飞秒激光组装一维纳米材料及其应用 下载: 2427次特邀综述
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 (
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.
1 引言
一维(1D)纳米材料,包括纳米线、纳米管和纳米带等,是径向方向为纳米尺度(通常小于100nm)、轴向方向为微观至宏观尺度的高长径比纳米材料,其含有天然的载流子传输通道,在光学、电学、磁学、热学和机械等方面具有优异的特性,被认为是构建微纳米功能性器件的基石。在纳米光电子领域,一维纳米材料的载流子限域效应使得辐射复合显著增强,并有效降低了激光激射阈值。因此,Yang等[1]通过合成规则排布的氧化锌纳米线(Zinc Oxide Nanowires,ZnO NWs)阵列,制备出了世界上最小的纳米线激光器,其激射阈值仅为40kW·cm-2,明显低于ZnO晶体和薄膜材料(300kW·cm-2)。在电学方面,一维纳米材料优异的电输运和场发射特性使其在场发射平板显示器等场发射器件方面具有巨大的应用潜力[2]。在能源领域,一维纳米材料因具有巨大的比表面积并含有天然的载流子通道,将其作为锂离子电池的电极材料,可以显著提高锂离子在电解质/电极界面中的扩散速率;并且其横向应变小,能够有效缓冲充放电循环过程中电极体积的变化,保持电极材料结构的稳定[3]。在热学性质方面,当材料尺寸降到纳米尺度,其熔点大大降低,这为在相对温和的环境下进行纳米材料的提纯、切割和焊接提供了可能[4]。磁性方面,一维磁性纳米材料的易磁化方向沿着纳米线轴向,具有高度的磁各向异性,是高密度垂直磁记录的理想介质。并且,磁纳米线阵列的热稳定极限远超传统存储介质,在新型存储器方面有着重要的应用[5]。机械特性方面,一维纳米材料相比于块体材料,单位长度的缺陷数量显著减小,机械强度明显增大。例如碳化硅纳米棒的弯曲强度达到了53.4GPa[6],可作为增韧组分来提高塑料、金属以及陶瓷基体的机械强度。
随着纳米科技的飞速发展,人们已经能够制备出众多具有优异性质的一维纳米材料。然而,在下一代量子器件和纳米结构器件需求的驱动下,纳米科技领域的研究热点逐渐从材料的生长制备转移到实现纳米材料的可控、有序的组装与集成。与杂乱无序的一维纳米材料网络相比,将一维纳米材料组装成高定向排列、规整有序的结构体,不仅能充分利用一维纳米材料优异的本征性能,还能开发出新颖的材料特性,这对于微观至宏观尺度下利用纳米构筑单元进行器件制备来说也是亟需的。目前,国际上针对一维纳米材料的传统组装方法可分为两大类:一类是基于光刻或电子束刻蚀等技术限定一维纳米材料生长位点或生长方向的原位生长组装法;另一类是生长后组装法,即利用外部作用力或外部驱动场,对生长好的一维纳米材料进行组装[7-13]。然而,现有的组装方法不论是原位生长组装法还是生长后组装法,都存在组装精度低、过程繁琐及难以实现真三维材料组装等不足。因此,实现一维纳米材料的高效可控的组装,特别是在二维/三维空间的高精度、高定向的组装集成,仍然是纳米功能器件制造领域所面临的挑战之一,也是实现未来应用的关键。
国内外研究学者针对现有一维纳米材料组装技术的不足,尝试采用飞秒激光直写的方法对一维纳米材料进行组装,以提高组装的精度和可控性。基于飞秒激光直写的双光子聚合(Two-Photon Polymerization,TPP)微纳制造技术具有超高的空间分辨率和真三维微纳制造能力,被认为是最有发展前景的微纳加工技术之一,同时也是一种富有应用前景的构建多功能三维微纳器件的激光制造技术[14-18]。双光子聚合是一种基于双光子吸收的三阶非线性效应,仅在激光焦点处光强达到聚合阈值的条件下才会引发光敏树脂聚合,因此具有超衍射极限的空间分辨率[19]。当飞秒激光作用于掺杂有功能性材料的复合光敏树脂时,纳米材料在飞秒激光强光场光镊力的作用下,移动、聚集且被束缚在激光焦点处,并随着激光的高速扫描,在光敏树脂的聚合作用下被固定在精细微纳结构中,从而实现功能性纳米材料在微纳结构中的定向分布[20-22]。进一步,将飞秒激光与二维振镜和三维压电位移平台相结合,根据预先设计的三维模型,可实现功能性纳米材料在任意三维结构中的可设计、高定向、高精度的材料组装。因此,相比于传统的组装方法,飞秒激光直写在一维纳米材料组装方面更具优势,有着广阔的应用前景和发展潜力。
本文首先简要回顾了传统的非激光直写组装一维纳米材料的方法,然后较详细地介绍了国际上关于飞秒激光直写技术组装一维纳米材料的研究进展,重点探讨了飞秒激光直写组装技术相比于传统的非激光直写组装方法的不同和优势。进一步,本文还讨论了飞秒激光直写组装纳米材料的机理以及器件应用。最后,本文总结了当前一维纳米材料组装领域所面临的挑战并展望了该领域未来的发展趋势和应用前景。
2 非激光直写组装一维纳米材料的研究
目前,根据纳米材料的生长和组装的顺序,传统的一维纳米材料的组装方法可分为原位生长组装法和生长后组装法。原位生长组装法有两种方式。一是通过自上而下的减材加工工艺(包括光刻和刻蚀等技术),对块体材料进行选择性刻蚀,从而形成规整有序的微纳结构。二是通过制备高精度模板,预先在目标衬底上形成材料的生长位点,从而对纳米材料的生长位置和方向进行限制和引导,再通过化学气相沉积(CVD)法、水热法及溶胶凝胶法等自下而上的生长技术制备图案化的一维纳米材料,如
图 1. 传统的一维纳米材料的组装方法。(a)原位生长组装法;(b)生长后组装法
Fig. 1. Traditional assembly methods of 1D nanomaterials. (a) In-situ assembly method; (b) post-growth assembly method
原位生长组装法的优点在于不需要通过后续工艺对纳米材料进行组装,采用成熟的光刻工艺即可实现大面积并行制造。另外,利用电子束光刻技术(Electron Beam Lithography,EBL)可以得到10nm以下的组装精度,如
图 2. 一维纳米材料非激光直写组装技术。(a)模板辅助生长法[28];(b)流体驱动组装法[7];(c)接触印刷法[8];(d)拉伸技术[23];(e)LB膜法[9,29];(f)介电泳法[10];(g)磁场驱动法[11];(h)电流体
Fig. 2. Assembly technology of 1D nanomaterials based on non-laser direct writing. (a) Template assisted method[28]; (b) fluid-flow method[7]; (c) contact printing method[8]; (d) stretching technique[23]; (e) LB technique[9,29]<
传统的一维纳米材料组装方法在实现纳米材料二维平面的组装方面已较为成熟,然而其在实现垂直于衬底的方向即纵向排布组装方面的研究鲜有报道。LB膜法[9]、接触印刷法[8,24]和电流体喷印法[25]可以通过逐层组装和堆叠下压的方式实现交叉堆叠的三维纳米线网络结构的制备。例如,Chen 等 [26]通过逐层旋转扭曲的方法定向排布纳米线阵列面,堆叠组装出与自然分层结构极为相似的仿生块状材料,所得的复合三维旋转堆叠结构具有良好的机械性能。Gao等 [27]利用冷冻干燥法实现了Ag纳米线宏观三维网络结构的组装。如
3 激光直写组装一维纳米材料的研究
