The lateral incorporation of graphene and hexagonal boron nitride (h-BN) onto a substrate surface creates in-plane h-BN/graphene heterostructures, which have promising applications in novel two-dimensional electronic and photoelectronic devices. The quality of h-BN/graphene domain boundaries depends on their orientation, which is crucial for device performances. Here, the heteroepitaxial growth of graphene along the edges of h-BN domains on Ni(111) surfaces as well as the growth dynamics of h-BN using chemical vapor deposition (CVD) are in situ investigated by surface imaging measurements. The nucleating seed effect of h-BN has been revealed, which contributes to the single orientation of heterostructures with epitaxial stitching. Further, the growth of h-BN prior to that of graphene is essential to obtain high-quality in-plane h-BN/graphene heterostructures on Ni(111). The "compact to fractal" shape transition of h-BN domains appears with the increasing surface concentration of the growth blocks, suggesting that the dynamic growth mechanism follows diffusion-limited aggregation (DLA) but not reaction-limited aggregation (RLA). Our results provide insights into the synthesis of well-defined h-BN/graphene heterostructures and deep understanding of the growth dynamics of h-BN on metal surfaces.

Two-dimensional (2D) cuprous oxide (Cu₂O) nanostructures (NSs) of monolayer thickness were synthesized on Au(111) and characterized using atomic-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations. The surface and edge structures of 2D Cu₂O were resolved at the atomic level and found to exhibit a graphene-like lattice structure. Cu₂O NSs grew preferentially at the face centered cubic (fcc) domains of Au(111). Depending on the annealing temperature, the shapes and structures of Cu₂O NSs were found to vary from elongated islands with a defective hexagonal lattice (mostly topological 5–7 defects) to triangular NSs with an almost-perfect hexagonal lattice. The edge structures of Cu₂O NSs also varied with the annealing temperature, from predominantly the arm-chair 56 structure at 400 K to almost exclusively the zig-zag structure at 600 K. DFT calculations suggested that the herringbone ridges of Au(111) confined the growth and structure of Cu₂O NSs on Au(111). As such, the arm-chair edges of Cu₂O NSs, which are less stable than the zig-zag edges, could be exposed preferentially at 400 K. Cu₂O NSs developed into the thermodynamically-favored triangular form and exposed zig-zag edges at 600 K, when the Au(111) substrate became mobile. The confined growth of 2D cuprous oxide on Au(111) demonstrated the importance of metal-oxide interactions in tuning the structures of supported 2D oxide NSs.

We present a facile and versatile method for introducing various non-precious metal nanoparticles (NPs) in small nanotubes, such as single-walled carbon nanotubes (SWNTs), including 3d-metals (V, Mn, Fe and Co), 4d-metals (Mo), and 5d-metals (W). This is realized by oxidizing encapsulated cycloalkene metal carbonyl complexes below their sublimation temperatures. This novel technique is significant because it avoids the diffusion and deposition of metal species on the outer walls of nanotubes, which has been challenging to achieve using the conventional filling methods. High-resolution transmission electron microscopy (HRTEM), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDX), Raman, and X-ray photoelectron spectroscopy (XPS) analyses revealed high filling efficiencies (> 95% SWNTs filled with metal NPs). This method also provides a unique approach to fabricate highly dispersed and uniform SWNT–metal nanoparticle encapsulates with lower valence states, which are often not stable in the bulk.

Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic resonance (NMR) studies on the effects of water on the adsorption and diffusion of methane in nanopores. Silica materials with one-dimensional pores of ZSM-22, MCM-41, and SBA-15, with pore sizes ranging from 0.5 to 6 nm, were chosen as models. Hyperpolarized (HP) ¹²⁹Xe NMR results show that water adsorption does not affect the pore sizes of ZSM-22 and MCM-41 but reduces that of SBA-15. The presence of water suppresses methane adsorption; this suppression effect is stronger in smaller pores. The self-diffusion coefficients of methane within ZSM-22 and MCM-41 are not significantly influenced by the presence of water, as measured by ¹H pulsed field gradient (PFG) NMR. However, within SBA-15, which has a pore size of 6 nm, the diffusion coefficient of methane increases as the amount of water adsorption increases, peaks, and then decreases to a constant value with further water adsorption. These experiments reveal the effects of the pore size and the presence of water on methane adsorption and diffusion in constrained spaces, which could have important implications for flow simulations of methane in shales.

