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Author

Hamin Park

Bio: Hamin Park is an academic researcher from KAIST. The author has contributed to research in topics: Materials science & Graphene. The author has an hindex of 10, co-authored 16 publications receiving 229 citations. Previous affiliations of Hamin Park include Center for Advanced Materials & Kwangwoon University.

Papers
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Journal ArticleDOI
TL;DR: This study produced highly uniform and scalable h-BN films by plasma-enhanced atomic layer deposition, which were characterized by various techniques including atomic force microscopy, transmission electron microscope, Raman spectroscopy, and X-ray diffraction.
Abstract: Hexagonal boron nitride (h-BN) has been previously manufactured using mechanical exfoliation and chemical vapor deposition methods, which make the large-scale synthesis of uniform h-BN very challenging. In this study, we produced highly uniform and scalable h-BN films by plasma-enhanced atomic layer deposition, which were characterized by various techniques including atomic force microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. The film composition studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy corresponded to a B:N stoichiometric ratio close to 1:1, and the band-gap value (5.65 eV) obtained by electron energy loss spectroscopy was consistent with the dielectric properties. The h-BN-containing capacitors were characterized by highly uniform properties, a reasonable dielectric constant (3), and low leakage current density, while graphene on h-BN substrates exhibited enhanced electrical performance such as the high carrier mobility and neutral Dirac voltage, which resulted from the low density of charged impurities on the h-BN surface.

56 citations

Journal ArticleDOI
22 May 2018
TL;DR: Using rotating-disk electrode measurements, it is confirmed that N-pGF undergoes a four-electron-transfer process during the ORR in alkaline and acidic media by possessing sufficient diffusion pathways and readily available ORR active sites for efficient mass transport.
Abstract: We report a simple approach to fabricate a pyridinic-N-doped graphene film (N-pGF) without high-temperature heat treatment from perforated graphene oxide (pGO). pGO is produced by a short etching treatment with hydrogen peroxide. GO perforation predominated in a short etching time (∼1 h), inducing larger holes and defects compared to pristine GO. The pGO is advantageous to the formation of a pyridinic N-doped graphene because of strong NH3 adsorption on vacancies with oxygen functional groups during the nitrogen-doping process, and the pyridinic-N-doped graphene exhibits good electrocatalytic activity for oxygen reduction reaction (ORR). Using rotating-disk electrode measurements, we confirm that N-pGF undergoes a four-electron-transfer process during the ORR in alkaline and acidic media by possessing sufficient diffusion pathways and readily available ORR active sites for efficient mass transport. A comparison between Pt/N-pGF and commercial Pt/C shows that Pt/N-pGF has superior performance, based on its...

38 citations

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TL;DR: In this paper, the enhancement of plasmonic coupling among metallic nanoparticles (NPs) uniformly spread out on both sides of a graphene spacer is experimentally and simulatively investigated.
Abstract: The plasmonic coupling, the enhanced electromagnetic field occurring through a uniform and small separation between metallic particles, is required for better application to localized surface plasmon resonance. Graphene has been studied as a good spacer candidate because of its precise controllability at subnanoscale. Here, the enhancement of plasmonic coupling among metallic nanoparticles (NPs) uniformly spread out on both sides of a graphene spacer is experimentally and simulatively investigated. Additionally, the post-evaporated flat structure is rippled along one direction to reduce the separation between nanoparticles. As the amount of rippling increases, the enhancement factor (EF) of the plasmonic coupling increases almost linearly or quadratically depending on the size of nanoparticles. Such a highly rippled nanostructure is believed to not only increase the plasmonic coupling in either side of the spacer but lead to a higher density of “hot spots” through the spacer gap also. The observed EFs of a structure with the MLG spacer are consistent with the simulation results obtained from the classical electrodynamics. On the other hand, the SLG case appears to be inconsistent with such a classical approach, indicating that the plasmon tunneling through the thin barrier is prevalent in the case of the SLG spacer.

32 citations

Journal ArticleDOI
Gwang Hyuk Shin1, Bondae Koo2, Bondae Koo1, Hamin Park1, Youngjun Woo1, Jae Eun Lee1, Sung-Yool Choi1 
TL;DR: A tunneling field-effect transistor based on a vertical heterostructure of highly p-doped silicon and n-type MoS2 shows a staggered band alignment in which the quantum mechanical band-to-band tunneling probability is enhanced.
Abstract: We present a tunneling field-effect transistor based on a vertical heterostructure of highly p-doped silicon and n-type MoS2. The resulting p-n heterojunction shows a staggered band alignment in which the quantum mechanical band-to-band tunneling probability is enhanced. The device functions in both tunneling transistor and conventional transistor modes, depending on whether the p-n junction is forward or reverse biased, and exhibits a minimum subthreshold swing of 15 mV/dec, an average of 77 mV/dec for four decades of the drain current, a high on/off current ratio of approximately 107 at a drain voltage of 1 V, and fully suppressed ambipolar behavior. Furthermore, low-temperature electrical measurements demonstrated that both trap-assisted and band-to-band tunneling contribute to the drain current. The presence of traps was attributed to defects within the interfacial oxide between silicon and MoS2.