飞秒激光具有超高峰值功率和超短脉宽,峰值功率可达1015 W。飞秒激光的高能脉冲与材料相互作用时,会引发材料的双光子或多光子非线性吸收,因此飞秒激光有着超光学衍射极限的分辨率,且具有广泛的材料加工能力,可引发光聚合、光还原、光致异构和烧蚀等多种光物理和光化学过程。另外,飞秒激光的超短脉宽使得材料的能量吸收时间远小于热弛豫时间,因此能够有效抑制激光作用区域的热效应,让激光能量可以精确聚焦到微小作用区域。由此可见,飞秒激光直写技术具有高精度、高定向和高度功能化的特点,在一维纳米材料组装方面相比于传统的一维纳米材料组装技术更具优势。
3.1 一维金属纳米材料
一维金属纳米材料既具有一维纳米材料相对于块体材料优良的尺寸效应,又兼具金属材料本身良好的导电性及其他优异的物理和化学特性,被广泛应用于集成电路[30]、场发射器件[31]、生物医学成像[32]和储氢[33]等,成为当前纳米材料研究领域的热点。将一维金属纳米材料进行组装后,组装体被赋予了耦合的光学、电学特性,因而表现出比单一的一维金属纳米材料更为优异的整体协同性质[34]。另外,金属纳米结构的局部表面等离子体基元共振(Localized Surface Plasmon Resonance,LSPRs)效应为新颖光子纳米技术的发展奠定了基础,被广泛应用于表面增强拉曼散射(Surface Enhanced Raman Scattering,SERS)[35-36]、生物和化学传感器[37-38]、手性材料[39-40]、光催化[41]、光波导[42]和纳米成像器件[32,43]等研究中。由于LSPRs过程中自由电子被限制在金属粒子内,共振效应与纳米结构的材料、形貌、取向以及周围环境密切相关。通过对金属纳米粒子的形貌和排布进行操控,可实现光场的精密调控。因此,开发新颖的微纳制造技术,实现任意复杂微纳结构的制备,使金属纳米材料得到定向排布组装等是等离子体基元技术发展迫切需要解决的难题。
3.1.1 金纳米线
Masui等[44]将金纳米线(Au NWs)掺杂到光刻胶中,利用飞秒激光双光子直写技术制备了金纳米线复合微纳结构,研究了Au NWs在飞秒激光作用下的聚集现象和LSPRs效应。如
图 3. 飞秒激光制备的Au纳米线聚集体微纳结构[44]。(a) Au纳米线聚集形成的示意图和物理机制;(b)不同激光功率密度下Au纳米线掺杂光刻胶的激光聚合形貌
Fig. 3. Femtosecond laser fabricated Au nanowire aggregate microstructures[44]. (a) Schematic of formation of Au nanowire aggregation and its mechanism; (b) morphologies of laser fabricated aggregates of Au nanowires doped photoresist under different laser power densities
张然等[45]利用飞秒激光直写的光镊作用力和双光子非线性吸收直接对金纳米棒(Au Nanorods, Au NRs)进行组装,无需化学修饰且不需要掺杂到光刻胶中,实现了金纳米棒图案化的组装,组装示意图如
图 4. 飞秒激光组装的Au纳米棒[45]。(a)飞秒激光组装Au纳米棒示意图;(b)变形金刚汽车标志和(c)螺旋线的SEM图; (d) 10 mW,(e) 25 mW,(f) 40 mW激光功率下组装微结构的Au纳米棒形貌
Fig. 4. Femtosecond laser assembled Au nanorods[45]. (a) Schematic of laser assembly of Au nanorods; SEM images of (b) Transformers car logo and (c) spiral ring; microstructural morphologies of Au nanorods fabricated under laser powers of (d)10mW, (e) 25mW, and (f) 40mW
考虑到LSPRs对一维金属纳米材料组装过程稳定性和纳米线方向操纵带来的影响, Do等[46]采用波长分别为532nm和1064nm的两束激光对聚乙二醇(PEG)修饰的单根Au NWs进行组装。组装过程和原理分别如
图 5. 双色激光打印单根金纳米线[46]。(a)双色激光打印装置图;(b)双色激光捕获和准直金纳米线示意图;(c)PEG修饰的金纳米线的归一化消光光谱;打印的金纳米线(d)“O” 和(e)“X”图案的SEM图;“OX”图案在(f)非偏振光、(g)垂直偏振光和(h)水平偏振光激发下的暗场白光瑞利散射图
Fig. 5. Two-color laser printing of individual Au nanowire[46]. (a) Schematic of two-color laser printing setup; (b) schematic of laser trapping and aligning of Au nanowires; (c) normalized extinction spectrum of PEG decorated Au nanowires; SEM images of (d) “O” and (e) “X” patterns of printed Au nanowires; dark-field white light Rayleigh scattering images of “OX” patterns excited by (f) non-polarized laser, (g) vertically polarized laser, and (h) horizo
3.1.2 银纳米线
银(Ag)被认为是一种理想的导电材料,其电导率高达6.3×107 S·m-1。具有高长径比的Ag纳米线(Ag NWs)含有天然的电荷传输通道,能够有效地传输电子,并且通过纳米线之间的熔接可以形成互联的高导电纳米线网络。Liu等 [47]将经硫醇分子(thiol)修饰过的Ag NWs掺杂到丙烯酸光刻胶中,制成了Ag NW-thiol-acrylate(ATA)复合光刻胶,如
图 6. Ag NWs硫醇功能化和ATA复合微纳结构[47]。(a)Ag NWs硫醇功能化示意图;(b)硫醇包覆Ag NWs的TEM图像;(c)纯丙烯酸树脂和ATA复合微纳结构的质谱图;(d)微螺旋光子晶体、(e)微弹簧和(f)微超级电容器的SEM图
Fig. 6. Ag NWs thiol functionalization and ATA composite micro/nanostructures[47]. (a) Schematic of Ag NWs thiol functionalization; (b) TEM image of thiol-capped Ag NWs; (c) mass spectra of structures fabricated using pure acrylate and ATA composite; SEM images of (d) spiral-like photonic crystal, (e) micro-coil, and (f) micro-capacitor
图 7. 激光在ATA复合微纳结构中纳米熔接Ag NWs[47]。(a)激光纳米熔接Ag NWs过程示意图,结点处经历了Ag原子活化、激发、扩散三个过程;Ag NW结点处在激光辐照熔接(b)之前和(c)之后的TEM图像和晶格衍射图;(d)AgNW熔接结点处TEM 放大图;(e)两根Ag NWs在(111)生长平面上的熔接示意图
