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Geometric Control of Visible Emitter Creation in Hexagonal Boron Nitride by Oblique Ion Irradiation
Authors:
Sagar Chowdhury,
Bhaveshkumar Kamaliya,
Ramachandra Bangari,
Caleb Whittier,
Joseph Spielbauer,
Nabil D. Bassim,
Thomas G. Folland,
Ravitej Uppu
Abstract:
Ion irradiation creates optically active defects in wide-bandgap van der Waals materials, yet most approaches tune defect formation by varying the ion species, energy, or fluence while leaving the incidence geometry fixed. The ion-incidence angle is established here as a geometric control parameter for engineering visible emitters in hexagonal boron nitride (hBN). The angle and ion fluence of a pl…
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Ion irradiation creates optically active defects in wide-bandgap van der Waals materials, yet most approaches tune defect formation by varying the ion species, energy, or fluence while leaving the incidence geometry fixed. The ion-incidence angle is established here as a geometric control parameter for engineering visible emitters in hexagonal boron nitride (hBN). The angle and ion fluence of a plasma-focused heavy-ion (Xe+) beam are varied across hBN flakes of different thickness, and the resulting photoluminescence is quantified. In thick flakes, oblique irradiation shifts the fluence for maximum emission by nearly two orders of magnitude relative to normal incidence, whereas thin flakes exhibit an angle-independent optimum. Ion-trajectory simulations attribute this thickness dependence to lateral redistribution of the collision cascade and enhanced oblique sputtering. Atomic force microscopy identifies distinct processing regimes that delineate the useful defect-creation window. Post-irradiation annealing quenches the emission and shifts the spectral weight toward the green-yellow band while preserving the angle-dependent activation trends. Spectrally resolved lifetime measurements show comparable biexponential dynamics for normal and oblique incidence, consistent with emission from related defect families rather than a geometry-specific emitter species. These results establish ion-incidence geometry as a materials-level knob for programming optical defect activation and spatial defect distributions in van der Waals photonic materials.
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Submitted 6 August, 2026;
originally announced August 2026.
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APTLAS: An Indexed APT Literature Repository
Authors:
Bavley Guerguis,
Nabil Bassim
Abstract:
Atom probe tomography (APT) literature is broad, rapidly growing, and dispersed across a wide range of journals, which can make it difficult to identify prior work on a given material system, instrument, or analytical approach. Conventional search engines (e.g., Google Scholar) excel at general retrieval but do not preserve the domain-specific metadata that often determines the relevance of an APT…
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Atom probe tomography (APT) literature is broad, rapidly growing, and dispersed across a wide range of journals, which can make it difficult to identify prior work on a given material system, instrument, or analytical approach. Conventional search engines (e.g., Google Scholar) excel at general retrieval but do not preserve the domain-specific metadata that often determines the relevance of an APT publication (e.g., analysis mode, laser wavelength, or instrument configuration). Herein, APTLAS is presented, which is an indexed repository of published APT literature. At present, the database contains ~2,300 records, each accompanied by metadata extracted from the source publication. The accompanying web tool, available at https://aptlas.bavleyguerguis.com/, allows users to browse and filter by material system, instrument, application, publication type, or keyword search.
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Submitted 29 May, 2026;
originally announced June 2026.
