Bilayer Research Articles

Fabrication of superhydrophobic and flame-retardant polyethylene terephthalate fabric through a fluorine-free layer-by-layer technique

Abstract Polyethylene terephthalate (PET) fabric materials are broadly applied in daily life. However, on one hand, they suffer problem of easy contamination by dust owing to their hydrophilicity, which largely reduce their lifetime. On the other hand, their inflammability will bring many potential safety hazards. Therefore, in this paper, PET fabric material with superior superhydrophobicity and flame retardance through a fluorine-free layer-by-layer (LBL) method was developed, which effectively extended its lifetime and range of applications. The LBL technique was realized through assembly of the mixed polyelectrolytes include chitosan (CS), phytic acid (PA), and ammonium polyphosphate (APP) for only two bilayers (BL), which endowed the fabric superior fire retardance. A final layer consisted of steel slag (SS) particles and octadecylamine (ODA) were further assembled onto the flame-retardant fabric, which successfully gave rise to superior superhydrophobicity with water contact angle (WCA) of 155° and water sliding angle (WSA) of 2°. Compared with the pure fabric, the limited oxygen index (LOI) values of the coated fabric were enhanced from 19.8% to 29.2%. The finally obtained fabric also showed excellent self-cleaning and anti-fouling capabilities. It could be used to highly efficiently separate various oil–water mixtures. It also could endure long-time heating treatment at high temperature of 180 °C without affecting the superhydrophobicity and flame retardance. This method was fluorine-free and made good use of waste SS particles. Such fabric was believed to find vary promising applications in water repellence, self-cleaning, flame retardance, anti-fouling, and liquid separation fields.

Growth-Promoting Mechanism of Bismuth-Doped Cu(In,Ga)Se2 Solar Cells Fabricated at 400 °C.

The classical high-temperature synthesis process of Cu(In,Ga)Se2 (CIGS) solar cells limits their applications on high-temperature intolerant substrates. In this study, a novel low-temperature (400 °C) fabrication strategy of CIGS solar cells is reported using the bismuth (Bi)-doping method, and its growth-promoting mechanism is systematically studied. Different concentrations of Bi are incorporated into pure chalcopyrite quaternary target sputtered-CIGS films by controlling the thickness of the Bi layer. Bi induces considerable grain growth improvement, and an average of approximately 3% absolute efficiency enhancement is achieved for Bi-doped solar cells in comparison with the Bi-free samples. Solar cells doped with a 50 nm Bi layer yield the highest efficiency of 13.04% (without any antireflective coating) using the low-temperature technology. The copper-bismuth-selenium compounds (Cu-Bi-Se, mainly Cu1.6Bi4.8Se8) are crucial in improving the crystallinity of absorbers during the annealing process. These Bi-containing compounds are conclusively observed at the grain boundaries and top and bottom interfaces of CIGS films. The growth promotion is found to be associated with the superior diffusion capacity of Cu-Bi-Se compounds in CIGS films, and these liquid compounds function as carriers to facilitate crystallization. Bi atoms do not enter the CIGS lattices, and the band gaps (Eg) of absorbers remain unchanged. Bi doping reduces the number of CIGS grain boundaries and increases the copper vacancy content in CIGS films, thereby boosting the carrier concentrations. Cu-Bi-Se compounds in grain boundaries significantly enhance the conductivity of grain boundaries and serve as channels for carrier transport. The valence band, Fermi energy level (EF), and conduction band of Bi-doped CIGS films all move downward. This band shift strengthens the band bending of the CdS/CIGS heterojunction and eventually improves the open circuit voltage (Voc) of solar cells. An effective doping method and a novel mechanism can facilitate the low-temperature preparation of CIGS solar cells.

Emergent Insulator-Metal Transition with Tunable Optical and Electrical Gap in Thin Films of a Molecular Conducting Composite.

