Laboratory High-Contrast X-ray Microscopy of Copper Nanostructures Enabled by a Liquid-Metal-Jet X-ray Source.

High-resolution imaging of Cu/low-k on-chip interconnect stacks in advanced microelectronic products is demonstrated using full-field transmission X-ray microscopy (TXM). The comparison of two lens-based laboratory X-ray microscopes that are operated at two different photon energies, 8.0 keV and 9.2 keV, shows a contrast enhancement for imaging of copper nanostructures embedded in insulating organosilicate glass of a factor of 5 if 9.2 keV photons are used. Photons with this energy (Ga-Kα radiation) are generated from a Ga-containing target of a laboratory X-ray source applying the liquid-metal-jet technology. The 5 times higher contrast compared to the use of Cu-Kα radiation (8.0 keV photon energy) from a rotating anode X-ray source is caused by the fact that the energy of the Ga-Kα emission line is slightly higher than that of the Cu-K absorption edge (9.0 keV photon energy). The use of Ga-Kα radiation is of particular advantage for imaging of copper interconnects with dimensions from several 100 nm down to several 10 nm in a Cu/SiO2 or Cu/low-k backend-of-line stack. Physical failure analysis and reliability engineering in the semiconductor industry will benefit from high-contrast X-ray images of sub-µm copper structures in microchips.

Laboratory X-ray Microscopy of 3D Nanostructures in the Hard X-ray Regime Enabled by a Combination of Multilayer X-ray Optics.

High-resolution imaging of buried metal interconnect structures in advanced microelectronic products with full-field X-ray microscopy is demonstrated in the hard X-ray regime, i.e., at photon energies > 10 keV. The combination of two multilayer optics-a side-by-side Montel (or nested Kirkpatrick-Baez) condenser optic and a high aspect-ratio multilayer Laue lens-results in an asymmetric optical path in the transmission X-ray microscope. This optics arrangement allows the imaging of 3D nanostructures in opaque objects at a photon energy of 24.2 keV (In-Kα X-ray line). Using a Siemens star test pattern with a minimal feature size of 150 nm, it was proven that features < 150 nm can be resolved. In-Kα radiation is generated from a Ga-In alloy target using a laboratory X-ray source that employs the liquid-metal-jet technology. Since the penetration depth of X-rays into the samples is significantly larger compared to 8 keV photons used in state-of-the-art laboratory X-ray microscopes (Cu-Kα radiation), 3D-nanopattered materials and structures can be imaged nondestructively in mm to cm thick samples. This means that destructive de-processing, thinning or cross-sectioning of the samples are not needed for the visualization of interconnect structures in microelectronic products manufactured using advanced packaging technologies. The application of laboratory transmission X-ray microscopy in the hard X-ray regime is demonstrated for Cu/Cu6Sn5/Cu microbump interconnects fabricated using solid-liquid interdiffusion (SLID) bonding.

Mitochondrial Dysfunction in Dopaminergic Neurons Derived from Patients with LRRK2- and SNCA-Associated Genetic Forms of Parkinson's Disease.

Parkinson's disease (PD) is the second most common neurodegenerative disease. Some cases of PD may be caused by genetic factors, among which mutations in the LRRK2 and SNCA genes play an important role. To develop effective neuroprotective strategies for PD, it is important to diagnose the disease at the earliest stages of the neurodegenerative process. Therefore, the detection of diagnostic and prognostic markers of Parkinson's disease (PD) is an urgent medical need. Advances in induced pluripotent stem cell (iPSC) culture technology provide new opportunities for the search for new biomarkers of PD and its modeling in vitro. In our work, we used a new technology for multiplex profiling of gene expression using barcoding on the Nanostring platform to assess the activity of mitochondrial genes on iPSC-derived cultures of dopaminergic neurons obtained from patients with LRRK2- and SNCA-associated genetic forms PD and a healthy donor. Electron microscopy revealed ultrastructural changes in mitochondria in both LRRK2 and SNCA mutant cells, whereas mitochondria in cells from a healthy donor were normal. In a culture with the SNCA gene mutation, the ratio of the area occupied by mitochondria to the total area of the cytoplasm was significantly lower than in the control and in the line with the LRRK2 gene mutation. Transcriptome analysis of 105 mitochondria proteome genes using the Nanostring platform revealed differences between the diseased and normal cells in the activity of genes involved in respiratory complex function, the tricarboxylic acid cycle, ATP production, mitochondria-endoplasmic reticulum interaction, mitophagy, regulation of calcium concentration, and mitochondrial DNA replication.

