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Defect-selective dry etching for quick and easy probing of hexagonal boron nitride domains
Wu, Qinke,Lee, Joohyun,Park, Sangwoo,Woo, Hwi Je,Lee, Sungjoo,Song, Young Jae IOP 2018 Nanotechnology Vol.29 No.12
<P>In this study, we demonstrate a new method to selectively etch the point defects or the boundaries of as-grown hexagonal boron nitride (hBN) films and flakes <I>in situ</I> on copper substrates using hydrogen and argon gases. The initial quality of the chemical vapor deposition-grown hBN films and flakes was confirmed by UV–vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy. Different gas flow ratios of Ar/H<SUB>2</SUB> were then employed to etch the same quality of samples and it was found that etching with hydrogen starts from the point defects and grows epitaxially, which helps in confirming crystalline orientations. However, etching with argon is sensitive to line defects (boundaries) and helps in visualizing the domain size. Finally, based on this defect-selective dry etching technique, it could be visualized that the domains of a polycrystalline hBN monolayer merged together with many parts, even with those that grew from a single nucleation seed.</P>
Wu, Qinke,Jung, Seong Jun,Jang, Sung Kyu,Lee, Joohyun,Jeon, Insu,Suh, Hwansoo,Kim, Yong Ho,Lee, Young Hee,Lee, Sungjoo,Song, Young Jae RSC Pub 2015 Nanoscale Vol.7 No.28
<P>Correction for 'Controllable poly-crystalline bilayered and multilayered graphene film growth by reciprocal chemical vapor deposition' by Qinke Wu et al., Nanoscale, 2015, 7, 10357-10361.</P>
Wu, Qinke,Jung, Seong Jun,Jang, Sung Kyu,Lee, Joohyun,Jeon, Insu,Suh, Hwansoo,Kim, Yong Ho,Lee, Young Hee,Lee, Sungjoo,Song, Young Jae RSC Pub 2015 Nanoscale Vol.7 No.23
<P>We report the selective growth of large-area bilayered graphene film and multilayered graphene film on copper. This growth was achieved by introducing a reciprocal chemical vapor deposition (CVD) process that took advantage of an intermediate h-BN layer as a sacrificial template for graphene growth. A thin h-BN film, initially grown on the copper substrate using CVD methods, was locally etched away during the subsequent graphene growth under residual H2 and CH4 gas flows. Etching of the h-BN layer formed a channel that permitted the growth of additional graphene adlayers below the existing graphene layer. Bilayered graphene typically covers an entire Cu foil with domain sizes of 10-50 μm, whereas multilayered graphene can be epitaxially grown to form islands a few hundreds of microns in size. This new mechanism, in which graphene growth proceeded simultaneously with h-BN etching, suggests a potential approach to control graphene layers for engineering the band structures of large-area graphene for electronic device applications.</P>
In situ chemical vapor deposition of graphene and hexagonal boron nitride heterostructures
Qinke Wu,Winadda Wongwiriyapan,Ji-Hoon Park,Sangwoo Park,Seong Jun Jung,Taehwan Jeong,Sungjoo Lee,이영희,Young Jae Song 한국물리학회 2016 Current Applied Physics Vol.16 No.9
Graphene and hexagonal boron nitride (hBN) heterostructures have attracted considerable attention in recent years to keep graphene's unique properties with ideal two-dimensional protective layers of h-BN for use in a wide range of potential applications. Depending on the application goals and the fabrication process, several structural configurations of graphene and hBN have been suggested; (1) lateral heterostructure incorporated in the in-plane direction on the same layer like graphene-hBN and (2) vertical heterostructures stacking a layer over different layers like graphene/hBN(GB), hBN/graphene(BG) or hBN/ graphene/hBN(BGB). These artificial heterostructures can induce new properties or preserve the ideal unique properties beyond the inevitable limit of pristine graphene caused during the conventional fabrication. In this perspective, recent advances in selective synthesis or controllable fabrication of graphene and hBN heterostructures are summarized. In particular, with practical scalability, high uniformity and quality, in situ chemical vapor deposition growth of in-plane and vertical graphene and hBN heterostructures are highlighted.
