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Two-dimensional series connected photovoltaic cells defined by ferroelectric domains
摘要： Recently, a large amount of effort has been devoted to bringing p- and n-type two-dimensional (2D) materials in close contact to promise a p–n junction for photodetectors and photovoltaic devices. However, all solar cells based on 2D materials are single p–n junctions so far, where the open circuit voltage is usually limited by the bandgap of semiconductor materials. Here, by using a scanning-probe domain patterning method to polarize the ferroelectric ?lm, we demonstrate a series connected MoTe2 photovoltaic cell with an additive open circuit voltage and output electrical power. The nonvolatile MoTe2 p–n diodes exhibit a recti?cation ratio of 100. As a photodetector, the device presents a responsivity of 220 mA/W and an external quantum ef?ciency of 41% without any gate or bias voltages. The open circuit voltage increases linearly with the number of series connected p–n junctions and can be beyond the bandgap of the multilayer MoTe2.
关键词： photovoltaic cells,MoTe2,open circuit voltage,two-dimensional materials,ferroelectric domains
更新于2025-09-23 15:19:57
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A Study of Eu Doping in Nanolayers of CsPbBr <sub/>3</sub> using Ab Initio Calculations to Understand <i>fa??f</i> Transitions in Eu <sup>3+</sup> -Doped Nanocrystals for Light-Emitting Diodes
摘要： Recent experiments on Eu doped nanocrystals of CsPbX3 (X = Cl, Br) show that Eu exists in 3+ oxidation state even though it substitutes Pb which is in 2+ state in these perovskites. Therefore, the question arises, what is it that leads to the formation of Eu3+ in nanocrystals of these materials? In order to understand this, we have studied the doping of Eu in a slab (~1.8 nm thick) of CsPbBr3 from ab initio calculations and explored various possibilities that could lead to the formation of Eu3+ and the occurrence of f-f transitions. These include: 1) the presence of a Cs vacancy, 2) the existence of H or OH due to moisture, 3) substitution of O at a surface halogen site, and 4) the possibility of excess halogen around Eu. It is found that the presence of surface oxygen is the most likely reason for the observation of Eu3+ in these nanolayers. Our results show the presence of partially occupied spin-up f states and 6.48 μB magnetic moment on Eu that could lead to the possibility of f-f transition in these doped systems. A similar result has also been obtained for Eu doped in CsPbCl3 nanolayers. The calculated change in energy when defects/impurities are present gives favourable indication of finding H, OH, and Br as interstitials and O as substitutional entities, but Cs vacancy is unlikely. Additionally, we find that the doping of Eu in nanolayers does not affect the atomic structure and the cost of doping is also very small making these perovskites very promising materials for light emitting diodes and other solid-state lighting applications.
关键词： Two-dimensional systems,Light emitting diodes,Solid state lighting,Density functional theory,Metal-halide perovskites,Nanolayers,Defects,f-f transitions
更新于2025-09-23 15:19:57
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Coupled plasmona??phonon modes in monolayer MoS <sub/>2</sub>
摘要： We present a theoretical study of the plasmon–phonon coupling in a suspended monolayer MoS2 and a MoS2 substrate system using a diagrammatic self-consistent field theory. The four coupled plasmon–phonon modes and the four plasmon-surface phonon modes are observed due to the spin–orbit and electron-optic phonon interactions. The two of coupled plasmon–phonon and plasmon-surface phonon modes are optic-like and the other two are acoustic-like. The plasmon are strongly coupled with the optic-phonon in MoS2 and the surface optic-phonon in the substrates as the electron density or wave-vector increases. The strong plasmon–phonon coupling shows that the optoelectronic properties of monolayer MoS2 are evidently modulated by electron–phonon interactions. The hybrid plasmon–phonon polaritons can be achieved by strong light-mater interactions. This study is relevant to the application of MoS2 as novel plasmonic and nanophotonic devices.
