Peter G. Gordon

Polarization-dependent properties of the cladding modes of a single mode fiber covered with gold nanoparticles.

The properties of the high order cladding modes of standard optical fibers are measured in real-time during the deposition of gold nanoparticle layers by chemical vapor deposition (CVD). Using a tilted fiber Bragg grating (TFBG), the resonance wavelength and peak-to-peak amplitude of a radially polarized cladding mode resonance located 51 nm away from the core mode reflection resonance shift by 0.17 nm and 13.54 dB respectively during the formation of a ~200 nm thick layer. For the spectrally adjacent azimuthally polarized resonance, the corresponding shifts are 0.45 nm and 16.34 dB. In both cases, the amplitudes of the resonance go through a pronounced minimum of about 5 dB for thickness between 80 and 100 nm and at the same time the wavelengths shift discontinuously. These effects are discussed in terms of the evolving metallic boundary conditions perceived by the cladding modes as the nanoparticles grow. Scanning Electron Micrographs and observations of cladding mode light scattering by nanoparticle layers of various thicknesses reveal a strong correlation between the TFBG polarized transmission spectra, the grain size and fill factor of the nanoparticles, and the scattering efficiency. This allows the preparation of gold nanoparticle layers that strongly discriminate between radially and azimuthally polarized cladding mode evanescent fields, with important consequences in the plasmonic properties of these layers.

Probing the Local Structure of Pure Ionic Liquid Salts with Solid‐ and Liquid‐State NMR

Room-temperature ionic liquids (RTILs) are gaining increasing interest and are considered part of the green chemistry paradigm due to their negligible vapour pressure and ease of recycling. Evidence of liquid-state order, observed by IR and Raman spectroscopy, diffraction studies, and simulated by ab initio methods, has been reported in the literature. Here, quadrupolar nuclei are used as NMR probes to extract information about the solid and possible residual order in the liquid state of RTILs. To this end, the anisotropic nature and field dependence of quadrupolar and chemical shift interactions are exploited. Relaxation time measurements and a search for residual second-order quadrupolar coupling were employed to investigate the molecular motions present in the liquid state and infer what kind of order is present. The results obtained indicate that on a timescale of approximately 10(-8) sec or longer, RTILs behave as isotropic liquids without residual order.

13C CP MAS NMR of halogenated (Cl, Br, I) pharmaceuticals at ultrahigh magnetic fields

This work reports significantly improved spectral resolution of 13C CP MAS NMR spectra of chlorinated, brominated and iodinated solid organic compounds when such spectra are recorded at ultrahigh magnetic field strengths. The cause of this is the residual dipolar coupling between carbon atoms and quadrupolar halogen nuclides (chlorine‐35/37, bromine‐79/81 or iodine‐127), an effect inversely proportional to the magnetic field strength which declines in importance markedly at 21.1 T as compared to lower fields. In favorable cases, the fine structure observed can be used for spectral assignment, e.g. for Cl‐substituted aromatics where the substituted carbon as well as the ortho‐carbons show distinct doublets. The experimental results presented are supported by theoretical modeling and calculations. The improved spectral resolution in the studied systems and similar halogenated materials will be of particular interest and importance for polymorph identification, drug discovery and quality control in the pharmaceutical industry. Copyright

35Cl Solid-State NMR of Halide Ionic Liquids at Ultrahigh Fields

This Letter describes recent work investigating the solid-state NMR spectra of (35)Cl nuclei in an assortment of ionic liquids under static and MAS conditions at field strengths of 9.4 and 21.1 T. At high field it was possible to resolve and extract information from multiple unique crystallographic sites and to resolve otherwise complex spectra that were analyzed to extract information regarding the electric field gradient (EFG) and chemical shift tensors, including their relative orientation. The NMR parameters were found to be typical of organic salts in general.

Recent Advances Using Guanidinate Ligands for Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD) Applications

Volatile metal complexes are important for chemical vapour deposition (CVD) and atomic layer deposition (ALD) to deliver metal components to growing thin films. Compounds that are thermally stable enough to volatilize but that can also react with a specific substrate are uncommon and remain unknown for many metal centres. Guanidinate ligands, as discussed in this review, have proven their utility for CVD and ALD precursors for a broad range of metal centres. Guanidinate complexes have been used to deposit metal oxides, metal nitrides and pure metal films by tuning process parameters. Our review highlights use of guanidinate ligands for CVD and ALD of thin films over the past five years, design trends for precursors, promising precursor candidates and discusses the future outlook of these ligands.

