Engineered low-symmetry colloidal crystals are emerging as promising performance-enhancing alternatives to natural materials for optical devices. However, current synthesis methods cannot precisely control structural features such as the orientation of the optical axes in these crystals. Here, DNA-modified nanorods and nanopentabipyramids were used as programmable atom equivalents to synthesize low-symmetry colloidal crystals. These crystals display three different lattice symmetries and crystal habits, aligning their optical axes in perpendicular, parallel, and oblique configurations relative to the crystal surface. The low lattice symmetries of the colloidal crystals define their optical anisotropies. Specifically, the rhombohedral colloidal crystals exhibit substantial polarization-dependent transmission and scattering characteristics. Optical measurements supported by simulations suggest that these colloidal crystals exhibit large optical anisotropy. This work expands the potential of programmable matter by developing a class of optically anisotropic materials engineered from DNA upon conjugation with relatively simple and readily available nanoparticle building blocks.

To simplify the treatment of real-life electromagnetic analysis problems that use integral equations, an alternative to the well-known integral equation discontinuous Galerkin (IEDG) method is proposed. This approach enables the creation of computer aided design and mesh models for separate subdomains, which can later be connected and analyze the problem as a whole, without caring about mesh conformity. The proposed extended multi-branch (EMB) basis functions allow for the analysis of nonconformal mesh problems, similar to IEDG, but with the advantage of avoiding the computation of the stabilization parameter beta (IEDG’s main drawback) while ensuring current continuity across tear lines. Several numerical experiments have been done to compare the results obtained from both methods (IEDG and EMB) with those from the equivalent conformal mesh model using RWG basis functions analyzed with the method of moments.

Chiral Au@Ag core-shell nanoparticles were synthesized by asymmetric Ag deposition on premade chiral Au nanorods and employed for enantioselective surface-enhanced Raman scattering (SERS) of bio-relevant chiral molecules. Electron tomography revealed nanoscale asymmetry arising during Ag shell growth, while circular dichroism spectroscopy and electromagnetic simulations confirmed strong optical activity. Differential SERS under circularly polarized light (CPL-SERS) demonstrated distinct spectral responses for L- and D-3,4-dihydroxyphenylalanine (L/D-DOPA), achieving enantiomeric discrimination exceeding 95% accuracy through principal-component linear-discriminant analysis. The combination of experimental and computational results reveals a direct structure-chirality-sensing correlation and establishes Au@Ag core-shell nanostructures as versatile platforms for ultrasensitive chiral detection.

Over the past decades, significant advancements have been made in computational electromagnetics, leading to highly efficient simulation methods. However, both the precision and computational efficiency of these simulations remain constrained by the discretization of geometric structures. The evaluation of highly sensitive parameters and the design of very low observability (VLO) targets necessitate a high-fidelity geometric representation, which, in turn, demands dense discretization and increased computational resources. To address this issue, adaptive meshing strategies, particularly h-refinement, have emerged as effective techniques [1]. This refinement approach begins with a coarse mesh and selectively enhances resolution in regions where errors are significant, guided by an error estimation mechanism. By dynamically subdividing these critical areas, h-refinement efficiently reduces global error, ensuring that the mesh meets the required accuracy.

The rapid advancement of scalable methods for solving Surface Integral Equations using the Method of Moments has equipped the computational electromagnetics community with powerful tools essential for modern engineering design. Accurate modeling of realistic complex platforms, such as ships and aircrafts, requires high-fidelity representations, especially for very low observability designs. However, these demands lead to multi-scale geometric challenges, dramatically increasing the number of unknowns and reducing solver performance. Existing solutions, such as macro-basis functions, higher-order basis functions, and curvilinear elements offer partial relief but face limitations in computational efficiency, mesh quality requirements, and geometric adaptability. In this work, we introduce generalized Rao-Wilton-Glisson (gRWG) functions as a novel higher-level basis to reduce the number of unknowns while preserving the geometric fidelity. These functions aggregate triangular elements into macro-cells and redefine RWG functions as linear combinations within these groups. The gRWG functions are excitation-independent, purely algebraic, and compatible with conventional MoM codes as a multiplicative preconditioner. This approach offers a computationally efficient and scalable solution for high-fidelity electromagnetic interference and radiation analyses in multi-scale environments.

