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ACS Appl Mater Interfaces ; 10(51): 44589-44602, 2018 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-30507162


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.

Anal Chem ; 89(17): 8772-8781, 2017 09 05.
Artigo em Inglês | MEDLINE | ID: mdl-28759194


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-Si1-xGexO2 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.

Anal Chem ; 88(10): 5225-33, 2016 05 17.
Artigo em Inglês | MEDLINE | ID: mdl-27104743


The effectivity of cryo-scanning transmission electron microscopy-electron energy loss spectroscopy was demonstrated for nanoscale analysis of the cross-section of the Cu/polyimide interface. The nanoscale Cu/Cu2O/CuO layer structure at the interface was clearly observed for the first time. In addition, a Cu atom was identified, embedded in the polyimide matrix, and the average valence of diffusing Cu atoms or nanoclusters was determined using (cryo-)scanning transmission electron microscopy-electron energy loss spectroscopy. On the basis of these results, we have proposed a mechanism for the diffusion of Cu atoms in polyimide. To the best of our knowledge, this is the first report of the observation of a metal atom embedded in an insulating amorphous polymer.

Microsc Microanal ; 21(6): 1398-1405, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26573381


To observe the fine distribution of minor aluminum and germanium dopants in the erbium-doped fiber (EDF) core of an optical amplifier, a sample thinning technique was applied for field emission electron probe microanalysis (FE-EPMA) together with wavelength-dispersive X-ray spectrometry. This technique significantly improved the spatial resolution without much degradation of the minimum detection limit for FE-EPMA. As such, this enabled us to observe the distribution of minor dopants in EDF. Moreover, we propose a very simple sample preparation to prevent electron-beam radiation damage, a problem involved with FE-EPMA of low-conductivity materials such as SiO2 glass, which is the main component of EDF.

Ultramicroscopy ; 157: 48-56, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26057834


The effect of sample thickness on the spatial resolution and minimum detection limit (MDL) has been investigated for field-emission electron probe microanalysis with wavelength dispersive X-ray spectroscopy (FE-EPMA-WDX). Indium gallium phosphide samples thinned to thicknesses of about 100, 130, 210, 310, and 430 nm provided effective thin-sample FE-EPMA-WDX in the resolution range of 40-350 nm and MDL range of 13,000-600 ppm (mass). A comparison of the FE-EPMA results for thin and bulk samples demonstrated that thin-sample FE-EPMA can achieve both higher sensitivity and better spatial resolution than is possible using bulk samples. Most of the X-rays that determine the MDL are generated in a surface region of the sample with a depth of approximately 300 nm. The spatial resolution and MDL can be tuned by the sample thickness. Furthermore, analysis of small amounts of Cl in SiO2 indicated that thin-sample FE-EPMA can realize a spatial resolution and MDL of 41 nm and 446 ppm at Iprob=50 nA, respectively, whereas bulk-sample FE-EPMA offers a resolution of only 348 nm and MDL of 426 ppm.

Ultramicroscopy ; 135: 64-70, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23876296


The minimum detection limit and spatial resolution for a thinned semiconductor sample were determined by electron probe microanalysis (EPMA) using a Schottky field emission (FE) electron gun and wavelength dispersive X-ray spectrometry. Comparison of the FE-EPMA results with those obtained using energy dispersive X-ray spectrometry in conjunction with scanning transmission electron microscopy, confirmed that FE-EPMA is largely superior in terms of detection sensitivity. Thin-sample FE-EPMA is demonstrated as a very effective method for high resolution, high sensitivity analysis in a laboratory environment because a high probe current and high signal-to-noise ratio can be achieved.