Directly Probing the Effects of Ions on Hydration Forces at Interfaces

Understanding the influence of water layers adjacent to interfaces is fundamental in order to fully comprehend the interactions of both biological and nonbiological materials in aqueous environments. In this study, we have investigated hydration forces at the mica–electrolyte interface as a function of ion valency and concentration using subnanometer oscillation amplitude frequency modulation atomic force microscopy (FM-AFM). Our results reveal new insights into the nature of hydration forces at interfaces due to our ability to measure high force gradients without instability and in the absence of lateral confinement due to the use of an atomically sharp tip. We demonstrate the influence of electrolytes on the properties of both primary and structural hydration forces and reveal new insights into the interplay between these phenomena in determining the interaction forces experienced by a nanoscale object approaching an interface. We also highlight the difficulty in directly comparing hydration force data from different measurement techniques where the nature of the perturbation induced by differing interaction geometries is likely to dramatically affect the results

Cycle-dependent morphology and surface potential of germanium nanowire anode electrodes

Germanium nanowire (GeNW) electrodes have shown great promise as high-power, fast-charging alternatives to silicon-based electrodes, owing to their vastly improved Li ion diffusion, electron mobility and ionic conductivity. Formation of the solid electrolyte interphase (SEI) on the anode surface is critical to electrode performance and stability but is not completely understood for NW anodes. Here, a systematic study characterizing pristine and cycled GeNWs in charged and discharged states with SEI layer present and removed is performed using Kelvin probe force microscopy in air. Correlating changes in the morphology of the GeNW anodes with contact potential difference mapping at different cycles provides insight into SEI layer formation and growth, and the effect of the SEI on battery performance.</p