Metal Nanoparticle Arrays Research Articles

Stick-and-play metasurfaces for directional light outcoupling

Periodic arrays of metallic nanoparticles act as metasurfaces to control light at the interface. Although the combination of a variety of functional materials with metasurfaces should open a rich scientific research field, the application degree of freedom is limited severely by the fabrication process. We developed a metasurface sticker that can be stuck on any surface and gives control over in- and outcoupling of light. We demonstrate a photoluminescence outcoupling by placing a sticker on the luminescent layers: the emission pattern is modulated both spatially and spectrally in a way defined by the metasurface sticker. The sticker is useful for enhancing optical response from many different surfaces including those that are incompatible with the nanofabrication processes and should help the integration of metasurfaces into functional devices.

Extinction cross section of dimer array of metallic nanoparticles

<sec>Surface lattice resonance (SLR) relies on both the lattice structure and its unit cell, which usually contains metallic nanoparticles. Since the full width half maximum of the lattice resonance is much narrower than that of localized surface plasmon resonance of a single particle, it is receiving attention increasingly. Based on the modified long-wavelength approximation, in this paper we derive an analytical expression for the extinction cross section of the dimer array of metallic nanoparticles.</sec><sec>Comparing with the single particle array, good tunability can be achieved by the lattice resonance of the dimer array, which is influenced by more factors, including the arrangement of the array, the structural parameter and the rotation of the dimer, the shape and size of the particles, etc. First, the polarizabilities of the two kinds of particles in the dimer array are adjusted by introducing a matrix of the array factors, which take into account the influence of dipole fields of every particle. Then a simple expression of the resonance condition for the SLR of the dimmer array is obtained. The proposed model can be applied to a wide variety of dimer arrays of ellipsoid particles, and the applied method can be generalized to more complicated structure like polymer arrays. In this paper we further discuss the polarization dependence and ability to modulate the lattice resonance, by changing the excitation condition and the structural parameters of the dimer array. It is found that the resonances of the dimmer array can be classified as three main categories. The resonance related to the particles is independent of the variation of the dimmer arrangement or the array structure. On the other hand, the resonances corresponding to the dimmer and the array rely crucially on the structural parameters. By carefully adjusting the structural parameters, we can modulate the specific resonance effectively. This research is of theoretical importance for studying the SLR for more complicated structures and may find potential applications in the design of new photoelectric chip via nanoparticle array.</sec>

Graphene on Rh(111): A template for growing ordered arrays of metal nanoparticles with different periodicities

The development of approaches to provide ordered networks of metal nanoparticles is a topic of great interest due to its potential contribution to the advent of a more efficient technology. The template-assisted formation of ordered nanoparticle arrays on graphene- or h-BN-metal surfaces has profiled as a promising approach because of the periodic interfacial modulations associated to the moiré patterns. Nevertheless, a complete understanding of the requirements that a moiré must meet to act as a good template is still challenging. In order to shed light on this issue, here, the graphene/Rh(111) surface is investigated as model template for the growth of metal nanoparticles due to its large variety of moiré patterns. Scanning tunneling microscopy experiments have revealed different Ir nanoparticle spatial distributions depending on the underlying moiré periodicity ranging from randomly scattered nanoparticles to well-ordered lattices with multiple periodicities. To unveil the origin of this behavior, density functional theory calculations have been performed on representative moiré patterns for the adsorption of both Ir individual adatoms and nanoparticles. We conclude that the presence of distinctive chemical environments throughout the moiré, which controls the size and the adsorption configuration of the nanoparticles, is crucial for the formation of ordered arrays.

Controllable Fabrication of Percolative Metal Nanoparticle Arrays Applied for Quantum Conductance-Based Strain Sensors.

