平面复合金属微纳结构的圆二色性研究

圆二色性效应在圆偏振器、光调制器及光电器件等方面具有广泛的应用.为提高平面金属微纳结构的圆二色性,本文设计了由无限长纳米线和G形微纳结构组成的平面复合金属微纳结构,并应用有限元方法研究了该阵列微纳结构的圆二色性特性.数值计算结果显示,在圆偏振光的激发下,G形微纳结构和平面复合金属微纳结构均出现了电偶极子、电四极子和电八极子等共振模式.当G形微纳结构与无限长纳米线连接时,各共振波长均发生红移,并且无限长纳米线增加了不同圆偏振光激发下的局域表面等离激元共振强度,从而使得平面复合微纳结构的圆二色性信号明显增强.此外,还研究了平面复合微纳结构阵列的几何参数对其圆二色性特性的影响.这些结果为提高平面手性微纳结构的圆二色性信号强度提供一定的指导思路和方法.     

双层开口环的圆二色性数值研究

基于琼斯矩阵的推导提出一种金属手性纳米结构-双层开口环阵列结构，其开口方向扭转一定角度以破坏对称性，并应用有限元方法研究圆二色性（CD）特性.研究表明：在左旋圆偏振光与右旋圆偏振光的激发下，该结构表现出巨大差异使得CD产生，其CD值达到0.34.结构的电流分布表明，在短波长处，上下层圆环的等效偶极子耦合可形成反键模式，在长波长处，上下层圆环的等效偶极子耦合可形成成键模式，研究结构参数对CD的影响.理解圆二色的物理机制，并提供一种设计手性结构的方法.     

蜂窝状椭圆孔洞吸收器圆二色性研究

手性结构的圆二色吸收已经被广泛应用于分析化学、工业制药、生物监测等领域.然而天然手性结构与光的相互作用很弱.等离激元光学纳米结构能大幅度增强光-物作用的能力.在制备可见-近红外手性等离激元超吸收结构的过程中,通常存在吸收率与样品制备面积的折中,即可大面积制备结构的圆二色性较小.为提高可大面积制备手性等离激元吸收器的圆二色性,本文设计了蜂窝状排列的椭圆孔洞吸收器,并研究了其吸收、圆二色性和光学g因子.通过合理的设计,数值计算结果显示,在手性光的激发下其圆二色值可达约0.8,对应光学g因子可达约1.7.巨大的圆二色性来源于倾斜椭圆结构对结构对称性的破坏,且倾斜角对圆二色性的影响很大.本结构可利用纳米球光刻法制备,对制备大规模手性等离激元吸收器具有一定的指导意义.     

TR I Z剪裁思想在科学研究中的应用

剪裁是现代TR I Z理论体系里的一个非常重要的分析问题工具. 在技术领域, 利用剪裁产生新问题, 解 决新问题以解决项目的初始问题. 在介绍剪裁工具基本思想的基础上, 综述了其在圆二色性研究中的具体体现. 将 使读者切实感受到剪裁在科学研究中的存在, 自觉应用TR I Z剪裁思想将有助于提高创新速度     

局域表面等离激元

局域表面等离激元使得贵金属纳米颗粒具有丰富的光学性质,其应用涵盖能源、生物医学、安全、信息、超材料等诸多领域。文章简要介绍局域表面等离激元的基本性质、贵金属纳米结构中的局域表面等离激元共振耦合以及具有局域表面等离激元特性的贵金属纳米结构的一些重要应用。     

局域表面等离激元

局域表面等离激元使得贵金属纳米颗粒具有丰富的光学性质,其应用涵盖能源、生物医学、安全、信息、超材料等诸多领域。文章简要介绍局域表面等离激元的基本性质、贵金属纳米结构中的局域表面等离激元共振耦合以及具有局域表面等离激元特性的贵金属纳米结构的一些重要应用。     

表面等离激元的聚焦与波导增强

近年来,表面等离激元学(plasmonics)已经形成一个新的学科热点.电子在金属与介质界面的集体振荡行为形成一种元激发——表面等离激元（surface plasomon polariton,SPP）.由于其具有特殊的耦合与传播性质,与SPP相关的器件设计与应用成为目前纳米光子学领域的国际前沿研究方向.文章介绍了利用微纳加工技术制备的SPP纳米结构,以及利用近场光学表征手段对SPP聚焦、波导、共振增强现象研究的进展.     

