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A major challenge limiting the practical applications of nanomaterials is that the activities of nanostructures (NSs) increase with reduced size, often sacrificing their stability in the chemical environment. Under oxidative conditions, NSs with smaller sizes and higher defect densities are commonly expected to oxidize more easily, since high-concentration defects can facilitate oxidation by enhancing the reactivity with O2 and providing a fast channel for oxygen incorporation. Here, using FeO NSs as an example, we show to the contrary, that reducing the size of active NSs can drastically increase their oxidation resistance. A maximum oxidation resistance is found for FeO NSs with dimensions below 3.2 nm. Rather than being determined by the structure or electronic properties of active sites, the enhanced oxidation resistance originates from the size-dependent structural dynamics of FeO NSs in O2. We find this dynamic size effect to govern the chemical properties of active NSs.

The formation of solid electrolyte interphase (SEI) and lithium ion intercalation are two crucial processes in lithium ion batteries. Given the complexity and challenges involved in investigating real batteries, a combination of model batteries comprising well-defined ultrathin graphite electrodes with surface-sensitive techniques can provide valuable information on these processes. Here, a comparative study of the performance of batteries using regular- and high-concentration electrolytes (RCE and HCE) is presented, aided by a myriad of correlative surface science techniques. It is found that the SEI formed in HCE possesses a thinner organic layer and more inorganic substances. Such an effective SEI protects the graphite electrode and facilitates the processes of Li+ intercalation/deintercalation, thereby improving the reversibility and cycling stability of the battery, superior to those with RCE. Moreover, the battery performance can be readily tuned by switching the electrolytes. The good cycling stability of the battery can still be maintained in RCE after the preformation of a robust SEI on the ultrathin graphite electrode in HCE. This work highlights the importance of electrolyte-modulated SEI formation to battery performance and provides powerful platforms to comprehensively study the SEI formation and ion intercalation processes. [ABSTRACT FROM AUTHOR]

Supported metal catalysts are widely used for chemical conversion, in which construction of high density metal‐oxide or oxide‐metal interface is an important means to improve their reaction performance. Here, Cu@ZnOx encapsulation structure has been in situ constructed through gas‐phase migration of Zn species from ZnO particles onto surface of Cu nanoparticles under CO2 hydrogenation atmosphere at 450 °C. The gas‐phase deposition of Zn species onto the Cu surface and growth of ZnOx overlayer is self‐limited under the high temperature and redox gas (CO2/H2) conditions. Accordingly, high density ZnOx‐Cu interface sites can be effectively tailored to have an enhanced activity in CO2 hydrogenation to methanol. This work reveals a new route for the construction of active oxide‐metal interface and classic strong metal‐support interaction state through gas‐phase migration of support species induced by high temperature redox reaction atmosphere. [ABSTRACT FROM AUTHOR]

Surface and interface play critical roles in energy storage devices, calling for operando characterization techniques to probe the electrified surfaces/interfaces. In this work, surface science methodology, including electron spectroscopy and scanning probe microscopy, has been successfully applied to visualize electrochemical processes at operating electrode surfaces in an Al/graphite model battery. Intercalation of anions together with cations is directly observed in the surface region of a graphite electrode with tens of nanometers thickness, the concentration of which is one order higher than that in bulk. An intercalation pseudocapacitance mechanism and a double specific capacity in the electrode surface region are expected based on the super-dense intercalants and anion/cation co-intercalation, which are in sharp contrast to the battery-like mechanism in the electrode bulk. The distinct electrochemical mechanism at the electrode surface is verified by performance tests of real battery devices, showing that a surface-dominant, nanometer-thick graphite cathode outperforms a bulk-dominant, micrometer-thick graphite cathode. Our findings highlight the important surface effect of working electrodes in charge storage systems. [ABSTRACT FROM AUTHOR]

The self-assembled structure of submonolayer manganese phthalocyanine (MnPc) on Pb(111) surface is investigated by using low-temperature scanning tunneling microscopy (STM). A 'holelike' superlattice, which is superimposed on the self-assembled nearly quadratic network, is observed. High resolution STM images reveal that there are two distinct azimuthal orientations of MnPc molecules. It is found that by taking the two different orientations the self-assembly can further be optimized energetically by maximizing intermolecular orbital overlapping. It is this intralayer energy minimization process that leads to the characteristic holelike superlattice. [ABSTRACT FROM AUTHOR]

