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Catalytic nanomotors with silica microbead heads and TiO(2) arms are systematically designed by dynamic shadowing growth. The swimming trajectories are fine tuned by altering the arm length and orientation exploiting geometry-dependent hydrodynamic interactions at low Reynolds number. The curvature, angular frequency, and radius of curvature of the trajectories change as a function of arm length. Simulations based on the method of regularized Stokeslets are also described and correctly capture the trends observed in the experiments.

The pitch height–dependent optical extinction spectra and the electric field enhancement of helical and multiring nanostructures are studied by the discrete dipole approximation method. For light incident along the axis of the helix, with the increase of the pitch height, the plasmon peak wavelengths redshift monotonically and the electric coupling between two adjacent pitches weakens. The plasmon peak can also be tuned by changing the polarization of the incident light, particularly by circularly polarized light. In most cases, the maximum electric field is distributed near the surface of the helix. As a comparison, since multiring structures do not have helicity, the extinction spectra are polarization independent and the maximum electrical fields always distribute on the top ring. These results show that the optical properties of helical structures are different when irradiated by left or right circular polarized light. Understanding and manipulating pitch height allow one to tune the plasmon peak and rearrange the electric field enhancement distribution of helical nanostructures. [ABSTRACT FROM AUTHOR]

Amorphous silicon nanocolumns, square nanospirals, and multilayer spiral/column rods are fabricated on bare Si substrates and monolayer colloid substrates by glancing angle deposition. The grown films are studied by scanning electron microscopy and transmission electron microscopy. The size of the deposited Si columns and spirals increases with the size of colloid particles for fixed incident angle of deposition flux. The feasibility of fabricating separated, well-ordered square spirals provides a cost effective and simple way to fabricate photonic crystals. [ABSTRACT FROM AUTHOR]

We have investigated the surface enhanced Raman scattering (SERS) from Au nanocombs and nanorods under different excitation conditions. The SERS intensity from nanocombs is always larger than that from nanorods, but the polarized SERS dependence is similar for the two nanostructures. These results agree quantitatively well with the local E-field calculations, and the nanospine in the nanocomb increases the local E-field over all surfaces of the nanocomb structure. The combination of experimental and numerical results predicts that the Raman enhancement at 633 nm excitation is estimated to be from seven to eight times that at 785 nm excitation. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role. [ABSTRACT FROM AUTHOR]

The extinction spectra and field distribution of Ag helical nanostructures have been calculated using the discrete dipole approximation method. The plasmon peak of the Ag helix can be tuned not only by the structural parameters but also by the polarizations of the incident light, especially the circular polarizations. In addition, the polarization direction of the incident light can change the spatial distribution of the maximum E field, which provides a simple way to spatially resolve analyte’s distribution on the nanostructures for sensing applications. [ABSTRACT FROM AUTHOR]

Substrates consisting of silver nanorod arrays with an irregular surface lattice (i.e., random nucleation sites) and with varying rod lengths were fabricated by an oblique angle vapor deposition method. These arrays were evaluated as potential surface-enhanced Raman spectroscopy (SERS) substrates using trans-1,2-bis(4-pyridyl)ethene as a reported molecule. SERS activity was shown to depend upon the length of the nanorods. The Ag nanorods with average lengths of 508.29±44.86 nm, and having aspect ratios of 5.69±1.49 exhibited the maximum SERS enhancement factors of greater than 108. Theoretical calculations indicate that this large SERS enhancement may be partially explained by the shape, density, and lateral arrangement of the Ag nanorod arrays. [ABSTRACT FROM AUTHOR]

Nanostructured materials have shown great potential in improving the sensitivity and reliability of chemical and biological sensors. The ability to control the geometric shape (size, separation, orientation, alignment, etc.) of nanostructures and to integrate nanostructures from different materials becomes one of the great challenges for sensor fabrication. Glancing angle deposition techniques can fabricate well-aligned three-dimensional nanostructures through computer programming. By rotating the substrate in both polar and azimuthal directions, one can fabricate desired nanostructures, such as nanorod arrays with different shapes, nanospring arrays, and even multilayer nanostructures. This method offers full three-dimensional control of the nanostructure with the additional capability of self-alignment and can be easily integrated into microdevices and optical devices. With the high surface area and high aspect ratio of those nanostructures, different sensors such as enzyme-based biosensors and optical sensors with higher sensitivity have been demonstrated. [ABSTRACT FROM AUTHOR]