Formation of highly oriented nanopores via crystallization of amorphous Nb2O5 and Ta2O5

Nakamura, Ryusuke; Ishimaru, Manabu; Sato, Kazuhisa; Tanaka, Kouhei; Nakajima, Hideo; Konno, Toyohiko J.

doi:10.1063/1.4822300

Cited by 7 publications

(6 citation statements)

References 19 publications

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“…We confirmed that the locations of the peaks and shoulders remain unchanged regardless of Q max , suggesting that the peaks and shoulders discussed here are not ghost but real ones. These peaks are in good agreement with the bond lengths of Ta-O, O-O, Ta-Ta (1), and Ta-Ta (2), respectively (the number in the parenthesis indicates the shorter and longer distance), in a-Ta 2 O 5 [21,25]. Therefore, the atomic distribution in a-Ta 2 O 6.6 S 0.7 prepared via anodization is essentially similar to that in a- Ta differs clearly from that of the as-anodized one.…”

Section: (A) For Comparison G(r) Of In Amorphous Ta 2 O 5 (A-ta 2 Osupporting

confidence: 72%

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Stability of amorphous Ta–O nanotubes prepared by anodization: Thermal and structural analyses

et al. 2014

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Amorphous Ta-O nanotubes (NTs) prepared by anodization in a sulfuric-acid-based solution have been found to contain considerable amounts of extra oxygen and sulfur. Their structural and thermal stability has been studied by combining X-ray diffractometry, transmission electron microscopy, and thermal analysis. The amorphous Ta-O, whose composition was estimated to be Ta 2 O 6.6 S 0.7 , crystallizes into orthorhombic β-Ta 2 O 5 at temperatures around 1073 K by an endothermic reaction, at which excess oxygen and impurity sulfur are released. The amorphous NTs were found to be thermally more stable than stoichiometric amorphous Ta 2 O 5 , whose crystallization temperature is around 973 K.Excess oxygen and impurity sulfur, which form chemical bonds with Ta atoms in the amorphous solid, must be the origin of the stability. The crystallization follows the out-diffusion of oxygen and sulfur from the solid at temperatures where the mobility of atoms is high enough, indicating that the crystallization is kinetically arrested.

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Section: (A) For Comparison G(r) Of In Amorphous Ta 2 O 5 (A-ta 2 Osupporting

confidence: 72%

“…The experimental details for sputtered samples are in Ref. [16,21]. g(r) of annealed a-Ta 2 O 5 is an original data for this publication.…”

Section: Discussionmentioning

confidence: 99%

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Stability of amorphous Ta–O nanotubes prepared by anodization: Thermal and structural analyses

et al. 2014

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“…Structural analysis Figure 1 shows cross-sectional TEM images and the corresponding SAED for 100 nm-thick specimens of amorphous 30 The structures of the specimens were confirmed to remain amorphous after annealing at the conditions. Therefore, the upper limit temperature for diffusionannealing experiments was considered to be these temperatures.…”

Section: Resultsmentioning

confidence: 99%

Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5

Nakamura

Toda

Tsukui

et al. 2014

Journal of Applied Physics

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was investigated along with structural analysis in terms of pair distribution function (PDF). The low activation energy, $1.2 eV, for diffusion in the oxides suggests a single atomic jump of oxygen ions mediated via vacancy-like defects. However, the pre-exponential factor for a-Ta 2 O 5 and a-Nb 2 O 5 with lower bond energy was two orders of magnitude larger than that for a-Al 2 O 3 with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta 2 O 5 and a-Nb 2 O 5 was more broadly distributed than that in a-Al 2 O 3 . Due to the larger variety of atomic configurations of a-Ta 2 O 5 and a-Nb 2 O 5 , these oxides have a higher activation entropy for diffusion than a-Al 2 O 3 . The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides. V C 2014 AIP Publishing LLC. [http://dx

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“…Based on the density functional theory, it has been reported that vacancies are preferentially trapped with Sn atoms in Ge. [20][21][22][23] In general, amorphous materials contain free volumes, [24][25][26] which presumably causes the Sn-vacancy pairs. As a consequence, substitutional Sn atoms, with a concentration that is much higher than the solubility limit, are stabilized in the crystalline Ge matrix.…”

Section: B Compositional Changes During Thermal Annealingmentioning

confidence: 99%

Behavior of Sn atoms in GeSn thin films during thermal annealing: Ex-situ and in-situ observations

Takase

Ishimaru

Uchida

et al. 2016

Journal of Applied Physics

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Thermally induced crystallization processes for amorphous GeSn thin films with Sn concentrations beyond the solubility limit of the bulk crystal Ge-Sn binary system have been examined by X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, and (scanning) transmission electron microscopy. We paid special attention to the behavior of Sn before and after recrystallization. In the as-deposited specimens, Sn atoms were homogeneously distributed in an amorphous matrix. Prior to crystallization, an amorphous-to-amorphous phase transformation associated with the rearrangement of Sn atoms was observed during heat treatment; this transformation is reversible with respect to temperature. Remarkable recrystallization occurred at temperatures above 400 °C, and Sn atoms were ejected from the crystallized GeSn matrix. The segregation of Sn became more pronounced with increasing annealing temperature, and the ejected Sn existed as a liquid phase. It was found that the molten Sn remains as a supercooled liquid below the eutectic temperature of the Ge-Sn binary system during the cooling process, and finally, β-Sn precipitates were formed at ambient temperature.

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Formation of highly oriented nanopores via crystallization of amorphous Nb2O5 and Ta2O5

Cited by 7 publications

References 19 publications

Stability of amorphous Ta–O nanotubes prepared by anodization: Thermal and structural analyses

Stability of amorphous Ta–O nanotubes prepared by anodization: Thermal and structural analyses

Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5

Behavior of Sn atoms in GeSn thin films during thermal annealing: Ex-situ and in-situ observations

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