Large-area synthesis of monolayered MoS(2(1-x))Se(2x) with a tunable band gap and its enhanced electrochemical catalytic activity.

PubMed

Yang, Lei; Fu, Qi; Wang, Wenhui; Huang, Jian; Huang, Jianliu; Zhang, Jingyu; Xiang, Bin

2015-06-21

"Band gap engineering" in two-dimensional (2D) materials plays an important role in tailoring their physical and chemical properties. The tuning of the band gap is typically achieved by controlling the composition of the semiconductor alloys. However, large-area preparation of 2D alloys remains a major challenge. Here, we report the large-area synthesis of high-quality monolayered MoS2(1-x)Se2x with a size coverage of hundreds of microns using a chemical vapor deposition method. The photoluminescence (PL) spectroscopy results confirm the tunable band gap in MoS2(1-x)Se2x, which is modulated by varying the Se content. Atomic-scale analysis was performed and the chemical composition was characterized using high-resolution scanning transmission electron microscopy and X-ray photoemission spectroscopy. With the introduction of Se into monolayered MoS2, it leads to enhanced catalytic activity in an electrochemical reaction for hydrogen generation, compared to monolayered MoS2 and MoSe2. It is promising as a potential alternative to expensive noble metals.

Uniform large-area growth of nanotemplated high-quality monolayer MoS2

NASA Astrophysics Data System (ADS)

Young, Justin R.; Chilcote, Michael; Barone, Matthew; Xu, Jinsong; Katoch, Jyoti; Luo, Yunqiu Kelly; Mueller, Sara; Asel, Thaddeus J.; Fullerton-Shirey, Susan K.; Kawakami, Roland; Gupta, Jay A.; Brillson, Leonard J.; Johnston-Halperin, Ezekiel

2017-06-01

Over the past decade, it has become apparent that the extreme sensitivity of 2D crystals to surface interactions presents a unique opportunity to tune material properties through surface functionalization and the mechanical assembly of 2D heterostructures. However, this opportunity carries with it a concurrent challenge: an enhanced sensitivity to surface contamination introduced by standard patterning techniques that is exacerbated by the difficulty in cleaning these atomically thin materials. Here, we report a templated MoS2 growth technique wherein Mo is deposited onto atomically stepped sapphire substrates through a SiN stencil with feature sizes down to 100 nm and subsequently sulfurized at high temperature. These films have a quality comparable to the best MoS2 prepared by other methodologies, and the thickness of the resulting MoS2 patterns can be tuned layer-by-layer by controlling the initial Mo deposition. The quality and thickness of the films are confirmed by scanning electron, scanning tunneling, and atomic force microscopies; Raman, photoluminescence, and x-ray photoelectron spectroscopies; and electron transport measurements. This approach critically enables the creation of patterned, single-layer MoS2 films with pristine surfaces suitable for subsequent modification via functionalization and mechanical stacking. Further, we anticipate that this growth technique should be broadly applicable within the family of transition metal dichalcogenides.

Inkjet printing ultra-large graphene oxide flakes

NASA Astrophysics Data System (ADS)

He, Pei; Derby, Brian

2017-06-01

Graphene oxide 2D materials inks with mean flake diameter 36 µm can be inkjet printed, with no significant blockage of the printer or apparent damage to the flakes, despite the mean flake size being  >50% of the printer nozzle diameter and the ink containing individual flakes considerably larger than the nozzle. Printed flakes show a similar level of wrinkle and fold defects as observed in flakes deposited by drop casting. Polarised light imaging of the ink in the printhead prior to printing shows alignment of the flakes in the shear flow and this is believed to allow passage without agglomeration or blocking of the nozzle. The bulk electrical conductivity of these ultra-large flake printed films is 2.48  ×  104 Sm-1 after reduction, which is comparable to that reported with printed pristine graphene. The conductivity of the printed films increases slightly with increasing flake size indicating that there is no increase in damage to electrical properties as the flakes approach and exceed the nozzle diameter.

Inversion layer MOS solar cells

NASA Technical Reports Server (NTRS)

Ho, Fat Duen

1986-01-01

Inversion layer (IL) Metal Oxide Semiconductor (MOS) solar cells were fabricated. The fabrication technique and problems are discussed. A plan for modeling IL cells is presented. Future work in this area is addressed.

Surface structure of bulk 2H-MoS2(0001) and exfoliated suspended monolayer MoS2: A selected area low energy electron diffraction study

NASA Astrophysics Data System (ADS)

Dai, Zhongwei; Jin, Wencan; Grady, Maxwell; Sadowski, Jerzy T.; Dadap, Jerry I.; Osgood, Richard M.; Pohl, Karsten

2017-06-01

We have used selected area low energy electron diffraction intensity-voltage (μLEED-IV) analysis to investigate the surface structure of crystalline 2H molybdenum disulfide (MoS2) and mechanically exfoliated and suspended monolayer MoS2. Our results show that the surface structure of bulk 2H-MoS2 is distinct from its bulk and that it has a slightly smaller surface relaxation at 320 K than previously reported at 95 K. We concluded that suspended monolayer MoS2 shows a large interlayer relaxation compared to the MoS2 sandwich layer terminating the bulk surface. The Debye temperature of MoS2 was concluded to be about 600 K, which agrees with a previous theoretical study. Our work has shown that the dynamical μLEED-IV analysis performed with a low energy electron microscope (LEEM) is a powerful technique for determination of the local atomic structures of currently extensively studied two-dimensional (2-D) materials.

Surface structure of bulk 2H-MoS 2 (0001) and exfoliated suspended monolayer MoS 2 : A selected area low energy electron diffraction study

DOE PAGES

Dai, Zhongwei; Jin, Wencan; Grady, Maxwell; ...

2017-02-10

Here, we used selected area low energy electron diffraction intensity-voltage (μLEED-IV) analysis to investigate the surface structure of crystalline 2H molybdenum disulfide (MoS 2) and mechanically exfoliated and suspended monolayer MoS 2. Our results show that the surface structure of bulk 2H-MoS 2 is distinct from its bulk and that it has a slightly smaller surface relaxation at 320 K than previously reported at 95 K. We concluded that suspended monolayer MoS 2 shows a large interlayer relaxation compared to the MoS 2 sandwich layer terminating the bulk surface. The Debye temperature of MoS 2 was concluded to be aboutmore » 600 K, which agrees with a previous theoretical study. Our work has shown that the dynamical μLEED-IV analysis performed with a low energy electron microscope (LEEM) is a powerful technique for determination of the local atomic structures of currently extensively studied two-dimensional (2-D) materials.« less

Synthesis of Epitaxial Single-Layer MoS2 on Au(111).

PubMed

Grønborg, Signe S; Ulstrup, Søren; Bianchi, Marco; Dendzik, Maciej; Sanders, Charlotte E; Lauritsen, Jeppe V; Hofmann, Philip; Miwa, Jill A

2015-09-08

We present a method for synthesizing large area epitaxial single-layer MoS2 on the Au(111) surface in ultrahigh vacuum. Using scanning tunneling microscopy and low energy electron diffraction, the evolution of the growth is followed from nanoscale single-layer MoS2 islands to a continuous MoS2 layer. An exceptionally good control over the MoS2 coverage is maintained using an approach based on cycles of Mo evaporation and sulfurization to first nucleate the MoS2 nanoislands and then gradually increase their size. During this growth process the native herringbone reconstruction of Au(111) is lifted as shown by low energy electron diffraction measurements. Within the MoS2 islands, we identify domains rotated by 60° that lead to atomically sharp line defects at domain boundaries. As the MoS2 coverage approaches the limit of a complete single layer, the formation of bilayer MoS2 islands is initiated. Angle-resolved photoemission spectroscopy measurements of both single and bilayer MoS2 samples show a dramatic change in their band structure around the center of the Brillouin zone. Brief exposure to air after removing the MoS2 layer from vacuum is not found to affect its quality.

Highly Enhanced Gas Adsorption Properties in Vertically Aligned MoS2 Layers.

PubMed

Cho, Soo-Yeon; Kim, Seon Joon; Lee, Youhan; Kim, Jong-Seon; Jung, Woo-Bin; Yoo, Hae-Wook; Kim, Jihan; Jung, Hee-Tae

2015-09-22

In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS2 compared to that of the conventional basal plane exposed MoS2 films. To compare the effect of the alignment of MoS2 on the gas adsorption properties, we synthesized three distinct MoS2 films with different alignment directions ((1) horizontally aligned MoS2 (basal plane exposed), (2) mixture of horizontally aligned MoS2 and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS2 (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS2 film shows about 5-fold enhanced sensitivity to NO2 gas molecules compared to horizontally aligned MoS2 film. Vertically aligned MoS2 has superior resistance variation compared to horizontally aligned MoS2 even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO2 binding energies are computed for multiple configurations near the edge sites of MoS2, which verifies that electrical response to target gas molecules (NO2) correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. We believe that this observation extends to other 2D TMD materials as well as MoS2 and can be applied to significantly enhance the gas sensor performance in these materials.

Combined photothermal and photodynamic therapy delivered by PEGylated MoS2 nanosheets

NASA Astrophysics Data System (ADS)

Liu, Teng; Wang, Chao; Cui, Wei; Gong, Hua; Liang, Chao; Shi, Xiaoze; Li, Zhiwei; Sun, Baoquan; Liu, Zhuang

2014-09-01

Single- or few-layered transitional metal dichalcogenides, as a new genus of two-dimensional nanomaterials, have attracted tremendous attention in recent years, owing to their various intriguing properties. In this study, chemically exfoliated MoS2 nanosheets are modified with lipoic acid-terminated polyethylene glycol (LA-PEG), obtaining PEGylated MoS2 (MoS2-PEG) with high stability in physiological solutions and no obvious toxicity. Taking advantage of its ultra-high surface area, the obtained MoS2-PEG is able to load a photodynamic agent, chlorin e6 (Ce6), by physical adsorption. In vitro experiments reveal that Ce6 after being loaded on MoS2-PEG shows remarkably increased cellular uptake and thus significantly enhanced photodynamic therapeutic efficiency. Utilizing the strong, near-infrared (NIR) absorbance of the MoS2 nanosheets, we further demonstrate photothermally enhanced photodynamic therapy using Ce6-loaded MoS2-PEG for synergistic cancer killing, in both in vitro cellular and in vivo animal experiments. Our study presents a new type of multifunctional nanocarrier for the delivery of photodynamic therapy, which, if combined with photothermal therapy, appears to be an effective therapeutic approach for cancer treatment.Single- or few-layered transitional metal dichalcogenides, as a new genus of two-dimensional nanomaterials, have attracted tremendous attention in recent years, owing to their various intriguing properties. In this study, chemically exfoliated MoS2 nanosheets are modified with lipoic acid-terminated polyethylene glycol (LA-PEG), obtaining PEGylated MoS2 (MoS2-PEG) with high stability in physiological solutions and no obvious toxicity. Taking advantage of its ultra-high surface area, the obtained MoS2-PEG is able to load a photodynamic agent, chlorin e6 (Ce6), by physical adsorption. In vitro experiments reveal that Ce6 after being loaded on MoS2-PEG shows remarkably increased cellular uptake and thus significantly enhanced photodynamic

Development of a measurement technique for qualitative analysis of MOS transistors using Kuhn's method for MOS varactors

NASA Astrophysics Data System (ADS)

Krautschneider, W.

The semiconductor junction region up to the oxidized surface layer is studied. The object of study is a MOS capacitor, but it is shown that the obtained values of the surface characteristics apply to more complicated MOS transistors. The metal oxide-silicon system is discussed in terms of an ideal varactor, the actual MOS structure, and the MOS system with p-n junction. The determination of the phase interface state density in MOS varactors and MOS transistors is addressed, as the quasistatic C(V) experiment of Kuhn (1970) is theoretically and experimentally extended from MOS varactors to MOS transistors. The surface recombination speed is treated, and the experimental results are compared with theoretical predictions.

Dispersive growth and laser-induced rippling of large-area singlelayer MoS2 nanosheets by CVD on c-plane sapphire substrate

PubMed Central

Liu, Hongfei; Chi, Dongzhi

2015-01-01

Vapor-phase growth of large-area two-dimensional (2D) MoS2 nanosheets via reactions of sulfur with MoO3 precursors vaporized and transferred from powder sources onto a target substrate has been rapidly progressing. Recent studies revealed that the growth yield of high quality singlelayer (SL) MoS2 is essentially controlled by quite a few parameters including the temperature, the pressure, the amount/weight of loaded source precursors, and the cleanup of old precursors. Here, we report a dispersive growth method where a shadow mask is encapsulated on the substrate to ‘indirectly’ supply the source precursors onto the laterally advancing growth front at elevated temperatures. With this method, we have grown large-area (up to millimeters) SL-MoS2 nanosheets with a collective in-plane orientation on c-plane sapphire substrates. Regular ripples (~1 nm in height and ~50 nm in period) have been induced by laser scanning into the SL-MoS2 nanosheets. The MoS2 ripples easily initiate at the grain boundaries and extend along the atomic steps of the substrate. Such laser-induced ripple structures can be fundamental materials for studying their effects, which have been predicted to be significant but hitherto not evidenced, on the electronic, mechanical, and transport properties of SL-MoS2. PMID:26119325

One-step fabrication of large-area ultrathin MoS2 nanofilms with high catalytic activity for photovoltaic devices.

PubMed

Liang, Jia; Li, Jia; Zhu, Hongfei; Han, Yuxiang; Wang, Yanrong; Wang, Caixing; Jin, Zhong; Zhang, Gengmin; Liu, Jie

2016-09-21

Here we report a facile one-step solution-phase process to directly grow ultrathin MoS2 nanofilms on a transparent conductive glass as a novel high-performance counter electrode for dye-sensitized solar cells. After an appropriate reaction time, the entire surface of the conductive glass substrate was uniformly covered by ultrathin MoS2 nanofilms with a thickness of only several stacked layers. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that the MoS2 nanofilms possess excellent catalytic activity towards tri-iodide reduction. When used in dye-sensitized solar cells, the MoS2 nanofilms show an impressive energy conversion efficiency of 8.3%, which is higher than that of a Pt-based electrode and very promising to be a desirable alternative counter electrode. Considering their ultrathin thickness, superior catalytic activity, simple preparation process and low cost, the as-prepared MoS2 nanofilms with high photovoltaic performance are expected to be widely employed in dye-sensitized solar cells.

Polarization-dependent optical absorption of MoS2 for refractive index sensing

PubMed Central

Tan, Yang; He, Ruiyun; Cheng, Chen; Wang, Dong; Chen, Yanxue; Chen, Feng

2014-01-01

As a noncentrosymmetric crystal with spin-polarized band structure, MoS2 nanomaterials have attracts increasing attention in many areas such as lithium ion batteries, flexible electronic devices, photoluminescence and valleytronics. The investigation of MoS2 is mainly focused on the electronics and spintronics instead of optics, which restrict its applications as key elements of photonics. In this work, we demonstrate the first observation of the polarization-dependent optical absorption of the MoS2 thin film, which is integrated onto an optical waveguide device. With this feature, a novel optical sensor combining MoS2 thin-film and a microfluidic structure has been constituted to achieve the sensitive monitoring of refractive index. Our work indicates the MoS2 thin film as a complementary material to graphene for the optical polarizer in the visible light range, and explores a new application direction of MoS2 nanomaterials for the construction of photonic circuits. PMID:25516116

Weight ratio effects on morphology and electrocapacitive performance for the MoS2/polypyrrole electrodes

NASA Astrophysics Data System (ADS)

Tu, Chao-Chi; Peng, Pei-Wen; Lin, Lu-Yin

2018-06-01

MoS2 is one of the promising electroactive materials for charge-storage devices. The charges cannot only be stored in the intersheet of MoS2 and the intrasheet of individual atomic layers, but also can be accumulated by conducting the Faradaic reactions on the Mo center. To further enhance the electrocapacitive performance of MoS2, incorporating conducting polymers is one of the feasible ways to improve the connection between MoS2 nanosheets. At the same time, the growth of conducting polymers can also be controlled via incorporating MoS2 nanosheets in the synthesis to enhance the conductivity and increase the specific surface area of the conducting polymers. In this work, layered structures of MoS2 nanosheets are successfully synthesized via a simple hydrothermal method, and pyrrole monomers are oxidative polymerized in the MoS2 solution to prepare the nanocomposites with different ratios of MoS2 and polypyrrole (Ppy). The optimized MoS2/Ppy electrode shows a specific capacitance (CF) of 182.28 F/g, which is higher than those of the MoS2 (40.58 F/g) and Ppy (116.95 F/g) electrodes measured at the same scan rate of 10 mV/s. The excellent high-rate capacity and good cycling stability with 20% decay on the CF value comparing to the initial value after the 1000 times repeated charge/discharge process are also achieved for the optimized MoS2/Ppy electrode. The better performance for the MoS2/Ppy electrode is resulting from the larger surface area for charge accumulation and the enhanced interconnection networks for charge transportation. The results suggest that combining two materials with complementary properties as the electrocapacitive material is one of the attractive ways to realize efficient charge-storage devices with efficient electrochemical performances and good cycling lifes.

Plasma-assisted synthesis of MoS2

NASA Astrophysics Data System (ADS)

Campbell, Philip M.; Perini, Christopher J.; Chiu, Johannes; Gupta, Atul; Ray, Hunter S.; Chen, Hang; Wenzel, Kevin; Snyder, Eric; Wagner, Brent K.; Ready, Jud; Vogel, Eric M.

2018-03-01

There has been significant interest in transition metal dichalcogenides (TMDs), including MoS2, in recent years due to their potential application in novel electronic and optical devices. While synthesis methods have been developed for large-area films of MoS2, many of these techniques require synthesis temperatures of 800 °C or higher. As a result of the thermal budget, direct synthesis requiring high temperatures is incompatible with many integrated circuit processes as well as flexible substrates. This work explores several methods of plasma-assisted synthesis of MoS2 as a way to lower the synthesis temperature. The first approach used is conversion of a naturally oxidized molybdenum thin film to MoS2 using H2S plasma. Conversion is demonstrated at temperatures as low as 400 °C, and the conversion is enabled by hydrogen radicals which reduce the oxidized molybdenum films. The second method is a vapor phase reaction incorporating thermally evaporated MoO3 exposed to a direct H2S plasma, similar to chemical vapor deposition (CVD) synthesis of MoS2. Synthesis at 400 °C results in formation of super-stoichiometric MoS2 in a beam-interrupted growth process. A final growth method relies on a cyclical process in which a small amount of Mo is sputtered onto the substrate and is subsequently sulfurized in a H2S plasma. Similar results could be realized using an atomic layer deposition (ALD) process to deposit the Mo film. Compared to high temperature synthesis methods, the lower temperature samples are lower quality, potentially due to poor crystallinity or higher defect density in the films. Temperature-dependent conductivity measurements are consistent with hopping conduction in the plasma-assisted synthetic MoS2, suggesting a high degree of disorder in the low-temperature films. Optimization of the plasma-assisted synthesis process for slower growth rate and better stoichiometry is expected to lead to high quality films at low growth temperature.

Photo-Sensitivity of Large Area Physical Vapor Deposited Mono and Bilayer MoS2 (Postprint)

DTIC Science & Technology

2014-07-01

layer MoS2 without any apparent rectifying junctions , making device fabrication straightforward. For bi-layers, no such effect was present, suggesting...layer MoS2 without any apparent rectifying junctions , making device fabrication straightforward. For bi-layers, no such effect was present, suggesting...pressure below 5×10−9 Torr for atomically sharp and clean interfaces. The mono and bi-layer specimens were grown on 100 nm thick thermal oxide coated silicon

Preparation and tribological properties of MoS2/graphene oxide composites

NASA Astrophysics Data System (ADS)

Song, Haojie; Wang, Biao; Zhou, Qiang; Xiao, Jiaxuan; Jia, Xiaohua

2017-10-01

A hydrothermal route is developed for the synthesis of MoS2/graphene oxide (GO) composites based on the hydrothermal reduction of Na2MoO4 and GO sheets with L-cysteine. The MoS2/GO composites in improving friction and wear of the sunshine oil on sliding steel surfaces under low or high applied load were demonstrated. In tests with sliding steel surfaces, the sunshine oil that contains small amounts of MoS2/GO composites exhibited the lowest specific friction coefficient and wear rate under all of the sliding conditions. Scanning electron microscopy and energy dispersive spectrometer performed to analyze the wear scar surfaces after friction confirmed that the outstanding lubrication performance of MoS2/GO composites could be attributed to their good dispersion stability and extremely thin laminated structure, which allow the MoS2/GO composites to easily enter the contact area, thereby preventing the rough surfaces from coming into direct contact.

Synthesis of MoS2/rGO nanosheets hybrid materials for enhanced visible light assisted photocatalytic activity

NASA Astrophysics Data System (ADS)

Pal, Shreyasi; Dutta, Shibsankar; De, Sukanta

2018-04-01

A facile hydrothermal method has been adopted to synthesize pure MoS2 nanosheets and MoS2/rGO nanosheets hybrid. The samples were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (HRTEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmett-Teller (BET). The photocatalytic performance and reusability of MoS2 nanosheets and MoS2/rGO hybrids was evaluated by discoloring of RhB under visible light irradiation. Results indicated that MoS2/rGO photocatalysts with large surface area of 69.5 m2 g-1 could completely degrade 50 mL of 8 mg L-1 RhB aqueous solution in 90 min with excellent recycling and structural stability as compared with pure MoS2 nanosheets (53%). Such enhanced performance could be explained due to the high surface area, enhanced light absorption and the increased dye adsorptivity and reduced electron-hole pair recombination with the presence of rGO.

Synthesis, characterization and photocatalytic performance of chemically exfoliated MoS2

NASA Astrophysics Data System (ADS)

Prabhakar Vattikuti, S. V.; Shim, Jaesool

2018-03-01

Two-dimensional (2D) layered structure transition metal dichalcogenides (TMDs) has gained huge attention and importance for photocatalytic energy conversion because of their unique properties. Molybdenum disulfide (MoS2) nanosheets were synthesized via one-pot method and exfoliated in (dimethylformamide) DMF solution. Subsequent exfoliated MoS2 nanosheets (e-MoS2) were used as photocatalysts for degradation of Rhodamine B (RhB) pollutant under solar light irradiation. The e-MoS2 nanosheets exhibited excellent photocatalytic activity than that of pristine MoS2, owing to high specific surface area with enormous active sites and light absorption capacity. In addition, e-MoS2 demonstrated remarkable photocatalytic stability.

Wafer-scale synthesis of monolayer and few-layer MoS2 via thermal vapor sulfurization

NASA Astrophysics Data System (ADS)

Robertson, John; Liu, Xue; Yue, Chunlei; Escarra, Matthew; Wei, Jiang

2017-12-01

Monolayer molybdenum disulfide (MoS2) is an atomically thin, direct bandgap semiconductor crystal potentially capable of miniaturizing optoelectronic devices to an atomic scale. However, the development of 2D MoS2-based optoelectronic devices depends upon the existence of a high optical quality and large-area monolayer MoS2 synthesis technique. To address this need, we present a thermal vapor sulfurization (TVS) technique that uses powder MoS2 as a sulfur vapor source. The technique reduces and stabilizes the flow of sulfur vapor, enabling monolayer wafer-scale MoS2 growth. MoS2 thickness is also controlled with great precision; we demonstrate the ability to synthesize MoS2 sheets between 1 and 4 layers thick, while also showing the ability to create films with average thickness intermediate between integer layer numbers. The films exhibit wafer-scale coverage and uniformity, with electrical quality varying depending on the final thickness of the grown MoS2. The direct bandgap of grown monolayer MoS2 is analyzed using internal and external photoluminescence quantum efficiency. The photoluminescence quantum efficiency is shown to be competitive with untreated exfoliated MoS2 monolayer crystals. The ability to consistently grow wafer-scale monolayer MoS2 with high optical quality makes this technique a valuable tool for the development of 2D optoelectronic devices such as photovoltaics, detectors, and light emitters.

New results of ground target based calibration of MOS on IRS

NASA Astrophysics Data System (ADS)

Schwarzer, Horst H.; Franz, Bryan A.; Neumann, Andreas; Suemnich, Karl-Heinz; Walzel, Thomas; Zimmermann, Gerhard

2002-09-01

The success of the Modular Optoelectronic Scanner MOS on the Indian Remote Sensing Satellite IRS-P3 during the 6 years mission time has been based on its sophisticated in-orbit calibration concept to a large extent. When the internal lamp and the sun calibration failed in September 2000 we tested the possibility of ground target based (or vicarious) calibration of the MOS instruments to continue the high data quality. This is essential for future watching of global changes of the ocean coastal zones (phytoplancton, sediments, pollution, etc.) using spectral measurements of the VIS/NIR MOS spectral channels. The investigations have shown the suitability of a part of the Great Eastern Erg in the Sahara desert for this purpose. The satellite crosses this very homogeneous area every 24 days. Because of the good cloudfree conditions we can use 6 - 8 overflys a year for calibration. The seasonal variability of the surface reflectance is very small so that we obtain relative calibration data of sufficient accuracy even without ground truth measurements for most of the channels. The trend of this "vicarious" calibration corresponds very well with the previous trend of the failed lamp and sun calibration. Dfferences between the three methods will be discussed. In the paper we will also present the results of a comparison between SeaWiFS and MOS data of comparable spectral channels from the Great Eastern Erg area. They confirm the suitability of this area for calibration purposes too.

Further study of inversion layer MOS solar cells

NASA Technical Reports Server (NTRS)

Ho, Fat Duen

1987-01-01

A group of inversion layer MOS solar cells has been fabricated. The highest value of open-circuit voltage obtained for the cells is 0.568V. One of the cells has produced a short-circuit current of 79.6 mA and an open-circuit voltage of 0.54V. It is estimated that the actual area AMO efficiency of this cell is 6.6 percent with an assumed value of 0.75 for its fill factor. Efforts made for fabricating an IL/MOS cell with reasonable efficiencies are reported. Future work for 4 sq cm IL cells and 25 sq cm IL cells is discussed.

Planarized thick copper gate polycrystalline silicon thin film transistors for ultra-large AMOLED displays

NASA Astrophysics Data System (ADS)

Yun, Seung Jae; Lee, Yong Woo; Son, Se Wan; Byun, Chang Woo; Reddy, A. Mallikarjuna; Joo, Seung Ki

2012-08-01

A planarized thick copper (Cu) gate low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) is fabricated for ultra-large active-matrix organic light-emitting diode (AMOLED) displays. We introduce a damascene and chemical mechanical polishing process to embed a planarized Cu gate of 500 nm thickness into a trench and Si3N4/SiO2 multilayer gate insulator, to prevent the Cu gate from diffusing into the silicon (Si) layer at 550°C, and metal-induced lateral crystallization (MILC) technology to crystallize the amorphous Si layer. A poly-Si TFT with planarized thick Cu gate exhibits a field effect mobility of 5 cm2/Vs and a threshold voltage of -9 V, and a subthreshold swing (S) of 1.4 V/dec.

Transistors and tunnel diodes enabled by large-scale MoS2 nanosheets grown on GaN

NASA Astrophysics Data System (ADS)

San Yip, Pak; Zou, Xinbo; Cho, Wai Ching; Wu, Kam Lam; Lau, Kei May

2017-07-01

We report growth, fabrication, and device results of MoS2-based transistors and diodes implemented on a single 2D/3D material platform. The 2D/3D platform consists of a large-area MoS2 thin film grown on SiO2/p-GaN substrates. Atomic force microscopy, scanning electron microscopy, and Raman spectroscopy were used to characterize the thickness and quality of the as-grown MoS2 film, showing that the large-area MoS2 nanosheet has a smooth surface morphology constituted by small grains. Starting from the same material, both top-gated MoS2 field effect transistors and MoS2/SiO2/p-GaN heterojunction diodes were fabricated. The transistors exhibited a high on/off ratio of 105, a subthreshold swing of 74 mV dec-1, field effect mobility of 0.17 cm2 V-1 s-1, and distinctive current saturation characteristics. For the heterojunction diodes, current-rectifying characteristics were demonstrated with on-state current density of 29 A cm-2 and a current blocking property up to -25 V without breakdown. The reported transistors and diodes enabled by the same 2D/3D material stack present promising building blocks for constructing future nanoscale electronics.

The formation of Colloidal 2D/3D MoS2 Nanostructures in Organic Liquid Environment

NASA Astrophysics Data System (ADS)

Durgun, Engin; Sen, H. Sener; Oztas, Tugba; Ortac, Bulend

2015-03-01

2D MoS2 nanosheets (2D MoS2 NS) and fullerene-like MoS2 nanostructures (3D MoS2 NS) with varying sizes are synthesized by nanosecond laser ablation of hexagonal crystalline 2H-MoS2 powder in methanol. Structural, chemical, and optical properties of MoS2 NS are characterized by optical microscopy, SEM, TEM, XRD, Raman and UV/VIS/NIR absorption spectroscopy techniques. Results of structural analysis show that the obtained MoS2 NS mainly present layered morphology from micron to nanometer surface area. Detailed analysis of the product also proves the existence of inorganic polyhedral fullerene-like 3D MoS2 NS generated by pulsed laser ablation in methanol. The possible factors which may lead to formation of both 2D and 3D MoS2 NS in methanol are examined by ab initio calculations and shown that it is correlated with vacancy formation. The hexagonal crystalline structure of MoS2 NS was determined by XRD analysis. The colloidal MoS2 NS solution presents broadband absorption edge tailoring from UV region to NIR region. Investigations of MoS2 NS show that the one step physical process of pulsed laser ablation-bulk MoS2 powder interaction in organic solution opens doors to the formation of ``two scales'' micron- and nanometer-sized layered and fullerene-like morphology MoS2 structures. This work was partially supported by TUBITAK under the Project No. 113T050 and Bilim Akademisi - The Science Academy, Turkey under the BAGEP program.

Highly sensitive MoS2 photodetectors with graphene contacts.

PubMed

Han, Peize; St Marie, Luke; Wang, Qing X; Quirk, Nicholas; El Fatimy, Abdel; Ishigami, Masahiro; Barbara, Paola

2018-05-18

Two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) are ideal candidates to create ultra-thin electronics suitable for flexible substrates. Although optoelectronic devices based on TMDs have demonstrated remarkable performance, scalability is still a significant issue. Most devices are created using techniques that are not suitable for mass production, such as mechanical exfoliation of monolayer flakes and patterning by electron-beam lithography. Here we show that large-area MoS 2 grown by chemical vapor deposition and patterned by photolithography yields highly sensitive photodetectors, with record shot-noise-limited detectivities of 8.7 × 10 14 Jones in ambient condition and even higher when sealed with a protective layer. These detectivity values are higher than the highest values reported for photodetectors based on exfoliated MoS 2 . We study MoS 2 devices with gold electrodes and graphene electrodes. The devices with graphene electrodes have a tunable band alignment and are especially attractive for scalable ultra-thin flexible optoelectronics.

Highly sensitive MoS2 photodetectors with graphene contacts

NASA Astrophysics Data System (ADS)

Han, Peize; St. Marie, Luke; Wang, Qing X.; Quirk, Nicholas; El Fatimy, Abdel; Ishigami, Masahiro; Barbara, Paola

2018-05-01

Two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) are ideal candidates to create ultra-thin electronics suitable for flexible substrates. Although optoelectronic devices based on TMDs have demonstrated remarkable performance, scalability is still a significant issue. Most devices are created using techniques that are not suitable for mass production, such as mechanical exfoliation of monolayer flakes and patterning by electron-beam lithography. Here we show that large-area MoS2 grown by chemical vapor deposition and patterned by photolithography yields highly sensitive photodetectors, with record shot-noise-limited detectivities of 8.7 × 1014 Jones in ambient condition and even higher when sealed with a protective layer. These detectivity values are higher than the highest values reported for photodetectors based on exfoliated MoS2. We study MoS2 devices with gold electrodes and graphene electrodes. The devices with graphene electrodes have a tunable band alignment and are especially attractive for scalable ultra-thin flexible optoelectronics.

Large-area, continuous and high electrical performances of bilayer to few layers MoS2 fabricated by RF sputtering via post-deposition annealing method

PubMed Central

Hussain, Sajjad; Singh, Jai; Vikraman, Dhanasekaran; Singh, Arun Kumar; Iqbal, Muhammad Zahir; Khan, Muhammad Farooq; Kumar, Pushpendra; Choi, Dong-Chul; Song, Wooseok; An, Ki-Seok; Eom, Jonghwa; Lee, Wan-Gyu; Jung, Jongwan

2016-01-01

We report a simple and mass-scalable approach for thin MoS2 films via RF sputtering combined with the post-deposition annealing process. We have prepared as-sputtered film using a MoS2 target in the sputtering system. The as-sputtered film was subjected to post-deposition annealing to improve crystalline quality at 700 °C in a sulfur and argon environment. The analysis confirmed the growth of continuous bilayer to few-layer MoS2 film. The mobility value of ~29 cm2/Vs and current on/off ratio on the order of ~104 were obtained for bilayer MoS2. The mobility increased up to ~173–181 cm2/Vs, respectively, for few-layer MoS2. The mobility of our bilayer MoS2 FETs is larger than any previously reported values of single to bilayer MoS2 grown on SiO2/Si substrate with a SiO2 gate oxide. Moreover, our few-layer MoS2 FETs exhibited the highest mobility value ever reported for any MoS2 FETs with a SiO2 gate oxide. It is presumed that the high mobility behavior of our film could be attributed to low charged impurities of our film and dielectric screening effect by an interfacial MoOxSiy layer. The combined preparation route of RF sputtering and post-deposition annealing process opens up the novel possibility of mass and batch production of MoS2 film. PMID:27492282

Attapulgite-CeO2/MoS2 ternary nanocomposite for photocatalytic oxidative desulfurization

NASA Astrophysics Data System (ADS)

Li, Xiazhang; Zhang, Zuosong; Yao, Chao; Lu, Xiaowang; Zhao, Xiaobing; Ni, Chaoying

2016-02-01

Novel attapulgite(ATP)-CeO2/MoS2 ternary nanocomposites were synthesized by microwave assisted assembly method. The structures of the nanocomposites were characterized by XRD, FT-IR, UV-vis, XPS and in situ TEM. The photocatalytic activities of ATP-CeO2/MoS2 composites were investigated by degradating dibenzothiophene (DBT) in gasoline under visible light irradiation. The effect of the mass ratio of CeO2 to MoS2 on photocatalytic activity was investigated. The results indicate that the three-dimensional network structure is firmly constructed by ATP skeleton, CeO2 particles and MoS2 nanosheet which effectively increase the surface area of the composites and promote the separation of electrons and holes by resulting electronic transmission channels of multi-channel in space. The degradation rate of DBT can reach 95% under 3 h irradiation when the mass ratio of CeO2/MoS2 is 4/10. A plausible mechanism for the photocatalytic oxidative desulfurization of this nanocomposite is put forward.

One-Step Preparation of Large Area Films of Oriented MoS2 Nanoparticles on Multilayer Graphene and Its Electrocatalytic Activity for Hydrogen Evolution

PubMed Central

He, Jinbao; Fernández, Cristina; Primo, Ana

2018-01-01

MoS2 is a promising material to replace Pt-based catalysts for the hydrogen evolution reaction (HER), due to its excellent stability and high activity. In this work, MoS2 nanoparticles supported on graphitic carbon (about 20 nm) with a preferential 002 facet orientation have been prepared by pyrolysis of alginic acid films on quartz containing adsorbed (NH4)2MoS4 at 900 °C under Ar atmosphere. Although some variation of the electrocatalytic activity has been observed from batch to batch, the MoS2 sample exhibited activity for HER (a potential onset between 0.2 and 0.3 V vs. SCE), depending on the concentrations of (NH4)2MoS4 precursor used in the preparation process. The loading and particle size of MoS2, which correlate with the amount of exposed active sites in the sample, are the main factors influencing the electrocatalytic activity. PMID:29361756

Digital MOS integrated circuits

NASA Astrophysics Data System (ADS)

Elmasry, M. I.

MOS in digital circuit design is considered along with aspects of digital VLSI, taking into account a comparison of MOSFET logic circuits, 1-micrometer MOSFET VLSI technology, a generalized guide for MOSFET miniaturization, processing technologies, novel circuit structures for VLSI, and questions of circuit and system design for VLSI. MOS memory cells and circuits are discussed, giving attention to a survey of high-density dynamic RAM cell concepts, one-device cells for dynamic random-access memories, variable resistance polysilicon for high density CMOS Ram, high performance MOS EPROMs using a stacked-gate cell, and the optimization of the latching pulse for dynamic flip-flop sensors. Programmable logic arrays are considered along with digital signal processors, microprocessors, static RAMs, and dynamic RAMs.

Electron tomography and fractal aspects of MoS2 and MoS2/Co spheres.

PubMed

Ramos, Manuel; Galindo-Hernández, Félix; Arslan, Ilke; Sanders, Toby; Domínguez, José Manuel

2017-09-26

A study was made by a combination of 3D electron tomography reconstruction methods and N 2 adsorption for determining the fractal dimension for nanometric MoS 2 and MoS 2 /Co catalyst particles. DFT methods including Neimarke-Kiselev's method allowed to determine the particle porosity and fractal arrays at the atomic scale for the S-Mo-S(Co) 2D- layers that conform the spherically shaped catalyst particles. A structural and textural correlation was sought by further characterization performed by x-ray Rietveld refinement and Radial Distribution Function (RDF) methods, electron density maps, computational density functional theory methods and nitrogen adsorption methods altogether, for studying the structural and textural features of spherical MoS 2 and MoS 2 /Co particles. Neimark-Kiselev's equations afforded the evaluation of a pore volume variation from 10 to 110 cm 3 /g by cobalt insertion in the MoS 2 crystallographic lattice, which induces the formation of cavities and throats in between of less than 29 nm, with a curvature radius r k  < 14.4 nm; typical large needle-like arrays having 20 2D layers units correspond to a model consisting of smooth surfaces within these cavities. Decreasing D P , D B , D I and D M values occur when Co atoms are present in the MoS 2 laminates, which promote the formation of smoother edges and denser surfaces that have an influence on the catalytic properties of the S-Mo-S(Co) system.

Enabling Colloidal Synthesis of Edge-Oriented MoS2 with Expanded Interlayer Spacing for Enhanced HER Catalysis.

PubMed

Sun, Yugang; Alimohammadi, Farbod; Zhang, Dongtang; Guo, Guangsheng

2017-03-08

By selectively promoting heterogeneous nucleation/growth of MoS 2 on graphene monolayer sheets, edge-oriented (EO) MoS 2 nanosheets with expanded interlayer spacing (∼9.4 Å) supported on reduced graphene oxide (rGO) sheets were successfully synthesized through colloidal chemistry, showing the promise in low-cost and large-scale production. The number and edge length of MoS 2 nanosheets per area of graphene sheets were tuned by controlling the reaction time in the microwave-assisted solvothermal reduction of ammonium tetrathiomolybdate [(NH 4 ) 2 MoS 4 ] in dimethylformamide. The edge-oriented and interlayer-expanded (EO&IE) MoS 2 /rGO exhibited significantly improved catalytic activity toward hydrogen evolution reaction (HER) in terms of larger current density, lower Tafel slope, and lower charge transfer resistance compared to the corresponding interlayer-expanded MoS 2 sheets without edge-oriented geometry, highlighting the importance of synergistic effect between edge-oriented geometry and interlayer expansion on determining HER activity of MoS 2 nanosheets. Quantitative analysis clearly shows the linear dependence of current density on the edge length of MoS 2 nanosheets.

Radio Frequency Transistors and Circuits Based on CVD MoS2.

PubMed

Sanne, Atresh; Ghosh, Rudresh; Rai, Amritesh; Yogeesh, Maruthi Nagavalli; Shin, Seung Heon; Sharma, Ankit; Jarvis, Karalee; Mathew, Leo; Rao, Rajesh; Akinwande, Deji; Banerjee, Sanjay

2015-08-12

We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations of fabricated MoS2 FETs yielded current densities exceeding 200 μA/μm and maximum transconductance of 38 μS/μm. A contact resistance corrected low-field mobility of 55 cm(2)/(V s) was achieved. Radio frequency FETs were fabricated in the ground-signal-ground (GSG) layout, and standard de-embedding techniques were applied. Operating at the peak transconductance, we obtain short-circuit current-gain intrinsic cutoff frequency, fT, of 6.7 GHz and maximum intrinsic oscillation frequency, fmax, of 5.3 GHz for a device with a gate length of 250 nm. The MoS2 device afforded an extrinsic voltage gain Av of 6 dB at 100 MHz with voltage amplification until 3 GHz. With the as-measured frequency performance of CVD MoS2, we provide the first demonstration of a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

Fabrication and electrical properties of MoS2 nanodisc-based back-gated field effect transistors.

PubMed

Gu, Weixia; Shen, Jiaoyan; Ma, Xiying

2014-02-28

Two-dimensional (2D) molybdenum disulfide (MoS2) is an attractive alternative semiconductor material for next-generation low-power nanoelectronic applications, due to its special structure and large bandgap. Here, we report the fabrication of large-area MoS2 nanodiscs and their incorporation into back-gated field effect transistors (FETs) whose electrical properties we characterize. The MoS2 nanodiscs, fabricated via chemical vapor deposition (CVD), are homogeneous and continuous, and their thickness of around 5 nm is equal to a few layers of MoS2. In addition, we find that the MoS2 nanodisc-based back-gated field effect transistors with nickel electrodes achieve very high performance. The transistors exhibit an on/off current ratio of up to 1.9 × 105, and a maximum transconductance of up to 27 μS (5.4 μS/μm). Moreover, their mobility is as high as 368 cm2/Vs. Furthermore, the transistors have good output characteristics and can be easily modulated by the back gate. The electrical properties of the MoS2 nanodisc transistors are better than or comparable to those values extracted from single and multilayer MoS2 FETs.

Modulating capacitive response of MoS2 flake by controlled nanostructuring through focused laser irradiation.

PubMed

Rani, Renu; Kundu, Anirban; Balal, Mohammad; Sheet, Goutam; Hazra, Kiran Shankar

2018-08-24

Unlike graphene nanostructures, various physical properties of nanostructured MoS 2 have remained unexplored due to the lack of established fabrication routes. Herein, we have reported unique electrostatic properties of MoS 2 nanostructures, fabricated in a controlled manner of different geometries on 2D flake by using focused laser irradiation technique. Electrostatic force microscopy has been carried out on MoS 2 nanostructures by varying tip bias voltage and lift height. The analysis depicts no contrast flip in phase image of the patterned nanostructure due to the absence of free surface charges. However, prominent change in phase shift at the patterned area is observed. Such contrast changes signify the capacitive interaction between tip and nanostructures at varying tip bias voltage and lift height, irrespective of their shape and size. Such unperturbed capacitive behavior of the MoS 2 nanostructures offer modulation of capacitance in periodic array on 2D MoS 2 flake for potential application in capacitive devices.

MOSFET and MOS capacitor responses to ionizing radiation

NASA Technical Reports Server (NTRS)

Benedetto, J. M.; Boesch, H. E., Jr.

1984-01-01

The ionizing radiation responses of metal oxide semiconductor (MOS) field-effect transistors (FETs) and MOS capacitors are compared. It is shown that the radiation-induced threshold voltage shift correlates closely with the shift in the MOS capacitor inversion voltage. The radiation-induced interface-state density of the MOSFETs and MOS capacitors was determined by several techniques. It is shown that the presence of 'slow' states can interfere with the interface-state measurements.

Reversible Phase Transition with Ultralarge Dielectric Relaxation Behaviors in Succinimide Lithium(I) Hybrids.

PubMed

Tang, Yun-Zhi; Wang, Bin; Zhou, Hai-Tao; Chen, Shao-Peng; Tan, Yu-Hui; Wang, Chang-Feng; Yang, Chang-Shan; Wen, He-Rui

2018-02-05

Dielectric relaxations have widely applied on high permittivity capacitors, dielectric switches, ferroelectrics, pyroelectrics, and electrical insulating materials. However, few investigations of large dielectric relaxation behaviors on organic-inorganic hybrid materials have been documented before. Here we present a novel two-dimensional succinimide lithium(I) hybrid compound, [Li(PDD) 2 ClO 4 ] n , 1, (PDD = 2,5-pyrrolidinedione = succinimide) which shows reversible phase transition behavior in the vicinity of 228 K accompanied by an unusual symmetry breaking from I4 1 /amd to C2/c. X-ray single crystal diffractions analysis indicates the twist motion of pyrrolidine heterocycles, and order-disorder motion of ClO 4 - anions triggered the reversible phase transition. By means of an intuitive crystallographic model (rattling ion model), we further illustrated the mechanism of the interesting reversible phase transition. Particularly, 1 shows ultralarge dielectric relaxation behavior in the vicinity of the phase transition by its dielectric constant dependence on temperatures and frequencies as well as its Cole-Cole relation.

Excitation intensity dependence of photoluminescence from monolayers of MoS2 and WS2/MoS2 heterostructures

NASA Astrophysics Data System (ADS)

Kaplan, D.; Gong, Y.; Mills, K.; Swaminathan, V.; Ajayan, P. M.; Shirodkar, S.; Kaxiras, E.

2016-03-01

A detailed study of the excitation dependence of the photoluminescence (PL) from monolayers of MoS2 and WS2/MoS2 heterostructures grown by chemical vapor deposition on Si substrates has revealed that the luminescence from band edge excitons from MoS2 monolayers shows a linear dependence on excitation intensity for both above band gap and resonant excitation conditions. In particular, a band separated by ∼55 meV from the A exciton, referred to as the C band, shows the same linear dependence on excitation intensity as the band edge excitons. A band similar to the C band has been previously ascribed to a trion, a charged, three-particle exciton. However, in our study the C band does not show the 3/2 power dependence on excitation intensity as would be expected for a three-particle exciton. Further, the PL from the MoS2 monolayer in a bilayer WS2/MoS2 heterostructure, under resonant excitation conditions where only the MoS2 absorbs the laser energy, also revealed a linear dependence on excitation intensity for the C band, confirming that its origin is not due to a trion but instead a bound exciton, presumably of an unintentional impurity or a native point defect such as a sulfur vacancy. The PL from the WS2/MoS2 heterostructure, under resonant excitation conditions also showed additional features which are suggested to arise from the interface states at the heteroboundary. Further studies are required to clearly identify the origin of these features.

Enhanced lithium-ion storage and hydrogen evolution reaction catalysis of MoS2/graphene nanoribbons hybrids with loose interlaced three-dimension structure

NASA Astrophysics Data System (ADS)

Wu, Xuan; Fan, Zihan; Ling, Xiaolun; Wu, Shuting; Chen, Xin; Hu, Xiaolin; Zhuang, Naifeng; Chen, Jianzhong

2018-06-01

Molybdenum disulfide hybridized with graphene nanoribbon (MoS2/GNR) was prepared by mild method. MoS2/GNR hybrids interlace loosely into a three-dimension structure. GNR hybridization can improve the dispersity of MoS2, reduce the grain size of MoS2 to 3-6 nm, increase the specific surface area, and broaden the interlamellar spacing of MoS2 (002) plane to 0.67-0.73 nm, which facilitates the transportation of Li+ ions for lithium-ion battery. MoS2/GNR hybrids have better cyclic durability, higher specific discharge capacity, and superior rate performance than MoS2. The electrocatalytic activity in hydrogen evolution reaction shows that MoS2/GNR hybrids have the lower overpotential and the larger current density with a negligible current loss after 2000 cycles. Hybridizing with GNRs enhances both the lithium-ion electrochemical storage and the electrocatalytic activity of MoS2. [Figure not available: see fulltext.

Salt-assisted clean transfer of continuous monolayer MoS2 film for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Cho, Heung-Yeol; Nguyen, Tri Khoa; Ullah, Farman; Yun, Jong-Won; Nguyen, Cao Khang; Kim, Yong Soo

2018-03-01

The transfer of two-dimensional (2D) materials from one substrate to another is challenging but of great importance for technological applications. Here, we propose a facile etching and residue-free method for transferring a large-area monolayer MoS2 film continuously grown on a SiO2/Si by chemical vapor deposition. Prior to synthesis, the substrate is dropped with water- soluble perylene-3, 4, 9, 10-tetracarboxylic acid tetrapotassium salt (PTAS). The as-grown MoS2 on the substrate is simply dipped in water to quickly dissolve PTAS to yield the MoS2 film floating on the water surface, which is subsequently transferred to the desired substrate. The morphological, optical and X-ray photoelectron spectroscopic results show that our method is useful for fast and clean transfer of the MoS2 film. Specially, we demonstrate that monolayer MoS2 film transferred onto a conducting substrate leads to excellent performance for hydrogen evolution reaction with low overpotential (0.29 V vs the reversible hydrogen electrode) and Tafel slope (85.5 mV/decade).

Recent advances in MoS2 nanostructured materials for energy and environmental applications - A review

NASA Astrophysics Data System (ADS)

Theerthagiri, J.; Senthil, R. A.; Senthilkumar, B.; Reddy Polu, Anji; Madhavan, J.; Ashokkumar, Muthupandian

2017-08-01

Molybdenum disulfide (MoS2), a layered transition metal dichalcogenide with an analogous structure to graphene, has attracted enormous attention worldwide owing to its use in a variety of applications such as energy storage, energy conversion, environmental remediation and sensors. MoS2 and graphene have almost similar functional properties such as high charge carrier transport, high wear resistance and good mechanical strength and friction. However, MoS2 is advantageous over graphene due to its low-cost, abundancy, tailorable morphologies and tuneable band gap with good visible light absorption properties. In this review, we have focussed mainly on recent advances in MoS2 nanostructured materials for the applications in the broad area of energy and environment. Special attention has been paid to their applications in dye-sensitized solar cells, supercapacitor, Li-ion battery, hydrogen evolution reaction, photocatalysis for the degradation of organic pollutants, chemical/bio sensors and gas sensors. Finally, the challenges to design MoS2 nanostructures suitable for energy and environmental applications are also highlighted.

Atomic-layer soft plasma etching of MoS2

PubMed Central

Xiao, Shaoqing; Xiao, Peng; Zhang, Xuecheng; Yan, Dawei; Gu, Xiaofeng; Qin, Fang; Ni, Zhenhua; Han, Zhao Jun; Ostrikov, Kostya (Ken)

2016-01-01

Transition from multi-layer to monolayer and sub-monolayer thickness leads to the many exotic properties and distinctive applications of two-dimensional (2D) MoS2. This transition requires atomic-layer-precision thinning of bulk MoS2 without damaging the remaining layers, which presently remains elusive. Here we report a soft, selective and high-throughput atomic-layer-precision etching of MoS2 in SF6 + N2 plasmas with low-energy (<0.4 eV) electrons and minimized ion-bombardment-related damage. Equal numbers of MoS2 layers are removed uniformly across domains with vastly different initial thickness, without affecting the underlying SiO2 substrate and the remaining MoS2 layers. The etching rates can be tuned to achieve complete MoS2 removal and any desired number of MoS2 layers including monolayer. Layer-dependent vibrational and photoluminescence spectra of the etched MoS2 are also demonstrated. This soft plasma etching technique is versatile, scalable, compatible with the semiconductor manufacturing processes, and may be applicable for a broader range of 2D materials and intended device applications. PMID:26813335

MoS2-InGaZnO Heterojunction Phototransistors with Broad Spectral Responsivity.

PubMed

Yang, Jaehyun; Kwak, Hyena; Lee, Youngbin; Kang, Yu-Seon; Cho, Mann-Ho; Cho, Jeong Ho; Kim, Yong-Hoon; Jeong, Seong-Jun; Park, Seongjun; Lee, Hoo-Jeong; Kim, Hyoungsub

2016-04-06

We introduce an amorphous indium-gallium-zinc-oxide (a-IGZO) heterostructure phototransistor consisting of solution-based synthetic molybdenum disulfide (few-layered MoS2, with a band gap of ∼1.7 eV) and sputter-deposited a-IGZO (with a band gap of ∼3.0 eV) films as a novel sensing element with a broad spectral responsivity. The MoS2 and a-IGZO films serve as a visible light-absorbing layer and a high mobility channel layer, respectively. Spectroscopic measurements reveal that appropriate band alignment at the heterojunction provides effective transfer of the visible light-induced electrons generated in the few-layered MoS2 film to the underlying a-IGZO channel layer with a high carrier mobility. The photoresponse characteristics of the a-IGZO transistor are extended to cover most of the visible range by forming a heterojunction phototransistor that harnesses a visible light responding MoS2 film with a small band gap prepared through a large-area synthetic route. The MoS2-IGZO heterojunction phototransistors exhibit a photoresponsivity of approximately 1.7 A/W at a wavelength of 520 nm (an optical power of 1 μW) with excellent time-dependent photoresponse dynamics.

Photothermoelectric and photovoltaic effects both present in MoS2

PubMed Central

Zhang, Youwei; Li, Hui; Wang, Lu; Wang, Haomin; Xie, Xiaomin; Zhang, Shi-Li; Liu, Ran; Qiu, Zhi-Jun

2015-01-01

As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice. PMID:25605348

Friction on a single MoS2 nanotube

PubMed Central

2012-01-01

Friction was measured on a single molybdenum disulfide (MoS2) nanotube and on a single MoS2 nano-onion for the first time. We used atomic force microscopy (AFM) operating in ultra-high vacuum at room temperature. The average coefficient of friction between the AFM tip and MoS2 nanotubes was found considerably below the corresponding values obtained from an air-cleaved MoS2 single crystal or graphite. We revealed a nontrivial dependency of friction on interaction strength between the nanotube and the underlying substrate. Friction on detached or weakly supported nanotubes by the substrate was several times smaller (0.023 ± 0.005) than that on well-supported nanotubes (0.08 ± 0.02). We propose an explanation of a quarter of a century old phenomena of higher friction found for intracrystalline (0.06) than for intercrystalline slip (0.025) in MoS2. Friction test on a single MoS2 nano-onion revealed a combined gliding-rolling process. PACS, 62.20, 61.46.Fg, 68.37 Ps PMID:22490562

Modeling of short channel MOS transistors

NASA Technical Reports Server (NTRS)

Lin, H. C.; Kokalis, D. P.; Bandy, W. R.

1976-01-01

Higher frequency response in MOS technology can be obtained by shortening the channel length. One approach for doing this involves an employment of higher resolution lithography technology. A second approach makes use of a double-diffused MOS transistor (DMOS). It is pointed out that the ordinary method of modeling the transistors used in both approaches is not accurate. An investigation is conducted of the questions which have to be considered for DMOS modeling. The modeling of a short channel MOS transistor is discussed, taking into account the derivation of the threshold voltage equation. Excellent agreement between theoretical and experimental data shows the accuracy of the described modeling approach.

High performance broadband photodetector based on MoS2/porous silicon heterojunction

NASA Astrophysics Data System (ADS)

Dhyani, Veerendra; Dwivedi, Priyanka; Dhanekar, Saakshi; Das, Samaresh

2017-11-01

A high speed efficient broadband photodetector based on a vertical n-MoS2/p-porous silicon heterostructure has been demonstrated. Large area MoS2 on electrochemical etched porous silicon was grown by sulphurization of a sputtered MoO3 thin film. A maximum responsivity of 9 A/W (550-850 nm) with a very high detectivity of ˜1014 Jones is observed. Transient measurements show a fast response time of ˜9 μs and is competent to work at high frequencies (˜50 kHz). The enhanced photodetection performance of the heterojunction made on porous silicon over that made on planar silicon is explained in terms of higher interfacial barrier height, superior light trapping property, and larger junction area in the MoS2/porous silicon junction.

Cosmology on ultralarge scales with intensity mapping of the neutral hydrogen 21 cm emission: limits on primordial non-Gaussianity.

PubMed

Camera, Stefano; Santos, Mário G; Ferreira, Pedro G; Ferramacho, Luís

2013-10-25

The large-scale structure of the Universe supplies crucial information about the physical processes at play at early times. Unresolved maps of the intensity of 21 cm emission from neutral hydrogen HI at redshifts z=/~1-5 are the best hope of accessing the ultralarge-scale information, directly related to the early Universe. A purpose-built HI intensity experiment may be used to detect the large scale effects of primordial non-Gaussianity, placing stringent bounds on different models of inflation. We argue that it may be possible to place tight constraints on the non-Gaussianity parameter f(NL), with an error close to σ(f(NL))~1.

One step hydrothermal synthesis of 3D CoS2@MoS2-NG for high performance supercapacitors

NASA Astrophysics Data System (ADS)

Meng, Qi; Chen, Yizhi; Zhu, Wenkun; Zhang, Ling; Yang, Xiaoyong; Duan, Tao

2018-07-01

A three-dimensional (3D) MoS2 coated CoS2-nitrogen doped graphene (NG) (CoS2@MoS2-NG) hybrid has been synthesized by a one step hydrothermal method as supercapacitor (SC) electrode material for the first time. Such a composite consists of NG embedded with stacked CoS2@MoS2 sheets. With a 3D skeleton, it prevents the agglomeration of CoS2@MoS2 nanoparticles, resulting in sound conductivity, rich porous structures and a large surface area. The results indicate that CoS2@MoS2-NG has higher specific capacitance (198 F g‑1 at 1 A g‑1), better rate performance (with about 56.57% from 1 to 16 A g‑1) and an improved cycle stability (with about 96.97% after 1000 cycles). It is an ideal candidate for SC electrode materials.

One step hydrothermal synthesis of 3D CoS2@MoS2-NG for high performance supercapacitors.

PubMed

Meng, Qi; Chen, Yizhi; Zhu, Wenkun; Zhang, Ling; Yang, Xiaoyong; Duan, Tao

2018-07-20

A three-dimensional (3D) MoS 2 coated CoS 2 -nitrogen doped graphene (NG) (CoS 2 @MoS 2 -NG) hybrid has been synthesized by a one step hydrothermal method as supercapacitor (SC) electrode material for the first time. Such a composite consists of NG embedded with stacked CoS 2 @MoS 2 sheets. With a 3D skeleton, it prevents the agglomeration of CoS 2 @MoS 2 nanoparticles, resulting in sound conductivity, rich porous structures and a large surface area. The results indicate that CoS 2 @MoS 2 -NG has higher specific capacitance (198 F g -1 at 1 A g -1 ), better rate performance (with about 56.57% from 1 to 16 A g -1 ) and an improved cycle stability (with about 96.97% after 1000 cycles). It is an ideal candidate for SC electrode materials.

Visible light responsive Cu2MoS4 nanosheets incorporated reduced graphene oxide for efficient degradation of organic pollutant

NASA Astrophysics Data System (ADS)

Rameshbabu, R.; Vinoth, R.; Navaneethan, M.; Harish, S.; Hayakawa, Y.; Neppolian, B.

2017-10-01

Visible light active copper molybdenum sulfide (Cu2MoS4) nanosheets were successfully anchored on reduced graphene oxide (rGO) using facile hydrothermal method. During the hydrothermal reaction, reduction of graphene oxide into rGO and the formation of Cu2MoS4 nanosheets were successfully obtained. The charge transfer interaction between the rGO sheets and Cu2MoS4 nanosheets extended the absorption to visible region in comparison with bare Cu2MoS4 nanosheets i.e without rGO sheets. Furthermore, the notable photoluminescence quenching observed for Cu2MoS4/rGO nanocomposite revealed the effective role of rGO towards the significant inhibition of electron-hole pair recombination. The photocatalytic efficiencies of bare Cu2MoS4 and Cu2MoS4/rGO nanocomposite was evaluated for the degradation of methyl orange dye under visible irradiation (λ > 420 nm). A maximum photodegradation efficiency of 99% was achieved for Cu2MoS4/rGO nanocomposite, while only 64% photodegradation was noted for bare Cu2MoS4. The enhanced optical absorption in visible region, high surface area, and low charge carrier recombination in the presence of rGO sheets were the main reasons for the enhancement in photodegardation of MO dye. In addition, the resultant Cu2MoS4/rGO nanocomposite was found to be reusable for five successive cycles without significant loss in its photocatalytic performance.

Parametric amplification in MoS2 drum resonator.

PubMed

Prasad, Parmeshwar; Arora, Nishta; Naik, A K

2017-11-30

Parametric amplification is widely used in diverse areas from optics to electronic circuits to enhance low level signals by varying relevant system parameters. Parametric amplification has also been performed in several micro-nano resonators including nano-electromechanical system (NEMS) resonators based on a two-dimensional (2D) material. Here, we report the enhancement of mechanical response in a MoS 2 drum resonator using degenerate parametric amplification. We use parametric pumping to modulate the spring constant of the MoS 2 resonator and achieve a 10 dB amplitude gain. We also demonstrate quality factor enhancement in the resonator with parametric amplification. We investigate the effect of cubic nonlinearity on parametric amplification and show that it limits the gain of the mechanical resonator. Amplifying ultra-small displacements at room temperature and understanding the limitations of the amplification in these devices is key for using these devices for practical applications.

BATMAN: MOS Spectroscopy on Demand

NASA Astrophysics Data System (ADS)

Molinari, E.; Zamkotsian, F.; Moschetti, M.; Spano, P.; Boschin, W.; Cosentino, R.; Ghedina, A.; González, M.; Pérez, H.; Lanzoni, P.; Ramarijaona, H.; Riva, M.; Zerbi, F.; Nicastro, L.; Valenziano, L.; Di Marcantonio, P.; Coretti, I.; Cirami, R.

2016-10-01

Multi-Object Spectrographs (MOS) are the major instruments for studying primary galaxies and remote and faint objects. Current object selection systems are limited and/or difficult to implement in next generation MOS for space and ground-based telescopes. A promising solution is the use of MOEMS devices such as micromirror arrays, which allow the remote control of the multi-slit configuration in real time. TNG is hosting a novelty project for real-time, on-demand MOS masks based on MOEMS programmable slits. We are developing a 2048×1080 Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the Galileo telescope, called BATMAN. It is a two-arm instrument designed for providing in parallel imaging and spectroscopic capabilities. With a field of view of 6.8×3.6 arcmin and a plate scale of 0.2 arcsec per micromirror, this astronomical setup can be used to investigate the formation and evolution of galaxies. The wavelength range is in the visible and the spectral resolution is R=560 for a 1 arcsec object, and the two arms will have 2k × 4k CCD detectors. ROBIN, a BATMAN demonstrator, has been designed, realized and integrated. We plan to have BATMAN first light by mid-2016.

