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Sample records for 6h-sic mos structures

  1. Design method for a digitally trimmable MOS transistor structure

    Ning, Feng; Bruun, Erik

    1996-01-01

    A digitally trimmable MOS transistor is a MOS transistor consisting of a drain, a source, and a main gate as well as several subgates. The transconductance of the transistor is tunabledigitally by means of connecting subgates either to the main gate or to the source terminal. In this paper, a...... systematic design method for a digitally trimmable MOS transistor structure is proposed. Using the proposed method, we have designed a digitally trimmable MOS transistor structure and prototype devices were fabricated in a 2.4 micron n-well CMOS technology. Through measurements on these devices, the design...... method has been experimentally confirmed. The trimmable MOS transistor structure has been applied to a high precision current mirror to reduce mismatch in the current mirror. With the trimmable transistor structure, the mismatch can be reduced by more than one order of magnitude....

  2. Design method for a digitally trimmable MOS transistor structure

    Ning, Feng; Bruun, Erik

    1996-01-01

    systematic design method for a digitally trimmable MOS transistor structure is proposed. Using the proposed method, we have designed a digitally trimmable MOS transistor structure and prototype devices were fabricated in a 2.4 micron n-well CMOS technology. Through measurements on these devices, the design...... method has been experimentally confirmed. The trimmable MOS transistor structure has been applied to a high precision current mirror to reduce mismatch in the current mirror. With the trimmable transistor structure, the mismatch can be reduced by more than one order of magnitude....

  3. Heavy-ion induced current in MOS structure

    The heavy-ion induced current in MOS structure has been investigated. We measured transient currents in MOS capacitors induced by 18 MeV Oxygen and 150 MeV Argon ions. The irradiation tests were carried out using the Single Ion Hit system and the current was measured using a Transient Ion Beam Induced Current measurement system. The current was calculated using device simulator and compared with measured data. It was confirmed that the transient current in MOS structure is dominated by a displacement current; that is caused by changing of surface potential under gate electrode due to the charges moved from ion-track region. (author)

  4. Effects of radiation on MOS structures and silicon devices

    A comprehensive view of radiation effects on MOS structures and silicon devices is given. In the introduction, the interaction of radiation with semiconductor material is presented. In the next section, the electrical degradation of semiconductor devices due to this interaction is discussed. The commonly used hardening techniques are shown. The last section deals with testing of radiation hardness of devices. (orig.)

  5. Atomic and electronic structure of MoS2 nanoparticles

    Bollinger, Mikkel; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet

    2003-01-01

    edges. The electronic structure of the edge states is studied and we discuss their influence on the chemical properties of the edges. In particular, we study the reactivity towards hydrogen and show that hydrogen may form stable chemical bonds with both the two low-Miller indexed edges of MoS2. A model...

  6. Influence of Ro radiation upon ion-implanted MOS structures

    The interaction of Ro radiation with defects in ion-implanted MOS structures is studied using the method of thermally stimulated charge release and C/V method. It is shown that preliminary treatment with Ro radiation decreases the temperature of thermal annealing of the radiation defects introduced by ion-implantation up to 4500C. (author)

  7. Atomic and electronic structure of MoS2 nanoparticles

    Bollinger, Mikkel; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet

    2003-01-01

    Using density-functional theory (DFT) we present a detailed theoretical study of MoS2 nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized at the edges. The electronic structure of the edge states is studied and we discuss their influence on the chemical properties of the edges. In particular, we study the reactivity towards hydrogen and show th...

  8. ELECTRONIC PROPERTIES OF MOS 2 MONOLAYER AND RELATED STRUCTURES

    ENYASHIN A.N.; Seifert, G.

    2014-01-01

    The present review provides an overview of the transition metal dichalcogenides discovered newly at the level of two dimensions. A special emphasis is given to the electronic structure of semiconducting representatives of this family, which can depend on many factors like thickness, environment, mechanical strain and structural imperfections of the layers. Both calculations and experimental data available to date on example of MoS 2 compound evidence that, semiconducting dichalcogenide layers...

  9. Band structural properties of MoS2 (molybdenite)

    Semiconductivity and superconductivity in MoS2 (molybdenite) can be understood in terms of the band structure of MoS2. The band structural properties of MoS2 are presented here. The energy dependence of nsub(eff) and epsilon(infinity)sub(eff) is investigated. Using calculated values of nsub(eff) and epsilon(infinity)sub(eff), the Penn gap has been determined. The value thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from the band structure. The Ravindra and Srivastava formula has been shown to give values for the isobaric temperature gradient of Esub(G)[(deltaEsub(G)/deltaT)sub(P)], which are in agreement with the experimental data, and the contribution to (deltaEsub(G)/deltaT)sub(P) due to the electron lattice interaction has been evaluated. In addition, the electronic polarizability has been calculated using a modified Lorentz-Lorenz relation. (author)

  10. Properties of MOS structures after B+ ion bombardment

    Some electrophysical properties of Si-SiO2 structures after boron ion implantation (E = 25 keV) through the oxide layer without subsequent annealing are investigated by the methods of C(U)-characteristics and the thermally stimulated charge release. The change of the electrophysical characteristics of MOS structures is shown to depend, in the definite implantation dose interval, on the position of distribution maximum of the implanted impurity relative to the Si-SiO2 interface; these characteristics are determined mainly by the radiation damage which induces the deep acceptor levels. The calculations made possible a qualitative explanation of the experimental results obtained. (author)

  11. The dual MOS-gated thyristor (DMGT) structure

    Flores, D.; Fernández, J.; Jordà, X.; Rebollo, J.; Godignon, P.; Hidalgo, S.; Millán, J.

    1998-04-01

    A new device concept, called the dual MOS-gated thyristor (DMGT), is presented in this paper and analyzed with the aid of 2D numerical simulations. The structure includes a vertical thyristor, a floating ohmic contact (FOC), and two N-channel MOSFETs (M1 and M2) which are controlled by independent gates. It can be operated either in a thyristor mode or in an IGBT regime, which provides the device a low on-state voltage drop and a good forward biased safe operating area. When a positive bias is applied to the M1 gate, the structure operates in the thyristor mode with a low on-state voltage drop. On the contrary, when a positive bias is applied to the M2 gate, the structure operates in the IGBT regime with the saturated current controlled by the positive voltage applied to the M1 gate.

  12. Ion implantation and MOS structures in SiC

    A theoretical study of stoichiometric disturbance (SMD) due to ion implantation in SiC is reported. In addition, experimental work on the material characterization of 3C SiC layers using Schottky diodes and metal-oxide-semiconductor (MOS) structures are presented. In studying theoretical aspects of ion implantation in SiC, a method is developed to calculate the depth distribution of the stoichiometric disturbance (SMD) resulting from this process. Projectile range distributions at intermediate energies are deduced from look-up tables of known range statistics. This results in a simpler method with little loss of accuracy as compared to existing procedures which use the Boltzmann transport equation. A calculation of the SMD for implantation of Al in SiC suggests that the SMD may be responsible for otherwise unexplained distortions in the annealed Al profile. In the efforts of the characterization of the 3C SiC material, the effects of oxidation of the SiC substrate have been studied at room temperature by capacitance-voltage (C-V) measurements on MOS structures formed by a double-contact mercury probe. Standard methods have been implemented to extract various device parameters from the C-V characteristics. These include the calculation of substrate doping profile, effective fixed oxide trap density, N1, and interface trap density, D/sub it/. The effective N/sub f/ value was found to be 4 to 7 x 1011 cm-2. The value of d/sub it/ is obtained from a comparison of the measured characteristics to a theoretical high-frequency curve and it reveals a concentration of approximately 1011 cm-2eV-1 across the energy gap, with a peak on the order of 1012 cm-2eV-1, centered at 0.6 eV below the conduction band edge

  13. Preparation and tunneling characteristics of MOS structures for Si-based IR light emitters

    Suckow, Stephan [IHP/BTU Joint Lab., Cottbus (Germany); Kittler, Martin; Seifert, Winfried; Arguirov, Tzanimir [IHP/BTU Joint Lab., Cottbus (Germany); IHP, Frankfurt (Oder) (Germany); Schmidt, Manfred; Stegemann, Bert; Angermann, Heike [Hahn-Meitner-Institut Berlin (Germany)

    2008-07-01

    Si based light emitters, such as MOS structures based on dislocation networks, are attractive candidates for the generation of electroluminescence in the IR spectral range to be applied e.g. in optical on-chip interconnects. In the present work the preparation of an appropriate MOS structure that facilitates efficient charge carrier injection is explored and its charge carrier tunneling and recombination characteristics are analyzed. In this respect MOS structures with ultra-thin tunnel oxides fabricated by wet-chemical oxidation of Si wafers and thermally deposited Ti contacts turned out to produce the most efficient and reliable results. Moreover, electroluminescence measurements revealed an anomalous temperature behavior of band-to-band recombination with enhanced intensity at higher temperature (300 K). As photoluminescence intensity inversely increases with decreasing temperature, this effect is clearly correlated to efficient minority charge carrier injection via the MOS contact and points towards an application as room temperature IR light emitter.

  14. Influence of Deposition Conditions on the Crystal Structure of MoS2 Coating

    Jihui WANG; Yang XIA; E.Wieers; L.M.Stals; X.Zhang; J.P.Celis

    2006-01-01

    MoS2 coatings were prepared using an unbalanced bipolar pulsed DC (direct current) magnetron sputtering apparatus under different targets, cathode current densities, power modes and bias voltages. The morphology,structure and growth characteristics of MoS2 coatings were observed and identified respectively by scanning electron microscopy, X-ray diffractometry and mass spectrometry. The results show that MoS2 coatings evolve with the (002) basal plane parallel to the surface by using cold pressed target with lower density, lower cathodic current density, bipolar pulse DC power and minus bias voltage, whereas the coatings deposited under hot pressed target, higher cathodic current density, simple DC power and positive bias voltage have the (002)basal plane perpendicular to the surface. The influence of deposition conditions on the crystal structure of MoS2 coating is implemented by altering its growth rate and the energy of sputtering-deposition particles.

  15. Sulfur bonding in MoS2 and Co-Mo-S structures

    Byskov, Line Sjolte; Hammer, Bjørk; Nørskov, Jens Kehlet;

    1997-01-01

    The structure and bonding in small MoS2 structures with and without Co is studied theoretically using self-consistent density functional theory with a non-local exchange-correlation energy. The structures model the catalysts used extensively in hydrotreating. We study in detail the structure and...... binding energies as a function of the amount of sulfur. The calculations show that extensive reconstructions occur at the two types of MoS2 edges where the sulfur dimerizes and occupies non-lattice positions. These structures are shown to be in good agreement with available experimental data. We also...

  16. High-pressure structure, decomposition, and superconductivity of MoS2

    Kohulák, Oto; MartoÅák, Roman; Tosatti, Erio

    2015-04-01

    The high pressure structural and electronic evolution of bulk MoS2, an important transition metal layered dichalchogenide, is currently under active investigation, particularly in search of superconductivity. Recent theoretical and experimental work predicted and verified a 2 Hc→2 Ha layer sliding structural transition at 20 GPa and a band overlap semiconductor-semimetal transition in the same pressure range. The poorly metallic and nonsuperconducting 2 Ha structure is known to persist up to a pressure of 81 GPa, but properties at higher pressures remain experimentally unknown. Here we predict, with a first-principles evolutionary search, that major structural and electronic transformations should take place in equilibrium at higher pressures near 130-140 GPa. The main motif is a decomposition into MoS + S, also heralded in a small bimolecular cell by the appearance of a metastable nonlayered metallic MoS2 structure with space group P 4 /m m m . Unlike semimetallic 2 Ha -MoS2, the new high pressure phases are expected to be fully metallic and superconducting with higher critical temperatures than even alkali-intercalated MoS2.

  17. Fabrication and atomic structure of size-selected, layered MoS2 clusters for catalysis.

    Cuddy, Martin J; Arkill, Kenton P; Wang, Zhi Wei; Komsa, Hannu-Pekka; Krasheninnikov, Arkady V; Palmer, Richard E

    2014-11-01

    Well defined MoS2 nanoparticles having a layered structure and abundant edges would be of considerable interest for applications including photocatalysis. We report the atomic structure of MoS2 size-selected clusters with mass in a range all the way from 50 to ∼2000 MoS2 units. The clusters were prepared by magnetron sputtering and gas condensation prior to size selection and soft landing on carbon supports. Aberration-corrected scanning transmission electron microscopy (STEM) in high-angle annular dark-field (HAADF) mode reveals a layered structure and Mo-Mo spacing similar to the bulk material. The mean number of layers in these lamellar clusters increases from one to three with increasing mass, consistent with density functional theory calculations of the balance between edge energies and interlayer binding. PMID:25226541

  18. Atomic-scale structure of single-layer MoS2 nanoclusters

    Helveg, S.; Lauritsen, J. V.; Lægsgaard, E.;

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2...... nanoparticles synthesized on Au(lll), and establishes a new picture of the active edge sires of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in general....

  19. Atomic-scale structure of single-layer MoS2 nanoclusters

    Helveg, S.; Lauritsen, J.V.; Lægsgaard, E.; Stensgaard, I.; Nørskov, Jens Kehlet; Clausen, B.S, Helveg S; Topsøe, H.; Besenbacher, Flemming

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2 nanoparticles synthesized on Au(lll), and establishes a new picture of the active edge sires of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in ...

  20. Modification of thin oxide films of MOS structure by high-field injection and irradiation

    Andreev, D. V.; Bondarenko, G. G.; Andreev, V. V.; Stolyarov, A. A.

    2016-02-01

    We have investigated processes of modification and changing of the charge state of MOS structures having a multilayer gate dielectric based on a thermal SiO2 film doped with phosphorus under conditions of different modes of high-field electron injection and an electron irradiation. We have determined that negative charge, accumulating in the phosphosilicate glass (PSG) ultra thin film of the MOS structures having the two-layer gate dielectric SiO2-PSG under conditions of both high-field tunneling injection of electrons and electron beam, could be used for a modification of devices having the same structure (e.g. correction of threshold voltage, increase of charge stability and breakdown voltage of MOS structure). We have shown that when thickness of PSG film increased, a raising of the electron traps density occurred, but the value of the cross-section of electron traps was the same. It was established that in order to obtain MOS structures with high thermal stability, one has to anneal them at 200° C after performing irradiation treatment.

  1. Effect of monolayer supports on the electronic structure of single-layer MoS2

    Ramirez-Torres, Alfredo; Le, Duy; Rahman, Talat S.

    2015-03-01

    We present results of density functional theory based calculations of the electronic structure of a single-layer of MoS2, as modified by three different single-layer materials used as support: hexagonal boron nitride (h-BN), graphene, and silicene, using the local density approximation (LDA), on the one hand, and a functional that explicitly includes van der Waals interactions (optB88-vdW), on the other hand. Because the lattice mismatch between the primitive cell of MoS2 and those of the supports is large, calculations are performed with as large a supercell as computationally feasible, so as to reduce the incommensurability between lattices. Even though van der Waals interactions are expected to play an important role in the binding between MoS2, and h-BN and graphene, we find that the band structure and related conclusions obtained by optB88-vdW and LDA are quite similar for the three heterostructures considered here. Single-layer MoS2 interacts weakly with h-BN and graphene, while covalent bonds are formed with silicene. Detailed analysis of the electronic density of states also indicates little effect of h-BN and graphene, while silicene severely modifies it by introducing additional states within the band gap. Furthermore, adsorption on graphene brings the conduction bands of MoS2 down to the Fermi level of graphene as a result of charge transfer from graphene to MoS2, while adsorption on silicene shifts both valence and conduction bands towards the Fermi level, in addition to inducing a gap of ~50 meV in silicene itself.

  2. Heavy ion effect on MOS and CMOS structures on insulator (CMOS/SOI)

    The effects of cosmic ions on Metal-Oxide-Semiconductor structures are described. Measurements done at different energies on MOS capacitors and CMOS on insulator transistors (CMOS/SOI) show a substrate funneling which gives rise to a transient current on device electrodes. The pulse amplitude is simply related to capacitor bias, lifetime of substrate minority carriers and range of the impinging ion

  3. Phosphorus ion implantation gettering effects in Mos structures

    The influence of some variables of phosphorus ion implantation gettering efficiency in Mos capacitors was investigated by the C-t measurement technique. The Si wafers were gettered by a 120 keV backside P ion implantation, into bare silicon and into silicon covered by a screen oxide 600-1200 Angstroms thick, with subsequent annealing at 900 Centigrade degrees for 30-150 min in N2. The generation lifetime was found to show maximum value after 120 min anneal. A marked tendency in the behavior of generation lifetime, when P was implanted into bare silicon and when it was implanted into silicon covered by an oxide, was not found. In both cases, the generation lifetime increases with the increase of oxide thickness. (Author)

  4. Modeling of tunneling current in ultrathin MOS structure with interface trap charge and fixed oxide charge

    Hu Bo; Huang Shi-Hua; Wu Feng-Min

    2013-01-01

    A model based on analysis of the self-consistent Poisson-Schrodinger equation is proposed to investigate the tunneling current of electrons in the inversion layer of a p-type metal-oxide-semiconductor (MOS) structure.In this model,the influences of interface trap charge (ITC) at the Si-SiO2 interface and fixed oxide charge (FOC) in the oxide region are taken into account,and one-band effective mass approximation is used.The tunneling probability is obtained by employing the transfer matrix method.Further,the effects of in-plane momentum on the quantization in the electron motion perpendicular to the Si-SiO2 interface of a MOS device are investigated.Theoretical simulation results indicate that both ITC and FOC have great influence on the tunneling current through a MOS structure when their densities are larger than 1012 cm-2,which results from the great change of bound electrons near the Si-SiO2 interface and the oxide region.Therefore,for real ultrathin MOS structures with ITC and FOC,this model can give a more accurate description for the tunneling current in the inversion layer.

  5. MOS structure fabrication by thermal oxidation of multilayer metal thin films

    Mohammad Orvatiniat; Atefeh Chahkoutahi

    2011-01-01

    A novel approach for the fabrication of a metal oxide semiconductor (MOS) structure was reported.The process comprises electrochemical deposition of aluminum and zinc layers on a base of nickel-chromium alloy.This two-layer structure was thermally oxidized at 400 ℃ for 40 min to produce thin layers of aluminum oxide as an insulator and zinc oxide as a semiconductor on a metallic substrate.Using deposition parameters,device dimensions and SEM micrographs of the layers,the device parameters were calculated.The resultant MOS structure was characterized by a C-V curve method.From this curve,the device maximum capacitance and threshold voltage were estimated to be about 0.74 nF and -2.9 V,respectively,which are in the order of model-based calculations.

  6. Surface Passivation of Germanium Using NH3 Ambient in RTP for High Mobility MOS Structure

    Anil G. Khairnar

    2013-05-01

    Full Text Available Ge CMOS is very striking for the post Si-CMOS technology. However, we have to attempt a number of challenges with regard to materials and their interface control. In this paper we have investigated the control of the interfacial properties of SiO2 / Ge gate stack structures by the thermal nitridation technique. Structural and electrical properties of SiO2 gate-dielectric metal-oxide-semiconductor (MOS capacitors deposited by sputtering on germanium are studied. The structural characterization confirmed that the thin film was free of physical defects and smooth surface of the films after PDA at 500 °C in N2 ambient. The smooth surface SiO2 thin films were used for Pt / SiO2 / GeON / Ge MOS structures fabrication. The MOS structure yields a low leakage current density of 9.16 × 10 – 6Acm – 2 at 1 V.

  7. New strategy of modeling inversion layer characteristics in MOS structure for ULSI applications

    马玉涛; 李志坚; 刘理天

    2001-01-01

    With the development of ULSI silicon technology, metal oxide semiconductor field effect transistor (MOSFET) devices are scaling down to nanometer regime. Energy of carriers in inversion layer in MOS structure is quantized and consequently, the physics and then the transport characteristics of inversion layer carriers are different from those in semi-classical theory. One essential matter is that the widely used concept of conduction band (valence band as well) effective density-of-states is no longer valid in quantized inversion layer. In this paper, an alternative concept, called surface layer effective density-of-states, is used to model the characteristics of MOS structure including threshold voltage, carrier sheet density, surface potential as well as capacitance.

  8. C-VCharacterization in MOS Structure Inversion Layer Including Quantum Mechanical Effects

    马玉涛; 刘理天; 李志坚

    2000-01-01

    A simplified method to calculate the band bending and subband energy is presented to investigate the Quantum Mechanical Effects (QMEs) in MOS structure inversion layer. The method is fairly unique compared with the published methods in the reversed nature of the iteration procedure. It has high efficiency and good convergence characteristics. Gate capacitance in MOS structure inversion region is formulated in both quantum mechanical cases and semi-classical cases and Quantum Mechanical Effects on gate capacitance have been analyzed. Results of different substrate doping levels are compared and the substrate doping concentration dependence of QMEs on gate capacitance is studied. It is shown that QMEs lead to a substantial decrease in gate capacitance in the strong inversion region. Results of different substrate doping levels indicate that the QMEs on gate capacitance are different substantially in the threshold region at different substrate doping levels but almost the same in the strong inversion region.

  9. Electron and γ-irradiation of ion implanted MOS structures with different oxide thickness

    Effects of high-energy electrons or gamma irradiation on the interface states of ion implanted MOS structures have been investigated by thermally stimulated charge method. The n-type Si-SiO2 samples with oxide thickness of 20, 200 and 300 are implanted with 50 keV boron ions to a dose of 1.5 x 1012 cm-2. Formed MOS structures are irradiated with 11 MeV electrons or 60Co γ-rays. The energy position and the concentration of the radiation-induced interface traps are determined. It is shown that the kinds of radiation-induced interface traps and their concentration depend on the disposition of the maximum of the previously implanted boron ions with respect to the Si-SiO2 interface

  10. Metal incorporation in sputter-deposited MoS2 films studied by extended x-ray adsorption fine structure

    Solid lubricant films produced by cosputtering metals with MoS2 and by forming metal/MoS2 multilayers are being planned for use in the next generation of solid lubricated devices on spacecraft, including gimbal and sensor bearings, actuators, and sliding electrical contacts. The films exhibit increased densities and wear lives compared to films without additives, but the mechanism of density enhancement is not well understood. The extended x-ray absorption fine structure (EXAFS) technique is ideal for elucidating the structure of these poorly crystalline films. We analyzed MoS2 films cosputtered with 0, 2, and 10% Ni, as well as Ni/MoS2 and Au(Pd)/MoS2 multilayer films. The results obtained at the Mo-K absorption edge showed that the metal-containing films comprised predominantly the same nanocrystalline phases present in similar films without added metals: pure MoS2 and a MoS2-xOx phase. MoS2-xOx is isostructural with MoS2, with O atoms substituting for S atoms in the MoS2 crystal lattice. For all Ni-containing films, EXAFS data obtained at the Ni--K absorption edge showed that the Ni had not chemically reacted with the MoS2-xOx and MoS2, but formed a disordered NiOx phase. However, Ni-cosputtered films showed decreasing Mo--Mo bond lengths in the MoS2-xOx phase with increasing Ni content, probably due to preferential oxidation of Ni compared to MoS2. EXAFS of these Ni-cosputtered films showed only a small decrease in short-range order with Ni content, while x-ray diffraction showed a concurrent large decrease in long-range order. The results indicate that film densification in Ni-cosputtered films is caused by NiOx formation at the edges of nucleating MoS2-xOx /MoS2 crystallites

  11. Investigations of physical properties of MOS-structure heavy ion counters

    Physical properties of the MOS-structure n-type silicon breakdown heavy ion counters with 50 mm2 sensitive area were investigated. Detection efficiency is approximately 100%. Heavy ion registration energy threshold is (22 +- 2) MeV/mg cm2 in silicon dioxide. Operation resource for the fission fragment registration does not exceed 3 X 106 fragm/cm2. The counters have good stability and have no background when irradiated with light charged particles. (Auth.)

  12. Formation of oxide-trapped charges in 6H-SiC MOS structures

    Yoshikawa, Masahito; Ohshima, Takeshi; Itoh, Hisayoshi; Nashiyama, Isamu [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment; Okumura, Hajime; Yoshida, Sadafumi

    1997-03-01

    The silicon and the carbon faces of hexagonal silicon carbide (6H-SiC) substrates were oxidized pyrogenically at 1100degC, and the metal-oxide-semiconductor structures were formed on these faces. The MOS capacitors developed using the silicon and the carbon faces were irradiated with {sup 60}Co gamma-rays under argon atmosphere at room temperature. The bias voltages with the different polarity were applied to the gate electrode during irradiation to examine the formation mechanisms of the trapped charges in the oxides of these MOS capacitors. The amount of the trapped charges in the oxide were obtained from capacitance pulse voltage characteristics. The generation of the trapped charges are affects with not only the absorbed dose but also the bias polarity applied to the gate electrodes during irradiation. The formation mechanisms of the trapped charges in the oxides were estimated in conjunction with the surface orientation of 6H-SiC substrates. (author)

  13. Utilization of monolayer MoS2 in Bragg stacks and metamaterial structures as broadband absorbers

    Mukherjee, Bablu; Simsek, Ergun

    2016-06-01

    We numerically study the possibility of using atomically thin transition metal dichalcogenides (TMDs) for applications requiring broadband absorption in the visible range of the electromagnetic spectrum. We demonstrate that when monolayer TMDs are positioned into a finite-period of multilayer Bragg stack geometry, they make broadband, wide-angle, almost polarization-independent absorbers. In our study, we consider molybdenum disulfide (MoS2) and silicon dioxide (SiO2) as semiconducting and dielectric thin film of alternate high- and low- index films, respectively. By optimizing the thickness of the SiO2 film, we find that monolayer MoS2 based Bragg stacks can absorb 94.7% of the incident energy in the visible (350-700 nm). Similar structures can be engineered to make perfect reflectors for saturable absorption applications. We also demonstrate that bandwidth of metamaterial absorbers can be expanded using monolayer TMDs.

  14. Surface Passivation of Germanium Using NH3 Ambient in RTP for High Mobility MOS Structure

    Anil G. Khairnar; Y.S. Mhaisagar; A.M. Mahajan

    2013-01-01

    Ge CMOS is very striking for the post Si-CMOS technology. However, we have to attempt a number of challenges with regard to materials and their interface control. In this paper we have investigated the control of the interfacial properties of SiO2 / Ge gate stack structures by the thermal nitridation technique. Structural and electrical properties of SiO2 gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering on germanium are studied. The structural characterizatio...

  15. Fundamental insights into the electronic structure of zigzag MoS2 nanoribbons.

    Yu, Shansheng; Zheng, Weitao

    2016-02-14

    The structural and electronic properties of zigzag MoS2 nanoribbons are investigated using first-principles density functional theory. Our models are motivated by the experimental observations, in which both Mo edges are terminated by S atoms. Our calculations show that the edge can introduce some extra states into the energy gap, which lead nanoribbons to exhibit a metallic characteristic. Such extra states around the Fermi level are flat or dispersed. Through detailed analyses, we identify and discriminate them based on the major contributors. By applying an external transverse electric field, Eext the extra states around the Fermi level can shift apparently, especially for those attributed to Mo-edge atoms. It can be explained by the charge redistribution in the MoS2 nanoribbons due to Eext. In addition, the nanoribbon can be changed from metal to an n/p-type semiconductor according to different edge hydrogenation. After full edge hydrogenation, we observe a characteristic of anti-bonding orbitals between H and S atoms at the Mo-edge. Interestingly, the energy of anti-bonding orbitals and electric conductivity of nanoribbons can be tailored by Eext. The results suggest a strategy controlling the performance of MoS2 for hydrogen evolution. PMID:26799649

  16. Effect of vacancies on structural, electronic and optical properties of monolayer MoS2: A first-principles study

    Highlights: • VMo induces an outward relaxation, whereas VS induces inward relaxation. • Monolayer MoS2 has changed from direct to indirect band gap after introduction of VMo0. • VMo induces acceptor-like level, whereas VS induces donor-like level. • Band gaps get smaller and defect levels get deeper as charge states of V increase. • Dielectric constants of defective monolayer MoS2 are larger than that of perfect one. - Abstract: Effects of vacancies on structural, electronic and optical properties of monolayer MoS2 were investigated using first-principles plane-wave pseudopotential method based on density functional theory. Results show that the band structure and band gap of perfect monolayer MoS2 are in good agreement with the available experimental and theoretical data. Structural analysis indicates that ions surrounding Mo vacancies show an outward relaxation, while that ions surrounding S vacancies exhibit slightly inward relaxation. Electronic analysis implies that the band gaps of defective monolayer MoS2 are smaller than that of perfect one. After introduction of neutral S-vacancy, monolayer MoS2 has changed from direct to indirect band gap. Mo vacancies bring about acceptor-like levels and p-type conductivities, whereas S vacancies lead to donor-like levels and n-type conductivities. With the increasing charge states of vacancies, the band gaps get smaller and the defect energy levels become deeper. Moreover, as the charge states of vacancies increase, the static dielectric constants of monolayer MoS2 with Mo vacancies decrease, whereas the static dielectric constants of monolayer MoS2 with S vacancies increase

  17. A MOS tunneling structure used as a photosensitive device with internal gain

    Avalanche photodiodes used in photosensitive devices with internal gain suffer some limitations due to their doping profiles and the reproducibility of their internal gain. Experiments were made on devices using very thin layers of SiO2. The basic structure being a MOS capacitance, it was shown that such a structure provides an internal gain when minority carriers are injected within the deep depletion layer just beneath the thin oxide in the silicon. Experimal results obtained on devices built using either aluminum and chromium electrodes are presented

  18. Kelvin probe force and scanning capacitance microscopy on MOS structures

    Baumgart, Christine; Helm, Manfred; Schmidt, Heidemarie [Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Dresden (Germany); Jaensch, Stefan [ElKiDo, Skjern (Denmark)

    2009-07-01

    As the size of semiconductor devices is decreasing permanently, new techniques are required to probe their dopant profile reliably on a nanometer scale. Kelvin probe force microscopy (KPFM) and scanning capacitance microscopy (SCM) are the most promising techniques for this demand. KPFM (LevelAFM from Anfatec) enables the detection of the contact potential difference (CPD) between tip and sample and SCM (DI3100 from Veeco Instruments) probes the capacitance of the metal oxide structures formed in contact. In order to demonstrate the complementary information obtained by KPFM and SCM measurements, we used the pn junction in a static random access memory integrated circuit device where the n-well with a donor concentration of 2.10{sup 17} cm{sup -3} has been fabricated by implanting the p-epi with a nominal acceptor concentration of 2.10{sup 16} cm{sup -3} with P{sup +} ions of energy 900 keV and a fluence of 1.7.10{sup 13} cm{sup -2}. As expected, KPFM yields a smooth variation of the CPD between the p-epi and the n-well amounting to 230 meV. SCM clearly shows the boxlike doping profile of this pn junction. The CPD variation can be modelled by assuming a partially compensated donor concentration in the n-well.

  19. Formation and annealing of radiation damage in boron ion implanted MOS structures

    Processes of accumulation of defects induced by radiation and annealing characteristics of 1.25 x 1012 cm-2 boron implanted MOS structures are investigated at implantation energy varied from 30 to 125 keV. Parameters of centres formed under these conditions at the SiO2-Si interface and in a thin surface region of silicon are determined by the method of thermally stimulated charge release. The anneal temperatures required to remove some types of defects are established. The dielectric-semiconductor interface is shown to affect significantly the anneal processes of traps induced by implantation. (author)

  20. Influence of the incident flux angles on the structures and properties of magnetron sputtered MoS2 films

    In this study, by adjusting the angle between the incident flux and the normal direction of the substrate’s surface, the MoS2 film prepared by magnetron sputtering was used as a model system to study the influence of incident flux angles on the structures and properties of deposited films. The morphological and structural evolutions of MoS2 films deposited at different angles ranging from 0 to 85 degrees were characterized and the corresponding mechanical and tribological properties were evaluated. The results show that a conversion of a continuous film structure to a separate columnar structure with high porosity is found as the incident flux angle increases. Although changing the incident flux angle plays a negligible effect on the crystal preferential orientation of deposited MoS2 films, the mechanical and tribological properties of these films degrade dramatically when the incident flux angle is larger than 60 degrees. (paper)

  1. Prediction of new stable structure, promising electronic and thermodynamic properties of MoS3: Ab initio calculations

    Pan, Yong; Guan, Weiming

    2016-09-01

    MoS3 has attracted considerable attention as potential hydrogen storage material due to the interaction between the hydrogen and unsaturated sulfur atoms. However, its structure and physical properties are unknown. By means of first-principles approach and Inorganic crystal structure Database (ISCD), we systematically investigated the structure, relevant physical and thermodynamic properties of MoS3. Phonon dispersion, electronic structure, band structure and heat capacity are calculated in detail. We predicted the orthorhombic B2ab (SrS3-type) and tetragonal P-421m (BaS3-type) structures of MoS3, which prefers to form the SrS3-type (Space group: B2ab, No.41) structure at the ground state. High pressure results in structural transition from SrS3-type structure to BaS3-type structure. This sulfide exhibits a degree of metallic behavior. The calculated heat capacity of MoS3 with SrS3-type structure is about of 39 J/(mol·K).

  2. Studies in electron phenomena in MOS structures: The pulsed C-V method. M.S. Thesis. Abstract Only

    Kaplan, G.

    1983-01-01

    The pulse hysteresis capacitance voltage (C-V) provides a straight forward technique for measuring the change of various charges in MOS structures and a tool for investigating the kinetics of various electron phenomena is developed and described. The method can be used for measuring the energy distribution and kinetics of surface states with the resolution of about 1/5 x 10 to the -9 power cm eV. Some transients in an MOS structure, particularly, the thermal generation of minority charge carriers via surface states and the relaxation of minority charge carriers supplied from the inversion layer outside the MOS structure are theoretically investigated. Analytical expressions which clearly present the physics of those electron phenomena are derived.

  3. Synthesis and Structural Characterization of Al2O3-Coated MoS2 Spheres for Photocatalysis Applications

    S. V. Prabhakar Vattikuti

    2015-01-01

    Full Text Available This paper reports the synthesis of novel monodisperse Al2O3-coated molybdenum disulfide nanospheres (i.e., core-shell structures using a one-step facile hydrothermal method. XPS analysis confirmed the purity and stable structure of the Al2O3-coated MoS2 nanospheres. A possible growth mechanism of the core-shell structure is also reported, along with their influence on the photodegradation process of rhodamine B (RhB. The Al2O3-coated MoS2 nanospheres demonstrate good photocatalytic activity and chemical stability compared to MoS2 spheres. TG-DTA analysis provided insight into the decomposition process of the precursor solution and the stability of the nanoparticles. The enhanced photocatalytic activity makes the Al2O3-coated MoS2 nanospheres a promising candidate as a photocatalyst that could be used in place of traditional Al2O3/MoS2 photocatalyst for the removal of pollutants from waste water.

  4. Evolution of band structures in MoS2-based homo- and heterobilayers

    Density functional theory calculations have been performed to elucidate the detailed evolution of band structures in MoS2-based homo- and heterobilayers. By constructing the energy-band alignments we observed that biaxial tensile and compressive strain in the constituent transition-metal dichalcogenide (TMD) monolayer shifts the states at the K C, Q C, and K V points down and up, respectively, while the states at the ΓV point are almost unaltered. In contrast, interlayer coupling tends to modify the states at the ΓV and Q C points by splitting the band-edge states of two strained or unstrained constituent TMD monolayers, while it does not affect the states at the K C and K V points. Considering the combined actions of strain and interlayer coupling, the relevant electronic parameters, especially the detailed evolution processes, of the band structures of the investigated bilayer systems can be clearly described. When further applying the extra biaxial strain to the three bilayer systems, it is found that energy differences ΔE(K C  −  Q C) and ΔE(K V  −  ΓV) decrease linearly as the increasing of the biaxial strain. According to the varying trends of ΔE(K C  −  Q C) and ΔE(K V  −  ΓV), MoS2 bilayer will maintain the indirect-bandgap character under any compressive or tensile strain. Differently, WS2/MoS2 heterobilayer transforms interestingly to the direct-bandgap material under the strain from  −1.6% to  −1.2% with the valence band maximum and conduction band minimum located at the K C and K V point respectively. The direct-to-indirect bandgap transition can be obtained for the WSe2/MoS2 heterobilayer when applying much larger extra tensile or compressive strain. The results offer an effective route to verify and tailor the electronic properties of TMD homo- and heterostructures and can be helpful in evaluating the performance of TMD-based electronic devices. (paper)

  5. Evolution of band structures in MoS2-based homo- and heterobilayers

    Zhu, H. L.; Zhou, C. J.; Huang, X. J.; Wang, X. L.; Xu, H. Z.; Lin, Yong; Yang, W. H.; Wu, Y. P.; Lin, W.; Guo, F.

    2016-02-01

    Density functional theory calculations have been performed to elucidate the detailed evolution of band structures in MoS2-based homo- and heterobilayers. By constructing the energy-band alignments we observed that biaxial tensile and compressive strain in the constituent transition-metal dichalcogenide (TMD) monolayer shifts the states at the K C, Q C, and K V points down and up, respectively, while the states at the ΓV point are almost unaltered. In contrast, interlayer coupling tends to modify the states at the ΓV and Q C points by splitting the band-edge states of two strained or unstrained constituent TMD monolayers, while it does not affect the states at the K C and K V points. Considering the combined actions of strain and interlayer coupling, the relevant electronic parameters, especially the detailed evolution processes, of the band structures of the investigated bilayer systems can be clearly described. When further applying the extra biaxial strain to the three bilayer systems, it is found that energy differences ΔE(K C  -  Q C) and ΔE(K V  -  ΓV) decrease linearly as the increasing of the biaxial strain. According to the varying trends of ΔE(K C  -  Q C) and ΔE(K V  -  ΓV), MoS2 bilayer will maintain the indirect-bandgap character under any compressive or tensile strain. Differently, WS2/MoS2 heterobilayer transforms interestingly to the direct-bandgap material under the strain from  -1.6% to  -1.2% with the valence band maximum and conduction band minimum located at the K C and K V point respectively. The direct-to-indirect bandgap transition can be obtained for the WSe2/MoS2 heterobilayer when applying much larger extra tensile or compressive strain. The results offer an effective route to verify and tailor the electronic properties of TMD homo- and heterostructures and can be helpful in evaluating the performance of TMD-based electronic devices.

  6. New data about dielectric breakdown counters on the MOS-structure base for heavy ion detection

    The fabrication technology of dielectric break-down counters based on a MOS structure and designed to record heavy ions is described. To produce counters use was made of low-resistant n-Si. The MOS structure was obtained by the method of thermal growing of a layer of SiO2 having a thickness of 1400 A on a chemically polished surface of the sample with further spraying of a forward aluminium electrode with a thickness of 500 A. One Si sample accomodated several counters. The rear electrode consisting in a layer of Al was common to all counters. By using the above-mentioned technology dielectric breakdown counters have been produced with a total area of the sensitive surface of up to 110 cm2. Results of investigations of such important counter characteristics as the detection efficiency, stability, reliability and reproducibility of counting characteristics in the process of counter fabrication are given. It has been found that the detection efficiency constitutes approximately 100%. The value of specific energy losses in SiO2, at which detection of heavy ions is still possible, is equal to 22+-2 MeVxcm2/mg. The maximum service life of counters in detecting fission fragments constituted approximately 3x10 cm-2. The results of multi-day tests of breakdown detectors showed good stability of their counting characteristics and efficiency

  7. Reduction of the annealing temperature of radiation-induced defects in ion-implanted MOS structures

    Si-SiO2 structures irradiated with 11-MeV electrons for 10 s and then implanted with B+ ions with an energy of 10 keV at a dose of 1.0 x 1012 cm-2 through the oxide were annealed at different temperatures. MOS capacitors including such oxide layers were studied by quasi-static C/V and thermally stimulated current (TSC) methods. A comparison of the radiation defect annealing of double-treated (electron-irradiated and ion-implanted) samples and of implanted-only samples was carried out. It is shown that a preceding low-dose high-energy electron irradiation of the samples leads to a lowering of the annealing temperature of radiation defects introduced by ion implantation. After annealing at 500 C for 15 min, no TSC spectra for the double-treated samples were observed. The spectra of the other samples (which were not previously irradiated) showed that after the same thermal treatment only some of the radiation defects introduced by ion implantation are annealed. The difference between the annealed interface state density of previously electron-irradiated and current MOS structures is also demonstrated. A possible explanation of the results is proposed. (orig.)

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

    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.

  9. Structural studies of seventh-deposited MoS2 solid lubricant films

    The relationship between the morphologies and crystal structures of sputter-deposited MoS2 films and their lubrication capabilities is discussed. In particular, aspects of plastic deformation processes are presented. Scanning electron microscopy (top surface and cross sectional), transmission electron microscopy (lattice imaging and dark field), and x-ray diffraction techniques were used to characterize film structure. The asdeposited morphology, which can be described in terms of zone models, was found to influence the initial nature of the wear debris and the loadbearing capabilities of the films. In many cases a highly deformed region confined to the surface of the films was found. Applied stress was found to reorient crystallites and to induce crystallization, with the degree of both processes being related to the initial structure of the film. Criteria are presented for selecting the film type and preparation conditions to fit various applications

  10. Monolithic Silicon Photodetector - Detector of Ionizing Radiation Based on Functional Integrated MOS Structures

    S.A. Legotin

    2014-07-01

    Full Text Available This paper describes the principle of operation, construction, architecture and fabrication of a new type of monolithic silicon coordinate photodetector - detector of optical and ionizing radiation (MSCP on the basis of functional integrated MOS structures. The analytical estimation of electrophysical characteristics MSCP is given. It is shown that MSCP is a specialized monolithic silicon VLSI containing two-dimensional pixel array with high and low voltage functionally integrated structures (FIS and peripheral electronic circuits of amplification and signal processing matrix. Estimations and presents comparative characteristics are presented. They show potential MSCP possibilities for registration of optical and ionizing radiation. Experimental results of α-particles and electrons registration. The possible areas of application, with the possibility of its use in a wide X-ray panels medical supplies, X-rays, etc are considered.

  11. High frequency characteristics and modelling of p-type 6H-silicon carbide MOS structures

    Fernández, J.; Godignon, P.; Berberich, S.; Rebollo, J.; Brezeanu, G.; Millán, J.

    1996-09-01

    This paper presents the high frequency electrical characteristics and modelling of Al/SiO 2/ p-type 6HSiC structures. The oxide was thermally grown under dry conditions. Capacitance and conductance vs bias and frequency measurements have been performed in daylight and exposing the capacitors to u.v. light. The experimental Cm- Vg and Gm- Vg characteristics show hysteresis effects, which are more important when the samples are exposed to 254 nm u.v. light. This behaviour can be explained in terms of interface traps. The MOS structure modelling is based on an interface trap model in which the interface trap levels are considered to be continuously distributed in the SiC bandgap and only charge exchange between interface trap levels and the SiC bands is allowed. From this formulation and from the Gm- f characteristics, the interface state density and the interface trap time constant have been determined.

  12. Effect of size and position of gold nanocrystals embedded in gate oxide of SiO2/Si MOS structures

    Chakraborty, Chaitali; Bose, Chayanika

    2016-02-01

    The influence of single and double layered gold (Au) nanocrystals (NC), embedded in SiO2 matrix, on the electrical characteristics of metal-oxide-semiconductor (MOS) structures is reported in this communication. The size and position of the NCs are varied and study is made using Sentaurus TCAD simulation tools. In a single NC-layered MOS structure, the role of NCs is more prominent when they are placed closer to SiO2/Si‑substrate interface than to SiO2/Al-gate interface. In MOS structures with larger NC dots and double layered NCs, the charge storage capacity is increased due to charging of the dielectric in the presence of NCs. Higher breakdown voltage and smaller leakage current are also obtained in the case of dual NC-layered MOS device. A new phenomenon of smearing out of the capacitance-voltage curve is observed in the presence of dual NC layer indicating generation of interface traps. An internal electric field developed between these two charged NC layers is expected to generate such interface traps at the SiO2/Si interface.

  13. Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board the XMM/NEWTON satellite

    We have used a mesh experiment in order to measure the sub-pixel structure of the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40 μm-square pixels which have an open electrode structure in order to improve the detection efficiency for low-energy X-rays. We obtained restored pixel images for various X-ray event grades (e.g. split-pixel events, single pixel events, etc.) at various X-ray energies. We confirmed that the open electrode structure results in a distorted horizontal pixel boundary. The open electrode region generates both single pixel events and vertically split events, but no horizontally split events. Because the single pixel events usually show the best energy resolution, we discuss a method of increasing the fraction of single pixel events from the open electrode region. Furthermore, we have directly measured the thickness of the electrodes and dead-layers by comparing spectra from the open electrode region with those from the other regions: electrodes, electrode finger and channel stop. We can say that EPIC MOS CCDs are more radiation hard than front-illumination chips of ACIS on-board Chandra X-ray Observatory because of their extra absorption thickness above the charge transfer channel. We calculated the mean pixel response and found that our estimation has a good agreement with that of the ground calibration of EPIC MOS CCD

  14. Effects of particle size and edge structure on the electronic structure, spectroscopic features, and chemical properties of Au(111)-supported MoS2 nanoparticles.

    Bruix, Albert; Lauritsen, Jeppe V; Hammer, Bjørk

    2016-07-01

    Materials based on MoS2 are widely used as catalysts and their structure usually consists of single-layered MoS2 nanoparticles whose edges are known to constitute the catalytically active sites. Methods based on density functional theory are used in this work to calculate the electronic structure of representative computational models of MoS2 nanoparticles supported on Au(111). By considering nanoparticles with different edge-terminations, compositions, and sizes, we describe how the electronic structure, Mo3d core-level shifts, and chemical properties (i.e. H adsorption and S vacancy formation) depend on the MoS2 nanoparticle size and structure. In addition, site-specific properties, largely inaccessible when using only slab models of MoS2 edges, are reported, which reveal that the edge sites are not uniform along the nanoparticle and largely depend on the proximity to the corners of the triangular NPs, especially when interacting with a metallic support. Furthermore, a structural motif where H atoms adsorb favourably in a bridging position between two Mo atoms is proposed as an active site for the hydrogen evolution reaction. PMID:27076269

  15. Li adsorption, hydrogen storage and dissociation using monolayer MoS2: an ab initio random structure searching approach.

    Putungan, Darwin Barayang; Lin, Shi-Hsin; Wei, Ching-Ming; Kuo, Jer-Lai

    2015-05-01

    Utilizing ab initio random structure searching, we investigated Li adsorption on MoS2 and hydrogen molecules on Li-decorated MoS2. In contrast to graphene, Li can be adsorbed on both sides of MoS2, with even stronger binding than on the single side. We found that high coverages of Li can be attained without Li clustering, which is essential for hydrogen storage and Li ion batteries. Moreover, regarding battery applications, Li diffusion was also found to be easy. The fully-lithiated MoS2 can then adsorb H2 with 4.4 wt%. Interestingly, our calculations revealed that hydrogen molecules can be dissociated at high Li coverage with a minimal energy barrier. We further showed that the dissociated hydrogen atom can readily diffuse on the surface, thus keeping the reaction site active. We therefore propose that Li-MoS2 could be an inexpensive alternative catalyst to noble metals in hydrogen dissociation reactions. PMID:25849099

  16. Changes in the composition, structure and friction property of sputtered MoS2 films by LEO environment exposure

    Highlights: • Sputtered MoS2 films were exposed in real low earth orbit (LEO) environment. • LEO exposure resulted in the oxidation and S loss of MoS2 film surface. • Depth affected by the LEO exposure was limited within 10 nm. • The exposed MoS2 film exhibited a slight increase in friction coefficient at initial sliding stage. - Abstract: Radio frequency-sputtered MoS2 films had been exposed for 43.5 h in real low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard China Shenzhou-7 manned spaceship. The composition, morphology, phase structure and friction property of the exposed films were investigated using X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray energy-dispersive spectroscopy (EDS) and ball-on-disk tribometer. XRD and EDS results revealed that the as-deposited MoS2 films were characterized by a MoSxOy phase structure, in which x and y values were determined to be ∼0.65 and 1.24, respectively. XPS analysis revealed that due to space atomic oxygen attack, the film surface was oxidized to MoO3 and MoSxOy with higher O concentration, while the partial S was lost. However, the affected depth was restricted within the surface layer because of protective function of the oxidation layer. As a result, the friction coefficient only exhibited a slight increase at initial stage of sliding friction

  17. Dispersion-Corrected Density Functional Theory Investigations of Structural and Electronic Properties of Bulk MoS2: Effect of Uniaxial Strain

    Nguyen, Chuong V.; Hieu, Nguyen N.; Nguyen, Duong T.

    2015-01-01

    Strain-dependent structural and electronic properties of MoS2 materials are investigated using first principles calculations. The structural and electronic band structures of the MoS2 with relaxed unit cells are optimized and calculated by the dispersion-corrected density functional theory (DFT-D2). Calculations within the local density approximation (LDA) and GGA using PAW potentials were also performed for specific cases for the purpose of comparison. The effect of strain on the band gap an...

  18. Nanoimprint-Assisted Shear Exfoliation (NASE) for Producing Multilayer MoS2 Structures as Field-Effect Transistor Channel Arrays.

    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. PMID:26302003

  19. Depth profiling of oxide-trapped charges in 6H-SiC MOS structures by slant etching method

    Saitoh, Kazunari; Takahashi, Yoshihiro; Ohnishi, Kazunori [Nihon Univ., Tokyo (Japan). Coll. of Science and Technology; Yoshikawa, Masahito; Ohshima, Takeshi; Itoh, Hisayoshi; Nashiyama, Isamu

    1997-03-01

    In this paper, we propose a method to evaluate the depth profile of trapped charges in an oxide layer on SiC. Using this method, 6H-SiC MOS structures with different oxide thickness were fabricated on the same substrate under the same oxidation condition, and the depth profile of oxide-trapped charges before and after {sup 60}Co-gamma ray irradiation were obtained. It is found, from the depth profiling, that the trapping mechanism of electrons and holes in the oxide strongly depends on the bias polarity during irradiation, and these charges are trapped near 6H-SiC/SiO{sub 2} interface. We believe that this method is very useful for estimation of the oxide-trapped charges in 6H-SiC MOS structures. (author)

  20. Characterization of SiON/InP MOS structure with sulfidation, fluorination, and hydrogenation

    Liquid phase deposited SiON film on InP with (NH4)2S treatment shows superior electrical characteristics due to the reduction of native oxides and sulfur passivation. Simultaneously, HF in SiON liquid phase deposition solution can effectively reduce residual native oxides on InP and provide fluorine passivation in SiON/InP film and interface. With post-metallization annealing (PMA), hydrogen ions can further passivate defects in SiON/InP film and interface. With these treatments, the PMA-LPD-SiON/(NH4)2S-treated InP MOS structure shows excellent electrical characteristics. With the physical thickness of 5.4 nm, the leakage current densities can be as low as 1.25 x 10-7 and 6.24 x 10-7 A/cm2 at ±2 V, and the interface state density is 3.25 x 1011 cm-2 eV-1. (orig.)

  1. DLTS study of annihilation of oxidation induced deep-level defects in Ni/SiO2/-Si MOS structures

    N Shashank; Sanjeev K Gupta; K V Madhu; J Akhtar; R Damle

    2011-12-01

    This paper describes the fabrication of MOS capacitor and DLTS study of annihilation of deeplevel defects upon thermal annealing. Ni/SiO2/-Si MOS structures fabricated on -type Si wafers were investigated for process-induced deep-level defects. The deep-level traps in Si substrates induced during the processing of Ni/SiO2/-Si have been investigated using deep-level transient spectroscopy (DLTS). A characteristic deep-level defect at C = 0.49 eV which was introduced during high-temperature thermal oxidation process was detected. The trap position was found to shift to different energy levels (C = 0.43, 0.46 and 0.34 eV) during thermal annealing process. The deep-level trap completely anneals at 350°C. Significant reduction in trap density with an increase in recombination life time and substrate doping concentration as a function of isochronal annealing were observed.

  2. The effect of 14.7 MeV neutrons on MOS structures

    Six MOS transistors on a common chip were irradiated with 14.7 MeV neutrons; the accompanying gamma radiation contributed 4% to the neutron dose. The mean energy of these photons was about 1 MeV. The dependence of the threshold voltage shift on the dose equivalent was investigated for several gate bias voltages. The MOS transistors irradiated with neutrons to a total dose equivalent of 188.40 Sv were also annealed isochronously in steps of 20 degC. The annealing curves are shown and activation energies of traps calculated therefrom. It was also found that the fading curve of fast-neutron-irradiated MOS transistors differed from that of photon irradiated ones. (J.B.)

  3. Structural and Electronic Properties of Germanene on MoS2

    Zhang, L.; Bampoulis, P.; Rudenko, A. N.; Yao, Q.; van Houselt, A.; Poelsema, B.; Katsnelson, M. I.; Zandvliet, H. J. W.

    2016-06-01

    To date germanene has only been synthesized on metallic substrates. A metallic substrate is usually detrimental for the two-dimensional Dirac nature of germanene because the important electronic states near the Fermi level of germanene can hybridize with the electronic states of the metallic substrate. Here we report the successful synthesis of germanene on molybdenum disulfide (MoS2), a band gap material. Preexisting defects in the MoS2 surface act as preferential nucleation sites for the germanene islands. The lattice constant of the germanene layer (3.8 ±0.2 Å ) is about 20% larger than the lattice constant of the MoS2 substrate (3.16 Å). Scanning tunneling spectroscopy measurements and density functional theory calculations reveal that there are, besides the linearly dispersing bands at the K points, two parabolic bands that cross the Fermi level at the Γ point.

  4. Effect of ion implantation on capacitance-voltage properties of MOS structures

    The effect of rare gas ions, such as Xe+ and Kr+, implanted in the oxide of MOS diodes on the capacitance-voltage properties and triangular voltage stressing has been studied. Results obtained are presented and discussed in terms of interface states and mobility of oxide charges

  5. Hierarchical MoS2 tubular structures internally wired by carbon nanotubes as a highly stable anode material for lithium-ion batteries

    Chen, Yu Ming; Yu, Xin Yao; Li, Zhen; Paik, Ungyu; Lou, Xiong Wen (David)

    2016-01-01

    Molybdenum disulfide (MoS2), a typical two-dimensional material, is a promising anode material for lithium-ion batteries because it has three times the theoretical capacity of graphite. The main challenges associated with MoS2 anodes are the structural degradation and the low rate capability caused by the low intrinsic electric conductivity and large strain upon cycling. Here, we design hierarchical MoS2 tubular structures internally wired by carbon nanotubes (CNTs) to tackle these problems. These porous MoS2 tubular structures are constructed from building blocks of ultrathin nanosheets, which are believed to benefit the electrochemical reactions. Benefiting from the unique structural and compositional characteristics, these CNT-wired MoS2 tubular structures deliver a very high specific capacity of ~1320 mAh g−1 at a current density of 0.1 A g−1, exceptional rate capability, and an ultralong cycle life of up to 1000 cycles. This work may inspire new ideas for constructing high-performance electrodes for electrochemical energy storage. PMID:27453938

  6. Theoretical analysis of a model for Na+ ion transport in the amorphous silicondioxide layer of MOS structures

    The authors introduce and calculate a simple phenomenological transport model for the movement of Na+ ions through the SiO2 layer of MOS structures. The gettering effect achieved by implantation of inert gas ions in the SiO2 layer is linked with the appearance of deep traps for the Na+ ions on the Al-SiO2 interface. The system of balance equations for the charge carriers involved and the Poisson equation for the internal electric field is solved numerically under corresponding boundary and initial conditions, and there is a discussion of the resultant current density-voltage curve. (author)

  7. High pressure effect on structure, electronic structure and thermoelectric properties of MoS$_2$

    Guo, Huaihong; Yang, Teng; Tao, Peng; Wang, Yong; Zhang, Zhidong

    2012-01-01

    We systematically study the effect of high pressure on the structure, electronic structure and transport properties of 2H-MoS$_2$, based on first-principles density functional calculations and the Boltzmann transport theory. Our calculation shows a vanishing anisotropy in the rate of structural change at around 25 GPa, in agreement with the experimental data. A conversion from van der Waals(vdW) to covalent-like bonding is seen. Concurrently, a transition from semiconductor to metal occurs at...

