Red-Ox Energy Partitioning of Light-Driven Electrons: From Laser Ablation to Plasmonics

Mu, Haoran; Huang, Hsin-Hui; Katkus, Tomas; Le, Nguyen Hoai An; Juodkazytė, Jurga; Nishijima, Yoshiaki; Juodkazis, Saulius

doi:10.3390/mi17080988

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Red-Ox Energy Partitioning of Light-Driven Electrons: From Laser Ablation to Plasmonics

by

Haoran Mu

^1,*

,

Hsin-Hui Huang

^1,2

,

Tomas Katkus

¹,

Nguyen Hoai An Le

¹,

Jurga Juodkazytė

³

,

Yoshiaki Nishijima

^4,5 and

Saulius Juodkazis

^1,6,*

¹

Optical Sciences Centre, Swinburne University of Technology, Hawthorn, VIC 3122, Australia

²

ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia

³

Center for Physical Sciences and Technology (FTMC), Saulėtekio Ave. 3, LT-10257 Vilnius, Lithuania

⁴

Institute of Advanced Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Kanagawa, Japan

⁵

PRESTO (Precursory Research for Embryonic Science and Technology), JST and Institute for Multidisciplinary Sciences, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Kanagawa, Japan

⁶

Laser Research Center, Physics Faculty, Vilnius University, Saulėtekio Ave. 10, LT-10223 Vilnius, Lithuania

^*

Authors to whom correspondence should be addressed.

Micromachines 2026, 17(8), 988; https://doi.org/10.3390/mi17080988

Submission received: 1 July 2026 / Revised: 18 August 2026 / Accepted: 20 August 2026 / Published: 21 August 2026

(This article belongs to the Section E：Engineering and Technology)

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Abstract

In femtosecond-laser processing of titania in water, light can induce reduction and oxidation simultaneously. We follow this redox energy partitioning, in this perspective, from colloidal titania synthesis to hot-electron devices. Femtosecond ablation/fragmentation of an aqueous anatase suspension (515 nm, 230 fs,

5 μ

J, fluence

F \approx 25.5

J cm

^{- 2}

/pulse at clamped intensity ∼

10^{13}

W cm

^{- 2}

) yields surface-reduced, Ti³⁺-rich bluish TiO_2-x, while the same optical breakdown generates reactive oxygen species (ROS), among them H2O2 and HO^. radicals, which compete by re-oxidising Ti³⁺. When the reduced titania is decorated with plasmonic nanoparticles (e.g., Au), an n-type plasmonic photo-electrode is realised:

s p

hot electrons are injected over the Schottky barrier, while the deep d-band supplies oxidising holes. The oxygen evolution reaction (OER) proceeds in stages at potentials well above the formal

1.23

V via the two-electron peroxide route (∼

1.77

V) or, for sufficiently energetic holes, via the one-electron HO^. route (∼

2.7

V). In a biased cell, H2 evolves on Pt through the adsorbed (H2⁺)_ad intermediate. The same Au/semiconductor physics on silicon enables sub-band-gap hot-electron photo-detection. Energy-level diagrams (flat-band and in-contact) and the

s p

- vs. d-band origin of the injected carriers are discussed.

Keywords: laser reduction of titania; water splitting; femtosecond laser ablation; hot electron injection; reactive oxygen species

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MDPI and ACS Style

Mu, H.; Huang, H.-H.; Katkus, T.; Le, N.H.A.; Juodkazytė, J.; Nishijima, Y.; Juodkazis, S. Red-Ox Energy Partitioning of Light-Driven Electrons: From Laser Ablation to Plasmonics. Micromachines 2026, 17, 988. https://doi.org/10.3390/mi17080988

AMA Style

Mu H, Huang H-H, Katkus T, Le NHA, Juodkazytė J, Nishijima Y, Juodkazis S. Red-Ox Energy Partitioning of Light-Driven Electrons: From Laser Ablation to Plasmonics. Micromachines. 2026; 17(8):988. https://doi.org/10.3390/mi17080988

Chicago/Turabian Style

Mu, Haoran, Hsin-Hui Huang, Tomas Katkus, Nguyen Hoai An Le, Jurga Juodkazytė, Yoshiaki Nishijima, and Saulius Juodkazis. 2026. "Red-Ox Energy Partitioning of Light-Driven Electrons: From Laser Ablation to Plasmonics" Micromachines 17, no. 8: 988. https://doi.org/10.3390/mi17080988

APA Style

Mu, H., Huang, H.-H., Katkus, T., Le, N. H. A., Juodkazytė, J., Nishijima, Y., & Juodkazis, S. (2026). Red-Ox Energy Partitioning of Light-Driven Electrons: From Laser Ablation to Plasmonics. Micromachines, 17(8), 988. https://doi.org/10.3390/mi17080988

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

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