W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Modellbildung Kohlenstoff-Modifikationen C 60 -Cluster Graphit graphenenanotubes Diamant

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Nobelpreis 1973 Leo Esaki The Nobel Prize in Physics (1973) was awarded in recognition of his pioneering work on electron tunneling in solids.

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Wavefunction engineering Wavefunction engineering - a new paradigm in the design of quantum semiconductor devices MBE Molecular beam epitaxy

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Wavefunction engineering

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Wavefunction engineering

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Wavefunction engineering The negative differential resistance shown by the I-V curve is a character- istic required for transistor action. With multipleresonant states, in the quantum well between the double barriers, we will have one peak for each resonant state. It has been shown by Capasso that two DBRTDs can replace 24 con- ventional transistors in logic circuits. Thus, we gain in functionality as well as in size, and hence in the speed of the device.

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Halbleitersupergitter Cross section SEM image of a PbEuTe microcavity structure. The top and bottom Bragg miror consists of 18 and 24 l/4 pairs, and the active region of 1000 A PbTe quantum well and 2200 A PbEuTe barriers. The layer structure is revealed by plasma etching, and the dark regions are layers with smaller Eu content.

W. Hergert Institut für Physik MLU Halle-Wittenberg Theorie B - Quantenmechanik V2 Potentialtöpfe Metalloberflächen Figure 3. (A) Top view of the Cu(111) surface with the Co adatom shown in its natural fcc binding site. (B) Schematic potential well for the Co atom in fcc and hcp sites: blue curve, native potential well, no tip- Co interaction; green curve, tip-induced potential well; red curve, native potential with added tip-induced potential. The potential at the hcp site increases in depth because of the increase in tip-Co interaction as the tip-Co distance decreases. The tip-induced potential well over the hcp site causes the Co atom to switch between the fcc and hcp sites, producing discrete changes in the tunnel current. (C to E) Schematic of manipulated atom tip height trace. Initially, with the tip over the fcc site, the force on the Co atom is vertical and the tip images the Co atom. As the tip moves down the side of the Co atom, a lateral force develops (D). When the tip reaches the hcp site, the lateral force is large enough to induce the Co atom to hop to the hcp site (E). STM – scanning tunneling microscope