Tunable Plasmonic Properties Research Articles

Optical properties of unoxidized and oxidized titanium nitride thin films

This study reports a pulsed laser deposition-assisted synthesis of highly metallic titanium nitride (TiN) and a series of semiconducting titanium oxynitride (TiNxOy) compounds in thin film form with tunable plasmonic properties by carefully altering the nitrogen (N)-oxygen (O) ratio. The N/O ratio was controlled from 0.3 (highest oxygen doping of TiN) to ~ 1.0 (no oxygen doping of TiN) by growing the TiN films under nitrogen pressures of 50, 35, and 10 mTorr and high vacuum conditions of 2 × 10−6 Torr with no external gas introduced. The presence of nitrogen in the deposition chamber during the film growth affects the gas phase oxidation of TiN to TiNxOy by increasing the mean free path-dependent N and O inter-collisions per second by two to three orders of magnitudes. The evidence of increased oxidation of TiN to TiNxOy with an increase in nitrogen deposition pressure was obtained using X-ray photoelectron spectroscopy analysis. While the TiN samples deposited in high vacuum conditions had the highest reflectance, TiNxOy thin films were also found to possess high reflectance at low frequency with a well-defined edge around 20,000 cm−1. Furthermore, the vacuum-deposited TiN samples showed a large negative dielectric constant of -330 and the largest frequency of zero-crossing at 25,000 cm−1; the TiNxOy samples deposited in the presence of nitrogen ambient also showed promising plasmonic applications at the near-mid infrared range. A comparison of the dielectric constant and loss function data of this research with the literature values for noble metals seems to indicate that TiN and TiNxOy have the potential to replace gold and silver in the visible and near-infrared spectral regions.

Investigating Sensor Properties of Plasmonic Gold Nanoparticles Produced By Pulsed Laser Deposition

Plasmonic gold nanoparticles exhibit exceptional optical properties, particularly Lo-calised Surface Plasmon Resonance, which makes them ideal candidates for sensor applications. These nanoparticles are highly sensitive to changes in their surrounding environment, allowing for precise detection of molecular interactions and environ-mental shifts. In this study, we investigate the sensor properties of gold nanoparticles produced via Pulsed Laser Deposition, a clean and versatile method that allows for precise control over particle size, morphology, and distribution without the need for chemical reagents. Pulsed Laser Deposition process was optimized by adjusting laser fluence, pulse duration, and deposition time to produce gold nanoparticles with tuna-ble plasmonic properties. The structural and optical characteristics of gold nanoparti-cles were analyzed using scanning electron microscopy, and UV-Vis spectroscopy, confirming that the size and morphology of the particles were controllable through the deposition parameters. The sensor performance of gold nanoparticles was evalu-ated through localised surface plasmon resonance measurements, which demonstrated their sensitivity to small changes in the refractive index of the surrounding medium. Specifically, the shift in localised surface plasmon resonance peak was measured up-on exposure to different analytes, including protein A where a wavelength shift of 50 nm measured, indicating the high sensitivity of these nanoparticles for biosensing ap-plications. The results suggest that Pulsed Laser Deposition-produced gold nanoparti-cles possess promising sensor properties for real-time detection and environmental monitoring, offering an efficient and reproducible platform for a wide range of sens-ing applications.

The Adsorption Kinetics of CTA+, Br-, and Ag+ Determining Anisotropic Growth of Gold Nanorods

Gold nanorods (AuNRs) have received significant attention due to their tunable plasmonic properties across the visible and near-infrared spectrum, large surface area to volume ratio, and chemical inertness, making them valuable in biomedical engineering and photochemistry. The physical properties of anisotropic AuNRs strongly depend on their aspect ratio, defined as the ratio of length to width. Previous studies have primarily focused on synthetic methods to precisely control the aspect ratio of AuNRs. Among various synthetic routes, the seed-mediated growth method in aqueous solution, comprising nucleation and further growth steps, is considered the best approach to obtain highly uniform AuNRs with a high yield. Notably, the method utilizing Ag+ with cetyltrimethylammonium cation (CTA+) and Br- during the growth step from Au nanoparticle seeds to NRs is the most convenient for controlling the aspect ratio of AuNRs. In this method, Ag+ acts as a key additive for symmetry breaking, ultimately modulating the aspect ratio of AuNRs. Despite advancements in synthetic methods, the underlying mechanism governing the cooperative interaction between additives (CTA+, Br-, and Ag+) and the anisotropic growth of AuNRs remains incompletely understood. Although computational simulations shed light on the detailed chemistry regarding the adsorption of additives, further investigation into the adsorption kinetics and their impact on the reduction of Au complexes is necessary. Due to the lack of information on the detailed chemistry during AuNR growth, synthetic results are sometimes inadequately explained by existing mechanisms. Therefore, this study aims to investigate the effect of CTA+, Br-, and Ag+ on the anisotropic growth of AuNRs. Electrochemical analyses will explore how Ag+ affects the adsorption behavior of CTA+ and Br-. This presentation will introduce the influence of each additive on Au reduction and the formation of suppression layers on AuNR surfaces across varying adsorption and growth durations.

