About

Naomi J. Halas is the Stanley C. Moore Professor in Electrical & Computer Engineering and also holds professorships in Biomedical Engineering, Chemistry, Physics & Astronomy. She is the Director of the Laboratory for Nanophotonics. Her academic credentials include a DSc from La Salle University obtained in 2007, a PhD in Physics from Bryn Mawr College earned in 1987, an MA in Physics from Bryn Mawr College in 1984, and a BA in Chemistry from La Salle College in 1980.

Research topics

• Optoelectronics
• Materials science
• Chemistry
• Nanotechnology
• Physics
• Photochemistry
• Chemical engineering
• Composite material
• Engineering
• Environmental science
• Optics
• Chemical physics
• Organic chemistry
• Molecular physics
• Inorganic chemistry
• Acoustics
• Atomic physics
• Thermodynamics
• Environmental engineering
• Electrical engineering
• Nuclear engineering
• Chromatography

Selected publications

• Optimizing Plasmonic Photocatalysis by Controlling the Temporal Distribution of Incident Photons

  ACS Catalysis · 2026-04-24

  articleSenior authorCorresponding

  Of central interest in plasmonic photocatalysis is efficiency, defined as the ratio of the rate of chemical transformation to the power of the incident light. Efforts to enhance efficiency have focused largely on optimizing the photocatalyst structure and composition, reaction conditions, and reactor design. Here, we show that the temporal distribution of incident photons is another parameter that can be used to optimize efficiency. We illustrate the concept by varying the repetition rate of incident laser light pulses. By increasing the repetition rate from 13 to 78 MHz while keeping both the total photon flux and temperature constant, we observe a 7-fold increase in external quantum efficiency for ammonia decomposition. An increase of up to 20-fold in the reaction rate per pulse for pulses of identical energy but shorter time delay between pulses is also observed, revealing nonlinearities in the photocatalytic process. Our findings broaden the approaches for light delivery in photocatalysis, offering insight into how photocatalytic efficiency can be maximized for a fixed incident light energy and expanding current concepts for dynamic control in plasmon-driven chemistry.

  PublisherDOI

• The dynamics of plasmon-induced hot carrier creation in colloidal gold

  Nature Communications · 2025-03-06 · 20 citations

  articleOpen access

  The generation and dynamics of plasmon-induced hot carriers in gold nanoparticles offer crucial insights into nonequilibrium states for energy applications, yet the underlying mechanisms remain experimentally elusive. Here, we leverage ultrafast X-ray absorption spectroscopy (XAS) to directly capture hot carrier dynamics with sub-50 fs temporal resolution, providing clear evidence of plasmon decay mechanisms. We observe the sequential processes of Landau damping (~25 fs) and hot carrier thermalization (~1.5 ps), identifying hot carrier formation as a significant decay pathway. Energy distribution measurements reveal carriers in non-Fermi-Dirac states persisting beyond 500 fs and observe electron populations exceeding single-photon excitation energy, indicating the role of an Auger heating mechanism alongside traditional impact excitation. These findings deepen the understanding of hot carrier behavior under localized surface plasmon resonance, offering valuable implications for applications in photocatalysis, photovoltaics, and phototherapy. This work establishes a methodological framework for studying hot carrier dynamics, opening avenues for optimizing energy transfer processes in nanoscale plasmonic systems.

  PublisherOA PDFDOI

• Optical and electrical probing of plasmonic metal-molecule interactions

  Science Advances · 2025-12-12 · 1 citations

  articleOpen access

  Plasmonic nanostructures enable efficient light-to-chemical energy conversion by concentrating optical energy into nanoscale volumes. A key mechanism in this process is chemical interface damping (CID), where surface plasmons are damped by adsorbed molecules, enabling the transfer of charge to adsorbed molecules. Here, we investigate the relationship between CID and adsorbate-induced changes in dc electrical resistivity for four molecular adsorbates on gold surfaces. Our results reveal two distinct CID regimes. On one hand, CID takes place via direct resonant electronic transitions to the lowest unoccupied molecular orbital. This mechanism is dependent on plasmon energy. In the second regime, plasmon damping takes place through inelastic electron scattering at the metal-molecule interface. This regime shows a weaker dependency on plasmon energy. This mechanism also leads to adsorbate-induced changes in dc resistivity. These findings provide previously unidentified insights into the microscopic origins of plasmon damping and offer a unified framework for understanding metal-adsorbate energy transfer.

