Nitrogen interstitials (N$_\mathrm{i}$) have the lowest formation energy among intrinsic defects of hexagonal boron nitride (hBN) under n-type and N-rich conditions. Using an optimized hybrid functional, which reproduces the gap and satisfies the generalized Koopmans condition, an N$_\mathrm{i}$ configuration is found which is lower in energy than the ones reported so far. The (0/-) charge transition level is also much deeper, so N$_\mathrm{i}$ acts as a very efficient compensating center in n-type samples. Its calculated photoluminescence (PL) at 3.0 eV agrees well with the position of an N-sensitive band measured at 3.1 eV. It has been also found that the nitrogen vacancy (V$_\mathrm{N}$) cannot be the origin of the three boron electron (TBC) electron paramagnetic resonance (EPR) center and in thermal equilibrium it cannot even exist in n-type samples.
A model of the interstitial diffusion of ion-implanted boron during rapid thermal annealing of silicon layers previously amorphized by implantation of germanium has been proposed. It is supposed that the boron interstitials are generated continuously during annealing due to dissolution or rearrangement of the clusters of impurity atoms which are formed in the ion-implanted layers with impurity concentration above the solubility limit. The local elastic stresses arising due to the difference of boron atomic radius and atomic radius of silicon also contribute to the generation of boron interstit…
It has been shown by means of impurity diffusion simulation that ion-implanted boron redistribution at the annealing temperatures 800^{\circ}C and lower is governed by the long-range migration of nonequilibrium impurity interstitials regardless of the methods used for the transient enhanced diffusion suppression. The relative amounts of impurity atoms, which are being transferred to the transient interstitial position, have been determined and time-average migration lengths of nonequilibrium boron interstitials have been obtained.
A model of interstitial impurity migration is proposed which explains the redistribution of ion-implanted boron in low-temperature annealing of nonamorphized silicon layers. It is supposed that nonequilibrium boron interstitials are generated either in the course of ion implantation or at the initial stage of thermal treatment and that they migrate inward and to the surface of a semiconductor in the basic stage of annealing. It is shown that the form of the "tail" in the boron profile with the logarithmic concentration axis changes from a straight line if the average lifetime of impurity inter…
By means of variable-composition evolutionary algorithm coupled with density functional theory and in combination with aberration-corrected high-resolution transmission electron microscopy experiments, we have studied and characterized the composition, structure and hardness properties of WB$_{3+x}$ ($x$ $<$ 0.5). We provide robust evidence for the occurrence of stoichiometric WB$_3$ and non-stoichiometric WB$_{3+x}$ both crystallizing in the metastable $hP$16 ($P6_3/mmc$) structure. No signs for the formation of the highly debated WB$_4$ (both $hP$20 and $hP$10) phases were found. Our results…
The subcarbides B12C3 and B13C2 known for their abrasive properties, can be structurally considered as carbon inserted rhombohedral alpha-B12 and expressed as B12{C-C-C} and B12(C-B-C). Using density functional theory DFT computations, the substitution of the central atom in the linear triatomic interstitials by N leads to an original new boron subcarbonitride B12C2N or B12(C-N-C) identified as slightly more cohesive than the two subcarbides. While B12C3 is insulating with a E(Gap) close to 0.2 eV, and B13C2 a weak metal with small density of state DOS at the Fermi level, B12C2N ground state i…
Extensive photochemical and spectroscopic properties of the $V_B^-$ defect in hexagonal boron nitride are calculated, concluding that the observed photoemission associated with recently observed optically-detected magnetic resonance is most likely of (1)3E" to (1)3A2' origin. Rapid intersystem crossing from the defect's triplet to singlet manifolds explains the observed short excited-state lifetime and very low quantum yield. New experimental results reveal smaller intrinsic spectral bandwidths than previously recognized, interpreted in terms spectral narrowing and zero-phonon-line shifting in…
A two stream model of boron diffusion in silicon has been developed. The model is intended for simulation of transient enhanced diffusion including redistribution of ion-implanted boron during low temperature annealing. The following mechanisms of boron diffusion were proposed, namely: the mechanism of a long-range migration of nonequilibrium boron interstitials and the mechanism due to the formation, migration, and dissolution of the "impurity atom - silicon self-interstitial" pairs. Based on the model, simulation of the redistribution of boron implanted into silicon substrates for annealing …
Photoluminescence of polycrystalline hexagonal boron nitride (hBN) was measured by means of time- and energy-resolved spectroscopy methods. The observed bands are related to DAP transitions, impurities and structural defects. The excitation of samples by high-energy photons above 5.4 eV enables a phenomenon of photostimulated luminescence (PSL), which is due to distantly trapped CB electrons and VB holes. These trapped charges are metastable and their reexcitation with low-energy photons results in anti-Stockes photoluminescence. The comparison of photoluminescence excitation spectra and PSL e…
We report on spectroscopic study of pyrolytic hBN (pBN) by means of time- and energy- resolved photoluminescence methods. A high purity of pBN samples (though low crystallinity) allows complementary information about excited states involved into the luminescence process. We affirm our recent conclusions about the impurity-related nature of most of the fluorescence bands in microcrystalline hBN. In addition, a broad band centred at 3.7 eV previously not considered because of its superposition with an intense structured impurity emission is attributed to the radiative recombination of deep DAPs.