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Aligning van der Waals heterostructures using electron backscatter diffraction
Authors:
R. Bangari,
M. Mosayebi,
J. Buchner,
J. D. Caldwell,
N. Bassim,
T. G. Folland
Abstract:
Precise and accurate determination of crystallographic orientation is crucial for engineering van der Waals heterostructures, where the twist angle between layers controls emergent electronic and optical properties. While Electron Backscatter Diffraction (EBSD) has been extensively used for bulk materials, its application to van der Waals materials remains largely unexplored. In this work, we demo…
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Precise and accurate determination of crystallographic orientation is crucial for engineering van der Waals heterostructures, where the twist angle between layers controls emergent electronic and optical properties. While Electron Backscatter Diffraction (EBSD) has been extensively used for bulk materials, its application to van der Waals materials remains largely unexplored. In this work, we demonstrate EBSD as a robust and versatile tool for determining crystallographic orientations of van der Waals materials with high precision. We show quantitative agreement between EBSD-determined orientations and facet orientations in orthorhombic α-MoO3 flakes on silicon substrates. We use Grain Reference Orientation Distribution (GROD) and Kernel Average Misorientation (KAM) across the flakes to demonstrate precision better than 0.2°. We extend this technique to other low-symmetry materials, specifically, monoclinic α-As2Te3, monoclinic GaTe and triclinic ReSe2, demonstrating broad applicability across van der Waals materials with different crystal structures. Finally, as a proof-of-concept application, we leverage EBSD-determined orientations to engineer twisted α-MoO3 heterostructure with precisely controlled twist angle, enabling observation of recently reported canalized phonon polaritons. Our results establish EBSD as a powerful characterization method for van der Waals materials, enabling precise orientation control essential for twistronics and twist-optics.
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Submitted 9 March, 2026;
originally announced March 2026.
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Controlled growth of rare-earth-doped TiO$_{2}$ thin films on III-V semiconductors for hybrid quantum photonic interfaces
Authors:
Henry C. Hammer,
Caleb Whittier,
Nathan A. Helvy,
Christopher Rouleau,
Nabil D. Bassim,
Ravitej Uppu
Abstract:
Quantum photonic networks require two distinct functionalities: bright single-photon sources and long-lived quantum memories. III-V semiconductor quantum dots excel as deterministic and coherent photon emitters, while rare-earth ions such as erbium (Er$^{3+}$) in crystalline oxides offer exceptional spin and optical coherence at telecom wavelengths. Combining these systems and their functionalitie…
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Quantum photonic networks require two distinct functionalities: bright single-photon sources and long-lived quantum memories. III-V semiconductor quantum dots excel as deterministic and coherent photon emitters, while rare-earth ions such as erbium (Er$^{3+}$) in crystalline oxides offer exceptional spin and optical coherence at telecom wavelengths. Combining these systems and their functionalities via direct epitaxy is challenging due to lattice mismatch and incompatible growth conditions. Here we demonstrate low-temperature pulsed laser deposition of Er$^{3+}$-doped TiO$_{2}$ thin films directly on GaAs and GaSb substrates. Controlled surface preparation with an arsenic cap and an oxygen-deficient buffer layer enables the growth of epitaxial anatase TiO$_{2}$ (001) at 390$^{o}$C with sub-300 pm surface roughness, while avoiding interface degradation. In contrast, high-temperature oxide desorption or growth temperatures drive the transition to rough, polycrystalline rutile film, as confirmed by transmission electron microscopy. Minimal coincident interface area (MCIA) modeling explains the orientation-selective growth on GaAs and GaSb. Raman and cryogenic photoluminescence excitation spectroscopy verify the crystal phase and optical activation of Er$^{3+}$ ions. This multi-parameter growth strategy helps preserve III-V quantum dot functionality and yields smooth surfaces suitable for low-loss nanophotonic structures. Our results establish a materials platform for monolithically integrating rare-earth quantum memories with semiconductor photon sources, paving the way toward scalable hybrid quantum photonic chips.
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Submitted 5 November, 2025;
originally announced November 2025.
