Extracting the Infrared Permittivity of SiO2 Substrates Locally by Near-Field Imaging of Phonon Polaritons in a van der Waals Crystal

Layered materials in which individual atomic layers are bonded by weak van der Waals forces (vdW materials) constitute one of the most prominent platforms for materials research. Particularly, polar vdW crystals, such as hexagonal boron nitride (h-BN), alpha-molybdenum trioxide (α-MoO3) or alpha-vanadium pentoxide (α-V2O5), have received significant attention in nano-optics, since they support phonon polaritons (PhPs)―light coupled to lattice vibrations― with strong electromagnetic confinement and low optical losses. Recently, correlative far- and near-field studies of α-MoO3 have been demonstrated as an effective strategy to accurately extract the permittivity of this material. Here, we use this accurately characterized and low-loss polaritonic material to sense its local dielectric environment, namely silica (SiO2), one of the most widespread substrates in nanotechnology. By studying the propagation of PhPs on α-MoO3 flakes with different thicknesses laying on SiO2 substrates via near-field microscopy (s-SNOM), we extract locally the infrared permittivity of SiO2. Our work reveals PhPs nanoimaging as a versatile method for the quantitative characterization of the local optical properties of dielectric substrates, crucial for understanding and predicting the response of nanomaterials and for the future scalability of integrated nanophotonic devices.

Download Full-text

Engineering phonon polaritons in van der Waals heterostructures to enhance in-plane optical anisotropy

Science Advances ◽

10.1126/sciadv.aau7171 ◽

2019 ◽

Vol 5 (4) ◽

pp. eaau7171 ◽

Cited By ~ 23

Author(s):

Kundan Chaudhary ◽

Michele Tamagnone ◽

Mehdi Rezaee ◽

D. Kwabena Bediako ◽

Antonio Ambrosio ◽

...

Keyword(s):

Optical Anisotropy ◽

Hexagonal Boron Nitride ◽

Near Field ◽

Van Der Waals ◽

Microscopy Study ◽

Refractive Indices ◽

Optical And Electrical Properties ◽

Nanophotonic Devices ◽

Two Dimensional Materials ◽

Phonon Polaritons

Van der Waals (vdW) heterostructures assembled from layers of two-dimensional materials have attracted considerable interest due to their novel optical and electrical properties. Here, we report a scattering-type scanning near-field optical microscopy study of hexagonal boron nitride on black phosphorus (h-BN/BP) heterostructures, demonstrating the first direct observation of in-plane anisotropic phonon polariton modes in vdW heterostructures. Notably, the measured in-plane optical anisotropy along the armchair and zigzag crystal axes exceeds the ratio of refractive indices of BP in the x-y plane. We explain that this enhancement is due to the high confinement of the phonon polaritons in h-BN. We observe a maximum in-plane optical anisotropy of αmax = 1.25 in the frequency spectrum at 1405 to 1440 cm−1. These results provide new insights into the behavior of polaritons in vdW heterostructures, and the observed anisotropy enhancement paves the way to novel nanophotonic devices and to a new way to characterize optical anisotropy in thin films.

Download Full-text

High-efficiency modulation of coupling between different polaritons in an in-plane graphene/hexagonal boron nitride heterostructure

Nanoscale ◽

10.1039/c8nr08334g ◽

2019 ◽

Vol 11 (6) ◽

pp. 2703-2709 ◽

Cited By ~ 7

Author(s):

Xiangdong Guo ◽

Hai Hu ◽

Debo Hu ◽

Baoxin Liao ◽

Ke Chen ◽

...

Keyword(s):

Boron Nitride ◽

High Efficiency ◽

Hexagonal Boron Nitride ◽

Van Der Waals ◽

Two Dimensional ◽

Low Loss ◽

Nanophotonic Devices ◽

Phonon Polaritons ◽

Graphene Plasmons

Two-dimensional van der Waals (vdW) materials have a full set of highly confined polariton modes, such as low-loss phonon polaritons and dynamically tunable graphene plasmons, which provide a solution for integrated nanophotonic devices by combining the unique advantages of different polaritons.

