Chen Jz

Nucleation and growth of nanoparticles during pulsed laser deposition in an ambient gas

We present a method to determine where the nanoparticles nucleate and grow during pulsed laser deposition in an ambient gas. Briefly, nanocrystalline Si films are systemically deposited on the substrates located at a distance from the plasma and placed in horizontal direction; meanwhile an external electric field is introduced perpendicularly to the plume. Based on the transportation dynamics of Si nanoparticles corresponding to different electric fields, the lateral nucleation range of 0.1 to 33.8xa0mm is determined for Si nanoparticles deposited in 10xa0Pa Ar gas at a laser fluence of 4xa0J/cm 2 . Further simulation of the mass and area density of Si nanoparticles demonstrates that both nucleation and growth probabilities in nucleation region are approximately Gauss-dependent of the lateral distance.

Enhancement effects of flat-mirror reflection on plasma radiation

Laser-induced breakdown spectroscopy quality can be improved by using a nanosecond Nd:YAG laser pulse to excite soil samples. To investigate how flat-mirror reflection affects the radiation characteristics of laser-induced plasma, emission spectra of sample elements were recorded using a grating spectrometer and photoelectric detection system. Placing a planar mirror vertically on the sample surface (10 mm mirror to plasma-center axis distance) for flat-mirror reflection increased spectral line intensities of Mg, Al, Fe, and Ba by 93.06%, 159.63%, 93.43%, and 94.61%, respectively. Signal-to-noise ratio increased by 17.56%, 40.21%, 31.29%, and 30%. The radiation enhancement mechanism was clarified using measured plasma parameters.

Effects of laser pulse sequence on laser-induced soil plasma emission

In this study, we investigated the effects of a sequence of laser pulses on the plasma emission intensity, plasma temperature, and electron density of laser-induced soil plasma. The experimental results indicate that the plasma radiation was gradually strengthened as the laser-pulse sequence progressed. The theoretical results show that the spectral line intensity and spectral signal-to-background ratio of the elements Fe, Mn, K, and Ti were strongest for plasma from the sixth laser pulse. These data suggest that repeatedly ablating the same surface position of a soil sample with a sequence of laser pulses can enhance the laser-induced breakdown spectroscopy signal.

The improved method to determine the nucleation region of Si nanoparticles formed during pulsed laser ablation

The determination of the nucleation region for Si nanoparticles synthesized by pulsed laser ablation was helpful to find proper parameter to obtain the high quality nanocrystalline silicon (nc-Si) thin films. A XeCl excimer laser was used to ablate high-resistively single crystalline Si target under a deposition pressure of 10 Pa. Glass or single crystalline (111) Si substrates, in parallel with the axial direction of silicon target, were located at a distance of 2.0 cm under the plasma to collect a series of nc-Si thin films. The Raman spectra, X-ray diffraction spectra (XRD) and Scanning electron microscopy (SEM) images show that Si nanoparticles deposited in substrates were only formed in the range 0.3~3.0cm away from the target. In this area, the size of the nanoparticles increased firstly and then reduced, meanwhile, the distributions for the size of the nanoparticles were also changed. According to the character of the beginning and the terminus of nucleation area, combining with the Horizontal Projectile Motion, the range and position of nucleation area were determination.