About

Jeffrey A. Fagan is the Isidor and Seville Sulzbacher Professor of Law at Columbia Law School, where he has taught since 2001. He is a leading expert on policing, crime, gun control, and race, with scholarly research that influences public policy. His work includes significant scholarship on capital punishment, the legal socialization of adolescents, neighborhoods and crime, juvenile crime and punishment, and police practices. Fagan's research on the New York Police Department’s stop-and-frisk practices, which found that more than 30 percent of the stops were legally unjustified or questionable, was central to a 2013 federal court decision that declared the policy unconstitutional. In addition to his role at Columbia Law, he holds a position as Professor of Epidemiology at the Mailman School of Public Health and has served as a visiting professor at Yale Law School. His contributions to the field have been recognized through awards and fellowships from institutions such as the Russell Sage Foundation, the Robert Wood Johnson Foundation, and the Open Society Institute’s Soros Justice Fellowship. Fagan has served on various editorial boards, contributed expert testimony, and participated in national panels examining policing and criminal justice issues.

Research topics

• Materials science
• Nanotechnology
• Optoelectronics
• Genetics
• Mathematics
• Physics
• Electrical engineering
• Optics
• Biology
• Chemistry
• Biological system
• Geometry

Selected publications

• Efficient Measurement of Length Distribution of 1D Nanoparticles in Solution <i>via</i> Optical Polarimetry

  ACS Nano · 2025-12-01

  articleOpen access

  The efficient measurement of the length distribution of nanotubes, nanowires, and other one-dimensional (1D) nanoparticles in solution is important to enable their incorporation into materials and devices and to optimize their processing for properties of interest, such as thermal/electrical conductivity or mechanical strength, in suspensions and composites. We report an electric-field (E-field)-assisted optical-polarimetry technique to measure the length distribution of ensembles of high-aspect-ratio particles in dilute suspension. The degree of alignment of polarizable 1D particles suspended in a fluid under Brownian motion explicitly depends on the E-field strength and the particle length. We show that it is possible to extract the length distribution of 1D nanoparticles suspended in an insulating fluid by applying a range of E-fields and using optical polarimetry to measure the corresponding alignment order parameter. Notably, the method is relatively insensitive to the diameter of the 1D particles, which can be poorly known or vary within a sample. The technique is validated with silver nanowires and carbon nanotubes of known lengths, as well as polymer-depletion-length-separated single-wall carbon nanotube samples with length distributions independently measured with analytical ultracentrifugation. Finally, we demonstrate the ability of the optical-polarimetry technique to quantify changes in the length distribution of ultranarrow, sub-nanometer-diameter single-wall carbon nanotubes under different types and durations of ultrasonication. Within its range of applicability (polarizable 1D nanoparticles in the 0.5 to 15 μm length range, constrained by the voltage stability of the media and the suspended particles), the E-field-assisted optical-polarimetry method is a particularly efficient and accurate method to measure the length distribution of nanowires and nanotubes in suspension.

  PublisherDOI

• Precise Partitioning of Metallic Single-Wall Carbon Nanotubes and Enantiomers through Aqueous Two-Phase Extraction

  ACS Nano · 2025-04-03 · 2 citations

  articleOpen accessSenior authorCorresponding

  Separation of single-chirality single-wall carbon nanotubes (SWCNTs) and their enantiomers holds significant potential for materials science and various applications but challenges in scalability and precision persist. In this study, we introduce a systematic approach to identify separation conditions for metallic SWCNTs in aqueous two-phase extraction (ATPE), precisely identifying improved conditions for isolating multiple armchair and chiral (n,m) species. We quantify these conditions by determining partition coefficient change condition (PCCC) values for both binary and ternary surfactant combinations. This information enables optimization for efficient separation of high-purity armchair nanotubes such as (6,6), (7,7), (8,8) and (9,9), and for isolation of enantiomeric nonarmchair nanotubes, including challenging metallic species such as the (8,5), (7,4), (9,3), (10,4) and (10,7). Lastly, separated single (n,m) populations are reseparated in ATPE at precise steps in both binary and ternary surfactant mixtures to resolve their enantiomers, extracting information on the underlying mechanism of metallic SWCNT ATPE and highlighting the utility of sodium cholate for achieving single enantiomer level separations.

