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Ordered Array of Metal Particles on Semishell Separated with Ultrathin Oxide: Fabrication and SERS Properties
摘要： Metal particles in gap cavities provide an interesting system to achieve hybrid local surface plasmon modes for local field enhancement. Here, we demonstrate a relatively simple method to fabricate Ag nanoparticles positioned on Ag semishells separated by a thin (~5 nm) dielectric layer. The obtained structure can provide strong local electric field enhancement for surface-enhanced Raman scattering (SERS). The fabrication of the ordered array structure was realized by nanosphere self-assembly, atomic layer deposition, and metal thin-film dewetting. Numerical simulation proved that, compared to the conventional metal semishell arrays, the additional Ag particles introduce extra hot spots particularly in the valley regions between adjacent Ag semishells. As a result, the SERS enhancement factor of the metal semishell-based plasmonic structure could be further improved by an order of magnitude. The developed novel plasmonic structure also shows good potential for application in plasmon-enhanced solar water-splitting devices.
关键词： particle in cavity,nanosphere lithography,surface-enhanced Raman scattering (SERS),surface plasmonic,monolayer self-assembly
更新于2025-09-23 15:22:29
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First-principle study on honeycomb fluorated-InTe monolayer with large Rashba spin splitting and direct bandgap
摘要： Rashba e?ect is much related to next-generation spintronic devices. It is highly desirable to search for Rashba materials with large Rashba spin splitting, which is considered as the key factor for the application of spin ?eld-e?ect transistor. Here, we design a two-dimensional monolayer of ?uorated-InTe (InTeF) with large Rashba spin splitting and direct bandgap on the basis of ?rst-principles calculations. InTeF monolayer is energetically and dynamically stable based on the calculations of cohesive energy and phonon dispersion. Remarkably, the Rashba parameter αR is about 1.08 eV·?, comparable to that of the BiTeI monolayer (1.86 eV·?). The direct bandgap is estimated to be 2.48 eV by HSE06 hybrid functional, which shows good prospects in light-emitting devices and photodetectors. To further explore the e?ect of substrates on the electronic structure of InTeF monolayer, we build two heterostructures, and the results show that the strength of Rashba e?ect and the direct bandgap nature in InTeF monolayer can be well preserved under the in?uence of substrates. Based on the above ?ndings in our work, InTeF monolayer is considered to be one of the promising 2D materials for the application of spintronics as well as optoelectronics.
关键词： Rashba spin splitting,InTeF monolayer,First-principle calculation,Direct bandgap
更新于2025-09-23 15:22:29
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Enhancement of monolayer SnSe light absorption by strain engineering: A DFT calculation
摘要： Strain effects on the electronic and optical properties of monolayer SnSe is studied by APW + lo method in DFT framework. The applied strains cause direct-indirect transition of SnSe band gap which is mainly constructed by s/p hybridization. The armchair εac and zigzag εzz reduce the unstrained band gap of 1.05 eV down to 0 eV at 12% compression, but at 12% tension, the band gap decreases to 0.726–0.804 eV. The band gap always increases under biaxial strain εb at at 12% compression to 12% tension. We observe an enhancement of real ε1(ω) and imaginary ε2(ω) parts of dielectric function by 14% ? 30% of magnitude, wider peak distribution to infrared and ultra-violet regions, and appearance of new peaks in the ε1(ω) and ε2(ω) spectrums. As a consequence, the light absorption α(ω) is significantly enhanced in the ultra-violet region and the absorption even starts at lower energy at infrared region.
关键词： Strain,Optical properties,Electronic band structure,First-principles,Monolayer SnSe
更新于2025-09-23 15:22:29
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Room temperature multi-phonon upconversion photoluminescence in monolayer semiconductor WS2
摘要： Photon upconversion is an anti-Stokes process in which an absorption of a photon leads to a reemission of a photon at an energy higher than the excitation energy. The upconversion photoemission has been already demonstrated in rare earth atoms in glasses, semiconductor quantum wells, nanobelts, carbon nanotubes and atomically thin semiconductors. Here, we demonstrate a room temperature upconversion photoluminescence process in a monolayer semiconductor WS2, with energy gain up to 150 meV. We attribute this process to transitions involving trions and many phonons and free exciton complexes. These results are very promising for energy harvesting, laser refrigeration and optoelectronics at the nanoscale.
