【作者】 温晓镭；

【导师】 明海； 王沛； 徐先凡；

【作者基本信息】 中国科学技术大学 ， 光学， 2014， 博士

【摘要】 光学天线因其新颖的物理现象和对光场的收集、发射及调控能力受到研究人员的广泛关注,在微纳光场调控、增强拉曼散射和增强荧光、近场成像及近场光刻等领域都有重要应用。金属纳米颗粒和纳米结构的局域表面等离子体(LSPs)效应是决定光学天线性质的基础,具有高度场局域和场增强特性。本文基于光学天线可调制分子发光性能的特性,设计了两种耦合型天线结构,并应用于表面增强拉曼散射(SERS)实验。研究了两种耦合结构的近远场光学性质及其与结构参数之间的关系。另外,根据光学天线的近场局域功能,使用蝴蝶结形光学天线进行近场超分辨光刻研究。基于该天线的近场光学性质,引入干涉式空间位相成像(ISPI)技术对掩膜板和光刻胶基底进行测距、调平,最终实现大规模并行超分辨光刻。本论文工作对于发展制备简单、灵敏度高的SERS基底,及分辨率高、产率大、成本低廉、可靠性好的微纳制造技术均有重要意义。具体研究内容如下：1.设计并制备了具有纳米级间隙的银纳米球帽-纳米小孔耦合型光学天线结构并应用于SERS实验。该结构制备方法简单,成本低廉。将耦合结构与非耦合的银纳米球帽单元结构进行对比研究,结合数值模拟手段分析知银纳米球帽和纳米小孔边缘的间隙中存在LSPs耦合效应,使能量高度局域在间隙区域内,增强电场强度,从而产生更多“热点”和更高的SERS增强因子,导致SERS信号大幅增强。研究还发现耦合效应强弱与耦合距离密切相关,通过改变蒸镀银膜厚度可调节该结构的耦合间隙大小,从而能改变SERS信号的强度,这为人为调控SERS基底的工作性能提供了有效途径。2.设计并制备了准三维的银纳米立方体-银纳米小孔阵列耦合结构,并应用于SERS实验。银纳米立方体通过化学合成法制备。银纳米小孔阵列结构则通过在具有周期孔洞结构的阳极氧化铝(AAO)模板上蒸镀银获得。使用纳米级厚度的PMMA薄膜作为间隔层,将银立方体和银小孔阵列结构纵向叠加在一起获得耦合结构。SERS实验和数值模拟结果显示,该结构可将银立方体和银小孔阵列结构的LSPs有效耦合并局域于PMMA间隔层中,影响掺杂在PMMA中的拉曼分子激发和辐射过程,从而可获得1.1×108的SERS增强因子。一系列单变量对比实验证明耦合效应对间隔层厚度、银膜厚度、小孔孔径及孔间距等特征结构参数敏感,为该结构今后的实际应用提供了多样化的调控手段。3.研究基于蝴蝶结形光学天线的近场扫描超分辨光刻技术。根据蝴蝶结形光学天线的近场局域特性和光斑发散特性,设计掩膜板结构、调平准直体系和光刻工艺,建立了一套基于该天线的近场光刻系统。通过实验和理论分析,系统地研究了光刻胶特性、光源、扫描速度、润滑剂等各项实验条件对光刻效果的影响。经过实验参数优化,最终获得可见光曝光条件下线宽分别为78nm和106nm的一维和二维任意图形超分辨近场扫描光刻结果。4.为提高近场光刻的生产效率,进行大规模并行近场光刻研究。在光刻系统中引入ISPI技术,用于对掩膜板与光刻胶基底进行精密测距和调平。通过ISPI调平可获得0.02mrad的掩膜板-基底空间平行度。建立了反馈控制机制,有效控制系统噪声,提高光刻胶基底移动过程中的系统稳定性。利用ISPI技术精确控制光学天线的工作距离,可进一步提高光刻分辨率,获得最小19nm线宽的光刻图形。使用改良的实验装置及掩膜板,实现了5×5(25个)和32×32(1024个)蝴蝶结形光学天线阵列的大规模并行近场二维扫描光刻。所获得的图形形貌均一,表面质量好,可靠性高。进一步提高扫描速度,可将产率相对于传统近场扫描光刻技术提高104倍以上。本论文的创新点在于：1.基于耦合型光学天线结构增强局域场的光学效应,设计制备了一种新颖的银纳米球帽-纳米小孔耦合天线结构,并应用于SERS实验。该结构的制备方法简单易行,可通过控制蒸镀银膜厚度的方法调节耦合间隙大小,从而对耦合效应和SERS信号强度起调制作用。2.提出一种新型的准三维耦合天线结构作为SERS基底。使用纳米级PMMA薄膜作为间隔层,将银纳米立方体和银纳米小孔阵列结构组装到一起。利用银小孔阵列结构增强对入射光的吸收,利用LSPs耦合效应将能量局域在耦合区域中,增强该区域内拉曼分子的激发和辐射效率,通过银立方体增强辐射,将近场拉曼信号发射至远场,便于被探测器收集。该耦合结构相比非耦合结构具有更好的拉曼增强效应,可获得1.1×108的SERS增强因子。3.首次将ISPI技术引入基于蝴蝶结形光学天线的近场扫描光刻体系,对掩膜板与光刻胶基底进行纳米级精密测距和调平,获得0.02mrad以上的掩膜板-基底平行度。系统地研究了近场扫描光刻过程中各技术参数对光刻结果的影响,使用ISPI技术精确控制天线工作距离,提高光刻分辨率,获得线宽最小可达19nm的光刻图形,并最终实现1024个天线阵列并行的大规模近场二维扫描超分辨光刻。该技术可将近场扫描光刻产率提高104倍。更多还原

