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When handling unsealed radioactive sources, radiological protection attention must be taken to avoid unnecessary exposure and radioactive contaminations, and an important and necessary practice to prevent such contaminations is the use of gloves when handling these sources. The present work aimed to determine the effectiveness of contamination protection provided by different types of disposable polymeric gloves used in Nuclear Medicine Service in Clinic Hospital of Porto Alegre, testing the main radiopharmaceuticals used at this site: [99mTc]sodium pertechnetate, [18F]FDG and [131I]sodium iodide. The analysis was performed using the wipe test inside gloves intentionally contaminated on the outside with these radiopharmaceuticals. The radiation detector used to measure the contamination was a NaI(Tl) scintillator well-type counter. The results indicate that three types of gloves analyzed protect the user from [99mTc]sodium pertechnetate and [18F]FDG contamination, for permanence times with the glove after contamination for up to 15 min (interval tested). For [131I]sodium iodide, gloves are completely effective in protection as long as they are used for a time interval after contamination of the external surface of up to: Latex – 5 min; Vinyl – 5 min; Nitrile – 10 min. Among them, the nitrile glove are the most effective, since contamination was not observed on the inner face for times equal to or less than 10 min; and, for an interval of 15 min, the percentage of permeation obtained was lower than the other two types: 3.3 times lower than vinyl glove permeation and 1.3 times lower of the latex glove permeation. It was also possible to estimate the skin dose rate due to contamination caused by iodine permeation for each glove case and time tested.

A series of heterogeneous metallocene catalysts were prepared by encapsulating Cp2ZrCl2 within silica-polystyrene hybrid support. Immobilization was performed through a non-hydrolytic sol–gel process in which polystyrene (PS) dissolved in toluene and metallocene (1% by wt) were combined. The effect of PS (0 to 5% by wt) and silicon tetrachloride (0.5 to 1.6 [TEOS]/[SiCl4]) was evaluated in terms of catalyst activity in ethylene polymerization with methylaluminoxane as the cocatalyst. According to FTIR measurements, an increase in PS content promoted a decrease in (SiO)6 content, which indicated the formation of more compact structures. Furthermore, homogeneous distributions of polymer and silica phases were observed both in bulk and on the support surface. The results showed very small surface areas (

The chemical nature of sub-monolayer phosphorous impurities at the SiC/SiO2 interface is a critical surface science problem related to device performance and other applications. In this study, SiO2 films containing phosphorus were deposited by sputtering on both the Si and C-faces of SiC substrates, and on silicon (Si(100)) substrates. After oxide removal by etching, a significant amount of phosphorus was retained on both SiC surfaces, while no phosphorus was observed on the Si surface. Chemical ambient investigation, quantification by XPS, and water contact angle measurements indicate that the phosphorus on the SiC surface is trivalent bonded, mainly to oxygen. Based on these results, a SiO2/SiC interfacial structure is proposed: Si-C-Si-|-O-P-O2-SiO2. These results provide new insights into the role of phosphorus, its incorporation, and stability, as a passivating agent in the performance of SiC MOS structures.

Surface energy modification and surface wettability of 4H silicon carbide (0001) as a function of nitrogen adsorption is reported. The surface wettability is shown to go from primarily hydrophilic to hydrophobic and the surface energy was significantly reduced with increasing nitrogen incorporation. These changes are investigated by x-ray photoelectron spectroscopy and contact angle measurements. The surface energy was quantitatively determined by the Fowkes model and interpreted primarily in terms of the variation of the surface chemistry with nitrogen coverage. Variable control of SiC surface energies with a simple and controllable atomic additive such as nitrogen that is inert to etching, stable against time, and also effective in electrical passivation, can provide new opportunities for SiC biomedical applications, where surface wetting plays an important role in the interaction with the biological interfaces.

Mesoporous nanoparticles and mixed-structure silica with existing nanometric and micrometric domains on their surface were prepared using SiCl4. TiCl4 was used as precursor to obtain nano- and mixed heterogeneous supported titania photocatalysts. The systems and, for comparative reasons, commercial (P25) were evaluated for Rhodamine B (RhB) photodegradation in deionized and lake water solution. The structural differences between nano- and mixed photocatalysts were observed and are due to the degree of particles structural organization, according to small-angle X-ray scattering (SAXS) profiles. The structural analysis obtained by fractal dimension (pL) showed that photocatalysts which were organized as mass fractal structures presented higher catalytic activity than the photocatalysts of rough surface fractal or non-fractal. A compressive discussion on surface topology, size, band gap, surface area, surface charge density, and catalysts amount was done to explain the effect of these features on the photocatalysts performance. The distribution of Ti-O-Si species on the support surface was determined by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). The higher photocatalytic activity for the degradation of RhB dye was achieved by SNCl5Ti sample. This catalyst achieved high efficiency factor, EF = mg of RhB degraded/ mg of catalyst, equal to 0.020 and 0.0132, under UV and Vis radiation, respectively, which is lower catalyst amount than the similar TiO2-SiO2 based systems reported in the literature. These findings broaden the opportunities to degrade other harmful pollutants in wastewater. This work also provides an insight on how structural properties are correlated to the efficiency of titania supported nano/micrometric catalysts.