Construction of model metal carbide surfaces is essential for surface catalysis studies over carbide‐based catalysts. Here, well‐controlled growth of tungsten carbide (WCx) layers on W(110) including carbon‐rich R(15×3)‐C/W(110) and carbon‐poor R(15×12)‐C/W(110) structures has been clearly demonstrated using chemical vapor deposition (CVD) on a clean W(110) surface or carbon segregation from the bulk. Low‐energy electron microscopy (LEEM) and micro‐region LEED (μ‐LEED) characterizations confirm that the R(15×12) structure forms first and then transforms to the R(15×3) structure by incorporating more carbon atoms in the CVD or surface segregation processes. Oxidation of the WCx/W(110) surfaces in O2 atmosphere removes surface carbon atoms, driving the structural transformation from R(15×3) to R(15×12) first and then to a two‐dimensional oxide surface. Our work provides a clear guide for well‐controlled growth of model WCx catalysts and the structural transformation between them. [ABSTRACT FROM AUTHOR]

Ultrathin ZnO nanostructures present interesting two-dimensional (2D) graphene-like structure in contrast to wurtzite structure in bulk ZnO. Growth on Au(111) has been regarded as a well-established route to the 2D ZnO layers while controlled growth of uniform ZnO nanostructures remains as a challenge. Here, reactive deposition of Zn in O3 and NO2 was employed, which is investigated by scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS). We demonstrate that uniform ZnO monolayer nanoislands and films can be obtained on Au(111) using O3 and uniform ZnO bilayer nanoislands and films form on Au(111) using NO2, respectively. Formation of atomic oxygen overlayers on Au(111) via exposure to O3 is critical to the formation of uniform ZnO monolayer nanostructures atop. Near ambient pressure XPS studies revealed that nearly full hydroxylation occurs on monolayer ZnO structures upon exposure to near ambient pressure water vapor or atomic hydrogen species, while partial surface hydroxylation happens on bilayer ZnO under the same gaseous exposure conditions. [ABSTRACT FROM AUTHOR]

Interaction of hexagonal boron nitride (h-BN) with gases is of great importance for its properties and applications. In the present work, the structural changes of h-BN overlayers on Pt(111) in oxidative atmospheres including O2 and NO2 have been investigated by using low energy electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS), and near ambient pressure XPS. We find that h-BN islands can be intercalated by oxygen in 10−6 Torr O2 at 200 °C, while oxygen intercalation of full layer h-BN around 200 °C requires near ambient pressure O2 (0.1 Torr) or such a strong oxidant as NO2 (10−6 Torr). h-BN overlayers can be etched away in the gases at much high temperatures, e.g. 800 °C. Upon mild oxidation in O2 or NO2 at temperatures of 400–450 °C, h-BN is transformed to boron oxide (BOx) overlayers, which can be converted back to h-BN by heating in NH3 at 800 °C. [ABSTRACT FROM AUTHOR]

Growth kinetics of epitaxial films often follows the diffusion-limited aggregation mechanism, which shows a “fractal-to-compact” morphological transition with increasing growth temperature or decreasing deposition flux. Here, we observe an abnormal “compact-to-fractal” morphological transition with increasing growth temperature for hexagonal boron nitride growth on the Ru(0001) surface. The unusual growth process can be explained by a reaction-limited aggregation (RLA) mechanism. Moreover, introduction of the subsurface Ar atoms has enhanced this RLA growth behavior by decreasing both reaction and diffusion barriers. Our work may shed light on the epitaxial growth of two-dimensional atomic crystals and help to control their morphology. [ABSTRACT FROM AUTHOR]

Understanding dynamic changes of catalytically active nanostructures under reaction conditions is a pivotal challenge in catalysis research, which has been extensively addressed in metal nanoparticles but is less explored in supported oxide nanocatalysts. Here, structural changes of iron oxide (FeOx) nanostructures supported on Pt in a gaseous environment were examined by scanning tunneling microscopy, ambient pressure X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy using both model systems and real catalysts. O–Fe (FeO) bilayer nanostructures can be stabilized on Pt surfaces in reductive environments such as vacuum conditions and H2-rich reaction gas, which are highly active for low temperature CO oxidation. In contrast, exposure to H2-free oxidative gases produces a less active O–Fe–O (FeO2) trilayer structure. Reversible transformation between the FeO bilayer and FeO2 trilayer structures can be achieved under alternating reduction and oxidation conditions, leading to oscillation in the catalytic oxidation performance. [ABSTRACT FROM AUTHOR]

