Ultrahigh-Resolution, Label-Free Hyperlens Imaging in the Mid-IR

He, Mingze; Iyer, Ganjigunte R. S.; Aarav, Shaurya; Sunku, Sai; Giles, Alexander J.; Folland, Thomas G.; Sharac, Nicholas; Sun, Xiaohang; Matson, Joseph; Liu, Song; Edgar, James H.; Fleischer, Jason W.; Basov, D. N.; Caldwell, Joshua D.

doi:10.1021/acs.nanolett.1c01808

Cited by 25 publications

(20 citation statements)

References 49 publications

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“…96 Note that monolayer hBN can also support ultrahigh momentum HPhPs. 103−105 The optic phonon origin of the HPhPs significantly reduced the optical losses in contrast to previously reported HMMs, resulting in significant improvements in hyperlens imaging resolution, 95,96,106 Q-factors, 8,107 and propagation lengths. 9,37,102,108−110 From Artificial to Natural Biaxial Hyperbolic Materials.…”

Section: ■ Introductionmentioning

confidence: 93%

“…Later work by Giles et al employed isotopically enriched hBN to enable the direct observation of these higher-order HPhPs propagating simultaneously at a fixed incident frequency using s-SNOM, with such modes previously only observed via Fourier transforms of s-SNOM linescans near hBN flake edges . Note that monolayer hBN can also support ultrahigh momentum HPhPs. − The optic phonon origin of the HPhPs significantly reduced the optical losses in contrast to previously reported HMMs, resulting in significant improvements in hyperlens imaging resolution, ,, Q -factors, , and propagation lengths. ,,,− …”

Section: Materials For Polariton Anisotropymentioning

confidence: 99%

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Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Folland

Duan

et al. 2022

ACS Photonics

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Anisotropy has been a key property employed in the design of optical components for hundreds of years. However, in recent years there has been growing interest in polaritons supported within anisotropic (low crystal symmetry) materials for their ability to compress light to smaller, deeply subwavelength dimensions. While historically the first anisotropic polaritons probed were hyperbolic modes, research into anisotropic materials has recently turned toward hybrid materials and optical modes, employing phenomena such as phonon confinement, polaritonic strong coupling, and Moiré structures to design the optical properties. In this Perspective, we will briefly introduce the physics and theories of polariton anisotropy, review recently investigated anisotropic and two-dimensional materials, and then move on to a discussion of approaches toward realizing hybrid modes and identifying new materials. Based on the results from the past few years, we extend these discussions to highlight outstanding challenges and outline what we perceive as promising paths to further explore the potential for polariton anisotropy and hybrid systems in future nanophotonic optical devices.

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Section: ■ Introductionmentioning

confidence: 93%

Section: Materials For Polariton Anisotropymentioning

confidence: 99%

Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Folland

Duan

et al. 2022

ACS Photonics

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“…The Q-factor compares the polariton propagation length to its modal confinement and is a useful metric of the practicality of a material for nanophotonics. [30] It is shown here as:…”

Section: Nanophotonic Resonatormentioning

confidence: 99%

“…Therefore, polar dielectric materials with large TO‐LO phonon splitting in the mid‐ to far‐IR and THz spectral ranges [ 19,26,27 ] are excellent candidates for devices such as on‐chip nanophotonics [ 17,18,28,29 ] and super‐resolution imaging. [ 2,30 ] This work investigates the TMD class of materials, which satisfies the above requirements, but have not been studied in depth in the far‐IR. [ 31 ]…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, polar dielectric materials with large TO-LO phonon splitting in the mid-to far-IR and THz spectral ranges [19,26,27] are excellent candidates for devices such as on-chip nanophotonics [17,18,28,29] and super-resolution imaging. [2,30] This work investigates the TMD class of materials, which satisfies the above requirements, but have not been studied in depth in the far-IR. [31] TMDs are an emerging group of materials with recent interest stemming from their 2D optical and electronic properties [32][33][34][35][36][37][38][39][40][41][42] in the visible to near-infrared spectrum.…”

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confidence: 99%

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Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS₂ and HfSe₂

