Pritika Reddy

Spectroscopic characterization of electron-beam evaporated V2O5 thin films

Thin films of vanadium pentoxide (V2O5) were prepared by electron beam evaporation at different deposition temperatures. The chemical composition and structural and optical properties were investigated employing spectroscopic techniques, viz. X-ray photo-electron spectroscopy (XPS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), infrared spectroscopy (IR), Raman spectroscopy (RS) and optical spectroscopy (OS). The influence of deposition temperature on the film properties were deduced from the spectroscopic measurements. The room temperature (303 K) electron-beam evaporated V2O5 films were nearly stoichiometric. The films formed at elevated temperatures were sub-stoichiometric as revealed (XPS) from the shift of the V(2p3/2) emission peak, the broadening of full width at half maximum (FWHM) and the decrease in the O(1s):V(2p3/2) ratio. The shift of vanadyl mode in the IR and Raman spectra, decrease of the optical band gap and increase in the near-infrared-broad band absorption also supported the sub-stoichimetric nature. Annealing of the films formed at Ts∼553K in an oxygen atmosphere (a partial pressure of 10−4 mbar) at 693 K led to the existence of vanadium in its highest oxidation state.

Optical constants of polycrystalline CuGaTe2 films

Abstract Thin films of CuGaTe2 with thicknesses in the range, 0.1–1.0 μm were deposited on Corning 7059 glass substrates by flash evaporation. The substrate temperatures, Ts, were maintained in the range 373–623 K. The transmittance of the films was recorded in the wavelength range 900–2500 nm. The dependence of the optical band gap, Eg, on substrate temperature showed that the value of Eg varied from 1.21 eV to 1.24 eV. The variation of refractive index and extinction coefficient with photon energy was studied from which the material properties such as the limiting value of dielectric constant, ϵ∞, plasma frequency, ωp, and hole effective mass, m h ∗ , were evaluated as ϵ∞ = 7.59, ωp = 1.47 × 1014 and m h ∗ = 1.25 m 0 .

Influence of substrate temperature on the composition and structural properties of electron beam evaporated V2O5 thin films

Abstract Thin films of vanadium pentoxide prepared by electron beam evaporation at different substrate temperatures were characterized by studying their structure and composition. The influence of the deposition temperature on the composition and structure of the films and the effect of heat treatment in an oxygen atmosphere were studied in detail and the deposition conditions were optimised to yield layered type V 2 O 5 thin films.

Investigations on polycrystalline CuGaTe2 thin films

Polycrystalline and single-phase CuGaTe2 thin films(0.4–1.0 μm thickness) were prepared by flashevaporation of the pre-reacted material, synthesized from its constituent elements. The filmswere deposited on glass substrates at temperatures in the range 303–623 K. The physical behaviour of the films was found to be highly influenced by the substrate temperature, T s. The films formed at Ts = 523–573 K were nearly stoichiometric and exhibited (112) preferred orientation with tetragonal structure. The evaluated lattice parameters were a = 6.025 A and c= 11.996 A. The electrical conductivity of the films varied in the range 10-102 ω cm. Two activation energies corresponding to shallow and deep acceptor levels were observed. The films showed a three-fold optical structure with the bandgaps at 1.23 eV, 1.28 eV and 1.98 eV. The optical constants, dielectric constant, plasma frequency and the effective mass of the charge carriers were computed. The results are discussed to study the suitability of CuGaTe2 films for solarcell application.

Characterization of p-AglnSe2/n-Zn0.35Cd0.65S polycrystalline thin film heterojunctions

Abstract Polycrystalline thin film p -AglnSe 2 / n -Zn 0.35 Cd 0.65 S heterojunctions were fabricated and the current density-voltage, capacitancevoltage and spectral response characteristics of the junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 425 mV, a short-circuit current density of 30 mA cm −2 and an electrical conversion efficiency of 7.5% have been obtained for a cell with an active area of 1 cm 2 under a solar input of 100 mW cm −2 .

Electrical properties of CuGaTe2 thin films

Abstract CuGaTe 2 thin films were prepared by the flash evaporation technique. The influence of substrate temperature ( T s ) on the electrical characteristics was studied. The films formed at T s = 523–573 K were polycrystalline, single phase and nearly stoichiometric. The films of 0.7 μm thickness showed an electrical resistivity of about 10 −2 Ω cm, a mobility of 55 cm 2 V −1 s −1 with a carrier concentration of 1.5 × 10 19 cm −3 . The electrical resistivity was found to decrease with film thickness, whereas the mobility increased. The activation energies were also determined in the temperature range 300–575 K.

Effectiveness of Tablet Learning in Online Courses at University of the South Pacific

In recent years, technology has become the game changer in the world of higher education. The handheld mobile devices are emerging as one of the most promising technologies and tools to support learning and venture into new pedagogies. This provides uncharted opportunities for educationists and facilitators to make learning pervasive and boost lifelong learning. Mobile devices like tablet computers have proven to be effective in accelerating student engagement, enhancing focus and supporting teacher interaction. To evaluate the effectiveness of tablet learning in a higher education institution, a study was conducted on a sample of 10 students who were picked on voluntarily basis from a seven weeks online course. The attitude of students to the new technological device was analysed. The study also considered the quality of tasks and assessments produced by the students and their success rate. The results of this study showed that students have a positive attitude towards tablet learning and there was an agreement that the mobile device was a good learning tool for the online courses. Interestingly, there was no significant difference noted with the success rates and the grades of the two groups.