Download Full-text

High-Q dark hyperbolic phonon-polaritons in hexagonal boron nitride nanostructures

Nanophotonics ◽

10.1515/nanoph-2020-0048 ◽

2020 ◽

Vol 9 (6) ◽

pp. 1457-1467 ◽

Cited By ~ 1

Author(s):

Georg Ramer ◽

Mohit Tuteja ◽

Joseph R. Matson ◽

Marcelo Davanco ◽

Thomas G. Folland ◽

...

Keyword(s):

Boron Nitride ◽

Cross Sections ◽

Hexagonal Boron Nitride ◽

Near Field ◽

High Q ◽

Surface Phonon Polaritons ◽

Previous Hypothesis ◽

Phonon Polaritons ◽

Field Reflectance ◽

Strong Confinement

AbstractThe anisotropy of hexagonal boron nitride (hBN) gives rise to hyperbolic phonon-polaritons (HPhPs), notable for their volumetric frequency-dependent propagation and strong confinement. For frustum (truncated nanocone) structures, theory predicts five, high-order HPhPs, sets, but only one set was observed previously with far-field reflectance and scattering-type scanning near-field optical microscopy. In contrast, the photothermal induced resonance (PTIR) technique has recently permitted sampling of the full HPhP dispersion and observing such elusive predicted modes; however, the mechanism underlying PTIR sensitivity to these weakly-scattering modes, while critical to their understanding, has not yet been clarified. Here, by comparing conventional contact- and newly developed tapping-mode PTIR, we show that the PTIR sensitivity to those weakly-scattering, high-Q (up to ≈280) modes is, contrary to a previous hypothesis, unrelated to the probe operation (contact or tapping) and is instead linked to PTIR ability to detect tip-launched dark, volumetrically-confined polaritons, rather than nanostructure-launched HPhPs modes observed by other techniques. Furthermore, we show that in contrast with plasmons and surface phonon-polaritons, whose Q-factors and optical cross-sections are typically degraded by the proximity of other nanostructures, the high-Q HPhP resonances are preserved even in high-density hBN frustum arrays, which is useful in sensing and quantum emission applications.

Download Full-text

Tin diselenide van der Waals materials as new candidates for mid-infrared waveguide chips

Nanoscale ◽

10.1039/c9nr04264d ◽

2019 ◽

Vol 11 (30) ◽

pp. 14113-14117 ◽

Cited By ~ 2

Author(s):

Mengfei Xue ◽

Qi Zheng ◽

Runkun Chen ◽

Lihong Bao ◽

Shixuan Du ◽

...

Keyword(s):

Near Field ◽

Van Der Waals ◽

Building Blocks ◽

Two Dimensional ◽

Mid Infrared ◽

Near Field Imaging ◽

Van Der Waals Materials ◽

Field Imaging

Near-field imaging of mid-infrared waveguide in SnSe2 slabs promotes two-dimensional van der Waals materials as building blocks for integrated MIR chips.

Download Full-text

Epitaxy of highly ordered organic semiconductor crystallite networks supported by hexagonal boron nitride

Scientific Reports ◽

10.1038/srep38519 ◽

2016 ◽

Vol 6 (1) ◽

Cited By ~ 17

Author(s):

Aleksandar Matković ◽

Jakob Genser ◽

Daniel Lüftner ◽

Markus Kratzer ◽

Radoš Gajić ◽

...

