Papers by Ting Fung Chung
Laser & Photonics Reviews, 2015
Plasmon resonances in nanopatterned singlelayer graphene nanoribbons (SL-GNRs), double-layer grap... more Plasmon resonances in nanopatterned singlelayer graphene nanoribbons (SL-GNRs), double-layer graphene nanoribbons (DL-GNRs) and triple-layer graphene nanoribbons (TL-GNRs) are studied experimentally using 'realistic' graphene samples. The existence of electrically tunable plasmons in stacked multilayer graphene nanoribbons was first experimentally verified by infrared microscopy. We find that the strength of the plasmonic resonance increases in DL-GNRs when compared to SL-GNRs. However, further increase was not observed in TL-GNRs when compared to DL-GNRs. We carried out systematic full-wave simulations using a finite-element technique to validate and fit experimental results, and extract the carrier-scattering rate as a fitting parameter. The numerical simulations show remarkable agreement with experiments for an unpatterned SLG sheet, and a qualitative agreement for a patterned graphene sheet. We conclude with our perspective of the key bottlenecks in both experiments and theoretical models.
Nano Letters, 2014
Pauli blocking of interband transistions gives rise to tunable optical properties in single layer... more Pauli blocking of interband transistions gives rise to tunable optical properties in single layer graphene (SLG). This effect is exploited in a graphene-nanoantenna hybrid device where Fano resonant plasmonic nanostructures are fabricated on top of a graphene sheet. The use of Fano resonant elements enhances the interaction of incident radiation with the graphene sheet and enables efficient electrical modulation of the plasmonic resonance. We observe electrically controlled damping in the Fano resonances occurring at approximately 2 μm, and the results are verified by full-wave 3D finite-element simulations. Our approach can be used for development of next generation of tunable plasmonic and hybrid nanophotonic devices.
Nano Letters, 2013
Two new Raman modes below 100 cm −1 are observed in twisted bilayer graphene grown by chemical va... more Two new Raman modes below 100 cm −1 are observed in twisted bilayer graphene grown by chemical vapor deposition. The two modes are observed in a small range of twisting angle at which the intensity of the G Raman peak is strongly enhanced, indicating that these low energy modes and the G Raman mode share the same resonance enhancement mechanism, as a function of twisting angle. The ∼94 cm −1 mode (measured with a 532 nm laser excitation) is assigned to the fundamental layer breathing vibration (ZO′ mode) mediated by the twisted bilayer graphene lattice, which lacks long-range translational symmetry. The dependence of this mode's frequency and line width on the rotational angle can be explained by the double resonance Raman process that is different from the previously identified Raman processes activated by twisted bilayer graphene superlattice. The dependence also reveals the strong impact of electronic-band overlaps of the two graphene layers. Another new mode at ∼52 cm −1 , not observed previously in the bilayer graphene system, is tentatively attributed to a torsion mode in which the bottom and top graphene layers rotate out-of-phase in the plane.
Carbon, 2014
ABSTRACT We study ultrafast dynamics in graphene grown by chemical vapor deposition, which presen... more ABSTRACT We study ultrafast dynamics in graphene grown by chemical vapor deposition, which presents a positive peak followed by a negative slow recovery process, and is different from the fully positive or negative dynamics reported. We discuss the diversity of ultrafast dynamics. A dynamic model of differential optical conductivity is developed to simulate ultrafast dynamics. It is found that the diversity of ultrafast dynamics originates from multiple parameter dependence. The appearance of ultrafast dynamics is mainly determined by the position of probed level with respect to static Fermi energy and/or momentum scattering time. The dynamic model is used to best fit the observed ultrafast dynamics to retrieve dynamic time constants. The thermalizing and cooling times of optical phonons are found consistent with the reported values, but a striking sub-femtosecond momentum scattering time and a sub-picosecond time of electron–hole recombination are obtained. The sub-femtosecond scattering time is much shorter than several to a few hundred femtoseconds accepted currently.
International Journal of Modern Physics B, 2013
The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intens... more The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interests. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapour deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this chapter, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapour deposition. We also discuss potential applications of such large scale synthetic graphene.
Applied Physics Letters, 2013
ABSTRACT Graphene field effect transistors (GFETs) fabricated by chemical vapor deposition graphe... more ABSTRACT Graphene field effect transistors (GFETs) fabricated by chemical vapor deposition graphene deposited onto SiC substrates exhibit sensitivity to broadband visible light. The hysteretic nature of this GFET type was studied utilizing a new current-voltage measurement technique in conjunction with current-time measurements. This measurement method accounts for hysteretic changes in graphene response and enables transfer measurements that can be attributed to fixed gate voltages. Graphene hysteresis is shown to be consistent with electrochemical p-type doping, and current-time measurements clearly resolve a hole to electron to hole carrier transition in graphene with a single large change in gate voltage.
