Biomimetically-inspired photonic nanomaterials

Nature has been kind enough to provide us with a 3-billion year old portfolio of an on-going experiment with living systems. There are well-optimised engineering solutions to mechanical, aerodynamic, hydrodynamic and optical problems all to be found in the living world Bar-Cohen (Bioinspir Biomim 1:P1–P12, 2006), Bhusan (Phil Trans Roy Soc A 367: 1445–1486, 2009). However, Nature is severely limited in the materials that are at its disposal so that as engineers we can improve on Nature’s solutions to particular problems by taking Nature’s design template as a starting point and then incorporating our own more appropriate materials, or metamaterials into that template design. We can also use Nature’s solutions as a starting point in our own “evolutionary algorithms” by taking Nature’s 3-billion year old solution as our initial starting point and then extrapolating that solution to (effectively) thousands of billions of years into the future using digital computers. This review article will consider just one particular application area of biomimetics—photonic nanomaterials Vukusic (Natural Photonics. Physics World pp. 35–39, 2004).     

Controlled growth and characterization methods of semiconductor nanomaterials

One-dimensional (1D) semiconductor nanomaterials attract much attention because they are ideal systems for investigation and studying the relationship between properties and structures and having extensive application future in the high technical field. They are expected to play an important role in fabrication of the next generation nanocircuits, nanotools, nanowires lasers, photon tunneling devices, near-field photo-waveguide devices, etc. This article described controlled growth, characterization of structures and morphologies and properties of 1D semiconductor nanomaterials based on our previous works. This article is organized into two parts: The first part is complicated nanostructures of semiconductors, which includes coaxial nanocables, heterostructure nanowires and nanowires with metal-semiconductor junction behavior, hierarchical structures, doping of the nanowires and nanobelts, porous materials and periodically twined nanowires and asymmetrical polytypic nanobelts. The second part contains semiconductor nanoarrays based on anodic alumina membrane (AAM) templates. Finally, we propose that further investigation of the influence of nanomaterial morphologies on properties and how to design the morphology of nanostructures to meet the property requirements of nanodevices are our future research directions in this field.     

高频热等离子体制备形状可控的一维结构纳米材料

介绍了采用高频热等离子体宏量制备ZnO、ZnS和A1N等一维结构纳米材料。研究了不同工艺条件对形貌的影响；采用锌粉为原料，成功制备了不同长径比的氧化锌纳米棒；同样，采用锌粉和硫粉混合物为原料，获得了均匀的棒状和四角状等不同形貌的一维结构纳米ZnS；采用铝粉与氨气在等离子体中的反应，获得了一维结构纳米A1N。通过控制不同的参数可以调控合成产物的大小、长径比和形貌等。在等离子体合成过程中，合成产物可以达到50g／min，而且，产物的大小和形貌均匀。XRD、SEM、HRTEM和拉曼光谱等表征了合成产物的结构和形貌。在高频常压热等离子体合成过程中，一维结构纳米材料的生长过程只有数秒，而合成的一维纳米材料的长度甚至可以达到几十微米。通过分析发现，在等离子体合成过程中，一维纳米材料的生长符合VS机制，而且，生长过程是双向进行的。     

Controlled manipulation of giant hybrid inorganic nanowire assemblies

The ultimate goal of nanotechnology is the design and fabrication of nanosize building blocks with multiple functionalities and their assembly into large-scale functional structures that can be controllably manipulated. Here we show that hybrid inorganic multisegmented nanowires, with hydrophobic carbon nanotube tails and hydrophilic metal nanowire heads, allow the assembly and manipulation of massive ordered structures in solution, reminiscent of the organic molecular micellar assembly. Further, properly designed assemblies can be manipulated using external stimuli such as magnetic field and light. The hybrid nanowires can have multiple segments including magnetic components, allowing the assembly to be manipulated by external magnetic field. The assembled structures can also be manipulated by modifying the hydrophobicity of the respective components via chemical functionalization and optical irradiation. This approach brings the concept of environment sensitive self-assembling nanomaterials closer to reality.     

Controlled AFM manipulation of small nanoparticles and assembly of hybrid nanostructures

We demonstrate controlled manipulation of semiconductor and metallic nanoparticles (NPs) with 5-15 nm diameters and assemble these NPs into hybrid structures. The manipulation is accomplished under ambient environment using a commercial atomic force microscope (AFM). There are particular difficulties associated with manipulating NPs this small. In addition to spatial drift, the shape of an asymmetric AFM tip has to be taken into account in order to understand the intended and actual manipulation results. Furthermore, small NPs often attach to the tip via electrostatic interaction and modify the effective tip shape. We suggest a method for detaching the NPs by performing a pseudo-manipulation step. Finally, we show by example the ability to assemble these small NPs into prototypical hybrid nanostructures with well-defined composition and geometry.     