  PublisherDOI

• A Multi-Institutional Study of Magnetic Resonance/Ultrasound Fusion–Guided Nanoparticle-Directed Focal Therapy for Prostate Ablation: Erratum

  The Journal of Urology · 2025-03-07 · 1 citations

  erratum
  PublisherDOI

• Ultrafast Energy Transfer Mechanisms in Nanophotonic Systems: Photocatalysis and Photothermal Cancer Therapy

  2025-01-01

  article

  This work investigates electromagnetic energy transfer mechanisms in nanophotonic systems, focusing on ultrafast plasmonic photocatalysis and optimized photothermal cancer therapy enabled by predictive modeling techniques. Key findings demonstrate how photothermal effects can be quantified and enhanced through tailored designs and time-dependent excitation.

  PublisherDOI

• Tuning the Reactivity of Al@TiO₂ Antenna–Reactor Plasmonic Photocatalysts by Controlling Oxygen Vacancies

  Nano Letters · 2025-08-25 · 4 citations

  articleSenior authorCorresponding

  Oxygen vacancies on a metal oxide surface enhance its catalytic activity. Here we investigate the controlled introduction of oxygen vacancies on core–shell Al@TiO2 antenna–reactor nanoparticle photocatalysts. Thermal annealing in an H2-reducing atmosphere creates more oxygen vacancies in the surface TiO2 layer of Al@TiO2 nanoparticles compared to the same process under inert (He) or oxidative (O2) ambients. The photocatalytic reactivity enhancement was evaluated by investigating two reactions: hole-mediated methanol decomposition and electron-mediated hydrogen dissociation. The ability to modify plasmonic nanoparticle photocatalyst reactivity in this simple and controllable manner demonstrates the potential of this approach to tailor and enhance the performance of plasmonic antenna–reactor photocatalysts.

  PublisherDOI

• <i>(Invited)</i> Light-Induced Nonlinearities Drive Plasmonic Photothermal Catalysis Under Pulsed Illumination

  ECS Meeting Abstracts · 2025-11-24

  article

  Photocatalysis with plasmonic nanostructures has established itself as a transformative paradigm to drive chemical reactions using light. At the surface of metallic nanoparticles, photoexcitation results in strong near fields, short-lived high-energy ‘hot’ carriers, and light-induced heating. This creates a local environment where reactions occur along thermal and nonthermal pathways with enhanced efficiency, in significantly milder conditions compared to conventional catalysis. Despite exceptional promises, the typical nano-reactors operate under continuous wave illumination, which inherently restricts rates, selectivity, and efficiency of the reactions. The use of pulsed illumination has therefore emerged as an attractive solution, further bolstered by the proven advantages of solid-state lighting sources, such as LEDs, for exciting photocatalytic nanostructures. Optical pulses, featuring high peak intensities over timescales (sub-ps to ns) comparable to those of the reaction elementary step, can unlock nonlinear interactions which are out of reach in the steady-state, with the potential to modify substantially the reaction rates. In this framework, it is critical to understand the nonequilibrium processes triggered by light, both at the electronic and thermal level. In this talk, we will first introduce an original modeling approach to gauge with spatial, temporal, and energy resolution, the ultrafast energy exchange from plasmonic hot carriers to molecular systems adsorbed on the metal nanoparticle surface, while consistently accounting for photothermal bond activation. Our numerical analysis allows for disentangling the contributions arising from the carriers and the heated lattice, and it shows that rates can strongly benefit from pulsed illumination. We then combine modelling and photocatalytic measurements to explore the impact of pulsed illumination on a prototypical reaction (ammonia decomposition using CuRu antenna-reactors), by tuning the temporal distance and energy of the pulses. We report on a 20-fold increase in the reaction rate per pulse (energy efficiency and external quantum efficiency, normalised by the total number of pulses) upon doubling the pulse repetition rate in the 13 – 78 MHz range, for the same pulse peak intensity and photocatalyst steady-state temperature. To rationalise this remarkable trend, we develop a quantitative model for the transient photoinduced temperature increase, and propose a concurrent light-driven nonlinear mechanism modulating the effective activation energy of the reaction, to explain such a stark super-linear improvement in the rate of hydrogen production. Taken together, our results provide key elements to advance the use of ultrashort light pulses in photocatalysis, to drive chemical events with unprecedented efficiencies in the nonequilibrium regime, beyond the steady-state limits.

