Growth Of LaRhO₃ Thin Films And Property Manipulation By Multi-Fields

In the perovskite transition metal oxide,due to the strong coupling between electrons,orbits,spins and lattices,there will be many rich and strange functions,such as high temperature superconductivity,colossal magnetoresistance effect and interface two-dimensional electron gas(2DEG),which inspired people's enthusiasm for the study of perovskite transition metal oxide materials.In the 4d perovskite transition metal oxide,because of the strong spin-orbit interaction,many novel properties have appeared,such as the discovery of unconventional superconductor in Sr2RuO4.And LaRhO3(LRO)not only shows the paramagnetic semiconductor behavior in,but also shows excellent catalytic performance and thermoelectric performance.Although the magnetic and electrical properties of LRO can be changed by doping,the introduction of other ions can cause trouble in the mechanism analysis.From the application point of view,thin film is more conducive to the miniaturization and integration of the device than the bulk material;from the perspective of physical research,thin film will appear some new phenomena different from the bulk material.First,we grew high-quality LRO thin films.Then,we use non-doping method(stress,light and gas)to adjust the property of LRO thin film.It can not only deepen understanding of 4d perovskite transition metal oxide materials,but also provide great potential for fabrication of devices in the future.This dissertation is divided into six chapters,mainly to study the properties of LRO thin films under various external fields control.The first chapter summarizes the basic knowledge and the background of perovskite transition metal oxide materials,then introduces the research progress of 4d rhodium oxide,and finally introduces three methods of stress,light and gas to regulate perovskite transition metal oxide materials.The second chapter introduces the growth method,characterization and self-build system.First introduce the knowledge of pulsed laser deposition(PLD)technology,including polycrystalline target preparation,substrate selection and the advantages and disadvantages of PLD in the fabrication of oxide thin films.Next,we introduce commonly used structural characterization methods for thin films,such as X-ray diffraction(XRD),Atomic Force Microscope(AFM),and commonly used physical property characterization methods,such as Physical Property Measurement System(PPMS)and Superconducting Quantum Interferometer(SQUID),and introduce two measurement systems about photoconductivity and gas sensing.Finally,we introduce the process of using photolithography technology for preparing devices.The third chapter introduces the growth of LRO film and its stress control research.In this chapter,we detail the process of growing high-quality LRO thin films,and then grow LRO samples on STO,LSAT,and LAO substrates,using the lattice mismatch between the film and the substrate to apply different degrees of stress.Finally,SQUID and MFM results show that the LRO film is ferromagnetic,which means stress successfully adjust the LRO material from paramagnetic to ferromagnetic.Chapter 4 introduces the research on the properties of LRO regulated by laser.According to the growth window of LRO film in Chapter 3,a high-quality LRO film was grown on the STO(110)substrate.Then the transient photoconductive(TPC)effect of LRO was tested under different laser wavelengths and different laser powers.When the laser wavelength is shortened,the TPC effect is enhanced;when the laser wavelength is fixed and the laser power is increased,the TPC effect is also enhanced.Finally,we also discuss the contribution of thermal effects to the TPC effect of LRO.Chapter 5 introduces the research on the properties of LRO regulated by organic vapors.When the LRO film is in ethanol gas atmosphere at different concentrations,its resistance will change significantly.Changing the thickness of the film,it was found that when the film thickness was 17 nm,the responsivity was the largest.Then the gold modification of the LRO film was carried out.When the thickness of the gold was 3 nm,the gas sensitivity to LRO was most obviously improved.Through XPS analysis,the proportion of adsorbed oxygen on the surface of LRO thin film increases greatly after gold modification,and the adsorbed oxygen can undergo a redox reaction with ethanol molecules,changing the sample resistance.The content of adsorbed oxygen will determine the performance of the gas sensor.Therefore,the gas sensitivity Au/LRO is greatly improved.By simply modifying the surface of the perovskite transition metal oxide thin film,its gas-sensing performance can be improved.This approach opens new ideas for the future preparation of gas sensors.Chapter 6 summarizes the work of this dissertation and the future.First,although the ferromagnetic of the LRO thin film has been achieved through stress,its generation mechanism is not yet clear and needs to be further resolved.Secondly,ultrafast optics is an effective way to study the ultrafast process inside the material,and the ultrafast kinetic process inside the LRO film is currently unclear.So,the ultrafast optical research of the LRO film is very meaningful.Finally,it is pointed out that the electric field is also a common way to manipulate thin film properties.Some new properties of LRO thin film are expected under the control of electric fields.