The synthesis of nonporous monodisperse chemically modified spherical silica particles was carried out according to the Stober method. The resulting hybrid silicas were employed in the preparation of supported Cp 2 ZrCl 2 . The resulting metal loading, determined by Rutherford Backscattering Spectrometry (RBS), was between 0.15 and 0.48 wt% Zr/SiO 2 . The systems were evaluated in ethylene polymerization with MAO as the co-catalyst. The presence of ligands can increase catalyst activity and the nature of the employed organosilane ligand on the hybrid silicas were shown to affect the molecular weight distribution leading to polyethylenes with broad polydispersity (Mw/Mn = 3.8) and even with bimodality (Mw/Mn = 12.6).

Phosphorus detection and quantification were obtained, using the 31P(α,p)34S nuclear reaction and Rutherford Backscattering Spectrometry, in deposited silicon oxide films containing phosphorus and in carbon substrates implanted with phosphorus. It was possible to determine the total amount of phosphorus using the resonance at 3.640 MeV of the 31P(α,p)34S nuclear reaction in samples with phosphorus present in up to 23 nm depth. Phosphorous amounts as low as 4 × 1014 cm−2 were detected. Results obtained by nuclear reaction were in good agreement with those from RBS measurements. Possible applications of phosphorus deposition routes used in this work are discussed.

Industrial galvanic bath residuals, residual silver-containing solutions from photography classes, residual metal-containing solutions from academic analytical chemistry classes, and residual Ziegler–Natta catalyst slurry from a petrochemical plant were employed as sources for photocatalysts. The residues were impregnated on silica, with subsequent calcination. The solids were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Rutherford backscattering spectrometry (RBS), diffuse reflectance spectroscopy in the ultraviolet (DRS-UV), small-angle X-ray scattering (SAXS), nitrogen porosimetry and zeta potential (ZP) measurements. The catalysts contained Zn, Ti, Ag, Cr or Cu. All the systems presented also included carbon in their composition. Metal content ranged from 0.01 to 0.60 wt%. The systems were evaluated by the photodegradation of Rhodamine B (RhB). For comparative reasons, P25 (Degussa) was also employed as a catalyst. The supported catalysts resulting from the residue of the petrochemical industry achieved the highest percentage of the dye degradation in the ultraviolet (67%) and visible (61%) radiation, while the commercial P25 achieved 93% and 14% for ultraviolet and visible radiation, respectively.

A new method to synthesize 18O standard samples to be used in nuclear reaction analyses is proposed and investigated. This method consists of obtaining a Si18O2 film on a Si substrate using a natural abundance SiO2 film as a passivation layer to prevent the isotopically enriched film to be exposed to the atmosphere and possibly degraded by it. For that, sequential oxidation steps are performed followed by a controlled etching in aqueous hydrofluoric acid. Details of these steps are discussed as well as the stability of the synthesized samples. Applications using these standard samples in the field of alternative semiconductors to Si (SiC and Ge), used in micro and nanoelectronics are also presented.

In this work, hybrid silica that contained an indenylpropyl organic moiety was synthesized using the sol–gel method from indenylpropylsilane and tetraethylorthosilicate (TEOS). These functionalized silica samples were used in the synthesis of supported metallocene catalysts that were active in the production of linear polyethylene. The reaction conditions, such as the catalyst type and reaction time, for the preparation of indenyl-functionalized silane influenced the incorporation of the organic precursor and the xerogel morphology. Hybrid materials that contained the indenidepropyl ligand were obtained at reaction times between 2 and 6 h with the use of HF or NH 3 as catalysts, which resulted in materials with different porosities, surface areas and morphologies. The indenyl-functionalized silica samples with organic contents greater than 10 wt% were thermally stable up to 350 °C. 13 C CP-MAS-NMR showed the presence of propyl and indenyl moieties in the hybrid materials. These organic precursors were reacted with ZrCl 4 ·2THF, which led to the formation of supported metallocene catalysts that, when tested in ethylene polymerization reactions, exhibited a dependence on the reaction temperature and the Al/Zr ratio.

The incorporation of hydrogen in dielectric/SiC structures and Pt/dielectric/SiC structures whose dielectric films were thermally grown in O 2 , NO, or O 2 followed by annealing in NO was investigated. The amount and the distribution of hydrogen incorporated and the capacitance-voltage characteristics were observed to be dependent on the thermal growth route employed. Hydrogen was mainly incorporated in the dielectric film/SiC interface region and larger amounts were incorporated when the Pt electrode was used. Annealing in hydrogen increased the negative shift in the flatband voltage, which was more pronounced when the Pt electrode was used in the case of NO-annealed SiO 2 /SiC sample.

The effect of sequential thermal treatments with growth/removal steps of SiO2 films intercalated with hydrogen peroxide treatments on the SiO2/4H-SiC interfacial region thickness were investigated on both Si and C faces. In the Si face case, samples that were submitted to more H2O2 treatments presented thinner interfacial region thicknesses. In the C face case, on the other hand, no significant alteration in this region was observed.

