About

Professor Stephen Burke Cronin received his Ph.D. in Physics from the Massachusetts Institute of Technology in 2002, where he worked in Professor Mildred Dresselhaus's research group measuring the transport properties of nanowires and quantum well structures. He conducted post-doctoral research at Harvard University with Professor Michael Tinkham, focusing on measuring single molecule optical spectroscopy and electron transport of individual carbon nanotubes. His research includes optical spectroscopy and electron transport of individual carbon nanotubes and graphene, as well as plasmon resonant enhancement of catalytic processes for solar fuel production.

Research topics

• Chemistry
• Materials science
• Physics
• Environmental science
• Molecular physics
• Organic chemistry
• Computational chemistry
• Physical chemistry
• Mechanics
• Photochemistry
• Nanotechnology
• Chemical engineering
• Inorganic chemistry
• Optoelectronics
• Optics

Selected publications

• Vibrational Spectroscopy of Ionic Liquids Electrochemically Intercalated into Multilayer Graphene

  ACS Applied Materials & Interfaces · 2026-05-14

  articleSenior authorCorresponding

  We report insights into the reversible electrochemical intercalation of ionic liquids into multilayer graphene (MLG) using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The studied device is comprised of an MLG/alumina membrane/copper stack, where the nanoporous alumina membrane is filled with ionic liquid [DEME+][TFSI–], forming a compact electrochemical cell. Upon application of a positive voltage, [TFSI–] anions intercalate into the interlayer regions of the MLG, despite the anion’s diameter (0.9 nm) being nearly 3 times the typical graphene interlayer spacing (0.355 nm). Pronounced spectral changes accompany this poorly understood intercalation. We observe a blue-shift of up to 21.2 cm–1 in several [TFSI–] vibrational modes, attributed to mechanical compression within the confined graphene layers and/or ion–ion interactions. Additionally, an infrared peak emerges at 1384 cm–1, corresponding to the symmetric bending mode of methyl (−CH3) groups, whose appearance suggests that symmetry breaking within the confined electrochemical environment activates otherwise forbidden transitions in the [DEME+] cation. These findings reveal the nanoscale structural and electronic perturbations induced by ionic liquid intercalation, identifying spectroscopic signatures to track intercalation dynamics in layered materials. Raman shifts observed in the graphene indicate doping levels on the order of 1021 cm–1, corresponding to a roughly 100-fold increase in free carrier concentration, thus providing evidence consistent with intercalation. However, these observations challenge our previous interpretation of the complete intercalation of ionic liquids into graphene. We additionally used density-functional tight-binding (DFTB) simulations to qualitatively determine the behavior of the [TFSI–] anion sandwiched between two graphene sheets for different separation distances from 7 to 10 Å with a 0.5 Å increment. The resulting frequency shifts at smaller separation distances exhibit qualitative agreement with experimental observations, and in the case of greater separation, the peak shifts diminish and plateau, transitioning toward the bulk anion.

  PublisherDOI

• A mechanistic study of transient plasma-enhanced combustion of ammonia and hydrogen via radical detection and reaction pathway analysis of experimental data

  Fuel · 2026-04-29

  articleSenior author
  PublisherDOI

• Probing the Real and Imaginary Dielectric Response of the Electric Double Layer Using Surface Plasmon Resonance Nanostructures

  The Journal of Physical Chemistry C · 2026-04-20

  articleSenior authorCorresponding

  Surface plasmon resonance (SPR) provides a sensitive optical probe of electric double layers (EDLs), yet conventional EC-SPR measurements typically report only resonance-angle shifts (Δθ), offering limited insight into the coupled dielectric and structural response of the interface. Here, we use plasmon-resonant gold grating nanostructures to simultaneously measure both Δθ and reflectance modulation (ΔR) in aqueous electrolytes and ionic liquids over a wide temperature range. By incorporating the full complex refractive index into finite-difference time-domain (FDTD) simulations, we reproduce the experimentally observed voltage-induced changes in both Δθ and ΔR, something not achievable with models that neglect optical absorption in the EDL. This integrated experiment-theory approach allows us to extract quantitative information about local dielectric screening, interfacial absorption, and the spatial extent of the perturbed EDL. Using known temperature-dependent dielectric functions of water and ionic liquids, our FDTD model accurately captures the thermal evolution of Δθ in concentrated aqueous solutions, consistent with an increase in the effective Debye screening length at elevated temperatures. In contrast, the same model fails to reproduce the anomalous temperature and voltage response of the ionic liquid [EMIM][TFSI], reflecting the breakdown of Debye-type screening in dense Coulomb fluids and the dominant role of ion–ion correlations and interfacial structuring. These results highlight that only by including the imaginary dielectric response and using full FDTD modeling can one quantitatively interpret EC-SPR measurements and distinguish classical screening behavior from the nonclassical electrostatics of ionic liquids.

