First-Principles Investigation of Size Effects on Cohesive Energies of Transition-Metal Nanoclusters.

The cohesive energy of transition-metal nanoparticles is crucial to understanding their stability and fundamental properties, which are essential for developing new technologies and applications in fields such as catalysis, electronics, energy storage, and biomedical engineering. In this study, we systematically investigate the size-dependent cohesive energies of all the 3, 4, and 5 transition-metal nanoclusters (small nanoparticles) based on a plane-wave-based method within general gradient approximation using first-principles density functional theory calculations. Our results show that the cohesive energies of nanoclusters decrease with decreasing size due to the increased surface-to-volume ratio and quantum confinement effects.

Interface Engineering at ScC MXene and Germanium Iodine Perovskite Interface: First-Principles Insights.

In recent years, Ge-based halide perovskite has gained increasing attention due to its potential in the development of lead-free perovskite solar cells. Here, through first-principles calculations, we explored the possibilities to enhance the optoelectronic properties of Ge-based perovskites via interfacial engineering between germanium iodine perovskite and 2D scandium-carbide MXene with various termination groups including F, O, and OH. We first evaluated the relative stability of the material interfaces and found that MAI-terminated interfaces are energetically more favorable than the GeI-terminated interfaces.

Perovskite superlattices with efficient carrier dynamics.

Compared with their three-dimensional (3D) counterparts, low-dimensional metal halide perovskites (2D and quasi-2D; BAMX, such as B = R-NH, A = HC(NH), Cs; M = Pb, Sn; X = Cl, Br, I) with periodic inorganic-organic structures have shown promising stability and hysteresis-free electrical performance. However, their unique multiple-quantum-well structure limits the device efficiencies because of the grain boundaries and randomly oriented quantum wells in polycrystals. In single crystals, the carrier transport through the thickness direction is hindered by the layered insulating organic spacers.

Elucidate interfacial disorder effects on the perpendicular magnetic anisotropy at Fe/MgO heterostructure from first-principles calculations.

The interfacial perpendicular magnetic anisotropy (PMA) plays a key role in spintronic applications such as memory recording and computational devices. Despite robust PMA being reported at the Fe/MgO interface, there are still inconsistencies in the disorder effects on the interfacial magnetic anisotropy. Here we reported a comprehensive study of the influence of the interfacial disorder, including the underoxidization, overoxidization, and oxygen migration, on the PMA of the Fe/MgO interface using first-principles calculations.

High-Throughput Design of Interfacial Perpendicular Magnetic Anisotropy at Heusler/MgO Heterostructures.

The perpendicular magnetic anisotropy (PMA) at ferromagnet/insulator interfaces has important technological applications, such as in the fields of magnetic recording and sensing devices. The perpendicular magnetic tunnel junctions (p-MTJs) with strong PMA have recently attracted increasing interest because they offer high stability and device performance toward low energy consumption. Heusler alloys are a large family of compounds that offer promising magnetic properties for developing p-MTJs.

Nonreciprocal Transport in a Bilayer of MnBiTe and Pt.

MnBiTe (MBT) is the first intrinsic magnetic topological insulator with the interaction of spin-momentum locked surface electrons and intrinsic magnetism, and it exhibits novel magnetic and topological phenomena. Recent studies suggested that the interaction of electrons and magnetism can be affected by the Mn-doped BiTe phase at the surface due to inevitable structural defects. Here, we report an observation of nonreciprocal transport, that is, current-direction-dependent resistance, in a bilayer composed of antiferromagnetic MBT and nonmagnetic Pt.

Two-Dimensional Electron Gas at the Spinel/Perovskite Interface: Suppression of Polar Catastrophe by an Ultrathin Layer of Interfacial Defects.

Two-dimensional electron gas (2DEG) at the interface between two insulating perovskite oxides has attracted much interest for both fundamental physics and potential applications. Here, we report the discovery of a new 2DEG formed at the interface between spinel MgAlO and perovskite SrTiO. Transport measurements, electron microscopy imaging, and first-principles calculations reveal that the interfacial 2DEG is closely related to the symmetry breaking at the MgAlO/SrTiO interface.

A fabrication process for flexible single-crystal perovskite devices.

Organic-inorganic hybrid perovskites have electronic and optoelectronic properties that make them appealing in many device applications. Although many approaches focus on polycrystalline materials, single-crystal hybrid perovskites show improved carrier transport and enhanced stability over their polycrystalline counterparts, due to their orientation-dependent transport behaviour and lower defect concentrations. However, the fabrication of single-crystal hybrid perovskites, and controlling their morphology and composition, are challenging.

Designing an All-Solid-State Sodium-Carbon Dioxide Battery Enabled by Nitrogen-Doped Nanocarbon.