Controlled replication of butterfly wings for achieving tunable photonic properties

The fine structure of the wing scale of a Morpho Peleides butterfly was examined carefully, and the entire configuration was completely replicated by a uniform Al(2)O(3) coating through a low-temperature ALD process. An inverted structure was achieved by removing the butterfly wing template at high temperature, forming a polycrystalline Al(2)O(3) shell structure with precisely controlled thickness. Other than the copy of the morphology of the structure, the optical property, such as the existence of PBG, was also inherited by the alumina replica. Reflection peaks at the violet/blue range were detected on both original wings and their replica, while a simple alumina coating shifted the reflection peak to longer wavelength because of the change of periodicity and refraction index. The alumina replicas also exhibited similar functional structures as waveguide and beam splitter, which may be used as the building blocks for photonic ICs with high reproducibility and lower fabrication cost compared to traditional lithography techniques.     

Controlled lateral manipulation of molecules on insulating films by STM

On metallic and semiconductor surfaces functional nanostructures can be built with atomic scale precision using the tip of an atomic force microscope/scanning tunneling microscope. In contrast, controlled lateral manipulation on insulators has not been reported. The traditional pushing and pulling based manipulation methods cannot be used for molecules adsorbed on insulating films because of the unfavorable ratio between diffusion barrier and desorption energy. Here, we demonstrate that molecules adsorbed on insulating films can be laterally manipulated in a controlled way by injecting inelastically tunneling electrons at well-defined positions in a molecule. The technique was successfully applied to several different molecules.     

Controlled growth of ZnO nanomaterials via hydrothermal method: effect of buffer layer

We report a facile solution-based method for the controlled growth of ZnO nanomaterials on an AIN/Si substrate. A ZnO buffer layer was coated on the substrate before growing the ZnO nano-materials. The shape of the ZnO nanomaterials changed from nanosheet to nanorod as the thickness of the ZnO buffer layer increased. Doping of the buffer layer with Ga decreased the average grain size of the ZnO buffer layer, which resulted in the growth of longer and thinner ZnO nanorods on the buffer layer. The UV sensing results of the ZnO nanorod-based device revealed that the aspect ratio of the ZnO nanorods is crucial for enhancing the performance of the device.     

Optical manipulation of photonic defect-modes in cholesteric liquid crystals induced by direct laser-lithography

Manipulation of photonic defect-modes in cholesteric liquid crystals (ChLCs), which are one-dimensional pseudo photonic band-gap materials have been demonstrated by an external optical field. A structural defect in which the pitch length of the ChLC in the bulk and the defect are different was introduced by inducing local polymerization in a photo-polymerizable ChLC material by a direct laser-lithography process, and infiltrating a different ChLC material as the defect medium. When an azobenzene dye-doped ChLC was infiltrated in the defect, the trans-cis isomerization of the dye upon ultraviolet (UV) exposure caused the pitch to shorten, changing the contrast in the pitch lengths at the bulk and the defect, leading to a consequent shifting of the defect-mode. The all-optical manipulation was reversible and had high reproducibility.     

Controlled bistability by using array defect layers in one-dimensional nonlinear photonic crystals

Using analytical modeling and detailed numerical simulations, we investigate the input-output transmission regimes in one-dimensional (1D) nonlinear photonic crystal including array defect layers. A coupled-mode system is derived from the Maxwell equations and analyzed for the stationary-transmission regime in the new proposed structure. Using the idea about introducing defect layers into 1D nonlinear photonic crystals, a new method for creating and controlling optical bistability is proposed. The periodic optical structures with array defect layers can be used as all optical switches between lower- and higher-transmissive states, whereas it possesses one jumping from a low-transmissive state to a transparent state.     

Controlled oxidative synthesis of Bi nanoparticles and emission centers in bismuth glass nanocomposites for photonic application

Here we demonstrate an oxidative process to control metallic bismuth (Bi⁰) nanoparticles (NPs) creation in bismuth glass nanocomposites by using K₂S₂O₈ as oxidant and enhanced transparency of bismuth glasses. Formation of Bi⁰ NPs has been monitored by their distinct surface plasmon resonance (SPR) band at 460 nm in the UV-visible absorption spectra. It is further confirmed by the transmission electron microscopy (TEM) images which disclose the formation of spherical Bi⁰ NPs whereas the selected area electron diffraction (SAED) pattern reveals their crystalline rhombohedral phase. These glasses are found to exhibit visible and near infrared (NIR) luminescence bands at 630 and 843 nm respectively on excitation at 460 nm of the SPR band. It is realized that the luminescence center of bismuth species is an uncertain issue, however, it is reasonable to consider that the emission band at 630 nm is due to the combination of ²D_5/2 → ⁴S_3/2 of Bi⁰ and ²P_3/2 (1) → ²P_1/2 of Bi²⁺ transitions, and that of NIR emission band at 843 nm is attributed to the ²D_3/2 → ⁴S_3/2 of Bi⁰ transition.     

