Surface plasmons on silver gratings transform pyrolytic carbon into luminescent graphitized carbon dots.

Plasmonic catalysis holds the promise of opening new reaction pathways that are inaccessible thermally or via direct UV-vis electronic transitions. Here, energetic carriers produced via the decay of surface plasmons excited by visible light at 532 nm (2.33 eV, green) on a Ag-grating-bearing pyrolytic carbon residue drive its transformation into light-emitting graphitized carbon dots.

Laser-machined thin copper films on silicon as physical unclonable functions.

Physical unclonable functions (PUFs) are receiving significant attention with the rise of cryptography and the drive towards creating unique structures for security applications and anti-counterfeiting. Specifically, nanoparticle based PUFs can produce a high degree of randomness through their size, shape, spatial distribution, chemistry, and optical properties, rendering them very difficult to replicate. However, nanoparticle PUFs typically rely on complex preparation procedures involving chemical synthesis in solution, therefore requiring dispersion, and embedding within a host medium for application.

Multiphoton laser-induced confined chemical changes in polymer films.

We report ultrafast-laser-induced photochemical, structural, and morphological changes in a polyimide film irradiated at the polymer-glass interface in back-incident geometry. Back-illumination creates locally hot material at the interface leading to a confined photochemical change at the interface and a morphological change through a blister formation. The laser-induced photochemical changes in polyimide resulted in new absorption and luminescence properties in the visible region.

Visible light driven plasmonic photochemistry on nano-textured silver.

Plasmon assisted generation of silver sulfate from dodecanethiol is demonstrated on a nano-textured silver substrate with a strong surface plasmon resonance in the visible range. The observed photo-physical processes are attributed to hot charge carriers that are generated from the excitation of surface plasmon resonances using 532 nm laser light. Excited charge carriers are responsible for cleaving the alkane chain, and for generating reactive oxygen species which rapidly photooxidize the exposed sulfur atoms.

A platform for colorful solar cells with enhanced absorption.

We demonstrate submicron thick platform integrating amorphous silicon nanowires and thin-films achieving vivid colors in transmission and reflection. The platform nearly doubles the absorption efficiency compared to the starting thin-film without much compromising with color diverseness. The structural colors can be changed over a wide range by changing the diameters of the nanowires while still keeping the absorption efficiency higher than starting thin-film.

Resonant photo-thermal modification of vertical gallium arsenide nanowires studied using Raman spectroscopy.

Gallium arsenide nanowires have shown considerable promise for use in applications in which the absorption of light is required. When the nanowires are oriented vertically, a considerable amount of light can be absorbed, leading to significant heating effects. Thus, it is important to understand the threshold power densities that vertical GaAs nanowires can support, and how the nanowire morphology is altered under these conditions.

Adjustable optical response of amorphous silicon nanowires integrated with thin films.

We experimentally demonstrate a new optical platform by integrating hydrogenated amorphous silicon nanowire arrays with thin films deposited on transparent substrates like glass. A 535 nm thick thin film is anisotropically etched to fabricate vertical nanowire arrays of 100 nm diameter arranged in a square lattice. Adjusting the nanowire length, and consequently the thin film thickness permits the optical properties of this configuration to be tuned for either transmission filter response or enhanced broadband absorption.

Enhanced photothermal conversion in vertically oriented gallium arsenide nanowire arrays.

The photothermal properties of vertically etched gallium arsenide nanowire arrays are examined using Raman spectroscopy. The nanowires are arranged in square lattices with a constant pitch of 400 nm and diameters ranging from 50 to 155 nm. The arrays were illuminated using a 532 nm laser with an incident energy density of 10 W/mm(2).

Color generation and refractive index sensing using diffraction from 2D silicon nanowire arrays.

Tunable structural color generation from vertical silicon nanowires arranged in different square lattices is demonstrated. The generated colors are adjustable using well-defined Bragg diffraction theory, and only depend on the lattice spacing and angles of incidence. Vivid colors spanning from bright red to blue are easily achieved.

Temperature and hydration dependence of proton MAS NMR spectra in MCM-41: model based on motion induced chemical shift averaging.

The proton MAS NMR spectra in MCM-41 at low hydration levels (less than hydration amounting to one water molecule per surface hydroxyl group) show complex proton resonance peak structures, with hydroxyl proton resonances seen in dry MCM-41 disappearing as water is introduced into the pores and new peaks appearing, representing water and hydrated silanol groups. Surface hydroxyl group-water molecule chemical exchange and chemical shift averaging brought about by a water molecule visiting different surface hydrogen bonding sites have been proposed as possible causes for the observed spectral changes. In this report a simple model based on chemical shift averaging, due to the making and breaking of hydrogen bonds as water molecules move on the MCM-41 surface, is shown to fully reproduce the NMR spectra, both as a function of hydration and temperature.