JOURNAL OF THEORETICAL AND APPLIED PHYSICS (IRANIAN PHYSICAL JOURNAL)
Year:2010 | Volume:4 | Issue:3|Papers Count:8

This work covers the analysis of the nonmagnetic-catalyzed plasma chemical vapor deposition (PCVD) of single walled carbon nanotubes (SWNTs). The selective growth of SWNTs by the nonmagnetic catalyst using PCVD is realized for the first time. Experimental investigations are presented, which allow to get a comprehensive picture of the nonmagnetic catalytic growth of SWNTs by PCVD. The PCVD growth of SWNTs is performed on an alumina supported Au catalyst using methane as a carbon source. The methodologies to accomplish the controlled growth of SWNTs, i.e., diameter, density, and chirality are investigated. The Au catalyst can afford the SWNTs growth with narrow diameter and chirality distribution with PCVD by carefully adjusting the experimental parameters. Methane PCVD on the Au catalyst under well-defined conditions produced predominantly (6,5) SWNTs according to Raman, UV-Vis-NIR absorption, and photoluminescence excitation/emission (PLE) spectroscopic characterizations. The high yield of (6,5) semiconducting SWNTs produced by the structure controlled synthesis described above is promoted us to directly use the as-synthesized SWNTs for constructing nanotube field effect transistors (FETs), which suggests the SWNTs grown from the nonmagnetic catalyst with PCVD display the best device performance in comparison with thermal chemical vapor deposition (TCVD) synthesized and magnetic catalyzed SWNTs based devices. Based on the magnetic measurements with the Au catalyzed SWNTs, we observe that the nonmagnetic catalyzed SWNTs show ferromagnetic features, which suggest that the ferromagnetic features might come from the SWNTs itself. Hence this narrow-chirality distributed Au catalyzed SWNTs selectively grown with PCVD could be attractive to both fundamental studies of intrinsic magnetic properties of SWNTs and industrial applications to nanoelectronics.

The electronic properties of double-wall zinc oxide nanotubes (DWZnONTs) are investigated via density functional theory. The DWZnONTs are separated into two categories¸ where the inner and outer nanotubes are armchairarmchair and zigzag-zigzag single-wall nanotubes. The band structure of the DWZnONTs is calculated. Our results show that the inter-wall coupling diminishes the energy gap in semiconducting nanotube. We found that the energy gap of DWZnONTs depends on the structure of the inner and outer walls.

In this paper, we have studied the transport properties of disordered four-terminal graphene nanodevice in the presence of perpendicular magnetic field, using Landauer approach and tight binding model. The results of our investigation imply that in the presence of random disorder the transport of the system decreases because of Anderson localization. Furthermore, the broadening widths of landau subbands become large in the presence of random disorder and magnetic field. The existence of divacancy and magnetic field creates additional band between landau levels, this appeared by increasing the transmission of the injected electron. In addition, we found that the coupling between two vacancies due to “vacancy molecule” and bonding between them can be tuned by the magnetic field. These theoretical studies can be useful to design the electronic nanodevice.

Two aspects of b-quark decays are investigated. First, according to the structure of penguin decays and second, according to the Effective Hamiltonian theory. In this work, the gluonic penguin term is calculated according to the structure of penguin for various b and `b quark decays. The total gluonic penguin amplitude to lowest order in as is used for the decay process, b®qkg ®qkq’`q (qkqi`q)i=j. The magnetic dipole gluonic penguin term for various b quark decays is calculated. The tree-level and gluonic penguin terms of b-quark are also added to calculated the decay rates of b and `b quark. It is shown that the gluonic penguin term is small for some decay. The decay rates of processes like b®cd`c (`b®cd`c(`b®`c`d),b®cs`c(`b®`c`sc) and b®us`u,(`b®`u`su) is obtained.

The growth of ZnO nanowires as a function of the thickness of Au thin layers, deposition temprature and surface properties through simple carbothermal evaporation method is studied. Investigations by X-ray diffraction (XRD) revealed the (002) plane as the preferred plane for the growth of ZnO nanowires. Our experiments indicated that the temperature range of 800-900°C under flow of 100 sccm N2 gas with Au catalyst layer, is the suitable condition for producing the most aligned nanowires. The Vepour – Liquid - Solid (VLS) mechanism more than other mechanisms is dominant for growth process.

A low cost corona gun plasma system that works at atmospheric pressure and operates with high voltage power supply was tested for its biocidal effect on Escherichia coli bacteria as Gram-negative bacteria and different microorganisms of commercial turmeric (curcuma longa) as a combination of both Gram-negative and Gram-positive bacteria and results are compared. In these experiments, the Escherichia coli bacteria with a population of 4.4 ´107 cfu/ml were perfectly sterilized after 5 seconds irradiation of plasma generated by the corona gun, while it took about 80 s for sterilizing the microorganisms of turmeric samples. Results show that, with increasing the discharge energy and plasma exposure time, the rate of sterilization increases. Their survival curves are straight lines with two slopes for Gram-negative bacteria and three slopes for microorganisms in turmeric.

The concept of local homogenization is employed for estimation of the relative permittivity scalars in copper Sculptured Thin Film (STFs). Three absorption transitions of dielectric to metal occur in the copper STFs. These transitions reduce to two in columns with circular cross section, when the volumetric fraction of metallic particles increases from zero to unity. The first transition occurs at low volumetric fraction of metallic inclusions and the other two transitions appear at high volumetric fraction of metallic inclusions. The influence of the column shape factors on the absorption transitions of dielectric to metal is also reported.

The ”massless” vector field equation in de Sitter (dS) 4-dimensional space is gauge invariant under some special gauge transformations. It is also gauge invariant in ambient space notations in which the field equation is written in terms of the Casimir operators of dS group. In this paper the "massless" vector field equation has been solved in the physical case. It has been shown that the solution can be written as the multiplication of a generalized polarization vector and a ”massless” conformally coupled scalar field in the ambient space notations. The physical vector twopoint function has been calculated using ambient space formalism and its zero curvature limit has been considered. It is shown that the physical vector two-point can be written in terms of the conformally coupled massless scalar two-point function in the ambient space notations. The two-point function is expressed in terms of dS intrinsic coordinates from its ambient space counterpart, which is dS-invariant and is free from any divergences.