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A major factor that hinders the realization of indium oxide (IO) as a potential gas/photosensor is the response time, which is quite poor. For instance, the photoresponse of dc sputtered IO films under UV and sub-bandgap illumination is known to exhibit bi-exponential decay with fast (10–100 min) and slow (∼3000 min) time constants. We demonstrate here that the response time can be greatly improved by the hot carriers generated through localized surface plasmon decay. Our study shows that when IO films are incorporated with gold nanoparticles (AuNPs), the fast and slow decay time constants are reduced by a factor of 20 and 30, respectively, at excitation wavelengths close to the localized surface plasmon resonance (LSPR) wavelength. We also show the possibility to achieve wavelength tunable reduction in the time constants by tuning the LSPR wavelength. We attribute the changes to the strong enhancement in the recombination rates facilitated by plasmon decay-mediated excess hot electrons injected into the conduction band of IO. We use a simple analytical model to explain the role of plasmon-mediated hot electrons in enhancing the recombination rate. We believe that the present results are of great significance to improve the response time of metal oxide based photodetectors/sensors, in general, since the underlying physical process depends primarily on the plasmonic nature of the AuNPs. [ABSTRACT FROM AUTHOR]

We report direct evidence of the role of stoichiometry of one-dimensional indium oxide (IO) nanostructures grown by vapor-phase evaporation method on the ethanol gas sensing properties. The stoichiometric crystalline In2O3 nanowires grown under oxidizing (water) ambient exhibit about two orders of magnitude higher sensor response value of 281 in comparison to nonstoichiometric (In/O ∼0.75) nanotubes grown under reducing (ethanol) ambient in presence of 1000 ppm ethanol gas at 300 °C. We propose that for a stoichiometric IO nanowire, Debye region completely depletes the nanowire from free charge carriers which results in a significant increase in the sensor response. [ABSTRACT FROM AUTHOR]

A black phosphorus (BP) ultrathin nanosheet has significant research values in broad fields ranging from nano-electronics/photonics to quantum physics. Here, a piezoelectric actuator is utilized to perform biaxial strain engineering for the investigation of anisotropic Raman response of the ultrathin BP transferred to the oxide dielectric substrate. Three characteristic peaks exhibit redshift when tensile strain is applied, while the peaks reveal blueshift under compressive strain. When applying compressive strain of −0.2%, the Raman shift rate of B2g mode can reach up to 15.3 cm−1/%. In contrast, with the application of 0.2% tensile strain, the B2g mode is shifted by −12.2 cm−1/%. Furthermore, we calculated the Grüneisen parameters to deduce the relationship between the tensile or compressive strain and phonon behavior of crystalline BP. The physical mechanism behind the observation of strained Raman response is discussed, which is related to the variations of bond angle and bond length in BP. Additionally, biaxial strain modulation may change the anisotropic dispersion of BP, revealing the significant potential of BP in innovative polarized light detection. [ABSTRACT FROM AUTHOR]

To realize the high efficiency potential of perovskite/chalcopyrite tandem solar cells in modules, hydrogenated In2O3 (IO:H) as electrode is investigated. IO:H with an electron mobility of 100cm²V-1s-1 is demonstrated. Compared to the conventional Sn doped In2O3 (ITO), IO:H exhibits a decreased electron concentration and leads to almost no sub-bandgap absorption up to the wavelength of 1200nm. Without a trade-off between transparency and lateral resistance in the IO:H electrode, the tandem cell keeps increasing in efficiency as the IO:H thickness increases and efficiencies above 22% are calculated. In contrast, the cells with ITO as electrode perform much worse due to the severe parasitic absorption in ITO. This indicates that IO:H has the potential to lead to high efficiencies, which is otherwise constrained by the parasitic absorptionin conventional transparent conductive oxide electrode for tandem solar cells in modules. [ABSTRACT FROM AUTHOR]

