Browsing by Author "Wang, Sheng-Tsung"

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Ambipolar MoTe2 Transistors and Their Applications in Logic Circuits
(2014-05-28)
Lin, Yen-Fu
;
Xu, Yong
;
Wang, Sheng-Tsung
;
Li, Song-Lin
;
Yamamoto, Mahito
We report ambipolar charge transport in a-molybdenum ditelluride (MoTe2) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed. The ambipolarity of the charge transport originated from the formation of Schottky barriers at the metal/MoTe2 contacts. The Schottky barrier heights as well as the current on/off ratio could be modified by modulating the electrostatic fields of the back-gate voltage (V-bg) and drain-source voltage (V-ds). Using these ambipolar MoTe2 transistors we fabricated complementary inverters and amplifiers, demonstrating their feasibility for future digital and analog circuit applications.
Dielectrophoretic placement of quasi-zero-, one-, and two-dimensional nanomaterials into nanogap for electrical characterizations
(2012-08-01)
Lin, Yen-Fu
;
Chiu, Shao-Chien
;
Wang, Sheng-Tsung
;
Fu, Sheng-Kai
;
Chen, Chien-Hsiang
DEP is one of promising techniques for positioning nanomaterials into the desirable location for nanoelectronic applications. In contrast, the lithography technique is commonly used to make ultra-thin conducting wires and narrow gaps but, due to the limit of patterning resolution, it is not feasible to make electrical contacts on ultra-small nanomaterials for a bottom-up device fabrication. Thus, integrating the lithography and dielectrophoresis, a real bottom-up fabrication can be achieved. In this work, the device with the nanogap in between two nanofinger-electrodes is made using electron-beam lithography from top down and the ultra-small nanomaterials, such as colloidal PbSe quantum dots, polyaniline nanofibers, and reduced-graphene-oxide flakes, are placed in the nanogap by DEP from bottom up. The threshold electric field for the DEP placement of PbSe nanocrystals was roughly estimated to be about 8.3 x 104 V/cm under our experimental configuration. After the DEP process, several procedures for reducing contact resistances are attempted and measurements of intrinsic electron transport in versatile nanomaterials are performed. It is experimentally confirmed that electron transport in both PbSe nanocrystal arrays and polyaniline nanofibers agrees well with Prof. Ping Sheng's model of granular metallic conduction. In addition, electron transport in reduced-graphene-oxide flakes follows Mott's 2D variable-range-hopping model. This study illustrates an integration of the electron-beam lithography and the DEP techniques for a precise manipulation of nanomaterials into electronic circuits for characterization of intrinsic properties.
"Dielectrophoretic placement of quasi-zero-, one-, and two-dimensional nanomaterials into nanogap for electrical characterizations"
(2012-08-01)
Lin, Yen-Fu
;
Chiu, Shao-Chien
;
Wang, Sheng-Tsung
;
Fu, Sheng-Kai
;
Chen, Chien-Hsiang
"DEP is one of promising techniques for positioning nanomaterials into the desirable location for nanoelectronic applications. In contrast, the lithography technique is commonly used to make ultra-thin conducting wires and narrow gaps but, due to the limit of patterning resolution, it is not feasible to make electrical contacts on ultra-small nanomaterials for a bottom-up device fabrication. Thus, integrating the lithography and dielectrophoresis, a real bottom-up fabrication can be achieved. In this work, the device with the nanogap in between two nanofinger-electrodes is made using electron-beam lithography from top down and the ultra-small nanomaterials, such as colloidal PbSe quantum dots, polyaniline nanofibers, and reduced-graphene-oxide flakes, are placed in the nanogap by DEP from bottom up. The threshold electric field for the DEP placement of PbSe nanocrystals was roughly estimated to be about 8.3 x 104 V/cm under our experimental configuration. After the DEP process, several procedures for reducing contact resistances are attempted and measurements of intrinsic electron transport in versatile nanomaterials are performed. It is experimentally confirmed that electron transport in both PbSe nanocrystal arrays and polyaniline nanofibers agrees well with Prof. Ping Sheng's model of granular metallic conduction. In addition, electron transport in reduced-graphene-oxide flakes follows Mott's 2D variable-range-hopping model. This study illustrates an integration of the electron-beam lithography and the DEP techniques for a precise manipulation of nanomaterials into electronic circuits for characterization of intrinsic properties."
Exposure of the Hidden Anti-ferromagnetism in Paramagnetic CdSe:Mn Nanocrystals
(2015-01-01)
Zou, Shou-Jyun
;
Wang, Sheng-Tsung
;
Wu, Ming-Fan
;
Jian, Wen-Bin
;
Cheng, Shun-Jen
We present theoretical and experimental investigations of the magnetism of paramagnetic semiconductor CdSe:Mn nanocrystals and propose an efficient approach to the exposure and analysis of the underlying anti-ferromagnetic interactions between magnetic ions therein. A key advance made here is the development of an analysis method with the exploitation of group theory technique that allows us to distinguish the anti-ferromagnetic interactions between aggregative Mn2+ ions from the overall pronounced paramagnetism of magnetic-ion-doped semiconductor nanocrystals. By using the method, we clearly reveal and identify the signatures of anti-ferromagnetism from the measured temperature-dependent magnetisms and furthermore determine the average number of Mn2+ ions and the fraction of aggregative ones in the measured CdSe:Mn nanocrystals.
Probing into the metal-graphene interface by electron transport measurements
(2013-01-21)
Lin, Yen-Fu
;
Wang, Sheng-Tsung
;
Pao, Chia-Chen
;
Li, Ya-Chi
;
Lai, Cheng-Chieh
Metal-graphene contact recently attracts much attention because of its effects on the performance and the operational speed of graphene field-effect transistor. Simple two-probe graphene devices on mechanically exfoliated graphene flakes are fabricated and the temperature behavior of resistance is measured from room temperature down to liquid helium temperature for the study of electron transport in the interface. Comparing experimental data with several different transport theories, it is confirmed that the model of fluctuation-induced tunneling conduction describes precisely the electron transport and indicates the existence of a thin insulating layer in the metal-graphene interface. Through the interface probing by electron transport measurements, the way to reduce the contact resistance is suggested. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789554]