I.J.R. Baumvol

High-resolution depth profiling in ultrathin Al2O3 films on Si

A combination of two complementary depth profiling techniques with sub-nm depth resolution, nuclear resonance profiling and medium energy ion scattering, and cross-sectional high-resolution transmission electron microscopy were used to study compositional and microstructural aspects of ultrathin (sub-10 nm) Al2O3 films on silicon. All three techniques demonstrate uniform continuous films of stoichiometric Al2O3 with abrupt interfaces. These film properties lead to the ability of making metal-oxide semiconductor devices with Al2O3 gate dielectric with equivalent electrical thickness in the sub-2 nm range.

Evidence of aluminum silicate formation during chemical vapor deposition of amorphous Al2O3 thin films on Si(100)

Using narrow nuclear reaction resonance profiling, aluminum profiles are obtained in ∼3.5 nm Al2O3 films deposited by low temperature (<400 °C) chemical vapor deposition on Si(100). Narrow nuclear resonance and Auger depth profiles show similar Al profiles for thicker (∼18 nm) films. The Al profile obtained on the thin film is consistent with a thin aluminum silicate layer, consisting of Al–O–Si bond units, between the silicon and Al2O3 layer. Transmission electron microscopy shows evidence for a two-layer structure in Si/Al2O3/Al stacks, and x-ray photoelectron spectroscopy shows a peak in the Si 2p region near 102 eV, consistent with Al–O–Si units. The silicate layer is speculated to result from reactions between silicon and hydroxyl groups formed on the surface during oxidation of the adsorbed precursor.

Reaction-diffusion in high-k dielectrics on Si

Abstract Thinning of the gate dielectric as required by scaling rules is currently inhibiting the so far outstanding evolution of the silicon age, owing to unacceptably high gate current (leakage current) arising from electron tunneling through the gate dielectric ultrathin layer. One possible solution is to use an alternative material to SiO2, which would interrupt more than 40 years of successful microelectronics technology based on Si and SiO2. This article discusses atomic scale investigation on the underlying difficulties of introducing ultrathin films of metal oxides, silicates, and oxynitrosilicates having dielectric constants much higher than that of SiO2—called high-k dielectrics—as gate dielectrics in advanced, Si-based metal-oxide–semiconductor field-effect transistor (MOSFET) fabrication. More specifically, we address atomic transport and chemical reaction processes generating instabilities in high-k dielectric films during different thermal processing fabrication steps following their deposition on (i) single-crystalline Si substrates or (ii) single-crystalline Si substrates on which SiO2, SiNx, or SiOxNy ultrathin films were either unintentionally formed during deposition or intentionally grown previously to high-k film deposition. A most typical reaction–diffusion situation is established in near-surface, bulk, and near-interface regions of this large family of amorphous ultrathin films deposited on Si, whose phenomenology, mathematical modeling, and atomic scale understanding constitute the subject of this article.

Enhanced initial growth of atomic-layer-deposited metal oxides on hydrogen-terminated silicon

A route is presented for activation of hydrogen-terminated Si(100) prior to atomic layer deposition. It is based on our discovery from in situ infrared spectroscopy that organometallic precursors can effectively initiate oxide growth. Narrow nuclear resonance profiling and Rutherford backscattering spectrometry show that surface functionalization by pre-exposure to 108 Langmuir trimethylaluminum at 300 °C leads to enhanced nucleation and to nearly linear growth kinetics of the high-permittivity gate dielectrics aluminum oxide and hafnium oxide.

Potential of medicinal plants from the Brazilian semi-arid region (Caatinga) against Staphylococcus epidermidis planktonic and biofilm lifestyles

ETHNOPHARMACOLOGICAL RELEVANCE Medicinal plants from the Caatinga, a Brazilian xeric shrubland, are used in folk medicine to treat infections. These ethnopharmacological data can contribute to obtaining new antimicrobial/antibiofilm extracts and natural product prototypes for the development of new drugs. The aim of this study was to investigate the antibiofilm and antibacterial activities of 45 aqueous extracts from 24 Caatinga plant species. MATERIALS AND METHODS The effect of aqueous extracts on planktonic cells and on biofilm formation by Staphylococcus epidermidis was studied by the OD(600) absorbance and by the crystal violet assay, respectively. Scanning electron microscopy (SEM) was used to generate comparative images of extract-treated and untreated biofilms. Chromatographic analyses were performed to characterize the active extracts. RESULTS The in vitro screening, at 0.4 mg/mL and 4.0mg/mL, showed 20 plants effective in preventing biofilm formation and 13 plants able to inhibit planktonic bacterial growth. SEM images demonstrated distinct profiles of bacterial adhesion, matrix production and cell morphology according to different treatments and surfaces. The phytochemical analysis of the selected active extracts indicates the polyphenols, coumarins, steroids and terpenes as possible active compounds. CONCLUSION This study describes the first antibiofilm and antibacterial screening of Caatinga plants against S. epidermidis. The evaluation presented in this study confirms several ethnopharmacological reports and can be utilized to identify new antibiofilm and antibacterial products against S. epidermidis from traditional Brazilian medicine.

