Comparative microscopic and spectroscopic analysis of temperature-dependent growth of WO3 and W0.95Ti0.05O3 thin films

We present a comparative microscopic and spectroscopic study of the morphology and composition of WO₃ and W_0.95Ti_0.05O₃ thin films, grown by radio-frequency magnetron reactive sputtering at substrate temperatures varied from room temperature to 500 °C, using atomic force microscopy (AFM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). With increasing growth temperature, the AFM results show increase in the average crystallite size and in the surface roughness for both undoped and doped samples. The AFM data, along with the Raman results, clearly indicate that for the given set of experimental conditions, higher growth temperatures are required to obtain crystalline Ti-doped WO₃ films than for WO₃ films. Also, the Raman results suggest a potential phase transformation from a monoclinic WO₃ structure to an orthorhombic, but more probably a tetragonal, configuration in the W_0.95Ti_0.05O₃ thin films. This remark is based on the observed shifting, with Ti doping, to lower frequencies of the Raman peaks corresponding to W–O–W stretching modes of WO₃ at 806 and 711 cm⁻¹ to 793 and 690 cm⁻¹, respectively. XPS data indicate that the doped material has a reduced WO_3−x stoichiometry at the surface, with the presence of W⁶⁺ and W⁵⁺ oxidation states; this observation could also be related to the existence of a different structural phase of this material, corroborating with the Raman measurements.     

Synthesis and characterization of Al2?xScx(WO4)3 ceramics for low-expansion infrared-transmitting windows

A low thermal-expansion material was synthesized with potential application in thermal-shock-resistant infrared-transmitting windows. The material is derived from a solid solution of Al₂(WO₄)₃, which has positive thermal expansion, and Sc₂(WO₄)₃ with a negative thermal expansion. An optimum composition of Al_0.5Sc_1.5(WO₄)₃ was identified by synthesizing solid solutions, Al_2−x Sc _x (WO₄)₃, by a solid-state route with compositions ranging from x = 0 to 2.0. A single orthorhombic phase was obtained at all compositions. A composition corresponding to x = 1.5 had a low coefficient of thermal expansion of −0.15 × 10⁻⁶/°C in the temperature range 25–700 °C. A low temperature solution combustion process was developed for this optimum composition, resulting in a single-phase powder with a surface area of ~14 m²/g and average particle size (as determined from surface area) of 92 nm. The powder was consolidated by slip-casting, sintering, and hot-isostatic pressing into visibly translucent disks with a peak in-line transmittance of 73 % at 2300 cm⁻¹. Significant infrared absorption in a 1-mm-thick disk of this material begins near 2200 cm⁻¹ and features three absorptions arising from 2-phonon transitions at 2002, 1847, and 1676 cm⁻¹. The infrared and Raman spectra are interpreted in terms of 1-, 2-, and 3-phonon vibrational transitions.     

Combustion synthesis and structural characterization of Li–Ti mixed nanoferrites

Polycrystalline samples of the mixed nanoferrites, Li_{0·5 + 0·5x} Ti _x Fe_{2·5 − 1·5x} O₄ (0·02 ≤ x ≤ 0·1), were prepared by combustion method at lower temperatures compared to the conventional high temperature sintering for the first time at low temperatures, using PEG which acts as a new fuel and oxidant. XRD patterns reveal a single-phase cubic spinel structure. The as synthesized Li–Ti ferrites are in nanocrystalline phase. The crystallite size was found to be in the range 16–27 nm. SEM images reveal rod-like morphology in all the samples with a discontinuous grain growth. The B–H loops have been traced using VSM technique, for all the compositions, at room temperature and the hysteresis parameters are calculated. Saturation magnetization decreases with increase in Ti content due to the fact that the Ti^4 + ion, which is a non-magnetic ion, replaces a magnetic Fe^3 + ion. The hysteresis loops show clear saturation at an applied field of ±10 kOe and the loops are highly symmetric in nature. The cation distribution is known indirectly by using saturation magnetization values.     

