The effects of residues introduced during the transfer of chemical vapor deposited graphene from a Cu substrate to an insulating (SiO 2) substrate on the physical and electrical of the transferred graphene are studied. X-ray photoelectron spectroscopy and atomic force microscopy show that this residue can be substantially reduced by annealing in vacuum. The impact of the removal of poly(methyl methacrylate) residue on the electrical properties of graphene field effect devices is demonstrated, including a nearly 2 Â increase in average mobility from 1400 to 2700 cm 2 /Vs. The electrical results are compared with graphene doping measurements by Raman spectroscopy. V

Field-effect transistors fabricated on graphene grown by chemical vapor deposition (CVD) often exhibit large hysteresis accompanied by low mobility, high positive backgate voltage corresponding to the minimum conductivity point (V(min)), and high intrinsic carrier concentration (n(0)). In this report, we show that the mobility reported to date for CVD graphene devices on SiO(2) is limited by trapped water between the graphene and SiO(2) substrate, impurities introduced during the transfer process and adsorbates acquired from the ambient. We systematically study the origin of the scattering impurities and report on a process which achieves the highest mobility (μ) reported to date on large-area devices for CVD graphene on SiO(2): maximum mobility (μ(max)) of 7800 cm(2)/(V·s) measured at room temperature and 12,700 cm(2)/(V·s) at 77 K. These mobility values are close to those reported for exfoliated graphene on SiO(2) and can be obtained through the careful control of device fabrication steps including minimizing resist residue and non-aqueous transfer combined with annealing. It is also observed that CVD graphene is prone to adsorption of atmospheric species, and annealing at elevated temperature in vacuum helps remove these species.

A detailed analysis of the extracted back gated FET mobility as a function of channel length, channel width, and underlying oxide thickness for both exfoliated and chemical vapor deposited (CVD) graphene is presented. The mobility increases with increasing channel length eventually saturating at a constant value for channel lengths of several micrometers. The length dependence is consistent with the transition from a ballistic to diffusive transport regime. The mobility as a function of channel width first increases and then decreases. The increase in mobility for very small channel widths is consistent with a reduction in edge scattering. The decrease in mobility for larger channel widths is observed to be strongly dependent on the oxide thickness suggesting that electrostatics associated with fringing fields is an important effect. This effect is further confirmed by a comparative analysis of the measured mobility of graphene devices with similar channel dimensions on oxides of different thicknesses. The observed electrical measurements are in excellent agreement with theoretical studies predicting the width dependence of conductivity and mobility. The mobility of CVD grown graphene is slightly lower than that of exfoliated graphene but shows similar trends with length and width. The mobility values reported in the literature are in agreement with the trend reported here. V

As the silicon industry continues to push the limits of device dimensions, tools such as Raman spectroscopy are ideal to analyze and characterize the doped silicon channels. The effect of intervalence band transitions on the zone center optical phonon in heavily p-type doped silicon is studied by Raman spectroscopy for a wide range of excitation wavelengths extending from the red (632.8 nm) into the ultra-violet (325 nm). The asymmetry in the one-phonon Raman lineshape is attributed to a Fano interference involving the overlap of a continuum of electronic excitations with a discrete phonon state. We identify a transition above and below the one-dimensional critical point (EΓ 1 = 3.4 eV) in the electronic excitation spectrum of silicon. The relationship between the anisotropic silicon band structure and the penetration depth is discussed in the context of possible device applications.

Current noise in electronic devices usually arises from uncorrelated charging events, with discrete transitions resolved only at low temperatures. However, in nanotube-based field effect transistors ͑FETs͒, we have observed random telegraph signal ͑RTS͒ with unprecedented amplitude at room temperature. This RTS is characteristically truncated, suggesting that the current blockade induced by one trap fully reverses through electrostatic interaction with another. These observations have motivated us to develop a robust quantum transport model that reveals how the fast varying, logarithmic gate potential along a one-dimensional channel makes it possible to detect correlated transitions arising from multiple charge traps. These results suggest applications including adsorbate detection and spectroscopy and the development of strategies to passivate traps and mitigate current noise in FETs.

The structure and vibrational spectrum of the novel endohedral fullerene Y2C2@C92 was studied by Raman spectroscopy, with particular emphasis on the rotational transitions of the diatomic C2 unit in the low energy Raman spectrum. We report evidence for tunneling of this unit through the C2 rotation plane and observe anomalous narrowing in a hindered rotational mode. We also report complementary density functional theory (DFT) calculations that support our conclusions and discuss potential applications to quantum computing and nonvolatile memory devices.

Proper analysis of the Schottky barrier height extraction methods shows that sulfur implantation followed by anneal does not effectively reduce the Schottky barrier height of NiSi/n-Si contacts. Instead, the results for sulfur implanted samples are consistent with enhanced field emission due to an increased doping density of the surface region of the silicon. Sulfur has a large impact on contact resistivity for silicon with low initial doping concentration (<∼1017 cm−3), but little impact for silicon with high initial doping density (>∼1017 cm−3). Internal photoemission measurements show that the Schottky barrier height remains unchanged with sulfur implantation.

The structure and vibrational spectrum of Gd 3 N@C 80 is studied through Raman and inelastic electron tunneling spectroscopy as well as density-functional theory and universal force field calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd 3 N-C 80 bond which reduces the ideal icosahedral symmetry of the C 80 cage. The vibrational modes involving the movement of the encapsulated species are a fingerprint of the interaction between the fullerene cage and the core complex. We present Raman data for the Gd 3 N@C 2n ͑40Յ n Յ 44͒ family as well as Y 3 N@C 80 , Lu 3 N@C 80 , and Y 3 N@C 88 for comparison. Conductance measurements have been performed on Gd 3 N@C 80 and reveal a Kondo effect similar to that observed in C 60 .