Vasilij Šmatko

Plasma treatment of particulate polymer composites for analyses by scanning electron microscopy. II. A study of highly filled polypropylene/calcium carbonate composites

Plasma treatment of fracture surfaces from particulate calcium carbonate/polypropylene composites has been shown to have potential as a means for exposing filler particles in the fracture surface, particularly where fracture occurs through the matrix. It has been found that the optimum time of plasma treatment is governed by the nature of the matrix and possibly by the type of filler-matrix bond. This method of exposing filler particles in composite surfaces provides a very convenient aid in the process of characterising filler particle size distributions and composite homogeneity/heterogeneity.

Thin YBCO films prepared by low-temperature spray pyrolysis

Thin YBCO films were prepared from aerosol by a low-temperature deposition process consisting of two steps-the deposition at atmospheric pressure and firing in vacuum degraded by partial pressure of oxygen-both at temperatures not exceeding 600 degrees C. A stoichiometric 1-2-3 aqueous nitrate solution of Y, Ba and Cu constituents was used as a source of aerosol. MgO and Al2O3 substrates were heated to 140 to 160 degrees C during deposition. The obtained films were 1 to 10 mu m thick with Tc>80 K and Jc=103 to 104 A cm-2. However, detailed TG, DTG and DTA studies performed by the authors and others showed that thermal decomposition of the nitrates used only starts at temperatures higher than 200 degrees C. The use of low substrate temperatures during deposition (140 to 160 degrees C in this case) is apparently the reason for rather low Jc values. Optimization of the preparation process is suggested, which could lead to higher Jc values at processing temperatures not exceeding 600 to 700 degrees C. Such temperatures are still interesting for substrates with elevated diffusivity into prepared films.

Highly oriented Y1Ba2Cu3O7 thin films prepared in situ by vacuum co-evaporation

The thin films YBa2Cu3O7 have been prepared on single crystal (100)-SrTiO3 and (200)-MgO substrates by vacuum co-evaporation of Y, BaF2 and Cu. The substrate temperature and total film thickness have been 650-700°C and 150 nm, respectively. The X-ray diffraction, scanning electron microscopy and low-temperature electrical measurements show that prepared films are highly c-axis oriented perpendicular to the substrate, the onset critical temperature Ton ≈ 90 K, zero-resistance critical temperature is TCO = 85 K, and critical current density jC ≈ 3x105 A/cm2 at 4.2 K and zero magnetic field.

Properties of SFS heterostructures prepared by a focused-ion-beam technique

We present a study of superconductor-ferromagnet (SF) bilayers and superconductor-ferromagnet-superconductor (SFS) heterostructures of nanometer dimensions prepared by a gallium focused-ion-beam (FIB) technique. The SFS heterostructures were implemented on the basis of high-Tc superconducting YBa2Cu3Ox (YBCO) and ferromagnetic La0.67Sr0.33MnO3 (LSMO) thin films deposited by magnetron sputtering on SrTiO3 (100) single crystal substrates. SFS weak link junctions require weak link dimensions in the range of nanometer size realizable by FIB patterning. On the other hand, the focused gallium ion beam might cause unacceptable degradation of the superconducting and ferromagnetic thin film properties. Our results confirm such influence of the FIB technology. However, protection of the structures by a gold thin film may effectively solve this problem, as is presented in the paper.

EFFECT OF GALLIUM FOCUSED ION BEAM IRRADIATION ON PROPERTIES OF YBa2Cu3Ox/La0.67Sr0.33MnO3 HETEROSTRUCTURES

Effect of Gallium Focused Ion Beam Irradiation on Properties of YBa2Cu3Ox/La0.67Sr0.33MnO3 Heterostructures We present initial investigation of the superconductor-ferromagnet-superconductor (SFS) heterostructures of nanometer dimensions prepared by the gallium focused ion beam (FIB) technology. The SFS heterostructures were realized on the basis of high-Tc superconducting YBa2Cu3Ox and ferromagnetic La0.67Sr0.33MnO3 thin films. SFS weak link junctions require dimensions of the weak link connection in the range of nanometer size realizable by FIB patterning. On the other side the gallium focused ion beam might bring about unacceptable degradation of the superconducting as well as ferromagnetic thin film properties. The presented results show that FIB offers a suitable procedure for realization of nanometer size devices but some degradation of the ferromagnetic and superconducting properties was observed. Solution of this problem will be achieved in the next stage of our investigations.

