Inside Front Cover: Optical Control and Patterning of Gold‐Nanorod–Poly(vinyl alcohol) Nanocomposite Films (Adv. Funct. Mater. 7/2005)

The micropatterning of optical structures into thin films of poly (vinyl alcohol) (PVA) containing gold nanorods is demonstrated by Pérez‐Juste, Liz‐Marzán, and co‐workers on p. 1065. The nanorods are uniformly distributed in the thin films and can be aligned by stretching the films. The inside cover shows how irradiation with a nanosecond laser, using a TEM grid as mask, selectively reshapes the nanorods into nanospheres (upper and lower TEM images, respectively). Gold nanorods with well‐defined aspect ratios are homogeneously incorporated within poly(vinyl alcohol) thin films and subsequently aligned by heating and stretching the nanocomposite films. The spatial alignment of the nanorods is directly proved using transmission electron microscopy. The polarization‐dependent optical response of the rods is measured and compared with a dipole model. Excellent agreement is found. Additionally, irradiation of the film with nanosecond laser pulses (1064 nm) leads to selective reshaping of the nanorods into nanospheres, and we demonstrate that this effect can be used to micropattern optical structures into the films.     

Optical Control and Patterning of Gold‐Nanorod–Poly(vinyl alcohol) Nanocomposite Films

Gold nanorods with well‐defined aspect ratios are homogeneously incorporated within poly(vinyl alcohol) thin films and subsequently aligned by heating and stretching the nanocomposite films. The spatial alignment of the nanorods is directly proved using transmission electron microscopy. The polarization‐dependent optical response of the rods is measured and compared with a dipole model. Excellent agreement is found. Additionally, irradiation of the film with nanosecond laser pulses (1064 nm) leads to selective reshaping of the nanorods into nanospheres, and we demonstrate that this effect can be used to micropattern optical structures into the films.     

Multisegment PtRu Nanorods: Electrocatalysts with Adjustable Bimetallic Pair Sites

Multisegment PtRu nanorods (Pt–Ru, Pt–Ru–Pt, Pt–Ru–Pt–Ru, Pt–Ru–Pt–Ru–Pt, Pt–Ru–Pt–Ru–Pt–Ru) with customizable lengths of the individual metals are obtained by the sequential electrodeposition of the metals into the pores of anodic aluminum oxide (AAO) membranes. Field‐emission scanning electron microscopy (FESEM) shows that the nanorods are about 200 nm in diameter and 1.2 μm long, with 900 nm of total platinum‐segment length. The alternating platinum and ruthenium segments can be easily differentiated using FESEM. X‐ray diffractometry reveals that the platinum and ruthenium in the bimetallic nanorods are polycrystalline with face‐centered cubic and hexagonal close‐packed crystal lattice structures, respectively. The presence of Pt⁰, Pt^II, Pt^IV, Ru⁰, and Ru^VI on the surface of the bimetallic nanorods is demonstrated via X‐ray photoelectron spectroscopy. The nanorods are catalytically active in the room‐temperature electro‐oxidation of methanol. The relative rates of reaction, recorded using chronoamperometry, show a linear relationship between the long‐time (near‐steady‐state) current density and the number of Pt–Ru interfaces. The use of segmented nanorods with a controlled number of Pt–Ru interfaces removes many of the ambiguities in the interpretation of experimental data from conventional alloy catalysts and has provided a direct demonstration of the role of pair sites in bifunctional catalysis.     

Penta‐Twinned Copper Nanorods: Facile Synthesis via Seed‐Mediated Growth and Their Tunable Plasmonic Properties

The use of seed‐mediated growth as a versatile approach to the synthesis of penta‐twinned Cu nanorods with uniform diameters and controllable aspect ratios is reported. The success of this approach relies on our recent synthesis of uniform Pd decahedra, with sizes in the range of 6–20 nm. The Pd decahedral seeds can direct the heterogeneous nucleation and growth of Cu along the fivefold axis to produce nanorods with uniform diameters defined by the lateral dimension of the original seeds. Due to a large mismatch in the lattice constants between Cu and Pd (7.1%), the deposited Cu is forced to grow along one side of the Pd decahedral seed, generating a nanorod with an asymmetric distribution of Cu, with the Pd seed situated at one of the two ends. According to extinction spectra, the as‐obtained Cu nanorods can be stored in water under the ambient conditions for at least six months without noticeable degradation. This excellent stability allows us to systematically investigate the size‐dependent surface plasmon resonance properties of the penta‐twinned Cu nanorods. With the nanorod transverse modes positioned at 560 nm, the longitudinal modes can be readily tuned from the visible to the near‐infrared region by controlling the aspect ratio.     

