N.A. Volchkov

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.

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.

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.

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.

Pulsed-laser deposition of “diamond-like” carbon coating on YBa2Cu3O7 high-Tc superconductor films

Abstract The possibility of fabrication of diamond-like coating on high- T c superconductors is investigated. Carbon thin films were deposited on single-crystal YBa 2 Cu 3 O 7 film substrates by pulsed-laser sputtering of graphite targets. Deposition at room temperature yields diamond-like films with high optical transmission, high resistivity, and good adhesion to unpretreated substrates. 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.

Conducting media with spatial dispersion in a microwave field: eigenvalue problem for permittivity operator

Conducting media with the spatial dispersion may be described formally by a singly operator – an operator of a dielectric permittivity, which completely defines a microwave response of conductors with the spatial dispersion. So the eigenvalue problem for the permittivity operator of conductors and superconductors possessing a strong spatial dispersion at low temperatures is of a great importance since the corresponding solutions are the stable waves for the constitutive equation in a self-consistent microwave field. Here a wave problem is formulated to search the solutions, which correspond to the eigenvalues of a permittivity operator, similar to the relationship and the general solutions are obtained. A significant role of the spatial-type conjugated. Dispersion relationship and general solutions are obtained. A significant role of the spatial-type force resonances is considered. Conditions for the spatial resonances are derived. The obtained resonances include particular solutions corresponding to the related to a polarization, two of which correspond to waves with an amplitude increasing into the depth of a conductor, and two else describes solutions with unusual properties.

The novel THz generation and detection possibilities of resonant-tunneling based semiconductor multiple-quantum well nanostructures

Development of physical principles of THz-wave amplification and oscillation is one of problems determining progress in modern solid state electronics towards high frequencies and ultrahigh performance. Novel perspectives are tied with use of resonant tunneling quantum effects, characterized by transient times less than 1 ps, comparable with fast response of superconducting devices. The information about these properties can be obtained from investigation of high-frequency oscillations or current-voltage switching phenomena in resonant-tunneling (RTD) nanostructures. In the paper the results of theoretical and experimental studies of high-frequency properties of RTD elements in subterahertz and terahertz frequency range are presented basing on developed theory of high-frequency response in RTD as well as on experimental high-frequency investigation data and current-voltage switching phenomena investigation results of effects correspondingly related to stationary current characteristics changes in single-quantum-well as well as in doublequantum- well resonant-tunneling diode nanostructures under external electromagnetic electrical field.

Control over the lateral distribution of hydrogen content in the pulsed-laser deposited diamond-like carbon films

We propose a method of controllable variation of the hydrogen content along the lateral direction of the pulsed-laser deposited DLC films. Hydrogen incorporates into the film by the adsorption of atmosphere hydrocarbon molecules on the growing surface in a vacuum chamber. The variation of hydrogen content is provided by use of the angular distribution of a carbon mass flow in a laser plume and by means of cleaning off the adsorbed hydrocarbons with help of impinging by laser-ablated carbon particles under oblique angles to the substrate. Deposition of DLC films at different angles of incidence of laser-ablated carbon flow reveals the decrease of the hydrogen content at the periphery of the film from 22 down to <3 at% as the angle changes from normal to the oblique one, while hydrogen content in the centre of the film remains nearly constant at a level of 10 at%.

Diamond-like coating prepared by pulsed laser sputtering of graphite in a high-vacuum environment

Abstract A method of diamond-like coating deposition on silicon and quartz, that can be compatible with growth processes of semiconductor and superconductor films, is described. These carbon thin films were prepared by pulsed laser sputtering of a graphite target in a high-vacuum (∼ 10−6 Torr) environment. Investigations by a variety of spectroscopic techniques demonstrate that the films have a high density (∼ 2.9 g/cm3) close to the density of diamond, a high ratio of sp3 to sp2 bonding ( 0.75 0.25 ), and IR transparency. The films were hard, adhesive to the substrate and had a high resistivity. It was found that hydrogen is incorporated into the films up to ∼ 10 at% due to reactions of sputtered carbon particles with residual hydrocarbons in the high-vacuum environment.

The spatially dispersive eigenvalues of permittivity operator and frequency-dependent surface impedance for conductors without the dc dissipation

An operator of the permittivity can completely describe alone a microwave response of conductors with the spatial dispersion. An eigenvalue problem for the nonself-adjoint permittivity operator Ễa was considered generally to search the wave solutions for conductors and superconductors. An appearance of additional solutions (additional waves) due to the spatial dispersion can strongly influence the properties of nanoelectronic devices or novel superconducting materials in the form of anomalous losses for example, and should be accounted in simulation and modeling of micro- and nanoelectronic devices. It was concluded that the modulus |Ž| of the surface impedance is proportional to the degree of frequency ω2/3 for all normal conductor solutions except that for the superconductor. There was some criticism related to the idea that the electrodynamics of superconductors should be in principle reduced to those for conductors as the temperature approaches and beyond the critical temperature. We demonstrate that appropriately taken into account effects of the spatial dispersion can give the general frequency dependence of the surface impedance for the obtained solutions including that for the superconductor. It is shown that an incorporation of the spatial dispersion leads to an appearance of the Meissner effect in perfect conductors in the same manner as in superconductors.