Wet-chemical etching of the barrier oxide layer of anodic aluminum oxide (AAO) was systematically investigated by using scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and a newly devised experimental setup that allows accurate in situ determination of the pore opening point during chemical etching of the barrier oxide layer. We found that opening of the barrier oxide layer by wet-chemical etching can be significantly influenced by anodization time (tanodi). According to secondary ion mass spectrometry (SIMS) analysis, porous anodic aluminum oxide (AAO) samples formed by long-term anodization contained a lower level of anionic impurity in the barrier oxide layer compared to the short-term anodized one and consequently exhibited retarded opening of the barrier oxide layer during the wet-chemical etching. The observed compositional dependence on the anodization time (tanodi) in the barrier oxide layer is attributed to the progressive decrease of the electrolyte concentration upon anodization. The etching rate of the outer pore wall at the bottom part is lower than that of the one at the top part due to the lower level of impurity content in that region. This indicates that a concentration gradient of anionic impurity in the outer pore wall oxide may be established along both the vertical and radial directions of cylindrical pores. Apart from the effect of electrolyte concentration on the chemical composition of the barrier oxide layer, significantly decreased current density arising from the lowered concentration of electrolyte during the long-term anodization (~120 h) was found to cause disordering of pores. The results of the present work are expected to provide viable information not only for practical applications of nanoporous AAO in nanotechnology but also for thorough understanding of the self-organized formation of oxide nanopores during anodization.
We investigate electric and magnetic properties of graphene with rotationally symmetric strain. The strain generates a large pseudomagnetic field with alternating sign in space, which forms a strongly confined quantum dot connected to six chiral channels. The orbital magnetism, degeneracy, and channel opening can be understood from the interplay between the real and pseudomagnetic fields which have different parities under time reversal and mirror reflection. While the orbital magnetic response of the confined state is diamagnetic, it can be paramagnetic if there is an accidental degeneracy with opposite mirror reflection parity. The recent successful preparation of a one-atom layer of carbons, graphene, 1,2 has provided the opportunity for theoretical and experimental research of a massless Dirac fermion in nanoelectronics. While quantum dots which confine quasiparticles in graphene are basic building blocks for its nanoelectronic application, the confinement turns out to be nontrivial. It is because, in graphene, where the quasiparticles are described by massless Dirac fermions, they can penetrate large and wide electrostatic barriers due to the effect of Klein tunneling.3 In principle, graphene dots can be realized by a spatially inhomogeneous magnetic field, but the required magnetic field for the confinement, however, is unreasonably strong 4 compared to usual electronics applications. Recently, strain engineering of graphene 5-7 has attracted great attention as an alternative tool for graphene electronics because the strain induces a strong pseudomagnetic field which guides electrons. Thus, for the strained graphene to work successfully in combination with existing technologies, it is now important to understand the physical properties of the pseudomagnetic field. In this Rapid Communication, we investigate the relative contribution of real and pseudomagnetic fields to the electric and magnetic properties of the graphene. We show that a reasonable size of strain can generate a strong pseudomagnetic field to form a graphene quantum dot with six chiral channels. It will be demonstrated that the different symmetry of real and pseudomagnetic fields give rises to rich properties of channel opening and orbital magnetism. The pseudomagnetic field appears since the variation of hopping energies by elastic strains enters the Dirac equation. [8][9][10][11][12][13] While the strong confinement is due to the fact that the pseudomagnetic field is very strong (∼10 T), the six chiral channels are due to the topology of the pseudomagnetic field, where charged particles propagate along the zero-field line. As we will show here, the real and pseudomagnetic fields have different parities under the symmetry operation, such as time reversal and mirror reflection. From the symmetry arguments, we prove that while the real magnetic field breaks the time-reversal symmetry in its Hamiltonian, it does not lift the valley degeneracy. We will demonstrate our theory by showing orbital diamagnetism of the confined state. It will be show...
Oxygen vacancies (V(O)) have profound effects on the physical and chemical performance of devices based on oxide materials. This is particularly true in the case of oxide-based resistive random access memories, in which memory switching operation under an external electrical stimulus is closely associated with the migration and ordering of the oxygen vacancies in the oxide material. In this paper, we report on a reliable approach to in situ control of the oxygen vacancies in TiOx films. Our strategy for tight control of the oxygen vacancy is based on the utilization of plasma-enhanced atomic layer deposition of titanium oxide under precisely regulated decomposition of the precursor molecules (titanium (IV) tetraisopropoxide, Ti[OCH(CH₃)₂]₄) by plasma-activated reactant mixture (N₂+O₂). From the various spectroscopic and microstructural analyses by using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, confocal Raman spectroscopy, and spectroscopic ellipsometry, we found that the precursor decomposition power (R(F)) of plasma-activated reactant mixture determines not only the oxygen vacancy concentration but also the crystallinity of the resulting TiO(x) film: nanocrystalline anatase TiO(x) with fewer oxygen vacancies under high R(F), while amorphous TiOx with more oxygen vacancies under low RF. Enabled by our controlling capability over the oxygen vacancy concentration, we were able to thoroughly elucidate the effect of oxygen vacancies on the resistive switching behavior of TiO(x)-based memory capacitors (Pt/TiO(x)/Pt). The electrical conduction behavior at the high resistance state could be explained within the framework of the trap-controlled space-charge-limited conduction with two characteristic transition voltages. One is the voltage (V(SCL)) for the transition from Ohmic conduction to space-charge-limited conduction, and the other is the voltage (V(TFL)) for transition from space-charge-limited conduction to trap-filled-limited conduction. In this work, we have disclosed for the first time the dependence of these two characteristic transition voltages (i.e., V(SCL) and V(TFL)) on the oxygen vacancy concentration.
Synchrotron-radiation x-ray photoelectron spectroscopy (XPS) has been used to analyze size-dependent Si 2p core-level spectra of Si nanocrystals (NCs) embedded in SiO2. The Si0 and suboxide XPS peaks of Si NCs shift to higher binding energies with decreasing NC size, which is based on the resolved spectra fitted by using Gaussian-Lorentzian lines for the Si oxidation states. It is also found that the shell region around Si NC bordered by SiO2 consists of the three Si suboxide states, Si1+, Si2+, and Si3+, whose densities are also strongly dependent on NC size. These results suggest that the analysis of the Si 2p core-level shift by XPS is useful for characterizing the size effect of Si NC at the Si NC∕SiO2 interfaces.
The characteristic interaction distance between Er3+ ions and carriers that excite them in Er-doped a-Si/SiO2 superlattices is investigated. Superlattice thin films consisting of 12 periods of a-Si/SiO2:Er/SiO2/SiO2:Er layers were deposited by ion sputtering and subsequent annealing at 950 °C. The dependence of the Er3+ photoluminescence intensity on the thickness of the Er-doped SiO2 layers is well-described by an exponentially decreasing Er-carrier interaction with a characteristic interaction distance of 0.5±0.1 nm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.