About

Danielle Reifsnyder Hickey is an Assistant Professor of Chemistry and of Materials Science and Engineering at Penn State University. She is associated with the Penn State Intercollege Graduate Degree Program (IGDP) in Materials Science and Engineering, where cross-disciplinary collaboration within research is highly valued. Her research interests include nanomaterials and aberration-corrected electron microscopy. Dr. Hickey's work involves exploring the properties and applications of nanomaterials, utilizing advanced electron microscopy techniques to analyze material structures at the atomic level. She contributes to the academic community through her role in graduate education and research within the Department of Materials Science and Engineering.

Research topics

• Chemistry
• Physics
• Optics
• Crystallography
• Nanotechnology
• Chemical physics
• Materials science
• Optoelectronics
• Quantum mechanics
• Condensed matter physics
• Particle physics
• Computational chemistry
• Composite material

Selected publications

• Stoichiometric FeTe is a Superconductor

  ArXiv.org · 2026-03-17

  articleOpen access

  Iron-based superconductors are a fascinating family of materials in which multiple electronic bands and strong antiferromagnetic (AFM) correlations are key ingredients for competing ground states, including antiferromagnetism, electronic nematicity, and unconventional superconductivity. FeTe, unlike its superconducting isostructural counterpart FeSe, has long been regarded as an AFM metal sans superconductivity. In this work, we employ molecular beam epitaxy to grow FeTe films and perform post-growth annealing under a Te flux. By performing spin-polarized scanning tunneling microscopy and spectroscopy, we demonstrate that the AFM order in as-grown FeTe films is induced by interstitial Fe atoms that disrupt the ideal 1:1 stoichiometry. Remarkably, the removal of these interstitial Fe atoms through Te annealing yields stoichiometric FeTe films that show no AFM order and instead exhibit robust superconductivity with a critical temperature of ~13.5K. This superconducting state is further confirmed by the observation of Cooper pair tunneling, zero electrical resistance, and the Meissner effect. Therefore, our results demonstrate that stoichiometric FeTe is inherently a superconductor, overturning a long-held view that it is an AFM metal. This work clarifies the origin of superconductivity in FeTe-based heterostructures and demonstrates the importance of stoichiometry control in understanding the competition between AFM and superconductivity in iron-based superconductors.

  PublisherOA PDF

• Intrinsic even-odd thickness-driven anomalous Hall effect in epitaxial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>MnBi</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi>Te</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> </mml:math> thin films

  Physical Review Materials · 2026-04-21

  article

  We demonstrate precise control of magnetism in ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ thin films through careful synthesis by molecular beam epitaxy, achieving minimal defects and accurate layer thickness control. By optimizing Mn-Bi-Te ratios and growth temperatures, we minimize detrimental self-doping effects and accurately target integer-layer films. X-ray diffraction and reflectivity provide quantitative measures of film quality and thickness. When these macroscale probes of structure and thickness are integrated with magnetotransport measurements, a striking even-odd layer dependence of the anomalous Hall effect is revealed. Odd-layer films exhibit a large hysteresis up to the N\'eel temperature ($\ensuremath{\sim}25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), consistent with noncompensated antiferromagnetism, while even-layer films show minimal response, as expected for an antiferromagnet. The sign of the anomalous Hall effect exhibits a sign reversal for intrinsic magnetism versus magnetism associated with defects. This work identifies critical factors for inducing pure, noncompensated ferromagnetism and reveals the characteristics of the intrinsic anomalous Hall effect in ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$, which together is a step toward realizing the zero-field quantum anomalous Hall effect in topological materials.

