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Research Activities:

1.   We have conducted systematic experimental investigation on the antireflection properties of bio-inspired antireflection coatings on both inorganic semiconductors (e.g., Si, GaAs, and GaSb) and transparent dielectrics (e.g., sol-gel glass and polymer). The structure-property relationship has been extensively studied.

2.   Three optical models, including a rigorous coupled-wave analysis (RCWA) model, a thin-film multilayer (TFM) model, and a finite-difference time-domain (FDTD) model, have been developed and implemented to simulate the specular optical reflection, diffraction, scattering, and transmission from periodic subwavelength antireflective structures.

3.   A roll-to-roll compatible doctor-blade coating technology for assembling large-area colloidal crystals for creating self-cleaning moth-eye antireflection coatings has been developed.

Educational Activities:

1.   I have developed and implemented two new experimental modules, including a templated fabrication of antireflection coatings and a fabrication and characterization of superhydrophobic coatings, in a graduate class (ECH 6937 – Material Self-Assembly Over All Length Scales) offered at the University of Florida during Spring 2009 and 2010 semesters.

2.   I have recruited three high school students (Ms. Grace Ooi, Mr. Patrick Terri, and Mr. Max Levy) to work in my lab on the antireflection coating project during the summers of 2008, 2009, and 2010).

3.   Four graduate and four undergraduate students have worked on the project.

4.   Three oral presentations have been made by the students at the AIChE annual meetings.

Findings:

1. We have successfully developed several inexpensive and scalable templating approaches for fabricating subwavelength-structured moth-eye antireflection coatings (ARCs) on a large variety of technologically important substrates, including Si (single-crystalline and multicrystalline), GaAs, GaSb, glass, and plastics.

2. We have demonstrated a novel doctor-blade-coating technology which is compatible with industrial-scale roll-to-roll fabrication for assembling large-area colloidal crystals. The resulting colloidal crystals can be used as structural templates for creating moth-eye ARCs. 

3. The templated moth-eye antireflection coatings exhibit much improved broadband antireflection properties than traditional quarter-wavelength dielectric coatings. Normal-incidence reflection of less than 2% has been achieved on silicon (both single-crystalline and multicrystalline), GaAs and GaSb substrates. Optical reflection of less than 0.5% for all optical wavelengths has been achieved on polymer and glass substrates.

4.   The moth-eye coating also exhibits superhydrophobic surface state once the aspect ratio of the nanopillars is higher than 10. We have demonstrated the self-cleaning function of these coatings by preventing bacterial contamination. This is important for developing self-cleaning ARCs for solar cells and many other optoelectronic devices.

5. The 3 theoretical models help better understanding of the optical diffraction from subwavelength gratings, as well as rational design of moth-eye antireflection coatings for different applications. We have shown that the RCWA and TFM models create almost equivalent results for subwavelenth-structured moth-eye gratings.

Contributions within Discipline:

1. The broadband antireflection coatings enabled by our spin-coating and doctor-blade coating technologies can significantly improve the conversion efficiency and reduce the manufacturing cost of crystalline silicon solar cell.

2.   The optical simulation tools (RCWA, TFM, and FDTD) developed from this project, which are freely available from the PI's group website, facilitate fundamental understanding of optical diffraction, reflection, scattering, and transmission from various subwavelength gratings. These free codes have been used by other groups to help develop new optoelectronic devices.

Contributions to Other Disciplines:

1.   The subwavelength antireflection coatings can be extended to improve the extraction efficiency of both inorganic and organic light emitting diodes. We are now exploring into this new research area.

2.   The open-sourced optical simulation codes can be implemented for other optical applications (e.g., plasmonics).

Impact on Student Education and Training:

 4 graduate and 4 undergraduate students have participated in the proposed research. The multidisciplinary nature of the research program has provided a rich intellectual and scientific training ground to these students.  They have worked closely with industry (including Emcore Corporation, Hewlett-Packard, and Jolar Technology) and other academic groups at UF as well as around the world to increase the breath of their education. Three Ph.D. students working on the project have already found jobs in prestigious semiconductor companies, like Intel.   

The results on biomimetic antireflection coatings have attracted great public interest. The publications have been featured on Nature, Laser Focus World, Materials Today, New England Cable TV, Popular Science, and more than thirty other public media. The PI received dozens of emails from high school students, teachers, and entrepreneurs asking about questions on the antireflection coatings and solar cells. We believe this will inspire interests of students and publics in science and engineering.

Contributions Beyond Science and Engineering:

The results on biomimetic antireflection coatings have attracted broad industrial interest from start-up (Nano Terra), mid-sized (e.g., Emcore), and big companies (e.g., REC Group, one of the biggest photovoltaics companies in Europe). REC Group is evaluating the technology for their solar cell manufacturing. We are also working with Emcore Corporation and Jolar Technology in transferring the antireflection technologies developed in the PI's lab to their commercial applications.

Impact on the PI's Career:

This ACS PRF helps to jump-start the PI's research career. Using the preliminary data obtained from this grant, the PI has successfully attracted more than one million dollars external funding from other federal agencies (including a prestigious NSF CAREER award, DTRA, DOE, and California Energy Commission). The work supported by this ACS PRF grant has also attracted a lot of public and industrial interest. This greatly facilitates the PI to commercialize the technologies developed in his group. A start-up company will be established by the PI in Gainesville, Florida in 2010 to commercial the antireflection technologies for making efficient solar cells. This ACS PRF grant also helps the PI to be early tenured and promoted to the associate professor rank.