Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency.

Silver nanoparticles (Ag NPs) have unique optical, electrical, and thermal properties and are being incorporated into products that range from photovoltaics to biological and chemical sensors. The production of silver nanoparticles has been increasing worldwide in the nanotechnology industry due to the variety of applications and are very likely to reach aquatic ecosystems damaging them. Due to their small size and high surface area to volume ratio of NPs, they can strongly interact with life cells and cause damage to tested animals. Based on the mentioned previously, it is necessary to evaluate the silver nanoparticle nanotoxicity in aquatic ecosystems to prevent possible ingestion or transfer to humans. Also, the research will benefit aquatic systems due to less pollution around aquatic organisms. The objectives of this research included: i) production and characterization of stable silver nanoparticles in water, ii) characterizing the optical properties by UV-Vis spectroscopy and morphology by HR-TEM and; iii) evaluate the toxicity of silver nanoparticles in aquatic organisms, i.e Artemia salina. Results obtained evidenced that Ag NPs showed an intense absorption peak at 448 nm. This broad peak is due to the phenomenon called surface plasmon resonance (SPR) that is responsible for a variety of phenomena, including nanoscale optical focusing, negative refraction, and surface-enhanced Raman scattering. HR-TEM measurements evidenced the spherical form of the nanoparticles and its small size at around 12-20 nm. In addition, Electron Diffraction analyses suggested the composition of the nanoparticle, which contained only Ag0. The toxicity assays were evaluated using different concentrations of purified Ag NPs. During the cytotoxicity assay, it was demonstrated that Ag NPs were not toxic to Artemia salina after 24 and 48 hours of exposure. However, silver (as silver nitrate) evidenced high toxicity to Artemia salina at larval stage.

Propagating inhomogeneous electromagnetic waves called surface plasmon polaritons (SPPs) can be excited by free-space beams on corrugated conducting surfaces at resonance angles determined by corrugation period, permittivity, and optical frequency. SPPs are coupled to and co-propagate with surface charge displacements. Complete electrical isolation of individual conducting corrugations prevents the charge displacement necessary to sustain an SPP, such that excitation resonances of traveling SPPs are absent. However, SPPs can be excited via electric induction if a smooth conducting surface exists below and nearby the isolated conducting corrugations. The dependence of SPP excitation resonances on that separation is experimentally investigated here at long-wave infrared wavelengths. We find that excitation resonances for traveling SPPs broaden and disappear as the dielectric’s physical thickness is increased beyond ~1% of the free-space wavelength. The resonance line width increases with refractive index and optical thickness of the dielectric.

Plasmonic metallic nanoparticles can significantly enhance the catalytic efficiency of semiconductors via plasmonic photocatalysis. In this study, a hybrid Ag/TiO2 photocatalyst was synthesized and tested for the photochemical reduction of bicarbonate to value-added formic acid. It was found that under solar irradiation, TiO2 is not very efficient, but formate production is significantly increased with the addition of silver nanoparticles. Under 365 nm irradiation, the photocatalytic efficiency of TiO2 is enhanced, but no effect was observed with the addition of silver nanoparticles. Under solar irradiation, Ag/TiO2 reached an apparent quantum efficiency (AQE) of 7.78 ± 0.04%, the highest AQE observed so far. Enhanced photocatalytic activity is attributed to the synergistic effect between UV photon excitation of TiO2 and surface plasmon resonance enhancement. To elucidate the mechanism of plasmon-enhanced photocatalysis, experiments were performed under solar irradiation and 365 nm irradiation. We propose that photo-excited electrons are transferred from above the Fermi level of the metal nanoparticle to the conduction band of the semiconductor through plasmon-induced electron transfer.

Graphene oxide serves as a precursor to various technologies, which include batteries, biosensors, solar cells, and supercapacitors. Gold nanoparticles exhibit excellent electrochemical and photophysical properties, allowing for electronic absorption and the ability to absorb light energy at the plasmonic wavelength. Palladium nanoparticles are highly sensitive and functional in room temperature, making it an ideal metal for catalytic applications. We report the synthesis of functional graphene oxide from graphite flakes followed by the insertion of gold and palladium nanoparticles through an oleylamine ligand. In this report, the fermi level of graphene oxide (GOx), gold-graphene oxide (Au-GOx), and palladium-graphene oxide (Pd-GOx) was shown to be effectively controlled. Additionally, each system showed complete solubility in ethanol and in the case of Au-GOx, enhanced solubility was seen in tetrahydrofuran as well.

