Precise placement of gold nanorods by capillary assembly

Capillary assembly was explored for the precise placement of 25 nm × 70 nm colloidal gold nanorods on prestructured poly(dimethylsiloxane) template surfaces. The concentration of nanorods and cationic surfactant cetyltrimethylammonium bromide (CTAB), the template wettability, and most critically the convective transport of the dispersed nanorods were tuned to study their effect on the resulting assembly yield. It is shown that gold nanorods can be placed into arrayed 120-nm diameter holes, achieving assembly yields as high as 95% when the local concentration of nanorods at the receding contact line is sufficiently high. Regular arrays of gold nanorods have several benefits over randomly deposited nanorod arrangements. Each assembled nanorod resides at a precisely defined location and can easily be found for subsequent characterization or direct utilization in a device. The former is illustrated by collecting scattering spectra from single nanorods and nanorod dimers, followed by subsequent SEM characterization without the need for intricate registration schemes.     

Biofunctional ZnO nanorod arrays grown on flexible substrates

A square pattern of thioctic acid self-assembled ZnO nanorod arrays was grown on a large 4-in. thermoplastic polyurethane (TPU) flexible substrate via an in situ soluthermal process at low temperature (348 K). With the addition of dimercaptosuccinic acid (DMSA), the surface chemistry forms a disordered ZnO phase, and the morphology of the ZnO-DMSA nanorods changes with various DMSA addition times. As evidenced by the Zn2p3/2, C1s, O1s, S2p, and N-1s scans of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), DMSA and proteins were conjugated on the single crystalline ZnO nanorods. The photoluminescence (PL) spectra indicated that the optical properties of ZnO nanorod arrays were changed while the DMSA was inserted, and proteins were conjugated. Furthermore, a control test found that the ZnO nanorods show a significant improvement in sensitive characterization over the ZnO film. As another proteins (e.g., human serum albumin, HSA) were bound onto the ZnO-bovine serum albumin (BSA) nanorod arrays, an enhanced ultraviolet emission intensity was detected. On the basis of these results, one might be expected to conjugate specific biomolecules on the biofunctional ZnO nanorod arrays to detect the complementary biomolecules by PL detecting.     

Plasmon coupling in nanorod assemblies: optical absorption, discrete dipole approximation simulation, and exciton-coupling model

The shape anisotropy of nanorods gives rise to two distinct orientational modes by which nanorods can be assembled, i.e., end-to-end and side-by-side, analogous to the well-known H and J aggregation in organic chromophores. Optical absorption spectra of gold nanorods have earlier been observed to show a red-shift of the longitudinal plasmon band for the end-to-end linkage of nanorods, resulting from the plasmon coupling between neighboring nanoparticles, similar to the assembly of gold nanospheres. We observe, however, that side-by-side linkage of nanorods in solution shows a blue-shift of the longitudinal plasmon band and a red-shift of the transverse plasmon band. Optical spectra calculated using the discrete dipole approximation method were used to simulate plasmon coupling in assembled nanorod dimers. The longitudinal plasmon band is found to shift to lower energies for end-to-end assembly, but a shift to higher energies is found for the side-by-side orientation, in agreement with the optical absorption experiments. The strength of plasmon coupling was seen to increase with decreasing internanorod distance and an increase in the number of interacting nanorods. For both side-by-side and end-to-end assemblies, the strength of the longitudinal plasmon coupling increases with increasing nanorod aspect ratio as a result of the increasing dipole moment of the longitudinal plasmon. For both the side-by-side and end-to-end orientation, the simulation of a dimer of nanorods having dissimilar aspect ratios showed a longitudinal plasmon resonance with both a blue-shifted and a red-shifted component, as a result of symmetry breaking. A similar result is observed for a pair of similar aspect ratio nanorods assembled in a nonparallel orientation. The internanorod plasmon coupling scheme concluded from the experimental results and simulations is found to be qualitatively consistent with the molecular exciton coupling theory, which has been used to describe the optical spectra of H and J aggregates of organic molecules. The coupled nanorod plasmons are also suggested to be electromagnetic analogues of molecular orbitals. Investigation of the plasmon coupling in assembled nanorods is important for the characterization of optical excitations and plasmon propagation in these nanostructures. The surface plasmon resonance shift resulting from nanorod assembly also offers a promising alternative for analyte-sensing assays.     