Fig. 7. Laser nano-joining of Ag NWs within ATA composites[47]. (a) Schematic of laser nano-joining of Ag NWs junctions including three processes of initiation, activation, and diffusion; TEM images and crystal lattice diffraction images of Ag NW junctions (b) before and (c) after laser irradiation fusion; (d) magnified TEM image of fused Ag NW junctions; (e) scheme of welding two Ag NWs over (111) growing plane
3.1.3 一维金属纳米材料的飞秒激光组装的特点
由于飞秒激光脉冲宽度窄、峰值功率高,因此在对一维金属纳米材料进行精密组装时,需要关注高能脉冲激光作用下激发金属产生的LSPRs效应。LSPRs效应会导致金属纳米材料周围局域电磁场急剧增强,进而光镊力作用随之增强,纳米材料更倾向于会聚到激光焦点处,有利于纳米材料捕获。另一方面,当利用飞秒激光双光子直写技术制备一维金属纳米材料复合微纳结构时,在LSPRs作用下局域电磁场的强度比初始的激光光场高几个数量级,会导致双光子聚合的功率阈值大幅降低,激光作用区域的光刻胶在极短的时间内迅速固化,只有在金属纳米材料表面才能实现稳定的双光子聚合,因此难以实现高定向、高精度的金属纳米线的三维组装。此外,由于一维金属纳米材料被聚合物紧密包覆,纳米线之间的互联和等离子体耦合往往受到阻碍,其应用受到限制。在不借助光刻胶成型的情况下,利用飞秒激光的光镊作用力,可直接对一维金属纳米材料进行组装,并且可以实现一维金属纳米材料如Au NRs[45]的二维图案化组装。该组装过程中的LSPRs效应会导致Au NWs的表面发生轻微熔化,从而实现一维金属纳米材料之间的熔合和互联,具有无接触、材料和衬底的热损伤较小等优点,因此飞秒激光直写技术可用于金属纳米材料的焊接与组装。然而,在LSPRs被激发的情况下,剧烈的等离子体振荡使得一维金属纳米材料的方向性难以控制,同时会诱导纳米线相互粘连,导致纳米线方向性的精确控制以及单根纳米线的操纵变得更为困难。因此,在需要对单根一维金属纳米材料实现稳定的捕获和方向性控制时,激光波长最好避开金属材料的共振波段。例如,Do等[46]分别采用Au共振波段附近和远离共振波段的两个不同波长的激光,通过多步操作实现了对单根Au NW的捕获和方向控制。因此,在利用飞秒激光对一维金属纳米材料进行组装时,需要综合考虑激光诱导的光镊作用力和LSPRs引起的热效应等因素带来的影响。
3.2 一维半导体纳米材料
3.2.1 碳纳米管
碳纳米管(CNTs)自1991年被日本科学家lijima[49]在电弧放电的阴极沉积物中发现后,因其具有独特的光、电、磁、热、力学和催化性质,在国际上引起了一股研究热潮,受到国内外光电子、能源、微机械和生物等领域研究学者的广泛关注。目前,关于CNTs的特性研究和制备方法已取得长足的进展,研究重点正逐渐转向规模化生产和实际应用。因CNTs物化性质呈现很强的各向异性,若要实现其器件集成并充分发挥它的优异特性,需对CNTs进行定向排布和有序组装。
Ushiba等 [13]将单壁碳纳米管(Single-Walled Carbon Nanotubes,SWNTs)掺杂到丙烯酸树脂中,制备成掺杂浓度(质量分数)为0.01%的SWNTs/聚合物复合材料,利用飞秒激光直写制备了SWNTs复合微纳结构并研究了SWNTs的定向排布特性,如
图 8. 飞秒激光直写制备SWNTs/聚合物复合结构[13]。(a)飞秒激光直写制备三维SWNT/聚合物复合物微纳结构示意图;(b)阵列线所组成的立方体微结构示意图和SEM图像;(c)极坐标下立方体G峰相对强度随偏振方向与激光扫描方向夹角的变化曲线;悬臂梁结构的(d)示意图和(e)SEM图像;(f)极坐标下G峰相对强度随激光偏振方向与悬臂梁轴向夹角的变化曲线
Fig. 8. Femtosecond laser direct writing of SWNTs/polymer composites[13]. (a) Schematic of femtosecond laser direct writing of 3D SWNTs/polymer composites; (b) SEM images and schematic of stereo structures made of nanowire arrays; (c) polar-diagram of G-band relative intensity versus angle between laser polarization direction and scanning direction; (d) schematic and (e) SEM image of alignment of suspended cantilever structure; (f) polar-diagram of G-ban
受飞秒激光组装SWNTs工作的启发,Xiong等[50]利用激光直写技术实现了多壁碳纳米管(Multi-Walled Carbon Nanotubes,MWNTs)的组装和器件制造,组装示意图如
图 9. 飞秒激光直写组装MWNTs[50]。(a)TPP制备实验装置图;(b)聚合的MA光刻胶(下)和MTA光刻胶(上)对比图;(c)新制备的和放置了一周的MTA光刻胶对比图;(d)可弯曲PET衬底上TPP加工的金电极图案; (e)微弹簧、(f)微金字塔、(g)螺旋光子晶体、(h)微电容器阵列和(i)微齿轮的SEM 图
Fig. 9. Femtosecond laser direct writing and assembly of MWTNs[50]. (a) Experimental setup of TPP fabrication; (b) comparison of polymerized MA photoresist (down) and MTA photoresist (up); (c) comparison of newly fabricated MTA photoresist and that after one week; (d) TPP fabricated Au electrode pattern on flexible PET substrate; SEM images of (e) micro-coil inductor, (f) micro-pyramid, (g) spiral photonic crystal, (h) micro-capacitor array, and (i) micr
图 10. 飞秒激光组装MWNTs电学和机械性能表征[51]。(a)退火后的MWNTs复合微米线结构的SEM图;(b)极坐标下微米线G峰相对强度随偏振方向与微米线轴向夹角的变化曲线;(c)不同激光扫描方向的长条形导电沟道SEM图;(d)长条形导电沟道的电流-电压特性曲线图;(e)MTA复合木堆结构的SEM 图;(f)MTA木堆结构的体积收缩率随MWNTs掺杂浓度的变化曲线
Fig. 10. Electrical and mechanical performance characterization of femtosecond laser assembled MWNTs[51]. (a) SEM micrograph of MWNTs micro-line structure after annealing; (b) polar-diagram of G-band relative intensity versus angle between laser polarization direction and micro-wire axial direction; (c) SEM micrographs of long rectangle bars fabricated under different laser scanning directions; (d) current-voltage characteristic curves of long rectangle b
