The Experts below are selected from a list of 2262 Experts worldwide ranked by ideXlab platform
F.m. Morales - One of the best experts on this subject based on the ideXlab platform.
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Surface oxidation of amorphous Si and Ge slanted columnar and mesoporous thin films: Evidence, scrutiny and limitations for infrared optics
Applied Surface Science, 2019Co-Authors: A.j. Santos, B. Lacroix, F. Maudet, A. Corvisier, F. Paumier, C. Dupeyrat, T. Girardeau, R. Garcia, F.m. MoralesAbstract:Issues on the superficial oxidation of mesoporous amorphous silicon and Germanium photonic layers generated at oblique angles are reported. Such films were designed to improve the transmittance of optical elements over the mid-IR window (3.6–4.9 μm) by removing the light reflection. These nanostructures were deposited on silicon substrates by e-beam evaporation at room temperature. IR ellipsometry and spectrophotometry studies combined with models based on effective medium approximations predicted the presence of silicon or Germanium Oxides. Such oxidation was evidenced by combining X-ray photoelectron spectroscopy and advanced (scanning-)transmission electron microscopy studies based on energy-dispersive X-rays and electron energy-loss spectroscopies. Both techniques also allowed to prove the formation of core-shell-type architectures consisting of pure Si or Ge surrounded by oxidized species, even for a Ge layer subsequently capped with a dense MgF2 coating. The different approaches used for preparing electron transparent specimens (tripod polishing and focused ion-beams) confirmed a fast oxidation of the Ge nanocolumns even for short air exposure periods, and allowed comparing it with the level of oxidation promoted from other pollutant sources. This work sheds light on the spontaneous undesired oxidation in Si or Ge slanted nanorods which can diminish the performances and limit further development of optical devices.
S. H. Lin - One of the best experts on this subject based on the ideXlab platform.
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Optical properties of oxygen vacancies in Germanium Oxides: quantum chemical modeling of photoexcitation and photoluminescence.
The Journal of Physical Chemistry A, 2007Co-Authors: A. S. Zyubin, And Alexander M. Mebel, S. H. LinAbstract:Photoabsorption and photoluminescence properties of single and double oxygen vacancy (OV and DOV) defects in quartz-like Germanium oxide have been investigated by high-level ab initio calculations. It has been found that photoabsorption for these systems occurs at lower energies as compared to the analogous defects in SiO 2 . For OV, the lowest electronic excitations with high oscillator strengths have energies of 6.7-7.0 eV, whereas for DOV, the lowest-energy photoabsorption band is calculated to be in the range of 5.5-5.9 eV. Significant geometry relaxation and large Stokes shift are inherent for these excited states and, as a result, their photoluminescence bands are predicted to peak at 3.1-3.3 eV for OV and at 2.6 eV for DOV. The double oxygen vacancy is suggested to be the most suitable candidate for generating bright blue photoluminescence observed experimentally for substoichiometric quartz-like GeO 2 nanowires, as the calculated optical properties of DOV are in close agreement with the features found in experiment.
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Photoluminescence of oxygen-deficient defects in Germanium Oxides: a quantum chemical study.
The Journal of Chemical Physics, 2006Co-Authors: A. S. Zyubin, A. M. Mebel, S. H. LinAbstract:The photoabsorption and photoluminescence (PL) properties of the surface E′ center, –GeX3, and the combined E′-center–oxygen vacancy, X3Ge–GeX2, defects in substoichiometric Germanium Oxides have been investigated by high-level ab initio calculations, including complete active space self-consistent field, multireference configuration interaction, and symmetry-adapted cluster configuration interaction methods. Both defects have been shown to give rise to photoabsorption bands between 4 and 6eV. Geometry relaxation is significant and the Stokes shifts are large for all calculated excited states. A removal of an electron from the Ge–Ge bond leads to its destruction, whereas the creation of an electron hole at lone pairs of O atoms results in elongations of the Ge–O–Ge bonds in the corresponding bridges. Most often, deexcitations of excited electronic states proceed radiationlessly, through crossing points of their potential energy surfaces with those of the lower states. The –GeX3 defect is able to generate ...