Biotin-streptavidin-induced aggregation of gold nanorods: tuning rod-rod orientation

We report herein biotin-streptavidin-mediated aggregation studies of long gold nanorods. We have previously demonstrated end-to-end linkages of gold nanorods driven by the biotin-streptavidin interaction (Caswell et al. J. Am. Chem. Soc. 2003, 125, 13914). In that report, the specific binding of biotin disulfide to the gold nanorod edges was achieved due to the preferred binding of thiol molecules to the Au[111] surface (gold nanorod ends) as opposed to the gold nanorod side faces. This led to the end-end linkage of gold nanorods upon subsequent addition of streptavidin. In this report we demonstrate a simple procedure to biotinylate the entire gold nanorod surface and subsequently form a 3-D assembly by addition of streptavidin. Gold nanorods were synthesized by the three-step seeding protocol documented in our previous articles. The surface of gold nanorods was further modified by a layer of a weak polyelectrolyte, poly(acrylic acid), PAA. A biotin molecule which has an amine group at one end (biotin-PEO-amine) was anchored to the carboxylic acid group of the polyelectrolyte using the well-known carbodiimide chemistry. This process biotinylates the entire gold nanorod surface. Addition of streptavidin further leads to aggregation of gold nanorods. A closer look at the aggregates reveals a preferential side-to-side assembly of gold nanorods. The gold nanorods were characterized at each stage by UV-vis spectroscopy, light scattering, and transmission electron microscopy (TEM) measurements.     

CdSe and CdSe/CdS nanorod solids

We demonstrate the self-organization of CdSe nanorods into nematic, smectic, and crystalline solids. Layered colloidal crystals of CdSe nanorods grow by slow destabilization of a nanocrystal solution upon allowing the diffusion of a nonsolvent into the colloidal solution of nanocrystals. The colloidal crystals of nanorods show characteristic birefringence, which we assign to specific spherulite-like texture of each nanorod assembly. To demonstrate the general character of nanorod self-assembly technique, CdSe/CdS heterostructure nanorods were organized into highly luminescent superlattices.     

Surface-functionalized CdSe nanorods for assembly in diblock copolymer templates

Poly(ethylene oxide)-covered CdSe nanorods were prepared and assembled in diblock copolymer templates by floating the block copolymer templates onto aqueous nanorod solutions. The assembly was enabled by consideration of the surface ligand coverage of the nanorods. Alkane-covered CdSe nanorods prepared by state-of-the-art techniques are not compatible with this assembly process. However, poly(ethylene oxide) (PEO)-functionalized CdSe nanorods were successfully used to assemble the nanorods into the channels and pores of diblock copolymer templates. Other water-dispersible CdSe nanorods, such as those covered with 11-mercaptoundecanoic acid (MUA), did not give the desired assemblies. These results are understood by considering the surface energies of the PEO-covered CdSe nanorods in this interfacial assembly process.     

Programmable Supra‐Assembly of a DNA Surface Adapter for Tunable Chiral Directional Self‐Assembly of Gold Nanorods

An important challenge in molecular assembly and hierarchical molecular engineering is to control and program the directional self‐assembly into chiral structures. Here, we present a versatile DNA surface adapter that can programmably self‐assemble into various chiral supramolecular architectures, thereby regulating the chiral directional “bonding” of gold nanorods decorated by the surface adapter. Distinct optical chirality relevant to the ensemble conformation is demonstrated from the assembled novel stair‐like and coil‐like gold nanorod chiral metastructures, which is strongly affected by the spatial arrangement of neighboring nanorod pair. Our strategy provides new avenues for fabrication of tunable optical metamaterials by manipulating the directional self‐assembly of nanoparticles using programmable surface adapters.     

