Jinho An

Publications (19)182.69 Total impact

• Article: Transfer of CVD-grown monolayer graphene onto arbitrary substrates.

  Ji Won Suk, Alexander Kitt, Carl W Magnuson, Yufeng Hao, Samir Ahmed, Jinho An, Anna K Swan, Bennett B Goldberg, Rodney S Ruoff
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  ABSTRACT: Reproducible dry and wet transfer techniques were developed to improve the transfer of large-area monolayer graphene grown on copper foils by chemical vapor deposition (CVD). The techniques reported here allow transfer onto three different classes of substrates: substrates covered with shallow depressions, perforated substrates, and flat substrates. A novel dry transfer technique was used to make graphene-sealed microchambers without trapping liquid inside. The dry transfer technique utilizes a polydimethylsiloxane frame that attaches to the poly(methyl methacrylate) spun over the graphene film, and the monolayer graphene was transferred onto shallow depressions with 300 nm depth. The improved wet transfer onto perforated substrates with 2.7 μm diameter holes yields 98% coverage of holes covered with continuous films, allowing the ready use of Raman spectroscopy and transmission electron microscopy to study the intrinsic properties of CVD-grown monolayer graphene. Additionally, monolayer graphene transferred onto flat substrates has fewer cracks and tears, as well as lower sheet resistance than previous transfer techniques. Monolayer graphene films transferred onto glass had a sheet resistance of ∼980 Ω/sq and a transmittance of 97.6%. These transfer techniques open up possibilities for the fabrication of various graphene devices with unique configurations and enhanced performance.
  ACS Nano 09/2011; 5(9):6916-24. · 10.77 Impact Factor
• Source

  Available from: Bert Freitag

  Article: Domain (grain) boundaries and evidence of "twinlike" structures in chemically vapor deposited grown graphene.

  Jinho An, Edgar Voelkl, Ji Won Suk, Xuesong Li, Carl W Magnuson, Lianfeng Fu, Peter Tiemeijer, Maarten Bischoff, Bert Freitag, Elmira Popova, Rodney S Ruoff
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  ABSTRACT: Understanding and engineering the domain boundaries in chemically vapor deposited monolayer graphene will be critical for improving its properties. In this study, a combination of transmission electron microscopy (TEM) techniques including selected area electron diffraction, high resolution transmission electron microscopy (HR-TEM), and dark field (DF) TEM was used to study the boundary orientation angle distribution and the nature of the carbon bonds at the domain boundaries. This report provides an important first step toward a fundamental understanding of these domain boundaries. The results show that, for the graphene grown in this study, the 46 measured misorientation angles are all between 11° and 30° (with the exception of one at 7°). HR-TEM images show the presence of adsorbates in almost all of the boundary areas. When a boundary was imaged, defects were seen (dangling bonds) at the boundaries that likely contribute to adsorbates binding at these boundaries. DF-TEM images also showed the presence of a "twinlike" boundary.
  ACS Nano 03/2011; 5(4):2433-9. · 10.77 Impact Factor
• Article: Raman measurements of thermal transport in suspended monolayer graphene of variable sizes in vacuum and gaseous environments.

  Shanshan Chen, Arden L Moore, Weiwei Cai, Ji Won Suk, Jinho An, Columbia Mishra, Charles Amos, Carl W Magnuson, Junyong Kang, Li Shi, Rodney S Ruoff
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  ABSTRACT: Using micro-Raman spectroscopy, the thermal conductivity of a graphene monolayer grown by chemical vapor deposition and suspended over holes with different diameters ranging from 2.9 to 9.7 μm was measured in vacuum, thereby eliminating errors caused by heat loss to the surrounding gas. The obtained thermal conductivity values of the suspended graphene range from (2.6 ± 0.9) to (3.1 ± 1.0) × 10(3) Wm(-1)K(-1) near 350 K without showing the sample size dependence predicted for suspended, clean, and flat graphene crystal. The lack of sample size dependence is attributed to the relatively large measurement uncertainty as well as grain boundaries, wrinkles, defects, or polymeric residue that are possibly present in the measured samples. Moreover, from Raman measurements performed in air and CO(2) gas environments near atmospheric pressure, the heat transfer coefficient for air and CO(2) was determined and found to be (2.9 +5.1/-2.9) and (1.5 +4.2/-1.5) × 10(4) Wm(-2)K(-1), respectively, when the graphene temperature was heated by the Raman laser to about 510 K.
  ACS Nano 01/2011; 5(1):321-8. · 10.77 Impact Factor
• Article: Mechanical properties of monolayer graphene oxide.

