arXiv subjects

Marek Maciaszek

Publications and source records attributed to Marek Maciaszek.

9 recordsLinked to original sources

arXiv2026

Towards Site-Selective Fabrication of Near-Infrared Emitters in hBN

Spatial control of near-infrared (NIR) emission from hexagonal boron nitride (hBN) would facilitate coupling atomic-scale light sources to photonic structures, yet oxygen-related NIR emitters are generally formed at stochastic locations. Here, we combine single-shot femtosecond laser writing with annealing in an oxygen-rich environment to bias NIR activation toward predefined coordinates in exfoliated hBN. Spectra acquired with 532, 635, and 785 nm excitations show narrow and multipeak emission extending to a wavelength of 1 um. Among the spectra collected at written sites, over 83% under 785 nm excitation and 71% under 635 nm excitation contain at least one resolved peak above 810 nm. The emission intensity increases monotonically with writing-pulse energy, suggesting tunability and indicating that the optimum for the single-emitter regime may require lower energies. Band-pass-resolved measurements show zero-delay correlation dips with g2(0) values indicative of single-photon emission but also reveal contributions from the spectral background. Spectrally resolved time series under 785 nm excitation show persistent bands over the recorded intervals as well as intermittent emission above 900 nm. This approach demonstrates NIR-emitter activation at predefined sites while identifying residual off-site activation and spectral multiplicity as the principal targets for further optimization.

physics.optics↗

arXiv2026

Optical Stability and Photophysics of NV Centers in Diamond up to 120 GPa

The nitrogen vacancy (NV) center has emerged as a powerful quantum sensor in high-pressure research, with the observation of optically detected magnetic resonance at megabar pressures. However, some aspects of NV physics require further investigation to optimize the development of NV-based sensing under pressure. Here, we study both experimentally and theoretically the optical properties of the NV center under hydrostatic pressure. We investigate the evolution of the zero-phonon line (ZPL) position, radiative lifetimes, optical lineshapes, and photoionization thresholds of the NV center under pressures up to ~120 GPa. We also provide spectroscopic guidelines for performing high-pressure optical experiments. Our results confirm that the NV center remains a robust quantum sensor under extreme hydrostatic pressures, especially for magnetic characterization.

quant-ph↗

arXiv2026

Substitutional oxygen as the origin of the 3.5 eV luminescence in hexagonal boron nitride

Although point defects in hexagonal boron nitride exhibiting single-photon emission attract considerable interest, a broader understanding of defect physics and chemistry in hBN remains limited, potentially hindering further development. Oxygen is among the most common impurities in hBN, and numerous studies have reported a pronounced photoluminescence band centered near 3.5 eV following oxygen incorporation, yet its microscopic origin has remained unresolved. Here, we demonstrate that this emission originates from hole capture by neutral oxygen substituting for nitrogen (ON). The transition mechanism is non-trivial, involving not only a change in charge state but also a substantial structural reconfiguration: the positive and neutral states exhibit markedly different geometries and symmetries. In the neutral state the defect adopts a low-symmetry configuration with out-of-plane displacements of the oxygen and neighboring atoms. The calculated emission energy (3.63 eV) and lineshape are in excellent agreement with experiment.

cond-mat.mtrl-sci↗

arXiv2025

CBVB-nH complexes as prevalent defects in metal-organic vapor-phase epitaxy-grown hexagonal boron nitride

Optically active defects in hexagonal boron nitride (hBN) are promising candidates for active components in emerging quantum technologies, such as single-photon emitters and spin centers. However, further progress in hBN-based quantum technologies requires a deeper understanding of the physics and chemistry of hBN defects. In this work, we employ ab initio calculations to investigate the thermodynamic stability and optical properties of defect complexes involving carbon, boron vacancies, and hydrogen. We demonstrate that the formation of CBVB-nH complexes (n from 0 to 3) is energetically favorable under nitrogen-rich conditions in the presence of carbon and hydrogen. The low formation energies and high binding energies of these complexes arise from the strong electrostatic attraction between the positively charged carbon substitutional defect (CB) and the negatively charged hydrogen-passivated boron vacancies (VB-nH). These complexes are particularly likely to form in metal-organic vapor-phase epitaxy (MOVPE)-grown samples, where growth occurs in the presence of carbon and hydrogen and is accompanied by a high density of boron vacancies. The optical properties of CBVB-nH complexes are analyzed and compared to recent photoluminescence measurements on MOVPE-grown hBN samples. In particular, we investigate the origin of the emission peaks at 1.90 eV and 2.24 eV and demonstrate that both the energies and lineshapes are consistent with hole capture by negatively charged CBVB and CBVB-H complexes.

