Nanoparticle Arrays Research Articles

(Invited) Near-Field Optics and Its Applications in Nanophotonic Devices: A Review

In our presentation, we will offer an overview of aperture-type scanning near field optical microscopy (SNOM) – a family of nano-optical imaging techniques derived from scanning probe microscopy which are capable of subwavelength resolution, and the development of three dimensional (3D) SNOM methods undertaken by our group to locally image the distribution of the electromagnetic radiation in the proximity of nanoparticles and nano-objects.[1] We will discuss a few applications in which we took advantage of 3D-SNOM to design specific optical nanosystems for light harvesting device applications. Specific case studies that will be presented include the design of plasmonic thin-film solar cells enhanced by random arrays of copper nanoparticles,[2] and the use of 3D-SNOM for characterizing evanescent waveguides self-assembled from of copper nanoparticles assembled on thin films of graphene.[3] In the final part of our talk, we will we present near-field scanning thermoreflectance imaging (NeSTRI), a new pump-probe technique invented in our group (see Figure 1) in which an aperture-type SNOM is used to contactlessly determine the thermal conductivity of inhomogeneous thin films and low-dimensional systems at the nanoscale for heat-spreading and thermoelectric applications.[4,5] These examples well represent the versatility of SNOM imaging and its potential for designing an even wider family of nano-optical devices.[1] P Bazylewski, S Ezugwu, G Fanchini, Applied Sciences 7 (2017) 973[2] S Ezugwu, H Ye, G Fanchini, Nanoscale 7 (2016) 252-260[3] T Ouyang, A Akbari-Sharbaf, J Park, R Bauld, MG Cottam, G Fanchini, RSC Advances 5 (2015) 98814-98821[4] S Ezugwu, S Kazemian, DYW Choi, G Fanchini, Nanoscale 9 (2017) 4097-4106[5] S Kazemian, S Ezugwu, G Fanchini, Proc. SPIE 10926, Quantum Sensing and Nano Electronics and Photonics XVI, 109260L (1 February 2019); doi: 10.1117/12.2509828 Figure 1

Asymmetric Transmission in Diffractive Chiral Metasurfaces Consisting of Nanoantennas

We have studied the asymmetric transmission in diffractive chiral metasurfaces consisting of nanoantennas. The study was made of lattice plasmon modes on the phenomenon of asymmetric transmission in chiral two dimensional arrays of plasmonic nanoparticles. It was demonstrated that asymmetric transmission resulted from contribution of higher order diffracted waves. It was shown that the isolated nanostructures has a fourfold rotational symmetry, the diffractive metasurfaces exhibited asymmetric transmission for normal incidence light within spectral range for which lattice plasmon modes were supported. It was found that lattice plasmon modes played role in enabling symmetric transmission in diffractive chiral metasurfaces. The symmetric transmission mechanism is due to different lattice plasmon mode excitation efficiencies of left circularly polarized and right circularly polarized and right circularly polarized light. The excitation efficiencies are controlled by tailoring the nano particles in plan distribution of scattered light for circularly polarized excitation and its alignment with the inplane diffraction orders of the metasurfaces. The phenomenon for a metasurface composed of an array of a chiral nanoparticles consisting of four nanoantennas. It was shown that the Rayleigh anomaly condition where the asymmetric transmission effect was strongest and metasurfaces supported lattice plasmon modes. It was found that the difference in the inplane scattered intensity varied as a function of the inplane angle around the nanostructure, rotating the nanostructure in the plane of the metasurface. The obtained results found in good agreement with previously obtained results.

Biomimetic Chiral Nanotopography for Manipulating Immunological Response

AbstractImmune response regulates implanted biomaterial−tissue integration and tissue regeneration, in which macrophages play a key role due to their plasticity and polarization. Chirality, an inherent property of carbon‐based life, can also exist in biomaterials such as gold monolayer. Constructing chiral nanostructured surfaces of implants can imitate the chirality of extracellular environment in a biomimetic manner, but the manipulation and mechanism of chiral nanotopography on macrophages remain poorly understood. Here, highly ordered gold nanoparticle arrays with 300 or 900 nm spacing are fabricated and modified with L‐ or D‐chirality. The D‐nanoarrays can promote M2 polarization and related cytokine secretion of macrophages, thus facilitating the reduction of inflammatory reaction and promoting tissue healing and regeneration. The mechanistic analysis further suggests that D‐nanoarrays proceeded these regulations through enhancing the expression of integrin αv/α8/β3‐p‐FAK pathway in macrophages, which may be largely attributed to its higher stereo‐affinity for fibronectin as revealed by quantitative experiments and molecular dynamics simulations. Overall, this study demonstrates that biomimetic chiral nanotopography can promote biomaterial−tissue integration by manipulating macrophage phenotype, bringing a novel strategy for immunomodulation.

