Manufacturing Bits: Jan. 31

Fiber-imprint patterning; measuring nanofibers.


Fiber-imprint patterning
The École polytechnique fédérale de Lausanne (EPFL)–a research institute/university in Lausanne, Switzerland–has put a new twist in nano-imprint patterning technology. It has devised a way to imprint tiny or nano-metric patterns on hollow polymer fiber.

Using a technique called thermal drawing, tiny patterns can be printed on both the inside and the outside of a fiber. Patterned fiber could be used to create certain optical effects on a fiber. In another application, the technology could make fiber more water resistant. In addition, patterned fibers could be used in nerve regeneration. Or it could be used to make smart bandages.

Researchers at EPFL have come up with a way of imprinting nanometric patterns on the inside and outside of polymer fibers. (Source: EPFL)

Researchers at EPFL have come up with a way of imprinting nanometric patterns on the inside and outside of polymer fibers. (Source: EPFL)

To make the patterns, EPFL uses a thermal drawing technology. This involves engraving or imprinting millimeter-sized patterns on a so-called “preform.” Based on a polymer, the preform is a macroscopic version of the targeted fiber.

In the flow, the imprinted preform is heated. Then, the preform is stretched into a long and thin fiber. Following those steps, the preform is allowed to harden again. Stretching causes the pattern to shrink. The problem? The pattern does not remain intact below the micrometer scale due to surface tension, according to EPFL.

To solve the problem, EPFL takes the preform. It sandwiches the preform in a sacrificial polymer material, which protects the pattern during the stretching process. Using this technique, research can pattern polymer fibers at lengths in the kilometer or longer range. Feature sizes down to a few hundred of nanometers have been demonstrated.

“We have achieved 300-nanometer patterns, but we could easily make them as small as several tens of nanometers,” said Fabien Sorin, a researcher at EPFL. “This technique enables (us) to achieve textures with feature sizes two orders of magnitude smaller than previously reported. It could be applied to kilometers of fibers at a highly reasonable cost.”

Applications for the technology include bioengineering, regenerative scaffolds, microfluidics, and smart textiles, according to EPFL. “Fibers that are rendered water-resistant by the pattern could be used to make clothes. Or we could give the fibers special optical effects for design or detection purposes. There is also much to be done with the many new microfluidic systems out there,” Sorin said.

Measuring nanofibers
The Joint Quantum Institute (JQI), the Army Research Laboratory (ARL) and the Naval Research Laboratory (NRL) have developed a way to measures how light propagates through a nanofiber.

Fiber optics are commonly used in communications systems. They enable data to travel at near the speed of light without loss.

In the lab, researchers have taken optical fibers and stretched them into tiny tapers, called nanofibers. Nanofibers could be used in the field of quantum optics and quantum information. Basically, quantum optics is the study of how photons interact with atoms and molecules. In simple terms, quantum information is data processing using a quantum computer.

Researchers, meanwhile, injected light into the nanofibers and found it still makes its way from point “A” to “B.” The nanofibers distort the light waves. Multiple patterns emerge from the interfering light shapes.

Light also travels outside the fiber’s exterior surface. This exterior light is called the evanescent field. The challenge is to fine-tune the evanescent light fields and measure them.

To characterize the evanescent light fields, JQI, ARL and NRL have devised a specialized probe or microfiber. This allows researchers to determine the nanofiber’s thickness to less than the width of an atom.

The goal is to make measurements of the interference patterns of the nanofiber structure itself. The nanofiber sits on a moving stage. Then, the structure crosses a probe at an oblique angle. Following those events, a tiny fraction of nanofiber light evanescently enters the second fiber and travels to a detector. All told, the probe reveals the behavior of all propagating modes.

Nanofiber evanescent light (red) entering probe fiber (larger glass cylinder). (Credit: E. Edwards)

Nanofiber evanescent light (red) entering probe fiber (larger glass cylinder). (Credit: E. Edwards)

“We are actually seeing the different light modes mix together and that sets the limits on determining the fiber waist—in this case sub-angstrom,” said Eliot Fenton, who is working on the project. “With our new method, we can avoid using SEM, which destroys the fiber with imaging chemicals and heating. By directly and sensitively measuring the interference (beating) of light without destroying the fiber, we can know exactly the kind of electromagnetic field that we would apply to atoms.”

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