Low-threshold tunable SPASER nanolaser based on plasmonic coupling enhancement effect

Localized surface plasmon resonances can increase the quantum efficiency of photon emitters through both absorption and spontaneous emission enhancement effects. Despite extensive studies, experimental results that clearly distinguish the two plasmonic enhancement effects are rarely available. Here, we present clear spectral signatures of the plasmonic enhancement effects on the absorption (excitation) and spontaneous emission (Purcell factor) by analyzing the temperature dependent photoluminescence (PL) properties of InGaAs/GaAs single quantum well (QW) coupled to colloidal gold nanorods (AuNRs) at different GaAs capping layer thickness (d). We find that when the emitting InGaAs layer is close to the AuNRs (d = 5 nm), the plasmonic enhancement effect on the QW PL is dominated by the Purcell factor that significantly increases the external quantum efficiency of the QW that otherwise barely emits. When d is increased to 10 nm, the temperature dependence of the PL enhancement factor (F) reflects absorption enhancement in the capping layer followed by carrier diffusion and capture by the well. First F increases with temperature and then decreases following the temperature dependence of the carrier diffusion coefficient in GaAs. By factoring out the contribution of the captured carriers to F, it is shown that carrier transfer to the well reaches saturation with increasing incident laser power. In addition to providing insight into the plasmonic enhancement mechanism, the results presented in this work suggest that colloidal plasmonic nanoparticles can be used as simple probes for understanding carrier transport phenomena in arbitrary semiconductor heterostructures.

Plasmon-induced photoluminescence and Raman enhancement in Pr:CaF2 crystal by embedded silver nanoparticles

Raman spectroscopy (RS) is a modern scientific analytic fingerprint technique that detects, examines, and analyzes the constituent chemical composition of various substances (solid–liquid–gas and plasmons) through interaction of laser light with matter. It is intelligent to present qualitative and quantitative information about the sample’s chemical composition, polymorphism, phase, crystallinity, stress/strain, and contamination and impurity/defects. The key mechanism is profoundly based on the Raman principle that was originally named after and discovered by the Indian primer scientist C.V Raman, who won the Nobel prize after the exposure of the Raman effect [Raman 1916; Krishnan 1928]. This review briefly presents the physical origin of Raman scattering explaining the key classical and quantum mechanical concepts. Molecular variations of the Raman effect will also be considered, including resonance, coherent, and enhanced Raman scattering. Further, we discuss the molecular origins of prominent bands often found in the Raman spectra of SPR (surface plasmon resonance) samples. Finally, we examine the several active variations of Raman spectroscopy techniques in practice, looking at their applications, strengths, and challenges. This review is intended to be a starting resource for scientists new to Raman spectroscopy, providing theoretical background and practical examples as the foundation for further study and exploration of SPR and surface-enhanced Raman spectroscopy (SERS) techniques. While RS is now used in biology and medicine for novel pandemic diseases, Raman spectroscopy found its first applications in physics and chemistry and was mainly used to study vibrations and structure of molecules. One early factor limiting the implementation of RS was the weak scattering signal. Large intensities of monochromatic light are required to excite a detectable signal. This requirement became much easier to realize following the invention of the laser in 1960. Over the past decades, Raman spectroscopy has been prominently exploited better in biological applications, where it is able to detect and analyze DNA and RNA molecules. Generally, there are four main types of Raman spectroscopy, but the most feasible in biological field is the SERS. The noble metal nanoclusters play an important role for nanobiomedical and modern optical devices. The present review explored the single and bi-metallic (silver (Ag), copper (Cu), silver–copper (Ag–Cu), and copper–silver (Cu–Ag)) nanoclusters embedded in soda–lime glass that is prepared by ion-exchange method. The ion-exchanged glasses are annealed by different methods (furnace and laser). These samples exhibit surface plasmon and surface enhancement effect. Optical absorption spectroscopic analysis was done on the metal nanocluster composite glasses, and the spectra are well studied as a function of various post ion-exchange treatments and different sizes. As size effects are an essential aspect of nanomaterials, the effect of size on the optical absorption metal nanoclusters was studied using theoretical models and correlated with the experimental results. Formation of embedded bi-metallic nanoclusters is also achieved by furnace annealing or laser irradiation of the sequential Cu–Ag and Ag–Cu ion-exchanged samples. The formations of core–shell structures or alloying between the metal species were confirmed from the optical absorption spectra. This review analyzes the influence of different parameters (nanocluster size, morphology, and composition as well as surface plasmon resonance (SPR) wavelength) on SERS. Experimental study of SERS substrates consists of silver, copper, and alloyed copper–silver (Cu–Ag) or silver–copper (Ag–Cu) nanoclusters of various sizes and compositions with the aim of finding the optimal conditions for fabricating substrates with maximum SERS enhancement factors. The primary aim of this work is focused on the development of novel SERS-active substrates and their applications in various research fields. The basic principle is borrowing the rough feature from the supported under layer to produce the rough noble meal surface and achieve the surface enhancement effect. The prepared substrates meet the following requirements, such as stable, reproducible, possessing large enhancement factor, and easiness for preparation. SERS opens up exciting opportunities in the field of biophysical and biomedical spectroscopy, where it provides ultrasensitive detection and characterization of biophysically/biomedically relevant molecules and processes as well as a vibrational spectroscopy with extremely high spatial resolution. This review explains many fundamental features of SERS and then describes the use of embedded nanocluster for the fabrication of highly reproducible and robust SERS substrates. The present review discusses the synthesis of single and bi-metallic nanocomposite glasses by the commercial ion-exchange technique followed by the suitable thermal treatments like furnace and laser annealing. Post treatment, the samples were subjected to various studies like optical absorption and SERS, FESEM, photoluminescence, and grazing incidence X-ray diffraction.

