Influence of anneal atmosphere on ZnO-nanorod photoluminescent and morphological properties with self-powered photodetector performance

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Raman G band in double-wall carbon nanotubes combining p doping and high pressure

We use sulfuric acid as pressure medium to extrapolate the G-band position of the inner and outer tubes of double-wall carbon nanotubes. Keeping the G-band position of the inner and outer tubes constant, we can determine the fraction of double-wall and single-wall tubes in samples containing a mixture of the two. A-band-related electronic interwall interaction at 1560 cm−1 is observed, which is associated with the outer tube walls. This band is observed to shift with pressure at the same rate as the G band of outer tubes and is not suppressed with chemical doping. Differences in the interwall interaction is discussed for double-wall carbon nanotubes grown by the catalytic chemical-vapor method and double-wall carbon nanotubes obtained through transformation of peapods

Investigating the Effect of Reaction Time on Carbon Dot Formation, Structure, and Optical Properties

Carbon dots, a young member of the carbon nanomaterial family, are quasi-spherical nanoparticles, which have fluorescent properties as their key characteristic. A wide range of starting materials and synthetic routes have been reported in the literature, divided into two main categories: a top-down and bottom-up approach. Moreover, a series of different parameters that affect the properties of carbon dots have been investigated, including temperature, starting pH, as well as precursor concentration. However, the effect of reaction time has not been extensively monitored. In our study, a biomass derivative was treated hydrothermally with varying reaction times to draw a solid formation mechanism. In addition, we monitored the effect of reaction time on optical and structural characteristics, as well as the chemical composition of our materials. Our key findings include a four-stage formation mechanism, a higher level of crystallinity, and an increasing brightness over reaction time

Charge transfer between carbon nanotubes and sulfuric acid as determined by Raman spectroscopy

The spontaneous interaction between sulfuric acid and carbon nanotubes is studied using Raman spectroscopy. We are able to determine the charge transfer without any additional parameter using the spectral signature of inner and outer walls of double-wall carbon nanotubes. While for the outer wall both the lattice contraction and the nonadiabatic effects contribute to the phonon shift, only the lattice contraction contributes for the inner nanotube. For the outer nanotube, we are able to separate these two contributions of the Raman G-band shift as a function of the charge transfer. We have carried out density functional theory calculations on graphene to see how different chemical species (HSO4-, H2SO4, H+) affect the electronic band structure and electron-phonon coupling. The Raman G band shift for the outer nanotube, Δω as a function of hole harge transfer per carbon atom, fC, is found to be Δω (cm−1) = (350 ± 20)fC + (101 ± 8)√fC

Microscale adhesion patterns for the precise localization of amoeba

In order to get a better understanding of amoeba-substrate interactions in the processes of cellular adhesion and directional movement, we engineered glass surfaces with defined local adhesion characteristics at a micrometric scale. Amoeba (Dictyostelium dicoideum) is capable to adhere to various surfaces independently of the presence of extracellular matrix proteins. This paper describes the strategy used to create selective adhesion motifs using an appropriate surface chemistry and shows the first results of locally confined amoeba adhesion. The approach is based on the natural ability of Dictyostelium to adhere to various types of surfaces (hydrophilic and hydrophobic) and on its inability to spread on inert surfaces, such as the block copolymer of polyethylene glycol and polypropylene oxide, named Pluronic. We screened diverse alkylsilanes, such as methoxy, chloro and fluoro silanes for their capacity to anchor Pluronic efficiently on a glass surface. Our results demonstrate that hexylmethyldichlorosilane (HMDCS) was the most appropriate silane for the deposition of Pluronic. A complex dependence between the physicochemistry of the silanes and the polyethylene glycol block copolymer deposition was observed. Using this method, we succeed in scaling down the micro-fabrication of pluronic-based adhesion motifs to the amoebaComment: Microelectronic Engineering (2008) in pres

Raman excitation spectroscopy of carbon nanotubes: effects of pressure medium and pressure

Raman excitation and emission spectra for the radial breathing mode (RBM) are reported, together with a preliminary analysis. From the position of the peaks on the two-dimensional plot of excitation resonance energy against Raman shift, the chiral indices (m, n) for each peak are identified. Peaks shift from their positions in air when different pressure media are added - water, hexane, sulphuric acid - and when the nanotubes are unbundled in water with surfactant and sonication. The shift is about 2 - 3 cm-1 in RBM frequency, but unexpectedly large in resonance energy, being spread over up to 100meV for a given peak. This contrasts with the effect of pressure. The shift of the peaks of semiconducting nanotubes in water under pressure is orthogonal to the shift from air to water. This permits the separation of the effects of the pressure medium and the pressure, and will enable the true pressure coefficients of the RBM and the other Raman peaks for each (m, n) to be established unambiguously.Comment: 6 pages, 3 Figures, Proceedings of EHPRG 2011 (Paris