  PublisherDOI

• Determination of the Fermi Energy of Diamond using Photoluminescence Spectral Analysis

  ArXiv.org · 2026-04-28

  articleOpen access

  Electronic band structures and the Fermi energy provide essential information for understanding the electronic properties of solids. In semiconductors, the Fermi energy level is determined by the donor and acceptor concentrations. For diamond, the relationship between the Fermi energy level and the donor-acceptor concentrations is highly nonlinear; therefore, experimental determination of the Fermi energy level is important. Here, we report a method to determine the Fermi energy of diamond based on photoluminescence (PL) measurement. The density-functional-theory (DFT) study by Deák et al.~\cite{deak2014formation} showed the relationship between the Fermi energy and the formation energies of nitrogen-vacancy centers in the negatively charged (NV-) and neutrally charged (NV0) charge states. In the present method, we measure the relative populations of the NV- and NV0 centers from PL spectral analysis and, using these populations and the DFT result, determine the Fermi energy of the diamond samples. Moreover, we show the application of the method to study the spin coherence and the stability against the charge state conversion of the NV centers on several diamond samples. We also extend the method for the Fermi energy determination using the silicon-vacancy (SiV) center in diamond. The PL-based method is advantageous for determining the Fermi energy with high spatial and fast time resolutions, even in extreme environments, and can be extended to determine various wide band gap semiconductors.

  PublisherOA PDF

• Fermi Level-Mediated Charge-State Control of Multicolor Diamond Microcrystals Using High-Voltage Pulses

  ACS Photonics · 2026-04-03

  articleSenior authorCorresponding

  Silicon-vacancy (SiV–) centers in diamond exhibit narrow optical transitions and favorable photophysical properties for quantum photonics and sensing. In microdiamonds, however, electrical control of color-center charge states remains challenging due to their small size, surface- and interface-dominated electronic structure, and the lack of reliable electrical contacts. Here, we report a noncontact strategy for electrically modulating microdiamond powders using nanosecond high-voltage pulses applied at kilohertz repetition rates across a hybrid architecture in which microdiamonds are deposited on electrically insulating bulk CVD diamond substrates. Sustained pulse excitation leads to pronounced and reversible suppression of zero-phonon-line emission from SiB, SiV–, and SiV0 centers under applied voltages up to 10 kV. Voltage-, frequency-, and temperature-dependent measurements indicate that the modulation arises from charge-redistribution-induced shifts of the local Fermi level within the microdiamond layer, which transiently destabilize the emissive negative charge states. Time-resolved PL reveals recovery dynamics on second time scales consistent with trap-assisted re-equilibration of the local Fermi level mediated by surface and interface states. Measurements across multiple substrates confirm that the response is intrinsic to the microdiamonds and exhibits the opposite polarity to the voltage-enhanced SiV– emission reported in bulk diamonds. This hybrid diamond platform establishes a scalable route to charge redistribution modulation control of nanoscale color centers, providing a versatile framework for probing charge-state dynamics in surface-dominated quantum nanomaterials.

  PublisherDOI

• Long‐Lived SiV ⁻ Center Induced by Nanosecond High‐Voltage Pulse Discharge

  Advanced Optical Materials · 2026-02-03 · 1 citations

  articleOpen accessCorresponding

  ABSTRACT Defect and impurity centers in diamond can exist in multiple charge states. A notable example is a negatively and neutrally charged nitrogen‐vacancy center in diamond, whose optical and spin properties are very different. Recent DFT studies show that an energetically favorable charge state can be controlled by adjusting the chemical potential of the diamond sample, which often requires significant materials engineering. This study presents an alternative approach for the control of charge states with the use of nanosecond high‐voltage pulse discharges. We demonstrate the control of silicon‐vacancy (SiV) centers in diamond. Using time‐resolved photoluminescence (PL) spectroscopy measurement of the SiV centers with the application of nanosecond high‐voltage pulses, we show the emergence of the negatively charged SiV − state. We also employ the time‐resolved PL measurements and show that the population of the induced SiV − charge state decays exponentially, and the lifetime of the charge state is determined by 200–1100 ms. The observed long‐lived charge state is potentially useful for applications based on the SiV − center. This method also paved the way to access various charge states of defect and impurity centers in diamond and wide‐bandgap semiconductors.

  PublisherOA PDFDOI

• Electronically Driven Combustion of Energetic Ionic Liquids in a Microcell Reactor

  ACS Omega · 2026-04-13

  articleOpen accessSenior authorCorresponding

  This study presents a microcell reactor platform designed to investigate the electronically driven combustion of energetic ionic liquids through nanosecond pulsed plasma discharges. A fuel mixture of 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]) and hydroxylammonium nitrate (HAN) with this system enables controlled ignition and characterization of intermediate species formed during plasma-assisted decomposition. The high throughput testing provided by the microcell reactor also enables rapid testing of variations of fuels to investigate combustion enhancements from dopants such as carbon nanotubes. The approach also enables us to differentiate between the thermally driven and plasma-driven processes involved in the combustion of [EMIM][EtSO4] and HAN through optical emission spectroscopy and Raman shift thermometry. This analysis allows for in situ diagnostics of reactive species and temperature evolution. Optical emission spectra reveal distinct reaction intermediates, including CN, C2, N2, and atomic H and N, and the mixture also exhibits broad spectral features indicative of exothermic combustion (i.e., continuum thermal radiation). Raman thermometry using a commercially available micro-Raman spectrometer, provides quantitative temperature measurements, enabling differentiation between thermally- and plasma-driven processes. The HAN+[EMIM][EtSO4] solution exhibits a higher temperature-induced shift, due to the nanosecond high voltage pulse excitation, than what was observed during the measurement of the individual ionic liquids. The microcell’s compact and reconfigurable design allows rapid assembly and testing of various oxidizer–fuel combinations. This offers a high-throughput approach for advancing green monopropellant research and understanding plasma-assisted reaction mechanisms.