Although perovskite solar cells have shown outstanding photovoltaic performance, there are still various obstacles that limit their performance and that remain as significant challenges. Weak optical absorption rate in the infrared region is a significant drawback for this kind of solar cell. In this paper, Au@SiO2@Graphene nanoparticles (NPs) as nano-photonic inclusions in the perovskite layer are proposed and investigated theoretically. Unlike conventional nanoparticles, these NPs exhibit strong, multiple plasmon resonances at low energies. The effect of geometrical parameters, periodicity, and the location of the Au@SiO2@Graphene NPs in the perovskite layer upon the performance of the PSCs are investigated. Under improved conditions, an absorption enhancement of 32% is obtained compared to pristine devices. Also, the result attained from coupled optical-electrical simulation of the improved device demonstrated 20.05% power conversion efficiency. These improvements have been achieved due to the plasmonic near-field enhancement effects of Au@SiO2@Graphene nanoparticles along with increased light-scattering from these NPs.

Copper nanoclusters embedded in soda lime glass are prepared by ion exchanged method. The ion exchanged glasses are annealed in air for 1 h at different temperature. These samples exhibit surface plasmon and surface enhancement effect. UV-visible optical absorption spectroscopic analysis shows the signature of the copper nanocluster in the ion exchanged glasses. Surface-enhanced Raman spectroscopy (SERS) technique is used to characterize the copper ion exchanged and annealed glasses. Additional results are obtained by SERS for optimizing the SERS substrate. The highest Raman enhancement is obtained for substrates with high cluster size. The micro-Raman scattering spectroscopic images of ion exchanged and different temperature annealed glasses support the optical absorption spectroscopy results.

Plasmonic bowtie nanostructures have been widely used to enhance electric fields by concentrating the electromagnetic field within nanoscale gaps. Various structural modifications of the bowtie geometry have been proposed to achieve stronger light confinement within the nanogaps. Among them, bowtie structures with curved arms have demonstrated a significantly higher enhancement factor (EF) compared to those with linear arms. However, although tip sharpness plays a critical role in electric field enhancement, the tip sharpness of the curved bowtie has not been systematically examined. In this study, we investigated the influence of tip sharpness on the EF of curved bowtie nanostructures using finite-difference time-domain (FDTD) simulations. We systematically optimized four structural parameters, including the tip sharpness and curvature of the side arms, and evaluated their impact on the resulting EF. The curved bowtie with sharp tips showed substantial increases in the EF (5.33 × 103), which is approximately 26% higher than that of the normal bowtie with sharp tips (4.23 × 103), whereas the bowtie with blunt tips exhibited an even lower EF than those with linear arms. These results highlight the critical role of the tip sharpness in achieving high-field enhancement. This study underscores the need for advanced nanofabrication techniques, such as domino lithography, to realize sharp tips, which are often limited by proximity effects in conventional photolithography and electron-beam lithography (EBL). Our findings provide valuable insight into the design of high-performance plasmonic nanostructures and pave the way for their practical applications in biosensing and nanophotonic technologies.

