Plasmonic Materials Research Articles

Optical Properties of Materials for Magnesium Plasmonics Described within DFT+U Approach

Optical Properties of Materials for Magnesium Plasmonics Described within DFT+U Approach

Accurate prediction of the optical properties of nanoalloys with both plasmonic and magnetic elements

The alloying process plays a pivotal role in the development of advanced multifunctional plasmonic materials within the realm of modern nanotechnology. However, accurate in silico predictions are only available for metal clusters of just a few nanometers, while the support of modelling is required to navigate the broad landscape of components, structures and stoichiometry of plasmonic nanoalloys regardless of their size. Here we report on the accurate calculation and conceptual understanding of the optical properties of metastable alloys of both plasmonic (Au) and magnetic (Co) elements obtained through a tailored laser synthesis procedure. The model is based on the density functional theory calculation of the dielectric function with the Hubbard-corrected local density approximation, the correction for intrinsic size effects and use of classical electrodynamics. This approach is built to manage critical aspects in modelling of real samples, as spin polarization effects due to magnetic elements, short-range order variability, and size heterogeneity. The method provides accurate results also for other magnetic-plasmonic (Au-Fe) and typical plasmonic (Au-Ag) nanoalloys, thus being available for the investigation of several other nanomaterials waiting for assessment and exploitation in fundamental sectors such as quantum optics, magneto-optics, magneto-plasmonics, metamaterials, chiral catalysis and plasmon-enhanced catalysis.

Obtaining Ligand-Free Aqueous Au-Nanoparticles Using Reversible CsPbBr3 ↔ Au@CsPbBr3 Nanocrystal Transformation.

Water-hexane interfacial preparation of photostable Au@CsPbBr3 (Au@CPB) hybrid nanocrystals (NCs) from pure CsPbBr3 (CPB) NCs is reported, with the coexistence of exciton and localized surface plasmon resonance with equal dominance. This enables strong exciton-plasmon coupling in these plasmonic perovskite NCs where not only the photoluminescence is quenched intrinsically due to ultrafast charge separation, but also the light absorption property increases significantly, covering the entire visible region. Using a controlled interfacial strategy, a reversible chemical transformation between CPB and Au@CPB NCs is shown, with the simultaneous eruption of larger-size ligand-free aqueous Au nanoparticles (NPs). An adsorption-desorption mechanism is proposed for the reversible transformation, while the overgrowth reaction of the Au NPs passes through the Au aggregation intermediate. This study further shows that the plasmonic Au@CPB hybrid NCs as well as ligand-free Au NPs exhibit clear surface enhanced Raman scattering (SERS) effect of a commercially available probe molecule. Overall, the beautiful interfacial chemistry delivers two independent plasmonic materials, i.e., Au@CPB NCs and ligand-free aqueous Au NPs, which may find important implications in photocatalytic and biomedical applications.

Ultrafast optical properties of stoichiometric and non-stoichiometric refractory metal nitrides TiNx, ZrNx, and HfNx.

Refractory metal nitrides have recently gained attention in various fields of modern photonics due to their cheap and robust production technology, silicon-technology compatibility, high thermal and mechanical resistance, and competitive optical characteristics in comparison to typical plasmonic materials like gold and silver. In this work, we demonstrate that by varying the stoichiometry of sputtered nitride films, both static and ultrafast optical responses of refractory metal nitrides can efficiently be controlled. We further prove that the spectral changes in ultrafast transient response are directly related to the position of the epsilon-near-zero region. At the same time, the analysis of the temporal dynamics allows us to identify three time components: the "fast" femtosecond one, the "moderate" picosecond one, and the "slow" at the nanosecond time scale. We also find out that the non-stoichiometry does not significantly decrease the recovery time of the reflectance value. Our results show the strong electron-phonon coupling and reveal the importance of both the electron and lattice temperature-induced changes in the permittivity near the ENZ region and the thermal origin of the long tail in the transient optical response of refractory nitrides.

