₂O₄ grains extensively surrounded by rare-earth ion-enriched grain boundaries. The photoluminescence properties of laser-produced SrAl₂O₄:Eu²⁺, Dy³⁺ materials are discussed. The results reported here suggest that this laser melting method is a promising route for the synthesis of ceramic phosphors. It is presented as an alternative to the conventional sol–gel and solid-state methods, which require the use of high-temperature furnaces, flux additives, and reducing atmospheres.     

Bifunctional mesoporous Cu–Al–MCM-41 materials for the simultaneous catalytic abatement of NOx and VOCs

This study explored the possibility of using waste organic solvent as the source of volatile organic compound (VOC) and it served as a reducing agent of selective catalytic reduction (SCR) deNO_x process, in which the VOC itself can be catalytically oxidized on the mesoporous Cu and/or Al substituted MCM-41 catalysts. The synthesized Cu–Al–MCM-41 catalysts were extensively characterized by powder low-angle X-ray diffraction (XRD), N₂ adsorption–desorption measurements, transmission electron microscopy (TEM), UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), ²⁷Al magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR), electron paramagnetic resonance spectroscopy (EPR) and inductively coupled plasma–mass spectrometer (ICP–MS) analysis. The XRD, TEM and N₂ adsorption–desorption studies clearly demonstrated the presence of a well ordered long range hexagonal array with uniform mesostructures. The Cu–Al–MCM-41 materials showed a better long-term-stability than that of copper ion-exchanged H–ZSM-5 (Cu–ZSM-5) zeolite. The Cu–Al–MCM-41 material was found to be an efficient catalyst than that of Cu–MCM-41 without aluminum for the simultaneous catalytic abatement of NO_x and VOCs, which was attributed to the presence of well dispersed and isolated Cu²⁺ ions on the Cu–Al–MCM-41 catalyst as observed by UV–Vis DRS and EPR spectroscopic studies. And the presence of aluminum (Al³⁺ ions) within the framework of Cu–Al–MCM-41 stabilized the isolated Cu²⁺ ions thus it led to higher and stabilized activity in terms of NO_x reduction.     

Fabrication,structural and vibrational properties,and physical and optical properties tailoring of nanocrystalline MoS2 films

The modification and tuning features of nanostructured films are of great interest because of controllable and distinctive inherent properties in these materials. Here, nanocrystalline MoS₂ films were fabricated on the stainless steels by a radio frequency magnetron sputtering at ambient temperature. X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Raman scattering spectroscopy were used to study the chemical state, chemical composition, crystal structure and vibrational properties of the fabricated MoS₂ films. The bias voltage dependent structural evolution and its influence on the optical properties of MoS₂ nanocrystalline films were systematically investigated. Besides, the residual stresses of MoS₂ nanocrystalline films were explored by employing sin²ψ approach. X-ray diffraction demonstrates that the nanocrystalline MoS₂ films have single-phase hexagonal crystal structure. All MoS₂ films are polycrystalline in nature. The bandgap values are found to be intensively dependent on bias voltage. Our findings show that the nanocrystalline MoS₂ films with different physical properties and intense quantum confinement effect can be realized through adjusting bias voltages. This work may provide deep insight for realizing transitional metal dichalcogenide-based nanostructured film optoelectronic devices with tunable physical properties through a traditional, very cost-effective, and large-scale fabrication method.