Abstract
The phase-transition dynamics of isopropanol (C3H8O) films with thicknesses on the order of 100 nm deposited on silicon wafers are investigated. A Nd : YAG nanosecond laser pulse is used to heat the substrate. Due to heat transfer, the fluid adjacent to the interface evaporates and the film on top is ejected as an intact liquid layer. The phase transition and the ejection process are monitored by reflectometry with a temporal resolution of about 200 ps and a spatial sensitivity on the nanometre-scale in the direction perpendicular to the substrate. We demonstrate that this approach allows us to determine the generated pressures, the achievable superheating and the relevant timescales of the process and as a consequence provides insights in the nature of the very early stages of the phase transition.
Highlights
Phase transitions of liquids in contact with a laser-heated solid surface are of fundamental importance for a variety of applications, such as Steam Laser Cleaning of nano-particles from sensitive surfaces [1, 2], laser desorption mass spectrometry [3] and laser surgery [4, 5]
The pulse is detected with a trigger diode and in conjunction with the reflectometer curve the film thickness in the moment of the phase transition can be determined with an accuracy of about 1 nm
The oscillations on the nanosecond timescale are caused by interference between the substrate surface and the intact liquid layer, which is ejected because of the phase transition
Summary
Phase transitions of liquids in contact with a laser-heated solid surface are of fundamental importance for a variety of applications, such as Steam Laser Cleaning of nano-particles from sensitive surfaces [1, 2], laser desorption mass spectrometry [3] and laser surgery [4, 5]. The dynamics of the phase transition are monitored by measuring the reflected intensity from an Ar+-cw-laser (λ = 488 nm, PAr+ = 500 mW) with a temporally highly resolving photo diode (rise time 200 ps).
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