Rational Design of Near‐infrared II Plasmonic Optofunctional Materials for Diagnostic and Therapeutic Applications

AbstractPlasmonic materials have aroused considerable interest in diagnostic and therapeutic biomedical applications because of their remarkable optical properties and the integration of multiple functionalities. Particularly, near‐infrared II (NIR‐II) plasmonic materials present great advantages for anticancer treatments, including deep tissue penetration, low tissue light scattering and autofluorescence, and high spatial resolution. Thus, NIR‐II plasmonic phototheranostics represents a promising approach for effective anticancer treatments through multi‐modal imaging‐guided therapy. Accordingly, tremendous efforts have recently been devoted to the development of NIR‐II plasmonic materials for highly efficient phototheranostics. In this review, the recent progress of NIR‐II plasmonic materials and their phototheranostic applications are overviewed. First, the localized surface plasmon resonance effect and the related optical properties such as the photothermal effect, photoacoustic effect, and surface‐enhanced Raman scattering (SERS) effect are introduced. Then, the unique features and the structure‐property relationship of various types of NIR‐II plasmonic materials are discussed. Finally, the recent progress of NIR‐II plasmonic material‐based multimodal phototheranostics with an emphasis on the integration of multiple functionalities are reviewed, and subsequently the current challenges and future research perspectives are discussed. This review will provide valuable guidelines for the rational design of NIR‐II plasmonic materials for highly efficient cancer phototheranostics in the future.

Detection of liquid chemical analytes using a novel PCF-SPR sensor based on the wavelength sensitivity measurement method

This paper proposes a novel, highly sensitive, dual-coated PCF-SPR sensor for harmful chemical detection. The sensor’s performance is investigated based on the measurement of the wavelength sensitivity method. Silver (Ag) is a plasmonic material, and Ta2O5 is used as an overlayer to enhance its performance. The impact of Ta2O5 thickness and structural parameter variation on sensor performance is also measured. The proposed plasmonic sensor measured the maximum wavelength sensitivity of 23000 nm/RIU. This investigation undoubtedly provides a new approach to designing a PCF-SPR sensor that tunes the range of chemical refractive indices by changing Ta2O5 thickness. Besides, the simplicity, flexibility, and fabrication-friendly design make it applicable for chemical analyte sensing.

Topological polarization singular enables multiple-system excellent circular dichroism via chiral bound states in the continuum with all-dielectric metasurfaces

The advancements in chiroptics have propelled applications beyond traditional optics, expanding its reach into domains such as heat and fluid mechanics. The current research predominantly focused on utilizing plasmonic materials in the photothermal and photofluidic systems. However, these systems face limitations in circular dichroism due to inherent Ohmic loss associated with plasmonic materials. Herein, we introduce the concept of topological polarization singularity in an all-dielectric structure, which supports chiral bound states in the continuum. The introduction of topological polarization singularity gives the structure an impressive chiral light absorption response. The BICs resonant mode achieves a 147-fold field enhancement, significantly improving the photothermal conversion efficiency of dielectric material. Moreover, the g factors of photothermal and optical fluids reach 1.9, approaching the theoretical limit value. Consequently, an exceptionally high degree of circular dichroism is realized in multiple systems including light absorption, photothermal, and photofluidic systems. Our proposed structures can potentially be used in chiral photothermal and chiral nanoparticle capture, as well as photofluidic applications related to biochemistry and clinical biology.

Sputtered SnTe Thin Films on Si and Ge as a Plasmonic Material

Sputtered SnTe Thin Films on Si and Ge as a Plasmonic Material

Intrinsic Visible Plasmonic Properties of Colloidal PtIn2 Intermetallic Nanoparticles.

Materials that intrinsically exhibit localized surface plasmon resonance (LSPR) in the visible region have been predominantly researched on nanoparticles (NPs) composed of coinage metals, namely Au, Ag, and Cu. Here, as a coinage metal-free intermetallic NPs, colloidal PtIn2 NPs with a C1 (CaF2 -type) crystal structure are synthesized by the liquid phase method, which evidently exhibit LSPR at wavelengths similar to face-centered cubic (fcc)-Au NPs. Computational simulations pointed out differences in the electronic structure and photo-excited electron dynamics between C1-PtIn2 and fcc-Au NPs; reduces interband transition and stronger screening with smaller number of bound d-electrons compare with fcc-Au are unique origins of the visible plasmonic nature of C1-PtIn2 NPs. These results strongly indicate that the intermetallic NPs are expected to address the development of alternative plasmonic materials by tuning their crystal structure and composition.