3.2.2 氧化锌纳米线
氧化锌(ZnO)作为一种II-VI宽禁带半导体材料,具有众多优异的特性。其激子束缚能高达60meV,远大于室温下的热能(26meV)且禁带宽度为3.37eV,因此在紫外发光和紫外探测等领域具有广泛的应用。另外,ZnO具有高等电位点,因此生物相容性良好。而一维ZnO纳米材料特别是ZnO纳米线(ZnO NWs)具有比宏观块体更为优异的特性,如具有巨大的比表面积且含有天然的载流子传输通道等,是一种理想的功能性材料,被广泛应用于光催化[52-53]、发光二极管[54]、光电探测器[55]、气体传感器[56]、生物化学传感器[57]、化学传感器、太阳能电池[58]和纳米压电发电机[59-60]等领域。而ZnO NWs的组装和功能器件的制造是发挥其性能的关键。
Fonseca等[61]将ZnO NWs掺杂到光敏树脂中,利用双光子聚合飞秒激光直写制造了ZnO NWs/聚合物复合三维微纳结构。如
图 11. 飞秒激光直写制备ZnO NWs/聚合物复合微纳结构[61]。(a)不同掺杂浓度的ZnO NWs/聚合物微立方体结构;(b)ZnO NWs/聚合物复合微纳结构的光电子能谱图;(c)ZnO NWs粉末(i),纯光敏树脂聚合物微纳结构(ii)和ZnO NWs/聚合物复合微纳结构(iii)的拉曼光谱;(d)ZnO NW粉末(i)和ZnO NWs/聚合物复合微纳结构(ii)的荧光光谱
Fig. 11. Femtosecond laser direct writing and fabrication of ZnO NWs/polymer composite micro/nanostructures [61]. (a) ZnO NWs/polymer stereo microstructures with different doping concentrations; (b) photoelectron spectra of ZnO NWs/polymer composite micro/nanostructures; (c) Raman spectra of ZnO NWs powder (i), pure resin polymer micro/nanostructures (ii) , and ZnO NWs/polymer composite micro/nanostructures (iii); (d) fluorescence spectra of ZnO NW powder
为了进一步提升ZnO NWs的组装质量和功能器件的制造,本课题组使用硅烷偶联剂[3-(三甲氧基甲硅基)甲基丙烯酸丙酯,silane]对ZnO NWs进行修饰,使其能均匀掺杂到光刻胶中。如
图 12. 飞秒激光直写组装ZnO NWs[62]。(a)纯丙烯酸酯树脂与ZNA复合树脂的比较图;(b)ZnO NWs经硅烷偶联剂修饰前后的水滴接触角测试对比图;(c)纯丙烯酸酯树脂与ZNA复合树脂的二次谐波光谱对比图;(d)(e)飞秒激光组装ZnO NWs原理示意图;(f)ZNA复合微纳结构的SEM图像,包括螺旋状光子晶体和视觉环
Fig. 12. Femtosecond laser direct writing and assembly of ZnO NWs [62]. (a) Comparison of pure acrylate resin and ZNA composite resin; (b) water contact angle diagrams of ZnO NWs before and after silane modification; (c) SHG spectra of pure acrylate resin and ZNA composite resin; (d)(e) schematic diagrams of femtosecond laser assembly of ZnO NWs; (f) SEM images of ZNA composite micro/nanostructures, including spiral photonic crystal and visual-ring
ZnO NWs是一种具有非中心对称结构的纤锌矿晶体,有着较强的二阶光学非线性[63]。并且,其偏振二次谐波(Polarized-Second Harmonic Generation,P-SHG)信号强度随着激发光的偏振方向和NWs轴线之间的夹角的变化而变化,夹角为0°即相互平行时强度最大,夹角为90°即相互垂直时强度最小。从ZNA花瓣结构[
图 13. ZNA复合微纳结构中ZnO NWs的定向排布表征[62]。 (a)ZNA 花瓣结构的光学显微图;ZNA花瓣结构的(b)P-SHG极化图和(c)(d)面扫描成像图;ZNA(e)网格和(f)木堆结构经过高温热处理后的SEM图像,右上角插图为木堆结构退火前的SEM图
Fig. 13. Alignment characterization of ZnO NWs in ZNA composite micro/nanostructures[62]. (a) Optical micrograph of ZNA flower pattern; (b) P-SHG polar-diagram and (c)(d) mapping images of ZNA flower pattern; (e) SEM images of ZNA (e) grid and (f) woodpile structures after high temperature thermal treatment and upper right corner is SEM image before annealing of woodpile structure
3.2.3 一维半导体纳米材料的飞秒激光组装特点
不同于一维金属纳米材料,一维半导体纳米材料飞秒激光组装过程不必过多考虑LSPRs效应。特别是金属氧化物一维半导体纳米材料,由于熔点高且飞秒激光脉宽窄,其在飞秒激光组装过程中受到的热损伤较小,因此激光诱导高定向组装过程较为稳定,可实现材料的精确定位和方向控制以及三维复合微纳结构的稳定制备。然而,一维半导体纳米材料的激光组装仅能得到纳米线之间的物理堆叠和搭接,难以实现晶体结构上的熔合和互联,这会影响组装结构整体性能的提升。例如在电学方面,组装的半导体纳米线不可避免存在接触空隙的情况,从而导致电子在经过纳米线传导时容易被阻断。另外,将半导体纳米材料掺杂到光刻胶中并利用飞秒激光进行组装时,一维纳米材料的尺寸和掺杂浓度对组装效果也有一定的影响。长度较长的纳米线以及浓度较高的纳米线复合光刻胶有利于形成致密的纳米线网络结构,提高组装效果和结构的导电性。然而,当纳米材料长度过长或掺杂浓度过高时,纳米线或纳米管如碳纳米管之间的缠绕和团聚效果会加剧,在复合光刻胶制备过程中容易离心沉降,反而导致纳米材料在复合光刻胶中的整体浓度较低,降低了组装质量;并且团聚的纳米材料极易在激光直写过程中引起微爆等现象,加剧激光组装制备过程的不稳定性。与此同时,对于纳米线的长度选择需要考虑微纳结构线宽的大小,本课题组在对ZnO NWs进行组装时[62],微纳结构的线宽在300nm左右,在纳米线的长度为300nm左右或小于该值的情况下,才可以保证纳米线能稳定束缚在微纳结构中。而当长度远大于结构的线宽时,纳米线的束缚和方向性控制会变得更为困难,因此选择合适的纳米线尺寸和掺杂浓度对飞秒激光组装一维半导体纳米材料是非常重要的。总体而言,相较于一维金属纳米材料,飞秒激光直写在组装一维半导体纳米材料时,具有组装过程稳定、热效应低且可实现三维高定向组装等优势。然而,因一维半导体纳米材料的熔点相对较高,组装过程中材料之间的激光诱导连接和熔合变得较为困难,这也是激光诱导材料组装领域将来需要重点解决的问题。