Two-dimensional MoS2 electromechanical actuators

NASA Astrophysics Data System (ADS)

Hung, Nguyen T.; Nugraha, Ahmad R. T.; Saito, Riichiro

2018-02-01

We investigate the electromechanical properties of two-dimensional MoS2 monolayers with 1H, 1T, and 1T‧ structures as a function of charge doping by using density functional theory. We find isotropic elastic moduli in the 1H and 1T structures, while the 1T‧ structure exhibits an anisotropic elastic modulus. Moreover, the 1T structure is shown to have a negative Poisson’s ratio, while Poisson’s ratios of the 1H and 1T‧ are positive. By charge doping, the monolayer MoS2 shows a reversible strain and work density per cycle ranging from  -0.68% to 2.67% and from 4.4 to 36.9 MJ m-3, respectively, making them suitable for applications in electromechanical actuators. We also examine the stress generated in the MoS2 monolayers and we find that 1T and 1T‧ MoS2 monolayers have relatively better performance than 1H MoS2 monolayer. We argue that such excellent electromechanical performance originate from the electrical conductivity of the metallic 1T and semimetallic 1T‧ structures and also from their high Young’s modulus of about 150-200 GPa.

Application of MOS-1 MESSR image to the investigation of wetlands in Poyang Lake

NASA Astrophysics Data System (ADS)

Chen, Shuisen; Li, Yan

1998-08-01

The lake beach and grass moor land is a kind of typical wetlands. The area varies greatly with season in Poyang Lake region. Moreover, the field investigation of wetlands is almost impossible as geographical features and difficulties in transportation. The notes address the potential role of remote sensing in the surveying of the lake beach and grass moor land. In particular, the notes reflect the characteristics relationships between MOS-1 MESSR image and the wetlands. The application results show that MOS-1 MESSR image is effective in surveying the wetland area variation and distribution (lake, river, grass moor, mud flat, sand beach, etc.). detecting lake base shape, and analyzing eco-environment surrounded.

Oxidation of atomically thin MoS2 on SiO2

NASA Astrophysics Data System (ADS)

Yamamoto, Mahito; Cullen, William; Einstein, Theodore; Fuhrer, Michael

2013-03-01

Surface oxidation of MoS2 markedly affects its electronic, optical, and tribological properties. However, oxidative reactivity of atomically thin MoS2 has yet to be addressed. Here, we investigate oxidation of atomic layers of MoS2 using atomic force microscopy and Raman spectroscopy. MoS2 is mechanically exfoliated onto SiO2 and oxidized in Ar/O2 or Ar/O3 (ozone) at 100-450 °C. MoS2 is much more reactive to O2 than an analogous atomic membrane of graphene and monolayer MoS2 is completely etched very rapidly upon O2 treatment above 300 °C. Thicker MoS2 (> 15 nm) transforms into MoO3 after oxidation at 400 °C, which is confirmed by a Raman peak at 820 cm-1. However, few-layer MoS2 oxidized below 400 °C exhibits no MoO3 Raman mode but etch pits are formed, similar to graphene. We find atomic layers of MoS2 shows larger reactivity to O3 than to O2 and monolayer MoS2 transforms chemically upon O3 treatment even below 100 °C. Work supported by the U. of Maryland NSF-MRSEC under Grant No. DMR 05-20741.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants.

PubMed

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-08-07

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

NASA Astrophysics Data System (ADS)

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-08-01

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry.

C-MOS array design techniques

NASA Technical Reports Server (NTRS)

Feller, A.

1978-01-01

The entire complement of standard cells and components, except for the set-reset flip-flop, was completed. Two levels of checking were performed on each device. Logic cells and topological layout are described. All the related computer programs were coded and one level of debugging was completed. The logic for the test chip was modified and updated. This test chip served as the first test vehicle to exercise the standard cell complementary MOS(C-MOS) automatic artwork generation capability.

Intrinsic electrical transport and performance projections of synthetic monolayer MoS2 devices

NASA Astrophysics Data System (ADS)

Smithe, Kirby K. H.; English, Chris D.; Suryavanshi, Saurabh V.; Pop, Eric

2017-03-01

We demonstrate monolayer (1L) MoS2 grown by chemical vapor deposition (CVD) with transport properties comparable to those of the best exfoliated 1L devices over a wide range of carrier densities (up to ˜1013 cm-2) and temperatures (80-500 K). Transfer length measurements decouple the intrinsic material mobility from the contact resistance, at practical carrier densities (>1012 cm-2). We demonstrate the highest current density reported to date (˜270 μA μm-1 or 44 MA cm-2) at 300 K for an 80 nm long device from CVD-grown 1L MoS2. Using simulations, we discuss what improvements of 1L MoS2 are still required to meet technology roadmap requirements for low power and high performance applications. Such results are an important step towards large-area electronics based on 1L semiconductors.

Epitaxial MoS2/GaN structures to enable vertical 2D/3D semiconductor heterostructure devices

NASA Astrophysics Data System (ADS)

Ruzmetov, D.; Zhang, K.; Stan, G.; Kalanyan, B.; Eichfeld, S.; Burke, R.; Shah, P.; O'Regan, T.; Crowne, F.; Birdwell, A. G.; Robinson, J.; Davydov, A.; Ivanov, T.

MoS2/GaN structures are investigated as a building block for vertical 2D/3D semiconductor heterostructure devices that utilize a 3D substrate (GaN) as an active component of the semiconductor device without the need of mechanical transfer of the 2D layer. Our CVD-grown monolayer MoS2 has been shown to be epitaxially aligned to the GaN lattice which is a pre-requisite for high quality 2D/3D interfaces desired for efficient vertical transport and large area growth. The MoS2 coverage is nearly 50 % including isolated triangles and monolayer islands. The GaN template is a double-layer grown by MOCVD on sapphire and allows for measurement of transport perpendicular to the 2D layer. Photoluminescence, Raman, XPS, Kelvin force probe microscopy, and SEM analysis identified high quality monolayer MoS2. The MoS2/GaN structures electrically conduct in the out-of-plane direction and across the van der Waals gap, as measured with conducting AFM (CAFM). The CAFM current maps and I-V characteristics are analyzed to estimate the MoS2/GaN contact resistivity to be less than 4 Ω-cm2 and current spreading in the MoS2 monolayer to be approx. 1 μm in diameter. Epitaxial MoS2/GaN heterostructures present a promising platform for the design of energy-efficient, high-speed vertical devices incorporating 2D layered materials with 3D semiconductors.

Indented Cu2MoS4 nanosheets with enhanced electrocatalytic and photocatalytic activities realized through edge engineering.

PubMed

Chen, Bang-Bao; Ma, De-Kun; Ke, Qing-Ping; Chen, Wei; Huang, Shao-Ming

2016-03-07

Edges often play a role as active centers for catalytic reactions in some nanomaterials. Therefore it is highly desirable to enhance catalytic activity of a material through modulating the microstructure of the edges. However, the study associated with edge engineering is less investigated and still at its preliminary stage. Here we report that Cu2MoS4 nanosheets with indented edges can be fabricated through a simple chemical etching route at room temperature, using Cu2MoS4 nanosheets with flat ones as sacrifice templates. Taking the electrocatalytic hydrogen evolution reaction (HER), photocatalytic degradation of rhodamine B (RhB) and conversion of benzyl alcohol as examples, the catalytic activity of Cu2MoS4 indented nanosheets (INSs) obtained through edge engineering was comparatively studied with those of Cu2MoS4 flat nanosheets (FNSs) without any modification. The photocatalytic tests revealed that the catalytic active sites of Cu2MoS4 nanosheets were associated with their edges rather than basal planes. Cu2MoS4 INSs were endowed with larger electrochemically active surface area (ECSA), more active edges and better hydrophilicity through the edge engineering. As a result, the as-fabricated Cu2MoS4 INSs exhibited an excellent HER activity with a small Tafel slope of 77 mV dec(-1), which is among the best records for Cu2MoS4 catalysts. The present work demonstrated the validity of adjusting catalytic activity of the material through edge engineering and provided a new strategy for designing and developing highly efficient catalysts.

Effect of post-annealing on sputtered MoS2 films

NASA Astrophysics Data System (ADS)

Wong, W. C.; Ng, S. M.; Wong, H. F.; Cheng, W. F.; Mak, C. L.; Leung, C. W.

2017-12-01

Typical routes for fabricating MoS2-based electronic devices rely on the transfer of as-prepared flakes to target substrates, which is incompatible with conventional device fabrication methods. In this work we investigated the preparation of MoS2 films by magnetron sputtering. By subjecting room-temperature sputtered MoS2 films to post-annealing at mild conditions (450 °C in a nitrogen flow), crystalline MoS2 films were formed. To demonstrate the compatibility of the technique with typical device fabrication processes, MoS2 was prepared on epitaxial magnetic oxide films of La0.7Sr0.3MnO3, and the magnetic behavior of the films were unaffected by the post-annealing process. This work demonstrates the possibility of fabricating electronic and spintronic devices based on continuous MoS2 films prepared by sputtering deposition.

Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS2 and HfO2 High-k Dielectric

PubMed Central

Xia, Pengkun; Feng, Xuewei; Ng, Rui Jie; Wang, Shijie; Chi, Dongzhi; Li, Cequn; He, Zhubing; Liu, Xinke; Ang, Kah-Wee

2017-01-01

Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS2 channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS2 and an ultra-thin HfO2 high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS2-HfO2 interface is responsible for the generation of interface states with a density (Dit) reaching ~7.03 × 1011 cm−2 eV−1. This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS2 bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in Dit could be achieved by thermally diffusing S atoms to the MoS2-HfO2 interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS2 devices with carrier transport enhancement. PMID:28084434

Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS2 and HfO2 High-k Dielectric.

PubMed

Xia, Pengkun; Feng, Xuewei; Ng, Rui Jie; Wang, Shijie; Chi, Dongzhi; Li, Cequn; He, Zhubing; Liu, Xinke; Ang, Kah-Wee

2017-01-13

Two-dimensional layered semiconductors such as molybdenum disulfide (MoS 2 ) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS 2 channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS 2 and an ultra-thin HfO 2 high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS 2 -HfO 2 interface is responsible for the generation of interface states with a density (D it ) reaching ~7.03 × 10 11  cm -2  eV -1 . This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS 2 bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in D it could be achieved by thermally diffusing S atoms to the MoS 2 -HfO 2 interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS 2 devices with carrier transport enhancement.

Mechanical and thermal properties of MoS2 reinforced epoxy nanocomposites

NASA Astrophysics Data System (ADS)

Madeshwaran, S. R.; Jayaganthan, R.; Velmurugan, R.; Gupta, N. K.; Manzhirov, A. V.

2018-04-01

The effects of molybdenum disulfide (MoS2) on thermal expansion and mechanical properties of epoxy composites were investigated. MoS2 nanosheets were exfoliated by ultra-sonication and reinforced into epoxy as nanofiller by mechanical stirring. Transmission electron microscopy observations demonstrated that MoS2 exhibited better dispersion in epoxy matrix. Thermal expansion measured by dilatometer has revealed that increasing MoS2 fractioninepoxy matrix significantly reduced the coefficient of thermal expansion (CTE). The 0.5wt% MoS2 incorporated epoxy composites shows 35.8% reduction in CTE as compared to neat epoxy. The addition of small fraction of MoS2(0.1wt%) in the composites increased the tensile and flexural strength 39.2% and 9.0% respectively. The glass transition temperature (Tg ) of 0.1wt% MoS2 incorporated epoxy composites shows 7.39% increase in Tg .

Charge transfer in crystalline germanium/monolayer MoS 2 heterostructures prepared by chemical vapor deposition

DOE PAGES

Lin, Yung-Chen; Bilgin, Ismail; Ahmed, Towfiq; ...

2016-09-21

Heterostructuring provides novel opportunities for exploring emergent phenomena and applications by developing designed properties beyond those of homogeneous materials. Advances in nanoscience enable the preparation of heterostructures formed incommensurate materials. Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides, are of particular interest due to their distinct physical characteristics. There have been recent changes in new research areas related to 2D/2D heterostructures. But, other heterostructures such as 2D/three-dimensional (3D) materials have not been thoroughly studied yet although the growth of 3D materials on 2D materials creating 2D/3D heterostructures with exceptional carrier transport properties has been reported. Here also wemore » report a novel heterostructure composed of Ge and monolayer MoS 2, prepared by chemical vapor deposition. A single crystalline Ge (110) thin film was grown on monolayer MoS 2. The electrical characteristics of Ge and MoS 2 in the Ge/MoS 2 heterostructure were remarkably different from those of isolated Ge and MoS 2. The field-effect conductivity type of the monolayer MoS 2 is converted from n-type to p-type by growth of the Ge thin film on top of it. Undoped Ge on MoS 2 is highly conducting. The observations can be explained by charge transfer in the heterostructure as opposed to chemical doping via the incorporation of impurities, based on our first-principles calculations.« less

Induction of Chirality in Two-Dimensional Nanomaterials: Chiral 2D MoS2 Nanostructures.

PubMed

Purcell-Milton, Finn; McKenna, Robert; Brennan, Lorcan J; Cullen, Conor P; Guillemeney, Lilian; Tepliakov, Nikita V; Baimuratov, Anvar S; Rukhlenko, Ivan D; Perova, Tatiana S; Duesberg, Georg S; Baranov, Alexander V; Fedorov, Anatoly V; Gun'ko, Yurii K

2018-02-27

Two-dimensional (2D) nanomaterials have been intensively investigated due to their interesting properties and range of potential applications. Although most research has focused on graphene, atomic layered transition metal dichalcogenides (TMDs) and particularly MoS 2 have gathered much deserved attention recently. Here, we report the induction of chirality into 2D chiral nanomaterials by carrying out liquid exfoliation of MoS 2 in the presence of chiral ligands (cysteine and penicillamine) in water. This processing resulted in exfoliated chiral 2D MoS 2 nanosheets showing strong circular dichroism signals, which were far past the onset of the original chiral ligand signals. Using theoretical modeling, we demonstrated that the chiral nature of MoS 2 nanosheets is related to the presence of chiral ligands causing preferential folding of the MoS 2 sheets. There was an excellent match between the theoretically calculated and experimental spectra. We believe that, due to their high aspect ratio planar morphology, chiral 2D nanomaterials could offer great opportunities for the development of chiroptical sensors, materials, and devices for valleytronics and other potential applications. In addition, chirality plays a key role in many chemical and biological systems, with chiral molecules and materials critical for the further development of biopharmaceuticals and fine chemicals, and this research therefore should have a strong impact on relevant areas of science and technology such as nanobiotechnology, nanomedicine, and nanotoxicology.

Flower-like N-doped MoS2 for photocatalytic degradation of RhB by visible light irradiation

NASA Astrophysics Data System (ADS)

Liu, Peitao; Liu, Yonggang; Ye, Weichun; Ma, Ji; Gao, Daqiang

2016-06-01

In this paper, the photocatalytic performance and reusability of N-doped MoS2 nanoflowers with the specific surface area of 114.2 m2 g-1 was evaluated by discoloring of RhB under visible light irradiation. Results indicated that the 20 mg fabricated catalyst could completely degrade 50 ml of 30 mg l-1 RhB in 70 min with excellent recycling and structural stability. The optimized N-doped MoS2 nanoflowers showed a reaction rate constant (k) as high as 0.06928 min-1 which was 26.4 times that of bare MoS2 nanosheets (k = 0.00262). In addition, it was about seven times that of P25 (k = 0.01) (Hou et al 2015 Sci. Rep. 5 15228). The obtained outstanding photocatalytic performance of N-doped MoS2 nanoflowers provides potential applications in water pollution treatment, as well as other related fields.

Electron beam interaction and its effect on crystalline 2H phase of MoS2

NASA Astrophysics Data System (ADS)

Reshmi, S.; Akshaya, M. V.; Basu, Palash Kumar; Bhattacharjee, K.

2018-04-01

Transition metal dichalcogenides (TMDs) in their two dimensional (2D) and nanostructured forms are of fundamentally and technologically important. TMDs can exist in various forms like mono- or few layers or in nanostructures like- nanospheres or rod like- structures whose band gap energy and carrier concentration varies depending on the crystalline phase and the structure. Tunableelectronic properties of the TMDs and the impact of controlled electron beam interaction on the TMDs can have dramatic performances in the area of energy storage, supercapacitors, electrocatalysis and for sensing applications. Here, we report of such electron beam interaction on the MoS2 nanostructures and propose a 1T-2H phase of MoS2 which might be responsible for comprising the post electron beam interaction phase of MoS2.

Comparing the Ocean Color Measurements Between MOS and SeaWiFS: A Vicarious Intercalibration Approach for MOS

NASA Technical Reports Server (NTRS)

Wang, Menghua; Franz, Bryan A.

1998-01-01

One of the primary goals of the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) project is to develop methods for meaningful comparison and possible merging of data products from multiple ocean color missions. The Modular Optoelectronic Scanner (MOS) is a German instrument that was launched in the spring of 1996 on the Indian IRS-P3 satellite. With the successful launch of NASA's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in the summer of 1997, there are now two ocean color missions in concurrent operation and there is interest within the scientific community to compare data from these two sensors. In this paper, we describe our efforts to retrieve ocean optical properties from both SeaWiFS and MOS using consistent methods. We first briefly review the atmospheric correction, which removes more than 90% of the observed radiances in the visible, and then describe how the atmospheric correction algorithm used for the SeaWiFS data can be modified for application to other ocean color sensors. Next, since the retrieved water-leaving radiances in the visible between MOS and SeaWiFS are significantly different, we developed a vicarious intercalibration method to recalibrate the MOS spectral bands based on the optical properties of the ocean and atmosphere derived from the coincident SeaWiFS measurements. We present and discuss the MOS retrieved ocean optical properties before and after the vicarious calibration, and demonstrate the efficacy of this approach. We show that it is possible and efficient to vicariously intercalibrate sensors between one and another.

Ultrathin MoS2 Nanosheets with Superior Extreme Pressure Property as Boundary Lubricants

PubMed Central

Chen, Zhe; Liu, Xiangwen; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2015-01-01

In this paper, a new kind of oil-soluble ultrathin MoS2 nanosheets is prepared through a one-pot process. A superior extreme pressure property, which has not been attained with other nano-additives, is discovered when the nanosheets are used as lubricant additives. The as-synthesized MoS2 nanosheet is only a few atomic layers thick and tens of nanometers wide, and it is surface-modified with oleylamine so it can be well dispersed in oil or lubricant without adscititious dispersants or surfactants. By adding 1 wt% ultrathin MoS2 nanosheets, at the temperature of 120 °C, the highest load liquid paraffin can bear is tremendously improved from less than 50 N to more than 2000 N. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism is proposed. It is believed that the good dispersion and the ultrathin shape of the nanosheets ensure that they can enter the contact area of the opposite sliding surfaces and act like a protective film to prevent direct contact and seizure between them. This work enriches the investigation of ultrathin MoS2 and has potential application in the mechanical industry. PMID:26249536

Large-Area Monolayer MoS2 for Flexible Low-Power RF Nanoelectronics in the GHz Regime.

PubMed

Chang, Hsiao-Yu; Yogeesh, Maruthi Nagavalli; Ghosh, Rudresh; Rai, Amritesh; Sanne, Atresh; Yang, Shixuan; Lu, Nanshu; Banerjee, Sanjay Kumar; Akinwande, Deji

2016-03-02

Flexible synthesized MoS2 transistors are advanced to perform at GHz speeds. An intrinsic cutoff frequency of 5.6 GHz is achieved and analog circuits are realized. Devices are mechanically robust for 10,000 bending cycles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Adsorption of DNA/RNA nucleobases onto single-layer MoS2 and Li-Doped MoS2: A dispersion-corrected DFT study

NASA Astrophysics Data System (ADS)

Sadeghi, Meisam; Jahanshahi, Mohsen; Ghorbanzadeh, Morteza; Najafpour, Ghasem

2018-03-01

The kind of sensing platform in nano biosensor plays an important role in nucleic acid sequence detection. It has been demonstrated that graphene does not have an intrinsic band gap; therefore, transition metal dichalcogenides (TMDs) are desirable materials for electronic base detection. In the present work, a comparative study of the adsorption of the DNA/RNA nucleobases [Adenine (A), Cytosine (C) Guanine (G), Thymine (T) and Uracil (U)] onto the single-layer molybdenum disulfide (MoS2) and Li-doped MoS2 (Li-MoS2) as a sensing surfaces was investigated by using Dispersion-corrected Density Functional Theory (D-DFT) calculations and different measure of equilibrium distances, charge transfers and binding energies for the various nucleobases were calculated. The results revealed that the interactions between the nucleobases and the MoS2 can be strongly enhanced by introducing metal atom, due to significant charge transfer from the Li atom to the MoS2 when Lithium is placed on top of the MoS2. Furthermore, the binding energies of the five nucleobases were in the range of -0.734 to -0.816 eV for MoS2 and -1.47 to -1.80 eV for the Li-MoS2. Also, nucleobases were adsorbed onto MoS2 sheets via the van der Waals (vdW) force. This high affinity and the renewable properties of the biosensing platform demonstrated that Li-MoS2 nanosheet is biocompatible and suitable for nucleic acid analysis.

On Valence-Band Splitting in Layered MoS2.

PubMed

Zhang, Youwei; Li, Hui; Wang, Haomin; Liu, Ran; Zhang, Shi-Li; Qiu, Zhi-Jun

2015-08-25

As a representative two-dimensional semiconducting transition-metal dichalcogenide (TMD), the electronic structure in layered MoS2 is a collective result of quantum confinement, interlayer interaction, and crystal symmetry. A prominent energy splitting in the valence band gives rise to many intriguing electronic, optical, and magnetic phenomena. Despite numerous studies, an experimental determination of valence-band splitting in few-layer MoS2 is still lacking. Here, we show how the valence-band maximum (VBM) splits for one to five layers of MoS2. Interlayer coupling is found to contribute significantly to phonon energy but weakly to VBM splitting in bilayers, due to a small interlayer hopping energy for holes. Hence, spin-orbit coupling is still predominant in the splitting. A temperature-independent VBM splitting, known for single-layer MoS2, is, thus, observed for bilayers. However, a Bose-Einstein type of temperature dependence of VBM splitting prevails in three to five layers of MoS2. In such few-layer MoS2, interlayer coupling is enhanced with a reduced interlayer distance, but thermal expansion upon temperature increase tends to decouple adjacent layers and therefore decreases the splitting energy. Our findings that shed light on the distinctive behaviors about VBM splitting in layered MoS2 may apply to other hexagonal TMDs as well. They will also be helpful in extending our understanding of the TMD electronic structure for potential applications in electronics and optoelectronics.

MoS2‐Based Nanocomposites for Electrochemical Energy Storage

PubMed Central

Wang, Tianyi; Chen, Shuangqiang; Xue, Huaiguo

2016-01-01

Typical layered transition‐metal chalcogenide materials, in particular layered molybdenum disulfide (MoS2) nanocomposites, have attracted increasing attention in recent years due to their excellent chemical and physical properties in various research fieldsHere, a general overview of synthetic MoS2 based nanocomposites via different preparation approaches and their applications in energy storage devices (Li‐ion battery, Na‐ion battery, and supercapacitor) is presented. The relationship between morphologies and the electrochemical performances of MoS2‐based nanocomposites in the three typical and promising rechargeable systems is also discussed. Finally, perspectives on major challenges and opportunities faced by MoS2‐based materials to address the practical problems of MoS2‐based materials are presented. PMID:28251051

Zero-static power radio-frequency switches based on MoS2 atomristors.

PubMed

Kim, Myungsoo; Ge, Ruijing; Wu, Xiaohan; Lan, Xing; Tice, Jesse; Lee, Jack C; Akinwande, Deji

2018-06-28

Recently, non-volatile resistance switching or memristor (equivalently, atomristor in atomic layers) effect was discovered in transitional metal dichalcogenides (TMD) vertical devices. Owing to the monolayer-thin transport and high crystalline quality, ON-state resistances below 10 Ω are achievable, making MoS 2 atomristors suitable as energy-efficient radio-frequency (RF) switches. MoS 2 RF switches afford zero-hold voltage, hence, zero-static power dissipation, overcoming the limitation of transistor and mechanical switches. Furthermore, MoS 2 switches are fully electronic and can be integrated on arbitrary substrates unlike phase-change RF switches. High-frequency results reveal that a key figure of merit, the cutoff frequency (f c ), is about 10 THz for sub-μm 2 switches with favorable scaling that can afford f c above 100 THz for nanoscale devices, exceeding the performance of contemporary switches that suffer from an area-invariant scaling. These results indicate a new electronic application of TMDs as non-volatile switches for communication platforms, including mobile systems, low-power internet-of-things, and THz beam steering.

Hydrothermal synthesis of flower-like MoS2 nanospheres for electrochemical supercapacitors.

PubMed

Zhou, Xiaoping; Xu, Bin; Lin, Zhengfeng; Shu, Dong; Ma, Lin

2014-09-01

Flower-like MoS2 nanospheres were synthesized by a hydrothermal route. The structure and surface morphology of the as-prepared MoS2 was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of MoS2 in 1 M KCl electrolyte was studied by means of cyclic voltammetry (CV), constant current charge-discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD results indicate that the as-prepared MoS2 has good crystallinity. SEM images show that the MoS2 nanospheres have uniform sizes with mean diameter about 300 nm. Many nanosheets growing on the surface make the MoS2 nanospheres to be a flower-like structure. The specific capacitance of MoS2 is 122 F x g(-1) at 1 A x g(-1) or 114 F x g(-1) at 2 mv s(-1). All the experimental results indicate that MoS2 is a promising electrode material for electrochemical supercapacitors.

High performance NO2 sensor using MoS2 nanowires network

NASA Astrophysics Data System (ADS)

Kumar, Rahul; Goel, Neeraj; Kumar, Mahesh

2018-01-01

We report on a high-performance NO2 sensor based on a one dimensional MoS2 nanowire (NW) network. The MoS2 NW network was synthesized using chemical transport reaction through controlled turbulent vapor flow. The crystal structure and surface morphology of MoS2 NWs were confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Further, the sensing behavior of the nanowires was investigated at different temperatures for various concentrations of NO2 and the sensor exhibited about 2-fold enhanced sensitivity with a low detection limit of 4.6 ppb for NO2 at 60 °C compared to sensitivity at room temperature. Moreover, it showed a fast response (16 s) with complete recovery (172 s) at 60 °C, while sensitivity of the device was decreased at 120 °C. The efficient sensing with reliable selectivity toward NO2 of the nanowires is attributed to a combination of abundant active edge sites along with a large surface area and tuning of the potential barrier at the intersections of nanowires during adsorption/desorption of gas molecules.

Direct laser-patterned micro-supercapacitors from paintable MoS2 films.

PubMed

Cao, Liujun; Yang, Shubin; Gao, Wei; Liu, Zheng; Gong, Yongji; Ma, Lulu; Shi, Gang; Lei, Sidong; Zhang, Yunhuai; Zhang, Shengtao; Vajtai, Robert; Ajayan, Pulickel M

2013-09-09

Micrometer-sized electrochemical capacitors have recently attracted attention due to their possible applications in micro-electronic devices. Here, a new approach to large-scale fabrication of high-capacitance, two-dimensional MoS2 film-based micro-supercapacitors is demonstrated via simple and low-cost spray painting of MoS2 nanosheets on Si/SiO2 chip and subsequent laser patterning. The obtained micro-supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ∼0.45 μm. The optimum MoS2 -based micro-supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm(-2) (volumetric capacitance of 178 F cm(-3) ) and excellent cyclic performance, superior to reported graphene-based micro-supercapacitors. This strategy could provide a good opportunity to develop various micro-/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro-electronic devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

ZrO2/MoS2 heterojunction photocatalysts for efficient photocatalytic degradation of methyl orange

NASA Astrophysics Data System (ADS)

Prabhakar Vattikuti, Surya Veerendra; Byon, Chan; Reddy, Chandragiri Venkata

2016-10-01

We report a simple solution-chemistry approach for the synthesis of ZrO2/MoS2 hybrid photocatalysts, which contain MoS2 as a cocatalyst. The material is usually obtained by a wet chemical method using ZrO(NO3)2 or (NH4)6Mo7O24·4H2O and C8H6S as precursors. The structural features of obtained materials were characterized by X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), thermal analysis (TG-DTA), N2 adsorption-desorption, and photoluminescence (PL). The influence on the photocatalytic activity of the MoS2 cocatalyst concentration with ZrO2 nanoparticles was studied. The MZr-2 hybrid sample had the highest photocatalytic activity for the degradation of methyl orange (MO), which was 8.45 times higher than that of pristine ZrO2 ascribed to high specific surface area and absorbance efficiency. Recycling experiments revealed that the reusability of the MZr-2 hybrid was due to the low photocorrosive effect and good catalytic stability. PL spectra confirmed the electronic interaction between ZrO2 and MoS2. The photoinduced electrons could be easily transferred from CB of ZrO2 to the MoS2 cocatalyst, which facilitate effective charge separation and enhanced the photocatalytic degradation in the UV region. A photocatalytic mechanism is proposed. It is believed that the ZrO2/MoS2 hybrid structure has promise as a photocatalyst with low cost and high efficiency for photoreactions.

Preparation of MoS2/TiO2 based nanocomposites for photocatalysis and rechargeable batteries: progress, challenges, and perspective.

PubMed

Chen, Biao; Meng, Yuhuan; Sha, Junwei; Zhong, Cheng; Hu, Wenbin; Zhao, Naiqin

2017-12-21

The rapidly increasing severity of the energy crisis and environmental degradation are stimulating the rapid development of photocatalysts and rechargeable lithium/sodium ion batteries. In particular, MoS 2 /TiO 2 based nanocomposites show great potential and have been widely studied in the areas of both photocatalysis and rechargeable lithium/sodium ion batteries due to their superior combination properties. In addition to the low-cost, abundance, and high chemical stability of both MoS 2 and TiO 2 , MoS 2 /TiO 2 composites also show complementary advantages. These include the strong optical absorption of TiO 2 vs. the high catalytic activity of MoS 2 , which is promising for photocatalysis; and excellent safety and superior structural stability of TiO 2 vs. the high theoretic specific capacity and unique layered structure of MoS 2 , thus, these composites are exciting as anode materials. In this review, we first summarize the recent progress in MoS 2 /TiO 2 -based nanomaterials for applications in photocatalysis and rechargeable batteries. We highlight the synthesis, structure and mechanism of MoS 2 /TiO 2 -based nanomaterials. Then, advancements and strategies for improving the performance of these composites in photocatalytic degradation, hydrogen evolution, CO 2 reduction, LIBs and SIBs are critically discussed. Finally, perspectives on existing challenges and probable opportunities for future exploration of MoS 2 /TiO 2 -based composites towards photocatalysis and rechargeable batteries are presented. We believe the present review would provide enriched information for a deeper understanding of MoS 2 /TiO 2 composites and open avenues for the rational design of MoS 2 /TiO 2 based composites for energy and environment-related applications.

Adsorption of radionuclides on the monolayer MoS2

NASA Astrophysics Data System (ADS)

Zhao, Qiang; Zhang, Zheng; Ouyang, Xiaoping

2018-04-01

How to remove radionuclides from radioactive wastewater has long been a difficult problem, especially in nuclear accidents. In this paper, the adsorption of radionuclides Cs, Sr, and Ba on the monolayer MoS2 was investigated by using the first principles calculation method. Through the calculation of adsorption energy and Hirshfeld charge of the radionuclides on the monolayer MoS2 at six adsorption sites, the results show that all of the radionuclides chemisorbed on the monolayer MoS2, and the adsorption strength of these three kinds of radionuclides on the monolayer MoS2 is Ba > Sr > Cs. This work might shed some light on the treatment of the radioactive wastewater.

Aptamer loaded MoS2 nanoplates as nanoprobes for detection of intracellular ATP and controllable photodynamic therapy

NASA Astrophysics Data System (ADS)

Jia, Li; Ding, Lin; Tian, Jiangwei; Bao, Lei; Hu, Yaoping; Ju, Huangxian; Yu, Jun-Sheng

2015-09-01

In this work we designed a MoS2 nanoplate-based nanoprobe for fluorescence imaging of intracellular ATP and photodynamic therapy (PDT) via ATP-mediated controllable release of 1O2. The nanoprobe was prepared by simply assembling a chlorine e6 (Ce6) labelled ATP aptamer on MoS2 nanoplates, which have favorable biocompatibility, unusual surface-area-to-mass ratio, strong affinity to single-stranded DNA, and can quench the fluorescence of Ce6. After the nanoprobe was internalized into the cells and entered ATP-abundant lysosomes, its recognition to ATP led to the release of the single-stranded aptamer from MoS2 nanoplates and thus recovered the fluorescence of Ce6 at an excitation wavelength of 633 nm, which produced a highly sensitive and selective method for imaging of intracellular ATP. Meanwhile, the ATP-mediated release led to the generation of 1O2 under 660 nm laser irradiation, which could induce tumor cell death with a lysosomal pathway. The controllable PDT provided a model approach for design of multifunctional theranostic nanoprobes. These results also promoted the development and application of MoS2 nanoplate-based platforms in biomedicine.In this work we designed a MoS2 nanoplate-based nanoprobe for fluorescence imaging of intracellular ATP and photodynamic therapy (PDT) via ATP-mediated controllable release of 1O2. The nanoprobe was prepared by simply assembling a chlorine e6 (Ce6) labelled ATP aptamer on MoS2 nanoplates, which have favorable biocompatibility, unusual surface-area-to-mass ratio, strong affinity to single-stranded DNA, and can quench the fluorescence of Ce6. After the nanoprobe was internalized into the cells and entered ATP-abundant lysosomes, its recognition to ATP led to the release of the single-stranded aptamer from MoS2 nanoplates and thus recovered the fluorescence of Ce6 at an excitation wavelength of 633 nm, which produced a highly sensitive and selective method for imaging of intracellular ATP. Meanwhile, the ATP

Scalable Patterning of MoS2 Nanoribbons by Micromolding in Capillaries.

PubMed

Hung, Yu-Han; Lu, Ang-Yu; Chang, Yung-Huang; Huang, Jing-Kai; Chang, Jeng-Kuei; Li, Lain-Jong; Su, Ching-Yuan

2016-08-17

In this study, we report a facile approach to prepare dense arrays of MoS2 nanoribbons by combining procedures of micromolding in capillaries (MIMIC) and thermolysis of thiosalts ((NH4)2MoS4) as the printing ink. The obtained MoS2 nanoribbons had a thickness reaching as low as 3.9 nm, a width ranging from 157 to 465 nm, and a length up to 2 cm. MoS2 nanoribbons with an extremely high aspect ratio (length/width) of ∼7.4 × 10(8) were achieved. The MoS2 pattern can be printed on versatile substrates, such as SiO2/Si, sapphire, Au film, FTO/glass, and graphene-coated glass. The degree of crystallinity of the as-prepared MoS2 was discovered to be adjustable by varying the temperature through postannealing. The high-temperature thermolysis (1000 °C) results in high-quality conductive samples, and field-effect transistors based on the patterned MoS2 nanoribbons were demonstrated and characterized, where the carrier mobility was comparable to that of thin-film MoS2. In contrast, the low-temperature-treated samples (170 °C) result in a unique nanocrystalline MoSx structure (x ≈ 2.5), where the abundant and exposed edge sites were obtained from highly dense arrays of nanoribbon structures by this MIMIC patterning method. The patterned MoSx was revealed to have superior electrocatalytic efficiency (an overpotential of ∼211 mV at 10 mA/cm(2) and a Tafel slope of 43 mV/dec) in the hydrogen evolution reaction (HER) when compared to the thin-film MoS2. The report introduces a new concept for rapidly fabricating cost-effective and high-density MoS2/MoSx nanostructures on versatile substrates, which may pave the way for potential applications in nanoelectronics/optoelectronics and frontier energy materials.

Flexible low-power RF nanoelectronics in the GHz regime using CVD MoS2

NASA Astrophysics Data System (ADS)

Yogeesh, Maruthi

Two-dimensional (2D) materials have attracted substantial interest for flexible nanoelectronics due to the overall device mechanical flexibility and thickness scalability for high mechanical performance and low operating power. In this work, we demonstrate the first MoS2 RF transistors on flexible substrates based on CVD-grown monolayers, featuring record GHz cutoff frequency (5.6 GHz) and saturation velocity (~1.8×106 cm/s), which is significantly superior to contemporary organic and metal oxide thin-film transistors. Furthermore, multicycle three-point bending results demonstrated the electrical robustness of our flexible MoS2 transistors after 10,000 cycles of mechanical bending. Additionally, basic RF communication circuit blocks such as amplifier, mixer and wireless AM receiver have been demonstrated. These collective results indicate that MoS2 is an ideal advanced semiconducting material for low-power, RF devices for large-area flexible nanoelectronics and smart nanosystems owing to its unique combination of large bandgap, high saturation velocity and high mechanical strength.

NO-sensing performance of vacancy defective monolayer MoS2 predicted by density function theory

NASA Astrophysics Data System (ADS)

Li, Feifei; Shi, Changmin

2018-03-01

Using density functional theory (DFT), we predict the NO-sensing performance of monolayer MoS2 (MoS2-MLs) with and without MoS3-vacancy/S-vacancy defects. Our theoretical results demonstrate that MoS3- and S-vacancy defective MoS2-MLs show stronger chemisorption and greater electron transfer effects than pure MoS2-MLs. The charge transfer analysis showed pure and defective MoS2-MLs all act as donors. Both MoS3-vacancy and S-vacancy defects induce dramatic changes of electronic properties of MoS2-MLs, which have direct relationship with gas sensing performance. In addition, S-vacancy defect leads to more electrons transfer to NO molecule than MoS3-vacancy defect. The H2O molecule urges more electrons transfer from MoS3- or S-vacancy defective MoS2-MLs to NO molecule. We believe that this calculation results will provide some information for future experiment.

Enhanced radiative emission from monolayer MoS2 films using a single plasmonic dimer nanoantenna

NASA Astrophysics Data System (ADS)

Palacios, Edgar; Park, Spencer; Butun, Serkan; Lauhon, Lincoln; Aydin, Koray

2017-07-01

By thinning transition metal dichalcogenides (TMDCs) to monolayer form, a direct bandgap semiconductor emerges which opens up opportunities for use in optoelectronic devices. However, absorption and radiative emission is drastically reduced which hinders their applicability for practical devices. One way to address this challenge is to design plasmonic resonators that localize electric fields within or near the two-dimensional (2D) material to confine excitation fields and increase Purcell factors. Previous studies have successfully utilized this method for enhancing radiative emission in 2D-TMDCs by using large area plasmonic arrays that exhibit complex plasmonic interactions due to near and far-field couplings that take place over many periods. In this study, we demonstrate the photoluminescence enhancements in monolayer MoS2 under single Au nanoantennas which only exhibit near-field interactions. Here, the enhancements originate from excitation of near-field plasmons confined within 20 nm of monolayer MoS2 which yields a peak photoluminescence enhancement of 8-fold and an area corrected photoluminescence enhancement >980 fold. Additionally, simulated enhancement trends are found to agree well with experimental results to understand the optimal design requirements. Our results will provide a better understanding of local emission enhancements in 2D materials over small areas of MoS2 that are essential for future applications of truly compact optoelectronic devices based on two-dimensional or reduced dimensionality materials.

Precision Voltage Referencing Techniques in MOS Technology.

NASA Astrophysics Data System (ADS)

Song, Bang-Sup

With the increasing complexity of functions on a single MOS chip, precision analog cicuits implemented in the same technology are in great demand so as to be integrated together with digital circuits. The future development of MOS data acquisition systems will require precision on-chip MOS voltage references. This dissertation will probe two most promising configurations of on-chip voltage references both in NMOS and CMOS technologies. In NMOS, an ion-implantation effect on the temperature behavior of MOS devices is investigated to identify the fundamental limiting factors of a threshold voltage difference as an NMOS voltage source. For this kind of voltage reference, the temperature stability on the order of 20ppm/(DEGREES)C is achievable with a shallow single-threshold implant and a low-current, high-body bias operation. In CMOS, a monolithic prototype bandgap reference is designed, fabricated and tested which embodies a curvature compensation and exhibits a minimized sensitivity to the process parameter variation. Experimental results imply that an average temperature stability on the order of 10ppm/(DEGREES)C with a production spread of less than 10ppm/(DEGREES)C feasible over the commercial temperature range.

Confocal absorption spectral imaging of MoS2: optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2.

PubMed

Dhakal, Krishna P; Duong, Dinh Loc; Lee, Jubok; Nam, Honggi; Kim, Minsu; Kan, Min; Lee, Young Hee; Kim, Jeongyong

2014-11-07

We performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra (over the range 1.5-3.2 eV) within regions having different numbers of layers and studied the variation of optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2 and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal absorption spectral imaging can provide comprehensive information on optical transitions of microscopic size intrinsic and doped two-dimensional layered materials.

MoS 2/TiO 2 heterostructures as nonmetal plasmonic photocatalysts for highly efficient hydrogen evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, L.; Yang, Z.; Marcus, K.

In this study, we report a nonmetal plasmonic MoS2@TiO2 heterostructure for highly efficient photocatalytic H2 generation. Large area laminated Z-scheme MoS2 in conjunction with TiO2 nanocavity arrays are achieved via carefully controlled anodization, physical vapor deposition, and chemical vapor deposition processes. Broad spectral response ranging from ultraviolet (UV)-visible (vis) to near-infrared (NIR) wavelengths and finite element frequency-domain simulation suggest that this MoS2@TiO2 heterostructured photocatalyst possesses an enhanced activity for H+ reduction. A high H2 yield rate of 580 mmol h-1 g-1 is achieved using a low catalyst loading mass of 10.2 μg. The spatially uniform heterostructure, correlated to plasmon-resonance throughmore » conformal coating MoS2 that effectively regulated charge transfer pathways, is proven to be vitally important for the unique solar energy harvesting and photocatalytic H2 production. As an innovative exploration, our study demonstrates that the photocatalytic activities of nonmetal, earth-abundant materials can be enhanced with plasmonic effects, which may serve as an excellent catalytic agent for solar energy conversion to chemical fuel. Periodically patterned MoS 2/TiO 2heterostructures were rationally designed as nonmetal plasmonic photocatalysts for highly efficient hydrogen evolution.« less

Probing Inflation Using Galaxy Clustering On Ultra-Large Scales

NASA Astrophysics Data System (ADS)

Dalal, Roohi; de Putter, Roland; Dore, Olivier

2018-01-01

A detailed understanding of curvature perturbations in the universe is necessary to constrain theories of inflation. In particular, measurements of the local non-gaussianity parameter, flocNL, enable us to distinguish between two broad classes of inflationary theories, single-field and multi-field inflation. While most single-field theories predict flocNL ≈ ‑5/12 (ns -1), in multi-field theories, flocNL is not constrained to this value and is allowed to be observably large. Achieving σ(flocNL) = 1 would give us discovery potential for detecting multi-field inflation, while finding flocNL=0 would rule out a good fraction of interesting multi-field models. We study the use of galaxy clustering on ultra-large scales to achieve this level of constraint on flocNL. Upcoming surveys such as Euclid and LSST will give us galaxy catalogs from which we can construct the galaxy power spectrum and hence infer a value of flocNL. We consider two possible methods of determining the galaxy power spectrum from a catalog of galaxy positions: the traditional Feldman Kaiser Peacock (FKP) Power Spectrum Estimator, and an Optimal Quadratic Estimator (OQE). We implemented and tested each method using mock galaxy catalogs, and compared the resulting constraints on flocNL. We find that the FKP estimator can measure flocNL in an unbiased way, but there remains room for improvement in its precision. We also find that the OQE is not computationally fast, but remains a promising option due to its ability to isolate the power spectrum at large scales. We plan to extend this research to study alternative methods, such as pixel-based likelihood functions. We also plan to study the impact of general relativistic effects at these scales on our ability to measure flocNL.

Ultrafast photocurrents in monolayer MoS2

NASA Astrophysics Data System (ADS)

Parzinger, Eric; Wurstbauer, Ursula; Holleitner, Alexander W.

Two-dimensional transition metal dichalcogenides such as MoS2 have emerged as interesting materials for optoelectronic devices. In particular, the ultrafast dynamics and lifetimes of photoexcited charge carriers have attracted great interest during the last years. We investigate the photocurrent response of monolayer MoS2 on a picosecond time scale utilizing a recently developed pump-probe spectroscopy technique based on coplanar striplines. We discuss the ultrafast dynamics within MoS2 including photo-thermoelectric currents and the impact of built-in fields due to Schottky barriers as well as the Fermi level pinning at the contact region. We acknowledge support by the ERC via Project 'NanoREAL', the DFG via excellence cluster 'Nanosystems Initiative Munich' (NIM), and through the TUM International Graduate School of Science and Engineering (IGSSE) and BaCaTeC.

Sequential structural and optical evolution of MoS2 by chemical synthesis and exfoliation

NASA Astrophysics Data System (ADS)

Kim, Ju Hwan; Kim, Jungkil; Oh, Si Duck; Kim, Sung; Choi, Suk-Ho

2015-06-01

Various types of MoS2 structures are successfully obtained by using economical and facile sequential synthesis and exfoliation methods. Spherically-shaped lumps of multilayer (ML) MoS2 are prepared by using a conventional hydrothermal method and were subsequently 1st-exfoliated in hydrazine while being kept in autoclave to be unrolled and separated into five-to-six-layer MoS2 pieces of several-hundred nm in size. The MoS2 MLs are 2nd-exfoliated in sodium naphthalenide under an Ar ambient to finally produce bilayer MoS2 crystals of ~100 nm. The sequential exfoliation processes downsize MoS2 laterally and reduce its number of layers. The three types of MoS2 allotropes exhibit particular optical properties corresponding to their structural differences. These results suggest that two-dimensional MoS2 crystals can be prepared by employing only chemical techniques without starting from high-pressure-synthesized bulk MoS2 crystals.

Interfacial chemical reactions between MoS2 lubricants and bearing materials

NASA Technical Reports Server (NTRS)

Zabinski, J. S.; Tatarchuk, B. J.

1989-01-01

XPS and conversion-electron Moessbauer spectroscopy (CEMS) were used to examine iron that was deposited on the basal plane of MoS2 single crystals and subjected to vacuum annealing, oxidizing, and reducing environments. Iron either intercalated into the MoS2 structure or formed oriented iron sulfides, depending on the level of excess S in the MoS2 structure. CEMS data demonstrated that iron sulfide crystal structures preferentially aligned with respect to the MoS2 basal plane, and that alignment (and potentially adhesion) could be varied by appropriate high-temperature annealing procedures.

Charge-Transfer-Induced p-Type Channel in MoS2 Flake Field Effect Transistors.

PubMed

Min, Sung-Wook; Yoon, Minho; Yang, Sung Jin; Ko, Kyeong Rok; Im, Seongil

2018-01-31

The two-dimensional transition-metal dichalcogenide semiconductor MoS 2 has received extensive attention for decades because of its outstanding electrical and mechanical properties for next-generation devices. One weakness of MoS 2 , however, is that it shows only n-type conduction, revealing its limitations for homogeneous PN diodes and complementary inverters. Here, we introduce a charge-transfer method to modify the conduction property of MoS 2 from n- to p-type. We initially deposited an n-type InGaZnO (IGZO) film on top of the MoS 2 flake so that electron charges might be transferred from MoS 2 to IGZO during air ambient annealing. As a result, electron charges were depleted in MoS 2 . Such charge depletion lowered the MoS 2 Fermi level, which makes hole conduction favorable in MoS 2 when optimum source/drain electrodes with a high work function are selected. Our IGZO-supported MoS 2 flake field effect transistors (FETs) clearly display channel-type conversion from n- to p-channel in this way. Under short- and long-annealing conditions, n- and p-channel MoS 2 FETs are achieved, respectively, and a low-voltage complementary inverter is demonstrated using both channels in a single MoS 2 flake.

HNO₃-assisted polyol synthesis of ultralarge single-crystalline Ag microplates and their far propagation length of surface plasmon polariton.

PubMed

Chang, Cheng-Wei; Lin, Fan-Cheng; Chiu, Chun-Ya; Su, Chung-Yi; Huang, Jer-Shing; Perng, Tsong-Pyng; Yen, Ta-Jen

2014-07-23

We developed a HNO3-assisted polyol reduction method to synthesize ultralarge single-crystalline Ag microplates routinely. The edge length of the synthesized Ag microplates reaches 50 μm, and their top facets are (111). The mechanism for dramatically enlarging single-crystalline Ag structure stems from a series of competitive anisotropic growths, primarily governed by carefully tuning the adsorption of Ag(0) by ethylene glycol and the desorption of Ag(0) by a cyanide ion on Ag(100). Finally, we measured the propagation length of surface plasmon polaritons along the air/Ag interface under 534 nm laser excitation. Our single-crystalline Ag microplate exhibited a propagation length (11.22 μm) considerably greater than that of the conventional E-gun deposited Ag thin film (5.27 μm).

Growth, structure and stability of sputter-deposited MoS2 thin films.

PubMed

Kaindl, Reinhard; Bayer, Bernhard C; Resel, Roland; Müller, Thomas; Skakalova, Viera; Habler, Gerlinde; Abart, Rainer; Cherevan, Alexey S; Eder, Dominik; Blatter, Maxime; Fischer, Fabian; Meyer, Jannik C; Polyushkin, Dmitry K; Waldhauser, Wolfgang

2017-01-01

Molybdenum disulphide (MoS 2 ) thin films have received increasing interest as device-active layers in low-dimensional electronics and also as novel catalysts in electrochemical processes such as the hydrogen evolution reaction (HER) in electrochemical water splitting. For both types of applications, industrially scalable fabrication methods with good control over the MoS 2 film properties are crucial. Here, we investigate scalable physical vapour deposition (PVD) of MoS 2 films by magnetron sputtering. MoS 2 films with thicknesses from ≈10 to ≈1000 nm were deposited on SiO 2 /Si and reticulated vitreous carbon (RVC) substrates. Samples deposited at room temperature (RT) and at 400 °C were compared. The deposited MoS 2 was characterized by macro- and microscopic X-ray, electron beam and light scattering, scanning and spectroscopic methods as well as electrical device characterization. We find that room-temperature-deposited MoS 2 films are amorphous, of smooth surface morphology and easily degraded upon moderate laser-induced annealing in ambient conditions. In contrast, films deposited at 400 °C are nano-crystalline, show a nano-grained surface morphology and are comparatively stable against laser-induced degradation. Interestingly, results from electrical transport measurements indicate an unexpected metallic-like conduction character of the studied PVD MoS 2 films, independent of deposition temperature. Possible reasons for these unusual electrical properties of our PVD MoS 2 thin films are discussed. A potential application for such conductive nanostructured MoS 2 films could be as catalytically active electrodes in (photo-)electrocatalysis and initial electrochemical measurements suggest directions for future work on our PVD MoS 2 films.

Growth, structure and stability of sputter-deposited MoS2 thin films

PubMed Central

Bayer, Bernhard C; Resel, Roland; Müller, Thomas; Skakalova, Viera; Habler, Gerlinde; Abart, Rainer; Cherevan, Alexey S; Eder, Dominik; Blatter, Maxime; Fischer, Fabian; Meyer, Jannik C; Polyushkin, Dmitry K; Waldhauser, Wolfgang

2017-01-01

Molybdenum disulphide (MoS2) thin films have received increasing interest as device-active layers in low-dimensional electronics and also as novel catalysts in electrochemical processes such as the hydrogen evolution reaction (HER) in electrochemical water splitting. For both types of applications, industrially scalable fabrication methods with good control over the MoS2 film properties are crucial. Here, we investigate scalable physical vapour deposition (PVD) of MoS2 films by magnetron sputtering. MoS2 films with thicknesses from ≈10 to ≈1000 nm were deposited on SiO2/Si and reticulated vitreous carbon (RVC) substrates. Samples deposited at room temperature (RT) and at 400 °C were compared. The deposited MoS2 was characterized by macro- and microscopic X-ray, electron beam and light scattering, scanning and spectroscopic methods as well as electrical device characterization. We find that room-temperature-deposited MoS2 films are amorphous, of smooth surface morphology and easily degraded upon moderate laser-induced annealing in ambient conditions. In contrast, films deposited at 400 °C are nano-crystalline, show a nano-grained surface morphology and are comparatively stable against laser-induced degradation. Interestingly, results from electrical transport measurements indicate an unexpected metallic-like conduction character of the studied PVD MoS2 films, independent of deposition temperature. Possible reasons for these unusual electrical properties of our PVD MoS2 thin films are discussed. A potential application for such conductive nanostructured MoS2 films could be as catalytically active electrodes in (photo-)electrocatalysis and initial electrochemical measurements suggest directions for future work on our PVD MoS2 films. PMID:28685112

Small-signal amplifier based on single-layer MoS2

NASA Astrophysics Data System (ADS)

Radisavljevic, Branimir; Whitwick, Michael B.; Kis, Andras

2012-07-01

In this letter we demonstrate the operation of an analog small-signal amplifier based on single-layer MoS2, a semiconducting analogue of graphene. Our device consists of two transistors integrated on the same piece of single-layer MoS2. The high intrinsic band gap of 1.8 eV allows MoS2-based amplifiers to operate with a room temperature gain of 4. The amplifier operation is demonstrated for the frequencies of input signal up to 2 kHz preserving the gain higher than 1. Our work shows that MoS2 can effectively amplify signals and that it could be used for advanced analog circuits based on two-dimensional materials.

Defects Engineered Monolayer MoS 2 for Improved Hydrogen Evolution Reaction

DOE PAGES

Ye, Gonglan; Gong, Yongji; Lin, Junhao; ...

2016-01-13

MoS 2 is a promising, low-cost material for electrochemical hydrogen production due to its high activity and stability during the reaction. Our work represents an easy method to increase the hydrogen production in electrochemical reaction of MoS 2 via defect engineering, and helps to understand the catalytic properties of MoS 2.

Experimental detection of active defects in few layers MoS2 through random telegraphic signals analysis observed in its FET characteristics

NASA Astrophysics Data System (ADS)

Fang, Nan; Nagashio, Kosuke; Toriumi, Akira

2017-03-01

Transition-metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), are expected to be promising for next generation device applications. The existence of sulfur vacancies formed in MoS2, however, will potentially make devices unstable and problematic. Random telegraphic signals (RTSs) have often been studied in small area Si metal-oxide-semiconductor field-effect transistors (MOSFETs) to identify the carrier capture and emission processes at defects. In this paper, we have systemically analyzed RTSs observed in atomically thin layer MoS2 FETs. Several types of RTSs have been analyzed. One is the simple on/off type of telegraphic signals, the second is multilevel telegraphic signals with a superposition of the simple signals, and the third is multilevel telegraphic signals that are correlated with each other. The last one is discussed from the viewpoint of the defect-defect interaction in MoS2 FETs with a weak screening in atomically confined two-dimensional electron-gas systems. Furthermore, the position of defects causing RTSs has also been investigated by preparing MoS2 FETs with multi-probes. The electron beam was locally irradiated to intentionally generate defects in the MoS2 channel. It is clearly demonstrated that the MoS2 channel is one of the RTS origins. RTS analysis enables us to analyze the defect dynamics of TMD devices.

Rotationally Commensurate Growth of MoS2 on Epitaxial Graphene

DTIC Science & Technology

2015-11-13

at the monolayer MoS2 edges. KEYWORDS: transition metal dichalcogenide, silicon carbide , scanning tunneling microscopy, synchrotron X-ray scattering... silicon from SiC not only offers uniform large-area synthesis of graphene but also provides technological advantages over alternative methods such as...Röhrl, J.; et al. Towards Wafer-Size Graphene Layers by Atmospheric Pressure Graphitization of Silicon Carbide . Nat. Mater. 2009, 8, 203−207. (18) Çelebi

Phosphorous doped p-type MoS2 polycrystalline thin films via direct sulfurization of Mo film

NASA Astrophysics Data System (ADS)

Momose, Tomohiro; Nakamura, Atsushi; Daniel, Moraru; Shimomura, Masaru

2018-02-01

We report on the successful synthesis of a p-type, substitutional doping at S-site, MoS2 thin film using Phosphorous (P) as the dopant. MoS2 thin films were directly sulfurized for molybdenum films by chemical vapor deposition technique. Undoped MoS2 film showed n-type behavior and P doped samples showed p-type behavior by Hall-effect measurements in a van der Pauw (vdP) configuration of 10×10 mm2 area samples and showed ohmic behavior between the silver paste contacts. The donor and the acceptor concentration were detected to be ˜2.6×1015 cm-3 and ˜1.0×1019 cm-3, respectively. Hall-effect mobility was 61.7 cm2V-1s-1 for undoped and varied in the range of 15.5 ˜ 0.5 cm2V-1s-1 with P supply rate. However, the performance of field-effect transistors (FETs) declined by double Schottky barrier contacts where the region between Ni electrodes on the source/drain contact and the MoS2 back-gate cannot be depleted and behaves as a 3D material when used in transistor geometry, resulting in poor on/off ratio. Nevertheless, the FETs exhibit hole transport and the field-effect mobility showed values as high as the Hall-effect mobility, 76 cm2V-1s-1 in undoped MoS2 with p-type behavior and 43 cm2V-1s-1 for MoS2:P. Our findings provide important insights into the doping constraints for transition metal dichalcogenides.

A pressure tuned stop-flow atomic layer deposition process for MoS2 on high porous nanostructure and fabrication of TiO2/MoS2 core/shell inverse opal structure

NASA Astrophysics Data System (ADS)

Li, Xianglin; Puttaswamy, Manjunath; Wang, Zhiwei; Kei Tan, Chiew; Grimsdale, Andrew C.; Kherani, Nazir P.; Tok, Alfred Iing Yoong

2017-11-01

MoS2 thin films are obtained by atomic layer deposition (ALD) in the temperature range of 120-150 °C using Mo(CO)6 and dimethyl disulfide (DMDS) as precursors. A pressure tuned stop-flow ALD process facilitates the precursor adsorption and enables the deposition of MoS2 on high porous three dimensional (3D) nanostructures. As a demonstration, a TiO2/MoS2 core/shell inverse opal (TiO2/MoS2-IO) structure has been fabricated through ALD of TiO2 and MoS2 on a self-assembled multilayer polystyrene (PS) structure template. Due to the self-limiting surface reaction mechanism of ALD and the utilization of pressure tuned stop-flow ALD processes, the as fabricated TiO2/MoS2-IO structure has a high uniformity, reflected by FESEM and FIB-SEM characterization. A crystallized TiO2/MoS2-IO structure can be obtained through a post annealing process. As a 3D photonic crystal, the TiO2/MoS2-IO exhibits obvious stopband reflecting peaks, which can be adjusted through changing the opal diameters as well as the thickness of MoS2 layer.

The use of hydrogenous material for sensitizing pMOS dosimeters to neutrons

NASA Astrophysics Data System (ADS)

Kronenberg, S.; Brucker, G. J.

1995-02-01

This paper is concerned with the application of pMOS dosimeters to measuring neutron dose by the use of hydrogenous materials to convert incident neutron flux to recoil protons. These latter charged particles can generate electron-hole pairs, and consequently, charge trapping takes place at the MOS interfaces, and threshold voltage shifts are produced. The use of pMOS devices for measuring gamma doses has been described extensively in the literature. Clearly, if measurable voltage shifts could be generated in a MOS device by neutrons, then a radiation detection instrument containing two MOS devices, back to back, with hydrogenous shields, and one MOS dosimeter without a converter would allow 4/spl pi/ measurements of neutron and gamma doses to be made. The results obtained in this study indicate that paraffin or polyethylene will convert incident, 2.82 MeV neutrons to recoil protons, which subsequently cause measurable voltage shifts.

Enhanced photoresponse of monolayer molybdenum disulfide (MoS2) based on microcavity structure

NASA Astrophysics Data System (ADS)

Lu, Yanan; Yang, Guofeng; Wang, Fuxue; Lu, Naiyan

2018-05-01

There is an increasing interest in using monolayer molybdenum disulfide (MoS2) for optoelectronic devices because of its inherent direct band gap characteristics. However, the weak absorption of monolayer MoS2 restricts its applications, novel concepts need to be developed to address the weakness. In this work, monolayer MoS2 monolithically integrates with plane microcavity structure, which is formed by the top and bottom chirped distributed Bragg reflector (DBR), is demonstrated to improve the absorption of MoS2. The optical absorption is 17-fold enhanced, reaching values over 70% at work wavelength. Moreover, the monolayer MoS2-based photodetector device with microcavity presents a significantly increased photoresponse, demonstrating its promising prospects in MoS2-based optoelectronic devices.

Validity and reliability of Arabic MOS social support survey.

PubMed

Dafaalla, Mohamed; Farah, Abdulraheem; Bashir, Sheima; Khalil, Ammar; Abdulhamid, Rabab; Mokhtar, Mousab; Mahadi, Mohamed; Omer, Zulfa; Suliman, Asgad; Elkhalifa, Mohammed; Abdelgadir, Hanin; Kheir, Abdelmoneim E M; Abdalrahman, Ihab

2016-01-01

We aimed to generate a valid reliable Arabic version of MOS social support survey (MOS-SSS). We did a cross sectional study in medical students of Faculty of Medicine in Khartoum, Sudan. We did a clustered random sampling in 500 students of which 487 were suitable for analysis. We followed the standard translation process for translating the MOS-SSS. We accomplished factor analysis to assess construct validity, and generated item-scales correlations to evaluate the convergent and discriminant validity. We extracted the Cronbach's α and Spearman Brown coefficient of spit half method to determine internal consistency. We measured stability by correlation between the scores of the MOS survey taken at two different occasions with ten days apart in 252 participants. All items correlated highly (0.788 or greater) with their hypothesized scales. All items in subscales correlated higher by two standard errors with their own scale than with any other scale. Principle component analysis with varimax rotation was conducted on the 19 items and examination of scree plot graphically suggested 4 predominant factors that account for 72 % of variance. It showed high loadings, ranging from 0.720 to 0.84 for items of emotional support, 0.699-0.845 for tangible support, 0.518-0.823 for affectionate support, and 0.740-0.816 for positive social interaction. Cronbach's alpha for overall MOS scale and subscales indicated high internal consistency. The test-retest correlation showed weak correlation between the test and retest (ranges from 0.04 to 0.104). The Arabic MOS-SSS had high validity and internal consistency.

Target capture during Mos1 transposition.

PubMed

Pflieger, Aude; Jaillet, Jerôme; Petit, Agnès; Augé-Gouillou, Corinne; Renault, Sylvaine

2014-01-03

DNA transposition contributes to genomic plasticity. Target capture is a key step in the transposition process, because it contributes to the selection of new insertion sites. Nothing or little is known about how eukaryotic mariner DNA transposons trigger this step. In the case of Mos1, biochemistry and crystallography have deciphered several inverted terminal repeat-transposase complexes that are intermediates during transposition. However, the target capture complex is still unknown. Here, we show that the preintegration complex (i.e., the excised transposon) is the only complex able to capture a target DNA. Mos1 transposase does not support target commitment, which has been proposed to explain Mos1 random genomic integrations within host genomes. We demonstrate that the TA dinucleotide used as the target is crucial both to target recognition and in the chemistry of the strand transfer reaction. Bent DNA molecules are better targets for the capture when the target DNA is nicked two nucleotides apart from the TA. They improve strand transfer when the target DNA contains a mismatch near the TA dinucleotide.

