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Abstract Advances in solid-state ionic materials theory, synthesis, characterization, and simulation over the past century have enabled development of quantitative frameworks and descriptors to describe defect populations, transport, and interfacial reactions that approximate observable behavior in dilute, crystalline compositions near equilibrium. Increasing development of nondilute, disordered, or extended-defect-laden materials, and new operating conditions further from equilibrium, particularly in emerging energy, manufacturing, and information contexts, motivate development of new theoretical frameworks. This article provides an overview of computational and experimental advances in understanding defect-mediated behavior in ionic materials for batteries, fuel/electrolysis cells, sensors, thermochemical reactors, artificial synapses, ionic nanomanufacturing, and related technologies. Topics include: (1) point defects in nondilute and complex solid-solution systems, (2) point-defect populations and transport in and near extended defects, (3) defect equilibria and mobility in the excited state, (4) developing theories for ionic transport, including high-field effects and dynamic descriptors, and (5) emerging descriptors for surface reaction kinetics at intermediate-high temperatures. Graphical Abstract 

ABSTRACT Two‐dimensional (2D) materials have opened new pathways for 3D thin‐film crystal engineering by overcoming the intrinsic limitations of conventional heteroepitaxy. Their atomically thin van der Waals surfaces enable interfacial interactions fundamentally distinct from those in 3D material systems, allowing the realization of crystal lattices, strain states, defect properties, and reconfigurable architectures unattainable with conventional epitaxy. Despite this promise, a critical gap remains in understanding and harnessing the full potential of 2D‐mediated crystal engineering. Most studies have focused on thin film growth above 2D layers for enhancing the crystallinity and heterogeneous integrability, whereas the equally powerful regimes below and between 2D materials remain largely unexplored. Here, we introduce crystal engineering pathways spanning ‘above (3D on 2D)’, ‘below (3D beneath 2D)’, and ‘between (3D confined within 2D layers)’ 2D layers, highlighting how these regimes collectively enable new crystals and interfaces largely inaccessible through conventional growth techniques. Through a comprehensive analysis of underlying mechanisms, experimental demonstrations, and remaining challenges, we provide a perspective on unlocking the full potential of 2D‐mediated crystal engineering for thin‐film growth and extending it into new regimes of mixed‐dimensional heterostructures. 

ABSTRACT Ferroelectric charged domain walls (CDWs) offer emergent electronic states that can serve as functional elements in high‐density nonvolatile memory and neuromorphic computing. Yet, poor conductivity, structural instability, and lack of deterministic control limit their practical use. Moreover, the CDWs are typically out‐of‐plane and buried interfaces, which prohibits electrical access and prevents gate control of their carrier density. This work demonstrates the fabrication of artificial in‐plane CDWs by stacking oppositely polarized flakes of van der Waals (vdW) ferroelectric ‐In₂Se₃. Edge contact is utilized to electrically access the CDWs and integrate them into CDW‐based field‐effect transistors (CDW‐FETs). CDW‐FETs exhibit room‐temperature conductance up to four orders of magnitude higher than single domains, exceeding previously reported CDWs by 2–9 orders of magnitude. Electron microscopy imaging reveals atomic reconstruction and interfacial heterogeneity in CDWs. Temperature and gate‐dependent electrical and magneto‐transport measurements confirm that interfacial band bending governs transport. Two transport mechanisms are identified in these CDW‐FETs: variable‐range hopping and thermally activated traps, showing a transition temperature of 80 K. These results establish artificial CDWs as on‐demand, designable conductive channels in vdW ferroelectrics, advancing the understanding of CDW conduction mechanisms and bridging the gap toward device integration. 

Abstract MoTe₂possesses two polymorphs: semiconducting (2H) and semi‐metallic (1T') phases, separated by a small energy barrier. The 1T' phase of MoTe₂provides an excellent platform for forming low‐resistance contacts with the 2H phase, where the low density of states in the semimetal suppresses metal‐induced gap states (MIGS) and reduces Fermi‐level pinning. However, existing fabrication methods encounter significant challenges in location control, contact quality, and device scaling. In this work, a new method is developed to synthesize 1T'‐2H heterophase structures using chemical vapor deposition (CVD). By depositing pre‐patterned molybdenum, seamless in‐plane 1T'‐2H MoTe₂heterophase junctions are synthesized in a single‐step process, achieving precise control over the location of each phase and uniform MoTe₂coverage across centimeter‐scale surfaces. Field‐effect transistors incorporating 1T' MoTe₂contacts and 2H MoTe₂channels show p‐type dominant transfer characteristics and exceptionally low contact resistance. The unique attributes of these 1T' MoTe₂contacts, including pristine interfaces, reduced Schottky barrier heights, and seamless edge contacts, combined with the pronounced ambipolarity of the grown 2H MoTe₂, demonstrate the commercial viability of this process for 2D transistors, addressing the long‐standing challenge of contact resistance in 2D transistor technology. 

Abstract In materials science, chiral perovskites stand out due to their exceptional optoelectronic properties and the versatility in their structure and composition, positioning them as crucial in the advances of technologies in spintronics and chiroptical systems. This review underlines the critical role of synthesizing and growing these materials, a process integral to leveraging their complex interplay between structural chirality and distinctive optoelectronic properties, including chiral-induced spin selectivity and chiroptical activity. The paper offers a comprehensive summary and discussion of the methods used in the synthesis and growth of chiral perovskites, delving into extensive growth techniques, fundamental mechanisms, and strategic approaches for the engineering of low-dimensional perovskites, alongside the creation of novel chiral ligands. The necessity of developing new synthetic approaches and maintaining precise control during the growth of chiral perovskites is emphasized, aiming to enhance their structural chirality and boost their efficiency in spin and chiroptical selectivity. 

