Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.224
Publication date: 18th July 2019
The microscopic description of the interface of colloidal nanoparticles (NPs) in solution is essential to understand and predict the stability of such systems, as well as their chemical and photochemical reactivity. However, the details of such an interface are still poorly understood and often rely on the use of simple electrostatic mean field models. Besides, surfaces are challenging to probe selectively as the bulk contribution often dominates, and in many cases the surface properties of a colloidal system cannot be inferred from studies of the corresponding planar surface.
Here we show that the electrical double layer of NPs in aqueous solution can be probed with polarimetric angle-resolved second harmonic scattering (AR-SHS). This nonlinear optical technique selectively probes the interfacial region and offers an all-optical alternative to surface‑sensitive techniques that usually require more sophisticated resources, as for example X-ray photoelectron spectroscopy.[1] Furthermore, AR-SHS gives access to quantities such as surface potential and water molecular orientation at the interface, two parameters not easily obtained experimentally, without the use of any labeling molecule nor a priori models for the structure of the interface. [2]
In this work, AR-SHS is applied to model SiO2 NPs as a proof of concept, and to semiconductor NPs such as TiO2. We are able to monitor surface changes as a function of pH and salt concentration, and show results under illumination for TiO2. An extension of AR-SHS to the time domain is discussed. This work provides a description of the structure and energetics of the NPs interface in different aqueous environments and highlights some of the electronic specificities of the semiconductor/aqueous interface.
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