Preparation And Properties Of SnO₂ Films

Porous metal oxide films,with ferromagnetism and resistive switching properties,may be multifunctional materials and they are expected to be applied in spintronic devices and multifunctional data storage.The porous tin oxide films as the research object is selected in this paper.These films have large specific surface areas,and there are many oxygen vacancies and metal ion vacancies in these films.Due to the difficulty in controlling the magnetism,a series of characterizations and studies were carried out based on porous tin oxide films.This paper mainly consists of two parts and the porous films are prepared by a sample and convenient electrochemical anodic oxidation method.Firstly,some films have structure color and its structure,optical and magnetic properties were studied.Secondly,the porous films were prepared by changing the oxidation voltage and time,its structure,magnetism and resistance were analyzed and the magnetism can be controlled by the applied electric field.This research provides theoretical and experimental basis for the development of storage.The research results are as follows:(1)Porous tin films were prepared by electrochemical anodic oxidation in 0.5 mol/L Na OH at room temperature.The films have saturation color in the visible light range.The result of SEM shows the porous structure and the thickness increasing with the oxidation time.Then,the relationship between color and time were studied,and these films were tested by UV-Vis.The color of these films are consistent with the maximum reflection peak and the corresponding wavelength and thickness conform to the principle of interference.(2)The magnetic properties of the films with structure color were tested by MPMS.Interestingly,the films can exhibit ferromagnetism,paramagnetism and diamagnetism.Moreover,the magnetism changes of the films are related to the direction of the applying magnetic field,showing obvious magnetic anisotropy.All the films have ferromagnetism at low field.With out-of-plane filed,the films show diamagnetism at high filed.But the films show paramagnetism with in-plane filed.(3)In order to further study the physical properties of these films,the porous films were prepared by changing the oxidation voltage and time.The results of HRTEM shows the prepared films crystallized well.These films measured by SEM and the thickness and pore size increase with the voltage,and the tube wall dissolves with the increasing voltage.The growth rate of these films at high voltage is several times than that of other metal films.(4)The films prepared at different voltages and time were tested by MPMS.These films also have ferromagnetism and magnetic anisotropy.The magnetism increases with the increasing of pore size,but decreases with the increasing of the thickness.The magnetic results are roughly consistent with the magnetic law of the structural color samples,but this law no longer exists when the films reach a certain thickness,which may be closely related to the sponge-like structure of these films.In this paper,the phenomenon is explained by combining the knowledge of solid state physics.This research will expand the application scope of porous tin films.(5)After annealing some samples in oxygen atmosphere,the porous films are tested by MPMS and PL.The results verified that oxygen vacancies are related to the generation of the ferromagnetism.ZFC/FC show the as-prepared samples have ferromagnetism.The Ag/Sn O₂/Sn resistive switching device was fabricated and the device has obvious bipolar resistive switching.The device has high-resistance and low-resistance state,and the magnetism in different states were studied.This result can shows the relationship of the resistance switching characteristics and ferromagnetism.This research shows the electric field can control the strength of ferromagnetism,which provides an important experimental basis for solving the physical mechanism of the magnetization controlled by the electric field in oxide semiconductor.It is expected to be widely used in the field of multi-functional data storage.