Chemistry Reference
In-Depth Information
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Figure 8.10
(a) Illustrations and micrographs showing formation of hierarchical
nanostructures driven by screw dislocation. Adapted with permission
from ref. 65. (Copyright 2013, ACS.) (b) Schematic illustration showing
the formation of helically arranged nanowire branches: (i) a nanowire
with an axial screw dislocation in the center. Both ends of the NW are
clamped. (ii) One end of the NWs is free to rotate, resulting in an
Eshelby twist. (iii) The branches are grown epitaxially onto the back-
bone nanowire by VLS growth. Adapted with permission from ref. 58.
(Copyright 2008, NPG.) (c) SEM image of a single helically branched
PbSe nanowire (inset, high-resolution SEM). Adapted with permission
from ref. 58. (Copyright 2008, NPG.)
growth, the supersaturation condition should be in a range where both layer-
by-layer growth and dislocation-driven growth coexist.
13
The dislocation-driven nanowire growth mechanism was also expanded to
other semiconducting materials such as ZnO,
61
In
2
O
3
,
62,63
CdS/CdSe
64
etc.
65
.
8.4.6 Laser-induced Hydrothermal Growth (LIHG)
Conventional hydrothermal growth involves heating in a furnace or con-
vection oven. However, furnace or oven heating is less energy-ecient and a
rather slow process requiring quite long heating/cooling time. In contrast,
laser provides a rapid heat source with ease of parametric control at a lo-
calized heating zone and furthermore enables selective heating by enabling
choice of desired wavelength. Exploiting these laser characteristics, Yeo
et al.
66
and In et al.
67
demonstrated laser-induced hydrothermal growth
(LIHG) of ZnO nanowires. Compared with conventional hydrothermal
growth, the nanowire growth rate dramatically increased and nanowire
structures could be deposited and even patterned on designated spots very
effectively and precisely by using a focused laser to induce a controlled
temperature rise as displayed in Figures 8.11(a) and (b). More interestingly,
very long ZnO nanowires, which have a high possibility of a significant in-
crease of the surface area at a given projected area, have been produced in a
short time with limited quantities of precursors (Figures 8.11(c) and (d)).
67
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