Atomic-resolution three-dimensional hydration structures on a heterogeneously charged surface

Kenichi Umeda,Adam S Foster,Peter Spijker,Hirofumi Yamada,Hiroaki Kominami,Kei Kobayashi,Juha Ritala,Lidija Zivanovic

doi:10.1038/s41467-017-01896-4

Abstract

Local hydration structures at the solid–liquid interface around boundary edges on heterostructures are key to an atomic-level understanding of various physical, chemical and biological processes. Recently, we succeeded in visualising atomic-scale three-dimensional hydration structures by using ultra-low noise frequency-modulation atomic force microscopy. However, the time-consuming three-dimensional-map measurements on uneven heterogeneous surfaces have not been achieved due to experimental difficulties, to the best of our knowledge. Here, we report the local hydration structures formed on a heterogeneously charged phyllosilicate surface using a recently established fast and nondestructive acquisition protocol. We discover intermediate regions formed at step edges of the charged surface. By combining with molecular dynamics simulations, we reveal that the distinct structural hydrations are hard to observe in these regions, unlike the charged surface regions, possibly due to the depletion of ions at the edges. Our methodology and findings could be crucial for the exploration of further functionalities.

Highlights

Local hydration structures at the solid–liquid interface around boundary edges on heterostructures are key to an atomic-level understanding of various physical, chemical and biological processes
We have opened the door to atomic-scale threedimensional (3D) mapping of the local hydration structures by ultra-low noise frequency-modulation atomic force microscopy (FM-AFM)[12, 13], which has been applied to various homogeneous samples[12,13,14,15,16,17,18]
Molecular-scale hydration structures on the terraces are visualised by 3D FMAFM in aqueous solution, which are reproduced by the molecular dynamics (MD) simulations

Summary

Introduction

Local hydration structures at the solid–liquid interface around boundary edges on heterostructures are key to an atomic-level understanding of various physical, chemical and biological processes. Heterostructures, nano-clusters, edges and defects are crucial in these processes, because these structures often amplify the reaction efficiencies due to quantum effects, low-coordinated atoms or concentrated electric fields[2,3,4, 7] Since they are always accompanied by local hydration changes reflecting the local structural and chemical changes of adsorption/ surface species, understanding the local hydration structures at such reactive places is essential. The hydration structures in complicated biological crystal samples have been extensively studied by X-ray/neutron crystallography, nuclear magnetic resonance and cryoelecton microscopy[8, 9] All of these measurements require samples in a crystalline state, of which the hydrations at such local structures are averaged out and often differ from those in liquid environments. We reveal the intermediate regions near the step edge on the positively charged terrace by 3D FM-AFM, presumably caused by the ion depletion near the step edge, which is predicted by the MD simulations

Methods

Results

Conclusion