Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation
Nanoscale Research Letters
Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation
Nurul Fariha Ahmad 0
Nurul Izni Rusli 3
Mohamad Rusop Mahmood 2
Kanji Yasui 4
Abdul Manaf Hashim 0 1
0 Malaysia-Japan International Institute of Technology , Universiti Teknologi Malaysia, Jalan Semarak, Kuala Lumpur 54100 , Malaysia
1 MIMOS Berhad, Technology Park Malaysia , Kuala Lumpur 57000 , Malaysia
2 Faculty of Electrical Engineering , Universiti Teknologi MARA, Shah Alam, Selangor 40450 , Malaysia
3 School of Electrical System Engineering , Universiti Malaysia Perlis, Kuala Perlis, Perlis 02000 , Malaysia
4 Department of Electrical Engineering, Nagaoka University of Technology , Kamitomioka-machi, Nagaoka, Niigata 940-2137 , Japan
We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O2 gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics.
Graphene; Thermal evaporation; Zinc oxide; Nanostructure; Hybrid integration
Background
In recent years, strong attentions have been paid in the
growth of semiconductor nanostructures on graphene
[
1-5
] for electronic and optoelectronic applications.
Nanostructures such as nanowires, nanorods, nanoneedles,
nanosheets, and nanowalls can offer additional
functionality to graphene for realizing advanced nanoscale
applications in photovoltaics, nanogenerators, field
emission devices, sensitive biological and chemical sensors,
and efficient energy conversion and storage devices [
6-8
].
This is due to the superb properties of nanostructures
such as high aspect ratio, extremely large
surface-tovolume ratio, and high porosity [
6-10
]. Graphene has a
great potential for novel electronic devices because of its
extraordinary electrical, thermal, and mechanical
properties, including carrier mobility exceeding 104 cm2/Vs and
a thermal conductivity of 103 W/mK [
11-14
]. Therefore,
with the excellent electrical and thermal characteristics of
graphene layers, growing semiconductor nanostructures
on graphene layers would enable their novel physical
properties to be exploited in diverse sophisticated device
applications. Graphene is a 2D hexagonal network of
carbon atoms which is formed by making strong
triangular σ-bonds of the sp2 hybridized orbitals. This
bonding structure is similar to the (111) plane of
zincblende structure and C plane of a hexagonal crystalline
structure. With this regard, the growth of
semiconductor nanostructures and thin films on graphene is
feasible. Recently, there are several works on the growth
and application of graphene/semiconductor nanocrystals
that show desirable combinations of these properties not
found in the individual components [
15-20
].
The 1D zinc oxide (ZnO) semiconducting
nanostructures are considered to be important multifunctional
building blocks for fabricating various nanodevices [
21,22
].
Since graphene is an excellent conductor and transparent
material, the hybrid structure of ZnO/graphene shall lead
to several device applications not only on Si substrate but
also on other insulating substrates such as transparent
glass and transparent flexible plastic. Owing to the unique
electronic and optical properties of ZnO nanostructures,
such hybrid structure can be used for sensing devices
[
23-25
], UV photodetector [26], solar cells [
27
], and
lightemitting diodes [
28
]. ZnO nanostructures have been
synthesized by various physical and chemical growth
techniques [
23
]. These techniques include thermal
evaporation [
5,29
], hydrothermal [
2,3
] and electrochemical
deposition [
4
], and metal-organic vapor-phase epitaxy (MOVPE)
[
1
]. In this paper, we report the seed/catalyst-free growth of
ZnO structures on multilayer (ML) graphene by thermal
evaporation. The dependence of substrate temperatures on
the properties of grown structures was studied. Based on
the obtained results, a growth mechanism was proposed.
Methods
A ML graphene on SiO2/Si (Graphene Laboratories Inc,
Calverton, NY, USA) was used as a substrate. Figure 1a
shows the measured Raman spectra of the ML graphene.
The 2D peaks at approximately 2,700 cm−1 of the Raman
spectra for graphite as shown by locations 1 and 4 have
broader and up-shifted 2D band indicating few layer
graphene [
30
]. Figure 1b shows the schematic of the
experimental setup. The growth was carried out by
thermal evaporation technique in dual zone furnace.
High-purity metallic Zn powder (99.85%) and oxygen
(O2) gas (...truncated)