3D Multi-Ion Corrosion Model in Hierarchically Structured Cementitious Materials Obtained from Nano-XCT Data.

Corrosion of steel reinforcements in concrete constructions is a worldwide problem. To assess the degradation of rebars in reinforced concrete, an accurate description of electric current, potential and concentrations of various species present in the concrete matrix is necessary. Although the concrete matrix is a heterogeneous porous material with intricate microstructure, mass transport has been treated in a homogeneous material so far, modifying bulk transport coefficients by additional factors (porosity, constrictivity, tortuosity), which led to so-called effective coefficients (e.g., diffusivity). This study presents an approach where the real 3D microstructure of concrete is obtained from high-resolution X-ray computed tomography (XCT), processed to generate a mesh for finite element method (FEM) computations, and finally combined with a multi-species system of transport and electric potential equations. This methodology allows for a more realistic description of ion movements and reactions in the bulk concrete and on the rebar surface and, consequently, a better evaluation of anodic and cathodic currents, ultimately responsible for the loss of reinforcement mass and its location. The results of this study are compared with a state-of-the-art model and numerical calculations for 2D and 3D geometries.

Spectromicroscopy of Nanoscale Materials in the Tender X-Ray Regime Enabled by a High Efficient Multilayer-Based Grating Monochromator.

The combination of near edge X-ray absorption spectroscopy with nanoscale X-ray imaging is a powerful analytical tool for many applications in energy technologies, catalysis, which are critical to combat climate change, as well as microelectronics and life science. Materials from these scientific areas often contain key elements, such as Si, P, S, Y, Zr, Nb, and Mo as well as lanthanides, whose X-ray absorption edges lie in the so-called tender photon energy range 1.5-5.0 keV. Neither conventional grazing incidence grating nor crystal monochromators have high transmission in this energy range, thereby yielding the tender photon energy gap. To close this gap, a monochromator setup based on a multilayer coated blazed plane grating and plane mirror is devised. The measurements show that this novel concept improves the photon flux in the tender X-ray regime by two-orders-of-magnitude enabling previously unattainable laboratory and synchrotron-based studies. This setup is applied to perform nanoscale spectromicroscopy studies. The high photon flux provides sufficient sensitivity to obtain the electronic structure of Mo in platinum-free MoNi4 nanoparticles for electrochemical energy conversion. Additionally, it is shown that the chemical bonding of nano-structures in integrated circuits can be distinguished by the electronic configuration at the Si-K edge.

Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth.

Invited for the cover of this issue are Maksym Opanasenko and co-workers at Charles University in Prague, IKTS and deepXscan GmbH in Dresden. The image depicts a controllable crystallization mechanism that can be switched from classical to reversed crystal growth by manipulating the interplay between silica particles and the structure-directing agent. Read the full text of the article at 10.1002/chem.202200590.

Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth.

Crystal growth mechanisms govern a wide range of properties of crystalline materials. Reversed crystal growth is one of the nonclassical mechanisms observed in many materials. However, the reversed crystallization starting from amorphous aggregates and the key factors driving this growth remain elusive. Here, we describe a characteristic model of reversed crystal growth representing the inner structure and crystallinity development of aggregates studied by microscopy and nano X-ray computed tomography. By adjusting the synthesis conditions, the fundamental function of the structure-directing agent, which determines the crystallization pathway, was revealed. As a result, the crystal growth mode can be "switched" from the classical route at a low ratio of SDA/framework elements to reversed growth at a high ratio. Our findings provide further insights into crystal growth control, which is crucial for improving synthesis protocols and designing various forms of crystalline materials.

Multi-scale microscopy study of 3D morphology and structure of MoNi4/MoO2@Ni electrocatalytic systems for fast water dissociation.

