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We investigate the chiral spectral singularities, i.e., laser threshold modes, in PT-symmetric dielectric metasurfaces originating from quasi-bound states in the continuum. The poles, referred to as the quasi-bound states in the continuum, of scattering matrix can move to the upper complex frequency plane from the lower half-plane by increasing the balanced gain and loss. The maximal intrinsic optical chirality of laser threshold mode has been theoretically demonstrated via the large transmission circular dichroism spectra. Our work paves the way for studying the enhanced optical chirality in non-Hermitian nanophotonics empowered by quasi-bound states in the continuum, together with various intriguing applications, such as chiral coherent perfect absorber and laser.

X-ray tomography is widely used in diverse research domains owing to its capacity for observing high-resolution three-dimensional structures nondestructively. However, ring artifacts appear in the tomographic reconstruction because of the inconsistent response of detector pixels, seriously affecting the image quality and causing nonuniform bias. To solve this problem, a method for correction of ring artifacts based on Swin-Conv-U-Net is proposed for x-ray tomography. When applied to simulation and experimental data, the proposed method achieves high accuracy and strong robustness and shows advantages over several classical methods in quantitative and qualitative evaluation.

Atomically thin two-dimensional (2D) materials make it possible to create a variety of van der Waals (vdW) heterostructures with different physical features and attributes, which enables the growth of innovative electronics and optoelectronics applications. The band alignment and charge transfer play a crucial role in the physical and optoelectrical properties of the vdW heterostructure. Here, we design a vdW heterojunction device comprising low-symmetric CrOCl to induce a stable anti-ambipolar behavior and polarization-sensitive photodetection performance. 2D CrOCl exhibits strong in-plane anisotropy and linear dichroism, and an anti-ambipolar transport behavior is observed in a MoTe2 channel due to the gate-tunable band bending and charge transfer at MoTe2/CrOCl interface. The devices also exhibit well photodetection performance with a responsivity of 1.05 A/W and a temporal response of 970 μs. Owing to the anisotropic CrOCl serving as a photosensitizing layer, the device achieves the capability of polarization-sensitive photodetection with a photocurrent dichroic ratio up to ∼6. This work offers a valid device model and design strategy to realize the versatile optoelectronics, including the anti-ambipolar transistor and polarimetric photodetectors.

Dual-band photodetectors have attracted intensive attention because of the requirement of multiband information [such as visible (VIS) and near-infrared (NIR)] in multicolor imaging technology, in which additional information beyond human vision could assist object identification and navigations. The use of 2D materials can break the limitation of high cost of conventional epitaxial semiconductors and a complex cryogenic cooling system for multi-band detection, but there is still much room to improve the performance, especially in responsivity and signal noise ratio. Herein, we have fabricated a VIS-NIR dual-band photodetector based on a multilayer Ta2NiSe5/GaSe heterojunction. Benefiting from the type-II heterojunction, the separation of photo-induced carriers is naturally enhanced, which promotes the responsivity of this dual-band photodetector to 4.8 A W−1 (VIS) and 0.15 A W−1 (NIR) at room temperature with a suppressed dark current at ∼4 pA. Our work suggests that the Ta2NiSe5/GaSe heterostructure is a promising candidate for ultrasensitive VIS-NIR dual-band photodetection.

Infrared detection by binary phosphides is of great interest due to their high carrier mobility, excellent stability, and high absorbance coefficient, as they have a wide range of applications in civil and military fields. As the only metastable phase in gold phosphide, Au2P3 has attracted great attention in fundamental research and optoelectronic applications. Here, we synthesized high-quality and environmentally stable Au2P3 nanosheets through a modified facile one-step mineralization-assisted chemical vapor transport method. Through systematic infrared photoluminescence characterizations, it is found that the as-synthesized Au2P3 nanosheets display an impressive mid-infrared luminescence band centered at about 6.64 μm (0.187 eV) at room temperature. Furthermore, Au2P3-based self-powered photodetectors display outstanding infrared detection performance with D* = 2.9 × 1010 Jones at 1550 nm and D* = 1.9 × 108 Jones at 2611 nm, respectively. Our results suggest that the synthesized Au2P3 nanosheets could be promising candidates for future chip-based infrared nanophotonic and optoelectronic circuitry.

