Synthetic
nanofluidic diodes with highly nonlinear current–voltage
characteristics are currently of particular interest because of their
potential applications in biosensing, separation, energy harvesting,
and nanofluidic electronics. We report the ionic current rectification
(ICR) characteristics of a porous anodic aluminum oxide membrane,
whose one end of the nanochannels is closed by a barrier oxide layer.
The membrane exhibits intriguing pH-dependent ion transport characteristics,
which cannot be explained by the conventional surface charge governed
ionic transport mechanism. We reveal experimentally and theoretically
that the space charge density gradient present across the 40-nm-thick
barrier oxide is mainly responsible for the evolution of ICR. Based
on our findings, we demonstrate the formation of a single 5–8-nm-sized
pore in each hexagonal cell of the barrier oxide. The present work
would provide valuable information for the design and fabrication
of future ultrathin nanofluidic devices without being limited by the
engineering of the nanochannel geometry or surface charge.
Charge doping to Mott insulators is critical to realize hightemperature superconductivity, quantum spin liquid state, and Majorana fermion, which would contribute to quantum computation. Mott insulators also have a great potential for optoelectronic applications; however, they showed insufficient photoresponse in previous reports. To enhance the photoresponse of Mott insulators, charge doping is a promising strategy since it leads to effective modification of electronic structure near the Fermi level. Intercalation, which is the ion insertion into the van der Waals gap of layered materials, is an effective charge-doping method without defect generation. Herein, we showed significant enhancement of optoelectronic properties of a layered Mott insulator, α-RuCl 3 , through electron doping by organic cation intercalation. The electron-doping results in substantial electronic structure change, leading to the bandgap shrinkage from 1.2 eV to 0.7 eV. Due to localized excessive electrons in RuCl 3 , distinct density of states is generated in the valence band, leading to the optical absorption change rather than metallic transition even in substantial doping concentration. The stable near-infrared photodetector using electronic modulated RuCl 3 showed 50 times higher photoresponsivity and 3 times faster response time compared to those of pristine RuCl 3 , which contributes to overcoming the disadvantage of a Mott insulator as a promising optoelectronic device and expanding the material libraries.
Photo-corrosion of anode participating in photo-electrochemical (PEC) water splitting is one of the obstacles for the long-term stability. To prevent the photo-corrosion, "electrically leaky" thick TiO2 film was deposited onto...
Herein, La2O3 films are fabricated on a Si substrate without a La–Sr intermixing layer at the La2O3/Si interface using a pulsed laser deposition method. X‐ray diffraction data shows only two discernible peaks of the La2O3 films: hexagonal La2O3 (10‐1) and cubic La2O3 (222), indicating polycrystalline character. During film growth, the reflection high‐energy electron diffraction pattern from the La2O3 surface changes from an initial column shape to a complicated distributed dot pattern with narrow lines, suggesting possible structural property changes in the La2O3 film. The occurrence of a structural transition is confirmed by high‐resolution transmission electron microscopy (HRTEM), which exhibits a clear crystalline phase change from an initial ≈10 nm thick amorphous La2O3 film to polycrystalline La2O3 film on Si. Rutherford backscattering shows a reduced La–Si intermixing between La2O3 and Si. Furthermore, the results of X‐ray photoelectron spectroscopy atomic depth profile analysis show that observation of La‐silicate over the whole La2O3 film indicates that Si diffuses through whole thick La2O3 films forming Si‐doped La2O3 films. This study of the well‐defined structural characteristics and sharp interface of La2O3/Si will enable further understanding of high dielectric constant materials grown on Si by the introduction of advanced film growth technique.
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