Shape-controlled synthesis of gold nanoparticles generally involves the use of surfactants, typically cetyltrimethylammonium (CTAX, X = Cl(-) , Br(-)), to regulate the nucleation growth process and to obtain colloidally stable nanoparticles. The surfactants adsorb on the nanoparticle surface making further functionalization difficult and therefore limit their use in many applications. Herein, the influence of CTAX on nanoparticle sensitivity to local dielectric environment changes is reported. It is shown, both experimentally and theoretically, that the CTAX bilayer significantly reduces the refractive index (RI) sensitivity of anisotropic gold nanoparticles such as nanocubes and concave nanocubes, nanorods, and nanoprisms. The RI sensitivity can be increased by up to 40% by removing the surfactant layer from nanoparticles immobilized on a solid substrate using oxygen plasma treatment. This increase compensates for the otherwise problematic decrease in RI sensitivity caused by the substrate effect. Moreover, the removal of the surfactants both facilitates nanoparticle biofunctionalization and significantly improves their catalytic properties. The strategy presented herein is a simple yet effective universal method for enhancing the RI sensitivity of CTAX-stabilized gold nanoparticles and increasing their potential as transducers in nanoplasmonic sensors, as well as in catalytic and biomedical applications.

Recently, Ag-Ag2S hybrid nanostructures have attracted a great deal of attention due to their enhanced chemical and thermal stability, in addition to their morphology- and composition-dependent tunable local surface plasmon resonances. Although Ag-Ag2S nanostructures can be synthesized via sulfidation of as-prepared anisotropic Ag nanoparticles, this process is poorly understood, often leading to materials with anomalous compositions, sizes, and shapes and, consequently, optical properties. In this work, we use theory and experiment to investigate the structural and plasmonic evolution of Ag-Ag2S nanoprisms during the sulfidation of Ag precursors. The previously observed red-shifted extinction of the Ag-Ag2S hybrid nanoprism as sulfidation occurs contradicts theoretical predictions, indicating that the reaction does not just occur at the prism tips as previously speculated. Our experiments show that sulfidation can induce either blue or red shifts in the extinction of the dipole plasmon mode, depending on reaction conditions. By elucidating the correlation with the final structure and morphology of the synthesized Ag-Ag2S nanoprisms, we find that, depending on the reaction conditions, sulfidation occurs on the prism tips and/or the (111) surfaces, leading to a core(Ag)-anisotropic shell(Ag2S) prism nanostructure. Additionally, we demonstrate that the direction of the shift in the dipole plasmon is a function of the relative amounts of Ag2S at the prism tips and Ag2S shell thickness around the prism.

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The integrated circuit (IC) chips are essential components in a variety of computing systems ranging from consumer electronics to high-security military devices. Hence, the authenticity of ICs is crucial. The pervasive nature of ICs and the need for their low-cost production has led to the globalization of IC design and manufacturing process, which has raised various security concerns including; (i) malicious tampering of ICs during fabrication to include Hardware Trojans (HT); and (ii) IC counterfeiting. To detect HTs and IC counterfeiting, we require an examination method to ensure the manufactured IC is consistent with the intended design. Here, we present a robust, rapid, and nondestructive IC authentication technique, which relies on imaging the optical watermarks embedded in predetermined locations in the IC. The watermark is a combination of unique signatures in the optical farfield reflection pattern created by modifying the physical layout of logic gates. These high-contrast optical signatures are enabled by embedding an innovative combination of plasmonic nanoantennas and grating structures directly in the metal-1 layer of the gate design. The uniqueness of logic gates' optical signatures is ensured through different plasmonic nanoantenna dimensions and periodicity of the surrounding gratings. For the rapid read-out of the watermarks, we present a confocal dark-field imaging technique utilizing modulated structured-illumination and lock-in signal acquisition. By combining these innovations in plasmonic nanoantennas and optical imaging, we demonstrate through numerical simulations a 30-fold contrast in polarization dependent reflectivity for each embedded optical signature allowing rapid read-out of watermarks and direct authentication of the IC design. INDEX TERMS Backside imaging, hardware trojan detection, IC counterfeit detection, integrated circuits, interference, lock-in measurement, plasmonic nanoantenna, structured-illumination.