Ni doping induced property enhancement in laser ablated BaSnO3 films suitable for optoelectronic applications.

Pulsed laser deposition is a straightforward approach for preparing films with superconducting to dielectric properties with atomic layer precision. The deep-seated mechanisms involved in the particle transport from target to substrate and subsequent film formation still need to be fully comprehended. This manuscript reports the property enhancement observed in laser ablated perovskite BaSnO3 films with Ni doping. Films' crystallinity improvement is observed, and an intensity enhancement of 1150% is observed on 3 mol% Ni-doping. The optimum Ni-doping concentration in BaSnO3 is found to be 3 mol%. Herein, Ni-doped BaSnO3 films deposited by PLD showed an unusual increase in film thickness (i.e., from 615 nm in the pure film to 1317 nm in the film with 7 mol% Ni-doping as revealed by lateral SEM analysis and spectroscopic ellipsometry). We propose an "Induced Magnetic field-assisted Particle Convergence (IMPC)" effect for this superficial growth enhancement. The film's optical properties are modified with an increased nickel doping level, and the bandgap energy shows renormalization. All the films show excellent transmittance (80-90%) in the Vis.-NIR region. Hall-effect measurement reveals the increased carrier concentration by three orders (2.98 × 1011 to 3.50 × 1014 cm-3). In addition, the enhancement in mobility from 3.13 to 20.93 cm2V-1s-1 and a decrease in electrical resistivity by six orders (i.e., from 4.05 × 109 to 1.13 × 103 Ω cm) are observed on 7 mol% Ni doping. XPS measurements reveals that the Ba, Sn and Ni ions are at 2+, 4+ and 2+ oxidation states. Using spectroscopic ellipsometric method, we estimated the optical constants of the films, the refractive index, dielectric constant, and extinction coefficient show a normal dispersion behavior. The high crystallinity, high transmittance, suitable surface topography, and improved electrical performances of the Ni-doped BaSnO3 films make them excellent candidates for optoelectronic devices and solar cells.

Tailoring the Emission Behavior of WO3 Thin Films by Eu3+ Ions for Light-Emitting Applications.

The article reports the successful fabrication of Eu3+-doped WO3 thin films via the radio-frequency magnetron sputtering (RFMS) technique. To our knowledge, this is the first study showing the tunable visible emission (blue to bluish red) from a WO3:Eu3+ thin film system using RFMS. X-ray diffractograms revealed that the crystalline nature of these thin films increased upto 3 wt% of the Eu3+ concentration. The diffraction peaks in the crystalline films are matched well with the monoclinic crystalline phase of WO3, but for all the films', micro-Raman spectra detected bands related to WO3 monoclinic phase. Vibrational and surface studies reveal the amorphous/semi-crystalline behavior of the 10 wt% Eu3+-doped sample. Valence state determination shows the trivalent state of Eu ions in doped films. In the 400-900 nm regions, the fabricated thin films show an average optical transparency of ~51-85%. Moreover, the band gap energy gradually reduces from 2.95 to 2.49 eV, with an enhancement of the Eu3+-doping content. The doped films, except the one at a higher doping concentration (10 wt%), show unique emissions of Eu3+ ions, besides the band edge emission of WO3. With an enhancement of the Eu3+ content, the concentration quenching process of the Eu3+ ions' emission intensities is visible. The variation in CIE chromaticity coordinates suggest that the overall emission color can be altered from blue to bluish red by changing the Eu3+ ion concentration.

Silver nanoparticles-incorporated Nb2O5 surface passivation layer for efficiency enhancement in dye-sensitized solar cells.

Guiding and capturing photons at the nanoscale by means of metal nanoparticles and interfacial engineering for preventing back-electron transfer are well documented techniques for performance enhancement in excitonic solar cells. Drifting from the conventional route, we propose a simple one-step process to integrate both metal nanoparticles and surface passivation layer in the porous photoanode matrix of a dye-sensitized solar cell. Silver nanoparticles and Nb2O5 surface passivation layer are simultaneously deposited on the surface of a highly porous nanocrystalline TiO2 photoanode, facilitating an absorption enhancement in the 465 nm and 570 nm wavelength region and a reduction in back-electron transfer in the fabricated dye-sensitized solar cells together. The TiO2 photoanodes were prepared by spray pyrolysis deposition method from a colloidal solution of TiO2 nanoparticles. An impressive 43% enhancement in device performance was accomplished in photoanodes having an Ag-incorporated Nb2O5 passivation layer as against a cell without Ag nanoparticles. By introducing this idea, we were able to record two benefits - the metal nanoparticles function as the absorption enhancement agent, and the Nb2O5 layer as surface passivation for TiO2 nanoparticles and as an energy barrier layer for preventing back-electron transfer - in a single step.

Ag@Nb2O5 plasmonic blocking layer for higher efficiency dye-sensitized solar cells.

