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利用射频磁控溅射的方法,在不同的工作气压(0.2Pa～4.0Pa)下,制备了一系列的本征TiO2薄膜。在2～340K的绝对温度下,测得所有制备态的本征TiO2薄膜均具有铁磁性,2.0Pa工作气压下制备的TiO2薄膜具有最大的室温饱和磁化强度为1.96emu/cm3。通过TiO2薄膜的X衍射(XRD)图谱观察到,在0.2Pa工作气压下,锐钛矿和金红石结构共存于TiO2多晶薄膜中;随着工作气压的增加,出现了金红石结构向锐钛矿结构的转变;当气压增加到2.0Pa时,TiO2薄膜的晶体结构由多晶态转变成非晶态。利用高分辨率透射电镜(HRTEM)分析TiO2薄膜的晶体结构,通过观察1.2Pa和2.0Pa工作气压下TiO2薄膜的电子衍射花样和HRTEM图,可以清楚地看到多晶态向非晶态的转变。利用分光光度计测试了TiO2薄膜样品的透过率曲线,可见光区平均透过率高于85%,伴随着晶体结构的非晶态转变,光学透过率曲线的吸收边向长波方向移动,光学带隙减小到3.14eV,由此可以证明,增加的结构缺陷是系统铁磁性产生的主要原因。并且,所有本征TiO2样品均为高阻态,电阻率高于107Ω.cm,可以排除以载流子为媒质的RKKY交换作用对系统铁磁性的影响。
A series of intrinsic TiO2 thin films were prepared by RF magnetron sputtering at different working pressures (0.2Pa ~ 4.0Pa). All of the as-prepared intrinsic TiO2 films were ferromagnetic at 2 ~ 340K absolute temperature. The maximum room-temperature saturation magnetization of TiO2 films prepared at 2.0 Pa was 1.96emu / cm3. The X-ray diffraction (XRD) pattern of TiO2 thin films shows that the anatase and rutile structures co-exist in the polycrystalline TiO2 films under the pressure of 0.2 Pa. With the increase of working pressure, the anatase and rutile structures appear in anatase When the pressure is increased to 2.0 Pa, the crystal structure of TiO2 thin film changes from polycrystalline to amorphous. The crystal structure of TiO2 thin film was analyzed by high resolution transmission electron microscopy (HRTEM). By observing the electron diffraction patterns and HRTEM images of TiO2 thin films at 1.2 Pa and 2.0 Pa, the transition from polycrystalline to amorphous state can be clearly seen . The transmittance curves of TiO2 thin films were measured by spectrophotometer. The average transmittance in visible light region was higher than 85%. With the amorphous transition of crystal structure, the absorption of the optical transmittance curve shifted to the long wavelength direction. The optical The bandgap is reduced to 3.14 eV, from which it can be shown that increased structural defects are the major cause of system ferromagnetism. Moreover, all the intrinsic TiO2 samples are in high impedance state and the resistivity is higher than 107Ω.cm, which can eliminate the effect of RKKY exchange mediated by carriers on the ferromagnetism of the system.