About

Professor Stephan Link is the Charles W. and Genevieve M. Walton Endowed Professor of Chemistry and Professor of Electrical & Computer Engineering at the University of Illinois. His research focuses on coupled nanostructures, hybrid plasmonic interfaces, and the dynamics of plasmon, hot carrier, and exciton decay. He is involved in exploring the fundamental mechanisms and applications of these nanostructures in various scientific and technological contexts.

Research topics

• Materials science
• Nanotechnology
• Optoelectronics
• Physics
• Optics
• Molecular physics
• Chemistry
• Chemical physics
• Atomic physics
• Computer Science
• Artificial Intelligence
• Acoustics
• Biological system
• Composite material
• Computational physics
• Photochemistry

Selected publications

• Resolving Single-Particle Absorption and Scattering by Plasmonic Magnesium Nanoparticles

  Nano Letters · 2026-04-01

  articleOpen accessSenior author

  Magnesium nanoparticles have emerged as a promising plasmonic material due to their low cost and biocompatibility, yet their optical absorption at the single-particle level is largely uncharacterized. While ensemble extinction measurements of 170 nm Mg spheroids show a broad extinction spectrum, we demonstrate through correlated single-particle dark-field scattering and photothermal absorption spectroscopies that individual nanoparticles support well-defined plasmon resonances in absorption and scattering. We found that the peaks in absorption and scattering occur at a similar wavelength average, with absorption consistently broader than scattering. Simulations reproduce these trends and confirm that the broader absorption line width arises from the large dispersion of the real part of Mg's dielectric function. These findings provide fundamental insights into the spectral differences in absorption and scattering by Mg nanoparticles and demonstrate the necessity of single-particle measurements for understanding their optical response, crucial for optimizing performance in diverse plasmonically powered applications.

  PublisherDOI

• Spectrometer Assembly and Python-Based Data Science Lab on the Reduction Kinetics of Methylene Blue

  Journal of Chemical Education · 2026-01-07 · 1 citations

  articleCorresponding

  Integrating data science and Python programming into secondary chemistry education addresses gaps in preparing students for STEM (science, technology, engineering, and mathematics) careers, where computational and analytical skills are essential. Traditional laboratories often treat instruments as “black boxes,” restricting students’ ability to grasp basic principles. High instrumentation costs and limited access to advanced data analysis tools restrict hands-on learning. We present a cost-effective laboratory module combining a do-it-yourself (DIY) spectrometer kit with data analysis using Python in Google Colaboratory (Colab). Students learn to plot data, perform least-squares fitting, calculate errors, and conduct kinetic studies, thereby developing analytical chemistry skills. These skills are applied in a problem-based learning environment to bridge introductory chemistry with quantitative analysis. Student feedback indicated a perceived improvement in understanding of instrumental components, calibration, and analytical techniques such as determining limits of linearity and dynamic range of detectors. By demystifying instruments and promoting chemical literacy and computational proficiency, this curriculum offers a model for integrating data science into secondary chemistry education.

  PublisherDOI

• Solvated Electron Generation from Coupled Plasmon Modes of Gold Nanoparticles Using Visible Light

  Nano Letters · 2026-04-10

  articleSenior authorCorresponding

  Solvated electrons are strong homogeneous reducing agents, and their generation with visible light can unlock new redox chemistry. Water imposes a high photoemission energy barrier for gold, restricting the accessible spectral window for plasmon-mediated solvated electron generation to the near-ultraviolet region. Here, we first demonstrate that by using hexamethylphosphoramide, an organic solvent that supports large applied cathodic potentials without decomposition, the photoemission threshold is lowered to provide access to the entire visible spectrum. Next, we achieve solvated electron yields up to 150-fold higher with coupled plasmon modes from clustered gold nanoparticles, as compared to a smooth gold electrode. The observed quantum yield correlates with the local electric field enhancement by gap plasmon modes for these nanostructured electrodes as identified by varying the particle density. Overall, this study offers mechanistic insights into how coupled plasmon modes and threshold optimization can be used to enhance solvated electron generation with visible light.

  PublisherDOI

• Enhancing Interfacial Charge Transport in Gold Nanoparticle@Polyaniline Hybrids via <i>N</i> ‐Heterocyclic Carbene Linkers

  Angewandte Chemie International Edition · 2026-05-11

  articleOpen access

  N-Heterocyclic carbenes (NHCs) have emerged as a unique class of ligands for gold nanoparticles (Au NPs), combining strong metal binding with intrinsic electronic conductivity. Yet over the past decade, studies on Au NP@NHC systems have primarily focused on their stability, while the conductivity of NHCs has remained largely unexplored due to synthesis challenges. Here, we present a synthetic strategy that addresses this gap by employing amino-functionalized NHC-Au complexes with in situ oxidative polymerization of polyaniline (PANI) to yield electronically coupled Au NP@NHC-PANI hybrids in aqueous media. This strategy enables both a controlled PANI shell growth and introduction of an electronically active NHC interlayer. Single-particle scattering spectroscopy reveals that NHCs improve the interfacial electronic coupling as evidenced by pronounced plasmonic linewidth broadening. Conductivity measurements further confirm that NHCs enhance charge transport: conductive atomic force microscopy (C-AFM) shows an increase in contact current from 14.6 to 99.4 pA under a 300-mV bias, while lateral four-probe conductance increases from 0.17 to 3.5 nS. These results provide the first direct experimental evidence of the conductive role of NHCs in hybrid NP-polymer systems, establishing a new interface-engineering strategy for the rational design of electronically delocalized nanostructures and their applications in nanoelectronics.

