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Plasmonic metasurfaces with giant chiral optical responses are good candidates for chirality study and application, which are usually composed of few-layer or three-dimensional nanostructures. Here, we demonstrate that hybrid bilayer plasmonic metasurfaces simply fabricated via a facile one-step nanofabrication process are good candidates for the realization of intrinsic chiral optical responses and spin-selective transmission. We prove that the intrinsic chiral optical response of the proposed metasurface, which can be easily manipulated, is attributed to the spin-selective collective interference of locally enhanced electric fields caused by the strong interlayer coupling. We further experimentally prove the advantages of fabricated hybrid bilayer plasmonic metasurfaces for optical encryption. With the advantages of compact design, chiral optical response easy to control and lower fabrication demand, the proposed metasurfaces can further expand the applications of chiral plasmonic nanostructures in the area of spin nanophotonics, nonlinear optics, and optical sensing.

Synchronization of electrical oscillators is a crucial step toward practical implementation of oscillator-based and bio-inspired computing. Here, we report the emergence of an unusual stochastic pattern in coupled spiking Mott nanodevices. Although a moderate capacitive coupling results in a deterministic alternating spiking, increasing the coupling strength leads counterintuitively to stochastic disruptions of the alternating spiking sequence. The disruptions of the deterministic spiking sequence are a direct consequence of the small intrinsic stochasticity in electrical triggering of the insulator–metal transition. Although the stochasticity is subtle in individual nanodevices, it becomes dramatically enhanced just in a single pair of coupled oscillators and, thus, dominates the synchronization. This is different from the stochasticity and multimodal coupling, appearing due to collective effects in large oscillator networks. The stochastic spiking pattern in Mott nanodevices results in a discrete inter-spike interval distribution resembling those in biological neurons. Our results advance the understanding of the emergent synchronization properties in spiking oscillators and provide a platform for hardware-level implementation of probabilistic computing and biologically plausible electronic devices.

Phase retrieval is a generic calculating phase method through intensity images and prior conditions. Usually, the image recording system requires stable mechanical movement and accurate alignment between different phase-shift images, which greatly limits the imaging speed and stability, resulting in mismatch or low phase retrieval quality. In this work, we propose a single-shot polarization-sensitive phase retrieval developed from triple transport of the intensity method with anisotropic metasurface. By applying gradient phase along the interface, three images with diffractive phase differences are projected on the recording plane. The three images are formed with known diffraction distances due to the conjugate Pancharatnam−Berry phase modulation of metasurface. The recorded images are calculated and post-processed using transport of intensity equation technique to obtain the phase of object. As a proof-of-principle, we demonstrate the phase imaging results through measuring phase-only objects with single-shot capture. Compared to traditional transport-of-intensity equation optical systems, our method requires no mechanical or system tuning, and polarization or electric controller switching. Thus, it can acquire three differently focused images with single-shot. This significantly improves the time efficiency of the experiments. Such compact metadevice with simplified manipulation and easy post-processing for phase retrieval can be applied to various applications, such as optical microscopy, fluid measurement, and on-ship integration.

Strain engineering, aiming to tune physical properties of semiconductors, provides a promising paradigm for modern micro/nanoelectronics. Two-dimensional materials (2DMs) are the ideal candidates for the next generation of strain engineered devices because of their intrinsic exceptional mechanical flexibility and strength. However, conventional strain modulation methods in 2DMs cannot satisfy the demand of future device applications, because strained structures by these methods lack consistency, reproducibility, and design flexibility. Here, based on the photoresist degeneration induced by electron irradiation, we present a non-contact approach to accurately and directly write the strains with designed patterns from the nanometer to micrometer scale in 2DMs. Profit from controllable manipulation of the electron beam, the developed strategy offers a capability for constructing tensile, compress, or complex strains in MoSe2 monolayers; hence, unique electronic structures for unique physical properties can be designed. Aside from 2DMs, this approach is also appropriate for other types of materials such as Au, α-Si, and Al2O3. Its flexibility and IC-compatibility allow our strain lithography methodology promising in accelerating the potential applications of 2DMs in extensive fields ranging from nanoelectromechanical systems, high-performance sensing, and nontraditional photovoltaics to quantum information science.

Ge2Sb2Te5 (GST) is a kind of non-volatile chalcogenide phase-change material, which has a significant difference in permittivity between its amorphous and crystalline states in the infrared range. On account of this remarkable property, the combination of GST and metamaterials has great potential in tunable meta-devices. In this paper, a perfect absorber based on a nanocross-resonator array stacked above a GST spacer layer and an Au mirror (i.e., a metal-dielectric-metal configuration) is designed and experimentally demonstrated. A thin indium tin oxide (ITO) protective layer is inserted between the GST spacer and the Au resonator to avoid heat-induced oxidation of the GST layer during phase transition. We found that the ITO layer not only can protect the GST layer from deterioration, but also allows a significant blue shift in the absorption peak from 1.808 μm to 1.559 μm by optimizing the thickness of the two dielectric layers without scaling down the size of the metal structure, which provides a more feasible idea in pushing the absorption peak to higher frequency. The LC circuit model is presented to explain this blue-shift phenomenon, which is mainly attributed to the engineering of the dielectric environment of the parallel plate capacitance. In addition, such good performance in dynamitic modulation makes this perfect absorber a robust candidate for optical switching and modulating in various situations.

