Thermocapillary Multidewetting of Thin Films

Abstract

Thermocapillary dewetting of liquids and molten films has recently emerged as a viable alternative to conventional microprocessing methods. As this thermal gradient-induced mechanism is universal, it can be applied to any material. This work explores the sequential dewetting of materials with varying melting points, including polymers and metals, to create aligned morphologies. The variation in melting point allows for the dewetting of single layers at a time or mobility-limited simultaneous dewetting. As a result, a variety of multimaterial structures can be produced with built-in alignment, such as arrays of concentric circles, lines with periodic segmentation, or islands on holes. This approach employs photothermal methods to induce the necessary thermal gradient, manipulating several variables in order to influence the consequent structures. Adjusting laser power and light intensity allows for the control of temperature for selective dewetting of films; altering beam size and exposure time affects the extent of dewetting in terms of diameter size; overlap effects and simultaneous dewetting can result in complex architectures. This controlled writing of patterns also presents a technique to create both masks at low temperatures for conductive multilayers as well as templates for electrospray deposition.

Self-limiting electrospray deposition on polymer templates

“…Through local softening, samples that are solid both before and after excitation lock in the effects of the exposure, such as dewetting 22 – 25 and/or zone annealing 26 – 28 . We have also shown that FLaSk has the ability to selectively pattern multilayers of material 29 . For the purposes of templating, FLaSk is developer-free and grayscale allowing for partial to complete dewetting in submicron feature sizes followed by immediate spray.…”

“…The microhole array on PS thin films was prepared by FLaSk dewetting as described previously 29 . Briefly, we sputtered a 35 nm gold film onto a 1-mm thick glass substrate using an Anatech Ltd Hummer X gold sputter.…”

“…For the purposes of templating, FLaSk is developer-free and grayscale allowing for partial to complete dewetting in submicron feature sizes followed by immediate spray. The size of the dewetted pattern has been determined to be dependent only on laser power and numerical aperture (NA) and the material's molecular weight 24,29 . FLaSk is also compatible with low T g materials, meaning that the templating process can be performed at low temperatures.…”

Self-Limiting Electrospray Deposition on Polymer Templates

“…This temperaturedependent patterning allows us to forego traditional lithographic patterning and etching techniques to pattern surfaces. Additionally, patterns formed via FLaSk dewetting are not limited to the masks used in conventional photolithography; translation of the laser stage and direct manipulation of laser parameters such as power and spot size allow precise control of 2D template size, with individual feature resolutions as small as 1.35 μm 22 . The size of the dewetted pattern has been determined to be dependent only on laser power and material molecular weight 22,23 .…”

“…Additionally, patterns formed via FLaSk dewetting are not limited to the masks used in conventional photolithography; translation of the laser stage and direct manipulation of laser parameters such as power and spot size allow precise control of 2D template size, with individual feature resolutions as small as 1.35 μm 22 . The size of the dewetted pattern has been determined to be dependent only on laser power and material molecular weight 22,23 . FLaSk is also compatible with low Tg materials, meaning that the templating process can be performed at low temperatures.…”