This work provides data corroborating the presence of silicon oxycarbides (SiOxCy) in the SiO2/SiC interface region. Besides, it presents results on the efficiency of hydrogen peroxide annealings for reducing the SiO2/SiC interfacial region thickness. Finally, influences of water vapor thermal treatments on dielectric films thermally grown are presented. In most of the samples, isotopes rare in nature (18O and 2H) were used in thermal treatments associated with ion beam analyses.

A series of supported metallocene catalysts were prepared by grafting Cp 2 ZrCl 2 on silica–magnesia xerogels, and then they were evaluated for the process of ethylene polymerization. The supports were characterized by a set of complementary techniques including small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N 2 adsorption–desorption. The supported catalysts were characterized by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared spectroscopy (DRIFTS). The use of silica–magnesia xerogels for immobilization of metallocene yielded systems with higher catalyst activity when compared to the results from metallocene grafted on bare silica. The resulting polymers showed a broader molecular weight distribution than those obtained by homogeneous Cp 2 ZrCl 2 and Cp 2 ZrCl 2 /SiO 2 , which potentially provides a better processing capacity of these alternative polyethylenes. In the case of polyethylene obtained with the system containing 16.0 wt.% Mg/Si, a fiber-like morphology was observed.

The consequences of thermal treatments in nitric oxide atmospheres on the characteristics of dielectric films / SiC structures was investigated by high-frequency capacitance-voltage measurements, X-ray photoelectron spectroscopy, and X-ray reflectometry techniques. It was observed that nitrogen incorporation in dielectric films / SiC structures leads to the formation of a thinner interfacial layer that contains carbon. This fact was related to the improvement of electrical properties of those structures.

A series of hybrid-supported catalysts was prepared by sequentially grafting Cp2ZrCl2 and (nBuCp)2ZrCl2 (1:3 ratio) onto synthesized silica–zirconia xerogel, alumino-silicates, alumina, chrysotile and commercial MAO (methylaluminoxane)-modified silica. Supported catalysts were characterized by Rutherford backscattering spectrometry, atomic force microscopy, extended X-ray absorption fine structure spectroscopy, X-ray diffraction and nitrogen adsorption. The grafted metal content was between 0.21 and 1.00 wt.% Zr/SiO2 or Zr/Al2O3. All of the systems were shown to be active in ethylene polymerization with methylaluminoxane as the cocatalyst. The catalyst activity and polymer molecular weight depended on the effects of the textural characteristics of the supports on the structure of the generated supported catalyst species. The highest activity in ethylene polymerization (ca. 6560 kgPE molZr−1 h−1) was reached with the supported catalyst using commercial MAO-modified silica and also presented the lowest surface roughness. Correlation between EXAFS data and polymer characteristics was extracted: the production of polyethylenes with higher molecular weight was associated with the reduction in the interatomic Zr–O distance of the supported catalysts, which was shown to be dependent on the nature of the support.

The immobilization of Cp2ZrCl2 was performed by entrapment within the binary oxide SiO2–WO3 using a non-hydrolytic sol–gel route. The catalyst and oxide matrix were characterized by complementary techniques (Rutherford backscattering spectrometry, ultraviolet–visible diffuse reflectance and infrared transmission spectroscopy, differential pulse voltammetry, adsorption–desorption of N2, and X-ray diffraction). The catalyst performance in terms of catalytic activity and polymer properties was evaluated by ethylene polymerization. Catalyst characterization suggested that the entrapped complex exhibited lower Zr electronic density than the corresponding unsupported metallocene. The polymerization results also revealed that this low Zr electronic density is optimized in terms of complex activation with low MAO concentration (low [Al/Zr] ratio) and reactivity. This fine tuning results in a catalyst system that is active with a low [Al/Zr] ratio and that achieves high catalytic activity. The results demonstrate that the entrapping method allows the generation of a catalyst system in which part of the activation process is attributed to the support. In this sense, the support may partially play MAO functions by stabilizing the active catalytic species.

Bis(cyclopentadienyl)zirconium dichloride was immobilized within binary oxides of SiO 2 –TiO 2 via a non-hydrolytic sol–gel route. Different coordinatively unsaturated Ti species were identified within the oxide structure depending on the TiO 2 content, which can interact with the encapsulated metallocene complex and affect its catalystic performance in ethylene polymerization. The catalysts were shown to be active in the polymerization using MAO as the cocatalyst in a low Al/Zr ratio. High molecular weight polymer was obtained, probably due to the suppression of chain termination reactions that occur by β-elimination. Furthermore, oxide network structures are suggested from analysis of the catalysts (via Rutherford backscattering spectrometry, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, diffuse pulse voltammetry), molecular simulation and polymerization performance.

A series of homogeneous metallocenes (Cp2ZrCl2, (nBuCp)2ZrCl2, (iBuCp)2ZrCl2, (tBuCp)2ZrCl2, Cp2TiCl2, Cp2HfCl2, EtInd2ZrCl2 and Et(IndH4)2ZrCl2) were immobilized within a silica matrix during its preparation using a non-hydrolytic sol–gel method. Supported metallocenes were characterized by small angle X-ray scattering (SAXS) and nitrogen adsorption. The results show that the silica particle was formed by the aggregation of primary structures having a diameter of about 160 nm. This was a result of the aggregation process, which was affected by the metallocene. This result suggests that the metallocene is surrounded by primary particles deep inside the silica matrix. The low polymer productivity exhibited by the less active metallocene catalysts could be related to the problems of particle fragmentation due to monomer mass transfer limitations along the partially fragmented particle, which would subsequently affect catalytic activity.

