Aluminum Plasmonics Research Articles

Controlling Cubic versus Octahedral Morphology in Plasmonic Aluminum Nanoparticle Synthesis with Titanocene Catalysts: A Systematic Study

Controlling Cubic versus Octahedral Morphology in Plasmonic Aluminum Nanoparticle Synthesis with Titanocene Catalysts: A Systematic Study

Enhanced deep ultraviolet light emission from AlGaN based nanowire with bowtie antenna array

The performance of conventional AlGaN based deep ultraviolet nanostructure has been hindered by low light emission efficiency. In this study, we demonstrate that the integration of a plasmonic aluminum (Al) bowtie antenna array with a high AlN content AlGaN based nanowire can potentially achieve a 42% and 45% enhancement in light emission at 275 nm under transverse electric (TE) and transverse magnetic (TM) polarization excitation, respectively. This enhancement is realized by carefully optimizing the nanowire diameter, as well as the size and position of the Al bowtie antenna array. The optimized dimensions of the nanowire facilitate light emission enhancement at 275 nm through dielectric resonance. Moreover, the integrated nanowire/antenna array system further increases light emission efficiency by exploiting local surface plasmon resonances. This integrated system holds promise for designing nano-photonic devices with precisely controlled responses.

Dynamic Behavior of Platinum Atoms and Clusters in the Native Oxide Layer of Aluminum Nanocrystals.

Strong metal-support interactions (SMSIs) are well-known in the field of heterogeneous catalysis to induce the encapsulation of platinum (Pt) group metals by oxide supports through high temperature H2 reduction. However, demonstrations of SMSI overlayers have largely been limited to reducible oxides, such as TiO2 and Nb2O5. Here, we show that the amorphous native surface oxide of plasmonic aluminum nanocrystals (AlNCs) exhibits SMSI-induced encapsulation of Pt following reduction in H2 in a Pt structure dependent manner. Reductive treatment in H2 at 300 °C induces the formation of an AlOx SMSI overlayer on Pt clusters, leaving Pt single-atom sites (Ptiso) exposed available for catalysis. The remaining exposed Ptiso species possess a more uniform local coordination environment than has been observed on other forms of Al2O3, suggesting that the AlOx native oxide of AlNCs presents well-defined anchoring sites for individual Pt atoms. This observation extends our understanding of SMSIs by providing evidence that H2-induced encapsulation can occur for a wider variety of materials and should stimulate expanded studies of this effect to include nonreducible oxides with oxygen defects and the presence of disorder. It also suggests that the single-atom sites created in this manner, when combined with the plasmonic properties of the Al nanocrystal core, may allow for site-specific single-atom plasmonic photocatalysis, providing dynamic control over the light-driven reactivity in these systems.

Photothermal Therapeutic Nanomaterials Composed of Plasmonic Aluminum Nanostructures for Effective Killing of Cells

Photothermal Therapeutic Nanomaterials Composed of Plasmonic Aluminum Nanostructures for Effective Killing of Cells

Efficiency enhancement of GaAs nanowire array-based solar cell by plasmonic Al nanoparticles

Gallium arsenide (GaAs) nanowire (NW) solar cells (SCs) have piqued the interest of researchers because they exhibit superior light-harvesting and anti-reflection properties along with reduced material consumption compared to their planar counterparts. However, the high surface-to-volume ratio associated with these NWs degrades their performance in practical applications. Light trapping is considered one of the most crucial parameters for producing low-cost high-efficiency NW-SCs. Thus, numerous light-trapping strategies have been explored, among which surface plasmon resonance (SPR) based optical absorption enhancement using metal nanoparticles (NPs) has emerged as a potential method. The role of plasmonic aluminum (Al) NPs in the efficiency enhancement of GaAs NW SC has not yet been explored. Therefore, in this study, a vertically aligned GaAs NW SC structure incorporated with Al NPs has been investigated using the finite-difference time-domain (FDTD) method. The sidewalls of GaAs NWs are embellished with uniformly arranged Al NPs with diameters ranging from 30 to 60 nm. The excitation of localized surface plasmon resonance in metal NPs results in significant light absorption enhancement at the GaAs near-band of the proposed structure. The results demonstrate that even with a low aspect ratio (D/P) of 0.3, optimizing the geometrical parameters of the NPs results in a 41.96 % increase in power conversion efficiency (PCE) and a 45 % increase in absorption efficiency at 800 nm for the proposed structure when compared to the bare structure. Hence, our suggested structure which utilizes the light-trapping mechanism of Al NPs proves to be a cost-effective and promising material combination for high-efficiency nanoscale SCs.

