Modern Physics Letters B

Resistive memories based on the resistive switching effect have promising application in the ultimate nonvolatile data memory field. This brief review focuses on the resistive switching phenomena in the perovskite oxide heterostructures, which originate from the modulation of the interface properties due to the movement of the oxygen vacancies and the ferroelectric polarization. Many recent experiments have been carried out to demonstrate the role of the oxygen vacancies by controlling the content of the oxygen vacancies in the oxide heterostructures with plenty of oxygen vacancies. The important role of the ferroelectric polarization was also carefully confirmed by analyzing the relationship between the current–voltage and polarization–voltage loops in the ferroelectric oxide heterostructures. The physical mechanisms have been revealed based on the developed numerical model.

In this paper, we study the intersubband impact ionization through conduction band states of quantum dot (QD) layers of an infrared photodetector. For this purpose, a photogenerated electron moving in high field active region of a p-i-n diode is assumed which can excite an electron from ground state of a QD by carrier–carrier scattering. The generated electron can escape the QD by tunneling and contribute in photocurrent giving avalanche gain to photodetector. The ionization rate and responsivity of detector are calculated from an analytical approach of intersubband transition rate equations. Results show increased responsivity in the order of several A/W.

CaMoO₄:Dy³⁺ used as solid-state laser single crystal, which operate in the yellow region, have important technological applications. In this paper, based on the crystal-field theory, the optical spectra of Dy³⁺ in CaMoO₄ crystal are calculated by diagonalizing the 42 × 42 energy matrix. The electron paramagnetic resonance (EPR) parameters g factors g_‖ and g_⊥ and hyperfine structure constants A_‖ and A_⊥ of ¹⁶¹Dy³⁺ and ¹⁶³Dy³⁺ isotopes in CaMoO₄ crystal are investigated using the perturbation formulas of the 4f⁹ ion in tetragonal symmetry. The needed crystal parameters are determined from the superposition model and the local structure of the studied system. The calculated results are in good agreement with the experimental values.

This paper presents a systematical analysis of the structure and electronic properties of armchair single-walled carbon nanotubes (SWCNTs) as well as single-walled silicon carbide nanotubes (SiCNTs) by using density functional theory. The geometries of all species were optimized at the B3LYP level of theory using the SVP basis set. The different behavior of C–C bonds "parallel" and "perpendicular" to the nanotube axis has been found. The HOMO–LUMO energy gap, ionization potential, electron affinity, electronegativity and hardness of studied tubes were compared. The influence of both SWCNTs and SiCNTs lengths on their electronic properties has been analyzed.

In this paper, single crystalline tetragonal MnO₂ nanorods have been synthesized by a simple hydrothermal method using MnSO₄⋅ H₂O and Na₂S₂O₈ as precursors. The crystalline phase, morphology, particle sizes and component of the as-prepared nanomaterial were characterized by employing X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy-dispersive X-ray spectroscopy (EDS). The photoluminescence (PL) emission spectrum of MnO₂ nanorods at room temperature exhibited a strong ultraviolet (UV) emission band at 380 nm, a prominent blue emission peak at 453 nm as well as a weak defect related green emission at 553 nm. Magnetization (M) as a function of applied magnetic field (H) curve showed that MnO₂ nanowires exhibited a superparamagnetic behavior at room temperature which shows the promise of synthesized MnO₂ nanorods for applications in ferrofluids and the contrast agents for magnetic resonance imaging. The magnetization versus temperature curve of the as-obtained MnO₂ nanorods shows that the Néel transition temperature is 94 K.

In this paper, we study the electronic structure of monolayer materials based on a double hexagonal geometry with (1×1) and superstructures. Inspired from the two-dimensional root system of an exceptional Lie algebra called G₂, this hexagonal atomic configuration involves two hexagons of unequal side length at angle 30°. The principal unit hexagonal cell contains twelve atoms instead of the usual configuration involving only six ones relying only on the (1×1) superstructure. Using ab initio calculations based on FPLO9.00-34 code, we investigate numerically the graphene and the germanene with the double hexagonal geometry. In particular, we find that the usual electronic properties and the lattice parameters of such materials are modified. More precisely, the lattice parameters are increased. It has been shown that, in the single hexagonal geometry, the grapheme and the germanene behave as a gapless semiconductor and a semi-metallic, respectively. In double hexagonal geometry however, both materials becomes metallic.

In this paper, we report the growth of carbon nanofibers (CNFs) by catalyst-free ultrasonic spray-pyrolysis of methanol, ethanol and 2-propanol. We found that the morphology of carbon deposition on the substrate strongly depended on the position of the substrate in the reaction tube and the carbon source species. When ethanol and 2-propanol were used as the carbon source, a slightly hollow structure CNFs were formed downstream in the reaction tube, whereas when the carbon source was methanol, an amorphous structure CNFs were formed at the center of the reaction tube. We consider the difference in CNFs growth between the alcohol types is presence of alkyl groups in alcohol.

In this paper, taking into account the effect of the induced interaction, we calculate the spectral function and hence density of states (DOS) of ultracold Fermi gases within the framework of non-self-consistent T-matrix approximation (nTMA) in the normal phase. The corresponding equations are calculated on the real-frequency axis directly with high accuracy. Our result shows that pseudogap phenomenon still exists in the spectral function and DOS.

In this paper, we report the field-dependent magnetization (M–H) and temperature-dependent magnetization (M–T) properties of hexagonal MnO₂ shrimps-like nanostructures which have been successfully synthesized by hydrothermal route using KMnO₄ and HNO₃ as precursors. The magnetic properties were characterized by vibrating sample magnetometer (VSM). Field-dependent magnetization (M–H) measured at 300 K exhibit paramagnetic nature of MnO₂ nanostructures, while an antiferromagnetic component is observed for the as-prepared product at 55 K. The Néel temperature (T_N) is calculated as 89 K by plotting temperature-dependent magnetization (M–T) curve for the as-prepared MnO₂ nanostructures. X-ray photoelectron spectroscopy (XPS) is employed to calculate the binding energies of Mn (2p_3/2, 2p_1/2) and O (1s) observed in the spectrum.

The determinant expression T^[N] of a new Darboux transformation (DT) for the Ablowitz–Kaup–Newell–Segur equation are given in this paper. By making use of this DT under the reduction r = q*, we construct determinant expressions of dark N-soliton solution for the defocusing NLS equation. Except known one-soliton, we provide smooth two-soliton and smooth N-soliton on a certain domain of parameter for the defocusing NLS equation.