表面等离激元的聚焦与波导增强

近年来,表面等离激元学（plasmonics）已经形成一个新的学科热点.电子在金属与介质界面的集体振荡行为形成一种元激发——表面等离激元（surface plasomon polariton,SPP）.由于其具有特殊的耦合与传播性质,与SPP相关的器件设计与应用成为目前纳米光子学领域的国际前沿研究方向.文章介绍了利用微...     

十字结构银纳米线的表面等离极化激元分束特性

金属纳米线波导可以将光局域在亚波长尺度内传播, 在纳米光子集成回路方面有着重要的作用. 本文应用有限元方法, 研究了十字结构银纳米线的表面等离极化激元分束特性. 结果表明, 不同模式的表面等离极化激元在十字结构三个分支的输出依赖于端面的几何结构参数. 此外, 研究还发现由于不同模式表面等离极化激元叠加, 在十字结构的分支上出现了周期性电场分布.     

金纳米棒核/贵金属壳杂化纳米结构的可控制备和性质调控

贵金属纳米颗粒由于其独特的光学及催化性能引起了人们的广泛关注,而这些性能与纳米颗粒的尺寸、形貌、结构组成等密切相关.目前如何有意识地控制晶体生长过程,以得到人们需要的纳米结构和组成,仍具有相当大的挑战性.文章重点介绍了利用具有特定形貌和晶面组成的金纳米棒(Au nanorods)作为种子,借助形成核/壳结构,诱导了Ag, Pd, Pt棒状纳米结构的形成,并实现了对杂化纳米结构光学和催化性能的调控,进一步扩展了贵金属纳米结构的应用范围.作者的研究结果表明,形成杂化纳米结构是性能调控的一种有效方式.     

Effect of size and morphology of Au nanostructures on boosting performance of organic photovoltaic devices: Plasmonic and non-plasmonic effects

We fabricated organic photovoltaic (OPV) devices containing various Au nanostructures mixed with hole-collecting buffer layer. The presence of the Au nanostructures results in enhancement of the external quantum efficiencies (EQE) at dissimilar wavelengths of visible light, which can be attributed to the modulated plasmonic absorption frequency of the Au nanostructures. In addition to this plasmonic effect induced by visible light absorption, an increase in the EQE was also found upon UV excitation, which can be attributed to scattering effects induced by Au particles. The optical response pattern of organic photovoltaic devices can be modulated in a wide range of visible and UV wavelengths, by controlling sizes and shapes of the Au nanostructures.     

Fabrication, characterization and some applications of graded chiral zigzag shaped nano-sculptured silver thin films

Graded chiral zig-zag shaped nano-sculptured silver thin films (GCZSSTF) were produced in two stages using oblique deposition technique together with rotation of substrate about its surface normal while a shadowing block was also fixed at the center of the substrate holder. Chrystallographic and morphological structure of these films were obtained using X-ray diffraction (XRD) and atomic force microscopy (AFM). Spectrophotometry was used to obtain their optical behavior while their application in both hydrophobicity and gas sensing was also investigated. XRD results showed a dominant (1 1 1) orientation growth on the zig arm of the structure while by addition of the second arm (zag) the crystallographical growth orientation changed to (2 2 0).The anisotropic nano-structure of these films was also distinguished through (1 − R) spectra. A common peak at about 350 nm related to the TM mode of plasmon resonances and a broad shoulder at about 420 nm for the s-polarized light and at 620 nm for the p-polarized light corresponding to the LM mode of plasmon resonances are observed. These peaks are directly related to the nano-columns topography. The film system used here proved to act as a physical method for producing layer-by-layer structure for obtaining enhanced hydrophobic surfaces rather than the usual chemical methods reported in the literature. In addition, the GCZSSTF also acted as good as reported results for nano-tubes when applied as cathode in the field ionization gas sensing setup.     

