Fig. 1. Applications of TiO₂ micro/nano structures and functional devices in energy materials and optical information fields

Fig. 2. Three crystal types of titanium dioxide. (a) Rutile; (b) anatase; (c) brookite

Fig. 3. Improving photochemistry performance of TiO₂ by different methods. (a) Reducing band gap^[4]; (b) preparation of functional surface structures^[2]

Fig. 4. Schematics of TiO₂ micro/nano structures processed using ultrafast laser. (a) Ultrafast laser ablation of material surface; (b) ultrafast laser induced periodic surface structure; (c) ultrafast laser induced phase transformation of TiO_2;(d) TiO₂ formation by ultrafast laser induced titanium oxidation

Fig. 5. Experimental and theoretical results of ultrafast laser ablation of TiO₂^[53]. (a) Optical microscope image of TiO₂ surface ablated using ultrafast laser with different pulse delays and laser energy fluxes; (b) distribution of free electron density calculated under different laser parameters; temporal dynamics of (c) laser intensity, calculated electron density, and (d) reflectivity of TiO₂

Fig. 6. Obtaining anatase with highly active crystal facets by femtosecond laser induced phase transformation of TiO₂ nanotubes^[47]. (a) Phase transformation diagrams of amorphous TiO₂ nanotubes induced by femtosecond laser; (b) comparison of TiO₂ phase transformations induced by femtosecond laser and heat treatment; (c)－(f) high resolution transmission electron microscopy images of TiO₂ nanotubes after femtosecond laser-induced phase transformation

Fig. 7. Fabricating patterned TiO₂ nanostructures by ultrafast laser-induced oxidation of titanium^[48]. (a) Schematic of ultrafast laser-induced oxidation of titanium; (b)(c) micro/nano patterns processed by ultrafast laser-induced oxidation of titanium

Fig. 8. Schematic of photoelectrochemistry water-splitting using TiO₂^[47]

Fig. 9. Photoelectrochemistry (PEC) performances of devices prepared using ultrafast laser^[47]. (a) Photocurrent density observed using chopped illumination; (b) photoluminescence spectra of photoelectrodes; (c) schematic of PEC water-　splitting; (d) conceptual schematics of high-resolution patterned photoelectrode for PEC water-splitting

Fig. 10. Fabrication of grating-type TiO₂ nanostructures and realization of patterned structure color ^[48]. (a) Schematic of proposed surface coloring; (b) color palettes with grating period of 500－1000 nm; (c) electron microscope image, (d) dark field microscope image and (e) local magnification of butterfly pattern composed of grating-type nanostructures; (f) dark field optical microscope images of grating-type nanostructures for resolution test; (g) measured gray values of neighboring nanostructures with periods of 600 nm, 800 nm and 1000 nm along y direction, respectively

Fig. 11. Optical encryption based on anisotropic optical behavior of grating-type TiO₂ nanostructures^[48]. (a) Decryption schematic of two hidden images by illumination from different directions; (b)－(k) decrypting hidden images by using directional dark field mode