Phase-referenced nonlinear spectroscopy of the α-quartz/water interface

• Published in: Nature communications Vol. 7; no. 1; pp. 13587 - 5
• Main Authors: Ohno, Paul E., Saslow, Sarah A., Wang, Hong-fei, Geiger, Franz M., Eisenthal, Kenneth B.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13.12.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 639/638/440/527; 639/638/542/971; ATOMIC AND MOLECULAR PHYSICS; Humanities and Social Sciences; multidisciplinary; optical spectroscopy; Science; Science (multidisciplinary); surface spectroscopy
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms13587

Probing the polarization of water molecules at charged interfaces by second harmonic generation spectroscopy has been heretofore limited to isotropic materials. Here we report non-resonant nonlinear optical measurements at the interface of anisotropic z -cut α-quartz and water under conditions of dynamically changing ionic strength and bulk solution pH. We find that the product of the third-order susceptibility and the interfacial potential, χ (3) × Φ(0), is given by ( χ 1 (3) − iχ 2 (3) ) × Φ(0), and that the interference between this product and the second-order susceptibility of bulk quartz depends on the rotation angle of α-quartz around the z axis. Our experiments show that this newly identified term, iχ (3) × Φ(0), which is out of phase from the surface terms, is of bulk origin. The possibility of internally phase referencing the interfacial response for the interfacial orientation analysis of species or materials in contact with α-quartz is discussed along with the implications for conditions of resonance enhancement. Probing the polarization of water molecules at charged interfaces reveals insights into surface behaviour, but current methods are limited to isotropic materials. Here the authors exploit the nonlinear optical properties of the α-quartz/water interface to expand the scope of such methods to non-isotropic materials.