Due to the high surface area and good bio-compatibility of nano structured ZnO, it finds good utility in biosensor applications. In this work we have fabricated highly dense ZnO nano bundles with the assistance of self assembled poly methylsilisesquoxane (PMSSQ) matrix which has been realized in a carpet like configuration with implanted ZnO nano-seeds. Such high aspect ratio structures (∼50) with carpet like layout have been realized for the first time using solution chemistry. Nanoparticles of PMMSQ are mixed with a nano-assembler Poly-propylene glycol (PPG) and Zinc Oxide nanoseeds (5-15 nm). The PPG acts by assembling the PMSSQ nanoparticles and evaporates from this film thus creating the highly porous nano-assembly of PMMSQ nanoparticles with implanted Zinc Oxide seeds. Nano-wire bundles with a high overall surface roughness are grown over this template by a daylong incubation of an aqueous solution of hexamethylene tetra amine and Zinc nitrate. Characterization of the fabricated structures has been extensively performed using FESEM, EDAX, and XRD. We envision these films to have potential of highly dense immobilization platforms for antibodies in immunosensors. The principle advantage in our case is a high aspect ratio of the nano-bundles and a high level of roughness in overall surface topology of the carpet outgrowing the zinc-oxide nanowire bundles. Antibody immobilization has been performed by modifying the surface with protein-G followed by Goat anti salmonella antibody. Antibody activity has been characterized by using 3D profiler, Bio-Rad Protein assay and UV-Visible spectrophotometer.

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Computer modeling of fluids in zeolites can provide a detailed molecular level understanding of the process of adsorption and diffusion under the influence of the 3-D potential field and the confinement offered by the crystal structure. We have shown that there is a strong link between the location, geometry and energetics of sites and the observed thermodynamics and spectroscopy of the adsorbates. Here we report on the modeling of Xe in zeolite Y, which is of interest both because it is commercially important and because it offers two distinct adsorption sites.

We have utilized a recently developed transient two-dimensional model for simulating localized beam-induced melting and solidification of thin silicon films on SiO2. Specifically, by tailoring the lateral beam profile, we simulate those situations that are encountered in the artificially-controlled superlateral growth (ACSLG) method, in which various techniques are utilized to irradiate the sample in preselected regions of a silicon film. The spatially and temporally localized character of heating is simulated by introducing a time-dependent two-dimensional heat-source function. The evolution of melt-creation and ensuing solidification is studied as a function of incident energy density and film thickness. The results show two distinct types of behavior as a function of incident energy density: at low energy densities, partial melting and predominantly vertical solidification occur; while at high energy densities, complete melting of the irradiated portion of the film is followed by rapid lateral solidification.

We have developed a two-dimensional numerical model of excimer-laser melting and solidification that properly takes into account the non-equilibrium and transient nature of the process. The model incorporates a novel explicit finite difference scheme for efficiently solving the heat conduction equation and an algorithm that incorporates the interface response function for properly simulating the evolution of phase domains. The model provides space- and time-resolved information regarding the thermal profile and phase domains from which nearly all of the important solidification details can be extracted (e.g., interface location, solidification velocity, interfacial undercooling, etc.). For the simple partial-melting-and-vertical-regrowth scenario, results from the model converge with the results from the well-established one-dimensional model. As a result of its two-dimensional and non-equilibrium formulation, which also respects the amorphous and inert nature of the underlying oxide surface, the model is unique in its capability for properly simulating those solidification scenarios that involve extensive lateral growth of solids, as for example those behind the super-lateral growth phenomenon and various artificially controlled super-lateral growth processes.

Raman scattering has been used to characterize lattice damage and impurity-induced compositional disordering in AlGaAs superlattice suitable for optical waveguiding. The degree of damage induced by both conventional ion beam (CIB) implantation and focused ion beam (FIB) implantation is studied using a spatial correlation model to interpret the Raman spectra. FIB implantation is found to induce slightly more damage than CIB implantation for doses of 8×1013 cm−2 and 4×1014 cm−2. and significantly more damage with 2×1015 cm2 compared to CIB implantations of the same dose. Suitable FIB implantation and rapid thermal annealing (RTA) conditions which provide compositional mixing were determined using Raman and photoluminescence spectroscopy. Using these conditions, an optical channel waveguide in AlGaAs superlattice formed by FIB-induced compositional intermixing is demonstrated.

Low temperature photoluminescence spectra have been used to characterize conventional ion beam (CIB) and focused ion beam (FIB) implanted superlattices. The excitation dependence of the single scan FIB is found to be significantly different from CIB and multiple scan FIB implantations which are similar. The peak position of the donor-acceptor transition is observed to change to higher energies significantly slower with excitation intensity for the single scan FIB case when compared to the multiple scan FIB and CIB cases. Simple models to describe these effects are briefly discussed.

The desorption kinetics of hydrogen from the β1 H2 -TPD state on Si(111)7×7 and Si(100)2×l were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Isothermal LITD studies of H2 desorption from Si(111)7×7 revealed second-order kinetics with a desorption activation energy of Ed = 62 ±4 kcal/mol and a preexponential factor of Vd = 92 ±10 cm2 /s. In contrast, H2 desorption from Si(100)2×l revealed first-order kinetics with an activation energy of Ed = 58 ±2 kcal/mol and a preexponential factor of Vd = 5.5 ±0.5 × 1015 s−1. The desorption kinetics yield similar upper limits for the Si-H bond energies but different desorption mechanisms on Si(lll)7×7 and Si(100)2×l.