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In this paper, the icephobic properties of superhydrophobic surfaces are investigated under dynamic flow conditions using a closed-loop low-temperature wind tunnel. Superhydrophobic surfaces were prepared by coating aluminum and steel substrate plates with nano-structured hydrophobic particles. The superhydrophobic plates, along with uncoated controls, were exposed to a wind tunnel air flow of 12 m/s and −7 °C with deviations of ±1 m/s and ±2.5 °C, respectively, containing micrometer-sized (∼50 μm in diameter) water droplets. The ice formation and accretion were observed by CCD cameras. Results show that the superhydrophobic coatings significantly delay ice formation and accretion even under the dynamic flow condition of highly energetic impingement of accelerated supercooled water droplets. It is found that there is a time scale for this phenomenon (delay in ice formation) which has a clear correlation with contact angle hysteresis and the length scale of the surface roughness of the superhydrophobic surface samples, being the highest for the plate with the lowest contact angle hysteresis and finest surface roughness. The results suggest that the key for designing icephobic surfaces under the hydrodynamic pressure of impinging droplets is to retain a non-wetting superhydrophobic state with low contact angle hysteresis, rather than to only have a high apparent contact angle (conventionally referred to as a “static” contact angle).

The recent observation of optical gain from silicon nanocrystals embedded in SiO2 opens an opportunity to develop a nanoscale silicon-based laser. However, the challenge remains to design and develop a laser architecture using CMOS-compatible materials. In this paper we present two designs for a waveguide laser in which silicon nanocrystals embedded in SiO2 are used as the optical gain media. One design employs a SiO2 membrane containing encapsulated Si nanocrystals. Preliminary calculations given here show that a highly resonant laser cavity can be produced in a SiO2 membrane using sub-wavelength structures. This photonic crystal architecture, used to guide and contain the light, can be combined with a gain medium of optically active Si nanocrystals synthesized in the SiO2 membrane using ion implantation/thermal annealing to produce a Si-based laser. The laser cavity dimensions can be matched to the near-infrared wavelengths where optical gain has been observed from Si nanocrystals. The second design utilizes silicon nanocrystals embedded in a distributed-feedback laser cavity fabricated in SiO2. Lasing action over a broad wavelength range centered at ∼770 nm should be possible in both of these configurations.

Nanocrystalline silicon (n-Si) is formed in a silicon dioxide thin-film matrix by ion implantation followed by thermal annealing in forming gas at 1100 °C for 1 hour. The ion implantation is performed using multiple implants with different implantation energies and doses to create a quasi-flat concentration of silicon atoms throughout the silicon dioxide film. These samples are then analyzed using spectroscopic ellipsometry to characterize their linear optical properties. Implantations with small doses (5 × 1020 Si atoms/cm3) increase the refractive index by a small amount (δn∼0.006 at 600nm), while implantations with moderate dose (5 × 1021 Si atoms/cm3) have a larger increase in refractive index and exhibit optical absorption above ∼1.9 eV (650 nm).