纳米材料的表征与测试方法

为促进纳米材料表征与测试技术体系的形成与发展,在查阅大量国内外文献、标准及相关法律法规的基础上,对纳米材料的分类、表征、重要测试技术进行介绍和综述,并对当前纳米材料表征与测试技术面临的挑战进行讨论,提出相关建议,在一定程度上能为解决纳米材料表征与测试技术难题、开展相关表征与测试工作、制定纳米材料表征与测试方法标准提供重要参考。     

Ion-induced manipulation of photochemical pathways in crown ether compounds based on fluorinated oligophenylenevinylenes: the border between ultrafast photoswitches and photoproduced nanomaterials

The photochemical and photophysical properties of the crown ethers trans,trans-1,4-bis[2-(3',4'-benzo 15-crown 5)ethenyl]-2,3,5,6-tetrafluorobenzene (1) and trans,trans-1,4-bis[2-(3',4'-benzo 18-crown 6) ethenyl]-2,3,5,6-tetrafluorobenzene (2) were investigated in the absence and presence of groups I and II metal ions. The photophysical methods used include steady state flurescence, uv spectroscopy, and ultrafast transient absorption spectroscopy. Both compounds showed solvatochromic behavior, due to intramolecular charge transfer state formation, and efficient fluorescence in polar solvents. Photophysical behavior was dependent on the metal ion. The addition of metal ions that completely fit into the crown ether cavity resulted in significant blue shifts in the fluorescence emission spectra (chemosensing properties). Partially fitting ions changed the fluorescence spectra slightly. Transient absorption measurements revealed fast and slow decay components with time constants of 10-20 and 500-600 ps for all fitting ions, respectively. The latter is assigned to a trans-cis photoisomerization process, which decreased in efficiency in the presence of partially fitting ions, i.e., increasing ion size. Steady state irradiation showed clear evidence of a change in the absorption spectra. Trans-cis photoisomerization and [2 + 2] photocycloaddition were found to compete with fluorescence. The ions Li+, Na+, and Ca2+, which fit into the cavity, direct the photoisomerization. Larger ions (K+, Rb+, Sr2+ and Ba2+) that partially fit the cavity cause photocycloaddition. Quantum yields of the photoreaction are between 0.1 and 0.3. Analysis of the photo-product obtained for the 1-Sr2+ system revealed a compound with a molecular weight of nanosize dimension, which was equivalent to seven mass units of 1. The higher molecular weight product was formed due to alternately stacked supramolecular assemblies.     

Molecular handles for the mechanical manipulation of single-membrane proteins in living cells

We have developed a procedure to selectively biotinylate a specific membrane protein, enabling its attachment to external force probes and thus allowing its mechanical manipulation within its native environment. Using potassium channels as model membrane proteins in oocytes, we have found that Maleimide-PEG3400-biotin is the crosslinker with highest conjugation selectivity and accessibility to external probes. Neutravidin-coated beads provide for directed attachment while avoiding nonspecific interactions with the cell. The technology was successfully tested by mechanical manipulation of biotinylated extracellular residues of channels in oocytes using an atomic force microscope under conditions which preserve function of the channels. Binding forces of /spl sim/80 pN at 100 nN/s were measured.     

Controlled chemical modification of the internal surface of photonic crystal fibers for application as biosensitive elements

Photonic crystal fibers (PCF) are one of the most promising materials for creation of constructive elements for bio-, drug and contaminant sensing based on unique optical properties of the PCF as effective nanosized optical signal collectors. In order to provide efficient and controllable binding of biomolecules, the internal surface of glass hollow core photonic crystal fibers (HC-PCF) has been chemically modified with silanol groups and functionalized with (3-aminopropyl) triethoxysilane (APTES). The shift of local maxima in the HC-PCF transmission spectrum has been selected as a signal for estimating the amount of silanol groups on the HC-PCF inner surface. The relationship between amount of silanol groups on the HC-PCF inner surface and efficiency of following APTES functionalization has been evaluated. Covalent binding of horseradish peroxidase (chosen as a model protein) on functionalized PCF inner surface has been performed successively, thus verifying the possibility of creating a biosensitive element.     

