Novel techniques to produce and deposit n-layer graphene: Their physical properties

A novel technique "electrostatic deposition of graphene" has been developed for transferring graphene (one atomically thick graphite layer) onto desired substrate. This method of graphene transfer is unique in the sense that the high voltage applied between the graphite and the substrate appears to overcome the repulsive part of the van der Waals interaction at small separation and thus produce monolayer thick graphene. In order to get a high-yield deposition of the graphene, the surface of the substrate can be modified. For example a corrugated silicon microfabricated trenches can be used instead of a flat silicon substrate. In this case the effective electric field is enhanced due to the sharp edges. The deposition involves no chemical additives eliminating a major source of contamination that previously had been difficult to remove and can be deposited with a specified number of layers, enabling the tuning of electronic properties More interestingly, this method can control (i) the number of layers by tuning the applied electric field; and (ii) lateral size of the graphene by depositing under controlled vacuum.;Also, the problem of fabrication graphene ribbons was solved. The gas jet impactor was made. The impactor produces the graphene ribbons of the controlled width. The width of the ribbons depends on the pressure difference between two chambers (gas velocity that carries metal clusters) and the metal type (indium, gallium, mercury) that can be used for the bombardment of graphite surface. Then employing electrostatic deposition technique the dislocated graphene ribbons can be transferred to the substrate. A detailed study was performed on different number of layers graphene sheets and ribbons by Atomic Force Microscopy, Raman Spectroscopy, Scanning Electron Microscopy and Optical Microscopy. Certain signature peaks for graphene were observed by using Raman spectroscopy and with combination of an AFM measurement that clearly identified the number of graphene layers deposited on substrate.;The investigation of the electric transport properties of the graphene reveals that graphene ribbons deposited on Si/SiO2 substrate and back gated shows p-type behavior under ambient conditions. This behavior can be reversed upon annealing at high temperature in a vacuum. N-type behavior under degassed conditions is attributed as due to the charge transfer from surface states on SiO2 to graphene. P-type behavior under ambient is believed to be due to electrochemically mediated charge transfer from graphene to oxygen. Charge transfer effects were observed when the degassed graphene was exposed to N2O and NH3.;It was demonstrated that atomic layers of graphene have stiffness E ∼ 1 TPa. These results show that single atomic sheets can be integrated with microfabricated structures to create a new class of atomic scale membrane-based devices.