Richard Sorbello is a leading theorist in the field of
electromigration. The phenomenon of electromigration is the transport of atoms
in a metallic system that is subjected to an electric field and the accompanying
"electron wind." It is a subject of great technological interest because the
unwanted migration of atoms in very large-scale integrated circuits (VLSI) leads
to degradation of the metallic fine lines comprising the backbone of the circuits, and this ultimately results in
device failure. Professor Sorbello has also worked in electron transport,
electronic structure, superconductivity, ultrasonic attenuation,
thermomigration, electronic response of small metal particles, and molecular
vibrations at metallic surfaces. Currently, he is also working in the theory of
resonant ultrasound spectroscopy.
In the field of electromigration, Professor Sorbello has published more
theoretical papers than any other researcher, and has introduced many important
insights and techniques. His work with P. Kumar placed the theory of
electromigration on a rigorous quantum mechanical foundation and has provided
theorists with a useful framework for further calculations. His
pseudopotential-based theory of the electron-wind force allowed treatment of
atomic configuration effects, and his work with B.B. Dasgupta introduced the
density matrix approach to electromigration and established the importance of
local field effects. Green's function studies with P. Rimbey showed that
band-polarization and virtual-bound states result in non-integral effective
valences associated with the direct electric field acting on the migrating atom.
Extensions of this work led to the first rigorous calculation of the electronic
contribution to thermomigration, which is the phenomenon of atom transport in a
thermal gradient. Additional work with A. Lodder introduced multiple-scattering
theory into the calculation of electromigration driving forces, and his work
with C.S. Chu introduced a local-field method which established a theoretical
framework for treating electromigration in mesoscopic systems. Further work with
I. Itskovich described the quantum dynamics of light-atom electromigration
within the formalism of many-body polaron theory. Recent work with his student
Z. Chen on local heating and atomic-recoil effects provides new insight into the
atomic migration process at the microscopic level. Professor Sorbello is a
member of the Laboratory for Surface Studies.