Precise measurement of gold nanorods by using depolarized dynamic light scattering apparatus

A precise and noninvasive method for the size and shape measurement of gold nanorods(GNRs) has been proposed based on depolarized dynamic light scattering(DDLS). A home-made DDLS apparatus has been established. By applying depolarized optical path with precise alignment method, the signal-to-noise ratio(SNR) of this apparatus is highly improved. GNRs with three different diameter and length has been precisely measured by using DDLS method as well as scanning electron microscopy(SEM). The thickness of adsorption layer of cetyltrimethylammonium bromide(CTAB) in solution has been taken into consideration. Results show that size measurement of GNRs by using DDLS method agrees very well with that by using SEM. In addition, it is shown that the extinction spectroscopy strongly limited the application of DDLS method by affecting the effective scattering light intensity. Proper laser wavelength should be chosen before the application of this method.     

A Simple and Effective Route for the Synthesis of Crystalline Silver Nanorods and Nanowires

A simple and effective approach to the aqueous‐phase synthesis of crystalline silver nanorods and nanowires is demonstrated, using which their diameters and aspect ratios can be effectively controlled. The synthesis involves a template‐less and non‐seed process to high‐quality nanoparticles, which is low‐cost and proceeds at moderate temperatures. The nanorods and nanowires were synthesized by the reduction of silver nitrate with tri‐sodium citrate in the presence of sodium dodecylsulfonate. The concentration of tri‐sodium citrate plays a critical role while sodium dodecylsulfonate, as a capping agent, only plays an assistant role in controlling the diameters and aspect ratios of the products. High‐resolution transmission electron microscopy (HRTEM) and selected‐area electron diffraction (SAED) investigations show that the silver nanocrystals are generated with a twinned crystalline structure. We also put forward a primary experimental model to shed light on their growth mechanisms.     

Mechanical and Structural Properties of BaCrO4 Nanorod Films under Confinement and Shear

Using an X‐ray surface forces apparatus (X‐SFA) we have investigated the effects of normal load (stress) and shear on the ordering and tribological properties of 10 nm × 30 nm surfactant‐coated BaCrO₄ nanorods in isooctane, confined within submicrometer films. The film structure and corresponding friction forces were monitored as a function of time and shearing distance at different gap sizes and loads. The X‐ray diffraction patterns indicate a cubic phase of nanorods coexisting with a surfactant phase that depends on the load, film thickness, shear rate, and shearing time. Atomic force microscopy and birefringence measurements performed on each surface after a shearing experiment showed ordered domains of nanorods over length scales of several tens of micrometers.     

Metal Nanocrystal‐Embedded Hollow Mesoporous TiO2 and ZrO2 Microspheres Prepared with Polystyrene Nanospheres as Carriers and Templates

Noble metal nanocrystals with different shapes and compositions are embedded in hollow mesoporous metal oxide microspheres through an ultrasonic aerosol spray. Polystyrene (PS) nanospheres are employed simultaneously as a hard template to create hollow interiors inside the oxide microspheres and as the carrier to bring pregrown metal nanocrystals, including Pd nanocubes, Au nanorods, and Au core/Pd shell nanorods, into the oxide microspheres. Calcination removes the PS template and causes the metal nanocrystals to adsorb on the inner surface of the hollow oxide microspheres. The catalytic performances of the Pd nanocube‐embedded TiO₂ and ZrO₂ microspheres are investigated using the reduction of 4‐nitrophenol as a model reaction. The presence of the mesopores in the oxide microspheres allows the reactant molecules to diffuse into the hollow interiors and subsequently interact with the Pd nanocubes. The embedding of the metal nanocrystals in the hollow oxide microspheres prevents the aggregation of the metal nanocrystals and reduces the loss of the catalyst during recycling. The Pd nanocube‐embedded ZrO₂ microspheres are found to exhibit a much higher catalytic activity, a much larger catalytic reaction rate, and a superior recyclability in comparison with a commercial Pd/C catalyst. This preparation approach could potentially be utilized to incorporate various types of mono‐ and multimetallic nanocrystals with different sizes, shapes, and compositions into hollow mesoporous oxide microspheres. Such a capability can facilitate the studies of the catalytic properties of various combinations of metal nanocrystals and metal oxide supports and therefore guide the design and creation of high‐performance catalysts.     

