TEM investigations of Ga(Sb,As) quantum dots grown on a seed layer of (In,Ga)As quantum dots

This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Peer Reviewe

A blueprint of ectoine metabolism from the genome of the industrial producer Halomonas elongata DSM 2581T

The halophilic γ-proteobacterium Halomonas elongata DSM 2581T thrives at high salinity by synthesizing and accumulating the compatible solute ectoine. Ectoine levels are highly regulated according to external salt levels but the overall picture of its metabolism and control is not well understood. Apart from its critical role in cell adaptation to halophilic environments, ectoine can be used as a stabilizer for enzymes and as a cell protectant in skin and health care applications and is thus produced annually on a scale of tons in an industrial process using H. elongata as producer strain. This paper presents the complete genome sequence of H. elongata (4 061 296 bp) and includes experiments and analysis identifying and characterizing the entire ectoine metabolism, including a newly discovered pathway for ectoine degradation and its cyclic connection to ectoine synthesis. The degradation of ectoine (doe) proceeds via hydrolysis of ectoine (DoeA) to Nα-acetyl-l-2,4-diaminobutyric acid, followed by deacetylation to diaminobutyric acid (DoeB). In H. elongata, diaminobutyric acid can either flow off to aspartate or re-enter the ectoine synthesis pathway, forming a cycle of ectoine synthesis and degradation. Genome comparison revealed that the ectoine degradation pathway exists predominantly in non-halophilic bacteria unable to synthesize ectoine. Based on the resulting genetic and biochemical data, a metabolic flux model of ectoine metabolism was derived that can be used to understand the way H. elongata survives under varying salt stresses and that provides a basis for a model-driven improvement of industrial ectoine production

HRTEM study of growth-correlated properties of (Si,Ge) islands

This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Peer Reviewe

L11 domain rearrangement upon binding to RNA and thiostrepton studied by NMR spectroscopy

Ribosomal proteins are assumed to stabilize specific RNA structures and promote compact folding of the large rRNA. The conformational dynamics of the protein between the bound and unbound state play an important role in the binding process. We have studied those dynamical changes in detail for the highly conserved complex between the ribosomal protein L11 and the GTPase region of 23S rRNA. The RNA domain is compactly folded into a well defined tertiary structure, which is further stabilized by the association with the C-terminal domain of the L11 protein (L11(ctd)). In addition, the N-terminal domain of L11 (L11(ntd)) is implicated in the binding of the natural thiazole antibiotic thiostrepton, which disrupts the elongation factor function. We have studied the conformation of the ribosomal protein and its dynamics by NMR in the unbound state, the RNA bound state and in the ternary complex with the RNA and thiostrepton. Our data reveal a rearrangement of the L11(ntd), placing it closer to the RNA after binding of thiostrepton, which may prevent binding of elongation factors. We propose a model for the ternary L11–RNA–thiostrepton complex that is additionally based on interaction data and conformational information of the L11 protein. The model is consistent with earlier findings and provides an explanation for the role of L11(ntd) in elongation factor binding

The refractive index in electron microscopy and the errors of its approximations

In numerical calculations for electron diffraction often a simplified form of the electron-optical refractive index, linear in the electric potential, is used. In recent years improved calculation schemes have been proposed, aiming at higher accuracy by including higher-order terms of the electric potential. These schemes start from the relativistically corrected Schrödinger equation, and use a second simplified form, now for the refractive index squared, being linear in the electric potential. The second and higher-order corrections thus determined have, however, a large error, compared to those derived from the relativistically correct refractive index. The impact of the two simplifications on electron diffraction calculations is assessed through numerical comparison of the refractive index at high-angle Coulomb scattering and of cross-sections for a wide range of scattering angles, kinetic energies, and atomic numbers

Untersuchungen der strukturellen Eigenschaften von InGaAs-GaAs-Übergittern und zur Rekonstruktion des projizierten Kristallpotentials in der hochauflösenden Elektronenmikroskopie