Target Capture during Mos1 Transposition*

PubMed Central

Pflieger, Aude; Jaillet, Jerôme; Petit, Agnès; Augé-Gouillou, Corinne; Renault, Sylvaine

2014-01-01

DNA transposition contributes to genomic plasticity. Target capture is a key step in the transposition process, because it contributes to the selection of new insertion sites. Nothing or little is known about how eukaryotic mariner DNA transposons trigger this step. In the case of Mos1, biochemistry and crystallography have deciphered several inverted terminal repeat-transposase complexes that are intermediates during transposition. However, the target capture complex is still unknown. Here, we show that the preintegration complex (i.e., the excised transposon) is the only complex able to capture a target DNA. Mos1 transposase does not support target commitment, which has been proposed to explain Mos1 random genomic integrations within host genomes. We demonstrate that the TA dinucleotide used as the target is crucial both to target recognition and in the chemistry of the strand transfer reaction. Bent DNA molecules are better targets for the capture when the target DNA is nicked two nucleotides apart from the TA. They improve strand transfer when the target DNA contains a mismatch near the TA dinucleotide. PMID:24269942

Ultra-broadband nonlinear saturable absorption of high-yield MoS2 nanosheets

NASA Astrophysics Data System (ADS)

Wei, Rongfei; Zhang, Hang; Hu, Zhongliang; Qiao, Tian; He, Xin; Guo, Qiangbing; Tian, Xiangling; Chen, Zhi; Qiu, Jianrong

2016-07-01

High-yield MoS2 nanosheets with strong nonlinear optical (NLO) responses in a broad near-infrared range were synthesized by a facile hydrothermal method. The observation of saturable absorption, which was excited by the light with photon energy smaller than the gap energy of MoS2, can be attributed to the enhancement of the hybridization between the Mo d-orbital and S p-orbital by the oxygen incorporation into MoS2. High-yield MoS2 nanosheets with high modulation depth and large saturable intensity generated a stable, passively Q-switched fiber laser pulse at 1.56 μm. The high output power of 1.08 mW can be attained under a very low pump power of 30.87 mW. Compared to recently reported passively Q-switched fiber lasers utilizing exfoliated MoS2 nanosheets, the efficiency of the laser for our passive Q-switching operation is larger and reaches 3.50%. This research may extend the understanding on the NLO properties of MoS2 and indicate the feasibility of the high-yield MoS2 nanosheets to passively Q-switched fiber laser effectively at low pump strengths.

Thermal management in MoS2 based integrated device using near-field radiation

NASA Astrophysics Data System (ADS)

Peng, Jiebin; Zhang, Gang; Li, Baowen

2015-09-01

Recently, wafer-scale growth of monolayer MoS2 films with spatial homogeneity is realized on SiO2 substrate. Together with the latest reported high mobility, MoS2 based integrated electronic devices are expected to be fabricated in the near future. Owing to the low lattice thermal conductivity in monolayer MoS2, and the increased transistor density accompanied with the increased power density, heat dissipation will become a crucial issue for these integrated devices. In this letter, using the formalism of fluctuation electrodynamics, we explored the near-field radiative heat transfer from a monolayer MoS2 to graphene. We demonstrate that in resonance, the maximum heat transfer via near-field radiation between MoS2 and graphene can be ten times higher than the in-plane lattice thermal conduction for MoS2 sheet. Therefore, an efficient thermal management strategy for MoS2 integrated device is proposed: Graphene sheet is brought into close proximity, 10-20 nm from MoS2 device; heat energy transfer from MoS2 to graphene via near-field radiation; this amount of heat energy then be conducted to contact due to ultra-high lattice thermal conductivity of graphene. Our work sheds light for developing cooling strategy for nano devices constructing with low thermal conductivity materials.

Two-dimensional MoS2: A promising building block for biosensors.

PubMed

Gan, Xiaorong; Zhao, Huimin; Quan, Xie

2017-03-15

Recently, two-dimensional (2D) layered nanomaterials have trigged intensive interest due to the intriguing physicochemical properties that stem from a quantum size effect connected with their ultra-thin structure. In particular, 2D molybdenum disulfide (MoS 2 ), as an emerging class of stable inorganic graphene analogs with intrinsic finite bandgap, would possibly complement or even surpass graphene in electronics and optoelectronics fields. In this review, we first discuss the historical development of ultrathin 2D nanomaterials. Then, we are concerned with 2D MoS 2 including its structure-property relationships, synthesis methods, characterization for the layer thickness, and biosensor applications over the past five years. Thereinto, we are highlighting recent advances in 2D MoS 2 -based biosensors, especially emphasize the preparation of sensing elements, roles of 2D MoS 2 , and assay strategies. Finally, on the basis of the current achievements on 2D MoS 2 and other ultrathin layered nanomaterials, perspectives on the challenges and opportunities for the exploration of 2D MoS 2 -based biosensors are put forward. Copyright © 2016 Elsevier B.V. All rights reserved.

Out-of-plane electron transport in finite layer MoS2

NASA Astrophysics Data System (ADS)

Holzapfel, R.; Weber, J.; Lukashev, P. V.; Stollenwerk, A. J.

2018-05-01

Ballistic electron emission microscopy (BEEM) has been used to study the processes affecting electron transport along the [0001] direction of finite layer MoS2 flakes deposited onto the surface of Au/Si(001) Schottky diodes. Prominent features present in the differential spectra from the MoS2 flakes are consistent with the density of states of finite layer MoS2 calculated using density functional theory. The ability to observe the electronic structure of the MoS2 appears to be due to the relatively smooth density of states of Si in this energy range and a substantial amount of elastic or quasi-elastic scattering along the MoS2/Au/Si(001) path. Demonstration of these measurements using BEEM suggests that this technique could potentially be used to study electron transport through van der Waals heterostructures, with applications in a number of electronic devices.

[MoS4]2- Cluster Bridges in Co-Fe Layered Double Hydroxides for Mercury Uptake from S-Hg Mixed Flue Gas.

PubMed

Xu, Haomiao; Yuan, Yong; Liao, Yong; Xie, Jiangkun; Qu, Zan; Shangguan, Wenfeng; Yan, Naiqiang

2017-09-05

[MoS 4 ] 2- clusters were bridged between CoFe layered double hydroxide (LDH) layers using the ion-exchange method. [MoS 4 ] 2- /CoFe-LDH showed excellent Hg 0 removal performance under low and high concentrations of SO 2 , highlighting the potential for such material in S-Hg mixed flue gas purification. The maximum mercury capacity was as high as 16.39 mg/g. The structure and physical-chemical properties of [MoS 4 ] 2- /CoFe-LDH composites were characterized with FT-IR, XRD, TEM&SEM, XPS, and H 2 -TPR. [MoS 4 ] 2- clusters intercalated into the CoFe-LDH layered sheets; then, we enlarged the layer-to-layer spacing (from 0.622 to 0.880 nm) and enlarged the surface area (from 41.4 m 2 /g to 112.1 m 2 /g) of the composite. During the adsorption process, the interlayer [MoS 4 ] 2- cluster was the primary active site for mercury uptake. The adsorbed mercury existed as HgS on the material surface. The absence of active oxygen results in a composite with high sulfur resistance. Due to its high efficiency and SO 2 resistance, [MoS 4 ] 2- /CoFe-LDH is a promising adsorbent for mercury uptake from S-Hg mixed flue gas.

Quantum transport through MoS2 constrictions defined by photodoping.

PubMed

Epping, Alexander; Banszerus, Luca; Güttinger, Johannes; Krückeberg, Luisa; Watanabe, Kenji; Taniguchi, Takashi; Hassler, Fabian; Beschoten, Bernd; Stampfer, Christoph

2018-05-23

We present a device scheme to explore mesoscopic transport through molybdenum disulfide (MoS 2 ) constrictions using photodoping. The devices are based on van-der-Waals heterostructures where few-layer MoS 2 flakes are partially encapsulated by hexagonal boron nitride (hBN) and covered by a few-layer graphene flake to fabricate electrical contacts. Since the as-fabricated devices are insulating at low temperatures, we use photo-induced remote doping in the hBN substrate to create free charge carriers in the MoS 2 layer. On top of the device, we place additional metal structures, which define the shape of the constriction and act as shadow masks during photodoping of the underlying MoS 2 /hBN heterostructure. Low temperature two- and four-terminal transport measurements show evidence of quantum confinement effects.

Quantum transport through MoS2 constrictions defined by photodoping

NASA Astrophysics Data System (ADS)

Epping, Alexander; Banszerus, Luca; Güttinger, Johannes; Krückeberg, Luisa; Watanabe, Kenji; Taniguchi, Takashi; Hassler, Fabian; Beschoten, Bernd; Stampfer, Christoph

2018-05-01

We present a device scheme to explore mesoscopic transport through molybdenum disulfide (MoS2) constrictions using photodoping. The devices are based on van-der-Waals heterostructures where few-layer MoS2 flakes are partially encapsulated by hexagonal boron nitride (hBN) and covered by a few-layer graphene flake to fabricate electrical contacts. Since the as-fabricated devices are insulating at low temperatures, we use photo-induced remote doping in the hBN substrate to create free charge carriers in the MoS2 layer. On top of the device, we place additional metal structures, which define the shape of the constriction and act as shadow masks during photodoping of the underlying MoS2/hBN heterostructure. Low temperature two- and four-terminal transport measurements show evidence of quantum confinement effects.

MoS2 @HKUST-1 Flower-Like Nanohybrids for Efficient Hydrogen Evolution Reactions.

PubMed

Wang, Chengli; Su, Yingchun; Zhao, Xiaole; Tong, Shanshan; Han, Xiaojun

2018-01-24

A novel MoS 2 -based flower-like nanohybrid for hydrogen evolution was fabricated through coating the Cu-containing metal-organic framework (HKUST-1) onto MoS 2 nanosheets. It is the first time that MoS 2 @HKUST-1 nanohybrids have been reported for the enhanced electrochemical performance of HER. The morphologies and components of the MoS 2 @HKUST-1 flower-like nanohybrids were characterized by scanning electron microscopy, X-ray diffraction analysis and Fourier transform infrared spectroscopy. Compared with pure MoS 2 , the MoS 2 @HKUST-1 hybrids exhibit enhanced performance on hydrogen evolution reaction with an onset potential of -99 mV, a smaller Tafel slope of 69 mV dec -1 , and a Faradaic efficiency of nearly 100 %. The MoS 2 @HKUST-1 flower-like nanohybrids exhibit excellent stability in acidic media. This design opens new possibilities to effectively synthesize non-noble metal catalysts with high performance for the hydrogen evolution reaction (HER). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced monolayer MoS2/InP heterostructure solar cells by graphene quantum dots

NASA Astrophysics Data System (ADS)

Wang, Peng; Lin, Shisheng; Ding, Guqiao; Li, Xiaoqiang; Wu, Zhiqian; Zhang, Shengjiao; Xu, Zhijuan; Xu, Sen; Lu, Yanghua; Xu, Wenli; Zheng, Zheyang

2016-04-01

We demonstrate significantly improved photovoltaic response of monolayer molybdenum disulfide (MoS2)/indium phosphide (InP) van der Waals heterostructure induced by graphene quantum dots (GQDs). Raman and photoluminescence measurements indicate that effective charge transfer takes place between GQDs and MoS2, which results in n-type doping of MoS2. The doping effect increases the barrier height at the MoS2/InP heterojunction, thus the averaged power conversion efficiency of MoS2/InP solar cells is improved from 2.1% to 4.1%. The light induced doping by GQD provides a feasible way for developing more efficient MoS2 based heterostructure solar cells.

Mechanism of Antiwear Property Under High Pressure of Synthetic Oil-Soluble Ultrathin MoS2 Sheets as Lubricant Additives.

PubMed

Chen, Zhe; Liu, Yuhong; Gunsel, Selda; Luo, Jianbin

2018-01-30

Wear occurs between two rubbing surfaces. Severe wear due to seizure under high pressure leads to catastrophic failures of mechanical systems and raises wide concerns. In this paper, a kind of synthetic oil-soluble ultrathin MoS 2 sheets is synthesized and investigated as lubricant additives between steel surfaces. It is found that, with the ultrathin MoS 2 sheets, the wear can be controlled under the nominal pressure of about 1 GPa, whereas the bearable nominal pressure for traditional lubricants is only a few hundred megapascals. It is found that when wear is under control, the real pressure between the asperities agrees with the breaking strength of ultrathin MoS 2 . Therefore, it is believed that, because of the good oil solubility and ultrasmall thickness, the ultrathin MoS 2 sheets can easily enter the contact area between the contacting asperities. Then, the localized seizure and further wear are prevented because there will be no metal-to-metal contact as long as the real pressure between the asperities is below the breaking strength of ultrathin MoS 2 . In this way, the upper limit pressure the lubricant can work is dependent on the mechanical properties of the containing ultrathin two-dimensional (2D) sheets. Additionally, ultrathin MoS 2 sheets with various lateral sizes are compared, and it is found that sheets with a larger size show better lubrication performance. This work discovers the lubrication mechanism of ultrathin MoS 2 sheets as lubricant additives and provides an inspiration to develop a novel generation of lubricant additives with high-strength ultrathin 2D materials.

Realization of high Curie temperature ferromagnetism in atomically thin MoS2 and WS2 nanosheets with uniform and flower-like morphology.

PubMed

Yang, Zhaolong; Gao, Daqiang; Zhang, Jing; Xu, Qiang; Shi, Shoupeng; Tao, Kun; Xue, Desheng

2015-01-14

High Curie temperature ferromagnetism has been realized in atomically thin MoS2 and WS2 nanosheets. The ultrathin nanosheet samples were prepared via a novel, simple and efficient chemical vapor deposition method; different kinds of transition metal disulfides (MoS2 and WS2) could be obtained by sulphuring the corresponding cation sources (MoO3 and WCl6). Through related morphological and structural characterization, we confirm that large-area, uniform, few-layer MoS2 and WS2 nanosheets were successfully synthesized by this method. Both nanosheet samples exhibit distinct ferromagnetic behavior. By careful measurement and fitting of the magnetization of MoS2 and WS2 samples at different temperatures, we deconstruct the magnetization into its diamagnetic, paramagnetic and ferromagnetic contributions. The ferromagnetic contributions persist until 865 K for MoS2 and 820 K for WS2. We attribute the observed ferromagnetic properties to the defects and dislocations produced during the growth process, as well as the presence of edge spins at the edge of the nanosheets.

Gap-Mode Surface-Plasmon-Enhanced Photoluminescence and Photoresponse of MoS2.

PubMed

Wu, Zhi-Qian; Yang, Jing-Liang; Manjunath, Nallappagar K; Zhang, Yue-Jiao; Feng, Si-Rui; Lu, Yang-Hua; Wu, Jiang-Hong; Zhao, Wei-Wei; Qiu, Cai-Yu; Li, Jian-Feng; Lin, Shi-Sheng

2018-05-22

2D materials hold great potential for designing novel electronic and optoelectronic devices. However, 2D material can only absorb limited incident light. As a representative 2D semiconductor, monolayer MoS 2 can only absorb up to 10% of the incident light in the visible, which is not sufficient to achieve a high optical-to-electrical conversion efficiency. To overcome this shortcoming, a "gap-mode" plasmon-enhanced monolayer MoS 2 fluorescent emitter and photodetector is designed by squeezing the light-field into Ag shell-isolated nanoparticles-Au film gap, where the confined electromagnetic field can interact with monolayer MoS 2 . With this gap-mode plasmon-enhanced configuration, a 110-fold enhancement of photoluminescence intensity is achieved, exceeding values reached by other plasmon-enhanced MoS 2 fluorescent emitters. In addition, a gap-mode plasmon-enhanced monolayer MoS 2 photodetector with an 880% enhancement in photocurrent and a responsivity of 287.5 A W -1 is demonstrated, exceeding previously reported plasmon-enhanced monolayer MoS 2 photodetectors. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CMOS-compatible batch processing of monolayer MoS2 MOSFETs

NASA Astrophysics Data System (ADS)

Xiong, Kuanchen; Kim, Hyun; Marstell, Roderick J.; Göritz, Alexander; Wipf, Christian; Li, Lei; Park, Ji-Hoon; Luo, Xi; Wietstruck, Matthias; Madjar, Asher; Strandwitz, Nicholas C.; Kaynak, Mehmet; Lee, Young Hee; Hwang, James C. M.

2018-04-01

Thousands of high-performance 2D metal-oxide-semiconductor field effect transistors (MOSFETs) were fabricated on wafer-scale chemical vapor deposited MoS2 with fully-CMOS-compatible processes such as photolithography and aluminum metallurgy. The yield was greater than 50% in terms of effective gate control with less-than-10 V threshold voltage, even for MOSFETs having deep-submicron gate length. The large number of fabricated MOSFETs allowed statistics to be gathered and the main yield limiter to be attributed to the weak adhesion between the transferred MoS2 and the substrate. With cut-off frequencies approaching the gigahertz range, the performances of the MOSFETs were comparable to that of state-of-the-art MoS2 MOSFETs, whether the MoS2 was grown by a thin-film process or exfoliated from a bulk crystal.

Effective size selection of MoS2 nanosheets by a novel liquid cascade centrifugation: Influences of the flakes dimensions on electrochemical and photoelectrochemical applications.

PubMed

Kajbafvala, Marzieh; Farbod, Mansoor

2018-05-14

Although liquid phase exfoliation is a powerful method to produce MoS 2 nanosheets in large scale, but its effectiveness is limited by the diversity of produced nanosheets sizes. Here a novel approach for separation of MoS 2 flakes having various lateral sizes and thicknesses based on the cascaded centrifugation has been introduced. This method involves a pre-separation step which is performed through low-speed centrifugation to avoid the deposition of large area single and few-layers by the heavier particles. The bulk MoS 2 powders were dispersed in an aqueous solution of sodium cholate (SC) and sonicated for 12 h. The main separation step was performed using different speed centrifugation intervals of 10-11, 8-10, 6-8, 4-6, 2-4 and 0.5-2 krpm by which nanosheets containing 2, 4, 7, 8, 14, 18 and 29 layers were obtained respectively. The samples were characterized using XRD, FESEM, AFM, TEM, DLS and also UV-vis, Raman and PL spectroscopy measurements. Dynamic light scattering (DLS) measurements have confirmed the existence of a larger number of single or few-layers MoS 2 nanosheets compared to when the pre-separation step was not used. Finally, Photocurrent and cyclic voltammetry of different samples were measured and found that the flakes with bigger surface area had larger CV loop area. Our results provide a method for the preparation of a MoS 2 monolayer enriched suspension which can be used for different applications. Copyright © 2018 Elsevier Inc. All rights reserved.

Atomically Thin-Layered Molybdenum Disulfide (MoS2) for Bulk-Heterojunction Solar Cells.

PubMed

Singh, Eric; Kim, Ki Seok; Yeom, Geun Young; Nalwa, Hari Singh

2017-02-01

Transition metal dichalcogenides (TMDs) are becoming significant because of their interesting semiconducting and photonic properties. In particular, TMDs such as molybdenum disulfide (MoS 2 ), molybdenum diselenide (MoSe 2 ), tungsten disulfide (WS 2 ), tungsten diselenide (WSe 2 ), titanium disulfide (TiS 2 ), tantalum sulfide (TaS 2 ), and niobium selenide (NbSe 2 ) are increasingly attracting attention for their applications in solar cell devices. In this review, we give a brief introduction to TMDs with a focus on MoS 2 ; and thereafter, emphasize the role of atomically thin MoS 2 layers in fabricating solar cell devices, including bulk-heterojunction, organic, and perovskites-based solar cells. Layered MoS 2 has been used as the hole-transport layer (HTL), electron-transport layer (ETL), interfacial layer, and protective layer in fabricating heterojunction solar cells. The trilayer graphene/MoS 2 /n-Si solar cell devices exhibit a power-conversion efficiency of 11.1%. The effects of plasma and chemical doping on the photovoltaic performance of MoS 2 solar cells have been analyzed. After doping and electrical gating, a power-conversion efficiency (PCE) of 9.03% has been observed for the MoS 2 /h-BN/GaAs heterostructure solar cells. The MoS 2 -containing perovskites-based solar cells show a PCE as high as 13.3%. The PCE of MoS 2 -based organic solar cells exceeds 8.40%. The stability of MoS 2 solar cells measured under ambient conditions and light illumination has been discussed. The MoS 2 -based materials show a great potential for solar cell devices along with high PCE; however, in this connection, their long-term environmental stability is also of equal importance for commercial applications.

Silicon superlattices. 2: Si-Ge heterostructures and MOS systems

NASA Technical Reports Server (NTRS)

Moriarty, J. A.

1983-01-01

Five main areas were examined: (1) the valence-and conduction-band-edge electronic structure of the thin layer ( 11 A) silicon-superlattice systems; (2) extension of thin-layer calculations to layers of thickness 11 A, where most potential experimental interest lies; (3) the electronic structure of thicker-layer (11 to 110 A) silicon superlattices; (4) preliminary calculations of impurity-scattering-limited electron mobility in the thicker-layer superlattices; and (5) production of the fine metal lines that would be required to produce on MOS superlattice.

Determination of band alignment at two-dimensional MoS2/Si van der Waals heterojunction

NASA Astrophysics Data System (ADS)

Goel, Neeraj; Kumar, Rahul; Mishra, Monu; Gupta, Govind; Kumar, Mahesh

2018-06-01

To understand the different mechanism occurring at the MoS2-silicon interface, we have fabricated a MoS2/Si heterojunction by exfoliating MoS2 on top of the silicon substrate. Raman spectroscopy and atomic force microscopy (AFM) measurement expose the signature of few-layers in the deposited MoS2 flake. Herein, the temperature dependence of the energy barrier and carrier density at the MoS2/Si heterojunction has been extensively investigated. Furthermore, to study band alignment at the MoS2/Si interface, we have calculated a valence band offset of 0.66 ± 0.17 eV and a conduction band offset of 0.42 ± 0.17 eV using X-ray and Ultraviolet photoelectron spectroscopy. We determined a type-II band alignment at the interface which is very conducive for the transport of photoexcited carriers. As a proof-of-concept application, we extend our analysis of the photovoltaic behavior of the MoS2/Si heterojunction. This work provides not only a comparative study between MoS2/p-Si and MoS2/n-Si heterojunctions but also paves the way to engineer the properties of the interface for the future integration of MoS2 with silicon.

Variability Analysis of MOS Differential Amplifier

NASA Astrophysics Data System (ADS)

Aoki, Masakazu; Seto, Kenji; Yamawaki, Taizo; Tanaka, Satoshi

Variation characteristics in MOS differential amplifier are evaluated by using the concise statistical model parameters for SPICE simulation. We find that the variation in the differential-mode gain, Adm, induced by the current factor variation, Δβ0, in the Id-variation of the differential MOS transistors is more than one order of magnitude larger than that induced by the threshold voltage variation, ΔVth, which has been regarded as a major factor for circuit variations in SoC's (2). The results obtained by the Monte Carlo simulations are verified by the theoretical analysis combined with the sensitivity analysis which clarifies the specific device parameter dependences of the variation in Adm.

High current density 2D/3D MoS2/GaN Esaki tunnel diodes

NASA Astrophysics Data System (ADS)

Krishnamoorthy, Sriram; Lee, Edwin W.; Lee, Choong Hee; Zhang, Yuewei; McCulloch, William D.; Johnson, Jared M.; Hwang, Jinwoo; Wu, Yiying; Rajan, Siddharth

2016-10-01

The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current density of 446 A/cm2 with repeatable room temperature negative differential resistance, peak to valley current ratio of 1.2, and minimal hysteresis was measured in the MoS2/GaN non-epitaxial tunnel diode. A high current density of 1 kA/cm2 was measured in the Zener mode (reverse bias) at -1 V bias. The GaN/MoS2 tunnel junction was also modeled by treating MoS2 as a bulk semiconductor, and the electrostatics at the 2D/3D interface was found to be crucial in explaining the experimentally observed device characteristics.

Design, Modeling, and Fabrication of Chemical Vapor Deposition Grown MoS2 Circuits with E-Mode FETs for Large-Area Electronics.

PubMed

Yu, Lili; El-Damak, Dina; Radhakrishna, Ujwal; Ling, Xi; Zubair, Ahmad; Lin, Yuxuan; Zhang, Yuhao; Chuang, Meng-Hsi; Lee, Yi-Hsien; Antoniadis, Dimitri; Kong, Jing; Chandrakasan, Anantha; Palacios, Tomas

2016-10-12

Two-dimensional electronics based on single-layer (SL) MoS 2 offers significant advantages for realizing large-scale flexible systems owing to its ultrathin nature, good transport properties, and stable crystalline structure. In this work, we utilize a gate first process technology for the fabrication of highly uniform enhancement mode FETs with large mobility and excellent subthreshold swing. To enable large-scale MoS 2 circuit, we also develop Verilog-A compact models that accurately predict the performance of the fabricated MoS 2 FETs as well as a parametrized layout cell for the FET to facilitate the design and layout process using computer-aided design (CAD) tools. Using this CAD flow, we designed combinational logic gates and sequential circuits (AND, OR, NAND, NOR, XNOR, latch, edge-triggered register) as well as switched capacitor dc-dc converter, which were then fabricated using the proposed flow showing excellent performance. The fabricated integrated circuits constitute the basis of a standard cell digital library that is crucial for electronic circuit design using hardware description languages. The proposed design flow provides a platform for the co-optimization of the device fabrication technology and circuits design for future ubiquitous flexible and transparent electronics using two-dimensional materials.

Enhanced photoresponse characteristics of transistors using CVD-grown MoS2/WS2 heterostructures

NASA Astrophysics Data System (ADS)

Shan, Junjie; Li, Jinhua; Chu, Xueying; Xu, Mingze; Jin, Fangjun; Fang, Xuan; Wei, Zhipeng; Wang, Xiaohua

2018-06-01

Semiconductor heterostructures based on transition metal dichalcogenides provide a broad platform to research two-dimensional nanomaterials and design atomically thin devices for fundamental and applied interests. The MoS2/WS2 heterostructure was prepared on SiO2/Si substrate by chemical vapor deposition (CVD) in our research. And the optical properties of the heterostructure was characterized by Raman and photoluminescence (PL) spectroscopy. The similar 2 orders of magnitude decrease of PL intensity in MoS2/WS2 heterostructures was tested, which is attribute to the electrical and optical modulation effects are connected with the interfacial charge transfer between MoS2 and WS2 films. Using MoS2/WS2 heterostructure as channel material of the phototransistor, we demonstrated over 50 folds enhanced photoresponsivity of multilayer MoS2 field-effect transistor. The results indicate that the MoS2/WS2 films can be a promising heterostructure material to enhance the photoresponse characteristics of MoS2-based phototransistors.

Strain and structure heterogeneity in MoS 2 atomic layers grown by chemical vapour deposition

DOE PAGES

Liu, Zheng; Amani, Matin; Najmaei, Sina; ...

2014-11-18

Monolayer molybdenum disulfide (MoS 2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices, and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS 2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS 2. Recently, large-size monolayer MoS 2 has been produced by chemical vapor deposition but has not yet been fully explored. Here we systematically characterize chemical vapor deposition grown MoS 2 by PL spectroscopy and mapping, and demonstrate non-uniform strain in single-crystalline monolayer MoS 2 and strain-induced band gap engineering. We also evaluatemore » the effective strain transferred from polymer substrates to MoS 2 by three-dimensional finite element analysis. In addition, our work demonstrates that PL mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS 2.« less

Extraordinary attributes of 2-dimensional MoS2 nanosheets

NASA Astrophysics Data System (ADS)

Rao, C. N. R.; Maitra, Urmimala; Waghmare, Umesh V.

2014-08-01

The discovery of the amazing properties of graphene has stimulated exploration of single- and few-layer structures of layered inorganic materials. Of all the inorganic 2D nanosheet structures, those of MoS2 have attracted great attention because of their novel properties such as the presence of a direct bandgap, good field-effect transistor characteristics, large spin-orbit splitting, intense photoluminescence, catalytic properties, magnetism, superconductivity, ferroelectricity and several other properties with potential applications in electronics, optoelectronics, energy devices and spintronics. MoS2 nanosheets have been used in lithium batteries, supercapacitors and to generate hydrogen. Highlights of the impressive properties of MoS2 nanosheets, along with their structural and spectroscopic features are presented in this Letter. MoS2 typifies the family of metal dichalcogenides such as MoSe2 and WS2 and there is much to be done on nanosheets of these materials. Linus Pauling would have been pleased to see how molybdenite whose structure he studied in 1923 has become so important today.

Plasma nanocoating of thiophene onto MoS2 nanotubes

NASA Astrophysics Data System (ADS)

Türkaslan, Banu Esencan; Dikmen, Sibel; Öksüz, Lütfi; Öksüz, Aysegul Uygun

2015-12-01

MoS2 nanotubes were coated with conductive polymer thiophene by atmospheric pressure radio-frequency (RF) glow discharge. MoS2 nanotubes were prepared by thermal decomposition of hexadecylamine (HDA) intercalated laminar MoS2 precursor on anodized aluminum oxide template and the thiophene was polymerized directly on surface of these nanotubes as in situ by plasma method. The effect of plasma power on PTh/MoS2 nanocomposite properties has been investigated by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM and EDX), and X-ray diffraction spectroscopy (XRD). The presence of PTh bands in the FTIR spectra of PTh/MoS2 nanotube nanocomposites corresponding XRD results indicates that the polythiophene coating onto MoS2 nanotube. The chemical structure of PTh is not changed when the plasma power of discharge differ from 117 to 360 W. SEM images of nanocomposites show that when the discharge power is increased between 117 and 360 W the average diameter of PTh/MoS2 nanotube nanocomposites are changed and the structure become more uniformly.

Strain-Enhanced p Doping in Monolayer MoS2

NASA Astrophysics Data System (ADS)

Choi, Minseok

2018-02-01

Achievement of desired p -type electrical properties in MoS2 remains a challenge. Here, we demonstrate that p doping in monolayer MoS2 can be enhanced in terms of strain manipulation, through first-principles hybrid functional calculations. Biaxial tensile strain and shear strain with smaller in-plane angles induce the dramatic reduction in formation energy of p dopants such as niobium and tantalum, providing the moderate doping contents required for applications. In addition, the formation of sulfur vacancies which are potential compensators of holes released from the dopants is suppressed by the strains. Our calculations pave an alternative strategy to overcome in the realization of p doping in monolayer MoS2 .

MOS1 Osmosensor of Metarhizium anisopliae Is Required for Adaptation to Insect Host Hemolymph▿

PubMed Central

Wang, Chengshu; Duan, Zhibing; St. Leger, Raymond J.

2008-01-01

Entomopathogenic fungi such as Metarhizium anisopliae infect insects by direct penetration of the cuticle, after which the fungus adapts to the high osmotic pressure of the hemolymph and multiplies. Here we characterize the M. anisopliae Mos1 gene and demonstrate that it encodes the osmosensor required for this process. MOS1 contains transmembrane regions and a C-terminal Src homology 3 domain similar to those of yeast osmotic adaptor proteins, and homologs of MOS1 are widely distributed in the fungal kingdom. Reverse transcription-PCR demonstrated that Mos1 is up-regulated in insect hemolymph as well as artificial media with high osmotic pressure. Transformants containing an antisense vector directed to the Mos1 mRNA depleted transcript levels by 80%. This produced selective alterations in regulation of genes involved in hyphal body formation, cell membrane stiffness, and generation of intracellular turgor pressure, suggesting that these processes are mediated by MOS1. Consistent with a role in stress responses, transcript depletion of Mos1 increased sensitivity to osmotic and oxidative stresses and to compounds that interfere with cell wall biosynthesis. It also disrupted developmental processes, including formation of appressoria and hyphal bodies. Insect bioassays confirmed that Mos1 knockdown significantly reduces virulence. Overall, our data show that M. anisopliae MOS1 mediates cellular responses to high osmotic pressure and subsequent adaptations to colonize host hemolymph. PMID:18055914

Strongly luminescent monolayered MoS2 prepared by effective ultrasound exfoliation.

PubMed

Štengl, Václav; Henych, Jiří

2013-04-21

Intense ultrasound in a pressurized batch reactor was used for preparation of monolayered MoS2 nanosheets from natural mineral molybdenite. Exfoliation of bulk MoS2 using ultrasound is an attractive route to large-scale preparation of monolayered crystals. To evaluate the quality of delamination, methods like X-ray diffraction, Raman spectroscopy and microscopic techniques (TEM and AFM) were employed. From single- or few-layered products obtained from intense sonication, MoS2 quantum dots (MoSQDs) were prepared by a one-pot reaction by refluxing exfoliated nanosheets of MoS2 in ethylene glycol under atmospheric pressure. The synthesised MoSQDs were characterised by photoluminescence spectroscopy and laser-scattering particle size analysis. Our easy preparation leads to very strongly green luminescing quantum dots.

Threshold Dependence of Deep- and Near-subwavelength Ripples Formation on Natural MoS2 Induced by Femtosecond Laser

PubMed Central

Pan, Yusong; Yang, Ming; Li, Yumei; Wang, Zhenhua; Zhang, Chunling; Zhao, Ying; Yao, Jianghong; Wu, Qiang; Xu, Jingjun

2016-01-01

Deep sub-wavelength ripples (DSRs) and near sub-wavelength ripples (NSRs) with uniform periods of ~160 nm and ~660 nm generated at the MoS2-vacuum interface is reported for the first time by the processing of femtosecond laser (800 nm, 120 fs, 1 kHz) in this paper. The DSRs and NSRs formation fluence thresholds are experimentally determined as 160 mJ/cm2 and 192 mJ/cm2, respectively. In addition, the ripple period is insensitive to the pulse number. Moreover, Raman analyses show that the MoS2 lattice in the irradiated area does not exhibit oxidation at room environment and the crystalline representation is well preserved in NSRs region. We attribute our result to the joint interactions of the spallation and sublimation of layered MoS2 together with the laser induced surface plasmon polaritons and propose an explanation to the threshold dependence of the ripple period. Our study provides some insights for ultrafast laser-matter interactions and indicates a simple effective method for future nano-fabrication of MoS2. PMID:26795074

Locality and rapidity of the ultra-large elastic deformation of Nb nanowires in a NiTi phase-transforming matrix

DOE PAGES

Wang, Shan; Cui, Lishan; Hao, Shijie; ...

2014-10-24

This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strainmore » of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design.« less

Biomining of MoS2 with Peptide-based Smart Biomaterials.

PubMed

Cetinel, Sibel; Shen, Wei-Zheng; Aminpour, Maral; Bhomkar, Prasanna; Wang, Feng; Borujeny, Elham Rafie; Sharma, Kumakshi; Nayebi, Niloofar; Montemagno, Carlo

2018-02-20

Biomining of valuable metals using a target specific approach promises increased purification yields and decreased cost. Target specificity can be implemented with proteins/peptides, the biological molecules, responsible from various structural and functional pathways in living organisms by virtue of their specific recognition abilities towards both organic and inorganic materials. Phage display libraries are used to identify peptide biomolecules capable of specifically recognizing and binding organic/inorganic materials of interest with high affinities. Using combinatorial approaches, these molecular recognition elements can be converted into smart hybrid biomaterials and harnessed for biotechnological applications. Herein, we used a commercially available phage-display library to identify peptides with specific binding affinity to molybdenite (MoS 2 ) and used them to decorate magnetic NPs. These peptide-coupled NPs could capture MoS 2 under a variety of environmental conditions. The same batch of NPs could be re-used multiple times to harvest MoS 2 , clearly suggesting that this hybrid material was robust and recyclable. The advantages of this smart hybrid biomaterial with respect to its MoS 2 -binding specificity, robust performance under environmentally challenging conditions and its recyclability suggests its potential application in harvesting MoS 2 from tailing ponds and downstream mining processes.

Two-dimensional hybrid materials: MoS2-RGO nanocomposites enhanced the barrier properties of epoxy coating

NASA Astrophysics Data System (ADS)

Chen, Chunlin; He, Yi; Xiao, Guoqing; Xia, Yunqin; Li, Hongjie; He, Ze

2018-06-01

By the way of hydrothermal reaction, the MoS2 nanoparticles were loaded on the surface of GO sheets uniformly. Then, the MoS2-RGO composites were modified with γ-(2,3-epoxypropoxy)propytrimethoxysilane (KH560), and followed by preparing the MoS2-RGO/epoxy composite coatings. The morphology and structure of MoS2-RGO were characterized though SEM, TEM, FT-IR and XPS. Besides, the corrosion resistance properties of the as-prepared MoS2-RGO/epoxy composite coatings were characterized by means of electrochemical impedance spectroscopy (EIS) and polarization curves analysis, and then the thermal stability and water permeability resistance of coatings were characterized. The results showed that the MoS2 could be loaded on the surface of GO uniformly when the ratio between MoS2 and GO is 1:1. The anti-corrosion property and permeability resistance of the MoS2-RGO/epoxy composites coating was enhanced significantly due to its excellent barrier property. Besides, the thermal property analysis exhibits that the lamellar structure of MoS2, GO and MoS2-RGO can effectively block the escape of the pyrolysis products, resulting in the maximum thermal weightlessness reduced.

One-pot synthesis of MoS2/In2S3 ultrathin nanoflakes with mesh-shaped structure on indium tin oxide as photocathode for enhanced photo-and electrochemical hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Sun, Baoliang; Shan, Fei; Jiang, Xinxin; Ji, Jing; Wang, Feng

2018-03-01

A bifunctional MoS2/In2S3 hybrid composite that has both photo- and electrocatalytic activity toward hydrogen evolution reaction (HER) is prepared by a facile one pot hydrothermal method. The characterizations by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM) and Photoluminescence (PL) shows that the MoS2/In2S3 hybrid exhibits ultrathin nanoflakes with mesh-shaped structure on transparent conductive substrates, and the as prepared catalyst composite obviously improves the separation of electro-hole pairs. The as prepared hybrid nanosheets with Mo:In of 1/2 integrate In-doped MoS2 to reduce the stacking and increase the active surface area. The novel mesh-shaped nanostructure with a moderate degree of disorder provides not only simultaneously intrinsic conductivity and defects but also higher electrochemically active surface area (ECSA). By electrochemical measurements, such as linear sweep voltammetry (LSV), electrochemical impedance spectroscope (EIS) and cyclic voltammetry (CV), we find that the MoS2/In2S3 hybrid possesses much better photo/electrochemical activity than pristine MoS2 or In2S3. MoS2/In2S3 ultrathin nanoflaks are anticipated to be a superior photoelectrocatalyst for PEC cells, and the rational use of the MoS2/In2S3 cathode offers a new avenue toward achieving effective photo-assistant electrocatalytic activity.

Single-poly EEPROM cell with lightly doped MOS capacitors

DOEpatents

Riekels, James E [New Hope, MN; Lucking, Thomas B [Maple Grove, MN; Larsen, Bradley J [Mound, MN; Gardner, Gary R [Golden Valley, MN

2008-05-27

An Electrically Erasable Programmable Read Only Memory (EEPROM) memory cell and a method of operation are disclosed for creating an EEPROM memory cell in a standard CMOS process. A single polysilicon layer is used in combination with lightly doped MOS capacitors. The lightly doped capacitors employed in the EEPROM memory cell can be asymmetrical in design. Asymmetrical capacitors reduce area. Further capacitance variation caused by inversion can also be reduced by using multiple control capacitors. In addition, the use of multiple tunneling capacitors provides the benefit of customized tunneling paths.

Functional thiols as repair and doping agents of defective MoS2 monolayers

NASA Astrophysics Data System (ADS)

Förster, Anja; Gemming, Sibylle; Seifert, Gotthard

2018-06-01

Recent experimental and theoretical studies indicate that thiols (R-SH) can be used to repair sulfur vacancy defects in MoS2 monolayers (MLs). This density functional theory study investigates how the thiol repair mechanism process can be used to dope MoS2 MLs. Fluorinated thiols as well as amine-containing ones are used to p- and n-dope the MoS2 ML, respectively. It is shown that functional groups are only physisorbed on the repaired MoS2 surface. This explains the reversible doping with fluorinated thiols.

Tuning Coupling Behavior of Stacked Heterostructures Based on MoS2, WS2, and WSe2

PubMed Central

Wang, Fang; Wang, Junyong; Guo, Shuang; Zhang, Jinzhong; Hu, Zhigao; Chu, Junhao

2017-01-01

The interlayer interaction of vertically stacked heterojunctions is very sensitive to the interlayer spacing, which will affect the coupling between the monolayers and allow band structure modulation. Here, with the aid of density functional theory (DFT) calculations, an interesting phenomenon is found that MoS2-WS2, MoS2-WSe2, and WS2-WSe2 heterostructures turn into direct-gap semiconductors from indirect-gap semiconductors with increasing the interlayer space. Moreover, the electronic structure changing process with interlayer spacing of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 is different from each other. With the help of variable-temperature spectral experiment, different electronic transition properties of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 have been demonstrated. The transition transformation from indirect to direct can be only observed in the MoS2-WS2 heterostructure, as the valence band maximum (VBM) at the Γ point in the MoS2-WSe2 and WS2-WSe2 heterostructure is less sensitive to the interlayer spacing than those from the MoS2-WS2 heterostructure. The present work highlights the significance of the temperature tuning in interlayer coupling and advance the research of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 based device applications. PMID:28303932

Probing photoresponse of aligned single-walled carbon nanotube doped ultrathin MoS2.

PubMed

Wang, Rui; Wang, Tianjiao; Hong, Tu; Xu, Ya-Qiong

2018-08-24

We report a facile method to produce ultrathin molybdenum disulfide (MoS 2 ) hybrids with polarized near-infrared (NIR) photoresponses, in which horizontally-aligned single-walled carbon nanotubes (SWNTs) are integrated with single- and few-layer MoS 2 through a two-step chemical vapor deposition process. The photocurrent generation mechanisms in SWNT-MoS 2 hybrids are systematically investigated through wavelength- and polarization-dependent scanning photocurrent measurements. When the incident photon energy is above the direct bandgap of MoS 2 , isotropic photocurrent signals are observed, which can be primarily attributed to the direct bandgap transition in MoS 2 . In contrast, if the incident photon energy in the NIR region is below the direct bandgap of MoS 2 , the maximum photocurrent response occurs when the incident light is polarized in the direction along the SWNTs, indicating that photocurrent signals mainly result from the anisotropic absorption of SWNTs. More importantly, these two-dimensional (2D) hybrid structures inherit the electrical transport properties from MoS 2 , displaying n-type characteristics at a zero gate voltage. These fundamental studies provide a new way to produce ultrathin MoS 2 hybrids with inherited electrical properties and polarized NIR photoresponses, opening doors for engineering various 2D hybrid materials for future broadband optoelectronic applications.

Chemical Vapor Sensing with Monolayer MoS2

DTIC Science & Technology

2013-01-04

show great potential for future nanoscale electronic devices. The high surface-to-volume ratio is a natural asset for applications such as chemical...For the devices in this study, 3 bulk sources of MoS2 were used. One piece was obtained from a colleague’s tribology research project (called the...devices were ~20 cm2/Vs. Although the conductance of our monolayer MoS2 devices can be increased significantly by application of a back gate

Irradiation of MOS-FET devices to provide desired logic functions

NASA Technical Reports Server (NTRS)

Danchenko, V.; Schaefer, D. H.

1972-01-01

Gamma, X-ray, electron, or other radiation is used to shift threshold potentials of MOS devices on logic circuits. Before irradiation MOS gates to be shifted are biased positive and other gates are grounded to substrate. Threshold lasts 10 years. Thermal annealing brings circuit back to original configuration.

Construction of MoS2/Si nanowire array heterojunction for ultrahigh-sensitivity gas sensor.

PubMed

Wu, Di; Lou, Zhenhua; Wang, Yuange; Xu, Tingting; Shi, Zhifeng; Xu, Junmin; Tian, Yongtao; Li, Xinjian

2017-10-27

Few-layer MoS 2 thin films were synthesized by a two-step thermal decomposition process. In addition, MoS 2 /Si nanowire array (SiNWA) heterojunctions exhibiting excellent gas sensing properties were constructed and investigated. Further analysis reveals that such MoS 2 /SiNWA heterojunction devices are highly sensitive to nitric oxide (NO) gas under reverse voltages at room temperature (RT). The gas sensor demonstrated a minimum detection limit of 10 ppb, which represents the lowest value obtained for MoS 2 -based sensors, as well as an ultrahigh response of 3518% (50 ppm NO, ∼50% RH), with good repeatability and selectivity of the MoS 2 /SiNWA heterojunction. The sensing mechanisms were also discussed. The performance of the MoS 2 /SiNWA heterojunction gas sensors is superior to previous results, revealing that they have great potential in applications relating to highly sensitive gas sensors.

Construction of MoS2/Si nanowire array heterojunction for ultrahigh-sensitivity gas sensor

NASA Astrophysics Data System (ADS)

Wu, Di; Lou, Zhenhua; Wang, Yuange; Xu, Tingting; Shi, Zhifeng; Xu, Junmin; Tian, Yongtao; Li, Xinjian

2017-10-01

Few-layer MoS2 thin films were synthesized by a two-step thermal decomposition process. In addition, MoS2/Si nanowire array (SiNWA) heterojunctions exhibiting excellent gas sensing properties were constructed and investigated. Further analysis reveals that such MoS2/SiNWA heterojunction devices are highly sensitive to nitric oxide (NO) gas under reverse voltages at room temperature (RT). The gas sensor demonstrated a minimum detection limit of 10 ppb, which represents the lowest value obtained for MoS2-based sensors, as well as an ultrahigh response of 3518% (50 ppm NO, ˜50% RH), with good repeatability and selectivity of the MoS2/SiNWA heterojunction. The sensing mechanisms were also discussed. The performance of the MoS2/SiNWA heterojunction gas sensors is superior to previous results, revealing that they have great potential in applications relating to highly sensitive gas sensors.

Electronic properties of hybrid monolayer-multilayer MoS2 nanostructured materials

NASA Astrophysics Data System (ADS)

Mlinar, Vladan

2017-12-01

The remarkable, layer-dependent properties of molybdenum disulphide (MoS2), such as an appropriately small and sizable bandgap or interplay between spin and the valley degrees of freedom, make it an attractive candidate for photodetectors, electrominescent devices, valleytronic devices, etc. Using nanostructuring to manipulate the size in lateral direction or number of layers of MoS2, we are opening a new playground for exploring and tuning properties of such systems. Here, we theoretically study the electronic properties of nanostructured MoS2 systems consisting of monolayer and multilayer MoS2 regions. In our analysis we consider hybrid systems in which monolayer region is surrounded by multilayer region and vice versa. We show how energy spectra and localization of carriers are influenced by the size and shape of the regions in lateral direction, number of MoS2 layers in the multilayer region, and the edge structure. Finally, we demonstrate how to control localization of carriers in these hybrid systems, which could make them appealing candidates for optoelectronic devices. Our findings are extracted from a tight-binding model that includes non-orthogonal sp3d5 orbitals, nearest-neighbor hopping matrix elements, and spin-orbit coupling.

Re-Engineering the Mission Operations System (MOS) for the Prime and Extended Mission

NASA Technical Reports Server (NTRS)

Hunt, Joseph C., Jr.; Cheng, Leo Y.

2012-01-01

One of the most challenging tasks in a space science mission is designing the Mission Operations System (MOS). Whereas the focus of the project is getting the spacecraft built and tested for launch, the mission operations engineers must build a system to carry out the science objectives. The completed MOS design is then formally assessed in the many reviews. Once a mission has completed the reviews, the Mission Operation System (MOS) design has been validated to the Functional Requirements and is ready for operations. The design was built based on heritage processes, new technology, and lessons learned from past experience. Furthermore, our operational concepts must be properly mapped to the mission design and science objectives. However, during the course of implementing the science objective in the operations phase after launch, the MOS experiences an evolutional change to adapt for actual performance characteristics. This drives the re-engineering of the MOS, because the MOS includes the flight and ground segments. Using the Spitzer mission as an example we demonstrate how the MOS design evolved for both the prime and extended mission to enhance the overall efficiency for science return. In our re-engineering process, we ensured that no requirements were violated or mission objectives compromised. In most cases, optimized performance across the MOS, including gains in science return as well as savings in the budget profile was achieved. Finally, we suggest a need to better categorize the Operations Phase (Phase E) in the NASA Life-Cycle Phases of Formulation and Implementation

A magnetic resonance study of MoS(2) fullerene-like nanoparticles.

PubMed

Panich, A M; Shames, A I; Rosentsveig, R; Tenne, R

2009-09-30

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS(2) nanoparticles. Spectra of bulk 2H-MoS(2) samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS(2) reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS(2) exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS(2) ones.

A magnetic resonance study of MoS2 fullerene-like nanoparticles

NASA Astrophysics Data System (ADS)

Panich, A. M.; Shames, A. I.; Rosentsveig, R.; Tenne, R.

2009-09-01

We report on the first nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) investigation of inorganic fullerene-like MoS2 nanoparticles. Spectra of bulk 2H-MoS2 samples have also been measured for comparison. The similarity between the measured quadrupole coupling constants and chemical shielding anisotropy parameters for bulk and fullerene-like MoS2 reflects the nearly identical local crystalline environments of the Mo atoms in these two materials. EPR measurements show that fullerene-like MoS2 exhibits a larger density of dangling bonds carrying unpaired electrons, indicative of them having a more defective structure than the bulk sample. The latter observation explains the increase in the spin-lattice relaxation rate observed in the NMR measurements for this sample in comparison with the bulk 2H- MoS2 ones.

Analysis of optical and electronic properties of MoS2 for optoelectronics and FET applications

NASA Astrophysics Data System (ADS)

Ullah, Muhammad S.; Yousuf, Abdul Hamid Bin; Es-Sakhi, Azzedin D.; Chowdhury, Masud H.

2018-04-01

Molybdenum disulfide (MoS2) is considered as a promising alternative to conventional semiconductor materials that used in the IC industry because of its novel properties. In this paper, we explore the optical and electronic properties of MoS2 for photodetector and transistors applications. This simulation is done using `DFT materials properties simulator'. Our findings show that mono- and multi-layer MoS2 is suitable for conventional and tunnel FET applications due to direct and indirect band-gap respectively. The bulk MoS2 crystal, which are composed of stacked layers have indirect bandgap and mono-layer MoS2 crystal form direct bandgap at the K-point of Brillouin zone. Indirect bandgap of bulk MoS2 crystal implies that phonons need to be involved in band-to-band tunneling (BTBT) process. Degenerately doped semiconductor, which is basically spinning the Fermi level, changing the DOS profile, and thinning the indirect bandgap that allow tunneling from valence band to conduction band. The optical properties of MoS2 is explored in terms of Absorption coefficient, extinction coefficient and refractive index. Our results shows that a MoS2 based photodetector can be fabricate to detect light in the visible range (below 500nm). It is also observed that the MoS2 is most sensitive for the light of wavelength 450nm.

A convenient method of manufacturing liquid-gated MoS2 field effect transistors

NASA Astrophysics Data System (ADS)

Lin, Kabin; Yuan, Zhishan; Yu, Yu; Li, Kun; Li, Zhongwu; Sha, Jingjie; Li, Tie; Chen, Yunfei

2017-10-01

In this paper, we present a simple and convenient method of manufacturing liquid-gated MoS2 field effect transistors (FETs). A Si3N4 chip is firstly fabricated by the semiconductor manufacturing process, then the mechanical exfoliation MoS2 is transferred onto the Si3N4 chip and is connected with the gold electrodes by depositing platinum to construct the MoS2 FETs. The liquid-gated is formed by injecting 0.1 M NaCl solution into reservoir to contact the back side of the Si3N4. Our measured results show that the contact properties between MoS2 and electrodes are in well condition and the liquid-gated MoS2 FETs have a high mobility that can reach up to 109 cm2 V-1 s-1.

Optical nonlinearities of excitons in monolayer MoS2

NASA Astrophysics Data System (ADS)

Soh, Daniel B. S.; Rogers, Christopher; Gray, Dodd J.; Chatterjee, Eric; Mabuchi, Hideo

2018-04-01

We calculate linear and nonlinear optical susceptibilities arising from the excitonic states of monolayer MoS2 for in-plane light polarizations, using second-quantized bound and unbound exciton operators. Optical selection rules are critical for obtaining the susceptibilities. We derive the valley-chirality rule for the second-order harmonic generation in monolayer MoS2 and find that the third-order harmonic process is efficient only for linearly polarized input light while the third-order two-photon process (optical Kerr effect) is efficient for circularly polarized light using a higher order exciton state. The absence of linear absorption due to the band gap and the unusually strong two-photon third-order nonlinearity make the monolayer MoS2 excitonic structure a promising resource for coherent nonlinear photonics.

Controlled p-doping of black phosphorus by integration of MoS2 nanoparticles

NASA Astrophysics Data System (ADS)

Jeon, Sumin; Kim, Minwoo; Jia, Jingyuan; Park, Jin-Hong; Lee, Sungjoo; Song, Young Jae

2018-05-01

Black phosphorus (BP), a new family of two dimensional (2D) layered materials, is an attractive material for future electronic, photonic and chemical sensing devices, thanks to its high carrier density and a direct bandgap of 0.3-2.0 eV, depending on the number of layers. Controllability over the properties of BP by electrical or chemical modulations is one of the critical requirements for future various device applications. Herein, we report a new doping method of BP by integration of density-controlled monolayer MoS2 nanoparticles (NPs). MoS2 NPs with different density were synthesized by chemical vapor deposition (CVD) and transferred onto a few-layer BP channel, which induced a p-doping effect. Scanning electron microscopy (SEM) confirmed the size and distribution of MoS2 NPs with different density. Raman and X-ray photoelectron spectroscopy (XPS) were measured to confirm the oxidation on the edge of MoS2 NPs and a doping effect of MoS2 NPs on a BP channel. The doping mechanism was explained by a charge transfer by work function differences between BP and MoS2 NPs, which was confirmed by Kelvin probe force microscopy (KPFM) and electrical measurements. The hole concentration of BP was controlled with different densities of MoS2 NPs in a range of 1012-1013 cm-2.

Mutual Photoluminescence Quenching and Photovoltaic Effect in Large-Area Single-Layer MoS2-Polymer Heterojunctions.

PubMed

Shastry, Tejas A; Balla, Itamar; Bergeron, Hadallia; Amsterdam, Samuel H; Marks, Tobin J; Hersam, Mark C

2016-11-22

Two-dimensional transition metal dichalcogenides (TMDCs) have recently attracted attention due to their superlative optical and electronic properties. In particular, their extraordinary optical absorption and semiconducting band gap have enabled demonstrations of photovoltaic response from heterostructures composed of TMDCs and other organic or inorganic materials. However, these early studies were limited to devices at the micrometer scale and/or failed to exploit the unique optical absorption properties of single-layer TMDCs. Here we present an experimental realization of a large-area type-II photovoltaic heterojunction using single-layer molybdenum disulfide (MoS 2 ) as the primary absorber, by coupling it to the organic π-donor polymer PTB7. This TMDC-polymer heterojunction exhibits photoluminescence intensity that is tunable as a function of the thickness of the polymer layer, ultimately enabling complete quenching of the TMDC photoluminescence. The strong optical absorption in the TMDC-polymer heterojunction produces an internal quantum efficiency exceeding 40% for an overall cell thickness of less than 20 nm, resulting in exceptional current density per absorbing thickness in comparison to other organic and inorganic solar cells. Furthermore, this work provides insight into the recombination processes in type-II TMDC-polymer heterojunctions and thus provides quantitative guidance to ongoing efforts to realize efficient TMDC-based solar cells.

Radiation damage in MOS integrated circuits, Part 1

NASA Technical Reports Server (NTRS)

Danchenko, V.

1971-01-01

Complementary and p-channel MOS integrated circuits made by four commercial manufacturers were investigated for sensitivity to radiation environment. The circuits were irradiated with 1.5 MeV electrons. The results are given for electrons and for the Co-60 gamma radiation equivalent. The data are presented in terms of shifts in the threshold potentials and changes in transconductances and leakages. Gate biases of -10V, +10V and zero volts were applied to individual MOS units during irradiation. It was found that, in most of circuits of complementary MOS technologies, noticable changes due to radiation appear first as increased leakage in n-channel MOSFETs somewhat before a total integrated dose 10 to the 12th power electrons/sg cm is reached. The inability of p-channel MOSFETs to turn on sets in at about 10 to the 13th power electrons/sq cm. Of the circuits tested, an RCA A-series circuit was the most radiation resistant sample.

MoS2 solid-lubricating film fabricated by atomic layer deposition on Si substrate

NASA Astrophysics Data System (ADS)

Huang, Yazhou; Liu, Lei; Lv, Jun; Yang, Junjie; Sha, Jingjie; Chen, Yunfei

2018-04-01

How to reduce friction for improving efficiency in the usage of energy is a constant challenge. Layered material like MoS2 has long been recognized as an effective surface lubricant. Due to low interfacial shear strengths, MoS2 is endowed with nominal frictional coefficient. In this work, MoS2 solid-lubricating film was directly grown by atomic layer deposition (ALD) on Si substrate using MoCl5 and H2S. Various methods were used to observe the grown MoS2 film. Moreover, nanotribological properties of the film were observed by an atomic force microscope (AFM). Results show that MoS2 film can effectively reduce the friction force by about 30-45% under different loads, indicating the huge application value of the film as a solid lubricant. Besides the interlayer-interfaces-sliding, the smaller capillary is another reason why the grown MoS2 film has smaller friction force than that of Si.

Direct observation of multiple rotational stacking faults coexisting in freestanding bilayer MoS2.

PubMed

Li, Zuocheng; Yan, Xingxu; Tang, Zhenkun; Huo, Ziyang; Li, Guoliang; Jiao, Liying; Liu, Li-Min; Zhang, Miao; Luo, Jun; Zhu, Jing

2017-08-16

Electronic properties of two-dimensional (2D) MoS 2 semiconductors can be modulated by introducing specific defects. One important type of defect in 2D layered materials is known as rotational stacking fault (RSF), but the coexistence of multiple RSFs with different rotational angles was not directly observed in freestanding 2D MoS 2 before. In this report, we demonstrate the coexistence of three RSFs with three different rotational angles in a freestanding bilayer MoS 2 sheet as directly observed using an aberration-corrected transmission electron microscope (TEM). Our analyses show that these RSFs originate from cracks and dislocations within the bilayer MoS 2 . First-principles calculations indicate that RSFs with different rotational angles change the electronic structures of bilayer MoS 2 and produce two new symmetries in their bandgaps and offset crystal momentums. Therefore, employing RSFs and their coexistence is a promising route in defect engineering of MoS 2 to fabricate suitable devices for electronics, optoelectronics, and energy conversion.

Using a Floating-Gate MOS Transistor as a Transducer in a MEMS Gas Sensing System

PubMed Central

Barranca, Mario Alfredo Reyes; Mendoza-Acevedo, Salvador; Flores-Nava, Luis M.; Avila-García, Alejandro; Vazquez-Acosta, E. N.; Moreno-Cadenas, José Antonio; Casados-Cruz, Gaspar

2010-01-01

Floating-gate MOS transistors have been widely used in diverse analog and digital applications. One of these is as a charge sensitive device in sensors for pH measurement in solutions or using gates with metals like Pd or Pt for hydrogen sensing. Efforts are being made to monolithically integrate sensors together with controlling and signal processing electronics using standard technologies. This can be achieved with the demonstrated compatibility between available CMOS technology and MEMS technology. In this paper an in-depth analysis is done regarding the reliability of floating-gate MOS transistors when charge produced by a chemical reaction between metallic oxide thin films with either reducing or oxidizing gases is present. These chemical reactions need temperatures around 200 °C or higher to take place, so thermal insulation of the sensing area must be assured for appropriate operation of the electronics at room temperature. The operation principle of the proposal here presented is confirmed by connecting the gate of a conventional MOS transistor in series with a Fe2O3 layer. It is shown that an electrochemical potential is present on the ferrite layer when reacting with propane. PMID:22163478

Structural effects on mechanical response of MoS2 nanostructures during compression

NASA Astrophysics Data System (ADS)

Bucholz, Eric W.; Sinnott, Susan B.

2013-07-01

In recent years, inorganic nanostructures, such as fullerene-like MoS2 and WS2 nanoparticles, have been shown to be promising candidates for friction and wear reduction in tribological applications. However, it has been demonstrated experimentally that the mechanical response of any given inorganic nanostructure varies depending on its individual structural characteristics such as size, shape, and crystallinity. Here, classical molecular dynamics simulations are performed that investigate the mechanical responses of different types of MoS2 nanostructures during uniaxial compression. The results illustrate the dependence of mechanical behavior on nanoparticle structure and, in particular, indicate that the mechanical properties of MoS2 nanostructures vary significantly with changes in the orientation of the MoS2 walls at the interface.

Generation of dual-wavelength square pulse in a figure-eight erbium-doped fiber laser with ultra-large net-anomalous dispersion.

PubMed

Shao, Zhihua; Qiao, Xueguang; Rong, Qiangzhou; Su, Dan

2015-08-01

A type of wave-breaking-free mode-locked dual-wavelength square pulse was experimentally observed in a figure-eight erbium-doped fiber laser with ultra-large net-anomalous dispersion. A 2.7 km long single-mode fiber (SMF) was incorporated as a nonlinear optical loop mirror (NOLM) and provided largely nonlinear phase accumulation and anomalous dispersion, which enhanced the four-wave-mixing effect to improve the stability of the dual-wavelength operation. In the NOLM, the long SMF with small birefringence supported the Sagnac interference as a filter to manage the dual-wavelength lasing. The dual-wavelength operation was made switchable by adjusting the intra-cavity polarization loss and phase delay corresponding to two square pulses. When the pump power was increased, the duration of the square pulse increased continuously while the peak pulse power gradually decreased. This square-type pulse can potentially be utilized for signal transmission and sensing.

Improving the Stability of High-Performance Multilayer MoS2 Field-Effect Transistors.