  PublisherDOI

• Combined Sustainable Water Purification and Remineralization Using an Off-Grid, Nanoparticle-Driven Solar Process

  ACS Sustainable Resource Management · 2025-08-28

  articleOpen accessSenior authorCorresponding

  The increasing demand for potable water worldwide necessitates scalable and sustainable approaches to water purification. Here, we demonstrate a solar-driven water purification system that combines nanoparticle-assisted, membrane-free solar distillation with remineralization through a natural sedimentary rock-filled condensation column. The solar distillation is accomplished using carbon black nanoparticles (CBNPs), whose broadband light absorption properties significantly enhance the evaporation rate during distillation. This is paired with a condensation-remineralization column incorporating sedimentary rocks, which effectively replenishes essential minerals such as calcium and magnesium (required for sustainable human consumption) and re-establishes water alkalinity. It achieves a 99% reduction of dissolved ions and restores calcium concentration to levels comparable to the World Health Organization (WHO) standards while also achieving effective microbial decontamination. Combining distillation and remineralization in one simple, low-tech system is a strategy that addresses the urgent demand for sustainably safe drinking water needed in many resource-limited communities and locations.

  PublisherOA PDFDOI

• Aluminum Nanocrystals Form Voids under Their Native Oxide

  Nano Letters · 2025-07-24

  articleSenior authorCorresponding

  Aluminum, the most abundant metal in the earth's crust, is protected and stabilized by a native surface oxide layer. Once the oxide is breached, rapid oxidation can occur, igniting Al in particulate form. By slowly heating and cooling Al nanocrystals of well controlled size and shape, we observe a localized void formation under the surface oxide, occurring on specific crystalline facets. These voids form during the slow cooling phase following heating, even for temperatures below the threshold of oxidation, in a manner sensitive to Al nanocrystal size and morphology, surface facet, and the degree of oxide porosity. Because of these sensitivities, this void formation may provide new strategies for modifying Al nanocrystal growth and developing Al nanocrystal-based hybrid materials.

  PublisherDOI

• In silico machine learning–enabled detection of polycyclic aromatic hydrocarbons from contaminated soil

  Proceedings of the National Academy of Sciences · 2025-05-08 · 4 citations

  articleOpen accessSenior authorCorresponding

  The detection and identification of polycyclic aromatic hydrocarbons (PAHs) and their modified derivatives in contaminated soil is challenging due to the chemical and microbial complexity of soil organic matter. To address these challenges, we developed an innovative analytical approach that combines Surface-enhanced Raman spectroscopy with a Raman spectral library constructed in silico using density functional theory (DFT)-calculated spectra. This method overcomes several limitations associated with traditional experimental libraries, including spectral background interference, solvent effects, and commercially unavailable or challenging to synthesize compounds. Our methodology employs a physics-informed machine learning pipeline that operates in two stages: the characteristic peak extraction (CaPE) algorithm, which isolates distinctive spectral features, and the characteristic peak similarity (CaPSim) algorithm, which identifies analytes with high robustness to spectral shifts and amplitude variations. Validation of this approach showed strong similarity values (>0.6) between DFT-calculated and experimental Surface-enhanced Raman spectra for multiple PAHs, confirming its accuracy and discriminative capability. This study establishes the viability of DFT-calculated spectra as reliable references for identifying analytes that lack experimental reference spectra, including those formed through environmental modification of PAHs. This advancement addresses a critical gap in environmental monitoring, providing a valuable tool for assessing public health risks associated with these contaminants.

  PublisherDOI

Recent grants

• REU Site: Research Experiences for Undergraduates at the Rice Quantum Institute

  NSF · $261k · 2008–2011

• NIH Grant U01CA15188601

  NIH · $388k · 2015

• MRI: Development of an Opto-electronic Characterization Instrument

  NSF · $998k · 2010–2013

• PFI-TT: Light Driven Evaporation System for Desalination

  NSF · $250k · 2020–2022

• Towards an Infrared Nanophotonic Nose: Ultracompact Spectroscopic Photodetection based on Plasmonic Nanoantenna-diodes

  NSF · $340k · 2016–2019

Frequent coauthors

• Peter Nordlander

  Rice University

  330 shared

• Sarah L. Westcott

  69 shared

• Steven J. Oldenburg

  NanoComposix (United States)

  56 shared

• Oara Neumann

  Rice University

  50 shared

• Richard D. Averitt

  University of California, San Diego

  48 shared

• Rizia Bardhan

  Iowa State University

  48 shared

• Henry O. Everitt

  48 shared

• Hongxing Xu

  Wuhan Institute of Technology

  46 shared

Labs

• Halas LabPI

  The Halas Lab focuses on nanophotonics and plasmonics.