1,637 research outputs found
On the Structural and Optical Properties of Sputtered Hydrogenated Amorphous Silicon Thin Films
The present work is essentially focused on the study of optical and
structural properties of hydrogenated amorphous silicon thin films (a-Si:H)
prepared by radio-frequency cathodic sputtering. We examine separately the
influence of hydrogen partial pressure during film deposition, and the effect
of post-deposition thermal annealings on the main optical characteristics of
the layers such as refraction index, optical gap and Urbach energy. Using the
grazing X-rays reflectometry technique, thin film structural properties are
examined immediately after films deposition as well as after surface oxidation
or annealing. We show that low hydrogen pressures allow a saturation of
dangling bonds in the layers, while high doses lead to the creation of new
defects. We show also that thermal annealing under moderate temperatures
improves the structural quality of the deposited layers. For the films examined
just after deposition, the role of hydrogen appears in the increase of their
density. For those analysed after a short stay in the ambient, hydrogen plays a
protective role against the oxidation of their surfaces. This role disappears
for a long time stay in the ambient.
Keywords
Amorphous silicon, Grazing incidence X-rays, Hydrogen, Optical properties,
Penetration depth, Reflectometry, Thermal annealing, Thin films.
PACS Numbers
61.10.K - 61.43.D - 68.55.JK - 68.55.81.15.AComment: 14 figures, 2 tables, 50 reference
Laser-Assisted Semi Relativistic Excitation of Atomic Hydrogen by Electronic Impact
The excitation of H () by electron impact in the presence and in the
absence of the laser field is studied in the framework of the first Born
approximation. The angular variation of the laser-assisted differential cross
section (DCS) for atomic hydrogen by electronic impact is presented at various
kinetic energies for the incident electron. The use of Darwin wave function as
a semirelativistic state to represent the atomic hydrogen gives interesting
results when the condition is fulfilled. A comparison with the non
relativistic theory and experimental data gives good agreement. It was observed
that beyond (2700 ) which represents the limit between the two approaches,
the non relativistic theory does not yield close agreement with our theory and
that, over certain ranges of energy, it can be in error by several orders of
magnitude. The sum rule given by Bunkin and Fedorov and by Kroll and Watson
\cite{22} has been verified in both nonrelativistic and relativistic regimes.Comment: 15 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:1211.0483; and text overlap with arXiv:physics/9911033 by other authors
without attributio
The Thermodynamic Aspect, the Temperature and the Solvent effects on the Chemical Reactivity of the Darzens Reaction between Isobutyraldehyde and Isopropyl Dibromoacetate: DFT Study.
The Darzens condensation is used to synthesize α-halogenoglycidic esters which are important compounds permits access to the bioactive molecules. Our aim in this work is to study the temperature effect in the chemical reactivity and in the thermodynamic aspect for the Darzens reaction between isobutyraldehyde and isopropyl dibromoacetate using density functional theory (DFT) on the B3LYP/6-311G (d, p) level. Therefore, we were interested in this study to comparing the ethanol solvent effect with 2-propanol solvent effect. Firstly, we optimized the reagents and products geometries. Secondly, we calculated the HOMO and LUMO energies; the electronic chemical potential; the global electrophilicity and the global nucleophilicity of the reagents; and Gibbs free energy. The local electrophilicity of isobutyraldehyde and local nucleophilicity of isopropyl dibromoacetate are calculated by the Parr function
A DFT computational study on the molecular mechanism of reaction between methyl 3-hydroxy-3-methyl-2 methylene butanoate and (E)-N-methyl-1-phenylethan-1-imine oxide
In this work we examined the regioselectivity and mechanism the of the cycloaddition reaction of methyl 3-hydroxy-3-methyl-2-methylenebutanoate and (E)-N-methyl-1-phenylethan-1-imine oxide within the DFT. This cycloaddition reaction evolved through non-concerted mechanism. Analysis of the relative free energies associated with the competitive reaction paths shows that the cycloaddition reactions of methyl 3-hydroxy-3-methyl-2-methylenebutanoate and (E)-N-methyl-1-phenylethan-1-imine oxide are highly stereoselective and regioselective, in clear agreement with the experimental outcomes
Quantum Study of the Reaction Between 2,5-Bis (Pyridin-2-yl) -1,3,4-Thiadiazole and Nickel(II) in the presence of Sodium Azide by Using DFT-B3LYP/6-31G
In the present work we used density functional theory (DFT) with B3LYP/6-31G to study the reaction between 2,5-bis (pyridin-2-yl) -1, 3,4-thiadiazole and sodium azide with nickel(II) triflateby determining theMulliken charges and the energies of the frontier molecular orbitals, chemical potentials, transfer charge quantities, and electrophilicity and nucleophilicity indices. We used the same method to calculate ionisation potentials, electronic affinities, hardness and softness of the various possible organo-metallic complexesobtained in the course of the reaction. We optimised the geometric parameters of the most stable conformers and compared them with those obtained experimentall
Electron's anomalous magnetic moment effects on laser assisted ionization of atomic hydrogen by electronic impact
Electron-impact ionization of atomic hydrogen with the electron's anomalous
mag- netic moment (AMM) effects are examined. The formulas for the
laser-assisted relativis- tic triple differential cross section (TDCS) in the
coplanar binary geometry developed earlier by Y. Attaourti and S. Taj [Phys.
