Symposium CM03 : Investigating Nanostructures with X-Rays---Fundamentals and Applications

Bragg Coherent Diffractive Imaging (BCDI) uses coherent X-ray beams for imaging the structure and dynamics of nanocrystals. While BCDI continues to develop at current and future new high brightness X-ray facilities, it is also adding new directions, such as reaching wavelength-limited resolution, higher energies and in-situ buried configurations of nanocrystals. In this talk I will address the potential application of BCDI to the problem of imaging domain structures. Domain structures occur widely in crystals which show superstructure ordering, such as ferroelastic domains in ferroelectric materials, or charge ordered domains in charge-density-wave (CDW) systems. When such a sample is measured with coherent X-rays, the broad superstructure peak becomes speckled because of interference between the domains. I will illustrate the phase domain problem with the example of a nano-sized bicrystal of Barium Titanate. The two domains each generate a BCDI pattern, but where these overlap in reciprocal space, additional speckles are generated which report the relative positions of the two halves of the bicrystal.

Progresses in area detector and x-ray optics technology combined with increased availability of high-end computational capabilities have transformed the relatively slow technique of scanning x-ray Laue microdiffraction at synchrotron facilities into a near real-time quantitative microstructural imaging tool enabling to rapidly map materials microstructure and deformation at the nanoscale in-situ. Fast data collection provided by state-of-the-art area detectors and fully automated diffraction pattern indexing algorithms optimized for speed make it possible to scan large portions of a sample and get quantitative images of the distribution of phases, crystal orientations (texture), misorientations, strains/stresses and defect densities. We will demonstrate the use of this technique to the study of laser 3D printed nickel-based superalloy samples.

Semiconductor nanowires (NWs) are promising nanostructures to achieved better photonic and electronic properties for later nanotechnologies applied in e.g. catalysis, microelectronics (nanosensors and nanotransistors), photonics and optical devices. Nevertheless defects and diffuse interfaces influence their properties.
As a first step, the defects as Inversion Domain Boundaries (IDBs) are investigated for GaN NWs with coherent X-ray diffraction in Bragg conditions. Several Bragg reflections have been measured at different heights of the wires using a nano-focused beam. Combined with phase retrieval algorithms, coherent X-ray diffraction yields non-destructive displacement field mapping with a spatial resolution better than 10 nm and a displacement accuracy of a few picometer.¹ The absolute polarity of the domains was unambiguously revealed. A rigid relative displacements of the domains and the absence of microscopic strain away from the IDBs were evidenced. Moreover, both, the IDBs configuration and the displacement field evolve along the wire. Additionally, the influence of the Si content will be discussed.
As a second step, the results on interdiffusion in Ge-Si Core-Shell NWs will be presented. Both, surface and interfacial structures are considered as the influencing factors on the enhanced emission efficiency of core-shell heterostructures at the nanoscale.² Notably, the short diffusion distances make nano-sized objects very susceptible to degradation. To follow atomic diffusion in individual Ge-Si core-shell NWs, In situ Bragg Coherent Diffraction Imaging was performed at certain stages to probe the evolution of the strain and compositional gradients in the interior of the NWs as a function of temperature up to 850°C. The occurrence of intermixing will be discussed considering the initial shape of the core.

¹ S. Labat, et al., ACS Nano 9, 9210 (2015).
² L. J. Lauhon, et al., Nature 420, 57 (2002).

Combination of coherent x-ray diffraction imaging (CXDI) and ptychograpy in Bragg geometry was used in order to determine the structural homogeneity of single core-shell-shell heterostructure nanowires (NWs) grown on (111) silicon substrate. The NWs were composed by 140nm GaAs core-10nm In_0.10Ga_0.90As inner shell and 30nm GaAs outer shell and are 2-3 micron in length. The experiment has been performed at beamline ID01 of the ESRF, Grenoble using coherent x-rays with the energy of 9keV and a beam size of 150x200nm² full width at half maximum (FWHM). CXDI was applied to record 3D reciprocal space maps (RSM) of the symmetric GaAs (111) reflection at different positions along the NW growth axis for two different NWs. In case of NW1 the 3D RSMs taken along the NW growth axis are same except the bottom part, revealing a rather uniform NW structure. On the other hand for NW2 the RSMs display local nonuniformities, because they are changing as a function of NW height. In addition to CXDI measurements, the very same NWs were investigated with 2D ptychography at the GaAs (111) Bragg reflection. In agreement with the RSM analysis ptychography reconstruction also shows the homogeneous structure (reconstructed homogeneous phase) at NW1 but phase change along the growth axis at NW2.

Ternary (In,Al,Ga)-As (III-As) nanowire (NW) heterostructures are promising near-infrared emitter/detectors for applications including on-chip photonic information transfer. However, they commonly exhibit nanoscale structural inhomogeneities such as nanofaceting, stacking faults, and polytype insertions, which cause modulations of the bandgap. Composition fluctuations and the resulting lattice strain can also modify the bandgap. Correlated measurements of strain, structure, and composition in three dimensions (3D) are necessary to understand nanowire electronic structure and how growth conditions influence the evolution of non-planar heterostructures. Towards this end, we will describe the application of coherent nano-focused x-rays for the non-destructive imaging of strain and local structural features in III-As nanowire heterostructures over a large field of view. We have developed a new approach to 3D coherent diffraction imaging, multi-angle Bragg projection ptychography (maBPP), that can probe strain and structural defects in 3D while utilizing fewer angles and coarser position alignment than traditional 3D Bragg ptychography. Utilizing maBPP implemented at the Hard X-ray Nanoprobe at NSLS-II, we reconstruct a 3D image of strain in a single InGaAs nanowire. Additionally, by accessing a second Bragg reflection sensitive to variations in the wurtzite stacking order, we image stacking defects with better than 3 nm resolution. Nanoscale 3D measurements are combined with coarse scanning nano-diffraction measurements to investigate single nanowires over multiple microns. Analysis of InGaAs quantum wells grown on GaAs nanowires using direct space nanoscale imaging with scanning diffraction x-ray microscopy at the Hard X-ray Nanoprobe at the Advanced Photon Source will also be discussed. Multiple strain components, as well as structural variations in individual nanowires, are correlated with spatially-resolved cathodoluminescence and 3D composition mapping using atom probe tomography to unravel the origins of their unusual emission characteristics.

Hard X-rays can be used to investigate electronic and optoelectronic devices in more or less realistic operational conditions, and modern X-ray optics reach the relevant length scales for nanoelectronic devices. We have developed methods to combine electrical measurements with nanofocused X-rays, where the X-rays are used both as pump and probe of semiconductor nanowires.

In the first experiment, local pumping with X-rays was used to investigate carrier collection properties of single nanowire solar cells. Single InP and InGaP nanowires with p-i-n junctions were contacted electrically, and locally excited with a 50-nm diameter X-ray beam. The absorbed X-rays excite electrons and holes in the semiconductor, which generate a current when they are separated by the internal electric field. This X-ray beam induced current (XBIC) was investigated as function of position, flux and applied electric bias. The subsequent analysis revealed the depletion region and the minority carrier diffusion lengths, as function of excitation and external bias. Furthermore, the secondary X-ray fluorescence was used to quantitatively map the p-doping.

In the second project, nanofocused hard X-rays were used to quantitatively probe both strain and bending in a single nanowire device under electric bias. Scanning X-ray diffraction was performed with 100 nm real-space resolution along the nanowire axis, also within the metal contacts. The device was then exposed to increasing bias voltages until breakdown, while simultaneously measuring the electrical current and performing scanning X-ray Bragg diffraction. The 3D shape of the nanowire was reconstructed from the XRD data. We observed that the nanowire changed shape, correlated with a reduction in electrical conductance.

Nanomechanical testing methods have drawn significant attention in both scientific and industrial research fields owing to unique deformation mechanisms in constrained volumes that underpin new property regimes. In-situ imaging equipment is now routinely employed to monitor the live evolution of material response during mechanical loading, with many of the testing developments tailored for electron microscopes (EMs). More recently, progress towards quantitative in-situ testing at synchrotron beamlines^1–3 enabled by innovations in source brightness, focusing optics, and large size detectors has been made. Novel techniques such as Bragg coherent X-ray diffraction promise 3D information with phase information related to displacement fields (elastic strain, defects) within the material. However, despite the rich information that can be collected, many challenges arise in the realization of in-situ imaging of single nanostructures using such methods, including meticulous sample preparation and complex data analysis in retrieving phase information.
In this work, we present the first successful systematic single nanowire tensile test while simultaneously recording 3D Bragg peaks using coherent X-rays. Defect free single crystalline <110> oriented Au nanowires were grown by physical vapor deposition⁴ and a 100 nm nanowire was harvested from the substrate and transferred to a nanotensile stage within a microelectromechanical system chip, which can be mounted to a coherent X-ray beamline. 3D Bragg peaks were recorded with nanofocused beam combined with 2D detector at each displacement step to discuss the evolution of strain and rotation of the nanowire during the tensile test. The movement of the peak sensitively depicted evolution of the deformation of the nanowire. In addition, the 3D Bragg coherent X-ray diffraction followed by phase retrieval has shown to reveal the internal strain state of nanostructure⁵ and this advanced technique is expected to reveal unique surface effects that mediate the overall mechanical performance of nano-scaled materials.
This research is supported by the A*MIDEX grant (ANR-11-IDEX-0001-02) funded by the French Government « Investissements d’Avenir » program and the European Synchrotron Radiation Facility (ESRF) for the allocated experiment at the BM32 and the ID01 beamlines as well as the National Science Foundation through a CAREER Award #DMR-1056293.

Semiconductor nanowires offer a large flexibility in combining different materials, and are thus highly promising candidates for next generation (opto)-electronic devices [1, 2]. For understanding and improving the performance of these future nano-devices, it is crucial to correlate the strain and defects to the electrical properties at the individual nanostructure level. Since device operation itself might also influence the structural properties of the materials due to heating or piezoelectricity, both ex situ and in situ experiments are needed to further explore the influence of the strain and defects distribution on the electrical properties of the nanowires.
X-ray diffraction as a non-destructive technique is suitable for experiments in operando. With recent advances at third generation synchrotron light sources, X-ray diffraction techniques, such as coherent Bragg diffraction imaging (CBDI) now provide information about the strain and defects distribution within individual nanostructures [3]. On the other hand, scanning tunneling microscopes (STM) are dedicated for measuring the electrical properties of individual nanostructures without any process steps [4]. Here we will present recent experiments where we combined these two techniques both ex situ and in situ.
In the ex situ experiment, wurtzite InAs nanowires containing only very few stacking faults were investigated. Using the STM tip as nanoprobe, the electrical conductivity of individual upstanding nanowires is measured. The stacking faults distribution within the same nanowires is investigated by CBDI, allowing to study the impact of stacking faults on the electrical conductivity on the individual nanowire level.
In situ electrical measurements are performed in combination with X-ray diffraction by mounting a specifically designed STM onto the goniometer of a nanofocus beamline. Here, we will present the concept of these experiments, aiming at the in situ characterization of Joule heating, piezoelectric response, or local strain induced by the nanoprobe, together with some initial results obtained on individual GaN nanowires.
[1] J. Wallentin, “InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit”, Science 339, 1057, 2013;
[2] E. Lind et al., ”III-V Heterostructure Nanowire Tunnel FETs”, IEEE J. El. Dev. Soc. 3, 96, 2015
[3] V. Favre-Nicolin et al., “Analysis of strain and stacking faults in single nanowires using Bragg coherent diffraction imaging,” New J. Phys., 12, 035013, 2010.
[4] R.Timm et al., ”Current-Voltage Characterization of Individual As-Grown Nanowires Using a Scanning Tunneling Microscope”, Nano Lett. 13, 5182, 2013.

