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Abstract Disentangling the limitations of O-O bond activation and OH* site-blocking effects on Pt sites is key to improving the intrinsic activity and stability of low-Pt catalysts for the oxygen reduction reaction (ORR). Herein, we integrate of PtFe alloy nanocrystals on a single-atom Fe-N-C substrate (PtFe@FeSAs-N-C) and further construct a ferromagnetic platform to investigate the regulation behavior of the spin occupancy state of the Pt d-orbital in the ORR. PtFe@FeSAs-N-C delivers a mass activity of 0.75 A mgPt −1 at 0.9 V and a peak power density of 1240 mW cm−2 in the fuel-cell, outperforming the commercial Pt/C catalyst, and a mass activity retention of 97%, with no noticeable current drop at 0.6 V for more than 220 h, is attained. Operando spectroelectrochemistry decodes the orbital interaction mechanism between the active center and reaction intermediates. The Pt dz 2 orbital occupation state is regulated to t 2g 6 e g 3 by spin-charge injection, suppressing the OH* site-blocking effect and effectively inhibiting H2O2 production. This work provides valuable insights into designing high-performance and low-Pt catalysts via spintronics-level engineering.

Abstract This work investigates the impact of pressure on the structural, optical properties, and electronic structure of CsPbBr3 quantum dots (QDs) using steady‐state photoluminescence, steady‐state absorption, and femtosecond transient absorption spectroscopy, reaching a maximum pressure of 3.38 GPa. The experimental results indicate that CsPbBr3 QDs undergo electronic state (ES) transitions from ES‐I to ES‐II and ES‐II to ES‐III at 0.38 and 1.08 GPa, respectively. Intriguingly, a mixed state of ES‐II and ES‐III is observed within the pressure range of 1.08–1.68 GPa. The pressure‐induced fluorescence quenching in ES‐II is attributed to enhanced defect trapping and reduced radiative recombination. Above 1.68 GPa, fluorescence vanishes entirely, attributed to the complete phase transformation from ES‐II to ES‐III in which radiative recombination becomes non‐existent. Notably, owing to stronger quantum confinement effects, CsPbBr3 QDs exhibit an impressive bandgap tuning range of 0.497 eV from 0 to 2.08 GPa, outperforming nanocrystals by 1.4 times and bulk counterparts by 11.3 times. Furthermore, this work analyzes various carrier dynamics processes in the pressure‐induced bandgap evolution and electron state transitions, and systematically studies the microphysical mechanisms of optical properties in CsPbBr3 QDs under pressure, offering insights for optimizing optical properties and designing novel materials.

Abstract Thermoelectric devices (TEDs) show great potential for waste heat energy recycling and sensing. However, existing TEDs cannot be self‐adapted to the complex quadratic surface, leading to significant heat loss and restricting their working scenario. Here, surface‐conformable origami‐TEDs (o‐TEGs) are developed through programmable crease‐designed origami substrates and the screen‐printing TE legs. Compared with “π” structured TEDs, the origami design (with heat conductive materials) changed the heat‐transferring direction of the laminated TE legs, resulting in an enhancement in enlarging ΔT/THot and Vout by 5.02 and 3.51 times. Four o‐TEDs with different creases designs are fabricated to verify the heat recycling ability on plane and central quadratic surfaces. Demonstrating a high Vout density (up to 0.98 −2at ΔT of 50 K) and good surface conformability, o‐TEDs are further used in thermal touch panels attached to multiple surfaces, allowing information to be wirelessly transferred on a remote display via finger‐writing.

Abstract Metallization has recently garnered significant interest due to its ability to greatly facilitate chemical reactions and dramatically change the properties of materials. Materials displaying metallization under low pressure are highly desired for understanding their potential properties. In this work, the effects of the pressure on the structural and electronic properties of lead‐free halide double perovskite (NH4)2PtI6 are investigated systematically. Remarkably, an unprecedented bandgap narrowing down to the Shockley–Queisser limit is observed at a very low pressure of 0.12 GPa, showing great promise in optoelectronic applications. More interestingly, the metallization of (NH4)2PtI6 is initiated at 14.2 GPa, the lowest metallization pressure ever reported in halide perovskites, which is related to the continuous increase in the overlap between the valence and conduction band of I 5p orbital. Its structural evolution upon compression before the metallic transition is also tracked, from cubic Fm‐3m to tetragonal P4/mnc and then to monoclinic C2/c phase, which is mainly associated with the rotation and distortions within the [PtI6]2– octahedra. These findings represent a significant step toward revealing the structure–property relationships of (NH4)2PtI6, and also prove that high‐pressure technique is an efficient tool to design and realize superior optoelectronic materials.

