Boron nitride for excitonics, nano photonics, and quantum technologies

We review the recent progress regarding the physics and applications of boron nitride bulk crystals and its epitaxial layers in various fields. First, we highlight its importance from optoelectronics side, for simple devices operating in the deep ultraviolet, in view of sanitary applications. Emphasis will be directed towards the unusually strong efficiency of the exciton-phonon coupling in this indirect band gap semiconductor. Second, we shift towards nanophotonics, for the management of hyper-magnification and of medical imaging. Here, advantage is taken of the efficient coupling of the electromagnetic field with some of its phonons, those interacting with light at 12 and 6 yin in vacuum. Third, we present the different defects that are currently studied for their propensity to behave as single photon emitters, in the perspective to help them becoming challengers of the NV centres in diamond or of the double vacancy in silicon carbide in the field of modern and developing quantum technologies.This work was financially supported in France by the contract BONASPES (ANR-19-CE30-0007-02) under the umbrella of the publicly funded Investissements d'Avenir program managed by the French ANR agency. This work has been supported in Spain the Spanish MINECO/FEDER under Contracts No. MAT2015-71035-R and No. MAT2016-75586-C4-1-P.Peer reviewe

Overtones of interlayer shear modes in the phonon-assisted emission spectrum of hexagonal boron nitride

We address the intrinsic optical properties of hexagonal boron nitride in deep ultraviolet. We show that the fine structure of the phonon replicas arises from overtones involving up to six low-energy interlayer shear modes. These lattice vibrations are specific to layered compounds since they correspond to the shear rigid motion between adjacent layers, with a characteristic energy of about 6-7 meV. We obtain a quantitative interpretation of the multiplet observed in each phonon replica under the assumption of a cumulative Gaussian broadening as a function of the overtone index, and with a phenomenological line broadening taken identical for all phonon types. We show from our quantitative interpretation of the full emission spectrum above 5.7 eV that the energy of the involved phonon mode is 6.8±0.5 meV, in excellent agreement with temperature-dependent Raman measurements of the low-energy interlayer shear mode in hexagonal boron nitride. We highlight the unusual properties of this material where the optical response is tailored by the phonon group velocities in the middle of the Brillouin zone. © 2017 American Physical Society.Peer reviewe

Electron effective mass and mobility in heavily doped n-GaAsN probed by Raman scattering

We investigate inelastic light scattering by longitudinal optic phonon-plasmon coupled modes LOPCMs in a series of heavily Se-doped, n-type GaAs1−xNx epilayers with x 0.4%. We perform a line shape analysis of the LOPCM spectra to estimate the optical effective mass, mopt , and the scattering time of the conduction electrons in GaAsN. We use these results to evaluate an effective carrier mobility for our samples. The values thus obtained, which we compare with measured electron Hall mobilities, indicate that the x-dependence of the mobility in GaAs1−xNx is dominated by the scattering time, rather than by the variation of the electron effective mass. The Raman analysis yields mopt values that are lower than those obtained from the band anticrossing model. © 2008 American Institute of Physics.This work is supported by the Spanish Government Projects MAT 2004-0664 and MAT2007-63617, and Ramon y Cajal Program and the EPSRC, United Kingdom. 1M. Henini, Dilute Nitride Semiconductors Elsevier Science, AmsterdamPeer reviewe

The effect of substrate on high-temperature annealing of GaN epilayers: Si versus sapphire

We have studied the effects of rapid thermal annealing at 1300¿°C on GaN epilayers grown on AlN buffered Si(111) and on sapphire substrates. After annealing, the epilayers grown on Si display visible alterations with craterlike morphology scattered over the surface. The annealed GaN/Si layers were characterized by a range of experimental techniques: scanning electron microscopy, optical confocal imaging, energy dispersive x-ray microanalysis, Raman scattering, and cathodoluminescence. A substantial Si migration to the GaN epilayer was observed in the crater regions, where decomposition of GaN and formation of Si3N4 crystallites as well as metallic Ga droplets and Si nanocrystals have occurred. The average diameter of the Si nanocrystals was estimated from Raman scattering to be around 3¿nm. Such annealing effects, which are not observed in GaN grown on sapphire, are a significant issue for applications of GaN grown on Si(111) substrates when subsequent high-temperature processing is required

Co(II) and Cu(II) fluorescent complexes with acridine based ligands

The condensation reaction of salicylaldehyde or 2‐hydroxynaphthaldehyde with a diamino organic group (Acridine Yellow or diaminoacridine) resulted in the Schiff‐base ligands ACRI‐1, ACRI‐2 and ACRI‐3, with the last two hitherto unknown. Fluorescent ACRI‐1, ACRI‐2 and ACRI‐3 were designed to provide iminophenolic binding pockets for two transition metals and ferromagnetic exchange between the metals. Following our report on the complex [Co2(ACRI‐1)2] (1Co), we report herein the reactions of ACRI‐1, ACRI‐2 and ACRI‐3 with CoII and CuII salts, which afforded the new fluorescent complexes [Cu2(ACRI‐1)2] (1Cu), [Co2(ACRI‐2)2] (2Co), [Cu2(ACRI‐2)2] (2Cu), [Co2(ACRI‐3)2(H2O)4] (3Co) and [Cu2(ACRI‐3)2] (3Cu

