Transition-metal dichalcogenides hosting multiple competing structural and electronic phases are thus ideal platforms for constructing polytype heterostructures with emergent quantum properties. However, controlling phase transitions to form diverse heterostructures inside a single crystal remains challenging. In this study, we realize vertical/lateral polytype heterostructures in a hole-doped Mott insulator via thermal annealing-induced structural transitions. Raman spectroscopy, atomic force microscopy and scanning Kelvin probe force microscopy confirm the coexistence of T-H polytype heterostructures. Atomic-scale scanning tunneling microscopy/spectroscopy measurements reveal the transparent effect in 1H/1T vertical heterostructures, where positive bias voltage induces in a pronounced superposition of the 13 & times;13 CDW of the 1T-layer on the 1H-layer. By systematically comparing the 1T/1H and 1T/1T interfaces, we demonstrate that the metallic 1H-layer induces a Coulomb screening effect on the 1T-layer, suppressing the formation of CDW domain walls and forming more ordered electronic states. These results clarify the interfacial coupling between distinct quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype heterostructures with tunable electronic properties.

Controlling mesoscale and nanoscale material structures and properties through self-organized atomic behavior is essential for atomic-scale manufacturing. However, direct and visual studies of the cross-scale effects of such atomic self-organization on mesoscopic structures remain scarce. Herein, we report the intertwined atomic-nanoscale-mesoscale structures via the intralayer Fe-chains in the sandwich-like layered FePd2Te2 crystal by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The hierarchical orthogonal corrugated morphologies are directly revealed and attributed to their chain-orientation-determined twinning-domain effect. Both Fe-chains of the middle-sublayer and two kinds of Te atoms of the top-sublayer are further atomically resolved, indicating the critical effects of Pd atoms/voids on the intralayer anisotropic Fe-chains and the interlayer structural alignment. The thermally induced and strain-related structural transitions of the surface layer are further investigated and discussed based on the proposed filling model of Pd-voids by the intralayer Pd atoms. Our work not only provides a deep understanding of this exotic layered magnetic material but also will inspire more perspectives for tailoring its anisotropic atomic-to-mesoscale structures and properties.

The delicate interfacial conditions and behaviors play critical roles in determining the valuable physical properties of two-dimensional materials and their heterostructures on substrates. However, directly probing these complex interfacial conditions remains challenging. Here, we reveal the coupled in-plane strain and out-of-plane bonding conditions in strain-engineered WS2 flakes by combining dual-harmonic electrostatic force microscopy (DH-EFM) and scanning microwave impedance microscopy (sMIM). A striking contradiction is observed between the compressive-strain-induced larger bandgap (lower electrical conductivity) detected by DH-EFM, and the enhanced conductivity probed by sMIM. Comparative measurements under different sMIM modes demonstrate that this contradiction originates from a tip-loading-force-induced dynamic puckering effect, which is governed by the interfacial bonding strength. Furthermore, the progressive accumulation and subsequent release of conductivity during forward/backward sMIM-contact scans further confirm this dynamic puckering behavior, revealing pronounced differences in interfacial conditions between the open-and closed-ring regions of WS2. This work establishes the correlation between electrical properties and interfacial conditions, and provides fundamental insights for interface-engineered devices.

Two-dimensional (2D) SnSe is an emerging 2D material exhibiting intriguing properties such as ferroelectricity and nonlinear optical responses. Here, high-quality single-crystalline SnSe nanosheets were synthesized via an NaCl-assisted chemical vapor deposition (CVD) method. NaCl acts as a nucleation promoter, markedly enhancing the nucleation density and surface coverage of the SnSe nanosheets while exerting little influence on their lateral size. The crystalline structure and composition of the as-grown nanosheets were characterized by XRD, Raman spectroscopy, and XPS. The ferroelectric domains in the SnSe nanosheets were directly visualized by piezoresponse force microscopy (PFM). The magnetic hysteresis loops of the SnSe nanosheets were measured at 2 K, which indicated weak ferromagnetism. A spin glass-like behavior was observed below 115 K, which is attributed to the presence of SnSe2 impurity. This work further establishes a controllable synthesis route for SnSe nanosheets, thereby paving the way for subsequent investigations of their ferroelectric properties.

