Laser-Induced Ultrafast Spin Injection in All-Semiconductor Magnetic CrI3/WSe2 Heterobilayer.

Spin injection stands out as a crucial method employed for initializing, manipulating, and measuring the spin states of electrons, which are fundamental to the creation of qubits in quantum computing. However, ensuring efficient spin injection while maintaining compatibility with standard semiconductor processing techniques is a significant challenge. Herein, we demonstrate the capability of inducing an ultrafast spin injection into a WSe2 layer from a magnetic CrI3 layer on a femtosecond time scale, achieved through real-time time-dependent density functional theory calculations upon a laser pulse. Following the peak of the magnetic moment in the CrI3 sublayer, the magnetic moment of the WSe2 layer reaches a maximum of 0.89 µB (per unit cell containing 4 WSe2 and 1 CrI3 units). During the spin dynamics, spin-polarized excited electrons transfer from the WSe2 layer to the CrI3 layer via type-II band alignment. The large spin splitting in conduction bands and the difference in the number of spin-polarized local unoccupied states available in the CrI3 layer lead to a net spin in the WSe2 layer. Furthermore, we confirmed that the number of available states, the spin-flip process, and the laser pulse parameters play important roles during the spin injection process. This work highlights the dynamic and rapid nature of spin manipulation in layered all-semiconductor systems, offering significant implications for the development and enhancement of quantum information processing technologies.

Ultrafast Laser Pulse Induced Transient Ferrimagnetic State and Spin Relaxation Dynamics in Two-Dimensional Antiferromagnets.

We employ real-time time-dependent density functional theory (rt-TDDFT) and ab initio nonadiabatic molecular dynamics (NAMD) to systematically investigate the ultrafast laser pulses induced spin transfer and relaxation dynamics of two-dimensional (2D) antiferromagnetic-ferromagnetic (AFM/FM) MnPS3/MnSe2 van der Waals heterostructures. We demonstrate that laser pulses can induce a ferrimagnetic (FiM) state in the AFM MnPS3 layer within tens of femtoseconds and maintain it for subpicosecond time scale before reverting to the AFM state. We identify the mechanism in which the asymmetric optical intersite spin transfer (OISTR) effect occurring within the sublattices of the AFM and FM layers drives the interlayer spin-selective charge transfer, leading to the transition from AFM to FiM state. Furthermore, the unequal electron-phonon coupling of spin-up and spin-down channels of AFM spin sublattice causes an inequivalent spin relaxation, in turn extending the time scale of the FiM state. These findings are essential for designing novel optical-driven ultrafast 2D magnetic switches.

Ultrafast Laser Control of Antiferromagnetic-Ferrimagnetic Switching in Two-Dimensional Ferromagnetic Semiconductor Heterostructures.

Realizing ultrafast control of magnetization switching is of crucial importance for information processing and recording technology. Here, we explore the laser-induced spin electron excitation and relaxation dynamics processes of CrCl3/CrBr3 heterostructures with antiparallel (AP) and parallel (P) systems. Although an ultrafast demagnetization of CrCl3 and CrBr3 layers occurs in both AP and P systems, the overall magnetic order of the heterostructure remains unchanged due to the laser-induced equivalent interlayer spin electron excitation. More crucially, the interlayer magnetic order switches from antiferromagnetic (AFM) to ferrimagnetic (FiM) in the AP system once the laser pulse disappears. The microscopic mechanism underpinning this magnetization switching is dominated by the asymmetrical interlayer charge transfer combined with a spin-flip, which breaks the interlayer AFM symmetry and ultimately results in an inequivalent shift in the moment between two FM layers. Our study opens up a new idea for ultrafast laser control of magnetization switching in two-dimensional opto-spintronic devices.

Highly Diastereoselective Synthesis of C-Glycosides from Glycal Anomers.

This Letter presents a highly diastereoselective synthesis of C-hydroxymethine glycosides from glycal anomers using a chiral N-heterocyclic carbene-copper catalyst. The high diastereoselectivity was synergistically controlled by the stereocenter of the substrate and chirality of the N-heterocyclic carbene-copper complex without being interrupted by the stereochemistry of C5 and the anomeric position. This approach enables the production of a diverse array of C-hydroxymethine glycosides using synthetically versatile glycals and various functionalized aldehydes.

