M.C. Santhosh Kumar

Co-evaporated SnS thin films for visible light photodetector applications

SnS thin films with different thicknesses have been deposited on glass substrates at a substrate temperature of 300 °C. The influence of thickness on structural, morphological, optical and electrical properties of the thin film has been investigated. X-ray diffraction (XRD) analysis and micro-Raman studies confirm the formation of single phase SnS films. Variation of surface morphology, roughness and average grain size of the as-deposited films have been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The optical properties such as film thickness (d), absorption coefficient (α), optical band gap (Eg), refractive index (n) and extinction coefficient (k) of the deposited thin films are estimated from the optical transmittance measurements. The optical energy band gap decreases from 1.51 eV to 1.24 eV with increase of film thickness. The electrical conductivity and photo-conductivity of the films increase by more than two orders with increase of film thickness from 170 nm to 915 nm. The visible photoresponsivity and specific detectivity of the films also increase with increase of film thickness. Hall effect measurements confirm the p-type nature of the as-prepared SnS thin films.

Investigation on P-N dual acceptor doped p-type ZnO thin films and subsequent growth of pencil-like nanowires

Phosphorous and nitrogen dual acceptor doped p-type ZnO (PNZO) have been deposited by spray pyrolysis method on glass substrates. An equimolar doping concentration of P and N were varied from 0.25?1.25 at% with a step of 0.25 at%. Preferred orientation along (002) planes with hexagonal wurzite structure was observed from structural analysis. Morphological analysis reveals uniform distributions of grains. Electrical studies showed dual acceptor doping of P and N in ZnO results in p-type behavior. The optimum doping concentration of P and N was found to be 0.75 at% which exhibited hole concentration of 4.48???1018 cm?3 and low resistivity value of 9.6 ?.cm. Photoluminescence (PL) studies revealed that, as-deposited films exhibit strong UV emission at 383 nm of the spectrum. The surface morphology of the optimum PNZO (0.75 at%) samples were further modified in the form of vertically aligned pencil-like nanowires by modified aqueous chemical growth (ACG) process. During ACG process, more acceptor related defects such as oxygen interstitials (Oi) were formed in the PNZO nanopencils. These acceptor defects induce enhanced emission in the visible region (400 nm to 700 nm) and also promote stable p-type characteristics.

Application of Taguchi method in the optimization of process parameters for a sol–gel-derived nano-alumina film

In this study, the Taguchi method is used to find the optimal process parameter combinations for realizing both lower film thickness and crystallite size and higher film thickness and crystallite size in a nano-alumina film prepared by sol–gel route. The process parameters evaluated were the molar concentration of the sol, dipping time, and sintering temperature. An orthogonal array, signal-to-noise ratio, and an analysis of variance were employed to analyze the effect of these process parameters. Surface profile measurement and X-ray diffraction techniques were used to measure the film thickness and crystallite size respectively. The analysis showed that the molar concentration of the sol was the most significant parameter on the film thickness and crystallite size, followed by dipping time and sintering temperature. Experimental results are supplied to exemplify the strength of this approach.

Room-temperature wide-range luminescence and structural, optical, and electrical properties of SILAR deposited Cu-Zn-S nano-structured thin films

We report the deposition of nanostructured Cu-Zn-S composite thin films by Successive Ionic Layer Adsorption and Reaction (SILAR) method on glass substrates at room temperature. The structural, morphological, optical, photoluminescence and electrical properties of Cu-Zn-S thin films are investigated. The results of X-ray diffraction (XRD) and Raman spectroscopy studies indicate that the films exhibit a ternary Cu-Zn-S structure rather than the Cu xS and ZnS binary composite. Scanning electron microscope (SEM) studies show that the Cu-Zn-S films are covered well over glass substrates. The optical band gap energies of the Cu-Zn-S films are calculated using UV-visible absorption measurements, which are found in the range of 2.2 to 2.32 eV. The room temperature photoluminescence studies show a wide range of emissions from 410 nm to 565 nm. These emissions are mainly due to defects and vacancies in the composite system. The electrical studies using Hall effect measurements show that the Cu-Zn-S films are having p-type conductivity.