Surface‐enhanced Raman imaging of intact cancer cell membrane on a rough aluminum substrate

AbstractThe plasma membrane of cancer cells displays differences in lipid and protein composition which distinguish them from healthy cells. Certain molecules have such prominent vibrational characteristics that they can be considered cancer biomarkers. Although Raman spectroscopy is a label‐free non‐invasive method of chemical analysis, it, however, has been limited by weak signals from the membrane compared to the bulk interior of cells. Surface‐enhanced Raman scattering (SERS) on plasmonic gold and silver substrates has previously been used to overcome this limitation. However, the high cost, poor repeatability, and toxicity of these noble metals hinder their practical applications. These challenges may be solved by using different materials and nanostructures. Here, we performed SERS imaging of ovarian cancer cells on rough aluminum substrates and extracted the Raman signals of intact cell membranes by comparing these with the corresponding measurements on Si substrates. We used atomic force microscopy (AFM) for Raman signal calibration. The comparison of cancer and normal cell membranes revealed the different lipid/protein peak ratios in cytoplasm and nucleus‐proximal areas. These Raman signatures of the ovarian cancer can be used as new biomarkers. This method may be extended to other types of cancer biosensing based on aluminum plasmonics.

Plasmonic Aluminum Nanostructures Synergizing with Oxygen Vacancies in Zinc Oxides for Enhanced Photoelectrocatalysis

Designing a highly efficient and stable electrode is of great importance for photoelectrochemical (PEC) water splitting, which is limited by light absorption and charge separation. Herein, a unique ZnO1–x/3D-Al composite photoanode consisting of low-cost 3D aluminum (3D-Al) plasmonic material and oxygen-vacant zinc oxide (ZnO1–x) nanoparticles was prepared for efficient PEC water splitting for the first time. The plasmonic 3D-Al nanostructure significantly improves the light absorption of the photoanode, which increases the number of photo-generated electron–hole pairs. Meanwhile, the presence of oxygen vacancies further facilitates the generation and separation of photon-induced electron–hole pairs in ZnO1–x. As a result, the integrated ZnO1–x/3D-Al photoanode delivers an enhanced photocurrent density of 70.1 μA cm–2 at 1.23 V versus RHE, 2.9 times greater than that of pristine ZnO/Al, attributed to the synergy effect between plasmon resonance in 3D aluminum nanostructures and oxygen vacancies in zinc oxides.

Up-to-Five-Photon Upconversion from Near-Infrared to Ultraviolet Luminescence Coupled to Aluminum Plasmonic Lattices.

The incorporation of upconversion luminescence (UCL) materials into various plasmonic structures promotes light-matter interactions in nanophotonic systems. It has been experimentally demonstrated that UCL enhancement entailing two photons exhibits a quadratic dependence on the excitation intensity. However, in the field of plasmonics, there have not been sufficient studies on high-order multi-photon upconversion processes. We report up-to-five-photon UCL, wherein λ = 1550 nm near-infrared light is converted to 382 nm ultraviolet light, from core-inert shell nanoparticles coupled to aluminum plasmonic lattices. The five-photon UCL intensity of nanoparticles on the plasmonic lattice is over 800 times stronger than that on the flat glass. We demonstrate that the enhancement of UCL scales with the nth power of the local field enhancement for n-photon process. These findings give a strategy to obtain high-order multi-photon UPL with aluminum plasmonic nanostructures and can contribute to anti-counterfeiting application.

Fluorophore-Induced Plasmonic Current Generation from Aluminum Nanoparticle Films.

In this paper we demonstrate fluorophore induced plasmonic current (FIPC) from aluminum nanoparticle films. It has been previously shown that near-field excited fluorophores are able to plasmonically couple with metal nanoparticle films (MNF's) and induce surface plasmons, which in turn leads to a direct measurable electrical current through the MNF. These currents have been detected and quantified in noble metal MNF's, however due to future envisioned cost considerations there has been a push to adapt FIPC for use with less expensive metals. Subsequently, we observe that plasmonic aluminum films are able to produce these current changes when in close proximity to excited fluorophores, and the magnitude of the current changes are respective to the magnitude of the extinction coefficients of the fluorophores themselves. These findings also further support recent literature reports showing the inverse relationship between metal-enhanced fluorescence (MEF) and FIPC.

