Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses

TL;DR

This paper investigates how thermocapillary stresses influence the spontaneous formation of nanopillar arrays in ultrathin viscous films, providing analytic, numerical, and simulation insights that align with experimental observations.

Contribution

It reveals the critical role of thermocapillary forces in nanopillar formation, challenging previous phonon reflection explanations, and offers predictive models for pillar spacing and growth rate.

Findings

Thermocapillary forces are essential for nanopillar formation.

Predicted pillar spacings match experimental data.

Simulations estimate pillar growth rates for applications.

Abstract

Experiments by several groups during the past decade have shown that a molten polymer nanofilm subject to a large transverse thermal gradient undergoes spontaneous formation of periodic nanopillar arrays. The prevailing explanation is that coherent reflections of acoustic phonons within the film cause a periodic modulation of the radiation pressure which enhances pillar growth. By exploring a deformational instability of particular relevance to nanofilms, we demonstrate that thermocapillary forces play a crucial role in the formation process. Analytic and numerical predictions show good agreement with the pillar spacings obtained in experiment. Simulations of the interface equation further determine the rate of pillar growth of importance to technological applications.