• Title/Summary/Keyword: core/shell nanowires

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Fabrication of $Al_2O_3$ nanotube with etching core material of one-dimensional ZnO/$Al_2O_3$ core/shell structure (1차원 ZnO/$Al_2O_3$ core/shell 구조에서 core 물질 식각방법에 의한 $Al_2O_3$ 나노튜브제작)

  • Hwang, Joo-Won;Min, Byung-Don;Lee, Jong-Su;Kim, Sang-Sig
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2003.07a
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    • pp.37-40
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    • 2003
  • Amorphous $Al_2O_3$ nanotubes have been fabricated by utilizing the ZnO nanowires as template with wet etching method. ZnO nanowires synthesized by thermal evaporation are conformally coated with $Al_2O_3$ by atomic-layer deposition(ALD) method. The $Al_2O_3$-coated ZnO nanowires are of core-shell structure; ZnO core nanowires and $Al_2O_3$ shells. When the $ZnO/Al_2O_3$ core-shell structure is dipped in $H_3PO_4$ solution at $25^{\circ}C$ for a 6 min, the core ZnO materials are completely etched, and only $Al_2O_3$ nanotubes are remained. This nanotube fabrication is technically easier than others, and simply approachable. Transmission electron microscopy shows that the $Al_2O_3$ nanotubes have various thicknesses that can be controlled.

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Fabrication of SnO2/Zn Core-shell Nanowires and Photoluminescence Properties

  • Kong, Myung Ho;Kwon, Yong Jung;Cho, Hong Yeon;Kim, Hyoun Woo
    • Applied Science and Convergence Technology
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    • v.23 no.5
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    • pp.301-307
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    • 2014
  • We have fabricated $SnO_2$/Zn core-shell nanowires by employing a sputtering technique with a Zn target. Scanning electron microscopy indicated that the surface of the nanowires became rougher by the coating. X-ray diffraction of the coated nanowires exhibited the hexagonal Zn diffraction peaks. TEM image of coated structures showed that shell layer was mainly comprised of hexagonal Zn phase. EDX spectra suggested that the shell layer consisted of Zn elements. The photoluminescence spectrum of the coated nanowires in conjunction with Gaussian fitting analysis revealed that the emission was disconvoluted with three Gaussian functions, which are centered at 2.1 eV in the yellow region, 2.4 eV in the green region, and 3.3 eV in the ultraviolet region. We speculated the possible mechanisms of these emission peaks.

One-dimensional Bi-Te core/shell structure grown by a stress-induced method for the enhanced thermoelectric properties

  • Kang, Joo-Hoon;Ham, Jin-Hee;Lee, Woo-Young
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.04b
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    • pp.47-47
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    • 2009
  • The formation of variable one-dimensional structures including core/shell structure is of particular significance with respect to potential applications for thermoelectric devices with the enhanced figure of merit ($ZT=S2{\sigma}T/{\kappa}$). We report the fabrication of Bi-Te core/shell nanowire based on a novel stress induced method. Fig. 1 schematically shows the nanowire fabrication process. Bi nanowires are grown on the Si substrate by the stress-induced method, and then Te is evaporated on the Bi nanowires. Fig. 2 is a transmission electron microscopy image clearly showing a core/shell structure for which effective phonon scattering and quantum confinement effect are expected. Electrical conductivity of the core/shell nanowire was measured at the temperatures from 4K to 300K, respectively. Our results demonstrate that Bi-Te core/shell nanowire can be grown successfully by the stress-induced method. Based on the result of electrical transport measurement and characteristic morphology of rough surface, Seebeck coefficient and thermal conductivity of Bi-Te core/shell nanowires are presented.

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Bi-Te Core/Shell Nanowires Synthesis Based on On-Film Formation of Nanowires Method for Thermoelectric Applications (압축응력에 의한 박막 위 나노선 성장법을 이용한 Bi-Te 코어/쉘 열전 나노선 합성)

  • Kang, Joohoon;Ham, Jinhee;Roh, Jong Wook;Noh, Jin-Seo;Lee, Wooyoung
    • Korean Journal of Metals and Materials
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    • v.48 no.5
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    • pp.445-448
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    • 2010
  • For an enhanced thermoelectric performance, one-dimensional heterostructure nanowires were created that consisted of aBi core and Te shell. The structure was fabricated by depositing Te in-situ onto a Bi nanowire grown by our unique OFF-ON (on-film formation of nanowires) method. After examining a cross-sectional TEM image, it was found that diffusive interface was formed between Bi and Te. Selected area electron diffraction revealed that the crystallinity of the Te shell was some what lower compared to the highly single-crystalline Bi core. The Bi-Te core/shell nanowires can be a smart structure that suppresses phonon transport by several scattering mechanisms, making the OFF-ON method the simplest way to realize that structure.