Plasmon-Enhanced Ultraviolet Luminescence in Colloid Solutions and Nanostructures Based on Aluminum and ZnO Nanoparticles.

Aluminum nanoparticles attract scientific interest as a promising low-cost material with strong plasmon resonance in the ultraviolet region, which can be used in various fields of photonics. In this paper, for the first time, ultraviolet luminescence of zinc oxide nanoparticles in colloid solutions and nanostructure films in the presence of plasmonic aluminum nanoparticles 60 nm in size with a metal core and an aluminum oxide shell were studied. Mixture colloids of ZnO and Al nanoparticles in isopropyl alcohol solution with concentrations from 0.022 to 0.44 g/L and 0.057 to 0.00285 g/L, correspondingly, were investigated. The enhancement of up to 300% of ZnO emission at 377 nm in colloids mixtures with metal nanoparticles due to formation of Al-ZnO complex agglomerates was achieved. Plasmon nanostructures with different configurations of layers, such as Al on the surface of ZnO, ZnO on Al, sandwich-like structure and samples prepared from a colloidal mixture of ZnO and Al nanoparticles, were fabricated by microplotter printing. We demonstrated that photoluminescence can be boosted 2.4-fold in nanostructures prepared from a colloidal mixture of ZnO and Al nanoparticles, whereas the sandwich-like structure gave only 1.1 times the amplification of luminescence. Calculated theoretical models of photoluminescence enhancement of ideal and weak emitters near aluminum nanoparticles of different sizes showed comparable results with the obtained experimental data.

Aluminum Plasmonic Nanoclusters for Paper-Based Surface-Enhanced Raman Spectroscopy.

Although surface-enhanced Raman spectroscopy (SERS) can rapidly identify molecular fingerprints and has great potential for analysis, the need for delicate plasmonic substrates and complex laboratory instruments seriously limits its applicability for on-site detection. This paper describes the development of an inexpensive aluminum nanoparticle (AlNP)-decorated paper that functions as a facile SERS-based detection platform (Al-PSERS). Polydopamine-protected AlNPs were chemically synthesized and then simply drop-cast onto a hydrophobic cellulose paper, forming a monolayer AlNP cluster array. Because of the abundance of hot spots arising from the plasmonic clusters, the inherent quasi-three-dimensional structure of the cellulose fibers, and the concentration effect of the hydrophobic surface, the Al-PSERS provided significant enhancements to the signal of various analytes, measured using a portable 785 nm Raman spectrometer. Near-field optical simulations and experimental spectroscopic results revealed that the local electric fields and corresponding SERS signal intensities of the AlNP array exhibited clear particle-length and cluster-size dependencies. Therefore, the Al-PSERS could be optimized to provide high sensitivity (enhancement factor: 2 × 103) and excellent reproducibility (variation: 8.72%). Moreover, the optimal Al-PSERS was capable of detecting colorants and environmental pollutants; for example, the detection limits of allura red and benzo[a]pyrene reached as low as 3.5 and 0.15 ppm, respectively. Furthermore, the Al-PSERS could rapidly identify illegal (rhodamine B) and edible (allura red, erythrosine) colorants from a mixture of multiple colorants or from adulterated candies. Because it facilitates rapid detection, is of low cost, and has minimal technical requirements, Al-PSERS should be applicable to on-site detection in, for example, food inspection and environmental monitoring.

Spectroscopy of nanoantenna-covered Cu2O : Towards enhancing quadrupole transitions in Rydberg excitons

Plasmonic antennas channel incoming light into a confined near field that comes along with strong field gradients at the edges. Transverse field gradients are capable of driving quadrupole transitions in a more effective way than the weak longitudinal field gradient in dipolar light. Cuprous oxide Rydberg excitons with principal quantum number $n$ between 5 and 15 are several tens to a few hundreds of nanometers in diameter and can have different orbital angular momentum quantum numbers. Usually, only $P$- and $F$-excitons are electric dipole allowed, while $S$- and $D$-excitons remain dark. Here, we use 30-nm-wide and 60- to 110-nm-long plasmonic aluminum nanoantennas deposited on the cuprous oxide crystal surface to create transverse field gradients in similar spatial dimensions as the size of the Rydberg excitons. This way, light field and matter wave function overlap spatially and quadrupole transitions of $S$excitons are enhanced. The relative enhancement of the $S$-exciton oscillator strength with respect to the $P$-exciton oscillator accounts for a factor of up to 1.4.

Tuning Light Emission Crossovers in Atomic-Scale Aluminum Plasmonic Tunnel Junctions.

