Shuangli Ye

Strain induced tetragonal SrTiO3 nanoparticles at room temperature

SrTiO3 nanoparticles with tetragonal phase at room temperature were fabricated using pulsed laser deposition method and rapid thermal annealing technique. High-resolution transmission electron microscope images demonstrate that SrTiO3 nanoparticle experiences a structural phase transition from cubic with indirect band gap to tetragonal with direct band gap with growing size. It has been found that the net deviatoric strain from Lu2O3 matrix can cause the rotation of the TiO6 octahedra and the change of the bond length, which is suggested to explain the structural phase transition. Strain engineering is an effective tool for tailoring the properties of SrTiO3 nanoparticles.

Equivalent Circuit-Level Model of Quantum Cascade Lasers: Influence of Doping Density on Steady State and Dynamic Responses

An equivalent circuit model of quantum cascade lasers (QCLs) is introduced by virtue of revised three-level rate equations. This model accounts for the influence of injector doping on electron dynamics of QCLs. Both the photon gain coefficient and the injection current efficiency depend on the injector doping density in this model. The nonradiative scattering times, radiative spontaneous relaxation time, and electron escape time are obtained by a fully nonequilibrium self-consistent Schrödinger-Poisson analysis of the scattering rate and energy balance equations. A general diode subcircuit is adopted to model the current-voltage relationship. Based on this new model, the steady and dynamic characteristics of devices with injector sheet doping densities in the range of 4 × 1011 ~ 6.5 × 1011 cm-2 are investigated by using a circuit simulator. Results indicate that doping density variations play an important role on threshold current and delay time of QCL devices.

Strain-gradient facilitated formation of confined Ge/GeO2 nanoparticles with a cracked shell and enhanced two-photon absorption

The formation of the cracked shell is confirmed by HRTEM for the Ge/GeO2 core/shell nanoparticles fabricated by the pulsed laser deposition method and a rapid thermal annealing technique. The determined two-photon absorption in Ge/GeO2 core/shell nanoparticles with a cracked shell is an instantaneous nonlinear process and is enhanced almost 2 times compared with that in pure Ge nanoparticles. Our simulation results illustrate that the oxidation of confined Ge/GeO2 core/shell nanoparticles results in the formation of cracks in GeO2 shells. It indicates that strain gradients induced in the confined GeO2 shell during the oxidation process can facilitate the formation of the cracked GeO2 shell and the shape evolution of Ge/GeO2 core/shell nanoparticles. These results demonstrate that the strain can manipulate the microstructure, morphology and optical properties of confined core/shell nanoparticles.

Shell Thickness-Dependent Strain Distributions of Confined Au/Ag and Ag/Au Core-Shell Nanoparticles

The shell thickness-dependent strain distributions of the Au/Ag and Ag/Au core-shell nanoparticles embedded in Al2O3 matrix have been investigated by finite element method (FEM) calculations, respectively. The simulation results clearly indicate that there is a substantial strain applied on both the Au/Ag and Ag/Au core-shell nanoparticles by the Al2O3 matrix. For the Au/Ag nanoparticles, it can be found that the compressive strain existing in the shell is stronger than that on the center of core and reaches the maximum at the interface between the shell and core. In contrast, for the Ag/Au nanoparticles, the compressive strain applied on the core is much stronger than that at the interface and that in the shell. With the shell thickness increasing, both of the strains in the Au/Ag and Ag/Au nanoparticles increase as well. However, the strain gradient in the shell decreases gradually with the increasing of the shell thickness for both of Ag/Au ad Au/Ag nanoparticles. These results provide an effective method to manipulate the strain distributions of the Au/Ag and Ag/Au nanoparticles by tuning the thickness of the shell, which can further have significant influences on the microstructures and physical properties of Au/Ag and Ag/Au nanoparticles.

Thickness-dependent strain effect on the deformation of the graphene-encapsulated Au nanoparticles

The strain effect on graphene-encapsulated Au nanoparticles is investigated. A finite-element calculation is performed to simulate the strain distribution and morphology of the monolayer and multilayer graphene-encapsulated Au nanoparticles, respectively. It can be found that the inhomogeneous strain and deformation are enhanced with the increasing shrinkage of the graphene shell. Moreover, the strain distribution and deformation are very sensitive to the layer number of the graphene shell. Especially, the inhomogeneous strain at the interface between the graphene shell and encapsulated Au nanoparticles is strongly tuned by the graphene thickness. For the mono- and bilayer graphene-encapsulated Au nanoparticles, the dramatic shape transformation can be observed. However, with increasing the graphene thickness further, there is hardly deformation for the encapsulated Au nanoparticles. These simulated results indicate that the strain and deformation can be designed by the graphene layer thickness, which provides an opportunity to engineer the structure and morphology of the graphene-encapsulated nanoparticles.

Effects of receiver parameters on the wireless power transfer system via magnetic resonance coupling

ABSTRACT The wireless system with four-coil resonators is a popular configuration for mid-range wireless power transfer via magnetic resonance coupling. It has broad range of applications. But it is difficult to make the parameters of receiver (including receiving coil and load coil) to be consistent with the parameters of transmitter (including driving coil and transmitting coil) in different application environments. The parameters of receiving coil and load coil have strong impacts on efficiency of the wireless power transfer system. In this work, a comprehensive study on effects of receiver (including receiving coil and load coil) parameters, such as coils radius, wire radius, number of turns and length of coil, is conducted. Some important observations on the effects of the receiver parameters are drawn based on theoretical studies and PSPICE simulation, which are also verified by experiments. It is shown that the radius of receiver has more significant impacts on the power transfer efficiency than other parameters.

A study on effects of coil locations in wireless power transfer

A study on effects of coil locations in the wireless system with four coils is presented by full-wave electromagnetic simulation. Three operational regions can be defined in terms of the distances between neighboring coils: over coupling, strong coupling and under coupling. It is shown that the distance between the receiving and load coils has significant impact on the power transfer efficiency in the strong coupling regime. Design guidelines for optimal coil locations are also presented.

Frequency effects of coil locations on wireless power transfer via magnetic resonance coupling

The wireless system with four coil resonators is a popular configuration for mid-range wireless power transfer via magnetic resonance coupling. The locations of four coils have strong impact on efficiency, resonant frequency and bandwidth of the wireless power transfer system. In this work, a comprehensive study on frequency effects of coil location parameters, such as the distances between neighboring coils, is conducted by virtue of full-wave electromagnetic solution. It is shown that the distance between the driving and transmitting coils may merely affect the bandwidth and the resonant frequency in the strong coupling regime. The distance between the transmitting and receiving coils can have strong impact on both the bandwidth and the resonant frequency. The research will provide design guidelines for optimal coil locations of the wireless power transfer system.

Strain distribution of Au and Ag nanoparticles embedded in Al 2 O 3 thin film

Au and Ag nanoparticles embedded in amorphous Al2O3 matrix are fabricated by the pulsed laser deposition (PLD) method and rapid thermal annealing (RTA) technique, which are confirmed by the experimental high-resolution transmission electron microscope (HRTEM) results, respectively. The strain distribution of Au and Ag nanoparticles embedded in the Al2O3 matrix is investigated by the finite-element (FE) calculations. The simulation results clearly indicate that both the Au and Ag nanoparticles incur compressive strain by the Al2O3 matrix. However, the compressive strain existing on the Au nanoparticle is much weaker than that on the Ag nanoparticle. This phenomenon can be attributed to the reason that Youngs modulus of Au is larger than that of Ag. This different strain distribution of Au and Ag nanoparticles in the same host matrix may have a significant influence on the technological potential applications of the Au-Ag alloy nanoparticles.