MedeA® Application Notes for Magnetic & Optical Properties

Structure and Bond Lengths in Titanium Dioxide (TiO₂)

In addition to the lattice parameters, the rutile structure has an additional degree of freedom, namely the position of the oxygen atom. This case study shows the simultaneous calculation of all these structural degrees of freedom.

 Structure and Bond Lengths in Titanium Dioxide (TiO₂)

Hydrogen-induced Nanotunnel Opening below the Surface of a Semiconductor, Silicon Carbide

Patrick Soukiassian, Erich Wimmer Edvige Celasco, Claudia Giallombardo, Simon Bonanni, Luca Vattuone, Letizia Savio, Anontio Tejeda, Mathieu Silly, Marie D’angelo, Fausto Sirotti, Mario Rocca

Nanostructuring a surface is a key and mandatory engineering step toward advances in nanotechnology. A team of french and italian scientists and of a franco-american company has just shown that hydrogen/deuterium (H/D) induces the opening of nanotunnels below the surface of an advanced semiconductor, silicon carbide (SiC). Such a finding is an especially interesting one, particularly in views of the specific properties of SiC. These investigations have been performed using advanced experimental tools such as synchrotron radiation and vibrational spectroscopy techniques, and state-of-the-art theoretical simulations. Depending on the H/D SiC surface exposures, these nanotunnels undergo through a sequence of semiconducting/metallic/semiconducting transitions. Such nanotunnels open very promising prospects toward applications in electronic, chemistry, storage, sensors and biotechnology.

Magnetism of Fe Surface

First-principles calculations reveal that the magnetic moments of atoms on an Fe(001) surface are 30% larger than in the bulk. This enhancement decays within about three layers towards the bulk, which demonstrates the highly localized character of enhanced surface magnetism in transition metals such as iron.

 Magnetism of Fe Surface

CO Adsorption on a TiO₂ Surface

This application shows the interaction of carbon monoxide with rutile.
An answer is given to the question whether CO binds with the carbon or the oxygen molecule to the surface.

 CO Adsorption on a TiO₂ Surface

Surface Reconstruction of Si(001)

Despite the enormous progress in experimental surface science, notably with spectroscopic
methods exploiting synchrotron radiation and scanning tunneling microscopy, computations
remain one of the most useful sources for accurate data on surface structures. In fact, quite often
it is the combination of experimental and computed results, which gives the most reliable data of
surface structures. As an example, let us apply MEDEA to the Si(001) surface. This surface is the
typical substrate in the manufacturing of semiconducting devices.

 Surface Reconstruction of Si(001)
CSV