cond-mat.mtrl-sci↗

arXiv2024

Optical lineshapes of the C-center in silicon from ab initio calculations: Interplay of localized modes and bulk phonons

In this work, we present a first-principles density functional theory (DFT) computational investigation of the luminescence and absorption lineshapes associated with the neutral carbon-oxygen interstitial pair (CiOi) defect in silicon. We obtain the lineshapes of the defect in the dilute limit using a computational methodology that constructs dynamical matrices of supercells containing tens of thousands of atoms, utilizing systems directly accessible through DFT. Both perturbed bulk phonons and localized vibrations contribute to the phonon sideband. We achieve excellent agreement with experimental luminescence data. Our findings further reinforce the attribution of the well-known C-line in silicon to the neutral CiOi complex.

cond-mat.mtrl-sci↗

arXiv2024

Blue quantum emitter in hexagonal boron nitride and carbon chain tetramer: proposition of identification

Single photon emitters in hexagonal boron nitride offer a gateway to the future of quantum technologies, yet their identification remains challenging and subject to ongoing debate. We demonstrate through ab initio calculations that the optical properties of a carbon chain tetramer are in excellent agreement with the characteristics of a blue quantum emitter in hexagonal boron nitride emitting at 435 nm. Its calculated zero-phonon line energy (2.77 eV) and radiative lifetime (1.6 ns) perfectly align with experimental observations. The relatively weak electron--phonon coupling (Huang-Rhys factor of 1.5) indicates intense emission at the zero-phonon line. Despite the absence of an inversion center in the carbon tetramer, we demonstrate that it exhibits a negligible linear Stark effect, consistent with experimental findings. Additionally, our hypothesis explains the experimental observation that the formation of blue emitters is only possible in samples containing numerous ultraviolet emitters, which are likely identical to carbon dimers.

cond-mat.mtrl-sci↗

arXiv2021

Thermodynamics of carbon point defects in hexagonal boron nitride

We present a first-principles computational study of the thermodynamics of carbon defects in hexagonal boron nitride (hBN). The defects considered are carbon monomers, dimers, trimers, and larger carbon clusters, as well as complexes of carbon with vacancies, antisites, and substitutional oxygen. Our calculations show that monomers ($\text{C}_{\text{B}}$, $\text{C}_{\text{B}}$), dimers, trimers, and $\text{C}_{\text{N}}\text{O}_{\text{N}}$ pairs are the most prevalent species under most growth conditions. Compared to these defects, larger carbon clusters, as well as complexes of carbon with vacancies and antisites, occur at much smaller concentrations. Our results are discussed in view of the relevance of carbon defects in single-photon emission in hBN.

cond-mat.mtrl-sci↗

arXiv2021

Photoionization of negatively charged NV centers in diamond: theory and ab initio calculations

We present ab-initio calculations of photoionization thresholds and cross sections of the negatively charged nitrogen-vacancy (NV) center in diamond from the ground $^{3}\!A_2$ and the excited $^{3}\!E$ states. We show that after the ionization from the $^{3}\!E$ level the NV center transitions into the metastable $^{4}\!A_2$ electronic state of the neutral defect. We reveal how spin polarization of $\mathrm{NV}^{-}$ gives rise to spin polarization of the $^{4}\!A_2$ state, providing an explanation of electron spin resonance experiments. We obtain smooth photoionization cross sections by employing dense $k$-point meshes for the Brillouin zone integration together with the band unfolding technique to rectify the distortions of the band structure induced by artificial periodicity of the supercell approach. Our calculations provide a comprehensive picture of photoionization mechanisms of $\mathrm{NV}^{-}$. They will be useful in interpreting and designing experiments on charge-state dynamics at NV centers. In particular, we offer a consistent explanation of recent results of spin-to-charge conversion of NV centers.

cond-mat.mtrl-sci↗

arXiv2019

Carbon dimer defect as a source of the 4.1 eV luminescence in hexagonal boron nitride

We propose that the carbon dimer defect in hexagonal boron nitride gives rise to the ubiquitous narrow luminescence band with a zero-phonon line of 4.08 eV (usually labeled the 4.1 eV band). Our first-principles calculations are based on hybrid density functionals that provide a reliable description of wide band-gap materials. The calculated zero-phonon line energy of 4.3 eV is close to the experimental value, and the deduced Huang-Rhys factor of ${S \approx 2.0}$, indicating modest electron-phonon coupling, falls within the experimental range. The optical transition occurs between two localized $π$-type defects states, with a very short radiative lifetime of 1.2 nanoseconds, in very good accord with experiments.

cond-mat.mtrl-sci↗