We report the fabrication of atomically abrupt interfaces of titanium dihydride (δ-TiH2) films and α-Al2O3(001) substrates. With the assistance from reactive hydrogen in plasma, single-phase δ-TiH2 epitaxial thin films were grown on α-Al2O3(001) substrates using the reactive magnetron sputtering technique. Scanning transmission electron microscopy measurements revealed an atomically abrupt interface at the δ-TiH2(111) film and Al2O3(001) substrate. These results indicate that the reactive magnetron sputtering has great potential to deposit various epitaxial thin films of hydrides restricted by the hydrogenation limit. The fabrication of high-quality hydride epitaxial thin films with atomically controlled interfaces paves the way for future hydride electronics.
Materials that are thermodynamically stable at ultrahigh pressures (>10 GPa) often exhibit unique physical properties. However, few studies have addressed the fabrication of epitaxial thin films of ultrahigh-pressure phases. Herein, we combine epitaxial thin film growth techniques with ultrahigh-pressure synthetic methods. We demonstrate the synthesis of single-phase epitaxial thin films of an ultrahigh-pressure polymorph of TiO2, α-PbO2-type TiO2. A rutile TiO2(100) epitaxial thin film is used as a precursor, and a structural phase transition is induced at 8 GPa and 800–1000 °C. This study demonstrates a new synthetic route to obtain ultrahigh-pressure-phase materials. The fabrication of epitaxial thin film ultrahigh-pressure phases paves the way for investigating the physical properties that arise at surfaces and interfaces of materials.
This paper reports the epitaxial growth of EuH 2 thin films with an ω-scan full width at half-maximum of 0.07°, the smallest value for metal hydride thin films reported so far. The thin films were deposited on yttria-stabilized ZrO 2 (111) substrates using reactive magnetron sputtering. The magnetization measurement showed that the saturation magnetization is ∼7 μ B /Eu atom, indicating that the EuH x films are nearly stoichiometric (x ≈ 2.0) and that the Curie temperature is ∼20 K. The optical measurements showed a bandgap of ∼1.81 eV. These values are similar to those previously reported for bulk EuH 2 . This study paves the way for the application of metal hydrides in the field of electronics through the fabrication of high-quality metal hydride epitaxial thin films.
We investigate the electron transport properties and structures of β-NbHx(010) epitaxial thin films on Al2O3(001) substrates with a variety of hydrogen contents. NbHx epitaxial thin films with x ≥ 0.77 exhibit a hysteresis loop in their resistance near room temperature. Notably, this hysteresis loop appears above the β–λ phase transition temperature. Detailed analysis of the temperature dependence of these structures suggests that the short-range ordering of hydrogen rearrangement in the λ-phase remains locally above the transition temperature, inducing the hysteresis in the resistance.
To observe a polymer chain deposited on a substrate by atomic force microscopy (AFM) at the molecular level, the substrate should be atomically flat and stable under laboratory conditions and adsorb polymer chains firmly. Therefore, substrates used under laboratory conditions are practically limited to mica, highly ordered pyrolytic graphite, and atomically stepped sapphire, and polymers observed by AFM at the molecular level are also limited. A silicon wafer is frequently used as a substrate for AFM observation for somewhat macroscopic observations, but the surface of the silicon wafer is too rough to observe polymer chains deposited on it at the molecular level. In this study, we prepared an atomically stepped Si(111) substrate via wet etching in NH 4 F and evaluated it as an AFM substrate. The Si(111) substrate was stable as an AFM substrate, and isolated poly(methyl methacrylate) (it-PMMA) chains and a crystalline monolayer deposited on the substrate were observed by AFM at the molecular level. An it-PMMA amorphous monolayer deposited on mica crystallized under high humidity, but that on the Si(111) substrate did not because of the difference in the surface nature and the crystal structure of the substrates. The Si(111) substrate was hydrophobic, and the it-PMMA monolayers could be deposited as a multilayer, which could not be formed on hydrophilic mica. The crystallization behavior of an it-PMMA amorphous multilayer and an amorphous/ crystalline mixed multilayer on the Si(111) substrate was also evaluated.
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