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February 28, 2025 September 9, 2026

Thermal emission of hydrogenated amorphous silicon microspheres in the mid-infrared - Notes

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Journal article

R. Fenollosa and F. Ramiro-Manzano

International Journal of Thermal Sciences Volume 213 Article 109829 2025

Published abstract

Hydrogenated amorphous silicon microspheres feature a pronounced phononic peak around 2000 cm-1 when they are thermally excited by means of a blue laser. This phononic signature corresponds to vibrational modes of silicon-hydrogen bonds and its emitted light can be coupled to Mie modes defined by the spherical cavity. The signal is apparently quite stable at moderate excitation intensities although there appeared some signs pointing to hydrides bonds reconfiguration and even hydrogen emission. Above a certain excitation threshold, a phase change from amorphous to poly-crystalline silicon occurs that preserves the good structural quality of the microspheres.

Figures

Original embedded field-emission scanning electron micrograph of a typical hydrogenated amorphous silicon microsphere with a one micrometre scale bar
Figure 1. Summary. Field Emission Scanning Electron Microscope (FESEM) image of a typical silicon microsphere utilized for thermal emission experiments.

From R. Fenollosa and F. Ramiro-Manzano, International Journal of Thermal Sciences 213, 109829 (2025), DOI 10.1016/j.ijthermalsci.2025.109829. © 2025 The Authors. CC BY 4.0.

Complete two-panel composition showing the thermal emission spectrum of an amorphous silicon microsphere and its corresponding interferogram
Figure 2. Summary. (a) Thermal emission spectrum of an amorphous silicon microsphere. (b) Corresponding interferogram.

From R. Fenollosa and F. Ramiro-Manzano, International Journal of Thermal Sciences 213, 109829 (2025), DOI 10.1016/j.ijthermalsci.2025.109829. © 2025 The Authors. CC BY 4.0.

Optical scattering spectra of an amorphous silicon microsphere before irradiation and after two successive irradiations
Figure 3. Summary. Optical scattering of an amorphous silicon microsphere performed before any irradiation and after two successive irradiations of 77 min for measuring the phonon emission of silicon hydrides.

From R. Fenollosa and F. Ramiro-Manzano, International Journal of Thermal Sciences 213, 109829 (2025), DOI 10.1016/j.ijthermalsci.2025.109829. © 2025 The Authors. CC BY 4.0.

Complete two-panel composition of emission spectra at increasing laser intensities and spectra illustrating the amorphous to polycrystalline phase change
Figure 4. Summary. (a) Emission spectra of an amorphous silicon microsphere at increasing laser excitation intensities from bottom-up. (b) Selected experimental spectra and a Mie-theory simulated emission spectrum illustrating the phase change.

From R. Fenollosa and F. Ramiro-Manzano, International Journal of Thermal Sciences 213, 109829 (2025), DOI 10.1016/j.ijthermalsci.2025.109829. © 2025 The Authors. CC BY 4.0.

Graph with complete left and right axes showing integrated emission intensity and peak centre versus laser intensity
Figure 5. Summary. Integral (black dots) and centre position (red dots) of the emission peak at 2000 cm-1 at different laser excitation intensities, corresponding to the spectra of Figure 4(a).

From R. Fenollosa and F. Ramiro-Manzano, International Journal of Thermal Sciences 213, 109829 (2025), DOI 10.1016/j.ijthermalsci.2025.109829. © 2025 The Authors. CC BY 4.0.

Complete two-panel composition comparing measured thermal emission spectra before and after phase transition with Mie-theory simulations
Figure 6. Summary. (a, b) Measured thermal emission spectra of two silicon microspheres before and after the amorphous-to-polycrystalline phase transition, with corresponding Mie-theory simulations.

From R. Fenollosa and F. Ramiro-Manzano, International Journal of Thermal Sciences 213, 109829 (2025), DOI 10.1016/j.ijthermalsci.2025.109829. © 2025 The Authors. CC BY 4.0.