Two-dimensional (2D) SnSe is an emerging 2D material exhibiting intriguing properties such as ferroelectricity and nonlinear optical response. Here, high-quality single-crystalline SnSe nanosheets were synthesized via NaCl-assisted chemical vapor deposition (CVD) method. The crystalline structure and composition of the nanosheets are confirmed by XRD, Raman spectroscopy, and XPS. Ferroelectric domains are directly observed in SnSe nanosheets using piezoresponse force microscopy (PFM). Magnetic measurements reveal a weak magnetic behavior with a Curie temperature of approximately 120 K. This work further establishes a controllable synthesis route for SnSe nanosheets, thereby paving the way for subsequent investigation of their multiferroic properties.

Fe3GeTe2, a two-dimensional (2D) van der Waals magnet with intrinsic long-range ferromagnetic ordering, has attracted great attention in recent years. However, the synthesis of large-area Fe3GeTe2 crystals by chemical vapor deposition (CVD) remains challenging, for it is difficult to control the reactions among three precursors. Herein, we demonstrate the growth of large-area van der Waals Fe3GeTe2 nanosheets via the subtractive element growth mechanism. Different from previous methods including three precursors, we selected GeTe and FeCl3 as precursors. The obtained nanosheets exhibit triangular or hexagonal shapes, with lateral sizes up to 162 μm and thicknesses down to 5.6 nm. XRD, Raman, HRTEM, and SAED were used to characterize the crystal structure and phase purity, while EDS, and XPS analyses further verified the chemical composition and valence states. Magnetic measurements reveal robust ferromagnetism with a Curie temperature of ∼230 K. This work establishes a feasible chemical strategy for the scalable preparation of 2D Fe3GeTe2, thereby advancing its prospects in spintronic applications.

Orbital-lattice coupling in transition-metal oxides is usually discussed within a given bonding framework, where orbital occupation is intertwined with local coordination, strain, or symmetry breaking. Here, we show that orbital occupation can also select the bonding framework itself, thereby determining structural dimensionality. Using first-principles calculations, we identify CrO as a prototype in which the single active 3d e_g electron of high-spin Cr^2+ gives rise to two competing orbital-structure states. The d_x^2-y^2 occupation favors a three-dimensionally connected covalent phase, whereas the d_z^2 occupation stabilizes a weakly coupled layered phase. Constrained-occupation calculations show that increasing the d_z^2 filling continuously contracts the in-plane lattice while expanding the structure along the layer normal. The two phases exhibit distinct magnetic ground states and ferroelastic responses. Moreover, the layered phase is robust against exchange-correlation functional and on-site (U) variations, remains dynamically stable down to the monolayer limit, and has a low exfoliation energy of 46 meV/Angstrom^2. Extending the analysis across related 3d binary oxides reveals a filling-dependence relation between accessible orbital filling and the preference for 2D or 3D connected bonding motifs, providing a microscopic basis for exploring low-dimensional oxide materials.

In this work, we systematically investigated temperature and time of substrate pre-annealing on the growth of GeTe nanosheets by chemical vapor deposition. It was found that thermal annealing in air was a useful way to reduce the density of nucleation site. As a result, the lateral size of nanosheets increased from similar to 5 mu m to similar to 30 mu m by increasing the temperature of pre-annealing. Meanwhile, the increasement of pre-annealing time increased lateral size from similar to 5 mu m to similar to 28 mu m. Furthermore, alpha-GeTe nanosheets hold room-temperature ferroelectric properties. This provides an effective method to control the growth of 2D ferroelectric materials on mica.

In recent years, kagome materials have attracted significant attention due to their rich emergent phenomena arising from the quantum interplay of geometry, topology, spin, and correlations. However, in the search for kagome materials, it has been found that bulk compounds with electronic properties related to the kagome lattice are relatively scarce, primarily due to the hybridization of kagome layers with adjacent layers. Therefore, researchers have shown increasing interest in the construction of two-dimensional (2D) kagome materials, aiming to achieve clean kagome bands near the Fermi level in monolayer or few-layer systems. Substantial advancements have already been made in this area. In this review, we summarize the current progress in the construction and development of 2D kagome lattices. We begin by introducing the geometric and electronic structures of the kagome lattice and its variants. This is followed by a discussion on the experimental realizations and electronic structure characterizations of 2D kagome materials. Finally, we provide an outlook on the future development of 2D kagome lattices.

Realizing room-temperature tunable skyrmionic objects in van der Waals ferromagnet offers unparalleled prospects for future spintronics. Here, we report an experimental investigation on the emergence and evolution of skyrmionic spin textures in the non-stoichiometric Fe3-xGaTe2 using magnetic force microscopy. The iron-deficiency-specific magnetic states of stripe, striped skyrmionium and striped skyrmion sack are observed. Through zero-field-cooling and field-cooling measurements, we observed distinct topological transitions and trivial transitions (distinguished by changes in topological charge) emerging during the stepwise evolution of topological spin textures, which enabled us to develop an evolution pathway model. Leveraging this model, the room-temperature stable composite topological spin textures of skyrmionium, skyrmion bag and sack states are further controllably realized via the exclusive topological-transition path (regulated by magnetic field and DMI intensity). Our work provides valuable insights into the room-temperature realization of topological spin textures in Fe3-xGaTe2, and inspires further exploration of their potential applications in heterostructure spintronics.

