SFB 616


Pictures SFB616

 Project C1:
Energy Dissipation of Ballistic Injected Electrons

 The goal of the project is the analysis of the ballistic transport of electrons through thin metallic layers as well as through individual molecules on top of the surface. Fig. 1 + Fig. 2 show the principle of Ballistic Electron Emission Microscopy (BEEM).


Fig. 1

 The electrons are injected from the tip of a scanning tunneling microscope with energies between the Fermi and the vacuum level. Those electrons which reach the Schottky barrier between the metal and the supporting n-type semiconductor may cross the barrier if their energy exceeds the height of the barrier. This can be measured directly at the back of the semiconductor.





Fig. 2

 Fig. 2 displays a schematic diagram of the combination of the tunneling barrier between the tip and the sample surface and the Schottky barrier at the interface between the metal and the semiconductor.









Fig. 3

 Fig. 3 shows the current of ballistic electrons as function of the energy E of the electrons. For the particular Bi(111) layer on Si(100) the Schottky barrier amounts to 0.58 eV. Above this threshold the current raises according to   (dashed line). The blue curve displays the data for the clean Bi-surface, the red curve for the Bi-surface covered by a monolayer of C60 . The reduction of the current of ballistic electrons as well as a second threshold at about 1.5 eV are clearly visible.






 Fig. 4 exhibits the lateral variation of the signal (B) in comparison to the topographic structure (A). For the triangular islands of closed packed C60 the ballistic transmission through the molecules is reduced, but reveals a ring-like pattern for each molecule as can be seen by the inset to the lower right in B.

Fig. 4

Currently the work focuses on the following projects:
- conservation of the lateral momentum of the electrons at the metal-semiconductor interface
- ballistic transmission of doped C60
- transmission of ballistic holes
- metallic heterostructures

 This project is in close collaborations with projects A1, A2, A3, B2, C2 and C4.


Internationaler Workshop 2008 I

Workshop 2008 I

C1 Bernhart et al.
PDF (1.0 MB)

Internationaler Workshop 2008 II

Workshop 2008 II

C1 Bernhart et al.
 PDF (1.4 MB)