Semiconductors nanotubes

Figure 20. The TEM micrograph of a WS2 nanotube with a polygonal cap at the end. Such nanotube can have a built-in metal (cap)-semiconductor (nanotube body) junction (8c). [Courtesy of A. Margolin, Weizmann Institute.]...

Fig. 14.13 A carbon nanotube Schottky barrier formed from an (8,0) semiconductor nanotube joined by a 5-7 defect to a (7,1) metallic nanotube.

E. Gracia-Espino, F. Lopez-Urfas, H. Terrones, M. Terrones, Doping (10, 0)-semiconductor nanotubes with nitrogen and vacancy defects, Mater. Express, vol. 1, pp. 127-135, 2011. 

The conductance of MWCNTs is quantized. The experimental setup to measure the conducting properties involved the replacement of an STM tip with a nanotube fiber that was lowered into a liquid metal to establish the electrical contact. The conductance value observed corresponded to one unit of quantum conductance (Go = 2e /h = 12.9 kQ ). This value may reflect the conductance of the external tube because, for energetic reasons, the different layers are electrically insulated [150]. Finally, the conductance of semiconductor nanotubes depends on the voltage applied to the gate electrode their band gap is a function of their diameter and helicity [145] and the ON/OFF ratio of the transistors fabricated with semiconductor nanotubes is typically 10 at room temperature and can be as high as 10 at... 

Takagi S, Eguchi M, Tryk DA, Inoue H. Porphyrin photochemistry in inorganic/organic hybrid materials clays, layered semiconductors, nanotubes and mesoporous materials. J Photochem Photobiol C Photochem Rev 2006 7 102-26. 

FETs are actually the basic building blocks of integrated circuits. To develop circuits using nanotubes, we first have to design nanotube-based transistors. Silicon nanowires represent one of the best characterized examples of semiconductor nanotubes with the structure, size, and electronic properties controlled reproducibly (Hu et al., 1999 Cui et al., 2001a). In particular, silicon nanowires can be prepared as single-crystal structures with controllable diameters as small as 2 to 3 nm (Cui et al., 2003 Wu, 2004). Both n- and p-type FET devices can be produced with well-defined and reproducible high-performance properties... 

As the nanotube diameter increases, more wave vectors become allowed for the circumferential direction, the nanotubes become more two-dimensional and the semiconducting band gap disappears, as is illustrated in Fig. 19 which shows the semiconducting band gap to be proportional to the reciprocal diameter l/dt. At a nanotube diameter of dt 3 nm (Fig. 19), the bandgap becomes comparable to thermal energies at room temperature, showing that small diameter nanotubes are needed to observe these quantum effects. Calculation of the electronic structure for two concentric nanotubes shows that pairs of concentric metal-semiconductor or semiconductor-metal nanotubes are stable [178]. 

Since the discovery of carbon nanotubes (CNTs) in 1991 [I], the band structures for CNTs have been calculated by a number of authors [2-7], They have predicted that CNTs can be metallic, narrow- or broad band-gap semiconductors. After macroscopic quantities of CNTs were synthesized [8], it has become possible to explore their practical properties. 

Porous Membranes of Nanoparticies from Templating Against AAO Membranes Using LB Technique. AAO-porous substrate has broad applications in making metal and semiconductor nanowires, aligned mesostructured nanorods, inorganic nanotubes. 

Of the various semiconductors tested to date, Ti02 is the most promising photocatalyst because of its appropriate electronic band structure, photostability, chemical inertness and commercial availability. But currently, a variety of nanostmctured Ti02 with different morphologies including nanorods, nanowires, nanostmctured films or coatings, nanotubes, and mesoporous/nanoporous structures have attracted much attention. 

For either conventional polycrystalline semiconductors or nanotubes and nanowires to be successful, the development of model and simulation tools that can be used for device and circuit design as well as for predictive engineering must be available. Since these devices are not necessarily based on single wires or single crystals, but rather on an ensemble of particles, the aggregate behavior must be considered. Initial efforts to provide the necessary physical understanding and device models using percolation theory have been reported.64,65... 

---