Highly Monodisperse Stable Gold Nanorod Powder for Optical Sensor.

Gold nanorods (GNRs) as plasmonic metal nanoparticles are valuable for optical applications due to their tunable plasmonic properties. However, conventional colloidal GNRs face significant optical instability during storage, which limits their practical use. In this work, we developed a highly dispersible GNR powder using an octadecyl trimethylammonium bromide (C18TAB)-assisted freeze-drying method, preserving the optical and chemical sensing properties of GNRs for over 4 months. Compared with C16TAB, C18TAB significantly enhances the GNRs dispersibility even at lower concentrations. Our study demonstrates that C18TAB forms a sponge-like crystal structure that prevents aggregation during the freeze-drying process. The resulting GNR powder retains its plasmonic features and water dispersibility, achieving near-identical optical properties to those of fresh GNR solutions. This stability enabled creation of a liquid-free colorimetric test kit with a long shelf life. This work marks a significant step forward in the use of GNRs as standard analytical reagents, opening new avenues for real-world applications.

Modeling of the tunable plasmonic properties of spherical and ellipsoidal silver nanoparticles in the matrix of an organic semiconductor

The object of research is the tunable plasmonic properties of spherical and ellipsoidal silver nanoparticles in the organic semiconductor matrix. The average absorption cross-sections, scattering cross-sections, and optical radiation efficiency of spherical and ellipsoidal silver nanoparticles have been simulated. The long-wave statistical approach has been used to model the optical parameters of the assembled spherical and ellipsoidal nanoparticles. Statistical averaging is used here, where absorption and scattering are considered from an «effective» particle with statistical properties. This approach avoids complex calculations considering the details of the spectral characteristics of single nanoparticles of different shapes. Taking into account the fact that the nanocomposite matrix will contain ensembles of spherical nanoparticles of different sizes, the peak of their absorption and scattering cross sections will be shifted to the short wavelength region of the spectrum compared to ensembles of the same spherical nanoparticles. In addition, there is a slight increase in the absorption cross-section and a decrease in the scattering cross-section, confirming the presence of smaller nanoparticles. A study was made of a composite material containing a randomly dispersed ensemble of silver ellipsoidal nanoparticles of the same and different shapes and sizes in an organic semiconductor matrix. An ensemble of identical ellipsoidal nanoparticles is characterized by the presence of two plasmon peaks, which corresponds to the characteristics of a single ellipsoidal nanoparticle. A completely different situation is observed if to consider that the nanocomposite will contain an ensemble of ellipsoidal nanoparticles of different shapes and sizes. Such nanoparticles will be characterized by a plasmon peak for both the absorption and scattering cross-sections. This can be explained by the fact that as the size of ellipsoidal nanoparticles decreases, the distance between the peaks responsible for the longitudinal and transverse modes of plasmon excitation decreases. An increase in the shape distribution leads to a broadening of the absorption and scattering cross-section spectra. The efficiency of the optical radiation increases as the size distribution increases. It is shown that a change in the refractive index of an organic semiconductor matrix mainly affects only the value of the scattering cross-section of an ensemble of ellipsoidal nanoparticles dispersed in it. This research is a preliminary step to studying the influence of these particles on the properties of organic light-emitting structures.

Engineering Carrier Density and Effective Mass of Plasmonic TiN Films by Tailoring Nitrogen Vacancies.

The introduction of nitrogen vacancies has been shown to be an effective way to tune the plasmonic properties of refractory titanium nitrides. However, its underlying mechanism remains debated due to the lack of high-quality single-crystalline samples and a deep understanding of electronic properties. Here, a series of epitaxial titanium nitride films with varying nitrogen vacancy concentrations (TiNx) were synthesized. Spectroscopic ellipsometry measurements revealed that the plasmon energy could be tuned from 2.64 eV in stoichiometric TiN to 3.38 eV in substoichiometric TiNx. Our comprehensive analysis of electrical and plasmonic properties showed that both the increased electronic states around the Fermi level and the decreased carrier effective mass due to the modified electronic band structures are responsible for tuning the plasmonic properties of TiNx. Our findings offer a deeper understanding of the tunable plasmonic properties in epitaxial TiNx films and are beneficial for the development of nitride plasmonic devices.