Cubic boron arsenide (BAs) is attracting greater attention due to the recent experimental demonstration of ultrahigh thermal conductivity \k{appa} above 1000 W/mK. However, its bandgap has not been settled and a simple yet effective method to probe its crystal quality is missing. Furthermore, traditional \k{appa} measurement methods are destructive and time consuming, thus they cannot meet the urgent demand for fast screening of high \k{appa} materials. After we experimentally established 1.82 eV as the indirect bandgap of BAs and observed room-temperature band-edge photoluminescence, we devel…
We report on a novel reconstruction of the alpha-boron (111) surface, discovered using an ab initio evolution structure search, and reveal that it has an unexpected neat structure and much lower surface energy than the recently proposed (111)-I_R,(a) surface. For this reconstruction, every single interstitial boron atom forms bridges with the unique polar-covalent bonds between neighboring B_12 icosahedra, which perfectly meet the electron counting rule and are responsible for the reconstruction-induced metal-semiconductor transition. The peculiar charge transfer between the interstitial atoms…
It has been shown that many of the phenomena related to the formation of "tails" in the low-concentration region of ion-implanted impurity distribution are due to the anomalous diffusion of nonequilibrium impurity interstitials. These phenomena include boron implantation in preamorphized silicon, a "hot" implantation of indium ions, annealing of ion-implanted layers et cetera. In particular, to verify this microscopic mechanism, a simulation of boron redistribution during low-temperature annealing of ion-implanted layers has been carried out under different conditions of transient enhanced dif…
On the basis of the Green function method, analytical solutions of the diffusion equation which describes nonstationary migration of nonequilibrium interstitial impurity atoms have been derived. It is supposed that the initial distribution of nonequilibrium impurity interstitials is formed due to ion implantation and, therefore, is described by the Gaussian function. The condition of the constant concentration of impurity interstitials (the Dirichlet boundary condition) or reflecting boundary condition was imposed on the surface of a semiconductor. The Dirichlet boundary condition was also enf…
Our ab initio study suggests that boron segregation to the Sigma 5(310)[001] grain boundary should strengthen the boundary up to 1.5 ML coverage (15.24 at/nm^2). The maximal effect is observed at 0.5 ML and corresponds to boron atoms filling exclusively grain boundary interstices. In copper bulk, B causes significant distortion both in interstitial and regular lattice sites for which boron atoms are either too big or too small. The distortion is compensated to large extent when the interstitial and substitutional boron combine together to form a strongly bound dumbell. Our prediction is that b…
It has been shown that during thermal treatments of silicon layers preamorphized by germanium implantation and then implanted with boron ions the transport of impurity atoms occurs right up to a temperature of 850^{\circ}C due to migration of the nonequilibrium boron interstitials.
We report optically detected magnetic resonance (ODMR) measurements of an ensemble of spin-1 negatively charged boron vacancies in hexagonal boron nitride. The photoluminescence decay rates are spin-dependent, with inter-system crossing rates of $1.02~\mathrm{ns^{-1}}$ and $2.03~\mathrm{ns^{-1}}$ for the $m_s=0$ and $m_s=\pm 1$ states, respectively. Time-gating the photoluminescence enhances the ODMR contrast by discriminating between different decay rates. This is particularly effective for detecting the spin of the optically excited state, where a zero-field splitting of $\vert D_{ES}\vert=2…
Single- and multi-walled molybdenum disulfide (MoS$_2$) nanotubes have been coaxially grown on small diameter boron nitride nanotubes (BNNTs) which were synthesized from heteronanotubes by removing single-walled carbon nanotubes (SWCNTs), and systematically investigated by optical spectroscopy. The strong photoluminescence (PL) from single-walled MoS$_2$ nanotubes supported by core BNNTs is observed in this work, which evidences a direct band gap structure for single-walled MoS$_2$ nanotubes with around 6 - 7 nm in diameter. The observation is consistent with our DFT results that the single-wa…
The results of XPS core-level and valence band measurements, photoluminescence spectra of a-SiO2 implanted by Zn-ions (E=30 keV, D=1*1017 cm^-2) and Density Functional Theory calculations of electronic structure as well as formation energies of structural defects in silica glass induced by Zn-ion implantation are presented. Both theory and experiment show that it is energetically more favorable for implanted zinc ions to occupy the interstitial positions instead of cation substitution. As a result, the Zn-ions embedded to interstitials, form chemical bonds with the surrounding oxygen atoms, fo…
