Meet Amro meet-amro

Name: Amro Alkhatib
Research interest: Electrical Transport Behavior in Ultra-thin Metallic Films and Nanostructures

Research Summary

Ultra-thin metallic films show interesting electrical phenomena as their thickness decreases. In particular, as the thickness reaches the nanoscale their electrical behavior has no precedents in the macroscale since they behave in a non-ohmic fashion. For example, the electrical resistivity of gold, which is a perfect or almost perfect conductor otherwise, can reach values which are orders of magnitude above their macroscale counterparts. Moreover, while the standard ohmic behavior is characterized by a linear relationship between current and voltage, the response of ultra thin films presents non-linearities between the latter that are not taken into account by standard theory. Here, we propose that such behavior is related to the discontinuity in the films below a certain thickness. Such discontinuities appear in lower thicknesses as the metallic film grows in an island growth mode before they start to merge later on when the thickness grows. As a result of the inherent discontinuity the current cannot find a continuous percolation path in the lateral direction of conduction. Electron tunneling was found to be the dominant mechanism of conduction in such thicknesses. A model for describing this behavior was developed based on Simmon’s model for tunneling in MIM junctions. Using that model we showed that two dominant iii tunneling regimes existed, dependent on the gold island separation and area of tunneling (related to the size of islands). Such interpretation for the observed behavior would be of great importance to enhance the current existing models for electrical conduction in thin metallic films.


Thin Film Growth
Left: Volmer-Weber (VW: island formation)
Middle: Frank-van der Merwe (FM: layer-by-layer)
Right: Stranski-Krastanov (SK: layer-plus-island)


Layered electrical/topography Maps:
Left: No correlation is observed between resistive areas and surface features
Right: High resistive areas should be related to inherent material behavior and  not  tip/surface interaction.


Current-Voltage  Spectroscopy


Discontinuity Hypothesis


Proof of discontinuities in lower thicknesses
SEM / EDX analysis showed black spaces Inside the metallic sheet (void/non-gold content)


Conductive AFM tip:
Silicon substrate – Aluminum reflective coating
Conductive coating ( Pt, Ir, Diamond, ..)
Tip radius of ~ 15 nm
(Image courtesy of Asylum Research)
Top: Gold Nanoparticles
Bottom: C-AFM setup.
Lateral configuration –  Vertical configuration
External resistance added (reduce joule heating effect and current density)


A. Alkhatib, T Souier, M. Chiesa “Non-ohmic transport behavior in ultra-thin gold films“ in Materials Science and Engineering: B, 2011.