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Article access and reuse

This is an open-access article published by Elsevier Masson SAS under the Creative Commons Attribution 4.0 International licence (CC BY 4.0). © 2025 The Authors; the authors retain copyright and grant Elsevier a licence to publish. The figures below were extracted from the local article PDF without enlargement or reconstruction and are reproduced with attribution. The licence permits sharing and adaptation provided appropriate credit is given, the licence is linked and changes are indicated. Elsevier copyright policy.

Related publications

Connections within F. Ramiro-Manzano's publication record, selected from shared research topics and evidence reviewed in the source papers.

SEM image showing a side view of as-synthesized polycrystalline silicon microspheres.
Journal article
Adv. Opt. Mater. 11(15), 2300135 (2023)
Silicon Microspheres for Super-Planckian Light Sources in the Mid Infrared
R. Fenollosa, F. Ramiro-Manzano, M. Garín and F. Meseguer

What the related paper adds

This earlier paper establishes a scientific basis for Thermal emission of hydrogenated amorphous silicon microspheres in the mid-infrared. This work carries resonant thermal emission into the mid infrared, where the lowest-order modes of two-to-three-micrometre silicon spheres are widely separated and approach the absorption-emission matching condition. Several peaks exceed the calculated black-body limit, establishing the spheres as compact, spectrally selective mid-infrared sources.

What this paper adds to the related work

Building on the earlier contribution Silicon Microspheres for Super-Planckian Light Sources in the Mid Infrared, this paper advances the research line. This paper distinguishes a new mid-infrared emission mechanism in hydrogenated amorphous silicon spheres. Vibrations of silicon-hydrogen bonds create a pronounced phononic band that can couple to the sphere resonances, while controlled laser heating reveals bond reconfiguration and the onset of transformation towards polycrystalline silicon.

Figure 1: experimental setup and temperature
Journal article
ACS Photonics 6(12), 3174-3179 (2019)
Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances
R. Fenollosa, F. Ramiro-Manzano, M. Garín and R. Alcubilla

What the related paper adds

This earlier paper establishes a scientific basis for Thermal emission of hydrogenated amorphous silicon microspheres in the mid-infrared. This study turns a single silicon microsphere into a resonant thermal emitter in the near infrared. Heating produces discrete Mie peaks instead of a smooth black-body spectrum, with quality factors around 400 and a predicted microsecond response, and points towards emission above the Planck limit in selected spectral intervals.

What this paper adds to the related work

Building on the earlier contribution Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances, this paper advances the research line. This paper distinguishes a new mid-infrared emission mechanism in hydrogenated amorphous silicon spheres. Vibrations of silicon-hydrogen bonds create a pronounced phononic band that can couple to the sphere resonances, while controlled laser heating reveals bond reconfiguration and the onset of transformation towards polycrystalline silicon.

Protocol Exchange
Protocol
Protocol Exchange (2013)
Processing and Characterization of Monodisperse Silicon Colloids
L. Shi, X. Lu, R. Fenollosa, I. Rodriguez, J. T. Harris, F. Ramiro-Manzano, B. A. Korgel and F. Meseguer

What the related paper adds

This earlier paper establishes a scientific basis for Thermal emission of hydrogenated amorphous silicon microspheres in the mid-infrared. This protocol makes the silicon-colloid platform reproducible at smaller and more uniform sizes. It describes how to fabricate monodisperse spheres in the 300 to 500 nanometre range and how to characterize individual particles with a purpose-built confocal microscope, linking controlled processing to well-resolved electric and magnetic Mie modes.

What this paper adds to the related work

Building on the earlier contribution Processing and Characterization of Monodisperse Silicon Colloids, this paper advances the research line. This paper distinguishes a new mid-infrared emission mechanism in hydrogenated amorphous silicon spheres. Vibrations of silicon-hydrogen bonds create a pronounced phononic band that can couple to the sphere resonances, while controlled laser heating reveals bond reconfiguration and the onset of transformation towards polycrystalline silicon.

Two silicon nanocavities illustrating mirror-image-induced magnetic modes
Article
ACS Nano 7(1), 664-668 (2013)
Mirror-Image-Induced Magnetic Modes
E. Xifré-Pérez, L. Shi, U. Tuzer, R. Fenollosa, F. Ramiro-Manzano, R. Quidant and F. Meseguer

What the related paper adds

This earlier paper establishes a scientific basis for Thermal emission of hydrogenated amorphous silicon microspheres in the mid-infrared. This paper shows that a silicon nanocavity can acquire a strongly enhanced magnetic-like optical response through interaction with its own image in a metallic mirror. The real particle and its virtual counterpart form an effective magnetic dipole, providing a route to amplify scattering without assembling two perfectly matched physical particles.

