High-quality uniform dry transfer of graphene to polymers.

In this paper we demonstrate high-quality, uniform dry transfer of graphene grown by chemical vapor deposition on copper foil to polystyrene. The dry transfer exploits an azide linker molecule to establish a covalent bond to graphene and to generate greater graphene-polymer adhesion compared to that of the graphene-metal foil. Thus, this transfer approach provides a novel alternative route for graphene transfer, which allows for the metal foils to be reused.

Colossal piezoresistance in phase separated manganites.

We have measured the strain dependent transport properties of phase separated manganite thin films. We subjected (La(1-y)Pr(y))(1-x)Ca(x)MnO(3) thin films grown on NdGaO(3)(110) substrates to direct external mechanical stress using a three-point beam bending method. The resultant change in resistance reveals a colossal piezoresistance (CPR) in manganites. Our experiments reveal that phase separation is a necessary but not sufficient condition for CPR. The maximum CPR is observed only when the phase boundaries are free to move in the fluid-like phase separated state. Our results show that both long-range strain interactions and quenched disorder play an important role in micrometer scale phase separation in manganites, albeit in different temperature ranges.

Measuring the Complex Optical Conductivity of Graphene by Fabry-Pérot Reflectance Spectroscopy.

We have experimentally studied the dispersion of optical conductivity in few-layer graphene through reflection spectroscopy at visible wavelengths. A laser scanning microscope (LSM) with a supercontinuum laser source measured the frequency dependence of the reflectance of exfoliated graphene flakes, including monolayer, bilayer and trilayer graphene, loaded on a Si/SiO2 Fabry-Pérot resonator in the 545-700 nm range. The complex refractive index of few-layer graphene, n - ik, was extracted from the reflectance contrast to the bare substrate. It was found that each few-layer graphene possesses a unique dispersionless optical index. This feature indicates that the optical conductivity does not simply scale with the number of layers, and that inter-layer electrodynamics are significant at visible energies.

Air-stable electron depletion of Bi(2)Se(3) using molybdenum trioxide into the topological regime.

We perform high-resolution photoelectron spectroscopy on in situ cleaved topological insulator Bi2Se3 single crystals and in situ transport measurements on Bi2Se3 films grown by molecular beam epitaxy. We demonstrate efficient electron depletion of Bi2Se3 via vacuum deposition of molecular MoO3, lowering the surface Fermi energy to within ∼100 meV of the Dirac point, well into the topological regime. A 100 nm MoO3 film provides an air-stable doping and passivation layer.