29 citations

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TL;DR: This study proposes the atomic-scale etching of h-BN for integration into devices based on 2D materials, using Ar plasma at room temperature, and fabricated a top-gate MoS2 field-effect transistor (FET) withh-BN gate dielectric, characterized by high electrical performance based on the on/off current ratio and carrier mobility.
Abstract: Hexagonal boron nitride (h-BN) is considered an ideal template for electronics based on two-dimensional (2D) materials, owing to its unique properties as a dielectric film. Most studies involving h-BN and its application to electronics have focused on its synthesis using techniques such as chemical vapor deposition, the electrical analysis of its surface state, and the evaluation of its performance. Meanwhile, processing techniques including etching methods have not been widely studied despite their necessity for device fabrication processes. In this study, we propose the atomic-scale etching of h-BN for integration into devices based on 2D materials, using Ar plasma at room temperature. A controllable etching rate, less than 1 nm min−1, was achieved and the low reactivity of the Ar plasma enabled the atomic-scale etching of h-BN down to a monolayer in this top-down approach. Based on the h-BN etching technique for achieving electrical contact with the underlying molybdenum disulfide (MoS2) layer of an h-BN/MoS2 heterostructure, a top-gate MoS2 field-effect transistor (FET) with h-BN gate dielectric was fabricated and characterized by high electrical performance based on the on/off current ratio and carrier mobility.

26 citations


Cited by
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19 Nov 2012

1,653 citations

Journal Article
TL;DR: In this paper, the authors demonstrate a novel technology for constructing large-scale electronic systems based on graphene/molybdenum disulfide (MoS2) heterostructures grown by chemical vapor deposition.
Abstract: Two-dimensional (2D) materials have generated great interest in the past few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS2), and insulating boron nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency, and favorable transport properties for realizing electronic, sensing, and optical systems on arbitrary surfaces. In this paper, we demonstrate a novel technology for constructing large-scale electronic systems based on graphene/molybdenum disulfide (MoS2) heterostructures grown by chemical vapor deposition. We have fabricated high-performance devices and circuits based on this heterostructure, where MoS2 is used as the transistor channel and graphene as contact electrodes and circuit interconnects. We provide a systematic comparison of the graphene/MoS2 heterojunction contact to more traditional MoS2-metal junctions, as well as a theoretical investigation, using density functional theory, of the origin of the Schottky barrier height. The tunability of the graphene work function with electrostatic doping significantly improves the ohmic contact to MoS2. These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics.

439 citations

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TL;DR: In this article, the most recent research works on the synthesis of heteroatom-doped graphene materials such as reduced graphene oxide, graphene oxide and graphene nanoribbons are surveyed.

335 citations

Journal ArticleDOI
TL;DR: In this article, a review comprehensively analyzes the relevant features of heteroatom-doped carbon composites used in batteries, supercapacitors, and the oxygen reduction reaction (ORR), and provides guidance for the design of more efficient materials.
Abstract: Heteroatom-doped carbon materials (HDCMs) have been widely studied as some of the most prominent material candidates for use in a wide range of applications, such as batteries, supercapacitors (SCs), and the oxygen reduction reaction (ORR) Over the past few years, various metal-free heteroatom-doped carbon composites have been developed via integrating different heteroatoms into carbon with different nanostructures, from single-atom doping (N, P, B, S, etc) to multiple heteroatom doping (N/P/S, N/S/B, etc) For the first time, this review comprehensively analyzes the relevant features of HDCMs used in batteries, SCs, and the ORR, and provides guidance for the design of more efficient materials By controlling the content and types of heteroatom-containing reagents, not only the physical and chemical properties of the material can be adjusted, but also the specific surface area and pore volume can be increased via controlling the morphology, thereby enhancing the electrochemical performance of the material Subsequently, this review summarizes the developments and the history of HDCMs, including synthesis methods, the relationship between doping (doping position and content) and performance, reaction mechanisms, and evaluations of systems In addition, the important role of oxygen doping is raised and discussed, to remind researchers not to ignore the role of oxygen in improving material properties Finally, future developments and challenges relating to key technologies in this thriving field are also discussed in this report

270 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed an AgNPs/graphene@AuNPs system with three-dimensional hot spots and tunable nanometer gap by changing the layer of graphene with a simple and facile method.
Abstract: Hot spots have been considered as a dominant role in surface enhancement Raman scattering (SERS). Its generation cannot be separated from the ultra-small nanogaps, which will tremendously contribute to the strong electromagnetic field. We propose a AgNPs/graphene@AuNPs system with three-dimensional hot spots and tunable nanometer gap by changing the layer of graphene with a simple and facile method. The excellent SERS behaviors of the proposed AgNPs/graphene@AuNPs substrate are demonstrated experimentally using rhodamine 6G (R6G) and crystal violet (CV) as probe molecules and theoretically using commercial COMSOL software. The excellent SERS behaviors can be attributed to the electromagnetic mechanism (EM) in all three dimensions introduced by the lateral nanogaps (AgNP-AgNP) and the vertical nanogaps (AgNP-AuNPs), and the chemical enhancement mechanism (CM) induced by the graphene film. For practical application, the prepared sensitive AgNPs/graphene@AuNPs SERS substrate was used to detect Malachite green (MG) in sea water, which provides a bran-new avenue for the detection of biological and chemical molecule.

200 citations