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|Title: ||Synthesis and characterization of II-IV group and silicon related nanomaterials|
|Other Titles: ||Yu gui xiang guan de er zhi si zu na mi cai liao de he cheng yu te xing miao shu|
|Authors: ||Ismathullakhan, Shafiq|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Master of Philosophy|
|Issue Date: ||2008|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Nanostructured materials.|
|Notes: ||CityU Call Number: TA418.9.N35 I86 2008|
xii, 94 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references.
|Abstract: ||Despite considerable efforts, rational synthesis of ZnO nanostructures with
tunable n-type conductivity is a challenging issue. On the other hand, as-synthesized
ZnO nanostructures are often randomly oriented, and thus have limited applications in
optoelectronic devices. Herein, we report a controlled growth and doping process of
well-aligned zinc oxide (ZnO) nanowire (NW) arrays via thermal evaporation.
Influence of Gallium (Ga) dopant on the growth direction of ZnO NWs was examined.
The growth direction of ZnO NWs was found to depend on the dopant content.
Electrical transport properties of ZnO NWs were studied by fabricating and
characterizing single nanowire field-effect transistors (FETs). It is shown that the ZnO
NW conductivity can be tuned by two orders of magnitude, through the way of
Doping is a widely used method to tailor the electrical and optical properties of
semiconductors by introducing discrete energy states in the band gap. In this regard,
the role of Indium (In) as a luminescence activator and as a compensator of n-type
materials is of considerable significance for II–VI compound semiconductors. In this
work, high quality n-type Indium doped cadmium sulphide (CdS) nanomaterials were
fabricated by doping through a simple thermal evaporation method.
Photoluminescence studies on the intrinsic and doped nanoribbons reveal the presence
of discrete exciton emission bands in doped samples. Studies on field emission
properties of doped CdS nanopens and nanopencils were also carried out. It is found
that the nanopens with sharp tip has less turn on field compared to the nanopencil
samples. Photoconductive response characteristics of single CdS nanoribbon (NR) to
various wavelengths were also investigated. It is shown that a single CdS NR photoconductor can be used as one switch in optoelectronic applications, because of
its reversible switching ability between high and low conductivities.
Manipulation of nanomaterials remains as another major challenge in the field of
nanotechnology, despite significant progress. The fabrication of integrated systems
using nanomaterial requires the site-specific growth or placement on relevant device
platforms. In addition, the formation of complex and multi-component structures are
needed for low-dimensional structures and electronic devices. In this dissertation,
heteroepitaxial growth of single-crystalline ZnSxSe1-x nanowire arrays on ZnS
nanoribbon substrates by the metal-catalyzed vapor-liquid-solid growth method were
carried out. ZnSxSe1-x nanowire arrays were aligned crosswise to the top surface and
vertically grown on side surfaces of ZnS nanoribbon substrates with variable
compositions making it having tunable optical properties. Photoluminescence
spectroscopy of the nanostructures reveals the lasing emission from the nanowires
beyond threshold excitation intensity and exciton emissions below threshold and at
Control of channel diameter and branching of a hierarchical tubular
nanostructure is important for developing nano-channels or nano-containers for
various applications. A simple thermo-evaporation synthesis and two-step method for
epitaxial growth of branched silicon oxide (SiO) nanotubes from ZnS/SiO core-shell
nanowire heterostructures using zinc sulfide (ZnS) and SiO as sources were studied.
ZnS nanowires were synthesized by Au-catalyzed vapor-liquid-solid growth, and
served as templates to form amorphous SiO nanotubes via evaporation of the ZnS
core. Successive SiO coating and ZnS wire removal was found to graft new branches
to the original tube and the diameter of the prepared porous SiO nanotube could be
post-processed by electron beam irradiation. The resulting core-shell structures were found to have uniform diameters, which are suitable for heterostructure nanodevices
fabrication. Low-temperature photoluminescence studies on the SiO nanotubes
sample reveal the visible-light emission centered at 612 nm. The present growth
template approach may be extended to assemble nano-fluidic channel network for
bioanalytical and chemical separations and branched field effect transistors.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2268744|
|Appears in Collections:||AP - Master of Philosophy |
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