In this paper we describe the formation and characterization of self-assembled monolayers of octadecylphosphonic acid (ODPA) on epitaxial (0001) GaN films on sapphire. By immersing the substrate in its toluene solution, ODPA strongly adsorbed onto UV/O 3-treated GaN to give a hydrophobic surface. Spectroscopic ellipsometry verified the formation of a well-packed monolayer of ODPA on the GaN substrate. In contrast, adsorption of other primarily substituted hydrocarbons (C n H 2 n+1 X; n = 16-18; X = -COOH, -NH 2, -SH, and -OH) offered less hydrophobic surfaces, reflecting their weaker interaction with the GaN substrate surfaces. A UV/O 3-treated N-polar GaN had a high affinity to the -COOH group in addition to ODPA, possibly reflecting the basic properties of the surface. These observations suggested that the molecular adsorption was primarily based on hydrogen bond interactions between the surface oxide layer on the GaN substrate and the polar functional groups of the molecules. The as-prepared ODPA monolayers were desorbed from the GaN substrates by soaking in an aqueous solution, particularly in a basic solution. However, ODPA monolayers heated at 160 degrees C exhibited suppressed desorption in acidic and neutral aqueous solution maybe due to covalent bond formation between ODPA and the surface. X-ray photoelectron spectroscopy provided insight into the effect of the UV/O 3 treatment on the surface composition of the GaN substrate and also the ODPA monolayer formation. These results demonstrate that the surface of a GaN substrate can be tailored with organic molecules having an alkylphosphonic acid moiety for future sensor and device applications.

The reflectance spectra of n-type GaAs samples with carrier densities from 3×1016 to 3×1018 cm−3 have been measured in the spectral range 55–1000 cm−1. Except for slight discrepancies in the vicinity of the reflectance minima, the classical Drude model provides an excellent description of the free-carrier effects in the reflectance. The discrepancies may be accounted for by a depletion layer at the surface or by a quantum-mechanical scattering theory. Inhomogeneities in the carrier density are measured by scanning the surface of the sample with a small aperture at a fixed frequency. The effect of mechanical polishing on the reflectance is analyzed in terms of a damaged layer. Reflectance measurements are also used to characterize samples consisting of epitaxial films of GaAs on GaAs substrates.

exactly 1 gallium vertex of another polyhedron. The Ga(22)-Ga(23) distance of 2.43 A is 0.1 A shorter than the next shortest Ga-Ga distance (Ga(4)-Ga(13) = 2.53 A), which when coupled with the lack of exopolyhedral bonds from Ga(22) and Ga(23) suggests a Ga( 22)=Ga( 23) double bond. If this is the case, the closed-shell electronic configuration for the edge-localized gallium satellite polyhedron depicted in Figure 2 in Ga1515-.

Interference effects, including multiple-beam and wide-angle, associated with luminescence from within a thin film are described. A simple geometrical model is used to calculate the s- and p-polarized luminescent light assuming electric-dipole radiation. The luminescence exhibits fringes when measured both as a function of the film thickness and as a function of the wavelength of the light. In the latter case the fringes can also show a beating effect. The model is applied to several experimental examples of cathodoluminescence in SiO(2) and an example of photoluminescence in a-Si.

We demonstrate that guided resonant modes can be readily observed in asymmetrical photonic crystal slabs on high-index substrates. In spite of the high radiative loss associated with all optical modes in these cases, the guided resonant modes are found to give rise to strong high-Q features in the transmission spectra. Since these photonic crystal structures are far more robust and easier to fabricate than the free-standing photonic crystal membranes used in previous studies of guided resonant modes, detailed studies of relevant optical phenomena and the implementation of proposed applications are greatly simplified.