Scanning Tunnelling Microscopy
Scanning tunneling microscopy (STM) was introduced in 1982 by Gerd Binnig and Heinrich Rohrer. For this achievement, they were awarded the Nobel Prize in Physics in 1986 shared with Ernst Ruska.
The STM technique allows to probe the electronic structure of a sample. It also yields information on the geometry and on the vibrations of the sample in real space. The principle of STM is based on quantum mechanical tunneling, whereby a tunneling current flows at a small sample-tip distance between a conducting sample and a conducting tip
Spectroscopy with STM
The STM allows two types of spectroscopic measurements. Measuring the first derivative of the tunneling current against the applied bias voltage, called STS (scanning tunneling spectroscopy), gives rise to the electronic structure of the sample. Measuring the second derivative, called IETS (inelastic electron tunneling spectroscopy), gives information about the vibrational excitation of the surface and adsorbed molecules.
Inelastic electron tunneling spectrosopy
Inelastic Electron Tunneling Spectroscopy (IETS) is used to investigate the vibrational properties of single molecules on surfaces. In contrast to STM as an imaging technique and STS, where only elastically tunneling electrons are taken into account (path a in Fig. 1), IETS considers the inelastically tunneling electrons.
IET manipulation
An electric current can induce inelastic effects in a system where vibrations can be excited. In STM, electrons that tunnel through adsorbates at the surface can induce molecular vibrations, occupy electronic orbitals, or both (vibronic excitation).
Femtochemistry on the nanoscale
By combining a femtosecond-laser with a low-temperature STM, we investigate femtochemistry down to single molecules. After imaging the adsorbed molecules and their adsorption geometry, the tip is retracted from the surface as far as possible to enable an ultra-short laser pulse to reach the sample without a change in the near field close to the surface.
FTIR Spectroscopy
Spectroscopy in general means the detection and analysis of an absorbed, emitted or scattered radiation by a substance. In case of infrared (IR) spectroscopy the absorption of IR radiation causes the excitation of molecular vibrations and rotations.
High resolution electron energy loss spectroscopy
High-resolution electron energy loss spectroscopy (HR-EELS) is an analytical method to investigate the vibrational properties of surfaces and adsorbates under UHV conditions.
X-ray photo electron spectroscopy (XPS)
X-Ray Photoelectron Spectroscopy (XPS, also known as Electron Spectroscopy for Chemical Analysis – ESCA) is used to determine the electronic structure of a sample surface under UHV conditions.
Controlled manipulation of single atoms and small molecules using the scanning tunnelling microscope
This article reviews manipulation of single molecules by
scanning tunnelling microscopes, in particular vertical manip-
ulation, lateral manipulation, and inelastic electron tunnelling
(IET) manipulation.