Control of Hot Carrier Cooling in Lead Halide Perovskites by Point Defects.

Hot carriers (HCs) in lead halide perovskites are prone to rapidly relax at the band edge and waste plentiful photon energy, severely limiting their conversion efficiency as HC photovoltaic devices. Here, the HC cooling dynamics of MAPbI3 perovskite with common vacancy point defects (e.g., MAv+ and Iv-) and an interstitial point defect (e.g., Ii-) is elucidated, and the underlying physics is explicated using ab initio nonadiabatic molecular dynamics. Contrary to vacancy point defects, the interstitial point defect reduces the band degeneracy, decreases the HC -phonon interaction, weakens the nonadiabatic coupling, and ultimately slows down hot electron cooling by a factor of 1.5-2. Furthermore, the band-by-band relaxation pathway and direct relaxation pathway are uncovered for hot electron cooling and hot hole cooling, respectively, explaining why hot electrons can store more energy than hot holes during the cooling process. Besides, oxygen molecules interacting with Ii- sharply accelerate the hot electron cooling, making it even faster than that of the pristine system and revealing the detrimental effect of oxygen on HC cooling. This work provides significant insights into the defect-dependent HC cooling dynamics and suggests a new strategy to design high-efficiency HC photovoltaic devices.

POD Nanozyme optimized by charge separation engineering for light/pH activated bacteria catalytic/photodynamic therapy.

The current feasibility of nanocatalysts in clinical anti-infection therapy, especially for drug-resistant bacteria infection is extremely restrained because of the insufficient reactive oxygen generation. Herein, a novel Ag/Bi2MoO6 (Ag/BMO) nanozyme optimized by charge separation engineering with photoactivated sustainable peroxidase-mimicking activities and NIR-II photodynamic performance was synthesized by solvothermal reaction and photoreduction. The Ag/BMO nanozyme held satisfactory bactericidal performance against methicillin-resistant Staphylococcus aureus (MRSA) (~99.9%). The excellent antibacterial performance of Ag/BMO NPs was ascribed to the corporation of peroxidase-like activity, NIR-II photodynamic behavior, and acidity-enhanced release of Ag+. As revealed by theoretical calculations, the introduction of Ag to BMO made it easier to separate photo-triggered electron-hole pairs for ROS production. And the conduction and valence band potentials of Ag/BMO NPs were favorable for the reduction of O2 to ·O2-. Under 1064 nm laser irradiation, the electron transfer to BMO was beneficial to the reversible change of Mo5+/Mo6+, further improving the peroxidase-like catalytic activity and NIR-II photodynamic performance based on the Russell mechanism. In vivo, the Ag/BMO NPs exhibited promising therapeutic effects towards MRSA-infected wounds. This study enriches the nanozyme research and proves that nanozymes can be rationally optimized by charge separation engineering strategy.

Rational Unraveling of Alkali Metal Concentration-Dependent Photovoltaic Performance of Halide Perovskites: Octahedron Distortion vs Surface Reconstruction.

Adding alkali metal in organic-inorganic halide perovskites effectively improves its photovoltaic performance, while excessive alkali metal incorporation would produce a detrimental effect. Through density functional theory and nonadiabatic molecular dynamics simulations, we demonstrate how and why the photogenerated carrier lifetime mutates with the increase of alkali metal concentration. A small amount of Rb doping in the lattice introduces a slight distortion of the octahedron, reducing the overlap of frontier orbitals and decreasing the nonadiabatic coupling, effectively enhancing the photogenerated carrier lifetime. In contrast, excessive Rb will introduce defect states, resulting in the low carrier lifetime by a factor of 2-3 orders of magnitude. Strikingly, the surface formamidinium (FA) cations exhibit unexpected responsibility for the carrier dynamics since its high-frequency thermal vibration strongly leads to the ultrafast hole trapping and carrier recombination. Our results provide new insight into the concentration-dependent photovoltaic performance of alkali metal cations in organic-inorganic halide perovskites.

Direct formation of interlayer exciton in two-dimensional van der Waals heterostructures.

