Shapes of Epitaxially Grown Quantum Dots

A variational model introduced by Spencer and Tersoff (Appl. Phys. Lett. 96:073114, 2010) to describe optimal faceted shapes of epitaxially deposited films is studied analytically in the case in which there are a non-vanishing crystallographic miscut and a lattice incompatibility between the film and the substrate. The existence of faceted minimizers for every volume of the deposited film is established. In particular, it is shown that there is no wetting effect for small volumes. Geometric properties including a faceted version of the zero contact angle are derived, and the explicit shapes of minimizers for small volumes are identified.     

Specific field emission properties of thin palladium films

The field emission current from thin palladium films deposited on insulating tips in UHV was measured as a function of film thickness at relatively low field strengths. The observed periodic oscillations of the field emission current can be interpreted as the quantum size effect.     

The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10^?5 and 10^?9 torr, and their resistivity ? measured as a function of film thicknessd≦500Å at temperaturesT=110K andT=300K. The ?(d) characteristics of films deposited at residual gas pressures of about 10^?6 torr with condensation rates of about 1Å/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ?(d) characteristics of films deposited at 10^?8 torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ?(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ?(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.

     

The quantum size effect in thin antimony films

Thin antimony films have been epitaxially deposited at 350K onto cleavage surfaces of mica at different residual gas pressures between 10⁻⁵ and 10⁻⁹ torr, and their resistivity ∂ measured as a function of film thicknessd≦500? at temperaturesT=110K andT=300K. The ∂(d) characteristics of films deposited at residual gas pressures of about 10⁻⁶ torr with condensation rates of about 1?/s showed generally decreasing slopes as film thicknesses increased, but irregularities in detail. The ∂(d) characteristics of films deposited at 10⁻⁸ torr with the same condensation rate decreasing with increasingd, too, show no such irregularities but very small regular variations of ∂(d) with constant oscillation length Δd between the maxima, and decreasing amplitudes with increasingd. These variations are better recognizable in a modified ∂(d) graph. We tend to interprete these variations by the quantum size effect as we found oscillation lengths and amplitudes compatibel with theory.     

Theory of the upper critical fieldH c2 in antiferromagnetic superconductors

The influence of antiferromagnetic order on the upper critical field of superconductors is investigated within the framework of Eliashberg theory. Below the Néel temperature the superconductor is characterized by Cooper pairs of quasiparticle states which are related by time reversal followed by a lattice translation. This leads to a change in the effective attraction between the quasiparticles which we calculate explicitely for the Chevrel phase compounds RE Mo₆S₈ (RE=Gd, Tb, and Dy). The results for the upper critical fields clearly show that our theory yields a consistent explanation of the experimentally observed anomalous behaviour.     

Effect-Directed Profiling of 17 Different Fortified Plant Extracts by High-Performance Thin-Layer Chromatography Combined with Six Planar Assays and High-Resolution Mass Spectrometry

An effect-directed profiling method was developed to investigate 17 different fortified plant extracts for potential benefits. Six planar effect-directed assays were piezoelectrically sprayed on the samples separated side-by-side by high-performance thin-layer chromatography. Multipotent compounds with antibacterial, α-glucosidase, β-glucosidase, AChE, tyrosinase and/or β-glucuronidase-inhibiting effects were detected in most fortified plant extracts. A comparatively high level of antimicrobial activity was observed for Eleutherococcus, hops, grape pomace, passiflora, rosemary and Eschscholzia. Except in red vine, black radish and horse tail, strong enzyme inhibiting compounds were also detected. Most plants with anti-α-glucosidase activity also inhibited β-glucosidase. Green tea, lemon balm and rosemary were identified as multipotent plants. Their multipotent compound zones were characterized by high-resolution mass spectrometry to be catechins, rosmarinic acid, chlorogenic acid and gallic acid. The results pointed to antibacterial and enzymatic effects that were not yet known for plants such as Eleutherococcus and for compounds such as cynaratriol and caffeine. The nontarget effect-directed profiling with multi-imaging is of high benefit for routine inspections, as it provides comprehensive information on the quality and safety of the plant extracts with respect to the global production chain. In this study, it not only confirmed what was expected, but also identified multipotent plants and compounds, and revealed new bioactivity effects.