Authors: Y-C Lee, C-H Chuang, D-B Wang, C-P Liu and F-B Hsiao
Affilation: National Cheng Kung University, Taiwan
Pages: 680 - 683
Keywords: laser assisted direct imprinting (LADI), nano-imprinting, imprinting mechanism, pulsed laser heating, elastodynamics
Laser Assisted Direct Imprinting (LADI) is an efficient and direct way for fabricating nanostructures. In short, a quartz mold with nano-features is first pressed against a sample. Upon radiating a short laser pulse on the sample surface through the quartz mold, near-surface material is molten momentarily. The pre-loaded contact pressure will then transfer the nanostructures onto the sample. The LADI has some advantages such as simplicity and efficiency since no further chemical etching process is needed. Apparently, the underlying mechanism of LADI is fairy complicated and is still not understood. In this study, the mechanism of LADI is investigated theoretically and experimentally. First of all, a numerical simulation of the pulsed laser heating is developed based on the laser-material interaction and a 1D thermal analysis. For given laser characteristics and material properties, the complete history of temperature and melting depth during the laser heating is obtained. Secondly, the imprinting process is modeled precisely based as elastodynamics and wave motion. From the analysis, the imprinting velocity of quartz surface as a function of time is obtained. By conjunction of the pulsed laser heating simulation and the surface movement equation, the relationship between the pre-loaded pressure and the imprinting depth can be quantitative determined. It is found that at lower contact pressure, the imprinting depth is almost linear proportional to the contact pressure, while at higher contact pressure is most determined by the laser fluence. Some preliminary experimental data are obtained which indicate similar trend as predicated by the proposed theory. This new theoretical model not only provides a good insight to the fundamental mechanism of LADI but also a useful tool for quantitative control or optimization of LADI processes.