We use gas phase deposition of well-defined nanoparticles (NPs) to fabricate closely-spaced Pd NP arrays on flexible membranes prepatterned with interdigital electrodes (IDEs). The evolution of the morphology and electron conductance of the NP arrays during deposition is analyzed. The growth of two-dimensional percolation clusters of interconnected NPs, which correlate with the percolation pathway for electron conduction in the NP deposits, is demonstrated. The percolative nature of the NP arrays permits us to finely control the percolation geometries and conductance of the NP film by controlling the NP deposition time so as to realize a precise and reproducible fabrication of sensing materials. Electron transport measurements reveal that the electrical conductance of the NP films is dominated by electron tunneling or hopping across the NP percolating networks. Based on the percolative and quantum tunneling nature, the closely-spaced Pd NP films on PET membranes are used as flexible strain sensors. The sensor demonstrates an excellent response ability to distinguish tiny deformations down to 5×10−4 strain and a high sensitivity with a large gauge factor of 200 up to 4% applied strain.

A non-invasive tool for early detection of acute leukemia in children using a paper-based optoelectronic nose based on an array of metallic nanoparticles

Volatile organic compounds (VOCs) in blood samples can be used as useful biomarkers to diagnose various human diseases. This study describes the potential of a paper-based sensor array for detecting leukemia using blood VOCs. Blood samples were collected from 59 new leukemia cases and 47 healthy cases as a control group. Each blood sample was divided into two parts; one for a laboratory test and the other was used in our study. Samples were mixed with heparin and then transferred to a sterile container, and a sensor was stacked on its cap. This sensor array contains 16 nanoparticles deposited on a sheet of hydrophobic paper in a 4 × 4 array format. Containers were stored in an oven at 60 °C for 4.5 h. Then, the image of sensors was recorded by a scanner and compared to the image before exposing the blood vapor. The sensor responses were subjected to different multivariate statistical methods to develop models that discriminate between control and leukemia samples. The interaction of nanoparticles with the volatile metabolome of blood caused aggregation and consequently changing in the color of nanoparticles. The color changes resulted in a specific pattern for blood samples with leukemia, which is different from those obtained from healthy specimens. The discrimination analysis was approved by pattern recognition methods such as principal component analysis with 97% accuracy. Among 59 patients, the mean age was 6.02 ± 4.55 years (range 1–16 y). The mean total response was 652.83 ± 117.02. The rock curve showed an accuracy of 96% for classifying patients from the control group. The logistic regression model showed that 93.6% of healthy and 93.2% of patients were classified correctly by using this method. These statistics agree with the classification results obtained by principal component analysis. For every 5000-unit increase in platelet count, the chance of leukemia decreased by 9%. Additionally, the chance of being categorized as a patient decreased by 10% for every 20-unit increase in total response. The electronic nose using VOC’s of blood is a non-invasive and inexpensive tool for detecting new cases of leukemia with high sensitivity and specificity. Platelet count is an essential para-clinical parameter determining the total response of the sensors. Follow up studies with a larger sample size are warranted to elucidate its clinical applicability.

Exceptionally narrow plasmonic surface lattice resonances in gold nanohemisphere array

Plasmonic surface lattice resonances (SLRs) supported by metal nanoparticle arrays have a range of appealing characteristics such as extremely narrow linewidths and greatly enhanced near fields, and thus are attractive in diverse applications. Improving the quality factor of SLRs is important for many applications and thus it has been the focus in this field. In this work, we report high quality out-of-plane SLRs supported by two-dimensional metal nanohemisphere arrays embedded in a symmetric dielectric environment. These SLRs, excited under oblique incidence with TM polarization, can have an ultra-narrow resonant linewidth (∼ 0.9 nm) at visible wavelengths around 715 nm. This corresponds to an exceptionally high quality factor of 794, which is ten times that of the widely-adopted nanorods. We attribute this striking performance to the nanohemisphere geometry, which greatly relaxes the stringent requirement on the height of nanoparticles for supporting out-of-plane SLRs, reducing the absorption loss, and in which the out-of-plane oscillations are much stronger than in-plane ones, leading to stronger inter-particle coupling. The tuning of the resonance wavelength and the quality factor can be explained by a qualitative approach based on the detuning between the Rayleigh anomaly and the localized surface plasmon resonance of an isolated nanoparticle. We expect this work will advance the engineering and applications of high quality SLRs.

