National Nano Fab Center

Yuseong gu, South Korea

National Nano Fab Center

Yuseong gu, South Korea
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PubMed | Ajou University, Dr Hari Singh Gour University, National Nano Fab Center, Sejong University and 2 more.
Type: | Journal: Scientific reports | Year: 2016

We report a simple and mass-scalable approach for thin MoS2 films via RF sputtering combined with the post-deposition annealing process. We have prepared as-sputtered film using a MoS2 target in the sputtering system. The as-sputtered film was subjected to post-deposition annealing to improve crystalline quality at 700C in a sulfur and argon environment. The analysis confirmed the growth of continuous bilayer to few-layer MoS2 film. The mobility value of ~29cm(2)/Vs and current on/off ratio on the order of ~10(4) were obtained for bilayer MoS2. The mobility increased up to ~173-181cm(2)/Vs, respectively, for few-layer MoS2. The mobility of our bilayer MoS2 FETs is larger than any previously reported values of single to bilayer MoS2 grown on SiO2/Si substrate with a SiO2 gate oxide. Moreover, our few-layer MoS2 FETs exhibited the highest mobility value ever reported for any MoS2 FETs with a SiO2 gate oxide. It is presumed that the high mobility behavior of our film could be attributed to low charged impurities of our film and dielectric screening effect by an interfacial MoOxSiy layer. The combined preparation route of RF sputtering and post-deposition annealing process opens up the novel possibility of mass and batch production of MoS2 film.

PubMed | Dr Hari Singh Gour University, Sejong University and National Nano Fab Center
Type: Journal Article | Journal: Nanoscale | Year: 2016

In this article, we report layer-controlled, continuous and large-area molydenum sulfide (MoS2) growth onto a SiO2/Si substrate by RF sputtering combined with sulfurization. A two-step process was employed to synthesize MoS2 films. In the first step, an atomically thin MoO3 film was deposited by RF magnetron sputtering at 300 C. Subsequently, the as-sputtered MoO3 film was further subjected to post-annealing and sulfurization processes at 650 C for 1 hour. It was observed that the number of layers of MoS2 can be controlled by adjusting the sputtering time. The fabricated MoS2 transistors exhibited high mobility values of 21 cm(2) V(-1) s(-1) (bilayer) and 25 cm(2) V(-1) s(-1) (trilayer), on/off ratios in the range of 10(7) (bilayer) and 10(4)-10(5) (trilayer), respectively. We believe that our proposed paradigm can start a new method for the growth of MoS2 in future electronics and optoelectronics applications.

Gwon H.,KAIST | Kim H.-S.,KAIST | Kim H.-S.,Samsung | Lee K.U.,KAIST | And 6 more authors.
Energy and Environmental Science | Year: 2011

Recently, great interest has been aroused in flexible/bendable electronic equipment such as rollup displays and wearable devices. As flexible energy conversion and energy storage units with high energy and power density represent indispensable components of flexible electronics, they should be carefully considered. However, it is a great challenge to fabricate flexible/bendable power sources. This is mainly due to the lack of reliable materials that combine both electronically superior conductivity and mechanical flexibility, which also possess high stability in electrochemical environments. In this work, we report a new approach to flexible energy devices. We suggest the use of a flexible electrode based on free-standing graphene paper, to be applied in lithium rechargeable batteries. This is the first report in which graphene paper is adopted as a key element applied in a flexible lithium rechargeable battery. Moreover graphene paper is a functional material, which does not only act as a conducting agent, but also as a current collector. The unique combination of its outstanding properties such as high mechanical strength, large surface area, and superior electrical conductivity make graphene paper, a promising base material for flexible energy storage devices. In essence, we discover that the graphene based flexible electrode exhibits significantly improved performances in electrochemical properties, such as in energy density and power density. Moreover graphene paper has better life cycle compared to non-flexible conventional electrode architecture. Accordingly, we believe that our findings will contribute to the full realization of flexible lithium rechargeable batteries used in bendable electronic equipments. © 2011 The Royal Society of Chemistry.

Mun J.H.,KAIST | Hwang C.,Korea Research Institute of Standards and Science | Lim S.K.,National Nano Fab Center | Cho B.J.,KAIST
Carbon | Year: 2010

The change of surface roughness during graphene synthesis on evaporated Ni thin films was monitored. It was found that Ni is highly agglomerated during high temperature annealing but the surface roughness is made smoother by the coverage of graphene. It is demonstrated that diffuse reflectance is a fast and convenient technique for evaluating surface roughness over a large area of graphene on a metal film, and specular reflectance is a good indicator of the coverage of graphene on the metal film. © 2009 Elsevier Ltd. All rights reserved.

