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Enhanced nucleation of germanium on graphene <i>via</i> dipole engineering
Yoo, Jinkyoung,Ahmed, Towfiq,Chen, Renjie,Chen, Aiping,Kim, Yeon Hoo,Kwon, Ki Chang,Park, Chan Woong,Kang, Hee Seong,Jang, Ho Won,Hong, Young Joon,Yang, Woo Seok,Lee, Chul-Ho The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.12
<P>The preparation of crystalline materials on incommensurate substrates has been a key topic of epitaxy. van der Waals (vdW) epitaxy on two-dimensional (2D) materials opened novel opportunities of epitaxial growth overcoming the materials compatibility issue. Therefore, vdW epitaxy has been considered as a promising approach for the preparation of building blocks of flexible devices and thin film-based devices at the nano/microscale. However, an understanding of vdW epitaxy has not been thoroughly established. Especially, controlling nucleation during vdW epitaxy has not been achieved although nucleation in vdW epitaxy is suppressed due to the absence of surface dangling bonds on 2D materials. Here we show an enhancement of nucleation probability of germanium on graphene <I>via</I> introducing an out-of-plane dipole moment without any change in the chemical nature of graphene. A graphene/hexagonal boron nitride stack and transferred graphene on a polarized ferroelectric thin film were employed to demonstrate the significant enhancement of Ge nucleation on graphene. Theoretical calculations and chemical vapor deposition were employed to elucidate the effect of the out-of-plane dipole moment on nucleation in vdW epitaxy.</P>
Metal-Lined Semiconductor Nanotubes for Surface Plasmon-Mediated Luminescence Enhancement
Yoo, Jinkyoung,Ma, Xuedan,Tang, Wei,Yi, Gyu-Chul American Chemical Society 2013 NANO LETTERS Vol.13 No.5
<P>Highly efficient solid-state light-emitting devices require semiconductor architectures equipped with high quantum efficiency and integratability on conductive substrates. Surface plasmon (SP)-mediated luminescence enhancement has been considered as one of the most promising solutions, because SP resonance can greatly improve the radiative recombination rate and be achieved using metal entities compatible with the electrode fabrication process. Nevertheless, metal/semiconductor heterostructures have had several fabrication-compatible issues due to metal as a potential contaminant of the semiconductor. We present here a simple fabrication scheme for a metal-lined semiconductor nanotube heterostructure, in which a metal layer is selectively formed on the inner wall of the semiconductor nanotube. The Ag-lining process in a ZnO nanotube resulted in 7.5-fold enhancement of the photoluminescence intensity at 11 K. This SP fabrication technique looks promising for highly efficient solid-state lighting based on semiconductor nanostructures without detrimental effects.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-5/nl400547z/production/images/medium/nl-2013-00547z_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl400547z'>ACS Electronic Supporting Info</A></P>
Yoo, Jinkyoung,Hong, Young Joon,Jung, Hye Seong,Kim, Yong-Jin,Lee, Chul-Ho,Cho, Jeonghui,Doh, Yong-Joo,Dang, Le Si,Park, Kyung Ho,Yi, Gyu-Chul WILEY-VCH Verlag 2009 Advanced Functional Materials Vol.19 No.10
<P>The position-controlled growth and structural and optical characteristics of ZnO nanotubes and their coaxial heterostructures are reported. To control both the shape and position of ZnO nanotubes, hole-patterned SiO<SUB>2</SUB> growth-mask layers on Si(111) substrates with GaN/AlN intermediate layers using conventional lithography are prepared. ZnO nanotubes are grown only on the hole patterns at 600 °C by catalyst-free metal–organic vapor-phase epitaxy. Furthermore, the position-controlled nanotube growth method allows the fabrication of artificial arrays of ZnO-based coaxial nanotube single-quantum-well structures (SQWs) on Si substrates. In situ heteroepitaxial growth of ZnO and Zn<SUB>0.8</SUB>Mg<SUB>0.2</SUB>O layers along the circumference of the ZnO nanotube enable an artificial formation of quantum-well arrays in a designed fashion. The structural and optical characteristics of the ZnO nanotubes and SQW arrays are also investigated using synchrotron radiation X-ray diffractometry and photoluminescence and cathodoluminescence spectroscopy.