Harvesting ubiquitous mechanical energy, an important energy resource, directly from the environment has been proposed as an effective approach to powering nanodevices. [1, 2] Numerous piezoelectric nanogenerators, such as zinc oxide (ZnO) nanowires, [3] indium nitride (InN) nanowires, [4] lead zirconate titanate nanofibers, [5] poly(vinylidene fluoride) nanofibers, [6] and cadmium sulfide (CdS) nanowires [7] have been explored for converting mechanical energy into electricity. For practical applications, low-cost, high-efficiency nanogenerators are demanded that can be fabricated on flexible substrates and require only simple integration processes.Graphene oxide (GO), a derivative of graphene, consists of a hexagonal ring of carbon network having both sp 2 -and sp 3 -hybridized carbon atoms bearing hydroxyl and epoxide functional groups on basal planes, as well as carbonyl and carboxyl groups at the edges of the sheet. [8,9] Those functional groups can extensively modify the electronic structure and chemical properties of GO, [10][11][12] enabling various applications. [14][15][16][17][18][19][20][21][22][23][24] Here, we report the exciting application of GO as a flexible, high-efficiency nanogenerator, realized through oxygen-containing functional groups which enable GO to store charges and harvest acoustic energy.In this study, GO exfoliated from a modified Hummer method [13,14] was used to fabricate a nanogenerator, which could convert acoustic energy to electricity at a high conversion efficiency of 12.1 %. The induced mean current is sensitively dependent on the pH values of the suspensions used to prepare the GO films. The findings reveal the exciting potential of GO for fabricating nanogenerators for energy harvesting, as well as a novel avenue for nanoelectronic applications.GO was synthesized from expandable graphitic flakes using the modified Hummer method. [13,14] Graphene was purchased from Sigma-Aldrich and used as received. The crystal structure of the samples was characterized with transmission electron microscopy (TEM, FEI Tecnai F20, 200 kV). Raman spectra were recorded using a confocal microprobe Raman system (HR800, Jobin Yvon) using a 633 nm HeNe laser. The electronic structure of carbon was characterized with X-ray photoemission spectroscopy (XPS, Kratos Axis UltraDLD, monochromatized Al K a source) operated at a base pressure of 5 10 À10 Torr. Atomic force microscopy (AFM) measurements were conducted with a Mutilmode V AFM system (Veeco). All the experimental processes are listed in the Supporting Information.The as-prepared GO suspensions from different pH solutions (adjusted with HCl and NaOH) and different concentrations were dropped onto a Teflon tape, followed by drying in a convection oven at 60 8C for 30 min to form GO films. The morphology of the GO films was characterized by scanning electron microscopy (SEM) with a FEI Quanta 200F SEM spectrometer. Microattenuated total-reflection (ATR)-Fourier transform infrared (FTIR) measurements were performed in air using a Bruker FTIR spec...

High-quality and wafer-scale graphene on insulating gate dielectrics is a prerequisite for graphene electronic applications. For such applications, graphene is typically synthesized and then transferred to a desirable substrate for subsequent device processing. Direct production of graphene on substrates without transfer is highly desirable for simplified device processing. However, graphene synthesis directly on substrates suitable for device applications, though highly demanded, remains unattainable and challenging. Here, we report a simple, transfer-free method capable of synthesizing graphene directly on dielectric substrates at temperatures as low as 600 °C using polycyclic aromatic hydrocarbons as the carbon source. Significantly, N-doping and patterning of graphene can be readily and concurrently achieved by this growth method. Remarkably, the graphene films directly grown on glass attained a small sheet resistance of 550 Ω/sq and a high transmittance of 91.2%. Organic light-emitting diodes (OLEDs) fabricated on N-doped graphene on glass achieved a current density of 4.0 mA/cm(2) at 8 V compared to 2.6 mA/cm(2) for OLEDs similarly fabricated on indium tin oxide (ITO)-coated glass, demonstrating that the graphene thus prepared may have potential to serve as a transparent electrode to replace ITO.

Anatase hierarchical TiO2 with innovative designs (hollow microspheres with exposed high-energy {001} crystal facets, hollow microspheres without {001} crystal facets, and solid microspheres without {001} crystal facets) were synthesized via a one-pot hydrothermal method and characterized. Based on these materials, gas sensors were fabricated and used for gas-sensing tests. It was found that the sensor based on hierarchical TiO2 hollow microspheres with exposed high-energy {001} crystal facets exhibited enhanced acetone sensing properties compared to the sensors based on the other two materials due to the exposing of high-energy {001} crystal facets and special hierarchical hollow structure. First-principle calculations were performed to illustrate the sensing mechanism, which suggested that the adsorption process of acetone molecule on TiO2 surface was spontaneous, and the adsorption on high-energy {001} crystal facets would be more stable than that on the normally exposed {101} crystal facets. Further characterization indicated that the {001} surface was highly reactive for the adsorption of active oxygen species, which was also responsible for the enhanced sensing performance. The present studies revealed the crystal-facets-dependent gas-sensing properties of TiO2 and provided a new insight into improving the gas sensing performance by designing hierarchical hollow structure with special-crystal-facets exposure.

We report the preparation of aand k-phase In 2 Se 3 nanowires by thermal evaporation and investigation of their phase transformations in situ by synchrotron radiation X-ray diffraction (XRD) during a thermal annealing process. The k-phase transformed into the a-phase at 500 C and eventually transformed to high temperature a-phase with a layered structure of 5 atoms-5 atoms at 700 C irreversibly. Different atomistic structures of In 2 Se 3 were modeled and optimized by DFT, which correlate well with the XRD results. The In 2 Se 3 nanowires also exhibit a large difference in resistivity before and after annealing.

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