Increasing growth time and temperature promoted high supersaturation and induced wedding cake growth of β-GeSe 2 nanosheets.

Cr2Te3 has recently emerged as a new class of two-dimensional (2D) materials due to its inherent long-range ferromagnetic order. Here, we report the synthesis of 2D Cr2Te3 nanosheets from a GeTe precursor by a cation replacement reaction. During the reaction, Cr ions preferentially bind to Te ions and replace Ge along the c-axis of the lattice. When Cr-Te bonds are formed, the binding energy is reduced due to the lower electronegativity of Cr. After the Ge atoms are substituted by Cr atoms, we successfully synthesized Cr2Te3 instead of CrGeTe3. Cr2Te3 nanosheets show a triangular structure with a lateral size of up to 10 mu m and a thickness of about 2.2 nm. The structure of Cr Te-2(3) nanosheets was confirmed by XRD, Raman spectroscopy, and HRTEM. Cr2Te3 nanosheets exhibit robust magnetic behavior with a Curie temperature (T-C) of about 161 K. This cation replacement strategy promotes the development of Cr2Te3 and paves an effective way to fabricate 2D magnetic materials.

Strain engineering offers a compelling route to modulate magnetism in two-dimensional (2D) materials, yet most approaches rely on externally applied strain. An in-plane anisotropic 2D-layered ferromagnet FePd2Te2 provides a suitable platform to study intrinsic strain-magnetism coupling due to its twinning domains. Here, we report spatially modulated internal compressive/tensile(C/T) strain regions in FePd2Te2 and their strong impact on local magnetic properties in real space by using atomic/magnetic force microscopy (AFM/MFM) combined with scanning tunneling microscopy (STM). Field- and strain-dependent spin transformations reveal the modulation of its intrinsic C/T regions. Notably, C regions retain intact Fe zigzag chains and exhibit larger, abruptly switching magnetic moments, while T regions display fragmented chains with reduced, gradually rotating spins. The intrinsic strain-induced intact ferromagnetic (FM), field-induced polarized-FM states, and their transitions are comparatively discussed during magnetic measurements. Temperature- and field-dependent evolution are further investigated in the FM and paramagnetic (PM) states and summarized to obtain an H-T phase diagram of FePd2Te2. Our work provides key results for understanding real-space tunable magnetic states through internal structural heterogeneity and suggests potential strategies for manipulating intrinsic strain-engineered magnetic devices.

The delicate interplay among the complex intra/inter-layer electron-electron and electron-lattice interactions is the fundamental prerequisite of these exotic quantum states, such as superconductivity, nematic order, and checkerboard charge order. Here, we explore the filling-dependent multiple stable intertwined electronic and atomic orders of the flat-band state of 1T-TaS2 encompassing hole order, phase orders, coexisting left- and right-chiral orders, and mixed phase/chiral orders via scanning tunneling microscopy (STM). Combining first-principles calculations, the emergent electronic/atomic orders can be attributed to the weakening of electron-electron correlations and stacking-dependent interlayer interactions. Moreover, achiral intermediate ring-like clusters and nematic charge density wave (CDW) states are successfully realized in intralayer chiral domain wall and interlayer heterochiral stacking regions through chiral overlap configurations. Our study not only deepens the understanding of filling-dependent electronic/atomic orders in flat-band systems but also offers perspectives for exploring exotic quantum states in correlated electronic systems.

Two-dimensional (2D) non-van der Waals (vdW) Cr5Te8 has attracted widespread research interest for its air stability and thickness-dependent magnetic properties. However, the growth of large-scale ultrathin 2D Cr5Te8 remains challenging. Here, we selected GaTe powder as the precursor to supply Te monomers and fabricated submillimeter 2D Cr5Te8 nanosheets. By optimizing the growth temperature and source-substrate distance (D SS), we successfully achieved Cr5Te8 nanosheets with a lateral size of up to similar to 0.19 mm and corresponding thickness down to similar to 4.8 nm. The role of GaTe is to enhance the efficient Te atom concentration, which promotes the lateral growth of Cr5Te8 nanosheets. Furthermore, our findings reveal the appearance of Cr5Te8 nanosheets exhibiting serrated edges and a stacked structure like those of wedding cakes. Magnetic property measurement revealed the intense out-of-plane ferromagnetism in Cr5Te8, with a Curie temperature (T C) of 172 K. This work paves the way for the controllable growth of submillimeter ultrathin 2D ferromagnetic crystals and lays the foundation for the future synthesis of millimeter ultrathin ferromagnets.

