A. I. Fedorenko

Schwarzschild soft-x-ray microscope for imaging of nonradiating objects

A soft-x-ray optical system based on multilayer mirrors was designed and fabricated for the production of magnified images of micro-objects with a spatial resolution of ~0.2 μm at a wavelength λ ≈ 20 nm. The system consists of a laser-produced plasma source, a condenser mirror, a 20× Schwarzschild objective, a filter set, and a detector. The quality of the x-ray optics and the precision of the system adjustment enabled us to achieve, for the first time to our knowledge, ~0.2-μm resolution using the full aperture (numerical aperture 0.2) of the objective and a single shot of a frequency-doubled Nd laser (pulse energy ~0.5 J, pulse duration ~1.5 ns).

(001)-oriented lead selenide films grown on silicon substrates

Abstract Lead selenide epitaxial films were grown on silicon substrates using a thin (⩽100 nm) YbS buffer layer. The films were (001)-oriented and had structural, electrical and photoelectrical properties comparable with those of PbSe bulk crystals. The X-ray rocking curve halfwidths were of 100–200 arcsec which are within similar values for PbSe/BaF2(CaF2)/Si films, thoroughly investigated for infrared detector array applications. The films investigated exhibit relatively large photosensitivity in the temperature range T = 80–300 K. Minority carrier lifetime values τ ≈ 10−6s at 80K and their temperature dependencies are preferably determined by the Schockley-Read-Hall recombination mechanism through the deep levels in the band gap.

The epitaxial growth of IV-VI heterostructures and superlattices on (001) Si

We report for the first time the use of rare-earth chalcogenides as buffer layers on silicon substrates prior to the high vacuum epitaxy of IV–VI compounds for the growth of thin film heterostructures and superlattices. The results of X-ray diffraction characterisation showed that YbS grows at 900–950 °C on (001) Si as a high-quality single crystal layer with an X-ray rocking curve half width δ = 300–500 arcsec. Such buffer layers allow us to grow single-crystal IV–VI films and various types of heterostructures and superlattices with crystal quality better than that achievable in the buffer layer (with δ = 100–300 arcsec), over a large area with good uniformity.

Band offsets in Eu-containing lead chalcogenides and lead chalcogenide superlattices from spectroscopic data

The results of an experimental study of the optical and photoelectrical properties of Eu-containing lead chalcogenides and superlattices are presented. From both sets of experiments band offset data for the lead chalcogenide-europium chalcogenide heterojunction are derived. The results are compared with the data obtained from a linear interpolation of the band structures between those of the binaries.

The galvanomagnetic properties of short-period SnTePbTe superlattices

Abstract (001) oriented SnTe PbTe superlattices (SLs) with the period in the range of 9–60 nm are grown. The temperature dependence of the conductivity, the Hall coefficient and the magnetoresistance anisotropy are investigated in the SLs in the temperature range of 1.5–300 K and magnetic fields up to 1.5 T. The SLs are of n-type with the apparent electron concentration in the range of 1019–1020 cm−3. The type II band ordering is concluded for the SLs. Below 6 K the SLs exhibit superconductivity. The superconductivity is suggested to have a local character and to be associated with the strained pseudomorphic SnTe layers.

Superconductivity in the novel semiconducting superlattices

Novel superconducting superlattices (SL) with transition temperature 4–6 K consisting only of semiconducting materials are discovered. Among them there are multilayers containing ferromagnetic chalcogenide EuS. Single films of the semiconducting materials constituting SL do not reveal superconductivity, and it appears only in multilayered systems. It is shown that superconductivity is confined to the interfaces between two semiconductors. The possible correlation between superconductivity and interfacial regualr grids of misfit dislocations is discussed.

Structural investigations of superconducting multilayers consisting of semiconducting materials

There are rather exotic semiconductor superlattices (SL) consisting of monochalcogenides of Pb, Sn, and rare-earth metals which exhibit superconductivity at temperature as high as 6 K. Here we report the results of precision x-ray diffractometry and TEM investigations as well as Auger spectroscopy data obtained on some of the epitaxially grown superconducting semiconductor SLs. It is established that the essential features of the SL structure determining the appearance of superconductivity are the perfect single-crystallinity of the samples and the presence of continuous dense grids of misfit dislocations on the interfaces between two semiconductors. The segregation of free Pb which was observed in some cases does not correlate, according to experimental data, with the appearance of superconductivity.

Oscillations and quantization of resistance at the temperature critical points of PbS-PbTe-PbS three-layer films on (001) KCl

Oscillations and a set of inflection points have been discovered in the temperature dependences of the resistance of single-crystal PbS-PbTe-PbS three-layer films on (001) KCl. Extrema and inflection points are observed at the temperatures (m/n)T0 (T0=5.238 K), and at these temperature critical points the resistance of the samples takes one of the values (p/q)RQ, where RQ=25812.8 Ω is the resistance quantum; and m, n, p, and q are integers.

HTSC-like superlattices PbTePbS microwave spectroscopy

Abstract For the first time magnetic field nonresonant microwave absorption at 9.4 GHz in the thin film superconductive superlattices (001) PbTePbS (Tc=5.5 K) was investigated. These superlattices may be considered as structural HTSC models. It was found that absorption in the superlattices has similar peculiarities to ones in HTSC thin films. The influence of modulating magnetic field on the conditions of formation of various hysteretic absorption signals was analysed.

Magnetic-field oscillations of the critical current and the pinning force in PbTe/PbS semiconductor superlattices and YBa2Cu3O7–δ films

The magnetic-field dependences of the critical current Ic and the pinning force Fp in single-crystal semiconductor PbTe/PbS superlattices on KCl and YBa2Cu3O7–δ films in magnetic fields oriented perpendicular to the plane of the samples or parallel to the current were investigated. Oscillations of Ic and Fp were observed for superlattices with a parallel orientation of the magnetic field and with two directions of the field for the YBa2Cu3O7–δ film. A model was proposed for the vortex structures which correspond to extrema of the pinning force in superlattices. It was shown that the single points (extrema and points of inflection) of the field dependences of Fp for superlattices and a YBa2Cu3O7–δ film appear for critical values of the magnetic field equal to Hcr = (p/q)H0, where p and q are integers, H0 = 838.37 Oe, and H0 = ch/π eR02 is determined by the length R0 = 88.607 nm, somewhat less than the reciprocal of the Rydberg constant R∞ = me4/πħ3c (R∞−1 = 91.127 nm). It was inferred on the basis of published data that the temperature and magnetic-field dependences of the properties of superlattices and HTSC materials follow general laws.