Quantitative powder diffraction using a (2+3) surface diffractometer and an area detector

X-ray diffractometers primarily designed for surface x-ray diffraction are often used to measure the diffraction from powders, textured materials, and fiber-texture samples in so-called $2\theta$ scans. Unlike high-energy powder diffraction only a fraction of the powder rings is typically measured and the data consists of many detector images across the $2\theta$ range. Such diffractometers typically scan in directions not possible on a conventional lab-diffractometer, which gives enhanced control of the scattering vector relative to the sample orientation. There are, however, very few examples where the measured intensity is directly used, such as for profile/Rietveld refinement, as is common with other powder diffraction data. Although the underlying physics is known, converting the data is time-consuming and the appropriate corrections are dispersed across several publications, often not with powder diffraction in mind. In this paper we present the angle calculations and correction factors required to calculate meaningful intensities for $2\theta$ scans with a (2+3)-type diffractometer and an area detector. We also discuss some of the limitations with respect to texture, refraction, and instrumental resolution, and what kind of information one can hope to obtain.Comment: Research paper, 15 pages, 12 figures, 3 table

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information

Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation

Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independentlyfrom the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscopeallows for local implantation and patterning down to the nanometer resolution, which is of interest for deviceapplications. We present here a study of bismuth ferrite (BiFeO3) films where strain was patterned locally byhelium implantation. Our combined Raman, x-ray diffraction, and transmission electron microscopy (TEM)study shows that the implantation causes an elongation of the BiFeO3unit cell and ultimately a transition towardsthe so-called supertetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset ofamorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phasetransition from the R-like to T-like BiFeO3appears as first-order in character, with regions of phase coexistenceand abrupt changes in lattice parameters

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information

In situ analysis of the nucleation of O-and Zn-polar ZnO nanowires using synchrotron-based X-ray diffraction

International audienceThe selection of the polarity of ZnO nanowires grown by chemical bath deposition offers a great advantage for their integration into a wide variety of engineering devices. However, the nucleation process of ZnO nanowires and its dependence on their polarity is still unknown despite its importance for optimizing their morphology and properties and thus to enhance the related device performances. To tackle this major issue, we combine an in situ analysis of the nucleation process of O-and Zn-polar ZnO nanowires on O-and Znpolar ZnO single crystals, respectively, using synchrotron radiation-based grazing incidence X-ray diffraction with ex situ transmission and scanning electron microscopy. We show that the formation of ZnO nanowires obeys three successive phases from the induction, through nucleation to growth phases. The characteristics of each phase, including the nucleation temperature, the shape and dimension of nuclei, as well as their radial and axial development are found to depend on the polarity of ZnO nanowires. A comprehensive description 2 reporting the dominant physicochemical processes in each phase and their dependence on the polarity of ZnO nanowires is presented, revisiting their formation process step-by-step. These findings provide a deeper understanding of the phenomena at work during the growth of ZnO nanowires by chemical bath deposition and open the perspective to develop a more accurate control of their properties at each step of the process