轴棱锥线聚焦特性对成像系统焦深的影响

利用时域有限差分(FDTD)法模拟了所设计的一种新 型劈裂纳米矩形结构消光光谱、近场增强和电荷分布情 况。研究了在劈裂金属纳米矩形中,Fano共振形成机理、结构参数对Fano共振峰的影响,以 及当入射场 偏振方向不同时在红外波长处形成的消光率同等强度骤增现象。研究表明,当改变周围环境 折射率时,Fano 共振峰有一个非常明显的移动,品质因数FoM可以达到11.8,这种新 型劈裂纳米矩形有很好的传感特性。 入射光沿不同偏振方向穿过劈裂金属纳米矩形时,在特定红外波长处形成同等强度的消光率 增强,对不同 偏振角激光强度形成统一衰减的特性使其在混合偏振角激光的强度衰减等光学方面有着重要 的应用价值。     

Photoluminescent Arrays of Nanopatterned Monolayer MoS2

Monolayer 2D MoS₂ grown by chemical vapor deposition is nanopatterned into nanodots, nanorods, and hexagonal nanomesh using block copolymer (BCP) lithography. The detailed atomic structure and nanoscale geometry of the nanopatterned MoS₂ show features down to 4 nm with nonfaceted etching profiles defined by the BCP mask. Atomic resolution annular dark field scanning transmission electron microscopy reveals the nanopatterned MoS₂ has minimal large‐scale crystalline defects and enables the edge density to be measured for each nanoscale pattern geometry. Photoluminescence spectroscopy of nanodots, nanorods, and nanomesh areas shows strain‐dependent spectral shifts up to 15 nm, as well as reduction in the PL efficiency as the edge density increases. Raman spectroscopy shows mode stiffening, confirming the release of strain when it is nanopatterned by BCP lithography. These results show that small nanodots (≈19 nm) of MoS₂ 2D monolayers still exhibit strong direct band gap photoluminescence (PL), but have PL quenching compared to pristine material from the edge states. This information provides important insights into the structure–PL property correlations of sub‐20 nm MoS₂ structures that have potential in future applications of 2D electronics, optoelectronics, and photonics.     

Magnetic Mesoporous Nanocarriers for Drug Delivery with Improved Therapeutic Efficacy

Mesoporous CoNi@Au core@shell nanorods are synthesized as magnetic drug nanocarriers by electrodeposition using ionic liquid‐in‐aqueous microemulsions. Mesoporous nanorods present a highly effective area (186 m² g^?1) and magnetic character that allows their manipulation, concentration, and retention by applying a magnetic field. The nanorods have been functionalized with thiol‐poly(ethyleneglycol) molecules, and molecules of Irinotecan, a drug used in chemotherapy, are retained in both the lattice of the linked thiol‐poly(ethyleneglycol) molecules and inside the interconnected nanorods pores. The nanorods' mesoporous character allows a high drug‐loading capability and magnetic behavior that allows the drug's controlled release. A high cellular viability of HeLa cells is obtained after their incubation with the nanorods functionalized with thiol‐poly(ethyleneglycol). However, when the nanorods function as carriers for Irinotecan, significant cell death is occurred when HeLa cells are incubated with the functionalized, drug‐loaded nanorods. Cell death is also produced by applying an alternating magnetic field due to both the effect of the release of Irinotecan from the carrier as to mechanical damage of cells by nanorods subjected to the effect of a magnetic field. The proposal to used mesoporous magnetic nanorods as drug carriers can thus dramatically reduce the amounts of both nanocarrier and drug needed to efficiently destroy cancer cells.     

