D. Mangelinck

Enhancement of thermal stability of NiSi films on (100)Si and (111)Si by Pt addition

The effect of a small amount of Pt (5 at. %) on the thermal stability of NiSi film on (100) and (111) Si substrates has been investigated both by in situ annealing inside an x-ray photoelectron spectroscopy system and by ex situ rapid thermal annealing. The addition of platinum increases the disilicide nucleation temperature to 900 °C leading to a better stability of NiSi at high temperatures. In the presence of Pt, NiSi films on both (111)Si and (100)Si substrates develop a texture with the relationship (100)NiSi∥(111)Si and (010)NiSi∥(100)Si. The increase in thermal stability has been explained in terms of the nucleation concept.

Morphological and phase stability of nickel–germanosilicide on Si1−xGex under thermal stress

Continuous and uniform Ni(Si,Ge) layers are formed on polycrystalline Si and Si0.42Ge0.58 substrate films at 500 degreesC by rapid thermal processing. The germanosilicide is identified as NiSi0.42G ...

Effect of Co, Pt, and Au additions on the stability and epitaxy of NiSi2 films on (111)Si

We studied the effect of the addition of cobalt, platinum, or gold on the cell parameter of NiSi2 deposited epitaxially on (111)Si. Namely, the formation and the microstructure of NiSi2 films containing one of these elements are compared to those of the pure disilicide. The solubility of Co, Pt, and Au in NiSi2 ranges from a total substitution to nickel in the case of cobalt to a very weak quantity (less than 1%) in the case of platinum. An intermediate behavior was observed for gold which can occupy more than 10% of the metal sites. This important solubility has been confirmed by analysis of bulk Ni(Au) disilicides and is understood as a consequence of the metastability of gold silicides. Cobalt, Pt, and Au additions change the temperature of formation of NiSi2: from 800 °C for reaction with pure nickel, this temperature is lowered to 650 °C by Co and Au additions while it is increased to 950 °C for Pt. These modifications are consistent with the nucleation controlled formation of NiSi2 and the effect of...

Increased nucleation temperature of NiSi2 in the reaction of Ni thin films with Si1−xGex

The formation of a ternary solid solution NiSi1−xGex, instead of a mixture of NiSi and NiGe, is found during solid-state interactions between Ni and various Si1−xGex films ranging from pure Si to pure Ge. The lattice parameters of the solid solution of orthorhombic structure increase linearly with Ge content (x) as: a=5.24+0.19x A, b=3.25+0.16x A, and c=5.68+0.15x A. The specific resistivity increases from 17 μΩ cm for NiSi to 21 μΩ cm for NiSi0.71Ge0.29 and NiSi0.42Ge0.58. Although the Ge content rapidly drops from 30–60 to about 10 at. % in the solid solutions formed above 600 °C, the crystallographic structure remains unchanged and no NiSi2 [or Ni(Si,Ge)2] is found in the Si1−xGex samples even after annealing at 850 °C. Without Ge, the NiSi completely disappears at 750 °C. These results indicate a strong effect of the entropy of mixing in NiSi–NiGe on the nucleation of NiSi2.

Differential scanning calorimetry analysis of the linear parabolic growth of nanometric Ni silicide thin films on a Si substrate

The formation of nanometric Ni silicide films on a Si wafer is analyzed using differential scanning calorimetry (DSC) and isothermal x-ray diffraction measurements. The sensitivity of DSC is remarkable even in this experimental configuration constituted of a Ni∕Si bilayer deposited on a Si substrate. Both methods confirm the sequential growth of Ni2Si and NiSi (for T<700°C). However the kinetics of growth of the first silicide formed (Ni2Si) cannot be fitted, for the two sets of measurements, by a simple parabolic law. Better agreement is obtained using a linear-parabolic growth law and a smaller activation energy for the linear term (0.8 eV) than for the parabolic one (1.5 eV).

Simultaneous growth of Ni5Ge3 and NiGe by reaction of Ni film with Ge

The reaction between nanometric Ni films and Ge is analyzed using isothermal x-ray diffraction measurements and transmission electron microscopy. It is found that NiGe is formed during deposition at room temperature. The metal rich phase that grows during heat treatment has been clearly identified to be Ni5Ge3. The simultaneous growths of Ni5Ge3 and NiGe have been observed on amorphous and polycrystalline germanium. This is in contrast with the usual sequential growth reported in thin films.