Ultra narrow PbS nanorods with intense fluorescence

We report on the narrowest "free" quantum rods of PbS with 1.7 nm diameter produced in a single step under bench-top reaction conditions. The nanorods exhibit molecule-like discrete narrow optical behavior with high fluorescence quantum yield. We propose a new macroscopic vortex assembly formation by simple spin casting route. Interestingly, the pattern generates fluorescence along its line from the nanorod domains. The ultra narrow nanorods with strong discrete fluorescence and robust stability could be useful in biological labeling, fluorescence resonance energy transfer, and optoelectronics applications, as well as to verify the theories in the very strong confinement regime.     

电沉积种子层化学控制生长氧化锌纳米棒和纳米管

采用水溶液法在电沉积的ZnO种子层上制备了高度取向的ZnO纳米棒阵列,并通过碱溶液化学腐蚀法获得了ZnO纳米管。对ZnO纳米棒和纳米管的溶液生长和腐蚀过程进行了分析。结果表明,种子层的结构和性能对ZnO纳米棒有着重要的影响,在-700 mV电位下沉积的种子层薄膜均匀性好,生长的纳米棒密度大、与基底垂直性好;碱溶液对纳米棒的腐蚀具有选择性,通过控制腐蚀液的浓度和时间,可获得中空的ZnO纳米管。     

Interfacial assembly of a series of cinnamoyl-containing bolaamphiphiles: spacer-controlled packing, photochemistry, and odd-even effect

A series of bolaamphiphiles with 4-hydroxycinnamoyl head groups and different length of the alkyl spacers (n = 6-12) were designed to investigate their photochemistry in the organized films obtained from the air/water interface. It has been found that both the length and odd-even number of the spacers can finely tune the molecular packing as well as the photochemistry. When the spacer length was changed from 6 to 12 methylene units, the assemblies changed from J aggregate to H aggregate. The molecules with even-numbered polymethylene spacer tend to form three-dimensional nanorod structure at the air/water interface. For the assembly of derivatives with odd-numbered spacers, diverse morphologies such as nanospirals and nanofibers were observed depending on the chain length and the surface pressures. The different packing of bolaamphiphiles could subsequently affect the photochemistry of the cinnamoyl groups in the organized films. The spacer effect in the assembly can be understood from the cooperation between H-bond of the phenolic hydroxyl and the amide groups, π-π stacking as well as the hydrophobic interactions of the alkyl spacer. A packing model was proposed to explain the phenomenon.     

Spectrally-resolved atomic-scale length variations of gold nanorods

Functionality of gold nanorod structures as ultra-sensitive optical rulers is demonstrated. Arrays of gold nanorods were fabricated by electron beam lithography and lift-off techniques with high accuracy and uniformity. Their longitudinal plasmon scattering spectra were found to exhibit extreme sensitivity to the length of the nanorods. This phenomenon enables optical detection of the nanorod length variations comparable to the thickness of a few atomic layers of gold.     

Field gradients can control the alignment of nanorods

This work is motivated by the unexpected experimental observation that field gradients can control the alignment of nonmagnetic nanorods immersed inside magnetic fluids. In the presence of local field gradients, nanorods were observed to align perpendicular to the external field at low field strengths, but parallel to the external field at high field strengths. The switching behavior results from the competition between a preference to align with the external field (orientational potential energy) and preference to move into regions of minimum magnetic field (positional potential energy). A theoretical model is developed to explain this experimental behavior by investigating the statistics of nanorod alignment as a function of both the external uniform magnetic field strength and the local magnetic field variation above a periodic array of micromagnets. Computational phase diagrams are developed which indicate that the relative population of nanorods in parallel and perpendicular states can be adjusted through several control parameters. However, an energy barrier to rotation was discovered to influence the rate kinetics and restrict the utility of this assembly technique to nanorods which are slightly shorter than the micromagnet length. Experimental results concerning the orientation of nanorods inside magnetic fluid are also presented and shown to be in strong agreement with the theoretical work.     

