Recent experiments that determine mass diffusion Ds on the close packed surfaces of vacuum compatible metals were reviewed. The results turn out to be approximately universal when scaled to homologous temperatures T/Tm, with Tm the melting temperature. A similar behavior of vacancy-driven diffusion in bulk metals was recognized for decades. Remarkably, the uncertainty with which this scaling occurred was only ~10%.

Why is Diffusion in Metals and on Metal Surfaces Universal? C.P.Flynn: Journal of Physics - Condensed Matter, 2006, 18[16], S439-45