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1.
In this paper, nitridation process of GaAs (1 0 0) substrates was studied in-situ using X-ray photoelectron spectroscopy (XPS) and ex-situ by means of electrical method I-V and photoluminescence surface state spectroscopy (PLS3) in order to determine chemical, electrical and electronic properties of the elaborated GaN/GaAs interfaces.The elaborated structures were characterised by I-V analysis. The saturation current IS, the ideality factor n, the barrier height ΦBn and the serial resistance RS are determined.The elaborated GaN/GaAs structures are also exhibited a high PL intensity at room temperature. From the computer-aided analysis of the power-dependent PL efficiency measurements (PLS3 technique), the value of the interface state density NSS(E) close to the mid-gap was estimated to be in the range of 2-4 × 1011 eV−1 cm−2, indicating a good electronic quality of the obtained interfaces.Correlation among chemical, electronic and electrical properties of the GaN/GaAs interface was discussed. 相似文献
2.
Bauduin C Moulin D Kaloun el B Darcel C Jugé S 《The Journal of organic chemistry》2003,68(11):4293-4301
The stereoselective synthesis of P-chirogenic chlorophosphine boranes 4 was investigated by HCl acidolysis of the corresponding aminophosphine boranes 10. The reaction afforded the P-N bond cleavage with inversion of the configuration at the phosphorus center, leading to the chlorophosphine boranes 4 with high to excellent enantiomeric purities (80-99% ee), except in the case of the chloro-1-naphthylphenylphosphine borane 4d. Reaction conditions and workup significantly influence the enantiomeric purity of the product, with the exception of the o-anisyl- and o-tolylchlorophenylphosphine boranes, 4b and 4c, which were found to be particularly stable even after purification by chromatography on silica gel. Reaction of the chlorophosphine boranes 4 with various nucleophiles, such as carbanions, phenolates, thiophenolates, or amides, afforded the corresponding organophosphorus borane complexes via P-C, P-O, P-S, and P-N bond formation, respectively, in 34-93% yield and with up to 99% ee. This work demonstrates the importance of chlorophosphine boranes 4 as new and powerful electrophilic building blocks for the highly stereoselective synthesis of P-chirogenic organophosphorus compounds. 相似文献
3.
Berrichi Amina Bailiche Zahra Bachir Redouane 《Research on Chemical Intermediates》2022,48(10):4119-4134
The AHA coupling of amines, haloalkane and alkynes under UV visible light was achieved with a higher yield in the presence of Au/Fe2O3. The catalyst was prepared by two methods using different gold content and then characterized by XRD, UV–vis, BET, TEM, ICP-OES and TPR spectroscopies. A comparative study of the ordinary and photocatalytic conditions, showed that the UV visible light could activate the gold nanoparticles and lead to the formation of CH2Cl? and Cl? radicals through CH2Cl2 fragmentation. The propargylamine was afforded at low temperature and a short time using 2% Au/Fe2O3. The catalyst was stable for five cycles with good photoactivity.
Graphical abstract4.
L.K. ElbouaananiB. Malaman R. Gérardin B. Ouladdiaf 《Journal of solid state chemistry》2002,164(1):71-80
Fe3P5SiO19 has been prepared by solid state reaction of Fe(PO3)3, FePO4, and SiO2 at 1000°C. The structure has been determined from a single crystal through direct methods and difference Fourier synthesis and refined to R=0.052. The unit cell is hexagonal, space group P63, with a=14.4804(8) Å, c=7.4256(2) Å, and Z=4. The three-dimensional framework is built up from [Fe2O9] units of two faces sharing octahedra and Si2O7 disilicates linked by PO4 tetrahedra. Fe3P5SiO19 is isotypic with V3P5SiO19. Fe3P5SiO19 is antiferromagnetic below TN=35 K. The magnetic structure has been determined by means of powder neutron diffraction methods: the magnetic moments are antiferromagnetically coupled inside the [Fe2O9] units, in agreement with the Goodenough rules. These units are linked to each other through several Fe-O-P-O-Fe super-superexchange pathways and form antiferromagnetic [001] rows. The moment direction lies in the (001) plane (μFe=4.56(5) μB at 2 K). There is a competition between the intra- and interunits interactions which all are antiferromagnetic and cannot be simultaneously satisfied without frustration. Mössbauer spectra are fitted with two doublets and two sextuplets in the paramagnetic and antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive effect. The magnetic interactions are discussed. 相似文献
5.
