Nanoparticle removal with a pulsed laser: thermoelastic transient surface acceleration simulations for analyzing edge effects

Abstract

Damage-free removal of nanoparticles and thin films from substrates is a critical requirement in micro- and nano-manufacturing. In laser cleaning, particles are removed by application of inertial forces at the particles attached to a substrate by means of surface acceleration. While the technique is promising, experimental results indicate that damage can occur in the process due to high levels of fluence. Potential damage mechanisms include surface breakage, interferometric interactions due to bumps/surface features, diffraction related focusing, micro-cracks, and peeling of top layers. To reduce and/or eliminate damage risk by avoiding excessive heat deposition, the absolute acceleration requirement must be well understood and accurately modeled. In the current work, a set of transient simulations for the thermoelastic response has been conducted to determine the surface acceleration vector and temperature elevation under a nanosecond pulsed-laser. It is known that in nanoparticle removal rolling motion-based removal requires the least amount of acceleration. The distribution of the acceleration field on the surface of a half-space is obtained. The magnitude of a jump in the radial acceleration component at the boundary of the irradiated area and the dark zone is determined, and its use in nanoparticle removal has been discussed and demonstrated. Preliminary experimental data for a novel removal method based on this acceleration localization is presented and discussed.

Keywords:

• Laser cleaning
• particle removal
• nanoparticles
• laser ultrasonics
• laser cleaning
• micromanufacturing
• nano-manufacturing.