Covalent functionalisation of graphene is a continuously progressing field of research. The optical properties of such derivatives attract particular attention. In virtually all optical responses, however, an enhancement in peak intensity with increase of sp3 carbon content, and a vanishing of the peak position shift in monolayer compared to few-layer systems, is observed. The understanding of these seemingly connected phenomena is lacking. Here we demonstrate, using Raman spectroscopy and in situ electrostatic doping techniques, that the intensity is directly modulated by an additional contribution from photoluminescent π-conjugated domains surrounded by sp3 carbon regions in graphene monolayers. The findings are further underpinned by a model which correlates the individual Raman mode intensities to the degree of functionalisation. We also show that the position shift in the spectra of solvent-based and powdered functionalised graphene derivatives originates predominantly from the presence of edge-to-edge and edge-to-basal plane interactions and is by large functionalisation independent.

Covalently functionalizing mechanical exfoliated mono- and bilayer graphenides with λ-iodanes led to the discovery that the monolayers supported on a SiO substrate are considerably more reactive than bilayers as demonstrated by statistical Raman spectroscopy/microscopy. Supported by DFT calculations we show that ditopic addend binding leads to much more stable products than the corresponding monotopic reactions as a result of the much lower lattice strain of the reactions products. The chemical nature of the substrate (graphene versus SiO ) plays a crucial role.

We report a straightforward chemical methodology for controlling the thickness of black phosphorus flakes down to the monolayer limit by layer-by-layer oxidation and thinning, using water as solubilizing agent.

When considering fluorinated graphene (FG)-based functional device technology, the device architectures must be chosen adequately. Typically, functionalized graphene devices can be envisaged as either large scale (area)-based thin film structures or as systems integrated from individual nanoobjects. This implies potentially significant qualitative and quantitative differences in the device response. Specifically, the presence of edges in graphene can be decisive. Considering the electrical conductivity of individual mono-and fewlayer flakes, it is dominated by the type, amount, and bonding position (basal or edge) of functional groups attached to the C(sp 2 ) matrix. In thin film-based systems, however, the charge transport also is largely affected by the properties of edge/edge, edge/plane, and plane/plane junctions. [22] Therefore, electrical characterization is a primary means to evaluate and benchmark whether or not a given derivative meets the requirements for selected applications.In the present work we study the impact of F content and bonding position on the electronic properties of graphene fluorinated by BrF 3 vapor at room temperature [8,20] in the range of 2.4-16.6 at%. We compared the electrical conductivity of thin films with the conductivity of corresponding individual FG flakes which constitute the former. We found a significant difference in the conductivity dependence on the degree of fluorination for the two device architectures: While in the case of thin films, a strong decrease in conductivity with fluorine content was observed, individual flakes showed an increase in conductivity and exhibited graphene-like bipolar transfer characteristics with electron and hole mobilities of the order of few 1000s cm 2 V −1 s −1 for F content approaching 17 at%. With further aid of scanning electron and Raman microscopy, this qualitative difference between films and single flakes was attributed to the circumstance that the preferred sites for fluorination are at the edges rather than basal planes of the FG.For the characterization of thin film devices, 3 mm long and 1 mm wide structures were defined using a hard-mask technique (Figure 1a). FG dispersions were sprayed onto Si wafers with 300 nm thermal SiO 2 on top, resulting in homogeneous and continuous films (Figure 1b), which were then electrically contacted with conducting silver paste. For electrical characterization of individual flakes, small amounts of the dispersionsThe conductivity of few-and monolayer graphene with covalently bound moieties is a key-point in the potential application of these materials in any electrical and optoelectronic device. In particular, fluorination of such graphene-based systems is of interest, as fluorine is expected to have a strong influence on the charge-carrier density due to its high electronegativity, and therefore modify the electrical transport properties significantly. Here it is shown that, depending on the device architecture, the electrical properties of fluorinated graphene-based devices are significantly d...

Electrical properties of contact-interfaces in germanium nanowire field effect transistor devices are studied. In contrast to planar bulk devices, it is shown that the active conduction channel and gate length extend between and underneath the contact electrodes. Furthermore, direct scaling of contact resistivity and Schottky barrier height with electrode metal function is observed. The associated pinning parameter was found to be γ=0.65 ± 0.03γ=0.65 ± 0.03, which demonstrates a significant suppression of Fermi level pinning in quasi-one-dimensional structures