Self-assembled GaN nanowires (NWs) prepared by molecular beam epitaxy typically possess lengths of up to several microns and diameters of 20-100 nm. These NWs elongate along the surface normal with a spread in orientations of 2-3°. The aim of the present work is to study the NW diameter distributions by small-angle X-ray scattering (SAXS). We analyze three different kinds of GaN NW ensembles which exhibit significantly different NW densities and diameters: (i) NW ensembles on Si with densities over 10¹⁰ cm^-2 and diameters of 20-100 nm, (ii) NW ensembles on Si thinned down to 6 nm in diameter using a post-growth thermal decomposition process, and (iii) NW ensembles on sputtered Ti films that possess densities of the order of 10⁹ cm^-2 and diameters of 20-50 nm.
The small-angle scattering measurements are performed with the incident x-ray beam directed normal to the NW axis, i.e., at a grazing angle to the substrate. We avoid the complications of the grazing incidence scattering by choosing the incidence angle notably larger than the critical angle. The analysis of the X-ray data requires development of new approaches since, unlike to the common case of small-angle scattering, NWs are aligned. The range of orientations is, however, notably broader than one meets in grazing incidence X-ray scattering studies of epitaxial islands, so that the characteristic features typical for scattering from these structures (like the facet truncation rods) are not observed.
We separate the scattered intensity from NWs from all kinds of parasitic scattering caused by surface roughness, 3D islands, etc. by taking into account that an angular spread of orientations of long NWs gives rise to a respective cone of intensity in the reciprocal space. The sharp facets of NWs should result in the Porod law for the intensity I(q) at large wave vectors, I(q)~q^-4. The plot of I(q)*q⁴ vs. q possesses a maximum that allows to determine the mean NW diameter directly from the measured intensity, even without a model fit. The fit provides the whole diameter distribution, which we compare with the scanning electron microscopy analysis, for the samples where the latter is possible.
Deviations of the measured intensity from the Porod law are however observed at large wave vectors q, despite the sharp NW facets. We find two different effects causing the Porod law violation in the respective samples. First, a combination of the finite NW lengths (albeit large compared with their diameters) with a finite range of their orientations gives rise to an increased intensity at large wave vectors. Secondly, NW bundling causes an interference between scattering from individual NWs in the bundle, which provides additional intensity in another range of wave vectors. Summarizing, we state that grazing incidence SAXS directly provides the GaN NW diameter distributions. Violation of the Porod law at larger wave vectors brings to light further features of the NW ensembles.

The morphology of GaAs Nanowires (NW), grown by the self-catalyzed method, is strongly influenced by the liquid Ga-droplet at the NW tip.¹ The size of the droplet correlates with the actual NW diameter.² Its composition and shape at the liquid-solid interface and the involved facets determine the micro-structure of the growing NW³, and certain control of the NW crystal structure at later stages of growth has been achieved recently⁴.
At the onset of growth however, the wetting conditions may change dramatically. Whereas the liquid droplet is in contact with the oxide-covered Si substrate prior to GaAs nucleation, it begins to wet the NW side-walls once the GaAs NW starts to grow. It has been shown, that the wetting conditions between droplet and substrate are crucial for NW growth in terms of vertical yield.⁵ Further, the wetting conditions between droplet and the NW have impact on the evolution of polytypism during growth.^1,3
Although there are reports about the impact of substrate treatment^5-8, an investigation of it the effect on the crystalline phase of the NWs, especially during the nucleation phase, is pending.
Here, we report on the growth of self-catalysed GaAs nanowires onto Silicon (111) substrates using the portable molecular beam epitaxy setup of LAS/IPS at KIT⁹, specially designed for in-situ growth studies by X-ray diffraction (XRD). We vary the size and shape of the liquid Ga droplets by pre-growth substrate treatment, and investigate the deposited Ga-droplets, that serve as seed particles for further NW growth.
Furthermore, we probe the crystallographic properties of the GaAs NW grown from these droplets by means of time-resolved in-situ Reflection-High-Energy-Electron-Diffraction. After the growth, the NWs are investigated by ex-situ Scanning-Electron-Microscopy (SEM) and XRD. We reveal differences in the crystalline phase composition of the grown NW samples in terms of polytypism.¹⁰ Employing a statistical model for the atomic stacking sequences in the NWs¹¹, we model the XRD data and find indications for polytypism beyond the 2H and 3C phases of self-catalyzed GaAs NWs.¹²

References
¹P. Krogstrup et al., Nano Lett., 10, (2010)
²B. O’Dowd et al., J. Appl. Phys., 116, (2014)
³P. Krogstrup et al., Phys.Rev. Lett., 106, (2011)
⁴L. Balaghi et al., Nano Lett., 16 (7), (2016)
⁵T. Tauchnitz et al., Cryst. Growth Des., 17, (2017)
⁶T. V. Hakkarainen et al., Nanotechnology, 26, (2015)
⁷Y. Zi et al., Nano Lett., 17, (2017)
⁸H. Küpers et al., Journal of Crystal Growth, 459, (2017)
⁹T. Slobodskyy et al., Rev. Sci. Instrum., 83, (2012)
¹⁰P. Schroth et al., Phys. Rev. Lett., 114, (2015)
¹¹M. Köhl et al., J Synchrotron Radiat., 23, (2016)
¹² We are grateful for David Reuther, Jörg Strempfer and Sonia Francoual at P09, Hans Gräfe, Bärbel Krause and Annette Weißhardt at IPS, KIT. We thank Simone Dehm at INT, KIT and Gernot Buth at SCD beamline at ANKA. The project was supported by German BMBF (05ES7CK and 05K13PS3).

Blending of soft polymer matrices with nanoparticles has led to nanocomposites with exceptional properties and therefore have a large potential for applications in materials science.^1,2 In particular, responsive polymeric nanocomposites that are able to adapt to different surrounding environments are playing an increasingly important role. Due to their unique magnetic properties, superparamagnetic iron oxide nanoparticles are perfectly suitable for the synthesis of magneto responsive nanocomposites.
However, synthesis of homogeneous polymer-NC nanocomposites is still one of the biggest problems, because of the immiscibility of the inorganic nanoparticles with their host matrix in the nanocomposite. Several approaches to overcome this difficulty exist, especially by grafting polymer chains on the particle surface of the same chemical nature as the host matrix.
Nevertheless, an unstable ligand shell often leads to phase separation, resulting in self-assembly of the nanoparticles into a variety of superstructures, thus changing the magnetic properties of the nanocomposite in a hardly reproducible manner. We developed a three-step approach to overcome this problem by introducing a robust ligand shell, which is cross-linked by covalent bonds and, therefore, provides maximum stability. Micellar encapsulation is based on the hydrophobic part of amphiphilic polymers (diblock copolymers) intercalating with the hydrophobic ligand shell of the particle while the hydrophilic part is reaching into the aqueous solution.³ The hydrophilic part often consists of poly(ethylene oxide) (PEO). The stability of the micelles can be further increased by crosslinking the hydrophobic part and this is a crucial parameter for the homogenous distribution of the nanoparticles within the polymer matrix. The crosslinking of the polymer shell by covalent bonds provides maximum stability during mixing step with the host matrix and results in uniform hybrid nanoparticles homogeneously dispersed in a poly(ethylene oxide) matrix. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) investigations demonstrate the presence of mostly single particles and a negligible amount of dyads.
The combination of advanced synthesis and encapsulation techniques using different diblock copolymers and the thiol-ene click reaction for crosslinking the polymeric shell results in homogenous magneto responsive nanocomposites.⁴
[1] W. Caseri, Macromol. Rapid Commun. 2000, 21, 705–722.
[2] A. C. Balazs, T. Emrick, T. P. Russell, Science (80-. ). 2006, 314, 1107–1110.
[3] E. Pöselt, C. Schmidtke, S. Fischer, K. Peldschus, J. Salamon, H. Kloust, H. Tran, A. Pietsch, M. Heine, G. Adam, et al., ACS Nano 2012, 6, 3346–3355.
[4] A. Feld, R. Koll, L. S. Fruhner, M. Krutyeva, W. Pyckhout-Hintzen, C. Weiß, H. Heller, A. Weimer, C. Schmidtke, M.-S. Appavou, et al., ACS Nano 2017, 11, 3767–3775.

The purpose of this research work is to gain a better understanding of the nanostructural properties of Molybdenum (Mo) thin films’ porosity, nanovoid heterogeneity and its volume fraction as the film growth sputtering pressure changes systematically. This knowledge shall assists in optimizing Mo film nano- and microstructural properties as desired for solar cells applications. Therefore, in this research work two separate series of Mo thin films (0.7 μm thick) were deposited on high purity (99.999%) Al-foil (10 μm thick), and Si/SiO₂ substrates using direct-current (DC) planar magnetron sputtering. The sputtering pressure was varied from 0.8 mT to 12 mT, with a sputtering power density of 1.2 W/cm². Small Angle Scattering (SAXS) technique was applied to examine the heterogeneity and existence of nano- and microvoids in the Mo-coated Al foils. Moreover, the porosity of the Mo films as a function of sputtering pressure was studied by transmission electron microscopy (TEM) on Mo-coated Si/SiO₂ substrates.
Preliminary results showed that all Mo films are characterized by columnar morphology where open grain-boundaries structure started to develop in the films at intermediate and high sputtering pressure. SAXS intensity I(q) as a function of the momentum transfer q for Mo films showed a systematic reduction in intensities as the sputter pressure is decreased. It revealed larger features in the films induced by the higher pressures, in addition to the existence of anisotropic scattering from non-spherical, oriented objects. The void volume fraction exhibited an increase from 0.4% (at 0.8 mT) to ∼ 7% (at 12 mT). The average void diameter was found to increase from 5.7 nm for the Mo films sputtered at 0.8 mT to 12.5 nm for those films sputtered at 12 mT. The oriented ellipsoid model was utilized and it was consistent with a columnar-like microstructure where the voids have an elongated shape and are located along the column boundaries. Also, the measured Porod parameter indicated significant scattering from larger features which can be due either to surface roughness or to even larger voids. It was observed that as the growth sputtering pressure increases, the calculated average microvoid number density ξ, at first increases up to 2.0 × 10¹⁶ cm^-3 at 2 mT; and then decreases to an average of about ∼0.6 × 10¹⁶ cm^-3 above 4 mT. Whereas the average microvoid volume V increases monotonically from 582 nm³ at 0.8 mT up to 10227 nm³ at 12 mT. Furthermore; in good agreement with SAXS results, TEM data revealed the existence of slit-like void that extended through the film thickness, which is not a single void, but rather a void network of about 10 nm in width. However, further data and interpretation of the results of this research work will be presented in the detailed paper, where a correlation between the Mo thin film sputtering pressure and the microvoids number density, its volume fraction, and its dimensions will be presented.