Spike Growth on Patterned Gold Nanoparticle Scaffolds.

This work reports a scaffold-templated, bottom-up synthesis of 3D anisotropic nanofeatures on periodic arrays of gold nanoparticles (AuNPs). Our method relies on substrate-bound AuNPs as large seeds with hemispherical shapes and smooth surfaces after the thermal annealing of as-fabricated particles. Spiky features were grown by immersing the patterned AuNPs into a growth solution consisting of a gold salt and Good's buffer; the number and length of spikes could be tuned by changing the solution pH and buffer concentration. Intermediate structures that informed the growth mechanism were characterized as a function of time by correlating the optical properties and spike features. Large-area (cm2) spiky AuNP arrays exhibited surface-enhanced Raman spectroscopy enhancement that was associated with increased numbers of high-aspect-ratio spikes formed on the AuNP seeds.

Laser Controlled Manipulation of Microbubbles on a Surface with Silica‐Coated Gold Nanoparticle Array (Small 49/2023)

Laser Controlled Manipulation of Microbubbles on a Surface with Silica‐Coated Gold Nanoparticle Array (Small 49/2023)

Laser Direct Writing of Crystallized TiO2 by Photothermal Effect Induced by Gold Nanoparticles

Near‐infrared (NIR) laser annealing is successfully used to crystallize TiO2 thin films from a sol–gel solution deposited on gold nanoparticle arrays (AuNPs). The AuNPs are used as nano‐heaters allowing a local temperature increase up to 500 °C in the film. The temperature reached under the laser is deduced from the presence of the anatase phase in the samples obtained by laser exposure, showing that crystallized TiO2 can be obtained by the photothermal effect. Different analytical techniques supported this study, such as grazing X‐ray diffraction (GIXRD), UV–vis, and Raman spectroscopy. The temperature increase is confirmed by a numerical model that emphasizes the role of NPs coupling in the photothermal effect. Direct laser patterning by NIR laser and in combination with Deep‐UV photolithography (DUV) are demonstrated. This fabrication method opens new perspectives in applications such as photonics, photocatalysis, or biosensing.

High Q-Factor Plasmonic Surface Lattice Resonances in Colloidal Nanoparticle Arrays.

Surface lattice resonances (SLRs) sustained by ordered metal arrays are characterized by their narrow spectral features, remarkable quality factors, and the ability to tune their spectral properties based on the periodicity of the array. However, the majority of these structures are fabricated using classical lithographic processes or require postannealing steps at high temperatures to enhance the quality of the metal. These limitations hinder the widespread utilization of these periodic metal arrays in various applications. In this work, we use the scalable technique of template-assisted assembly of metal colloids to produce plasmonic supercrystals over centimeter areas capable of sustaining SLRs with high Q factors reaching up to 270. Our approach obviates the need for any postprocessing, offering a streamlined and efficient fabrication route. Furthermore, our method enables extensive tunability across the entire visible and near-infrared spectral ranges, empowering the design of tailored plasmonic resonant structures for a wide range of applications.

Assembly of nanoparticles at symmetric coffee stain locations

The precise picture of the nanoparticle array deposits on the substrate surface is crucial since many uses for nanostructures are dependent on how the assembled array's collective behavior responds to various physicochemical properties. The well-known seed-mediated approach was used to synthesize gold nanorods stabilized by CTAB molecules. Due to the Helium Ion Microscope’s (HIM) remarkable ability to reveal the real nature of the deposited entities, gold nanorod arrays at symmetrical parts of the coffee-stain ring have been studied using this technique. The object of this study is to evaluate three different positions within the coffee-stain ring at the convective symmetric locations. In the context of the self-assembled mechanism, the formation of various liquid crystalline phases induced by the evaporating symmetric convective flow inside the sessile droplet have been examined and compared at the symmetric positions within the ring.