Composites exhibit unique synergistic properties emerging when components with different properties are combined. The tuning of the energy bandgap in the electronic structure of the material allows designing tailor-made systems with desirable mechanical, electrical, optical, and/or thermal properties. Here, we study an emergent insulator–metal transition at room temperature in bilayered (BL) thin-films comprised of polycarbonate/molecular-metal composites. Temperature-dependent resistance measurements allow monitoring of the electrical bandgap, which is in agreement with the optical bandgap extracted by optical absorption spectroscopy. The semiconductor-like properties of BL films, made with bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF or ET) α-ET2I3 (nano)microcrystals as two-dimensional molecular conductor on one side and insulator polycarbonate as a second ingredient, are attributed to an emergent phenomenon equivalent to the transition from an insulator to a metal. This made it possible to obtain semiconducting BL films with tunable electrical/optical bandgaps ranging from 0 to 2.9 eV. A remarkable aspect is the similarity close to room temperature of the thermal and mechanical properties of both composite components, making these materials ideal candidates to fabricate flexible and soft sensors for stress, pressure, and temperature aiming at applications in wearable human health care and bioelectronics.

Conformation-dependent thermoelectric power factor of multilayer nanocomposites

Polyelectrolyte multilayer thin films, assembled by sequentially depositing bilayer (BL) of poly(allyamine hydrochloride) (PAH) and double-walled carbon nanotubes (DWNT) stabilized in polyacrylic acid (PAA) using the layer-by-layer assembly technique, are studied in an effort to establish the relationships between the conformational changes and thermoelectric performances. Controlling the charge density of weak polyelectrolytes with assembly pH conditions gives rise to a different physical, structural, and mechanical properties. The 7.5PAH/3.5(DWNT-PAA) films exhibit an exponentially-grown thickness behavior due to in-and-out diffusion of the partially charged polyelectrolytes with coiled polymeric conformation, which results in randomly distributed nanotubes within the multilayers. Films made with the same sequences, but with extended polymeric conformation due to high charge density along the polymer chain (PAH at pH 6 and PAA at pH 6.5), show the linear growth behavior with a uniformly oriented nanotube structure and relatively higher elastic modulus. The precise control of the polymeric conformation upon charge density at the nanoscale level significantly affects the thermoelectric performances. A 14 BL 6PAH/6.5(DWNT-PAA) film exhibits an electrical conductivity of 417 S cm−1 and Seebeck coefficient of 85 μV K−1. This translates to a power factor of 301 μW m−1 K−2, which is 75 times higher than the same films made at pH 7.5/3.5.

Magnetic domain configurations of pulsed laser deposited MnBi hard magnetic films

Hard magnetic MnBi films were obtained by appropriate heat treatments of pulsed laser deposited (PLD) (Bi/Mn) films. X-ray diffraction patterns indicated a slight texture of MnBi crystallites and magnetometry measurements showed a slight preferential growth of the crystallites with their c-axis perpendicular to the film plane. Magnetic force microscopy (MFM) measurements displayed the presence of magnetic domains, whose size was in the micrometer range, and which were correlated to the MnBi grains observed in the sample. The addition of extra Mn layers did not modify significantly the previous structural and magnetic results. Nevertheless, the size of the magnetic domains increased to a few microns. However, on adding extra Bi layers, upon annealing, the MnBi grains grew with their c-axes perpendicular to the film plane. A perpendicular to the film magnetic anisotropy was deduced from the hysteresis loops, where an increase in the remanence of the magnetization was measured when the magnetic field was applied perpendicular to the film plane. In these samples, by measuring the magnetic domain configuration of the samples by MFM, we observed that the size of the magnetic domains exceeded the dimensions of the grains. This change in the magnetic structure of the films was assumed to be due to the coupling of the magnetization in the neighboring grains, and it was responsible for the decrease of the coercivity in the Bi rich samples.