Oxides with perovskite-like structure represent a fascinating class of advanced materials which have been extensively studied in the past decades since they exhibit a variety of functionalities, e.g., ferromagnetism, ferroelectricity or ferroelasticity. In ferroelectric materials phase symmetry and structural distortions are strongly coupled to piezoelectric properties. Periodic domain structures are of particular interest from both fundamental and technological point of view. Such periodic polarization modulations on a nanometer scale can be engineered by the use of substrates with suitable (anisotropic) misfit strains. However, understanding and controlling of ferroelectric phases and dimensions of the domain pattern is still challenging.

We focus on (K,Na)NbO₃ thin films grown on various rare earth scandate substrates using metal-organic chemical vapor deposition (MOCVD). Highly regular one dimensional ferroelectric domains pattern are formed with a lateral periodicity of typically 50 nm. The monoclinic symmetry of the domains is controlled by the anisotropic epitaxial lattice strain. Using piezoresponse force microscopy and conventional x-ray diffraction the monoclinic M_c phase can identified, which is associated with both a strong vertical and lateral electrical polarization component.

Interestingly, depending on the lattice strain induced by the underlying substrate and the MOCVD growth conditions four structural variants of superdomains are found, which differ in the three-dimensional arrangement of the domain walls and the corresponding electrical polarization vectors. These superdomains with typical lateral sizes of a few micrometers were individually characterized by a focused 100 nm x-ray beam as provided by highly brilliant synchrotron radiation sources (ESRF, PETRA III). Distinct differences (e.g. strain state, monoclinic shearing angle, domain wall angles) between the superdomain variants were observed and will be discussed in more detail.

Photo-rechargeable lithium-ion batteries, which are able to both harvest and store solar energy within electrodes, are a promising technology for a more efficient use of intermittent solar radiation [1]. However, there is a lack of understanding on how the light-induced lithium extraction reaction occurs within the electrode host lattice. In fact, this technology is based on bifunctional nanostructured electrodes, which undergo simultaneous complex modifications : structural reorganization through lithium-ion insertion and photo-excited charges creation through solar illumination.

In order to get more insight on the mechanism governing the photo-recharge of a single device based on a TiO₂ thin film electrode made of mesoporous anatase, we perform ex-situ glancing-incidence XRD experiments. Using laboratory glancing incidence diffraction, and implementing proper corrections for the instrumental broadening of this diffraction geometry in the Rietveld refinement software XND, it was possible to extract quantitative information about the structure (lattice strain and atomic positions) and the microstructure (crystallite size and micro-strain), selectively probing the material on a depth of few nanometers.

We believe that electrodes composition and architecture, nanocrystals orientation and constraints play an important role in the dynamics of the light-induced processes. In this poster, we will present how the grazing-incidence XRD can be used before and after electrodes cycling under illumination to better understand the impact of these parameters on the photo-recharge kinetics in a view of making performant devices.

[1] O. Nguyen, E. Courtin, F. Sauvage, N. Krins, C. Sanchez, C. Laberty-Robert, Shedding light on the light-driven lithium ion deinsertion reaction: towards the design of a photorechargeable battery, J. Mater. Chem. A 5 (2017) 5927-5933

Development of materials and engineering solutions in fusion technologies support the use of high-Z elements as Plasma Facing Component. Tungsten is among the most promising candidates for these applications. It is then important to assess the structure and strain of thick W coatings as those parameters influence the adhesion on various substrates. Glancing incidence X-ray diffraction can be used to study W polycrystalline textured films, obtain information about their structure, and establish a depth profiling of residual strain. The actual strain at different depths within the coating can be extracted from the measured averaged strain using the inverse Laplace transform method applied to a set of measurements at different angles of the impinging X-ray beam. This work was supported by grant Investissements d’Avenir of LabEx PALM (ANR-10- LABX-0039-PALM) and by the Region Ile-de-France in the framework of DIM Nano-K.

Tourmaline is an important function material due to its excellent physical properties such as spontaneous polarization, pyroelectricity, infrared radiations, and can serve as a petrogenetic monitor of the origin and evolution [1]. Because of the diverse composition and crystal defect from different origins, natural tourmaline is difficult to explore its potential in applications. Till now, many scientists have synthesized tourmaline containing many elements (K, Li, and NH4) through hydrothermal method with high pressure and temperature [2-4]. However, extreme reaction condition and minor sizes of the synthetic crystal (only several microns) are required in such methods. To solve these issues, a new high pressure solid-state method was present and dravite has been firstly synthesized in the present work. It provides an creative synthetic method for the synthesis of tourmaline and shed light upon the large-scale applications of tourmaline.
In this paper, polycrystalline dravite was prepared by using a solid-state reaction method under high pressure and temperature. Synthesis involved a solid-state method at 770-900K and a pressure of 5-7 GPa in mixture of powered Na₂O₂, Mg(OH)₂, MgO, Al₂O₃, SiO₂ and B₂O₃ with high purity. The growing crystal size is up to Æ0.1mm. Based on XRD and EMPA, it can conclude that dravite was successfully synthesized with a small quantity of SiO₂ and Al₂O₃. The mole ratio of chemical composition are emerged as n(Na): n(Mg) : n(Al): n(Si): n(B) : n(H)=1.032: 2.987: 6.017: 5.982: 3: 4, consistent with the mole ratio of the general formula. Pyroelectricity of the synthetic dravite and natural dravite were measured by TF3000 ferroelectric analyzer. According to the comparison of their pyroelectric coefficient, the pyroelectricity of synthetic dravite are found to be enormously enhanced than natural dravite. These findings provide important insight into the synthesis of bulky tourmaline with different chemical compositions and serve as the role of extending the wide application of tourmaline.

Reference
[1] Encarnación roda-robles, William simmons, et al. AM MINERAL 100, 95-109(2015).
[2] Eleanor J. Berryman, Bernd Wunder, et al. Contrib Mineral Petrol 169, 539-542(2015).
[3] Martin Kutzschbach, Bernd Wunder, et al. Phys Chem Minerals 44, 353-363(2017).
[4] Bernd Wunder, Eleanor Berryman, et al. AM MINERAL 100, 250-256(2015).

In the field of semiconductor electronic packaging, lead-based eutectic solder alloy is prevailing and cost friendly. However, lead soldering contacts cannot operate at high temperatures and its toxicity also has significant environmental impact. The functionality and mechanical integrity of a lead-free, nano-silver die-attachment has been demonstrated when it is sintered under high temperature and pressure. Nevertheless, the pressure-assisted sintering process increases the cost and it remains challenging to prevent the silicon die from cracking under pressure when the die is thinner and with rougher surface. It is thus desirable to utilize a pressure-less and lower-temperature sintering process. However, mechanical properties of the nano-silver die-attachment sintered at lower-temperature and pressure-less conditions tends to fail mechanically near the interfaces between the silver di-attachment and the substrate, in particular when gold is used as a metallization layer. To understand the underlying failure behaviors and mechanisms, we visualized and quantified the 3D structure of sintered nano-silver for die-attachment using x-ray ptychography and full field x-ray nano-tomography. The feature size distribution of the different phases, porosity, and the shape of the silver phase were determined as a function of metallization substrates, sintering pressure, types of nano-silver particles and thermal aging conditions. This analysis and the die shear test provided understanding in the failure mechanism within the sintered nano-silver powder structure.

Three-dimensional (3D) pore microstructure was investigated for six types of carbon nanotube (CNT) reinforced magnesium (Mg) composite foams with various porosities (i.e. 29%, 39%, and 49%) and compositions (0.05 wt.% CNT and 1 wt.% CNT) using a nondestructive x-ray micro-computed tomography technique. The data were analyzed to explore the effect of overall porosity and carbon composition on 3D pore microstructure such as the number of large pores, pore connectivity, pore size, pore size distribution, pore shape distribution, and specific surface area. The increase of overall porosity resulted in more large and connected pores, and a larger specific surface area. For all studied composite foams, pore size varies in the range of several microns to hundreds of microns; over 80% of the pores have the aspect ratio ≤ 2 and over 96% of the pores have the aspect ratio ≤ 3. The volume fractions are very low for the pores with the smallest and biggest sizes. The volume fraction for pores with a size ≥ 40 μm (i.e. the average size of raw Mg powders) increases from almost 40% to about 50% and then to almost 80% when the overall porosity increases from 29% to 39% and then to 49%. A critical pore size was defined and extracted for each of the studied foams and this size increases with the increase of overall porosity. Additionally, the variation of CNT concentration only slightly affects the pore microstructure.

Liquid crystalline polymers (LCP’s) comprise a class of performance materials that exhibit high mechanical strength, chemical inertness, flame retardancy and frequency-stable dielectric response. These favorable properties make LCP’s ideal candidates for various engineering applications, such as semiconductor packaging, high-frequency electronics, and high strength-to-weight ratio components. The characteristic LCP behavior arises from a unique microstructure, which in contrast to conventional amorphous polymers, consists of aligned crystalline domains in both the melt and solid phases. The resulting long-range molecular ordering gives rise to anisotropic behavior of the bulk material, which can be problematic from an industrial perspective. Thus, the ability to simulate the driving forces behind this morphology is essential to the design of processes for isotropic material production.
Goldbeck-Wood, et al. introduced a method for modeling the directionality, or orientation, of LCP’s on a mesoscopic scale. This hybrid method is carried out in two steps: first, the LCP rheology is simulated with conventional numerical methods, and second, the calculation of directionality is performed, using the data from the rheological modeling, assuming the LCP can be approximated as small molecule liquid crystals. Although Goldbeck-Wood, et al. demonstrated the ability of this technique to simulate LCP orientation on structured lattice grids, the methodology can be extended to unstructured meshes using modern finite element or finite volume solvers, to simulate complex geometric domains.
In this investigation, the evolution of LCP directionality during an injection molding process was modeled. The commercial solver, ANSYS FLUENT, was used to simulate the flow of a commercial LCP during injection molding. The resulting rheological outputs were then applied to user-defined calculations in MATLAB governing LCP directionality. These calculations captured three primary factors driving the final orientation state, namely: rheological (shear stresses), elastic (distortional interactions between crystals), and translational (bulk fluid flow).
To validate the model, the simulation results were compared to wide-angle x-ray scattering (WAXS) measurements of orientation in injection molded LCP plaque samples. An order parameter and anisotropy factor were calculated from the scattering data, as well as from the modeling results, to serve metrics for comparison between the two. Plaques of two thicknesses were both simulated and fabricated for the analysis, and it was hypothesized that decreasing the plaque thickness would result in a larger shear gradient driving crystal ordering in the material. The WAXS analysis found that the thinner plaque exhibited a higher degree of orientation with respect to the the flow direction, and the corresponding model predicted greater crystalline alignment with the flow than in the thicker simulation.

We use two non-destructive, synchrotron-based techniques—X-ray absorption tomography (XRAT) and near-field high-energy X-ray diffraction microscopy (HEDM)—to assess the character of grain boundaries resistant to hydrogen embrittlement in Ni-base alloy 725. Our study yields the grain size distribution and the full, five-parameter grain boundary character distribution. These analyses show that the microstructure of alloy 725 comprises elevated densities of Σ9 and coherent Σ3 grain boundaries. We also use the registered HEDM and XRAT reconstructions to connect the grain boundary character to intergranular fracture inside a hydrogen-embrittled Ni-base alloy 725 sample. This investigation provides unprecedented insight into the connection between the crystallographic character and susceptibility to hydrogen-assisted fracture of individual grain boundaries. We find that boundaries formed along planes with low Miller-index facets are especially resistant to hydrogen-assisted crack propagation and their presence results in toughening of the microstructure. Our investigation opens new paths toward predicting and improving the performance of Ni-base alloys exposed to hydrogen.