In atomically thin two-dimensional van der Waals (2D vdW) heterostructures, spatially separated interlayer excitons play an important role in the optoelectronic performance and show great potential for the exploration of many-body quantum phenomena. A commonly accepted formation mode for interlayer excitons is via a two-step intralayer exciton transfer mechanism, namely, photo-excited intralayer excitons are initially generated in individual sublayers, and photogenerated electrons and holes are then separated into opposite sublayers based on the type-II band alignment. Herein, we expand the concept of interlayer exciton formation and reveal that bright interlayer excitons can be generated in one step by direct interlayer photoexcitation in 2D vdW heterostructures that have strong interlayer coupling and a short photoexcitation channel. First-principles and many-body perturbation theory calculations demonstrate that indium selenide/antimonene and indium selenide/black phosphorus heterostructures are two promising systems that show an exceptionally large interlayer transition probability (>500 Debye2). This study enriches the understanding of interlayer exciton formation and provides a new avenue to acquiring strong interlayer excitons in artificial 2D vdW heterostructures.

Spin-constrained optoelectronic functionality in two-dimensional ferromagnetic semiconductor heterojunctions.

Two-dimensional (2D) van der Waals (vdW) engineering has brought about many extraordinary and new physics concepts and potential applications. Herein, we propose a new type of spin-constrained optoelectronic device developed using 2D ferromagnetic semiconductor heterostructures (FMSs). It is based on a photoexcited double-band-edge transition model, involved coupling between the interlayer magnetic order and the spin-polarized band structure and can achieve the reversible switch of band alignment via reversal of magnetization. We demonstrate that such a unique magnetic optoelectronic device can be realized with a CrBr3/CrCl3 heterojunction and other 2D FMS heterojunctions that have the same direction as the easy magnetization axis and have a switchable band alignment that allows reconfiguration. This study opens a new application window for 2D vdW heterostructures and enables the possibility for fully vdW-based ultra-compact spintronics devices.

Photocatalytic conversion of CO to fuels with water by B-doped graphene/g-C3N4 heterostructure.

Photocatalytic reduction of carbon monoxide (CO) is a promising route to the production of high-value chemicals and fuels, as a supplement to high energy-input Fischer-Tropsch synthesis (FTS) and a key step in direct photo/electro-reduction CO2 to multi-carbon products. However, many current research efforts for high-efficiency FTS/CO2 reduction mainly focus on the metal-based catalysts, while metal-free and solar-driven photocatalysts are rarely explored. Here, by means of Lewis acid sites, a metal-free composite photocatalyst for CO reduction, namely boron (B) doped-graphene/g-C3N4 heterostructure, is proposed. First-principles calculations show that the dopants (B) as catalytic sites can effectively capture and activate CO molecules and reduce CO to CH3OH and CH4 in different doping content. It is worth noting that C2 products, i.e., C2H5OH, can be produced with low free energy barriers on para-doped graphene/g-C3N4. Meanwhile, the competitive hydrogen evolution reaction (HER) can be greatly suppressed, leading to the high selectivity of CO reduction. Moreover, the formation of a built-in electric field in heterostructure enhances the separation of photogenerated electrons and holes, which further accelerates the transmission of photogenerated electrons to the catalytic sites and improves the reaction efficiency. Overall, this work not only proposes a new strategy from a new perspective to solve problems of high energy consumption and low selectivity of FTS, but also provides a tandem strategy to solve problems of CO2 to multi-carbon products.

Bi2WO6-BiOCl heterostructure with enhanced photocatalytic activity for efficient degradation of oxytetracycline.

