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Surface diffusion experiments with STM: equilibrium correlations and non-equilibrium low temperature growth.

M C Tringides¹, M Hupalo

¹Ames Laboratory-USDOE, Iowa State University, Ames, IA 50011, USA.

Journal of Physics. Condensed Matter : an Institute of Physics Journal

|March 10, 2011

Summary

Surface diffusion measurements reveal distinct behaviors in equilibrium and non-equilibrium states. Scanning tunneling microscopy (STM) enables the study of collective diffusion and novel low-temperature mechanisms, explaining self-organization in thin films.

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Area of Science:

Surface Science
Statistical Mechanics
Materials Science

Background:

Surface diffusion is critical in determining material properties and self-organization.
Understanding diffusion mechanisms is essential for controlling thin film growth and surface phenomena.
Distinguishing between equilibrium and non-equilibrium diffusion is key to accurate theoretical modeling.

Purpose of the Study:

To investigate surface diffusion in both equilibrium and non-equilibrium conditions using Scanning Tunneling Microscopy (STM).
To measure the collective diffusion coefficient D(c) in 2-d overlayers and compare with theoretical predictions.
To explore novel diffusion mechanisms present in non-equilibrium growth experiments at low temperatures.

Main Methods:

Utilized STM to perform equilibrium measurements of surface diffusion by analyzing tunneling current fluctuations.
Conducted growth experiments at low temperatures and high flux rates to probe non-equilibrium diffusion.
Investigated the role of wetting layers in island formation and self-organization during thin film growth.

Main Results:

Successfully measured the collective diffusion coefficient D(c) from autocorrelation of tunneling current fluctuations.
Observed unusually uniform island heights in Pb/Si(111) and In/Si(111) systems, indicating novel low-temperature diffusion.
Revealed the significant role of the wetting layer in the self-organization of growing islands.

Conclusions:

STM is a versatile tool for studying both equilibrium and non-equilibrium surface diffusion.
Novel low-temperature diffusion mechanisms contribute to high degrees of self-organization in specific thin film systems.
The wetting layer plays a crucial role in the evolution and stability of islands during growth.