We present the thickness-dependent electrical properties of mechanically exfoliated single crystal Ta4Pd3Te16 nanoribbons. By decreasing the nanoribbon thickness in the range of 500–20 nm, we observed a suppression of superconductivity driven by both the thickness and the external magnetic field. In particular, for the thinner nanoribbons with the thickness less than 40 nm, there is a non-zero resistance state extending down to low temperature, followed by the loss of superconductivity when the thickness is decreased to the order of the coherence length. We found that the theory of a thermally activated phase slip can well describe the temperature dependence of the resistance below Tc. The disorder-induced enhanced Coulomb interaction with the decrease in the thickness is expected to be dominant in the gradual crossover behavior from superconducting to normal or very weakly insulating behavior in the low-dimensional system.

We demonstrate theoretically and experimentally a plasmonic metasurface operating as a broadband polarization converter with adequate efficiency which can transform linearly polarized light into its orthogonal polarization in the near-infrared region. The unit cell of the specifically designed metasurfaces is composed of an asymmetric split-ring resonator (SRR) within a square metallic hole. The adequate polarization conversion rate arises from the enhancement of the cross-polarized electric field and the decrease in the co-polarized electric field induced by the symmetry breaking of the SRR. Furthermore, a broad operating frequency range results from the overlap of multiple polarization rotation responses, which are generated in the combined symmetry-breaking SRRs and square metallic holes. This ultrathin single-layer metasurface avoids the complicated fabrication process of multilayered and tridimensional polarization converters and offers more intriguing possibilities to design high-performance plasmon...

Oxide heterostructures with the broken translational symmetry often trigger a two-dimensional quantum confinement and associated unique electronic properties that cannot be observed in bulk constituents. Particular interest is devoted to the formation of two-dimensional electron gas (2DEG) at heterointerfaces between two insulators, which offers a fertile ground for fabricating advanced electronic devices. Here, we combine atomic force microscopy, transmission electron microscopy, and atomistic first-principles calculations to demonstrate that the (100) BiFeO3/SrTiO3 interface takes on a metallic nature and a 2DEG is generated at this interface. Our findings also reveal that the electronic reconstruction due to the polar discontinuity and the variation in valence state of Ti arising from diffusion of Ti cations in SrTiO3 to Fe sites of BiFeO3 are critical to the formation of 2DEG at the heterointerface.

This paper demonstrated the flexible control of positive and negative electrocaloric effects (ECEs) in ⟨001⟩-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 single crystal, and a dual cooling cycle is proposed using their combination to improve cooling capacity. The ECE exhibits a complex evolution of positive-negative-positive within 20–140 °C, where the negative ECE originates from the electric field-induced transition from rhombohedral phase to high-symmetric tetragonal phase. Since the coexistence of different ECEs at some temperatures, the positive and negative ECEs alternately appear in neighboring cycles under proper applied fields, i.e., dual cooling. A significant improvement of ∼150% in cooling capacity is directly characterized by the isothermal heat flow measurement.

Manipulating electromagnetic waves with artificial nanostructures has garnered great interest for their properties and potential applications. However, existing devices performing various desired operations at different wavelengths usually require cascading with different geometry patterns, which does not offer satisfactory simplicity. Here, we theoretically and experimentally demonstrate that an ultrathin, multifunctional metasurface, consisting of an array of nanorods, can perform various functions at different wavelengths. Simulated and experimental results indicate that nearly perfect absorption, linear-to-circular conversion, and linear cross-polarization conversion can be integrated into one multifunctional metasurface. Furthermore, the multifunctional metasurface can maintain very high performance across a large range of incident angles. The proposed configuration is extremely compact and easy to fabricate; these qualities should support the development of practical applications.

Most applications of graphene need a suitable support substrate to present its excellent properties. But transferring graphene onto insulators or growing graphene on foreign substrates could cause properties diminishing. This paper reports the graphene growth directly out of diamond (111) by B doping, guided by first-principles calculations. The spontaneous graphene formation occurred due to the reconstruction of the diamond surface when the B doping density and profile are adequate. The resulting materials are defect free with high phase purity/carrier mobility, controllable layer number, and good uniformity, which can be potentially used directly for device fabrication, e.g., high-performance devices requiring good thermal conductivity.