The 3D morphology of hierarchically structured electrocatalytic systems is determined based on multi-scale X-ray computed tomography (XCT), and the crystalline structure of electrocatalyst nanoparticles is characterized using transmission electron microscopy (TEM), supported by X-ray diffraction (XRD) and spatially resolved near-edge X-ray absorption fine structure (NEXAFS) studies. The high electrocatalytic efficiency for hydrogen evolution reaction (HER) of a novel transition-metal-based material system - MoNi4 electrocatalysts anchored on MoO2 cuboids aligned on Ni foam (MoNi4/MoO2@Ni) - is based on advantageous crystalline structures and chemical bonding. High-resolution TEM images and selected-area electron diffraction patterns are used to determine the crystalline structures of MoO2 and MoNi4. Multi-scale XCT provides 3D information of the hierarchical morphology of the MoNi4/MoO2@Ni material system nondestructively: Micro-XCT images clearly resolve the Ni foam and the attached needle-like MoO2 micro cuboids. Laboratory nano-XCT shows that the MoO2 micro cuboids with a rectangular cross-section of 0.5 × 1 µm2 and a length of 10-20 µm are vertically arranged on the Ni foam. MoNi4 nanoparticles with a size of 20-100 nm, positioned on single MoO2 cuboids, were imaged using synchrotron radiation nano-XCT. The application of a deep convolutional neural network (CNN) significantly improves the reconstruction quality of the acquired data.

Monitored Tomographic Reconstruction-An Advanced Tool to Study the 3D Morphology of Nanomaterials.

Detailed and accurate three-dimensional (3D) information about the morphology of hierarchically structured materials is derived from multi-scale X-ray computed tomography (XCT) and subsequent 3D data reconstruction. High-resolution X-ray microscopy and nano-XCT are suitable techniques to nondestructively study nanomaterials, including porous or skeleton materials. However, laboratory nano-XCT studies are very time-consuming. To reduce the time-to-data by more than an order of magnitude, we propose taking advantage of a monitored tomographic reconstruction. The benefit of this new protocol for 3D imaging is that the data acquisition for each projection is interspersed by image reconstruction. We demonstrate this new approach for nano-XCT data of a novel transition-metal-based materials system: MoNi4 electrocatalysts anchored on MoO2 cuboids aligned on Ni foam (MoNi4/MoO2@Ni). Quantitative data that describe the 3D morphology of this hierarchically structured system with an advanced electrocatalytically active nanomaterial are needed to tailor performance and durability of the electrocatalyst system. We present the framework for monitored tomographic reconstruction, construct three stopping rules for various reconstruction quality metrics and provide their experimental evaluation.

Anisotropy of Mechanical Properties of Pinctada margaritifera Mollusk Shell.

The mechanical properties such as compressive strength and nanohardness were investigated for Pinctada margaritifera mollusk shells. The compressive strength was evaluated through a uniaxial static compression test performed along the load directions parallel and perpendicular to the shell axis, respectively, while the hardness and Young modulus were measured using nanoindentation. In order to observe the crack propagation, for the first time for such material, the in-situ X-ray microscopy (nano-XCT) imaging (together with 3D reconstruction based on the acquired images) during the indentation tests was performed. The results were compared with these obtained during the micro-indentation test done with the help of conventional Vickers indenter and subsequent scanning electron microscopy observations. The results revealed that the cracks formed during the indentation start to propagate in the calcite prism until they reach a ductile organic matrix where most of them are stopped. The obtained results confirm a strong anisotropy of both crack propagation and the mechanical strength caused by the formation of the prismatic structure in the outer layer of P. margaritifera shell.

3D Diatom-Designed and Selective Laser Melting (SLM) Manufactured Metallic Structures.

Diatom frustules, with their diverse three-dimensional regular silica structures and nano- to micrometer dimensions, represent perfect model systems for biomimetic fabrication of materials and devices. The structure of a frustule of the diatom Didymosphenia geminata was nondestructively visualized using nano X-ray computed tomography (XCT) and transferred into a CAD file for the first time. Subsequently, this CAD file was used as the input for an engineered object, which was manufactured by applying an additive manufacturing technique (3D Selective Laser Melting, SLM) and using titanium powder. The self-similarity of the natural and the engineered objects was verified using nano and micro XCT. The biomimetic approach described in this paper is a proof-of-concept for future developments in the scaling-up of manufacturing based on special properties of microorganisms.