Abstract High‐performance flexible pressure sensors have attracted a great deal of attention, owing to its potential applications such as human activity monitoring, man–machine interaction, and robotics. However, most high‐performance flexible pressure sensors are complex and costly to manufacture. These sensors cannot be repaired after external mechanical damage and lack of tactile feedback applications. Herein, a high‐performance flexible pressure sensor based on MXene/polyurethane (PU)/interdigital electrodes is fabricated by using a low‐cost and universal spray method. The sprayed MXene on the spinosum structure PU and other arbitrary flexible substrates (represented by polyimide and membrane filter) act as the sensitive layer and the interdigital electrodes, respectively. The sensor shows an ultrahigh sensitivity (up to 509.8 kPa–1), extremely fast response speed (67.3 ms), recovery speed (44.8 ms), and good stability (10 000 cycles) due to the interaction between the sensitive layer and the interdigital electrodes. In addition, the hydrogen bond of PU endows the device with the self‐healing function. The sensor can also be integrated with a circuit, which can realize tactile feedback function. This MXene‐based high‐performance pressure sensor, along with its designing/fabrication, is expected to be widely used in human activity detection, electronic skin, intelligent robots, and many other aspects.

Ferroelectric tunnel junction (FTJ) has attracted considerable attention for its potential applications in nonvolatile memory and neuromorphic computing. However, the experimental exploration of FTJs with high ON/OFF ratios is a challenging task due to the vast search space comprising of ferroelectric and electrode materials, fabrication methods and conditions and so on. Here, machine learning (ML) is demonstrated to be an effective tool to guide the experimental search of FTJs with high ON/OFF ratios. A dataset consisting of 152 FTJ samples with nine features and one target attribute (i.e., ON/OFF ratio) is established for ML modeling. Among various ML models, the gradient boosting classification model achieves the highest prediction accuracy. Combining the feature importance analysis based on this model with the association rule mining, it is extracted that the utilizations of {graphene/graphite (Gra) (top), LaNiO3 (LNO) (bottom)} and {Gra (top), Ca[Formula: see text]Ce[Formula: see text]MnO3 (CCMO) (bottom)} electrode pairs are likely to result in high ON/OFF ratios in FTJs. Moreover, two previously unexplored FTJs: Gra/BaTiO3 (BTO)/LNO and Gra/BTO/CCMO, are predicted to achieve ON/OFF ratios higher than 1000. Guided by the ML predictions, the Gra/BTO/LNO and Gra/BTO/CCMO FTJs are experimentally fabricated, which unsurprisingly exhibit [Formula: see text]1000 ON/OFF ratios ([Formula: see text]8540 and [Formula: see text]7890, respectively). This study demonstrates a new paradigm of developing high-performance FTJs by using ML.

Constructing a heterogeneous interface using different components is one of the effective measures to achieve the bifunctionality of nanocatalysts, while synergistic interactions between multiple interfaces can further optimize the performance of single-interface nanocatalysts. The non-precious metal nanocatalysts MoS2/NiSe2/reduced graphene oxide (rGO) bilayer sandwich-like nanostructure with multiple well-defined interfaces is prepared by a simple hydrothermal method. MoS2 and rGO are layered nanostructures with clear boundaries, and the NiSe2 nanoparticles with uniform size are sandwiched between both layered nanostructures. This multiple-interfaced sandwich-like nanostructure is prominent in catalytic water splitting with low overpotential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and almost no degradation in performance after a 20 h long-term reaction. In order to simulate the actual overall water splitting process, the prepared nanostructures are assembled into MoS2/NiSe2/rGO||MoS2/NiSe2/rGO modified two-electrode system, whose overpotential is only 1.52 mV, even exceeded that of noble metal nanocatalyst (Pt/C||RuO2~1.63 mV). This work provides a feasible idea for constructing multi-interface bifunctional electrocatalysts using nanoparticle-doped bilayer-like nanostructures.