Formation of one-dimensional arrays of nanoparticles using segmented polyurethane nanofibers prepared by electrospinning

The number density and the arrangement of metal nanoparticles in composite materials have a significant effect on their performance and hence their suitability for use in sensors and devices. Forming one-dimensional arrays of metal nanoparticles is one way of controlling their number density and arrangement in the devices. In this study, we fabricated one-dimensional arrays of gold nanoparticles by adsorbing them on linearly distributed hard segments present on the surfaces of segmented polyurethane nanofibers, which were produced by electrospinning under a stretching force. The length of the one-dimensional array was approximately 500 nm. Furthermore, the interparticle distance was almost constant at approximately 14 nm. Thus, the proposed method is suitable for fabricating one-dimensional arrays of metal nanoparticles with high precision.

Super- and Subradiant Lattice Resonances in Bipartite Nanoparticle Arrays.

Lattice resonances, the collective modes supported by periodic arrays of metallic nanoparticles, give rise to very strong and spectrally narrow optical responses. Thanks to these properties, which emerge from the coherent multiple scattering enabled by the periodic ordering of the array, lattice resonances are used in a variety of applications such as nanoscale lasing and biosensing. Here, we investigate the lattice resonances supported by bipartite nanoparticle arrays. We find that, depending on the relative position of the two particles within the unit cell, these arrays can support lattice resonances with a super- or subradiant character. While the former result in large values of reflectance with broad lineshapes due to the increased radiative losses, the latter give rise to very small linewidths and maximum absorbance, consistent with a reduction of the radiative losses. Furthermore, by analyzing the response of arrays with finite dimensions, we demonstrate that the subradiant lattice resonances of bipartite arrays require a much smaller number of elements to reach a given quality factor than the lattice resonances of arrays with single-particle unit cells. The results of this work, in addition to advancing our knowledge of the optical response of periodic arrays of nanostructures, provide an efficient approach to obtain narrow lattice resonances that are robust to fabrication imperfections.

Deterministic aperiodic photonic crystal with a 2D array of metallic nanoparticles as polarization-sensitive dichroic filter

We demonstrate the possibility of using a two-dimensional array of spheroidal metallic nanoparticles embedded in a one-dimensional photonic crystal to obtain a narrow-bandpass, polarization-sensitive dichroic filter operating in the near-UV and visible domains. The optical anisotropy of the array of identically oriented nanoparticles results in two spectrally distinct plasmon resonances independently excited for two mutually orthogonal linear polarization states of light, which ensures polarization and spectral selectivity of the composite structure. The narrow transmission bands of the filter are defect modes due to a layer located at the center of the structure and hosting the nanoparticle array. In order to suppress these transmission windows, it is essential that the defect modes closely coincide with the plasmon resonances excited in the array. We show that the use of deterministic aperiodic distributed reflectors surrounding the defect layer makes it possible to adjust the spectral positions of two defect modes in two separate bandgaps in order to achieve such a coincidence. Among the various parameters governing the precise position of transmittivity windows of the filter, we establish the strong influence of the thickness of the defect layer. We also show that a strong localization of the optical field in the plane of the nanoparticle array is essential to enhance the efficiency of plasmonic excitation and obtain the desired control of the defect modes. Our study opens up possibilities for the further development of polarization-controlled nanophotonic devices.

Mesoporous Silica Encapsulated Metal-Organic Frameworks for Heterogeneous Catalysis

Encapsulation of metal-organic frameworks (MOFs) with a shell of mesoporous silica can boost overall performance of MOFs, offering versatility for synthetic architecture of integrated nanocatalysts with reactor-like features. Recently, Yu et al. report a green approach to make yolk-shell nanoreactors.

Topological edge and corner states in a two-dimensional photonic Su-Schrieffer-Heeger lattice

Abstract Implementation of topology on photonics has opened new functionalities of photonic systems such as topologically protected boundary modes. We theoretically present polarization-dependent topological properties in a 2D Su-Schrieffer-Heeger lattice by using a metallic nanoparticle array and considering the polarization degree of freedom. We demonstrate that when eigenmodes are polarized parallel to the plane of the 2D lattice, it supports longitudinal edge modes that are isolated from the bulk states and transverse edge modes that are overlapped with the bulk states. Also, the in-plane polarized modes support a second-order topological phase under an open boundary condition by breaking the four-fold rotational symmetry. This work will offer polarization-based multifunctionality in compact photonic systems that have topological features.