Single photon emitters (SPEs) in solids have emerged as promising candidates for quantum photonic sensing, communications, and computing. Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with the material's local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nano-beam electron diffraction. Across 40 emitters and 15 samples, we observe zero ph…
Heterostructures made from van der Waals materials provide a template to investigate proximity effects at atomically sharp heterointerfaces. In particular, near-field charge and energy transfer in heterostructures made from semiconducting transition metal dichalcogenides (TMD) have attracted interest to design model 2D "donor-acceptor" systems and new optoelectronic components. Here, using of Raman scattering and photoluminescence spectroscopies, we report a comprehensive characterization of a molybedenum diselenide (MoSe$_2$) monolayer deposited onto hexagonal boron nitride (hBN) and capped b…
Recent discoveries of supposedly pure alpha-tetragonal boron require to revisit its structure. The system is also interesting with respect to a new type of geometrical frustration in elemental crystals, which was found in beta-rhombohedral boron. Based on density functional theory calculations, the present study has resolved the structural and thermodynamic characteristics of pure alpha-tetragonal boron. Different from beta-rhombohedral boron, the conditions for stable covalent bonding (a band gap and completely filled valence bands) are almost fulfilled at a composition B_52 with two 4c inter…
Beta cells generate electric power as carrier-producing beta irradiation from incorporated radioisotopes bombard a series of p-n-junctions. However, radiation damage to the semiconductors commonly used in solar cells limits beta cells to extremely weak irradiations that generate concomitantly miniscule electric powers, e.g. micro-Watts. By contrast, beta cells that generate many orders-of-magnitude larger powers are possible with icosahedral boron-rich semiconductors since their bombardment-induced atomic displacements spontaneously self-heal. Furthermore, substitutions for Mg and Al atoms of …
The generation of single-photon emitters in hexagonal boron nitride around 2 eV emission is experimentally well-recognized; however the atomic nature of these emitters is unknown. In this paper, we use first-principles calculations to demonstrate that $C_2C_N$ is a possible source of 2 eV single-photon emitter. We showcase the calculations of a complete set of static and dynamical properties related to defects, including exciton-defect couplings and electron-phonon interactions. In particular, we show it is critical to consider nonradiative processes when comparing with experimental lifetime f…
A recent study associate carbon with single photon emitters (SPEs) in hexagonal boron nitride (h-BN). This observation, together with the high mobility of carbon in h-BN suggest the existence of SPEs based on carbon clusters. Here, by means of density-functional theory calculations we studied clusters of substitutional carbon atoms up to tetramers in hexagonal boron nitride. Two different conformations of neutral carbon trimers have zero-point line energies and shifts of the phonon sideband compatible with typical photoluminescence spectra. Moreover, some conformations of two small C clusters …
Quantum emitters in layered hexagonal boron nitride (hBN) have recently attracted a great attention as promising single photon sources. In this work, we demonstrate resonant excitation of a single defect center in hBN, one of the most important prerequisites for employment of optical sources in quantum information application. We observe spectral linewidths of hBN emitter narrower than 1 GHz while the emitter experiences spectral diffusion. Temporal photoluminescence measurements reveals an average spectral diffusion time of around 100 ms. On-resonance photon antibunching measurement is also r…
Optical centers in cubic boron nitride and diamond: remarkable similarities
Central European Institute of Technology, Brno University of Technology（中欧技术研究所，布尔诺理工大学）；Jilin Diamond Technology Research & Development（吉林金刚石技术研发有限公司）
A serious concern in the safety and economy of a pressurized water nuclear reactor is related to the accumulation of boron inside the metal oxide (mostly NiFe${}_{2}$O${}_{4}$ spinel) deposits on the upper regions of the fuel rods. Boron, being a potent neutron absorber, can alter the neutron flux causing anomalous shifts and fluctuations in the power output of the reactor core. This phenomenon reduces the operational flexibility of the plant and may force the down-rating of the reactor. In this work an innovative approach is used to combine first-principles calculations with thermodynamic dat…
An electron spin resonance (ESR) and photoluminescence signal is observed in the as grown single crystal of stishovite indicating the presence of defects in the non-irradiated sample. Photoluminescence of the as received stishovite single crystals exhibits two main bands - a blue at 3 eV and an UV at 4.75 eV. Luminescence is excited in the range of optical transparency of stishovite (below 8.75 eV) and, therefore, is ascribed to defects. A wide range of decay kinetics under a pulsed excitation is observed. For the blue band besides the exponential decay with a time constant of about 18 μs an a…