The application of BiOCl in photocatalysis has been restricted by its low utilization of solar energy and fast recombination of charge carriers. In this study, zero-dimensional (0D) Bi2WO6 nanoparticles/two-dimensional (2D) layered BiOCl heterojunction composite was successfully constructed by facile hydrothermal and solvothermal methods. The most favorable sunlight photocatalytic activity was achieved for the as-prepared Bi2WO6-BiOCl composites with a ratio of 1%. The photocatalytic rate and mineralization efficiency of one typical antibiotic (i.e., oxytetracycline) over 1% Bi2WO6-BiOCl was about 2.7 and 5.3 times as high as that of BiOCl. Both experimental characterizations and density functional theory (DFT) calculations confirmed that the excellent photocatalytic performance mainly arised from the effective charge separation along the Bi2WO6 and BiOCl heterojunction interface. The effective electron transfer was driven by the internal electric field at the interfacial junction. In addition, 1% Bi2WO6-BiOCl exhibited excellent stability, and no apparent deactivation was observed after 4 test cycles. Therefore, the 0D/2D Bi2WO6-BiOCl heterojunction showed a great potential for the photocatalytic degradation of emerging organic pollutants.

Aqueous acid-based synthesis of lead-free tin halide perovskites with near-unity photoluminescence quantum efficiency.

Recently, lead halide perovskites with outstanding emission performance have become new candidate materials for light-emitting devices and displays; however, the toxicity of lead and instability of halide perovskites remain significant challenges. Herein, we report the aqueous acid-based synthesis of highly emissive two-dimensional (2D) tin halide perovskites, (octylammonium)2SnX4 (X = Br, I, or mixtures thereof), which displayed a high absolute photoluminescence (PL) quantum yield of near-unity in the solid-state, PL emission centered at 600 nm with a broad bandwidth (136 nm), a large Stokes shift (250 nm), long-lived luminescence (τ = 3.3 µs), and zero overlap between their absorption and emission spectra. Significantly, the stability study of 2D tin halide perovskites monitored by the PL quantum yield showed no changes after 240 days of storage at room temperature under ambient air and humidity conditions. The PL emission of the 2D tin halide perovskites was tuned from yellow to deep red by controlling halide composition. Furthermore, new yellow phosphors with superior optical properties are used to fabricate UV pumped white light emitting diodes (WLEDs). We expect these results to facilitate the development of new environmentally friendly and high-performance phosphors for future lighting and display technologies.

Greatly Enhanced Photoabsorption and Photothermal Conversion of Antimonene Quantum Dots through Spontaneously Partial Oxidation.

Two-dimensional quantum dots (2DQDs), as promising photothermal agents (PTAs) in photothermal therapy (PTT) to malignant tumors, have been widely studied experimentally, whereas the superior photoabsorption and photothermal conversion mechanisms remain unclear. In this work, we present the first excited-state dynamics study on the PTT of 2D antimonene (AM) QDs by employing time-dependent density functional theory and ab initio nonadiabatic molecular dynamics calculations. Surprisingly, pristine AMQDs themselves are not good PTAs due to weak photoabsorption and low photothermal conversion performance. The superior PTT capacity of AMQDs actually derives from the spontaneously partial oxidation. The partial oxidation introduces additional band edge states, which not only broaden the optical absorption range but also strengthen the transition dipole moment. More importantly, the oxidation doubles the nonradiative transition rate arising from the increased nonradiative coupling, which greatly promotes the release of photogenerated electron energy and accelerates the photothermal conversion efficiency. The in-depth insight unveiled here should be of fundamental importance and benefit for efficient utilization of 2DQDs in biomedical field.

Photocatalytic performance of few-layer graphitic C3N4: enhanced by interlayer coupling.

For atomically thin two-dimensional materials, van der Waals interlayer coupling is a crucial factor to tune or produce novel physicochemical properties. In terms of photocatalysis, however, researching into the interlayer coupling effect is still in its infancy, especially that involving excited state dynamics. Here, by performing many-body perturbation theory and ab initio nonadiabatic molecular dynamics, we find that metal-free few-layer graphitic C3N4 (g-C3N4) possesses a better photocatalytic hydrogen evolution performance due to interlayer coupling compared with ultrathin monolayer g-C3N4. Specifically, few-layer g-C3N4 activates the electronic transition channel around the Fermi level and transforms dark excitation to bright excitation, which broadens the solar light absorption region. Meanwhile, few-layer g-C3N4 can effectively weaken the strong binding energy between nitrogen and hydrogen by means of intralayer charge transfer, and can enhance the activity of hydrogen evolution reactive sites. Furthermore, the interlayer coupling tends to localize photogenerated electrons at the reactive sites, which can provide more active electrons to participate in the catalytic reaction.