In den letzten Jahrzehnten haben Halbleiterbauelemente, deren Herstellung auf Kombinationen von Gruppe-lV-Elementen, Ill-V -Verbindungshalbleitern und II-VI-Verbindungshalbleitern, sowie ihren ternären und quaternären Verbindungen beruht, neuartige technologische Perspektiven eröffnet und eine Reihe materialwissenschaftlicher Fragestellungen aufgeworfen. Das technologische Potential beruht darauf, daß die elektrischen und optoelektronischen Eigenschaften vieler Verbindungshalbleiter durch die Existenz einer direkten Bandlücke bestimmt werden, und einige Verbindungshalbleiter eine sehr hohe Ladungsträgerbeweglichkeit aufweisen [117]. Das Maßschneidern elektrischer Eigenschaften, sowie das Erreichen einer hohen Integrationsdichte von erfordert ausnahmslos strukturelle Perfektionauf sehr kleinen Längenskalen, bis hinunter auf die Ebene. Ein wichtiger Elementarprozeß bei der Bauelementherstellung ist das Aufwachsen eines kristallinen Materials auf ein anderes kristallines Material, wobei die aufwachsende Schicht die kristallographische Orientierung des Substrats übernimmt. Diese $\textit{Heteroepitaxie}$ zweier verschiedener Materialien ist technologisch in einer Reihe von Verfahren realisiert, wie der Molekularstrahlepitaxie ($\textit{molecular beam epitaxy}$, MBE), der Flüssigphasenepitaxie ($\textit{liquid phase epitaxy}$, LPE), der Deposition aus der Gasphase ($\textit{chemical vapour deposition}$, CVD), sowie Hybridverfahren, die nach der Zusammensetzung der Quellen oder nach der Art der Prozeßführung benannt sind: Molekularstrahlepitaxie mit metallorganischen Verbindungen ($\textit{metal organic molecular beam epitaxy}$, MOMBE), Niedrigdruck-Gasphasendeposition ($\textit{low pressure chemical vapour deposition}$, LPCVD), und so fort. Die grundlegende Problematik der Halbleiter-Heteroepitaxie liegt in den oft sehr unterschiedlichen strukturellen und mechanischen Eigenschaften der beteiligten Materialien, wie zum Beispiel der Kristallstruktur, der Gitterkonstante, des Schubmoduls und des thermischen Ausdehnungskoeffizienten. In einer Vielzahl von Fällen istdie Kristallstruktur der beteiligten Materialien jedoch gleich, nämlich vom Diamantoder Zinkblende-Typ. In diesem Fall wächst die Schicht in der kristallographischenOrientierung auf, die durch die Substratoberfläche vorgegeben wird. Häufig unterscheiden sich jedoch die Gitterkonstanten der beiden Materialien voneinander, so daß ein defektfreies, gitterangepaßtes Wachstum nur dann möglich ist, wenn das aufwachsende Material die Gitterkonstante des Substratmaterials annimmt. Die dabei auftretende elastische [...

Reconstruction of the projected electrostatic potential in high-resolution transmission electron microscopy including phenomenological absorption

The projected electrostatic potential is reconstructed from a high-resolution exit wave function through a maximum-likelihood refinement algorithm. The theory of an already existing algorithm [1] is extended to include the effects of phenomenological absorption. Various tests with a simulated exit wave function of YBa2Cu3O7 in [1 0 0] orientation used as a source show that the reconstruction is successful, regardless of the strongly differing scattering power of atomic columns, even for the case of strong dynamical diffraction. Object thickness, the amount of absorption, and a residual defocus aberration of the wave function—parameters often unknown or difficult to measure in experiments—can be determined accurately with the aid of the refinement algorithm in a self-consistent way. For the next generation of instruments, with information limits of 0.05 nm and better, reconstruction accuracies of better than 2% can be expected, which is sufficient to measure and display the structural and chemical information with the aid of an accurate projected potential map

Relativistic correction of atomic scattering factors for high-energy electron diffraction

Relativistic electron diffraction depends on linear and quadratic terms in the electric potential, the latter being neglected in the frequently used relativistically corrected Schrödinger equation. The quadratic electric potential term modifies atomic scattering amplitudes in particular for large-angle scattering and backscattering. The respective correction increases with increasing scattering angle, increasing atomic number and increasing kinetic energy. Conventional tabulations for electron scattering and its large-angle extrapolations can be amended in closed form by a universal correction based on the screened Coulomb potential squared

No surprise in the first Born approximation for electron scattering

In a recent article it is argued that the far-field expansion of electron scattering, a pillar of electron diffraction theory, is wrong (Treacy and Van Dyck, 2012 [1]). It is further argued that in the first Born approximation of electron scattering the intensity of the electron wave is not conserved to first order in the scattering potential. Thus a “mystery of the missing phase” is investigated, and the supposed flaw in scattering theory is seeked to be resolved by postulating a standing spherical electron wave (Treacy and Van Dyck, 2012 [1]). In this work we show, however, that these theses are wrong. A review of the essential parts of scattering theory with careful checks of the underlying assumptions and limitations for high-energy electron scattering yields: (1) the traditional form of the far-field expansion, comprising a propagating spherical wave, is correct; (2) there is no room for a missing phase; (3) in the first Born approximation the intensity of the scattered wave is conserved to first order in the scattering potential. The various features of high-energy electron scattering are illustrated by wave-mechanical calculations for an explicit target model, a Gaussian phase object, and for a Si atom, considering the geometric conditions in high-resolution transmission electron microscopy

Spin-Dependent Nonlinear Contrast Transfer in Transmission Electron Microscopy

In this study, the spin-dependent nonlinear contrast transfer in transmission electron microscopy is derived from the eikonal expansion of the Dirac equation. The transmission cross-coefficient of the standard imaging theory is amended by a spin-dependent factor, whose effect is investigated for single scattering in the object by an electrical field under polarized and unpolarized illumination, and it is illustrated with numerical results and plots for a kinetic energy of 80 keV. The resulting image displacement and image convolution increase with decreasing kinetic energy but are always smaller than a wavelength. General features of the cross-coefficient are discussed to identify favorable conditions for the measurement of the small spin effects, possibly in an unmodified instrument