V. Damodara Das

Bio: V. Damodara Das is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Thin film & Electrical resistivity and conductivity. The author has an hindex of 20, co-authored 89 publications receiving 1145 citations.

Effect of annealing and surface treatment on the efficiency of photoelectrochemical (PEC) solar cells with vacuum-deposited n-InSe thin film electrode

Abstract: Three hundred-nanometre thick films of n-InSe have been vacuum-deposited by flash evaporation on conducting indium oxide film coated clean glass substrates held at 373 K at 6.6 × 10−3 Pa pressure. These InSe films have been used as photoelectrodes in a photoelectrochemical (PEC) cell with graphite as the counter electrode, the saturated calomel electrode as the reference electrode and aqueous polyiodide electrolyte (with different pHs) as the redox electrolyte. PEC cells have been characterised by making I–V and C-V measurements under different experimental conditions, i.e., using the as-grown InSe films as photoelectrodes before and after surface treatment and after annealing and/or etching and for different pHs of the electrolyte. The optimum pH has been found to be about 6.2. It is also found that surface treatment and annealing leads to increase in the efficiency of the PEC solar cell. The open circuit voltage and photo current density are found to be of the order of 580 mV and 3000 μA/cm2, respectively under AM1 condition.

Ageing studies of discontinuous copper and silver thin films

Abstract: The results of experiments carried out on the post-deposition resistance changes in discontinuous films of copper and silver with and without overlayers of SiO and Al2O3 are presented. The changes in the sheet resistance of the films with time and pressure were studied for the above combinations. Mobility coalescence is assumed to be responsible for the resistance increase of an uncovered copper film of initial resistance 1.9 MΩ/□. On exposure to the atmosphere, it was found that an Ag/SiO combination of initial resistance of 0.1 MΩ/□ achieved stability in the sheet resistance much quicker than a Cu/Al2O3 combination of initial resistance 20 MΩ/□. The fall in resistance of the Cu/Al2O3 composite is attributed to the formation of Al2(OH)6 due to the interaction of Al2O3 with the water vapour in atmosphere. Copper films with and without overlayers of Al2O3 show an abrupt increase in the sheet resistance as a function of pressure at a pressure of about 5 × 10−2 torr with the maximum rate of change of resistance occurring at higher pressure for the higher resistance film. This indicates that the overlayer of Al2O3 is very porous in nature. Field effect studies were carried out on an uncovered copper film of initial resistance 10 MΩ/□ and the behaviour was found to be ohmic up to a field of 800 V cm−1.

A review on thermoelectric renewable energy: Principle parameters that affect their performance

Abstract: Developing thermoelectric materials with superior performance means tailoring interrelated thermoelectric physical parameters – electrical conductivities, Seebeck coefficients, and thermal conductivities – for a crystalline system. High electrical conductivity, low thermal conductivity, and a high Seebeck coefficient are desirable for thermoelectric materials. Therefore, knowledge of the relation between electrical conductivity and thermal conductivity is essential to improve thermoelectric properties. In general, research in recent years has focused on developing thermoelectric structures and materials of high efficiency. The importance of this parameter is universally recognized; it is an established, ubiquitous, routinely used tool for material, device, equipment and process characterization both in the thermoelectric industry and in research. In this paper, basic knowledge of thermoelectric materials and an overview of parameters that affect the figure of merit ZT are provided. The prospects for the optimization of thermoelectric materials and their applications are also discussed.

Vortex formation in neutron-irradiated superfluid 3He as an analogue of cosmological defect formation

Abstract: TOPOLOGICAL defects formed during a rapid symmetry-breaking phase transition in the early Universe1,2 could be responsible for seeding large-scale structure, for the anisotropy of the microwave background radiation, and for the predominance of matter over antimatter3,4. The theory describing this cosmological phase transition is formally analogous to that describing the transition to the superfluid state in liquid 3He, so that in principle the process of cosmological defect formation can be modelled in the laboratory. Here we report the results of an experiment in which the 'primordial fireball' is mimicked using a neutron-induced nuclear reaction (n + 3He → p + 3He + 0.76 MeV) to heat small regions of superfluid 3He above the superfluid transition temperature. These bubbles of normal liquid cool extremely rapidly, and we find that their transition back to the superfluid state is accompanied by the formation of a random network of vortices (the superfluid analogue of cosmic strings). We monitor the evolution of this defect state by rotating the superfluid sample, allowing vortices to escape from the network and thus be probed individually. Our results provide clear confirmation of the idea that topological defects form at a rapid second-order phase transition, and give quantitative support to the Kibble–Zurek mechanism5,6 of cosmological defect formation.

Investigation of the optical and electronic properties of Ge2Sb2Te5 phase change material in its amorphous, cubic, and hexagonal phases

Abstract: Ge–Sb–Te alloys are widely used for data recording based on the rapid and reversible amorphous-to-crystalline phase transformation that is accompanied by increases in the optical reflectivity and the electrical conductivity. However, uncertainties about the optical band gaps and electronic transport properties of these phases have persisted because of inappropriate interpretation of reported data and the lack of definitive analytical studies. In this paper we characterize the most widely used composition, Ge2Sb2Te5, in its amorphous, face-centered-cubic, and hexagonal phases, and explain the origins of inconsistent or unphysical results in previous reports. The optical absorption in all of these phases follows the relationship αhν∝(hν−Egopt)2, which corresponds to the optical transitions in most amorphous semiconductors as proposed by Tauc, Grigorovici, and Vancu [Tauc et al., Phys. Status Solidi 15, 627 (1966)], and to those in indirect-gap crystalline semiconductors. The optical band gaps of the amorpho...

Functional inks and printing of two-dimensional materials.

Abstract: Graphene and related two-dimensional materials provide an ideal platform for next generation disruptive technologies and applications. Exploiting these solution-processed two-dimensional materials in printing can accelerate this development by allowing additive patterning on both rigid and conformable substrates for flexible device design and large-scale, high-speed, cost-effective manufacturing. In this review, we summarise the current progress on ink formulation of two-dimensional materials and the printable applications enabled by them. We also present our perspectives on their research and technological future prospects.

Effect of magnetic dipolar interactions on nanoparticle heating efficiency: Implications for cancer hyperthermia

Abstract: Nanostructured magnetic systems have many applications, including potential use in cancer therapy deriving from their ability to heat in alternating magnetic fields. In this work we explore the influence of particle chain formation on the normalized heating properties, or specific loss power (SLP) of both low- (spherical) and high- (parallelepiped) anisotropy ferrite-based magnetic fluids. Analysis of ferromagnetic resonance (FMR) data shows that high particle concentrations correlate with increasing chain length producing decreasing SLP. Monte Carlo simulations corroborate the FMR results. We propose a theoretical model describing dipole interactions valid for the linear response regime to explain the observed trends. This model predicts optimum particle sizes for hyperthermia to about 30% smaller than those previously predicted, depending on the nanoparticle parameters and chain size. Also, optimum chain lengths depended on nanoparticle surface-to-surface distance. Our results might have important implications to cancer treatment and could motivate new strategies to optimize magnetic hyperthermia.