Non-equilibrium phonon generation and detection in microstructure devices

Hertzberg, Jared; Otelaja, Obafemi; Yoshida, Naoki; Robinson, Richard D.

doi:10.1063/1.3652979

Cited by 9 publications

(14 citation statements)

References 35 publications

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“…Since we expect that 34 + is likely to be the same for all spectrometers on the same sample chip (see preceding discussion), a convenient way to measure 34 + is through a spectrometer in which a trench is etched into the mesa to completely block the line-of-sight path for phonons, but is otherwise identical to the other spectrometers on the chip. 8 Where this was not possible, we estimate 34 + (-) instead by measuring / of a phonon source and detector that are separated by ~100 μm on the same chip and do not share a line-of-sight. For such a source/detector pair, the trajectory for scattering from the bottom of the chip (~ 500 μm away) is much the same as for a more closely separated source/detector pair.…”

Section: Supplementary Discussion 3: Description Of Measurement Of Background Level >4 ?1mentioning

confidence: 99%

Direct Measurements of Surface Scattering in Si Nanosheets Using a Microscale Phonon Spectrometer: Implications for Casimir-Limit Predicted by Ziman Theory

et al. 2014

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Thermal transport in nanostructures is strongly affected by phonon-surface interactions, which are expected to depend on the phonon's wavelength and the surface roughness. Here we fabricate silicon nanosheets, measure their surface roughness (∼ 1 nm) using atomic force microscopy (AFM), and assess the phonon scattering rate in the sheets with a novel technique: a microscale phonon spectrometer. The spectrometer employs superconducting tunnel junctions (STJs) to produce and detect controllable nonthermal distributions of phonons from ∼ 90 to ∼ 870 GHz. This technique offers spectral resolution nearly 10 times better than a thermal conductance measurement. We compare measured phonon transmission rates to rates predicted by a Monte Carlo model of phonon trajectories, assuming that these trajectories are dominated by phonon-surface interactions and using the Ziman theory to predict phonon-surface scattering rates based on surface topology. Whereas theory predicts a diffuse surface scattering probability of less than 40%, our measurements are consistent with a 100% probability. Our nanosheets therefore exhibit the so-called "Casimir limit" at a much lower frequency than expected if the phonon scattering rates follow the Ziman theory for a 1 nm surface roughness. Such a result holds implications for thermal management in nanoscale electronics and the design of nanostructured thermoelectrics.

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Section: Supplementary Discussion 3: Description Of Measurement Of Background Level >4 ?1mentioning

confidence: 99%

Direct Measurements of Surface Scattering in Si Nanosheets Using a Microscale Phonon Spectrometer: Implications for Casimir-Limit Predicted by Ziman Theory

et al. 2014

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“…The microfabricated phonon spectrometer has the advantage of probing nanoscale effects such as phonon confinement [3], end-coupling diffraction [22], and surface scattering [23], with submicron spatial resolution. We have recently demonstrated a prototype microfabricated spectrometer for emission and detection of non-equilibrium phonons with frequencies ranging from 0 to ~200 GHz [24], and have now tuned the phonon source (emitter) to emit phonons with frequency ranging from 0 to ~870 GHz. The spectrometer comprises a pair of aluminum-aluminum oxide-aluminum (Al-Al x O y -Al) superconducting tunnel junctions serving as phonon emitter and phonon detector on opposite sides of a silicon microstructure.…”

Section: Importance Of Nanoscale Phonon Spectroscopymentioning

confidence: 99%

“…(Because the mean free path of phonons at our experimental temperature and frequencies is >>1 mm [25], the detected phonons will also include phonons that backscatter from the bottom of the substrate.) The ballistic path along the <110> direction between emitter and detector may be blocked by etching a trench into the mesa in order to determine this contribution of backscattered phonons [24]. This phonon transport measurement platform also enables the monolithic integration of nanostructures into the mesa.…”

Section: Spectrometer Designmentioning

confidence: 99%

Design and operation of a microfabricated phonon spectrometer utilizing superconducting tunnel junctions as phonon transducers

et al. 2013

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In order to fully understand nanoscale heat transport it is necessary to spectrally characterize phonon transmission in nanostructures. Toward this goal we have developed a microfabricated phonon spectrometer. We utilize microfabricated superconducting tunnel junction (STJ)-based phonon transducers for the emission and detection of tunable, non-thermal and spectrally resolved acoustic phonons, with frequencies ranging from ∼100 to ∼870 GHz, in silicon microstructures. We show that phonon spectroscopy with STJs offers a spectral resolution of ∼15-20 GHz, which is ∼20 times better than thermal conductance measurements, for probing nanoscale phonon transport. The STJs are Al-Al x O y -Al tunnel junctions and phonon emission and detection occurs via quasiparticle excitation and decay transitions that occur in the superconducting films. We elaborate on the design geometry and constraints of the spectrometer, the fabrication techniques and the low-noise instrumentation that are essential for successful application of this technique for nanoscale phonon studies. We discuss the spectral distribution of phonons emitted by an STJ emitter and the 3 Current address:

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“…We note that the dynamics of electrons coupled to phonons has been extensively studied in the context of thermalization of "hot electrons" [54][55][56][57][58][59][60][61][62] . Relatively less attention has been paid to the dynamics of the phonons coupled to fermions [63][64][65][66][67] . We note that the evolution of the one-particle distribution functions have been treated before using Kadanoff-Baym equations 27 .…”

Section: Introductionmentioning

confidence: 99%

Non-equilibrium scalar field dynamics starting from Fock states: Absence of thermalization in one dimensional phonons coupled to fermions

Islam,

Sensarma

2021

Preprint

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We propose a new method to study non-equilibrium dynamics of scalar fields starting from non-Gaussian initial conditions using Keldysh field theory. We use it to study dynamics of phonons coupled to bosonic and fermionic baths, starting from initial Fock states. We find that in one dimension long wavelength phonons coupled to fermionic baths do not thermalize both at low and high bath temperatures. At low temperature, constraints from energy-momentum conservation lead to a narrow bandwidth of particle-hole excitations and the phonons effectively do not feel the effects of this bath. On the other hand, the strong band edge divergence of particle-hole density of states leads to an undamped "polariton-like" mode of the dressed phonons above the band edge of the particle-hole excitations. These undamped modes contribute to the lack of thermalization of long wavelength phonons at high temperatures. In higher dimensions, these constraints and the divergence of density of states are weakened and leads to thermalization at all wavelengths.

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Non-equilibrium phonon generation and detection in microstructure devices

Cited by 9 publications

References 35 publications

Direct Measurements of Surface Scattering in Si Nanosheets Using a Microscale Phonon Spectrometer: Implications for Casimir-Limit Predicted by Ziman Theory

Direct Measurements of Surface Scattering in Si Nanosheets Using a Microscale Phonon Spectrometer: Implications for Casimir-Limit Predicted by Ziman Theory

Design and operation of a microfabricated phonon spectrometer utilizing superconducting tunnel junctions as phonon transducers

Non-equilibrium scalar field dynamics starting from Fock states: Absence of thermalization in one dimensional phonons coupled to fermions

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