Device simulation of GeSe homojunction and vdW GeSe/GeTe heterojunction TFETs for high-performance application

Compared with a two-dimensional (2D) homogeneous channel, the introduction of a 2D/2D homojunction or heterojunction is a promising method to improve the performance of a tunnel field-effect transistor (TFET), mainly by controlling the tunneling barrier. We simulate 10-nm-Lg double-gated GeSe homojunction TFETs and van der Waals (vdW) GeSe/GeTe heterojunction TFETs based on a ballistic quasi-static ab initio quantum transport simulation. Two device configurations are considered for both the homojunction and heterojunction TFETs by placing the bilayer (BL) GeSe or vdW GeSe/GeTe heterojunction as the source or drain, while the channel and the remaining drain or source use monolayer (ML) GeSe. The on-state current (Ion) values of the optimal n-type BL GeSe source homojunction TFET and the optimal p-type vdW GeSe/GeTe drain heterojunction TFET are 2320 and 2387 μA μm−1, respectively, which are 50% and 64% larger than Ion of the ML GeSe homogeneous TFET. Notably, the device performance (Ion, intrinsic delay time τ, and power dissipation PDP) of both the optimal n-type GeSe homojunction and p-type vdW GeSe/GeTe heterojunction TFETs meets the requirements of the International Roadmap for Devices and Systems for high-performance devices for the year 2034 (2020 version).

Masking Ability of Monolithic and Layered Zirconia Crowns on Discolored Substrates.

There is scarce information on the colorimetric behavior of monolithic and layered zirconia crowns in combination with various abutment colors. This study evaluated the masking ability on discolored substrates of monolithic and layered zirconia crowns. Anterior crowns were fabricated using 3Y-TZP zirconia and layering ceramic and divided into three groups: monolithic (ML), bi-layer (BL), and tri-layer (TL). The crowns were placed over eleven substrates (ND1-ND9, zirconia, metal), and CIE L*, a*, b*, C*, and h° color coordinates were measured in the cervical, middle, and incisal areas with a spectrophotometer. Masking ability was calculated using the color difference formula, and values were interpreted according to the perceptibility and acceptability thresholds. Data were analyzed statistically (α = 0.001). The L* coordinate was not significantly different between BL and TL crowns, regardless of the measurement area or substrate (p ≥ 0.001). In the middle area, the L* coordinate of the ML group was statistically different from the BL and TL groups only for zirconia and metal substrates, while in the incisal area, only for ND7 and metal substrates. The a* coordinate was significantly different between the ML and layered crowns for all measurement areas and substrates (except zirconia). The b* and C* coordinates differed significantly between the groups only in the cervical area (p < 0.001). The ML crown had better masking ability than the BL and TL crowns. However, the color differences for ML crowns were below the acceptability threshold for ND2, ND3, and ND7 substrates in the cervical and middle areas and below perceptibility threshold only for the incisal area. The lowest masking ability of the crowns was found for ND9 and metal substrates in all measurement areas.

High-energy–density carbon-coated bismuth nanodots on hierarchically porous molybdenum carbide for superior lithium storage

The use of carbon-based supports, such as graphene and porous carbon, is a well-established approach to overcome the rapid capacity fading issues associated with alloy-based anode materials in lithium-ion batteries (LIBs). However, adopting carbonaceous materials that typically exhibit a low density eventually diminishes the primary purpose of alloys as high-energy–density anode materials. In this study, we introduce three-dimensional hierarchically porous molybdenum carbide (PMC) with high energy density, robust mechanical strength, and high electronic conductivity, which make it a promising alternative support for suppressing the huge volume expansion of alloying-based materials. Carbon-coated, ultrasmall Bi nanodots with an average size of 6.4 nm are uniformly embedded on the PMC surface (denoted as C-Bi/PMC) by facilitating heterogeneous nucleation. When tested as an anode in an LIB, the C-Bi/PMC electrode exhibits a high reversible capacity of 422 mAh g−1 at 50 mA g−1, high-rate capacity of 268 mAh g−1 at 1000 mA g−1, and long-term stability of 400 mAh g−1 at 250 mA g−1 over 500 cycles followed by 0.002 mAh g−1 decay per cycle at 5000 mA g−1 over subsequent 1000 cycles. When paired with LiNi0.5Co0.2Mn0.3O2 cathode as full-cell LIBs, the C-Bi/PMC anode deliver high gravimetric and volumetric energy densities of 352 Wh kg−1 and 563 Wh L–1, respectively. In-situ X-ray diffraction patterns captured during cycling reveal that the Li+-ion insertion mechanism in the voltage plateau region at 0.7–1.0 V consists of the intercalation between Bi layers followed by the formation of triclinic LiBi phase and the subsequent transition of triclinic LiBi to cubic Li3Bi phase.