Rev. A 69, 063411 (2004)] are used to check the consistency of our computations
when the anomaly is taken to be zero. We show that the contribution of
the terms containing the AMM effects even in the first Born approximation has
an important contribution, so it must be included in any reliable analysis. A
full analytical calculation for the TDCS is presented.Comment: One latex file and five eps figure
Fractional Quantum Hall Filling Factors from String Theory using Toric Geometry
Using toric Cartan matrices as abelian gauge charges, we present a class of
stringy fractional quantum Hall effect (FQHE) producing some recent
experimental observed filling factor values. More precisely, we derive the
corresponding Chern-Simons type models from M-theory compactified on four
complex dimensional hyper-K\"{a}hler manifolds X^4. These manifolds, which are
viewed as target spaces of a particular N=4 sigma model in two dimensions, are
identified with the cotangent bundles over intersecting 2-dimensional toric
varieties V_i^2 according to toric Cartan matrices. Exploring results of string
dualities, the presented FQHE can be obtained from D6-banes wrapping on such
intersecting toric varieties interacting with R-R gauge fields. This string
theory realization provides a geometric interpretation of the filling factors
in terms of toric and Euler characteristic topological data of the compactified
geometry. Concretely, explicit bilayer models are worked out in some details.Comment: 17 pages, late
Optical characterization of a-Si:H thin films grown by Hg-Photo-CVD
Mercury-Sensitized Photo-Assisted Chemical Vapor Deposition (Hg-Photo-CVD)
technique opens new possibilities for reducing thin film growth temperature and
producing novel semiconductor materials suitable for the future generation of
high efficiency thin film solar cells onto low cost flexible plastic
substrates. This paper provides some experimental data resulting from the
optical characterization of hydrogenated amorphous silicon thin films grown by
this deposition technique. Experiments have been performed on both as-deposited
layers and thermal annealed ones.
Keywords: Photovoltaic, Solar Cell, Thin films, Nano-Crystalline Silicon,
Hydrogenated Amorphous Silicon, Optical Properties, Thermal Annealing PACS
Numbers: 68.60.Dv, 78.66.Jg, 78.66.-w, 73.50.Pz, 81.15.-z, 84.60.JtComment: 17 pages, 8 figures, 73 references. ICTP Preprint, August 2006
(Submitted to the Moroccan Journal of Condensed Matte
UNDERSTANDING THE MECHANISM OF THE REGIOSELECTIVITY OF 1,3-DIPOLAR CYCLOADDITION REACTIONS BETWEEN PROP-2- YN-1-OL AND AZIDO COMPOUNDS USING DFT COMPUTATIONS
The mechanism of the regioselectivity of 1,3-dipolar cycloaddition reactions between prop-2-yn-1-ol 4 and azido-benzene, 4-azido-benzonitrile and 1-azido-4-nitro-benzene have been theoretically studied using DFT methods at the B3LYP/6-311 G(d, p) computational level. The possible ortho/meta regioselective channels were explored and characterized. Analysis of the free energies associated with the different reaction pathways indicates that these reactions are highly meta regioselectives, in agreement with the experimental results
A THEORETICAL STUDY OF THE MECHANISM AND REGIOSELECTIVITY OF THE 1,3-DIPOLAR CYCLOADDITION REACTION OF AZIDES WITH ALKYNES
The mechanism and regioselectivities of the [3+2] cycloaddition reactions of the ethynylbenzene 4 and azide compounds 1, 2 and 3, have been theoretically studied using DFT methods at the B3LYP/6-31G(d) computational level. The possible ortho/meta regioselective channels were explored and characterized. The low polar character of these 32CA reactions is the consequence of the high nucleophilic character of both reagents. Analysis of the free energies associated with the different reaction pathways indicates that the 32CA reactions of the ethynyl-benzene 4 and azide compounds 1, 2 and 3 are highly meta regioselective, in agreement with the experimental observations
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