  Ji Won Suk, Richard D Piner, Jinho An, Rodney S Ruoff
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  ABSTRACT: Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young's modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for "pristine" graphene. The prestress (39.7-76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.
  ACS Nano 10/2010; 4(11):6557-64. · 10.77 Impact Factor
• Source

  Available from: E. M. Vogel

  Article: Graphene films with large domain size by a two-step chemical vapor deposition process.

  Xuesong Li, Carl W Magnuson, Archana Venugopal, Jinho An, Ji Won Suk, Boyang Han, Mark Borysiak, Weiwei Cai, Aruna Velamakanni, Yanwu Zhu, Lianfeng Fu, Eric M Vogel, Edgar Voelkl, Luigi Colombo, Rodney S Ruoff
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  ABSTRACT: The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters. Transmission electron microscopy further shows that the domains are crystallographically rotated with respect to each other with a range of angles from about 13 to nearly 30°. Electrical transport measurements performed on back-gated FETs show that overall films with larger domains tend to have higher carrier mobility up to about 16,000 cm(2) V(-1) s(-1) at room temperature.
  Nano Letters 10/2010; 10(11):4328-34. · 13.20 Impact Factor
• Source

  Available from: utexas.edu

  Article: Site-Specific Deposition of Au Nanoparticles in CNT Films by Chemical Bonding.

  Aruna Velamakanni, Carl W Magnuson, K J Ganesh, Yanwu Zhu, Jinho An, Paulo J Ferreira, Rodney S Ruoff
  ACS Nano 08/2010; 4(8):4962. · 10.77 Impact Factor
• Source

  Available from: Vikas Berry

  Article: Biocompatible, robust free-standing paper composed of a TWEEN/graphene composite.

  Sungjin Park, Nihar Mohanty, Ji Won Suk, Ashvin Nagaraja, Jinho An, Richard D Piner, Weiwei Cai, Daniel R Dreyer, Vikas Berry, Rodney S Ruoff
  Advanced Materials 04/2010; 22(15):1736-40. · 13.88 Impact Factor
• Source

  Available from: bucky-central.me.utexas.edu

  Article: Thin Film Fabrication and Simultaneous Anodic Reduction of Deposited Graphene Oxide Platelets by Electrophoretic Deposition

  Sung Jin An, Yanwu Zhu, Sun Hwa Lee, Meryl D. Stoller, Tryggvi Emilsson, Sungjin Park, Aruna Velamakanni, Jinho An, Rodney S. Ruoff
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  ABSTRACT: We report the deposition of films composed of overlapped and stacked platelets of graphene oxide (G-O) reduced by an electrophoretic deposition (EPD) process. The oxygen functional groups of G-O were significantly removed by the EPD process, and the as-deposited G-O film by EPD showed improved electrical conductivity (1.43 × 104 S·m−1) over G-O papers made by the filtration method (0.53 × 10−3 S·m−1). This method for reducing G-O without added reducing agents has the potential for high-yield, large-area, low-cost, and environmentally friendly production of films composed of reduced G-O platelets.Keywords (keywords): graphene; reduced graphene oxide; electrophoretic deposition (EPD); electrochemical reduction; reduced graphene oxide film
  03/2010;
• Source

  Available from: Toshiyuki Hashida

  Article: The influence of nanoscale defects on the fracture of multi-walled carbon nanotubes under tensile loading

  Go Yamamoto, Ji Won Suk, Jinho An, Richard D Piner, Toshiyuki Hashida, Toshiyuki Takagi, Rodney S Ruoff
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  ABSTRACT: We report the mechanical behavior of a unique type of multi-walled carbon nanotube (MWCNT) and an acid-treated version of this MWCNT type that have nanoscale defects on their surfaces from the acid treatment. These defects, from scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging have a 'channel-like' appearance, as if a ring of material was cut away from the MWCNT around the circumference. The mechanical properties of individual MWCNTs have been experimentally shown to strongly depend on their structure and structural disorder can drastically reduce the mechanical properties. Tensile-loading experiments using a nanomanipulator tool operated inside a SEM revealed that the tensile strengths of 10 pristine MWCNTs ranged from ∼ 2 to ∼ 48 GPa (mean 20 GPa). For 10 acid-treated MWCNTs with channel-like defects, tensile strengths ranged from ∼ 1 to ∼ 18 GPa (mean 6 GPa, thus roughly 70% lower than those of the pristine MWCNTs). Microstructural observations revealed that the fracture of the acid-treated MWCNTs occurred at a channel-like defect region in 8 of the 10 samples. This indicates that the channel-like defects associated with the acid etching are typically going to be the weakest points in the acid-treated MWCNT structure and that stress concentration is present at the defect region. © 2010 Published by Elsevier B.V.
  03/2010;
• Source

