Strong Band Gap Blueshift in Copper (I) Oxide Semiconductor via Bioinspired Route

Semiconductors have numerous applications in both science and technology. Several methods have been developed to engineer their band gap, which is one of the most important parameters of semiconductors. Here, it is shown that the incorporation of various amino acids into the crystal lattice of copper (I) oxide, akin to the way living organisms incorporate organic macromolecules into minerals during biomineralization, leads to significant shrinkage in the volume of the host unit cell and a strong blueshift in the band gap of up to ≈18%. In examining the potential location of the bio‐organic molecules within the inorganic host's lattice, a very good fit between the proposed model of incorporation and experimental findings is found. The bioinspired phenomenon of band gap widening is thought to be attributable to the void‐induced quantum confinement effect, even though observed in micrometer‐sized crystals. This hypothesis is supported by developing a tight‐binding model that is found to fit well with the experimental data. The outcome of this research could profoundly impact the fields of light‐emitting and spin‐based devices as well as opens up a new bioinspired route to tune the band gap of semiconductors.     

Lithiumpyridinyl‐Driven Synthesis of High‐Purity Zero‐Valent Iron Nanoparticles and Their Use in Follow‐Up Reactions

The synthesis of zero‐valent iron (Fe(0)) nanoparticles in pyridine using lithium bipyridinyl ([LiBipy]) or lithium pyridinyl ([LiPy]) is presented. FeCl₃ is used as the most simple starting material and reduced either in a [LiBipy]‐driven two‐step approach or in a [LiPy]‐driven one‐pot synthesis. High‐quality nanoparticles are obtained with uniform, spherical shape, and mean diameters of 2.9 ± 0.5 nm ([LiBipy]) or 4.1 ± 0.7 nm ([LiPy]). The as‐prepared, high purity Fe(0) nanoparticles are monocrystalline. In addition to particle characterization (high‐resolution transmission electron microscopy, scanning transmission electron microscopy, dynamic light scattering), composition and purity are examined in detail based on electron diffraction, X‐ray powder diffraction, elemental analysis, infrared spectroscopy, ⁵⁷Fe Mössbauer spectroscopy, and magnetic measurements. Due to their small size and high purity, the Fe(0) nanoparticles are highly reactive. They can be used in follow‐up reactions to obtain a variety of iron compounds, which is exemplarily shown for the transformation to iron carbide (Fe₃C) nanoparticles, the reaction with sulfur to obtain FeS nanoparticles, or the direct reaction with pentamethylcyclopentadiene to FeCp*₂ (Cp*: pentamethylcyclopentadienyl).     

Biosynthesis of the Fluorinated Natural Product Nucleocidin in Streptomyces calvus Is Dependent on the bldA‐Specified Leu‐tRNAUUA Molecule

Nucleocidin is one of the very few natural products known to contain fluorine. Mysteriously, the nucleocidin producer Streptomyces calvus ATCC 13382 has not been observed to synthesize the compound since its discovery in 1956. Here, we report that complementation of S. calvus ATCC 13382 with a functional bldA‐encoded Leu‐tRNA^UUA molecule restores the production of nucleocidin. Nucleocidin was detected in culture extracts by ¹⁹F NMR spectroscopy, HPLC‐ESI‐MS, and HPLC‐continuum source molecular absorption spectroscopy for fluorine‐specific detection. The molecule was purified from a large‐scale culture and definitively characterized by NMR spectroscopy and high‐resolution MS. The nucleocidin biosynthetic gene cluster was identified by the presence of genes encoding the 5′‐O‐sulfamate moiety and confirmed by gene disruption. Two of the genes within the nucleocidin biosynthetic gene cluster contain TTA codons, thus explaining the dependence on bldA and resolving a 60‐year‐old mystery.     

Super‐Efficient Exciton Funneling in Layer‐by‐Layer Semiconductor Nanocrystal Structures

In semiconductor nanocrystals the electronic energy gap is determined not only by the material but also by the size of the nanocrystals. This allows the construction of an energy‐gap gradient normal to multiple layers of nanocrystals where the diameters of the nanocrystals are monotonically increasing or decreasing in subsequent layers. In such devices we observe a highly efficient funneling of excitation energy from layers comprising smaller nanocrystals towards the layer with the largest nanocrystals in the center of the funnel. Most importantly, not only are excitons in radiative states transferred, but also excitons from trapped states, usually lost for luminescence, can be effectively recycled, hence increasing the overall luminescence yield.     

Fully employing software inspections data

Software inspections provide a proven approach to quality assurance for software products of all kinds, including requirements, design, code, test plans, among others. Common to all inspections is the aim of finding and fixing defects as early as possible, and thereby providing cost savings by minimizing the amount of rework necessary later in the life cycle. Measurement data, such as the number and type of found defects and the effort spent by the inspection team, provide not only direct feedback about the software product to the project team, but are also valuable for process improvement activities. In this paper, we discuss NASA??s use of software inspections and the rich set of data that has resulted. In particular, we present results from analysis of inspection data that illustrate the benefits of fully utilizing that data for process improvement at several levels. Examining such data across multiple inspections or projects allows team members to monitor and trigger cross project improvements. Such improvements may focus on the software development processes of the whole organization as well as improvements to the applied inspection process itself.     

Hybrid Colloidal Heterostructures of Anisotropic Semiconductor Nanocrystals Decorated with Noble Metals: Synthesis and Function

This Feature Article offers an overview of hybrid colloidal heterostructures of anisotropic semiconductor nanocrystals decorated with metals; primarily gold and platinum. The nonspherical shapes of the semiconductor components create a great variety of metal‐decorated hybrid nanostructures, whose synthesis and morphology are considered here. Due to the current interest in photocatalytic systems able to utilize solar energy for water‐splitting, the use of Pt‐decorated CdS‐based nanorods for hydrogen generation is specifically addressed. Great flexibility of the colloidal synthesis leading to well‐defined hybrid semiconductor–metal nanostructures drastically increases the possibility of their integration into functional nanosystems with novel synergetic properties, making them promising candidates for a variety of photovoltaic, catalytic, and sensing applications.     

Ostwald Ripening of precipitates and self similarity of size distributions in reaction controlled growth

We present a mathematical model to describe competitive growth of spherical precipitates in reaction-controlled systems. In this model the flux of solute atoms through the interface depends on the interface migration velocity and on the differences of chemical potential at the interface. The growth-rate obtained is dependent on the precipitate radius, much like in the diffusion-controlled case. Numerical simulations were performed using a modified finite-difference approach where the time-step increase changes during evolution to avoid dissolution of more than one precipitate each step. By using the continuity equation we obtained an analytical function that represents the self-similar shape of the precipitate-size distribution dependent of the growth-parameter ν. The effect of ν on the coarsening evolution was investigated. Our results show that the precipitate size distribution obtained from the numerical simulations agrees well with the analytical solution. As predicted by the theory, we obtained the growth parameter (ν = 4) and the temporal dependence of the mean-radius (t ^1/2) different of the diffusion case, ν = 6.75 and t ^1/3. We also show that the self-similarity of the PSD is independent of the initial PSD. Presented at the V Symposium of the Brazil-MRS. Florianópolis, 8–12 October 2006.