Xiasheng Guo

Pulsed laser deposition and characterization of optical waveguiding (Pb,La)(Zr,Ti)O3 thin films

The ferroelectric (Pb,La)(Zr,Ti)O3 optical waveguiding thin films have been prepared on MgO coated (100)LiF substrates by pulsed laser deposition. X‐ray θ‐2θ scans revealed that the films are single‐phase pseudocubic perovskite and highly 〈100〉 textured. The surface chemical composition of the as‐grown films was determined by x‐ray photoelectron spectroscopy. The ferroelectric properties of the films as grown on Pt/Ti coated silicon were demonstrated by using a modified Sawyer–Tower circuit, and the optical waveguiding properties of the films were characterized by using a rutile prism coupling method. The as‐grown films have an average transmittance of 75% in the wavelength range of 400–2000 nm and a refractive index of 2.2 at 632.8 nm close to the bulk PLZT. The distinct m lines of the guided TM and TE modes of the films as grown on MgO coated LiF substrates have been observed.

Acoustic non-diffracting Airy beam

The acoustic non-diffracting Airy beam as its optical counterpart has unique features of self-bending and self-healing. The complexity of most current designs handicaps its applications. A simple design of an acoustic source capable of generating multi-frequency and broad-band acoustic Airy beam has been theoretically demonstrated by numerical simulations. In the design, a piston transducer is corrugated to induce spatial phase variation for transducing the Airy function. The pistons surface is grooved in a pattern that the width of each groove corresponds to the half wavelength of Airy function. The resulted frequency characteristics and its dependence on the size of the piston source are also discussed. This simple design may promote the wide applications of acoustic Airy beam particularly in the field of medical ultrasound.

Investigation on the inertial cavitation threshold and shell properties of commercialized ultrasound contrast agent microbubbles

The inertial cavitation (IC) activity of ultrasound contrast agents (UCAs) plays an important role in the development and improvement of ultrasound diagnostic and therapeutic applications. However, various diagnostic and therapeutic applications have different requirements for IC characteristics. Here through IC dose quantifications based on passive cavitation detection, IC thresholds were measured for two commercialized UCAs, albumin-shelled KangRun(®) and lipid-shelled SonoVue(®) microbubbles, at varied UCA volume concentrations (viz., 0.125 and 0.25 vol. %) and acoustic pulse lengths (viz., 5, 10, 20, 50, and 100 cycles). Shell elastic and viscous coefficients of UCAs were estimated by fitting measured acoustic attenuation spectra with Sarkars model. The influences of sonication condition (viz., acoustic pulse length) and UCA shell properties on IC threshold were discussed based on numerical simulations. Both experimental measurements and numerical simulations indicate that IC thresholds of UCAs decrease with increasing UCA volume concentration and acoustic pulse length. The shell interfacial tension and dilatational viscosity estimated for SonoVue (0.7 ± 0.11 N/m, 6.5 ± 1.01 × 10(-8) kg/s) are smaller than those of KangRun (1.05 ± 0.18 N/m, 1.66 ± 0.38 × 10(-7) kg/s); this might result in lower IC threshold for SonoVue. The current results will be helpful for selecting and utilizing commercialized UCAs for specific clinical applications, while minimizing undesired IC-induced bioeffects.

Pulsed laser deposition of /MgO bilayered films on Si wafer in waveguide form

Strontium barium niobate (SBN) thin films were grown on Si (111) substrates coated with MgO buffer by the pulsed laser deposition (PLD) technique. The thickness of SBN and MgO films were of the order of 1200 nm and 840 nm respectively. X-ray energy dispersive spectrometry (XREDS) showed that SBN films have stoichiometric composition identical to the target material, and no Si diffusion into the SBN film was found. X-ray diffraction (XRD) scans indicated that MgO films were highly (111) textured, but the SBN films were polycrystalline without preferential orientation. The surface of the SBN film was smooth, dense and crack-free and no large droplets were observed when studied under a scanning electron microscope (SEM). A favourable optical waveguiding property of the bilayered films was demonstrated by a prism coupler method.

Modeling and optimization of an acoustic diode based on micro-bubble nonlinearity

The first acoustic diode (AD), which is composed by integrating a super lattice (SL) with a nonlinear medium (NLM), has recently been proposed to make a one-way street for the acoustic energy flux. This device prohibits the acoustic waves from one direction, but allows the transmission of the second harmonic wave (generated from the NLM) from the other direction. To improve its performance, it is crucial to transfer more acoustic energy from the stop-band of the acoustic filter (i.e., the SL) to its pass-band with the help of the NLM. In this work, a finite difference time domain model is developed to study the dynamic behaviors of the AD, in which a micro-bubble suspension takes the role of the NLM. Based on this model, the method of optimizing the nonlinearity-based AD is investigated by examining its performance with respect to several parameters, such as the periodicity number of the SL, the bubble size distribution, the bubble shell parameters, and the bubble concentration. It is also suggested that, instead of the rectification ratio, it might be more reasonable to characterize the performance of the AD with the energy attenuation coefficients (or transmission loss) for both incident directions.

