Tham khảo tài liệu 'the materials science of thin films episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 378 Interdiffusion and Reactions In Thin Films Figure 8-13a. Compound film thickness versus square root of time for AuAl2 and Au2A1 at different annealing temperatures. b. O4 200 I75 I50 I25 I00__75 C io3 t k Figure 8-13b. Arrhenius plots for the kinetics of formation of AuAl2 and Au2Al compounds. From Ref. 20 . ness-time1 2 curves are proportional to the ubiquitous Boltzmann factor. Therefore by plotting these slopes actually the logs of the square of the slope in this case versus 1 7 K in the usual Arrhenius manner Fig. 8-13b we obtain activation energies for compound growth. The values of and eV can be roughly compared with the systematics given for FCC metals to elicit some clue as to the mass-transport mechanism for compound formation. Based on Au these energies translate into equivalent Boltzmann factors of exp .9Tm T and exp ỒATM T respectively suggesting a GB-as-sisted diffusion mechanism. Lastly it is interesting to note how the sequence of . Electromigration In Thin Films 379 Figure 8-14. Schematic diagrams illustrating compound formation sequence in Al-Au thin film couples. End phases depend on whether dM dAu or JAu dM. compound formation Fig. 8-14 correlates with the equilibrium phase diagram not shown . When the film thickness of Al exceeds that of Au then the latter will be totally consumed leaving excess Al. The observed equilibrium between Al and AuA12 layers is consistent with the phase diagram. Similarly excess Au is predicted to finally equilibrate with the Au4 Al phase as observed. . Electromigration in Thin Films Electromigration a phenomenon not unlike electrolysis involves the migration of metal atoms along the length of metallic conductors carrying large direct current densities. It was observed in liquid metal alloys well over a century ago and is a mechanism responsible for failure of tungsten light-bulb filaments. Bulk metals approach the melting point when powered with current densities J of about 104 A cm2. On the .
