General approaches for shear-correcting coordinate transformations in Bragg coherent diffraction imaging: Part 2

X-ray Bragg coherent diffraction imaging has been demonstrated as a powerful three-dimensional (3D) microscopy approach for the investigation of sub-micrometer-scale crystalline particles. It is based on the measurement of a series of coherent diffraction intensity patterns that are numerically inverted to retrieve an image of the spatial distribution of relative phase and amplitude of the Bragg structure factor of the scatterer. This 3D information, which is collected through an angular rotation of the sample, is necessarily obtained in a non-orthogonal frame in Fourier space that must be eventually reconciled. To deal with this, the currently favored approach (detailed in Part I) is to perform the entire inversion in conjugate non-orthogonal real and Fourier space frames, and to transform the 3D sample image into an orthogonal frame as a post-processing step for result analysis. In this article, a direct follow-up of Part I, we demonstrate two different transformation strategies that enable the entire inversion procedure of the measured data set to be performed in an orthogonal frame. The new approaches described here build mathematical and numerical frameworks that apply to the cases of evenly and non-evenly sampled data along the direction of sample rotation (the rocking curve). The value of these methods is that they rely on and incorporate significantly more information about the experimental geometry into the design of the phase retrieval Fourier transformation than the strategy presented in Part I. Two important outcomes are 1) that the resulting sample image is correctly interpreted in a shear-free frame, and 2) physically realistic constraints of BCDI phase retrieval that are difficult to implement with current methods are easily incorporated. Computing scripts are also given to aid readers in the implementation of the proposed formalisms

Nondestructive three-dimensional imaging of crystal strain and rotations in an extended bonded semiconductor heterostructure

International audienceWe report the 3D mapping of strain and tilts of crystal planes in an extended InP nanostructured layer bonded onto silicon, measured without sample preparation. Our approach takes advantages of 3D x-ray Bragg ptychography combined to an optimized inversion process. The excellent agreement with the sample nominal structure validates the reconstruction while the evidence of spatial fluctuations hardly observable by other means, underlines the specificities of Bragg ptychography

Cell cyclins: triggering elements of cancer or not?

Cyclins are indispensable elements of the cell cycle and derangement of their function can lead to cancer formation. Recent studies have also revealed more mechanisms through which cyclins can express their oncogenic potential. This review focuses on the aberrant expression of G1/S cyclins and especially cyclin D and cyclin E; the pathways through which they lead to tumour formation and their involvement in different types of cancer. These elements indicate the mechanisms that could act as targets for cancer therapy

Chronic p53-independent p21 expression causes genomic instability by deregulating replication licensing

The cyclin-dependent kinase inhibitor p21WAF1/CIP1 (p21) is a cell-cycle checkpoint effector and inducer of senescence, regulated by p53. Yet, evidence suggests that p21 could also be oncogenic, through a mechanism that has so far remained obscure. We report that a subset of atypical cancerous cells strongly expressing p21 showed proliferation features. This occurred predominantly in p53-mutant human cancers, suggesting p53-independent upregulation of p21 selectively in more aggressive tumour cells. Multifaceted phenotypic and genomic analyses of p21-inducible, p53-null, cancerous and near-normal cellular models showed that after an initial senescence-like phase, a subpopulation of p21-expressing proliferating cells emerged, featuring increased genomic instability, aggressiveness and chemoresistance. Mechanistically, sustained p21 accumulation inhibited mainly the CRL4–CDT2 ubiquitin ligase, leading to deregulated origin licensing and replication stress. Collectively, our data reveal the tumour-promoting ability of p21 through deregulation of DNA replication licensing machinery—an unorthodox role to be considered in cancer treatment, since p21 responds to various stimuli including some chemotherapy drugs

Molecular marks for epigenetic identification of developmental and cancer stem cells