High-Entropy Alloys (HEAs) are in the focus of materials science due to their high strength, good ductility and excellent resistance to wear, corrosion and softening at high temperatures. HEAs are disordered solid solutions, containing at least four chemical elements with similar concentrations. The goal of our study was to investigate the lattice defect structure in nanocrystalline HEAs by X-ray diffraction peak profile analysis. The X-ray line profile analysis was complemented by electron backscatter diffraction and transmission electron microscopy. The spatial distribution of constituents was studied by energy-dispersive X-ray spectroscopy. The dislocation density and the twin-fault probability in the nanocrystalline HEAs were determined by X-ray line profile analysis. The chemical heterogeneities and the disordered structure in HEAs yielded an additional diffraction peak broadening in addition to the line breadths caused by the finite crystallite size and the lattice defects. Therefore, the evaluation method of X-ray line profiles was modified for HEAs accordingly. The average yield strength was estimated as one-third of the hardness and correlated to the defect structure. The influence of the concentration fluctuations on the mechanical properties was investigated by micro-pillar compression tests. The correlation between the mechanical performance and the defect structure for nanocrystalline HEAs is discussed in detail.

The ability to grow boron-doped diamond epilayers of high crystalline quality is a prerequisite for the fabrication of diamond power electronic devices, in particular high voltage diodes and metal-oxide-semiconductor (MOS) transistors. Boron and intrinsic diamond layers are homoepitaxially overgrown by microwave assisted chemical vapour deposition (MWCVD) on single crystal high pressure, high temperature (HPHT) grown bulk diamond substrates. Various epilayer thicknesses were grown, with dopant concentrations ranging from 10²¹ atom/cm³ at nanometer thickness in the case of 'delta doping', up 10¹⁶ atom/cm³ and 50µm thickness or high electric field drift regions. The crystalline quality of these overgrown layers as regards defects, strain, distortion… is critical for the device performance through its relation to the final electrical properties (Hall mobility, breakdown voltage...). In addition to the optimization of the epilayer growth conditions in the MWCVD reactor, other important questions related to the crystalline quality of the overgrown layer(s) are:
1. what is the dependence on the bulk quality and surface preparation methods of the HPHT diamond substrate;
2. how do defects already present in the substrate crystal propagate into the overgrown layer;
3. what types of new defects are created during overgrowth, what are their growth mechanisms, and how can these defects be avoided;
4. how can we relate in a quantitative manner parameters related to the measured crystalline quality of the boron doped layer to the electronic properties of final processed devices;
We describe synchrotron-based techniques developed to address these questions. These techniques allow the visualization of local defects and crystal distortion which complements the data obtained by other well-established analysis methods such as AFM, SIMS, Hall conductivity… We have used Grazing Incidence X-ray Diffraction (GIXRD) at the ID01 beamline of the ESRF to study lattice parameters and damage (strain, tilt and mosaic spread) both in diamond substrate near surface layers and in thick (10–50 µm) overgrown boron doped diamond epi-layers. Micro- and nano-section topography has been carried out at both the BM05 and ID06 - ESRF) beamlines using rocking curve imaging techniques to study defects which have propagated from the substrate into the overgrown layer(s) and their influence on final electronic device performance. These studies were performed using various commercially sourced HPHT grown diamond substrates, with the MWCVD overgrowth carried out at the Fraunhofer IAF-Germany. The synchrotron results are in good agreement with low-temperature (5K) cathodoluminescence spectroscopy carried out on the grown samples using an Inspect F5O FESEM fitted with an IHR spectrometer.

Coherent diffraction continues to develop into a mature technique capable of imaging single nanoparticles and thin film grains in a variety of environments. Its unique sensitivity to structural perturbations, and in particular dislocations, has made it the premier imaging tool for crystalline specimens with sizes of 100 nm to 1 micron. In this talk, I will initially review coherent diffraction in both Bragg and transmission geometries and then spend the majority of the time on applications of the techniques to two materials science systems that share many similarities in their underlying thermodynamics: advanced battery cathodes and hydrogen storage materials. The ultimate goal of this talk is to open new collaborations to address important outstanding questions in physics, chemistry, and materials science.

Low temperature scanning tunneling microscopy (STM) combined with synchrotron based X-rays is a surface sensitive technique to measure elemental, chemical and magnetic contrast at unprecedented resolution. A functionalized tip at a tip-sample junction works as a detector to collect localized information. Recently, we demonstrated that the technique can be utilized to obtain chemical fingerprint of monolayer metal islands [1] and localized magnetic contrast by utilizing polarized beams [2]. Here, we present measurements of chemical distributions on a battery anode material using SX-STM technique. The capability to probe depth sensitive chemical information at high spatial resolution opens door to study localized chemistry on surfaces.

References
[1] N. Shirato et al., Nano Letters 14, 6499 (2014).
[2] A. DiLullo et al., J. Synchrotron Rad. 23, 574 (2016).

Two soft-x-ray spectromicroscopes, scanning photoelectron microscope (SPEM) and scanning transmission x-ray microscope (STXM), are operational at the Pohang Light Source, enabling us to investigate element-, chemical state-, valence state-, crystal structure-, electronic structure-specific local distribution within a sample with a space resolution down to hundreds of nm in SPEM and tens of nm in STXM. As a nano-focused x-ray photoelectron spectroscopy (200 – 1,000 nm x-ray size at the sample), SPEM is operating at 400 – 1,000 eV photon energy and is surface sensitive (less than ~2nm probing depth). SPEM has been practically applied to investigate local chemical states and electronic structure of graphene layers, functionalized graphene layers, single layer of CVD synthesized MoS₂, h-BN encapsulated WSe₂, and laser-illumination-induced phase-changed MoTe₂. As an absorption spectroscopy, STXM normally operates in transmission mode and probes crystal structure, chemical state, and valence state through the sample. The sample thickness is ~hundreds of nm at the photon energy of strong absorption or several micrometers to even thicker at non-absorbing photon energy. Usable photon energy of the STXM ranges from ~200 eV to ~1600 eV. The space resolution is ~30 nm by using a 25 nm outermost zone-wide zone plate in the photon energy range from ~250 eV to ~850 eV, with worse space resolution at higher photon energy. The data acquisition time for one image is typically ~1 min. and thus in-situ or operando investigation is feasible, such as to investigate charging and discharging details of the lithium ion battery materials. Applications to nano-bio materials, energy storage materials, catalyst materials are becoming very active. Recently, we have added a soft x-ray fluorescence measurement setup in order to probe thicker samples’ elemental distribution as well as chemical state information, at a space resolution of ~50 nm. Also, we have implemented Ptychography setup in order to improve the space resolution down to less than 10 nm.

With the advent of high quality x-ray optics, several techniques have been proposed to exploit the imaging under Bragg conditions at synchrotron sources. Within the framework of the ESRF upgrade, a new dedicated instrument has been implemented on beamline ID01 at The European Synchrotron (ESRF). Since April 2017 this instrument is fully operational and has supplied users with Full Field Diffraction X-ray Microscopy (FFDXM) imaging adapted to various sample environments. Compared to more established scanning diffraction techniques, FFDXM offers fast, spatially resolved images on a large sample area without mechanical motions, perfectly suited for in situ and operando experiments.
The concept of FFDXM will be first demonstrated. A set of objective lens is placed downstream the sample to make a dark field image of the diffracted beam. At 6.5 meters away, the illuminated sample area (Field of View : 200×200 μm^{<span style="font-size:10.8333px">2</span>}) is magnified and spatially resolved on a CCD camera with a resolution of 100 nm. Essentially an x-ray strain microscope, the FFDXM is capable of probing lattice tilt, strain and grain orientation at surfaces, buried interfaces or inside functioning devices, which is often unreachable for electron microscopy techniques.
Results of several user and in house experiments will be given next, to illustrate the principle of diffraction topography (strained STO), mosaicity (InGaN nano-pyramids) and strain (buried gas cavities in implanted Si wafers) mapping using FFDXM. Typical image acquisition time is around 1 sec; a complete set of measurement takes just a few minutes.
Thanks to its large FoV, short acquisition time and suitable resolution, the FFDXM is ideal for in situ and operando experiments. This is further demonstrated by two successful examples. In the first experiment, the evolution of strain and lattice tilt of the Si surrounding Cu Through Si Via (TSV) was studied during in situ annealing up to 500°C and during subsequent cooling. In the second experiment, the failure mechanism (defect formation) of planar Si anode was studied during operando cycling of a Li-ion battery.

The growth of metal-surface oxides and its roles in surface reactions have been continuously studied (and debated) as it provide fundamental knowledge on how the surface reaction occurs in the presence of oxides. Among many of those studies, the surface oxides of Pt and Pd have been intensively studied and two different reaction mechanisms, i.e. Langmuir-Hinshelwood mechanism and Mars-van-Krevelen mechanism, have been employed to explain CO oxidation reaction.

Recently, we revisited the study of CO oxidation on Pt(110) and Pd(100) surface using AP-XPS. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure, the presence of surface oxides is observed on both surfaces. Due to exothermic nature of CO oxidation, the temperature of both Pt and Pd surfaces increases as CO oxidation takes places. Interestingly, the gas phase peaks of oxygen behave differently from Pt surface to Pd surface under oxygen rich condition, reflecting opposite reaction properties of surface oxides. The origin of the reaction properties of Pt and Pd will be discussed.

Condensed phase matter in the atmosphere is of paramount importance for hydrology, biogeochemical cycles, climate, ecosystems and human health. Ice in snow and cirrus clouds, aqueous solutions in aerosol particles and clouds, and salt, organics and mineral oxides in other particulate matter suspended in the air are some examples. Increased interest about chemical and physical processes at or near the condensed phase – air interface has led to in situ techniques capable of probing relevant surfaces at the molecular scale (at depths of a few nanometer at most) and the interior of atmospheric particles with submicron resolution. Atmospheric material properties are a strong function of the water vapor partial pressure in the mbar range, while most chemically relevant trace gases are in the 10^-6 mbar range and below. Therefore, in situ techniques must provide chemical selectivity and either sensitivity for the surface or high spatial resolution, while at the same time being able to cope with a high water vapor pressure. For the purpose of addressing interfacial chemistry we have recently developed an in situ cell for ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to study the interaction of trace gases with ice, mineral oxides and aqueous solutions that allows equilibrating these materials at relevant relative humidity and at the same time features fast response times to sticky trace gases. For the purpose of addressing the internal physical and chemical structure of aerosol particles, we have used an environmental cell in conjunction with scanning transmission X-ray microspectroscopy (STXM) to investigate the behavior of authentic and proxy aerosol particles in response to chemical or photochemical stimuli that induce changes in morphology and chemical composition. Recent results obtained with both techniques will be presented.

References

Alpert, P. A., Ciuraru, R., Rossignol, S., Passananti, M., Tinel, L., Perrier, S., Dupart, Y., Steimer, S. S., Ammann, M., Donaldson, D. J., and George, C.: Fatty Acid Surfactant Photochemistry Results in New Particle Formation, Scientific Reports, 7, 12693, 2017.

