Epitaxial Ag(001) grown on MgO(001) and TiN(001): Twinning, surface morphology, and electron surface scattering

Epitaxial Ag(001) layers were deposited on MgO(001) in order to study electron surface scattering. X-ray reflection indicates 3D layer nucleation with a high rms surface roughness of 1.0 nm for a layer thickness d1⁄4 3.5 nm. X-ray diffraction shows that f111g twins form at d< 11 nm, followed by 2nd generation twinning for 11 nm< d< 120 nm. Increasing the growth temperature from 25 to 150 C suppresses 2nd generation twinning and reduces the twin density by 2 orders of magnitude. In situ deposition of epitaxial 2.5-nm-thick TiN(001) underlayers prior to Ag deposition results in twin-free single-crystal Ag(001) with 10 smoother surfaces for d1⁄4 3.5 nm. This is attributed to a better wetting on the higher energy TiN(001) than MgO(001) surface, resulting in the absence of 3D nuclei with exposed f111g facets, which facilitate twin nucleation. The twinned Ag/MgO layers have a higher resistivity q than the single crystal Ag/TiN layers at both 298 and 77 K, due to electron scattering at grain and twin boundaries. The q for single-crystal Ag layers increases with decreasing d, which is well explained with known surface scattering models and provides specularity parameters for the Ag-vacuum and the Ag-air interfaces of p1⁄4 0.86 0.1 and 0.46 0.1, respectively. A comparison with corresponding epitaxial Cu(001) layers shows that qAg< qCu for d> 50 nm, consistent with known bulk values. However, qAg>qCu for d< 40 nm. This is attributed to the larger electron mean free path for electron-phonon scattering and a correspondingly higher resistivity contribution from surface scattering in Ag than Cu. In contrast, air exposure causes qAg< qCu for all d, due to diffuse scattering at the oxidized Cu surface and the correspondingly higher Cu resistivity. VC 2012 American Institute of Physics. [doi:10.1063/1.3684976]