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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. 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.

  13. 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)

  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. 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.

  11. 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.

  12. 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

  13. 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.

  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. 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

  12. 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

  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. 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.

  16. 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

  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. 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.

  19. 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.

  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

    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

    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.

  11. 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

  12. 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.

  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. 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.

  15. 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

  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. 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.

  6. 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.

  7. 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.

  8. 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

  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. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  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. 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

  8. 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

  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. 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...

  11. 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...

  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. 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.

  7. 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)

  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

    2016-01-01

    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

  9. 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.

  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. 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

  13. 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

  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. 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.

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

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

    2016-03-01

    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.

  3. 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

  4. 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.

  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. 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.

  11. 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...

  12. 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...

  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. 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.

  1. 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

  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. 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

  8. 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.

  9. 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)

  10. 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

  11. 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.

  12. 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.

  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.