Passivation of Plasmonic Colors on Bulk Silver by Atomic Layer Deposition of Aluminum Oxide

We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer deposition (ALD) of thin films of aluminum oxide. The colors are rendered by silver nanoparticles produced by laser ablation and redeposition on silver. We then apply a two-step approach to aluminum oxide conformal film formation via ALD. In the first step, a low-density film is deposited at low temperature to preserve and pin the silver nanoparticles. In the second step, a second denser film is deposited at a higher temperature to provide tarnish protection. This approach successfully protects the silver and plasmonic colors against tarnishing, humidity, and temperature, as demonstrated by aggressive exposure trials. The processing time associated with deposition of the conformal passivation layers meets industry requirements, and the approach is compatible with mass manufacturing.

Plasmonic coloring of noble metals rendered by picosecond laser exposure

We show the angle-independent coloring of metals in air arising from nanoparticle distributions on metal surfaces created via picosecond laser processing. Each of the colors is linked to a unique total accumulated fluence, rendering the process compatible with industry. We report the coating of the colored metal surfaces using atomic layer deposition which is shown to preserve colors and provide mechanical and chemical protection Laser bursts are composed of closely time-spaced pulses separated by 12.8 ns. The coloring of silver using burst versus non-burst is shown to increase the Chroma, or color saturation, by 50% and broaden the color Lightness range by up to 60%. The increase in Chroma and Lightness are accompanied by the creation of 3 kinds of different laser-induced periodic surface structures (LIPSS). One of these structures is measured to be 10 times the wavelength of light and are not yet explained by conventional theories. Two temperature model simulations of laser bursts interacting with the metal surface show a significant increase in the electron-phonon coupling responsible for the well-defined LIPSS observed on the surface of silver. Finite-difference time-domain simulations of nanoparticles distributed on the high-spatial frequency LIPSS (HSFL) explain the increase in color saturation (i.e. Chroma of the colors) by the enhanced absorption and enriched plasmon resonances.

Chemical Vapor Deposition of Anisotropic Ultrathin Gold Films on Optical Fibers: Real-time Sensing by Tilted Fiber Bragg Gratings and Use of a Dielectric Pre-coating

Tilted fiber Bragg gratings (TFBGs) are refractometry-based sensor platforms that have been employed herein as devices for the real-time monitoring of chemical vapour deposition (CVD) in the near-infrared range (NIR). The coreguided light launched within the TFBG core is back-reflected off a gold mirror sputtered onto the fiber-end and is scattered out into the cladding where it can interact with a nucleating thin film. Evanescent fields of the growing gold nanostructures behave differently depending on the polarization state of the core-guided light interrogating the growing film, therefore the resulting spectral profile is typically decomposed into two separate peak families for the orthogonal S- and P-polarizations. Wavelength shifts and attenuation profiles generated from gold films in the thickness regime of 5-100 nm are typically degenerate for deposition directly onto the TFBG. However, a polarization-dependence can be imposed by adding a thin dielectric pre-coating onto the TFBG prior to using the device for CVD monitoring of the ultrathin gold films. It is found that addition of the pre-coating enhances the sensitivity of the P-polarized peak family to the deposition of ultrathin gold films and renders the films optically anisotropic. It is shown herein that addition of the metal oxide coating can increase the peak-to-peak wavelength separation between orthogonal polarization modes as well as allow for easy resonance tracking during deposition. This is also the first reporting of anisotropic gold films generated from this particular gold precursor and CVD process. Using an ensemble of x-ray techniques, the local fine structure of the gold films deposited directly on the TFBG is compared to gold films of similar thicknesses deposited on the Al2O3 pre-coated TFBG and witness slides.

Chemical Vapour Deposition and Atomic Layer Deposition: Metals for Optical Fibres

Deposition of metal thin films is well-established for vapour-based methods like atomic layer deposition (ALD) and chemical vapour deposition (CVD). The chemistry of the

Characterization and assessment of a novel hybrid organic/inorganic metal-insulator-semiconductor structure for photovoltaic applications

Hybrid organic/inorganic photovoltaic devices have recently emerged as a possible solution to the stability, charge transfer and mobility issues that have been limiting the lifetimes and efficiencies of the organic solar cells. The purpose of the project presented here is to assess the potential of a new hybrid metal-insulator-semiconductor (MIS) photovoltaic device design developed at Carleton University. The silicon substrate is nanostructured with a wet chemical etch resulting in about 1:1 aspect ratio structures of roughly 300nm in size. The interface is passivated with a thin dielectric tunnel barrier of alumina or silica. A layer of transparent conducting polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT), is added through in-situ polymerization. The structure is then completed with a printed silver/polymer composite collection electrode. The electrical current-voltage (I-V) and capacitance-voltage(C-V) characteristics along with the effect of nanostructuring the substrate on the performance of such a solar cell is explored by comparison with unstructured devices. The C-V and I-V measurements are used to estimate changes in the effective device junction due to the structuring. The quality of the insulator layer as well as its optimal thickness are studied. The fabricated structures show photovoltaic behavior with the structuring yielding a significant increase in efficiency. The test structures show promise for the use in photovoltaics and further optimization of such a structure may yield fruitful results in solar applications.