Abstract
Heterogeneous interfaces exhibit the unique phenomena by the redistribution of charged species to equilibrate the chemical potentials. Despite recent studies on the electronic charge ...accumulation across chemically inert interfaces, the systematic research to investigate massive reconfiguration of charged ions has been limited in heterostructures with chemically reacting interfaces so far. Here, we demonstrate that a chemical potential mismatch controls oxygen ionic transport across TiO
2
/VO
2
interfaces, and that this directional transport unprecedentedly stabilizes high-quality rutile TiO
2
epitaxial films at the lowest temperature (≤ 150 °C) ever reported, at which rutile phase is difficult to be crystallized. Comprehensive characterizations reveal that this unconventional low-temperature epitaxy of rutile TiO
2
phase is achieved by lowering the activation barrier by increasing the “effective” oxygen pressure through a facile ionic pathway from VO
2-δ
sacrificial templates. This discovery shows a robust control of defect-induced properties at oxide interfaces by the mismatch of thermodynamic driving force, and also suggests a strategy to overcome a kinetic barrier to phase stabilization at exceptionally low temperature.
Abstract
Unrestricted integration of single-crystal oxide films on arbitrary substrates has been of great interest to exploit emerging phenomena from transition metal oxides for practical ...applications. Here, we demonstrate the release and transfer of a freestanding single-crystalline rutile oxide nanomembranes to serve as an epitaxial template for heterogeneous integration of correlated oxides on dissimilar substrates. By selective oxidation and dissolution of sacrificial VO
2
buffer layers from TiO
2
/VO
2
/TiO
2
by H
2
O
2
, millimeter-size TiO
2
single-crystalline layers are integrated on silicon without any deterioration. After subsequent VO
2
epitaxial growth on the transferred TiO
2
nanomembranes, we create artificial single-crystalline oxide/Si heterostructures with excellent sharpness of metal-insulator transition (
$$\triangle \rho /\rho$$
△
ρ
/
ρ
> 10
3
) even in ultrathin (<10 nm) VO
2
films that are not achievable via direct growth on Si. This discovery offers a synthetic strategy to release the new single-crystalline oxide nanomembranes and an integration scheme to exploit emergent functionality from epitaxial oxide heterostructures in mature silicon devices.
The use of gate bias to control electronic phases in VO2, an archetypical correlated oxide, offers a powerful method to probe their underlying physics, as well as for the potential to develop novel ...electronic devices. Up to date, purely electrostatic gating in 3‐terminal devices with correlated channel shows the limited electrostatic gating efficiency due to insufficiently induced carrier density and short electrostatic screening length. Here massive and reversible conductance modulation is shown in a VO2 channel by applying gate bias VG at low voltage by a solid‐state proton (H+) conductor. By using porous silica to modulate H+ concentration in VO2, gate‐induced reversible insulator‐to‐metal (I‐to‐M) phase transition at low voltage, and unprecedented two‐step insulator‐to‐metal‐to‐insulator (I‐to‐M‐to‐I) phase transition at high voltage are shown. VG strongly and efficiently injects H+ into the VO2 channel without creating oxygen deficiencies; this H+‐induced electronic phase transition occurs by giant modulation (≈7%) of out‐of‐plane lattice parameters as a result of H+‐induced chemical expansion. The results clarify the role of H+ on the electronic state of the correlated phases, and demonstrate the potentials for electronic devices that use ionic/electronic coupling.
Gate‐induced massive and reversible phase transition is demonstrated in VO2 channels using solid‐state proton electrolytes. Applying gate bias effectively injects large numbers of H+ ions without creating oxygen deficiencies and causes a two‐step insulator‐to‐metal‐to‐insulator phase transition and a hydrogen‐defect‐induced chemical expansion at room temperature. This observation presents an opportunity to develop new types of three‐terminal electronic devices.
