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 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.

Fe5GeTe2 single crystals can be divided into nonquenched (NQ) and quench-cooled (QC) phases with different magnetic properties. A comprehensive understanding of the magnetic property variations in the NQ and QC phases is imperative for guiding Fe5GeTe2 towards spintronics applications; however, it remains elusive. Here, we report a real-space study on the structural and magnetic properties of these two magnetic phases using cryogenic magnetic force microscopy and scanning tunneling microscopy. The thermal history introduces disorder and order to the Fe(1) sites, resulting in the NQ and QC phases exhibiting global and broken inversion symmetry, respectively. The observed magnetic domain transitions (branching to labyrinthine) in the spin reorientation process and the distinct 3D spin textures stabilized by magnetic dipolar interaction observed in field-dependent studies allow the NQ phase to exhibit a more resilient global magnetic state. In contrast, the QC phase exhibits enhanced magnetic anisotropy, resulting in a higher TC. Meanwhile, the Dzyaloshinskii-Moriya interaction (DMI) introduced by the broken inversion symmetry causes the QC phase to exhibit a localized magnetic state: no domain transformation occurs during spin reorientation, and irregular domain states are observed in field-related studies. Our work provides an important reference for understanding the complex magnetic properties in Fe5GeTe2.

Atom tracking technology enhanced with innovative algorithms has been implemented in this study, utilizing a comprehensive suite of controllers and software independently developed domestically. Leveraging an on-board field-programmable gate array (FPGA) with a core frequency of 100 MHz, our system facilitates reading and writing operations across 16 channels, performing discrete incremental proportional-integral-derivative (PID) calculations within 3.4 microseconds. Building upon this foundation, gradient and extremum algorithms are further integrated, incorporating circular and spiral scanning modes with a horizontal movement accuracy of 0.38 pm. This integration enhances the real-time performance and significantly increases the accuracy of atom tracking. Atom tracking achieves an equivalent precision of at least 142 pm on a highly oriented pyrolytic graphite (HOPG) surface under room temperature atmospheric conditions. Through applying computer vision and image processing algorithms, atom tracking can be used when scanning a large area. The techniques primarily consist of two algorithms: the region of interest (ROI)-based feature matching algorithm, which achieves 97.92% accuracy, and the feature description-based matching algorithm, with an impressive 99.99% accuracy. Both implementation approaches have been tested for scanner drift measurements, and these technologies are scalable and applicable in various domains of scanning probe microscopy with broad application prospects in the field of nanoengineering.

Quantum materials with tunable correlated and/or topological electronic states, such as the electronic Kagome lattice, provide an ideal platform to study the exotic quantum properties. However, the real-space investigations on the correlated electronic Kagome lattice have been rarely reported. Herein, we report on the electronic Kagome lattice emerging in the correlated charge-density-wave (CDW) state of 1T-TaS$_2$ at ~200 K via variable-temperature scanning tunneling microscopy (VT-STM). This emergent Kagome lattice can be considered a fractional electron-filling superstructure with reduced translational and rotational symmetries, confirmed by STM measurements and density functional theory simulations. The characteristic band structure and density of states of this electronic Kagome lattice are further explored based on theoretical calculations. Our results demonstrate a self-organized electronic Kagome lattice from the correlated CDW state via the effective tuning parameter of temperature and provide a platform to directly explore the interplay of correlated electrons and topological physics.

We developed a new scheme for cryogen-free cooling down to sub-3 K temperature range and ultra-low vibration level. An ultra-high-vacuum cryogen-free scanning probe microscope (SPM) system was built based on the new scheme. Instead of mounting a below-decoupled cryocooler directly onto the system, the new design was realized by integrating a Gifford-McMahon cryocooler into a separate liquefying chamber, providing two-stage heat exchangers in a remote way. About 10 L of helium gas inside the gas handling system was cooled, liquefied in the liquefying chamber, and then transferred to a continuous-flow cryostat on the SPM chamber through an ∼2 m flexible helium transfer line. The exhausted helium gas from the continuous-flow cryostat was then returned to the liquefying chamber for reliquefaction. A base temperature of ∼2.84 K at the scanner sample stage and a temperature fluctuation of almost within ±0.1 mK at 4 K were achieved. The cooling curves, tunneling current noise, variable-temperature test, scanning tunneling microscopy and non-contact atomic force microscopy imaging, and first and second derivatives of I(V) spectra are characterized to verify that the performance of our cryogen-free SPM system is comparable to the bath cryostat-based low-temperature SPM system. This remote liquefaction close-cycle scheme shows conveniency to upgrade the existing bath cryostat-based SPM system, upgradeability of realizing even lower temperature down to sub-1 K range, and great compatibility of other physical environments, such as high magnetic field and optical accesses. We believe that the new scheme could also pave a way for other cryogenic applications requiring low temperature but sensitive to vibration.

