MODELLING THE STRUCTURE AND DYNAMICS OF H-BOND NETWORKS AT OXIDE-WATER INTERFACES: FROM NEUTRON SPECTROSCOPY TO SUM FREQUENCY GENERATION
Open Access
- Author:
- Dellostritto, Mark Joseph
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 28, 2017
- Committee Members:
- Jorge Sofo, Dissertation Advisor/Co-Advisor
Jorge Sofo, Committee Chair/Co-Chair
Milton Cole, Committee Member
Mauricio Terrones, Committee Member
Lasse Jensen, Outside Member - Keywords:
- water
oxide
molecular dynamics
sum frequency generation
hydrogen bond
network
neutron
polarizability
density functional theory - Abstract:
- In this thesis I review the structure and dynamics of H-bond networks at oxide-water interfaces. I progress from simple, local measures of the H-bond network to more complex, non-local measures, reviewing studies of specific oxide-water interfaces as examples. In all examples, I use density functional theory molecular dynamics (DFT-MD) simulations to extract both structural and vibrational information which I use to correlate experimentally measured vibrational spectra with the microscopic structure. I first introduce the vibrational density of states (VDOS) measured with inelastic neutron scattering (INS) and show how it can be used to reveal strong, anisotropic H-bonds at the SnO<sub>2</sub>(110)-H<sub>2</sub>O interface. Moving beyond the local VDOS, I then use a network description of the H-bond network and a ``residence'' definition of the H-bond to study how cations affect structural correlations of the H-bond network at the SiO<sub>2</sub>(110)-H<sub>2</sub>O interface. I then introduce a non-local measure of the vibrational spectrum of an interface, Sum Frequency Generation (SFG), and review the theory behind this surface-specific nonlinear optical vibrational probe. As calculation of the SFG spectrum requires knowledge of the polarizability of an interface, I then introduce an Atomic Interaction Model (AIM) for efficient, accurate calculations of the polarizability which take into account local interactions. Finally, I calculate the SFG response of the Al<sub>2</sub>O<sub>3</sub>(001)-H<sub>2</sub>O interface and show that multiple, independent simulations are necessary for converged results for interfaces, that the calculated response matches the measured response, and that the two peaks are due to H<sub>2</sub>O and surface OH groups separately, not solely H<sub>2</sub>O molecules as previously thought.