Colloidal Gold Nanorings and Their Plasmon Coupling with Gold Nanospheres

Gold nanorings are attractive as plasmonic metal nanocrystals because they have a hollow inner cavity. Their enhanced electric field inside the ring cavity is accessible, which is highly desirable for assembling with other optical components and studying their plasmon‐coupling behaviors. However, the lack of robust methods for synthesizing size‐controllable and uniform Au nanorings severely impedes the study of their attractive plasmonic properties and plasmon‐driven applications. Herein, an improved wet‐chemistry method is reported for the synthesis of monodisperse colloidal Au nanorings. Using circular Au nanodisks with different thicknesses and diameters as templates, Au nanorings are synthesized with thicknesses varied from ≈30 to ≈50 nm and cavity sizes varied from ≈90 to ≈40 nm. The produced Au nanorings are assembled with colloidal Au nanospheres to yield Au nanoring–nanosphere heterodimers in sphere‐in‐ring and sphere‐on‐ring configurations on substrates. The sphere‐in‐ring heterodimers exhibit the interesting feature of plasmonic Fano resonance upon the excitation of the dark quadrupolar plasmon mode of the Au nanorings. The open cavity in a nanoring holds a great promise for studying plasmon‐coupled systems, which will facilitate the construction of advanced metamaterials and high‐performance Fano‐based devices.     

Effects of lateral asymmetry on electronic structure of strained semiconductor nanorings in a magnetic field

The influence of lateral asymmetry on the electronic structure and optical transitions in elliptical strained InAs nanorings is analyzed in the presence of a perpendicular magnetic field. Two-dimensional rings are assumed to have elliptical inner and outer boundaries oriented in mutually orthogonal directions. The influence of the eccentricity of the ring on the energy levels is analyzed. For large eccentricity of the ring, we do not find any Aharonov-Bohm effect, in contrast to circular rings. Rather, the single-particle states of the electrons and the holes are localized as in two laterally coupled quantum dots formed in the lobes of the nanoring. Our work indicates that the control of shape is important for the existence of the Aharonov-Bohm effect in semiconductor nanorings.     

Switching of ± 360° domain wall states in a nanoring by an azimuthal Oersted field

We demonstrate magnetic switching between two 360° domain wall vortex states in cobalt nanorings, which are candidate magnetic states for robust and low power magnetoresistive random access memory (MRAM) devices. These 360° domain wall (DW) or 'twisted onion' states can have clockwise or counterclockwise circulation, the two states for data storage. Reliable switching between the states is necessary for any realistic device. We accomplish this switching by applying a circular Oersted field created by passing current through a metal atomic force microscope tip placed at the center of the ring. After initializing in an onion state, we rotate the DWs to one side of the ring by passing a current through the center, and can switch between the two twisted states by reversing the current, causing the DWs to split and meet again on the opposite side of the ring. A larger current will annihilate the DWs and create a perfect vortex state in the rings.     

Ordered arrays of lead zirconium titanate nanorings

Periodic arrays of nanorings of morphotropic phase boundary lead zirconium titanate (PZT) have been successfully fabricated using a novel self-assembly technique: close-packed monolayers of latex nanospheres were deposited onto Pt-coated silicon substrates, and then plasma cleaned to form ordered arrays of isolated nanospheres, not in contact with each other. Subsequent pulsed laser deposition of PZT, high angle argon ion etching and thermal annealing created the arrays of isolated nanorings, with diameters of ～100?nm and wall thicknesses of ～10?nm. Energy dispersive x-ray analysis confirms that the rings are compositionally morphotropic phase boundary PZT, and high resolution transmission electron microscopy imaging of lattice fringes demonstrates some periodicities consistent with perovskite rather than pyrochlore material. The dimensions of these nanorings, and the expected 'soft' behaviour of the ferroelectric material from which they are made, means that they offer the most likely opportunity to date for observing whether or not vortex arrangements of electrical dipoles, analogous to those seen in ferromagnetic nanostructures, actually exist.     

Structures and Images of Novel Derivatives of Carbon Nanotubes, Fullerenes and Related New Carbon Forms

In the light of the finding that carbon nanotubes get functionalized on reaction with acid and other oxidizing agents, the structures and shapes of nanotube derivatives resulting from possible reaction between functionalized nanotubes, are obtained by an energy minimization procedure and the structures, so obtained, are compared with the observed microscopic images. The shapes of fullerene -like and nanotupe - like structures containing seven - membered rings, in addition to six and five - membered rings, are depicted along with the structures of bent nanotubes containing similar ring systems. Diamond - graphite hybrid structures which constitute an important class of carbon materials are also investigated.     