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Two-dimensional Indium Oxide at the Epitaxial Graphene/SiC Interface: Synthesis, Structure, Properties, and Devices
Authors:
Furkan Turker,
Bohan Xu,
Chengye Dong,
Michael Labella III,
Nadire Nayir,
Natalya Sheremetyeva,
Zachary J. Trdinich,
Duanchen Zhang,
Gokay Adabasi,
Bita Pourbahari,
Wesley E. Auker,
Ke Wang,
Mehmet Z. Baykara,
Vincent Meunier,
Nabil Bassim,
Adri C. T. van Duin,
Vincent H. Crespi,
Joshua A. Robinson
Abstract:
High-quality two-dimensional (2D) dielectrics are crucial for fabricating 2D/3D hybrid vertical electronic devices such as metal-oxide-semiconductor (MOS) based Schottky diodes and hot electron transistors, the production of which is constrained by the scarcity of bulk layered wide bandgap semiconductors. In this research, we present the synthesis of a new 2D dielectric, monolayer InO2, which diff…
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High-quality two-dimensional (2D) dielectrics are crucial for fabricating 2D/3D hybrid vertical electronic devices such as metal-oxide-semiconductor (MOS) based Schottky diodes and hot electron transistors, the production of which is constrained by the scarcity of bulk layered wide bandgap semiconductors. In this research, we present the synthesis of a new 2D dielectric, monolayer InO2, which differs in stoichiometry from its bulk form, over a large area (>300 um2) by intercalating at the epitaxial graphene (EG)/SiC interface. By adjusting the lateral size of graphene through optical lithography prior to the intercalation, we tune the thickness of InO2 where predominantly (~85%) monolayer InO2 is formed. The preference for monolayer formation of InO2 is explained using ReaxFF reactive molecular dynamics and density functional theory (DFT) calculations. Additionally, the band gap of InO2 is calculated to be 4.1 eV, differing from its bulk form (2.7 eV). Furthermore, MOS-based Schottky diode measurements on InO2 intercalated EG/n-SiC demonstrate that the EG/n-SiC junction transforms from ohmic to a Schottky junction upon intercalation, with a barrier height of 0.87 eV and a rectification ratio of ~10^5. These findings introduce a new addition to the 2D dielectric family, showing significant potential for monolayer InO2 to be used as a barrier in vertical electronic devices.
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Submitted 10 November, 2025; v1 submitted 12 April, 2025;
originally announced April 2025.
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Multi-Length-Scale Dopants Analysis of an Image Sensor via Focused Ion Beam-Secondary Ion Mass Spectrometry and Atom Probe Tomography
Authors:
Bavley Guerguis,
Ramya Cuduvally,
Alexander Ost,
Morvarid Ghorbani,
Sabaa Rashid,
Wilson Machado,
Dan McGrath,
Chris Pawlowicz,
Brian Langelier,
Nabil Bassim
Abstract:
The following article presents a multi-length-scale characterization approach for investigating doping chemistry and spatial distributions within semiconductors, as demonstrated using a state-of-the-art CMOS image sensor. With an intricate structural layout and varying doping types/concentration levels, this device is representative of the current challenges faced in measuring dopants within confi…
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The following article presents a multi-length-scale characterization approach for investigating doping chemistry and spatial distributions within semiconductors, as demonstrated using a state-of-the-art CMOS image sensor. With an intricate structural layout and varying doping types/concentration levels, this device is representative of the current challenges faced in measuring dopants within confined volumes using conventional techniques. Focused ion beam-secondary ion mass spectrometry is applied to produce large-area compositional maps with a sub-20 nm resolution, while atom probe tomography is used to extract atomic-scale quantitative dopant profiles. Leveraging the complementary capabilities of the two methods, this workflow is shown to be an effective approach for resolving nano- and micro- scale dopant information, crucial for optimizing the performance and reliability of advanced semiconductor devices.
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Submitted 15 April, 2025; v1 submitted 15 January, 2025;
originally announced January 2025.
