RECEIVED DATE (automatically inserted by publisher); ayan@iisertvm.ac.in Structural and electronic properties of the all-Si analogue of graphene, silicene have elucidated through DFT calculations. Silicene differs considerably from graphene in being 'chair-type' puckered in each 6-membered ring which leads to ordered ripples across the surface. Binding energies suggest stability for such rippled silicenes and are predicted to behave as a finite gap semi-conductor with electron-hole symmetry quenched. Inter-layer coupling between the silicenes is suggested as the mechanism for the formation of the bulk-Si in it's only known diamond form.Graphene has attracted immense interest in the present decade due to its remarkable chemical, physical, mechanical, electronic and magnetic properties. 1-3 This nanoscale 2-D system provides a wonderful starting material for fabricating materials in the nano dimension. Apart from its novel prospects, the fundamental structural aspects of graphene are also very interesting. 4-5 Though expected to be ideally planar, recent experiments and computations suggest that graphene is not really planar and distinct ripples are observed. 6-8 This is also expected from the Mermin-Wagner theorem predicting that thermal fluctuations should destroy long-range order in 2-D systems and instabilities should appear. This phenomenon is similar to the established Peierls distortion in polyacetylene and other 1-D systems. 9 The all silicon analogue of graphene, silicene has generated recent interest. Silicon nanoribbons have been studied through STM studies and DFT calculations. 10-11 Even though there is an immediate possibility of application of silicene based nano-materials in existing Simicroelectronics, the fundamental structural aspects are yet to be elucidated. In this communication, we report the rich structural and electronic aspects in nanosheets of polysilo-acenes and silicenes based on DFT calculations. In marked contrast to graphene, the ground-state of silicene show large, short-range and periodically ordered ripples even in the absence of thermal fluctuations. This effect is a direct consequence of the puckering distortion in the six-membered rings that leads to a gap opening in silicene, unlike the zero-gap semiconductor like behavior in graphene.

The electronic properties of graphene, such as high charge carrier concentrations and mobilities, make it a promising candidate for next-generation nanoelectronic devices. In particular, electrons and holes can undergo ballistic transport on the sub-micrometre scale in graphene and do not suffer from the scale limitations of current MOSFET technologies. However, it is still difficult to produce single-layer samples of graphene and bulk processing has not yet been achieved, despite strenuous efforts to develop a scalable production method. Here, we report a versatile solution-based process for the large-scale production of single-layer chemically converted graphene over the entire area of a silicon/SiO(2) wafer. By dispersing graphite oxide paper in pure hydrazine we were able to remove oxygen functionalities and restore the planar geometry of the single sheets. The chemically converted graphene sheets that were produced have the largest area reported to date (up to 20 x 40 microm), making them far easier to process. Field-effect devices have been fabricated by conventional photolithography, displaying currents that are three orders of magnitude higher than previously reported for chemically produced graphene. The size of these sheets enables a wide range of characterization techniques, including optical microscopy, scanning electron microscopy and atomic force microscopy, to be performed on the same specimen.

We report the development of useful chemical sensors from chemically converted graphene dispersions using spin coating to create single-layer films on interdigitated electrode arrays. Dispersions of graphene in anhydrous hydrazine are formed from graphite oxide. Preliminary results are presented on the detection of NO 2 , NH 3 , and 2,4-dinitrotoluene using this simple and scalable fabrication method for practical devices. Current versus voltage curves are linear and ohmic in all cases, studied independent of metal electrode or presence of analytes. The sensor response is consistent with a charge transfer mechanism between the analyte and graphene with a limited role of the electrical contacts. A micro hot plate sensor substrate is also used to monitor the temperature dependence of the response to nitrogen dioxide. The results are discussed in light of recent literature on carbon nanotube and graphene sensors.