Molecular rods designed for surface chirality studies have been synthesized in high yields. The molecules are composed of oligo(naphthylene-ethynylene) skeletons and functionalized at their two termini with carboxylic acids and hydrophobic groups. The molecular skeletons were constructed by means of palladium-catalyzed Sonogashira reactions between naphthyl halides and acetylenes. The triazene functionality was used as a protected iodine precursor to allow linear extension of the molecular rods during the syntheses. The carboxylic acid groups in the target molecules were protected as esters during the synthesis to keep the large aromatic molecules soluble during their syntheses. These rigid oligomers were designed to form lamella-like structures when adsorbed on a surface, through which multiple distinguishable surface conformations should be obtainable. Preliminary scanning tunneling microscopy imaging confirmed these properties. [ABSTRACT FROM AUTHOR]

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity‐stability trade‐off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas‐catalyst‐support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25‐500 °C under dry conditions and 200‐800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h. [ABSTRACT FROM AUTHOR]

Epitaxial growth of ultrathin overlayers on solid substrate is critically dependent on the surface structure, and in this work near‐surface doping is identified as another important growth factor. It is shown that growth of hexagonal boron nitride (h‐BN) on Ni(111) through chemical vapor deposition or surface ammonization can be strongly modulated by near‐surface B doping. Epitaxial h‐BN islands form on clean Ni(111) surface, while both epitaxial and nonepitaxial h‐BN islands grow on Ni(111) containing near‐surface B atoms. Quantitative correlation of epitaxial growth and near‐surface doping is unambiguously demonstrated. In situ spatially resolved surface science measurements based on photoemission electron microscopy and low energy electron microscopy in combination with density function calculations reveal that near‐surface B atoms weaken the interaction between h‐BN overlayer and Ni surface, which favor the nonepitaxial and metastable h‐BN structures. The present work suggests that near‐surface doping acts as an effective route to influence epitaxial growth of two‐dimensional (2D) material overlayers on solids. [ABSTRACT FROM AUTHOR]

An enclosed nanospace often shows a significant confinement effect on chemistry within its inner cavity, while whether an open space can have this effect remains elusive. Here, we show that the open surface of TiO 2 creates a confined environment for In 2 O 3 which drives spontaneous transformation of free In 2 O 3 nanoparticles in physical contact with TiO 2 nanoparticles into In oxide (InO x ) nanolayers covering onto the TiO 2 surface during CO 2 hydrogenation to CO. The formed InO x nanolayers are easy to create surface oxygen vacancies but are against over-reduction to metallic In in the H 2 -rich atmospheres, which thus show significantly enhanced activity and stability in comparison with the pure In 2 O 3 catalyst. The formation of interfacial In-O-Ti bonding is identified to drive the In 2 O 3 dispersion and stabilize the metastable InO x layers. The InO x overlayers with distinct chemistry from their free counterpart can be confined on various oxide surfaces, demonstrating the important confinement effect at oxide/oxide interfaces.

Interfacial interaction plays a crucial rule in catalysis over supported catalysts, and the catalyst-support interaction needs to be explored at microscopic scale. Here, we use the scanning tunneling microscope (STM) tip to manipulate Cr 2 O 7 dinuclear clusters on Au(111) and find that the Cr 2 O 7 -Au interaction can be weakened by an electric field in the STM junction, facilitating rotation and translation of the individual clusters at the imaging temperature (78 K). Surface alloying with Cu makes the manipulation of the Cr 2 O 7 clusters hard due to the enhanced Cr 2 O 7 -substrate interaction. Density functional theory calculations reveal that barrier for translation of a Cr 2 O 7 cluster on the surface can be increased by surface alloying, influencing the tip manipulation. Our study demonstrates that the oxide-metal interfacial interaction can be probed by STM tip manipulation of supported oxide clusters, which provides a new method to investigate the interfacial interaction.