Engineering photons on a nanoscale via guidance and localization by metal nanostructures has a profound influence on the performance of devices that try to mimic the process of photosynthesis. The conventional route for the synthesis of plasmonic nanoparticles and their integration into the porous structure of the photoanode either directly or after being capped with a dielectric material not only adds to the complexity but also to the cost of the cell. The present study introduces the concept of a plasmonic blocking layer that concurrently acts as a light harvester and an electron-blocking layer in a dye-sensitized solar cell (DSSC), wherein the plasmonic silver nanoparticles are incorporated into an Nb2O5 blocking layer by a simple one-step process. The cell with the plasmonic blocking layer achieves an efficiency of 9.24% when compared with a cell with a non-plasmonic blocking layer (7.6%), registering an impressive enhancement in the efficiency by 22%. Moreover, the cell with the plasmonic blocking layer shows an improvement in the efficiency by 49% when compared with the cell without a blocking layer (6.19%).

Effect of thermal annealing on the phase evolution of silver tungstate in Ag/WO3 films.

Silver/tungsten oxide multi-layer films are deposited over quartz substrates by RF magnetron sputtering technique and the films are annealed at temperatures 200, 400 and 600°C. The effect of thermal annealing on the phase evolution of silver tungstate phase in Ag/WO3 films is studied extensively using techniques like X-ray diffraction, micro-Raman analysis, atomic force microscopy and photoluminescence studies. The XRD pattern of the as-deposited film shows only the peaks of cubic phase of silver. The film annealed at 200°C shows the presence of XRD peaks corresponding to orthorhombic phase of Ag2WO4 and peaks corresponding to cubic phase of silver with reduced intensity. It is found that, as annealing temperature increases, the volume fraction of Ag decreases and that of Ag2WO4 phase increases and becomes highest at a temperature of 400°C. When the temperature increases beyond 400°C, the volume fraction of Ag2WO4 decreases, due to its decomposition into silver and oxygen deficient phase Ag2W4O13. The micro-Raman spectra of the annealed films show the characteristic bands of tungstate phase which is in agreement with XRD analysis. The surface morphology of the films studied by atomic force microscopy reveals that the particle size and r.m.s roughness are highest for the sample annealed at 400°C. In the photoluminescence study, the films with silver tungstate phase show an emission peak in blue region centered around the wavelength 441 nm (excitation wavelength 256 nm).

Alteration of architecture of MoO3 nanostructures on arbitrary substrates: growth kinetics, spectroscopic and gas sensing properties.

MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.

A detailed perceptive on the growth and characterization studies of para amino hippuric acid (PAHA) single crystals.

Single crystals of para amino hippuric acid (PAHA) were grown by slow evaporation technique. The spectral and its structural properties of the crystals were studied by FT-IR, micro-Raman and factor group analysis. The optical transparency in the UV-Visible regions was found to be good for non-linear optics (NLO) applications. Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA) showed that the compound decomposes beyond 300°C. The dielectric behavior of the compound predicts low dielectric loss at high frequency applied whereas in the case of mechanical behavior of the specimen hardness increases with increasing applied load. After certain weight increase, hardness gets saturated in the region of ≥110. Relative second harmonic efficiency of the compound is found to be 1.8 times greater than that of potassium di-phosphate reference.

Structural, spectroscopic and electrical studies of nanostructured porous ZnO thin films prepared by pulsed laser deposition.

ZnO thin films are grown on quartz substrates at various substrate temperatures (ranging from 573 to 973 K) under an oxygen ambience of 0.02 mbar by using pulsed laser ablation. Influence of substrate temperature on the structural, morphological, optical and electrical properties of the ZnO thin films are investigated. The XRD and micro-Raman spectra reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye-Scherer equation and the average size of the crystallites are found to be in the range 17-29 nm. The AFM study reveals that the surface morphology of the film depends strongly on the substrate temperature. UV-Visible transmittance spectra show highly transparent nature of the films in visible region. The calculated optical band gap energy is found to be decrease with increase in substrate temperatures. The complex dielectric constant, the loss factor and the distribution of the volume and surface energy loss of the ZnO thin films prepared at different substrate temperatures are calculated. All the films are found to be highly porous in nature. The PL spectra show very strong emission in the blue region for all the films. The dc electrical resistivity of the film decreases with increase in substrate temperature. The temperature dependent electrical measurements done on the film prepared at substrate temperature 573 K reveals that the electric conduction is thermally activated and the activation energy is found to be 0.03911 eV which is less than the reported values for ZnO films.

Effect of zinc oxide doping on the structural and optical characterization of nanostructured molybdenum oxide films.