Low energy ion irradiation induced Au/Ag multilayer nanostructured substrates for SERS-based molecular sensing

Au and Ag are the most prominent plasmonic materials to study Surface-Enhanced Raman Spectroscopy (SERS) because of their wide tuning of localized surface plasmon resonance in the broad wavelength range. In the present work, the formation of nanostructures of Au single-layer, Au/Ag bi-layer, and Au/Ag/Au/Ag four-layer thin films on silicon substrates by low energy Kr++ ion irradiation with fluences of 1 × 1015 and 3 × 1015 ions/cm2 was systematically studied and were used for the detection of dye molecules. The surface morphology and microstructural analysis indicated the formation of different nanostructures with different ion fluences by atomic force microscopy and field emission scanning electron microscopy. Rutherford backscattering spectrometry results indicate a considerable change in film thickness after ion irradiation, mainly due to the removal of surface atoms due to sputtering. The maximum enhancement in Raman intensity of R6G was observed in the Bi-layer Au–Ag substrate compared to other substrates with an enhancement factor of 4.78 × 106 corresponding to a 1516 cm−1 characteristic peak in SERS analysis. Coumarin 343 molecules trace amount were detected to determine the versatility of the substrate. A finite-difference time-domain simulation was performed to provide a better understanding of the nanostructure hot-spots formation and support the obtained SERS results.

Enhanced charge transport and broadband photoresponse of MoS2 photodetectors with sparsely distributed Ag@SiO2 core–shell nanostructures

Integrating metal nanostructures with two-dimensional (2D) material photodetectors has been demonstrated that can greatly improve device performance owning to various extraordinary optoelectronic phenomena. For example, metal nanostructures are served as ideal plasmonic materials to maximize local electromagnetic fields leading to light absorption of 2D materials. In this work, other than the widely reported plasmonic effects, we discover the contribution of metal nanostructures in charge transport engineering in 2D material photodetectors, which is important but always ignored in previous studies by others. Notable improvements of carrier mobility and carrier concentration attributing to the integration of sparsely distributed Ag@SiO2 core–shell nanoparticles on the MoS2 detector were experimentally established, originating from reduced carrier scattering and interfacial gating. Consequently, a 1.5-fold broadband (400–1100 nm) uniform photocurrent enhancement was observed, which was entirely derived from the improved charge transport. These findings open up a new research perspective for the precise identification and objective evaluation of different effects of metal nanostructures on optoelectronic devices.

Plasmonic-based electrochromic materials and devices

Abstract The development of electrochromic (EC) materials has paved the way for a wide range of devices, such as smart windows, color displays, optical filters, wearable camouflages, among others. However, the advancement of electrochromism faces a significant hurdle due to its poor stability and limited color options. This lack of stability is primarily attributed to the substantial alteration in the dielectric properties of EC materials during cycling. Consequently, the design of advanced plasmonic materials is a key strategy to achieve a stable EC device. In this review, we provide an overview of the current state-of-the-art designs of plasmonic-based EC materials and devices. We discuss their working principles, techniques for structure/morphology engineering, doping methods, and crystal phase design. Furthermore, we explore the integration of plasmonic materials with other EC materials to create advanced EC devices. Finally, we outline the challenges that need to be addressed and present an outlook on the development of high-performance EC devices.

Surface engineered nanohybrids in plasmonic photothermal therapy for cancer: Regulatory and translational challenges.

