Environmental Engineering Reference
In-Depth Information
in defect band emission. Various metal nanoparticles such as Au, Pt,
Ag, Ti, Pb, Al and Zn were successfully decorated over ZnO nanowire
[169-174]. A good control on photoluminescence and photoconductiv-
ity is observed by metal surface coating. h e metal work function plays
an important role in deciding the nature of emission spectra; enhanced/
reduced UV emissions are observed for dif erent metals. A p-type nature
has also been observed in Ti-coated nanowire and it was proposed that
Ti decoration on ZnO nanowires led to the formation of a TiOx layer,
which reveals p-type conducting performance due to the existence of
electron captured oxygen molecules [169]. Surface modii cations were
also performed by various metal oxide/semiconductors coatings; CdTe
quantum dots,
MgO nanoparticles, ZnS nanoparticles, amorphous-Si
and a-SiNx:H layer have been successfully demonstrated [175-179].
h e ZnO/CdSSe, ZnO/Al
2
O
3
, ZnO-ZnGa
2
O
4
and ZnO/ZnSe type of
core-shell structures have also been proposed to manipulate electrical
properties of ZnO nanowires [180-184]. Suppressed defect emission
and enhanced electrical conduction is observed in core-shell structures
and they also showed relatively high stable nanowire compared with
bare ZnO. h us, we can say that, various surface treatments can lead
to manipulation of the defects density, which ultimately controls the
electrical conduction in nanowire i lms.
16.6
ZnO Nanowires for Energy Conversion Devices
Our daily activities are such that household applications, transport systems
and many other industrial applications require a huge amount of energy.
h e conventional sources of energy such as fuel, coal and natural gases
are very limited and also cause pollution in the environment [185]. h e
production of various greenhouse gases is the result of consumption of
these conventional energy sources [185]. Sunlight, wind, rain, tides, waves
and geothermal heat are renewable sources of energy and can fuli ll our
need for energy; however, storage and conversion of energy in the proper
form is a major challenge [186]. Solar energy is very important and can
be stored easily in various forms by using dif erent energy conversion and
storage devices [187]. In this section of the chapter, we will look at the
application of ZnO nanowire i lms in various energy conversion devices.
Some examples are the conversion of solar energy into electrical energy by
using photovoltaic devices and conversion of solar energy to hydrogen by
using water splitting process through electrochemical cell. h ermal and
mechanical energy can also be utilized to generate electric power using
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