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Work function changes induced by charged adsorbates: origin of the polarity asymmetry
Paul S Bagus1, Daniel Käfer, Gregor Witte
1Department of Chemistry, University of North Texas, Denton, Texas 76203-5070, USA.
Physical Review Letters
|June 4, 2008
Summary
Charged adsorbates on metal surfaces exhibit polarity asymmetry. Theoretical analysis explains this phenomenon, showing negatively charged species can paradoxically decrease work function.
Area of Science:
- Surface Science
- Theoretical Chemistry
- Condensed Matter Physics
Background:
- Experimental observations show polarity asymmetry in charged adsorbates on metal surfaces.
- The underlying reasons for this asymmetry and its impact on work function changes have remained poorly understood.
Purpose of the Study:
- To theoretically analyze the polarity asymmetry of charged adsorbates on metal surfaces.
- To elucidate the contributing factors to interface dipole changes and work function alterations.
- To explain the physical and chemical origins of these phenomena for specific cases.
Main Methods:
- Theoretical analysis of charged adsorbates on metal surfaces.
- Examination of terms contributing to interface dipole changes.
- Case study using iodine (I) on copper (Cu(111)).
Main Results:
- A pronounced polarity asymmetry was revealed between electropositive and electronegative adsorbates.
- Analysis identified and quantified several, often canceling, terms affecting interface dipole and work function changes (Δφ).
- For I on Cu(111), the magnitudes and signs of these terms were explained by their physical and chemical origins.
Conclusions:
- The theoretical framework successfully reproduces the observed polarity asymmetry.
- The cancellation of contributing terms leads to unexpected work function changes.
- Negatively charged adsorbates can result in a decrease in work function (Δφ<0), contrary to expectations (Δφ>0).
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