Heterostructures of GaN with SiC and ZnO enhance carrier stability and separation in framework semiconductors

A computational approach, using the density functional theory, is employed to describe the enhanced electron-hole stability and separation in a novel class of semiconducting composite materials, with the so-called double bubble structural motif, which can be used for photocatalytic applications. We examine the double bubble containing SiC mixed with either GaN or ZnO, as well as related motifs that prove to have low formation energies. We find that a 24-atom SiC sodalite cage inside a 96-atom ZnO cage possesses electronic properties that make this material suitable for solar radiation absorption applications. Surprisingly stable, the inverse structure, with ZnO inside SiC, was found to show a large deformation of the double bubble and a strong localisation of the photo-excited electron charge carriers, with the lowest band gap of ca. 2.15 eV of the composite materials considered. The nanoporous nature of these materials could indicate their suitability for thermoelectric applications

Origin of three-body resonances

We expose the relation between the properties of the three-body continuum states and their two-body subsystems. These properties refer to their bound and virtual states and resonances, all defined as poles of the $S$-matrix. For one infinitely heavy core and two non-interacting light particles, the complex energies of the three-body poles are the sum of the two two-body complex pole-energies. These generic relations are modified by center-of-mass effects which alone can produce a Borromean system. We show how the three-body states evolve in $^6$He, $^6$Li, and $^6$Be when the nucleon-nucleon interaction is continuously switched on. The schematic model is able to reproduce the main properties in their spectra. Realistic calculations for these nuclei are shown in detail for comparison. The implications of a core with non-zero spin are investigated and illustrated for $^{17}$Ne ($^{15}$O+p+p). Dimensionless units allow predictions for systems of different scales.Comment: 15 pages, 7 figure

Thermodynamically accessible titanium clusters TiN, N = 2–32

We have performed a genetic algorithm search on the tight-binding interatomic potential energy surface (PES) for small TiN (N = 2–32) clusters. The low energy candidate clusters were further refined using density functional theory (DFT) calculations with the PBEsol exchange–correlation functional and evaluated with the PBEsol0 hybrid functional. The resulting clusters were analysed in terms of their structural features, growth mechanism and surface area. The results suggest a growth mechanism that is based on forming coordination centres by interpenetrating icosahedra, icositetrahedra and Frank–Kasper polyhedra. We identify centres of coordination, which act as centres of bulk nucleation in medium sized clusters and determine the morphological features of the cluster

Why Are Polar Surfaces of ZnO Stable?

We probe and rationalize the complex surface chemistry of wurtzite ZnO by employing interatomic potential calculations coupled with a Monte Carlo procedure that sampled over 0.5 million local minima. We analyze the structure and stability of the (0001) and (0001̅) ZnO surfaces, rationalizing previous patterns found in STM images and explaining the (1 × 1) periodicity reported by LEED analysis. The full range of Zn/O surface occupancies was covered for a (5 × 5) supercell, keeping |<i>m</i>_Zn – <i>m</i>_O|/<i>N</i> ≈ 0.24 where <i>m</i> and <i>N</i> are the numbers of occupied surface sites and total surface sites, respectively. Our calculations explain why the (5 × 5) reconstructions seen in some experiments and highlight the importance of completely canceling the inherent dipole of the unreconstructed polar surfaces. The experimentally observed rich reconstruction patterns can be traced from the lowest occupancy, showing the thermodynamically most stable configurations of both polar surfaces. Triangular and striped reconstructions are seen, <i>inter alia</i>, on both polar surfaces, and hexagonal patterns also appear on the O terminated surface. Our results explain the main experimental structures observed on these complex surfaces. Moreover, grand canonical simulations of ZnO polar surfaces reveal that disorder is favored and, thus, configurational entropic factors is the the cause of their stability

Nine-ring angular fused biscarbazoloanthracene displaying a solid state based excimer emission suitable for OLED application

A new biscarbazoloanthracene consisting of nine fused aromatic rings, including two pyrrole units, has been obtained in a straightforward and convergent synthesis. Computational chemistry and conformational analysis revealed that the semiconductor’s molecule is not planar, the two carbazole moieties being helical twisted from the plane of the anthracene unit. Photophysical and electrochemical measurements showed that this angular fused heteroacene has a low lying HOMO energy level with a wide band gap despite its extended p-conjugated molecular framework. Based on its relatively low-lying HOMO level, the semiconductor promises a high environmental stability in comparison to other related linear fused acenes and heteroacenes. The biscarbazoloanthracene has been applied as the light emitting layer in a white light emitting diode (WOLED). It is proposed that the white OLED feature is due to dual light emission properties from the active semiconductor layer being based on both the molecular luminescence of the small molecule and a discrete excimer emission made possible by suitable aggregates in the solid state. Noteworthy, this is the first reported example of such a behavior observed in a small molecule heteroacene rather than an oligomer or a polymer

The choice of legal form of business from the point of view of tax burden

The aim of this thesis is to assess the possibilities of tax optimization in relation to the different legal forms of business. The thesis describes the various legal forms of business and tax system according to the valid legislation of the Czech Republic. The next step is analyze tax burden on individual forms, especially in terms of income tax. The methodology of thesis includes a procedure for determining of the tax burden, actually the tax obligations and available resources. A substantial part of the thesis are tax optimization options and their impact on tax obligation. The practical part of thesis deals with some forms of business and compares their tax burden and the available resources that are available after the payment of compulsory payments. The conclusion of thesis contains a summary and comparison of results from the practical part, the advantages and disadvantages of forms and recommendations. This recommendation should provide guidance to future businessmen when choosing a legal form of business if they are making a decisions on the basis of the above mentioned two aspects, namely the tax burden and the resources available after payment of compulsory payments