Zinc Oxide Nanowire Films: Solution Growth, Defect States and Electrical Conductivity - Advanced Materials for Agriculture, Food and Environmental Safety - page 456

understood, and few researchers believe that HMT acts as a buf er [52].
Ashfold et al. have proposed that the rate of decomposition of HMT is
independent of the reaction and acts as a kinetic buf er [51]. Primarily, the
pH and the concentration of Zn 2+ ions are maintained in such a way that
the ZnO growth starts with the formation of Zn(OH) 2 . When pH is gradu-
ally increased, the concentration of the Zn ions decreases and Zn(OH) 2
becomes thermodynamically unstable. Sugunan et al. have suggested a
dif erent approach, that HMT prefers to attach on the non-polar facets
rather than the polar facets, and leads to one-dimensional epitaxial growth
on substrate [53]. h e HMT therefore acts more like a shape-inducing
polymer surfactant rather than as a buf er.
h e ZnO 1D nanostructures have been successfully grown in the pres-
ence of dif erent surfactants such as polyvinyl alcohol (PVA), polyethylene
glycol (PEG), sodium dodecyl sulphate (SDS) and cetyltrimethyl ammo-
nium bromide (CTAB) [49, 54]. h e use of PVA resulted in more regu-
lar and defect free rods than PEG, SDS and CTAB. Li et al. have reported
CTAB assisted hydrothermal growth resulted in tapered ZnO nanowires
with diameter decreasing from 400 nm at the body to about 80 nm at the
tip [55]. Figure 16.1 shows low temperature hydrothermal grown ZnO
Figure 16.1 Scanning electron microscopic images of low temperature hydrothermally
grown ZnO nanowires. (a) Top view, (b) 20 degree tilt view, (c) cross-sectional view, and
(d) high resolution tilt image.