A series of hybrid supported catalysts was prepared by sequentially grafting Cp2ZrCl2 and (nBuCp)2ZrCl2 (1:3 ratio) onto alumino-silicates (MCM-41, SBA-15, MCM-22, ITQ-2), alumina and chrysotiles (native and leached). Supports and catalysts were characterized by Rutherford backscattering spectrometry, atomic force microscopy and nitrogen adsorption. Grafted metal content laid between 0.2 and 0.8 wt.% Zr/SiO2 and 0.9 wt.% Zr/Al2O3. All the systems were shown to be active in ethylene polymerization with methylaluminoxane as the cocatalyst. Catalyst activity and molecular weight were shown to depend on the textural characteristic of the silicas, namely grain size and pore diameter. The highest activity in ethylene polymerization (ca. 3200 kg PE mol Zr−1 h−1) was obtained with the supported catalyst using SBA-15 with average particle size around 0.21 μm. Resulting polymers were characterized by gel permeation chromatography and differential scanning calorimetry.

A series of hybrid supported catalysts was prepared by sequentially grafting Cp 2 ZrCl 2 and ( n BuCp) 2 ZrCl 2 (1:3 ratio) onto synthesized xerogel, aerogel and commercial silicas. Supports and catalysts were characterized by Rutherford backscattering spectrometry, energy-dispersive X-ray scanning electron microscopy, atomic force microscopy and nitrogen adsorption. Grafted metal content laid between 0.15 and 0.5 wt.% Zr/SiO 2 . All the systems were shown to be active in ethylene polymerization with methylaluminoxane as the co-catalyst. Catalyst activity and molecular weight were shown to depend on the textural characteristic of the silicas, namely grain size and pore diameter. The highest activity in ethylene polymerization (ca. 5310 kg PE mol Zr −1 h −1 ) was obtained with the supported catalyst using commercial silicas with average particle size around 50 μm. Particles with sizes of 80–90 μm obtained less activity. Resulting polymers were characterized by gel permeation chromatography and differential scanning calorimetry.

Summary: Concomitant immobilization of zirconocene (Cp2ZrCl2) into a silica matrix was performed during the SiO2 synthesis through non-hydrolytic sol-gel method. Two different routes, varying the SiCl4:Si(OEt)4 ratio were evaluated in terms of zirconocene content and catalyst activity in ethylene polymerization, using methylaluminoxane (MAO) as cocatalyst. The catalysts were characterized by Rutherford backscattering spectrometry, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy and X-ray dispersive spectroscopy. The zirconocene content laid between 0.60 and 1.02 wt.% Zr/SiO2, depending upon the components ratio employed in the sol-gel synthesis. Catalyst grains presented of irregular shape (20–100 mm size) and zirconocene distribution was not uniform. Both routes led to supported catalysts active in ethylene polymerization. Catalyst activity was intermediate between that exhibited by the homogeneous and the grafted zirconocene on silica. Resulting polyethylenes presented narrow molecular weight distribution and molecular weight slightly higher than that observed in the case of polymer produced with the homogeneous system.

A method for the determination of Ti and V using inductively coupled plasma atomic emission spectrometry (ICP OES) in Ziegler-Natta polymerization catalysts is proposed. The concentrations of both Ti and V are efficiently determined after catalyst acid digestion with a mixture of HNO3 + HCl + HF and heating (160 degrees C for 6 h) or with 10% (v/v) H2SO4 and heating (160 degrees C for 6 h) or with 10% (v/v) H2SO4 and sonication (during 2 min). The V and Ti detection limits are 0.002% and 0.08%, respectively, using 0.20 g of catalyst sample in 50 ml. The method is validated by a comparison with the Rutherford backscattering spectrometry (RBS) technique. In this case, catalyst samples are only pressed as pellets before analyte determination. Despite the fact that both the V and Ti concentrations cannot be determined individually by means of RBS, because the atomic numbers of Ti and V are very close, the sum of the V and Ti contents is in accordance with that attained by means of ICP OES. According to scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) it is observed that the Ti distribution on the catalyst grain is not homogenous.

Silica (350 m2 g−1) was chemically modified with Cp2ZrCl2 and (nBuCp)2ZrCl2 by grafting. Hybrid silica bearing surface indene groups was synthesized by the sol–gel method, followed by metallation with ZrCl4⋅2THF. The resulting phases were characterized by Rutherford backscattering spectrometry (RBS), 13C and 29Si magic angle spin nuclear magnetic resonance, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. According to RBS measurements, metal content was 0.2- to 0.3-wt% Zr/SiO2 for the grafted systems and 4.5-wt% Zr/SiO2 for the phase prepared by the sol–gel method. The solid phases were evaluated for the adsorption/preconcentration of lindane and heptachlor epoxide from aqueous solution. For comparative reasons, the commercial LC-18 phase was also evaluated. Analyte concentration was monitored by gas chromatography electron capture detection. For the grafted phases, the coordination sphere around the metal center seems not to influence the adsorption/desorption properties of these phases vis-a-vis the studied analytes. In the case of the phases prepared by the sol–gel method, recovery results were comparable to those observed for LC-18. Experiments using ZrO2 and ZrO2/SiO2 phases led to lower recovery results.

