Tuning Magnetism of Metal Porphyrazine Molecules by a Ferroelectric In2Se3 Monolayer

Nonvolatile Electric Control of Rashba Spin Splitting in Sb/In2Se3 Heterostructure

Ferroelectric Rashba semiconductors (FRS) are highly demanded for their potential capability for nonvolatile electric control of electron spins. An ideal FRS is characterized by a combination of room temperature ferroelectricity and a strong Rashba effect, which has, however, been rarely reported. Herein, we designed a room-temperature FRS by vertically stacking a Sb monolayer on a room-temperature ferroelectric In2Se3 monolayer. Our first-principles calculations reveal that the Sb/In2Se3 heterostructure exhibits a clean Rashba splitting band near the Fermi level and a strong Rashba effect coupled to the ferroelectric order. Switching the electric polarization direction enhances the Rashba effect, and the flipping is feasible with a low energy barrier of 22 meV. This Rashba-ferroelectricity coupling effect is robust against changes of the heterostructure interfacial distance and external electric fields. Such a nonvolatile electrically tunable Rashba effect at room temperature enables potential applications in next-generation data storage and logic devices operated under small electrical currents.

Robust Magnetoelectric Coupling in FeTiO3/Ga2O3 Non-van der Waals Heterostructures

Magnetoelectric coupling represents a significant breakthrough for next-generation electronics, offering the ability to achieve nonvolatile magnetic control via electrical means. In this comprehensive investigation, leveraging first-principles calculations, we unveil a robust magnetoelectric coupling within multiferroic heterostructures (HSs) by ingeniously integrating a non-van der Waals (non-vdW) magnetic FeTiO3 monolayer with the ferroelectric (FE) Ga2O3. Diverging from conventional van der Waals (vdW) multiferroic HSs, the magnetic states of the FeTiO3 monolayer can be efficiently toggled between ferromagnetic (FM) and antiferromagnetic (AFM) configurations by reversing the polarization of the Ga2O3 monolayer. This intriguing phenomenon arises from polarization-dependent substantial interlayer electron transfers and the interplay between superexchange and direct-exchange magnetic couplings of the iron atoms. The carrier-mediated interfacial interactions induce crucial shifts in Fermi level positions, decisively imparting distinct electronic characteristics near the Fermi level of composite systems. These novel findings offer exciting prospects for the future of magnetoelectric technology.

Research progress on photocatalytic reduction of CO2 based on ferroelectric materials

Transforming CO2 into renewable fuels or valuable carbon compounds could be a practical means to tackle the issues of global warming and energy crisis. Photocatalytic CO2 reduction is more energy-efficient and environmentally friendly, and offers a broader range of potential applications than other CO2 conversion techniques. Ferroelectric materials, which belong to a class of materials with switchable polarization, are attractive candidates as catalysts due to their distinctive and substantial impact on surface physical and chemical characteristics. This review provides a concise overview of the fundamental principles underlying photocatalysis and the mechanism involved in CO2 reduction. Additionally, the composition and properties of ferroelectric materials are introduced. This review expands on the research progress in using ferroelectric materials for photocatalytic reduction of CO2 from three perspectives: directly as a catalyst, by modification, and construction of heterojunctions. Finally, the future potential of ferroelectric materials for photocatalytic CO2 reduction is presented. This review may be a valuable guide for creating reasonable and more effective photocatalysts based on ferroelectric materials.

Ferroelectric Materials and Their Applications in Activation of Small Molecules

The demand for renewable and environmentally friendly energy sources has attracted extensive research on high-performance catalysts. Ferroelectrics, a class of materials with switchable polarization, are unique and promising catalyst candidates due to the significant effects of polarization on surface chemistry and physics. The band bending at the ferroelectric/semiconductor interface induced by the polarization flip promotes charge separation and transfer, thereby enhancing the photocatalytic performance. More importantly, the reactants can be selectively adsorbed on the surface of ferroelectric materials depending on the polarization direction, which can effectively lift the basic limitations as imposed by Sabatier's principle on catalytic activity. This Review summarizes the latest developments of ferroelectric materials and introduces ferroelectric-related catalytic applications. The possible research directions of 2D ferroelectric materials in chemical catalysis are discussed at the end. The Review is expected to inspire extensive research interests from physical, chemical, and materials science communities.

