Spatially Resolved Raman Spectroscopy of Single- and Few-Layer Graphene

We present Raman spectroscopy measurements on single- and few-layer graphene flakes. Using a scanning confocal approach we collect spectral data with spatial resolution, which allows us to directly compare Raman images with scanning force micrographs. Single-layer graphene can be distinguished from double- and few-layer by the width of the D' line: the single peak for single-layer graphene splits into different peaks for the double-layer. These findings are explained using the double-resonant Raman model based on ab-initio calculations of the electronic structure and of the phonon dispersion. We investigate the D line intensity and find no defects within the flake. A finite D line response originating from the edges can be attributed either to defects or to the breakdown of translational symmetry

Raman spectroscopy on etched graphene nanoribbons

We investigate etched single-layer graphene nanoribbons with different widths ranging from 30 to 130 nm by confocal Raman spectroscopy. We show that the D-line intensity only depends on the edge-region of the nanoribbon and that consequently the fabrication process does not introduce bulk defects. In contrast, the G- and the 2D-lines scale linearly with the irradiated area and therefore with the width of the ribbons. We further give indications that the D- to G-line ratio can be used to gain information about the crystallographic orientation of the underlying graphene. Finally, we perform polarization angle dependent measurements to analyze the nanoribbon edge-regions

Raman imaging of doping domains in graphene on SiO2

We present spatially resolved Raman images of the G and 2D lines of single-layer graphene flakes. The spatial fluctuations of G and 2D lines are correlated and are thus shown to be affiliated with local doping domains. We investigate the position of the 2D line -- the most significant Raman peak to identify single-layer graphene -- as a function of charging up to |n|~4 10^12 cm^-2. Contrary to the G line which exhibits a strong and symmetric stiffening with respect to electron and hole-doping, the 2D line shows a weak and slightly asymmetric stiffening for low doping. Additionally, the line width of the 2D line is, in contrast to the G line, doping-independent making this quantity a reliable measure for identifying single-layer graphene

Research Note: Benefits and Drawbacks of Pre-bloom Applications of Gibberellic Acid (GA3) for Stem Elongation in Sauvignon blanc

Dense grape clusters have a high predisposition to bunch rot. An elongation of cluster stems could resultin a loosening of the cluster structure. To achieve such an elongation, gibberellic acid (GA3; 10 ppm)was applied to Sauvignon blanc either when three, five, seven, nine, 11 or 13 leaves were unfolded or atfull bloom in the 2010 season. In the present season, all applications led to stem elongation, a reductionof cluster compactness as well as a reduction of bunch rot severity. The density index proved to be anefficient tool to describe the predisposition of grape clusters to bunch rot. Best success was achieved if theapplication took place when seven leaves were unfolded. In the subsequent season (2011; the year followingthe year of application), the number of inflorescences per shoot, the length of the clusters, as well as theyield were considerably reduced, especially in the treatments with promising positive effects on the clusterstructure and disease severity. Hence, the present study shows the loosening potential as well as the riskof pre-bloom gibberellic acid applications. Due to the observed negative resultant effects, the pre-bloomapplication of GA3 at the present concentration (10 ppm) cannot yet be recommended for practical use inSauvignon blanc

Tunable Coulomb blockade in nanostructured graphene

We report on Coulomb blockade and Coulomb diamond measurements on an etched, tunable single-layer graphene quantum dot. The device consisting of a graphene island connected via two narrow graphene constrictions is fully tunable by three lateral graphene gates. Coulomb blockade resonances are observed and from Coulomb diamond measurements a charging energy of ~3.5 meV is extracted. For increasing temperatures we detect a peak broadening and a transmission increase of the nanostructured graphene barriers

Coulomb oscillations in three-layer graphene nanostructures

We present transport measurements on a tunable three-layer graphene single electron transistor (SET). The device consists of an etched three-layer graphene flake with two narrow constrictions separating the island from source and drain contacts. Three lateral graphene gates are used to electrostatically tune the device. An individual three-layer graphene constriction has been investigated separately showing a transport gap near the charge neutrality point. The graphene tunneling barriers show a strongly nonmonotonic coupling as function of gate voltage indicating the presence of localized states in the constrictions. We show Coulomb oscillations and Coulomb diamond measurements proving the functionality of the graphene SET. A charging energy of $\approx 0.6$ meV is extracted.Comment: 10 pages, 6 figure

Local gating of a graphene Hall bar by graphene side gates

We have investigated the magnetotransport properties of a single-layer graphene Hall bar with additional graphene side gates. The side gating in the absence of a magnetic field can be modeled by considering two parallel conducting channels within the Hall bar. This results in an average penetration depth of the side gate created field of approx. 90 nm. The side gates are also effective in the quantum Hall regime, and allow to modify the longitudinal and Hall resistances

Topological Influence and Locality in Swap Schelling Games

Residential segregation is a wide-spread phenomenon that can be observed in almost every major city. In these urban areas residents with different racial or socioeconomic background tend to form homogeneous clusters. Schelling’s famous agent-based model for residential segregation explains how such clusters can form even if all agents are tolerant, i.e., if they agree to live in mixed neighborhoods. For segregation to occur, all it needs is a slight bias towards agents preferring similar neighbors. Very recently, Schelling’s model has been investigated from a game-theoretic point of view with selfish agents that strategically select their residential location. In these games, agents can improve on their current location by performing a location swap with another agent who is willing to swap. We significantly deepen these investigations by studying the influence of the underlying topology modeling the residential area on the existence of equilibria, the Price of Anarchy and on the dynamic properties of the resulting strategic multi-agent system. Moreover, as a new conceptual contribution, we also consider the influence of locality, i.e., if the location swaps are restricted to swaps of neighboring agents. We give improved almost tight bounds on the Price of Anarchy for arbitrary underlying graphs and we present (almost) tight bounds for regular graphs, paths and cycles. Moreover, we give almost tight bounds for grids, which are commonly used in empirical studies. For grids we also show that locality has a severe impact on the game dynamics