Kwon M.-S.,Ulsan National Institute of Science and Technology | Shin J.-S.,Korea Advanced Institute of Science and Technology | Shin S.-Y.,Korea Advanced Institute of Science and Technology | Lee W.-G.,National Nano Fab Center
Optics Express | Year: 2012

We investigate experimentally metal-insulator-silicon-insulatormetal (MISIM) waveguides that are fabricated by using fully standard CMOS technology. They are hybrid plasmonic waveguides, and they have a feature that their insulator is replaceable with functional material. We explain a fabrication process for them and discuss fabrication results based on 8-inch silicon-on-insulator wafers. We measured the propagation characteristics of the MISIM waveguides that were actually fabricated to be connected to Si photonic waveguides through symmetric and asymmetric couplers. When incident light from an optical source has transverse electric (TE) polarization and its wavelength is 1318 or 1554 nm, their propagation losses are between 0.2 and 0.3 dB/μm. Excess losses due to the symmetric couplers are around 0.5 dB, which are smaller than those due to the asymmetric couplers. Additional measurement results indicate that the MISIM waveguide supports a TE-polarized hybrid plasmonic mode. Finally, we explain a process of removing the insulator without affecting the remaining MISIM structure to fabricate 30-nm-wide nanochannels which may be filled with functional material. © 2012 Optical Society of America.

PubMed | Chungnam National University, Hanyang University, National Nano Fab Center and Korea Advanced Institute of Science and Technology
Type: | Journal: Scientific reports | Year: 2016

High-mobility zinc oxynitride (ZnON) semiconductors were grown by RF sputtering using a Zn metal target in a plasma mixture of Ar, N2, and O2 gas. The RF power and the O2 to N2 gas flow rates were systematically adjusted to prepare a set of ZnON films with different relative anion contents. The carrier density was found to be greatly affected by the anion composition, while the electron mobility is determined by a fairly complex mechanism. First-principles calculations indicate that excess vacant nitrogen sites (VN) in N-rich ZnON disrupt the local electron conduction paths, which may be restored by having oxygen anions inserted therein. The latter are anticipated to enhance the electron mobility, and the exact process parameters that induce such a phenomenon can only be found experimentally. Contour plots of the Hall mobility and carrier density with respect to the RF power and O2 to N2 gas flow rate ratio indicate the existence of an optimum region where maximum electron mobility is obtained. Using ZnON films grown under the optimum conditions, the fabrication of high-performance devices with field-effect mobility values exceeding 120cm(2)/Vs is demonstrated based on simple reactive RF sputtering methods.

An H.,Institute of Nano and Advanced Materials Engineering | Lee W.-G.,National Nano Fab Center | Jung J.,Institute of Nano and Advanced Materials Engineering
Current Applied Physics | Year: 2012

A new method for implementing graphene ribbons using selective graphene growth on metal-sidewall by chemical vapor deposition has been proposed. In this method, Ni catalyst is pre-patterned before chemical vapor deposition, and graphene film is selectively grown on the sidewall of the nickel for graphene ribbons. The graphene ribbons were confirmed by TEM image and Raman spectroscopy, and the fabricated graphene ribbon transistors showed well gate-modulated output characteristics. We believe this sidewall-graphene could be useful for applications such as graphene sensors which require high surface area of graphene. © 2011 Elsevier B.V. All rights reserved.

Kim E.,Sejong University | An H.,Sejong University | Jang H.,Sejong University | Cho W.-J.,Kwangwoon University | And 3 more authors.
Chemical Vapor Deposition | Year: 2011

Few-layered sheets of graphene were synthesized on polycrystalline thin Co and Ni films by low pressure chemical vapor deposition. On average, thinner layers of graphene were synthesized on Co than on the conventional Ni at the same process conditions, but slightly higher defects were detected on Co-grown graphene layers than on Ni-grown ones. Possible explanations for this are suggested. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kim E.,Sejong University | Lee W.-G.,National Nano Fab Center | Jung J.,Sejong University
Electronic Materials Letters | Year: 2011

The agglomeration effect of thin metal catalyst on graphene film grown via CVD was investigated. Among Ni and Co catalysts with 200 nm to 400 nm thickness, 200 nm-Ni exhibits the highest agglomeration and the worst non-uniformity of the synthesized graphene film. Agglomeration induces roughness of catalysts and in turn degrades thickness uniformity of graphene film due to non-uniform dissolution and precipitation of carbon across the catalyst film. Increasing catalyst thickness suppresses the agglomeration and improves uniformity of graphene film. Co shows higher resistant to agglomeration than Ni and improves uniformity of the synthesized graphene film. © 2011 The Korean Institute of Metals and Materials and Springer Netherlands.

Choi J.,Sejong University | Seo Y.-S.,Sejong University | Lee W.-G.,National Nano Fab Center | Jung J.,Sejong University
Current Applied Physics | Year: 2013

The high contact resistance of organic thin film transistors (OTFTs), due to the work function difference between metal electrode and organic channel, seriously decreases the electrical properties. Graphene electrode could reduce the contact resistance and improve the electrical performance of OTFTs. However, the high chemical vapor deposition (CVD) temperature (900-1000°C) limits the available OTFT substrate in the case of direct graphene growth on S/D metal electrodes. Furthermore, the application of a transferred graphene electrode induces significant problems due to the transfer process. In this work, thin graphite sheet was directly grown on a metal electrode by the inductively coupled plasma-chemical vapor deposition (ICP-CVD) method at as low temperature as 400, 500°C. We show that OFETs with thin graphite sheet/metal, grown at 400, 500°C, exhibit much lower contact resistance than OFETs with metal-only electrode. © 2013 Elsevier B.V. All rights reserved.

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