Vibrational properties and ultrafast photocarrier dynamics of 2H–TaS2 under pressures are studied by the experiments of Raman scattering and femtosecond time resolved spectroscopy. With increasing pressure, the linewidth of two-phonon Raman mode broadens, especially features with a sudden rapid increase above 10 GPa. Meanwhile, the ultrafast dynamics show that the fast decay through optical phonon scattering is significantly suppressed in amplitude and prolonged in lifetime; however, the weight of the slow decay component originating from acoustic phonon scattering is enhanced at high pressures. Furthermore, the electron-phonon (e-ph) coupling constant, λq, and the density of states (DOS) near the Fermi level, N(0), are evaluated qualitatively, which reveals a drastic decrease in e-ph coupling strength and a sudden increase in the DOS beyond 10 GPa. This turning pressure is consistent with the critical point where T c of superconductivity peaks while the charge density wave (CDW) vanishes, indicating the direct correlations between λq, N(0), superconductivity, and the CDW under pressure. The anomaly of the DOS may imply the occurrence of a topological transition of the electronic structure. Our work not only provides valuable information for the understanding of competition between the CDW and superconductivity in 2H–TaS2 but also may open up a routine to unveil the pressure-induced electronic topological transition.

Photodetection in the visible and near-infrared (NIR) spectral regions offers a wide range of applications, such as image arrays of high pixel density and artificial intelligence. In this work, broadband organic photodiodes (OPDs) are developed with performance comparable to that of crystalline silicon-based commercial devices. Through the strategy of combining an NIR-absorbing non-fullerene acceptor and a thick junction, the resulting devices show significantly improved performance parameters, with a suppressed dark current density of 0.35 nA/cm2, an enhanced spectral response covering 300–1000 nm, and external quantum efficiency over 60% el/ph. Owing to the low dark current noise and high responsivity to NIR wavelengths, an unexpectedly high specific detectivity of 5.1 × 1013 Jones at 930 nm is obtained together with a linear dynamic range of 157 dB and a −3 dB cutoff frequency of 4.5 kHz. These results reveal that the NIR OPD has great potential for 2D and 3D imaging applications with a high frame rate and multiple band selection.

In this work, the starting nominal Ti25Zr25Hf25Nb25 high entropy alloy (HEA) has two body centered cubic (BCC) phases with a volume percentage about 100:1, with the primary phase having a much larger bulk modulus (incompressible) than the uniform single-phase HEA. We found that these two phases merged into one single BCC phase at pressures beyond 36 GPa, whose bulk modulus dropped to that of the normal homogeneous HEA. After decompressing, the new phase can be sustained to ambient conditions. This abnormal pressure-induced softening was largely related to the lattice distortion evolution and interfacial energy during compression.

Subnanosecond switching speed from an amorphous state with stable crystal precursors to the crystalline state was recently achieved in amorphous Sc-doped Sb2Te3 (a-SST) phase change materials (PCMs), which is about two orders of magnitude faster than that in the well-studied Ge2Sb2Te5 and Ge1Sb2Te4 PCMs. However, the phase change mechanism and phase stability of a-SST remain unknown. Here, we prepared amorphous Sc0.3Sb2Te3 nanocomposites within a minute amount of face-centered-cubic (FCC) type nanograins embedded in the amorphous matrix. Using in situ high-pressure synchrotron X-ray diffraction, we found that nanograins were frustrated under high pressure and gradually dissolved into the matrix around 11.0 GPa. Beyond 11.0 GPa, the a-SST matrix transformed into a uniform high density metallic like amorphous state with a five orders of magnitude drop in electric resistivity compared to the pristine materials. When further compressed to 23.97 GPa, the high density amorphous (HDA) phase switched into a body-centered-cubic (BCC) high-pressure structure, a different phase from the ambient pressure crystalline structure. Upon decompression back to ambient pressure, a pure amorphous phase was sustained. The present study provides additional insight into the phase change mechanism of amorphous nanocomposites.

