Supramolecular Polyurethane "Ligaments" Enabling Room-Temperature Self-Healing Flexible Perovskite Solar Cells and Mini-Modules.

Flexible perovskite solar cells (F-PSCs) have emerged as promising alternatives to conventional silicon solar cells for applications in portable and wearable electronics. However, the mechanical stability of inherently brittle perovskite, due to residual lattice stress and ductile fracture formation, poses significant challenges to the long-term photovoltaic performance and device lifetime. In this paper, to address this issue, a dynamic "ligament" composed of supramolecular poly(dimethylsiloxane) polyurethane (DSSP-PPU) is introduced into the grain boundaries of the PSCs, facilitating the release of residual stress and softening of the grain boundaries. Remarkably, this dynamic "ligament" exhibits excellent self-healing properties and enables the healing of cracks in perovskite films at room temperature. The obtained PSCs have achieved power conversion efficiencies of 23.73% and 22.24% for rigid substrates and flexible substrates, respectively, also 17.32% for flexible mini-modules. Notably, the F-PSCs retain nearly 80% of their initial efficiency even after subjecting the F-PSCs to 8000 bending cycles (r = 2 mm), which can further recover to almost 90% of the initial efficiency through the self-healing process. This remarkable improvement in device stability and longevity holds great promise for extending the overall lifetime of F-PSCs.

Constructing Type-II and S-Scheme Heterojunctions of Cu2O@Cu4(SO4)(OH)6·H2O Polyhedra by In Situ Etching Cu2O with Different Exposed Facets for Enhanced Photocatalytic Sterilization and Degradation Performance.

The construction of type-II or S-scheme heterojunctions can effectively accelerate the directional migration of charge carriers and inhibit the recombination of electron-hole pairs to improve the catalytic performance of the composite catalyst; therefore, the construction and formation mechanism of a heterojunction are worth further investigation. Herein, Cu2O@Cu4(SO4)(OH)6·H2O core-shell polyhedral heterojunctions were fabricated via in situ etching Cu2O with octahedral, cuboctahedral, and cubic shapes by sodium thiosulfate (Na2S2O3). Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions demonstrated obviously enhanced sterilization and degradation performance than the corresponding single Cu2O polyhedra and Cu4(SO4)(OH)6·H2O. When Cu2O with a different morphology contacts with Cu4(SO4)(OH)6·H2O, a built-in electric field is established at the interface due to the difference in Fermi level (Ef); meanwhile, the direction of band bending and the band alignment are determined. These lead to the different migration pathways of electrons and holes, and thereby, a type-II or S-scheme heterojunction is constructed. The results showed that octahedral o-Cu2O@Cu4(SO4)(OH)6·H2O is an S-scheme heterojunction; however, cuboctahedral co-Cu2O@Cu4(SO4)(OH)6·H2O and cubic c-Cu2O@Cu4(SO4)(OH)6·H2O are type-II heterojunctions. By means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), diffuse reflectance spectra (DRS), and Mott-Schottky analyses, the band alignments, Fermi levels, and band offsets (ΔECB, ΔEVB) of Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions were estimated; the results indicated that the catalytic ability of the composite catalyst is determined by the type of heterojunction and the sizes of band offsets. Cubic c-Cu2O@Cu4(SO4)(OH)6·H2O has the strongest driving force (namely, biggest band offsets) to accelerate charge migration and effectively separate charge carriers, so it exhibits the strongest catalytic bactericidal and degrading abilities.

Enhancement of ferroelectricity and homogeneity of orthorhombic phase in Hf0.5Zr0.5O2thin films.

By adoption of a high permittivity ZrO2capping layer (ZOCL), enhanced ferroelectric properties were achieved in the Hf0.5Zr0.5O2(HZO) thin films. For HZO thin film with 10 Å ZOCL, the 2Prvalue can reach as high as ∼43.1µC cm-2under a sweep electric field of 3 MV cm-1. In addition, a reduced coercive field of 1.5 MV cm-1was observed, which is comparable to that of HZO with metallic CL. Furthermore, the homogeneity of ferroelectric orthorhombic phase in HZO films was observed to be clearly increased, as evidenced by nanoscale piezoelectric force microscopy measurements. These results demonstrate that ZOCL is very favorable for high performance ferroelectric HZO films and their future device applications.