PubMed

Liu, Na; Baek, Jongyeol; Kim, Seung Min; Hong, Seongin; Hong, Young Ki; Kim, Yang Soo; Kim, Hyun-Suk; Kim, Sunkook; Park, Jozeph

2017-12-13

In this study, we propose a method for improving the stability of multilayer MoS 2 field-effect transistors (FETs) by O 2 plasma treatment and Al 2 O 3 passivation while sustaining the high performance of bulk MoS 2 FET. The MoS 2 FETs were exposed to O 2 plasma for 30 s before Al 2 O 3 encapsulation to achieve a relatively small hysteresis and high electrical performance. A MoO x layer formed during the plasma treatment was found between MoS 2 and the top passivation layer. The MoO x interlayer prevents the generation of excess electron carriers in the channel, owing to Al 2 O 3 passivation, thereby minimizing the shift in the threshold voltage (V th ) and increase of the off-current leakage. However, prolonged exposure of the MoS 2 surface to O 2 plasma (90 and 120 s) was found to introduce excess oxygen into the MoO x interlayer, leading to more pronounced hysteresis and a high off-current. The stable MoS 2 FETs were also subjected to gate-bias stress tests under different conditions. The MoS 2 transistors exhibited negligible decline in performance under positive bias stress, positive bias illumination stress, and negative bias stress, but large negative shifts in V th were observed under negative bias illumination stress, which is attributed to the presence of sulfur vacancies. This simple approach can be applied to other transition metal dichalcogenide materials to understand their FET properties and reliability, and the resulting high-performance hysteresis-free MoS 2 transistors are expected to open up new opportunities for the development of sophisticated electronic applications.

Metallization and superconductivity in Ca-intercalated bilayer MoS2

NASA Astrophysics Data System (ADS)

Szczȱśniak, R.; Durajski, A. P.; Jarosik, M. W.

2017-12-01

A two-dimensional molybdenum disulfide (MoS2) has attracted significant interest recently due to its outstanding physical, chemical and optoelectronic properties. In this paper, using the first-principles calculations, the dynamical stability, electronic structure and superconducting properties of Ca-intercalated bilayer MoS2 are investigated. The calculated electron-phonon coupling constant implies that the stable form of investigated system is a strong-coupling superconductor (λ = 1.05) with a low value of critical temperature (TC = 13.3 K). Moreover, results obtained within the framework of the isotropic Migdal-Eliashberg formalism proved that Ca-intercalated bilayer MoS2 exhibits behavior that goes beyond the scope of the conventional BCS theory.

Vacuum ultraviolet radiation effects on two-dimensional MoS2 field-effect transistors

NASA Astrophysics Data System (ADS)

McMorrow, Julian J.; Cress, Cory D.; Arnold, Heather N.; Sangwan, Vinod K.; Jariwala, Deep; Schmucker, Scott W.; Marks, Tobin J.; Hersam, Mark C.

2017-02-01

Atomically thin MoS2 has generated intense interest for emerging electronics applications. Its two-dimensional nature and potential for low-power electronics are particularly appealing for space-bound electronics, motivating the need for a fundamental understanding of MoS2 electronic device response to the space radiation environment. In this letter, we quantify the response of MoS2 field-effect transistors (FETs) to vacuum ultraviolet (VUV) total ionizing dose radiation. Single-layer (SL) and multilayer (ML) MoS2 FETs are compared to identify differences that arise from thickness and band structure variations. The measured evolution of the FET transport properties is leveraged to identify the nature of VUV-induced trapped charge, isolating the effects of the interface and bulk oxide dielectric. In both the SL and ML cases, oxide trapped holes compete with interface trapped electrons, exhibiting an overall shift toward negative gate bias. Raman spectroscopy shows no variation in the MoS2 signatures as a result of VUV exposure, eliminating significant crystalline damage or oxidation as possible radiation degradation mechanisms. Overall, this work presents avenues for achieving radiation-hard MoS2 devices through dielectric engineering that reduces oxide and interface trapped charge.

CVD-grown monolayer MoS2 in bioabsorbable electronics and biosensors.

PubMed

Chen, Xiang; Park, Yong Ju; Kang, Minpyo; Kang, Seung-Kyun; Koo, Jahyun; Shinde, Sachin M; Shin, Jiho; Jeon, Seunghyun; Park, Gayoung; Yan, Ying; MacEwan, Matthew R; Ray, Wilson Z; Lee, Kyung-Mi; Rogers, John A; Ahn, Jong-Hyun

2018-04-27

Transient electronics represents an emerging technology whose defining feature is an ability to dissolve, disintegrate or otherwise physically disappear in a controlled manner. Envisioned applications include resorbable/degradable biomedical implants, hardware-secure memory devices, and zero-impact environmental sensors. 2D materials may have essential roles in these systems due to their unique mechanical, thermal, electrical, and optical properties. Here, we study the bioabsorption of CVD-grown monolayer MoS 2 , including long-term cytotoxicity and immunological biocompatibility evaluations in biofluids and tissues of live animal models. The results show that MoS 2 undergoes hydrolysis slowly in aqueous solutions without adverse biological effects. We also present a class of MoS 2 -based bioabsorbable and multi-functional sensor for intracranial monitoring of pressure, temperature, strain, and motion in animal models. Such technology offers specific, clinically relevant roles in diagnostic/therapeutic functions during recovery from traumatic brain injury. Our findings support the broader use of 2D materials in transient electronics and qualitatively expand the design options in other areas.

Efficient evaluation of epitaxial MoS2 on sapphire by direct band structure imaging

NASA Astrophysics Data System (ADS)

Kim, Hokwon; Dumcenco, Dumitru; Fregnaux, Mathieu; Benayad, Anass; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier; Lanes Group, Epfl Team; Leti, Cea Team

The electronic band structure evaluation of two-dimensional metal dichalcogenides is critical as the band structure can be greatly influenced by the film thickness, strain, and substrate. Here, we performed a direct measurement of the band structure of as-grown monolayer MoS2 on single crystalline sapphire by reciprocal-space photoelectron emission microscopy with a conventional laboratory ultra-violet He I light source. Arrays of gold electrodes were deposited onto the sample in order to avoid charging effects due to the insulating substrate. This allowed the high resolution mapping (ΔE = 0.2 eV Δk = 0.05 Å-1) of the valence states in momentum space down to 7 eV below the Fermi level. The high degree of the epitaxial alignment of the single crystalline MoS2 nuclei was verified by the direct momentum space imaging over a large area containing multiple nuclei. The derived values of the hole effective mass were 2.41 +/-0.05 m0 and 0.81 +/-0.05 m0, respectively at Γ and K points, consistent with the theoretical values of the freestanding monolayer MoS2 reported in the literature. HK acknowledges the french CEA Basic Technological Research program (RTB) for funding.

Ultrafast charge transfer between MoTe2 and MoS2 monolayers

NASA Astrophysics Data System (ADS)

Pan, Shudi; Ceballos, Frank; Bellus, Matthew Z.; Zereshki, Peymon; Zhao, Hui

2017-03-01

High quality and stable electrical contact between metal and two-dimensional materials, such as transition metal dichalcogenides, is a necessary requirement that has yet to be achieved in order to successfully exploit the advantages that these materials offer to electronics and optoelectronics. MoTe2, owing to its phase changing property, can potentially offer a solution. A recent study demonstrated that metallic phase of MoTe2 connects its semiconducting phase with very low resistance. To utilize this property to connect other two-dimensional materials, it is important to achieve efficient charge transfer between MoTe2 and other semiconducting materials. Using MoS2 as an example, we report ultrafast and efficient charge transfer between MoTe2 and MoS2 monolayers. In the transient absorption measurements, an ultrashort pump pulse is used to selectively excite electrons in MoTe2. The appearance of the excited electrons in the conduction band of MoS2 is monitored by using a probe pulse that is tuned to the resonance of MoS2. We found that electrons transfer to MoS2 on a time scale of at most 0.3 ps. The transferred electrons give rise to a large transient absorption signal at both A-exciton and B-exciton resonances due to the screening effect. We also observed ultrafast transfer of holes from MoS2 to MoTe2. Our results suggest the feasibility of using MoTe2 as a bridge material to connect MoS2 and other transition metal dichalcogenides, and demonstrate a new transition metal dichalcogenide heterostructure involving MoTe2, which extends the spectral range of such structures to infrared.

Conduction quantization in monolayer MoS2

NASA Astrophysics Data System (ADS)

Li, T. S.

2016-10-01

We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

Vibrational and optical properties of MoS2: From monolayer to bulk

NASA Astrophysics Data System (ADS)

Molina-Sánchez, Alejandro; Hummer, Kerstin; Wirtz, Ludger

2015-12-01

Molybdenum disulfide, MoS2, has recently gained considerable attention as a layered material where neighboring layers are only weakly interacting and can easily slide against each other. Therefore, mechanical exfoliation allows the fabrication of single and multi-layers and opens the possibility to generate atomically thin crystals with outstanding properties. In contrast to graphene, it has an optical gap of ~1.9 eV. This makes it a prominent candidate for transistor and opto-electronic applications. Single-layer MoS2 exhibits remarkably different physical properties compared to bulk MoS2 due to the absence of interlayer hybridization. For instance, while the band gap of bulk and multi-layer MoS2 is indirect, it becomes direct with decreasing number of layers. In this review, we analyze from a theoretical point of view the electronic, optical, and vibrational properties of single-layer, few-layer and bulk MoS2. In particular, we focus on the effects of spin-orbit interaction, number of layers, and applied tensile strain on the vibrational and optical properties. We examine the results obtained by different methodologies, mainly ab initio approaches. We also discuss which approximations are suitable for MoS2 and layered materials. The effect of external strain on the band gap of single-layer MoS2 and the crossover from indirect to direct band gap is investigated. We analyze the excitonic effects on the absorption spectra. The main features, such as the double peak at the absorption threshold and the high-energy exciton are presented. Furthermore, we report on the the phonon dispersion relations of single-layer, few-layer and bulk MoS2. Based on the latter, we explain the behavior of the Raman-active A1g and E2g1 modes as a function of the number of layers. Finally, we compare theoretical and experimental results of Raman, photoluminescence, and optical-absorption spectroscopy.

Hierarchical MoS2-coated three-dimensional graphene network for enhanced supercapacitor performances

NASA Astrophysics Data System (ADS)

Zhou, Rui; Han, Cheng-jie; Wang, Xiao-min

2017-06-01

Layered molybdenum disulfide (MoS2) owns graphene-like two-dimensional structure, and when used as the electrode material for energy storage devices, the intercalation of electrolyte ions is permitted. Herein, a simple dipping and drying method is employed to stack few-layered MoS2 nanosheets on a three-dimensional graphene network (3DGN). The structure measurement results indicate that the assembled hierarchical MoS2 nanosheets own expanded interlayer spacing (∼0.75 nm) and are stacked on the surface of 3DGN uncontinuously. The composite can achieve 110.57% capacitance retention after 4000 cycles of galvanostatic charge/discharge tests and 76.73% capacitance retention with increasing the current density from 1 A g-1 to 100 A g-1. Moreover, the asymmetric coin cell supercapacitor using MoS2@3DGN and active carbon as electrode materials is assembled. This device could achieve a working voltage window of 1.6 V along with the power and energy densities of 400.0-8001.6 W kg-1 and 36.43-1.12 Wh kg-1 respectively. The enhanced electrochemical performance can be attributed to: (1) the expanded interlayer spacing of hierarchical MoS2 nanosheets which can facilitate the fast intercalation/deintercalation of electrolyte cations, (2) the uncontinuous deposition of hierarchical MoS2 nanosheets which facilitates more contact between electrolyte and the section of MoS2 nanosheets to provide more gates for the intercalation/deintercalation.

Compact modeling of total ionizing dose and aging effects in MOS technologies

DOE PAGES

Esqueda, Ivan S.; Barnaby, Hugh J.; King, Michael Patrick

2015-06-18

This paper presents a physics-based compact modeling approach that incorporates the impact of total ionizing dose (TID) and stress-induced defects into simulations of metal-oxide-semiconductor (MOS) devices and integrated circuits (ICs). This approach utilizes calculations of surface potential (ψs) to capture the charge contribution from oxide trapped charge and interface traps and to describe their impact on MOS electrostatics and device operating characteristics as a function of ionizing radiation exposure and aging effects. The modeling approach is demonstrated for bulk and silicon-on-insulator (SOI) MOS device. The formulation is verified using TCAD simulations and through the comparison of model calculations and experimentalmore » I-V characteristics from irradiated devices. The presented approach is suitable for modeling TID and aging effects in advanced MOS devices and ICs.« less

NO2 sensing at room temperature using vertically aligned MoS2 flakes network

NASA Astrophysics Data System (ADS)

Kumar, Rahul; Goel, Neeraj; Kumar, Mahesh

2018-04-01

To exploit the role of alignment of MoS2 flake in chemical sensing, here, we have synthesized the horizontally and vertically aligned MoS2 flake network using conventional chemical vapor deposition technique. The morphology and number of layers were confirmed by SEM and Raman spectroscopy, respectively. The sensing performance of horizontally aligned and vertically aligned flake network was investigated to NO2 at room temperature. Vertically aligned MoS2 based sensor showed higher sensitivity 51.54 % and 63.2 % compared to horizontally aligned MoS2 sensor' sensitivity of 35.32 % and 45.2 % to 50 ppm and 100 ppm NO2, respectively. This high sensitivity attributed to the high aspect ratio and high adsorption energy on the edge site of vertically aligned MoS2.

Radiation effects on MOS devices - dosimetry, annealing, irradiation sequence, and sources

NASA Technical Reports Server (NTRS)

Stassinopoulos, E. G.; Brucker, G. J.; Van Gunten, O.; Knudson, A. R.; Jordan, T. M.

1983-01-01

This paper reports on some investigations of dosimetry, annealing, irradiation sequences, and radioactive sources, involved in the determination of radiation effects on MOS devices. Results show that agreement in the experimental and theoretical surface to average doses support the use of thermo-luminescent dosimeters (manganese activated calcium fluoride) in specifying the surface dose delivered to thin gate insulators of MOS devices. Annealing measurements indicate the existence of at least two energy levels,,s or a activation energies, for recovery of soft oxide MOS devices after irradiation by electrons, protons, and gammas. Damage sensitivities of MOS devices were found to be independent of combinations and sequences of radiation type or energies. Comparison of various gamma sources indicated a small dependence of damage sensitivity on the Cobalt facility, but a more significant dependence in the case of the Cesium source. These results were attributed to differences in the spectral content of the several sources.

High performance MoS2 TFT using graphene contact first process

NASA Astrophysics Data System (ADS)

Chang Chien, Chih-Shiang; Chang, Hsun-Ming; Lee, Wei-Ta; Tang, Ming-Ru; Wu, Chao-Hsin; Lee, Si-Chen

2017-08-01

An ohmic contact of graphene/MoS2 heterostructure is determined by using ultraviolet photoelectron spectroscopy (UPS). Since graphene shows a great potential to replace metal contact, a direct comparison of Cr/Au contact and graphene contact on the MoS2 thin film transistor (TFT) is made. Different from metal contacts, the work function of graphene can be modulated. As a result, the subthreshold swing can be improved. And when VgMoS2 TFT, a new method using graphene contact first and MoS2 layer last process that can avoid PMMA residue and high processing temperature is applied. MoS2 TFT using this method shows on/off current ratio up to 6×106 order of magnitude, high mobility of 116 cm2/V-sec, and subthreshold swing of only 0.515 V/dec.

Anisotropic MoS2 Nanosheets Grown on Self-Organized Nanopatterned Substrates.

PubMed

Martella, Christian; Mennucci, Carlo; Cinquanta, Eugenio; Lamperti, Alessio; Cappelluti, Emmanuele; Buatier de Mongeot, Francesco; Molle, Alessandro

2017-05-01

Manipulating the anisotropy in 2D nanosheets is a promising way to tune or trigger functional properties at the nanoscale. Here, a novel approach is presented to introduce a one-directional anisotropy in MoS 2 nanosheets via chemical vapor deposition (CVD) onto rippled patterns prepared on ion-sputtered SiO 2 /Si substrates. The optoelectronic properties of MoS 2 are dramatically affected by the rippled MoS 2 morphology both at the macro- and the nanoscale. In particular, strongly anisotropic phonon modes are observed depending on the polarization orientation with respect to the ripple axis. Moreover, the rippled morphology induces localization of strain and charge doping at the nanoscale, thus causing substantial redshifts of the phonon mode frequencies and a topography-dependent modulation of the MoS 2 workfunction, respectively. This study paves the way to a controllable tuning of the anisotropy via substrate pattern engineering in CVD-grown 2D nanosheets. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct TEM observations of growth mechanisms of two-dimensional MoS2 flakes

PubMed Central

Fei, Linfeng; Lei, Shuijin; Zhang, Wei-Bing; Lu, Wei; Lin, Ziyuan; Lam, Chi Hang; Chai, Yang; Wang, Yu

2016-01-01

A microscopic understanding of the growth mechanism of two-dimensional materials is of particular importance for controllable synthesis of functional nanostructures. Because of the lack of direct and insightful observations, how to control the orientation and the size of two-dimensional material grains is still under debate. Here we discern distinct formation stages for MoS2 flakes from the thermolysis of ammonium thiomolybdates using in situ transmission electron microscopy. In the initial stage (400 °C), vertically aligned MoS2 structures grow in a layer-by-layer mode. With the increasing temperature of up to 780 °C, the orientation of MoS2 structures becomes horizontal. When the growth temperature reaches 850 °C, the crystalline size of MoS2 increases by merging adjacent flakes. Our study shows direct observations of MoS2 growth as the temperature evolves, and sheds light on the controllable orientation and grain size of two-dimensional materials. PMID:27412892

Effect of interfaces on electron transport properties of MoS2-Au Contacts

NASA Astrophysics Data System (ADS)

Aminpour, Maral; Hapala, Prokop; Le, Duy; Jelinek, Pavel; Rahman, Talat S.; Rahman's Group Collaboration; Nanosurf Lab Collaboration

2014-03-01

Single layer MoS2 is a promising material for future electronic devices such as transistors since it has good transport characteristics with mobility greater than 200 cm-1V-1s-1 and on-off current ratios up to 108. However, before MoS2 can become a mainstream electronic material for the semiconductor industry, the design of low resistive metal-semiconductor junctions as contacts of the electronic devices needs to be addressed and studied systematically. We have examined the effect of Au contacts on the electronic transport properties of single layer MoS2 using density functional theory in combination with the non-equilibrium Green's function method. The Schottky barrier between Au contact and MoS2, transmission spectra, and I-V curves will be reported and discussed as a function of MoS2 and Au interfaces of varying geometry. This work is supported in part by the US Department of Energy under grant DE-FG02-07ER15842.

Preparation of nanostructured and nanosheets of MoS2 oxide using oxidation method.

PubMed

Amini, Majed; Ramazani S A, Ahmad; Faghihi, Morteza; Fattahpour, Seyyedfaridoddin

2017-11-01

Molybdenum disulfide (MoS 2 ), a two-dimensional transition metal has a 2D layered structure and has recently attracted attention due to its novel catalytic properties. In this study, MoS 2 has been successfully intercalated using chemical and physical intercalation techniques, while enhancing its surface properties. The final intercalated MoS 2 is of many interests because of its low-dimensional and potential properties in in-situ catalysis. In this research, we report different methods to intercalate the layers of MoS 2 successfully using acid-treatment, ultrasonication, oxidation and thermal shocking. The other goal of this study is to form SO bonds mainly because of expected enhanced in-situ catalytic operations. The intercalated MoS 2 is further characterized using analyses such as Fourier Transform Infrared Spectroscopy (FTIR), Raman, Contact Angle, X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Microanalysis (EDAX), Transmission electron microscopy (TEM), and BET. Copyright © 2017. Published by Elsevier B.V.

Note: All-digital CMOS MOS-capacitor-based pulse-shrinking mechanism suitable for time-to-digital converters

NASA Astrophysics Data System (ADS)

Chen, Chun-Chi; Hwang, Chorng-Sii; Lin, You-Ting; Liu, Keng-Chih

2015-12-01

This paper presents an all-digital CMOS pulse-shrinking mechanism suitable for time-to-digital converters (TDCs). A simple MOS capacitor is used as a pulse-shrinking cell to perform time attenuation for time resolving. Compared with a previous pulse-shrinking mechanism, the proposed mechanism provides an appreciably improved temporal resolution with high linearity. Furthermore, the use of a binary-weighted pulse-shrinking unit with scaled MOS capacitors is proposed for achieving a programmable resolution. A TDC involving the proposed mechanism was fabricated using a TSMC (Taiwan Semiconductor Manufacturing Company) 0.18-μm CMOS process, and it has a small area of nearly 0.02 mm2 and an integral nonlinearity error of ±0.8 LSB for a resolution of 24 ps.

Investigation of noise insensitive electronic circuits for automotive applications with particular regard to MOS circuits

NASA Astrophysics Data System (ADS)

Gorille, I.

1980-11-01

The application of MOS switching circuits of high complexity in essential automobile systems, such as ignition and injection, was investigated. A bipolar circuit technology, current hogging logic (CHL), was compared to MOS technologies for its competitiveness. The functional requirements of digital automotive systems can only be met by technologies allowing large packing densities and medium speeds. The properties of n-MOS and CMOS are promising whereas the electrical power needed by p-MOS circuits is in general prohibitively large.

Low-Temperature Atomic Layer Deposition of MoS2 Films.

PubMed

Jurca, Titel; Moody, Michael J; Henning, Alex; Emery, Jonathan D; Wang, Binghao; Tan, Jeffrey M; Lohr, Tracy L; Lauhon, Lincoln J; Marks, Tobin J

2017-04-24

Wet chemical screening reveals the very high reactivity of Mo(NMe 2 ) 4 with H 2 S for the low-temperature synthesis of MoS 2 . This observation motivated an investigation of Mo(NMe 2 ) 4 as a volatile precursor for the atomic layer deposition (ALD) of MoS 2 thin films. Herein we report that Mo(NMe 2 ) 4 enables MoS 2 film growth at record low temperatures-as low as 60 °C. The as-deposited films are amorphous but can be readily crystallized by annealing. Importantly, the low ALD growth temperature is compatible with photolithographic and lift-off patterning for the straightforward fabrication of diverse device structures. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hysteresis in the transfer characteristics of MoS2 transistors

NASA Astrophysics Data System (ADS)

Di Bartolomeo, Antonio; Genovese, Luca; Giubileo, Filippo; Iemmo, Laura; Luongo, Giuseppe; Foller, Tobias; Schleberger, Marika

2018-01-01

We investigate the origin of the hysteresis observed in the transfer characteristics of back-gated field-effect transistors with an exfoliated MoS2 channel. We find that the hysteresis is strongly enhanced by increasing either gate voltage, pressure, temperature or light intensity. Our measurements reveal a step-like behavior of the hysteresis around room temperature, which we explain as water-facilitated charge trapping at the MoS2/SiO2 interface. We conclude that intrinsic defects in MoS2, such as S vacancies, which result in effective positive charge trapping, play an important role, besides H2O and O2 adsorbates on the unpassivated device surface. We show that the bistability associated to the hysteresis can be exploited in memory devices.

Investigation on nonlinear optical properties of MoS2 nanoflake, grown on silicon and quartz substrates

NASA Astrophysics Data System (ADS)

Bayesteh, S.; Mortazavi, S. Z.; Reyhani, A.

2018-03-01

In this study, MoS2 was directly synthesized by one-step thermal chemical vapour deposition (TCVD), on different substrates including Si/SiO2 and quartz, using MoO3 and sulfide powders as precursor. The XRD patterns demonstrate the high crystallinity of MoS2 on Si/SiO2 and quartz substrates. SEM confirmed the formation of MoS2 grown on both substrates. According to line width and frequency difference between the E1 2g and A1g in Raman spectroscopy, it is inferred that the MoS2 grown on Si/SiO2 substrate is monolayer and the MoS2 grown on quartz substrate is multilayer. Moreover, by assessment of MoS2 nanoflake band gap via UV-visible analysis, it verified the formation of few layer structures. In addition, the open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the synthesized MoS2. All experiments were performed using a diode laser with a wavelength of 532 nm as light source. The monolayer MoS2 synthesized on Si/SiO2, display considerable two-photon absorption. However, the multilayer MoS2 synthesized on quartz displayed saturable absorption (SA). It is noticeable that both samples demonstrate obvious self-defocusing behaviour.

Patterned growth of p-type MoS 2 atomic layers using sol-gel as precursor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Wei; Lin, Junhao; Feng, Wei

2D layered MoS 2 has drawn intense attention for its applications in flexible electronic, optoelectronic, and spintronic devices. Most of the MoS 2 atomic layers grown by conventional chemical vapor deposition techniques are n-type due to the abundant sulfur vacancies. Facile production of MoS 2 atomic layers with p-type behavior, however, remains challenging. Here, a novel one-step growth has been developed to attain p-type MoS 2 layers in large scale by using Mo-containing sol–gel, including 1% tungsten (W). Atomic-resolution electron microscopy characterization reveals that small tungsten oxide clusters are commonly present on the as-grown MoS 2 film due to themore » incomplete reduction of W precursor at the reaction temperature. These omnipresent small tungsten oxide clusters contribute to the p-type behavior, as verified by density functional theory calculations, while preserving the crystallinity of the MoS 2 atomic layers. The Mo containing sol–gel precursor is compatible with the soft-lithography techniques, which enables patterned growth of p-type MoS 2 atomic layers into regular arrays with different shapes, holding great promise for highly integrated device applications. Lastly, an atomically thin p–n junction is fabricated by the as-prepared MoS 2, which shows strong rectifying behavior.« less

Patterned growth of p-type MoS 2 atomic layers using sol-gel as precursor

DOE PAGES

Zheng, Wei; Lin, Junhao; Feng, Wei; ...

2016-07-19

2D layered MoS 2 has drawn intense attention for its applications in flexible electronic, optoelectronic, and spintronic devices. Most of the MoS 2 atomic layers grown by conventional chemical vapor deposition techniques are n-type due to the abundant sulfur vacancies. Facile production of MoS 2 atomic layers with p-type behavior, however, remains challenging. Here, a novel one-step growth has been developed to attain p-type MoS 2 layers in large scale by using Mo-containing sol–gel, including 1% tungsten (W). Atomic-resolution electron microscopy characterization reveals that small tungsten oxide clusters are commonly present on the as-grown MoS 2 film due to themore » incomplete reduction of W precursor at the reaction temperature. These omnipresent small tungsten oxide clusters contribute to the p-type behavior, as verified by density functional theory calculations, while preserving the crystallinity of the MoS 2 atomic layers. The Mo containing sol–gel precursor is compatible with the soft-lithography techniques, which enables patterned growth of p-type MoS 2 atomic layers into regular arrays with different shapes, holding great promise for highly integrated device applications. Lastly, an atomically thin p–n junction is fabricated by the as-prepared MoS 2, which shows strong rectifying behavior.« less

Tunable magnetic coupling in Mn-doped monolayer MoS2 under lattice strain

NASA Astrophysics Data System (ADS)

Miao, Yaping; Huang, Yuhong; Bao, Hongwei; Xu, Kewei; Ma, Fei; Chu, Paul K.

2018-05-01

First-principles calculations are conducted to study the electronic and magnetic states of Mn-doped monolayer MoS2 under lattice strain. Mn-doped MoS2 exhibits half-metallic and ferromagnetic (FM) characteristics in which the majority spin channel exhibits metallic features but there is a bandgap in the minority spin channel. The FM state and the total magnetic moment of 1 µ B are always maintained for the larger supercells of monolayer MoS2 with only one doped Mn, no matter under tensile or compressive strain. Furthermore, the FM state will be enhanced by the tensile strain if two Mo atoms are substituted by Mn atoms in the monolayer MoS2. The magnetic moment increases up to 0.50 µ B per unit cell at a tensile strain of 7%. However, the Mn-doped MoS2 changes to metallic and antiferromagnetic under compressive strain. The spin polarization of Mn 3d orbitals disappears gradually with increasing compressive strain, and the superexchange interaction between Mn atoms increases gradually. The results suggest that the electronic and magnetic properties of Mn-doped monolayer MoS2 can be effectively modulated by strain engineering providing insight into application to electronic and spintronic devices.

Ganoderma-Like MoS2 /NiS2 with Single Platinum Atoms Doping as an Efficient and Stable Hydrogen Evolution Reaction Catalyst.

PubMed

Guan, Yongxin; Feng, Yangyang; Wan, Jing; Yang, Xiaohui; Fang, Ling; Gu, Xiao; Liu, Ruirui; Huang, Zhengyong; Li, Jian; Luo, Jun; Li, Changming; Wang, Yu

2018-05-27

Herein, a unique ganoderma-like MoS 2 /NiS 2 hetero-nanostructure with isolated Pt atoms anchored is reported. This novel ganoderma-like heterostructure can not only efficiently disperse and confine the few-layer MoS 2 nanosheets to fully expose the edge sites of MoS 2 , and provide more opportunity to capture the Pt atoms, but also tune the electronic structure to modify the catalytic activity. Because of the favorable dispersibility and exposed large specific surface area, single Pt atoms can be easily anchored on MoS 2 nanosheets with ultrahigh loading of 1.8 at% (the highest is 1.3 at% to date). Owing to the ganoderma-like structure and platinum atoms doping, this catalyst shows Pt-like catalytic activity for the hydrogen evolution reaction with an ultralow overpotential of 34 mV and excellent durability of only 2% increase in overpotential for 72 h under the constant current density of 10 mA cm -2 . © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

MoS2 thin films prepared by sulfurization

NASA Astrophysics Data System (ADS)

Sojková, M.; Chromik, Å.; Rosová, A.; Dobročka, E.; Hutár, P.; Machajdík, D.; Kobzev, A. P.; Hulman, M.

2017-08-01

Sulfurization of a Mo layer is one of the most used methods for preparation of thin MoS2 films. In the method, a sulfur powder and Mo covered substrate are placed in different positions within a furnace, and heated separately. This requires a furnace having at least two zones. Here, we present a simplified version of the method where a one-zone tube furnace was used. A molybdenum film on a substrate and a sulfur powder were placed in the center of the furnace and heated at temperatures above 800°C. Mo films transform into MoS2 in vapors of sulphur at high temperatures. As-prepared films were characterized by number of techniques including X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman, Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS). It appears that one-zone sulfurization, with just one annealing temperature used, is a suitable method for fabrication of MoS2 thin films. This method is fast, cheap and easy to scale up.

Chemistry of one-dimensional metallic edge states in MoS2 nanoclusters

NASA Astrophysics Data System (ADS)

Lauritsen, J. V.; Nyberg, M.; Vang, R. T.; Bollinger, M. V.; Clausen, B. S.; Topsøe, H.; Jacobsen, K. W.; Lægsgaard, E.; Nørskov, J. K.; Besenbacher, F.

2003-03-01

Nanostructures often have unusual properties that are linked to their small size. We report here on extraordinary chemical properties associated with the edges of two-dimensional MoS2 nanoclusters, which we show to be able to hydrogenate and break up thiophene (C4H4S) molecules. By combining atomically resolved scanning tunnelling microscopy images of single-layer MoS2 nanoclusters and density functional theory calculations of the reaction energetics, we show that the chemistry of the MoS2 nanoclusters can be associated with one-dimensional metallic states located at the perimeter of the otherwise insulating nanoclusters. The new chemistry identified in this work has significant implications for an important catalytic reaction, since MoS2 nanoclusters constitute the basis of hydrotreating catalysts used to clean up sulfur-containing molecules from oil products in the hydrodesulfurization process.

Influence of the Metal-MoS2 interface on MoS2 Transistor Performance

NASA Astrophysics Data System (ADS)

Yuan, Hui; Cheng, Guangjun; Hight Walker, Angela; You, Lin; Kopanski, Joseph J.; Li, Qiliang; Richter, Curt A.

2015-03-01

We compare the electrical characteristics of MoS2 field-effect transistors (FETS) with Ag source/drain contacts with transistors with Ti contacts, and we demonstrate that the metal-MoS2 interface is crucial to the final device performance. The topography of 5nm Au/5nm Ag (contact layer) and 5nm Au/5nm Ti metal films deposited onto mono- and few-layer MoS2 was characterized by using scanning electron microscopy and atomic force microscopy. The surface morphology of the Au/Ti films on MoS2 shows a rough, dewetting pattern while Au/Ag forms smooth, dense films. These smoother and denser Au/Ag contacts lead to improved carrier transport efficiency. FETs with Ag contacts show more than 60 times higher on-state current and a steeper subthreshold slope. Raman spectroscopy of MoS2 covered with Au/Ag or Au/Ti films revealed that the contact layer is Ag or Ti, respectively. In addition, there is a dramatic difference in the heat transfer between the MoS2 and the two metals: while laser heating is observed in Au/Ti covered MoS2, no heating effects are seen in Au/Ag covered MoS2. It is reasonable to conclude that the smoother and denser Ag contact leads to higher carrier transport efficiency and contributes to the improved thermal properties.

Surface plasmon-enhanced optical absorption in monolayer MoS2 with one-dimensional Au grating

NASA Astrophysics Data System (ADS)

Song, Jinlin; Lu, Lu; Cheng, Qiang; Luo, Zixue

2018-05-01

The optical absorption of a composite photonic structure, namely monolayer molybdenum disulfide (MoS2)-covered Au grating, is theoretically investigated using a rigorous coupled-wave analysis algorithm. The enhancement of localized electromagnetic field due to surface plasmon polaritons supported by Au grating can be utilized to enhance the absorption of MoS2. The remarkable enhancement of absorption due to exciton transition can also be realized. When the period of grating is 600 nm, the local absorption of the monolayer MoS2 on Au grating is nearly 7 times higher than the intrinsic absorption due to B exciton transition. A further study reveals that the absorption properties of Au grating can be tailored by altering number of MoS2 layers, changing to a MoS2 nanoribbon array, and inserting a hafnium dioxide (HfO2) spacer. This work will contribute to the design of MoS2-based optical and optoelectronic devices.

Luminescent monolayer MoS2 quantum dots produced by multi-exfoliation based on lithium intercalation

NASA Astrophysics Data System (ADS)

Qiao, Wen; Yan, Shiming; Song, Xueyin; Zhang, Xing; He, Xueming; Zhong, Wei; Du, Youwei

2015-12-01

An effective multi-exfoliation method based on lithium (Li) intercalation has been demonstrated for preparing monolayer molybdenum disulfide (MoS2) quantum dots (QDs). The cutting mechanism of MoS2 QDs may involve the complete breakup around the defects and edges during the reaction of LixMoS2 with water and its following ultrasonication process. The multiply exfoliation make the MoS2 fragile and easier to break up. After the third exfoliation, a large number of monolayer MoS2 QDs is formed. The as-prepared MoS2 QDs show photoluminescence (PL) inactive due to the existence of 1T phase. After heating treatment, the PL intensity excited at 300 nm is enhanced by five times. The MoS2 QDs solution has an excitation-dependent luminescence emission which shifts to longer wavelengths when the excitation wavelength changes from 280 nm to 370 nm. The optical properties are explored based on the quantum confinement and edge effect.

Doping effect on monolayer MoS2 for visible light dye degradation - A DFT study

NASA Astrophysics Data System (ADS)

Cheriyan, Silpa; Balamurgan, D.; Sriram, S.

2018-04-01

The electronic and optical properties of, Nitrogen (N), Cobalt (Co), and Co-N co-doped monolayers of MoS2 has been studied by using density functional theory (DFT) for visible light photocatalytic activity. From the calculations, it has been observed that the band gap of monolayer MoS2 has been reduced while doping. However, the band gaps of pristine and N doped MoS2 monolayers only falls in the visible region while for Co and Co-N co-doped systems, the band gap shifted to IR region. The optical calculation also confirms the results. The formation energy values of the doped system reaveal that MoS2 monolayer drops its stability while doping. To evaluate the photocatalytic response, band edge potentials of pristine and N-MoS2 are calculated, and the observed results show that compared to N-doped MoS2 monolayer, pure MoS2 is highly suitable for visible light photocatalytic dye degradation.

Characterization of MoS2-Graphene Composites for High-Performance Coin Cell Supercapacitors.

PubMed

Bissett, Mark A; Kinloch, Ian A; Dryfe, Robert A W

2015-08-12

Two-dimensional materials, such as graphene and molybdenum disulfide (MoS2), can greatly increase the performance of electrochemical energy storage devices because of the combination of high surface area and electrical conductivity. Here, we have investigated the performance of solution exfoliated MoS2 thin flexible membranes as supercapacitor electrodes in a symmetrical coin cell arrangement using an aqueous electrolyte (Na2SO4). By adding highly conductive graphene to form nanocomposite membranes, it was possible to increase the specific capacitance by reducing the resistivity of the electrode and altering the morphology of the membrane. With continued charge/discharge cycles the performance of the membranes was found to increase significantly (up to 800%), because of partial re-exfoliation of the layered material with continued ion intercalation, as well as increasing the specific capacitance through intercalation pseudocapacitance. These results demonstrate a simple and scalable application of layered 2D materials toward electrochemical energy storage.

Facile, substrate-scale growth of mono- and few-layer homogeneous MoS2 films on Mo foils with enhanced catalytic activity as counter electrodes in DSSCs.

PubMed

Antonelou, Aspasia; Syrrokostas, George; Sygellou, Lamprini; Leftheriotis, George; Dracopoulos, Vassileios; Yannopoulos, Spyros N

2016-01-29

The growth of MoS2 films by sulfurization of Mo foils at atmospheric pressure is reported. The growth procedure provides, in a controlled way, mono- and few-layer thick MoS2 films with substrate-scale uniformity across square-centimeter area on commercial foils without any pre- or post-treatment. The prepared few-layer MoS2 films are investigated as counter electrodes for dye-sensitized solar cells (DSSCs) by assessing their ability to catalyse the reduction of I3(-) to I(-) in triiodide redox shuttles. The dependence of the MoS2 catalytic activity on the number of monolayers is explored down to the bilayer thickness, showing performance similar to that of, and stability against corrosion better than, Pt-based nanostructured film. The DSSC with the MoS2-Mo counter electrode yields a photovoltaic energy conversion efficiency of 8.4%, very close to that of the Pt-FTO-based DSSC, i.e. 8.7%. The current results disclose a facile, cost-effective and green method for the fabrication of mechanically robust and chemically stable, few-layer MoS2 on flexible Mo substrates and further demonstrate that efficient counter electrodes for DSSCs can be prepared at thicknesses down to the 1-2 nm scale.

MOS 2.0: The Next Generation in Mission Operations Systems

NASA Technical Reports Server (NTRS)

Bindschadler, Duane L.; Boyles, Carole A.; Carrion, Carlos; Delp, Chris L.

2010-01-01

A Mission Operations System (MOS) or Ground System constitutes that portion of an overall space mission Enterprise that resides here on Earth. Over the past two decades, technological innovations in computing and software technologies have allowed an MOS to support ever more complex missions while consuming a decreasing fraction of Project development budgets. Despite (or perhaps, because of) such successes, it is routine to hear concerns about the cost of MOS development. At the same time, demand continues for Ground Systems which will plan more spacecraft activities with fewer commanding errors, provide scientists and engineers with more autonomous functionality, process and manage larger and more complex data more quickly, all while requiring fewer people to develop, deploy, operate and maintain them. One successful approach to such concerns over this period is a multimission approach, based on the reuse of portions (most often software) developed and used in previous missions. The Advanced Multi-Mission Operations System (AMMOS), developed for deep-space science missions, is one successful example of such an approach. Like many computing-intensive systems, it has grown up in a near-organic fashion from a relatively simple set of tools into a complexly interrelated set of capabilities. Such systems, like a city lacking any concept of urban planning, can and will grow in ways that are neither efficient nor particularly easy to sustain. To meet the growing demands and unyielding constraints placed on ground systems, a new approach is necessary. Under the aegis of a multi-year effort to revitalize the AMMOS's multimission operations capabilities, we are utilizing modern practices in systems architecting and model-based engineering to create the next step in Ground Systems: MOS 2.0. In this paper we outline our work (ongoing and planned) to architect and design a multimission MOS 2.0, describe our goals and measureable objectives, and discuss some of the benefits

Chemically deposited nano grain composed MoS(2) thin films for supercapacitor application.

PubMed

Pujari, R B; Lokhande, A C; Shelke, A R; Kim, J H; Lokhande, C D

2017-06-15

Low temperature soft chemical synthesis approach is employed towards MoS 2 thin film preparation on cost effective stainless steel substrate. 3-D semispherical nano-grain composed surface texture of MoS 2 film is observed through FE-SEM technique. Electrochemical supercapacitor performance of MoS 2 film is tested from cyclic voltammetry (CV) and galvanostatic charge discharge (GCD) techniques in 1M aqueous Na 2 SO 4 electrolyte. Specific capacitance (C s ) of 180Fg -1 with CV cycling stability of 82% for 1000 cycles is achieved. Equivalent series resistance (R s ) of 1.78Ωcm -2 observed through Nyquist plot shows usefulness of MoS 2 thin film for charge conduction in supercapacitor application. Copyright © 2016. Published by Elsevier Inc.

Models of MOS and SOS devices

NASA Technical Reports Server (NTRS)

Gassaway, J. D.; Mahmood, Q.; Trotter, J. D.

1980-01-01

Quarterly report describes progress in three programs: dc sputtering machine for aluminum and aluminum alloys; two dimensional computer modeling of MOS transistors; and development of computer techniques for calculating redistribution diffusion of dopants in silicon on sapphire films.

Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride

PubMed Central

Lin, Shisheng; Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhang, Shengjiao; Zhong, Huikai; Wu, Zhiqian; Xu, Wenli; Chen, Hongsheng

2015-01-01

MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells. PMID:26458358

Strain transfer across grain boundaries in MoS2 monolayers grown by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Niehues, Iris; Blob, Anna; Stiehm, Torsten; Schmidt, Robert; Jadriško, Valentino; Radatović, Borna; Čapeta, Davor; Kralj, Marko; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf

2018-07-01

Monolayers of transition metal dichalcogenides (TMDC) mechanically exfoliated from bulk crystals have exceptional mechanical and optical properties. They are extremely flexible, sustaining mechanical strain of about 10% without breaking. Their optical properties dramatically change with applied strain. However, the fabrication of a large number of mechanical devices is tedious due to the micromechanical exfoliation process. Alternatively, monolayers can be grown by chemical vapor deposition (CVD) on the wafer scale, with the drawback of cracks and grain boundaries in the material. Therefore, it is important to investigate the mechanical properties of CVD-grown material and its potential as a material for mass production of nanomechanical devices. Here, we measure the optical absorption of CVD-grown MoS2 monolayers with applied uniaxial tensile strain. We derive a strain-dependent shift for the A exciton of  ‑42 meV/%. This value is identical to MoS2 monolayers, which are mechanically exfoliated from natural molybdenite crystals. Using angle-resolved second-harmonic generation spectroscopy, we find that the applied uniaxial tensile strain is fully transferred across grain boundaries of the CVD-grown monolayer. Our work demonstrates that large-area artificially grown MoS2 monolayers are promising for mass-produced nanomechanical devices.

MoS2-clad microfibre laser delivering conventional, dispersion-managed and dissipative solitons

PubMed Central

Cui, Yudong; Lu, Feifei; Liu, Xueming

2016-01-01

Molybdenum disulfide (MoS2), whose monolayer possesses a direct band gap, displays promising applications in optoelectronics, photonics, and lasers. Recent researches have demonstrated that MoS2 has not only a significant broadband saturable absorption performance, but also a higher optical nonlinear response than graphene. However, MoS2 shows much lower optical damage threshold owing to the poorer thermal conductivity and mechanical property. Here, we exploit a MoS2-clad microfibre (MCM) as the saturable absorber (SA) for the generation of ultrashort pulses under different dispersion conditions. The improved evanescent field interaction scheme can overcome the laser-induced thermal damage, as well as take full advantage of the strong nonlinear effect of MoS2. With the MCM SA, conventional, dispersion-managed, and dissipative solitons are generated around 1600 nm in Er-doped fibre lasers with anomalous, near-zero, and normal cavity dispersions, respectively. Our work paves the way for applications of 2D layered materials in photonics, especially in laser sources. PMID:27456468

Two-dimensional Si nanosheets with local hexagonal structure on a MoS(2) surface.

PubMed

Chiappe, Daniele; Scalise, Emilio; Cinquanta, Eugenio; Grazianetti, Carlo; van den Broek, Bas; Fanciulli, Marco; Houssa, Michel; Molle, Alessandro

2014-04-02

The structural and electronic properties of a Si nanosheet (NS) grown onto a MoS2 substrate by means of molecular beam epitaxy are assessed. Epitaxially grown Si is shown to adapt to the trigonal prismatic surface lattice of MoS2 by forming two-dimensional nanodomains. The Si layer structure is distinguished from the underlying MoS2 surface structure. The local electronic properties of the Si nanosheet are dictated by the atomistic arrangement of the layer and unlike the MoS2 hosting substrate they are qualified by a gap-less density of states. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lattice strain effects on the optical properties of MoS2 nanosheets

PubMed Central

Yang, Lei; Cui, Xudong; Zhang, Jingyu; Wang, Kan; Shen, Meng; Zeng, Shuangshuang; Dayeh, Shadi A.; Feng, Liang; Xiang, Bin

2014-01-01

“Strain engineering” in functional materials has been widely explored to tailor the physical properties of electronic materials and improve their electrical and/or optical properties. Here, we exploit both in plane and out of plane uniaxial tensile strains in MoS2 to modulate its band gap and engineer its optical properties. We utilize X-ray diffraction and cross-sectional transmission electron microscopy to quantify the strains in the as-synthesized MoS2 nanosheets and apply measured shifts of Raman-active modes to confirm lattice strain modification of both the out-of-plane and in-plane phonon vibrations of the MoS2 nanosheets. The induced band gap evolution due to in-plane and out-of-plane tensile stresses is validated by photoluminescence (PL) measurements, promising a potential route for unprecedented manipulation of the physical, electrical and optical properties of MoS2. PMID:25008782

MoS2 monolayers on nanocavities: enhancement in light-matter interaction

NASA Astrophysics Data System (ADS)

Janisch, Corey; Song, Haomin; Zhou, Chanjing; Lin, Zhong; Elías, Ana Laura; Ji, Dengxin; Terrones, Mauricio; Gan, Qiaoqiang; Liu, Zhiwen

2016-06-01

Two-dimensional (2D) atomic crystals and van der Waals heterostructures constitute an emerging platform for developing new functional ultra-thin electronic and optoelectronic materials for novel energy-efficient devices. However, in most thin-film optical applications, there is a long-existing trade-off between the effectiveness of light-matter interactions and the thickness of semiconductor materials, especially when the materials are scaled down to atom thick dimensions. Consequently, enhancement strategies can introduce significant advances to these atomically thick materials and devices. Here we demonstrate enhanced absorption and photoluminescence generation from MoS2 monolayers coupled with a planar nanocavity. This nanocavity consists of an alumina nanolayer spacer sandwiched between monolayer MoS2 and an aluminum reflector, and can strongly enhance the light-matter interaction within the MoS2, increasing the exclusive absorption of monolayer MoS2 to nearly 70% at a wavelength of 450 nm. The nanocavity also modifies the spontaneous emission rate, providing an additional design freedom to control the interaction between light and 2D materials.

Metallic Contact between MoS2 and Ni via Au Nanoglue.

PubMed

Shi, Xinying; Posysaev, Sergei; Huttula, Marko; Pankratov, Vladimir; Hoszowska, Joanna; Dousse, Jean-Claude; Zeeshan, Faisal; Niu, Yuran; Zakharov, Alexei; Li, Taohai; Miroshnichenko, Olga; Zhang, Meng; Wang, Xiao; Huang, Zhongjia; Saukko, Sami; González, Diego López; van Dijken, Sebastiaan; Alatalo, Matti; Cao, Wei

2018-05-01

A critical factor for electronics based on inorganic layered crystals stems from the electrical contact mode between the semiconducting crystals and the metal counterparts in the electric circuit. Here, a materials tailoring strategy via nanocomposite decoration is carried out to reach metallic contact between MoS 2 matrix and transition metal nanoparticles. Nickel nanoparticles (NiNPs) are successfully joined to the sides of a layered MoS 2 crystal through gold nanobuffers, forming semiconducting and magnetic NiNPs@MoS 2 complexes. The intrinsic semiconducting property of MoS 2 remains unchanged, and it can be lowered to only few layers. Chemical bonding of the Ni to the MoS 2 host is verified by synchrotron radiation based photoemission electron microscopy, and further proved by first-principles calculations. Following the system's band alignment, new electron migration channels between metal and the semiconducting side contribute to the metallic contact mechanism, while semiconductor-metal heterojunctions enhance the photocatalytic ability. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Edge-spin-derived magnetism in few-layer MoS2 nanomeshes

NASA Astrophysics Data System (ADS)

Kondo, G.; Yokoyama, N.; Yamada, S.; Hashimoto, Y.; Ohata, C.; Katsumoto, S.; Haruyama, J.

2017-12-01

Magnetism arising from edge spins is highly interesting, particularly in 2D atomically thin materials in which the influence of edges becomes more significant. Among such materials, molybdenum disulfide (MoS2; one of the transition metal dichalcogenide (TMD) family) is attracting significant attention. The causes for magnetism observed in the TMD family, including in MoS2, have been discussed by considering various aspects, such as pure zigzag atomic-structure edges, grain boundaries, and vacancies. Here, we report the observation of ferromagnetism (FM) in few-layer MoS2 nanomeshes (NMs; honeycomb-like array of hexagonal nanopores with low-contamination and low-defect pore edges), which have been created by a specific non-lithographic method. We confirm robust FM arising from pore edges in oxygen(O)-terminated MoS2-NMs at room temperature, while it disappears in hydrogen(H)-terminated samples. The observed high-sensitivity of FM to NM structures and critical annealing temperatures suggest a possibility that the Mo-atom dangling bond in pore edge is a dominant factor for the FM.

Transfer matrix approach to electron transport in monolayer MoS2/MoO x heterostructures

NASA Astrophysics Data System (ADS)

Li, Gen

2018-05-01

Oxygen plasma treatment can introduce oxidation into monolayer MoS2 to transfer MoS2 into MoO x , causing the formation of MoS2/MoO x heterostructures. We find the MoS2/MoO x heterostructures have the similar geometry compared with GaAs/Ga1‑x Al x As semiconductor superlattice. Thus, We employ the established transfer matrix method to analyse the electron transport in the MoS2/MoO x heterostructures with double-well and step-well geometries. We also considere the coupling between transverse and longitudinal kinetic energy because the electron effective mass changes spatially in the MoS2/MoO x heterostructures. We find the resonant peaks show red shift with the increasing of transverse momentum, which is similar to the previous work studying the transverse-momentum-dependent transmission in GaAs/Ga1‑x Al x As double-barrier structure. We find electric field can enhance the magnitude of peaks and intensify the coupling between longitudinal and transverse momentums. Moreover, higher bias is applied to optimize resonant tunnelling condition to show negative differential effect can be observed in the MoS2/MoO x system.

Lubrication with sputtered MoS2 films: Principles, operation, limitations

NASA Technical Reports Server (NTRS)

Spalvins, T.

1991-01-01

The present practices, limitations, and understanding of thin sputtered MoS2 films are reviewed. Sputtered MoS2 films can exhibit remarkable tribological properties such as ultralow friction coefficients (0.01) and enhanced wear lives (millions of cycles) when used in vacuum or dry air. To achieve these favorable tribological characteristics, the sputtering conditions during deposition must be optimized for adequate film adherence and appropriate structure (morphology) and composition.

Molecule desorption induced by gate-voltage application in MOS structure

NASA Astrophysics Data System (ADS)

Hirota, Nozomu; Hattori, Ken; Daimon, Hiroshi; Hattori, Azusa N.; Tanaka, Hidekazu

2016-04-01

For the first time, we demonstrate desorption from a MOS surface by applying gate voltages (V G). We observed CH4, CO, and CO2 desorption from a MOS (Fe nanofilm/a-SiO2/Si) surface in vacuum only when applying negative V G, suggesting the occurrence of electronic excitation by hot-hole injection. This demonstration is the first step in the application of MOSs to electrically controlled catalysts.

Selective growth of MoS2 for proton exchange membranes with extremely high selectivity.

PubMed

Feng, Kai; Tang, Beibei; Wu, Peiyi

2013-12-26

Proton conductivity and methanol permeability are the most important transport properties of proton exchange membranes (PEMs). The ratio of proton conductivity to methanol permeability is usually called selectivity. Herein, a novel strategy of in situ growth of MoS2 is employed to prepare MoS2/Nafion composite membranes for highly selective PEM. The strong interactions between the Mo precursor ((NH4)2MoS4) and Nafion's sulfonic groups in a suitable solvent environment (DMF) probably lead to a selective growth of MoS2 flakes mainly around the ionic clusters of the resultant MoS2/Nafion composite membrane. Therefore, it would significantly promote the aggregation and hence lead to a better connectivity of these ionic clusters, which favors the increase in proton conductivity. Meanwhile, the existence of MoS2 in the ionic channels effectively prevents methanol transporting through the PEM, contributing to the dramatic decrease in the methanol permeability. Consequently, the MoS2/Nafion composite membranes exhibit greatly increased selectivity. Under some severe conditions, such as 50 °C with 80 v/v% of methanol concentration, an increase in the membrane selectivity by nearly 2 orders of magnitude compared with that of the recast Nafion membrane could be achieved here, proving our method as a very promising way to prepare high-performance PEMs. All these conclusions are confirmed by various characterizations, such as (FE-) SEM, TEM, AFM, IR, Raman, TGA, XRD, etc.

A Facile Strategy for the Preparation of MoS3 and its Application as a Negative Electrode for Supercapacitors.

PubMed

Zhang, Tong; Kong, Ling-Bin; Dai, Yan-Hua; Yan, Kun; Shi, Ming; Liu, Mao-Cheng; Luo, Yong-Chun; Kang, Long

2016-09-06

Owing to their graphene-like structure and available oxidation valence states, transition metal sulfides are promising candidates for supercapacitors. Herein, we report the application of MoS3 as a new negative electrode for supercapacitors. MoS3 was fabricated by the facile thermal decomposition of a (NH4 )2 MoS4 precursor. For comparison, samples of MoS3 &MoS2 and MoS2 were also synthesized by using the same method. Moreover, this is the first report of the application of MoS3 as a negative electrode for supercapacitors. MoS3 displayed a high specific capacitance of 455.6 F g(-1) at a current density of 0.5 A g(-1) . The capacitance retention of the MoS3 electrode was 92 % after 1500 cycles, and even 71 % after 5000 cycles. In addition, an asymmetric supercapacitor assembly of MoS3 as the negative electrode demonstrated a high energy density at a high potential of 2.0 V in aqueous electrolyte. These notable results show that MoS3 has significant potential in energy-storage devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fabrication of TiO2/MoS2@zeolite photocatalyst and its photocatalytic activity for degradation of methyl orange under visible light

NASA Astrophysics Data System (ADS)

Zhang, Weiping; Xiao, Xinyan; Zheng, Lili; Wan, Caixia

2015-12-01

TiO2/MoS2@zeolite composite photocatalysts with visible-light activity were fabricated via a simple ultrasonic-hydrothermal synthesis method, using TiCl4 as Ti source, MoS2 as a direct sensitizer, glycerol water solution with certain dispersion agent as hydrolytic agent, and zeolite as carrier. The structure, morphology, composition, optical properties, and specific surface area of the as-prepared photocatalysts were characterized by using XRD, FTIR, SEM-EDS, TEM, XPS, UV-vis, PL and BET analyzer, respectively. And the photocatalytic degradation of methyl orange (MO) in aqueous suspension has been employed to evaluate the photocatalytic activity and degradation kinetics of as-prepared photocatalysts with xenon lamp as irradiation source. The results indicate that: (1) TiO2/MoS2@zeolite composite photocatalysts exhibit enhanced photocatalytic activities for methyl orange (MO) degradation compared to Degussa P25; (2) photocatalytic degradation of MO obeys Langmuir-Hinshelwood kinetic model (pseudo-first order reaction), and its degradation rate constant (kapp) (2.304 h-1) is higher than that of Degussa P25 (0.768 h-1); (3) the heterostructure consisted of zeolite, MoS2 and TiO2 nanostructure could provide synergistic effect for degradation of MO due to the efficient electron transfer process and better absorption property of TiO2/MoS2@zeolite composite photocatalyst.

Electrical properties of HfO2 high- k thin-film MOS capacitors for advanced CMOS technology

NASA Astrophysics Data System (ADS)

Khairnar, A. G.; Patil, L. S.; Salunke, R. S.; Mahajan, A. M.

2015-11-01

We deposited the hafnium dioxide (HfO2) thin films on p-Si (100) substrates. The thin films were deposited with deposition time variations, viz 2, 4, 7 and 20 min using RF-sputtering technique. The thickness and refractive index of the films were measured using spectroscopic ellipsometer. The thicknesses of the films were measured to be 13.7, 21.9, 35.38 and 92.2 nm and refractive indices of 1.90, 1.93, 1.99 and 1.99, respectively, of the films deposited for 2, 4, 7 and 20 min deposition time. The crystal structures of the deposited HfO2 thin films were determined using XRD spectra and showed the monoclinic structure, confirmed with the ICDD card no 34-0104. Aluminum metallization was carried to form the Al/HfO2/ p-Si MOS structures by using thermal evaporation system with electrode area of 12.56 × 10-4 cm2. Capacitance voltage and current voltage measurements were taken to know electrical behavior of these fabricated MOS structures. The electrical parameters such as dielectric constant, flat-band shift and interface trap density determined through CV measurement were 7.99, 0.11 V and 6.94 × 1011 eV-1 cm-2, respectively. The low leakage current density was obtained from IV measurement of fabricated MOS structure at 1.5 V is 4.85 × 10-10 Acm-2. Aforesaid properties explored the suitability of the fabricated HfO2 high- k-based MOS capacitors for advanced CMOS technology.

Metal Oxide Silicon /MOS/ transistors protected from destructive damage by wire

NASA Technical Reports Server (NTRS)

Deboo, G. J.; Devine, E. J.

1966-01-01

Loop of flexible, small diameter, nickel wire protects metal oxide silicon /MOS/ transistors from a damaging electrostatic potential. The wire is attached to a music-wire spring, slipped over the MOS transistor case, and released so the spring tensions the wire loop around all the transistor leads, shorting them together. This allows handling without danger of damage.

Development of spontaneous magnetism and half-metallicity in monolayer MoS2

NASA Astrophysics Data System (ADS)

Rahman, Altaf Ur; Rahman, Gul; García-Suárez, Víctor M.

2017-12-01

Half-metallic behavior and ferromagnetism are predicted in strained MoS2 with different light elements adsorbed using density functional theory. We find that strain increases the density of states at the Fermi energy for Y doping (Y = H, Li, and F) at the S sites and strain-driven magnetism develops in agreement with the Stoner mean field model. Strain-driven magnetism requires less strain (∼3%) for H doping as compared with F and Li doping. No saturation of the spin-magnetic moment is observed in Li-doped MoS2 due to less charge transfer from the Mo d electrons and the added atoms do not significantly increase the Spin-orbit coupling. Half-metallic ferromagnetism is predicted in H and F-doped MoS2. Fixed magnetic moments calculations are also performed, and the DFT computed data is fitted with the Landau mean field theory to investigate the emergence of spontaneous magnetism in Y-doped MoS2. We predict spontaneous magnetism in systems with large (small) mag netic moments for H/F (Li) atoms. The large (small) magnetic moments are atttributed to the electronegativity difference between S and Y atoms. These results suggest that H and F adsorbed monolayer MoS2 is a good candidate for spin-based electronic devices.

Micro-dressing of a carbon nanotube array with MoS2 gauze

NASA Astrophysics Data System (ADS)

Lim, Sharon Xiaodai; Woo, Kah Whye; Ng, Junju; Lu, Junpeng; Kwang, Siu Yi; Zhang, Zheng; Tok, Eng Soon; Sow, Chorng-Haur

2015-10-01

Few-layer MoS2 film has been successfully assembled over an array of CNTs. Using different focused laser beams with different wavelengths, site selective patterning of either the MoS2 film or the supporting CNT array is achieved. This paves the way for applications and investigations into the fundamental properties of the hybrid MoS2/CNT material with a controlled architecture. Through Raman mapping, straining and electron doping of the MoS2 film as a result of interaction with the supporting CNT array are detected. The role of the MoS2 film was further emphasized with a lower work function being detected from Ultra-violet Photoelectron Spectrsocopy (UPS) measurements of the hybrid material, compared to the CNT array. The effect of the changes in the work function was illustrated through the optoelectronic behavior of the hybrid material. At 0 V, 3.49 nA of current is measured upon illuminating the sample with a broad laser beam emitting laser light with a wavelength of 532 nm. With a strong response to external irradiation of different wavelengths, and changes to the power of the excitation source, the hybrid material has shown potential for applications in optoelectronic devices.

Low-temperature plasma-enhanced atomic layer deposition of 2-D MoS2: large area, thickness control and tuneable morphology.

PubMed

Sharma, Akhil; Verheijen, Marcel A; Wu, Longfei; Karwal, Saurabh; Vandalon, Vincent; Knoops, Harm C M; Sundaram, Ravi S; Hofmann, Jan P; Kessels, W M M Erwin; Bol, Ageeth A

2018-05-10

Low-temperature controllable synthesis of monolayer-to-multilayer thick MoS2 with tuneable morphology is demonstrated by using plasma enhanced atomic layer deposition (PEALD). The characteristic self-limiting ALD growth with a growth-per-cycle of 0.1 nm per cycle and digital thickness control down to a monolayer are observed with excellent wafer scale uniformity. The as-deposited films are found to be polycrystalline in nature showing the signature Raman and photoluminescence signals for the mono-to-few layered regime. Furthermore, a transformation in film morphology from in-plane to out-of-plane orientation of the 2-dimensional layers as a function of growth temperature is observed. An extensive study based on high-resolution transmission electron microscopy is presented to unravel the nucleation mechanism of MoS2 on SiO2/Si substrates at 450 °C. In addition, a model elucidating the film morphology transformation (at 450 °C) is hypothesized. Finally, the out-of-plane oriented films are demonstrated to outperform the in-plane oriented films in the hydrogen evolution reaction for water splitting applications.

