Materials Horizons最新文献

The recent synthesis of goldene, a 2D atomic monolayer of gold, has opened new avenues in exploring novel materials. However, the question of when multilayer goldene transitions into bulk gold remains unresolved. This study used density functional theory calculations to address this fundamental question. Our findings reveal that multilayer goldene retains an AA-like stacking configuration of up to six layers, with no observation of Bernal-like stacking as seen in graphene. Goldene spontaneously transitions to a bulk-like gold structure at seven layers, adopting a rhombohedral (ABC-like) stacking characteristic of bulk face-centered cubic (FCC) gold. The atomic arrangement converges entirely to the bulk gold lattice for more than ten layers. Quantum confinement significantly impacts the electronic properties, with monolayer and bulk goldene exhibiting levels with linear dispersion at the X-point of the Brillouin zone. In contrast, multilayer goldene shows levels with linear dispersions at the X- and Y-points. Monolayer goldene exhibits anisotropic optical absorption, which is absent in bulk gold. This study provides a deeper understanding of multilayer goldene's structural and electronic properties and stacked 2D materials in general.

Hardware neural networks could perform certain computational tasks orders of magnitude more energy-efficiently than conventional computers. Artificial neurons are a key component of these networks and are currently implemented with electronic circuits based on capacitors and transistors. However, artificial neurons based on memristive devices are a promising alternative, owing to their potentially smaller size and inherent stochasticity. But despite their promise, demonstrations of memristive artificial neurons have so far been limited. Here we demonstrate a fully on-chip artificial neuron based on microscale electrodes and halide perovskite semiconductors as the active layer. By connecting a halide perovskite memristive device in series with a capacitor, the device demonstrates stochastic leaky integrate-and-fire behavior, with an energy consumption of 20 to 60 pJ per spike, lower than that of a biological neuron. We simulate populations of our neuron and show that the stochastic firing allows the detection of sub-threshold inputs. The neuron can easily be integrated with previously-demonstrated halide perovskite artificial synapses in energy-efficient neural networks.

Conductive hydrogels with stable sensing performance are highly required in soft electronic devices. However, these hydrogels tend to solidify and experience structural damage at sub-zero temperatures, leading to material breakdown and device malfunction. The main challenge lies in effectively designing the micro/nano-structure to enhance mechanical properties and stable strain sensing while preventing freezing in hydrogels. Here, we present a rapid strategy for developing a MXene bridging double-network structure-based strain sensor using polyacrylamide and agar hydrogels that can maintain stable functionality even at an extremely low temperature of -30 °C. By incorporating MXenes as a catalyst to expedite free radical polymerization, we achieve outstanding mechanical and strain sensing properties at room temperature (a high response range of 1000%, a response signal linearity of 0.998, and a gauge factor (GF) value of 1.41). This sensing performance surpasses those reported for many other hydrogels. Importantly, we also observe that the stable micro-nanostructure in the hydrogel at an extreme temperature of approximately -30 °C results in exceptional strain-detection performance (a stable response range of up to 250%) with a linearity of 0.995 and a GF value of 1.25 due to its remarkably low freezing point (<-80 °C). These findings highlight the application of our hydrogel-based tactile sensor in low-temperature environments.

Realizing spin-orbit torque (SOT)-driven magnetization switching offers promising opportunities for the advancement of next-generation spintronics. However, the relatively low charge-spin conversion efficiency accompanied by an ultrahigh critical switching current density (J_c) remains a significant obstacle to the further development of SOT-based storage elements. Herein, spin absorption engineering at the ferromagnet/nonmagnet interface is firstly proposed to achieve high SOT efficiency in Pt/Co/Ir trilayers. The J_c value was significantly decreased to 7.5 × 10⁶ A cm^-2, achieving a maximum reduction of 58% when a 4.0-nm Gd layer was inserted into the Co/Ir interface. A similar trend was observed in the trilayers with various rare metal insertions, suggesting the universality of this approach. Simultaneously, the highest effective spin Hall angle of 0.29 was obtained in the Pt/Co/Gd (4.0 nm)/Ir multilayers, which was approximately three times greater than that obtained in the Pt/Co/Ir trilayer. First-principles calculations together with polarized neutron reflectivity results revealed that spin mixed conductivity can be significantly enhanced due to a spontaneous interfacial CoGd alloy, which is critical for high SOT efficiency. In addition, the deterministic field-free switching polarity can be tuned by introducing Gd insertion. These findings provide a promising pathway for deeply understanding the spin-charge conversion mechanism, and further enable the design of low-consumption spintronic circuits.

This study focuses on fabricating photonic crystals (PCs) by surfactant-based particle capture at the gas-liquid interface of evaporating sessile droplets. The captured particles form interfacial films, resulting in ordered monolayer depositions manifesting iridescent structural colors. The particle dynamics behind the ordered arrangement is delineated. This arrangement is influenced by the alteration in particles' hydrophobicity, charge, and internal flow introduced by the surfactant addition. The influence of surfactant and particle concentrations on the phenomenon is also investigated. The work demonstrates a drop-by-drop technique to scale up the formation of PCs. Furthermore, the work is extended towards demonstrating the utilization of this mechanism to fabricate arbitrary PCs efficiently by direct writing technique. The particle coverage in directly written patterns is influenced by printing speed and particle concentration, which are adjusted to achieve covert photonic patterns. Finally, the replication of colloidal PC onto a flexible polymer with minimal colloid transfer is demonstrated using soft lithography.