Fabrication of Large-Area Fully Alloyed Ag/Au Nanoparticle Arrays

Fabrication of Large-Area Fully Alloyed Ag/Au Nanoparticle Arrays

Triangular Au nanoparticle arrays based on flexible materials as temperature-sensitive SERS substrates

In this study, PS microspheres were used as masks to obtain tip-connected triangular Au nanoparticle arrays on the surface of Cu films by thermal evaporation. Then transferred to flexible polydimethylsiloxane (PDMS), triangular Au nanoparticle arrays (Au NPAs/PDMS) were obtained by increasing the temperature using concentrated stress to cause fracture at the junction. The prepared Au NPAs/PDMS was used as an active substrate for surface-enhanced Raman spectroscopy (SERS), and the Raman signal of probe molecule rhodamine 6G (R6G) was collected while the substrate was heated. Due to the thermal expansion of PDMS, the gap of Au NPAs/PDMS changes with increasing temperature, enabling dynamic SERS detection. When the temperature reaches 64 °C, the substrate achieves the optimal Raman enhancement with a low RSD value of 5.8 % and a detection limit of 10−8 M for R6G. Furthermore, we modified the substrate hydrophobic, and finally obtained a low concentration of 10−10 M, with an enhancement factor of 3.5 × 108, to achieve highly sensitive SERS signal detection. In addition, due to the high optical transmittance and flexibility, the PDMS can be well-fitted to the surface of the object, indicating the potential of the fabricated substrates for in-situ detection.

Nanopores limited domain and PVA film used to assist the SERS property of gold nanoparticle arrays

The combination of nanopores and noble metal nanoparticles has been the focus of research in recent years, and their synergistic effect enabled the substrate exhibit excellent SERS property. In this paper, the array porous silicon structures embedded with gold nanoparticles have been prepared by using the polystyrene (PS) microsphere template assisted gold annealing process and metal assisted chemical etching techniques (AuNPs@nanopore). Polyvinyl alcohol (PVA) thin film was introduced as a molecular adsorption layer to be spin coated on the surface and formed composite structure (AuNPs@nanopore @PVA) to enrich more detection molecules. Through the SERS analysis of different depths of gold nanoparticles by Rhodamine 6G (R6G) probe molecules, the optimal etching time, that is, the optimal depth that gold nanoparticles should be in, was determined. Under the etching time of 2 min, the AuNPs@nanopore @PVA structure base with pore depth of 245 nm and diameter of gold nanoparticles of 181 nm showed high sensitivity, high uniformity and the best SERS property. It can realize the low concentration detection of 10−10 mol/L R6G molecule and 10−11 mol/L methylene blue (MB) molecule, and the enhancement factor is up to 1.20 × 107. The substrate can also be used to detect the pesticide thiabendazole molecule, the detection limit of 10−8 mol/L.

Confined In-Situ Encapsulation of Co/C Composites with Increased Heterogeneous Interface Polarization for Enhanced Electromagnetic Performance.

It is an urgent problem to realize reliable microwave absorption materials (MAMs) with low density. To address this issue, a series of controlled experiments w ere carried out, which indicated that the tubular structure enables excellent microwave absorption properties with a lower powder filling rate. This performance is attributable to the combined dielectric and magnetic loss mechanisms provided by Co/C and the interface polarization facilitated by multiple heterogeneous interfaces. Particularly, Co@C nanotubes, benefiting from the enhanced heterointerface polarization due to their abundant specific surface area and the reduced electron migration barrier induced by their 1D stacked structure, effectively achieved a dual enhancement of dielectric loss and polarization loss at lower powder filling ratios. Furthermore, the magnetic coupling effect of magnetic nanoparticle arrays in tubular structures is demonstrated by micromagnetic simulation, which have been few reported elsewhere. These propertied enable Co@C nanotubes to achieve minimum reflection lossand maximum effective absorption broadband values of 61.0dB and 5.5GHz, respectively, with a powder filling ratio of 20wt% and a thickness of 1.94mm. This study reveals the significance of designing 1D structures in reducing powder filling ratio and matching thickness, providing valuable insights for developing MAMs with different microstructures.

Conduction Mechanism Switching from Coulomb Blockade to Classical Critical Percolation Behavior in Disordered Nanoparticle Array

AbstractLarge, open‐gate transistors made from metal nanoparticle arrays offer possibilities to build new electronic devices, such as sensors. A nanoparticle necklace network (N3) of Au particles from 300 K to cryogenic temperatures exhibit a nonohmic I–Vd behavior, I ≈ (Vd–VT)ζ, where VT is a conduction gap and ζ is a constant critical exponent. The conduction gap in N3, made from disordered networks of 1D chains of 10 nm diameter Au particles exhibits room temperature (RT) gating. Although the I–Vd behavior at RT is identical to Coulomb blockade, the conduction is modulated by field‐assisted tunneling exhibiting classical critical behavior. In this study, based on three results, invariance of VT on gating, invariance of VT on temperature, and zero–bias conductance, a sharp transition temperature at ≈140 K is discovered where the conduction mechanism switches from Coulomb blockade to classical critical percolation behavior. The N3 architecture allows the reconciliation of the Coulomb blockade versus activation process as a sharp thermal transition to serve as a model system to study the exotic behavior in nanogranular‐metallic materials. The novel global critical behavior to local Coulomb blockade governed transition in these N3 architectures may potentially lead to novel sensors and biosensors.