Single-particle catalysis aims at determining factorsthat dictatethe nanoparticle activity and selectivity. Existing methods oftenuse fluorescent model reactions at low reactant concentrations, operateat low pressures, or rely on plasmonic enhancement effects. Hence,methods to measure single-nanoparticle activity under technicallyrelevant conditions and without fluorescence or other enhancementmechanisms are still lacking. Here, we introduce nanofluidic scatteringmicroscopy of catalytic reactions on single colloidal nanoparticlestrapped inside nanofluidic channels to fill this gap. By detectingminuscule refractive index changes in a liquid flushed trough a nanochannel,we demonstrate that local H2O2 concentrationchanges in water can be accurately measured. Applying this principle,we analyze the H2O2 concentration profiles adjacentto single colloidal Pt nanoparticles during catalytic H2O2 decomposition into O2 and H2Oand derive the particles’ individual turnover frequencies fromthe growth rate of the O2 gas bubbles formed in their respectivenanochannel during reaction.

It is well established that the presence of metallic surfaces or particles in the vicinity of a fluorophore can dramatically increase the radiative decay rate, and consequently the quantum efficiency, of the fluorophore. This effect, which depends on parameters such as metal particle size and fluorophore-particle separation, is manifest as a substantial enhancement in fluorescence emission intensity. This presentation will focus on optimisation strategies to maximise the enhancement for important applications such as fluorescence-based biochip platforms. Ordered arrays of metallic nano-islands were fabricated on a range of substrates by a process of natural lithography using monodisperse polystyrene nanospheres. The metal particle dimensions were tailored in order to match the plasmon resonance wavelength to the spectral absorption of the fluorophore. The fluorophore Cy5 dye, which is widely used in optical immunoassays and has a medium quantum efficiency (~0.3), was used in this study of the plasmonic enhancement effect. The morphology of the metallic arrays was investigated using scanning electron microscope (SEM) and atomic force microscope (AFM). Absorption and emission spectroscopies were used to elucidate the enhancement effect and its dependence on metal island morphology. Results were correlated with existing theoretical models. The applicability of this important technique to sensor platforms, such as fluorescence-based biochips, will be discussed.

The combination of the integrated waveguide and phase-change materials (PCMs) provides a promising platform for reconfigurable and multifunctional photoelectric devices. Through plasmonic enhancement and the low loss propagation of the waveguide, the footprint and power consumption of the photoelectric device can be effectively improved. In this work, a metal double-ring structure embedded with phase change materials was proposed to utilize the plasmonic effect for enhancement of the light-matter interaction. In particular, the overall temperature difference in the PCM cell can be confined within 2 °C during the crystallization process, thus avoiding the interior heterogeneous crystallization. The insertion loss of the cell in amorphous and crystalline states at a wavelength of 1550 nm are 2.3 dB and 1.0 dB, respectively. A signal contrast ratio of 15.8% is achieved under the ultra-small footprint (50 × 90 nm2) at a wavelength of 1550 nm.

