Bulk MoS Research Articles

Effect of Bulk MoS₂ on the Metabolic Profile of Yeast.

MoS2, a kind of two-dimensional material with unique performances, has been widely used in many fields. However, an in-depth understanding of its toxicity is still needed, let alone its effects on the environmental microorganism. Herein, we used different methods, including metabolomics technology, to investigate the influence of bulk MoS2 (BMS) on yeast cells. The results indicated that high concentrations (1 mg/L and more) of BMS could destroy cell membrane and induce ROS accumulation. When exposed to a low concentration of BMS (0.1 mg/L), the intracellular concentrations of many metabolites (e.g., fumaric acid, lysine) increased. However, most of their concentrations descended significantly as the yeast cells were treated with BMS of high concentrations (1 mg/L and more). Metabolomics analysis further revealed that exposure to high concentrations of BMS could significantly affect some metabolic pathways such as amino acid and citrate cycle related metabolism. These findings will be beneficial for MoS2 toxicity assessment and further applications.

Probing Interaction between Individual Submonolayer Nanoislands and Bulk MoS2 Using Ambient TERS

Tip-enhanced Raman spectroscopy (TERS) has shown that detecting single molecules with a high spatial resolution is possible in ultrahigh vacuum (UHV) at low temperature with plasmonic metallic substrates. It is still challenging to probe interactions of molecules with semiconductors, which is important in biosensing, photovoltaics, and many other applications. Here we demonstrate that in ambient conditions it is possible to obtain Raman signals from submonolayer molecular islands on bulk MoS2 using TERS. Analysis of relative Raman signal intensity ratio and Raman spectral peak position from spatial TERS mapping showed differences in the adsorbate–adsorbate and adsorbate–substrate interactions on Au and MoS2 substrates. The Raman transition which involves the vibration of the metal center of the CuPc molecule experienced a change in the relative Raman signal intensity ratio due to the differences in the molecule–substrate charge transfer interaction. In comparison to the other vibrational modes, the vibrat...

Electronic-dimensionality reduction of bulk MoS2 by hydrogen treatment

A reduction in the electronic-dimensionality of materials is one method for achieving improvements in material properties. Here, a reduction in electronic-dimensionality is demonstrated using a simple hydrogen treatment technique. Quantum well states from hydrogen-treated bulk 2H-MoS2 are observed using angle resolved photoemission spectroscopy (ARPES). The electronic states are confined within a few MoS2 layers after the hydrogen treatment. A significant reduction in the band-gap can also be achieved after the hydrogen treatment, and both phenomena can be explained by the formation of sulfur vacancies generated by the chemical reaction between sulfur and hydrogen.

Integrating sleep and pass transistor logic for leakage power reduction in FinFET circuits

This work impacts on the huge potential of FinFET technology, which can replace bulk MOS below 32 nm. Here, two new techniques are introduced to mitigate leakage power as leakage controlling pass transistor P-type LCPT (P) and leakage controlling pass transistor N-type LCPT(N) techniques. Some existing and proposed circuits are simulated in high performance (HP) and lower standby power FinFET library at 20, 16, 14, 10, and 7 nm by using the Berkley predictive technology module for the sake of comparison. Simulation results of a two-input NAND gate using proposed techniques at 10 MHz frequency using FinFET technology saves a maximum of leakage power using LCSPT (P) at input vector 11 of 98.90% compared with a conventional NAND gate. Similarly LCSPT (N) saves a maximum of leakage power of 98.44% at 10 input vectors compared with LECTOR technique at 20 nm in HP model. Also maximum saving of dynamic power by LCSPT (P) is 59.6% at 14 nm as compared to conventional NAND gate.

Tip-Enhanced Raman Scattering on Bulk MoS2Substrate

Surface-enhanced Raman scattering (SERS) has many applications in nanotechnology, biophotonics, and sensing. Conventional SERS is based on surface plasmon resonances of noble metal nanostructures that enhance molecular Raman signals via electromagnetic mechanism and on molecule-substrate interaction via chemical mechanism. Recent studies used 2-D materials as atomically flat SERS substrates based on the chemical mechanism. Here, we use tip-enhanced Raman scattering (TERS) to enhance Raman signals from copper phthalocyanine molecules deposited on a bulk MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrate by a nanosized gold tip via electromagnetic enhancement. We present a comparative study of MoS2, gold, and SiO2 substrates. MoS2 changes relative intensities of molecular vibrations and provides additional gap-mode enhancement of TERS via interaction with the gold tip. Our results can be used to improve sensitivity and resolution in single molecule detection and imaging on flat substrates.