Morphology of periodic nanostructures for photonic crystals grown by glancing angle deposition

An enhancement of the glancing angle deposition (GLAD) technique called PhiSweep was used to grow slanted columns of silicon and titanium dioxide onto patterned substrates. The PhiSweep technique involves periodically rotating the substrate back and forth during the deposition process, which reduces column fanning caused by anisotropy in the shadowing conditions. The patterned substrates consisted of a tetragonal array of hillocks with 100, 200, and 300 nm periodicities and were fabricated using electron beam lithography. The PhiSweep method alters the tilt angle of the slanted columns compared with those grown using traditional GLAD. We present a derivation of the tilt angle of the slanted columns as a function of the parameters of the PhiSweep technique. The tilt angles of the silicon and titanium dioxide films were measured and agree with the predicted values. The films fabricated using the PhiSweep method are compared with similar films grown using traditional GLAD. The PhiSweep technique produced films with substantially less column fanning than those grown by traditional GLAD. This reduction in column fanning has extended the size range over which periodic GLAD structures, such as square spiral photonic crystals, can be grown.     

Plasmonic waveguiding properties of the gap plasmon mode with a dielectric substrate

The plasmonic waveguiding properties of the gap plasmon mode between two adjacent silver nanowires with a substrate are theoretically investigated using finite element method. The results show that there is a critical gap distance between two silver nanowires which approximately equals to the radius of the nanowires. When the gap distance is less than the critical distance, the influence of the substrate on the gap plasmon mode can be neglected. The gap plasmon mode has a combination of high confinement and long propagation length. Moreover, the plasmonic waveguiding properties of the gap plasmon mode are not sensitive to the wire-to-substrate distance between silver nanowires and the substrate.     

Superhydrophobic hierarchical surfaces fabricated by anodizing of oblique angle deposited Al-Nb alloy columnar films

A combined process of oblique angle magnetron sputtering and anodizing has been developed to tailor superhydrophobic surfaces with hierarchical morphology. Isolated submicron columns of single-phase Al-Nb alloys are deposited by magnetron sputtering at several oblique deposition angles on a scalloped substrate surface, with the gaps between columns increasing with an increase in the deposition angle from 70° to 110°. Then, the columnar films have been anodized in hot phosphate-glycerol electrolyte to form a nanoporous anodic oxide layer on each column. Such surfaces with submicron-/nano-porous structure have been coated with a fluoroalkyl phosphate layer to reduce the surface energy. The porous surface before coating is superhydrophilic with a contact angle for water is less than 10°, while after coating the contact angles are larger than 150°, being superhydrophobic. The beneficial effect of dual-scale porosity to enhance the water repellency is found from the comparison of the contact angles of the submicron columnar films with and without nanoporous oxide layers. The larger submicron gaps between columns are also preferable to increase the water repellency.     

数值模拟二维间隙表面等离子波导传输特性

利用表面等离子激元的新颖特性,设计了二维间隙表面等离子波导.以这种结构为基础通过变形和组合形成90°直角弯曲波导、T型光功率分配器和光开光,采用时域有限差分法研究了它们的传输特性.结果表明:不同于介质光波导的弯曲损耗来自于辐射泄漏,90°直角弯曲间隙表面等离子波导的能量损耗主要来自于金属中的欧姆热损耗.在间隙达到40 nm以上后,当直行段的长度适当时,弯曲段的透射率较相同长度的直波导的透射率要大.T型光功率分配器在两输出波导的间隙宽度比达到0.6及以上时,不同于传统介质波导的分光原则,能量主要沿等效折射率较小的输出臂流出.当两输入光的相位反相时,T型光开关处于输出截止的状态,当两输入光的相位同相时,T型光开关处于输出导通的状态.所有波导间隙均小于衍射极限,实现了超衍射极限传播,可用于未来了超大规模集成光路中.     

