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HIGH IMPEDANCE PROPERTIES OF TWO-DIMENSIONAL COMPOSITE RIGHT/LEFT-HANDED TRANSMISSION LINES
摘要： The electromagnetic characteristics of two-dimensional composite right/left-handed transmission lines (2D CRLH TLs) were investigated for the normal incidence of plane waves. The measured characteristic impedance and re?ection phases exhibited resonant high impedance properties (equivalent to zero re?ection phase) at a frequency within the left-handed mode for one-dimensional CRLH TL. An equivalent circuit was proposed to explain the measured characteristics. The relationship between the resonant frequency and the circuit parameters for 2D CRLH TLs was clari?ed by deriving an approximate equation for the resonant frequency.
关键词： equivalent circuit,plane waves,resonant frequency,two-dimensional composite right/left-handed transmission lines,high impedance properties
更新于2025-09-09 09:28:46
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Phase velocity of drifting spin wave packets in semiconductor two-dimensional electron gas
摘要： We investigated the drift and diffusion dynamics of spin wave packets under spin–orbit effective magnetic fields in two-dimensional electron systems. A simplified model with a spin drift-diffusion equation predicted that the spin phase velocity will change over time from a large negative value to a small positive value. Kerr rotation microscopy revealed the trend we expected for the phase velocity in spin wave packets in a GaAs quantum well. Monte-Carlo simulations agreed with the experiment and showed that the phase velocity can be simply characterized by the spin–orbit parameters and the size ratio between the instantaneous and initial wave packets.
关键词： two-dimensional electron systems,spin wave packets,Kerr rotation microscopy,Monte-Carlo simulations,spin–orbit effective magnetic fields
更新于2025-09-09 09:28:46
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High-performance lead-free two-dimensional perovskite photo transistors assisted by ferroelectric dielectrics
摘要： The purpose of this research was to understand the effect of a built-in ferroelectric field on the performance of two-dimensional (2D) lead-free perovskite material-based phototransistor applications. In this work, ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and two-dimensional (2D) lead-free perovskite ((C6H5C2H4NH3)2SnI4) were utilized as a dielectric layer and a channel layer, respectively. We observed that large hysteresis was successfully eliminated in the transfer curve, as well as the subthreshold swing being significantly reduced by one order of magnitude after P(VDF-TrFE) was introduced as a dielectric layer. Under polarization ‘‘up’’ and ‘‘down’’ states, the device achieved a high photo-switching on/off ratio (4100) and a short photoresponse time (50 ms), respectively. In addition to that, the device also demonstrated a high responsivity of 14.57 A W?1 and a high detectivity of 1.74 × 1012 Jones under the polarization ‘‘up’’ state with an illumination intensity of 21 mW cm?2. In addition, low temperature solution-processed P(VDF-TrFE) and (C6H5C2H4NH3)2SnI4 (except for the contacts of Au electrodes) in this work are considered to be suitable and compatible for flexible-based phototransistor applications in the future.
关键词： lead-free,phototransistor,two-dimensional perovskite,ferroelectric dielectrics
更新于2025-09-09 09:28:46
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Temperature-Dependent Transport in Ultrathin Black Phosphorus Field-Effect Transistors
摘要： This paper studies the temperature-dependent transport properties of ultrathin black phosphorus (BP). We present measurements of BP Schottky-barrier (SB) metal-oxide-semiconductor field-effect-transistors (MOSFETs) with various channel lengths, constructed from a single BP sample with nanoscale uniformity in thickness and width. The electrical characterization reveals a reversal in the temperature dependence of drain current as a function of gate voltage. This reversal indicates a transition in the charge conduction limiting mechanisms as the device is swept from the off-state into the on-state. In the off-state, charge transport is limited by thermionic emission over the energy barriers at the source/drain SB contacts, and drain current increases with temperature. In the on-state, carriers can easily tunnel across the SB at the contacts, and charge transport is limited by scattering in the channel. As a result, drain current decreases with temperature in the on-state, as scattering increases with temperature. Using Landauer transport theory we derive a closed-form expression for thermionic emission current in SB-MOSFETs with 2-D channels. We use this expression to extract the SB height at metal contact interface with BP, and demonstrate the impact of scattering on the extraction. We then use a comprehensive BP SB-MOSFET model to analyze on-state current as a function of temperature, and demonstrate the effects of charged impurity and phonon scattering on the transport properties of BP through extractions of mobility at fixed carrier density.
关键词： transistor,two-dimensional,black phosphorus,MOSFET,transport,2D materials
更新于2025-09-09 09:28:46
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High-Performance 2D MoS <sub/>2</sub> Phototransistor for Photo Logic Gate and Image Sensor
摘要： Two-dimensional (2D) MoS2 is a representative n-type transition-metal dichalcogenide (TMD) semiconductor that has great potential for future nanoscale electronic and optoelectronic applications. Here, we report a high-performance MoS2 phototransistor that exhibits a photoresponse in the 400?700 nm range with the maximum responsivity of over 1 × 104 A/W. As a more sophisticated optoelectronic application than a simple unit device, it is implemented in a photoinverter (NOT logic gate) connected to an external resistor, which clearly shows photoinduced static and dynamic characteristics. Furthermore, we demonstrate a prototype visible imager using the MoS2 photoinverter as imaging pixels as an excellent example of advanced developments in an optoelectronic system based on the 2D semiconductors.