Plasmonic materials as non-invasive and selective treatment strategies are gaining increasing attention in the healthcare sector due to their remarkable optical and electronic properties, where the interface between matter and light becomes enhanced and highly localized. Some attractive applications of plasmonic materials in healthcare include drug delivery to target specific tissues or cells, hence reducing the side effects of the drug and improving their efficacy; enhancing the contrast and resolution in bioimaging; and selectively heating and destroying the cancerous cells while parting the healthy cells. Despite such advancements in photothermal therapy for cancer treatment, some limitations are still challenging. These include poor photothermal conversion efficiency, heat resistance, less accumulation in the tumor microenvironment, poor biosafety of photothermal agents, damage to the surrounding healthy tissues, post-treatment inflammatory responses, etc. Even though the clinical application of photothermal therapy is primarily restricted due to poor tissue penetration of excitation light, enzyme therapy is hindered due to less therapeutic efficacy. Several multimodal strategies, including chemotherapy, radiotherapy, photodynamic therapy, and immunotherapy were developed to circumvent these side effects associated with plasmonic photothermal agents for effective mild-temperature photothermal therapy. It can be prophesied that the nanohybrid platform could pave the way for developing cutting-edge multifunctional precise nanomedicine via an ecologically sustainable approach towards cancer therapy. In the present review, we have highlighted the significant challenges of photothermal therapy from the laboratory to the clinical setting and their struggle to get approval from the Food and Drug Administration (FDA).

Analytical developments in the synergism of copper particles and cysteine: a review.

Cysteine, a sulfur-containing amino acid, is a vital candidate for physiology. Coinage metal particles (both clusters and nanoparticles) are highly interesting for their spectacular plasmonic properties. In this case, copper is the most important candidate for its cost-effectiveness and abundance. However, rapid oxidation destroys the stability of copper particles, warranting the necessity of suitable capping agents and experimental conditions. Cysteine can efficiently carry out such a role. On the contrary, cysteine sensing is a vital step for biomedical science. This review article is based on a comparative account of copper particles with cysteine passivation and copper particles for cysteine sensing. For the deep understanding of readers, we discuss nanoparticles and nanoclusters, properties of cysteine, and importance of capping agents, along with various synthetic protocols and applications (sensing and bioimaging) of cysteine-capped copper particles (cysteine-capped copper nanoparticles and cysteine-capped copper nanoclusters). We also include copper nanoparticles and copper nanoclusters for cysteine sensing. As copper is a plasmonic material, fluorometric and colorimetric methods are mostly used for sensing. Real sample analysis for both copper particles with cysteine and copper particles for cysteine sensing are also incorporated in this review to demonstrate their practical applications. Both cysteine-capped copper particles and copper particles for cysteine sensing are the main essence of this review. The aspect of the synergism of copper and cysteine (unlike other amino acids) is quite promising for future researchers.

Label-free biosensing with singular-phase-enhanced lateral position shift based on atomically thin plasmonic nanomaterials

Rapid plasmonic biosensing has attracted wide attention in early disease diagnosis and molecular biology research. However, it was still challenging for conventional angle-interrogating plasmonic sensors to obtain higher sensitivity without secondary amplifying labels such as plasmonic nanoparticles. To address this issue, we developed a plasmonic biosensor based on the enhanced lateral position shift by phase singularity. Such singularity presents as a sudden phase retardation at the dark point of reflection from resonating plasmonic substrate, leading to a giant position shift on reflected beam. Herein, for the first time, the atomically thin layer of Ge2Sb2Te5 (GST) on silver nanofilm was demonstrated as a novel phase-response-enhancing plasmonic material. The GST layer was not only precisely engineered to singularize phase change but also served as a protective layer for active silver nanofilm. This new configuration has achieved a record-breaking largest position shift of 439.3 μm measured in calibration experiments with an ultra-high sensitivity of 1.72 × 108 nm RIU−1 (refractive index unit). The detection limit was determined to be 6.97 × 10−7 RIU with a 0.12 μm position resolution. Besides, a large figure of merit (FOM) of 4.54 × 1011 μm (RIU∙°)−1 was evaluated for such position shift interrogation, enabling the labelfree detection of trace amounts of biomolecules. In targeted biosensing experiments, the optimized sensor has successfully detected small cytokine biomarkers (TNF-α and IL-6) with the lowest concentration of 1 × 10−16 M. These two molecules are the key proinflammatory cancer markers in clinical diagnosis, which cannot be directly screened by current clinical techniques. To further validate the selectivity of our sensing systems, we also measured the affinity of integrin binding to arginylglycylaspartic acid (RGD) peptide (a key protein interaction in cell adhesion) with different Mn2+ ion concentrations, ranging from 1 nM to 1 mM.

