Local fields in conductor surface electromigration: A first-principles study in the low-bias ballistic limit

Abstract

Utilizing first-principles quantum transport calculations, we investigate the role of local fields in conductor surface electromigration. A nanometer thick Ag(100) thin film is adopted as our prototypical conductor, where we demonstrate the existence of intense local electric fields at atomic surface defects under an external bias. It is shown that such local fields can play an important role in driving surface electromigration and electrical breakdown. The intense fields originate from the relatively short (atomic-scale) screening lengths common to most elemental metals. This general short-range screening trend is established self-consistently within an intuitive picture of linear response electrostatics. The findings shed new light on the underlying physical origins of surface electromigration and point to the possibility of harnessing local fields to engineer electromigration at the nanoscale.

Electromigration and the structure of metallic nanocontacts

“…This is in agreement with a more recent approach, where a screening of 5%-25% is found (Lodder, 2005). The electrostatic fields near impurities have been recalculated using first-principles calculations and were found to be very intense due to the short-range nature of the screening in metals (Bevan et al, 2012).…”

Quasi-Fermi level splitting in nanoscale junctions from ab initio

“…Note that, because the electron states are not explicitly generated within DFT-NEGF, QFLs have been extracted as a post-processing procedure based on certain approximations on the form of the averaged local electrochemical potential. [11][12]17 Within the MS-DFT formalism, we now adopt finite-sized L and R electrodes (micro-canonical ensembles) and explicitly extract the Kohn-Sham (KS) states by performing the multi-space constrained-search procedure or total-energy minimizations with the constraint of 𝑒𝑉 # = 𝜇 & − 𝜇 ( . A key step is then, during the self-consistent construction of non-equilibrium charge densities, variationally occupying the KS states with a proper occupation rule.…”

“…which could be a representative scheme of generating the local electrochemical potential that was found to be useful for post-processing analysis. [11][12]17 Carrying out the MS-DFT calculations for the single-molecule junction models based on the HDT and HTDT molecules and benchmarking the DFT-NEGF calculation results, we now heuristically determine the validity of the above two occupation rules. In modeling the junctions (Fig.…”

“…However, the standard approach combining density-functional theory (DFT) with non-equilibrium Green's function (NEGF) formalism within the Landauer picture has been less successful in extracting the QFL profiles because it does not explicitly provide information on single-electron wavefunctions and their occupations. [11][12] Herein, carrying out first-principles non-equilibrium electronic structure and quantum transport calculations within the multi-space constrained-search DFT (MS-DFT) formalism we have recently developed, 13 we report the firstprinciples calculations of QFL profiles in single-molecule junctions and their correlations with finite-bias transmissions. For nanoscale constrictions where the Landauer picture can be invoked, the MS-DFT method is established by (i) adopting a micro-canonical picture that considers finite electrodes (rather than semi-infinite electrodes within the Landauer picture) and (ii) mapping the finite-bias quantum transport process to the drain-to-source multi-electrode electronic excitation (optical analogy).…”

A first principles scanning tunneling potentiometry study of an opaque graphene grain boundary in the ballistic transport regime

“…On the other hand, if we are measuring the electrochemical potential then the gradient does not necessarily measure the local electric field. As discussed in [16,31] and [33], at low bias the electrostatic potential profile ϕ r ( ) can be related to the electrochemical potential profile in equation ( 7) through the linear response expression of Poissonʼs equation where ε r is the relative static permittivity and ε 0 is the vacuum permittivity. Importantly, only when the electrochemical potential varies on a length scale similar to that of the screening length (i.e.…”