Polymorphic structures of transition metal dichalcogenides (TMDs) host exotic electronic states, like charge density wave and superconductivity. However, the number of these structures is limited by crystal symmetries, which poses a challenge to achieving tailored lattices and properties both theoretically and experimentally. Here, we report a coloring-triangle (CT) latticed MoTe 2 monolayer, termed CT-MoTe 2 , constructed by controllably introducing uniform and ordered mirror-twin-boundaries into a pristine monolayer via molecular beam epitaxy. Low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) together with theoretical calculations reveal that the monolayer has an electronic Janus lattice, i.e., an energy-dependent atomic-lattice and a Te pseudo-sublattice, and shares the identical geometry with the Mo 5 Te 8 layer. Dirac-like and flat electronic bands inherently existing in the CT lattice are identified by two broad and two prominent peaks in STS spectra, respectively, and verified with density-functional-theory calculations. Two types of intrinsic domain boundaries were observed, one of which maintains the electronic-Janus-lattice feature, implying potential applications as an energy-tunable electron-tunneling barrier in future functional devices.

The layered transition metal dichalcogenide 1T -TaS2 has evoked great interest owing to its particularly rich electronic phase diagram including different charge density wave (CDW) phases. However, few studies have focused on its hysteretic electronic phase transitions based on the in-depth discussion of the delicate interplay among temperature-dependent electronic interactions. Here, we report a sequence of spatial electronic phase transitions in the hysteresis temperature range (160-230 K) of 1T-TaS2 via variable-temperature scanning tunneling microscopy. Several emergent electronic states are investigated at multiscale during the commensurate CDW-triclinic CDW (CCDW-TCDW) phase transitions: a spotty-CDW state above similar to 160 K, a network-CDW (NCDW) state above similar to 180 K during the warmup process, a belt-TCDW state below similar to 230 K, a NCDW state below similar to 200 K, and finally a mosaic-CDW state below similar to 160 K during cooldown from the TCDW phase. These emergent electronic states are associated with the delicate temperature-dependent competition and/or cooperation of stacking-dependent interlayer interactions, intralayer electron-electron correlations, and electron-phonon (e-ph) coupling of 1T-TaS2. Our results not only provide insight to understand the hysteretic electronic phase transitions in the correlated CDW state, but also pave a way to realize more exotic quantum states by accurately and effectively tuning various interior interactions in correlated materials.

Strain engineering plays a crucial role in controlling thephysical properties of two-dimensional (2D) materials. However, themechanical behavior of stressed 2D crystals has not been fully understood.In this study, the fracture behavior and accompanying properties of astrained single-crystal monolayer WS2of submicron scale were investigatedusing a theoretical-experimental joint study. After thermal strain, the WS2monolayer was split into different forms by several cracks, with the cause ofthe crack formation being studied usingfinite element analysis (FEA). Thecracks were initiated from the vertex of the nucleation center, extendingalong the stronger von Mises stress isolines and terminating at the edges ofthe monolayers. Within the separate sections, ripple regions were observed,forming several typical nanopatterns. The band gap, frictional, viscosity,and elasticity characteristics of the different strain regions were alsoinvestigated. The nanopattern should enableflexibility in the design of more sophisticated devices based on 2D materials.

Recently, many exotic electronic states, such as quantum spin liquid (QSL) and superconductivity (SC), have been extensively discovered and introduced in layered transition metal dichalcogenides 1T-TaS2 by controlling their complex correlated charge-density-wave (CDW) states. However, few studies have focused on its hysteretic electronic phase transitions based on the in-depth discussion of the delicate interplay among temperature-dependent electronic interactions. Here, we reported a sequence of spatial electronic phase transitions in the hysteresis temperature range of 1T-TaS2 via variable-temperature scanning tunneling microscopy (VT-STM). The emergence, evolution, coexistence, and separation of diverse novel electronic states within the commensurate CDW/triclinic CDW (CCDW/TCDW) phase are investigated in detail through the warming/cooling process. These novel emergent electronic states can be attributed to the delicate temperature-dependent competition and/or cooperation of interlayer interactions, intralayer electron-electron correlation, and electron-phonon (e-ph) coupling of 1T-TaS2. Our results not only provide a novel insight to understand the hysteretic electronic phase transitions of correlated CDW state, but also pave a way to realize more exotic quantum states by accurately and effectively controlling various interactions in correlated materials.

