K. K. Viswanathan

Phase transition kinetics and surface binding states of methylammonium lead iodide perovskite

We have presented a detailed analysis of the phase transition kinetics and binding energy states of solution processed methylammonium lead iodide (MAPbI3) thin films prepared at ambient conditions and annealed at different elevated temperatures. It is the processing temperature and environmental conditions that predominantly control the crystal structure and surface morphology of MAPbI3 thin films. The structural transformation from tetragonal to cubic occurs at 60 °C with a 30 minute annealing time while the 10 minute annealed films posses a tetragonal crystal structure. The transformed phase is greatly intact even at the higher annealing temperature of 150 °C and after a time of 2 hours. The charge transfer interaction between the Pb 4f and I 3d oxidation states is quantified using XPS.

Stacked Cu1.8S nanoplatelets as counter electrode for quantum dot-sensitized solar cell

It is found that the electrocatalytic activity of Cu2−xS thin films used in quantum dot-sensitized solar cells (QDSSCs) as counter electrode (CE) for the reduction of polysulfide electrolyte depends on the surface active sulfide and disulfide species and the deficiency of Cu. The preferential bonding between Cu2+ and S2−, leading to the selective formation of a Cu1.8S stacked platelet-like morphology, is determined by the cetyl trimethyl ammonium bromide surfactant and deposition temperature; the crab-like Cu–S coordination bond formed dictates the surface area to volume ratio of the Cu1.8S thin films and their electrocatalytic activity. The Cu deficiency enhances the conductivity of the Cu1.8S thin films, which exhibit near-infrared localized surface plasmon resonance due to free carriers, and UV-vis absorption spectra show an excitonic effect due to the quantum size effect. When these Cu1.8S thin films were employed as CEs in QDSSCs, a robust photoconversion efficiency of 5.2% was obtained for the film deposited at 60 °C by a single-step chemical bath deposition method.

Growth mechanisms and origin of localized surface plasmon resonance coupled exciton effects in Cu2−xS thin films

We have demonstrated a robust protocol to prepare Cu2−xS thin films with a controlled crystal phase and size which exhibit localized surface plasmon resonance (LSPR) coupled exciton effects by a simple template free single step wet chemical method without any surfactant. The LSPR frequency can be tuned in the Cu2−xS thin films by the growth temperature and time which controls the free carrier density. These selectively grown Cu2−xS thin films possess a tunable band gap (2.6–1.4 eV) due to the quantum size effect. The origin of the LSPR coupled exciton effects are discussed.

Free vibration of anti-symmetric angle-ply cylindrical shell walls using first-order shear deformation theory

In the present study, free vibration of anti-symmetric angle-ply cylindrical shell walls is investigated under first-order shear deformation theory using the spline method. Assuming the displacement components in a separable form, a system of coupled equations on three displacement and two rotational functions are obtained. A generalized eigenvalue problem is obtained using the collocation procedure and applying the spline function approximation for displacement and rotational function. The resulting eigenvalue problem is solved for the frequency parameters to get as many eigenvalues as required starting from the least. The eigenvectors are the spline coefficients from which the mode shapes can be constructed. The parametric study showed the effect of length parameter, circumferential node number, ply angles, number of lay-ups, lamination materials and different boundary conditions on the shell frequency.

Buckling Analysis of Rectangular Plates with Variable Thickness Resting on Elastic Foundation

Buckling of rectangular plates of variable thickness resting in elastic foundation is analysed using a quintic spline approximation technique. The thickness of the plate varies in the direction of one edge and the variations are assumed to be linear, exponential and sinusoidal. The plate is subjected to in plane load of two opposite edges. The buckling load and the mode shapes of buckling are computed from the eigenvalue problem that arises. Detailed parametric studies are made with different boundary conditions and the results are presented through the diagram and discussed.

Vibration of Antisymmetric Angle-Ply Laminated Plates of Higher-Order Theory with Variable Thickness

Free vibration of antisymmetric angle-ply laminated plates with variable thickness is studied. Higher-order shear deformation plate theory (HSDT) is introduced in the present method to remove the shear correction factors and improve the accuracy of transverse shear stresses. The thickness variations are assumed to be linear, exponential, and sinusoidal. The coupled differential equations are obtained in terms of displacement and rotational functions and approximated using cubic and quantic spline. A generalized eigenvalue problem is obtained and solved numerically by employing the eigensolution techniques with eigenvectors as spline coefficients to obtain the required frequencies. The results of numerical calculations are presented for laminated plates with simply supported boundary conditions. Comparisons of the current solutions and those reported in literature are provided to verify the accuracy of the proposed method. The effects of aspect ratio, number of layers, ply-angles, side-to-thickness ratio, and materials on the free vibration of cylindrical plates are discussed in detail.

Effects on MHD Flow of Oldroyd-B Fluid in a Porous Space via G-Jitter Combined with Heat and Mass Transfer

The effects of stimulated g-jitter which come together with heat and mass transfer by mixed convection in microgravity situation on MHD flow of Oldroyd - B fluid in porous space is investigated for a particular system. The system comprises of a pair of heated up perpendicular parallel infinite plates maintained at constant although various concentrations and temperatures. By using modified Darcy’s law, the equations governing the flow are modelled. These equations are solved exactly for the distributions of stimulated velocity, temperature and concentration. Interestingly the solutions for second grade and Maxwell fluids are recovered as new limiting cases of the present general results. Similar result in the relevant literature relating to Newtonian fluid is also obtained as a special case of the present solution. Finally particular attention is given to the graphical results for the velocity profiles of the oscillating flow in the channel. The analysis on the variations of embedded flow parameters in the solution expressions are presented and discussed.