Interfacial superstructures and chemical bonding transitions at metal-ceramic interfaces

Abstract

Metal-ceramic interfaces are scientifically interesting and technologically important. However, the transition of chemical bonding character from a metal to a nonoxide ceramic is not well understood. The effects of solute segregation and interfacial structural transitions are even more elusive. In this study, aberration-corrected electron microscopy is combined with atomic-resolution energy-dispersive x-ray and electron energy loss spectroscopy to investigate Ti-, V-, and Cr-segregated WC-Co interfaces as model systems. The experiments reveal the general anisotropic formation of reconstructed trilayer-like superstructures with segregant-specific compositional profiles that facilitate the transition from covalent to metallic electronic structures. Density functional theory calculations confirm the gradual increasing metallicity from WC to Co in the interfacial trilayers via increasing metallic solute concentration. This study uncovers unprecedented details of the sophisticated interfacial superstructures at metal-ceramic interfaces. It sheds light on how a metal transits to a ceramic at a “general” interface with strong segregation.

Ethanol on Graphite: Ordered Structures and Delicate Balance of Interfacial and Intermolecular Forces

“…It is known that structures at interfaces where different materials and/or molecules meet have fundamental impacts on materials properties and behavior, interfacial phenomena, and even device performance in practical applications. − For small molecules, especially those capable of forming hydrogen bonds such as water, methanol, ethanol, and so on, knowledge of their interfacial structures has particular importance due to their broad existence as common solvents and in fuel cells, catalysis, macromolecular systems, and interstellar matter. − Given the relatively large strength and directional nature among intermolecular forces, hydrogen bonds play an important role in the organization of assembly structures, which may be in competition or sometimes cooperation with substrate–molecule interactions. Hence, to reveal interfacial structural details as a result of a delicate balance of all forces involved, it is crucial to use structure-probing techniques with suitable surface sensitivity, for example, scanning probe microscopy, , reflection–absorption infrared spectroscopy, − and reflection diffraction methods. − In recent years, reflection high-energy electron diffraction (RHEED) has been used to elucidate unanticipated ordered assemblies and unusual phase-transformation behavior of small molecules physisorbed or chemisorbed on different surfaces. − The technique’s strengths of a (sub)­nanometer thick penetration depth at grazing incidence angles and resulting surface sensitivity make noncontacting RHEED highly suitable for temperature- and thickness-dependent studies of interfacial structures and phase transitions of molecular systems, beside its typical use during thin-film fabrications in materials science.…”

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