Integrated Calendar

Inorganic-organic semiconductor hybrid structures for opto-electronics and photonics

Sylke Blumstengel

Institute of Physics, Humboldt University Berlin, Newtonstr. 15, 12489 Berlin

In this seminar I will summarize our recent efforts to fabricate heterostructures based on ZnO and various conjugated organic materials as well as to tailor their electronic and optical properties. Growth by molecular beam epitaxy of both material components ensures well-defined interfaces and highest structural quality. A unique feature of ZnO and its ternaries ZnCdO and ZnMgO is that films and quantum structures with very good crystalline and optical properties can be epitaxially grown at low temperatures (50°C!) compatible with the stability of organic materials. Thus, not only organic-on-inorganic, but also inorganic-on-organic epitaxy can be performed. Relevant growth mechanisms are discussed. Interfacial energy level alignment including band-offset engineering through molecular morphology is presented. Direct electronic coupling of the fundamental excitations (Frenkel and Wannier-Mott excitons) across the interface occurs with coupling constants on the meV-energy scale. The superior optoelectronic function of sandwich-type hybrids is demonstrated by the achievement of stimulated emission of the enclosed organic layer at markedly reduced pump thresholds due to efficient energy transfer from ZnO.

Abstract: Peptides play critical roles in human physiology. Conformational flexibility limits, however, characterization of peptides which bind to biologically relevant membrane proteins. Mining protein receptors, we have pioneered an approach to identify allosteric modulators as leads for peptide-based drugs. Novel solution- and solid-phase organic chemistry for producing peptide mimics has been employed to study the secondary structure responsible for the biological activity of these modulators. For example, methodology will be presented for making peptide analogs possessing amino-lactam, aza-amino acid and azabicycloalkanone residues. Results from screening such analogs as receptor ligands will be discussed to illustrate efforts to identify biologically active conformers of the parent peptide and to construct mimics with improved physiological properties for drug discovery.