Morphology and growth mechanism of aligned ZnO nanorods grown by catalyst-free MOCVD

We report on ZnO nanorods grown by catalyst-free metal-organic chemical vapour deposition (MOCVD) in a commercial Epigress reactor using diethylzinc and N₂O as precursors. Well-aligned ZnO nanorods with uniform diameter, length and density have been grown perpendicularly to the sapphire (0 0 0 1) surface. Scanning electron microscopy (SEM) has been used to observe the morphology of the ZnO nanorods and X-ray diffraction and transmission electron microscopy (TEM) to investigate the crystalline structure of the nanorods. TEM observation as well as photoluminescence measurements confirm the very good crystalline quality of the nanorods. SEM observation on samples that have been prepared with various deposition times has been used in order to investigate the growth mechanism. Three types of ZnO morphologies have been identified: a thin two-dimensional ZnO layer formed at the sapphire surface, covered by three-dimensional hexagonal-shaped islands and hexagonal nanorods on top of them.     

Poly(3‐hexylthiophene) Nanorods with Aligned Chain Orientation for Organic Photovoltaics

A structured polymer solar cell architecture featuring a large interface between donor and acceptor with connecting paths to the respective electrodes is explored. To this end, poly‐(3‐hexylthiophene) (P3HT) nanorods oriented perpendicularly to indium tin oxide (ITO) glass are fabricated using an anodic aluminum oxide template. It is found that the P3HT chains in bulk films or nanorods are oriented differently; perpendicular or parallel to the ITO substrate, respectively. Such chain alignment of the P3HT nanorods enhanced the electrical conductivity up to tenfold compared with planar P3HT films. Furthermore, the donor/acceptor contact area could be maximised using P3HT nanorods as donor and C60 as acceptor. In a photovoltaic device employing this structure, remarkable photoluminescence quenching (88%) and a seven‐fold efficiency increase (relative to a device with a planar bilayer) are achieved.     

Morphological and spectroscopic studies on the vertically aligned zinc oxide nanorods grown on low and high temperature deposited seed layer

Vertically aligned zinc oxide nanorods were grown on low and high temperature deposited aluminium doped zinc oxide seed layer by hydrothermal method and annealed to improve crystallinity. The morphology of the seed layer and the grown nanorods were studied by field emission scanning electron microscopy characterization technique. The properties of the zinc oxide nanorods were analyzed using laser spectroscopic studies. Resonant Raman spectroscopy reveals the unique increase in the A₁(LO) mode of vibration with increase in count. The luminescence property of the nanorods was studied with photoluminescence spectrometer. The vertically aligned zinc oxide nanorods show, the very high band edge emission in the ultraviolet region of the electromagnetic spectrum.     

Spectral encoding on Gold Nanorods Doped in a Silica Sol–Gel Matrix and Its Application to High‐Density Optical Data Storage

Metallic nanorods exhibit fascinating optical properties due to surface plasmons—collective oscillation of the electron cloud within a particle. They exhibit two principle absorption bands that correspond to surface plasmon resonance (SPR) along the longitudinal and transverse directions of the nanorod. Most importantly, the longitudinal band can be tuned with the aspect ratio of the rod, making it a spectrally tuneable optical material, which can be applied to a variety of devices from bioimaging to high‐density optical storage. Here, spectral encoding for high‐density optical storage applications is demonstrated on two sizes of gold nanorods (aspect ratios of three and five) doped in a silica sol–gel matrix by femtosecond pulsed laser irradiation. It is widely known that high‐power pulsed laser irradiation causes metal nanorods to undergo shape transformations via the process of melting or fragmentation. The process is enhanced if the laser wavelength is tuned at the longitudinal surface plasmon resonance peak of the nanorods, which results in a significant reduction or shift in the surface plasmon resonance peak. As such a shape change occurs only on the subpopulation of rods that have a longitudinal plasmon band matching the laser wavelength, a size‐ or spectrum‐selective shape transition is possible in a rod mixture with varying aspect ratios. The current spectral encoding technology can be incorporated into existing optical disc technology, such as three‐dimensional bit‐by‐bit and holographic, and can increase the capacity limit by utilizing the spectral domain.     