锂离子电池用α-Fe2O3-Ag复合纳米棒负极材料的制备及储锂性能

采用FeOOH纳米棒为前驱体,通过层层自组装法及随后的热处理过程制备出α-Fe2O3-Ag复合纳米棒.采用透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)和电化学性能测试对样品的形貌、结构及电化学性能进行了表征.结果表明,Ag纳米颗粒均匀地分布在α-Fe2O3纳米棒的表面.作为锂离子电池负极材料,α-Fe2O3-Ag复合纳米棒表现出了较好的循环性能和较高的比容量.180个循环后,其比容量高达549.8 mA.h/g.     

Electrodeposition and characterization of assembly of Sn on Cu nanorods for Li-ion microbattery application

Assembly of Sn on Cu Nanorods as anode for Li-ion microbatteries was prepared by a two-step electrodeposition design. Firstly, Cu nanorods arrays were grown on copper substrate by anodic aluminum oxide template-assisted growth method. Then, Sn was deposited onto Cu nanorods arrays by galvanostatic deposition. X-ray diffraction and scanning electron microscopy measurements reveal that Cu nanorod arrays are covered with Sn. Electrochemical performances of prepared electrodes were evaluated by charge/discharge cycle measurement. The assembly of Sn on Cu nanorods electrode exhibited highly reversible specific capacity and superior capacity retention resulting from the three-dimensionally nano-architectured design, which exhibits a large surface area, shortened Li-ion diffusion distance, Cu?CSn alloying, and can accommodate the volume expansion of Sn during cycling. Deposition time is an important parameter for fabricating the assembly of Sn on Cu nanorods electrode with suitable structure and morphology.     

Electrodeposition and characterization of assembly of Sn on Cu nanorods for Li-ion microbattery application

Assembly of Sn on Cu Nanorods as anode for Li-ion microbatteries was prepared by a two-step electrodeposition design. Firstly, Cu nanorods arrays were grown on copper substrate by anodic aluminum oxide template-assisted growth method. Then, Sn was deposited onto Cu nanorods arrays by galvanostatic deposition. X-ray diffraction and scanning electron microscopy measurements reveal that Cu nanorod arrays are covered with Sn. Electrochemical performances of prepared electrodes were evaluated by charge/discharge cycle measurement. The assembly of Sn on Cu nanorods electrode exhibited highly reversible specific capacity and superior capacity retention resulting from the three-dimensionally nano-architectured design, which exhibits a large surface area, shortened Li-ion diffusion distance, Cu–Sn alloying, and can accommodate the volume expansion of Sn during cycling. Deposition time is an important parameter for fabricating the assembly of Sn on Cu nanorods electrode with suitable structure and morphology.

     

Synthesis of ZnO nanorods and their application in quantum dot sensitized solar cells

ZnO nanorod thin films of different thicknesses and CdS quantum dots have been prepared by chemical method. X-ray diffraction pattern reveals that the CdS quantum dot and ZnO nanorods are of hexagonal structure. Field emission scanning electron microscope images show that the diameter of hexagonal shaped ZnO nanorods ranges from 110 to 200 nm and the length of the nanorod vary from 1.3 to 4.7 μm. CdS quantum dots with average size of 4 nm have been deposited onto ZnO nanorod surface using successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with ZnO nanorod has been used as photo-electrode in quantum dot sensitized solar cells. The efficiency of the fabricated CdS quantum dot-sensitized ZnO nanorod-based solar cell is 1.10 % and is the best efficiency reported so far for this type of solar cells.     

