Surface with well-defined components and structures possesses unique electronic, magnetic, optical and chemical properties. As a result, surface chemistry research plays a crucial role in various fields such as catalysis, energy, materials, quantum, and microelectronics. Surface science mainly investigates the correspondence between surface property and functionality. Scanning probe microscopy (SPM) techniques are important tools to characterize surface properties because of the capability of atomic-scale imaging, spectroscopy and manipulation at the single-atom level. In this review, we summarize recent advances in surface electronic, magnetic and optical properties characterized mainly by SPM-based methods. We focus on elucidating the π-magnetism in graphene-based nanostructures, construction of spin qubits on surfaces, topology properties of surface organic structures, STM-based light emission, tip-enhanced Raman spectroscopy and integration of machine learning in SPM studies.

X-ray photoelectron spectroscopy (XPS) is a widely used technique in material characterization, enabling the acquisition of chemical information by measuring the core-level electron binding energy (BE) of target elements. Theoretical simulations of XPS typically provide a streamlined and condition-free methodology for obtaining material XPS data. However, for iron-based systems, the complex magnetic properties, strong electron-electron correlation interactions, and the absence of standard sample pose a significant challenge to establish an efficient and accurate simulation approach. This work introduces a high-throughput framework designed for the standardization and efficient calculation of the Fe 2p core-level BE shifts. With this framework, the reliability of the theoretical method was comprehensively evaluated, encompassing an all-electron extension of the delta self-consistent field method and orbital energy approximation methods based on the pseudopotential. Furthermore, a series of standard samples of iron compounds were prepared under ultrahigh-vacuum conditions to provide measured XPS values as references to evaluate the theoretical simulations. Through this evaluation, the FSn method with the PBE functional was established as the most suitable for simulating XPS in iron-based materials, demonstrating a remarkable accuracy with an error of merely 0.02 eV. Our methodology offers a standardized approach for the analysis of iron compounds, laying the groundwork for quantitative analysis of more complex systems in future investigations.

Surface chemistry focuses on the investigation of the adsorption, migration, assembly, activation, reaction, and desorption of atoms and molecules at surfaces. Surface chemistry plays the pivotal roles in both fundamental science and applied technology. This review will summarize the recent progresses on surface assembly, synthesis and catalysis investigated mainly by scanning tunneling microscopy and atomic force microscopy. Surface assemblies of water and small biomolecules, construction of Sierpiński triangles and surface chirality are summarized. On-surface synthesis of conjugated carbo- and heterocycles and other kinds of carbon nanostructures are surveyed. Surface model catalysis, including single-atom catalysis and electrochemical catalysis, are discussed at the single-atom level.

Cryo-electron microscopy (cryo-EM) has been widely used to reveal the structures of proteins at atomic resolution. One key challenge is that almost all proteins are predominantly adsorbed to the air-water interface during standard cryo-EM specimen preparation. The interaction of proteins with air-water interface will significantly impede the success of reconstruction and achievable resolution. Here, we highlight the critical role of impenetrable surfactant monolayers in passivating the air-water interface problems, and develop a robust effective method for high-resolution cryo-EM analysis, by using the superstructure GSAMs which comprises surfactant self-assembled monolayers (SAMs) and graphene membrane. The GSAMs works well in enriching the orientations and improving particle utilization ratio of multiple proteins, facilitating the 3.3-Å resolution reconstruction of a 100-kDa protein complex (ACE2-RBD), which shows strong preferential orientation using traditional specimen preparation protocol. Additionally, we demonstrate that GSAMs enables the successful determinations of small proteins (<100 kDa) at near-atomic resolution. This study expands the understanding of SAMs and provides a key to better control the interaction of protein with air-water interface. Air-water interface hinders cryo-EM reconstruction and achievable resolution. Here, a superstructure called GSAMs is developed to alleviate the air-water interface effect and improve the efficiency of cryo-EM analysis.

Acetylene production from mixed alpha-olefins emerges as a potentially green and energy-efficient approach with significant scientific value in the selective cleavage of C-C bonds. On the Pd(100) surface, it is experimentally revealed that C2 to C-4 alpha-olefins undergo selective thermal cleavage to form surface acetylene and hydrogen. The high selectivity toward acetylene is attributed to the 4-fold hollow sites which are adept at severing the terminal double bonds in alpha-olefins to produce acetylene. A challenge arises, however, because acetylene tends to stay at the Pd(100) surface. By using the surface alloying methodology with alien Au, the surface Pd d-band center has been successfully shifted away from the Fermi level to release surface-generated acetylene from alpha-olefins as a gaseous product. Our study actually provides a technological strategy to economically produce acetylene and hydrogen from alpha-olefins.

Polyethylene production through catalytic ethylene polymerization is one of the most common processes in the chemical industry. The popular Cossee-Arlman mechanism hypothesizes that the ethylene be directly inserted into the metal-carbon bond during chain growth, which has been awaiting microscopic and spatiotemporal experimental confirmation. Here, we report an in situ visualization of ethylene polymerization by scanning tunneling microscopy on a carburized iron single-crystal surface. We observed that ethylene polymerization proceeds on a specific triangular iron site at the boundary between two carbide domains. Without an activator, an intermediate, attributed to surface-anchored ethylidene (CHCH3), serves as the chain initiator (self-initiation), which subsequently grows by ethylene insertion. Our finding provides direct experimental evidence of the ethylene polymerization pathway at the molecular level.

Thermally deposited picene (C22H14) molecules on a monolayered CuO film were grown at a Cu(110) self-assemble into side-on molecular strips extending along the [1 (1) over bar0] direction, as revealed by scanning tunneling microscopy (STM). The picene molecules are closely stacked on and anchored to the Cu-O chains via their armchair edges. They form two stacking modes and stick to the substrate via their long (Pic-I) and short (Pic-II) armchair edges. Such configurations are reversibly switchable by either an applied STM bias voltage pulse or continuous tip navigation. Scanning tunneling spectroscopies acquired above the Pic-I and Pic-II strips reveal different electronic states, showing a clear relationship between their electronic structures and their stacking modes on the substrate.

Formic acid adsorption and decomposition on clean Cu(100) and two atomic oxygen pre-covered Cu(100) surfaces have been studied using surface science techniques including scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy, and infrared reflection-absorption spectroscopy. The two atomic oxygen pre-covered Cu(100) surfaces include an O-(22 ×2)R45° Cu(100) surface and an oxygen modified Cu(100) surface with a local O-c(2 × 2) structure. The results show that the O-(22 ×2)R45° Cu(100) surface is inert to the formic acid adsorption at 300 K. After exposing to formic acid at 300 K, bidentate formate formed on the clean Cu(100) and local O-c(2 × 2) area of the oxygen modified Cu(100) surface. However, their adsorption geometries are different, being vertical to the surface plane on the former surface and inclined with respect to the surface normal with an ordered structure on the latter surface. The temperature programmed desorption spectra indicate that the formate species adsorbed on the clean Cu(100) surface decomposes into H2 and CO2 when the sample temperature is higher than 390 K. Differently, the proton from scission of the C-H bond of formate reacts with the surface oxygen, forming H2O on the oxygen modified Cu(100) surface. The CO2 signal starts increasing at about 370 K, which is lower than that on clean Cu(100), indicating that the surface oxygen affiliates formate decomposition. Combining all these results, we conclude that the surface oxygen plays a crucial role in formic acid adsorption and formate decomposition.