Synthesis of Fe-Doped TiO2/α-Fe2O3 Core-Shell Nanowires Using Co-Electrospinning and Their Magnetic Property (복합 전기방사법을 이용한 Fe-doped TiO2/α-Fe2O3 이중구조 나노와이어의 합성 및 자성 특성)

  • Koo, Bon-Ryul;Ahn, Hyo-Jin
    • Korean Journal of Materials Research
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    • v.24 no.8
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    • pp.423-428
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    • 2014
  • We synthesized Fe-doped $TiO_2/{\alpha}-Fe_2O_3$ core-shell nanowires(NWs) by means of a co-electrospinning method and demonstrated their magnetic properties. To investigate the structural, morphological, chemical, and magnetic properties of the samples, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used, as was a vibrating sample magnetometer. The morphology of the nanostructures obtained after calcination at $500^{\circ}C$ exhibited core/shell NWs consisting of $TiO_2$ in the core region and ${\alpha}-Fe_2O_3$ in the shell region. In addition, the XPS results confirmed the formation of Fe-doped $TiO_2$ by the doping effect of $Fe^{3+}$ ions into the $TiO_2$ lattice, which can affect the ferromagnetic properties in the core region. For comparison, pure ${\alpha}-Fe_2O_3$ NWs were also fabricated using an electrospinning method. With regard to the magnetic properties, the Fe-doped $TiO_2/{\alpha}-Fe_2O_3$ core-shell NWs exhibited improved saturation magnetization(Ms) of approximately ~2.96 emu/g, which is approximately 6.1 times larger than that of pure ${\alpha}-Fe_2O_3$ NWs. The performance enhancement can be explained by three main mechanisms: the doping effect of Fe ions into the $TiO_2$ lattice, the size effect of the $Fe_2O3_$ nanoparticles, and the structural effect of the core-shell nanostructures.

Synthesis of Vertically Aligned SiNW/Carbon Core-shell Nanostructures

  • Kim, Jun-Hui;Kim, Min-Su;Kim, Dong-Hwan
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.488.2-488.2
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    • 2014
  • Carbon-based materials such as carbon nanotubes and graphene have emerged as promising building blocks in applications for nanoelectronics and energy devices due to electrical property, ease of processability, and relatively inert electrochemistry. In recent years, there has been considerable interest in core-shell nanomaterials, in which inorganic nanowires are surrounded by inorganic or organic layers. Especially, carbon encapsulated semiconductor nanowires have been actively investigated by researchers in lithium ion batteries. We report a method to synthesize silicon nanowire (SiNW) core/carbon shell structures by chemical vapor deposition (CVD), using methane (CH4) as a precursor at growth temperature of $1000{\sim}1100^{\circ}C$. Unlike carbon-based materials synthesized via conventional routes, this method is of advantage of metal-catalyst free growth. We characterized these materials with FE-SEM, FE-TEM, and Raman spectroscopy. This would allow us to use these materials for applications ranging from optoelectronics to energy devices such as solar cells and lithium ion batteries.

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3D Hierarchical Heterostructure of TiO2 Nanorod/Carbon Layer/NiMn-Layered Double Hydroxide Nanosheet

  • Zhao, Wei;Jung, Hyunsung
    • Journal of the Korean institute of surface engineering
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    • v.51 no.6
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    • pp.365-371
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    • 2018
  • 1D core-shell nanostructures have attracted great attention due to their enhanced physical and chemical properties. Specifically, oriented single-crystalline $TiO_2$ nanorods or nanowires on a transparent conductive substrate would be more desirable as the building core backbone. However, a facile approach to produce such structure-based hybrids is highly demanded. In this study, a three-step hydrothermal method was developed to grow NiMn-layered double hydroxide-decorated $TiO_2$/carbon core-shell nanorod arrays on transparent conductive fluorine-doped tin oxide (FTO) substrates. XRD, SEM, TEM, XPS and Raman were used to analyze the obtained samples. The in-situ fabricated hybrid nanostructured materials are expected to be applicable for photoelectrode working in water splitting.

