Jing Kong

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (37)287.08 Total impact

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    ABSTRACT: Highly porous metal nanowire aerosponges are produced by direct assembly of the Cu nanowire in situ during their synthesis. Such a method offers not only great simplicity, but also excellent properties such as extremely low densities, high electrical conductivities, and remarkable mechanical properties. Furthermore, these Cu aerosponges exhibit excellent wicking behavior, suggesting their potential for heat exchange applications in heat pipes.
    No preview · Article · Dec 2015 · Advanced Materials
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    ABSTRACT: D nanomaterials have been found to show surface-dominant phenomena and understanding this behavior is crucial for establishing a relationship between a material's structure and its properties. Here, the transition of molybdenum disulfide (MoS2) from a diffusion-controlled intercalation to an emergent surface redox capacitive behavior is demonstrated. The ultrafast pseudocapacitive behavior of MoS2 becomes more prominent when the layered MoS2 is downscaled into nanometric sheets and hybridized with reduced graphene oxide (RGO). This extrinsic behavior of the 2D hybrid is promoted by the fast Faradaic charge-transfer kinetics at the interface. The heterostructure of the 2D hybrid, as observed via high-angle annular dark field–scanning transmission electron microscopy and Raman mapping, with a 1T MoS2 phase at the interface and a 2H phase in the bulk is associated with the synergizing capacitive performance. This 1T phase is stabilized by the interactions with the RGO. These results provide fundamental insights into the surface effects of 2D hetero-nanosheets on emergent electrochemical properties.
    No preview · Article · Oct 2015 · Advanced Energy Materials
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    ABSTRACT: Abrupt switching behavior and near-zero leakage current of nanoelectromechanical (NEM) switches are advantageous properties through which NEMs can outperform conventional semiconductor electrical switches. To date, however, typical NEMs structures require high actuation voltages and can prematurely fail through permanent adhesion (defined as stiction) of device components. To overcome these challenges, in the present work we propose a NEM switch, termed a "squitch," which is designed to electromechanically modulate the tunneling current through a nanometer-scale gap defined by an organic molecular film sandwiched between two electrodes. When voltage is applied across the electrodes, the generated electrostatic force compresses the sandwiched molecular layer, thereby reducing the tunneling gap and causing an exponential increase in the current through the device. The presence of the molecular layer avoids direct contact of the electrodes during the switching process. Furthermore, as the layer is compressed, the increasing surface adhesion forces are balanced by the elastic restoring force of the deformed molecules which can promote zero net stiction and recoverable switching. Through numerical analysis, we demonstrate the potential of optimizing squitch design to enable large on-off ratios beyond 6 orders of magnitude with operation in the sub-1 V regime and with nanoseconds switching times. Our preliminary experimental results based on metal-molecule-graphene devices suggest the feasibility of the proposed tunneling switching mechanism. With optimization of device design and material engineering, squitches can give rise to a broad range of low-power electronic applications.
    No preview · Article · Aug 2015 · ACS Nano
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    ABSTRACT: The incorporation of heteroatoms into carbon nanomaterials is extremely crucial for tuning their electronic and surface properties, but phosphorus (P) incorporation into hierarchical structure remains challenging and its charge storage mechanism is obscure. Herein, we investigate surface redox charge storage of hierarchically structured, P-incorporated graphene architectures (hpGAs). As probed by in-situ and ex-situ spectroscopic techniques and density functional theory, the P=O site of C–P=O bonding with the most favorable proton binding energy is identified and associated with highly reversible and fast pseudocapacitive behavior. As a consequence of synergistic effects arising from compositional and structural features, the hpGAs show dramatic improvements in capacitance, rate capability, and cyclic stability. This work broadens our knowledge about the unique surface charge storage phenomenon originating from the controlled heteroatom chemistry using combined spectroscopic and computational methods.
    No preview · Article · May 2015 · Nano Energy
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    ABSTRACT: Monolayer nanoporous graphene represents an ideal membrane for molecular separations, but its practical realization is impeded by leakage through defects in the ultrathin graphene. Here, we report a multiscale leakage-sealing process that exploits the nonpolar nature and impermeability of pristine graphene to selectively block defects, resulting in a centimeter-scale membrane that can separate two fluid reservoirs by an atomically thin layer of graphene. After introducing subnanometer pores in graphene, the membrane exhibited rejection of multivalent ions and small molecules and water flux consistent with prior molecular dynamics simulations. The results indicate the feasibility of constructing defect-tolerant monolayer graphene membranes for nanofiltration, desalination, and other separation processes.
