Research La _0.9 Sr _0.1 CoO ₃ Laser Induced Thermoelectric Voltage Film Effects And Humidity Characteristics

Strontium doped oxide La1.xSrxCoO3belongs to ABO3-typed cubic perovskite oxides, it is a kind of mixed conductor of high temperature electrons and ions, which exhibites abundant physical properties such as:high temperature superconducting property, colossal magnetoresistance effect. At present, few reports demonstrated that it also has laser induced thermoelectric voltage effect (LITV) and humidity sensitive property. The study of Lao.9Sr0.1CoO3thin films contributes to exploring efficient and useful materials. In this paper, we systematic studied the LITV effect and humidity sensitive property of La0.9Sr0.1CoO3thin films. The work’s main contents and results are as follows:1. The strontium-doped La0.9Sr0.1CoO3ceramic targets were prepared by a conventional solid state reaction method. We used XRD characterization. Compared with the standard PDF card (28-1229) of La0.9Sr0.1CoO3, the ceramic target was really La0.9Sr0.iCo03. Then we used PLD technique deposited La0.9Sr0.1CoO3thin films grown on5°vicinal cut LaAlO3(100) substrates. The Lao.9SrO.1CoO3thin films were oriented growth along (110), their surface was compact and uniformly, and the crystallinity was very good.2. We measured LITV signals of the La0.9Sr0.1CoO3thin films grown on LaAlO3(100) substrates. When the inclination angle of LaAlO3(100) substrate was5°, the full width at half maximum of LITV signal was45ns and the rise time of LITV signals was only18ns, the response time was extremely rapid, which exhibited that La0.9Sr0.1CoO3thin films can be used to prepare fast response time laser energy/power meter. The peaks voltage had a good liner relationship of peak voltage with pulse laser energy, which can be used to prepare high precision detector. When the pulse laser energy irradiated on the La0.9Sr0.1CoO3thin films was8.57mJ, the peak voltages of LITV signals reached up to3.76V, exceed La0.9Sr0.1CoO3thin films with other doped proportion. it showed that La0.9Sr0.1CoO3thin films had high sensitivity which can be used to fabricate photosensitive device. Due to above characteristics, light detectors fabricated by La0.9Sr0.1CoO3thin films were superior to bulk light detectors fabricated by silicon photo materials, thermal sensitive ceramic materials, et al.3.For the further studied the influence of different titling angles to the LITV signals, we prepared the La0.9Sr0.1CoO3thin films grown on3°、5°、10°、15°vicinal cut LAO (100) substrates. Through the measurement of LITV signals, we obtained that when the titling angles was5°, the peak voltage with pulse laser energy had the best liner relationship,that is the precision was the highest; when the titling angles was15°, the rake ratio was the largest, which exhibiting the best sensitivity.4. The La0.9Sr0.1CoO3thin films not only exhibited LITV effect of fast response time, high precision and high sensitivity, but also showed humidity sensitive property which resistance exchanged with humidity. In order to study the relations of substrate and humidity sensitive property of La0.9Sr0.1CoO3thin films, we introduced a humidity sensitive coefficient a=ΔR/(R0x ARH%). Calculated the a of La0.9Sr0.1CoO3films grown on AI2O3substrate, SiO2substrate, LaAlO3substrate, Si substrate and AAO template, we obtained that the a of La0.9Sr0.1CoO3films grown on AI2O3substrate was the largest, which showed that the humidity sensitive property of the films prepared was the best. Further, the resistance of the La0.9Sr0.1CoO3thin films grown on Al2O3substiates was exponential increase with humidity, and we briefly studied the sensing mechanism of positive wet sensitive features.5. For the La0.9Sr0.1CoO3thin films grown on Al2O3substrate had the best humidity sensitive property, we studied the influence of different titling angles to humidity sensitive property of the La0.9Sr0.1CoO3thin films. Through the introduced humidity sensitive coefficient α, we obtained that the humidity sensitive coefficient of La0.9Sr0.1CoO3thin films grown on10°Al2O3substrate was the largest, which was more sensitive to humidity. Then we prepared La0.9Sr0.1CoO3thin films with no post-annealing dispose and400℃、500℃、600℃、800℃post-annealing temperature, to studied the influence of different post-annealing temperature to humidity sensitivity. We found that when there was no post-annealing dispose and the post-annealing temperature from400℃to600℃, the resistance of the La0.9Sr0.1CoO3thin films was exponential increase with humidity, showed positive wet sensitive features; when the post-annealing temperature was800℃, the resistance of the La0.9Sr0.1CoO3thin films was exponential decrease with humidity, showed negative wet sensitive features. This showed that when the post-annealing temperature was800℃, the crystal structure of the La0.9Sr0.1CoO3thin films changed. The systematic study for humidity sensitive property of the La0.9Sr0.1CoO3thin films grown on Al2O3substrates laid a good foundation for humidity sensor.