R. K. Bedi

Electrical properties of flash-evaporated tin selenide films

Abstract The electrical properties of tin selenide films deposited by flash evaporation onto glass, mica and KCl substrates are reported. It has been observed that the electrical resistivity of the flash-evaporated films is lower than those of films deposited by conventional thermal evaporation. The films deposited in KCl substrates have a lower resistivity than those deposited on glass and mica substrates. The films are found to be p type. Hall mobility and carrier concentration are observed to increase with increase in temperature.

SnO2 thick films for room temperature gas sensing applications

Porous nanosized SnO2 powder has been synthesized by a simple nonaqueous sol gel method using SnCl2⋅2H2O and C2H5OH as precursors. Thermal stabilization of the gel is investigated by thermogravimetric/differential thermal analysis. SnO2 powder has been obtained by calcining the gel at 500°C for 3h and studied for its structural properties using x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). XRD observations confirm the formation of rutile structured SnO2. On an average, 35nm size particles have been found in TEM micrographs of SnO2 powder. FESEM of the powder reveals the formation of a porous network formed by weak aggregation of nanoparticles. An attempt has been made to fabricate gas sensor by depositing thick SnO2 films on glass substrate. Gas sensing studies show that the sensing response of SnO2 sensor toward ammonia is comparatively higher at room temperature as compared to that toward acetone and ethanol.

Multifractal characterization of water soluble copper phthalocyanine based films surfaces

This paper presents a multifractal approach to characterize the structural complexity of 3D surface roughness of CuTsPc films on the glass and quartz substrate, obtained with atomic force microscopy (AFM) analysis. CuTsPc films prepared by drop cast method were investigated. CuTsPc films surface roughness was studied by AFM in tapping-mode™, in an aqueous environment, on square areas of 100 μm2 and 2500 μm2. A detailed methodology for CuTsPc films surface multifractal characterization, which may be applied for AFM data, was also presented. Analysis of surface roughness revealed that CuTsPc films have a multifractal geometry at various magnifications. The generalized dimension Dq and the singularity spectrum f(α) provided quantitative values that characterize the local scale properties of CuTsPc films surface morphology at nanometer scale. Multifractal analysis provides different yet complementary information to that offered by traditional surface statistical parameters.

Characterization of AgInTe2 films grown by a hot wall epitaxy technique on KCl substrates

Abstract AgInTe 2 films have been grown by a hot wall epitaxy technique onto KCl substrates kept at different temperatures in a vacuum of 1.3×10 −3 Pa. Experimental conditions were optimized to obtain better crystallinity in the films. The films thus prepared were studied for their electrical conductivity, Hall mobility, carrier concentration, as well as structural and optical properties. Observations reveal that the electrical conductivity and carrier concentration of films increases with increasing temperature of the substrate during deposition, while the Hall mobility decreases. The results indicate that the films are p-type, thus indicating holes as dominant charge carriers. The scanning electron micrographs of the films show an increase in grain size with increasing substrate temperature. Analysis of optical absorption studies on the films indicate the band gap energies lie in the range 1.12–1.26 eV.

Growth and properties of aluminium antimonide films produced by hot wall epitaxy on single-crystal KCl

Abstract Aluminium antimonide (AlSb) films have been grown by hot wall epitaxy on KCl substrates kept at different temperatures in vacuum of 1 × 10−5 Torr. The experimental conditions are optimised to obtain better crystallinity of the films. The electrical conductivity. Hall mobility and carrier concentration are determined. The films appear to be p-type: thus, indicating holes as dominant charge carriers. Scanning electron microscopy shows an increase in grain size with substrate temperature. Transmission electron micrographs indicate a better crystallinity of AlSb films as compared to those grown by thermal co-evaporation.

Effect of the crystallinity of silver nanoparticles on surface plasmon resonance induced enhancement of effective absorption cross-section of dyes

The effective absorption cross-section of dye, and therefore, the efficiency of dye-sensitized solar cell can be increased by surface plasmon resonance (SPR) of metal nanoparticles with enhanced dephasing time. Further, the dephasing time is proportional to the enhancement factor of electric field in the vicinity of nanoparticle surface, and is governed by size, shape, and dielectric constant of surrounding medium. In this paper, we demonstrate that crystallinity of silver nanoparticles plays an important role in enhancing the dephasing time of SPR. Our theoretical formulation indicates that the dephasing time is higher for single crystalline silver nanoparticles as compared to that of polycrystalline nanoparticles, which is attributed to the presence of scattering centers in the latter. This suggests that single crystalline silver nanoparticles are interesting candidates for the enhancement of effective absorption cross-section of dyes. In order to validate our theoretical formulation, we have synthesized single crystalline and polycrystalline silver nanoparticles and studied their effect on absorption cross-section of N719 dye. We observed that dye incorporated with single crystalline silver nanoparticles showed a significant enhancement as compared to polycrystalline silver nanoparticles (24.42% in solution, 21.01% in thin film form in single crystalline silver nanoparticles while 8.52% in solution, 7.97% in thin film form in polycrystalline silver nanoparticles, respectively).

