F. A. Pudonin

Anomalously high low-frequency effective permittivity in a system of metal nanoislands

The low-frequency effective permittivity in a system of Co, W, and FeNi metal nanoislands in an electric field is investigated. The permittivity of films is determined from analyzing the dependences of the susceptance of the films on the temperature and the electric field. It is found that the effective permittivity of the structures under investigation has an anomalously high positive value (107–108) and that an increase in the electric field leads to a decrease in the effective permittivity and an increase in the electrical conductivity of the films. The nature of the high effective permittivity of the structures is governed by the island structure of the metal films and associated with the polarization of dipoles formed by pairs of negatively and positively charged metal nanoislands.

Detection of photoconductivity in hyperfine metal films in the visible and infrared spectral regions

Photoelectric phenomena in island metal films are investigated. The electrical conductivity and photoconductivity are measured in island films of Ti, W, FeNi, and others grown by the method of radio-frequency sputtering in argon. The photoconductivity effect is observed in metal films whose resistivity varies with temperature by the activation law of ρ ∝ exp(T0/T)0.5. This law is interpreted within the model of variable range hopping conductivity in the region of a Coulomb quasi-gap. The photoconductivity in metal films is detected in the visible and near-infrared spectral regions. The mechanisms of photoconductivity in an island metal film are discussed.

Activation conduction in metallic Island films

The differential conductivity of metallic island films of Ti, Co, W, and FeNi is investigated in the vicinity of liquid nitrogen temperatures. It is found that the temperature dependence of the conductivity of metallic island films in the insulator phase varies in accordance with the activation law σ ∝Tnexp(−E/kT). It is shown that the power of temperature in the preexponential factor varies from n = 2 to 1 upon an increase in the film thickness. In thicker films, in which a transition from the insulator to the metal conductivity phase takes place, the temperature dependence of the conductivity increases in proportion to temperature. The mechanism of conduction in metallic island films is discussed.

Effect of weak electric fields on the conduction in thin metal films

The variation of conduction in island metallic Ti, Co, W, and FeNi films in weak electric field is studied. The variation of the differential conductivity of island metallic films with an electric field at temperatures from T = 77 to 300 K is measured, as well as the temperature dependence of the differential conductivity in the same temperature range. It is shown that a thermally activated conduction mode is realized in such structures. The mechanism of variation of conductivity of island metallic films in a weak electric field is discussed.

Manifestation of quantum size effects in optics of ultrathin niobium films

The optical properties of ultrathin (∼nm) niobium films enriched with oxygen are studied by the methods of phase spectroscopy of surface electromagnetic waves (in the far-IR spectral region), IR absorption (in the mid-IR spectral region), and ellipsometry (in the visible spectral region). The films were deposited onto crystal calcium fluoride substrates by the method of high-frequency cathode sputtering. The complex permittivity of the films is calculated from the experimental data. The dependences of both the imaginary and real parts of the permittivity on the film thickness exhibit oscillations with a period of 9 Å, the real part sign being changed during oscillations.

Detection of the metal–insulator transition in disordered systems of magnetic nanoislands

We have studied the conductivity and permittivity of a series of nanoisland-type FeNi films with an effective thickness of up to 3.2 nm on different substrates. It has been observed that the quantity Re ε changes its sign at effective thickness d* ≈ 1.5–1.8 nm, because of the metal–insulator transition. Analysis of the temperature dependences of the conductivity has confirmed the existence of the metal–insulator transition at the same thickness d*. It has been concluded that the introduced effective permittivity can serve as a characteristic of island metal systems.