Rational design of highly stable and active metal catalysts requires a deep understanding of metal-support interactions at the atomic scale. Here, ultrathin films of FeO and FeO 2- x grown on Pt(111) are used as templates for the construction of well-defined metal nanoclusters. Periodic arrays of Cu clusters in the form of monomers and trimers are preferentially located at FCC domains of FeO/Pt(111) surface, while the selective location of Cu clusters at FeO 2 domains is observed on FeO 2- x /Pt(111) surface. The preferential nucleation and formation of well-ordered Cu clusters are driven by different interactions of Cu with the Fe oxide domains in the sequence of FeO 2 -FCC > FeO-FCC > FeO-HCP > FeO-TOP, which is further validated by density functional theory calculations. It has been revealed that the p -band center as a reactivity descriptor of surface O atoms determines the interaction between metal adatoms and Fe oxides. The modulated metal-oxide interaction provides guidance for the rational design of supported single-atom and nanocluster catalysts., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Ambient atmosphere is critical for the surface/interface chemistry of electrodes that governs the operation and failure in energy storage devices (ESDs). Here, taking an Al/graphite battery as an example, both the relaxation and failure processes in the working graphite electrodes have been dynamically monitored by multiple in situ surface and interface characterization methods within various well-controlled atmospheres. Relaxation effects are manifested by recoverable stage-structure change and electronic relaxation occurring in anhydrous inert atmospheres and O 2 , which are induced by the anion/cation redistribution within the neighboring graphene layers and have slight influence on the long-term cycling. In contrast, rapid and unrecoverable failure behaviors happen in hydrous atmospheres as shown by the stage-structure degradation and electronic decoupling between guest ions and host graphite, which are caused by the hydrolysis between newly intercalated H 2 O molecules and intercalants. Consistent with the characterization results, exposure to H 2 O can cause nearly 100% capacity loss. The methodology and concept adopted in this work to unravel the battery mechanism under ambient conditions are universal and significant to investigate many ESDs.

A newly developed instrument comprising a near ambient pressure (NAP) photoemission electron microscope (PEEM) and a tunable deep ultraviolet (DUV) laser source is described. This NAP-PEEM instrument enables dynamic imaging of solid surfaces in gases at pressures up to 1 mbar. A diode laser (976 nm) can illuminate a sample from the backside for in situ heating in gases up to 1200 K in minutes. The DUV laser with a tunable wavelength between 175 nm and 210 nm is perpendicularly incident onto the sample surface for PEEM imaging of a wide spectrum of solids with different surface work functions. Using this setup, we have first demonstrated spatiotemporal oscillation patterns of CO oxidation reaction on Pt(110) from high vacuum to NAPs and gas-induced restructuring of metal nanostructures in millibar gases. The new facility promises important applications in heterogeneous catalysis, electrochemical devices, and other surface processes under nearly working conditions.

During graphene growth on various transition metals in the periodic table, metal carbides always emerge to behave as complex intermediates. On VIII metals, metastable carbides usually evolve and then transform into graphene along the phase interfaces, and even no metal carbides can form on IB-IIB metals. In contrast, during graphene growth on group IVB-VIB metals, carbides are usually generated even before the evolution of graphene and stably exist throughout the whole growth process. However, for the remaining transition metals, e.g., group VIIB, located in between IVB-VIB and VIII, the interplay between graphene and carbide is still vague. Herein, on Re(0001) (VIIB), we have revealed a novel transition from graphene to metal carbide (reverse to that on VIII metals) for the first time. This transition experienced graphene decomposition, dissolution, and carbon segregation processes, as evidenced by scanning tunneling microscopy (STM) and on-site, variable-temperature low electron energy diffraction (LEED) characterizations. This work thus completes the picture about the interplay between graphene and carbide on/in transition metals in the periodic table, as well as discloses a new territory for the growth of carbon-related materials, especially the metal carbide.

The controlled fabrication of nanostructures has often used a substrate template to mediate and control the growth kinetics. Electronic substrate-mediated interactions have been demonstrated to guide the assembly of organic molecules or the nucleation of metal atoms but usually at cryogenic temperatures, where the diffusion has been limited. Combining STM, STS, and DFT studies, we report that the strong electronic interaction between transition metals and oxides could indeed govern the growth of low-dimensional oxide nanostructures. As a demonstration, a series of FeO triangles, which are of the same structure and electronic properties but with different sizes (side length >3 nm), are synthesized on Pt(111). The strong interfacial interaction confines the growth of FeO nanostructures, leading to a discrete size distribution and a uniform step structure. Given the same interfacial configuration, as-grown FeO nanostructures not only expose identical edge/surface structure but also exhibit the same electronic properties, as manifested by the local density of states and local work functions. We expect the interfacial confinement effect can be generally applied to control the growth of oxide nanostructures on transition metal surfaces. These oxide nanostructures of the same structure and electronic properties are excellent models for studies of nanoscale effects and applications.