CLEO: 2013, 2013
ABSTRACT We demonstrate strong electrical control of plasmonic Fano resonances in dolmen structur... more ABSTRACT We demonstrate strong electrical control of plasmonic Fano resonances in dolmen structures using tunable interband transitions in graphene. Such graphene-plasmonic hybrid devices can have applications in light modulation and sensing.
Nano Letters, 2012
Graphene has many promising physical properties. It has been discovered that local strain in a gr... more Graphene has many promising physical properties. It has been discovered that local strain in a graphene sheet can alter its conducting properties and transport gaps. It is of great importance to develop scalable strain engineering techniques to control the local strains in graphene and understand the limit of the strains. Here, we present a scalable manufacturing process to generate three-dimensional (3D) nanostructures and thus induce local strains in the graphene sheet. This process utilizes laser-induced shock pressure to generate 3D tunable straining in the graphene sheet. The size dependent straining limit of the graphene and the critical breaking pressure are both studied. It is found that the graphene film can be formed to a circular mold (∼50 nm in diameter) with an aspect ratio of 0.25 and strain of 12%, and the critical breaking pressure is 1.77 GPa. These values were found to be decreasing with the increase of mold size. The local straining and breaking of graphene film are verified by Raman spectra. Large scale processing of the graphene sheet into nanoscale patterns is presented. The process could be scaled up to roll-to-roll process by changing laser beam size and scanning speed. The presented laser shock straining approach is a fast, tunable, and low-cost technique to realize strain engineering of graphene for its applications in nanoelectrical devices.
Conference on Lasers and Electro-Optics 2012, 2012
Surface Science, 2000
Graphene oxide (GO) sheets, suspended in an aqueous solution, were deposited on freshly cleaved h... more Graphene oxide (GO) sheets, suspended in an aqueous solution, were deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG) and studied using Raman spectroscopy, atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM phase imaging shows a distinct contrast between GO and the underlying HOPG substrate. Raman spectroscopy clearly showed the presence of GO sheets on the top of
Surface Science, 2011
Graphene Oxide (GO) sheets, suspended in an aqueous solution, were deposited on freshly cleaved h... more Graphene Oxide (GO) sheets, suspended in an aqueous solution, were deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG) and studied using Raman spectroscopy, atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM phase imaging shows a distinct contrast between GO and the underlying HOPG substrate. Raman spectroscopy clearly showed the presence of GO sheets on the top of HOPG substrate. The AFM and STM images also reveal wrinkling, folding, and tearing of individual GO sheets after depositing onto an HOPG substrate. We have also observed a distinct cracking of a GO sheet after folding. We attribute this new cracking phenomenon to a weakening of C-C bonds during the oxidation of a graphene sheet.
Nature Materials, 2011
The strong interest in graphene has motivated the scalable production of high quality graphene an... more 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.
Arxiv preprint arXiv: …, 2010
Qingkai Yu 1,2,$,* , Luis A. Jauregui 3,4,$ , Wei Wu 1,2,# , Robert Colby 3,5,# , Jifa Tian 3,6,#... more Qingkai Yu 1,2,$,* , Luis A. Jauregui 3,4,$ , Wei Wu 1,2,# , Robert Colby 3,5,# , Jifa Tian 3,6,# , ... Zhihua Su 2 , Helin Cao 3,6 , Zhihong Liu 2 , Deepak Pandey 3,6 , Dongguang Wei 7 , Ting Fung ... Chung 3,6 , Peng Peng 1,2 , Nathan Guisinger 8 , Eric A. Stach 3,5,9 , Jiming ...
Scientific Reports, 2014
Corrosion of metal in biomedical devices could cause serious health problems to patients. Current... more Corrosion of metal in biomedical devices could cause serious health problems to patients. Currently ceramics coating materials used in metal implants can reduce corrosion to some extent with limitations. Here we proposed graphene as a biocompatible protective film for metal potentially for biomedical application. We confirmed graphene effectively inhibits Cu surface from corrosion in different biological aqueous environments. Results from cell viability tests suggested that graphene greatly eliminates the toxicity of Cu by inhibiting corrosion and reducing the concentration of Cu 21 ions produced. We demonstrated that additional thiol derivatives assembled on graphene coated Cu surface can prominently enhance durability of sole graphene protection limited by the defects in graphene film. We also demonstrated that graphene coating reduced the immune response to metal in a clinical setting for the first time through the lymphocyte transformation test. Finally, an animal experiment showed the effective protection of graphene to Cu under in vivo condition. Our results open up the potential for using graphene coating to protect metal surface in biomedical application.
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Papers by Ting Fung Chung