Quantitation of metal content in the silver-assisted growth of gold nanorods

The seed-mediated approach to making gold nanorods in aqueous surfactant solutions has become tremendously popular in recent years. Unlike the use of strong chemical reductants to make spherical gold nanoparticles, the growth of gold nanorods requires weak reducing conditions, leading to an unknown degree of gold reduction. The metal content of gold nanorods, made in high yield in the presence of silver ion, is determined by inductively coupled plasma atomic emission spectroscopy. Through the use of the known gold concentration in nanorods, molar extinction coefficients are calculated for nanorods of varying aspect ratios from 2.0 to 4.5. The extinction coefficients at the longitudinal plasmon band peak maxima for these nanorods vary from 2.5x10(9) to 5.5x10(9) M-1 cm-1, respectively, on a per-particle basis. Many of the gold ions present in the growth solution remain unreacted; insights into the growth mechanism of gold nanorods are discussed.     

Observation of a Quadrupole Surface Plasmon Mode for Au Nanorods: Effects of Surface Roughness and Crystal Facets

This paper describes how the surface roughness and synthetic methods of Au nanorods affect the optical properties that are often associated with localized surface plasmon resonances. We synthesized Au nanorods with different aspect ratios and surface roughness by using two different synthetic strategies to observe surface plasmon resonance bands. One set of nanorods was prepared in high yield by using a seed‐mediated dropwise‐addition method with a growth‐directing surfactant in aqueous solution (Au nanorods in aqueous phase, GNRA). The other set of Au nanorods were synthesized by the electrochemical deposition of Au onto an anodized aluminum oxide (AAO) template (Au nanorods by AAO template, GNRT). The length of the nanorods was controlled by changing the total charge that was passed through the cell and their diameter was monitored by changing the diameter of the template channel. The as‐prepared Au nanorods were optimized to observe a quadrupole mode, which is one of the higher‐order surface plasmon bands. Our results showed differences between the optical properties of GNRA and GNRT. The roughness and crystal structure of the Au nanorods affected their optical properties. Smooth and single‐crystal surface on GNRA had larger and sharper peaks than GNRT. The discrete dipole approximation (DDA) method was used to calculate the optical properties of the Au nanorods and these results were in good agreement with our experimental results.     

Templated synthesis of metal nanorods in silica nanotubes

We report a general method for the synthesis of noble metal nanorods, including Au, Ag, Pt, and Pd, based on their seeded growth in silica nanotube templates. The controlled growth of the metals occurs exclusively on the seeds inside the silica nanotubes, which act as hard templates to confine the one-dimensional growth of the metal nanorods and define their aspect ratios. This method affords large quantities of noble metal nanorods with well-controlled aspect ratios and high yield, which may find wide use in the fields of nanophotonics, catalysis, sensing, imaging, and biomedicine.     

Fine-tuning the synthesis of ZnO nanostructures by an alcohol thermal process

A simple and efficient alcohol thermal technique was applied to control the growth of the dimensions and morphology of ZnO nanostructures under mild conditions, where surfactant was not necessary. The size of ZnO nanocrystals increased with growth temperature and they transformed into nanorods with different aspect ratios through tuning the reaction time. The length of nanorods increased significantly with the reaction time, but their thickness only slightly increased. The as-prepared ZnO nanocrystals were monocrystalline and the growth orientation of ZnO nanorods was [001]. Photoluminescence measurements showed a blue shift in violet emission with a reduction in crystal size and revealed the quantum confinement effect. Electron irradiation induced structural damage was observed in the ZnO nanorods synthesized at 120 degrees C. Experimental results proved that the possible growth mechanism of ZnO nanostructures was oriented attachment.     

Structural characteristics and growth of pentagonal silver nanorods prepared by a surfactant method

The crystal structure and growth mechanism of silver nanorods prepared by a seed-mediated surfactant method using the cationic surfactant cetyltrimethylammonium tosylate (CTAT) and its wormlike micelles are characterized by conventional and high-resolution transmission electron microscopy. Depending on the nanorod orientations, two types of electron diffraction patterns are obtained from a truncated decahedral structure consisting of five crystal units packing along [111] twining planes with five [111] planes on each end and five circumferential [001] side surfaces parallel to a <110> longitudinal direction. High-resolution images of the nanorods and the corresponding Fourier transform patterns confirm the results from the morphological and diffraction analyses. The silver nanorods grow only from multiply twinned decahedral seeds, and the high selectivity of surfactant attachment results in a barrier to the transfer of silver atoms from the solution to the circumferential [100] planes. Blockage of circumferential growth causes the aspect ratio of the rod to grow.     