4 飞秒激光组装一维纳米材料的应用
在飞秒激光的作用下,一维纳米材料可从杂乱无序的状态转变为有序的结构体,这不仅能优化材料的内在特性,而且还能开发出新的物理和化学性能。通过高精度纳米材料组装和功能化二维及三维结构的构建,可以充分发挥一维纳米材料结构单元之间的协同作用,从而使其具有更大的应用价值。
4.1表面增强拉曼探测
表面增强拉曼散射(Surface-Enhanced Raman Scattering,SERS)是一种使用金属纳米结构衬底来增强待测样品Raman光谱信号的表面敏感技术。当分子接近或吸附在贵金属纳米材料表面时,Raman光谱信号将增强104~1015倍,可实现单分子检测。SERS可提供分子振动的指纹信息,不需要其他的标记信号,根据指纹特征就可以直接确定其结构组成。SERS作为一项直接的、灵敏的探测技术,得到了广泛的研究。另外,SERS信号增强的大小与纳米结构的材料、尺寸、形状、激发波长及偏振密切相关。因此,通过设计纳米材料的结构和形貌,对其分布进行操纵,可调制表面等离子体的共振特征,提高SERS单分子检测灵敏度。
Zhang等[45]将组装的金纳米棒微纳结构应用于微流控芯片的SERS探测,并将组装有金纳米棒的基片进行封装,实时探测溶液经过金纳米棒后探针分子的信号,如
图 14. 飞秒激光组装Au纳米棒用于SERS探测[45]。(a)基于金纳米棒微纳结构的微流控芯片的SERS 探测示意图;(b)R6G探测分子的拉曼光谱
Fig. 14. Femtosecond laser assembly of Au nanorods used for SERS detection [45]. (a) Schematic of SERS detection of microfluidic chip based on Au nanorod micro/nanostructure; (b) Raman spectrum of R6G probe molecules
4.2 热敏开关
Liu等 [47]基于飞秒激光作用下形成的高导电Ag NWs网络,对ATA复合微纳结构的热敏性能进行了研究,揭示了ATA复合结构的导电机制并实现了功能器件的制造。如
图 15. ATA复合微纳结构的温度相关导电性表征[47]。导电性测试的(a)示意图和(b)装置图;(c)纯丙烯酸树酯和ATA复合结构在激光焊接和523 K情况下的电流-电压曲线图;(d)ATA复合微纳结构的温度循环导电性测试曲线
Fig. 15. Temperature-dependent electrical conductivity characterization of ATA composite micro/nanostructures [47]. (a)Schematic and (b) setup for electrical conductivity test; (b) current-voltage curves of ATA composite structure and pure pure acrylate resin under laser welding and 523 K; (d) temperature-dependent electrical conductivity of ATA composite micro/nanostructure
与纯光敏树脂相比,基于ATA光刻胶制备成的Ag NWs复合结构在经过飞秒激光熔接处理并实现电阻跳变后, 电导率提高了10个数量级。无论是与导体还是与绝缘体相比,ATA复合微纳结构都呈现出了独特的导电特性。该项研究所展示的纳米材料的组装和连接方法为今后开发多功能器件和设备提供了新的思路,有望应用于3D电子设备、温度传感器、忆阻器和生物医学设备等。
4.3 微电子器件
Xiong等[50] 基于MTA 复合材料在激光直写组装下所呈现的高导电性,制作了一系列功能微电子器件,如
图 16. TPP飞秒激光直写制备的MWNTs功能性器件[50]。(a) MWNTs复合聚合物线阵列经过真空热退火后的SEM图像,插图为组装的MWNT束的SEM放大图;(b) MWNTs复合聚合物线阵列退火前后的电流-电压曲线;(c) Au对电极间电容器阵列的光学显微图像,插图展示了单个电容器的SEM图像;(d)电容器阵列的磁滞回线;(e)锯齿形电阻阵列的光学显微图像,插图展示了单个锯齿形电阻的SEM图像;(f) MTA复合结构传导线和铜传输线的频率响应特性曲线
Fig. 16. TPP-based femtosecond laser direct writing and fabrication of MWNTs-based functional devices [50]. (a) SEM image of MWNTs composite polymer array after vacuum thermal annealing and magnified SEM image of assembled MWNT bundle shown in inset; (b) current-voltage curves of MWNTs composite polymer line array before and after thermal annealing; (c) optical micrograph of capacitor array between two Au electrodes and SEM image of single capacitor shown
4.4 偏振紫外光探测器
本课题组以ZnO NWs为例制备了电阻式的紫外光电导探测器[62],器件示意图和光学显微图分别如
图 17. TPP飞秒激光直写制备的ZnO NWs偏振相关紫外探测器[62]。(a)示意图;(b)光学显微图;(c)器件的时间分辨响应;(d)不同紫外光偏振角度下器件的光电流
Fig. 17. ZnO NWs-based polarized UV photodetectors fabricated by TPP-based femtosecond laser direct writing [62]. (a) Schematic; (b)optical micrograph; (c) time-resolved response of device; (d) photocurrents of device under different UV polarization angles
5 飞秒激光组装一维纳米材料的机理和影响因素
飞秒激光组装一维纳米材料时,激光焦点处的一维纳米材料被光学梯度力捕获,倾向于沿着激光偏振方向偏转。当激光高速扫描时,会在纳米线与光刻胶的界面产生剪切力,该剪切力会诱导一维纳米材料朝着激光扫描的方向偏转并使其准直。另外,激光作用区域的光刻胶在聚合的同时,聚合结构会产生体积收缩,体积收缩带来的内应力同样会诱导一维纳米材料朝着激光扫描的方向定向排布。与此同时,一维纳米材料在偏转、准直的过程中也会受到光刻胶黏滞力的阻碍作用。并且,飞秒激光作用区域的温度会迅速升高,将导致激光焦点处纳米材料的布朗运动加剧,反过来会对纳米材料的可控组装造成负面影响,因此必须对激光组装过程进行系统研究和控制。