Spectral ellipsometry of binary optic gratings

The coupled wave method (CWM) has been applied to the description of electromagnetic wave propagation in binary optic gratings. The electromagnetic field and the permittivity profile are expanded into two-fold Fourier series. The reflection coefficients of 2D periodical structures have been specified and the ellipsometric angles of discussed shapes have been computed. The theoretical results computed for SiO2 and Si3N4 dots are compared with experimental data obtained for the square silicon nitride dots on the Si substrate. The measurements were performed using computer controlled four zone null ellipsometer in spectral range from 240 nm to 700 nm. The influences of Si02 ultrathin oxidation layer and dot thickness on spectral ellipsometric angles are also discussed.

Selective deposition of epitaxial YBCO films on substrate and titanium oxide mask applicable for patterning of stable microbridges

Crystallographic and physical properties of epitaxial (YBCO) films selectively grown on the titanium oxide mask and buffer layer are presented. The deposition process was realized on a sapphire single-crystal substrate. It took place as an in situ deposition from the moment when a system, Ti film, was available. It involved plasma oxidation of Ti to titanium oxide at and deposition of YBCO at the same temperature, but in a gas mixture: argon + oxygen. Epitaxial thin YBCO layers were deposited by magnetron sputtering. The evaporated titanium oxide mask on showed no significant incorporation of YBCO slab, while deposition of YBCO on the buffer layer produced a superconducting film. These properties predetermine the use of the stable mask for patterning of lasting submicrometre bridges. Estimation of the oxygen content in from the x-ray pattern is also briefly described.

Doping of Bi-Sr-Ca-Cu-O superconductors with Pb, Sn and Ag

Basic and substituted superconductors in the homologous series Bi2Sr2Can−1Cun O2n+4+y, Bi2−x/2Sr2−x/2LxCan−1CunO2n+4+y and Bi2Sr2−xLxCan−1CunO2n+4+y(L=Sn, Pb or Ag,x=0−0.4,n=2, 3 or 4) have been synthesized. All the prepared ceramic samples show superconducting behaviour with zero resistance atTc=70 to 85 K. The compounds withn=3 or 4 showed onset temperature around 115K indicating involvement of a disproportionate solid-state reaction and formation of a two-phase system. The phase involving tin or lead oxides showed similar superconducting properties. Final rapid quenching of samples contributed to preservation of the high temperature equilibria with higher solubility of tin oxide in the quaternary system Bi-Sr-Ca-Cu-O. Silver was not soluble but precipitated in a colloidal form at interfaces between the crystalline grains.

New Experimental Approach to Measure the Photocatalytic Activity of the TiO 2 Nanosamples

Titanium dioxide (TiO2) samples are important industrial nano-objects with wide applications. For example nowadays TiO2 is the most abundantly used white pigment. The pigment is still in use, both in the production of contemporary art and for the conservation of older artwork as a retouching pigment. But next to its positive characteristics, the pigment has a major potential drawback: its photo-catalytic activity that can cause degradation of artworks in which it is used. So it is important to create methods to test the photo-catalytic activity of different quality of titanium dioxide samples. In this paper a new experimental set-up to measure the photo-catalytic activity of TiO2 samples is described.

Recognition of the carbon thin films sub-structures: thermo-optical measurements

Carbon thin films oxidation was investigated on-line by high-sensitivity optical transmission (OT) method. The films have been prepared by common vacuum arc discharge and subsequently air oxidized at linear heating rates until temperatures of their complete gasification. The shape of the optical curves acquired was interpreted in light of deduced partial optical changes, each of them being ascribed by simple sigmoidal dependence. The dependencies converted to their derivative form ordered respective to the temperature scale conveniently represent an inter-relationship among the sequentially evolved films’ optical events, considered as being closely related to the individual carbon-replenishing steps. The dependencies correspond well to the ones obtained on thicker films by means of the thermogravimetry (TG) measurements.