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In situ neutron diffraction experiments have been performed to investigate the deformation mechanisms on CoCrFeNi high entropy alloys (HEAs) with various amounts of doped Cu. Lattice strain evolution and diffraction peak analysis were used to derive the stacking fault probability, stacking fault energy, and dislocation densities. Such diffraction analyses indirectly uncovered that a lower degree of Cu doping retained the twinning behavior in undoped CoCrFeNi HEAs, while increasing the Cu content increased the Cu clusterings which suppressed twinning and exhibited prominent dislocation strengthening. These results agree with direct observations by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

III–V Indium Arsenide (InAs) nanowire photodetectors have attracted intensive research attention due to their high carrier mobility, direct and narrow bandgap, and nanoscale dimensions, offering immense potential in nanoscale optoelectronics, particularly for applications in photonic integrated circuits. Despite extensive studies on the properties of InAs nanowires, their photoresponse remains intricate, displaying bipolar behavior (i.e., positive and negative photoresponse) within the same device under varying conditions. However, the underlying driving mechanism remains unclear. In this work, we have systematically studied the transition between the negative photoresponse and positive photoresponse in the InAs nanowire photodetector under different conditions. We found the bipolar photoresponse is directly related to the occupation status of the surface trap states, and it could be effectively regulated by the gate voltage, power intensity, as well as the illumination duration. Furthermore, we developed a waveguide-integrated InAs nanowire photodetector using electron photoresist with an optical loss as low as 0.122 dB/μm. This achievement underscores its potential for application in photonic integrated photodetectors, laying the groundwork for future integration of InAs nanowire photodetectors into photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Acoustic emission, AE, spectroscopy identifies dislocation avalanches and crack propagation in high-purity Cu with self-stabilized dislocation networks. These samples were produced by additive manufacturing where thermal gradients form cellular structures. These structures confine avalanches of dislocation movements (∼confined dislocations) with an energy exponent ε = 1.82 ± 0.04. Free dislocation movement follows force-integrated mean-field behavior with ε = 1.6 ± 0.02. Additional crack propagation under tension exhibits a critical failure exponent of ε = 1.45 ± 0.01. These three mechanisms combine to generate sample failure under tension. We use this example to demonstrate how different avalanche mechanisms can be disentangled in AE spectroscopy of additive manufactured metal and how the specific self-stabilized dislocation networks influence these avalanche dynamics. [ABSTRACT FROM AUTHOR]

Metal oxide-based memristors usually exhibit robust resistive switching characteristics but poor mechanical tolerance, limiting their applications in wearable intelligent electronics. Here, we report a highly flexible and robust hafnium oxide-based memristor by using the ultrathin substrate for wearable in-memory computing. The fabricated memristor can display reliable resistive switching behaviors, including low switching voltage, good endurance, and excellent uniformity, under an extremely bending state with the radius of 0.8 mm. The mechanical behavior of the flexible memristor with varying substrate thickness is systematically analyzed using the finite element method. Moreover, typical synaptic plasticity including long-term potentiation and long-term depression was verified under the extremely bending state. Based on the highly flexible and robust memristor device, a three-layer neural network was constructed using a software simulator, achieving a recognition accuracy of 90.49% for handwritten digit recognition under the bending state. These results demonstrate our robust memristor synapse shows high mechanical flexibility, paving a promising way to realizing wearable in-memory computing. [ABSTRACT FROM AUTHOR]

We report on electrical gating of superconducting bilayer NbSe2 using dual-gate field-effect transistors constructed by the van der Waals assembly of mechanically exfoliated NbSe2 and SrTiO3 thin films grown by molecular beam epitaxy. Charge carrier doping, but not a pure electric field, was found to induce changes to the superconducting resistive transition, reaching a 190 mK modulation of the critical temperature and excluding the Rashba effect. The phase space for the superconducting state beyond the Pauli limit under in-plane magnetic fields expands when the critical temperature is enhanced. Quantitative comparison with theory suggests the presence of intervalley scattering, which competes with Ising spin–orbit coupling to set the superconducting-normal phase boundary. The gating method demonstrated here may be applied to study other van der Waals layered superconductors. [ABSTRACT FROM AUTHOR]

We present a report on hybrid InSb–Pb nanowires that combine high spin–orbit coupling with a high critical field and a large superconducting gap. Material characterization indicates the Pb layer of high crystal quality on the nanowire side facets. Hard induced superconducting gaps and gate-tunable supercurrent are observed in the hybrid nanowires. These results showcase the promising potential of this material combination for a diverse range of applications in hybrid quantum transport devices. [ABSTRACT FROM AUTHOR]

