communications GrapheneIn order to realize solar cells with technologically useful performance, intensive efforts are being directed towards the development of novel device architectures and components. So far, high power conversion effi ciencies exceeding 5% have been reached with dye-sensitized [ 1 ] or polymer blend-based solar cells, [ 2 ] wherein very fast interfacial charge transfer occurs. However, charge transport is often limiting the performance of these devices. In particular for blendbased solar cells, the photocurrent depends strongly on the properties of the percolation network. [ 3 ] A promising strategy to overcome this limitation involves nano-structured solar cells which provide well-defi ned, separate pathways for carrier transport, thus minimizing recombination losses. Examples include vertically aligned arrays of ZnO, [ 4 ] TiO 2 , [ 5 ] Si nanowires, [ 6 ] or TiO 2 functionalized CNTs. [ 7 ] Especially promising are CNTs decorated with semiconductor nanoparticles, since the former provide a close-to-ideal transport pathway for carriers. However, it is diffi cult to obtain a high quality electrical connection between nanotube and semiconductor without disrupting the carbon framework of the nanotubes. Accordingly, studying the interface between sp 2 -bonded carbon materials and semiconductors is important for further improving the performance of CNT based solar cells. More recently, also the closely related graphene has attracted increasing interest toward photovoltaic applications. [ 8 ] It has been chemically modifi ed by the attachment of TiO 2 nanoparticles [ 9 ] or CdS quantum dots, [ 10 ] albeit only little is known about the interface between graphene and inorganic or organic semiconductors, in contrast to the metal-graphene interaction. [ 11 -13 ] In fact, while ultrafast electron transfer from CdS dots to graphene has been detected by time-resolved photoluminescence spectroscopy, [ 14 ] the suitability of these nanocomposites for light harvesting applications remains to be evaluated.Here, we investigate the photoelectric properties of the interface between graphene as a carbon nanostructure and CdS as a widely used II-VI semiconductor. In this model system, the graphene sheet is contacted with a CdS nanowire which serves to transport electrons to the opposite metal contact. The lateral device confi guration allows scanning photocurrent microscopy (SPCM) to be used to map the generated photocurrents with sub-micrometer resolution. In contrast to bulk solar cells, this opens the possibility to distinguish between photoresponses of the involved interfaces at the nanoscale. Although due to the ultrasmall photoactive interfacial area in these devices, they naturally exhibit only low photoconversion effi ciencies, they provide a valuable platform to explore strategies for chemical interface tailoring.The fi nal device structure is illustrated by the atomic force microscopy (AFM), optical microscopy and optical refl ection images in Figure 1 a. In this device, the contacted graphene consist...
InAs quantum dots (QDs) on InP were implemented as active layers in laser structures completely grown by metal organic vapor phase epitaxy (MOVPE). In laser structures due to growth of the upper InP cladding layers onto the QDs, a marked blueshift of the emission wavelength and a simultaneous degradation of photoluminescence intensity were observed. This behavior was systematically investigated using thermal treatment to simulate the growth of the upper cladding layer. Using an adequate growth procedure emission behavior was achieved that has proven to be fairly insensitive to over-/regrowth steps. Broad-area 1.55μm emitting laser devices were fabricated by incorporating seven QD layers in an all-MOVPE grown structure. Transparency current densities per dot layer of 80Acm−2 were achieved which is close to values of multiple quantum well lasers processed in the same way.
Widespread human SARS-CoV-2 infections pose a constant risk for virus transmission to animals. Here, we serologically investigated 1000 cattle samples collected in late 2021 in Germany. Eleven sera tested antibody-positive, indicating that cattle may be occasionally infected by contact to SARS-CoV-2-positive keepers, but there is no indication of further spreading.
In the present study, we show that, in human cells, after heterologous expression of GFP-Ypt11 (where GFP stands for green fluorescent protein), the protein is targeted to transferrin-positive recycling endosomes. This compartment has been shown to form extensive tubular networks on applying the drug Brefeldin A. We also show, by confocal fluorescent microscopy, that these networks also contain Rab11 in cells expressing CFP-Rab11a (where CFP stands for cyan fluorescent protein) fusion protein and that these structures are identical with those targeted by GFP-Ypt11.
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