Active-phase engineering is regularly utilized to tune the selectivity of metal nanoparticles (NPs) in heterogeneous catalysis. However, the lack of understanding of the active phase in electrocatalysis has hampered the development of efficient catalysts for CO₂ electroreduction. Herein, we report the systematic engineering of active phases of Pd NPs, which are exploited to select reaction pathways for CO₂ electroreduction. In situ X-ray absorption spectroscopy, in situ attenuated total reflection-infrared spectroscopy, and density functional theory calculations suggest that the formation of a hydrogen-adsorbed Pd surface on a mixture of the α- and β-phases of a palladium-hydride core (α+β PdH_x@PdH_x) above -0.2 V (vs. a reversible hydrogen electrode) facilitates formate production via the HCOO^* intermediate, whereas the formation of a metallic Pd surface on the β-phase Pd hydride core (β PdH_x@Pd) below -0.5 V promotes CO production via the COOH^* intermediate. The main product, which is either formate or CO, can be selectively produced with high Faradaic efficiencies (> 90%) and mass activities in the potential window of 0.05 to -0.9 V with scalable application demonstration.

Hexagonal boron nitride (h-BN) is often prepared by epitaxial growth on metals, and stability of the formed BN/metal interfaces in gaseous environment is a key issue for physicochemical properties of the BN overlayers. As an illustration here, the structural change of a BN/Ru(0001) interface upon exposure to O₂ has been investigated using in situ photoemission electron microscopy (PEEM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). We demonstrate the occurrence of oxygen intercalation of the BN overlayers in O₂ atmosphere, which decouples the BN overlayer from the substrate. Comparative studies of oxygen intercalation at BN/Ru(0001) and graphene/Ru(0001) surfaces indicate that the oxygen intercalation of BN overlayers happens more easily than graphene. This finding will be of importance for future applications of BN-based devices and materials under ambient conditions.

A PtFe/C catalyst has been synthesized by impregnation and high-temperature reduction followed by acid-leaching. X-ray diffraction, X-ray photoelectron spectroscopy and X-ray atomic near edge spectroscopy characterization reveal that Pt₃Fe alloy formation occurs during high-temperature reduction and that unstable Fe species are dissolved into acid solution. The difference in Fe concentration from the core region to the surface and strong O-Fe bonding may drive the outward diffusion of Fe to the highly corrugated Pt-skeleton, and the resulting highly dispersed surface FeO_x is stable in acidic medium, leading to the construction of a Pt₃Fe@Pt-FeO_x architecture. The as prepared PtFe/C catalyst demonstrates a higher activity and comparable durability for the oxygen reduction reaction compared with a Pt/C catalyst, which might be due to the synergetic effect of surface and subsurface Fe species in the PtFe/C catalyst.

Surface functionalization of epitaxial graphene overlayers on 6H-SiC(0001) has been attempted through thermal reactions in NH₃. X-ray photoelectron spectroscopy and micro-region low energy electron diffraction results show that a significant amount of N is present at the NH₃-treated graphene surface, which results in strong band bending at the SiC surface as well as decoupling of the graphene overlayers from the substrate. The majority of the surface N species can be removed by annealing in vacuum up to 850 ℃, weakening the surface band bending and resuming the strong coupling of graphene with the SiC surface. The desorbed N atoms can be attributed to the intercalated species between graphene and SiC. Low temperature scanning tunneling spectroscopy and density functional theory simulations confirm the presence of N dopants in the graphene lattice, which are in the form of graphitic substitution and can be stable above 850 ℃. This is the first report of simultaneous N intercalation and N doping of epitaxial graphene overlayers on SiC, and it may be employed to alter the surface physical and chemical properties of epitaxial graphene overlayers.

A two-dimensional (2D) Si film can form between a graphene overlayer and a Ru(0001) substrate through an intercalation process. At the graphene/2D-Si/Ru(0001) surface, the topmost graphene layer is decoupled from the Ru substrate and becomes quasi-freestanding. The interfacial Si layers show high stability due to the protection from the graphene cover. Surface science measurements indicate that the surface Si atoms can penetrate through the graphene lattice, and density functional theory calculations suggest a Si-C exchange mechanism facilitates the penetration of Si at mild temperatures. The new mechanism may be involved for other elements on graphene, if they can bond strongly with carbon. This finding opens a new route to form 2D interfacial layers between graphene and substrates.