Narrow Results

The Fermi level for a multiwalled carbon nanotube is determined analytically by using the Fermi velocity obtained from the particle-in-a-box model. Fermi energy is found to be quantized so that the corresponding quantum number coincides with the wall number. In addition, the classical limit is discussed.

We have investigated the electronic and magnetic properties of GaC_1-xMn₃ (x = 0, 0.125, 0.25) using first-principles density functional theory within the generalized gradient approximation (GGA) + U schemes. The crystal structures of the compounds are cubic for x = 0, 0.125, 0.25. The lattice parameters and unit cell volume decrease as the C vacancy increase. Our spin polarized calculations give metallic ground state for x = 0, 0.125, 0.25. The magnetic structure for x = 0, 0.125 are antiferromagnetic, while for x = 0.25 it is ferromagnetic. From the density of states (DOS), the hybridization between the C 2p and Mn 3d state is the main reason for magnetic transition.

The processes of charge transport on alternating current in ${({\mathrm{\text{TlGaSe}}}_2)}_{1-x}{({\mathrm{\text{TlInSe}}}_2)}_x$ solid solutions have been studied. It has been established that in weak alternating electric fields, there is a hopping mechanism of charge transfer over localized states in the vicinity of the Fermi level. A quantitative assessment of parameters was made in the framework of the effective medium theory and the Mott approximation. The use of impedance spectroscopy methods in ${({\mathrm{\text{TlGaSe}}}_2)}_{1-x}{({\mathrm{\text{TlInSe}}}_2)}_x$ solid solutions in the frequency range of 25–106 Hz, at temperatures of 180, 240 and 300 K charge transfer processes has been investigated. It was found that at 300 K in the low-frequency region, there are additional contributions to the conductivity, which, apparently, is associated with diffuse ion transfer near the boundary of the solid electrolyte and the electrode. Impedance locus curves, at low frequencies and at a temperature of 300 K, are characteristic of Warburg diffuse impedance.

The frequency dependence of the thallium sulfide (TlS) crystal impedance is analyzed in wide frequency and temperature range for the hopping and superionic conduction mechanisms. It has been established that in weak alternating electric fields, there is a hopping mechanism of charge transfer. The use of impedance spectroscopy methods in TlS crystals, at temperatures of 300, 350 and 400 K in the frequency range of 2*10⁶ Hz and subjected to $\gamma$-irradiation doses 0, 0.25 and 0.75 MGy charge transfer processes, has been investigated. Hodographs constructed from the data of experimental measurements of 400 K, in the low-frequency region ($>10^3$ Hz) and regardless of the absorbed gamma quanta, indicating additional contributions to the conductivity, presumably corresponds to the fact that in the frequency range of the applied signal, carrier diffusion does not reach the diffuse layer. This type of hodographs at low frequencies is characteristic of the Warburg impedance.

Magnetic properties of Ag₂S doped with 3d-transition metals were studied using density functional theory (DFT). It was found that magnetic elements such as Co, Cr and Mn cause magnetism in the structure. The nature of this magnetism is mainly from the 3d-states of the magnetic elements. The magnetic moment of supercells containing various concentrations (x= 2.08%, 4.1%, 8.3%) of dopant atoms has been studied. It was determined that the contribution of the magnetic elements is significant in the total magnetic moment of supercells. Calculation results reveal that when doped with impurity atoms, supercells show half metallicity and ferromagnetic (FM) nature which makes them the best candidate to be used in the field of spintronics.

Oxygen adsorption on the surface of polycrystalline palladium has been studied by the photoelectron spectroscopy method in a wide range of oxygen exposure and temperatures, starting with the earliest stages of adsorption to the formation of the surface compound of PdO-type. Based on the analysis of the experimental data and the calculation of the density of states carried out by the TB-LMTO-ASA method, the attempt to elucidate the electronic mechanism of adsorption and oxidation power of palladium was made.

We report on the fabrication of carbon nanotube field effect transistors (CNTFETs) from dispersed single-walled CNTs using OCMC (O-Carboxymethylchitosan) as the surfactant. The as-prepared devices exhibit p-type as well as ambipolar characteristics due to oxygen adsorption at the metal/nanotube contacts. The Raman scattering from the SWCNTs shows that OCMC disperses CNTs efficiently. Rapid thermal annealing (RTA) at 400°C for 5 min is found to partially remove OCMC from the surface of SWCNTs.

We have explored the interaction of Ni/Cr with pyridinic N-doped graphene and its influence on the electronic and magnetic characteristics of graphene using a density functional theory (DFT) approach. A $5\times 5$ graphene supercell with a single vacancy is modeled. Initially, the concentration of nitrogen atoms is varied in the pyridinic configuration of graphene. The structures, thus obtained, are decorated with Ni/Cr atoms. For configurations without transition metals (TMs), the calculated electronic band structures show a downward shift in Fermi level that decreases as nitrogen concentration increases. Furthermore, it is found that these structures manifest metallic behavior along with some flat bands near the Fermi level. With the addition of Ni/Cr atoms, the movement of the Fermi level toward the conduction band is noticed. The opening of the bandgap at the K-point also varies slightly with the concentration of N atoms and/or the presence of TM atoms. The structures P1N-Ni and P2N-Ni transmute into semiconductors. A significant increase in the magnetic moment is found with the adsorption of the Ni/Cr atom. The analysis of spin-polarized partial density of states proves that higher magnetic moments following TM absorption are mainly on account of the Ni/Cr-3d orbitals and their hybridization with C-2p orbitals. These findings suggest that functionalizing TMs on pyridinic N (Nitrogen)-doped graphene can drastically alter their electronic and magnetic properties.