Ultrafast detection of infectious bacteria using optoelectronic nose based on metallic nanoparticles

Developing an accurate and sensitive method for detection of waterborne pathogens and urinary tract infection are important environmental and clinical challenges. We report a colorimetric assay based on arrays of nanoparticles for identification of 10 infectious bacteria strains belonging to both gram positive and gram-negative species. The detection system works based on the interaction of the volatile metabolites emitted from bacteria with the arrays of metallic nanoparticles deposited on paper substrate. The color changes, monitored by a flatbed scanner, are analyzed by statistical pattern recognition methods. A unique colorimetric pattern is achieved for each bacteria strain. We could detect bacteria at very low concentrations (around 100 bacteria/mL) in less than 10 min, which is the fastest method reported ever. The sensor can be used successfully for detection of bacteria in drinking water as well as human urine (containing 177 healthy and 123 patient samples) in less than 50 min, which is dramatically faster than urine culture. The provided detection system opens a new way to develop simple, small, sensitive and rapid devices for detecting pathogens in various clinical samples.

(Invited) Nanoscale Llight Management Using Three-Dimensional Scanning Near-Field Optical Microscopy

In this talk, we will present an overview of aperture and apertureless type scanning near-field optical microscopy (SNOM) techniques that have been developed for the characterization of photonics-grade nanoscale materials, with a focus on three-dimensional (3D) SNOM methods. 3D SNOM has been undertaken to image the local distribution (within ~100 nm of the surface) of the electromagnetic radiation scattered by random and deterministic arrays ofmetal nanostructures or photonic crystal waveguides. Individual metal nanoparticles and metal nanoparticle arrays exhibit unique effects under light illumination, including plasmon resonance and waveguiding properties, which can be directly investigated using 3D-SNOM. In the second part of this article, we will review a few applications in which 3D-SNOM has proven to be useful for designing and understanding specific nano-optoelectronic structures and photonic materials. Examples will include the analysis of the nano-optical response phonetic crystal waveguides, aperture antennae and metal nanoparticle arrays, as well as the design of plasmonic solar cells incorporating random arrays of copper nanoparticles as an optical absorption enhancement layer, and the use of 3D-SNOM to probe multiple components of the electric and magnetic near-fields without requiring specially designed probe tips. A common denominator of these examples is the added value provided by 3D-SNOM in predicting the properties-performance relationship of nanostructured systems in photonics grade materials.

Resonant Optical Phenomena in Heterogeneous Plasmon Nanostructures of Noble Metals: A Review

The interaction of electromagnetic radiation with ordered and disordered arrays of noble metal nanoparticles, leading to the excitation of various modes of surface plasmon states in them, is analyzed. The dipole localized surface plasmon resonance in isolated nanoparticles and the influence of various size effects on its optical response are considered. The effect of dipole-dipole interaction between gold and silver nanoparticles on the optical properties of various nanosized and nanostructured objects is discussed. It is shown that both localized and delocalized (propagated) surface plasmon modes can be excited in composite gold and silver nanosystems, in particular, in porous films. The prospects for the practical application of nanostructures with arrays of gold and silver nanoparticles in sensor technology, surface-enhanced Raman spectroscopy, and modern optoelectronics are examined.

Chiral Surface Lattice Resonances.

Collective excitation of periodic arrays of metallic nanoparticles by coupling localized surface plasmon resonances to grazing diffraction orders leads to surface lattice resonances with narrow line width. These resonances may find numerous applications in optical sensing and information processing. Here, a new degree of freedom of surface lattice resonances is experimentally investigated by demonstrating handedness-dependent excitation of surface lattice resonances in arrays of chiral plasmonic crescents. The self-assembly of particles used as mask and modified colloidal lithography is applied to produce arrays of planar and 3D gold crescents over large areas. The excitation of surface lattice resonances as a function of the interparticle distance and the degree of order within the arrays is investigated. The chirality of the individual 3D crescents leads to the formation of chiral lattice modes, that is, surface lattice resonances that exhibit optical activity.