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Altermagnetic Polar Metallic phase in Ultra-Thin Epitaxially-Strained RuO2 Films
Authors:
Seung Gyo Jeong,
In Hyeok Choi,
Sreejith Nair,
Luca Buiarelli,
Bita Pourbahari,
Jin Young Oh,
Nabil Bassim,
Daigorou Hirai,
Ambrose Seo,
Woo Seok Choi,
Rafael M. Fernandes,
Turan Birol,
Liuyan Zhao,
Jong Seok Lee,
Bharat Jalan
Abstract:
Altermagnetism refers to a wide class of magnetic orders featuring magnetic sublattices with opposite spins related by rotational symmetries, resulting in non-trivial spin splitting and magnetic multipoles. However, the direct observation of the altermagnetic order parameter remains elusive. Here, by combining theoretical analysis, electrical transport, X-ray and optical spectroscopies, we establi…
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Altermagnetism refers to a wide class of magnetic orders featuring magnetic sublattices with opposite spins related by rotational symmetries, resulting in non-trivial spin splitting and magnetic multipoles. However, the direct observation of the altermagnetic order parameter remains elusive. Here, by combining theoretical analysis, electrical transport, X-ray and optical spectroscopies, we establish a phase diagram in hybrid molecular beam epitaxy-grown RuO2/TiO2 (110) films, mapping symmetries along with altermagnetic/electronic/structural phase transitions as functions of film thickness and temperature. This features a novel altermagnetic metallic polar phase in epitaxially-strained 2 nm films, extending the concept of multiferroicity to altermagnets. Such a clear signature of a magnetic phase transition at ~500 K is observed exclusively in ultrathin strained films, unlike in bulk RuO2 single crystals. These results demonstrate the potential of epitaxial heterostructure design to induce altermagnetism, paving the way for emergent novel phases with multifunctional properties.
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Submitted 13 February, 2025; v1 submitted 9 May, 2024;
originally announced May 2024.
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Elucidating the Mechanism of Large Phosphate Molecule Intercalation Through Graphene Heterointerfaces
Authors:
Jiayun Liang,
Ke Ma,
Xiao Zhao,
Guanyu Lu,
Jake V. Riffle,
Carmen Andrei,
Chengye Dong,
Turker Furkan,
Siavash Rajabpour,
Rajiv Ramanujam Prabhakar,
Joshua A. Robinson,
Magdaleno R. Vasquez Jr.,
Quang Thang Trinh,
Joel W. Ager,
Miquel Salmeron,
Shaul Aloni,
Joshua D. Caldwell,
Shawna M. Hollen,
Hans A. Bechtel,
Nabil Bassim,
Matthew P. Sherburne,
Zakaria Y. Al Balushi
Abstract:
Intercalation is a process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on intercalating metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains highly unexplored. In this work, we present a new mechanism for intercalating large molecules thr…
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Intercalation is a process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on intercalating metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains highly unexplored. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface. We investigate the intercalation of phosphorus pentoxide (P2O5) molecules directly from the vapor phase and confirm the formation of confined P2O5 at the graphene heterointerface using various techniques. Density functional theory (DFT) corroborate the experimental results and reveal the intercalation mechanism, whereby P2O5 dissociates into small fragments catalyzed by defects in the graphene that then permeates through lattice defects and reacts at the heterointerface to form P2O5. This process can also be used to form new confined metal phosphates (e.g., 2D InPO4). While the focus of this study is on P2O5 intercalation, the possibility of intercalation from pre-dissociated molecules catalyzed by defects in graphene may exist for other types of molecules as well. This study is a significant milestone in advancing our understanding of intercalation routes of large molecules via the basal plane of graphene, as well as heterointerface chemical reactions leading to the formation of distinctive confined complex oxide compounds.
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Submitted 4 April, 2023;
originally announced April 2023.
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Large-Area Intercalated 2D-Pb/Graphene Heterostructure as a Platform for Generating Spin-Orbit Torque
Authors:
Alexander Vera,
Boyang Zheng,
Wilson Yanez,
Kaijie Yang,
Seong Yeoul Kim,
Xinglu Wang,
Jimmy C. Kotsakidis,
Hesham El-Sherif,
Gopi Krishnan,
Roland J. Koch,
T. Andrew Bowen,
Chengye Dong,
Yuanxi Wang,
Maxwell Wetherington,
Eli Rotenberg,
Nabil Bassim,
Adam L. Friedman,
Robert M. Wallace,
Chaoxing Liu,
Nitin Samarth,
Vincent H. Crespi,
Joshua A. Robinson
Abstract:
A scalable platform to synthesize ultrathin heavy metals may enable high efficiency charge-to-spin conversion for next-generation spintronics. Here we report the synthesis of air-stable, epitaxially registered monolayer Pb underneath bilayer graphene on SiC (0001) by confinement heteroepitaxy (CHet). Diffraction, spectroscopy, and microscopy reveal CHet-based Pb intercalation predominantly exhibit…
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A scalable platform to synthesize ultrathin heavy metals may enable high efficiency charge-to-spin conversion for next-generation spintronics. Here we report the synthesis of air-stable, epitaxially registered monolayer Pb underneath bilayer graphene on SiC (0001) by confinement heteroepitaxy (CHet). Diffraction, spectroscopy, and microscopy reveal CHet-based Pb intercalation predominantly exhibits a mottled hexagonal superstructure due to an ordered network of Frenkel-Kontorova-like domain walls. The system's air stability enables ex-situ spin torque ferromagnetic resonance (ST-FMR) measurements that demonstrate charge-to-spin conversion in graphene/Pb/ferromagnet heterostructures with a 1.5x increase in the effective field ratio compared to control samples.