  8. Structures of a 17,19-hexatriacontadiyne and sashlike polydiacetylene monolayer on MoS2(0001) studied by UHV-STM

    We have observed a 17,19-hexatriacontadiyne (HTDY) monolayer on MoS2(0001) and sashlike polydiacetylene atomic sash (AS) molecules derived from the monolayer by scanning tunnelling microscopy under ultrahigh vacuum. HTDY molecules adsorbed at 150 K start to move around on the surface above 240 K to form relatively unstable columnar structures. The column is converted into the AS by UV irradiation. In most AS molecules on MoS2(0001), the alkyl chains are in all-trans conformation but their carbon planes are tilted to the polydiacetylene backbone. This conformer, which is one of the most stable structures for an isolated AS molecule, appears on MoS2(0001) because of very weak molecule-substrate interactions

  9. C-V and G-V characteristics of ion-implanted MOS structures depending upon the geometrical structure of the implanted region

    It is found that the capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of MOS capacitors, into which ions of the opposite conductivity type are implanted, depend strongly upon the geometrical structure of the ion-implanted region. This phenomenon can be analyzed in terms of lateral current flow which connects an inversion layer formed in the ion-implanted region to a surrounding nonimplanted substrate. On the basis of this model, the C-V and G-V characteristics are calculated using a simple equivalent circuit, and general relationships inherent in this model are obtained. MOS capacitors with an ion-implanted layer of different geometries have been prepared to measure their C-V and G-V characteristics. Comparison of experimental measurements with theory substantiates the lateral current flow model

  10. Capacitance transients in p-type GaAs MOS structures and application to lifetime mapping during solar cell fabrication

    Vitale, G.; Loferski, J. J.; Ercil, Y.

    1979-01-01

    Fabrication on p-type GaAs of MOS structures in which the quality of the oxide is such that the surface can be driven into deep inversion by a voltage pulse is reported. The capacitance transients in such MOS capacitors as a function of step amplitude and temperature were measured and the transients were analyzed by an extension of a method for silicon. The oxides were produced by plasma oxidation on an LPE-grown p-type GaAs specimen with N sub A of 3x10 to the 17th power/cu cm. The capacitors were produced by depositing 50 microns-diameter gold dots over the native oxide and, therefore, the lifetime is localized to the area under the dot. The method permits extraction of both the bulk lifetime and the interface recombination velocity. These parameters on samples with different N sub A were measured and a correlation between tau sub g and N sub A was found.

  11. Crystal structure and electric resistance of MoS2-NbS2 alloys produced by self-propagating high temperature synthesis

    MoS2-NbS2 alloys produced by means of self-propagating high-temperature synthesis are studied for dependence of their crystal structure on conditions of charge preparation and alloy position in reactionary cake. It is shown that solid solutions of Nb in MoS2 may be obtained when diluting the starting charge either with a final product or with MoS2 and Nb (in the latter case substitution of Nb atoms for Mo atoms is less intensive). Formation of the solid solutions is shown to occur at a distance of 0.5-0.7 cm from the reactionary cake surface where charge is melted. It is found out that substitution of Nb atoms for Mo atoms in MoS2 leads to a sharp decrease in electric resistance as Nb is an acceptor impurity for MoS2; with a 5% substitution electric resistance falls to (1-2)x10-3 Ωxcm, i. e. to the graphite level

  12. Controlled, defect-guided, metal-nanoparticle incorporation onto MoS2 via chemical and microwave routes: electrical, thermal, and structural properties.

    Sreeprasad, T S; Nguyen, Phong; Kim, Namhoon; Berry, Vikas

    2013-09-11

    Ultrathin (0.3-3 nm) metal dichalcogenides exhibit confinement of carriers, evolution of band-structure and photophysical properties with thickness, high on/off rectification (in MoS2, WS2, and so forth) and high thermal absorption. Here, we leverage the stable sulfur/nobel-metal binding to incorporate highly capacitive gold nanoparticles (Au NPs) onto MoS2 to raise the effective gate-voltage by an order of magnitude. Functionalization is achieved via both diffusion limited aggregation and instantaneous reaction arresting (using microwaves) with selective deposition on crystallographic edges (with 60° displacement). The electrical, thermal, and Raman studies show a highly capacitive interaction between Au NP and MoS2 flakes (CAu-MoS2 = 2.17 μF/cm(2)), a low Schottky barrier (14.52 meV), a reduced carrier-transport thermal-barrier (253 to 44.18 meV after Au NP functionalization), and increased thermal conductivity (from 15 to 23 W/mK post NP deposition). The process could be employed to attach electrodes to heterostructures of graphene and MoS2, where a gold film could be grown to act as an electron-tunneling gate-electrode connected to MoS2. PMID:23927716

  13. Thiol click chemistry on gold-decorated MoS2: elastomer composites and structural phase transitions

    Topolovsek, Peter; Cmok, Luka; Gadermaier, Christoph; Borovsak, Milos; Kovac, J.; Mrzel, Ales

    2016-05-01

    We show that gold decorated MoS2 flakes are amenable to thiol chemistry by blending them with a cross-linkable thiolated polysiloxane (PMMS). PMMS prevents restacking of dispersed MoS2 when transforming the metallic to the semiconducting phase. Cross-linking PMMS yields an elastomer of good optical quality, containing individual, mostly single-layer MoS2 flakes.We show that gold decorated MoS2 flakes are amenable to thiol chemistry by blending them with a cross-linkable thiolated polysiloxane (PMMS). PMMS prevents restacking of dispersed MoS2 when transforming the metallic to the semiconducting phase. Cross-linking PMMS yields an elastomer of good optical quality, containing individual, mostly single-layer MoS2 flakes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01490a

  14. Electronic structure of MoSe2, MoS2, and WSe2. I. Band-structure calculations and photoelectron spectroscopy

    Coehoorn, R.; Haas, C.; Dijkstra, J.; Flipse, C.J.F.; de Groot, R. A.; Wold, A.

    1987-01-01

    The band structures of the semiconducting layered compounds MoSe2, MoS2, and WSe2 have been calculated self-consistently with the augmented-spherical-wave method. Angle-resolved photoelectron spectroscopy of MoSe2 using He I, He II, and Ne I radiation, and photon-energy-dependent normal-emission photoelectron spectroscopy using synchrotron radiation, show that the calculational results give a good description of the valence-band structure. At about 1 eV below the top of the valence band a dis...

  15. Generation lifetime investigation of ion-damage gettered silicon using MOS structure

    Gettering of undesirable generation impurities by O and Ar implant damage layer has been investigated by transient response of MOS capacitors. One-half of each Si wafer was masked against the implanting ion beam and comparison was made between the two halves of each wafer by deducing the generation lifetime from the C-t measurements. The implant dosage was 1016 cm-2 and ion energy 200 keV. The gettering anneal at 10700C was also the gate oxidation. The generation lifetime from 1 to 15 μs of the control half was increased to as high as 200 μs after both O and Ar implants. The results with O were more reproducible than with the Ar-implanted Si wafers; however, the largest increase in generation lifetime was observed with the Ar getterered wafer. It is proposed that there are generation centers other than the generation impurity centers that cannot be removed by gettering methods

  16. Design considerations of a MOS-bipolar Darlington structure: The vertical insulated base transistor (IBT)

    Godignon, P.; Fernández, J.; Flores, D.; Hidalgo, S.; Rebollo, J.; Millán, J.; Chante, J. P.

    1996-12-01

    The analysis of a vertical insulated base transistor (MOS-bipolar Darlington power device with cellular layout) is discussed. The device operation is investigated in the framework of a schematic representation of the output characteristics and by means of 2D numerical simulation. A new design using a P --diffusion interconnecting the P-type regions is proposed to improve the device breakdown voltage. Several cellular and stripe geometries were implemented with a double metal layer technology. Experiments corroborate the simulation results pointing out that the IBT shows a low on-resistance and fast switching times. For the sake of comparison of their electrical characteristics VDMOS and IGBTs were also fabricated with the same process.

  17. Synthesis and Crystal Structure of a Novel Mixed Nido-like and Half-open Cubane-like Cluster [(n-Bu)4N]3[MoS4Cu5Br6

    LIU,Quai(刘泉); XU,Qing-Feng(徐庆锋); ZHANG,Yong(张勇); CHEN,Jin-Xiang(陈金香); ZHOU,Zhi-Feng(周志峰); LANG,Jian-Ping(郎建平)

    2002-01-01

    Reaction of (NH4)2MoS4 with [Cu(MeCN)4] (BF4) and (nBu)4NBr in CH2Cl2 afforded a new hexanuclear cluster [ ( nBu)4N]3[MoS4Cu5Br6] (1). 1 crystallizes in the monoclinic system, space group P21/c, with lattice parameters a =1.17383(4) nm, b = 2.40136(4) nm, c = 2.64112(5) nm,β =94.2020(5)°, V=7.4247(5) nm3andZ=4. The structure of the [MoS4Cu5Br6]3- trianion of 1 is composed of one nidolike [MoS3Cu3] core and one half-open cubane-like [MoS3Cu3Br] core, which are interconnected by sharing the of 0.2622(6)-0.2692(5) nm.

  18. Structures of exfoliated single layers of WS2, MoS2, and MoSe2 in aqueous suspension

    Gordon, R. A.; Yang, D.; Crozier, E. D.; Jiang, D. T.; Frindt, R. F.

    2002-03-01

    Single layers of the transition-metal dichalcogenides WS2, MoS2, and MoSe2 were formed as aqueous suspensions by lithium intercalation and exfoliation of crystalline powders and examined by x-ray diffraction and x-ray absorption fine structure (XAFS) spectroscopy. The two-dimensional characteristics of these systems were readily apparent through the absence of any (hkl) peaks (l≠0) and in the strong asymmetry of the (hk0) peaks in the diffraction patterns. Indexing the diffraction patterns with rectangular unit cells revealed the diselenide as the most distorted from the hexagonal structures of the parent materials, with the Mo atoms forming a ``zigzag'' structure which is also corrugated perpendicular to the layers. Mo K-edge and W L3-edge XAFS analysis using WTe2-related structural models enabled the determination of the short, intermediate, and long metal-metal near-neighbor distances with the shortest metal-metal distances contracted approximately 0.4 Å compared to parent reference materials. Shifts in the Mo K-absorption-edge energy in MoSe2 correlated with changing Se-Se interactions. Combining the XAFS and diffraction results enabled an estimation of the layer puckering and atomic positions in three-dimensional models of the unit cells. Selenium K-edge XAFS also identified two selenium-oxygen scattering paths from water or OH- ions coordinating the layers of exfoliated MoSe2.

  19. Structural and electrical characteristics of RF-sputtered HfO 2 high-k based MOS capacitors

    Tirmali, P. M.; Khairnar, Anil G.; Joshi, Bhavana N.; Mahajan, A. M.

    2011-08-01

    The HfO 2 high-k thin films have been deposited on p-type (1 0 0) silicon wafer using RF magnetron sputtering technique. The XRD, AFM and Ellipsometric characterizations have been performed for crystal structure, surface morphology and thickness measurements respectively. The monoclinic structured, smooth surface HfO 2 thin films with 9.45 nm thickness have been used for Al/HfO 2/p-Si metal-oxide-semiconductor (MOS) structures fabrication. The fabricated Al/HfO2/Si structure have been used for extracting electrical properties viz dielectric constant, EOT, barrier height, doping concentration and interface trap density through capacitance voltage and current-voltage measurements. The dielectric constant, EOT, barrier height, effective charge carriers, interface trap density and leakage current density are determined are 22.47, 1.64 nm, 1.28 eV, 0.93 × 10 10, 9.25 × 10 11 cm -2 eV -1 and 9.12 × 10 -6 A/cm 2 respectively for annealed HfO 2 thin films.

  20. Influence of structural defects in subsurface layers of silicon on charge carrier mobility in the channel of MOS-transistors threshold voltage

    The influence of structural imperfections, the impurity composition, and the doping inhomogeneity on the basic parameters of the I - V characteristics of MOS-transistors has been found out with aid of modern research methods. Oxygen and carbon are the basic impurities in initial and oxidized silicons. Oxygen reveals electrical activity and influences the parameters of structural defects that, in turn, affect the charge carrier mobility and the threshold voltage

  1. Three-Dimensional Structures of MoS2@Ni Core/Shell Nanosheets Array toward Synergetic Electrocatalytic Water Splitting.

    Xing, Zhicai; Yang, Xiurong; Asiri, Abdullah M; Sun, Xuping

    2016-06-15

    Hydrogen evolution reaction (HER) in alkaline media using non-noble metal catalysts with great efficiency represents a critical challenge in current water-alkaline and chlor-alkali electrolyzers. Herein, we demonstrate that the MoS2@Ni core/shell nanosheets array vertically aligned on carbon cloth (MoS2@Ni/CC) is a highly active electrocatalyst for HER. In alkaline solutions, MoS2@Ni/CC needs overpotentials of 91, 118, and 196 mV to approach current densities of 10, 20, and 100 mA cm(-2), respectively, exceeding behavior of commercial Pt/C catalyst at high current densities. Additionally, this catalyst also exhibits excellent electrocatalytic activity toward HER in neutral electrolytes. Such high hydrogen evolution activities are due to synergistic electrocatalytic effects between MoS2 core and Ni shell. PMID:27211232

  2. Structure design and film process optimization for metal-gate stress in 20 nm nMOS devices

    The optimizations to metal gate structure and film process were extensively investigated for great metal-gate stress (MGS) in 20 nm high-k/metal-gate-last (HK/MG-last) nMOS devices. The characteristics of advanced MGS technologies on device performances were studied through a process and device simulation by TCAD tools. The metal gate electrode with different stress values (0 to −6 GPa) was implemented in the device simulation along with other traditional process-induced-strain (PIS) technologies like e-SiC and nitride capping layer. The MGS demonstrated a great enhancing effect on channel carriers transporting in the device as device pitch scaling down. In addition, the novel structure for a tilted gate electrode was proposed and relationships between the tilt angle and channel stress were investigated. Also with a new method of fully stressed replacement metal gate (FSRMG) and using plane-shape-HfO to substitute U-shape-HfO, the effect of MGS was improved. For greater film stress in the metal gate, the process conditions for physical vapor deposition (PVD) TiNx were optimized. The maximum compressive stress of −6.5 GPa TiNx was achieved with thinner film and greater RF power as well as about 6 sccm N ratio. (semiconductor technology)

  3. Structure design and film process optimization for metal-gate stress in 20 nm nMOS devices

    Zuozhen, Fu; Huaxiang, Yin; Xiaolong, Ma; Shumin, Chai; Jianfeng, Gao; Dapeng, Chen

    2013-06-01

    The optimizations to metal gate structure and film process were extensively investigated for great metal-gate stress (MGS) in 20 nm high-k/metal-gate-last (HK/MG-last) nMOS devices. The characteristics of advanced MGS technologies on device performances were studied through a process and device simulation by TCAD tools. The metal gate electrode with different stress values (0 to -6 GPa) was implemented in the device simulation along with other traditional process-induced-strain (PIS) technologies like e-SiC and nitride capping layer. The MGS demonstrated a great enhancing effect on channel carriers transporting in the device as device pitch scaling down. In addition, the novel structure for a tilted gate electrode was proposed and relationships between the tilt angle and channel stress were investigated. Also with a new method of fully stressed replacement metal gate (FSRMG) and using plane-shape-HfO to substitute U-shape-HfO, the effect of MGS was improved. For greater film stress in the metal gate, the process conditions for physical vapor deposition (PVD) TiNx were optimized. The maximum compressive stress of -6.5 GPa TiNx was achieved with thinner film and greater RF power as well as about 6 sccm N ratio.

  4. Electron microscopy studies on MoS2 nanocrystals

    Hansen, Lars Pilsgaard

    Industrial-style MoS2-based hydrotreating catalysts are studied using electron microscopy. The MoS2 nanostructures are imaged with single-atom sensitivity to reveal the catalytically important edge structures. Furthermore, the in-situ formation of MoS2 crystals is imaged for the first time....

  5. A Novel Depletion-Mode MOS Gated Emitter Shorted Thyristor

    张鹤鸣; 戴显英; 张义门; 马晓华; 林大松

    2000-01-01

    A Novel MOS-gated thyristor, depletion-mode MOS gated emitter shorted thyristor (DMST),and its two structures are proposed. In DMST,the channel of depletion-mode MOS makes the thyristor emitter-based junction inherently short. The operation of the device is controlled by the interruption and recovery of the depletion-mode MOS P channel. The perfect properties have been demonstrated by 2-D numerical simulations and the tests on the fabricated chips.

  6. Effect of non-doping ion implantation into the oxide of MOS structures on electrical behaviour of the Si-SiO2 interface

    The influence of implantation of Ar+, Al+, and Cl- ion beams with radiation doses of 1013 to 1015 1/cm2 in oxides of MOS structures was investigated by means of HF-C(V) and quasistatistic C(V) methods. The minority carrier lifetime tau was calculated from C(t) curves. The density of mobile alkali ions was determined by the TVS method

  7. In Situ XPS Chemical Analysis of MnSiO3 Copper Diffusion Barrier Layer Formation and Simultaneous Fabrication of Metal Oxide Semiconductor Electrical Test MOS Structures.

    Byrne, Conor; Brennan, Barry; McCoy, Anthony P; Bogan, Justin; Brady, Anita; Hughes, Greg

    2016-02-01

    Copper/SiO2/Si metal-oxide-semiconductor (MOS) devices both with and without a MnSiO3 barrier layer at the Cu/SiO2 interface have been fabricated in an ultrahigh vacuum X-ray photoelectron spectroscopy (XPS) system, which allows interface chemical characterization of the barrier formation process to be directly correlated with electrical testing of barrier layer effectiveness. Capacitance voltage (CV) analysis, before and after tube furnace anneals of the fabricated MOS structures showed that the presence of the MnSiO3 barrier layer significantly improved electric stability of the device structures. Evidence of improved adhesion of the deposited copper layer to the MnSiO3 surface compared to the clean SiO2 surface was apparent both from tape tests and while probing the samples during electrical testing. Secondary ion mass spectroscopy (SIMS) depth profiling measurements of the MOS test structures reveal distinct differences of copper diffusion into the SiO2 dielectric layers following the thermal anneal depending on the presence of the MnSiO3 barrier layer. PMID:26732185

  8. Photo-induced tunneling currents in MOS structures with various HfO2/SiO2 stacking dielectrics

    Chin-Sheng Pang

    2014-04-01

    Full Text Available In this study, the current conduction mechanisms of structures with tandem high-k dielectric in illumination are discussed. Samples of Al/SiO2/Si (S, Al/HfO2/SiO2/Si (H, and Al/3HfO2/SiO2/Si (3H were examined. The significant observation of electron traps of sample H compares to sample S is found under the double bias capacitance-voltage (C-V measurements in illumination. Moreover, the photo absorption sensitivity of sample H is higher than S due to the formation of HfO2 dielectric layer, which leads to larger numbers of carriers crowded through the sweep of VG before the domination of tunneling current. Additionally, the HfO2 dielectric layer would block the electrons passing through oxide from valance band, which would result in less electron-hole (e−-h+ pairs recombination effect. Also, it was found that both of the samples S and H show perimeter dependency of positive bias currents due to strong fringing field effect in dark and illumination; while sample 3H shows area dependency of positive bias currents in strong illumination. The non-uniform tunneling current through thin dielectric and through HfO2 stacking layers are importance to MOS(p tunneling photo diodes.

  9. Structural, mechanical and electronic properties of in-plane 1T/2H phase interface of MoS2 heterostructures

    Xiaoyan Guo

    2015-09-01

    Full Text Available Two-dimensional (2D molybdenum disulfide (MoS2 phase hybrid system composed by 2H and 1T phase is a natural metal/semiconductor heterostructures and promised a wide range of potential applications. Here, we report the first principle investigations on the structural, mechanical and electronic properties of hybrid system with armchair (AC and zigzag (ZZ interfaces. The ZZ type 1T/2H interface are more energy favorable than AC type interface with 3.39 eV/nm. Similar with that of bulked 1T MoS2, the intrinsic strengths of the heterostructures are lower than that of the bulk 2H, especially for that with ZZ interface. Analysis of density of states shows that the electronic properties gradually transmitted from the metallic 1T phase to the semiconducting 2H phase for the structural abrupt interface. The present theoretical results constitute a useful picture for the 2D electronic devices using current MoS2 1T/2H heterostructures and provide vital insights into the other 2D hybrid materials.

  10. Structural, mechanical and electronic properties of in-plane 1T/2H phase interface of MoS2 heterostructures

    Two-dimensional (2D) molybdenum disulfide (MoS2) phase hybrid system composed by 2H and 1T phase is a natural metal/semiconductor heterostructures and promised a wide range of potential applications. Here, we report the first principle investigations on the structural, mechanical and electronic properties of hybrid system with armchair (AC) and zigzag (ZZ) interfaces. The ZZ type 1T/2H interface are more energy favorable than AC type interface with 3.39 eV/nm. Similar with that of bulked 1T MoS2, the intrinsic strengths of the heterostructures are lower than that of the bulk 2H, especially for that with ZZ interface. Analysis of density of states shows that the electronic properties gradually transmitted from the metallic 1T phase to the semiconducting 2H phase for the structural abrupt interface. The present theoretical results constitute a useful picture for the 2D electronic devices using current MoS2 1T/2H heterostructures and provide vital insights into the other 2D hybrid materials

  11. Electrical characteristics of MoS2 field-effect transistor with ferroelectric vinylidene fluoride-trifluoroethylene copolymer gate structure

    Kobayashi, Takuhei; Hori, Naoki; Nakajima, Takashi; Kawae, Takeshi

    2016-03-01

    Ferroelectric field-effect transistors (FeFET) based on MoS2 have recently been shown to exhibit considerable potential for use in nano sized non-volatile memory devices. Here, we demonstrated fabrication and characterization of FeFET based on MoS2 channel with vinylidene fluoride (VDF)-trifluoroethylene (TrFE) copolymer as back-gate insulator. In this device, counterclockwise hysteresis behavior was observed in the drain current-gate voltage curve, which is indicative of interaction between MoS2 carrier modulation and ferroelectric polarization switching. Furthermore, our VDF-TrFE/MoS2 FeFET exhibited only n-type behavior, a maximum linear mobility of 625 cm2/V s, a large memory window width of 16 V, and a high on/off current ratio of 8 × 105.

  12. Effects of nitrogen plasma treatment on the electrical property and band structure of few-layer MoS2

    Few-layer MoS2 prepared by the chemical vapor deposition method was treated with nitrogen plasma under different radio-frequency (rf) power conditions in order to experimentally study the change in the electrical property. Control of the rf power could change the work function of MoS2 from 5.40 eV to 5.06 eV. It is shown that the increased rf power leads to the increased (reduced) number of nitrogen (oxygen) atoms, increasing the electron concentration and shifting the Fermi level toward conduction band. The sensitivity of the work function to the rf power provides an opportunity to tune the work function of MoS2

  13. MOS integrated circuit design

    Wolfendale, E

    2013-01-01

    MOS Integral Circuit Design aims to help in the design of integrated circuits, especially large-scale ones, using MOS Technology through teaching of techniques, practical applications, and examples. The book covers topics such as design equation and process parameters; MOS static and dynamic circuits; logic design techniques, system partitioning, and layout techniques. Also featured are computer aids such as logic simulation and mask layout, as well as examples on simple MOS design. The text is recommended for electrical engineers who would like to know how to use MOS for integral circuit desi

  14. Dopant density from maximum-minimum capacitance ratio of implanted MOS structures

    For uniformly doped structures, the ratio of the maximum to the minimum high frequency capacitance determines the dopant ion density per unit volume. Here it is shown that for implanted structures this 'max-min' dopant density estimate depends upon the dose and depth of the implant through the first moment of the depleted portion of the implant. A a result, the 'max-min' estimate of dopant ion density reflects neither the surface dopant density nor the average of the dopant density over the depletion layer. In particular, it is not clear how this dopant ion density estimate is related to the flatband capacitance. (author)

  15. High energy electron irradiation of ion implanted MOS structures with different oxide thickness

    The effects of 11 MeV electron irradiation of boron ion implanted Si-SiO2 structures with different oxide thickness have been investigated by thermally stimulated charge (TSC) method. It has been shown that electron irradiation of implanted with 20 keV boron ions structures results in the formation of a trap spectrum which locates in the same temperature range as the spectrum of the as-implanted samples. The density of radiation-induced interface traps after electron irradiation has been found to depend on the disposition of the maximum of the previously implanted boron ions with respect to the Si-SiO2 interface

  16. Atomic-scale structures and electronic states of defects on Ar+-ion irradiated MoS2

    Highlights: ► MoS2 surfaces bearing defects generated by Ar+ bombardment at a low density were observed by STM. ► STS results revealed that the two types of defects have different spectra. ► The bright feature is assigned to hybridized Mo states beneath the feature. ► The concave defect is monolayer removal of MoS2 with the mid-gap electronic state at the edge. -- Abstract: We observed MoS2 surfaces bearing defects generated by Ar+-ion bombardment at the density of 2.75 × 10−3 ions/nm2 by scanning tunneling microscopy (STM) and measured local electronic state by scanning tunneling spectroscopy (STS). Two types of concave surface defects, one with a bright feature and one without, were observed in STM images. STS revealed that the two features have different spectra. We elucidated the origins of these defects by comparison of the experimental results with electronic states obtained from density functional theory (DFT) calculation. The dI/dV curve measured at the center of the bright feature has a mid-gap state, which can be assigned to Mo beneath the feature. The bright feature was composed of several S vacancies, leaving a surface with metallic character. The concave defect without the bright feature is interpreted as being formed by layer-by-layer removal of MoS2. The dI/dV curve measured at the center of this type of concave defect showed a semiconducting property similar to that of a clean MoS2 surface, and the edge of the concave region shows a peak at −0.5 V from the Fermi level

  17. Electronic structure of MoSe2, MoS2, and WSe2. II. The nature of the optical band gaps

    Coehoorn, R.; Haas, C.; de Groot, R. A.

    1987-01-01

    From band-structure calculations it is shown that MoSe2, MoS2, and WSe2 are indirect-gap semiconductors. The top of the valence band is at the Γ point and the bottom of the conduction band is along the line T of the hexagonal Brillouin zone, halfway between the points Γ and K. The A and B excitons correspond to the smallest direct gap at the K point. This assignment of the exciton peaks is shown to be consistent with the polarization dependence of their intensities, their effective masses, an...

  18. Electronic Structures and Magnetic Properties of MoS2 Nanostructures: Atomic Defects, Nanoholes, Nanodots and Antidots

    Zhou, Yungang; Yang, Ping; Zu, Haoyue; Gao, Fei; Zu, Xiaotao

    2013-04-24

    MoS2-based nanostructures, including atomic defect, nanohole, nanodot and antidot, are characterized with spin-polarized density functional theory. The S-vacancy defect is more likely to form than the Mo-vacancy defect due to the formation of Mo-Mo metallic bonds. Among different shaped nanoholes and nanodots, triangle ones associated with ferromagnetic characteristic are the most energetically favorable, and exhibit unexpected large spin moment that is scaled linearly with edged length.

  19. Degradation of the electrical characteristics of MOS structures with erbium, gadolinium, and dysprosium oxides under the effect of an electric field

    The degradation of the characteristics of silicon metal-oxide-semiconductor (MOS) structures with oxides of rare-earth elements under the effect of electric fields with intensities of 0.1–4 MV/cm during the course of electroforming is studied. A specific feature of electroforming consists in the possibility of multiple switching of the structures from the insulating state to the low-resistivity one and back. The temporal characteristics of the degradation of MOS structures during the course of electroforming are exponential. The current-voltage characteristics follow the power law in the range of 0.2–3 V; the effect of an electric field brings about a variation in the distribution of the energy density of traps responsible for currents limited by space charge. It is established that multiple cycles of electroforming lead to an increase in the density of surface states at the Si-oxide interface and to a variation in the energy position of the trap levels, which affects the charge state of the traps

  20. Transformation of metallic boron into substitutional dopants in graphene on 6H-SIC(0001)

    Sforzini, J.; Telychko, Mykola; Krejčí, Ondřej; Vondráček, Martin; Švec, Martin; Bocquet, F.C.; Tautz, F.S.

    2016-01-01

    Roč. 93, č. 4 (2016), "041302-1"-"041302-4". ISSN 1098-0121 R&D Projects: GA ČR GA15-07172S Institutional support: RVO:68378271 Keywords : heavily nitrogenated graphene * chemisorbed molecules * recent progress * performance Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.736, year: 2014

  1. Structural, optical and compositional stability of MoS2 multi-layer flakes under high dose electron beam irradiation

    Rotunno, E.; Fabbri, F.; Cinquanta, E.; Kaplan, D.; Longo, M.; Lazzarini, L.; Molle, A.; Swaminathan, V.; Salviati, G.

    2016-06-01

    MoS2 multi-layer flakes, exfoliated from geological molybdenite, have been exposed to high dose electron irradiation showing clear evidence of crystal lattice and stoichiometry modifications. A massive surface sulfur depletion is induced together with the consequent formation of molybdenum nanoislands. It is found that a nanometric amorphous carbon layer, unwillingly deposited during the transmission electron microscope experiments, prevents the formation of the nanoislands. In the absence of the carbon layer, the formation of molybdenum grains proceeds both on the top and bottom surfaces of the flake. If carbon is present on both the surfaces then the formation of Mo grains is completely prevented.

  2. Gold nanoparticles on MoS2 layered crystal flakes

    Inorganic layered crystal MoS2 is considered as one of the most promising and efficient semiconductor materials for future transistors, photoelectronics, and electrocatalysis. To boost MoS2-based material applications, one direction is to grow physically and chemically reactive nanoparticles onto MoS2. Here we report on a simple route to synthesis crystalized MoS2–Au complexes. The gold nanoparticles were grown on MoS2 flakes through a wet method in the oxygen free environment at room temperature. Nanoparticles with diameters varying from 9 nm to 429 nm were controlled by the molar ratios of MoS2 and HAuCl4 precursors. MoS2 host flakes keep intrinsic honeycomb layered structures and the Au nanoparticles cubic-center crystal microstructures. From product chemical states analysis, the synthesis was found driven by redox reactions between the sulphide and the chloroauric acid. Photoluminescence measurement showed that introducing Au nanoparticles onto MoS2 stacks substantially prompted excitonic transitions of stacks, as an analogy for doping Si wafers with dopants. Such composites may have potential applications in wide ranges similar as the doped Si. - Highlights: • The Au nanoparticles were decorated on MoS2 in oxygen free ambiences via a wet method. • The Au nanoparticles are size-controllable and crystalized. • Chemical reaction scheme was clarified. • The MoS2–Au complexes have strong photoluminescent properties

  3. Optical and Electrical Performance of MOS-Structure Silicon Solar Cells with Antireflective Transparent ITO and Plasmonic Indium Nanoparticles under Applied Bias Voltage

    Wen-Jeng Ho

    2016-08-01

    Full Text Available This paper reports impressive improvements in the optical and electrical performance of metal-oxide-semiconductor (MOS-structure silicon solar cells through the incorporation of plasmonic indium nanoparticles (In-NPs and an indium-tin-oxide (ITO electrode with periodic holes (perforations under applied bias voltage. Samples were prepared using a plain ITO electrode or perforated ITO electrode with and without In-NPs. The samples were characterized according to optical reflectance, dark current voltage, induced capacitance voltage, external quantum efficiency, and photovoltaic current voltage. Our results indicate that induced capacitance voltage and photovoltaic current voltage both depend on bias voltage, regardless of the type of ITO electrode. Under a bias voltage of 4.0 V, MOS cells with perforated ITO and plain ITO, respectively, presented conversion efficiencies of 17.53% and 15.80%. Under a bias voltage of 4.0 V, the inclusion of In-NPs increased the efficiency of cells with perforated ITO and plain ITO to 17.80% and 16.87%, respectively.

  4. Comparison of the generation of interface states in MOS structures due to 60Co and VUV irradiation accompanied with photo-injection of electrons

    The buildup of interface states in MOS structures with differently annealed oxides is studied under vacuum ultraviolet (VUV) and 60Co irradiation. A larger creation of interface states is observed if photoinjection of electrons is applied simultaneously with the VUV irradiation. The presence of electrons at the Si/SiO2 interface favors the generation and explains the larger amount of interface states after 60Co irradiation. After VUV irradiation the interface state density increases in n-samples to a specific saturation value which is reached earlier if gate voltage is made more positive or samples are exposed to photoinjection. This is due to the increase of the radiation peak which is located in the upper half of the silicon gap. The impact of post oxidation annealing on the interface state generation is investigated due to VUV and 60Co irradiation. (author). 26 refs., 9 figs., 1 tab

  5. Correlation between mechanical stress and hydrogen-related effects on radiation-induced damage in MOS structures

    Correlation between mechanical stress and hydrogen effects on radiation damage in polycide-gate MOS capacitors was investigated as a function of gate-oxide thickness. The compressive stress magnitude was altered by varying the silicide (TiSi2 or WSi2) thickness in the polycide-gate electrode, and hydrogen introduction into gate-SiO2 film was carried out by diffusion from plasma-deposited silicon-nitride passivation film (SiN-Cap). In a MOS capacitor without passivation film (No-Cap sample), it was found that compressive stress on gate-SiO2 reduces both positive charge build-up (ΔQot) and interface-trap generation (ΔDit). Radiation induced shift, ΔQot exhibits a smaller stress effect as compared with ΔDit. As gate-SiO2 thickness decreases, the stress effect on ΔQot increases, while this effect on ΔDit remains nearly constant. This compressive stress effect was inhibited by hydrogen diffusion, especially in ΔDit. In addition, both stress effects on ΔQot and ΔDit in SiN-Cap samples show a gate-oxide thickness dependence similar to that on ΔQot in No-Cap samples. The stress effect observed in No-Cap samples can be explained on the basis of the bond reformation process at the SiO2Si interface and near the electrodeSiO2 interface. In a SiN-Cap sample, hydrogen is highly distributed at the SiO2Si interface region and hydrogen-related interface-trap generation may occur at this interface region. As a result, only the stress effect near the gate-electrode was observed in SiN-Cap samples

  6. Torsional Deformations in Subnanometer MoS Interconnecting Wires.

    Koh, Ai Leen; Wang, Shanshan; Ataca, Can; Grossman, Jeffrey C; Sinclair, Robert; Warner, Jamie H

    2016-02-10

    We use aberration-corrected transmission electron microscopy to track the real time atomic level torsional dynamics of subnanometer wires of MoS interconnecting monolayer regions of MoS2. An in situ heating holder is used inside the transmission electron microscope to raise the temperature of the sample to 400 °C to increase crystallization rates of the wires and reduce contamination effects. Frequent rotational twisting of the MoS wire is captured, demonstrating elastic torsional deformation of the MoS wires. We show that torsional rotations of the crystal structure of the MoS wires depend upon the specific atomic structure of the anchored sections of the suspended wire and the number of unit cells that make up the wire length. Elastic torsional flexibility of the MoS wires is revealed to help their self-adapting connectivity during the structural changes. Plastic torsional deformation is also seen for MoS wires that contain defects in their crystal structure, which produce small scale rotational disorder within the wires. Upon removal of the defects, the wire returns back to pristine form. These results provide detailed insights into how the atomic structure of the anchoring site significantly influences the nanowire configurations relative to the monolayered MoS2. PMID:26785319

  7. Theoretical study on electronic properties of MoS2 antidot lattices

    Motivated by the state of the art method for etching hexagonal array holes in molybdenum disulfide (MoS2), the electronic properties of MoS2 antidot lattices (MoS2ALs) with zigzag edge were studied with first-principles calculations. Monolayer MoS2ALs are semiconducting and the band gaps converge to constant values as the supercell area increases, which can be attributed to the edge effect. Multilayer MoS2ALs and chemical adsorbed MoS2ALs by F atoms show metallic behavior, while the structure adsorbed with H atoms remains to be semiconducting with a tiny bandgap. Our results show that forming periodically repeating structures in MoS2 can develop a promising technique for engineering nano materials and offer new opportunities for designing MoS2-based nanoscale electronic devices and chemical sensors.

  8. The creation of the magnetic and metallic characteristics in low-width MoS 2 nanoribbon (1D MoS 2): A DFT study

    Shidpour, Reza; Manteghian, Merhrdad

    2009-06-01

    A basic understanding of the catalytic performance is needed to probe the physical properties that change with a reduction in the catalytic clusters size. It has been shown that the edge of low-width MoS2 nanoribbon has a metallic characteristic, while that of bulk MoS2 has a semi-conductive characteristic. For probing the observations, we constructed the models representing the surface atoms and the edge atoms of the MoS2 nanoribbon. The nanoribbon-like model can also be used to model the edge atoms of the nanocluster MoS2 .Then we calculated the density of states (DOS) of infinitely two-dimensional MoS2 and of the structure corresponding to the edge atoms of the MoS2 nanoribbon-like structure with Wien2K software. The magnetic moment of structures was calculated for identifying the magnetic structure. We found that the bulk MoS2 and infinitely two-dimensional MoS2 are semi-conductive and not magnetic, while the computation model corresponding to MoS2 nanoribbon is metallic. The calculation anticipates that the edges of the MoS2 nanocluster and the low-width MoS2 nanoribbon are strongly magnetic.

  9. Two-bit memory and quantized storage phenomenon in conventional MOS structures with double-stacked Pt-NCs in an HfAlO matrix.

    Zhou, Guangdong; Wu, Bo; Liu, Xiaoqin; Li, Ping; Zhang, Shuangju; Sun, Bai; Zhou, Ankun

    2016-03-01

    A two-bit memory and quantized storage phenomenon are observed at room temperature for a device based on the traditional MOS structure with double-stacked Pt-nanocrystals (Pt-NCs). A 2.68 and 1.72 V flat band voltage shift (memory window) has been obtained when applying a ±7 V programming/erasing voltage to the structures with double-stacked Pt-NCs. The memory windows of 2.40 and 1.44 V can be retained after stress for 10(5) seconds, which correspond to 89.55% and 83.72% stored charges reserved. The quantized charge storage phenomenon characterized by current-voltage (J-V) hysteresis curves was detected at room temperature. The shrinkage of the memory window results from the decreasing tunneling probability, which strongly depends on the number of stacks. The traps, de-traps and quantum confinement effects of Pt-NCs may contribute to the improvement of dielectric characteristics and the two-bit memory behavior. The multi-bit memory and quantized storage behavior observed in the Pt-NCs stacks structure at room temperature might provide a feasible method for realizing the multi-bit storage in non-volatile flash memory devices. PMID:26864686

  10. Parametric Conversion Using Custom MOS Varactors

    Iniewski Krzysztof (Kris

    2006-01-01

    Full Text Available The possible role of customized MOS varactors in amplification, mixing, and frequency control of future millimeter wave CMOS RFICs is outlined. First, the parametric conversion concept is revisited and discussed in terms of modern RF communications systems. Second, the modeling, design, and optimization of MOS varactors are reconsidered in the context of their central role in parametric circuits. Third, a balanced varactor structure is proposed for robust oscillator frequency control in the presence of large extrinsic noise expected in tightly integrated wireless communicators. Main points include the proposal of a subharmonic pumping scheme based on the MOS varactor, a nonequilibrium elastance-voltage model, optimal varactor layout suggestions, custom m-CMOS varactor design and measurement, device-level balanced varactor simulations, and parametric circuit evaluation based on measured device characteristics.

  11. All in-situ GaSb MOS structures on GaAs (001): Growth, passivation and high-k oxides

    Tokranov, V.; Madisetti, S.; Yakimov, M.; Nagaiah, P.; Faleev, N.; Oktyabrsky, S.

    2013-09-01

    The GaSb-on-GaAs growth was optimized for the fabrication of metal-oxide-semiconductor (MOS) capacitors (Caps) with low interface state trap density (Dit) using in-situ deposited amorphous silicon (a-Si) interface passivation layer (IPL) and high-k oxides. The best top surface with the average roughness Ra=0.37 nm and with spiral type "step-flow" growth mode was observed in the GaSb structure with the initial 0.5 μm grown at 410 °C and the top 0.5 μm grown at 485 °C. N- and p-type GaSb MOSCaps with reasonable capacitance-voltage(C-V) characteristics at room temperature (RT) were demonstrated using all in-situ 0.5 nm a-Si IPL and 10 nm Al2O3+HfO2 or Al2O3. A-Si IPL was found essential for n-MOSCaps but not in the case of p-MOSCaps where comparable C-V characteristics with a similarly low Dit=1-2×1012 cm-2 eV-1were demonstrated without IPL.

  12. Synthesis and characterization of MoS2 nanosheets

    Deokar, G.; Vignaud, D.; Arenal, R.; Louette, P.; Colomer, J.-F.

    2016-02-01

    Here, we report on the synthesis of MoS2 nanosheets using a simple two-step additive-free growth technique. The as-synthesized nanosheets were characterized to determine their structure and composition, as well as their optical properties. The MoS2 nanosheets were analyzed by scanning electron microscopy, transmission electron microscopy (TEM), including high-resolution scanning TEM imaging and energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL). The as-produced MoS2 nanosheets are vertically aligned with curved edges and are densely populated. The TEM measurements confirmed that the nanosheets have the 2H-MoS2 crystal structure in agreement with the Raman results. The XPS results revealed the presence of high purity MoS2. Moreover, a prominent PL similar to mechanically exfoliated few and mono-layer MoS2 was observed for the as-grown nanosheets. For the thin (≤50 nm) nanosheets, the PL feature was observed at the same energy as that for a direct band-gap monolayer MoS2 (1.83 eV). Thus, the as-produced high-quality, large-area, MoS2 nanosheets could be potentially useful for various optoelectronic and catalysis applications.

  13. A generic tight-binding model for monolayer, bilayer and bulk MoS2

    Ferdows Zahid; Lei Liu; Yu Zhu; Jian Wang; Hong Guo

    2013-01-01

    Molybdenum disulfide (MoS2) is a layered semiconductor which has become very important recently as an emerging electronic device material. Being an intrinsic semiconductor the two-dimensional MoS2 has major advantages as the channel material in field-effect transistors. In this work we determine the electronic structures of MoS2 with the highly accurate screened hybrid functional within the density functional theory (DFT) including the spin-orbit coupling. Using the DFT electronic structures ...

  14. Interfacial chemical reactions between MoS2 lubricants and bearing materials

    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.

  15. Phonon Bandgap Engineering of Strained Monolayer MoS2

    Jiang, Jin-Wu

    2014-01-01

    The phonon band structure of monolayer MoS2 is characteristic for a large energy gap between acoustic and optical branches, which protects the vibration of acoustic modes from being scattered by optical phonon modes. Therefore, the phonon bandgap engineering is of practical significance for the manipulation of phonon-related mechanical or thermal properties in monolayer MoS2. We perform both phonon analysis and molecular dynamics simulations to investigate the tension effect on the phonon ban...

  16. Broadband ultra-high transmission of terahertz radiation through monolayer MoS$_{2}$

    Deng, Xue-Yong; Su, Fu-Hai; Liu, Nian-Hua; Liu, Jiang-Tao

    2015-01-01

    In this study, terahertz (THz) absorption and transmission of monolayer MoS$_{2}$ was calculated under different carrier concentrations. Results showed that the THz absorption of monolayer MoS$_{2}$ is very small even under high carrier concentrations and large incident angle. Equivalent loss of the THz absorption is the total sum of reflection and absorption that is one to three grades lower than that of graphene. The monolayer MoS$_{2}$ transmission is much larger than that of the traditional GaAs and InAs two-dimensional electron gas. The field-effect tubular structure formed by the monolayer MoS$_{2}$-insulation-layer-graphene is investigated. In this structure the THz absorption of graphene to reach saturation under low voltage. Meantime, the maximum THz absorption of monolayer MoS$_{2}$ was limited to approximately 5\\%. Thus, monolayer MoS$_{2}$ is a kind of ideal THz Transparent Electrodes.

  17. DLTS analysis of amphoteric interface defects in high-TiO{sub 2} MOS structures prepared by sol-gel spin-coating

    Kumar, Arvind; Mondal, Sandip; Rao, K. S. R. Koteswara, E-mail: ksrkrao@physics.iisc.ernet.in, E-mail: raoksrk@gmail.com [Department of Physics, Indian Institute of Science, Bangalore, 560012 (India)

    2015-11-15

    High-κ TiO{sub 2} thin films have been fabricated from a facile, combined sol – gel spin – coating technique on p and n type silicon substrate. XRD and Raman studies headed the existence of anatase phase of TiO{sub 2} with a small grain size of 18 nm. The refractive index ‘n’ quantified from ellipsometry is 2.41. AFM studies suggest a high quality, pore free films with a fairly small surface roughness of 6 Å. The presence of Ti in its tetravalent state is confirmed by XPS analysis. The defect parameters observed at the interface of Si/TiO{sub 2} were studied by capacitance – voltage (C – V) and deep level transient spectroscopy (DLTS). The flat – band voltage (V{sub FB}) and the density of slow interface states estimated are – 0.9, – 0.44 V and 5.24×10{sup 10}, 1.03×10{sup 11} cm{sup −2}; for the NMOS and PMOS capacitors, respectively. The activation energies, interface state densities and capture cross – sections measured by DLTS are E{sub V} + 0.30, E{sub C} – 0.21 eV; 8.73×10{sup 11}, 6.41×10{sup 11} eV{sup −1} cm{sup −2} and 5.8×10{sup −23}, 8.11×10{sup −23} cm{sup 2} for the NMOS and PMOS structures, respectively. A low value of interface state density in both P- and N-MOS structures makes it a suitable alternate dielectric layer for CMOS applications. And also very low value of capture cross section for both the carriers due to the amphoteric nature of defect indicates that the traps are not aggressive recombination centers and possibly can not contribute to the device operation to a large extent.

  18. Highly stretchable MoS2 kirigami

    Hanakata, Paul Z.; Qi, Zenan; Campbell, David K.; Park, Harold S.

    2015-12-01

    We report the results of classical molecular dynamics simulations focused on studying the mechanical properties of MoS2 kirigami. Several different kirigami structures were studied based upon two simple non-dimensional parameters, which are related to the density of cuts, as well as the ratio of the overlapping cut length to the nanoribbon length. Our key findings are significant enhancements in tensile yield (by a factor of four) and fracture strains (by a factor of six) as compared to pristine MoS2 nanoribbons. These results, in conjunction with recent results on graphene, suggest that the kirigami approach may be generally useful for enhancing the ductility of two-dimensional nanomaterials.

  19. Formation Energies of the Lithium Intercalations in MoS2

    Aiyu LI; Huiying LIU; Zizhong ZHU; Meichun HUANG; Yong YANG

    2006-01-01

    First-principles calculations have been performed to study the lithium intercalations in MoS2. The formation energies, changes of volumes, electronic structures and charge densities of the lithium intercalations in MoS2 are presented. Our calculations show that during lithium intercalations in MoS2, the lithium intercalation formation energies per lithium atom are between 2.5 eV to 3.0 eV, The volume expansions of MoS2 due to lithium intercalations are relatively small

  20. Hierarchical MoS2-rGO nanosheets with high MoS2 loading with enhanced electro-catalytic performance

    Zhou, Jing; Xiao, Han; Zhou, Bowen; Huang, Feifan; Zhou, Shoubin; Xiao, Wei; Wang, Dihua

    2015-12-01

    Incorporation of high-loading redox-active materials with small amounts of graphene is a general protocol to achieve high-performance catalysts. Herein, hierarchical MoS2-reduced graphene oxide nanosheet (denoted as MoS2-rGO nanosheets) hybrids with a loading of MoS2 as high as 94 wt% are synthesized. The obtained hierarchical MoS2-rGO nanosheets simultaneously integrate the structural and compositional design rationales for high-efficiency and durable electrocatalysts based on high weight ratio of MoS2 in hybrid composite, highly stable/conducting rGO, well-dispersed two-dimensional ultrathin MoS2 nanosheets, more exposed edge sites and micro/nano hierarchical structure. When evaluated as electrocatalysts for hydrogen evolution and oxygen reduction reactions, the hierarchical MoS2-rGO nanosheets demonstrates enhanced activity and excellent stability, promising their applications in MoS2 based electrochemical, photo-catalytic and photo-elecrocatalytic cells.

  1. Band gap engineering of MoS2 upon compression

    López-Suárez, Miquel; Neri, Igor; Rurali, Riccardo

    2016-04-01

    Molybdenum disulfide (MoS2) is a promising candidate for 2D nanoelectronic devices, which shows a direct band-gap for monolayer structure. In this work we study the electronic structure of MoS2 upon both compressive and tensile strains with first-principles density-functional calculations for different number of layers. The results show that the band-gap can be engineered for experimentally attainable strains (i.e., ±0.15). However, compressive strain can result in bucking that can prevent the use of large compressive strain. We then studied the stability of the compression, calculating the critical strain that results in the on-set of buckling for free-standing nanoribbons of different lengths. The results demonstrate that short structures, or few-layer MoS2, show semi-conductor to metal transition upon compressive strain without bucking.

  2. Effects of plasma treatment on surface properties of ultrathin layered MoS2

    Kim, Suhhyun; Choi, Min Sup; Qu, Deshun; Ra, Chang Ho; Liu, Xiaochi; Kim, Minwoo; Song, Young Jae; Jong Yoo, Won

    2016-09-01

    This work investigates the use of oxygen plasma (O2) treatment, applied as an inductively coupled plasma, to control the thickness and work function of a MoS2 layer. Plasma-etched MoS2 exhibited a surface roughness similar to that of the pristine MoS2. The MoS2 field effect transistors fabricated using the plasma-etched MoS2 displayed a higher n-type doping concentration than that of pristine MoS2. The x-ray photoelectron spectroscopy was performed to analyze chemical composition to demonstrate the minimum level of chemical reactions occurred upon plasma treatment. Moreover, Kelvin probe force microscopy measurements were conducted to probe the changes in the work function that could be attributed to the changes in the surface potential. The measured work functions suggest the modification of a band structure and n-doping effect after plasma treatments that depended on the number of MoS2 layers. This study suggests that the O2 plasma can control the layer number of the MoS2 as well as the electronic properties of a MoS2 film.

  3. Examination of the radiation induced damage in-depth profile in silicon after ion implantation by means of MOS-structure

    A new non-destructive technique for the determination of radiation damage in-depth profile in silicon after ion implantation is developed. The locally enhanced generation rate according to the SRH-theory of the deep depleted MOS diode as an image of radiation damage is used. It is evaluated by the measurement of the C(V) pulse capacitance and hf pulse capacitance transient response C(t). Results of high and low energy experiments with Hsub(e)+, P+ and O+ are reported. Furthermore, in the case of Hsub(e)+, the deep trap evolution influenced by the Si/SiO2 interface is examined. (orig.)

  4. Surface Defects on Natural MoS2.

    Addou, Rafik; Colombo, Luigi; Wallace, Robert M

    2015-06-10

    Transition metal dichalcogenides (TMDs) are being considered for a variety of electronic and optoelectronic devices such as beyond complementary metal-oxide-semiconductor (CMOS) switches, light-emitting diodes, solar cells, as well as sensors, among others. Molybdenum disulfide (MoS2) is the most studied of the TMDs in part because of its availability in the natural or geological form. The performance of most devices is strongly affected by the intrinsic defects in geological MoS2. Indeed, most sources of current transition metal dichalcogenides have defects, including many impurities. The variability in the electrical properties of MoS2 across the surface of the same crystal has been shown to be correlated with local variations in stoichiometry as well as metallic-like and structural defects. The presence of impurities has also been suggested to play a role in determining the Fermi level in MoS2. The main focus of this work is to highlight a number of intrinsic defects detected on natural, exfoliated MoS2 crystals from two different sources that have been often used in previous reports for device fabrication. We employed room temperature scanning tunneling microscopy (STM) and spectroscopy (STS), inductively coupled plasma mass spectrometry (ICPMS), as well as X-ray photoelectron spectroscopy (XPS) to study the pristine surface of MoS2(0001) immediately after exfoliation. ICPMS used to measure the concentration of impurity elements can in part explain the local contrast behavior observed in STM images. This work highlights that the high concentration of surface defects and impurity atoms may explain the variability observed in the electrical and physical characteristics of MoS2. PMID:25980312

  5. Synthesis of coaxial nanotubes of MoS2 and carbon

    The di chalcogenides WS2 and MoS2 by their tubular properties were combined. It was synthesized coaxial structures of MoS2 with C with the purpose to studying the possible structural changes of the MoS2 nano tubes at was submitted to a propylene gas flux as carbon precursor in a thermal treatment. Studies of structural characterization by Transmission Electron Microscopy (Tem) were realized. The theoretical simulation of the structure was realized using an algorithm type multilayer. The possibility of the nano tubes are applied to gas storage as can be the hydrogen arouse interest by the energy production. (Author)

  6. Improved photoelectrical properties of MoS(2) films after laser micromachining.

    Lu, Junpeng; Lu, Jia Hui; Liu, Hongwei; Liu, Bo; Chan, Kim Xinhui; Lin, Jiadan; Chen, Wei; Loh, Kian Ping; Sow, Chorng Haur

    2014-06-24

    Direct patterning of ultrathin MoS2 films with well-defined structures and controllable thickness is appealing since the properties of MoS2 sheets are sensitive to the number of layer and surface properties. In this work, we employed a facile, effective, and well-controlled technique to achieve micropatterning of MoS2 films with a focused laser beam. We demonstrated that a direct focused laser beam irradiation was able to achieve localized modification and thinning of as-synthesized MoS2 films. With a scanning laser beam, microdomains with well-defined structures and controllable thickness were created on the same film. We found that laser modification altered the photoelectrical property of the MoS2 films, and subsequently, photodetectors with improved performance have been fabricated and demonstrated using laser modified films. PMID:24863730

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

    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. PMID:25924398

  8. MOS VLSI reliability and yield trends

    Woods, Murray H.

    1986-12-01

    Trends in yield and reliability of new technologies for MOS devices both drive and are a consequence of at least six major, highly interactive technology trends - tending toward (1) more complex device structures and materials, (2) reduced device dimensions and feature sizes, (3) larger wafer sizes, (4) factory automation, (5) higher pin count packages and larger die sizes, and (6) increasingly sophisticated CAD tools. Technology decisions now often involve trading off one reliabilty failure mechanism for another. The implications are that the dominant reliability mechanisms may change in the future, and wearout will start to impinge on reliability life.

