Ryszard Czajka

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.

Observation of C60 film formation on a highly oriented pyrolitic graphite substrate via scanning tunnelling microscopy

We have investigated the early stages in the adsorption process of C60 molecules on a highly oriented pyrolitic graphite (HOPG) substrate. C60 powder was thermally evaporated in UHV of 10−8 Pa conditions onto a freshly cleaved HOPG surface. We did not observe individual fullerenes on the substrate for the case of short deposition times and low evaporation rates. However, small islands of C60 molecules with an fcc structure could be observed when the deposition rate was about 0.2 nm/min and the total thickness was above 1 nm. The islands did not grow in the vicinity of the HOPG steps. The typical lateral dimensions of these islands were of the order of a few hundred square nanometers, having thickness of up to five monolayers. We modified the shapes and positions of these islands by the STM tip, using a small (less than 1 V) bias voltage.

Interface and nanostructure evolution of cobalt germanides on Ge(001)

Cobalt germanide (CoxGey) is a candidate system for low resistance contact modules in future Ge devices in Si-based micro and nanoelectronics. In this paper, we present a detailed structural, morphological, and compositional study on CoxGey formation on Ge(001) at room temperature metal deposition and subsequent annealing. Scanning tunneling microscopy and low energy electron diffraction clearly demonstrate that room temperature deposition of approximately four monolayers of Co on Ge(001) results in the Volmer Weber growth mode, while subsequent thermal annealing leads to the formation of a Co-germanide continuous wetting layer which evolves gradually towards the growth of elongated CoxGey nanostructures. Two types of CoxGey nanostructures, namely, flattop- and ridge-type, were observed and a systematic study on their evolution as a function of temperature is presented. Additional transmission electron microscopy and x-ray photoemission spectroscopy measurements allowed us to monitor the reaction between ...

Atomic force microscopy and friction force microscopy studies of ferroelastic crystal surfaces

Abstract Topography and frictional properties of freshly cleaved surfaces of ferroelastic crystals: K 3 Na(SeO 4 ) 2 (KNSe), and NH 4 LiH 3 (SO 4 ) 4 (ALHS), and Gd 2 (MoO 4 ) 3 (GMO) were investigated by combined scanning and friction force microscopy (FFM) under ambient and UHV conditions. Atomic force microscopy (AFM) images revealed stepped surfaces with step heights corresponding to the multiplication height of crystal lattice constant fractions e.g., c /2 or c /4. A frictional contrast was observed between terraces which are separated by steps and between different domains of ferroelastic crystals. We suggest that the frictional contrast is due to different molecular orientations at different terraces and/or at different domains of a ferroelastic crystal, in the case of GMO, surface bends at the domain boundary with the angle estimated to be about 2.35°. It was also shown that the ALHS crystal surface can be modified (e.g., by changing the step profile and creation of the artificial bumps) by an AFM tip imaging with normal force above 100 nN.

AFM investigation of bismuth doped silicate glasses

Abstract Bismuth doped glasses were reduced in hydrogen atmosphere at temperatures above 250 °C. This process leads to changes in stoichiometry of the glass in the region close to the glass surface. Relatively high surface conductivity of 10 −6 S allows this material to be applied to channeltron production. AFM investigations of freshly cleaved bismuth doped glasses were done in constant and friction force modes. The AFM topographical images show the presence of different concentrations of nanocrystals vs distance from the glass surface. Atomic resolution images obtained in both modes of these nanocrystals, together with XRD data, suggest that they are composed of bismuth.

Growth and evolution of nickel germanide nanostructures on Ge(001)

Nickel germanide is deemed an excellent material system for low resistance contact formation for future Ge device modules integrated into mainstream, Si-based integrated circuit technologies. In this study, we present a multi-technique experimental study on the formation processes of nickel germanides on Ge(001). We demonstrate that room temperature deposition of ∼1 nm of Ni on Ge(001) is realized in the Volmer-Weber growth mode. Subsequent thermal annealing results first in the formation of a continuous NixGey wetting layer featuring well-defined terrace morphology. Upon increasing the annealing temperature to 300 °C, we observed the onset of a de-wetting process, characterized by the appearance of voids on the NixGey terraces. Annealing above 300 °C enhances this de-wetting process and the surface evolves gradually towards the formation of well-ordered, rectangular NixGey 3D nanostructures. Annealing up to 500 °C induces an Ostwald ripening phenomenon, with smaller nanoislands disappearing and larger ones increasing their size. Subsequent annealing to higher temperatures drives the Ni-germanide diffusion into the bulk and the consequent formation of highly ordered, {111} faceted Ni-Ge nanocrystals featuring an epitaxial relationship with the substrate Ni-Ge (101); (010) || Ge(001); (110).

Graphene-based magnetoresistance device utilizing strip pattern geometry

The idea of a raster pattern magnetoresistor made of thin films of III–V compounds and a metallic layer has been known for over fifty years. Based on this knowledge, we present the construction of a magnetoresistor made of combined graphene and metallic strip patterns. The presented device is implemented using a monolayer of graphene epitaxially grown on a semi-insulating substrate. A graphene strip pattern magnetoresistor gives a promising wide range of practical applications due to its very high sensitivity combined with the mono-atomic thickness of the sensitive layer, the simplicity of realization, and a very convenient principle of sensor operation assuming only the usage of two electrical terminals.

STM/STS investigation of carbon nanotubes deposited on Bi2Te3 surface

This paper reports our scanning tunneling microscopy and spectroscopy (STM/STS) study of double-walled and multi-walled carbon nanotubes (CNTs) of different diameter deposited on Bi2Te3 (narrow gap semiconductor). The approximate diameter of the studied double-walled and multi-walled CNTs was 2 nm and 8 nm, respectively. Crystalline Bi2Te3 was used as a substrate to enhance the contrast between the CNTs and the substrate in the STS measurements performed to examine peculiarities of CNT morphology, such as junctions, ends or structural defects, in terms of their electronic structure.

STM investigation of cobalt silicide nanostructures’ growth on Si(111)-(√19 Ã- √19) substrate

Continuing miniaturization of electronic devices necessarily requires assembly of several different objects or devices in a small space. Therefore, besides thin films growth, the possibility of fabricating wires and dots [1, 2] at the nanometre scale composed of metal silicides is of the top interest. This report is about the STM/STS investigation of cobalt silicides’ nanostructures created on Si(111)-(√19 × √19) substrates via Co evaporation and post deposition annealing. This (√19 × √19) reconstruction was induced by Ni doping. Less than 1ML of Co on surface was obtained. Surface reconstruction induced growth of agglomerates of clusters rather than an uniform layer. The post deposition annealing of a crystal sample (up to 670 K, 770 K, 870 K, 970 K, 1070 K and 1170 K) led to creation of silicides’ nanostructures. Measurements showed that coalescence of Co nanoislands begun around 970 K. Annealing above 1070 K led to alloying of a Co, Ni and Si. As a consequence the Si(111)-(7×7) reconstruction occurred at the cost of Si(111)-(√19 × √19).

AFM investigations of K3Na(SeO4)2 single crystals

Abstract K3Na(SeO4)2 single crystal cleaved surfaces were imaged by means of an atomic force microscope in air. The images revealed atomically flat terraces 500 nm wide, with steps, this height being the multiple of the K3Na(SeO4)2 c 2 lattice constant. For the first time, atomic resolution was observed on the KNSe crystal surface in air. Correlation between the images obtained and crystal structure is discussed.