Gallium Phosphide Nanoparticles for Low‐Loss Nanoantennas in Visible Range

Abstract

as a low-loss nanoantenna. [1,2] Differently from plasmonic nanoantennas, they exhibit magnetic-type resonances as well as electric-type ones. Existence of magnetic and electric multipole resonances provides a large degree of freedom for tailoring light-matter interactions. [3][4][5][6][7][8][9] Up to now, the most studied dielectric material for a nanoantenna is Si because of the high refractive index (n > 3.5) in the whole visible to near IR (NIR) range and the low extinction coefficient in the red to NIR range (Figure 1). [10,11] However, the extinction coefficient of Si increases at shorter wavelength, and below ≈600 nm, the quality factor (Q-factor) of the resonance degrades and the albedo, that is the ratio of scattering to extinction efficiencies, decreases. This limits the performance of a nanoantenna in the short wavelength range. An alternative material of a nanoantenna operating in a short wavelength range is GaP. It has a moderately high refractive index (n > 3) and a small extinction coefficient at >470 nm (Figure 1a) because of the much larger indirect band gap 2.26 eV (≈550 nm) [12][13][14][15][16][17][18] than that of Si (1.12 eV). For example, the extinction coefficient of GaP at 514 nm is 0.004, which is an order of magnitude smaller than that of Si (0.06). However, despite the expected high performance, research on GaP nanoantennas is very scarce. [13,16,19] For example, even the highest symmetry nanoantenna, i.e., a spherical GaP nanoparticle, has not been developed and the antenna performance has not been studied.In this work, we develop colloidal solution of spherical GaP NP nanoantennas operating below 600 nm. We produce spherical GaP NPs by the combination of mechanical milling and a pulsed laser melting in solution process. In general, the Q-factor of Mie resonances of a spherical NP nanoantenna is higher than that of irregular-shape NP nanoantennas. We first study the effect of the shape on the Mie resonances by single particle scattering spectroscopy and electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). We then discuss scattering spectra of single GaP NPs with different sizes and demonstrate the existence of distinctive Mie resonances below 600 nm when the diameter is above ≈200 nm. Finally, we show Purcell enhancement of fluorescence of dye molecules by a GaP nanoantenna.

Silicon eccentric shell nanoparticles fabricated by template-assisted deposition for Mie magnetic resonances enhanced light confinement

“…Nanoparticles (NPs) of high refractive index materials offering Mie resonances in the visible to near infrared range have been widely explored to manipulate light-matter interaction at the nanoscale [1,2]. The high-index NPs naturally sustaining intense magnetic and electric Mie resonances opens the way to extraordinary properties such as cloaking, negative refraction, sensing, perfect lensing, and broadband total transmission or reflection [3][4][5][6]. Among high-index dielectrics, Silicon (Si) is the most attractive material because of its high compatibility to semiconductor industry, as well as the high environmental friendliness, earth abundance, etc.…”

Photosensitizing Metasurface Empowered by Enhanced Magnetic Field of Toroidal Dipole Resonance

“…Although a large number of researches have been conducted for the enhancement of S 0 →S 1 transition of a molecule, [14][15][16] those for the enhancement of S 0 →T 1 transition by enhanced magnetic field are limited. Promising materials for magnetic nanoantennas in the optical frequency are high refractive index dielectrics, such as silicon (Si), [17][18][19][20] gallium phosphide (GaP), [21][22][23] titanium dioxide (TiO 2 ), [24,25] etc., because they exhibit magnetic Mie resonances as well as the electric ones in the optical frequency. The enhanced magnetic field accompanied by the magnetic-type Mie resonances enhances the magnetic dipole transition rate of a molecule via the magnetic Purcell effect.…”

Solving Maxwell’s Equations Using Polarimetry Alone

“…In other words, we deal with axially symmetric objects whose optical response is described by a single multipolar order. We recall that such objects have been widely studied in Nanophotonics. − ,− In this setting ( scriptl normalm is fixed), let us insert the far-field limit ( kr → ∞ ) of eq into eqs and ). After some algebra (see Supporting Information S1), we get ( centertrue | a l m | 2 | b l m | 2 R false{ a scriptl m b scriptl m * false} I false{ a scriptl m b scriptl m * false} ) = U scriptl m ( centertrue s 0 s 1 ...…”

“…At this point, we show the accuracy of our method to solve the Maxwell equations in the radiation zone with a realistic material. Particularly, we consider a Gallium Phosphide (GaP) nanoparticle of radius a = 75 nm excited by a circularly polarized plane wave . We select GaP as it is a material with high potential for metasurface-based devices operating across the visible, as it presents a high-refractive index ( m > 3.3) and negligible losses …”

“…In other words, we deal with axially symmetric objects whose optical response is described by a single multipolar order. We recall that such objects have been widely studied in Nanophotonics. − ,− In this setting ( is fixed), let us insert the far-field limit ( kr → ∞ ) of eq into eqs and ). After some algebra (see Supporting Information S1), we get Equation shows that all the quadratic combinations of { , } can be attained from a single Stokes vector measurement in the far-field.…”