Simultaneous Spectroscopic and Topographic Near-Field Imaging of TiO₂ Single Surface States and Interfacial Electronic Coupling

Abstract

We have probed single surface states and the involved interfacial charge transfer coupling on the TiO(2) surface using confocal as well as tip-enhanced near-field topographic-spectroscopic imaging analysis on a niobium-doped rutile TiO(2)(110) surface. The confocal images excited with a radially polarized donut mode render ring-shaped excitation patterns typical for quantum systems with two perpendicular transition dipole moments. The tip-enhanced near-field optical images of single surface states are visualized by the strong exciton plasmon-polariton coupling localized at the subdomain boundaries with a spatial resolution of ∼15 nm (far beyond the optical diffraction limit). We suggest that the abundant surface states in the doped TiO(2) generate excitons under laser excitation which are strongly coupled to the surface plasmon-polaritons of the Au tip. Moreover, the interfacial electronic molecule-substrate coupling has been characterized by probing the molecule-perturbed surface states distribution and the associated specific Raman vibrational modes. The imaging and characterization of the surface states and their distributions on TiO(2) surfaces at nanoscale are critically relevant to a deep understanding of interfacial electron transfer dynamics and energetics involving in solar energy conversion, photocatalysis, and mechanistic understanding of surface-enhanced Raman scattering spectroscopy.

Nanoscale Chemical Imaging Using Tip‐Enhanced Raman Spectroscopy: A Critical Review

“…Tools for the chemical analysis of thin‐film solar cell materials at the micro‐ and nanometer scale are definitively needed, because there are still many remaining questions concerning the relationship between fabrication/processing, micro‐ and nanostructure, and solar cell efficiency. The potential of tip‐enhanced spectroscopy for studying single surface states in inorganic semiconductors, such as Nb‐doped rutile (TiO 2 ), has recently been demonstrated by Sevinc et al 128…”

Probing the inhomogeneity and intermediates in the photosensitized degradation of rhodamine B by Ag3PO4 nanoparticles from an ensemble to a single molecule approach

“…Single-molecule, single-particle uorescence and single molecule uorescence lifetime imaging microscopy (FLIM) have been proved to be the very powerful tools for investigating heterogeneous processes because of their high sensitivity and selectivity, simplicity of data collection, and high spatial and temporal resolution. [14][15][16][17][18] Indeed, Majima and coworkers used single-molecule dynamical observations and proposed that the reaction sites in the effective reduction of probe molecules are located on the facets with a higher surface energy. 19 The IET processes between a single dye molecule and TiO 2 nanoparticle surface demonstrate an inhomogeneity and sensitizing efficiency.…”

Enhanced Vibrational Spectroscopies as Tools for Small Molecule Biosensing

“…TERS has already demonstrated its performances in the characterization of several materials as carbon nanotube [ 94 , 95 , 96 , 97 ], graphene [ 98 , 99 , 100 ], semiconductors layers (InN [ 101 ], Si(001) [ 102 ], GaAs(001) [ 103 ]), oxides layers (BaTiO 3 [ 104 ], TiO 2 [ 105 ]) or molecular monolayers (copper porphyrin [ 106 ], copper phthalocyanine (CuPc) [ 107 ], thiol compounds [ 108 , 109 ]), and biomolecules (proteins [ 110 ], peptides [ 111 , 112 ], single RNA strands [ 113 ], cytochrome [ 114 ], lipid domains [ 115 ], alginate biofilms [ 116 ], insulin amyloid fibrils [ 117 , 118 , 119 ]).…”