Bilayer borophene synthesized on Ag(111) film: Physical mechanism and applications for optical sensor and thermoelectric devices

In this letter, we theoretically investigate the physical mechanism of bilayer (BL) borophene synthesized on Ag (111) film, stimulating by recent experimental report [Borophene synthesis beyond the single-atomic-layer limit. Nature Materials, 21, 35–40 (2022)]. Our results reveal that strong hybrid coupling interaction and interfacial charge transfer between BL borophene and Ag (111) film results in the interlayer covalent bond by the van der Waals interaction. Interlayer covalent chemical bond results in the two Dirac points in BL borophene, as electric cage, which can efficiently confine electrons. We propose the potential applications of BL borophene for optical sensor and thermoelectric devices, based on the physical properties of BL borophene.

Oxygen Vacancy Transition in HfOx‐Based Flexible, Robust, and Synaptic Bi‐Layer Memristor for Neuromorphic and Wearable Applications

AbstractIn this work, a reliable bilayer flexible memristor is demonstrated using TaOx/HfOx Bi‐layer (BL) to mimic synaptic characteristics by using oxygen concentration engineering in the oxide layers. Due to low Gibbs free energy of TaOx layer and stable properties of the single layer memristor, TaOx is inserted in the HfOx‐based memristor for making the BL flexible device. Such device exhibits stable gradual switching behavior with low set/reset voltages (1 V/−1 V) and multilevel cell characteristic making it favorable for synaptic application. The presence of oxide layers and change in oxygen vacancy concentration in two layers are examined by transmission electron microscopy and X‐ray photoelectron spectroscopy, respectively. Further, the device shows potentiation and depression epochs for more than 10 000 pulses and switching up to bending radius of 4 mm for 1000 bending cycles. The device mimics biological synaptic time‐dependent plasticity (STDP) operation when presynaptic and postsynaptic pulses are applied on top and bottom electrodes, respectively. The relationship between nonlinearity coefficient and control parameters in STDP is derived and established. It achieves more that 96% accuracy only after 20 iterations for neuromorphic application when a system of 2500 synapses incorporating 50 × 50 pixel image for recognition is deployed.

In Situ Atomic Force Microscopy Analysis of the Corrosion Processes at the Buried Interface of an Epoxy‐like Model Organic Film and AA2024‐T3 Aluminum Alloy

The application of characterization methods with high spatial resolution to the analysis of buried coating/metal interfaces requires the design and use of model systems. Herein, an epoxy‐like thin film is used as a model coating resembling the epoxy‐based coatings and adhesives widely used in technical applications. Spin coating is used for the deposition of a 30 nm‐thin bilayer (BL) composed of poly‐(ethylenimine) (PEI) and poly[(o‐cresyl glycidyl ether)‐co‐formaldehyde] (CNER). Fourier‐transform infrared spectroscopy (FTIR) results confirm that the exposure of coated AA2024‐T3 (AA) samples to the corrosive electrolyte solution does not cause the degradation of the polymer layer. In situ atomic force microscopy (AFM) studies are performed to monitor local corrosion processes at the buried interface of the epoxy‐like film and the AA2024‐T3 aluminum alloy surface in an aqueous electrolyte solution. Hydrogen evolution due to the reduction of water as the cathodic corrosion reaction leads to local blister formation. Based on the results of the complementary energy‐dispersive X‐ray spectroscopy (EDX) analysis performed at the same region of interest, most of the hydrogen evolved originates at the vicinity of Mg‐containing intermetallic particles.