Plasmonic effects on CO2 reduction over bimetallic Ni-Au catalysts

Various graphene-based Au nanocomposites have been developed as surface-enhanced Raman scattering (SERS) substrates recently. However, efficient use of SERS has been impeded by the difficulty of tuning SERS enhancement effects induced from chemical and plasmonic enhancement by different preparation methods of graphene. Herein, we developed graphene-based Au hybrids through physical sputtering gold NPs on monolayer graphene prepared by chemical vapor deposition (CVD) as a CVD-G/Au hybrid, as well as graphene oxide-gold (GO/Au) and reduced-graphene oxide (rGO/Au) hybrids prepared using the chemical in situ crystallization growth method. Plasmonic and chemical enhancements were tuned effectively by simple methods in these as-prepared graphene-based Au systems. SERS performances of CVD-G/Au, rGO/Au and GO/Au showed a gradually monotonic increasing tendency of enhancement factors (EFs) for adsorbed Rhodamine 6G (R6G) molecules, which show clear dependence on chemical bonds between graphene and Au, indicating that the chemical enhancement can be steadily controlled by chemical groups in a graphene-based Au hybrid system. Most notably, we demonstrate that the optimized GO/Au was able to detect biomolecules of adenine, which displayed high sensitivity with a detection limit of 10(-7) M as well as good reproducibility and uniformity.

Graphene-based noble metal nanocomposites have attracted tremendous research interest in the fields of surface-enhanced Raman scattering (SERS) recently. However, efficient utilization as SERS substrates has been impeded by the difficulty of tuning SERS enhancement effects induced from chemical and plasmonic enhancement by different preparation methods of graphene. Herein, three kinds of graphene-based Au hybrid, CVD-G/Au, GO/Au and rGO/Au, which were synthesized by physical sputtering and chemical in-situ crystallization growth methods, were fabricated to evaluate as SERS substrates. Simple methods were developed to enhance the Raman signals effectively by tuning both plasmonic and chemical enhancement, respectively. Besides, the prepared rGO/Au nanocomposites were used as SERS substrates to monitor the process of plasmon-driven surface-catalyzed reaction from 4-nitrobenzenethiol (4-NBT) to p,p'-dimercaptoazobenzene (DMAB). According to systematic comparisons during power- and time-dependent SERS experiments, rGO/Au was demonstrated to be with lower power threshold and higher catalytic efficiency than Au nanoparticles (NPs) toward the reaction, which provide clues to understand the interaction between metal and graphene as well as further study of plasmon-driven chemical reactions for further.

Local-plasmon-enhanced up-conversion fluorescence from copper phthalocyanine

Plasmonic coupling provides a highly localized electromagnetic field in the gap of noble metals when illuminated by a light. The plasmonic field enhancement is generally known to be inversely proportional to the gap distance. Given such a relation, reducing the gap distance appears to be necessary to achieve the highest possible field enhancement. At the sub-nanometer scale, however, quantum mechanical effects have to be considered in relation to plasmonic coupling. Here, we use graphene as a spacer to observe plasmonic field enhancement in sub-nanometer gap. The gap distance is precisely controlled by the number of stacked graphene layers. We propose that the sudden drop of field enhancement for the single layer spacer is originated from the plasmon tunneling through the thin spacer. Numerical simulation which incorporates quantum tunneling is also performed to support the experimental results. From the fact that field enhancement with respect to the number of graphene layers exhibits different behavior in two wavelengths corresponding to on- and off-resonance conditions, tunneling phenomenon is thought to destroy the resonance conditions of plasmonic coupling.

The self‐powered photothermoelectric photodetector is promising for diverse military and civilian applications. However, the substandard mechanical flexibility and high manufacturing costs limit its promotion in wearable electronics. Herein, a cost‐effective route is demonstrated for manufacturing a flexible photothermoelectric photodetector using industrial waste. By the precipitation reaction under the coupling of ultrasonic waves and shear force, waste copper etching solution is successfully recycled into copper sulfide nanoparticles. The resulting plasmonic Cu 9 S 8 nanoparticles, with an average size of ≈10 nm, exhibit strong near‐infrared light absorption as well as the high photothermal conversion efficiency of 48% due to the plasmonic enhancement effects. Then, the flexible photothermoelectric device is fabricated by depositing the Cu 9 S 8 thin film on Nylon filter membranes. The simplified device demonstrates a responsivity of 0.3 mA W −1 and a rapid response time of 4.1 s (rise) and 3.0 s (fall) to 808 nm infrared light. Furthermore, microcrack engineering within the Cu 9 S 8 thin film enhances the device's mechanical durability. The flexible photodetector shows almost no degradation in photoresponse even after 1000 bending‐releasing cycles. This work not only provides a way to turn waste etching solution into treasure, but also opens up a new path for low‐cost preparation of flexible photodetectors.