The age-specific mating incidence and mating behaviour of an aphidophagous ladybird beetle Coelophora saucia Mulsant were studied. Males started mating at the age of 4 days. Newly emerged females mated with older males albeit forcibly. The incidence of mating was 100% at the age of 10 days. Courtship involved five steps, viz. approach, watch, examine, mount and attempt, and was male dominated under laboratory conditions. Results indicate that physical cues probably play a role in the initiation of courtship, while chemical signals are probably involved in the continuation of courtship, culminating in intromission. The mating duration, latent period and number of bouts gradually decreased with increase in the number of matings; however, the interval between bouts slightly increased. Pseudo-mating with dead mates was observed in C. saucia. The oviposition period, fecundity and % egg viability were highest in females mated multiple times, while lowest in those that mated once.

We have utilized the fact that syndiotactic and isotactic Poly(methyl methacrylate) {PMMA} form a stereocomplex to spin semi-crystalline PMMA fibers. Our goal is to produce oriented semi-crystalline fibers with a high enough melting point to withstand atactic-PMMA processing conditions. We successfully developed stereocomplex PMMA fibers by wet spinning and gel spinning, and characterized their properties by means of differential scanning calorimetry, optical/electron microscopy, mechanical testing and X-ray crystallography. Stereocomplex fibers from gel spinning have highest melting points and polymer chain orientation, hence are the best reinforcing agents. We are currently working on producing self-reinforced composites using these fibers.

Organic light emitting diodes (OLEDs) require a transparent conducting oxide (TCO) electrode for injection of charge carriers and the emitted light to come out. In order to exploit the full flexibility of organic semiconductor based large area electronic devices, the deposition of TCO on plastic substrates is essential, which prohibits high temperature processing. Therefore, low temperature deposition of Indium tin oxide (ITO) films is very important for flat panel displays and solar cells. Here we have carried out a systematic study of ITO deposition on plastic substrates using RF magnetron sputtering. For the optimization of structural, electrical and optical properties of ITO, various experiments such as X-ray diffractometer, transmission measurements, sheet resistance and AFM were employed. These properties were investigated as a function of substrate temperature, deposition time and RF power. From these experiments, we obtained a reasonably low sheet resistance (˜ 14;Ω / □) and high transmittance (˜75%) in the visible region on plastic substrates. We also observed that these films are not much affected by atmosphere and does not degrade with time. These ITO films deposited by RF magnetron sputtering on plastic substrates can be use as anode for flexible organic light emitting displays.

The photoluminescence (PL) intensity first increases with anodization time (ta) and then decreases at very large ta. The increase in PL intensity with ta may be understood if the PL intensity is taken to be proportional to the effective volume of porous silicon (PS) layer under the probe laser beam. The effective volume of PS layer will be proportional to its thickness and reciprocal to the porosity. For a fixed anodization condition, the thickness and porosity both increase with ta. The increase in thickness increases the effective PS volume, while the increase in porosity causes the effective volume to decrease. Therefore, the intensity variation is governed by these two parameters: thickness and porosity. The observed results suggest that the thickness dominates the PL intensity initially and then the porosity becomes more important for very long ta. The PS layers prepared under ambient light illumination also exhibited the similar behaviour. The intensity variation with ta was explained as the interplay of thickness and porosity variations with ta.

The optical degradation of polysilane copolymer has been studied in spin cast thin films and solutions using light source of 325 nm wavelength. The room temperature photoluminescence (PL) spectrum of these films show a sharp emission at 368 nm when excited with a source of 325 nm. However, the PL intensity deteriorates with time upon light exposure. Further the causes of this degradation have been examined by characterizing the material for its transmission behaviour and changes occurring in molecular weight as analysed by GPC data.

Al/PS junctions are non-rectifying and quasi-linear whereas Al/PS/c-Si junctions are weakly rectifying. The rectifying behavior is due to PS/c-Si heterojunction. The diode ideality factor (n) is about 8 for bias ≤0.5 V (about 50 for bias ≤5 V) at forward bias and nearly 1 for ≤0.5 V at reverse bias. As the temperature decreases, n at both forward and reverse biases increases. Different current transport mechanisms are found to be operating across the PS/c-Si junctions under forward and reverse biases. The barrier height measured from I-V data for ≤0.5 V is higher for forward bias than that for reverse bias. For high reverse biases (>5 V), the reverse current increases slowly following In(I)∝ V1/2 law. I-V results on PS/c-Si junctions are explained by a multi tunneling-recombination model for forward bias while carrier generation-recombination and barrier lowering effects for reverse bias.

The dark conductivity (σd) has been measured from 300 to 440K on undoped hydrogenated microcrystalline silicon (μc-Si:H) films having different thicknesses. The carrier transport is found to be thermally activated with single activation energy (Ea) in all the samples. The Ea increases as the film thickness decreases. At the same time logarithmic of dark conductivity prefactor (σo) is found to follow a linear relation with activation energy, known as the Meyer-Neldel rule (MNR). Results are explained in terms of increased degree of disorder in thinner samples. Thus change in Ea with the film thickness is directly related to the density of localized states at the Fermi level in grain boundary (GB). Therefore varying the film thickness and, hence, the exponential density of states induces a statistical shift of Fermi level which gives rise to the observed MNR.

We present the results of an X-ray scattering study on partially confined smectic-A (layered) LC films. This partial confinement is achieved by placing the LC material inside the open grooves of a glass grating. Samples prepared in this manner are confined in the direction perpendicular to the gratings. Samples in which the LC is contained entirely inside the grooves develop an induced molecular tilt, which results in a compression of the smectic layers. The molecular tilt varies as the amount of the LC material increases, eventually forming a thin overlayer film above the gratings. As the thickness varies, a second region develops in the films. The layer spacing in this region is close to the bulk layer spacing. This structural evolution is coupled to a variation in the nematic-to-smectic-A phase transition temperature of the samples from the bulk. In addition, the nature of the phase transition is driven first order. The effects of partial confinement on a sm-C* LC film is discussed briefly.

Internal photoemission is used to investigate the mobility edges in high quality, undoped, hydrogenated amorphous silicon (a-Si:H). The detailed studies carried out on intimate metal/ a- Si:H Schottky barriers are described and results on the electron barrier heights of these contacts formed on a-Si:H having different bandgaps are presented. The observed dependence of the barrier heights on changes in the optical gap due to hydrogen incorporation indicates that not all of these changes are due to the shifts of the valence band edges. The first results on the injection of holes into the valence band of a-Si:H are reported.