Oxygen reaction-diffusion in metalorganic chemical vapor deposition HfO2 films annealed in O2

Composition, atomic transport, and chemical reaction were investigated following annealing in O2 of ultrathin HfO2 films deposited on Si substrates thermally nitrided in NO. The as-prepared thin film composition was established by Rutherford backscattering spectrometry, nuclear reaction analysis, and x-ray photoelectron spectroscopy as a HfO2 film on an intermediate layer containing silicon oxynitride, hafnium silicate, and possibly hafnium–silicon oxynitride. O penetration, incorporation in the bulk of the HfO2/SiOxNy structure, and oxidation of the substrate forming SiO2 were observed.

Initial stages of SiC oxidation investigated by ion scattering and angle-resolved x-ray photoelectron spectroscopies

Initial stages of oxidation of single-crystal, Si-faced silicon carbide were investigated using ion scattering and angle-resolved x-ray photoelectron spectroscopies. The very first oxidation products are shown to be silicon oxycarbides (SiCxOy), while, for longer oxidation times, a mixture of SiCxOy and SiO2 is formed in the near-surface region of the growing oxide film. The composition of the near-surface region of such thin films is very similar to that reported in previous investigations for the near-interface region when thicker oxides films are grown on SiC.

Ruthenium dioxide nanoparticles in ionic liquids: synthesis, characterization and catalytic properties in hydrogenation of olefins and arenes

A reacao de NaBH 4 com RuCl 3 dissolvido no liquido ionico 1-n-butil-3-metilimidazolio hexafluorfosfato (BMI.PF 6 ) e um metodo simples e reprodutivel para a sintese de nanoparticulas de RuO 2 estaveis com distribuicao estreita e diâmetro da particula entre 2-3 nm. As nanoparticulas de RuO 2 foram caracterizadas por XRD, XPS, EDS e TEM. Estas nanoparticulas mostraram alta atividade catalitica tanto na catalise heterogenea quanto na hidrogenacao bifasica liquido-liquido de olefinas e arenos sob condicoes moderadas de reacao. Experimentos de envenenamento com Hg(0) e CS 2 , e analises de XRD e TEM de particulas isoladas apos a catalise indicaram a formacao de nanoparticulas de Ru(0). As nanoparticulas podem ser reutilizadas em condicoes de catalise heterogenea ate 10 vezes na hidrogenacao de 1-hexeno rendendo um numero total de ciclos cataliticos de 175.000 para atomos de Ru expostos. The reaction of NaBH 4 with RuCl 3 dissolved in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF 6 ) ionic liquid is a simple and reproducible method for the synthesis of stable RuO 2 nanoparticles with a narrow size distribution within 2-3 nm. RuO 2 nanoparticles were characterized by XRD, XPS, EDS and TEM. These nanoparticles showed high catalytic activity either in the solventless or liquid-liquid biphasic hydrogenation of olefins and arenes under mild reaction conditions. Hg(0) and CS 2 poisoning experiments and XRD and TEM analysis of particles isolated after catalysis indicated the formation of Ru(0) nanoparticles. The nanoparticles could be re-used in solventless conditions up to 10 times in the hydrogenation of 1-hexene yielding a total turnover number for exposed Ru atoms of 175,000.

Comparison of nitrogen incorporation in SiO2/SiC and SiO2/Si structures

The nitrogen content of SiO2/SiC (4H) structures annealed in NO and N2O has been measured using nuclear reaction analysis. Samples were annealed in 15N18O or 15N2O at 1000 °C at a static pressure of 10 mbar for either 1 or 4 h. Annealing in N2O incorporates ∼1013 cm−2 of N and annealing in NO incorporates ∼1014 cm−2, both of which are an order of magnitude lower than in SiO2/Si. In the NO anneal, N is predominantly incorporated near the SiO2/SiC interface with an atomic concentration of ∼0.5%. As in the nitridation of SiO2/Si, two features are observed in SiO2/SiC after the NO anneal: a surface exchange of O in the oxide with the gas phase and NO diffusion and reaction at the interface. The surface exchange reaction in SiO2/SiC is similar to SiO2/Si, but there is a large difference in the incorporation of N at the interface.

Nitrogen bonding, stability, and transport in AlON films on Si

The chemical environment of N in nitrided aluminum oxide films on Si(001) was investigated by angle-resolved x-ray photoelectron spectroscopy. Two different bonding configurations were identified, namely N–Al and N–O–Al, suggesting the formation of the AlN and AlO2N compounds. The near-surface region is N-rich and AlN compounds therein are more abundant than AlO2N, whereas in bulk regions the proportions of these two compounds are comparable. Rapid thermal annealing at 1000 °C for 10 s in vacuum or in low-pressure oxygen atmosphere led to the breakage of N–Al bonds in AlN, releasing N and Al. The mobile N is partly lost by desorption from the surface and partly fixed by reacting with the network to form AlO2N. The released Al atoms, which remain immobile, react with oxygen from the film or from the gas phase. Characterization of the films outermost surfaces by low-energy ion scattering revealed that the migration of Si atoms from the substrate across the films, reaching the surface and being oxidized ther...