Titanium‐Coated Extremely Sensitive SPR Biosensor for Cancer Cell Detection

In this study, a D‐shaped, extremely sensitive surface plasmon resonance (SPR) sensor with a blue shift characteristic is proposed that can be used to identify various malignant cancer cells. A sensing layer made of titanium is inserted to produce intense sensitivity. For the simulation and numerical evaluation of the proposed biosensor, we used the finite element method (FEM) and the COMSOL Multiphysics 5.6 software. To regulate how much light passes through the sensor, which incites the released electrons at the surface of the plasmonic material, air holes in different radii are used. The characteristics that make our proposed sensor superior to other D‐shaped SPR sensors are—it gives an excellent amplitude sensitivity (AS) of 200 RIU−1 also ensures extremely high wavelength sensitivity (WS) spanning from 34,350 to 42,145 nm/RIU with an outstanding spectral resolution of 2.37 × 10−6 RIU. Furthermore, the R2 (0.9966) value is also extremely close to 1 which ensures the quality of our sensor regarding its performance. The given sensor is tailored for four vital human cancers, which are blood cancer, skin cancer, cervical cancer, and adrenal gland cancer. Here, optimization of the structural geometric parameters, plasmonic materials, and material thickness are also conducted in search of the best functionality of the sensor. The offered structure, nonetheless, can be an obvious prologue in the case of the crucial human cancer detection platform due to its mild sensing performances.

Synergistic effect of Zn-AgIn5S8/CdS Z-scheme heterojunction and S-doped rGO for efficient removal of chromium from contaminated water.

This study aimed to synthesize a Zn-AgIn5S8/CdS/SrGO nanocomposite for Cr(vi) removal from contaminated water under solar irradiation. To prevent photo corrosion of CdS, a Z-scheme heterojunction was formed between CdS and Zn-AgIn5S8. The introduction of Ag2+ plasmonic materials extended the light absorption range and stabilized the photocatalyst. Further, to improve the catalytic surface area, electrical conductivity, and minimize the rate of electron and hole pair recombination, the Zn-AgIn5S8/CdS Z-scheme heterojunction was loaded onto S-doped rGO. The morphological and structural analysis of the synthesized nanomaterials (NMs) was done using various techniques, including XRD, FT-IR, UV-vis DRS, FESEM, TEM, EDAX, photoluminescence, and Raman spectroscopy. Results revealed that the Zn-AgIn5S8/CdS/SrGO nanocomposite removed 85% of Cr(vi) at an initial concentration of 50 mg L-1 in 180 min when exposed to solar irradiation. The simulated first-order kinetic model fitted to the experimental data for Cr(vi) reduction by the nanocomposite exhibits a high correlation coefficient (R 2 ≥ 0.97) and the K app value for Zn-AgIn5S8/CdS/SrGO (K app = 0.0114 min-1) is around 1.6 times larger than that of bare ZnAgIn5S8. Moreover, Zn-AgIn5S8/CdS/SrGO heterojunctions show excellent reusability up to 4 cycles. Further, the possible photocatalytic mechanism of Cr(vi) reduction has been proposed. Therefore, the Zn-AgIn5S8/CdS/SrGO nanocomposite could serve as an alternative photocatalyst system driven by solar light for Cr(vi) reduction.

Plasmonic Optical Fiber Based Continuous in-Vivo Glucose Monitoring for ICU/CCU Setup.