Magnetoresistance behavior of ferromagnetic nanorings in a ring-wire hybrid configuration

We present a technique for probing the magnetic configurations in ferromagnetic rings electrically without placing the electrical contact leads directly on the nanorings, but on wires attached to the ring structures. The magnetic configurations in pseudo spin valve rectangular and elliptical rings of width in the range from 60 to 300?nm have been systematically mapped using this technique. The giant magnetoresistance (GMR) responses for both the rings exhibit distinct switching fields and features corresponding to identifiable magnetization states in different segments of the nanostructures.     

Controlled synthesis of cadmium carbonate nanowires, nanoribbons, nanorings and sphere like architectures via hydrothermal method

Crystalline nanowires, nanoribbons, nanorings and sphere like architectures of cadmium carbonate have been synthesized with the spontaneous self-assembly of nanocrystals in aqueous solution under hydrothermal condition. The powder X-ray diffraction (PXRD) patterns of these materials exhibit phase pure hexagonal structure. The perfect circular nanorings with radius 375-437 nm, as a new member of nanostructured cadmium carbonate family are being reported for the first time. The width of the cadmium carbonate nanowires/nanoribbons and nanorings, respectively are found to be in the range 11-30 and 26-50 nm as observed by transmission electron microscope (TEM). The effect of temperature and concentration of urea on the cadmium carbonate morphology is discussed. The plausible growth mechanism for the formation of nanorings is also proposed.     

Effects of geometrical and loading parameters on wave propagation in a circular ring

A theoretical investigation into the transient elastic response of a circular ring under radial impact is undertaken. The effects of ring curvature, cross-section geometry and impact duration on the resulting shear force, axial force and bending moment distributions and ring deformation are examined. This extends an earlier effort (Shim, Quah, J. Appl. Mech. 65 (1998) 569–579) which employed classical Timoshenko beam theory, coupled with the method of characteristics, to analyse propagation of flexural waves in rings. The present study shows that curvature and ring cross-sectional geometry do not significantly affect the development of bending moments and shear forces but influence axial forces induced and the deformed shape. It is found that for a given impulse, propagation of generalised forces and the deformation geometry depend on impact duration. Wave speeds relating to different deformation modes are governed primarily by curvature and cross-sectional geometry.     

Optimised inner boundary shapes in circular rings under diametral compression

Using a method developed by the authors, the configuration of the inside boundary of circular rings, subjected to diametral compression, has been optimised, keeping cleared the space enclosed by the original circular inside boundary. The range of diameters studied was 0.33ID/OD0.7. In comparison with circular rings of the same ID/OD, the stress concentrations have been reduced by about 30%, the weight has been reduced by about 10% and coefficients of efficiency of about 0–96 have been attained. The maximum values of compressive and tensile stresses on the edge of the hole, are approximately equal, there are practically no gradients of stress along the edge of the hole, and sharp corners exhibit zero stress. The geometries for each ID/OD design are given in detail.     

Arrays of ultrasmall metal rings

In this paper, we present a simple method to fabricate ultra-high-density hexagonal arrays of ferromagnetic nanorings having 13?nm outer diameter, 5?nm inner diameter and 5 nm thickness. Cobalt magnetic nanorings were fabricated using a self-assembled diblock copolymer template with an angular evaporation of metal followed by an ion-beam etching. Magnetic measurements and theoretical calculations suggest that, at low fields, only the single domain and vortex states are important for rings of this size. The measured magnetization as a function of applied field shows a hysteresis that is consistent. These ultrasmall ferromagnetic rings have potential use in magnetic memory devices due to the simplicity of the preparation coupled with the ultra-high-density and geometry-controlled switching. This fabrication technique can be extended to other materials for applications in optics, sensing and nanoscale research.     

The influence of reinforcement ring width on the buckling response of carbon fibre composite panels with circular cut-outs

This paper investigates the influence of cut-out diameter and the width of the circular reinforcement rings upon the buckling stability of square CFRP panels. The study undertaken at Cranfield University uses MSC/NASTRAN Finite Element Analysis (FEA) extensively for this investigation. The FEA results have been compared with results from practical tests and good agreement was found. Diagrams showing the influence of cut-out diameter and reinforcement ring width on the buckling stability of simply supported CFRP panels are presented. The results are shown for approx. 2 mm-thick ((± 45/0)_s)_s square CFRP panels with 0–50 mm wide reinforcement rings bonded around the central circular cut-outs. The panels are loaded in pure shear or in compression. The results presented can be used to find the optimum reinforcement ring width for square CFRP panels with central circular cut-outs.     