This study examined the metal-induced fluorescence properties of three-dimensionally ordered macroporous silver inverse opal (IO) films. Electrochemically synthesized silver IO films with a micrometer cavity exhibited notable fluorescence enhancement at the silver frame, and a decrease in fluorescence lifetime. Numerical calculations supported the observations of a higher fluorescence efficiency at the frame than in the cavity. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy of hydrogen-doped indium oxide (IO) tubular nanostructures shows presence of paramagnetic oxygen vacancies (VO) at room temperature. For temperatures below 80 K, the EPR spectra exhibit two distinct split resonances correspond to S=12 hydrogen electron spin. Interestingly, presence of hydrogen EPR resonances is accompanied by absence of EPR signal of VO, which is restored above 80 K with the concomitant disappearance of signature resonances from hydrogen. The temperature dependent donor and passivation behavior of hydrogen has been directly observed in metal oxide. This could provide valuable explanations of various VO induced controversial properties of IO nanostructures. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) coated BiVO4 inverse opal (io-BiVO4) structure that shows dramatic improvement of photoelectrochemical hydrogen generation has been fabricated using electrodeposition with a template. The io-BiVO4 maximizes photon trapping through slow light effect, while maintaining adequate surface area for effective redox reactions. CQDs are then incorporated to the io-BiVO4 to further improve the photoconversion efficiency. Due to the strong visible light absorption property of CQDs and enhanced separation of the photoexcited electrons, the CQDs coated io-BiVO4 exhibit a maximum photo-to-hydrogen conversion efficiency of 0.35%, which is 6 times higher than that of the pure BiVO4 thin films. This work is a good example of designing composite photoelectrode by combining quantum dots and photonic crystal. [ABSTRACT FROM AUTHOR]

The near-infrared (NIR) emission of Er3+ ions has been extensively studied owing to their significance in optical communication applications. However, studies concerning the incorporation of lanthanide ions into the two-dimensional (2D) matrix are still in the early stages. In this work, we developed an ingenious two-step vapor-phase-transfer method to synthesize Er3+ doped MoS2 single-crystalline monolayers. The NIR emission at 1530 nm was observed from the doped MoS2 nanosheets under 980 nm diode laser excitation, corresponding to the energy transition from 4I13/2 to 4I11/2 of the Er3+ dopant. The concentration quenching effect was demonstrated with an optimal Er content of around 4 mol. %. To further understand the effect of lanthanide doping on the 2D MoS2 host matrix in terms of the growth mechanism and electronic structures, theoretical analysis was performed on Er-doped monolayer MoS2 using the density functional theory calculation. The computed band structure with the superimposed Dieke diagram was in good accordance with our experimental results. Our work offers the possibility to develop doping strategies in the 2D limit and provides an in-depth understanding of the lanthanide doping in atomically thin materials. [ABSTRACT FROM AUTHOR]

A sixfold decrease in photoluminescence signal intensity at 590 nm with increase in deposition time from 3 to 12 h has been observed in single crystalline indium oxide octahedron structures grown by vapor-phase evaporation method. Electron paramagnetic resonance and energy dispersive x-ray analysis confirm that the concentration of oxygen vacancies increases with deposition time. These results are contrary to the previous reports where oxygen vacancies were shown to be responsible for photoluminescence in indium oxide structures. Our results indicate that indium interstitials and their associated complex defects other than oxygen vacancies are responsible for the photoluminescence in In2O3 microstructures. [ABSTRACT FROM AUTHOR]

BiVO4 photonic crystal inverse opals (io-BiVO4) with highly dispersed Ag nanoparticles (NPs) were prepared by the nanosphere lithography method combining the pulsed current deposition method. The incorporation of the Ag NPs can significantly improve the photoelectrochemical and photocatalytic activity of BiVO4 inverse opals in the visible light region. The photocurrent density of the Ag/io-BiVO4 sample is 4.7 times higher than that of the disordered sample without the Ag NPs, while the enhancement factor of the corresponding kinetic constant in photocatalytic experiment is approximately 3. The improved photoelectrochemical and photocatalytic activity is benefited from two reasons: one is the enhanced light harvesting owing to the coupling between the slow light and localized surface plasmon resonance effect; the other is the efficient separation of charge carriers due to the Schottky barriers. [ABSTRACT FROM AUTHOR]

