Nanoscale materials nanorods

This review focuses on nanoparticles, namely objects that are roughly spherical. We use the commonly accepted definition for nanoscale objects of having a dimension below 100 nm, and so identify nanoparticles as objects with a diameter of 100 nm or smaller. The review does not focus on larger aspect ratio nanoscale materials such as nanotubes and nanorods, though they are mentioned in some cases. 

Ohsaka s group has extensively examined the electrochemical behavior of both chemically and electrochemically deposited Mn02, both as discrete NPs and as nanostructured interfacial materials [61,64—81]. We focus here on two of their studies that exemplify the electrocatalytic nature of these nanoscale materials. In the first effort, El-Deab and Ohsaka explored the electrocatalytic behavior of MnOOH nanorods that had been electrodeposited onto Pt electrodes by oxidation of Mn(II) in an aqueous solution of manganese acetate [76]. The nanorods had average diameters of 20 nm and aspect ratios of 45 (i.e. average lengths of 900 nm) and covered nearly... 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

The various methods of preparation employed to prepare nanoscale clusters include evaporation in inert-gas atmosphere, laser pyrolysis, sputtering techniques, mechanical grinding, plasma techniques and chemical methods (Hadjipanyas Siegel, 1994). In Table 3.5, we list typical materials prepared by inert-gas evaporation, sputtering and chemical methods. Nanoparticles of oxide materials can be prepared by the oxidation of fine metal particles, by spray techniques, by precipitation methods (involving the adjustment of reaction conditions, pH etc) or by the sol-gel method. Nanomaterials based on carbon nanotubes (see Chapter 1) have been prepared. For example, nanorods of metal carbides can be made by the reaction of volatile oxides or halides with the nanotubes (Dai et al., 1995). 

With the advent of nanomaterials, different types of polymer-based composites developed as multiple scale analysis down to the nanoscale became a trend for development of new materials with new properties. Multiscale materials modeling continue to play a role in these endeavors as well. For example, Qian et al. [257] developed multiscale, multiphysics numerical tools to address simulations of carbon nanotubes and their associated effects in composites, including the mechanical properties of Young s modulus, bending stiffness, buckling, and strength. Maiti [258] also used multiscale modeling of carbon nanotubes for microelectronics applications. Friesecke and James [259] developed a concurrent numerical scheme to evaluate nanotubes and nanorods in a continuum. 

It has been well known that HRTEM is a powerful tool to investigate structures of low-dimensional oxides, such as nanoparticles, nanowires, nanorods and nanotubes, while the information from powder dilfraction of these low-dimensional materials is normally very Hmited merely because their small crystaUite sizes. For the nanoscale oxides, HRTEM can give useful information on particle size, crystal structure, particle morphology, structural defects and possible inter-particle connections. 

One-dimensional (ID) nanostructures such as nanowires, nanorods and nanobelts, provide good models to investigate the dependence of electronic transport, optical, mechanical and other properties on size confinement and dimensionality. Nanowires are likely to play a crucial role as interconnects and active components in nanoscale devices. An important aspect of nanowires relates to the assembly of individual atoms into such unique ID nanostructures in a controlled fashion. Excellent chemical methods have been developed for generating zero-dimensional nanostructures (nanocrystals or quantum dots) with controlled sizes and from a wide range of materials (see earlier chapters of this book). The synthesis of nanowires with controlled composition, size, purity and crystallinity, requires a proper understanding of the nucleation and growth processes at the nanometer regime. 

Metallic nanorods are highly interesting materials from many points of view as elements in future nanoscale electronic circuits as sensors as catalysts as optical elements in future nanoscale optical devices. Gold and silver nanorods have distinct visible absorption and scattering spectra that are tunable with aspect ratio. Many workers have developed wet synthetic routes to these nanomaterials, with control of aspect ratio a key improvement compared to the synthesis of simple nanospheres. Another key area for which improvements need to be made is the understanding of the atomic arrangements of the different faces of crystalline... 

One-dimensional nanostructured polymer composite materials include nanowires, nanorods, nanotubes, nanobelts, and nanoribbons. Compared to the other three dimensions, the first characteristic of one-dimensional nanostructure is its smaller dimension structure and high aspect ratio, which could efficiently transport electrical carriers along one controllable direction, thus is highly suitable for moving charges in integrated nanoscale systems (Tran et al., 2009). The second characteristic of one-dimensional nanostructure is its device function, which can be exploited as device elements in many kinds of nanodevices. With a rational synthetic design, nanostructures with different diameters/... 

Nanomaterials represent today s cutting edge in the development of novel advanced materials, which promise tailor-made functionality for unique applications in all important industrial sectors. Nanomaterials can be clusters of atoms, grains 100 nm in size, fibers that are less than 100 nm in diameter, films that are less than 100 nm in thickness, nanoholes, and composites that are a combination of these. In other words, it implies that the microstructures (crystallites, crystal boundaries) are nanoscale [1]. Nanomaterials include atom clusters, nanoparticles, nanotubes, nanorods, nanowires, nanobelts, nanofilms, compact nanostructured bulk materials, and nanoporous materials [2]. Materials in nanosize range exhibit... 

M.-C Wu, et al.. Nanoscale morphology and performance of molecular-weight-dependent poly(3-hexylthiophene)/Ti02 nanorod hybrid solar cells. Journal of Materials Chemistry, 2008. 18(34) p. 4097-4102. 

When one of the dimensions of the material is in nanoscale, the material is known as a nanomaterial. Depending on the procedure for synthesis, the shape and size of the polymeric nanomaterial is altered. Hence the optimization process in the synthesis of any polymeric nanomaterial is critically important for its reproducibility. Various morphologies possessed by the electronically conducting polymeric nanomaterials are nanoparticles, thin films, nanotubes, nanorods, etc. Some special kinds of morphologies such as flower-like, dendritic, fibril-like, etc., are also foimd to exist. Some of the three-dimensional architectures contain the combination of various morphologies of the same polymeric material. The various structures are particularly important to their application. For example, for electrode purposes, the materials should have large surface area and hence three-dimensional nanostructures are preferred. 

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