All-solid-state sodium-carbon dioxide (Na-CO) battery is an emerging technology that effectively utilizes the greenhouse gas, CO, for energy storage with the virtues of minimized electrolyte leakage and suppressed Na dendrite growth for the Na metal anode. However, the sluggish reduction/evolution reactions of CO on the solid electrolyte/CO cathode interface have caused premature battery failure. Herein, nitrogen (N)-doped nanocarbon derived from metal-organic frameworks is designed as a cathode catalyst to solve this challenge.

Stability diagrams, defect tolerance, and absorption coefficients of hybrid halide semiconductors: High-throughput first-principles characterization.

On the basis of the screened 29 hybrid halide compounds from our prior study [Y. Li and K. Yang, Energy Environ.

Strain engineering and epitaxial stabilization of halide perovskites.

Strain engineering is a powerful tool with which to enhance semiconductor device performance. Halide perovskites have shown great promise in device applications owing to their remarkable electronic and optoelectronic properties. Although applying strain to halide perovskites has been frequently attempted, including using hydrostatic pressurization, electrostriction, annealing, van der Waals force, thermal expansion mismatch, and heat-induced substrate phase transition, the controllable and device-compatible strain engineering of halide perovskites by chemical epitaxy remains a challenge, owing to the absence of suitable lattice-mismatched epitaxial substrates.

First-principles studies of polar perovskite KTaO surfaces: structural reconstruction, charge compensation, and stability diagram.

Polar perovskite oxides are of considerable interest for developing advanced functional materials with exceptional electronic properties for their unique polar characters. A cleavage of polar perovskite oxides along the charged layers leads to an electrostatic instability on the cleaved surfaces, and a charge compensation is required to stabilize these surfaces. In this work, we have systemically studied 25 types of surface models of polar KTaO3 perovskite oxide, including (001), (110), and (111) surfaces with various types of surface terminations, using first-principles electronic structure calculations.

Tuning Interfacial Magnetic Ordering via Polarization Control in Ferroelectric SrTiO/PbTiO Heterostructure.

The electromagnetic properties at the interface of heterostructure are sensitive to the interfacial crystal structure and external field. For example, the two-dimensional magnetic states at the interface of LaAlO/SrTiO are discovered and can further be controlled by electric field. Here, we study two types of heterostructures, TiO/PbTiO and SrTiO/PbTiO, using first-principle electronic structure calculations.

Size effects and odd-even effects in MoS nanosheets: first-principles studies.

Molybdenum disulfide (MoS) nanostructures have been widely used as catalysts in the petroleum refinery industry for the hydrodesulfurization process, in which sulfur vacancies play a critical role in determining the catalytic activity. Here we report size effects and odd-even effects on the formation of sulfur vacancies in the triangular MoS nanosheets using first-principles calculations. By modeling four types of edge structures of MoS nanosheets, S-terminated edges are found to be energetically more favorable than Mo-terminated edges, and are then selected for studying energetics of sulfur vacancies.

Comparison Studies of Interfacial Electronic and Energetic Properties of LaAlO/TiO and TiO/LaAlO Heterostructures from First-Principles Calculations.

By using first-principles electronic structure calculations, we studied electronic and energetic properties of perovskite oxide heterostructures with different epitaxial growth order between anatase TiO and LaAlO. Two types of heterostructures, i.e.

Interfacial Multiferroics of TiO/PbTiO Heterostructure Driven by Ferroelectric Polarization Discontinuity.

Novel phenomena appear when two different oxide materials are combined together to form an interface. For example, at the interface of LaAlO/SrTiO, two-dimensional conductive states form to avoid the polar discontinuity, and magnetic properties are found at such an interface. In this work, we propose a new type of interface between two nonmagnetic and nonpolar oxides that could host a magnetic state, where it is the ferroelectric polarization discontinuity instead of the polar discontinuity that leads to the charge transfer, forming the interfacial magnetic state.

High-mobility two-dimensional electron gas in SrGeO- and BaSnO-based perovskite oxide heterostructures: an ab initio study.

We explored the possibility of producing a high-mobility two-dimensional electron gas (2DEG) in the LaAlO/SrGeO and LaGaO/BaSnO heterostructures using first-principles electronic structure calculations. Our results show that the 2DEG occurs at n-type LaAlO/SrGeO and LaGaO/BaSnO interfaces. Compared to the prototype LaAlO/SrTiO, LaAlO/SrGeO and LaGaO/BaSnO systems yield comparable total interfacial charge carrier density but much lower electron effective mass (nearly half the value of LaAlO/SrTiO), thus resulting in about twice larger electron mobility and enhanced interfacial conductivity.

