Showing papers by "Olivier J. F. Martin published in 2023"
TL;DR: In this article , a unified framework was provided to understand the interaction between an oscillating electric field with a particle of matter. And the authors provided useful parallels between these two techniques, discuss the different and often unstated assumptions they are based upon, and illustrate key applications in the fields of physical and analytical chemistry, biosensing, and colloidal science.
Abstract: Electromagnetic forces and torques enable many key technologies, including optical tweezers or dielectrophoresis. Interestingly, both techniques rely on the same physical process: the interaction of an oscillating electric field with a particle of matter. This work provides a unified framework to understand this interaction both when considering fields oscillating at low frequencies—dielectrophoresis—and high frequencies—optical tweezers. We draw useful parallels between these two techniques, discuss the different and often unstated assumptions they are based upon, and illustrate key applications in the fields of physical and analytical chemistry, biosensing, and colloidal science.
5 citations
TL;DR: In this paper , the response of simple plasmonic nanorods to polarized illumination is studied in detail, where a broad variety of colors can be produced that cover half of the chromaticity diagram.
Abstract: The response of simple plasmonic nanorods to polarized illumination is studied in detail. Depending on the orientation of that polarization with respect to the symmetry axes of the nanostructure, a chiral response can occur, which can be analyzed through a second polarizer, in order to control the spectral response of the system. Specifically, for the Ag nanorods fabricated here, a broad variety of colors can be produced that cover half of the chromaticity diagram. Depending on the illumination and detection polarizations, these colors range from white to vivid colors or even black, in spite of the fact that the material at hand does not absorb much light. By exploiting two additional degrees of freedom, namely the nanorod length and its orientation within the unit cell, it is possible to produce a very rich palette of optical effects that are controlled by the polarization of light. Their utilization to reproduce artworks is demonstrated, together with their operation as encrypting system, where the polarizations are used as keys and the message is encrypted in a quaternary color subset.
1 citations
TL;DR: In this article , an original DEP platform and test the Hölzel-Pethig empirical model for protein DEP was constructed and three different proteins were studied: lysozyme, BSA, and lactoferrin.
Abstract: Dielectrophoresis (DEP) is a versatile tool for the precise microscale manipulation of a broad range of substances. To unleash the full potential of DEP for the manipulation of complex molecular-sized particulates such as proteins requires the development of appropriate theoretical models and their comprehensive experimental verification. Here, we construct an original DEP platform and test the Hölzel–Pethig empirical model for protein DEP. Three different proteins are studied: lysozyme, BSA, and lactoferrin. Their molecular Clausius–Mossotti function is obtained by detecting their trapping event via the measurement of the fluorescence intensity to identify the minimum electric field gradient required to overcome dispersive forces. We observe a significant discrepancy with published theoretical data and, after a very careful analysis to rule out experimental errors, conclude that more sophisticated theoretical models are required for the response of molecular entities in DEP fields. The developed experimental platform, which includes arrays of sawtooth metal electrode pairs with varying gaps and produces variations of the electric field gradient, provides a versatile tool that can broaden the utilization of DEP for molecular entities.
1 citations
TL;DR: In this article , the plasmon modes of gold nanorods (as short as ∼100 nm) on a nonmetallic conductive substrate using scanning tunneling microscope-induced light emission (STM-LE) with a nonplasmonic tungsten tip at room temperature in high vacuum (10 −7 mbar).
Abstract: We study the plasmon modes of gold nanorods (as short as ∼100 nm) on a nonmetallic conductive substrate using scanning tunneling microscope-induced light emission (STM-LE) with a nonplasmonic tungsten tip at room temperature in high vacuum (10–7 mbar). The far-field light is identified as the radiative decay of plasmon modes on the nanorods excited by inelastic electron tunneling. The spatial intensity distributions of the first three longitudinal multipolar modes on nanorods are spatially resolved on the order of 10–20 nm. These intensity distributions are related to the radiative electromagnetic local density of states and agree very well with numerical simulations. We discover that the presence of the tungsten tip with a high-dielectric constant influences the line shapes of the plasmon spectra and enhances the strength of the plasmon peaks.