Undoped and zinc oxide (ZnO) doped molybdenum oxide (MoO3) films were prepared by RF magnetron sputtering technique. The influence of doping and post annealing temperature on the structural and optical properties of these films were investigated systematically using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-VIS spectroscopy and photoluminescence spectroscopy (PL). The XRD patterns indicate the presence of stoichiometric orthorhombic alpha-MoO3 phase in the annealed (573 and 673 K) undoped molybdenum oxide films and in ZnO doped molybdenum oxide film (annealed at 673 K). The crystalline grain size in the films was investigated using Debye Scherrer formula and corrected using Hall-Williamson equation. The SEM and AFM images revealed the distribution of nano leafs, nanorods and nanograins. Nanorods of length 1.4 microm and diameter 149 nm can be observed in ZnO doped films. The optical band gap energy was found to increase with increase in annealing temperature and particle size. These nanostructures show a room temperature PL emission in the UV and visible region.

Micro-structural, electrical and spectroscopic investigations of pulsed laser ablated palladium incorporated nanostructured tungsten oxide films.

Pure and Pd incorporated (0.5, 1 and 5 wt%) WO3 films are prepared on quartz substrates using pulsed laser ablation (PLD) technique in an oxygen ambient of 0.12 mbar, at a substrate temperature (Ts) of 873 K. Palladium incorporation effects on the microstructure, optical and electrical properties of tungsten oxide films are systematically investigated using techniques like X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), micro-Raman spectroscopy, UV-Vis absorption spectroscopy and temperature dependent electrical resistivity measurements. The micro-structural analysis by XRD and micro-Raman indicates that Pd addition can perturb the tungsten oxide lattice and suppress the grain growth. Optical band gap values of the films increases from 3.17 eV for pure WO3 to 3.29 eV for 5 wt% Pd incorporated WO3 films. All the films present high transparency in the visible spectral range. The electrical resistivity studies of the pure and Pd incorporated films done at room temperature and for the range of temperature; 170-450 K reveal that Pd addition can lower the resistivity of the WO3 thin films. Room temperature resistivity as well as activation energy of the film decreases exponentially with Pd incorporation concentration. Highly transparent, nanocrystalline and semiconducting WO3 films with low resistivity obtained by Pd incorporation can make WO3 suitable for microelectronics industry and for gas sensing applications.

Optimum wavelength for the differentiation of brain tumor tissue using autofluorescence spectroscopy.

OBJECTIVE: The role of autofluorescence spectroscopy in the detection and staging of benign and malignant brain tumors is being investigated in this study, with an additional aim of determining an optimum excitation wavelength for the spectroscopic identification of brain tumors. MATERIALS AND METHODS: The present study involves in-vitro autofluorescence monitoring of different human brain tumor samples to assess their spectroscopic properties. The autofluorescence measurement at four different excitation wavelengths 320, 370, 410, and 470 nm, were carried out for five different brain tumor types: glioma, astrocytoma, meningioma, pituitary adenoma, and schwannoma. RESULTS: The fluorescence spectra of tumor tissues showed significant differences, both in intensity and in spectral profile, from those of adjacent normal brain tissues at all four excitation wavelengths. The data were then subjected to multivariate statistical analysis and the sensitivities and specificities were calculated for each group. Of the four excitation wavelengths being considered, 470 nm appeared to be the optimal wavelength for detecting tissue fluorescence of brain tumor tissues. CONCLUSIONS: In conclusion, the spectroscopic luminescence measurements carried out in this study revealed significant differences between tumor tissue and adjacent normal tissue of human brains for all the tumor types tested, except for pituitary adenoma. From the results of this study we conclude that excitation wavelengths ranging from 410-470 nm are most suitable for the detection of brain tumor tissue. Moreover, in this particular study, only excitation at 470 nm indicated that samples we considered to be normal tissue were not normal, and that these were indeed pituitary adenoma tissues. This distinction was not clear at other excitation wavelengths.

Infrared and polarized Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O.

FTIR and single crystal Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O have been recorded at 300 and 90 K and analysed. The shifting of nu1 mode to higher wavenumber and its appearance in Bg species contributing to the alpha(xz) and alpha(yz) polarizability tensor components indicate the distortion of SO4 tetrahedra. The presence of nu1 and nu2 modes in the IR spectrum and the lifting of degeneracies of nu2, nu3, and nu4 modes are attributed to the lowering of the symmetry of the SO4(2-) ion. Coincidence of the IR and Raman bands for different modes suggest that DMA+ ion is orientationally disordered. One of the H atoms of the NH2 group of the DMA+ ion forms moderate hydrogen bonds with the SO4(2-) anion. Al(H2O)6(3+) ion is also distorted in the crystal. The shifting of the stretching modes to lower wavenumbers and the bending mode to higher wavenumber suggest that H2O molecules form strong hydrogen bonds with SO4(2-) anion. The intensity enhancement and the narrowing of nu1SO4, deltaC2N and Al(H2O)6(3+) modes at 90 K confirm the settling down of the protons in the hydrogen bonds formed with H2O molecules and NH2 groups. This may be one of the reasons for the phase transition observed in the crystal.