title: Phase-referenced nonlinear spectroscopy of the α-quartz/water interface.
abstract: 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 (χ1(3)-iχ2(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.
authors.affiliation: Department of Chemistry, Northwestern University, Technological Institute Room KG68, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Paul E
authors.identifier: 0000-0003-4192-1888
authors.initials: PE
authors.lastname: Ohno
authors.affiliation: Department of Chemistry, Northwestern University, Technological Institute Room KG68, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Sarah A
authors.identifier: 0000-0002-8385-2676
authors.initials: SA
authors.lastname: Saslow
authors.affiliation: Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Hong-Fei
authors.identifier: 0000-0001-8238-1641
authors.initials: HF
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Northwestern University, Technological Institute Room KG68, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Franz M
authors.initials: FM
authors.lastname: Geiger
authors.affiliation: Department of Chemistry, Columbia University, New York, New York 10027, USA.
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Eisenthal