Lajos Daróczi

Magnetic properties of ball milled nanocrystalilne Ni and Fe

Abstract Magnetic properties of pure nanocrystalline nickel and iron produced by ball milling were investigated by low field magnetization measurements and by Barkhausen-noise technique at room temperature. The coercivity He followed the predictions of the random anisotropy model, shows a peak in the nanocrystalline region. The saturation magnetization is practically independent of the grain size in iron and similar behaviour can be deduced for nickel if the effect of iron contamination (caused by ball milling) is extracted from the magnetization curve.

Comparative Microstructural Study of the Diffusion Zone between NiCr Alloy and Different Dental Ceramics

Our knowledge on the bonding mechanisms between the metal and ceramic parts of dental systems is very limited. This work tested the hypothesis that the details of the interface processes can be described in the framework of a chemical diffusion model. The development of interfacial phases was investigated by cross-sectional analytical transmission electron microscopy between a NiCr (Wiron 99) alloy and three different dental ceramics (Carat, Vita VMK 95, and Vision). All systems were investigated at normal firing conditions (suggested by the manufacturer) and at increased firing times as well. The conclusions are based on the results that the formation of a nanocrystalline Cr2O3 layer and amorphous silicon oxide inclusions were detected in the early stage of the firing process in all investigated systems, and that, in the case of Carat and Vision ceramics, formation of complex NiCr and NiCrTi oxides was also observed at longer annealing times. It is shown by transmission electron microscopy that, in the reaction processes taking place at the NiCr alloy/dental ceramics interface, nanocrystalline Cr2O3 first forms and amorphous silicon oxide inclusions appear, then, at longer firing times, complex NiCr and NiCrTi oxides form.

Production and magnetic properties of nanocrystalline Fe and Ni

Abstract Magnetic properties of pure nanocrystalline iron produced by ball-milling and heavy cold deformation are investigated, using low field magnetization measurements at low temperatures and Barkhausen-noise technique at room temperature. It was observed that the saturation magnetization was practically constant up to the grain size of D = 7 nm. On the other hand, the coercive force, H, determined from the Barkhausen-noise curves, was very sensitive to the grain size. Furthermore, the Barkhausen-noise values showed a systematic, but different behavior with the grain size for the ball-milled powders and for the cold-worked wires. Similar measurements were carried out for cold-worked nickel wires.

Ni diffusion in near-equiatomic Ni-Ti and Ni-Ti(-Cu) alloys

Tracer volume diffusion of 63 Ni in Ni-50.07 at.% Ti binary and Ni-48.83 at.% Ti-9.29 at.% Cu ternary alloys have been measured between 783 and 1288 K. The temperature dependence of the diffusion coefficients can be well described by a straight Arrhenius function This illustrates that a diffusional anomaly (typical in some bcc metallic alloys and related to the well-known phonon softening), if there is any in this system, is negligible. On the other hand, the small activation energy (about half the value expected from simulations for the commonly accepted mechanism with thermally activated vacancies) shows that the mechanism of diffusion is probably mediated by structural vacancies.

Nanoscale investigations of shift of individual interfaces in temperature induced processes of Ni–Si system by secondary neutral mass spectrometry

We describe a method for measurement of nanoscale shift of interfaces in layered systems by a combination of secondary neutral mass spectrometry and profilometer. We demonstrate it by the example of the investigation of interface shifts during the solid state reaction in Ni/amorphous-Si system. The kinetics of the shrinkage of the initial nanocrystalline Ni film and the amorphous Si layer as well as the average growth kinetics of the product phases were determined at 503 K. The results show that nanoscale resolution can be reached and the method is promising for following solid state reactions in different thin film systems.