Electrochemical properties of electrospun MoS2@C nanofiber as electrode material for high-performance supercapacitor application

Abstract The superior cycle life and power density exhibited by supercapacitors stimulate the research interest towards discovering new electrode materials with high specific capacitance and 100% cycle life. Here we demonstrate an enhancement in the electrochemical performance of MoS 2 @C composite nanofibers with reversibility over 2000 cycles towards supercapacitor application. MoS 2 @C composite nanofibers are synthesized by carbonization of stabilized electrospun MoS 2 /PVA composite mat and studied its morphology, composition, and crystal structure through various characterizations. The electrochemical performance of the MoS 2 @C electrode studied in 6 M KOH electrolyte shows a significant enhancement of specific capacitance than bulk MoS 2 . The MoS 2 @C nanofibers exhibit a high specific capacitance of 355.6 Fg −1 at a scan rate of 5 mV s −1 and long cycling stability with specific capacitance retention of 93% up to 2000 cycles.

MoS$_2$ Broadband Coherent Perfect Absorber for Terahertz Waves

We present a comprehensive analysis of terahertz waves propagation through a bulk MoS $_2$ crystal slab. It is shown that broadband coherent perfect absorption can be achieved and the coherent absorptivity can be adjusted from 1.57% to 99.97% by means of phase modulation. Moreover, the relative bandwidth for over 90% coherent absorptivity can be as wide as 179%. By increasing the doping rate in MoS $_2$ crystal, the coherent absorptivity spectrum exhibits a clear blueshift whilst the peak coherent absorptivity remains over 99.9%. Full-wave numerical simulations are further carried out to confirm the validity of our theoretical analysis.

Momentum-resolved hot electron dynamics at the2H−MoS2surface

The layered transition-metal dichalcogenide MoS${}_{2}$ as well as related compounds, such as WS${}_{2}$ and WSe${}_{2}$, undergo a transition from an indirect to a direct band-gap semiconductor when thinned down to a single layer. This unexpected observation, which goes along with substantial changes in electronic and optical properties, has stimulated numerous recent studies on this compound class, including pump-probe time-domain studies addressing fundamental aspects of hot carrier relaxation. So far, mainly all-optical methods have been applied to probe the ultrafast dynamics in a rather comprehensive manner. Due to intermixing of different processes and a lack of momentum-resolution, the interpretation of such data is, however, not necessarily straightforward. In order to complement these studies, the authors present here results of a time- and angle-resolved photoemission (trARPES) experiment on bulk MoS${}_{2}$, a technique that provides the most direct view onto hot electron dynamics in energy and momentum space. Surprisingly, the new data agree well with past results of monolayer MoS${}_{2}$ as opposed to bulk MoS${}_{2}$. The authors interpret this finding in terms of the high density of surface defects in MoS${}_{2}$ samples, which substantially affect hot carrier relaxation due to trapping. In contrast to all optical studies, trARPES is very efficient in probing such processes owing to the extreme surface sensitivity of photoemission.

Study of temperature variation on threshold voltage and sub-threshold slope of E $$\delta$$ δ DC MOS transistor including quantum corrections and reduction techniques

For low power System-on-Chip applications, where cost is a critical factor, recently proposed epitaxial delta doped channel (E\(\delta\)DC) structure is a promising alternative architecture within the planar bulk MOS transistor technology due to enhanced electrostatic integrity and reduced threshold voltage variability Sengupta and Pandit (IEEE Trans Electron Dev 63(2):551–557, 2016). In this paper we present a comprehensive analytical and technology computer-aided design (TCAD) simulation study of the effects of variation of temperature on the threshold voltage and sub-threshold slope of an n-type E\(\delta\)DC MOS transistor in the wide range of 100–500 K. We assume Berkeley Short Channel IGFET Model (BSIM) framework for the analytical model. The quantum correction of the threshold voltage is considered while developing the analytical model. The amount of short channel effects at low and high drain bias increase linearly with temperature above 300 K and reduces with reduction in temperature below 300 K. The sub-threshold slope varies linearly with temperature. Another important contribution of this work is that, we also discuss two strategies for reducing the effect of temperature variations on the threshold voltage at the device design level and at the circuit design level.