【Abstract】 Optical antenna has been widely investigated due to their novel optical phenomena and capability of manipulating light field at the nanometer scale. It has been used in many fields such as nano-scale light manipulation, surface enhanced Raman spectroscopy (SERS), fluorescence enhancement, near-field imaging and near-field optical nanolithography. Its properties are based on the localized surface plasmons (LSPs) that are supported by metal nanoparticles or nanostructures. In our work, two kinds of antennas consist of LSPs coupling structures were designed for SERS experiments, which can significantly increase the Raman signals due to the excitation and radiation enhancement of the molecules. On the other hand, based on the localization property, near-field optical nanolithography was investigated using bowtie aperture antennas. We studied the optical near-field properties of the bowtie aperture antenna and established a nanolithography system. To improve the lithography resolution and quality, interferometric-spatial-phase-imaging (ISPI) technique was introduced into this system, and finally assisted to realize high-throughput parallel near-field scanning optical lithography with diffraction-unlimited resolution. Our work has great potentials on developing easy-fabricated and low-cost SERS substrates and high-resolution, high-throughput, low-cost and reliable nano-manufacture technologies.The details of this thesis are shown as following:1. Ag nanocap-nanohole coupling antenna was designed for SERS experiments. This structure was fabricated through a facile and low-cost method. Both the SERS measurements and numerical simulations show that the cap-hole structure produces much stronger Raman signal than the non-coupling structures which is due to the plasmonic coupling effect within the gap between the cap and the hole. The coupling effect localized the energy in the gap so that can produce more "hot spots" and higher SERS enhancement factor. Additionally, the coupling effect is sensitive to the gap size, which can be controlled by the Ag layer thickness during the evaporation process. It provides an effective way to control the SERS performance for further applications.2. A quasi-3D system composed of Ag nanocubes and Ag nanohole arrays was designed and fabricated. The Ag nanocubes were synthesized through chemical reaction. The Ag nanohole arrays were obtained by evaporating Ag onto anodic aluminum oxide (AAO) templates, which have self-organized hexagonally-ordered hole arrays. PMMA film with nanoscale thichness was used as a spacer layer to separate the cubes and the hole array. SERS measurements and numerical simulation show that this structure supports LSPs coupling effect within the spacer. The intense local field can affect the excitation and radiation of Raman molecules doped in PMMA, which produced1.1×108SERS enhancement. A series of experiments were performed to investigate the sensitivity of the coupling effect to the structure parameters (such as the spacer thickness, the Ag film thickness, the hole diameter and the hole period). It provides varies ways to modulate the SERS performance of this kind of structure.3. Near-field scanning optical nanolithography was studied using bowtie aperture antennas. The near-field optical properties of the bowtie antenna were investigated for the reference of the mask design, the alignment procedure and the lithography technique. A near-field scanning optical lithography system was established using bowtie antennas as focusing elements. The effects of experimental parameters such as the photoresist properties, exposing source, scanning speed and the lubricant were analyzed through experiments. After optimizing the parameters,1D and2D arbitrary patterns with diffraction-unlimited resolution (78nm and106nm, respectively) were achieved under visible exposing light.4. To improve the throughput of near-field scanning nanolithography, parallel lithography technique was studied. Interferometric-spatial-phase-imaging (ISPI) technique was introduced into the lithography system to realize accurate gap detection and alignment. Through the ISPI alignment for the mask and photoresist substrate,0.02mrad parallelism can be achieved. The ISPI technique was also utilized to establish a feed-back system to suppress the noise during lithography process, which improved the stability of the whole system. The experimental setup and mask structure is developed according to the ISPI-assistant lithography strategy, and the working distance of the antennas can be well controlled to achieve a lithography resolution as small as19nm. High-throughput parallel near-field nanolithography using massive antenna arrays (e.g.25and1024antennas) were successfully realized with good quality, uniformity and reliability. By additionally speeding up the scanning movement, the throughput can be further increased to104times higher than the traditional near-field scanning lithography technique. The innovations of this thesis are listed following:1. Based on the local field enhancement of the LSPs coupling effect, Ag nanocap-nanohole coupling antenna was designed for SERS. The fabrication of this structure is facile and low-cost, and is able to control the gap size through the thickness of the Ag layer, which provides a easy way to modulate the SERS effect of this kind of structure.2. A quasi-3D plasmonic coupling antenna structure which is consist of Ag nanocubes and Ag nanohole arrays was realized using a PMMA film as spacer layer. An idea was performed to use Ag nanohole array to increase the absorption of the incident light energy and localize it in the coupling area. While the Ag cubes can enhance the radiation of the Raman signal and transfer it to far field for detection. This structure produced1.1×108SERS enhancement.3. Near-field scanning optical nanolithography using bowtie aperture antannas was studied thoroughly by investigating the influence of each technical parameter. ISPI technique was introduced into the lithography system to detect the distance between the mask and photoresist substrate and align them with a high accuracy (0.02mrad) so that the problems caused by the near-field property of the antenna can be solved. The ISPI technique can precisely control the working distance of the antenna, which helps to achieve a lithography resolution as small as19nm and finally realize massive parallel lithography for1D and2D arbitrary patterns. The throughput can reach104times of the traditional near-field lithography method.更多还原