Plasmonic superlattices constructed by coupling electronic systems with metal nanoparticle arrays

We investigate the produced superlattice in electronic systems when coupled with metal nanoparticle arrays. The periodic potential is formed by the induced plasmonic excitations in the metal nanoparticles, with the period changing from several to hundreds of nanometers for either one- or two-dimensional cases. The theoretical method to calculate the periodic potential is presented analytically. Landau–Zener tunneling is studied in the one-dimensional case. The results show that the energy band structures of the superlattice could be designed or modified in a variety of ways, such as changing the structure parameters, combining different kinds of metal nanoparticles, and tuning the strength of the excitation field. These advantages make it a prospective platform to simulate condensed matter physics.

Formation of nanoparticles from thin silver films under a liquid layer by single-shot nanosecond laser action

In this study, we show that Ag thin films (10 nm thickness) deposited on a glass substrate can be transformed into nanoparticles by laser-induced dewetting using a pulsed Nd:YAG laser operated at λ = 532 nm. The film could be entirely dewetted by a single pulse, and the required fluence was about 100 mJ/cm2. The properties of fabricated nanostructures are investigated by scanning electron microscopy and optical spectroscopy. The size distribution of produced particles and the absorption spectra of dewetted films were found. This process provides a facile and scalable method of forming metal nanoparticle arrays for plasmonic and other applications.

Three-Terminal Tandem Solar Cells With a Back-Contact-Type Bottom Cell Bonded Using Conductive Metal Nanoparticle Arrays

To address three-terminal tandem solar cells composed of a back-contact-type Si bottom cell, which, in principle, has a tolerance against spectral variation, we fabricate the three-terminal GaAs/Si tandem device bonded using conductive metal nanoparticle arrays and measure the power extraction. A power equivalent to the sum of the power generated by the top and bottom subcells is extracted even under varying spectral conditions, which indicates advantages in three-terminal tandem solar cells with a back-contact-type bottom cell for terrestrial applications.

Strong coupling between organic dye molecules and lattice modes of a dielectric nanoparticle array

Abstract Plasmonic structures interacting with light provide electromagnetic resonances that result in a high degree of local field confinement, enabling the enhancement of light-matter interaction. Plasmonic structures typically consist of metals, which, however, suffer from very high ohmic losses and heating. High-index dielectrics, meanwhile, can serve as an alternative material due to their low-dissipative nature and strong scattering abilities. We studied the optical properties of a system composed of all-dielectric nanoparticle arrays covered with a film of organic dye molecules (IR-792) and compared these dielectric arrays with metallic nanoparticle arrays. We tuned the light-matter interaction by changing the concentration in the dye film and reported the system to be in the strong coupling regime. We observed a Rabi splitting between the surface lattice resonances of the nanoparticle arrays and the absorption line of the dye molecules of up to 253 and 293 meV, for the dielectric and metallic nanoparticles, respectively. The Rabi splitting depends linearly on the square root of the dye molecule concentration, and we further assessed how the Rabi splitting depends on the film thickness for a low dye molecule concentration. For thinner films of thicknesses up to 260 nm, we observed no visible Rabi splitting. However, a Rabi splitting evolved at thicknesses from 540 to 990 nm. We performed finite-difference time-domain simulations to analyze the near-field enhancements for the dielectric and metallic nanoparticle arrays. The electric fields were enhanced by a factor of 1200 and 400, close to the particles for gold and amorphous silicon, respectively, and the modes extended over half a micron around the particles for both materials.

An ultrahigh resolution pressure sensor based on percolative metal nanoparticle arrays

Tunneling conductance among nanoparticle arrays is extremely sensitive to the spacing of nanoparticles and might be applied to fabricate ultra-sensitive sensors. Such sensors are of paramount significance for various application, such as automotive systems and consumer electronics. Here, we represent a sensitive pressure sensor which is composed of a piezoresistive strain transducer fabricated from closely spaced nanoparticle films deposited on a flexible membrane. Benefited from this unique quantum transport mechanism, the thermal noise of the sensor decreases significantly, providing the opportunity for our devices to serve as high-performance pressure sensors with an ultrahigh resolution as fine as about 0.5 Pa and a high sensitivity of 0.13 kPa−1. Moreover, our sensor with such an unprecedented response capability can be operated as a barometric altimeter with an altitude resolution of about 1 m. The outstanding behaviors of our devices make nanoparticle arrays for use as actuation materials for pressure measurement.