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Author

Wei Wu

Other affiliations: Center for Advanced Materials
Bio: Wei Wu is an academic researcher from University of Houston. The author has contributed to research in topics: Graphene & Chemical vapor deposition. The author has an hindex of 24, co-authored 38 publications receiving 4783 citations. Previous affiliations of Wei Wu include Center for Advanced Materials.

Papers
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TL;DR: It is shown that grain boundaries give a significant Raman 'D' peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.
Abstract: Chemical vapour deposition is a promising route for large-scale graphene growth. It is now shown that—through the use of seeds—high-quality, large, single-crystal domains can be grown on a patterned arrangement, and can be used to carefully study the transport across grain boundaries.

1,385 citations

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TL;DR: In this paper, single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu are studied and individual boundaries between coalescing grains affect graphene's electronic properties.
Abstract: The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. Since large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman "D" peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.

1,294 citations

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TL;DR: In this paper, the authors used a 4 mm × 3 mm size graphene film with a 1 nm palladium film deposited for hydrogen detection and showed high sensitivity, fast response and recovery, and can be used with multiple cycles.
Abstract: Graphene with a large area was synthesized on Cu foils by chemical vapor deposition under ambient pressure. A 4 �� × 4 �� graphene film was transferred onto a 6 �� Si wafer with a thermally grown oxide film. Raman mapping indicates monolayer graphene dominates the transferred graphene film. Gas sensors were fabricated on a 4 mm × 3 mm size graphene film with a 1 nm palladium film deposited for hydrogen detection. Hydrogen in air with concentrations in 0.0025-1% (25-10,000 ppm) was used to test graphene- based gas sensors. The gas sensors based on palladium-decorated graphene films show high sensitivity, fast response and recovery, and can be used with multiple cycles. The mechanism of hydrogen detection is also discussed.

245 citations

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TL;DR: In this paper, the electrical characteristics of field effect transistors (FETs) with single-crystal molybdenum disulfide (MoS2) channels synthesized by chemical vapor deposition (CVD) were reported.
Abstract: We report the electrical characteristics of field-effect transistors (FETs) with single-crystal molybdenum disulfide (MoS2) channels synthesized by chemical vapor deposition (CVD). For a bilayer MoS2 FET, the field-effect mobility is ∼17 cm2 V−1 s−1 and the on/off current ratio is ∼108, which are much higher than those of FETs based on CVD polycrystalline MoS2 films. By avoiding the detrimental effects of the grain boundaries and the contamination introduced by the transfer process, the quality of the CVD MoS2 atomic layers deposited directly on SiO2 is comparable to or better than the exfoliated MoS2 flakes. The result shows that CVD is a viable method to synthesize high quality MoS2 atomic layers.

240 citations

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TL;DR: In this article, the electronic properties of graphene synthesized by chemical vapor deposition (CVD) on copper then transferred to SiO2/Si were reported, showing ambipolar field effect (with on/off ratio ∼5 and carrier mobilities up to ∼3000 cm2/V
Abstract: We report on electronic properties of graphene synthesized by chemical vapor deposition (CVD) on copper then transferred to SiO2/Si. Wafer-scale (up to 4 in.) graphene films have been synthesized, consisting dominantly of monolayer graphene as indicated by spectroscopic Raman mapping. Low temperature transport measurements are performed on microdevices fabricated from such CVD graphene, displaying ambipolar field effect (with on/off ratio ∼5 and carrier mobilities up to ∼3000 cm2/V s) and “half-integer” quantum Hall effect, a hall-mark of intrinsic electronic properties of monolayer graphene. We also observe weak localization and extract information about phase coherence and scattering of carriers.

211 citations


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TL;DR: The roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates are reported, showing high quality and sheet resistances superior to commercial transparent electrodes such as indium tin oxides.
Abstract: The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.

7,709 citations

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TL;DR: An overview of the key aspects of graphene and related materials, ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries are provided.
Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

2,560 citations

Journal ArticleDOI
18 Jul 2011-Small
TL;DR: The synthesis, characterization, properties, and applications of graphene-based materials are discussed and the promising properties together with the ease of processibility and functionalization make graphene- based materials ideal candidates for incorporation into a variety of functional materials.
Abstract: Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

2,246 citations

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TL;DR: Electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin akin to human skin.
Abstract: Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

1,950 citations

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TL;DR: In this paper, single-crystal islands and polycrystals containing tilt and mirror twin grain boundaries are characterized, and the influence of the grain boundaries on the material properties of molybdenum disulphide is assessed.
Abstract: Despite recent progress in the synthesis and characterization of molybdenum disulphide, little is yet known about its microstructure. Using refined chemical vapour deposition synthesis, high-quality crystals of monolayer molybdenum disulphide have now been grown. Single-crystal islands and polycrystals containing tilt and mirror twin grain boundaries are characterized, and the influence of the grain boundaries on the material properties of molybdenum disulphide is assessed.

1,911 citations