http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Lee, Eun Kyung,Yin, Liang,Lee, Yongjin,Lee, Jong Woon,Lee, Sang Jin,Lee, Junho,Cha, Seung Nam,Whang, Dongmok,Hwang, Gyeong S.,Hippalgaonkar, Kedar,Majumdar, Arun,Yu, Choongho,Choi, Byoung Lyong,Kim, J American Chemical Society 2012 NANO LETTERS Vol.12 No.6
<P>The strongly correlated thermoelectric properties have been a major hurdle for high-performance thermoelectric energy conversion. One possible approach to avoid such correlation is to suppress phonon transport by scattering at the surface of confined nanowire structures. However, phonon characteristic lengths are broad in crystalline solids, which makes nanowires insufficient to fully suppress heat transport. Here, we employed Si–Ge alloy as well as nanowire structures to maximize the depletion of heat-carrying phonons. This results in a thermal conductivity as low as ∼1.2 W/m-K at 450 K, showing a large thermoelectric figure-of-merit (ZT) of ∼0.46 compared with those of SiGe bulks and even ZT over 2 at 800 K theoretically. All thermoelectric properties were “simultaneously” measured from the same nanowires to facilitate accurate ZT measurements. The surface-boundary scattering is prominent when the nanowire diameter is over ∼100 nm, whereas alloying plays a more important role in suppressing phonon transport for smaller ones.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-6/nl300587u/production/images/medium/nl-2012-00587u_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl300587u'>ACS Electronic Supporting Info</A></P>
Lee, Dongmok,Kwon, Gi Duk,Kim, Jung Ho,Moyen, Eric,Lee, Young Hee,Baik, Seunghyun,Pribat, Didier The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.21
<P>We have studied the influence of the surface roughness of copper foils on the sheet resistance of graphene sheets grown by chemical vapor deposition. The surface roughness of the copper foils was reproducibly controlled by electropolishing. We have found that the graphene sheet resistance monotonically decreases as the surface roughness of the copper foils decreases. We show that a pre-annealing treatment combined with an optimized electropolishing process of the Cu foils and a fast CVD growth prevents the evolution of the Cu surface roughness during graphene synthesis. This combination of fabrication conditions produces small grain polycrystalline graphene films with a sheet resistance of 210 Ω □<SUP>−1</SUP>and carrier mobility values as high as 5450 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP>after transfer onto SiO2/Si.</P>
Lee, Jong Woon,Lee, Junho,Yi, Su-in,Seo, Young Min,Choi, Byoung Lyong,Yu, Choongho,Yang, Cheol-Woong,Hwang, Sungwoo,Kim, Sungjin,Whang, Dongmok,Lee, Eun Kyung The Royal Society of Chemistry 2014 Journal of Materials Chemistry A Vol.2 No.31
<▼1><P>Core–shell Si1−xGex alloy nanowires can suppress the phonon propagation without reducing the electrical conductivity.</P></▼1><▼2><P>We demonstrate for the first time core–shell Si1−xGex alloy nanowires that can suppress the phonon propagation in nanowires without reducing the electrical conductivity. Non-uniformly distributed structural defects in the outer shells of the Si1−xGex nanowires enhance boundary scattering during phonon transport, while a defect-free core provides a current path for electrical carriers.</P></▼2>
One-pot size-controlled growth of graphene-encapsulated germanium nanocrystals
Lee, Jae-Hyun,Lee, Eun-Kyung,Kang, Seog-Gyun,Jung, Su-Ho,Son, Seok-Kyun,Nam, Woo Hyun,Kim, Tae-Hoon,Choi, Byong Lyong,Whang, Dongmok Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.440 No.-
<P><B>Abstract</B></P> <P>To realize graphene-encapsulated semiconductor nanocrystals (NCs), an additional graphene coating process, which causes shape destruction and chemical contamination, has so far been inevitable. We report herein one-pot growth of uniform graphene-germanium core–shell nanocrystals (Ge@G NCs) in gram scale by the addition of methane as a carbon source during the thermal pyrolysis of germane. The methane plays a critical role in the growth of the graphene shell, as well as in the determination of the nucleation density and diameter of the NCs, similar to a surfactant in the liquid-phase growth of monodisperse NCs. By adjusting the gas ratio of precursors, a mixture of germane and methane, we can control the size of the Ge@G NCs in the range of ∼5–180 nm. The Ge@G NCs were characterized by various