On-Surface Chemistry Induced by Long-Lived Excitons: (NO)2 Dissociation on C60.

Solid-state excitonic excitations play an increasingly important role in optoelectronic and light harvesting processes due to their ubiquitous presence in dipolar two-dimensional materials. Here we show that long-lived solid-state excitons induce chemical reactions in adsorbed molecules and thus convert light into chemical energy. For the model system (NO)2 dimer adsorbed on ordered c(4×4) C60 films, time-of-flight measurements following UV laser excitation reveal a slow and a fast dissociative desorption channel, which are assigned to intersystem crossing and internal conversion, respectively, by time-dependent density functional theory calculations.

UV-induced formation of oxygen-derived dangling bonds on hydroxyl-terminated SiC.

A combined theoretical and multi-technique experimental study was employed to comprehensively determine the electronic structure of 6H-SiC(0 0 0 1) surfaces upon hydroxyl and oxygen termination. We demonstrate the UV-induced formation of single-coordinated oxygen radicals in on-top sites above the atoms of the uppermost silicon layer of the substrate on initially hydroxyl-terminated SiC. Such a configuration of oxygen radicals represents an unprecedented adsorbate-derived system of unpaired electrons, bearing analogy to silicon and carbon dangling bonds on clean, unreconstructed SiC surfaces. We evidence the presence of adsorbate-derived surface states within the fundamental band gap for both hydroxyl- and oxygen-terminated SiC. For hydroxyl termination, a hydrogen-induced unoccupied surface state is revealed consistently by inverse photoemission spectroscopy and density-functional theory calculations employing self-interaction-corrected pseudopotentials (DFT-SIC). The formation of oxygen dangling bonds is accompanied by the occurrence of an occupied surface state derived from p x - and p y -orbitals associated with the unpaired electrons as proven by both ultraviolet photoemission spectroscopy and DFT-SIC.

Functionalization of amorphous SiO2 and 6H-SiC(0001) surfaces with benzo[ghi]perylene-1,2-dicarboxylic anhydride via an APTES linker.

The successful covalent functionalization of quartz and n-type 6H-SiC with organosilanes and benzo[ghi]perylene-1,2-dicarboxylic dye is demonstrated. In particular, wet-chemically processed self-assembled layers of aminopropyltriethoxysilane (APTES) and benzo[ghi]perylene-1,2-dicarboxylic anhydride are investigated. The structural and chemical properties of these layers are studied by contact angle measurements, attenuated total reflection infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The optical properties are measured by confocal microscopy. The wetting angles observed for the organic layers are α = 68° for the APTES-functionalized surface, while angles of α = 85° and 78° are determined for dye-functionalized quartz and 6H-SiC surfaces, respectively. However, not all amino groups of the APTES-functionalized surfaces react to bind dye molecules. Further dye functionalization is not uniform throughout the surface, showing different island sizes of the dye and including different chemical environments. The quartz surface exhibits a higher packing density of dyes than the 6H-SiC surface. The fluorescence lifetimes of the surface-attached dye show double exponential decays of about 1.4 and 4.2 ns, largely independent of the substrates.