| Tin doped indium oxide(ITO) transparent conducting thin films are widely used in optoelectronic devices such as flat panel displays, solar cells and surface heaters owing to their performances containing low resistivity, high transmittance for visible light and high reflectance in infrared spectrum, and show great value in military applications such as electromagnetic shield and infrared stealth due to the unique property of effective attenuation to microwave. In actual applications, ITO thin films are required to have excellent optical and electrical performances. Certain instruments demand ITO thin films coated uniformly on special-shaped surface, and possess excellent mechanical properties and film-substrate adhesion in order to adapt various applications in harsh load-conditions. Previous researches showed that physical properties of ITO thin films were primarily affected by microstructure features, and the microstructure features were determined by the growth process of films. Therefore, ITO thin films were fabricated by ion-assisted electron beam evaporation method, the growth process, microstructure, optoelectrical properties, mechanical properties and hemispherical substrate coating were investigated aimed at aforementioned theoretical and practical problems, the innovative works and primary conclusions including:Electron diffraction and high resolution transmission electron microscopy measurements were performed on diverse-thickness ITO thin films deposited at different deposition rate, the growth process and structural development of ITO thin films were studied detailedly, the results showed that: ITO thin film deposited at relatively low deposition rate mainly consisted of crystal grains with [100] and [111] preferred orientation initially, and the [111] preferred orientation enhanced as the film thickness increased; Film deposited at relatively high deposition rate consisted of nanowires initially, the nanowires degraded as the deposition precess proceeded, the film atoms recrystallized and formed into cubic shaped grains grown along [100] crystallography orientation; ITO thin film with intensive(222) preferred orientation showed resistivity as low as 2.58×10-4 Ω·cm, and transmittance greater than 85% in visible range.Mechanical properties such as nano-hardness, elastic modulus and film-substrate adhesion of ITO thin films were investigated systematicly, the stress conditions of polycrystalline ITO thin films were calculated using related mechanics theory with lattice diffraction data. The results showed that the nano-hardness of ITO thin film with appropriate microstructure could be up to 13.8 GPa, which was greater than nano-hardness of glass substrate; ITO thin films obtained were all in the state of compressive stress, which was attributed to intrinsic stress induced by structural defects; Film-substrate adhesion degraded as the deposition rate increased.Thickness distribution of film on hemispherical substrate was calculated through relevant calculation principle combined with ITO evaporation characteristics; A planetary fixture with variable tilt angle was designed and manufactured, ITO thin film was evaporated on large size glass hemispherical substrate adopted optimized deposition parameters by aforementioned planetary fixture. Investigations revealed that the physical properties of ITO thin film on hemispherical substrate changed as the variations of incident angles of evaporation beam and assisted oxygen ion beam, the microstructure of ITO thin film showed large difference as the coated position changed from the top center to the edge of hemispherical substrate. |
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