Second Harmonic Phonon Spectroscopy of α-Quartz

Winta, Christopher; Gewinner, Sandy; Schöllkopf, Wieland; Wolf, Martin; Paarmann, Alexander

doi:10.1364/cleo_qels.2016.ftu4a.5

Cited by 4 publications

(10 citation statements)

References 36 publications

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“…Thus, we employed IR SHG, − collecting spectra from the AlN/GaN SL using the IR emission from a free-electron laser . This technique was recently shown to provide clear identification of phonon modes in multimode systems since it allows the direct measurement of phonon peaks on a nominally flat spectral background.…”

Section: Resultsmentioning

confidence: 99%

“…IR SHG and reflectance spectra were collected from three locations on Sample A with varying AlN and GaN layer thicknesses and are shown in Figure a and b, respectively. Within the SHG spectra, each E 1 (TO) phonon is observed with large contrast . Additionally, A 1 (LO) phonons of the SL can be closely approximated via the Berreman effect, which produces subtle dips in the reflectance near the spectral position where the real part of the permittivity crosses through zero (the so-called epsilon-near-zero condition).…”

Section: Resultsmentioning

confidence: 99%

“…Within the SHG spectra, each E 1 (TO) phonon is observed with large contrast. 44 Additionally, A 1 (LO) phonons of the SL can be closely approximated via the Berreman effect, 45 which produces subtle dips in the reflectance near the spectral position where the real part of the permittivity crosses through zero (the so-called epsilon-near-zero condition). The strong confinement of the electromagnetic fields of the Berreman modes 46,47 also results in pronounced peaks in the SHG Subscripts in the legend denote the average number of monolayers.…”

Section: Resultsmentioning

confidence: 99%

“…Second Harmonic Spectroscopy. The second-harmonic phonon spectra 38,44 were obtained using an IR free-electron laser (FEL) 43 as a light source, which provided widely tunable, ∼0.5% bandwidth laser pulses in the mid-to far-IR. Using a noncollinear autocorrelator geometry in reflection, both FEL beams were focused onto the SL wafer in spatial and temporal overlap, incident at angles α 1 i = 28°and α 2 i = 62°, respectively.…”

Section: Methodsmentioning

confidence: 99%

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Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

et al. 2019

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Surface phonon polaritons (SPhPs), the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons, offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. However, once a particular material is chosen, the SPhP characteristics are fixed by the spectral positions of the optic phonon frequencies. Here, we provide a demonstration of how the frequency of these optic phonons can be altered by employing atomic-scale superlattices (SLs) of polar semiconductors using AlN/GaN SLs as an example. Using second harmonic generation (SHG) spectroscopy, we show that the optic phonon frequencies of the SLs exhibit a strong dependence on the layer thicknesses of the constituent materials. Furthermore, new vibrational modes emerge that are confined to the layers, while others are centered at the AlN/GaN interfaces. As the IR dielectric function is governed by the optic phonon behavior in polar materials, controlling the optic phonons provides a means to induce and potentially design a dielectric function distinct from the constituent materials and from the effective-medium approximation of the SL. We show that atomic-scale AlN/GaN SLs instead have multiple Reststrahlen bands featuring spectral regions that exhibit either normal or extreme hyperbolic dispersion with both positive and negative permittivities dispersing rapidly with frequency. Apart from the ability to engineer the SPhP properties, SL structures may also lead to multifunctional devices that combine the mechanical, electrical, thermal, or optoelectronic functionality of the constituent layers. We propose that this effort is another step toward realizing user-defined, actively tunable IR optics and sources.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

et al. 2019

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“…For sufficiently strong external fields, atomic vibrations in solids and molecules can be pushed beyond the harmonic regime, thus exhibiting a nonlinear behavior. Surprisingly, harmonic generation associated with atomic vibrations has only been poorly explored, with just a few works focusing on this phenomenon at terahertz frequencies, − as well as a parallel effort on parametric amplification of optical phonons in SiC . The strength of vibrational nonlinear effects is a key question that determines the range of applications, but this line of research is still open, in search of robust materials with an intense response.…”

