Dongdong Zhang

National Center for Nanoscience and Technology, Peping, Beijing, China

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Publications (3)18.76 Total impact

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    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.
    The Journal of Physical Chemistry C. 05/2012; 116(19):10702–10707.
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    ABSTRACT: Defects were introduced precisely to exfoliated graphene (G) sheets on a SiO(2)/n(+) Si substrate to modulate the local energy band structure and the electron pathway using solution-phase oxidation followed by thermal reduction. The resulting nanoscale charge distribution and band gap modification were investigated by electrostatic force microscopy and spectroscopy. A transition phase with coexisting submicron-sized metallic and insulating regions in the moderately oxidized monolayer graphene were visualized and measured directly. It was determined that the delocalization of electrons/holes in a graphene "island" is confined by the surrounding defective C-O matrix, which acts as an energy barrier for mobile charge carriers. In contrast to the irreversible structural variations caused by the oxidation process, the electrical properties of graphene can be restored by annealing. The defect-patterned graphene and graphene oxide heterojunctions were further characterized by electrical transport measurement.
    Nanoscale 03/2012; 4(8):2651-7. · 6.73 Impact Factor
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    ABSTRACT: Air-stable, n-doped or p-doped graphene sheets on a chip were achieved by modifying the substrates with self-assembled layers of silane and polymer. The interfacial effects on the electronic properties of graphene were investigated using micro-Raman and Kelvin probe force microscopy (KPFM). Raman studies demonstrated that the phonon vibrations were sensitive to the doping level of graphene on the various substrates. Complementary information on the charge transfer between the graphene and substrate was extracted by measuring the surface potential of graphene flakes using KPFM, which illustrated the distribution of carriers in different graphene layers as well as the formation of dipoles at the interface. The Fermi level of single layer graphene on the modified substrates could be tuned in a range from -130 to 90 mV with respect to the Dirac point, corresponding to the doped carrier concentrations up to 10(12) cm(-2).
    ACS Nano 01/2011; 5(1):408-12. · 12.03 Impact Factor