MoS2 Heterojunctions by Thickness Modulation

PubMed Central

Tosun, Mahmut; Fu, Deyi; Desai, Sujay B.; Ko, Changhyun; Seuk Kang, Jeong; Lien, Der-Hsien; Najmzadeh, Mohammad; Tongay, Sefaattin; Wu, Junqiao; Javey, Ali

2015-01-01

In this work, we report lateral heterojunction formation in as-exfoliated MoS2 flakes by thickness modulation. Kelvin probe force microscopy is used to map the surface potential at the monolayer-multilayer heterojunction, and consequently the conduction band offset is extracted. Scanning photocurrent microscopy is performed to investigate the spatial photocurrent response along the length of the device including the source and the drain contacts as well as the monolayer-multilayer junction. The peak photocurrent is measured at the monolayer-multilayer interface, which is attributed to the formation of a type-I heterojunction. The work presents experimental and theoretical understanding of the band alignment and photoresponse of thickness modulated MoS2 junctions with important implications for exploring novel optoelectronic devices. PMID:26121940

Ultrathin MoS2-coated Ag@Si nanosphere arrays as an efficient and stable photocathode for solar-driven hydrogen production

NASA Astrophysics Data System (ADS)

Zhou, Qingwei; Su, Shaoqiang; Hu, Die; Lin, Lin; Yan, Zhibo; Gao, Xingsen; Zhang, Zhang; Liu, Jun-Ming

2018-03-01

Solar-driven photoelectrochemical (PEC) water splitting has attracted a great deal of attention recently. Silicon (Si) is an ideal light absorber for solar energy conversion. However, the poor stability and inefficient surface catalysis of Si photocathodes for the hydrogen evolution reaction (HER) have remained key challenges. Alternatively, MoS2 has been reported to exhibit excellent catalysis performance if sufficient active sites for the HER are available. Here, ultrathin MoS2 nanoflakes are directly synthesized to coat arrays of Ag-core Si-shell nanospheres (Ag@Si NSs) by using chemical vapor deposition. Due to the high surface area ratio and large curvature of these NSs, the as-grown MoS2 nanoflakes can accommodate more active sites. In addition, the high-quality coating of MoS2 nanoflakes on the Ag@Si NSs protects the photocathode from damage during the PEC reaction. An photocurrent density of 33.3 mA cm-2 at a voltage of -0.4 V is obtained versus the reversible hydrogen electrode. The as-prepared nanostructure as a hydrogen photocathode is evidenced to have high stability over 12 h PEC performance. This work opens up opportunities for composite photocathodes with high activity and stability using cheap and stable co-catalysts.

Ultrathin MoS2-coated Ag@Si nanosphere arrays as an efficient and stable photocathode for solar-driven hydrogen production.

PubMed

Zhou, Qingwei; Su, Shaoqiang; Hu, Die; Lin, Lin; Yan, Zhibo; Gao, Xingsen; Zhang, Zhang; Liu, Jun-Ming

2018-01-30

Solar-driven photoelectrochemical (PEC) water splitting has attracted a great deal of attention recently. Silicon (Si) is an ideal light absorber for solar energy conversion. However, the poor stability and inefficient surface catalysis of Si photocathodes for the hydrogen evolution reaction (HER) have remained key challenges. Alternatively, MoS 2 has been reported to exhibit excellent catalysis performance if sufficient active sites for the HER are available. Here, ultrathin MoS 2 nanoflakes are directly synthesized to coat arrays of Ag-core Si-shell nanospheres (Ag@Si NSs) by using chemical vapor deposition. Due to the high surface area ratio and large curvature of these NSs, the as-grown MoS 2 nanoflakes can accommodate more active sites. In addition, the high-quality coating of MoS 2 nanoflakes on the Ag@Si NSs protects the photocathode from damage during the PEC reaction. An photocurrent density of 33.3 mA cm -2 at a voltage of -0.4 V is obtained versus the reversible hydrogen electrode. The as-prepared nanostructure as a hydrogen photocathode is evidenced to have high stability over 12 h PEC performance. This work opens up opportunities for composite photocathodes with high activity and stability using cheap and stable co-catalysts.

Investigation on nonlinear optical properties of MoS2 nanoflakes grown on silicon and quartz substrates

NASA Astrophysics Data System (ADS)

Bayesteh, Samaneh; Zahra Mortazavi, Seyedeh; Reyhani, Ali

2018-05-01

In this study, MoS2 nanoflakes were directly grown on different substrates—Si/SiO2 and quartz—by one-step thermal chemical vapor deposition using MoO3 and sulfide powders as precursors. Scanning electron microscopy and x-ray diffraction patterns demonstrated the formation of MoS2 structures on both substrates. Moreover, UV-visible and photoluminescence analysis confirmed the formation of MoS2 few-layer structures. According to Raman spectroscopy, by assessment of the line width and frequency shift differences between the and A 1g, it was inferred that the MoS2 grown on the silicon substrate was monolayer and that grown on the quartz substrate was multilayer. In addition, open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the grown MoS2. All experiments were performed using a diode laser with a wavelength of 532 nm as the light source. It is noticeable that both samples demonstrate obvious self-defocusing behavior. The monolayer MoS2 grown on the silicon substrate displayed considerable two-photon absorption while, the multilayer MoS2 synthesized on the quartz exhibited saturable absorption. In general, few-layered MoS2 would be useful for the development of nanophotonic devices like optical limiters, optical switchers, etc.

Robust Denaturation of Villin Headpiece by MoS2 Nanosheet: Potential Molecular Origin of the Nanotoxicity

NASA Astrophysics Data System (ADS)

Gu, Zonglin; Yang, Zaixing; Kang, Seung-Gu; Yang, Jerry R.; Luo, Judong; Zhou, Ruhong

2016-06-01

MoS2 nanosheet, a new two-dimensional transition metal dichalcogenides nanomaterial, has attracted significant attentions lately due to many potential promising biomedical applications. Meanwhile, there is also a growing concern on its biocompatibility, with little known on its interactions with various biomolecules such as proteins. In this study, we use all-atom molecular dynamics simulations to investigate the interaction of a MoS2 nanosheet with Villin Headpiece (HP35), a model protein widely used in protein folding studies. We find that MoS2 exhibits robust denaturing capability to HP35, with its secondary structures severely destroyed within hundreds of nanosecond simulations. Both aromatic and basic residues are critical for the protein anchoring onto MoS2 surface, which then triggers the successive protein unfolding process. The main driving force behind the adsorption process is the dispersion interaction between protein and MoS2 monolayer. Moreover, water molecules at the interface between some key hydrophobic residues (e.g. Trp-64) and MoS2 surface also help to accelerate the process driven by nanoscale drying, which provides a strong hydrophobic force. These findings might have shed new light on the potential nanotoxicity of MoS2 to proteins with atomic details, which should be helpful in guiding future biomedical applications of MoS2 with its nanotoxicity mitigated.

Prospects of zero Schottky barrier height in a graphene-inserted MoS2-metal interface

NASA Astrophysics Data System (ADS)

Chanana, Anuja; Mahapatra, Santanu

2016-01-01

A low Schottky barrier height (SBH) at source/drain contact is essential for achieving high drive current in atomic layer MoS2-channel-based field effect transistors. Approaches such as choosing metals with appropriate work functions and chemical doping are employed previously to improve the carrier injection from the contact electrodes to the channel and to mitigate the SBH between the MoS2 and metal. Recent experiments demonstrate significant SBH reduction when graphene layer is inserted between metal slab (Ti and Ni) and MoS2. However, the physical or chemical origin of this phenomenon is not yet clearly understood. In this work, density functional theory simulations are performed, employing pseudopotentials with very high basis sets to get insights of the charge transfer between metal and monolayer MoS2 through the inserted graphene layer. Our atomistic simulations on 16 different interfaces involving five different metals (Ti, Ag, Ru, Au, and Pt) reveal that (i) such a decrease in SBH is not consistent among various metals, rather an increase in SBH is observed in case of Au and Pt; (ii) unlike MoS2-metal interface, the projected dispersion of MoS2 remains preserved in any MoS2-graphene-metal system with shift in the bands on the energy axis. (iii) A proper choice of metal (e.g., Ru) may exhibit ohmic nature in a graphene-inserted MoS2-metal contact. These understandings would provide a direction in developing high-performance transistors involving heteroatomic layers as contact electrodes.

Two-dimensional electronic transport and surface electron accumulation in MoS2.

PubMed

Siao, M D; Shen, W C; Chen, R S; Chang, Z W; Shih, M C; Chiu, Y P; Cheng, C-M

2018-04-12

Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. Van der Waals crystals are expected to have an inert surface because of the absence of dangling bonds. However, here we show that the surface of high-quality synthesized molybdenum disulfide (MoS 2 ) is a major n-doping source. The surface electron concentration of MoS 2 is nearly four orders of magnitude higher than that of its inner bulk. Substantial thickness-dependent conductivity in MoS 2 nanoflakes was observed. The transfer length method suggested the current transport in MoS 2 following a two-dimensional behavior rather than the conventional three-dimensional mode. Scanning tunneling microscopy and angle-resolved photoemission spectroscopy measurements confirmed the presence of surface electron accumulation in this layered material. Notably, the in situ-cleaved surface exhibited a nearly intrinsic state without electron accumulation.

Synthesis and characterization of three-dimensional MoS2@carbon fibers hierarchical architecture with high capacity and high mass loading for Li-ion batteries.

PubMed

Shan, Xinyuan; Zhang, Shen; Zhang, Na; Chen, Yujin; Gao, Hong; Zhang, Xitian

2018-01-15

Three-dimensional (3D) MoS 2 @carbon fibers (CFs) hierarchical architectures are successfully synthesized via a simple hydrothermal method and subsequent annealing. MoS 2 nanoflakes are grown on the twine carbon fibers of the carbonized waste cotton cloth. The twine CFs can provide a short diffusion path for ions in electrolyte, enhance the specific surface area, and improve the conductivity of the 3D MoS 2 @CFs hierarchical architectures with high mass loading of 4.4mgcm -2 . The 3D MoS 2 @CFs hierarchical architectures as the electrode material can achieve a high reversible areal capacity (5.2mAhcm -2 at 2.5mAcm -2 ) and exhibit an excellent rate performance. In addition, CFs are prepared by simply carbonizing the waste cotton and then used as carbon source, which is low-cost and eco-friendly. We also found that the Mo nanoparticles produced during the charge/discharge process exist in the hierarchical architectures during cycling and can improve the conductivity of the entire system as well as the cycling stability. Therefore, MoS 2 @CFs nanocomposites as electrode materials manifest a significant application potential for high-performance Li-ion batteries. Copyright © 2017 Elsevier Inc. All rights reserved.

Word Criticality Analysis MOS: 76W. Skill Levels 1 & 2

DTIC Science & Technology

1981-09-01

some degree of criticality in the training/performance of tasks contained in the respective MOS Soldier’s Manual (SM). These critical words were...printout. The prime users of this document were fully cognizant of its contents and required no special instructioft for interpretation . However, for the...Skill Level II However, due to the way some Soldier Manuals are constructed, the WCA for some MOS have both Skill Levels merged into one report. Each

Industrial Technology of Decontamination of Liquid Radioactive Waste in SUE MosSIA 'Radon' - 12371

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adamovich, Dmitry V.; Neveykin, Petr P.; Karlin, Yuri V.

SUE MosSIA 'RADON' - this enterprise was created more than 50 years ago, which deals with the recycling of radioactive waste and conditioning of spent sources of radiation in stationary and mobile systems in the own factory and operating organizations. Here is represented the experience SUE MosSIA 'Radon' in the field of the management with liquid radioactive waste. It's shown, that the activity of SUE MosSIA 'RADON' is developing in three directions - improvement of technical facilities for treatment of radioactive waters into SUE MosSIA 'RADON' development of mobile equipment for the decontamination of radioactive waters in other organizations, developmentmore » of new technologies for decontamination of liquid radioactive wastes as part of various domestic Russian and international projects including those related to the operation of nuclear power and nuclear submarines. SUE MosSIA 'RADON' has processed more than 270 thousand m{sup 3} of radioactive water, at that more than 7000 m{sup 3} in other organizations for more than 50 years. It is shown that a number of directions, particularly, the development of mobile modular units for decontamination of liquid radioactive waste, SUE MosSIA 'RADON' is a leader in the world. (authors)« less

Anti-site defected MoS2 sheet-based single electron transistor as a gas sensor

NASA Astrophysics Data System (ADS)

Sharma, Archana; Husain, Mushahid; Srivastava, Anurag; Khan, Mohd. Shahid

2018-05-01

To prevent harmful and poisonous CO gas molecules, catalysts are needed for converting them into benign substances. Density functional theory (DFT) calculations have been used to study the adsorption of CO and CO2 gas molecules on the surface of MoS2 monolayer with Mo atom embedded at S-vacancy site (MoS). The strong interaction between Mo metal with pristine MoS2 sheet suggests its strong binding nature. Doping Mo into MoS2 sheet enhances CO and CO2 adsorption strength. The sensing response of MoS-doped MoS2 system to CO and CO2 gas molecules is obtained in the single electron transistor (SET) environment by varying bias voltage. Doping reduces charging energy of the device which results in fast switching of the device from OFF to ON state.

Modification of the optoelectronic properties of two-dimensional MoS2 crystals by ultraviolet-ozone treatment

NASA Astrophysics Data System (ADS)

Yang, Hae In; Park, Seonyoung; Choi, Woong

2018-06-01

We report the modification of the optoelectronic properties of mechanically-exfoliated single layer MoS2 by ultraviolet-ozone exposure. Photoluminescence emission of pristine MoS2 monotonically decreased and eventually quenched as ultraviolet-ozone exposure time increased from 0 to 10 min. The reduction of photoluminescence emission accompanied reduction of Raman modes, suggesting structural degradation in ultraviolet-ozone exposed MoS2. Analysis with X-ray photoelectron spectroscopy revealed that the formation of Ssbnd O and Mosbnd O bonding increases with ultraviolet-ozone exposure time. Measurement of electrical transport properties of MoS2 in a bottom-gate thin-film transistor configuration suggested the presence of insulating MoO3 after ultraviolet-ozone exposure. These results demonstrate that ultraviolet-ozone exposure can significantly influence the optoelectronic properties of single layer MoS2, providing important implications on the application of MoS2 and other two-dimensional materials into optoelectronic devices.

An inductorless active mixer using stacked nMOS/pMOS configuration and LO shaping technique

NASA Astrophysics Data System (ADS)

Guo, Benqing; Chen, Jun; Wang, Xuebing; Chen, Hongpeng

2018-04-01

In this paper, a CMOS active down-conversion mixer is presented for wideband applications. Specifically, a LO generation chain is suggested to convert AC LO signal to shaped trapezoid burst, which reduces the sinusoidal LO power level requirement by the mixer. The current-reuse technique by stacked nMOS/pMOS architecture is used to save the power consumption of the circuit. Moreover, this complementary configuration is also employed to compensate second-order nonlinearity of the circuit. Implemented in a 0.18-μm CMOS process, post-simulations show that, driven by only ‑10 dBm sinusoidal LO signal, the proposed inductorless mixer provides a maximal conversion gain of 15.7 dB and a noise figure (NF) of 9.1-12 dB across RF input frequency range 0.5-1.6 GHz. The IIP3 and IP1dB of 3.5 dBm and ‑4.8 dBm are obtained, respectively. The mixer core only consumes 3.6 mW from a 1.8-V supply.

Radiative energy transfer from MoS2 excitons to surface plasmons

NASA Astrophysics Data System (ADS)

Kang, Yimin; Li, Bowen; Fang, Zheyu

2017-12-01

In this work, we demonstrated the energy transfer process from few-layer MoS2 to gold dimer arrays via ultrafast pump-probe spectroscopy. With the overlap between the MoS2 exciton and the designed plasmon dipolar modes in the frequency domain, the exciton energy can be radiatively transferred to plasmonic structures, excited the localized surface plasmon resonance, and then enhanced the oscillation of coherent acoustic phonons. Power-dependent differential reflection signals and an analytical model based on the rate equation of exciton density were carried out to quantitatively study the energy transfer process. Our finding explores the energy flow between MoS2 excitons and surface plasmons, and can be contributed to the design of exciton-plasmon structures utilizing ultrathin materials.

Three-Dimensional Tubular MoS2/PANI Hybrid Electrode for High Rate Performance Supercapacitor.

PubMed

Ren, Lijun; Zhang, Gaini; Yan, Zhe; Kang, Liping; Xu, Hua; Shi, Feng; Lei, Zhibin; Liu, Zong-Huai

2015-12-30

By using three-dimensional (3D) tubular molybdenum disulfide (MoS2) as both an active material in electrochemical reaction and a framework to provide more paths for insertion and extraction of ions, PANI nanowire arrays with a diameter of 10-20 nm can be controllably grown on both the external and internal surface of 3D tubular MoS2 by in situ oxidative polymerization of aniline monomers and 3D tubular MoS2/PANI hybrid materials with different amounts of PANI are prepared. A controllable growth of PANI nanowire arrays on the tubular MoS2 surface provides an opportunity to optimize the capacitive performance of the obtained electrodes. When the loading amount of PANI is 60%, the obtained MoS2/PANI-60 hybrid electrode not only shows a high specific capacitance of 552 F/g at a current density of 0.5 A/g, but also gives excellent rate capability of 82% from 0.5 to 30 A/g. The remarkable rate performance can be mainly attributed to the architecture with synergistic effect between 3D tubular MoS2 and PANI nanowire arrays. Moreover, the MoS2/PANI-60 based symmetric supercapacitor also exhibits the excellent rate performance and good cycling stability. The specific capacitance based on the total mass of the two electrodes is 124 F/g at a current density of 1 A/g and 79% of its initial capacitance is remained after 6000 cycles. The 3D tubular structure provides a good and favorable method for improving the capacitance retention of PANI electrode.

Three-dimensional nanoporous MoS2 framework decorated with Au nanoparticles for surface-enhanced Raman scattering

NASA Astrophysics Data System (ADS)

Sheng, Yingqiang; Jiang, Shouzhen; Yang, Cheng; Liu, Mei; Liu, Aihua; Zhang, Chao; Li, Zhen; Huo, Yanyan; Wang, Minghong; Man, Baoyuan

2017-08-01

The three-dimensional (3D) MoS2 decorated with Au nanoparticles (Au NPs) hybrids (3D MoS2-Au NPs) for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. SEM, Raman spectroscopy, TEM, SAED, EDX and XRD were performed to characterize 3D MoS2-Au NPs hybrids. Rhodamine 6G (R6G), fluorescein and gallic acid molecules were used as the probe for the SERS detection of the 3D MoS2-Au NPs hybrids. In addition, we modeled the enhancement of the electric field of MoS2-Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.

Performance of an Advanced MOS System in the 1996-97 National Collegiate Weather Forecasting Contest.

NASA Astrophysics Data System (ADS)

Vislocky, Robert L.; Fritsch, J. Michael

1997-12-01

A prototype advanced model output statistics (MOS) forecast system that was entered in the 1996-97 National Collegiate Weather Forecast Contest is described and its performance compared to that of widely available objective guidance and to contest participants. The prototype system uses an optimal blend of aviation (AVN) and nested grid model (NGM) MOS forecasts, explicit output from the NGM and Eta guidance, and the latest surface weather observations from the forecast site. The forecasts are totally objective and can be generated quickly on a personal computer. Other "objective" forms of guidance tracked in the contest are 1) the consensus forecast (i.e., the average of the forecasts from all of the human participants), 2) the combination of NGM raw output (for precipitation forecasts) and NGM MOS guidance (for temperature forecasts), and 3) the combination of Eta Model raw output (for precipitation forecasts) and AVN MOS guidance (for temperature forecasts).Results show that the advanced MOS system finished in 20th place out of 737 original entrants, or better than approximately 97% of the human forecasters who entered the contest. Moreover, the advanced MOS system was slightly better than consensus (23d place). The fact that an objective forecast system finished ahead of consensus is a significant accomplishment since consensus is traditionally a very formidable "opponent" in forecast competitions. Equally significant is that the advanced MOS system was superior to the traditional guidance products available from the National Centers for Environmental Prediction (NCEP). Specifically, the combination of NGM raw output and NGM MOS guidance finished in 175th place, and the combination of Eta Model raw output and AVN MOS guidance finished in 266th place. The latter result is most intriguing since the proposed elimination of all NGM products would likely result in a serious degradation of objective products disseminated by NCEP, unless they are replaced with equal

Ultrahigh-performance pseudocapacitor based on phase-controlled synthesis of MoS2 nanosheets decorated Ni3S2 hybrid structure through annealing treatment

NASA Astrophysics Data System (ADS)

Huang, Long; Hou, Huijie; Liu, Bingchuan; Zeinu, Kemal; Zhu, Xiaolei; Yuan, Xiqing; He, Xiulin; Wu, Longsheng; Hu, Jingping; Yang, Jiakuan

2017-12-01

In this work, a hierarchical Ni3S2@MoS2 hybrid structure was synthesized by an effective strategy with a combined hydrothermal route and subsequent annealing treatment. When tested as supercapacitor electrodes, the Ni3S2@MoS2 composites exhibited high specific capacitance of 1418.5 F g-1 at 0.5 A g-1, which also showed a good capacitance retention of 75.8% at 5 A g-1 after 1250 cycles. The Ni3S2@MoS2 composites demonstrated 1.9 fold higher specific capacitance compared to the amorphous shell counterpart (NixSy@MoS2). Furthermore, the assembled asymmetric supercapacitor (Ni3S2@MoS2//rGO) also demonstrated a capacitance of 61 F g-1 at 0.5 A g-1, with energy and power densities of 21.7 Wh kg-1 at 400 W kg-1 and 12 Wh kg-1 at 2400 W kg-1 under an operating window of 1.6 V. The asymmetric supercapacitor also showed a favorable cycle stability with 72% capacity retention over 4000 cycles at 10 A g-1. The improved electrochemical performance is attributed to the synergetic effect of the large accessible surface area and optimal contacts between the MoS2 and the electrolyte, as well as high capacitance of the metallic Ni3S2 core.

Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

PubMed

Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

2016-02-16

A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4.

Word Criticality Analysis MOS: 17B. Skill Levels 1 & 2.

DTIC Science & Technology

1981-09-01

DPFO Curl -___ .... F ...... COPIES ATOP .o’,. 109.1 ,.,,,o .4i,1,.~ .. d.,--. - , selll efle *,5,ed. !* DISCLAIMER NOTICE THIS DOCUMENT IS BEST QUALITY...Manual (SM). These critical words were selected by subject matter/job experts knowledgeable in their MOS. The vocabulary set used as the basis for critical...following 5 point rating scale was used by a team of up to 3 subject matter experts fzum Army MOS proponent schools to rate each word selected as having

Doping of two-dimensional MoS2 by high energy ion implantation

NASA Astrophysics Data System (ADS)

Xu, Kang; Zhao, Yuda; Lin, Ziyuan; Long, Yan; Wang, Yi; Chan, Mansun; Chai, Yang

2017-12-01

Two-dimensional (2D) materials have been demonstrated to be promising candidates for next generation electronic circuits. Analogues to conventional Si-based semiconductors, p- and n-doping of 2D materials are essential for building complementary circuits. Controllable and effective doping strategies require large tunability of the doping level and negligible structural damage to ultrathin 2D materials. In this work, we demonstrate a doping method utilizing a conventional high-energy ion-implantation machine. Before the implantation, a Polymethylmethacrylate (PMMA) protective layer is used to decelerate the dopant ions and minimize the structural damage to MoS2, thus aggregating the dopants inside MoS2 flakes. By optimizing the implantation energy and fluence, phosphorus dopants are incorporated into MoS2 flakes. Our Raman and high-resolution transmission electron microscopy (HRTEM) results show that only negligibly structural damage is introduced to the MoS2 lattice during the implantation. P-doping effect by the incorporation of p+ is demonstrated by Photoluminescence (PL) and electrical characterizations. Thin PMMA protection layer leads to large kinetic damage but also a more significant doping effect. Also, MoS2 with large thickness shows less kinetic damage. This doping method makes use of existing infrastructures in the semiconductor industry and can be extended to other 2D materials and dopant species as well.

MOS 2.0: Modeling the Next Revolutionary Mission Operations System

NASA Technical Reports Server (NTRS)

Delp, Christopher L.; Bindschadler, Duane; Wollaeger, Ryan; Carrion, Carlos; McCullar, Michelle; Jackson, Maddalena; Sarrel, Marc; Anderson, Louise; Lam, Doris

2011-01-01

Designed and implemented in the 1980's, the Advanced Multi-Mission Operations System (AMMOS) was a breakthrough for deep-space NASA missions, enabling significant reductions in the cost and risk of implementing ground systems. By designing a framework for use across multiple missions and adaptability to specific mission needs, AMMOS developers created a set of applications that have operated dozens of deep-space robotic missions over the past 30 years. We seek to leverage advances in technology and practice of architecting and systems engineering, using model-based approaches to update the AMMOS. We therefore revisit fundamental aspects of the AMMOS, resulting in a major update to the Mission Operations System (MOS): MOS 2.0. This update will ensure that the MOS can support an increasing range of mission types, (such as orbiters, landers, rovers, penetrators and balloons), and that the operations systems for deep-space robotic missions can reap the benefits of an iterative multi-mission framework.12 This paper reports on the first phase of this major update. Here we describe the methods and formal semantics used to address MOS 2.0 architecture and some early results. Early benefits of this approach include improved stakeholder input and buy-in, the ability to articulate and focus effort on key, system-wide principles, and efficiency gains obtained by use of well-architected design patterns and the use of models to improve the quality of documentation and decrease the effort required to produce and maintain it. We find that such methods facilitate reasoning, simulation, analysis on the system design in terms of design impacts, generation of products (e.g., project-review and software-delivery products), and use of formal process descriptions to enable goal-based operations. This initial phase yields a forward-looking and principled MOS 2.0 architectural vision, which considers both the mission-specific context and long-term system sustainability.

MoS 2 Heterojunctions by Thickness Modulation

DOE PAGES

Tosun, Mahmut; Fu, Deyi; Desai, Sujay B.; ...

2015-06-30

In this work, we report lateral heterojunction formation in as-exfoliated MoS 2 flakes by thickness modulation. Kelvin probe force microscopy is used to map the surface potential at the monolayer-multilayer heterojunction, and consequently the conduction band offset is extracted. Scanning photocurrent microscopy is performed to investigate the spatial photocurrent response along the length of the device including the source and the drain contacts as well as the monolayer-multilayer junction. The peak photocurrent is measured at the monolayer-multilayer interface, which is attributed to the formation of a type-I heterojunction. Finally, the work presents experimental and theoretical understanding of the band alignmentmore » and photoresponse of thickness modulated MoS 2 junctions with important implications for exploring novel optoelectronic devices.« less

Single-layer MoS2 - electrical transport properties, devices and circuits

NASA Astrophysics Data System (ADS)

Kis, Andras

2013-03-01

After quantum dots, nanotubes and nanowires, two-dimensional materials in the shape of sheets with atomic-scale thickness represent the newest addition to the diverse family of nanoscale materials. Single-layer molybdenum disulphide (MoS2) , a direct-gap semiconductor is a typical example of these new graphene-like materials that can be produced using the adhesive-tape based cleavage technique originally developed for graphene. The presence of a band gap in MoS2 allowed us to fabricate transistors that can be turned off and operate with negligible leakage currents. Furthermore, our transistors can be used to build simple integrated circuits capable of performing logic operations and amplifying small signals. I will report here on our latest 2D MoS2 transistors with improved performance due to enhanced electrostatic control, showing improved currents and transconductance as well as current saturation. We also record electrical breakdown of our devices and find that MoS2 can support very high current densities, exceeding the current carrying capacity of copper by a factor of fifty. Furthermore, I will show optoelectronic devices incorporating MoS2 with sensitivity that surpasses similar graphene devices by several orders of magnitude. Finally, I will present temperature-dependent electrical transport and mobility measurements that show clear mobility enhancement due to the suppression of the influence of charge impurities with the deposition of an HfO2 capping layer. Financially supported by grants from Swiss National Science Foundation, EU-FP7, EU-ERC and Swiss Nanoscience Institute.

Mace-like hierarchical MoS2/NiCo2S4 composites supported by carbon fiber paper: An efficient electrocatalyst for the hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Sun, Lan; Wang, Tao; Zhang, Long; Sun, Yunjin; Xu, Kewei; Dai, Zhengfei; Ma, Fei

2018-02-01

The rational design and preparation of earth-abundant, stable and efficient electrocatalysts for hydrogen production is currently the subject in extensive scientific and technological researches toward the future of a clean-energy society. Herein, a mace-like MoS2/NiCo2S4 hierarchical structure is designed and synthesized on carbon fiber paper via a facile hydrothermal method, and evaluated as electrocatalyst for hydrogen evolution reaction. In the MoS2/NiCo2S4/carbon fiber paper hierarchical structures, MoS2 nanosheets are dispersively distributed on the surface of NiCo2S4 nanowires, which provides an enlarged surface area, abundant interfaces and catalytic active sites. As for hydrogen evolution reaction, such MoS2/NiCo2S4/carbon fiber paper heterostructures give rise to a hydrogen evolution reaction catalytic current density of 10 mA cm-2 with a lower overpotential of 139 mV and a smaller Tafel slope of 37 mV·dec-1 than those of MoS2/carbon fiber paper and NiCo2S4/carbon fiber paper counterparts, exhibiting a prominent electrocatalytic performance. Moreover, the electrocatalytic properties change little after 5000 CV cycles and continual electrolysis for 12 h without obvious decay, respectively, demonstrating high durability and stability. The excellent hydrogen evolution reaction performances endow the hierarchical configuration MoS2/NiCo2S4/carbon fiber paper with promising alternative in HER and other related renewable energy fields.

Observing Ambipolar Behavior and Bandgap Engineering of MoS2 with Transport Measurements

NASA Astrophysics Data System (ADS)

Morris, Rachael; Wilson, Cedric; Hamblin, Glen; Tsuchikawa, Ryuichi; Deshpande, Vikram V.

Molybdenum disulfide is a transition metal semiconductor with a relatively large bandgap about 1.8 eV. In MoS2\\ it is expected that the bandgap is layer dependent and changes with the application of strain. In this talk I will outline our attempt to make simple field effect transistors with thin MoS2 on flexible substrates. Our aim was to see the bandgap of MoS2 directly via transport measurements using electrolytic gating, then apply uniaxial strain to a single layer MoS2 device to see the bandgap change. This was to be one way of confirming theoretical expectations, as well as compare with experimental results already obtained through photoluminescence spectroscopy. Though we did not obtain our target result with this stage of the experiment, future experimental work is planned. I will discuss the experimental method, the challenges of obtaining data and the results we obtained.

Improving the tribological and corrosive properties of MoS2-based coatings by dual-doping and multilayer construction

NASA Astrophysics Data System (ADS)

Shang, Kedong; Zheng, Shaoxian; Ren, Siming; Pu, Jibin; He, Dongqing; Liu, Shuan

2018-04-01

The pure MoS2 coating always performs high friction coefficient and short service life when used in high humidity or after long-time storage in humid atmospheric environment. In this study, the MoS2/Pb-Ti composite and MoS2/Pb-Ti multilayer coatings are deposited to improve the corrosion resistance in 3.5 wt% NaCl solution and tribological performance in high humidity condition. The electrochemical impedance spectra and salt spray test shown that the MoS2/Pb-Ti composite and multilayer coatings can inhibit the permeation of oxygen and other corrosive elements, thus resulting a high corrosion resistance. Furthermore, compared with pure MoS2 coating, the tribological performance of the MoS2/Pb-Ti composite and multilayer coatings is also improved significantly owing to the high mechanical properties and compact structure. Moreover, the heterogenous interfaces in MoS2/Pb-Ti multilayer coating play an important role to improve the corrosion resistance and tribological performance of coatings. Overall, the dual-doping and multilayer construction are promising approaches to design the MoS2 coatings as the environmentally adaptive lubricants.

Characterization of atomic-layer MoS2 synthesized using a hot filament chemical vapor deposition method

NASA Astrophysics Data System (ADS)

Ying-Zi, Peng; Yang, Song; Xiao-Qiang, Xie; Yuan, Li; Zheng-Hong, Qian; Ru, Bai

2016-05-01

Atomic-layer MoS2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy (AFM), x-ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation (002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasi-honeycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS2. The stoichiometric mole ratio of S/Mo is about 2.0-2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS2 under our experimental conditions. Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant Nos. LY16F040003 and LY16A040007) and the National Natural Science Foundation of China (Grant Nos. 51401069 and 11574067).

Balancing the Hydrogen Evolution Reaction, Surface Energetics, and Stability of Metallic MoS 2 Nanosheets via Covalent Functionalization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benson, Eric E.; Zhang, Hanyu; Schuman, Samuel A.

We modify the fundamental electronic properties of metallic (1T phase) nanosheets of molybdenum disulfide (MoS 2) through covalent chemical functionalization, and thereby directly influence the kinetics of the hydrogen evolution reaction (HER), surface energetics, and stability. Chemically exfoliated, metallic MoS 2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS 2 functionalized with the most electron donating functional group (p-(CH 3CH 2) 2NPh-MoS 2) is the most efficient catalyst for HER in this series, with initial activity that is slightly worse compared to the pristine metallic phase of MoS 2. The p-(CHmore » 3CH 2) 2NPh-MoS 2 is more stable than unfunctionalized metallic MoS 2 and outperforms unfunctionalized metallic MoS 2 for continuous H 2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the functional group. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS 2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS 2 nanosheet. The functional groups preserve the metallic nature of the MoS 2 nanosheets, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when mildly annealed in a nitrogen atmosphere. We propose that the electron density and, therefore, reactivity of the MoS 2 nanosheets are controlled by the attached functional groups. Functionalizing nanosheets of MoS 2 and other transition metal dichalcogenides provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state.« less

The Role of Interfacial Electronic Properties on Phonon Transport in Two-Dimensional MoS 2 on Metal Substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Zhequan; Chen, Liang; Yoon, Mina

2016-11-08

In this paper, we investigate the role of interfacial electronic properties on the phonon transport in two-dimensional MoS 2 adsorbed on metal substrates (Au and Sc) using first-principles density functional theory and the atomistic Green’s function method. Our study reveals that the different degree of orbital hybridization and electronic charge distribution between MoS 2 and metal substrates play a significant role in determining the overall phonon–phonon coupling and phonon transmission. The charge transfer caused by the adsorption of MoS 2 on Sc substrate can significantly weaken the Mo–S bond strength and change the phonon properties of MoS 2, which resultmore » in a significant change in thermal boundary conductance (TBC) from one lattice-stacking configuration to another for same metallic substrate. In a lattice-stacking configuration of MoS 2/Sc, weakening of the Mo–S bond strength due to charge redistribution results in decrease in the force constant between Mo and S atoms and substantial redistribution of phonon density of states to low-frequency region which affects overall phonon transmission leading to 60% decrease in TBC compared to another configuration of MoS 2/Sc. Strong chemical coupling between MoS 2 and the Sc substrate leads to a significantly (~19 times) higher TBC than that of the weakly bound MoS 2/Au system. Our findings demonstrate the inherent connection among the interfacial electronic structure, the phonon distribution, and TBC, which helps us understand the mechanism of phonon transport at the MoS 2/metal interfaces. Finally, the results provide insights for the future design of MoS 2-based electronics and a way of enhancing heat dissipation at the interfaces of MoS 2-based nanoelectronic devices.« less

Balancing the Hydrogen Evolution Reaction, Surface Energetics, and Stability of Metallic MoS 2 Nanosheets via Covalent Functionalization

DOE PAGES

Benson, Eric E.; Zhang, Hanyu; Schuman, Samuel A.; ...

2017-12-27

We modify the fundamental electronic properties of metallic (1T phase) nanosheets of molybdenum disulfide (MoS 2) through covalent chemical functionalization, and thereby directly influence the kinetics of the hydrogen evolution reaction (HER), surface energetics, and stability. Chemically exfoliated, metallic MoS 2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS 2 functionalized with the most electron donating functional group (p-(CH 3CH 2) 2NPh-MoS 2) is the most efficient catalyst for HER in this series, with initial activity that is slightly worse compared to the pristine metallic phase of MoS 2. The p-(CHmore » 3CH 2) 2NPh-MoS 2 is more stable than unfunctionalized metallic MoS 2 and outperforms unfunctionalized metallic MoS 2 for continuous H 2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the functional group. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS 2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS 2 nanosheet. The functional groups preserve the metallic nature of the MoS 2 nanosheets, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when mildly annealed in a nitrogen atmosphere. We propose that the electron density and, therefore, reactivity of the MoS 2 nanosheets are controlled by the attached functional groups. Functionalizing nanosheets of MoS 2 and other transition metal dichalcogenides provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state.« less

Balancing the Hydrogen Evolution Reaction, Surface Energetics, and Stability of Metallic MoS2 Nanosheets via Covalent Functionalization.

PubMed

Benson, Eric E; Zhang, Hanyu; Schuman, Samuel A; Nanayakkara, Sanjini U; Bronstein, Noah D; Ferrere, Suzanne; Blackburn, Jeffrey L; Miller, Elisa M

2018-01-10

We modify the fundamental electronic properties of metallic (1T phase) nanosheets of molybdenum disulfide (MoS 2 ) through covalent chemical functionalization, and thereby directly influence the kinetics of the hydrogen evolution reaction (HER), surface energetics, and stability. Chemically exfoliated, metallic MoS 2 nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS 2 functionalized with the most electron donating functional group (p-(CH 3 CH 2 ) 2 NPh-MoS 2 ) is the most efficient catalyst for HER in this series, with initial activity that is slightly worse compared to the pristine metallic phase of MoS 2 . The p-(CH 3 CH 2 ) 2 NPh-MoS 2 is more stable than unfunctionalized metallic MoS 2 and outperforms unfunctionalized metallic MoS 2 for continuous H 2 evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the functional group. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS 2 nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS 2 nanosheet. The functional groups preserve the metallic nature of the MoS 2 nanosheets, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when mildly annealed in a nitrogen atmosphere. We propose that the electron density and, therefore, reactivity of the MoS 2 nanosheets are controlled by the attached functional groups. Functionalizing nanosheets of MoS 2 and other transition metal dichalcogenides provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state.

Metalorganic Vapor-Phase Epitaxy Growth Parameters for Two-Dimensional MoS2

NASA Astrophysics Data System (ADS)

Marx, M.; Grundmann, A.; Lin, Y.-R.; Andrzejewski, D.; Kümmell, T.; Bacher, G.; Heuken, M.; Kalisch, H.; Vescan, A.

2018-02-01

The influence of the main growth parameters on the growth mechanism and film formation processes during metalorganic vapor-phase epitaxy (MOVPE) of two-dimensional MoS2 on sapphire (0001) have been investigated. Deposition was performed using molybdenum hexacarbonyl and di- tert-butyl sulfide as metalorganic precursors in a horizontal hot-wall MOVPE reactor from AIXTRON. The structural properties of the MoS2 films were analyzed by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. It was found that a substrate prebake step prior to growth reduced the nucleation density of the polycrystalline film. Simultaneously, the size of the MoS2 domains increased and the formation of parasitic carbonaceous film was suppressed. Additionally, the influence of growth parameters such as reactor pressure and surface temperature is discussed. An upper limit for these parameters was found, beyond which strong parasitic deposition or incorporation of carbon into MoS2 took place. This carbon contamination became significant at reactor pressure above 100 hPa and temperature above 900°C.

Enhanced performance of lithium-sulfur batteries with an ultrathin and lightweight MoS2/carbon nanotube interlayer

NASA Astrophysics Data System (ADS)

Yan, Lingjia; Luo, Nannan; Kong, Weibang; Luo, Shu; Wu, Hengcai; Jiang, Kaili; Li, Qunqing; Fan, Shoushan; Duan, Wenhui; Wang, Jiaping

2018-06-01

Ultrathin and lightweight MoS2/carbon nanotube (CNT) interlayers are developed to effectively trap polysulfides in high-performance lithium-sulfur (Li-S) batteries. The MoS2/CNT interlayer is constructed by loading MoS2 nanosheets onto a cross-stacked CNT film. The CNT film with excellent conductivity and superior mechanical properties provides the Li-S batteries with a uniform conductive network, a supporting skeleton for the MoS2 nanosheets, as well as a physical barrier for the polysulfides. Moreover, chemical interactions and bonding between the MoS2 nanosheets and the polysulfides are evident. The electrode with the MoS2/CNT interlayer delivers an attractive specific capacity of 784 mA h g-1 at a high capacity rate of 10 C. In addition, the electrode demonstrates a high initial capacity of 1237 mA h g-1 and a capacity fade as low as -0.061% per cycle over 500 charge/discharge cycles at 0.2 C. The problem of self-discharge can also be suppressed with the introduction of the MoS2/CNT interlayer. The simple fabrication procedure, which is suitable for commercialization, and the outstanding electrochemical performance of the cells with the MoS2/CNT interlayer demonstrate a great potential for the development of high-performance Li-S batteries.

Enhancement of photodetection characteristics of MoS2 field effect transistors using surface treatment with copper phthalocyanine.

PubMed

Pak, Jinsu; Jang, Jingon; Cho, Kyungjune; Kim, Tae-Young; Kim, Jae-Keun; Song, Younggul; Hong, Woong-Ki; Min, Misook; Lee, Hyoyoung; Lee, Takhee

2015-11-28

Recently, two-dimensional materials such as molybdenum disulfide (MoS2) have been extensively studied as channel materials for field effect transistors (FETs) because MoS2 has outstanding electrical properties such as a low subthreshold swing value, a high on/off ratio, and good carrier mobility. In this study, we characterized the electrical and photo-responsive properties of MoS2 FET when stacking a p-type organic copper phthalocyanine (CuPc) layer on the MoS2 surface. We observed that the threshold voltage of MoS2 FET could be controlled by stacking the CuPc layers due to a charge transfer phenomenon at the interface. Particularly, we demonstrated that CuPc/MoS2 hybrid devices exhibited high performance as a photodetector compared with the pristine MoS2 FETs, caused by more electron-hole pairs separation at the p-n interface. Furthermore, we found the optimized CuPc thickness (∼2 nm) on the MoS2 surface for the best performance as a photodetector with a photoresponsivity of ∼1.98 A W(-1), a detectivity of ∼6.11 × 10(10) Jones, and an external quantum efficiency of ∼12.57%. Our study suggests that the MoS2 vertical hybrid structure with organic material can be promising as efficient photodetecting devices and optoelectronic circuits.

Measuring charge nonuniformity in MOS devices

NASA Technical Reports Server (NTRS)

Maserjian, J.; Zamani, N.

1980-01-01

Convenient method of determining inherent lateral charge non-uniformities along silicon dioxide/silicon interface of metal-oxide-semiconductor (MOS) employs rapid measurement of capacitance of interface as function of voltage at liquid nitrogen temperature. Charge distribution is extracted by fast-Fourier-transform analysis of capacitance voltage (C-V) measurement.

Two-dimensional MoS2-graphene hybrid nanosheets for high gravimetric and volumetric lithium storage

NASA Astrophysics Data System (ADS)

Deng, Yakai; Ding, Lixin; Liu, Qixing; Zhan, Liang; Wang, Yanli; Yang, Shubin

2018-04-01

Two-dimensional (2D) MoS2-graphene (MoS2-G) hybrid is fabricated simultaneously and scalablely with an efficient electrochemical exfoliation approach from the combined bulk MoS2-graphite wafer. The as-prepared 2D MoS2-G hybrid is tightly covered with each other with lateral sizes of 600 nm to few micrometers and can be directly assembled to flexible films for lithium storage. When used as anode material for lithium ion battery, the resultant MoS2-G hybrid film exhibits both high gravimetric (750 mA h g-1 at 50 mA g-1) and volumetric capacities (1200 mA h cm-3 at 0.1 mA cm-2). Such excellent electrochemical performance should attributed to the unique 2D structure and good conductive graphene network, which not only facilitates the diffusion of lithium ions, but also improves the fast transfer of electrons, satisfying the kinetics requirements for rapid lithium storage.

Layer Dependence and Light Tuning Surface Potential of 2D MoS2 on Various Substrates.

PubMed

Li, Feng; Qi, Junjie; Xu, Minxuan; Xiao, Jiankun; Xu, Yuliang; Zhang, Xiankun; Liu, Shuo; Zhang, Yue

2017-04-01

Here surface potential of chemical vapor deposition (CVD) grown 2D MoS 2 with various layers is reported, and the effect of adherent substrate and light illumination on surface potential of monolayer MoS 2 are investigated. The surface potential of MoS 2 on Si/SiO 2 substrate decreases from 4.93 to 4.84 eV with the increase in the number of layer from 1 to 4 or more. Especially, the surface potentials of monolayer MoS 2 are strongly dependent on its adherent substrate, which are determined to be 4.55, 4.88, 4.93, 5.10, and 5.50 eV on Ag, graphene, Si/SiO 2 , Au, and Pt substrates, respectively. Light irradiation is introduced to tuning the surface potential of monolayer MoS 2 , with the increase in light intensity, the surface potential of MoS 2 on Si/SiO 2 substrate decreases from 4.93 to 4.74 eV, while increases from 5.50 to 5.56 eV on Pt substrate. The I-V curves on vertical of monolayer MoS 2 /Pt heterojunction show the decrease in current with the increase of light intensity, and Schottky barrier height at MoS 2 /Pt junctions increases from 0.302 to 0.342 eV. The changed surface potential can be explained by trapped charges on surface, photoinduced carriers, charge transfer, and local electric field. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

As-prepared MoS2 quantum dot as a facile fluorescent probe for long-term tracing of live cells

NASA Astrophysics Data System (ADS)

Zhou, Kai; Zhang, Yue; Xia, Zhining; Wei, Weili

2016-07-01

Recently, the newly emerged two-dimensional nanomaterials, layered transition metal dichalcogenide (e.g. MoS2) nanosheets, have drawn tremendous attentions due to their extraordinary electronic and optical properties, and MoS2 quantum dots (MoS2 QDs) with lateral sizes less than 10 nm have been found to be highly luminescent. In the present study, a facile approach for large-scale preparation of MoS2 QDs by Na intercalation reaction without using any toxic organic reagents is proposed. MoS2 QDs were carefully characterized by various techniques including transmission electron microscopy, atomic force microscopy, dynamic light scattering, spectroscopy, in vitro cytotoxicology, and capillary electrophoresis. The as-prepared MoS2 QDs were strongly fluorescent, highly photo-stable, low in cytotoxicity, and readily reactive to thiols. These inherent properties of MoS2 QDs make them excellent fluorescent probes for long-term live cell tracing. The results of live cells imaging indicated that MoS2 QD stained cells remained highly fluorescent after long-term culture, and could be easily traced from other co-cultured cell lines.

Fabrication of a temperature-responsive and recyclable MoS2 nanocatalyst through composting with poly (N-isopropylacrylamide)

NASA Astrophysics Data System (ADS)

Liu, Yan; Chen, Pengpeng; Nie, Wangyan; Zhou, Yifeng

2018-04-01

A temperature-responsive, recyclable nanocatalyst was fabricated by composting the exfoliated molybdenum disulfide (MoS2) nanosheets with poly (N-isopropylacry lamide) (PNIPAM). The structure and morphology of MoS2/PNIPAM nanocatalyst was fully characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Thermogravimetry analysis (TGA), Scanning electron microscope (SEM) and Transmission electron microscopy (TEM). The temperature-responsive properties of the MoS2/PNIPAM nanocatalyst were confirmed by Dynamic Light Scattering (DLS) and Ultraviolet-visible ((UV-vis)) absorption spectroscopy. The catalytic activities of the MoS2/PNIPAM nanocatalyst were studied using the reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as the model reaction. Results showed that the catalytic activity of the MoS2/PNIPAM nanocatalyst could be regulated by temperature. Furthermore, when the temperature went higher than the low critical solution temperature (LCST) of PNIPAM, the MoS2/PNIPAM nanocatalyst tended to aggregated to form bulk materials from homogeneous suspension.

Cold cathode emission studies on topographically modified few layer and single layer MoS2 films

NASA Astrophysics Data System (ADS)

Gaur, Anand P. S.; Sahoo, Satyaprakash; Mendoza, Frank; Rivera, Adriana M.; Kumar, Mohit; Dash, Saroj P.; Morell, Gerardo; Katiyar, Ram S.

2016-01-01

Nanostructured materials, such as carbon nanotubes, are excellent cold cathode emitters. Here, we report comparative field emission (FE) studies on topographically tailored few layer MoS2 films consisting of ⟨0001⟩ plane perpendicular (⊥) to c-axis (i.e., edge terminated vertically aligned) along with planar few layer and monolayer (1L) MoS2 films. FE measurements exhibited lower turn-on field Eto (defined as required applied electric field to emit current density of 10 μA/cm2) ˜4.5 V/μm and higher current density ˜1 mA/cm2, for edge terminated vertically aligned (ETVA) MoS2 films. However, Eto magnitude for planar few layer and 1L MoS2 films increased further to 5.7 and 11 V/μm, respectively, with one order decrease in emission current density. The observed differences in emission behavior, particularly for ETVA MoS2 is attributed to the high value of geometrical field enhancement factor (β), found to be ˜1064, resulting from the large confinement of localized electric field at edge exposed nanograins. Emission behavior of planar few layers and 1L MoS2 films are explained under a two step emission mechanism. Our studies suggest that with further tailoring the microstructure of ultra thin ETVA MoS2 films would result in elegant FE properties.

Enhanced hydrogen generation by hydrolysis of Mg doped with flower-like MoS2 for fuel cell applications

NASA Astrophysics Data System (ADS)

Huang, Minghong; Ouyang, Liuzhang; Liu, Jiangwen; Wang, Hui; Shao, Huaiyu; Zhu, Min

2017-10-01

In this work, flower-like MoS2 spheres are synthesized via a hydrothermal method and the catalytic activity of the as-prepared and bulk MoS2 on hydrolysis of Mg is systematically investigated for the first time. The Mg-MoS2 composites are prepared by ball milling and the hydrogen generation performances of the composites are investigated in 3.5% NaCl solution. The experimental results suggest that the as-prepared MoS2 exhibits better catalytic effect on hydrolysis of Mg compared to bulk MoS2. In particular, Mg-10 wt% MoS2 (as-prepared) composite milled for 1 h shows the best hydrogen generation properties and releases 90.4% of theoretical hydrogen generation capacity within 1 min at room temperature. The excellent catalytic effect of as-prepared MoS2 may be attributed to the following aspects: three-dimensional flower-like MoS2 architectures improve its dispersibility on Mg particles; make the composite more reactive; hamper the generated Mg(OH)2 from adhering to the surface of Mg; and increase the galvanic corrosion of Mg. In addition, a hydrogen generator based on the hydrolysis reaction of Mg-0.2 wt% MoS2 composite is manufactured and it can supply a maximum hydrogen flow rate of 2.5 L/min. The findings here demonstrate the as-prepared flower-like MoS2 can be a promising catalyst for hydrogen generation from Mg.

Word Frequency Analysis. MOS: 54E. Skill Levels 1 & 2.

DTIC Science & Technology

1981-05-01

REPRODUCE LEGIBLY. qi l)NCLASSTFTFD SECURITY CLASSIFICATION OF THIS PAGE (ൌ n Date Entered) REPORT DOCUMENTATION PAGE REoLNSTUCT{IONS B.ROE COMPNETI...mid Identify by block numbr) MOS Vocabulary Readab ili ty Comprehension of text Curriculum Development A,~ A-65rA Cc .e o ld., n ~lt, block ntibe This...vocabulary set is only a sampling of the entire MOS vocabulary and is subject to change. N -Albry ItvCe DnesVAi 4- ^ -- I I i i i I t |w o• I HEADQUARTERS

Stacking stability of MoS2 bilayer: An ab initio study

NASA Astrophysics Data System (ADS)

Tao, Peng; Guo, Huai-Hong; Yang, Teng; Zhang, Zhi-Dong

2014-10-01

The study of the stacking stability of bilayer MoS2 is essential since a bilayer has exhibited advantages over single layer MoS2 in many aspects for nanoelectronic applications. We explored the relative stability, optimal sliding path between different stacking orders of bilayer MoS2, and (especially) the effect of inter-layer stress, by combining first-principles density functional total energy calculations and the climbing-image nudge-elastic-band (CI-NEB) method. Among five typical stacking orders, which can be categorized into two kinds (I: AA, AB and II: AA', AB', A'B), we found that stacking orders with Mo and S superposing from both layers, such as AA' and AB, is more stable than the others. With smaller computational efforts than potential energy profile searching, we can study the effect of inter-layer stress on the stacking stability. Under isobaric condition, the sliding barrier increases by a few eV/(ucGPa) from AA' to AB', compared to 0.1 eV/(ucGPa) from AB to [AB]. Moreover, we found that interlayer compressive stress can help enhance the transport properties of AA'. This study can help understand why inter-layer stress by dielectric gating materials can be an effective means to improving MoS2 on nanoelectronic applications.

Magnetic MoS2 on multiwalled carbon nanotubes for sulfide sensing.

PubMed

Li, Chunxiang; Zhang, Dan; Wang, Jiankang; Hu, Pingan; Jiang, Zhaohua

2017-07-04

A novel hybrid metallic cobalt insided in multiwalled carbon nanotubles/molybdenum disulfide (Co@CNT/MoS 2 ) modified glass carbon electrode (GCE) was fabricated with a adhesive of Nafion suspension and used as chemical sensors for sulfide detection. Single-layered MoS 2 was coated on CNTs through magnetic traction force between paramagnetic monolayer MoS 2 and Co particles in CNTs. Co particles faciliated the collection of paramagnetic monolayer MoS 2 exfoliated from bulk MoS 2 in solution. Amperometric analysis, cycle voltammetry, cathodic stripping analysis and linear sweep voltammetry results showed the Co@CNT/MoS 2 modified GCE exhibited excellent electrochemical activity to sulfide in buffer solutions, but amperometric analysis was found to be more sensitive than the other methods. The amperometric response result indicated the Co@CNT/MoS 2 -modified GCE electrode was an excellent electrochemical sensor for detecting S 2- with a detection limit of 7.6 nM and sensitivity of 0.23 mA/μM. The proposed electrode was used for the determination of sulfide levels in hydrogen sulfide-pretreated fruits, and the method was also verified with recovery studies. Copyright © 2017 Elsevier B.V. All rights reserved.

Performance Investigation of Multilayer MoS2 Thin-Film Transistors Fabricated via Mask-free Optically Induced Electrodeposition.

PubMed

Li, Meng; Liu, Na; Li, Pan; Shi, Jialin; Li, Guangyong; Xi, Ning; Wang, Yuechao; Liu, Lianqing

2017-03-08

Transition metal dichalcogenides, particularly MoS 2 , have recently received enormous interest in explorations of the physics and technology of nanodevice applications because of their excellent optical and electronic properties. Although monolayer MoS 2 has been extensively investigated for various possible applications, its difficulty of fabrication renders it less appealing than multilayer MoS 2 . Moreover, multilayer MoS 2 , with its inherent high electronic/photonic state densities, has higher output driving capabilities and can better satisfy the ever-increasing demand for versatile devices. Here, we present multilayer MoS 2 back-gate thin-film transistors (TFTs) that can achieve a relatively low subthreshold swing of 0.75 V/decade and a high mobility of 41 cm 2 ·V -1 ·s -1 , which exceeds the typical mobility value of state-of-the-art amorphous silicon-based TFTs by a factor of 80. Ag and Au electrode-based MoS 2 TFTs were fabricated by a convenient and rapid process. Then we performed a detailed analysis of the impacts of metal contacts and MoS 2 film thickness on electronic performance. Our findings show that smoother metal contacts exhibit better electronic characteristics and that MoS 2 film thickness should be controlled within a reasonable range of 30-40 nm to obtain the best mobility values, thereby providing valuable insights regarding performance enhancement for MoS 2 TFTs. Additionally, to overcome the limitations of the conventional fabrication method, we employed a novel approach known as optically induced electrodeposition (OIE), which allows the flexible and precise patterning of metal films and enables rapid and mask-free device fabrication, for TFT fabrication.

Optically tuned terahertz modulator based on annealed multilayer MoS2.

PubMed

Cao, Yapeng; Gan, Sheng; Geng, Zhaoxin; Liu, Jian; Yang, Yuping; Bao, Qiaoling; Chen, Hongda

2016-03-08

Controlling the propagation properties of terahertz waves is very important in terahertz technologies applied in high-speed communication. Therefore a new-type optically tuned terahertz modulator based on multilayer-MoS2 and silicon is experimentally demonstrated. The terahertz transmission could be significantly modulated by changing the power of the pumping laser. With an annealing treatment as a p-doping method, MoS2 on silicon demonstrates a triple enhancement of terahertz modulation depth compared with the bare silicon. This MoS2-based device even exhibited much higher modulation efficiency than the graphene-based device. We also analyzed the mechanism of the modulation enhancement originated from annealed MoS2, and found that it is different from that of graphene-based device. The unique optical modulating properties of the device exhibit tremendous promise for applications in terahertz switch.

Measuring the Refractive Index of Highly Crystalline Monolayer MoS2 with High Confidence

PubMed Central

Zhang, Hui; Ma, Yaoguang; Wan, Yi; Rong, Xin; Xie, Ziang; Wang, Wei; Dai, Lun

2015-01-01

Monolayer molybdenum disulphide (MoS2) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS2 on SiO2/Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS2. The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO2 thickness and incident light wavelength for monolayer MoS2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application. PMID:25676089

Measuring the refractive index of highly crystalline monolayer MoS2 with high confidence.

PubMed

Zhang, Hui; Ma, Yaoguang; Wan, Yi; Rong, Xin; Xie, Ziang; Wang, Wei; Dai, Lun

2015-02-13

Monolayer molybdenum disulphide (MoS2) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS2 on SiO2/Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS2. The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO2 thickness and incident light wavelength for monolayer MoS2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application.

Measuring the Refractive Index of Highly Crystalline Monolayer MoS2 with High Confidence

NASA Astrophysics Data System (ADS)

Zhang, Hui; Ma, Yaoguang; Wan, Yi; Rong, Xin; Xie, Ziang; Wang, Wei; Dai, Lun

2015-02-01

Monolayer molybdenum disulphide (MoS2) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS2 on SiO2/Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS2. The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO2 thickness and incident light wavelength for monolayer MoS2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application.

Chemical Doping Effects in Multilayer MoS2 and its Application in Complementary Inverter.

PubMed

Yoo, Hocheon; Hong, Seongin; On, Sungmin; Ahn, Hyungju; Lee, Han-Koo; Hong, Young Ki; Kim, Sunkook; Kim, Jae-Joon

2018-06-19

Multilayer MoS2 has been gaining interests as a new semiconducting material for flexible displays, memory devices, chemical/bio sensors, and photodetectors. However, conventional multilayer MoS2 devices have exhibited limited performances due to the Schottky barrier (SB) and defects. Here, we demonstrate PDPP3T doping effects in multilayer MoS2, which results in improved electrical characteristics (~3.2X mobility compared to the baseline and a high current on/off ratio of 106). Synchrotron-based study using X-ray photoelectron spectroscopy (XPS) and grazing-incidence wide-angle X-ray diffraction (GIWAXD) provides mechanisms that align the edge-on crystallites (97.5 %) of the PDPP3T as well as a larger interaction with MoS2 that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a hybrid CMOS inverter using the PDPP3T-doped MoS2 and organic DNTT transistors as n- and p-channels, respectively. The proposed hybrid inverter offers an ultra-high voltage gain of ~205 V/V.

Controllable Growth of Large-Size Crystalline MoS2 and Resist-Free Transfer Assisted with a Cu Thin Film.

PubMed

Lin, Ziyuan; Zhao, Yuda; Zhou, Changjian; Zhong, Ren; Wang, Xinsheng; Tsang, Yuen Hong; Chai, Yang

2015-12-21

Two-dimensional MoS2 is a promising material for future nanoelectronics and optoelectronics. It has remained a great challenge to grow large-size crystalline and high surface coverage monolayer MoS2. In this work, we investigate the controllable growth of monolayer MoS2 evolving from triangular flakes to continuous thin films by optimizing the concentration of gaseous MoS2, which has been shown a both thermodynamic and kinetic growth factor. A single-crystal monolayer MoS2 larger than 300 μm was successfully grown by suppressing the nuclei density and supplying sufficient source. Furthermore, we present a facile process of transferring the centimeter scale MoS2 assisted with a copper thin film. Our results show the absence of observable residues or wrinkles after we transfer MoS2 from the growth substrates onto flat substrates using this technique, which can be further extended to transfer other two-dimensional layered materials.

Controllable Growth of Large-Size Crystalline MoS2 and Resist-Free Transfer Assisted with a Cu Thin Film

NASA Astrophysics Data System (ADS)

Lin, Ziyuan; Zhao, Yuda; Zhou, Changjian; Zhong, Ren; Wang, Xinsheng; Tsang, Yuen Hong; Chai, Yang

2015-12-01

Two-dimensional MoS2 is a promising material for future nanoelectronics and optoelectronics. It has remained a great challenge to grow large-size crystalline and high surface coverage monolayer MoS2. In this work, we investigate the controllable growth of monolayer MoS2 evolving from triangular flakes to continuous thin films by optimizing the concentration of gaseous MoS2, which has been shown a both thermodynamic and kinetic growth factor. A single-crystal monolayer MoS2 larger than 300 μm was successfully grown by suppressing the nuclei density and supplying sufficient source. Furthermore, we present a facile process of transferring the centimeter scale MoS2 assisted with a copper thin film. Our results show the absence of observable residues or wrinkles after we transfer MoS2 from the growth substrates onto flat substrates using this technique, which can be further extended to transfer other two-dimensional layered materials.

Room temperature ammonia gas sensing properties of MoS2 nanostructured thin film

NASA Astrophysics Data System (ADS)

Sharma, Shubham; Kumar, Arvind; Kaur, Davinder

2018-05-01

Here, we have fabricated the MoS2 nanostructure thin films on the Si (100) substrate using DC magnetron sputtering technique. The MoS2 thin film sensor shows the selective responses towards the ammonia gas (NH3) under low detection range 10-500 ppm. The sensor displays a significantly high sensing response (Rg/Ra ˜2.2) towards 100 ppm ammonia gas with a very fast response and recovery time of 22 sec and 30 sec respectively. Selectivity and stability investigations exhibit the excellent sensing properties of MoS2 thin film sensor. The working principle and sensing mechanism behind their remarkable performance was also investigated in detail.

Solution processable mixed-solvent exfoliated MoS2 nanosheets for efficient and robust organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Liu, Chia-Wei; Wang, Chia; Liao, Chia-Wei; Golder, Jan; Tsai, Ming-Chih; Young, Hong-Tsu; Chen, Chin-Ti; Wu, Chih-I.

2018-04-01

We demonstrate the use of solution-processed molybdenum trioxide (MoO3) nanoparticle-decorated molybdenum disulfide (MoS2) nanosheets (MoS2/MoO3) as hole injection layer (HIL) in organic lighting diodes (OLEDs). The device performance is shown to be significantly improved by the introduction of such MoS2/MoO3 HIL without any post-ultraviolet-ozone treatment, and is shown to better the performance of devices fabricated using conventional poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and MoO3 nanoparticle HILs. The MoS2/MoO3 nanosheets form a compact film, as smooth as PEDOT:PSS films and smoother than MoO3 nanoparticle films, when simply spin-coated on indium tin oxide substrates. The improvement in device efficiency can be attributed to the smooth surface of the nanostructured MoS2/MoO3 HIL and the excellent conductivity characteristics of the two-dimensional (2D) layered material (MoS2), which facilitate carrier transport in the device and reduce the sheet resistance. Moreover, the long-term stability of OLED devices that use such MoS2/MoO3 layers is shown to be improved dramatically compared with hygroscopic and acidic PEDOT:PSS-based devices.