Kowalski

Nolen

Varnavides

et al. 2022

Advanced Optical Materials

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spectral windows due to the lack of an established optical infrastructure. Spectroscopy in this range can be a difficult task, due to the lack of efficient radiation sources within the so-called "terahertz gap" that extends beyond the range where blackbody sources can provide sufficient power. Despite recent developments to create powerful radiation within this region, accessing solid-state properties at these frequencies remains challenging. [4][5][6] Passive optical components in the mid-to far-IR also suffer from undesirable dispersion due to the optic phonon resonances of the material. This dispersion is associated with high absorption losses and optical performance that is strongly frequency dependent, resulting in a non-uniform transmission intensity over the spectral band of interest. [7] Materials with suitable spectral properties exist, but they all suffer from other challenges. For example, cesium iodide (CsI) has extremely lowenergy vibrational modes outside of this spectral range giving rise to suitable transmission, [8][9][10] but it is hygroscopic and therefore must be operated under vacuum or kept within other inert atmospheres. While thin polymer coatings can be applied over CsI optics as a protective layer, these induce additional vibrational resonances,The far-infrared (far-IR) remains a relatively underexplored region of the electromagnetic spectrum extending roughly from 20 to 100 µm in free-space wavelength. Research within this range has been restricted due to a lack of optical materials that can be optimized to reduce losses and increase sensitivity, as well as by the long free-space wavelengths associated with this spectral region. Here the exceptionally broad Reststrahlen bands of two Hf-based transition metal dichalcogenides (TMDs) that can support surface phonon polaritons (SPhPs) within the mid-infrared (mid-IR) into the terahertz (THz) are reported. In this vein, the IR transmission and reflectance spectra of hafnium disulfide (HfS 2 ) and hafnium diselenide (HfSe 2 ) flakes are measured and their corresponding dielectric functions are extracted. These exceptionally broad Reststrahlen bands (HfS 2 : 165 cm −1 ; HfSe 2 : 95 cm −1 ) dramatically exceed that of the more commonly explored molybdenum-(Mo) and tungsten-(W) based TMDs (≈5-10 cm −1 ), which results from the over sevenfold increase in the Born effective charge of the Hf-containing compounds. This work therefore identifies a class of materials for nanophotonic and sensing applications in the mid-to far-IR, such as deeply sub-diffractional hyperbolic and polaritonic optical antennas, as is predicted via electromagnetic simulations using the extracted dielectric function.

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A Review of Scalable Hexagonal Boron Nitride (h‐BN) Synthesis for Present and Future Applications

2022

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Ga-N, In-P, etc. Crystalline BN has typically been perceived as a purely synthetic material, [1] however geological findings provide evidence of structures similar to BN in rocks. [2] BN exhibits several stable crystal forms (see Figure 1A), for example, i) sp 3 bonded cubic and wurtzite forms; and ii) sp 2 bonded hexagonal and rhombohedral forms. [3] The cubic BN (c-BN) form has "zincblende" type crystal structure consisting of overlapping fcc cubic lattices consisting of B and N atoms. The c-BN crystal structure is analogous to that of diamond. The wurtzite form of BN (w-BN) is also sp 3 bonded like c-BN, however the wurtzite form consists of a hexagonal lattice with each ring sitting in a boat configuration. The w-BN crystal structure is analogous to that of the rare lonsdaleite, a carbon allotrope formed from graphite under immense heat and pressure. [4] Hexagonal boron nitride (h-BN) is a layered hexagonal crystal (a = 2.505 Å and c = 6.653 Å) belonging to the P6 3 /mmc space group with a structure analogous to that of graphite. [11,12] Alternating B and N atoms are sp 2 bonded in-plane to form a hexagonal lattice and several such layers are stacked to form the bulk h-BN crystal (Figure 1B). [11,12] The BN sp 2 bonding results in strong in-plane σ bonds leading to high in-plane thermal conductivity, chemical stability and strength, while empty π orbitals make h-BN electrically insulating (bandgap ≈ 5.955 eV). [3,13] The in-plane BN bonds exhibit ionic behavior due to the stronger electronegativity of the N atoms and results in layer to layer interactions between h-BN layers leading to AA′ stacking configuration, that is, each N atom in one layer is directly above the B atoms of the next layer (Figure 1B). [14] In addition to AA′ stacking, AB stacking (Bernal stacking) has also been occasionally observed in thin h-BN films even though this is a higher energy configuration. [15,5] Finally, BN is also observed in rhombohedral form (r-BN). Each layer of r-BN is the same crystal structure as that of h-BN (Figure 1A), however r-BN follows an ABC stacking configuration whereby boron still sits atop nitrogen atoms, except layers are offset such that the 1 and 3 atoms (N and N for example) sit atop the 4 and 6 atoms (B and B in this example) of the ring below. [3] Hexagonal boron nitride (h-BN) is a layered inorganic synthetic crystal exhibiting high temperature stability and high thermal conductivity. As a ceramic material it has been widely used for thermal management, heat shielding, lubrication, and as a filler material for structural composites. Recent scientific advances in isolating atomically thin monolayers from layered van der Waals crystals to study their unique properties has propelled research interest in mono/few layered h-BN as a wide bandgap insulating support for nanoscale electronics, tunnel barriers, communications, neutron detectors, optics, sensing, novel separations, quantum emission from defects, among others. Realizing these futuristic applications hinges on scalable cost-effective high-qual...

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Ultrahigh-Resolution, Label-Free Hyperlens Imaging in the Mid-IR

Cited by 25 publications

References 49 publications

Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS₂ and HfSe₂

A Review of Scalable Hexagonal Boron Nitride (h‐BN) Synthesis for Present and Future Applications

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Ultrahigh-Resolution, Label-Free Hyperlens Imaging in the Mid-IR

Cited by 25 publications

References 49 publications

Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Anisotropy and Modal Hybridization in Infrared Nanophotonics Using Low-Symmetry Materials

Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS2 and HfSe2

A Review of Scalable Hexagonal Boron Nitride (h‐BN) Synthesis for Present and Future Applications

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Mid‐ to Far‐Infrared Anisotropic Dielectric Function of HfS₂ and HfSe₂