Electrostatic models of insulator-metal and metal-insulator concentration phase transitions in Ge and Si crystals doped by hydrogen-like impurities

Two electrostatic models have been developed that allow calculation of the critical concentration of hydrogen-like impurities in three-dimensional crystalline semiconductors corresponding to the insulator-metal and metal-insulator transition in the zero temperature limit. The insulator-metal transition manifests itself as a divergence of the static permittivity observed in lightly compensated semiconductors as the concentration of polarizable impurities increases to the critical level. The metal-insulator transition is signaled by the divergence of the dc electrical resistivity in heavily doped semiconductors as the compensation of the majority impurity increases (or its concentration decreases). The critical impurity concentration corresponds to the coincidence of the percolation level for the majority carriers with the Fermi level. The results of the calculations made with these models fit the experimental data obtained for n-and p-type silicon and germanium within a broad range of their doping levels and impurity compensation.     

Ramo-Shockley relation for a series <Emphasis Type="Italic">RCL</Emphasis> circuit

The current induced by the passage of an external point charge through a plane vacuum capacitor in an RCL circuit free of current (voltage) sources is calculated. The case is also analyzed when an internal point charge is emitted by one of the capacitor plates, moves to the other plate, and is absorbed by it. A technique is proposed to measure the internal charge and its velocity component perpendicular to the capacitor plates in a passive RCL circuit.     

Screening of an Electric Field and the Quasi-Static Capacitance of an Induced Charge in Semiconductors with Hopping Conductivity

Expressions for the screening length of an external electrostatic field in a crystalline semiconductor are derived in the Debye–Hückel and Mott–Schottky approximations taking into account electron (hole) hopping via hydrogen-like donors (acceptors). The feasibility of determining the Debye–Hückel screening length from measurements of a quasi-static capacitance with low and high degrees of basic dopant compensation has been demonstrated even in a strong field, that is, in the Mott–Schottky approximation. To measure the capacitance, the electric signal frequency must be much less than the average frequency of electron hopping via donors.     

Interwall conductance in double-walled armchair carbon nanotubes

The dependence of the interwall conductance on distance between walls and relative positions of walls are calculated at the low voltage by Bardeen method for (n,n)@(2n,2n) double-walled carbon nanotubes (DWCNTs) with n=5,6,…,10. The calculations show that interwall conductance does not depend on temperature (for T?500 K) and current-voltage characteristic is linear. The conductance decreases by 6 orders of magnitude when the interwall distance is doubled. Thus, depending on the interwall distance, DWCNTs can be used as temperature stable nanoresistors or nanocapacitors.     

Electrochemical co-deposition for the synthesis of PtPb electrocatalysts

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Totally symmetric vibrational modes of fullerene C60

Semiempirical molecular orbital calculations are carried out for the totally symmetric vibrations of the C₆₀ molecule. The calculated equilibrium geometry coincides with the precision experimental data to within measurement error. The ratio of force constants calculated for the two different types of C-C bonds in fullerene is equal to 1.389. A comparison of the computational results with the Raman scattering data indicates that there may be Fermi resonance between the totally symmetric vibrations.     

Coulomb Distortion of Carbododecahedron C20 2+

The electronic structure, geometry, and potential energy surface of the dication of carbododecahedron C₂₀ ²⁺ have been investigated by the PM3 semiempirical method of molecular orbitals. An analog of the Jahn–Teller dynamic effect for this system is revealed, caused by the repulsion of uncompensated positive charges on carbon atoms (Coulomb distortion). The D ₃ symmetry of the ground state of C₂₀ ²⁺ is predicted. The IR vibrational spectrum of the dication of carbododecahedron is calculated, the observation of which could confirm the predicted effect. Evaluational calculations of C₂₀ ⁺ and C₂₀ are also carried out.