Keyword(s):

Boron Nitride ◽

Organic Semiconductors ◽

Organic Semiconductor ◽

Density Functional ◽

Hexagonal Boron Nitride ◽

Van Der Waals ◽

Dielectric Substrate ◽

Force Microscopy ◽

Dielectric Substrates ◽

Field Effect Devices

Abstract This study focuses on hexagonal boron nitride as an ultra-thin van der Waals dielectric substrate for the epitaxial growth of highly ordered crystalline networks of the organic semiconductor parahexaphenyl. Atomic force microscopy based morphology analysis combined with density functional theory simulations reveal their epitaxial relation. As a consequence, needle-like crystallites of parahexaphenyl grow with their long axes oriented five degrees off the hexagonal boron nitride zigzag directions. In addition, by tuning the deposition temperature and the thickness of hexagonal boron nitride, ordered networks of needle-like crystallites as long as several tens of micrometers can be obtained. A deeper understanding of the organic crystallites growth and ordering at ultra-thin van der Waals dielectric substrates will lead to grain boundary-free organic field effect devices, limited only by the intrinsic properties of the organic semiconductors.

Download Full-text

Photon Tunneling via Coupling Graphene Plasmons With Phonon Polaritons of Hexagonal Boron Nitride in Reststrahlen Bands

ASME 2021 Heat Transfer Summer Conference ◽

10.1115/ht2021-62180 ◽

2021 ◽

Author(s):

Ruiyi Liu ◽

Xiaohu Wu ◽

Zheng Cui

Keyword(s):

Boron Nitride ◽

Chemical Potential ◽

Hexagonal Boron Nitride ◽

Near Field ◽

Tunneling Probability ◽

Coupling Mechanism ◽

Work Study ◽

Photon Tunneling ◽

Phonon Polaritons ◽

Graphene Plasmons

Abstract The photon tunneling probability is the most important thing in near-field radiative heat transfer (NFRHT). This work study the photon tunneling via coupling graphene plasmons with phonon polaritons in hexagonal boron nitride (hBN). We consider two cases of the optical axis of hBN along z-axis and x-axis, respectively. We investigate the NFRHT between graphene-covered bulk hBN, and compare it with that of bare bulk hBN. Our results show that in Reststrahlen bands, the coupling of graphene plasmons and phonon polaritons in hBN can either suppress or enhance the photon tunneling probability, depending on the chemical potential of graphene and frequency. This conclusion holds when the optiacal axis of hBN is either along z-axis or x-axis. The findings in this work not only deepen our understanding of coupling mechanism between graphene plasmons with phonon polaritons, but also provide a theoretical basis for controlling photon tunneling in graphene covered hyperbolic materials.

Download Full-text

Near-Field Radiative Heat Transfer Between Two α-MoO3 Biaxial Crystals

Journal of Heat Transfer ◽

10.1115/1.4046968 ◽

2020 ◽

Vol 142 (7) ◽

Cited By ~ 1

Author(s):

Xiaohu Wu ◽

Ceji Fu ◽

Zhuomin M. Zhang

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Radiative Heat Transfer ◽

Radiative Heat ◽

Hexagonal Boron Nitride ◽

Near Field ◽

Radiative Heat Flux ◽

Relative Rotation ◽

Maximum Heat ◽

Phonon Polaritons

Abstract The near-field radiative heat transfer (NFRHT) between two semi-infinite α-MoO3 biaxial crystals is investigated numerically based on the fluctuation–dissipation theorem combined with the modified 4 × 4 transfer matrix method in this paper. In the calculations, the near-field radiative heat flux (NFRHF) along each of the crystalline directions of α-MoO3 is obtained by controlling the orientation of the biaxial crystals. The results show that much larger heat flux than that between two semi-infinite hexagonal boron nitride can be achieved in the near-field regime, and the maximum heat flux is along the [001] crystalline direction. The mechanisms for the large radiative heat flux are explained as due to existence of hyperbolic phonon polaritons (HPPs) inside α-MoO3 and excitation of hyperbolic surface phonon polaritons (HSPhPs) at the vacuum/α-MoO3 interfaces. The effect of relative rotation between the emitter and the receiver on the heat flux is also investigated. It is found that the heat flux varies significantly with the relative rotation angle. The modulation contrast can be as large as two when the heat flux is along the [010] direction. We attribute the large modulation contrast mainly to the misalignment of HSPhPs and HPPs between the emitter and the receiver. Hence, the results obtained in this work may provide a promising way for manipulating near-field radiative heat transfer between anisotropic materials.

Download Full-text