  PublisherDOI

• Stoichiometric FeTe is a Superconductor

  arXiv (Cornell University) · 2026-03-17

  preprintOpen access

  Iron-based superconductors are a fascinating family of materials in which multiple electronic bands and strong antiferromagnetic (AFM) correlations are key ingredients for competing ground states, including antiferromagnetism, electronic nematicity, and unconventional superconductivity. FeTe, unlike its superconducting isostructural counterpart FeSe, has long been regarded as an AFM metal sans superconductivity. In this work, we employ molecular beam epitaxy to grow FeTe films and perform post-growth annealing under a Te flux. By performing spin-polarized scanning tunneling microscopy and spectroscopy, we demonstrate that the AFM order in as-grown FeTe films is induced by interstitial Fe atoms that disrupt the ideal 1:1 stoichiometry. Remarkably, the removal of these interstitial Fe atoms through Te annealing yields stoichiometric FeTe films that show no AFM order and instead exhibit robust superconductivity with a critical temperature of ~13.5K. This superconducting state is further confirmed by the observation of Cooper pair tunneling, zero electrical resistance, and the Meissner effect. Therefore, our results demonstrate that stoichiometric FeTe is inherently a superconductor, overturning a long-held view that it is an AFM metal. This work clarifies the origin of superconductivity in FeTe-based heterostructures and demonstrates the importance of stoichiometry control in understanding the competition between AFM and superconductivity in iron-based superconductors.

  PublisherDOI

• Intrinsic Even-Odd Thickness-Driven Anomalous Hall in Epitaxial MnBi2Te4 Thin Films

  arXiv (Cornell University) · 2026-03-11

  preprintOpen access

  We demonstrate precise control of magnetism in MnBi2Te4 thin films through careful synthesis by molecular beam epitaxy, achieving minimal defects and accurate layer thickness control. By optimizing Mn-Bi-Te ratios and growth temperatures, we minimize detrimental self-doping effects and accurately target integer-layer films. X-ray diffraction and reflectivity provide quantitative measures of film quality and thickness. When these macroscale probes of structure and thickness are integrated with magnetotransport measurements, a striking even-odd layer dependence of the anomalous Hall effect is revealed. Odd-layer films exhibit a large hysteresis up to the Néel temperature (~25K), consistent with non-compensated antiferromagnetism, while even-layer films show minimal response, as expected for an antiferromagnet. The sign of the anomalous Hall effect exhibits a sign reversal for intrinsic magnetism versus magnetism associated with defects. This work identifies critical factors for inducing pure, non-compensated ferromagnetism and reveals the character of the intrinsic anomalous Hall effect in MnBi2Te4, which together is a step towards realizing the zero-field quantum anomalous Hall effect in topological materials.

  PublisherDOI

• Mesoscale Epitaxy in Two-Dimensional Anisotropic ReS ₂ /MoS ₂ Vertical Heterostructures

  Nano Letters · 2026-02-06

  article

  Effects of lattice mismatch and twist on epitaxy in two-dimensional (2D) vertical heterostructures are well-explored, whereas the effects of in-plane anisotropy are largely unknown. Here, we report the synthesis of ReS2/MoS2 vertical heterostructures using chemical vapor deposition, combining anisotropic (triclinic) ReS2 and isotropic (hexagonal) MoS2. A combination of scanning/transmission electron microscopy (S/TEM) and density functional theory calculations are used to elucidate the microstructure of ReS2/MoS2 heterostructures and reveal a complex interplay of interfacial epitaxy, lattice mismatch strain, and anisotropy. We observe that the heterostructure system’s ability to relax interlayer registry differs in the crystallographic directions of larger and smaller lattice mismatch. It nevertheless obtains an overall effective lattice registry on the longest length scales by means of variations in the Re chain direction that create a quilt-like pattern of stripe domains, a phenomenon we describe as mesoscale epitaxy.

  PublisherDOI

• Nucleation and Antiphase Twin Control in Bi ₂ Se ₃ via Step‐Terminated Al ₂ O ₃ Substrates (Adv. Funct. Mater. 22/2026)

  Advanced Functional Materials · 2026-03-01

  article

  Quantum Materials In their Research Article (10.1002/adfm.202513054), Alessandro R. Mazza, Matthew Brahlek, and co-workers show how atomic step edges take control of the growth of 2D materials. Stepped surfaces guide how the topological material Bi2Se3 grows by molecular beam epitaxy, suppressing defects and unlocking new material motifs that can transform quantum materials from the ground up.

