International Journal of Modern Physics B

Analytical polar optical phonon states in a wurtzite ZnO-based cylindrical coupling quantum dots (CQDs) with arbitrary number of quantum dots (QDs) are deduced and analyzed. It is found that there are four types of polar mixing optical phonon modes, i.e., the z-IO/ρ-QC modes, the z-PR/ρ-IO modes, the z-QC/ρ-QC modes and the z-HS/ρ-IO modes coexisting in the ZnO-based CQDs. Within the framework of the macroscopic dielectric continuum model, the dispersive equations are derived by using the transferring matrix method. And the Fröhlich electron–phonon interaction Hamiltonians are obtained via a standard procedure of field quantization. The relationships between the present ZnO-based CQDs and the ZnO-based quantum wells (QWs) or the nanowires (NWs) are analyzed, and the general features of phonon modes in ZnO-based low-dimensional quantum structures are concluded and discussed. Under certain conditions, the present theoretical results in wurtzite ZnO-based CQDs can be naturally degenerate into those in wurtzite ZnO-based single or double QDs, wurtzite NWs and QWs and even into cubic quantum confined structures. This just embodies the intrinsic consistency of phonon mode theories in low-dimensional confined systems with different confined dimensions. Due to the ternary mixing effect of Mg_xZn_1-xO crystal, the dielectric functions of Mg_xZn_1-xO crystals are quite complicated, and the phonon modes in ZnO-based quantum structures have both the features of phonon modes in anisotropic wurtzite confined systems and isotropic rock-salt crystal quantum systems. The characteristics of electron–phonon coupling strength in ZnO-based quantum systems are summarized. Very strong polaronic effect could be prognosticated and anticipated in ZnO-based low-dimensional quantum structures because of their quite large electron–phonon coupling constants. The theoretical results and conclusions described in this paper also can be looked on as a summary of phonon states and their general features in ZnO-based quantum confined systems.

The mean escape time of Brownian particles from a metastable potential well is investigated under the influence of a thermal time derivative Ornstein–Uhlenbeck noise, which can induce ballistic diffusion of force-free Brownian particles. Compared with the usual Ornstein–Uhlenbeck noise, some new characteristics are obtained. The Brownian particles escape fast remarkably for a larger correlation time of the Ornstein–Uhlenbeck noise. The mean escape time increases as the correlation time decreases, which is contrary to the Ornstein–Uhlenbeck noise case. The escape time for derivative Ornstein–Uhlenbeck noise is longer than that of Ornstein–Uhlenbeck noise for small strength of noise and small correlation time of Ornstein–Uhlenbeck noise. These features are explained by the spectrum features of derivative Ornstein–Uhlenbeck noise and the corresponding dynamical effects.

Recent experiment [Xie et al., Catal. Commun., 27, 21 (2012)] reported that LaOF is an active catalyst for water reduction: the catalytic activity per surface area of LaOF is about ten times higher than that of anatase TiO₂. First-principles density functional theory (DFT) calculations have been performed on Ln-doped LaOF (Ln = Ce, Pr, Nd and Pm) to evaluate the effect of lanthanide doping on the electronic and optical properties. It is found that the lowest conduction band (CB) edge potential of LaOF is less than zero (versus normal hydrogen electrode (NHE)), confirming it has enough driving force for photocatalytic water splitting. The band gap of LaOF could be reduced significantly by lanthanide doping. Electronic structure analysis shows that the impurity states appear deep inside the band gap of LaOF, which is in favor of the separation center of photogenerated carriers due to large effective mass differences between electron and hole. Moreover, doping both Pm and Nd into LaOF is an effective approach to extend the optical absorption edge to the visible light. These findings suggest that LaOF doped with lanthanide element is a promising candidate for the photocatalytic hydrogen generation from water and pollutant decomposition.