Abstract Flexible thermoelectric generators (f‐TEGs) have demonstrated great potential in wearable self‐powered health monitoring devices. However, the existing wearable f‐TEGs are neither flexible enough to bend and stretch while maintaining the device's integrity with a good TE performance nor directly compatible with clothes materials. Here, ultraflexible fabric‐based thermoelectric generators (uf‐TEGs) are proposed with conductive cloth electrodes and elastic fabric substrate. The patterned elastic fabric substrate fits the rigid cuboids well, together with serpentine structured cloth electrodes, rendering uf‐TEG with excellent integrity and flexibility, thereby achieving a highly functional TE performance when strain reaches 30% or on arbitrarily shaped heat sources. The uf‐TEGs show a large peak power of 64.10 μW for a temperature difference of 33.24 K with a high voltage output of 111.49 mV, which is superior compared to previously reported fabric‐based TEG devices, and it is still functional after the water immersion test. Besides the energy harvesting function, with both the temperature sensing ability and the touch perception, this uf‐TEG is demonstrated as the electrical skin when mounted on a robot. Moreover, due to the wind‐sensitive performance and self‐power ability, the uf‐TEGs are assembled on cloth as wearable health and motion monitoring devices.

Abstract Understanding hot carrier dynamics between plasmonic nanomaterials and its adsorbate is of great importance for plasmon‐enhanced photoelectronic processes such as photocatalysis, optical sensing and spectroscopic analysis. However, it is often challenging to identify specific dominant mechanisms for a given process because of the complex pathways and ultrafast interactive dynamics of the photoelectrons. Here, using CO2 reduction as an example, the underlying mechanisms of plasmon‐driven catalysis at the single‐molecule level using time‐dependent density functional theory calculations is clearly probed. The CO2 molecule adsorbed on two typical nanoclusters, Ag20 and Ag147, is photoreduced by optically excited plasmon, accompanied by the excitation of asymmetric stretching and bending modes of CO2. A nonlinear relationship has been identified between laser intensity and reaction rate, demonstrating a synergic interplay and transition from indirect hot‐electron transfer to direct charge transfer, enacted by strong localized surface plasmons. These findings offer new insights for CO2 photoreduction and for the design of effective pathways toward highly efficient plasmon‐mediated photocatalysis.

As the star material among nonprecious electrocatalysts, molybdenum disulfide (MoS2) has received much attention. However, the catalytic inertness of the basal plane, low conductivity of its steady state (2H phase), and the agglomeration of lamellar structures have seriously hindered its catalytic performance. It is very essential to design and modulate the morphology and phase of MoS2 to improve the above issues by synergistic regulation of electrical structure and defect engineering. Herein, MoS2 was delicately composited on CoP nanoframe derived from a typical metal–organic frame nanostructure (ZIF-67), forming the hollow CoP@MoS2 hetero-nanoframe. This exquisite externally layered and internally hollow CoP@MoS2 electrocatalyst demonstrated excellent catalytic performance for the hydrogen evolution reaction, with a low overpotential of 119 mV at 10 mA cm−2, a small Tafel slope of 49 mV dec−1, a large electric double-layer capacitance of 10.28 mF cm−2, and prominent long-term stability. The remarkable catalytic performance of hollow CoP@MoS2 hetero-nanoframe can be attributed to the unique architecture of the hetero-nanostructures, appropriate component ratios, strong interaction between CoP and MoS2, and large-scale defects and disorder. First-principles density-functional theory calculations can prove the above arguments adequately, the hydrogen adsorption free energy of CoP@MoS2 is close to zero.

Abstract Lead‐free halide double perovskites (HDPs) are promising candidates for high‐performance solar cells because of their environmentally‐friendly property and chemical stability in air. The power conversion efficiency of HDPs‐based solar cells needs to be further improved before their commercialization in the market. It requires a thoughtful understanding of the correlation between their specific structure and property. Here, the structural and optical properties of an important HDP‐based (NH4)2SeBr6 are investigated under high pressure. A dramatic piezochromism is found with the increase in pressure. Optical absorption spectra reveal the pressure‐induced red‐shift in bandgap with two distinct anomalies at 6.57 and 11.18 GPa, and the energy tunability reaches 360 meV within 20.02 GPa. Combined with structural characterizations, Raman and infrared spectra, and theoretical calculations using density functional theory, results reveal that, the first anomaly is caused by the formation of a Br‐Br bond among the [SeBr6]2− octahedra, and the latter is attributed to a cubic‐to‐tetragonal phase transition. These results provide a clear correlation between the chemical bonding and optical properties of (NH4)2SeBr6. It is believed that the proposed strategy paves the way to optimize the optoelectronic properties of HDPs and further stimulate the development of next‐generation clear energy based on HDPs solar cells.

