Influence of laser beam on transport dynamics of Si nanoparticles by laser ablation

Abstract

To investigate nucleation area and transport dynamics of Si nanoparticles, nanocrystalline silicon films were prepared by pulsed laser ablation. Subsequently, the additional laser beam as energy source was introduced, which crossed vertically the plasma plume from the top down in front of the target at a distance of 0.5 cm under same experiment condition. In this region, due to collision between the photon and the plasma plume, the transport of Si nanoparticles was impacted by the cross-laser beam. The Raman and x-ray diffraction spectra (XRD), scanning electron microscopy (SEM) images of the films showed that Si nanoparticles were formed in a certain range, and the average size of Si nanoparticles monotonically decreases with the increase of distance. Obviously, the range of Si nanoparticles deposited in substrates became narrower due to the influence of additional laser beam. Experimental results were analyzed in terms of the nucleation area model. 1.INTRODUCTIONThe synthesis and study of nanocrystalline silicon (nc-Si) films containing Si nanoparticles is of great interest for both photoelectric integration application and fundamental research [1] . Traditionally, nc-Si films have been produced by many kinds of techniques [2][3] . Pulsed laser ablation (PLA), one of methods preparing nc-Si films, has received more and more attention due to its unique advantages such as rapid thermogenic speed and small surface contaimination [4] . For nanosecond laser, to obtain Si nanoparticles in the film without post-annealing, PLA process is usually carried out in an inert gas with constant pressure [5] . The characteristics of synthesized particles largely depend on fabrication conditions such as the distance between an ablated target and a collecting substrate, the ambient gas, the pressure of the ambient gas, and so on. In order to optimize and control the synthesis process, detailed information on where and when the particles are formed in the ablation plume and how they are transported onto the substrate is required [6] .We systematically investigated the size dependence and distribution of Si nanoparticles prepared in a high-purity gas of He, Ar or Ne, and "nucleation area" model [7] was proposed to explain the experiment result. According to this model, the narrower "nucleation area" can induce the smaller and more uniform nanoparticles. Evidently, It is crucial to determine the range of "nucleation area", which is helpful for both the controlling of the grain size of Si nanoparticles and the understanding of PLA dynamics.In this letter, the nanocrystalline Si films were systemically deposited on glass or single crystalline (111) Si substrates located at a distance of 2.0 cm under the plasma. The relation of the average size and distribution of Si nanoparticles with the distance to target was studied. In order to determine accurately the range of nucleation area, the other laser [8] as energy source interacting with transport of Si nanoparticles was introduced. We analyzed theoretically the results of experiment, wh...

Angular Distribution of Damping Coefficient of Ablated Particle in Pure He, Ne, and Ar Gases

“…Moreover, the average sizes of nanoparticles in all the films prepared under the three gases are maximal at 0 • , namely, at the position facing the plume. Because the substrate is not heated, the nanoparticles are formed by undergoing gas phase nucleation [21]. After the pulse laser ablates the single crystalline Si target, ablation particles are ejected out to all directions, with velocities approximately satisfying the Maxwell velocity distribution [22], and then transported and deposited on the substrates.…”