Yang-Bo Zhou

Self-powered, ultrafast, visible-blind UV detection and optical logical operation based on ZnO/GaN nanoscale p-n junctions.

Ultrafast-response (20 μs) UV detectors, which are visible-blind and self-powered, in devices where an n-type ZnO nanowire partially lies on a p-type GaN film, are demonstrated. Moreover, a CdSe-nanowire red-light detector powered by a nanoscale ZnO/GaN photovoltaic cell is also demonstrated, which extends the device function to a selective multiwavelength photodetector and shows the function of an optical logical AND gate.

Graphene/ZnO nanowire/graphene vertical structure based fast-response ultraviolet photodetector

time, and recovery speed of our UV detectors are 8 � 10 2 , 0.7s, and 0.5s, respectively, which are significantly improved compared to the conventional ZnO NWs photodetectors. The improved performance is attributed to the existence of Schottky barriers between ZnO NW and graphene electrodes. The graphene/ZnO NW/graphene vertical sandwiched structures may be promising candidates for integrated optoelectronic sensor devices. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4724208] ZnO, as a wide direct band gap (3.37eV) compound semiconductor with large exciton binding energy (60meV), has been widely investigated for its potential applications in optoelectronic devices, gas and chemical sensors. 1,2 Due to large surface-to-volume ratio, ZnO nanowires (NWs) exhibit highly susceptible photoelectric properties by means of electron-hole generation or recombination during ultraviolet (UV) illumination. Therefore, ZnO NWs have great potential in high sensitivity and fast-response UV sensors, 3 environmental monitors, and optical communications. 4 Recently, Hu et al. 5 reported ZnO NW based UV sensors using Schottky contact formed between ZnO and Pt electrode and the device performance such as the sensitive and UV response, is much higher than that of the traditional ZnO NW photoconductivity based UV sensors. The UV detectors based on Schottky barriers formed between ZnO NW and other metal electrodes, such as gold electrodes, have also been studied. 6,7 Nevertheless, metal electrodes are poor in transparency and can dramatically influence the absorption efficiency of the UV sensors. Graphene, a monolayer sp 2 carbon atoms with unique physical properties, such as high mobility and conductivity, 8 high optical transparency 9 and mechanical flexibility, 10 etc., has attracted great research interest recently. The high conductive and optical transparent properties make graphene an ideal candidate for the application in transparent electrode. The Schottky barrier is also expected to be existed at the interface between ZnO nanowire and graphene, and it has been utilized for light-emitting diodes 11 and transparent nanogenerators. 12 In this letter, we have fabricated a vertical sandwich structure of graphene/ZnO NW/graphene. We demonstrate the high performance of our ZnO NW based vertical UV photodetector due to the existence of Schottky barriers between graphene electrodes and ZnO NW. The current on-off ratio of the UV detector is up to 8 � 10 2 at a illumination power density of 50lw/lm 2 , the photocurrent

Strain dependent resistance in chemical vapor deposition grown graphene

The strain dependence of conductance of monolayer graphene has been studied experimentally here. The results illustrate the notable transitions: the slight increase, the dramatic decrease, and the sudden dropping of the conductance by gradually increasing the uniaxial strain. The graphene conductance behaves reversibly by tuning of the elastic tensile strain up to 4.5%, while it fails to recover after the plastic deformation at 5%. The change in conductance due to strain is surprisingly high, which indicates the potential applications in electromechanical devices.

Single ZnO Nanowire/p‐type GaN Heterojunctions for Photovoltaic Devices and UV Light‐Emitting Diodes

We fabricate heterojunctions consisting of a single n-type ZnO nanowire and a p-type GaN film. The photovoltaic effect of heterojunctions exhibits open-circuit voltages ranging from 2 to 2.7 V, and a maximum output power reaching 80 nW. Light-emitting diodes with UV electroluminescence based on the heterojunctions are demonstrated.

