Development of coatings to minimize unwanted surface adsorption is extremely important for their use in applications, such as sensors and medical implants. Self-assembled monolayers (SAMs) are an excellent choice for coatings that minimize nonspecific adsorption because they can be uniform and have a very high surface coverage. Another equally important characteristic of such coatings is their stability. In the present study, both the bonding mechanism and the stability of stearic acid SAMs on two aluminum oxides (single-crystal C-plane aluminum oxide (sapphire) and amorphous aluminum oxide (alumina)) are investigated. The adsorption mechanism is investigated by ex situ X-ray photoelectron spectroscopy and infrared (IR) spectroscopy. The results revealed that stearic acid binds to sapphire surfaces via a bidentate interaction of carboxylate with two oxygen atoms while it binds to alumina surfaces via both bidentate and monodentate interactions. Desorption kinetics of stearic acid self-organized on both aluminum oxide surfaces into water is explored by ex situ tapping mode atomic force microscopy, IR spectroscopy, and contact angle measurements. The results exhibit that the SAMs of stearic acid formed on sapphire are not stable in water and are continuously lost through desorption. Water contact angle measurements of SAMs that are immersed in water further indicate that the desorption rate of adsorbates from atomically smooth terrace sites is substantially faster than that of adsorbates from the sites of surface defects due to weaker molecular interaction with the smooth surface. A time-dependent desorption profile of SAMs grown on amorphous alumina reveals that contact angles decrease monotonically without any regional distinction, providing further evidence for the presence of adsorption sites with different types of affinity on the amorphous alumina surface.

The need for small form factor, portable biosensing platforms is prevalent across a wide range of medical, environmental, and defense applications. This paper presents the design of a novel, integrated optofluidic photonic crystal biosensor architecture that shows potential for meeting the single molecule detection requirements of these application areas. GaN is being targeted as the photonic crystal slab material due to its transparency in the visible spectral range and also the potential for creating high aspect ratio photonic crystal lattices via polarity inverted MBE growth. Results of optical modeling efforts indicating 10-15x resonant enhancement of fluorescent emission and polarity inversion GaN growth techniques will be discussed.

Fabrication of high index contrast waveguide stacks for biosensing and other applications require nanometer scale thickness control. Nanoscale dielectric films from electron-beam evaporation can be difficult to obtain due to the resulting porosity and poor stoichiometry of the films. An alternative approach is the reactive deposition of the film from a metal source in the presence of oxygen ions. Using spectroscopic ellipsometry, we have shown that greater control over thickness and index of refraction of silicon dioxide depositions can be obtained through reactive depositions as compared to depositions from SiO2 dielectric source material itself. Through Fourier Transform Infrared Spectroscopy (FT-IR), the Si-O in-phase stretching peak at 1078 cm-1 can be traced, allowing us to determine the stoichiometry of the film.The effects of performing depositions of aluminum oxide dielectric source material in the presence of oxygen ions has also been investigated. Through the use of the oxygen ion source, greater control over index of refraction and optical losses has been observed. By controlling ion source parameters, the aluminum oxide films’ index of refraction can be engineered within a range of 1.58 to 1.64, and waveguide losses can be reduced to as low as 2.0 dB/cm.