In situ growth of nano-structures by metal-organic vapour phase epitaxy

Using spontaneous self-organization effects is an efficient way to produce nano-structures, as for instance quantum wires and quantum dots. This article is focused on the strain-induced self-organization, or “self-assembling” effect, producing quantum dots. Particularly the following aspects will be addressed: (i) the phenomenology of the 2D–3d morphology transition, (ii) the effects of materials choices and growth conditions on density, size and homogeneity of dots, and (iii) manipulations to get laterally aligned and vertically stacked dot structures.     

Curvature coupling dependence of membrane protein diffusion coefficients

We consider the lateral diffusion of a protein interacting with the curvature of the membrane. The interaction energy is minimized if the particle is at a membrane position with a certain curvature that agrees with the spontaneous curvature of the particle. We employ stochastic simulations that take into account both the thermal fluctuations of the membrane and the diffusive behavior of the particle. In this study, we neglect the influence of the particle on the membrane dynamics, thus the membrane dynamics agrees with that of a freely fluctuating membrane. Overall, we find that this curvature coupling substantially enhances the diffusion coefficient. We compare the ratio of the projected or measured diffusion coefficient and the free intramembrane diffusion coefficient, which is a parameter of the simulations, with analytical results that rely on several approximations. We find that the simulations always lead to a somewhat smaller diffusion coefficient than that from our analytical approach. A detailed study of the correlations of the forces acting on the particle indicates that the diffusing inclusion tries to follow favorable positions on the membrane such that forces along the trajectory are on average smaller than they would be for random particle positions.     

A new search for the atomic EDM of 129Xe at FRM-II

Permanent electric dipole moments (EDMs) arise due to the breaking of time-reversal or, equivalently, CP-symmetry. Although EDM searches have so far only set upper limits, which are many orders of magnitude larger than Standard Model (SM) predictions, the motivation for more sensitive searches is stronger than ever. A new effort at FRM-II incorporating ¹²⁹Xe and ³He as a co-magnetometer can potentially improve the current limit. The noble gas mixture of ¹²⁹Xe and ³He is simultanously polarized by spin-exchange optical pumping and then transferred into a high-performance magnetically shielded room. Inside, both species can freely precess in the presence of applied magnetic and electric fields. The precession signals are detected by LTc SQUID sensors. In EDM cells with silicon electrodes we observed spin lifetimes in excess of 2500 s without and with high-voltage applied. This meets one requirement to achieve our goal of improving the EDM limit on ¹²⁹Xe by several orders of magnitude.     

Rates of decay in the classical Katznelson-Tzafriri theorem

The Katznelson-Tzafriri Theorem states that, given a power-bounded operator T, ∥Tⁿ(I ? T)∥ → 0 as n → ∞ if and only if the spectrum σ(T) of T intersects the unit circle T in at most the point 1. This paper investigates the rate at which decay takes place when σ(T) ∩ T = {1}. The results obtained lead, in particular, to both upper and lower bounds on this rate of decay in terms of the growth of the resolvent operator R(e^iθ, T) as θ → 0. In the special case of polynomial resolvent growth, these bounds are then shown to be optimal for general Banach spaces but not in the Hilbert space case.     

Small angle X-ray scattering measurements probe water nanodroplet evolution under highly non-equilibrium conditions

Our in situ small angle X-ray scattering (SAXS) measurements yield an unprecedented and detailed view of rapidly evolving H(2)O nanodroplets formed in supersonic nozzles. The SAXS experiments produce spectra in a few seconds that are comparable to small angle neutron scattering (SANS) spectra requiring several hours of integration time and the use of deuterated compounds. These measurements now make it possible to quantitatively determine the maximum nucleation and growth rates of small droplets formed under conditions that are far from equilibrium. Particle growth is directly followed from about 10 micros to 100 micros after particle formation with growth rates of approximately 0.2 to 0.02 nm micros(-1). The peak H(2)O nucleation rates lie between 10(17) and 10(18) cm(-3) s(-1).     

Femtosecond pump-probe investigation of ultrafast silver nanoparticle deformation in a glass matrix

Single-color femtosecond pump-probe experiments were performed to investigate the time dependence of laser-induced ultrafast desorption and deformation processes of silver nanoparticles in glass. After laser excitation at wavelengths close to the surface plasmon resonance, transient extinction changes were found to exhibit dynamics on quite different time scales ranging from sub-picoseconds to some hundred ps. The slowest observed decay component is identified as characteristic for the deformation/desorption processes. Possible mechanisms for these processes are discussed. Received: 3 April 2000 / Revised version: 3 July 2000 / Published online: 20 September 2000     

Das System KCl/ErCl3 und die Modifikationen der Verbindungen K3LnCl6 (Ln = Ce–Lu,Y)

The System KCl/ErCl₃ and the Modifications of Compounds K₃LnCl₆ (Ln = Ce–Lu, Y) The phase diagram of the system KCl/ErCl₃ was investigated by DTA and XRD. Two compounds exist: KEr₂Cl₇ incongruently and K₃ErCl₆ congruently melting. Their thermodynamic functions for the formation from KCl and ErCl₃ were determined by solution calorimetry and emf vs T measurements in a galvanic cell for solid electrolytes. Both compounds are stable down to 0 K. – K₃ErCl₃ exists in three modifications. The structure of T–K₃ErCl₆ was determined by single crystal measurements: S.G. P2₁/c; Z = 4; a = 1309.8(5), b = 767.1(3), c = 1252.6(4) pm, β = 109.94(2)°. – A survey of all known results on compounds K₃LnCl₆ reveals, that from Ln = Ce to Ln = Ho they only are stable at higher temperatures, > 521 °C (Ce) and > –27 °C (Ho), resp.     

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