The remarkably high electromagnetic fields that can be induced by the optical stimulation of surface plasmons in
plasmonic nanostructures can induce large enhancements to Raman scattering. The Surface-enhanced Raman Scattering
(SERS) effect offers great potential for the development of molecular sensors with low false alarm rates and high
sensitivity. Although research in this field has grown at a very fast pace in recent years, most of this work has focused
on attaining the highest enhancements at highly localized hot-spots, which while providing large peak enhancements,
exhibit very low average enhancement factors, making their use for most sensing applications unlikely. Here we report
on Au-coated Si nanopillar arrays where we probe the dependence of the SERS enhancement on both the nanopillar
diameter and the interpillar gap over a range extending from 30 to 245 nm and 20 to 165 nm, respectively. This
approach allows for the optimization of the SPR condition relative to the incident laser wavelength chosen, enabling an
optimized SERS sensor. As the interparticle gaps approach 20 nm, we also explored arrays of nanopillars where
interparticle plasmonic coupling should exist, however, it remains unclear if any such collective effects are present. The
arrays created do illustrate very large highly uniform (<30% deviation) SERS enhancement factors (G), with G in excess
of 1x10<sup>7</sup> being reported. In addition, we explored the role of the nanoparticle geometry, where we determined that a
higher G is observed for circle in comparison to square nanopillars of similar dimensions. The SERS enhancement was
found to have a very distinct dependence on the nanopillar diameter, while only a monotonic increase was observed with
increasing interpillar gap. These results suggest great suitability of plasmo-photonic large-area nanopillar arrays for
SERS vapor and liquid sensor applications.
The doping of Eu into MgS as well as CaS:Eu thinfilms, produced by Chemically Controlled Pulsed Laser
Deposition (CCPLD), offer a lot of potential for the development of ultra-high density; (Terabits per sq. in.) spectral
storage devices. These storage capacities are made possible by the use of spectral holeburning technique where many
spectral holes can be burned into the inhomogeneously broadened Zero Phonon Line (ZPL) of 4f-5d electronic transition
of the Eu ions inside the MgS and CaS lattice. It is shown that one can tailor different optical centers by introducing trace
amounts of impurities in the alkaline earth sulfide lattice, especially if these impurities occupy sites close to the
europium ion. The effect of doping on MgS and CaS thinfilms with oxygen impurity has been presented. Laser excited
fluorescence results have been presented that demonstrate possible atomic tailoring of calcium and magnesium sulfides
in creating new oxygen associated europium centers. Such centers are of prime importance in increasing the spectral
storage capacity of multilayer thinfilm structures based on these materials.
Despite surface-enhanced Raman scattering (SERS) being first observed in the late 1970s, efforts to provide
reproducible SERS-based chemical sensors have been hindered by the inability to make large-area devices with a
uniform SERS response. Furthermore, variations in the observed spectra occur due to the variable interactions and
orientations of the analyte with the textured SERS surfaces. Here we report on periodic arrays of Ag- and Au-coated
vertical silicon nanopillars fabricated by e-beam lithography and reactive ion etching for use as SERS sensor templates
that provide both large and uniform enhancement factors (up to 1×10<sup>8</sup>) over the structure surface area. We discuss the
impact of the overall geometry of the structures, by varying both the diameter and the edge-to-edge spacing in an effort
to optimize the SERS response for a given excitation laser wavelength. Calculations of the electromagnetic field
distributions within such structures were also performed and support the behavior observed experimentally.
Rare earth doped thin-films have been produced using laser pulse vapor deposition technique. By changing the thin film growth environment inside the chamber, we were able to create several optical centers. Emission and absorption spectroscopy measurements performed on these structures confirm that that these thinfilms are suitable candidates to be used for ultra-high density spectral storage applications. Scanning electron microscopy studies of these thinfilms were conducted to study degradation in their optical quality upon long-term storage. Results on microscopy show that the deterioration is initiated by nano-gaps and cracks in the capping layer of zinc sulfide.
The fabrication of spectral storage materials presents a great challenge of tailoring the optical properties of a solid at
the atomic scale. We show that by a careful choice of a host material and the luminescent rare earth centers created in it,
thin film structures can be fabricated using pulsed laser deposition. It is shown that these structures can be tailored to
satisfy the material requirements for the power-gated spectral holeburning, one of the most successful techniques for the
spectral storage. In the form of multilayer thin film structures, these tailored materials can provide surface storage
densities exceeding a terabit per square inch. Possibilities of tailoring new rare earth centers that can further multiply the
storage densities have been discussed. Experimental data has been presented for the fabrication and characterization of
such impurity based europium centers in MgS and CaS by chemically controlled pulsed laser deposition.
Spectral Storage using optical holeburning has the potential of providing ultrahigh densities approaching terabits per
square inch. The progress on multilayer spectral storage in Eu-doped sulfides has been presented. It is shown that
atomic scale tailoring of these structures is possible in order to design several different europium optical centers. In
the spectrum of these centers, ultrahigh density storage can be achieved with the simultaneous optimization of other
performance parameters. Results are also presented for tailoring the barrier and the capping layers.
Pulsed Laser Chemical Vapor Deposition (PLCVD) has been used to fabricate single atoms doped nanoparticles of magnesium sulfide. These particles were dispersed in optically transparent Poly-methyl-methacrylate (PMMA) films for near field nano-microscopy such that each nanoparticle doped with a single europium atom falls in the focusing range of the near field microscope. By atomic tailoring, the concentration of the doubly ionized europium, Eu<sup>2+</sup>, has been maximized in these nanoparticles. The energy and the oscillator strength of the 4f<sup>7</sup>-4f<sup>6</sup>5d<sup>1</sup> electronic transition has been tailored to maximize its addressing by photons in single atom spectroscopy experiments. Results have been presented on the fabrication of these single atom doped nanoparticles and their spectroscopy by laser excited fluorescence technique. Studies of a single Eu<sup>2+</sup> ion by confocal micro-spectroscopy are in progress.