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Lai S.,SKKU Advanced Institute of Nanotechnology SAINT | Jeon J.,SKKU Advanced Institute of Nanotechnology SAINT | Song Y.-J.,SKKU Advanced Institute of Nanotechnology SAINT | Lee S.,SKKU Advanced Institute of Nanotechnology SAINT | And 2 more authors.
RSC Advances | Year: 2016

The transfer of two-dimensional (2D) material layers to arbitrary substrates from growth substrates is critical for many applications. Although several studies of transfer processes have been reported, a transfer method that does not degrade 2D layers and damage growth substrates is still required. In this paper, we report a method that with the assistance of water penetration enables the mechanical transfer of MoS2, one of the most widely studied 2D materials, from the growth substrate to a target substrate without any etching of the growth substrate or leaving any polymer residue on the MoS2 layer. The difference between the adhesion forces of the MoS2 and carrier films and the difference between the hydrophobicities of MoS2 and the growth substrate means that water can easily penetrate the interspace at the MoS2/growth substrate interface generated by the peeling off process. We also experimentally confirmed the usefulness of Cu carrier films as a contact material for MoS2 that enables its clean separation. Our transfer method protects the original quality and morphology of large area MoS2 without leaving any polymer residue, and enables the reuse of the growth substrate. This clean transfer approach is expected to facilitate the realization of industrial applications of MoS2 and other 2D materials. © 2016 The Royal Society of Chemistry.

Xu J.,SKKU Advanced Institute of Nanotechnology SAINT | Xu J.,Center for Human Interface Nanotechnology | Jang S.K.,SKKU Advanced Institute of Nanotechnology SAINT | Jang S.K.,Center for Human Interface Nanotechnology | And 6 more authors.
Journal of Physical Chemistry C | Year: 2014

We report a new method for the codoping of boron and nitrogen in a monolayer graphene film. After the CVD synthesis of monolayer graphene, BN-doped graphene is prepared by performing power-controlled plasma treatment and thermal annealing with borazine. BN-doped graphene films with various doping levels, which were controlled by altering the plasma treatment power, were found with Raman and electrical measurements to investigate exhibit p-doping behavior. Transmission electron microscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy were used to demonstrate that the synthesized BN-doped graphene films have a sp2 hybridized hexagonal structure. This approach to tuning the distribution and doping levels of boron and nitrogen in monolayer sp2 hybridized BN-doped graphene is expected to be very useful for applications requiring large-area graphene with an opened band gap. © 2014 American Chemical Society.

Lai S.,SKKU Advanced Institute of Nanotechnology SAINT | Lai S.,Center for Human Interface Nanotechnology | Kyu Jang S.,SKKU Advanced Institute of Nanotechnology SAINT | Jae Song Y.,SKKU Advanced Institute of Nanotechnology SAINT | And 4 more authors.
Applied Physics Letters | Year: 2014

We report a simple and accurate method for detecting graphene defects that utilizes the mild, dry annealing of graphene/Cu films in air. In contrast to previously reported techniques, our simple approach with optical microscopy can determine the density and degree of dislocation of defects in a graphene film without inducing water-related damage or functionalization. Scanning electron microscopy, confocal Raman and atomic force microscopy, and X-ray photoelectron spectroscopy analysis were performed to demonstrate that our nondestructive approach to characterizing graphene defects with optimized thermal annealing provides rapid and comprehensive determinations of graphene quality. © 2014 AIP Publishing LLC.

Wang M.,SKKU Advanced Institute of Nanotechnology SAINT | Wang M.,Center for Human Interface Nanotechnology | Jang S.K.,SKKU Advanced Institute of Nanotechnology SAINT | Song Y.J.,SKKU Advanced Institute of Nanotechnology SAINT | And 4 more authors.
Materials Research Bulletin | Year: 2015

We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO2, show the carrier mobility up to approximately 2250 cm2 V-1 s-1. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems. © 2014, Elsevier Ltd. All rights reserved.

Park H.-Y.,Sungkyunkwan University | Dugasani S.R.,Sungkyunkwan University | Kang D.-H.,Sungkyunkwan University | Jeon J.,Sungkyunkwan University | And 6 more authors.
ACS Nano | Year: 2014

(Figure Presented). Deoxyribonucleic acid (DNA) and two-dimensional (2D) transition metal dichalcogenide (TMD) nanotechnology holds great potential for the development of extremely small devices with increasingly complex functionality. However, most current research related to DNA is limited to crystal growth and synthesis. In addition, since controllable doping methods like ion implantation can cause fatal crystal damage to 2D TMD materials, it is very hard to achieve a low-level doping concentration (nondegenerate regime) on TMD in the present state of technology. Here, we report a nondegenerate doping phenomenon for TMD materials (MoS2 and WSe2, which represent n- and p-channel materials, respectively) using DNA and slightly modified DNA by metal ions (Zn2+, Ni2+, Co2+, and Cu2+), named as M-DNA. This study is an example of interdisciplinary convergence research between DNA nanotechnology and TMD-based 2D device technology. The phosphate backbone (PO4 -) in DNA attracts and holds hole carriers in the TMD region, n-doping the TMD films. Conversely, M-DNA nanostructures, which are functionalized by intercalating metal ions, have positive dipole moments and consequently reduce the electron carrier density of TMD materials, resulting in p-doping phenomenon. N-doping by DNA occurs at ∼6.4 × 1010 cm-2 on MoS2 and ∼7.3 × 109 cm-2 on WSe2, which is uniform across the TMD area. p-Doping which is uniformly achieved by M-DNA occurs between 2.3 × 1010 and 5.5 × 1010 cm-2 on MoS2 and between 2.4 × 1010 and 5.0 × 1010 cm-2 on WSe2. These doping levels are in the nondegenerate regime, allowing for the proper design of performance parameters of TMD-based electronic and optoelectronic devices (VTH, on-/off-currents, field-effect mobility, photoresponsivity, and detectivity). In addition, by controlling the metal ions used, the p-doping level of TMD materials, which also influences their performance parameters, can be controlled. This interdisciplinary convergence research will allow for the successful integration of future layered semiconductor devices requiring extremely small and very complicated structures. © 2014 American Chemical Society.

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