2 research outputs found
Enhanced Electrical Conduction in Anatase TaON via Soft Chemical Lithium Insertion toward Electronics Application
Metal oxynitride
semiconductors with the d<sup>0</sup> or d<sup>10</sup> electron configuration
are promising materials for nontoxic
pigments and photocatalysts, but their electrical properties have
scarcely been studied. Anatase TaON (δ-TaON) is a metastable
polymorph of TaON, and its epitaxial thin films show good semiconducting
properties such as a wide tunability of electrical conductivity and
a rather high electron mobility comparable to that of anatase TiO<sub>2</sub>. However, the density of carrier electrons (<i>n</i><sub>e</sub>) provided by anion vacancies is limited to ∼1
× 10<sup>20</sup> cm<sup>–3</sup>, so establishing a method
for carrier doping of anatase TaON remains a critical issue for its
use in electronics applications. In this report, we used soft chemical
insertion of Li into interstitial sites of anatase TaON epitaxial
thin films by using an <i>n</i>-butyllithium solution, and
the resulting material showed a higher <i>n</i><sub>e</sub> (3.5 × 10<sup>20</sup> cm<sup>–3</sup>) than anion-deficient
anatase TaON films. Additionally, the Li-inserted anatase TaON showed
an enhanced Hall mobility (μ<sub>H</sub>) of over 30 cm<sup>2</sup>V<sup>–1</sup>s<sup>–1</sup> and a lower resistivity
of 6.7 × 10<sup>–4</sup> Ωcm at room temperature.
In contrast, direct vapor phase deposition of Li-doped TaON caused
Li substitution for Ta, where a large difference in charges between
Li<sup>+</sup> and Ta<sup>5+</sup> was compensated by an increase
in the O/N ratio. These results indicate that soft chemical insertion
of Li after growth of the host crystal is an effective method for
carrier doping of anatase TaON
Reversible Changes in Resistance of Perovskite Nickelate NdNiO<sub>3</sub> Thin Films Induced by Fluorine Substitution
Perovskite
nickel oxides are of fundamental as well as technological interest
because they show large resistance modulation associated with phase
transition as a function of the temperature and chemical composition.
Here, the effects of fluorine doping in perovskite nickelate NdNiO<sub>3</sub> epitaxial thin films are investigated through a low-temperature
reaction with polyvinylidene fluoride as the fluorine source. The
fluorine content in the fluorinated NdNiO<sub>3–<i>x</i></sub>F<sub><i>x</i></sub> films is controlled with precision
by varying the reaction time. The fully fluorinated film (<i>x</i> ≈ 1) is highly insulating and has a bandgap of
2.1 eV, in contrast to NdNiO<sub>3</sub>, which exhibits metallic
transport properties. Hard X-ray photoelectron and soft X-ray absorption
spectroscopies reveal the suppression of the density of states at
the Fermi level as well as the reduction of nickel ions (valence state
changes from +3 to +2) after fluorination, suggesting that the strong
Coulombic repulsion in the Ni 3d orbitals associated with the fluorine
substitution drives the metal-to-insulator transition. In addition,
the resistivity of the fluorinated films recovers to the original
value for NdNiO<sub>3</sub> after annealing in an oxygen atmosphere.
By application of the reversible fluorination process to transition-metal
oxides, the search for resistance-switching materials could be accelerated