飞秒激光组装一维纳米材料及其应用

一维纳米材料具有众多优异的特性,是构建微纳米功能性器件的基石。实现一维纳米材料在二维和三维空间的高精度和高定向组装是充分发挥其应用潜力的关键,同时也是制造难点。在众多纳米材料组装技术中,飞秒激光直写诱导组装技术具有独特优势,可实现一维纳米材料在任意三维结构中的可设计、高定向及高精度的组装。首先简要介绍了一维纳米材料组装研究的背景,并总结了非激光直写组装技术的研究现状和存在的挑战,然后较详细介绍了飞秒激光直写技术在一维纳米材料组装研究中的进展,重点回顾了金属(包括Au和Ag纳米线)、半导体(包括CNTs和ZnO)一维纳米材料的飞秒激光直写组装及微纳光电子功能器件的制造。并讨论了诱导一维纳米材料定向排布的光学力和非光学力(包括剪切力、体积收缩应力和空间限制)的作用机理,理论计算和实验研究结果验证了飞秒激光诱导的非光学力作用是导致一维纳米材料定向排布的主要原因。最后探讨了目前飞秒激光组装技术面临的一些问题和未来在高精度纳米材料组装和三维功能器件集成方面的发展趋势。

Femtosecond Laser Assembly of One-Dimensional Nanomaterials and Their Application

Significance One-dimensional(1D)nanomaterials,such as nanowires(NWs),nanorods(NRs)and nanotubes(NTs),are the smallest units for achieving the efficient transportation of electrons and excitons,which are considered to be the ideal building blocks for constructing micro/nano functional devices.1D nanomaterials have potential application prospects in nano-optoelectronics,nanosensing,energy storage,biomedicine,and other such fields because of their unique optical,electrical,magnetic,thermal,and mechanical characteristics as well as other excellent characteristics.Currently,the techniques used to synthesize the ordered 1D nanomaterials are quite mature.However,the efficient assembly of 1D nanomaterials remains a challenge that must be urgently solved.The gaps between 1D nanomaterials and integrated devices in various fields can be bridged by assembling 1D nanomaterials into two-dimensional(2D)or three-dimensional(3D)micro/nanoarchitectures.In addition,the properties of 1D nanomaterials must be completely utilized.Thus,to realize the high-precision and highly directional assembly of 1D nanomaterials in 2D/3D spaces is the key to explore their potential applications.Various methods,such as the lithography and etching technologies,the methods in which external force or field approaches,the template-assisted methods,the biorecognition methods involving near-field manipulation,and the electro-hydrodynamic(EHD)printing method,are used for assembling 1D nanomaterials into 2D and 3D ordered mesoscale structures.Unfortunately,the inherent disadvantages associated with these methods considerably limit their wider applications.In case of the usage of the external force approach,it is difficult to precisely control the density and placement of NWs using the shear force-based approaches.The application of the magnetic field-based method is only restricted to the ferromagnetic and super-paramagnetic material-based NWs.In addition,the electric field-based method requires the highly unified process conditions and the preparation of electrodes in advance.Furthermore,the assembly of 1D nanomaterials in 3D space is still in the initial research stage.The traditional assembly methods such as the Langmuir-Blodgett(LB),contact printing,and EHD printing methods,can used to realize the deposition of 2D and 2.5D structures,such as arrays and mesh grids,by stacking 1D nanomaterials.However,it is still difficult to accurately control the vertical assembly of 1D nanomaterials using these traditional assembly methods.Therefore,the high precision,highly directional,and controllable assembly of 1D nanomaterials in 3D space requires a further investigation.Recently,two-photon polymerization(TPP)laser direct writing has emerged as a promising technique for assembling nanomaterials owing to its real 3D nanofabrication capability and sub-diffraction-limited resolution.TPP fabrication can achieve designable,highly directional,and high-precision assembly of 1D nanomaterials in 3D space because of the laser-induced trapping force and micro/nanoscale laser writing resolution.Currently,some research groups have assembled 1D nanomaterials,including Au NRs,Ag NWs,CNTs,and ZnO NWs,via laser direct writing.However,some challenges remain with respect to the highly directional assembly,integration and application of the assembled nanomaterials and the LSPRs of metal nanomaterials.Hence,the existing research must be summarized for guiding the future development of this field in a rational manner.Progress In this study,first,the background of 1D nanomaterial assembly techniques is introduced.In addition,the mechanism and state of the art of non-laser assembly techniques are summarized.Furthermore,the existing challenges associated with this field are discussed.Second,the recent progress of the laser assembly techniques of 1D nanomaterials is reviewed.Both 1D metallic and semiconducting nanomaterials,including Au NRs,Ag NWs,CNTs,and ZnO NWs,are reviewed and discussed.For assembling 1D metal nanomaterials,Do et al.have deposited an individual Au NW from an optical trap using two different laser wavelengths to avoid the influence of LSPRs(Fig.5).Liu et al.have fabricated 3D Ag NW-based micro/nanostructures via TPP fabrication followed by a femtosecond laser nanojoining process(Figs.6 and 7).In case of 1D semiconductor nanomaterials,Xiong et al.have fabricated various MWNT-based microelectronic devices,including capacitors and resistors,via TPP laser direct writing(Figs.9 and 10).Long et al.have achieved the highly directional assembly of ZnO NWs in 2D and 3D micro/nanostructures via laser direct writing and fabricated a ZnO-NW-based polarization-resolved photodetector(Figs.12 and 13).Third,the factors that influence the directional assembly of 1D nanomaterials including the optical and non-optical forces are discussed.The laser-induced non-optical force is proven to be the dominant factor that causes the directional assembly of 1 Dnanomaterials through the theoretical calculations and experimental tests.Finally,the existing challenges and development trends associated with femtosecond laser assembly techniques are discussed.Conclusion and Prospect Compared with the traditional non-laser assembly techniques,the laser assembly methods,especially the femtosecond laser direct writing technology,exhibit advantages on the assembly of 1D nanomaterials because of their high spatial resolution and true 3D micro-nano manufacturing capability.A femtosecond laser exhibits high peak power and short pulse duration,and thus the nanomaterials can be accurately controlled with respect to its energy and momentum.Although the femtosecond laser direct writing technology has made some progresses on the assembly of 1D nanomaterials,several problems remain to be resolved,including some irregularities observed in the assembled 1D nanomaterials,the LSPRs of metal nanomaterials,and the low efficiency of the laser assembly methods.Thus,the regularity,flexibility,and efficiency of the laser direct writing technology may be further improved by modifying the components of the 1D nanomaterial composite resin,introducing vectorial electromagnetic fields,or employing parallel laser direct writing manufacturing.