ABSTRACT:Hydrogen atom in a cylindrical cavity is the simplest model for describing electronic states of the atom encapsulated into the nanotube. In the present work, simple analytical estimates for the electronic energy change under longitudinal and transversal shifts of the nucleus are made, using the first-order perturbation theory with the radius of the cavity as a perturbation parameter. Predicted signature of the electronic energy for the variety of atomic states agrees in essential details with the direct numerical estimations by finite difference and collocation procedures.

Effect of gate oxidation method on electrical properties of metal-oxide-semiconductor field-effect transistors fabricated on 4H-SiC C (0001) face Appl.The key stages of the dry oxidation of the SiC͑0001͒ surface are analyzed based on first-principles calculations. It is found that an abrupt SiC/ SiO 2 interface model results in a large activation barrier of oxygen penetration to the silicon carbide, and thus the penetration is probably the rate-limiting step for the entire dry-oxidation process. The subsequent reactions of SiC oxidation after oxygen penetration are investigated, and it is found that CO release is competing with carbon dimer formation. These dimers probably are responsible for near-interface traps in the silica layer generated during SiC oxidation. The possible passivation reactions of a carbon dimer defect by active species, such as O 2 , NO, and H 2 are investigated. It is found that an oxygen molecule can break a Si-C bond via dissociation in the triplet state and finally can produce two CO molecules from the carbon dimer defect. The NO molecule can easily break a Si-C bond of a carbon dimer defect and form cyano groups -CN, which can finally recombine to form a C 2 N 2 molecule. This molecule can hardly diffuse in silica matrix, and it is suggested that it is further oxidized by an NO molecule to CO and N 2 molecules. It is suggested that the process of passivation by O 2 and NO molecules is restricted by the incorporation of these molecules in small voids near the carbon defect. Based on the calculated results, a simple kinetic mechanism of dry SiC oxidation is proposed and kinetic modeling of the oxidation process is performed. It is found that in the framework of this mechanism, the carbon defect density should weakly depend on temperature.

The problem of a hydrogen atom in an impenetrable spherical cavity of small radius R is considered on the basis of the first-order perturbational treatment of the electron-nucleus interaction taking explicit account of the boundary condition. An approximate analytic expression is derived for the electronic energy as a function of the shift of the nucleus off the centre. The estimations obtained are in good qualitative and semiquantitative agreement with the results of the finite-difference calculations. Some general features of the energy dependences are discussed qualitatively.

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Electronic states of the cylindrically confined hydrogen atom are studied numerically by the finite difference (FD) approach. Energies of the low-lying states of the system are estimated vs. the radius R and length Z of the cylinder, as well as the position of the nucleus at the axis. Under the isotropic stretch of the cylinder with the constant ratio R ϭ Z/2, the energy level picture reminds us that in the spherically confined atom: the energies of all states regularly grow up when decreasing the size of the cavity, and the states with the same principal n, but higher values of the angular l quantum number correspond to lower energies almost everywhere. Anisotropic stretch of the cylinder from prolate to the oblate one with constant volume causes numerous level intersections and avoided crossings, with the levels ordered as 1, 2, 3␦, 2,. . ., in the prolate limit case, and as 1, 2, 2, 3␦, 3, 3,. . ., in the oblate limit case. The results of numerical calculations are in excellent agreement with qualitative consideration of the one-electron system in the impenetrable cavity by using both variational and perturbative approaches.