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Invisible excitations and the story of luminescence in hexagonal Boron Nitride

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Invisible excitations
and the story of luminescence
in Hexagonal Boron Nitride

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Invisible excitations and the story of luminescence in hexagonal Boron Nitride

  1. 1. Invisible excitations and the story of luminescence in hexagonal Boron Nitride Claudio Attaccalite
  2. 2. Hexagonal Boron Nitride h­BN is a  layered  crystal homo­structural to graphite. As graphite, h­BN can be easily exfoliated, and for this  reason it finds applications as lubrificant .
  3. 3. Hexagonal Boron Nitride h­BN has a large band  gap and it’s transparent  h­BN emits light in the  ultraviolet
  4. 4. Breaking news on h-BN !!! Direct­bandgap properties and evidence for  ultraviolet lasing of h­BN single crystal K. Watanabe et al. Nature Materials 3, 404 (2004)*
  5. 5. Breaking news on h-BN !!! Direct­bandgap properties and evidence for  ultraviolet lasing of h­BN single crystal K. Watanabe et al. Nature Materials 3, 404 (2004)* Hexagonal boron nitride is an indirect band­gap  semiconductor G. Cassabois et al.,  Nature Photonics, 10, 262 (2016)* *) results from Luminescence measurements
  6. 6. Internal quantum yield 50% ZnO Direct and indirect excitons with high binding energies in hBN. L. Schue et al. arXiv preprint arXiv:1803.03766 (2018)
  7. 7. Internal quantum yield Direct and indirect excitons with high binding energies in hBN. L. Schue et al. arXiv preprint arXiv:1803.03766 (2018) 50% 0.1% ZnO Diamond
  8. 8. Internal quantum yield 15% 0.1% ZnO DiamondhBN 50% Direct and indirect excitons with high binding energies in hBN. L. Schue et al. arXiv preprint arXiv:1803.03766 (2018)
  9. 9. h­BN band structure and ARPES Direct observation of the band structure in bulk hexagonal boron nitride H. Henck, et al. PRB 95, 085410(2017)
  10. 10. h­BN optical properties Excitons in boron nitride nanotubes: dimensionality effects." Wirtz, Ludger, Andrea Marini, and Angel Rubio. " PRL 96, 126104 (2006)
  11. 11. Electron loss spectroscopy on h­BN
  12. 12. Origin of the EELS peaks Loss function  Peaks of L(q, ω) can be put in relation  to inter­band excitations (  Im[∝ ε(q, ω)]) and plasmon resonances (|ε|   0)≈ Exciton interference in hexagonal boron nitride L. Sponza, H. Amara, C. Attaccalite, F. Ducastelle, A. Loiseau PRB 97 (7), 075121(2017) Direct Observation of the Lowest Indirect Exciton State in the Bulk of Hexagonal Boron Nitride R. Schuster C. Habenicht, M. Ahmad, M. Knupfer, B. Büchner, PRB 97, 041201 (2018)
  13. 13. Origin of the EELS peaks Exciton interference in hexagonal boron nitride L. Sponza, H. Amara, C. Attaccalite, F. Ducastelle, A. Loiseau PRB 97 (7), 075121(2017) Loss function  Peaks of L(q, ω) can be put in relation  to inter­band excitations (  Im[∝ ε(q, ω)]) and plasmon resonances (|ε|   0)≈ Direct Observation of the Lowest Indirect Exciton State in the Bulk of Hexagonal Boron Nitride R. Schuster C. Habenicht, M. Ahmad, M. Knupfer, B. Büchner, PRB 97, 041201 (2018)
  14. 14. What about luminescence?
  15. 15. Luminescence Theory Theory of photoluminescence in semiconductors  K. Hannewald, S. Glutsch, and F. Bechstedt  PRB 62, 4519 (2000). Non­equilibrium Bethe­Salpeter  equation  Absorption Emission
  16. 16. Which phonons are involved  in luminescence?
  17. 17. Exciton­phonon scattering   Infrared absorption spectrum of germanium LH. Hall, J. Bardeen, FJ. Blatt  Phys. Rev., 95, 559 (1954) Electron–phonon coupling from finite differences B. Monserrat J. of Phys.: Cond. Matt. 30, 083001(2018) perturbative correction of the  BSE due to the electron­ phonon coupling + electron­phonon matrix  elements calculated  by finite difference We constructed a non­diagonal  supercell that maps K and M  points at 
  18. 18. Luminescence in h­BN Theory Experiment Hexagonal boron nitride is an  indirect band­gap  semiconductor G. Cassabois et al.,  Nature  Photonics, 10, 262 (2016) Theory of phonon­assisted  luminescence in solids: application  to hexagonal boron nitride E Cannuccia,et al. arXiv preprint arXiv:1807.11797
  19. 19. Conclusions Codes  ● Exciton interference in hexagonal boron nitride L. Sponza, H. Amara, C. Attaccalite, F. Ducastelle, A. Loiseau Phys. Rev. B 97, 075121 (2017) ● Theory of phonon-assisted luminescence in solids: application to hexagonal boron nitride E. Cannuccia, B. Monserrat and C. Attaccalite arXiv preprint arXiv:1807.11797 ● Direct and indirect excitons in boron nitride polymorphs: a story of atomic configuration and electronic correlation L Sponza, H Amara, C Attaccalite, S Latil, T Galvani, F Paleari, L Wirtz, F. Ducastelle arXiv preprint arXiv:1806.06201 ● Two-photon absorption in two-dimensional materials: The case of hexagonal boron nitride C. Attaccalite, M Grüning, H Amara, S Latil, F Ducastelle arXiv preprint arXiv:1803.10959 ● Excitons responsible for luminescence can be probed by EELS ● We extended luminescence theory to include phonon scattering and reproduce the luminescence spectra References 
  20. 20. Acknowledgments  Lorenzo Sponza François Ducastelle Hakim Amara Elena Cannuccia Bartomeu Monserrat Elena Cannuccia L. Wirtz,   M. Gruning,   F. Paleari,   S. Latil 
  21. 21. What next?  Higher­order  phonon sidebands  Temperature  dependence of  luminescence Direct and indirect excitons with high binding energies in hBN. L. Schue et al. arXiv preprint arXiv:1803.03766 (2018) Overtones of interlayer shear modes in the phonon-assisted emission spectrum of hexagonal boron nitride. T. Q. P. Vuong et al, PRB, 95(4), 045207 (2017)
  22. 22. Luminescence intensity  from bulk to monolayer This ratio in MoS2  is about 104 Dimensionality effects on the luminescence properties of hBN L. Schué et al.,  Nanoscale 8, 6986 (2016). "Excitons in few­layer hexagonal boron nitride: Davydov splitting  and surface localization”  F. Paleari,  et al.  2D Materials 5, 045017 (2018)
  23. 23. Theory vs experiments Angular resolved electron energy loss spectroscopy in hexagonal boron nitride F. Fossard et al. Phys. Rev. B 96 115304 (2017)
  24. 24. Direct Observation of the Lowest Indirect Exciton State in the Bulk of Hexagonal Boron Nitride R. Schuster C. Habenicht, M. Ahmad, M. Knupfer, B. Büchner, PRB 97, 041201 (2018) May we probe indirect nature of h­BN  with EELS?
  25. 25. Theory: how to calculate e(w)  Excitons in boron nitride single layer T. Galvani et al., Phys. Rev. B 94, 125303 (2016)G. Strinati, Nuovo Cimento 11, 1 (1988)
  26. 26. EELS ­ theory and experiments  Exciton interference in hexagonal boron nitride L. Sponza, et al. PRB 97(7), 075121(2017)

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