Improved electrical properties of silicon-incorporated anodic niobium oxide formed on porous Nb-Si substrate

In the present study, porous Nb-Si alloy films with isolated nano-column morphology have been successfully developed by oblique angle magnetron sputtering on to aluminum substrate with concave cell structure. The deposited films are amorphous with the 15 at% silicon supersaturated into niobium. The porous Nb-15 at% Si films, as well as niobium films with similar morphology, are anodized at several voltages up to 50 V in 0.1 mol dm⁻³ ammonium pentaborate electrolyte. Due to the presence of sufficient gaps between neighboring columns, the gaps are not filled with anodic oxide, despite the large Pilling-Bedworth ratio (for instance, 2.6 for Nb/Nb₂O₅) and hence, a linear correlation between the reciprocal of capacitance and formation voltage is obtained for the Nb-15 at% Si. From the comparison with the anodic films formed on porous niobium films, it has been found that silicon addition improves the thermal stability of anodic niobium oxide; the change in capacitance and increase in leakage current become small for the Nb-Si. The findings indicate the potential of oblique angle deposition to tailor porous non-equilibrium niobium alloy films for high performance niobium-base capacitor.     

Chirality of molecular nanostructures on surfaces via molecular assembly and reaction: manifestation and control

The formation of chiral nanostructures via molecular assembly and reaction on solid surfaces is a ubiquitous surface process due to the symmetry-breaking at 2D surface. Studying chirality during the adsorption, assembly, and reaction of molecules on 2D solid surfaces at molecular level not only sheds deep insights into the enantioselective heterogeneous catalysis, chiral recognition, origin and evolution of chirality, and many important physical chemistry processes but also provides an important strategy to create chiral nanostructures. Here, we give a survey of recent advances in chiral expression and control in molecular assemblies and reactions on surfaces. We firstly give a brief introduction to the general concepts of chiral molecular nanostructures on surfaces. And then we focus on the induction and control of chirality expressed in molecular assemblies. The recent developments in the control strategies such as chiral co-adsorber, chiral auxiliary, chiral solvent, chiral templated surfaces, as well as the underlying mechanism to achieve the chiral induction and amplification, are reviewed. After that, we review the studies of chirality expressed in on-surface synthesis which has been proved to be a promising strategy to fabricate covalently bonded low-dimensional nanostructures and materials. In this respect, we introduce the chiral expression in the intramolecular and intermolecular coupling reactions on surfaces. In addition, we survey the methods to steer the stereoselectivity of on-surface reactions including the design of precursor structure, steric hindrance effect, substrate, kinetic parameters et al. Finally, the future outlook in this field is discussed.     

金纳米空心半球壳膜的可调谐光学性质研究

以单层聚苯乙烯微球阵列为模板,通过控制其表面金膜蒸镀时间,制备了具有不同厚度的空心半球壳结构的金纳米膜.利用扫描电子显微镜和自制光谱仪分别测量了金膜表面形貌和其透射光谱,并分析了金膜形貌与其光学性质间的关系,同时以4-巯基苯胺为探针分子测定了金膜的表面增强喇曼散射效应.结果表明,该金纳米膜的表面等离子体共振波长随膜厚度增大而发生红移,在可见与近红外波段较宽范围内可调谐,并且,当金膜共振波长与入射激发光波长较近时,探针分子可产生出较强的表面增强喇曼信号.同时,对该现象的产生机制也进行了理论解释.     

Dielectric properties of anodic films on sputter-deposited Ti-Si porous columnar films

For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti-7 at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti-7 at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are ∼500 nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100-200 nm. When the porous Ti-7 at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to ∼35 V, while it is limited to less than 6 V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti-7 at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti-7 at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film.