First-Principles Prediction of Two-Dimensional Electron Gas Driven by Polarization Discontinuity in Nonpolar/Nonpolar AHfO/SrTiO (A = Ca, Sr, and Ba) Heterostructures.

By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) in nonpolar/nonpolar AHfO/SrTiO (A = Ca, Sr, and Ba) heterostructures. Two types of nonpolar/nonpolar interfaces, (AO)/(TiO) and (HfO)/(SrO), each with AO and HfO surface terminations, are modeled, respectively. The polarization domain and resulting interfacial electronic property are found to be more sensitive to the surface termination of the film rather than the interface model.

High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Polar/Nonpolar Perovskite Oxide Heterostructures.

The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO and SrTiO (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests.

Creating Two-Dimensional Electron Gas in Polar/Polar Perovskite Oxide Heterostructures: First-Principles Characterization of LaAlO3/A(+)B(5+)O3.

By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) at the polar/polar (LaO)(+)/(BO2)(+) interface in the LaAlO3/A(+)B(5+)O3 (A = Na and K, B = Nb and Ta) heterostructures (HS). Unlike the prototype polar/nonpolar LaAlO3/SrTiO3 HS system where there exists a least film thickness of four LaAlO3 unit cells to have an insulator-to-metal transition, we found that the polar/polar LaAlO3/A(+)B(5+)O3 HS systems are intrinsically conducting at their interfaces without an insulator-to-metal transition. The interfacial charge carrier densities of these polar/polar HS systems are on the order of 10(14) cm(-2), much larger than that of the LaAlO3/SrTiO3 system.

Polarization effects on the interfacial conductivity in LaAlO3/SrTiO3 heterostructures: a first-principles study.

We studied the influence of uniaxial [100] strain (-1% to +1%) on the electron transport properties of a two-dimensional electron gas (2DEG) at the n-type interface of the LaAlO3/SrTiO3(LAO/STO) heterostructure (HS)-based slab system from the perspective of polarization effects via first-principles density functional theory calculations. We first analyzed the unstrained system, and found that the induced polarization toward the vacuum in the LAO film leads to a small charge carrier density on the order of 10(13) cm(-2) (less than the theoretical value of 3.3 × 10(14) cm(-2) from the superlattice-model-based polar catastrophe mechanism), which is in excellent agreement with the experimental values of oxygen-annealed LAO/STO HS samples.

Creating Two-Dimensional Electron Gas in Nonpolar/Nonpolar Oxide Interface via Polarization Discontinuity: First-Principles Analysis of CaZrO3/SrTiO3 Heterostructure.

We studied strain-induced polarization and resulting conductivity in the nonpolar/nonpolar CaZrO3/SrTiO3 (CZO/STO) heterostructure (HS) system by means of first-principles electronic structure calculations. By modeling four types of CZO/STO HS-based slab systems, i.e.

Energetic stability, oxidation states, and electronic structure of Bi-doped NaTaO3: a first-principles hybrid functional study.

We studied the defect formation energies, oxidation states of the dopants, and electronic structures of Bi-doped NaTaO3 using first-principles hybrid density functional theory calculations. Three possible structural models, including Bi-doped NaTaO3 with Bi at the Na site (Bi@Na), with Bi at the Ta site (Bi@Ta), and with Bi at both Na and Ta sites [Bi@(Na,Ta)], are constructed. Our results show that the preferred doping sites of Bi are strongly related to the preparation conditions of NaTaO3.

Nb and Ta layer doping effects on the interfacial energetics and electronic properties of LaAlO3/SrTiO3 heterostructure: first-principles analysis.

The two-dimensional electron gas (2DEG) formed at the n-type (LaO)(+1)/(TiO2)(0) interface in the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) has emerged as a prominent research area because of its great potential for nanoelectronic applications. Due to its practical implementation in devices, desired physical properties such as high charge carrier density and mobility are vital. In this respect, 4d and 5d transition metal doping near the interfacial region is expected to tailor electronic properties of the LAO/STO HS system effectively.

Interface Energetics and Charge Carrier Density Amplification by Sn-Doping in LaAlO3/SrTiO3 Heterostructure.

Tailoring the two-dimensional electron gas (2DEG) at the n-type (TiO2)(0)/(LaO)(+1) interface between the polar LaAlO3 (LAO) and nonpolar SrTiO3 (STO) insulators can potentially provide desired functionalities for next-generation low-dimensional nanoelectronic devices. Here, we propose a new approach to tune the electronic and magnetic properties in the n-type LAO/STO heterostructure (HS) system via electron doping. In this work, we modeled four types of layer doped LAO/STO HS systems with Sn dopants at different cation sites and studied their electronic structures and interface energetics by using first-principles electronic structure calculations.