Electronic Properties of Fe Clusters on GaAs(110)
Considerable interest lies in the electronic properties of small metal
particles as a probe of the evolution of the electronic structure toward that
of the solid state. Small particles with n=10-100 atoms span the regime
where the electronic properties develop from atomic-like to metallic
characteristics with increasing particle size. In our studies of Fe growth on
GaAs(110), we have observed electron tunneling characteristics which depend on
the size of Fe clusters on the GaAs surface.
Fe clusters form naturally when depositing Fe on GaAs(110) at room temperature,
as shown in Fig. 1. STM contours show several different cluster heights
indicating 3D cluster growth. The volumes of the clusters shown in Fig. 1
range from 0.1 to 1.5 nm3 corresponding to 9-127 atoms per
cluster.
Figure 1: STM image, 40 nm x 38 nm, of 0.01 nm
of Fe on p-GaAs(110).
For Fe clusters of volumes ~0.15 nm3, corresponding to ~13 atoms, we observe a finite gap in the tunneling characteristics. This can be interpreted as due to non-metallic properties of the Fe cluster or possibly due to Coulomb charging effects. Larger clusters with > 35 atoms begin to show metallic characteristics. Tunneling into the GaAs surface in the vicinity of the Fe cluster has revealed the evanescent decay of midgap states.
Figure 2: Tunneling current vs voltage characteristics of Fe on
p-GaAs(110). The four curves correspond to (a) 1.7 nm Fe film,
(b) 1.15 nm3 cluster, and (d) GaAs(110) surface,
4.0 nm from the nearest cluster. The curves have been shifted vertically
for display.
Metallicity and Gap States in Tunneling to Fe Clusters on GaAs(110)
Dispersion of Evanescent Band Gap States in Fe Clusters on GaAs(110)
Characterization of Epitaxial Fe on GaAs(110) By Scanning Tunneling Microscopy
Joseph A. Stroscio
Daniel T. Pierce
Robert J. Celotta
Robert Dragoset - NIST
Phillip First - Georgia Institute of Technology
Lloyd Whitman - Naval Research Laboratory
Supported in part by the Office of Naval Research
Online: May 1996
Last Updated: February 2008
egpwebmaster@nist.gov