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Synthesis and Characterization of 1-dimensional nanostructure 원문보기

  • 저자

    배승용

  • 학위수여기관

    고려대학교 대학원

  • 학위구분

    국내박사

  • 학과

    소재화학과

  • 지도교수

  • 발행년도

    2004

  • 총페이지

    x, 150p.

  • 키워드

    1-dimensional Nanostructure Gallium nitride nanowires;

  • 언어

    eng

  • 원문 URL

    http://www.riss.kr/link?id=T10074218&outLink=K  

  • 초록

    Nanostructures, having at a least one-dimension(1-D) between 1 and 100nm, have received steadily growing interests as a result of their peculiar and fascinating properties, and applications superior to their bulk counterparts. Recently, 1-D nanostructures such as wires, rods, belts, and tubes have also become the focus of intensive research owing to their unique applications in mesoscopic physics and fabrication of nanoscale devices. It is generally accepted that 1-D nanostructures provide a good system to investigate the dependence of electrical and thermal transport or mechanical properties on dimensionality and size reduction(or quantum confinement). We devote the most attention to 1D nanostructures, such as wires, rods, belts, tubes, cables, and heterostructures, that have been synthesized using chemical vapor deposition methods. One of the crucial factors in the synthesis of 1-D nanostructures is the control of size, shape, growth direction, crystallinity, and composition. Scanning electron microscopy(SEM), transmission electron microscopy(TEM), electron diffraction(ED), x-ray diffraction(XRD), electron energy loss spectroscopy(EELS), Raman spectroscopy, and photoluminescence(PL) were used to investigate the structural and optical properties of the various 1-D nanostructures. We also controlled size and shape of the 1-D nanostructures by the adjusting catalyst and temperature and elucidated their atomic/electronic structure by X-ray photoelectron spectroscopy(XPS). Chapter 1 describes the synthesis of boron nitride(BN) nanotubes. The diameter of nanotubes is in the range of 40-100nm. The nanotubes grown below 1100℃ possess exclusively a bamboo-like structure. As the temperature increases to 1200℃, almost all nanotubes show a cylindrical structure in which the BN sheets are tilted to the tube axis by an angle of about 25 deg. Electron energy-loss spectroscopy identifies that the ratio of B and N is almost one. The Raman scattering peak associated with the E_(2g) mode shifts to the higher frequency and narrows as the growth temperature increases. The results indicate that the growth temperature can be a crucial growth parameter in controlling the structure and crystallinity of BN nanotubes. On the basis of the structural features, we suggest a base-growth mechanism for both bamboo-like and cylindrical BN nanotubes. In the chapter 2-4, we have studied the synthesis and characterization of controlled gallium nitride(GaN) nanostructures having porous structure, treelike shape with uniform[001] growth directiont and sheath coated with the boron carbonitride(BCN) layers. Porous structured GaN nanowires were synthesized using Ga/Ga₂O_(3)/B₂O_(3)/C mixture under NH_(3) flow. The average diameter is 40nm and the length is up to 1mm. The porous GaN nanowires consist of the wurtzite single crystal grown with the[011] direction parallel to the wire axis. The size of pores is 5-20nm. The porous GaN crystals are partially coated with nearly amorphous BCN layers. The PL exhibits a broad band in the energy range of2.1-3.6eV. Tree-like GaN nanowires whose growth direction is[001], were synthesized via a chemical vapor deposition of Ga/GaN/B₂O_(3) mixture under NH_(3) atmosphere. The majority of nanowires are extremely thin and long; the diameter is 5-10nm and the length is 40-50㎛. The larger diameter nanowires exhibit a zigzag configuration with amorphous B outerlayers. XRD and Raman spectroscopy reveal no significant strains inside the nanowires. GaN nanocables coated BCN outer layers were synthesized using a thennal chemical vapor deposition method. The average diameter is 30nm and the length is up to 1mm. Less than 20 graphitic sheets coat the single-crystalline wurtzite structured GaN nanowires. The graphitic outerlayers are composed of B, C, and N atoms with a ratio of about 1:2:1. The PL exhibit a broad band in the energy range of 2.1-3.6eV, suggesting a contribution of the emission from the graphitic BCN outerlayers. Chapter 5 describes the coaxial nanocables of gallium phosphide(GaP) core with a variety of outerlayers, i.e., SiO_(x), C, SiO_(x)/C, BCN. The GaP/SiO_(x) and GaP/C nanocables were directly grown on the Au nanopartic1es deposited on the substrates and the outer diameter is below 50nm. The C deposition on the pre-grown GaP/SiO_(x) nanocables produces the GaP/SiO(_x)/C nanocables. The thickness and crystallinity of the C outerlayers were controllable by the deposition time and temperature. The GaP nanorods encapsulated with the mutiwalled BCN nanotubes were also directly synthesized and the diameter of these GaPlBCN nanocables is 70 nm. The BCN outerlayers have a thickness of 5nm with a composition ratio of about B:C:N=4:1:4. The acid treatment of the nanocables selectively produces the GaP nanowires as well as the hollow BCN nanotubes. The growth process and the structure control of these nanocables have been discussed based on the vapor-liquid-solid mechanism. Chapter 6 describes various heterostructured zinc oxide(ZnO) nanorods grown on pre-grown 1-D nanostructures, such as C nanotubes, GaN nanowires, GaP nanowires, SiC nanowires, and SiC core-C shell coaxial nanocables. The diameter of ZnO nanorods is in the range of 80-150nm, and the maximum length is about 3 ㎛. The ZnO nanorods align vertically on the wall of 1D nanostructures, with uniform growth direction of[001]. We suggest a vaporliquid-solid growth mechanism that Zn vapor deposits on the 1D nanostructures and produces the outer layers encapsulating the 1D nanostructures; the Zno nanorods are grown out from the outer layers of nanocable structure. The length and density of ZnO nanorods is controllable by the deposition time. All these heterostructures exhibit intense UV emission of PL and cathodoluminescence(CL). The green emission intensity is correlated with the density of Zno nanorods. In the chapter 7 and 8, we have studied sulfer (S)-and indium (In)-doped ZnO nanowires. High-density Zno nanowires doped with 4 atom % sulfur(S) and pure ZnO nanowires were grown vertically aligned on a silicon substrate. They were synthesized via chemical vapor deposition of a Zn or Zn/8 powder mixture at 500℃. The S-doped ZnO nanowires usually form bundles. The average diameter of the S-doped Zno nanowires and ZnO nanowires is 20 and 50nm, respectively. They consist of single-crystalline wurtzite ZnO crystals with a unifonn growth direction of[001]. Elemental mapping reveals that the S doping takes place mainly at the surface of the nanowires with a thickness of a few nanometers. XRD data suggest that the incorporation of S would expand the lattice constants of ZnO. The PL and CL of S-doped Zno nanowires exhibit a significantly enhanced green emission band that comes from the S-doped surface region of the nanowires. Indium (In)-doped zinc oxide (ZnO) nanowires whose In content [In/(Zn+In) atomic ratio] is 15 and 25%, were synthesized by thennal evaporation method. They consist of a single-crystalline wurtzite structure with unifonn[010] growth direction. X-ray diffraction reveals the structural defects caused by the In doping. High-resolution X-ray photoelectron spectrum(XPS) analysis suggests that the doped In withdraw the electrons from Zn and increase the dangling-bond O 2p states. The lower-energy shift and green band enhancement of photoluminescence are well correlated with the results of XRD and XPS.


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