Corrélations entre méthode de préparation, hauteur de barrière et états d'interface dans les contacts métal-GaAs

Interface states distribution in metal-semiconductor contacts can be determined by studying variations of Schottky diode capacitance as a function of frequency, temperature and forward bias. This method, called Schottky Capacitance Spectroscopy is applied to contacts between Ag, Au, Al and diversely prepared surfaces : cleavage under ultra-high vacuum or controlled gazeous atmosphere, cleavage followed by ion-bombardment, chemical etch, molecular beam epitaxy. So, the rôle played by a great number of physical parameters on interface states distribution and barrier height can be determined. It is established that only the creation of a severely perturbed interfacial zone of a few angströms width can significantly modify the properties of the barrier.La distribution des états d'interface dans un contact métal-semiconducteur peut être déterminée à partir de l'étude du comportement de la capacité dynamique d'une diode Schottky sous polarisation directe en fonction de la fréquence, la température et la tension appliquée. Cette méthode, appelée Spectroscopie de Capacité Schottky est appliquée à des dépôts d'Ag, Au et Al sur des surfaces de GaAs préparées de manières très diverses : clivage sous ultravide ou sous gaz, clivage suivi de bombardement ionique, nettoyage chimique, épitaxie par jets moléculaires. Ceci permet de tester le rôle joué par un grand nombre de paramètres sur la distribution des états d'interface et la hauteur de barrière. On constate que ces propriétés ne sont affectées de manière importante que par la création d'une zone interfaciale fortement perturbée, s'étendant sur plusieurs couches atomiques

Limoniastrum guyonianum aqueous gall extract induces apoptosis inhuman cervical cancer cells involving p16INK4A re-expression related to UHRF1 and DNMT1 down-regulation

International audienc

Green Synthesis of Highly Monodisperse and Spherical Ag Nanoparticles by a Combination of Teucrium ramosissimum Desf. (Lamiaceae) Extracts with Emphasis on the Stabilizing and Capping Biomolecules

Here, the aqueous (Taquo) and hydroethanolic (Thydro) extracts of the Teucrium ramosissimum Desf. are used for the synthesis of one of the most spherical and monodisperse Ag nanoparticles (Ag NPs) reported by green chemistry. Several parameters, such as pH, amount of extract, reaction time, and reaction temperature, are investigated. The optimized Ag NPs are obtained at a pH value of ca. 10, using 1 mL of extract, a reaction time of 4 h, at 60 °C, and allowing an incubation period at room temperature. The average particle size ranged between 18 and 22 nm in all cases, and no significant differences were observed between the Taquo or the Thydro extracts. Apart from that, the principal bioactive molecules responsible for the reduction process were identified by nuclear magnetic resonance spectroscopy, and the molecules incorporated on the Ag surface were determined by headspace-solid phase microextraction (HS-SPME), followed by gas chromatography/quadrupole-mass spectrometry (GC–qMS). In both cases, we found that phenolic acids, phenylpropanoids, citric acid, and malic acid are molecules involved in the reduction process, and some of them are found on the Ag NPs surface in their oxidized form. Moreover, a stabilization study as a function of pH is also presented that confirms the high stability of our fabricated Ag NPs. UV–vis analysis confirmed the presence of the Ag plasmon band as well as the particle stability, and transmission electron microscopy images demonstrate that our synthesized Ag NPs are some of the most spherical and monodisperse biobased Ag nanosystems presented in the literature. Ag NPs were also analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, selected area electron diffraction, and Fourier-transform infrared spectroscopy