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Submitted 20 August, 2024; v1 submitted 13 May, 2022;
originally announced May 2022.
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Tunable Two-Dimensional Group-III Metal Alloys
Authors:
Siavash Rajabpour,
Alexander Vera,
Wen He,
Benjamin N. Katz,
Roland J. Koch,
Margaux Lassaunière,
Xuegang Chen,
Cequn Li,
Katharina Nisi,
Hesham El-Sherif,
Maxwell T. Wetherington,
Chengye Dong,
Aaron Bostwick,
Chris Jozwiak,
Adri C. T. van Duin,
Nabil Bassim,
Jun Zhu,
Gwo-Ching Wang,
Ursula Wurstbauer,
Eli Rotenberg,
Vincent Crespi,
Su Ying Quek,
Joshua A. Robinson
Abstract:
Chemically stable quantum-confined 2D metals are of interest in next-generation nanoscale quantum devices. Bottom-up design and synthesis of such metals could enable the creation of materials with tailored, on-demand, electronic and optical properties for applications that utilize tunable plasmonic coupling, optical non-linearity, epsilon-near-zero behavior, or wavelength-specific light trapping.…
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Chemically stable quantum-confined 2D metals are of interest in next-generation nanoscale quantum devices. Bottom-up design and synthesis of such metals could enable the creation of materials with tailored, on-demand, electronic and optical properties for applications that utilize tunable plasmonic coupling, optical non-linearity, epsilon-near-zero behavior, or wavelength-specific light trapping. In this work, we demonstrate that the electronic, superconducting and optical properties of air-stable two-dimensional metals can be controllably tuned by the formation of alloys. Environmentally robust large-area two-dimensional InxGa1-x alloys are synthesized by Confinement Heteroepitaxy (CHet). Near-complete solid solubility is achieved with no evidence of phase segregation, and the composition is tunable over the full range of x by changing the relative elemental composition of the precursor. The optical and electronic properties directly correlate with alloy composition, wherein the dielectric function, band structure, superconductivity, and charge transfer from the metal to graphene are all controlled by the indium/gallium ratio in the 2D metal layer.
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Submitted 31 May, 2021;
originally announced June 2021.
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Unexpected Near-Infrared to Visible Non-linear Optical Properties from Two-Dimensional Polar Metals
Authors:
Megan A. Steves,
Yuanxi Wang,
Natalie Briggs,
Tian Zhao,
Hesham El-Sherif,
Brian Bersch,
Shruti Subramanian,
Chengye Dong,
Timothy Bowen,
Ana De La Fuente Duran,
Katharina Nisi,
Margaux Lassaunière,
Ursula Wurstbauer,
Nabil Bassim,
Jose J. Fonseca,
Jeremy T. Robinson,
Vincent Crespi,
Joshua Robinson,
Kenneth L. Knappenberger Jr
Abstract:
Near-infrared-to-visible second harmonic generation from air-stable two-dimensional polar gallium and indium metals is described. The photonic properties of 2D metals - including the largest second-order susceptibilities reported for metals (approaching 10nm$^2$/V) - are determined by the atomic-level structure and bonding of two-to-three-atom-thick crystalline films. The bond character evolved fr…
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Near-infrared-to-visible second harmonic generation from air-stable two-dimensional polar gallium and indium metals is described. The photonic properties of 2D metals - including the largest second-order susceptibilities reported for metals (approaching 10nm$^2$/V) - are determined by the atomic-level structure and bonding of two-to-three-atom-thick crystalline films. The bond character evolved from covalent to metallic over a few atomic layers, changing the out-of-plane metal-metal bond distances by approximately ten percent (0.2 $\unicode{x212B}$), resulting in symmetry breaking and an axial electrostatic dipole that mediated the large nonlinear response. Two different orientations of the crystalline metal atoms, corresponding to lateral displacements < 2 $\unicode{x212B}$, persisted in separate micron-scale terraces to generate distinct harmonic polarizations. This strong atomic-level structure-property interplay suggests metal photonic properties can be controlled with atomic precision.