  PublisherDOI

• How to RSoXS

  The Journal of Chemical Physics · 2025-08-12 · 2 citations

  articleOpen access

  Resonant Soft X-ray Scattering (RSoXS) has emerged as a powerful technique for investigating compositional and orientational heterogeneity in organic thin films. By exploiting the variation in optical constants near atomic absorption edges, RSoXS enables unprecedented contrast between organic materials and unique sensitivity to molecular orientation. Despite its growing importance over the past 15 years, particularly in organic electronics research, detailed guidance on proper implementation and analysis has been limited. This tutorial provides a comprehensive introduction to the technique, starting with the fundamental principles of near edge x-ray absorption fine structure spectroscopy and RSoXS contrast mechanisms. Using multi-walled carbon nanotubes as an illustrative example, we walk through best practices for sample preparation, measurement procedures, and data analysis. We present both model-free analysis approaches and detailed modeling using the open-source NIST RSoXS simulation suite. We intend this tutorial to serve as a practical resource for both new practitioners and experienced researchers, enabling quantitative analysis of molecular-scale structure in soft materials.

  PublisherOA PDFDOI

• The Resonance Structure of Raman Scattering for Emitted and Absorbed Phonons in Chirality-Pure Carbon Nanotube Films

  ACS Nano · 2025-11-14

  articleOpen accessSenior author

  Chirality-pure single-wall carbon nanotubes (SWCNTs) are ideal samples for resonant Raman scattering (RS) as they have sharp optical transitions and are strong Raman scatterers, having diameter and chirality specific resonances in the visible and in the near-infrared. Recently, it has become possible to rapidly obtain broadband maps of many vibrational modes of SWCNTs and their excitation resonances. Here, we use a full spectrum Raman excitation mapping technique to obtain experimental Raman excitation maps for several species of SWCNT [(7,6), (7,5), and (6,5)] purified by two different methods, mapping both phonon emission (Stokes) RS and phonon absorption (anti-Stokes) RS. These experimental maps show intricate patterns which match well with some of the predictions of quantum models of RS, and strong signals enhanced ≈3000× over graphite G bands near incident photon resonance. All RS bands necessarily have different excitation structure, but Stokes and anti-Stokes pairs are closely symmetrical, yielding an overall butterfly shaped pattern interpretable in terms of excitonic resonances with incident photons and scattered photons. Temperature provides the phonon population for anti-Stokes RS and is critical to interpreting relative feature intensity compared to Stokes RS. SWCNTs are robust and strong RS, both Stokes and anti-Stokes and their ratio, can be obtained over orders of magnitude in laser power, which we show is a critical variable affecting relative response based on sample preparation factors.

  PublisherDOI

• Aligned Boron Nitride Nanotube Thin Films and Their Cocomposites with Single-Wall Carbon Nanotubes through Slow Vacuum Filtration

  ACS Nanoscience Au · 2025-06-17 · 1 citations

  articleOpen accessSenior authorCorresponding

  Boron nitride nanotubes (BNNTs) are a promising nanomaterial due to their remarkable optical and mechanical properties, chemical robustness, and extended aspect ratios. Herein, we report the formation of strongly biaxially aligned thin films of BNNTs using automated slow vacuum filtration (SVF), as well as their cocomposites with single-wall carbon nanotubes (SWCNTs). Pure BNNT SVF-generated films are found to differ in optimization conditions from those identified previously for SWCNTs but display similar improvements in alignment and uniformity with advanced purification for nanotube length and homogeneity, with globally aligned films observed. Mixed, cocomposite, biaxially aligned films of BNNTs with SWCNTs are also described. Such films provide effective and efficient hosting capabilities for unique morphologies of distributed and individualized SWCNTs aligned by a wide-bandgap BNNT matrix. Concentrations upward of 25% SWCNT mass fraction were found to reside within majority-BNNT films without significantly disrupting the global composite structure; the SWCNT fraction, in turn, enabled probing of both local and global nematic alignment through their use as spectroscopic reporters. Leveraging the thickness and alignment control provided by our SVF implementation, both neat BNNT and composite films show great promise for advancing novel photonic and other thin-film nanocomposite applications requiring tailorable mechanical, thermal, optical, and electronic functionalities.