Thickness-dependent topological phase transition and Rashba-like preformed topological surface states of α-Sn(001) thin films on InSb(001)

Topological materials, possessing spin-momentum locked topological surface states (TSS), have attracted much interest due to their potential applications in spintronics. \ensuremath{\alpha}-phase Sn (\ensuremath{\alpha}-Sn), being one of them, displays enriched topological phases via band-gap engineering through a strain or confinement effect. In this work, we investigated the band evolution of in-plane compressively strained \ensuremath{\alpha}-Sn(001) thin films on InSb(001) in a wide range of thickness from 3 bilayers (BL) to 370 BL by combining angle-resolved photoemission spectra and first-principles calculations. Gapped surface states evolved to a linearly dispersive TSS at a critical thickness of 6 BL, indicating that the system undergoes a phase transition from topologically trivial to nontrivial. For films thicker than 30 BL, additional Rashba-like surface states (RSS) were identified. These RSS served as preformed TSS in another strain-induced topological phase transition. In thick films, 370-BL \ensuremath{\alpha}-Sn(001), so as to preclude the confinement effect in thin films, our results were consistent with a Dirac semimetal phase with Dirac nodes located along $\mathrm{\ensuremath{\Gamma}}--Z$. This thickness-dependent band-structure study deepens our understanding of topological phase transitions and the evolution of Dirac states. Furthermore, the coexistence of TSS and RSS in a Dirac semimetal \ensuremath{\alpha}-Sn might significantly enhance the potential for spintronic applications.

Existence of two-dimensional hole gas at the interface of Bi(Zn, Ti)O[formula omitted]/SrTiO[formula omitted] heterostructures: An ab-initio study

We present first-principles calculations for a system consisting of a varying number of layers of the ferroelectric semiconductor Bi(Zn, Ti)O3 (BZT) on top of SrTiO3 (STO) substrate. To begin with, we assume that a TiO2 layer in STO is connected to a BiO layer in BZT. We show that atomic relaxation has a significant effect on the electronic properties of the heterostructure. In the absence of relaxation, due to the large polarization in BZT, a two-dimensional electron gas is formed at the interface when one unit cell of BZT is placed on top of STO. When relaxation is taken into account, the polarization in BZT is reduced in value and reversed in direction; in this case the insulator-to-metal transition occurs when the number of BZT unit cells reaches four, and a two-dimensional hole gas is formed at the interface. We also consider the case where an SrO layer in STO connects to a (Zn, Ti)O2 layer in BZT, and show that, when three unit cells of BZT are added on top of STO, a two-dimensional electron gas is formed near the interface.

Thin Ag/Bi coatings as epsilon-near-zero material with low optical losses

The work presents a study of the influence of the deposition conditions and the composition on the optical and structural properties of thin Ag/Bi coatings. Two methods for thin films deposition were used for this purpose: co-evaporation of silver and bismuth and deposition of multilayer coatings by alternating very thin layers of both metals. The results from the X-ray analyses showed that both methods allow the realization of thin Ag–Bi layers with controlled composition. The complex permittivity, ε = ε’+i.ε” of the thin films was determined by spectral ellipsometry. A significant reduction in the values of ε” was observed at a bismuth content of 20–50 at. % in the thin Ag–Bi films, while the ε′ values stay negative and vary between 0 and -1 in a wide spectral range 0.6–3.5 eV. The analysis of the dielectric loss function, Im{-1/ε} showed that the silver-bismuth interface influences significantly the properties of Ag–Bi thin films.