  PublisherDOI

• Emergent anisotropic three-phase order in critically doped superconducting diamond films

  Proceedings of the National Academy of Sciences · 2026-05-11

  preprintOpen access

  Two decades since its discovery, superconducting heavily boron-doped diamond (HBDD) still poses fundamental questions that need to be answered to unlock its full potential for quantum applications. We use electrical magnetotransport measurements of critically doped homoepitaxial single crystal HBDD films to reveal signatures of intrinsically granular superconductivity. By studying the dependence of electrical resistivity on temperature and magnetic field vector, we infer that this granularity arises from doping induced disorder. We observe an unexpected three-phase anisotropy in the magnetoresistance, accompanied by a spontaneous transverse voltage (Hall anomaly). Our findings indicate the emergence of an anisotropic order in an otherwise isotropic single crystal HBDD film, offering insights into the mechanism of superconductivity in this quantum material.

  PublisherDOI

• Stoichiometric FeTe is a superconductor

  Nature · 2026-04-01 · 1 citations

  articleOpen access
  PublisherOA PDFDOI

• Intrinsic Even-Odd Thickness-Driven Anomalous Hall in Epitaxial MnBi2Te4 Thin Films

  ArXiv.org · 2026-03-11

  articleOpen access

  We demonstrate precise control of magnetism in MnBi2Te4 thin films through careful synthesis by molecular beam epitaxy, achieving minimal defects and accurate layer thickness control. By optimizing Mn-Bi-Te ratios and growth temperatures, we minimize detrimental self-doping effects and accurately target integer-layer films. X-ray diffraction and reflectivity provide quantitative measures of film quality and thickness. When these macroscale probes of structure and thickness are integrated with magnetotransport measurements, a striking even-odd layer dependence of the anomalous Hall effect is revealed. Odd-layer films exhibit a large hysteresis up to the Néel temperature (~25K), consistent with non-compensated antiferromagnetism, while even-layer films show minimal response, as expected for an antiferromagnet. The sign of the anomalous Hall effect exhibits a sign reversal for intrinsic magnetism versus magnetism associated with defects. This work identifies critical factors for inducing pure, non-compensated ferromagnetism and reveals the character of the intrinsic anomalous Hall effect in MnBi2Te4, which together is a step towards realizing the zero-field quantum anomalous Hall effect in topological materials.

  PublisherOA PDF

• Atomic-Resolution Insights into Colloidal Inorganic Nanocrystal Surfaces and Transformations

  ECS Meeting Abstracts · 2025-11-24

  article1st authorCorresponding

  The size- and shape-dependent properties of inorganic nanocrystals have given rise to many fascinating physical phenomena and enabled new applications that cannot be achieved in bulk materials. Therefore, it is important to explore the roles of different crystal facets, how they interact with species on the surfaces, and how they transform under stimuli. A number of applications, including catalysis and plasmonics, depend on exactly which facets are accessible, and how these facets are able to interact with the surrounding environment. This presentation will explore the role of facets in surface functionalization and the in situ transformations of crystal morphologies and phases. The work presented will demonstrate how atomic-resolution transmission electron microscopy can provide precise information about surfaces, interfaces, and atomic transformations. It will highlight the important role of surface structures, crystal packing, and the underlying nanocrystal morphology.

  PublisherDOI

Frequent coauthors

• Nasim Alem

  Pennsylvania State University

  25 shared

• K. Andre Mkhoyan

  University of Minnesota

  24 shared

• N. Samarth

  Pennsylvania State University

  18 shared

• Saiphaneendra Bachu

  Pennsylvania State University

  17 shared

• Joan M. Redwing

  Pennsylvania State University

  16 shared

• Joon Sue Lee

  16 shared

• Anthony Richardella

  Pennsylvania State University

  11 shared

• Tanushree H. Choudhury

  10 shared

Awards & honors

• Taylor Lecture
• Tressler Lecture
• McFarland Award