Materials Science Forum Vol. 736

Abstract: Whereas single crystal silicon limited to 300 mm in diameter dominates the bulk of electronic devices, when electronics is required on a larger scale we have to rely on either amorphous or multi-crystalline materials. In this category, the organic semiconductors have made rapid in-roads. Among their applications, most notable successes are organic light emitting diodes (OLEDs) based displays. But, these OLEDs could also be made to emit in ultraviolet (UV) as shown through polysilanes devices. Two materials that we have investigated emit in UV or near UV. The emission spectrum could be manipulated by modifying the side groups on the main Si chain. Further discussed in the paper are full colour passive matrix displays we have made and development of thin films transistor for moving towards active matrix displays.

Abstract: Inkjet printing of organic thin film transistors is an enabling technology for many applications requiring low cost electronics such as RFID tags, sensors, e-paper, and displays. This review summarizes the achievements and remaining challendges in the field. An all inkjet printed organic thin film transistor is feasible, but manufacturability needs to be improved. Often, a hybrid process in which only some layers are inkjet printed is used. Development of devices requires optimization of (1) ink chemistry, (2) inkjet process, (3) substrate ink interaction, and (4) new device structures. Several conducting, dielectric and semiconducting materials have been used to formulate ink. It appears that metal nanoparticle based conducting ink and PEDOT:PSS are widely used materials to fabricate source, drain and gate electrodes. PVPh is the most popular dielectric material for inkjet printing. To print semiconducting layer, both polymers and oligomers/small molecules are used. Many high performance organic semiconductors are p-type, but few n-type organic semiconductors show excellent performance. In addition to improved materials, challenges inherent in the inkjet process also need solutions. These are registration, alignment of the source,and drain with gate, resolution, reducing off-state current, and roll-to-roll processing.

Abstract: Since the introduction of Electroless (EL) coating in 1946 by Brenner and Riddle, the process has been the subject of steady growth. It is one of the most elegant methods available for the production of alloy coatings on surface. The technique involves the autocatalytic reduction, at the substrate/solution interface, of cations by EL bath released from suitable chemical reducing agents. EL coating technique is simple one, as can be manifested just by controlling pH and temperature of the coating bath. Such coatings are reported to provide excellent physical and mechanical properties. The electroless coatings are being studied at Indian Institute of Technology Roorkee since 1985. The structural and morphological behavior of Ni-P coatings for different phosphorous contents has been extensively studied. Sub-micron size coating islands and their transformations have been deduced. The metallography studies using hot stage within TEM to follow the phase transformations occurring at various temperatures have been studied for Ni-B EL coatings. The realization of mechanical bonding along with chemical bonding between EL coating and the substrate has been explained by coated copper on ceramic powder. As a forward step towards composite coatings, Ni-P-C, Ni-P-Al₂O₃, Ni-P-ZrO₂ has been developed by EL co-deposition technique. Ag-graphite coatings produced by EL technique exhibits nearly five times higher wear resistance and nearly two times better corrosion resistance apart from a good electrical conductor. The tribological behavior of electroless Ni-P-X and Ni-P coatings on steel and aluminium substrates in different conditions i.e., as coated, heat treated at various temperatures at different extents of time with different normal loads, have been studied in terms of dry sliding friction and wear against counter face of case hardened steel. In Ni-P-X nanocoating (X= ZrO₂-Al₂O₃-Al₃Zr), X has been produced in-situ and are of nanosize particles. Such coating could be done on carbon fibre of 7µ diameter uniformly. Ni-P-ferrite nanocoatings with thickness less than nearly 1mm thick, is exhibiting good absorption of microwave in the range of 12-18 GHz which can be exploited for radar applications. Micro-thickness coatings are paying ways to nanocoatings. Nanocoatings are the coatings in which either the thickness of the coating is in nanolevel or second phase that dispersed in the coat matrix is of nanosize. To further explore the field of EL nanocomposite coatings, now days, a work on EL Ni-P-ZnO, TiO₂, Al₂O₃, ZrO₂ and Ni-B-ZrO₂ for its mechanical properties has been carried out.

Abstract: The oxidation behavior of HVOF sprayed Cr₃C₂NiCr coatings on 310S stainless steel for 50 cycles in air at 700°C under cyclic conditions has been investigated in the present work. The microstructure, hardness and porosity of the coating were characterised. X-ray diffraction, field emission scanning electron microscope with energy dispersive spectroscopy and X-ray mapping were used to analyze the scales formed on the surface of the oxidised samples. The microstructure of the as sprayed coating showed uniformly distributed chrome carbide-rich ceramic grains attached with nickel chrome-rich binder phase. The Cr₃C₂-25% NiCr coated specimen exihibit negligible microspalling of the scales upon oxidation. The improved oxidation resistance of Cr₃C₂NiCr coatings may be attributed to the formation of oxides of chromium, nickel, and spinels of nickel and chromium.

Abstract: The effects of aqueous delithiation of lithium cobalt oxide crystals on the crystal texture and etching patterns has been studied by electron microscopy, x-ray and neutron diffraction at high resolution. The delithiation proceeds to exfoliation and in the process textural patterns that appear have been associated with periodic strains in the crystals developed by the delithiation.

Abstract: Mg alloys show limited room temperature formability compared to its lightweight counterpart aluminium alloys, which is a main obstacle in using this metal for most of the structural applications. However, it is known that grain refinement and texture control are the two possibilities for the improvement of formability of magnesium alloys. Amongst the approaches attempted for the texture weakening, additions through of rare-earth (RE) elements have been found most effective. The relationship between the texture and ductility is well established. In this paper, the effect of rare earth addition on texture weakening has been summarized for various magnesium alloys under the two most common modes of deformation methods.

Abstract: My entry to the professional world of academics was more of straying into it when I had been trying to find a suitable profession where I could spend my life without boredom. Continuing studies till Ph.D. was partly due to inertia and partly due to the enjoyment of a carefree student life. After completing Ph.D. only two options were available – joining research laboratories or higher academic institutions of teaching and research. Initially, I joined research laboratories and soon I was tired of listening everyday to the frustrations of my colleagues and their dissatisfaction with their bosses. The possibility of spending my life in such an environment started to haunt me and I was afraid to become one of them eventually. I decided to jump out of it and join the academic world of higher education. I got fascinated by this environment, which has an ever-changing component of student community, which helps one to remain young in mind. The academic world also has its share of negativities. But one has the freedom of creating an insulated space where you may do your academic work happily along with your students and collaborators and build a barrier outside