Xue-Yi Zhu

The microstructure studies of bismuth sulfide nanorods prepared by sonochemical method

In this work, the microstructures of Bi2S3 single crystal nanorods were investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HREM) in detail. The mechanism of the formation of Bi2S3 nanorods prepared by a sonochemical method is explored.

High-resolution electron microscopy investigations on stacking faults in SrBi2Ta2O9 ferroelectric thin films

Structural planar defects in the SrBi2Ta2O9 (SBT) films with 10 mol % excess Bi grown in Pt/TiO2/SiO2/Si substrates by metalorganic deposition have been observed by high-resolution electron microscopy. It was found that these stacking defects were planar defects with extra Bi–O planes normal to the c axis. These structural defects are expected to effectively improve the ferroelectric response and fatigue-resistance characteristics of SBT films because of the extra Bi–O planes having higher strucutral flexibility and alleviating the mechanical stresses and strains as well as injected-charge problems.

Asymmetric diffraction based on a passive parity-time grating

Optical structures with balanced loss and gain provide an efficient platform to study the features of light propagation under non-Hermitian parity-time symmetry. Here, we report a feasible design of one-dimensional parity-time symmetric diffraction grating, where the real and imaginary parts of refractive index are separately modulated. Due to the spontaneous breaking of parity-time symmetry at the exceptional point, asymmetric diffractions are observed between a pair of oblique incident light. This asymmetric phenomenon, determined by the modulation direction of the introduced parity-time symmetry, is also polarization-dependent. The coupled-mode theory is implemented to theoretically analyze the polarization dependent asymmetric diffraction, showing consistence with numerical simulations. Our findings may provide a feasible way for manipulating light and instructively inspire the development of diffraction optics.

Broadband and wide angle infrared wire-grid polarizer

An infrared polarizer consisting of metal-insulator-metal (MIM) gratings is designed with transmittance exceeding 85% and polarization extinction ratio (ER) higher than 70 dB in the wavelength range from 1.5 to 8 μm. Moreover, the polarizer retains excellent performance even when the incident angle increases to as large as 80°. The MIM gratings support magnetic polariton (MP) in the near-infrared regime and operate non-resonantly in the mid-infrared regime, both of which result in the advantages of high extinction ratio, broadband, and wide angle. The proposed structure can find applications in polarizer, beam-splitter, filter, and isolator in the infrared range.

Optimizing growth parameters for highly luminescent Er:Al 2 O 3 thin films that act as a base to fabricate a PT laser

Recently PT symmetric devices, a new class of artificial optical materials, found a tremendous interest in research where PT symmetry is maintained by balancing gain and loss regions, and therefore combined PT operation leads to interchange loss and gain and leaves the system invariant. Based on this gain/loss modulation concept, we demonstrate both experimentally and theoretically a PT symmetric laser fabricated out of a grating structure on the top surface of erbium doped alumina thin films deposited by Co-sputtering technique. Erbium doped in alumina act as one of the best choice to fabricate such an active device because Al2O3 effectively improves the erbium ion doping concentration and hence increasing fluorescence lifetime giving a large optical gain in a smaller device size. In order to fabricate such grating structure, firstly we have optimized the growth parameters for depositing homogeneous and highly luminescent Er:Al2O3 thin films on thermally oxidized silicon substrates. The main subject of investigation includes the effect of change in various deposition parameters like substrate heating, RF power and oxygen pressure inside the chamber while deposition. Co-sputtering is found to be very promising technique for fabrication of such films as CVD and sol-gel techniques suffer from the presence of hydroxyl groups that incorporates inside the film during deposition and that induce luminescence quenching. In this paper, high quality as-deposited films with various Er concentrations and low carbon contents have been confirmed by XPS. Substrate heating ~ 500°C was found to be very effective in getting highly dense films with high refractive index of 1.70 in 1530-1565nm band. The films showed highly intense PL peak at 1550nm even without any post deposition annealing treatment.

Atomic-scale surface structures and structural defects of hydrothermal batio3 nanoparticles revealed by HRTEM

We report on the effects of reactive conditions on the formation of BT nanoparticles via hydrothermal process with a focus on their atomic-scale surface microstructures and structural defects characterized by HRTEM. The results showed that large Ba/Ti molar ratios in the precursors could lead to large particles with a cubic morphology. Smaller particles with a weaker agglomeration behavior were observed in the products synthesized via solvothermal process using ethylene glycol (EG) as reaction medium, in comparison to using either pure water or water-EG mixed solution as reactive medium. A terrace-ledge-kink surface structure and structural defects such as anti-phase boundaries (APBs) and edge dislocations with Burgers vector of or were observed at the edges of the nanoparticles. The {110} surfaces were found to be reconstructed and composed of the corners bound by the {100} mini-faces. APBs near the edges of BT nanoparticles were formed by the intersection of two crystalline parts with displacement deviation from each other by

Electron microscopy study of ferroelectric domains and microstructural defects in Bi- and Zn-modified Pb(Ni 1/3 Nb 2/3 )O 3 -PbZrO 3 -PbTiO 3 piezoelectric ceramics

Ferroelectric domain configurations and microstructural defects in the Bi- and Zn-modified Pb(Ni1/3Nb2/3)O3-PbZrO3-PbTiO3 piezoelectric ceramics were investigated by transmission electron microscopy (TEM) and selected area electron diffraction. In the samples with tetragonal symmetry, labyrinthic domain configurations with 90° a-c domains were observed besides the herringbone-like configuration, parallel band-shaped and/or wedge-shaped domains. Polar nanodomains with local random contrast were observed in the samples with rhombohedral symmetry but close to the paraelectric phase region, and the effects of electron beam irradiation on the local random diffraction contrast were also studied. Microstructural defect such as anti-phase boundaries in this piezoelectric system was also revealed by TEM.