  PublisherDOI

• Rapid Broadband Raman Excitation Mapping of Chirality-Pure Carbon Nanotubes

  ECS Meeting Abstracts · 2025-07-11

  articleSenior author

  Each chirality of SWCNT has its own set of optical absorption (OA) resonances in the visible and near infrared ( vis -NIR), and also has its own vibrational modes, some chirality-specific, many chirality-non-specific. These resonances and modes give rise to Raman scattering (RS) in the vis -NIR which is strongly laser wavelength dependent. The variation of the intensity of RS with incident laser energy for a given band is the (resonant) Raman excitation profile (REP). Importantly, each resonant RS band has its own, distinct REP. The map of the scattering intensity as a function of ingoing photon energy and outgoing photon energy can be called the Raman excitation map (REM). The REM is a two dimensional or even multidimensional fingerprint of each analyte and its physical/chemical state, with great analytical potential. Progress in optical technology now makes it much more practical than ever before to obtain REMs rapidly over a broad band of excitation wavelengths. Furthermore, progress in separation science means that highly pure chirality-sorted SWCNT samples are available with specific, well defined, electronic structure. So, it is becoming possible to rapidly obtain broadband REMs from particular, known chiral species of SWCNTs. Here we show experimental broadband REMs of various species of SWCNTs which were prepared by two different sorting techniques: aqueous two-phase extraction and conjugated polymer extraction. We show the structure of REPs from various RS bands, and investigate how features of the REMs compare to our expectations. Uncommon RS bands are clearly observed. We show some connections of RS to OA and photoluminescence excitation. We demonstrate the real-time acquisition of high signal-to-noise REMs in broadband at sub-second timescales, enabling the practical investigation of the time evolution of the REM. The dynamics of the REM under photo-driven defect production will be presented.

  PublisherDOI

• Brief of Amici Curiae Professors of Constitutional and Criminal Law in Support of Petitioner (Whitton v. Dixon - 25-580)

  eYLS (Yale Law School) · 2025-12-01

  articleOpen access

  Brief in support of Petitioner. SUMMARY OF ARGUMENT: This Court has “consistently held that a conviction obtained by the knowing use of perjured testimony is fundamentally unfair” because it “involve[s] a corruption of the truth-seeking function of the trial process.” United States v. Agurs, 427 U.S. 97, 103–04 (1976). Here, the Eleventh Circuit acknowledged that the state committed a Giglio violation when it permitted a jailhouse informant to falsely testify at trial that he lacked a violent criminal record despite prosecutors knowing that he did. The Eleventh Circuit deemed this violation harmless, however, based on its erroneous consideration of a DNA test which was conducted years after the trial and was never admitted into evidence or subjected to adversarial testing. But, as this Court has explained, “it is not the appellate court’s function . . . to speculate upon probable reconviction and decide according to how the speculation comes out.” Kotteakos v. United States, 328 U.S. 750, 763 (1946). By doing precisely that, the Eleventh Circuit erred, and its decision conflicts with the decisions of this Court, other circuits and state courts. Review of the Eleventh Circuit’s decision is especially warranted because it raises serious Confrontation Clause concerns. It is inconsistent with due process principles for an appellate court’s harmless error analysis in a death penalty case to consider unadmitted allegedly inculpatory DNA evidence that was never presented to a jury or subject to cross-examination.

  PublisherOA PDF

• <i>(Invited)</i> Calibrating Chiroptical Response of Enantiomer-Sorted Single-Wall Carbon Nanotubes Using Hyperspectral Fluorescence Microscopy

  ECS Meeting Abstracts · 2025-07-11

  article

  Recent advancements in the sorting of SWCNTs have created a vast library of samples varying in diameter, roll-up angle, handedness and filling state. While this diversity is intriguing due to the rich choice of structure-dependent properties, many samples lack high enantiomeric purity hindering advanced applications such as next-generation electronics or biosensing [1]. Chiroptical spectroscopy, notably Electronic Circular Dichroism (ECD) or Raman optical activity (ROA), has emerged as a preferred method for rapidly characterizing enantiomer samples. Although it identifies well the (n,m) structure, establishing a direct correlation between chiroptical intensities and the exact enantiomeric purity of the samples currently poses challenges. In this study, we combine ECD and ROA with hyperspectral fluorescence microscopy on the same enantiomer-sorted (6,5) SWCNTs. By utilizing the fluorescence shift in the hyperspectral data arising from the interaction of SWCNT enantiomers with the chiral surfactant [2], we reliably quantify the SWCNT enantiomeric purity and subsequently calibrate intensities in ECD and ROA spectra. Our results enable a reliable determination of enantiomeric purity of SWCNTs through chiroptical spectroscopy, promising future advancements in enantiomer sorting and the development of chiroptical characterization methods. [1] Yang et al. , Chem. Rev. 2020 , 120, 5, 2693–2758 [2] M. Erkens et al. , ACS Nano 2024 , 18, 14532–14545