Characteristics of Graphene Quantum Dot-Based Oxide Substrate for InGaN/GaN Micro-LED Structure (InGaN/GaN Micro-LED구조를 위한 그래핀 양자점 기반의 산화막 기판 특성)

  • Hwang, Sung Won
    • Journal of the Semiconductor & Display Technology
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    • v.20 no.3
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    • pp.167-171
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    • 2021
  • The core-shell InGaN/GaN Multi Quantum Well-Nanowires (MQW-NWs) that were selectively grown on oxide templates with perfectly circular hole patterns were highly crystalline and were shaped as high-aspect-ratio pyramids with semi-polar facets, indicating hexagonal symmetry. The formation of the InGaN active layer was characterized at its various locations for two types of the substrates, one containing defect-free MQW-NWs with GQDs and the other containing MQW-NWs with defects by using HRTEM. The TEM of the defect-free NW showed a typical diode behavior, much larger than that of the NW with defects, resulting in stronger EL from the former device, which holds promise for the realization of high-performance nonpolar core-shell InGaN/GaN MQW-NW substrates. These results suggest that well-defined nonpolar InGaN/GaN MQW-NWs can be utilized for the realization of high-performance LEDs.

Synthesis and Characterization of SnO2-CoO/carbon-coated CoO Core/shell Nanowire Composites (SnO2-CoO/carbon-coated CoO core/shell 나노선 복합체의 합성 및 구조분석)

  • Lee, Yu-Jin;Koo, Bon-Ryul;Ahn, Hyo-Jin
    • Journal of Powder Materials
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    • v.21 no.5
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    • pp.360-365
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    • 2014
  • $SnO_2-CoO$/carbon-coated CoO core/shell nanowire composites were synthesized by using electrospinning and hydrothermal methods. In order to obtain $SnO_2-CoO$/carbon-coated CoO core/shell nanowire composites, $SnO_2-Co_3O_4$ nanowire composites and $SnO_2-Co_3O_4$/polygonal $Co_3O_4$ core/shell nanowire composites are also synthesized. To demonstrate their structural, chemical bonding, and morphological properties, field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out. These results indicated that the morphologies and structures of the samples were changed from $SnO_2-Co_3O_4$ nanowires having cylindrical structures to $SnO_2-Co_3O_4/Co_3O_4$ core/shell nanowires having polygonal structures after a hydrothermal process. At last, $SnO_2-CoO$/carbon-coated CoO core/shell nanowire composites having irregular and high surface area are formed after carbon coating using a polypyrrole (PPy). Also, there occur phases transformation of cobalt phases from $Co_3O_4$ to CoO during carbon coating using a PPy under a argon atmosphere.

Thermal Conductivity Measurement of Ge-SixGe1-x Core-Shell Nanowires Using Suspended Microdevices (뜬 마이크로 디바이스를 이용한 Ge-SixGe1-x Core-Shell Nanowires 의 열전도율 측정)

  • Park, Hyun Joon;Nah, Jung hyo;Tutuc, Emanuel;Seol, Jae Hun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.10
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    • pp.825-829
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    • 2015
  • Theoretical calculations suggest that the thermoelectric figure of merit (ZT) can be improved by introducing a core-shell heterostructure to a semiconductor nanowire because of the reduced thermal conductivity of the nanowire. To experimentally verify the decrease in thermal conductivity in core-shell nanowires, the thermal conductivity of Ge-SixGe1-x core-shell nanowires grown by chemical vapor deposition (CVD) was measured using suspended microdevices. The silicon composition (Xsi) in the shells was measured to be about 0.65, and the remainder of the germanium in the shells was shown to play a role in decreasing defects originating from the lattice mismatch between the cores and shells. In addition to the standard four-point current- voltage (I-V) measurement, the measurement configuration based on the Wheatstone bridge was attempted to enhance the measurement sensitivity. The measured thermal conductivity values are in the range of 9-13 W/mK at room temperature and are lower by approximately 30 than that of a germanium nanowire with a comparable diameter.