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Abstract The type‐II band‐aligned van der Waals (vdW) heterostructures are favorable for photocarrier separation and are often used for designing high‐performance photodetectors. Inspired by this, a metal‐mirror electrode enhanced HfSe2‐InSe vdW heterostructure photodetector is designed and demonstrated excitement performance in UV light detection. It is demonstrated the moderate bandgap heterostructure can be configured as a high‐performance UV photodetector with excellent light on/off ratio of 106, high photoresponsivity of 47.3 AW−1, competitive high specific detectivity of 3.2 × 1012 cmHz1/2W−1 and very low noise equivalent power of 2.8 × 10−16 WHz−1/2. Notably, the photoresponse speed of the device is very fast, with a rise time of 4.1 µs and a decay time of 5.4 µs. The results indicate that 2D HfSe2‐InSe vdW heterostructure possesses great potential applications in UV photodetection.

Abstract Broadband photodetectors based on 2D layered materials provide great potential applications in night vision, sensing, and communications. However, it remains a challenge for detectors to achieve both high photoresponsivity and fast response. Here, a high‐sensitive photodetector based on ReS2/BP van der Waals (vdW) heterodiode with fast speed, rising time (τr) of 770 ns, and decay time (τd) of 760 ns under a 637 nm laser is reported. The detection range is covered from visible to mid‐wave infrared (MWIR) 0.405–3.753 μm. In the visible range, a high photoresponsivity of 107.1 AW−1, competitive specific detectivity (D*) of 1.89 × 1010 cm Hz1/2 W−1, and a low noise equivalent power of 3.03 × 10−14 W Hz−1/2 are obtained. In the MWIR the D* of 3.26 × 108 cm Hz1/2 W−1 is demonstrated in the photovoltaic model. Notably, the photodiode realizes a high external quantum efficiency of 71.8%, and a high power conversion efficiency of 2.0%. This work provides a way to design broadband response and fast‐speed self‐driven photodetectors with great potential applications in weak light intensity.

Bismuth ferrite–based ferroelectric ceramics are considered strong competitors in high–temperature piezoelectric applications that benefits from their high depolarization temperature (Td), but problems of large conductivity and low piezoelectric coefficient (d33) should be tackled. BiFeO3PbTiO3–x(Sr0.7Bi0.2□0.1)TiO3 (BF–PT–xSBT) ternary system are designed in this work that successfully resolves this tough paradox. Rietveld refinements show that this system exhibits multiphase coexistence with complex structural transition among rhombohedral, tetragonal and pseudocubic phase. Interestingly, a high Td ∼320 °C and d33 ∼ 236 pC/N are synergistically optimized in x=0.20 composition near pseudo–phase boundary, which are indicated by multi–scale techniques (phase structure, dielectric analysis etc.). What's more, dual electrostrain peaks appear at separate phase boundaries for x=0.20 and 0.66 compositions with distinct piezo/ferroelectric properties. Rayleigh law and piezoelectric force microscopy analysis clarify that the optimal electrostrain performance for both critical compositions are dominated by intrinsic (x=0.20) and extrinsic (x=0.66) contributions, respectively. This work not only provides a new BF–PT–xSBT system with a high Td and superior d33 that are promising candidates in high–temperature actuator and sensor applications, but also presents a possibility of multiphase–coexistence established exotic macroscopic performances.

In this work, we focused on engineering the bandgap of the MoS2–MoSe2 heterobilayer via either stacking type or induced magnetic moment with the aid of density functional theory. We have computed the electronic properties of different stacking MoS2–MoSe2 heterobilayers and their magnetization components, in which all situations retain spin-valley locking. Calculations show that different stacking types can cause a bandgap change of a maximum of 0.1 eV. On the other hand, a micro-enhanced magnetic moment in the heterobilayer increases the bandgap (in some cases, there are changes close to 0.3 eV) significantly. Results suggest that the stacking type and induced magnetic moment make MoS2–MoSe2 heterobilayers potential candidates for valleytronics applications. This study provides a new pathway in tuning spin-valley polarization of valleytronics devices.

BiFeO3–based ceramics possess an advantage over large spontaneous polarization and high Curie temperature, and are thus widely explored in the field of high–temperature lead–free piezoelectrics and actuators. However, poor piezoelectricity/resistivity and thermal stability of electrostrain make them less competitive. To address this problem, (1 − x) (0.65BiFeO3–0.35BaTiO3)–xLa0.5Na0.5TiO3 (BF–BT–xLNT) systems are designed in this work. It is found that piezoelectricity is significantly improved with LNT addition, which is contributed by the phase boundary effect of rhombohedral and pseudocubic phase coexistence. The small–signal and large–signal piezoelectric coefficient (d33 and d33*) peaks at x = 0.02 with 97 pC/N and 303 pm/V, respectively. The relaxor property and resistivity are enhanced as well. This is verified by Rietveld refinement, dielectric/impedance spectroscopy and piezoelectric force microscopy (PFM) technique. Interestingly, a good thermal stability of electrostrain is obtained at x = 0.04 composition with fluctuation η = 31% (Smax'−SRTSRT×100%), in a wide temperature range of 25–180 °C, which is considered as a compromise of negative temperature dependent electrostrain for relaxors and the positive one for ferroelectric matrix. This work provides an implication for designing high–temperature piezoelectrics and stable electrostrain materials.

Excess interstitial Fe atoms in as-grown FeSe1−xTex single crystals are unavoidable in the self-flux growing procedure. As harmful defects to the study of superconductivity and Majorana fermions, the excess Fe atoms are usually removed by the post-annealing procedure. This two-step method is mostly used to obtain high quality FeSe1−xTex single crystals in present studies. Here, we carried out a one-step way to synthesize FeSe1−xTex single crystals without excess Fe content using a chemical vapor transport method. By combining transport measurement, magnetic measurement, and local scanning tunneling microscopy measurement, we prove that there is no excess Fe content in our one-step grown FeSe0.45Te0.55 single crystals. This work provides a new convenient way to obtain pure FeSe0.45Te0.55 single crystals and may be helpful to better study this exotic material.