We present a robust, compact, and transportable instrument that measures the iodine monoxide atmospheric radical at extremely low concentration, down to 40 ppqv (parts per quadrillion by volume, 1:1015). As nitrogen dioxide is strongly absorbed in the same spectral region it could be simultaneously measured down to 4 pptv (parts per trillion by volume, 1:1012). Relying on 'mode locked cavity-enhanced absorption spectroscopy,' the instrument makes use of a free-running commercial femtosecond Titane Saphir laser. We demonstrate that this multiplex detection scheme provides shot noise limited spectra for acquisition times as long as 5 min. Moreover, this instrument is very versatile as it can be potentially tuned from the infrared to the ultraviolet (1080-340 nm) to reach various molecular absorptions. It has been recently deployed at the Station Biologique de Roscoff on the North West Atlantic coast of France. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic properties of molybdenum-doped (0–5 wt %) indium oxide films deposited on (100) MgO substrates using pulsed-laser deposition technique. Interestingly these films were found to reveal room-temperature ferromagnetism, where the magnetization increases with Mo doping. The maximum saturation magnetization of ∼6.6 emu/cc was found for ∼5 wt % Mo doping, providing approximately five times enhancement in comparison to the undoped film. We believe that this enhancement is ascribed to the magnetic moments of Mo ions occupied in the In sites. [ABSTRACT FROM AUTHOR]

Reports on the fabrication and properties of cobalt/alumina/iron oxide tunnel junctions. Magnetoresistance effects observed at room temperature and 4.2 K; Magnetoresistance's origination from the activation of tunneling channels through spin polarized states.

We show that epitaxial graphene on silicon carbide (epigraphene) grown at high temperatures (T >1850 °C) readily acts as material for implementing solar-blind ultraviolet (UV) detectors with outstanding performance. We present centimeter-sized epigraphene metal–semiconductor–metal (MSM) detectors with a peak external quantum efficiency of η ∼ 85% for wavelengths λ = 250–280 nm, corresponding to nearly 100% internal quantum efficiency when accounting for reflection losses. Zero bias operation is possible in asymmetric devices, with the responsivity to UV remaining as high as R = 134 mA/W, making this a self-powered detector. The low dark currents Io ∼ 50 fA translate into an estimated record high specific detectivity D = 3.5 × 1015 Jones. The performance that we demonstrate, together with material reproducibility, renders epigraphene technologically attractive to implement high-performance planar MSM devices with a low processing effort, including multi-pixel UV sensor arrays, suitable for a number of practical applications. [ABSTRACT FROM AUTHOR]

A model of the negative bias illumination stress instability in InGaZn oxide is presented, based on the photo-excitation of electrons from oxygen interstitials. The O interstitials are present to compensate hydrogen donors. The O interstitials are found to spontaneously form in O-rich conditions for Fermi energies at the conduction band edge, much more easily that in related oxides. The excited electrons give rise to a persistent photoconductivity due to an energy barrier to recombination. The formation energy of the O interstitials varies with their separation from the H donors, which leads to a voltage stress dependence on the compensation. [ABSTRACT FROM AUTHOR]

In this letter, we report an observation of room temperature electrical oscillation in vanadium dioxide (VO2), a representative strongly correlated material showing a metal-insulator transition. An electric circuit for the oscillation is simply composed of a voltage source and two-terminal VO2 thin film device serially connected with a standard resistor. The systematic procedures where the oscillation occurred were explained based on the electrical relationship between the VO2 device and resistor, and the generation window of the oscillation was determined. In particular, the oscillation frequency could be controlled by adjusting an external voltage and increased up to >0.5 MHz. [ABSTRACT FROM AUTHOR]