Commercial polyethylenes produced by Ziegler-Natta, Philips and metallocene technology were analyzed by X-ray fluorescence spectroscopy. Synthetic standards using wax matrix was shown to be suitable for the calibration curve in comparison to those prepared by milling and grinding virgin polymer mixed with standard metal oxide as matrix. The detection limits obtained for the studied metal in the different polymers were: 12 mg kg −1 for Mg, 0.8 mg kg −1 for Ti, 1.6 mg kg −1 for Cr, 1.2 mg kg −1 for Zr and 1.9 mg kg −1 for V. For comparative reasons, the determination of residual metal content by Rutherford backscattering spectrometry (RBS) and total-reflection X-ray fluorescence spectrometry (TXRF) is also discussed.

The mechanisms of oxygen incorporation during dry thermal oxidation of 6H-SiC wafers were investigated. Isotopic tracing of oxygen was performed by sequential oxidations in dry O2 enriched or not in the 18O isotope and subsequent determinations of the 18O profiles. The results obtained with SiC substrates were compared with those of Si, evidencing different mechanisms of oxygen incorporation and transport. The gradual nature of the SiO2/SiC interface was also evidenced. A probable explanation for this gradual SiO2/SiC interface is shown to be the formation of C clusters during oxidation.

A series of hybrid supported catalysts were prepared by combining (iBuCp)2ZrCl2 and {TpMs*}TiCl3 complex (TpMs* = HB(3-mesityl-pyrazolyl)2(5-mesityl-pyrazolyl)−) sequentially grafted onto MAO (methylaluminoxane)-modified silica according to a Plackett Burmann 23 design. Supported catalysts were prepared taking into account the immobilization order, silica pretreatment temperature, and grafting temperature. Grafted metal content was comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectronic spectroscopy (XPS), and inductively coupled plasma–optical emission spectroscopy (ICP–OES). The resulting catalysts were evaluated in terms of catalyst activity and polymer properties. According to RBS measurements, grafted metal content remained comprised between 0.1 and 0.5 wt % Zr/SiO2 and 0.1 and 0.3 wt % Ti/SiO2 depending on the immobilization order and on silica pretreatment temperature. All the systems were shown to be active in ethylene polymerization having external MAO as cocatalyst. Catalyst activity seemed to be governed by the zirconocene species, influenced slightly by Ti ones. Resulting polymers were characterized by DSC and GPC. The polyethylenes mostly presented higher molecular weight than those produced by homogeneous catalysts or by zirconocene grafted on bare or on MAO-modified silica. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Metal contents in supported zirconocene catalysts were comparatively determined by x-ray fluorescence spectroscopy and Rutherford backscattering spectrometry. A series of supported zirconocenes was prepared by grafting sequentially Cp2ZrCl2 (Cp = cyclopentadienyl) and (nBuCp)2ZrCl2 on to silica. The addition order and molar ratio of the two catalysts were varied. The grafted metal content was shown to be coherent between the two techniques and was between 0.37 and 0.53 wt% Zr/SiO2. The steric effect played by the ligand influences the final zirconocene grafted content. No influence of the grafting order was observed. Nevertheless, catalyst systems in which (nBuCp)2ZrCl2 was either immobilized in the first place or at a higher molar ratio were shown to be more active in ethylene polymerization. Extended x-ray absorption fine structure analysis in the Zr-edge showed that systems bearing Cp2ZrCl2 and (nBuCp)2ZrCl2 in a 1:3 molar ratio afforded a more disoriented system. According to electron probe microanalysis, the metal distribution in the catalyst particle was more uniform than that resulting from the immobilization of solely (nBuCp)2ZrCl2 on silica. Copyright © 2004 John Wiley & Sons, Ltd.

Chemical modification of low density polyethylene (LDPE) with vinyltriethoxysilane (VTES) was studied. The melt reactions were performed in a mixer and were initiated by thermal decomposition of a peroxide. The degree of functionalization was determined by Fourier transform infrared spectroscopy and Rutherford backscattering spectrometry. It was verified that the degree of functionalization increased with VTES and peroxide concentrations showing high conversion, up to 86 wt.%. No functionalization was observed in the absence of peroxide. Functionalized products showed some gel content and lower crystallinity than the parent homopolymer, affecting the stress/strain behavior. Yielding stress, elongation at break and elastic modulus decreased for the modified PE.

( n BuCp) 2 ZrCl 2 was grafted on a series of modified silica and evaluated in ethylene/1-hexene copolymerization and their performance was compared with the homogenous system and with that resulting from its immobilization on bare silica. Silica was modified by polymethylhydrosiloxane (PMHS), Me 3 SiCl, Ph 3 SiOH, SnCl 4 , isodrin and aldrin. ( n BuCp) 2 ZrCl 2 grafted on PMHS-modified silica afforded the catalyst with the highest activity. Comonomer incorporation, melting point and polydispersity was shown to be dependent on the catalyst nature. Bimodality was observed in the case of ethylene homopolymerization employing PMHS-silica-based catalysts.