  9. First-principles analysis of MoS2/Ti2C and MoS2/Ti2CY2 (Y=F and OH) all-2D semiconductor/metal contacts

    Gan, Li-Yong

    2013-06-13

    First-principles calculations are used to explore the geometry, bonding, and electronic properties of MoS2/Ti2C and MoS2/Ti2CY2 (Y = F and OH) semiconductor/metal contacts. The structure of the interfaces is determined. Strong chemical bonds formed at the MoS2/Ti2C interface result in additional states next to the Fermi level, which extend over the three atomic layers of MoS2 and induce a metallic character. The interaction in MoS2/Ti2CY2, on the other hand, is weak and not sensitive to the specific geometry, and the semiconducting nature thus is preserved. The energy level alignment implies weak and strong n-type doping of MoS2 in MoS2/Ti2CF2 and MoS2/Ti2C(OH)2, respectively. The corresponding n-type Schottky barrier heights are 0.85 and 0.26 eV. We show that the MoS2/Ti2CF2 interface is close to the Schottky limit. At the MoS2/Ti2C(OH)2 interface, we find that a strong dipole due to charge rearrangement induces the Schottky barrier. The present interfaces are well suited for application in all-two-dimensional devices.

  10. Photoconductivities in MoS2 Nanoflake Photoconductors.

    Shen, Wei-Chu; Chen, Ruei-San; Huang, Ying-Sheng

    2016-12-01

    Photoconductivities in molybdenum disulfide (MoS2) layered nanostructures with two-hexagonal crystalline structure prepared by mechanical exfoliation were investigated. The photoconductor-type MoS2 nanoflakes exhibit remarkable photoresponse under the above bandgap excitation wavelength of 532 nm at different optical intensity. The photocurrent responsivity and photoconductive gain of nanoflakes can reach, respectively, 30 AW(-1) and 103 at the intensity of 50 Wm(-2), which are several orders of magnitude higher than those of their bulk counterparts. The vacuum-enhanced photocurrent and power-independent responsivity/gain indicate a surface-controlled photoconduction mechanism in the MoS2 nanomaterial. PMID:26935304

  11. Thermal conductivity of MoS2 polycrystalline nanosheets

    Sledzinska, M.; Graczykowski, B.; Placidi, M.; Reig, D. Saleta; Sachat, A. El; Reparaz, J. S.; Alzina, F.; Roche, S.; B. Mortazavi; Quey, R.; Torres, C. M. Sotomayor

    2016-01-01

    We report a technique for transferring large areas of the CVD-grown, few-layer MoS2 from the original substrate to another arbitrary substrate and onto holey substrates, in order to obtain free-standing structures. The method consists of a polymer- and residue-free, surface-tension-assisted wet transfer, in which we take advantage of the hydrophobic properties of the MoS2. The methods yields better quality transferred layers, with fewer cracks and defects, and less contamination than the wide...

  12. Co-precipitation synthesis and characterization of faceted MoS2 nanorods with controllable morphologies

    Molybdenum disulfide (MoS2) nanopowder has been prepared using a co-precipitation method. This paper describes the thermal effect on the morphology enhancement of MoS2 sphere-like structures into nanorods with a winding structure. For the reduction in precursors, the as-obtained MoS2 nanopowder was calcinated at 250, 400, 600, and 800 C for 1 h in an N2 environment. The calcined samples were characterized using a particle size analyzer, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with X-ray analysis (EDAX) and transmission electron microscopy, HRTEM and X-ray photoelectron spectroscopy. The results show the MoS2 sphere-like structure with diameter in the range of 50-100 nm and rod-like winding structure with diameter in the range of 20-150 nm, and a few tens of micrometers in length with a high degree of size homogeneity. The FT-IR spectra show the obtained bands at 480 and 900 cm-1 are corresponding to the Mo-S bond and the S-S bond. The TG-DTA curves confirm the thermal stability of the prepared samples. It is observed that the band gap energy for the MoS2 nanorods is lower than for the nanospherical structure MoS2, which leads to achieve high electron and hole recombination rate. (orig.)

  13. Facile Synthesis of Hollow MoS2 Microspheres/Amorphous Carbon Composites and Their Lithium Storage Properties

    Graphical abstract: - Highlights: • Hollow MoS2 MACCs have been successfully synthesized. • Initial discharge capacity of 1545 mAhg−1 is obtained at 100 mAg−1. • Hollow MoS2 MACCs show enhanced cycling stability and rate capability. • Amorphous carbon can improve electrochemical performance. - Abstract: In this paper, we report a facile process to synthesize hollow MoS2 microspheres/amorphous carbon composites (MACCs) by hydrothermal method and their improved electrochemical performance in Lithium ion batteries (LIBs). The composites prepared are characterized by XRD, SEM, HRTEM and EDS. MoS2 nanosheets are uniformly grow on the surface of amorphous carbon. The interlayer-distance of the adjacent MoS2 nanosheets in the composites is about 0.64 nm. As an electrode material for the LIBs, hollow MoS2 MACCs exhibit excellent cyclic stability with 1147 mAhg−1 at 100 mAg−1 after 100 cycles, which displays more prominent performance than that of the hollow MoS2 microspheres. Moreover, the reversible capacity for the hollow MoS2 MACCs can be still maintain at 876 mAhg−1 at 1000 mAg−1. The enhanced electrochemical performance of hollow MoS2 MACCs could be attributed to their unique hollow structure, large specific surface area, the increased interlayer-distance and the synergistic effects between hollow MoS2 microspheres and amorphous carbon

  14. Graphite edge controlled registration of monolayer MoS2 crystal orientation

    Transition metal dichalcogenides such as the semiconductor MoS2 are a class of two-dimensional crystals. The surface morphology and quality of MoS2 grown by chemical vapor deposition are examined using atomic force and scanning tunneling microscopy techniques. By analyzing the moiré patterns from several triangular MoS2 islands, we find that there exist at least five different superstructures and that the relative rotational angles between the MoS2 adlayer and graphite substrate lattices are typically less than 3°. We conclude that since MoS2 grows at graphite step-edges, it is the edge structure which controls the orientation of the islands, with those growing from zig-zag (or armchair) edges tending to orient with one lattice vector parallel (perpendicular) to the step-edge

  15. Thermoelectric performance of restacked MoS2 nanosheets thin-film

    Wang, Tongzhou; Liu, Congcong; Xu, Jingkun; Zhu, Zhengyou; Liu, Endou; Hu, Yongjing; Li, Changcun; Jiang, Fengxing

    2016-07-01

    MoS2 has been predicted to be an excellent thermoelectric material due to its large intrinsic band gap and high carrier mobility. In this work, we exfoliated bulk MoS2 by the assistance of lithium intercalation and fabricated the restacked MoS2 thin-film using a simple filtration technique. These MoS2 thin-films with different thickness showed different thermoelectric performance. It was found that with the increase of thickness, carrier concentration, electrical conductivity and Seebeck coefficient all showed an increasing trend. In particular, the maximum Seebeck coefficient was able to reach 93.5 μV K‑1. This high thermopower indicates that MoS2 will have ideal thermoelectric performance in the future through optimizing its structure. The highest figure of merit (ZT = 0.01) is calculated in this experiment.

  16. A first-principles study of van der Waals interactions and lattice mismatch at MoS2/metal interfaces

    Farmanbar, M.; Brocks, G.

    2015-01-01

    We explore the adsorption of MoS2 on a range of metal substrates by means of first-principles density functional theory calculations. Including van der Waals forces in the density functional is essential to capture the interaction between MoS2 and a metal surface, and obtain reliable interface potential steps and Schottky barriers. Special care is taken to construct interface structures that have a mismatch between the MoS2 and the metal lattices of

  17. Large-Area Buckled MoS2 Films on the Graphene Substrate.

    Kim, Seon Joon; Kim, Dae Woo; Lim, Joonwon; Cho, Soo-Yeon; Kim, Sang Ouk; Jung, Hee-Tae

    2016-06-01

    In this study, a novel buckled structure of edge-oriented MoS2 films is fabricated for the first time by employing monolayer graphene as the substrate for MoS2 film growth. Compared to typical buckling methods, our technique has several advantages: (1) external forces such as heat and mechanical strain are not applied; (2) uniform and controllable buckling over a large area is possible; and (3) films are able to be transferred to a desired substrate. Dual MoS2 orientation was observed in the buckled film where horizontally aligned MoS2 layers of 7 nm thickness were present near the bottom graphene surface and vertically aligned layers dominated the film toward the outer surface, in which the alignment structure was uniform across the entire film. The catalytic ability of the buckled MoS2 films, measured by performing water-splitting tests in acidic environments, shows a reduced onset potential of -0.2 V versus reversible hydrogen electrode (RHE) compared to -0.32 V versus RHE for pristine MoS2, indicating that the rough surface provided a higher catalytic activity. Our work presents a new method to generate a buckled MoS2 structure, which may be extended to the formation of buckled structures in various 2D materials for future applications. PMID:27144288

  18. MOS integrated circuit fault modeling

    Sievers, M.

    1985-01-01

    Three digital simulation techniques for MOS integrated circuit faults were examined. These techniques embody a hierarchy of complexity bracketing the range of simulation levels. The digital approaches are: transistor-level, connector-switch-attenuator level, and gate level. The advantages and disadvantages are discussed. Failure characteristics are also described.

  19. The OverMOS project

    Das, D.; Dopke, J.; McMahon, S. J.; Turchetta, R.; Villani, G.; Wilson, F.; Worm, S.

    2016-07-01

    The OverMOS project aims to create a fast radiation hard tracking detector sensor, based on High Resistivity CMOS technology. In a first prototype submission, different pixel and charge collection node geometries have been produced, which have lately been returned from fabrication and are currently under test.

  20. A 77 K MOS magnetic field detector

    Murphy, R S; Torres, A. [Instituto Nacional de Astrofisica Optica y Electronica, Puebla (Mexico); Garcia, P.J. [Universidad Veracruzana, Veracruz (Mexico); Gutierrez, E.A. [Motorola, Puebla (Mexico)

    2001-12-01

    An integrated MOS (metal-oxide-semiconductor)-compatible magnetic field detector (split-drain MAGFET) for operation at liquid-nitrogen temperature LNT (77 K) is presented. The measured relative magnetic sensibility (S{sub a}) is approximately 14%/T (double the value ever reported) using a non-optimized MAGFET structure (W/L) = (100 mm/125 mm). The cryo-magnetic structure was tested without a built-in preamplifier. It presents a power consumption of the order of mW. [Spanish] A traves de este articulo se presenta un detector de campo magnetico (split-drain MAGFET), basado en el transistor de efecto de campo MOS (metal-oxido-semiconductor), y totalmente compatible con procesos de fabricacion de circuitos integrados CMOS. La operacion optima de este detector es a temperaturas criogenicas. Aqui se presentan los resultados experimentales de la caracterizacion de una estructura no optimizada con dimensiones (W / L) = (100 mm/125 mm) a la temperatura del nitrogeno liquido (77 K). La sensibilidad relativa medida es de cerca del 14 % T, casi el doble del valor maximo antes reportado en la literatura. El dispositivo se midio sin un pre-amplificador integrado, mostrando un consumo de potencia del orden de microwatts.

  1. Effect of MoO3 constituents on the growth of MoS2 nanosheets by chemical vapor deposition

    Wang, Xuan; Zhang, Yong Ping; Qian Chen, Zhi

    2016-06-01

    The highly crystalline and uniform MoS2 film was grown on Si substrate by a low-pressure chemical vapor deposition method using S and MoO3 as precursors at an elevated temperature. The structures and properties of MoS2 nanosheets vary greatly with the content of MoO3 constituents in the films. The nanostructured MoS2 film exhibits strong photoluminescence in the visible range. This work may provide a pathway to synthesizing MoS2 nanosheets and facilitate the development of applicable devices.

  2. The casein kinase II beta subunit binds to Mos and inhibits Mos activity.

    Chen, M.; D. Li; Krebs, E G; Cooper, J. A.

    1997-01-01

    Mos is a germ cell-specific serine/threonine kinase and is required for Xenopus oocyte maturation. Active Mos stimulates a mitogen-activated protein kinase (MAPK) by directly phosphorylating and activating MAPK kinase (MKK). We report here that the Xenopus homolog of the beta subunit of casein kinase II (CKII beta) binds to and regulates Mos. The Mos-interacting region of CKII beta was mapped to the C terminus. Mos bound to CKII beta in somatic cells ectopically expressing Mos and CKII beta a...

  3. Design requirement, qualification tests and integration of a thin solid lubricant film of MoS2 for the cold mass support structure of the steady state superconducting tokamak SST-1

    The SST-1 is a superconducting tokamak, which is in the commissioning phase and will soon be ready for plasma operation. The superconducting magnet system of SST-1 comprises toroidal field (TF) and poloidal field (PF) coils. The 16 TF coils are nosed and clamped towards the in-board side and are supported toroidally with the inter-coil structure at the out-board side, forming a rigid body system. The 9 PF coils are clamped on the TF coils structure. The integrated system of TF coils and PF coils forms the cold mass of 50 ton weight. This cold mass system (CMS) is freely supported on the rigid support ring at 16 locations and the support ring in turn is supported on the 8 columns of the machine support structure. This CMS is accommodated inside the high vacuum chamber (cryostat). During the operation this cold mass attains a cryogenic temperature of 4.2 K in the hostile environment of high vacuum. During the cool down, the thermal excursion of cold mass and its supporting structure generates severe frictional forces at the sliding surfaces of the support. There is a design requirement of introducing a thin layer of solid lubricant film of molybdenum disulfide having coefficient of friction 0.05 between the sliding surfaces to control the stress contribution due to the friction. To ascertain the compatibility of molybdenum disulphide (MoS2) as a solid lubricant in a high vacuum and very low temperature environment, we have carried out qualification tests on various samples and measured the coefficient of friction in both room temperature conditions and at high vacuum and after thermal shocking at a temperature of 4.2 K in a high vacuum environment to simulate the actual working condition. After successful qualification tests and process establishment, the actual components are fabricated and integrated in the cold mass support structure assembly. The design requirement and qualification tests performed at 4.2 K and room temperature as well as details about the

  4. Plasma nanocoating of thiophene onto MoS2 nanotubes

    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.

  5. Electronic and magnetic properties of MoS2 nanoribbons with sulfur line vacancy defects

    Han, Yang; Zhou, Jian; Dong, Jinming

    2015-08-01

    Motivated by the recent experimental result that single sulfur vacancies in monolayer MoS2 are mobile under the electron beam and easily agglomerate into the sulfur line vacancy defects [Physical Review B 88, 035301(2013)] , the structural, electronic and magnetic properties of one dimensional zigzag (ZZ) and armchair (AC) edge MoS2 nanoribbons with single or double staggered sulfur line vacancy defects (hereafter, abbreviated as SV or DV, respectively), parallel to their edges, have been investigated systematically by density functional theory calculations. It is very interesting to find that the bond strains induced by the sulfur line vacancy defect can cause a much larger out-of plane distortions in the ZZ edge MoS2 nanoribbon than in the AC edge counterpart. Besides, the defective ZZ edge MoS2 nanoribbons with SV or DV are both metals, having their two respective degenerate ground states with the same energy, among which one is ferromagnetic (FM " + +") and the other is antiferromagnetic (AFM " + -"). But the AC edge MoS2 nanoribbons with SV or DV are both nonmagnetic semiconductors, having very different gap values. Finally, the sulfur line vacancy defects would induce some defect states in the electronic structures of the defective MoS2 nanoribbons. All these important results could provide a new route of tuning the electronic properties of MoS2 nanoribbons and its derivatives for their promising applications in nanoelectronics and optoelectronics.

  6. Wettability and friction of water on a MoS2 nanosheet

    Luan, Binquan; Zhou, Ruhong

    2016-03-01

    The molybdenum disulfide (MoS2) nanosheet is a promising two-dimensional (2D) material and has recently been used in biological sensing. While the electronic structure of 2D MoS2 sheet has been actively studied, the role of its atomic structure and thus the interfacial interactions with bio-fluids are still elusive. Using Molecular dynamics simulations, we developed MoS2 force field parameters to reproduce the experimentally determined water contact angle of the MoS2 nanosheet and then predicted the slip-length of water that has not been measured in experiment yet. Simulation results suggest that the MoS2 nanosheet is a hydrophobic and low-friction surface, despite its seemingly significant charges of surface atoms and relatively strong strength of van der Waals potentials. We expect that the developed force fields for depicting surface atoms of MoS2 will facilitate future research in understanding biomolecule-MoS2 interactions in MoS2-based biosensors.

  7. Synthesis of Vertically Standing MoS2 Triangles on SiC.

    Lan, Feifei; Lai, Zhanping; Xu, Yongkuan; Cheng, Hongjuan; Wang, Zaien; Qi, Chengjun; Chen, Jianli; Zhang, Song

    2016-01-01

    Layered material MoS2 has been attracting much attention due to its excellent electronical properties and catalytic property. Here we report the synthesis of vertically standing MoS2 triangles on silicon carbon(SiC), through a rapid sulfidation process. Such edge-terminated films are metastable structures of MoS2, which may find applications in FinFETs and catalytic reactions. We have confirmed the catalytic property in a hydrogen evolution reaction(HER). The Tafel slope is about 54mV/decade. PMID:27550237

  8. A Multiple—Valued Algebra for Modeling MOS VLSI Circuits at Switch—Level

    胡谋

    1992-01-01

    A multiple-valued algebra for modeling MOS VLSI circuits at switch-level is proposed in this paper,Its structure and properties are studied.This algebra can be used to transform a MOS digital circuit to a swith-level algebraic expression so as to generate the truth table for the circuit and to derive a Boolean expression for it.In the paper,methods to construct a switch-level algebraic expression for a circuit and methods to simplify expressions are given.This algebra provides a new tool for MOS VLSI circuit design and analysis.

  9. All Chemical Vapor Deposition Growth of MoS2:h-BN Vertical van der Waals Heterostructures.

    Wang, Shanshan; Wang, Xiaochen; Warner, Jamie H

    2015-05-26

    Vertical van der Waals heterostructures are formed when different 2D crystals are stacked on top of each other. Improved optical properties arise in semiconducting transition metal dichalcogenide (TMD) 2D materials, such as MoS2, when they are stacked onto the insulating 2D hexagonal boron nitride (h-BN). Most work to date has required mechanical exfoliation of at least one of the TMDs or h-BN materials to form these semiconductor:insulator structures. Here, we report a direct all-CVD process for the fabrication of high-quality monolayer MoS2:h-BN vertical heterostructured films with isolated MoS2 domains distributed across 1 cm. This is enabled by the use of few-layer h-BN films that are more robust against decomposition than monolayer h-BN during the MoS2 growth process. The MoS2 domains exhibit different growth dynamics on the h-BN surfaces compared to bare SiO2, confirming that there is strong interaction between the MoS2 and underlying h-BN. Raman and photoluminescence spectroscopies of CVD-grown MoS2 are compared to transferred MoS2 on both types of substrates, and our results show directly grown MoS2 on h-BN films have smaller lattice strain, lower doping level, cleaner and sharper interfaces, and high-quality interlayer contact. PMID:25895108

  10. Thermal transport in MoS2/Graphene hybrid nanosheets.

    Zhang, Zhongwei; Xie, Yuee; Peng, Qing; Chen, Yuanping

    2015-09-18

    Heat dissipation is a very critical problem for designing nano-functional devices, including MoS2/graphene heterojunctions. In this paper we investigate thermal transport in MoS2/graphene hybrid nanosheets under various heating conditions, by using molecular dynamics simulation. Diverse transport processes and characteristics, depending on the conducting layers, are found in these structures. The thermal conductivities can be tuned by interlayer coupling, environment temperature, and interlayer overlap. The highest thermal conductivity at room temperature is achieved as more than 5 times of that of single-layer MoS2 when both layers are heated and 100% overlapped. Different transport mechanisms in the hybrid nanosheets are explained by phonon density of states, temperature distribution, and interlayer thermal resistance. Our results could not only provide clues to master the heat transport in functional devices based on MoS2/graphene heterojunctions, but are also useful for analyzing thermal transport in other van der Waals hybrid nanosheets. PMID:26313739

  11. Single-layer MoS2 transistors.

    Radisavljevic, B; Radenovic, A; Brivio, J; Giacometti, V; Kis, A

    2011-03-01

    Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting. PMID:21278752

  12. Composition dependent Fermi level shifting of Au decorated MoS2 nanosheets

    In the present work, shifting of Fermi level of MoS2 nanosheets due to decoration of Au nanoparticles (Au NPs) is reported. Au NPs are grown on MoS2 nanosheets by chemical reduction method. The structural analysis of pristine MoS2 and Au NPs decorated MoS2 has been done using X-ray diffraction and transmission electron microscopy. The effect of Au NPs decoration on the Fermi energy level of MoS2 nanosheets have been monitored by scanning Kelvin probe microscopy, which measures the work function in terms of contact potential difference. The work function of pristine MoS2 is found to be 4.994 eV, and it increases linearly for Au-MoS2 with increasing concentration of Au NPs. The gradual increase in the work function values indicate a systematic shifting of Fermi energy level of MoS2 towards valence band due to decoration of Au NPs

  13. Ab initio study of MoS2 nanotube bundles

    Verstraete, Matthieu; Charlier, Jean-Christophe

    2003-07-01

    Recently, the synthesis of a new phase of MoS2I1/3 stoichiometry was reported [M. Remskar, A. Mrzel, Z. Skraba, A. Jesih, M. Ceh, J. Demšar, P. Stadelmann, F. Lévy, and D. Mihailovic, Science 292, 479 (2001)]. Electron microscope images and diffraction data were interpreted to indicate bundles of sub-nanometer-diameter single-wall MoS2 nanotubes. After experimental characterization, the structure was attributed to an assembly of “armchair” nanotubes with interstitial iodine. Using first-principles total-energy calculations, bundles of MoS2 nanotubes with different topologies and stoichiometries are investigated. All of the systems are strongly metallic. Configurations with “zigzag” structures are found to be more stable energetically than the “armchair” ones, though all of the structures have similar stabilities. After relaxation, there remain several candidates which give a lattice parameter in relative agreement with experiment. Further, spin-polarized calculations indicate that a structure with armchair tubes iodine atoms in their center acquires a very large spontaneous magnetic moment of 12μB, while the other structures are nonmagnetic. Our ab initio calculations show that in most of the other structures, the tubes are very strongly bound together, and that the compounds should be considered as a crystal, rather than as a bundle of tubes in the habitual sense.

  14. Lubrication with sputtered MoS2 films: Principles, operation, limitations

    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.

  15. Facile Hydrothermal Synthesis of Monodispersed MoS2 Ultrathin Nanosheets Assisted by Ionic Liquid Brij56

    Guan-Qun Han

    2015-01-01

    Full Text Available Monodispersed MoS2 ultrathin nanosheets have been successfully fabricated by a facile hydrothermal process assisted by ionic liquid Brij56. The effect of Brij56 on the morphology and structure of MoS2 has been obviously observed. XRD shows that the as-prepared MoS2 assisted by Brij56 has the weak and broad peak of (002 planes, which implies the small size and well dispersed structure of MoS2 nanosheets. TEM and SEM images reveal that MoS2 ultrathin nanosheets have small size and few stacking layers with the adding of Brij56. HRTEM images prove that MoS2 appears to have a highly monodispersed morphology and to be monolayer ultrathin nanosheets with the length about 5–8 nm, which can provide more exposed rims and edges as active sites for hydrogen evolution reaction. Brij56 has played a crucial role in preparing monodispersed MoS2 ultrathin nanosheets as excellent electrocatalysts. The growth mechanism of monodispersed MoS2 has been discussed in detail.

  16. Operation and modeling of the MOS transistor

    Tsividis, Yannis

    2011-01-01

    Operation and Modeling of the MOS Transistor has become a standard in academia and industry. Extensively revised and updated, the third edition of this highly acclaimed text provides a thorough treatment of the MOS transistor - the key element of modern microelectronic chips.

  17. Large-area MoS2 grown using H2S as the sulphur source

    Dumcenco, Dumitru; Ovchinnikov, Dmitry; Lopez Sanchez, Oriol; Gillet, Philippe; Alexander, Duncan T. L.; Lazar, Sorin; Radenovic, Aleksandra; Kis, Andras

    2015-12-01

    We report on the growth of molybdenum disulphide (MoS2) using H2S as a gas-phase sulfur precursor that allows controlling the domain growth direction of domains in both vertical (perpendicular to the substrate plane) and horizontal (within the substrate plane), depending on the H2S:H2 ratio in the reaction gas mixture and temperature at which they are introduced during growth. Optical and atomic force microscopy measurements on horizontal MoS2 demonstrate the formation of monolayer triangular-shape domains that merge into a continuous film. Scanning transmission electron microscopy of monolayer MoS2 shows a regular atomic structure with a hexagonal symmetry. Raman and photoluminescence spectra confirm the monolayer thickness of the material. Field-effect transistors fabricated on MoS2 domains that are transferred onto Si/SiO2 substrates show a mobility similar to previously reported exfoliated and chemical vapor deposition-grown materials.

  18. Monolayers of MoS2 and WS2 as oxidation protective nanocoating materials

    Sen, Huseyin Sener; Durgun, Engin; Sahin, Hasan; Peeters, Francois

    2014-03-01

    First-principles simulation techniques are employed to analyse the interaction of oxygen with MoS2 and WS2 monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulphur atoms, oxygen molecule only weakly interact with the system. The penetration of oxygen atom and molecule through MoS2 monolayer require a very high energy barrier indicating that MoS2 can serve as protective layer from oxidation. Not only ideal structures but also possible defect formations are considered and penetration/diffusion barriers of oxygen are calculated for each case. The study is extended for WS2 as well, and obtained results are compared. Our predictions indicate that ideal and/or defected MoS2 and WS2 monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be used as an efficient nanocoating material.

  19. MoS2 Enhanced T-Phase Stabilization and Tunability Through Alloying.

    Raffone, Federico; Ataca, Can; Grossman, Jeffrey C; Cicero, Giancarlo

    2016-07-01

    Two-dimensional MoS2 is a promising material for nanoelectronics and catalysis, but its potential is not fully exploited since proper control of its multiple phases (H, T, ZT) and electronic properties is lacking. In this theoretical study, alloying is proposed as a method to stabilize the MoS2 T-phase. In particular, MoS2 is alloyed with another material that is known to exist in a monolayer MX2 T-structure, and we show that the formation energy difference among phases decreases even for low impurity concentrations in MoS2, and a relationship between impurity concentration and alloy band gap is established. This method can be potentially applied to many two-dimensional materials to tune/enhance their electronic properties and stabilities in order to suit the desired application. PMID:27225447

  20. Z2 Invariance of Germanene on MoS2 from First Principles

    Amlaki, Taher; Bokdam, Menno; Kelly, Paul J.

    2016-06-01

    We present a low energy Hamiltonian generalized to describe how the energy bands of germanene (Ge ¯ ) are modified by interaction with a substrate or a capping layer. The parameters that enter the Hamiltonian are determined from first-principles relativistic calculations for Ge ¯ |MoS2 bilayers and MoS2|Ge ¯ |MoS2 trilayers and are used to determine the topological nature of the system. For the lowest energy, buckled germanene structure, the gap depends strongly on how germanene is oriented with respect to the MoS2 layer(s). Topologically nontrivial gaps for bilayers and trilayers can be almost as large as for a freestanding germanene layer.

  1. A magnetic resonance study of MoS2 fullerene-like nanoparticles

    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.

  2. Performance Analysis of Strained Monolayer MoS$_{2}$ MOSFET

    Sengupta, Amretashis; Ghosh, Ram Krishna; Mahapatra, Santanu

    2013-01-01

    We present a computational study on the impact of tensile/compressive uniaxial ($\\varepsilon_{xx}$) and biaxial ($\\varepsilon_{xx}=\\varepsilon_{yy}$) strain on monolayer MoS$_{2}$ NMOS and PMOS FETs. The material properties like band structure, carrier effective mass and the multi-band Hamiltonian of the channel, are evaluated using the Density Functional Theory (DFT). Using these parameters, self-consistent Poisson-Schr\\"{o}dinger solution under the Non-Equilibrium Green's Function (NEGF) fo...

  3. Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures.

    Pierucci, Debora; Henck, Hugo; Avila, Jose; Balan, Adrian; Naylor, Carl H; Patriarche, Gilles; Dappe, Yannick J; Silly, Mathieu G; Sirotti, Fausto; Johnson, A T Charlie; Asensio, Maria C; Ouerghi, Abdelkarim

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential. PMID:27281693

  4. Two-dimensional lateral heterojunction through bandgap engineering of MoS2 via oxygen plasma

    Choudhary, Nitin; Islam, Muhammad R.; Kang, Narae; Tetard, Laurene; Jung, Yeonwoong; Khondaker, Saiful I.

    2016-09-01

    The present study explores the structural, optical (photoluminescence (PL)), and electrical properties of lateral heterojunctions fabricated by selective exposure of mechanically exfoliated few layer two-dimensional (2D) molybdenum disulfide (MoS2) flakes under oxygen (O2)-plasma. Raman spectra of the plasma exposed MoS2 flakes show a significant loss in the structural quality due to lattice distortion and creation of oxygen-containing domains in comparison to the pristine part of the same flake. The PL mapping evidences the complete quenching of peak A and B consistent with a change in the exciton states of MoS2 after the plasma treatment, indicating a significant change in its band gap properties. The electrical transport measurements performed across the pristine and the plasma-exposed MoS2 flake exhibit a gate tunable current rectification behavior with a rectification ratio up to 1.3  ×  103 due to the band-offset at the pristine and plasma-exposed MoS2 interface. Our Raman, PL, and electrical transport data confirm the formation of an excellent lateral heterojunction in 2D MoS2 through its bandgap modulation via oxygen plasma.

  5. MOS dosemeter using bismuth oxide (Bi2O3) and copper phthalocyanine (CuPc) polymer thick film

    A metal-oxide-silicon (MOS)-capacitor having an Ag/Bi2O3/CuPc/Ag and an MOS-transistor with Ag (gate)-Bi2O3 (gate insulator)-CuPc (semiconductor)-CdO (drain and source) structure were fabricated using screen-printing polymer thick film. The effects of gamma irradiation on the characteristics of both MOS-capacitor and MOS-transistor were investigated. The flat band voltage (VFB) of the MOS-capacitor showed a shift towards the negative gate voltage when exposed to gamma rays. The IDS-VGs characteristics displayed enhancement mode transistor for such devices. The threshold voltage was found to be 4.25 V, which displayed a linear and gradual decrease in ΔVT=0.5 V at VDS=0 V and ΔVT=1.0 V at VDS=2 V when exposed to gamma rays of dose step of 60 Gy. (authors)

  6. Synergistic effect of bias and target currents for magnetron sputtered MoS2-Ti composite films

    In terms of modification of the properties of MoS2-Ti composite films, especially tribological properties, significant advances have recently been recorded. However, the commercially production of MoS2-Ti composite films is still limited, because the production of desirable MoS2-Ti composite coating is only possible by using closed field unbalanced magnetron systems and by the selection of convenient deposition parameters. This requirement has focused the researchers' attention on optimization of deposition parameters. This study is concentrating on the effect of the bias voltage and the target currents for MoS2-Ti composite films deposited by pulsed magnetron sputtering (PMS). It is found that the bias and the target currents clearly affect the mechanical, structural and tribological properties of MoS2-Ti films.

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

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

    2016-01-01

    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. PMID:27312409

  8. Reductive hybridization route with exfoliated graphene oxide and MoS2 nanosheets to efficient electrode materials

    Highlights: • Homogeneous hybridization of MoS2 and graphene can occur with exfoliated nanosheet precursors. • Graphene oxide is more effective for hybridization with MoS2 than reduced graphene oxide. • Mesoporous MoS2-graphene nanohybrid shows excellent anode performance in Li-ion battery. - Abstract: Mesoporous MoS2–graphene nanohybrid with excellent electrode activity can be synthesized by the reductive hybridization of exfoliated MoS2 and graphene oxide (G-O) nanosheets under hydrothermal condition. The use of G-O precursor is crucial in synthesizing homogeneously hybridized MoS2–graphene materials with mesoporous stacking structure. The MoS2–graphene nanohybrid prepared with G-O shows promising electrode performance for lithium ion batteries with large discharge capacity of ∼1400 mA h g−1 for the 100th cycle and excellent rate performance, which is much superior to that of the homologue prepared with rG-O precursor and also restacked MoS2 nanosheets. The present results clearly demonstrate the usefulness of G-O precursor in the hydrothermal synthesis of graphene-based hybrid materials

  9. Theoretical study of thermoelectric properties of MoS2

    We systematically studied the thermoelectric properties of MoS2 with doping based on the Boltzmann transport theory and first-principles calculations. We obtained an optimal doping region (around 1019 cm−3) for thermoelectric properties along in-plane and cross-plane directions. MoS2 in the optimal doping region has a vanishingly small anisotropy of thermopower possibly due to the decoupling of in-plane and cross-plane conduction channels, but big anisotropies of electrical conductivity σ and electronic thermal conductivity κe arising from the anisotropic electronic scattering time. The κe is comparable to the lattice counterpart κ1 in the plane, while κ1 dominates over κe across the plane. The figure of merit ZT can reach 0.1 at around 700 K with in-plane direction preferred by doping. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  10. Electron Emission from Ultra-Large Area MOS Electron Emitters

    Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm;

    2009-01-01

    Ultralarge metal-oxide-semiconductor (MOS) devices with an active oxide area of 1 cm2 have been fabricated for use as electron emitters. The MOS structures consist of a Si substrate, a SiO2 tunnel barrier (~5 nm), a Ti wetting layer (3–10 Å), and a Au top layer (5–60 nm). Electron emission from the...... layer is varied from 3 to 10 Å which changes the emission efficiency by more than one order of magnitude. The apparent mean free path of ~5 eV electrons in Au is found to be 52 Å. Deposition of Cs on the Au film increased the electron emission efficiency to 4.3% at 4 V by lowering the work function....... Electron emission under high pressures (up to 2 bars) of Ar was observed. ©2009 American Vacuum Society...

  11. Neutron induced degradation in nitrided pyrogenic field oxide MOS capacitors

    Vaidya, S J; Shaikh, A M; Chandorkar, A N

    2002-01-01

    Neutron induced oxide charge trapping and generation of interface states in MOS capacitors with pyrogenic and nitrided pyrogenic field oxides have been studied. In order to assess the damage due to neutrons alone, it is necessary to account for the damage produced by the accompanying gamma rays from neutron radiation. This is done by measuring the intensity of gamma radiation accompanying neutrons at different neutron fluences at the irradiation position. MOS capacitor structures were subjected to neutron radiation in a swimming pool type of reactor. Other samples from the same batch were then subjected to an equivalent dose of gamma radiation from a Co sup 6 sup 0 source. The difference in the damage observed was used to characterize the damage caused by neutrons. It is observed that neutrons, though uncharged, are capable of causing ionization damage. This damage is found to be significant when the radiation is performed under biased conditions. Nitridation in different ambients is found to improve the radi...

  12. Highly Stretchable MoS2 and Phosphorene Kirigami

    Campbell, David; Hanakata, Paul; Park, Harold

    Several recent works have shown how nanomesh and kirigami patterning can be used to increase the ductility of monolayer graphene and thin film electrodes, suggesting that this approach should be useful for other 2D materials. We have studied the effects of kirigami patterning on the mechanical properties of MoS2 and phosphorene ``monolayers,'' using classical molecular dynamics simulations. We have explored several different kirigami structures, focusing on two simple non-dimensional parameters found to be relevant in our previous study of graphene. These parameters are related to the density of cuts and to the ratio of the overlapping cut length to the nanoribbon length. We found that these membranes, despite not having the single atomic layer planar structure of graphene, show a significantly enhanced ductility that can be understood in terms of the two geometric parameters. For instance, fracture strains of MoS2 kirigami can be enhanced by a factor of six relative to pristine MoS2 nanoribbons. Our findings suggest that the kirigami cuts are the key to changing the morphology of 2D membranes to allow out of plane deflection and to prevent early failure

  13. Development of a new molecular dynamics method for tribochemical reaction and its application to formation dynamics of MoS2 tribofilm

    Recently we have developed a novel molecular dynamics program NEW-RYUDO-CR, which can deal with chemical reactions. The developed method has been applied to the study of tribochemical reaction dynamics of MoS2 tribofilm on iron surface. The initially amorphous MoS2 layer self-organized its structure as result of the tribochemical reactions and formed layered MoS2 tribofilm. The friction coefficient significantly decreased as the MoS2 tribofilm was formed. Besides, sliding was observed between sulfur layers of MoS2 tribofilms which occurred due to repulsive Coulombic interaction forces between sulfur atoms. This indicates that the formation of the layered MoS2 tribofilm is important to achieve better lubrication properties

  14. Mouse Mos protooncogene product is present and functions during oogenesis.

    Paules, R S; Buccione, R; Moschel, R C; Vande Woude, G F; Eppig, J.J.

    1989-01-01

    We have identified the mouse Mos-encoded protein product, p39mos, in maturing mouse oocytes and have shown that it is indistinguishable from the product expressed in Mos-transformed NIH 3T3 cells. p39mos is detected in oocytes arrested in the first meiotic prophase, during germinal-vesicle breakdown, metaphase I, anaphase I, and in ovulated eggs. We show that microinjection of three different Mos antisense (but not sense) oligodeoxyribonucleotides into germinal vesicle-stage oocytes prevents ...

  15. Synthesis of MoS2 and MoO2 for their applications in H2 generation and lithium ion batteries: a review

    Yufei Zhao, Yuxia Zhang, Zhiyu Yang, Yiming Yan and Kening Sun

    2013-01-01

    Scientists increasingly witness the applications of MoS2 and MoO2 in the field of energy conversion and energy storage. On the one hand, MoS2 and MoO2 have been widely utilized as promising catalysts for electrocatalytic or photocatalytic hydrogen evolution in aqueous solution. On the other hand, MoS2 and MoO2 have also been verified as efficient electrode material for lithium ion batteries. In this review, the synthesis, structure and properties of MoS2 and MoO2 are briefly summarized accord...

  16. Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction

    Wang, Haotian; Lu, Zhiyi; Xu, Shicheng; Kong, Desheng; Cha, Judy J.; Zheng, Guangyuan; Hsu, Po-Chun; Yan, Kai; Bradshaw, David; Prinz, Fritz B.; Cui, Yi

    2013-01-01

    The electronic structures of two-dimensional materials can be tuned for a variety of applications by guest species intercalation into the van der Waals gaps. Using Li electrochemical intercalated MoS2 as an example here, we correlate the continuously tuned electronic structure of lithiated MoS2 with the corresponding enhanced hydrogen evolution reaction activity, and thus construct the electronic structure–catalytic activity relationship. This work offers a unique thinking of tuning the elect...

  17. Memristive Phenomena in Polycrystalline Single Layer MoS2

    Sangwan, Vinod; Jariwala, Deep; Kim, In-Soo; Chen, Kan-Sheng; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark; Hersam Laboratory Team

    Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, single layer transition metal dichalcogenides (e.g. MoS2) present a host of attractive features such as high electrical conductivity, tunable band-gap, and strong light-matter interaction. However, available growth methods produce large-area polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions. In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS2 transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS2. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to ~103. Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Complementary electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism.

  18. Scalable Patterning of MoS2 Nanoribbons by Micromolding in Capillaries.

    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. PMID:27462874

  19. Thickness dependence of spin polarization and electronic structure of ultra-thin films of MoS2 and related transition-metal dichalcogenides

    Chang, Tay-Rong; Lin, Hsin; Jeng, Horng-Tay; Bansil, Arun

    2015-03-01

    Thickness dependence of electronic structures of transition-metal dichalcogenides (TMDs) MX2 (M=Mo or W; X=S, Se or Te) is investigated using first-principles calculations. When spin-orbit coupling (SOC) is included in the computations, the electronic structure of monolayer MX2 films exhibits significant band splittings due to the breaking of spatial inversion symmetry. In particular, spin-split states appear around the valence band maximum with nearly 100% out-of-the-plane spin polarization with the spin oriented oppositely at the K and K' symmetry points in the Brillouin zone. For bilayer films, the spin-polarization can be tuned by an out-of-the-plane electric field, and the spin-polarized states are weakly coupled between the layers with small kz dispersion. We confirm a transition from an indirect to a direct band gap as the thickness is reduced to a monolayer in MoX2, in agreement with recent experimental findings. Our study provides insight into the thickness dependence of electronic structure and the degree of spin polarization of the valence bands in ultra-thin TMD films and their viability for spintronics applications.

  20. Suspended MoS2 devices

    Jin, Taiyu; Kang, Jinyoung; Liu, Renlong; Kim, Youngchan; Lee, Changgu

    2013-03-01

    Single or a few layer MoS2 sheets have been reported to have high electric mobility and current on/off ratio comparable to those of silicon due to its semiconductor properties with bandgap of 1.3 ~ 1.9eV. However, its extremely high surface to volume ratio and low thickness prohibits it from reproducing its electronic properties on SiO2 substrates possibly because of charge scattering by surface charges and phonons. In order to investigate these surface effects, we fabricated MoS2 devices suspended from the SiO2 and characterized their electronic transport properties. We exfoliated single or a few layer MoS2 on SiO2 substrates first, and fabricated field effect transistors using e-beam lithography. After that, we suspended MoS2 sheets by etching SiO2 with hydrofluoric acid. We measured mobility and current on/off ratio before and after the etching process. We found that mobility of MoS2 devices increased by factor of 5-10 after etching for all devices. However, on/off ratio did not show significant variation. Our measurements suggest that atomically thin MoS2 devices are significantly affected by substrate surface and environment.

  1. Bandgap engineering of monolayer MoS2 under strain: A DFT study

    Li, Can; Fan, Bowen; Li, Weiyi; Wen, Luowei; Liu, Yan; Wang, Tao; Sheng, Kuang; Yin, You

    2015-06-01

    In this paper, density functional theory calculations are used to investigate the monolayer MoS2 in terms of the strain by analyzing the structure parameters: the bandgap, the density of states (DOS) and the Milliken charges. The calculations indicate that an increasing external stain tends to depress the ripple structure with a shorter S-S interlayer spacing and to enlarge the length of the Mo-S bond. Tensile strain dramatically alteres the bandgap; however, compressive strain almost does not. The change in the bandgap is explained by an analysis of the DOS, the partial density of states (PDOS), the structure parameters and the Mulliken charge distribution. The effects of strain on the Mulliken charge and the length of the Mo-S band cause bandgap differences under tensile and compressive strain.

  2. A generic tight-binding model for monolayer, bilayer and bulk MoS2

    Ferdows Zahid

    2013-05-01

    Full Text Available Molybdenum disulfide (MoS2 is a layered semiconductor which has become very important recently as an emerging electronic device material. Being an intrinsic semiconductor the two-dimensional MoS2 has major advantages as the channel material in field-effect transistors. In this work we determine the electronic structures of MoS2 with the highly accurate screened hybrid functional within the density functional theory (DFT including the spin-orbit coupling. Using the DFT electronic structures as target, we have developed a single generic tight-binding (TB model that accurately produces the electronic structures for three different forms of MoS2 - bulk, bilayer and monolayer. Our TB model is based on the Slater-Koster method with non-orthogonal sp3d5 orbitals, nearest-neighbor interactions and spin-orbit coupling. The TB model is useful for atomistic modeling of quantum transport in MoS2 based electronic devices.

  3. Radiation damage in MOS varactors at low temperatures

    A description of the build-up of charges at low temperatures (T = 80 K) in SiO2 (MOS-structures) induced by ionizing radiation is presented. The damage is characterized by CV measurements and an expanded analysis is developed. A non-homogeneous distribution of frozen holes in the SiO2 appears corresponding to the energy deposition. When the radiation is terminated a field dependent (≥ 2 MV/cm) hole transport to the interfaces is observed. Only after warming (T ≥ 240 K) the structure interface states are created. (orig./HP)

  4. High-k Al2O3 MOS structures with Si interface control layer formed on air-exposed GaAs and InGaAs wafers

    This paper attempts to realize unpinned high-k insulator-semiconductor interfaces on air-exposed GaAs and In0.53Ga0.47As by using the Si interface control layer (Si ICL). Al2O3 was deposited by ex situ atomic layer deposition (ALD) as the high-k insulator. By applying an optimal chemical treatment using HF acid combined with subsequent thermal cleaning below 500 deg. C in UHV, interface bonding configurations similar to those by in situ UHV process were achieved both for GaAs and InGaAs after MBE growth of the Si ICL with no trace of residual native oxide components. As compared with the MIS structures without Si ICL, insertion of Si ICL improved the electrical interface quality, a great deal both for GaAs and InGaAs, reducing frequency dispersion of capacitance, hysteresis effects and interface state density (Dit). A minimum value of Dit of 2 x 1011 eV-1 cm-2 was achieved both for GaAs and InGaAs. However, the range of bias-induced surface potential excursion within the band gap was different, making formation of electron layer by surface inversion possible in InGaAs, but not possible in GaAs. The difference was explained by the disorder induced gap state (DIGS) model.

  5. MOS capacitance-voltage characteristics and dielectric properties of ion implanted thermal oxides on silicon

    Structural damage created in thermal oxides on silicon as a result of exposure to energetic ion beams leads to a change of its dielectric and chemical properties. Adverse effects on the oxide-silicon interface in the form of creation of interface states are also to be expected. Ion implanted oxides in MOS structures are studied with the help of MOS capacitance- and conductance-voltage characteristics, reactions of these oxides in etchant solutions, and ellipsometry. Interesting pattern of recovery of these properties is seen when the ion implanted samples are annealed at increasing temperatures. (author)

  6. Field-effect piezoresistors for vibration detection of nanobeams by using monolithically integrated MOS capacitors

    A novel piezoresistive sensing method is presented herein for the detection of nanobeam resonator based on a monolithically integrated MOS (metal–oxide–semiconductor) capacitor structure. The bottom layer of the nanobeam located beneath the MOS capacitor is utilized as a piezoresistor for the detection of internal stress resulting from nanobeam deformation, and therefore the challenging process of ultra-shallow junction doping is avoided. When a bias voltage applied on the MOS gate exceeds the threshold, the depletion layer width is built up to the maximum, and the piezoresistive cancellation effect beside the neutral plane is eliminated. Based on a conventional microelectromechanical (MEMS) process, an MOS capacitor is fabricated at the terminal of a double-clamped nanobeam with dimensions of 46 µm × 7 µm × 149 nm. The measured R–V curve of this MOS structure presents a 64.7 nm thick piezoresistor which closely agrees with the design. This double-clamped nanobeam is excited into mechanical resonance by mounting it on a piezoelectric ceramic, and the amplitude–frequency response is measured by a network analyzer. The measured resonant frequency is 3.97 MHz and the quality (Q)-factor is 82 in atmosphere environment. Besides, this piezoresistive sensing method is verified by a laser-Doppler vibrometry. (paper)

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

    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

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

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

    2016-07-01

    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.

  9. MoS2 nanotube exfoliation as new synthesis pathway to molybdenum blue

    Graphical abstract: . Display Omitted Highlights: ► New synthesis approach to obtaining molybdenum blue via exfoliated MoS2 nanotubes. ► Material is prone to self assembly and is stable in high vacuum. ► Molecules are as small as 2 nm and their clusters are up to tens of nanometers. ► Change in absorption and oxidation states from the precursor MoS2. -- Abstract: Molybdenum blue-type materials are usually obtained by partially reducing MoVI+ in acidic solutions, while in the presented method it is formed in ethanol solution of exfoliated MoS2 nanotubes, where the MoS2 flakes are the preferential location for their growth. Material was investigated by means of scanning electron and atomic force microscopy, showing the structure and self assembly, while also confirming that it is stable in high vacuum with molecules as small as 1.6 nm and the agglomerates of few tens of nanometres. The ultraviolet–visible and photoelectron spectrometry show the change in absorption properties and oxidation states from MoS2 structure to molybdenum blue, while the presence of sulphur suggests that this is a new type of molybdenum blue material.

  10. Attapulgite-CeO2/MoS2 ternary nanocomposite for photocatalytic oxidative desulfurization

    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.

  11. Radiation effects on custom MOS devices

    This Thesis consists of four chapters: The first is primarily for background information on the effects of radiation on MOS devices and the theory of wafer bonding; the second gives a full discussion of all practical work carried out for manufacture of Field Effect test Capacitors, the third discusses manufacture of vacuum insulator Field Effect Transistors (FET's) and the fourth discusses the testing of these devices. Using a thermally bonded field effect capacitor structure, a vacuum dielectric was studied for use in high radiation environments with a view to manufacturing a CMOS compatible, micro machined transistor. Results are given in the form of high frequency C-V curves before and after a 120 kGy(Si), 12 MRad(Si), dose from a Co60 source showing a 1 Volt shift. The work is then extended to the design and manufacture of a micro machined, under-etch technique, Field Effect Transistor for use in high radiation areas. Results are shown for Threshold, Subthreshold and Transfer characteristics before and after irradiation up to a total dose of 100kGy or 10MRad. The conclusion from this work is that it should be possible to commercially manufacture practical vacuum dielectric field effect transistors which are radiation hard to at least 120 kGy(Si). (author)

  12. Hole transport in MOS oxides

    Hole and electron transport are reported for three different kinds of MOS oxides: wet, dry, and ion-implanted. The electron-hole pairs are generated in the bulk of the oxide by a 3 ns x-ray pulse and the separation of the electron and hole photocurrents is made possible by the large difference in mobility. The electrons are so mobile that they are swept from the oxide (or trapped in a heavily ion-implanted region) during the x-ray pulse. The holes, on the other hand, have much lower mobilities which depend strongly on the preparation of the oxide. In the dry oxide the nominal mobility at room temperature is several orders of magnitude higher than in the wet oxide. The mobility is strongly activated by temperature in the oxides, and at liquid N2 temperature no hole motion could be detected even though the electrons are still swept out. The low temperature charging of oxides can be understood in terms of the bulk trapped holes, but room temperature charging seems to be dominated by trapping close to the Si/SiO2 interface rather than the transport of the holes from the bulk to the interface. Ion implantation provides electron traps which seem to be associated with the lattice damage rather than the ion. The electron traps can be successfully annealed out at 9000C in 20 minutes

  13. Few-layer MoS2: a promising layered semiconductor.

    Ganatra, Rudren; Zhang, Qing

    2014-05-27

    Due to the recent expanding interest in two-dimensional layered materials, molybdenum disulfide (MoS2) has been receiving much research attention. Having an ultrathin layered structure and an appreciable direct band gap of 1.9 eV in the monolayer regime, few-layer MoS2 has good potential applications in nanoelectronics, optoelectronics, and flexible devices. In addition, the capability of controlling spin and valley degrees of freedom makes it a promising material for spintronic and valleytronic devices. In this review, we attempt to provide an overview of the research relevant to the structural and physical properties, fabrication methods, and electronic devices of few-layer MoS2. Recent developments and advances in studying the material are highlighted. PMID:24660756

  14. The cryogenic MOS unit for LUCIFER

    Hofmann, Reiner; Gemperlein, Hans; Grimm, Bernhard; Jutte, Marcus; Mandel, Holger; Polsterer, Kai; Weisz, Harald

    2004-09-01

    The LUCIFER MOS unit has been designed to exchange long-slit and multi-slit masks between two mask storage cabinets and the focal plane area. In combination with auxiliary cryostats, the MOS unit also permits the exchange of cold mask cabinets between LUCIFER and the auxiliary cryostats. Main functional components of the MOS unit are: a focal plane interface accepting the active mask, a mask handling unit transporting the masks between the focal plane mount and their storage locations, a stationary and an exchangeable cabinet holding 10 longslit and 23 multi-slit masks respectively, the translation drives for the exchangeable cabinet and the mask handling unit, and the mask locking unit securing the masks in their cabinets. For mask cabinet exchange, the LUCIFER cryostat as well as the auxiliary cryostats are equipped with 32 cm clear diameter gate valves. A test cryostat has been built to test all MOS unit functions at LN2 temperature. Most of the MOS unit components have been completed. System tests at ambient have started. First results are presented.

  15. MOS OF CANADA: A FOODSERVICE INDUSTRY ANALYSIS OF GREATER VANCOUVER

    Ryomoto, Craig

    2009-01-01

    This paper analyzes the Greater Vancouver commercial food industry and whether the market is ideal for MOS Food Services to fulfil its “MOS of the World” strategy by opening a MOS Burger restaurant in Greater Vancouver. To assess the future viability of MOS Burger opening in Greater Vancouver, this paper identifies and analyzes market size, drivers of demand, various customer segments, key competitors, the strength of key industry forces, and the key sources of advantage for the foodservice i...

  16. MOSFET and MOS capacitor responses to ionizing radiation

    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.

  17. Periodic Modulation of the Doping Level in Striped MoS2 Superstructures.

    Zhou, Xiebo; Shi, Jianping; Qi, Yue; Liu, Mengxi; Ma, Donglin; Zhang, Yu; Ji, Qingqing; Zhang, Zhepeng; Li, Cong; Liu, Zhongfan; Zhang, Yanfeng

    2016-03-22

    Although the recently discovered monolayer transition metal dichalcogenides exhibit novel electronic and optical properties, fundamental physical issues such as the quasiparticle bandgap tunability and the substrate effects remain undefined. Herein, we present the report of a quasi-one-dimensional periodically striped superstructure for monolayer MoS2 on Au(100). The formation of the unique striped superstructure is found to be mainly modulated by the symmetry difference between MoS2 and Au(100) and their lattice mismatch. More intriguingly, we find that the monolayer MoS2 is heavily n-doped on the Au(100) facet with a bandgap of 1.3 eV, and the Fermi level is upshifted by ∼0.10 eV on the ridge (∼0.2 eV below the conduction band) in contrast to the valley regions (∼0.3 eV below the conduction band) of the striped patterns after high-temperature sample annealing process. This tunable doping effect is considered to be caused by the different defect densities over the ridge/valley regions of the superstructure. Additionally, an obvious bandgap reduction is observed in the vicinity of the domain boundary for monolayer MoS2 on Au(100). This work should therefore inspire intensive explorations of adlayer-substrate interactions, the defects, and their effects on band-structure engineering of monolayer MoS2. PMID:26913990

  18. Perspective: Highly ordered MoS2 thin films grown by multi-step chemical vapor deposition process

    S. N. Heo

    2016-03-01

    Full Text Available We established a process for growing highly ordered MoS2 thin films. The process consists of four steps: MoO3 thermal evaporation, first annealing, sulfurization, and second annealing. The main feature of this process is that thermally deposited MoO3 thin films are employed as a precursor for the MoS2 films. The first deposition step enabled us to achieve precise control of the resulting thickness of the MoS2 films with high uniformity. The crystalline structures, surface morphologies, and chemical states at each step were characterized by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Based on these characterizations and a careful optimization of the growth conditions, we successfully produced a highly oriented MoS2 thin film with a thickness of five monolayers over an entire one-centimeter-square sapphire substrate.

  19. Recent Advancement on the Optical Properties of Two-Dimensional Molybdenum Disulfide (MoS2 Thin Films

    Mingxiao Ye

    2015-03-01

    Full Text Available The emergence of two-dimensional (2D materials has led to tremendous interest in the study of graphene and a series of mono- and few-layered transition metal dichalcogenides (TMDCs. Among these TMDCs, the study of molybdenum disulfide (MoS2 has gained increasing attention due to its promising optical, electronic, and optoelectronic properties. Of particular interest is the indirect to direct band-gap transition from bulk and few-layered structures to mono-layered MoS2, respectively. In this review, the study of these properties is summarized. The use of Raman and Photoluminescence (PL spectroscopy of MoS2 has become a reliable technique for differentiating the number of molecular layers in 2D MoS2.

  20. A density functional study of strong local magnetism creation on MoS2 nanoribbon by sulfur vacancy

    Shidpour, Reza; Manteghian, Merhrdad

    2010-08-01

    In this study a low-width MoS2 ribbon has been used for probing the electronic structure and local magnetic moment near vacancies. A theoretical study with the full-potential Density Functional Theory (DFT) approach (Wien2K code) have shown that when the dimension of MoS2 is reduced from 2-D to 1-D the nonmagnetic semi-conductor MoS2 becomes a magnetic conductor. Our study has shown that a vacancy on the S-edge with 50% coverage intensifies the magnetization of the edge of the MoS2 nanoribbon but such a vacancy on S-edge with 100% coverage causes this magnetic property to disappear. It is concluded that in both of them, there are positive or negative strong gradients of local magnetic moment near the vacancy. This may explain why lattice defects are essential for catalysis processes.