Antimonene is a recently discovered two-dimensional semiconductor with high carrier mobility, suitable bandgap, and strong spin–orbit coupling, which is of great interest for future electronic, optoelectronic, and spintronics device applications. However, as the basic properties of materials, the electronic structure of antimonene is not fully understood. In this work, the whole and anisotropic electronic structures of antimonene modulated by a horizontal crystal field have been studied in detail by angle-resolved photoemission spectroscopy. The valence band of antimonene for semiconductor properties is characterized by a three-dimensional anisotropic “M”-shape with hexagonal deformation in (E, kx, ky) space. Moreover, the surface state of antimonene for metallic properties is characterized by an upward conelike structure with a stronger warping effect. The anisotropic electronic structure of antimonene is systematically depicted along the high symmetric direction and constant energy contours.

Measurements of electrical transport and Raman spectroscopy are performed on 2H-TaS2 to study the formation and the character of the charge density wave. The entry of the charge-density-wave state below the lock-in temperature is detected by the sudden change of the resistivity slope with temperature, the sharp rise of the magneto-resistivity, and the significant change in the Hall coefficient. Meanwhile, the frequency of the two-phonon mode decreases with decreasing temperature. When approaching the lock-in temperature, the formation of the charge density wave is also evidenced by the disappearance of the two-phonon mode. In the charge density wave state, the newly born charge-density-wave modes in the E2g- and A1g-symmetries exhibit a blue-shift with decreasing temperature. These results suggest that the combined techniques of electrical transport measurement and Raman spectroscopy are powerful in studying the charge-density-wave order in materials with strong electron-phonon coupling.

We perform a long distance measurement up to 1.2 km on the outdoor baseline by electro-optic dual-comb interferometry. A frequency comb pair is developed by phase modulating a continuous laser with a narrow linewidth, and the slightly different repetition frequencies are synchronized to the Rb clock via the signal generators. A RF electrical comb can be generated by multi-wavelength heterodyne interferometry, and thus, a series of synthetic wavelengths can be obtained, whose phases can be used to determine the distances. Compared with the reference values, the experimental results show an agreement within 379 μm in the 1180 m range. In the long-time experiments, the Allan deviation can be below 20 μm with an averaging time of 10 s, and can be further improved to be less than 600 nm when the averaging time is above 350 s at 435 m and 1180 m, respectively.

The interfacial charge transfer between mechanically exfoliated few-layer graphene and Cr2O3 (0001) surfaces has been investigated. Electrostatic force microscopy and Kelvin probe force microscopy studies point to hole doping of few-layer graphene, with up to a 150 meV shift in the Fermi level, an aspect that is confirmed by Raman spectroscopy. Density functional theory calculations furthermore confirm the p-type nature of the graphene/chromia interface and suggest that the chromia is able to induce a significant carrier spin polarization in the graphene layer. A large magnetoelectrically controlled magneto-resistance can therefore be anticipated in transistor structures based on this system, a finding important for developing graphene-based spintronic applications.

Extensive attention has been drawn in generating multimode quantum states in recent years. Many efforts have been made during the last decade to produce such states. In this paper, we have experimentally demonstrated a scheme for generating a multi-spatial-mode quantum light source by a non-degenerated four-wave mixing process with a conical pump and a conical probe in a hot atomic vapor cell. The degree of the intensity-difference squeezing between the generated twin beams is about −4.1 dB. Due to the similar conical shape of the concentric quantum correlated beams, both the amplified probe and the generated conjugate beams can be decomposed into many angular modes. We have also experimentally verified the multi-spatial-mode nature of the generated quantum correlation by comparing the noise levels' variation tendencies of global attenuation and local cutting attenuations. In addition, we have also found the optimal values of each parameter in this scheme for further applications. Due to our scheme's advantages such as compactness, phase-insensitivity, and easy scalability, we have already shown a promising candidate for generating multi-spatial-mode quantum states, which may find potential applications in quantum metrology and quantum imaging, such as quantum-enhanced superresolution and the generation of multiple quantum correlated images.