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Photoluminescence of oxygen-containing surface defects in Germanium Oxides: A theoretical study
The Journal of Chemical Physics, 2005Co-Authors: A. S. Zyubin, A. M. Mebel, S. H. LinAbstract:Photoabsorption and photoluminescence properties of nonbridging oxygen –O–Ge(NBO), –OO–Ge (peroxy radical), OGe, and (O2)Ge defects in Germanium Oxides have been investigated by high-level ab initio calculations. Geometry optimization for excited electronic states of model clusters simulating these defects was carried out at the complete-active-space self-consistent-field level, and relative energies were calculated by various methods including time-dependent density-functional theory, outer-valence Green’s functions, equation-of-motion coupled cluster theory with single and double excitations, symmetry-adapted cluster configuration interaction, multireference second-order perturbation theory, and multireference configuration interaction. The results demonstrate that the considered excited states of the aforementioned defects normally exhibit large Stokes shifts and that, with few exceptions, UV photoabsorption is accompanied by red or IR photoluminescence.
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Quantum-chemical simulation of the optical properties of O=X< and O2X< point defects in silicon and Germanium Oxides
Russian Journal of Inorganic Chemistry, 2005Co-Authors: A. S. Zyubin, A. M. Mebel, S. H. LinAbstract:TD-DFT, EOM-CCSD, CAS-PT2, and MRCI calculations of the first excited singlet states of O=X< and O 2 X< point defects in silicon and Germanium Oxides were performed for the simulation of their photoabsorption and luminescence properties. It was found that these systems exhibit a large Stokes shift and their first absorption bands lie in the near ultraviolet region, whereas the corresponding luminescence bands lie in the optical and IR regions.
A.j. Santos - One of the best experts on this subject based on the ideXlab platform.
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Surface oxidation of amorphous Si and Ge slanted columnar and mesoporous thin films: Evidence, scrutiny and limitations for infrared optics
Applied Surface Science, 2019Co-Authors: A.j. Santos, B. Lacroix, F. Maudet, A. Corvisier, F. Paumier, C. Dupeyrat, T. Girardeau, R. Garcia, F.m. MoralesAbstract:Issues on the superficial oxidation of mesoporous amorphous silicon and Germanium photonic layers generated at oblique angles are reported. Such films were designed to improve the transmittance of optical elements over the mid-IR window (3.6–4.9 μm) by removing the light reflection. These nanostructures were deposited on silicon substrates by e-beam evaporation at room temperature. IR ellipsometry and spectrophotometry studies combined with models based on effective medium approximations predicted the presence of silicon or Germanium Oxides. Such oxidation was evidenced by combining X-ray photoelectron spectroscopy and advanced (scanning-)transmission electron microscopy studies based on energy-dispersive X-rays and electron energy-loss spectroscopies. Both techniques also allowed to prove the formation of core-shell-type architectures consisting of pure Si or Ge surrounded by oxidized species, even for a Ge layer subsequently capped with a dense MgF2 coating. The different approaches used for preparing electron transparent specimens (tripod polishing and focused ion-beams) confirmed a fast oxidation of the Ge nanocolumns even for short air exposure periods, and allowed comparing it with the level of oxidation promoted from other pollutant sources. This work sheds light on the spontaneous undesired oxidation in Si or Ge slanted nanorods which can diminish the performances and limit further development of optical devices.
A. S. Zyubin - One of the best experts on this subject based on the ideXlab platform.
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Optical properties of oxygen vacancies in Germanium Oxides: quantum chemical modeling of photoexcitation and photoluminescence.
The Journal of Physical Chemistry A, 2007Co-Authors: A. S. Zyubin, And Alexander M. Mebel, S. H. LinAbstract:Photoabsorption and photoluminescence properties of single and double oxygen vacancy (OV and DOV) defects in quartz-like Germanium oxide have been investigated by high-level ab initio calculations. It has been found that photoabsorption for these systems occurs at lower energies as compared to the analogous defects in SiO 2 . For OV, the lowest electronic excitations with high oscillator strengths have energies of 6.7-7.0 eV, whereas for DOV, the lowest-energy photoabsorption band is calculated to be in the range of 5.5-5.9 eV. Significant geometry relaxation and large Stokes shift are inherent for these excited states and, as a result, their photoluminescence bands are predicted to peak at 3.1-3.3 eV for OV and at 2.6 eV for DOV. The double oxygen vacancy is suggested to be the most suitable candidate for generating bright blue photoluminescence observed experimentally for substoichiometric quartz-like GeO 2 nanowires, as the calculated optical properties of DOV are in close agreement with the features found in experiment.
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Photoluminescence of oxygen-deficient defects in Germanium Oxides: a quantum chemical study.
