scholarly journals Spectroscopic Analysis of Rare-Earth Silicide Structures on the Si(111) Surface

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4104
Author(s):  
Simone Sanna ◽  
Julian Plaickner ◽  
Kris Holtgrewe ◽  
Vincent M. Wettig ◽  
Eugen Speiser ◽  
...  
Keyword(s):  
Rare Earth ◽  
Density Functional ◽  
Ohmic Contacts ◽  
Spectroscopic Analysis ◽  
Structural Model ◽  
Phonon Modes ◽  
Strong Argument ◽  
Silicide Layer ◽  
Atomistic Calculations ◽  
Rare Earth Silicide

Two-dimensional rare-earth silicide layers deposited on silicon substrates have been intensively investigated in the last decade, as they can be exploited both as Ohmic contacts or as photodetectors, depending on the substrate doping. In this study, we characterize rare-earth silicide layers on the Si(111) surface by a spectroscopic analysis. In detail, we combine Raman and reflectance anisotropy spectroscopy (RAS) with first-principles calculations in the framework of the density functional theory. RAS suggests a weakly isotropic surface, and Raman spectroscopy reveals the presence of surface localized phonons. Atomistic calculations allow to assign the detected Raman peaks to phonon modes localized at the silicide layer. The good agreement between the calculations and the measurements provides a strong argument for the employed structural model.

scholarly journals Phonons in Short-Period GaN/AlN Superlattices: Group-Theoretical Analysis, Ab initio Calculations, and Raman Spectra

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 286
Author(s):  
Valery Davydov ◽  
Evgenii Roginskii ◽  
Yuri Kitaev ◽  
Alexander Smirnov ◽  
Ilya Eliseyev ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Raman Spectra ◽  
Density Functional ◽  
Structural Characteristics ◽  
Vibrational Modes ◽  
Phonon Modes ◽  
Short Period ◽  
Group Theoretical Analysis

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.

scholarly journals Adsorption and Desorption Mechanisms of Rare Earth Elements (REEs) by Layered Double Hydroxide (LDH) Modified with Chelating Agents

2019 ◽  
Vol 9 (22) ◽  
pp. 4805 ◽  
Author(s):  
Shuang Zhang ◽  
Naoki Kano ◽  
Kenji Mishima ◽  
Hirokazu Okawa
Keyword(s):  
Rare Earth ◽  
Quantum Chemistry ◽  
Rare Earth Elements ◽  
Adsorption Capacity ◽  
Density Functional ◽  
Stable State ◽  
Experimental Result ◽  
Adsorption And Desorption ◽  
Adsorption Affinity ◽  
Quantum Chemistry Calculations

In order to obtain the adsorption mechanism and adsorption structures of Rare Earth Elements (REEs) ions adsorbed onto layered double hydroxides (LDH), the adsorption performance of LDH and ethylenediaminetetraacetic acid (EDTA) intercalated LDH for REEs was investigated by batch experiments and regeneration studies. In addition to adsorption capacity, the partition coefficient (PC) was also evaluated to assess their true performance metrics. The adsorption capacity of LDH increases from 24.9 μg·g−1 to 145 μg·g−1 for Eu, and from 20.8 μg·g−1 to 124 μg·g−1 for La by intercalating EDTA in this work; and PC increases from 45.5 μg·g−1·uM−1 to 834 μg·g−1·uM−1 for Eu, and from 33.6 μg·g−1·μM−1 to 405 μg·g−1·μM−1 for La. Comparison of the data indicates that the adsorption affinity of EDTA-intercalated LDH is better than that of precursor LDH no matter whether the concept of adsorption capacity or that of the PC was used. The prepared adsorbent was characterized by XRD, SEM-EDS and FT-IR techniques. Moreover, quantum chemistry calculations were also performed using the GAUSSIAN09 program package. In this calculation, the molecular locally stable state structures were optimized by density functional theory (DFT). Both the quantum chemistry calculations and the experimental data showed that REEs ions adsorbed by EDTA-intercalated LDH are more stable than those adsorbed by precursor LDH. Furthermore, the calculation results of adsorption and desorption rates show that adsorption rates are larger for Eu(III) than for La(III), which agrees with the experimental result that Eu(III) has a higher adsorption ability under the same conditions. The LDHs synthesized in this work have a high affinity for removing REEs ions.

Ordered arrays of rare-earth silicide nanowires on Si(001)

2003 ◽  
Vol 251 (1-4) ◽  
pp. 657-661 ◽  
Author(s):  
Regina Ragan ◽  
Yong Chen ◽  
Douglas A.A. Ohlberg ◽  
Gilberto Medeiros-Ribeiro ◽  
R.Stanley Williams
Keyword(s):  
Rare Earth ◽  
Ordered Arrays ◽  
Rare Earth Silicide

Magnetic properties of rare earth silicide single crystals RSi2− (R = Pr, Nd, Gd)

1990 ◽  
Vol 89 (1-2) ◽  
pp. 86-96 ◽  
Author(s):  
J. Pierre ◽  
S. Auffret ◽  
E. Siaud ◽  
R. Madar ◽  
E. Houssay ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Rare Earth ◽  
Single Crystals ◽  
Rare Earth Silicide

Density Functional Theory and X-ray Analysis of the Structural Variability in η5,η5,η1-Tris(ring) Rare Earth/Actinide Tetramethylpyrrolyl Complexes, (C5Me5)2M(NC4Me4)