  Available from: kaist.ac.kr

  Article: Polymer Brushes via Controlled, Surface-Initiated Atom Transfer Radical Polymerization (ATRP) from Graphene Oxide.

  Sun Hwa Lee, Daniel R Dreyer, Jinho An, Aruna Velamakanni, Richard D Piner, Sungjin Park, Yanwu Zhu, Sang Ouk Kim, Christopher W Bielawski, Rodney S Ruoff
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  ABSTRACT: A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface-grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.
  Macromolecular Rapid Communications 02/2010; 31(3):281-8. · 4.60 Impact Factor
• Source

  Available from: utexas.edu

  Article: Graphene-based actuators.

  Sungjin Park, Jinho An, Ji Won Suk, Rodney S Ruoff
  Small 11/2009; 6(2):210-2. · 8.35 Impact Factor
• Article: TEM Measurements of Grain Orientation in Nanoscale Cu Interconnects using ACT

  Jinho An, Jeff Pickering, K. J. Ganesh, P. J. Ferreira
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  ABSTRACT: Transmission electron microscope (TEM) is used in conjunction with an Automated Crystallography for TEM (ACT) to index the crystal orientation of 180 nm wide Cu interconnects using the Nano Beam Diffraction (NBD) mode in the TEM. An FEM software, OOF2, was used to simulate the local quasi‐hydrostatic stresses in the interconnect lines based on the local orientation data, and was compared results obtained from stress induced void (SIV) formation in 180 nm Cu interconnects studied through in‐situ TEM (Transmission Electron Microscope) heating. SIV were induced at temperatures of around 230° C. Correlation between the stress simulations and the experimental results show that point of high local stresses and high stress gradients seem to influence the formation of the SIV in the Cu interconnect lines. A description of a new technique, called D‐STEM that allows for obtaining diffraction patterns from crystals only a few nanometers in size is also given, that will allow for characterizing even smaller width Cu interconnects for future generation microelectronic devices.
  AIP Conference Proceedings. 06/2009; 1143(1):166-171.
• Source

  Available from: arxiv.org

  Article: Large-area synthesis of high-quality and uniform graphene films on copper foils.

  Xuesong Li, Weiwei Cai, Jinho An, Seyoung Kim, Junghyo Nah, Dongxing Yang, Richard Piner, Aruna Velamakanni, Inhwa Jung, Emanuel Tutuc, Sanjay K Banerjee, Luigi Colombo, Rodney S Ruoff
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  ABSTRACT: Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single-layer graphene, with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on silicon/silicon dioxide substrates showed electron mobilities as high as 4050 square centimeters per volt per second at room temperature.
  Science 05/2009; 324(5932):1312-4. · 31.20 Impact Factor
• Source

  Available from: utexas.edu

  Article: Colloidal suspensions of highly reduced graphene oxide in a wide variety of organic solvents.

  Sungjin Park, Jinho An, Inhwa Jung, Richard D Piner, Sung Jin An, Xuesong Li, Aruna Velamakanni, Rodney S Ruoff
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  ABSTRACT: We report that homogeneous colloidal suspensions of chemically modified graphene sheets were readily produced in a wide variety of organic solvent systems. Two different sets of solubility parameters are used to rationalize when stable colloidal suspensions of graphene oxide sheets and, separately, of reduced graphene oxide sheets in a given solvent type are possible and when they are not. As an example of the utility of such colloidal suspensions, "paperlike" materials generated by very simple filtration of the reduced graphene oxide sheets had electrical conductivity values as high as 16,000 S/m.
  Nano Letters 05/2009; 9(4):1593-7. · 13.20 Impact Factor
• Source

  Available from: utexas.edu

  Article: Aqueous Suspension and Characterization of Chemically Modified Graphene Sheets

  Sungjin Park, Jinho An, Richard D. Piner, Inhwa Jung, Dongxing Yang, Aruna Velamakanni, SonBinh T. Nguyen, Rodney S. Ruoff
  10/2008;
• Source

  Available from: utexas.edu

  Article: Graphene-based ultracapacitors.