The Journal of Chemical Physics, 2006Co-Authors: A. S. Zyubin, A. M. Mebel, S. H. LinAbstract:The photoabsorption and photoluminescence (PL) properties of the surface E′ center, –GeX3, and the combined E′-center–oxygen vacancy, X3Ge–GeX2, defects in substoichiometric Germanium Oxides have been investigated by high-level ab initio calculations, including complete active space self-consistent field, multireference configuration interaction, and symmetry-adapted cluster configuration interaction methods. Both defects have been shown to give rise to photoabsorption bands between 4 and 6eV. Geometry relaxation is significant and the Stokes shifts are large for all calculated excited states. A removal of an electron from the Ge–Ge bond leads to its destruction, whereas the creation of an electron hole at lone pairs of O atoms results in elongations of the Ge–O–Ge bonds in the corresponding bridges. Most often, deexcitations of excited electronic states proceed radiationlessly, through crossing points of their potential energy surfaces with those of the lower states. The –GeX3 defect is able to generate ...
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Photoluminescence of oxygen-containing surface defects in Germanium Oxides: A theoretical study
The Journal of Chemical Physics, 2005Co-Authors: A. S. Zyubin, A. M. Mebel, S. H. LinAbstract:Photoabsorption and photoluminescence properties of nonbridging oxygen –O–Ge(NBO), –OO–Ge (peroxy radical), OGe, and (O2)Ge defects in Germanium Oxides have been investigated by high-level ab initio calculations. Geometry optimization for excited electronic states of model clusters simulating these defects was carried out at the complete-active-space self-consistent-field level, and relative energies were calculated by various methods including time-dependent density-functional theory, outer-valence Green’s functions, equation-of-motion coupled cluster theory with single and double excitations, symmetry-adapted cluster configuration interaction, multireference second-order perturbation theory, and multireference configuration interaction. The results demonstrate that the considered excited states of the aforementioned defects normally exhibit large Stokes shifts and that, with few exceptions, UV photoabsorption is accompanied by red or IR photoluminescence.
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Quantum-chemical simulation of the optical properties of O=X< and O2X< point defects in silicon and Germanium Oxides
Russian Journal of Inorganic Chemistry, 2005Co-Authors: A. S. Zyubin, A. M. Mebel, S. H. LinAbstract:TD-DFT, EOM-CCSD, CAS-PT2, and MRCI calculations of the first excited singlet states of O=X< and O 2 X< point defects in silicon and Germanium Oxides were performed for the simulation of their photoabsorption and luminescence properties. It was found that these systems exhibit a large Stokes shift and their first absorption bands lie in the near ultraviolet region, whereas the corresponding luminescence bands lie in the optical and IR regions.
C. Dupeyrat - One of the best experts on this subject based on the ideXlab platform.
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Surface oxidation of amorphous Si and Ge slanted columnar and mesoporous thin films: Evidence, scrutiny and limitations for infrared optics
Applied Surface Science, 2019Co-Authors: A.j. Santos, B. Lacroix, F. Maudet, A. Corvisier, F. Paumier, C. Dupeyrat, T. Girardeau, R. Garcia, F.m. MoralesAbstract:Issues on the superficial oxidation of mesoporous amorphous silicon and Germanium photonic layers generated at oblique angles are reported. Such films were designed to improve the transmittance of optical elements over the mid-IR window (3.6–4.9 μm) by removing the light reflection. These nanostructures were deposited on silicon substrates by e-beam evaporation at room temperature. IR ellipsometry and spectrophotometry studies combined with models based on effective medium approximations predicted the presence of silicon or Germanium Oxides. Such oxidation was evidenced by combining X-ray photoelectron spectroscopy and advanced (scanning-)transmission electron microscopy studies based on energy-dispersive X-rays and electron energy-loss spectroscopies. Both techniques also allowed to prove the formation of core-shell-type architectures consisting of pure Si or Ge surrounded by oxidized species, even for a Ge layer subsequently capped with a dense MgF2 coating. The different approaches used for preparing electron transparent specimens (tripod polishing and focused ion-beams) confirmed a fast oxidation of the Ge nanocolumns even for short air exposure periods, and allowed comparing it with the level of oxidation promoted from other pollutant sources. This work sheds light on the spontaneous undesired oxidation in Si or Ge slanted nanorods which can diminish the performances and limit further development of optical devices.