关键词： two-dimensional van der Waals materials,MoS2,image sensor,phototransistor,graphene contact,photoinverter
更新于2025-09-09 09:28:46
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Relaxation and domain formation in incommensurate two-dimensional heterostructures
摘要： We introduce con?guration space as a natural representation for calculating the mechanical relaxation patterns of incommensurate two-dimensional (2D) bilayers. The approach can be applied to a wide variety of 2D materials through the use of a continuum model in combination with a generalized stacking fault energy for interlayer interactions. We present computational results for small-angle twisted bilayer graphene and molybdenum disul?de (MoS2), a representative material of the transition-metal dichalcogenide family of 2D semiconductors. We calculate accurate relaxations for MoS2 even at small twist-angle values, enabled by the fact that our approach does not rely on empirical atomistic potentials for interlayer coupling. The results demonstrate the ef?ciency of the con?guration space method by computing relaxations with minimal computational cost. We also outline a general explanation of domain formation in 2D bilayers with nearly aligned lattices, taking advantage of the relationship between real space and con?guration space. The con?guration space approach also enables calculation of relaxations in incommensurate multilayer systems.
关键词： incommensurate,domain formation,MoS2,bilayers,two-dimensional,relaxation,graphene
更新于2025-09-09 09:28:46
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Semiconducting defect-free polymorph of borophene: Peierls distortion in two dimensions
摘要： In contrast to the well-defined lattices of various two-dimensional (2D) systems, the atomic structure of borophene is sensitive to growth conditions and type of the substrate which results in rich polymorphism. By employing ab initio methods, we reveal a thermodynamically stable borophene polymorph without vacancies which is a semiconductor unlike the other known boron sheets, in the form of an asymmetric centered-washboard structure. Our results indicate that asymmetric distortion is induced due to Peierls instability which transforms a symmetric metallic system into a semiconductor. We also show that applying uniaxial or biaxial strain gradually lowers the obtained band gap and the symmetric configuration is restored following the closure of the band gap. Furthermore, while the Poisson’s ratio is calculated to be high and positive in the semiconducting regime, it switches to negative once the metallicity is retrieved. The realization of semiconducting borophene polymorphs without defects and tunability of its electronic and mechanical response can extend the usage of boron sheets in a variety of nanoelectronic applications.
关键词： Peierls distortion,strain engineering,two-dimensional materials,semiconductor,borophene
更新于2025-09-09 09:28:46
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Simulating Fluorescence Detected Two-Dimensional Electronic Spectroscopy of Multi-Chromophoric Systems
摘要： We present a theory for modeling fluorescence detected two-dimensional electronic spectroscopy of multichromophoric systems. The theory is tested by comparison of the predicted spectra of the light-harvesting complex LH2 with experimental data. A qualitative explanation of the strong cross-peaks as compared to conventional two-dimensional electronic spectra is given. The strong cross-peaks are attributed to the clean ground state signal that is revealed when the annihilation of exciton pairs created on the same LH2 complex cancels oppositely-signed signals from the doubly-excited state. This annihilation process occurs much faster than the non-radiative relaxation. Furthermore, the lineshape difference is attributed to slow dynamics, exciton delocalization within the bands and intraband exciton-exciton annihilation. This is in line with existing theories presented for model systems. We further propose the use of time-resolved fluorescence detected two-dimensional spectroscopy to study state resolved exciton-exciton annihilation.
关键词： fluorescence detected two-dimensional electronic spectroscopy,multichromophoric systems,light-harvesting complex LH2,exciton-exciton annihilation,time-resolved fluorescence detected two-dimensional spectroscopy
更新于2025-09-04 15:30:14
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Building two-dimensional materials one row at a time: Avoiding the nucleation barrier
摘要： Assembly of two-dimensional (2D) molecular arrays on surfaces produces a wide range of architectural motifs exhibiting unique properties, but little attention has been given to the mechanism by which they nucleate. Using peptides selected for their binding affinity to molybdenum disulfide, we investigated nucleation of 2D arrays by molecularly resolved in situ atomic force microscopy and compared our results to molecular dynamics simulations. The arrays assembled one row at a time, and the nuclei were ordered from the earliest stages and formed without a free energy barrier or a critical size. The results verify long-standing but unproven predictions of classical nucleation theory in one dimension while revealing key interactions underlying 2D assembly.
关键词： two-dimensional materials,atomic force microscopy,nucleation,peptides,molecular dynamics simulations
更新于2025-09-04 15:30:14
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Two-dimensional semimetal in HgTe quantum well under hydrostatic pressure
摘要： We report results of systematic measurements of charge transport properties of the 20.5-nm-wide HgTe-based quantum well in perpendicular magnetic ?eld, performed under hydrostatic pressures up to 15.1 kbar. At ambient pressure, transport is well described by the two-band semiclassical model. In contrast, at elevated pressure, we observed nonmonotonic pressure dependence of resistivity at the “charge neutrality point.” For pressures lower than ≈9 kbar, resistivity grows with pressure, in accord with expectations from the band structure calculations and the model incorporating effects of disorder on transport in two-dimensional (2D) semimetals with indirect band overlap. For higher pressures, the resistivity saturates and starts decreasing upon further increase of pressure. Above ≈14 kbar the resistance value and the magnetoresistance character sharply change, which may indicate signi?cant change of electronic structure due to new electronic phase formation or some structural transitions. The data also reveal strong in?uence of disorder on transport in 2D electron-hole system with a small band overlap.
关键词： HgTe quantum well,charge transport,hydrostatic pressure,magnetoresistance,two-dimensional semimetal
更新于2025-09-04 15:30:14