Domain Patterned Ferroelectric Surfaces for Selective Deposition Via Photochemical Reaction

Abstract

In this work, the use of domain patterned ferroelectric materials as a template to direct the assembly of nanostructures via photochemical reactions as well as to direct the assembly of polar molecules is presented. A distinct characteristic of ferroelectric materials is existence of a reversible spontaneous polarization. The direction of the spontaneous polarization can be reversed with the application of an electric field; thus, conductive tip atomic force microscopy (AFM) was employed to "write" nanoscale domain patterns in the ferroelectric and subsequently to visualize the configuration with piezoresponse force microscopy (PFM).

Domain patterned lithium niobate and lithium tantalate, which are known as oxygen octahedra ferroelectrics, were used as templates. These materials exhibit unique surface electronic properties resulting from screening of the bound polarization charge, which dictate local reactivity on the surface. The effect of composition (stoichiometry and doping) on photochemical reactions at the surface is explored. Depending on the composition of the material, deposition can occur on the surface of domains or domain boundaries leading to a "bottom-up" method of nanowire formation. Nanowires of various shapes and sizes can be fabricated, as these parameters are dependent only upon the underlying domain configuration. Domain specific adsorption of polar molecules is achieved by utilizing the pyroelectric nature of ferroelectric materials. Surfaces may also be passivated with these polar molecules; subsequent UV irradiation induces photodecomposition of the molecules, which results in the formation of trenches at domain boundaries. Additionally, a scanning Kelvin probe microscopy (SKPM) study of the charge distribution on the surface of lithium niobate emphasizes the external screening mechanism and demonstrates the instability and screening of surface charges.