Tunable surface plasmon properties of hollow cylindrical nanocomposite structures

Tunable surface plasmon properties of hollow cylindrical nanocomposite structures

Low-loss plasmons in Weyl semimetals Mn3Sn

We report the optical reflectance measurement for Weyl semimetal Mn3Sn single crystal at room temperature. We observe a low-loss plasmon in the UV energy ranges. This low plasmonic loss is associated with a large electron scattering rate contributed by electron-electron interaction and scattering of conduction electrons by Mn atoms. The incorporation of more Mn atoms simultaneously adds more elastic scattering centers and increases the strength of electron-electron correlation which generates multiple plasmons with lower plasmonic loss in Mn3+xSn1-x. The UV tunable plasmonic properties in Mn3+xSn1-x have great potential for plasmonic and spintronic applications. We also discuss the plasmonic loss in Mn3Sn to the other conducting materials including correlated and non-correlated systems establishing the crucial role of electron correlation on the plasmonic loss. Our result suggests novel and effective strategies for obtaining lower plasmonic loss in the class of correlated materials.

Design of Biopolymer-Coated Gold Nanorods as Biorelevant Photothermal Agents.

Gold nanorods (AuNRs) are emerging metallic nanoparticles utilized to generate heat for photothermal therapy (PTT) in cancer. The tunable plasmonic properties of AuNRs make them a remarkable candidate for hyperthermia. However, the cytotoxicity of AuNRs limits its biological applicability due to the existence of cetyltrimethylammonium bromide (CTAB) on the surface as a common surfactant. In this study, AuNRs are synthesized by seed-mediated growth and then the optical properties are optimized by altering AgNO3 concentration. Afterward, CTAB is replaced with biopolymers which are BSA:Dextran and BSA:Guar Gum conjugates resulting in enhanced cellular viability, enabling to use of them as biologically relevant photothermal agents. The biocompatibility of AuNRs is improved to utilize them at high concentrations for laser studies, in which similar heat generation success of CTAB- and biopolymer-coated AuNRs are shown for potential PTT applications. CTAB and biopolymer-coated AuNRs in concentrations of 0.5 and 1mg mL-1 are irradiated under NIR light at 808nm laser at 0.5, 0.75, and 1W cm-2 for 300 s. The biopolymer-coated gold nanorods with different coatings preserve photothermal properties while reducing the cytotoxicity effects of CTAB and thus they are promising photothermal agents for potential PTT.

Self-Assembled TiN-Metal Nanocomposites Integrated on Flexible Mica Substrates towards Flexible Devices.

The integration of nanocomposite thin films with combined multifunctionalities on flexible substrates is desired for flexible device design and applications. For example, combined plasmonic and magnetic properties could lead to unique optical switchable magnetic devices and sensors. In this work, a multiphase TiN-Au-Ni nanocomposite system with core-shell-like Au-Ni nanopillars embedded in a TiN matrix has been demonstrated on flexible mica substrates. The three-phase nanocomposite film has been compared with its single metal nanocomposite counterparts, i.e., TiN-Au and TiN-Ni. Magnetic measurement results suggest that both TiN-Au-Ni/mica and TiN-Ni/mica present room-temperature ferromagnetic property. Tunable plasmonic property has been achieved by varying the metallic component of the nanocomposite films. The cyclic bending test was performed to verify the property reliability of the flexible nanocomposite thin films upon bending. This work opens a new path for integrating complex nitride-based nanocomposite designs on mica towards multifunctional flexible nanodevice applications.

Welded Gold Nanoparticle Assemblies Defined Plasmonic Coupling.

Nanoparticle assemblies with interparticle ohmic contacts are crucial for nanodevice fabrication. Despite tremendous progress in DNA-programmable nanoparticle assemblies, seamlessly welding discrete components into welded continuous three-dimensional (3D) configurations remains challenging. Here, we introduce a single-stranded DNA-encoded strategy to customize welded metal nanostructures with tunable morphologies and plasmonic properties. We demonstrate the precise welding of gold nanoparticle assemblies into continuous metal nanostructures with interparticle ohmic contacts through chemical welding in solution. We find that the welded gold nanoparticle assemblies show a consistent morphology with welded efficiency over 90%, such as the rod-like, triangular, and tetrahedral metal nanostructures. Next, we show the versatility of this strategy by welding gold nanoparticle assemblies of varied sizes and shapes. Furthermore, the experiment and simulation show that the welded gold nanoparticle assemblies exhibit defined plasmonic coupling. This single-stranded DNA encoded welding system may provide a new route for accurately building functional plasmonic nanomaterials and devices.

