超快激光加工二氧化钛微纳结构及功能器件研究进展

Research Progress in Ultrafast Laser Processing of Titanium Dioxide Micro/nano Structures and Functional Devices

二氧化钛兼具优异的光化学性质和光学性质,被广泛应用于能源材料、光学信息等领域的微纳功能器件中。二氧化钛的微纳加工与成形技术是二氧化钛微纳功能器件制备的关键技术基础。超快激光由于具有超短脉宽和超高能量峰值等特性而成为理想的微纳制造工具之一,近年来在二氧化钛的微纳加工领域中得到了广泛的关注。综述了超快激光加工二氧化钛微纳结构及功能器件的研究进展,包括二氧化钛的性质及应用、超快激光与二氧化钛的作用机理、二氧化钛微纳结构的超快激光加工技术,介绍了利用这些技术加工的二氧化钛光解水制氢器件、图案化结构色器件和光学加密器件等微纳功能器件,并对超快激光微纳加工技术在二氧化钛微纳结构及功能器件加工领域中的应用前景进行了展望。

Significance Because of the outstanding photochemical and optical properties, the titanium dioxide(TiO_(2)) has been used for applications such as energy materials and optical information. Compared to other semiconductor photocatalysts, TiO_(2)has attracted more attentions since the report of its ability for water splitting. In the recent half century, TiO_(2)is considered one of the ideal semiconductor photocatalysts because of its abundance, high stability, nontoxicity, and low cost. Because of its characteristics of high transmittance and high refractive index, TiO_(2)also has application prospects in the field of optical information. With the development of micro/nano technology, advanced micro/nano processing technologies have been used to prepare TiO_(2)micro/nano structures and functional devices(Fig. 1). In the field of energy materials, TiO_(2)micro/nano structures can be used for photoelectrochemistry water-splitting, dye-sensitized solar cells, photocatalysis, photovoltaic cells, photodetectors, and lithium-ion batteries. In the field of optical information, TiO_(2)micro/nano structures can be used for metasurface structure color, optical encryption, holography, and optical metadevices. The micro/nano processing of TiO_(2)is essential for the applications of TiO_(2)micro/nano functional devices.The ultrafast laser processing minimizes heat affected zone due to its ultra-short interaction time with the material. The ultrafast laser can be used to process almost any material due to the ultra-high power density. This provides an ideal choice for the processing of TiO_(2)micro/nano structures and functional devices. The ultrafast laser micro/nano processing of TiO_(2)has attracted attention in recent years. In this review, we introduce the research progress of ultrafast laser processing of TiO_(2)micro/nano structures and functional devices. Processing approaches and applications of TiO_(2)micro/nano structures are discussed. In addition, the prospects of ultrafast laser processing of TiO_(2)micro/nano structures and functional devices are discussed.Progress Four ultrafast laser processing approaches are commonly used for TiO_(2)micro/nano structures(Fig. 4), including ultrafast laser ablation of material surface, laser-induced periodic surface structure, ultrafast laser induced phase transformation of TiO_(2)and ultrafast laser writing TiO_(2)micro/nano structures on titanium. Numerical calculation models for ultrafast laser ablation of TiO_(2)have been established. The ablation thresholds are calculated, and the results are consistent with the experimental results(Fig. 5). A method is developed to achieve processing of amorphous TiO_(2)nanotubes and their transformation to anatase using the ultrafast laser(Fig. 6). Compared with thermal annealed pure TiO_(2)nanotubes, TiO_(2)nanotubes with exposed reactive anatase {010} facets are prepared after the ultrafast laser induced phase transformation. Based on the method of laser induced in situ growth of TiO_(2), a "THU” pattern with height smaller than the laser wavelength is realized(Fig. 7). TiO_(2)micro/nano functional devices, such as devices for photoelectrochemistry water-splitting, structural color, and optical encryption, are also discussed. TiO_(2)nanotubes with exposed reactive anatase {010} facets can be prepared by the ultrafast laser. Due to the exposure of reactive facets, the TiO_(2)nanotubes show an improved photocurrent density about five times of those of the thermal annealed pure anatase TiO_(2)nanotubes(Fig. 9). Based on the method of laser induced in situ growth of TiO_(2), grating-type TiO_(2)nanostructures with various periods can be processed. The grating-type TiO_(2)nanostructures is used for grating-based structural colors in the visible range. The observed colors are determined by the grating period with a fixed incident angle(Fig. 10). Due to the anisotropic optical behavior of grating-type structures, an optical encryption strategy is developed. The horizontal and vertical nanostructures demonstrate a remarkable difference in scattered intensity when visualized under a dark field optical microscope. The scattered intensity is the strongest when the nanostructures are illuminated along the direction perpendicular to the nanostructures. While it is the weakest when the nanostructures are illuminated along the direction parallel to them. Two different images can be encrypted on the same position(Fig. 11).Conclusions and Prospects We introduce the research progress of ultrafast laser processing of TiO_(2)micro/nano structures and functional devices. The photochemical and optical properties of TiO_(2)are introduced. The photochemical and optical properties of TiO_(2)can be adjusted by preparing TiO_(2)with different micro/nano structures. A model of transient local electron density is established. The theoretical predictions of ablation threshold and diameters are realized. Different approaches, including ultrafast laser ablation of material surface, laser-induced periodic surface structure, ultrafast laser induced phase transformation of TiO_(2)and ultrafast laser writing TiO_(2)micro/nano structures on the surface of titanium plate, have been studied for the processing of TiO_(2)micro/nano structures and functional devices. Ultrafast laser provides a choice for the processing of TiO_(2)micro/nano structures and functional devices. The method shows promising applications in fields such as photoelectrochemistry water-splitting, structural color, and optical encryption devices. The processing of TiO_(2)micro/nano structures and functional devices using the ultrafast laser also has some challenges, for example, the efficiency needs to be improved. With the further research on the mechanism and processing technology, it is expected to further expand the application ranges of TiO_(2)micro/nano structures and functional devices.