Substituting the doped amorphous silicon films at the front of silicon heterojunction solar cells with wide-bandgap transition metal oxides can mitigate parasitic light absorption losses. This was recently proven by replacing p-type amorphous silicon with molybdenum oxide films. In this article, we evidence that annealing above 130°C--often needed for the curing of printed metal contacts-- detrimentally impacts hole collection of such devices. We circumvent this issue by using electrodeposited copper front metallization and demonstrate a silicon heterojunction solar cell with molybdenum oxide hole collector, featuring a fill factor value higher than 80% and certified energy conversion efficiency of 22.5%. [ABSTRACT FROM AUTHOR]

We report p-type conductivity in intrinsic indium oxide (IO) films deposited by magnetron sputtering on fused quartz substrates under oxygen-rich ambient. Highly oriented (111) films were studied by x-ray diffraction, optical absorption, and Hall effect measurements. We fabricated p-n homojunctions on these films. [ABSTRACT FROM AUTHOR]

The magnetic and transport properties of a single layer of La0.7Ca0.3MnO3 are compared with one topped with magnetic nanodots formed from oxides of iron. Remarkably enhanced magnetization and metal-insulator transition temperature were observed for the decorated film capped with In2O3. The saturation magnetization increased by ∼35%, and the metal-insulator transition temperature increased from 75 K to 145 K at zero field. However, no enhancement was observed for either the La0.7Ca0.3MnO3 film with uncapped magnetic dots or the bilayer formed from La0.7Ca0.3MnO3 and In2O3. [ABSTRACT FROM AUTHOR]

This work presents an alternative experimental approach to directly measure propagation losses of surface plasmon polaritons (SPPs) in a single silver nanowire (AgNW). The methodology synergistically combines several techniques, including single nanowire optical shaping, accurate triggering of SPPs by upconversion nanocrystals (NCs), and precise deposition of sub-micrometer-size droplets with emitters. Indeed, a femtoliter volume of colloidal NCs deposited at one end of the nanowire and excited with a laser through an objective provides a stable source of polaritons, which propagate in the nanowire. The intensity of radiation released by the SPPs scattered out at the opposite AgNW end is a direct measure of propagation losses. This is enabled through a method of precise laser cutting of the nanowire, where the length of the nanowire can be gradually reduced by an optically controlled melting process. At the same time, both the length and diameter of the nanowire are constantly monitored using optical imaging of the complex interaction between the nanowire and polarized Gaussian beam. The optical cutting technique, implemented in this experiment, shows great potential for advanced and inexpensive shaping of the metallic nanostructures for nanophotonic applications. [ABSTRACT FROM AUTHOR]

We investigated the time-dependent current-voltage curves of the forming process in unipolar resistance switching. We applied triggered-voltage triangular-waveform (pulse-waveform) signals with varied sweep rate (amplitude) to Pt/SrTiOx/Pt capacitors. By investigating their temperature dependences, we found that the forming process was driven by two different mechanisms, depending on the sweep rate (amplitude): a purely electrical dielectric breakdown and a thermally assisted dielectric breakdown. For the latter process, we observed precursory changes in the current I(t) before the forming process. By fitting the time-dependent precursory changes with I(t)=Io-A exp(-t/τ), we suggest that the thermally activated migration of oxygen vacancies/ions could help the thermally assisted dielectric breakdown. [ABSTRACT FROM AUTHOR]

Absorption at 355 nm, with a pulsed frequency tripled yttrium-aluminum-garnet laser as light source, is used to monitor the time evolution of the Cl2 density in high-density inductively coupled plasmas. The detection limit over a 0.1 s acquisition time is about 0.2 mTorr of Cl2. This technique is well suited for monitoring chlorine density when studying elementary processes in Cl2 containing plasmas. Furthermore, it can be applied to control the process drift in industrial etch reactors resulting from the modification of the chamber walls conditions: by measuring the Cl2 density in a reference Cl2 plasma before etching a wafer, it can be determined if the chamber wall conditions are kept identical from one wafer to another. [ABSTRACT FROM AUTHOR]

Presents a study of intersubband transitions in a doped asymmetric double quantum well structure under a direct current bias. Description on the basis of the system; Components of the intersubband transitions; Report on the important electroabsorption and electro-optical coefficients.