Effect of Pt addition on Ni silicide formation at low temperature: Growth, redistribution, and solubility

The formation of Ni silicide during the reaction between Ni(5% Pt) and a Si(100) substrate has been analyzed by differential scanning calorimetry (DSC), in situ x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), and H4e+ Rutherford backscattering. The DSC measurements show evidence of the Ni2Si nucleation followed by lateral growth formation. In situ XRD and TEM have been used to investigate the sequence of formation of the silicides. These experiments show that the formations of Ni2Si and NiSi occur simultaneously in the presence of the Pt alloy. The redistribution of platinum at different stages of the Ni silicide growth has been determined. We have estimated the solubility limit of platinum (1 at. % at 573 K) in the Ni2Si phase by extrapolation from a measured value at 1073 K. This redistribution is explained in terms of the solubility limits and the diffusion of Pt in the Ni2Si and NiSi phases. Pt is more likely to reside at the silicide grain boundaries and the interface...

Formation of Ni silicide from Ni(Au) films on (111)Si

The solid state reaction between a Ni (7 at. % Au) film and a Si substrate at temperatures ranging from 250 to 800 °C is examined by scanning electron microscopy, x‐ray diffraction, and Rutherford backscattering spectrometry. Compared to the usual features for thin film reaction of Ni with Si, we observed the following. (i) The simultaneous growth of Ni2Si and NiSi, and the growth of NiSi at the expense of both Ni2Si and Ni. This is related to Au accumulation in the metal layer. (ii) Au precipitation at 300 °C followed by the dissolution of the clusters thus created above the Au–Si eutectic temperature (370 °C). (iii) A decrease of the temperature of formation of NiSi2 and the appearance of thickness oscillations that are characteristic of nucleation. These different effects are interpreted by taking into account the metallurgy of the system: segregation of Au in the Ni film, Au solubility in the different silicides, change in surface and interface energies, and chemical interactions with Si.The solid state reaction between a Ni (7 at. % Au) film and a Si substrate at temperatures ranging from 250 to 800 °C is examined by scanning electron microscopy, x‐ray diffraction, and Rutherford backscattering spectrometry. Compared to the usual features for thin film reaction of Ni with Si, we observed the following. (i) The simultaneous growth of Ni2Si and NiSi, and the growth of NiSi at the expense of both Ni2Si and Ni. This is related to Au accumulation in the metal layer. (ii) Au precipitation at 300 °C followed by the dissolution of the clusters thus created above the Au–Si eutectic temperature (370 °C). (iii) A decrease of the temperature of formation of NiSi2 and the appearance of thickness oscillations that are characteristic of nucleation. These different effects are interpreted by taking into account the metallurgy of the system: segregation of Au in the Ni film, Au solubility in the different silicides, change in surface and interface energies, and chemical interactions with Si.

First stages of the formation of Ni silicide by atom probe tomography

Atom probe tomography assisted by femtosecond laser pulses has been performed on a Ni(Pt) film on (100)Si. Two phases with different compositions were found to form during deposition at room temperature: a NiSi layer with a relatively constant thickness of approximately 2nm and a particle of Ni2Si. The shape of the Ni2Si particle is in accordance with nucleation followed by lateral growth formation. This confirms the growth model deduced from calorimetric measurement of silicides and intermetallics and from atom probe tomography studies of the Al∕Co system. A nonuniform redistribution of Pt was also observed.

Revealing martensitic transformation and α/β interface evolution in electron beam melting three-dimensional-printed Ti-6Al-4V.

As an important metal three-dimensional printing technology, electron beam melting (EBM) is gaining increasing attention due to its huge potential applications in aerospace and biomedical fields. EBM processing of Ti-6Al-4V as well as its microstructure and mechanical properties were extensively investigated. However, it is still lack of quantitative studies regarding its microstructural evolution, indicative of EBM thermal process. Here, we report α′ martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography. Quantitative chemical composition analysis suggests a general phase transformation sequence. By increasing in-fill hatched thickness, elemental partitioning ratios arise and β volume fraction is increased. Furthermore, we observe kinetic vanadium segregation and aluminum depletion at interface front and the resultant α/β interface widening phenomenon. It may give rise to an increased α/β lattice mismatch and weakened α/β interfaces, which could account for the degraded strength as printing thickness increases.