Access to Substituted Indenol Ethers via a Regioselective Intermolecular Carbopalladation Cascade.

Alkyne carbopalladation reactions can rapidly generate multiple new C-C bonds; however, regioselectivity is challenging for intermolecular variants. Using ynol ethers, we observe complete regiocontrol of migratory insertion followed by a second migratory insertion with a pendant alkene to turn-over the catalytic cycle. The resulting products are oligosubstituted 1-indenol ethers with defined stereochemistry based on the initial alkene geometry. Blocking ß-hydride elimination allowed for C-H and C-C reductive elimination steps for catalyst turnover.

Epitaxial III-V films and surfaces for photoelectrocatalysis.

Efficient photoelectrochemical devices for water splitting benefit from the highest material quality and dedicated surface preparation achieved by epitaxial growth. InP(100)-based half-cells show significant solar-to-hydrogen efficiencies, but require a bias due to insufficient voltage. Tandem absorber structures may provide both adequate potential and efficient utilization of the solar spectrum. We propose epitaxial dilute nitride GaPNAs photocathodes on Si(100) substrates to combine close-to-optimum limiting efficiency, lattice-matched growth, and established surface preparation. Prior to a discussion of the challenging III-V/Si(100) heterojunction, we describe the closely related epitaxial preparation of InP(100) surfaces and its beneficial impact on photoelectrochemical water-splitting performance. Analogies and specific differences to GaP(100) surfaces are discussed based on in situ reflectance anisotropy and on two-photon photoemission results. Preliminary experiments regarding GaP/Si(100) photoelectrochemistry and dilute nitride GaPN heteroepitaxy on Si(100) confirm the potential of the GaPNAs/Si tandem absorber structure for future water-splitting devices.

Fundamental aspects of electrodeposition for the realization of plasmonic nanostructures.

Electrodeposition is used for the preparation of nanoparticles and nanostructures that allow, in principle, surface plasmon excitation. The (photo)electrodeposition process of Rh and Au nanoparticles as well as of heterodimeric enzymes onto silicon surfaces is investigated and the resulting structures are discussed with regard to applications in photoelectroctalysis and biosensing. Electrodeposition of Rh onto H-terminated p-Si surfaces generates nanostructures of the metal nanoparticles with simultaneous oxidation of the substrate thus forming nano-dimensioned metal-oxide-semiconductor (MOS)-type contacts. The excess minority carrier harvesting in these nanoemitter structures, where semispherical space charge layers underneath the metal exist are discussed based on spectral sensitivity and capacitance measurements The deposition of Au nanoparticles by a combined chemical-electrochemical method on Si is presented as an example for sensing actuators where the resonance frequency is changed by adsorption. Similarly, site-selective deposition of the enzyme reverse transcriptase onto nanostructured (step-bunched) silicon serves as precursor experiment for biosensing in a Kretschmann-type ATR configuration. Future applications based on plasmonically active structures are outlined.