Scanning tunnelling microscopy (STM) has proved to be a fascinating and powerful technique in the field of surface science. The fact that sets the STM apart from most other surface sensitive techniques is its ability to resolve the structure of surfaces on an atomic scale, that is atom-by-atom, and furthermore its ability to study the dynamics of surface processes. This article presents a survey of recent STM studies of well characterized single crystal metal surfaces under ultra-high vacuum conditions. It particularly addresses STM investigations of clean metal surfaces, adsorbates on metal surfaces, adsorbate-induced restructuring of metal surfaces, chemical reactions on metal surfaces, metal-on-metal growth and finally studies of electron confinement and quantum size effects on metal surfaces.

https://iopscience.iop.org/article/10.1088/0034-4885/59/12/004/pdf

Scanning tunnelling microscopy studies of metal surfaces

Self-surfactant effect on Fe/Au(100):: place exchange plus Au self-diffusion

Much of the fascination of Scanning Tunneling Microscopy (STM) results from its ability to directly image atomic and molecular structures of a wide variety of materials. Since its inception, one purpose of STM has been to go beyond imaging by performing local experiments with individual nanoscopic objects addressed by the STM tip [5.1]. The concept of the technique to be presented in this chapter is to use the tip of a STM as a source of low-energy electrons or holes to locally excite photon emission and thus study luminescence1 phenomena on nanometer-sized structures of metals, semiconductors and molecules [5.2]. This combination of STM with optical methods offers several attractive features. First, photons represent a particularly versatile channel of information in addition to the tunneling current. Their intensity, spectral distribution, angular emission pattern, polarization status, and time correlation are accessible by sensitive optical methods and represent unique probes of the tunneling region. Spatial mapping of these physical quantities permits the addition of “true color” to STM images. Second, the emission of visible or infrared light is a chemically specific characteristic of many excitations of solids and molecules.

Photon Emission from the Scanning Tunneling Microscope

The transient tunneling current induced by pulsed laser irradiation of a scanning tunneling microscope (STM) tunneling gap was observed to occur over a 100 μs time scale range in response to a 20 ns duration of the laser pulse. The amplitude of the transient current varies exponentially with laser power, confirming our previous suggestion that thermal expansion of the STM tip is the main source of the transient increase of tunneling current. This thermal expansion mechanism is also supported by the observation of a qualitatively similar variation of the tunneling current during the piezo-driven decrease of the tip-sample separation.

Transient tunneling current in laser-assisted scanning tunneling microscopy

Molecular level studies of solid-gas and solid-liquid interfaces

Tunneling spectroscopy of Au(100)‐(5×20) and Fe on Au(100) surfaces has been studied. Using a well‐defined tunneling tip, I–S, I–V, and V/I*dI/dV–V spectra were obtained. The results confirm that the characteristics of the spectra resemble those of previously reported semiconductors. From I–S relations, it was found that the tunneling barrier decreases abruptly when the tunneling gap is <6 A.

P. J. Silverman

Papers

Scanning tunneling spectroscopy of metal surfaces