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Nonvolatile molecular memory with the multilevel states based on MoS2 nanochannel field effect transistor through tuning gate voltage to control molecular configurations
(2020-04-17)
Lan, Yann-Wen
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Hong, Chuan-Jie
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Chen, Po-Chun
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Lin, Yun-Yan
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Yang, Chih-Hao
A new flexible memory element is crucial for mobile and wearable electronics. A new concept for memory operation and innovative device structure with new materials is certainly required to address the bottleneck of memory applications now and in the future. We report a new nonvolatile molecular memory with a new operating mechanism based on two-dimensional (2D) material nanochannel field-effect transistors (FETs). The smallest channel length for our 2D material nanochannel FETs was approximately 30 nm. The modified molecular configuration for charge induced in the nanochannel of the MoS2 FET can be tuned by applying an up-gate voltage pulse, which can vary the channel conductance to exhibit memory states. Through controlling the amounts of triggered molecules through either different gate voltage pulses or gate duration time, multilevel states were obtained in the molecular memory. These new molecular memory transistors exhibited an erase/program ratio of more than three orders of current magnitude and high sensitivity, of a few picoamperes, at the current level. Reproducible operation and four-level states with stable retention and endurance were achieved. We believe this prototype device has potential for use in future memory devices.
Experimentally Determining the Top and Edge Contact Resistivities of Two-Step Sulfurization Nb-Doped MoS2 Films Using the Transmission Line Measurement
(2019-10-01)
Chung, Yun-Yan
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Li, Chi-Feng
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Lin, Chao-Ting
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Ho, Yen-Teng
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Chien, Chao-Hsin
This study determined the top (vertical) and edge (horizontal) resistivities of metal-MoS2 contact based on the experimental results obtained using the transmission line measurement structure. A novel two-step sulfurization scheme was conducted for forming Nb-doped MoS2 films on a sapphire substrate. The edge contact resistivity, rho(C_edge), was almost two orders of magnitude lower than the top contact resistivity, rho(C_top). Our findings highlight a simple and effective method to accurately determine the edge and top contact resistances of a metal-two-dimensional material contact.
Monolayer MoSe2 Grown by Chemical Vapor Deposition for Fast Photodetection
(2014-08-01)
Chang, Yung-Huang
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Zhang, Wenjing
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Zhu, Yihan
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Han, Yu
;
Pu, Jiang
Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.
Large-Scale Transparent Molybdenum Disulfide Plasmonic Photodetector Using Split Bull Eye Structure
(2018-10-18)
Sourav, Adhikary
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Li, Zhiwen
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Huang, Zhonghui
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Botcha, Venkata Divakar
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Hu, Cong
A high performance photodetector array on transparent substrate is highly sought after for enabling next-generation imaging technology at the visible wavelengths. 2D materials such as molybdenum disulfide (MoS2) are attractive for such application owing to its superior optoelectronic properties and transparency when scaled to atomic thinness. Here, direct growth of MoS2 on centimeter-scale transparent Al2O3 substrate is reported using a high yield and scalable chemical vapor deposition approach. This enables a large area photodetector array to be demonstrated, wherein aluminum split bull eye (SBE) plasmonic structure is integrated to achieve further performance boost due to surface plasmon resonance (SPR) effect. For a wavelength of 405 nm, the plasmonic MoS2 detector achieves an ultralow noise equivalent power of approximate to 6.2 x 10-14 W Hz(-1/2) and a high responsivity of 7.26 A W-1 at a small bias of 1.0 V, which is more than 6x larger than the reference detector due to SPR effect. Finite-difference time-domain simulation confirms a higher concentration of optical field distribution at the center of the SBE structure, which is responsible for the enhancement of photocurrent and sensitivity even at low-light condition.
Boron Doped Graphene Quantum Structure and MoS2 Nanohybrid as Anode Materials for Highly Reversible Lithium Storage
(2019-03-13)
Riyanto
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Sahroni, Imam
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Bindumadhavan, Kartick
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Chang, Pei-Yi
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Doong, Ruey-an
Herein, the boron-doped graphene quantum structure (BGQS), which contains both the advantages of 0-D graphene quantum dot and 2-D reduced graphene oxide, has been fabricated by top-down hydrothermal method and then mixed with molybdenum sulfide (MoS2) to serve as an active electrode material for the enhanced electrochemical performance of lithium ion battery. Results show that 30 wt% of BGQS/MoS2 nanohybrid delivers the superior electrochemical performance in comparison with other BGQS/MoS2 and bare components. A highly reversible capacity of 3,055 mAh g(-1) at a current density of 50mA g(-1) is achieved for the initial discharge and a high reversible capacity of 1,041 mAh g(-1) is obtained at 100mA g(-1) after 50 cycles. The improved electrochemical performance in BGQS/MoS2 nanohybrid is attributed to the well exfoliated MoS2 structures and the presence of BGQS, which can provide the vitally nano-dimensional contact for the enhanced electrochemical performance. Results obtained in this study clearly demonstrate that BGQS/MoS2 is a promising material for lithium ion battery and can open a pathway to fabricate novel 2-D nanosheeted nanocomposites for highly reversible Li storage application.
