Electron work function – a probe for interfacial diagnosis

Abstract

A poor interface or defected interfacial segment may trigger interfacial cracking, loss of physical and mechanical functions, and eventual failure of entire material system. Here we show a novel method to diagnose local interphase boundary based on interfacial electron work function (EWF) and its gradient across the interface, which can be analyzed using a nano-Kelvin probe with atomic force microscope. It is demonstrated that a strong interface has its electron work function gradually changed across the interface, while a weaker one shows a steeper change in EWF across the interface. Both experimental and theoretical analyses show that the interfacial work function gradient is a measure of the interaction between two sides of the interface. The effectiveness of this method is demonstrated by analyzing sample metal-metal and metal-ceramic interfaces.

Tuning the Conductivity and Electron Work Function of a Spin-Coated PEDOT:PSS/PEO Nanofilm for Enhanced Interfacial Adhesion

“…The interactions between different types of material such as ceramics-polymer are generally weak. A previous study on ceramics-metal pair shows that the interaction at interface comes from the formation of a dipole layer induced by the difference in electron work function between the materials in contact, which is also influenced by the freedom of electrons. Figure illustrates the situation when two materials are in contact.…”

“…As shown in Figure 8a, when the two different types of materials are in contact with little or without atomic diffusion, their Fermi levels at the interface would converge, thus developing a potential difference, ΔV = (φ B − φ A )/e 0 , where e 0 is the unit charge. 16 Under the potential difference, electrons move from the material having a lower work function (φ A ) to the one having a high work function (φ B ) to achieve equilibrium in the system. As a result, a dipole layer forms at the A/B interface as Figure 8b illustrates, which induces the interfacial interaction or interfacial bonding.…”

“…A dipole layer may form at interfaces to enhance the interfacial bonding without the involvement of diffusion. 16 With methanol post-treatment, the conductivity of PE-DOT:PSS increases from 0.3 S cm −1 to about 1,362 S cm −1 . 17 Other solvents can also be used with differing effects on PEDOT:PSS conductivity.…”

“…Upon contacting with the base metal, a Schottky diode is formed due to the difference in the electron work function (EWF) present across the interface. A dipole layer may form at interfaces to enhance the interfacial bonding without the involvement of diffusion …”

New insights into the kinetics of metal|electrolyte interphase growth in solid-state-batteries via an operando XPS analysis - part II: modelling

“…As a photoelectron leaves the NZSP phase, it will undergo acceleration in accordance with the magnitude of the interfacial voltage. The shift in photoelectron kinetic energy (E k ) is therefore equivalent to the interfacial voltage:14,15…”