Vortex ring propagation and interactions studies

This paper experimentally investigates the vortex ring propagation and interactions with thin cylindrical and flat surfaces. Dye-based visualization technique is adopted for the interaction studies. Vortex rings are generated from a circular nozzle of 19 mm diameter with the stroke length ratios (length of the fluid slug to nozzle diameter, L_N/D_N) of 1 to 5, and ejection velocities in the range of 0.05 to 0.2 m/s. Vortex interaction studies are carried out with two different bodies; firstly, with the circular cylinders having the diameters of 0.2, 0.6, 1.5 and 2.5 mm, and secondly with a flat solid surface. Results indicate that the trails in the vortex ring start following at L_N/D_N = 4. The influence of the initial velocity is found to be insignificant on the vortex ring diameter, however, found to depend on stroke length ratio. Vortex-cylinder interaction studies indicated that vortex velocity decreases with increase in cylinder diameter after the interaction. Reconnections of vortex rings are observed in lower cylinder diameter cases. In case of vortex ring interaction with the flat surface, stretching of the vortex core is observed leading to a considerable increase in the vortex ring diameter.     

非均匀加筋圆柱薄壳圆截面内振动的径向模态机械阻抗分析

提出圆柱薄壳的圆截面内运动假设,从声学角度将环肋对壳体的作用等效为径向作用力,根据Hamilton原理建立了简支非均匀加筋圆柱壳的振动控制方程,利用驻波形式解对其径向模态机械阻抗进行了研究。分析表明:对于加筋圆柱壳,环肋与圆柱薄壳的径向模态机械阻抗具有串联连接方式,通过调整环肋的几何参数增大环肋自身的径向模态机械阻抗,可以达到壳体减振降噪的目的,并指出了利用环肋的反共振特性进行加筋圆柱壳结构减振的设计方向。     

双曲冷却塔结构特性新认识

通过动力特性分析和等效静风荷载作用下响应分析,并借鉴简单圆环结构和悬臂结构的结构特性,对双曲冷却塔结构特性进行了阐述。研究发现,作为圆截面高耸空间薄壁结构,双曲冷却塔的静动力结构特性同时体现了简单水平圆环结构和子午向悬臂结构的特点:对于低阶模态,其振型是上下弹性支撑水平圆环结构(条带)和左右弹性支撑子午向悬臂结构(条带)振型的耦合,且频率主要受环向刚度控制;风荷载作用下塔筒位移和内力的环向分布与外表面风压分布模式一致,各荷载效应的最值主要受迎风区和侧风区风压影响并受环向风压分布的不均匀性所控制;子午向轴力的环向分布提供了整体抗倾覆弯矩,因此表现出明显的向下积聚现象,这也是悬臂结构顺风向整体倾覆弯矩的体现,并且这种积聚效应与子午线型有关。     

Excitonic Aharonov–Bohm Oscillations in Core–Shell Nanowires

Phase coherence in nanostructures is at the heart of a wide range of quantum effects such as Josephson oscillations between exciton–polariton condensates in microcavities, conductance quantization in 1D ballistic transport, or the optical (excitonic) Aharonov–Bohm effect in semiconductor quantum rings. These effects only occur in structures of the highest perfection. The 2D semiconductor heterostructures required for the observation of Aharonov–Bohm oscillations have proved to be particularly demanding, since interface roughness or alloy fluctuations cause a loss of the spatial phase coherence of excitons, and ultimately induce exciton localization. Experimental work in this field has so far relied on either self‐assembled ring structures with very limited control of shape and dimension or on lithographically defined nanorings that suffer from the detrimental effects of free surfaces. Here, it is demonstrated that nanowires are an ideal platform for studies of the Aharonov–Bohm effect of neutral and charged excitons, as they facilitate the controlled fabrication of nearly ideal quantum rings by combining all‐binary radial heterostructures with axial crystal‐phase quantum structures. Thanks to the atomically flat interfaces and the absence of alloy disorder, excitonic phase coherence is preserved even in rings with circumferences as large as 200 nm.     