Ultrathin MoS2-coated Ag@Si nanosphere arrays as an efficient and stable photocathode for solar-driven hydrogen production.

Solar-driven photoelectrochemical (PEC) water splitting has attracted a great deal of attention recently. Silicon (Si) is an ideal light absorber for solar energy conversion. However, the poor stability and inefficient surface catalysis of Si photocathodes for the hydrogen evolution reaction (HER) have remained key challenges. Alternatively, MoS2 has been reported to exhibit excellent catalysis performance if sufficient active sites for the HER are available. Here, ultrathin MoS2 nanoflakes are directly synthesized to coat arrays of Ag-core Si-shell nanospheres (Ag@Si NSs) by using chemical vapor deposition. Due to the high surface area ratio and large curvature of these NSs, the as-grown MoS2 nanoflakes can accommodate more active sites. In addition, the high-quality coating of MoS2 nanoflakes on the Ag@Si NSs protects the photocathode from damage during the PEC reaction. An photocurrent density of 33.3 mA cm-2 at a voltage of -0.4 V is obtained versus the reversible hydrogen electrode. The as-prepared nanostructure as a hydrogen photocathode is evidenced to have high stability over 12 h PEC performance. This work opens up opportunities for composite photocathodes with high activity and stability using cheap and stable co-catalysts.

Interface Engineering of Domain Structures in BiFeO3 Thin Films.

A wealth of fascinating phenomena have been discovered at the BiFeO3 domain walls, examples such as domain wall conductivity, photovoltaic effects, and magnetoelectric coupling. Thus, the ability to precisely control the domain structures and accurately study their switching behaviors is critical to realize the next generation of novel devices based on domain wall functionalities. In this work, the introduction of a dielectric layer leads to the tunability of the depolarization field both in the multilayers and superlattices, which provides a novel approach to control the domain patterns of BiFeO3 films. Moreover, we are able to study the switching behavior of the first time obtained periodic 109° stripe domains with a thick bottom electrode. Besides, the precise controlling of pure 71° and 109° periodic stripe domain walls enable us to make a clear demonstration that the exchange bias in the ferromagnet/BiFeO3 system originates from 109° domain walls. Our findings provide future directions to study the room temperature electric field control of exchange bias and open a new pathway to explore the room temperature multiferroic vortices in the BiFeO3 system.

Temperature-dependent transport and hysteretic behaviors induced by interfacial states in MoS2 field-effect transistors with lead-zirconate-titanate ferroelectric gating.

We report the temperature and gate-voltage-dependent electrical properties of lead-zirconate-titanate-gated MoS2 field-effect transistors (MoS2-PZT FETs) within a temperature range of 300 to 380 K. The MoS2 transistors with PZT gating exhibit large reproducible clockwise hysteresis, which is induced by the dynamic charge-trapping/de-trapping process of interfacial states between PZT films and MoS2 channels under the modulation of ferroelectric polarization of PZT films. In this way, the modulation of the gate effect on the hysteresis behavior has been achieved by activating the dynamic charge-trapping/de-trapping process in the interfacial states under different V gs . Moreover, the temperature dependence of the current in the range of 300 to 380 K indicates thermally activated hysteretic behaviors. The hysteresis in the transfer characteristics of MoS2-PZT FETs shows a simultaneous enlargement with increasing temperature, which can be attributed to the thermally sensitive dynamic trapping/de-trapping process of interfacial states.

High-density ordered Ag@Al2O3 nanobowl arrays in applications of surface-enhanced Raman spectroscopy.