The application of wavelength‐dependent differential circularly polarized light‐induced surface‐enhanced Raman scattering (CPL‐SERS) is reported for codification and encryption, using colloidal chiral plasmonic nanoparticles. This study demonstrates that intrinsically chiral Au nanorods (c‐AuNRs) encoded with achiral Raman reporters display unique optical activity. Right‐handed and left‐handed c‐AuNRs show positive or negative CPL‐SERS depending on the illumination wavelength (633 and 785 nm in this case), in correlation with their respective circular dichroism (CD) spectra. This effect enables c‐AuNR enantiomeric differentiation through evaluation of the CPL‐SERS response for each excitation wavelength. To showcase the potential of this approach, four encoded c‐AuNR dispersions were prepared, each with distinct handedness and Raman reporter combinations, and used to encode a four‐letter message on paper, which can be selectively decoded through CPL‐SERS, even when using only two Raman reporters. By switching between excitation wavelengths of 633 and 785 nm, inverted CPL‐SERS signals were recorded, therefore enhancing the versatility of the coding. The integration of chiral plasmonic nanoparticles and CPL‐SERS represents a highly tunable platform for advanced sensing, encryption, and codification, thereby expanding the functionality of plasmonic nanostructures in optical technologies.

Colloidal chiral plasmonic nanoparticles are garnering growing interest due to their interaction with circularly polarized light, offering advanced optical applications. Their circular dichroism (CD) spectra are significantly narrower and more defined than extinction spectra, making them ideal for refractive index-based sensing. Despite progress in colloidal synthesis, this field remains relatively underexplored. In this work, a one-step, seed-mediated route to chiral Au nanorods is introduced in which the molar ratio Au3(+)/Au-0 enables continuous control of the CD response (intensity, sign, and position), using L- and D-cysteine as chiral inducers. CD-based refractive index sensitivity (RIS) measurements reveal a figure of merit (FoM = RIS/linewidth) exceeding 1000 RIU-1, outperforming the conventional extinction-based approaches. Thin films of C-AuNRs fabricated via a layer-by-layer assembly retain the bisignate CD response and show RIS values comparable to colloidal samples. These films demonstrate excellent stability, reusability, and resilience in highly absorbing media. All the experimental data are supported by advanced calculations performed using full-wave M3 Maxwell's solver and using electron tomography reconstructions as direct input. Finally, their applicability in RI-based quantitative detection of bovine serum albumin (BSA) is demonstrated, highlighting their potential for biomolecular sensing.

In this communication, we present the combination of a high scalability implementation of the multibranch-multiresolution preconditioner with the domain decomposition method for the electromagnetic analysis of geometrically complex strutures with different levels of multi-scale features and discretized with a possible non-conformal mesh. Finally, a numerical experiment is shown to illustrate the great efficiency of the proposed approach for the solution of large multi-scale objects.

In computational electromagnetics, the accuracy of simulations is significantly influenced by the meshing quality of the structures under analysis. Higher mesh density generally translates into higher accuracy as it provides a more detailed representation of the structure, although at the expense of greater demands on computational resources. This is particularly true in multiscale problems, where the different levels of detail make the impact of mesh density and quality even more critical. In this context, adaptive meshing techniques, especially through h-refinement, arise as a powerful tool for addressing these problems [1, 2]. H-refinement involves locally refining the mesh in areas lacking accuracy depending on an error estimation process. This method allows for targeted subdivisions in regions with higher errors, thereby systematically reducing the overall error and achieving the desired level of accuracy.

The interest in the electromagnetic behavior of periodic structures has significantly increased due to their crucial role in advancing cutting-edge applications in nanoscale and metasurface devices in scattering networks, plasmonic crystals, and nanophotonics. The rise of these technologies makes the improvement of the state-of-the-art methods in computational electromagnetics for the efficient solution of these kind of periodic structures even more crucial than ever. Traditional approaches predominantly centered on methods tailored for infinite periodic structures based on Floquet’s theorem and the Ewald transformation. However, although these methods have been demonstrated as powerful tools in the design process, they are not suitable for integration with other systems and sensors due to the limitation of infinite periodic structures or the accurate modeling of complex physical phenomena like edge effects and standing waves, vital phenomena for certain applications.

In this communication, we present the combination of a high scalability implementation of the multibranch-multiresolution preconditioner with the domain decomposition method for the electromagnetic analysis of geometrically complex structures with different levels of multiscale features and discretized with a possible nonconformal mesh. Finally, a numerical experiment is shown to illustrate the great efficiency of the proposed approach for the solution of large multiscale objects.