Artiglia, L., Edebeli, J., Orlando, F., Chen, S., Lee, M.-T., Corral Arroyo, P., Gilgen, A., Bartels-Rausch, T., Kleibert, A., Vazdar, M., Andres Carignano, M., Francisco, J. S., Shepson, P. B., Gladich, I., and Ammann, M.: A surface-stabilized ozonide triggers bromide oxidation at the aqueous solution-vapour interface, Nature Communications, 8, 700, 2017.


Kong, X., Waldner, A., Orlando, F., Artiglia, L., Huthwelker, T., Ammann, M., and Bartels-Rausch, T.: Coexistence of Physisorbed and Solvated HCl at Warm Ice Surfaces, The Journal of Physical Chemistry Letters, 4757-4762, 2017.

For state-of-the-art rechargeable batteries, the working principle is commonly based on the reversible insertion of alkali metal ions into a host structure, usually a layered transition metal oxide for the positive electrode (cathode). The nature of the alkali insertion reaction into the host structure is a key issue for the performance of the electrode material, such as electrode potential and reversible capacity. Both are intimately coupled to the electronic structure of the material and its evolution upon deintercalation. In the past, the electronic structure of intercalation materials has been inferred from the performance of the material such as its electrode potential at different state of charge (SOC), or has been experimentally determined using electrodes which were electrochemically deintercalated using liquid electrolyte and then analyzed after emersion by XPS and XAS (“post mortem analysis”). The results of these studies are subject to uncertainties due to the large surface sensitivity of the measurement techniques. For post mortem studies of cathode materials that were in contact with liquid electrolytes, surface contamination by electrolyte residuals and the solid electrolyte interface (SEI) layer are inevitable and oppose an unambiguous interpretation of the data.

In this contribution we present an in operando XPS study of the cathode material Na_xCoO₂, which to our knowledge is the first study of this kind dealing with a layered oxide cathode material. An all-solid-state-battery with a Na_xCoO₂ cathode was assembled under UHV conditions in such a way that it was possible to measure XPS of the bare cathode surface in operando while cycling the battery. In addition, batteries were precharged in situ and transferred under UHV conditions to the synchrotron facility BESSY II to measure XAS at the cathode surfaces at various charge states.

In the XPS and XAS measurements using the all-solid-state-battery approach we were able to follow the charge process in the core levels (Co2p, O1s, Na1s) as well as in the valence band region without uncertainties caused by electrode-electrolyte interactions. During charging a decrease in alkali content and change in cobalt oxidation state of the cathode material is clearly visible. Already at comparably low deintercalation states -within the reversible region- changes in the O2p orbitals were measured. Correlation of XPS/XAS and electrochemical data indicate a reflection of the electronic structure evolution by the charge curve.

Atomic layer deposition (ALD) and chemical vapour deposition (CVD) are very important methods that enable a highly controlled growth of thin films [1]. The surface chemistry of the underlying processes remains, however, little understood. While idealised reaction mechanisms have been developed, they represent postulates rather than models based on the factual identification of surface species and kinetics [2]. New in situ and operando methods offer the prospect of gaining a much more thorough understanding of the involved molecular and atomic surface processes and (dynamic) structures, which, in turn, means that a much better knowledge basis can be achieved for the future improvement of materials and growth recipes (see, e.g. [3,4]). One such operando method, which can be applied to the investigation of ALD and CVD, is synchrotron-based ambient pressure x-ray photoelectron spectroscopy (APXPS). While conventional x-ray photoelectron spectroscopy (XPS) is limited to vacuum pressures of 10^-5 mbar and below, APXPS can be carried out at realistic pressure. Today, most APXPS machines can operate at pressures up to the 10 mbar regime, which is an ideal match to the pressure regime used in standard ALD reactors.
Here, I will report on our recent efforts to apply synchrotron-based APXPS to the ALD/CVD of oxides (TiO₂, SiO₂, and HfO₂) on semiconductor (InAs and Si) and oxide surfaces (TiO₂, RuO₂) [3-5]. I will show that APXPS allows the identification of the surface species occurring during thin film growth and the real-time monitoring of their evolution, presently with a time resolution of around 1 s. I will also report on our efforts to further improve instrumentation with the goal of achieving a much closer match of the APXPS sample environment with the geometries used in conventional ALD reactors. The development will also open for the use of a wider range of precursors and growth protocols. Further, we work on making the millisecond timescale attainable in the APXPS study of ALD.

[1] V. Miikkulainen et al., J. Appl. Phys. 113 (2013) 021301.
[2] F. Zaera, Coord. Chem. Rev. 257 (2013) 3177.
[3] B. A. Sperling et al. Appl. Spectrosc. 67 (2013) 1003.
[4] K. Devloo-Casier et al., J. Vac. Sci. Technol. 32 (2014) 010801.
[3] S. Chaudhary et al. , J. Phys. Chem. C 119 (2015) 19149.
[4] A. R. Head et al. , J. Phys. Chem. C 120 (2016) 243.
[5] R. Timm et al., submitted (2017).

Characterising the structural properties (strain gradients, chemical composition, crystal orientation and defects) inside nanostructures is a grand challenge in materials science. Bragg coherent diffraction imaging (Bragg CDI) can be utilized to address this challenge for crystalline nanostructures. A resolution of the structural properties of less than 10 nm is achieved up-to-date [1]. The capabilities of the Bragg CDI technique will be demonstrated on single nanoparticles during thermal annealing and for enhanced catalysis. The experiments have been performed at the beamline ID01 at The European Synchrotron (ESRF), where a Fresnel zone-plate was used to focus the beam with energy of 8 keV to a spotsize of 100 nm (V) × 300 (H) nm².
The Bragg CDI technique allows understanding the interplay between shape, size, strain, faceting [2], composition and defects at the nanoscale. For example, we will demonstrate that Bragg CDI on a single particle model catalyst makes it possible to map its local strain/defect field and directly images strain build-up close to the facets. The localized strain modifies sorption energies of the reactants. In situ [3] and operando Bragg CDI was also performed: it was possible to track a single particle in gas phase environment, to monitor its facet changes and to measure its strain response to gas.
This technique opens pathways to determine and control the internal structure of nanoparticles to tune and optimize them during catalytic and other chemical reactions.

[1] S. Labat, M.-I. Richard, M. Dupraz, M. Gailhanou, G. Beutier, M. Verdier, F. Mastropietro, T. W. Cornelius, T. U. Schülli, J. Eymery, and O. Thomas, ACS Nano 9, 9210 (2015).
[2] M.-I. Richard, S. Fernandez, J. Eymery, J.-P. Hofmann, L. Gao, J. Carnis, S. Labat, V. Favre-Nicolin, E. J. M. Hensen, O. Thomas, T. Schülli, and S. J. Leake, Submitted (2017).
[3] M.-I. Richard, S. Fernández, J. P. Hofmann, L. Gao, G. A. Chahine, S. J. Leake, H. Djazouli, Y. De Bortoli, L. Petit, P. Boesecke, S. Labat, E. J. M. Hensen, O. Thomas, and T. Schülli, Rev. Sci. Instrum. 88, 093902 (2017).

Tracking structural changes down to the atomic level in a catalyst under operando conditions is crucial to gain a fundamental insight into the catalytic process [1]. We report on structural changes in a pre-selected single platinum (Pt) nanoparticle epitaxially grown on a (100)-oriented strontium titanate (STO) single crystal as observed by in-situ coherent X-ray diffraction imaging (CXDI) during catalytic CO oxidation at near ambient pressure and elevated temperature.
(111)-oriented Pt nanoparticles were grown on the STO substrate by e-beam evaporation. Scanning electron microscopy (SEM) was used to pre-select an isolated Pt nanoparticle that was marked in its vicinity by Pt-containing nano-crystalline markers using electron-beam induced deposition (E-BID). The in-situ catalytic CXDI experiment was conducted at the beamline ID01 at ESRF in Grenoble, France, using an X-ray energy of 8.5 keV and focusing Fresnel zone plates [2]. The hierarchical position markers and a transfer and positioning protocol developed in the framework of the European user platform Nanoscience Foundries Fine Analysis (NFFA Europe) [3] permitted us to re-localize the pre-selected Pt nanoparticle. CXDI signals of the Pt(111) Bragg peak were collected in a gas flow of 20 ml/min and a pressure of 50 mbar in inert Ar and in a stoichiometric 2:1 mixture of CO and O2.
The facet signals around the Pt(111) Bragg peak in Ar at room temperature showed that the Pt nanoparticle surface was facetted. Alterations in the facet signals at elevated temperature and in a catalytic CO/O2 atmosphere indicate that applying these conditions induced structural changes in the Pt nanoparticle. These are evident by reconstructing the CXDI data and comparing the resulting real space particle in the different environments. In particular, we discuss the observed particle shape-changes, atomic displacements and a dislocation inside the Pt nanoparticle also in respect to complementary molecular dynamics simulations of the Pt nanoparticle under the applied catalytic CO oxidation conditions.

References

[1] U. Hejral, P. Mueller, O. Balmes, D. Pontoni, A. Stierle, Tracking the Shape-Dependent Sintering of Platinum-Rhodium Model Catalysts under Operando Conditions, Nature Communications 7, 10964 (2016) http://www.nature.com/articles/ncomms10964
[2] M. I. Richard, M. H. Zoellner, G. A. Chahine, P. Zaumseil, G. Capellini, M. Haeberlen, P. Storck, T. U. Schulli, T. Schroeder, Structural Mapping of Functional Ge Layers Grown on Graded SiGe Buffers for sub-10 nm CMOS Applications Using Advanced X-ray Nanodiffraction, ACS Appl. Mater. Interfaces 7, 26696 (2015). http://pubs.acs.org/doi/10.1021/acsami.5b08645
[3] EU H2020 framework programme for research and innovation under grant agreement n. 654360. http://www.nffa.eu/

Ion exchanged zeolites are promising heterogeneous catalysts in selective reduction chemistry and in vehicle exhaust purification. The chemically active site of the zeolite channels acts as an ion trap and supplies an ion to reactants selectively. Local strain affects the pore size and the channel connectivity of the zeolite catalyst related to the catalytic efficiency. Here, we report the kinetics of local deformation field distribution of Cu-ZSM-5 zeolites during the nitrogen oxide reduction catalysis using in situ time resolved coherent X-ray diffraction imaging with an X-ray Free Electron Laser. The adsorption of hydrocarbons to Cu-ZSM-5 catalysts, essential component for activating the Cu ions at low temperature, generates unusual lattice displacement. It reflects inhomogeneity of the host crystals and then is released during the subsequent steps of the catalytic process of the nitrogen oxide reduction. The observed time dependence should therefore be considered as a major factor in the design of future catalytic materials.

