Experimental and Theoretical Joint Study on the Electronic and Structural Properties of Silicon Nanocrystals Embedded in SiO2: active Role of the Interface Region

2003 ◽  
Vol 770 ◽  
Author(s):  
N. Daldosso ◽  
M. Luppi ◽  
G. Dalba ◽  
L. Pavesi ◽  
F. Rocca ◽  
...  
Keyword(s):  
Total Energy ◽  
Silicon Nanocrystals ◽  
Density Functional ◽  
Light Emission ◽  
Local Environment ◽  
Active Role ◽  
Localized States ◽  
Total Electron ◽  
Energy Calculations ◽  
Si Content

AbstractThe local environment of light emitting silicon nanocrystals (Si-nc) embedded in amorphous SiO2 has been studied by x-ray absorption spectroscopy (XAS) and by ab-initio total energy calculations. Si-nc have been formed by PECVD deposition of SiOx with different Si content (from 35 to 42 at.%) and thermal annealing at high temperature (1250 °C). The comparison between total electron yield (TEY) and photoluminescence yield (PLY) spectra has allowed the identification of a modified region of SiO2 (about 1 nm thick) surrounding the Si-nc, which participates to the light emission of Si-nc. Total energy calculations, within the density functional theory, clearly show that Si-nc are surrounded by a cap-shell of stressed SiO2 with a thickness of about 1 nm. The optoelectronic properties show the appearance of localized states not only in the Si-nc core region but also in the modified SiO2 region.

scholarly journals Density-functional Based Tight-binding Calculations on Thiophene Polymorphism

VLSI Design ◽  
2001 ◽  
Vol 13 (1-4) ◽  
pp. 393-397
Author(s):  
J. Widany ◽  
G. Daminelli ◽  
A. Di Carlo ◽  
P. Lugli
Keyword(s):  
Total Energy ◽  
Intermolecular Interaction ◽  
Density Functional ◽  
Tight Binding ◽  
Methyl Groups ◽  
Direct Function ◽  
Energy Calculations ◽  
Polymorphic Modifications

Total energy calculations based on a density-functional tight-binding scheme have been performed on polymorphic modifications of various thiophene crystals. The investigated structures include sulphanyl-substituted quater-thiophene and methyl-substituted sexithiophene, in the monoclinic and triclinic modifications. Attention has been focused on the intermolecular interaction between the molecular units. Despite the similarities in the backbone geometries, the strength and nature of intermolecular interaction differs largely in the various polymorphs. Sulphur atoms belonging to the thiophene rings are strongly involved in the interaction. Sulphanyl substituents play an important role, while methyl groups do not contribute. The strength of intermolecular interaction is not a direct function of atom distance.

DISSOCIATION OF PH3 AND AsH3 ON Ge(100)(2x1) SURFACE

2007 ◽  
Vol 14 (03) ◽  
pp. 507-515 ◽  
Author(s):  
ŞENAY KATIRCIOĞLU
Keyword(s):  
Density Functional Theory ◽  
Total Energy ◽  
Density Functional ◽  
Functional Theory ◽  
Energy Calculations ◽  
Dissociation Path ◽  
Stable Structures ◽  
Relative Total Energy

The most stable structures for the dissociation of phosphine and arsine on Ge (100)(2x1) surface have been investigated by relative total energy calculations based on Density Functional Theory. It has been found that the thermodynamically preferred structures in the dissociation path of phosphine and arsine are the same; PH 2 and AsH 2 products prefer to be on a single Ge dimer bond, but PH and AsH prefer to be between the adjacent Ge dimers. According to the optimization calculations, the dissociation path started with the adsorption of PH 3( AsH 3) on the electron deficient side of the Ge dimer bond is ended with the formation of P – P ( As – As ) dimers parallel to the dimers of Ge .

New Insight in Scandium-Mediated Growth Techniques: Sc-Related Defects in 4H-SiC and 6H-SiC

2007 ◽  
Vol 556-557 ◽  
pp. 469-472 ◽  
Author(s):  
Uwe Gerstmann ◽  
Siegmund Greulich-Weber ◽  
E. Rauls ◽  
Johann Martin Spaeth ◽  
Ekaterina N. Kalabukhova ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Total Energy ◽  
Density Functional ◽  
Epr Spectra ◽  
Functional Theory ◽  
Energy Calculations ◽  
Large Anisotropy

Scandium can be used to influence the stoichiometry of SiC during growth of the hexagonal polytypes. Using PL-EPR and total energy calculations in the framework of density functional theory, scandium is predicted to be built in predominantly at the Si-sublattice in form of ScSi acceptors with acceptor levels at 0.55 eV (6H-SiC) and 0.48 eV (4H-SiC). In addition, new PL-EPR spectra are found with a large anisotropy in the g-tensor suggesting defect pairs as an origin.

NONEMPIRICAL SIMULATIONS OF Σ3 TUNGSTEN GRAIN BOUNDARY WITH BORON ATOMS

1999 ◽  
Vol 06 (05) ◽  
pp. 705-718 ◽  
Author(s):  
DAVID FUKS ◽  
KLEBER MUNDIM ◽  
VLAD LIUBICH ◽  
SIMON DORFMAN
Keyword(s):  
Density Functional Theory ◽  
Grain Boundary ◽  
Total Energy ◽  
Ab Initio ◽  
Density Functional ◽  
Atomistic Simulations ◽  
Interatomic Potentials ◽  
Potential Approximation ◽  
Functional Theory ◽  
Energy Calculations

We perform the atomistic simulations of the properties of the Σ3< 111> grain boundary in W and demonstrate the influence of boron additive on the resistance of the grain boundary with respect to different shifts. The interatomic potentials used in these simulations are obtained from ab initio total energy calculations. These calculations are carried out in the framework of density functional theory in the coherent potential approximation. The recursion procedure to extract A–B type interatomic potentials is suggested.