1 citations
26 May 2023
TL;DR: In this paper , achiral nano-particles, such as flat helices, may be subjected to an optical torque even when illuminated by normally incident linearly polarized light.
Abstract: It has been observed that achiral nano-particles, such as flat helices, may be subjected to an optical torque even when illuminated by normally incident linearly polarized light. However, the origin of this fascinating phenomenon has so far remained mostly unexplained. We therefore propose an exhaustive discussion that provides a clear and rigorous explanation for the existence of such a torque. Using multipolar theory, and taking into account nonlocal interactions, we find that this torque stems from multipolar pseudochiral responses that generate both spin and orbital angular momenta. We also show that the nature of these peculiar responses makes them particularly dependent on the asymmetry of the particles. By elucidating the origin of this type of torque, this work may prove instrumental for the design of high-performance nano-rotors.
TL;DR: In this paper , the authors demonstrate reflectivity modulation based on a nanostructured, mechanically tunable, metasurface, consisting of an amorphous silicon nanopillar array and a suspended ammorphous silicon membrane with integrated electrostatic actuators.
Abstract: Reflectivity modulation is a critical feature for applications in telecommunications, 3D imaging and printing, advanced laser machining, or portable displays. Tunable metasurfaces have recently emerged as a promising implementation for miniaturized and high-performance tunable optical components. Commonly, metasurface response tuning is achieved by electro-optical effects. In this work, we demonstrate reflectivity modulation based on a nanostructured, mechanically tunable, metasurface, consisting of an amorphous silicon nanopillar array and a suspended amorphous silicon membrane with integrated electrostatic actuators. With a membrane displacement of only 150 nm, we demonstrate reflectivity modulation by Mie resonance enhanced absorption in the pillar array, leading to a reflectivity contrast ratio of 1:3 over the spectral range from 400–530 nm. With fast, low-power electrostatic actuation and a broadband response in the visible spectrum, this mechanically tunable metasurface reflectivity modulator could enable high frame rate dynamic reflective displays.
TL;DR: In this article , an interference-based method of creating microscopic structural color pixels using a single-mask process using standard UV photolithography on an all-dielectric substrate was proposed.
Abstract: While interference colors have been known for a long time, conventional color filters have large spatial dimensions and cannot be used to create compact pixelized color pictures. Here we report a simple yet elegant interference-based method of creating microscopic structural color pixels using a single-mask process using standard UV photolithography on an all-dielectric substrate. The technology makes use of the varied aperture-controlled physical deposition rate of low-temperature silicon dioxide inside a hollow cavity to create a thin-film stack with the controlled bottom layer thickness. The stack defines which wavelengths of the reflected light interfere constructively, and thus the cavities act as micrometer-scale pixels of a predefined color. Combinations of such pixels produce vibrant colorful pictures visible to the naked eye. Being fully CMOS-compatible, wafer-scale, and not requiring costly electron-beam lithography, such a method paves the way toward large scale applications of structural colors in commercial products.
TL;DR: In this paper , the authors used optical tweezers to trap a gold nanoparticle and statistically analyze the particle's movement in response to various surfactant concentrations, evidencing the rearrangement of surfactants adsorbed on glass surfaces.
Abstract: Understanding the behavior of surfactants at interfaces is crucial for many applications in materials science and chemistry. Optical tweezers combined with trajectory analysis can become a powerful tool for investigating surfactant characteristics. In this study, we perform trap-and-track analysis to compare the behavior of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) at water–glass interfaces. We use optical tweezers to trap a gold nanoparticle and statistically analyze the particle’s movement in response to various surfactant concentrations, evidencing the rearrangement of surfactants adsorbed on glass surfaces. Our results show that counterions have a significant effect on surfactant behavior at the interface. The greater binding affinity of bromide ions to CTA+ micelle surfaces reduces the repulsion among surfactant head groups and enhances the mobility of micelles adsorbed on the interface. Our study provides valuable insights into the behavior of surfactants at interfaces and highlights the potential of optical tweezers for surfactant research. The development of this trap-and-track approach can have important implications for various applications, including drug delivery and nanomaterials.