Ushiba等[13]在组装SWNTs时,研究了直写结构线宽对SWNTs定向性的影响。
图 18. SWMTs/聚合物复合微纳结构中SWMTs定向排布强度的表征[13]。(a)不同线宽悬空纳米线的SEM图像;(b)SWNTs的准直系数随着悬空纳米线线宽的变化;(c)沿相互垂直激光扫描方向分别加工的微立方块结构的SEM图,左侧立方块由沿x轴方向排布的NWs组成,右侧立方块由沿y轴方向排布的NWs组成;(d)微立方块结构示意图;(e)微立方块结构的偏振SHG极化图
Fig. 18. Alignment intensity characterization of SWNTs in SWNTs/polymer composite microstructures[13]. (a) SEM images of suspended nanowires with different wire widths; (b) nematic order parameter versus wire width; (c) SEM images of micro-cubes fabricated along mutually perpendicular laser scanning direction, in which left cube is made of NWs arranged along x-axis and right cube is made of NWs arranged along y-axis; (d) structural diagram o
本课题组在进行ZnO NWs组装的同时,探究了激光直写实验参数对ZnO NWs组装效果的影响。结果表明,硅烷偶联剂修饰的纳米线在功率小于7.5mW、扫描间距大于400nm时可以得到最佳的线性排布效果,形貌具有良好的定向排布效果,并且与衬底结合紧密。而当功率大于7.5mW或扫描速度小于50μm/s时,光刻胶在高功率激光或激光长时间作用下快速固化,导致纳米线来不及在光学梯度力下沿着激光扫描路径偏转方向。而当激光功率小于7.5mW或扫描速度高于50μm/s时,激光扫描速度过快,导致激光辐照时间太短,纳米线来不及克服黏滞力的影响,无法偏转到激光扫描的方向。另外,激光扫描的线间距也会对纳米线的排布产生影响,当线间距大于400nm时,才会呈现良好的线性排布效果。而当线间距过小时,相邻线之间在激光扫描的过程中会发生干扰,从而导致定向排布效果不明显。
飞秒激光组装ZnO NWs的过程和机理如
为了探究飞秒激光组装ZnO NWs时诱导纳米线定向排布的主要因素,研究者开展了理论计算和实验测试。当激光功率为10mW和扫描速度为50μm/s时,瑞利模型[67]下光学梯度力最大值约为20.5fN。与此同时,利用斯托克斯定律[10,25],得到纳米线在偏转到激光扫描方向的过程中需要克服的黏滞力大概为44.3pN。可以看出,光学梯度力明显小于黏滞力,因此单纯的光镊力难以克服偏转过程中黏滞力的影响,即难以实现定向排布。考虑到光学梯度力作用下一维纳米材料倾向于沿着激光偏振的方向偏转[68],本实验采用水平偏振光和垂直偏振光对纳米线进行组装测试。实验结果如
图 19. 飞秒激光组装ZnO NWs的示意图[62]。(a)组装机理图;(b)不同扫描路径和偏振方向下激光加工的正方形结构以及相对应的偏振SHG面扫描图像
Fig. 19. Schematic of femtosecond laser assembly of ZnO NWs [62]. (a) Schematic of assembly mechanism; (b) square structures fabricated under different laser scanning routes and polarization directions and their polarized SHG mapping images
6 结束语
主要回顾了一维纳米材料组装研究的背景,总结了现有组装技术的研究现状和存在的挑战,详细介绍了基于飞秒激光直写技术的金属(包括Au、Ag纳米线)、半导体(包括CNTs、ZnO)组装和功能器件制造的研究。与传统非激光组装技术相比,激光直写组装技术特别是飞秒激光直写技术具有超高空间分辨率和真三维微纳制造能力,在一维纳米材料组装方面具有明显的优势。飞秒激光的高峰值功率和短脉冲的特性使其可以从能量和动量上实现对纳米材料的精确调控。即一方面可产生紧聚焦的光梯度场,从而对纳米材料进行有效捕获和方向控制,并且超短脉宽使得材料的能量吸收时间远小于热弛豫时间,能够有效抑制激光作用区域的热效应,使得能量可以精确聚焦到微小作用区域,组装精度高。另一方面,激光焦点处的能量高度集中,可激发多种光物理和光化学过程,从而实现对一维纳米材料的形貌、分布及连接状况的调控。由此可见,飞秒激光直写可实现一维微纳材料在任意三维空间的高定向、高精度的组装,以及微纳光电子功能器件的制造。
尽管飞秒激光直写技术在一维纳米材料组装方面取得了可喜进展,但仍存在以下几个亟待解决的问题:1)一维纳米材料的轴向排布组装仍然存在一些不规则性,高度准直的激光组装技术和物理机制还有待深入研究;2)多种一维纳米材料的三维组装以及集成功能器件的制造仍需进一步发展;3)一维金属纳米材料因表面等离子体基元共振效应的影响,往往难以实现高定向、可控的材料组装,需要进一步深入研究;4) 目前激光直写组装效率偏低,还有待提高。针对以上问题,可对一维纳米材料复合树脂的组分进行进一步优化,以减小其在沿激光扫描方向旋转排布时需要克服的黏滞力;在激光组装过程中,通过引入激光光束偏振态控制,实现对一维纳米材料的更加精准的定向排布操纵。另外,采用激光直写并行加工技术等,可进一步提高一维纳米材料的组装效率。
综上,一维纳米材料的可控三维组装和功能化集成是实现纳米材料应用的关键。功能性微纳结构的构建以及功能器件的制造迫切需要合理的纳米材料组装策略和技术手段。飞秒激光直写技术具有真三维、可设计和高精度的材料组装等特点,为实现一维纳米材料的功能化结构制造与器件集成提供了一条切实可行的道路,有望在MEMS/NEMS、柔性电子、传感器、光开关和超材料等领域中得到广泛应用。
[1] Yang P, Yan H, Mao S, et al. Controlled growth of ZnO nanowires and their optical properties[J]. Advanced Functional Materials, 2002, 12(5): 323-331.
[2] Pan Z, Lai H L. Au F C K, et al. Oriented silicon carbide nanowires: Synthesis and field emission properties[J]. Advanced Materials, 2000, 12(16): 1186-1190.
[3] Chan C K, Peng H, Liu G, et al. High-performance lithium battery anodes using silicon nanowires[J]. Nature Nanotechnology, 2008, 3(1): 31-35.
[4] Zhang Y J, Ago H, Liu J, et al. The synthesis of In, In2O3 nanowires and In2O3 nanoparticles with shape-controlled[J]. Journal of Crystal Growth, 2004, 264(1/2/3): 363-368.