Surfactant-ligand co-assisted solvothermal technique for the synthesis of different-shaped CdS nanorod-based materials

1-D nanorods, twinrods, golfclubs, and tripods of CdS were prepared via a surfactant-ligand co-assisted solvothermal method at 160°C. The surfactant of S-dodecylisothiounium bromide (C₁₂) used in the process was favorable for synthesis of different-shaped CdS nanorod with high aspect ratio. X-ray diffraction (XRD) and TEM images showed that the 1-D nanorods had wurtzite phase and others had a zinc blende core and wurtzite arms. The morphologies of CdS prepared under different conditions suggested the “template-assistance” of the surfactant and that the nonaqueous organic media are important for the self-assembling of inorganic components at atomic level.     

One-step synthesis of large-aspect-ratio single-crystalline gold nanorods by using CTPAB and CTBAB surfactants

Gold nanorods were prepared in high yields by using a one-step seed-mediated process in aqueous cetyltripropylammonium bromide (CTPAB) and cetyltributylammonium bromide (CTBAB) solutions in the presence of silver nitrate. The diameters of the nanorods range from 3 to 11 nm, their lengths are in the range of 15 to 350 nm, and their aspect ratios are in the range of 2 to 70. The diameters of the Au nanorods obtained from one growth batch in CTPAB solutions decrease as their lengths increase, and their volumes decrease as the aspect ratios increase. The diameters of the Au nanorods obtained from one growth batch in CTBAB solutions first decrease and then slightly increase as their lengths increase, and their volumes increase as the aspect ratios increase. These Au nanorods are single-crystalline and are seen to be oriented in either the [100] or [110] direction under transmission electron microscopy imaging, irrespective of their sizes. To the best of our knowledge, this is the first report of the preparation by using wet-chemistry methods of single-crystalline Au nanorods with aspect ratios larger than 15.     

阴离子表面活性剂作为添加剂种子生长法制备尺寸可调的单分散金纳米棒

以不同阴离子表面活性剂作为添加剂种子生长法制备金纳米棒, 并考察阴离子表面活性剂种类对金纳米棒形貌及光学性质的影响。在十二烷基苯基磺酸钠(SDBS)存在下, 金纳米棒的产率明显高于使用十二烷基磺酸钠的反应体系。对添加SDBS的种子生长法制备金纳米棒的反应条件进行优化, 得到十六烷基三甲基溴化铵、SDBS、抗坏血酸和硝酸银的最佳浓度分别为0.04 mol·L^-1、2.4 mmol·L^-1、1.2 mmol·L^-1和0.08 mmol·L^-1。在此条件下, 金纳米棒的生长在30 min内完成, 所制备的金纳米棒表面等离子共振吸收峰位于823 nm, 其横纵比为(5±0.03)。当改变生长液中硝酸银浓度时, 金纳米棒的尺寸也随之发生改变。此外, 我们还探讨了SDBS的作用机理。相对于经典种子生长法, 新方法制备纳米金棒在尺寸可调性、单分散性和生物毒性方面明显改善, 可广泛应用于各种光学及生物分析。     

单金纳米棒的光散射分析化学:径向比与分析灵敏度的关系

单纳米颗粒作为信号感应单元在化学与生物传感应用中已引起广泛关注.本文通过暗场显微成像(iDFM)研究了不同径向比金纳米棒的光散射性质.将iDFM与扫描电子显微镜(SEM)结合表征种子生长法制备的金纳米棒,结果发现,因局域表面等离子体共振而展示出的红色散射光随单个金纳米棒的径向比增大逐渐红移,且金纳米棒对其周围介质折光率(RI)变化的敏感程度随径向比增大而增大.这一结果对设计高灵敏的生物纳米传感器、提高分析检测的灵敏度具有很好的指导意义.     

阴离子表面活性剂作为添加剂种子生长法制备尺寸可调的单分散金纳米棒

以不同阴离子表面活性剂作为添加剂种子生长法制备金纳米棒,并考察阴离子表面活性剂种类对金纳米棒形貌及光学性质的影响。在十二烷基苯基磺酸钠(SDBS)存在下,金纳米棒的产率明显高于使用十二烷基磺酸钠的反应体系。对添加SDBS的种子生长法制备金纳米棒的反应条件进行优化,得到十六烷基三甲基溴化铵、SDBS、抗坏血酸和硝酸银的最佳浓度分别为0.04 mol.L-1、2.4 mmol.L-1、1.2 mmol.L-1和0.08 mmol.L-1。在此条件下,金纳米棒的生长在30 min内完成,所制备的金纳米棒表面等离子共振吸收峰位于823 nm,其横纵比为(5±0.03)。当改变生长液中硝酸银浓度时,金纳米棒的尺寸也随之发生改变。此外,我们还探讨了SDBS的作用机理。相对于经典种子生长法,新方法制备纳米金棒在尺寸可调性、单分散性和生物毒性方面明显改善,可广泛应用于各种光学及生物分析。     

