AmericanChemicalSociety.com

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 extremely low scattering in a perforated silver film with tunable resonance wavelengths and widths. We also discovered electric field enhancement and confinement between two silver films. In collaboration with Dr. Ming Su, we simulated the etching of multi-component glass films.

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. The achievements from the projects had been used preliminary results for external funding applications. For example, the PI's NSF career proposal will based on the results obtained from the award. The PI is preparing a proposal to the Air force research department using the preliminary results achieved from the award.

2. Educational impact

Two graduate students, one undergraduate student, and one visiting scholar were involved in the project. Graduate student Haining Wang calculated the extremely low scattering cross section of a perforated silver film and was involved in the electric field confinement and ehancement between two silver films which was finished by graduate student Feng Yu. Haining Wang also model the gain and loss of propagating electromagnetic wave along hollow silver rods. Undergraduate student, Jennifer Reed, was trained to learn about the discrete dipole approximation method and got familiar with simulations of the optical properties of silver films and ring structures. Visiting scholar, Yicun Ni, finished the simulations of an etched glass structure which was experimentally fabricated by our collaborator, Ming Su, in the Nanoscience and technology center at the University of Central Florida, and is useful for the development of surfaces with reduced scattering.

3. Research achievements

3.1 Extremely low scattering efficiency of a perforated silver film.

Using the discrete dipole approximation method, we investigated the scattering cross section of a perforated silver film. We found that extremely low scattering cross section can be achieved at tunable wavelengths and widths. The results may help harvesting sun light in the visible wavelengths. In the simulations, the thickness of the film is 100 nm, holes are arranged in a square lattice array with different size, shape, and separation. The simulations shown that the scattering efficiency can be reduced to close to zero when the distance between hole is set to be 400 nm. We found that rectangular hole will generate more significant scattering reduction in comparison to cylindrical hole. The resonance wavelength shifts to red when the edge length of the hole along the polarization direction is reduced. The resonance wavelength also shift to red when the hole center to center distance along the polarization direction increases. We calculated the electric field around a hole and found that the electric field was enhanced and confined around hole area.

3.2 Electric field confinement and enhancement between two silver layers.

Using an analytical method, we investigated the extinction, scattering, and absorption spectra of a two layer silver film. We also calculated the electric field between the two layers. The finding may help the design of multi-layer structures with enhanced absorption efficiency and enhanced electric field in a confined space. In the simulations, we changed the distance between the two silver layers and the thickness of the two layers. The distance between the two layers is varied from 100 nm to 300 nm. The thicknesses of the two layers are varied between 10 to 80 nm. We found that the thickness of the first layer plays an important role in determining the optical properties of the system. When the thickness of the first layer is between 30 to 40 nm, light may penetrate through the first layer and trapped between the two layers due to the back and forth reflection between the two layers. The electric field |E|² between the two layers can be enhanced and an enhancement of 50 was achieved when the thickness of the first layer is 40 nm and that of the second layer is 80 nm.