Thermodynamic and kinetic study of solid state reactions in the Cu–Si system

Abstract

It has been shown that significant changes in the course of solid state reactions can be realized by decreasing length scale, temperature, or by varying parent microstructures. In the case of the formation of Cu 3 Si by interdiffusion of Cu and Si, previous research has shown that over a large temperature range reaction rates are determined by the rate of grain boundary diffusion of Cu through the growing Cu 3 Si phase. We have examined the effect of replacing crystalline Si with amorphous Si (a-Si) on these solid state reactions, as well as the effect of decreasing the temperatures and length scales of the reactions. Multilayered thin film diffusion couples of Cu and a-Si were prepared by sputter deposition, with most average composite stoichiometries close to that of the equilibrium phase Cu 3 Si. Layer thicknesses of the two materials were changed such that the modulation (sum of the thickness of one layer of Cu and a-Si), λ, varied between 5 and 160 nm. Xray diffraction analysis and transmission electron microscopy analysis were used to identify phases present in as prepared and reacted diffusion couples. Complete reactions to form a single phase or mixtures of the three low temperature equilibrium silicides (Cu 3 Si, Cu 15 Si 4 and Cu 5 Si) were observed. Upon initial heating of samples from room temperature, heat flow signals were observed with differential scanning calorimetry corresponding to the growth of Cu 3 Si. At higher temperatures (> 525 K) and in the presence of excess Cu, the more Cu rich silicides, Cu 15 Si 4 and Cu 5 Si formed. Based on differential scanning calorimetry results for samples with average stoichiometry of the phases Cu 3 Si and Cu 5 Si, enthalpies of formation of these compounds were measured. Considering the reaction of these phases forming from Cu and a-Si, the enthalpies were found to be-13.6±0.3 kJ/mol for Cu 3 Si and-10.5±0.6 kJ/mol for Cu 5 Si. The growth of Cu 3 Si was found to obey a parabolic growth law:

Growth of Crystalline Copper Silicide Nanowires in High Yield within a High Boiling Point Solvent System

“…30 The majority of reports to date studying Cu silicides have presented the formation of the orthorhombic Cu 3 Si η′′ phase rather than the other low temperature equilibrium phases Cu 15 Si 4 and Cu 5 Si. 18,35 Previously, the formation of higher Cu ratio silicides has required reaction temperatures of greater than 525 K and the presence of excess Cu. 35 The formation of the Cu 15 Si 4 phase here may thus be due to these two conditions being satisfied.…”

“…18,35 Previously, the formation of higher Cu ratio silicides has required reaction temperatures of greater than 525 K and the presence of excess Cu. 35 The formation of the Cu 15 Si 4 phase here may thus be due to these two conditions being satisfied. In the case of the Ge NWs previously grown in our system from Cu foil, the intermediate Cu germanide phase formed on top of the cubic Cu foil was Cu 3 Ge (orthorhombic).…”

Investigations of Interface Properties in Copper-Silicon Carbide Composites

“…2, proves that part of Si has dissolved in the Cu. Due to the phenomenon of contamination carbon linear distribution results should be treated approximately as a supplement to other results.The observed effect of silicon dissolution has been studied and reported in many papers [9][10][11][12]. Even such small disadvantageous changes at metal-ceramic boundary result in the decrease of global thermal conductivity, which is visible in case of coated SiC particles.…”

Phase separation of a microsized powder mixture of Si and SiC by Cu–Si alloying

“…The Cu-Si binary alloy system has been well established (Olesinski and Abbaschian, 1986), and the thermodynamic characterization of each phases is described in many references (Chromik et al, 1999;Lüdecke, 1987;Mattern et al, 2007;Meschel and Kleppa, 1991). The primary intermetallic compounds at room temperature include η″ (Cu 3 Si), ε (Cu 15 Si 4 ), and γ (Cu 5 Si), and the eutectic temperature is 802 1C with a composition of 69.9 at.% Cu.…”