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Yanjun Guo

Bio: Yanjun Guo is an academic researcher. The author has contributed to research in topics: Graphene foam & Quantum dot. The author has an hindex of 1, co-authored 1 publications receiving 22 citations.

Papers
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TL;DR: In this paper, a precisely controlled chemical modification of exfoliated graphene on a substrate was achieved by solution-phase oxidation, which exhibited an energy band gap of 2 eV.
Abstract: A precisely controlled chemical modification of exfoliated graphene on a substrate was achieved by solution-phase oxidation. The structural and electrical evolution of graphene induced by oxygen-related defects was investigated using micro-Raman and photoluminescence spectroscopy. The sp2-hybrid carbon network in monolayer graphene was found to gradually decrease with increasing degree of oxidation. The size of the graphene quantum dots was finally reduced to about 1 nm, which exhibited an energy band gap of 2 eV. The double-layer graphene showed a symmetry breaking induced by the defects. The process of solution modification may provide a facile method to tailor the electrical properties of graphene on a chip for constructing carbon-based nanoelectronics.

26 citations


Cited by
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Journal ArticleDOI
01 Mar 2013-Carbon
TL;DR: In this article, the formation of different types of oxygen containing functional groups in GO and their influences on its structure were analyzed using X-ray diffraction (XRD), Fourier transform infra-red spectra, x-ray photoelectron spectra (XPS), zeta potential analysis and Raman spectroscopy.

1,428 citations

Journal ArticleDOI
TL;DR: The ability to tune the selectivity of graphene through controlled generation of subnanometer pores addresses a significant challenge in the development of advanced nanoporous graphene membranes for nanofiltration, desalination, gas separation, and other applications.
Abstract: We report selective ionic transport through controlled, high-density, subnanometer diameter pores in macroscopic single-layer graphene membranes. Isolated, reactive defects were first introduced into the graphene lattice through ion bombardment and subsequently enlarged by oxidative etching into permeable pores with diameters of 0.40 ± 0.24 nm and densities exceeding 1012 cm–2, while retaining structural integrity of the graphene. Transport measurements across ion-irradiated graphene membranes subjected to in situ etching revealed that the created pores were cation-selective at short oxidation times, consistent with electrostatic repulsion from negatively charged functional groups terminating the pore edges. At longer oxidation times, the pores allowed transport of salt but prevented the transport of a larger organic molecule, indicative of steric size exclusion. The ability to tune the selectivity of graphene through controlled generation of subnanometer pores addresses a significant challenge in the dev...

706 citations

Journal ArticleDOI
11 Apr 2013-ACS Nano
TL;DR: A well-defined graphene pattern is demonstrated by using ozone photolithography, in which the ozone-treated graphene electrodes are monolithic but separated by insulating GO regions, indicating the promising use of ozone treatment to achieve high-performance graphene-based optoelectronic devices.
Abstract: Tunable electrical and optical properties of graphene are vital to promote its use as film electrodes in a variety of devices. We developed an etching-free ozone treatment method to continuously tune the electrical resistance and optical transmittance of graphene films by simply varying the time and temperature of graphene exposure to ozone. Initially, ozone exposure dramatically decreases the electrical resistance of graphene films by p-doping, but this is followed by increases in the resistance and optical transmittance as a result of surface oxidation. The rate of resistance increase can be significantly increased by raising the treatment temperature. The ozone-oxidized graphene is not removed but is gradually transformed to graphene oxide (GO). On the basis of such effects of ozone treatment, we demonstrate a well-defined graphene pattern by using ozone photolithography, in which the ozone-treated graphene electrodes are monolithic but separated by insulating GO regions. Such a monolithic graphene pat...

94 citations

Journal ArticleDOI
TL;DR: By combining coarse-grained molecular dynamics and newly developed accurate models of GO, the driving forces that lead to the various morphologies are resolved and computational methods to design directed synthesis routes for diverse self-assemblies and applications are provided.
Abstract: Controlling the structure of graphene and graphene oxide (GO) phases is vitally important for any of its widespread intended applications: highly ordered arrangements of nanoparticles are needed for thin-film or membrane applications of GO, dispersed nanoparticles for composite materials, and 3D porous arrangements for hydrogels. By combining coarse-grained molecular dynamics and newly developed accurate models of GO, the driving forces that lead to the various morphologies are resolved. Two hydrophilic polymers, poly(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA), are used to illustrate the thermodynamically stable morphologies of GO and relevant dispersion mechanisms. GO self-assembly can be controlled by changing the degree of oxidation, varying from fully aggregated over graphitic domains to intercalated assemblies with polymer bilayers between sheets. The long-term stability of a dispersion is extremely important for many commercial applications of GO composites. For any degree of oxidation, GO does not disperse in PVA as a thermodynamic equilibrium product, whereas in PEG dispersions are only thermodynamically stable for highly oxidized GO. These findings-validated against the extensive literature on GO systems in organic solvents-furnish quantitative explanations for the empirically unpredictable aggregation characteristics of GO and provide computational methods to design directed synthesis routes for diverse self-assemblies and applications.

81 citations

Journal ArticleDOI
TL;DR: An electrochemical approach involving phenyl-diazonium salts is used to systematically probe electronic modification in MLG and BLG with increasing functionalization for the first time, obtaining the highest conversion values to date.
Abstract: A central question in graphene chemistry is to what extent chemical modification can control an electronically accessible band gap in monolayer and bilayer graphene (MLG and BLG). Density functional theory predicts gaps in covalently functionalized graphene as high as 2 eV, while this approach neglects the fact that lattice symmetry breaking occurs over only a prescribed radius of nanometer dimension, which we label the S-region. Therefore, high chemical conversion is central to observing this band gap in transport. We use an electrochemical approach involving phenyl-diazonium salts to systematically probe electronic modification in MLG and BLG with increasing functionalization for the first time, obtaining the highest conversion values to date. We find that both MLG and BLG retain their relatively high conductivity after functionalization even at high conversion, as mobility losses are offset by increases in carrier concentration. For MLG, we find that band gap opening as measured during transport is lin...

67 citations