Guan Li

Characteristics of Plasma Shock Waves Generated in the Pulsed Laser Ablation Process

We modify the Sedov theory to describe plasma shock waves generated in a pulsed laser ablating process. We also study the propagation characteristics of plasma shock waves during the preparation process of functional thin films deposited by a pulsed laser. In particular, we discuss in detail the temporal behaviour of energy causing the difference of the propagation characteristics between the plasma shock wave and the ideal shock wave in the point explosion model. Under the same experimental conditions, the theoretical results calculated with our modified Sedov theory are in good agreement with the existing experimental data.

A Fractal Model for the Effective Thermal Conductivity of Granular Flow with Non-uniform Particles*

The equipartition of energy applied in binary mixture of granular flow is extended to granular flow with non-uniform particles. Based on the fractal characteristic of granular flow with non-uniform particles as well as energy equipartition, a fractal velocity distribution function and a fractal model of effective thermal conductivity are derived. Thermal conduction resulted from motions of particles in the granular flow, as well as the effect of fractal dimension on effective thermal conductivity, is discussed.

Monte Carlo Simulation of Growth of Thin Film Prepared by Pulsed Laser

We use the Monte Carlo simulation method to perform the early growth stage of thin film prepared by pulsed laser deposition. We focus on the number of point defects on the substrate surface varying with the energy density of laser and substrate temperature. The results show that the laser energy and the substrate temperature strongly affect the morphology and size of the growth islands and the deposition rate of thin film. Our results are in good agreement with the related experimental results.

A New Synthetical Model of High-Power Pulsed Laser Ablation

We develop a new synthetical model of high-power pulsed laser ablation, which considers the dynamic absorptance, vaporization, and plasma shielding. And the corresponding heat conduction equations with the initial and boundary conditions are given. The numerical solutions are obtained under the reasonable technical parameter conditions by taking YBa2Cu3O7 target for example. The space-dependence and time-dependence of temperature in target at a certain laser fluence are presented, then, the transmitted intensity through plasma plume, space-dependence of temperature and ablation rate for different laser fluences are significantly analyzed. As a result, the satisfactorily good agreement between our numerical results and experimental results indicates that the influences of the dynamic absorptance, vaporization, and plasma shielding cannot be neglected. Taking all the three mechanisms above simultaneously into account for the first time, we cause the present model to be more practical.

Effect of Incident Intensity on Films Growth in Pulsed Laser Deposition

Incident intensity, defined by the amount of particles deposited per pulse, is an important parameter in the film growth process of pulsed laser deposition (PLD). Different from previous models, we investigate the irreversible and reversible growth processes by using a kinetic Monte Carlo method and find that island density and film morphology strongly depend on pulse intensity. At higher pulse intensities, lots of adatoms instantaneously diffuse on the substrate surface, and then nucleation easily occurs between the moving adatoms resulting in more smaller-size islands. In contrast, at the lower pulse intensities, nucleation event occurs preferentially between the single adatom and existing islands rather than forming new islands, and therefore the average island size becomes larger in this case. Additionally, our results show that substrate temperature plays an important role in film growth. In particular, it can determine the films shape and weaken the effect of pulse intensity on film growth at the lower temperatures by controlling the mobility rate of atoms. Our results can match the related theoretical and experimental results.