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Objective and summary of achievements: The objective of the proposal is to understand the nano-structure dependence of metal and semi-conductor film using electrodynamics theory. We achieved unit absorption efficiency at tunable wavelengths using a two layer silver film. We also developed a coupled dipole method to study the energy transfer between metallic nanoparticles and quantum dots and fluorophore molecules. In collaboration with Drs. Yan and Liu at Arizona State University, we obtained quantitative agreement between the theoretically calculated data and experimental measurements.

1. Impact to the PI's research

The award helps the early career development of the PI and members in the PI's group. Three papers were published as a result of the award in the year 2009-2010. The achievements from the projects had been used as preliminary results for external funding applications. For example, the PI's NSF career proposal will based on the results obtained from the award.

2. Educational impact

Two graduate students and one visiting scholar were involved in the project. Graduate student Haining Wang and Feng Yu calculated the scattering and absorption spectra of a two layer silver film and obtained unit absorption efficiency at tunable wavelengths. Haining Wang also modeled the energy transfer between metallic nanoparticles and quantum dots and fluorophore molecules.

3. Research achievements

3.1 Efficient and Tunable Light Trapping Thin Films.

Using the discrete dipole approximation method, we investigated the scattering and absorption spectra of a two layer silver film. The film was composed of a perforated layer perforated with asymmetric holes and a solid layer to block all the incident light. Unit absorption efficiency can be obtained in the visible wavelengths. The scattering efficiency is close to zero at the resonance wavelength. The resonance wavelength may be tuned when the distance between the two layers and the periodic distance of the perforated hole arrays are varied. We also found that geometries of conical frustum shaped holes in the first layer are critical for the improved absorption efficiencies. When the hole bottom diameter equals the periodic distance and the upper diameter is about one-third of the bottom diameter, close to unit absorption efficiency can be obtained.

3.2 Energy transfer between metallic nanoparticles and quantum dots and fluorophore molecules.

We developed a coupled dipole method to study the energy transfer between metallic nanoparticles and quantum dots and fluorophore molecules.  The aim of the studies is to understand how the energy is transferred between a metallic nanoparticle and quantum dots or fluorophore molecules so that the transferred energy can be used by a solar cell.  In collaboration with experimental groups, Drs. Yan and Liu at Arizona State University, we obtained quantitative agreement between the experimentally measured signals and theoretically calculated data.