We demonstrate a simple all-optical patterning method for graphene, based on laser induced two-photon oxidation. By tuning the intensity and dose of irradiation, the level of oxidation is controlled, the band gap is introduced and electrical and optical properties are continuously tuned. Complex patterning is performed for air-suspended monolayer graphene and for graphene on substrates. The presented concept allows development of all-graphene electronic and optoelectronic devices with an all-optical method.

Atomically thin materials, such as graphene, are the ultimate building blocks for nanoscale devices. But although their synthesis and handling today are routine, all efforts thus far have been restricted to flat natural geometries, since the means to control their three-dimensional (3D) morphology has remained elusive. Here we show that, just as a blacksmith uses a hammer to forge a metal sheet into 3D shapes, a pulsed laser beam can forge a graphene sheet into controlled 3D shapes in the nanoscale. The forging mechanism is based on laser-induced local expansion of graphene, as confirmed by computer simulations using thin sheet elasticity theory.

ABSTRACT:The mechanism of the reaction of olefins and hydrogen with dimetallenes ArMMAr (Ar = aromatic group; M = Al or Ga) was studied by density functional theory calculations and experimental methods. The digallenes, for which the most experimental data are available, are extensively dissociated to gallanediyl monomers :GaAr in hydrocarbon solution, but we found that they do not react as the more open dissociated species. Instead, the calculations and experimental data show that they react with simple olefins such as ethylene as intact ArGaGaAr dimers via two stepwise [2 + 2] cycloadditions due to their considerably lower activation barriers vis-à-vis the gallanediyl monomers, :GaAr. This mechanism was preferred over the [2 + 2] cycloaddition of ethylene to a monomeric :GaAr to form a gallacyclopropane ring which could in principle then dimerize to form the 1,2-digallacyclobutane intermediate and, subsequently, the 1,4-digallacyclohexane product. In addition, calculations show that the addition of H2 to digallene proceeds by a different mechanism involving the initial addition of one equivalent of H2 to form a 1,2-dihydride intermediate. This reacts with a second equivalent of H2, to give two ArGaH2 fragments which recombine to give the observed product with terminal and bridging H-atoms, Ar(H)Ga(-H)2Ga(H)Ar.2

Chemical composition of two-photon oxidized single-layer graphene is studied by micrometer X-ray photoelectron spectroscopy (XPS). Oxidized areas with a size of 2 x 2 µm 2 are patterned on graphene by tightly focused femtosecond pulsed irradiation under air atmosphere. The degree of oxidation is controlled by varying the irradiation time. The samples are characterized by four wave mixing (FWM) imaging and Raman spectroscopy/imaging. Micrometer-XPS is used to study local chemical composition of

ABSTRACT. Mechanism of two-photon induced oxidation of single-layer graphene on Si/SiO 2 substrates is studied by atomic force microscopy (AFM) and Raman microspectroscopy and imaging. AFM imaging of areas oxidized by using a tightly focused femtosecond laser beam shows that oxidation is not homogeneous but oxidized and non-oxidized graphene segregate into separate domains over the whole irradiated area. Oxidation process starts from point-like "seeds" 2 which grow into islands finally coalescing together. The size of islands before coalescence is 30 -40 nm and the density of the islands is on the order of 10 11 cm -2 . Raman spectroscopy reveals growth of the D/G band ratio along the oxidation. Sharpness of the D-band which persists over large range of oxidation and the maximal value of the intensity ratio of the D-and G-bands (~0.8) indicates that graphene oxidation proceeds by increase of the oxidized area rather than progression of oxidized areas to fully disordered structure. A phenomenological model is developed which explains the observations. According to the model, the probability for oxidation of a site next to already oxidized site is five orders of magnitude higher than oxidation of pristine graphene. Irradiation of an extended area by raster scanning leads to a formation of an irregular nanomesh of oxide islands with a narrow size distribution. The phenomenological model yields similar results as the experiment. This study forms a basis for controlled use of two-photon oxidation for tailoring properties of graphene and patterning it with sub-micrometer resolution.