Preparation and characterizations of tungsten oxide electrochromic nanomaterials

Nanoscaled tungsten oxide thin films were fabricated by galvanostatic electrodeposition. The effect of preparation parameters such as tungsten ions concentration, pH, current density and annealing on the properties and performance of WO₃ thin films electrochromic materials was investigated. XRD, SEM–EDS, TEM, FTIR, UV–VIS spectrophotometry, and electrochemical measurements were utilized to characterize the structural and compositional properties as well as the electrochromic behaviour of the prepared thin films. Triclinic WO₃ structure was prepared at 0.1 M W⁺ and current density of 0.5 mA cm⁻², while at 0.2 M W⁺ and 1 mA cm⁻², orthorhombic structure was revealed. High energy gap of 3.5 eV with diffusion coefficient of 6.81 × 10⁻¹¹ cm² S⁻¹ and coloration efficiency of 62.68 cm² C⁻¹ were obtained for the films prepared at pH 2, 1 mA cm⁻², and 0.1 M W⁺.     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

Infrared Reflectivity Spectra of Manganite Thin Films Grown on Different Substrates

We have measured the reflectivity infrared (IR) spectra of R_1−x Ca _x MnO₃ (R = La, Pr) manganite thin films grown on different substrates (SrTiO₃ (STO), LaAlO₃ (LAO) and SrLaGaO₄ (SLGO)) manganites over a wide frequency (50–5000 cm⁻¹) range. In the Far IR (FIR) region the substrates dominate over the manganite spectrum. However, the previously observed infrared active modes or mode pairs could be identified. In the mid-IR (MIR) region, a characteristic insulating gap at ∼700 cm⁻¹ is always present for all thin film studied, which shows substrate and thickness dependence.     

Amorphous Li–B–W–O solid-state electrolyte thin film for a solid-state ionic power sources

Li–B–W–O thin film serving as a solid-state electrolyte layer for a solid-state thin film battery has been deposited on a stainless steel (SUS)/Si substrate by thermal evaporation deposition at room temperature. By energy dispersive X-ray spectroscopy and inductively coupled plasma-atomic emission spectrometer measurements, the as-grown thin film showed a stoichiometry of Li_2.99BW_1.8O₉. The as-grown Li–B–W–O solid-state electrolyte thin film possessed an amorphous structure as confirmed by X-ray diffraction. Field emission scanning electron microscopy measurements of the film cross section showed a dense structure that did not have any large defects such as cracks or voids. For a cell structure of SUS/Li–B–W–O/SUS/Si, an impedance measurement conducted at room temperature revealed an ionic conductivity of 2.15 × 10⁻⁷ S cm⁻¹ with activation energy of 0.52 eV, which suggests that Li–B–W–O thin film can possibly be used as an electrolyte in solid-state thin film batteries.     

Supercapacitive performance of hydrous ruthenium oxide (RuO<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) thin films deposited by SILAR method

The amorphous hydrous ruthenium oxide (RuO₂·nH₂O) thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. These films were characterized for their structural, surface morphological, and compositional study by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDAX) techniques. The wettability test was carried out by measuring the water contact angle. The scanning electron microscopy study showed small RuO₂ particles are grouped together to form porous agglomerates. The FT-IR study confirmed the formation of hydrous ruthenium oxide films. The hydrophilic nature of ruthenium oxide (RuO₂·nH₂O) thin films was observed from water contact angle measurement. The presence of Ru and O in the film was confirmed by EDAX analysis. The supercapacitor behavior of these films studied in 0.5 M H₂SO₄ electrolyte showed maximum specific capacitance of 162 F g⁻¹ at 10 mV s⁻¹ scan rate. These films exhibit 80% cycling performance after 2,000 cycles. The charge–discharge studies carried at 1 mA cm⁻² current density revealed the specific power of 3.5 KW kg⁻¹ and specific energy of 29.7 W Kg⁻¹ with 93% coulombic efficiency.     

