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971.
Marina Cornejo Bashkim Ziberi Christoph Meinecke Dietmar Hirsch Jürgen W. Gerlach Thomas Höche Frank Frost Bernd Rauschenbach 《Applied Physics A: Materials Science & Processing》2011,102(3):593-599
This report focuses on the effect of simultaneous Fe incorporation in the self-organized pattern formation on Si(001) by low-energy
ion-beam sputtering. Experimental observations giving evidence for the correlation between different ion-beam parameters,
Fe concentration on the substrate, and the resulting topography are shown. It was observed that the incorporation of Fe affects
the evolution of the topography and it is a requisite for the formation of ripples at near-normal incidence. It is shown also
that Fe is not homogeneously distributed on the surface, but there is a higher concentration at the crests of the ripples
than at the valleys. For the experimental setup used for this study, the Fe flux that reaches the surface is determined mainly
by the acceleration voltage (U
acc), while the ion energy (E
ion) and ion-beam incidence angle (α) control the concentration of Fe in the steady state. The adjustment of these operational parameters of the ion source enables
the fine-tuning of surface patterns. 相似文献
972.
We study fundamental spectral properties of random block operators that are common in the physical modelling of mesoscopic disordered systems such as dirty superconductors. Our results include ergodic properties, the location of the spectrum, existence and regularity of the integrated density of states, as well as Lifshits tails. Special attention is paid to the peculiarities arising from the block structure such as the occurrence of a robust gap in the middle of the spectrum. Without randomness in the off-diagonal blocks the density of states typically exhibits an inverse square-root singularity at the edges of the gap. In the presence of randomness we establish a Wegner estimate that is valid at all energies. It implies that the singularities are smeared out by randomness, and the density of states is bounded. We also show Lifshits tails at these band edges. Technically, one has to cope with a non-monotone dependence on the random couplings. 相似文献
973.
Nicola Mingirulli Jan Haschke Ralf Gogolin Rafel Ferré Tim F. Schulze J. Düsterhöft Nils‐Peter Harder Lars Korte Rolf Brendel Bernd Rech 《固体物理学:研究快报》2011,5(4):159-161
We present back‐contacted amorphous/crystalline silicon heterojunction solar cells (IBC‐SHJ) on n‐type substrates with fill factors exceeding 78% and high current densities, the latter enabled by a SiNx /SiO2 passivated phosphorus‐diffused front surface field. Voc calculations based on carrier lifetime data of reference samples indicate that for the IBC architecture and the given amorphous silicon layer qualities an emitter buffer layer is crucial to reach a high Voc, as known for both‐side contacted silicon heterojunction solar cells. A back surface field buffer layer has a minor influence. We observe a boost in solar cell Voc of 40 mV and a simultaneous fill factor reduction introducing the buffer layer. The aperture‐area efficiency increases from 19.8 ± 0.4% to 20.2 ± 0.4%. Both, efficiencies and fill factors constitute a significant improvement over previously reported values. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
974.
We establish optimal estimates of Gelfand numbers or Gelfand widths of absolutely convex hulls cov(K) of precompact subsets ${K\subset H}$ of a Hilbert space H by the metric entropy of the set K where the covering numbers ${N(K, \varepsilon)}$ of K by ${\varepsilon}$ -balls of H satisfy the Lorentz condition $$ \int\limits_{0}^{\infty} \left(\log N(K,\varepsilon) \right)^{r/s}\, d\varepsilon^{s} < \infty $$ for some fixed ${0 < r, s \le \infty}$ with the usual modifications in the cases r = ∞, 0 < s < ∞ and 0 < r < ∞, s = ∞. The integral here is an improper Stieltjes integral. Moreover, we obtain optimal estimates of Gelfand numbers of absolutely convex hulls if the metric entropy satisfies the entropy condition $$\sup_{\varepsilon >0 }\varepsilon \left(\log N(K,\varepsilon) \right)^{1/r}\left(\log(2+\log N(K,\varepsilon))\right)^\beta < \infty$$ for some fixed 0 < r < ∞, ?∞ < β < ∞. Using inequalities between Gelfand and entropy numbers we also get optimal estimates of the metric entropy of the absolutely convex hull cov(K). As an interesting feature of the estimates, a sudden jump of the asymptotic behavior of Gelfand numbers as well as of the metric entropy of absolutely convex hulls occurs for fixed s if the parameter r crosses the point r = 2 and, if r = 2 is fixed, if the parameter β crosses the point β = 1. The results established in Hilbert spaces extend and recover corresponding results of several authors. 相似文献
975.
We prove that a transitive permutation group of degree n with a cyclic point stabilizer and whose order is n(n-1) is isomorphic to the affine group of degree 1 over a field with n elements. More generally we show that if a finite group G has an abelian and core-free Hall subgroup Q, then either Q has a small order (2|Q|2 < |G|) or G is a direct product of 2-transitive Frobenius groups. 相似文献
976.
Bernd Ulrich Wolmer V. Vasconcelos 《Transactions of the American Mathematical Society》2005,357(2):425-442
The computation of the integral closure of an affine ring has been the focus of several modern algorithms. We will treat here one related problem: the number of generators the integral closure of an affine ring may require. This number, and the degrees of the generators in the graded case, are major measures of cost of the computation. We prove several polynomial type bounds for various kinds of algebras, and establish in characteristic zero an exponential type bound for homogeneous algebras with a small singular locus.
977.
Fabrice Guittonneau Abdesselam Abdelouas Bernd Grambow Sandrine Huclier 《Ultrasonics sonochemistry》2010,17(2):391-398
Ultrasound treatment was used to study the decrease of the granulometry of graphite, due to the cavitation, which allows the erosion by separating grains. At a smaller scale, cavitation bubble implosion tears apart graphite sheets as shown by HRTEM, while HO and H radicals produced from water sonolysis, generate oxidative and reductive reactions on these sheet fragments. Such reactions form smaller species, e.g. dissolved organic matter. The methodology proposed is very sensitive to unambiguously identifying the in situ composition of organic compounds in water. The use of the atmospheric pressure chemical ionization (APCI) Fourier transform mass spectrometry (FTMS) technique minimizes the perturbation of the organic composition and does not require chemical treatment for analysis. The structural features observed in the narrow range (m/z < 300) were mainly aromatic compounds (phenol, benzene, toluene, xylene, benzenediazonium, etc.), C4–C6 alkenes and C2–C10 carboxylic acids. Synthesis of small compounds from graphite sonication has never been reported and will probably be helpful to understand the mechanisms involved in high energy radical reactions. 相似文献
978.
Veit Preidel Daniel Lockau Tobias Sontheimer Franziska Back Eveline Rudigier‐Voigt Bernd Rech Christiane Becker 《固体物理学:研究快报》2013,7(12):1045-1049
We present a design study of 3D photonic poly‐Si microarchitectures on 2 µm periodically textured glass substrates for application as absorber layers in crystalline Si thin‐film solar cells. Different arrays of microholes and microcones were fabricated in a low‐cost process, by combining high rate electron beam evaporation, nanoimprint technology and self‐organized solid phase crystallization. Two promising designs exhibiting strong absorption enhancement were identified by optical analysis. High angular acceptance and calculated maximum achievable short‐circuit current density of 27.6 mA/cm2 for an effective Si thickness of 1.1 µm highlight the optical potential of these microarchitectures as broadband absorbers in polycrystalline Si thin‐film solar cells.
979.
We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments. 相似文献
980.