Investigations of diffusion kinetics in Si/Ta/Cu/W and Si/Co/Ta systems by secondary neutral mass spectrometry

Proper understanding of the degradation mechanisms and diffusion kinetics of copper and cobalt interconnections for advanced microelectronics is important from the point of view of fundamental research and technology as well. In this paper Si(substrate)/Ta(10 nm)/Cu(25 nm)/W(10 nm) and Si(substrate)/Co(150 nm)/Ta(10 nm) samples, prepared by DC magnetron sputtering, were in investigated. The samples were annealed at several temperatures ranging from 423 K to 823 K for various times. The composition distributions were detected by means of Secondary Neutral Mass Spectrometry (SNMS). Microstructural characterization of samples was carried out by means of Transmission Electron Microscopy (TEM). It is shown that the changes in the composition profiles were mainly caused by grain boundary, GB, diffusion and the effective GB diffusion coefficients of Ta in Cu were determined both by the ‘‘first appearance’’ and ‘‘centre-gradient’’ methods. The activation energy is 100 kJ/mol. The importance of the Ta penetration into the Cu and its accumulation at the Cu/W interface can lead to an increase of the Ta content in the copper film. This can be an important factor in the change/degradation of the physical parameters (e.g. the electrical resistance) of interconnects. Furthermore a Ta segregation factor in Cu was evaluated. Preliminary results in the Si(substrate)/Co(150 nm)/Ta(10 nm) indicate fast (GB) diffusion of the Si into the Co layer, formation of a cobalt silicide layer at the Co/Si interface and Si accumulation first at the Ta/Co interface and later a retarded accumulation at the free Ta surface. 2010 Elsevier Ltd. All rights reserved.

Nano-sized clusters of a teicoplanin ψ-aglycon-fullerene conjugate. Synthesis, antibacterial activity and aggregation studies

Glycopeptide antibiotic derivative teicoplanin ψ-aglycone has been bound covalently to a fullerenopyrrolidine derivative using azide-alkyne 1,3-dipolar cycloaddition reaction. The aggregation of the antibiotic-fullerene conjugate in aqueous solution has been studied. The conjugate exhibited antibacterial activity against enterococci resistant to teicoplanin.

Determination of grain-boundary diffusion coefficients by Auger electron spectroscopy

Abstract Surface accumulation method, called the Hwang–Balluffi method [J.C.M. Hwang, J.D. Pan and R.W. Balluffi, J. Appl. Phys., 50(3), 1979, 1339], was applied to measure the grain-boundary diffusion of Ag at low temperatures (413 and 428 K) in a nanocrystalline Cu film. Ag atoms from the Ag layer diffused through the copper nanocrystalline film along the grain boundaries to the opposite surface (i.e. the accumulation surface) where they spread out by rapid surface diffusion and accumulated. The rate of accumulation was detected by Auger Electron Spectroscopy (AES). It was shown that the results are not sensitive to the supposition whether accumulation takes place in one or two monolayers of the surface. TEM observations have been made in the same time before and after heat treatment to check the stability of the nanostructure.

Differential platelet deposition onto collagen in cone-and-plate and parallel plate flow chambers

To routinely test the formation of thrombi and the effect of drugs modifying it, proper test systems are needed. Their design should rely on the laws of rheology and the physiology of laminar flow. To best model physiological or pathological shear conditions, parallel/linear and rotational type flow chambers are developed. We have compared the initial phase of platelet thrombus formation in a parallel plate flow chamber (PPC) and a cone-and-plate chamber (CPC) under von Willebrand dependent shear conditions. Blood was allowed to flow through human collagen type III surfaces at a shear rate of 1000 s−1 for 150 s. Thrombus deposition was characterized by surface coverage, average area and height of thrombi. VWF distribution within thrombi was analyzed with confocal laser scanning microscopy. Reduced surface-specific platelet adhesion and aggregation (surface coverage and average thrombus size) were observed in CPC along with a significant increase in single platelet disappearance from the circulating blood. Our data suggest that the higher rate of platelet consumption in this device, as opposed to PPC, is limiting the adhesion to the surface. Consequently, surface-specific processes and aggregation in the flowing blood are both assessed using CPC, while comprehensive evaluation of surface-specific processes is best achieved with PPC. Therefore, the choice of chamber type as a diagnostic tool is purpose-dependent.

Study of interdiffusion in amorphous Si/Ge multilayers by Rutherford backscattering spectrometry

Abstract Amorphous Si/Ge multilayers of 10–40 nm repeat length were prepared by DC magnetron sputtering and annealed at 683 K. Rutherford backscattering spectrometry (RBS) with increased depth resolution was applied to study the intermixing of the elements. The interdiffusion coefficient was determined by measuring the intensity of the first Ge peak in the RBS spectrum as a function of annealing time. An attempt was made to observe the theoretically predicted change of dimensions of the Si/Ge layers caused by the diffusion asymmetry.