关键词： photoluminescence,monolayer semiconductor,phonons,energy gain,room temperature,WS2,excitons,trions,upconversion
更新于2025-09-23 15:22:29
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Screening Effect of Ultrathin Gold Films on Excitons in Monolayer WS2
摘要： Screening plays an important role in determining the energy levels and binding energies of excitons in two-dimensional (2D) semiconductors. However, the photoelectric properties of 2D materials deposited upon metal films are often assumed to remain unaffected by the screening effect. Herein, we derive the reflectance contrast spectra of monolayer WS2 on different thicknesses of ultrathin gold films by using the transfer matrix method, and investigate the screening effect of ultrathin gold films on excitons in monolayer WS2. We show that the exciton binding energy of the ground state gradually decreases as the gold film thickness increases due to the enhanced screening effect. Nevertheless, it may be due to the impact of free-electron scattering on the permittivities of gold films: exciton resonance energies of the ground state and the first excited state gradually increase as the gold film thickness increases, which are different from previously reported variation trend of exciton energy levels with the thickness of screening media of 2D materials. As a consequence, the electronic bandgap of the exciton only presents a small variation range of less than 4 meV with thickening of the gold film from 0.0 to 40 nm. These findings shed light on understanding to what extent the screening effect of gold films affects the excitons in 2D materials.
关键词： Ultrathin gold film,Transfer matrix method,Excitonic properties,Monolayer WS2,Dielectric screening effect
更新于2025-09-23 15:22:29
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Electronic and Magnetic Properties of Transition-Metal-Doped WS? Monolayer; First-Principles Investigations
摘要： The electronic structures and magnetic properties of the transition-metal (TM)-doped WS2 monolayers are investigated by using the first-principles calculations within the density functional theory. The W atoms of the pristine WS2 monolayer are partially replaced by the 3d TMs of Mn, Fe, Co, and Cu with the impurity concentration of about 4%. For the uniformly distributed doping, the ferromagnetic phases are found to be stabilized with the total spin magnetic moments of 1.00, 2.00, 3.00, and 1.00 μB for the Mn-, Fe-, Co-, and Cu-doping, respectively, where not only the spin moments of the TM dopants but also the induced spin moments of the W and S atoms contribute significantly depending on the dopant type as well as on the relaxation. All systems are found to be half-metallic with the spin gap of 0.10–0.53 eV. Among them, the biggest spin gap is found for the doping of Co which is the ingredient of the well-known half-metallic Heusler alloys. When the TM dopants were brought closer keeping the same impurity concentration, the preference of the substitutional doping site and the magnetic phase is changed sensitively depending on the type of doping and the interatomic distance between the TM dopants.
关键词： spin density,transition-metal (TM) dopant,Magnetic state,WS2 monolayer.
更新于2025-09-23 15:22:29
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Electronic properties and optical behaviors of bulk and monolayer ZrS2: A theoretical investigation
摘要： In this paper, we study the di?erence in electronic and optical properties of bulk and monolayer zirconium sul?de by applying the APW + lo method in the framework of density functional theory. All calculation is performed at the energy level of visual light and higher ranging from 0 eV to 15 eV. Our results demonstrates that except for the underestimated band gap like other GGA calculation, the remain properties like dielectric function, the re?ectivity, absorption and loss energy are close to experiment. The valence band is constructed by mainly sulfur s/p-states and the lower portion of zirconium s/p/d-states. The conduction band is mostly donated by zirconium d-state. In contrast with bulk structure, the valence band maximum in monolayer has the triple peak at Γ point, making its monolayer be more sensitive to light absorption. The di-electric function has the highest peak at about 1.5–2.5 eV with remarkable anisotropy, beyond this level to the ultraviolet region the anisotropy decreases and almost disappears at energy larger than 10 eV. The absorption is at 106 x 10 cm4 for energy range 5–10 eV, while the re?ectivity is at its highest value of 30 %–50 % in the energy range from 0 to 8 eV. The energy loss of monolayer is higher than those of bulk. For optical and electronic properties, the monolayer show sharper peaks and their clear separation indicate the progressive application of monolayer zirconium sul?de.
