Jing Kong

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (31)203.46 Total impact

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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.
    Nano Letters 04/2015; 15(5). DOI:10.1021/acs.nanolett.5b00456 · 12.94 Impact Factor
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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.
    Carbon 11/2014; 84:82-90. DOI:10.1016/j.carbon.2014.11.040 · 6.16 Impact Factor
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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.
    Nano Letters 10/2014; 14(11). DOI:10.1021/nl503104n · 12.94 Impact Factor
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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).
    Nano Letters 06/2014; 14(7). DOI:10.1021/nl500602n · 12.94 Impact Factor
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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).
    CLEO: Science and Innovations; 06/2014
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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.
    Nano Letters 03/2014; 14(5). DOI:10.1021/nl500158y · 12.94 Impact Factor
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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.
    Small 03/2014; 10(6). DOI:10.1002/smll.201302081 · 7.51 Impact Factor
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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.
    Nano Letters 02/2014; 14(3). DOI:10.1021/nl404118f · 12.94 Impact Factor
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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.
    Nano Letters 12/2013; 14(1). DOI:10.1021/nl403751p · 12.94 Impact Factor
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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.
    CLEO: Science and Innovations; 06/2013
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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.
    CLEO: QELS_Fundamental Science; 06/2013
  • Scientific Reports 03/2013; 3:1423. DOI:10.1038/srep01423 · 5.58 Impact Factor
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    ABSTRACT: Plasmonic antennas enable the conversion of light from free space into subwavelength volumes and vice versa, which facilitates the manipulation of light at the nanoscale. Dynamic control of the properties of antennas is desirable for many applications, including biochemical sensors, reconfigurable meta-surfaces and compact optoelectronic devices. The combination of metallic structures and graphene, which has gate-voltage dependent optical properties, is emerging as a possible platform for electrically controlled plasmonic devices. In this paper, we demonstrate in situ control of antennas using graphene as an electrically tunable load in the nanoscale antenna gap. In our experiments, we demonstrate electrical tuning of graphene-loaded antennas over a broad wavelength range of 650 nm (∼140 cm-1, ∼10% of the resonance frequency) in the mid-infrared (MIR) region. We propose an equivalent circuit model to quantitatively analyze the tuning behavior of graphene-loaded antenna pairs and derive an analytical expression for the tuning range of resonant wavelength. In a separate experiment, we used doubly resonant antenna arrays to achieve MIR optical intensity modulation with maximum modulation depth of more than 30% and bandwidth of 600 nm (∼100 cm-1, 8% of the resonance frequency). This study shows that combining graphene with metallic nanostructures provides a route to electrically tunable optical and optoelectronic devices.
    Nano Letters 02/2013; 13(3). DOI:10.1021/nl3047943 · 12.94 Impact Factor
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    ABSTRACT: We engineered functional cardiac patches by seeding neonatal rat cardiomyocytes onto carbon nanotube (CNT) incorporated photocrosslinkable gelatin methacrylate (GelMA) hydrogel. The resulting cardiac constructs showed excellent mechanical integrity and advanced electrophysiological functions. Specifically, myocardial tissues cultured on 50 μm thick CNT-GelMA showed 3 times higher spontaneous synchronous beating rates and 85% lower excitation threshold, compared to those cultured on pristine GelMA hydrogels. Our results indicate that the electrically conductive and nanofibrous networks formed by CNTs within a porous gelatin framework is the key characteristics of CNT-GelMA leading to improved cardiac cell adhesion, organization, and cell-cell coupling. Centimeter-scale patches were released from glass substrates to form 3D biohybrid actuators, which showed controllable linear cyclic contraction/extension, pumping, and swimming actuations. In addition, we demonstrate for the first time that cardiac tissues cultured on CNT-GelMA resist damage by a model cardiac inhibitor as well as a cytotoxic compound. Therefore, incorporation of CNTs into gelatin, and potentially other biomaterials, could be useful in creating multifunctional cardiac scaffolds for both therapeutic purposes and in vitro studies. These hybrid materials could also be used for neuron and other muscle cells to create tissue constructs with improved organization, electroactivity, and mechanical integrity.
    ACS Nano 01/2013; 7(3). DOI:10.1021/nn305559j · 12.03 Impact Factor
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    ABSTRACT: Aerogels have numerous applications due to their high surface area and low densities. However, creating aerogels from a large variety of materials has remained an outstanding challenge. Here, we report a new methodology to enable aerogel production with a wide range of materials. The method is based on the assembly of anisotropic nano-objects (one-dimensional (1D) nanotubes, nanowires, or two-dimensional (2D) nanosheets) into a cross-linking network from their colloidal suspensions at the transition from the semi-dilute to the isotropic concentrated regime. The resultant aerogels have highly porous and ultrafine three-dimensional (3D) networks consisting of 1D (Ag, Si, MnO(2), single-walled carbon nanotubes (SWNTs)) and 2D materials (MoS(2), graphene, h-BN) with high surface areas, low densities, and high electrical conductivities. This method opens up a facile route for aerogel production with a wide variety of materials and tremendous opportunities for bio-scaffold, energy storage, thermoelectric, catalysis, and hydrogen storage applications.