Electronic properties of superatomic crystals have not been sufficiently explored due to the versatility of their building units; moreover, their interunit couplings are even poorly understood. Here, we present a joint experiment-theory investigation of a rationally designed layered superatomic crystal of Au6Te12Se8 (ATS) cubes stacked by noncovalent intercube quasibonds. We find a sequential-emerged anisotropic triple-cube charge density wave (TCCDW) and polarized metallic states below 120 K, as revealed via scanning tunneling microscopy and spectroscopy, angle-resolved photoemission spectroscopy, transport measurement, Raman spectra, and density-functional theory. The polarized states are locked in an antiparallel configuration, which is required for maintaining the inversion symmetry of the center cube in the TCCDW. The antipolar metallic states are thus interweaved by the CDW and the polarized metallic states, and primarily ascribed to electronic effects via theoretical calculations. This work not only demonstrates a microscopic picture of the interweaved CDW and polarized charge orders in the superatomic crystal of ATS, but also sheds light on expanding the existing category of quantum materials to noncovalent solids.

Synthesis of emergent crystals is the foundation of discovering novel phenomena and exploring intriguing properties. Comparing to the diverse exotic quantum states of covalent crystals, the unique super-atomic crystals are far from being extensively investigated in the case of their versatile superatoms (building blocks) and inter-superatom coupling (non-covalent interactions). Here, we investigate the correlated electronic structures in the layered super-atomic crystal of AuTe2Se4/3 (ATS), which can be assumed as three-dimensional triclinic stacking of the cube super-atoms (Au6Te12Se8, 0D) with the anisotropic covalent-like inter-cube Te...Te bonds. The sequential-emerged anisotropic triple CDW charge modulation, antipolar charge orders and quasi-2D Fermi surface were discovered in ATS using scanning tunneling microscopy/spectroscopy (STM/STS) in combination with angle-resolved photoemission spectroscopy (ARPES), transport measurement and Raman spectra. DFT calculations disclose the emerging and correlation mechanism of CDW and antipolar charge orders via the unique layered super-atomic crystal geometry and electronic structures. This work not only provides an unprecedented microscopic picture of novel electronic phase in the ATS, but also suggests a new category of super-atom layered materials with manipulatable properties through their high and precise tunability of super-atomic units and inter-unit interactions.

Surface ripple, as an important factor of corrugations in two-dimensional (2D) atomic crystals, plays important roles in determining their mechanical and physical properties. Here, we systematically investigated the strain-engineered rippling structure and manipulation of the rippling domain in monolayer WS2 flakes via atomic force microscopy (AFM). The rippling structure was introduced by the in-plane compression applied through the underlying SiO2/Si substrate during the rapid cooling process of post-growth. The zigzag-orientated rippling domains with three-equivalent directions were visualized by transverse shear microscopy (TSM) and friction force microscopy and further determined via angle-dependent TSM. Furthermore, these rippling domains can be precisely manipulated by controlling the AFM scanning, and various rippling patterns were formed by the AFM lithography. The manipulation mechanisms were phenomenally discussed based on their strain-induced anisotropic mechanical properties, the film-substrate mechanical model, and the dynamic strain-induced anisotropic puckering effects. Our study will be beneficial in understanding and controlling not only the rippling structures but also the rippling-related electronic and optical properties of 2D materials.

The interplay of symmetry-breaking ordered states, such as superconductivity, charge density waves (CDW), magnetism and pseudogap, is a fundamental issue in correlated system. CDW and antiferromagnetism often coexist in the proximity of phase diagram region in cuprates. It is also worthy nothing that different order states appear in a situation on comparable temperature scales, so these orders are intertwined and competing on the same footing. The magnetism of vdW material Fe 5- x GeTe 2 with the one of the highest reported bulk Curie temperatures, is found to be sensitive to thermal history and external magnetic field. However, the temperature-dependent magnetization with two characteristic points still lacks a unified picture to describe. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy, magnetic properties measurements, and the first-principles calculations, the complex yet intriguing magnetic behaviors are gradually unveiled. A competition mechanism between charge order and ferromagnetism is proposed and firmly observed by experimental measurements. As the ferromagnetic order strengthens at low temperature, the charge order will be suppressed. Exchange splitting in itinerant ferromagnetism plays a significant role in the temperature evolution of band structure and causes a Lifshitz transition, which provides more control means to realize novel devices at room temperature.

