Photochemical Reaction Patterns on Heterostructures of ZnO on Periodically Poled Lithium Niobate.
The internal electric field in LiNbO3provides a driving force for heterogeneous photocatalytic reactions, where photoexcited holes or electrons can participate in redox reactions on positive (+c) and negative (-c) domain surfaces and at the domain boundaries. One method to characterize the surface chemical reactivity is to measure photoinduced Ag deposition by immersing the LiNbO3in an aqueous AgNO3solution and illuminating with above bandgap light. Reduction of Ag+ions leads to the formation of Ag nanoparticles at the surface, and a high density of Ag nanoparticles indicates enhanced surface photochemical reactions. In this study, an n-type semiconducting ZnO layer is deposited on periodically poled LiNbO3(PPLN) to modulate the surface electronic properties and impact the surface redox reactions. After plasma enhanced atomic layer deposition (PEALD) of 1, 2, 4, and 10 nm ZnO thin films on PPLN substrates, the substrates were immersed in aqueous AgNO3and illuminated with above band gap UV light. The Ag nanoparticle density increased for 1 and 2 nm ZnO/PPLN heterostructures, indicating an enhanced electron density at the ZnO/PPLN surface. However, increasing the ZnO thickness beyond 2 nm resulted in a decrease in the Ag nanoparticle density. The increase in nanoparticle density is related to the photoexcited charge density at the ZnO/PPLN interface and the presence of a weakly adsorbed Stern layer at the ZnO surface. The decrease in the nanoparticle density for thicker ZnO is attributed to photoexcited electron screening in the ZnO layer that suppresses electron flow from the LiNbO3to ZnO surface.
School for Engineering of Matter, Transport and Energy, Arizona State University , Tempe, Arizona 85287-6106, United States.
Manpuneet
M
Kaur
School for Engineering of Matter, Transport and Energy, Arizona State University , Tempe, Arizona 85287-6106, United States.
Qianlang
Q
Liu
School for Engineering of Matter, Transport and Energy, Arizona State University , Tempe, Arizona 85287-6106, United States.
Peter A
PA
Crozier
Department of Physics, Arizona State University , Tempe, Arizona 85287-1504, United States.
Robert J
RJ
Nemanich
AFM; PEALD; PFM; PPLN; ZnO; heterostructure; lithium niobate; photoinduced