Total Ionizing Dose Effects in MOS Oxides and Devices

NASA Technical Reports Server (NTRS)

Oldham, Timothy R.; McLean, F. B.

2003-01-01

The development of military and space electronics technology has traditionally been heavily influenced by the commercial semiconductor industry. The development of MOS technology, and particularly CMOS technology, as dominant commercial technologies has occurred entirely within the lifetime of the NSREC. For this reason, it is not surprising that the study of radiation interactions with MOS materials, devices and circuits has been a major theme of this conference for most of its history. The basic radiation problem in a MOS transistor is illustrated. The application of an appropriate gate voltage causes a conducting channel to form between the source and drain, so that current flows when the device is turned on. In Fig. lb, the effect of ionizing radiation is illustrated. Radiation-induced trapped charge has built up in the gate oxide, which causes a shift in the threshold voltage (that is, a change in the voltage which must be applied to turn the device on). If this shift is large enough, the device cannot be turned off, even at zero volts applied, and the device is said to have failed by going depletion mode.

Templated synthesis of plate-like MoS2 nanosheets assisted with HNTs and their tribological performance in oil

NASA Astrophysics Data System (ADS)

Wu, Pei-Rong; Cheng, Zhi-Lin; Kong, Ying-Chao; Ma, Zhan-Sheng; Liu, Zan

2018-05-01

Two-dimensional MoS2 nanosheets were synthesized by using halloysite nanotubes (HNTs) as template under the hydrothermal synthesis. The structure and morphology of the as-synthesized MoS2 nanosheets were determined by a series of characterizations. The results showed that the as-synthesized MoS2 nanosheets were of the plate-like structure with about five layers, and the basal spacing was about 0.63 nm. It was demonstrated that HNTs played a crucial template role in the formation of the plate-like MoS2 nanosheets. The formation mechanism was proposed. Furthermore, the tribological performance of the as-prepared MoS2 nanosheets in oil was intensively examined on the ball-on-ball wear tester. The testing results verified that the as-prepared MoS2 nanosheets as additive could significantly improve the friction performance of oil, which exhibited the good antifriction, antiwear, and load-carrying properties.

2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Rowley-Neale, Samuel J.; Brownson, Dale A. C.; Smith, Graham C.; Sawtell, David A. G.; Kelly, Peter J.; Banks, Craig E.

2015-10-01

We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode

Flower-like PEGylated MoS2 nanoflakes for near-infrared photothermal cancer therapy

PubMed Central

Feng, Wei; Chen, Liang; Qin, Ming; Zhou, Xiaojun; Zhang, Qianqian; Miao, Yingke; Qiu, Kexin; Zhang, Yanzhong; He, Chuanglong

2015-01-01

Photothermal cancer therapy has attracted considerable interest for cancer treatment in recent years, but the effective photothermal agents remain to be explored before this strategy can be applied clinically. In this study, we therefore develop flower-like molybdenum disulfide (MoS2) nanoflakes and investigate their potential for photothermal ablation of cancer cells. MoS2 nanoflakes are synthesized via a facile hydrothermal method and then modified with lipoic acid-terminated polyethylene glycol (LA-PEG), endowing the obtained nanoflakes with high colloidal stability and very low cytotoxicity. Upon irradiation with near infrared (NIR) laser at 808 nm, the nanoflakes showed powerful ability of inducing higher temperature, good photothermal stability and high photothermal conversion efficiency. The in vitro photothermal effects of MoS2-PEG nanoflakes with different concentrations were also evaluated under various power densities of NIR 808-nm laser irradiation, and the results indicated that an effective photothermal killing of cancer cells could be achieved by a low concentration of nanoflakes under a low power NIR 808-nm laser irradiation. Furthermore, cancer cell in vivo could be efficiently destroyed via the photothermal effect of MoS2-PEG nanoflakes under the irradiation. These results thus suggest that the MoS2-PEG nanoflakes would be as promising photothermal agents for future photothermal cancer therapy. PMID:26632249

Flower-like PEGylated MoS2 nanoflakes for near-infrared photothermal cancer therapy

NASA Astrophysics Data System (ADS)

Feng, Wei; Chen, Liang; Qin, Ming; Zhou, Xiaojun; Zhang, Qianqian; Miao, Yingke; Qiu, Kexin; Zhang, Yanzhong; He, Chuanglong

2015-12-01

Photothermal cancer therapy has attracted considerable interest for cancer treatment in recent years, but the effective photothermal agents remain to be explored before this strategy can be applied clinically. In this study, we therefore develop flower-like molybdenum disulfide (MoS2) nanoflakes and investigate their potential for photothermal ablation of cancer cells. MoS2 nanoflakes are synthesized via a facile hydrothermal method and then modified with lipoic acid-terminated polyethylene glycol (LA-PEG), endowing the obtained nanoflakes with high colloidal stability and very low cytotoxicity. Upon irradiation with near infrared (NIR) laser at 808 nm, the nanoflakes showed powerful ability of inducing higher temperature, good photothermal stability and high photothermal conversion efficiency. The in vitro photothermal effects of MoS2-PEG nanoflakes with different concentrations were also evaluated under various power densities of NIR 808-nm laser irradiation, and the results indicated that an effective photothermal killing of cancer cells could be achieved by a low concentration of nanoflakes under a low power NIR 808-nm laser irradiation. Furthermore, cancer cell in vivo could be efficiently destroyed via the photothermal effect of MoS2-PEG nanoflakes under the irradiation. These results thus suggest that the MoS2-PEG nanoflakes would be as promising photothermal agents for future photothermal cancer therapy.

Widely-tunable, passively Q-switched erbium-doped fiber laser with few-layer MoS2 saturable absorber.

PubMed

Huang, Yizhong; Luo, Zhengqian; Li, Yingyue; Zhong, Min; Xu, Bin; Che, Kaijun; Xu, Huiying; Cai, Zhiping; Peng, Jian; Weng, Jian

2014-10-20

We propose and demonstrate a MoS2-based passively Q-switched Er-doped fiber laser with a wide tuning range of 1519.6-1567.7 nm. The few-layer MoS2 nano-platelets are prepared by the liquid-phase exfoliation method, and are then made into polymer-composite film to construct the fiber-compatible MoS2 saturable absorber (SA). It is measured at 1560 nm wavelength, that such MoS2 SA has the modulation depth of ∼ 2% and the saturable optical intensity of ∼ 10 MW/cm(2). By further inserting the filmy MoS2-SA into an Er-doped fiber laser, stable Q-switching operation with a 48.1 nm continuous tuning from S- to C-waveband is successfully achieved. The shortest pulse duration and the maximum pulse energy are 3.3 μs and 160 nJ, respectively. The repetition rate and the pulse duration under different operation conditions have been also characterized. To the best of our knowledge, it is the first demonstration of MoS2 Q-switched, widely-tunable fiber laser.

Tailoring the charge carrier in few layers MoS2 field-effect transistors by Au metal adsorbate

NASA Astrophysics Data System (ADS)

Singh, Arun Kumar; Pandey, Rajiv K.; Prakash, Rajiv; Eom, Jonghwa

2018-04-01

It is an essential to tune the charge carrier concentrations in semiconductor in order to approach high-performance of the electronic and optoelectronic devices. Here, we report the effect of thin layer of gold (Au) metal on few layer (FL) molybdenum disulfide (MoS2) by atomic force microscopy (AFM), Raman spectroscopy and electrical charge transport measurements. The Raman spectra and charge transport measurements show that Au thin layer affect the electronic properties of the FL MoS2. After deposition of Au thin layer, the threshold voltages of FL MoS2 field-effect transistors (FETs) shift towards positive gate voltages, this reveal the p-doping in FL MoS2 nanosheets. The shift of peak frequencies of the Raman bands are also analyzed after the deposition of Au metal films of different thickness on FL MoS2 nanosheets. The surface morphology of Au metal on FL MoS2 is characterized by AFM and shows the smoother and denser film in comparison to Au metal on SiO2.

Effects of Electron Beam Irradiation and Thiol Molecule Treatment on the Properties of MoS2 Field Effect Transistors

NASA Astrophysics Data System (ADS)

Choi, Barbara Yuri; Cho, Kyungjune; Pak, Jinsu; Kim, Tae-Young; Kim, Jae-Keun; Shin, Jiwon; Seo, Junseok; Chung, Seungjun; Lee, Takhee

2018-05-01

We investigated the effects of the structural defects intentionally created by electron-beam irradiation with an energy of 30 keV on the electrical properties of monolayer MoS2 field effect transistors (FETs). We observed that the created defects by electron beam irradiation on the MoS2 surface working as trap sites deteriorated the carrier mobility and carrier concentration with increasing the subthreshold swing value and shifting the threshold voltage in MoS2 FETs. The electrical properties of electron-beam irradiated MoS2 FETs were slightly improved by treating the devices with thiol-terminated molecules which presumably passivated the structural defects of MoS2. The results of this study may enhance the understanding of the electrical properties of MoS2 FETs in terms of creating and passivating defect sites.

Molecular adsorption properties of CO and H2O on Au-, Cu-, and AuxCuy-doped MoS2 monolayer

NASA Astrophysics Data System (ADS)

Kadioglu, Yelda; Gökoğlu, Gökhan; Üzengi Aktürk, Olcay

2017-12-01

In this study, we investigate the adsorption properties of Au, Cu, and AuxCuy nanoclusters on MoS2 sheet and the interactions of the adsorbed systems with CO and H2O molecules by using first principles calculations. Results indicate that Au, Cu, or AuxCuy strongly binds to MoS2 monolayer resulting in enhanced chemical activity and sensitivity toward CO and H2O molecules compared to bare MoS2 monolayer. Although both CO and H2O molecules bind weakly to pristine MoS2 monolayer, CO strongly binds to MoS2 sheet in the presence of Au, Cu atoms or AuxCuy clusters. Semiconductor MoS2 monolayer turns into metal upon Au or Cu adsorption. AuxCuy nanocluster adsorption decreases the band gap of MoS2 monolayer acting as a n-type dopant. AuxCuy-doped MoS2 systems have improved adsorption properties for CO and H2O molecules, so the conclusions provided in this study can be useful as a guide for next generation device modeling.

Adsorption of gas molecules on Cu impurities embedded monolayer MoS2: A first- principles study

NASA Astrophysics Data System (ADS)

Zhao, B.; Li, C. Y.; Liu, L. L.; Zhou, B.; Zhang, Q. K.; Chen, Z. Q.; Tang, Z.

2016-09-01

Adsorption of small gas molecules (O2, NO, NO2 and NH3) on transition-metal Cu atom embedded monolayer MoS2 was investigated by first-principles calculations based on the density-functional theory (DFT). The embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS2 with a high diffusion barrier. The stable adsorption geometry, charge transfer and electronic structures of these gas molecules on monolayer MoS2 embedded with transition-metal Cu atom are discussed in detail. It is found that the monolayer MoS2 with embedded Cu atom can effectively capture these gas molecules with high adsorption energy. The NH3 molecule acts as electron donor after adsorption, which is different from the other gas molecules (O2, NO, and NO2). The results suggest that MoS2-Cu system may be promising for future applications in gas molecules sensing and catalysis, which is similar to those of the transition-metal embedded graphene.

Effects of adding metals to MoS2 in a ytterbium doped Q-switched fiber laser

NASA Astrophysics Data System (ADS)

Khaleque, Abdul; Liu, Liming

2018-03-01

Molybdenum disulfide (MoS2) is widely used in lubricants, metallic alloys and in electronic and optical components. It is also used as saturable absorbers (SAs) in lasers (e.g. fiber lasers): a simple deposition of MoS2 on the fiber end can create a saturable absorber without the necessity of extensive alignment of the optical beam. In this article, we study the effects of adding different metals (Cr, Au, and Al) to MoS2 in a ytterbium (Yb)-doped Q-switched fiber laser. Experimental results show that the addition of a thin layer of gold and aluminium can reduce pulse durations to about 5.8 μs and 8.5 μs, respectively, compared with pure MoS2 with pulse duration of 12 μs. Experimental analysis of the combined metal and MoS2 based composite SAs can be useful in fiber laser applications where it may also find applications in medical, three dimensional (3D) active imaging and dental applications.

Richardson constant and electrostatics in transfer-free CVD grown few-layer MoS2/graphene barristor with Schottky barrier modulation >0.6eV

NASA Astrophysics Data System (ADS)

Jahangir, Ifat; Uddin, M. Ahsan; Singh, Amol K.; Koley, Goutam; Chandrashekhar, M. V. S.

2017-10-01

We demonstrate a large area MoS2/graphene barristor, using a transfer-free method for producing 3-5 monolayer (ML) thick MoS2. The gate-controlled diodes show good rectification, with an ON/OFF ratio of ˜103. The temperature dependent back-gated study reveals Richardson's coefficient to be 80.3 ± 18.4 A/cm2/K and a mean electron effective mass of (0.66 ± 0.15)m0. Capacitance and current based measurements show the effective barrier height to vary over a large range of 0.24-0.91 eV due to incomplete field screening through the thin MoS2. Finally, we show that this barristor shows significant visible photoresponse, scaling with the Schottky barrier height. A response time of ˜10 s suggests that photoconductive gain is present in this device, resulting in high external quantum efficiency.

Point Defects and Grain Boundaries in Rotationally Commensurate MoS 2 on Epitaxial Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiaolong; Balla, Itamar; Bergeron, Hadallia

2016-03-28

With reduced degrees of freedom, structural defects are expected to play a greater role in two-dimensional materials in comparison to their bulk counterparts. In particular, mechanical strength, electronic properties, and chemical reactivity are strongly affected by crystal imperfections in the atomically thin limit. Here, ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) are employed to interrogate point and line defects in monolayer MoS2 grown on epitaxial graphene (EG) at the atomic scale. Five types of point defects are observed with the majority species showing apparent structures that are consistent with vacancy and interstitial models. The total defect densitymore » is observed to be lower than MoS2 grown on other substrates and is likely attributed to the van der Waals epitaxy of MoS2 on EG. Grain boundaries (GBs) with 30° and 60° tilt angles resulting from the rotational commensurability of MoS2 on EG are more easily resolved by STM than atomic force microscopy at similar scales due to the enhanced contrast from their distinct electronic states. For example, band gap reduction to ~0.8 and ~0.5 eV is observed with STS for 30° and 60° GBs, respectively. In addition, atomic resolution STM images of these GBs are found to agree well with proposed structure models. This work offers quantitative insight into the structure and properties of common defects in MoS2 and suggests pathways for tailoring the performance of MoS2/graphene heterostructures via defect engineering.« less

Role of Hole Trap Sites in MoS2 for Inconsistency in Optical and Electrical Phenomena.

PubMed

Tran, Minh Dao; Kim, Ji-Hee; Kim, Hyun; Doan, Manh Ha; Duong, Dinh Loc; Lee, Young Hee

2018-03-28

Because of strong Coulomb interaction in two-dimensional van der Waals-layered materials, the trap charges at the interface strongly influence the scattering of the majority carriers and thus often degrade their electrical properties. However, the photogenerated minority carriers can be trapped at the interface, modulate the electron-hole recombination, and eventually influence the optical properties. In this study, we report the role of the hole trap sites on the inconsistency in the electrical and optical phenomena between two systems with different interfacial trap densities, which are monolayer MoS 2 -based field-effect transistors (FETs) on hexagonal boron nitride (h-BN) and SiO 2 substrates. Electronic transport measurements indicate that the use of h-BN as a gate insulator can induce a higher n-doping concentration of the monolayer MoS 2 by suppressing the free-electron transfer from the intrinsically n-doped MoS 2 to the SiO 2 gate insulator. Nevertheless, optical measurements show that the electron concentration in MoS 2 /SiO 2 is heavier than that in MoS 2 /h-BN, manifested by the relative red shift of the A 1g Raman peak. The inconsistency in the evaluation of the electron concentration in MoS 2 by electrical and optical measurements is explained by the trapping of the photogenerated holes in the spatially modulated valence band edge of the monolayer MoS 2 caused by the local strain from the SiO 2 /Si substrate. This photoinduced electron doping in MoS 2 /SiO 2 is further confirmed by the development of the trion component in the power-dependent photoluminescence spectra and negative shift of the threshold voltage of the FET after illumination.

2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction.

PubMed

Rowley-Neale, Samuel J; Brownson, Dale A C; Smith, Graham C; Sawtell, David A G; Kelly, Peter J; Banks, Craig E

2015-11-21

We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.

Facile synthesis of Sb2S3/MoS2 heterostructure as anode material for sodium-ion batteries.

PubMed

Zhang, Zhendong; Zhao, Jiachang; Xu, Meilan; Wang, Hongxia; Gong, Yanmei; Xu, Jingli

2018-05-18

A novel Sb2S3/MoS2 heterostructure in which Sb2S3 nanorods are coated with MoS2 nanosheets to form core-shell structure has been fabricated via a facile two-step hydrothermal process. The Sb2S3/MoS2 heterostructure utilized as anode of sodium-ion batteries (SIBs) shows higher capacity, superior rate capability and better cycling performance compared with individual Sb2S3 nanorods and MoS2 nanosheets. Specifically, the Sb2S3/MoS2 electrode shows an initial reversible capacity of 701 mAh g-1 at the current density of 100 mA g-1, which is remained 80.1% of the initial perforance after 100 cycles at the same current density. This outstanding electrochemical performance indicates Sb2S3/MoS2 heterostructure is a very promising anode material for high-performance SIBs. © 2018 IOP Publishing Ltd.

Direct measurement of the thickness-dependent electronic band structure of MoS2 using angle-resolved photoemission spectroscopy.

PubMed

Jin, Wencan; Yeh, Po-Chun; Zaki, Nader; Zhang, Datong; Sadowski, Jerzy T; Al-Mahboob, Abdullah; van der Zande, Arend M; Chenet, Daniel A; Dadap, Jerry I; Herman, Irving P; Sutter, Peter; Hone, James; Osgood, Richard M

2013-09-06

We report on the evolution of the thickness-dependent electronic band structure of the two-dimensional layered-dichalcogenide molybdenum disulfide (MoS2). Micrometer-scale angle-resolved photoemission spectroscopy of mechanically exfoliated and chemical-vapor-deposition-grown crystals provides direct evidence for the shifting of the valence band maximum from Γ to K, for the case of MoS2 having more than one layer, to the case of single-layer MoS2, as predicted by density functional theory. This evolution of the electronic structure from bulk to few-layer to monolayer MoS2 had earlier been predicted to arise from quantum confinement. Furthermore, one of the consequences of this progression in the electronic structure is the dramatic increase in the hole effective mass, in going from bulk to monolayer MoS2 at its Brillouin zone center, which is known as the cause for the decreased carrier mobility of the monolayer form compared to that of bulk MoS2.

A Confirmatory Factor Analysis of an Abbreviated Social Support Instrument: The MOS-SSS

ERIC Educational Resources Information Center

Gjesfjeld, Christopher D.; Greeno, Catherine G.; Kim, Kevin H.

2008-01-01

Objective: Confirm the factor structure of the original 18-item Medical Outcome Study Social Support Survey (MOS-SSS) as well as two abbreviated versions in a sample of mothers with a child in mental health treatment. Method: The factor structure, internal consistency, and concurrent validity of the MOS-SSS were assessed using a convenience sample…

Impact of Microstructure on MoS 2 Oxidation and Friction

DOE PAGES

Curry, John F.; Wilson, Mark A.; Luftman, Henry S.; ...

2017-07-31

In this work, we demonstrate the role of microstructure in the friction and oxidation behavior of the lamellar solid lubricant molybdenum disulfide (MoS 2). We report on systematic investigations of oxidation and friction for two MoS 2 films with distinctively different microstructures—amorphous and planar/highly-ordered—before and after exposure to atomic oxygen (AO) and high-temperature (250 °C) molecular oxygen. A combination of experimental tribology, molecular dynamics simulations, X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) was used to reveal new insights about the links between structure and properties of these widely utilized low-friction materials. Initially, ordered MoS 2 films showedmore » a surprising resistance to both atomic and molecular oxygens (even at elevated temperature), retaining characteristic low friction after exposure to extreme oxidative environments. Finally, XPS shows comparable oxidation of both coatings via AO; however, monolayer resolved compositional depth profiles from HS-LEIS reveal that the microstructure of the ordered coatings limits oxidation to the first atomic layer.« less

Impact of Microstructure on MoS 2 Oxidation and Friction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Curry, John F.; Wilson, Mark A.; Luftman, Henry S.

In this work, we demonstrate the role of microstructure in the friction and oxidation behavior of the lamellar solid lubricant molybdenum disulfide (MoS 2). We report on systematic investigations of oxidation and friction for two MoS 2 films with distinctively different microstructures—amorphous and planar/highly-ordered—before and after exposure to atomic oxygen (AO) and high-temperature (250 °C) molecular oxygen. A combination of experimental tribology, molecular dynamics simulations, X-ray photoelectron spectroscopy (XPS), and high-sensitivity low-energy ion scattering (HS-LEIS) was used to reveal new insights about the links between structure and properties of these widely utilized low-friction materials. Initially, ordered MoS 2 films showedmore » a surprising resistance to both atomic and molecular oxygens (even at elevated temperature), retaining characteristic low friction after exposure to extreme oxidative environments. Finally, XPS shows comparable oxidation of both coatings via AO; however, monolayer resolved compositional depth profiles from HS-LEIS reveal that the microstructure of the ordered coatings limits oxidation to the first atomic layer.« less

MoS2 /Carbon Nanotube Core-Shell Nanocomposites for Enhanced Nonlinear Optical Performance.

PubMed

Zhang, Xiaoyan; Selkirk, Andrew; Zhang, Saifeng; Huang, Jiawei; Li, Yuanxin; Xie, Yafeng; Dong, Ningning; Cui, Yun; Zhang, Long; Blau, Werner J; Wang, Jun

2017-03-08

Nanocomposites of layered MoS 2 and multi-walled carbon nanotubes (CNTs) with core-shell structure were prepared by a simple solvothermal method. The formation of MoS 2 nanosheets on the surface of coaxial CNTs has been confirmed by scanning electron microscopy, transmission electron microscopy, absorption spectrum, Raman spectroscopy, and X-ray photoelectron spectroscopy. Enhanced third-order nonlinear optical performances were observed for both femtosecond and nanosecond laser pulses over a broad wavelength range from the visible to the near infrared, compared to those of MoS 2 and CNTs alone. The enhancement can be ascribed to the strong coupling effect and the photoinduced charge transfer between MoS 2 and CNTs. This work affords an efficient way to fabricate novel CNTs based nanocomposites for enhanced nonlinear light-matter interaction. The versatile nonlinear properties imply a huge potential of the nanocomposites in the development of nanophotonic devices, such as mode-lockers, optical limiters, or optical switches. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogenated MoS2 QD-TiO2 heterojunction mediated efficient solar hydrogen production.

PubMed

Saha, Arka; Sinhamahapatra, Apurba; Kang, Tong-Hyun; Ghosh, Subhash C; Yu, Jong-Sung; Panda, Asit B

2017-11-09

Herein, we report the development of a hydrogenated MoS 2 QD-TiO 2 (HMT) heterojunction as an efficient photocatalytic system via a one-pot hydrothermal reaction followed by hydrogenation. This synthetic strategy facilitates the formation of MoS 2 QDs with an enhanced band gap and a proper heterojunction between them and TiO 2 , which accelerates charge transfer process. Hydrogenation leads to oxygen vacancies in TiO 2 , enhancing the visible light absorption capacity through narrowing its band gap, and sulfur vacancies in MoS 2 , which enhance the active sites for hydrogen adsorption. Due to the band gap reduction of hydrogenated TiO 2 and the band gap enhancement of the MoS 2 QDs, the energy states are rearranged to create a reverse movement of electrons and holes facilitated the charge transfer process which enhance life-time of photo-generated charges. The photocatalyst showed stable, efficient and exceptionally high noble metal free sunlight-induced hydrogen production with a maximum rate of 3.1 mmol g -1 h -1 . The developed synthetic strategy also provides flexibility towards the shape of the MoS 2 , e.g. QDs/single or few layers, on TiO 2 and offers the opportunity to design novel visible light active photocatalysts for different applications.

Resistive switching effect of N-doped MoS2-PVP nanocomposites films for nonvolatile memory devices

NASA Astrophysics Data System (ADS)

Wu, Zijin; Wang, Tongtong; Sun, Changqi; Liu, Peitao; Xia, Baorui; Zhang, Jingyan; Liu, Yonggang; Gao, Daqiang

2017-12-01

Resistive memory technology is very promising in the field of semiconductor memory devices. According to Liu et al, MoS2-PVP nanocomposite can be used as an active layer material for resistive memory devices due to its bipolar resistive switching behavior. Recent studies have also indicated that the doping of N element can reduce the band gap of MoS2 nanosheets, which is conducive to improving the conductivity of the material. Therefore, in this paper, we prepared N-doped MoS2 nanosheets and then fabricated N-doped MoS2-PVP nanocomposite films by spin coating. Finally, the resistive memory [C. Tan et al., Chem. Soc. Rev. 44, 2615 (2015)], device with ITO/N-doped MoS2-PVP/Pt structure was fabricated. Study on the I-V characteristics shows that the device has excellent resistance switching effect. It is worth mentioning that our device possesses a threshold voltage of 0.75 V, which is much better than 3.5 V reported previously for the undoped counterparts. The above research shows that N-doped MoS2-PVP nanocomposite films can be used as the active layer of resistive switching memory devices, and will make the devices have better performance.

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS2

PubMed Central

Trainer, Daniel J.; Putilov, Aleksei V.; Di Giorgio, Cinzia; Saari, Timo; Wang, Baokai; Wolak, Mattheus; Chandrasena, Ravini U.; Lane, Christopher; Chang, Tay-Rong; Jeng, Horng-Tay; Lin, Hsin; Kronast, Florian; Gray, Alexander X.; Xi, Xiaoxing X.; Nieminen, Jouko; Bansil, Arun; Iavarone, Maria

2017-01-01

Recent progress in the synthesis of monolayer MoS2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS2 as a function of the number of layers at the nanoscale and show in-depth how the band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS2. PMID:28084465

Role of oxygen adsorption in modification of optical and surface electronic properties of MoS2

NASA Astrophysics Data System (ADS)

Shakya, Jyoti; Kumar, Sanjeev; Mohanty, Tanuja

2018-04-01

In this work, the effect of surface oxidation of molybdenum disulfide (MoS2) nanosheets induced by hydrogen peroxide (H2O2) on the work function and bandgap of MoS2 has been investigated for tuning its optical and electronic properties. Transmission electron microscopy studies reveal the existence of varying morphologies of few layers of MoS2 as well as quantum dots due to the different absorbing effects of two mixed solvents on MoS2. The X-ray diffraction, electron paramagnetic resonance, and Raman studies indicate the presence of physical as well as chemical adsorption of oxygen atoms in MoS2. The photoluminescence spectra show the tuning of bandgap arising from the passivation of trapping centers leading to radiative recombination of excitons. The value of work function obtained from scanning Kelvin probe microscopy of MoS2 in mixed solvents of H2O2 and N-methyl-2-pyrrolidone increases with an increase in the concentration of H2O2. A linear relationship could be established between H2O2 content in mixed solvent and measured values of work function. This work gives the alternative route towards the commercial use of defect engineered transition metal dichalcogenide materials in diverse fields.

Inter-layer coupling induced valence band edge shift in mono- to few-layer MoS 2

DOE PAGES

Trainer, Daniel J.; Putilov, Aleksei V.; Di Giorgio, Cinzia; ...

2017-01-13

In this study, recent progress in the synthesis of monolayer MoS 2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here,we report a study of highly crystalline islands of MoS 2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS 2 as a function of the number of layers at the nanoscale and show in-depth how themore » band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS 2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS 2.« less

Zinc Oxide Coating Effect for the Dye Removal and Photocatalytic Mechanisms of Flower-Like MoS2 Nanoparticles

NASA Astrophysics Data System (ADS)

Tian, Qingyong; Wu, Wei; Yang, Shuanglei; Liu, Jun; Yao, Weijing; Ren, Feng; Jiang, Changzhong

2017-03-01

Flower-like MoS2 nanoparticles (NPs) consist of ultra-thin MoS2 nanosheets are synthesized via a facile one-pot hydrothermal method. The MoS2/ZnO p-n heterostructure is formed by coating n-type ZnO on the surface of flower-like MoS2 NPs through the seed-mediate route and post-annealing treatment. The effects for the dye removal and photocatalytic performances after ZnO coating are systematically investigated. The results demonstrated that the coating of ZnO nanoparticles has a positive promotion to the photodegrading properties while negative effect on the adsorption capacity of the MoS2/ZnO heterostructures. The related mechanisms on the relationship of adsorption capacity and photocatalysis are discussed in detail.

Hierarchical heterostructure of MoS2 flake anchored on TiO2 sphere for supercapacitor application

NASA Astrophysics Data System (ADS)

Chanda, K.; Thakur, S.; Maiti, S.; Acharya, A.; Paul, T.; Besra, N.; Sarkar, S.; Das, A.; Sardar, K.; Chattopadhyay, K. K.

2018-05-01

Hierarchical architectures realized via rational coupling of several components not only boast synergy driven raised functionality compared to their structural constituents also exhibit noble interface phenomena, thus made them significantly pertinent from research and technological point of view. Here in, geometrically intricate hierarchical nanoform constituting MoS2 nanoflakes anchored on TiO2 sphere was realized via two steps hydrothermal protocol. Initially TiO2 sphere was synthesized using titanium isopropoxide assisted hydrothermal route followed by which the sphere was used as scaffold for secondary growth of MoS2. As synthesized hybrid sample displayed much improved electrochemical behavior than pristine TiO2 sphere. Assessed value of specific capacitance for the hybrid is found to 152.22 F/g at current density of 0.1A/g which is 30 fold than TiO2 sphere. This electrochemical performance enhancement can be accredited to high surface area of the hybrid sample.

Dramatic switching behavior in suspended MoS2 field-effect transistors

NASA Astrophysics Data System (ADS)

Chen, Huawei; Li, Jingyu; Chen, Xiaozhang; Zhang, David; Zhou, Peng

2018-02-01

When integrating MoS2 flakes into scaling-down transistors, the short-channel effect, which is severe in silicon technology below 5-nanometer, can be avoided effectively. MoS2 transistors not only exhibit a high on/off ratio but also demonstrate a rapid switching speed. According to the theoretical calculation, the thermionic limit subthreshold slope (SS) of the ideal device could reach 60 mV/dec. However, due to the confinement of defects from substrates or contamination during the process, the SS deteriorates to more than 300 mV/dec, causing serious power consumption. In this work, we optimize the SS through structure design of MoS2 transistors. The suspended transistors exhibit a high on/off ratio of 107 and a minimum SS of 63 mV/dec with an ultralow standby power at room temperature. This study demonstrates the promising potential of structure design for electronic devices with ultralow-power switching behaviors.

Exploring biological effects of MoS2 nanosheets on native structures of α-helical peptides

NASA Astrophysics Data System (ADS)

Gu, Zonglin; Li, Weifeng; Hong, Linbi; Zhou, Ruhong

2016-05-01

Recent reports of mono- and few-layer molybdenum disulfide (MoS2), a representative transition metal dichacogenide (TMD), as antibacterial and anticancer agents have shed light on their potential in biomedical applications. To better facilitate these promising applications, one needs to understand the biological effects of these TMDs as well, such as their potential adverse effects on protein structure and function. Here, we sought to understand the interaction of MoS2 nanosheets with peptides using molecular dynamics simulations and a simple model polyalanine with various lengths (PAn, n = 10, 20, 30, and 40; mainly α - helices). Our results demonstrated that MoS2 monolayer has an exceptional capability to bind all peptides in a fast and strong manner. The strong attraction from the MoS2 nanosheet is more than enough to compensate the energy needed to unfold the peptide, regardless of the length, which induces drastic disruptions to the intra-peptide hydrogen bonds and subsequent secondary structures of α - helices. This universal phenomenon may point to the potential nanotoxicity of MoS2 when used in biological systems. Moreover, these results aligned well with previous findings on the potential cytotoxicity of TMD nanomaterials.

Mechanically delaminated few layered MoS2 nanosheets based high performance wire type solid-state symmetric supercapacitors

NASA Astrophysics Data System (ADS)

Krishnamoorthy, Karthikeyan; Pazhamalai, Parthiban; Veerasubramani, Ganesh Kumar; Kim, Sang Jae

2016-07-01

Two dimensional nanostructures are increasingly used as electrode materials in flexible supercapacitors for portable electronic applications. Herein, we demonstrated a ball milling approach for achieving few layered molybdenum disulfide (MoS2) via exfoliation from their bulk. Physico-chemical characterizations such as X-ray diffraction, field emission scanning electron microscope, and laser Raman analyses confirmed the occurrence of exfoliated MoS2 sheets with few layers from their bulk via ball milling process. MoS2 based wire type solid state supercapacitors (WSCs) are fabricated and examined using cyclic voltammetry (CV), electrochemical impedance spectroscopy, and galvanostatic charge discharge (CD) measurements. The presence of rectangular shaped CV curves and symmetric triangular shaped CD profiles suggested the mechanism of charge storage in MoS2 WSC is due to the formation of electrochemical double layer capacitance. The MoS2 WSC device delivered a specific capacitance of 119 μF cm-1, and energy density of 8.1 nW h cm-1 with better capacitance retention of about 89.36% over 2500 cycles, which ensures the use of the ball milled MoS2 for electrochemical energy storage devices.

Improved dehydrogenation performance of LiBH4 by 3D hierarchical flower-like MoS2 spheres additives

NASA Astrophysics Data System (ADS)

Zhao, Yan; Liu, Yongchang; Liu, Huiqiao; Kang, Hongyan; Cao, Kangzhe; Wang, Qinghong; Zhang, Chunling; Wang, Yijing; Yuan, Huatang; Jiao, Lifang

2015-12-01

In this work, 3D hierarchical flower-like MoS2 spheres are successfully fabricated via a hydrothermal method followed by a heat treatment. The obtained product is composed of few-layered MoS2 nanosheets with enlarged interlayer distance (ca. 0.66 nm) of the (002) plane. Meanwhile, the hydrogen storage properties of the as-prepared MoS2 ball milled with LiBH4 are systematically investigated. The results of temperature programmed desorption (TPD) and isothermal measurement suggest that the LiBH4-MoS2 (as-prepared) mixture exhibits favorable dehydrogenation properties in both lowering the hydrogen release temperature and improving kinetics of hydrogen release rate. LiBH4-MoS2 (as-prepared) sample (the preparation mass ratio is 1:1) starts to release hydrogen at 171 °C, and roughly 5.6 wt% hydrogen is released within 1 h when isothermally heated to 320 °C, which presents superior dehydrogenation performance compared to that of the bulk LiBH4. The excellent dehydrogenation performance of the LiBH4-MoS2 (as-prepared) mixture may be attributed to the high active site density and enlarged interlayer distance of the MoS2 nanosheets, 3D architectures and hierarchical structures.

A measurement technique of time-dependent dielectric breakdown in MOS capacitors

NASA Technical Reports Server (NTRS)

Li, S. P.

1974-01-01

The statistical nature of time-dependent dielectric breakdown characteristics in MOS capacitors was evidenced by testing large numbers of capacitors fabricated on single wafers. A multipoint probe and automatic electronic visual display technique are introduced that will yield statistical results which are necessary for the investigation of temperature, electric field, thermal annealing, and radiation effects in the breakdown characteristics, and an interpretation of the physical mechanisms involved. It is shown that capacitors of area greater than 0.002 sq cm may yield worst-case results, and that a multipoint probe of capacitors of smaller sizes can be used to obtain a profile of nonuniformities in the SiO2 films.

Atomic layer MoS2-graphene van der Waals heterostructure nanomechanical resonators.

PubMed

Ye, Fan; Lee, Jaesung; Feng, Philip X-L

2017-11-30

Heterostructures play significant roles in modern semiconductor devices and micro/nanosystems in a plethora of applications in electronics, optoelectronics, and transducers. While state-of-the-art heterostructures often involve stacks of crystalline epi-layers each down to a few nanometers thick, the intriguing limit would be hetero-atomic-layer structures. Here we report the first experimental demonstration of freestanding van der Waals heterostructures and their functional nanomechanical devices. By stacking single-layer (1L) MoS 2 on top of suspended single-, bi-, tri- and four-layer (1L to 4L) graphene sheets, we realize an array of MoS 2 -graphene heterostructures with varying thickness and size. These heterostructures all exhibit robust nanomechanical resonances in the very high frequency (VHF) band (up to ∼100 MHz). We observe that fundamental-mode resonance frequencies of the heterostructure devices fall between the values of graphene and MoS 2 devices. Quality (Q) factors of heterostructure resonators are lower than those of graphene but comparable to those of MoS 2 devices, suggesting interface damping related to interlayer interactions in the van der Waals heterostructures. This study validates suspended atomic layer heterostructures as an effective device platform and provides opportunities for exploiting mechanically coupled effects and interlayer interactions in such devices.

Ultraclean and Direct Transfer of a Wafer-Scale MoS2 Thin Film onto a Plastic Substrate.

PubMed

Phan, Hoang Danh; Kim, Youngchan; Lee, Jinhwan; Liu, Renlong; Choi, Yongsuk; Cho, Jeong Ho; Lee, Changgu

2017-02-01

An ultraclean method to directly transfer a large-area MoS 2 film from the original growth substrate to a flexible substrate by using epoxy glue is developed. The transferred film is observed to be free of wrinkles and cracks and to be as smooth as the film synthesized on the original substrate. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selective Amplification of the Primary Exciton in a MoS_{2} Monolayer.

PubMed

Lee, Hyun Seok; Kim, Min Su; Jin, Youngjo; Han, Gang Hee; Lee, Young Hee; Kim, Jeongyong

2015-11-27

Optoelectronics applications for transition-metal dichalcogenides are still limited by weak light absorption and their complex exciton modes are easily perturbed by varying excitation conditions because they are inherent in atomically thin layers. Here, we propose a method of selectively amplifying the primary exciton (A^{0}) among the exciton complexes in monolayer MoS_{2} via cyclic reexcitation of cavity-free exciton-coupled plasmon propagation. This was implemented by partially overlapping a Ag nanowire on a MoS_{2} monolayer separated by a thin SiO_{2} spacer. Exciton-coupled plasmons in the nanowire enhance the A^{0} radiation in MoS_{2}. The cumulative amplification of emission enhancement by cyclic plasmon traveling reaches approximately twentyfold selectively for the A^{0}, while excluding other B exciton and multiexciton by significantly reduced band filling, without oscillatory spectra implying plasmonic cavity effects.

Order of magnitude enhancement of monolayer MoS 2 photoluminescence due to near-field energy influx from nanocrystal films

DOE PAGES

Guo, Tianle; Sampat, Siddharth; Zhang, Kehao; ...

2017-02-03

Two-dimensional transition metal dichalcogenides (TMDCs) like MoS 2 are promising candidates for various optoelectronic applications. The typical photoluminescence (PL) of monolayer MoS 2 is however known to suffer very low quantum yields. We demonstrate a 10-fold increase of MoS 2 excitonic PL enabled by nonradiative energy transfer (NRET) from adjacent nanocrystal quantum dot (NQD) films. The understanding of this effect is facilitated by our application of transient absorption (TA) spectroscopy to monitor the energy influx into the monolayer MoS 2 in the process of ET from photoexcited CdSe/ZnS nanocrystals. In contrast to PL spectroscopy, TA can detect even non-emissive excitons,more » and we register an order of magnitude enhancement of the MoS 2 excitonic TA signatures in hybrids with NQDs. The appearance of ET-induced nanosecond-scale kinetics in TA features is consistent with PL dynamics of energy-accepting MoS 2 and PL quenching data of the energy-donating NQDs. The observed enhancement is attributed to the reduction of recombination losses for excitons gradually transferred into MoS 2 under quasi-resonant conditions as compared with their direct photoproduction. Furthermore, the TA and PL data clearly illustrate the efficacy of MoS 2 and likely other TMDC materials as energy acceptors and the possibility of their practical utilization in NRET-coupled hybrid nanostructures.« less

Experimental Study of Floating-Gate-Type Metal-Oxide-Semiconductor Capacitors with Nanosize Triangular Cross-Sectional Tunnel Areas for Low Operating Voltage Flash Memory Application

NASA Astrophysics Data System (ADS)

Liu, Yongxun; Guo, Ruofeng; Kamei, Takahiro; Matsukawa, Takashi; Endo, Kazuhiko; O'uchi, Shinichi; Tsukada, Junichi; Yamauchi, Hiromi; Ishikawa, Yuki; Hayashida, Tetsuro; Sakamoto, Kunihiro; Ogura, Atsushi; Masahara, Meishoku

2012-06-01

The floating-gate (FG)-type metal-oxide-semiconductor (MOS) capacitors with planar (planar-MOS) and three-dimensional (3D) nanosize triangular cross-sectional tunnel areas (3D-MOS) have successfully been fabricated by introducing rapid thermal oxidation (RTO) and postdeposition annealing (PDA), and their electrical characteristics between the control gate (CG) and FG have been systematically compared. It was experimentally found in both planar- and 3D-MOS capacitors that the uniform and higher breakdown voltages are obtained by introducing RTO owing to the high-quality thermal oxide formation on the surface and etched edge regions of the n+ polycrystalline silicon (poly-Si) FG, and the leakage current is highly suppressed after PDA owing to the improved quality of the tetraethylorthosilicate (TEOS) silicon dioxide (SiO2) between CG and FG. Moreover, a lower breakdown voltage between CG and FG was obtained in the fabricated 3D-MOS capacitors as compared with that of planar-MOS capacitors thanks to the enhanced local electric field at the tips of triangular tunnel areas. The developed nanosize triangular cross-sectional tunnel area is useful for the fabrication of low operating voltage flash memories.

Electrohydrodynamic printing for scalable MoS2 flake coating: application to gas sensing device

NASA Astrophysics Data System (ADS)

Lim, Sooman; Cho, Byungjin; Bae, Jaehyun; Kim, Ah Ra; Lee, Kyu Hwan; Kim, Se Hyun; Hahm, Myung Gwan; Nam, Jaewook

2016-10-01

Scalable sub-micrometer molybdenum disulfide ({{MoS}}2) flake films with highly uniform coverage were created using a systematic approach. An electrohydrodynamic (EHD) printing process realized a remarkably uniform distribution of exfoliated {{MoS}}2 flakes on desired substrates. In combination with a fast evaporating dispersion medium and an optimal choice of operating parameters, the EHD printing can produce a film rapidly on a substrate without excessive agglomeration or cluster formation, which can be problems in previously reported liquid-based continuous film methods. The printing of exfoliated {{MoS}}2 flakes enabled the fabrication of a gas sensor with high performance and reproducibility for {{NO}}2 and {{NH}}3.

Flexible integrated circuits and multifunctional electronics based on single atomic layers of MoS2 and graphene

NASA Astrophysics Data System (ADS)

Amani, Matin; Burke, Robert A.; Proie, Robert M.; Dubey, Madan

2015-03-01

Two-dimensional materials, such as graphene and its analogues, have been investigated by numerous researchers for high performance flexible and conformal electronic systems, because they offer the ultimate level of thickness scaling, atomically smooth surfaces and high crystalline quality. Here, we use layer-by-layer transfer of large area molybdenum disulphide (MoS2) and graphene grown by chemical vapor deposition (CVD) to demonstrate electronics on flexible polyimide (PI) substrates. On the same PI substrate, we are able to simultaneously fabricate MoS2 based logic, non-volatile memory cells with graphene floating gates, photo-detectors and MoS2 transistors with tunable source and drain contacts. We are also able to demonstrate that these flexible heterostructure devices have very high electronic performance, comparable to four point measurements taken on SiO2 substrates, with on/off ratios >107 and field effect mobilities as high as 16.4 cm2 V-1 s-1. Additionally, the heterojunctions show high optoelectronic sensitivity and were operated as photodetectors with responsivities over 30 A W-1. Through local gating of the individual graphene/MoS2 contacts, we are able to tune the contact resistance over the range of 322-1210 Ω mm for each contact, by modulating the graphene work function. This leads to devices with tunable and multifunctional performance that can be implemented in a conformable platform.

Flexible integrated circuits and multifunctional electronics based on single atomic layers of MoS2 and graphene.

PubMed

Amani, Matin; Burke, Robert A; Proie, Robert M; Dubey, Madan

2015-03-20

Two-dimensional materials, such as graphene and its analogues, have been investigated by numerous researchers for high performance flexible and conformal electronic systems, because they offer the ultimate level of thickness scaling, atomically smooth surfaces and high crystalline quality. Here, we use layer-by-layer transfer of large area molybdenum disulphide (MoS2) and graphene grown by chemical vapor deposition (CVD) to demonstrate electronics on flexible polyimide (PI) substrates. On the same PI substrate, we are able to simultaneously fabricate MoS2 based logic, non-volatile memory cells with graphene floating gates, photo-detectors and MoS2 transistors with tunable source and drain contacts. We are also able to demonstrate that these flexible heterostructure devices have very high electronic performance, comparable to four point measurements taken on SiO2 substrates, with on/off ratios >10(7) and field effect mobilities as high as 16.4 cm(2) V(-1) s(-1). Additionally, the heterojunctions show high optoelectronic sensitivity and were operated as photodetectors with responsivities over 30 A W(-1). Through local gating of the individual graphene/MoS2 contacts, we are able to tune the contact resistance over the range of 322-1210 Ω mm for each contact, by modulating the graphene work function. This leads to devices with tunable and multifunctional performance that can be implemented in a conformable platform.

Preparation of yolk-shell MoS2 nanospheres covered with carbon shell for excellent lithium-ion battery anodes

NASA Astrophysics Data System (ADS)

Guo, Bangjun; Feng, Yu; Chen, Xiaofan; Li, Bo; Yu, Ke

2018-03-01

Molybdenum disulfide is regarded as one of the most promising electrode materials for high performance lithium-ion batteries. Designing firm basal structure is a key point to fully utilize the high capacity of layered MoS2 nanomaterials. Here, yolk-shell structured MoS2 nanospheres is firstly designed and fabricated to meet this needs. This unique yolk-shell nanospheres are transformed from solid nanospheres by a simply weak alkaline etching method. Then, the yolk-shell MoS2/C is synthesized by a facile process to protect the outside MoS2 shell and promote the conductivity. Taking advantages of high capacity and well-defined cavity space, allowing the core MoS2 to expand freely without breaking the outer shells, yolk-shell MoS2/C nanospheres delivers long cycle life (94% of capacity retained after 200 cycles) and high rate behaviour (830 mA h g-1 at 5 A g-1). This design of yolk-shell structure may set up a new strategy for preparing next generation anode materials for LIBs.

Electronic properties of ZnPSe3-MoS2 Van der Waals heterostructure

NASA Astrophysics Data System (ADS)

Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

2018-04-01

We present a comparative study of electronic properties of ZnPSe3-MoS2 heterostructure using GGA-PBE functional and DFT-D2 method within the framework of density functional theory (DFT). Electronic band structure for the considered heterostructure shows a direct band gap semiconducting character. A decrease in band gap is observed with the heterostructuring as compared to their constituent pristine monolayers. The alignment of valance band maxima and conduction band minima on different layers in heterostructure indicate the physical separation of charge carriers. A work function of 5.31 eV has been calculated for ZnPSe3-MoS2 heterostructure. These results provide a physical basis for the potential applications of these ZnPSe3-MoS2 heterostructure in optoelectronic devices.

Atomic-Monolayer MoS2 Band-to-Band Tunneling Field-Effect Transistor.

PubMed

Lan, Yann-Wen; Torres, Carlos M; Tsai, Shin-Hung; Zhu, Xiaodan; Shi, Yumeng; Li, Ming-Yang; Li, Lain-Jong; Yeh, Wen-Kuan; Wang, Kang L

2016-11-01

The experimental observation of band-to-band tunneling in novel tunneling field-effect transistors utilizing a monolayer of MoS 2 as the conducting channel is demonstrated. Our results indicate that the strong gate-coupling efficiency enabled by two-dimensional materials, such as monolayer MoS 2 , results in the direct manifestation of a band-to-band tunneling current and an ambipolar transport. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhancing Photoresponsivity of Self-Aligned MoS2 Field-Effect Transistors by Piezo-Phototronic Effect from GaN Nanowires.

PubMed

Liu, Xingqiang; Yang, Xiaonian; Gao, Guoyun; Yang, Zhenyu; Liu, Haitao; Li, Qiang; Lou, Zheng; Shen, Guozhen; Liao, Lei; Pan, Caofeng; Lin Wang, Zhong

2016-08-23

We report high-performance self-aligned MoS2 field-effect transistors (FETs) with enhanced photoresponsivity by the piezo-phototronic effect. The FETs are fabricated based on monolayer MoS2 with a piezoelectric GaN nanowire (NW) as the local gate, and a self-aligned process is employed to define the source/drain electrodes. The fabrication method allows the preservation of the intrinsic property of MoS2 and suppresses the scattering center density in the MoS2/GaN interface, which results in high electrical and photoelectric performances. MoS2 FETs with channel lengths of ∼200 nm have been fabricated with a small subthreshold slope of 64 mV/dec. The photoresponsivity is 443.3 A·W(-1), with a fast response and recovery time of ∼5 ms under 550 nm light illumination. When strain is introduced into the GaN NW, the photoresponsivity is further enhanced to 734.5 A·W(-1) and maintains consistent response and recovery time, which is comparable with that of the mechanical exfoliation of MoS2 transistors. The approach presented here opens an avenue to high-performance top-gated piezo-enhanced MoS2 photodetectors.

Psychometric testing of the Chinese version of the medical outcomes study social support survey (MOS-SSS-C).

PubMed

Yu, Doris S F; Lee, Diana T F; Woo, Jean

2004-04-01

The purpose of this study was to assess the psychometric properties of the Chinese version of the Medical Outcomes Study Social Support Survey (MOS-SSS-C) in a sample of 110 patients. Criterion-related and construct validities of the MOS-SSS-C were evaluated by correlations with the Chinese version of the Multidimensional Perceived Social Support Survey (r =.82) and the Hospital Anxiety and Depression Scale (r = -.58). Confirmatory factor analysis affirmed the four-factor structure of the MOS-SSS-C in measuring the functional aspects of perceived social support. Cronbach's alphas for the subscales ranged from.93 to.96, whereas the alpha for the overall scale was.98. The 2-week test-retest reliability of the MOS-SSS-C as measured by the intraclass correlation coefficient was.84. The MOS-SSS-C is a psychometrically sound multidimensional measure for the evaluation of functional aspects of perceived social support by Chinese patients with chronic disease. Copyright 2004 Wiley Periodicals, Inc.

Wafer-scale production of highly uniform two-dimensional MoS2 by metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Kim, TaeWan; Mun, Jihun; Park, Hyeji; Joung, DaeHwa; Diware, Mangesh; Won, Chegal; Park, Jonghoo; Jeong, Soo-Hwan; Kang, Sang-Woo

2017-05-01

Semiconducting two-dimensional (2D) materials, particularly extremely thin molybdenum disulfide (MoS2) films, are attracting considerable attention from academia and industry owing to their distinctive optical and electrical properties. Here, we present the direct growth of a MoS2 monolayer with unprecedented spatial and structural uniformity across an entire 8 inch SiO2/Si wafer. The influences of growth pressure, ambient gases (Ar, H2), and S/Mo molar flow ratio on the MoS2 layered growth were explored by considering the domain size, nucleation sites, morphology, and impurity incorporation. Monolayer MoS2-based field effect transistors achieve an electron mobility of 0.47 cm2 V-1 s-1 and on/off current ratio of 5.4 × 104. This work demonstrates the potential for reliable wafer-scale production of 2D MoS2 for practical applications in next-generation electronic and optical devices.

Chemical Vapor Deposition of High-Quality Large-Sized MoS2 Crystals on Silicon Dioxide Substrates.

PubMed

Chen, Jianyi; Tang, Wei; Tian, Bingbing; Liu, Bo; Zhao, Xiaoxu; Liu, Yanpeng; Ren, Tianhua; Liu, Wei; Geng, Dechao; Jeong, Hu Young; Shin, Hyeon Suk; Zhou, Wu; Loh, Kian Ping

2016-08-01

Large-sized MoS 2 crystals can be grown on SiO 2 /Si substrates via a two-stage chemical vapor deposition method. The maximum size of MoS 2 crystals can be up to about 305 μm. The growth method can be used to grow other transition metal dichalcogenide crystals and lateral heterojunctions. The electron mobility of the MoS 2 crystals can reach ≈30 cm 2 V -1 s -1 , which is comparable to those of exfoliated flakes.

Direct Growth of High Mobility and Low-Noise Lateral MoS2 -Graphene Heterostructure Electronics.

PubMed

Behranginia, Amirhossein; Yasaei, Poya; Majee, Arnab K; Sangwan, Vinod K; Long, Fei; Foss, Cameron J; Foroozan, Tara; Fuladi, Shadi; Hantehzadeh, Mohammad Reza; Shahbazian-Yassar, Reza; Hersam, Mark C; Aksamija, Zlatan; Salehi-Khojin, Amin

2017-08-01

Reliable fabrication of lateral interfaces between conducting and semiconducting 2D materials is considered a major technological advancement for the next generation of highly packed all-2D electronic circuitry. This study employs seed-free consecutive chemical vapor deposition processes to synthesize high-quality lateral MoS 2 -graphene heterostructures and comprehensively investigated their electronic properties through a combination of various experimental techniques and theoretical modeling. These results show that the MoS 2 -graphene devices exhibit an order of magnitude higher mobility and lower noise metrics compared to conventional MoS 2 -metal devices as a result of energy band rearrangement and smaller Schottky barrier height at the contacts. These findings suggest that MoS 2 -graphene in-plane heterostructures are promising materials for the scale-up of all-2D circuitry with superlative electrical performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Size effect on the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2 nanoribbon

NASA Astrophysics Data System (ADS)

Wen, Yan-Ni; Xia, Ming-Gang; Zhang, Sheng-Li

2016-05-01

By using the VASP, we studied the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2-nanoribbons (WS2-MoS2-NRs). Our results show that the NRs' edge chirality and width affect significantly its magnetic and electronic properties. The monolayer lateral hetero-junction ZZ-WS2-MoS2-NRs(ZZ: zigzag) exhibitmetallic behavior and have considerable magnetic moment. Their magnetic moments decrease in the order of Nz = 2, 6 and 4 (the width of NRs). While, the magnetic moment decreases with the increased rz (the number of the Mo-S chains, rz ≠ 0 and rz ≠ Nz) at the same width Nz. The NA-AC-WS2-NR (AC: armchair) and NA-AC-WS2-MoS2-NR-1 (the number of the Mo-S chain is 1) show metallic behavior when NA = 3 (the width of NRs). The other monolayer lateral hetero-junction AC-WS2-MoS2-NRs remain the nonmagnetic and semiconductingbehavior as bulk. But they are indirect band-gap except for the NA = 3, rA = 2 (the number of the Mo-S chains) and NA = 7, rA = 0 when NA < 9. However they are direct band-gap when NA ≥ 9. Their lowest and highest band gaps are 0.150 eV and 0.581 eV, respectively. These unique magnetic and electronic properties will provide guidanceon the WS2-MoS2 hetero-junction application in nanodevice.

Chemistry of MOS-LSI radiation hardening

NASA Technical Reports Server (NTRS)

Grunthaner, P.

1985-01-01

The objective of this task was to obtain chemical information on MOS test samples. Toward this end, high resolution X-ray photoemission spectroscopy (XPS) has been the primary techniques used to characterize the chemistry and structure of the SiO2/Si interface for a variety of MOS structures with differing degrees of susceptibility to damage by ionizing radiation. The major accomplishments of this program are: (1) the identification of a structurally distinct region of SiO2 in the near-interfacial region of thermal SiO2 on Si; (2) the identification in the near-interfacial region of SiO2 structural differences between radiation hard and soft gate oxides; (3) the direct observation of radiation-induced damage sites in thermal SiO2 with XPS using in situ electron stress; (4) the correlation of suboxide state distributions at the SiO2/Si interface with processing parameters and radiation susceptibility; (5) the development of a chemical mechanism for radiation-induced interface state generation in SiO2/Si structures; and (6) the development benign chemical profiling techniques which permit the investigation of oxide/semiconductor structures using surface sensitive electron spectroscopic techniques.

Role of graphene inter layer on the formation of the MoS2-CZTS interface during growth

NASA Astrophysics Data System (ADS)

Vishwakarma, Manoj; Thota, Narayana; Karakulina, Olesia; Hadermann, Joke; Mehta, B. R.

2018-05-01

The growth of MoS2 layer near the Mo/CZTS interface during sulphurization process can have an impact on back contact cell parameters (series resistance and fill factor) depending upon the thickness or quality of MoS2. This study reports the dependence of the thickness of interfacial MoS2 layer on the growth of graphene at the interface between molybdenum back contact and deposited CZTS layer. The graphene layer reduces the accumulation of Zn/ZnS, Sn/SnO2 and formation of pores near the MoS2-CZTS interface. The use of graphene as interface layer can be potentially useful for improving the quality of Mo/MoS2/CZTS interface.

MoS2 interactions with 1.5 eV atomic oxygen

NASA Technical Reports Server (NTRS)

Martin, J. A.; Cross, J. B.; Pope, L. E.

1989-01-01

Exposures of MoS2 to 1.5-eV atomic oxygen in an anhydrous environment reveal that the degree of oxidation is essentially independent of crystallite orientation, and that the surface-adsorbed reaction products are MoO3 and MoO2. A mixture of oxides and sulfide exists over a depth of about 90 A, and this layer has a low diffusion rate for oxygen. It is concluded that a protective oxide layer forms on MoS2 on exposure to the atomic-oxygen-rich environment of LEO.

Energetic distributions of interface states Dit(phi sub s) of MOS transistors in extension of Kuhn's quasistatic C(V)-method

NASA Astrophysics Data System (ADS)

Krautschneider, W.; Wagemann, H. G.

1983-10-01

Kuhn's quasi-static C(V)-method has been extended to MOS transistors by considering the capacitances of the source and drain p-n junctions additionally to the MOS varactor circuit model. The width of the space charge layers w(phi sub s) is calculated as a function of the surface potential phi sub s and applied to the MOS capacitance as a function of the gate voltage. Capacitance behavior for different channel length is presented as a model and compared to measurement results and evaluations of energetic distributions of interface states Dit(phi sub s) for MOS transistor and MOS varactor on the same chip.

Effects of van der Waals interaction and electric field on the electronic structure of bilayer MoS2.

PubMed

Xiao, Jin; Long, Mengqiu; Li, Xinmei; Zhang, Qingtian; Xu, Hui; Chan, K S

2014-10-08

The modification of the electronic structure of bilayer MoS2 by an external electric field can have potential applications in optoelectronics and valleytronics. Nevertheless, the underlying physical mechanism is not clearly understood, especially the effects of the van der Waals interaction. In this study, the spin orbit-coupled electronic structure of bilayer MoS2 has been investigated using the first-principle density functional theory. We find that the van der Waals interaction as well as the interlayer distance has significant effects on the band structure. When the interlayer distance of bilayer MoS2 increases from 0.614 nm to 0.71 nm, the indirect gap between the Γ and Λ points increases from 1.25 eV to 1.70 eV. Meanwhile, the energy gap of bilayer MoS2 transforms from an indirect one to a direct one. An external electric field can shift down (up) the energy bands of the bottom (top) MoS2 layer and also breaks the inversion symmetry of bilayer MoS2. As a result, the electric field can affect the band gaps, the spin-orbit interaction and splits the valance bands into two groups. The present study can help us understand more about the electronic structures of MoS2 materials for potential applications in electronics and optoelectronics.

Charging effect at grain boundaries of MoS2

NASA Astrophysics Data System (ADS)

Yan, Chenhui; Dong, Xi; Li, Connie H.; Li, Lian

2018-05-01

Grain boundaries (GBs) are inherent extended defects in chemical vapor deposited (CVD) transition metal dichalcogenide (TMD) films. Characterization of the atomic structure and electronic properties of these GBs is crucial for understanding and controlling the properties of TMDs via defect engineering. Here, we report the atomic and electronic structure of GBs in CVD grown MoS2 on epitaxial graphene/SiC(0001). Using scanning tunneling microscopy/spectroscopy, we find that GBs mostly consist of arrays of dislocation cores, where the presence of mid-gap states shifts both conduction and valence band edges by up to 1 eV. Our findings demonstrate the first charging effect near GBs in CVD grown MoS2, providing insights into the significant impact GBs can have on materials properties.

Probing the biocompatibility of MoS2 nanosheets by cytotoxicity assay and electrical impedance spectroscopy

NASA Astrophysics Data System (ADS)

Shah, Pratikkumar; Narayanan, Tharangattu N.; Li, Chen-Zhong; Alwarappan, Subbiah

2015-08-01

Transition metal dichalgogenides such as MoS2 have recently emerged as hot two-dimensional (2D) materials due to their superior electronic and catalytic properties. Recently, we have reported the usefulness of MoS2 nanosheets toward the electrochemical detection of neurotransmitters and glucose (Narayanan et al 2014 Nanotechnology 25 335702). Furthermore, there are reports available in the literature that demonstrate the usefulness of MoS2 nanosheets for biosensing and energy storage applications (Zhu et al 2013 J. Am. Chem. Soc. 135 5998-6001 Pumera and Loo 2014 Trends Anal. Chem. 61 49-53 Lee et al 2014 Sci. Rep. 4 7352; Stephenson et al 2014 Energy Environ. Sci. 7 209-31). Understanding the cytotoxic effect of any material is very important prior to employing them for any in vivo biological applications such as implantable sensors, chips, or carriers for drug delivery and cell imaging purposes. Herein, we report the cytotoxicity of the MoS2 nanosheets based on the cytotoxic assay results and electrical impedance analysis using rat pheochromocytoma cells (PC12) and rat adrenal medulla endothelial cells (RAMEC). Our results indicated that the MoS2 nanosheets synthesized in our work are safe 2D nanosheets for futuristic biomedical applications.

Influence of water vapor on the electronic property of MoS2 field effect transistors.