Synthesis, crystal structure, and topology of a polycatenated bismuth coordination polymer

Abstract Solvothermal reaction of Bi(NO3)3·5H2O with the flexible ligand 1,3,5-tris[4-(carboxyphenyl)oxamethyl]-2,4,6-trimethylbenzene (H3TBTC) in methanol at 120 °C for 1 h led to the formation of a novel coordination polymer (CP) with the composition of Bi(TBTC). The structure of the microcrystalline material was determined through three-dimensional electron diffraction (3DED) measurements and phase purity was confirmed by a Pawley refinement, elemental analysis, and thermal analysis. The compound crystallizes in the triclinic space group P 1 ‾ $P\overline{1}$ with one Bi3+ cation and one TBTC3− trianion in the asymmetric unit. Edge-sharing of BiO7 polyhedra leads to the formation of dinuclear Bi2O12 units, which through coordination to six TBTC3− ions form a layered two-periodic structure. Upon heating the material in air, the unit cell volume contracts by 9%, which is attributed to a shift in the inter-layer arrangement and to the flexibility of the building units of the structure. The compound starts to decompose at ∼300 °C. Topological analysis revealed layers consisting of 3-c and 6-c nodes, consistent with the two-periodic kgd net – the dual of the Kagome net (kgm). However, due to the non-planar nature of the Bi(TBTC) layers, adjacent layers are interlaced by polycatenation.

Water Formation Reaction under Interfacial Confinement: Al0.25Si0.75O2 on O-Ru(0001).

Confined nanosized spaces at the interface between a metal and a seemingly inert material, such as a silicate, have recently been shown to influence the chemistry at the metal surface. In prior work, we observed that a bilayer (BL) silica on Ru(0001) can change the reaction pathway of the water formation reaction (WFR) near room temperature when compared to the bare metal. In this work, we looked at the effect of doping the silicate with Al, resulting in a stoichiometry of Al0.25Si0.75O2. We investigated the kinetics of WFR at elevated H2 pressures and various temperatures under interfacial confinement using ambient pressure X-ray photoelectron spectroscopy. The apparent activation energy was lower than that on bare Ru(0001) but higher than that on the BL-silica/Ru(0001). The apparent reaction order with respect to H2 was also determined. The increased residence time of water at the surface, resulting from the presence of the BL-aluminosilicate (and its subsequent electrostatic stabilization), favors the so-called disproportionation reaction pathway (*H2O + *O ↔ 2 *OH), but with a higher energy barrier than for pure BL-silica.

Exfoliating silica bilayers via intercalation at the silica/transition metal interface

The growth of the silica (SiO2) bilayer (BL) films on transition metal (TM) surfaces creates a new class of two-dimensional (2D) crystalline, self-contained materials that interact weakly with the TM substrate. The BL-silica/TM heterojunction has shown unique physical and chemical properties that can lead to new chemical reaction mechanisms under the sub-nm confinement and broad potential applications ranging from surface protection, nano transistors, molecular sieves to nuclear waste removal. Novel applications of BL-silica can be further explored as a constituent of van der Waals assembly of 2D materials. Key to these applications is an unmet technical challenge to exfoliate and transfer BL-silica films in a large area from one substrate to another without material damage. In this study, we propose a new exfoliation mechanism based on gas molecule intercalation from density functional theory studies of the BL-silica/TM heterojunction. We found that the intercalation of O atoms and CO molecules at the BL-silica/TM interface weakens the BL-silica—TM hybridization, which results in an exponential decrease of the exfoliation energy against the interface distance as the coverage of interfacial species increases. This new intercalation mechanism opens up the opportunity for non-damaging exfoliation and transfer of large area silica bilayers.