The phase behavior of two components p-quaterphenyl (QP) and polymethyl methacrylate (PMMA)/heptadecanoic acid (HA)) in the Langmuir monolayer was characterized. The surface pressure versus area per molecule isotherms revealed that the area per molecule systematically changed with increasing mole fractions of QP, indicating that repulsive types of interactions were involved between the QP and the matrix molecules (PMMA/HA), leading to the phase separation which in turn stimulated the aggregate formation. Absorption spectroscopy, complemented with scanning electron microscopy (SEM), confirmed the aggregation of QP molecules in the mixed films.

In this paper, quantum solitons in the Fermi–Pasta–Ulam (FPU) model are investigated analytically. By using the canonical transform method and number-conserving approximation, we obtain the normal form of the phonon-conserving quantized Hamiltonian. In order to convert the quantized Hamiltonian into the coordinate space, we employ the inverse Fourier transform. With the help of the Hartree approximate and the semidiscrete multiple-scale method, the nonlinear Schrödinger (NLS) equation is derived. The results show that quantum solitons may exist in the FPU model. Moreover, it is found that moving quantum solitons become quantum intrinsic localized modes under certain condition. In addition, we obtain the energy level of quantum solitons, which indicates that the energy of such quantum solitons is quantized.

Several different pH of Al₂O₃ nano-fluid were prepared using dispersant and doped into polyvinyl alcohol (PVA)/acrylamide (AA) based photopolymers where the photopolymers were exposed with 647 nm Ar⁺Kr⁺ laser to study its holographic properties. The research shows that the incorporation of Al₂O₃ nanoparticles (NPs) improves the holographic characteristics of sample, where the pH has an effect to the dispersion of Al₂O₃ NPs in the photopolymer. When the pH of Al₂O₃ nano-fluid is about 7, the diffraction efficiency of the sample can be raised to 93.8%, the maximum refractive index modulation can be increased to 2.28×10^-3, the shrinkage can be depressed to 0.8%, the Bragg mismatch is 0.04°, and the concentration of 10 nm Al₂O₃ nano-fluid modified by high definition (HD) dispersant must be 1.02×10^-3mol⋅L^-1.

An open quantum system is studied consisting of a particle moving in a spherical space with an infinite wall. With the theory of Lindblad the system is described by a density matrix which gets affected by operators with diffusive and dissipative properties depending on the linear momentum and density matrix only. It is shown that an infinite number of basis states leads to an infinite energy because of the infinite unsteadiness of the potential energy at the infinite wall. Therefore only a solution with a finite number of basis states can be performed. A slight approximation is introduced into the equation of motion in order that the trace of the density matrix remains constant in time. The equation of motion is solved by the method of searching eigenvalues. As a side-product two sums over the zeros of spherical Bessel functions are found.

The semiconductor ZnO of large gap of 3,4 eV is of great interest for the technological applications as chemical sensors, UV light emission, optical memories, laser emission, solar cells, etc. These applications depend on the electron structure of material. We adopt the density functional theory (DFT) calculation by using the program Wien2K, within the Generalized Gradient Approximation (GGA) and modified Becke–Johnson (mBJ) for studying the electron behavior of ZnO. The features of the valence band derived from the hybridization of Zn-3d and O-2p states. The electron charge density calculated by these simulation methods indicates a charge transfer between zinc and oxygen inducing a difference in electronegativity between both species (Zn and O), responsible to ionic character of bonding in ZnO. The predictions based on the GGA and mBJ calculations are confirmed by the results of the experimental spectroscopic analysis Auger Electron Spectroscopy (AES) and Electron Energy Loss Spectroscopy (EELS).

The full potential linearized augmented plane wave method within the framework of density functional theory (DFT) is employed to investigate the structural, magnetic, electronic and optical properties of Ti-doped ZnTe and CdTe in the zinc blende phase. In this approach the local spin density approximation (LSDA) is used for the exchange-correlation (XC) potential. Results are provided for the lattice constant, bulk modulus, pressure derivative, magnetic moment, band structure, density of states and refractive indices. Our results are compared with other theoretical works and good agreement is shown.