  1. Heating-up Synthesis of MoS2 Nanosheets and Their Electrical Bistability Performance

    Li, Xu; Tang, Aiwei; Li, Jiantao; Guan, Li; Dong, Guoyi; Teng, Feng

    2016-03-01

    Molybdenum disulfide (MoS2) nanosheets were synthesized by using a simple heating-up approach, in which 1-dodecanethiol (DDT) was used not only as a sulfur source but also as the surface ligand. The sheet-like morphology was confirmed by the transmission electron microscopy (TEM) and atomic force microscopy (AFM) results, and the X-ray diffraction (XRD) patterns and Raman spectrum were employed to characterize the structure of the as-synthesized MoS2 nanosheets. The as-obtained MoS2 nanosheets blending with a polymer could be used to fabricate an electrically bistable device through a simple spin-coating method, and the device exhibited an obvious electrical bistability in the I-V curve. The charge transport of the device was discussed based on the organic electronic models.

  2. Heating-up Synthesis of MoS2 Nanosheets and Their Electrical Bistability Performance.

    Li, Xu; Tang, Aiwei; Li, Jiantao; Guan, Li; Dong, Guoyi; Teng, Feng

    2016-12-01

    Molybdenum disulfide (MoS2) nanosheets were synthesized by using a simple heating-up approach, in which 1-dodecanethiol (DDT) was used not only as a sulfur source but also as the surface ligand. The sheet-like morphology was confirmed by the transmission electron microscopy (TEM) and atomic force microscopy (AFM) results, and the X-ray diffraction (XRD) patterns and Raman spectrum were employed to characterize the structure of the as-synthesized MoS2 nanosheets. The as-obtained MoS2 nanosheets blending with a polymer could be used to fabricate an electrically bistable device through a simple spin-coating method, and the device exhibited an obvious electrical bistability in the I-V curve. The charge transport of the device was discussed based on the organic electronic models. PMID:27033847

  3. The Interface between Gd and Monolayer MoS2: A First-Principles Study

    Zhang, Xuejing

    2014-12-08

    We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

  4. Stretching and breaking of monolayer MoS2—an atomistic simulation

    Lorenz, Tommy; Joswig, Jan-Ole; Seifert, Gotthard

    2014-06-01

    We report on the simulation of the nanoindentation process of monolayer MoS2 using molecular-dynamics simulations and a density-functional based tight-binding method. A circular sheet of MoS2 with clamped boundaries was indented by a slowly moved tip, which deformed and finally pierced the layer. We found the Young’s modulus of monolayer MoS2 to be 262 GPa, which is in good agreement with experimental observations. Furthermore, the energetic and structural behavior during the indentation process was analyzed. Elasticity theory supplies the necessary equations to explain the experiment. Thereby, the nature of the linear term in the force-deflection relation is discussed.

  5. Atomistic simulation of the electronic states of adatoms in monolayer MoS2

    Chang, Jiwon; Larentis, Stefano; Tutuc, Emanuel; Register, Leonard F.; Banerjee, Sanjay K.

    2013-01-01

    Using an ab initio density functional theory (DFT) based electronic structure method, we study the effects of adatoms on the electronic properties of monolayer transition metal dichalcogenide (TMD) Molybdenum-disulfide (MoS2). We consider the 1st (Li, Na, K) and 7th (F, Cl, Br) column atoms and metals (Sc, Ti, Ta, Mo, Pd, Pt, Ag, Au). Three high symmetry sites for the adatom on the surface of monolayer MoS2 are examined as starting points to search for the most energetically stable configurat...

  6. Analysis of electron beam damage of exfoliated MoS2 sheets and quantitative HAADF-STEM imaging

    In this work we examined MoS2 sheets by aberration-corrected scanning transmission electron microscopy (STEM) at three different energies: 80, 120 and 200 kV. Structural damage of the MoS2 sheets has been controlled at 80 kV according a theoretical calculation based on the inelastic scattering of the electrons involved in the interaction electron–matter. The threshold energy for the MoS2 material has been found and experimentally verified in the microscope. At energies higher than the energy threshold we show surface and edge defects produced by the electron beam irradiation. Quantitative analysis at atomic level in the images obtained at 80 kV has been performed using the experimental images and via STEM simulations using SICSTEM software to determine the exact number of MoS2 layers. - Highlights: • MoS2 sheets were exfoliated by using hydrogen gas flow to separate the MoS2 layers. • The optimum energy to avoid structural damage was calculated. • Cs-corrected STEM imaging was used to obtain atomic resolution images. • Three energies were used in STEM imaging: 80, 120 and 200 kV. • A quantitative method for determining the number of layers has been applied

  7. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    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. PMID:26797320

  8. Photo-Promoted Platinum Nanoparticles Decorated MoS2@Graphene Woven Fabric Catalyst for Efficient Hydrogen Generation.

    Li, Xiao; Zhang, Li; Zang, Xiaobei; Li, Xinming; Zhu, Hongwei

    2016-05-01

    Hydrogen production from water splitting has been considered as an effective and sustainable method to solve future energy related crisis. Molybdenum sulfides (e.g., MoS2) show promising catalytic ability in hydrogen evolution reaction (HER). Combining MoS2 with conductive carbon-based materials has aroused tremendous research interest recently. In this work, a highly efficient multiple-catalyst is developed for HER by decorating Pt nanoparticles (Pt NPs) on MoS2@graphene protected nickel woven fabrics (NiWF) substrate, which comprises the following components: (i) Graphene protected NiWF acts as the underlying substrate, supporting the whole structure; (ii) MoS2 nanoplates serve as a central and essential photosensitive component, forming a heterostructure with graphene simultaneously; and (iii) on the basis of the intrinsic photoluminescence effect of MoS2, together with the photoelectric response at the MoS2/graphene interface, Pt NPs are successfully deposited on the whole structure under illumination. Particularly and foremost, this work emphasizes on discussion and verification of the underlying mechanism for photopromoted electroless Pt NPs deposition. Due to this assembly approach, the usage amount of Pt is controlled at ∼5 wt % (∼0.59 at. %) with respect to the whole catalyst. MoS2@Substrate with Pt NPs deposited under 643 nm illumination, with the synergistic effect of MoS2 active sites and Pt NPs, demonstrates the most superior electrocatalytic performance, with negligible overpotential and low Tafel slope of 39.4 mV/dec. PMID:27070762

  9. Direct synthesis of large-scale hierarchical MoS2 films nanostructured with orthogonally oriented vertically and horizontally aligned layers.

    Zhang, Xiaoyan; Zhang, Saifeng; Chen, Bohua; Wang, Hao; Wu, Kan; Chen, Yang; Fan, Jintai; Qi, Shen; Cui, Xiaoli; Zhang, Long; Wang, Jun

    2016-01-01

    Hierarchical MoS2 thin films nanostructured with orthogonally oriented vertically and horizontally aligned layers were designed and excellent passive Q-switching behavior in a fiber laser was demonstrated. A special solvothermal system containing a small amount of water was applied to synthesize such hierarchical MoS2 nanofilms, in which the reaction rate is carefully controlled by the diffusion rate of the sulfur precursor. Wafer-scale MoS2 thin films with hierarchical structures are formed on various substrates. Moreover, the hierarchical MoS2 thin films consisting of both vertical and horizontal layers can be tuned to possess only horizontally aligned layers by controlling the solvothermal time. To show the potential application proof-of-concept, the nonlinear optical performance of the hierarchical MoS2 was investigated. Superior passive Q-switching behavior in a fiber laser with a minimum pulse width of 2.2 μs was observed. PMID:26620263

  10. An offset-trimmable array of magnetic-field-sensitive MOS transistors (MAGFETs)

    Ning, Feng; Bruun, Erik

    1997-01-01

    paper we present a new combination of an offset compensating circuit and a MAGFET cascade circuit with increased sensitivity. The offset compensation utilizes a digitally trimmable current mirror implemented by a multiple-gate MOS transistor structure. A prototype circuit has been fabricated in a 2.4 mu...

  11. Low Noise Bias Current/Voltage References Based on Floating-Gate MOS Transistors

    Igor, Mucha

    1997-01-01

    The exploitation of floating-gate MOS transistors as reference current and voltage sources is investigated. Test structures of common source and common drain floating-gate devices have been implemented in a commercially available 0.8 micron double-poly CMOS process. The measurements performed...

  12. Formation of MOS-transistors with isolation of active elements by oxiden porous silicon

    Novosyadlyi S. P.

    2009-06-01

    Full Text Available The superthin functional layers of MOS-transistors require qualitative isolation of active elements. The new method of formation of epitaksial structures for technology «silicon - on-isolator» is offered on the basis of porous silicon. It will allow to form three kinds of transistors — bipolar, SМОS, DМОS.

  13. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J.; Atkin, Paul; Berean, Kyle J.; Clark, Rhiannon M.; Cole, Ivan S.; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-01

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4]2- anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of

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

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

    2015-11-01

    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 × 1010 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.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

  15. Interface properties of CVD grown graphene transferred onto MoS2(0001)

    Coy Diaz, Horacio; Addou, Rafik; Batzill, Matthias

    2013-12-01

    Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting devices. We show that solution transfer results in water trapping at the interface which may be removed by annealing to ~300 °C in a vacuum. After removal of the water, by high temperature annealing, ultraflat graphene is obtained on MoS2 with only a very weak moiré pattern observable in scanning tunneling microscopy images due to lattice mismatch and random alignment of graphene with respect to the MoS2 substrate. Photoemission spectroscopy indicates interface dipole formation, p-type doping of graphene by ~0.09 eV downward shift of the Fermi-level below the Dirac point, and a negative space charge region in bulk MoS2. Interestingly, valence band spectra of the graphene covered MoS2 surface indicate a band gap narrowing of the MoS2 surface by ~0.1 eV. This band gap reduction at the surface is further evidence that interlayer van der Waals interactions critically influence the band structure of 2D-layered dichalcogenides and suggest that interfacing with dissimilar van der Waals materials allows tuning of their electronic properties.Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting

  16. Quantitative evaluation of slow traps near Ge MOS interfaces by using time response of MOS capacitance

    Tanaka, Katsuhisa; Zhang, Rui; Takenaka, Mitsuru; Takagi, Shinichi

    2015-04-01

    Time-dependent changes in current and threshold voltage due to slow traps near Ge metal-oxide-semiconductor (MOS) interfaces is one of the most serious problems in Ge metal-oxide-semiconductor field-effect transistors (MOSFETs). In this study, we propose a new evaluation method of slow traps near MOS interfaces utilizing the time response of capacitance in MOS capacitors at a constant gate voltage, allowing us to evaluate the density and time constant of slow traps. We apply this method to Au/Al2O3/GeOx/Ge MOS capacitors and evaluate the density and average time constant of slow traps. The slow trap density of n-Ge MOS capacitors is found to be much larger than that of p-Ge MOS capacitors, indicating that a higher density of slow traps exists near the conduction band edge. We also examine the effects of post deposition annealing in a variety of ambient gases, including several hydrogen-based species, on the properties of slow traps.

  17. Resistance thermometers with MOS field effect transistors

    The temperature-dependent resistance change of n- as well as p-type MOS transistors has been investigated. Implantation of He ions increases the temperature sensitivity of the n-channel devices. The influence of magnetic fields up to 80 kG has been studied. (author)

  18. Reconfigurable Threshold Logic Element with SET and MOS Transistors

    WEI Rong-Shan; CHEN Jin-Feng; CHEN Shou-Chang; HE Ming-Hua

    2012-01-01

    A novel reconfigurable threshold logic element (TLE) using single-electron transistors (SETs) and metal-oxide semiconductor (MOS) transistors is proposed.The proposed TLE is highly reconfigurable,which can perform all two-variable logic functions directly or indirectly,including OR,NOR,AND,NAND,XOR and XNOR.The reconfiguration of the TLE is realized by simply configuring the input bits without changing the device parameters.The design methodology can also be applied in the design of a multi-variable TLE.The reconfigurable TLE demonstrates good performance at room temperature with a compact structure and ultralow power dissipation.The reconfigurable TLE can be useful in high-density high-performance reconfigurable systems and artificial neural networks.%A novel reconfigurable threshold logic element (TLE) using single-electron transistors (SETs) and metal-oxide-semiconductor (MOS) transistors is proposed. The proposed TLE is highly reconfigurable, which can perform all two-variable logic functions directly or indirectly, including OR, NOR, AND, NAND, XOR and XNOR. The reconfiguration of the TLE is realized by simply configuring the input bits without changing the device parameters. The design methodology can also be applied in the design of a multi-variable TLE. The reconfigurable TLE demonstrates good performance at room temperature with a compact structure and ultralow power dissipation. The reconfigurable TLE can be useful in high-density high-performance reconfigurable systems and artificial neural networks.

  19. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates.

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J; Atkin, Paul; Berean, Kyle J; Clark, Rhiannon M; Cole, Ivan S; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-16

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4](2-) anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications. PMID:27263805

  20. Monolayer MoS2-Graphene Hybrid Aerogels with Controllable Porosity for Lithium-Ion Batteries with High Reversible Capacity.

    Jiang, Lianfu; Lin, Binghui; Li, Xiaoming; Song, Xiufeng; Xia, Hui; Li, Liang; Zeng, Haibo

    2016-02-01

    Monolayer MoS2 nanosheets (NSs) are promising anode materials for lithium-ion batteries because all redox reactions take place at the surface without lithium-ion diffusion limit. However, the expanded band gap of monolayer MoS2 NSs (∼1.8 eV) compared to their bulk counterparts (∼1.2 eV) and restacking tendency due to the van der Waals forces result in poor electron transfer and loss of the structure advantage. Here, a facile approach is developed to fabricate the MoS2-graphene aerogels comprising controlled three-dimensional (3D) porous architectures constructed by interconnected monolayer MoS2-graphene hybrid NSs. The robust 3D architectures combining with the monolayer feature of the hybrid NSs not only prevent the MoS2 and graphene NSs from restacking, but also enable fast electrode kinetics due to the surface reaction mechanism and highly conductive graphene matrix. As a consequence, the 3D porous monolayer MoS2-graphene composite aerogels exhibit a large reversible capacity up to 1200 mAh g(-1) as well as outstanding cycling stability and rate performance, making them promising as advanced anode materials for lithium-ion batteries. PMID:26761564

  1. The origin of the enhanced performance of nitrogen-doped MoS2 in lithium ion batteries

    Liu, Qiuhong; Weijun, Xia; Wu, Zhenjun; Huo, Jia; Liu, Dongdong; Wang, Qiang; Wang, Shuangyin

    2016-04-01

    MoS2 with a similar layered structure to graphene has been widely applied in various areas including lithium ion batteries. However, low conductivity, capacity fading and poor rate performance are still the main challenges for MoS2 anode materials. In this work, for the first time, we prepared nitrogen-doped MoS2 (N-MoS2) nanosheets through a simple two-step method involving the preparation of MoS2 with defects by the hydrothermal method, followed by sintering in a NH3 atmosphere. Our electrochemical characterizations and density functional theory calculations demonstrated that nitrogen doping could enhance the electron conductivity and showed higher specific capacity than pristine MoS2 as anode materials of lithium ion batteries, which can be attributed to the faster transportation of electrons and ions because of nitrogen doping. This work helps us understand the origin of the enhanced performance of N-doped MoS2 in lithium ion batteries.

  2. Interface properties of CVD grown graphene transferred onto MoS2(0001).

    Coy Diaz, Horacio; Addou, Rafik; Batzill, Matthias

    2014-01-21

    Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting devices. We show that solution transfer results in water trapping at the interface which may be removed by annealing to ~300 °C in a vacuum. After removal of the water, by high temperature annealing, ultraflat graphene is obtained on MoS2 with only a very weak moiré pattern observable in scanning tunneling microscopy images due to lattice mismatch and random alignment of graphene with respect to the MoS2 substrate. Photoemission spectroscopy indicates interface dipole formation, p-type doping of graphene by ~0.09 eV downward shift of the Fermi-level below the Dirac point, and a negative space charge region in bulk MoS2. Interestingly, valence band spectra of the graphene covered MoS2 surface indicate a band gap narrowing of the MoS2 surface by ~0.1 eV. This band gap reduction at the surface is further evidence that interlayer van der Waals interactions critically influence the band structure of 2D-layered dichalcogenides and suggest that interfacing with dissimilar van der Waals materials allows tuning of their electronic properties. PMID:24297086

  3. Mechanistic Insight into the Stability of HfO2 -Coated MoS2 Nanosheet Anodes for Sodium Ion Batteries.

    Ahmed, Bilal; Anjum, Dalaver H; Hedhili, Mohamed N; Alshareef, Husam N

    2015-09-01

    It is demonstrated for the first time that surface passivation of 2D nanosheets of MoS2 by an ultrathin and uniform layer of HfO2 can significantly improve the cyclic performance of sodium ion batteries. After 50 charge/discharge cycles, bare MoS2 and HfO2 coated MoS2 electrodes deliver the specific capacity of 435 and 636 mAh g(-1) , respectively, at current density of 100 mA g(-1) . These results imply that batteries using HfO2 coated MoS2 anodes retain 91% of the initial capacity; in contrast, bare MoS2 anodes retain only 63%. Also, HfO2 coated MoS2 anodes show one of the highest reported capacity values for MoS2 . Cyclic voltammetry and X-ray photoelectron spectroscopy results suggest that HfO2 does not take part in electrochemical reaction. The mechanism of capacity retention with HfO2 coating is explained by ex situ transmission electron microscope imaging and electrical impedance spectroscopy. It is illustrated that HfO2 acts as a passivation layer at the anode/electrolyte interface and prevents structural degradation during charge/discharge process. Moreover, the amorphous nature of HfO2 allows facile diffusion of Na ions. These results clearly show the potential of HfO2 coated MoS2 anodes, which performance is significantly higher than previous reports where bulk MoS2 or composites of MoS2 with carbonaceous materials are used. PMID:26061915

  4. Prebiotic (Mannanoligosaccharide- MOS in fish nutrition: effects on nile-tilapia Oreochromis niloticus performance

    Flávio Endrigo Cechim

    2012-12-01

    observed no influence of this prebiotic on fish growth. The use of prebiotics as mannanoligosaccharides to improve growth and health status in fish still needs further research for better explanation of contradictory results. The complex carbohydrate structure in the cell wall of yeast, different strains and fermentation conditions, processing methods can all alter their function, as well as MOS concentration, administration period and population status (age, sex, gonadal maturation. For instance, in this experiment, dietary MOS supplementation did not show prebiotic properties such as positive effects on juvenile Nile tilapia growth.

  5. Beneficial effect of Re doping on the electrochemical HER activity of MoS2 fullerenes.

    Chhetri, Manjeet; Gupta, Uttam; Yadgarov, Lena; Rosentsveig, Rita; Tenne, Reshef; Rao, C N R

    2015-10-01

    Electrochemical generation of hydrogen by non-precious metal electrocatalysts at a lower overpotential is a focus area of research directed towards sustainable energy. The exorbitant costs associated with Pt-based catalysts is the major bottleneck associated with commercial-scale hydrogen generation. Strategies for the synthesis of cost-effective and stable catalysts are thus key for a prospective 'hydrogen economy'. In this report, we highlight a novel and general strategy to enhance the electrochemical activity of molybdenum disulfide (MoS2) in a fullerene structure (IF-). In particular, pristine (undoped) and rhenium-doped nanoparticles of MoS2 with fullerene-like structures (IF-MoS2) were studied, and their performance as catalysts for the hydrogen evolution reaction (HER) was compared to that of 2H-MoS2 particles (platelets). The current density of the IF-MoS2 was higher by one order of magnitude than that of few-layer (FL-) MoS2, due to the enhanced density of the edge sites. Furthermore, Re doping of as low as 100 ppm in IF-MoS2 decreased the onset potential by 60-80 mV and increased the activity by 60 times compared with that of the FL-MoS2. The combined synergistic effect of Re doping and the IF structure not only changes the intrinsic nature of the MoS2 but also increases its reactivity. This strategy highlights the potential use of the IF structure and Re doping in electrocatalytic hydrogen evolution using MoS2-based catalysts. PMID:26308554

  6. Additional electric field in real trench MOS barrier Schottky diode

    Mamedov, R. K.; Aslanova, A. R.

    2016-04-01

    In real trench MOS barrier Schottky diode (TMBS diode) additional electric field (AEF) the whole is formed in the near contact region of the semiconductor and its propagation space is limited with the barrier metal and the metallic electrodes of MOS structures. Effective potential barrier height TMBS diode is formed via resulting electric field of superposition AEF and electric field of space charge region (SCR) semiconductor. The dependence of the resulting electric field intensity of the distance towards the inside the semiconductor is nonlinear and characterized by a peak at a certain distance from the interface. The thickness of the SCR in TMBS diode becomes equal to the trench depth. Force and energy parameters of the AEF, and thus resulting electric field in the SCR region, become dependent on the geometric design parameters TMBS diode. The forward I-V characteristic TMBS diode is described by the thermionic emission theory as in conventional flat Scottky diode, and in the reverse bias, current is virtually absent at initial voltage, appears abruptly at a certain critical voltage.

  7. Towards a uniform and large-scale deposition of MoS2 nanosheets via sulfurization of ultra-thin Mo-based solid films

    Vangelista, Silvia; Cinquanta, Eugenio; Martella, Christian; Alia, Mario; Longo, Massimo; Lamperti, Alessio; Mantovan, Roberto; Basso Basset, Francesco; Pezzoli, Fabio; Molle, Alessandro

    2016-04-01

    Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor-solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm2-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (<750 °C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000 °C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.

  8. Synthesis of MoS2/g-C3N4 nanocomposites with enhanced visible-light photocatalytic activity for the removal of nitric oxide (NO).

    Wen, M Q; Xiong, T; Zang, Z G; Wei, W; Tang, X S; Dong, F

    2016-05-16

    Molybdenum disulfide and graphitic carbon nitride (MoS2-g-C3N4) nanocomposites with visible-light induced photocatalytic activity were successfully synthesized by a facile ultrasonic dispersion method. The crystalline structure and morphology of the MoS2-g-C3N4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM). The optical property of the as-prepared nanocomposites was studied by ultraviolet visible diffusion reflection (UV-vis) and photoluminescence(PL) spectrum. It could be observed from the TEM image that the MoS2 nanosheets and g-C3N4 nanoparticles were well combined together. Moreover, the photocatalytic activity of MoS2-g-C3N4 composites was evaluated by the removal of nitric oxide under visible light irradiation (>400nm). The experimental results demonstrated that the nanocomposites with the MoS2 content of 1.5 wt% exhibited optimal photocatalytic activity and the corresponding removal rate of NO achieved 51.67%, higher than that of pure g-C3N4 nanoparticles. A possible photocatalytic mechanism for the MoS2-g-C3N4 nanocomposites with enhanced photocatalytic activity could be ascribed to the hetero-structure of MoS2 and g-C3N4. PMID:27409846

  9. Three-dimensional spirals of atomic layered MoS2.

    Zhang, Liming; Liu, Kaihui; Wong, Andrew Barnabas; Kim, Jonghwan; Hong, Xiaoping; Liu, Chong; Cao, Ting; Louie, Steven G; Wang, Feng; Yang, Peidong

    2014-11-12

    Atomically thin two-dimensional (2D) layered materials, including graphene, boron nitride, and transition metal dichalcogenides (TMDs), can exhibit novel phenomena distinct from their bulk counterparts and hold great promise for novel electronic and optoelectronic applications. Controlled growth of such 2D materials with different thickness, composition, and symmetry are of central importance to realize their potential. In particular, the ability to control the symmetry of TMD layers is highly desirable because breaking the inversion symmetry can lead to intriguing valley physics, nonlinear optical properties, and piezoelectric responses. Here we report the first chemical vapor deposition (CVD) growth of spirals of layered MoS2 with atomically thin helical periodicity, which exhibits a chiral structure and breaks the three-dimensional (3D) inversion symmetry explicitly. The spirals composed of tens of connected MoS2 layers with decreasing areas: each basal plane has a triangular shape and shrinks gradually to the summit when spiraling up. All the layers in the spiral assume an AA lattice stacking, which is in contrast to the centrosymmetric AB stacking in natural MoS2 crystals. We show that the noncentrosymmetric MoS2 spiral leads to a strong bulk second-order optical nonlinearity. In addition, we found that the growth of spirals involves a dislocation mechanism, which can be generally applicable to other 2D TMD materials. PMID:25343743

  10. MoS2 coated hollow carbon spheres for anodes of lithium ion batteries

    Zhang, Yufei; Wang, Ye; Yang, Jun; Shi, Wenhui; Yang, Huiying; Huang, Wei; Dong, Xiaochen

    2016-06-01

    With the assistance of resorcinol-formaldehyde, MoS2 coated hollow carbon spheres (C@MoS2) were synthesized through a facile hydrothermal route followed by heat and alkali treatments. The measurements indicate that the hollow carbon spheres with an average diameter of 300 nm and shell thickness of 20 nm. And the hollow core are uniformly covered by ultrathin MoS2 nanosheets with a length increased to 400 nm. The unique hollow structure and the synergistic effect between carbon layer and MoS2 nanosheets significantly enhance the rate capability and electrochemical stability of C@MoS2 spheres as anode material of lithium-ion battery. The synthesized C@MoS2 delivered a capacity of 750 mAh g-1 at a current density of 100 mA g-1. More importantly, the C@MoS2 maintained a reversible capacity of 533 mAh g-1 even at a high current density of 1000 mA g-1. The study indicated that MoS2 coated hollow carbon spheres can be promising anode material for next generation high-performance lithium-ion batteries.

  11. Ultrafast charge transfer in MoS2/WSe2 p–n Heterojunction

    Peng, Bo; Yu, Guannan; Liu, Xinfeng; Liu, Bo; Liang, Xiao; Bi, Lei; Deng, Longjiang; Chien Sum, Tze; Loh, Kian Ping

    2016-06-01

    Atomically thin and sharp van der Waals heterojunction can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) onto n-type molybdenum disulfide (MoS2). Theory predicts that stacked MoS2 and WSe2 monolayer forms type II p–n junction, creating a built-in electric field across the interface which facilitates electron–hole separation and transfer. Gaining insights into the dynamics of charge transfer across van der Waals heterostructure is central to understanding light-photocurrent conversion at these ultrathin interfaces. Herein, we investigate the exciton dissociation and charge transfer in a MoS2/WSe2 van der Waals hetero-structure. Our results show that ultrafast electron transfer from WSe2 to MoS2 take place within 470 fs upon optical excitation with 99% charge transfer efficiency, leading to drastic photoluminescence quenching and decreased lifetime. Our findings suggest that van der Waals heterostructure may be useful as active components in ultrafast optoelectronic devices.

  12. Stacking stability of MoS2 bilayer: An ab initio study

    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. (condensed matter: structural, mechanical, and thermal properties)

  13. Pristine Basal- and Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties.

    Tan, Shu Min; Ambrosi, Adriano; Sofer, Zdenĕk; Huber, Štěpán; Sedmidubský, David; Pumera, Martin

    2015-05-01

    The layered structure of molybdenum disulfide (MoS2 ) is structurally similar to that of graphite, with individual sheets strongly covalently bonded within but held together through weak van der Waals interactions. This results in two distinct surfaces of MoS2 : basal and edge planes. The edge plane was theoretically predicted to be more electroactive than the basal plane, but evidence from direct experimental comparison is elusive. Herein, the first study comparing the two surfaces of MoS2 by using macroscopic crystals is presented. A careful investigation of the electrochemical properties of macroscopic MoS2 pristine crystals with precise control over the exposure of one plane surface, that is, basal plane or edge plane, was performed. These crystals were characterized thoroughly by AFM, Raman spectroscopy, X-ray photoelectron spectroscopy, voltammetry, digital simulation, and DFT calculations. In the Raman spectra, the basal and edge planes show anisotropy in the preferred excitation of E2g and A1g phonon modes, respectively. The edge plane exhibits a much larger heterogeneous electron transfer rate constant k(0) of 4.96×10(-5) and 1.1×10(-3)  cm s(-1) for [Fe(CN)6 ](3-/4-) and [Ru(NH3 )6 ](3+/2+) redox probes, respectively, compared to the basal plane, which yielded k(0) tending towards zero for [Fe(CN)6 ](3-/4-) and about 9.3×10(-4)  cm s(-1) for [Ru(NH3 )6 ](3+/2+) . The industrially important hydrogen evolution reaction follows the trend observed for [Fe(CN)6 ](3-/4-) in that the basal plane is basically inactive. The experimental comparison of the edge and basal planes of MoS2 crystals is supported by DFT calculations. PMID:25821017

  14. Resonant Raman spectroscopy study of swift heavy ion irradiated MoS2

    Guo, Hang; Sun, Youmei; Zhai, Pengfei; Zeng, Jian; Zhang, Shengxia; Hu, Peipei; Yao, Huijun; Duan, Jinglai; Hou, Mingdong; Liu, Jie

    2016-08-01

    Molybdenum disulphide (MoS2) crystal samples were irradiated by swift heavy ions (209Bi and 56Fe). Hillock-like latent tracks were observed on the surface of irradiated MoS2 by atomic force microscopy. The modifications of properties of irradiated MoS2 were investigated by resonant Raman spectroscopy and ultraviolet-visible spectroscopy (UV-Vis). A new peak (E1u2, ∼385.7 cm-1) occurs near the in-plane E2g1 peak (∼383.7 cm-1) after irradiation. The two peaks shift towards lower frequency and broaden due to structural defects and stress with increasing fluence. When irradiated with high fluence, two other new peaks appear at ∼ 190 and ∼ 230 cm-1. The peak at ∼230 cm-1 is disorder-induced LA(M) mode. The presence of this mode indicates defects induced by irradiation. The feature at ∼460 cm-1 is composed of 2LA(M) (∼458 cm-1) and A2u (∼466 cm-1) mode. With increasing fluence, the integrated intensity ratio between 2LA(M) and A2u increases. The relative enhancement of 2LA(M) mode is in agreement with the appearance of LA(M) mode, which both demonstrate structural disorder in irradiated MoS2. The ∼423-cm-1 peak shifts toward lower frequency due to the decrease in exciton energy of MoS2, and this was demonstrated by the results of UV-Vis spectra. The decrease in exciton energy could be due to introduction of defect levels into band gap.

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

    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.

  16. Origin of the n -type and p -type conductivity of MoS 2 monolayers on a SiO 2 substrate

    Dolui, Kapildeb

    2013-04-02

    Ab initio density functional theory calculations are performed to study the electronic properties of a MoS2 monolayer deposited over a SiO 2 substrate in the presence of interface impurities and defects. When MoS2 is placed on a defect-free substrate, the oxide plays an insignificant role since the conduction band top and the valence band minimum of MoS2 are located approximately in the middle of the SiO2 band gap. However, if Na impurities and O dangling bonds are introduced at the SiO2 surface, these lead to localized states, which modulate the conductivity of the MoS2 monolayer from n- to p-type. Our results show that the conductive properties of MoS2 deposited on SiO 2 are mainly determined by the detailed structure of the MoS 2/SiO2 interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS2-based devices. © 2013 American Physical Society.

  17. High pressure effect on MoS2 and MoSe2 single crystals grown by CVT method

    Madhavi Dave; Rajiv Vaidya; S G Patel; A R Jani

    2004-04-01

    Single crystals of MoS2 and MoSe2 were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS2 and MoSe2 do not undergo any structural transitions under pressure.

  18. Porous tremella-like MoS2/polyaniline hybrid composite with enhanced performance for lithium-ion battery anodes

    Graphical abstract: Display Omitted -- Abstract: Molybdenum disulfide (MoS2) is one of the most attractive anode materials for lithium-ion batteries (LIBs) due to its high theoretical specific capacity, but its poor cyclic stability need further optimization for its practical application. In this study, porous MoS2/polyaniline (MoS2/PANI) composite with a tremella-like hierarchical structure was synthesized via a facile polymerization and hydrothermal method. The homogeneously distributed PANI can not only improve the conductivity of MoS2, but also rebuild a hierarchical porous structure thus enhance rapid Li+ transport during the Li+ insertion/extraction reaction. As an anode material of LIBs, this composite exhibits a high initial reversible capacity of 910 mAh/g with an initial Coulombic efficiency of ∼80% at 0.1 A/g. Even at a high current density of 4 A/g, the reversible capacity of the MoS2/PANI composite still remains at 369 mAh/g. Moreover, this composite retains an impressive high capacity of 915 mAh/g after 200 cycles at a high current density of 1 A/g, demonstrating its potential for applications in LIBs

  19. In-Situ hydrothermal synthesis of a MoS2 nanosheet electrode for electrochemical energy storage applications

    Patel, Rajkumar; Inamdar, Akbar I.; Kim, Hyung Bae; Im, Hyunsik; Kim, Hyungsang

    2016-06-01

    A molybdenum disulfide (MoS2) nanosheet film was grown directly on a stainless-steel substrate by using an in-situ hydrothermal growth technique at 200 °C. The formation of an MoS2 hexagonal structure with a nanosheet-like morphology was confirmed by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) while a layered MoS2 nanosheet structure was observed under an energy-filtering transmission electron microscope (EF-TEM). The electrochemical supercapacitor properties of the MoS2 nanosheet electrode were measured in 1-M aqueous Na2SO4 electrolyte by using cyclic voltammetry (CV) and charge/discharge technique, and the electrode's specific capacitances were 91.29 F/g and 146.15 F/g, respectively. The concurrent double-layer capacitance and pseudo-capacitance behaviors of the electrode manifested themselves in the rectangular shape and redox peaks of the CV curve. The mesoporous MoS2 nanosheets were electrochemically stable for up to 1000 charge/discharge cycles.

  20. Magnetoresistance in Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions.

    Zhang, Han; Ye, Meng; Wang, Yangyang; Quhe, Ruge; Pan, Yuanyuan; Guo, Ying; Song, Zhigang; Yang, Jinbo; Guo, Wanlin; Lu, Jing

    2016-06-28

    Semiconducting single-layer (SL) and few-layer MoS2 have a flat surface, free of dangling bonds. Using density functional theory coupled with non-equilibrium Green's function method, we investigate the spin-polarized transport properties of Co/2D MoS2/Co and Ni/2D MoS2/Ni junctions with MoS2 layer numbers of N = 1, 3, and 5. Well-defined interfaces are formed between MoS2 and metal electrodes. The junctions with a SL MoS2 spacer are almost metallic owing to the strong coupling between MoS2 and the ferromagnets, while those are tunneling with a few layer MoS2 spacer. Both large magnetoresistance and tunneling magnetoresistance are found when fcc or hcp Co is used as an electrode. Therefore, flat single- and few-layer MoS2 can serve as an effective nonmagnetic spacer in a magnetoresistance or tunneling magnetoresistance device with a well-defined interface. PMID:27257639

  1. Synthesis of MoS2 and MoO2 for their applications in H2 generation and lithium ion batteries: a review

    Yufei Zhao, Yuxia Zhang, Zhiyu Yang, Yiming Yan and Kening Sun

    2013-01-01

    Full Text Available Scientists increasingly witness the applications of MoS2 and MoO2 in the field of energy conversion and energy storage. On the one hand, MoS2 and MoO2 have been widely utilized as promising catalysts for electrocatalytic or photocatalytic hydrogen evolution in aqueous solution. On the other hand, MoS2 and MoO2 have also been verified as efficient electrode material for lithium ion batteries. In this review, the synthesis, structure and properties of MoS2 and MoO2 are briefly summarized according to their applications for H2 generation and lithium ion batteries. Firstly, we overview the recent advancements in the morphology control of MoS2 and MoO2 and their applications as electrocatalysts for hydrogen evolution reactions. Secondly, we focus on the photo-induced water splitting for H2 generation, in which MoS2 acts as an important co-catalyst when combined with other semiconductor catalysts. The newly reported research results of the significant functions of MoS2 nanocomposites in photo-induced water splitting are presented. Thirdly, we introduce the advantages of MoS2 and MoO2 for their enhanced cyclic performance and high capacity as electrode materials of lithium ion batteries. Recent key achievements in MoS2- and MoO2-based lithium ion batteries are highlighted. Finally, we discuss the future scope and the important challenges emerging from these fascinating materials.

  2. Synthesis of MoS2 and MoO2 for their applications in H2 generation and lithium ion batteries: a review

    Scientists increasingly witness the applications of MoS2 and MoO2 in the field of energy conversion and energy storage. On the one hand, MoS2 and MoO2 have been widely utilized as promising catalysts for electrocatalytic or photocatalytic hydrogen evolution in aqueous solution. On the other hand, MoS2 and MoO2 have also been verified as efficient electrode material for lithium ion batteries. In this review, the synthesis, structure and properties of MoS2 and MoO2 are briefly summarized according to their applications for H2 generation and lithium ion batteries. Firstly, we overview the recent advancements in the morphology control of MoS2 and MoO2 and their applications as electrocatalysts for hydrogen evolution reactions. Secondly, we focus on the photo-induced water splitting for H2 generation, in which MoS2 acts as an important co-catalyst when combined with other semiconductor catalysts. The newly reported research results of the significant functions of MoS2 nanocomposites in photo-induced water splitting are presented. Thirdly, we introduce the advantages of MoS2 and MoO2 for their enhanced cyclic performance and high capacity as electrode materials of lithium ion batteries. Recent key achievements in MoS2- and MoO2-based lithium ion batteries are highlighted. Finally, we discuss the future scope and the important challenges emerging from these fascinating materials. (review)

  3. Luminescence from Er and Tb implanted into MOS tunnel diodes

    We have demonstrated the 1.5 μm electroluminescence from implanted Er ions inside the SiO2 insulator of a silicon metal-oxide-semiconductor (MOS) structure under forward bias. The Er ions are excited by the direct impact from electrons tunneling through the oxide at electric fields larger than 6 MV/cm. We measured an excitation cross-section of 6x10-15 cm2 and a total lifetime of 1.5 ms. In order to change the emission wavelength into the visible regime, we changed to Tb ions. Photoluminescence data show a broad defect luminescence band and several sharp lines due to the Tb transitions. We find a noticeable influence of Tb-Tb-cross-relaxation which favours the green lines over the blue luminescence lines

  4. X-ray irradiation of ion-implanted MOS capacitors

    He+ ion-implanted metal-oxide-semiconductor (MOS) capacitors with two different oxide thickness have been irradiated by X-rays and the depth distribution of the implant damage in the Si-SiO2 structures have been examined. The efficiency of X-ray annealing of electronic traps caused by implantation and changes in charge populations are reported. The experiment shows that (in the case when defects introduced by implantation are located at the Si-SiO2 interface) only defects corresponding to the deep levels in the Si can be affected by X-ray irradiation. When defects introduced by ion implantation are located deeper within the Si substrate complete annealing of these defects is observed

  5. Bonding between graphene and MoS2 monolayers without and with Li intercalation

    We performed density functional theory (DFT) calculations for a bi-layered heterostructure combining a graphene layer with a MoS2 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 MoS2 monolayer. For the combined graphene/MoS2 bi-layer, we observe interesting electronic structure and density of states (DOS) characteristics near the Fermi energy, showing both the gap like features of the MoS2 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 MoS2. 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 MoS2 monolayers). Moreover, we calculate the dielectric function of the Li intercalated graphene/MoS2 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/MoS2 heterostructure

  6. Thermally activated trap charges responsible for hysteresis in multilayer MoS2 field-effect transistors

    Park, Youngseo; Baac, Hyoung Won; Heo, Junseok; Yoo, Geonwook

    2016-02-01

    Hysteresis, which is induced by both extrinsic and intrinsic causes, is often observed in molybdenum disulphide (MoS2) field-effect transistors (FETs), and several extrinsic hysteresis effects have been reported in unpassivated bottom-gate MoS2 device structures. In this study, interface-trap-induced hysteresis and other electrical properties are examined. We experimentally investigate thermally activated trap charges near a silicon-dioxide (SiO2)-MoS2 interface that gives rise to hysteresis in a multilayer MoS2 FET in a temperature region of 10-300 K. The threshold voltage (VTH) and field-effect mobility (μFE) decrease with the increase in temperature, regardless of the gate-bias sweep direction. The hysteresis that coincides with the trend of subthreshold swing increases sharply above T = 150 K as the released charges from interface traps become dominant over the fixed charges. Based on a temperature-dependent hysteresis analysis, we discussed the activation energy of interface traps and maximum interface trap density of the fabricated multilayer MoS2 FET.

  7. Spin-dependent transport properties of Fe3O4/MoS2/Fe3O4 junctions

    Wu, Han-Chun; Coileáin, Cormac Ó.; Abid, Mourad; Mauit, Ozhet; Syrlybekov, Askar; Khalid, Abbas; Xu, Hongjun; Gatensby, Riley; Jing Wang, Jing; Liu, Huajun; Yang, Li; Duesberg, Georg S.; Zhang, Hong-Zhou; Abid, Mohamed; Shvets, Igor V.

    2015-11-01

    Magnetite is a half-metal with a high Curie temperature of 858 K, making it a promising candidate for magnetic tunnel junctions (MTJs). Yet, initial efforts to exploit its half metallic nature in Fe3O4/MgO/Fe3O4 MTJ structures have been far from promising. Finding suitable barrier layer materials, which keep the half metallic nature of Fe3O4 at the interface between Fe3O4 layers and barrier layer, is one of main challenges in this field. Two-dimensional (2D) materials may be good candidates for this purpose. Molybdenum disulfide (MoS2) is a transition metal dichalcogenide (TMD) semiconductor with distinctive electronic, optical, and catalytic properties. Here, we show based on the first principle calculations that Fe3O4 keeps a nearly fully spin polarized electron band at the interface between MoS2 and Fe3O4. We also present the first attempt to fabricate the Fe3O4/MoS2/Fe3O4 MTJs. A clear tunneling magnetoresistance (TMR) signal was observed below 200 K. Thus, our experimental and theoretical studies indicate that MoS2 can be a good barrier material for Fe3O4 based MTJs. Our calculations also indicate that junctions incorporating monolayer or bilayer MoS2 are metallic.

  8. MOS: The Critical Elements of Doing Effective Classroom Demonstrations

    Shmaefsky, Brian R.

    2005-01-01

    MOS, or Minds-On-Science, is the foundation of conducting educationally valuable science demonstrations. It is a teaching strategy equally effective as hands-on-learning. Plus, it proves much more effective at reinforcing abstract science concepts than traditional lectures, readings, and audiovisual presentations. Adding MOS to a demonstration…

  9. Heterostructures based on graphene and MoS2 layers decorated by C60 fullerenes

    Chernozatonskii, Leonid A.; Kvashnin, Alexander G.; Sorokin, Pavel B.

    2016-09-01

    Here we present a comprehensive investigation of various novel composite structures based on graphene (G) and molybdenum disulphide (MoS2) monolayers decorated by C60 fullerenes, which can be successfully applied in photovoltaics as a solar cell unit. Theoretical studies of the atomic structure, stability and electronic properties of the proposed G/C60, MoS2/C60 and G/MoS2/C60/G nanostructures were carried out. We show that making the G/MoS2/C60/G heterostructure from the 2D films considered here will lead to the appearance of particular properties suitable for application in photovoltaics due to the broad energetic region of high electronic density of states.

  10. Covalent functionalization of MoS2

    Stanislav Presolski

    2016-04-01

    Full Text Available MoS2 nanosheets have been used extensively in catalytic, electronic, optoelectronic and electrochemical research due to their diverse properties that are often determined by the method of fabrication. Fine tuning of the colloidal behaviour, specific interactions and further reactivity of the materials is typically achieved by subsequent surface modifications. Arguably the most permanent of these involve covalent attachment of molecules to either the molybdenum or the sulphur atoms in the lattice. Here we review of the nascent field of transition metal dichalcogenide (TMD covalent functionalization and explore the prospective avenues for hybrid organic-inorganic nanomaterials.

  11. MoS2-reduced graphene oxide composites via microwave assisted synthesis for sodium ion battery anode with improved capacity and cycling performance

    MoS2-reduced graphene oxide (RGO) composites were synthesized via a facile microwave assisted reduction of graphene oxide in MoS2 precursor solution and subsequent annealing in N2/H2 atmosphere at 800 °C for 2 h. Their morphology, structure and electrochemical performance were characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, N2 adsorption-desorption isotherm, cyclic voltammetry and electrochemical impedance spectroscopy. The MoS2-RGO composites with different RGO loadings were applied as anode materials of sodium ion batteries (SIBs) and they exhibit a maximum reversible specific capacity of about 305 mAh g−1 at a current density of 100 mA g−1 after 50 cycles and excellent rate performance. The results demonstrate that MoS2-RGO could be a potential electrode material for rechargeable SIBs

  12. Van der Waals epitaxial growth of MoS2 on SiO2/Si by chemical vapor deposition

    Cheng, Yingchun

    2013-01-01

    Recently, single layer MoS2 with a direct band gap of 1.9 eV has been proposed as a candidate for two dimensional nanoelectronic devices. However, the synthetic approach to obtain high-quality MoS2 atomic thin layers is still problematic. Spectroscopic and microscopic results reveal that both single layers and tetrahedral clusters of MoS2 are deposited directly on the SiO2/Si substrate by chemical vapor deposition. The tetrahedral clusters are mixtures of 2H- and 3R-MoS2. By ex situ optical analysis, both the single layers and tetrahedral clusters can be attributed to van der Waals epitaxial growth. Due to the similar layered structures we expect the same growth mechanism for other transition-metal disulfides by chemical vapor deposition. © 2013 The Royal Society of Chemistry.

  13. UHV-STM manipulation of single flat gold nano-islands for constructing interconnection nanopads on MoS2

    We demonstrate manipulation of metallic islands containing nearly a million atoms with a precision of one lattice spacing on a MoS2 surface, one at a time. Optimizing the growth conditions yields triangular shape metallic nano-islands 40 nm in lateral size and 12 nm in height on the MoS2 surface. The manipulation of these nano-islands is done one at a time using the scanning tunneling microscope, and a fully planar 4 pad nanostructure is demonstrated, where one apex of each triangular nano-island is pointing towards a central working MoS2 area of 12 nm x 24 nm in which atomic cleanliness is preserved. The feedback loop conditions to achieve this manipulation are discussed. This fully planar 4 pads nano-structure is ready to be interconnected by a multi-tip system

  14. Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

    YUE YuanZheng; HAO Yue; FENG Qian; ZHANG JinCheng; MA XiaoHua; NI JinYu

    2009-01-01

    We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al2O3 as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process, a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AIGaN/GaN HEMT of similar design, better interface property, lower leakage current, and smaller capacitance-voltage (C-V) hysteresis were obtained, and the superiority of this MOS-HEMT device structure with ALD Al2O3 gate dielectric was exhibited.

  15. Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

    2009-01-01

    We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al2O3 as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process,a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design,better interface property,lower leakage current,and smaller capacitance-voltage (C-V) hysteresis were obtained,and the superiority of this MOS-HEMT device structure with ALD Al2O3 gate dielectric was exhibited.

  16. Ab initio study of bilateral doping within the MoS2-NbS2 system

    Ivanovskaya, Viktoriya V.; Zobelli, Alberto; Gloter, Alexandre; Brun, Nathalie; Serin, Virginie; Colliex, Christian

    2008-01-01

    We present a systematic study on the stability and the structural and electronic properties of mixed molybdenum-niobium disulphides. Using density functional theory we investigate bilateral doping with up to 25 % of MoS2 (NbS2) by Nb (Mo) atoms, focusing on the precise arrangement of dopants within the host lattices. We find that over the whole range of considered concentrations, Nb doping of MoS2 occurs through a substitutional mechanism. For Mo in NbS2 both interstitial and substitutional d...

  17. Radiation hardness of graphene and MoS2 field effect devices against swift heavy ion irradiation

    We have investigated the deterioration of field effect transistors based on two-dimensional materials due to irradiation with swift heavy ions. Devices were prepared with exfoliated single layers of MoS2 and graphene, respectively. They were characterized before and after irradiation with 1.14 GeV U28+ ions using three different fluences. By electrical characterization, atomic force microscopy, and Raman spectroscopy, we show that the irradiation leads to significant changes of structural and electrical properties. At the highest fluence of 4 × 1011 ions/cm2, the MoS2 transistor is destroyed, while the graphene based device remains operational, albeit with an inferior performance.

  18. A route to synthesis molybdenum disulfide-reduced graphene oxide (MoS2-RGO) composites using supercritical methanol and their enhanced electrochemical performance for Li-ion batteries

    Choi, Mugyeom; Koppala, Siva Kumar; Yoon, Dohyeon; Hwang, Jieun; Kim, Seung Min; Kim, Jaehoon

    2016-03-01

    A simple and effective approach for the tight anchoring of molybdenum disulfide (MoS2) to the surface of supercritical-alcohol-reduced graphene oxide (SRGO) is developed. The MoS2-SRGO composites are synthesized by the one-pot deposition of MoO2 on SRGO and simultaneous reduction of GO to SRGO in supercritical methanol followed by sulfurization. The obtained MoS2-SRGO composites contain a crystalline MoS2 phase comprising 11-14 layers of MoS2. In addition, the composites have mesoporous structures with high porosities, ranging between 55 and 57%. In comparison with bare MoS2 and SRGO, the MoS2-SRGO composites have enhanced electrochemical performances due to their mesoporous structures and the synergetic effect between MoS2 and SRGO sheets. When tested as the anode in a secondary lithium battery, it shows high reversible capacity of 896 mAh g-1 at 50 mA g-1 after 50 cycles, a high rate capacity of 320 mAh g-1 at a high charge-discharge rate of 2.5 A g-1, and long-term cycling of 724 mAh g-1 at 50 mA g-1 after 200 cycles. This unique synthetic approach effectively and tightly anchors MoS2 nanoparticles to the SRGO surface, resulting in improved structural integrity, electron transfer efficiency between the SRGO sheets and MoS2, and Li-ion diffusion kinetics.

  19. Analytical Charge Voltage Model in MOS Inversion Layer Based on Space Charge Capacitance

    2000-01-01

    The concept of Space Charge Capacitance (SCC) is proposed and used to make a novel analytical charge model of quantized inversion layer in MOS structures. Based on SCC,continuous expressions of surface potential and inversion layer carrier density are derived.Quantum mechanical effects on both inversion layer carrier density and surface potential are extensively included. The accuracy of the model is verified by the numerical solution to Schrodinger and Poisson equation and the model is demonstrated,too.

  20. Atomic and electronic properties of quasi-one-dimensional MoS2 nanowires

    Fernandez Seivane, Lucas; Barron, Hector; Botti, Silvana; Lopes Marques, Miguel Alexandre; Rubio Secades, Ángel; López-Lozano, Xóchitl

    2013-01-01

    The structural, electronic, and magnetic properties of quasi-one-dimensional MoS2nanowires (NWs), passivated by extra sulfur, have been determined using ab initio density functional theory. The nanostructures were simulated using several different models based on experimental electron microscopy images and theoretical literature. It is found that independently of the geometrical details and the coverage of extra sulfur at the Mo edge, quasi-one-dimensional metallic states are predominant in a...

  1. Porous Hybrid Composites of Few-Layer MoS2 Nanosheets Embedded in a Carbon Matrix with an Excellent Supercapacitor Electrode Performance.

    Ji, Hongmei; Liu, Chao; Wang, Ting; Chen, Jing; Mao, Zhengning; Zhao, Jin; Hou, Wenhua; Yang, Gang

    2015-12-22

    Porous hierarchical architectures of few-layer MoS2 nanosheets dispersed in carbon matrix are prepared by a microwave-hydrothermal method followed by annealing treatment via using glucose as C source and structure-directing agent and (NH4 )2 MoS4 as both Mo and S sources. It is found that the morphology and size of the secondary building units (SBUs), the size and layer number of MoS2 nanosheets as well as the distribution of MoS2 nanosheets in carbon matrix, can be effectively controlled by simply adjusting the molar ratio of (NH4 )2 MoS4 to glucose, leading to the materials with a low charge-transfer resistance, many electrochemical active sites and a robust structure for an outstanding energy storage performance including a high specific capacitance (589 F g(-1) at 0.5 A g(-1) ), a good rate capability (364 F g(-1) at 20 A g(-1) ), and an excellent cycling stability (retention 104% after 2000 cycles) for application in supercapacitors. The exceptional rate capability endows the electrode with a high energy density of 72.7 Wh kg(-1) and a high power density of 12.0 kW kg(-1) simultaneously. This work presents a facile and scalable approach for synthesizing novel heterostructures of MoS2 -based electrode materials with an enhanced rate capability and cyclability for potential application in supercapacitor. PMID:26551452

  2. A compact plasmonic MOS-based 2x2 electro-optic switch

    Ye, Chenran; Soref, Richard A; Sorger, Volker J

    2015-01-01

    We report on a three-waveguide electro-optic switch for compact photonic integrated circuits and data routing applications. The device features a plasmonic metal-oxide-semiconductor (MOS) mode for enhanced light-matter-interactions. The switching mechanism originates from a capacitor-like design where the refractive index of the active medium, Indium-Tin-Oxide, is altered via shifting the plasma frequency due to carrier accumulation inside the waveguide-based MOS structure. This light manipulation mechanism controls the transmission direction of transverse magnetic polarized light into either a CROSS or BAR waveguide port. The extinction ratio of 18 dB (7) dB for the CROSS (BAR) state, respectively, is achieved via a gating voltage bias. The ultrafast broadband fJ/bit device allows for seamless integration with Siliconon- Insulator platforms to for low-cost manufacturing.

  3. A compact plasmonic MOS-based 2×2 electro-optic switch

    Ye, Chenran; Liu, Ke; Soref, Richard A.; Sorger, Volker J.

    2015-01-01

    We report on a three-waveguide electro-optic switch for compact photonic integrated circuits and data routing applications. The device features a plasmonic metal-oxide-semiconductor (MOS) mode for enhanced light-matter-interactions. The switching mechanism originates from a capacitor-like design where the refractive index of the active medium, indium-tin-oxide, is altered via shifting the plasma frequency due to carrier accumulation inside the waveguide-based MOS structure. This light manipulation mechanism controls the transmission direction of transverse magnetic polarized light into either a CROSS or BAR waveguide port. The extinction ratio of 18 (7) dB for the CROSS (BAR) state, respectively, is achieved via a gating voltage bias. The ultrafast broadband fJ/bit device allows for seamless integration with silicon-on-insulator platforms for low-cost manufacturing.

  4. Photoluminescence of MoS2 Prepared by Effective Grinding-Assisted Sonication Exfoliation

    Jing-Yuan Wu

    2014-01-01

    Full Text Available Exfoliation of bulk molybdenum disulfide (MoS2 using sonication in appropriate solvent is a promising route to large-scale preparation of few-layered or monolayered crystals. Grinding-assisted sonication exfoliation was used for preparing monolayered MoS2 nanosheets from natural mineral molybdenite. By controlling the sonication time, larger crystallites could be further exfoliated to smaller as well as thinner nanosheets without damaging their structures. The concentration of 1.6 mg mL−1 of final solution could be achieved. Several microscopic techniques like scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were employed to evaluate the exfoliation results. Strong photoluminescence with the peak centered at 440 nm was also observed in the resulting dispersion which included several small lateral-sized (~3 nm nanostructures.

