Cu surface segregation in Ni/Cu system

Surface Science, 2002

The eect of segregation on the dissolution of a thin Ni layer (3±14 equivalent-monolayers (eq-ML)) into a semi-in®nite Cu substrate has been investigated at dierent temperatures (600±730 K) by Auger electron spectroscopy. Computer simulations have also been carried out to understand the details of the dissolution and a sophisticated method is proposed to analyse the experimental kinetics. The simulations indicated a step-wise character of dissolution and an interesting interference between segregation and dissolution. Because of the strong concentration dependence (there is a fast diusion in Cu and there is practically no diusion into Ni), the interface remains sharp and shifts proportionally with time until it does not reach the next-to-the-last Ni layer. Then the dissolution continues by the saturation of Cu in the topmost layer, according to the segregation isotherm. After the complete coverage of the surface by Cu, the ®nal homogenisation takes place by the total dissolution of the next-to-the-last layer. According to these results, it was possible to separate the dissolution from the segregation and to determine the average speed of the interface shift, which is proportional to the intrinsic diusion coecient.

Journal of Alloys and Compounds, 2014

NiTi alloys are shape memory alloys (SMAs) which combine two very unique properties, shape memory effect and super-elasticity. These properties depend strongly on the composition and structure. In this research volume diffusion of Cu in bulk Ni 50.8 Ti 49.2 alloy with B2 ordered structure has been measured and diffusion phenomenon on a bi-layer Ni-Ti thin film was also studied. The penetration profiles were determined by two techniques: secondary ion mass spectroscopy (SIMS) and energy dispersive X-ray analysis (EDS). Cu diffusivity in NiTi-Ni rich bulk was found to follow linear Arrhenius dependencies with the pre-exponential factor of 5.8 ± 1 Â 10 À14 m 2 /s and the activation energy of 40 ± 4 kJ/mol. Anti-site defect diffusion mechanism is suggested to provide diffusion of copper in NiTi alloy. The diffusion coefficient of Cu in Ni-Ti Ni-rich was used to estimate the gradient composition in the bi-layer thin film (Ni-rich/NiTiCu) after annealing. The bi-layer thin film was deposited on Si (1 1 1) using DC magnetron sputtering and annealed at 773 K for 1 h. The crystallization temperature and microstructure of the thin film were characterized using differential scanning calorimeter (DSC) and X-ray diffractometer (GIXRD). The results depicted that estimation of the concentration gradient in the bi-layer thin film using the diffusion equation obtained from the NiTi bulk samples shows good agreement with the measured concentration gradient in the bi-layer.

Physical Review B, 2009

High kinetic-energy photoelectron spectroscopy ͑HIKE͒ or hard x-ray photoelectron spectroscopy has been used to investigate the alloying of Ni/Cu ͑100͒ multilayers. Relative intensities of the corelevels and their chemical shifts derived from binding energy changes are shown to give precise information on physicochemical properties and quality of the buried layers. Interface roughening, including kinetic properties such as the rate of alloying, and temperature effects on the processes can be analyzed quantitatively. Using HIKE, we have been able to precisely follow the deterioration of the multilayer structure at the atomic scale and observe the diffusion of the capping layer into the multilayer structure which in turn is found to lead to a segregation in the ternary system. This is of great importance for future research on multilayered systems of this kind. Our experimental data are supplemented by first-principles theoretical calculations of the core-level shifts for a ternary alloy to allow for modeling of the influence of capping materials on the chemical shifts.

Journal of Materials Research, 1992

The kinetics of the formation of intermetallics in the Cu–In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form CuIn intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of CuIn intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with CuIn to form Cu9In4. Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained fr...

Defect and Diffusion Forum, 2009

A nanostructured surface layer with a gradient microstructure was produced on a Cu plate by means of the surface mechanical attrition treatment (SMAT). Diffusion of Ni in the nanostructured layer was investigated by the radiotracer technique at temperatures from 383 to 438 K. The measured diffusion profiles consist of two distinct sections with different slopes, the steep one corresponding to the top surface layer with the grain size of 10 to 25 nm and the shallow one corresponding to a subsurface layer with a grain size of 25 to 100 nm. The effective diffusivities derived from both sections are more than 2 orders of magnitudes higher than the grain boundary diffusivities in coarse-grained Cu. The significantly accelerated diffusion rates are expected to be associated with the "non-equilibrium" states of interfaces in the nanostructured surface layer induced by SMAT. The difference between the diffusivities in the top and sub-surface layer might result from the fact that most interfaces developed from twin boundaries in the former while produced by dislocation activities in the latter.

International Journal of Quantum Chemistry, 2002

Cu(1 0 0)-c(2 Â 2)N surface was studied by a first-principles calculation. The optimized atomic structure of Cu(1 0 0)c(2 Â 2)N surface had the fourfold symmetry. The calculated diffusion path and the barrier of an isolated nitrogen atom on Cu(1 0 0) surface was the path through the bridge site and 1.5-1.7 eV, respectively. The scanning tunneling microscope (STM) image of Cu(1 0 0)-c(2 Â 2)N surface was simulated in consistent with an STM experiment. Effective interaction energy on this surface among nitrogen atoms was calculated and was found to be attractive one as suggested by experiments.

Applied Surface Science, 2010

Physical Review B Condensed Matter and Materials Physics, 2001

Surface and interface properties of Cu thin films (1-4 monolayers) deposited on Ni(100) have been extracted by means of x-ray absorption spectroscopy and analyzed in combination with ab initio density-functional calculations. An unoccupied Cu surface state is identified in an x-ray absorption spectra and studied as a function of film thickness. Experimental data is supported by calculations of the layer-resolved density of states and the results from this combined theoretical-experimental effort show that the surface state is almost entirely located on the atomic layer closest to the vacuum. Our results also indicate strong hybridization between unoccupied states at the Cu/Ni interface boundary.

Intermetallics, 2015

The paper presents new results concerning the influence of nickel addition (1 and 5 at.%) into tin on the development of the Cu/(Sn,Ni) interface area in diffusion couple experiment. The morphology and chemical composition of the intermetallic phases growing in the Cu/(Sn,Ni) diffusion couples were examined by means of the scanning (SEM) and transmission (TEM) electron microscopy after annealing at 215 C in vacuum for different period time. It was shown that even 1 at.% of nickel addition into tin resulted in formation of intermetallics of complex microstructure. The presence of (Cu 1Àx Ni x) 6 Sn 5 in two morphological and compositional variants was noted. The discontinuous layer consisting up to 7.2 at.% of Ni closer to copper end-member coexisted with needle-like and faceted precipitates with even 22.3 at.% of Ni, which intensively detached from the interface. At the Cu/(Cu 1Àx Ni x) 6 Sn 5 interface the formation of Cu 3 Sn wavy layer compound was observed in all examined diffusion couples which became thicker with time. The porosity within the both formed intermetallic phases existed irrespective of the amount of added nickel.

Physical Review B, 2001

Surface and interface properties of Cu thin films ͑1-4 monolayers͒ deposited on Ni͑100͒ have been extracted by means of x-ray absorption spectroscopy and analyzed in combination with ab initio densityfunctional calculations. An unoccupied Cu surface state is identified in an x-ray absorption spectra and studied as a function of film thickness. Experimental data is supported by calculations of the layer-resolved density of states and the results from this combined theoretical-experimental effort show that the surface state is almost entirely located on the atomic layer closest to the vacuum. Our results also indicate strong hybridization between unoccupied states at the Cu/Ni interface boundary.