Hydrothermal Preparation And Optical Properties Of The Oriented TiO₂Thin Films

Second-order nonlinear optical thin films have widespread application in thefields of optical communication, optical information processing and optical datastorage. Basing on the reports that bulk rutile TiO2(110) and (001) crystallographicplanes have significant second-harmonic generation (SHG), Two kinds of orientedrutile TiO2films was tentatively designed to grow along the [110] or [001] directionrespectively, expecting to obtain strong SHG, in the aim of searching candidate filmmaterials for the development of opto-electrical functional devices.Using glass or FTO glass as substrates, series of rutile TiO2thin films wereprepared by hydrothermal synthetic method in this article. Through UV-Vis-NIRspectrum and Maker fringe method, the effects of different titanium sources andhydrothermal time on optical transmittance performance and SHG of the TiO2filmswere studied. Then the origin of SHG of the films was analyzed by XRD and FESEMcharacterizations. The main results are listed as follows:(1) Second-harmonic (SH) intensity of the films prepared on glass slide substrateincreases as extending hydrothermal time, SH intensity of the films prepared withtitanium butoxide (TBOT) as titanium source nearly reach1.4times of the Y-cutquartz, the corresponding1064nm and532nm transmittances are54%and46%respectively. SH intensity of the films prepared with titanium tetrachloride(TiCl4) astitanium source almost achieve2.3times of the Y-cut quartz, the corresponding1064nm and532nm transmittances are12%and10%respectively. XRD patternsindicate that films are rutile TiO2with (110) diffraction peak is strongest and (002)diffraction peak is very weak. FESEM images indicate that film is composed of manytetragonal-shaped rods grown along every direction. The four side surfaces of eachrod are (110) plane. SHG of the films was considered come from Ti(γ)-O(α)-Ti(γ)-O(α) zigzag chains arranging along [001] direction.(2) SH intensity of the films fabricated on FTO substrate increases as prolonginghydrothermal time, SH intensity of the films with TBOT as titanium source almost asstrong as the Y-cut quartz, the corresponding1064nm and532nm transmittances are28%and27%respectively. SH intensity of the films with TiCl4as titanium sourcenearly achieve3times of the Y-cut quartz, the corresponding1064nm and532nmtransmittances are62%and53%respectively. XRD data display that films are rutile TiO2with (110) diffraction peak is not exist, but (002) diffraction peak is thestrongest, which shows preferred (001) orientation. FESEM images exhibit that filmis composed of nanorods growing along the [001] direction, the top surface of eachnanorod is (001) crystal plane. SHG of the films was thought come from Ti(t)-O(b)-Ti(o)-O(b)-Ti(t) chains arranging along [110] direction.