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1. Tailorable Optical Response of Au–LiNbO ₃ Hybrid Metamaterial Thin Films for Optical Waveguide Applications

   https://doi.org/10.1002/adom.201800510  

   Huang, Jijie; Jin, Tiening; Misra, Shikhar; Wang, Han; Qi, Zhimin; Dai, Yaomin; Sun, Xing; Li, Leigang; Okkema, Joseph; Chen, Hou‐Tong; et al (July 2018, Advanced Optical Materials)

   Abstract Photonic integrated circuits require various optical materials with versatile optical properties and easy on‐chip device integration. To address such needs, a well‐designed nanoscale metal‐oxide metamaterial, that is, plasmonic Au nanoparticles embedded in nonlinear LiNbO₃(LNO) matrix, is demonstrated with tailorable optical response. Specifically, epitaxial and single‐domain LNO thin films with tailored Au nanoparticle morphologies (i.e., various nanoparticle sizes and densities), are grown by a pulsed laser deposition method. The optical measurement presents obvious surface plasmon resonance and dramatically varied complex dielectric function because of the embedded Au nanoparticles, and its response can be well tailored by varying the size and density of Au nanoparticles. An optical waveguide structure based on the thin film stacks of a‐Si on SiO₂/Au‐LNO is fabricated and exhibits low optical dispersion with an optimized evanescent field staying in the LNO‐Au active layer. The hybrid Au‐LNO metamaterial thin films provide a novel platform for tunable optical materials and their future on‐chip integrations in photonic‐based integrated circuits. 

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2. Large‐Scale Plasmonic Hybrid Framework with Built‐In Nanohole Array as Multifunctional Optical Sensing Platforms

   https://doi.org/10.1002/smll.201906459  

   Wang, Xuejing; Ma, Xuedan; Shi, Enzheng; Lu, Ping; Dou, Letian; Zhang, Xinghang; Wang, Haiyan (February 2020, Small)

   Abstract Light coupling with patterned subwavelength hole arrays induces enhanced transmission supported by the strong surface plasmon mode. In this work, a nanostructured plasmonic framework with vertically built‐in nanohole arrays at deep‐subwavelength scale (6 nm) is demonstrated using a two‐step fabrication method. The nanohole arrays are formed first by the growth of a high‐quality two‐phase (i.e., Au–TiN) vertically aligned nanocomposite template, followed by selective wet‐etching of the metal (Au). Such a plasmonic nanohole film owns high epitaxial quality with large surface coverage and the structure can be tailored as either fully etched or half‐way etched nanoholes via careful control of the etching process. The chemically inert and plasmonic TiN plays a role in maintaining sharp hole boundary and preventing lattice distortion. Optical properties such as enhanced transmittance and anisotropic dielectric function in the visible regime are demonstrated. Numerical simulation suggests an extended surface plasmon mode and strong field enhancement at the hole edges. Two demonstrations, including the enhanced and modulated photoluminescence by surface coupling with 2D perovskite nanoplates and the refractive index sensing by infiltrating immersion liquids, suggest the great potential of such plasmonic nanohole array for reusable surface plasmon‐enhanced sensing applications. 

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3. Electromagnetic Thermal Energy Transfer in Nanoparticle Assemblies Below Diffraction Limit

   https://doi.org/10.1115/1.4047631  

   Yuksel, Anil; Yu, Edward T.; Cullinan, Michael; Murthy, Jayathi (April 2021, Journal of Thermal Science and Engineering Applications)

   Abstract Fabrication of micro- and nanoscale electronic components has become increasingly demanding due to device and interconnect scaling combined with advanced packaging and assembly for electronic, aerospace, and medical applications. Recent advances in additive manufacturing have made it possible to fabricate microscale, 3D interconnect structures but heat transfer during the fabrication process is one of the most important phenomena influencing the reliable manufacturing of these interconnect structures. In this study, optical absorption and scattering by three-dimensional (3D) nanoparticle packings are investigated to gain insight into micro/nano heat transport within the nanoparticles. Because drying of colloidal solutions creates different configurations of nanoparticles, the plasmonic coupling in three different copper nanoparticle packing configurations was investigated: simple cubic (SC), face-centered cubic (FCC), and hexagonal close packing (HCP). Single-scatter albedo (ω) was analyzed as a function of nanoparticle size, packing density, and configuration to assess effect for thermo-optical properties and plasmonic coupling of the Cu nanoparticles within the nanoparticle packings. This analysis provides insight into plasmonically enhanced absorption in copper nanoparticle particles and its consequences for laser heating of nanoparticle assemblies. 

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4. A Hybrid Desktop Process for Integrated Deposition and Low-cost, In-situ Sintering of Conductive Silver Nanoparticles

   Bhandari, Roshan; Bansal, Shalu; Dexter, Michael; Malhotra, Rajiv (March 2017, World Congress on Micro and Nano Manufacturing)

   Microscale continuous thin films or patterned conductive structures find applications in thin film electronics, energy generation and functional sensor systems. An emerging alternative to conventional vacuum based deposition of such structures is the additive deposition and sintering of conductive nanoparticles, to enable low temperature, low-cost and low energy fabrication. While significant work has gone into additive deposition of nanoparticles the realization of the above potential needs nanoparticle sintering methods that are equally low-cost, in-situ, ambient condition and desktop-sized in nature. This work demonstrates the integration of non-laser based, low-cost and small footprint optical energy sources for ambient condition sintering of conductive nanoparticles, with wide-area aerosol jet based additive printing of nanoparticle inks. The nanoparticle sintering is characterized by quantifying the sintering temperatures, sintered material conductivity, crystallinity, optical properties, thickness and microscale morphology in terms of the sintering parameters. It is shown that such optical sintering sources can be further integrated with inkjet printing as well, and the implications on new paradigms for hybrid additive- 

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5. Programmable Self‐Regulation with Wrinkled Hydrogels and Plasmonic Nanoparticle Lattices

   https://doi.org/10.1002/smll.202103865  

   Lee, Young‐Ah Lucy; Mousavikhamene, Zeynab; Amrithanath, Abhishek Kottaram; Neidhart, Suzanne M.; Krishnaswamy, Sridhar; Schatz, George C.; Odom, Teri W. (November 2021, Small)

   Abstract This paper describes a self‐regulating system that combines wrinkle‐patterned hydrogels with plasmonic nanoparticle (NP) lattices. In the feedback loop, the wrinkle patterns flatten in response to moisture, which then allows light to reach the NP lattice on the bottom layer. Upon light absorption, the NP lattice produces a photothermal effect that dries the hydrogel, and the system then returns to the initial wrinkled configuration. The timescale of this regulatory cycle can be programmed by tuning the degree of photothermal heating by NP size and substrate material. Time‐dependent finite element analysis reveals the thermal and mechanical mechanisms of wrinkle formation. This self‐regulating system couples morphological, optical, and thermo‐mechanical properties of different materials components and offers promising design principles for future smart systems. 

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