The role of pH, metal ions and their hydroxides in charge reversal of protein-coated nanoparticles

In this study, we investigated charge inversion of protein-coated Au nanoparticles caused by the addition of metal ions. The addition of hydrolyzable metal ions (Lewis acids) can induce drastic pH changes and depending on this pH, the metal ions (e.g. M3+) are readily converted into the hydrolyzed species (MOH2+, M(OH)2+) or even into hydroxides (M(OH)3). Adsorbed metal hydroxides were identified to cause the charge inversion of the NPs by using a combination of cryo-TEM, EFTEM and ζ-potential measurements

Testing the universality of free fall with rubidium and ytterbium in a very large baseline atom interferometer

We propose a very long baseline atom interferometer test of Einstein's equivalence principle (EEP) with ytterbium and rubidium extending over 10m of free fall. In view of existing parametrizations of EEP violations, this choice of test masses significantly broadens the scope of atom interferometric EEP tests with respect to other performed or proposed tests by comparing two elements with high atomic numbers. In a first step, our experimental scheme will allow reaching an accuracy in the E\"otv\"os ratio of $7\times 10^{-13}$. This achievement will constrain violation scenarios beyond our present knowledge and will represent an important milestone for exploring a variety of schemes for further improvements of the tests as outlined in the paper. We will discuss the technical realisation in the new infrastructure of the Hanover Institute of Technology (HITec) and give a short overview of the requirements to reach this accuracy. The experiment will demonstrate a variety of techniques which will be employed in future tests of EEP, high accuracy gravimetry and gravity-gradiometry. It includes operation of a force sensitive atom interferometer with an alkaline earth like element in free fall, beam splitting over macroscopic distances and novel source concepts

Quantum Test of the Universality of Free Fall

We simultaneously measure the gravitationally-induced phase shift in two Raman-type matter-wave interferometers operated with laser-cooled ensembles of $^{87}$Rb and $^{39}$K atoms. Our measurement yields an E\"otv\"os ratio of $\eta_{\text{Rb,K}}=(0.3\pm 5.4)\times 10^{-7}$. We briefly estimate possible bias effects and present strategies for future improvements

Main defect reactions behind phosphorus diffusion gettering of iron

Phosphorus diffusion is well known to getter effectively metal impurities during silicon solar cell processing. However, the main mechanisms behind phosphorus diffusion gettering are still unclear. Here, we analyze the impact of oxygen, phosphosilicate glass as well as active and clustered phosphorus on the gettering efficiency of iron. The results indicate that two different mechanisms dominate the gettering process. First, segregation of iron through active phosphorus seems to correlate well with the gettered iron profile. Secondly, immobile oxygen appears to act as an effective gettering sink for iron further enhancing the segregation effect. Based on these findings, we present a unifying gettering model that can be used to predict the measured iron concentrations in the bulk and in the heavily phosphorus doped layers and explains the previous discrepancies reported in the literature.Peer reviewe

A Unified Parameterization of the Formation of Boron Oxygen Defects and their Electrical Activity

AbstractThe magnitude of light-induced degradation of solar cells based on Czochralski grown silicon strongly depends on material properties. We have performed experiments to describe the activation and recombination activity of boron oxygen defects in boron compensated n-type silicon. Compensated n-type material enables flexible assessment of charge carrier influences on the defect that cannot be distinguished on p-type material. The results can be generalized to p-type material and thus provide valuable insights to the defect. Our measurements demonstrate the two-level defect nature of the slow-formed boron oxygen defect component and allow the study of the dopant dependency of the defect concentrations. Our findings strongly support a revision of the existing model of the defect composition.Based on the experimental results and literature data we have created a parameterization of the lifetime limitation in silicon due to BO defects. Established findings from literature for uncompensated p-type silicon are taken into account and ensure general validity. The parameterization is useful to discuss BO defect influences and can serve to predict material properties after LID

Quantum versus classical dynamics in spin models:Chains, ladders, and square lattices

We present a comprehensive comparison of spin and energy dynamics in quantum and classical spin models on different geometries, ranging from one-dimensional chains, over quasi-one-dimensional ladders, to two-dimensional square lattices. Focusing on dynamics at formally infinite temperature, we particularly consider the autocorrelation functions of local densities, where the time evolution is governed either by the linear Schrödinger equation in the quantum case or the nonlinear Hamiltonian equations of motion in the case of classical mechanics. While, in full generality, a quantitative agreement between quantum and classical dynamics can therefore not be expected, our large-scale numerical results for spin-1/2 systems with up to N=36 lattice sites in fact defy this expectation. Specifically, we observe a remarkably good agreement for all geometries, which is best for the nonintegrable quantum models in quasi-one or two dimensions, but still satisfactory in the case of integrable chains, at least if transport properties are not dominated by the extensive number of conservation laws. Our findings indicate that classical or semiclassical simulations provide a meaningful strategy to analyze the dynamics of quantum many-body models, even in cases where the spin quantum number S=1/2 is small and far away from the classical limit S→∞.</p

Enzymatic Catalysis at Nanoscale: Enzyme-Coated Nanoparticles as Colloidal Biocatalysts for Polymerization Reactions

Enzyme-catalyzed controlled radical polymerization represents a powerful approach for the polymerization of a wide variety of water-soluble monomers. However, in such an enzyme-based polymerization system, the macromolecular catalyst (i.e., enzyme) has to be separated from the polymer product. Here, we present a compelling approach for the separation of the two macromolecular species, by taking the catalyst out of the molecular domain and locating it in the colloidal domain, ensuring quasi-homogeneous catalysis as well as easy separation of precious biocatalysts. We report on gold nanoparticles coated with horseradish peroxidase that can catalyze the polymerization of various monomers (e.g., N-isopropylacrylamide), yielding thermoresponsive polymers. Strikingly, these biocatalyst-coated nanoparticles can be recovered completely and reused in more than three independent polymerization cycles, without significant loss of their catalytic activity

Analysis of Different Models of Iron Precipitation in Multicrystalline Silicon

Simulation of solar cell processing enables inexpensive and rapid process optimization. Over the last twenty years, several models describing the distribution and behavior of iron point defects and iron-silicide precipitates have been developed and incorporated into process simulations. The goal of this work is to elucidate what physics are needed to accurately describe industry-relevant as-grown impurity and defect distributions and processing conditions by simulating different material-processing combinations with each model. This rigorous comparison helps scientists and engineers choose the appropriate level of model complexity, and consequently simulation run time, based on material characteristics and processing conditions.Peer reviewe