Research
Research Areas
Graphene Electronics
Graphene (graphite + -ene) is a mono layer of graphite arranged in a honeycomb lattice structure. Thus, thickness of graphene is only about 0.2nm ~ 0.4nm. With this amazing thin thickness, graphene has numerous greater properties than any other conventionally used materials.
The development of various methods for producing graphene has stimulated a vast amount of research in recent years because graphene has remarkable physical, thermal, and electrical properties. Furthermore, graphene is suitable for flexible electronics because of its stretchable and bendable properties. We are studying on graphene with these superior properties to alternate high cost ITO (Indium Tin Oxide) as an electrode. However, it is difficult to make uniformly flat 2D structure graphene with high conductivity. In this reason, we are trying to fabricate graphene having high conductivity in a simple method without catalysts.
-
Application to electronic devices
Growth of graphene from CVD process is one of the most widely used one because of its large-scale production. We are performing researches on organic electronics such as organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs) by employing the CVD-grown graphenes as the electrode
• Graphene is a good candidate for flexible anode material due to following several reasons.
1) Good transparency (~98%) of graphene monolayer.
2) High electron mobility : ~20,000 cm2 V-1 s-1 even at RT.
3) Extremely stronger than diamond, iron and CNT.
• Therefore, we apply the graphene layer to organic devices as the electrode.
[References]
1. Nature Photonics (2012), 6, 105
-
New process for graphene fabrication
Since the first fabrication of the isolated graphene from mechanical exfoliation of graphite crystals was found, many other methods that can produce graphene have been generated. We are trying to make graphene in a new way to earn a qualified and large-scaled one that have not discovered yet before.
We have been demonstrated new way to fabricate graphene without using CH4gases which can easily explosive. We fabricate graphene using polymer as a carbon source and capping the polymer layer with metal capping layer. we demonstrated a cost-effective, scalable and sustainable process to fabricate graphene films from polymer thin films on inert substrates under a metal capping layer.
[References]
1. J. Phys. Chem. Lett. (2011), 2, 493
2. Scientific Reports (2015), 5, 16710
-
Rapid and Scalable production of Aligned Graphene Nano Ribbon
Graphene has superior electronic, physical, and chemical properties, but its zero bandgaprestricts many of its applications in future electronics. However, the bandgapis expected to open when graphene is patterned into a narrow ribbon to confine carriers to a quasi-one-dimensional system. However, industrial applications of GNRs are still hampered by limitations to scalable fabrication and designable alignment of GNRs.
we demonstrate an innovative method of producing GNRs in large area: electro-hydrodynamic nanowire lithography (e-NW lithography). This method is fast and inexpensive, and can be used to fabricate GNRs on a large scale while designing their aligment
[References]
1. Advanced Materials (2014), 26, 3459
-
N-doping of graphene
Although graphene can be easily p-doped by various adsorbates, developing stable n-doped graphene that is very useful for practical device applications is a difficult challenge. Chemical doping is one of the most feasible methods to control the carrier type (thus the Dirac point) and concentration in graphene.
We studied the doping effect of solution-processed (4-(1,3-dimethyl-2,3-dihydro-1 H -benzoimidazol-2-yl)phenyl)dimethylamine(N-DMBI) on chemicalvapor-deposited (CVD) graphene. Strong n-type doping is confirmed by Raman
spectroscopy and the electrical transport characteristics of graphene field-effect transistors. The work function was uniform on a large scale. Stable electrical properties are observed in a device aged in air for more than one month.
[References]
1. Small (2014), 10, 1999
2. Advanced Materials (2015), 27, 9, 1619
-
P-doping of graphene
Although conventional p-type doping on graphene decreases the sheet resistance (Rsh) of graphene, the doped graphene has suffered from severe increase of Rsh in ambient conditions, which has been considered as a biggest bottleneck for practical application of graphene electrodes; furthermore, the work function (WF) of p-doped graphene is still far below the WF required for an anode in organic optoelectronics. Here, we report an extremely environmentally-stable graphene electrode doped with fluorinated acid as a chemical p-type dopant.
[References]
1. Angew. chem. Int. Ed. (2016), 55, 6197