<i>In situ</i> chemical vapor deposition of graphene and hexagonal boron nitride heterostructures
Wu, Qinke,Wongwiriyapan, Winadda,Park, Ji-Hoon,Park, Sangwoo,Jung, Seong Jun,Jeong, Taehwan,Lee, Sungjoo,Lee, Young Hee,Song, Young Jae Elsevier 2016 CURRENT APPLIED PHYSICS Vol.16 No.9
<P>Graphene and hexagonal boron nitride (hBN) heterostructures have attracted considerable attention in recent years to keep graphene's unique properties with ideal two-dimensional protective layers of h-BN for use in a wide range of potential applications. Depending on the application goals and the fabrication process, several structural configurations of graphene and hBN have been suggested; (1) lateral heterostructure incorporated in the in-plane direction on the same layer like graphene-hBN and (2) vertical heterostructures stacking a layer over different layers like graphene/hBN(GB), hBN/graphene(BG) or hBN/graphene/hBN(BGB). These artificial heterostructures can induce new properties or preserve the ideal unique properties beyond the inevitable limit of pristine graphene caused during the conventional fabrication. In this perspective, recent advances in selective synthesis or controllable fabrication of graphene and hBN heterostructures are summarized. In particular, with practical scalability, high uniformity and quality, in situ chemical vapor deposition growth of in-plane and vertical graphene and hBN heterostructures are highlighted. (C) 2016 Elsevier B.V. All rights reserved.</P>
Wu, Qinke,Lee, Joohyun,Sun, Jia,Song, Young Jae Elsevier 2018 Carbon Vol.138 No.-
<P><B>Abstract</B></P> <P>Here, we report the <I>in situ</I> direct growth of a graphene/hexagonal boron nitride (hBN) heterostructure on a SiO<SUB>2</SUB> substrate without a metal catalyst by chemical vapor deposition (CVD). The hBN could be grown easily on a SiO<SUB>2</SUB> substrate, while graphene growth was difficult and time-consuming as graphite could be grown only partially on the dielectric substrate, even after 5 h. Graphene was grown directly on this hBN/SiO<SUB>2</SUB> substrate sequentially, which demonstrated easy and quick growth of a fully covered and high-quality graphene multilayer film within 40 min. The effect of hydrogen on the direct growth of hBN on a SiO<SUB>2</SUB> substrate was also studied, and it was found that when a higher flow rate of hydrogen was used, the domain size was larger and higher quality of hBN could be grown. The quality of the grown hBN and graphene/hBN samples were confirmed by UV–vis, Raman, and atomic force microscopy (AFM). This new method can be used for graphene multilayer coating on dielectric substrates, on which it is difficult to grow graphene directly, for industrial or scientific applications.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Wu, Qinke,Song, Young Jae The Royal Society of Chemistry 2018 Chemical communications Vol.54 No.69
<P>The environmental stability of large-sized and single-crystalline antimony flakes was systematically investigated with temperature and time dependence at fixed humidity. The antimony flakes used in this work were grown by chemical vapor deposition (CVD) directly on SiO2 substrates, where antimonene layers were stacked to a few tens of nm thickness with a typical area of ∼40 μm.</P>
Jeong, Taehwan,Piao, Huiyan,Park, Sangwoo,Yang, Jae-Hun,Choi, Goeun,Wu, Qinke,Kang, Hyunmin,Woo, Hwi Je,Jung, Seong Jun,Kim, Hanchul,Shin, Bong Gyu,Kim, Youngkuk,Hwang, Euy Heon,Choy, Jin-Ho,Song, You Elsevier 2019 Applied catalysis. B, Environmental Vol.256 No.-
<P><B>Abstract</B></P> <P>Industrial demands for sustainable and renewable energy resources have inspired studies on photonic and electronic properties of graphitic-carbon nitride (<I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB>) as a promising photocatalyst without precious metal. The absorption and the yield by metal-free pristine <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> are, however, still limited with hydrogen/oxygen evolution reaction (HER/OER) mostly around ultraviolet-light. Here, we propose the graphene-decorated <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> as a metal-free photocatalyst under visible-light, based on our atomic-scale measurements and calculations. The <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> nanosheets on highly-oriented pyrolytic graphite (HOPG) exhibit band-gaps appropriate for visible-light absorption and work-functions tuned for band alignments to supply electrons and holes for HER/OER. Scanning probe microscopy (SPM) measurements for local density of states (LDOS) in atomic scale and work-functions in nanometer scale with ab initio calculations confirmed the various electronic transitions for each nitrogen and carbon atom in different atomic registries. The graphene-decorated <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB>, therefore, could provide a breakthrough enabling the efficient water-splitting reactions under visible-light without precious metal.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The potocatalytic mechanism of graphene/<I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB> was unveiled by STM measurements and DFT calculations at the atomic scale. </LI> <LI> This heterostructure has a direct and indirect band-gaps of 2.51 and 1.64 eV, representing the best fit to a visible light. </LI> <LI> Band alignments appropriate for HER and OER could be confirmed by thickness-dependent CPD measurements by KPFM and STS. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Summary of the research: Graphene-decorated graphitic carbon nitride (<I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB>) can be a metal-free photocatalyst for hydrogen and oxygen evolution reaction (HER/OER) under visible light. Epitaxially-stacked graphene can induce an appropriate bandgap and work-function on <I>g</I>-C<SUB>3</SUB>N<SUB>4</SUB>. The role of carbon and different nitrogen atoms for bandgap and work-function modulations could be described by scanning tunneling microscopy/spectroscopy (STM/STS) measurements in atomic scale along with DFT calculations.</P> <P>[DISPLAY OMISSION]</P>