We directly monitored the lattice dynamics in PbSe quantum dots (QD) induced by laser excitation using ultrafast electron diffraction. The energy relaxation between the carriers and the lattice took place within 10 ps, showing no evidence of any significant phonon bottleneck effect. Meanwhile, the lattice dilation exhibited some unusual features that could not be explained by the available mechanisms of photon-induced acoustic vibrations in semiconductors alone. The heat transport between the QDs and the substrate deviates significantly from Fourier's Law, which opens questions about the heat transfer under nonequilibrium conditions in nanoscale materials.

We report a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in about 4 ps and a subsequent slower transformation in 90 ps and longer timescales. The fast process is designated as the initial melting of orthorhombic phase induced by the Mn-O bond change that is most likely driven by the quenching of the dynamic Jahn-Teller distortion following the photo-excitation. The slow process is attributed to the growing of newly formed structure domain from the photo-excited sites to the neighboring non-excited orthorhombic sites.

The terahertz (THz) response from vertically aligned few-layer graphene samples with and without femtosecond optical excitation was investigated. The frequency-dependent optical conductivity of the photoexcited vertically aligned few-layer graphene had a strong free carrier response. Upon photoexcitation, a transient decrease in THz transmission on the subpicosecond timescale was observed. A modulation depth of nearly 16% was demonstrated in the range of the photoexcitation power used. The photoinduced ultrafast response presented here is distinct from previous studies on horizontally grown graphene. The mechanism underlying this photoconductive ultrafast response was investigated by measuring the transmission properties and by calculating the carrier density. The results of these studies are promising for the development of high-performance THz modulators and ultrafast switchable THz photoelectric devices.

High-quality continuous uniform monolayer graphene was grown on polycrystalline PtRh20 alloy foils by low pressure chemical vapor deposition. The morphology of graphene was investigated by Raman spectroscopy, scanning electron microscopy, and atomic force microscopy. Analysis results confirm that high quality single-layer graphene was fabricated on PtRh20 foil at 1050 °C using a lower flux of methane under low pressure. Graphene films were transferred onto the SiO2/Si substrate by the bubbling transfer method. The mobility of a test field effect transistor made of the graphene grown on PtRh20 was measured and reckoned at room temperature, showing that the carrier mobility was about 4000 cm2 V−1 s−1. The results indicate that desired quality of single-layer graphene grown on PtRh20 foils can be obtained by tuning reaction conditions.

We report few-layer SnSe2 field effect transistors (FETs) with high current on/off ratios. By trying different gate configurations, 300 nm SiO2 and 70 nm HfO2 as back gate only and 70 nm HfO2 as back gate combined with a top capping layer of polymer electrolyte, few-layer SnSe2 FET with a current on/off ratio of 104 can be obtained. This provides a reliable solution for electrically modulating quasi-two-dimensional materials with high electron density (over 1013 cm−2) for field-effect transistor applications.

In this paper, we demonstrate the combination of nematic liquid crystal with a binary silicon nanohole array to realize a high performance Fano resonance based optical modulator. The simulations using a finite difference time domain method reveal that the sharp Fano profile in the binary array originates from the interaction of the in-phased and anti-phased lattice collective resonance hybridized through lattice coupling effects. Experimental results agree very well with the simulations and demonstrate the strong dependence of the Q factor and spectral contrast of the resonance on the radius difference of the two nanohole arrays. Infiltrated with nematic liquid crystal, E7, the Fano profile can be dynamically and continuously tuned by an applied voltage, and an unprecedented modulation depth up to 85% is achieved.

We present the underlying theory, the design specifications, and the experimental demonstration of the broadband diodelike asymmetric transmission of linearly polarized light in the near-infrared regime. This result is achieved through the use of a two-layer hybrid metamaterial, composed of an L-shaped metallic particle and a double nano antenna. The experimental results are shown to agree well with the theoretical predictions and the simulated transmission spectra. The realization of the diodelike asymmetric transmission can be attributed to the combination of two independently functioning metallic structures, which are shown to perform their respective function even when shifted away from perfect alignment. This work offers a further step in developing broadband diodelike asymmetric transmission for use in electromagnetic devices.

To realize linear-like dielectric characteristics in normal ferroelectric poly(vinylidene-co-trifluoroethylene) (P(VDF-TrFE)), poly(ethyl methacrylate) (PEMA) was grafted onto poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) as side chains. The introduction of rigid PEMA segments resulted in the decreased crystallinity, crystal and ferroelectric domain size. As a result, reduced dielectric loss and improved modulus, therefore enhanced breakdown strength was obtained in the graft copolymers. Moreover, low energy loss (about 16.6%) and relatively high energy density (19.3 J cm−3) under high electric field (675 MV m−1) was achieved since the hysteresis induced by the ferroelectric relaxation of P(VDF-TrFE) has been completely eliminated.