X-ray ptychography is a method of coherent X-ray diffractive imaging that applies translational diversity, in which the object of interest is scanned in small steps by an overlapping probe, providing redundancy in collected data. So far, X-ray ptychography has been applied to structural imaging of various specimens in biology and materials science at the nanoscale. X-ray ptychography can also provide us with chemical information of a sample by using an X-ray absorption edge, which is often referred to as X-ray spectro-ptychography. Recently, the X-ray absorption fine structure (XAFS) of nanomaterials has been reconstructed by soft X-ray spectro-ptychography[1]. Extending this approach to the hard X-ray region will enable us to visualize the chemical state of nanostructures buried within bulk materials. However, a limitation of this method is the weak absorption of incident X-rays in the hard X-ray region. To improve the convergence of the phase retrieval for complex-valued images in X-ray spectro-ptychography, we proposed and demonstrated the addition of a constraint based on the Kramers–Kronig relation (KKR constraint) to the phase retrieval algorithm[2]. A numerical simulation showed that the speed of convergence was increased by using the improved algorithm with the KKR. We successfully demonstrated its usefulness in a proof-of-principle experiment using a test sample at SPring-8. We applied hard X-ray spectro-ptychography to visualize the oxidation state of oxygen storage and release particles, CZx (Ce₂Zr₂O_x, 7≦x≦8), which are used in automobile exhaust gas cleaning systems owing to their high oxygen storage and release property. Twenty-eight energies were selected between 5.717 keV and 5.817 keV around the Ce L₃ absorption edge. Diffraction patterns were measured with 4 s exposure at each scan position. After reconstructing the object functions at each energy using the KKR constraint, an oxidation state mapping was derived with 13 nm pixel resolution by linear combination of the XAFS spectra of fully reduced CZ7 and oxidized CZ8. Nanodomain structures due to the heterogeneous oxidation state in CZ7.6 particles were clearly visualized[3].

References
[1] D. A. Shapiro et al., Nat. Photonics 8, 765-769 (2014).
[2] M. Hirose, K. Shimomura, N. Burdet, and Y. Takahashi, Opt. Express 25, 8593-8603 (2017).
[3] M. Hirose, N. Ishiguro, K. Shimomura, N. Burdet, H. Matsui, M. Tada, and Y. Takahashi, submitted

Magnetite (Fe₃O₄ nanoparticles) was known to be present in Amyloid plaques in Alzheimer patient. In vitro this nanoparticle induces Aβ-fibril formation under saturated concentration. Redox activity of iron depends on its ionic status, and plays an important role in toxicity of Aβ-fibril/amyloid plaque. We have attempted to image the magnetite distribution in a macrophage cell and nanoradiator-based ROS formation using zone-plate based synchrotron X-ray STXM-XAS method, which allows focusing of Fe L-edge X-ray beam as 30 nm, irradiating almost single nanoparticles in a single cell, and producing low-energy electron and measurement of redox activity of iron: Fe(II) (redox active), Fe(III)(redox inactive). In the presence Aβ₄₂ peptide, FeCl₃ induced Aβ fibril, rendering redox active Fe(II), while traversing proton irradiation converted into redox inactive Fe(III) with disrupted Aβ-fibril which was confirmed TEM imaging. In this connection, we investigated magnetite-mediated induction of Aβ-fibril formation and its redox status of Fe(II), and after proton irradiation, major redox status of magnetite was monitored which in turn turned into Fe(III) compared to initial overriding Fe (II) in Aβ-fibril before proton irradiation. These results suggest traversing proton beam may be used for novel redox change therapy in the amyloid plaque in Alzheimer disease patient.

X-ray techniques have grown in popularity over the past decade. Owing to the high penetrating power and non-destructive capabilities of X-ray radiation, these techniques have opened new frontiers for material characterization. In spite of these advantages, however, conventional laboratory X-ray instrumentation is intrinsically limited by the brightness of the illuminating x-rays, which, in turn, limits the detection sensitivity and spatial resolution of commercial X-ray fluorescence spectrometers (XRFs). Conventional laboratory micro-XRFs are typically limited to detection sensitivities in the ppm range, with analytical spot sizes on the order of 10s to 100s of microns. For higher sensitivities or finer spatial resolutions, researchers typically must select alternative techniques, such as LA-ICP-MS or EDS; however, these techniques have the disadvantage of either being destructive (as in the case of LA-ICP-MS) or limited in sensitivity and to surface features only (as for EDS).

In designing a new generation of laboratory micro-XRFs, we began by redesigning the X-ray source. Using a fine array of micro-drilled targets embedded in diamond, the heat dissipation has been significantly enhanced, producing an X-ray source that is over 50x brighter than conventional micro-XRF laboratory sources. This novel source technology is then paired with a twin paraboloidal X-ray mirror lens, fabricated with minimal slope errors and smoothness on the order of single-digit angstroms, providing achromatic focusing with long working distances (~30 mm) and enabling high-spatial resolutions to be achieved. In order to maximize the x-ray fluorescence flux and detection sensitivity, the source is typically customized with the most appropriate X-ray target material(s), may be selected and tuned for each characterization study, varying the x-ray fluorescence cross section by several orders of magnitude.

Combining this high brightness X-ray source with the precision X-ray optics has produced a unique approach to laboratory micro-XRF, providing spatial resolutions on the order of single-digit microns and detection sensitivities in the sub-femtogram (attogram) regime. This system is also designed with a variety of X-ray detectors, enabling correlative in situ X-ray radiography and spectroscopy, in order to quickly identify regions of interest and analyze them with micro-XRF. Here, we will review the design principles of this novel micro-XRF, describing in more detail how the paired X-ray source and twin paraboloidal optics work together to provide enhanced detection sensitivities and spatial resolutions. We will then demonstrate the application of this technique to a range of studies, including advanced material characterization, microelectronics inspection, and environmental contamination, as time permits.

On the basis of the in-situ photoemission spectroscopy (PES) system, we propose a novel, direct diagnosis method for the characterization of graphene (Gr) doping states at the organic semiconductor (OSC)/electrode interface. Our in-situ PES system enables ultraviolet/X-ray photoelectron spectroscopy (UPS/XPS) measurements in the OSC growth or removal process. We directly deposit C₆₀ film on three different p-type doped Gr—the gold chloride doped Gr (AuCl₃_Gr), (trifuoromethyl-sulfonyl)imide (TFSI) and nitric acid (HNO₃) doped Gr (TFSI_Gr), and nitric acid doped Gr (HNO₃_Gr). We periodically characterize the chemical/electronic state changes of C₆₀/Gr structures during their aging processes under ambient conditions. In other word, we perform cyclic UPS/XPS measurements and these results provide significant information regarding the variations of chemical and electronic states in the C₆₀/Gr structures, according to aging time under ambient conditions. In addition, the OSC can also act as a passivating layer to prevent severe degradation of dopants with negligible change in doping state over one month, while the p-type doped Gr without OSC degrades a lot in one-month aging. Consequently, all the p-type doped Gr layers in different C₆₀/Gr structures undergo significant transitions in the doping states over time, in spite of the passivation effect of C₆₀ films. Our result concludes that the chemical/electronic structures of the Gr layer are completely reflected in the energy level alignments at the C₆₀/Gr interfaces. Therefore, we determine a strong correlation between the energy level alignment at the C₆₀/Gr interface and the Gr doping state; and therefore, we strongly believe that the variation of energy level alignments at the OSC/graphene interface is a key standard for determining the doping state of graphene after a certain period of aging time.

Self-assembled semiconductor quantum dots (QDs), such as Ge QD on Si and InAs QD on GaAs exhibit size and composition dependent optical and electrical properties. The prime challenge remains to determine the growth parameters to obtain predictable composition and strain profiles within a QD and size-distribution of QDs so that optoelectronic properties of these quantum structures can be tuned with fundamental physics calculations. It has been pointed out that the confinement length of the carriers depends upon the composition profile within a QD and not just on their size. Structure-spectroscopy correlation allowed us to address these problems with accuracy.

We have studied the growth process of Ge Inverted Quantum Hut (IQH) structures, embedded in a silicon lattice, using anomalous x-ray scattering techniques [1]. The results showed that the deposited Ge layer relaxes strain by uniform intermixing with the previously deposited lower Si layer to form a SiGe alloy wet layer and the IQH structure forms just below the wet layer with its tip pointing towards the substrate. The interfacial strain in such IQH structures is greatly reduced, leading to a Type - I band-alignment at the hetero-interface, which is different from that obtained for conventional QDs [2], and hence these are significant for application in optoelectronics. We have also studied the in-plane density dependent properties of InAs QDs grown on GaAs substrate. We showed that composition and strain profile of the QDs can be tuned by controlling in-plane density of the dots over the substrate with the help of substrate-temperature profile [3].

Anomalous grazing incidence x-ray diffraction (GIXD) study of the Ge IQH structures on Si substrate grown by Molecular Beam Epitaxy technique will be presented. GIXD measurements were performed at Petra III, DESY, Germany by tuning the incident X-ray beam at two different energies corresponding to Ge K-edge (11103eV) and away from it (11043eV), in order to improve the sensitivity of Ge. Measurements were performed to probe (400) and (800) in-plane diffraction peaks at both the energies and their intensities were compared. The study allows us to directly determine the composition variation in such structures and also mapping of strain in the different regions constituting them. Important morphological details of the IQH structure have been revealed by the analysis of x-ray reflectivity data by Born-approximation. The results are supported by cross-sectional transmission electron microscopy images of the IQH structures.

References:
[1] M. Sharma, M. K. Sanyal, B. Satpati, O. H. Seeck and S. K. Ray, Physical Review B, 89, 205304 (2014).
[2] M. Sharma, M. K. Sanyal, A. Katiyar and S. K. Ray, Applied Physics A, 119, 55 (2015).
[3] M. Sharma, M. K. Sanyal, I. Farrer, D. Ritchie, A. B. Dey, A. Bhattacharyya, O. H. Seeck, J. S. Szymanska, M. Felle, A. J. Bennett and A. J. Shields, Scientific Reports, 5, 15732 (2015).

As the X-ray microscopy approaching higher spatial resolution, the associated depth of field dramatically shrinks, which limits the sample thickness without sacrificing resolution. A recent development on multi-slice ptychography method decomposes the X-ray-sample interaction into a series of planes, and on each plane the projection approximation satisfies. This approach effectively extends the achievable depth of field. However, since the depth resolution is provided by the z-component of high-q diffraction signal projected on the curved Ewald sphere, typical multi-slice ptychography measurements with X-rays requires 10s of seconds dwell time per scan point to collect adequate high-q signal. Here, we present an approach to conduct multi-slice ptychography measurement using nano-focused beam from multilayer Laue lenses. Using the data inside the intense holographic area, the dwell time can be reduced to 0.05 second level, while reaching 8 nm lateral resolution and 10 um depth resolution. This approach is successfully integrated with on-the-fly scan mode, which greatly improves the throughput of multi-slice ptychography method as a high-resolution 3D imaging technique.

Coherent x-ray diffractive imaging (CXDI) can now reach down to sub ten nanometer structural imaging of materials[1]. When done in the Bragg geometry one can also image distortions of the lattice with 10⁻⁵ sensitivity [2, 3]. Bragg CDI is also highly compatible with in-situ and operando studies of materials owing to the relatively large free space around the sample.
Recently we have conducted imaging experiments with both catalytic systems and ultrafast laser pump – x-ray probe of energy transport by phonons in nanomaterials[4]. To quantify the response seen in the materials there is an increased requirement for image analysis to understand the physical processes occurring.
Advanced image analysis and molecular dynamics (MD) simulations are now scaling in the opposite direction of CXDI. These computational methods are reaching UP to the length/time scales achieved in the imaging experiments. Image meshing techniques can be used to create models of the actual samples in an experiment, which can then feed into multi-million atom MD and finite element simulations over hundreds of picoseconds[5].
Building a complete workflow to understand nanoscale phenomena with atomistic origins is the goal the MAUI (Modeling, Analysis and Ultrafast Imaging) project at Argonne National Laboratory. Specialists in coherent imaging, ultrafast laser science, 4D image analysis, math and computer science have teamed up with molecular dynamics simulations experts to develop these tools.
This talk will focus on recent efforts and results coming out of the MAUI team.


