The Growth Of Perovskite Structure Thin Films And In Situ Electronic Structure Measurement

A series of perovskite oxide thin films LaFe_1-xCr_xO₃ (x = 0.1¹.0) have been fabricated using laser molecular beam epitaxy (Laser MBE), and investigated on its electronic structures by in situ Synchronization Radiation Photoemission Spectroscopy (SRPES).The main contents and results are as follows. Part â… 1.1 Powders of LaFe_1-xCr_xO₃ (x = 0.1¹.0) were synthesized by solid reaction processes, then its structures were characterized by XRD and EXAFS. The data show that all samples are with a single phase. The lattice constants (a, b and c) decrease with the content of Cr increasing. The FeO₆ octahedra of LaFe_1-xCr_xO₃. systems present small changes, i.e.(Fe-0 bond and volume of the FeO₆ octahedra) but the La atoms shift larger. Finaly,these oxide powders were sinterd into the targets of Laser-MBE by the spark plasma sintering (SPS).1.2 We have also investigated on the methods to treat of commercial SrTiO₃ (STO), which is an important substrate for atomic scale epitaxy. The experimental measurements of Atomic force microscopy (AFM) and reflection high energy electron diffraction (RHEED) show that it is very effetive to obtain atomic smooth surface by annealing in oxygen atmosphere and homoepitaxy of STO.1.3 Perovskite thin films LaFe_1-xCr_xO₃ with the thickness of 10 run have been successfully fabricated by continuous RHEED intensity oscillations monitoring. Part â…¡2.1 The core levels of three films(LaCrO₃,LaFe_0.5Cr_0.5O₃,LaFeO₃) were detected using the photoemission spectrum (PES). We didn't observe any impurity peaks. The available results illustrate that the valences of Fe and Cr in the oxides were still in +3 while the doping. And the O Is core level shifts about 2 eV, contributing to the charge exchange between the O 2p orbit and the 3d orbits of FeandCr.2.2 The Fe and Cr 3d obit electronic structure of LaFei.xCrxO3 thin films were studied by resonance photoemission spectrum (RPES). The data show that the Fe-O-Cr bonding structure exist. And the Fe 3d eg electrons transferred to Cr 3d obit through the O 2p obit while the Cr doping.2.3 We studied the behavior of d obits (La, Fe and Cr) on conduction band, and concluded that the energy gaps in LaFei-xCrxO3 became small from LaCrO3 to LaFeO3.2.4 The La 4d and 4f X ray absorption spectrum(XAS) were analyzed. And we discussed the reasons of giant band of 4f excitation state 'Pi. The results show that the changes of ligand field effect the La 4f obit, which is supported by first-principles electronic structure calculations.