Photoluminescence and Raman studies in swift heavy ion irradiated polycrystalline aluminum oxide

Polycrystalline aluminum oxide is synthesized by combustion technique and XRD studies of the sample revealed the α-phase. The synthesized sample is irradiated with 120 MeV swift Au⁹⁺ ions for the fluence in the range from 1 × 10¹¹ to 1 × 10¹³ ions cm⁻². A broad photoluminescence (PL) emission with peak at ∼ 447 nm and two sharp emissions with peak at ∼ 679 and ∼ 695 nm are observed in pristine when sample was excited with 326 nm. However, in the irradiated samples the PL intensity at ∼ 447, 679 and 695 nm decreases with increase in ion fluence. The α-Al₂O₃ gives rise to seven Raman modes with Raman intensity with peaks at ∼ 253, 396, 417, 546, 630, 842, 867 cm⁻¹ observed in pristine. The intensity of these modes decreases with increase in ion fluence. However, the Raman modes observed at lower fluences are found to disappear at higher fluence.     

Characterization of NaPO3–SnO–WO3 glasses prepared by microwave heating

Phosphate glasses containing tin and tungsten oxides were produced by microwave heating under a nitrogen protective atmosphere. Microwaves permit to heat the raw materials at temperatures close to 1000 °C in short time and to obtain homogeneous glasses in less than 10 min. All samples were characterized from thermal and mechanical point of view as function of metal oxide proportions. The equimolar addition of SnO and WO₃ in sodium phosphate matrix involves a linear evolution of the different properties (T _g, CTE, density, mechanical properties, and durability). Thus, we have shown a progressive strengthening of the network. The glass transition temperature does not exceed 405 °C, and the chemical durability is improved to four orders of magnitude. The dissolution rate is equal to 3.4 × 10⁻⁷ g cm⁻² min⁻¹ for 40NaPO₃–30SnO–30WO₃ glass composition and is comparable with those of the window glass.     

AC impedance and dielectric spectroscopic studies of Mg<Superscript>2 + </Superscript> ion conducting PVA–PEG blended polymer electrolytes

Polyvinyl alcohol (PVA)–polyethylene glycol (PEG) based solid polymer blend electrolytes with magnesium nitrate have been prepared by the solution cast technique. Impedance spectroscopic technique has been used, to characterize these polymer electrolytes. Complex impedance analysis was used to calculate bulk resistance of the polymer electrolytes. The a.c.-impedance data reveal that the ionic conductivity of PVA–PEG–Mg(NO₃)₂ system is changed with the concentration of magnesium nitrate, maximum conductivity of 9·63 × 10^− 5 S/cm at room temperature was observed for the system of PVA–PEG–Mg(NO₃)₂ (35–35–30). However, ionic conductivity of the above system increased with the increase of temperature, and the highest conductivity of 1·71 × 10^− 3 S/cm was observed at 100°C. The effect of ionic conductivity of polymer blend electrolytes was measured by varying the temperature ranging from 303 to 373 K. The variation of imaginary and real parts of dielectric constant with frequency was studied.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years     

Formation of In nanoparticles on InP wafers by laser-assisted etching

Indium nanoparticles were formed by laser etching an InP (100) wafer in a 10% chlorine–helium atmosphere maintained at ~5–8 × 10⁻⁵ Torr. The wafer was irradiated by a homogenized ultraviolet beam with a series of 50–4500 pulses at a fluence of 230 mJ/cm². The surface was also irradiated using fluences from 50 to 340 mJ/cm² with 600 pulses. The irradiated surfaces were studied using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. Raman spectroscopy confirmed that the irradiated surface layer remains crystalline. According to EDS analysis, the surface particles are composed primarily of indium. SEM images show that the number of pulses and the pulse intensity can control the size distribution of the particles.     

Insulating ZnO film on silicon for MIS application

High resistive zinc oxide thin film (∼ 0·5 μm) was deposited on single crystalp-silicon (100) wafers by an inexpensive spray-CVD method and was characterized both optically and electrically. Al/ZnO/Si (MIS) device structure was subsequently fabricated and bothI − V andC − V characteristics were studied. The semiconductor-insulator interface charge density (D _it) was calculated by Terman method and was found to be 3·85 × 10¹¹ cm⁻²eV⁻¹.     

