倾斜底涂法制备聚苯乙烯胶体晶体及其光学特性研究

采用倾斜底涂法将单分散的聚苯乙烯胶体微球自组装生长成为胶体晶体,并用扫描电子显微镜和紫外-可见光分光光度计对其形貌和光学特性进行测量。结果表明,聚苯乙烯微球自组装为面心立方密堆积结构,胶体晶体的光子带隙位于可见光波段。分别对不同胶体颗粒的粒径、悬浮液的浓度、基片倾斜角度及环境温度等制备条件下生成的聚苯乙烯光子晶体样品逐一分类对比,分析了影响光子带隙宽度和深度的因素。     

二维金纳米阵列制备及其光学响应

有序贵金属纳米结构由于其本身所特有的光学响应及灵活调控能力,在微纳光电子材料与器件研究领域得到了广泛应用。在众多相关研究中,如何实现金（Au）纳米周期结构的大面积快速制备是人们关心的重要问题之一。采用纳米球自组装刻蚀方法,在大孔周期结构模板内部成功制备了新型二维Au纳米阵列,并有效避免了杂散Au纳米颗粒的产生。通过进一步的工艺优化和参量控制,实现了Au纳米颗粒尺寸的灵活调控,并探讨了其结构形成的物理机理。光学测试研究结果揭示了二维Au纳米阵列的表面等离子体吸收与散射响应,并证明其在近红外飞秒脉冲激励下具有显著的双光子吸收（饱和）效应。该研究结果在太阳能电池,光开关及材料微纳制备等领域具有潜在应用。     

二维光子晶体的制备及应用

主要论述二维光子晶体的制备方法和二维光子晶体器件，并着重讨论了光子晶体在未来的光学器件集成方面广阔的应用前景．     

基于二维有序分立胶体晶体模板制备的金属薄膜透射谱的研究

We studied the infrared transmission properties of gold films on ordered two-dimensional nonclose- packed polystyrene （PS） colloidal crystal. The gold films consist of gold half-shells on the PS spheres and gold film with 2D arrays of holes on the glass substrate. An extraordinary optical transmission phenomenon could be found in such a structure. Simulations with the finite-difference time-domain method were also employed to get the transmission spectra and electric field distribution. The transmission response of the samples can be adjusted by controlling the thickness of the gold films. Angle-resolved measurements were performed using polarized light to obtain more information about the surface plasmon polariton resonances of the gold films. As the angle changes, the transmission spectra change a lot. The transmission spectra of p-polarized light have quite different properties compared to those of s-polarized light.     

二维光子晶体的制备及应用

主要论述二维光子晶体的制备方法和二维光子晶体器件,并着重讨论了光子晶体在未来的光学器件集成方面广阔的应用前景。     

稀土La自组装纳米膜的制备及表征

电子封装表面材料采用分子自组装技术制备了稀土La纳米膜,采用AFM(原子力显微镜)对组装膜的表面形貌进行表征,表征结果该稀土纳米膜表面形貌致密,表面粒子尺寸为20～30nm;场发射扫描电镜测试表明,该组装膜的成分为La;     

单分散性sio2胶体微球自组装光子晶体的实验研究

光子晶体是一种周期性电介质材料,具有光子带隙和光子局域等一系列优异的光学特性。制备了多种不同直径的单分散二氧化硅胶体微球,采用垂直沉积法将不同直径,以及同一直径不同浓度的二氧化硅胶体微球自组装成多种光子晶体薄膜,并用扫描电子显微镜和紫外—可见—近红外分光光度计对其微观结构和光学特性进行了表征,结果表明所得晶体薄膜具有三维有序结构,其表面存点、线缺陷。自组装得到的光子晶体薄膜存在明显的光子带隙特征,带隙位置与二氧化硅胶体微球直径有关,带隙中心波长与理论值一致。随着二氧化硅胶体微球浓度的增加,光子带隙深度增加,特性更好,但是,当浓度大于10%时,光子带隙的深度反而减小。     

二维纳米结构银膜表面增强拉曼散射基底的制备与研究

采用电解法制备了粒径分布为(50±8)nm,表面呈正电性的纳米银粒子.基于该纳米银粒子,采用静电自组装技术在经过特殊处理、表面呈负电性的玻璃基底上生成了具有高效、稳定性的二维纳米结构银膜.该银膜外层纳米银粒子平均粒径约200 nm,相邻纳米银粒子之间形成了不规则的纳米微区,平均尺寸达到200 nm左右.基于该纳米银膜,采用便携式拉曼光谱仪对20个正常人血清样本进行了表面增强拉曼散射(SERS)光谱的检测.同时,也对同一正常人血清基于同种条件下制备的不同纳米银膜的SERS光谱进行了检测.实验发现:该纳米银膜对人血清的拉曼散射具有较好的增强效果,有望为人血清的研究提供新的途径.     

