Understanding the interface between silicon-based materials and water: Molecular-dynamics exploration of infrared spectra

José A Martinez-Gonzalez,Niall J English,Aoife A Gowen

doi:10.1063/1.4999086

Abstract

Molecular-dynamics simulations for silicon, hydrogen- and hydroxyl-terminated silicon in contact with liquid water, at 220 and 300 K, display water-density ‘ordering’ along the laboratory z-axis, emphasising the hydrophobicity of the different systems and the position of this first adsorbed layer. Density of states (DOS) of the oxygen and proton velocity correlation functions (VACFs) and infrared (IR) spectra of the first monolayer of adsorbed water, calculated via Fourier transformation, indicate similarities to more confined, ice-like dynamical behaviour (redolent of ice). It was observed that good qualitative agreement is obtained between the DOS for this first layer in all systems. The DOS for the lower-frequency zone indicates that for the interface studied (i.e., the first layer near the surface), the water molecules try to organise in a similar form, and that this form is intermediate between liquid water and ice. For IR spectra, scrutiny of the position of the highest-intensity peaks for the stretching and bending bands indicate that such water molecules in the first solvating layer are organised in an intermediate fashion between ice and liquid water.

Highlights

The study of aqueous solutions in contact with different types of materials and bio-materials has become a subject of substantial interest, addressing open questions relating to how water organisation changes depending on the hydrophobicity of the surface
Classical molecular dynamics simulations were carried out according the procedure outlined above
The vibrational density of states (VDOS) spectra may be divided according to regions of stretching, bending and translational-librational components

Summary

Introduction

The study of aqueous solutions in contact with different types of materials and bio-materials has become a subject of substantial interest, addressing open questions relating to how water organisation changes depending on the hydrophobicity of the surface. Water in close contact with surfaces of these materials, called interfacial water, plays important roles in biology,[1] meteorology,[2] geology,[3] and nanotechnology. Liquid water behaviour as it comes in contact with a solid surface is an interfacial phenomenon that helps us to understand membrane channels.[4] water organisation, together with surface chemistry, influences many biological phenomena, such as bio-adhesion.[1,5]. The level of organisation for these interfacial water molecules is key to discerning wetting phenomena.[6] such interfaces provide a rich environment for unravelling how confinement of water molecules’ motion is affected by the properties of the material, which can be observed in the variation of transport and vibrational properties. Understanding the role of hydrogen bonding between interfacial water molecules and the surface/bulk of water is important to reveal more clues about wetting phenomena

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Conclusion