Microhardness measurements have been carried out on high purity Cu samples with average grain sizes ranging from ∼10 to ∼200nm, over temperatures from liquid nitrogen to ambient, and dwell-times of the indenter in the sample from 5 s to 39 h. The Vickers hardness diminishes approximately linearly with the logarithm of the dwell-time. At short dwell-times the hardness increases significantly with decreasing grain size and with decreasing temperature, but the influence of these variables substantially diminishes at longer times. Investigation by transmission electron microscopy shows that rapid grain growth under the indenter most likely is responsible for the strong and long-lasting indentation creep.

A whipple shield using Al/PTFE (polytetrafluoroethylene) energetic material to protect against space debris is presented. The hypervelocity impact characteristics were investigated experimentally using a two-stage light gas gun at velocities between 3 and 6 km/s. A good protection of the shield was obtained through comparative experiments which used the same bumper areal density. The results showed that the critical projectile diameter can be improved by 28% by contrast with the Christiansen ballistic limit equations. The Al/PTFE energetic material bumper can break up the projectile into smaller, less massive, and slower projectiles due to the combined effect of impact and explosion, thereby producing a sharp rise in the spacecraft protection ability.

A phase sensitive Raman scattering was experimentally demonstrated by injecting a Stokes light seed into an atomic ensemble, whose internal state is set in such a way that it is coherent with the input Stokes seed. Such phase sensitive characteristic is a result of interference effect due to the phase correlation between the injected Stokes light field and the internal state of the atomic ensemble in the Raman process. Furthermore, the constructive interference leads to a Raman efficiency larger than other kinds of Raman processes such as stimulated Raman process with Stokes seed injection alone or uncorrelated light-atom seeding. It may find applications in precision spectroscopy, quantum optics, and precise measurement.

Metal-Oxide-Semiconductor (MOS) capacitors with Bi2Te3 thin film sandwiched and embedded inside the oxide layer have been fabricated and studied. The capacitors exhibit ferroelectric-like hysteresis which is a result of the robust, reversible polarization of the Bi2Te3 thin film while the gate voltage sweeps. The temperature-dependent capacitance measurement indicates that the activation energy is about 0.33 eV for separating the electron and hole pairs in the bulk of Bi2Te3, and driving them to either the top or bottom surface of the thin film. Because of the fast polarization speed, potentially excellent endurance, and the complementary metal–oxide–semiconductor compatibility, the Bi2Te3 embedded MOS structures are very interesting for memory application.

Resonant tunneling is observed in double barrier resonant tunneling diodes with semimetallic ErAs quantum wells. Magnetic field dependence distinguishes two different resonant channels while the thickness dependence of the voltage for resonant tunneling strongly suggests that the electrons tunnel through hole states in the semimetal quantum well.

The effectiveness of suppressing Be out‐diffusion from a Be‐doped GaAs layer by strained InGaAs layers using secondary ion mass spectroscopy has been evaluated. The experimental structures consist of an 800 A Be‐doped (∼1×1019 cm−3) GaAs layer sandwiched between 80 A InxGa1−xAs (x=0,0.1,0.25) layers. The samples were subjected to rapid thermal annealing (RTA) at 750 °C for 6 min. It is clearly observed that Be diffusion beyond the InGaAs layers is the fastest for the structure with x=0 and the slowest for the structure with x=0.25.

We have grown C‐doped GaAs and (In,Ga)As epitaxial layers of device quality in a standard solid source molecular beam epitaxy system using carbon tetrabromide (CBr4) as the carbon source. Dopant incorporation was relatively efficient for both GaAs and (In,Ga)As, requiring a CBr4 beam pressure of about 1×10−6 Torr to achieve a hole density of 1.5×1020/cm3. For doping in the 1019/cm3 range, hole mobilities were comparable to or slightly higher than those of Be‐doped layers with the same carrier concentrations. Modulation‐doped structures grown immediately after heavily C‐doped GaAs layers exhibited reduced two‐dimensional electron gas mobility, but the mobility recovered to previous values within 24 h. (Al,Ga)As/GaAs heterojunction bipolar transistors (emitter size=25 μm×50 μm) with C‐doped bases (p=1.2×1019 cm−3) had common emitter small signal current gains averaging 86 at an emitter current density of 970 A/cm2. The relatively low gas load during growth, the lack of long‐term memory effect, and the acceptable device performance indicate that CBr4 is an attractive alternative to Be for GaAs and (In,Ga)As devices grown by solid source molecular beam epitaxy.