银纳米棒光学性质的离散偶极近似计算

The optical properties of metal nanoparticles are quite different from those of the bulk materials mainly due to the collective oscillations of their conduction electrons known as the surface plasmon resonance（SPR）,which is strongly dependent on the particle shape and size,and the dielectric properties of the local environment where the nanoparticles are embedded in. Based on the discrete dipole approximation（DDA）method,we studied the optical properties of silver nanorods with different aspect ratios in some special dielectric environment including air,water,acetone,methylene chloride and pyridine. The DDA simulation of the ultraviolet-visible（UV-Vis）extinction spectra of silver nanorods with varying aspect ratios shows the plasmons absorption splits into two bands corresponding to the oscillation of the free electrons along and perpendicular to the long axis of the rods. The transverse mode shows almost a fixed resonance at about 350 nm while the resonance of the longitudinal mode is red-shifted and strongly depends on the aspect ratio of the nanorods. An empirical formula was given to predict the peak position of the longitudinal palsmon band of the silver nanorods with different aspect ratios in the air. The calculation result also shows the maximum of the longitudinal plasmon band of a silver nanorod with a fixed aspect ratio depends on the medium dielectric constant in a linear way. The TEM image and corresponding UV-Vis extinction spectrum of silver nanosphere and nanorods synthesized by our lab are in good agreement with the DDA simulation results.     

Thorough tuning of the aspect ratio of gold nanorods using response surface methodology

In the present work a central composite design based on response surface methodology (RSM) is employed for fine tuning of the aspect ratios of seed-mediated synthesized gold nanorods (GNRs). The relations between the affecting parameters, including ratio of l-ascorbic acid to Au³⁺ ions, concentrations of silver nitrate, CTAB, and CTAB-capped gold seeds, were explored using a RSM model. It is observed that the effect of each parameter on the aspect ratio of developing nanorods highly depends on the value of the other parameters. The concentrations of silver ions, ascorbic acid and seeds are found to have a high contribution in controlling the aspect ratios of NRs. The optimized parameters led to a high yield synthesis of gold nanorods with an ideal aspect ratio ranging from 1 (spherical particle) to 4.9. In addition, corresponding tunable surface Plasmon absorption band has been extended to 880 nm. The resulted nanorods were characterized by UV–visible spectrometry and transmission electron microscopy.     

Epitaxial growth and photochemical annealing of graded CdS/ZnS shells on colloidal CdSe nanorods

We report the preparation and structural characterization of core/shell CdSe/CdS/ZnS nanorods. A graded shell of larger band gap is grown around CdSe rods using trioctylphosphine oxide as a surfactant. Interfacial segregation is used to preferentially deposit CdS near the core, providing relaxation of the strain at the core/shell interface. The reported synthesis allows for variation of the shell thickness between one and six monolayers, on core nanorods ranging from aspect ratios of 2:1 to 10:1. After an irreversible photochemical annealing process, the core/shell nanorods have increased quantum efficiencies and are stable in air under visible or UV excitation. In addition to their robust optical properties, these samples provide an opportunity for the study of the evolution of epitaxial strain as the shape of the core varies from nearly spherical to nearly cylindrical.     

Hydrothermal synthesis of one-dimensional ZnO nanostructures with different aspect ratios

1-D ZnO nanorods with different aspect ratios were synthesized by a one-step, hydrothermal method. The ZnO nanorods grow along the [0001] direction to form single crystals. The experimental results reveal that the growth of polar inorganic crystals is sensitive to the reaction solvents.     

金纳米棒的生长及与FeCl_3的作用

采用三氯化铁选择性刻蚀法获得了预定长径比的金纳米棒.相比于晶种生长法,三氯化铁选择性刻蚀法可以更加简便快捷地调控金纳米棒形貌.以三氯化铁为刻蚀剂的刻蚀反应优先发生在金纳米棒尖端,这是因为金纳米棒尖端反应活性更高且表面活性剂钝化作用更弱.通过控制刻蚀反应时间及刻蚀剂浓度,可以精确调控金纳米棒的长径比.实验结果表明,增加刻蚀剂浓度、卤素离子浓度以及升高反应温度可以加快刻蚀反应速率.进一步讨论了金属离子的刻蚀作用机理.     