Tunable Plasmonic Properties of Spatially Overlapping Asymmetric Nanoparticle Dimers

Tunable Plasmonic Properties of Spatially Overlapping Asymmetric Nanoparticle Dimers

INFLUENCE OF THE REDUCING AGENTS ON MORPHOLOGY AND PROPERTIES OF SIVER STRUCTURES ON PAPER

Abstract. A paper-based SERS substrate with tunable plasmonic properties and excellent flexibility has been applied in various fields. These SERS substrates were prepared using a direct chemical reduction synthesis method for the present work. The isotropic and anisotropic morphology of silver structures on cellulose paper fiber were controlled by the types of reducing agents: (1) sodium borohydride (NaBH4), (2) ascorbic acid (L-AA), (3) glucose, (4) formaldehyde (HCHO). The plasmon characterization of silver structures on paper was systematically investigated. The fabricated paper-based SERS substrates were used to detect melamine in an aqueous solution and determine the influence of type reducing agents on the enhancement factor (EF) and signal uniformity of SERS substrates.

Controlled formation of gold nanoparticles with tunable plasmonic properties in tellurite glass

Silicate glasses with metallic nanoparticles (NPs) have been of intense interest in art, science and technology as the plasmonic properties of these NPs equip glass with light modulation capability. The so-called striking technique has enabled precise control of the in situ formation of metallic NPs in silicate glasses for applications from coloured glasses to photonic devices. Since tellurite glasses exhibit the unique combination of comparably easy fabrication, low phonon energy, wide transmission window and high solubility of luminescent rare earth ions, there has been a significant amount of work over the past two decades to adapt the striking technique to form gold or silver NPs in tellurite glasses. Despite this effort, the striking technique has remained insufficient for tellurite glasses to form metal NPs suitable for photonic applications. Here, we first uncover the challenges of the traditional striking technique to create gold NPs in tellurite glass. Then, we demonstrate precise control of the size and concentration of gold NPs in tellurite glass by developing new approaches to both steps of the striking technique: a controlled gold crucible corrosion technique to incorporate gold ions in tellurite glass and a glass powder reheating technique to subsequently transform the gold ions to gold NPs. Using the Mie theory, the size, size distribution and concentration of the gold NPs formed in tellurite glass are determined from the plasmonic properties of the NPs. This fundamental research provides guidance for designing and manipulating the plasmonic properties in tellurite glass for photonics research and applications.

Plasmonic Nano‐Rotamers with Programmable Polarization‐Resolved Coloration

Abstract3D‐shaped artificial Mg nano‐rotamers with a programmable dihedral angle between two plasmonic arms, designed to exhibit both programmable linear and circular polarization properties, are presented. The nanoscale physical shadow growth technique offers precise control over the angular alignment in these nanostructures with 1° angular precision, thus controlling their symmetry from achiral C2v and C2h to chiral C2. As a result, they give rise to a wide range of polarization‐resolved coloration, spanning from invisible to visible colors with 46% transmission contrast for linear polarization while exhibiting 0.08 g‐factor in visible for circular polarization. These nano‐rotamers hold great potential for various applications in adaptive photonic filters, memory, and anticounterfeiting devices, benefiting from their tunable plasmonic properties.

Hybrid Integration of Au Nanoplates and Ag Nanoparticles with Controlled Nanogaps via Cu2O‐mediated Galvanic Replacement Reaction: Plasmonic Catalysis and Photothermal Conversion

AbstractRational assembling of different noble metal nanocrystals with controlled nanogaps in one entity allows the efficient coupling of electromagnetic fields of each component and versatile manipulation over the overall physiochemical properties. In the present study, we report a stepwise synthetic strategy to hybridlike assemble Au nanoplate and Ag nanoparticles without direct physical contact. Particularly, the success of current work relies on the conformal coating of Cu2O over the Au nanoplate as an intermediate layer, followed by the in situ formation of Ag nanoparticles via the galvanic replacement reaction between Cu2O and Ag+. With the anchoring of Ag nanoparticles over the Cu2O‐wrapped Au nanoplate, the resulting hybrid nanostructures exhibit noticeable multiple plasmonic absorptions across the UV‐vis‐NIR region. The potential use as the plasmonic catalyst for current Au@Cu2O‐Ag hybrid products is validated using reduction of 4‐nitrophenol as the model reaction, where the catalytic performance is greatly improved by the UV‐vis light irradiation. They also exhibit satisfactory photothermal conversion performance under the irradiation of Xe lamp. The current work provides a niche strategy to create noble‐metal hybrid nanostructures with controlled interparticle distance and tunable plasmonic properties, could be extended to other noble metal or alloys.