What this paper adds to the related work

Building on the earlier contribution Mirror-Image-Induced Magnetic Modes, this paper advances the research line. This paper distinguishes a new mid-infrared emission mechanism in hydrogenated amorphous silicon spheres. Vibrations of silicon-hydrogen bonds create a pronounced phononic band that can couple to the sphere resonances, while controlled laser heating reveals bond reconfiguration and the onset of transformation towards polycrystalline silicon.

Complete original Figure 2 composition extracted directly from the article PDF
Journal article
J. Appl. Phys. 109, 102424 (2011)
Silicon colloids: A new enabling nanomaterial
F. Meseguer, R. Fenollosa, I. Rodriguez, E. Xifre-Perez, F. Ramiro-Manzano, M. Garin and M. Tymczenko

What the related paper adds

This earlier paper establishes a scientific basis for Thermal emission of hydrogenated amorphous silicon microspheres in the mid-infrared. This paper defines silicon colloids as a material platform rather than a single device. It surveys polycrystalline, amorphous and porous spherical particles, explains their strong low-order Mie resonances and infrared light confinement, and opens applications ranging from optical filtering to light-controlled forces between particles.

What this paper adds to the related work

Building on the earlier contribution Silicon colloids: A new enabling nanomaterial, this paper advances the research line. This paper distinguishes a new mid-infrared emission mechanism in hydrogenated amorphous silicon spheres. Vibrations of silicon-hydrogen bonds create a pronounced phononic band that can couple to the sphere resonances, while controlled laser heating reveals bond reconfiguration and the onset of transformation towards polycrystalline silicon.

Research fields

Bottom-up

Hydrogenated amorphous-silicon microspheres provide the material platform. Their gas-phase synthesis produces smooth, micrometre-scale particles whose silicon-hydride content supplies the mid-infrared vibrational emission investigated in the work.

Simulations & fits

Mie calculations connect the resonant peaks that emerge after laser-induced crystallisation with the diameter and optical response of the resulting silicon cavity, separating those resonances from the broader hydride-related emission.

Characterization

Single-particle interferometric emission and visible-to-near-infrared scattering measurements follow the same microsphere before and after controlled laser exposure. The comparison resolves hydride emission near 2000 cm⁻¹ and the subsequent appearance of crystalline-silicon Mie modes.

RESEARCH TOPICS

CouplingThe microsphere does more than emit a broad thermal background. Figures 4 and 6 make that connection visible: once the emission regime changes, narrow resonant peaks appear, and their spectral positions are compared with Mie-theory calculations for crystalline-silicon spheres.EmissionAt moderate excitation, the most distinctive signal is a mid-infrared band associated with silicon-hydrogen vibrations rather than the free-carrier spectrum normally expected from hot crystalline silicon. Figure 5 then follows how the integrated intensity and centre of this band evolve as the 405 nm laser power is increased, before the spectrum changes irreversibly.MaterialsThe optical experiment also acts as a probe of a material transformation. The sphere therefore preserves its geometry while its internal structure and refractive response change.ResonatorsThese 3-4 μm particles are sufficiently spherical and refractive to behave as Mie resonators without an externally fabricated mirror. In Figure 6 the authors reproduce their positions with Mie simulations for crystalline-silicon spheres of 3540 and 3130 nm diameter, allowing the spectral pattern to be connected to particle size and refractive index rather than treated as an unexplained emission structure.SetupsThe measurement isolates the weak emission of one microsphere. A liquid-nitrogen-cooled MCT detector and lock-in amplifier recover the modulated signal, while a separate chopped HeNe beam monitors optical-path displacement.ChemistryThe spectrum contains information about which hydrogen configurations survive inside the amorphous matrix. At higher excitation, the disappearance of these signatures accompanies irreversible dehydrogenation and crystallisation.
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