Epigenetic regulations of genes by reversible methylation of DNA (at the carbon-5 of cytosine) and numerous reversible modifications of histones play important roles in normal physiology and development, and epigenetic deregulations are associated with developmental disorders and various disease states, including cancer. Stem cells have the capacity to self-renew indefinitely. Similar to stem cells, some malignant cells have the capacity to divide indefinitely and are referred to as cancer stem cells. In recent times, direct correlation between epigenetic modifications and reprogramming of stem cell and cancer stem cell is emerging. Major discoveries were made with investigations on reprogramming gene products, also known as master regulators of totipotency and inducer of pluoripotency, namely, OCT4, NANOG, cMYC, SOX2, Klf4, and LIN28. The challenge to induce pluripotency is the insertion of four reprogramming genes (Oct4, Sox2, Klf4, and c-Myc) into the genome. There are always risks of silencing of these genes by epigenetic modifications in the host cells, particularly, when introduced through retroviral techniques. In this contribution, we will discuss some of the major discoveries on epigenetic modifications within the chromatin of various genes associated with cancer progression and cancer stem cells in comparison to normal development of stem cell. These modifications may be considered as molecular signatures for predicting disorders of development and for identifying disease states

Microscopie quantitative tri-dimensionnelle de nanostructures cristallines

Ptychography is a coherent diffraction imaging technique which aims in retrieving the lost phase from intensity-only far-field measurements. The versatility of the approach has proved an important asset for 3D mapping of different physical quantities, like the electron density of micrometer-sized specimens with resolution in the 10 - 100nm range. In this work, we explored the possibility to push further the current limits of 3D Bragg ptychography, by addressing the case of an extended InP/InGaAs nanostructured thin film, bonded on a silicon wafer. The experiment was performed at the ID13 beamline at ESRF, with a monochromatic beam focused down to 100nm. 2D intensity patterns were acquired at several incidence angles in the vicinity of the InP (004) Bragg peak, stacking up a three dimensional dataset. Numerical analysis of the given problem was performed beforehand in order to optimize the inversion strategy and study the possibility of introducing additional physical constraints through regularization approaches. Inversions of the dataset were done using a ptychographical gradient-based optimization phase retrieval algorithm. The developed strategy was applied on the experimental data which led to the retrieval of a complex-valued 3D image. The result exhibits the high crystallinity quality of the sample with the expected values of thickness and lattice mismatch, nevertheless, small local lattice tilts have been observed - in the order of 0.02°- and confirmed by numerical modeling. This result demonstrates the high sensitivity of the technique, as well as its exciting perspectives for imaging complex organic and inorganic nanostructured materials.La ptychographie est une technique d’imagerie par diffraction cohérente qui vise à récupérer la phase perdue, uniquement par des mesures d’intensité en champ lointain. Cette technique permet l’imagerie des champs de déformation dans des cristaux périodiques avec des résolutions sous-faisceau. Dans ce travail, la ptychographie de Bragg en 3D est utilisée pour étudier les propriétés d’une couche cristalline nanostructurée de InP/InGaAs collée sur un substrat de silicium. L’expérience a été réalisée sur la ligne ID13 de l’ESRF, avec un faisceau monochromatique concentré à 100nm. Les intensités 2D ont été acquises avec plusieurs angles d’incidence dans le voisinage du pic de Bragg InP (004), empilant un jeu de données tridimensionnelles. L’analyse numérique du problème donné a été effectuée à l’avance afin d’optimiser la stratégie d’inversion et d’étudier la possibilité d’introduire des contraintes physiques supplémentaires basées sur des approches de régularisation. L’inversion de l’ensemble des données a été effectuée en utilisant un algorithme ptychographique de reconstruction de phase. L’image 3D récupérée représente la haute qualité cristalline de l’échantillon, avec les valeurs de l’épaisseur et du désaccord de maille attendus en moyenne. Néanmoins, de petites inclinaisons locales de mailles ont été observées - de l’ordre de 0.02°- et confirmées par modélisation numérique. Les résultats démontrent la sensibilité de la technique, ainsi que ses perspectives passionnantes pour l’imagerie des matériaux organiques et inorganiques nanostructurés complexes

Local piezoelectric properties of Na0.5Bi0.5TiO3 thin films by X-ray microdiffraction