Investigates the gate-electric breakdown in small n-channel metal-oxide-semiconductor field-effect transistors. Acceleration of the breakdown; Effect of the rapid thermal nitridation of the gate oxide in the transistors; Increase of the charge to the breakdown.

Nanosecond scale threshold switching is investigated with conducting atomic force microscopy (AFM) for an amorphous GeSe film. Switched bits exhibit 2-3 orders of magnitude variations in conductivity, as demonstrated in phase change based memory devices. Through the nm-scale AFM probe, this crystallization was achieved with pulse durations of as low as 15 ns, the fastest reported with scanning probe based methods. Conductance AFM imaging of the switched bits further reveals correlations between the switched volume, pulse amplitude, and pulse duration. The influence of film heterogeneities on switching is also directly detected, which is of tremendous importance for optimal device performance. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) ferroelectrics has emerged as a promising building block for nonvolatile memory devices. In this work, we demonstrate the out-of-plane ferroelectricity of 2D CuCrP2S6 (CCPS) at the room temperature and the switchable diode effect in 2D CCPS-based ferroelectric nanodevices. The spontaneous out-of-plane ferroelectric polarization switching and hysteresis loops are directly evidenced by the piezoresponse force microscopy. The intrinsic ferroelectricity originates from the non-centrosymmetric structure of 2D CCPS, which is confirmed by optical second-harmonic generation technique. A ferroelectric tunnel junction was built up by using 2D CCPS as a function layer. The observed diode-like forward rectification effect of CCPS diode is opposite to the direction of remnant polarization, which is attributed to the ferroelectric polarization modulation of Schottky barrier. Our work highlights the great potential of 2D CCPS in ultrathin ferroelectric memory device and motivates the development of multifunctional nanodevices. [ABSTRACT FROM AUTHOR]

Engineering the admittance of external environments connected to superconducting qubits is essential, as increasing the measurement speed introduces spontaneous emission loss to superconducting qubits, known as Purcell loss. Here, we report a broadband Purcell filter within a small footprint, which effectively suppresses Purcell loss without losing the fast measurement speed. We characterize the filter's frequency response at 4.3 K and also estimate Purcell loss suppression by finite-element-method simulations of superconducting planar circuit layouts with the proposed filter design. The filter is fabricated with 200 nm-thick niobium films and shows the measured bandwidth over 790 MHz within 0.29 mm2 of compact size owing to densely packed spiral resonators. The estimated lifetime enhancement indicates the effective protection of the qubit from Purcell loss. The presented filter design is expected to be easily integrated on existing superconducting quantum circuits for fast and multiplexed readout without occupying large footprint. [ABSTRACT FROM AUTHOR]

We present a broadband enhanced single photon source device of Gaussian-shaped GaAs microlens (ML) arrays coupled with a gold bottom mirror hybrid structure. The extrapolated light extraction efficiency of (60.6 ± 1.5)% at maximum (for collection numerical aperture = 0.45 and based on the an actually measured raw detection efficiency of ∼0.775%) and a broad spectral band of 890–960 nm were obtained. The ML-Au structure with embedded epitaxial quantum dots exhibits a high single-photon purity of (96.6 ± 0.7)% [g(2)(0) = 0.034 ± 0.003] under pulsed excitation with 20% saturation. Wet-etched microlenses with smooth surfaces achieve simultaneous enhancement of both XX and X exciton emissions, which is prerequisite for promising entangled photon pair generation. This work proposes the bright potential of integrated hybrid structures to enable further photon pair entanglement applications. [ABSTRACT FROM AUTHOR]