    Scientific Reports 11/2012; 2:849. DOI:10.1038/srep00849 · 5.58 Impact Factor
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    ABSTRACT: We report graphene composite membranes with nominal areas more than 25 mm(2) fabricated by transfer of a single layer of CVD graphene onto a porous polycarbonate substrate. A combination of pressure-driven and diffusive transport measurements provides evidence of size-selective transport of molecules through the membrane, which is attributed to the low-frequency occurrence of intrinsic 1-15 nm diameter pores in the CVD graphene. Our results present the first step toward the realization of practical membranes that use graphene as the selective material.
    ACS Nano 10/2012; 6(11). DOI:10.1021/nn303869m · 12.03 Impact Factor
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    ABSTRACT: Graphene wires have been fabricated from large-area multilayer graphene sheets grown by chemical vapor deposition. As the methane concentration increases, a larger percentage of thicker graphene layers are grown. The multilayer graphene sheets have an average thickness of 10-20 nm with sheet resistances between 500 and 1000 Ω/sq. The sheet resistance shows a strong correlation with the average surface roughness. This letter reports measured breakdown current densities up to 4×10<sup>7</sup> A/cm<sup>2</sup>, where resistive heating is proposed as the main breakdown mechanism. Increasing the uniformity of the graphene layers is important in achieving a higher breakdown current density.
    IEEE Electron Device Letters 05/2011; 32(4-32):557 - 559. DOI:10.1109/LED.2011.2108259 · 3.02 Impact Factor
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    ABSTRACT: In this paper, we characterize the performance of monolithically integrated graphene interconnects on a prototype 0.35-μm CMOS chip. The test chip implements an array of transmitter/receivers to analyze the end-to-end data communication on graphene wires. Large-area graphene sheets are first grown by chemical vapor deposition, which are then subsequently processed into narrow wires up to 1 mm in length. A low-swing signaling technique is applied, which results in a transmitter energy of 0.3-0.7 pJ/b·mm-1 and a total energy of 2.4-5.2 pJ/b·mm-1. Bit error rates below 2 × 10-10 are measured using a 231 - 1 pseudorandom binary sequence. Minimum voltage swings of 100 mV at 1.5-V supply and 500 mV at 3.3-V supply have also been demonstrated. At present, the graphene wire is largely limited by its growth quality and high sheet resistance.
    IEEE Transactions on Electron Devices 12/2010; 57(12):3418-3425. DOI:10.1109/TED.2010.2083667 · 2.36 Impact Factor
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    ABSTRACT: Carbon-based nanomaterials such as metallic single-walled carbon nanotubes, multiwalled carbon nanotubes (MWCNTs), and graphene have been considered as some of the most promising candidates for future interconnect technology because of their high current-carrying capacity and conductivity in the nanoscale, and immunity to electromigration, which has been a great challenge for scaling down the traditional copper interconnects. Therefore, studies on the performance and optimization of carbon-based interconnects working in a realistic operational environment are needed in order to advance the technology beyond the exploratory discovery phase. In this paper, we present the first demonstration of graphene interconnects monolithically integrated with industry-standard complementary metal-oxide-semiconductor technology, as well as the first experimental results that compare the performance of high-speed on-chip graphene and MWCNT interconnects. The graphene interconnects operate up to 1.3-GHz frequency, which is a speed that is commensurate with the fastest high-speed processor chips today. A low-swing signaling technique has been applied to improve the speed of carbon interconnects up to 30%.
    IEEE Transactions on Electron Devices 12/2010; DOI:10.1109/TED.2010.2069562 · 2.36 Impact Factor
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    ABSTRACT: Graphene has been considered as one of the most promising candidates for future interconnect technology. In spite of the promising theoretical predictions and DC characterization results about the excellent current-carrying capability of graphene nanoribbons, experimental demonstration and characterization of high speed signaling performance of graphene interconnects is still very limited. Here we present the first monolithic integration of graphene with commercial CMOS technology and the first experimental demonstration of on-chip graphene interconnects that operates above 1 GHz. We also studied the the dependence of high frequency performance on graphene interconnect physical dimensions. Important physical parameters like mean free path of graphene are extracted from experimental data. We compared our experimental results with previous theoretical predictions and gave experimental performance projection of on-chip graphene nanoribbon interconnects with linewidth smaller than 100nm.

Publication Stats

886 Citations
203.46 Total Impact Points

Institutions

  • 2006–2015
    • Massachusetts Institute of Technology
      • Department of Electrical Engineering and Computer Science
      Cambridge, Massachusetts, United States
  • 2010
    • Stanford University
      • Center for Integrated Systems
      Palo Alto, California, United States