Surface-supported, low-dimensional gold nanostructures are of interest for plasmonic applications. Low dimensional nanostructures are readily accessible by solution-phase growth, where shape control through the addition of growthdirecting surfactants is well established. Yet, shape control in chemical vapour deposition (CVD) has not been well explored, and metallic gold films are typically limited to nanoparticulate or thin film morphologies. This article describes the self-seeded growth of high aspect ratio gold plates and wires by CVD. A directed growth mechanism is proposed, where growth is directed by the coordinating N-heterocyclic carbene (NHC) and phosphine ligands originating from the thermal decomposition of the two gas-phase precursors, [Au(HMDS)(NHC)] (HMDS = hexamethyldisilazide, NHC = 1,3-diisopropyl-imidazolidin-2-ylidene) and [Au(HMDS)(PMe 3 )]. These ligands acted as transient surfactants for plate growth between 370 and 460°C and at high precursor flux. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) evidence indicates that hydroxyl terminated substrate surfaces are passivated with trimethylsilyl (TMS) moieties originating from the HMDS ligand in both precursors, which promoted island type growth and directed precursor decomposition to occur on gold surfaces. Secondary nucleation is observed on all gold structures, and is a crucial component to gas-phase surfactant-mediated CVD growth. This work identifies the potential to use precursor-bound coordinative ligands or gas-phase surfactants to direct growth of metal nanocrystals by CVD.

Formic acid can undergo dehydration or dehydrogenation with variable selectivity over a range of metal catalysts. The selectivity among these reactions depends on the reaction mechanism and reaction conditions pertinent on each surface. This work provides mechanistic insight on the decomposition of formic acid on cobalt at high and low temperature regimes. The adsorption and decomposition of formic acid on a Co(0001) single crystal was studied in ultra-high vacuum by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Insight is provided using DFT calculations. In the low temperature regime, formic acid adsorbs molecularly on the surface at 130 K. Partial decomposition produces CO at 140 K, and at 160 K the decomposition of formic acid into formate, which is a thermodynamic sink, is dominant. Water can be formed at low temperature via bimolecular processes. At high temperature (>400 K) the similar barriers for decomposition of the formate species lead to the concomitant production of CO, CO2 and H2. The correlation between experiment and theory provides a framework for the interpretation of surface species and reaction path operating in different regimes.

The combined effect of nanoscale dielectric and metallic layers prepared by atomic layer deposition (ALD) and chemical vapor deposition (CVD) on the refractometric properties of tilted optical fiber Bragg gratings (TFBG) is studied. A high index intermediate layer made up of either 50 nm or 100 nm layers of Al2O3 (refractive index near 1.62) was deposited by ALD and followed by thin gold layers (30-65 nm) deposited from a known single-source gold (I) iminopyrrolidinate CVD precursor. The fabricated devices were immersed in different surrounding refractive indices (SRI) and the spectral transmission response of the TFBGs was measured. Preliminary results indicate that the addition of the dielectric Al2O3 pre-coating enhances the SRI sensitivity by up to 75% but this enhancement is highly dependent on the polarization and dielectric thickness. In fact, the sensitivity decreases by up to 50% for certain cases. These effects are discussed with support from TFBG simulations and models, by quantifying the penetration of the evanescently coupled light out of the fiber through the various coating layers. Additional characterization studies have been carried out on these samples to further correlate the optical behaviour of the coated TFBGs with the physical properties of the gold and Al2O3 layers, using atomic force microscopy x-ray photoelectron spectroscopy and an ensemble of other optical and x-ray absorption spectroscopy techniques. The purity, roughness, and morphology of gold thin films deposited by CVD onto the dielectric-TFBG surface are also provided.

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