In this paper, we demonstrate a high-performance surface-enhanced Raman scattering (SERS) substrate based on high-density ordered Ag@Al2O3 nanobowl arrays. By ion beam etching (IBE) the anodized aluminum oxide (AAO) and subsequent Ag coating, ordered Ag@Al2O3 nanobowl arrays were created on the Si substrate. Unlike the 'hot spots' generated between adjacent metallic nanostructures, the Ag@Al2O3 nanobowl introduced 'hot spots' on the metal boundary of its hemispherical cavity. Based on the analysis of SERS signals, the optimized SERS substrate of Ag@Al2O3 nanobowl arrays had both high sensitivity and large-area uniformity. A detection limit as low as 10(-10) M was obtained using chemisorbed p-thiocresol (p-Tc) molecules, and the SERS signal was highly reproducible with a small standard deviation. The method opens up a new way to create highly sensitive SERS sensors with high-density 'hot spots', and it could play an important role in device design and corresponding biological and food safety monitoring applications.

Unique nano-domain structures in self-assembled BiFeO3 and Pb(Zr,Ti)O3 ferroelectric nanocapacitors.

In this work, self-assembled ferroelectric BiFeO3 (BFO) and Pb(Zr,Ti)O3 (PZT) nanocapacitors were fabricated by a one-step pulsed-laser deposition process. Each individual nanocapacitor consists of a SrRuO3 or LaSrMnO3 bottom electrode layer, an epitaxial ferroelectric middle layer and a self-assembled nanoisland of conductive Bi2O3 or PbO2 as the top nanoelectrode. The nanoelectrodes have a lateral size of 10-100 nm depending on various deposition equivalent thickness. The as-fabricated nanocapacitors exhibit unique so-called anti-domain structures, with opposite polarization orientation to that of the naked ferroelectric films, which can be understood by the different interface built-in-voltages between their neighboring layers. They also show apparent reduced coercive fields and enhanced piezoelectricity compared to the naked films, as revealed by the switching spectroscopy piezoresponse force microscopy (SSPFM) and band-excitation mapping. Besides that, individual addressable polarization writing and erasing properties were also observed in these nanocapacitors and the written domain can maintain stability up to 12 h, which is promising for data storage devices.

Fabrication of high-density BiFeO3 nanodot and anti-nanodot arrays by anodic alumina template-assisted ion beam etching.

Efficient and cost-competitive fabrication of high-quality ferroelectric and multiferroic nanostructures is of general interest. In this work, a top-down nano-patterning technique is developed by the Ar+ ion beam etching in combination with the sacrificed ultrathin anodic alumina (AAO) mask. This technique is demonstrated by preparation of the epitaxial BiFeO3 (BFO) nanostructures of various geometries, including nanodot and anti-nanodot arrays. The lateral dot size is as small as ∼60 nm and an ultrahigh dot density of ∼60 Gbit/inch2 is achieved. It is revealed that the etching process involves sequential shape evolution of both the AAO mask and the underlying BFO film, resulting in the nanodots and anti-nanodots arrays of various geometries. The as-etched BFO nanodots array exhibits well-established ferroelectric domain structures and reversible polarization switching, as examined by piezoresponse force microscopy (PFM). It is suggested that this technique is extendable to fabrication of a wide range of functional oxide nanostructures for potential nanoelectronic applications.

Highly reproducible surface-enhanced Raman scattering substrate for detection of phenolic pollutants.

The ordering degree of nanostructures is the key to determining the uniformity of surface-enhanced Raman scattering (SERS). However, fabrication of large-area ordered nanostructures remains a challenge, especially with the ultrahigh-density (>1010 cm-2). Here, we report a fabrication of large-area ultrahigh-density ordered Ag@Al2O3/Ag core-shell nanosphere (NS) arrays with tunable nanostructures. The ultrahigh-density (2.8 × 1010 cm-2) ordered NS arrays over a large-area capability (diameter >4.0 cm) enable the uniform SERS signals with the relative standard deviation of less than 5%. The as-fabricated highly reproducible SERS substrate can be applied to detect trace phenolic pollutants in water. This work does not only provide a new route for synthesizing the ultrahigh-density ordered nanostructures, but also create a new class of SERS substrates with high sensitivity and excellent reproducibility.

Epitaxial growth of vertically free-standing ultra-thin silicon nanowires.