Single-Cell Analysis with Silver-Coated Pipette by Combined SERS and SICM.

The study of individual cell processes that occur both on their surface and inside is highly interesting for the development of new medical drugs, cytology and cell technologies. This work presents an original technique for fabricating the silver-coated pipette and its use for the cell analysis by combination with surface-enhanced Raman spectroscopy (SERS) and scanning ion-conducting microscopy (SICM). Unlike the majority of other designs, the pipette opening in our case remains uncovered, which is important for SICM. SERS-active Ag nanoparticles on the pipette surface are formed by vacuum-thermal evaporation followed by annealing. An array of nanoparticles had a diameter on the order of 36 nm and spacing of 12 nm. A two-particle model based on Laplace equations is used to calculate a theoretical enhancement factor (EF). The surface morphology of the samples is investigated by scanning electron microscopy while SICM is used to reveal the surface topography, to evaluate Young's modulus of living cells and to control an injection of the SERS-active pipettes into them. A Raman microscope-spectrometer was used to collect characteristic SERS spectra of cells and cell components. Local Raman spectra were obtained from the cytoplasm and nucleus of the same HEK-293 cancer cell. The EF of the SERS-active pipette was 7 × 105. As a result, we demonstrate utilizing the silver-coated pipette for both the SICM study and the molecular composition analysis of cytoplasm and the nucleus of living cells by SERS. The probe localization in cells is successfully achieved.

Quasi-Random Multimetallic Nanoparticle Arrays.

This paper describes a nanofabrication procedure that can generate multiscale substrates with quasi-random microregions of nanoparticle arrays having different periodicities and metals. We combine cycles of large-area nanoparticle array fabrication with solvent-assisted wrinkle lithography to mask and etch quasi-random areas of prefabricated nanoparticles to control the fill factors of the arrays. The approach is highly flexible, and parameters, including nanoparticle size and material, array geometry, and fill factor, can be tailored independently. Multimetallic nanoparticle arrays can support surface lattice resonances at fill factors as low as 20% and can function as nanoscale cavities for lasing action with as few as 10% of the nanoparticles in an array. We demonstrated that multimetallic nanoparticle substrates that combine two or three arrays with different periodicities can exhibit lasing responses over visible and near-infrared wavelengths. Our work showcases the robust optical responses of multimetallic and periodic devices for broadband light manipulation.

Direct observation of NMR transverse relaxation in nanopatterned clusters of iron oxide particles.

We aim to verify predictions showing T2 relaxation rate of nanoparticle clusters and its dependence on spacing, size, geometry, and pulse sequence. We performed a laboratory validation study using nanopatterned arrays of iron oxide nanoparticles to precisely control cluster geometry and image diverse samples using a 4.7T MRI scanner with a T2 -weighted fast spin-echo multislice sequence. We applied denoising and normalization to regions of interest and estimated relative R2 for each relevant nanoparticle array or nanocluster array. We determined significance using an unpaired two-tailed t-test or one-way analysis of variance and performed curve fitting. We measured a density-dependent T2 effect (p = 8.9976 × 10-20 , one-way analysis of variance) and insignificant effect of cluster anisotropy (p = 0.5924, unpaired t-test) on T2 relaxation. We found negative quadratic relationships (-0.0045[log τD ]2 -0.0655[log τD ]-2.7800) for single nanoparticles of varying sizes and for clusters (-0.0045[log τD ]2 -0.0827[log τD ]-2.3249) for diffusional correlation time τD = rp 2 /D. Clusters show positive quadratic relationships for large (3.8615 × 10-6 [dpp /rp ]2 -9.3853 × 10-5 [dpp /rp ]-2.0393) and exponential relationships for small (-2.0050[dpp /rp ]0.0010 ) clusters. Calculated R2 peak values also align well with in silico predictions (7.85 × 10-4 ms compared with 1.47 × 10-4 , 4.23 × 10-4 , and 5.02 × 10-4 ms for single iron oxide nanoparticles, 7.88 × 10-4 ms compared with 5.24 × 10-4 ms for nanoparticle clusters). Our verification affirms longstanding in silico predictions and demonstrates aggregation-dependent behavior in agreement with previous Monte Carlo simulation studies.

