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Large enhancement of infrared absorption due to trimer comprised of doping-N and S-S divacancies in the imperfect monolayer MoS2: A first-principles study
摘要： In this study, we systematically study on crystal and electronic structures and optical absorption properties of perfect monolayer MoS2 (M), M with S vacancy (M@SV), M with N doping at S site (M@ND) and M with both S vacancy and N doping at S site (M@V-D) using first-principles method. It is showed that the N atom is tend to located between Mo and S layers, leaving one vacancy at original site, to form interstitial N atom. Thus, the interstitial N atom and the S vacancy make up the NI-VS dimer. We study M@V-D with five atomic configurations and find the most stable structure having the NI-VS-VS trimer. It is showed that the absorbance for the stable M@V-D in the most infrared region is obviously higher than that for the other systems. It is revealed that large enhancement of infrared absorption for the stable M@V-D is mainly attributable to the special electronic structure determined by the crystal structure with the trimer. It is considered that M@V-D could be the promising candidate for infrared materials.
关键词： Monolayer MoS2,Infrared absorption
更新于2025-09-04 15:30:14
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Electronic and magnetic properties of Al-doped WS <sub/>2</sub> monolayer under strain
摘要： Magnetic properties of Al-doped WS2 monolayer under strain are investigated by ab initio methods. Without strain, the Al-doped WS2 monolayer is a nonmagnetic nano material. We applied strain to Al-doped WS2 monolayer from –10% to 10%. Under tensile strain, ranging from 3% to 10%, the system always keeps nonmagnetic and changes from semiconductor to metal-like material. The magnetic moment gets a maximum value of 3.03 lB at –3% compressive strain. However, the magnetic moment of system decreases to zero gradually as the compressive strain increases. The coupling among the 3s states of Al, 5d states of W and 3p states of S is responsible for the strong strain effect on the magnetic properties. Our studies predict Al-doped WS2 monolayer under strain to be candidates for application in spintronics.
关键词： strain,DFT calculations,nonmagnetic metal,WS2 monolayer
更新于2025-09-04 15:30:14
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Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides
摘要： Monolayer transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) semiconductors for application in optoelectronics. Their optical properties are dominated by two series of photo-excited exciton states—A (XA) and B (XB)1,2—that are derived from direct interband transitions near the band extrema. These exciton states have large binding energies and strong optical absorption3–6, and form an ideal system to investigate many-body effects in low dimensions. Because spin–orbit coupling causes a large splitting between bands of opposite spins, XA and XB are usually treated as spin-polarized Ising excitons, each arising from interactions within a specific set of states induced by interband transitions between pairs of either spin-up or spin-down bands (TA or TB). Here, by using monolayer MoS2 as a prototypical system and solving the first-principles Bethe–Salpeter equations, we demonstrate a strong intravalley exchange interaction between TA and TB, indicating that XA and XB are mixed states instead of pure Ising excitons. Using 2D electronic spectroscopy, we observe that an optical excitation of the lower-energy TA induces a population of the higher-energy TB, manifesting the intravalley exchange interaction. This work elucidates the dynamics of exciton formation in monolayer TMDCs, and sheds light on many-body effects in 2D materials.
关键词： intravalley exchange interaction,2D electronic spectroscopy,exciton states,many-body effects,monolayer transition metal dichalcogenides
更新于2025-09-04 15:30:14
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Temporally Resolving Synchronous Degenerate and Nondegenerate Two-Photon Absorption in 2D Semiconducting Monolayers
摘要： Degenerate and nondegenerate two-photon absorption (TPA) in WS2 and MoSe2 monolayers are synchronously induced and temporally resolved by femtosecond laser pump-probe. Di?erential transmission signals in the ?rst 500 fs consist of negative and positive components, that originate from direct probe depletion via nondegenerate TPA and carrier accumulation via degenerate TPA, respectively. Temporal cross-correlation of pump and probe pulses allows us to fully decouple the ultrafast nondegenerate and degenerate TPA signals. Subsequently, degenerate and nondegenerate TPA coe?cients are calculated as a function of pump irradiance. Under nonresonant pumping, 100 ± 10 and 250 ± 25 cm GW?1 are obtained for degenerate and nondegenerate TPA coe?cients of monolayer WS2, respectively, which both present linearly decreasing trends as increasing pump irradiances. However, under resonant pumping of 2 p excitonic states in monolayer MoSe2, degenerate TPA coe?cients exponentially decrease from 800 to 80 cm GW?1 as increasing pump irradiances, due to the interplay between band-renormalization and band-?lling e?ects, while nondegenerate TPA coe?cient is about 650 ± 50 cm GW?1. For comparison, a trilayer MoSe2 is also investigated. These results set a foundation for precisely measuring TPA coe?cients and actively controlling nonlinear excitonic dynamics via TPA in 2D semiconducting monolayers.