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confidence: 99%

Nonlinear Tunable Vibrational Response in Hexagonal Boron Nitride

2021

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Nonlinear light-matter interactions in structured materials are the source of exciting properties and enable vanguard applications in photonics. However, the magnitude of nonlinear effects is generally small, thus requiring high optical intensities for their manifestation at the nanoscale. Here, we reveal a large nonlinear response of monolayer hexagonal boron nitride (hBN) in the mid-infrared phonon-polariton region, triggered by the strongly anharmonic potential associated with atomic vibrations in this material. We present robust first-principles theory predicting a threshold light field ∼ 40 MV/m to produce order-unity effects in Kerr nonlinearities and harmonic generation, which are made possible by a combination of the long lifetimes exhibited by optical phonons and the strongly asymmetric landscape of the configuration energy in hBN. We further foresee polariton blockade at the few-quanta level in nanometer-sized structures. In addition, by mixing static and optical fields, the strong nonlinear response of monolayer hBN gives rise to substantial frequency shifts of optical phonon modes, exceeding their spectral width for in-plane DC fields that are attainable using lateral gating technology. We therefore predict a practical scheme for electrical tunability of the vibrational modes with potential interest in mid-infrared optoelectronics. The strong nonlinear response, low damping, and robustness of hBN polaritons set the stage for the development of applications in light modulation, sensing, and metrology, while triggering the search for intense vibrational nonlinear response in other ionic materials.

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Structure and Reactivity of α-Al₂O₃(0001) Surfaces: How Do Al–I and Gibbsite-like Terminations Interconvert?

et al. 2022

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The α-Al 2 O 3 (0001) surface has been extensively studied because of its significance in both fundamental research and application. Prior work suggests that in ultra-high-vacuum (UHV), in the absence of water, the so-called Al−I termination is thermodynamically favored, while in ambient, in contact with liquid water, a Gibbsite-like layer is created. While the view of the α-Al 2 O 3 (0001)/H 2 O(l) interface appears relatively clear in theory, experimental characterization of this system has resulted in estimates of surface acidity, i.e., isoelectric points, that differ by 4 pH units and surface structure that in some reports has non-hydrogen-bonded surface aluminol (Al−OH) groups and in others does not. In this study, we employed vibrational sum frequency spectroscopy (VSFS) and density functional theory (DFT) simulation to study the surface phonon modes of the differently terminated α-Al 2 O 3 (0001) surfaces in both UHV and ambient. We find that, on either water dosing of the Al−I in UHV or heat-induced dehydroxylation of the Gibbsite-like in ambient, the surfaces do not interconvert. This observation offers a new explanation for disagreements in prior work on the α-Al 2 O 3 (0001)/liquid water interface�different preparation methods may create surfaces that do not interconvert�and shows that the surface phonon spectral response offers a novel probe of interfacial hydrogen bonding structure.

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Second Harmonic Phonon Spectroscopy of α-Quartz

Abstract: We demonstrate mid-infrared second harmonic generation spectroscopy as a novel type of phonon spectroscopy for α-quartz. The immense tunability of an infrared free-electron laser gives access to optical phonons in the range of 350-1400 cm^-1

Cited by 4 publications

References 36 publications

Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

Nonlinear Tunable Vibrational Response in Hexagonal Boron Nitride

Structure and Reactivity of α-Al₂O₃(0001) Surfaces: How Do Al–I and Gibbsite-like Terminations Interconvert?

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Second Harmonic Phonon Spectroscopy of α-Quartz

Abstract: We demonstrate mid-infrared second harmonic generation spectroscopy as a novel type of phonon spectroscopy for α-quartz. The immense tunability of an infrared free-electron laser gives access to optical phonons in the range of 350-1400 cm-1

Cited by 4 publications

References 36 publications

Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

Nonlinear Tunable Vibrational Response in Hexagonal Boron Nitride

Structure and Reactivity of α-Al2O3(0001) Surfaces: How Do Al–I and Gibbsite-like Terminations Interconvert?

Contact Info

Product

Resources

About

Abstract: We demonstrate mid-infrared second harmonic generation spectroscopy as a novel type of phonon spectroscopy for α-quartz. The immense tunability of an infrared free-electron laser gives access to optical phonons in the range of 350-1400 cm^-1

Structure and Reactivity of α-Al₂O₃(0001) Surfaces: How Do Al–I and Gibbsite-like Terminations Interconvert?