Thermoelectric materials, based on photo-thermoelectric effect (PTE), may be promising in photo-detection because of their self-power, extremely broad-band, and free of cryogenic attachments. Up to now, the performance of PTE is mainly optimized through enhancement of extrinsic absorption such as using optical metamaterials. Instead, we here improve the PTE through materials engineering, accordingly systematically investigated the PTE of both P- and N-type SnSe crystals with different carrier concentrations (1017–1019 cm−3). P-type SnSe has much better photo-thermoelectric performance than the N-type one. Among P-type SnSe, the SnSe crystal with the largest carrier concentration (∼1019 cm−3 at room temperature) demonstrates the highest photo-thermoelectric performance. Analysis by a modified two-temperature model suggests that the key parameter of enhanced PTE is the high electrical conductivity, which leads to large optical absorption and large temperature difference. Our work provides a guideline on how to engineer thermoelectric materials to enhance their photo-thermoelectric performance. [ABSTRACT FROM AUTHOR]

Here, we report the growth of (Sr, Ca) Nd2Fe2O7 single crystals with the Ruddlesden–Popper structure using an optical floating-zone method. A significantly anisotropic magneto-dielectric effect (MD), ab-plane and c-axial MD coefficients reaching −12.3% and −8.4% measured at 103 Hz in a 1 T magnetic field, can be obtained in a SrNd2Fe2O7 crystal at room temperature. The corresponding anisotropic MD ratio can be reached as high as 1.46. With an increase in the Ca concentration, the MD effect decreases dramatically and is eventually completely suppressed in both directions. Analysis of magnetic properties and 57Fe Mössbauer spectra suggests that the anisotropic MD effects in SrNd2Fe2O7 can be attributed to polaronic hopping between two neighboring Fe3+ ions through oxygen vacancies in an anisotropically antiferromagnetic matrix; the disappearance of the MD effect in Ca-doped SrNd2Fe2O7 is a consequence of the suppression of the antiferromagnetism. Our work suggests that the significantly anisotropic MD effect in SrNd2Fe2O7 crystals at room temperature can be used in magneto-dielectric controlled devices. [ABSTRACT FROM AUTHOR]

It is necessary but challenging to verify topological surface states of α-Sn by electrical transport. In this work, we demonstrate conclusive transport evidence on topological properties of an α-Sn film grown on a CdTe substrate by molecular beam epitaxy. A Berry phase determined from Shubnikov–de Haas oscillations is 0.98π. A two-dimensional (2D) Fermi surface is clearly demonstrated by angle-dependent oscillations. We believe the nontrivial topology originates from the 2D Dirac fermions of the topological surface states. In addition, both anisotropic magneto-resistance and planar Hall effect have negative amplitudes at higher fields, which we attribute to the spin-flip backscattering in the topological surface states. We also show that these topological surface states have a long relaxation time of ∼95 fs, making α-Sn a potential candidate for high-efficiency spintronics. [ABSTRACT FROM AUTHOR]

The allotrope of carbon, biphenylene, was prepared experimentally recently [Fan et al., Science 372, 852–856 (2021)]. In this Letter, we perform first-principles simulation to understand the bonding nature and structure stability of the possible in-plane heterostructure built by graphene and biphenylene. We found that the graphene–biphenylene in-plane heterostructure only exhibits along the armchair direction, which is connected together by strong covalent bonds and energetically stable. Then, the non-equilibrium molecular dynamics calculations are used to explore the interfacial thermal properties of the graphene/biphenylene heterostructure. It is found that the graphene/biphenylene in-plane heterostructure possesses an excellent interfacial thermal conductance of 2.84 × 109 W·K−1·m−2 at room temperature. Importantly, the interfacial thermal conductance presents different temperature dependence under opposite heat flux direction. This anomalous temperature dependence results in increased thermal rectification ratio with temperature about 40% at 350 K. This work provides comprehensive insight into the graphene–biphenylene heterostructure and suggests a route for designing a thermal rectifier with high efficiency. [ABSTRACT FROM AUTHOR]