关键词： 2D monolayer,transition metal dichalcogenide,femtosecond laser pump-probe,nondegenerate two-photon absorption,degenerate two-photon absorption
更新于2025-09-04 15:30:14
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Monolayer rubrene functionalized graphene-based eletrochemiluminscence biosensor for serum cystatin C detection with immunorecognition-induced 3D DNA machine
摘要： Only surficial molecules of eletrochemiluminscent (ECL) nanomaterials are the most reactive species in the typical ECL reaction. Herein, monolayer rubrene was assembled on the surface of graphene sheet to obtain monolayer rubrene functionalized graphene composite (G/mRub) with strong ECL emission by maximizing the surficial rubrene molecules. Based on G/mRub as the strong ECL emitter, an ultrasensitive “on-off” biosensor was developed to detect cystatin C (Cys C) in human serum with the help of a novel immunorecognition-induced enzyme-free 3D DNA machine. Benefiting from the strong ECL emission of G/mRub and the efficient signal amplification of 3D DNA machine, the established biosensor achieved high sensitivity for Cys C detection with linear range from 1.0 fg mL-1 to 10 ng mL-1 and limit of detection down to 0.38 fg mL-1. In addition, this enzyme-free biosensing method was adopted to successfully detect the concentration of Cys C in human serum. Therefore, the G/mRub based ECL biosensor might provide a potential tool for protein detection in clinical diagnosis and a new avenue to prepare high-performance luminescent nanomaterials.
关键词： electrochemiluminescence,graphene,cystatin C,monolayer rubrene,3D DNA machine
更新于2025-09-04 15:30:14
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Tunable Direct Semiconductor Gap and High Carrier Mobility of Mo <sub/>6</sub> Br <sub/>6</sub> S <sub/>3</sub> Monolayer
摘要： Two-dimensional materials with direct semiconductor gaps and high mobilities can play an important role in future electronic and optical applications. Here we propose that Mo6Br6S3 monolayer as a new two-dimensional material is stable and can be exfoliated from corresponding layered bulk. Our first-principles results show that the monolayer has a direct semiconductor gap beyond 1 eV (between PBE and HSE values) and a very high electron mobility (6880 cm2V?1s?1), and these can be tuned through in-plane strain by applying uniaxial stress. Furthermore, we show that the Mo6Br6S3/graphene heterostructure makes a p-type Schottky barrier and the amplitude of band bending (0.03 eV) is extremely low compared to other similar junctions because the Mo6Br6S3 monolayer has a close work function to graphene. With all these useful properties and functions, the Mo6Br6S3 monolayer can be very promising for nanoelectronic and optical applications.
关键词： Mo6Br6S3 monolayer,p-type Schottky barrier,optical applications,Two-dimensional materials,electron mobility,high mobilities,first-principles,direct semiconductor gaps,nanoelectronic
更新于2025-09-04 15:30:14
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[IEEE 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Chengdu, China (2018.5.7-2018.5.11)] 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - A Perfect Absorber Based on Monolayer MoS2 and Nano-Silver in the Visible Regime
摘要： The monolayer MoS2 offer wide band gap and has great potential in energy storage, sensor, photonics. In this paper, we design and simulate a perfect absorber based on the local surface plasmon resonance and the coupling properties between the Ag pattern and the monolayer MoS2. The absorption value is almost 100% at peak, and the bandwidth of the absorption greater than 90% can reach 20THz. It is also polarization independent due to the fourfold rotational structural symmetry. The absorption value still remains over 90% when the incident angle increases to 60 degrees. The absorber has a great potential in many applications such as photodetectors, solar cell, sensors.