In situ, real-time monitoring of a dehydration of poly(vinyl alcohol) (PVA) film is researched. The technique based on the incorporation plasmonic nanocages (NCs) between the two identical layers of PVA, (PVA)/NCs/(PVA) film, and its sensitivity to the variation of the refractive index of the surrounding PVA film via desorption water. The dehydration time increases from 180 (s) to 1800 (s) as the content of the PVA in the films increases twice, from (PVA)/NCs/(PVA) to (PVA)2/NCs/(PVA)2. Such effect could be explained by different rate of the molecules desorption from the PVA based films. Specifically, the dehydration rate is of 0.22 (vol% per s) and 0.026 (vol% per s) for (PVA)/NCs/(PVA) and (PVA)2/NCs/(PVA)2 films, respectively. The dehydration rate constant reduces from -50×10-4 (s-1) to -4.3 ×10-4 (s-1) as the content of PVA increases from (PVA)/NCs/(PVA) to (PVA)2/NCs/(PVA)2 films, respectively.

Sparsely distributed and self-organized gold-nanocones are fabricated by broad argon ion beam sputtering on the gold surface with grazing incident angle. The rotation of the sample with respect to the vertical axis has found to influence the morphology of the obtained nanostructures. Ion beam irradiation of the sample leads to formation of nanoripples when the sample is held stationary, otherwise nanocones are formed if the sample is rotated during irradiation. A hybrid gold-nanocone/graphene/gold-nanohole based surface-enhanced Raman scattering (SERS) sensor is proposed and shown to exhibit an enhancement factor of 109 via finite-difference time-domain (FDTD) simulations.

Metal–insulator–metal (MIM) resonant absorbers comprise a conducting ground plane, a dielectric of thickness t, and thin separated metal top-surface structures of dimension l. The fundamental resonance wavelength is predicted by an analytic standing-wave model based on t, l, and the dielectric refractive index spectrum. For the dielectrics SiO2, AlN, and TiO2, values for l of a few microns give fundamental resonances in the 8-12 μm long-wave infrared (LWIR) wavelength region. Agreement with theory is better for t/l exceeding 0.1. Harmonics at shorter wavelengths were already known, but we show that there are additional resonances in the far-infrared 20 - 50 μm wavelength range in MIM structures designed to have LWIR fundamental resonances. These new resonances are consistent with the model if far-IR dispersion features in the index spectrum are considered. LWIR fundamental absorptions are experimentally shown to be optimized for a ratio t/l of 0.1 to 0.3 for SiO2- and AlN-based MIM absorbers, respectively, with TiO2-based MIM optimized at an intermediate ratio.

Transdimensional photonics has emerged as a new field of science and engineering that explores the optical properties of materials and nanostructures in the translational regime between two and three dimensions. In the present work, we study an example of such transdimensional lattice consisting of nanoparticle array, and we aim at a direct comparison of lattice resonances excited in the periodic lattices of either plasmonic (gold) or silicon nanoparticles of the same size and interparticle spacing. We numerically analyze extinction cross-sections and reflection from the array, and we include electric and magnetic dipoles and electric quadrupoles into consideration. Lattice resonances are excited at the wavelength close to Rayleigh anomaly which is defined by the array periodicity, and different multipoles respond to one or another period of rectangular array depending on incident light polarization. We show that lattice resonances originating from dipole moments are extended to the larger spectral range than electric-quadrupole lattice resonances. Overlap of resonances causes a decrease in reflection (generalized Kerker effect) and, in the case of electric quadrupole and magnetic dipole moments, the coupling of the multipoles is enabled by the lattice.

