Modification of Graphene Properties due to Electron-Beam Irradiation

The authors report micro-Raman investigation of changes in the single and bilayer graphene crystal lattice induced by the low and medium energy electron-beam irradiation (5 and 20 keV). It was found that the radiation exposures results in appearance of the strong disorder D band around 1345 1/cm indicating damage to the lattice. The D and G peak evolution with the increasing radiation dose follows the amorphization trajectory, which suggests graphene's transformation to the nanocrystalline, and then to amorphous form. The results have important implications for graphene characterization and device fabrication, which rely on the electron microscopy and focused ion beam processing.Comment: 13 pages and 4 figure

Ab initio calculations of edge-functionalized armchair graphene nanoribbons: Structural, electronic, and vibrational effects

We present a theoretical study on narrow armchair graphene nanoribbons (AGNRs) with hydroxyl functionalized edges. Although this kind of passivation strongly affects the structure of the ribbon, a high degree of edge functionalization proves to be particularly stable. An important consequence of the geometric deviations is a severe reduction of the band-gap of the investigated 7-AGNR. This shift follows a linear dependence on the number of added hydroxyl groups per unit cell and thus offers the prospect of a tunable band-gap by edge functionalization. We furthermore cover the behavior of characteristic phonons for the ribbon itself as well as fingerprint modes of the hydroxyl groups. A large down-shift of prominent Raman active modes allows the experimental determination of the degree of edge functionalization.Comment: 6 pages, 9 figure

Determination of nanogram microparticles from explosives after real open-air explosions by confocal Raman microscopy

Explosives are increasingly being used for terrorist attacks to cause devastating explosions. The detection of their post-blast residues after an explosion is a high challenge, which has been barely investigated, particularly using spectroscopic techniques. In this research, a novel methodology using confocal Raman microscopy has been developed for the analysis of post-blast residues from ten open-air explosions caused by ten different explosives (TNT, RDX, PETN, TATP, HMTD, dynamite, black powder, ANFO, chloratite, and ammonal) commonly used in improvised explosive devices. The methodology for the determination of post-blast particles from explosives consisted of examining the samples surfaces with both the naked eye, first, and microscopically (10x and 50x), immediately afterward; and finally, analysing the selected residues by confocal Raman spectroscopy in order to identify the post-blast particles from explosives. Interestingly, confocal Raman microscopy has demonstrated to be highly suitable to rapidly, selectively and non-invasively analyse post-blast microscopic particles from explosives up to the nanogram range

Highly Tunable Nanostructures in a Doubly pH-Responsive Pentablock Terpolymer in Solution and in Thin Films

Multiblock copolymers with charged blocks are complex systems that show great potential for enhancing the structural control of block copolymers. A pentablock terpolymer PMMA-b-PDMAEMA-b-P2VP-b-PDMAEMA-b-PMMA is investigated. It contains two types of midblocks, which are weak cationic polyelectrolytes, namely poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(2-vinylpyridine) (P2VP). Furthermore, these are end-capped with short hydrophobic poly(methyl methacrylate) (PMMA) blocks in dilute aqueous solution and thin films. The self-assembly behavior depends on the degrees of ionization α of the P2VP and PDMAEMA blocks, which are altered in a wide range by varying the pH value. High degrees of ionization of both blocks prevent structure formation, whereas microphase-separated nanostructures form for a partially charged and uncharged state. While in solutions, the nanostructure formation is governed by the dependence of the P2VP block solubility of the and the flexibility of the PDMAEMA blocks on α, in thin films, the dependence of the segregation strength on α is key. Furthermore, the solution state plays a crucial role in the film formation during spin-coating. Overall, both the mixing behavior of the 3 types of blocks and the block sequence, governing the bridging behavior, result in strong variations of the nanostructures and their repeat distances

The 3-3-1 model with S_4 flavor symmetry

We construct a 3-3-1 model based on family symmetry S_4 responsible for the neutrino and quark masses. The tribimaximal neutrino mixing and the diagonal quark mixing have been obtained. The new lepton charge \mathcal{L} related to the ordinary lepton charge L and a SU(3) charge by L=2/\sqrt{3} T_8+\mathcal{L} and the lepton parity P_l=(-)^L known as a residual symmetry of L have been introduced which provide insights in this kind of model. The expected vacuum alignments resulting in potential minimization can origin from appropriate violation terms of S_4 and \mathcal{L}. The smallness of seesaw contributions can be explained from the existence of such terms too. If P_l is not broken by the vacuum values of the scalar fields, there is no mixing between the exotic and the ordinary quarks at the tree level.Comment: 20 pages, revised versio

The behaviour of inositol 1,3,4,5,6-pentakisphosphate in the presence of the major biological metal cations

The inositol phosphates are ubiquitous metabolites in eukaryotes, of which the most abundant are inositol hexakisphosphate (InsP6) and inositol 1,3,4,5,6-pentakisphosphate [Ins(1,3,4,5,6)P5)]. These two compounds, poorly understood functionally, have complicated complexation and solid formation behaviours with multivalent cations. For InsP6, we have previously described this chemistry and its biological implications (Veiga et al. in J Inorg Biochem 100:1800, 2006; Torres et al. in J Inorg Biochem 99:828, 2005). We now cover similar ground for Ins(1,3,4,5,6)P5, describing its interactions in solution with Na+, K+, Mg2+, Ca2+, Cu2+, Fe2+ and Fe3+, and its solid-formation equilibria with Ca2+ and Mg2+. Ins(1,3,4,5,6)P5 forms soluble complexes of 1:1 stoichiometry with all multivalent cations studied. The affinity for Fe3+ is similar to that of InsP6 and inositol 1,2,3-trisphosphate, indicating that the 1,2,3-trisphosphate motif, which Ins(1,3,4,5,6)P5 lacks, is not absolutely necessary for high-affinity Fe3+ complexation by inositol phosphates, even if it is necessary for their prevention of the Fenton reaction. With excess Ca2+ and Mg2+, Ins(1,3,4,5,6)P5 also forms the polymetallic complexes [M4(H2L)] [where L is fully deprotonated Ins(1,3,4,5,6)P5]. However, unlike InsP6, Ins(1,3,4,5,6)P5 is predicted not to be fully associated with Mg2+ under simulated cytosolic/nuclear conditions. The neutral Mg2+ and Ca2+ complexes have significant windows of solubility, but they precipitate as [Mg4(H2L)]·23H2O or [Ca4(H2L)]·16H2O whenever they exceed 135 and 56 μM in concentration, respectively. Nonetheless, the low stability of the [M4(H2L)] complexes means that the 1:1 species contribute to the overall solubility of Ins(1,3,4,5,6)P5 even under significant Mg2+ or Ca2+ excesses. We summarize the solubility behaviour of Ins(1,3,4,5,6)P5 in straightforward plots