Abstract Artificial superlattices constructed with ferromagnetic La0.7Sr0.3MnO3 layer and ferroelectric Ba0.7Sr0.3TiO3 layer were designed and fabricated on SrTiO3 substrates. An epitaxial growth with sharp interfaces between La0.7Sr0.3MnO3 and Ba0.7Sr0.3TiO3 layers was confirmed by scanning transmission electron microscopy and x-ray diffraction. An unambiguous charge transfer involving an electron transferring from the La0.7Sr0.3MnO3 layers to Ba0.7Sr0.3TiO3 layers (Mn3+→Mn4+; Ti4+→Ti3+) across the interface were resolved by electron energy loss spectra analysis. These observations are attributed to the possible modification in the stereochemistry of the Ti and Mn ions in the interfacial region. The out-of-plane lattice parameter, Curie temperature, and magnetoresistance are strongly affected by the thicknesses of the La0.7Sr0.3MnO3 and Ba0.7Sr0.3TiO3 layers. Huge magnetoresistance subsisting to low temperature was also observed in the La0.7Sr0.3MnO3/Ba0.7Sr0.3TiO3 superlattices. All spectral changes identified at a nanometer scale and their potential effect on the degradation of magnetic and transport properties at a macroscopic level. These findings highlight the importance of dependence on sublayer thickness, illustrating the high degree of tenability in these artificially low-dimensional oxide materials.

Oxygen vacancy in different oxide systems shows up as a crucial parameter in modulation of the emerging application-oriented functionalities. A systematic exploration on the relation between oxygen vacancy and electronic structure of the La0.2Sr0.8MnO3 (LSMO) thin film has been carried out through sequential surface treatments followed by a series of wide scan XPS, O 1s XPS, O-K edge XAS, Mn-L edge XAS and work function measurements. Experimental results demonstrate mutual corroborative certifying evidences in between the different photoemission spectral measurements on the evolution and influence of the oxygen vacancy. Spectral characteristic features observed in the work are applicable using as justification fingerprint for the existence, modulation, or elimination of the oxygen vacancy in similar perovskite type oxide systems.

Nickel oxide (NiO) nanotubes were synthesized via a thermal oxidation process from Ni nanowires. The effects of oxidation temperature on the morphology, microstructures, and composition of nanowires were investigated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show that the Ni nanowires convert initially to Ni/NiO core-shell nanowires with increasing annealing temperatures, and then to the nanotubes at the critical transition temperature of about 425 °C. Our findings provide useful information for the preparation of NiO nanotubes to meet the required applications.

Thin films of BaNb(sub x)Ti(sub 1-x)O(sub 3) were epitaxially grown on MgO substrates by laser molecular beam epitaxy. The resistivity of BaNb(sub x)Ti(sub 1-x)O(sub 3) epitaxial thin films deposited under low oxygen pressure monotonously decreased with Nb concentration.

Thin films of BaNbxTi1-xO3 (0

The phase transition behavior of BaNbxTi1-xO3 (BNTO) (0.0<=x<=0.50) thin films grown on MgO substrates by laser molecular beam epitaxy was systematically investigated by using x-ray diffraction (XRD) and micro-Raman spectroscopy. The asymmetric rocking XRD scan measurements show that with an increase of Nb-doped content, the lattice parameters c and a increase while c/a ratio decreases, indicating a decrease of tetragonality of the BNTO films. The intensity of Raman signal decreases and the width of the bands broaden with increase of Nb-doped content. The results of XRD and Raman spectra indicate that at room temperature BNTO thin films with Nb<=10 at. % have tetragonal structure, however, for Nb>=20 at. %, BNTO thin films exhibit typical disordering cubic structure. [ABSTRACT FROM AUTHOR]

We report the optical properties of p-type SrIn[sub x]Ti[sub 1-x]O[sub 3] (x=0.1 and 0.2) films prepared by laser molecular beam epitaxy under different oxygen pressures. The results of x-ray diffraction and near-field scanning optical microscopy indicate that the films have high crystallinity, smoothness, and uniformity. Hall measurement confirms that the films are p-type semiconductors. The optical transmittance spectra reveal that the films are highly transparent in most of the visible region. A blueshift of the absorption edge with an increase in oxygen pressure during deposition has been observed and discussed. Moreover, the first-order Raman scattering peaks of the optical phonons in these In-doped SrTiO[sub 3] films are presented, and they are Raman inactive in bulk SrTiO[sub 3] single crystal. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of thin film matrix and substrate on the coercivity and blocking temperature of self-assembled Ni nanoparticles is examined. The studies have shown that the Ni nanoparticle size can be controlled by tailoring the deposition time as the films have grown in the respective thin film matrix.

