David Fuks

Atomistic study of interaction zone at copper-carbon interfaces

Abstract Formation of Cu–C composite is a difficult technological problem: carbon is practically insoluble in copper. We show that the heat treatment of the Cu–C composite leads to the formation of thin (approximately 50 nm) interface, which provides the bonding between fiber and matrix. The high-resolution scanning electron microscopy (HR SEM) study displays the formation of the interaction zone. Monte Carlo simulations with repulsive Cu–C interatomic potentials study this zone on the interface.

Glucose determination using a re-usable enzyme-modified ion track membrane sensor

A novel concept for a glucose biosensor based on the enzyme glucose oxidase covalently linked to nanopores of etched nuclear track membranes is presented. This device can be used to detect physiologically relevant glucose concentrations between 10 microM and 1 M. The sensitive catalytic sensor can be made re-usable due to the production of diffusible products from the oxidative biomolecular recognition event. We have demonstrated both the simplicity with which this sensor can be produced and the stability of the enzyme embedded in the nanopores. We strongly believe that the approach could be expanded for different enzymes and variable configurations of sensing and catalysis using membranes with nanopores for biocatalysis and enrichment of substrates and products. This is the first time that such devices are being used for biocatalytic transformations.

Theory of the growth mode for a thin metallic film on an insulating substrate

We have developed a novel theory predicting the growth mode of a thin metallic film on an insulating substrate. This combines ab initio electronic structure calculations for several ordered metal/insulator interfaces (varying both coverage and substrate lattice constant), with a thermodynamic approach based on microscopic calculations. We illustrate this approach for Ag film deposited on MgO(0 0 1) substrate. Ab initio calculations predict high mobility of adsorbed silver atoms on the perfect magnesia surface even at low temperatures. Our theoretical analysis clearly demonstrates that the growth of metallic islands is predominant at the initial stage of silver deposition, which agrees with the experimental data. 2001 Published by Elsevier Science B.V.

Microstructure of Cu–C interface in Cu-based metal matrix composite

Abstract Existence of dilute copper–carbon solid solutions is one of the characteristic features of the interfaces of the metal matrix composites widely used in the electrical applications. Experimental high-resolution SEM study allows to visualize the formation of the interaction zone on carbon fibre. We model interstitial solid solutions formed in this interaction zone non-empirically within the embedded-cluster and supercell approaches. Atomistic approach allows selection of the geometry of the solid solution. Electronic structure studies show that the most favourable position of the carbon atom is shifted along the [110] direction from the centre of the octahedral position. Investigation of this physical phenomenon allows us to understand the nature of the chemical bonding in copper-based solid solutions with carbon.

Formation of nano-crystalline structure at the interface in Cu–C composite

Abstract Formation of Cu–C composite is a difficult technological problem: carbon is practically insoluble in copper. We show that the heat treatment of the Cu–C composite leads to the formation of a thin (approximately 50 nm) interface which provides the bonding between fiber and matrix. The HR SEM study displays the formation of small copper nano-crystals in the interaction zone. This structure of the interface is predicted by molecular dynamic and Monte Carlo simulations with semi-empirical repulsive Cu–C interatomic potentials. We show that inclusion of a small amount of carbon in fcc copper leads to strong deformation of the copper host matrix in the vicinity of carbon. Decrease of stresses in the lattice may be reached by the formation of the developed surface in nano-crystalline structure.

Diffusivity of carbon in the copper matrix. Influence of alloying

Abstract The heights of diffusion barriers for copper-based composite materials with carbon whiskers or fibers are calculated. It is shown that the alloying of the matrix by an additional element, substituting copper in an interstitial Cu C solid solution, changes the value of the barrier and the migration entropy. This substitutional impurity influences the diffusion of the carbon-copper matrix. Zirconium as the best alloying element for preventing the diffusion of carbon in Cu C alloy is predicted.

A new model for the diffusion behavior of hydrogen in metallic glasses

Both experimental and simulation results have indicated the deviation from Arrhenius law of the diffusion coefficient of hydrogen in metallic glasses. This deviation was traditionally explained by the existence of various kinds of jumps or in terms of continuous distributions of activation energies due to different kinds of disorder. A new model is suggested, which relates this deviation to the temperature dependence of the short-range order (SRO). The suggested model is applied to simulate the diffusion behavior of hydrogen in dilute amorphous Fe-H, Fe-Si-H and Fe-B-H alloys. The effect of the alloying elements on the activation energy of hydrogen diffusion in amorphous iron is discussed in terms of their electronic structure and mean volume.

Interstitial carbon in copper: Electronic and mechanical properties

The effects of interstitial carbon on the electronic and mechanical properties of copper are studied theoretically. Semiempirical methodology, atomistic simulations and first-principles density-functional embedded-cluster schemes are combined to extract some understanding of the diffusion process and related degradation of Cu-C composite materials under extremes of temperature and stress. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu-C interface.

Carbon in copper and silver: Diffusion and mechanical properties

Abstract The effects of interstitial carbon on the diffusion and mechanical properties of copper and silver are studied theoretically. Semiempirical methodology, atomistic simulations, and first-principles density functional schemes are combined to extract some understanding of the diffusion process and lattice reconstruction in extremely dilute interstitial Cu–C and Ag–C alloys. It is demonstrated that carbon inclusion in the host matrix leads to sufficient non-uniform dilatation of the lattice. We also show that an account of static displacements is important in the calculations of the activation energy for the diffusion of the interstitial atoms. The “embedded” cluster scheme is suggested to simulate the relaxation in extremely dilute alloys. High-resolution scanning electron microscopy results are presented, which demonstrate the existence of a solid solution zone at the Cu–C interface.

Atomistic simulation of the [001]surface structure in BaTiO3

Abstract We simulate the effect of the surface relaxation on the polarization of the layers of paraelectric phase in the vicinity of the [001] surface in BaTiO 3 in the framework of the shell-model potentials. We observe large polarization of ions in the first two layers of the surface. Our simulations confirm the possibility of existence of Ti- and Ba-containing top layers in [001] BaTiO 3 surfaces.