Migration enhanced epitaxy (MEE) was used in this work to grow p+‐GaAs at the substrate temperature of 300 °C for the base of AlGaAs/GaAs heterojunction bipolar transistors. The results indicated that the low‐temperature MEE‐grown p+‐GaAs epitaxial layers (p=1×1019–1×1020 cm−3) exhibited a crystalline quality comparable to those grown by standard MBE at a substrate temperature of 570 °C. AlGaAs/GaAs HBTs with low‐temperature MEE‐grown bases doped at p≊2×1019 cm−3 were fabricated by using a self‐alignment technique. For the devices with the conventional MBE‐grown base, secondary ion mass spectroscopy depth profiles showed a significant Be diffusion into the AlGaAs emitter and as a consequence, the devices showed no current gain. For the devices with the low‐temperature MBE‐grown base, there was a negligible Be penetration into the emitter and the devices exhibited a common‐emitter dc current gain of 13.

The realization of controllable wrinkle pattern on a thin membrane is of great importance to micro/nanoengineering and aerospace engineering. Here, we report a straightforward method that achieves this outcome by introducing simple microstructures such as holes into the membrane. For a two-end clamped stretched membrane, the presence of holes redistributes stress field in the membrane, therefore monitors the buckling mode and wrinkle pattern of the membrane. Experiment, numerical simulation, and analytical model are provided to quantify this idea, and several wrinkle patterns are demonstrated. The results can provide insightful ideas to understand wrinkling phenomenon of microstructured membranes and to tailor wrinkle patterns used in various disciplines such as membrane manufacturing, cell differentiation, and film antenna in aerospace engineering.

Temperature-dependent surface current measurements were performed to analyze the mechanism of surface conductance of AlGaN/GaN channel high-electron-mobility transistors by utilizing process-optimized double gate structures. Different temperatures and electric field dependence have been found in surface current measurements. At low electric field, the mechanism of surface conductance is considered to be two-dimensional variable range hopping. At elevated electric field, the Frenkel–Poole trap assisted emission governs the main surface electrons transportation. The extracted energy barrier height of electrons emitting from trapped state near Fermi energy level into a threading dislocations-related continuum state is 0.38 eV. SiN passivation reduces the surface leakage current by two order of magnitude and nearly 4 orders of magnitude at low and high electric fields, respectively. SiN also suppresses the Frenkel–Poole conductance at high temperature by improving the surface states of AlGaN/GaN. A surface treatment process has been introduced to further suppress the surface leakage current at high temperature and high field, which results in a decrease in surface current of almost 3 orders of magnitude at 476 K.

Forward gate-bias stress experiments are performed to investigate the variation of trap states under Schottky contact in GaN-based high electron mobility transistors. Traps with activation energy ET ranging from 0.22 eV to 0.31 eV are detected at the gate-semiconductor interface by dynamic conductance technique. Trap density decreases prominently after stressing, particularly for traps with ET > 0.24 eV. X-ray photoelectron spectroscopy measurements reveal a weaker Ga-O peak on the stressed semiconductor surface. It is postulated that oxygen is stripped by Ni to form NiO upon electrical stress, contributing to the decrease in ON donor sates under the gate contact.

Frequency dependent capacitance and conductance measurements were performed to analyze the trap states in the AlGaN channel high-electron-mobility transistors (HEMTs). The trap state density in the AlGaN channel HEMTs decreases from 1.26 × 1013 cm−2eV−1 at the energy of 0.33 eV to 4.35 × 1011 cm−2eV−1 at 0.40 eV. Compared with GaN channel HEMTs, the trap states in the AlGaN channel HEMTs have deeper energy levels. The trap with deeper energy levels in the AlGaN channel HEMTs is another reason for the reduction of the reverse gate leakage current besides the higher Schottky barrier height.