Enhanced Photocarrier Generation with Selectable Wavelengths by M-Decorated-CuInS2 Nanocrystals (M = Au and Pt) Synthesized in a Single Surfactant Process on MoS2 Bilayers
(2019-02-22)
Tang, Shin-Yi
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Medina, Henry
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Yen, Yu-Ting
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Chen, Chia-Wei
;
Yang, Tzu-Yi
A facile approach for the synthesis of Au- and Pt-decorated CuInS2 nanocrystals (CIS NCs) as sensitizer materials on the top of MoS2 bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS2 bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20-40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS2 bilayers-based photodetectors. Remarkably, by using Pt- or Au-decorated CIS NCs, the photocurrent enhancement of MoS2 photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS2-based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.
A novel hybrid artificial photosynthesis system using MoS2 embedded in carbon nanofibers as electron relay and hydrogen evolution catalyst
(2017-08-01)
Niu, Fujun
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Dong, Chung-Li
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Zhu, Changbao
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Huang, Yu-Cheng
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Wang, Miao
Inspired by photosynthesis in nature, artificial photosynthesis (AP) systems have been widely investigated in the context of energy and environmental research. Here we report a noble-metal-free AP system for visible-light-driven H-2 generation from aqueous solutions consisting of fluorescein (FL) as photosensitizer, single-layer ultrasmall MoS2 nanoplates embedded in carbon nanofibers (CNF) as electron relay and redox catalyst, and triethanolamine (TEOA) as sacrificial electron donor. This CNF-MoS2/FL system exhibits outstanding H-2 evolution performance, with an H-2 generation rate that exceeds not only both MoS2/FL (by 100%) and CNF/FL (by 1100%), but also the Pt/FL system (by 40%). The excellent photocatalytic activity of this CNF-MoS2/FL system can be ascribed to the synergistic effects of CNF and MoS2 coupling: (1) the simultaneous presence of MoS2 with its delocalized and increased Mo 4d unoccupied states and of CNF with increased graphitic characteristics enables electron transfer from FL* to MoS2 via CNF electron relay; (2) the single-layered ultrasmall MoS2 nanoplates with short effective lengths for electron transfer and high density of reactive S-edges effectively catalyze the H-2 evolution reaction (HER). The presented work successfully fabricated a highly efficient AP system for solar H-2 production from a fully aqueous solution and indicated CNF-MoS2 as a promising candidate to replace Pt for solar fuel conversion. (C) 2017 Elsevier Inc. All rights reserved.
PBTI Investigation of MoS2 n-MOSFET With Al2O3 Gate Dielectric
(2017-05-01)
Yuan, Hui-Wen
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Shen, Hui
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Li, Jun-Jie
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Shao, Jinhai
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Huang, Daming
For the first time, we report the positive bias temperature instability of the back gated multilayer MoS2 n-MOSFETs with Al2O3 gate dielectric. In the stress phase, the Id-Vg curve shifts to the positive gate bias. In the recovery phase, it shifts back to the negative gate bias. After 5000 s recovery, it completely recovers to that of the fresh device. The results indicate that the voltage shift is solely due to trapping and detrapping of the pre-existing border traps in the Al2O3 dielectric. The traps consist of fast and slow components with the capture time constants of 7 and 1.8 x 10(2) s and the emission time constants of 15 and 1.0 x 10(3) s, respectively. The results from first-order trapping and detrapping calculations are in overall agreements with 12 measured Delta Vg curves including six under stress voltages and six in the recovery phases. The energy densities for the fast and slow traps are derived to be in the order of 10(13) cm(- 2) eV(-1) above the bottom of the MoS2 conduction band.
High Mobility MoS2 Transistor with Low Schottky Barrier Contact by Using Atomic Thick h-BN as a Tunneling Layer
(2016-10-05)
Wang, Jingli
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Yao, Qian
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Huang, Chun-Wei
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Zou, Xuming
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Liao, Lei
High-performance MoS2 transistors are developed using atomic hexagonal boron nitride as a tunneling layer to reduce the Schottky barrier and achieve low contact resistance between metal and MoS2. Benefiting from the ultrathin tunneling layer within 0.6 nm, the Schottky barrier is significantly reduced from 158 to 31 meV with small tunneling resistance.
Investigation of Traps at MoS2/Al2O3 Interface in nMOSFETs by Low-Frequency Noise
(2016-04)
Yuan, Hui-Wen
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Shen, Hui
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Li, Jun-Jie
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Shao, Jinhai
;
Huang, Daming
A new method is proposed to distinguish the contributions of the low-frequency noise (LFN) from the channel and the source/drain Schottky contacts in MOS devices. The method is applied to back-gated nMOSFETs with MoS2 channel and Al2O3 gate dielectric. To avoid a possible noise signal contamination from the top MoS2 surface by oxygen or water molecules absorption, the nMOSFETs with multilayer MoS2 are fabricated, and the measurements are carried out in the vacuum. The trap density Not at the MoS2/Al2O3 interface is derived for the first time using the proposed method. It is found that the Not responsible to LFN depends strongly on the surface potential, ranging from 4 x 10(10) cm(-2) in the weak over-drive region to 5 x 10(11) cm(-2) in the strong over-drive region.

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