Coulomb Blockade and Hopping Conduction in Graphene Quantum Dots Array

We show that the low temperature electron transport properties of chemically functionalized graphene can be explained as sequential tunneling of charges through a two dimensional array of graphene quantum dots (GQD). Below 15 K, a total suppression of current due to Coulomb blockade through GQD array was observed. Temperature dependent current-gate voltage characteristics show Coulomb oscillations with energy scales of 6.2-10 meV corresponding to GQD sizes of 5-8 nm while resistance data exhibit an Efros-Shklovskii variable range hopping arising from structural and size induced disorder.Comment: The document will be appeared in Physics Review

High yield fabrication of chemically reduced graphene oxide field effect transistors by dielectrophoresis

We demonstrate high yield fabrication of field effect transistors (FET) using chemically reduced graphene oxide (RGO) sheets suspended in water assembled via dielectrophoresis. The two terminal resistances of the devices were improved by an order of magnitude upon mild annealing at 200 0C in Ar/H2 environment for 1 hour. With the application of a backgate voltage, all of the devices showed FET behavior with maximum hole and electron mobilities of 4.0 and 1.5 cm2/Vs respectively. This study shows promise for scaled up fabrication of graphene based nanoelectronic devices.Comment: 8 pages, 6 figure

Space charge limited conduction with exponential trap distribution in reduced graphene oxide sheets

We elucidate on the low mobility and charge traps of the chemically reduced graphene oxide (RGO) sheets by measuring and analyzing temperature dependent current-voltage characteristics. The RGO sheets were assembled between source and drain electrodes via dielectrophoresis. At low bias voltage the conduction is Ohmic while at high bias voltage and low temperatures the conduction becomes space charge limited with an exponential distribution of traps. We estimate an average trap density of 1.75x10^16 cm^-3. Quantitative information about charge traps will help develop optimization strategies of passivating defects in order to fabricate high quality solution processed graphene devices.Comment: 6 pages, 3 figures, 1 tabl

Polymer-Derived Non-Oxide Ceramic Fibers-Past, Present and Future

Polymer-derived ceramics (PDCs) are a class of multifunctional ceramics synthesized by the thermal decomposition of polymeric precursors. The direct polymer-to-ceramic processing route makes the materials very suitable for the fabrication of complex shaped components and devices through hybrid processing/shaping technologies. Such process has led to significant technology breakthrough in ceramics including the development of ceramic fibers, coatings and thermal stable ceramics. Non-oxide ceramic fibers have been widely used as the skeletal structures in ceramic matrix composites (CMCs) for high temperature applications where the metallic materials suffer serious corrosion and mechanical property deterioration. Fabricating non-oxide ceramic fibers from polymer precursors offers excellent control of the mechanical and chemical properties of the ceramic fibers by manipulating the composition and physical properties of the polymer precursors. A series of high performance ceramic fibers with diameter from nanometers to micrometers have been produced through such polymer-derived ceramic fiber process. Well-designed synthesis of the precursors, materials processing and characterization play the key role in producing ceramic fibers with desired properties. The incorporation of functional materials including carbon nanotubes and polymers into the preceramic polymers can introduce difference functionalities and generate interesting nanosize structures to the ceramic fibers, providing new applications such as catalyzing and energy storage devices. This review highlights the synthesis of polymer precursors and the development of non-oxide ceramic fibers from different polymer precursors through melt-spinning and electrospinning, presents recent progress in fabricating ceramic fibers with nanosize structures, and discusses the advantage, challenge and future direction of the research in this field

Position dependent photodetector from large area reduced graphene oxide thin films

We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemically synthesis and interconnecting sheets

FUNCTIONALIZATION OF REGIOREGULAR HEAD-TO-TAIL POLY(3-ALKYLTHIOPHENES) SIDE CHAIN

Conjugated polymers possess several intriguing properties including high electrical conductivity, fast and large nonlinear optical responses and visible wavelength chromaticity. Layer by layer conducting polymer structures are even more interesting because they offer many potentia