We report epitaxial growth of ultra-thin vertically free-standing silicon nanowires (Si NWs) on Si(111) and Si(110) substrate, by an ultra-high vacuum chemical vapor deposition method. The epitaxial growth direction of Si NWs with sub-10 nm diameters was found to be dependent upon the orientation type of the Si substrate. The 〈112〉 and 〈110〉 epitaxial growth directions are crystallographically preferred on Si(111) and Si(110) substrates, respectively. Especially, for the epitaxy on Si(110), most of the Si NWs are grown vertically in the [110] direction with sub-5 nm diameters. Based on transmission electron microscope investigations, a growth model for ultra-thin Si NWs was deduced from the morphology of interface between catalyst and nanowire, and the growth direction at a very early stage of epitaxy was determined.

Silver catalyzed gallium phosphide nanowires integrated on silicon and in situ Ag-alloying induced bandgap transition.

In this work, we demonstrate a silver catalyzed heteroepitaxial growth of gallium phosphide nanowires (GaP NWs) on silicon. The morphology and growth direction of GaP NWs on differently orientated Si substrates were investigated. From crystallographic analysis, we inferred that Ag from catalyst is incorporated into the GaP during the chemical beam epitaxy (CBE) process. Using the PL spectrum and time-resolved emission spectroscopy, the optical properties of Ag-catalyzed GaP NWs were greatly modified, with bandgap transitions in the blue range. The Raman characterizations further confirmed the Ag incorporation into GaP during the growth. From the bandgap calculations, it was deduced that Ag was substituted on the Ga site with bandgap broadening. The in situ Ag-alloying during the growth of Ag-catalyzed GaP NWs greatly modified the band structure of GaP, and could lead to further applications in optoelectronics for low-dimensional GaP-based nanomaterials.

Room-temperature sub-100 nm Néel-type skyrmions in non-stoichiometric van der Waals ferromagnet Fe3-xGaTe2 with ultrafast laser writability.

Realizing room-temperature magnetic skyrmions in two-dimensional van der Waals ferromagnets offers unparalleled prospects for future spintronic applications. However, due to the intrinsic spin fluctuations that suppress atomic long-range magnetic order and the inherent inversion crystal symmetry that excludes the presence of the Dzyaloshinskii-Moriya interaction, achieving room-temperature skyrmions in 2D magnets remains a formidable challenge. In this study, we target room-temperature 2D magnet Fe3GaTe2 and unveil that the introduction of iron-deficient into this compound enables spatial inversion symmetry breaking, thus inducing a significant Dzyaloshinskii-Moriya interaction that brings about room-temperature Néel-type skyrmions with unprecedentedly small size. To further enhance the practical applications of this finding, we employ a homemade in-situ optical Lorentz transmission electron microscopy to demonstrate ultrafast writing of skyrmions in Fe3-xGaTe2 using a single femtosecond laser pulse. Our results manifest the Fe3-xGaTe2 as a promising building block for realizing skyrmion-based magneto-optical functionalities.

Ionic Liquid Bridge Assisting Bifacial Defect Passivation for Efficient All-Inorganic Perovskite Cells with High Open-Circuit Voltage.

Serious open-circuit voltage (Voc) loss originating from nonradiative recombination and mismatch energy level at TiO2/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) perovskite solar cells (PSCs) fabricated through low-temperature methods. Here, an ionic liquid (IL) bridge is constructed by introducing 1-butyl-3-methylimidazolium acetate (BMIMAc) IL to treat the TiO2/perovskite buried interface, bilaterally passivate defects and modulate energy alignment. Therefore, the Voc of all-inorganic CsPbIBr2 PSCs modified by BMIMAc (Target-1) significantly increases by 148 mV (from 1.213 to 1.361 V), resulting in the efficiency increasing to 10.30% from 7.87%. Unsealed Target-1 PSCs show outstanding long-term and thermal stability. During the accelerated degradation process (85 °C, RH: 50∼60%), the Target-1 PSCs achieve a champion PCE of 11.94% with a remarkable Voc of 1.403 V, while the control PSC yields a promising PCE of 10.18% with a Voc of 1.319 V. In particular, the Voc of 1.403 V is the highest Voc reported so far in carbon-electrode-based CsPbIBr2 PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI2Br PSCs to achieve a Voc of 1.295 V and a champion efficiency of 15.20%, which is close to the reported highest PCE of 15.48% for all-inorganic CsPbI2Br PSCs prepared by a low-temperature process. This study provides a simple BMIMAc IL bridge to assist bifacial defect passivation and elevate the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) PSCs.

