András Szász

Microstructure and its relaxation in FeB amorphous system simulated by moleculular dynamics

A computer simulation by molecular dynamics for the system Fe85B15 is presented, to explore the dynamics of structural transformation from liquid to amorphous state by a rapid quench. The truncated Morse potential is used to simulate the atomic interactions. Possible models of the actual amorphous structures are suggested based on the statistical analysis of Voronoi polyhedra. The obtained metastable state depend on the methods of sample preparation.

On the formation of electroless amorphous layers. I. Phenomenological description of NiP deposited on Cu and Fe substrates

Abstract The formation of amorphous NiP coating by electroless deposition on to copper and iron substrates has been followed by soft X-ray emission spectroscopy (SXES), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Three different stages of formation can be distinguished. The first period is nucleation in an essentially two-dimensional layer where the formation of nuclei depends on the number and properties of the active sites on the underlying substrate layer. There is a three-dimensional spherical growth in the second stage. The concentration of phosphorus increased in the interspherical area. A relatively slow two-dimensional growth is characteristic of the third stage giving rise to a bright outer surface of the coating.

On electronic structure and metastability

Abstract A model is proposed in which nearly spherical ‘deformed’ Joneszone polyhedra are formed in k-space when translational symmetry is lost in real space for disordered materials. This leads to an electronic origin for metastability in a large category of disordered materials whose stability is identified with icosahedral-seeking symmetry.

The process of formation of amorphous Ni-P layers made by electroless deposition☆

Abstract The composition, electronic states and structure of thin Ni-P layers deposited by the electroless method were studied by soft X-ray emission spectroscopy, differential thermal analysis, secondary ion emission, X-ray diffraction and auxiliary microscopic investigations. The first centres of the layer consisted of pure crystalline nickel nuclei. With increasing growth, the deviation from crystallinity increased, with continous changes in the composition. Also, diffusion processes take place transporting aluminium and silicon from the underlying substrate.

Soft X-ray Emission Depth Profile Analysis: SXDA

Abstract A nondestructive deep profile analytical method called Soft X-ray Emission Depth Analysis (SXDA) is developed on the basis of Soft X-ray Emission Spectroscopy (SXES). The theoretical basis, methods of calculations, apparatus and typical examples are given. All the advantages of SXES are included and in addition SXDA provides qualitative and quantitative elementary analysis, nondestructive detection of chemical bonding states is and can be used for surface layers in the depth range between 10−3 and 3 μm. Examples of applications are taken from the fields of surface oxide investigations, catalysis, and alloy analysis.

Factors affecting the adhesion of electroless coatings

Abstract In this paper, we study the factors affecting the first stage of autocatalytic (electroless) growth: the nucleation processes. The initiation of the process was achieved with the nickel electroless method on iron and copper substrates. Both acidic and alkaline baths were used for generalization of the layers.

On the electronic stability of amorphous alloys

The metastability of amorphous alloys has been investigated in dependence on the electron/atom ratio (e/a). A linear dependence of the thermodynamic parameters (crystallization temperature, transition heat) versus electronic concentration has been observed and is discussed.

Mechanisms of formation and stability in electroless deposition of nickel-phosphorus

Abstract Phase characteristics and chemical bonding are examined in electroless deposited amorphous nickel-phosphorus layers. The metastability of the amorphous structure and microscopic and macroscopic mechanisms of the phase transformation during growth are discussed. Both chemical bonding and stability change during growth. The changes are studied in terms of their dependence on electronic structure and atomic arrangement during the phase transition. The electronic structure plays a dominant role in stabilizing the amorphous phase. The growth kinetics are examined in terms of an ‘Avrami’ equation.

Surface composition of Pt-Pd alloys treated in hydrogen

Abstract Pd enrichment is observed in Pd-Pt alloy sheets when heated in He and in H2. The surface composition was monitored by soft X-ray emission spectroscopy (SXES) and by work function measurements. A regular solution model is used to calculate the expected composition of the surface atomic layers, with and without adsorbed hydrogen, and the calculated and measured values for Pd-enrichment are compared. The possible effect of subsurface adsorbed hydrogen is discussed.

On the characteristic structural clustering in metal-metalloid amorphous systems

Abstract A Voronoi analysis of selected Feue5f8B, Feue5f8P, Niue5f8B and Niue5f8P amorphous alloys is made. The alloys were modeled by molecular dynamics, using pseudo- and Morse-pair potentials. Characteristic properties of the cluster formation are discussed.