  PublisherDOI

• Enhancing Interfacial Charge Transport in Gold Nanoparticle@Polyaniline Hybrids via <i>N</i> ‐Heterocyclic Carbene Linkers

  Angewandte Chemie · 2026-05-12

  articleOpen access

  ABSTRACT N ‐Heterocyclic carbenes (NHCs) have emerged as a unique class of ligands for gold nanoparticles (Au NPs), combining strong metal binding with intrinsic electronic conductivity. Yet over the past decade, studies on Au NP@NHC systems have primarily focused on their stability, while the conductivity of NHCs has remained largely unexplored due to synthesis challenges. Here, we present a synthetic strategy that addresses this gap by employing amino‐functionalized NHC‐Au complexes with in situ oxidative polymerization of polyaniline (PANI) to yield electronically coupled Au NP@NHC‐PANI hybrids in aqueous media. This strategy enables both a controlled PANI shell growth and introduction of an electronically active NHC interlayer. Single‐particle scattering spectroscopy reveals that NHCs improve the interfacial electronic coupling as evidenced by pronounced plasmonic linewidth broadening. Conductivity measurements further confirm that NHCs enhance charge transport: conductive atomic force microscopy (C‐AFM) shows an increase in contact current from 14.6 to 99.4 pA under a 300‐mV bias, while lateral four‐probe conductance increases from 0.17 to 3.5 nS. These results provide the first direct experimental evidence of the conductive role of NHCs in hybrid NP‐polymer systems, establishing a new interface‐engineering strategy for the rational design of electronically delocalized nanostructures and their applications in nanoelectronics.

  PublisherDOI

• Plasmon-Induced Resonance Energy Transfer in Hybrid Nanomaterials

  ACS Energy Letters · 2026-02-18 · 2 citations

  articleCorresponding

  Plasmon-induced resonance energy transfer (PIRET) has emerged as a powerful mechanism for harnessing and redirecting plasmon energy before it dissipates into hot carriers or heat. By matching plasmon resonance frequencies with acceptor absorption bands, PIRET extends plasmon-driven processes beyond the charge transfer pathway, enabling selective energy flow into excitonic transitions. This review highlights important progress in elucidating the fundamental plasmon decay processes and transitioning them into hybrid nanomaterials under PIRET. Employing specialized single-particle spectroscopic techniques based on scattering, extinction, and emission enables demonstration of PIRET in the face of competing mechanisms, such as interfacial charge transfer and thermalization. Finally, we complete this review by addressing strategies for active modulation of PIRET and present applications, ranging from plasmon photocatalysis to intracellular biochemical sensing.

  PublisherDOI

• Laser-Induced Enhancement of Acoustic Mode Quality Factor Revealed by Correlated Single-Particle Optical and Electron Microscopy

  The Journal of Physical Chemistry C · 2026-02-18

  articleSenior authorCorresponding

  Acoustic modes in plasmonic nanostructures provide fundamental insights into their optomechanical behavior at the nanoscale, enabling emerging applications in plasmon-enhanced optomechanics, ultrasensitive sensing, and nanoscale energy transduction. Here we explore the modulation of acoustic phonon dynamics in lithographically fabricated gold nanodisks via laser-induced photothermal annealing. Using a correlated approach that utilizes both single-particle transient extinction spectroscopy and advanced electron microscopy, we directly link nanoscale structural transformations to changes in mechanical properties as probed through the coherence of the excited acoustic modes. Specifically, ultrafast pump–probe microscopy reveals an enhancement in the acoustic mode quality factor of annealed gold nanodisks, indicative of reduced damping and improved vibrational coherence. Structural characterization via scanning electron microscopy and electron backscatter diffraction confirms that photoinduced annealing results in smoother surface morphology and overall enhanced crystallinity. The improved crystalline order reduces defect and crystal boundary scattering, which we suggest as the reason underlying the lower quality factor before annealing. These findings demonstrate that targeted structural engineering at the nanoscale offers a powerful strategy for optimizing the optomechanical performance of plasmonic nanostructures, with broad implications for the design of next-generation nanophotonic and optomechanical systems.