  PublisherDOI

• Electrically Tunable Excitonic-Hyperbolicity in Chirality-Pure Carbon Nanotubes

  ArXiv.org · 2025-09-29

  preprintOpen access

  Metamaterials exhibiting hyperbolic dispersion enable unprecedented control over light-matter interactions, from sub-diffraction imaging to enhanced spontaneous emission. However, conventional plasmonic hyperbolic metamaterials suffer from limited tunability and lack intrinsic emission capabilities, constraining their utility for active photonic devices. Here, we demonstrate the first room-temperature, electrically tunable, excitonic hyperbolic metamaterial using aligned films of chirality-pure semiconducting carbon nanotubes. Unlike plasmonic systems, these excitonic metamaterials of aligned nanotubes combine strong optical anisotropy with dynamic electrostatic tunability. Spectroscopic ellipsometry reveals that the hyperbolic dispersion window can be electrically shifted by 53 meV, enabling real-time switching between hyperbolic and elliptical regimes. Theory predicts that this tunability translates to the propagation angle being modulated by 34°, driven by a momentum enhancement 3.11 times that of free space, limited primarily by material losses that can be mitigated through improved alignment. In addition, simulations of the system exhibit a high Purcell factor of 1550 and a modulation of 37 % without an optical cavity for a dipole placed 5 nm above the aligned nanotubes. These findings establish excitonic carbon nanotubes as a versatile platform for dynamically reconfigurable photonic metamaterials, opening pathways for adaptive optical devices, electrically-controlled spontaneous emission, and tunable hyper-lenses operating at room temperature.

  PublisherOA PDFDOI

• Analytical Ultracentrifugation Characterization of Differential Sedimentation Size‐Separated Graphene Dispersions

  Small · 2025-04-11 · 1 citations

  articleOpen accessSenior authorCorresponding

  Analytical ultracentrifugation (AUC) is applied to the characterization of as-dispersed graphene nanoplatelet dispersions and differential sedimentation separated daughter dispersions. The liquid-phase characterization of AUC is demonstrated to resolve both the broad sedimentation coefficient distributions of as-dispersed samples and changes in daughter dispersions determined by a protocol of applied differential sedimentation process steps. Comparison is made to measurements on deposited samples by scanning electron microscopy and atomic force microscopy. The value of AUC to rapidly monitor changes in the sedimentation distribution of each particle population is demonstrated to allow tailoring of the differential sedimentation protocol to produce significantly narrower population distributions. This rapid characterization is particularly important for technologies in which dispersed nanoparticles cannot be removed from a solvent solution for microscopy analysis.

  PublisherOA PDFDOI

Frequent coauthors

• Angela R. Hight Walker

  99 shared

• Ming Zheng

  72 shared

• Erik K. Hobbie

  North Dakota State University

  61 shared

• Tom R. Tyler

  58 shared

• Amanda Geller

  University of California, Irvine

  54 shared

• Elizabeth S. Piper

  University of Puget Sound

  38 shared

• Jason K. Streit

  UES (United States)

  38 shared

• Yu-Teh Cheng

  37 shared

Education

• Ph.D., Criminology

  Columbia University

  1983

• M.A., Sociology

  Columbia University

  1979

• B.A., Sociology

  University of California, Berkeley

  1976

Awards & honors

• National Associate, National Research Council and Institute…
• Fellow, Earl Warren Legal Institute, School of Law, Universi…
• Power of One Award, Racial Justice Award, Center on Race Cri…
• Lillie and Nathan Ackerman Lecture in Equality and Justice,…
• Fellow, Davenport College, Yale University