[5] Kou X M, Fan X, Dumas R K, et al. Memory effect in magnetic nanowire arrays[J]. Advanced Materials, 2011, 23(11): 1393-1397.
[6] Wong E W, Sheehan P E, Lieber C M. Nanobeam mechanics: Elasticity, strength, and toughness of nanorods and nanotubes[J]. Science, 1997, 277(5334): 1971-1975.
[7] Huang Y. Directed assembly of one-dimensional nanostructures into functional networks[J]. Science, 2001, 291(5504): 630-633.
[8] Fan Z, Ho J C, Jacobson Z A, et al. Wafer-scale assembly of highly ordered semiconductor nanowire arrays by contact printing[J]. Nano Letters, 2008, 8(1): 20-25.
[9] Wang D, Chang Y L, Liu Z, et al. Oxidation resistant germanium nanowires: Bulk synthesis, long chain alkanethiol functionalization, and Langmuir-Blodgett assembly[J]. Journal of the American Chemical Society, 2005, 127(33): 11871-11875.
[10] Freer E M, Grachev O, Duan X, et al. High-yield self-limiting single-nanowire assembly with dielectrophoresis[J]. Nature Nanotechnology, 2010, 5(7): 525-530.
[11] Hangarter C M, Rheem Y, Yoo B, et al. Hierarchical magnetic assembly of nanowires[J]. Nanotechnology, 2007, 18(20): 205305.
[12] Lee J, Wang A, Rheem Y, et al. DNA assisted assembly of multisegmented nanowires[J]. Electroanalysis, 2007, 19(22): 2287-2293.
[13] Ushiba S, Shoji S, Masui K, et al. Direct laser writing of 3D architectures of aligned carbon nanotubes[J]. Advanced Materials, 2014, 26(32): 5653-5657.
[14] Tan D F, Li Y, Qi F J, et al. Reduction in feature size of two-photon polymerization using SCR500[J]. Applied Physics Letters, 2007, 90(7): 071106.
[15] Kawata S, Sun H B, Tanaka T, et al. Finer features for functional microdevices[J]. Nature, 2001, 412(6848): 697-698.
[16] 史杨, 许兵, 吴东, 等. 飞秒激光直写技术制备功能化微流控芯片研究进展[J]. 中国激光, 2019, 46(10): 1000001.
[17] 杨雪, 孙会来, 岳端木, 等. 飞秒激光制备微透镜阵列的研究进展[J]. 激光与光电子学进展, 2021, 58(5): 050005.
Yang X, Sun H L, Yue D M, Wu D, et al. Research progress on femtosecond laser fabrication microlens array[J]. Laser & Optoelectronics Progress, 2021, 58(5): 050005.
[18] 李金健, 刘一, 曲士良. 飞秒激光微纳加工光纤功能器件研究进展[J]. 激光与光电子学进展, 2020, 57(11): 111402.
[19] Gan Z, Cao Y, Evans R A, et al. Three-dimensional deep sub-diffraction optical beam lithography with 9nm feature size[J]. Nature Communications, 2013, 4: 2061.
[20] Ishitobi H, Shoji S, Hiramatsu T, et al. Two-photon induced polymer nanomovement[J]. Optics Express, 2008, 16(18): 14106-14114.
[21] Sun Z B, Dong X Z, Chen W Q, et al. Multicolor polymer nanocomposites: In situ synthesis and fabrication of 3D microstructures[J]. Advanced Materials, 2008, 20(5): 914-919.
[22] Xia H, Wang J, Tian Y, et al. Ferrofluids for fabrication of remotely controllable micro-nanomachines by two-photon polymerization[J]. Advanced Materials, 2010, 22(29): 3204-3207.
[23] Hsieh G W, Wang J J, Ogata K, et al. Stretched contact printing of one-dimensional nanostructures for hybrid inorganic-organic field effect transistors[J]. The Journal of Physical Chemistry C, 2012, 116(12): 7118-7125.
[24] Javey A, Nam S, Friedman R S, et al. Layer-by-layer assembly of nanowires for three-dimensional, multifunctional electronics[J]. Nano Letters, 2007, 7(3): 773-777.
[25] Lee H, Seong B, Kim J, et al. Direct alignment and patterning of silver nanowires by electrohydrodynamic jet printing[J]. Small, 2014, 10(19): 3918-3922.
[26] Chen S M, Gao H L, Zhu Y B, et al. Biomimetic twisted plywood structural materials[J]. National Science Review, 2018, 5(5): 703-714.
[27] Gao H L, Xu L, Long F, et al. Macroscopic free-standing hierarchical 3D architectures assembled from silver nanowires by ice templating[J]. Angewandte Chemie International Edition, 2014, 53(18): 4561-4566.
[28] Pevzner A, Engel Y, Elnathan R, et al. Confinement-guided shaping of semiconductor nanowires and nanoribbons: “writing with nanowires”[J]. Nano Letters, 2012, 12(1): 7-12.
[29] Liu X, Long Y Z, Liao L, et al. Large-scale integration of semiconductor nanowires for high-performance flexible electronics[J]. ACS Nano, 2012, 6(3): 1888-1900.
[30] Lin J H, Cretu O, Zhou W, et al. Flexible metallic nanowires with self-adaptive contacts to semiconducting transition-metal dichalcogenide monolayers[J]. Nature Nanotechnology, 2014, 9(6): 436-442.
[31] Wang S L, He Y H, Fang X S, et al. Structure and field-emission properties of sub-micrometer-sized Tungsten-Whisker arrays fabricated by vapor deposition[J]. Advanced Materials, 2009, 21(23): 2387-2392.
[32] Huang X H. El-Sayed I H, Qian W, et al. Cancer cell imaging and photothermal therapy in the near-infrared region by using gold nanorods[J]. Journal of the American Chemical Society, 2006, 128(6): 2115-2120.
[33] Lee E P, Peng Z M, Cate D M, et al. Growing Pt nanowires as a densely packed array on metal gauze[J]. Journal of the American Chemical Society, 2007, 129(35): 10634-10635.
[34] Chen M S, Phang I Y, Lee M R, et al. Layer-by-layer assembly of Ag nanowires into 3D woodpile-like structures to achieve high density "hot spots" for surface-enhanced Raman scattering[J]. Langmuir, 2013, 29(23): 7061-7069.
[35] Zijlstra P, Paulo P M, Orrit M. Optical detection of single non-absorbing molecules using the surface plasmon resonance of a gold nanorod[J]. Nature Nanotechnology, 2012, 7(6): 379-382.
[36] Chaney S B, Shanmukh S, Dluhy R A, et al. Aligned silver nanorod arrays produce high sensitivity surface-enhanced Raman spectroscopy substrates[J]. Applied Physics Letters, 2005, 87(3): 031908.