Hysteresis reversion in graphene field-effect transistors

To enhance performances of graphene/SiO(2) based field-effect transistors (FETs), understanding of the transfer of carriers through the graphene/SiO(2) interface is crucial. In this paper, we have studied the temperature dependent transfer characters of graphene FETs. Hysteresis loop is shown to be dominated by trapping/detrapping carriers through the graphene/SiO(2) interface.

Synthesis and Quantum Transport Properties of Bi2Se3 Topological Insulator Nanostructures

Bi2Se3 nanocrystals with various morphologies, including nanotower, nanoplate, nanoflake, nanobeam and nanowire, have been synthesized. Well-distinguished Shubnikov-de Haas (SdH) oscillations were observed in Bi2Se3 nanoplates and nanobeams. Careful analysis of the SdH oscillations suggests the existence of Berrys phase π, which confirms the quantum transport of the surface Dirac fermions in both Bi2Se3 nanoplates and nanobeams without intended doping. The observation of the singular quantum transport of the topological surface states implies that the high-quality Bi2Se3 nanostructures have superiorities for investigating the novel physical properties and developing the potential applications.

Layer-by-layer assembly of vertically conducting graphene devices

Graphene has various potential applications owing to its unique electronic, optical, mechanical and chemical properties, which are primarily based on its two-dimensional nature. Graphene-based vertical devices can extend the investigations and potential applications range to three dimensions, while interfacial properties are crucial for the function and performance of such graphene vertical devices. Here we report a general method to construct graphene vertical devices with controllable functions via choosing different interfaces between graphene and other materials. Two types of vertically conducting devices are demonstrated: graphene stacks sandwiched between two Au micro-strips, and between two Co layers. The Au|graphene|Au junctions exhibit large magnetoresistance with ratios up to 400% at room temperature, which have potential applications in magnetic field sensors. The Co|graphene|Co junctions display a robust spin valve effect at room temperature. The layer-by-layer assembly of graphene offers a new route for graphene vertical structures.

Ion irradiation induced structural and electrical transition in graphene

The relationship between the electrical properties and structure evolution of single layer graphene was studied by gradually introducing the gallium ion irradiation. Raman spectrums show a structural transition from nano-crystalline graphene to amorphous carbon as escalating the degree of disorder of the graphene sample, which is in correspondence with the electrical transition from a Boltzmann diffusion transport to a carrier hopping transport. The results show a controllable method to tune the properties of graphene.

Site‐Specific Transfer‐Printing of Individual Graphene Microscale Patterns to Arbitrary Surfaces

massless Dirac fermions, [ 3 ] extremely high mobility, [ 4 ] special quantum Hall effect, [ 3 ] and gate voltage tunable optical transitions. [ 5 ] Those remarkable electrical and optical properties make it an attractive candidate for potential applications in integrated bipolar fi eld-effect transistors (FETs), [ 6 ] transparent electrodes for solar cells, [ 7,8 ] as well as other microscale functional devices. [ 9 ]

Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer Helium Ion Beam

We report subnanometer modification enabled by an ultrafine helium ion beam. By adjusting ion dose and the beam profile, structural defects were controllably introduced in a few-layer molybdenum disulfide (MoS2) sample and its stoichiometry was modified by preferential sputtering of sulfur at a few-nanometer scale. Localized tuning of the resistivity of MoS2 was demonstrated and semiconducting, metallic-like, or insulating material was obtained by irradiation with different doses of He(+). Amorphous MoSx with metallic behavior has been demonstrated for the first time. Fabrication of MoS2 nanostructures with 7 nm dimensions and pristine crystal structure was also achieved. The damage at the edges of these nanostructures was typically confined to within 1 nm. Nanoribbons with widths as small as 1 nm were reproducibly fabricated. This nanoscale modification technique is a generalized approach that can be applied to various two-dimensional (2D) materials to produce a new range of 2D metamaterials.