Phthalocyanine based nanowires and nanoflowers as highly sensitive room temperature Cl2 sensors

Nanowires of Zn(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (ZnPcOC8) and nanoflowers of Cu(II) 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (CuPcOC8) have been uniformly grown onto glass substrate by employing a cost effective solution based self-assembly technique. The nanowires and nanoflowers were characterized by XRD, SEM and UV-Visible absorption spectroscopy. It has been demonstrated that these nanowires and nanoflowers were highly sensitive towards Cl2 at room temperature with a detection limit as low as 5 ppb. The response of nanowires and nanoflowers varied linearly from 93% to 715% and 85% to 550% for 5–1500 ppb of Cl2. Raman spectroscopic and XPS studies revealed that the central metal ions of ZnPcOC8 and CuPcOC8 were the predominant absorption sites for Cl2. The results emphasized the application of these nanostructures as low cost and highly sensitive room temperature Cl2 sensors.

Characterization of AgInSe2 Films Deposited by Hot-Wall Vacuum Evaporation Method

Hot-wall technique was used to prepare AgInSe2 films that work close to thermodynamic equilibrium and, therefore, are considered most suitable for growth at low temperatures. The samples were grown on the glass substrate kept at 135°C. The technique can be described as semiclosed growth reactor consisting of a vertically mounted quartz cylinder heated by three separately temperature-controlled ovens and is closed on the top by the substrate. The first oven heats the source material and controls the growth rate, while the second oven heats the wall between source and substrate, and the substrate temperature is controlled by the third one. The structural and optical properties of AgInSe2 films grown by hot-wall technique were studied. X-ray diffraction (XRD) pattern indicates that the prepared films are highly oriented in the (112) direction. The band gap was found to be 1.19 and 2.09 eV, which is due to the fundamental absorption edge and transition originating from crystal field splitting, respectively. The crystallite size of 47 nm and 94% transparency at 890 nm wavelength was observed for the films.

Characterization of ZnO Films Based Sensors Prepared by Different Techniques

In the present research, zinc oxide (ZnO) films have been prepared by simple solution method and spray pyrolysis on different substrates (glass and sapphire) for different molar concentrations (0.2M & 0.25M). The films were subjected to different substrate temperatures (400 °C and 450 °C respectively. These were characterized for SEM and XRD and the average size of the crystallites were in range of 300 and 200nm for the films on Saphire and glass at higher substrate temperature. FTIR analysis has been carried out and optimization conditions were used in order to confirm the significant peaks and phase transformation. The films were subjected to ethanol gas for these substrates and corresponding electrical properties were carried out by two probe method and was found that the films for sapphire substrate prepared by spray pyrolysis method showed more conductance at higher temperatures than glass. Optical properties were also studied for these films and was found that films prepared by spray on sapphire shows less transmittance at higher substrate temperatures in comparison to the films on glass.

Structural, optical, and electrical characterization of hot wall epitaxy grown 1-methoxy-8-hydroxy-9,10-anthraquinone films

1-methoxy-8-hydroxy-9,10-anthraquinone compound has been synthesized and its films are grown by the hot wall epitaxy technique onto the glass substrates kept at different temperatures in a vacuum of 10−5 Torr. The experimental conditions are optimized to obtain better crystallinity of the films. The films so prepared have been studied for their structural, optical, and electrical properties. Observations reveal that the crystallinity of the films increases with an increase in substrate temperature. Crystallites as large as 3.30 μm are observed in the case of films deposited at 348 K. Analysis of optical absorption measurements on the films indicate that the interband transition energies lies in the range 1.87–2.02 eV. The conduction in these films is found to be ohmic in nature and appears to take place by thermally activated hopping above intermolecular barriers. The electrical resistivity of films decreases with the increase in temperature, while carrier concentration increases.