Preparation of nanocrystalline SnO2 thin films used in chemisorption sensors by pulsed laser reactive ablation

Nanocrystalline SnO2 thin films were fabricated by pulsed laser reactive ablation using a metallic Sn target. Oxidation of Sn to SnO2 occurred principally on the substrate surface and was negligible during transportation of Sn atoms in the ablated plume from the target to the film. Therefore, the substrate temperature was the most important parameter to influence the phase constitution of the films. When the substrate temperature was higher than the melting point of metal Sn (230 °C), SnO2 phase was obtained. Otherwise the films were β-Sn dominant. X-ray diffraction and transmission electron microscopy techniques were used to determine the grain size in the films, which was in the range 10–30 nm, depending upon the substrate temperature and the subsequent annealing. For chemisorption performance, films with a thickness up to 24 nm showed a higher sensitivity than the films 38 nm and 96 nm thick. Excellent chemisorption properties have been achieved on the very thin nanocrystalline films.

Pulsed laser deposition of c-orientedLiNbO3LiTaO3 optical waveguiding bilayered films on silicon wafers

LiNbO3(LN)LiTaO3(LT) bilayered films were grown on a p-type Si(111) wafer coated with a SiO2 buffer by a pulsed laser deposition (PLD) technique. The XPS measurement showed that the stoichiometries of the LN and LT films were in good agreement with the target materials. The crystallinity of the as-grown films was analysed by XRD, which indicated that LN and LT were highly c-oriented while the SiO2 buffer was amorphous. The surface of the as-grown films was mirror-like, dense and crack-free; no large droplets were observed by scanning electron microscope (SEM). The thicknesses of the LN, LT and SiO2 films were about 960, 360 and 1800 nm, respectively. The interface between the LN and LT films was sharp. The X-ray energy dispersive spectrometer (XREDS) analysis to the different areas of the LN film showed that there was no variation of composition with depth. The optical waveguiding properties of the films were demonstrated by a prism coupler method.

Controllable in vivo hyperthermia effect induced by pulsed high intensity focused ultrasound with low duty cycles

High intensity focused ultrasound (HIFU)-induced hyperthermia is a promising tool for cancer therapy. Three-dimensional nonlinear acoustic-bioheat transfer-blood flow-coupling model simulations and in vivo thermocouple measurements were performed to study hyperthermia effects in rabbit auricular vein exposed to pulsed HIFU (pHIFU) at varied duty cycles (DCs). pHIFU-induced temperature elevations are shown to increase with increasing DC. A critical DC of 6.9% is estimated for temperature at distal vessel wall exceeding 44 °C, although different tissue depths and inclusions could affect the DC threshold. The results demonstrate clinic potentials of achieving controllable hyperthermia by adjusting pHIFU DCs, while minimizing perivascular thermal injury.

Mechanical and dynamic characteristics of encapsulated microbubbles coupled by magnetic nanoparticles as multifunctional imaging and drug delivery agents

Development of magnetic encapsulated microbubble agents that can integrate multiple diagnostic and therapeutic functions is a key focus in both biomedical engineering and nanotechnology and one which will have far-reaching impact on medical diagnosis and therapies. However, properly designing multifunctional agents that can satisfy particular diagnostic/therapeutic requirements has been recognized as rather challenging, because there is a lack of comprehensive understanding of how the integration of magnetic nanoparticles to microbubble encapsulating shells affects their mechanical properties and dynamic performance in ultrasound imaging and drug delivery. Here, a multifunctional imaging contrast and in-situ gene/drug delivery agent was synthesized by coupling super paramagnetic iron oxide nanoparticles (SPIOs) into albumin-shelled microbubbles. Systematical studies were performed to investigate the SPIO-concentration-dependence of microbubble mechanical properties, acoustic scattering response, inertial cavitation activity and ultrasound-facilitated gene transfection effect. These demonstrated that, with the increasing SPIO concentration, the microbubble mean diameter and shell stiffness increased and ultrasound scattering response and inertial cavitation activity could be significantly enhanced. However, an optimized ultrasound-facilitated vascular endothelial growth factor transfection outcome would be achieved by adopting magnetic albumin-shelled microbubbles with an appropriate SPIO concentration of 114.7 µg ml(-1). The current results would provide helpful guidance for future development of multifunctional agents and further optimization of their diagnostic/therapeutic performance in clinic.

Low biased voltage induced textured growth of LiNbO3 films on silicon wafer

Abstract In this work, it has been found that a low electric biased voltage of up to 120 V applied during pulsed laser deposition of LiNbO3 films has a significant influence on the orientation of LiNbO3 films. By applying a biased voltage of about 110 V (7–8 V/cm) in LiNbO3 film, completely c-oriented LiNbO3 films with their poling direction parallel to the biased electric field have been achieved on fused silica and amorphous SiO2 coated silicon wafer. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize the microstructure of the films. The films are single phased, smooth and nearly stoichiometric. The effects of biased voltage on the orientation of the films were analyzed based on the theory of the nucleation of LiNbO3 with spontaneous polarization under the influence of electric field.