Tag Archives: The Optical Society

Chinese scientists develop a novel 3D fabrication technique for bio-inspired hierarchical structures

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An April 14, 2016 news item on phys.org describes a new 3D fabrication technique devised by Chinese scientists,

Nature is no doubt the world’s best biological engineer, whose simple, exquisite but powerful designs have inspired scientists and engineers to tackle the challenges of technologies for centuries. Scientists recently mimicked the surface structure of a moth’s eye, a unique structure with an antireflective property, to develop a highly light-absorbent graphene material. This is breakthrough [sic] in solar cell technology. Rice leaves and butterfly wings also have unique self-cleaning surface characteristics, which inspire scientists to develop novel materials resistant to biofouling. The bio-inspired periodic multi-scale structures, called hierarchical structures, have recently caught broad attention among scientists in various applications such as solar cells, Light-emitting diodes (LEDs), biomaterials and anti-bacterial surfaces.

An April 14, 2016 Optical Society of American news release (also on EurekAlert), which originated the news item, provides more detail,

Although a number of techniques for fabricating bio-inspired hierarchical structures already exist, most conventional methods either involve complicated processes or are highly time-consuming and low cost-efficiency for industrial applications. Now, a team of researchers from Changchun University of Science and Technology, China, have developed a novel method for the rapid and maskless fabrication of bio-inspired hierarchical structures, using a technique called laser interference lithography.

Specifically, the researchers use the interference pattern of three-and four-beam lasers to fabricate ordered multi-scale surface structures on silicon substrates, with the pattern of hierarchical structures controllable by adjusting the parameters of incident light. In accordance with the theoretical and computer analysis, the researchers have experimentally demonstrated the novel technique’s potential in large-area, low-cost and high-volume 3D fabrication of micro and nanostructures. …

“We presented a flexible and direct method for fabricating ordered multi-scale 3D structures using three- and four-beam interference lithography,” said Zuobin Wang, the primary author and a professor of International Research Centre for Nano Handling and Manufacturing of China at the Changchun University of Science and Technology, China. “Compared with other patterning technologies, our method is simple and efficient in terms of obtaining bio-inspired hierarchical structures.”

Wang mentioned that for certain complicated surface structures, conventional techniques such as electron beam lithography may take several hours or a day to fabricate the pattern, while the laser interference approach only takes several minutes to generate the structure, which makes the technique suitable for high-volume industrial production.

“Laser interference lithography is a maskless patterning technique that uses the interference patterns generated from two or several coherent laser beams to fabricate micro and nanometer periodic patterns over large areas,” Wang said. Different from conventional patterning techniques like electron beam lithography, the laser interference technique enables fabricating the entire substrate surface with one single exposure or one-step lithography.

For example, in Wang’s experiment, the one-dimension multi-scale structure, that is, one-dimension oriented arrangement with the sinusoidal grooves covered with periodic line-like structures was fabricated by exposing the silicon substrate to three or four interfered beams for one time. The resultant surface pattern, though arranged in one direction, has three-dimension spatial structure. To obtain more complicated structures such as two-dimension oriented multi-scale structures, the researchers simply rotated the substrate by 90 degrees in the plane and applied second laser exposure to the surface.

“Laser interference lithography is capable of fabricating homogeneous micro and nanometer structured patterns over areas more than one square meter, which is either impossible or highly time or cost consuming for conventional techniques,” Wang said. These features make laser interference lithography superior to other techniques in terms of efficiency and high-volume production.

According to Wang, their experimental process is simple: a high power laser beam was split into three or four equal beams, which then were directed by mirrors to generate interference patterns to fabricate the surface structures. The laser parameters such as incident angle and azimuthal angle of each beam were adjusted by beam splitters and mirror positions. Other optical devices such as quarter-wave plates and polarizers were used to select the polarization mode and control the energy of laser beams.

“The laser beam parameters are selected according to the desired surface structure and corresponding interference energy distribution calculated from theoretical simulation. In other words, the shapes or patterns of hierarchical structures in our method are controllable by adjusting the parameters of each incident beams,” Wang noted.

According to Wang, the proposed technique could be used to fabricate optical or medical devices such as solar cells, antireflective coatings, self-cleaning and antibacterial surfaces and long-life artificial hip joints.

The researchers’ next step is to develop functional surface structures with controllable wettability, adhesion and reflectivity properties for optical, medical and mechanical applications.

Here’s a link to and a citation for the paper,

Bio-inspired hierarchical patterning of silicon by laser interference lithography by Yaowei Hu, Zuobin Wang, Zhankun Weng, Miao Yu, and Dapeng Wang. Applied Optics Vol. 55, Issue 12, pp. 3226-3232 (2016) doi: 10.1364/AO.55.003226

I believe this paper is behind a paywall.

