Nele Moelans

Plasma-enhanced chemical vapour deposition growth of Si nanowires with low melting point metal catalysts: an effective alternative to Au-mediated growth

Au nanoparticles are efficient catalysts for the vapour?solid?liquid (VLS) growth of semiconductor nanowires, but Au poses fundamental reliability concerns for applications in Si semiconductor technology. In this work we show that the choice of catalysts for Si nanowire growth can be broadened when the need for catalytic precursor dissociation is eliminated through the use of plasma enhancement. However, in this regime the incubation time for the activation of VLS growth must be minimized to avoid burying the catalyst particles underneath an amorphous Si layer. We show that the combined use of plasma enhancement and the use of a catalyst such as In, already in a liquid form at the growth temperature, is a powerful method for obtaining Si nanowire growth with high yield. Si nanowires grown by this method are monocrystalline and generally oriented in the direction.

Thermodynamic optimization of the lead-free solder system Bi–In–Sn–Zn

Abstract The Bi–In–Sn–Zn system is an important alloy system in lead-free soldering. Thermodynamic descriptions for the ternary systems Bi–In–Sn, Bi–In–Zn, Bi–Sn–Zn and In–Sn–Zn are optimized, using the CALPHAD method and combined to obtain a description of the quaternary Bi–In–Sn–Zn. All available experimental data from the literature are taken into consideration in the optimization. Calculated liquidi, isothermal and vertical sections and thermodynamic properties are compared with experimental data. Ternary and quaternary invariant reactions are also calculated.

Quantitative analysis of grain boundary properties in a generalized phase field model for grain growth in anisotropic systems

A good choice of model formulation and model parameters is one of the most important and difficult aspects in mesoscale modeling and requires a systematic and quantitative analysis. In this paper, it is studied how the model parameters of a generalized phase field model affect the landscape of the free-energy density functional, the phase field profiles at the grain boundaries, and the corresponding trajectory along the free-energy landscape. The analysis results in quantitative relations between the model parameters, on one hand, and grain boundary energy and mobility, on the other hand. Based on these findings, a procedure is derived that generates a suitable set of model parameters that reproduces accurately a materials grain boundary energy and mobility for arbitrary misorientation and inclination dependence. The misorientation and inclination dependence are formulated so that the diffuse interface width is constant, resulting in uniform stability and accuracy conditions for the numerical solution. The proposed model formulation and parameter choice allow us to perform quantitative simulations with excellent controllability of the numerical accuracy and therefore of the material behavior.

Origin and sedimentation of Cu-droplets sticking to spinel solids in pyrometallurgical slags

Cu-droplet losses in slags are an important problem in Cu-industry, limiting the metal recovery. An important cause responsible for the entrainment of copper droplet losses in slags is their sticking behaviour to spinel solids. In the present study, the interaction between spinel solids and Cu-droplets is investigated in an industrially relevant slag system (PbO–CaO–SiO2–Cu2O–Al2O3–FeO–ZnO) using two complementary experimental set-ups. Firstly the influence of the sedimentation time is studied and secondly the presence of entrained (sticking) droplets is studied as a function of height in the slag layer. Based on the experimental results, a mechanism that explains the sticking Cu-droplets is proposed. Finally, a model describing the sedimentation of sticking and non-sticking droplets is formulated based on the experimental data.

Wetting behaviour of Cu based alloys on spinel substrates in pyrometallurgical context

Metal droplet losses in slags are an important issue in copper industry. One significant aspect that promotes the entrainment of metal droplets in the slag is their attachment to spinel solids. In the present study, the wetting behaviour of copper alloys on spinel substrates has been investigated in the presence and absence of a slag phase. At first, the attachment was investigated using a synthetic slag containing spinel particles. Microstructural analysis of quenched slag reveals the presence of microdroplets sticking onto a surface of the spinel particles. Second, the metal–spinel interaction was investigated using the sessile drop technique. Wetting angle measurements were performed between Cu–Ag alloys and MgAl2O4 substrates. A non-wetting behaviour between the alloys and substrates was observed. The results suggest that the oxygen partial pressure and the amount of Ag in the alloy both influence the wetting behaviour.

