Reactive compatibilization of recycled low- or high-density polyethylenes (LDPE and HDPE, respectively) and ground tire rubber (GTR) via chemical interactions of pre-functionalized components in their blend interface has been carried out. Polyethylene component was functionalized with maleic anhydride (MAH); as well, the rubber component was modified via functionalization with MAH or acrylamide (AAm) using chemically or irradiation (gamma-rays) induced grafting techniques. The grafting degree and molecular mass distribution of the functionalized polymers have been measured via FTIR and Size Exclusion Chromatography (SEC) analyses, respectively. Additional coupling agents such as p-phenylene diamine (PDA) and polyamide fiber were used for producing some thermoplastic elastomer (TPE). Thermoplastic elastomer materials based on synthesized reactive polyethylenes and GTR as well as ethylene-propylene-diene monomer rubber (EPDM) were prepared by dynamic vulcanization of the rubber phase inside thermoplastic (polyethylene) matrix and their phase structure, and main properties have been studied using DSC, DMTA and mechanical testing. As a result, high performance thermoplastic elastomers based on functionalized polyethylene and ground rubber with improved mechanical properties have been developed.

The spectral and temperature characteristics of the magnetooptical Kerr effect and the optical properties of an La0.7Ca0.25Ba0.05MnO3 single crystal are studied. The data obtained are used to calculate the components of the permittivity tensor, whose behavior is interpreted within the framework of the known models of the electronic structure of manganites.

We report the influence of light irradiation on the electrical properties of oxygen deficient La0.7Pbx □0.3 − x MnO3 − δ thin films with (x = 0.1) and without (x = 0.3) cation vacancies (noted by □). Transient photoconductivity and photoinduced insulator–metal transition occurs at low temperatures in these thin films. Introducing cation vacancies does not increase the Mn4+/Mn3+ ratio but creates a sheared structure that decreases the oxygen content and can explain our transport and photoconductivity results.

Light illumination produces major, interesting changes of the electrical properties of oxygen deficient ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin films. At small oxygen deficiency, the classical insulator-metal $(I\ensuremath{-}M)$ transition at a temperature ${T}_{p}$ decreases with increasing oxygen deficiency. The low-temperature metallic behavior in darkness shows a persistent increase of the conductivity with light. This photoconductivity increases with oxygen deficiency (from a few to $60%).$ At large oxygen deficiency, the films are semiconducting in darkness, from helium to room temperature and light induces a transient photoconductivity and a low-temperature $I\ensuremath{-}M$ transition. The intriguing possibility of collective light induced magnetism is discussed.

L.T.E. CNRS UMR 6595, Universite ́ de Nice-Sophia Antipolis, Parc Valrose 06108 Nice Cedex 02, France L.P.M.C. CNRS UMR 6622, Universite ́ de Nice-Sophia Antipolis, Parc Valrose 06108 Nice Cedex 02, France Unité Mixte de Physique CNRS/Thomson-CSF (UMR 0137), 91404 Orsay, France Physics Department-0319, University of California –San Diego, La Jolla, California 92093-0319 ~Received 18 July 2000; revised manuscript received 15 December 2000; published 10 April 2001 !

Light illumination produces major, interesting changes of the electrical properties of oxygen deficient La2/3Sr1/3MnO3-delta thin films. At small oxygen deficiency, the classical insulator-metal (I-M) transition at a temperature T-p decreases with increasing oxygen deficiency. The low-temperature metallic behavior in darkness shows a persistent increase of the conductivity with light. This photoconductivity increases with oxygen deficiency (from a few to 60%). At large oxygen deficiency, the films are semiconducting in darkness, from helium to room temperature and light induces a transient photoconductivity and a low-temperature I-M transition. The intriguing possibility of collective light induced magnetism is discussed.

We report the analogies between the electrical properties at low temperatures of oxygen deficient cuprates and manganites thin films under illumination by UV or visible light. For the cuprates, a decrease of the oxygen content decreases the critical temperature of the transition from the normal to the superconducting state while for the manganites it decreases the transition temperature at which the insulator-metal transition occurs. For full oxygenated cuprates and manganites thin films there is no effect of the illumination on the electrical properties of the films. For small oxygen deficient cuprates (in the normal state) and manganites thin films, light increases substantially the conductivity leading to a persistent photoinduced conductivity (PPC) and the effect of persistent photoconductivity increases with oxygen deficiency. For high oxygen deficiency, the cuprates and the manganites are insulating. In that case, a transient photoconductivity is observed in the cuprates and manganites. Moreover, a photoinduced insulator-metal (I-M) transition appears in these insulating thin films.