Silver-based plasmonic nanoparticles and their application as biosensor

The silver nanoparticles (AgNPs) exhibit unique and tunable plasmonic properties. The size and shape of these particles can manipulate their localized surface plasmon resonance (LSPR) property and their response to the local environment. The LSPR property of nanoparticles is exploited by their optical, chemical, and biological sensing. This is an interdisciplinary area that involves chemistry, biology, and materials science. In this paper, a polymer system is used with the optimization technique of blending two polymers. The two polymer composites polystyrene/poly (4-vinylpyridine) (PS/P4VP) (50:50) and (75:25) were used as found suitable by their previous morphological studies. The results of 50, 95, and 50, 150 nm thicknesses of silver nanoparticles deposited on PS/P4VP (50:50) and (75:25) were explored to observe their optical sensitivity. The nature of the polymer composite embedded with silver nanoparticles affects the size of the nanoparticle and its distribution in the matrix. The polymer composites used are found to have a uniform distribution of nanoparticles of various sizes. The optical properties of Ag nanoparticles embedded in suitable polymer composites for the development of the latest plasmonic applications, owing to their unique properties, were explored. The sensing capability of a particular polymer composite is found to depend on the size of the nanoparticle embedded in it. The optimum result has been found for silver nanoparticles of 150 nm thickness deposited on PS/P4VP (75:25).

Cysteine-assisted overgrowth of gold nanorods to prepare highly branched gold nanoantennas with tunable morphological and plasmonic properties

In this work, gold nanoantennas with high branching properties were prepared by cysteine-assisted overgrowth of gold nanorods (AuNRs).

Near-infrared light activatable niosomes loaded with indocyanine green and plasmonic gold nanorods for theranostic applications.

Light-mediated theranostic platforms involve the use of agents (small molecules/nanomaterials), which can absorb light to produce either heat or reactive chemical species (RCS) and emit fluorescence. Such platforms are advantageous in the field of personalized medicine, as they provide enhanced diagnostic capabilities, improved therapeutic efficiencies, and can also simultaneously monitor the treatment outcomes using imaging modalities. Specifically, agents absorbing near-infrared (NIR) light can provide minimal scattering, low autofluorescence, superior spatio-temporal resolution, and deeper tissue penetration depths. Gold nanorods (GNR) and indocyanine green (ICG) are two agents known to absorb light in the NIR region. GNR can provide tunable plasmonic properties, while ICG is an FDA-approved NIR fluorophore. However, the use of ICG and GNR suffers from various limitations, such as photobleaching, non-specificity, toxicity, and aggregation in solution. To overcome these limitations, herein, we report on NIR light-activatable niosomes loaded with GNR and ICG for cancer theranostic applications. Both agents were encapsulated into non-ionic surfactant-based biocompatible niosomes to form ICG-GNR@Nio with superior loading efficiencies and enhanced properties. ICG-GNR@Nio offers excellent storage stability, photostability, elevated temperature rise and generation of reactive oxygen species (ROS) upon 1064 nm laser irradiation. Subsequently, the enhanced phototherapeutic capabilities mediated by ICG-GNR@Nio were validated in the in vitro cellular experiments. Overall, ICG-GNR@Nio-based theranostic platforms can provide a significant benchmark in the improved diagnosis and therapeutic capabilities for biomedical clinicians to tackle various diseases.

Low-cost and simple fabrication of hierarchical Al nanopit arrays for deep ultraviolet refractive index sensing

Herein, we proposed a simple non-lithographic way to fabricate hierarchical Al nanopit arrays performed as deep ultraviolet (DUV, 200–300 nm) refractive index sensing. Only by adjusting the Al deposition thickness on the Al nanopit array, the hierarchical Al nanopit arrays with tunable plasmonic properties in the DUV region were obtained. The prepared hierarchical Al nanopit arrays are of very good time stability and its RI sensitivity and concentration detection limit of adenine ethanol solution reach 311 nm/RIU and respectively, as the Al deposition thickness is 60 nm. Furthermore, the electric field distribution simulation results show that high RI sensing characteristic are mainly attributed to the local surface plasmon resonance. This investigation provides a facile way to develop low cost, high efficient and easily fabricated Al-based RI sensor in the DUV region.