  5. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

    Chiu, Ming-Hui

    2015-07-16

    The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

  6. Remote Plasma Oxidation and Atomic Layer Etching of MoS2.

    Zhu, Hui; Qin, Xiaoye; Cheng, Lanxia; Azcatl, Angelica; Kim, Jiyoung; Wallace, Robert M

    2016-07-27

    Exfoliated molybdenum disulfide (MoS2) is shown to chemically oxidize in a layered manner upon exposure to a remote O2 plasma. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) are employed to characterize the surface chemistry, structure, and topography of the oxidation process and indicate that the oxidation mainly occurs on the topmost layer without altering the chemical composition of underlying layer. The formation of S-O bonds upon short, remote plasma exposure pins the surface Fermi level to the conduction band edge, while the MoOx formation at high temperature modulates the Fermi level toward the valence band through band alignment. A uniform coverage of monolayer amorphous MoO3 is obtained after 5 min or longer remote O2 plasma exposure at 200 °C, and the MoO3 can be completely removed by annealing at 500 °C, leaving a clean ordered MoS2 lattice structure as verified by XPS, LEED, AFM, and scanning tunneling microscopy. This work shows that a remote O2 plasma can be useful for both surface functionalization and a controlled thinning method for MoS2 device fabrication processes. PMID:27386734

  7. Nanopatterning and Electrical Tuning of MoS2 Layers with a Subnanometer Helium Ion Beam.

    Fox, Daniel S; Zhou, Yangbo; Maguire, Pierce; O'Neill, Arlene; Ó'Coileáin, Cormac; Gatensby, Riley; Glushenkov, Alexey M; Tao, Tao; Duesberg, Georg S; Shvets, Igor V; Abid, Mohamed; Abid, Mourad; Wu, Han-Chun; Chen, Ying; Coleman, Jonathan N; Donegan, John F; Zhang, Hongzhou

    2015-08-12

    We report subnanometer modification enabled by an ultrafine helium ion beam. By adjusting ion dose and the beam profile, structural defects were controllably introduced in a few-layer molybdenum disulfide (MoS2) sample and its stoichiometry was modified by preferential sputtering of sulfur at a few-nanometer scale. Localized tuning of the resistivity of MoS2 was demonstrated and semiconducting, metallic-like, or insulating material was obtained by irradiation with different doses of He(+). Amorphous MoSx with metallic behavior has been demonstrated for the first time. Fabrication of MoS2 nanostructures with 7 nm dimensions and pristine crystal structure was also achieved. The damage at the edges of these nanostructures was typically confined to within 1 nm. Nanoribbons with widths as small as 1 nm were reproducibly fabricated. This nanoscale modification technique is a generalized approach that can be applied to various two-dimensional (2D) materials to produce a new range of 2D metamaterials. PMID:26154305

  8. Photoelectron spectroscopic imaging and device applications of large-area patternable single-layer MoS2 synthesized by chemical vapor deposition.

    Park, Woanseo; Baik, Jaeyoon; Kim, Tae-Young; Cho, Kyungjune; Hong, Woong-Ki; Shin, Hyun-Joon; Lee, Takhee

    2014-05-27

    Molybdenum disulfide (MoS2) films, which are only a single atomic layer thick, have been synthesized by chemical vapor deposition (CVD) and have gained significant attention due to their band-gap semiconducting properties. However, in order for them to be useful for the fabrication of practical devices, patterning processes that can be used to form specific MoS2 structures must be integrated with the existing synthetic approaches. Here, we report a method for the synthesis of centimeter-scale, high-quality single-layer MoS2 that can be directly patterned during CVD, so that postpatterning processes can be avoided and device fabrication can be streamlined. Utilizing X-ray photoelectron spectroscopic imaging, we characterize the chemical states of these CVD-synthesized single-layer MoS2 films and demonstrate that the triangular-shaped MoS2 are single-crystalline single-domain monolayers. We also demonstrate the use of these high-quality and directly patterned MoS2 films in electronic device applications by fabricating and characterizing field effect transistors. PMID:24730654

  9. Synthesis of MoS2/g-C3N4 nanosheets as 2D heterojunction photocatalysts with enhanced visible light activity

    Li, Juan; Liu, Enzhou; Ma, Yongning; Hu, Xiaoyun; Wan, Jun; Sun, Lin; Fan, Jun

    2016-02-01

    g-C3N4 nanosheets coupled with MoS2 nanosheets as 2D heteroconjuction were prepared via a facile impregnation and calcination method. The structure characterization clearly indicated that MoS2 nanosheets were successfully horizontal loaded on g-C3N4 nanosheets. The investigation indicated that the formation of 2D heterojunction between the g-C3N4 nanosheets and MoS2 nanosheets promoted the charge transfer and enhanced separation efficiency of photoinduced electron-hole pairs. Furthermore, the measurement of photocatalytic activity for the degradation of rhodamine B and methyl orange revealed that the as-prepared 2D MoS2/g-C3N4 heterojunction exhibited the significantly enhanced photocatalytic activity and considerable stability under visible light irradiation. The 2D MoS2/g-C3N4 heterojunction prepared with 3 wt% of MoS2 exhibited the optimal photodegradable efficiency. The present work shows that the formation of 2D heterojunction should be a good strategy to design efficient photocatalysts.

  10. Towards a uniform and large-scale deposition of MoS2 nanosheets via sulfurization of ultra-thin Mo-based solid films.

    Vangelista, Silvia; Cinquanta, Eugenio; Martella, Christian; Alia, Mario; Longo, Massimo; Lamperti, Alessio; Mantovan, Roberto; Basset, Francesco Basso; Pezzoli, Fabio; Molle, Alessandro

    2016-04-29

    Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor-solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm(2)-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing. PMID:26984949

  11. Growth and characteristics of self-assembled MoS2/Mo-S-C nanoperiod multilayers for enhanced tribological performance

    Xu, Jiao; He, Tengfei; Chai, Liqiang; Qiao, Li; Wang, Peng; Liu, Weimin

    2016-05-01

    Highly ordered MoS2/Mo-S-C nanoperiod multilayers are synthesized by a novel self-assembling mechanism in simultaneous sputtering of MoS2 and graphite targets. The sequential formation of MoS2-riched domain layers and Mo-S-C compositional mixed capping layers reveals no correspondence to the sample stage rotation but is caused by the low energy ion bombardment enhanced interdiffusion. The HRTEM observation shows that the phase segregation normal to the film surface is initiated from substrate-film interlayer with clear contrasts in the first few bi-layers, and then diffuses mutually in a quasiperiodic pattern between two altered sub-layers. Compared with sputtered MoS2 film, the bulk film of multilayers exhibit largely improved toughness under a normal load, and the preferential orientation of sputtered MoS2 in (002) basal planes is significantly enhanced, both of which render the film excellent loads-bearing capacity and lubricant properties. The nano-scratching tests performed on a nanoindentation system suggest that the nano-tribological performance of multilayers is directly determined by the altered structure and properties of neighboring sub-layers until stable tribofilms are formed. Meanwhile, the pin-on-disk tribotests in ambient air, low vacuum and high vacuum provide comparably low friction coefficient yet distinct wear lives in different atmospheres due to the partially restricted humid-sensitivity of sputtered MoS2 phase.

  12. Large-Scale Synthesis of a Uniform Film of Bilayer MoS2 on Graphene for 2D Heterostructure Phototransistors.

    Chen, Chuanmeng; Feng, Zhihong; Feng, Yiyu; Yue, Yuchen; Qin, Chengqun; Zhang, Daihua; Feng, Wei

    2016-07-27

    The large-scale synthesis of atomically thin, layered MoS2/graphene heterostructures is of great interest in optoelectronic devices because of their unique properties. Herein, we present a scalable synthesis method to prepare centimeter-scale, continuous, and uniform films of bilayer MoS2 using low-pressure chemical vapor deposition. This growth process was utilized to assemble a heterostructure by growing large-scale uniform films of bilayer MoS2 on graphene (G-MoS2/graphene). Atomic force microscopy, Raman spectra, and transmission electron microscopy characterization demonstrated that the large-scale bilayer MoS2 film on graphene exhibited good thickness uniformity and a polycrystalline nature. A centimeter-scale phototransistor prepared using the G-MoS2/graphene heterostructure exhibited a high responsivity of 32 mA/W with good cycling stability; this value is 1 order of magnitude higher than that of transferred MoS2 on graphene (2.5 mA/W). This feature results from efficient charge transfer at the interface enabled by intimate contact between the grown bilayer MoS2 (G-MoS2) and graphene. The ability to integrate multilayer materials into atomically thin heterostructures paves the way for fabricating multifunctional devices by controlling their layer structure. PMID:27381011

  13. Identification of protein tyrosine phosphatase 1B and casein as substrates for 124-v-Mos

    Stabel Silvia; Proikas-Cezanne Tassula; Riethmacher Dieter

    2002-01-01

    Abstract Background The mos proto-oncogene encodes a cytoplasmic serine/threonine-specific protein kinase with crucial function during meiotic cell division in vertebrates. Based on oncogenic amino acid substitutions the viral derivative, 124-v-Mos, displays constitutive protein kinase activity and functions independent of unknown upstream effectors of mos protein kinase. We have utilized this property of 124-v-Mos and screened for novel mos substrates in immunocomplex kinase assays in vitro....

  14. Breakdown properties of irradiated MOS capacitors

    The authors have studied the effects of ionizing and non-ionizing radiation on the breakdown properties of different types of MOS capacitors, with thick (200 nm) and thin (down to 8 nm) oxides. In general, no large variations of the average breakdown field, time-to-breakdown at constant voltage, or charge-to-breakdown at constant voltage, or charge-to-breakdown values have been observed after high dose irradiation (20 Mrad(Si) 9 MeV electrons on thin and thick oxides, 17(Si) Mrad Co60 gamma and 1014 neutrons/cm2 only on thick oxides). However, some modifications of the cumulative failure distributions have been observed in few of the oxides tested

  15. Enhanced photovoltaic performances of graphene/Si solar cells by insertion of a MoS2 thin film

    Tsuboi, Yuka; Wang, Feijiu; Kozawa, Daichi; Funahashi, Kazuma; Mouri, Shinichiro; Miyauchi, Yuhei; Takenobu, Taishi; Matsuda, Kazunari

    2015-08-01

    Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell.Transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their characteristic band structure. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with the increasing number of graphene layers and the decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03046c

  16. Enhanced saturation current sensitivities to charge trapping and illumination in MOS tunnel diode by inserting metal in gate dielectric

    Chen, Jun-Yao; Kao, Wei-Chih; Hwu, Jenn-Gwo

    2016-06-01

    The enlarged two-state phenomenon in the current-voltage (I-V) characteristic of metal-oxide-semiconductor (MOS) tunnel diode (TD) after negative/positive constant voltage stress (negative/positive CVS) was investigated. It was found that the reverse saturation tunnel current of MOS TD is proportional to the Schottky barrier height of holes, which is determined by the intensity of fringing field (FF) at device edge. With the aid of high permittivity dielectric and screening effect by embedded metal in the MOS structure, the FF was enhanced, which was confirmed by TCAD simulations. Because of the FF enhancement, after proper electrical treatments of voltage stressing, the intensified quantity of electron trapping/de-trapping was found at device edge, which augmented the modulation of Schottky barrier height of holes. As a result, much variation of reverse saturation tunnel current was exhibited, and hence, the enlarged two-state behavior was achieved. The endurance characteristics were also demonstrated to show that the trapped electrons are more stable in the MOS structure with embedded aluminum. Moreover, benefited from FF enhancement, the enlarged photosensitivity of the I-V characteristics of the sample with high permittivity dielectric and embedded aluminum was obtained. The mechanisms of the enlarged split of current behaviors after suitable CVS and illumination treatments are also discussed for these observations.

  17. Polystyrene-Templated Aerosol Synthesis of MoS2 -Amorphous Carbon Composite with Open Macropores as Battery Electrode.

    Choi, Seung Ho; Kang, Yun Chan

    2015-07-01

    MoS2 -amorphous carbon (MoS2 -AC) composite microspheres with macroporous structure were fabricated by one-pot spray pyrolysis. Single- or few-layered MoS2 were uniformly dispersed and oriented in random directions in the amorphous carbon microsphere with macropores sizes between 50 and 90 nm. The macroporous microspheres having a high contact area with liquid electrolyte exhibited overall superior Li- and Na-ion storage properties compared with those of the dense microspheres. After 250 charge/discharge cycles at a current density of 1.5 A g(-1) , the discharge capacities of the MoS2 -AC microspheres with dense and macroporous structures for Li-ion storage were 694 and 896 mAh g(-1) , respectively. In the case of Na-ion storage, discharge capacities of 336 and 425 mAh g(-1) were achieved for the dense and macroporous microspheres, respectively, after 100 cycles at 0.3 A g(-1) . PMID:26098539

  18. Monolayer MoS2 heterojunction solar cells

    Tsai, Menglin

    2014-08-26

    We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS 2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS 2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices. © 2014 American Chemical Society.

  19. Electrical tuning of valley magnetic moment through symmetry control in bilayer MoS2

    Wu, Sanfeng [University of Washington, Seattle; Ross, Jason [University of Washington, Seattle; Liu, G. B. [University of Hong Kong, The; Aivazian, Grant [University of Washington, Seattle; Jones, Aaron [University of Washington, Seattle; Fei, Zaiyao [University of Washington, Dept Phys, Seattle, WA; Zhu, Wenguang [University of Tennessee, Knoxville (UTK); Xiao, Di [ORNL; Yao, Wang [University of Hong Kong, The; Cobden, David [University of Washington, Dept Phys, Seattle, WA; Xu, Xiaodong [University of Washington

    2013-01-01

    Crystal symmetry governs the nature of electronic Bloch states. For example, in the presence of time-reversal symmetry, the orbital magnetic moment and Berry curvature of the Bloch states must vanish unless inversion symmetry is broken1. In certain two-dimensional electron systems such as bilayer graphene, the intrinsic inversion symmetry can be broken simply by applying a perpendicular electric field2,3. In principle, this offers the possibility of switching on/off and continuously tuning the magnetic moment and Berry curvature near the Dirac valleys by reversible electrical control4,5. Here we investigate this possibility using polarization-resolved photoluminescence of bilayer MoS2, which has the same symmetry as bilayer graphene but has a bandgap in the visible spectrum6,7 allowing direct optical probing5,8 12. We find that in bilayer MoS2 the circularly polarized photoluminescence can be continuously tuned from 15% to 15% as a function of gate voltage, whereas in structurally non-centrosymmetric monolayer MoS2 the photoluminescence polarization is gate independent. The observations are well explained as resulting from the continuous variation of orbital magnetic moments between positive and negative values through symmetry control.

  20. Ab-initio study of dynamical properties of two dimensional MoS2 under strain

    Himadri Soni

    2015-10-01

    Full Text Available In this paper, we report the biaxial strain induced modifications in the phonon dispersion curves of monolayer MoS2 using first principles calculations in the framework of density functional perturbation theory. We have used the ultrasoft psedopotentials and the exchange correlation energies have been approximated by the local density approximation. There are significant changes in the phonon dispersion curves under strain. A systematic decrease in the optical phonon modes is observed with strain percentage. The longitudinal and transverse acoustic phonon modes of monolayer MoS2 show linear dependency for both without and with strain cases. However, the out of plane acoustic mode (ZA which behaves quadratically with wave vector k- turns linear under strain. We have also linked ripple in single layer (SL MoS2 by ZA mode with strain using shell elasticity theory. The strain induced softening of linear behaviour of ZA mode with strain indicates the absence of rippling under strain. At a very high strain there is a possibility of structural phase transition as the ZA mode at zone centre turns imaginary above 15% strain. Our results indicate a close relationship between the morphology and properties enabling the device tailoring and bandgap engineering in SL-MoS2 by manipulating the strain.

  1. Extraordinary Bending Effects in MoS2 , Phosphorene, and Graphene Nanoribbons

    Yu, Liping; Ruzsinszky, Adrienn; Perdew, John

    The two-dimensional (2D) materials show great potential for flexible electronics and energy applications. They have remarkable mechanical, electronic, thermal and optical properties, which are often coupled to each other. In this talk, we shall present our first principles study on the bending effects in the electronic structure of MoS2, phosphorene, and graphene nanoribbons. We predict that mechanical bending, as a unique attribute of thin 2D materials, can be used to control conductivity and Fermi-level shift. We find that bending can control the charge localization of top valence bands in both MoS2 and phosphorene nanoribbons. The donor-like in-gap edge-states of armchair MoS2 ribbon and their associated Fermi-level pinning can be removed by bending. A bending-controllable new in-gap state and accompanying direct-indirect gap transition are predicted in armchair phosphorene nanoribbon. We demonstrate that such emergent bending effects are realizable in experiment and can be attributed to the highly non-uniform and enormously large local in-plane strains induced by bending. The bending stiffness as wells as the effective thickness of 2D materials are also derived from first principles. The work was supported as part of the Center for the Computational Design of Functional Layered Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

  2. Deuterium-incorporated gate oxide of MOS devices fabricated by using deuterium ion implantation

    In the aspect of metal-oxide-semiconductor (MOS) device reliability, deuterium-incorporated gate oxide could be utilized to suppress the wear-out that is combined with oxide trap generation. An alternative deuterium process for the passivation of oxide traps or defects in the gate oxide of MOS devices has been suggested in this study. The deuterium ion is delivered to the location where the gate oxide resides by using an implantation process and subsequent N2 annealing process at the back-end of metallization process. A conventional MOS field-effect transistor (MOSFET) with a 3-nm-thick gate oxide and poly-to-ploy capacitor sandwiched with 20-nm-thick SiO2 were fabricated in order to demonstrate the deuterium effect in our process. An optimum condition of ion implantation was necessary to account for the topography of the overlaying layers in the device structure and to minimize the physical damage due to the energy of the implanted ion. Device parameter variations, the gate leakage current, and the dielectric breakdown phenomenon were investigated in the deuterium-ion-implanted devices. We found the isotope effect between hydrogen- and deuterium-implanted devices and an improved electrical reliability in the deuterated gate oxide. This implies that deuterium bonds are generated effectively at the Si/SiO2 interface and in the SiO2 bulk.

  3. Photovoltaic heterojunctions of fullerenes with MoS2 and WS 2 monolayers

    Gan, Liyong

    2014-04-17

    First-principles calculations are performed to explore the geometry, bonding, and electronic structures of six ultrathin photovoltaic heterostructures consisting of pristine and B- or N-doped fullerenes and MoS2 or WS2 monolayers. The fullerenes prefer to be attached with a hexagon parallel to the monolayer, where B and N favor proximity to the monolayer. The main electronic properties of the subsystems stay intact, suggesting weak interfacial interaction. Both the C60/MoS 2 and C60/WS2 systems show type-II band alignments. However, the built-in potential in the former case is too small to effectively drive electron-hole separation across the interface, whereas the latter system is predicted to show good photovoltaic performance. Unfortunately, B and N doping destroys the type-II band alignment on MoS2 and preserves it only in one spin channel on WS2, which is unsuitable for excitonic solar cells. Our results suggest that the C60/WS 2 system is highly promising for excitonic solar cells. © 2014 American Chemical Society.

  4. Enhanced electrochemical performance of Li1.2Mn0.54Ni0.13Co0.13O2 by surface modification with graphene-like lithium-active MoS2

    Highlights: • MoS2 is used as a novel coating material for Li1.2Mn0.54Ni0.13Co0.13O2 via thermolysis of (NH4)2MoS4. • MoS2 coating layer is crystalline with the hexagonal phase. • MoS2 coated LMNCO exhibits the improved high-rate capability and cyclic stability, even at elevated temperature. - Abstract: In order to improve the high-rate capacity and cycleability, the graphene-like structured MoS2 is successfully coated on Li1.2Mn0.54Ni0.13Co0.13O2 via wet chemical method followed by a solid state reaction. Transmission electron microscopy and energy dispersive X-ray spectrometry indicate that the surface of cathode particles is uniformly covered with a crystalline MoS2 layer (∼5 nm thick) after 3 wt% MoS2 surface coating. Compared with the bare sample, MoS2-coated electrode exhibits the improved Coulombic efficiency, cycleability and rate capability in the voltage range of 2.0–4.8 V, even at elevated temperature. Based on the analysis from cyclic voltammetry and electrochemical impedance spectra, the remarkably improved electrochemical performances of the surface-modified electrode are ascribed to the presence of lithium-active MoS2 coating with the layered structure, which could not only suppress the undesirable side reaction and increasing impedance, and enhance the structural stability of host material, but also provide the additional sites for insertion of extracted lithium to compensate the lost Li sites during the activation of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 to effectively increase the initial Coulombic efficiency

  5. Hot-wire vapor deposition of amorphous MoS2 thin films

    Amorphous, as shown by X-ray diffraction measurements, MoS2 films (a-MoS2) were deposited by heating a molybdenum wire at temperatures between 500 and 700 C in H2S at 1 Torr. As shown by Scanning Electron Microscopy measurements, the morphology of samples depends significantly on the filament temperature; at low temperature samples are homogeneous and smooth, at intermediate temperatures they exhibit a granular microstructure and at high temperatures a columnar one. X-ray photoelectron spectroscopy measurements have shown S/Mo ratios in films varying between 2.5 and 1.5 dependent on filament temperature. Films also contain oxygen at atomic contents of 8 to 12%. As shown by XPS and Raman spectroscopy, at a filament temperature of 600 C films are mainly composed of MoS2 also containing oxygen at an atomic ratio of 8%. Spectroscopic ellipsometry measurements made on a-MoS2 films have shown that their band gap is of the order of 1.4 eV, slightly higher than that for the bulk crystalline material. Photoluminescence spectroscopy measurements have shown that samples exhibit a doublet of peaks at 2.8 and 3 eV blue shifted relatively to MoS2 samples composed of one or two mono-layers. The above indicate that the electronic structure of crystalline atomic-layer thick MoS2 is preserved in a-MoS2 films. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Charakterisierung und Optimierung selektiv gewachsener vertikaler Silizium-MOS-Feldeffekttransistoren

    Klaes, D.

    1999-01-01

    Characterization and Optimization of Selectively Grown Vertical Si-MOS Transistors The subject of this thesis was the process development, characterization and optimization of silicon based MOS field-effect transistors. The active transistor region was grown using selective epitaxy. Two different layouts have been investigated and optimized in respect of their electrical characteristics. For one of them (V-FET) only weIl established self-aligning standard technology is used,...

  7. Synthesis of molybdenum disulfide (MoS2) for lithium ion battery applications

    This paper reports the use of a rheological phase reaction method for preparing MoS2 nanoflakes. The characterization by powder X-ray diffraction indicated that MoS2 had been formed. High resolution electron microscopy observation revealed that the as-prepared MoS2 nanoflakes had started to curve and partly form MoS2 nanotubes. The lithium intercalation/de-intercalation behavior of as-prepared MoS2 nanoflake electrode was also investigated. It was found that the MoS2 nanoflake electrode exhibited higher specific capacity, with very high cycling stability, compared to MoS2 nanoparticle electrode. The possible reasons for the high electrochemical performance of the nanoflakes electrodes are also discussed. The outstanding electrochemical properties of MoS2 nanoflakes obtained by this method make it possible for MoS2 to be used as a promising anode material.

  8. The Effect of VMoS3 Point Defect on the Elastic Properties of Monolayer MoS2 with REBO Potentials.

    Li, Minglin; Wan, Yaling; Tu, Liping; Yang, Yingchao; Lou, Jun

    2016-12-01

    Structural defects in monolayer molybdenum disulfide (MoS2) have significant influence on the electric, optical, thermal, chemical, and mechanical properties of the material. Among all the types of structural defects of the chemical vapor phase-grown monolayer MoS2, the VMoS3 point defect (a vacancy complex of Mo and three nearby S atoms) is another type of defect preferentially generated by the extended electron irradiation. Here, using the classical molecular dynamics simulation with reactive empirical bond-order (REBO) potential, we first investigate the effect of VMoS3 point defects on the elastic properties of monolayer MoS2 sheets. Under the constrained uniaxial tensile test, the elastic properties of monolayer MoS2 sheets containing VMoS3 vacancies with defect fraction varying from 0.01 to 0.1 are obtained based on the plane anisotropic constitutive relations of the material. It is found that the increase of VMoS3 vacancy concentration leads to the noticeable decrease in the elastic modulus but has a slight effect on Poisson's ratio. The maximum decrease of the elastic modulus is up to 25 %. Increasing the ambient temperature from 10 K to 500 K has trivial influences on the elastic modulus and Poisson's ratio for the monolayer MoS2 without defect and with 5 % VMoS3 vacancies. However, an anomalous parabolic relationship between the elastic modulus and the temperature is found in the monolayer MoS2 containing 0.1 % VMoS3 vacancy, bringing a crucial and fundamental issue to the application of monolayer MoS2 with defects. PMID:27000023

  9. Stability and electronic properties of SiC nanowire adsorbed on MoS2 monolayer

    Sharma, Munish; Pooja, Kumar, Ashok; Ahluwalia, P. K.

    2015-06-01

    Structural stability and electronic properties of silicon carbide (SiC) nano-wire on MoS2 monolayer are investigated within the framework of density functional theory (DFT). The preferred binding site for the SiC nano-wire is predicted to be hollow site of monolayer. In the electronic band structure the states in valence band near Fermi level are mainly due to nano-wire leading to reduction of band gap relative to monolayer. These results provide a platform for their applications in optoelectronic devices.

  10. Characterization of the system MoS2 + C, HAADF vs Tem conventional

    A study is presented about the synthesis and characterization of unidimensional nano systems composed of MoS2 and C with potential use as solid lubricant. The synthesis process was developed for the mold method, via thermal decomposition, which uses a film of nano porous aluminium oxide. Such systems were characterized by two analysis methods that involve Transmission Electron Microscopy, HRTEM (Conventional TEM) and HAADF (Z Contrast). The results obtained in the structural and morphological characterization were supplemented to determine the structure type obtained in the unidimensional systems. (Author)

  11. Monolayer MoS2/GaAs heterostructure self-driven photodetector with extremely high detectivity

    Xu, Zhijuan; Li, Xiaoqiang; Zhang, Shengjiao; Wu, Zhiqian; Xu, Wenli; Lu, Yanghua; Xu, Sen

    2015-01-01

    Two dimensional material/semiconductor heterostructures offer alternative platforms for optoelectronic devices other than conventional Schottky and p-n junction devices. Herein, we use MoS2/GaAs heterojunction as a self-driven photodetector with wide response band width from ultraviolet to visible light, which exhibits high sensitivity to the incident light of 650 nm with responsivity as 446 mA/W and detectivity as 5.9E13 Jones (Jones = cm Hz^1/2 W^-1), respectively. Employing interface design by inserting h-BN and photo-induced doping by covering Si quantum dots on the device, the responsivity is increased to 582 mA/W for incident light of 650 nm. Distinctly, attributing to the low dark current of the MoS2/h-BN/GaAs sandwich structure based on the self-driven operation condition, the detectivity shows extremely high value of 3.2E14 Jones for incident light of 650 nm, which is higher than all the reported values of the MoS2 based photodetectors. Further investigations reveal that the MoS2/GaAs based photodete...

  12. Back-gated Nb-doped MoS2 junctionless field-effect-transistors

    Gioele Mirabelli

    2016-02-01

    Full Text Available Electrical measurements were carried out to measure the performance and evaluate the characteristics of MoS2 flakes doped with Niobium (Nb. The flakes were obtained by mechanical exfoliation and transferred onto 85 nm thick SiO2 oxide and a highly doped Si handle wafer. Ti/Au (5/45 nm deposited on top of the flake allowed the realization of a back-gate structure, which was analyzed structurally through Scanning Electron Microscopy (SEM and Transmission Electron Microscopy (TEM. To best of our knowledge this is the first cross-sectional TEM study of exfoliated Nb-doped MoS2 flakes. In fact to date TEM of transition-metal-dichalcogenide flakes is extremely rare in the literature, considering the recent body of work. The devices were then electrically characterized by temperature dependent Ids versus Vds and Ids versus Vbg curves. The temperature dependency of the device shows a semiconductor behavior and, the doping effect by Nb atoms introduces acceptors in the structure, with a p-type concentration 4.3 × 1019 cm−3 measured by Hall effect. The p-type doping is confirmed by all the electrical measurements, making the structure a junctionless transistor. In addition, other parameters regarding the contact resistance between the top metal and MoS2 are extracted thanks to a simple Transfer Length Method (TLM structure, showing a promising contact resistivity of 1.05 × 10−7 Ω/cm2 and a sheet resistance of 2.36 × 102 Ω/sq.

  13. Back-gated Nb-doped MoS2 junctionless field-effect-transistors

    Mirabelli, Gioele; Schmidt, Michael; Sheehan, Brendan; Cherkaoui, Karim; Monaghan, Scott; Povey, Ian; McCarthy, Melissa; Bell, Alan P.; Nagle, Roger; Crupi, Felice; Hurley, Paul K.; Duffy, Ray

    2016-02-01

    Electrical measurements were carried out to measure the performance and evaluate the characteristics of MoS2 flakes doped with Niobium (Nb). The flakes were obtained by mechanical exfoliation and transferred onto 85 nm thick SiO2 oxide and a highly doped Si handle wafer. Ti/Au (5/45 nm) deposited on top of the flake allowed the realization of a back-gate structure, which was analyzed structurally through Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). To best of our knowledge this is the first cross-sectional TEM study of exfoliated Nb-doped MoS2 flakes. In fact to date TEM of transition-metal-dichalcogenide flakes is extremely rare in the literature, considering the recent body of work. The devices were then electrically characterized by temperature dependent Ids versus Vds and Ids versus Vbg curves. The temperature dependency of the device shows a semiconductor behavior and, the doping effect by Nb atoms introduces acceptors in the structure, with a p-type concentration 4.3 × 1019 cm-3 measured by Hall effect. The p-type doping is confirmed by all the electrical measurements, making the structure a junctionless transistor. In addition, other parameters regarding the contact resistance between the top metal and MoS2 are extracted thanks to a simple Transfer Length Method (TLM) structure, showing a promising contact resistivity of 1.05 × 10-7 Ω/cm2 and a sheet resistance of 2.36 × 102 Ω/sq.

  14. MoS2 nanoribbons as promising thermoelectric materials

    The thermoelectric properties of MoS2 armchair nanoribbons with different width are studied by using first-principles calculations and Boltzmann transport theory, where the relaxation time is predicted from deformation potential theory. Due to the dangling bonds at the armchair edge, there is obvious structure reconstruction of the nanoribbons which plays an important role in governing the electronic and transport properties. The investigated armchair nanoribbons are found to be semiconducting with indirect gaps, which exhibit interesting width-dependent oscillation behavior. The smaller gap of nanoribbon with width N = 4 (Here, N represents the number of dimer lines or zigzag chains across the ribbon width) leads to a much larger electrical conductivity at 300 K, which outweighs the relatively larger electronic thermal conductivity when compared with those of N = 5, 6. As a result, the ZT values can be optimized to 3.4 (p-type) and 2.5 (n-type) at room temperature, which significantly exceed the performance of most laboratory results reported in the literature.

  15. Electric field effects on armchair MoS2 nanoribbons.

    Dolui, Kapildeb; Pemmaraju, Chaitanya Das; Sanvito, Stefano

    2012-06-26

    Ab initio density functional theory calculations are performed to investigate the electronic structure of MoS(2) armchair nanoribbons in the presence of an external static electric field. Such nanoribbons, which are nonmagnetic and semiconducting, exhibit a set of weakly interacting edge states whose energy position determines the band gap of the system. We show that, by applying an external transverse electric field, E(ext), the nanoribbon band gap can be significantly reduced, leading to a metal-insulator transition beyond a certain critical value. Moreover, the presence of a sufficiently high density of states at the Fermi level in the vicinity of the metal-insulator transition leads to the onset of Stoner ferromagnetism that can be modulated, and even extinguished, by E(ext). In the case of bilayer nanoribbons we further show that the band gap can be changed from indirect to direct by applying a transverse field, an effect that might be of significance for opto-electronics applications. PMID:22546015

  16. MoS2 nanoribbons as promising thermoelectric materials

    Fan, D. D.; Liu, H. J.; Cheng, L.; Jiang, P. H.; Shi, J.; Tang, X. F.

    2014-09-01

    The thermoelectric properties of MoS2 armchair nanoribbons with different width are studied by using first-principles calculations and Boltzmann transport theory, where the relaxation time is predicted from deformation potential theory. Due to the dangling bonds at the armchair edge, there is obvious structure reconstruction of the nanoribbons which plays an important role in governing the electronic and transport properties. The investigated armchair nanoribbons are found to be semiconducting with indirect gaps, which exhibit interesting width-dependent oscillation behavior. The smaller gap of nanoribbon with width N = 4 (Here, N represents the number of dimer lines or zigzag chains across the ribbon width) leads to a much larger electrical conductivity at 300 K, which outweighs the relatively larger electronic thermal conductivity when compared with those of N = 5, 6. As a result, the ZT values can be optimized to 3.4 (p-type) and 2.5 (n-type) at room temperature, which significantly exceed the performance of most laboratory results reported in the literature.

  17. Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence

    Yuan, Cailei; Cao, Yingjie; Luo, Xingfang; Yu, Ting; Huang, Zhenping; Xu, Bo; Yang, Yong; Li, Qinliang; Gu, Gang; Lei, Wen

    2015-10-01

    The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis.

  18. Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence.

    Yuan, Cailei; Cao, Yingjie; Luo, Xingfang; Yu, Ting; Huang, Zhenping; Xu, Bo; Yang, Yong; Li, Qinliang; Gu, Gang; Lei, Wen

    2015-11-01

    The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis. PMID:26439853

  19. Chitosan-assisted fabrication of ultrathin MoS2/graphene heterostructures for Li-ion battery with excellent electrochemical performance

    Graphical abstract: Display Omitted -- Highlights: •2D ultrathin MoS2/graphene heterostructures have been prepared by a chitosan-assisted hydrothemal and a subsequent calcination method. •MoS2 nanosheets in heterostructures are characteristic of few-layered structrues of 3–4 layers. •As an anode material for LIBs, this MoS2/graphene heterostructure deliveres a high reversible specific capacity ∼1100 mAh g−1, excellent cyclic stability and significantly enhanced rate capability (∼800 mAh g−1 at 1A g−1). -- Abstract: A convenient chitosan-assisted hydrothermal and postannealing strategy was successfully developed to fabricate 2D ultrathin MoS2/graphene heterostructures. The resultant heterostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption-desorption. It was found that the ultrathin MoS2 nanosheets were of few-layered structures (3–4 layers) and were well anchored on the large flexible graphene flakes to form heterostructures, which had more uniform mesoporosity and larger surface area than the pristine MoS2. As a result, the obtained MoS2/graphene heterostructure electrode exhibited superior electrochemical lithium-storage performances such as high reversible specific capacity (∼1100 mAh g−1), excellent cyclic stability and significantly enhanced rate capability. The prominent electrochemical performance could be attributed to the robust 2D mesoporous heterostructures composed of ultrathin few-layered MoS2 nanosheets and highly conductive graphene as well as the resultant positive synergistic effect between them

  20. MOS Current Mode Logic Near Threshold Circuits

    Alexander Shapiro

    2014-06-01

    Full Text Available Near threshold circuits (NTC are an attractive and promising technology that provides significant power savings with some delay penalty. The combination of NTC technology with MOS current mode logic (MCML is examined in this work. By combining MCML with NTC, the constant power consumption of MCML is reduced to leakage power levels that can be tolerated in certain modern applications. Additionally, the speed of NTC is improved due to the high speed nature of MCML technology. A 14 nm Fin field effect transistor (FinFET technology is used to evaluate these combined circuit techniques. A 32-bit Kogge Stone adder is chosen as a demonstration vehicle for feasibility analysis. MCML with NTC is shown to yield enhanced power efficiency when operated above 1 GHz with a 100% activity factor as compared to standard CMOS. MCML with NTC is more power efficient than standard CMOS beyond 9 GHz over a wide range of activity factors. MCML with NTC also exhibits significantly lower noise levels as compared to standard CMOS. The results of the analysis demonstrate that pairing NTC and MCML is efficient when operating at high frequencies and activity factors.

  1. Identification of protein tyrosine phosphatase 1B and casein as substrates for 124-v-Mos

    Stabel Silvia

    2002-04-01

    Full Text Available Abstract Background The mos proto-oncogene encodes a cytoplasmic serine/threonine-specific protein kinase with crucial function during meiotic cell division in vertebrates. Based on oncogenic amino acid substitutions the viral derivative, 124-v-Mos, displays constitutive protein kinase activity and functions independent of unknown upstream effectors of mos protein kinase. We have utilized this property of 124-v-Mos and screened for novel mos substrates in immunocomplex kinase assays in vitro. Results We generated recombinant 124-v-Mos using the baculovirus expression system in Spodoptera frugiperda cells and demonstrated constitutive kinase activity by the ability of 124-v-Mos to auto-phosphorylate and to phosphorylate vimentin, a known substrate of c-Mos. Using this approach we analyzed a panel of acidic and basic substrates in immunocomplex protein kinase assays and identified novel in vitro substrates for 124-v-Mos, the protein tyrosine phosphatase 1B (PTP1B, alpha-casein and beta-casein. We controlled mos-specific phosphorylation of PTP1B and casein in comparative assays using a synthetic kinase-inactive 124-v-Mos mutant and further, tryptic digests of mos-phosphorylated beta-casein identified a phosphopeptide specifically targeted by wild-type 124-v-Mos. Two-dimensional phosphoamino acid analyses showed that 124-v-mos targets serine and threonine residues for phosphorylation in casein at a 1:1 ratio but auto-phosphorylation occurs predominantly on serine residues. Conclusion The mos substrates identified in this study represent a basis to approach the identification of the mos-consensus phosphorylation motif, important for the development of specific inhibitors of the Mos protein kinase.

  2. Antibacterial activity of two-dimensional MoS2 sheets

    Yang, Xi; Li, Jie; Liang, Tao; Ma, Chunyan; Zhang, Yingying; Chen, Hongzheng; Hanagata, Nobutaka; Su, Huanxing; Xu, Mingsheng

    2014-08-01

    Graphene-like two-dimensional materials (2DMats) show application potential in optoelectronics and biomedicine due to their unique properties. However, environmental and biological influences of these 2DMats remain to be unveiled. Here we reported the antibacterial activity of two-dimensional (2D) chemically exfoliated MoS2 (ce-MoS2) sheets. We found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the raw MoS2 powders used for the synthesis of ce-MoS2 sheets possibly due to the 2D planar structure (high specific surface area) and higher conductivity of the ce-MoS2. We investigated the antibacterial mechanisms of the ce-MoS2 sheets and proposed their antibacterial pathways. We found that the ce-MoS2 sheets could produce reactive oxygen species (ROS), different from a previous report on graphene-based materials. Particularly, the oxidation capacity of the ce-MoS2 sheets toward glutathione oxidation showed a time and concentration dependent trend, which is fully consistent with the antibacterial behaviour of the ce-MoS2 sheets. The results suggest that antimicrobial behaviors were attributable to both membrane and oxidation stress. The antibacterial pathways include MoS2-bacteria contact induced membrane stress, superoxide anion (O2&z.rad;-) induced ROS production by the ce-MoS2, and the ensuing superoxide anion-independent oxidation. Our study thus indicates that the tailoring of the dimension of nanomaterials and their electronic properties would manipulate antibacterial activity.Graphene-like two-dimensional materials (2DMats) show application potential in optoelectronics and biomedicine due to their unique properties. However, environmental and biological influences of these 2DMats remain to be unveiled. Here we reported the antibacterial activity of two-dimensional (2D) chemically exfoliated MoS2 (ce-MoS2) sheets. We found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the raw MoS2 powders

  3. Phonon thermal conductivity of monolayer MoS2

    Wang, Xiaonan; Tabarraei, Alireza

    2016-05-01

    We use nonequilibrium molecular dynamics modeling using Stillinger-Weber interatomic potential to investigate the thermal properties of monolayer molybdenum disulfide (MoS2) nanoribbons. We study the impact of factors such as length, edge chirality, monovacancies, and uniaxial stretching on the thermal conductivity of MoS2 nanoribbons. Our results show that longer ribbons have a higher thermal conductivity, and the thermal conductivity of infinitely long zigzag and armchair MoS2 nanoribbons is, respectively, 54 W/mK and 33 W/mK. This is significantly lower than the thermal conductivity of some other graphene-like two-dimensional materials such as graphene and boron nitride. While the presence of molybdenum or sulfur vacancies reduces the thermal conductivity of ribbons, molybdenum vacancies have a more deteriorating effect on thermal conductivities. We also have studied the impact of uniaxial stretching on the thermal conductivity of MoS2 nanoribbons. The results show that in contrast to three dimensional materials, thermal conductivity of MoS2 is fairly insensitive to stretching. We have used the phonon dispersion curves and group velocities to investigate the mechanism of this unexpected behavior. Our results show that tensile strain does not alter the phonon dispersion curves and hence the thermal conductivity does not change.

  4. Plasma-edge diagnostics based on Pd-MOS diodes

    Pd metal-oxide-semiconductor (MOS) devices can be used to detect energetic hydrogen atoms. H isotopes implanted into a Pd-MOS diode quickly diffuse through the Pd layer and are accommodated at available Pd-SiO2 interface sites, causing an increase in the leakage current through the device. We find that a diode's response to energetic hydrogen is rapid, sensitive, dosimetric, and reproducible. Pd-MOS diodes can be regenerated when saturated with hydrogen by heating to 100-2000C for a few minutes. These properties make Pd-MOS diodes useful for plasma-edge diagnosis of hydrogen particle fluence when the energy distribution of the incident hydrogen is known. Pd-MOS diode sensors have been used in the laboratory and in the ZT-40M reversed-field pinch to measure energetic hydrogen fluxes. Their small size allows placement in locations inaccessible to conventional diagnostics and should provide a means for remote monitoring of hydrogen fluxes to plasma-facing surfaces. (orig.)

  5. Microinjection of antisense c-mos oligonucleotides prevents meiosis II in the maturing mouse egg.

    O'Keefe, S J; Wolfes, H; Kiessling, A A; Cooper, G M

    1989-01-01

    Injection of antisense oligonucleotides was used to investigate the function of c-mos in murine oocytes. Oocytes injected with antisense c-mos oligonucleotides completed the first meiotic division but failed to initiate meiosis II. Instead, loss of c-mos function led to chromosome decondensation, reformation of a nucleus after meiosis I, and cleavage to two cells. Therefore, c-mos is required for meiosis II during murine oocyte maturation.

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

    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.

  7. Constructing Highly Oriented Configuration by Few-Layer MoS2: Toward High-Performance Lithium-Ion Batteries and Hydrogen Evolution Reactions.

    Zhang, Sanpei; Chowdari, B V R; Wen, Zhaoyin; Jin, Jun; Yang, Jianhua

    2015-12-22

    Constructing three-dimensional (3D) architecture with oriented configurations by two-dimensional nanobuilding blocks is highly challenging but desirable for practical applications. The well-oriented open structure can facilitate storage and efficient transport of ion, electron, and mass for high-performance energy technologies. Using MoS2 as an example, we present a facile and effective hydrothermal method to synthesize 3D radially oriented MoS2 nanospheres. The nanosheets in the MoS2 nanospheres are found to have less than five layers with an expanded (002) plane, which facilitates storage and efficient transport of ion, electron, and mass. When evaluated as anode materials for rechargeable Li-ion batteries, the MoS2 nanospheres show an outstanding performance; namely, a specific capacity as large as 1009.2 mA h g(-1) is delivered at 500 mA g(-1) even after 500 deep charge/discharge cycles. Apart from promising the lithium-ion battery anode, this 3D radially oriented MoS2 nanospheres also show high activity and stability for the hydrogen evolution reaction. PMID:26549425

  8. A study of gamma radiation induced changes in electrical properties of Al/TeO2/n-Si/Al MOS capacitor for dosimetric applications

    The study of the effects of ionizing radiation on MOS devices has been an active area of research due to their wide range applications. Some attempts have recently been made to investigate the influence of ionizing radiation on properties of the MOS capacitor prepared by replacing SiO2 layer by any metal oxide layer of large band gap and then to understand its response. The effect of gamma radiation on electrical properties of the Al/TeO2/n-Si/Al MOS capacitor has been studied in detail for the first time in the present work in order to understand its applicability in the post-exposure gamma radiation dosimetry. The effect of gamma radiation on the real and imaginary parts of the permittivity, dielectric loss, series resistance, ac conductivity and surface state density has been determined. These properties have been obtained by analyzing C-V and G/ω-V characteristics, recorded at a frequency 1.0 MHz of the small ac signal, for the MOS structure exposed to different levels of the gamma radiation dose. The linear variation of the dielectric constant with the gamma radiation dose over a wide range of doses, observed corresponding to the accumulation region of the MOS capacitor, possesses high potential for its application as the post-exposure gamma radiation dosimeter. (author)

  9. A novel technique to measure interface trap density in a GaAs MOS capacitor using time-varying magnetic fields

    Choudhury, Aditya N. Roy; Venkataraman, V.

    2016-05-01

    Interface trap density (Dit) in a GaAs metal-oxide-semiconductor (MOS) capacitor can be measured electrically by measuring its impedance, i.e. by exciting it with a small signal voltage source and measuring the resulting current through the circuit. We propose a new method of measuring Dit where the MOS capacitor is subjected to a (time-varying) magnetic field instead, which produces an effect equivalent to a (time-varying) voltage drop across the sample. This happens because the electron chemical potential of GaAs changes with a change in an externally applied magnetic field (unlike that of the gate metal); this is not the voltage induced by Faraday's law of electromagnetic induction. So, by measuring the current through the MOS, Dit can be found similarly. Energy band diagrams and equivalent circuits of a MOS capacitor are drawn in the presence of a magnetic field, and analyzed. The way in which a magnetic field affects a MOS structure is shown to be fundamentally different compared to an electrical voltage source.

  10. On the Mechanical Properties of WS2 and MoS2 Nanotubes and Fullerene-Like Nanoparticles: In Situ Electron Microscopy Measurements

    Kaplan-Ashiri, Ifat; Tenne, Reshef

    2016-01-01

    Since the discovery of the first inorganic fullerene-like nanoparticles and nanotubes made of WS2 and then MoS2, many more compounds which produce such nanostructures have been discovered and added to the ever expanding list of this group of the layered nanomaterials. Scaling-up the synthesis of the nano-phases of WS2 and MoS2 together with their incredible mechanical properties has turned them into a most promising product for the lubrication industry. Fundamental studies on the mechanical properties of WS2 and MoS2 inorganic fullerene-like nanoparticles and nanotubes are presented in this review. A wide range of mechanical testing was conducted on WS2 and MoS2 nanoparticles. The main focus of this review will be on single nanoparticle experiments in situ electron microscopy as it enables simultaneous structure and properties characterization. Although it is quite challenging, the single nanoparticle approach provides us with the ability to elucidate the intrinsic properties of WS2 and MoS2 inorganic fullerenes and nanotubes.

  11. MoS2/CdS Nanosheets-on-Nanorod Heterostructure for Highly Efficient Photocatalytic H2 Generation under Visible Light Irradiation.

    Yin, Xing-Liang; Li, Lei-Lei; Jiang, Wen-Jie; Zhang, Yun; Zhang, Xiang; Wan, Li-Jun; Hu, Jin-Song

    2016-06-22

    Semiconductor-based photocatalytic H2 generation as a direct approach of converting solar energy to fuel is attractive for tackling the global energy and environmental issues but still suffers from low efficiency. Here, we report a MoS2/CdS nanohybrid as a noble-metal-free efficient visible-light driven photocatalyst, which has the unique nanosheets-on-nanorod heterostructure with partially crystalline MoS2 nanosheets intimately but discretely growing on single-crystalline CdS nanorod. This heterostructure not only facilitates the charge separation and transfer owing to the formed heterojunction, shorter radial transfer path, and fewer defects in single-crystalline nanorod, thus effectively reducing the charge recombination, but also provides plenty of active sites for hydrogen evolution reaction due to partially crystalline structure of MoS2 as well as enough room for hole extraction. As a result, the MoS2/CdS nanosheets-on-nanorod exhibits a state-of-the-art H2 evolution rate of 49.80 mmol g(-1) h(-1) and an apparent quantum yield of 41.37% at 420 nm, which is the advanced performance among all MoS2/CdS composites and CdS/noble metal photocatalysts. These findings will open opportunities for developing low-cost efficient photocatalysts for water splitting. PMID:27237623

  12. Tunable electronic and magnetic properties of a MoS2 monolayer with vacancies under elastic planar strain: Ab initio study

    Salami, N.; Shokri, A. A.; Elahi, S. M.

    2016-03-01

    Electronic and magnetic properties of a molybdenum disulfide (MoS2) monolayer with some intrinsic and extrinsic vacancies are investigated using ab initio method in the presence of planar strain distributions. The calculations are carried out within the density functional theory (DFT) as implemented in SIESTA package. By using fully relaxed structures and applying a full spin-polarized description to the system, we concentrate on created magnetic moment due to the vacancies under different planar strains. The results show that the extrinsic MoS6 vacancy induces a net magnetic moment of 6.00 μB per supercell. Also, it is found that the pure MoS2 monolayer for the most cases does not show any magnetic properties under the planar strain. While the net magnetic moment of MoS2 monolayer with the vacancies enhances as the planar tensile strain is applied. The tunable magnetic moment of MoS2 monolayer may be utilized for the development of spintronic and flexible electronic nano-devices.

  13. Electronic and dielectric properties of MoS2-MoX2 heterostructures

    We present a comparative study of electronic and dielectric properties of MoS2−MoX2 heteostructures (where X=S, Se, Te) within the framework of density functional theory (DFT). Electronic band structure, real and imaginary part of dielectric function, electron energy loss spectra and static dielectric constant have been calculated for each system and compared with one another. A systematic decrease/increase in band gap/static dielectric constant is observed as the X changes from S to Te. These results provide a physical basis for the potential applications of these heterostructures in optoelectronic devices

  14. Electronic and dielectric properties of MoS2-MoX2 heterostructures

    Sharma, Munish; Jamdagni, Pooja; Kumar, Ashok; Ahluwalia, P. K.

    2015-05-01

    We present a comparative study of electronic and dielectric properties of MoS2-MoX2 heteostructures (where X=S, Se, Te) within the framework of density functional theory (DFT). Electronic band structure, real & imaginary part of dielectric function, electron energy loss spectra and static dielectric constant have been calculated for each system and compared with one another. A systematic decrease/increase in band gap/static dielectric constant is observed as the X changes from S to Te. These results provide a physical basis for the potential applications of these heterostructures in optoelectronic devices.

  15. Magnetic edge states in MoS2 characterized using density-functional theory

    Vojvodic, Aleksandra; Hinnemann, B; Nørskov, Jens Kehlet

    2009-01-01

    It is known that the edges of a two-dimensional slab of insulating MoS2 exhibit one-dimensional metallic edge states, the so-called "brim states." Here, we find from density-functional theory calculations that several edge structures, which are relevant for the hydrodesulfurization process, are magnetic. The magnetism is an edge phenomenon associated with certain metallic edge states. Interestingly, we find that among the two low-index edges, only the S edge displays magnetism under hydrodesu...

  16. Magnetic edge states in MoS2 characterized using density-functional theory

    Vojvodic, Aleksandra; Hinnemann, B.; Nørskov, Jens Kehlet

    2009-01-01

    It is known that the edges of a two-dimensional slab of insulating MoS2 exhibit one-dimensional metallic edge states, the so-called "brim states." Here, we find from density-functional theory calculations that several edge structures, which are relevant for the hydrodesulfurization process, are...... magnetic. The magnetism is an edge phenomenon associated with certain metallic edge states. Interestingly, we find that among the two low-index edges, only the S edge displays magnetism under hydrodesulfurization conditions. In addition, the implications of this on the catalytic activity are investigated...

  17. Shallow donor in natural MoS2

    Using electron paramagnetic resonance and density functional theory calculations, we show that the shallow donor responsible for the n-type conductivity in natural MoS2 is rhenium (Re) with a typical concentration in the low 1017 cm-3 range and the g -values: g parallel = 2.0274 and g perpendicular to = 2.2642. In bulk MoS2, the valley-orbit (VO) splitting and ionization energy of the Re shallow donor are determined to be ∝3 meV and ∝27 meV, respectively. Calculations show that the VO splitting of Re approaches the value in bulk if the number of MoS2 layers is larger than four and increases to 97.9 meV in a monolayer. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Synthesis of Large Scale MoS2 -Graphene Heterostructures

    McCreary, Kathleen; Hanbicki, Aubrey; Friedman, Adam; Robinson, Jeremy; Jonker, Berend

    2014-03-01

    A rapidly progressing field involves the stacking of multiple two dimensional materials to form heterostructures. These heterosctructures have exhibited unique and interesting properties. For the most part, heterostructure devices are produced via mechanical exfoliation followed by careful aligning and stacking of the various components, limiting dimensions to micron-scale devices. Chemical vapor deposition (CVD) has proven to be a useful tool in the production of graphene and has very recently been investigated as a means for the growth of other 2D materials such as MoS2, hexagonal boron nitride and WS2. Using a two-step CVD process we are able to synthesize MoS2 on CVD grown graphene. AFM and Raman microscopy of the MoS2-graphene heterostructure show a uniform and continuous film on the cm scale.

  19. MoS2 nanotube field effect transistors

    M. Strojnik

    2014-09-01

    Full Text Available We report on electric field effects on electron transport in multi-walled MoS2 nanotubes (NTs, fabricated using a two-step synthesis method from Mo6SxI9-x nanowire bundle precursors. Transport properties were measured on 20 single nanotube field effect transistor (FET devices, and compared with MoS2 layered crystal devices prepared using identical fabrication techniques. The NTs exhibited mobilities of up to 0.014 cm2V−1s−1 and an on/off ratio of up to 60. As such they are comparable with previously reported WS2 nanotube FETs, but materials defects and imperfections apparently limit their performance compared with multilayer MoS2 FETs with similar number of layers.

  20. He+ ion radiation effect in MOS transistors under operation

    Attempt was carried out to resolve the mechanisms of the characteristic degradation of MOS FET's by using VdG accelerator. The system that is capable to control the irradiation dose exactly established. The sample used was n-channel MOS FET with 69371 μm channel width, 13 μm channel length and 1200 A oxide thickness. MOS FET's under operation were irradiated with 1.5 MeV He ions with 0.5 nA beam current for about 1000 μS and the drain voltage during the irradiation was monitored. The drain voltage shifted and its amplitude varied depending on the irradiation dose. Induced electron-hole pair within a substrate turned into additional current. (author)

  1. MoS2 nanotube field effect transistors

    We report on electric field effects on electron transport in multi-walled MoS2 nanotubes (NTs), fabricated using a two-step synthesis method from Mo6SxI9-x nanowire bundle precursors. Transport properties were measured on 20 single nanotube field effect transistor (FET) devices, and compared with MoS2 layered crystal devices prepared using identical fabrication techniques. The NTs exhibited mobilities of up to 0.014 cm2V−1s−1 and an on/off ratio of up to 60. As such they are comparable with previously reported WS2 nanotube FETs, but materials defects and imperfections apparently limit their performance compared with multilayer MoS2 FETs with similar number of layers

  2. Plasmons on the edge of MoS2 nanostructures

    Andersen, Kirsten; Jacobsen, Karsten W.; Thygesen, Kristian S.

    2014-10-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S edges of the ribbon are clearly distinguishable in calculated spatially resolved electron energy loss spectrum owing to the different plasmonic properties of the two edges. The edge plasmons could potentially be utilized for tuning the photocatalytic activity of MoS2 nanoparticles.