Raman temperature dependence analysis of carbon-doped titanium dioxide nanoparticles synthesized by ultrasonic spray pyrolysis technique

Carbon-doped titanium dioxide nanoparticles were prepared by ultrasonic spray pyrolysis technique using titanium tetra-ethoxide as a precursor and glucose as a dopant. The as-synthesized nanoparticles were then characterized using high resolution transmission electron microscopy for the structural properties and temperature dependence Raman spectroscopy for the optical properties. High resolution transmission electron microscopy analysis shows that the ultrasonic synthesized carbon-doped titanium dioxide nanoparticles have an interplanar d-spacing of 0.352 nm, a value close to 0.374 nm of the pure undoped anatase titanium dioxide (bulk). The fast Fourier transform (FFT) of the selected electron diffraction images, of the selected areas, display the fact that only the main diffraction (reflection) plane of Miller indices (101) in titanium dioxide is responsible for diffraction pattern. Raman spectroscopy confirms the titanium dioxide polymorph to be anatase with the intense phonon frequency at 153 cm⁻¹ blue-shifted from 141 cm⁻¹ due to both carbon doping and particle size decrease. The temperature dependence analysis of the spectra shows an initial linear dependence of the Raman shift for the E _g(1) mode at 152.7 cm⁻¹ with increase in temperature up to a critical temperature 450 °C, after which we observe a decrease with increase in temperature. The other Raman modes [B _1g and E _g(3)] exhibit a different temperature dependence in that the B _1g displays a somewhat sinusoidal behavior and the E _g(3) mode shows a linear decrease of Raman shift with an increase in temperature. Temperature dependence analysis of peak width for the E _g(1) indicates the peak width of the as prepared nanoparticle to be 20 cm⁻¹ which is far much larger than that for single crystal of 7 cm⁻¹ at room temperature.     

Characterization of La1 −x Sr1 +x Cu5 −x Fe x O12 + δ (0 ≤x ≤ 1·0) by dc electrical conductivity,magnetic susceptibility and EPR measurements(0 ≤x ≤ 1·0) by dc electrical conductivity,magnetic susceptibility and EPR measurements

The DC electrical resistivity results of La_{4 −x} Sr_{1 +x} Cu_{5 −x} Fe _x O_{12 + δ} (0 ≤x ≤ 1·0) showed that for S1 (x = 0) and S2 (x = 0·25) the temperature coefficient of resistivity (TCR), dρ/dT, is positive and slightly increases with increasing temperature in the range 20–270 K. This shows the metallic nature of S1 and S2. For the samples S3(x = 0·5) and S4 (x = 0·75), TCR slightly increases in the range 20–270 K, with change in sign from negative to positive at ∼ 80 K and ∼ 130 K, respectively. These results show the metal-insulator type transition in S3 and S4. For the sample S5 (x = 1·0), the TCR is negative and gradually increases in the range 20–270 K, which shows its semiconductor-like behaviour. The activation energy for S5 is found to be 0·21 × 10⁻² eV. Furthermore, the DC resistivity results of S1–S5 in the range 350–660 K are in conformity with the low temperature results. The very weak temperature dependence of magnetic susceptibility results of S1–S3 show Pauli-paramagnetic behaviour in the range 77K–400 K, while S4 and S5 exhibit Pauli-paramagnetic behaviour in the range 77–850 K. Long-range antiferromagnetic interaction is observed in S5 (x = 1·0) belowT _c ∼ 100 K. The room temperature EPR lineshapes gradually improve from metallic S1 (x = 0) to semiconductor-like S5(x = 1·0). Negativeg-shift is observed in the samples S2–S5 with increasing trend ing _iso-values of 1·880 in S2 to 1·961 in S5. However, theg _iso-value for S1 could not be observed due to very poor lineshape.     

