Photoinduced charging and spatially selective photochemistry on ferroelectric surfaces

Abstract

Ferroelectric surfaces exhibit polarization-dependent photoreactivity and provide a route to program chemical patterns through local electrical control of polarization. Observations accumulated over several decades show reaction products in domain interiors, at domain boundaries, and in other selected regions, indicating that the mechanisms extend beyond a single polarization-induced band-bending picture. Here we analyze light-induced charging and interfacial reactions on uniformly polarized ferroelectrics and domain patterns, for dry surfaces and surfaces in contact with an electrochemically active solution. A common semiconductor transport and charge-conservation framework distinguishes five cases: an isolated dry ferroelectric, a dry ferroelectric connected to a carrier reservoir, a blocking ferroelectric-electrolyte junction, a reactive interface with an external carrier return, and two opposite domains coupled through the solid and electrolyte. Analytical solutions and numerical evaluations connect stationary potentials versus illumination to differential optical spectra and finite light-step responses. We further examine the doping effects on static potentials in all five cases and dynamic photovoltage in the isolated film and a fixed-polarization, bare-surface contacted-film variant. For reactive interfaces, the same framework determines reduction and oxidation rates, their spatial distributions, and accumulated reaction amount. The analysis covers surface charging and photochemical conversion beyond deposition, while retaining the electrical and chemical boundaries that distinguish finite charging from sustained turnover, and explains the observed range of photodeposition morphologies. Finally, this framework builds the theoretical foundation for the modulated photovoltage imaging methods that can readily be realized in SPM under illumination.