    No preview · Article · Apr 2015 · Nano Letters
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    ABSTRACT: Water vapor condensation is commonly observed in nature and routinely used as an effective means of transferring heat, with dropwise condensation on non-wetting surfaces exhibiting heat transfer improvement compared to filmwise condensation on wetting surfaces. However, state-of-the-art techniques to promote dropwise condensation rely on functional hydrophobic coatings which either have challenges with chemical stability or are so thick that any potential heat transfer improvement is negated due to the added thermal resistance of the coating. In this work, we show the effectiveness of ultra-thin scalable chemical vapor deposited (CVD) graphene coatings to promote dropwise condensation while offering robust chemical stability and maintaining low thermal resistance. Heat transfer enhancements of 4x were demonstrated compared to filmwise condensation, and the robustness of these CVD coatings was superior to typical hydrophobic monolayer coatings. Our results indicate that graphene is a promising surface coating to promote dropwise condensation of water in industrial conditions, with the potential for scalable application via CVD.
    No preview · Article · Mar 2015 · Nano Letters
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    Jin‐Yong Hong · Jing Kong · Sung Hyun Kim
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    ABSTRACT: The article describes a novel graphitization method for GO sheets that allows better removal for the oxygen species and enhanced degree of graphitization via a green mechanical approach. In addition, a micro-patterned rGO sheets could be prepared at relatively low temperatures and was found to be applicable to flexible plastic substrates. The adjacent GO sheet layers connect to each other more closely and create a large number of graphitic joint through the pressure-assisted thermal graphitization. The electrical properties of the reduced graphene oxide sheets were minutely investigated according to the number of spin-coating and transparency. The surface resistance of rGO and GrGO sheets decreased gradually as the number of spin-coating increased, indicating the change in the number of spin-coatings was also capable of tuning the sheet resistance finely.
    Full-text · Article · Dec 2014 · Small
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    ABSTRACT: High porosity combined with mechanical durability in conductive materials is in high demand for special applications in energy storage under limiting conditions, and it is fundamentally important for establishing a relationship between the structure/chemistry of these materials and their properties. Herein, polymer-assisted self-assembly and cross-linking are combined for reduced graphene oxide (rGO)-based aerogels with reversible compressibility, high elasticity, and extreme durability. The strong interplay of cross-linked rGO (x-rGO) aerogels results in high porosity and low density due to the re-stacking inhibition and steric hinderance of the polymer chains, yet it makes mechanical durability and structural bicontinuity possible even under compressive strains because of the coupling of directional x-rGO networks with polymer viscoelasticity. The x-rGO aerogels retain >140% and >1400% increases in the gravimetric and volumetric capacitances, respectively, at 90% compressive strain, showing reversible change and stability of the volumetric capacitance under both static and dynamic compressions; this makes them applicable to energy storage devices whose volume and mass must be limited.
    No preview · Article · Dec 2014 · Advanced Functional Materials
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    ABSTRACT: The influence of transfer parameters on the final structure, morphology and electrical properties of graphene were investigated in this work. Optical microscopy and atomic force microscopy (AFM) images showed that a double layer of PMMA can enhance or degrade graphene quality depending on its concentration. When properly diluted (15% in anisole, resulting in a PMMA layer of 1.35%) the transfer technique using double layer PMMA pro-duces high quality graphene with fewer PMMA residues, non-cracked surface and sheet resistance around 247 ohm/square. We also investigated the influence of different baking times and temperature, and observed that the increase in baking time can degrade graphene quality thus leaving higher amounts of PMMA residues. Several works regarding graphene transfer are reported in the literature, but PMMA-based transfer processes still present challenges in yielding a clean and high quality graphene.
    No preview · Article · Nov 2014 · Carbon
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    ABSTRACT: Dynamically reconfigurable metasurfaces open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping, hyperspectral imaging and adaptive optics. The realization of high performance metasurface-based devices remains a great challenge due to very limited tuning ranges and modulation depths. Here we show that a widely tunable metasurface composed of optical antennas on graphene can be incorporated into a subwavelength-thick optical cavity to create an electrically-tunable perfect absorber. By switching the absorber in and out of the critical coupling condition via the gate voltage applied on graphene, a modulation depth of up to 100% can be achieved. In particular, we demonstrated ultra-thin (thickness < λ0/10) high speed (up to 20 GHz) optical modulators over a broad wavelength range (5-7 µm). The operating wavelength can be scaled from the near infrared to the terahertz by simply tailoring the metasurface and cavity dimensions.
    Full-text · Article · Oct 2014 · Nano Letters
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    ABSTRACT: We demonstrated electrical tuning of optical antennas over a broad wavelength range (~1100 nm, ~20% of the resonance frequency) and achieved optical modulators at the mid-infrared wavelength range with nanosecond response time.