The complexation of 2-hydroxy-1,4-naphtho-quinone and 3-hydroxy-2-methyl-4-pyrone with zirconium tetrachloride yielded complexes containing bidentate alkoxide ligands. In the presence of MAO or TIBA these complexes were found to be active for ethylene polymerization, producing polymers with high molecular weight. Both catalytic systems were also shown to be active when supported on silica or on MAO-modified silica.

A series of metallocenes differing in the metal center (M=Zr, Ti, Hf), in the coordination sphere (RCp, with R=H, Me, iBu, nBu; Indenyl) and the bridge (Et, Me2Si) were studied as homogeneous systems and supported on silica and MAO-mediated (2.0 wt.% Al/SiO2) silica. The effect of these parameters were evaluated in the grafted metal content, in catalyst activity and in polymer properties. Metal content was determined by Rutherford backscattering spectrometry (RBS) and X-ray photoelectronic spectroscopy (XPS). Alkyl ligands seemed not to affect sensitively the final metal content, but indenyl complexes led to higher grafted metal content. Immobilization on MAO-mediated systems afforded higher metal contents. XPS measurements evidenced a reduction in Zr, Ti or Hf binding energy (BE) after immobilization on silica or on MAO-modified silica, in the latter two different species being observed after signal deconvolution. Monitoring of the surface reaction by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that at this aluminum content residual silanol groups still remains, bearing probably two kind of species: one supported on silanol groups and another on MAO counterpart. Inductive effects from substituent on ligands influence in the catalyst activity, but this electronic effect is reduced in comparison to the steric effect played by the silica surface. Resulting polymers showed higher molecular weight than those produced by the soluble systems.

A series of supported catalysts were prepared by combining ( n BuCp) 2 ZrCl 2 and Cp 2 ZrCl 2 sequentially grafted on silica in different ratio (1:1 and 1:3) and immobilization order. Catalyst systems were characterized by Rutherford backscattering spectrometry (RBS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Grafted metal content remained comprised between 0.37 and 0.53 wt.% Zr/SiO 2 . All the systems were shown to be active in ethylene homopolymerization having methylaluminoxane as co-catalyst. Catalyst activity was shown to be dependent on the metallocene nature, but not on the addition order or molar ratio. The highest activity was achieved with Cp 2 ZrCl 2 /( n BuCp) 2 ZrCl 2 (1:3) catalyst system (ca. 4.26 kg PE (mmol Zr h) −1 ). Resulting polymers were characterized by GPC and DSC. In spite of bearing two catalyst centers, no bimodality was observed in the resulting polymers.

Propylene homopolymerization was carried out with Me2Si(Ind)2ZrCl2 immobilized on commercial MAO-modified silica by the in situ supporting technique. Adsorption isotherm determination for this metallocene on silica indicated that the saturation level is reached at 2.0 wt.% Zr/SMAO. Catalyst systems were shown to be active in the absence of external MAO, being activated by common alkylaluminum cocatalysts, namely triethylaluminum (TEA), isoprenylaluminum (IPRA) and triisobutylaluminum (TIBA). The effect of the nature and concentration of cocatalyst on catalyst activity and on polypropylene (PP) properties was evaluated. Best catalyst activity was observed in low concentration of IPRA (1.4 kg PP/g cat h). The resulting polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), 13 C nuclear magnetic resonance (NMR) spectroscopy, and scanning electronic microscopy (SEM). © 2003 Elsevier Science B.V. All rights reserved.

We investigated the limiting step of thermal growth of SiO2 on SiC. For that we determined the incorporation of oxygen during different stages of the oxidation process of 6H-SiC wafers as well as of Si wafers, for comparison. Oxidations in natural dry O2 followed by oxidations in isotopically enriched oxygen ( 18 O 2 ) were performed. Different times of oxidation in natural gas and chemical etching of the grown oxides were used to obtain samples representing different starting conditions. 18 O depth profiles were determined using the 18 O (p,α) 15 N nuclear reaction in the 151 keV resonance region of the cross-section curve. The results evidence that in the thickness range studied, thermal growth of SiO2 on SiC is limited by reaction of O2 with SiC, whereas, on Si the growth is limited by diffusion of O2 in the growing oxide film.

In the present work Et(IndH 4 ) 2 ZrCl 2 was immobilized on silica previously modified with different chemical compounds, namely VOCl 3 , SnCl 4 , Bu 3 SnH, Me 2 SiHCl, polymethylhydrosiloxane (PMHS) and such systems were compared to methylaluminoxane (MAO) pretreated systems. Bu 3 SnH-modified silica led to the highest zirconocene grafted content. Zr 3d 5/2 binding energy determined by X-ray spectroscopy (XPS) was shown to increase for Et(IndH 4 ) 2 ZrCl 2 supported on silica modified with VOCl 3 , MAO and Bu 3 SnH, suggesting the generation of more electron deficient surface species. All systems were shown to be active in ethylene–propylene copolymerization, presenting higher activity than those prepared by grafting the zirconocene on bare silica. Aging test with MAO-mediated systems showed that the catalyst bearing 2.0 wt.% Al/SiO 2 kept its catalyst activity at least for 3 months after preparation.

