Meet Amro

Name: Amro Alkhatib
Research interest: Electrical Transport Behavior in Ultra-thin Metallic Films and Nanostructures
Email: aalkhatib@masdar.ac.ae

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)

Publications

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