Polarization-sensitive photodetectors have received considerable attention for their exceptional optoelectronic properties that depend on polarization. It is an excellent method to reduce energy consumption, system's sizes, and cost by constructing self-powered heterojunctions using the two-dimensional materials with asymmetry structure. In this report, we present a self-powered MoS2/WSe2 heterojunction capable of polarized photodetection. The heterojunction exhibits both photovoltaic and pyroelectric effects, which are correlated with the polarized signals. Interestingly, there is a 90° polarization angle between the photovoltaic and pyroelectric effects due to the introduction of in-plane structural polarization. The photovoltaic effect achieves the highest specific detectivity (D*) of about 5 × 1012 Jones when the light polarization is parallel to the in-plane structural polarization. Conversely, the pyroelectric effect dominates and yields the highest D* of about 6 × 109 Jones when the light polarization is perpendicular to the in-plane structural polarization. These findings demonstrate that the specific detectivity of the heterojunction can vary based on the orientation of the light polarization relative to the in-plane structural polarization due to distinct physical mechanisms. Moreover, the self-powered MoS2/WSe2 heterojunction enables simultaneous detection of optical power density and its change rate for polarized light. This study highlights the potential application of two-dimensional heterojunctions for polarization-sensitive self-powered photodetection in the future. [ABSTRACT FROM AUTHOR]

The built-in electric field at the heterojunction interface can effectively separate electron–hole pairs, which can effectively increase the photocurrent and suppress the dark current. The p–n junction can provide a good depletion layer, so p–n junction photodetectors based on two-dimensional materials are rapidly developing. In this study, Nb-doped MoS2 as a p-type semiconductor and n-type α-In2Se3 were used to form a van der Waals heterojunction photodetector. This photodetector achieves photodetection in the visible to near-infrared range with a responsivity (R) of 87 A/W and a specific detectivity (D*) of 7.5 × 1011 Jones. The carriers introduced by doping make the device less suppressive to dark currents, but maintain a high photoresponsivity. This study adopts doping modulation of the conductive properties for p–n junction photodetectors, and the results are expected to further enhance the photodetection performance. [ABSTRACT FROM AUTHOR]

We present a highly efficient self-powered silicon metal–semiconductor–metal (MSM) photodetector (PD). The key feature of our device lies in its asymmetric electrode design, which induces an asymmetry in the Schottky barrier heights at the MSM interface. We utilize a built-in electric field that originates from the larger electrode and extends toward the smaller electrode due to the presence of trapped holes on the larger electrode side. This approach facilitates efficient charge carrier separation and collection, leading to self-powered operation across a wavelength range of 300–1000 nm at 0 V bias. The PD exhibits a high responsivity of 513 mA/W and detectivity of 2.04 × 1011 Jones at a wavelength of 1000 nm. Furthermore, the normalized photocurrent-to-dark current ratio (NPDR) analysis reveals the PD's superior dark current suppression capabilities, resulting in high sensitivity and reliable detection. [ABSTRACT FROM AUTHOR]

Silicon-based near-infrared (NIR) light sources with a simple structure are significant for circuit integration and fiber optic communications. Herein, 1530-nm electroluminescence (EL) from p-Ga2S3:Er/n+-Si junction light-emitting devices (LEDs) is reported with Er-doped Ga2S3 nanofilms as the photoemission layer and heavily doped n-type silicon as the substrate. The 1530-nm EL emission is attributed to the energy transfer between the Ga2S3 host and the Er3+ dopant, and it reaches its maximum at Er-doping concentration of 1 mol. % as the device works at −4.8 mA. The Er-related NIR EL occurs only at reverse voltages because the holes and electrons for recombination in Ga2S3:Er come from the Zener tunneling in the depletion region and the direct ITO injection, respectively. The realization of 1530-nm p-Ga2S3:Er/n+-Si LEDs offers opportunities for silicon-based integrated light sources. [ABSTRACT FROM AUTHOR]

