Raman analyses of the lifetimes of phonons in GaN and AlN crystallites of wurtzite structure are presented. In order to ensure the accuracy of the measurement of the phonon lifetimes, an experimental procedure to eliminate the broadening due to the finite slit width was performed. The lifetime analyses indicate that the phonon lifetimes in AlN as well as in GaN fall into two main time regimes: a relatively long time of the E 2 1 mode and much shorter times of the E 2 2 , E1͑TO͒, and A1͑TO͒ modes. The lifetimes of the E 2 1 , E 2 2 , E1͑TO͒, A1͑TO͒, and A1͑LO͒ modes of an high-quality AlN crystallite are 4.4, 0.83, 0.91, 0.76, and 0.45 ps, respectively. Moreover, the lifetime of the A1͑LO͒ mode found in this study is consistent with the current phonondecay model of that mode in wurtzite structure materials. The lifetimes of E 2 1 , E 2 2 , E1͑TO͒, and A1͑TO͒ of a GaN crystallite were found to be 10.1, 1.4, 0.95, and 0.46 ps, respectively. The A1͑LO͒ mode in the GaN was not observed and its absence is attributed to plasmon damping. The lifetime shortening due to impurities was also studied: the lifetimes of the Raman modes of an AlN crystallite, which contains about two orders of magnitude more Si and C impurities relative to the concentration of the high-quality crystallite were found to be 50% shorter. ͓S0163-1829͑99͒04419-7͔

We employed a simple and effective electroless (EL) plating approach to produce silver nanoparticles (NPs) on bare silicon, on dielectric ZnO nanowires (NWs) and on Si NWs, respectively. The surface stability of the homogeneous Ag NPs formed on the ZnO NW surfaces was investigated by surface enhanced Raman spectroscopy (SERS), which show that the attachment of thiol to the Ag surface can slow down the oxidation process, and the SERS signal remains strong for more than ten days. To further examine the Ag NP oxidation process in air, the oxygen content in the silicon nanowire core/Ag sheath composites was monitored by the energy dispersive x-ray (EDX) method. The amount of oxygen in the system increases with time, indicating the silver NPs were continuously oxidized, and it is not clear if saturation is reached in this time period. To investigate the influence of the Ag NPs size distribution on the oxidation process, the oxygen amount in the NPs formed by EL deposition and e-beam (EB) evaporation on a bare silicon surface was compared. Results indicate a faster oxidation process in the EL formed Ag NPs than those produced by EB evaporation. We attribute this observation to the small diameter of the EL produced silver particles, which results in a higher surface energy.

This article presents a study of the quasi-longitudinal optical and quasi-transverse optical modes in wurtzite AlN which originate from the interaction of phonons belonging to the A1 and E1 symmetry groups. In order to analyze the allowed quasi as well as pure Raman modes, the modes were observed in a rotating crystallographic coordinate system, and the Raman tensors of the wurtzite crystal structure were calculated as a function of the crystallographic rotation. The frequencies of the quasimodes of wurtzite AlN were also analyzed in terms of the interaction of the polar phonons with the long range electrostatic field model. The experimental values of the Raman frequencies of the quasiphonons concur with these expected from the model, implying that the long range electrostatic field dominates the short range forces for polar phonons in AlN.

We report on ultraviolet Raman spectroscopy of InxGa1−xN thin films grown on sapphire by metal-organic chemical vapor deposition. The A1(LO) and E2 phonon mode behavior was investigated over a large compositional range (0<x<0.50). Compelling evidence is presented for one-mode behavior for the A1(LO) phonon, and data suggestive of two-mode behavior are presented for the E2 phonon.

Semiconductor nanostructures in biological applications are discussed. Results are presented on the use of colloidal semiconductor quantum dots both as biological tags and as structures that interact with and influence biomolecules. Results are presented on the use of semiconducting carbon nanotubes in biological applications.

We have developed dielectric core/metal sheath nanowire (NW) composites for surface-enhanced Raman scattering (SERS), in which an electroless (EL) Ag plating approach was employed. The NW surface was uniformly covered with a high density of 3D silver islands, having a diameter in the 20-30 nm range and spaced less than approximately 10 nm apart. In comparison with the silver deposition via e-beam evaporation, the EL coating approach has the advantage of full metal coverage of the NWs. This approach also provides a fast and simple way to completely cover any nanostructures with Ag, including nanowires, regardless of the orientation or shape. SERS measurements were performed using benzene thiol and the SERS signal strength of the EL-coated NW composites was significantly greater than expected, since the surface plasmon resonance (SPR) of 20 nm Ag nanospheres is weak and in the UV, while our measurements were performed using a 514.5 nm laser line. However, we have modeled this system using our electric field calculations and the results indicate that the strong SERS signal is due to plasmonic coupling of neighboring closely spaced islands, as well as an enhanced substrate effect. In addition, the nanowire core serves as a template for the formation of these small, closely spaced Ag islands, resulting in the strong SERS signal.

There is currently a major international effort aimed at integrating semiconductor nanostructures with biological structures. This paper reports the functionalization of cadmium sulfide quantum dots with peptides that facilitate the selective binding of these quantum-dot-peptide complexes to integrins in the membranes of cancer cells of the MDA-MB-435 cell line. In addition, this paper focuses on the roles that biological environments play in altering and determining the optical and vibrational properties of these nanostructures.

In this paper we report a study of phase separation in bulk InxGa1−xN films grown by metal organic chemical-vapor deposition using mid-UV Raman spectroscopy. Evidence of phase separation is observed by the occurrence of low frequency shoulders identified as minority phase in the A1(LO) Raman mode. A phase transition in the alloy from the metastable to unstable region was found to be occurring at an indium concentration of about 25%. Raman spectroscopic results also indicate that the compositional inhomogenity in our samples increase, as would be expected, with depth in the film. A direct correspondence is also found between the percentage of indium concentration in the film and the amount of compositional inhomogenity.