Synthetic membranes made with help from Mother Nature

Significance 

An artificial membrane, is a synthetically created membrane which is usually intended for separation purposes in laboratory or in industry. With recent technological advances, synthetic membranes are increasingly forming part of many microelectronic devices. In fact, they have become commonplace in a variety of microelectromechanical systems and microfluidic applications. For instance, they are used in pressure sensors, resonant sensors, thermal actuators, ion-sensitive field-effect transistors, micromirrors, and microfluidic pumps; all of which rely on membrane motion. In addition, exciting applications such as biomolecular analysis using nanopores formed within membranes and other biosensors rely on membranes as molecular gates and filters, often mimicking structures and processes found in nature. However, the construction of membranes with nanoscale thicknesses has been a challenge, especially for membranes intended to be interfaced with microscale elements like fluid channels, optical waveguides, or electronic circuitry. Robust silicon-nitride nanoscale membranes can be made using bulk micromachining through a silicon substrate; nonetheless, this process is best used for isolated membranes.

More readily integrated surface micromachining that attempts to stretch membranes over sacrificial regions has suffered from abrupt edges at interfaces between materials. In particular, these non-continuous boundaries, even when different by only nanometers, create stress and cracking in overlaid membranes. To address these challenges, Brigham Young University researchers Zach Walker, Tanner Wells, Kalliyan Lay and Professor Aaron Hawkins, in collaboration with Mohammad Julker Neyen Sampad and Professor Holger Schmidt at the University of California developed a novel method to create robust, nanoscale solid-state membranes using the natural shape of a liquid meniscus as a template. Their work is currently published in the research journal, Nanotechnology.

In their approach, a narrow, open channel was etched into a silicon substrate and then a photoresist polymer was introduced into the channel through spontaneous capillary action. The natural concave meniscus formed by the polymer was then covered by a thin chemical vapor deposited membrane. Lastly, the polymer was removed by sacrificial etching, leaving behind a suspended membrane.

In essence, the outlined design highlighted the robust nature of a membrane fabricated on a smooth surface formed by a natural meniscus. Such a meniscus can be created without an abrupt step at material interfaces. The researchers reported that by employing the reported technique, membranes were constructed for a variety of different channel widths, lengths and membrane thicknesses.

In summary, the study demonstrated the successful fabrication of thin silicon dioxide membranes on a natural meniscus formed by a liquid polymer, by way of spontaneous capillary effect. Remarkably, the fabrication process for designing membranes was proven to be robust and could create strong membranes that can be used for a variety of different applications. In a statement to Advances in Engineering, Professor Aaron Hawkins explained that the new technique enables a new class of micro and nano-scale devices with larger area membranes than previously thought possible.

Reference

Zach Walker, Tanner Wells, Kalliyan Lay, Mohammad Julker Neyen Sampad, Holger Schmidt, Aaron Hawkins. Solid-state membranes formed on natural menisci. Nanotechnology; volume 31 (2020) 445303 (6pp).

Go To Nanotechnology

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