Galvanically replaced artificial interfacial layer for highly reversible zinc metal anodes

Interface modification is considered as a straightforward strategy to regulate the electrochemical environment of metal anodes and to provide a physically protective interphase. Herein, we develop galvanically replaced artificial interfacial layers, where Sn, Sb, and Bi layers are uniformly grown on Zn anodes, for use in high-performance aqueous rechargeable zinc batteries. The corrosion and dendrite formation of Zn metal are inhibited by manipulating the uniform Zn deposition behavior and facile plating/stripping, as verified by electrochemical characterizations and postmortem, in situ optical, and computational analyses. Considering that the thickness, morphology, and crystallinity of the interfacial layers vary depending on their chemical identity, the Sn modified Zn anode (Zn|Sn) exhibits the optimum electrochemical performance owing to its highest Zn affinity and hierarchical structure. Consequently, symmetric cells with Zn|Sn anodes demonstrate stable plating/stripping over 2200 h at 1 mA cm−2 and a long cycle life of 2000 h at a high current density of 4 mA cm−2. In particular, the full cells by pairing Zn|Sn with β-MnO2 deliver a high capacity of 92.8 mA h g−1 even at a high current rate of 5000 mA g−1, 73% capacity retention after 1000 cycles at 1000 mA g−1, and improved cycle stability under low N/P ratio (&amp;lt;50) and high cathode mass loading (∼15.8 mg cm−2).

The quantum size and spin-orbit coupling effects in BiVO4 with several atomic layers studied by density functional theory.

The quantum size and spin-orbit coupling (SOC) effects play an important role in the electronic structure of photocatalytic materials with heavy elements such as Bi, Pb, Ir, Te, Sb, Sn, etc. How these two effects affect the conduction band (CB) or the valence band (VB) edge of a photocatalyst is not well understood. In this work, we investigated the quantum size and SOC effects on the CB and VB edges of BiVO4 (BVO) with a thickness of several atomic layers. The BVO is a good water oxidation photocatalyst but doesn't have the hydrogen reduction ability. We find that when the thickness of a BVO layer is smaller than 0.64 nm, the CB edge upshifts significantly because of the quantum size effect. But after including the SOC effect, the CB edge remains almost unchanged. The CB edge of BVO upshifts above the equilibrium redox potentials for H2/H2O with a thickness of ∼0.64 to 1.28 nm. Within this thickness, only the quantum size effect dominates and the SOC effect is very weak. Both the quantum size and SOC effects are insignificant as the thickness of the BVO layers increases to be larger than 1.28 nm. The results presented here provide an essential step toward the understanding and rational design of photocatalysts from both the quantum size and SOC effects.

A Comparative Investigation of the Mechanical Properties of Single and Bi Layer MoS2 Structures: Influences of Defect, Strain Rate and Temperature

In this paper, the mechanical properties of single and bi layer molybdenum disulfide (MoS2) structures are investigated using uniaxial tensile molecular dynamics (MD) simulation. According to the results of MD simulations, these structures show superior mechanical properties (failure strain, ultimate tensile strength and Young’s modulus) for various applications of nanodevice. The mechanical properties of single and bi layer MoS2 structures are studied at four different temperatures between 300 K and 900 K and different strain rates from 107 s-1 to 109 s-1. As temperature increases up to 900 K, the mechanical properties of single and bi layer MoS2 structures gradually decrease, due to the high temprerature’s weakening effect. Also, changing of temperatures shows more effect on the bi layer MoS2 structure than single layer MoS2 structure. Furthermore, MD results show that the mechanical properties of single and bi layer MoS2 structures demonstrate increasing trend when the strain rate increases. Different strain rates indicate similar effects on the mechanical properties of single and bi layer MoS2 structures. On the other hand, the mechanical properties of these structures are adversely affected by structural defects. Accordingly, the influences of two different S atom types vacancy defect on the mechanical properties of single and bi layer MoS2 structures are examined. When the vacancy defect concentrations in MoS2 structures increase, the mechanical properties of these structures decrease significantly. In addition, S atom bi vacancy defects type exerts more effect on the mechanical properties of single and bi layer MoS2 structures than S atom single vacancy defect type do by increasing concentration. Additionally, vacancy defects indicate more influence on the bi layer MoS2 structure than single layer MoS2 structure. Finally, the results of this study make them excellent candidate for nano-mechanical systems.