The researchers have provided this image as an illustration of their concept,

Caption: This is a Scanning Electron Microscope (SEM) image of a moth eye. Credit: Zuobin Wang/Changchun University of Science and Technology, China


Caption: This is a Scanning Electron Microscope (SEM) image of a moth eye. Credit: Zuobin Wang/Changchun University of Science and Technology, China

From Australia: a recipe for baking lenses

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Here’s the recipe from an April 24, 2014 Optical Society news release on EurekAlert,

All that’s needed is an oven, a microscope glass slide and a common, gel-like silicone polymer called polydimethylsiloxane (PDMS). First, drop a small amount of PDMS onto the slide. Then bake it at 70 degrees Celsius to harden it, creating a base. Then, drop another dollop of PDMS onto the base and flip the slide over. Gravity pulls the new droplet down into a parabolic shape. Bake the droplet again to solidify the lens. More drops can then be added to hone the shape of the lens that also greatly increases the imaging quality of the lens. “It’s a low cost and easy lens-making recipe,” Lee [ Steve Lee from the Research School of Engineering at Australian National University] says.

I’m still marveling over this image,

Caption: This photo shows a single droplet lens suspended on a fingertip. Credit: Stuart Hay. Courtesy: The Optical Society

Caption: This photo shows a single droplet lens suspended on a fingertip. Credit: Stuart Hay. Courtesy: The Optical Society

For anyone who doesn’t know much about producing lenses and why these baked droplets could improve lives, the Optical Society news release provides some insight,

A droplet of clear liquid can bend light, acting as a lens. Now, by exploiting this well-known phenomenon, researchers have developed a new process to create inexpensive high quality lenses that will cost less than a penny apiece.

Because they’re so inexpensive, the lenses can be used in a variety of applications, including tools to detect diseases in the field, scientific research in the lab and optical lenses and microscopes for education in classrooms.

“What I’m really excited about is that it opens up lens fabrication technology,” says Steve Lee from the Research School of Engineering at Australian National University (ANU) …

…

Many conventional lenses are made the same way lenses have been made since the days of Isaac Newton—by grinding and polishing a flat disk of glass into a particular curved shape. Others are made with more modern methods, such as pouring gel-like materials molds. But both approaches can be expensive and complex, Lee says. With the new method, the researchers harvest solid lenses of varying focal lengths by hanging and curing droplets of a gel-like material—a simple and inexpensive approach that avoids costly or complicated machinery.

“What I did was to systematically fine-tune the curvature that’s formed by a simple droplet with the help of gravity, and without any molds,” he explains.

Although people have long recognized that a droplet can act as a lens, no one tried to see how good a lens it could be. Now, the team has developed a process that pushes this concept to its limits, Lee says.

…

The researchers made lenses about a few millimeters thick with a magnification power of 160 times and a resolution of about 4 microns (millionths of a meter)—two times lower in optical resolution than many commercial microscopes, but more than three orders of magnitude lower in cost. “We’re quite surprised at the magnification enhancement using such a simple process,” he notes.

An April 24, 2014 Australian National University (ANU) news release on EurekAlert adds more details to the story,

The lenses are made by using the natural shape of liquid droplets.

“We put a droplet of polymer onto a microscope cover slip and then invert it. Then we let gravity do the work, to pull it into the perfect curvature,” Dr Lee said.

“By successively adding small amounts of fluid to the droplet, we discovered that we can reach a magnifying power of up to 160 times with an imaging resolution of four micrometers.”

The polymer, polydimethylsiloxane (PDMS), is the same as that used for contact lenses, and it won’t break or scratch.

“It would be perfect for the third world. All you need is a fine tipped tool, a cover slip, some polymer and an oven,” Dr Lee said.

The first droplet lens was made by accident. [emphasis mine]

“I nearly threw them away. [emphasis mine] I happened to mention them to my colleague Tri Phan, and he got very excited,” Dr Lee said.

“So then I decided to try to find the optimum shape, to see how far I could go. When I saw the first images of yeast cells I was like, ‘Wow!'”

Dr Lee and his team worked with Dr Phan to design a lightweight 3D-printable frame to hold the lens, along with a couple of miniature LED lights for illumination, and a coin battery.

The technology taps into the current citizen science revolution [emphasis mine], which is rapidly transforming owners of smart phones into potential scientists. There are also exciting possibilities for remote medical diagnosis.

Dr Phan said the tiny microscope has a wide range of potential uses, particularly if coupled with the right smartphone apps.

“This is a whole new era of miniaturisation and portability – image analysis software could instantly transform most smartphones into sophisticated mobile laboratories,” Dr Phan said.

“I am most able to see the potential for this device in the practice of medicine, although I am sure specialists in other fields will immediately see its value for them.”

Dr Lee said the low-cost lens had already attracted interest from a German group interested in using disposable lenses for tele-dermatology.

“There are also possibilities for farmers,” he said. “They can photograph fungus or insects on their crops, upload the pictures to the internet where a specialist can identify if they are a problem or not.”

That Lee created his first droplet by accident and almost threw it away echoes many, many other science stories. In addition to that age old science story, I love the simplicity of the idea, the reference to Isaac Newton, and the inclusion of citizen science.

Here’s a link to and a citation for the paper,

Fabricating low cost and high performance elastomer lenses using hanging droplets by W. M. Lee, A. Upadhya, P. J. Reece, and Tri Giang Phan. Biomedical Optics Express, Vol. 5, Issue 5, pp. 1626-1635 (2014) http://dx.doi.org/10.1364/BOE.5.001626

This paper is open access.

I wish Lee and his team great success in making this technology available, assuming that it lives up to its promise.