Joseph P. Moening

Formation of conical silicon tips with nanoscale sharpness by localized laser irradiation

The formation of conical silicon tips with nanoscale sharpness as a result of single-pulse localized laser irradiation is presented in this work. A Q-switched neodymium doped yttrium aluminum garnet nanosecond-pulse laser, emitting at its fourth harmonic of 266 nm, and a mask projection technique were used to generate circular laser spots, several microns in diameter. The irradiation of silicon-on-insulator films was performed in ambient, vacuum, or argon atmospheres, with the resulting structures and underlying substrate examined via atomic force microscopy and scanning electron microscopy. The laser fluence range within which tip formation occurs is strongly dependent on the irradiated spot size. Within this range, the height of the resulting tip increases with the fluence level, while nearly preserving the aspect ratio. The formation mechanism of these structures is briefly discussed in view of these results and other, related published work.

Focused ion beam and electron microscopy characterization of nanosharp tips and microbumps on silicon and metal thin films formed via localized single-pulse laser irradiation

Cross-sections of laser fabricated nanosharp tips and microbumps on silicon and metal thin films are produced and examined in this work. These structures are formed with a Q-switched neodymium doped yttrium aluminum garnet nanosecond-pulse laser, emitting at its fourth harmonic of 266 nm, using a mask projection technique to generate circular laser spots, several microns in diameter. Cross-section of selected structures were produced using a focused ion beam and were characterized via electron microscopy. The diffraction patterns of the silicon samples indicate that the laser formed tip maintains the same single crystal structure as the original silicon film. Examinations of the laser formed structures in metal films confirm that the microbumps are hollow, while revealing that the vertical protrusions are solid.

Microstructure and electronic properties of zinc nitride thin films

Results from an initial study on the preparation, microstructure, and optical and electrical properties of zinc nitride films are presented. Zinc nitride has a lower bandgap than ZnO and can be fabricated in a thin film form by sputtering and other methods. This material has a potential as a new semiconductor material in photovoltaic, optoelectronic and other applications, offering additional advantages such as environment-friendly processing and potentially low fabrication cost. A main goal of our studies, which are still in progress, is establishing correlations between the fabrication conditions and the structure and relevant properties. Junctions and interfaces with metals or zinc oxide will be of interest as well.

Formation of microbumps and protrusions on metal thin films by localized laser irradiation

We present results on the formation of microbumps, and high-aspect-ratio nano-scale protrusions on metal films as a result of single-pulse localized laser irradiation. A Q-switched nanosecond-pulse Nd:YAG laser, emitting at its fourth harmonic of 266 nm, was employed. Gold or platinum films with thicknesses of several hundred nanometers were irradiated in ambient or under low-vacuum conditions, with circular laser spots, several micrometers in diameter. A mask projection technique was used to generate these spot patterns. The resulting structures were examined by scanning electron microscopy. The formation mechanism of these structures is briefly discussed.

Low-X BIPV window enabled by infrared mirror film

A low concentration Building Integrated PhotoVoltaic (BIPV) window utilizing PV cells in conjunction with 3M Brand Prestige Window Film is presented. The goal was to provide a proof of concept showing how photovoltaics and the film can be integrated into windows to allow for both energy production and daylighting. Unlike most other BIPV windows, the PV cell angle is adjustable. The system was shown to be comparable to a typical window in terms of daylighting. Long-term energy production testing is needed for a conclusive analysis, but simulated results showed an increase in power compared to a vertical BIPV system.