Chemistry Reference
In-Depth Information
which is far lower than the on/off ratio exhibited in the current switching
transistor. The enhancement of resistance tunability is strongly desired in
order to realize high-performance in atomic graphene transistors [5].
Therefore, further investigation of the gate voltage characteristics in the
graphene is required [6-10].
Here, we introduced our experiments to fabricate graphene transistor
on SiO
2
/Si substrate to investigate electric conduction under a high
electric field. An original graphene mapping method on the SiO
2
/Si
substrate and a fabrication method of gate electrode have been
introduced. We also experimentally investigated the transport properties
in the fabrication of graphene transistors with top and back gates.
2. EXPERIMENTAL
2.1.
Quick and precise judgment method for number of layers
The graphite films are prepared using the micromechanical cleavage
method
[1] from kish, HOPG, or natural graphite on a highly doped
silicon wafer with a 300-nm-thick or 90-nm-thick SiO
2
layer. On the
SiO
2
surface, thin graphite films with various thicknesses, including the
graphenes, are randomly spread around. Among the graphite films,
suitable graphene films should be efficiently selected. Monolayer
graphene is commonly judged from the color of the optical-microscope
image [1,11,12]. Precise determination of the number of layers by
Raman spectroscopy [13,14] shows that the optical-microscope method
is reliable and reproducible for an experienced observer. It is known that
a green optical filter improves visibility of thin layers in the optical
microscope observations [11,12]. Oostinga et al. successfully distinguished
between the monolayer and bilayer graphene by using the absolute green
intensity in digital images [15].
We use a charge-coupled device (CCD) mounted on an optical
microscope to obtain direct green images of graphene films. The light
detected by the CCD is separated into red, green, and blue (RGB)
components for each pixel. Each component is recorded in 256