Atomic-sized plasmonic tunnel junctions are of fundamental interest, with great promise as the smallest on-chip light sources in various optoelectronic applications. Several mechanisms of light emission in electrically driven plasmonic tunnel junctions have been proposed, from single-electron or higher-order multielectron inelastic tunneling to recombination from a steady-state population of hot carriers. By progressively altering the tunneling conductance of an aluminum junction, we tune the dominant light emission mechanism through these possibilities for the first time, finding quantitative agreement with theory in each regime. Improved plasmonic resonances in the energy range of interest increase photon yields by 2 orders of magnitude. These results demonstrate that the dominant emission mechanism is set by a combination of tunneling rate, hot carrier relaxation time scales, and junction plasmonic properties.

Selective Photodetoxification of a Sulfur Mustard Simulant Using Plasmonic Aluminum Nanoparticles.

Plasmonic nanostructures have attracted increasing interest in the fields of photochemistry and photocatalysis for their ability to enhance reactivity and tune reaction selectivity, a benefit of their strong interactions with light and their multiple energy decay mechanisms. Here we introduce the use of earth-abundant plasmonic aluminum nanoparticles as a promising renewable detoxifier of the sulfur mustard simulant 2-chloroethylethylsulfide through gas phase photodecomposition. Analysis of the decomposition products indicates that C-S bond breaking is facilitated under illumination, while C-Cl breaking and HCl elimination are favored under thermocatalytic (dark) conditions. This difference in reaction pathways illuminates the potential of plasmonic nanoparticles to tailor reaction selectivity toward less hazardous products in the detoxification of chemical warfare agents. Moreover, the photocatalytic activity of the Al nanoparticles can be regenerated almost completely after the reaction concludes through a simple surface treatment.

Hybrid Graphene-Supported Aluminum Plasmonics.

Controlled fabrication of devices for plasmonics on suspended graphene enables obtaining tunable localized surface plasmon resonances (LSPRs), reducing the red-shift of LSPRs, and creating hybrid 3D–2D systems promising for adjustable dipole–dipole coupling and plasmon-mediated catalysis. Here, we apply a low-cost fabrication methodology to produce patterned aluminum nanostructures (bowties and tetramers) on graphene monolayers via electron-beam lithography and trap platinum (Pt) nanoclusters (NCs) within their hotspots by thermal annealing. We reveal the LSPRs of aluminum plasmonics on graphene using electron energy-loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) in a monochromated scanning transmission electron microscope (STEM). The LSPRs of these nanostructures are measured to be between visible and ultraviolet regions of the spectrum and are confirmed by electromagnetic simulations. The antibonding dipole and bonding dipole modes of both structures are tuned by controlling their gap size. The tetramers enable the simultaneous excitation of both antibonding and bonding dipole modes at the poles of nanoprisms, while bowties allow us to excite these modes separately either at the poles or within the hotspot. We further show that the hybrid nanocavity–NC systems are in the intermediate coupling regime providing an enhanced plasmon absorption in the Pt NCs via the energy transfer from the antibonding dipole mode to the Pt NCs. The dipole LSPR of Pt NCs also couples to the bonding-type breathing mode in bowties. Our findings suggest that these hybrid nanocavity–graphene systems are of high application potential for plasmon-mediated catalysis, surface-enhanced fluorescence, and quantum technologies.

Uncovering the Evolution of Low-Energy Plasmons in Nanopatterned Aluminum Plasmonics on Graphene.

We report adjusting the charge-transfer-plasmon (CTP) resonances of aluminum (Al) bowties on suspended monolayer graphene via controlled nanofabrication and focused electron-beam irradiation. CTP resonances of bowties with a conductive junction blue-shift with an increase in junction width, whereas their 3λ/2 and λ resonances barely red-shift. These plasmon modes are derived and confirmed by an LC circuit model and electromagnetic simulations performed with boundary-element and frequency-domain methods. A monotonic decay of the CTP lifetime is observed, while the junction width is extended. Instead, the lifetimes of 3λ/2 and λ resonances are nearly independent of junction width. When the junction is shrunk by electron-beam irradiation, all antenna resonances red-shift. Having created an electron-beam-induced sub 5 nm gap in bowties, we monitor the unambiguous transition of a CTP into a bonding-type gap mode, which is highly sensitive to the separation distance. Meanwhile, the 3λ/2 and λ resonances evolve into dipolar bright and dipolar dark modes.