Long-Lived Phonon Polaritons in Hyperbolic Materials

Natural hyperbolic materials with dielectric permittivities of opposite signs along different principal axes can confine long-wavelength electromagnetic waves down to the nanoscale, well below the diffraction limit. Confined electromagnetic waves coupled to phonons in hyperbolic dielectrics including hexagonal boron nitride (hBN) and α-MoO3 are referred to as hyperbolic phonon polaritons (HPPs). HPP dissipation at ambient conditions is substantial, and its fundamental limits remain unexplored. Here, we exploit cryogenic nanoinfrared imaging to investigate propagating HPPs in isotopically pure hBN and naturally abundant α-MoO3 crystals. Close to liquid-nitrogen temperatures, losses for HPPs in isotopic hBN drop significantly, resulting in propagation lengths in excess of 8 μm, with lifetimes exceeding 5 ps, thereby surpassing prior reports on such highly confined polaritonic modes. Our nanoscale, temperature-dependent imaging reveals the relevance of acoustic phonons in HPP damping and will be instrumental in mitigating such losses for miniaturized mid-infrared technologies operating at liquid-nitrogen temperatures.Research at Columbia is supported by Vannevar Bush Faculty Fellowship ONR-VB: N00014-19-1-2630. We thank A. Sternbach and S. Zhang for helpful discussions. Exfoliation and transfer of hBN onto desired substrates and electron beam lithography of gold disks were performed by J.T.M. and supported by the National Science Foundation (DMR1904793). Additional structure fabrication was supported by the Center on Precision-Assembled Quantum Materials, funded through the U.S. National Science Foundation (NSF) Materials Research Science and Engineering Centers (award no. DMR-2011738). Initial simulations and experimental design from Vanderbilt were provided by J.D.C. in collaboration with the Columbia team (D.N.B. and G.N.) and was supported by the Office of Naval Research (N00014-18-1-2107). The hBN phonon band structure calculation was performed by R.C. and L.A. and supported by the Spanish MINECO/FEDER grant (MAT2015-71035- R). Cryogenics nano-optics experiments at Columbia were solely supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0019443. D.N.B is the Gordon and Betty Moore Foundation’s EPiQS Initiative Investigator no. 9455.Peer reviewe

Jardins per a la salut

Facultat de Farmàcia, Universitat de Barcelona. Ensenyament: Grau de Farmàcia. Assignatura: Botànica farmacèutica. Curs: 2014-2015. Coordinadors: Joan Simon, Cèsar Blanché i Maria Bosch.Els materials que aquí es presenten són el recull de les fitxes botàniques de 128 espècies presents en el Jardí Ferran Soldevila de l’Edifici Històric de la UB. Els treballs han estat realitzats manera individual per part dels estudiants dels grups M-3 i T-1 de l’assignatura Botànica Farmacèutica durant els mesos de febrer a maig del curs 2014-15 com a resultat final del Projecte d’Innovació Docent «Jardins per a la salut: aprenentatge servei a Botànica farmacèutica» (codi 2014PID-UB/054). Tots els treballs s’han dut a terme a través de la plataforma de GoogleDocs i han estat tutoritzats pels professors de l’assignatura. L’objectiu principal de l’activitat ha estat fomentar l’aprenentatge autònom i col·laboratiu en Botànica farmacèutica. També s’ha pretès motivar els estudiants a través del retorn de part del seu esforç a la societat a través d’una experiència d’Aprenentatge-Servei, deixant disponible finalment el treball dels estudiants per a poder ser consultable a través d’una Web pública amb la possibilitat de poder-ho fer in-situ en el propi jardí mitjançant codis QR amb un smartphone

Computational Study on the Deaminative Hydrogenation of Amides Catalyzed by Base Metal Complexes

Catalytic hydrogenation of amides could be an excellent option for the green atom efficient formation of alcohols and amines. However, the low reactivity of amides has been a big drawback for this reaction. In the last decade, the emergence of bifunctional catalysts for hydrogenation reactions improved the conditions for amide hydrogenation and made them feasible on larger scales. Still, the reaction mechanisms remained underinvestigated. In the course of his PhD studies, the candidate has elucidated the reaction mechanisms and bottlenecks by computational simulations at a quantum scale. With that information, the candidate proposed new catalysts that avoided such bottlenecks. Later, experimental studies proved the increased performance of the predicted catalysts

Isotope effects on the intra- and inter-layer phonons in layered van der Waals crystals: influence on the h-BN phonon lifetimes

9th International Conference on Low Dimensional Structures and Devices in Puerto Varas (Chile), 2-6 December 2019.Research funded by Ministerio de Ciencia, Innovación y Universidades , (MAT2015-71035R

Temperature dependence of Raman-active phonons and anharmonic interactions in layered hexagonal BN

We present a Raman scattering study of optical phonons in hexagonal BN for temperatures ranging from 80 to 600 K. The experiments were performed on high-quality, single-crystalline hexagonal BN platelets. The observed temperature dependence of the frequencies and linewidths of both Raman active E2g optical phonons is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional theory calculations. With increasing temperature, the E2ghigh mode displays strong anharmonic interactions, with a linewidth increase that indicates an important contribution of four-phonon processes and a marked frequency downshift that can be attributed to a substantial effect of the four-phonon scattering processes (quartic anharmonicity). In contrast, the E2glow mode displays a very narrow linewidth and weak anharmonic interactions, with a frequency downshift that is primarily accounted for by the thermal expansion of the interlayer spacing. © 2016 American Physical Society.This work has been financially supported by the Spanish MINECO under Contract No. MAT2015-71035-R. and by the network GaNeX (ANR-11-LABX-0014).Peer reviewe