PubMed

Shu, Jiapei; Wu, Gongtao; Gao, Song; Liu, Bo; Wei, Xianlong; Chen, Qing

2017-05-19

The influence of water vapor on the electronic property of MoS 2 field effect transistors (FETs) is studied through controlled experiments. We fabricate supported and suspended FETs on the same piece of MoS 2 to figure out the role of SiO 2 substrate on the water sensing property of MoS 2 . The two kinds of devices show similar response to water vapor and to different treatments, such as pumping in the vacuum, annealing at 500 K and current annealing, indicating the substrate does not play an important role in the MoS 2 water sensor. Water adsorption is found to decrease the carrier mobility probably through introducing a scattering center on the surface of MoS 2 . The threshold voltage and subthreshold swing of the FETs do not change obviously after introducing water vapor, indicating there is no obvious doping and trap introducing effects. Long time pumping in a high vacuum and 500 K annealing show negligible effects on removing the water adsorption on the devices. Current annealing at high source-drain bias is found to be able to remove the water adsorption and set the FETs to their initial states. The mechanism is proposed to be through the hot carriers at high bias.

Ultrathin MoS2 and WS2 layers on silver nano-tips as electron emitters

NASA Astrophysics Data System (ADS)

Loh, Tamie A. J.; Tanemura, Masaki; Chua, Daniel H. C.

2016-09-01

2-dimensional (2D) inorganic analogues of graphene such as MoS2 and WS2 present interesting opportunities for field emission technology due to their high aspect ratio and good electrical conductivity. However, research on 2D MoS2 and WS2 as potential field emitters remains largely undeveloped compared to graphene. Herein, we present an approach to directly fabricate ultrathin MoS2 and WS2 onto Ag nano-tips using pulsed laser deposition at low temperatures of 450-500 °C. In addition to providing a layer of chemical and mechanical protection for the Ag nano-tips, the growth of ultrathin MoS2 and WS2 layers on Ag led to enhanced emission properties over that of pristine nano-tips due to a reduction of the effective barrier height arising from charge injection from Ag to the overlying MoS2 or WS2. For WS2 on Ag nano-tips, the phasic mixture was also an important factor influencing the field emission performance. The presence of 1T-WS2 at the metal-WS2 interface in a hybrid film of 2H/1T-WS2 leads to improvement in the field emission capabilities as compared to pure 2H-WS2 on Ag nano-tips.

Synthesis of MoS2-reduced graphene oxide/Fe3O4 nanocomposite for enhanced electromagnetic interference shielding effectiveness

NASA Astrophysics Data System (ADS)

Prasad, Jagdees; Singh, Ashwani Kumar; Shah, Jyoti; Kotnala, R. K.; Singh, Kedar

2018-05-01

This article presents a facile two step hydrothermal process for the synthesis of MoS2-reduced graphene oxide/Fe3O4 (MoS2-rGO/Fe3O4) nanocomposite and its application as an excellent electromagnetic interference shielding material. Characterization tools like; scanning electron microscope, transmission electron microscope, x-ray diffraction, and Raman spectroscopy were used to confirm the formation of nanocomposite and found that spherical Fe3O4 nanoparticles are well dispersed over MoS2-rGO composite with average particle size ∼25–30 nm was confirmed by TEM. Structural characterization done by XRD was found inconsistent with the known lattice parameter of MoS2 nanosheet, reduced graphene oxide and Fe3O4 nanoparticles. Electromagnetic shielding effectiveness of MoS2-rGO/Fe3O4 nanocomposite was evaluated and found to be an excellent EMI shielding material in X-band range (8.0–12.0 GHz). MoS2-rGO composite shows poor shielding capacity (SET ∼ 3.81 dB) in entire range as compared to MoS2-rGO/Fe3O4 nanocomposite (SET ∼ 8.27 dB). It is due to interfacial polarization in the presence of EM field. The result indicates that MoS2-rGO/Fe3O4 nanocomposite provide a new stage for the next generation in high-performance EM wave absorption and EMI shielding effectiveness.

Tm-doped fiber laser mode-locking with MoS2-polyvinyl alcohol saturable absorber

NASA Astrophysics Data System (ADS)

Cao, Liming; Li, Xing; Zhang, Rui; Wu, Duanduan; Dai, Shixun; Peng, Jian; Weng, Jian; Nie, Qiuhua

2018-03-01

We have designed an all-fiber passive mode-locking thulium-doped fiber laser that uses molybdenum disulfide (MoS2) as a saturable absorber (SA) material. A free-standing few-layer MoS2-polyvinyl alcohol (PVA) film is fabricated by liquid phase exfoliation (LPE) and is then transferred onto the end face of a fiber connector. The excellent saturable absorption of the fabricated MoS2-based SA allows the laser to output soliton pulses at a pump power of 500 mW. Fundamental frequency mode-locking is realized at a repetition frequency of 13.9 MHz. The central wavelength is 1926 nm, the 3 dB spectral bandwidth is 2.86 nm and the pulse duration is 1.51 ps. Additionally, third-order harmonic mode-locking of the laser is also achieved. The pulse duration is 1.33 ps, which is slightly narrower than the fundamental frequency mode-locking bandwidth. The experimental results demonstrate that the few-layer MoS2-PVA SA is promising for use in 2 μm laser systems.

Chemical vapor deposition of high-quality large-sized MoS 2 crystals on silicon dioxide substrates

DOE PAGES

Chen, Jianyi; Tang, Wei; Tian, Bingbing; ...

2016-03-31

Large-sized MoS 2 crystals can be grown on SiO 2/Si substrates via a two-stage chemical vapor deposition method. The maximum size of MoS 2 crystals can be up to about 305 μm. The growth method can be used to grow other transition metal dichalcogenide crystals and lateral heterojunctions. Additionally, the electron mobility of the MoS 2 crystals can reach ≈30 cm 2 V –1 s –1, which is comparable to those of exfoliated flakes.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos.

PubMed

Vitale, Ilio; Senovilla, Laura; Jemaà, Mohamed; Michaud, Mickaël; Galluzzi, Lorenzo; Kepp, Oliver; Nanty, Lisa; Criollo, Alfredo; Rello-Varona, Santiago; Manic, Gwenola; Métivier, Didier; Vivet, Sonia; Tajeddine, Nicolas; Joza, Nicholas; Valent, Alexander; Castedo, Maria; Kroemer, Guido

2010-04-07

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

Coaxial metal-oxide-semiconductor (MOS) Au/Ga2O3/GaN nanowires.

PubMed

Hsieh, Chin-Hua; Chang, Mu-Tung; Chien, Yu-Jen; Chou, Li-Jen; Chen, Lih-Juann; Chen, Chii-Dong

2008-10-01

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

Enhanced photo-assistant electrocatalysis of anodization TiO2 nanotubes via surrounded surface decoration with MoS2 for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Tian, Yuanyuan; Song, Ye; Dou, Meiling; Ji, Jing; Wang, Feng

2018-03-01

A highly ordered TiO2 nanotube array covered with MoS2 is fabricated through a facile anodization of a metallic Ti followed by electrochemical deposition approach. The morphologies characterization of v-TiO2@MoS2 indicate that a whole scale of 1D TiO2nanotube uniformly covered with the MoS2 layer inside and outside, and the pathway inside the TiO2nanotube is kept flow-through. The as-synthesized v-TiO2@MoS2 hybrid exhibits higher efficient and stable visible light activities than that of either pure TiO2 nanotubes or nv-TiO2@MoS2 nanostructures. By electrochemical measurements such as linear sweep voltammetry(LSV) and electrochemical impedance spectroscope (EIS) under light illumination or in dark, we find that the v-TiO2@MoS2hybrid shows markedly enhanced photoelectrochemical performance. Furthermore, we compare the electrocatalytic behavior of v-TiO2@MoS2under illumination in H2SO4/Lactic acid within Na2S/NaSO3 solution. The results show that the photo-assistant electrocatalytic activity in acidic environment is much better than in alkaline environment. The highly directional and orthogonal separation of charge carriers between TiO2 nanotubes and MoS2 layer, together with maximally exposed MoS2 edges, light harvesting and junctions formed between TiO2 and MoS2 is supposed to be mainly responsible for the enhanced photo-assistant electrocatalytic activity of v-TiO2@MoS2.

2D Space-Confined Synthesis of Few-Layer MoS2 Anchored on Carbon Nanosheet for Lithium-Ion Battery Anode.

PubMed

Zhou, Jingwen; Qin, Jian; Zhang, Xiang; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun; Zhao, Naiqin; He, Chunnian

2015-04-28

A facile and scalable 2D spatial confinement strategy is developed for in situ synthesizing highly crystalline MoS2 nanosheets with few layers (≤5 layers) anchored on 3D porous carbon nanosheet networks (3D FL-MoS2@PCNNs) as lithium-ion battery anode. During the synthesis, 3D self-assembly of cubic NaCl particles is adopted to not only serve as a template to direct the growth of 3D porous carbon nanosheet networks, but also create a 2D-confined space to achieve the construction of few-layer MoS2 nanosheets robustly lain on the surface of carbon nanosheet walls. In the resulting 3D architecture, the intimate contact between the surfaces of MoS2 and carbon nanosheets can effectively avoid the aggregation and restacking of MoS2 as well as remarkably enhance the structural integrity of the electrode, while the conductive matrix of 3D porous carbon nanosheet networks can ensure fast transport of both electrons and ions in the whole electrode. As a result, this unique 3D architecture manifests an outstanding long-life cycling capability at high rates, namely, a specific capacity as large as 709 mAh g(-1) is delivered at 2 A g(-1) and maintains ∼95.2% even after 520 deep charge/discharge cycles. Apart from promising lithium-ion battery anode, this 3D FL-MoS2@PCNN composite also has immense potential for applications in other areas such as supercapacitor, catalysis, and sensors.

Tuning on-off current ratio and field-effect mobility in a MoS(2)-graphene heterostructure via Schottky barrier modulation.

PubMed

Shih, Chih-Jen; Wang, Qing Hua; Son, Youngwoo; Jin, Zhong; Blankschtein, Daniel; Strano, Michael S

2014-06-24

Field-effect transistor (FET) devices composed of a MoS2-graphene heterostructure can combine the advantages of high carrier mobility in graphene with the permanent band gap of MoS2 for digital applications. Herein, we investigate the electron transfer, photoluminescence, and gate-controlled carrier transport in such a heterostructure. We show that the junction is a Schottky barrier, whose height can be artificially controlled by gating or doping graphene. When the applied gate voltage (or the doping level) is zero, the photoexcited electron-hole pairs in monolayer MoS2 can be split by the heterojunction, significantly reducing the photoluminescence. By applying negative gate voltage (or p-doping) in graphene, the interlayer impedance formed between MoS2 and graphene exhibits an 100-fold increase. For the first time, we show that the gate-controlled interlayer Schottky impedance can be utilized to modulate carrier transport in graphene, significantly depleting the hole transport, but preserving the electron transport. Accordingly, we demonstrate a new type of FET device, which enables a controllable transition from NMOS digital to bipolar characteristics. In the NMOS digital regime, we report a very high room temperature on/off current ratio (ION/IOFF ∼ 36) in comparison to graphene-based FET devices without sacrificing the field-effect electron mobilities in graphene. By engineering the source/drain contact area, we further estimate that a higher value of ION/IOFF up to 100 can be obtained in the device architecture considered. The device architecture presented here may enable semiconducting behavior in graphene for digital and analogue electronics.

Copper nanoparticle interspersed MoS2 nanoflowers with enhanced efficiency for CO2 electrochemical reduction to fuel.

PubMed

Shi, Guodong; Yu, Luo; Ba, Xin; Zhang, Xiaoshu; Zhou, Jianqing; Yu, Ying

2017-08-15

Electrocatalytic conversion of carbon dioxide (CO 2 ) has been considered as an ideal method to simultaneously solve the energy crisis and environmental issue around the world. In this work, ultrasmall Cu nanoparticle interspersed flower-like MoS 2 was successfully fabricated via a facile microwave hydrothermal method. The designed optimal hierarchical Cu/MoS 2 composite not only exhibited remarkably enhanced electronic conductivity and specific surface area but also possessed improved CO 2 adsorption capacity, resulting in a significant increase in overall faradaic efficiency and a 7-fold augmentation of the faradaic efficiency of CH 4 in comparison with bare MoS 2 . In addition, the Cu/MoS 2 composite had superior stability with high efficiency retained for 48 h in the electrochemical process. It is anticipated that the designed Cu/MoS 2 composite electrocatalyst may provide new insights for transition metal sulfides and non-noble particles applied to CO 2 reduction.

Electron transfer kinetics on natural crystals of MoS2 and graphite.

PubMed

Velický, Matěj; Bissett, Mark A; Toth, Peter S; Patten, Hollie V; Worrall, Stephen D; Rodgers, Andrew N J; Hill, Ernie W; Kinloch, Ian A; Novoselov, Konstantin S; Georgiou, Thanasis; Britnell, Liam; Dryfe, Robert A W

2015-07-21

Here, we evaluate the electrochemical performance of sparsely studied natural crystals of molybdenite and graphite, which have increasingly been used for fabrication of next generation monolayer molybdenum disulphide and graphene energy storage devices. Heterogeneous electron transfer kinetics of several redox mediators, including Fe(CN)6(3-/4-), Ru(NH3)6(3+/2+) and IrCl6(2-/3-) are determined using voltammetry in a micro-droplet cell. The kinetics on both materials are studied as a function of surface defectiveness, surface ageing, applied potential and illumination. We find that the basal planes of both natural MoS2 and graphite show significant electroactivity, but a large decrease in electron transfer kinetics is observed on atmosphere-aged surfaces in comparison to in situ freshly cleaved surfaces of both materials. This is attributed to surface oxidation and adsorption of airborne contaminants at the surface exposed to an ambient environment. In contrast to semimetallic graphite, the electrode kinetics on semiconducting MoS2 are strongly dependent on the surface illumination and applied potential. Furthermore, while visibly present defects/cracks do not significantly affect the response of graphite, the kinetics on MoS2 systematically accelerate with small increase in disorder. These findings have direct implications for use of MoS2 and graphene/graphite as electrode materials in electrochemistry-related applications.

Effect of Dielectric Interface on the Performance of MoS2 Transistors.

PubMed

Li, Xuefei; Xiong, Xiong; Li, Tiaoyang; Li, Sichao; Zhang, Zhenfeng; Wu, Yanqing

2017-12-27

Because of their wide bandgap and ultrathin body properties, two-dimensional materials are currently being pursued for next-generation electronic and optoelectronic applications. Although there have been increasing numbers of studies on improving the performance of MoS 2 field-effect transistors (FETs) using various methods, the dielectric interface, which plays a decisive role in determining the mobility, interface traps, and thermal transport of MoS 2 FETs, has not been well explored and understood. In this article, we present a comprehensive experimental study on the effect of high-k dielectrics on the performance of few-layer MoS 2 FETs from 300 to 4.3 K. Results show that Al 2 O 3 /HfO 2 could boost the mobility and drain current. Meanwhile, MoS 2 transistors with Al 2 O 3 /HfO 2 demonstrate a 2× reduction in oxide trap density compared to that of the devices with the conventional SiO 2 substrate. Also, we observe a negative differential resistance effect on the device with 1 μm-channel length when using conventional SiO 2 as the gate dielectric due to self-heating, and this is effectively eliminated by using the Al 2 O 3 /HfO 2 gate dielectric. This dielectric engineering provides a highly viable route to realizing high-performance transition metal dichalcogenide-based FETs.

Transition metal dichalcogenide (WS2 and MoS2) saturable absorbers for Q-switched Er-doped fiber lasers

NASA Astrophysics Data System (ADS)

Li, Lu; Lv, Ruidong; Liu, Sicong; Wang, Xi; Wang, Yonggang; Chen, Zhendong; Wang, Jiang

2018-05-01

This report demonstrates a stable Q-switched Er-doped fiber laser with MoS2 (WS2)-based saturable absorber (SA) in the net normal dispersion regime. The SA is obtained by mixing MoS2 (WS2) nanosheets with polyvinyl alcohol (PVA) into polystyrene cells, and then evaporating them to form MoS2 (WS2)/PVA film. The modulation depth values for MoS2/PVA and WS2/PVA are measured to be 2.7% and 2.1% respectively. Employing the MoS2 (WS2)/PVA film in the Er-doped fiber laser cavity, stable Q-switching operation is achieved with central wavelength of 1560 nm. The shortest pulse durations of the two Q-switched fiber lasers are, respectively, 3.97 and 3.71 µs, and their maximum single pulse energies are measured to be 131.52 and 126.96 nJ. The experimental results clearly show that MoS2 (WS2) is a promising nonlinear material, and that improvements in Q-switching performance due to two SAs in the net normal dispersion regime might be helpful in the design of fiber lasers.

Half-metallic ferromagnetism prediction in MoS2-based two-dimensional superlattice from first-principles

NASA Astrophysics Data System (ADS)

Wen, Yan-Ni; Gao, Peng-Fei; Xia, Ming-Gang; Zhang, Sheng-Li

2018-03-01

Half-metallic ferromagnetism (HMFM) has great potential application in spin filter. However, it is extremely rare, especially in two-dimensional (2D) materials. At present, 2D materials have drawn international interest in spintronic devices. Here, we use ab initio density functional theory (DFT) calculations to study the structural stability and electrical and magnetic properties of the MoS2-based 2D superlattice formed by inserting graphene hexagonal ring in 6 × 6 × 1 MoS2 supercell. Two kinds of structures with hexagonal carbon ring were predicted with structural stability and were shown HMFM. The two structures combine the spin transport capacity of graphene with the magnetism of the defective 2D MoS2. And they have strong covalent bonding between the C and S or Mo atoms near the interface. This work is very useful to help us to design reasonable MoS2-based spin filter.

Fabrication of flexible MoS2 thin-film transistor arrays for practical gas-sensing applications.

PubMed

He, Qiyuan; Zeng, Zhiyuan; Yin, Zongyou; Li, Hai; Wu, Shixin; Huang, Xiao; Zhang, Hua

2012-10-08

By combining two kinds of solution-processable two-dimensional materials, a flexible transistor array is fabricated in which MoS(2) thin film is used as the active channel and reduced graphene oxide (rGO) film is used as the drain and source electrodes. The simple device configuration and the 1.5 mm-long MoS(2) channel ensure highly reproducible device fabrication and operation. This flexible transistor array can be used as a highly sensitive gas sensor with excellent reproducibility. Compared to using rGO thin film as the active channel, this new gas sensor exhibits much higher sensitivity. Moreover, functionalization of the MoS(2) thin film with Pt nanoparticles further increases the sensitivity by up to ∼3 times. The successful incorporation of a MoS(2) thin-film into the electronic sensor promises its potential application in various electronic devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Facile Synthesis of 1D/2D Core-Shell Structured Sb2S3@MoS2 Nanorods with Enhanced Photocatalytic Performance

NASA Astrophysics Data System (ADS)

Xu, Meilan; Zhao, Jiachang

2018-07-01

Herein, a novel core-shell heterojunction structure of molybdenum disulfide (MoS2) nanosheets coated antimony trisulfide (Sb2S3) nanorods (Sb2S3@MoS2) are designed and fabricated by a two-step hydrothermal method. The Sb2S3@MoS2 heterostructure consists of one-dimension (1D) Sb2S3 nanorods coated by two-dimension (2D) MoS2 nanosheets. When utilized as a photocatalyst under simulated sunlight, compared with pure Sb2S3 nanorods and MoS2 nanosheets, Sb2S3@MoS2 nanorods perform an enhanced photoactivity in degrading Rhodamine B (RhB) with a decomposition efficiency of 99%. The excellent photocatalytic property is attributed to the properly constructed heterojunction between Sb2S3 and MoS2, which can broaden the photoadsorption range. Furthermore, not only can the unique hybrid 1D/2D core-shell structures possess more reaction active sites, but also the compact interfaces between Sb2S3 and MoS2 provide rapid charge transfer channels for charge separation.

A theoretical study on reaction mechanisms and kinetics of thiophene hydrodesulfurization over MoS 2 catalysts

DOE PAGES

Jin, Qiu; Chen, Biaohua; Ren, Zhibo; ...

2018-02-10

In the present study, thiophene hydrodesulphurization (HDS) over the Mo-edge, the S-edge, and the Mo-S connection edge of MoS 2 catalyst with 50% sulfur coverage was studied using first-principles based microkinetic modeling. Two parallel HDS routes, i.e., direct desulfurization (DDS) and hydrogenation (HYD) were taken into account. It has been found that the major reaction route of thiophene HDS on the Mo- and the Mo-S edges is temperature dependent. In the low temperature range of 500–600 K, the HYD route is dominant, leading to the C 4H 8 formation. As the temperature increases, the DDS route becomes competitive with themore » HYD route. At the temperature above 650 K, the DDS route will be the dominant HDS reaction route on the Mo- and the Mo-S edges. The DDS route leading to the formation of C 4H 6 is the major thiophene HDS reaction route on the S-edge in the entire temperature range of 500–750 K. The microkinetic modeling results show the overall HDS activity on the S-edge is lower than it on the Mo- and the Mo-S edges. The Mo-S edge also provides a preferential reaction pathway, which facilitates 2-hydrothiophene migration from the Mo-edge to the S-edge, followed by remaining elementary steps with lower activation barriers in the DDS route.« less

A theoretical study on reaction mechanisms and kinetics of thiophene hydrodesulfurization over MoS 2 catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Qiu; Chen, Biaohua; Ren, Zhibo

In the present study, thiophene hydrodesulphurization (HDS) over the Mo-edge, the S-edge, and the Mo-S connection edge of MoS 2 catalyst with 50% sulfur coverage was studied using first-principles based microkinetic modeling. Two parallel HDS routes, i.e., direct desulfurization (DDS) and hydrogenation (HYD) were taken into account. It has been found that the major reaction route of thiophene HDS on the Mo- and the Mo-S edges is temperature dependent. In the low temperature range of 500–600 K, the HYD route is dominant, leading to the C 4H 8 formation. As the temperature increases, the DDS route becomes competitive with themore » HYD route. At the temperature above 650 K, the DDS route will be the dominant HDS reaction route on the Mo- and the Mo-S edges. The DDS route leading to the formation of C 4H 6 is the major thiophene HDS reaction route on the S-edge in the entire temperature range of 500–750 K. The microkinetic modeling results show the overall HDS activity on the S-edge is lower than it on the Mo- and the Mo-S edges. The Mo-S edge also provides a preferential reaction pathway, which facilitates 2-hydrothiophene migration from the Mo-edge to the S-edge, followed by remaining elementary steps with lower activation barriers in the DDS route.« less

Fabrication and investigation of the optoelectrical properties of MoS2/CdS heterojunction solar cells

PubMed Central

2014-01-01

Molybdenum disulfide (MoS2)/cadmium sulfide (CdS) heterojunction solar cells were successfully synthesized via chemical bath deposition (CBD) and chemical vapor deposition (CVD). The as-grown CdS film on a fluorine tin oxide (FTO) substrate deposited by CBD is continuous and compact. The MoS2 film deposited by CVD is homogeneous and continuous, with a uniform color and a thickness of approximately 10 nm. The optical absorption range of the MoS2/CdS heterojunction covers the visible and near-infrared spectral regions of 350 to 800 nm, which is beneficial for the improvement of solar cell efficiency. Moreover, the MoS2/CdS solar cell exhibits good current-voltage (I-V) characteristics and pronounced photovoltaic behavior, with an open-circuit voltage of 0.66 V and a short-circuit current density of 0.227 × 10-6 A/cm2, comparable to the results obtained from other MoS2-based solar cells. This research is critical to investigate more efficient and stable solar cells based on graphene-like materials in the future. PMID:25593552

Contact-Engineered Electrical Properties of MoS2 Field-Effect Transistors via Selectively Deposited Thiol-Molecules.

PubMed

Cho, Kyungjune; Pak, Jinsu; Kim, Jae-Keun; Kang, Keehoon; Kim, Tae-Young; Shin, Jiwon; Choi, Barbara Yuri; Chung, Seungjun; Lee, Takhee

2018-05-01

Although 2D molybdenum disulfide (MoS 2 ) has gained much attention due to its unique electrical and optical properties, the limited electrical contact to 2D semiconductors still impedes the realization of high-performance 2D MoS 2 -based devices. In this regard, many studies have been conducted to improve the carrier-injection properties by inserting functional paths, such as graphene or hexagonal boron nitride, between the electrodes and 2D semiconductors. The reported strategies, however, require relatively time-consuming and low-yield transfer processes on sub-micrometer MoS 2 flakes. Here, a simple contact-engineering method is suggested, introducing chemically adsorbed thiol-molecules as thin tunneling barriers between the metal electrodes and MoS 2 channels. The selectively deposited thiol-molecules via the vapor-deposition process provide additional tunneling paths at the contact regions, improving the carrier-injection properties with lower activation energies in MoS 2 field-effect transistors. Additionally, by inserting thiol-molecules at the only one contact region, asymmetric carrier-injection is feasible depending on the temperature and gate bias. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Faster Electron Injection and More Active Sites for Efficient Photocatalytic H2 Evolution in g-C3 N4 /MoS2 Hybrid.

PubMed

Shi, Xiaowei; Fujitsuka, Mamoru; Kim, Sooyeon; Majima, Tetsuro

2018-03-01

Herein, the structural effect of MoS 2 as a cocatalyst of photocatalytic H 2 generation activity of g-C 3 N 4 under visible light irradiation is studied. By using single-particle photoluminescence (PL) and femtosecond time-resolved transient absorption spectroscopies, charge transfer kinetics between g-C 3 N 4 and two kinds of nanostructured MoS 2 (nanodot and monolayer) are systematically investigated. Single-particle PL results show the emission of g-C 3 N 4 is quenched by MoS 2 nanodots more effectively than MoS 2 monolayers. Electron injection rate and efficiency of g-C 3 N 4 /MoS 2 -nanodot hybrid are calculated to be 5.96 × 10 9 s -1 and 73.3%, respectively, from transient absorption spectral measurement, which are 4.8 times faster and 2.0 times higher than those of g-C 3 N 4 /MoS 2 -monolayer hybrid. Stronger intimate junction between MoS 2 nanodots and g-C 3 N 4 is suggested to be responsible for faster and more efficient electron injection. In addition, more unsaturated terminal sulfur atoms can serve as the active site in MoS 2 nanodot compared with MoS 2 monolayer. Therefore, g-C 3 N 4 /MoS 2 nanodot exhibits a 7.9 times higher photocatalytic activity for H 2 evolution (660 µmol g- 1 h -1 ) than g-C 3 N 4 /MoS 2 monolayer (83.8 µmol g -1 h -1 ). This work provides deep insight into charge transfer between g-C 3 N 4 and nanostructured MoS 2 cocatalysts, which can open a new avenue for more rationally designing MoS 2 -based catalysts for H 2 evolution. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effects of surface polarity and dangling bonds on the electronic properties of MoS2 on SiO2

NASA Astrophysics Data System (ADS)

Sung, Ha-Jun; Choe, Duk-Hyun; Chang, Kee Joo

2015-03-01

MoS2 has recently attracted much attention due to its intriguing physical phenomena and possible applications for the next generation electronic devices. In pristine monolayer MoS2, strong spin-orbit coupling and inversion symmetry breaking allow for an effective coupling between the spin and valley degrees of freedom, inducing valley polarization at the K valleys. However, the spin-valley coupling disappears in bilayer MoS2 because the inversion symmetry is restored. In this work, we investigate the effects of surface polarity and dangling bonds on the electronic properties of MoS2 on α-quartz SiO2 through first-principles calculations. In monolayer MoS2, a transition can take place from the direct-gap to indirect-gap semiconductor in the presence of O dangling bonds. In bilayer MoS2, O dangling bonds induce dipole fields across the interface and thus break the inversion symmetry, resulting in the valley polarization, similar to that of pristine monolayer MoS2. Based on the results, we discuss the origin of the valley polarization observed in MoS2 deposited on SiO2 This work was supported by National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and by Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

Achieving Ohmic Contact for High-quality MoS2 Devices on Hexagonal Boron Nitride

NASA Astrophysics Data System (ADS)

Cui, Xu

MoS2, among many other transition metal dichalcogenides (TMDCs), holds great promise for future applications in nano-electronics, opto-electronics and mechanical devices due to its ultra-thin nature, flexibility, sizable band-gap, and unique spin-valley coupled physics. However, there are two main challenges that hinder careful study of this material. Firstly, it is hard to achieve Ohmic contacts to mono-layer MoS2, particularly at low temperatures (T) and low carrier densities. Secondly, materials' low quality and impurities introduced during the fabrication significantly limit the electron mobility of mono- and few-layer MoS2 to be substantially below theoretically predicted limits, which has hampered efforts to observe its novel quantum transport behaviours. Traditional low work function metals doesn't necessary provide good electron injection to thin MoS2 due to metal oxidation, Fermi level pinning, etc. To address the first challenge, we tried multiple contact schemes and found that mono-layer hexagonal boron nitride (h-BN) and cobalt (Co) provide robust Ohmic contact. The mono-layer spacer serves two advantageous purposes: it strongly interacts with the transition metal, reducing its work function by over 1 eV; and breaks the metal-TMDCs interaction to eliminate the interfacial states that cause Fermi level pinning. We measure a flat-band Schottky barrier of 16 meV, which makes thin tunnel barriers upon doping the channels, and thus achieve low-T contact resistance of 3 kohm.um at a carrier density of 5.3x10. 12/cm. 2. Similar to graphene, eliminating all potential sources of disorder and scattering is the key to achieving high performance in MoS2 devices. We developed a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within h-BN and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. The h-BN-encapsulation provides excellent protection from environmental factors, resulting in

Three-Dimensional Hierarchical MoS2 Nanosheets/Ultralong N-Doped Carbon Nanotubes as High-Performance Electromagnetic Wave Absorbing Material.

PubMed

Liu, Lianlian; Zhang, Shen; Yan, Feng; Li, Chunyan; Zhu, Chunling; Zhang, Xitian; Chen, Yujin

2018-04-25

Here, we report a simple method to grow thin MoS 2 nanosheets (NSs) on the ultralong nitrogen-doped carbon nanotubes through anion-exchange reaction. The MoS 2 NSs are grown on ultralong nitrogen-doped carbon nanotube surfaces, leading to an interesting three-dimensional hierarchical structure. The fabricated hybrid nanotubes have a length of approximately 100 μm, where the MoS 2 nanosheets have a thickness of less than 7.5 nm. The hybrid nanotubes show excellent electromagnetic wave attenuation performance, with the effective absorption bandwidth of 5.4 GHz at the thicknesses of 2.5 mm, superior to the pure MoS 2 nanosheets and the MoS 2 nanosheets grown on the short N-doped carbon nanotube surfaces. The experimental results indicate that the direct growth of MoS 2 on the ultralong nitrogen-doped carbon nanotube surfaces is a key factor for the enhanced electromagnetic wave attenuation property. The results open the avenue for the development of ultralong transition metal dichalcogenides for electromagnetic wave absorbers.

Structure and optical properties of 2D layered MoS2 crystals implemented with novel friction induced crystal growth

NASA Astrophysics Data System (ADS)

Tanabe, Tadao; Ito, Takafumi; Oyama, Yutaka

2018-03-01

We used X-ray diffraction, and Raman and photoluminescence (PL) spectroscopies to examine the structure and optical properties of molybdenum disulfide (MoS2) crystals grown by friction at the interface between two materials. MoS2 is produced chemically from molybdenum dithiocarbamates (MoDTC) in synthetic oil under sliding friction conditions. The X-ray diffraction (XRD) patterns indicate that the structure of the MoS2 is layered with the c-axis perpendicular to the surface. The MoS2 layer was formed on stainless steel and germanium by friction at the interface between these materials and high carbon chromium bearing steel. The number of layers is estimated to be N (N > 6) from the distance between the Raman frequencies of the E12g and A1g modes. For MoS2 grown on stainless steel, exciton peak is observed in the PL spectrum at room temperature. These results show that this friction induced crystal growth method is viable for synthesizing atomic layers of MoS2 at solid surfaces.

MoS2-coated microspheres of self-sensitized carbon nitride for efficient photocatalytic hydrogen generation under visible light irradiation

NASA Astrophysics Data System (ADS)

Gu, Quan; Sun, Huaming; Xie, Zunyuan; Gao, Ziwei; Xue, Can

2017-02-01

We have successfully coated the self-sensitized carbon nitride (SSCN) microspheres with a layer of MoS2 through a facile one-pot hydrothermal method by using (NH4)2MoS4 as the precursor. The resulted MoS2-coated SSCN photocatalyst appears as a core-shell structure and exhibits enhanced visible-light activities for photocatalytic H2 generation as compared to the un-coated SSCN and the standard g-C3N4 reference with MoS2 coating. The photocatalytic test results suggest that the oligomeric s-triazine dyes on the SSCN surface can provide additional light-harvesting capability and photogenerated charge carriers, and the coated MoS2 layer can serve as active sites for proton reduction towards H2 evolution. This synergistic effect of surface triazine dyes and MoS2 coating greatly promotes the activity of carbon nitride microspheres for vishible-light-driven H2 generation. This work provides a new way of future development of low-cost noble-metal-free photocatalysts for efficient solar-driven hydrogen production.

Efficient and stable MoS2 catalyst integrated on Si photocathodes by photoreduction and post-annealing for water splitting

NASA Astrophysics Data System (ADS)

Zhou, Jungui; Dai, Song; Dong, Wen; Su, Xiaodong; Fang, Liang; Zheng, Fengang; Wang, Xiongdong; Shen, Mingrong

2016-05-01

MoS2 has been studied as an efficient and cheap hydrogen evolution reaction (HER) catalyst; however, its effective integration with a photocathode remains a challenge. Here, crystalline MoS2 catalyst was deposited on top of a ˜2 nm Al2O3 protected n+p-Si photocathode using a simple photoreduction method following a post-annealing. The amount of MoS2 is optimized for HER of the photocathode, balanced between its catalytic effect and light absorption. High efficiency with 0.35 V onset potential vs. reversible hydrogen electrode and 34.5 mA/cm2 saturated photocurrent and high stability after 2 min ultrasonication or under 40 h continuous HER were observed. Such properties are much superior to the corresponding photocathodes coated by the traditional electrodeposited amorphous MoS2. Furthermore, the MoS2 layer is also an effective support for Pt nanoparticles with considerable reduction in the Pt amount while keeping the photoelectrochemical reactivity. This study indicates that the cheap-made MoS2 can be an efficient and stable HER catalyst for the Si photocathode.

Atmospheric pressure chemical vapor deposition: an alternative route to large-scale MoS2 and WS2 inorganic fullerene-like nanostructures and nanoflowers.

PubMed

Li, Xiao-Lin; Ge, Jian-Ping; Li, Ya-Dong

2004-11-19

Large-scale MoS2 and WS2 inorganic fullerene-like (IF) nanostructures (onionlike nanoparticles, nanotubes) and elegant three-dimensional nanoflowers (NF) have been selectively prepared through an atmospheric pressure chemical vapor deposition (APCVD) process with the reaction of chlorides and sulfur. The morphologies were controlled by adjusting the deposition position, the deposition temperature, and the flux of the carrier gas. All of the nanostructures have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A reaction mechanism is proposed based on the experimental results. The surface area of MoS2 IF nanoparticles and the field-emission effect of as-prepared WS2 nanoflowers is reported.

Humate-assisted Synthesis of MoS2/C Nanocomposites via Co-Precipitation/Calcination Route for High Performance Lithium Ion Batteries

NASA Astrophysics Data System (ADS)

Geng, Qin; Tong, Xin; Wenya, Gideon Evans; Yang, Chao; Wang, Jide; Maloletnev, A. S.; Wang, Zhiming M.; Su, Xintai

2018-04-01

A facile, cost-effective, non-toxic, and surfactant-free route has been developed to synthesize MoS2/carbon (MoS2/C) nanocomposites. Potassium humate consists of a wide variety of oxygen-containing functional groups, which is considered as promising candidates for functionalization of graphene. Using potassium humate as carbon source, two-dimensional MoS2/C nanosheets with irregular shape were synthesized via a stabilized co-precipitation/calcination process. Electrochemical performance of the samples as an anode of lithium ion battery was measured, demonstrating that the MoS2/C nanocomposite calcinated at 700 °C (MoS2/C-700) electrode showed outstanding performance with a high discharge capacity of 554.9 mAh g- 1 at a current density of 100 mA g- 1 and the Coulomb efficiency of the sample maintained a high level of approximately 100% after the first 3 cycles. Simultaneously, the MoS2/C-700 electrode exhibited good cycling stability and rate performance. The success in synthesizing MoS2/C nanocomposites via co-precipitation/calcination route may pave a new way to realize promising anode materials for high-performance lithium ion batteries.

Schottky Barrier Height of Pd/MoS2 Contact by Large Area Photoemission Spectroscopy.

PubMed

Dong, Hong; Gong, Cheng; Addou, Rafik; McDonnell, Stephen; Azcatl, Angelica; Qin, Xiaoye; Wang, Weichao; Wang, Weihua; Hinkle, Christopher L; Wallace, Robert M

2017-11-08

MoS 2 , as a model transition metal dichalcogenide, is viewed as a potential channel material in future nanoelectronic and optoelectronic devices. Minimizing the contact resistance of the metal/MoS 2 junction is critical to realizing the potential of MoS 2 -based devices. In this work, the Schottky barrier height (SBH) and the band structure of high work function Pd metal on MoS 2 have been studied by in situ X-ray photoelectron spectroscopy (XPS). The analytical spot diameter of the XPS spectrometer is about 400 μm, and the XPS signal is proportional to the detection area, so the influence of defect-mediated parallel conduction paths on the SBH does not affect the measurement. The charge redistribution by Pd on MoS 2 is detected by XPS characterization, which gives insight into metal contact physics to MoS 2 and suggests that interface engineering is necessary to lower the contact resistance for the future generation electronic applications.

Imaging Electron Motion in a Few Layer MoS2 Device

NASA Astrophysics Data System (ADS)

Bhandari, S.; Wang, K.; Watanabe, K.; Taniguchi, T.; Kim, P.; Westervelt, R. M.

2017-06-01

Ultrathin sheets of MoS2 are a newly discovered 2D semiconductor that holds great promise for nanoelectronics. Understanding the pattern of current flow will be crucial for developing devices. In this talk, we present images of current flow in MoS2 obtained with a Scanned Probe Microscope (SPM) cooled to 4 K. We previously used this technique to image electron trajectories in GaAs/AlGaAs heterostructures and graphene. The charged SPM tip is held just above the sample surface, creating an image charge inside the device that scatters electrons. By measuring the change in resistance ΔR while the tip is raster scanned above the sample, an image of electron flow is obtained. We present images of electron flow in an MoS2 device patterned into a hall bar geometry. A three-layer MoS2 sheet is encased by two hBN layers, top and bottom, and patterned into a hall-bar with multilayer graphene contacts. An SPM image shows the current flow pattern from the wide contact at the end of the device for a Hall density n = 1.3×1012 cm-2. The SPM tip tends to block flow, increasing the resistance R. The pattern of flow was also imaged for a narrow side contact on the sample. At density n = 5.4×1011 cm-2; the pattern seen in the SPM image is similar to the wide contact. The ability to image electron flow promises to be very useful for the development of ultrathin devices from new 2D materials.

Measuring oral health during pregnancy: sensitivity and specificity of a maternal oral screening (MOS) tool.

PubMed

George, Ajesh; Dahlen, Hannah G; Blinkhorn, Anthony; Ajwani, Shilpi; Bhole, Sameer; Ellis, Sharon; Yeo, Anthony; Elcombe, Emma; Sadozai, Ayesha; Johnson, Maree

2016-11-09

Midwives can play a key role in promoting the oral health of pregnant women and assessing their oral health status. A maternal oral assessment tool (MOS) was developed and pilot tested by the study investigators to assist midwives in this role and the results were promising. The aim of this study was to undertake further sensitivity and specificity assessment of the MOS tool using two-comparison approaches- the longer oral health screening tool known as the Oral Health Impact Profile (OHIP-14) and an oral assessment by trained study dentists. Pregnant women were recruited for this study as part of a larger randomised controlled trial of a Midwifery Initiated Oral Health (MIOH) program. Pregnant women completed the MOS and OHIP-14 as part of their initial assessment undertaken by 38 trained and accredited midwives. A dental assessment was conducted for all women in the intervention group using three trained study dentists with high inter rater reliability. Two hundred and eleven pregnant women participated in the validation of the MOS tool. Results from both approaches found the MOS tool to have high sensitivity, correctly identifying 88-94 % of women at risk of poor dental health, and low specificity (14-21 %). This study has shown that the MOS tool can be successfully implemented by midwives during a woman's first antenatal visit and can identify up to 94 % of women at risk of poor oral health and needing a dental referral. The tool has the potential to be transferable to other antenatal care providers and could be incorporated into hospital obstetric database systems. ACTRN12612001271897 , 6 th Dec 2012, retrospectively registered.

Nanoimprint-Assisted Shear Exfoliation (NASE) for Producing Multilayer MoS2 Structures as Field-Effect Transistor Channel Arrays.

PubMed

Chen, Mikai; Nam, Hongsuk; Rokni, Hossein; Wi, Sungjin; Yoon, Jeong Seop; Chen, Pengyu; Kurabayashi, Katsuo; Lu, Wei; Liang, Xiaogan

2015-09-22

MoS2 and other semiconducting transition metal dichalcogenides (TMDCs) are of great interest due to their excellent physical properties and versatile chemistry. Although many recent research efforts have been directed to explore attractive properties associated with MoS2 monolayers, multilayer/few-layer MoS2 structures are indeed demanded by many practical scale-up device applications, because multilayer structures can provide sizable electronic/photonic state densities for driving upscalable electrical/optical signals. Currently there is a lack of processes capable of producing ordered, pristine multilayer structures of MoS2 (or other relevant TMDCs) with manufacturing-grade uniformity of thicknesses and electronic/photonic properties. In this article, we present a nanoimprint-based approach toward addressing this challenge. In this approach, termed as nanoimprint-assisted shear exfoliation (NASE), a prepatterned bulk MoS2 stamp is pressed into a polymeric fixing layer, and the imprinted MoS2 features are exfoliated along a shear direction. This shear exfoliation can significantly enhance the exfoliation efficiency and thickness uniformity of exfoliated flakes in comparison with previously reported exfoliation processes. Furthermore, we have preliminarily demonstrated the fabrication of multiple transistors and biosensors exhibiting excellent device-to-device performance consistency. Finally, we present a molecular dynamics modeling analysis of the scaling behavior of NASE. This work holds significant potential to leverage the superior properties of MoS2 and other emerging TMDCs for practical scale-up device applications.

Current-mode subthreshold MOS implementation of the Herault-Jutten autoadaptive network

NASA Astrophysics Data System (ADS)

Cohen, Marc H.; Andreou, Andreas G.

1992-05-01

The translinear circuits in subthreshold MOS technology and current-mode design techniques for the implementation of neuromorphic analog network processing are investigated. The architecture, also known as the Herault-Jutten network, performs an independent component analysis and is essentially a continuous-time recursive linear adaptive filter. Analog I/O interface, weight coefficients, and adaptation blocks are all integrated on the chip. A small network with six neurons and 30 synapses was fabricated in a 2-microns n-well double-polysilicon, double-metal CMOS process. Circuit designs at the transistor level yield area-efficient implementations for neurons, synapses, and the adaptation blocks. The design methodology and constraints as well as test results from the fabricated chips are discussed.

[A validation of the MOS-HIV quality of life measure in HIV-infected patients in Mexico].

PubMed

Peña de León, Edilberto; Aguilar Gaytán, Sandra Socorro; Suárez Mendoza, Aldo Antonio; Reyes Terán, Gustavo

2007-05-01

To validate the Medical Outcomes Study HIV Health Survey (MOS-HIV) quality of life instrument for its application in clinical research in Mexico. The data for this study were collected between April, 2002, and February, 2004. An expert committee combined two Spanish-language translations of the MOS-HIV questionnaire. The new questionnaire's feasibility was assessed in a group of 32 HIV-infected persons by measuring how long they took to complete the questionnaire and the numbers of items they left unanswered. The questionnaire was then applied to a group of 120 HIV-positive patients and to a control group of 102 HIV-negative individuals. The following questionnaire characteristics were evaluated: (1) internal reliability (Cronbach alpha coefficient), (2) discriminant validity (the receiver operating characteristic (ROC) curves derived from the scores of the two groups), and (3) convergent validity (the Spearman correlation coefficients for the scores of the HIV-positive patients on the 11 MOS-HIV dimensions and their scores on the analog visual scale of the European Quality of Life 5-Dimensional format (EQ-5D) questionnaire, a list of symptoms, the viral load, and the CD4 cell count). The mean response time with the questionnaire was 10 minutes and 22 seconds, and the mean number of unanswered items was 0.62. With each of the 11 dimensions of the questionnaire, the Cronbach alpha coefficient was at least 0.75. The mean scores obtained by the two groups were different for 9 of the 11 dimensions, and the 95% confidence intervals of the areas under the ROC curves did not include the value of 0.5 for 8 of the dimensions. The absolute value of the Spearman correlation coefficient was less than 0.3 for the CD4 cell count and for the viral load, and it was greater than 0.3 for each dimension and the scores on the list of symptoms and on the analog visual scale of the EQ-5D questionnaire. The MOS-HIV measure is valid for use in clinical research among HIV-infected persons

Biocompatible PEGylated MoS2 nanosheets: controllable bottom-up synthesis and highly efficient photothermal regression of tumor.

PubMed

Wang, Shige; Li, Kai; Chen, Yu; Chen, Hangrong; Ma, Ming; Feng, Jingwei; Zhao, Qinghua; Shi, Jianlin

2015-01-01

Two-dimensional transition metal dichalcogenides, particularly MoS2 nanosheets, have been deemed as a novel category of NIR photothermal transducing agent. Herein, an efficient and versatile one-pot solvothermal synthesis based on "bottom-up" strategy has been, for the first time, proposed for the controlled synthesis of PEGylated MoS2 nanosheets by using a novel "integrated" precursor containing both Mo and S elements. This facile but unique PEG-mediated solvothermal procedure endowed MoS2 nanosheets with controlled size, increased crystallinity and excellent colloidal stability. The photothermal performance of nanosheets was optimized via modulating the particulate size and surface PEGylation. PEGylated MoS2 nanosheets with desired photothermal conversion performance and excellent colloidal and photothermal stability were further utilized for highly efficient photothermal therapy of cancer in a tumor-bearing mouse xenograft. Without showing observable in vitro and in vivo hemolysis, coagulation and toxicity, the optimized MoS2-PEG nanosheets showed promising in vitro and in vivo anti-cancer efficacy. Copyright © 2014 Elsevier Ltd. All rights reserved.

Lateral MoS2 p-n junction formed by chemical doping for use in high-performance optoelectronics.

PubMed

Choi, Min Sup; Qu, Deshun; Lee, Daeyeong; Liu, Xiaochi; Watanabe, Kenji; Taniguchi, Takashi; Yoo, Won Jong

2014-09-23

This paper demonstrates a technique to form a lateral homogeneous 2D MoS2 p-n junction by partially stacking 2D h-BN as a mask to p-dope MoS2. The fabricated lateral MoS2 p-n junction with asymmetric electrodes of Pd and Cr/Au displayed a highly efficient photoresponse (maximum external quantum efficiency of ∼7000%, specific detectivity of ∼5 × 10(10) Jones, and light switching ratio of ∼10(3)) and ideal rectifying behavior. The enhanced photoresponse and generation of open-circuit voltage (VOC) and short-circuit current (ISC) were understood to originate from the formation of a p-n junction after chemical doping. Due to the high photoresponse at low VD and VG attributed to its built-in potential, our MoS2 p-n diode made progress toward the realization of low-power operating photodevices. Thus, this study suggests an effective way to form a lateral p-n junction by the h-BN hard masking technique and to improve the photoresponse of MoS2 by the chemical doping process.

High-temperature performance of MoS2 thin-film transistors: Direct current and pulse current-voltage characteristics

NASA Astrophysics Data System (ADS)

Jiang, C.; Rumyantsev, S. L.; Samnakay, R.; Shur, M. S.; Balandin, A. A.

2015-02-01

We report on fabrication of MoS2 thin-film transistors (TFTs) and experimental investigations of their high-temperature current-voltage characteristics. The measurements show that MoS2 devices remain functional to temperatures of at least as high as 500 K. The temperature increase results in decreased threshold voltage and mobility. The comparison of the direct current (DC) and pulse measurements shows that the direct current sub-linear and super-linear output characteristics of MoS2 thin-films devices result from the Joule heating and the interplay of the threshold voltage and mobility temperature dependences. At temperatures above 450 K, a kink in the drain current occurs at zero gate voltage irrespective of the threshold voltage value. This intriguing phenomenon, referred to as a "memory step," was attributed to the slow relaxation processes in thin films similar to those in graphene and electron glasses. The fabricated MoS2 thin-film transistors demonstrated stable operation after two months of aging. The obtained results suggest new applications for MoS2 thin-film transistors in extreme-temperature electronics and sensors.

Simulating Excitons in MoS2 with Time-Dependent Density Functional Theory

NASA Astrophysics Data System (ADS)

Flamant, Cedric; Kolesov, Grigory; Kaxiras, Efthimios

Monolayer molybdenum disulfide, owing to its graphene-like two-dimensional geometry whilst still having a finite bandgap, is a material of great interest in condensed matter physics and for potential application in electronic devices. In particular, MoS2 exhibits significant excitonic effects, a desirable quality for fundamental many-body research. Time-dependent density functional theory (TD-DFT) allows us to simulate dynamical effects as well as temperature-based effects in a natural way given the direct treatment of the time evolution of the system. We present a TD-DFT study of monolayer MoS2 exciton dynamics, examining various qualitative and quantitative predictions in pure samples and in the presence of defects. In particular, we generate an absorption spectrum through simulated pulse excitation for comparison to experiment and also analyze the response of the exciton in an external electric field.In this work we also discuss the electronic structure of the exciton in MoS2 with and without vacancies.

Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer

PubMed Central

Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J.

2016-01-01

Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack. PMID:27279454

Improved Gate Dielectric Deposition and Enhanced Electrical Stability for Single-Layer MoS2 MOSFET with an AlN Interfacial Layer.

PubMed

Qian, Qingkai; Li, Baikui; Hua, Mengyuan; Zhang, Zhaofu; Lan, Feifei; Xu, Yongkuan; Yan, Ruyue; Chen, Kevin J

2016-06-09

Transistors based on MoS2 and other TMDs have been widely studied. The dangling-bond free surface of MoS2 has made the deposition of high-quality high-k dielectrics on MoS2 a challenge. The resulted transistors often suffer from the threshold voltage instability induced by the high density traps near MoS2/dielectric interface or inside the gate dielectric, which is detrimental for the practical applications of MoS2 metal-oxide-semiconductor field-effect transistor (MOSFET). In this work, by using AlN deposited by plasma enhanced atomic layer deposition (PEALD) as an interfacial layer, top-gate dielectrics as thin as 6 nm for single-layer MoS2 transistors are demonstrated. The AlN interfacial layer not only promotes the conformal deposition of high-quality Al2O3 on the dangling-bond free MoS2, but also greatly enhances the electrical stability of the MoS2 transistors. Very small hysteresis (ΔVth) is observed even at large gate biases and high temperatures. The transistor also exhibits a low level of flicker noise, which clearly originates from the Hooge mobility fluctuation instead of the carrier number fluctuation. The observed superior electrical stability of MoS2 transistor is attributed to the low border trap density of the AlN interfacial layer, as well as the small gate leakage and high dielectric strength of AlN/Al2O3 dielectric stack.

Bonding between graphene and MoS 2 monolayers without and with Li intercalation

DOE PAGES

Ahmed, Towfiq; Modine, N. A.; Zhu, Jian-Xin

2015-07-27

We performed density functional theory (DFT) calculations for a bi-layered heterostructure combining a graphene layer with a MoS 2 layer with and without intercalated Li atoms. Our calculations demonstrate the importance of the van der Waals (vdW) interaction, which is crucial for forming stable bonding between the layers. Our DFT calculation correctly reproduces the linear dispersion, or Dirac cone, feature at the Fermi energy for the isolated graphene monolayer and the band gap for the MoS 2 monolayer. For the combined graphene/MoS 2 bi-layer, we observe interesting electronic structure and density of states (DOS) characteristics near the Fermi energy, showingmore » both the gap like features of the MoS 2 layer and in-gap states with linear dispersion contributed mostly by the graphene layer. Our calculated total DOS in this vdW heterostructure reveals that the graphene layer significantly contributes to pinning the Fermi energy at the center of the band gap of MoS 2. We also find that intercalating Li ions in between the layers of the graphene/MoS2 heterostructure enhances the binding energy through orbital hybridizations between cations (Li adatoms) and anions (graphene and MoS 2 monolayers). Moreover, we calculate the dielectric function of the Li intercalated graphene/MoS 2 heterostructure, the imaginary component of which can be directly compared with experimental measurements of optical conductivity in order to validate our theoretical prediction. We observe sharp features in the imaginary component of the dielectric function, which shows the presence of a Drude peak in the optical conductivity, and therefore metallicity in the lithiated graphene/MoS 2 heterostructure.« less

Electrical transport and structural characterization of epitaxial monolayer MoS2 /n- and p-doped GaN vertical lattice-matched heterojunctions

NASA Astrophysics Data System (ADS)

Ruzmetov, D.; O'Regan, T.; Zhang, K.; Herzing, A.; Mazzoni, A.; Chin, M.; Huang, S.; Zhang, Z.; Burke, R.; Neupane, M.; Birdwell, Ag; Shah, P.; Crowne, F.; Kolmakov, A.; Leroy, B.; Robinson, J.; Davydov, A.; Ivanov, T.

We investigate vertical semiconductor junctions consisting of monolayer MoS2 that is epitaxially grown on n- and p-doped GaN crystals. Such a junction represents a building block for 2D/3D vertical semiconductor heterostructures. Epitaxial, lattice-matched growth of MoS2 on GaN is important to ensure high quality interfaces that are crucial for the efficient vertical transport. The MoS2/GaN junctions were characterized with cross-sectional and planar scanning transmission electron microscopy (STEM), scanning tunneling microscopy, and atomic force microscopy. The MoS2/GaN lattice mismatch is measured to be near 1% using STEM. The electrical transport in the out-of-plane direction across the MoS2/GaN junctions was measured using conductive atomic force microscopy and mechanical nano-probes inside a scanning electron microscope. Nano-disc metal contacts to MoS2 were fabricated by e-beam lithography and evaporation. The current-voltage curves of the vertical MoS2/GaN junctions exhibit rectification with opposite polarities for n-doped and p-doped GaN. The metal contact determines the general features of the current-voltage curves, and the MoS2 monolayer modifies the electrical transport across the contact/GaN interface.

Spectroscopic signatures of AA' and AB stacking of chemical vapor deposited bilayer MoS 2

DOE PAGES

Xia, Ming; Li, Bo; Yin, Kuibo; ...

2015-11-04

We discuss prominent resonance Raman and photoluminescence spectroscopic differences between AA'and AB stacked bilayer molybdenum disulfide (MoS 2) grown by chemical vapor deposition are reported. Bilayer MoS 2 islands consisting of the two stacking orders were obtained under identical growth conditions. Also, resonance Raman and photoluminescence spectra of AA' and AB stacked bilayer MoS 2 were obtained on Au nanopyramid surfaces under strong plasmon resonance. Both resonance Raman and photoluminescence spectra show distinct features indicating clear differences in interlayer interaction between these two phases. The implication of these findings on device applications based on spin and valley degrees of freedom.

Two-dimensional Layered MoS2 Biosensors Enable Highly Sensitive Detection of Biomolecules

NASA Astrophysics Data System (ADS)

Lee, Joonhyung; Dak, Piyush; Lee, Yeonsung; Park, Heekyeong; Choi, Woong; Alam, Muhammad A.; Kim, Sunkook

2014-12-01

We present a MoS2 biosensor to electrically detect prostate specific antigen (PSA) in a highly sensitive and label-free manner. Unlike previous MoS2-FET-based biosensors, the device configuration of our biosensors does not require a dielectric layer such as HfO2 due to the hydrophobicity of MoS2. Such an oxide-free operation improves sensitivity and simplifies sensor design. For a quantitative and selective detection of PSA antigen, anti-PSA antibody was immobilized on the sensor surface. Then, introduction of PSA antigen, into the anti-PSA immobilized sensor surface resulted in a lable-free immunoassary format. Measured off-state current of the device showed a significant decrease as the applied PSA concentration was increased. The minimum detectable concentration of PSA is 1 pg/mL, which is several orders of magnitude below the clinical cut-off level of ~4 ng/mL. In addition, we also provide a systematic theoretical analysis of the sensor platform - including the charge state of protein at the specific pH level, and self-consistent channel transport. Taken together, the experimental demonstration and the theoretical framework provide a comprehensive description of the performance potential of dielectric-free MoS2-based biosensor technology.

Enhancement of photovoltaic response in multilayer MoS2 induced by plasma doping.

PubMed

Wi, Sungjin; Kim, Hyunsoo; Chen, Mikai; Nam, Hongsuk; Guo, L Jay; Meyhofer, Edgar; Liang, Xiaogan

2014-05-27

Layered transition-metal dichalcogenides hold promise for making ultrathin-film photovoltaic devices with a combination of excellent photovoltaic performance, superior flexibility, long lifetime, and low manufacturing cost. Engineering the proper band structures of such layered materials is essential to realize such potential. Here, we present a plasma-assisted doping approach for significantly improving the photovoltaic response in multilayer MoS2. In this work, we fabricated and characterized photovoltaic devices with a vertically stacked indium tin oxide electrode/multilayer MoS2/metal electrode structure. Utilizing a plasma-induced p-doping approach, we are able to form p-n junctions in MoS2 layers that facilitate the collection of photogenerated carriers, enhance the photovoltages, and decrease reverse dark currents. Using plasma-assisted doping processes, we have demonstrated MoS2-based photovoltaic devices exhibiting very high short-circuit photocurrent density values up to 20.9 mA/cm(2) and reasonably good power-conversion efficiencies up to 2.8% under AM1.5G illumination, as well as high external quantum efficiencies. We believe that this work provides important scientific insights for leveraging the optoelectronic properties of emerging atomically layered two-dimensional materials for photovoltaic and other optoelectronic applications.

Double gate impact ionization MOS transistor: Proposal and investigation

NASA Astrophysics Data System (ADS)

Yang, Zhaonian; Zhang, Yue; Yang, Yuan; Yu, Ningmei

2017-02-01

In this paper, a double gate impact ionization MOS (DG-IMOS) transistor with improved performance is proposed and investigated by TCAD simulation. In the proposed design, a second gate is introduced in a conventional impact ionization MOS (IMOS) transistor that lengthens the equivalent channel length and suppresses the band-to-band tunneling. The OFF-state leakage current is reduced by over four orders of magnitude. At the ON-state, the second gate is negatively biased in order to enhance the electric field in the intrinsic region. As a result, the operating voltage does not increase with the increase in the channel length. The simulation result verifies that the proposed DG-IMOS achieves a better switching characteristic than the conventional is achieved. Lastly, the application of the DG-IMOS is discussed theoretically.

A theoretical prediction of super high-performance thermoelectric materials based on MoS2/WS2 hybrid nanoribbons

NASA Astrophysics Data System (ADS)

Zhang, Zhongwei; Xie, Yuee; Peng, Qing; Chen, Yuanping

2016-02-01

Modern society is hungry for electrical power. To improve the efficiency of energy harvesting from heat, extensive efforts seek high-performance thermoelectric materials that possess large differences between electronic and thermal conductance. Here we report a super high-performance material of consisting of MoS2/WS2 hybrid nanoribbons discovered from a theoretical investigation using nonequilibrium Green’s function methods combined with first-principles calculations and molecular dynamics simulations. The hybrid nanoribbons show higher efficiency of energy conversion than the MoS2 and WS2 nanoribbons due to the fact that the MoS2/WS2 interface reduces lattice thermal conductivity more than the electron transport. By tuning the number of the MoS2/WS2 interfaces, a figure of merit ZT as high as 5.5 is achieved at a temperature of 600 K. Our results imply that the MoS2/WS2 hybrid nanoribbons have promising applications in thermal energy harvesting.

A theoretical prediction of super high-performance thermoelectric materials based on MoS2/WS2 hybrid nanoribbons

PubMed Central

Zhang, Zhongwei; Xie, Yuee; Peng, Qing; Chen, Yuanping

2016-01-01

Modern society is hungry for electrical power. To improve the efficiency of energy harvesting from heat, extensive efforts seek high-performance thermoelectric materials that possess large differences between electronic and thermal conductance. Here we report a super high-performance material of consisting of MoS2/WS2 hybrid nanoribbons discovered from a theoretical investigation using nonequilibrium Green’s function methods combined with first-principles calculations and molecular dynamics simulations. The hybrid nanoribbons show higher efficiency of energy conversion than the MoS2 and WS2 nanoribbons due to the fact that the MoS2/WS2 interface reduces lattice thermal conductivity more than the electron transport. By tuning the number of the MoS2/WS2 interfaces, a figure of merit ZT as high as 5.5 is achieved at a temperature of 600 K. Our results imply that the MoS2/WS2 hybrid nanoribbons have promising applications in thermal energy harvesting. PMID:26884123

Comparitive study of fluorescence lifetime quenching of rhodamine 6G by MoS2 and Au-MoS2

NASA Astrophysics Data System (ADS)

Shakya, Jyoti; Kasana, Parath; Mohanty, T.

2018-04-01

Time resolved fluorescence study of Rhodamine 6G (R6G) in the presence of Molybdenum disulfide (MoS2) nanosheets and gold doped MoS2 (Au-MoS2) have been carried out and discussed. We have analyzed the fluorescence decay curves of R6G and it is observed that Au-MoS2 is a better fluorescence lifetime quencher as compare to MoS2 nanosheets. Also, the energy transfer efficiency and energy transfer rate from R6G to MoS2 and Au-MoS2 has been calculated and found higher for Au-MoS2.

Tribological properties of sputtered MoS sub 2 films in relation to film morphology

NASA Technical Reports Server (NTRS)

Spalvins, T.

1980-01-01

Thin sputter deposited MoS2 films in the 2000 to 6000 A thickness range have shown excellent lubricating properties, when sputtering parameters and substrate conditions are properly selected and precisely controlled. The lubricating properties of sputtered MoS2 films are strongly influenced by their crystalline-amorphous structure, morphology and composition. The coefficient of friction can range from 0.04 which is effective lubrication to 0.4 which reflects an absence of lubricating properties. Visual screening and slight wiping of the as-sputtered MoS2 film can identify the integrity of the film. An acceptable film displays a black-sooty surface appearance whereas an unacceptable film has a highly reflective, gray surface and the film is hard and brittle.

