Studies On Strain Tuning Of Transport And Photoelectric Properties Of Oxide Thin Films Based On Mica Substrates

Functional oxide thin films have attracted the wide attention of researchers due to their rich functional properties.As a control method,lattice strain can greatly affect the coupling between lattice degree of freedom and other degrees of freedom and induce many novel physical phenomena.Based on van der Waals epitaxial film fabrication technology,exploring the control of mechanical bending strain on the functional properties of oxide films can not only explore novel physical phenomena caused by bending strains but also provide certain guidelines for the development and application based on flexible film materials.In this paper,two types of oxide thin films——Cr doped In2O3 and perovskite structure doped manganese oxide are selected as the research objects to study the tuning of bending strain on their electronic transport and photoelectric properties.Through experiments and firstprinciples calculations,exploring the tuning mechanism of bending strain.The main researches are listed as follows:(1)The Cr:In2O3 film was grown on the flexible(001)mica substrate.By applying different compressive or tensile bending strains on the sample,the effects of strains on electronic transport and photoelectric properties of the film were studied.The results show that the Cr:In2O3 film exhibits lateral photoelectric properties that are sensitive to the position.When mechanical bending is applied,the resistance and lateral photoelectric response sensitivity of the film decrease and increase,respectively.Under-0.084%compressive and 0.083%tensile bending strains,the resistance decreases by 8.9%and 4.6%,the sensitivity of the lateral resistance increases by 74.6%and 60.5%,respectively,and the signal response time significantly increases.The analysis shows that the lateral photoelectric effect of the film is mainly based on the thermoelectric effect.The flexoelectric effect induced by bending strain tunes the related parameters of the thermoelectric properties of the Cr:In2O3 film,and enhances the conductivity and lateral photoelectric effect of the Cr:In2O3.These results show that bending strain is an effective way to improve the lateral photoelectric properties of the Cr:In2O3 film.(2)The La0.67Sr0.33MnO3 film was grown on the flexible(001)mica substrate,and the effects of bending strain on the electronic transport and photoelectric properties of the films were studied.The results show that bending strains can significantly control the electronic transport and photoelectric properties of the La0.67Sr0.33MnO3 film.As the bending strains increase,the resistance and photoresistance of the film gradually decrease and increase,respectively.At room temperature,the photoresistance of the La0.67Sr0.33MnO3 film is increased by 95.88%and 92.14%at-0.047%compressive and 0.045%tensile bending strains,respectively,and the signal response time significantly increases.Meanwhile,bending strains and illumination also can tune the insulator-metal transition in La0.67Sr0.33MnO3.The insulatormetal transition in film disappears by applying bending strains.By adjusting the carrier concentration,illumination reduces the insulator-metal transition temperature by 50 K.Based on first-principles calculations,the compressive/tensile bending strains make the electronic density of states of the Mn-3d and O-2p orbitals of the La0.67Sr0.33MnO3 move towards low/high energy,respectively,which causes the increase of the electronic density of states near the Fermi energy level and enhances the conductivity.Besides,Jahn-Teller distortion becomes more obvious as the bending strains increase,which suppresses the insulator-metal transition in La0.67Sr0.33MnO3.(3)The La0.9Hf0.1MnO3 film was grown on the(001)PMN-PT single crystal substrate,the tuning of the in-plane lattice strain in situ induced by the polarization electric field on the resistance and photoelectric properties of the La0.9Hf0.1MnO3 film was studied.And we compared the difference between non-bending strain tuning and bending strain tuning.The results show that the polarization electric field can significantly control the resistance and photoelectric properties of the epitaxial La0.9Hf0.1MnO3 film based on the inverse piezoelectric effect of the ferroelectric single-crystal substrate PMN-PT.At room temperature,as the in-plane compressive strain increases,the resistance and photoresistance of the film gradually decreases and increases,respectively.The difference from bending strains is that in-plane strain does not change the response time of the signals.Besides,as the temperature decreases,the curves of the resistance of the film with the applied bipolar cyclic polarization electric field gradually change from "butterfly" to "square".High-power illumination can turn the "square" curves into"butterfly" curves.These indicate that the tuning effect of the polarization electric field shows the competition mechanism of the ferroelectric field effect and the strain effect.The strain effect is shown when the carrier concentration is high,and the electric field effect is shown when the carrier concentration is low.