Assemblies from metallic and semiconducting nanocrystals

Optical properties of nanomaterials such as semiconductor and metal quantum dots are important for sensors and photovoltaic applications. We report on optical, microscopic, and AFM investigations on bulk and single nanoobjects such as metal and semiconducting nanoparticles. Firstly, of special interest is the investigation of Ag metal nanoaggregates formed in zeolites. Here, the defined structure of the zeolite serves both as size directing and a stabilizing agent. The size selected Ag aggregates fluoresce in the zeolite cages even after storage under ambient conditions for almost one year. In addition, single Ag particles escape the cages and can be investigated by fluorescence microscopy also with respect to sensor applications. Secondly, with respect to photovoltaic applications, energy transfer among organic dye molecules and semiconductor quantum dots is of great importance. We report on the extension of the optical absorption of ZnSe quantum dots into the UV regime and investigate excitation energy transfer within self-assembled nanoaggregates of surface functionalized QDs and fluorescent styrylpyridine dyes.     

Ultrasonic sensor for predicting sugar concentration using multivariate calibration

This paper presents a multivariate regression method for the prediction of maltose concentration in aqueous solutions. For this purpose, time and frequency domain of ultrasonic signals are analyzed. It is shown, that the prediction of concentration at different temperatures is possible by using several multivariate regression models for individual temperature points. Combining these models by a linear approximation of each coefficient over temperature results in a unified solution, which takes temperature effects into account. The benefit of the proposed method is the low processing time required for analyzing online signals as well as the non-invasive sensor setup which can be used in pipelines. Also the ultrasonic signal sections used in the presented investigation were extracted out of buffer reflections which remain primarily unaffected by bubble and particle interferences.     

Limit on the electron electric dipole moment in gadolinium-iron garnet

A new method for the detection of the electron electric dipole moment (EDM) using a solid is described. The method involves the measurement of a voltage induced across the solid by the alignment of the sample's magnetic dipoles in an applied magnetic field, H. A first application of the method to GdIG has resulted in a limit on the electron EDM of 5 x 10(-24)e cm, which is a factor of 40 below the limit obtained from the only previous solid-state EDM experiment. The result is limited by the imperfect discrimination of an unexpectedly large voltage that is even upon the reversal of the sample magnetization.     

One-dimensional confinement in heterogeneous catalysis: Trapped oxygen on RuO2(110) model catalysts

With temperature programmed reaction (TPR) experiments and kinetic Monte Carlo (kMC) simulations of coadsorbed oxygen and HCl on the RuO₂(110) surface we studied the thermal stabilization of dissociatively adsorbed oxygen. Due to one-dimensional confinement single surface O atoms can be trapped by surface chlorine atoms so that surface oxygen is not able to desorb from the RuO₂(110) surface at the expected temperature of 420 K. Trapped oxygen needs desorption temperatures as high as 700 K where it recombines with bridging O from RuO₂(110) to form O₂. Kinetic modeling of catalytic reactions with dimensional confinement of their reaction intermediates on the catalyst's surface requires the application of kinetic Monte Carlo simulations which are beyond the mean field approach.     

The World According to Quantum Mechanics (Or the 18 Errors of Henry P. Stapp)

Several errors in Stapp's interpretation of quantum mechanics and its application to mental causation (Henry P. Stapp, Quantum theory and the role of mind in nature, Foundations of Physics 31, 1465–1499 (2001)) are pointed out. An interpretation of (standard) quantum mechanics that avoids these errors is presented.     

Traveling Salesman Problem with Clustering

In the original traveling salesman problem, the traveling salesman has the task to find the shortest closed tour through a proposed set of nodes, touching each node exactly once and returning to the initial node at the end. For the sake of the tour length to be minimized, nodes close to each other might not be visited one after the other but separated in the tour. However, for some practical applications, it is useful to group nodes to clusters, such that all nodes of a cluster are visited contiguously. Here we present an approach which leads to an automatic clustering with a clustering parameter governing the sizes of the clusters.     

Determination of Interatomic Potentials for the X0(+), A0(+), and B1 States of HgKr from Fluorescence and Excitation Spectra

We present an analysis of the A0(+)(6(3)P(1))-->X0(+)(6(1)S(0)) bound-bound and bound-free fluorescence spectrum, and of the A0(+)(6(3)P(1))<--X0(+)(6(1)S(0)) and B1(6(3)P(1))<--X0(+)(6(1)S(0)) bound-bound excitation spectrum of the HgKr van der Waals molecule. The A-->X fluorescence spectrum, which was observed for the first time, as well as the excitation spectra were recorded using a pulsed supersonic molecular beam crossed with a pulsed dye laser beam. An analysis of the A(v')<--X(v"), B(v')<--X(v"), and A(v'=8)-->X(v") bound-bound bands indicates that a Morse function combined with a long-range approximation represents the interatomic potential energy curve of the A, B, and X states below the dissociation limit. In the simulation of the A(v'=8)-->X bound-free spectrum the Morse, Lennard-Jones (n-6), and Maitland-Smith (n(0), n(1)) functions were tested, and the Maitland-Smith (11.39, 10.50) potential was found to be a good representation of the repulsive part of the X-state PE curve above the dissociation limit, over the internuclear separation range R=2.85-3.55 ?. The spectroscopic characteristics for the A, B, and X states obtained in this work are compared with other available experimental and theoretical results. Copyright 2001 Academic Press.     

Angular distributions of s-subshell electrons in open-shell atoms: 3s photoionization of atomic chlorine

A determination of the angular distribution parameter beta of the atomic chlorine 3s photoelectrons over the photon-energy range from 29 to 70 eV has been carried out using electron spectrometry in conjunction with synchrotron radiation. Our results confirm the basic theoretical predictions that beta, for s-subshell photoionization in open-shell atoms, is in general term and photon-energy dependent, in contrast to closed-shell atoms where beta is always 2 nonrelativistically. However, our measurements of beta for the Cl+ 3s((1,3)P) channels demonstrate that significant details are not handled well by simple Hartree-Fock theory.