二维光子晶体三角形结构带隙研究

通过改变二维光子晶体三角形结构的晶格元胞半径、晶格周期和厚度,模拟其带隙变 化,分析变化规律,为二维光子晶体集成波导提供理论基础。     

Chiral 2D Colloidal Semiconductor Quantum Wells

Induced chirality in colloidal semiconductor nanoparticles has raised significant attention in the past few years as an extremely sensitive spectroscopic tool and due to the promising applications of chiral quantum dots in sensing, quantum optics, and spintronics. Yet, the origin of the induced chiroptical effects in semiconductor nanoparticles is still not fully understood, partly because almost all the theoretical and experimental studies to date are based on the simple model system of a spherical nanocrystal. Here, the realization of induced chirality in atomically flat 2D colloidal quantum wells is shown. A strong circular dichroism (CD) response as well as an absorptive‐like CD line shape is observed in chiral CdSe nanoplatelets (NPLs), significantly differing from that previously observed in spherical dots. Furthermore, this intense CD signal almost completely disappears after coating with a very thin CdS shell. In contrast, CdSe‐CdS core‐crown NPLs exhibit a spectral response which seems to originate independently from the core and the crown regions of the NPL. This work on the one hand further advances the understanding of the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, and on the other opens a pathway toward applications using chiroptical materials.     

2D van der Waals Heterojunction Nanophotonic Devices: From Fabrication to Performance

2D van der Waals heterojunctions (vdWhs) are a novel type of metamaterial that are flexible, adjustable, and easy to assemble. Using weak van der Waals forces (vdWfs), layered 2D materials can stack freely to form vdWhs with atomic level flat interfaces. By using different 2D materials and specific stacking methods, their unique properties can be organically combined, to exhibit more abundant optical properties. In fact, nanophotonic devices based on 2D vdWhs have developed rapidly and made significant progress. Therefore, the main progress of 2D vdWhs nanophotonic devices in recent years, including the preparation methods of 2D vdWhs and the performance improvements of various nanophotonic devices, is reviewed. Lastly, the prospects of 2D vdWhs nanophotonic devices are discussed.     

Artificial Helical Screws of 2D Materials with Archimedean Spiral Arrangement

Helix structures, which are frequently observed in nature, act as versatile structural templates for complex functionalities with asymmetry and anisotropy. However, atomically thin 2D materials, including graphene, transition metal dichalcogenides (TMDs), and MXenes, do not have inherent chirality in their planar geometry and cannot easily form such a structure. This study presents the macroscopic self-assembly of 2D materials for helical screws with an Archimedean spiral arrangement. The naturally triggered spontaneous rotation upon the 1D fiber assembly of 2D materials forms helical screws consisting of multiple helices and perversions. For a clear understanding of the morphological evolution of helical screws, variations in the helical pitch and angle are systematically analyzed considering thermodynamic and kinetic conditions. Subsequently, the influence of spontaneous helix formation on the properties of the 2D assembled fibers is investigated in terms of the solvent-driven actuator performance and electrical and electrothermal properties. The suggested approach provides a new perspective on the directed self-assembly of inherently achiral 2D materials toward chiral helix formation.     

Fabrication and Characterization of Two‐Photon Polymerized Features in Colloidal Crystals

The fabrication and characterization of two‐photon polymerized features written within and outside of colloidal crystals is presented. Two‐photon polymerization (TPP) response diagrams are introduced and developed to map the polymerization and damage thresholds for features written via modulated beam rastering. The use of tris[4‐(7‐benzothiazol‐2‐yl‐9,9‐diethylfluoren‐2‐yl)phenyl]amine (AF‐350) as an initiator for TPP is demonstrated for the first time and TPP response diagrams illustrate the polymerization window. These diagrams also demonstrate that the polymerization behavior within and outside of colloidal crystals is similar and electron microscopy reveals nearly identical resolution. Fluorescence confocal microscopy further enables visualization of non‐self‐supporting, three‐dimensional TPP features within self‐assembled photonic crystals. Finally, microspot spectroscopy is collected from a two‐photon feature written within a colloidal crystal and this is compared with simulation.     