Sound absorption is important for room acoustics and remediation of noise. Acoustic metamaterials have recently emerged as one of the most promising platforms for sound absorption. However, the working bandwidth is severely limited because of the strong dispersion in the spectrum caused by local resonance. Utilizing the coupling effect among resonators can improve the absorbers' performance, but the requirement of collecting coupling effects among all resonators, not only the nearest-neighbor coupling, makes the system too complex to explore analytically. This Letter describes deep learning based acoustic metamaterials for achieving broadband sound absorption with no visible oscillation in a targeted frequency band. We numerically and experimentally achieve an average absorption coefficient larger than 97% within the ultra-broadband extending from 860 to 8000 Hz, proving the validity of the deep learning based acoustic metamaterials. The excellent ultra-broadband and near-perfect absorption performance allows the absorber for versatile applications in noise-control engineering and room acoustics. Our work also reveals the significance of modulating coupling effects among resonators, and the deep learning approach may blaze a trail in the design strategy of acoustic functional devices. [ABSTRACT FROM AUTHOR]

Hafnium-oxide-based materials are considered a promising candidate for next-generation nonvolatile memory devices owing to their good CMOS compatibility and robust ferroelectricity at the nanoscale. In this work, we synthesize highly (111)-oriented La-doped HfO2 (HLO) ferroelectric thin films via pulsed laser deposition. Furthermore, the effect of La dopant concentration, thickness, and growth temperature on the ferroelectricity of HLO films is investigated in detail. A maximum remnant polarization of ∼9 μC/cm2 is achieved for only the 5-nm-thick 3 mol. % HLO films without a wake-up process. The 180° inversion of the domain, the butterfly-shaped capacitance–voltage curve, and typical ferroelectric displacement current curve further demonstrate the robust ferroelectricity at the nanoscale. Moreover, the phase evolves from the monoclinic to the orthorhombic and subsequently to the cubic phase with increasing La concentration, which is due to the combined action of oxygen vacancy, epitaxial strain, and chemical pressure. Additionally, in the interface configuration of HLO/La0.7Sr0.3MnO3 (LSMO), the MnO20.7− layer is substituted by the HLO layer on the MnO2-terminated surface of LSMO, which can be attributed to the fact that the HLO layer with higher electronegativity replaces the MnO20.7− layer with the same electronegativity in the HLO film. Therefore, this study provides a reliable pathway for directly obtaining a lightly doped HLO ferroelectric thin film, which can help to broaden the understanding of the ferroelectric physical mechanisms with element doping. [ABSTRACT FROM AUTHOR]

Manipulation of carrier types in SnSe crystals is quite advantageous to fabricate SnSe-based homojunction devices such as thermoelectric modules. However, tuning the n-type charge carrier at an optimal level of SnSe is quite challenging because of its natural p-type without intentional doping. Here, we report the realization of the n-type SnSe through halogens or Ce doping. Importantly, heavily electron doped SnSe single crystals (∼1019 cm−3) can be obtained by Ce-doping through the Bridgeman method. The electrical conductivity of as-grown SnSe crystals evolves from thermally activated behavior to the metallic one when the electron concentrations are increased from 1016 to 1019 cm−3. Remarkably, the power-factor and electronic quality factor of heavily electron Ce-doped SnSe crystals can reach 1.59 and 0.44 μW cm−1 K−2 at 300 K, respectively, which is one of the best thermoelectric n-type SnSe. This work suggests that Ce-doping through the Bridgeman method is an ideal route for further improving the thermoelectric property of n-type SnSe crystals. [ABSTRACT FROM AUTHOR]

Transformation-induced plasticity (TRIP) high-entropy alloys (HEAs) have drawn great attention as they present excellent mechanical properties, and their phase stability is critical for the underlying deformation mechanisms and the application temperature range. In this study, the kinetic phase transformation behavior of a dual-phase TRIP-HEA Fe50Mn30Co10Cr10 (at. %) was probed by in situ neutron diffraction during thermal cycling between 293 and 425 K. Continuous austenitic and martensitic transformation were visualized through the evolution of hexagonal close-packed phase fraction during thermal cycling. Specifically, thanks to the magnetic sensitivity of neutron diffraction, it was found that the martensitic transformation under cooling became suppressed when the antiferromagnetic ordering started at ∼326 K. This temperature was further confirmed as the Néel temperature by magnetization measurements. Thermodynamic calculations revealed that the suppression effect on martensitic transformation is attributed to the consumption of the chemical driving force by the magnetic ordering. The magnetic ordering at such relatively high temperature is associated with the high Mn content. These findings shed light on a potential strategy to achieve better mechanical properties of Mn-containing alloys by manipulating the magnetic property through tuning the Mn content. [ABSTRACT FROM AUTHOR]

