cfaed Seminar Series

The success of graphene has not only shown that it is possible to create stable, single atom thick
sheets from a layered crystalline solid, but also that these materials have fundamentally different
properties than their bulk counterparts. Much theoretical work on the matter of 2D elements
different from carbon was performed in recent years. The most probable candidates are the heavy
elements of the 4. main group – Si, Ge and Sn, the heavy elements of the 5. main group – P, As
and Sb, and boron, as the only element of the of the 3. main group, that may be stable in the ultrathin
form. The experimental work has focused on the epitactically grown sheets on catalytically
active metal surfaces. The synthesis of free-standing sheets, on the other hand, is highly
desirable, but not an easy goal to achieve. Consider, for example, the 2D form of silicon – the
silicene. The mechanical methods, like the scotch-tape method, will not work with bulk silicon due
to its purely sp3 bonding nature. The bonding between planes therein is rather strong, as
compared to graphite and other van der Waals layered solids. Furthermore, a problem for all
surface-rich materials is their instability, because the surface atoms are considerably more reactive
than those in the bulk material. This holds especially true for rather electropositive elements, like
silicon, so it is reasonable that the oxidation of silicene in air must be addressed to realize the full
potential of silicene in technological applications. Experiments with silicene grown on surfaces
revealed its fast oxidation after contact with air. Oxidation of the Si stripes starts at their extremities
– the edge atoms and porous in-plane defects, where the Si atoms with dangling bonds are
present. This was called the “burning-match process” by G. LeLay and B. Aufray, who have
pioneered the epitactical growth of silicene on metallic surfaces. So if one wants to create
processable free-standing silicene, those moieties must be chemically protected. In the present
talk, I would like to introduce my own experimental work in the field of the chemical preparation of
the free-standing sheets of the elements B, Si, Ge, Sn and P.