  PublisherDOI

• Plasma-enhanced electrostatic precipitation (PE-ESP) of restaurant smoke emissions

  Environmental Science and Pollution Research · 2026-01-30 · 1 citations

  articleSenior author
  PublisherDOI

• Role of Transient-Plasma Generated Free Radicals in Hydrogen Combustion: Spectroscopic and Theoretical Insights

  Fuel · 2026-02-14

  articleOpen accessSenior authorCorresponding

  • TPI produces fast, non-equilibrium discharges generating abundant H· radicals. • Optical spectroscopy captures H α as direct evidence of radical formation. • Kinetic modeling shows H· accelerates OH· formation and H 2 oxidation. • TPI flames propagate faster than CSI beyond flame-wrinkling effects. • Lagrangian simulations reveal distinct TPI radical pathways. Transient plasma ignition is known to improve the combustion of various fuels. Here, we compare the combustion mechanisms of carbon-free fuels containing mixtures of H 2 and O 2 via transient plasma ignition and conventional spark ignition. The transient plasma ignition is produced by five 20 ns pulses at a frequency of 1 kHz with an amplitude of 20 kV. Compared to conventional spark ignition (CSI), TPI ignited four times faster at a lean equivalence ratio (ϕ = 0.4). Optical diagnostics confirmed the presence of H α emission during TPI, providing direct evidence of atomic hydrogen radicals generated by nanosecond plasma discharges. These radicals, coupled with electrostatic flow effects, reduced ignition delay and accelerated flame propagation beyond enhancements attributable to flame wrinkling alone. Complementary kinetic modeling with Cantera and one-dimensional Lagrangian simulations revealed that plasma-generated H· radicals bypass high-temperature initiation pathways. This shortens induction times and promotes earlier OH· formation, thereby accelerating H 2 oxidation and water production under both adiabatic and non-adiabatic conditions. Together, these findings demonstrate that TPI enhances hydrogen combustion by coupling radical-driven kinetics with fluid-dynamic effects, offering a promising strategy to improve ignition reliability and efficiency in carbon-free propulsion systems.

  PublisherDOI

• Electronically-Throttleable, Catalyst-free Combustion of Ionic Liquid-based Polymers using Transient Plasma Discharge

  SSRN Electronic Journal · 2026-01-01

  preprintOpen accessSenior author
  PublisherDOI

Recent grants

• CAS: Mechanistic Study of Reaction Intermediates in Nanoparticle-Enhanced Plasma-Assisted Catalysis

  NSF · $311k · 2020–2024

• CAREER: Enhanced Catalytic Phenomena via Surface Plasmon Resonant Excitation

  NSF · $400k · 2009–2014

• Collaborative Research: In Situ Surface Spectroscopy of 2D Material-based Electrocatalysis and Photoelectrocatalysis

  NSF · $300k · 2020–2024

• Collaborative Research: Plasma-enhanced Electrostatic Precipitation of Diesel Particulates using High Voltage Nanosecond Pulses

  NSF · $210k · 2021–2024

• Collaborative Research: A Mechanistic Study of Chemical Enhancement in Surface Enhanced Raman Spectroscopy and Graphene Enhanced Raman Spectroscopy

  NSF · $265k · 2017–2021

Frequent coauthors

• M. S. Dresselhaus

  Massachusetts Institute of Technology

  93 shared

• Adam Bushmaker

  The Aerospace Corporation

  63 shared

• Haotian Shi

  State Key Laboratory of Supramolecular Structure and Materials

  55 shared

• Bingya Hou

  48 shared

• Jihan Chen

  Advanced Semiconductor Engineering (Taiwan)

  41 shared

• Rohan Dhall

  39 shared

• Lang Shen

  Shanghai Electric (China)

  39 shared

• G. Dresselhaus

  Massachusetts Institute of Technology

  39 shared

Education

• Ph.D., Electrical Engineering

  University of Southern California

  1990

• M.S., Electrical Engineering

  University of Southern California

  1986

• B.S., Electrical Engineering

  University of Southern California

  1984

Awards & honors

• 2010 University of Southern California USC Viterbi School of…
• 2009 National Science Foundation NSF CAREER Award
• 2007 USC Stevens Institute for Innovation USC Stevens Curric…
• 2007 Air Force AFOSR Young Investigator Award
• 2006 USC James H. Zumberge Research and Innovation Award