ZnO/graphene hybrid system: optical, electrical and gas sensing properties
F. Rigoni
1,2
, C. Baratto
2,1
, R. Maiti
1
, M. Donarelli
1,2
, N. Cattabiani
1,2
, E. Comini
1,2
,
M. Ferroni
1,2
, D. Zappa
1,2
, A. Ponzoni
2
, G. Sberveglieri
1,2
and G. Faglia
1,2
1
Sensor Lab, Department of Information Engineering, University of Brescia, Italy
2
Sensor Lab,
National Research Council CNR-INO, Brescia, Italy
E-mail:
Both nanostructured metal oxides and graphene are known and widely used as suitable materials in
photovoltaics, optoelectronics and gas sensing applications.
As a wide-bandgap semiconducting metal oxide (SMOX), ZnO turns out to be an attractive candidate
for blue and UV optoelectronics. SMOX materials like n-type ZnO have been proposed for many
applications, including single-nanowire transistors, gas sensors and, once put in contact with a p-type
materials to create p-n junctions, nano-optoelectronic devices, e.g. UV LED. The gas sensing
properties of ZnO thin films are also very well known, and nanostructured ZnO, e.g. nanowires, can
enhance both the stability of the device and the gas sensing properties.
Graphene is a promising material for the fabrication of ultrasensitive and ultrafast electronic sensors
due to its large specific surface area, low electrical noise associated with its unique high crystalline
single-atom thick two-dimensional structure, and exceptionally high carrier mobility (up to 2×10
5
cm
2
V
-1
cm
-1
) at room temperature (RT). Thanks to all these exciting properties, graphene and
graphene-based hybrid systems have attracted great interest for a wide range of applications.
Chemoresistive gas sensing is one of them.
The possibility to develop nanostructured architectures based on hybrid systems composed of metal
oxide, e.g. ZnO, and graphene can provide novel functionalities or enhance sensing and optical
response to gases with respect to the bare parent compounds.
In the present work, ZnO/Graphene hybrid systems, obtained by a very easy transfer procedure, have
been tested as gas sensors upon exposure to several gases in different humidity conditions. CVD-
grown graphene on Cu foil has been transferred on SiO
2
substrate or directly on ZnO nanowires to
fabricate gas sensing devices. Furthermore, by photoluminescence (PL) and Raman spectroscopy, we
have been able to investigate how the optical properties of these hybrid materials change in different
gas atmospheres. ZnO/Graphene hybrid system shows an enhanced PL and Raman intensities of the
peaks with respect to the bare ZnO.
We have studied the sensing behavior at room temperature (RT) of the ZnO/Graphene device in the
presence of oxidizing and reducing target gases (NO
2
, NH
3
, Acetone, Ethanol, CO and H
2
) in various
relative humidity environments, under 254 nm UV light illumination and in dark conditions. Under
UV light, we have observed improved relative response during gas exposures and the recovery of the
baseline signal after gas exposure, in contrast to what happens in dark conditions.
The research leading to these results has received funding from NATO project SPS 985043
O 3
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