A.L. Karuzskii

Studies of nanoscale structure and its transformation in pulsed-laser deposited dense diamond-like carbon films

Abstract Dense diamond-like carbon (DLC) thin films were deposited at room and liquid nitrogen temperatures on Si and SiO 2 substrates by pulsed-laser sputtering of a graphite target in a high-vacuum (≈10 −6 Torr) chamber. The high density (≈3.05 g/cm 3 ) of the films was evaluated by comparison of the intensity of carbon core electron excitation energy peaks in X-ray photoelectron spectra (XPS), measured for diamond, graphite and DLC films. Direct experimental evidence is presented for the first time that DLC films deposited at room temperature are essentially amorphous. Graphite nanocluster formation is observed as the appearance of a graphitic nanocluster system suspended in a dense sp 3 amorphous matrix. Data obtained by Raman spectroscopy, IR vibrational spectroscopy, XPS, electron energy-loss spectroscopy (EELS) and transmission electron microscopy (TEM) show that the transformation of the amorphous mixture of sp 3 and sp 2 bonded carbon atoms into the graphitic nanocluster system occurs as a result of the ordering of the sp 2 bonded carbon atoms in the process of annealing at temperatures which are only about two times higher than the temperature of deposition.

Measurements of the effective electrodynamical parameters of Nb microstrip resonator

Abstract An experimental method for simultaneous determination of the effective dielectric permittivity and the effective length of a microstrip resonator is developed. The method is based on partial filling of a resonator cavity by the dielectric medium with low, controllably variable permittivity. For microstrip resonators partially filled with helium, the reciprocal linear dependence of squared frequency on helium permittivity was found experimentally. Coefficients of this linear dependence have been related to the effective permittivity and the effective length of the microstrip resonator. The proposed technique for prompt and precise determination of the effective parameters of a microwave unit needs neither special test fixtures and circuit standardization nor additional model assumptions. Effective parameters have been measured for superconducting halfware microstrip resonators in microwaves.

Additional microwave modes in systems with conductivity of metals and superconductors

Semiclassical model, which takes into consideration the spatial dispersion effects in conductivity and permittivity, demonstrates the possible appearance of additional waves in conducting media, which are known to exist in transparent dielectrics near a narrow absorption band. The dispersion law of additional waves for modelling media (one-dimensional conductance) with parameters of Cu and Nb is obtained, which predicts the novel phenomenon—the possibility for additional microwave modes to propagate in metals with low enough attenuation at cryogenic temperatures.

Resonant tunneling and intersubband population inversion effects in asymmetric wide quantum-well structures

Abstract Theoretical estimates and the results of vertical transport and optical investigations in GaAs/AlGaAs structures show that resonant tunneling can lead efficiently to selective depopulation of the levels, resulting in a population inversion and possible stimulated emission due to intersubband transitions between the lowest states in wide-quantum-well structures.

Polariton-like interaction between microwaves and electronic subsystem of metal oxide superconductor

Abstract In studying the microwave (10 GHz) response of both single crystal and ceramic samples of the YBa 2 Cu 3 O 7 in Nb resonator we have found dielectric permittivity dependent strongly on wave-vector resulting in appearance of the new dielectric resonances with hysteretic temperature behaviour. Data show the importance of the non-conducting “bound” electron polarization in strong local fields and spatial dispersion, which lead to the polariton-like interaction between microwaves and electrons in a high-T c superconductor. The effects of the polariton-like microwave excitations on the limiting mechanisms in superconducting cavities are discussed.

Phenomenological model of microwave electrodynamics of high-Tc superconductor metal oxides

Abstract Phenomenological model of microwave electrodynamics of the metal oxide high-T c superconductors (HTSC) is presented. The model takes into account the effects of the finite complex dielectric permittivity and of the local (acting) electric fields in semiclassical interpretation of the current carrier dynamics. The effects should be significant due to the layered structure and the metal-insulator type instability of HTSC metal oxides. Microwave electrodynamics of the superconducting state of HTSC is described on the base of the general two-fluid principles. The full expressions for the complex dielectric permittivity and for the surface impedance are derived and used to relate the current carrier parameters with the data of microwave measurements.

Microwave nonlinear effects in He-cooled superconducting microstrip resonators

Abstract Nonlinear phenomena in superconducting niobium microstrip-like resonators filled by liquid helium are studied in microwaves. The found nonlinear resonance is explained by thermally induced variations of the helium dielectric permittivity caused by the microwave power losses in superconductor. A number of interesting manifestations of this thermal instability have been observed including the parametric pulse generation of the monochromatic microwave signal, generation of acoustic pulses.

Pulsed-laser deposited protective ‘diamond-like’ carbon coatings on high-Tc superconductors

Abstract The fabrication of diamond-like coating on high- T c superconductors is investigated. Carbon thin films were deposited on YBa 2 Cu 3 O 7 single-crystal film by pulse-laser sputtering of graphite targets. Deposition at room temperature yields diamond-like films with high optical transmission, high resistivity, and good adhesion to unpretreated YBa 2 Cu 3 O 7 . Degradation of superconducting properties or deterioration of mechanical characteristics of YBa 2 Cu 3 O 7 films was not observed after carbon deposition and subsequent low temperature thermocycling. The water-protective properties of these diamond-like coatings were investigated.

Intersubband population inversion under resonance tunnelling in wide quantum well structures

The possibility of intersubband population inversion and the necessary conditions for its achievement in wide quantum well structures with the energy space between the lowest states being lower than the optical phonon energy are considered. Two possible designs are proposed, both using resonant tunnelling for selective depopulation of the lowest subband. The analysis of resonance tunnelling times and intersubband relaxation rates due to various scattering processes is carried out, demonstrating the possibility, at sufficiently low carrier concentrations, of inverted carrier distributions over the lowest subbands under optical pumping or electrical injecting conditions.

Experimental evidence for spatial dispersion effects and the change of sign of dieletric permittivity in superconductors from microwave measurements

Abstract Short-scale spatial modulation of the resonance field in a microstrip resonator revealed by experiment was used to study the spatial dispersion effects in dielectric properties of Nb and YBa2Cu3O7 superconductors. The results show a negative sign of a real part of e(ω,k) the dielectric permittivity, which absolute value drastically depends on configuration of the electric field, suggesting strong spatial dispersion effects in these materials.