LiNbO₃surfaces from a microscopic perspective

Abstract

A large number of oxides has been investigated in the last twenty years as possible new materials for various applications ranging from opto-electronics to heterogeneous catalysis. In this context, ferroelectric oxides are particularly promising. The electric polarization plays a crucial role at many oxide surfaces, and it largely determines their physical and chemical properties. Ferroelectrics offer in addition the possibility to control/switch the electric polarization and hence the surface chemistry, allowing for the realization of domain-engineered nanoscale devices such as molecular detectors or highly efficient catalysts. Lithium niobate (LiNbO) is a ferroelectric with a high spontaneous polarization, whose surfaces have a huge and largely unexplored potential. Owing to recent advances in experimental techniques and sample preparation, peculiar and exclusive properties of LiNbO surfaces could be demonstrated. For example, water films freeze at different temperatures on differently polarized surfaces, and the chemical etching properties of surfaces with opposite polarization are strongly different. More important, the ferroelectric domain orientation affects temperature dependent surface stabilization mechanisms and molecular adsorption phenomena. Various ab initio theoretical investigations have been performed in order to understand the outcome of these experiments and the origin of the exotic behavior of the lithium niobate surfaces. Thanks to these studies, many aspects of their surface physics and chemistry could be clarified. Yet other puzzling features are still not understood. This review gives a résumé on the present knowledge of lithium niobate surfaces, with a particular view on their microscopic properties, explored in recent years by means of ab initio calculations. Relevant aspects and properties of the surfaces that need further investigation are briefly discussed. The review is concluded with an outlook of challenges and potential payoff for LiNbO based applications.

Second harmonic microscopy of poled x-cut thin film lithium niobate: Understanding the contrast mechanism

“…The domain growth started from the bottom electrodes, to which the positive voltage was applied. This is a behavior typical observed during electric field poling of LN, where growth starts from the positive electrodes 62 . Figure 10(a) shows a simulated line scan for the given film and numerical aperture parameters for a vertical DW.…”

Magnetism and multiferroic properties at MnTiO3 surfaces: A DFT study

“…From a technological point of view, this result is exciting because the control of (0 0 1) surface properties of many perovskite (ABO 3 ) materials has been intensively explored during recent years. Moreover, some reports for multiferroic BiFeO 3 based-material show the existence of a (0 0 1) surface plane in the reported morphologies, and the z-cut of LiNbO 3 (R3c) exhibits an intriguing mechanism associated with the dependence of ferroelectric ordering [10,[69][70][71].…”

“…1. Below the Curie temperature, the A cations are displaced from the central positions of oxygen octahedral cages-i.e., [AO 6 ] cluster-resulting in a spontaneous polarization along the (0 0 1) direction [10,19]. This distortion also induces a singular crystal-field splitting, especially for A-site cations, owing to the existence of a trigonal prismatic arrangement (D 3h ) that splits the t 2g levels into nondegenerated a 1g and double-degenerated states, whereas e g becomes .…”

“…In addition, several studies have exploited the electrical field at the ferroelectric surfaces, indicating that the surface polarity can be switched by an external electric field that controls the bulk spontaneous polarization [1][2][3]. In this case, the chemical and physical properties associated with the surfaces can be controlled, resulting in several interesting applications-for instance, the dynamic control of catalysis, photocatalysis and artificial photosynthesis, and switchable chemical sensors [3][4][5][6][7][8][9][10][11].…”

Ab initio Calculations of YAlO3 and ABO3 Perovskite (001), (011) and (111) Surfaces, Interfaces and Defects

“…Surface and interface phenomena, taking place in the ABO 3 perovskites as well as their nanostructures, the complex nature of their surface and interface states, the novel mechanisms of surface electronic processes are the key topics in nowadays solid state physics [1][2][3][4][5][6][7]. CaTiO 3 (CTO), SrTiO 3 (STO), PbTiO 3 (PTO), BaTiO 3 (BTO), SrZrO 3 (SZO) and PbZrO 3 (PZO) materials are so-called ABO 3 perovskites, and they have a large amount of technologically important applications, such as, for example, capacitors, actuators, and charge storage devices, and many others [8], for which the surface quality and structure are essential.…”