Dynamics of Strong Coupling Between Free Charge Carriers in Organometal Halide Perovskites and Aluminum Plasmonic States.

We have investigated a strong coupled system composed of a MAPbIxCl3-x perovskite film and aluminum conical nanopits array. The hybrid states formed by surface plasmons and free carriers, rather than the traditional excitons, is observed in both steady-state reflection measurements and transient absorption spectra. In particular, under near upper band resonant excitation, the bleaching signal from the band edge of uncoupled perovskite was completely separated into two distinctive bleaching signals of the hybrid system, which is clear evidence for the formation of strong coupling states between the free carrier–plasmon state. Besides this, a Rabi splitting up to 260 meV is achieved. The appearance of the lower bands can compensate for the poor absorption of the perovskite in the NIR region. Finally, we found that the lifetime of the free carrier–SP hybrid states is slightly shorter than that of uncoupled perovskite film, which can be caused by the ultrafast damping of the SPs modes. These peculiar features on the strong coupled hybrid states based on free charge carriers can open new perspectives for novel plasmonic perovskite solar cells.

Purcell radiative rate enhancement of label-free proteins with ultraviolet aluminum plasmonics

The vast majority of proteins are intrinsically fluorescent in the ultraviolet, thanks to the emission from their tryptophan and tyrosine amino-acid constituents. However, the protein autofluorescence quantum yields are generally very low due to the prevailing quenching mechanisms by other amino acids inside the protein. This motivates the interest to enhance the radiative emission rate of proteins using nanophotonic structures. Although there have been numerous reports of Purcell effect and local density of optical states control in the visible range using single dipole quantum emitters, the question remains open to apply these concepts in the UV on real proteins containing several tryptophan and tyrosine amino acids arranged in a highly complex manner. Here, we report the first complete characterization of the Purcell effect and radiative rate enhancement for the UV intrinsic fluorescence of label-free β-galactosidase and streptavidin proteins in plasmonic aluminum nanoapertures. We find an excellent agreement with a calibration performed using a high quantum yield UV fluorescent dye. Demonstrating and intensifying the Purcell effect is essential for the applications of UV plasmonics and the label-free detection of single proteins.

Preventing Corrosion of Aluminum Metal with Nanometer-Thick Films of Al2O3 Capped with TiO2 for Ultraviolet Plasmonics

Extending plasmonics into the ultraviolet range imposes the use of aluminum to achieve the best optical performance. However, water corrosion is a major limiting issue for UV aluminum plasmonics, as this phenomenon occurs significantly faster in presence of UV light, even at low laser powers of a few microwatts. Here we assess the performance of nanometer-thick layers of various metal oxides deposited by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) on top of aluminum nanoapertures to protect the metal against UV photocorrosion. The combination of a 5 nm Al2O3 layer covered by a 5 nm TiO2 capping provides the best resistance performance, while a single 10 nm layer of SiO2 or HfO2 is a good alternative. We also report the influence of the laser wavelength, the laser operation mode and the pH of the solution. Properly choosing these conditions significantly extends the range of optical powers for which the aluminum nanostructures can be used. As application, we demonstrate the label-free detection of streptavidin proteins with improved signal to noise ratio. Our approach is also beneficial to promote the long-term stability of the aluminum nanostructures. Finding the appropriate nanoscale protection against aluminum corrosion is the key to enable the development of UV plasmonic applications in chemistry and biology.

Plasmon-Enhanced Sunlight Harvesting in Thin-Film Solar Cell by Randomly Distributed Nanoparticle Array.

In this paper, a randomly distributed plasmonic aluminum nanoparticle array is introduced on the top surface of conventional GaAs thin-film solar cells to improve sunlight harvesting. The performance of such photovoltaic structures is determined through monitoring the modification of its absorbance due to changing its structural parameters. A single Al nanoparticle array is integrated over the antireflective layer to boost the absorption spectra in both visible and near-infra-red regimes. Furthermore, the planar density of the plasmonic layer is presented as a crucial parameter in studying and investigating the performance of the solar cells. Then, we have introduced a double Al nanoparticle array as an imperfection from the regular uniform single array as it has different size particles and various spatial distributions. The comparison of performances was established using the enhancement percentage in the absorption. The findings illustrate that the structural parameters of the reported solar cell, especially the planar density of the plasmonic layer, have significant impacts on tuning solar energy harvesting. Additionally, increasing the plasmonic planar density enhances the absorption in the visible region. On the other hand, the absorption in the near-infrared regime becomes worse, and vice versa.