The ID01 beamline has been built to combine Bragg diffraction with imaging techniques to produce a strain and mosaicity microscope for materials in their native or operando state. A scanning probe ...with nano‐focused beams, objective‐lens‐based full‐field microscopy and coherent diffraction imaging provide a suite of tools which deliver micrometre to few nanometre spatial resolution combined with 10−5 strain and 10−3 tilt sensitivity. A detailed description of the beamline from source to sample is provided and serves as a reference for the user community. The anticipated impact of the impending upgrade to the ESRF – Extremely Brilliant Source is also discussed.
The ID01 beamline has been built to combine Bragg diffraction with imaging techniques to produce a strain and mosaicity microscope for materials in their native or operando state. A detailed description of the beamline from source to sample is provided and serves as a reference for the user community.
Domains within the multienzyme polyketide synthases are linked by noncatalytic sequences of variable length and unknown function. Recently, the crystal structure was reported of a portion of the ...linker between the acyltransferase (AT) and ketoreductase (KR) domains from module 1 of the erythromycin synthase (6‐deoxyerythronolide B synthase), as a pseudodimer with the adjacent ketoreductase (KR). On the basis of this structure, the homologous linker region between the dehydratase (DH) and enoyl reductase (ER) domains in fully reducing modules has been proposed to occupy a position on the periphery of the polyketide synthases complex, as in porcine fatty acid synthase. We report here the expression and characterization of the same region of the 6‐deoxyerythronolide B synthase module 1 AT‐KR linker, without the adjacent KR domain (termed ΔN AT1‐KR1), as well as the corresponding section of the DH‐ER linker. The linkers fold autonomously and are well structured. However, analytical gel filtration and ultracentrifugation analysis independently show that ΔN AT1‐KR1 is homodimeric in solution; site‐directed mutagenesis further demonstrates that linker self‐association is compatible with the formation of a linker‐KR pseudodimer. Our data also strongly indicate that the DH‐ER linker associates with the upstream DH domain. Both of these findings are incompatible with the proposed model for polyketide synthase architecture, suggesting that it is premature to allocate the linker regions to a position in the multienzymes based on the solved structure of animal fatty acid synthase.
The 1.4-A crystal structure of the oxidized state of a Y25S variant of cytochrome cd(1) nitrite reductase from Paracoccus pantotrophus is described. It shows that loss of Tyr(25), a ligand via its ...hydroxy group to the iron of the d(1) heme in the oxidized (as prepared) wild-type enzyme, does not result in a switch at the c heme of the unusual bishistidinyl coordination to the histidine/methionine coordination seen in other conformations of the enzyme. The Ser(25) side chain is seen in two positions in the d(1) heme pocket with relative occupancies of approximately 7:3, but in neither case is the hydroxy group bound to the iron atom; instead, a sulfate ion from the crystallization solution is bound between the Ser(25) side chain and the heme iron. Unlike the wild-type enzyme, the Y25S mutant is active as a reductase toward nitrite, oxygen, and hydroxylamine without a reductive activation step. It is concluded that Tyr(25) is not essential for catalysis of reduction of any substrate, but that the requirement for activation by reduction of the wild-type enzyme is related to a requirement to drive the dissociation of this residue from the active site. The Y25S protein retains the d(1) heme less well than the wild-type protein, suggesting that the tyrosine residue has a role in stabilizing the binding of this cofactor.
Solid‐state‐based quantum technologies, such as electronic spin‐qubits, constitute a leading approach to the realization of quantum computation. Electronic spin‐qubits hosted in semiconductor ...heterostructures demand the highest crystalline quality, specifically with respect to the structure and formation of in‐plane misfit dislocations (MDs). Here, the formation mechanisms of MD networks in such Si/SiGe heterostructures are investigated. For this purpose, strained Si layers on relaxed Si0.7Ge0.3 with thicknesses above the critical thickness are grown by molecular beam epitaxy to allow for the formation of MDs. MDs are mapped out by electron channeling contrast imaging and the experimental results are compared to MD networks calculated by Monte Carlo simulations. The simulations show that the ratio between the threading dislocation density (TDD) and the average length of MDs is a constant for a given set of parameters, here 2.9 for sufficiently large dislocation statistics and simultaneous extension of MDs. Further, the fractal dimension of the MD network determined by the box‐counting method as an alternative quantity to characterize MD networks is introduced. This allows to infer the formation mechanism of MDs in real devices and hence the quantification of resulting average relaxation within the Si‐quantum well.
Herein, the formation mechanisms of misfit dislocation (MD) networks in strained Si layers grown on relaxed SiGe heterostructures are investigated. For this purpose, geometric Monte Carlo simulations of dislocation formation together with electron channeling contrast imaging are employed to show that the ratio of threading to misfit dislocation spacings (MDSs) is constant and related to the relaxation of the layer.
Silicon nanowire‐based sensors find many applications in micro‐ and nano‐electromechanical systems, thanks to their unique characteristics of flexibility and strength that emerge at the nanoscale. ...This work is the first study of this class of micro‐ and nano‐fabricated silicon‐based structures adopting the scanning X‐ray diffraction microscopy technique for mapping the in‐plane crystalline strain (ϵ044) and tilt of a device which includes pillars with suspended nanowires on a substrate. It is shown how the micro‐ and nanostructures of this new type of nanowire system are influenced by critical steps of the fabrication process, such as electron‐beam lithography and deep reactive ion etching. X‐ray analysis performed on the 044 reflection shows a very low level of lattice strain (<0.00025 Δd/d) but a significant degree of lattice tilt (up to 0.214°). This work imparts new insights into the crystal structure of micro‐ and nanomaterial‐based sensors, and their relationship with critical steps of the fabrication process.
A multiscale analytical approach is presented for understanding the structure of micro‐ and nano‐fabricated nanowire‐based sensors. Using scanning X‐ray diffraction microscopy, crystal deformation is evaluated with respect to lattice strain and tilt caused by the manufacturing process of a silicon monolith.
Germanium–tin (GeSn) microdisks are promising structures for complementary metal–oxide–semiconductor‐compatible lasing. Their emission properties depend on Sn concentration, strain, and operating ...temperature. Critically, the band structure of the alloy varies along the disk due to different lattice deformations associated with mechanical constraints. An experimental and numerical study of Ge1−xSnx microdisk with Sn concentration between 8.5 and 14 at% is reported. Combining finite element method calculations, micro‐Raman and X‐ray diffraction spectroscopy enables a comprehensive understanding of mechanical deformation, where computational predictions are experimentally validated, leading to a robust model and insight into the strain landscape. Through micro‐photoluminescence experiments, the temperature dependence of the bandgap of Ge1−xSnx is parametrized using the Varshni formula with respect to strain and Sn content. These results are the input for spatially dependent band structure calculations based on deformation potential theory. It is observed that Sn content and temperature have comparable effects on the bandgap, yielding a decrease of more than 20 meV for an increase of 1 at% or 100 K, respectively. The impact of the strain gradient is also analyzed. These findings correlate structural properties to emission wavelength and spectral width of microdisk lasers, thus demonstrating the importance of material‐related consideration on the design of optoelectronic microstructures.
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