Recent advances in interfacial solar steam generation have made direct solar desalination a promising approach for providing cost-effective and environmentally friendly clean water solutions. However, developing highly effective, salt-resistant solar absorbers for long-term desalination at high efficiencies and evaporation rates remains a significant challenge. We present a Janus hydrogel-based absorber featuring a surface modified with thermo-responsive hydroxypropyl cellulose (HPC) and a hydrogel matrix containing photothermal conversion units, MXene, specifically designed for long-term seawater desalination. At the lower critical solution temperature, HPC undergoes phase separation, which results in the formation of a rough hydrophobic surface. This process creates a Janus evaporator structure that exhibits a high evaporation rate, excellent salt resistance, and long-term stability. Consequently, the hydrogel absorbers achieve an impressive evaporation rate (3.11 kg m^-2 h^-1) under one-sun irradiation. Salt residues are deposited only at the edges of the super-hydrophilic bottom. This process ensures long-term evaporator stability for continuous solar evaporation (>30 hours) in simulated seawater at an average evaporation rate of ∼2.58 kg m^-2 h^-1. With its unique structural design, achieved via a straightforward design process, the flexible Janus absorber serves as an efficient, salt-resistant, and stable solar steam generator for direct solar desalination.

Quantum dots have garnered significant interest in perovskite solar cells (PSCs) due to their stable chemical properties, high carrier mobility, and unique features such as multiple exciton generation and excellent optoelectronic characteristics resulting from quantum confinement effects. This review explores quantum dot properties and their applications in photoelectronic devices, including their synthesis and deposition processes. This sets the stage for discussing their diverse roles in the carrier transport, absorber, and interfacial layers of PSCs. We thoroughly examine advances in defect passivation, energy band alignment, perovskite crystallinity, device stability, and broader light absorption. In particular, novel approaches to enhance the photoelectric conversion efficiency (PCE) of quantum dot-enhanced perovskite solar cells are highlighted. Lastly, based on a comprehensive overview, we provide a forward-looking outlook on advanced quantum dot fabrication and its impact on enhancing the photovoltaic performance of solar cells. This review offers insights into fundamental mechanisms that endorse quantum dots for improved PSC performance, paving the way for further development of quantum dot-integrated PSCs.

Two-dimensional transition metal dichalcogenides (2D TMDCs) can be combined with organic semiconductors to form hybrid van der Waals heterostructures. Specially, non-fullerene acceptors (NFAs) stand out due to their excellent absorption and exciton diffusion properties. Here, we couple monolayer tungsten diselenide (ML-WSe₂) with two well performing NFAs, ITIC, and IT-4F (fluorinated ITIC) to achieve hybrid architectures. Using steady state and time resolved spectroscopic techniques, we reveal sub-picosecond free charge generation in the heterostructure of ML-WSe₂ with ITIC, where however, bimolecular recombination of spin uncorrelated charge carriers with possible contributions from geminate charge recombination cause rapid formation of low-lying triplet (T₁) states in ITIC. Importantly, this unwanted process is effectively suppressed when the fluorinated derivative of ITIC, IT-4F, is deposited on ML-WSe₂. We observe a similar scenario when replacing the ML-TMDC with copper thiocyanate (CuSCN) as the hole acceptor meaning that triplet state formation is not driven by the spin-orbit coupling of ML-WSe₂. From ab initio calculations based on density functional theory, we interpret the high triplet formation in the ML-WSe₂/ITIC hybrid bilayer due to changes in the nature and energies of the interfacial charge transfer (CT) levels. Our results highlight the delicate balance between excitons and charges in such inorganic/NFA heterostructures.

Dynamic responsive structural colored materials have drawn increased consideration in a wide range of applications, such as colorimetric sensors and high-safety tags. However, the sophisticated interactions among the individual responsive parts restrict the advanced design of multimodal responsive photonic materials. Inspired by stimuli-responsive color change in chameleon skin, a simple and effective photo-crosslinking strategy is proposed to construct hydroxypropyl cellulose (HPC) based hydrogels with multiple responsive structured colors. By controlling UV exposure time, the structural color of HPC hydrogels can be effectively controlled in a full-color spectrum. At the same time, HPC hydrogels showcase temperature and mechanical dual-responsive structural colors. In particular, the microstructure of HPC hydrogels undergoes a transition from the chiral nematic phase to the nematic phase under the action of external stretching, leading to a significant reflection of circularly polarized light (CPL) to linearly polarized light (LPL). Given the diverse responsiveness exhibited by HPC hydrogels and their unique structural transition properties under external forces, we have explored their potential applications as dynamic anti-counterfeiting labels and optical skins. This work reveals the great possibility of using structural colored cellulose hydrogels in multi-sensing and optical displays, opening up a new path for the exploration of next-generation flexible photonic devices.

Given that optical thermometers are widely used due to their unique advantages, this study aims to address critical challenges in existing technologies, such as insufficient sensitivity, limited temperature measurement ranges, and poor signal recognition capabilities. Herein, we develop a thermometer based on the fluorescence intensity ratio (FIR) of Sb-doped Cs₂NaInCl₆ (Cs₂NaInCl₆:Sb). As the temperature increases from 203 to 323 K, the thermally induced transition from triplet to singlet self-trapped excitons (STEs) leads to enhanced 455 nm photoluminescence (PL) from singlet STE recombination. Thus, the FIR monotonically depends on temperature, allowing for temperature sensing with a high absolute sensitivity (S_A) of 0.0575 K^-1 and the maximum relative sensitivity (S_R) of 1.005% K^-1. We demonstrate that spatial temperature distribution can be measured by mapping the PL spectra, even with a transparent medium screening the target. Furthermore, blue emissive Cs₂NaInCl₆:Sb is mixed with yellow emissive Cs₂AgInCl₆:Sb with a thermal quenching feature. The fluorescence color of the mixture dramatically depends on temperature, enabling a user-friendly colorimetric temperature sensing. Therefore, two operational modes are proposed to meet various practical application demands.