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Organizing the pentacene molecules with respect to the substrate is an essential prerequisite for achieving high field effect mobility in organic thin film transistors. Here, we report electrical characteristics of bottom gate, top contact Sin++/SiO2/pentacene/gold thin film transistors using electric field assisted thermal evaporation of pentacene. We find that the field assisted devices exhibit a five-fold enhancement in the field effect mobility, along with improvement in the saturation current as compared with a standard device. Simulation of electric field distribution in the substrate-electrode arrangement due to the application of external voltage during pentacene deposition shows an existence of a non-uniform electric field in the bottom gate top contact configuration and hence another configuration that avoids metal before pentacene deposition is proposed. The observed improvement in the transistor characteristics of field assisted device is explained by ab-initio calculation of anisotropy in the polarizability of isolated pentacene molecule, followed by an estimate of molecules that would align due to the field. Furthermore, the preferential molecular alignment in field deposited pentacene films is confirmed using X-ray diffraction and atomic force microscopy.

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Hydroxyapatite (HA) is a widely used bioceramic known for its chemical similarity with that of bone and teeth (Ca/P ratio of 1.67). But, owing to its extreme brittleness, a-Al 2 O 3 is reinforced with HA and processed as a coating via pulsed laser deposition (PLD). Reinforcement of a-Al 2 O 3 (50 wt.%) in HA via PLD on 316L steel substrate has shown modulus increase by 4% and hardness increase by 78%, and an improved adhesion strength of 14.2 N (improvement by 118%). Micro-scratching has shown an increase in the coefficient-of-friction from 0.05 (pure HA) to 0.17 (with 50 wt.% Al 2 O 3 ) with enhancement in the crack propagation resistance (CPR) up to 4.5 times. Strong adherence of PLD HA-Al 2 O 3 coatings ($4.5 times than that of HA coating) is attributed to efficient release of stored tensile strain energy ($17 9 10 À3 J/m 2 ) in HA-Al 2 O 3 composites, making it a potential damagetolerant bone-replacement surface coating.