</P> <B>Graphic Abstract</B> <P>Position-controlled ZnO nanotubes and their coaxial nanotube quantum structure arrays are fabricated by selective metal–organic vapor-phase epitaxy (see image). Both the position-controlled nanotube and associated coaxial heterostructures arrays exhibit excellent luminescent characteristics. This simple, precise, well-controlled “bottom-up” fabrication provides a general and rational route to integrate vertical nanodevices for nanometer-scale electronics and optoelectronics. <img src='wiley_img/1616301X-2009-19-10-ADFM200801123-content.gif' alt='wiley_img/1616301X-2009-19-10-ADFM200801123-content'> </P>
Yoo, Jinkyoung,Ahmed, Towfiq,Tang, Wei,Kim, Yong-Jin,Joon Hong, Young,Lee, Chul-Ho,Yi, Gyu-Chul IOP 2017 Nanotechnology Vol.28 No.39
<P>ZnO radial <I>p–n</I> junction architecture has the potential for forward-leap of light-emitting diode (LED) technology in terms of higher efficacy and economical production. We report on ZnO radial <I>p–n</I> junction-based light emitting diodes prepared by full metalorganic chemical vapour deposition (MOCVD) with hydrogen-assisted <I>p</I>-type doping approach. The <I>p</I>-type ZnO(P) thin films were prepared by MOCVD with the precursors of dimethylzinc, tert-butanol, and tertiarybutylphosphine. Controlling the precursor flow for dopant results in the systematic change of doping concentration, Hall mobility, and electrical conductivity. Moreover, the approach of hydrogen-assisted phosphorous doping in ZnO expands the understanding of doping behaviour in ZnO. Ultraviolet and visible electroluminescence of ZnO radial <I>p–n</I> junction was demonstrated through a combination of position-controlled nano/microwire and crystalline <I>p</I>-type ZnO(P) radial shell growth on the wires. The reported research opens a pathway of realisation of production-compatible ZnO <I>p–n</I> junction LEDs.</P>
Controlled epitaxial growth modes of ZnO nanostructures using different substrate crystal planes
Hong, Young Joon,Yoo, Jinkyoung,Doh, Yong-Joo,Kang, Suk Hoon,Kong, Ki-jeong,Kim, Miyoung,Lee, Dong Ryeol,Oh, Kyu Hwan,Yi, Gyu-Chul Royal Society of Chemistry 2009 Journal of materials chemistry Vol.19 No.7
<P>A combined experimental and theoretical investigation has clarified the nanometre-scale vapour-phase epitaxial growth of ZnO nanostructures on different crystal planes of GaN substrates. Under typical growth conditions, ZnO nanorods grow perpendicular to the GaN(0001) plane, but thin flat films form on GaN(101&cmb.macr;1), (101&cmb.macr;0) and (112&cmb.macr;0). High-resolution X-ray diffraction data and transmission electron microscopy confirm the heteroepitaxial relationship between the ZnO nanostructures and GaN substrates. These results are consistent with first-principles theoretical calculations, indicating that the ZnO surface morphologies are mainly influenced by highly anisotropic GaN/ZnO interface energies. As a result of the large surface energy gradients, different ZnO nanostructures grow by preferential heteroepitaxial growth on different facets of regular GaN micropattern arrays. High-resolution transmission electron microscopy shows that ZnO nanotubes develop epitaxially on micropyramid tips, presumably as a result of enhanced nucleation and growth about the edges.</P> <P>Graphic Abstract</P><P>Combined experimental and theoretical investigations have clarified the controlled catalyst-free vapour-phase epitaxial growth mode of ZnO nanorods, nanotubes, and thin films on different crystal planes of GaN substrates. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b816034a'> </P>