One-dimensional (1D) chains offer unique opportunities for nanoelectronics and spintronics, yet their experimental realization remains challenging because 1D motifs are often thermodynamically disfavored relative to higher-dimensional phases. Here we present a high-throughput first-principles exploration of 1D single-atomic transition-metal chalcogenide and halide chains, screening 6,832 candidates constructed from binary combinations of 28 metals and 8 non-metals. To assess kinetic accessibility, we compare the formation energetics of 1D chains with competing two-dimensional polymorphs at the nucleation stage across relevant chemical-potential windows, using nucleation-stage thermodynamic selectivity as a proxy. This workflow identifies 183 kinetically accessible 1D chains. Interpretable machine-learning analysis reveals two simple stability descriptors as key drivers of 1D stabilization. The accessible chains exhibit diverse magnetic configurations with different magnetic characters. We further uncover their pronounced magnetoelastic couplings, exemplified by CrTe with giant magnetostriction reaching 5.93

Two-dimensional (2D) magnetic materials have predominantly exhibited easy-axis or easy-plane anisotropy and display a high sensitivity to the underlying crystal structure and lattice symmetry. Recently, an in-plane anisotropic 2D ferromagnet of FePd2Te2 has been discovered with intriguing structure and quasi-one-dimensional spin system. Here, we report a real-space investigation of its twinning structure and magnetic states using atomic/magnetic force microscopy (AFM/MFM) combined with scanning tunneling microscopy (STM). The atomic to mesoscale hierarchical structures with the orthogonal and corrugated compressive /tensile(C/T) regions are directly observed due to the intrinsic twinning-domain characteristic. The structure-related intact ferromagnetic (FM), field-induced polarized-FM states and their transitions are comparatively discussed at the mesoscale with the corresponding macroscopic magnetic measurements. Temperature- and field-dependent evolution of magnetic phase are further investigated at the FM and PM states, and summarized to obtain a unique H-T phase diagram of FePd2Te2. Our work provides key results for understanding the complicated magnetic properties of FePd2Te2, and suggests new directions for manipulating magnetic states through the atomic and mesoscale structure engineering.

The localized (particle-like) correlated electrons deserve particular attention as they govern various exotic quantum phenomena, such as quantum spin liquids, Wigner crystals, and Mott insulators in correlated systems. However, direct observation and manipulation of these particle-like electrons at the atomic or single-electron scale remain highly challenging. Here, we successfully realize and directly visualize particle-like correlated electrons in 1T-TaS2 through hole doping. The potential-dependent local electronic structure of single particle-like electron is revealed by angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) combined with theoretical calculations. The complex correlated interactions including nearest-neighbor attractive interactions and many-body repulsive interactions are further demonstrated and discussed based on the spatial distribution of particle-like electrons. Furthermore, the tentative manipulation of the particle-like electrons is successfully achieved by the energy-excitation mechanism. Our results not only provide profound insights into particle-like electrons in correlated systems, but also establish a versatile platform for designing and controlling quantum states at the atomic scale.

Although 2D self-intercalated Cr5Te8 has been successfully synthesized via chemical vapor deposition (CVD), its etching behavior remains largely unexplored. Etching, as the inverse process of material growth, is essential for understanding growth mechanisms and fabricating nanosheet patterns. Herein, we explore the anisotropic etching of 2D Cr5Te8 assisted by an excess Te supply. The etching process initiates from both the surface and the edge, creating distinct holes and nanoribbons with triangular or hexagonal shapes. To the best of our knowledge, this is the first report on controllable anisotropic etching patterns in 2D Cr5Te8. Furthermore, magnetic measurements reveal ferromagnetism in the etched nanosheets with a Curie temperature (T C) of 164 K, slightly lower than that of the unetched nanosheets. The etched nanosheets exhibit an enhanced saturated magnetic field of 38.5 kOe, approximately 3.2 times that of the unetched nanosheets. This enhancement in the saturated magnetic field is attributed to the pattern-induced strengthening of the reentrant stray field. This study offers a new direction for preparing patterned 2D materials and opens a novel avenue for modulating 2D magnetism.