关键词： monolayer MoS2,coupling,absorber,nano-Ag,broad-angle
更新于2025-09-04 15:30:14
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Carbon Nanomembranes
摘要： This chapter describes the formation and properties of one nanometer thick carbon nanomembranes (CNMs), made by electron induced cross-linking of aromatic self-assembled monolayers (SAMs). The cross-linked SAMs are robust enough to be released from the surface and placed on solid support or over holes as free-standing membranes. Annealing at ~1000K transforms CNMs into graphene accompanied by a change of mechanical stiffness and electrical resistance. The developed fabrication approach is scalable and provides molecular level control over thickness and homogeneity of the produced CNMs. The mechanisms of electron-induced cross-linking process are discussed in details. A variety of polyaromatic thiols: oligophenyls as well as small and extended condensed polycyclic hydrocarbons have been successfully employed, demonstrating that the structural and functional properties of the resulting nanomembranes are strongly determined by the structure of molecular monolayers. The mechanical properties of CNMs (Young’s modulus, tensile strength and prestress) are characterized by bulge testing. The interpretation of the bulge test data relates the Young’s modulus to the properties of single molecules and to the structure of the pristine SAMs. The gas transport through the CNM is measured onto polydimethylsiloxane (PDMS) - thin film composite membrane. The established relationship of permeance and molecular size determines the molecular sieving mechanism of permeation through this ultrathin sheet.
关键词： Helium Ion Microscopy,radiation induced cross-linking,Self-Assembled Monolayer,Carbon Nanomembrane (CNM),Graphene
更新于2025-09-04 15:30:14
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H2S and NH3 Detection with Langmuir-Schaefer Monolayer Organic Field-Effect Transistors
摘要： In this work gas sensing properties of Langmuir-Schaefer monolayer organic field-effect transistors (LS OFETs) prepared from organosilicon derivative of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) have been investigated. The monolayer has been deposited using Langmuir-Schaefer method, which results in a uniform low-defect monolayer with excellent electrical performance, hole mobility up to 7 × 10?2 cm2 V?1 s?1, the threshold voltage around 0 V and on-off ratio of 104. Developed sensors demonstrate a long-term stability of a half-year storage under ambient conditions. Preliminary investigations demonstrated that the LS OFETs give instantaneous response on ammonia and hydrogen sulfide at low concentrations. The results reported open new perspectives for the OFET-based gas-sensing technology.
关键词： OFETs,monolayer,organic electronics,chemical sensing,Langmuir-Schaefer
更新于2025-09-04 15:30:14
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Resonant Plasmon-Enhanced Upconversion in Monolayers of Core-Shell Nanocrystals: Role of Shell Thickness
摘要： The upconversion luminescence (UCL) of colloidal lanthanide-doped upconversion nanocrystals (UCNCs) can be improved either by precise encapsulation of the surface by optically inert shells around the core, by an alteration of the nearby environment via metal nanoparticles, or by a combination of both. Considering their potential importance in crystalline silicon photovoltaics,the present study investigates both effects for two-dimensional arrangements of UCNCs. Using excitation light of 1500 nm wavelength, we study the variation in the upconversion luminescence from an Er3+-doped NaYF4 core as a function of the thickness of a NaLuF4 shell in colloidal solutions as well as in spin-cast-assisted self-assembled monolayers of UCNCs. The observed UCL yields and decay times of Er3+ ions of the UCNCs increase with increasing shell thickness in both cases, and nearly no variation in decay times is observed in the transition of the UCNCs from solution to film configurations. The luminescence efficiency of the UCNC monolayers is further enhanced by electron-beam-lithographic-designed Au-nanodiscs deposited either on top or buried within of the monolayer. It is observed that the improvement by the nanocrystal shells is greater than that of the Au-nanodiscs.
关键词： shell thickness,core-shell nanocystals,monolayer,upconversion,Plasmon enhancement
更新于2025-09-04 15:30:14