关键词： Monolayer ZrS2,Strain,First-principles,Band structure,Optical properties
更新于2025-09-23 15:21:21
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Flexoelectricity in Monolayer Transition Metal Dichalcogenides
摘要： Flexoelectricity, the coupling effect of the strain gradient and charge polarization, is an important route to tune electronic properties of low-dimensional materials. Here our extensive first-principles calculations reveal that structural wrinkling and corrugation will cause significant flexoelectricity in transition metal dichalcogenide (TMD) monolayers. The flexoelectricity is induced by the strain gradients created along the finite thickness of the wrinkled TMD monolayers and becomes more dominant in determining out-of-plane polarizations with decreasing wavelengths of the TMD wrinkles. According to the first-principles calculations and whole structural symmetry, a theoretical model is developed to describe the total out-of-plane polarizations and flexoelectric effect of the wrinkled TMD monolayers. The unveiled flexoelectricity in monolayer TMDs highlights a potential for their application in energy conversion devices.
关键词： energy conversion,monolayer,strain gradient,flexoelectricity,polarization,transition metal dichalcogenides
更新于2025-09-23 15:21:21
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Collective strong light-matter coupling in hierarchical microcavity-plasmon-exciton systems
摘要： Polaritons are compositional light-matter quasiparticles that arise as a result of strong coupling between the vacuum field of a resonant optical cavity and electronic excitations in quantum emitters. Reaching such a regime is often hard, as it requires materials possessing high oscillator strengths to interact with the relevant optical mode. Two-dimensional transition metal dichalcogenides (TMDCs) have recently emerged as promising candidates for realization of strong coupling regime at room temperature. However, these materials typically provide coupling strengths in the range of 10-40 meV, which may be insufficient for reaching strong coupling with low quality factor resonators. Here, we demonstrate a universal scheme that allows a straightforward realization of strong coupling with 2D materials and beyond. By intermixing plasmonic excitations in nanoparticle arrays with excitons in a WS2 monolayer inside a resonant metallic microcavity, we fabricate a hierarchical system with the collective microcavity-plasmon-exciton Rabi splitting exceeding ~500 meV at room temperature. Photoluminescence measurements of the coupled systems show dominant emission from the lower polariton branch, indicating the participation of excitons in the coupling process. Strong coupling has been recently suggested to affect numerous optical- and material-related properties including chemical reactivity, exciton transport and optical nonlinearities. With the universal scheme presented here, strong coupling across a wide spectral range is within easy reach and therefore exploring these exciting phenomena can be further pursued in a much broader class of materials.
关键词： TMDC,Strong plasmon-exciton coupling,collective Rabi splitting,monolayer WS2
更新于2025-09-23 15:21:21
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Monolayer Attachment of Metallic MoS <sub/>2</sub> on Restacked Titania Nanosheets for Efficient Photocatalytic Hydrogen Generation
摘要： Monolayer attachment of metallic MoS2 (1T) on restacked titania (Ti0.87O2 0.52?) nanosheets was attained via a facile two-step flocculation process of their colloidal suspensions with the aid of the difference in critical H+ concentrations required for inducing flocculation of the respective nanosheets. The process produced porous flaky aggregates of restacked Ti0.87O2 0.52? nanosheets covered with monolayer MoS2, which serves as the electron collector and provides abundant catalytically active sites for proton reduction reaction. The MoS2-modified restacked-Ti0.87O2 0.52? nanosheets showed a remarkably high photocatalytic efficiency for hydrogen generation (1.2 mmol h-1 g-1), being superior to those of the restacked Ti0.87O2 0.52? nanosheets and P25-TiO2 nanoparticles conventionally modified with MoS2 (0.38, and 0.4 mmol h-1 g-1, respectively). The extensive molecular-level interfacial coupling of Ti0.87O2 0.52?/MoS2 nanosheets facilitates efficient charge separation and fast electron transfer, resulting in the significantly enhanced photocatalytic activity.
关键词： 2D heterointerface,photocatalysis,hydrogen evolution,two-step flocculation process,monolayer co-catalyst
更新于2025-09-23 15:21:21