A Channel Stress-Profile-Based Compact Model for Threshold Voltage Prediction of Uniaxial Strained HKMG nMOS Transistors

In this paper, a physics-based compact model for the longitudinal and transverse stress profile in the channel of an uniaxially strained bulk MOS transistor is presented. The stress in the channel of a MOS transistor is not uniform and this nonuniform stress distribution results in higher average channel stress with reduction in the gate length. The developed model accurately predicts the average channel stress for different stress liners and transistor dimensions like gate length, gate height, and spacer width. The modeled average stress is then used to calculate the strain induced threshold voltage shift in HKMG nMOS transistors for different stress liners (fixed transistor dimensions) and for different transistor dimensions (fixed stress liner). The accuracy of the model is verified by comparing the threshold voltage shift with the experimental data obtained from the transistors fabricated in the 28 nm HKMG CMOS technology.

Comparison of self-heating and its effect on analogue performance in 28 nm bulk and FDSOI

In this work self-heating and its effect on analogue device parameters are compared in 28nm technology bulk and FDSOI MOS devices. It is shown that for self-heating characterisation in advanced MOSFETs the RF extraction technique is more suitable than the pulsed I–V. It is found that the thermal resistance is ∼3.4 times higher and the temperature rise is ∼2.5 times higher in 28nm gate length FDSOI than in bulk. However, in spite of stronger self-heating, FDSOI devices outperform bulk over a wide frequency range. Moreover, device parameters degradation with temperature is attenuated in FDSOI transistors.

Negative refraction in molybdenum disulfide.

Recently, negative refractions have been demonstrated in uniaxial crystals with no necessary of negative permittivity and permeability. However, the small anisotropy parameterγin the uniaxial crystals limits the negative refraction occurrence only in a small range of the incident light angle, retarding its practical applications. In this paper, we report negative refraction induced by a pronounced anisotropic behavior in the bulk MoS(2). Using the first-principles, the dielectric function and refractive index calculations confirm a uniaxial trait of MoS(2) with a calculated anisotropy parameterγlarger than 2.5 in the entire range of visible wavelength. The critical incident angle to trigger a negative refraction in the bulk MoS(2) is calculated up to 90°. The finite-difference time-domain simulations prove that the incident light with a density of 59.5% can be negatively refracted in a MoS(2) slab with a thickness of 0.1 µm. Our results open up a new pathway for MoS(2)-like materials to a novel field of optical integration.

High-pressure structure, decomposition, and superconductivity ofMoS2

The high pressure structural and electronic evolution of bulk MoS$_2$, an important transition metal layered dichalchogenide, is currently under active investigation. Recent theoretical and experimental work predicted and verified a 2H$_c \to$ 2H$_a$ layer sliding structural transition at 20 GPa and a band overlap semiconductor-semimetal transition in the same pressure range. The 2H$_a$ structure is known to persist up to pressure of 81 GPa but properties at higher pressures remain experimentally unknown. Here we predict, with a reliable first-principles evolutionary search, that major structural 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 non-layered metallic MoS$_2$ structure with space group \textit{P4/mmm}. Unlike semimetallic 2H$_a$-MoS$_2$, both this phase and sulphur in the fully phase separated system are fully metallic and superconducting with higher critical temperatures than alkali-intercalated MoS$_2$.

Flux method growth of bulk MoS2single crystals and their application as a saturable absorber

A 3 mm × 5 mm crystal of MoS2is grown by the Sn flux method.

INTERLAYER INTERACTION AND SCREENING IN MoS2

Electronic band structures and phonon bands of bulk, bilayer and monolayer MoS 2 are studied by DFT and GW methods and discussed in the framework of applicability of the 2D model for layered systems. The MoS 2 monolayer is found to be a direct gap semiconductor with the top of the valence band and the bottom of the conduction band at K-point. For a bulk MoS 2, the bandgap, estimated within GW, agrees with the indirect bandgap obtained in experiment. However, for a MoS 2 monolayer, the GW-derived gap exceeds the energy of the photoluminescence line by ~0.9 eV. In contrast, the LDA value (1.84 eV) is consistent with the position of the photoluminescence line as well as with absorption spectroscopy and photoconductivity experiments. A significant overlap of the LDA-derived electron densities (in contrast to GGA results) indicates that the interlayer interaction in MoS 2 can be explained by the exchange interaction. Phonon bands, calculated for MoS 2 monolayer and bilayer within LDA, are consistent with Raman spectra, thus indicating the capability of LDA to correctly describe interactions in the layered system, including the interlayer interactions usually attributed to van der Waals forces.