  3. MoS2/Nitrogen-doped graphene as efficient electrocatalyst for oxygen reduction reaction

    Graphical abstract: A simple yet effective method was developed for generating an electrocatalyst for oxygen reduction reaction by deposited MoS2 sheets on nitrogen-doped graphene (NG). Due to the synergistic effect of MoS2 and NG, enhancement of electrocatalytic oxygen-reduction was realized. Display Omitted -- Highlights: • MoS2/Nitrogen-doped graphene (NG) composites were obtained by physically mixing method. • MoS2 sheets deposited NG could be used as effective electrocatalyst for ORR. • Enhanced electrocatalytic activity is due to the synergistic effect of MoS2 and NG. • The ORR is a four-electron process based on Koutecky-Levich equation. -- Abstract: A simple yet effective strategy was developed to generate a non-precious oxygen electrode electrocatalyst of MoS2/nitrogen-doped graphene (NG) by physical mixing MoS2 sheets with NG. The micrometer-sized MoS2 sheets were obtained through ultrasonication exfoliation of the bulk MoS2, only showing little oxygen reduction reaction (ORR) activity. MoS2/NG hybrid was obtained by loading MoS2 sheets onto NG through ultrasonication, and the resulting nanocomposites exhibited improved electrocatalytic activity for ORR with dominant 4 electron pathway in alkaline solutions. The exposed active edges as well as the synergistic effect and reduced resistance connection jointly make the MoS2/NG composite a highly competitive ORR catalyst

  4. Large-Area Epitaxial Monolayer MoS2.

    Dumcenco, Dumitru; Ovchinnikov, Dmitry; Marinov, Kolyo; Lazić, Predrag; Gibertini, Marco; Marzari, Nicola; Lopez Sanchez, Oriol; Kung, Yen-Cheng; Krasnozhon, Daria; Chen, Ming-Wei; Bertolazzi, Simone; Gillet, Philippe; Fontcuberta i Morral, Anna; Radenovic, Aleksandra; Kis, Andras

    2015-04-28

    Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging potential applications in electronics, optoelectronics, and energy harvesting. Large-area growth methods are needed to open the way to applications. Control over lattice orientation during growth remains a challenge. This is needed to minimize or even avoid the formation of grain boundaries, detrimental to electrical, optical, and mechanical properties of MoS2 and other 2D semiconductors. Here, we report on the growth of high-quality monolayer MoS2 with control over lattice orientation. We show that the monolayer film is composed of coalescing single islands with limited numbers of lattice orientation due to an epitaxial growth mechanism. Optical absorbance spectra acquired over large areas show significant absorbance in the high-energy part of the spectrum, indicating that MoS2 could also be interesting for harvesting this region of the solar spectrum and fabrication of UV-sensitive photodetectors. Even though the interaction between the growth substrate and MoS2 is strong enough to induce lattice alignment via van der Waals interaction, we can easily transfer the grown material and fabricate devices. Local potential mapping along channels in field-effect transistors shows that the single-crystal MoS2 grains in our film are well connected, with interfaces that do not degrade the electrical conductivity. This is also confirmed by the relatively large and length-independent mobility in devices with a channel length reaching 80 μm. PMID:25843548

  5. Ferromagnetism in Transitional Metal-Doped MoS2 Monolayer.

    Fan, Xiao-Li; An, Yu-Rong; Guo, Wen-Jun

    2016-12-01

    Manipulating electronic and magnetic properties of two-dimensional (2D) transitional-metal dichalcogenides (TMDs) MX2 by doping has raised a lot of attention recently. By performing the first-principles calculations, we have investigated the structural, electronic, and magnetic properties of transitional metal (TM)-doped MoS2 at low and high impurity concentrations. Our calculation result indicates that the five elements of V-, Mn-, Fe-, Co-, and Cu-doped monolayer MoS2 at low impurity concentration all give rise to the good diluted magnetic semiconductors. By studying various configurations with different TM-TM separations, we found that the impurity atoms prefer to stay together in the nearest neighboring (NN) configuration, in which the doped TM atoms are FM coupling except for Fe doping at 12 % concentration. For V, Mn, and Fe doping, the total magnetic moment is smaller than the local magnetic moment of the dopants because the induced spins on the nearby host atoms are antiparallel to that of the doped atoms. In contrast, Co and Cu doping both give the higher total magnetic moment. Especially, Cu doping induces strong ferromagnetism relative to the local spins. However, the atomic structures of Co- and Cu-doped MoS2 deviate from the original prismatic configuration, and the magnetic moments of the doped systems decrease at 12 % impurity concentration although both elements give higher magnetic moments at 8 % impurity concentration. Our calculations indicate that V and Mn are promising candidates for engineering and manipulating the magnetism of the 2D TMDs. PMID:27000022

  6. Ultrafast Li-storage of MoS2 nanosheets grown on metal-organic framework-derived microporous nitrogen-doped carbon dodecahedrons

    Shao, Jie; Gao, Tian; Qu, Qunting; Shi, Qiang; Zuo, Zhichen; Zheng, Honghe

    2016-08-01

    The nanocomposites of MoS2 nanosheets and microporous nitrogen-doped carbon dodecahedron (MNCD) are prepared through the pyrolysis of metal-organic framework (MOF) and subsequent growth of MoS2. The porous and active surface of MNCDs enables uniform growth of ultrathin MoS2 nanosheets. When the MNCD@MoS2 composite is used as the anode material of Li-ion batteries, a reversible capacity of 915 mAh g-1 can be obtained even at the extremely high current density of 10 A g-1. The ultrafast charge/discharge ability of MNCD@MoS2 can be attributed to its unique core-shell structure with the inner MNCDs serving as the reservoir of Li-ions and transport media of electrons.

  7. MoS2 nanotube field effect transistors

    M. Strojnik; A. Kovic; Mrzel, A; J. Buh; Strle, J.; Mihailovic, D.

    2014-01-01

    We report on electric field effects on electron transport in multi-walled MoS2 nanotubes (NTs), fabricated using a two-step synthesis method from Mo6SxI9-x nanowire bundle precursors. Transport properties were measured on 20 single nanotube field effect transistor (FET) devices, and compared with MoS2 layered crystal devices prepared using identical fabrication techniques. The NTs exhibited mobilities of up to 0.014 cm2V−1s−1 and an on/off ratio of up to 60. As such they are comparable with p...

  8. Online MOS Capacitor Characterization in LabVIEW Environment

    Chinmay K Maiti

    2009-08-01

    Full Text Available We present an automated evaluation procedure to characterize MOS capacitors involving high-k gate dielectrics. Suitability of LabVIEW environment for online web-based semiconductor device characterization is demonstrated. Developed algorithms have been successfully applied to automate the MOS capacitor measurements for Capacitance-Voltage, Conductance-Voltage and Current-Voltage characteristics. Implementation of the algorithm for use as a remote internet-based characterization tool where the client and server communicate with each other via web services is also shown.

  9. Nanocrystalline MoS2 through directional growth along the (0 0 2) crystal plane under high pressure

    Highlights: · MoS2 crystals are uncovered to grow along (0 0 2) plane by XRD techniques. · XRD peaks abnormal broadening is attributed to the layers disorder of MoS2. ·Scherrer equation could not be suitable for layer-disordered nano-MoS2. - Abstract: The directional growth experiments of graphite-like structured MoS2 crystallites have been conducted by utilizing a designed sample cell assembly under high pressure (2.0 and 5.0 GPa) and high temperature (700 deg. C). X-ray diffraction (XRD) and scanning electron microscope (SEM) are used to characterize the samples. The results show that the prepared nanocrystalline MoS2 (n-MoS2) crystals have a hexagonal layered structure. The crystal is uncovered to grow preferentially along the (0 0 2) plane, which indicates that the low-energy surface is the (0 0 2) plane of the crystal. The striking diffuse/broadening nature of Bragg reflection is also analyzed in details, and considered to be associated with the defect structures of the layers stacking and rotational disorder. Measurements of crystallite/grain size are performed by using XRD technique and SEM observation. The measurement results suggest that the traditional peak broadening analysis techniques, including Williamson-Hall formula and Scherrer equation, may not be suitable for the present poorly crystallized n-MoS2 situation. The results may be conducive to have an insight into the growth mechanism and defects analysis of the layer-structured materials.

  10. MOS2 has redundant function with its homolog MOS2H and is required for proper splicing of SNC1

    Copeland, Charles; Xu, Shaohua; Qi, Yijun; Li, Xin

    2013-01-01

    Plant immunity is essential for plant survival and resistance (R) proteins serve essential roles in pathogen detection and defense signal initiation. A gain-of-function mutation in SNC1, a TIR-type R gene, results in a characteristic autoimmune phenotype in Arabidopsis. From a forward genetic suppressor screen using snc1, MOS2 (MODIFIER of snc1), which encodes an RNA-binding protein, was identified. When MOS2 function is lost, the autoimmunity caused by snc1 is abolished and basal resistance ...

  11. Enhanced absorption of monolayer MoS2 with resonant back reflector

    Liu, Jiang-Tao; Li, Xiao-Jing; Liu, Nian-Hua

    2014-01-01

    By extracting the permittivity of monolayer MoS2 from experiments, the optical absorption of monolayer MoS2 prepared on top of one-dimensional photonic crystal (1DPC) or metal films is investigated theoretically. The 1DPC and metal films act as resonant back reflectors that can enhance absorption of monolayer MoS2 substantially over a broad spectral range due to the Fabry-Perot cavity effect. The absorption of monolayer MoS2 can also be tuned by varying either the distance between the monolayer MoS2 and the back reflector or the thickness of the cover layers.

  12. Photoluminescence of freestanding single- and few-layer MoS2

    Scheuschner, Nils; Ochedowski, Oliver; Kaulitz, Anne-Marie; Gillen, Roland; Schleberger, Marika; Maultzsch, Janina

    2013-01-01

    We present a photoluminescence study of freestanding and Si/SiO2 supported single- and few-layer MoS2. The single-layer exciton peak (A) is only observed in freestanding MoS2. The photoluminescence of supported single-layer MoS2 is instead originating from the A- (trion) peak as the MoS2 is n-type doped from the substrate. In bilayer MoS2, the van der Waals interaction with the substrate is decreasing the indirect band gap energy by up to ~ 80 meV. Furthermore, the photoluminescence spectra o...

  13. Theoretical analysis of the combined effects of sulfur vacancies and analyte adsorption on the electronic properties of single-layer MoS2

    Akdim, Brahim; Pachter, Ruth; Mou, Shin

    2016-05-01

    We report a first-principles theoretical investigation on the electronic structure and electron transport of defective single-layer (SL) MoS2, as well as of corresponding structures adsorbed with benzyl viologen (BV), which was shown to provide improved performance of a field effect transistor. O2 adsorption was included to gain an understanding of the response upon air-exposure. Following analysis of the structure and stability of sulfur single vacancy and line defects in SL MoS2, we investigated the local transport at the adsorbed sites via a transport model that mimics a scanning tunneling spectroscopy experiment. Distinct current-voltage characteristics were indicated for adsorbed oxygen species at a sulfur vacancy. The electronic structures of defective MoS2 indicated the emergence of impurity states in the bandgap due to sulfur defects and oxygen adsorption. Electron transport calculations for the MoS2 surface with an extended defect in a device setting demonstrated that physisorption of BV enhances the output current, while facile chemisorption by O2 upon air-exposure causes degradation of electron transport.

  14. Structural and optical properties of ZnO films grown on silicon and their applications in MOS devices in conjunction with ZrO2 as a gate dielectric

    S K Nandi; S Chakraborty; M K Bera; C K Maiti

    2007-06-01

    Photoluminescence (PL) properties of undoped ZnO thin films grown by rf magnetron sputtering on silicon substrates have been investigated. ZnO/Si substrates are characterized by Rutherford backscattering (RBS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). ZrO2 thin films have been deposited on ZnO using microwave plasma enhanced chemical vapour deposition at a low temperature (150°C). Using metal insulator semiconductor (MIS) capacitor structures, the reliability and the leakage current characteristics of ZrO2 films have been studied both at room and high temperatures. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Good electrical and reliability properties suggest the suitability of deposited ZrO2 thin films as an alternative as gate dielectric on ZnO/-Si heterostructure for future device applications.

  15. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis

    Tadi, Kiran Kumar; Palve, Anil M.; Pal, Shubhadeep; Sudeep, P. M.; Narayanan, Tharangattu N.

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

  16. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

    Tadi, Kiran Kumar; Palve, Anil M; Pal, Shubhadeep; Sudeep, P M; Narayanan, Tharangattu N

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here. PMID:27231837

  17. Layer-by-layer self-assembly of polyelectrolyte functionalized MoS2 nanosheets.

    Shen, Jianfeng; Pei, Yu; Dong, Pei; Ji, Jin; Cui, Zheng; Yuan, Junhua; Baines, Robert; Ajayan, Pulickel M; Ye, Mingxin

    2016-05-01

    Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems. PMID:27102889

  18. Magnetoresistance in molybdenite (MoS2) crystals

    The principal magnetoresistance ratios of molybdenite (MoS2), the naturally occurring semiconducting crystal, have been investigated at magnetic fields ranging from 4.5 KOe and within the temperature range 3000K to 7000K. Unlike some previous observations, magnetoresistance has been found to be negative. (author)

  19. Threshold voltage shift of mos transistors by ion implantation

    The simple theory of the use of ion implantation of mos transistors to shift threshold voltage is outlined. Discrepancies between theory and practice are discussed. A modified model is proposed in which all implanted ions contribute to the threshold voltage shift irrespective of energy levels. (U.K.)

  20. Cube-like Cu2MoS4 photocatalysts for visible light-driven degradation of methyl orange

    Zhang, Ke; Chen, Wenxing; Wang, Yu; Li, Jiong; Chen, Haiping; Gong, Zhiyu; Chang, Shuo; Ye, Fei; Wang, Tianxing; Chu, Wangsheng; Zou, Chongwen; Song, Li

    2015-07-01

    Cube-like Cu2MoS4 nanoparticles with low-index facets and high crystallinity were fabricated via a hydrothermal method. The as-obtained nanocubes with an average size of 40-60 nm are composed of stacking-Cu2MoS4 layers separated by a weak Van der Waals gap of 0.5 nm. A strong absorption at visible light region is observed in the nanocube aqueous solution, indicating its optical-band gap of 1.78 eV. The photocatalytic measurements reveal that the nanocubes can thoroughly induce the degradation of methyl orange under visible light irradiation with good structural stability. Our finding may provide a way in design and fabrication of transition metal dichalcogenide nanostructures for practical applications.

  1. Cube-like Cu2MoS4 photocatalysts for visible light-driven degradation of methyl orange

    Cube-like Cu2MoS4 nanoparticles with low-index facets and high crystallinity were fabricated via a hydrothermal method. The as-obtained nanocubes with an average size of 40-60 nm are composed of stacking-Cu2MoS4 layers separated by a weak Van der Waals gap of 0.5 nm. A strong absorption at visible light region is observed in the nanocube aqueous solution, indicating its optical-band gap of 1.78 eV. The photocatalytic measurements reveal that the nanocubes can thoroughly induce the degradation of methyl orange under visible light irradiation with good structural stability. Our finding may provide a way in design and fabrication of transition metal dichalcogenide nanostructures for practical applications

  2. Nitrogen-Doped Carbon Embedded MoS2 Microspheres as Advanced Anodes for Lithium- and Sodium-Ion Batteries.

    Xie, Dong; Xia, Xinhui; Wang, Yadong; Wang, Donghuang; Zhong, Yu; Tang, Wangjia; Wang, Xiuli; Tu, Jiangping

    2016-08-01

    Rational design and synthesis of advanced anode materials are extremely important for high-performance lithium-ion and sodium-ion batteries. Herein, a simple one-step hydrothermal method is developed for fabrication of N-C@MoS2 microspheres with the help of polyurethane as carbon and nitrogen sources. The MoS2 microspheres are composed of MoS2 nanoflakes, which are wrapped by an N-doped carbon layer. Owing to its unique structural features, the N-C@MoS2 microspheres exhibit greatly enhanced lithium- and sodium-storage performances including a high specific capacity, high rate capability, and excellent capacity retention. Additionally, the developed polyurethane-assisted hydrothermal method could be useful for the construction of many other high-capacity metal oxide/sulfide composite electrode materials for energy storage. PMID:27355199

  3. Monitoring the formation of inorganic fullerene-like MoS2 nanostructures by laser ablation in liquid environments

    Laser ablation of solid targets in liquid media is emerging as a simple, clean and reproducible way to generate a large number of intriguing nanometric structures with peculiar properties. In this work we present some results on the formation of MoS2 fullerene-like nanoparticles (10-15 nm diameter) obtained by the ablation of crystalline targets in water. Such a top-down approach can be considered greener than standard sulphidization reactions and represents an intriguing single step procedure. The generation of the MoS2 nanostructures is in competition with that of oxide clusters and strongly depends on the oxidative environment created by the plasma plume. The size, shape and crystalline phase of the obtained nanoparticles are studied by microscopy while X-Ray Photoelectron Spectroscopy is used to investigate the chemical state of produced nanostructures and to propose mechanisms for their growth.

  4. Cube-like Cu2MoS4 photocatalysts for visible light-driven degradation of methyl orange

    Ke Zhang

    2015-07-01

    Full Text Available Cube-like Cu2MoS4 nanoparticles with low-index facets and high crystallinity were fabricated via a hydrothermal method. The as-obtained nanocubes with an average size of 40-60 nm are composed of stacking-Cu2MoS4 layers separated by a weak Van der Waals gap of 0.5 nm. A strong absorption at visible light region is observed in the nanocube aqueous solution, indicating its optical-band gap of 1.78 eV. The photocatalytic measurements reveal that the nanocubes can thoroughly induce the degradation of methyl orange under visible light irradiation with good structural stability. Our finding may provide a way in design and fabrication of transition metal dichalcogenide nanostructures for practical applications.

  5. Thermal transport properties of MoS2 and MoSe2 monolayers

    Kandemir, Ali; Yapicioglu, Haluk; Kinaci, Alper; Çağın, Tahir; Sevik, Cem

    2016-02-01

    The isolation of single- to few-layer transition metal dichalcogenides opens new directions in the application of two-dimensional materials to nanoelectronics. The characterization of thermal transport in these new low-dimensional materials is needed for their efficient implementation, either for general overheating issues or specific applications in thermoelectric devices. In this study, the lattice thermal conductivities of single-layer MoS2 and MoSe2 are evaluated using classical molecular dynamics methods. The interactions between atoms are defined by Stillinger-Weber-type empirical potentials that are developed to represent the structural, mechanical, and vibrational properties of the given materials. In the parameterization of the potentials, a stochastic optimization algorithm, namely particle swarm optimization, is utilized. The final parameter sets produce quite consistent results with density functional theory in terms of lattice parameters, bond distances, elastic constants, and vibrational properties of both single-layer MoS2 and MoSe2. The predicted thermal properties of both materials are in very good agreement with earlier first-principles calculations. The discrepancies between the calculations and experimental measurements are most probably caused by the pristine nature of the structures in our simulations.

  6. Atomistic modeling of the metallic-to-semiconducting phase boundaries in monolayer MoS2

    Saha, Dipankar; Mahapatra, Santanu

    2016-06-01

    Recent experimental demonstration on the coexistence of metallic and semiconducting phases in the same monolayer MoS2 crystal has attracted much attention for its use in ultra-low contact resistance-MoS2 transistors. However, the electronic structures of the metallic-to-semiconducting phase boundaries, which appear to dictate the carrier injection in such transistors, are not yet well understood. In this letter, interfacing the 2H and 1T' polytypes appropriately, we first model the "beta" (β) and the "gamma" (γ) phase boundaries, and demonstrate good agreement with experiential results. We then apply first-principles based density functional theory to calculate the electronic structures for those optimized geometries. We further employ non equilibrium Green's function formalism to evaluate the transmission spectra and the local density of states (LDOS) in order to assess the Schottky barrier nature of the phase boundaries. Our study reveals that while the γ boundary yields p-type Schottky barrier, the β boundary leads to the distinct symmetric Schottky barrier with an atomically sharp transition region. This understanding could be useful for designing high performance transistors using phase-engineered MoS2 crystals.

  7. Tunable Molecular MoS2 Edge-Site Mimics for Catalytic Hydrogen Production.

    Garrett, Benjamin R; Polen, Shane M; Click, Kevin A; He, Mingfu; Huang, Zhongjie; Hadad, Christopher M; Wu, Yiying

    2016-04-18

    Molybdenum sulfides represent state-of-the-art, non-platinum electrocatalysts for the hydrogen evolution reaction (HER). According to the Sabatier principle, the hydrogen binding strength to the edge active sites should be neither too strong nor too weak. Therefore, it is of interest to develop a molecular motif that mimics the catalytic sites structurally and possesses tunable electronic properties that influence the hydrogen binding strength. Furthermore, molecular mimics will be important for providing mechanistic insight toward the HER with molybdenum sulfide catalysts. In this work, a modular method to tune the catalytic properties of the S-S bond in MoO(S2)2L2 complexes is described. We studied the homogeneous electrocatalytic hydrogen production performance metrics of three catalysts with different bipyridine substitutions. By varying the electron-donating abilities, we present the first demonstration of using the ligand to tune the catalytic properties of the S-S bond in molecular MoS2 edge-site mimics. This work can shed light on the relationship between the structure and electrocatalytic activity of molecular MoS2 catalysts and thus is of broad importance from catalytic hydrogen production to biological enzyme functions. PMID:27022836

  8. A novel optical property induced by MO, S vacancy and V-doped in monolayer MoS2

    Xu, Wei-bin; Li, Ping; Li, Sheng-shi; Huang, Bao-jun; Zhang, Chang-wen; Wang, Pei-ji

    2015-09-01

    The electronic structure and optical properties of Mo, S vacancy and V doping in MoS2 monolayer will be investigated through first-principles calculations based on the density functional theory. The results indicate that the MoS2 with Mo, S vacancy and V doping (Mo14VS32, Mo15VS31 and Mo14VS31) will gain the property of magnetic semiconductor with the magnetic moment of 1 μB, 1 μB and 0.95 μB, respectively. The optical properties of these V-doped and vacancy defect structures all reflect the phenomenon of red shift. The absorption edge of pure monolayer molybdenum disulfide is 0.8 eV, whereas the absorption edges of Mo14VS32, Mo15VS31 and Mo14VS31 become 0 eV, 0.2 eV and 0.16 eV, respectively. As a potential material, MoS2 is widely used in many fields such as the production of optoelectronic devices, military devices and civil devices.

  9. Optimal electron irradiation as a tool for functionalization of MoS2: Theoretical and experimental investigation

    We demonstrate the utility of electron irradiation as a tool to enhance device functionality of graphene-analogous MoS2. With the help of first-principles based calculations, vacancy-induced changes of various electronic properties are shown to be a combined result of crystal-field modification and spin-orbital coupling. A comparative theoretical study of various possible vacancy configurations both in bulk and monolayer MoS2 and related changes in their respective band-structures help us to explain plausible irradiation induced effects. Experimentally, various structural forms of MoS2 in bulk, few layered flakes, and nanocrystals are observed to exhibit important modification of their magnetic, transport, and vibrational properties, following low doses of electron irradiation. While irradiated single crystals and nanocrystals show an enhanced magnetization, transport properties of few-layered devices show a significant increase in their conductivity, which can be very useful for fabrication of electronic devices. Our theoretical calculations reveal that this increase in n-type conductivity and magnetization can be correlated with the presence of sulfur and molybdenum vacancies

  10. Coherently stacked MoS2/WSe2 heterostructures: Moiré pattern and its effect on interlayer couplings

    Zhang, Chendong; Li, Ming-Yang; Chuu, Chih-Piao; Chou, Mei-Yin; Li, Lain-Jong; Shih, Chih-Kang

    Vertically stacked heterojunctions (HJs) of transition metal dichalcogenides (TMDs) have been proposed as fundamental building blocks for several novel electronic and photonic devices. Although such HJs can be easily achieved by sequential transferring of different TMDs, this approach is not scalable, and the orientation relationship between the layers is difficult to control. A much more desirable approach is to directly grow one kind of TMD on top of the other. In addition to being a scalable platform, the epitaxial approach also results in a well-defined orientation relationship. A very important question to ask is ``What is the role of the interlayer coupling on the electronic structures of such a bilayer stack?'' By using scanning tunneling microscopy/spectroscopy (STM/S) and first-principles calculations, we investigate the MoS2/WSe2 vertical heterojunctions formed by direct epitaxial growth. The different lateral lattice constants between MoS2 and WSe2 lead to the formation of a well-ordered Moire pattern with a superlattice constant of ~8.5 nm. This superlattice reflects the variation of the lateral alignment between the MoS2 and WSe2 lattices. STS shows very large variations of interlayer coupling, as a function of the lateral alignment. More interestingly, depending on the location in the BZ, the interlayer coupling has very different consequences on the electronic structures.

  11. Location and coordination of promoter atoms in Co- and Ni-promoted MoS2-based hydrotreating catalysts

    Lauritsen, J.V.; Kibsgaard, J.; Olesen, G.H.; Moses, Poul Georg; Hinnemann, Berit; Helveg, S.; Nørskov, Jens Kehlet; Clausen, B.S.; Topsøe, H.; Lægsgaard, E.; Besenbacher, F.

    2007-01-01

    In this study, we used scanning tunneling microscopy (STM) and density functional theory (DFT) to investigate the atomic-scale structure of the active Co- or Ni-promoted MoS2 nanoclusters in hydrotreating catalysts. Co-promoted MoS2 nanoclusters (Co–Mo–S) are found to adopt a hexagonal shape, with...... nanocluster size. Larger clusters (type A) are structurally similar to Co–Mo–S exposing fully Ni-substituted () edges with a 50% S coverage. Smaller clusters (type B) show dodecagonal shapes terminated by three different edges, all of which contain Ni-promoter atoms fully or partially substituting the Mo...... Co atoms preferentially located at () edges with a 50% sulfur coverage. The first atom-resolved STM images of the Ni-promoted MoS2 nanoclusters (Ni–Mo–S) reveal that the addition of Ni also leads to truncated morphologies, but the degree of truncation and the Ni sites are observed to depend on the...

  12. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals

    Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.

    2016-06-01

    Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

  13. Epitaxial Growth of Lattice-Mismatched Core-Shell TiO2 @MoS2 for Enhanced Lithium-Ion Storage.

    Dai, Rui; Zhang, Anqi; Pan, Zhichang; Al-Enizi, Abdullah M; Elzatahry, Ahmed A; Hu, Linfeng; Zheng, Gengfeng

    2016-05-01

    Core-shell structured nanohybrids are currently of significant interest due to their synergetic properties and enhanced performances. However, the restriction of lattice mismatch remains a severe obstacle for heterogrowth of various core-shells with two distinct crystal structures. Herein, a controlled synthesis of lattice-mismatched core-shell TiO2 @MoS2 nano-onion heterostructures is successfully developed, using unilamellar Ti0.87 O2 nanosheets as the starting material and the subsequent epitaxial growth of MoS2 on TiO2 . The formation of these core-shell nano-onions is attributed to an amorphous layer-induced heterogrowth mechanism. The number of MoS2 layers can be well tuned from few to over ten layers, enabling layer-dependent synergistic effects. The core-shell TiO2 @MoS2 nano-onion heterostructures exhibit significantly enhanced energy storage performance as lithium-ion battery anodes. The approach has also been extended to other lattice-mismatched systems such as TiO2 @MoSe2 , thus suggesting a new strategy for the growth of well-designed lattice-mismatched core-shell structures. PMID:27062267

  14. Nanocomposite of MoS2 on ordered mesoporous carbon nanospheres: A highly active catalyst for electrochemical hydrogen evolution

    Bian, Xiaojun; Zhu, Jie; Liao, Lei; Scanlon, Micheál D.; Ge, Peiyu; JI, CHANG; Girault, Hubert H.; Liu, Baohong

    2012-01-01

    An efficient electrocatalyst for hydrogen evolution has been developed based upon in situ reduction of MoS2 on ordered mesoporous carbon nanospheres (MoS2/MCNs). The properties of MoS2/MCNs were characterised by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Polarisation curves and electrochemical impedance measurements were obtained for MoS2/MCNs modified glassy carbon electrodes. The MoS2/MCNs exhibit high catalytic activity for hydrogen...

  15. Few-layer MoS2-anchored graphene aerogel paper for free-standing electrode materials

    Lee, Wee Siang Vincent; Peng, Erwin; Loh, Tamie Ai Jia; Huang, Xiaolei; Xue, Jun Min

    2016-04-01

    To reduce the reliance on polymeric binders, conductive additives, and metallic current collectors during the electrode preparation process, as well as to assess the true performance of lithium ion battery (LIB) anodes, a free-standing electrode has to be meticulously designed. Graphene aerogel is a popular scaffolding material that has been widely used with embedded nanoparticles for application in LIB anodes. However, the current graphene aerogel/nanoparticle composite systems still involve decomposition into powder and the addition of additives during electrode preparation because of the thick aerogel structure. To further enhance the capacity of the system, MoS2 was anchored onto a graphene aerogel paper and the composite was used directly as an LIB anode. The resultant additive-free MoS2/graphene aerogel paper composite exhibited long cyclic performance with 101.1% retention after 700 cycles, which demonstrates the importance of free-standing electrodes in enhancing cyclic stability.To reduce the reliance on polymeric binders, conductive additives, and metallic current collectors during the electrode preparation process, as well as to assess the true performance of lithium ion battery (LIB) anodes, a free-standing electrode has to be meticulously designed. Graphene aerogel is a popular scaffolding material that has been widely used with embedded nanoparticles for application in LIB anodes. However, the current graphene aerogel/nanoparticle composite systems still involve decomposition into powder and the addition of additives during electrode preparation because of the thick aerogel structure. To further enhance the capacity of the system, MoS2 was anchored onto a graphene aerogel paper and the composite was used directly as an LIB anode. The resultant additive-free MoS2/graphene aerogel paper composite exhibited long cyclic performance with 101.1% retention after 700 cycles, which demonstrates the importance of free-standing electrodes in enhancing cyclic

  16. Dual role of monolayer MoS2 in enhanced photocatalytic performance of hybrid MoS2/SnO2 nanocomposite

    Ding, Shuang-Shuang; Huang, Wei-Qing; Yang, Yin-Cai; Zhou, Bing-Xin; Hu, Wang-Yu; Long, Meng-Qiu; Peng, P.; Huang, Gui-Fang

    2016-05-01

    The enhanced photocatalytic performance of various MoS2-based nanomaterials has recently been observed, but the role of monolayer MoS2 is still not well elucidated at the electronic level. Herein, focusing on a model system, hybrid MoS2/SnO2 nanocomposite, we first present a theoretical elucidation of the dual role of monolayer MoS2 as a sensitizer and a co-catalyst by performing density functional theory calculations. It is demonstrated that a type-II, staggered, band alignment of ˜0.49 eV exists between monolayer MoS2 and SnO2 with the latter possessing the higher electron affinity, or work function, leading to the robust separation of photoexcited charge carriers between the two constituents. Under irradiation, the electrons are excited from Mo 4d orbitals to SnO2, thus enhancing the reduction activity of latter, indicating that the monolayer MoS2 is an effective sensitizer. Moreover, the Mo atoms, which are catalytically inert in isolated monolayer MoS2, turn into catalytic active sites, making the monolayer MoS2 to be a highly active co-catalyst in the composite. The dual role of monolayer MoS2 is expected to arise in other MoS2-semiconductor nanocomposites. The calculated absorption spectra can be rationalized by available experimental results. These findings provide theoretical evidence supporting the experimental reports and pave the way for developing highly efficient MoS2-based photocatalysts.

  17. Modeling accumulation capacitance-voltage characteristic of MoS2 thin flake transistors

    We report a theoretical investigation on the accumulation capacitance in MoS2 thin flake transistors using a two-valley band structure. To obtain the relevant two-valley band structure parameters, first-principles calculations are performed. Then, the capacitance-voltage characteristic in the accumulation layer is simulated by a self-consistent Poisson–Schrödinger solution. It is found that the occupation of the K valley in the conduction band has a significant contribution to the accumulation capacitance, especially in the strong accumulation layer. More importantly, the calculated results using a two-valley band structure is in good agreement with the published experimental data without any fitting parameters, highlighting that the inclusion of both the Q and K conduction band valley is necessary to understand the accumulation capacitance in the strong accumulation region. (paper)

  18. The capacity fading mechanism and improvement of cycling stability in MoS2-based anode materials for lithium-ion batteries

    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

  19. Enhanced second harmonic generation of MoS2 layers on a thin gold film.

    Zeng, Jianhua; Yuan, Maohui; Yuan, Weiguang; Dai, Qiaofeng; Fan, Haihua; Lan, Sheng; Tie, Shaolong

    2015-08-28

    The linear and nonlinear optical properties of thin MoS2 layers exfoliated on an Au/SiO2 substrate were investigated both numerically and experimentally. It was found that the MoS2 layers with different thicknesses exhibited different colors on the gold film. The reflection spectra of the MoS2 layers with different thicknesses were calculated by using the finite-difference time-domain technique and the corresponding chromaticity coordinates were derived. The electric field enhancement factors at both the fundamental light and the second harmonic were calculated and the enhancement factors for second harmonic generation (SHG) were estimated for the MoS2 layers with different thicknesses. Different from the MoS2 layers on a SiO2/Si substrate where the maximum SHG was observed in the single-layer MoS2, the maximum SHG was achieved in the 17 nm-thick MoS2 layer on the Au/SiO2 substrate. As compared with the MoS2 layers on the SiO2/Si substrate, a significant enhancement in SHG was found for the MoS2 layers on the Au/SiO2 substrate due to the strong localization of the electric field. More interestingly, it was demonstrated experimentally that optical data storage can be realized by modifying the SHG intensity of a MoS2 layer through thinning its thickness. PMID:26204257

  20. Adding the combination of CNTs and MoS2 into halogen-free flame retarding TPEE with enhanced the anti-dripping behavior and char forming properties

    Highlights: • Introduction the combination of the CNTs and MoS2 into P–N flame retarding TPEE. • Binary synergists for P–N flame retardants in TPEE. • Increase of char yield and form the stable carbonaceous char. - Abstract: In this paper, the nanocomposites thermoplastic polyester-ether elastomer (TPEE) with phosphorus–nitrogen (P–N) flame retardants, carbon nanotubes (CNTs) and molybdenum disulfide (MoS2) was prepared by melt blending. TPEE containing P–N flame retardant, CNTs and MoS2 achieved UL94 V-0 rating due to the better barrier effect of the special structure. The structure was supported by the result of rheological properties. The thermal stability was studied by thermal gravimetric analysis (TGA) and char residue characterization was investigated by SEM–EDX measurements. The results demonstrated that the combination of CNTs and MoS2 results in the increase of char yield and the formation of the thermally stable char which can effectively prevent in the dripping behavior during the burning process

  1. Photoluminescence wavelength variation of monolayer MoS2 by oxygen plasma treatment

    We performed nanoscale confocal photoluminescence (PL), Raman, and absorption spectral imaging measurements to investigate the optical and structural properties of molybdenum disulfide (MoS2) monolayers synthesized by chemical vapor deposition method and subjected to oxygen plasma treatment for 10 to 120 s under high vacuum (1.3 × 10−3 Pa). Oxygen plasma treatment induced red shifts of ~ 20 nm in the PL emission peaks corresponding to A and B excitons. Similarly, the peak positions corresponding to A and B excitons of the absorption spectra were red-shifted following oxygen plasma treatment. Based on the confocal PL, absorption, and Raman microscopy results, we suggest that the red-shifting of the A and B exciton peaks originated from shallow defect states generated by oxygen plasma treatment. - Highlights: • Effects of oxygen plasma on optical properties of monolayer MoS2 were investigated. • Confocal photoluminescence, Raman, and absorption spectral maps are presented. • Wavelength tuning up to ~ 20 nm for the peak emission wavelength was achieved

  2. Atomic defect states in monolayers of MoS2 and WS2

    Salehi, Saboura; Saffarzadeh, Alireza

    2016-09-01

    The influence of atomic vacancy defects at different concentrations on electronic properties of MoS2 and WS2 monolayers is studied by means of Slater-Koster tight-binding model with non-orthogonal sp3d5 orbitals and including the spin-orbit coupling. The presence of vacancy defects induces localized states in the bandgap of pristine MoS2 and WS2, which have potential to modify the electronic structure of the systems, depending on the type and concentration of the defects. It is shown that although the contribution of metal (Mo or W) d orbitals is dominant in the formation of midgap states, the sulphur p and d orbitals have also considerable contribution in the localized states, when metal defects are introduced. Our results suggest that Mo and W defects can turn the monolayers into p-type semiconductors, while the sulphur defects make the system a n-type semiconductor, in agreement with ab initio results and experimental observations.

  3. Thermoelectric Powerfactor and Density of States in 2D MoS2

    Hippalgaonkar, Kedar; Wang, Ying; Ye, Yu; Zhu, Hanyu; Wang, Yuan; Moore, Joel; Zhang, Xiang

    Efficient thermoelectric devices require high voltage generation from a temperature gradient and a large electrical conductivity, while maintaining a low thermal conductivity. For a given thermal conductivity and temperature, thermoelectric powerfactor is determined by the electronic structure of the material. Low dimensionality (1D and 2D) opens new routes to high powerfactor due to unique density of states (DOS) of confined electrons and holes. Emerging 2D transition metal dichalcogenide (TMDC) semiconductors represent a new class of thermoelectric materials not only because of their discretized density of states, but also due to their large effective masses and high carrier mobilities. We report a measured powerfactor of MoS2 as large as 8.5 mWm-1K-2 at room temperature, which is amongst the highest among all thermoelectric materials and we show that the powerfactor scales with mobility for 1L and 2L samples. Moreover, measurement of thermoelectric properties of monolayer MoS2 allows us to determine the confined 2D DOS near the conduction band edge and in the insulating state, which cannot be measured by electrical conductivity alone. The demonstrated record high electronically tunable powerfactor in 2D TMDCs holds promise for efficient thermoelectric energy conversion.

  4. Microscopic and spectroscopic investigation of MoS2 nanotubes/P3HTnanocomposites

    Blends of conductive polymer poly(3-hexylthiophene) (P3HT) and size controlled MoS2 nanotubes (NTs) were prepared focusing on procedures which do not alter the electrical and optical properties of nanotubes, i.e., without surfactants. After disassembly of as-grown hedgehog-like self-assemblies of the MoS2 NTs, relatively homogeneous dispersions of the NTs in P3HT were prepared. Thin films of these blends were prepared via spin coating. The NTs were found efficiently wetted by the P3HT and nearly completely immersed in the films. The surface structure was composed of pure P3HT lamellae. Photoluminescence spectra taken on P3HT/MoS2 NT thin films revealed a quenching effect, which depends on the concentration of NTs. Results of optical microscopy and spectroscopy investigations, scanning tunnelling microscopy and scanning electron microscopy studies are shown. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Graphene - ferroelectric and MoS2 - ferroelectric heterostructures for memory applications

    Lipatov, Alexey; Sharma, Pankaj; Gruverman, Alexei; Sinitskii, Alexander

    In recent years there has been an unprecedented interest in two-dimensional (2D) materials with unique physical and chemical properties that cannot be found in their three-dimensional (3D) counterparts. One of the important advantages of 2D materials is that they can be easily integrated with other 2D materials and functional films, resulting in multilayered structures with new properties. We fabricated and tested electronic and memory properties of field-effect transistors (FETs) based on a single-layer graphene combined with lead zirconium titanate (PZT) substrate. Previously studied graphene-PZT devices exhibited an unusual electronic behavior such as clockwise hysteresis of electronic transport, in contradiction with counterclockwise polarization dependence of PZT. We investigated how the interplay of polarization and interfacial phenomena affects the electronic behavior and memory characteristics of graphene-PZT FETs, explain the origin of unusual clockwise hysteresis and experimentally demonstrate a reversed polarization-dependent hysteresis of electronic transport. In addition we fabricated and tested properties of MoS2-PZT FETs which exhibit a large hysteresis of electronic transport with high ON/OFF ratios. We demonstrate that MoS2-PZT memories have a number of advantages over commercial FeRAMs, such as nondestructive data readout, low operation voltage, wide memory window and the possibility to write and erase them both electrically and optically.

  6. Pd-gate MOS sensor for detection of methanol and propanol

    Preeti Pandey; J.K.Srivastava; V.N.Mishra; R.Dwivedi

    2011-01-01

    The present paper focused on the detection of methanol and propanol using Pd-gate metal-oxide-semiconductor(MOS)sensor.Surface morphology and composition of the gate film were studied by scanning electron microscopy(SEM)and atomic force microscopy(AFM).The response of the sensor for propanol and methanol was measured as shift in capacitance-voltage(C-V) and conductance-voltage(G-V) curves of the MOS structure.The sensitivity of the sensor towards methanol was found to be greater than that towards propanol.It was 58.2% for methanol and 32% for propanol(at 0.6 V,1 MHz)in terms of capacitance measurements,while in terms of conductance results the sensitivity was found to be 57.2% for methanol and 38.9% for propanol at 1 kHz.The discontinuities or cracks present in the microstructure of the gate material are believed to be mainly responsible for the high sensitivity of the sensor,going with the decomposition of gas molecules and subsequent hydrogen permeation through Pd.

  7. DPFFs: C2MOS Direct Path Flip-Flops for Process-Resilient Ultradynamic Voltage Scaling

    Myeong-Eun Hwang

    2016-01-01

    Full Text Available We propose two master-slave flip-flops (FFs that utilize the clocked CMOS (C2MOS technique with an internal direct connection along the main signal propagation path between the master and slave latches and adopt an adaptive body bias technique to improve circuit robustness. C2MOS structure improves the setup margin and robustness while providing full compatibility with the standard cell characterization flow. Further, the direct path shortens the logic depth and thus speeds up signal propagation, which can be optimized for less power and smaller area. Measurements from test circuits fabricated in 130 nm technology show that the proposed FF operates down to 60 mV, consuming 24.7 pW while improving the propagation delay, dynamic power, and leakage by 22%, 9%, and 13%, respectively, compared with conventional FFs at the iso-output-load condition. The proposed FFs are integrated into an 8×8 FIR filter which successfully operates all the way down to 85 mV.

  8. MOS correction of GCM- and RCM-simulated daily precipitation

    Eden, Jonathan; Widmann, Martin; Wong, Geraldine; Maraun, Douglas; Vrac, Mathieu; Kent, Thomas

    2013-04-01

    Understanding long-term changes in daily precipitation characteristics, particularly those associated with extreme events, is an important component of climate change science and impact assessment. Estimates of such changes are required at local scales where impacts are most keenly felt. However, the limited spatial resolution of General Circulation Models (GCMs) makes direct estimates of future daily precipitation unrealistic. A popular downscaling approach is to use GCMs to drive high-resolution Regional Climate Models (RCMs). Whilst able to simulate precipitation characteristics at smaller scales, RCMs do not represent local variables and remain limited by systematic errors and biases. It is possible to apply statistical corrections, known as Model Output Statistics (MOS), to RCM-simulated precipitation. The simplest form of MOS (including bias correction) follows a 'distribution-wise' approach in which the statistical link is derived between long-term distributions of simulated and observed variables. However, more sophisticated MOS methods may be performed 'event-wise' using, for example, multiple linear regression to derive links between simulated and observed sequences of day-to-day weather. This approach requires a fitting period in which the simulated temporal evolution of large-scale weather states matches that of the real world and is thus limited to either reanalysis-driven RCMs or nudged GCM simulations. It is unclear to what extent MOS can be used to correct daily precipitation directly from GCMs, thus removing the computationally challenging RCM step from the downscaling process. Here, we present and cross-validate a stochastic, event-wise MOS method for both GCM- and RCM-simulated precipitation. A 'mixture' model, combining gamma and generalised Pareto distributions, is used to represent the complete (extreme and non-extreme) precipitation distribution. This is combined with a vector generalised linear model (VGLM) in order to estimate the

  9. Broadband and enhanced nonlinear optical response of MoS2/graphene nanocomposites for ultrafast photonics applications

    Jiang, Yaqin; Miao, Lili; Jiang, Guobao; Chen, Yu; Qi, Xiang; Jiang, Xiao-Fang; Zhang, Han; Wen, Shuangchun

    2015-11-01

    Due to their relatively high compatibility with specific photonic structures, strong light-matter interactions and unique nonlinear optical response, two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides, are attractive for ultrafast photonics applications. Here, we fabricate MoS2/graphene nanocomposites by a typical hydrothermal method. In addition, we systematically investigate their nonlinear optical responses. Our experiments indicate that the combined advantages of ultrafast relaxation, a broadband response from graphene, and the strong light-matter interaction from MoS2, can be integrated together by composition. The optical properties in terms of carrier relaxation dynamics, saturation intensity and modulation depth suggest great potential for the MoS2/graphene nanocomposites in photonics applications. We have further fabricated 2D nanocomposites based optical saturable absorbers and integrated them into a 1.5 μm Erbium-doped fiber laser to demonstrate Q-switched and mode-locked pulse generation. The fabrication of 2D nanocomposites assembled from different types of 2D materials, via this simple and scalable growth approach, paves the way for the formation and tuning of new 2D materials with desirable photonic properties and applications.

  10. GaN MOS-HEMT Using Ultra-Thin Al2O3 Dielectric Grown by Atomic Layer Deposition

    YUE Yuan-Zheng; HAO Yue; FENG Qian; ZHANG Jin-Cheng; MA Xiao-Hua; NI Jin-Yu

    2007-01-01

    @@ We report a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with atomic layer deposited (ALD) Al2O3 gate dielectric. Based on the previous work [Appl. Phys. Lett. 86 (2005) 063501] of Ye et al. By decreeing the thickness of the gate oxide to 3.5nm and optimizing the device fabrication process, the device with maximum transconductance of 150mS/mm is produced and discussed in comparison with the result of 100mS/mm of Ye et al. The corresponding drain current density in the 0.8-μm-gate-length MOS-HEMT is 800mA/mm at the gate bias of 3.0 V. The gate leakage is two orders of magnitude lower than that of the conventional AlGaN/GaN HEMT. The excellent characteristics of this novel MOS-HEMT device structure with ALD Al2O3 gate dielectric are presented.

  11. Polymer-Derived Ceramic Functionalized MoS2 Composite Paper as a Stable Lithium-Ion Battery Electrode

    David, L.; Bhandavat, R.; Barrera, U.; Singh, G.

    2015-04-01

    A facile process is demonstrated for the synthesis of layered SiCN-MoS2 structure via pyrolysis of polysilazane functionalized MoS2 flakes. The layered morphology and polymer to ceramic transformation on MoS2 surfaces was confirmed by use of electron microscopy and spectroscopic techniques. Tested as thick film electrode in a Li-ion battery half-cell, SiCN-MoS2 showed the classical three-stage reaction with improved cycling stability and capacity retention than neat MoS2. Contribution of conversion reaction of Li/MoS2 system on overall capacity was marginally affected by the presence of SiCN while Li-irreversibility arising from electrolyte decomposition was greatly suppressed. This is understood as one of the reasons for decreased first cycle loss and increased capacity retention. SiCN-MoS2 in the form of self-supporting paper electrode (at 6 mg.cm-2) exhibited even better performance, regaining initial charge capacity of approximately 530 mAh.g-1 when the current density returned to 100 mA.g-1 after continuous cycling at 2400 mA.g-1 (192 mAh.g-1). MoS2 cycled electrode showed mud-cracks and film delamination whereas SiCN-MoS2 electrodes were intact and covered with a uniform solid electrolyte interphase coating. Taken together, our results suggest that molecular level interfacing with precursor-derived SiCN is an effective strategy for suppressing the metal-sulfide/electrolyte degradation reaction at low discharge potentials.

  12. New quantum spin Hall insulator in two-dimensional MoS2 with periodically distributed pores

    Liu, Peng-Fei; Zhou, Liujiang; Frauenheim, Thomas; Wu, Li-Ming

    2016-02-01

    MoS2, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS2 (g-MoS2), consisting of MoS2 squares and hexagons. g-MoS2 has a nontrivial gap as large as 109 meV, comparable with previously reported 1T'-MoS2 (80 meV) and so-MoS2 (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS2 originates from the pure d-d band inversion, different from the conventional band inversion between s-p, p-p or d-p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications.MoS2, one of the transition metal dichalcogenides (TMDs), has gained a lot of attention due to its excellent semiconductor characteristics and potential applications. Here, based on density functional theory methods, we predict a novel 2D QSH insulator in the porous allotrope of monolayer MoS2 (g-MoS2), consisting of MoS2 squares and hexagons. g-MoS2 has a nontrivial gap as large as 109 meV, comparable with previously reported 1T'-MoS2 (80 meV) and so-MoS2 (25 meV). We demonstrate that the origin of the 2D QSH effect in g-MoS2 originates from the pure d-d band inversion, different from the conventional band inversion between s-p, p-p or d-p orbitals. The new polymorph greatly enriches the TMD family and its stabilities are confirmed using phonon spectrum analysis. In particular, its porous structure endows it with the potential for efficient gas separation and energy storage applications. Electronic supplementary information (ESI) available: Geometry for graphene, T-graphene, graphenylene, h-MoS2, so-MoS2 and g-MoS2, ab initio molecular dynamics simulations, shapes of the three

  13. Covalent Modification of MoS2 with Poly(N-vinylcarbazole) for Solid-State Broadband Optical Limiters.

    Cheng, Hongxia; Dong, Ningning; Bai, Ting; Song, Yi; Wang, Jun; Qin, Yuanhao; Zhang, Bin; Chen, Yu

    2016-03-18

    New soluble MoS2 nanosheets covalently functionalized with poly(N-vinylcarbazole) (MoS2-PVK) were in situ synthesized for the first time. In contrast to MoS2 and MoS2 /PVK blends, both the solution of MoS2 -PVK in DMF and MoS2-PVK/poly(methyl methacrylate) (PMMA) film show superior nonlinear optical and optical limiting responses. The MoS2-PVK/PMMA film shows the largest nonlinear coefficients (βeff) of about 917 cm GW(-1) at λ=532 nm (cf. 100.69 cm GW(-1) for MoS2/PMMA and 125.12 cm GW(-1) for MoS2/PVK/PMMA) and about 461 cm GW(-1) at λ=1064 nm (cf. -48.92 cm GW(-1) for MoS2/PMMA and 147.56 cm GW(-1) for MoS2/PVK/PMMA). A larger optical limiting effect, with thresholds of about 0.3 GW cm(-2) at λ=532 nm and about 0.5 GW cm(-2) at λ=1064 nm, was also achieved from the MoS2-PVK/PMMA film. These values are among the highest reported for MoS2-based nonlinear optical materials. These results show that covalent functionalization of MoS2 with polymers is an effective way to improve nonlinear optical responses for efficient optical limiting devices. PMID:26891470

  14. Nanoscale plasmonic phenomena in CVD-grown MoS(2) monolayer revealed by ultra-broadband synchrotron radiation based nano-FTIR spectroscopy and near-field microscopy.

    Patoka, Piotr; Ulrich, Georg; Nguyen, Ariana E; Bartels, Ludwig; Dowben, Peter A; Turkowski, Volodymyr; Rahman, Talat S; Hermann, Peter; Kästner, Bernd; Hoehl, Arne; Ulm, Gerhard; Rühl, Eckart

    2016-01-25

    Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum disulfide (MoS(2)) on silicon dioxide (SiO(2)) are reported. A scattering type scanning near-field optical microscope (s-SNOM) with a broadband synchrotron radiation (SR) infrared source was used. We also present complementary optical mapping using tunable CO(2)-laser radiation. Specifically, there is a correlation of the topography of well-defined MoS(2) islands grown by chemical vapor deposition, as determined by atomic force microscopy, with the infrared (IR) signature of MoS(2). The influence of MoS(2) islands on the SiO(2) phonon resonance is discussed. The results reveal the plasmonic character of the MoS(2) structures and their interaction with the SiO(2) phonons leading to an enhancement of the hybridized surface plasmon-phonon mode. A theoretical analysis shows that, in the case of monolayer islands, the coupling of the MoS(2) optical plasmon mode to the SiO(2) surface phonons does not affect the infrared spectrum significantly. For two-layer MoS(2), the coupling of the extra inter-plane acoustic plasmon mode with the SiO(2) surface transverse phonon leads to a remarkable increase of the surface phonon peak at 794 cm(-1). This is in agreement with the experimental data. These results show the capability of the s-SNOM technique to study local multiple excitations in complex non-homogeneous structures. PMID:26832499

  15. Rare-earth implanted MOS devices for silicon photonics. Microstructural, electrical and optoelectronic properties

    Rebohle, Lars; Skorupa, Wolfgang [Forschungszentrum Rossendorf e.V. (FZR), Dresden (Germany). Inst. fuer Ionenstrahlphysik und Materialforschung

    2010-07-01

    The book concentrates on the microstructural, electric and optoelectronic properties of rare-earth implanted MOS structures and their use as light emitters in potential applications. It describes the structural formation processes in the gate oxide during fabrication and under operation, how this microstructure development will affect the electrical device performance and how both microstructure and electrical characteristics determine the optoelectronic features of the light emitters. However, most of the discussed physical processes as well as the described fabrication methods and device characterization techniques are of general interest and are beyond the scope of this type of light emitter. The book will be of value to engineers, physicists, and scientists dealing either with Si based photonics in particular or optoelectronic device fabrication and characterization in general. (orig.)

  16. Diffusion-Mediated Synthesis of MoS2/WS2 Lateral Heterostructures.

    Bogaert, Kevin; Liu, Song; Chesin, Jordan; Titow, Denis; Gradečak, Silvija; Garaj, Slaven

    2016-08-10

    Controlled growth of two-dimensional transition metal dichalcogenide (TMD) lateral heterostructures would enable on-demand tuning of electronic and optoelectronic properties in this new class of materials. Prior to this work, compositional modulations in lateral TMD heterostructures have been considered to depend solely on the growth chronology. We show that in-plane diffusion can play a significant role in the chemical vapor deposition of MoS2/WS2 lateral heterostructures leading to a variety of nontrivial structures whose composition does not necessarily follow the growth order. Optical, structural, and compositional studies of TMD crystals captured at different growth temperatures and in different diffusion stages suggest that compositional mixing versus segregation are favored at high and low growth temperatures, respectively. The observed diffusion mechanism will expand the realm of possible lateral heterostructures, particularly ones that cannot be synthesized using traditional methods. PMID:27438807

  17. Developments in MOS CCDs for X-ray astronomy

    Pool, P J; Burt, D J; Holland, A D

    1999-01-01

    MOS CCDs with excellent X-ray spectroscopic performance have been supplied to both the EPIC and RGS instruments on XMM. Future X-ray astronomy instruments are planned with larger focal planes, for use with high throughput optics. To perform useful imaging spectroscopy, the array will require large area devices, optimised for the application and operated at significantly higher data rates than in previous instruments, but with similar noise performance. Most of the enabling technologies for the realisation of such arrays have been demonstrated in MOS CCDs. This paper will provide examples of advances that have already been demonstrated since X-ray CCDs of the current generation were designed and will describe developments which can be expected in the near future. In particular, we will refer to device size, construction of multi-chip arrays, read noise and quantum efficiency.

  18. Effects on focused ion beam irradiation on MOS transistors

    The effects of irradiation from a focused ion beam (FIB) system on MOS transistors are reported systematically for the first time. Three MOS transistor technologies, with 0.5, 1, and 3 μm minimum feature sizes and with gate oxide thicknesses ranging from 11 to 50 nm, were analyzed. Significant shifts in transistor parameters (such as threshold voltage, transconductance, and mobility) were observed following irradiation with a 30 keV Ga+ focused ion beam with ion doses varying by over 5 orders of magnitude. The apparent damage mechanism (which involved the creation of interface traps, oxide trapped charge, or both) and extent of damage were different for each of the three technologies investigated

  19. Effects on focused ion beam irradiation on MOS transistors

    Campbell, A.N.; Peterson, K.A.; Fleetwood, D.M.; Soden, J.M.