2012 ◽  
Vol 52 (7) ◽  
pp. 3565-3572 ◽  
Author(s):  
Christopher L. Webster ◽  
Jefferson E. Bates ◽  
Ming Fang ◽  
Joseph W. Ziller ◽  
Filipp Furche ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Rare Earth ◽  
Density Functional ◽  
Functional Theory ◽  
X Ray ◽  
Structural Variability

The structure and activity of potassium supported on SBA-15 molecular sieve: Density functional theory study

2014 ◽  
Vol 13 (01) ◽  
pp. 1350076 ◽  
Author(s):  
Bing Liu ◽  
Daxi Wang ◽  
Zhongxue Wang ◽  
Zhen Zhao ◽  
Yu Chen ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Lewis Acid ◽  
Molecular Sieve ◽  
Active Sites ◽  
Density Functional ◽  
Structural Model ◽  
Vibrational Frequencies ◽  
Oxygen Molecule ◽  
Lewis Base ◽  
Functional Theory

The geometries, vibrational frequencies, electronic properties and reactivity of potassium supported on SBA-15 have been theoretically investigated by the density functional theory (DFT) method. The structural model of the potassium supported on SBA-15 was constructed based on our previous work [Wang ZX, Wang DX, Zhao Z, Chen Y, Lan J, A DFT study of the structural units in SBA-15 mesoporous molecular sieve, Comput. Theor. Chem.963, 403, 2011]. This paper is the extension of our previous work. The most favored location of potassium atom was obtained by the calculation of substitution energy. The calculated vibrational frequencies of K /SBA-15 are in good agreement with the experimental results. By analyzing the properties of electronic structure, we found that the O atom of Si - O (2)- K group acts as the Lewis base center and the K atom acts as the Lewis acid center. The reactivity of K /SBA-15 was investigated by calculating the activation of oxygen molecule. The oxygen molecule can be activated by K /SBA-15 with an energy barrier of 103.2 kJ/mol. In the final state, the activated oxygen atoms become new Lewis acid centers, which are predicted to act as the active sites in the catalytic reactions. This study provides a deep insight into the properties of supported potassium catalysts and offers fundamental information for further research.

scholarly journals Demystifying the Soai Reaction

2019 ◽  
Author(s):  
Soumitra Athavale ◽  
Adam Simon ◽  
Kendall N. Houk ◽  
Scott Denmark
Keyword(s):  
Density Functional ◽  
Spectroscopic Analysis ◽  
Chiral Symmetry Breaking ◽  
Kinetic Studies ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Group Transfer ◽  
Linear Behavior ◽  
Structural Mutations ◽  
Soai Reaction

The extraordinary Soai reaction has profoundly impacted chemists’ perspective of chiral symmetry breaking, absolute asymmetric synthesis and its role in the origin of biological homochirality. Herein, we describe the unprecedented observation of asymmetry amplifying autocatalysis in the alkylation of 5-(trimethylsilylethynyl)pyridine-3-carbaldehyde using diisopropylzinc. Kinetic studies with a “Trojan-horse” substrate and spectroscopic analysis of a series of zinc-alkoxides that incorporate specific structural mutations reveal a ‘pyridine-assisted cube escape’. The new cluster functions as a catalyst that activates the ‘floor-to-floor’ bound aldehyde and poises a coordinated diisopropylzinc moiety for alkyl group transfer. Transitionstate models leading to both the homochiral and heterochiral products were validated by density functional theory calculations. Moreover, experimental and computational analysis of the heterochiral complex provides a definitive explanation for the non-linear behavior of this system. Our deconstruction of the Soai system contributes substantially to understanding the mechanism of this transformation that has stood as a longstanding challenge in chemistry.<br>

scholarly journals Computational Modelling of Structural, Electronic, Optical and Vibrational Properties of PVK/C60 Nanoheterostructure Interfaces

2020 ◽  
Vol 11 (3) ◽  
pp. 10864-10884
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Computational Modelling ◽  
Phonon Modes ◽  
Functional Studies ◽  
Density Functional Perturbation Theory ◽  
Structural Differences ◽  
Dynamical Lattice ◽  
Quantum Espresso ◽  
Stacking Patterns

In this work, we present first-principles density functional studies of the dynamical properties of three nanoheterostructure interfaces of poly(9-vinylcarbazole)/fullerene (PVK/C60): PVK/C60(α), PVK/C60(β), and PVK/C60(γ). Linear response within density functional perturbation theory (DFPT), as implemented in the Quantum Espresso code, has been employed to explore the nature of permittivity, Born effective charges, polarizabilities, and vibrational frequency modes. The vibrational frequencies for the three nanoheterostructure interfaces were computed and their modes assigned. The phonon modes were also classified, and we showed that some important frequency modes are associated with C-C, CH2, and C−N stretching modes, among others. In addition, computed values of polarizability and permittivity for the nanoheterostructures were seen to have comparable values to that of literature for conjugated polymers. Conspicuous differing characteristics were noticed in the computed infrared and Raman absorption spectra for the three nanoheterostructures, which was due to the structural differences arising from their different stacking patterns. It is noted that the presence of the nitrogen atom plays a significant role in determining their dynamical lattice properties. The permittivity and polarizability tensors of PVK/C60(α), PVK/C60(β), and PVK/C60(γ) nanoheterostructures were found to be strongly anisotropic.

Sign in / Sign up

Export Citation Format

Share Document