Observation of out-of-plane vibrations in few-layer graphene

We report the observation of layer breathing mode (LBM) vibrations in few-layer graphene (FLG) samples of thickness from 2 to 6 layers, exhibiting both Bernal (AB) and rhombohedral (ABC) stacking order. The LBM vibrations are identified using a Raman combination band lying around 1720 cm-1. From double resonance theory, we identify the feature as the LOZO' combination mode of the out-of-plane LBM (ZO') and the in-plane longitudinal optical mode (LO). The LOZO' Raman band is found to exhibit multiple peaks, with a unique line shape for each layer thickness and stacking order. These complex line shapes of the LOZO'-mode arise both from the material-dependent selection of different phonons in the double-resonance Raman process and from the detailed structure of the different branches of LBM in FLG.Comment: 17 pages, 7 figures, supplemental material include

Oxidation induced shifts of Raman modes of carbon nanotubes

We investigate the influence of different oxidation methods on carbon nanotubes by Raman spectroscopy and HR-TEM. Besides the known D/G ratio as a sign for amorphous carbon and defects, we observe an oxidation induced shift of the D* mode. As in previous experiments, the D* mode is found to be of higher intensity than the D mode and might be an alternative characterizing the quality and properties of individual CNTs. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Oxidation induced defects in CVD grown carbon nanotubes

Abstract — This paper addresses the issue of allocating risk amongst agents in distributed chance-constrained planning algorithms. Building on previous research that extended chanceconstrained planning to stochastic multi-agent multi-task missions, this paper presents a framework for risk allocation and proposes several strategies for distributing risk in homogeneous and heterogeneous teams. In particular, the contributions of this work include proposing risk allocation strategies that exploit domain knowledge of agent score distributions to improve team performance, and providing insights about what stochastic parameters and features affect the allocations and the overall mission score/performance. Results are provided showing improved performance over previously published heuristic techniques in environments with given allowable risk thresholds. I

Defects induced on chemical vapour deposition carbon nanotubes during peapod synthesis on substrates

Individual carbon nanotubes are filled with fullerene molecules directly on the substrate. Two different oxidation techniques for opening the tubes prior to the filling, annealing in air, and acid treatment, are compared. High-resolution transmission electron microscopy images indicate that both methods induce defects on the sidewalls of the nanotubes. In the case of acid treatment, the inner walls can be damaged without affecting the outer walls, while the inner walls are opened along with the outer ones by heating in air. The effect of acid treatment on the tubes is much stronger than known from bulk samples. In contrast to previous studies, we find amorphous carbon inside the nanotubes after oxidation, and an additional high-temperature annealing step is needed to remove these plugs in order to open the tubes for filling