Selective sensing properties and enhanced ferromagnetism in CrI3monolayer via gas adsorption

Recent fabrication of chromium triiodide (CrI₃) monolayers has raised potential prospects of developing two-dimensional (2D) ferromagnetic materials for spintronic device applications. The low Curie temperature has stimulated further interest for improving the ferromagnetic stability of CrI₃monolayer. Here, based on density functional theory calculations, we investigated the adsorption energy, charge transfer, electronic and magnetic properties of gases (CO, CO₂, N₂, NH₃, NO, NO₂, O₂, and SO₂) adsorption on the CrI₃monolayer. It is found that CrI₃is sensitive to the NH₃, NO, and NO₂adsorption due to the high adsorption energy and large charge transfer. The electrical transport results show that the conductivity of CrI₃monolayer is significantly reduced with the adsorption of N-based gases, suggesting that CrI₃exhibits superior sensitivity and selectivity toward N-based gases. In addition, the ferromagnetic stability and Curie temperature (T_C) of CrI₃monolayer can be effectively enhanced by the adsorption of magnetic gases (NO, NO₂, O₂). This work not only demonstrates that CrI₃monolayer can be used as a promising candidate for gas sensing, but also brings further interest to tune the electronic and magnetic properties of 2D ferromagnetic materials via gas adsorption.

Ferroelectric control of band alignments and magnetic properties in the two-dimensional multiferroic VSe2/In2Se3

Our first-principles evidence shows that the two-dimensional (2D) multiferroic VSe₂/In₂Se₃experiences continuous change of electronic structures, i.e. with the change of the ferroelectric (FE) polarization of In₂Se₃, the heterostructure can possess type-I, -II, and -III band alignments. When the FE polarization points from In₂Se₃to VSe₂, the heterostructure has a type-III band alignment, and the charge transfer from In₂Se₃into VSe₂induces half-metallicity. With reversal of the FE polarization, the heterostructure enters the type-I band alignment, and the spin-polarized current is turned off. When the In₂Se₃is depolarized, the heterostructure has a type-II band alignment. In addition, influence of the FE polarization on magnetism and magnetic anisotropy energy of VSe₂was also analyzed, through which we reveal the interfacial magnetoelectric coupling effects. Our investigation about VSe₂/In₂Se₃predicts its wide applications in the fields of both 2D spintronics and multiferroics.

Remarkable ferroelectricity-modulated electronic and magnetic properties in a 2H-VS2/BiAlO3(0001) hybrid system

In the present work, a 2H-VS₂/BiAlO₃(0001) hybrid system is constructed to perform first-principles density functional theory (DFT) calculations. The results reveal that, in addition to the ionic-vdW interface coupling, the ferromagnetic semiconductive 2H-VS₂ monolayer on the ferroelectric BiAlO₃(0001) substrate exhibits n-type or p-type doping behavior and even half-metal characteristics. Furthermore, the magnetoelectric coefficient (α_S) for the 2H-VS₂/BiAlO₃(0001) structures can reach a value of 10^-10 G cm² V^-1 with ferroelectric polarization reversal. The estimated Curie temperatures (T_c) of the 2H-VS₂ monolayer on the BiAlO₃(0001) Z+ (positive), Z+↓ (polarization-reversed Z+), Z- (negative), and Z-↑ (polarization-reversed Z-) polar surfaces were found to be 176, 276, 266, and 87 K, respectively. This indicates that the magnetic properties of the 2H-VS₂ monolayer are remarkably tunable using a ferroelectric BiAlO₃(0001) knob. These important findings provide a distinctive treatment option for controllable and adjustable nanoelectronic, photoelectronic, and spintronic devices based on a 2H-VS₂ monolayer.