  PublisherDOI

• Machine Learning to Adaptively Predict Gold Nanorod Sizes on Different Substrates

  The Journal of Physical Chemistry C · 2025-03-18 · 4 citations

  articleSenior authorCorresponding

  Correlating a nanoparticle’s morphology with its optical properties is essential and is achieved by a combination of electron microscopy and optical spectroscopy. Machine learning has gained attention for enhancing in situ measurements and enabling inverse nanoparticle design. However, new training data for each specific condition are often required when testing data differ from training data. We propose a method to adapt existing training data for predicting the size of gold nanorods (AuNRs) on different substrates. This method is based on simulated spectra of AuNRs on glass and indium tin oxide-coated glass (ITO), adapting the resonance energy between substrates. Using the adapted data, we train a decision tree regressor to predict AuNR sizes on ITO and test it with experimental data on ITO. This correction achieves comparable accuracy in predicting AuNR length to a decision tree trained directly on ITO. In addition, we apply the correction method to predict AuNR sizes on Al2O3, despite the lack of extensive training data, leading to an improvement in length prediction as well. Our analysis reveals that length prediction is more sensitive to the change in the resonance energy, suggesting that substrate differences mostly affect the length prediction. Overall, adapting training data enables real-time size determination across various environments without additional training data.

  PublisherDOI

• Single-Particle Correlated Imaging Reveals Multiple Chromophores in Carbon Dot Fluorescence

  Journal of the American Chemical Society · 2025-05-16 · 12 citations

  articleSenior authorCorresponding

  Carbon dots are remarkable nanomaterials with many applications, but the sources of their emission are still uncertain. Carbon dots exhibit complex behaviors such as excitation-dependent emission due to their heterogeneous composition and structure. Most studies have been carried out on the ensemble level, where sample heterogeneity remains hidden. Understanding the complex emission of carbon dots requires single-particle measurements. Here, we determined that for red-emitting carbon dots made from two bottom-up precursors, there is a significant population of dots with more than one emitting moiety. Polarization-resolved, single-dot emission microscopy revealed subpopulations of carbon dots based on their emission intensity and polarization. For the multichromophoric carbon dots, we found an average of about four emitters. Single-particle spectroscopy, acquired in parallel to the emission trajectories, and molecular dynamics simulations furthermore established that the countable chromophores in the carbon dots are chemically similar, considering the rather narrow room-temperature emission line width and the absence of significant spectral diffusion.

  PublisherDOI

• Bovine-Hemoglobin Detection by Single-Particle Plasmon-Coupled Circular Dichroism

  Nano Letters · 2025-05-16 · 3 citations

  articleSenior authorCorresponding

  Plasmon-coupled circular dichroism enables chiral molecule detection by inducing circular dichroism at the plasmon resonance through interactions with a plasmonic sensor. Coupled nanoparticles offer potentially higher sensitivities due to stronger plasmonic fields at the junctions. However, ensemble-level sensitivity is limited by signal averaging, and the structural chirality of the sensor itself can obscure the molecular response. To overcome these issues, we combine single-particle dark-field scattering with electron microscopy. Individual gold nanosphere dimers, selected to avoid interference from structural chirality, yield unambiguous plasmon-coupled circular dichroism for hemoglobin as an analyte, while monomers give no detectable signal. We explain these results based on their difference in refractive index sensitivities with respect to hemoglobin's circular birefringence, as supported by electrodynamic simulations. This study sheds new light on the mechanism of plasmon-coupled circular dichroism by isolating the response of individual nanostructures and thereby avoiding ensemble averaging over a heterogeneous mixture of nanostructure geometries.

  PublisherDOI

Recent grants

• DMREF: Collaborative Research: Nanoscale Temperature Manipulation via Plasmonic Fano Interferences

  NSF · $563k · 2017–2022

• COLLABORATIVE RESEARCH: DMREF: Designing Plasmonic Nanoparticle Assemblies For Active Nanoscale Temperature Control By Exploiting Near- And Far-Field Coupling

  NSF · $612k · 2021–2024

• Chiral Plasmonics at the Single Nanoparticle and Single Molecule Level

  NSF · $428k · 2015–2019

• Probing Dynamics and Structure of the Nanoparticle Protein Corona to Understand Its Impacts on Environmental Health and Safety

  NSF · $300k · 2014–2017

• CAREER: Novel Plasmonic Properties of Individual Nanoparticle Chains Investigated by Correlated Structural Imaging and Single Particle Spectroscopy

  NSF · $620k · 2010–2015

Frequent coauthors

• Wei‐Shun Chang

  University of Massachusetts Dartmouth

  101 shared

• Christy F. Landes

  University of Illinois Urbana-Champaign

  74 shared

• Mostafa A. El‐Sayed

  University of Glasgow

  48 shared

• Peter Nordlander

  Rice University

  43 shared

• Naomi J. Halas

  Rice University

  29 shared

• Martin Bröring

  Technische Universität Braunschweig

  26 shared

• Behnaz Ostovar

  University of Illinois Urbana-Champaign

  24 shared

• Liane S. Slaughter

  21 shared

Labs

• Link Research GroupPI

Awards & honors

• Fellow, American Association for the Advancement of Science…