Nb2O5 quantum dots (QDs) were grown using a simple technique of vacuum thermal evaporation. QDs were found to be crystalline in nature by selected area electron diffraction (SAED) in TEM. Samples with thickness up to 20 nm did not show any significant residual strain. Residual stress effect on band gap of crystalline Nb2O5 was studied for films thicker than 20 nm. Residual strain was determined using SAED of the films with reference to powder X-ray diffraction (XRD). Films thicker than 45 nm become amorphous as analyzed by both SAED and XRD. The optical absorption of films in the range 25–60 nm indicates significantly varying optical band gap of films. The varying band gap with film thickness scales linearly very well with the variation of residual stress with film thickness. The residual stress dependence of band gap of crystalline films yields stress free band gap as 3.37 eV with pressure coefficient of band gap (∂Eg/∂P)T = −29.3 meV/GPa. From this study, the crystalline to amorphous transformation in tetragonal form of M-Nb2O5 has been determined to be at about 14 GPa. Both pressure coefficient of band gap and crystalline to amorphous transition for tetragonal M-Nb2O5 have been determined for the first time in the literature.

Self-assembled InAs quantum dots (QDs) were grown on germanium substrates by metal organic chemical vapor deposition technique. Effects of growth temperature and InAs coverage on the size, density, and height of quantum dots were investigated. Growth temperature was varied from 400 to 450°C and InAs coverage was varied between 1.40 and 2.35 monolayers (MLs). The surface morphology and structural characteristics of the quantum dots analyzed by atomic force microscope revealed that the density of the InAs quantum dots first increased and then decreased with the amount of InAs coverage; whereas density decreased with increase in growth temperature. It was observed that the size and height of InAs quantum dots increased with increase in both temperature and InAs coverage. The density of QDs was effectively controlled by growth temperature and InAs coverage on GaAs buffer layer.

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CaCu 3 Ti 4 O 12 ( CCTO ) ceramics were prepared by the solid-state reaction route. Effect of sintering time was studied on the polarization (P) versus electric field (E) behavior. Unlike conventional ferroelectric hysteresis loop, PE hysteresis behavior in CCTO ceramics was observed to exhibit ferroelectric-like loop where polarization does not saturate but gives a maximum value. Remnant polarization and maximum polarization was observed to increase with sintering time. Current (I)–voltage (V) characteristics shows a nonlinear behavior making them useful for varistor applications. Coefficient of non-linearity (α) is also found to depend on sintering duration.