The homopolymerization of ethylene was investigated using the catalysts of (nBuCp)2ZrCl2 supported on PMHS-modified silicas (PMHS=polymethylhydrosiloxane). The effect of the amount of the organosilane polymer on the metallocene grafted content was studied in loadings of PMHS from 0.0 to 3.0 wt.% Si/SiO2, in which the grafted Zr content was from 0.9 to 0.3 wt.% Si/SiO2. The metal contents were determined by Rutherford backscattering spectrometry (RBS), while the catalyst stepwise preparation was monitored by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The chemical environment of the zirconocene surface species were further probed by X-ray spectroscopy (XPS) and the metal distribution was studied by Electron probe microanalysis (EPMA). These catalyst systems produced polyethylenes with a narrow molecular weight distribution using methylaluminoxane as co-catalyst, and their catalyst activities were three times greater than the one obtained with (nBuCp)2ZrCl2 supported on the bare SiO2. Effects of the support structure and the chemical modification on the catalyst performance are presented and discussed.

To minimize electrical degradation from thermal oxidation of 4H-SiC, a thin and stoichiometric SiO2 film was thermally grown, monitored by X-ray photoelectron spectroscopy. To obtain thicker films, SiO2 was deposited by sputtering. Reduction in the flatband voltage was observed when compared to SiO2 films thermally grown or deposited directly on 4H-SiC. Post-deposition annealing in Ar reduced the flatband voltage of the samples but induced an electrical degradation in the SiO2/4H-SiC interface. Nuclear reaction analyzes proved that the thin film thermally grown was not stable during the annealing, exchanging O atoms with the deposited film and with the gaseous ambient.

The incorporation of water vapor in SiO2 films thermally grown on 6H-SiC(0 0 0 1) and on Si (0 0 1) was investigated using nuclear reaction analyses. Water isotopically enriched in deuterium (2H or D) and in 18O was used. The dependence of incorporated D with the water annealing temperature and initial oxide thickness were inspected. The D amount in SiO2/SiC structures increases continuously with temperature and with initial oxide thickness, being incorporated in the surface, bulk, and interface regions of SiO2 films. However, in SiO2/Si, D is observed mostly in near-surface regions of the oxide and no remarkable dependence with temperature or initial oxide thickness was observed. At any annealing temperature, oxygen from water vapor was incorporated in all depths of the oxide films grown on SiC, in contrast with the SiO2/Si.

Metal contents in polymerization catalysts were comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) spectroscopy. Catalysts were prepared by grafting metallocene onto bare silica or onto silica chemically modified with methylaluminoxane (MAO). Catalysts were compressed as self-supporting pellets (RBS and XRF), or mounted on adhesive copper tape (XPS). The proximity of the mass of the atomic nuclei did not allow resolution by RBS of the signals corresponding to Zr and Nb, nor Si and Al in catalyst systems such as ( n BuCp) 2 ZrCl 2 /Cp 2 NbCl 2 /MAO/SiO 2 . On the other hand, Zr, Nb, Si and Al lines were completely resolved in an XRF spectrum. For supported metallocenes on bare silica, XPS measurement was ca . 40% higher than that obtained by RBS. Silica-supported zirconocene showed good agreement in Zr content determination by XRF and RBS.

Initial stages of in situ oxidation of a n-type 6H–SiC(0 0 0 1) sample were investigated using low energy ion scattering (LEIS) and angle resolved X-ray photoelectron spectroscopy. The very first oxidation products are shown to be silicon oxycarbides (SiC x O y ), while for longer oxidation times a mixture of SiC x O y and SiO 2 is formed in the near-surface region of the growing film. The composition profile of a much thicker oxide thermally grown on Ar + irradiated SiC was also investigated. The environment of Si atoms was probed as a function of depth by sequential LEIS and X-ray photoelectron spectroscopy measurements followed by HF etching. The results indicate the existence of a transition region, containing SiC x O y , between a pure stoichiometric layer of SiO 2 and the substrate. The analyses also indicate that the SiO 2 /SiC interface is rough.

We report on the use of the narrow and isolated resonance at 404.9 keV in the cross-section curve of the 27 Al(p,γ)28Si nuclear reaction for profiling Al in ultrathin aluminum oxide films on Si. The samples were characterized as-deposited and after thermal annealing, so that Al transport could be studied. An estimated depth resolution of approximately 0.4 nm near the surface of the films could be obtained owing to: (i) the very small resonance width; (ii) the high stopping power of Al2O3 for 404.9 keV protons; (iii) the high energy stability of the proton beam provided by the 500 kV HVEE ion implanter at Porto Alegre; and (iv) an apparent thickness magnification by a factor between 2.0 and 2.4 with the use of glancing incidence. This technique is compared to other methods for Al profiling like medium energy ion scattering and some sputtering-based techniques.