Origin of band bending at domain boundaries of MoS2: First-principles study

NASA Astrophysics Data System (ADS)

Kaneko, Tomoaki; Saito, Riichiro

2018-04-01

Using first-principles calculations based on density functional theory, the energetics and electronic structure of domain boundaries of MoS2, in which the same polar edges face each other, are investigated. We find that the interface model with homoelemental bonds is not energetically preferred in this system. The domain boundaries have defect levels that have wide distributions inside the band gap of MoS2. The upshift (or downshift) of the MoS2 energy band occurs around the domain boundaries when the occupation number of electrons in the defect levels increases (or decreases). The charge transfer of electrons from the graphite substrate plays an important role in band bending, which is observed in the recent experiments by scanning tunneling microscopy/spectroscopy.

The Synergistic Effects of MoS2 and Liquid Lubrication

NASA Astrophysics Data System (ADS)

Buttery, M.; Roberts, E.; Stanley, S.; Murer, J.

2015-09-01

We present an overview of a three-stage program on the potential for hybrid lubrication of MoS2 and PFPE fluids (Fomblin Z25 & Braycote 601EF) performed at the European Space Tribology Laboratory (ESTL).Tests were performed using a spiral orbit tribometer (SOT) and a pin-on-disc tribometer (POD), demonstrating encouraging results. Hybrid lubrication allows for extended periods of in-air running of MoS2 with no detrimental effect to the subsequent in-vacuum lifetime. In addition, hybrid lubrication was shown to be synergistic, with the lifetime of the hybrid fluid/MoS2 lubrication extended in comparison to the individual constituents, with no detriment to the friction.

Structural stability of coplanar 1T-2H superlattice MoS2 under high energy electron beam.

PubMed

Reshmi, S; Akshaya, M V; Satpati, Biswarup; Basu, Palash Kumar; Bhattacharjee, K

2018-05-18

Coplanar heterojunctions composed of van der Waals layered materials with different structural polymorphs have drawn immense interest recently due to low contact resistance and high carrier injection rate owing to low Schottky barrier height. Present research has largely focused on efficient exfoliation of these layered materials and their restacking to achieve better performances. We present here a microwave assisted easy, fast and efficient route to induce high concentration of metallic 1T phase in the original 2H matrix of exfoliated MoS 2 layers and thus facilitating the formation of a 1T-2H coplanar superlattice phase. High resolution transmission electron microscopy (HRTEM) investigations reveal formation of highly crystalline 1T-2H hybridized structure with sharp interface and disclose the evidence of surface ripplocations within the same exfoliated layer of MoS 2 . In this work, the structural stability of 1T-2H superlattice phase during HRTEM measurements under an electron beam of energy 300 keV is reported. This structural stability could be either associated to the change in electronic configuration due to induction of the restacked hybridized phase with 1T- and 2H-regions or to the formation of the surface ripplocations. Surface ripplocations can act as an additional source of scattering centers to the electron beam and also it is possible that a pulse train of propagating ripplocations can sweep out the defects via interaction from specific areas of MoS 2 sheets.

Structural stability of coplanar 1T-2H superlattice MoS2 under high energy electron beam

NASA Astrophysics Data System (ADS)

Reshmi, S.; Akshaya, M. V.; Satpati, Biswarup; Basu, Palash Kumar; Bhattacharjee, K.

2018-05-01

Coplanar heterojunctions composed of van der Waals layered materials with different structural polymorphs have drawn immense interest recently due to low contact resistance and high carrier injection rate owing to low Schottky barrier height. Present research has largely focused on efficient exfoliation of these layered materials and their restacking to achieve better performances. We present here a microwave assisted easy, fast and efficient route to induce high concentration of metallic 1T phase in the original 2H matrix of exfoliated MoS2 layers and thus facilitating the formation of a 1T-2H coplanar superlattice phase. High resolution transmission electron microscopy (HRTEM) investigations reveal formation of highly crystalline 1T-2H hybridized structure with sharp interface and disclose the evidence of surface ripplocations within the same exfoliated layer of MoS2. In this work, the structural stability of 1T-2H superlattice phase during HRTEM measurements under an electron beam of energy 300 keV is reported. This structural stability could be either associated to the change in electronic configuration due to induction of the restacked hybridized phase with 1T- and 2H-regions or to the formation of the surface ripplocations. Surface ripplocations can act as an additional source of scattering centers to the electron beam and also it is possible that a pulse train of propagating ripplocations can sweep out the defects via interaction from specific areas of MoS2 sheets.

A label-free ultrasensitive electrochemical DNA sensor based on thin-layer MoS2 nanosheets with high electrochemical activity.

PubMed

Wang, Xinxing; Nan, Fuxin; Zhao, Jinlong; Yang, Tao; Ge, Tong; Jiao, Kui

2015-02-15

A label-free and ultrasensitive electrochemical DNA biosensor, based on thin-layer molybdenum disulfide (MoS2) nanosheets sensing platform and differential pulse voltammetry detection, is constructed in this paper. The thin-layer MoS2 nanosheets were prepared via a simple ultrasound exfoliation method from bulk MoS2, which is simpler and no distortion compared with mechanical cleavage and lithium intercalation. Most importantly, this procedure allows the formation of MoS2 with enhanced electrochemical activity. Based on the high electrochemical activity and different affinity toward ssDNA versus dsDNA of the thin-layer MoS2 nanosheets sensing platform, the tlh gene sequence assay can be performed label-freely from 1.0 × 10(-16)M to 1.0 × 10(-10)M with a detection limit of 1.9 × 10(-17)M. Without labeling and the use of amplifiers, the detection method described here not only expands the application of MoS2, but also offers a viable alternative for DNA analysis, which has the priority in sensitivity, simplicity, and costs. Moreover, the proposed sensing platform has good electrocatalytic activity, and can be extended to detect more targets, such as guanine and adenine, which further expands the application of MoS2. Copyright © 2014 Elsevier B.V. All rights reserved.

Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi2S3@MoS2: experiments and theory

PubMed Central

Li, Mengjiao; Wang, Junyong; Zhang, Peng; Deng, Qinglin; Zhang, Jinzhong; Jiang, Kai; Hu, Zhigao; Chu, Junhao

2017-01-01

The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567). PMID:28211893

MoS2 Nanosheet-Modified CuInS2 Photocatalyst for Visible-Light-Driven Hydrogen Production from Water.

PubMed

Yuan, Yong-Jun; Chen, Da-Qin; Huang, Yan-Wei; Yu, Zhen-Tao; Zhong, Jia-Song; Chen, Ting-Ting; Tu, Wen-Guang; Guan, Zhong-Jie; Cao, Da-Peng; Zou, Zhi-Gang

2016-05-10

Exploiting photocatalysts respond to visible light is of huge challenge for photocatalytic H2 production. Here, we synthesize a new composite material consisting of few-layer MoS2 nanosheets grown on CuInS2 surface as an efficient photocatalyst for solar H2 generation. The photocatalytic results demonstrate that the 3 wt % MoS2 /CuInS2 photocatalyst exhibits the highest H2 generation rate of 316 μmol h(-1)  g(-1) under visible light irradiation, which is almost 28 times higher than that of CuInS2 . Importantly, the MoS2 /CuInS2 photocatalyst shows a much higher photocatalytic activity than that of Pt-loaded CuInS2 photocatalyst. The enhanced photocatalytic activities of MoS2 /CuInS2 photocatalysts can be attributed to the improved charge separation at the interface of MoS2 and CuInS2, which is demonstrated by the significant enhancement of photocurrent responses in MoS2 /CuInS2 photoelectrodes. This work presents a noble-metal-free photocatalyst that responds to visible light for solar H2 generation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Instructional Innovation - MOS: A Model Involving Student Participation.

ERIC Educational Resources Information Center

Malloy, Elizabeth; O'Donnell, Terrence P.

1987-01-01

Asserts that new models of instructional methodology are needed to meet the demands of a changing world community. Describes a small-group teaching method called MOS, which calls for students to read, analyze, and shape meaning gained from material while instructors encourage and provide insight. (BSR)

Optical properties of thickness-controlled MoS2 thin films studied by spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Li, Dahai; Song, Xiongfei; Xu, Jiping; Wang, Ziyi; Zhang, Rongjun; Zhou, Peng; Zhang, Hao; Huang, Renzhong; Wang, Songyou; Zheng, Yuxiang; Zhang, David Wei; Chen, Liangyao

2017-11-01

As a promising candidate for applications in future electronic and optoelectronic devices, MoS2 has been a research focus in recent years. Therefore, investigating its optical properties is of practical significance. Here we synthesized different MoS2 thin films with quantitatively controlled thickness and sizable thickness variation, which is vital to find out the thickness-dependent regularity. Afterwards, several characterization methods, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman spectroscopy, photoluminescence (PL), optical absorption spectra, and spectroscopic ellipsometry (SE), were systematically performed to character the optical properties of as-grown samples. Accurate dielectric constants of MoS2 are obtained by fitting SE data using point-by-point method, and precise energies of interband transitions are directly extracted from the Lorentz dispersion model. We assign these energies to different interband electronic transitions between the valence bands and conduction bands in the Brillouin zone. In addition, the intrinsic physical mechanisms existing in observed phenomena are discussed in details. Results derived from this work are reliable and provide a better understanding of MoS2, which can be expected to help people fully employ its potential for wider applications.

A Novel SPM Probe with MOS Transistor and Nano Tip for Surface Electric Properties

NASA Astrophysics Data System (ADS)

Lee, Sang H.; Lim, Geunbae; Moon, Wonkyu

2007-03-01

In this paper, the novel SPM (Scanning Probe Microscope) probe with the planar MOS (Metal-Oxide-Semiconductor) transistor and the FIB (Focused Ion Beam) nano tip is fabricated for the surface electric properties. Since the MOS transistor has high working frequency, the device can overcome the speed limitation of EFM (Electrostatic Force Microscope) system. The sensitivity is also high, and no bulky device such as lock-in-amplifier is required. Moreover, the nano tip with nanometer scale tip radius is fabricated with FIB system, and the resolution can be improved. Therefore, the probe can rapidly detect small localized electric properties with high sensitivity and high resolution. The MOS transistor is fabricated with the common semiconductor process, and the nano tip is grown by the FIB system. The planar structure of the MOS transistor makes the fabrication process easier, which is the advantage on the commercial production. Various electric signals are applied using the function generator, and the measured data represent the well-established electric properties of the device. It shows the promising aspect of the local surface electric property detection with high sensitivity and high resolution.

[Validity of the questionnaire MOS-SSS of social support in neoplastic patients].

PubMed

Costa Requena, Gema; Salamero, Manuel; Gil, Francisco

2007-05-12

Previous studies have pointed out how the perception of social support benefits the wellbeing of patients. The main objective in this study is to adapt and validate the MOS-SSS (Medical Outcomes Study-Social Support Survey) questionnaire to measure social support. In a sample of 400 oncology out-patients, in order to validate the MOS-SSS questionnaire, we have applied a exploratory factorial analysis. The factors were extracted by principal components and varimax rotation. Then, we compared the dimensions of the questionnaire with other variables as size of social network, sex and age. We have observed a high reliability of the MOS-SSS questionnaire, with the alpha coefficient around 0.94 . By a factorial analysis, we have extracted 3 factors: emotional/informational support, affective support and instrumental support. The fourth dimension included in the original questionnaire, positive social interaction, was included in the emotional/informational support dimension. Comparing the mean scores of the 3 dimensions with other variables (number of members in the family and friends, sex and age), we have observed that a high number of relatives and friends were related with a higher perception of social support. However, the men received more instrumental and emotional/informational support than women; and the age was not related with the perception of social support in patients with cancer. The MOS-SSS questionnaire is a valid instrument to assess the multidimensionality of the perception of social support in Spanish cancer patients.

All the catalytic active sites of MoS 2 for hydrogen evolution

DOE PAGES

Li, Guoqing; Zhang, Du; Qiao, Qiao; ...

2016-11-29

MoS 2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS 2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. Here, the intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated tomore » be 7.5 s –1 (65–75 mV/dec), 3.2 s –1 (65–85 mV/dec), and 0.1 s –1 (120–160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7–10%, and the number of sulfur vacancies in high crystalline quality MoS 2 is higher than that in low crystalline quality MoS 2, which may be related with the proximity of different local crystalline structures to the vacancies.« less

Mechanistic studies on the reactions of PhS(-) or [MoS(4)](2)(-) with [M(4)(SPh)(10)](2)(-) (M = Fe or Co).

PubMed

Cui, Zhen; Henderson, Richard A

2002-08-12

Kinetic studies, using stopped-flow spectrophotometry, on the reactions of [M(4)(SPh)(10)](2)(-) (M = Fe or Co) with PhS(-) to form [M(SPh)(4)](2)(-) are described, as are the reactions between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) to form [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). The kinetics of the reactions with PhS(-) are consistent with an initial associative substitution mechanism involving attack of PhS(-) at one of the tetrahedral M sites of [M(4)(SPh)(10)](2)(-) to form [M(4)(SPh)(11)](3)(-). Subsequent or concomitant cleavage of a micro-SPh ligand, at the same M, initiates a cascade of rapid reactions which result ultimately in the complete rupture of the cluster and formation of [M(SPh)(4)](2)(-). The kinetics of the reaction between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) indicate an initial dissociative substitution mechanism at low concentrations of [MoS(4)](2)(-), in which rate-limiting dissociation of a terminal thiolate from [M(4)(SPh)(10)](2)(-) produces [M(4)(SPh)(9)](-) and the coordinatively unsaturated M site is rapidly attacked by a sulfido group of [MoS(4)](2)(-). It is proposed that subsequent chelation of the MoS(4) ligand results in cleavage of an M-micro-SPh bond, initiating a cascade of reactions which lead to the ultimate break-up of the cluster and formation of the products, [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). With [Co(4)(SPh)(10)](2)(-), at higher concentrations of [MoS(4)](2)(-), a further substitution pathway is evident which exhibits a second order dependence on the concentration of [MoS(4)](2)(-). The mechanistic picture of cluster disruption which emerges from these studies rationalizes the "all or nothing" reactivity of [M(4)(SPh)(10)](2)(-).

Resonant enhancement of band-to-band tunneling in in-plane MoS2/WS2 heterojunctions

NASA Astrophysics Data System (ADS)

Kuroda, Tatsuya; Mori, Nobuya

2018-04-01

The band-to-band (BTB) tunneling current J through in-plane MoS2/WS2 heterojunctions is calculated by the nonequilibrium Green function method combined with tight-binding approximation. Types A and B of band configurations are considered. For type-A (type-B) heterojunctions, a potential notch exists (or is absent) at the heterointerface. Both type-A and type-B MoS2/WS2 heterojunctions can support a higher BTB current than MoS2 and WS2 homojunctions. For type-A heterojunctions, the resonant enhancement of J occurs resulting in a significantly higher BTB tunneling current.

One-pot mass preparation of MoS2/C aerogels for high-performance supercapacitors and lithium-ion batteries.

PubMed

Zhang, Yan; He, Ting; Liu, Guanglei; Zu, Lianhai; Yang, Jinhu

2017-07-20

In this paper, we report the successful design and synthesis of a hierarchically porous MoS 2 /C composite aerogel by simple one-pot mass preparation. The synthesis involves the in situ formation of MoS 2 nanosheets on agarose molecular chains, the gelation of MoS 2 -deposited agarose monomers to generate a composite hydrogel, and in situ transformation of the composite hydrogel into a MoS 2 /C composite aerogel through carbonization. This composite aerogel can be used as a high-performance electrode material for supercapacitors and lithium-ion batteries. When tested as a supercapacitor electrode, it achieves a high specific capacitance of 712.6 F g -1 at 1 A g -1 and 97.3% capacity retention after 13 000 cycles at 6 A g -1 . In addition, as a lithium-ion battery electrode, it exhibits a superior rate capability (653.2 mA h g -1 at 0.1 A g -1 and 334.5 mA h g -1 at 5.0 A g -1 ) and an ultrahigh capacity retention of nearly 100% after 1000 cycles at 1 A g -1 . These performances may be ascribed to the unique structure of the MoS 2 /C composite aerogel, such as hierarchical pores, (002) plane-expanded MoS 2 and interconnected carbon networks embedded uniformly with MoS 2 nanosheets. This work may provide a general and simple approach for mass preparation of composite aerogel materials and pave the way for promising materials applied in both supercapacitors and lithium-ion batteries.

Toward DNA electrochemical sensing by free-standing ZnO nanosheets grown on 2D thin-layered MoS2.

PubMed

Yang, Tao; Chen, Meijing; Kong, Qianqian; Luo, Xiliang; Jiao, Kui

2017-03-15

Very recently, the 2-dimensional MoS 2 layer as base substrate integrated with other materials has caused people's emerging attention. In this paper, a thin-layered MoS 2 was prepared through an ultrasonic exfoliation method from bulk MoS 2 and then the free-standing ZnO nanosheet was electrodeposited on the MoS 2 scaffold for DNA sensing. The ZnO/MoS 2 nanocomposite revealed smooth and vertical nanosheets morphology by scanning electron microscopy, compared with the sole MoS 2 and sole ZnO. Importantly, the partially negative charged MoS 2 layer is beneficial to the nucleation and growth of ZnO nanosheets under the effect of electrostatic interactions. Classic methylene blue, which possesses different affinities to dsDNA and ssDNA, was adopted as the measure signal to confirm the immobilization and hybridization of DNA on ZnO nanosheets and pursue the optimal synthetic conditions. And the results demonstrated that the free-standing ZnO/MoS 2 nanosheets had low detection limit (6.6×10 -16 M) and has a positive influence on DNA immobilization and hybridization. Copyright © 2016 Elsevier B.V. All rights reserved.

Unexpected optical limiting properties from MoS2 nanosheets modified by a semiconductive polymer.

PubMed

Zhao, Min; Chang, Meng-Jie; Wang, Qiang; Zhu, Zhen-Tong; Zhai, Xin-Ping; Zirak, Mohammad; Moshfegh, Alireza Z; Song, Ying-Lin; Zhang, Hao-Li

2015-08-07

Direct solvent exfoliation of bulk MoS2 with the assistance of poly(3-hexylthiophene) (P3HT) produces a novel two-dimensional organic/inorganic semiconductor hetero-junction. The obtained P3HT-MoS2 nanohybrid exhibits unexpected optical limiting properties in contrast to the saturated absorption behavior of both P3HT and MoS2, showing potential in future photoelectric applications.

Highly sensitive MOS photodetector with wide band responsivity assisted by nanoporous anodic aluminum oxide membrane.

PubMed

Chen, Yungting; Cheng, Tzuhuan; Cheng, Chungliang; Wang, Chunhsiung; Chen, Chihwei; Wei, Chihming; Chen, Yangfang

2010-01-04

A new approach for developing highly sensitive MOS photodetector based on the assistance of anodic aluminum oxide (AAO) membrane is proposed, fabricated, and characterized. It enables the photodetector with the tunability of not only the intensity but also the range of the response. Under a forward bias, the response of the MOS photodetector with AAO membrane covers the visible as well as infrared spectrum; however, under a reverse bias, the near-infrared light around Si band edge dominates the photoresponse. Unlike general MOS photodetectors which only work under a reverse bias, our MOS photodetectors can work even under a forward bias, and the responsivity at the optical communication wavelength of 850nm can reach up to 0.24 A/W with an external quantum efficiency (EQE) of 35%. Moreover, the response shows a large enhancement factor of 10 times at 1050 nm under a reverse bias of 0.5V comparing with the device without AAO membrane. The underlying mechanism for the novel properties of the newly designed device has been proposed.

Schottky Barrier Height Engineering for Electrical Contacts of Multilayered MoS2 Transistors with Reduction of Metal-Induced Gap States.

PubMed

Kim, Gwang-Sik; Kim, Seung-Hwan; Park, June; Han, Kyu Hyun; Kim, Jiyoung; Yu, Hyun-Yong

2018-06-06

The difficulty in Schottky barrier height (SBH) control arising from Fermi-level pinning (FLP) at electrical contacts is a bottleneck in designing high-performance nanoscale electronics and optoelectronics based on molybdenum disulfide (MoS 2 ). For electrical contacts of multilayered MoS 2 , the Fermi level on the metal side is strongly pinned near the conduction-band edge of MoS 2 , which makes most MoS 2 -channel field-effect transistors (MoS 2 FETs) exhibit n-type transfer characteristics regardless of their source/drain (S/D) contact metals. In this work, SBH engineering is conducted to control the SBH of electrical top contacts of multilayered MoS 2 by introducing a metal-interlayer-semiconductor (MIS) structure which induces the Fermi-level unpinning by a reduction of metal-induced gap states (MIGS). An ultrathin titanium dioxide (TiO 2 ) interlayer is inserted between the metal contact and the multilayered MoS 2 to alleviate FLP and tune the SBH at the S/D contacts of multilayered MoS 2 FETs. A significant alleviation of FLP is demonstrated as MIS structures with 1 nm thick TiO 2 interlayers are introduced into the S/D contacts. Consequently, the pinning factor ( S) increases from 0.02 for metal-semiconductor (MS) contacts to 0.24 for MIS contacts, and the controllable SBH range is widened from 37 meV (50-87 meV) to 344 meV (107-451 meV). Furthermore, the Fermi-level unpinning effect is reinforced as the interlayer becomes thicker. This work widens the scope for modifying electrical characteristics of contacts by providing a platform to control the SBH through a simple process as well as understanding of the FLP at the electrical top contacts of multilayered MoS 2 .

Highly sensitive wide bandwidth photodetector based on internal photoemission in CVD grown p-type MoS2/graphene Schottky junction.

PubMed

Vabbina, PhaniKiran; Choudhary, Nitin; Chowdhury, Al-Amin; Sinha, Raju; Karabiyik, Mustafa; Das, Santanu; Choi, Wonbong; Pala, Nezih

2015-07-22

Two dimensional (2D) Molybdenum disulfide (MoS2) has evolved as a promising material for next generation optoelectronic devices owing to its unique electrical and optical properties, such as band gap modulation, high optical absorption, and increased luminescence quantum yield. The 2D MoS2 photodetectors reported in the literature have presented low responsivity compared to silicon based photodetectors. In this study, we assembled atomically thin p-type MoS2 with graphene to form a MoS2/graphene Schottky photodetector where photo generated holes travel from graphene to MoS2 over the Schottky barrier under illumination. We found that the p-type MoS2 forms a Schottky junction with graphene with a barrier height of 139 meV, which results in high photocurrent and wide spectral range of detection with wavelength selectivity. The fabricated photodetector showed excellent photosensitivity with a maximum photo responsivity of 1.26 AW(-1) and a noise equivalent power of 7.8 × 10(-12) W/√Hz at 1440 nm.

Band-offset-induced lateral shift of valley electrons in ferromagnetic MoS2/WS2 planar heterojunctions

NASA Astrophysics Data System (ADS)

Ghadiri, Hassan; Saffarzadeh, Alireza

2018-03-01

Low-energy coherent transport and a Goos-Hänchen (GH) lateral shift of valley electrons in planar heterojunctions composed of normal MoS2 and ferromagnetic WS2 monolayers are theoretically investigated. Two types of heterojunctions in the forms of WS2/MoS2/WS2 (type-A) and MoS2/WS2/MoS2 (type-B) with incident electrons in the MoS2 region are considered in which the lateral shift of electrons is induced by band alignments of the two constituent semiconductors. It is shown that the type-A heterojunction can act as an electron waveguide due to electron confinement between the two WS2/MoS2 interfaces which cause the incident electrons with an appropriate incidence angle to propagate along the interfaces. In this case, the spin- and valley-dependent GH shifts of totally reflected electrons from the interface lead to separated electrons with distinct spin-valley indexes after traveling a sufficiently long distance. In the type-B heterojunction, however, transmission resonances occur for incident electron beams passing through the structure, and large spin- and valley-dependent lateral shift values in propagating states can be achieved. Consequently, the transmitted electrons are spatially well-separated into electrons with distinct spin-valley indexes. Our findings reveal that the planar heterojunctions of transition metal dichalcogenides can be utilized as spin-valley beam filters and/or splitters without external gating.

Electrical characteristics of multilayer MoS2 FET's with MoS2/graphene heterojunction contacts.

PubMed

Kwak, Joon Young; Hwang, Jeonghyun; Calderon, Brian; Alsalman, Hussain; Munoz, Nini; Schutter, Brian; Spencer, Michael G

2014-08-13

The electrical properties of multilayer MoS2/graphene heterojunction transistors are investigated. Temperature-dependent I-V measurements indicate the concentration of unintentional donors in exfoliated MoS2 to be 3.57 × 10(11) cm(-2), while the ionized donor concentration is determined as 3.61 × 10(10) cm(-2). The temperature-dependent measurements also reveal two dominant donor levels, one at 0.27 eV below the conduction band and another located at 0.05 eV below the conduction band. The I-V characteristics are asymmetric with drain bias voltage and dependent on the junction used for the source or drain contact. I-V characteristics of the device are consistent with a long channel one-dimensional field-effect transistor model with Schottky contact. Utilizing devices, which have both graphene/MoS2 and Ti/MoS2 contacts, the Schottky barrier heights of both interfaces are measured. The charge transport mechanism in both junctions was determined to be either thermionic-field emission or field emission depending on bias voltage and temperature. On the basis of a thermionic field emission model, the barrier height at the graphene/MoS2 interface was determined to be 0.23 eV, while the barrier height at the Ti/MoS2 interface was 0.40 eV. The value of Ti/MoS2 barrier is higher than previously reported values, which did not include the effects of thermionic field emission.

Surface Optical Rectification from Layered MoS2 Crystal by THz Time-Domain Surface Emission Spectroscopy.

PubMed

Huang, Yuanyuan; Zhu, Lipeng; Zhao, Qiyi; Guo, Yaohui; Ren, Zhaoyu; Bai, Jintao; Xu, Xinlong

2017-02-08

Surface optical rectification was observed from the layered semiconductor molybdenum disulfide (MoS 2 ) crystal via terahertz (THz) time-domain surface emission spectroscopy under linearly polarized femtosecond laser excitation. The radiated THz amplitude of MoS 2 has a linear dependence on ever-increasing pump fluence and thus quadratic with the pump electric field, which discriminates from the surface Dember field induced THz radiation in InAs and the transient photocurrent-induced THz generation in graphite. Theoretical analysis based on space symmetry of MoS 2 crystal suggests that the underlying mechanism of THz radiation is surface optical rectification under the reflection configuration. This is consistent with the experimental results according to the radiated THz amplitude dependences on azimuthal and incident polarization angles. We also demonstrated the damage threshold of MoS 2 due to microscopic bond breaking under the femtosecond laser irradiation, which can be monitored via THz time-domain emission spectroscopy and Raman spectroscopy.

Synthesis of MoS2 and MoO2 for their applications in H2 generation and lithium ion batteries: a review.

PubMed

Zhao, Yufei; Zhang, Yuxia; Yang, Zhiyu; Yan, Yiming; Sun, Kening

2013-08-01

Scientists increasingly witness the applications of MoS 2 and MoO 2 in the field of energy conversion and energy storage. On the one hand, MoS 2 and MoO 2 have been widely utilized as promising catalysts for electrocatalytic or photocatalytic hydrogen evolution in aqueous solution. On the other hand, MoS 2 and MoO 2 have also been verified as efficient electrode material for lithium ion batteries. In this review, the synthesis, structure and properties of MoS 2 and MoO 2 are briefly summarized according to their applications for H 2 generation and lithium ion batteries. Firstly, we overview the recent advancements in the morphology control of MoS 2 and MoO 2 and their applications as electrocatalysts for hydrogen evolution reactions. Secondly, we focus on the photo-induced water splitting for H 2 generation, in which MoS 2 acts as an important co-catalyst when combined with other semiconductor catalysts. The newly reported research results of the significant functions of MoS 2 nanocomposites in photo-induced water splitting are presented. Thirdly, we introduce the advantages of MoS 2 and MoO 2 for their enhanced cyclic performance and high capacity as electrode materials of lithium ion batteries. Recent key achievements in MoS 2 - and MoO 2 -based lithium ion batteries are highlighted. Finally, we discuss the future scope and the important challenges emerging from these fascinating materials.

Involvement of Mos-MEK-MAPK pathway in cytostatic factor (CSF) arrest in eggs of the parthenogenetic insect, Athalia rosae.

PubMed

Yamamoto, Daisuke S; Tachibana, Kazunori; Sumitani, Megumi; Lee, Jae Min; Hatakeyama, Masatsugu

2008-01-01

Extensive survey of meiotic metaphase II arrest during oocyte maturation in vertebrates revealed that the mitogen-activated protein kinase (MAPK) pathway regulated by the c-mos proto-oncogene product, Mos, has an essential role in cytostatic activity, termed cytostatic factor (CSF). In contrast, little is known in invertebrates in which meiotic arrest occurs in most cases at metaphase I (MI arrest). A parthenogenetic insect, the sawfly Athalia rosae, in which artificial egg activation is practicable, has advantages to investigate the mechanisms of MI arrest. Both the MAPK/extracellular signal-regulated protein kinase kinase (MEK) and MAPK were phosphorylated and maintained active in MI-arrested sawfly eggs, whereas they were dephosphorylated soon after egg activation. Treatment of MI-arrested eggs with U0126, an inhibitor of MEK, resulted in dephosphorylation of MAPK and MI arrest was resumed. The sawfly c-mos gene orthologue encoding a serine/threonine kinase was cloned and analyzed. It was expressed in nurse cells in the ovaries. To examine CSF activity of the sawfly Mos, synthesized glutathione S-transferase (GST)-fusion sawfly Mos protein was injected into MI-resumed eggs in which MEK and MAPK were dephosphorylated. Both MEK and MAPK were phosphorylated again upon injection. In these GST-fusion sawfly Mos-injected eggs subsequent mitotic (syncytial) divisions were blocked and embryonic development was ceased. These results demonstrated that the MEK-MAPK pathway was involved in maintaining CSF arrest in sawfly eggs and Mos functioned as its upstream regulatory molecule.

The quasi-equilibrium response of MOS structures: Quasi-static factor

NASA Astrophysics Data System (ADS)

Okeke, M.; Balland, B.

1984-07-01

The dynamic response of a MOS structure driven into a non-equilibrium behaviour by a voltage ramp is presented. In contrast to Khun's quasi-static technique it is shown that any ramp-driven MOS structure has some degree of non-equilibrium. A quasi staticity factor μAK which serves as a measure of the degree of quasi-equilibrium, has been introduced for the first time. The mathematical model presented in the paper allows a better explanation of the experimental recordings. It is shown that this model could be used to analyse the various features of the response of the structure and that such physical parameters as the generation-rate, trap activation energy, and the effective capture constants could be obtained.

Anti-site defected MoS2 sheet for catalytic application

NASA Astrophysics Data System (ADS)

Sharma, Archana; Husain, Mushahid; Khan, Mohd. Shahid

2018-04-01

To prevent harmful and poisonous CO gas molecules, catalysts are needed for converting them into benign substances. Density functional theory (DFT) calculations have been used to investigate CO oxidation on the surface of MoS2 monolayer with Mo atom embedded at S-vacancy site (anti-site defect). The stronger interaction between Mo metal with O2 molecule as compared with CO molecule suggests high catalytic activity. The complete oxidation of CO is studied in a two-step procedure using Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms with a low overall energy barrier of 0.35 eV. Creation of anti-site defect makes the surface of MoS2 nanosheet catalytically active for the CO oxidation to take place.

Controlled growth of MoS2 nanopetals on the silicon nanowire array using the chemical vapor deposition method

NASA Astrophysics Data System (ADS)

Chen, Shang-Min; Lin, Yow-Jon

2018-01-01

In order to get a physical/chemical insight into the formation of nanoscale semiconductor heterojunctions, MoS2 flakes are deposited on the silicon nanowire (SiNW) array by chemical vapor deposition (CVD). In this study, H2O2 treatment provides a favorable place where the formation of Sisbnd O bonds on the SiNW surfaces that play important roles (i.e., the nucleation centers, catalyst control centers or ;seeds;) can dominate the growth of MoS2 on the SiNWs. Using this configuration, the effect of a change in the S/MoO3 mass ratio (MS/MMoO3) on the surface morphology of MoS2 is studied. It is shown that an increase in the value of MS/MMoO3 leads to the increased nucleation rate, increasing the size of MoS2 nanopetals. This study provides valuable scientific information for directly CVD-grown edge-oriented MoS2/SiNWs heterojunctions for various nanoscale applications, including hydrogen evolution reaction and electronic and optoelectronic devices.

Compressive Sensing Cluster Expansion Studies of Lithium Intercalation and Phase Transformation in MoS2 for Energy Storage

NASA Astrophysics Data System (ADS)

Liu, Chi-Ping; Zhou, Fei; Ozolins, Vidvuds; University of California, Los Angeles Collaboration; Lawrence livermore national laboratory Collaboration

2015-03-01

Bulk molybdenum disulfide (MoS2) is a good electrode material candidate for energy storage applications, such as lithium ion batteries and supercapacitors due to its high theoretical energy and power density. First-principles density-functional theory (DFT) calculations combined with cluster expansion are an effective method to study thermodynamic and kinetic properties of electrode materials. In order to construct accurate models for cluster expansion, it is important to effectively choose clusters with significant contributions. In this work, we employ a compressive sensing based technique to select relevant clusters in order to build an accurate Hamiltonian for cluster expansion, enabling the study of Li intercalation in MoS2. We find that the 2H MoS2 structure is only stable at low Li content while 1T MoS2 is the preferred phase at high Li content. The results show that the 2H MoS2 phase transforms into the disordered 1T phase and the disordered 1T structure remains after the first Li insertion/deinsertion cycle suggesting that disordered 1T MoS2 is stable even at dilute Li content. This work also highlights that cluster expansion treated with compressive sensing is an effective and powerful tool for model construction and can be applied to advanced battery and supercapacitor electrode materials.

ReaxFF Reactive Force-Field Study of Molybdenum Disulfide (MoS2).

PubMed

Ostadhossein, Alireza; Rahnamoun, Ali; Wang, Yuanxi; Zhao, Peng; Zhang, Sulin; Crespi, Vincent H; van Duin, Adri C T

2017-02-02

Two-dimensional layers of molybdenum disulfide, MoS 2 , have been recognized as promising materials for nanoelectronics due to their exceptional electronic and optical properties. Here we develop a new ReaxFF reactive potential that can accurately describe the thermodynamic and structural properties of MoS 2 sheets, guided by extensive density functional theory simulations. This potential is then applied to the formation energies of five different types of vacancies, various vacancy migration barriers, and the transition barrier between the semiconducting 2H and metallic 1T phases. The energetics of ripplocations, a recently observed defect in van der Waals layers, is examined, and the interplay between these defects and sulfur vacancies is studied. As strain engineering of MoS 2 sheets is an effective way to manipulate the sheets' electronic and optical properties, the new ReaxFF description can provide valuable insights into morphological changes that occur under various loading conditions and defect distributions, thus allowing one to tailor the electronic properties of these 2D crystals.

Equivalent input spectrum and drain current spectrum for 1/ƒ noise in short channel MOS transistors

NASA Astrophysics Data System (ADS)

Gentil, P.; Mounib, A.

1981-05-01

Flicker noise in MOS transistors can be evaluated by measuring the spectrum SID of the drain current fluctuation or the spectrum Sve of an equivalent gate fluctuation. We show here that experimental variations of {S I D}/{Sve} are in good agreement with gm2 by considering a model of the transconductance gm which takes into account the variations of the channel carriers mobility with the surface electric field. The model agrees with the experimental results obtained on short channel MOS transistors which exhibit large variations of mobility with the gate voltage. The validity of physical interpretations of noise data on MOS transistors is examined.

Quantitative analysis of trap states through the behavior of the sulfur ions in MoS2 FETs following high vacuum annealing

NASA Astrophysics Data System (ADS)

Bae, Hagyoul; Jun, Sungwoo; Kim, Choong-Ki; Ju, Byeong-Kwon; Choi, Yang-Kyu

2018-03-01

Few-layer molybdenum disulfide (MoS2) has attracted a great deal of attention as a semiconductor material for electronic and optoelectronic devices. However, the presence of localized states inside the bandgap is a critical issue that must be addressed to improve the applicability of MoS2 technology. In this work, we investigated the density of states (DOS: g(E)) inside the bandgap of MoS2 FET by using a current-voltage (I-V) analysis technique with the aid of high vacuum annealing (HVA). The g(E) can be obtained by combining the trap density and surface potential (ψ S) extracted from a consistent subthreshold current (I D-sub). The electrical performance of MoS2 FETs is strongly dependent on the inherent defects, which are closely related to the g(E) in the MoS2 active layer. By applying the proposed technique to the MoS2 FETs, we were able to successfully characterize the g(E) after stabilization of the traps by the HVA, which reduces the hysteresis distorting the intrinsic g(E). Also, the change of sulfur ions in MoS2 film before and after the HVA treatment is investigated directly by Auger electron spectroscopy analysis. The proposed technique provides a new methodology for active channel engineering of 2D channel based FETs such as MoS2, MoTe2, WSe2, and WS2.

Oscillations in MOS tunneling

NASA Technical Reports Server (NTRS)

Lewicki, G.; Maserjian, J.

1975-01-01

Oscillatory deviations from Fowler-Nordheim tunneling currents were measured in MOS capacitors with oxide thicknesses ranging from 30 to 75 A. The observed variation of oscillation phases and amplitudes with oxide thickness indicates that the Si-SiO2 interface is independent of oxide thickness only for thicknesses greater than 65 A. At lower thicknesses, the barrier height at the interface decreases gradually with oxide thickness at a rate on the order of 10 mV/A. At higher thicknesses, the barrier height is 4.08 eV. The energy dispersion relation with the SiO2 conduction band is parabolic. The mean free path within the SiO2 conduction band is on the order of 13 A.

Deconvoluting the Photonic and Electronic Response of 2D Materials: The Case of MoS2.

PubMed

Zhang, Kehao; Borys, Nicholas J; Bersch, Brian M; Bhimanapati, Ganesh R; Xu, Ke; Wang, Baoming; Wang, Ke; Labella, Michael; Williams, Teague A; Haque, Md Amanul; Barnard, Edward S; Fullerton-Shirey, Susan; Schuck, P James; Robinson, Joshua A

2017-12-05

Evaluating and tuning the properties of two-dimensional (2D) materials is a major focus of advancing 2D science and technology. While many claim that the photonic properties of a 2D layer provide evidence that the material is "high quality", this may not be true for electronic performance. In this work, we deconvolute the photonic and electronic response of synthetic monolayer molybdenum disulfide. We demonstrate that enhanced photoluminescence can be robustly engineered via the proper choice of substrate, where growth of MoS 2 on r-plane sapphire can yield >100x enhancement in PL and carrier lifetime due to increased molybdenum-oxygen bonding compared to that of traditionally grown MoS 2 on c-plane sapphire. These dramatic enhancements in optical properties are similar to those of super-acid treated MoS 2 , and suggest that the electronic properties of the MoS 2 are also superior. However, a direct comparison of the charge transport properties indicates that the enhanced PL due to increased Mo-O bonding leads to p-type compensation doping, and is accompanied by a 2x degradation in transport properties compared to MoS 2 grown on c-plane sapphire. This work provides a foundation for understanding the link between photonic and electronic performance of 2D semiconducting layers, and demonstrates that they are not always correlated.

Deconvoluting the Photonic and Electronic Response of 2D Materials: The Case of MoS 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Kehao; Borys, Nicholas J.; Bersch, Brian M.

Evaluating and tuning the properties of two-dimensional (2D) materials is a major focus of advancing 2D science and technology. While many claim that the photonic properties of a 2D layer provide evidence that the material is "high quality", this may not be true for electronic performance. In this work, we deconvolute the photonic and electronic response of synthetic monolayer molybdenum disulfide. We demonstrate that enhanced photoluminescence can be robustly engineered via the proper choice of substrate, where growth of MoS 2 on r-plane sapphire can yield > 100x enhancement in PL and carrier lifetime due to increased molybdenum-oxygen bonding comparedmore » to that of traditionally grown MoS 2 on c-plane sapphire. These dramatic enhancements in optical properties are similar to those of super-acid treated MoS 2 , and suggest that the electronic properties of the MoS 2 are also superior. However, a direct comparison of the charge transport properties indicates that the enhanced PL due to increased Mo-O bonding leads to p-type compensation doping, and is accompanied by a 2x degradation in transport properties compared to MoS 2 grown on c-plane sapphire. This work provides a foundation for understanding the link between photonic and electronic performance of 2D semiconducting layers, and demonstrates that they are not always correlated.« less

Deconvoluting the Photonic and Electronic Response of 2D Materials: The Case of MoS 2

DOE PAGES

Zhang, Kehao; Borys, Nicholas J.; Bersch, Brian M.; ...

2017-12-05

Evaluating and tuning the properties of two-dimensional (2D) materials is a major focus of advancing 2D science and technology. While many claim that the photonic properties of a 2D layer provide evidence that the material is "high quality", this may not be true for electronic performance. In this work, we deconvolute the photonic and electronic response of synthetic monolayer molybdenum disulfide. We demonstrate that enhanced photoluminescence can be robustly engineered via the proper choice of substrate, where growth of MoS 2 on r-plane sapphire can yield > 100x enhancement in PL and carrier lifetime due to increased molybdenum-oxygen bonding comparedmore » to that of traditionally grown MoS 2 on c-plane sapphire. These dramatic enhancements in optical properties are similar to those of super-acid treated MoS 2 , and suggest that the electronic properties of the MoS 2 are also superior. However, a direct comparison of the charge transport properties indicates that the enhanced PL due to increased Mo-O bonding leads to p-type compensation doping, and is accompanied by a 2x degradation in transport properties compared to MoS 2 grown on c-plane sapphire. This work provides a foundation for understanding the link between photonic and electronic performance of 2D semiconducting layers, and demonstrates that they are not always correlated.« less

Tunable Electrical and Optical Characteristics in Monolayer Graphene and Few-Layer MoS2 Heterostructure Devices.

PubMed

Rathi, Servin; Lee, Inyeal; Lim, Dongsuk; Wang, Jianwei; Ochiai, Yuichi; Aoki, Nobuyuki; Watanabe, Kenji; Taniguchi, Takashi; Lee, Gwan-Hyoung; Yu, Young-Jun; Kim, Philip; Kim, Gil-Ho

2015-08-12

Lateral and vertical two-dimensional heterostructure devices, in particular graphene-MoS2, have attracted profound interest as they offer additional functionalities over normal two-dimensional devices. Here, we have carried out electrical and optical characterization of graphene-MoS2 heterostructure. The few-layer MoS2 devices with metal electrode at one end and monolayer graphene electrode at the other end show nonlinearity in drain current with drain voltage sweep due to asymmetrical Schottky barrier height at the contacts and can be modulated with an external gate field. The doping effect of MoS2 on graphene was observed as double Dirac points in the transfer characteristics of the graphene field-effect transistor (FET) with a few-layer MoS2 overlapping the middle part of the channel, whereas the underlapping of graphene have negligible effect on MoS2 FET characteristics, which showed typical n-type behavior. The heterostructure also exhibits a strongest optical response for 520 nm wavelength, which decreases with higher wavelengths. Another distinct feature observed in the heterostructure is the peak in the photocurrent around zero gate voltage. This peak is distinguished from conventional MoS2 FETs, which show a continuous increase in photocurrent with back-gate voltage. These results offer significant insight and further enhance the understanding of the graphene-MoS2 heterostructure.

A theoretical modeling of photocurrent generation and decay in layered MoS2 thin-film transistor photosensors

NASA Astrophysics Data System (ADS)

Hur, Ji-Hyun; Park, Junghak; Jeon, Sanghun

2017-02-01

A model that universally describes the characteristics of photocurrent in molybdenum disulphide (MoS2) thin-film transistor (TFT) photosensors in both ‘light on’ and ‘light off’ conditions is presented for the first time. We considered possible material-property dependent carrier generation and recombination mechanisms in layered MoS2 channels with different numbers of layers. We propose that the recombination rates that are mainly composed of direct band-to-band recombination and interface trap-involved recombination change on changing the light condition and the number of layers. By comparing the experimental results, it is shown that the model performs well in describing the photocurrent behaviors of MoS2 TFT photosensors, including the photocurrent generation under illumination and a hugely long time persistent trend of the photocurrent decay in the dark condition, for a range of MoS2 layer numbers.

Gap-mode enhancement on MoS2 probed by functionalized tip-enhanced Raman spectroscopy

NASA Astrophysics Data System (ADS)

Alajlan, Abdulrahman M.; Voronine, Dmitri V.; Sinyukov, Alexander M.; Zhang, Zhenrong; Sokolov, Alexei V.; Scully, Marlan O.

2016-09-01

Surface enhancement of molecular spectroscopic signals has been widely used for sensing and nanoscale imaging. Because of the weak electromagnetic enhancement of Raman signals on semiconductors, it is motivating but challenging to study the electromagnetic effect separately from the chemical effects. We report tip-enhanced Raman scattering measurements on Au and bulk MoS2 substrates using a metallic tip functionalized with copper phthalocyanine molecules and demonstrate similar gap-mode enhancement on both substrates. We compare the experimental results with theoretical calculations to confirm the gap-mode enhancement on MoS2 using a well-established electrostatic model. The functionalized tip approach allows for suppressing the background and is ideal for separating electromagnetic and chemical enhancement mechanisms on various substrates. Our results may find a wide range of applications in MoS2-based devices, sensors, and metal-free nanoscale bio-imaging.

Total Ionizing Dose Effects on Strained Ge pMOS FinFETs on Bulk Si

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, En Xia; Fleetwood, Daniel M.; Hachtel, Jordan A.

2016-12-02

In this paper, we have characterized the total ionizing dose response of strained Ge p MOS FinFETs built on bulk Si using a fin replacement process. Devices irradiated to 1.0 Mrad(SiO 2) show minimal transconductance degradation (less than 5%), very small V th shifts (less than 40 mV in magnitude) and very little ON/OFF current ratio degradation (<5%), and only modest variation in radiation response with transistor geometry (typically less than normal part-to-part variation). Both before and after irradiation, the performance of these strained Ge p MOS FinFETs is far superior to that of past generations of planar Ge pmore » MOS devices. Finally, these improved properties result from significant improvements in processing technology, as well as the enhanced gate control provided by the strained Ge FinFET technology.« less

Assessment Alternatives for a High Skill MOS. Volume I. Problem Procedures and Results. Volume II. Appendices.

ERIC Educational Resources Information Center

Frederickson, Edward W.; And Others

The development and evaluation of prototype hands-on equipment, job sample performance tests for a high skilled technical Military Occupational Specialty (MOS) are described. An electronic maintenance MOS (26C20) was used as the research vehicle. The results led to the conclusion that valid and reliable performance tests could be constructed, but…

Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation.

PubMed

Song, Xiufeng; Liu, Xuhai; Yu, Dejian; Huo, Chengxue; Ji, Jianping; Li, Xiaoming; Zhang, Shengli; Zou, Yousheng; Zhu, Gangyi; Wang, Yongjin; Wu, Mingzai; Xie, An; Zeng, Haibo

2018-01-24

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr 3 nanosheets with MoS 2 atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr 3 to the MoS 2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS 2 /CsPbBr 3 . Resultantly, such a hybrid MoS 2 /CsPbBr 3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 10 10 Jones because of the high efficient photoexcited carrier separation at the interface of MoS 2 and CsPbBr 3 . The photoresponsivity of this hybrid device presents an improvement of 3 orders of magnitude compared with that of a MoS 2 device without CsPbBr 3 . The response time of the device is also shortened from 65.2 to 0.72 ms after coupling with MoS 2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high-performance optoelectronic devices.

Influence of Gas Adsorption and Gold Nanoparticles on the Electrical Properties of CVD-Grown MoS2 Thin Films.

PubMed

Cho, Yunae; Sohn, Ahrum; Kim, Sujung; Hahm, Myung Gwan; Kim, Dong-Ho; Cho, Byungjin; Kim, Dong-Wook

2016-08-24

Molybdenum disulfide (MoS2) has increasingly attracted attention from researchers and is now one of the most intensively explored atomic-layered two-dimensional semiconductors. Control of the carrier concentration and doping type of MoS2 is crucial for its application in electronic and optoelectronic devices. Because the MoS2 layers are atomically thin, their transport characteristics may be very sensitive to ambient gas adsorption and the resulting charge transfer. We investigated the influence of the ambient gas (N2, H2/N2, and O2) choice on the resistance (R) and surface work function (WF) of trilayer MoS2 thin films grown via chemical vapor deposition. We also studied the electrical properties of gold (Au)-nanoparticle (NP)-coated MoS2 thin films; their R value was found to be 2 orders of magnitude smaller than that for bare samples. While the WF largely varied for each gas, R was almost invariant for both the bare and Au-NP-coated samples regardless of which gas was used. Temperature-dependent transport suggests that variable range hopping is the dominant mechanism for electrical conduction for bare and Au-NP-coated MoS2 thin films. The charges transferred from the gas adsorbates might be insufficient to induce measurable R change and/or be trapped in the defect states. The smaller WF and larger localization length of the Au-NP-coated sample, compared with the bare sample, suggest that more carriers and less defects enhanced conduction in MoS2.

Role of vacancy sites and UV-ozone treatment on few layered MoS2 nanoflakes for toxic gas detection

NASA Astrophysics Data System (ADS)

Burman, Debasree; Ghosh, Ruma; Santra, Sumita; Ray, Samit Kumar; Guha, Prasanta Kumar

2017-10-01

Various issues like global warming and environmental pollutions have led to the research of toxic gas detection worldwide. In this work, we have tried to develop a molybdenum disulfide (MoS2) based gas sensor to detect toxic gases like ammonia and NO. MoS2, an inorganic analog of graphene, has attracted lots of attention for many different applications recently. This paper reports the use of liquid exfoliated MoS2 nanoflakes as the sensing layer in a handheld, resistive toxic gas sensor. The nanoflakes were exfoliated from MoS2 bulk powder using a sonication based exfoliation technique at room temperature. The successful exfoliation of the nanoflakes was characterized using different techniques e.g., optical microscopy, atomic force microscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy and ultraviolet-visible spectrophotometry. The characterization results showed that few-layered nanoflakes have successfully been exfoliated. The MoS2 nanoflakes showed reasonable sensing towards ammonia and NO. In order to explore the effect of particle size on ammonia sensing, the MoS2 flakes were also exfoliated using different sonication times. We also observed that various factors like presence of vacancy sites, ambient oxygen, humidity, different contact electrodes have significant effect on the sensing characteristics. In fact, the response of the sensing layer against 400 ppm of ammonia increased from 54.1% to ˜80% when it was UV-ozone treated. This work holds promises to developing cost-effective, reliable and highly sensitive MoS2 based ammonia sensors.

The Arabidopsis THO/TREX component TEX1 functionally interacts with MOS11 and modulates mRNA export and alternative splicing events.

PubMed

Sørensen, Brian B; Ehrnsberger, Hans F; Esposito, Silvia; Pfab, Alexander; Bruckmann, Astrid; Hauptmann, Judith; Meister, Gunter; Merkl, Rainer; Schubert, Thomas; Längst, Gernot; Melzer, Michael; Grasser, Marion; Grasser, Klaus D

2017-02-01

We identify proteins that associate with the THO core complex, and show that the TEX1 and MOS11 components functionally interact, affecting mRNA export and splicing as well as plant development. TREX (TRanscription-EXport) is a multiprotein complex that plays a central role in the coordination of synthesis, processing and nuclear export of mRNAs. Using targeted proteomics, we identified proteins that associate with the THO core complex of Arabidopsis TREX. In addition to the RNA helicase UAP56 and the mRNA export factors ALY2-4 and MOS11 we detected interactions with the mRNA export complex TREX-2 and multiple spliceosomal components. Plants defective in the THO component TEX1 or in the mRNA export factor MOS11 (orthologue of human CIP29) are mildly affected. However, tex1 mos11 double-mutant plants show marked defects in vegetative and reproductive development. In tex1 plants, the levels of tasiRNAs are reduced, while miR173 levels are decreased in mos11 mutants. In nuclei of mos11 cells increased mRNA accumulation was observed, while no mRNA export defect was detected with tex1 cells. Nevertheless, in tex1 mos11 double-mutants, the mRNA export defect was clearly enhanced relative to mos11. The subnuclear distribution of TEX1 substantially overlaps with that of splicing-related SR proteins and in tex1 plants the ratio of certain alternative splicing events is altered. Our results demonstrate that Arabidopsis TEX1 and MOS11 are involved in distinct steps of the biogenesis of mRNAs and small RNAs, and that they interact regarding some aspects, but act independently in others.

Relation between film thickness and surface doping of MoS2 based field effect transistors

NASA Astrophysics Data System (ADS)

Lockhart de la Rosa, César J.; Arutchelvan, Goutham; Leonhardt, Alessandra; Huyghebaert, Cedric; Radu, Iuliana; Heyns, Marc; De Gendt, Stefan

2018-05-01

Ultra-thin MoS2 film doping through surface functionalization with physically adsorbed species is of great interest due to its ability to dope the film without reduction in the carrier mobility. However, there is a need for understanding how the thickness of the MoS2 film is related to the induced surface doping for improved electrical performance. In this work, we report on the relation of MoS2 film thickness with the doping effect induced by the n-dopant adsorbate poly(vinyl-alcohol). Field effect transistors built using MoS2 films of different thicknesses were electrically characterized, and it was observed that the ION/OFF ratio after doping in thin films is more than four orders of magnitudes greater when compared with thick films. Additionally, a semi-classical model tuned with the experimental devices was used to understand the spatial distribution of charge in the channel and explain the observed behavior. From the simulation results, it was revealed that the two-dimensional carrier density induced by the adsorbate is distributed rather uniformly along the complete channel for thin films (<5.2 nm) contrary to what happens for thicker films.

Defect-mediated transport and electronic irradiation effect in individual domains of CVD-grown monolayer MoS 2

DOE PAGES

Durand, Corentin; Zhang, Xiaoguang; Fowlkes, Jason; ...

2015-01-16

We study the electrical transport properties of atomically thin individual crystalline grains of MoS 2 with four-probe scanning tunneling microscopy. The monolayer MoS 2 domains are synthesized by chemical vapor deposition on SiO 2/Si substrate. Temperature dependent measurements on conductance and mobility show that transport is dominated by an electron charge trapping and thermal release process with very low carrier density and mobility. The effects of electronic irradiation are examined by exposing the film to electron beam in the scanning electron microscope in an ultrahigh vacuum environment. The irradiation process is found to significantly affect the mobility and the carriermore » density of the material, with the conductance showing a peculiar time-dependent relaxation behavior. It is suggested that the presence of defects in active MoS 2 layer and dielectric layer create charge trapping sites, and a multiple trapping and thermal release process dictates the transport and mobility characteristics. The electron beam irradiation promotes the formation of defects and impact the electrical properties of MoS 2. Finally, our study reveals the important roles of defects and the electron beam irradiation effects in the electronic properties of atomic layers of MoS 2.« less

Anisotropic thermoelectric behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications

PubMed Central

Arab, Abbas; Li, Qiliang

2015-01-01

In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 in both armchair and zigzag orientations. Density functional theory (DFT) using non-equilibrium Green’s function (NEGF) method has been implemented to calculate the transmission spectra of mono- and fewlayer MoS2 in armchair and zigzag directions. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In general, a thermoelectric generator is composed of thermocouples made of both n-type and p-type legs. Based on our calculations, monolayer MoS2 in armchair orientation is found to have the highest ZT value for both p-type and n-type legs compared to all other armchair and zigzag structures. We have proposed a thermoelectric generator based on monolayer MoS2 in armchair orientation. Moreover, we have studied the effect of various dopant species on thermoelectric current of our proposed generator. Further, we have compared output current of our proposed generator with those of Silicon thin films. Results indicate that thermoelectric current of MoS2 armchair monolayer is several orders of magnitude higher than that of Silicon thin films. PMID:26333948

Anisotropic thermoelectric behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications.

PubMed

Arab, Abbas; Li, Qiliang

2015-09-03

In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 in both armchair and zigzag orientations. Density functional theory (DFT) using non-equilibrium Green's function (NEGF) method has been implemented to calculate the transmission spectra of mono- and fewlayer MoS2 in armchair and zigzag directions. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In general, a thermoelectric generator is composed of thermocouples made of both n-type and p-type legs. Based on our calculations, monolayer MoS2 in armchair orientation is found to have the highest ZT value for both p-type and n-type legs compared to all other armchair and zigzag structures. We have proposed a thermoelectric generator based on monolayer MoS2 in armchair orientation. Moreover, we have studied the effect of various dopant species on thermoelectric current of our proposed generator. Further, we have compared output current of our proposed generator with those of Silicon thin films. Results indicate that thermoelectric current of MoS2 armchair monolayer is several orders of magnitude higher than that of Silicon thin films.

The capacity fading mechanism and improvement of cycling stability in MoS2-based anode materials for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Shu, Haibo; Li, Feng; Hu, Chenli; Liang, Pei; Cao, Dan; Chen, Xiaoshuang

2016-01-01

Two-dimensional (2D) layered MoS2 nanosheets possess great potential as anode materials for lithium ion batteries (LIBs), but they still suffer from poor cycling performance. Improving the cycling stability of electrode materials depends on a deep understanding of their dynamic structural evolution and reaction kinetics in the lithiation process. Herein, thermodynamic phase diagrams and the lithiation dynamics of MoS2-based nanostructures with the intercalation of lithium ions are studied by using first-principles calculations and ab initio molecular dynamics simulations. Our results demonstrate that the continuous intercalation of Li ions induces structural destruction of 2H phase MoS2 nanosheets in the discharge process that follows a layer-by-layer dissociation mechanism. Meanwhile, the intercalation of Li ions leads to a structural transition of MoS2 nanosheets from the 2H to the 1T phase due to the ultralow transition barriers (~0.1 eV). We find that the phase transition can slow down the dissociation of MoS2 nanosheets during lithiation. The result can be applied to explain extensive experimental observation of the fast capacity fading of MoS2-based anode materials between the first and the subsequent discharges. To suppress the dissociation of MoS2 nanosheets in the lithiation process, we propose a strategy by constructing a sandwich-like graphene/MoS2/graphene structure that indicates high chemical stability, superior conductivity, and high Li-ion mobility in the charge/discharge process, implying the possibility to induce an improvement in the anode cycling performance. This work opens a new route to rational design layered transition-metal disulfide (TMD) anode materials for LIBs with superior cycling stability and electrochemical performance.Two-dimensional (2D) layered MoS2 nanosheets possess great potential as anode materials for lithium ion batteries (LIBs), but they still suffer from poor cycling performance. Improving the cycling stability of

Top-Down and Bottom-Up Approaches in Engineering 1 T Phase Molybdenum Disulfide (MoS2 ): Towards Highly Catalytically Active Materials.

PubMed

Chua, Chun Kiang; Loo, Adeline Huiling; Pumera, Martin

2016-09-26

The metallic 1 T phase of MoS2 has been widely identified to be responsible for the improved performances of MoS2 in applications including hydrogen evolution reactions and electrochemical supercapacitors. To this aim, various synthetic methods have been reported to obtain 1 T phase-rich MoS2 . Here, the aim is to evaluate the efficiencies of the bottom-up (hydrothermal reaction) and top-down (chemical exfoliation) approaches in producing 1 T phase MoS2 . It is established in this study that the 1 T phase MoS2 produced through the bottom-up approach contains a high proportion of 1 T phase and demonstrates excellent electrochemical and electrical properties. Its performance in the hydrogen evolution reaction and electrochemical supercapacitors also surpassed that of 1 T phase MoS2 produced through a top-down approach. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of buffer layer on photoresponse of MoS2 phototransistor

NASA Astrophysics Data System (ADS)

Miyamoto, Yuga; Yoshikawa, Daiki; Takei, Kuniharu; Arie, Takayuki; Akita, Seiji

2018-06-01

An atomically thin MoS2 field-effect transistor (FET) is expected as an ultrathin photosensor with high sensitivity. However, a persistent photoconductivity phenomenon prevents high-speed photoresponse. Here, we investigate the photoresponse of a MoS2 FET with a thin Al2O3 buffer layer on a SiO2 gate insulator. The application of a 2-nm-thick Al2O3 buffer layer greatly improves not only the steady state properties but also the response speed from 1700 to 0.2 s. These experimental results are well explained by the random localized potential fluctuation model combined with the model based on the recombination of the bounded electrons around the trapped hole.

Principles to Products: Toward Realizing MOS 2.0

NASA Technical Reports Server (NTRS)

Bindschadler, Duane L.; Delp, Christopher L.

2012-01-01

This is a report on the Operations Revitalization Initiative, part of the ongoing NASA-funded Advanced Multi-Mission Operations Systems (AMMOS) program. We are implementing products that significantly improve efficiency and effectiveness of Mission Operations Systems (MOS) for deep-space missions. We take a multi-mission approach, in keeping with our organization's charter to "provide multi-mission tools and services that enable mission customers to operate at a lower total cost to NASA." Focusing first on architectural fundamentals of the MOS, we review the effort's progress. In particular, we note the use of stakeholder interactions and consideration of past lessons learned to motivate a set of Principles that guide the evolution of the AMMOS. Thus guided, we have created essential patterns and connections (detailed in companion papers) that are explicitly modeled and support elaboration at multiple levels of detail (system, sub-system, element...) throughout a MOS. This architecture is realized in design and implementation products that provide lifecycle support to a Mission at the system and subsystem level. The products include adaptable multi-mission engineering documentation that describes essentials such as operational concepts and scenarios, requirements, interfaces and agreements, information models, and mission operations processes. Because we have adopted a model-based system engineering method, these documents and their contents are meaningfully related to one another and to the system model. This means they are both more rigorous and reusable (from mission to mission) than standard system engineering products. The use of models also enables detailed, early (e.g., formulation phase) insight into the impact of changes (e.g., to interfaces or to software) that is rigorous and complete, allowing better decisions on cost or technical trades. Finally, our work provides clear and rigorous specification of operations needs to software developers, further

EMC analysis of MOS-1

NASA Astrophysics Data System (ADS)

Ishizawa, Y.; Abe, K.; Shirako, G.; Takai, T.; Kato, H.

The electromagnetic compatibility (EMC) control method, system EMC analysis method, and system test method which have been applied to test the components of the MOS-1 satellite are described. The merits and demerits of the problem solving, specification, and system approaches to EMC control are summarized, and the data requirements of the SEMCAP (specification and electromagnetic compatibility analysis program) computer program for verifying the EMI safety margin of the components are sumamrized. Examples of EMC design are mentioned, and the EMC design process and selection method for EMC critical points are shown along with sample EMC test results.