Δημοσιεύσεις

Project Acronym: AIMONACA
Title: Ab initio modelling of nanoparticle catalysts
Affiliation: aristotle university of thessaloniki
Pi: Joseph Kioseoglou
Research Field: chemical sciences and materials

Observation of the Direct Energy Band Gaps of Defect-Tolerant Cu3N by Ultrafast Pump-Probe Spectroscopy
by M Zervos, A Othonos, M Sergides, T Pavloudis, J Kioseoglou
Abstract:
Cu$_3$N with a cubic crystal structure has been prepared from Cu on fused SiO$_2$ under a flow of NH$_3$:O$_2$ between 400 and 600 °C. All Cu$_3$N layers exhibited distinct maxima in differential transmission at ∼500, 550, and 630, 670 nm with the same spectral structure and shape on a ps timescale as shown by ultrafast pump-probe spectroscopy. We show that the maxima at 630 (≡1.97 eV) and 670 nm (≡1.85 eV) correspond to the M and R direct energy band gaps of Cu$_3$N, in excellent agreement with density functional theory calculations of the electronic band structure. These findings are corroborated further by the fact that Cu$_3$N as-deposited by reactive sputtering under 100% N$_2$ at 25 °C and 10–2 mbar did not exhibit a fine spectral structure due to a smeared density of states, poor crystallinity, and a high density of defects, but annealing under NH$_3$:H$_2$ at 300 °C revealed a similar spectral structure to Cu$_3$N obtained from Cu under NH$_3$:O$_2$. In contrast to the above, we suggest that the peaks at 500 (≡2.48 eV) and 550 nm (≡2.25 eV) might correspond to the M and R direct gaps of certain regions of Cu$_3$N under strain that changes the lattice constant and band gap. We discuss the charge carrier generation and recombination mechanisms in terms of Cu interstitials and vacancies that are known to be energetically located near the band edges, thus allowing the observation of the direct energy band gaps in this defect tolerant semiconductor.
Reference:
Observation of the Direct Energy Band Gaps of Defect-Tolerant Cu3N by Ultrafast Pump-Probe Spectroscopy (M Zervos, A Othonos, M Sergides, T Pavloudis, J Kioseoglou), In The Journal of Physical Chemistry C, volume 124, 2020.
Bibtex Entry:
@article{doi:10.1021-acs.jpcc.9b10303,
 author = {M Zervos, A Othonos, M Sergides, T Pavloudis, J Kioseoglou},
 doi = {10.1021/acs.jpcc.9b10303},
 url = {https://doi.org/10.1021/acs.jpcc.9b10303},
 year = {2020},
 bibyear = {2020},
 journal = {The Journal of Physical Chemistry C},
 abstract = {Cu$_3$N with a cubic crystal structure has been prepared from Cu on fused SiO$_2$ under a flow of NH$_3$:O$_2$ between 400 and 600 °C. All Cu$_3$N layers exhibited distinct maxima in differential transmission at ∼500, 550, and 630, 670 nm with the same spectral structure and shape on a ps timescale as shown by ultrafast pump-probe spectroscopy. We show that the maxima at 630 (≡1.97 eV) and 670 nm (≡1.85 eV) correspond to the M and R direct energy band gaps of Cu$_3$N, in excellent agreement with density functional theory calculations of the electronic band structure. These findings are corroborated further by the fact that Cu$_3$N as-deposited by reactive sputtering under 100\% N$_2$ at 25 °C and 10–2 mbar did not exhibit a fine spectral structure due to a smeared density of states, poor crystallinity, and a high density of defects, but annealing under NH$_3$:H$_2$ at 300 °C revealed a similar spectral structure to Cu$_3$N obtained from Cu under NH$_3$:O$_2$. In contrast to the above, we suggest that the peaks at 500 (≡2.48 eV) and 550 nm (≡2.25 eV) might correspond to the M and R direct gaps of certain regions of Cu$_3$N under strain that changes the lattice constant and band gap. We discuss the charge carrier generation and recombination mechanisms in terms of Cu interstitials and vacancies that are known to be energetically located near the band edges, thus allowing the observation of the direct energy band gaps in this defect tolerant semiconductor.},
 volume = {124},
 number = {6},
 pages = {3459-3469},
 title = {Observation of the Direct Energy Band Gaps of Defect-Tolerant Cu3N by Ultrafast Pump-Probe Spectroscopy },
}