58 σ.Το λαμπρότερο σύγχροτρο ακτίνων Χ αυτή τη στιγμή στον κόσμο θεωρείται το ESRF (European Synchrotron Radiation Facility), με παραγόμενη δέσμη της τάξης των 10^20 φωτόνια/sec/mrad^2/mm^2/0.1% bandwidth με την ασύλληπτη ικανότητα να διεισδύει σε βάθος στην ύλη καινα αποκαλύπτει τα μυστικά της σε επίπεδο δεκάτου του νανομέτρου ή ισοδύναμα 1 άνγκστρομ. Με τη χρήση μιας τέτοιας δέσμης και βασιζόμενοι σε διαφορετικά φαινόμενα οπτικής-ηλεκτρομαγνητικής φύσεως, μπορούμε πλέον να δούμε τι συμβαίνει στον μικρόκοσμο. Με την περίθλαση Bragg και άλλες τεχνικές μπορούμε πληροφορίες για τη δομή ή τη σύσταση ενός υλικού, ακόμα και να παρακολουθήσουμε ζωντανάτις βιολογικές εργασίες που λαμβάνουν χώρα σε ένα δείγμα πρωτεϊνών. Μέσα από την ανάγκη εύρεσης νέων σιδηροηλεκτρικών και πιεζοηλεκτρικών υλικών που χρησιμοποιούνται στων χώρο των Η/Υ και αλλού,θα μελετήσουμε ένα ιδιαίτερα δυνατό υποψήφιο, ικανό να αντικαταστήσει τα σημερινά υλικά που περιέχουν σημαντικές ποσότητες μολύβδου, πράγμα που τα καθιστά επιβλαβή για την ανθρώπινη υγεία. Σε αυτή την εργασία θα δούμε πως η ακτινοβολία συγχρότρου μπορεί να συνδυαστεί με την τεχνολογία ενός μικροσκοπίου ακίδας ώστε να επιτευχθούν όσο γίνεται περισσότερο τοπικές μετρήσεις της ηλεκτρικής πόλωσης και του πιεζοηλεκτρικού φαινομένου σε ένα τέτοιο σιδηροηλεκτρικό υλικό, με άλλα λόγια να μετρηθούν φυσικά μεγέθη όπως η παραμένουσα πόλωση, το συνακτικό πεδίο και τα ρεύματα διαρροής, καθώς και η αλλαγή διαστάσεων της μοναδιαίας κυψελίδας στη διεύθυνση του εξωτερικού ηλεκτρικού πεδίου, η οποία εκφράζεται από την πιεζοηλεκτρική σταθερά d33.Sodium bismuth titanate (NBT) is a promising candidate among ferroelectric and piezoelectric materials, to replace the now widely used PZT and other leadbased compounds in applications such as piezoelectric actuators, sensors, transducers and even Ferroelectric-RAMs. Because of environmental issues, lead content must be reduced in such applications and NBT appears to be a suitable replacement material while it has interesting ferroelectric (Pr=38mC/cm2, Ec=73kV/cm) and piezoelectric properties (d33=79pC/N). In this report, we focus on two things. First, we study the piezoelectric properties of NBT thin films and more specifically, we analyse the technique we used for measuring the d33 piezoelectric coefficient. Second, we make an effort to correlate the different PFM experimental values of the d33 coefficient that we get on grains with different crystallographic orientation. Meaning that from previous Piezorespose Force Microscopy studies on 0.95Na0:5Bi0:5TiO3- 0.05BaTiO3 compounds, it is found that piezoelectric effect is not the same on crystallites with different orientation - for example, the d33 coefficient for the (100) oriented crystallites was found 280pC/N, for the (110) 160pC/N and for the (111) 90pC/N. So, we tried to observe the reverse piezoelectric effect in a size of a few nanometers, in order to see any difference in the behaviour of a single grain. We applied an external electric field with the use of an alternating voltage source, by creating a contact between an AFM tip and a platinum electrode deposited on top of our sample. As the electric field caused the sample to expand or contract, we illuminated the sample with hard X-rays (E=8.9kV) and saw how the Bragg peak moves, while the lattice parameter changes with time. Then, from the Bragg relation we could calculate the lattice parameter and as a result, measure the strain. The whole idea of the local measurements is based on the fact that the tip of the AFM has a typical radius of 1-4mm and the size of the X-ray beam is equal to 300nmx200nm, comparable the grain size. The result of our study is a unique measurement of a distribution of properties in a non-homogeneous ferroelectric thin film. The different response of the grains can be attributed to a different local environment. As a future perspective, an accurate analysis of the intrinsic strain state of single grains should be performed to correlate it with the piezoresponse.Αναστάσιος Η. Πατέρα