Copper is the current interconnect metal of choice in integrated circuits. As interconnect dimensions decrease, the resistivity of copper increases dramatically because of electron scattering from surfaces, impurities, and grain boundaries (GBs) and threatens to stymie continued device scaling. Lacking direct measurements of individual scattering sources, understanding of the relative importance of these scattering mechanisms has largely relied on semiempirical modeling. Here we present the first ever attempt to measure and calculate individual GB resistances in copper nanowires with a one-to-one correspondence to the GB structure. Large resistance jumps are directly measured at the random GBs with a value far greater than at coincidence GBs and first-principles calculations. The high resistivity of the random GB appears to be intrinsic, arising from the scaling of electron mean free path with the size of the lattice relaxation region. The striking impact of random GB scattering adds vital information for understanding nanoscale conductors.

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a b s t r a c tInterdiffusion and impurity diffusion in Mg binary solid solutions, Mg(Al) and Mg(Zn) were investigated at temperatures ranging from 623 to 723 K. Interdiffusion coefficients were determined via the Boltzmann-Matano Method using solid-to-solid diffusion couples assembled with polycrystalline Mg and Mg(Al) or Mg(Zn) solid solutions. In addition, the Hall method was employed to extrapolate the impurity diffusion coefficients of Al and Zn in pure polycrystalline Mg. For all diffusion couples, electron microprobe analysis was utilized for the measurement of concentration profiles. The interdiffusion coefficient in Mg(Zn) was higher than that of Mg(Al) by an order of magnitude. Additionally, the interdiffusion coefficient increased significantly as a function of Al content in Mg(Al) solid solution, but very little with Zn content in Mg(Zn) solid solution. The activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg(Al) solid solution were determined to be 186.8 (±0.9) kJ/mol and 7.69 Â 10 À1 (±1.80 Â 10 À1 ) m 2 /s, respectively, while those determined for Mg(Zn) solid solution were 139.5 (±4.0) kJ/mol and 1.48 Â 10 À3 (±1.13 Â 10 À3 ) m 2 /s. In Mg, the Zn impurity diffusion coefficient was an order of magnitude higher than the Al impurity diffusion coefficient. The activation energy and pre-exponential factor for diffusion of Al impurity in Mg were determined to be 139.3 (±14.8) kJ/mol and 6.25 Â 10 À5 (±5.37 Â 10 À4 ) m 2 /s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 (±6.3) kJ/mol and 2.90 Â 10 À5 (±4.41 Â 10 À5 ) m 2 /s.

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