TL;DR: In this paper , the authors propose a framework that connects the spatial symmetries of a metasurface to its material parameter tensors and its scattering matrix, and demonstrate the existence of multipolar extrinsic chirality in geometrically achiral structures sensitive to field gradients, even at normal incidence.
Abstract: We propose a framework that connects the spatial symmetries of a metasurface to its material parameter tensors and its scattering matrix. This provides a simple and universal way to effortlessly determine the properties of a metasurface scattering response, such as chirality or asymmetric transmission, and which of its effective material parameters should be taken into account in the prospect of a homogenization procedure. In contrast to existing techniques, this approach does not require any a priori knowledge of group theory or complicated numerical simulation schemes, hence making it fast, easy to use and accessible. Its working principle consists in recursively solving symmetry-invariance conditions that apply to dipolar and quadrupolar material parameters, which include nonlocal interactions, as well as the metasurface scattering matrix. The overall process thus only requires listing the spatial symmetries of the metasurface. Using the proposed framework, we demonstrate the existence of multipolar extrinsic chirality, which is a form of chiral response that is achieved in geometrically achiral structures sensitive to field gradients, even at normal incidence.
TL;DR: In this article , the authors demonstrate a nonlinear plasmonic metasurface that exhibits strongly asymmetric second-harmonic generation: nonlinear scattering is efficient upon excitation in one direction, and it is substantially suppressed when the excitation direction is reversed, thus enabling a diode-like functionality.
Abstract: We demonstrate a nonlinear plasmonic metasurface that exhibits strongly asymmetric second-harmonic generation: nonlinear scattering is efficient upon excitation in one direction, and it is substantially suppressed when the excitation direction is reversed, thus enabling a diode-like functionality. A significant (approximately 10 dB) extinction ratio of SHG upon opposite excitations is measured experimentally, and those findings are substantiated with full-wave simulations. This effect is achieved by employing a combination of two commonly used metals—aluminum and silver—producing a material composition asymmetry that results in a bianisotropic response of the system, as confirmed by performing homogenization analysis and extracting an effective susceptibility tensor. Finally, we discuss the implications of our results from the more fundamental perspectives of reciprocity and time-reversal asymmetry.
DOI•
15 Mar 2023
TL;DR: In this article , it was demonstrated that the magnetic dipole in dielectrics can be entirely suppressed for small interparticle distances by the near-field produced by a nearby metal nanostructure.
Abstract: Among the material families used in nanophotonics, the fundamental mode for metal nanostructures is electric, while that for dielectric nanostructures is magnetic. Here, we consider hybrid nanophotonics, an emerging field of research that mixes both materials into one hybrid structure to benefit from the best of both worlds. It is demonstrated that the magnetic dipole in dielectrics can be entirely suppressed for small interparticle distances by the near-field produced by a nearby metal nanostructure. The explanation of the observed effect is given by considering the formation of a standing wave between the incident field and the light scattered from the metal particle. The analytical coupled electric and magnetic dipole method (CEMD) along with the full wave surface integral equation method (SIE) are used to examine this phenomenon. The conditions required for the observation of the magnetic dipole suppression in the visible range for high refractive index dielectric nanoparticles are described. The influence of the effect on the ability to control the directivity of the radiation in the far-field is considered. We further show that the electric and magnetic responses can be enhanced or suppressed by positioning the dielectric particle in the nodes of the standing wave formed by the metallic particle. This controlled near-field interaction provides a handle on the far-field response of the system, with possible applications as optical switches.