Aiming to understand the processes involved in the formation of the transition region between SiO2 and SiC, known as the interfacial region, early steps of SiC oxidation were investigated using mainly nuclear reaction analyses. Oxidation kinetics reveals that an abrupt change in the oxidation mechanism is observed in C-face oxide films when their thickness is around 10 nm, while a continuous change in the oxidation mechanism is observed in Si-face oxide films with thicknesses up to about 4 nm. This last thickness corresponds to the maximum width of the interfacial region. Changes observed in the oxidation mechanism were related to oxidation reaction and interfacial atom emission that may take place during oxide film growth. Besides, the activation energies of such processes were obtained.

Dielectric films on Si or SiC were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS) and ion beam analysis techniques, namely high and low energy ion scattering (RBS and LEIS) and narrow nuclear resonance profiling (NRP) combined with isotopic substitution. For the Si substrate, attention was focused on the thermal stability of materials candidate to replacing SiO 2 in Si-based microelectronic devices (so-called "high-k dielectrics"): Al 2 O 3, ZrSi x O y, ZrAl x O y, HfSi x O y, and GdSi x O y. Mobility of different atomic species — especially Si and O — was observed at both the surface of the films and the interface with Si. Such atomic transport may have serious consequences concerning application of these materials in the microelectronics industry. For the SiC substrate, attention was focused on the initial stages of thermal oxidation in O 2, seeking an understanding of its poorer electrical quality as compared to SiO 2– Si . It was found that the initial oxidation products are silicon oxycarbides ( SiC x O y), while for longer oxidation times a mixture of SiC x O y and SiO2 is formed in the near surface region of the growing 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.

We report on N doses and profiles in Si and (ultra)thin SiO 2 films on Si nitrided by plasma or ion beam processing in the 3–1000 eV energy range. Accurate elemental quantification was performed by nuclear reaction analysis (NRA), and elemental profiling with subnanometer depth resolution was achieved by narrow nuclear resonance profiling (NNRP) or medium energy ion scattering (MEIS). Heavy and shallow nitrogen incorporation was observed up to 0.7 N/(N + O) and peak N concentrations at 2 nm and less from the sample surface. Device-quality films were produced with post-nitridation annealing in O 2 , as indicated by C – V and I – V measurements.

We developed a low energy ion beam deposition system for isotope-selective modification of materials. It consists of a conventional ion implanter (HVEE 500 kV) and an attachable deceleration system. 29 (N 2 ) + ion beams were used for the nitridation of Si(0 0 1) and the resulting 15 N retained doses and profiles were determined by narrow nuclear resonance profiling. 29 Si was deposited on amorphous carbon films on Si(0 0 1) and the doses evaluated by channeled α particle beams with detection of scattered α at grazing angles. 29 Si was also deposited on Si(0 0 1) and the resulting profiles determined by narrow nuclear resonance.

Proton and deuteron beams were used to induce nuclear reactions ( 18 O ( p , α ) 15 N and 16 O ( d , p 0 ) 17 O ) in order to determine the areal densities of 18 O and 16 O in ultrathin films of SiO2 thermally grown on Si in 18 O 2 at low temperatures (700°C and 800°C) and pressures (0.7, 7.0 and 70.0 mbar). It was observed that film thickness increases with time, temperature and O2 pressure. Moreover, O2 partial pressure was seen to be determinant in a process that leads to a reversal in the growth kinetics behavior of SiO2 films for the two Si crystalline orientations tested: (0 0 1) and (1 1 1). In the sequence, experimental kinetics were fitted using a diffusion–reaction model (de Almeida et al., Phys. Rev. B 61 (2000) 12 992). In some cases good agreement was observed, allowing the determination of diffusivities of the oxidizing species through the oxide films.

Ultrathin films of Al2O3 deposited on Si were submitted to rapid thermal annealing in vacuum or in oxygen atmosphere, in the temperature range from 600 to 800 degrees C. Nuclear reaction profiling with subnanometric depth resolution evidenced mobility of O, Al, and Si species, and angle-resolved x-ray photoelectron spectroscopy revealed the formation of Si-Al-O compounds in near-surface regions, under oxidizing atmosphere at and above 700 degrees C. Under vacuum annealing all species remained essentially immobile. A model is presented based on diffusion-reaction equations capable of explaining the mobilities and reproducing the obtained profiles.

Thermal growth of silicon oxide films on Si in dry ${\mathrm{O}}_{2}$ is modeled as a dynamical system, assuming that it is basically a reaction-diffusion phenomenon. Relevant findings of the last decade are incorporated, as structure and composition of the oxide/Si interface and ${\mathrm{O}}_{2}$ transport and reaction at initial stages of growth. The present model departs from the well-established Deal and Grove framework [B. E. Deal and A. S. Grove, J. Appl. Phys. 36, 3770 (1965)] indicating that its basic assumptions, steady-state regime, and reaction between ${\mathrm{O}}_{2}$ and Si at a sharp oxide/Si interface are only attained asymptotically. Scaling properties of these model equations are explored, and experimental growth kinetics, obtained for a wide range of growth parameters including the small thickness range, are shown to be well described by the model.