B-doped ultrananocrystalline diamond (UNCD) films are grown using hot-filament chemical vapor deposition method, and their electrical transport properties varying with temperature are investigated. When the B-doped concentration of UNCD film is low, a step-like increase feature of the resistance is observed with decreasing temperature, reflecting at least three temperature-modified electronic state densities at the Fermi level according to three-dimensional Mott's variable range hopping transport mechanism, which is very different from that of reported B-doped nanodiamond. With increasing B-doped concentration, a superconductive transformation occurs in the UNCD film and the highest transformation temperature of 5.3 K is observed, which is higher than that reported for superconducting nanodiamond films. In addition, the superconducting coherence length is about 0.63 nm, which breaks a reported theoretical and experimental prediction about ultra-nanoscale diamond's superconductivity.

We present the design, characterization, and experimental demonstration of a polarization-insensitive wide-angle plasmonically induced transparency (PIT) planar metamaterial (MM) in the near-infrared regime. A four-level plasmonic system is proposed to explain and analyze the forming mechanisms of the PIT planar MM, whose results agree closely with the simulated and experimental results. This shows that the local asymmetrical nanostructure leading to the plasmon-assisted interaction is the key to producing PIT, but it does not mean that PIT cannot be achieved by the whole symmetrical nanostructure. This work offers a further step in developing optical modulation.

Two-dimensional transition-metal dichalcogenides such as MoS2 are promising channel materials for transistor scaling. Here, we report the performance and environmental effects on back-gated bi-layer MoS2field-effect transistors. The devices exhibit Ohmic contacts with titanium at room temperature, on/off ratio higher than 107, and current saturation. Furthermore, we show that the devices are sensitive to oxygen and water in the ambient. Exposure to ambient dramatically reduces the on-state current by up to 2 orders of magnitude likely due to additional scattering centers from chemisorption on the defect sites of MoS2. We demonstrate that vacuum annealing can effectively remove the absorbates and reversibly recover the device performances. This method significantly reduces the large variations in MoS2 device caused by extrinsic factors.

We present the design, characterization, and experimental demonstration of a polarization insensitive and omnidirectional broadband near perfect planar metamaterial absorber (MA) in the near infrared regime, which does not need to stack multilayer composite structures. Experimental result shows that greater than 80% absorption is obtained across a wavelength range of 0.41 μm, which is in reasonable agreement with the simulation. The electromagnetic response of the MA is theoretically investigated. The broadband planar MA is polarization insensitive and the absorption remains high even at large incident angles.

The temporal evolution of residual charges during laser ablation of metal and dielectric materials was investigated by measuring the correlated transient electric field using femtosecond electron shadow imaging and deflectometry. The results indicate that residual charges in metals can redistribute themselves almost instantly, abiding by the boundary conditions and Maxwell equations in the same way as they would at electrostatic equilibrium condition, but residual charges in dielectrics are confined within the excited area for hundreds of picoseconds and beyond. These observations provide an experimental support to the alleged Coulomb explosion phenomenon in previous studies as well as a reference for modeling residual charge dynamics.

Using an ultrafast electron probe capable of four-dimensional diagnosis, the initial stage of fast evolving plasmas produced by a 1014 W/cm2 laser irradiation of a metal target was investigated in real time with picosecond time resolution. The associated strong transient electric field was identified to have two components, which either focus or defocus the probe electron beam. The effects of this field on the probe electron beam can be reproduced by a self-expanding charge cloud containing about 5×107 suprathermal electrons with the outermost layer expanding at an average speed of 1.2×107 m/s.

In a recent letter [Appl. Phys. Lett. 92, 011901 (2008)], Tang reported a simulation of structural dynamics in metal films induced by ultrafast laser heating using the two-temperature model [P. B. Allen, Phys. Rev. Lett. 59, 1460 (1987) and R. W. Schoenlein et al., Phys. Rev. Lett. 58, 1680 (1987)] and one-dimensional anharmonic chain model [E. Fermi J. Pasta S. Ulam, No. LA-1940 (1955)]. In this comment, we would like to point out several issues in the physical concepts and formulations in the simulation which we strongly disagree with the author. Consequently, we believe that the main conclusion of Tang's paper that the interpretation of ultrafast diffraction data requires both nonlocal collective atomic motion and the conventional linear thermal expansion lacks physical justification and is questionable.

We report the measurement of the electronic Gruneisen parameter γe of the ferromagnetic transition metal nickel. In this measurement, the electronic thermal expansion was differentiated from other thermal contributions by simultaneously monitoring the laser-induced ultrafast stress and structural dynamics in the time domain using femtosecond electron diffraction. This method overcomes the restriction of traditional low temperature methods and offers a unique path to study electronic thermal expansion in magnetic metals. The result indicates that the local magnetic moment, which persists in the paramagnetic state of nickel, does not significantly contribute to the thermal expansion.