Two-dimensional InSb/GaAs- and InSb/InP-based tandem photovoltaic device with matched bandgap

The past several years have witnessed remarkable research efforts to develop high-performance photovoltaics (PVs), to curtail the energy crisis by avoiding dependence on traditional fossil fuels. In this regard, there is an urgent need to accelerate research progress on new low-dimensional semiconductors with superior electronic and optical properties. Herein, combining abundant related PV experimental data in the literature and our systematic theoretical calculations, we propose two-dimensional (2D) InSb/GaAs and InSb/InP-based tandem PVs with high solar-to-electric efficiency up to near 30.0%. Firstly, according to first-principles calculations, the stability, electronic and optical properties of single-layer group-III-V materials (XY, X = Ga and In, Y = N, P, As, Sb, and Bi) are systematically introduced. Next, due to the high bandgap (E_g) of GaAs and InP being a perfect match with the low E_g of InSb, InSb/GaAs- and InSb/InP-based tandem PVs are constructed. In addition, the complementary absorption spectra of these two subcells can facilitate the achievement of high tandem power conversion efficiency. Furthermore, we have analyzed in detail the influencing factors for PCE and the physical mechanism of the optimized match between the top and bottom subcells in the tandem configurations. Our designed 2D-semiconductor-based PVs can be expected to bring a new perspective for future commercialized high-efficiency energy devices.

Large perpendicular magnetic anisotropy of transition metal dimers driven by polarization switching of two-dimensional ferroelectric In2Se3 substrate

Large perpendicular magnetic anisotropy (MA) is highly desirable for realizing atomic-scale magnetic data storage which represents the ultimate limit of the density of magnetic recording. In this work, we study...

Mechano-ferroelectric coupling: stabilization enhancement and polarization switching in bent AgBiP2Se6 monolayers

Two-dimensional (2D) van der Waals (vdW) ferroelectrics are core candidates for the development of next-generation non-volatile storage devices, which rely highly on ferroelectric stability and feasible approaches to manipulate the ferroelectric polarization and domain. Here, based on density functional theory calculations, we demonstrate that the bending deformation can not only manipulate the polarization direction and domain size of AgBiP₂Se₆ monolayers but also significantly improve the ferroelectric stability. The ordered polarization in the bent AgBiP₂Se₆ monolayers can be well maintained at a temperature of 200 K in molecular dynamics simulations; by contrast, it is broken at only 100 K for their freestanding counterparts. These phenomena can be attributed to synergic effects from the asymmetric strain energy induced by a strain gradient and a reduced migration barrier of Ag ions from convex to concave surfaces. More interestingly, a ferroelectric bubble can be induced in the monolayer under biaxial compression strain. This mechano-ferroelectric coupling represents a new mechanism and feasible route towards stabilization and polarization flip in 2D ferroelectrics.

Controllable CO2 electrocatalytic reduction via ferroelectric switching on single atom anchored In2Se3 monolayer

Efficient and selective CO₂ electroreduction into chemical fuels promises to alleviate environmental pollution and energy crisis, but it relies on catalysts with controllable product selectivity and reaction path. Here, by means of first-principles calculations, we identify six ferroelectric catalysts comprising transition-metal atoms anchored on In₂Se₃ monolayer, whose catalytic performance can be controlled by ferroelectric switching based on adjusted d-band center and occupation of supported metal atoms. The polarization dependent activation allows effective control of the limiting potential of CO₂ reduction on TM@In₂Se₃ (TM = Ni, Pd, Rh, Nb, and Re) as well as the reaction paths and final products on Nb@In₂Se₃ and Re@In₂Se₃. Interestingly, the ferroelectric switching can even reactivate the stuck catalytic CO₂ reduction on Zr@In₂Se₃. The fairly low limiting potential and the unique ferroelectric controllable CO₂ catalytic performance on atomically dispersed transition-metals on In₂Se₃ clearly distinguish them from traditional single atom catalysts, and open an avenue toward improving catalytic activity and selectivity for efficient and controllable electrochemical CO₂ reduction reaction.