microscopic and spectroscopic tools, which indicated that the Ge core is single crystalline, and is completely covered by the graphene shell. We further investigated the merits of the graphene shell, which can enhance the electrical conductivity of nanocrystalline materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Ge-graphene core-shell nanocrystals (Ge@G NCs) are synthesized in gram scale. </LI> <LI> The role of CH<SUB>4</SUB> is critical for determination of the density and diameter of the NCs. </LI> <LI> The size of the Ge@G NCs can be controlled by tuning the gas ratio of GeH<SUB>4</SUB> and CH<SUB>4</SUB>. </LI> <LI> The graphene shell enhances the electrical conductivity of NCs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Jong Woon,Lee, Junho,Jung, Su-Ho,Jang, Yamujin,Choi, Byoung Lyong,Yang, Cheol-Woong,Whang, Dongmok,Lee, Eun Kyung IOP 2016 Nanotechnology Vol.27 No.30
<P>We demonstrate silicon germanium (SiGe) alloy nanowires (NWs) with Ge nanoparticles (GeNPs) embedded in a SiO<SUB>2</SUB> shell as a material for decreasing thermal conductivity. During thermal oxidation of SiGe NWs to form SiGe–SiO<SUB>2</SUB> core–shell structures, Ge atoms were diffused into the SiO<SUB>2</SUB> shell to relax the strain in the SiGe core, and agglomerated as a few nanometer-sized particles. This structure leads to a large reduction in thermal conductivity due to the GeNP–phonon interaction, while electrical conductivity is sustained because the core of the SiGe alloy NW provides a current path for the charged carriers. The thermal conductivity of the SiGe alloy NWs wrapped with a GeNP-embedded SiO<SUB>2</SUB> shell is 0.41 W m<SUP>−1</SUP> K<SUP>−1</SUP> at 300 K.</P>
Dependence of the In-Plane Thermal Conductivity of Graphene on Grain Misorientation
Lee, Dongmok,Lee, Sanghoon,An, Byeong-Seon,Kim, Tae-Hoon,Yang, Cheol-Woong,Suk, Ji Won,Baik, Seunghyun American Chemical Society 2017 Chemistry of materials Vol.29 No.24
<P>The thermal transport across the grain boundary (GB) is inevitably encountered for large-area polycrystalline graphene. However, the influence of GB configuration on thermal transport is not well understood. Here we investigated the effect of grain misorientation angle on the in-plane thermal conductivity (κ) of suspended graphene by using the optothermal Raman technique. Graphene with well-defined grain orientation was synthesized on an electropolished, annealed, and oxygen plasma-treated single-crystalline Cu(111) substrate by low-pressure chemical vapor deposition. The κ was primarily dependent on the grain size of single-, bi-, and polycrystalline graphene, consistent with the Boltzmann transport model. Surprisingly, κ of bicrystalline graphene dramatically decreased with a slight misorientation (<4°) between two neighboring grains. This phonon-boundary scattering was successfully simulated by the GB misorientation model. The GB length or shape also affected κ as a tertiary parameter. The GB misorientation angle and length, in addition to the grain size, were determining factors of κ, which may be applicable for other two-dimensional materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2017/cmatex.2017.29.issue-24/acs.chemmater.7b03821/production/images/medium/cm-2017-03821d_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm7b03821'>ACS Electronic Supporting Info</A></P>
Thermoelectric Properties of Nanowires with a Graphitic Shell.
Lee, Jong Woon,Lee, Eun Kyung,Kim, Byung Sung,Lee, Jae Hyun,Kim, Hee Goo,Jang, Hyeon Sik,Hwang, Sung Woo,Choi, Byoung Lyong,Whang, Dongmok Wiley-VCH 2015 ChemSusChem Vol.8 No.14
<P>A thermoelectric device that can generate electricity from waste heat can play an important role in a global energy solution. However, the strongly correlated thermoelectric properties have remained a major hurdle for the highly efficient conversion of thermoelectric energy. Herein, the electrical and thermal properties of Si and SiO2 nanowires with few-layer graphitic shells are demonstrated; these structures exhibit enhanced electrical properties but no increase in thermal conductivity. The main path of the phonons through the structures is the core nanowire, which has a large cross-sectional area relative to that of the graphitic shell layer. However, the electrical conductivities of the nanowires with shell structures are high because of the good electrical conductivity of the graphitic shell, despite its small cross-sectional area.</P>