    1997-04-01

    The effects of irradiation from a focused ion beam (FIB) system on MOS transistors are reported systematically for the first time. Three MOS transistor technologies, with 0.5, 1, and 3 {mu}m minimum feature sizes and with gate oxide thicknesses ranging from 11 to 50 nm, were analyzed. Significant shifts in transistor parameters (such as threshold voltage, transconductance, and mobility) were observed following irradiation with a 30 keV Ga{sup +} focused ion beam with ion doses varying by over 5 orders of magnitude. The apparent damage mechanism (which involved the creation of interface traps, oxide trapped charge, or both) and extent of damage were different for each of the three technologies investigated.

  20. Focused Ion Beam Induced Effects on MOS Transistor Parameters

    Abramo, Marsha T.; Antoniou, Nicholas; Campbell, Ann N.; Fleetwood, Daniel M.; Hembree, Charles E.; Jessing, Jeffrey R.; Soden, Jerry M.; Swanson, Scot E.; Tangyunyong, Paiboon; Vanderlinde, William E.

    1999-07-28

    We report on recent studies of the effects of 50 keV focused ion beam (FIB) exposure on MOS transistors. We demonstrate that the changes in value of transistor parameters (such as threshold voltage, V{sub t}) are essentially the same for exposure to a Ga+ ion beam at 30 and 50 keV under the same exposure conditions. We characterize the effects of FIB exposure on test transistors fabricated in both 0.5 {micro}m and 0.225 {micro}m technologies from two different vendors. We report on the effectiveness of overlying metal layers in screening MOS transistors from FIB-induced damage and examine the importance of ion dose rate and the physical dimensions of the exposed area.

  1. Atomic-layer soft plasma etching of MoS2

    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 (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.

  2. Micro-irradiation experiments in MOS transistors using synchrotron radiation

    Spatially-resolved total-dose degradation has been performed in MOS transistors by focusing x-ray synchrotron radiation on the gate electrode with micrometer resolution. The influence of the resulting permanent degradation on device electrical properties has been analyzed using current-voltage and charge pumping measurements, in concert with optical characterization (hot-carrier luminescence) and one-dimensional device simulation. (authors)

  3. Characteristics of tungsten gate devices for mos VLSIs

    Recently, refractory metals, such as W and Mo, with low resistivity and high melting points have received keen interest as materials for gate electrodes and interconnects for MOS VLSI devices. It is commonly believed that MOS devices with refractory metal gates deposited from sputter sources have low reliability due to mobile ion contamination. In this work, it was confirmed that W gates with commercially available W sputtering targets introduced high level mobile charges into the gate oxide. It was also found that the rates of degradation of W gate MOS transistors due to hot carriers were higher than those of poly Si gates, and the internal stresses in W gates increased the degradation rates. Therefore, the authors have developed a high-purity W sputtering target fabrication technique through the use of electron melting. A W gate annealing technique was developed to reduce internal stress in W films. Through these techniques, the above-mentioned problems can be eliminated and W gate devices with characteristics comparable to those of poly Si gates can be produced. The minimum feature size of very large scale integrated (VLSI) circuits has been reduced to one micrometer or less, while at the same time the number of elements per chip continues to increase. Under the present D-RAM developmental situation, a 256kb D-RAM has reached the stage of practical use, and 1Mb D-RAM prototypes have been examined and tested by a number of LSI manufacturers. These developments have impose severe demands on the materials and interconnects in MOS VLSIs

  4. MOS PARAMETER EXTRACTION AND OPTIMIZATION WITH GENETIC ALGORITHM

    BAŞAK, M.Emin; KUNTMAN, Ayten; Kuntman, Hakan

    2010-01-01

    Extracting an optimal set of parameter values for a MOS device is great importance in contemporary technology is acomplex problem. Traditional methods of parameter extraction can produce far from optimal solutions because of thepresence of local optimum in the solution space. Genetic algorithms are well suited for finding near optimal solutions inirregular parameter spaces.In this study*, We have applied a genetic algorithm to the problem of device model parameter extraction and are able topr...

  5. A Low-Voltage Floating-Gate MOS Biquad

    Rodríguez-Villegas, Esther O.; Alberto Yúfera; Adoración Rueda

    2001-01-01

    A second-order gm-C filter based on the Floating-Gate MOS (FGMOS) technique is presented. It uses a new fully differential transconductor and works at 2 V of voltage supply with a full differential input linear range and a THD below 1%. Programming and tuning are performed by means of a single voltage signal. The transconductor incorporates a novel Common-Mode Feedback Circuit (CMFB) based also on FGMOS transistors.

  6. Unusual reactivity of MoS2 nanosheets

    Mondal, Biswajit; Som, Anirban; Chakraborty, Indranath; Baksi, Ananya; Sarkar, Depanjan; Pradeep, Thalappil

    2016-05-01

    The reactivity of the 2D nanosheets of MoS2 with silver ions in solution, leading to their spontaneous morphological and chemical transformations, is reported. This unique reactivity of the nanoscale form of MoS2 was in stark contrast to its bulk counterpart. While the gradual morphological transformation involving several steps has been captured with an electron microscope, precise chemical identification of the species involved was achieved by electron spectroscopy and mass spectrometry. The energetics of the system investigated supports the observed chemical transformation. The reaction with mercury and gold ions shows similar and dissimilar reaction products, respectively and points to the stability of the metal-sulphur bond in determining the chemical compositions of the final products.The reactivity of the 2D nanosheets of MoS2 with silver ions in solution, leading to their spontaneous morphological and chemical transformations, is reported. This unique reactivity of the nanoscale form of MoS2 was in stark contrast to its bulk counterpart. While the gradual morphological transformation involving several steps has been captured with an electron microscope, precise chemical identification of the species involved was achieved by electron spectroscopy and mass spectrometry. The energetics of the system investigated supports the observed chemical transformation. The reaction with mercury and gold ions shows similar and dissimilar reaction products, respectively and points to the stability of the metal-sulphur bond in determining the chemical compositions of the final products. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00878j

  7. Enhancement mode AlGaN/GaN MOS high-electron-mobility transistors with ZrO2 gate dielectric deposited by atomic layer deposition

    Anderson, Travis J.; Wheeler, Virginia D.; Shahin, David I.; Tadjer, Marko J.; Koehler, Andrew D.; Hobart, Karl D.; Christou, Aris; Kub, Francis J.; Eddy, Charles R., Jr.

    2016-07-01

    Advanced applications of AlGaN/GaN high-electron-mobility transistors (HEMTs) in high-power RF and power switching are driving the need for insulated gate technology. We present a metal–oxide–semiconductor (MOS) gate structure using atomic-layer-deposited ZrO2 as a high-k, high-breakdown gate dielectric for reduced gate leakage and a recessed barrier structure for enhancement mode operation. Compared to a Schottky metal-gate HEMT, the recessed MOS-HEMT structure demonstrated a reduction in the gate leakage current by 4 orders of magnitude and a threshold voltage shift of +6 V to a record +3.99 V, enabled by a combination of a recessed barrier structure and negative oxide charge.

  8. Monolayer MoS2 self-switching diodes

    Al-Dirini, Feras; Hossain, Faruque M.; Mohammed, Mahmood A.; Hossain, Md Sharafat; Nirmalathas, Ampalavanapillai; Skafidas, Efstratios

    2016-01-01

    This paper presents a new molybdenum disulphide (MoS2) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS2 monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS2 results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70.

  9. Bending response of single layer MoS2

    Xiong, Si; Cao, Guoxin

    2016-03-01

    Using molecular mechanics (or dynamics) simulations, three different approaches, including the targeted molecular mechanics, four-point bending and nanotube methods, are employed to investigate the bending response of single layer MoS2 (SLMoS2), among which four-point bending is the most accurate approach to determine the bending stiffness according to the continuum theory. It is found that when the bending curvature radius is large enough (e.g. >4 nm), three approaches will give the same bending stiffness of SLMoS2 and the bending behavior is isotropic for SLMoS2, whereas the nanotube method with small tubes (e.g. theory, the revised Stillinger-Weber (SW) and reactive empirical bond-order (REBO) potentials can give the reasonable bending stiffness of SLMoS2 (8.7-13.4 eV) as well as the effective deformed conformation. In addition, since the Mo-S bond deformation of SLMoS2 under bending is similar to that under in-plane tension/compression, the continuum bending theory can quite accurately predict the bending stiffness of SLMoS2 if a reasonable thickness of SLMoS2 is given. For SLMoS2, the reasonable thickness should be larger than the distance between its two S atomic planes and lower than the distance between two Mo atomic planes of bulk MoS2 crystal, e.g. 0.375-0.445 nm.

  10. Monolayer MoS2 self-switching diodes

    This paper presents a new molybdenum disulphide (MoS2) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS2 monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS2 results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70

  11. c-Mos forces the mitotic cell cycle to undergo meiosis II to produce haploid gametes

    Tachibana, Kazunori; Tanaka, Daisuke; Isobe, Tomohiro; Kishimoto, Takeo

    2000-01-01

    The meiotic cycle reduces ploidy through two consecutive M phases, meiosis I and meiosis II, without an intervening S phase. To maintain ploidy through successive generations, meiosis must be followed by mitosis after the recovery of diploidy by fertilization. However, the coordination from meiotic to mitotic cycle is still unclear. Mos, the c-mos protooncogene product, is a key regulator of meiosis in vertebrates. In contrast to the previous observation that Mos f...

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

    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.

  13. Synthesis of MoS2 @C Nanotubes Via the Kirkendall Effect with Enhanced Electrochemical Performance for Lithium Ion and Sodium Ion Batteries.

    Zhang, Xueqian; Li, Xiaona; Liang, Jianwen; Zhu, Yongchun; Qian, Yitai

    2016-05-01

    A MoS2 @C nanotube composite is prepared through a facile hydrothermal method, in which the MoS2 nanotube and amorphous carbon are generated synchronically. When evaluated as an anode material for lithium ion batteries (LIB), the MoS2 @C nanotube manifests an enhanced capacity of 1327 mA h g(-1) at 0.1 C with high initial Coulombic efficiency (ICE) of 92% and with capacity retention of 1058.4 mA h g(-1) (90% initial capacity retention) after 300 cycles at a rate of 0.5 C. A superior rate capacity of 850 mA h g(-1) at 5 C is also obtained. As for sodium ion batteries, a specific capacity of 480 mA h g(-1) at 0.5 C is achieved after 200 cycles. The synchronically formed carbon and stable hollow structure lead to the long cycle stability, high ICE, and superior rate capability. The good electrochemical behavior of MoS2 @C nanotube composite suggests its potential application in high-energy LIB. PMID:26997521

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

    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 m(2) 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. PMID:27108967

  15. Magnetic MoS2 pizzas and sandwiches with Mnn (n = 1-4) cluster toppings and fillings: A first-principles investigation

    Zhang, Meng; Huang, Zhongjia; Wang, Xiao; Zhang, Hongyu; Li, Taohai; Wu, Zhaolong; Luo, Youhua; Cao, Wei

    2016-01-01

    The inorganic layered crystal (ILC) MoS2 in low dimensions is considered as one of the most promising and efficient semiconductors. To enable the magnetism and keep intrinsic crystal structures, we carried out a first-principles study of the magnetic and semiconductive monolayer MoS2 adsorbed with the Mnn (n = 1-4) clusters, and bilayer MoS2 intercalated with the same clusters. Geometric optimizations of the Mnn@MoS2 systems show the complexes prefer to have Mnn@MoS2(M) pizza and Mnn@MoS2(B) sandwich forms in the mono- and bi-layered cases, respectively. Introductions of the clusters will enhance complex stabilities, while bonds and charge transfers are found between external Mn clusters and the S atoms in the hosts. The pizzas have medium magnetic moments of 3, 6, 9, 4 μB and sandwiches of 3, 2, 3, 2 μB following the manganese numbers. The pizzas and sandwiches are semiconductors, but with narrower bandgaps compared to their corresponding pristine hosts. Direct bandgaps were found in the Mnn@MoS2(M) (n = 1,4) pizzas, and excitingly in the Mn1@MoS2(B) sandwich. Combining functional clusters to the layered hosts, the present work shows a novel material manipulation strategy to boost semiconductive ILCs applications in magnetics.

  16. Effect of processing parameters on microstructure of MoS2 ultra-thin films synthesized by chemical vapor deposition method

    Yang Song

    2015-06-01

    Full Text Available MoS2 ultra-thin layers are synthesized using a chemical vapor deposition method based on the sulfurization of molybdenum trioxide (MoO3. The ultra-thin layers are characterized by X-ray diffraction (XRD, photoluminescence (PL spectroscopy and atomic force microscope (AFM. Based on our experimental results, all the processing parameters, such as the tilt angle of substrate, applied voltage, heating time and the weight of source materials have effect on the microstructures of the layers. In this paper, the effects of such processing parameters on the crystal structures and morphologies of the as-grown layers are studied. It is found that the film obtained with the tilt angle of 0.06° is more uniform. A larger applied voltage is preferred to the growth of MoS2 thin films at a certain heating time. In order to obtain the ultra-thin layers of MoS2, the weight of 0.003 g of source materials is preferred. Under our optimal experimental conditions, the surface of the film is smooth and composed of many uniformly distributed and aggregated particles, and the ultra-thin MoS2 atomic layers (1∼10 layers covers an area of more than 2 mm×2 mm.

  17. Simultaneous Hosting of Positive and Negative Trions and the Enhanced Direct Band Emission in MoSe2/MoS2 Heterostacked Multilayers.

    Kim, Min Su; Seo, Changwon; Kim, Hyun; Lee, Jubok; Luong, Dinh Hoa; Park, Ji-Hoon; Han, Gang Hee; Kim, Jeongyong

    2016-06-28

    Heterostacking of layered transition-metal dichalcogenide (LTMD) monolayers (1Ls) offers a convenient way of designing two-dimensional exciton systems. Here we demonstrate the simultaneous hosting of positive trions and negative trions in heterobilayers made by vertically stacking 1L MoSe2 and 1L MoS2. The charge transfer occurring between the 1Ls of MoSe2 and MoS2 converted the polarity of trions in 1L MoSe2 from negative to positive, resulting in the presence of positive trions in the 1L MoSe2 and negative trions in the 1L MoS2 of the same heterostacked bilayer. Significantly enhanced MoSe2 photoluminescence (PL) in the heterostacked bilayers compared to the PL of 1L MoSe2 alone suggests that, unlike other previously reported heterostacked bilayers, direct band transition of 1L MoSe2 in heterobilayer was enhanced after the vertical heterostacking. Moreover, by inserting hexagonal BN monolayers between 1L MoSe2 and 1L MoS2, we were able to adjust the charge transfer to maximize the MoSe2 PL of the heteromultilayers and have achieved a 9-fold increase of the PL emission. The enhanced optical properties of our heterostacked LTMDs suggest the exciting possibility of designing LTMD structures that exploit the superior optical properties of 1L LTMDs. PMID:27187667

  18. Construction of 3D flower-like MoS2 spheres with nanosheets as anode materials for high-performance lithium ion batteries

    In this work, we constructed 3D flower-like MoS2 spheres with nanosheets (less than 10 nm) by a simple alcohol-assisted solvothermal route. It was found that the presence of alcohol enhanced the dispersity of MoS2 samples, and the distilled water facilitated the formation of nanosheets through varying the volume ratio of alcohol and distilled water. The prepared MoS2 samples delivered high initial discharge capacity (1346 mA h g−1 at a current density of 100 mA g−1), good coulombic efficiency (77.49% retention for the first cycle and ∼100% for the subsequent cycles), excellent cycling performance (947 mA h g−1 at 100 mA g−1 after 50 cycles) and remarkable rate behavior as anode materials for lithium ion batteries. The superior behavior of MoS2 samples for lithium ion batteries can be ascribed to the thin nanosheets, high specific surface area and their unique layered structure

  19. Potential application of mono/bi-layer molybdenum disulfide (MoS2) sheet as an efficient transparent conducting electrode in silicon heterojunction solar cells

    Chaudhary, Rimjhim; Patel, Kamlesh; Sinha, Ravindra K.; Kumar, Sanjeev; Tyagi, Pawan K.

    2016-07-01

    In this paper, we have simulated the structure of n-type MoS2/silicon heterojunction solar cell and studied its function under different conditions. The optimization of parameters of the cell's layer has been carried out by using AFORS-HET software. In the present study, MoS2 has been considered as 3-D in nature instead of the reported 2-D nature. In order to ensure the formation of Schottky junction, electric contact has been made along the c-axis to collect the minority charge carriers. After optimizing the various parameters of n-type single layer MoS2, power efficiency of 12.44% has been achieved at the room temperature, which has further decreased to 9.042% as the layer number has increased up to 40. Furthermore, after optimizing the parameters of silicon wafer maximum efficiency of 16.4% has been achieved. Temperature dependence of the cell performance has also been studied and the maximum efficiency has been achieved at 300 K. In the present study, we have demonstrated that n-type ultrathin layer of MoS2 can be used as an excellent transparent conducting electrode.

  20. Radiation effects on MOS and bipolar devices by 8 MeV protons, 60 MeV Br ions and 1 MeV electrons

    The radiation effects of the metal-oxide-semiconductor (MOS) and the bipolar devices are characterised using 8 MeV protons, 60 MeV Br ions and 1 MeV electrons. Key parameters are measured in-situ and compared for the devices. The ionising and nonionising energy losses of incident particles are calculated using the Geant4 and the stopping and range of ions in matter code. The results of the experiment and energy loss calculation for different particles show that different incident particles may give different contributions to MOS and bipolar devices. The irradiation particles, which cause a larger displacement dose within the same chip depth of bipolar devices at a given total dose, would generate more severe damage to the voltage parameters of the bipolar devices. On the contrary, the irradiation particles, which cause larger ionising damage in the gate oxide, would generate more severe damage to MOS devices. In this investigation, we attempt to analyse the sensitivity to radiation damage of the different parameter of the MOS and bipolar devices by comparing the irradiation experimental data and the calculated results using Geant4 and SRIM code. (condensed matter: structure, thermal and mechanical properties)

  1. Cross-Calibration of the XMM-Newton EPIC pn & MOS On-Axis Effective Areas Using 2XMM Sources

    Read, A. M.; Guainazzi, M.; Sembay, S.

    2014-01-01

    We aim to examine the relative cross-calibration accuracy of the on-axis effective areas of the XMM-Newton EPIC pn and MOS instruments. Spectra from a sample of 46 bright, high-count, non-piled-up isolated on-axis point sources are stacked together, and model residuals are examined to characterize the EPIC MOS-to-pn inter-calibration. The MOS1-to-pn and MOS2-to-pn results are broadly very similar. The cameras show the closest agreement below 1 keV, with MOS excesses over pn of 0-2% (MOS1/pn) ...

  2. Density functional theory calculation of edge stresses in monolayer MoS$_2$

    Qi, Zenan; Cao, Penghui; Park, Harold S.

    2013-01-01

    We utilize density functional theory to calculate the edge energy and edge stress for monolayer MoS$_{2}$ nanoribbons. In contrast to previous reports for graphene, for both armchair and zigzag chiralities, the edge stresses for MoS$_{2}$ nanoribbons are found to be tensile, indicating that their lowest energy configuration is one of compression in which Mo-S bond lengths are shorter than those in a bulk, periodic MoS$_{2}$ monolayer. The edge energy and edge stress is found to converge for b...

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

    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

  4. Photothermoelectric and photovoltaic effects both present in MoS2

    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.

  5. Towards intrinsic phonon transport in single-layer MoS2

    Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuanfeng; Zhang, Xiangchao; Zhu, Heyuan

    2016-06-01

    The intrinsic lattice thermal conductivity of MoS$_2$ is an important aspect in the design of MoS$_2$-based nanoelectronic devices. We investigate the lattice dynamics properties of MoS$_2$ by first principles calculations. The intrinsic thermal conductivity of single-layer MoS$_2$ is calculated using the Boltzmann transport equation for phonons. The obtained thermal conductivity agrees well with the measurements. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. The size dependence of thermal conductivity is investigated as well.

  6. Tuning the threshold voltage of MoS2 field-effect transistors via surface treatment.

    Leong, Wei Sun; Li, Yida; Luo, Xin; Nai, Chang Tai; Quek, Su Ying; Thong, John T L

    2015-06-28

    Controlling the threshold voltage (Vth) of a field-effect transistor is important for realizing robust logic circuits. Here, we report a facile approach to achieve bidirectional Vth tuning of molybdenum disulfide (MoS2) field-effect transistors. By increasing and decreasing the amount of sulfur vacancies in the MoS2 surface, the Vth of MoS2 transistors can be left- and right-shifted, respectively. Transistors fabricated on perfect MoS2 flakes are found to exhibit a two-fold enhancement in mobility and a very positive Vth (18.5 ± 7.5 V). More importantly, our elegant hydrogen treatment is able to tune the large Vth to a small value (∼0 V) without any performance degradation simply by reducing the atomic ratio of S : Mo slightly; in other words, it creates a certain amount of sulfur vacancies in the MoS2 surface, which generate defect states in the band gap of MoS2 that mediates conduction of a MoS2 transistor in the subthreshold regime. First-principles calculations further indicate that the defect band's edge and width can be tuned according to the vacancy density. This work not only demonstrates for the first time the ease of tuning the Vth of MoS2 transistors, but also offers a process technology solution that is critical for further development of MoS2 as a mainstream electronic material. PMID:26036230

  7. Density functional theory calculation of edge stresses in monolayer MoS2

    Qi, Zenan; Cao, Penghui; Park, Harold S.

    2013-10-01

    We utilize density functional theory to calculate the edge energy and edge stress for monolayer MoS2 nanoribbons. In contrast to previous reports for graphene, for both armchair and zigzag chiralities, the edge stresses for MoS2 nanoribbons are found to be tensile, indicating that their lowest energy configuration is one of compression in which Mo-S bond lengths are shorter than those in a bulk, periodic MoS2 monolayer. The edge energy and edge stress is found to converge for both chiralities for nanoribbon widths larger than about 1 nm.

  8. Self-Assembly-Induced Alternately Stacked Single-Layer MoS2 and N-doped Graphene: A Novel van der Waals Heterostructure for Lithium-Ion Batteries.

    Zhao, Chenyang; Wang, Xu; Kong, Junhua; Ang, Jia Ming; Lee, Pooi See; Liu, Zhaolin; Lu, Xuehong

    2016-01-27

    In this article, a simple self-assembly strategy for fabricating van der Waals heterostructures from isolated two-dimensional atomic crystals is presented. Specifically, dopamine (DOPA), an excellent self-assembly agent and carbon precursor, was adsorbed on exfoliated MoS2 monolayers through electrostatic interaction, and the surface-modified monolayers self-assembled spontaneously into DOPA-intercalated MoS2. The subsequent in situ conversion of DOPA to highly conductive nitrogen-doped graphene (NDG) in the interlayer space of MoS2 led to the formation of a novel NDG/MoS2 nanocomposite with well-defined alternating structure. The NDG/MoS2 was then studied as an anode for lithium-ion batteries (LIBs). The results show that alternating arrangement of NDG and MoS2 triggers synergistic effect between the two components. The kinetics and cycle life of the anode are greatly improved due to the enhanced electron and Li(+) transport as well as the effective immobilization of soluble polysulfide by NDG. A reversible capacity of more than 460 mAh/g could be delivered even at 5 A/g. Moreover, the abundant voids created at the MoS2-NDG interface also accommodate the volume change during cycling and provide additional active sites for Li(+) storage. These endow the NDG/MoS2 heterostructure with low charge-transfer resistance, high sulfur reservation, and structural robustness, rendering it an advanced anode material for LIBs. PMID:26745784

  9. Cross-Calibration of the XMM-Newton EPIC pn & MOS On-Axis Effective Areas Using 2XMM Sources

    Read, A M; Sembay, S

    2014-01-01

    We aim to examine the relative cross-calibration accuracy of the on-axis effective areas of the XMM-Newton EPIC pn and MOS instruments. Spectra from a sample of 46 bright, high-count, non-piled-up isolated on-axis point sources are stacked together, and model residuals are examined to characterize the EPIC MOS-to-pn inter-calibration. The MOS1-to-pn and MOS2-to-pn results are broadly very similar. The cameras show the closest agreement below 1 keV, with MOS excesses over pn of 0-2% (MOS1/pn) and 0-3% (MOS2/pn). Above 3 keV, the MOS/pn ratio is consistent with energy-independent (or only mildly increasing) excesses of 7-8% (MOS1/pn) and 5-8% (MOS2/pn). In addition, between 1-2 keV there is a `silicon bump' - an enhancement at a level of 2-4% (MOS1/pn) and 3-5% (MOS2/pn). Tests suggest that the methods employed here are stable and robust. The results presented here provide the most accurate cross-calibration of the effective areas of the XMM-Newton EPIC pn and MOS instruments to date. They suggest areas of furt...

  10. Hydrogenation-induced edge magnetization in armchair MoS2 nanoribbon and electric field effects

    We performed density functional theory study on the electronic and magnetic properties of armchair MoS2 nanoribbons (AMoS2NR) with different edge hydrogenation. Although bare and fully passivated AMoS2NRs are nonmagnetic semiconductors, it was found that hydrogenation in certain patterns can induce localized ferromagnetic edge state in AMoS2NRs and make AMoS2NRs become antiferromagnetic semiconductors or ferromagnetic semiconductors. Electric field effects on the bandgap and magnetic moment of AMoS2NRs were investigated. Partial edge hydrogenation can change a small-sized AMoS2NR from semiconductor to metal or semimetal under a moderate transverse electric field. Since the rate of edge hydrogenation can be controlled experimentally via the temperature, pressure and concentration of H2, our results suggest edge hydrogenation is a useful method to engineer the band structure of AMoS2NRs

  11. A tight-binding model for MoS2 monolayers

    Ridolfi, Emilia; Le, Duy; Rahman, Talat; Mucciolo, Eduardo; Lewenkopf, Caio

    We propose an accurate tight-binding parametrization for the band structure of MoS2 monolayers near the main energy gap. We introduce a generic and straightforward derivation for the band energies equations that could be employed for other monolayer dichalcogenides. A parametrization that includes spin-orbit coupling is also provided. The proposed set of model parameters reproduce both the correct orbital compositions and location of valence and conductance band in comparison with ab initio calculations. The model gives a suitable starting point for realistic large-scale atomistic electronic transport calculations. Supported by the Brazilian funding agencies CNPq, CAPES, FAPERJ, and the Ciencia sem Fronteiras program. DL and TSR are supported in part by the DOE Grant DE-FG02-07ER46354.

  12. Phase transition, effective mass and carrier mobility of MoS2 monolayer under tensile strain

    We report a computational study on the impact of tensile strain on MoS2 monolayer. The transition between direct and indirect bandgap structure and the transition between semiconductor and metal phases in the monolayer have been investigated with tensile strain along all direction configurations with both x-axis and y-axis components εxy (εx and εy). Electron effective mass and the hole effective mass are isotropic for biaxial strain εxy = εx = εy and anisotropic for εxy with εx ≠ εy. The carrier effective mass behaves differently along different directions in response to the tensile strain. In addition, the impact of strain on carrier mobility has been studied by using the deformation potential theory. The electron mobility increases over 10 times with the biaxial strain: εx = εy = 9.5%. Also, the mobility decreases monotonically with the increasing temperature as μ ∼ T−1. These results are very important for future nanotechnology based on two-dimensional materials

  13. Total-dose effects of γ-ray irradiation on SOI-MOS transistors

    A measurement of total-dose radiation effects of SOI-MOS transistors is presented. The motivation of this study is to understand radiation effects of a single transistor, which is fabricated with the same structure (BESOI) as a preamplifier planned to be used for the silicon vertex detector in the KEK BELLE experiment. Results are given with the threshold voltage shift (ΔVth), mobility degradation and increase of the 1/f noise. We decomposed ΔVth into the oxide trap and interface trap components. Using this decomposition result, we found good agreement of data for the mobility degradation versus interface traps and the 1/f noise increase versus oxide trapped charges with the empirical relations. (orig.)

  14. Giant valley drifts in uniaxially strained monolayer MoS2

    Zhang, Qingyun

    2013-12-30

    Using first-principles calculations, we study the electronic structure of monolayer MoS2 under uniaxial strain. We show that the energy valleys drift far off the corners of the Brillouin zone (K points), about 12 times the amount observed in graphene. Therefore, it is essential to take this effect into consideration for a correct identification of the band gap. The system remains a direct band gap semiconductor up to 4% uniaxial strain, while the size of the band gap decreases from 1.73 to 1.54 eV. We also demonstrate that the splitting of the valence bands due to inversion symmetry breaking and spin-orbit coupling is not sensitive to strain.

  15. First-principle study of hydrogenation on monolayer MoS2

    Xu, Yong; Li, Yin; Chen, Xi; Zhang, Chunfang; Zhang, Ru; Lu, Pengfei

    2016-07-01

    The structural and electronic properties of hydrogenation on 1H-MoS2 and 1T-MoS2 have been systematically explored by using density functional theory (DFT) calculations. Our calculated results indicate an energetically favorable chemical interaction between H and MoS2 monolayer for H adsorption when increasing concentration of H atoms. For 1H-MoS2, single H atom adsorption creates midgap approaching the fermi level which increases the n-type carrier concentration effectively. As a consequence, its electrical conductivity is expected to increase significantly. For 1T-MoS2, H atoms adsorption can lead to the opening of a direct gap of 0.13eV compared to the metallic pristine 1T-MoS2.

  16. Short channel, low noise UHF MOS-FET's utilizing molybdenum-gate masked ion-implantation

    A low noise high cutoff frequency dual-gate MOS-FET with a Mo-gate is fabricated using gate-masked ion-implantation. In the high frequency region, low noise performance is achieved with a short channel and minimum resistive parasitics such as gate and source resistances. To reduce the effect of the gate resistance, a new comb type structure with low resistive Mo film is realized. The dual-gate FET with a channel length of 1.3 μ as the 1st channel and 2.5 μ as the 2nd channel, a channel width of 1.2 mm and a gate oxide thickness of 600 A, was operated at 800 MHz with a minimum noise figure of 2.4 dB and a power gain of 19 dB. Good cross modulation characteristic was also confirmed. (auth.)

  17. Hydrogenation-induced edge magnetization in armchair MoS2 nanoribbon and electric field effects

    Ouyang, Fangping; Yang, Zhixiong; Ni, Xiang; Wu, Nannan; Chen, Yu; Xiong, Xiang

    2014-02-01

    We performed density functional theory study on the electronic and magnetic properties of armchair MoS2 nanoribbons (AMoS2NR) with different edge hydrogenation. Although bare and fully passivated AMoS2NRs are nonmagnetic semiconductors, it was found that hydrogenation in certain patterns can induce localized ferromagnetic edge state in AMoS2NRs and make AMoS2NRs become antiferromagnetic semiconductors or ferromagnetic semiconductors. Electric field effects on the bandgap and magnetic moment of AMoS2NRs were investigated. Partial edge hydrogenation can change a small-sized AMoS2NR from semiconductor to metal or semimetal under a moderate transverse electric field. Since the rate of edge hydrogenation can be controlled experimentally via the temperature, pressure and concentration of H2, our results suggest edge hydrogenation is a useful method to engineer the band structure of AMoS2NRs.

  18. Reaction mechanism of core–shell MoO2/MoS2 nanoflakes via plasma-assisted sulfurization of MoO3

    Kumar, Prabhat; Singh, Megha; Sharma, Rabindar K.; Reddy, G. B.

    2016-05-01

    The sulfurization of MoO3 in an H2S/Ar plasma atmosphere has been experimentally studied and a reaction mechanism has been proposed based on the results obtained. Nanostructured thin films (NTFs) of MoO3 were sulfurized at different temperatures varying from 150 °C to 550 °C. High-resolution transmission electron microscopy (TEM) images depict core–shell nanoflakes with varying shell thicknesses as the sulfurization temperature (T sn) is varied. The shells consist of MoS2 and the core is MoO2/MoO3. X-ray diffraction (XRD) and Raman analysis have been used to study the structural changes as MoO3 is sulfurized. The analyses showed two phases, MoO2 and MoS2, at low temperatures (≤350 °C), whereas the films sulfurized at higher temperatures show predominantly MoS2. The scanning electron microscopy (SEM) results show no noticeable changes in the surface morphology of the NTFs after sulfurization. X-ray photoelectron spectroscopy (XPS) was carried out to calculate the relative percentages of MoO3, MoO2 and MoS2. It is revealed that sulfurization of MoO3 in the plasma is affected by T sn. The sulfurization process occurs in two steps, involving the reduction of MoO3 to form MoO2 in the first step, followed by MoO2 being converted into MoS2. It is also evident that the reduction of MoO3 is more a result of the reactive species of hydrogen (H*) than the replacement of oxygen by sulfur in the second step.

  19. Thickness-dependent electron mobility of single and few-layer MoS2 thin-film transistors

    Ji Heon Kim

    2016-06-01

    Full Text Available We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ∼107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ∼10 to ∼18 cm2V−1s−1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness.

  20. Thickness-dependent electron mobility of single and few-layer MoS2 thin-film transistors

    Kim, Ji Heon; Kim, Tae Ho; Lee, Hyunjea; Park, Young Ran; Choi, Woong; Lee, Cheol Jin

    2016-06-01

    We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ˜107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ˜10 to ˜18 cm2V-1s-1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness.

  1. Efficient exfoliation of MoS2 with volatile solvents and their application for humidity sensor. .

    Zhang, Shao-Lin; Jung, Hyun; Huh, Jeung-Soo; Yu, Joon-Boo; Yang, Woo-Chul

    2014-11-01

    Liquid-phase exfoliation is likely to be feasible for practical fabrication of few-layer MoS2 nanosheets in large quantities. However, this method generally involves the organic solvents with high boiling point; new strategy using low-boiling-point solvents to obtain high MoS2 concentration is still highly required. In this study, using the strategy of Hansen solubility parameters (HSP), a method based on exfoliation of MoS2 in chloroform/acetonitrile mixtures is demonstrated to fabricate high concentration MoS2 nanosheet solution. The highest concentration of few-layer MoS2 nanosheets and nanoparticles up to 0.4 mg/ml is achieved with the optimum composition of mixture. The MoS2 nanosheet thin film is also investigated in terms of their sensing properties towards humidity. The exfoliated MoS2 based thin film sensor exhibited excellent sensitivity, quick response and recovery, and good reproducibility comparing to their bulk counterpart. The excellent sensing performance of exfoliated MoS2 is generally attributed to the high surface-to-volume-ratio and increased ratio of edge sites and basal plane sites after exfoliation. PMID:25958556

  2. Tunable volatile organic compounds sensor by using thiolated ligand conjugation on MoS2.

    Kim, Jong-Seon; Yoo, Hae-Wook; Choi, Hyung Ouk; Jung, Hee-Tae

    2014-10-01

    One of the most important issues in the development of gas sensors for breath analysis is the fabrication of gas sensor arrays that possess different responses for recognizing patterns for volatile organic compounds (VOCs). Here, we develop a high-performance chemiresistor with a tunable sensor response and high sensitivity for representative VOC groups by using molybdenum disulfide (MoS2) and by conjugating a thiolated ligand (mercaptoundecanoic acid (MUA)) to MoS2 surface. Primitive and MUA-conjugated MoS2 sensing channels exhibit distinctly different sensor responses toward VOCs. In particular, the primitive MoS2 sensor presents positive responses for oxygen-functionalized VOCs, while the MUA-conjugated MoS2 sensor presents negative responses for the same analytes. Such characteristic sensor responses demonstrate that ligand conjugation successfully adds functionality to a MoS2 matrix. Thus, this will be a promising approach to constructing a versatile sensor array, by conjugating a wide variety of thiolated ligands on the MoS2 surface. Furthermore, these MoS2 sensors in this study exhibit high sensitivity to representative VOCs down to a concentration of 1 ppm. This approach to fabricating a tunable and sensitive VOC sensor may lead to a valuable real-world application for lung cancer diagnosis by breath analysis. PMID:25191976

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

    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

  4. Layered MoS2 grown on c-sapphire by pulsed laser deposition

    Layered growth of molybdenum disulphide (MoS2) was successfully achieved by pulsed laser deposition (PLD) method on c -plane sapphire substrate. Growth of monolayer to a few monolayer MoS2, dependent on the pulsed number of excimer laser in PLD is demonstrated, indicating the promising controllability of layer growth. Among the samples with various pulse number deposition, the frequency difference (A1g-E12g) in Raman analysis of the 70 pulse sample is estimated as 20.11 cm-1, suggesting a monolayer MoS2 was obtained. Two-dimensional (2D) layer growth of MoS2 is confirmed by the streaky reflection high energy electron diffraction (RHEED) patterns during growth and the cross-sectional view of transmission electron microscopy (TEM). The in-plane relationship, (0006) sapphire//(0002)MoS2 and [2 anti 1 anti 10] sapphire//[0 anti 1 anti 10]MoS2 is determined. The results imply that PLD is suitable for layered MoS2 growth. Additionally, the oxide states of Mo 3d core level spectra of PLD grown MoS2, analysed by X-ray photoelectron spectroscopy (XPS), can be effectively reduced by adopting a post sulfurization process. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. MOS current gain cells with electronically variable gain and constant bandwidth

    Klumperink, Eric A.M.; Seevinck, Evert

    1989-01-01

    Two MOS current gain cells are proposed that provide linear amplification of currents supplied by several linear MOS V-I converters. The gain is electronically variable by a voltage or a current and can be made insensitive to temperature and IC processing. The gain cells have a constant (gain-indepe

  6. MOS current gain cells with electronically variable gain and constant bandwidth

    Klumperink, Eric A.M.; Seevinck, Evert

    1989-01-01

    Two MOS current gain cells are proposed that provide linear amplification of currents supplied by several linear MOS V-I converters. The gain is electronically variable by a voltage or a current and can be made insensitive to temperature and IC processing. The gain cells have a constant (gain-independent) bandwidth

  7. Patterned Peeling 2D MoS2 off the Substrate.

    Zhao, Jing; Yu, Hua; Chen, Wei; Yang, Rong; Zhu, Jianqi; Liao, Mengzhou; Shi, Dongxia; Zhang, Guangyu

    2016-07-01

    The performance of two-dimensional (2D) MoS2 devices depends largely on the quality of the MoS2 itself. Existing fabrication process for 2D MoS2 relies on lithography and etching. However, it is extremely difficult to achieve clean patterns without any contaminations or passivations. Here we report a peel-off pattering of MoS2 films on substrates based on a proper interface engineering. The peel-off process utilizes the strong adhesion between gold and MoS2 and removes the MoS2 film contact with gold directly, leading to clean MoS2 pattern generation without residuals. Significantly improved electrical performances including high mobility ∼17.1 ± 8.3 cm(2)/(V s) and on/off ratio ∼5.6 ± 3.6 × 10(6) were achieved. Such clean fabrication technique paves a way to high quality MoS2 devices for various electrical and optical applications. PMID:27314173

  8. General Thermal Texturization Process of MoS2 for Efficient Electrocatalytic Hydrogen Evolution Reaction.

    Kiriya, Daisuke; Lobaccaro, Peter; Nyein, Hnin Yin Yin; Taheri, Peyman; Hettick, Mark; Shiraki, Hiroshi; Sutter-Fella, Carolin M; Zhao, Peida; Gao, Wei; Maboudian, Roya; Ager, Joel W; Javey, Ali

    2016-07-13

    Molybdenum disulfide (MoS2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS2 because the pristine MoS2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS2, it is essential to activate the basal plane. Here, we report a general thermal process in which the basal plane is texturized to increase the density of HER-active edge sites. This texturization is achieved through a simple thermal annealing procedure in a hydrogen environment, removing sulfur from the MoS2 surface to form edge sites. As a result, the process generates high HER catalytic performance in pristine MoS2 across various morphologies such as the bulk mineral, films composed of micron-scale flakes, and even films of a commercially available spray of nanoflake MoS2. The lowest overpotential (η) observed for these samples was η = 170 mV to obtain 10 mA/cm(2) of HER current density. PMID:27322506

  9. Mos1 transposon-based transformation of fish cell lines using baculoviral vectors

    Yokoo, Masako [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan); Fujita, Ryosuke [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan); Innate Immunity Laboratory, Graduate School of Life Science and Creative Research Institution, Hokkaido University, Sapporo 001-0021 (Japan); Nakajima, Yumiko [Functional Genomics Group, COMB, Tropical Biosphere Research Center, University of the Ryukyus, Okinawa 903-0213 (Japan); Yoshimizu, Mamoru; Kasai, Hisae [Faculty of Fisheries Sciences, Hokkaido University, Hakodate 041-8611 (Japan); Asano, Shin-ichiro [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan); Bando, Hisanori, E-mail: hban@abs.agr.hokudai.ac.jp [Laboratory of Applied Molecular Entomology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589 (Japan)

    2013-09-13

    Highlights: •The baculovirus vector infiltrates the cells of economic important fishes. •Drosophila Mos1 transposase expressed in fish cells maintains its ability to localize to the nucleus. •The baculoviral vector carrying Mos1 is a useful tool to stably transform fish cells. -- Abstract: Drosophila Mos1 belongs to the mariner family of transposons, which are one of the most ubiquitous transposons among eukaryotes. We first determined nuclear transportation of the Drosophila Mos1-EGFP fusion protein in fish cell lines because it is required for a function of transposons. We next constructed recombinant baculoviral vectors harboring the Drosophila Mos1 transposon or marker genes located between Mos1 inverted repeats. The infectivity of the recombinant virus to fish cells was assessed by monitoring the expression of a fluorescent protein encoded in the viral genome. We detected transgene expression in CHSE-214, HINAE, and EPC cells, but not in GF or RTG-2 cells. In the co-infection assay of the Mos1-expressing virus and reporter gene-expressing virus, we successfully transformed CHSE-214 and HINAE cells. These results suggest that the combination of a baculovirus and Mos1 transposable element may be a tool for transgenesis in fish cells.

  10. DNA base detection using a single-layer MoS2.

    Farimani, Amir Barati; Min, Kyoungmin; Aluru, Narayana R

    2014-08-26

    Nanopore-based DNA sequencing has led to fast and high-resolution recognition and detection of DNA bases. Solid-state and biological nanopores have low signal-to-noise ratio (SNR) ( 5 nm) to be able to read at single-base resolution. A nanopore in graphene, a 2-D material with sub-nanometer thickness, has a SNR of ∼3 under DNA ionic current. In this report, using atomistic and quantum simulations, we find that a single-layer MoS2 is an extraordinary material (with a SNR > 15) for DNA sequencing by two competing technologies (i.e., nanopore and nanochannel). A MoS2 nanopore shows four distinct ionic current signals for single-nucleobase detection with low noise. In addition, a single-layer MoS2 shows a characteristic change/response in the total density of states for each base. The band gap of MoS2 is significantly changed compared to other nanomaterials (e.g., graphene, h-BN, and silicon nanowire) when bases are placed on top of the pristine MoS2 and armchair MoS2 nanoribbon, thus making MoS2 a promising material for base detection via transverse current tunneling measurement. MoS2 nanopore benefits from a craftable pore architecture (combination of Mo and S atoms at the edge) which can be engineered to obtain the optimum sequencing signals. PMID:25007098

  11. Electrical and optical properties of Co-doped and undoped MoS2

    Ko, Tsung-Shine; Huang, Cheng-Ching; Lin, Der-Yuh; Ruan, Yan-Jia; Huang, Ying Sheng

    2016-04-01

    Co-doped and undoped layered MoS2 crystals were grown by the chemical vapor transport method using iodine as the transport agent. Both reflectance and piezoreflectance measurements reveal two exciton transitions of the direct band edge around 1.86 and 2.06 eV for undoped MoS2 and 1.84 and 2.03 eV for Co-doped MoS2. Hall effect measurements show that the Co-doped MoS2 sample has a lower carrier concentration and mobility than the undoped sample. These differences between undoped and Co-doped MoS2 were attributed to the effect of cobalt atoms causing a small lattice distortion, lattice imperfections and/or impurity states that form trap states between the conduction band and valence band. Furthermore, photoconductivity (PC) and persistent PC results show that Co-doped MoS2 has a longer time constant and better responsivity than undoped MoS2. This work discusses the advantages of Co-doped MoS2 for photodetector applications.

  12. Exfoliated MoS2 in Water without Additives.

    Forsberg, Viviane; Zhang, Renyun; Bäckström, Joakim; Dahlström, Christina; Andres, Britta; Norgren, Magnus; Andersson, Mattias; Hummelgård, Magnus; Olin, Håkan

    2016-01-01

    Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants and other funtionalization agents. Pure water should be an ideal solvent, however, it is generally believed, based on solubility theories that stable dispersions of water could not be achieved and systematic studies are lacking. Here we describe the use of water as a solvent and the stabilization process involved therein. We introduce an exfoliation method of molybdenum disulfide (MoS2) in pure water at high concentration (i.e., 0.14 ± 0.01 g L-1). This was achieved by thinning the bulk MoS2 by mechanical exfoliation between sand papers and dispersing it by liquid exfoliation through probe sonication in water. We observed thin MoS2 nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of the nanosheets were around 200 nm, the same range obtained in organic solvents. Electrophoretic mobility measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. A probability decay equation was proposed to compare the stability of these dispersions with the ones reported in the literature. Water can be used as a solvent to disperse nanosheets and although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable. PMID:27120098

  13. Ionizing radiation M.O.S. dosimeters: sensibility and stability

    This thesis is a contribution to the study of the ionizing radiation responsivity of P.O.M.S. dosimeters. Unlike the development of processing hardening techniques, our works goal were to increase, on the one hand, the M.O.S. dosimeters sensitivity in order to detect small radiation doses and on the other hand, the stability with time and temperature of the devices, to minimize the absorbed-dose estimation errors. With this aim in mind, an analysis of all processing parameters has been carried out: the M.O.S. dosimeter sensitivity is primarily controlled by the gate oxide thickness and the irradiation electric field. Thus, P.M.O.S. transistors with 1 and 2 μm thick silica layers have been fabricated for our experiments. The radiation response of our devices in the high-field mode satisfactorily fits a Dox2 power law. The maximum sensitivity achieved (9,2 V/Gy for 2μm devices) is close to the ideal value obtained when considering only an unitary carrier-trapping level, and allows to measure about 10-2 Gy radiation doses. Read-time stability has been evaluated under bias-temperature stress conditions: experiments underscore slow fading, corresponding to 10-3 Gy/h. The temperature response has also been studied: the analytical model we have developed predicts M.O.S. transistors threshold voltage variations over the military specifications range [-50 deg. C, + 150 deg. C]. Finally, we have investigated the possibilities of irradiated dosimeters thermal annealing for reusing. It appears clearly that radiation-induced damage annealing is strongly gate bias dependent. Furthermore, dosimeters radiation sensitivity seems not to be affected by successive annealings. (author). 146 refs., 58 figs., 9 tabs

  14. Exfoliated MoS2 in Water without Additives

    Forsberg, Viviane; Zhang, Renyun; Bäckström, Joakim; Dahlström, Christina; Andres, Britta; Norgren, Magnus; Andersson, Mattias; Hummelgård, Magnus; Olin, Håkan

    2016-01-01

    Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants and other funtionalization agents. Pure water should be an ideal solvent, however, it is generally believed, based on solubility theories that stable dispersions of water could not be achieved and systematic studies are lacking. Here we describe the use of water as a solvent and the stabilization process involved therein. We introduce an exfoliation method of molybdenum disulfide (MoS2) in pure water at high concentration (i.e., 0.14 ± 0.01 g L−1). This was achieved by thinning the bulk MoS2 by mechanical exfoliation between sand papers and dispersing it by liquid exfoliation through probe sonication in water. We observed thin MoS2 nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of the nanosheets were around 200 nm, the same range obtained in organic solvents. Electrophoretic mobility measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. A probability decay equation was proposed to compare the stability of these dispersions with the ones reported in the literature. Water can be used as a solvent to disperse nanosheets and although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable. PMID:27120098

  15. Exfoliated MoS2 in Water without Additives.

    Viviane Forsberg

    Full Text Available Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants and other funtionalization agents. Pure water should be an ideal solvent, however, it is generally believed, based on solubility theories that stable dispersions of water could not be achieved and systematic studies are lacking. Here we describe the use of water as a solvent and the stabilization process involved therein. We introduce an exfoliation method of molybdenum disulfide (MoS2 in pure water at high concentration (i.e., 0.14 ± 0.01 g L-1. This was achieved by thinning the bulk MoS2 by mechanical exfoliation between sand papers and dispersing it by liquid exfoliation through probe sonication in water. We observed thin MoS2 nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of the nanosheets were around 200 nm, the same range obtained in organic solvents. Electrophoretic mobility measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. A probability decay equation was proposed to compare the stability of these dispersions with the ones reported in the literature. Water can be used as a solvent to disperse nanosheets and although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable.

  16. Layer-by-layer self-assembly of polyelectrolyte functionalized MoS2 nanosheets

    Shen, Jianfeng; Pei, Yu; Dong, Pei; Ji, Jin; Cui, Zheng; Yuan, Junhua; Baines, Robert; Ajayan, Pulickel M.; Ye, Mingxin

    2016-05-01

    Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems.Few-layered polyelectrolyte functionalized MoS2 nanosheets were obtained for the first time through in situ polymerization of MoS2 nanosheets with poly(acrylic acid) and poly(acrylamide), both of which demonstrated excellent dispersibility and stability in water. After designing and optimizing the components of this series of polyelectrolyte functionalized MoS2 nanosheets, by exploiting the electrostatic interactions present in the modified MoS2 nanosheets, we further created a series of layer-by-layer (LBL) self-assembling MoS2-based films. To this end, uniform MoS2 nanosheet-based LBL films were precisely deposited on substrates such as quartz, silicon, and ITO. The polyelectrolyte functionalized MoS2 nanosheet assembled LBL film-modified electrodes demonstrated enhanced electrocatalytic activity for H2O2. As such, they are conducive to efficient sensors and advanced biosensing systems. Electronic supplementary information (ESI) available: SEM, AFM and TEM characterization of PAA-MoS2 and PAM-MoS2 nanocomposites. More characterization and electrochemical properties of LBL films

  17. A νMOS soft-maximum current mirror

    Minch, Bradley A.; Diorio, Chris; Hasler, Paul; Mead, Carver

    1995-01-01

    In this paper, we describe a novel circuit consisting of N+1 MOS transistors and a single floating gate which computes a soft maximum of N current inputs and reflects the result in the output transistor. An intuitive description of the operation of the circuit is given. Data from a working two-input version of the circuit is presented and discussed. The circuit features a high output voltage swing and an interesting feedback mechanism which causes its output impedance to be comparable to that...

  18. Adjustment of threshold voltage of MOS devices by ion implantation

    In this paper we report the effect of oxide thickness, implant energy and dose on threshold voltage shift Δ Vsub(T). The implant parameters e.g. stopping power, projected range, straggle and the energy loss per micron for an ion in the substrate lattice are calculated using the WHB potential. The junction depth beneath the oxide semiconductor surface is calculated using a two layer model. The parameters are then used in a theoretical calculation of threshold shift of MOS devices. Experimental threshold voltages for unimplanted and implanted samples were obtained from C-V plots, showing fairly good agreement with theory. (author)

  19. Plasmons on the edge of MoS2 nanostructures

    Andersen, Kirsten; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer

    2015-01-01

    Using ab initio calculations we predict the existence of one-dimensional (1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon. The strongest plasmon originates from a metallic edge state localized on the sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the dielectric function reveals that the observed deviations from the ideal 1D plasmon behavior result from single-particle transitions between the metallic edge state and the valence and conduct...

  20. 650V CoolMOS CFD2:MOSFET

    2011-01-01

    英飞凌推出了650V CoolMOS CFD2,它是漏源击穿电压为650V并且集成了快速体二极管的高压晶体管。器件延续了600VCFD产品的特点,不仅可以提高能效,而且具备更软的交换功能,从而降低了电磁干扰(EMI)。

  1. Optically pumped terahertz wave modulation in MoS2-Si heterostructure metasurface

    Zheng, Wei; Fan, Fei; Chen, Meng; Chen, Sai; Chang, Sheng-Jiang

    2016-07-01

    An optically pumped terahertz (THz) modulator based on a MoS2-Si heterostructure metasurface are fabricated and investigated in this paper. The THz wave modulation in MoS2 metasurface has been demonstrated by THz time domain spectroscopy experiment and numerical simulation, which can reach over 90% under the continuous wave laser pumping of 4W/cm2 power density. Importantly, the catalysis of photocarrier generation in MoS2-Si heterostructure has been proved by the comparsion between the modulation depth of metasurface with and without MoS2 nanosheet under the same pumping power, and we found that the strcuture of metasurface and polariztion direction can also influence the photocarrier density in MoS2 metasurface. This novel THz modulator based on 2D material has a high effective modulation on THz waves under a low pumping power, which has a bright potential in THz applications.

  2. Plasma treatment introduced memory properties in MoS2 field-effect transistors

    Zhang, Miaomiao; Tong, Yanhong; Tang, Qingxin; Liu, Yichun

    2016-01-01

    We present a facile method to obtain MoS2-based nonvolatile memory field-effect transistors by oxygen plasma treatment on the MoS2 surface that is in contact with a dielectric. The oxygen plasma treatment provides a way of introducing deep defects into the MoS2 surface. Only those deep defects located at the semiconductor/dielectric interface can behave as charge trapping sites to develop the memory capability. No memory properties can be observed when the MoS2 surface far from the conductive channel was treated with oxygen plasma. This method brings promising advantages to MoS2-based memory devices obtained using a simple fabrication method and small device dimensions.

  3. Defect passivation induced strong photoluminescence enhancement of rhombic monolayer MoS2.

    Su, Weitao; Jin, Long; Qu, Xiaodan; Huo, Dexuan; Yang, Li

    2016-05-18

    Growing high quality monolayer MoS2 with strong photoluminescence (PL) is essential to produce light-emitting devices on the atomic scale. In this study we show that rhombic monolayer MoS2 with PL intensity 8 times stronger than those of chemical vapour deposition (CVD)-grown triangular and mechanically exfoliated (ME) monolayer MoS2 can be prepared by using CVD. Both Raman and PL measurements indicate low density of defects in rhombic monolayer MoS2 with enhanced PL intensity. Density functional theory (DFT) calculations show that passivation of defects in MoS2 removes trapping gap states, which may finally result in PL enhancement. PMID:27152375

  4. Surface oxidation energetics and kinetics on MoS2 monolayer

    In this work, surface oxidation of monolayer MoS2 (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method. Oxygen interaction with MoS2 shows that, thermodynamically, the surface tends to be oxidized. However, the dissociative absorption of molecular oxygen on the MoS2 surface is kinetically limited due to the large energy barrier at low temperature. This finding elucidates the air stability of MoS2 surface in the atmosphere. Furthermore, the presence of defects significantly alters the surface stability and adsorption mechanisms. The electronic properties of the oxidized surface have been examined as a function of oxygen adsorption and coverage as well as substitutional impurities. Our results on energetics and kinetics of oxygen interaction with the MoS2 monolayer are useful for the understanding of surface oxidation, air stability, and electronic properties of transition-metal dichalcogenides at the atomic scale

  5. Thermal Conductance at the 2D MoS2-hexagonal Boron Nitride Interface

    Liu, Yi; Hippalgaonkar, Kedar; Ong, Zhun Yong; Thong, John Tl; Qiu, Chengwei

    In recent years, a number of 2D heterostructure devices have emerged, including graphene/hexagonal boron nitride (h-BN), graphene/MoS2 and MoS2/ h-BN. Among them, MoS2/ h-BN field-effect transistors with MoS2 channels and h-BN dielectric have been reported to have higher carrier mobility and reduced hysteresis compared to MoS2 on SiO2. Despite relatively high in-plane thermal conductivity of MoS2 and h-BN, heat dissipation from these 2D devices is mainly limited by heat transfer in the vertical direction. Consequently, their operating temperatures are strongly influenced by the interface thermal conductance. In this work, we demonstrate the measurement of interface thermal conductance between MoS2 and h-BN. This is realized by electrically heating MoS2 and monitoring their temperatures through Raman spectroscopy. The obtained interface thermal conductance between MoS2 and h-BN is 1.77 MW/m2K, smaller than the reported value for the graphene/ h-BN interface, due to the weak coupling of phonon modes between MoS2 and h-BN based on our NEGF calculation. The low interface thermal conductance value suggests this interface is not favorable for heat dissipation, and should be considered carefully for the design of electronic and optoelectronic devices based on MoS2/ h-BN heterostructures.