关键词： plasmon–phonon coupling,plasmon,two dimensional materials
更新于2025-09-23 15:19:57
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Ultrathin two-dimensional conjugated metala??organic framework single-crystalline nanosheets enabled by surfactant-assisted synthesis
摘要： Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have recently emerged for potential applications in (opto-)electronics, chemiresistive sensing, and energy storage and conversion, due to their excellent electrical conductivity, abundant active sites, and intrinsic porous structures. However, developing ultrathin 2D c-MOF nanosheets (NSs) for facile solution-processing and integration into devices remains a great challenge, mostly due to unscalable synthesis, low yield, limited lateral size and low crystallinity. Here, we report a surfactant-assisted solution synthesis toward ultrathin 2D c-MOF NSs, including HHB-Cu (HHB=hexahydroxybenzene), HHB-Ni and HHTP-Cu (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene). For the first time, we achieve single-crystalline HHB-Cu(Ni) NSs featured with a thickness of 4-5 nm (~8-10 layers) and a lateral size of 0.25-0.65 μm2, as well as single-crystalline HHTP-Cu NSs with a thickness of ~5.1±2.6 nm (~10 layers) and a lateral size of 0.002-0.02 μm2. Benefiting from the ultrathin feature, the synthetic NSs allow fast ion diffusion and high utilization of active sites. As a proof of concept, when serving as a cathode material for Li-ion storage, HHB-Cu NSs deliver a remarkable rate capability (charge within 3 min) and long-term cycling stability (90% capacity retention after 1000 cycles), superior to the corresponding bulk materials and other reported MOF cathodes.
关键词： Li-ion batteries,Two-dimensional conjugated metal-organic frameworks,electrochemical performance,surfactant-assisted synthesis,ultrathin nanosheets
更新于2025-09-23 15:19:57
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Gate Tunable Symmetric Bipolar Junction Transistor Fabricated via Femtosecond Laser Processing
摘要： Two-dimensional (2D) bipolar junction transistor (BJT) with van der Waals heterostructures plays an important role in the development of future nanoelectronics. Herein, a convenient method is introduced for fabricating a symmetric bipolar junction transistor (SBJT) constructed with black phosphorus and MoS2 with femtosecond laser processing. This SBJT exhibits good bidirectional current amplification thanks to its symmetric structure. Next, we place a top gate on one side of the SBJT to change the difference in the major carrier concentration between the emitter and collector in order to further investigate the effect of electrostatic doping on the device’s performance. The SBJT can also act as a gate tunable phototransistor with good photodetectivity and photocurrent gain of β ~ 21. Scanning photocurrent images are used to determine the mechanism governing photocurrent amplification in the phototransistor. These results promote the development of the applications of multifunctional nanoelectronics based on 2D materials.
关键词： Femtosecond laser processing,Phototransistor,Two-dimensional materials,Bipolar junction transistor,Gate tunable
更新于2025-09-23 15:19:57
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A self-powered photodetector based on two-dimensional boron nanosheets
摘要： Owing to their intriguing characteristics, the ongoing pursuit of emerging mono-elemental two-dimensional (2D) nanosheets beyond graphene is an exciting research area for next-generation applications. Herein, we demonstrate that highly crystalline 2D boron (B) nanosheets can be efficiently synthesized by employing a modified liquid phase exfoliation method. Moreover, carrier dynamics has been systematically investigated by using femtosecond time-resolved transient absorption spectroscopy, demonstrating an ultrafast recovery speed during carrier transfer. Based on these results, the optoelectronic performance of the as-synthesized 2D B nanosheets has been investigated by applying them in photoelectrochemical (PEC)-type and field effect transistor (FET)-type photodetectors. The experimental results revealed that the as-fabricated PEC device not only exhibited a favourable self-powered capability, but also a high photoresponsivity of 2.9–91.7 μA W?1 in the UV region. Besides, the FET device also exhibited a tunable photoresponsivity in the range of 174–281.3 μA W?1 under the irradiation of excited light at 405 nm. We strongly believe that the current work shall pave the path for successful utilization of 2D B nanosheets in electronic and optoelectronic devices. Moreover, the proposed method can be utilized to explore other mono-elemental 2D nanomaterials.
关键词： two-dimensional boron nanosheets,optoelectronic devices,carrier dynamics,liquid phase exfoliation,photodetector
更新于2025-09-23 15:19:57
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Digital holography for non-invasive quantitative imaging of two-dimensional materials
摘要： Digital holography has found applications in many walks of life, from medicine to metrology, due to its ability to measure complex fields. Here, we use the power of digital holography to quantitatively image two-dimensional Transition Metal Dichalcogenides (TMDs) such as MoS2 and WS2 placed on a SiO2/Si substrate and determine their complex refractive indices or layer thicknesses. By considering the different refractive indices of the TMDs as they are thinned down from bulk to monolayers and by holographically capturing both the amplitude and the phase of reflected light, single atomic layers of TMDs, about 0.7 nm thick, can be resolved. Using holography, we also predict the number of layers contained within a thick TMD flake, which shows agreement with results obtained using Atomic Force Microscopy (AFM). A Bland–Altman analysis was performed to compare our experimental results with the standard AFM measurements, yielding a limit of agreement <5 nm for samples with thicknesses ranging from 15 to 60 nm. Our technique is non-contact, non-invasive, does not require scanning, and produces a field of view of a few hundred micrometers by a few hundred micrometers in a single capture. To further our study, we also perform simulations to demonstrate how the thickness of the SiO2 layer and the laser wavelength are critical in optimizing the amplitude and phase response of a two-dimensional material. These simulations can be used as a roadmap to determine the ideal wavelength and SiO2 layer thickness that should be used to accurately determine the refractive index or thickness of any given sample.
