Optical characterisation of plasmonic nanostructures on planar substrates using second-harmonic generation.

Off-normal, polarization dependent second-harmonic generation (SHG) measurements were performed ex situ on plasmonic nanostructures grown by self-assembly on nanopatterned templates. These exploratory studies of Ag nanoparticle (NP) arrays show that the sensitivity of SHG to the local fields, which are modified by the NP size, shape and distribution, makes it a promising fixed wavelength characterization technique that avoids the complexity of spectroscopic SHG. The off-normal geometry provides access to the out-of-plane SH response, which is typically an order-of-magnitude larger than the in-surface-plane response measured using normal incidence, for example in SHG microscopy.

An analytic approach to modeling the optical response of anisotropic nanoparticle arrays at surfaces and interfaces.

Anisotropic nanoparticle (NP) arrays with useful optical properties, such as localized plasmon resonances (LPRs), can be grown by self-assembly on substrates. However, these systems often have significant dispersion in NP dimensions and distribution, which makes a numerical approach to modeling the LPRs very difficult. An improved analytic approach to this problem is discussed in detail and applied successfully to NP arrays from three systems that differ in NP metal, shape and distribution, and in substrate and capping layer.

Optical fingerprints of Si honeycomb chains and atomic gold wires on the Si(111)-(5×2)-Au surface.

The intensively studied Si(111)-(5×2)-Au surface is reexamined using reflectance anisotropy spectroscopy and density functional theory simulations. We identify distinctive spectral features relating directly to local structural motifs such as Si honeycomb chains and atomic gold wires that are commonly found on Au-reconstructed vicinal Si(111) surfaces. Optical signatures of chain dimerization, responsible for the observed (×2) periodicity, are identified.

Manipulating and probing the growth of plasmonic nanoparticle arrays using light.

Highly ordered self-assembled silver nanoparticle (NP) arrays have been produced by glancing angle deposition on faceted c-plane Al2O3 templates. The NP shape can be tuned by changing the substrate temperature during deposition. Reflectance anisotropy spectroscopy has been used to monitor the plasmonic evolution of the sample during the growth.

Controlled in situ growth of tunable plasmonic self-assembled nanoparticle arrays.

Self-assembled silver nanoparticle (NP) arrays were produced by deposition at glancing angles on transparent stepped Al2O3 templates. The evolution of the plasmonic resonances has been monitored using reflection anisotropy spectroscopy (RAS) during growth. It is demonstrated that the morphology of the array can be tailored by changing the template structure, resulting in a large tunability of the optical resonances.

Probing surface and interface structure using optics.

Optical techniques for probing surface and interface structure are introduced and recent developments in the field are discussed. These techniques offer significant advantages over conventional surface probes: all pressure ranges of gas-condensed matter interfaces are accessible and liquid-liquid, liquid-solid and solid-solid interfaces can be probed, due to the large penetration depth of the optical radiation. Sensitivity and discrimination from the bulk are the two challenges facing optical techniques in probing surface and interface structure.

Using surface and interface optics to probe the capping, with amorphous Si, of Au atom chains grown on vicinal Si(111).

The distinct optical signatures of aligned single and double Au atom chain structures, grown on vicinal Si(111) substrates, have been identified using reflectance anisotropy spectroscopy (RAS). Deposition of 0.04 monolayers (ML) of amorphous Si (a-Si) at room temperature perturbs the anisotropic optical response of the double chain structure.

Structure of si(111)-in nanowires determined from the midinfrared optical response.

The anisotropic optical response of Si(111)-(4x1)/(8x2)-In in the midinfrared, where ab initio studies predict significant changes in the band structure between competing models of this important quasi-1D system, has been measured using infrared spectroscopic ellipsometry (IRSE) and reflection anisotropy spectroscopy (RAS). Both IRSE and RAS of the (8x2) phase show that the anisotropic Drude tail of the (4x1) phase is replaced by two peaks at 0.50 and 0.

Magnetic second-harmonic generation from the terraces and steps of aligned magnetic nanostructures grown on low symmetry interfaces.

Aligned magnetic nanostructures grown on low symmetry interfaces are generally inhomogeneous, with different magnetic species, such as terrace and step atoms, contributing to the overall magnetic response from the interfacial regions. It is shown that the presence of different magnetic regions can be detected by means of normal incidence (NI) magnetic second-harmonic generation (MSHG). A phenomenological model of NI MSHG at magnetic interfaces of 1m symmetry is developed and a methodology is described for optimizing the signal-to-noise ratio of extracted hysteresis curves by adjusting the input polarization angle.

Optical reflectance anisotropy of buried Fe nanostructures on vicinal W(110).

The optical anisotropy of Au protected Fe layers grown on a vicinal W(110) surface has been investigated using reflectance anisotropy spectroscopy (RAS). Iron nanostripes formed at submonolayer coverage, as well as Fe layers up to 3 ML coverage, were protected by 12 and 16 nm gold caps and measured ex situ under ambient conditions. The RAS is dominated by structures originating in the interfacial W(110) region, modified by the absorption in the Au cap and possibly by uniaxial strain in the Au cap itself.