环状永磁体表面径向磁通密度分布的模拟计算

利用AutoCAD软件构建四极磁环的三维模型,采用Ansoft Maxwell软件的有限元分析法对各向异性粘结钕铁硼(NdFeB)四极环状磁体表面径向磁通密度分布进行数值模拟。研究了各向异性粘结NdFeB永磁材料的剩磁B_r和矫顽力H_(cb)及环状磁体的高度、厚度和内外径,对环状磁体表面径向磁通密度与磁特性的影响。结果表明,环状磁体表面径向磁通密度与NdFeB材料的矫顽力H_(cb)及磁体的厚度密切相关,而NdFeB材料的剩磁B_r及磁体的高度对其影响较小。     

Unique Tube–Ring Interactions: Complexation of Single‐Walled Carbon Nanotubes with Cycloparaphenyleneacetylenes

Carbon nanotubes (CNTs) interlocked by cyclic compounds through supramolecular interaction are promising rotaxane‐like materials applicable as 2D and 3D networks of nanowires and disease‐specific theranostic agents having multifunctionalities. Supramolecular complexation of CNTs with cyclic compounds in a “ring toss'' manner is a straightforward method to prepare interlocked CNTs; however, to date, this has not been reported on. Here, the “ring toss” method to prepare interlocked CNTs by using π‐conjugated carbon nanorings: [8]‐, [9]‐, and [10]cycloparaphenyleneacetylene (CPPA) is reported. CPPAs efficiently interact with CNTs to form CNT@CPPA complexes, while uncomplexed CPPAs can be recovered without decomposition. CNTs, which tightly fit in the cavities of CPPAs through convex–concave interaction, efficiently afford “tube‐in‐ring”‐type CNT@CPPA complexes. “Tube‐in‐ring”‐type and “ring‐on‐tube”‐type complexation modes are successfully distinguished by spectroscopic, thermogravimetric, and microscopic analyses.     

Graphitic nanorings for super-long lifespan lithium-ion capacitors

Porous graphitic carbon nanorings (PGCNs) are proposed by smart catalytic graphitization of nano-sized graphene quantum dots (GQDs). The as-prepared PGCNs show unique ring-like morphology with diameter around 10 nm, and demonstrate extraordinary mesoporous structure, controllable graphitization degree and highly defective nature. The mechanism from GQDs to PGCNs is proven to be a dissolution-precipitation process, undergoing the procedure of amorphous carbon, intermediate phase, graphitic carbon nanorings and graphitic carbon nanosheets. Further, the relationship between particles size of GQDs precursor and graphitization degree of PGCNs products is revealed. The unique microstructure implies PGCNs a broad prospect for energy storage application. When applied as negative electrode materials in dual-carbon lithium-ion capacitors, high energy density (77.6 Wh·kg⁻¹) and super long lifespan (89.5% retention after 40,000 cycles at 5.0 A·g⁻¹) are obtained. The energy density still maintains at 24.5 Wh·kg⁻¹ even at the power density of 14.1 kW·kg⁻¹, demonstrating excellent rate capability. The distinct microstructure of PGCNs together with the strategy for catalytic conversion from nanocarbon precursors to carbon nanorings opens a new window for carbon materials in electrochemical energy storage.

     

Evolution of composition distribution of Si-capped Ge islands on Si(001)

The evolution of the composition distribution and microstructures of Ge islands on Si(001) during the Si overgrowth was investigated by atomic force microscopy combined with selective wet etching procedures. With increasing Si coverage to 5.4 nm, the uncapped Ge islands were found to change their shapes dramatically from domes to truncated pyramids, nanorings and eventually to the fully buried islands. Different atomic composition profiles in SiGe islands were observed at different Si coverages. Especially, the nanorings were found to have a Ge-rich core with a Si-rich periphery. Based on the experimental results, the Ge redistribution in islands during Si capping is not only correlated with the intermixing between Si capping layer and Ge islands, but also a strain-driven process.     

Polymer-assisted fabrication of gold nanoring arrays

In this paper,we report a new strategy for the fabrication of gold nanoring arrays via colloidal lithography and polymer-assisted self-assembly of gold nanoparticles (Au NPs).First,multi-segmented polymer nanorod arrays were fabricated via colloidal lithography.They were then used as templates for Au NP adsorption,which resulted in nanoparticles on the poly(4-vinyl pyridine) (P4VP) segments.Continuous gold nanorings were formed after electroless deposition of gold.The diameter,quantity,and spacing of the gold nanorings could be tuned.Three dimensional coaxial gold nanorings with varying diameters could be fabricated on a polymer nanorod by modifying the etch parameters.The nanorings exhibited optical plasmonic resonances at theoretically predicted wavelengths.In addition,the polymer-assisted gold nanorings were released from the substrate to generate a high yield of free-standing nanorings.This simple,versatile method was also used to prepare nanorings from other metals such as palladium.