The scattering of charge carriers by line defects, i.e., threading dislocations (TDs), severely limits electron mobility in epitaxial semiconductor films grown on dissimilar substrates. The density ...of TDs needs to be decreased to further enhance electron mobility in lattice-mismatched epitaxial films and heterostructures for application in high-performance electronic devices. Here, we report a strategy for the post-treatment of epitaxial La-doped BaSnO3 (LBSO) films by delicately controlling the oxygen partial pressure p(O2), which achieved a significant increase in the room temperature (RT) electron mobility (μe) to μe = 122 cm2 V−1 s−1 at a carrier concentration of 1.1 × 1020 cm−3. This mobility enhancement is mostly attributed to an oxygen vacancy-assisted recovery process that reduces the density of TDs by accelerating the movement of dislocations in ionic crystals under a p(O2)-controlled treatment despite an increase in the density of charged point defects. Our finding suggests that accurate control of the interactions between point defects and line defects can reduce dominant carrier scattering by charged dislocations in epitaxial oxide semiconductors that have dissimilar substrates. This method provides alternative approaches to achieving perovskite oxide heterostructures that have high RT μe values.
Abstract
We report direct evidence that oxygen vacancies affect the structural and electrical parameters in tensile-strained NdNiO
3−δ
epitaxial thin films by elaborately adjusting the amount of ...oxygen deficiency (δ) with changing growth temperature
T
D
. The modulation in tensile strain and
T
D
tended to increase oxygen deficiency (δ) in NdNiO
3−δ
thin films; this process relieves tensile strain of the thin film by oxygen vacancy incorporation. The oxygen deficiency is directly correlated with unit-cell volume and the metal-insulator transition temperature (
T
MI
), i.e., resulting in the increase of both unit-cell volume and metal-insulator transition temperature as oxygen vacancies are incorporated. Our study suggests that the intrinsic defect sensitively influences both structural and electronic properties, and provides useful knobs for tailoring correlation-induced properties in complex oxides.
High‐performance UV photodetectors call for sensitive and energy‐efficient signal detection in extreme environments. To satisfy the requirement of a UV detection without an external power ...consumption, self‐powered UV photodetectors must be realized by an optimal combination of heterostructure with maximum built‐in potential using novel wide‐bandgap materials. Here, self‐powered UV photodiodes are designed via the band engineering of a wide‐bandgap Sr(Sn,Ni)O3/BaSnO3 heterojunction for the first time. Based on the theoretical concept of acceptor doping by Ni substitution in SrSnO3, remarkably, this heterojunction with a conduction band offset of 0.94 eV shows strong nonlinear electrical characteristics with extremely low Idark (≈100 fA) owing to the spatial gradient of the potential barrier across the interfaces, outstanding photo‐to‐dark current ratio (>107 at 25 °C and > 104 at 300 °C), and high stability under various extreme conditions upon UV illumination even without external bias (V = 0 V). This study suggests a novel strategy that utilizes band engineering to maximize sensitivity and minimize energy consumption in harsh environments for UV imaging using the newly discovered wide‐bandgap semiconductors.
High performance self‐powered np photodiodes have been demonstrated using perovskite stannate BaSnO3/Sr(Sn,Ni)O3 heterojunction. Outstanding photo‐to‐dark current ratio (> 107 at 25 °C) even at high temperature (> 104 at 300 °C) without an external power supply is achieved by exploiting excellent thermal/chemical stability of perovskite stannate and band engineering at the interface of np junction.
This article proposes a new interference-compensating magnetometer calibration scheme aided by a gyroscope sensor, which could reduce the effect of induced magnetic interference due to nearby onboard ...current flow. By using the innovation process and a linear matrix inequality approach, mean and variance of the induced magnetic interference are estimated to ensure that their physical meaningful values are taken to be closest to the empirically measured ones. The values are reflected in the update step of the extended Kalman filter in order to accurately estimate the calibration parameters and the corresponding direction. Results of experiments performed using a real unmanned aerial vehicle (UAV) demonstrate that the proposed calibration scheme compensates well for the disturbing magnetic interference arising from the UAV's onboard current and hence reduces the estimation error of its yaw angle, or its heading direction, by approximately two-thirds of that obtained using the existing scheme.
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