We show that the unitary group of a separable Hilbert space has
Kazhdan's Property (T), when it is equipped with the strong operator
topology. More precisely, for every integer m
2, we give an
explicit Kazhdan set consisting of m unitary operators and determine
an optimal Kazhdan constant for this set. Moreover, we show that a
locally compact group with Kazhdan's Property (T) has a finite Kazhdan
set if and only if its Bohr compactification has a finite Kazhdan
set. As a consequence, if a locally compact group with Property (T)
is minimally almost periodic, then it has a finite Kazhdan set. 相似文献
6.
Nawel Cheikh Didier Villemin Nathalie Bar Jean-François Lohier Nourredine Choukchou-Braham Bachir Mostefa-Kara Jana Sopkova 《Tetrahedron》2013,69(3):1234-1247
In the course of our studies on Cerpegin analogues synthesis, a serendipitous reactivity of enaminolactone nitrile has been observed. Instead of expecting iminocerpegins, we have gained new class of substituted 2-aminopyridines. The methodology has been applied on a wide range of primary amines, as aliphatic, aromatic, heteroaromatic and also, diamines, hydrazines and chiral amines. 相似文献
7.
The geometric and electronic structures of a series of hypothetical compounds of the types CpM(C13H9N) and (CO)3M(C13H9N) (M = first row transition metal and C13H9N = 7,8-benzoquinoline) have been investigated by means of density functional theory (DFT). The benzoquinoline ligand can bind to the metal through η1-η6 coordination modes, adopting structures of types a, b and c, in agreement with the electron count and the nature of the metal. In the investigated species, the most favored closed-shell count is 18-MVE, except for the Ti and V models which prefer the open-shell 16-MVE configuration. This study has shown the difference in the coordination ability of this heteropolycyclic ligand and coordination of the inner C6 ring is less favored than the outer C6 and C5N rings, in agreement with the π-electron density localization. 相似文献
8.
Regueiro-Figueroa M Bensenane B Ruscsák E Esteban-Gómez D Charbonnière LJ Tircsó G Tóth I de Blas A Rodríguez-Blas T Platas-Iglesias C 《Inorganic chemistry》2011,50(9):4125-4141
In this contribution we present two ligands based on a do3a platform containing a picolinate group attached to the fourth nitrogen atom of the cyclen unit, which are designed for stable lanthanide complexation in aqueous solutions. Potentiometric measurements reveal that the thermodynamic stability of the complexes is very high (log K = 21.2-23.5), being comparable to that of the dota analogues. Luminescence lifetime measurements performed on solutions of the Eu(III) and Tb(III) complexes indicate that the complexes are nine coordinate with no inner-sphere water molecules. A combination of density functional theory (DFT) calculations and NMR measurements shows that for the complexes of the heaviest lanthanides there is a major isomer in solution consisting of the enantiomeric pair Λ(δδδδ) and Δ(λλλλ), which provides square antiprismatic coordination (SAP) around the metal ion. Analysis of the Yb(III)-induced paramagnetic shifts unambiguously confirms that these complexes have SAP coordination in aqueous solution. For the light lanthanide ions however both the SAP and twisted-square antiprismatic (TSAP) isomers are present in solution. Inversion of the cyclen ring appears to be the rate-determining step for the Λ(δδδδ) ? Δ(λλλλ) enantiomerization process observed in the Lu(III) complexes. The energy barriers obtained from NMR measurements for this dynamic process are in excellent agreement with those predicted by DFT calculations. The energy barriers calculated for the arm-rotation process are considerably lower than those obtained for the ring-inversion path. Kinetic studies show that replacement of an acetate arm of dota by a picolinate pendant results in a 3-fold increase in the formation rate of the corresponding Eu(III) complexes and a significant increase of the rates of acid-catalyzed dissociation of the complexes. However, these rates are 1-2 orders of magnitude lower than those of do3a analogues, which shows that the complexes reported herein are remarkably inert with respect to metal ion dissociation. 相似文献
9.
Youcef Bouizem Salah Boulaaras Bachir Djebbar 《Mathematical Methods in the Applied Sciences》2019,42(7):2465-2474
The paper deals with some existence results for an elliptic equation of Kirchhoff‐type with changing sign data and a logarithmic nonlinearity by direct variational method, Galerkin approach, and sub‐super solutions method. Our results are natural extension of Boulaaras' work in (Math Methods Appl Sci; 41(13):5203‐5210). 相似文献