The piezoelectric properties of 4-(4-dimethylaminostyryl) methylpyridine p-toluene sulfonate (DAST)-polydimethylsiloxane (PDMS) composite thin film was investigated. Flexible nanogenerators based on zinc oxide (ZnO) nanowire (NW) arrays/DAST-PDMS were fabricated. DAST holds organic crystal structure, and it can possess piezoelectric properties, and it can enhance the piezoelectric properties of ZnO NW arrays. PDMS can not only mix DAST powder with a liquid to prepare a thin film but also protect ZnO NW arrays and DAST from deterioration. When applying pressure with a balance weight of 100 g, the flexible nanogenerator based on ZnO NW arrays/DAST-PDMS can generate an output voltage of 2.3 V, which is much larger than that of the nanogenerator based on ZnO NW arrays. The effect of the strength of vertical external force, frequency of vertical external force, and degree of bending deformation on the ZnO NW arrays/DAST-PDMS flexible nanogenerators were investigated in this Letter. In our experiments, the output voltage of the ZnO NW arrays/DAST-PDMS flexible nanogenerators can reach 3.3 V. After bending the nanogenerator 20 times, the energy collection device based on the ZnO NW arrays/DAST-PDMS flexible nanogenerator was able to light an LED bulb. [ABSTRACT FROM AUTHOR]

Nonvolatile multiferroic coupling that can be controlled by electric fields has a wide range of future electronic multistate applications. Through first-principles calculations, we have revealed such magnetoelectric effect in van der Waals heterostructure systems consisting of CuCrP2Se6 and VS2. The distinct magnetic moments for Se atoms on the upper and lower surfaces of the CuCrP2Se6 substrate lead to different interlayer magnetic coupling configurations. Meanwhile, by varying the number of substrate layers, we can manipulate the direction of V's magnetic moment during ferroelectric reversal. This intricate interplay of ferroelectricity, magnetism, and ferrovalley enables the creation of electric switchable states. These findings provide ideas for nonvolatile memories controlled directly through electric fields. [ABSTRACT FROM AUTHOR]

Ferroelectricity in van der Waals (vdW) layered material has attracted a great deal of interest recently. CuInP2S6 (CIPS), the only vdW layered material whose ferroelectricity in the bulk was demonstrated by direct polarization measurements, was shown to remain ferroelectric down to a thickness of a few nanometers. However, its ferroelectric properties have just started to be explored in the context of potential device applications. We report here the preparation and measurements of metal-ferroelectric semiconductor-metal heterostructures using nanosheets of CIPS obtained by mechanical exfoliation. Four bias voltage and polarization dependent resistive states were observed in the current–voltage characteristics, which we attribute to the formation of ferroelectric Schottky diode, along with switching behavior. [ABSTRACT FROM AUTHOR]

A large-area single-photon detector with a high maximum count rate (MCR) is expected by LiDAR application for a large dynamic range and high coupling efficiency. Superconducting nanowire single-photon detectors (SNSPDs) are very competitive for high quantum efficiency at near infrared wavelengths. However, it is a great challenge to balance the efficiency, area, and MCR of SNSPDs due to the long superconducting nanowire architecture. In this article, we design a large-area SNSPD with a high MCR for LiDAR applications. The SNSPD has four independent channels, and each of them is composed of four parallel nanowires. The photosensitive area has a diameter of 60 μm and can be coupled with a 200-μm multimode fiber through a lens. At the same time, we analyze the origin of the detector latching under high count rates and propose a discharge acceleration circuit to alleviate it. In the experiment, an MCR of 147 Mcps is achieved in this SNSPD. The product of area and MCR for each channel of this SNSPD is twice higher than previously reported results. We highlight that this work is of great significance for the application of SNSPD in LiDAR. [ABSTRACT FROM AUTHOR]

Mechanisms and influence factors of surface optical (SO) phonon-mode-assisted exciton photoluminescence (PL) spectroscopy in quasi-1-dimensional (Q1D) nitride nanostructures remain a subject of debate. In this work, using momentum and energy conservation laws, a constraint relationship for the frequency and wave number of SO phonon-mode-assisted exciton PL is established. Using the dispersion relationships of SO modes in anisotropic wurtzite nanowires, the frequency and wave number of SO-mode-assisted exciton PL emission are determined. The present theoretical scheme and numerical results not only explain a current experimental discrepancy but could also be used to predict and design exciton PL spectroscopy with SO phonon modes in Q1D nanostructures. [ABSTRACT FROM AUTHOR]