Herein, we reported on the study of percolation dynamics in thermoset-based die attach (DA) materials and its effect on percolation conductivity. Two types of percolation mechanism in thermoset based DA were discovered, i.e., the curing reaction-induced percolation and the physical aging-induced percolation. The former features in a fast percolation network growth rate, which is one order of magnitude higher than the latter. It is demonstrated that the percolation kinetics largely affects the apparent percolation conductivity under the traditional packaging conditions; and reaction-induced percolation allows ultrahigh efficiency in reaching the volume fraction-limiting percolation conductance, resulting in enhanced thermal performance of DA.

We report on the ultraviolet (UV)-radiation sensing of pulsed-laser deposited In2O3:SnO2:ZnO films grown on glass substrates. The films demonstrate sharp increase (∼0.35 Ω) in electrical resistance on UV illumination. The resistance of the films shows strong spectral (in the vicinity of 325 nm) and power dependence. This is explained due to the presence of defects located at lattice disorders that generate levels within the semiconductor band gap and originate depletion region around them when charged. This reduces the effective conduction region, increasing the effective resistance. These results show new possibilities for the low-cost high performance UV radiation sensors for biosafety.

We report on the feasible fabrication of microfluidic devices for noncontact particle trapping. A half-wavelength resonator was constructed using standard soft lithography to generate ultrasonic standing waves through a miniature piezoelectric transducer. Microparticles (400nm to 10μm in diameter) flowing through polydimethylsiloxane microchannels were efficiently trapped to levitate in the middle depth of a resonance cavity. Such a device could potentially offer a flexible platform for particle-based assays for a large variety of applications.

The authors report the fabrication of p-n junctions, consisting of n-type SrTiO3 or BaTiO3 and p-type Si substrates, by the pulsed-laser deposition technique. The BaTiO3∕Si junction exhibits excellent rectifying behavior and significantly reduced leakage current at 300K exceeding breakdown voltage of −25V with leakage current

We report the synthesis of epitaxial As-doped ZnO and Mn-doped (ZnAs)O films by pulsed-laser deposition technique. The grain size in (ZnAs)O films decreases from 40 to less than 10nm upon Mn doping, illustrating that Mn acts as a potential catalyst to create nanosize grains. Temperature dependent electrical resistance shows metal-insulator transition and metal-semiconductor transition (MST) at 165 and 115K, respectively, in (ZnAs)O, although Mn doping suppresses MST completely. Both ionization efficiency on oxygen vacancies and percolation of charge carriers may be responsible for such transitions. In addition, electrical conduction in these films shows strong aging effects.

There have been long-standing concerns about the stability of the internal structure of nanocrystalline metals. In this letter we examine grain growth in nanocrystalline Cu under the microhardness indenter, examining the influence of temperature of indentation and sample purity. Surprisingly, it is found that grain coarsening is even faster at cryogenic temperatures than at room temperature. Sample purity is seen to play an important role in determining the rate of grain growth. Fast grain coarsening can affect the outcome of mechanical tests, especially if they involve large stresses and high-purity samples.

We report on the observation of remarkable room-temperature ferromagnetism in nanocrystalline epitaxial Co:TiO2 films grown on sapphire (0001) substrates by a pulsed-laser deposition technique using high-density targets. The films were characterized by x-ray measurements, atomic force microscopy, micro-Raman, electron-paramagnetic resonance, and magnetization studies. The films exhibit three-dimensional islandlike growth that contains nanocrystalline particles. Our experimental results suggest that the remarkable ferromagnetism in Co:TiO2 films is controlled either by the interstitial Co2+ ions or small clusters, which are mainly present at the interface and on the surface of the films. Our work clearly indicates that Co interstitials and nanoclusters cause room-temperature ferromagnetism in Co-doped TiO2.

We report on the integration of epitaxial colossal magnetoresistive La0.67Ba0.33MnO films on Si(100) semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals the superior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3 template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology, magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating the ferromagnetic nature of the film and possible device applications at room temperature.