Dislocation breakaway from nanoparticle array linear complexions: Plasticity mechanisms and strength scaling laws

Linear complexions are stable defect states, where the stress field associated with a dislocation induces a local phase transformation that remains restricted to nanoscale dimensions. As these complexions are born at the defects which control plasticity in metals, it is crucial to understand their impact on subsequent mechanical properties. In this work, atomistic modeling is used to understand how dislocation mechanics are altered by the presence of nanoparticle array linear complexions in a Ni-Al alloy. Molecular dynamics simulations are used to identify the critical shear stress needed to drive dislocation breakaway, first for nanoparticle arrays formed by Monte Carlo/molecular dynamics methods to represent realistic configurations and subsequently for simplified models that allow the effects of particle spacing and size to be varied in a controlled manner. A combined bowing and progressive unpinning mechanism is uncovered, leading to the demonstration of a new strength scaling law that differs in keys ways from classical Orowan bowing.

Multiple surface lattice resonances of overlapping nanoparticle arrays with different lattice spacing.

Multiple surface lattice resonances generated with nanoparticle arrays are promising to enhance light-matter interactions at different spectral positions simultaneously, and it is important to tailor these resonances to desired frequencies for practical applications such as multi-modal nanolasing. To this end, this study proposes to generate multiple surface lattice resonances using overlapping nanoparticle arrays with different lattice spacing. Both full-wave numerical simulations and analytical coupled dipole approximation calculations reveal that for the overlapping structures composed with two different gold nanosphere arrays, both surface lattice resonances for the element structures are effectively excited. Considering that the optical responses are governed by the dipole-dipole interactions between the nanoparticles, it is interesting to find that the multiple surface lattice resonances are almost invariant by adjusting the relative shifts between the two arrays, which can be useful to tailor the high-quality factor resonances to desired spectral positions. In addition, due to the same reason, it is also shown that the multiple surface lattice resonances can be further finely tuned by selectively removing specific nanoparticles in the array. We anticipate that the tolerance to generate multiple surface lattice resonances and the flexible tunability make the overlapping nanoparticle arrays useful to design high performance linear and nonlinear nanophotonic devices.

Super-resolution imaging based on cascaded microsphere compound lenses.

In this paper, a cascaded microsphere compound lens (CMCL) is introduced, in which a 20-µm-diameter barium titanate glass (BTG) primary microsphere and a 250-nm-diameter or 200-nm-diameter polystyrene (PS) secondary microsphere array constitute CMCL1 and CMCL2, respectively. The field of view (FOV) depends on the size of the BTG microsphere, while the waist of the photon nanojet (PNJ) can be adjusted by the size of the PS microsphere. The narrower the waist of the PNJ, the higher the imaging resolution. In the experiment, a 200-nm-diameter hexagonally close-packed PS nanoparticle array is successfully observed by the CMCL with a high magnification of ∼11.6× and a FOV of ∼14µm, while the single BTG microsphere is incapable of observing the array. The point spread function is used to quantify the resolution of the CMCL. A well-designed CMCL can improve the imaging performances of a microsphere-assisted microscope.

Multi-mode detection of iodine based on Au@Ag nanoparticle array with highly sensibility and stability using plasmonic surface lattice resonances

Designing a sensor to rapidly and simply detect iodine (I2) in liquid and gaseous phase with excellent sensitivity, high stability, and low cost at room temperature is highly desirable. Herein, a two-dimensional Au@Ag nanoparticle ordered array was prepared by template method combined with chemical reduction for detecting I2 at room temperature. Due to the ordered structure, a plasmonic surface lattice resonances (PSLR) peak appeared in extinction spectrum of the Au@Ag nanoparticle ordered array. When the ordered array exposed to I2, the Ag shell would react with I2 to form AgI, thus leading to a change in the dielectric medium surrounding the Au nanoparticles. This change would cause a variation of color and a shift of PSLR peak, realizing multi-mode detection of liquid and gaseous I2 at room temperature without any sophisticated instrument. With the increase of I2 concentration, the color of the Au@Ag nanoparticle array changed from red to yellow-green. Meantime, the PSLR peak displayed highly sensitive redshift with a larger offset (about 156 nm) and intense signal strength. Moreover, due to the ordered array structure, the PSLR peak possessed good uniformity and stability. Therefore, the PSLR peak was more suitable for detecting I2 in a large concentration region. Furthermore, the practical application of the present prepared Au@Ag nanoparticle array was explored by detecting gaseous I2 at room temperature. It was found that the Au@Ag nanoparticle array possessed high sensitivity to gaseous I2 with a detection limit reaching to trace level (1 ppb), suggesting tremendous potential for real-world application.