2D Metal-Organic Complex Luminescent Crystals

2D emissive crystals have attracted tremendous research interests due to their outstanding compatibility with an integrated planar photonic system, which ideally meet the requirement for versatile photonic device applications, such as lasers, light-emitting devices, and optical waveguides. Among 2D emissive materials, metal-organic complex crystals are highly desirable because of their strong charge-transfer interactions and enhanced optical absorption that benefit superior luminescence efficiency. Here, the in-air sublimation method is adopted to synthesize 2D Ge-TCNQ microplate crystals (TCNQ, 7,7,8,8-tetracyanoquinodimethane) with thickness down to 13.4 nm. Such ultrathin Ge-TCNQ crystals exhibit an exciton binding energy of 40.7 meV and a decent photoluminescence (PL) quantum efficiency of 5.53%. The fitting slope of excitation power-dependent PL intensity displays a transition from linear to superlinear characteristics that reveals both trap-assisted recombination and free carrier recombination are present in the luminescence process. The energy band structure of Ge-TCNQ is examined by ultraviolet photoelectron spectroscopy and UV–vis spectroscopy to elucidate the physical mechanism of photo excitation and fluorescence processes. The emissive Ge-TCNQ crystals are further employed as high-performance optical waveguides with a small optical loss coefficient of 0.078 dB µm⁻¹. This work opens new avenues using 2D metal-organic complex crystals to develop advanced optoelectronic devices.     

Fabrication of Bioinspired Hierarchical Functional Structures by Using Honeycomb Films as Templates

A facile approach to the fabrication of bioinspired hierarchical functional structures by using honeycomb films with controllable micropores as templates is described here. Taking advantage of the breath figure method, honeycomb films with manipulable micropores can be conveniently fabricated by modulating the experimental conditions such as duration of the moist gas flow, temperature, and stretching of the film, which further serve as templates to induce the assembly of subsequently introduced silica nanoparticles for the construction of hierarchical functional structures in a controlled fashion. The resultant hierarchical functional structures not only present a viewing angle independent property, but also exhibit improved hydrophobicity and unique wetting behaviors depending on the morphologies of their building units. It is believed that the work will provide plenty of inspiration for the fabrication of novel high‐performance optical devices for display, as well as functionalized surfaces for waterproof and self‐cleaning.     

Fabrication of Photonic Microbricks via Crack Engineering of Colloidal Crystals

Evaporation‐induced self‐assembly of colloidal particles is one of the most versatile fabrication routes to obtain large‐area colloidal crystals; however, the formation of uncontrolled “drying cracks” due to gradual solvent evaporation represents a significant challenge of this process. While several methods are reported to minimize crack formation during evaporation‐induced colloidal assembly, here an approach is reported to take advantage of the crack formation as a patterning tool to fabricate microscopic photonic structures with controlled sizes and geometries. This is achieved through a mechanistic understanding of the fracture behavior of three different types of opal structures, namely, direct opals (colloidal crystals with no matrix material), compound opals (colloidal crystals with matrix material), and inverse opals (matrix material templated by a sacrificial colloidal crystal). This work explains why, while direct and inverse opals tend to fracture along the expected {111} planes, the compound opals exhibit a different cracking behavior along the nonclose‐packed {110} planes, which is facilitated by the formation of cleavage‐like fracture surfaces. The discovered principles are utilized to fabricate photonic microbricks by programming the crack initiation at specific locations and by guiding propagation along predefined orientations during the self‐assembly process, resulting in photonic microbricks with controlled sizes and geometries.     

Wafer‐Scale Fabrication of Ordered Binary Colloidal Monolayers with Adjustable Stoichiometries

Colloidal monolayers with high order and increased complexity beyond plain hexagonal packing geometries are useful for 2D templating of surface nanostructures and lithographic applications. Here, binary colloidal monolayers featuring a close‐packed monolayer of large spheres (L) with a superlattice of small particles (S) are prepared in a single step using a Langmuir trough. Adjustment of the stoichiometry of the two particle types at the air–water interface leads to a high degree of control over the occupation of the interstitial sites in the close‐packed layer of large spheres by the small colloids. Thus, large areas of binary 2D crystals with LS₂, LS₆, and LS₉ structures are fabricated in a controlled way. The process allows the formation of binary crystals over a wide range of particle size ratios from 0.19 to 0.40. The pH value of the subphase can be used to enhance the crystallization process by changing the contact angle of the particles at the interface. An interfacial polymerization of butyl cyanoacrylate is used to directly image the contact angle of the colloids at the interface. Transfer to solid substrates is achieved by a surface lowering technique. A variety of substrates with arbitrary topographies can thus be decorated with colloidal monolayers. Applied to a lithographic process, such monolayer architectures allow the generation of complex patterns, not accessible with conventional close‐packed monolayers.     

二维三角晶格空气孔光子晶体直线型波导的TE波传输特性研究

本文利用了时域有限差分法(FDTD)研究了TE波在二维三角晶格空气孔光子晶体线缺陷形成的直线型波导中的传输特性,给出了在TE极化下缺陷的结构参量变化与波导的频带宽度、波导中心频率的变化关系,为制作二维三角晶格空气孔线缺陷形成的波导提供了理论依据.