Parabolic Flights @ Home

We developed an unmanned air vehicle (UAV) suitable for small parabolic-flight experiments. The flight speed of 100 m s^− 1 is sufficient for zero-gravity parabolas of 16 s duration. The flight path’s length of slightly more than 1 km and 400 m difference in altitude is suitable for ground controlled or supervised flights. Since this fits within the limits set for model aircraft, no additional clearance is required for operation. Our UAV provides a cost-effective platform readily available for low-g experiments, which can be performed locally without major preparation. A payload with a size of up to 0.9 ×0.3 ×0.3 m³ and a mass of ∼5 kg can be exposed to 0 g ₀–5 g ₀, with g ₀ being the gravitational acceleration of the Earth. Flight-duration depends on the desired acceleration level, e.g. 17 s at 0.17 g ₀ (lunar surface level) or 21 s at 0.38 g ₀ (Martian surface level). The aircraft has a mass of 25 kg (including payload) and a wingspan of 2 m. It is powered by a jet engine with an exhaust speed of 450 m s^− 1 providing a thrust of 180 N. The parabolic-flight curves are automated by exploiting the advantages of sophisticated micro-electronics to minimize acceleration errors.     

Spectroscopic studies of TeO<Subscript>2</Subscript>–ZnO–Er<Subscript>2</Subscript>O<Subscript>3</Subscript> glass system

Series of glass based on the (80 − x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ≤ x ≤ 2.5 mol%) has successfully been made by melt quenching technique. The optical properties of glass have been investigated by means of IR and Raman spectroscopy. It is observed that as the Er₂O₃ content is being increased, the sharp IR absorption peaks are consistently shifted from 650 to 672 cm⁻¹ while the Raman shift intensity around 640–670 cm⁻¹ is decreases but increases around 720–740 cm⁻¹. It is found out that both phenomenons are related to the structural changes between the stretching vibration mode of TeO₄ tbp and TeO₃ tp, and bending vibration mode of Te–O bonds in the glass linkages.     

Preparation, proton conduction, and application in ammonia synthesis at atmospheric pressure of La0.9Ba0.1Ga1– x Mg x O3–α

La_0.9Ba_0.1Ga_1–x Mg _x O_3–α (0 ≤ x ≤ 0.25) was prepared by the microemulsion method. A single phase of LaGaO₃ perovskite structure was formed when x was ≥0.15. Electrochemical hydrogen permeation (hydrogen pumping) proved that La_0.9Ba_0.1Ga_1–x Mg _x O_3–α had proton conduction, and the proton conduction was measured by AC impedance spectroscopy method from 400 to 800 °C in hydrogen atmospheres. Among these samples, La_0.9Ba_0.1Ga_0.8Mg_0.2O_3–α has the highest proton conductivity with the values of 9.51 × 10⁻⁴ to 4.68 × 10⁻² S cm⁻¹ at 400–800 °C. Ammonia was synthesized from nitrogen and hydrogen at atmospheric pressure in an electrolytic cell using La_0.9Ba_0.1Ga_0.8Mg_0.2O_3–α as electrolyte. The rate of NH₃ formation was 1.89 × 10⁻⁹ mol s⁻¹ cm⁻² at 520 °C upon imposing a current of 1 mA through the cell.     

Sol–gel synthesis and electrical characterization of (Pb, Ca)TiO3 thin films

Calcium modified lead titanate films have been prepared on Pt/Ti/SiO₂/Si substrates using a sol–gel route. The sols were prepared from propanediol solutions of Pb(CH₃COO)₂·xH₂O, Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂ and Ca(NO₃)₂·xH₂O. Tetragonal phase (Pb, Ca)TiO3 films could be produced by firing the coatings at 650°C for 30 min. The limiting thickness of crack-free single layers was ∼0.4 μm, but 3 μm thick films could be made by a multiple deposition technique. Dielectric and ferroelectric parameters were determined for single layer 0.5 μm films for compositions up to 30 mol% Ca. The average values of remanent polarization, P_r and coercive field, E_c decreased with increasing Ca content from ∼11 μC cm⁻² and ∼125 Kv cm⁻¹ for a 10 mol% Ca composition to ∼8 μC cm⁻² and 80 kV cm⁻¹ for 30 mol% Ca films. It was noted that the statistical variation in electrical values across each film was greater than in PZT films made by a similar sol–gel route. Reasons for this are discussed in terms of the incidence of physical defects in the films. This revised version was published online in November 2006 with corrections to the Cover Date.