The construction of two-dimensional heterojunctions has significantly expanded the modulation degrees of freedom in two-dimensional materials, which has led to the emergence of numerous advanced microelectronics and optoelectronic devices. Extensive research has been conducted on the photovoltaic and photoconductivity effects to achieve higher photodetection performance in heterojunction-based devices. However, the bulk photovoltaic effect, which has excellent potential for applications in self-powered optoelectronics, microelectronics, and energy conversion devices, has not received enough attention. Herein, we construct a two-dimensional ferroelectric heterojunction using multi-layered CuInP2S6 (CIPS) and MoS2 nanoflakes and investigate its photoconductivity effect for photodetection. Furthermore, we observe and analyze the bulk photovoltaic effect in the heterojunction. The photoelectric effect in the MoS2 layer contributes to the photoconductivity effect of the heterojunction, while the room-temperature polar ordering in CIPS contributes to the bulk photovoltaic effect. The heterojunction exhibits high specific detectivity (D*) of 1.89 × 109 Jones, when the optical power intensity is 4.71 mW/cm2. Moreover, the short-circuit photocurrent density is high, reaching about 1.23 mA/cm2 when the optical power intensity is 0.35 W/cm2. This work highlights the potential application of two-dimensional ferroelectric materials in multifunction devices with self-powered detection and energy conversion capabilities. [ABSTRACT FROM AUTHOR]

Functional dielectrics are a group of materials possessing interesting electro-active behaviors, such as variable permittivity, high breakdown strength, ferroelectricity, piezoelectricity, and pyroelectricity, resulting from their capacity to generate and respond to electric fields in a nonlinear manner. These properties make them highly desirable for energy conversion and storage applications. [ABSTRACT FROM AUTHOR]

The alignment agent plays a crucial role in the electro-optical characteristics of an electro-optic liquid crystal (LC) device. Conventionally, rubbed polyimide (PI) layers have been utilized as alignment agents in LC devices. However, these organic PI layers are sensitive to UV rays and high temperatures. The rubbing procedure involved in preparing PI layers also introduces drawbacks, including non-uniform brightness due to uneven rubbing mechanisms and the presence of residual fiber dust. In our recent research, we demonstrated that various hexagonal 2D (inorganic) materials, such as monolayer graphene, monolayer tungsten diselenide (WSe2), and monolayer hexagonal boron nitride (h-BN) nanosheets, can effectively serve as planar-alignment agents in electro-optic LC devices. In this Perspective, we review the rubbing-free LC alignment process, which relies on the coherent overlay of the benzene rings of LC molecules on the hexagonal lattice structure of 2D materials. We review our recent results on LC devices utilizing 2D materials as alignment agents, highlighting their potential advantages. Furthermore, we discuss the challenges associated with this research field. Finally, we provide our perspectives on the future directions and opportunities for advancing this area of study, aiming to overcome challenges and extend the benefits of employing 2D materials as planar-alignment agents in electro-optic LC devices. [ABSTRACT FROM AUTHOR]

Exploring the semiconductor materials with suitable gap and chemical stability is the key to developing solar-blind ultraviolet photodetectors with high stability, responsivity, and detectivity. However, available materials are limited currently, hindering the development of solar-blind detectors greatly. Rare earth oxides (Yb2O3) have the bandgap and high-dielectric constants suitable for solar-blind detection, but its potential of being applied to broadband gap semiconductors has not been deeply studied. Therefore, to activate the semiconductor characteristics of Yb2O3, this work builds a p-Gr/i-Yb2O3/n-Si heterojunction solar-blind ultraviolet photodetector by introducing single-layer graphene. Through tests, this device has an absorption cutoff wavelength of 271 nm, which can almost cover the entire solar-blind ultraviolet band, and a high responsivity of 9.78 mA/W under 0 V bias with the rise and fall time as short as 87 and 73 ms, respectively. This work not only prepares a high-performance solar-blind UV photodetector but also presents the potential application of Yb2O3 in the solar-blind ultraviolet light detection. The high-dielectric performance of rare earth oxides makes it expected to be used for the photoelectric chip unit in future integrated circuit. [ABSTRACT FROM AUTHOR]