Tuning Multipolar Mie Scattering of Particles on a Dielectric-Covered Mirror

Optically resonant particles are key building blocks of many nanophotonic devices such as optical antennas and metasurfaces. Because the functionalities of such devices are largely determined by the optical properties of individual resonators, extending the attainable responses from a given particle is highly desirable. Practically, this is usually achieved by introducing an asymmetric dielectric environment. However, commonly used simple substrates have limited influences on the optical properties of the particles atop. Here, we show that the multipolar scattering of silicon microspheres can be effectively modified by placing the particles on a dielectric-covered mirror, which tunes the coupling between the Mie resonances of microspheres and the standing waves and waveguide modes in the dielectric spacer. This tunability allows selective excitation, enhancement, and suppression of the multipolar resonances and enables scattering at extended wavelengths, providing new opportunities in controlling light-matter interactions for various applications. We further demonstrate with experiments the detection of molecular fingerprints by single-particle mid-infrared spectroscopy, and, with simulations strong optical repulsive forces that could elevate the particles from a substrate.Comment: 16 pages, 4 figure

Room-temperature observation of near-intrinsic exciton linewidth in monolayer WS2

The homogeneous exciton linewidth, which captures the coherent quantum dynamics of an excitonic state, is a vital parameter in exploring light-matter interactions in two-dimensional transition metal dichalcogenides (TMDs). An efficient control of the exciton linewidth is of great significance, and in particular of its intrinsic linewidth, which determines the minimum timescale for the coherent manipulation of excitons. However, such a control has rarely been achieved in TMDs at room temperature (RT). While the intrinsic A exciton linewidth is down to 7 meV in monolayer WS2, the reported RT linewidth was typically a few tens of meV due to inevitable homogeneous and inhomogeneous broadening effects. Here, we show that a 7.18 meV near-intrinsic linewidth can be observed at RT when monolayer WS2 is coupled with a moderate-refractive-index hydrogenated silicon nanosphere in water. By boosting the dynamic competition between exciton and trion decay channels in WS2 through the nanosphere-supported Mie resonances, we have managed to tune the coherent linewidth from 35 down to 7.18 meV. Such modulation of exciton linewidth and its associated mechanism are robust even in presence of defects, easing the sample quality requirement and providing new opportunities for TMD-based nanophotonics and optoelectronics.J.F., K.Y., and Y.Z. acknowledge the financial support of the National Aeronautics and Space Administration Early Career Faculty Award (80NSSC17K0520), the National Science Foundation (NSF-ECCS-2001650), and the National Institute of General Medical Sciences of the National Institutes of Health (DP2GM128446). M.W. and A.A. acknowledge the financial support of the Air Force Office of Scientific Research MURI program (FA9550-17-1-0002), the Vannevar Bush Faculty Fellowship, and the Simons Foundation. T.Z. and M.T. acknowledge the financial support of the Air Force Office of Scientific Research (FA9550-18-1-0072). T.J. and B.A.K. acknowledge the financial support of the Robert A. Welch Foundation (F-1464), and the Center for Dynamics and Control of Materials (CDCM), Materials Research Science and Engineering Center (MRSEC) (DMR-1720595).Center for Dynamics and Control of Material

Opto-thermoelectric pulling of light-absorbing particles

Optomechanics arises from the photon momentum and its exchange with low-dimensional objects. It is well known that optical radiation exerts pressure on objects, pushing them along the light path. However, optical pulling of an object against the light path is still a counter-intuitive phenomenon. Herein, we present a general concept of optical pulling—opto-thermoelectric pulling (OTEP)—where the optical heating of a light-absorbing particle using a simple plane wave can pull the particle itself against the light path. This irradiation orientation-directed pulling force imparts self-restoring behaviour to the particles, and three-dimensional (3D) trapping of single particles is achieved at an extremely low optical intensity of 10 −2 mW μm−2. Moreover, the OTEP force can overcome the short trapping range of conventional optical tweezers and optically drive the particle flow up to a macroscopic distance. The concept of self- induced opto-thermomechanical coupling is paving the way towards freeform optofluidic technology and lab-on-a- chip devices.L.L., P.S.K., A.K., Y.L., X.P. and Y.Z. acknowledge the financial support of the National Science Foundation (NSF-CMMI-1761743), the Army Research Office (W911NF-17-1-0561), the National Aeronautics and Space Administration Early Career Faculty Award (80NSSC17K0520), and the National Institute of General Medical Sciences of the National Institutes of Health (DP2GM128446). B.A.K. and T.J. acknowledge financial support of this work from the Robert A. Welch Foundation (Grant no. F-1464) and the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No. DMR-1720595. L.L. acknowledges support from the Youth Thousand Talent Programme of ChinaCenter for Dynamics and Control of Material

Broadband forward light scattering by architectural design of core–shell silicon particles

A goal in the field of nanoscale optics is the fabrication of nanostructures with strong directional light scattering at visible frequencies. Here, we demonstrate the synthesis of Mie-resonant coreshell particles with overlapping electric and magnetic dipole resonances in the visible spectrum. The core consists of silicon surrounded by a lower index silicon oxynitride (SiOxNy) shell with an adjustable thickness. Optical spectroscopies coupled to Mie theory calculations give the first experimental evidence that the relative position and intensity of the magnetic and electric dipole resonances are tuned by changing the core-shell architecture. Specifically, coating a high-index particle with a low-index shell coalesces the dipoles, while maintaining a high scattering efficiency, thus generating broadband forward scattering. This synthetic strategy opens a route towards metamaterial fabrication with unprecedented control over visible light manipulation.Advanced Materials by DesignInitiative d'excellence de l'Université de BordeauxDéveloppment d'une infrastructure française distribuée coordonné

Mechanical Properties of Hydrogenated Amorphous Silicon (A-Si:H) Particles

A nanoindenter was used to compress individual particles of hydrogenated amorphous silicon (a-Si:H) ranging in diameter from 290 nm to 780 nm. The colloidal synthesis used to produce the particles enables the hydrogen content to be manipulated over a wide range, from about 5 at. % to 50 at. %, making these a-Si:H particles promising for applications in lithium ion batteries, hydrogen storage, and optical metamaterials. Force-displacement curves generated using a tungsten probe flattened with focused ion beam exhibited elastic and then plastic deformations, followed by fracture and crushing of the particles. For particles with 5% and 50% H, Young\u27s moduli, yield strengths, and compressive strengths were 73.5(±19.5) GPa, 5.8 GPa, and 3.2(±0.1)-9.3(±0.6) GPa and 31.2(±9.0) GPa, 2.5 GPa, and 1.8 (±0.3)-5.3(±0.8) GPa, respectively. Particles with more hydrogen were significantly more compliant and weaker. This is consistent with atomistically detailed molecular dynamics simulations, which revealed compression forms of an interphase of H atom clusters that weakens the material