Molecular conformational flexibility can play an important role in supramolecular self-assembly on surfaces, affecting not least chiral molecular assemblies. To explicitly and systematically investigate the role of molecular conformational flexibility in surface self-assembly, we synthesized a three-bit conformational switch where each of three switching units on the molecules can assume one of two distinct binary positions on the surface. The molecules are designed to promote C-H···N type hydrogen bonds between the switching units. While supramolecular self-assembly based on strong hydrogen-bonding interactions has been widely explored, less is known about the role of such weaker directional interactions for surface self-assembly. The synthesized molecules consist of three nitrogen-containing isoquinoline (IQ) bits connected by ethynylene spokes and terminated by tert-butyl (tBu) groups. Using high-resolution scanning tunnelling microscopy, we investigate the self-assembly of the IQ-tBu molecules on a Au(111) surface under ultrahigh-vacuum conditions. The molecules form extended domains of brick-wall structure where the molecular backbones are packed regularly but without selection of specific molecular conformations. However, statistical analysis of the extended network demonstrates alignment/correlation for the orientations of the switching units indicating specific interactions. The primary interaction motifs in the structure are quantified from DFT calculations, showing that the brick-wall structure is indeed stabilized by two types of weak C-H···N bonds, involving either aromatic hydrogens on the IQ groups or nonaromatic hydrogens on the tBu groups. Analysis of the C-H···N interactions in the brick-wall structure explains the observed distribution and alignment of molecular conformations as well as the overall organization of the molecular surface structures.

Understanding dynamic changes of catalytically active nanostructures under reaction conditions is a pivotal challenge in catalysis research, which has been extensively addressed in metal nanoparticles but is less explored in supported oxide nanocatalysts. Here, structural changes of iron oxide (FeO(x)) nanostructures supported on Pt in a gaseous environment were examined by scanning tunneling microscopy, ambient pressure X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy using both model systems and real catalysts. O-Fe (FeO) bilayer nanostructures can be stabilized on Pt surfaces in reductive environments such as vacuum conditions and H2-rich reaction gas, which are highly active for low temperature CO oxidation. In contrast, exposure to H2-free oxidative gases produces a less active O-Fe-O (FeO2) trilayer structure. Reversible transformation between the FeO bilayer and FeO2 trilayer structures can be achieved under alternating reduction and oxidation conditions, leading to oscillation in the catalytic oxidation performance.

A noble metal (NM) can stabilize monolayer-dispersed surface oxide phases with metastable nature. The formed "oxide-on-metal" inverse catalyst presents better catalytic performance than the NM because of the introduction of coordinatively unsaturated cations at the oxide-metal boundaries. Here we demonstrate that an ultrathin NM layer grown on a non-NM core can impose the same constraint on the supported oxide as the bulk NM. Cu@Pt core-shell nanoparticles (NPs) decorated with FeO patches use much less Pt but exhibit performance similar to that of Pt NPs covered with surface FeO patches in the catalytic oxidation of CO. The "oxide-on-core@shell" inverse catalyst system may open a new avenue for the design of advanced nanocatalysts with decreased usage of noble metals.

Adsorption and self-assembly of cobalt phthalocyanine (CoPc) molecules on Pb(111) thin films with a thickness ranging from 10 atomic monolayers (ML) to 20 ML were investigated by using scanning tunneling microscopy and spectroscopy (STM/STS). Unprecedented thickness-selective oscillating adsorption and self-assembly behavior of the molecules on the films were observed. STS measurement reveals that this oscillatory behavior arises from quantum size effect. The strong quantum confinement of electron motion in the Pb films modulates the electronic density of states at the Fermi level (DOS(EF)), leading to preferential adsorption at thicknesses of higher DOS(EF). The work provides an unambiguous evidence for quantum modulation of surface reactivities of a metal thin film.