Study On Plasma Shielding And Ablating Mechanism In The PLD Process

Pulsed laser deposition is one of the most attractive new techniques for the growth of thin films. In 1960's, pulsed laser deposition technique appeared after the ruby laser was produced, but developed slowly because of the limiting of laser. In 1987, high-Tc superconducting thin films were prepared in the Bell laboratory. From then on, the PLD technique attracted much more attention and developed quickly. The PLD technique has so many advantages, such as high pulsed laser energy density, similarity between target and prepared thin film components, the high deposition rate, and lower substrate temperature. In the past two decade years, varieties of functional thin films have been deposited by PLD technique. At the same time, the development of the relevant physics mechanism research of the PLD technique has flourished.This dissertation summarizes the systemic and integrated models of the PLD mechanism at present, including Singh-Narayan model, the Zhang-Li model, the Zhang-Guan model, and LSAW model.In this paper, we investigate deeply the physics mechanism of PLD technique and discuss in detail the separate regimes of the PLD process. The contents studied as follows:1. According to the theory of energy balance, we have studied systematically the process of the high power pulsed laser ablating target, and the dependence of the ablating surface position on the time is obtained. 2. By using the appropriate dynamic boundary conditions, we have solved the heat flow equation with heat generation term, and we have studied in detail the temperature distribution in the target before melting as well as after melting. The interface position of solid and liquid phase after melting is also obtained. The temperature distribution in the target after melting is given by analytical expressions. And then, we have obtained the results about the ablation of target Si. Finally, the comparison with related experiments indicates that the conclusions of the paper are in good agreement with the results of the experiments.3. We have systematically studied a theoretical model to analysis the ablation characteristics during the whole laser-target interaction process. The process of energy accumulation can be classified into two separate stages on the basis of the actual situation. By the numerical simulations, we obtain the results as follows:1) The plasma length increases with increasing the plasma temperature under the condition of the same incident energy density.2) Assuming that the value of the reflectivity for the laser emission is zero, the variation of the transmitted intensity has been distinguished into two regions: (i) the absolute transmitted region in which the laser instantaneous incident energy is absorbed absolutely, and (ii) the absorbing region in which the transmitted intensity decreases with increasing the plasma temperature.3) The ablation depths of sample exposed to 25 ns square excimer laser pulse for three most common wavelengths are in good agreement with the related experimental results.4) Due to the plasma shielding to the instantaneous incident energy lead to the effect of the ablation depth,the increment of the ablation depth decreases as the pulse number increase, at the same time, the value of increases as the number of laser pulses increases.