Self-organized patterning on Si(001) by ion sputtering with simultaneous metal incorporation

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.     

Convariant q-Differential Calculus and its Deformations at qN = 1

We construct the generalized version of covariant Z₃-graded differential calculus introduced by one of us (R.K.) and then extend it to the case of arbitrary Z_N grading. Here our main purpose is to establish the recurrence formulae for the Nth power of covariant q-differential D_q=d_q + A and to analyze more closely the particular case of q being an Nth primitive root of unity. The generalized notions of connection and curvature are introduced and several examples of realization are displayed for N=3 and 4. Finally we briefly discuss the idea of infinitesimal deformations of the parameter q in the complex plane.     

Chemistry and microstructure of PLD (Ti,Al)CxN1-x coatings deposited at room temperature

The aim of the present work was the improvement of titanium-aluminium nitride (TiAlN) coatings by the solid-solution hardening with carbon atoms leading to titanium-aluminium carbon-nitride (Ti,Al)C_xN_1-x coatings with varying carbon (x) and nitrogen contents. The request of low deposition temperatures necessary for the coating of heat sensitive materials like tool steels of high hardness and polymers was reached by the application of the room temperature pulsed laser deposition (PLD) technique. A Nd:YAG laser of 1064 nm wavelength operated at two different laser pulse energies was used in the ablation experiments of pure TiAl targets (50 at.% Al) in various C₂H₂-Ar gas mixtures. Different pulse energies of the laser resulted in changes of the ratio of Ti/Al atoms in the grown coatings. Furthermore, the results reveal a strong proportionality of the gas mixture to the C and N content of the coatings. In the coatings deposited at low C₂H₂ gas flows the XRD investigations showed crystalline phases with fcc TiN type lattices, whereas high acetylene flows during deposition resulted in the formation of fully amorphous coatings and carbon precipitation or cluster boundaries found in Raman investigations. PACS 81.15.Fg; 46.55.+d     

Dynamical conductivity at the dirty superconductor-metal quantum phase transition

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.     

The effect of high power ultrasound on an aqueous suspension of graphite

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.     

Random Block Operators

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.     

Heavy atomic-layer doping of B in low-temperature Si epitaxial growth on Si(1 0 0) by ultraclean low-pressure chemical vapor deposition

Electrical characteristics of B atomic-layer doped Si epitaxial films on Si(1 0 0) formed by B atomic-layer formation on Si(1 0 0) at 180 °C and subsequent capping Si deposition at 500 °C using ultraclean low-pressure chemical vapor deposition were investigated. From evaluation results of carrier concentration in the films, by low-temperature SiH₄ exposure at 180-300 °C before the capping Si deposition at 500 °C, 70% improvement of B electrical activity was confirmed, and it is suggested that lowering the temperatures for B atomic-layer formation on Si(1 0 0) as well as SiH₄ exposure before the capping Si deposition is effective to suppress B clustering and to achieve B atomic-layer doped Si films with extremely high carrier concentration.     

Structural Insight into IAPP-Derived Amyloid Inhibitors and Their Mechanism of Action

Designed peptides derived from the islet amyloid polypeptide (IAPP) cross-amyloid interaction surface with Aβ (termed interaction surface mimics or ISMs) have been shown to be highly potent inhibitors of Aβ amyloid self-assembly. However, the molecular mechanism of their function is not well understood. Using solution-state and solid-state NMR spectroscopy in combination with ensemble-averaged dynamics simulations and other biophysical methods including TEM, fluorescence spectroscopy and microscopy, and DLS, we characterize ISM structural preferences and interactions. We find that the ISM peptide R3-GI is highly dynamic, can adopt a β-like structure, and oligomerizes into colloid-like assemblies in a process that is reminiscent of liquid–liquid phase separation (LLPS). Our results suggest that such assemblies yield multivalent surfaces for interactions with Aβ40. Sequestration of substrates into these colloid-like structures provides a mechanistic basis for ISM function and the design of novel potent anti-amyloid molecules.