References
[1] Y. Takahashi et al., English, Physical Review B 80, 054103 (Aug. 2009).
[2] M. A. Pfeifer et al., Nature 442, 63–66 (July 2006).
[3] I. Robinson et al., Nat Mater 8, 291–298 (Apr. 2009).
[4] A. Ulvestad et al., J. Phys. Chem. Lett. 7 (15), 3008–3013 (Jul. 2016).
[5] Y. Li et al., Scientific reports 5 (2015).

Bragg coherent x-ray diffraction imaging (BCDI) has been employed on various nanoscaled crystalline materials to image the distribution of strain and lattice distortion with non-destructive measurements. In-situ and/or operando imaging became a major driver for BCDI to address scientific questions on physics and chemistry in recent years. Many efforts have been made to surpass the current state-of-art of BCDI and world leading synchrotrons, such as APS, ESRF, and Petra IV, are planning to upgrade x-ray sources to deliver more coherent photons which is essential for BCDI.
In this study, I will introduce current status of BCDI as well as a new approach for BCDI that exploit tunable x-ray wavelengths to eliminate the requirement of the sample rotation for 3D imaging which often bothers in-situ or operando experiments. We have measured 3D coherent diffraction patterns around Au (111) Bragg peak with energy scans and successfully reconstructed the image of the sample with new phase retrieval algorithm. In addition, I will talk about the way for collecting 3D dataset within short time using broadband x-rays and the experimental setup which disperses diffracted polychromatic x-rays into monochromatic patterns in parallel with a stack of analyzers. In the last part, BCDI with upgraded x-ray sources in the future will be discussed.

Three-dimensional coherent diffraction imaging methods including Bragg ptychography (BP) and single-particle Bragg coherent diffraction imaging (BCDI) have tremendous potential to elucidate dynamic structural properties in nanoscale crystalline volumes with especially fine sensitivity to lattice imperfections. However, especially in in-situ environments, uncertainty due to thermal drift and vibrations can affect not only the position of particle / beam, but also the incident angle. Both have detrimental effects on the final reconstructed image. In this abstract we focus on correcting angular uncertainties, and we show that the approach can be used both for BCDI and Bragg ptychography.

The novelty of our approach, inspired in the steepest descent gradient method successfully applied in transmission Bragg ptychography, lies in the calculation of a generalized gradient of the error which enables its minimization by simultaneously improving the reconstructed object and correcting for the beam position/incident angle uncertainties. This method to correct for the angular position of the diffraction pattern collected over a rocking curve scan has a wide application in the post-processing procedure of BCDI and BP measured data since the high precision control of the beam position/incident angle which is required for a high quality reconstruction is often difficult to achieve.

Spatial resolution of strain in bulk polycrystal volumes requires coherent diffractive imaging (CDI) capabilities at high X-ray energies, typically greater than 50 keV. We describe here a data recovery scheme to treat coarsely resolved diffraction signals from such experiments. The general numerical methodology is applicable to scattering data collected under a variety of restrictive experimental conditions. Our method is detailed here in the context of Bragg-mode CDI measurements of a single crystal. We describe certain mathematical properties of the wave field from such a scatterer, and how these can be exploited to achieve a resolution of the signal that is not limited by the detector pixel size. Our focus specifically is on two variants of the conventional experimental setup, and how application of our numerical ‘sparse recovery’ method allows one to relax certain experimental constraints and affords one flexibility in the data acquisition process. We see the development of such enhanced signal processing tools as complementary to the current hardware upgrade programs at next-generation synchrotrons around the world.

Components of any system, from suspension bridges to computer chips, must be designed to withstand the stresses they will experience. At the macroscopic scale, stress is well understood and methods for characterizing these stresses using neutron and high-energy X-ray diffraction are well established. Microscopic stresses within complex microstructures and devices are less well understood, largely because methods for characterizing stresses at micrometer and sub-micrometer length scales are lacking. As just one example, it has been estimated that thermo-mechanically induced stress is responsible for approximately 65% of all microelectronic device failures, but almost all studies of these stresses use finite element simulations with no direct experimental validation. Recent advances in synchrotron X-ray techniques by researchers at the National Institute of Standards and Technology and the Advanced Photon Source (APS) at Argonne National Laboratory have provided an unprecedented capability for probing phases, microstructure, and full strain/strain tensors with micrometer, and even submicrometer, spatial resolution within complex real-world materials. An overview of these microbeam measurement capabilities at beamline 34ID-E at the APS will be presented, along with example studies of microscopic stresses within microelectronics, plastically deformed metals, and additive manufactured metal components. Finally, prospects for future developments in this area will be described.

Leading-edge CMOS technology nodes use transistors with down-scaled dimensions, and simultaneously, challenge design and materials integration of on-chip interconnect stacks. Particularly insulating ultra low-k (ULK) materials with low Young’s modulus and fracture toughness weaken the mechanical behavior of the backend-of-line (BEoL) stack. Chip-package interaction (CPI) and the related thermomechanical stress increase the risk of failure caused by delamination along Cu/dielectrics interfaces (adhesive failure) and fracture in dielectrics (cohesive failure). In order to avoid mechanical chip damage, so-called crack-stop structures are integrated [1]. Transmission X-ray microscopy (TXM) with sub-100nm resolution and nano X-ray computed tomography (nano-XCT) are a unique techniques to image crack propagation in interconnect stacks. We demonstrate in-situ crack propagation studies in BEoL structures. Based on 3D data sets, weak interfaces in the BEoL stack are identified and the effectiveness of crack stop structures is evaluated. The study of the crack evolution was performed in a laboratory-based X-ray microscope (Xradia) using a micro double cantilever beam (micro-DCB) test [2] and using synchrotron radiation (BESSY II Berlin) using an indenter manipulation [3]. Conclusions will be discussed in the frame of fracture mechanics.

[1] X. Zhang, R. S. Smith, R. Huang, P. S. Ho, “Chip package interaction and crack-stop study for Cu ultra low-k interconnects”, AIP Conf. Proc. 1143, 197 (2009)
[2] S. Niese, “Lab-based in-situ X-ray microscopy – Methodical developments and applications in materials science and microelectronics“, PhD thesis, BTU Cottbus (2015)
[3] K. Kutukova, J. Gluch, Y. Standke, E. Zschech, “Crack evolution in Cu/low-k stacks and crack stop evaluation using in-situ micro-DCB in a nano-XCT tool“, FCMN conference, March 2017, Monterey/CA (2017)

Ever since the storming rise of graphene, the expanding list of two dimensional material family as predicted by theorists has been experimentally verified almost in every few months in the last years. Most fundamental properties of 2D atomic thin crystals, such as morphology/geometric profiles, electronic/magnetic transports and optoelectronic responses can be investigated by various optically excited and surface force sensitive techniques like Raman/IR spectroscopy and AFM/STM probes. However, determining atomic structures of versatile 2D crystal surfaces and interfaces in the burgeoning 2D heterostructure materials remains very challenging. So far, high-resolution cross-section TEM is still the most popular and viable method to map out surface/interface atomic structures of 2D crystal and other derivative materials although the delicate interface bonding can be undesirably vulnerable to electron-beam effects. Synchrotron-based surface X-ray diffraction, in particular crystal truncation rod (CTR) technique, can render a complete and precise atomic structure of single crystals and high quality epitaxial thin films/heterostructures in non-destructive manner. Nevertheless, the miniature lateral dimension (e.g. less than a few to tens of microns) of most 2D flakes and heterostructures makes conventional surface X-ray diffraction almost impractical to map out the complete Bragg rod so as to extract the complete atomic structures. Moreover, structural and electronic phases of some unique 2D crystals are strikingly controllable by strain applied by the underlying substrate or support when it has a large surface curvature, which for certain throws another big technical barrier for any surface-sensitive X-ray techniques.

High-brilliance, high flux synchrotron source and state-of-art focusing optics capable of routinely realizing nanobeam below 100 nm makes X-ray nanodiffraction, even surface X-ray nanodiffraction become practical and user-accessible. In this talk, I will discuss the feasibility of surface X-ray nanodiffraction measurements, and then demonstrate two most recent intriguing practices on investigating 2D atomic thin crystal and Lego-style 2D heterstructures. In one case, surface nanodiffraction helps to map out the complete specular CTR of a high quality graphene-hexagon BN heterostructure. The resolved interfacial atomic structures suggest a subtle variation of interfacial van-der-waals bonding between exfoliated and CVD grown 2D thin crystals. In another example, surface nanodiffraction allowed for precise determining in-plane lattice expansion of miniature MoS₂ 2D flakes vapor grown on highly curved glass spheres, which provides an excitingly new approach to effectively manipulate electronic band valley structures. In summary, surface X-ray nanodiffraction brings about significant opportunities for us to explore new two-dimensional materials, unravel emergent phenomena, and develop novel functionalities.

X-ray diffraction and X-ray imaging have for one century mostly been regarded as two distinct applications of the same type of radiation. Traditionally X-ray diffraction is considered as a method with poor spatial resolution yielding only spatial averages as useful results. Very recent developments in the use of highly focused beams produced on the most advanced synchrotron sources show however a great and rapidly developing potential of diffraction imaging techniques. These are much improving the resolution of traditional X-ray imaging and topography but are as well combined with X-ray diffraction. In this way a new portfolio of techniques emerges, coupling the information of strain and texture with spatial information. As so far most of these new imaging techniques are brilliance limited they are naturally developed at synchrotrons. With the rapid development of the availability of synchrotron and in interaction with the very active user community in this field, new imaging techniques rapidly gain practically all fields of materials science, chemistry and device physics. While X-ray optics typically limit today’s practical resolution to about 50 nm, technological progress in this field, as well as the use of reconstruction techniques pave already the way towards nanometric resolution in space while preserving the structural information available through diffraction. With new source projects at the horizon these exciting imaging techniques will be established on a growing number of beamlines.
With the completion of the first phase of the upgrade of the European Synchrotron Radiation Facility (ESRF), several spectro-nanoprobes and diffraction imaging beamlines have returned successfully to user operation.
In the future, the field of diffraction imaging will supply unique information on the atomic structure of samples while preserving the operando capacity of X-rays with their penetration power and tolerance of sample environments.
The Talk will present the state of the art of scanning and full field diffraction imaging tools with examples of recent application in the imaging of semiconductor devices and applied materials.

Coherent x-ray diffraction imaging techniques are nowadays reaching sufficient maturity to be applied to increasing complex scientific cases. A key point has been the progressive improvement of the reconstruction algorithms and the experimental setup stability and capabilities in the last years. Up to quite recently, these techniques were confined to be exploited by the expert users in the coherence community, but this is rapidly evolving and the field is welcoming new communities interested in applying these techniques to address a variety of open questions, particularly in the field of Materials Science. Furthermore, the advent of Diffraction Limited Storage Rings will bring new possibilities to perform coherent diffraction imaging on materials during in-situ and in operando conditions, particularly in the two areas where it excels: strain and structural disorder mapping of materials, and imaging of domains (for instance, during phase transitions).
Here, we present recent examples of strain imaging by Bragg coherent diffraction imaging (Bragg CDI) at beamline CRISTAL, at Synchrotron SOLEIL: strain mapping in semiconductor heterogeneous nanostructures; and study of the relationship between strain and catalytic sites in nanocatalyst particles performed in operando and in situ conditions.

