Nanowire materials, physical properties

One-dimensional (ID) nanostructures have also been the focus of extensive studies because of their unique physical properties and potential to revolutionize broad areas of nanotechnology. First, ID nanostructures represent the smallest dimension structure that can efficiently transport electrical carriers and, thus, are ideally suited for the ubiquitous task of moving and routing charges (information) in nanoscale electronics and optoelectronics. Second, ID nanostructures can also exhibit a critical device function and thus can be exploited as both the wiring and device elements in architectures for functional nanosystems.20 In this regard, two material classes, carbon nanotubes2131 and semiconductor nanowires,32"42 have shown particular promise. 

The fundamental physical properties of nanowire materials can be improved even more to surpass their bulk counterpart using precisely engineered NW heterostructures. It has been recently demonstrated that Si/Ge/Si core/shell nanowires exhibit electron mobility surpassing that of state-of-the-art technology.46 Group III-V nitride core/shell NWs of multiple layers of epitaxial structures with atomically sharp interfaces have also been demonstrated with well-controlled and tunable optical and electronic properties.47,48 Together, the studies demonstrate that semiconductor nanowires represent one of the best-defined nanoscale building block classes, with well-controlled chemical composition, physical size, and superior electronic/optical properties, and therefore, that they are ideally suited for assembly of more complex functional systems. 

Nanocrystal and cluster science is the study of the chemical synthesis and physical properties of individual nanocrystals and nanotubes. It seeks to understand the evolution of molecular properties into solid state properties with increasing size. Methods include so-called bottom-up chemical synthesis of nanocrystals, nanowires, and very large species, as well as physical molecular beam approaches. Advanced physical characterization of single nano-objects by local probe methods and optics is critical here. The area is intrinsically interdisciplinary at the junction of physics, chemistry, and materials science. Outstanding chemical research in nanocrystal science is often found in a wide variety of science and engineering departments. 

The divergences of dielectric permittivity and correlation radius at the critical value of the flexoelectric coefficient (related to the critical radius) give new possibilities to control the physical properties of ferroelectric materials. The effect of the correlation radius renormalization by the flexoelectric effect alters the intrinsic width of domain walls. The predicted effects are useful for design of ferroelectric nanowires with radius up to several nanometers, which have ultra-thin domain walls and reveal polar properties close to those in bulk samples. 

In recent years, nanotechnology has opened a new window on the physical-chemical properties of semiconductor materials nanostructuration. The development of nanostructured materials (nanowires, nanotubes, nanoparticles etc.) enables improvements in the response and recovery times of the sensor signal, due to the reduction of gas diffusion effects in the bulk of the material. Additionally, the sensitivity and the sensor response are also improved by the changes in the conduction mechanisms at the nanoscale and, finally, the reduction of the dimensions of the device allows the reduction of the power consumption by the system. 

When the size of a material is reduced to the nanoscale, their physical and chemical properties are dramatically changed. The separated nanostructure of polymer composites is expected to bring important improvements for polymer electronics because the size reduction of materials increases the contact surface area and lowers the interfacial impedance between the electrode and the electrolyte, and decreases the transport pathways for both electrons and ions (Shi et al., 2015). In addition, the mechanical properties for strain accommodation as well as the flexibility will be improved. A variety of nanostructures of polymer composites have been developed including zero-dimensional nanoparticles, one-dimensional nanowires/rods/belts, two-dimensional nanosheets/plates, and three-dimensional porous frameworks/networks. 

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