Incorporation of metallic nanoparticles (NPs) in polymer matrix has been used to enhance and control dissolution and release of drugs, for targeted drug delivery, as antimicrobial agents, localized heat sources, and for unique optoelectronic applications. Gold NPs in particular exhibit a plasmonic response that has been utilized for photothermal energy conversion. Because plasmonic nanoparticles typically exhibit a plasmon resonance frequency similar to the visible light spectrum, they present as good candidates for direct photothermal conversion with enhanced solar thermal efficiency in these wavelengths. In our work, we have incorporated ∼3-nm-diameter colloidal gold (Auc) NPs into electrospun polyethylene glycol (PEG) fibers to utilize the nanoparticle plasmonic response for localized heating and melting of the polymer to release medical treatment. Auc and Auc in PEG (PEG+Auc) both exhibited a minimum reflectivity at 522 nm or approximately green wavelengths of light under ultraviolet-visible (UV-Vis) spectroscopy. PEG+Auc ES fibers revealed a blue shift in minimum reflectivity at 504 nm. UV-Vis spectra were used to calculate the theoretical efficiency enhancement of PEG+Auc versus PEG alone, finding an approximate increase of 10 % under broad spectrum white light interrogation, and ∼14 % when illuminated with green light. Auc enhanced polymers were ES directly onto resistance temperature detectors and interrogated with green laser light so that temperature change could be recorded. Results showed a maximum increase of 8.9 °C. To further understand how gold nanomaterials effect the complex optical properties of our materials, spectroscopic ellipsometry was used. Using spectroscopic ellipsometry and modeling with CompleteEASE® software, the complex optical constants of our materials were determined. The complex optical constant n (index of refraction) provided us with optical density properties related to light wavelength divided by velocity, and k (extinction coefficient) was used to show the absorptive properties of the materials.

Colloidal gold-palladium (Au-Pd) bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) photo-oxidation cycle, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Au-Pd bimetallic alloy and core-shell nanoparticles were prepared to synergistically couple a plasmonic absorber (Au) with a catalytic metal (Pd) with composite optical and catalytic properties tailored towards promoting photocatalytic oxidation. Catalysts utilizing metals that exhibit localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement for small molecule oxidation via augmented photocarrier generation/separation and photothermal conversion. The coupling of Au to Pd in an alloy or core-shell nanostructure maintains SPR-induced charge separation, mitigates the poisoning effects on Pd, and allows for improved EtOH oxidation. The Au-Pd nanoparticles were coupled to semiconducting titanium dioxide photocatalysts to probe their effects on plasmonically-assisted photocatalytic oxidation of EtOH. Complete oxidation of EtOH to CO2 under solar simulated-light irradiation was confirmed by monitoring the yield of gaseous products. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.

We visually observed color changes of discontinuous gold surfaces on paper substrates through localized surface plasmon resonance (LSPR) at room temperature due to surface diffusion of gold nanostructures. Isolated nanoparticles and an uncompleted nanosheet of gold were obtained by thermal vapor deposition. After preservation for 8 months in air at room temperature, the particle sizes and shapes remarkably changed with color changes. The surface diffusion of the discontinuous gold on the paper would be derived from solid-state dieting, resulting in the growth of the nanosheet defect and coalescence of the nanoparticles. This is due to the total energy minimization of the surfaces of gold nanostructures and the paper and the interface between gold and the paper.

Deposition of size-selected copper and silver nanoparticles (NPs) on polymers using cluster beam technique is studied. It is shown that ratio of particle embedment in the film can be controlled by simple thermal annealing. Combining electron beam lithography, cluster beam deposition, and heat treatment allows to form specific patterns (arrays) of metal NPs on polymer films. Plasticity and flexibility of polymer host and specific properties added by coinage metal NPs open a way for different applications of such composite materials, in particular, for the formation of plasmonic structures with required configurations which can be applied for wave-guiding, resonators, in sensor technologies, and surface enhanced Raman scattering.

A fully two-dimensional theoretical study of the electromagnetic wave propagation through Metal–Liquid Crystal–Metal (M–LC–M) waveguide structure is presented. Dispersion relations corresponding to both symmetric and antisymmetric-coupled surface plasmons polaritons modes in M–LC–M structure are derived and numerically solved. The effects of LC tilt angles on the effective refractive index and propagation length are proposed. The analytical method is in good agreement with those obtained from finite-difference time-domain simulation. The obtained analytic formula can be used as an efficient element in designing tunable ultrahigh nanoscale integrated plasmonic devices.