Catalysis based on ferroelectrics: controllable chemical reaction with boosted efficiency

Catalysts, which can accelerate chemical reactions, show promising potential to alleviate environmental pollution and the energy crisis. However, their wide application is severely limited by their low efficiency and poor selectivity due to the recombination of photogenerated electron-hole pairs, the back-reaction of interactants. Accordingly, ferroelectrics have emerged as promising catalysts to address these issues with the advantages of promoted light adsorption, boosted catalytic efficiency as a result of their intrinsic polarization, suppressed electron-hole pair recombination, and superior selectivity via the ferroelectric switch. This review summarizes the recent research progress of catalytic studies based on ferroelectric materials and highlights the controllability of catalytic activity by the ferroelectric switch. More importantly, we also comprehensively highlight the underlying working mechanism of ferroelectric-controlled catalysis to facilitate a deep understanding of this novel chemical reaction and guide future experiments. Finally, the perspectives of catalysis based on ferroelectrics and possible research opportunities are discussed. This review is expected to inspire wide research interests and push ferroelectric catalysis to practical applications.

Nonvolatile electrical control of 2D Cr2Ge2Te6 and intrinsic half metallicity in multiferroic hetero-structures

The electrical control of two-dimensional (2D) van der Waals ferromagnets is a step forward for the realization of spintronic devices. However, using this approach for practical applications remains challenging due to its volatile memory. Herein, we adopt an alternative strategy, where the bistable ferroelectric switches (P↑ and P↓) of Sc₂CO₂ (SCO) assist the ferromagnetic states of Cr₂Ge₂Te₆ (CGT) in order to achieve non-volatile memories. Moreover, MXene SCO, being an aided layer in multiferroic CGT/SCO hetero-structures, also modifies the electronic properties of CGT to half metal by its polarized P↓ state. In contrast, the P↑ state does not change the semiconducting nature of CGT. Hence, non-volatile, electrical-controlled switching of ferromagnetic CGT can be engineered by the two opposite ferroelectric states of single layer SCO. Importantly, the magnetic easy axis of CGT switches from in-plane to out-of-plane when the direction of electric polarization of SCO is altered from P↓ to P↑.

Penta-Hexa-Graphene Nanoribbons: Intrinsic Magnetism and Edge Effect Induce Spin-Gapless Semiconducting and Half-Metallic Properties

Two-dimensional materials with intrinsic long-range ordered magnetic moments have drawn a lot of attention. However, for practical applications, whether or not the magnetism is stable in their nanostructures has not been revealed. Here, based on the recently proposed magnetic penta-hexa-graphene, we study the electronic and magnetic properties of its nanoribbons (named PHGNRs). The results show that the PHGNRs have intrinsic robust magnetic moments that are different from zigzag graphene nanoribbons, where the magnetic moments caused by the edge effect are vulnerable. Moreover, the magnetic ground states, namely, ferromagnetic (FM) or antiferromagnetic (AFM), can be transformed by changing the width of PHGNRs. Most interestingly, under the FM ground state, the spin-polarized electronic properties reveal that the zigzag PHGNRs transform from spin-gapless semiconductors (SGSs) to half-metals, as the width of nanoribbons increases, while all the armchair PHGNRs are magnetic semiconductors. Furthermore, by considering different edge effects caused by the residual carbon atoms on the edges, the PHGNRs can further derive different types of SGSs, as well as half-metals. Our work suggests that the PHGNRs possessing intrinsic robust magnetic moments have potential applications in the field of spintronic devices.

Switchable Asymmetric Moiré Patterns with Strongly Localized States

Most moiré pattern structures are constructed by twisting the angle of two similar 2D materials. The corresponding electronic structures are fixed in device applications. Here we study moiré patterns constructed with monolayers of InSe and ferroelectric In₂Se₃. The ferroelectricity of In₂Se₃ induces deep electron trap states and allows the switch of moiré pattern by an applied electric field. Using a unique linear scaling computational method, we systematically studied the electronic structures, localized state sizes, and strong correlation effects of switchable moiré patterns of systems containing close to 10 000 atoms.