Femtosecond laser-assisted fabrication of chalcopyrite micro-concentrator photovoltaics.

Micro-concentrator solar cells offer an attractive way to further enhance the efficiency of planar-cell technologies while saving absorber material. Here, two laser-based bottom-up processes for the fabrication of regular arrays of CuInSe2 and Cu(In,Ga)Se2 microabsorber islands are presented, namely one approach based on nucleation and one based on laser-induced forward transfer. Additionally, a procedure for processing these microabsorbers to functioning micro solar cells connected in parallel is demonstrated. The resulting cells show up to 2.9% efficiency and a significant efficiency enhancement under concentrated illumination.

Water oxidation by amorphous cobalt-based oxides: volume activity and proton transfer to electrolyte bases.

Water oxidation in the neutral pH regime catalyzed by amorphous transition-metal oxides is of high interest in energy science. Crucial determinants of electrocatalytic activity were investigated for a cobalt-based oxide film electrodeposited at various thicknesses on inert electrodes. For water oxidation at low current densities, the turnover frequency (TOF) per cobalt ion of the bulk material stayed fully constant for variation of the thickness of the oxide film by a factor of 100 (from about 15 nm to 1.5 µm). Thickness variation changed neither the nanostructure of the outer film surface nor the atomic structure of the oxide catalyst significantly. These findings imply catalytic activity of the bulk hydrated oxide material. Nonclassical dependence on pH was observed. For buffered electrolytes with pKa values of the buffer base ranging from 4.7 (acetate) to 10.3 (hydrogen carbonate), the catalytic activity reflected the protonation state of the buffer base in the electrolyte solution directly and not the intrinsic catalytic properties of the oxide itself. It is proposed that catalysis of water oxidation occurs within the bulk hydrated oxide film at the margins of cobalt oxide fragments of molecular dimensions. At high current densities, the availability of a proton-accepting base at the catalyst-electrolyte interface controls the rate of water oxidation. The reported findings may be of general relevance for water oxidation catalyzed at moderate pH by amorphous transition-metal oxides.

Water oxidation by electrodeposited cobalt oxides--role of anions and redox-inert cations in structure and function of the amorphous catalyst.

For the production of nonfossil fuels, water oxidation by inexpensive cobalt-based catalysts is of high interest. Films for the electrocatalysis of water oxidation were obtained by oxidative self-assembly (electrodeposition) from aqueous solutions containing, apart from Co, either K, Li or Ca with either a phosphate, acetate or chloride anion. X-ray absorption spectroscopy (XAS) at the Co K-edge revealed clusters of edge-sharing CoO(6) octahedra in all films, but the size or structural disorder of the Co-oxido clusters differed. Whereas potassium binding is largely unspecific, CaCo(3) O(4) cubanes, which resemble the CaMn(3) O(4) cubane of the biological catalyst in oxygenic photosynthesis, may form, as suggested by XAS at the Ca K-edge. Cyclic voltammograms in a potassium phosphate buffer at pH 7 revealed that no specific combination of anions and redox-inactive cations is required for catalytic water oxidation. However, the anion type modulates not only the size (or order) of the Co-oxido clusters, but also electrodeposition rates, redox potentials, the capacity for oxidative charging, and catalytic currents. On these grounds, structure-activity relations are discussed.

Oxidation of Au by surface OH: nucleation and electronic structure of gold on hydroxylated MgO(001).

The nucleation and electronic structure of vapor-deposited Au on hydroxylated MgO(001) surfaces has been investigated under ultrahigh vacuum conditions. Hydroxylated MgO(001) surfaces with two different hydroxyl coverages, 0.4 and 1 monolayer, respectively, were prepared by exposure to water (D(2)O) at room temperature. Scanning tunneling microscopy experiments show significantly higher gold particle densities and smaller particle sizes on the hydroxylated MgO surface as compared to gold deposited on clean MgO(001). Infrared spectroscopy and X-ray photoelectron spectroscopy experiments were performed to reveal details about the initial nucleation of gold. Gold atoms are found to chemically interact with a specific type of hydroxyl groups on the MgO surface, leading to the formation of oxidized gold particles. The enhanced adhesion of Au particles, which is due to the formation of strong Au-O interfacial bonds, is responsible for the observed higher stability of small Au clusters toward thermal sintering on hydroxylated MgO surfaces. The results are compared to similar studies on Au/TiO(2)(110) model systems and powder samples prepared by the deposition-precipitation route.

Rapid purification of myxoma virus DNA.

A rapid and efficient procedure for the purification of myxoma virus DNA from infected cell cultures is described. The traditional method used for recovery of myxoma virus DNA involves multiple freeze-thawing cycles to disrupt cells and release virions followed by ultracentrifugation to concentrate virions for DNA extraction. Freeze-thaw cycles are time consuming and reduce viral titers, while ultracentrifugation steps limit the number of samples that can be processed at one time, reducing efficiency. In this report an optimized method circumventing the time-consuming techniques and replacing them with rapid, efficient steps adequate for the processing of larger numbers of samples is described. The traditional method was compared with the optimized protocol, which was found to be more efficient in terms of time required to complete the process and in the quantities of DNA purified.

Rapid identification of myxoma virus variants by long-range PCR and restriction fragment length polymorphism analysis.

A long-range PCR method directed at the Myxoma virus (MV) left hand and right hand terminal inverted repeats (TIRs) for rapid amplification of genomic DNA and MV isolate differentiation by restriction fragment length polymorphism (RFLP) analysis is described. The efficacy of this method was tested by comparing the results from full genome RFLPs with those from TIRs amplified separately using reference strain Lausanne (Lu) and a field MV strain characterised previously for its virulence in rabbits. The usefulness of this method was also demonstrated by amplifying MV DNA directly from the eyelid tissue of an infected rabbit and comparative RFLP analysis with respect to Lu. The results proved the long-range PCR technique to be a simple highly efficient method for identifying mutations between MV genomes by RFLP analyses of the amplified TIRs and may be used in future studies to identify variable regions for phylogenetic studies.