To explore the bandgap tunability in strain-compensated superlattices, we have grown a series of InAs/AlAs strain-compensated short-period superlattices (SPSs) with different period lengths by molecular beam epitaxy. Although the average indium composition of the InAs/AlAs SPS samples remains the same, the bandgaps of these SPSs measured by photoluminescence show a strong dependence on the period length, ranging from 1.41 to 1.01 eV as the period length varies from 4 ML to 10 ML. This fine control on the period length can extend the cutoff wavelength of this digital-alloy-like InAlAs (lattice matched to InP) material up to 1230 nm at room temperature. Multiple transitions are observed in Fourier transform infrared spectra, which agree well with the calculation and confirm the confinement in this structure. The strain effect in tuning the band structures and the band alignments is demonstrated, showing that longer period length together with smaller conduction band offset has led to the smaller effective bandgap of the InAs/AlAs SPS. [ABSTRACT FROM AUTHOR]

Intermittent avalanches in a multitude of materials are characterized by acoustic emission, AE, where local events lead to strain relaxations and generate shock waves (so-called "jerks"), which are measured at the sample surface. The bane of this approach is that several avalanche mechanisms may contribute to the same AE spectrum so that a detailed analysis of each individual contribution becomes virtually impossible. It is, hence, essential to develop tools to separate signals from different dynamical processes, such as ferroic domain switching, collapse of porous inclusions, dislocation movements, entanglements, and so on. Particularly, difficult cases are dynamical microstructures in fcc alloys where the AE signal strength is weak. Nevertheless, using profile analysis of AE signals, we can distinguish between two mechanisms, namely, dislocation movements and dynamic entanglements in fcc 316L stainless steel. In this approach, we are able to measure the statistical AE durations of both subsets separately. The fingerprint for superposed avalanches with different durations is seen by the scaling between the energy E and the maximum amplitude A of each avalanche E ∼ Ax with x = 2. While the same exponent x applies for both mechanisms, the scaling relation shows two branches with different absolute energy values. The two mechanisms are then confirmed by separating the energy distributions P(E) ∼ E−ε for the two mechanisms with ε = 1.55 for dislocation movements and ε = 1.36 for entanglements. [ABSTRACT FROM AUTHOR]

Nanoceramics may have different structural and physical properties compared to their coarse-grained counterparts. Here, we report the high-pressure study of micro- and nano-crystalline MgAl2O4 in order to examine the effect of particle size on the structural stability. A reversible pressure-induced phase transition (cubic to tetragonal) is observed in MgAl2O4 nanocrystals under non-hydrostatic pressure at room temperature, in contrast to the previously reported structural transition of MgAl2O4 at high pressure and high temperature. It is also found that the compressed MgAl2O4 microcrystals do not fracture further below 60 nm, suggesting a plastic deformation mechanism transition. MgAl2O4 with a grain size above ∼60 nm exhibits normal cracking behaviors, but shows metal-like plastic deformation behaviors below this critical size. It is implied that combined ductility and strength can be achieved in nanoceramic MgAl2O4. [ABSTRACT FROM AUTHOR]

Chirality is present as a trend of research in biological and chemical communities for it has a significant effect on physiological properties and pharmacological effects. Further, manipulating specific morphological chirality recently has emerged as a promising approach to design metamaterials with tailored mechanical, optical, or electromagnetic properties. However, the realization of many properties found in nature, such as switchable and hierarchical chirality, which allows electromagnetic control of the polarization of light and enhancement of mechanical properties, in man-made structures has remained a challenge. Here, we present helical structures with switchable and hierarchical chirality inspired by origami techniques. We propose eggbox-based chiral units for constructing homogeneous and heterogeneous chiral structures and demonstrate a theoretical approach for tuning the chirality of these structures by modulating their geometrical parameters and for achieving chirality switching through mechanism bifurcation. Finally, by introducing a helical tessellation between the chiral units, we design hierarchical structures with chirality transferring from construction elements to the morphological level and discover a helix with two zero-height configurations during the unwinding process. We anticipate that our design and analysis approach could facilitate the development of man-made metamaterials with chiral features, which may serve in engineering applications, including switchable electromagnetic metamaterials, morphing structures, and bionic robots. [ABSTRACT FROM AUTHOR]