Enhancement of persistent photoconductivity of ZnO nanorods under polyvinyl alcohol encapsulation

We report on the observation of enhanced and persistent ultraviolet (UV) photoconductivity of polyvinyl alcohol (PVA) encapsulated ZnO nanorods. A simple aqueous solution growth technique is adopted to grow ZnO nanorods in the form of thin film as well as powder. The morphological features of nanorods (before and after PVA coating) have been studied using electron microscopy. Both bare and PVA coated nanorods are found to exhibit photoconductivity under UV light illumination. PVA encapsulation of nanorods has led to the lower adsorption of oxygen molecules on the surface of nanorods leading to the exhibition of high dark current and a slower growth in photocurrent under steady illumination. The appealing aspect of the present investigation lies in the observation of highly enhanced persistent photoconductivity in the encapsulated nanorods. Based on the fact of confinement of the desorbed oxygen molecules, a new mechanism has been proposed to support the encapsulation led enhancement in persistent photoconductivity. The encapsulation led confinement of the desorbed oxygen molecules around the nanorods results in the faster development of surface built-in potential and hence exhibits enhanced persistent photoconductivity, thereby indicating the uniqueness of the proposed mechanism.     

热氧化法制备ZnO纳米棒及其结构表征

在无催化剂条件下,采用热蒸发Zn源,以N2为载气体,在SiO2衬底上反应沉积制备出单晶氧化锌纳米棒。XRD研究表明纳米棒为结晶完好的纤锌矿结构,并且为非定向生长,非定向生长的氧化锌纳米棒减弱了棒之间的屏蔽效应,表现出较好的场发射效果,为未来场发射电子器件的实际应用提供了可靠依据。     

Effect of Gold Nanorods on the Remote Decapsulation of Liposomal Capsules Using Ultrashort Electric Pulses

Decapsulation of nanocomposite liposomal capsules due to the effect of ultrashort electric pulses is obtained when the liposomal sheaths of the capsules are bound to significantly anisotropic gold nanoparticles (nanorods). Destruction of the liposomal sheath is interpreted using the rotational displacement of gold nanorods in the presence of the pulsed electric field. Such an interpretation is used to derive an expression for the critical electric field that determines the threshold level of the effect. The calculated critical field is in agreement with the experimental results. It is shown that the decapsulation is related to the presence of the gold nanorods in the sheath of liposomal capsules and is not obtained in the absence of the nanorods.     

Uniform 3D hydrothermally deposited zinc oxide nanorods with high haze ratio

We present low cost hydrothermally deposited uniform zinc oxide (ZnO) nanorods with high haze ratios for the a-Si thin film solar cells. The problem of low transmittance and conductivity of hydrothermally deposited ZnO nanorods was overcome by using RF magnetron sputtered aluminum doped zinc oxide (ZnO:Al ~300 nm) films as a seed layer. The length and diameters of the ZnO nanorods were controlled by varying growth times from 1 to 4 h. The length of the ZnO nanorods was varied from 1 to 1.5 µm, while the diameter was kept larger than 300 nm to obtain various aspect ratios. The uniform ZnO nanorods showed higher transmittance (~89.07%) and haze ratio in the visible wavelength region. We also observed that the large diameters (>300 nm) and average aspect ratio (3–4) of ZnO nanorods favored the light scattering in the longer wavelength region. Therefore, we proposed uniformly deposited ZnO nanorods with high haze ratio for the future low cost and large area amorphous silicon thin film solar cells.     

Al掺杂ZnO纳米棒的性能研究及其在太阳能电池中的应用

通过水热法制备了不同质量分数(0%,0.5%,1.0%和1.5%)的Al 3+掺杂ZnO纳米棒,扫描电镜(SEM)、X射线衍射(XRD)、紫外-可见(UV-vis)吸收光谱等测试结果表明,通过这种方法得到了较为规整的ZnO纳米阵列,结晶良好、具有明显的c轴生长取向;掺杂浓度的增加对产物的形貌和晶体结构产生了明显的影响。通过瞬态光谱和面电阻测试发现,Al 3+掺杂提高了ZnO传导电子的能力。将Al 3+掺杂的ZnO纳米棒同时作为电极与电子传输层,应用于有机太阳能电池器件中,在低浓度(0.5at.%)掺杂时得到最佳的器件性能,相比于未掺杂的ZnO纳米棒,短路电流提高了30%,光电转化效率提高了50%。