Imagine how long it would have taken to produce vinyl record albums if, instead of pressing them from master molds, the grooves had to be etched into each individual LP? Well, that's pretty much been the case when it comes to creating devices from porous nanomaterials - the microscopic patterns necessary for their functioning have had to be applied to each individual nanodevice, requiring considerable time and a perfect environment. Now, however, researchers from Nashville's Vanderbilt University have developed a system for quickly stamping out whole batches of the devices.
Porous nanomaterials, first of all, are a class of rigid materials that are full of microscopic holes. Substances such as gold, silicon, alumina, and titanium oxide all come in nanoporous forms. The holes give the materials unique optical, electrical, chemical and mechanical properties, making them useful in applications such as drug delivery, chemical and biological sensors, solar cells and battery electrodes.
Typically, the manufacturing of devices from these materials must be performed in a clean room. The nanoporous surface is painted with a coating known as a resist, then exposed to ultraviolet light or scanned with an electron beam to create the necessary pattern. The material is then subjected to a series of chemical treatments, either to engrave the surface, or to apply new material.
A team led by Vanderbilt associate professor of electrical engineering Sharon M. Weiss has invented a new production system, that is much quicker, easier and less costly.
While they still start with the traditional method, they use it to create a master stamp. That stamp can then be used to press out additional copies in less than a minute each, at room temperature and atmospheric pressure, regardless of their complexity. The process is called direct imprinting of porous substrates, or DIPS.
The team's first creation was a biosensor, that can identify organic molecules such as DNA, proteins and viruses. It features a grating made from porous silicon, that can be treated so that a target molecule will stick to it. If that molecule is present in a liquid sample, then it will cause laser light shined on the grating to diffract in a specific pattern.
They have since used DIPS to create highly-sensitive chemical sensors, and to produce shaped microparticles - this is done by using the stamp to cut right through the porous nanomaterial, like a cookie cutter. Microparticles made from porous silicon could find use as anodes in lithium-ion batteries, which would have a higher capacity than conventional li-ions, but not much more weight.
Weiss' team has reportedly already used some stamps over 20 times, with no signs of deterioration. The smallest pattern they have made so far measured in the tens of nanometers, or about the size of a fatty acid molecule.
The research was recently published in the journal Nano Letters.