Low temperature homogenization in nanocrystalline PdCu thin film system

Abstract

AbstactDiffusion and solid state reactions were investigated in Pd-Cu nanocrystalline films by means of secondary neutral mass spectrometry depth profiling technique. The heat treatments were made at low temperatures (where the volume diffusion was frozen in) for long enough annealing times to reach saturation. In the early stage there is a grain boundary interdiffusion. At longer times first a Pd plateau developed inside the Cu layer. Later on the Cu penetration was also more and more extended in the Pd, even the average composition of Cu in Pd became higher than the average Pd composition in Cu. Depending on the ratio of the initial thicknesses, the system (for thickness ratios corresponding to 50/50 Cu/Pd or to 75/25 Cu/Pd) arrived either at the mixture of pure Pd and β-CuPd phase or to the mixture of α′-Cu 3 Pd and β-CuPd phases, respectively, as dictated by the phase diagram. The process is interpreted as grain boundary diffusion induced solid state reaction.

Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry

“…In addition, in the literature mainly the alloying in the slower component (in B) was investigated and only few results on alloying on the other (faster) side can be found [12,13]. In a more recent series of experimental investigations in our laboratory [14][15][16][17][18][19][20] it was indicated that the compositions in the DIGM zones can be determined by secondary neutral mass spectrometry (SNMS) depth profiling. It was shown that i) as it was illustrated in the Cu/Ni system already in 1983 [21], alloying can also take place in the faster component, similarly as in the slower one of the Ag/Au system [16] and ii) if the grain size is less than half of the average sweeping distance of the GBs, L, a full homogenization is possible, with a saturation at compositions determined by the concentrations left behind the sweeping boundaries.…”

“…In order to get clear conclusions about the validity of above predictions it is plausible to make a distinction between systems forming solid solutions and systems forming compound. In the latter cases the DIGM drives the system to phase equilibrium, dictated by the bulk phase diagram [19,20], and the description of these systems should go beyond, e.g., the theoretical model of [4], providing the relations in Equation 1 or Equation 2. On the other hand in systems forming solid solutions, according to Equation 1 and Equation 2, the saturation values should be different on the two sides of the couple, predicting a higher value in the slower component (in B).…”

Determination of the compositions of the DIGM zone in nanocrystalline Ag/Au and Ag/Pd thin films by secondary neutral mass spectrometry

“…In addition, in the literature mainly the alloying in the slower component (in B) was investigated and only few results on alloying on the other (faster) side can be found [ 12 – 13 ]. In a more recent series of experimental investigations in our laboratory [ 14 – 20 ] it was indicated that the compositions in the DIGM zones can be determined by secondary neutral mass spectrometry (SNMS) depth profiling. It was shown that i) as it was illustrated in the Cu/Ni system already in 1983 [ 21 ], alloying can also take place in the faster component, similarly as in the slower one of the Ag/Au system [ 16 ] and ii) if the grain size is less than half of the average sweeping distance of the GBs, L , a full homogenization is possible, with a saturation at compositions determined by the concentrations left behind the sweeping boundaries.…”

“…In order to get clear conclusions about the validity of above predictions it is plausible to make a distinction between systems forming solid solutions and systems forming compound. In the latter cases the DIGM drives the system to phase equilibrium, dictated by the bulk phase diagram [ 19 – 20 ], and the description of these systems should go beyond, e.g., the theoretical model of [ 4 ], providing the relations in Eq. 1 or Eq.…”