W.D. Song

Laser-induced cavitation bubbles for cleaning of solid surfaces

When a high-power laser beam is focused into liquid, it results in a shock wave emission and cavitation bubble generation. Upon inserting a rigid substrate into the liquid, the bubbles migrate towards the substrate due to the Bjerknes attractive force. Due to bubble–substrate and/or bubble–free-surface interaction, a high-speed liquid jet is formed during bubble collapse, and a collapse shock wave is generated at the moment of bubble collapse near the substrate. These shock waves and liquid jet induce large forces acting on the substrate to remove particles from it. For a substrate several millimeters away from the laser focus point, the collapse shock wave and liquid jet play key roles in removal of particles. The cleaning efficiency increases with an increase of laser fluence and decreases with an increase of distance between substrate surface and laser beam focus point or depth below liquid surface. In a case of bubbles close to substrate and liquid-surface boundaries, implosion of the bubbles will giv...

Growth and characterization of dual-beam pulsed-laser-deposited Zn1−xCoxO thin films

Dual beam pulsed laser deposition was used to synthesize Zn1−xCoxO thin films with a large range of Co concentrations. In this paper, the influence of growth temperature on the crystal structures, magnetic properties, and semiconductor properties of these films was studied. It was found that the growth temperature has a significant effect on dopant concentration, as well as the structure and properties of the films. The optimum growth temperature is around 650°C. The thin films were of single crystal especially at low Co concentrations. Epitaxial growth of the thin films was observed. No precipitates were observed at low Co concentrations. Magnetic hysteresis loops were observed at room temperature, indicating that magnetism can be realized with Co doped into ZnO. However, the improvement was limited. The Hall resistivity tended to increase, while carrier density tended to decrease with Co concentration until a certain Co concentration (10%) is achieved. When the growth temperature was greater than 650°C,...

Anomalous Hall effect and origin of magnetism in Zn1−xCoxO thin films at low Co content

A small anomalous Hall effect signal of a Zn1−xCoxO (x=0.05) thin film was observed, indicating that there presents sp-d interactions in the Zn1−xCoxO thin film. However, under a self-held setup, we did not obtain observable differences between the M-H curves when the near band electrons were changed. Integrated with our previous results, possible mechanisms for the magnetism of Zn1−xCoxO thin films were proposed based on a picture of spins in a carrier sea.

Ferroelectrical properties of W-doped lead zirconate titanate

Effects of the dopant W on the ferroelectric properties of Pb(Zr0.3Ti0.7)O3 (PZT) have been studied. The PZT and PZT doped with W (PZTW) thin films were deposited on LaNiO3 bottom electrodes by pulsed laser deposition at an oxygen partial pressure of 300mTorr. X-ray diffraction of PZTW films revealed pure perovskite structure with increased (110) orientation, compared to that of PZT films with high (l00) orientation. Both secondary ion mass spectrometry and x-ray photoelectron spectra tests confirmed the existence of W ions in the PZTW films. Although the PZTW film showed decreased remnant polarization, the saturation polarization is increased and the coercive field was greatly lowered. Moreover, the PZTW film demonstrated an improved fatigue behavior than PZT film. The W dopants are believed to contribute to the improvement of the ferroelectric behavior of PZT thin films. Ab initio calculation indicated that the formation energy of the oxygen vacancies in PZT lattice under Pb-deficient conditions can be ...

Laser cleaning of printed circuit boards

Abstract Laser cleaning of printed circuit boards (PCB) has been studied in this paper. It is demonstrated that laser cleaning is a powerful tool to remove resin contaminants from printed circuit boards. A Nd:YAG laser is used as a light source for laser cleaning. The beam profile of the YAG laser is reshaped and homogenized into a square beam with uniform energy distribution in the focal plane of the focusing lens by using an optical system. The printed circuit board surfaces before and after laser cleaning were inspected by an optical microscope, analysed by X-ray photoelectron spectroscopy and monitored by an acoustic wave detection method. The cleaning threshold is about 75xa0mJ/cm 2 and no damage is observed below 400xa0mJ/cm 2 .

Comparative study of effects of Mo and W dopants on the ferroelectric property of Pb(Zr0.3Ti0.7) thin films

Pb(Zr0.3Ti0.7)O3 thin films, respectively, doped with 1 mol% W and 1 mol% Mo have been deposited on the LaNiO3 bottom electrodes using pulse laser deposition. The x-ray diffraction analyses revealed that both dopants induced (1 1 0) orientation of the perovskite structures. Compared with the undoped PZT films, the doped PZT films showed smoother and denser surfaces. The XPS measurements indicated that W possessed a valence state of +6 in the PZTW films, but Mo showed mixed valence states of +4 and +6. The hysteresis loops and fatigue results of the undoped, the W-doped (PZTW) and the Mo-doped PZT (PZTM) films were obtained. While both the two doped films revealed better fatigue behaviour than undoped PZT, the PZTW film had a slow fatigue rate in comparison with the PZTM film, which is consistent with our previous theoretical predictions.

Characterization of La-doped (Ba0.85 Sn0.15)TiO3 thin films grown by pulsed laser deposition

In the present study, 1 mol.% La-doped Ba(Ti0.85Sn0.15)O3 (BLaTS) thin films have been deposited on LaNiO3 (LNO)/SiO2 /Si substrates by PLD. X-ray diffraction analyses revealed that the films grow with a highly (h00) textured orientation. Higher crystallization quality was obtained at higher deposition temperatures. FE-SEM cross-sectional images and the SIMS test both confirm the sharp interface between as-deposited BLaTS thin films and the bottom LNO layers. The XPS measurement results indicated that La showed a pure +3 valence. The lower loss tangent in the low frequency range is attributed to the reduction in oxygen vacancies caused by La doping. The pyroelectric results showed that BLaTS thin films are suitable candidates for thermal applications.