Evaluation of tailored magnetic composite films for near-field electromagnetic noise suppression

The effects of permeability and permittivity of the magnetic nanorods filled in composite films have been studied in the broadband radio-frequency range from 0.5 to 10 GHz on a microstrip line. The transmission power absorption of the composite film on a microstrip line was simulated using 3D FEM HFSS program. The model of microstrip line was designed based on IEC standard (IEC 62333-2). The permeability of composite film with magnetic nanorods could be controlled by the aspect ratio of nanorods. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by the Landau–Lifshitz–Gilbert equation. Given the bulk magnetization of 5 kG, the power loss frequency region has exhibited the 2.5–7 GHz broadband frequency by mixing of nanorods with various aspect ratios from 2 to 10. The permittivity effects have been evaluated by changing the real part of permittivity with a fixed imaginary part value and vice versa. The power losses were increased with the proportional to the imaginary part of permittivity and did not show any significant change with the increment of the real part of permittivity. The conduction electromagnetic noise in near field can be suppressed by controlling complex permeability with various aspect ratios of the magnetic nanorods in the composite.

     

Ultrafast studies of gold, nickel, and palladium nanorods

Steady state and ultrafast transient absorption studies have been carried out for gold, nickel, and palladium high aspect ratio nanorods. For each metal, nanorods were fabricated by electrochemical deposition into approximately 6 microm thick polycarbonate templates. Two nominal pore diameters(10 and 30 nm, resulting in nanorod diameters of about 40 and 60 nm, respectively) were used, yielding nanorods with high aspect ratios (>25). Static spectra of nanorods of all three metals reveal both a longitudinal surface plasmon resonance (SPR(L)) band in the mid-infrared as well as a transverse band in the visible for the gold and larger diameter nickel and palladium nanorods. The appearance of SPR(L) bands in the infrared for high aspect ratio metal nanorods and the trends in their maxima for the different aspect ratios and metals are consistent with calculations based on the Gans theory. For the gold and nickel samples, time resolved studies were performed with a subpicosecond resolution using 400 nm excitation and a wide range of probe wavelengths from the visible to the mid-IR as well as for infrared excitation (near 2000 cm(-1)) probed at 800 nm. The dynamics observed for nanorods of both metals and both diameters include transients due to electron-phonon coupling and impulsively excited coherent acoustic breathing mode oscillations, which are similar to those previously reported for spherical and smaller rod-shaped gold nanoparticles. The dynamics we observe are the same within the experimental uncertainty for 400 nm and infrared (5 microm) excitation probed at 800 nm. The transient absorption using 400 nm excitation and 800 nm probe pulses of the palladium nanorods also reveal coherent acoustic oscillations. The results demonstrate that the dynamics for high aspect ratio metal nanorods are similar to those for smaller nanoparticles.     

Synthesis and optical properties of small Au nanorods using a seedless growth technique

Gold nanoparticles have shown potential in photothermal cancer therapy and optoelectronic technology. In both applications, a call for small size nanorods is warranted. In the present work, a one-pot seedless synthetic technique has been developed to prepare relatively small monodisperse gold nanorods with average dimensions (length × width) of 18 × 4.5 nm, 25 × 5 nm, 15 × 4.5 nm, and 10 × 2.5 nm. In this method, the pH was found to play a crucial role in the monodispersity of the nanorods when the NaBH(4) concentration of the growth solution was adjusted to control the reduction rate of the gold ions. At the optimized pH and NaBH(4) concentrations, smaller gold nanorods were produced by adjusting the CTAB concentration in the growth solution. In addition, the concentration of silver ions in the growth solution was found to be pivotal in controlling the aspect ratio of the nanorods. The extinction coefficient values for the small gold nanorods synthesized with three different aspect ratios were estimated using the absorption spectra, size distributions, and the atomic spectroscopic analysis data. The previously accepted relationships between the extinction coefficient or the longitudinal band wavelength values and the nanorods' aspect ratios found for the large nanorods do not extend to the small size domain reported in the present work. The failure of extending these relationships over larger sizes is a result of the interaction of light with the large rods giving an extinction band which results mostly from scattering processes while the extinction of the small nanorods results from absorption processes.     

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.     

Synthesis and characterization of wurtzite ZnTe nanorods with controllable aspect ratios

ZnTe nanorods with controllable aspect ratios were synthesized using polytellurides a tellurium precursor. The use of polytellurides which allow nucleation and growth at relatively low temperature is the key to formation of wurtzite phase and controlled anisotropic growth along c-axis. The aspect ratio of the resulting ZnTe nanorods was controlled by tuning the temperature that in turn controls the kinetics of the nanocrystal growth. A diameter dependent quantum confinement effect in ZnTe nanorods was observed by UV-vis absorption spectroscopy. Transient absorption measurements show ultrafast charge injection dynamics from ZnTe nanorods, suggesting their strong potential for applications in photocatalysis.