Abstract Mixed‐conducting perovskites are workhorse electrochemically active materials, but typical high‐temperature processing compromises their catalytic activity and chemo‐mechanical integrity. Low‐temperature pulsed laser deposition of amorphous films plus mild thermal annealing is an emerging route to form homogeneous mixed conductors with exceptional catalytic activity, but little is known about the evolution of the oxide‐ion transport and transference numbers during crystallization. Here the coupled evolution of ionic and electronic transport behavior and structure in room‐temperature‐grown amorphous (La,Sr)(Ga,Fe)O_3‐xfilms as they crystallize is explored.In situ ac‐impedance spectroscopy with and without blocking electrodes, simultaneous capturingsynchrotron‐grazing‐incidence X‐ray diffraction, dc polarization, transmission electron microscopy, and molecular dynamics simulations are combined to evaluate isothermal and non‐isothermal crystallization effects and the role of grain boundaries on transference numbers. Ionic conductivity increases by ≈2 orders of magnitude during crystallization, with even larger increases in electronic conductivity. Consequently, as crystallinity increases, LSGF transitions from a predominantly ionic conductor to a predominantly electronic conductor. The roles of evolving lattice structural order, microstructure, and defect chemistry are examined. Grain boundaries appear relatively nonblocking electronically but significantly blocking ionically. The results demonstrate that ionic transference numbers can be tailored over a wide range by tuning crystallinity and microstructure without having to change the cation composition. 

Abstract Source/Drain extension doping is crucial for minimizing the series resistance of the ungated channel and reducing the contact resistance of field‐effect transistors (FETs) in complementary metal–oxide–semiconductor (CMOS) technology. 2D semiconductors, such as MoS₂and WSe₂, are promising channel materials for beyond‐silicon CMOS. A key challenge is to achieve extension doping for 2D monolayer FETs without damaging the atomically thin material. This work demonstrates extension doping with low‐resistance contacts for monolayer WSe₂p‐FETs. Self‐limiting oxidation transforms a bilayer WSe₂into a hetero‐bilayer of a high‐work‐function WO_xSe_yon a monolayer WSe₂. Then, damage‐free nanolithography defines an undoped nano‐channel, preserving the high on‐current of WO_xSe_y‐doped FETs while significantly improving their on/off ratio. The insertion of an amorphous WO_xSe_yinterlayer under the contacts achieves record‐low contact resistances for monolayer WSe₂over a hole density range of 10¹²to 10¹³cm⁻²(1.2 ± 0.3 kΩ µm at 10¹³cm⁻²). The WO_xSe_y‐doped extension exhibits a sheet resistance as low as 10 ± 1 kΩ □⁻¹. Monolayer WSe₂p‐FETs with sub‐50 nm channel lengths reach a maximum drain current of 154 µA µm⁻¹with an on/off ratio of 10⁷–10⁸. These results define strategies for nanometer‐scale selective‐area doping in 2D FETs and other 2D architectures. 

Abstract The ongoing reduction in transistor sizes drives advancements in information technology. However, as transistors shrink to the nanometer scale, surface and edge states begin to constrain their performance. 2D semiconductors like transition metal dichalcogenides (TMDs) have dangling‐bond‐free surfaces, hence achieving minimal surface states. Nonetheless, edge state disorder still limits the performance of width‐scaled 2D transistors. This work demonstrates a facile edge passivation method to enhance the electrical properties of monolayer WSe₂nanoribbons, by combining scanning transmission electron microscopy, optical spectroscopy, and field‐effect transistor (FET) transport measurements. Monolayer WSe₂nanoribbons are passivated with amorphous WO_xSe_yat the edges, which is achieved using nanolithography and a controlled remote O₂plasma process. The same nanoribbons, with and without edge passivation are sequentially fabricated and measured. The passivated‐edge nanoribbon FETs exhibit 10 ± 6 times higher field‐effect mobility than the open‐edge nanoribbon FETs, which are characterized with dangling bonds at the edges. WO_xSe_yedge passivation minimizes edge disorder and enhances the material quality of WSe₂nanoribbons. Owing to its simplicity and effectiveness, oxidation‐based edge passivation could become a turnkey manufacturing solution for TMD nanoribbons in beyond‐silicon electronics and optoelectronics. 

Abstract Two-dimensional van der Waals materials such as graphene present an opportunity for band structure engineering using custom superlattice potentials. In this study, we demonstrate how self-assemblies of magnetic iron-oxide (Fe₃O₄) nanospheres stacked on monolayer graphene generate a proximity-induced magnetic superlattice in graphene and modify its band structure. Interactions between the nanospheres and the graphene layer generate superlattice Dirac points in addition to a gapped energy spectrum near the K and K′ valleys, resulting in magnetic confinement of quasiparticles around the nanospheres. This is evidenced by gate-dependent resistance oscillations, observed in our low temperature transport measurements, and confirmed by self-consistent tight binding calculations. Furthermore, we show that an external magnetic field can tune the magnetic superlattice potential created by the nanospheres, and thus the transport characteristics of the system. This technique for magnetic-field-tuned band structure engineering using magnetic nanostructures can be extended to a broader class of 2D van der Waals and topological materials.