Ab initio total energy studies of minerals using density functional theory and the local density approximation

1995 ◽  
Vol 59 (397) ◽  
pp. 589-596 ◽  
Author(s):  
Björn Winkler ◽  
Victor Milman ◽  
Michael C. Payne
Keyword(s):  
Total Energy ◽  
Ab Initio ◽  
Local Density Approximation ◽  
Density Functional ◽  
Local Density ◽  
Lattice Energy ◽  
Density Approximation ◽  
Proton Proton ◽  
Energy Calculations ◽  
Good Agreement

AbstractAb initio total energy calculations based on the local density approximation (LDA) and using a conjugate-gradient solver for the Kohn-Sham equations have been performed for cordierite, brucite, (Mg(OH)2) and diaspore (AlOOH). The calculated fractional coordinates of all structures are in good agreement with experimental diffraction data. The angle of the non-linear hydrogen bond in diaspore is reproduced well. The Raman active OH stretching frequency in brucite has been calculated using the frozen phonon approach and the calculated stretching frequency is in very good agreement with the observed value. The energetically most favourable calculated orientation of the proton-proton vector of an H2O molecule incorporated in the structural channels of cordierite agrees with findings deduced from spectroscopic data, and the calculated energy of hydration is in reasonable agreement with calorimetric data. It is therefore concluded that ab initio total energy calculations can confidently be used to predict properties of hydrogen bonded structures, which is difficult with conventional parameterized static lattice energy minimization calculations. An extension to the model is necessary to improve the agreement of the predicted to the observed lattice parameters for small structures.

Total Energy Calculations of RfCl4and Homologues in the Framework of Relativistic Density Functional Theory

2000 ◽  
Vol 104 (27) ◽  
pp. 6495-6498 ◽  
Author(s):  
S. Varga ◽  
B. Fricke ◽  
M. Hirata ◽  
T. Baştuǧ ◽  
V. Pershina ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Total Energy ◽  
Density Functional ◽  
Functional Theory ◽  
Energy Calculations

Nanometer Scale Spectroscopic Visualization of Catalytic Sites During a Hydrogenation Reaction on a Pd/Au Bimetallic Catalyst

2020 ◽  
Author(s):  
hao yin ◽  
Liqing Zheng ◽  
Wei Fang ◽  
Yin-Hung Lai ◽  
Nikolaus Porenta ◽  
...  
Keyword(s):  
Catalytic Hydrogenation ◽  
Density Functional ◽  
Hydrogen Transfer ◽  
Bimetallic Catalyst ◽  
Local Environment ◽  
Hydrogenation Reaction ◽  
Boundary Density ◽  
Catalytic Sites ◽  
Powerful Analytical Tool ◽  
Tip Enhanced Raman Spectroscopy

<p>Understanding the mechanism of catalytic hydrogenation at the local environment requires chemical and topographic information involving catalytic sites, active hydrogen species and their spatial distribution. Here, tip-enhanced Raman spectroscopy (TERS) was employed to study the catalytic hydrogenation of chloro-nitrobenzenethiol on a well-defined Pd(sub-monolayer)/Au(111) bimetallic catalyst (<i>p</i><sub>H2</sub>=1.5 bar, 298 K), where the surface topography and chemical fingerprint information were simultaneously mapped with nanoscale resolution (≈10 nm). TERS imaging of the surface after catalytic hydrogenation confirms that the reaction occurs beyond the location of Pd sites. The results demonstrate that hydrogen spillover accelerates hydrogenation at the Au sites within 20 nm from the bimetallic Pd/Au boundary. Density functional theory was used to elucidate the thermodynamics of interfacial hydrogen transfer. We demonstrate that TERS as a powerful analytical tool provides a unique approach to spatially investigate the local structure-reactivity relationship in catalysis.</p>

Nanometer Scale Spectroscopic Visualization of Catalytic Sites During a Hydrogenation Reaction on a Pd/Au Bimetallic Catalyst

2020 ◽  
Author(s):  
Hao Yin ◽  
Liqing Zheng ◽  
Wei Fang ◽  
Yin-Hung Lai ◽  
Nikolaus Porenta ◽  
...  
Keyword(s):  
Catalytic Hydrogenation ◽  
Density Functional ◽  
Hydrogen Transfer ◽  
Bimetallic Catalyst ◽  
Local Environment ◽  
Hydrogenation Reaction ◽  
Boundary Density ◽  
Catalytic Sites ◽  
Powerful Analytical Tool ◽  
Tip Enhanced Raman Spectroscopy

<p>Understanding the mechanism of catalytic hydrogenation at the local environment requires chemical and topographic information involving catalytic sites, active hydrogen species and their spatial distribution. Here, tip-enhanced Raman spectroscopy (TERS) was employed to study the catalytic hydrogenation of chloro-nitrobenzenethiol on a well-defined Pd(sub-monolayer)/Au(111) bimetallic catalyst (<i>p</i><sub>H2</sub>=1.5 bar, 298 K), where the surface topography and chemical fingerprint information were simultaneously mapped with nanoscale resolution (≈10 nm). TERS imaging of the surface after catalytic hydrogenation confirms that the reaction occurs beyond the location of Pd sites. The results demonstrate that hydrogen spillover accelerates hydrogenation at the Au sites within 20 nm from the bimetallic Pd/Au boundary. Density functional theory was used to elucidate the thermodynamics of interfacial hydrogen transfer. We demonstrate that TERS as a powerful analytical tool provides a unique approach to spatially investigate the local structure-reactivity relationship in catalysis.</p>

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