High-Resolution Identification of Chemical States in Individual Metal Clusters in an Insulating Amorphous Polymer

Nondestructive initial-profile-free 3D elemental mapping in multilayer thin film structures based on EDX and a quadratic programming problem

We have demonstrated a new data analysis method that enables nondestructive depth profiling of a multilayer thin-film sample from energy-dispersive X-ray spectroscopy (EDX) data without the assumption of initial profiles. This method is based on a quadratic programming problem and allows for three-dimensional elemental mapping in the sample without destroying it, by performing depth profiling for all the pixels in the EDX two-dimensional mapping data. In this paper, first nondestructive depth profiling of two samples with different multilayer structures was performed using the proposed method. The results were compared with those obtained by cross-sectional observation to validate the accuracy and usefulness of the proposed method. Next, an example of the three-dimensional elemental mapping based on the proposed method was demonstrated. This method allows us to nondestructively obtain three-dimensional elemental distribution within a sample over a wide area on the order of mm, which is impossible to obtain using other analytical methods. The way to determine the hyperparameters, which significantly affects the calculation results, is fully described in this paper.

Fabrication of a Bilayer Structure of Cu and Polyimide To Realize Circuit Microminiaturization and High Interfacial Adhesion in Flexible Electronic Devices

With commercialization of the fifth-generation mobile communication system and the further spread of the Internet of Things, industrial innovation is arriving with new business fields related to concepts such as high-speed communication, self-driving vehicles, and remote medicine. One of the challenges is the realization of flexible devices with high-definition circuits, which requires new fabrication techniques for Cu films on polymer substrates to meet demands and an understanding of Cu/polymer interfacial nanostructure to assure product quality. We have developed a promising technique for the fabrication of Cu film on polyimide (PI), which consists mainly of very simple semiconductor device processes. This technique allows for control of the Cu thickness with nanometer precision to form miniaturized Cu circuits with potential advantages in terms of interfacial adhesion and material/production costs. The Cu/PI interfaces fabricated by conventional vapor deposition and the new technique are systematically analyzed using synchrotron hard X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and time-of-flight secondary ion mass spectroscopy. With conventional vapor deposition, it was discovered that evaporated Cu atoms decompose the PI and an oxidation layer with a thickness of several nanometers that deteriorates the interfacial adhesion could be visualized at the Cu/PI interface. With the new technique, the decomposition of PI and interfacial oxidation are significantly suppressed. Furthermore, the proposed technique can be broadly applied to the investigation of metal/polymer interfaces fabricated by polymer coating on a metal substrate, which has so far been impossible.

Quantitative Cryo-Scanning Transmission Electron Microscopy of Biological Materials

Electron tomography provides a detailed view into the 3D structure of biological cells and tissues. Physical fixation by vitrification of the aqueous medium provides the most faithful preservation of biological specimens in the native, fully hydrated state. Cryo-microscopy is challenging, however, because of the sensitivity to electron irradiation and due to the weak electron scattering of organic material. Tomography is even more challenging because of the dependence on multiple exposures of the same area. Tomographic imaging is typically performed in wide-field transmission electron microscopy (TEM) mode with phase contrast generated by defocus. Scanning transmission electron microscopy (STEM) is an alternative mode based on detection of scattering from a focused probe beam, without imaging optics following the specimen. While careful configuration of the illumination and detectors is required to generate useful contrast, STEM circumvents the major restrictions of phase contrast TEM to very thin specimens and provides a signal that is more simply interpreted in terms of local composition and density. STEM has gained popularity in recent years for materials science. The extension of STEM to cryomicroscopy and tomography of cells and macromolecules is summarized herein.

Nanoscale Phase-Separated Structure in Core-Shell Nanoparticles of SiO2-Si1-xGexO2 Glass Revealed by Electron Microscopy

SiO₂-based optical fibers are indispensable components of modern information communication technologies. It has recently become increasingly important to establish a technique for visualizing the nanoscale phase-separated structure inside SiO₂-GeO₂ glass nanoparticles during the manufacturing of SiO₂-GeO₂ fibers. This is because the rapidly increasing price of Ge has made it necessary to improve the Ge yield by clarifying the detailed mechanism of Ge diffusion into SiO₂. However, direct observation of the internal nanostructure of glass particles has been extremely difficult, mainly due to electrostatic charging and the damage induced by electron and X-ray irradiation. In the present study, we used state-of-the-art scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDX) to examine cross-sectional samples of SiO₂-GeO₂ particles embedded in an epoxy resin, which were fabricated using a broad Ar ion beam and a focused Ga ion beam. These advanced techniques enabled us to observe the internal phase-separated structure of the nanoparticles. We have for the first time clearly determined the SiO₂-Si_1-xGe_xO₂ core-shell structure of such particles, the element distribution, the degree of crystallinity, and the quantitative chemical composition of microscopic regions, and we discuss the formation mechanism for the observed structure. The proposed imaging protocol is highly promising for studying the internal structure of various core-shell nanoparticles, which affects their catalytic, optical, and electronic properties.