关键词： digital holography,Atomic Force Microscopy,layer thicknesses,Bland–Altman analysis,Transition Metal Dichalcogenides,two-dimensional materials,complex refractive indices
更新于2025-09-23 15:19:57
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Two-Dimensional Quantum Transport in Free-Standing InSb Nanosheets
摘要： Low-dimensional narrow band gap III?V compound semiconductors, such as InAs and InSb, have attracted much attention as one of promising platforms for studying Majorana zero modes and non-Abelian statistics relevant for topological quantum computation. So far, most of experimental studies were performed on hybrid devices based on one-dimensional semiconductor nanowires. In order to build complex topological circuits toward scalable quantum computing, exploring high-mobility two-dimensional (2D) III?V compound electron system with strong spin?orbit coupling is highly desirable. Here, we study quantum transport in high-mobility InSb nanosheet grown by molecular-beam epitaxy. The observations of Shubnikov-de Hass oscillations and quantum Hall states, together with the angular dependence of magnetotransport measurements, provide the evidence for the 2D nature of electronic states in InSb nanosheet. The presence of strong spin?orbit coupling in the InSb nanosheet is veri?ed by the low-?eld magnetotransport measurements, characterized by weak antilocalization e?ect. Finally, we demonstrate the realization of high-quality InSb nanosheet?superconductor junctions with transparent interface. Our results not only advance the study of 2D quantum transport but also open up opportunities for developing hybrid topological devices based on 2D semiconducting nanosheets with strong spin?orbit coupling.
关键词： spin?orbit interaction,quantum Hall effect,InSb nanosheet,two-dimensional transport,Josephson junction
更新于2025-09-23 15:19:57
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Resonant modal analysis and dual-mode tailoring in high refractive index contrast two-dimensional nanorod arrays
摘要： Resonant modal analysis and dual-mode tailoring in high refractive index contrast two-dimensional (2-D) nanorod arrays are proposed. The specific modes of the guided mode resonances (GMRs) excited by the 2-D nanorod arrays can be distinguished based on the equivalent medium theory (EMT) and the analysis of the electric/magnetic fields. The broadband reflection and enhanced transmission can be obtained by the tailoring between the resonant dual-mode of the 2-D nanorod arrays. It is shown that the 2-D nanorod arrays can support the excitation of the resonant dual-mode with low-quality factor (low-Q) TM0 and high quality factor (high-Q) TE0 modes on a reflection broadband. The coupling of the edges of the resonant dual-mode can be tailored to create the resonant transmission with polarization independence near 1.31 μm. By merely changing the angle of incidence, one can achieve triple transmission channels due to the interaction of the nondegenerate resonant dual-modes.
关键词： Dual-mode tailoring,Modal analysis,Two-dimensional nanorod arrays,Guided mode resonance
更新于2025-09-23 15:19:57
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Two-dimensional Janus PtSSe for photocatalytic water splitting under the visible or infrared light
摘要： Recently, two-dimensional Janus materials have attracted increasing research interest due to their particular structure and great potential in electronics, optoelectronics and piezoelectronics. Here, we propose 2D Janus PtSSe with compelling photocatalytic properties which were investigated by means of first-principles calculations. 2D Janus PtSSe exhibits high thermal, dynamic and mechanical stability. Most remarkably, single-layer PtSSe exhibits an indirect band gap of 2.19 eV, high absorption coefficients in the visible light region, appropriate band edge positions and strong ability for carrier separation and transfer, thus rendering it a promising candidate for photocatalytic water splitting. Moreover, double-layer PtSSe compounds with different stacking configurations are extraordinary photocatalysts for water splitting even under infrared light, owing to their small band gaps as well as the built-in electrical field. Our results reveal 2D PtSSe with high experimental feasibility as a new platform for the overall water splitting reaction.
关键词： two-dimensional Janus materials,first-principles calculations,photocatalytic water splitting,visible light,infrared light
更新于2025-09-23 15:19:57