Temperature is a key thermodynamic parameter that drives many phase transformations in functional films. Phase transitions in phase change materials (PCM) are deeply studied to develop Phase Change Random Access Memory (PCRAM)¹. The use of PCMs for non-volatile data storage relies on their physical properties exhibiting a reversible temperature induced transition between amorphous and crystalline phases with distinctly different electrical and optical properties. Typically the amorphous (resp. crystalline) phase possesses low (resp. high) optical reflectivity, low (resp. high) mass density and very high (resp. low) electrical resistivity. Such phase transitions are usually studied by in-situ techniques as X-ray diffraction and reflectivity (XRD, XRR), wafer curvature for stress study and sheet resistance (Rs). These techniques are often used separately, thus the correlation between all the physical properties is often ambiguous. GeTe is a prototypical PCM particularly interesting due to its large resistivity window, high crystallization speed and better stability in amorphous state¹. Its large density change upon crystallization raises, however, important issues because of the large mechanical stresses occurring during memory cycling. Furthermore its crystallization process is not still fully understood.
We developed 2 combined experiments (at DiffAbs beamline-Synchrotron SOLEIL-France) to characterize in-situ and simultaneously electrical, mechanical and structural changes occurring during phase transitions of thin or nanostructured PCM films: i) combined wafer curvature, XRR and XRD performed simultaneously^2,3 to follow the concomitant stress buildup during the phase transition as well as the structural properties (structure, lattice parameter, grain size, thickness, density), the strain and phase segregation occurring in crystalline phases; ii) combined in-situ Rs measurements and X-ray scattering techniques (XRD and XRR)⁴ allowing to simultaneously follow both structural and electrical parameters. Both experiments were applied to study the crystallization process of GeTe alloy as a function of 1D confinement, by performing experiments during heating of thin layers down to 5 nm. This contribution will focus on the interest of such coupling for the fundamental understanding of 3 key phenomena governing the reliability of PCRAMs: i) the increase of crystallization temperature with increasing confinement considering the role of both nucleation and oxidation; ii) phase segregation⁵ and iii) stress buildup upon crystallization and further heating⁶.
This study has been funded by ANR-SESAME ANR-15-CE24-002; the authors thank P.Noé -CEA-LETI-France for providing samples.
¹ V.L. Deringer et al. Adv. Funct. Mater. 25 (2015) 6343–6359
² C. Rivero et al. APL 87 (2005) 041904
³ T. Ouled-Khachroum et al. Thin Solid Films 617 (2016) 44–47
⁴ M. Putero et al. J. Appl. Cryst. 44 (2011) 858–864
⁵ M. Putero et al. APL 108 (2016) 101909
⁶ M.S. Amara et al. To be submitted

Gels are formed when particles in solution aggregate to form a mechanically rigid system spanning network upon varying the concentration and/ or the strength of attraction between the particles. Subtle changes in these parameters can alter the formation times and the mechanical properties of the resultant gel by orders of magnitude. This sensitivity creates both a scientific challenge central to the field of soft matter but also an opportunity for designing suspensions tailored for specific applications. Such control is crucial to technologies in a diverse range of areas including ceramics, food processing, pharmaceuticals, etc. We examine the fluid to solid transition for a model system composed of nanometer scale octadecyl silica particles in decahydronaphthalene (82 nm and 110 nm, volume fraction = 0.2) that undergoes thermoreversible gelation. Taking advantage of newly developed x-ray scattering capabilities and the ability to tune precisely the strength of the particle attractions, we track the evolution in the microscopic organization and mobility of the particles and correlate them with the time-dependent macroscopic mechanical behavior of the suspensions. We find that the suspensions proceed through identical intermediate states of microscopic and macroscopic behavior even as the gel formation times vary by orders of magnitude upon changing the temperature (or, equivalently, strength of attraction) 0 – 2 K below the gel point. We propose a model of gel formation in the regime of weak attraction in which network formation is a hierarchical process whose initiation depends on the creation and stability of small clusters in which the particles arrange in locally favorable configurations. Finally, we introduce a scaling parameter that captures the similarity in the evolution of the gel as it forms at different strengths of attraction.

The periodicity and symmetries of an atomic lattice define its electronic band structure and strongly influences the resulting physical properties, e.g. electron or phonon transport, light absorption or emission, anisotropic elasticity etc… Therefore the ability to precisely measure lattice strain and orientation is much needed by physicists and materials scientists. A large number of techniques have been developed to measure lattice strain and orientation, using different kinds of radiation (electrons, neutrons, visible and X-ray photons) and with different merits. In particular, the relatively recent development of new generation of X-ray sources such as synchrotrons or free electron lasers, and the inherent benefits of X-rays (capability to focus down to nanometers sizes, large probing depth, controllable polarization, large coherence length…) have spurred the development of innovative techniques as well as the improvement of existing ones much beyond their initial promises.
This talk will be dedicated to the X-ray techniques used on beamline BM32 (IF) at the European Synchrotron Radiation Facility in Grenoble, France and will be divided in two parts. The first part will deal with the recent developments of the micro-Laue diffraction instrument on the beamline. Laue diffraction was the first X-ray diffraction observed and understood, yet it is constantly improved and enhanced using additional features, such as energy resolution for full strain tensor resolution or depth resolution for 3D reconstruction.
The constant need for a finer comprehension of ever more complex physical mechanisms has also driven the development of operando studies, where materials are being studied in situ in functioning devices. This type of studies will be illustrated in the second part of the talk, in the field of energy materials using the example of the lithiation Si nanoparticles as electrodes for next-generation Li-ion batteries.

Nanoparticles of tungsten oxides have a range of important applications in e.g. gas-sensing, catalysis and in supercapacitors[1]. Tungsten oxides show rich structural chemistry due to rich redox chemistry and a range of stable crystal structures. The properties are highly dependent on the size and structure of the material, and in order to obtain a ‘tailor-made’ material, it is crucial to understand the mechanisms that dictate the formation of the material during synthesis. X-ray total scattering with Pair Distribution Function (PDF) analysis allows following the structural changes that take place all the way from precursor cluster over nucleation clusters to the final crystalline particles[2].
We here present a study of WO_x nanostructures formed in a solvothermal synthesis by thermal decomposition of ammonium metatungstate hydrate under different experimental conditions. Using Ex Situ and In Situ X-ray Total Scattering and Pair Distribution Function analysis, we study how different experimental conditions induces changes in the final size and crystal structure of the nanomaterials. We also observe how different reaction conditions influence the precursor and induce two distinct crystallisation pathways. We determine the changes in molecular geometries as the system moves from polyanion clusters to crystalline nanoparticles. Using small box modelling we determine the structure of the ionic clusters present at all stages of the reaction, revealing complex equilibria between different polyoxometalate structures. Furthermore we determine the atomic structuture of crystalline nanoparticles.

1. Zheng, H., et al., Nanostructured Tungsten Oxide – Properties, Synthesis, and Applications. Advanced Functional Materials, 2011. 21(12): p. 2175-2196.
2. Jensen, K.M.Ø., et al., In Situ Studies of Solvothermal Synthesis of Energy Materials, ChemSusChem, 2014. 7(6): p. 1594-1611.

Nano-sized particles of MoO₂ are studied for applications both as anode material for Li/Na batteries and in catalysis. The properties of the nanoparticles are intimately tied to the MoO₂ structure. Therefore, knowledge of the structure is vital to improve the material performance in any application. Bulk MoO₂ crystallizes in a distorted rutile structure. However, the structure of nano-sized MoO₂ is currently not well characterized. The bulk structural model does not describe the atomic arrangement in the MoO₂ nanoparticles, and the particle small size challenges conventional crystallographic techniques in determining the structure.¹ The aim of this study is to elucidate the structure of nano-sized MoO₂.

Several structural trends exist within the molybdenum oxide and rutile systems. The building blocks for molybdenum oxide structures are [MoO₆]-octahedra, and the octahedra share corners and edges in various ways to form different crystal structures. Early studies of molybdenum oxides found a large homologous ‘Magneli’ series of molybdenum oxide phases² (Mo_nO_3n-m) where the structures vary by the introduction of ordered crystallographic shear planes. A similar homologous series is also seen in rutile titanium oxide.

Here, we use X-ray total scattering with Pair Distribution Function (PDF) to investigate the structure of molybdenum oxide particles in sizes ranging from c. 2 nm to 100 nm synthesized via a simple one-step solvothermal synthesis. Taking advantage of the knowledge of the Magneli series, PDF analysis allows us to develop a new structural model for even the smallest nanoparticles of MoO₂. We are able to show that the structural transformation of the nano-sized MoO₂ is caused by a high concentration of crystallographic shear planes, which greatly alters the atomic arrangement on global and local scale compared to bulk MoO₂. The 100 nm MoO₂-particles also exhibit shear planes, but to a smaller degree resulting in unchanged long-range atomic correlations. In addition to determining the structure of nano-sized MoO₂ this project showcases the strength of having both local and global structural information available by using total scattering techniques.


S. J. L. Billinge, I. Levin, Science, 2007, 316, 561-565
A. Magnéli, Acta Cryst, 1953, 6, 495

Coherent diffractive imaging (CDI) is a growing technique in photon science. CDI has been demonstrated to be a powerful tool for visualizing cells and organelles using synchrotron radiation. X-ray free-electron lasers (XFELs) with femtosecond pulse durations further extends the ability of CDI to achieve spatial resolution beyond the conventional radiation-damage limitation. We performed live cell nano-imaging using a Japanese XFEL facility, SACLA. We employed pulsed coherent X-ray solution scattering (PCXSS), a form of X-ray CDI, developed by our group [1,2]. A unique feature of PCXSS is to keep solution sample under a controlled environment in micro-liquid enclosure array (MLEA) chips. We succeeded in reconstructing a live cell image from a coherent diffraction pattern recorded with a single XFEL shot. The reconstructed image quantitatively revealed the internal structures, e.g. high image intensity structure indicative of dense DNA [2]. PCXSS can also be effectively applied to nano-imaging of materials functional in solution. For example, we successfully imaged gold nanoparticle self-assemblies, developed as drug delivery carriers, in solution [3,4]. We also initiated industrial application of PCXSS in collaboration with Toyota Motor Corp [5]. Furthermore, as recent developments in PCXSS, we report on time-resolved pump-probe measurement, temperature-controlled measurement, utilization of ~100-nm focused XFEL, etc.

[1] J. Pérez and Y. Nishino, “Advances in X-ray scattering: from solution SAXS to achievements with coherent beams”, Curr. Opin. Struct. Biol. 22, 670 (2012).
[2] T. Kimura et al., “Imaging live cell in micro-liquid enclosure by X-ray laser diffraction”, Nature Commum. 5, 3052 (2014).
[3] R. Iida et al., “Synthesis of Janus-Like Gold Nanoparticles with Hydrophilic/Hydrophobic Faces by Surface Ligand Exchange and Their Self-Assemblies in Water”, Langmuir 31, 4054 (2015).
[4] J. Wei et al., “Yolk/Shell Assembly of Gold Nanoparticles by Size Segregation in Solution”, J. Am. Chem. Soc. 138, 3274 (2016).
[5] R. Yoshida et al., “Extending the potential of x-ray free-electron lasers to industrial applications – an initiatory attempt at coherent diffractive imaging on car-related nanomaterials”, J. Phys. B 48, 244008 (2015).