The investigation of acoustic emission (AE) reveals mixing of avalanche processes in porous 316L stainless steel. One avalanche mechanism relates to the movement of dislocations, the other to crack propagation. Both mechanisms occur under different external tensions: small tension dislodges dislocations while crack propagation occurs at much higher tension close to the mechanical failure point. In an intermediate overlap regime, both effects occur simultaneously. The avalanche related power laws show a mixing behavior where the higher avalanche exponents form an upper limit for the mixing curve and the lower exponent is approached asymptotically for strong AE signals. The power law probability distribution functions, show a characteristic upwards bend near the crossover between the two mechanisms. The three regimes, namely, the dislocation movement, mixing, and crack propagation, are confirmed by other avalanche characteristics: the sparseness of the AE spectra, the avalanche exponents of energy, amplitude, and duration. Only the crack propagation follows mean field predictions, while the dislocation movements (in confined spaces) deviates significantly from mean field behavior with much greater exponents than those predicted in this approximation. We demonstrate that apparent deviations from scale invariance are, in reality, the result of two superimposed avalanche processes whereby each of them remains scale invariant. The seeming deviations from scale invariance are actually superposition effects. [ABSTRACT FROM AUTHOR]

Lithium niobate on insulator (LNOI) is a unique platform for integrated photonic applications and especially for high-efficiency nonlinear frequency converters because of the strong optical field confinement. In this work, we fabricated a 6-mm-long periodically poled LNOI ridge waveguide with an optimized duty cycle (50:50) using an active domain structure monitoring method. The performance of the single-pass second-harmonic generation and difference-frequency generation in the nanophotonic waveguide was characterized, and the normalized conversion efficiencies were ∼80% of the theoretical values. These high-quality frequency conversion devices can pave the way for the application of LNOI in nonlinear integrated photonics. [ABSTRACT FROM AUTHOR]

Recently, a large amount of effort has been devoted to bringing p- and n-type two-dimensional (2D) materials in close contact to promise a p–n junction for photodetectors and photovoltaic devices. However, all solar cells based on 2D materials are single p–n junctions so far, where the open circuit voltage is usually limited by the bandgap of semiconductor materials. Here, by using a scanning-probe domain patterning method to polarize the ferroelectric film, we demonstrate a series connected MoTe2 photovoltaic cell with an additive open circuit voltage and output electrical power. The nonvolatile MoTe2 p–n diodes exhibit a rectification ratio of 100. As a photodetector, the device presents a responsivity of 220 mA/W and an external quantum efficiency of 41% without any gate or bias voltages. The open circuit voltage increases linearly with the number of series connected p–n junctions and can be beyond the bandgap of the multilayer MoTe2. [ABSTRACT FROM AUTHOR]

A HfO2-based thin film is a nanoscale ferroelectric material with a high-k dielectric and CMOS compatibility, which make it a promising candidate for high-performance electronics. Here, we demonstrate the synthesis of a ferroelectric Y-doped HfO2 (HYO) thin film by pulsed laser deposition. This HYO thin film is gradient doped by alternately depositing a HfO2 ceramic target and a Y2O3 ceramic target. In the films, the orthorhombic phase, ferroelectric phase, is proved by grazing incidence x-ray diffraction and scanning transmission electron microscopy measurements. Moreover, the HYO thin film embraces outstanding ferroelectric and dielectric properties, its remanent polarization is up to 10.5 μC/cm2, and the dielectric constant is 27. The 180° inversion of the domain can be observed in a piezoelectric power microscopy image, while the phase contrast of the write domain fades with time. Therefore, this work provides a reliable approach to obtain a ferroelectric HYO thin film, which enables great potential in future high-performance nanoelectronics. [ABSTRACT FROM AUTHOR]

Oxide-based binary resistive switching memories using metal nitride as one of the electrodes usually have a limited ratio of the resistances of the high- and low-resistance states. Here, we propose a competing mechanism to enhance the switching ratio by modifying the high-resistance state with extra inherent interfacial oxygen diffusion against what happens at the oxide/nitride interface. This is implemented in Pt/ZrO2/Ta2O5/TaN bilayer structures, where a resistance ratio above 104, about one to two orders of magnitude greater than that in Pt/Ta2O5/TaN monolayer structures, is achieved. This competing mechanism is further corroborated by the failed enhancement in the switching ratio when using an altered stacking arrangement of the two oxide layers. [ABSTRACT FROM AUTHOR]

In this work, we present light-controlled resistive switches with p-Si/HfO2/Pt structures, in which the resistance can be controlled by a combination of electrical pulses and light. The devices have a large switching ratio (over 104) and good uniformity. Connecting two devices with a conventional resistor enables one to implement light-controlled material implication (IMP). Based on the light-controlled IMP logic, light-controlled NAND and light-controlled OR logic operations were also executed in the same devices. [ABSTRACT FROM AUTHOR]