Microstructure and degradation performance of biodegradable Mg-Si-Sr implant alloys

In this work the microstructure and degradation behavior of several as-cast alloy compositions belonging to the Mg rich corner of the Mg-Si-Sr system are presented and related. The intermetallic phases are identified and analyzed describing the microstructure evolution during solidification. It is intended in this work to obtain insight in the behavior of the ternary alloys in in vitro tests and to analyze the degradation behavior of the alloys under physiologically relevant conditions. The as-cast specimens have been exposed to immersion tests, both mass loss (ML) and potentiodynamic polarization (PDP). The degradation rate (DR) have been assessed and correlated to microstructure features, impurity levels and alloy composition. The initial reactions resulted to be more severe while the degradation stabilizes with time. A higher DR is related with a high content of the Mg17Sr2 phase and with the presence of coarse particles of the intermetallics Mg2Si, MgSiSr and MgSi2Sr. Specimens with a higher DR typically have higher levels of impurities and alloy contents.

Phase-field simulations of the interaction between a grain boundary and an evolving second-phase particle

We performed phase-field simulations to analyse the interaction of a migrating grain boundary with an evolving second-phase particle. It is found that depending on the difference between the interfacial energies of the particle–matrix interface for the two grain orientations involved and the driving force for grain boundary movement, particles with a particle size well above the critical limit can dissolve due to passage of the boundary.

Sessile drop evaluation of high temperature copper/spinel and slag/spinel interactions

Abstract Metal droplets sticking to spinel solids, present in metallurgical slag systems, play an important role in hindering the sedimentation of copper in slags. To understand this phenomenon, the interaction between spinel particles with Cu on one hand and with slag, on the other hand, was evaluated. A dedicated approach was applied, using an industrially relevant synthetic slag system PbO–FeO–SiO 2 –CaO–Al 2 O 3 –Cu 2 O–ZnO, pure copper and MgAl 2 O 4 substrates to represent the industrial slag, the entrained copper droplets and the spinel solids, respectively. Both the copper–MgAl 2 O 4 and the slag–MgAl 2 O 4 interaction were studied using sessile drop measurements, combined with an extensive microstructural analysis. Additionally, the effect of time on the slag–MgAl 2 O 4 interaction was studied using immersion experiments. Copper displayed a non-wetting behaviour on MgAl 2 O 4 , whereas slag displayed a reactive wetting and an interaction layer of (Mg, Fe, Zn)(Al, Fe) 2 O 4 spinel was formed at the interface, which was also observed in the immersion experiments. Moreover, the diffusion of MgO and Al 2 O 3 from the spinel substrate into the slag droplets was noted.

Microstructure simulation of grain growth in Cu through silicon vias using phase-field modeling

In this paper, a time-efficient 3D phase-field model, for simulating grain growth in Through Silicon Via (TSV) is presented. This model is modified to model grain growth in the cylindrical shape of a TSV to capture the effect of temperature in its microstructure. The data generated from this simulation is used to explain large distribution of Cu pumping (i.e. non reversible thermal expansion of TSV). To achieve this, generated results must be used as an input in a Finite Element Model of a TSV structure to study the effect of grain growth and asymmetry in distribution of Cu pumping. Results generated from a sample FEM model with grain structure input confirms this capability.

A Phase Field Model for grain Growth and Thermal Grooving in Thin Films with Orientation Dependent Surface Energy

A phase field model for simulating grain growth and thermal grooving in thin films is presented. Orientation dependence of the surface free energy and misorientation dependence of the grain boundary free energy are included in the model. Moreover, the model can treat different mechanisms for groove formation, namely through volume diffusion, surface diffusion, evaporation-condensation, or a combination of these mechanisms. The evolution of a groove between two grains has been simulated for different surface and grain boundary energies and different groove formation mechanisms.