Organic-Inorganic Hybrid Perovskite Ferroelectric Nanosheets Synthesized by a Room-Temperature Antisolvent Method.

Over the past years, the application potential of ferroelectric nanomaterials with unique physical properties for modern electronics is highlighted to a large extent. However, it is relatively challenging to fabricate inorganic ferroelectric nanomaterials, which is a process depending on a vacuum atmosphere at high temperatures. As significant complements to inorganic ferroelectric nanomaterials, the nanomaterials of molecular ferroelectrics are rarely reported. Here a low-cost room-temperature antisolvent method is used to synthesize free-standing 2D organic-inorganic hybrid perovskite (OIHP) ferroelectric nanosheets (NSs), that is, (CHA)2PbBr4 NSs (CHA = cyclohexylammonium), with an average lateral size of 357.59 nm and a thickness ranging from 10 to 70 nm. This method shows high repeatability and produces NSs with excellent crystallinity. Moreover, ferroelectric domains in single NSs can be clearly visualized and manipulated using piezoresponse force microscopy (PFM). The domain switching and PFM-switching spectroscopy indicate the robust in-plane ferroelectricity of the NSs. This work not only introduces a feasible, low-cost, and scalable method for preparing molecular ferroelectric NSs but also promotes the research on molecular ferroelectric nanomaterials.

Strain-Induced Reversible Motion of Skyrmions at Room Temperature.

Magnetic skyrmions are topologically protected swirling spin textures with great potential for future spintronic applications. The ability to induce skyrmion motion using mechanical strain not only stimulates the exploration of exotic physics but also affords the opportunity to develop energy-efficient spintronic devices. However, the experimental realization of strain-driven skyrmion motion remains a formidable challenge. Herein, we demonstrate that the inhomogeneous uniaxial compressive strain can induce the movement of isolated skyrmions from regions of high strain to regions of low strain at room temperature, which was directly observed using an in situ Lorentz transmission electron microscope with a specially designed nanoindentation holder. We discover that the uniaxial compressive strain can transform skyrmions into a single domain with in-plane magnetization, resulting in the coexistence of skyrmions with a single domain along the direction of the strain gradient. Through comprehensive micromagnetic simulations, we reveal that the repulsive interactions between skyrmions and the single domain serve as the driving force behind the skyrmion motion. The precise control of skyrmion motion through strain provides exciting opportunities for designing advanced spintronic devices that leverage the intricate interplay between strain and magnetism.

Current-Induced Reversible Split of Elliptically Distorted Skyrmions in Geometrically Confined Fe3 Sn2 Nanotrack.

Skyrmions are swirling spin textures with topological characters promising for future spintronic applications. Skyrmionic devices typically rely on the electrical manipulation of skyrmions with a circular shape. However, manipulating elliptically distorted skyrmions can lead to numerous exotic magneto-electrical functions distinct from those of conventional circular skyrmions, significantly broadening the capability to design innovative spintronic devices. Despite the promising potential, its experimental realization so far remains elusive. In this study, the current-driven dynamics of the elliptically distorted skyrmions in geometrically confined magnet Fe3 Sn2 is experimentally explored. This study finds that the elliptical skyrmions can reversibly split into smaller-sized circular skyrmions at a current density of 3.8 × 1010 A m-2 with the current injected along their minor axis. Combined experiments with micromagnetic simulations reveal that this dynamic behavior originates from a delicate interplay of the spin-transfer torque, geometrical confinement, and pinning effect, and strongly depends on the ratio of the major axis to the minor axis of the elliptical skyrmions. The results indicate that the morphology is a new degree of freedom for manipulating the current-driven dynamics of skyrmions, providing a compelling route for the future development of spintronic devices.

Significantly Improved Efficiency and Stability of Pure Tin-Based Perovskite Solar Cells with Bifunctional Molecules.

