A study of iodine adlayers on polycrystalline gold electrodes by in situ electrochemical Rutherford backscattering (ECRBS)

A review of ion scattering spectroscopy studies at liquid interfaces with noble gas ion projectiles

Ion scattering spectroscopy (ISS) is an analytical tool that provides direct structural, topographical, and atomic compositional information at interfaces when ions are used as projectiles. Since its development in 1967, ISS is commonly used to obtain quantitative information about solid interfaces. Over the last couple of decades, ISS has emerged as an important technique to probe liquid interfaces and their studies employing ISS has become not uncommon, more so with Neutral impact collision ion scattering spectroscopy (NICISS). Therefore, here the principle of ISS with a particular focus on NICISS and its data evaluation are summarised while reviewing some important studies at vapor-liquid interfaces that provide direct information for molecular orientation of liquids (including ionic liquids), composition and distribution of atoms (or solutes) and charges as a function of depth to gain vast variety of thermodynamical information. Employing ISS such information can be achieved with high depth resolution of ∼1-2 Å (depending on the nature of the experiment). These examples highlight the significance of ISS and show potential for its application for studies related to specific ion effects, atmospheric reaction in aerosol and sea water droplets, and even determining the fate of environmental pollutants like heavy metal ions and per-fluoroalkyl substances (PFAS). Furthermore, some limitations of ISS are also discussed relating to investigation of high-vapor pressure liquids and probing buried interfaces like liquid-liquid interfaces while presenting progresses made in probing solid-liquid interfaces.

Microscale Electrochemical Corrosion of Uranium Oxide Particles

Understanding the corrosion of spent nuclear fuel is important for the development of long-term storage solutions. However, the risk of radiation contamination presents challenges for experimental analysis. Adapted from the system for analysis at the liquid-vacuum interface (SALVI), we developed a miniaturized uranium oxide (UO2)-attached working electrode (WE) to reduce contamination risk. To protect UO2 particles in a miniatured electrochemical cell, a thin layer of Nafion was formed on the surface. Atomic force microscopy (AFM) shows a dense layer of UO2 particles and indicates their participation in electrochemical reactions. Particles remain intact on the electrode surface with slight redistribution. X-ray photoelectron spectroscopy (XPS) reveals a difference in the distribution of U(IV), U(V), and U(VI) between pristine and corroded UO2 electrodes. The presence of U(V)/U(VI) on the corroded electrode surface demonstrates that electrochemically driven UO2 oxidation can be studied using these cells. Our observations of U(V) in the micro-electrode due to the selective semi-permeability of Nafion suggest that interfacial water plays a key role, potentially simulating a water-lean scenario in fuel storage conditions. This novel approach offers analytical reproducibility, design flexibility, a small footprint, and a low irradiation dose, while separating the α-effect. This approach provides a valuable microscale electrochemical platform for spent fuel corrosion studies with minimal radiological materials and the potential for diverse configurations.

Revealing the formation dynamics of the electric double layer by means of in-situ Rutherford backscattering spectrometry

We report on a new versatile experimental setup for in situ Rutherford backscattering spectrometry at solid-liquid interfaces which enables investigations of electric double layers directly and in a quantitative manner. A liquid cell with a three-electrode arrangement is mounted in front of the beam line, and a thin Si₃N₄ window (thickness down to 150 nm) separates the vacuum of the detector chamber from the electrolyte in the cell. By minimizing the contribution of the window to the measurement, a large variety of elements at the solid-liquid interface with sensitivities far below one monolayer can be monitored. The attachment of Ba onto the Si₃N₄ surface as a function of contact time and pH value of the electrolyte solution was chosen as an example system. From our measurement, we can not only follow the evolution of the double layer but also derive limits for the point of zero charge for the Si₃N₄ surface. Our findings of 5.7≤pH_PZC≤6.2 are in good agreement with values found in the literature obtained by other techniques. Despite focusing on a specific system in this work, the presented setup allows for a large variety of in situ investigations at solid-liquid interfaces such as, but not limited to, tracing electrochemical reactions and monitoring segregation, adsorption, and dissolution and corrosion processes.

Thin film depth profiling by ion beam analysis

The analysis of thin films is of central importance for functional materials, including the very large and active field of nanomaterials. Quantitative elemental depth profiling is basic to analysis, and many techniques exist, but all have limitations and quantitation is always an issue. We here review recent significant advances in ion beam analysis (IBA) which now merit it a standard place in the analyst's toolbox. Rutherford backscattering spectrometry (RBS) has been in use for half a century to obtain elemental depth profiles non-destructively from the first fraction of a micron from the surface of materials: more generally, "IBA" refers to the cluster of methods including elastic scattering (RBS; elastic recoil detection, ERD; and non-Rutherford elastic backscattering, EBS), nuclear reaction analysis (NRA: including particle-induced gamma-ray emission, PIGE), and also particle-induced X-ray emission (PIXE). We have at last demonstrated what was long promised, that RBS can be used as a primary reference technique for the best traceable accuracy available for non-destructive model-free methods in thin films. Also, it has become clear over the last decade that we can effectively combine synergistically the quite different information available from the atomic (PIXE) and nuclear (RBS, EBS, ERD, NRA) methods. Although it is well known that RBS has severe limitations that curtail its usefulness for elemental depth profiling, these limitations are largely overcome when we make proper synergistic use of IBA methods. In this Tutorial Review we aim to briefly explain to analysts what IBA is and why it is now a general quantitative method of great power. Analysts have got used to the availability of the large synchrotron facilities for certain sorts of difficult problems, but there are many much more easily accessible mid-range IBA facilities also able to address (and often more quantitatively) a wide range of otherwise almost intractable thin film questions.

In situ chemical probing of the electrode-electrolyte interface by ToF-SIMS

A portable vacuum interface allowing direct probing of the electrode-electrolyte interface was developed. A classical electrochemical system consisting of a gold working electrode, platinum counter electrode, platinum reference electrode, and potassium iodide electrolyte was used to demonstrate real-time observation of the gold iodide adlayer on the electrode and chemical species as a result of redox reactions using cyclic voltammetry (CV) and time-of-flight secondary ion mass spectrometry (ToF-SIMS, a vacuum-based surface technique) simultaneously. This microfluidic electrochemical probe provides a new way to investigate the surface region with adsorbed molecules and the region of the diffused layer with chemical speciation in liquids in situ by surface sensitive techniques.