Center for Nanoscale Science & Technolgy home page NIST home page Electron Physics Group home page Electron Physics Group Research Areas page Electron Physics Group Publications page Collaborative Research Facilities pageElectron Physics Group Staff page Electron Physics Group What's New page
• Nanomagnetics
• Atomic scale characterization & fabrication
• Modeling nanostructures in mesoscopic environments
• Nanoscale measurement & fabrication using laser-controlled atoms
• Atom Optics
• Magneto-Optic Microscopy
• Magnetic Force Microscopy
• Nanoscale Physics
• SEMPA
• UHV STM

Electronic Properties of 1-d, 2-d, and 3-d Cs Structures

Considerable interest exists in the study of alkali-metal adsorption on semiconductor surfaces as model systems for understanding metal-semiconductor interfaces. In our study of Cs on cleaved GaAs(110) and InSb(110) surfaces, we have discovered a novel system for the formation of alkali structures which range in dimensionality from 1-d, 2-d, and 3-d, depending on the coverage of Cs on these surfaces. Figure 1(a) shows a large area image of 1-d Cs chains on GaAs(110), including chains that are over 100 nm long. Note that the chains tend to be separated by tens of nanometers and have no long range order along the [001] direction, demonstrating that they are truly 1-d structures. The higher-resolution image shown in Fig. 1(b) reveals that the Cs structures are single-atom zig-zag chains in registry with the GaAs(110) surface. Similar 1-d structures are observed on the InSb(110), as shown in Fig. 1(c).

Figure 1
Figure 1. (upper left) STM image, 137x137 nm, of 1-d Cs zig-zag chains on GaAs(110); (upper right) 7x7 nm image of a single Cs zig-zag chain on GaAs(110); (lower left) 20x20 nm image of Cs chains on InSb(110); (lower right) schematic drawing of Cs zig-zag chains.

With increasing Cs coverage, 2-d and 3-d phases also form on the (110) surfaces of GaAs and InSb. The possibility of the 1-d Cs structures being metallic is very interesting, since bulk Cs lies near the metal-insulator transition. To probe for metallic characteristics tunneling spectroscopy measurements were performed to examine the tunneling conductivity at zero bias, which is a measure of the density of states at the Fermi level. As shown in Fig. 2, both the 1-d and 2-d phases show insulating characteristics, and the onset of metallicity does not occur until the formation of the 3-d structures of Cs. In addition to these novel electronic properties, we have observed that the alkali atoms can be manipulated with the STM probe tip by utilizing the interaction of the dipole moment of the alkali atom with the electric field gradient in the STM tunnel junction.

Figure 2
Figure 2. Current-vs-voltage measurements over various Cs structures on GaAs(110).


Publications
Atomic Manipulation of Polarizable Atoms by Electric Field Directional Diffusion
Alkali Metals on III-V (110) Semiconductor Surfaces: Overlayer Properties and Manipulation Via STM
Atomic and Molecular Manipulation With the Scanning Tunneling Microscope
Insulating Cs Overlayer on InSb(110)
Geometric and Electronic Properties of Cs Structures on III-V (110) Surfaces: From 1-D and 2-D Insulators to 3-D Metals
Manipulation of Adsorbed Atoms and Creation of New Structures on Room-temperature Surfaces with a Scanning Tunneling Microscope
A Scanning Tunneling Microscopy Study of Clean and Cs-Covered InSb(110)
Scanning Tunneling Microscopy Study of InSb(110)
Structure of Cs on GaAs(110) as Determined by STM

Staff listings
Joseph A. Stroscio
Daniel T. Pierce
Robert J. Celotta

Former staff listing
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