B. Susła

Superconductivity in PrBa2Cu3O7-δ single crystals after high-temperature thermal treatment

Abstract The influence of post-growth treatment, consisting of high-temperature reduction, quench and oxidation, on the structural, electrical and magnetic properties of PrBa 2 Cu 3 O 7− δ single crystals, obtained in Al 2 O 3 and ZrO 2 crucibles by the self-flux method, was examined. We report on the observation of inhomogeneous superconductivity in several Al-doped crystals from the ac magnetic susceptibility and resistivity measurements. Superconducting crystals were characterised by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Room-temperature scanning tunnelling microscopy (STM) was used to study the topography and local electric conductivity of the crystal surface after thermal treatment. We attribute the onset of the superconductivity in our samples to the structural changes after high-temperature reduction in argon atmosphere providing the decrease in number of Pr on Ba site defects and enhanced by the existence of Al-rich clusters in the material.

Effect of Heat Treatment on Phase Behaviour and Molecular Dynamics of Mineral-Filled PPS

Abstract Investigation concerning the structure and molecular dynamics of a nanocomposite made up of poly(p-phenylene sulfide) and silicon dioxide (SiO2) has been conducted by means of atomic force microscopy (AFM) and nuclear magnetic resonance (NMR). AFM and NMR studies of samples PPS in the neat and composite forms show that during annealing the fragmentation of big agglomerates of PPS take place. Between agglomerates and smaller aggregates there exist repulsion forces which are probably the source of fragmentation in the polymer network. The work has also proved that inside agglomerates and smaller aggregates of PPS dipolar magnetic interaction exist, whereas the electrostatic one occurs between them.

Conductance quantization in nanowires formed at the metal-semiconductor interface

We demonstrate that step-like conductance traces resulting from quantum efiects such as the conductance quantization or formation of single-atom contacts are possible in the nanowires formed at the metal-semiconductor junction. In the macroscopic metal-semiconductor interfaces the Schottky barrier is usually risen. For the nanowires formed at the contact between the germanium surface and cobalt or gold tip, the conductance traces are characterized by a high reproducibility and long duration of the conductance plateaus. The current-voltage characteristics of these contacts are strongly nonlinear similarly to a junction with the Schottky barrier.

Atomic image of Bi2Sr2CaCu2O8+x cleaved surface

Abstract The results of the scanning tunneling microscopy/spectroscopy as well as transmission electron microscopy measurements on the bismuth cuprate superconductors Bi2Sr2CaCu2O8+x in the ab-plane are reported. STM high-resolution images of cleaved single crystal reveal an atomic lattice and a superimposed incommensurate superstructure. We have also clearly seen this superstructure in high-resolution electron micrographs. Scanning tunneling microscopy of the deposited clusters yield information on the cluster shape. Scanning tunneling spectroscopy at low temperature allows identifying quantum size effect in individual Ni clusters.

Nanostructural investigations of cuprate superconductors by scanning probe methods

A brief review of the basic principles and the theory of scanning tunneling microscopy (STM) and spectroscopy (STS) as well as atomic force microscopy (AFM) is presented with emphasis on materials problem. The detailed spectroscopy and characteristic features of Bi2Sr2CaCu2O8 and Nd2-xCexCuO4-y (NCCO) single crystals in normal state are also discussed. In addition to STS studies, some examples of STM and AFM surface topography of NCCO single crystals are given.

A SPECTROSCOPIC STUDY OF THE LAYERED STRUCTURE IN BI2SR2CACU2O8

Abstract This paper reports scanning tunneling spectroscopy (STS) and the Raman scattering (RS) investigations of Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) single crystals. STS measurements of the local I-V characteristics on the cleaved surface of BSCCO show both the metallic CuO and semiconducting BiO features. The width of the semiconducting gap was estimated to be 0.3 eV at room temperature. The Raman scattering spectra for BSCCO were obtained at two different temperatures and for two different exciting lines. The observed two-magnon excitation from BSCCO lies around 3 J exch .

The effects of growth conditions on superconducting properties of Nd1Ba2Cu3O7−δ single crystals

Abstract The influence of thermal treatment conditions on the structure and superconducting properties of single crystal Nd 1 Ba 2 Cu 3 O 7− δ growths has been studied. The crystals were grown in air by the flux method. The microstructure of the crystals was studied using scanning electron microscopy and scanning tunnelling microscopy. To examine the superconducting properties of the crystals measurements of the DC magnetic moment in applied magnetic fields were performed. A superconducting transition was not observed in any of the samples. This may have been a result of Nd/Ba or Cu/Al substitution.

Scanning tunneling microscopy/spectroscopy of ferromagnetic Ni clusters on graphite and BSCCO high-Tc superconductor

Abstract A brief description of the basic principles of the theory of scanning tunneling microscopy and spectroscopy is given. This paper presents results of our experimental investigations of Ni clusters deposited on ab-surface of Bi2Sr2CaCu2O8+y (BSCCO) single crystals or highly oriented pyrolytic graphite (HOPG) substrates. The microclusters were produced by the plasma gas condensation or evaporator with integral flux monitor. The scanning tunneling spectroscopy was performed at 24 K and at room temperature. The spectra measured above the Ni clusters and directly above the substrate reveal remarkable differences. Point contact tunneling (PCT) measurements on the overdoped regime Bi2Sr2CaCu2O8+y single crystals show sharp zero bias conductance peak (ZBCP) at zero bias voltage. The ZBCP observation gives strong evidence that the order parameter is of d-wave symmetry for overdoped BSCCO single crystals.

Scanning probe microscopy/spectroscopy and its applications for nanotechnology

We present results of experimental investigations of Ni clusters deposited on ab surface of Bi2Sr2CaCu2O8+y (BSCCO) single crystals or highly oriented pyrolytic graphite (HOPG) substrates. The micro clusters were produced by the plasma gas condensation or evaporator with integral flux monitor. The scanning tunneling spectroscopy was performed at 24K and at room temperature. The spectra reveal differences between the curves measured above the Ni clusters and substrate, respectively. The relationship between surface atomic scale and local density of states in the materials is also discussed.

Electrical conductivity of the ZnS:Mn,Cu thin films

Electrical properties of the electroluminescent thin film cells based on zinc sulfide were investigated. Current-voltage characteristics for whole electroluminescent cell and part of the cell were measured at room temperature. Current-voltage characteristics due to part of the cell were performed by point contact tunneling method. In both the kind of current-voltage characteristics memory effect has been observed. Different mechanisms of the charge transport through the cells and thin ZnS:Mn,Cu films were taken into account. We have found that it is more than one mechanism of electrical conductivity in the thin films.