Hexagonal boron nitride (h-BN) is an attractive van der Waals material for studying fluorescent defects due to its large bandgap. In this work, we demonstrate enhanced pink color due to neutron irradiation and perform electron paramagnetic resonance (EPR) measurements. The new point defects are tentatively assigned to doubly- occupied nitrogen vacancies with (S = 1) and a zero-field splitting (D = 1.2 GHz). These defects are associated with a broad visible optical absorption band and near infrared photoluminescence band centered at ~ 490 nm and 820 nm, respectively. The EPR signal intensities …
We report on the fabrication and characterization of a single-crystal diamond device for the electrical stimula- tion of light emission from nitrogen-vacancy (NV0) and other defect-related centers. Pairs of sub-superficial graphitic micro-electrodes embedded in insulating diamond were fabricated by a 6 MeV C3+ micro-beam irra- diation followed by thermal annealing. A photoluminescence (PL) characterization evidenced a low radiation damage concentration in the inter-electrode gap region, which did not significantly affect the PL features domi- nated by NV centers. The operation of the device in…
Improved Electrochemical Performance and Diffusion kinetics by Boron-doping in Na$_{0.66}$Mn$_{0.8}$Fe$_{0.2}$O$_{2}$ Layered Cathodes for Sodium-Ion Batteries
Indian Institute of Technology Delhi（印度德里理工学院）；Hindu College, University of Delhi（德里大学印度教学院）；Indian Institute of Technology Delhi-Abu Dhabi（印度德里理工学院阿布扎比分校）
Single photon emitters in 2D hexagonal boron nitride (hBN) have attracted a considerable attention because of their highly intense, stable, and strain-tunable emission. However, the precise source of this emission, in particular the detailed atomistic structure of the involved crystal defect, remains unknown. In this work, we present first-principles calculations of the vibrationally resolved optical fingerprint of the spin-triplet (2)(_^3)B_1 to (1)(_^3)B_1 transition of the VNCB point defect in hBN. Based on the excellent agreement with experiments for key spectroscopic quantities such as th…
The ability to locally activate or generate quantum emitters in two-dimensional materials is of major interest for the realization of integrated quantum photonic devices. In particular, hexagonal boron nitride (hBN) has recently been shown to allow a variety of techniques for obtaining quantum emitters at desired locations. Here, we use cathodoluminescence (CL) to monitor in situ the local activation of color centers by an electron beam in hBN. We observe that the CL signal saturates at a given surface dose, independently of the electron current density. Based on photoluminescence and photon c…
Spin defects in solid-state materials are strong candidate systems for quantum information technology and sensing applications. Here we explore in details the recently discovered negatively charged boron vacancies ($V_B^-$) in hexagonal boron nitride (hBN) and demonstrate their use as atomic scale sensors for temperature, magnetic fields and externally applied pressure. These applications are possible due to the high-spin triplet ground state and bright spin-dependent photoluminescence (PL) of the $V_B^-$. Specifically, we find that the frequency shift in optically detected magnetic resonance …
Micro-environment of the Eu interstitial in $β$-SiAlON:Eu$^{2+}$ green phosphor
Institute of Condensed Matter and Nanosciences, Université catholique de Louvain（凝聚态物质与纳米科学研究所，天主教鲁汶大学）；Matgenix（马特格尼克斯公司）；WEL Research Institute（WEL研究所）；Yanshan University（燕山大学）；Mitsubishi Chemical Corporation（三菱化学株式会社）
Non-radiative energy transfer between boron vacancies in hexagonal boron nitride and other 2D materials
Université de Toulouse, INSA-CNRS-UPS（图卢兹大学，INSA-CNRS-UPS）；Ioffe Institute, Russian Academy of Sciences（约费研究所，俄罗斯科学院）；Laboratoire Charles Coulomb, Université de Montpellier and CNRS（夏尔·库隆实验室，蒙彼利埃大学和法国国家科学研究中心）；Institut Universitaire de France（法兰西学院）
We have studied the temperature dependencies of the photoluminescence (PL) intensity of 4.1 eV in microcrystalline powder of hexagonal boron nitride in the range of 7-1100 K. The results obtained have been analyzed within the band model of energy levels of associated donor-acceptor pairs based on impurity (ONCN) complexes. Luminescence enhancement processes at T<200 K and two independent channels of external thermal activation quenching are typical of the observable luminescence mechanisms under direct (4.26 eV) excitations of the samples. It has been shown that, at T>220 K, when directly exci…
In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline anisotropy which may compete with shape anisotropy. Probing this theoretical suggestion experimentally, epitaxial films are examined. A spontaneous strain up to 5 % lattice distortion is obtained for B contents up to 4 at%, which leads to uniaxial anis…
