The Optical And Transport Properties Modulation And Applications Of Ferroelectric Materials

The distinct physical properties of ferroelectric materials and the multiple-properties coupling upon these materials,attract much attentions not only on the fundamental physics researches but also on the application fields.It is considered to have potential benefit on ferroelectric photovoltaic device,ferroelectic random access memory,piezoelectric material,ferroelectric tunnel junction,etc.This thesis systematically research about the optics-electron characteristic and transport behaviors of multiferroic Bi Fe O₃,and propose the possible applications based on these researches.Besides,the electron doping on a common ferroelectric material Pb Ti O₃ is experimentally explored in order to find a candidate for ferroelectric metal,which was predicted decades ago,but has few members up to now.The main results are listed as follows:1.Ferroelectric Bi Fe O₃ films were deposited on the?001?-oriented Sr Ti O₃ substrates by Laser molecular-beam epitaxy technique.By introducing a laser beam into the combination of piezoelectric force microscopy and Kelvin Probe Force Microscopy,we demonstrate that the surface potential contrast of Bi Fe O₃ films can be recovered based on the mechanism of ferroelectric photovoltaic effect.The redistribution of the photo-induced charges driven by the internal polarization field results in the recovery of the surface potential contrast.Our theoretical calculations reproduce our experimental results,revealing the basic recovering mechanism.It is promising that a novel photo-assistant non-destructive read-out method in ferroelectric thin film by using non-contact surface potential can be realized as non-volatile ferroelectric memory.2.The dynamics of surface screening charges on Bi Fe O₃ films with pre-written stripes of domains was studied with surface potential measurements by Kelvin Probe Force Microscopy.The screening effect decays exponentially with time,and this decay is slower in the arrays with wider domains or larger intervals of domains,indicating that the in-plane diffusion of the surface screening charges plays a major role in the decay dynamics.The good agreement between experimental data and theoretical results based on diffusion-drift model confirms the mechanism of in-plane diffusion of the screening charges in the decay dynamics.Our work could provide a pathway to control the data stability of charge storage by artificially designing the ferroelectric domains.3.An intuitively persistent enhancement of the local surface potential of Bi Fe O₃ films was observed by the Kelvin probe force microscopy technique after the illumination.This photo-induced enhanced surface potential can maintain as long as 15 hours after the illumination.We attributed this super-long-time relaxation of photo-induced influence to a photo-induced depolarization in the Bi Fe O₃ thin films.Our findings provide a peculiar understanding into the photo-induced phenomena on the widely researched ferroelectric systems4.We report the coexistence of metallicity and polar distortion in a new candidate for ferroelectric metal Pb Ti1-x Nbx O₃ via doping engineering.The ferroelectric-like local polar distortion in all the doped Pb Ti1-x Nbx O₃ samples,where x is ranging from 0.04 to 0.12,was confirmed by piezoresponse force microscopy and scanning transmission electron microscopy measurements.Pb Ti1-x Nbx O₃ films become more conductive with increasing the doping level,and emerge a metallic behavior when x reaches 0.12.We believe that these results confirm the feasibility of realizing the coexistence of metallicity and polar distortion in common ferroelectrics.