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Ngoc HV, Tung NT, Nguyen DK, On VV, Rivas-Silva J, Cocoletzi GH, Hoat D. First-principles calculations to investigate Structural, electronic, and optical properties of MgF2 monolayer in 1T-phase and 2H-phase using hybrid functional. Chem Phys 2022. [DOI: 10.1016/j.chemphys.2022.111473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Yagmurcukardes M, Sozen Y, Baskurt M, Peeters FM, Sahin H. Interface-dependent phononic and optical properties of GeO/MoSO heterostructures. NANOSCALE 2022; 14:865-874. [PMID: 34985489 DOI: 10.1039/d1nr06534c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The interface-dependent electronic, vibrational, piezoelectric, and optical properties of van der Waals heterobilayers, formed by buckled GeO (b-GeO) and Janus MoSO structures, are investigated by means of first-principles calculations. The electronic band dispersions show that O/Ge and S/O interface formations result in a type-II band alignment with direct and indirect band gaps, respectively. In contrast, O/O and S/Ge interfaces give rise to the formation of a type-I band alignment with an indirect band gap. By considering the Bethe-Salpeter equation (BSE) on top of G0W0 approximation, it is shown that different interfaces can be distinguished from each other by means of the optical absorption spectra as a consequence of the band alignments. Additionally, the low- and high-frequency regimes of the Raman spectra are also different for each interface type. The alignment of the individual dipoles, which is interface-dependent, either weakens or strengthens the net dipole of the heterobilayers and results in tunable piezoelectric coefficients. The results indicate that the possible heterobilayers of b-GeO/MoSO asymmetric structures possess various electronic, optical, and piezoelectric properties arising from the different interface formations and can be distinguished by means of various spectroscopic techniques.
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Affiliation(s)
- M Yagmurcukardes
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Y Sozen
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
| | - M Baskurt
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - H Sahin
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
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Kaltsas D, Pappas P, Tsetseris L. Formation and properties of iodine- and acetonitrile-functionalized two-dimensional Si materials: a Density Functional Theory study. Phys Chem Chem Phys 2021; 24:411-418. [PMID: 34897312 DOI: 10.1039/d1cp03442a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Topotactic transformations of suitable layered three-dimensional precursors are among the most robust methods to prepare two-dimensional (2D) materials based on silicon or germanium. Here we use Density Functional Theory calculations to probe the mechanisms underlying the formation of 2D-Si sheets functionalized with iodine atoms (SiI) or acetonitrile molecules [Si(MeCN)] starting from a layered CaSi2 precursor. We identify the sequence of exothermic surface reactions that enable the adsorption of, not only iodine atoms, but, surprisingly, also of solvent acetonitrile molecules on both sides of the top layer of a Si-terminated CaSi2 surface and its ensuing exfoliation as a standalone 2D sheet. In the acetonitrile case, the as-formed 2D material exhibits intriguing structural and electronic properties with an unusual quasi-one-dimensional substructure of silicon chains and a Dirac-like cone in the energy band diagram. The results elucidate the atomic-scale details of the established experimental technique of topotactic synthesis of functionalized silicene and identify new structural motifs for 2D materials.
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Affiliation(s)
- Dimitrios Kaltsas
- Department of Physics, National Technical University of Athens, Heroon Polytechniou 9 Zographou Campus, 15780, Athens, Greece.
| | - Panagiotis Pappas
- Department of Physics, National Technical University of Athens, Heroon Polytechniou 9 Zographou Campus, 15780, Athens, Greece.
| | - Leonidas Tsetseris
- Department of Physics, National Technical University of Athens, Heroon Polytechniou 9 Zographou Campus, 15780, Athens, Greece.
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Plokker MP, van der Knijff IC, de Wit AV, Voet B, Woudstra T, Khanin V, Dorenbos P, van der Kolk E. Experimental and numerical analysis of Tm 2+excited-states dynamics and luminescence in Ca X2( X= Cl, Br, I). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:255701. [PMID: 33882460 DOI: 10.1088/1361-648x/abfa5d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 04/21/2021] [Indexed: 06/12/2023]
Abstract
The prospect of using Tm2+-doped halides for luminescence solar concentrators (LSCs) requires a thorough understanding of the temperature dependent Tm2+excited states dynamics that determines the internal quantum efficiency (QE) and thereby the efficiency of the LSC. In this study we investigated the dynamics in CaX2:Tm2+(X= Cl, Br, I) by temperature- and time-resolved measurements. At 20 K up to four distinct Tm2+emissions can be observed. Most of these emissions undergo quenching via multi-phonon relaxation below 100 K. At higher temperatures, only the lowest energy 5d-4f emission and the 4f-4f emission remain. Fitting a numerical rate equation model to the data shows that the subsequent quenching of the 5d-4f emission is likely to occur initially via multi-phonon relaxation, whereas at higher temperatures additional quenching via interband crossing becomes thermally activated. At room temperature only the 4f-4f emission remains and the related QE becomes close to 30%. Possible reasons for the quantum efficiency not reaching 100% are provided.
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Affiliation(s)
- M P Plokker
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - I C van der Knijff
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - A V de Wit
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - B Voet
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - T Woudstra
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - V Khanin
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - P Dorenbos
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
| | - E van der Kolk
- Luminescence Materials Research Group, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
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Affiliation(s)
- Xiaoyang Zhu
- Department of Chemistry, Columbia University, New York, New York 10027, USA
| | - David R Reichman
- Department of Chemistry, Columbia University, New York, New York 10027, USA
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Harutyunyan VS. Correlation of the Madelung constant and I-M-I bonding angle with cohesive energy contributions in layered metal diiodides (MI 2) with CdI 2 (2H polytype) structure. ACTA CRYSTALLOGRAPHICA SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS 2020; 76:1045-1054. [PMID: 33289716 DOI: 10.1107/s2052520620013463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2020] [Accepted: 10/07/2020] [Indexed: 06/12/2023]
Abstract
This study uses theoretically methods to investigate, for metal diiodides MI2 (M = Mg, Ca, Mn, Fe, Cd, Pb) with CdI2 (2H polytype) structure, the mutual correlation between the structure-characterizing parameters (the flatness parameter of monolayers f, the Madelung constant A, and bonding angle I-M-I) and correlation of these parameters with contributions of the Coulomb and covalent energies to cohesive energy. The energy contributions to cohesive energy are determined with the use of empirical atomic potentials. It is demonstrated that the parameters f and A, and the bonding angle I-M-I are strictly correlated and increase in the same order: FeI2 < PbI2 < MnI2 < CdI2 < MgI2 < CaI2. It is found that with an increase of parameter A and bonding angle I-M-I the relative contribution of the Coulomb energy to cohesive energy increases, whereas the relative contribution of the covalent energy decreases. For a hypothetical MX2 layered compound with the CdI2 (2H polytype) structure, composed of regular MX6 octahedra (angle X-M-X = 90°), the flatness parameter and the Madelung constant are found to be freg = 2.449 and Areg = 2.183, respectively. Correlation of the covalent energy with the type of distortion of MI6 octahedra (elongation or compression) with respect to regular configuration (angle I-M-I = 90°) is also analyzed.
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Affiliation(s)
- Valeri S Harutyunyan
- Solid State Physics, Yerevan State University, A. Manukian 1/ 0025, Yerevan, 0025, Armenia
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