Modeling of Fume Formation from Shielded Metal Arc Welding Process

In this study, a semi-empirical model of fume formation rate (FFR) from a shielded metal arc welding (SMAW) process has been developed. The model was developed for a DC electrode positive (DCEP) operation and involves the calculations of droplet temperature, surface area of the droplet, and partial vapor pressures of the constituents of the droplet to predict the FFR. The model was further extended for predicting FFR from nano-coated electrodes. The model estimates the FFR for Fe and Mn assuming constant proportion of other elements in the electrode. Fe FFR was overestimated, while Mn FFR was underestimated. The contribution of spatters and other mechanism in the arc responsible for fume formation were neglected. A good positive correlation was obtained between the predicted and experimental FFR values which highlighted the usefulness of the model.

Control of exposure to hexavalent chromium concentration in shielded metal arc welding fumes by nano-coating of electrodes

Abstract Background: Cr(VI) is a suspected human carcinogen formed as a by-product of stainless steel welding. Nano-alumina and nano-titania coating of electrodes reduced the welding fume levels. Objective: To investigate the effect of nano-coating of welding electrodes on Cr(VI) formation rate (Cr(VI) FR) from a shielded metal arc welding process. Methods: The core welding wires were coated with nano-alumina and nano-titania using the sol-gel dip coating technique. Bead-on plate welds were deposited on SS 316 LN plates kept inside a fume test chamber. Cr(VI) analysis was done using an atomic absorption spectrometer (AAS). Results: A reduction of 40% and 76%, respectively, in the Cr(VI) FR was observed from nano-alumina and nano-titania coated electrodes. Increase in the fume level decreased the Cr(VI) FR. Discussion: Increase in fume levels blocked the UV radiation responsible for the formation of ozone thereby preventing the formation of Cr(VI).

Fabrication and characterization of p-ZnO:(P,N)/n-ZnO:Al homojunction ultra-violet (UV) light emitting diodes (Presentation Recording)

ZnO possess distinctive characteristics such as low cost, wide band gap (3.36 eV) and large exciton binding energy (60meV). As the band gap lies in ultra violet (UV) region, ZnO is considered as a novel material for the fabrication of ultra violet light emitting diodes (UV-LEDs). However, ZnO being intrinsic n-type semiconductor the key challenge lies in realization of stable and reproducible p-type ZnO. In the present research dual acceptor group-V elements such as P and N are simultaneously doped in ZnO films to obtain the p-type characteristics. The deposition is made by programmable spray pyrolysis technique upon glass substrates at 697K. The optimum doping concentration of P and N were found to be 0.75 at% which exhibits hole concentration of 4.48 x 10^18 cm-3 and resistivity value of 9.6 Ω.cm. The deposited p-ZnO were found to be stable for a period over six months. Highly conducting n-type ZnO films is made by doping aluminum (3 at%) which exhibits higher electron concentration of 1.52 x 10^19 cm-3 with lower electrical resistivity of 3.51 x 10-2 Ω.cm. The structural, morphological, optical and electrical properties of the deposited n-ZnO and p-ZnO thin films are investigated. An efficient p-n homojunction has been fabricated using the optimum p-ZnO:(P,N) and n-ZnO:Al layers. The current–voltage (I–V) characteristics show typical rectifying characteristics of p-n junction with a low turn on voltage. Electroluminescence (EL) studies reveals the fabricated p-n homojunction diodes exhibits strong emission features in ultra-violet (UV) region around 378 nm.

Realization of highly transparent conducting CdO thin films by R.F. Magnetron sputtering for optoelectronic applications

Cadmium Oxide (CdO) thin films with low electrical resistivity and higher transparency has been deposited by r.f. magnetron sputtering on glass substrates. Sputtering process was carried out at r.f. power of 40W and with varying substrate temperatures. The structural, morphological, electrical and optical properties of the deposited films are investigated. The structral properties reveals that the as-deposited CdO films shows preferential orientation along (111) plane exhibiting face centered cubic structure. The surface morphology shows that all the films possess well defined grain boundaries with high uniformity. CdO samples deposited at substrate temperature of 150°C with r.f. power of 40W exhibits above 95% transparency in the visible region with lower electrical resistivity value in the order of 10-4 Ω.cm. The comparatevely high value of the figure of merit for the optimum sample of CdO deposited at 150°C indicates that these films are suitable for optoelectronic device applications.