金纳米棒组装体表面等离子体共振耦合效应的FDTD模拟

贵金属纳米结构的光学性质与其尺寸、形貌、介质环境等因素的相关性是基础研究领域的重要内容.本文利用时域有限差分(FDTD)方法,计算了不同构型二聚体和多聚体的表面等离子体共振(SPR)特性.研究了金纳米棒结构和组装方式对SPR耦合效应的影响,模拟结果与实验规律比较吻合.金纳米棒二聚体的光吸收结果表明:对于肩并肩(S-S)的组装体,随着间隙的减小,金纳米棒的横向SPR(SPRT)峰有较小的红移,而纵向SPR(SPRL)峰显著蓝移.对于端对端(E-E)的组装体,随着组装体间隙的减小,金纳米棒的SPRT峰无明显移动,而SPRL峰显著红移,并在近红外较长波段范围内出现新的共振峰,其强度随着间隙的减小而增强;结合弹簧振子模型和纳米颗粒在外电场作用下的极化,对组装体共振吸收峰的移动和新的耦合共振峰的出现提出了初步的解释.     

Silica-coated Au/Ag nanorods with tunable surface plasmon bands for nanoplasmonics with single particles

We present the synthesis and analysis of silica-coated Au/Ag bimetallic nanorods with controlled surface plasmon bands. Depending on the thickness of Ag shell deposited on the Au nanorod surface, there is a blue-shift on the longitudinal surface plasmon band of Au nanorods, which can be expressed by an approximate formula derived from the absorption profile of light in Ag films using finite difference time domain simulations. The subsequent coating of silica shell not only enhances the stability of the Au/Ag bimetallic nanorods but also provides a mesoporous host for optically active species. Minute red-shifts of the longitudinal resonance mode, induced by stepwise increased silica shell volumes, are shown. Application as carrier for fluorescent rhodamine B molecules is demonstrated by photoluminescence analysis. On the single-particle level, dark field microscopy of Au/Ag-silica nanorods was finally employed. This introduces a route towards revealing the relation between structure, shape, and optical (plasmonic) properties of complex composite metal particles as well as fabrication strategies for nanoassemblies of tailored structures in the field of nanoplasmonics.     

Electrochemical formation of crooked gold nanorods and gold networked structures by the additive organic solvent

Crooked gold nanorods (CGNRs) and gold network structures are fabricated using a simple electrochemical approach. The growth solution is prepared by surfactant solution as micelle templates with isopropanol (IPA) solvent. The shape of crooked nanorods and networks structure depend on the amount of added IPA solvent. To investigate the influence of isopropanol solvent on the CGNRs, the amount of IPA was varied in the range from 0.05 to 0.2 mL. It was found that the aspect ratios (gamma) of CGNRs were in the range from 1.06 to 1.46, and the UV-vis absorption measurement revealed a pronounced red-shift of the surface plasmon resonance (SPR) band from 532 to 560 nm. High-resolution transmission electron microscopy (HRTEM) showed that the formation of crooked nanorod structure was induced by aggregation of many small gold nuclei between the several large gold nanoparticles during growth, causing the small gold nuclei to link the gold nanoparticles. The CGNRs have a polycrystalline structure via the analysis from selected-area electron diffraction (SAED).     

DNA-Mediated Self-Assembly and Metallization of Semiconductor Nanorods for the Fabrication of Nanoelectronic Interfaces

DNA nanostructures provide a powerful platform for the programmable assembly of nanomaterials. Here, this approach is extended to semiconductor nanorods that possess interesting electrical properties and could be utilized for the bottom-up fabrication of nanoelectronic building blocks. The assembly scheme is based on an efficient DNA functionalization of the nanorods. A complete coverage of the rod surface with DNA ensures a high colloidal stability while maintaining the rod size and shape. It furthermore supports the assembly of the nanorods at defined docking positions of a DNA origami platform with binding efficiencies of up to 90 % as well as the formation of nanorod dimers with defined relative orientations. By incorporating orthogonal binding sites for gold nanoparticles, defined metal-semiconductor heterostructures can be fabricated. Subsequent application of a seeded growth procedure onto the gold nanoparticles (AuNPs) allows for to establish a direct metal-semiconductor interface as a crucial basis for the integration of semiconductors in self-assembled nanoelectronic devices.