    No preview · Conference Paper · Jul 2014
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    ABSTRACT: Graphene is an attractive photoconductive material for optical detection due to its broad absorption spectrum and ultra-short response time. However, it remains a great challenge to achieve high responsivity in graphene detectors because of graphene's weak optical absorption (only 2.3% in the monolayer graphene sheet) and short photo-carrier lifetime (< 1 ps). Here we show that metallic antenna structures can be designed to simultaneously improve both light absorption and photo-carrier collection in graphene detectors. The coupled antennas concentrate free space light into the nano-scale deep-subwavelength antenna gaps, where the graphene light interaction is greatly enhanced as a result of the ultra-high electric field intensity inside the gap. Meanwhile, the metallic antennas are designed to serve as electrodes that collect the generated photo-carriers very efficiently. We also elucidate the mechanism of photoconductive gain in the graphene detectors and demonstrate mid-infrared (mid-IR) antenna-assisted graphene detectors at room temperature with more than 200 times enhancement of responsivity (~0.4 V/W at λ_0=4.45 μm) compared to devices without antennas (<2 mV/W).
    Full-text · Article · Jun 2014 · Nano Letters
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    ABSTRACT: We demonstrated antenna-assisted mid-infrared graphene detectors at room temperature with more than 200 times enhancement of responsivity ( 0.4 V/W at λ0=4.45 µm) compared to devices without antennas (<2 mV/W).
    No preview · Conference Paper · Jun 2014
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    ABSTRACT: We introduce far-infrared graphene plasmonic crystals. Periodic structural perturbation--in a proof-of-concept form of hexagonal lattice of apertures--of a continuous graphene medium alters delocalized plasmonic dynamics, creating plasmonic bands in a manner akin to photonic crystals. Fourier transform infrared spectroscopy demonstrates band formation, where far-infrared irradiation excites a unique set of plasmonic bands selected by phase matching and symmetry-based selection rules. This band engineering may lead to a new class of graphene plasmonic devices.
    Full-text · Article · Mar 2014 · Nano Letters
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    ABSTRACT: Label-free MoS2 nanosheet-based field-effect biosensor detects cancer marker protein Prostate Specific Antigen in real time with high sensitivity and selectivity, exhibiting great potential in point-of-care diagnostics application.
    Full-text · Article · Mar 2014 · Small
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    ABSTRACT: We report selective ionic transport through controlled, high-density, sub-nanometer 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 10(12) 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 changed 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 sub-nanometer pores addresses a significant challenge in the development of advanced nanoporous graphene membranes for nanofiltration, desalination, gas separations, and other applications.
    No preview · Article · Feb 2014 · Nano Letters
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    ABSTRACT: Graphene is emerging as a broadband optical material which can be dynamically tuned by electrostatic doping. However, direct application of grapheme sheets in optoelectronic devices is challenging due to its small thickness and the resultant weak interaction with light. By combining metal and graphene in a hybrid plasmonic structure, it is possible to enhance graphene-light interaction and thus achieve in situ control of the optical response. We show that the effective mode index of the bonding plasmonic mode in metal-insulator-metal (MIM) waveguides is particularly sensitive to the change in the optical conductivity of a graphene layer in the gap. By incorporating such MIM structures in optic antenna designs, we demonstrate an electrically tunable coupled antenna array on graphene with a large tuning range (1100 nm, i.e. 250 cm-1, nearly 20% of the resonance frequency) of the antenna resonance wavelength at the mid-infrared (MIR) region. Our device exhibits a 3dB cut-off frequency of 30 MHz, which can be further increased into the GHz range. This study confirms that hybrid metal-graphene structures are promising elements for high-speed electrically controllable optical and optoelectronic devices.
    Full-text · Article · Dec 2013 · Nano Letters
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    ABSTRACT: We demonstrate electrical tuning of graphene-loaded optical antennas over a broad wavelength range (~650 nm, 10% of the resonance frequency) and optical intensity modulation with a bandwidth of 600 nm in the Mid-infrared wavelength range.
    Full-text · Conference Paper · Jun 2013
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    ABSTRACT: We demonstrate electro-optical modulation of mid-infrared Si photonic crystal cavities using the tuning of graphene. A wavelength shift of 4 nm is seen around a wavelength of 4.47 µm, demonstrating the feasibility of on-chip electro-optic modulation for the mid-infrared.
    No preview · Conference Paper · Jun 2013
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    Preview · Article · Mar 2013 · Scientific Reports