IMPROVEMENT IN MOBILITY AND CONDUCTIVITY OF FEW-LAYER MoS2 FILMS

We present a study of the influence of annealing and doping on the electrical properties of few-layer (FL) MoS 2 films on Si and quartz substrates deposited using a self-designed metal sulfide chemical vapor deposition (MSCVD) system. FL MoS 2 slices obtained through MSCVD, in the size range of 50–200 nm, were found to be uniformly scattered on the substrates. The conductivity and mobility of these films are greatly enhanced after annealing at 650–850°C. The largest mobility measured for pure MoS 2 on quartz substrate is 6.4×103 cm 2/ Vs , almost two orders of magnitude larger than that of bulk MoS 2 (500 cm2/Vs). We deduce that the superior charge carrier mobility in our sample is mainly attributed to reduced phonon scattering because of a lower carrier density (1010-1011 cm -2) compared to previously documented values (1012-1013 cm -2). Additionally, the conductivity and carrier concentration of FL MoS 2 films were enhanced by about two orders of magnitude compared to those of the as-grown films doped with Cu , Na and Ag ions but not doped with B ions. The films doped with Na and Ag exhibit characteristic p-type conductivity, while those doped with Cu and B exhibit n-type conductivity. Moreover, the MoS 2/ Si heterojunction exhibited good rectification characteristics and excellent conductivity, indicating that the FL MoS 2 films will find many applications in high-efficiency nanodevices.

Production of few-layer MoS2nanosheets through exfoliation of liquid N2–quenched bulk MoS2

An efficient method for the production of few-layer MoS2nanosheets through exfoliation of bulk MoS2compounds that were subject to quenching in liquid N2and subsequent ultrasonication.

A review: the method for synthesis MoS&lt;SUB align="right"&gt;2 monolayer

Until now, there were kinds of methods that had been reported to prepare monolayer MoS 2 , such as solvothermal approach, self-propagating high-temperature synthesis, pulsed electrodeposition, soft chemistry method, laser ablation, liquid exfoliation of bulk MoS 2 , etching MoS 2 , physical vapour deposition, chemical vapour deposition(CVD) and exfoliation etc. But among them, most of the gained MoS 2 are few layers and in a small size of micron meters, except low-pressure chemical vapour deposition (LPCVD) method. After analysis, it can be easily concluded that when the chosen substrate owning a crystal structure similar to MoS 2 , like mica, the gained MoS 2 monolayer can reach a size of several millimetres, this can be explained by the weak bonding between layer and strong bonding existing in the layer of these kind of crystal. The corresponding experiments showed that this large size monolayer prepared by LPCVD own high quality, which can successfully be exploited for a variety of future applications.

Effect of spin-orbit interaction on the optical spectra of single-layer, double-layer, and bulk MoS2

We present converged ab-initio calculations of the optical absorption spectra of single-layer, bi-layer, and bulk MoS$_2$. Both the quasiparticle-energy calculations (on the level of the GW approximation) and the calculation of the absorption spectra (on the level of the Bethe-Salpeter equation) explicitly include spin-orbit coupling, using the full spinorial Kohn-Sham wave-functions as input. Without excitonic effects, the absorption spectra would have the form of a step-function, corresponding to the joint-density of states of a parabolic band-dispersion in 2D. This profile is deformed by a pronounced bound excitonic peak below the continuum onset. The peak is split by spin-orbit interaction in the case of single-layer and (mostly) by inter-layer interaction in the case of double-layer and bulk MoS$_2$. The resulting absorption spectra are thus very similar in the three cases but the interpretation of the spectra is different. Differences in the spectra can be seen around 3 eV where the spectra of single and double-layer are dominated by a strongly bound exciton.

Effects of confinement and environment on the electronic structure and exciton binding energy of MoS2from first principles

Using $GW$ first-principles calculations for few-layer and bulk MoS${}_{2}$, we study the effects of quantum confinement on the electronic structure of this layered material. By solving the Bethe-Salpeter equation, we also evaluate the exciton energy in these systems. Our results are in excellent agreement with the available experimental data. Exciton binding energy is found to dramatically increase from 0.1 eV in the bulk to 1.1 eV in the monolayer. The fundamental band gap increases as well, so that the optical transition energies remain nearly constant. We also demonstrate that environments with different dielectric constants have a profound effect on the electronic structure of the monolayer. Our results can be used for engineering the electronic properties of MoS${}_{2}$ and other transition-metal dichalcogenides and may explain the experimentally observed variations in the mobility of monolayer MoS${}_{2}$.