The LaAlO(sub 3) thin films were deposited on Si(100) substrates by laser molecular beam epitaxy (LMBE) under various oxygen pressures and these films were amorphous. With increasing oxygen pressures, the oxygen vacancies decreased, the leakage current and the flatband voltage decreased .

Wall-thickness-controllable multiferroic bismuth ferrite (BiFeO3) nanotubes were synthesized by a sol-gel method combined with an anodic aluminum oxide (AAO) template. By connecting the template with a negative pressure system tuned by a gas flowmeter, BiFeO3 nanotubes with wall thicknesses of about 28 and 15 nm were obtained if the flowmeter speed was adjusted to 0.4 and 2 m³/h, respectively. The resulting nanotubes were characterized by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. It is shown that the nanotubes present a rhombohedral distorted perovskite BiFeO3 structure. Meanwhile, the wall thickness of BiFeO3 nanotubes became smaller at higher flowmeter speed, which was caused by the increase in the differential pressure on the solution. [ABSTRACT FROM AUTHOR]

The properties of perovskite nickelates are very sensitive to their oxygen content, which allows us to tune their electronic structures by varying the oxygen partial pressure during film deposition. Under the optimized condition, we have obtained GdNiO3 films that are sensitive to a wide spectrum of light. By combining the GdNiO3 film with Nb-doped SrTiO3 to form a heterojunction, we design a self-powered photodetector with high sensitivity toward light with a wavelength between 650 nm and 365 nm. Under 365 nm illumination (50 μW/cm2), the device shows a responsivity of 0.23 A/W at 0V bias, comparable to or even better than the ultraviolet photodetectors made of semiconductor materials such as GaN or ZnO. The photo-dark ratio can be close to 103 when the power light density reaches 0.6 mW/cm2. Moreover, the device performance is very stable without any decay after 6 months. [ABSTRACT FROM AUTHOR]

Surface double-layer structure different from the interior was found in BiFeO3 thin film grown on SrRuO3 covered SrTiO3 (110) substrate by pulsed laser deposition. It was shown that BiFeO3 film exhibits epitaxial phase with single domain. X-ray reflectivity and X-ray photoelectron spectroscopy results revealed a skin layer of less than 1 nm with a reduced electron density and different surface state. Grazing incidence x-ray diffraction convinced a surface multi-domain structure of several nm beneath the surface skin layer. The double-layer near surface structure would be originated from the large depolarization field produced by the single-domain structure with strain. [ABSTRACT FROM AUTHOR]

BiFeO3 (BFO) ultrathin films with nominal thicknesses from 2 to 12 nm were grown with a SrRuO3 (SRO) buffer layer on TiO2-terminated (001) SrTiO3 (STO) substrates using pulsed laser deposition. The surface morphologies and domain configurations of the thin films were investigated using atomic force microscopy and piezoelectric force microscopy. Periodical one-dimensional finger-like nanostripes of BFO on the SRO covered STO substrates were observed. With increasing thickness, the BFO ultrathin films develop from the finger-like nanostripes to an atomically flat surface. The formation of the finger-like nanostructures of BFO is related to the atomic step or terrace structure of the substrate. The BFO nanostripes and the atomically flat thin films both show good ferroelectricity. The as-grown domain orientations of the BFO ultrathin films are ascribed to the chemical terminations at the surface of the SRO layer. These results indicate that the surface morphologies and the domain configurations of BFO ultrathin films can be artificially designed by using substrates with optimized terrace structures and chemical termination, and these films are potentially useful in multifunctional nanoelectronic devices. [ABSTRACT FROM AUTHOR]

ABO3 perovskite is a kind of very important functional material with versatile physical properties. Although B-site chemical substitution with various magnetic ions has been widely investigated, the A-site doping with magnetic transition metal is little known. Here we report AA'3B2B'2O12-type A- and B-site ordered ferrimagnet CaCu3Fe2Os2O12 with magnetic transition metals occupying three different atomic sites (A', B, and B' sites). This compound is synthesized by a special high-pressure annealing process. It possesses a much higher Curie temperature TC of 580 K compared with that of the B-site-only ordered Ca2FeOsO6 (TC=320K) without magnetic ion at the A site. First-principles numerical calculations reveal that this enhancement primarily originates from the additional spin interaction between the A'-site Cu2+ and the B'-site Os5+, generating a strong Cu2+(↑)Fe3+(↑)Os5+(↓) ferrimagnetic spin coupling. This work opens up an alternative way for enhancing the spin ordering temperature by introducing A-site magnetic ions. [ABSTRACT FROM AUTHOR]