Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Water Droplets direct Self-assembly Process in Thin-film Materials

You can think of it as origami – very high-tech origami.

Researchers at the University of Illinois have developed a technique for fabricating three-dimensional, single-crystalline silicon structures from thin films by coupling photolithography and a self-folding process driven by capillary interactions.

The films, only a few microns thick, offer mechanical bendability that is not possible with thicker pieces of the same material.

“This is a completely different approach to making three-dimensional structures,” said Ralph G. Nuzzo, the G. L. Clark Professor of Chemistry at Illinois. “We are opening a new window into what can be done in self-assembly processes.”

Nuzzo is corresponding author of a paper accepted for publication in the Proceedings of the National Academy of Sciences. The paper is to be posted on the journal’s Early Edition Web site the week of November 23.

As a demonstration of the new capillary-driven, self-assembly process, Nuzzo and colleagues constructed spherical and cylindrical shaped silicon solar cells and evaluated their performance.

The researchers also developed a predictive model that takes into account the type of thin film to be used, the film’s mechanical properties and the desired structural shape.

“The model identifies the critical conditions for self-folding of different geometric shapes,” said mechanical science and engineering professor K. Jimmy Hsia. “Using the model, we can improve the folding process, select the best material to achieve certain goals, and predict how the structure will behave for a given material, thickness and shape.”

To fabricate their free-standing solar cells, the researchers began by using photolithography to define the desired geometric shape on a thin film of single-crystalline silicon, which was mounted on a thicker, insulated silicon wafer. Next, they removed the exposed silicon with etchant, undercut the remaining silicon foil with acid, and released the foil from the wafer. Then they placed a tiny drop of water at the center of the foil pattern.

As the water evaporated, capillary forces pulled the edges of the foil together, causing the foil to wrap around the water droplet.

To retain the desired shape after the water had fully evaporated, the researchers placed a tiny piece of glass, coated with an adhesive, at the center of the foil pattern. The glass “froze” the three-dimensional structure in place, once it had reached the desired folded state.

“The resulting photovoltaic structures, not yet optimized for electrical performance, offer a promising approach for efficiently harvesting solar energy with thin films,” said Jennifer A. Lewis, the Thurnauer Professor of Materials Science and Engineering and director of the university’s Frederick Seitz Materials Research Laboratory.

Unlike conventional, flat solar cells, the curved, three-dimensional structures also serve as passive tracking optics by absorbing light from nearly all directions.

“We can look forward from this benchmark demonstration to photovoltaic structures made from thin films that behave as though they are optically dense, and much more efficient,” Lewis said.

The new self-assembly process can be applied to a variety of thin-film materials, not just silicon, the researchers noted in their paper.

With Nuzzo, Hsia and Lewis, co-authors of the paper are graduate students Xiaoying Guo and Huan Li, and postdoctoral researchers Bok Yeop Ahn and Eric B. Douss.

Hsia is associate dean of the Graduate College and is affiliated with the university’s Micro and Nanotechnology Laboratory.

Lewis is affiliated with the department of chemical and biomolecular engineering and the Micro and Nanotechnology Laboratory.

Nuzzo is affiliated with the Institute for Genomic Biology, the Micro and Nanotechnology Laboratory, the materials science and engineering department, and the Frederick Seitz Materials Research Laboratory.

The U.S. Defense Advanced Research Projects Agency, the Department of Energy and the National Science Foundation funded the work.

James E. Kloeppel | University of Illinois
Further information:

More articles from Physics and Astronomy:

nachricht Sharpening the X-ray view of the nanocosm
23.03.2018 | Changchun Institute of Optics, Fine Mechanics and Physics

nachricht Drug or duplicate?
23.03.2018 | Fraunhofer-Institut für Angewandte Festkörperphysik IAF

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Space observation with radar to secure Germany's space infrastructure

Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.

The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

New solar solutions for sustainable buildings and cities

23.03.2018 | Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

Latest News

For graphite pellets, just add elbow grease

23.03.2018 | Materials Sciences

Unique communication strategy discovered in stem cell pathway controlling plant growth

23.03.2018 | Agricultural and Forestry Science

Sharpening the X-ray view of the nanocosm

23.03.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>