Speaker: Taishi Takenobu
Affiliation: Waseda University, Tokyo
Abstract Details: Recently, the transition metal dichalcogenide (TMDC) monolayers, such as MoS2, MoSe2 and WSe2, have attracted considerable interest because of its high carrier mobility, mechanical strength, large intrinsic bandgap and optical properties [1,2]. Although many researches have been done by mechanically exfoliated TMDC monolayers, the chemical growth of TMDC thin films that could be transferred onto other arbitrary substrates was reported, thereby providing a path forward to develop large-area CMOS electronics built onto flexible plastic and stretchable rubber substrates [2-6].
Here, we firstly demonstrate the fabrication of chemically grown MoS2 thin-film transistors (TFTs) using ion gel as elastic gate dielectrics [5]. Because these transistors revealed good performance (mobility of 60 cm2/Vs and On/Off ratio of 105), we transferred MoS2 films on flexible plastic substrates and realized excellent flexibility down to a curvature radius of 0.75 mm [5]. We also fabricated MoS2 transistors on stretchable rubber substrates and achieved high stretchability under 5% channel strain without significant degradation of the carrier mobility and on/off current ratio, which might be owing to a relaxation of ripples [6]. As the next step, we challenged to expand material variation and successfully fabricated high-performance chemically grown WSe2 transistors (mobility of 90 cm2/Vs and On/Off ratio of 107) and simple resistor-loaded inverters [4]. Finally, by the combination of MoS2 and WSe2 TFTs, we also demonstrated TMDC CMOS inverters, opening a route for atomically thin electronics on flexible and stretchable substrates. In addition, these TMDC transistors revealed ambipolarity, in which both hole and electron are mobile [4]. Very recently, using such ambipolar transport, we realized p-n junction by electrostatic carrier doping and observed diode properties under low temperature [6]. Such p-n junction also opens a route for optoelectronic devices of TMDC films.
[1] M. Chhowalla et al., Nature Chemistry 5, 263 (2013).[2] Q. H. Wang et al., Nature Nanotechnology 7, 699 (2012).[3] K. K. Liu, L.-J. Li et al., Nano Letters 12, 1538 (2012).[4] J.-K. Huang, J. Pu, T. Takenobu, L.-J. Li et al., arXiv:1304.7365.[5] J. Pu, L.-J. Li, T. Takenobu et al., Nano Letters 12, 4013 (2012).[6] J. Pu, L.-J. Li, T. Takenobu et al., Applied Physics Letters, 023505 (2013).[7] Y. J. Zhang, T. Takenobu, Y. Iwasa et al., Nano Letters 13, 3023 (2013).
About the Speaker: Taishi Takenobu received his Ph.D. (materials science) from Japan Advanced Institute of Science and Technology (JAIST) in 2001 under the direction of Professor Yoshihiro Iwasa. Since April 2001, he has worked in SONY corporation. From December 2001, as an assistant professor of Institute for Materials Research, Tohoku University. And, from 2007-2010, he was an associate professor of Institute for Materials Research, Tohoku University. He also held various visiting positions, including Delft University of Technology (the Netherlands), University of Sussex (England), Nanyang Technological University (Singapore), Kyoto University (Japan) and Institute for Molecular Science (Japan). From April 2010, he is an associate professor of Department of Applied Physics, Waseda University, and, from 2013, he is currently professor of Waseda University. His current research interests include (1) novel functionalities in two-dimensional materials, (2) realization of electrical driven organic laser devise based on single-crystal ambipolar transistor, and (3) flexible and ink-jet printable electronics based on single-walled carbon nanotube film transistor.
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