  6. An infant with mos45,X/46,XY/47,XYY/48,XYYY: Genetic and clinical findings

    Fox, J.; Blumenthal, D.; Brock, W. [Long Island Jewish Medical Center, New Hyde Park, NY (United States)] [and others

    1994-09-01

    We report on an infant with mos45,X/46,XY/47,XYY/48,XYYY who presented with ambiguous genitalia. The patient was the 2,637 gram product of a 38 week gestation and elective repeat C-section born to a 35 year old G3P2 mother. The pregnancy was complicated by placenta previa. There was no history of maternal health problems or drug or steroid use. At birth bilateral epicanthal folds and overfolded helices were noted without webbing of the neck or lymphedema. There was a phallic structure measuring 1.5 cm with dorsal hood and midline cleft with a normal female introitus, urethra, and vagina. Congenital adrenal hyperplaxia was excluded. Renal ultrasound was normal. Periperal blood chromosomes revealed a mos45,X(38%)/47,XYY(29%)/48,XYYY(33%) karyotype. Echocardiography revealed coarctation of the aorta and a bicuspid aortic valve. An additional cell line, 46,XY, was identified in aortic tissue obtained at the time of surgery. At age 15 months she was 25% in height and weight and had bilateral ptosis. Her development was within normal limits, but no words except {open_quotes}Mama{close_quotes} or {open_quotes}Dada{close_quotes} were spoken. A left intraabdominal testis with epididymis and dilated tubules and bilateral Fallopian tubes were removed at laparoscopy/reconstruction. Cell cultures were initiated from gonadal tissue, and karyotypes are pending. Patients with mosaic Y chromosome aneuploidy involving 2 Y chromosomes are rare. Eighteen patients with 45,X/47,XYY have been described; prenatally diagnosed cases appeared to be normal male whereas cases diagnosed postnally presented with ambiguous genitalia and/or other anomalies. The phenotype of Y chromosome aneuploidy with 3 Y chromosomes is even more unpredictable due to the paucity of reported cases. To our knowledge this is the first patient described with this unusual karyotype, thus adding to the limited information of patients with rare mosaic Y chromosome aneuploidy.

  7. Germanium MOS technology for infra-red detectors

    Ruddell, Fred H. [Northern Ireland Semiconductor Research Centre, Queen' s University Belfast, Stranmillis Road, Belfast BT9 5AH (United Kingdom)]. E-mail: f.ruddell@qub.ac.uk; Montgomery, John H. [Northern Ireland Semiconductor Research Centre, Queen' s University Belfast, Stranmillis Road, Belfast BT9 5AH (United Kingdom); Gamble, Harold S. [Northern Ireland Semiconductor Research Centre, Queen' s University Belfast, Stranmillis Road, Belfast BT9 5AH (United Kingdom); Denvir, Donal [Andor Technology, 7 Millenium Way, Springvale Business Park, Belfast BT12 7AL (United Kingdom)

    2007-04-01

    Fabrication of an electrically stable dielectric is a key enabling technology in the production of a Ge detector with enhanced response in the near infra-red spectrum. This work investigates the physical and electrical properties of silicon dioxide (SiO{sub 2}) dielectrics deposited on Ge substrates. The deposited SiO{sub 2} (silox) layers have been densified at 600 and 800 deg. C. Significant Ge outdiffusion from the substrate into the densifying silox layer has been observed for the 800 deg. C process, and the diffusivity has been estimated as 1.5x10{sup -4} {mu}m{sup 2}/min. The C-V characteristics of Ge MOS capacitors incorporating this silox dielectric display the onset of 'low frequency' operation at a relatively high frequency of 100 kHz, and the capacitor C-t response suggests that Ge carrier lifetime is much shorter than that measured for Si MOS capacitors. These phenomena are shown to result from the narrow band gap of Ge, and this work therefore emphasises that increased cooling will be required to exploit the infra-red detector properties of a practical Ge device.

  8. ELT-MOS White Paper: Science Overview & Requirements

    Evans, Chris; Barbuy, Beatriz; Bastian, Nate; Bonifacio, Piercarlo; Caffau, Elisabetta; Cuby, Jean-Gabriel; Dalton, Gavin; Davies, Ben; Dunlop, Jim; Flores, Hector; Hammer, Francois; Kaper, Lex; Lemasle, Bertrand; Morris, Simon; Pentericci, Laura; Petitjean, Patrick; Schaerer, Daniel; Telles, Eduardo; Welikala, Niraj; Ziegler, Bodo

    2013-01-01

    The workhorse instruments of the 8-10m class observatories have become their multi-object spectrographs (MOS), providing comprehensive follow-up to both ground-based and space-borne imaging. With the advent of deeper imaging surveys from, e.g., the HST and VISTA, there are a plethora of spectroscopic targets which are already beyond the sensitivity limits of current facilities. This wealth of targets will grow even more rapidly in the coming years, e.g., after the completion of ALMA, the launch of the JWST and Euclid, and the advent of the LSST. Thus, one of the key requirements underlying plans for the next generation of ground-based telescopes, the Extremely Large Telescopes (ELTs), is for even greater sensitivity for optical and infrared spectroscopy. Here we revisit the scientific motivation for a MOS capability on the European ELT, combining updated elements of science cases advanced from the Phase A instrument studies with new science cases which draw on the latest results and discoveries. These science...

  9. BATMAN: a DMD-based MOS demonstrator on Galileo Telescope

    Zamkotsian, Frédéric; Spanò, Paolo; Bon, William; Riva, Marco; Lanzoni, Patrick; Nicastro, Luciano; Molinari, Emilio; Cosentino, Rosario; Ghedina, Adriano; Gonzalez, Manuel; Di Marcantonio, Paolo; Coretti, Igor; Cirami, Roberto; Manetta, Marco; Zerbi, Filippo; Tresoldi, Daniela; Valenziano, Luca

    2012-09-01

    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 groundbased 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. We are developing a Digital Micromirror Device (DMD) - based spectrograph demonstrator called BATMAN. We want to access the largest FOV with the highest contrast. The selected component is a DMD chip from Texas Instruments in 2048 x 1080 mirrors format, with a pitch of 13.68μm. Our optical design is an all-reflective spectrograph design with F/4 on the DMD component. This demonstrator permits the study of key parameters such as throughput, contrast and ability to remove unwanted sources in the FOV (background, spoiler sources), PSF effect, new observational modes. This study will be conducted in the visible with possible extension in the IR. A breadboard on an optical bench, ROBIN, has been developed for a preliminary determination of these parameters. The demonstrator on the sky is then of prime importance for characterizing the actual performance of this new family of instruments, as well as investigating the operational procedures on astronomical objects. BATMAN will be placed on the Nasmyth focus of Telescopio Nazionale Galileo (TNG) during next year.

  10. Thiophene hydrodesulfurization on MoS 2; Theoretical aspects

    Zonnevylle, Marjanne C.; Hoffmann, Roald; Harris, Suzanne

    Hydrodesulfurization (HDS), the removal of sulfur in the form of H 2S from petroleum, is a crucial step in the industrial refinement process. Using the extended Hückel tight binding method, we have examined the nature of the active site and the mechanism of desulfurization in the case of thiophene on MoS 2. The η 5-bound sites, in which the thiophene ring lies parallel to the surface, are particularly advantageous to weakening the SC bond. η 1-bound sites are less active. The removal of sorrounding surface sulfurs increases the HDS potential of the η 5 geometry, but is ineffective at promoting the poorer adsorption modes. Surface reconstruction has also been examined; the possibility of MoMo pairing is suggested. The effect of poisons and promoters is considered. The role they play in HDS catalysis may be determined by the position they occupy in the MoS 2 lattice. Metals which replace a surface molybdenum tend to poison HDS, whereas those which "pseudo-intercalate" between the SS layers can serve to promote the reaction.

  11. MoS2 memristor with photoresistive switching.

    Wang, Wei; Panin, Gennady N; Fu, Xiao; Zhang, Lei; Ilanchezhiyan, P; Pelenovich, Vasiliy O; Fu, Dejun; Kang, Tae Won

    2016-01-01

    A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques. PMID:27492593

  12. MoS2 memristor with photoresistive switching

    Wang, Wei; Panin, Gennady N.; Fu, Xiao; Zhang, Lei; Ilanchezhiyan, P.; Pelenovich, Vasiliy O.; Fu, Dejun; Kang, Tae Won

    2016-08-01

    A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques.

  13. Nanoscale mapping of excitonic processes in single-layer MoS2 using tip-enhanced photoluminescence microscopy

    Su, Weitao; Kumar, Naresh; Mignuzzi, Sandro; Crain, Jason; Roy, Debdulal

    2016-05-01

    In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural and excitonic properties.In two-dimensional (2D) semiconductors, photoluminescence originating from recombination processes involving neutral electron-hole pairs (excitons) and charged complexes (trions) is strongly affected by the localized charge transfer due to inhomogeneous interactions with the local environment and surface defects. Herein, we demonstrate the first nanoscale mapping of excitons and trions in single-layer MoS2 using the full spectral information obtained via tip-enhanced photoluminescence (TEPL) microscopy along with tip-enhanced Raman spectroscopy (TERS) imaging of a 2D flake. Finally, we show the mapping of the PL quenching centre in single-layer MoS2 with an unprecedented spatial resolution of 20 nm. In addition, our research shows that unlike in aperture-scanning near field microscopy, preferential exciton emission mapping at the nanoscale using TEPL and Raman mapping using TERS can be obtained simultaneously using this method that can be used to correlate the structural

  14. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    Wei-Ting eLai

    2016-02-01

    Full Text Available We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5−90 nm, the SiO2 thickness (3−4 nm, and as well the SiGe-shell thickness (2−15 nm has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5 in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge MOS nanoelectronic and nanophotonic applications.

  15. Gate-stack engineering for self-organized Ge-dot/SiO2/SiGe-shell MOS capacitors

    Lai, Wei-Ting; Yang, Kuo-Ching; Liao, Po-Hsiang; George, Tom; Li, Pei-Wen

    2016-02-01

    We report the first-of-its-kind, self-organized gate-stack heterostructure of Ge-dot/SiO2/SiGe-shell on Si fabricated in a single step through the selective oxidation of a SiGe nano-patterned pillar over a Si3N4 buffer layer on a Si substrate. Process-controlled tunability of the Ge-dot size (7.5‑90 nm), the SiO2 thickness (3‑4 nm), and as well the SiGe-shell thickness (2‑15 nm) has been demonstrated, enabling a practically-achievable core building block for Ge-based metal-oxide-semiconductor (MOS) devices. Detailed morphologies, structural, and electrical interfacial properties of the SiO2/Ge-dot and SiO2/SiGe interfaces were assessed using transmission electron microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent high/low-frequency capacitance-voltage measurements. Notably, NiGe/SiO2/SiGe and Al/SiO2/Ge-dot/SiO2/SiGe MOS capacitors exhibit low interface trap densities of as low as 3-5x10^11 cm^-2·eV^-1 and fixed charge densities of 1-5x10^11 cm^-2, suggesting good-quality SiO2/SiGe-shell and SiO2/Ge-dot interfaces. In addition, the advantage of having single-crystalline Si1-xGex shell (x > 0.5) in a compressive stress state in our self-aligned gate-stack heterostructure has great promise for possible SiGe (or Ge) MOS nanoelectronic and nanophotonic applications.

  16. Fluorescent MoS2 Quantum Dots: Ultrasonic Preparation, Up-Conversion and Down-Conversion Bioimaging, and Photodynamic Therapy.

    Dong, Haifeng; Tang, Songsong; Hao, Yansong; Yu, Haizhu; Dai, Wenhao; Zhao, Guifeng; Cao, Yu; Lu, Huiting; Zhang, Xueji; Ju, Huangxian

    2016-02-10

    Small size molybdenum disulfide (MoS2) quantum dots (QDs) with desired optical properties were controllably synthesized by using tetrabutylammonium-assisted ultrasonication of multilayered MoS2 powder via OH-mediated chain-like Mo-S bond cleavage mode. The tunable up-bottom approach of precise fabrication of MoS2 QDs finally enables detailed experimental investigations of their optical properties. The synthesized MoS2 QDs present good down-conversion photoluminescence behaviors and exhibit remarkable up-conversion photoluminescence for bioimaging. The mechanism of the emerging photoluminescence was investigated. Furthermore, superior (1)O2 production ability of MoS2 QDs to commercial photosensitizer PpIX was demonstrated, which has great potential application for photodynamic therapy. These early affording results of tunable synthesis of MoS2 QDs with desired photo properties can lead to application in fields of biomedical and optoelectronics. PMID:26761391

  17. Unravelling merging behaviors and electrostatic properties of CVD-grown monolayer MoS2 domains.

    Hao, Song; Yang, Bingchu; Gao, Yongli

    2016-08-28

    The presence of grain boundaries is inevitable for chemical vapor deposition (CVD)-grown MoS2 domains owing to various merging behaviors, which greatly limits its potential applications in novel electronic and optoelectronic devices. It is therefore of great significance to unravel the merging behaviors of the synthesized polygon shape MoS2 domains. Here we provide systematic investigations of merging behaviors and electrostatic properties of CVD-grown polycrystalline MoS2 crystals by multiple means. Morphological results exhibit various polygon shape features, ascribed to polycrystalline crystals merged with triangle shape MoS2 single crystals. The thickness of triangle and polygon shape MoS2 crystals is identical manifested by Raman intensity and peak position mappings. Three merging behaviors are proposed to illustrate the formation mechanisms of observed various polygon shaped MoS2 crystals. The combined photoemission electron microscopy and kelvin probe force microscopy results reveal that the surface potential of perfect merged crystals is identical, which has an important implication for fabricating MoS2-based devices. PMID:27586938

  18. Effect of precursor on growth and morphology of MoS2 monolayer and multilayer

    Ganorkar, Shraddha; Kim, Jungyoon; Kim, Young-Hwan; Kim, Seong-II

    2015-12-01

    The rise of two-dimensional (2D) material is one of the results of successful efforts of researchers which laid the path to the new era of electronics. One of the most exciting materials is MoS2. Synthesis has been always a major issue as electronic devices need reproducibility along with similar properties for mass productions. Chemical vapor deposition (CVD) is one of the successful methods for 2D materials including graphene. Furthermore, the choice of starting materials for Mo and S source is crucial. The different source has different effects on the layers and morphology of MoS2 films. In this work, we have extensively studied the CVD technique to grow few layers of MoS2 with two precursors MoO3 and MoCl5, show remarkable changes. The MoO3 source gives a triangular shaped MoS2 monolayer while that of MoCl5 can achieve uniform MoS2 without triangle. The absence of geometric shapes with MoCl5 is poorly understood. We tried to explain with MoCl5 precursor, the formation of continuous monolayer of MoS2 without any triangle on the basis of chemical reaction formalism mostly due to one step reaction process and formation of MoS2 from gas phase to the solid phase. The film synthesized by MoCl5 is more continuous and it would be a good choice for device applications.

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

    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.

  20. Synthesis of Highly Uniform Molybdenum-Glycerate Spheres and Their Conversion into Hierarchical MoS2 Hollow Nanospheres for Lithium-Ion Batteries.

    Wang, Yawen; Yu, Le; Lou, Xiong Wen David

    2016-06-20

    Highly uniform Mo-glycerate solid spheres are synthesized for the first time through a solvothermal process. The size of these Mo-glycerate spheres can be easily controlled in the range of 400-1000 nm by varying the water content in the mixed solvent. As a precursor, these Mo-glycerate solid spheres can be converted into hierarchical MoS2 hollow nanospheres through a subsequent sulfidation reaction. Owing to the unique ultrathin subunits and hollow interior, the as-prepared MoS2 hollow nanospheres exhibit appealing performance as the anode material for lithium-ion batteries. Impressively, these hierarchical structures deliver a high capacity of about 1100 mAh g(-1) at 0.5 A g(-1) with good rate retention and long cycle life. PMID:27095261

  1. Synthesis and characterization of MoS2/Ti composite coatings on Ti6Al4V prepared by laser cladding

    Rongjuan Yang

    2013-02-01

    Full Text Available The MoS2/Ti composite coating with sub-micron grade structure has been prepared on Ti6Al4V by laser method under argon protection. The morphology, microstructure, microhardness and friction coefficient of the coating were examined. The results indicated that the molybdenum disulfide was decomposed during melting and resolidification. The phase organization of composite coating mainly consisted of ternary element sulfides, molybdenum sulfides and titanium sulfides. The friction coefficient of and the surface roughness the MoS2/Ti coating were lower than those of Ti6Al4V. The composite coating exhibits excellent adhesion to the substrates, less surface roughness, good wear resistance and harder surface.

  2. Towards intrinsic MoS2 devices for high performance arsenite sensing

    Li, Peng; Zhang, Dongzhi; Sun, Yan'e.; Chang, Hongyan; Liu, Jingjing; Yin, Nailiang

    2016-08-01

    Molybdenum disulphide (MoS2) is one of the most attractive two dimensional materials other than graphene, and the exceptional properties make it a promising candidate for bio/chemical sensing. Nevertheless, intrinsic properties and sensing performances of MoS2 are easily masked by the presence of the Schottky barrier (SB) at source/drain electrodes, and its impact on MoS2 sensors remains unclear. Here, we systematically investigated the influence of the SB on MoS2 sensors, revealing the sensing mechanism of intrinsic MoS2. By utilizing a small work function metal, Ti, to reduce the SB, excellent electrical properties of this 2D material were yielded with 2-3 times enhanced sensitivity. We experimentally demonstrated that the sensitivity of MoS2 is superior to that of graphene. Intrinsic MoS2 was able to realize rapid detection of arsenite down to 0.1 ppb without the influence of large SB, which is two-fold lower than the World Health Organization (WHO) tolerance level and better than the detection limit of recently reported arsenite sensors. Additionally, accurately discriminating target molecules is a great challenge for sensors based on 2D materials. This work demonstrates MoS2 sensors encapsulated with ionophore film which only allows certain types of molecules to selectively permeate through it. As a result, multiplex ion detection with superb selectivity was realized. Our results show prominent advantages of intrinsic MoS2 as a sensing material.

  3. Fabrication of 3 D Mesoporous Black TiO2 /MoS2 /TiO2 Nanosheets for Visible-Light-Driven Photocatalysis.

    Liu, Xuefeng; Xing, Zipeng; Zhang, Hang; Wang, Wenmei; Zhang, Yan; Li, Zhenzi; Wu, Xiaoyan; Yu, Xiujuan; Zhou, Wei

    2016-05-23

    A novel 3 D mesoporous black TiO2 (MBT)/MoS2 /MBT sandwich-like nanosheet was successfully fabricated using a facile mechanochemical process combined with an in situ solid-state chemical reduction approach, followed by mild calcination (350 °C) under an argon atmosphere. The MBT/MoS2 /MBT exhibits a 3 D sandwich-like nanosheet structure and heterojunctions are formed at the interfaces between MoS2 and black TiO2 . The significantly narrowed band gap of MBT/MoS2 /MBT is attributed to the introduction of MoS2 and the formed Ti(3+) species in the frameworks. The visible-light photocatalytic degradation rate of methyl orange and the hydrogen production rate are as high as 89.86 % and 0.56 mmol h(-1)  g(-1) , respectively. The introduction of MoS2 and Ti(3+) in the frameworks favors the visible-light absorption and the separation of photogenerated charges, and the 3 D sandwich-like heterojunction structure facilitates the transfer of photogenerated charges. PMID:27111114

  4. Optical signatures of states bound to vacancy defects in monolayer MoS$_2$

    Erementchouk, Mikhail; Khan, M A; Leuenberger, Michael N.

    2015-01-01

    We show that pristine MoS$_2$ single layer (SL) exhibits two bandgaps $E_{g\\parallel}=1.9$ eV and $E_{g\\perp}=3.2$ eV for the optical in-plane and out-of-plane susceptibilities $\\chi_\\parallel$ and $\\chi_\\perp$, respectively. In particular, we show that odd states bound to vacancy defects (VDs) lead to resonances in $\\chi_\\perp$ inside $E_{g\\perp}$ in MoS$_2$ SL with VDs. We use density functional theory, the tight-binding model, and the Dirac equation to study MoS$_2$ SL with three types of ...

  5. Flexible MoS2 Field-Effect Transistors for Gate-Tunable Piezoresistive Strain Sensors.

    Tsai, Meng-Yen; Tarasov, Alexey; Hesabi, Zohreh R; Taghinejad, Hossein; Campbell, Philip M; Joiner, Corey A; Adibi, Ali; Vogel, Eric M

    2015-06-17

    Atomically thin molybdenum disulfide (MoS2) is a promising two-dimensional semiconductor for high-performance flexible electronics, sensors, transducers, and energy conversion. Here, piezoresistive strain sensing with flexible MoS2 field-effect transistors (FETs) made from highly uniform large-area films is demonstrated. The origin of the piezoresistivity in MoS2 is the strain-induced band gap change, which is confirmed by optical reflection spectroscopy. In addition, the sensitivity to strain can be tuned by more than 1 order of magnitude by adjusting the Fermi level via gate biasing. PMID:26010011

  6. Electrostatic properties of few-layer MoS2 films

    Guolin Hao

    2013-04-01

    Full Text Available Two-dimensional MoS2-based materials are considered to be one of the most attractive materials for next-generation nanoelectronics. The electrostatic properties are important in designing and understanding the performance of MoS2-based devices. By using Kelvin probe force microscopy, we show that few-layer MoS2 sheets exhibit uniform surface potential and charge distributions on their surfaces but have relatively lower surface potentials on the edges, folded areas as well as defect grain boundaries.

  7. Two-step synthesis of luminescent MoS2-ZnS hybrid quantum dots

    Clark, Rhiannon M.; Carey, Benjamin J.; Daeneke, Torben; Atkin, Paul; Bhaskaran, Madhu; Latham, Kay; Cole, Ivan S.; Kalantar-Zadeh, Kourosh

    2015-10-01

    A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing applications.A surfactant assisted technique has been used to promote the exfoliation of molybdenum disulphide (MoS2) in a water-ethanol mixture, to avoid the use of harsh organic solvents, whilst still producing sufficient concentration of MoS2 in suspension. The exfoliated flakes are converted into MoS2 quantum dots (QDs), through a hydrothermal procedure. Alternatively, when the flakes are processed with precursors for zinc sulphide (ZnS) synthesis, a simultaneous break-down and composite growth is achieved. The products are separated by centrifugation, into large ZnS spheres (200-300 nm) and small MoS2-ZnS hybrid QD materials (QDs, respectively. The PL emission from MoS2-ZnS QDs is of high energy and is more intense than the bare MoS2 flakes or QDs, with a quantum yield as high as 1.96%. The emission wavelength is independent from the excitation wavelength and does not change over time. Due to such properties, the developed hybrid QDs are potentially suitable for imaging and sensing

  8. Near-infrared photodetectors utilizing MoS2-based heterojunctions

    Near-infrared photodetectors are developed using graphene/MoS2 and WSe2/MoS2 vertical heterojunctions. These heterojunctions exhibit diode-rectifying behavior in the dark and enhanced photocurrent upon near-infrared irradiation. The photocurrent increases with increasing near-infrared power, leading to the photoresponsibility of 0.14 and 0.3 A W−1 for the graphene/MoS2 and WSe2/MoS2 heterojunctions, respectively, which are much higher than the photoresponsibility reported for a multilayer MoS2 phototransistor

  9. High temperature ferromagnetism in Cu-doped MoS2 nanosheets

    Xia, Baorui; Guo, Qing; Gao, Daqiang; Shi, Shoupeng; Tao, Kun

    2016-04-01

    The synthesis of 2D metal chalcogenide based on ferromagnetic nanosheets is in high demand for modern electronics and spintronics applications. Herein, Cu-doped MoS2 nanosheets were successfully prepared by a hydrothermal method. Magnetic measurement results indicate that the doping of Cu ions can introduce ferromagnetism into MoS2 nanosheets, where saturate magnetization increases with increased Cu concentration. Further, the hysteresis curves measured at different temperatures demonstrate a high Curie temperature of 930 K for the Cu-doped MoS2 nanosheets. This result opens a new path to exploring spintronics in pristine 2D nanostructures by non-magnetic atom doping.

  10. Quantum confinement effects across two-dimensional planes in MoS2 quantum dots

    The low quantum yield (∼10−5) has restricted practical use of photoluminescence (PL) from MoS2 composed of a few layers, but the quantum confinement effects across two-dimensional planes are believed to be able to boost the PL intensity. In this work, PL from 2 to 9 nm MoS2 quantum dots (QDs) is excluded from the solvent and the absorption and PL spectra are shown to be consistent with the size distribution. PL from MoS2 QDs is also found to be sensitive to aggregation due to the size effect

  11. Mutation analysis of the c-mos proto-oncogene in human ovarian teratomas.

    de Foy, K. A.; Gayther, S A; Colledge, W.H.; Crockett, S; Scott, I V; Evans, M.J.; Ponder, B A

    1998-01-01

    Female transgenic mice lacking a functional c-mos proto-oncogene develop ovarian teratomas, indicating that c-mos may behave as a tumour-suppressor gene for this type of tumour. We have analysed the entire coding region of the c-MOS gene in a series of human ovarian teratomas to determine whether there are any cancer-causing alterations. DNA from twenty teratomas was analysed by single-strand conformational analysis (SSCA) and heteroduplex analysis (HA) to screen for somatic and germline muta...

  12. MoS2 and semiconductors in the flatland

    Oleg V. Yazyev

    2015-01-01

    Full Text Available The fascinating properties of graphene, the first two-dimensional (2D material, and the accompanying strong activity in the research community have sparked a renewed interest in related layered crystalline materials with unique electronic and optical properties. Their superb mechanical properties, optical transparency, direct band gap and large degree of electrostatic control due to their atomic scale thickness make them interesting inorganic nanosystems for a wide variety of applications. In this review we will present a short history of research in the synthesis, band properties and potential applications of 2D semiconductors with a particular emphasis on MoS2, the prototypical and best-studied material from this family.

  13. Epitaxial CoSi2 on MOS devices

    Lim, Chong Wee (Urbana, IL); Shin, Chan Soo (Daejeon, KR); Petrov, Ivan Georgiev (Champaign, IL); Greene, Joseph E. (Champaign, IL)

    2005-01-25

    An Si.sub.x N.sub.y or SiO.sub.x N.sub.y liner is formed on a MOS device. Cobalt is then deposited and reacts to form an epitaxial CoSi.sub.2 layer underneath the liner. The CoSi.sub.2 layer may be formed through a solid phase epitaxy or reactive deposition epitaxy salicide process. In addition to high quality epitaxial CoSi.sub.2 layers, the liner formed during the invention can protect device portions during etching processes used to form device contacts. The liner can act as an etch stop layer to prevent excessive removal of the shallow trench isolation, and protect against excessive loss of the CoSi.sub.2 layer.

  14. MoS2-Titanium Contact Interface Reactions.

    McDonnell, Stephen; Smyth, Christopher; Hinkle, Christopher L; Wallace, Robert M

    2016-03-01

    The formation of the Ti-MoS2 interface, which is heavily utilized in nanoelectronic device research, is studied by X-ray photoelectron spectroscopy. It is found that, if deposition under high vacuum (∼1 × 10(-6) mbar) as opposed to ultrahigh vacuum (∼1 × 10(-9) mbar) conditions are used, TiO2 forms at the interface rather than Ti. The high vacuum deposition results in an interface free of any detectable reaction between the semiconductor and the deposited contact. In contrast, when metallic titanium is successfully deposited by carrying out depositions in ultrahigh vacuum, the titanium reacts with MoS2 forming Ti(x)S(y) and metallic Mo at the interface. These results have far reaching implications as many prior studies assuming Ti contacts may have actually used TiO2 due to the nature of the deposition tools used. PMID:26967016

  15. Ultralarge area MOS tunnel devices for electron emission

    Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm;

    2007-01-01

    A comparative analysis of metal-oxide-semiconductor (MOS) capacitors by capacitance-voltage (C-V) and current-voltage (I-V) characteristics has been employed to characterize the thickness variations of the oxide on different length scales. Ultralarge area (1 cm(2)) ultrathin (similar to 5 nm oxide...... density. Oxide thicknesses have been extracted by fitting a model based on Fermi-Dirac statistics to the C-V characteristics. By plotting I-V characteristics in a Fowler plot, a measure of the thickness of the oxide can be extracted from the tunnel current. These apparent thicknesses show a high degree...... capacitors with different oxide areas ranging from 1 cm(2) to 10 mu m(2), using the slope from Fowler-Nordheim plots of the I-V characteristics as a measure of the oxide thickness, points toward two length scales of oxide thickness variations being similar to 1 cm and similar to 10 mu m, respectively....

  16. Lessons learned from decommissioning experience in Mos SIA Radon

    The Center of Radioactive Waste Transportation and Emergency Works was established at Mos SIA Radon in 1994. The Center is responsible for: preparation of decontamination plans and decision making for site decontamination, developing of advanced decontamination techniques, full scale decontamination service for sites located in the Central Part of Russian Federation, and waste transportation. Its main tasks are: Removal of radioactive wastes (RAW); Cleanup of radioactive contamination; Transportation of RAW and spent radioactive sources; Radiation control and inspections; Decontamination, dismantling and decommissioning of contaminated facilities and sites; Decontamination/ laundering of protective clothes; Development of new decontamination/demolishing methods. Its achievements since 1994 include: More than 650 historical sites decontaminated; More than 23000 cubic meters of radwastes transported for treatment and storage; More than 800 emergency calls; More than 10 industrial/research sites decommissioned. (author)

  17. Bandgap tuning in armchair MoS2 nanoribbon

    Yue, Qu; Chang, Shengli; Kang, Jun; Zhang, Xueao; Shao, Zhengzheng; Qin, Shiqiao; Li, Jingbo

    2012-08-01

    We report on the first-principles calculations of bandgap modulation in armchair MoS2 nanoribbon (AMoS2NR) by transverse and perpendicular electric fields respectively. In the monolayer AMoS2NR case, it is shown that the bandgap can be significantly reduced and be closed by transverse field, whereas the bandgap modulation is absent under perpendicular field. The critical strength of transverse field for gap closure decreases as ribbon width increases. In the multilayer AMoS2NR case, in contrast, it is shown that the bandgap can be effectively reduced by both transverse and perpendicular fields. Nevertheless, it seems that the two fields exhibit different modulation effects on the gap. The critical strength of perpendicular field for gap closure decreases with increasing number of layers, while the critical strength of transverse field is almost independent of it.

  18. Density functional theory study of chemical sensing on surfaces of single-layer MoS2 and graphene

    In this work, density functional theory (DFT) calculations have been used to investigate chemical sensing on surfaces of single-layer MoS2 and graphene, considering the adsorption of the chemical compounds triethylamine, acetone, tetrahydrofuran, methanol, 2,4,6-trinitrotoluene, o-nitrotoluene, o-dichlorobenzene, and 1,5-dicholoropentane. Physisorption of the adsorbates on free-standing surfaces was analyzed in detail for optimized material structures, considering various possible adsorption sites. Similar adsorption characteristics for the two surface types were demonstrated, where inclusion of a correction to the DFT functional for London dispersion was shown to be important to capture interactions at the interface of molecular adsorbate and surface. Charge transfer analyses for adsorbed free-standing surfaces generally demonstrated very small effects. However, charge transfer upon inclusion of the underlying SiO2 substrate rationalized experimental observations for some of the adsorbates considered. A larger intrinsic response for the electron-donor triethylamine adsorbed on MoS2 as compared to graphene was demonstrated, which may assist in devising chemical sensors for improved sensitivity

  19. Synthesizing 2D MoS2 Nanofins on carbon nanospheres as catalyst support for Proton Exchange Membrane Fuel Cells.

    Hu, Yan; Chua, Daniel H C

    2016-01-01

    Highly dense 2D MoS2 fin-like nanostructures on carbon nanospheres were fabricated and formed the main catalyst support structure in the oxygen reduction reaction (ORR) for polymer electrolyte membrane (PEM) fuel cells. These nanofins were observed growing perpendicular to the carbon nanosphere surface in random orientations and high resolution transmission electron microscope confirmed 2D layers. The PEM fuel cell test showed enhanced electrochemical activity with good stability, generating over 8.5 W.mgPt(-1) as compared to standard carbon black of 7.4 W.mgPt(-1) under normal operating conditions. Electrochemical Impedance Spectroscopy confirmed that the performance improvement is highly due to the excellent water management of the MoS2 lamellar network, which facilitates water retention at low current density and flood prevention at high current density. Reliability test further demonstrated that these nanofins are highly stable in the electrochemical reaction and is an excellent ORR catalyst support. PMID:27302135

  20. Versatile MoS2 Nanosheets in ITO-Free and Semi-transparent Polymer Power-generating Glass

    Hu, Xiaotian; Chen, Lie; Tan, Licheng; Zhang, Yong; Hu, Lin; Xie, Bing; Chen, Yiwang

    2015-07-01

    Chemical exfoliated ultra-thin MoS2 nanosheets (NSs) with well 2D structure were demonstrated for interfacial layers and Ag nanowires composite transparent electrode in polymer solar cells (PSCs). The smooth and uniform n-type and p-type (after the plasma treatment) MoS2 NSs could improve fill factor of devices and light absorption in active layer. The optimized Ag nanowires-MoS2 NSs (AgNW-MoS2 NSs) transparent electrode presented a low sheet resistance of 9.8 Ω sq-1, and the corresponding transmittance also exhibited a high value of 93.1% at 550 nm. As a result, ITO-free PSCs based on AgNW-MoS2 NSs/n-MoS2 NSs cathode and p-MoS2 NSs/Ag anode achieved a highest PCE of 8.72%. Furthermore, a high efficiency (6.55%), large area and low cost semi-transparent power-generating glass was obtained, after reducing the thickness of top Ag electrode from 100 nm to 30 nm. To our best knowledge, it is the highest performance for semi-transparent PSCs devices reported up to now. The novel semi-transparent power-generating glass showed good performance and color purity for commercial applications in the near future.

  1. High energy (MeV) ion beam modifications of sputtered MoS2 coatings on sapphire

    The present article reports on the results of our investigations of high-energy (MeV) ion irradiation on the microstructural and tribological properties of dc magnetron sputtered MoS2 films. Films of thicknesses 500-7500 A were deposited on NaCl, Si and sapphire substrates and subsequently ion irradiated by 2 MeV Ag+ ions at a dose of 5x1015 cm-2. Scanning and transmission electron microscopy. Rutherford backscattering and X-ray diffraction techniques were utilized to study the structural, morphological and compositional changes of the film due to ion irradiation. The friction coefficient and sliding life were determined by pin-on-disc tests. Both as-deposited and ion-irradiated films were found to be amorphous having a stoichiometry of MoS1.8. A low friction coefficient in the range 0.03-0.04 was measured for both as-deposited and ion-irradiated films. However, the sliding life of ion-irradiated film was found to increase more than tenfold compared to as-deposited films indicating improved bonding at the interface. (orig.)

  2. Synthesizing 2D MoS2 Nanofins on carbon nanospheres as catalyst support for Proton Exchange Membrane Fuel Cells

    Hu, Yan; Chua, Daniel H. C.

    2016-06-01

    Highly dense 2D MoS2 fin-like nanostructures on carbon nanospheres were fabricated and formed the main catalyst support structure in the oxygen reduction reaction (ORR) for polymer electrolyte membrane (PEM) fuel cells. These nanofins were observed growing perpendicular to the carbon nanosphere surface in random orientations and high resolution transmission electron microscope confirmed 2D layers. The PEM fuel cell test showed enhanced electrochemical activity with good stability, generating over 8.5 W.mgPt‑1 as compared to standard carbon black of 7.4 W.mgPt‑1 under normal operating conditions. Electrochemical Impedance Spectroscopy confirmed that the performance improvement is highly due to the excellent water management of the MoS2 lamellar network, which facilitates water retention at low current density and flood prevention at high current density. Reliability test further demonstrated that these nanofins are highly stable in the electrochemical reaction and is an excellent ORR catalyst support.

  3. A low power cryogenic 512 × 512-pixel infrared readout integrated circuit with modified MOS device model

    Zhao, Hongliang; Liu, Xinghui; Xu, Chao

    2013-11-01

    A low power cryogenic readout integrated circuit (ROIC) for 512 × 512-pixel infrared focal plane array (IRFPA) image system, is presented. In order to improve the precision of the circuit simulation at cryogenic temperatures, a modified MOS device model is proposed. The model is based on BSIM3 model, and uses correction parameters to describe carrier freeze-out effect at low temperatures to improve the fitting accuracy for low temperature MOS device simulation. A capacitive trans-impedance amplifier (CTIA) with inherent correlated double sampling (CDS) configuration is employed to realize a high performance readout interfacing circuit in a pixel area of 30 × 30 μm2. Optimized column readout timing and structure are applied to reduce the power consumption. The experimental chip fabricated by a standard 0.35 μm 2P4M CMOS process shows more than 10 MHz readout rate with less than 70 mW power consumption under 3.3 V supply voltage at 77-150 K operated temperatures. And it occupies an area of 18 × 17 mm2.

  4. The Pore Confinement Effect of FDU-12 Mesochannels on MoS2 Active Phases and Their Hydrodesulfurization Performance

    Cong Liu

    2016-01-01

    Full Text Available FDU-12 silica with highly ordered face-centered cubic mesoporous structure is developed as support to prepare Mo/FDU-12 catalysts for hydrodesulfurization (HDS of dibenzothiophene (DBT. A series of Mo/FDU-12 catalysts are synthesized by using incipient wetness impregnation method with different MoO3 loadings (6, 8, 10, 12, and 15 wt.%. The objective of this work is to explore the pore confinement effect of FDU-12 mesochannels on the MoS2 morphology with various metal loadings. It is found that, as increasing MoO3 loadings from 6 to 15 wt.%, the MoS2 nanocrystallites transform from monolayer to multilayer and the morphology changes from straight layered to curved and then to ring-like and finally to spherical-like morphology due to the restriction of cage-like pore channels of FDU-12 support. The HDS results show that the catalytic activity increases first and then decreases with the best HDS performance at the MoO3 loading of 10 wt.%. In addition, we compared the HDS activity of Mo catalyst supported on FDU-12 with that on the commercial γ-Al2O3 and SBA-15; the result exhibits that FDU-12 is superior to the other two supports due to its large pore size and ordered three-dimensional open pore channels.

  5. Heterojunction hybrid devices from vapor phase grown MoS2.

    Yim, Chanyoung; O'Brien, Maria; McEvoy, Niall; Riazimehr, Sarah; Schäfer-Eberwein, Heiko; Bablich, Andreas; Pawar, Ravinder; Iannaccone, Giuseppe; Downing, Clive; Fiori, Gianluca; Lemme, Max C; Duesberg, Georg S

    2014-01-01

    We investigate a vertically-stacked hybrid photodiode consisting of a thin n-type molybdenum disulfide (MoS2) layer transferred onto p-type silicon. The fabrication is scalable as the MoS2 is grown by a controlled and tunable vapor phase sulfurization process. The obtained large-scale p-n heterojunction diodes exhibit notable photoconductivity which can be tuned by modifying the thickness of the MoS2 layer. The diodes have a broad spectral response due to direct and indirect band transitions of the nanoscale MoS2. Further, we observe a blue-shift of the spectral response into the visible range. The results are a significant step towards scalable fabrication of vertical devices from two-dimensional materials and constitute a new paradigm for materials engineering. PMID:24975741

  6. Morphology evolution of MoS2: From monodisperse nanoparticles to self-assembled nanobelts

    Yu, Ting; Luo, Xingfang; Han, Shuming; Cao, Yingjie; Yuan, Cailei; Yang, Yong; Li, Qinliang

    2016-02-01

    The MoS2 nanobelts were successfully synthesized on SiO2/Si substrates using a vapor phase sulfurization process. Atomic force microscopy (AFM) techniques are employed to comprehensively study the morphology evolution of MoS2 from monodisperse nanoparticles to self-assembled nanobelts on the SiO2/Si substrates. A possible three-step morphology evolution process, which includes initial nucleation process, self-assembly process, and subsequent crystal growth process (Ostwald ripening), is proposed to explain the formation of MoS2. Moreover, MoS2 nanobelts are characterized by Raman spectroscopy and photo-luminescence (PL). These results provide the possibility to develop an easier-to-cooperate and morphology-controllable approach to fabricate novel architectures.

  7. Monolayers of MoS2 as an oxidation protective nanocoating material

    First-principle calculations are employed to investigate the interaction of oxygen with ideal and defective MoS2 monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulfur atoms, the oxygen molecule only weakly interacts with the surface. The penetration of oxygen atoms and molecules through a defect-free MoS2 monolayer is prevented by a very high diffusion barrier indicating that MoS2 can serve as a protective layer for oxidation. The analysis is extended to WS2 and similar coating characteristics are obtained. Our calculations indicate that ideal and continuous MoS2 and WS2 monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be considered as an efficient nanocoating material

  8. Monolayers of MoS2 as an oxidation protective nanocoating material

    Sen, H. Sener; Sahin, H.; Peeters, F. M.; Durgun, E.

    2014-08-01

    First-principle calculations are employed to investigate the interaction of oxygen with ideal and defective MoS2 monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulfur atoms, the oxygen molecule only weakly interacts with the surface. The penetration of oxygen atoms and molecules through a defect-free MoS2 monolayer is prevented by a very high diffusion barrier indicating that MoS2 can serve as a protective layer for oxidation. The analysis is extended to WS2 and similar coating characteristics are obtained. Our calculations indicate that ideal and continuous MoS2 and WS2 monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be considered as an efficient nanocoating material.

  9. Electrophoretic deposition of pure MoS2 dry film lubricant coatings

    Electrophoresis can be employed to deposit a wide variety of materials including MoS2 coatings that exhibit properties comparable to the properties of sputtered MoS2 coatings used as lubricants for vacuum applications. Coatings which display coefficients of friction as low as 0.03 can be deposited from an aqueous suspension containing approximately 2.5 wt %, micrometer-sized MoS2 particles stablized with approximately 500 ppm of a nonionic surfactant. Uniform coatings with appropriate thicknesses can be deposited on nonplanar surfaces in minutes with minimal equipment. The morphology of the as-deposited coatings suggest that MoS2 is electrophoretically active as a result of a net positive surface charge along the basal plane

  10. MoS2 functionalization for ultra-thin atomic layer deposited dielectrics

    The effect of room temperature ultraviolet-ozone (UV-O3) exposure of MoS2 on the uniformity of subsequent atomic layer deposition of Al2O3 is investigated. It is found that a UV-O3 pre-treatment removes adsorbed carbon contamination from the MoS2 surface and also functionalizes the MoS2 surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS2 surface and provides nucleation sites for atomic layer deposition of Al2O3. The enhanced nucleation is found to be dependent on the thin film deposition temperature

  11. Orientation Dependent Thermal Conductance in Single-Layer MoS2

    Jiang, Jin-Wu; Zhuang, Xiaoying; Rabczuk, Timon

    2013-07-01

    We investigate the thermal conductivity in the armchair and zigzag MoS2 nanoribbons, by combining the non-equilibrium Green's function approach and the first-principles method. A strong orientation dependence is observed in the thermal conductivity. Particularly, the thermal conductivity for the armchair MoS2 nanoribbon is about 673.6 Wm-1 K-1 in the armchair nanoribbon, and 841.1 Wm-1 K-1 in the zigzag nanoribbon at room temperature. By calculating the Caroli transmission, we disclose the underlying mechanism for this strong orientation dependence to be the fewer phonon transport channels in the armchair MoS2 nanoribbon in the frequency range of [150, 200] cm-1. Through the scaling of the phonon dispersion, we further illustrate that the thermal conductivity calculated for the MoS2 nanoribbon is esentially in consistent with the superior thermal conductivity found for graphene.

  12. Scalable fabrication of a hybrid field-effect and acousto-electric device by direct growth of monolayer MoS2/LiNbO3

    Preciado, Edwin; Schülein, Florian J. R.; Nguyen, Ariana E.; Barroso, David; Isarraraz, Miguel; von Son, Gretel; Lu, I.-Hsi; Michailow, Wladislaw; Möller, Benjamin; Klee, Velveth; Mann, John; Wixforth, Achim; Bartels, Ludwig; Krenner, Hubert J.

    2015-10-01

    Lithium niobate is the archetypical ferroelectric material and the substrate of choice for numerous applications including surface acoustic wave radio frequencies devices and integrated optics. It offers a unique combination of substantial piezoelectric and birefringent properties, yet its lack of optical activity and semiconducting transport hamper application in optoelectronics. Here we fabricate and characterize a hybrid MoS2/LiNbO3 acousto-electric device via a scalable route that uses millimetre-scale direct chemical vapour deposition of MoS2 followed by lithographic definition of a field-effect transistor structure on top. The prototypical device exhibits electrical characteristics competitive with MoS2 devices on silicon. Surface acoustic waves excited on the substrate can manipulate and probe the electrical transport in the monolayer device in a contact-free manner. We realize both a sound-driven battery and an acoustic photodetector. Our findings open directions to non-invasive investigation of electrical properties of monolayer films.

  13. Pressure evolution of the potential barriers of phase transition of MoS2, MoSe2 and MoTe2.

    Fan, Xaiofeng; Singh, David J; Jiang, Q; Zheng, W T

    2016-04-28

    Two-dimensional crystals with weak layer interactions, such as twisted graphene, have been a focus of research recently. As a representative example, transitional metal dichalcogenides show a lot of fascinating properties due to stacking orders and spin-orbit coupling. We analyzed the dynamic energy barrier of possible phase transitions in MoX2 (X = S, Se and Te) with first-principles methods. In the structural transition from 2Hc to 2Ha, the energy barrier is found to be increased following an increase of pressure which is different from the phase transition in usual semiconductors. Among MoS2, MoSe2 and MoTe2, the energy barrier of MoS2 is the lowest and the stability of both 2Hc and 2Ha is reversed under pressure for MoS2. It is found that the absence of a phase transition in MoSe2 and MoTe2 is due to the competition between van der Waals interaction of layers and the coulomb interaction of Mo and X in nearest-neighbor layer of Mo in both phases. PMID:27074155

  14. Laser Direct Writing Process for Making Electrodes and High-k Sol-Gel ZrO2 for Boosting Performances of MoS2 Transistors.

    Kwon, Hyuk-Jun; Jang, Jaewon; Grigoropoulos, Costas P

    2016-04-13

    A series of two-dimensional (2D) transition metal dichalcogenides (TMDCs), including molybdenum disulfide (MoS2), can be attractive materials for photonic and electronic applications due to their exceptional properties. Among these unique properties, high mobility of 2D TMDCs enables realization of high-performance nanoelectronics based on a thin film transistor (TFT) platform. In this contribution, we report highly enhanced field effect mobility (μ(eff) = 50.1 cm(2)/(V s), ∼2.5 times) of MoS2 TFTs through the sol-gel processed high-k ZrO2 (∼22.0) insulator, compared to those of typical MoS2/SiO2/Si structures (μ(eff) = 19.4 cm(2)/(V s)) because a high-k dielectric layer can suppress Coulomb electron scattering and reduce interface trap concentration. Additionally, in order to avoid costly conventional mask based photolithography and define the patterns, we employ a simple laser direct writing (LDW) process. This process allows precise and flexible control with reasonable resolution (up to ∼10 nm), depending on the system, and enables fabrication of arbitrarily patterned devices. Taking advantage of continuing developments in laser technology offers a substantial cost decrease, and LDW may emerge as a promising technology. PMID:27011225

  15. Free MoS2 Nanoflowers Grown on Graphene by Microwave-Assisted Synthesis as Highly Efficient Non-Noble-Metal Electrocatalysts for the Hydrogen Evolution Reaction

    Cao, Jiamu; Zhang, Xuelin; Zhang, Yufeng; Zhou, Jing; Chen, Yinuo; Liu, Xiaowei

    2016-01-01

    Advanced approaches to preparing non-noble-metal electrocatalysts for the hydrogen evolution reaction (HER) are considered to be a significant breakthrough in promoting the exploration of renewable resources. In this work, a hybrid material of MoS2 nanoflowers (NFs) on reduced graphene oxide (rGO) was synthesized as a HER catalyst via an environmentally friendly, efficient approach that is also suitable for mass production. Small-sized MoS2 NFs with a diameter of ca. 190 nm and an abundance of exposed edges were prepared by a hydrothermal method and were subsequently supported on rGO by microwave-assisted synthesis. The results show that MoS2 NFs were distributed uniformly on the remarkably reduced GO and preserved the outstanding original structural features perfectly. Electrochemical tests show that the as-prepared hybrid material exhibited excellent HER activity, with a small Tafel slope of 80 mV/decade and a low overpotential of 170 mV. PMID:27556402

  16. Density functional theory study of Li, Na, and Mg intercalation and diffusion in MoS2 with controlled interlayer spacing

    Shuai, Jing; Deog Yoo, Hyun; Liang, Yanliang; Li, Yifei; Yao, Yan; Grabow, Lars C.

    2016-06-01

    Layered materials, such as the transition metal dichalcogenide molybdenum disulfide (MoS2), are promising materials for ion storage in electrodes of rechargeable batteries. To extend the application range of these materials to ions beyond lithium-ions, we used van der Waals corrected density functional theory simulations to study the intercalation and diffusion of lithium (Li), sodium (Na), and magnesium (Mg) in the 2H structure of MoS2 as a function of interlayer spacing. All three species exhibit an optimal intercalation energy, which is reached at about 11% expansion for Li and Mg, and 23% expansion for Na. Similarly, the slow diffusion kinetics of large Na and divalent Mg-ions can be improved by layer expansion. When the interlayer spacing is increased by about 35% from its equilibrium value, the diffusion of Na and Mg-ions becomes more facile than the diffusion of small, monovalent Li-ions, with diffusion barriers similar to those of Li in graphene. Our results indicate that interlayer expansion is a promising technique to improve intercalation kinetics and thermodynamics for large and/or multivalent ions in MoS2, which can be a major limitation to battery performance. The rationalization of our results in terms of bonding geometries forms the basis of a battery electrode design framework with applications for a wide range of layered materials.

  17. Investigations on MgO-dielectric GaN/AlGaN/GaN MOS-HEMTs by using an ultrasonic spray pyrolysis deposition technique

    Lee, Ching-Sung; Hsu, Wei-Chou; Liu, Han-Yin; Wu, Ting-Ting; Sun, Wen-Ching; Wei, Sung-Yen; Yu, Sheng-Min

    2016-05-01

    This work investigates GaN/Al0.24Ga0.76N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) grown on a Si substrate with MgO gate dielectric by using the non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. The oxide layer thickness is tuned to be 30 nm with the dielectric constant of 8.8. Electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), transmission electron microscopy (TEM), C-V, low-frequency noise spectra, and pulsed I-V measurements are performed to characterize the interface and oxide quality for the MOS-gate structure. Improved device performances have been successfully achieved for the present MOS-HEMT (Schottky-gate HEMT) design, consisting of a maximum drain-source current density (I DS, max) of 681 (500) mA/mm at V GS = 4 (2) V, I DS at V GS = 0 V (I DSS0) of 329 (289) mA/mm, gate-voltage swing (GVS) of 2.2 (1.6) V, two-terminal gate-drain breakdown voltage (BV GD) of -123 (-104) V, turn-on voltage (V on) of 1.7 (0.8) V, three-terminal off-state drain-source breakdown voltage (BV DS) of 119 (96) V, and on/off current ratio (I on/I off) of 2.5 × 108 (1.2 × 103) at 300 K. Improved high-frequency and power performances are also achieved in the present MOS-HEMT design.

  18. Effects of heat and UV radiation on the mobilization of transposon mariner-Mos1.

    Jardim, Sinara Santos; Schuch, André Passaglia; Pereira, Camila Moura; Loreto, Elgion Lucio Silva

    2015-09-01

    There are many complex interactions between transposable elements (TEs) and host genomes. Environmental changes that induce stressful conditions help to contribute for increasing complexity of these interactions. The transposon mariner-Mos1 increases its mobilization under mild heat stress. It has putative heat shock elements (HSEs), which are probably activated by heat shock factors (HSFs). Ultraviolet radiation (UVC) is a stressor that has been suggested as able to activate heat shock protein genes (Hsp). In this study, we test the hypothesis that if UVC induces Hsp expression, as heat does, it could also promote mariner-Mos1 transposition and mobilization. The Drosophila simulans white-peach is a mutant lineage that indicates the mariner-Mos1 transposition phenotypically through the formation of mosaic eyes. This lineage was exposed to UVC or mild heat stress (28 °C) in order to evaluate the induction of mariner-Mos1 expression by RT-qPCR, as well as the mariner-Mos1 mobilization activity based on the count number of red spots in the eyes. The effects of both treatments on the developmental time of flies and cell cycle progression were also investigated. Both the analysis of eyes and mariner-Mos1 gene expression indicate that UVC radiation has no effect in mariner-Mos1 transposition, although heat increases the expression and mobilization of this TE soon after the treatment. However, the expression of Hsp70 gene increased after 24 h of UVC exposure, suggesting different pathway of activation. These results showed that heat promotes mariner-Mos1 mobilization, although UVC does not induce the expression or mobilization of this TE. PMID:26092118

  19. Active control of surface plasmon resonance in MoS2-Ag hybrid nanostructures

    Zu, Shuai; Li, Bowen; Gong, Yongji; Ajayan, Pulickel M.; Fang, Zheyu

    2016-01-01

    Molybdenum disulfide (MoS2) monolayers have attracted much attention for their novel optical properties and efficient light-matter interactions. When excited by incident laser, the optical response of MoS2 monolayers was effectively modified by elementary photo-excited excitons owing to their large exciton binding energy, which can be facilitated for the optical-controllable exciton-plasmon interactions. Inspired by this concept, we experimentally investigated active light control of surface ...

  20. Lattice Vibrational Modes and Phonon Thermal Conductivity of Monolayer MoS2

    Cai, Yongqing; Lan, Jinghua; Zhang, Gang; Zhang, Yong-Wei

    2013-01-01

    The anharmonic behavior of phonons and intrinsic thermal conductivity associated with the Umklapp scattering in monolayer MoS2 sheet are investigated via first-principles calculations within the framework of density functional perturbation theory. In contrast to the negative Gruneissen parameter occurring in low frequency modes in graphene, positive Gruneissen parameter in the whole Brillouin zone is demonstrated in monolayer MoS2 with much larger Gruneissen parameter for acoustic modes than ...