  Meryl D Stoller, Sungjin Park, Yanwu Zhu, Jinho An, Rodney S Ruoff
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  ABSTRACT: The surface area of a single graphene sheet is 2630 m(2)/g, substantially higher than values derived from BET surface area measurements of activated carbons used in current electrochemical double layer capacitors. Our group has pioneered a new carbon material that we call chemically modified graphene (CMG). CMG materials are made from 1-atom thick sheets of carbon, functionalized as needed, and here we demonstrate in an ultracapacitor cell their performance. Specific capacitances of 135 and 99 F/g in aqueous and organic electrolytes, respectively, have been measured. In addition, high electrical conductivity gives these materials consistently good performance over a wide range of voltage scan rates. These encouraging results illustrate the exciting potential for high performance, electrical energy storage devices based on this new class of carbon material.
  Nano Letters 10/2008; 8(10):3498-502. · 13.20 Impact Factor
• Source

  Available from: presolar.wustl.edu

  Article: Synthesis and Solid-State NMR Structural Characterization of 13C-Labeled Graphite Oxide

  Weiwei Cai, Richard D. Piner, Frank J. Stadermann, Sungjin Park, Medhat A. Shaibat, Yoshitaka Ishii, Dongxing Yang, Aruna Velamakanni, Sung Jin An, Meryl Stoller, Jinho An, Dongmin Chen, Rodney S. Ruoff
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  ABSTRACT: The detailed chemical structure of graphite oxide (GO), a layered material prepared from graphite almost 150 years ago and a precursor to chemically modified graphenes, has not been previously resolved because of the pseudo-random chemical functionalization of each layer, as well as variations in exact composition. Carbon-13 (13C) solid-state nuclear magnetic resonance (SSNMR) spectra of GO for natural abundance 13C have poor signal-to-noise ratios. Approximately 100% 13C-labeled graphite was made and converted to 13C-labeled GO, and 13C SSNMR was used to reveal details of the chemical bonding network, including the chemical groups and their connections. Carbon-13–labeled graphite can be used to prepare chemically modified graphenes for 13C SSNMR analysis with enhanced sensitivity and for fundamental studies of 13C-labeled graphite and graphene.
  Science 09/2008; 321(5897):1815-1817. · 31.20 Impact Factor
• Source

  Available from: Matthew Pelton

  Article: Characterization of Thermally Reduced Graphene Oxide by Imaging Ellipsometry

  Inhwa Jung, Matthias Vaupel, Matthew Pelton, Richard Piner, Dmitriy A. Dikin, Sasha Stankovich, Jinho An, Rodney S. Ruoff
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  ABSTRACT: The dispersion functions for the refractive index and the extinction coefficient of single- and multiple-layer graphene oxide samples were measured by imaging spectroscopic ellipsometry in the wavelength range of 350−1000 nm and were compared to previously reported results measured by confocal microscopy. The dispersion functions for thin platelets were also compared to those obtained by standard spectroscopic ellipsometry on a deposit consisting of many overlapping graphene oxide layers. Changes were observed in both the thickness of the deposits and the values of the dispersion parameters following heating. A model is proposed to explain these observations, based on the removal of water between the graphene-oxide layers upon thermal treatment.
  05/2008;
• Article: Hydrazine-reduction of graphite- and graphene oxide

  Sungjin Park, Jinho An, Jeffrey R. Potts, Aruna Velamakanni, Shanthi Murali, Rodney S. Ruoff
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  ABSTRACT: We prepared hydrazine-reduced materials from both graphite oxide (GO) particles, which were not exfoliated, and completely exfoliated individual graphene oxide platelets, and then analyzed their chemical and structural properties by elemental analysis, XPS, TGA, XRD, and SEM. Both reduced materials showed distinctly different chemical and structural properties from one another. While hydrazine reduction of graphene oxide platelets produced agglomerates of exfoliated platelets, the reduction of GO particles produced particles that were not exfoliated. The degree of chemical reduction of reduced GO particles was lower than that of reduced graphene oxide and the BET surface area of reduced GO was much lower than that of reduced graphene oxide.
  Carbon. 49(9):3019-3023.