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Submitted 24 August, 2020; v1 submitted 3 April, 2020;
originally announced April 2020.
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Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures
Authors:
Daniel C. Ratchford,
Christopher J. Winta,
Ioannis Chatzakis,
Chase T. Ellis,
Nikolai C. Passler,
Jonathan Winterstein,
Pratibha Dev,
Ilya Razdolski,
Joseph G. Tischler,
Igor Vurgaftman,
Michael B. Katz,
Neeraj Nepal,
Matthew T. Hardy,
Jordan A. Hachtel,
Juan Carlos Idrobo,
Thomas L. Reinecke,
Alexander J. Giles,
D. Scott Katzer,
Nabil D. Bassim,
Rhonda M. Stroud,
Martin Wolf,
Alexander Paarmann,
Joshua D. Caldwell
Abstract:
Surface phonon polaritons (SPhPs) - the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons - offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. Here, we present a novel approach to overcome the major limitation of SPhPs, namely the narrow, material-specific spectral range where SPhPs can be…
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Surface phonon polaritons (SPhPs) - the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons - offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. Here, we present a novel approach to overcome the major limitation of SPhPs, namely the narrow, material-specific spectral range where SPhPs can be supported, called the Reststrahlen band. We use an atomic-scale superlattice (SL) of two polar semiconductors, GaN and AlN, to create a hybrid material featuring layer thickness-tunable optic phonon modes. As the IR dielectric function is governed by the optic phonon behavior, such control provides a means to create a new dielectric function distinct from either constituent material and to tune the range over which SPhPs can be supported. This work offers the first glimpse of the guiding principles governing the degree to which the dielectric function can be designed using this approach.
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Submitted 18 June, 2018;
originally announced June 2018.
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Perfect interference-less absorption at infrared frequencies by a van der Waal's crystal
Authors:
D. G. Baranov,
J. H. Edgar,
Tim Hoffman,
Nabil Bassim,
Joshua D. Caldwell
Abstract:
Traditionally, efforts to achieve perfect absorption have required the use of complicated metamaterial-based structures as well as relying on destructive interference to eliminate back reflections. Here, we have demonstrated both theoretically and experimentally that such perfect absorption can be achieved using a naturally occurring material, hexagonal boron nitride (hBN) due to its high optical…
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Traditionally, efforts to achieve perfect absorption have required the use of complicated metamaterial-based structures as well as relying on destructive interference to eliminate back reflections. Here, we have demonstrated both theoretically and experimentally that such perfect absorption can be achieved using a naturally occurring material, hexagonal boron nitride (hBN) due to its high optical anisotropy without the requirement of interference effects to absorb the incident field. This effect was observed for p-polarized light within the mid-infrared spectral range, and we provide the full theory describing the origin of the perfect absorption as well as the methodology for achieving this effect with other materials. Furthermore, while this is reported for the uniaxial crystal hBN, this is equally applicable to biaxial crystals and more complicated crystal structures. Interference-less absorption is of fundamental interest to the field of optics; moreover, such materials may provide additional layers of flexibility in the design of frequency selective surfaces, absorbing coatings and sensing devices operating in the infrared.
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Submitted 13 October, 2015;
originally announced October 2015.