Tin-based perovskite solar cells (TPSCs) have become one of the most prospective photovoltaic materials due to their remarkable optoelectronic properties and relatively low toxicity. Nevertheless, the rapid crystallization of perovskites and the easy oxidization of Sn2+ to Sn4+ make it challenging to fabricate efficient TPSCs. In this work, a piperazine iodide (PI) material with -NH- and -NH2+- bifunctional groups is synthesized and introduced into the PEA0.1FA0.9SnI3-based precursor solution to tune the microstructure, charge transport, and stability of TPSCs. Compared with piperazine (PZ) containing only the -NH- group, the PI additive displays better effects on regulating the microstructure and crystallization, inhibiting Sn2+ oxidation and reducing trap states, resulting in an optimal efficiency of 10.33%. This is substantially better than that of the reference device (6.42%). Benefiting from the fact that PI containing -NH- and -NH2+- groups can passivate both positively charged defects and negatively charged halogen defects, unencapsulated TPSCs modified with the PI material can maintain about 90% of their original efficiency after being kept in a N2 atmosphere for 1000 h, much higher than the value of 47% in reference TPSCs without additives. This work provides a practical method to prepare efficient and stable pure TPSCs.

All-ferroelectric implementation of reservoir computing.

Reservoir computing (RC) offers efficient temporal information processing with low training cost. All-ferroelectric implementation of RC is appealing because it can fully exploit the merits of ferroelectric memristors (e.g., good controllability); however, this has been undemonstrated due to the challenge of developing ferroelectric memristors with distinctly different switching characteristics specific to the reservoir and readout network. Here, we experimentally demonstrate an all-ferroelectric RC system whose reservoir and readout network are implemented with volatile and nonvolatile ferroelectric diodes (FDs), respectively. The volatile and nonvolatile FDs are derived from the same Pt/BiFeO3/SrRuO3 structure via the manipulation of an imprint field (Eimp). It is shown that the volatile FD with Eimp exhibits short-term memory and nonlinearity while the nonvolatile FD with negligible Eimp displays long-term potentiation/depression, fulfilling the functional requirements of the reservoir and readout network, respectively. Hence, the all-ferroelectric RC system is competent for handling various temporal tasks. In particular, it achieves an ultralow normalized root mean square error of 0.017 in the Hénon map time-series prediction. Besides, both the volatile and nonvolatile FDs demonstrate long-term stability in ambient air, high endurance, and low power consumption, promising the all-ferroelectric RC system as a reliable and low-power neuromorphic hardware for temporal information processing.

Performance estimation for the memristor-based computing-in-memory implementation of extremely factorized network for real-time and low-power semantic segmentation.

Nowadays many semantic segmentation algorithms have achieved satisfactory accuracy on von Neumann platforms (e.g., GPU), but the speed and energy consumption have not meet the high requirements of certain edge applications like autonomous driving. To tackle this issue, it is of necessity to design an efficient lightweight semantic segmentation algorithm and then implement it on emerging hardware platforms with high speed and energy efficiency. Here, we first propose an extremely factorized network (EFNet) which can learn multi-scale context information while preserving rich spatial information with reduced model complexity. Experimental results on the Cityscapes dataset show that EFNet achieves an accuracy of 68.0% mean intersection over union (mIoU) with only 0.18M parameters, at a speed of 99 frames per second (FPS) on a single RTX 3090 GPU. Then, to further improve the speed and energy efficiency, we design a memristor-based computing-in-memory (CIM) accelerator for the hardware implementation of EFNet. It is shown by the simulation in DNN+NeuroSim V2.0 that the memristor-based CIM accelerator is ∼63× (∼4.6×) smaller in area, at most ∼9.2× (∼1000×) faster, and ∼470× (∼2400×) more energy-efficient than the RTX 3090 GPU (the Jetson Nano embedded development board), although its accuracy slightly decreases by 1.7% mIoU. Therefore, the memristor-based CIM accelerator has great potential to be deployed at the edge to implement lightweight semantic segmentation models like EFNet. This study showcases an algorithm-hardware co-design to realize real-time and low-power semantic segmentation at the edge.