飞秒激光加工低维纳米材料及应用

Significance Low-dimensional nanomaterials exhibit quantum confinement effects because of their unique size and atomic structures, which enable them to have advanced physical and chemical properties. Therefore, they can be widely applied in nanoelectronics, nanooptics, biochemical sensing, energy devices, and many other fields, indicating their great development potential. Low-dimensional nanomaterials can be divided into zero-, one-, and two-dimensional nanomaterials based on their three-dimensional size. They possess many adjustable parameters, including size, distribution, elemental composition, and functional surface. Therefore, the controllable preparation and property modulation of low-dimensional nanomaterials are essential for ensuring their multifield applications. The current mainstream preparation methods can be categorized as physical and chemical methods depending on the occurrence of chemical reactions. Physical methods primarily include magnetron sputtering, plasma treatment, physical vapor deposition, and electron beam lithography, whereas chemical methods primarily include the hydrothermal method, the template method, electrochemical etching, and liquid phase stripping. Generally, physical methods have complicated processing conditions and high design costs. Through chemical methods, other dangerous chemical reagents can be easily introduced, hindering environmental protection. Therefore, these methods cannot be applied to all materials. Hence, a green, controllable, and material universal method is considerably important for the processing and applications of low-dimensional nanomaterials. Laser processing is a flexible, controllable, and environmentally friendly manufacturing method, which prefers loose processing conditions (no need for high temperature or pressure). Unlike traditional lasers, femtosecond lasers exhibit ultrashort pulse widths, ultrahigh instantaneous power density, and nonlinear processing, resulting in the reduced heat effect, higher processing precision, and the clearer edge of the nanomaterial. They can process almost all types of materials (metals, semiconductors, dielectrics, etc.) and process transparent materials internally. They have unique advantages with respect to the preparation and precision processing of low-dimensional nanomaterials, which are conveniently aimed at targeted position and patterned nanomaterials. Therefore, they are always used to fabricate or process diversified, multiscale, high-precision functional nanomaterials. Progress Zero-dimensional nanoparticles are prepared by femtosecond laser processing mainly based on the system of femtosecond laser liquid ablation. The size, distribution, and crystal form of quantum dots can be modulated by controlling the energy, wavelength, pulse number, and other parameters of femtosecond lasers. In addition, the adjustment of the temporally shaped parameters of femtosecond lasers considerably influences the multilevel photoexfoliation of single-layer quantum dots (Fig. 1) and the photochemical reduction of precursors to prepare amorphous quantum dots (Fig. 3). This is conducive for the preparation of quantum dots with small size, uniform distribution, and high surface activity. Femtosecond lasers can also selectively induce the breakage and rearrangement of chemical bonds, realize the dissociation of chemical reactions and the development of reaction channels in the specified direction (Fig. 2). Thus, the target chemical reaction intermediate products are obtained and the specified functional nanoparticles are achieved. The femtosecond laser preparation of one-dimensional nanowires is mainly achieved via sintering or photoreduction. However, this always involves the introduction of other reagents, necessitating material selection. Wang et al. proposed a method of regulating the spatial parameters of femtosecond lasers to process a gold nanowire with minimum line width of 56 nm which breaks the diffraction limit (Fig. 5). Furthermore, the spatial distribution of one-dimensional nanomaterials is meaningful for their functional applications. Xiong et al. investigated a method for functionalizing the multiwalled carbon nanotubes (MWNTs) to develop a type of two photon polymerization(TPP)-compatible MWNT-thiol-acrylate (MTA) resin, significantly enhancing the electrical and mechanical properties of the three-dimensional micro/nanostructures (Fig. 6). The femtosecond laser processing of two-dimensional films is mainly divided into two categories: modification and ablation. Modification can induce the dissociation of the functional groups on the film surface (Fig. 15), whereas ablation can induce chemical bond rupture to produce highly active defects (Fig. 9). Therefore, the quantum dots prepared using femtosecond lasers exhibit high catalytic activity and are mostly used for electrocatalysis or photoelectrocatalytic hydrogen production. The fabricated nanowires exhibit high resolution and good conductivity and are mostly used for preparing transparent electrodes. The ultrathin films processed using femtosecond lasers contain several surface defect sites, which lead to applications in functional surface preparation, such as superhydrophobic surface, and surface-enhanced Raman scatting(SERS) detection. Conclusion and Prospect In this study, we review the current research status of the preparation and processing of low-dimensional nanomaterials using femtosecond lasers. We introduce the functional quantum dots, nanowires, and two-dimensional thin films prepared using temporally and spatially shaped femtosecond pulsed lasers and their applications in the fields of catalysis, biochemical detection, biocompatibility, and electronic devices. The current technical difficulties associated with the preparation of nanomaterials have been analyzed, and the temporal or spatial parameters of the femtosecond laser affecting the preparation and application performance of nanomaterials have been summarized. Further, the morphological and physical requirements associated with different application fields of nanoparticles have been discussed, and corresponding femtosecond laser processing strategies and future research trends have been proposed.