Nanowires Subject

A phase diagram of the EuTiOs 1-nm nanowire (R 2.5 lattice constants) in coordinates temperature T — radial stress Opp = —p,// is illustrated in Fig. 4.43a for the temperature range of 0-300 K. Figure 4.43b is a magnified in view of Fig. 4.43a for temperatures lower than 30 K, which shows the multiferroic phase boundaries at lower temperatures. The FE + PM, FE + FM and FE + AFM phases appear in the nanowires subjected to the intrinsic surface stress Opp = — i R, in contrast to the bulk material with ct = 0, which can attain PM + PE and AFM + PE phases only. The FE and FM phase transition temperatures increase with the increase in the surface stress, which in turn is inversely proportional to the wire radius in the continuous theory. 

It is important to point out that if plating is terminated before solid Au nanowires are obtained, Au nanotubules that span the complete thickness of the template membrane are deposited within the pores. We have shown that these nanotubule membranes have interesting ion [71] and molecular [72] transport properties. This will be subject of the following section. 

Synthesis forms a vital aspect of the science of nanomaterials. In this context, chemical methods have proved to be more effective and versatile than physical methods and have therefore, been employed widely to synthesize a variety of nanomaterials, including zero-dimensional nanocrystals, one-dimensional nanowircs and nanotubes as well as two-dimensional nanofilms and nanowalls. Chemical synthesis of inorganic nanomaterials has been pursued vigorously in the last few years and in this article we provide a perspective on the present status of the subject. The article includes a discussion of nanocrystals and nanowires of metals, oxides, chalcogenides and pnictides. In addition, inorganic nanotubes and nanowalls have been reviewed. Some aspects of core-shell particles, oriented attachment and the use of liquid-liquid interfaces are also presented. 

The research of the properties of Si nanostructures has been promoted by recent progress in fabrication of low-dimensional semiconductors in the nanometric scale for applications in transistor and memory devices. The electrical properties of Si nanowires, nanopillars and arrays of dots are the subject of current research. Porous Si seems now promising for applications in the field of photonics and sensing including important perspectives in biosensing. 

TTie subject of nanotechnology thus now covers the search for and synthesis of new materials of advanced technology which possess the sizes of nanometres the determination of their characteristics, and their practical application. Nanostructures are the bridge between individual atoms and molecules, where the laws of quantum mechanics apply, and bulk phases, whose properties usually result from the collective behaviour of billions of atoms. Individual nanostructures may be clusters, nanomolecules, nanocrystals, so-called quantum points, nanowires and nanotubes. They possess orderly structures and some large molecules can form single nanostructures [2], The quantum sizes and shapes of nanomolecules affect their mechanical, chemical, electrical, nuclear-electronic, electric-optical and dynamic properties. They may exhibit new, unique physicoehemical phenomena, quantitatively different from those of the bulk phase. This leads to the possible control of the action and application of nanostructures... 

While the previously mentioned processes require complex instruments and high voltages up to 20 kV with limited scale, an alternative fabrication process is realized through a template wetting. Dissolved or molten PVDF is soaked into a nanoporous template (Fig. 5.7D) (Bhavanasi et al., 2014 Whiter et al., 2014). During the formation of nanowires, the PVDF is subjected to substantial stresses which result in preferential formation of a ferroelectric p-phase. Suitable templates include anodized aluminum oxide that is available commercially with a range of sizes, pore diameters, and pore densities. Furthermore, it is possible to free the nanowire from the template via a selective etch in phosphoric acid... 

Fig. 4.41 (a) Schematics of a high aspect ratio nanowire, where P3 is the polarization along the Z-direction and p is the polar radius, (b) The stress-free EUTLO3 unit ceU in a bulk material in the antiferromagnetic phase, (c) EuTiOs unit cells subjected to the surface stress (Laplace tension) [11]... 

Not only nanoparticles of AB semiconductors can be synthesized, but also nanowires. Therefore, these have also been the subject of theoretical studies. These include the recent density-functional study of Carter et who studied the properties of GaN nanowires as a function of their diameter. These authors used two different density-functional codes, i.e., SIESTA and DMol, and studied systems whose strueture was obtained as relaxed cut-outs of the infinite, periodic crystal. 

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