Awnish Gupta

Reversible fluorination of graphene: Evidence of a two-dimensional wide bandgap semiconductor

We report the synthesis and evidence of graphene fluoride, a two-dimensional wide bandgap semiconductor derived from graphene. Graphene fluoride exhibits hexagonal crystalline order and strongly insulating behavior with resistance exceeding

New aspects in the oxidative stabilization of PAN-based carbon fibers: II

10\text{ }\text{G}\ensuremath{\Omega}

Probing graphene edges via Raman scattering.

at room temperature. Electron transport in graphene fluoride is well described by variable range hopping in two dimensions due to the presence of localized states in the band gap. Graphene obtained through the reduction of graphene fluoride is highly conductive, exhibiting a resistivity of less than

Nondispersive Raman D band activated by well-ordered interlayer interactions in rotationally stacked bilayer graphene

100\text{ }\text{k}\ensuremath{\Omega}

Curvature-induced D-band Raman scattering in folded graphene

at room temperature. Our approach provides a pathway to reversibly engineer the band structure and conductivity of graphene for electronic and optical applications.

Use of single-walled carbon nanotubes to increase the quality factor of an AT-cut micromachined quartz resonator

Abstract Oxidative stabilization studies on PAN-based copolymer fibers indicate the presence of at least two distinct reactions occurring at temperatures below 380 °C. Techniques such as thermal stress, percentage shrinkage, differential scanning calorimetry, wide-angle X-ray diffraction and small-angle X-ray scattering have been used to elucidate the mechanisms involved. Reactions initiate in the amorphous part of the copolymer at temperatures below 200 °C and contribute to the major portion of the macroscopic shrinkage. This corresponds to the first “amorphous” peak observed in DSC. Crystalline morphology is largely maintained during this stage, although considerable randomization of crystal lamellae take place. Reactions propagate to crystalline components at higher temperatures and proceed to completion at ~380 °C, giving rise to the second “crystalline” DSC peak. Additionally, a broad shoulder on the second peak is observed. Although its origin is not clear, it is speculated that it corresponds to certain intermolecular cross-linking reactions. The importance of using copolymer PAN as a carbon fiber precursor is outlined. Additionally, new models for morphological development during stabilization are proposed. Macroscopic shrinkage along the fiber axis is seen to be primarily an entropy-driven process, with “chemical” effects serving to only modify the entropie response. Intramolecular cyclization reactions serve as the basis for initial stabilization, with intermolecular cross-linking occurring in the presence of oxygen above ~300 °C for oxidatively stabilized fibers.

On the Possibility of a Graphene Based Chemical Sensor

We present results of a Raman scattering study from the region near the edges of n-graphene layer films. We find that a Raman band (D) located near 1344 cm(-1) (514.5 nm excitation) originates from a region next to the edge with an apparent width of approximately 70 nm (upper bound). The D-band was found to exhibit five important characteristics: (1) a single Lorentzian component for n = 1, and four components for n = 2-4, (2) an intensity I(D) approximately cos(4) theta, where theta is the angle between the incident polarization and the average edge direction, (3) a local scattering efficiency (per unit area) comparable to the G-band, (4) dispersive behavior ( approximately 50 cm(-1)/eV for n = 1), consistent with the double resonance (DR) scattering mechanism, and (5) a scattering efficiency that is almost independent of the crystallographic orientation of the edge. High-resolution transmission electron microscope images reveal that our cleaved edges exhibit a sawtooth-like roughness of approximately 3 nm (i.e., approximately 20 times the C-C bond length). We propose that in the double resonance Raman scattering process the photoelectron scatters diffusely from our edges, obscuring the recently proposed strong variation in the scattering from armchair versus zigzag symmetry edges based on theoretical arguments.

Improvement in Q-factor of AT-cut quartz crystal resonators using single walled carbon nanotubes

Raman measurements on monolayer graphene folded back upon itself into skewed bilayer (i.e., with interlayer rotation) presents a mechanism for Raman scattering in

Micromachined quartz resonator functionalized with single walled carbon nanotubes

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Improvement of the elastic modulus of micromachined structures using carbon nanotubes

carbons in the