In this communication, the performance of the generalized minimum residual method (GMRES) preconditioned by a domain decomposition method (DDM) scheme embedded in a surface integral equation (SIE) formulation is studied. In realistic large multiscale problems the individual subdomain solutions, which in a DDM scheme acts as the preconditioners, have to be obtained by Krylov subspace iterative processes with a decisive influence on the outcome of the overall iterative process that deals with subdomains mutual couplings. The convergence and accuracy of the global solution, as well as the degree of correlation between them, are studied for left, right and flexible-right preconditioned GMRES to draw conclusions which maximize the efficiency in the application of the SIE-DDM implementation to challenging problems.

Discontinuous Galerkin (DG) approaches [1] used to connect two non-conformal surfaces in the Method of Moments typical employ Interior Penalty (IP) methods to mitigate charge accumulation along the half RWG basis functions connection boundary. These IP approaches are introduced via a combined impedance matrix $(Z-\beta$. $I P$). Alternatively in soft non-conforming problems, Multi-branch (MB-RWG) basis functions can be utilized [2]. Generalizations of multibranch basis functions can lead to higher degress of nonconformality as the use of $N^{+}-N^{-}$ branches MB_RWG [3] when $N^{+}$ and $N^{-}$ triangles have common vertices at the endpoints of the shared countour, but not along the contour.

The production of colloidal metal nanostructures with complex geometries usually involves shape-directing additives, such as metal ions or thiols, which stabilize high-index facets. These additives may however affect the nanoparticles' surface chemistry, hindering applications, e.g., in biology or catalysis. We report herein the preparation of gold bipyramids with no need for additives and shape yields up to 99%, using pentatwinned Au nanorods as seeds and cetyltrimethylammonium chloride as surfactant. For high-growth solution:seed ratios, the bipyramids exhibit an unusual "belted" structure. Three-dimensional electron microscopy revealed the presence of high-index {117}, {115}, and {113} side facets, with {113} and {112} facets at the belt. Belted bipyramids exhibit strong near-field enhancement and high extinction in the near-infrared, in agreement with electromagnetic simulations. These Ag-free bipyramids were used to seed chiral overgrowth using 1,1 '-binaphthyl-2,2 '-diamine as a chiral inducer, with g-factor up to 0.02, likely the highest reported for bipyramid seeds so far.

Computational electromagnetics (CEM) has become an indispensable tool for engineers in a wide range of applications in the aerospace and naval industries. The complexity of these industries, with challenges such as advanced antenna design, Electromagnetic Environmental Effects (E3), and radar cross section (RCS) control, demands the use of powerful simulation tools. However, new times bring new advances to the industry and, with them, new challenges to the computational electromagnetic field. Seeking cutting-edge advances in very low observability (VLO) techniques and E3 in modern platforms further underscores the need for these tools, capable of dealing with multiple scales and all kinds of novel modern materials (metamaterials).

The development of new surface integral equations (SIEs) methods able to efficiently solve non-conformal discretization has become a source of extensive studies in recent years in search for an accurate method able to simplify the CAD generation processes, especially when dealing with realistic projects involving piecewise objects.

Fabrication and transmission of plasmonic chirality is a rapidly developing area of research. While nanoscale chirality is reasonably well explored, research on intrinsically chiral nanostructures, that has ramifications to origin of homochirality, is still in its infancy. Herein, we report the synthesis of dog-bone shaped chiral gold nanostructures using a chiral cationic surfactant with excess ascorbic acid. Chiral growth is attributed to the specific binding and structure breaking ability of chiral surfactant and ascorbic acid. The controlled assembly of particles facilitated tuning and enhancement of chiral signals. Experimental observations were validated with theoretical simulations modelled in frequency domain with a surface integral-equation parameterization. Work highlighting the generation and tuning of plasmonic chirality provides new insights into the understanding of intrinsic chirality and paves way for their application in enantioselective catalysis and biosensing.

The development of a multitrace method including an automatic and multilevel quasi-Helmholtz decomposition, until now only applied to perfect electrical conductors, is here presented for the simulation, via the method of moments, of arbitrary complex geometries composed of piecewise homogeneous composite objects in order to improve the conditioning. A numerical experiment demonstrates the flexibility of the proposed approach for the solution of objects composed of multiple materials.

Non-conformal surface integral equation (SIE) methods have received considerable attention from the research community in recent years, in search of procedures to simplify the generation of computer-aided-design (CAD) and mesh models for electromagnetic solution of complex problems or in the context of collaborative projects.