Sean M. Casey

Chemistry of arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy probed by simultaneous laser flux monitoring and reflection high-energy electron diffraction

Arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy is studied in situ with laser single‐photon ionization time‐of‐flight mass spectrometry and reflection high‐energy electron diffraction (RHEED). Incident and scattered fluxes of Ga and Asn species in front of the growing GaAs wafer are ionized repetitively by a pulsed laser beam of 118 nm (10.5 eV) photons. The methods to obtain and interpret time‐of‐flight mass spectra and the simultaneous RHEED measurements are described. The real time behaviors of incident Ga and desorbing As2 and As4, obtained without mass spectral cracking, are studied during growth of GaAs layers with As4 and when growth is arrested as a function of substrate temperature and Ga/As4 flux ratio. During growth only with As4, both As2 and As4 are desorbed or scattered in varying amounts depending on flux and substrate temperature conditions. Without an incident gallium flux, desorbing As4 decreases while desorbing As2 increases with increasing surface temperature. During...

Novel Dichroic Polarizing Materials and Approaches to Large-Area Processing

We have developed new polarizing coating materials and processes which enable the fabrication of polarizers for large-area liquid-crystal displays. The polarizing materials are novel discotic surfactants which self-assemble in aqueous solutions to provide a stable liquid-crystalline phase within a wide range of concentrations and temperatures. These lyotropic liquid crystals in an aqueous medium can be spread on a substrate surface by a variety of techniques including a knife-like doctor blade, a rolling cylinder, or a roll-to-roll method. Under the shearing force applied during deposition, the liquid crystals align on the substrate forming a dichroic polarizer. This alignment process allows continuous production of large-area polarizing films at low cost compared with the current technology that requires stretching of the films. Thin coatings can be applied to flexible plastic films, glass, or rigid plastic substrates. Direct coating of the polarizing material on glass eliminates several process steps in liquid-crystal display production since lamination of the polarizing film is no longer required. These new polarizing films have a high optical performance including a polarizing efficiency of above 98% and a dichroic ratio as high as 7.7.

Gas phase chemomechanical modification of silicon

In this work we demonstrate the gas phase chemomechanical functionalization of silicon. This work streamlines the preparation of chemomechanically modified surfaces, in comparison with previously described liquid phase modifications. Scribing was performed in the presence of ethylene, acetylene, and a control (air). X-ray photoelectron spectroscopy, wetting, and time-of-flight secondary ion mass spectrometry (scores and loadings from principal components analysis) results are consistent with expectations and with previous analysis of samples scribed under liquid alkenes and alkynes. Thermal desorption spectroscopy analysis supports the Si(100) model for scribed silicon.