This paper reports a sensor architecture for continuous monitoring of biomarkers directly in the blood, especially for ICU/CCU patients requiring critical care and rapid biomarker measurement. The sensor is based on a simple optical fiber that can be inserted through a catheter into the bloodstream, wherein gold nanoparticles are attached at its far distal end as a plasmonic material for highly sensitive opto-chemical sensing of target biomolecules (glucose in our application) via the excitation of surface plasmon polaritons. For specificity, the nanoparticles are functionalized with a specific receptor enzyme that enables the localized surface plasmon resonance (LSPR)-based targeted bio-sensing. Further, a micro dialysis probe is introduced in the proposed architecture, which facilitates continuous monitoring for an extended period without fouling the sensor surface with cells and blood debris present in whole blood, leading to prolonged enhanced sensitivity and limit of detection, relative to existing state-of-the-art continuous monitoring devices that can conduct direct measurements in blood. To establish this proof-of-concept, we tested the sensor device to monitor glucose in-vivo involving an animal model, where continuous monitoring was done directly in the circulation of living rats. The sensor's sensitivity to glucose was found to be 0.0354 a.u./mg.dl-1 with a detection limit of 50.89 mg/dl.

Hollow cubic CuSe@CdS with tunable size for plasmon-induced Vis-NIR driven photocatalytic properties.

The rational design of the dimension and geometry of a plasmonic semiconductor cocatalyst is vitally important for efficient utilization of near-infrared (NIR) light and superior photocatalytic hydrogen generation. Herein, hollow cubic CuSe@CdS composites with different sizes and strong localized surface plasmon resonance (LSPR) were prepared by selenizing size-tunable Cu2O templates and loading CdS nanoparticles. The size of hollow cubic CuSe can affect the surface area and the conduction band potential through the size effect, regulating the carrier behavior of the CuSe@CdS heterojunction. The CuSe@CdS composites show enhanced and wide absorption in the full spectrum due to the LSPR effect of CuSe. Meanwhile, the composites show excellent photocatalytic hydrogen capacity in the full spectrum in a 0.35 M Na2S/0.25 M Na2SO3 sacrificial reagent solution. The best hydrogen production rate of CSCE2 is 1.518 mmol g-1 h-1 (5.54 times higher than that of CdS) under Vis light (780 > λ > 420 nm) irradiation and 0.28 mmol g-1 h-1 under NIR light (λ > 780 nm) illumination. Interestingly, the photocatalytic activity for H2 under Vis-NIR light (λ > 420 nm) is about 3 times (up to 4.45 mmol g-1 h-1) higher than that without NIR light assistance, due to the photothermal effect. Various analyses and DFT calculations demonstrate that the p-n heterojunction formed in the composites consists of p-type CuSe and n-type CdS, which achieves efficient carrier transfer and separation under the synergistic effect of the size effect and the photothermal effect. In addition, the expansion of the photocatalytic performance to the NIR range is mainly due to the "hot-electron" injection mechanism induced by the LSPR effect of CuSe. The reasonable design coupled with the plasmonic materials offers a new path to achieving the highly efficient conversion of solar energy to hydrogen energy.

Influence of molecular structure on the coupling strength to a plasmonic nanoparticle and hot carrier generation.

Strong coupling between metal nanoparticles and molecules mixes their excitations, creating new eigenstates with modified properties such as altered chemical reactivity, different relaxation pathways or modified phase transitions. Here, we explore excited state plasmon-molecule coupling and discuss how strong coupling together with a changed orientation and number of an asymmetric molecule affects the generation of hot carriers in the system. We used a promising plasmonic material, magnesium, for the nanoparticle and coupled it with CPDT molecules, which are used in organic optoelectronic materials for organic electronic applications due to their facile modification, electron-rich structure, low band gap, high electrical conductivity and good charge transport properties. By employing computational quantum electronic tools we demonstrate the existence of a strong coupling mediated charge transfer plasmon whose direction, magnitude, and spectral position can be tuned. We find that the orientation of CPDT changes the nanoparticle-molecule gap for which maximum charge separation occurs, while larger gaps result in trapping hot carriers within the moieties due to weaker interactions. This research highlights the potential for tuning hot carrier generation in strongly coupled plasmon-molecule systems for enhanced energy generation or excited state chemistry.