The strain has been employed for controlled modification of electronical and mechanical properties of two-dimensional (2D) materials. However, the thermal strain-engineered behaviors of the CVD-grown MoS2 have not been systematically explored. Here, we investigated the strain-induced structure and properties of CVD-grown triangular MoS2 flakes by several advanced atomic force microscopy. Two different kinds of flakes with sharp-corner or vein-like nanostructures are experimentally discovered due to the size-dependent strain behaviors. The critical size of these two kinds of flakes can be roughly estimated at ∼17 μm. Within the small flakes, the sharp-corner regions show specific strain-modified properties due to the suffering of large tensile strain. While in the large MoS2 flakes, the complicated vein-like nanoripple structures were formed due to the interface slipping process under the larger tensile strain. Our work not only demonstrates the size-specific strain behaviors of MoS2 flakes but also sheds light on the artificial design and preparation of strain-engineered nanostructures for the devices based on the 2D materials.

The bismuth-antimony (Bi-Sb) alloys with some specific Sb concentrations are three-dimensional topological insulators (3D TIs). For the thin Bi-Sb alloy films, the quantum confinement effect can suppress the bulk conduction channels and enhance the transport of the topological surface states. However, the fabrication of Bi-Sb films is still challenging. Here, we have successfully prepared the Bi-Sb alloy films by surface Bi-alloying of the epitaxial Sb nanofilm on highly oriented pyrolytic graphite (HOPG) substrate. The morphology, atomic structure, and electronic structure of the Bi-Sb alloy films were characterized by a combination of scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning tunneling microscopy/spectroscopy (STM/STS). The formation of hexagonal Bi-Sb surface alloy was confirmed by the atomic-resolution STM images. The quantum-well states (QWS) were directly observed in the STS spectra of Bi-Sb films due to the strong quantum confinement effect. The standing-wave patterns of QWS are further observed in the real-space spectra maps. Our work suggests a promising route to fabricate Bi-Sb alloy films and lays the foundation for further exploring their topological electronic structures.

Transition-metal chalcogenides (TMCs) materials have attracted increasing interest both for fundamental research and industrial applications. Among all these materials, two-dimensional (2D) compounds with honeycomb-like structure possess exotic electronic structures. Here, we report a systematic study of TMC monolayer AgTe fabricated by direct depositing Te on the surface of Ag(111) and annealing. Few intrinsic defects are observed and studied by scanning tunneling microscopy, indicating that there are two kinds of AgTe domains and they can form gliding twin-boundary. Then, the monolayer AgTe can serve as the template for the following growth of Te film. Meanwhile, some Te atoms are observed in the form of chains on the top of the bottom Te film. Our findings in this work might provide insightful guide for the epitaxial growth of 2D materials for study of novel physical properties and for future quantum devices.

The ultrathin β-Sn(001) films have attracted tremendous attention owing to its topological superconductivity (TSC), which hosts Majorana bound state (MBSs) for quantum computation. Recently, β-Sn(001) thin films have been successfully fabricated via phase transition engineering. However, the understanding of structural phase transition of β-Sn(001) thin films is still elusive. Here, we report the direct growth of ultrathin β-Sn(001) films epitaxially on the highly oriented pyrolytic graphite (HOPG) substrate and the characterization of intricate structural-transition-induced superstructures. The morphology was obtained by using atomic force microscopy (AFM) and low-temperature scanning tunneling microscopy (STM), indicating a structure-related bilayer-by-bilayer growth mode. The ultrathin β-Sn film was made of multiple domains with various superstructures. Both high-symmetric and distorted superstructures were observed in the atomic-resolution STM images of these domains. The formation mechanism of these superstructures was further discussed based on the structural phase transition of β to α-Sn at the atomic-scale thickness. Our work not only brings a deep understanding of the structural phase transition of Sn film at the two-dimensional limit, but also paves a way to investigate their structure-sensitive topological properties.

Nanocontact properties of two-dimensional (2D) materials are closely dependent on their unique nanomechanical systems, such as the number of atomic layers and the supporting substrate. Here, we report a direct observation of toplayer-dependent crystallographic orientation imaging of 2D materials with the transverse shear microscopy (TSM). Three typical nanomechanical systems, MoS2 on the amorphous SiO2/Si, graphene on the amorphous SiO2/Si, and MoS2 on the crystallized Al2O3, have been investigated in detail. This experimental observation reveals that puckering behaviour mainly occurs on the top layer of 2D materials, which is attributed to its direct contact adhesion with the AFM tip. Furthermore, the result of crystallographic orientation imaging of MoS2/SiO2/Si and MoS2/Al2O3 indicated that the underlying crystalline substrates almost do not contribute to the puckering effect of 2D materials. Our work directly revealed the top layer dependent puckering properties of 2D material, and demonstrate the general applications of TSM in the bilayer 2D systems.