Mechanical control of nanomaterials and nanosystems

In situations of power outage or shortage, such as periods just following a seismic disaster, the only reliable power source available is the most fundamental of forces i.e., manual mechanical stimuli. Although there are many macroscopic mechanical tools, mechanical control of nanomaterials and nanosystems has not been an easy subject to develop even by using advanced nanotechnological concepts. However, this challenge has now become a hot topic and many new ideas and strategies have been proposed recently. This report summarizes recent research examples of mechanical control of nanomaterials and nanosystems. Creation of macroscopic mechanical outputs by efficient accumulation of molecular-level phenomena is first briefly introduced. We will then introduce the main subject: control of molecular systems by macroscopic mechanical stimuli. The research described is categorized according to the respective areas of mechanical control of molecular structure, molecular orientation, molecular interaction including cleavage and healing, and biological and micron-level phenomena. Finally, we will introduce two more advanced approaches, namely, mechanical strategies for microdevice fabrication and mechanical control of molecular machines. As mechanical forces are much more reliable and widely applicable than other stimuli, we believe that development of mechanically responsive nanomaterials and nanosystems will make a significant contribution to fundamental improvements in our lifestyles and help to maintain and stabilize our society.     

SiO2/CdS光子晶体的制备及其光学性能

用化学浴沉淀法(CBD)在SiO2胶体晶体中生长了CdS半导体材料, 并用UV-VIS-NIR光谱仪和荧光光分度计测试了其光学性能.测试结果表明,在SiO2胶体晶体中随着CdS填充量的增加,光子带隙向长波段方向移动且变宽;当发射出的光与基体材料的光子带隙相匹配时,可控制半导体材料的光致发光,同时,可通过控制SiO2胶体颗粒粒经的大小来调节CdS的光致发光性能.     

ZnO一维纳米材料的制备与表征

首先以乙醇为溶剂,乙酸锌为前驱体,油酸钠为表面修饰剂,采用溶液化学法,制得ZnO纳米粒子。以自制ZnO纳米粒子为基体,通过煅烧方法制备针状ZnO纳米线束。通过紫外-可见吸收光谱(UVVis)、荧光光谱(FL)、透射电子显微镜(TEM)、X射线衍射(XRD)和扫描电子显微镜(SEM)等方法对合成的样品进行表征。结果表明,所合成ZnO纳米粒子样品UV-Vis吸收光谱在355nm给出ZnO纳米粒子的特征吸收峰,FL光谱显示在400和550nm处产生荧光发射。ZnO纳米粒子尺寸约为5nm且粒径分布较窄。自制ZnO纳米粒子样品经500℃煅烧后可得到针状ZnO纳米线束。纳米线为六方晶系纤锌矿结构ZnO单晶纳米线,长度约为10μm,直径约为100nm,长径比约为100,且具有良好的紫外发光性能。     

PZT纳米材料低温合成及性能研究

用Pb(NO3)2、ZrOCl28H2O(或Zr(NO3)4·5H2O)与TiO2在160℃反应4 h生成PZT纳米材料.对制备的PZT纳米材料进行了XRD、TEM、SEM、XRF及热分析研究.生成的PZT晶粒为大小均匀的球形颗粒,平均直径为5～10nm,这些纳米颗粒团聚成规则的方形.通过调节反应条件可改变PZT产物的形貌,得到PZT的片或棒.并对水热反应PZT纳米材料晶体生长的机制进行了探讨.对PZT纳米粉体制备的块体材料进行了烧结和介电性能研究.其烧结温度大大降低,在1150℃即可烧结成瓷,样品收缩率为9.3%.烧结后PZT的晶粒形貌与烧结温度有关.其介电性能随频率的稳定性好.     

Nanotribology, nanomechanics and nanomaterials characterization

Nanotribology and nanomechanics studies are needed to develop fundamental understanding of interfacial phenomena on a small scale and to study interfacial phenomena in magnetic storage devices, nanotechnology and other applications. Friction and wear of lightly loaded micro/nanocomponents are highly dependent on the surface interactions (a few atomic layers). These structures are generally coated with molecularly thin films. Nanotribology and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures and provide a bridge between science and engineering. An atomic force microscope (AFM) tip is used to simulate a single-asperity contact with a solid or lubricated surface. AFMs are used to study the various tribological phenomena that include surface roughness, adhesion, friction, scratching, wear and boundary lubrication. In situ surface characterization of local deformation of materials and thin coatings can be carried out using a tensile stage inside an AFM. Mechanical properties such as hardness, Young's modulus of elasticity and creep/relaxation behaviour can be determined on micro- to picoscales using a depth-sensing indentation system in an AFM.