[37] Tang L J, Li S, Han F, et al. SERS-active Au@Ag nanorod dimers for ultrasensitive dopamine detection[J]. Biosensors and Bioelectronics, 2015, 71: 7-12.
[38] Strickland A D, Batt C A. Detection of carbendazim by surface-enhanced Raman scattering using cyclodextrin inclusion complexes on gold nanorods[J]. Analytical Chemistry, 2009, 81(8): 2895-2903.
[39] Lan X, Lu X, Shen C, et al. Au nanorod helical superstructures with designed chirality[J]. Journal of the American Chemical Society, 2015, 137(1): 457-462.
[40] Guerrero-Martínez A, Auguié B. Alonso-Gómez J L, et al. Intense optical activity from three-dimensional chiral ordering of plasmonic nanoantennas[J]. Angewandte Chemie International Edition, 2011, 50(24): 5499-5503.
[41] Hartland G V, Besteiro L V, Johns P, et al. What's so hot about electrons in metal nanoparticles?[J]. ACS Energy Letters, 2017, 2(7): 1641-1653.
[42] Neira A D, Wurtz G A, Ginzburg P, et al. Ultrafast all-optical modulation with hyperbolic metamaterial integrated in Si photonic circuitry[J]. Optics Express, 2014, 22(9): 10987-10994.
[43] Kawata S, Ono A, Verma P. Subwavelength colour imaging with a metallic nanolens[J]. Nature Photonics, 2008, 2(7): 438-442.
[44] Masui K, Shoji S, Asaba K, et al. Laser fabrication of Au nanorod aggregates microstructures assisted by two-photon polymerization[J]. Optics Express, 2011, 19(23): 22786-22796.
[45] 张然, 肖鑫泽, 吕超, 等. 金纳米棒的飞秒激光组装研究[J]. 物理学报, 2014, 63(1): 014206.
Zhang R, Xiao X Z. L C, et al. Assembling of gold nanorods by femtosecond laser fabrication[J]. Acta Physica Sinica, 2014, 63(1): 014206.
[46] Do J, Fedoruk M, Jäckel F, et al. Two-color laser printing of individual gold nanorods[J]. Nano Letters, 2013, 13(9): 4164-4168.
[48] Chen H Y, Gao Y, Zhang H R, et al. Transmission-electron-microscopy study on fivefold twinned silver nanorods[J]. The Journal of Physical Chemistry B, 2004, 108(32): 12038-12043.
[49] Iijima S. Helical microtubules of graphitic carbon[J]. Nature, 1991, 354(6348): 56-58.
[50] Xiong W, Liu Y, Jiang L J, et al. Laser-directed assembly of aligned carbon nanotubes in three dimensions for multifunctional device fabrication[J]. Advanced Materials, 2016, 28(10): 2002-2009.
[51] Park C, Ounaies Z, Watson K A, et al. Dispersion of single wall carbon nanotubes by in situ polymerization under sonication[J]. Chemical Physics Letters, 2002, 364(3/4): 303-308.
[52] Kumar S G, Rao K S. Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications[J]. RSC Advances, 2015, 5(5): 3306-3351.
[53] Choi J, Chan S, Joo H, et al. Three-dimensional (3D) palladium-zinc oxide nanowire nanofiber as photo-catalyst for water treatment[J]. Water Research, 2016, 101: 362-369.
[54] Liu X Y, Shan C X, Jiao C, et al. Pure ultraviolet emission from ZnO nanowire-based p-n heterostructures[J]. Optics Letters, 2014, 39(3): 422-425.
[55] Zeng Y Y, Pan X H, Lu B, et al. Fabrication of flexible self-powered UV detectors based on ZnO nanowires and the enhancement by the decoration of Ag nanoparticles[J]. RSC Advances, 2016, 6(37): 31316-31322.
[56] Tiwale N. Zinc oxide nanowire gas sensors: fabrication, functionalisation and devices[J]. Materials Science and Technology, 2015, 31(14): 1681-1697.
[57] Zhou W, Dai X C, Lieber C M. Advances in nanowire bioelectronics[J]. Reports on Progress in Physics, 2017, 80(1): 016701.
[58] Chen H N, Yang S H. Hierarchical nanostructures of metal oxides for enhancing charge separation and transport in photoelectrochemical solar energy conversion systems[J]. Nanoscale Horizons, 2016, 1(2): 96-108.
[59] Wu W, Wen X, Wang Z L. Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging[J]. Science, 2013, 340(6135): 952-957.
[60] Wang Z, Pan X M, He Y H, et al. Piezoelectric nanowires in energy harvesting applications[J]. Advances in Materials Science and Engineering, 2015, 2015: 1-21.
[61] Fonseca R D, Correa D S, Paris E C, et al. Fabrication of zinc oxide nanowires/polymer composites by two-photon polymerization[J]. Journal of Polymer Science Part B: Polymer Physics, 2014, 52(4): 333-337.
[62] Long J, Xiong W, Wei C, et al. Directional assembly of ZnO nanowires via three-dimensional laser direct writing[J]. Nano Letters, 2020, 20(7): 5159-5166.
[63] Johnson J C, Yan H Q, Schaller R D, et al. Near-field imaging of nonlinear optical mixing in single zinc oxide nanowires[J]. Nano Letters, 2002, 2(4): 279-283.
[64] Stallinga P. Electronic transport in organic materials: Comparison of band theory with percolation/(variable range) hopping theory[J]. Advanced Materials, 2011, 23(30): 3356-3362.
[65] Waser R, Aono M. Nanoionics-based resistive switching memories[J]. Nature Materials, 2007, 6(11): 833-840.
[66] Jeong D S, Thomas R, Katiyar R S, et al. Emerging memories: Resistive switching mechanisms and current status[J]. Reports on Progress in Physics, 2012, 75(7): 076502.
[67] Harada Y, Asakura T. Radiation forces on a dielectric sphere in the Rayleigh scattering regime[J]. Optics Communications, 1996, 124(5/6): 529-541.
[68] Reece P J, Toe W J, Wang F, et al. Characterization of semiconductor nanowires using optical tweezers[J]. Nano Letters, 2011, 11(6): 2375-2381.
Article Outline
龙婧, 焦玢璋, 范旭浩, 刘耘呈, 邓磊敏, 曲良体, 熊伟. 飞秒激光组装一维纳米材料及其应用[J]. 中国激光, 2021, 48(2): 0202017. Jing Long, Binzhang Jiao, Xuhao Fan, Yuncheng Liu, Leimin Deng, Liangti Qu, Wei Xiong. Femtosecond Laser Assembly of One-Dimensional Nanomaterials and Their Application[J]. Chinese Journal of Lasers, 2021, 48(2): 0202017.