We report two types of photoconductivity effects observed by illumination of oxygen deficient manganites thin films with UV or visible light. One is the persistent photoconductivity effect observed at low temperature (T < 30 K) when the thin film is in the metallic state. This effect is analog to the persistent photoconductivity observed in the high T c superconductors particularly in oxygen deficient YBaCuO thin films. The other type of effect is a photo-induced transition to metallic state at temperatures T < 100 K observed in Pr2/3Sr1/3MnO3 thin film which stays always in the semiconducting state in the darkness. This photo induced metallic transition from a semiconducting state leads to a non persistent colossal photoconductivity (several orders of magnitude of decrease of the resistivity).

We report, for the first time, experiments of persistent photoconductivity (PPC) in thin films of manganese perovskites La0.7Ca0.25Ba0.05MnO3 and La0.7Ca0.2Ba0.1MnO3 showing a persistent decrease of a few percent of the resistance after illumination with visible light. These persistent photoinduced effects are seen only in a range of low temperatures (< 25 K) well below the insulator-metal transition at respectively T-c=173 K and T-c=120 K. In this low temperature range, the transport mechanism is rather of activated hopping type regime.

Positron-beam experiments have been carried out to characterize defects in metal-organic vapor-phase-epitaxially grown GaAs layers on (100)GaAs and (100)Si substrates. The Te-doped GaAs/GaAs layer (n = 2 X 10(15) cm-3) appears to be free of vacancies which are present in similarly doped bulk n-type GaAs crystals. The heteroepitaxial GaAs/Si layer with the low (< 10(7) cm-2) dislocation density is also free of positron trapping. At a higher dislocation density of 10(7)-10(8) cm-2 positrons detect Si clusters. In the epilayer with the dislocation density 10(8) cm-2 vacancies and small vacancy clusters at the concentration < 10(17) cm-3 are found. In addition, in this epilayer a 0.3-mum layer next to the interface has a high concentration of Si clusters which trap all positrons stopped there. The findings are in agreement with the earlier observations of Si diffusion in GaAs/Si epilayers and vacancy-type point defects in deformed bulk GaAs.

The possibility of growing strained GaAs layers on GaAs (100) substrates using a nonpseudomorphic GaAs1−xPx buffer layers is examined. It is demonstrated that by varying the phosphorus content in a thick buffer (significantly thicker than the critical thickness for strain relaxation), uniform biaxial stress magnitude can be monitored in GaAs, e.g., 8 kbar biaxial compression can be achieved by a P composition of 0.16 in the alloy. After an x-ray diffraction study of strain relaxation in the buffers, low temperature photoluminescence measurements are used to evaluate the effect of such a stress upon monitoring the near band gap properties of GaAs layers.

An investigation of GaAs films grown on Si substrates for solar cells is presented. Two types of layered structures are examined. One is GaAs grown on Ge (2–3 µm) coated Si substrate; GaAs/Ge/Si structure. The other is a direct growth of GaAs on Si using an original AlAs nucleating layer (10nm). Both type materials exhibit good structural and electrical characteristics. The solar cell fabricated using the AlAs nucleating layer showed 12.2% (AMO) conversion efficiency.

A novel technique, based on a stress balance principle, is proposed to control residual stress magnitude in GaAs layers grown on Si substrates. It is demonstrated that, using a suitable GaAs1−xPx buffer layer, room (300 K) or low (2 K) temperature stress-free GaAs can be grown on Si (100).

It is demonstrated that, using a suitable GaAs1-xPx buffer layer, stress free GaAs can be grown on Si (100) substrates. In fact the lattice mismatch between GaAs and GaAs1-xPx will introduce a (100) biaxial compressive stress component in the GaAs top layer. The magnitude of this lattice mismatch induced stress can be monitored from 1 to 7 Kbar by varying the P content of the buffer from x = 0.02 to x = 0.15. Results on GaAs/ GaAs1-xPx/ Si (100) ( but also on strained GaAs grown on GaAs1-xPx/GaAs(100)) are discussed in the light of photoluminescence and X-ray diffraction experiments. It is shown that, by adjusting the P composition in such buffer, the lattice mismatch induced stress can exactly compensate the thermoelastic stress, leading thus to an almost stress free GaAs at room (300K) or at low (2K) temperature.

Excited and ground states of carbon, silicon and germanium acceptor impurities in GaAs on Si are studied using selective donor-acceptor pair luminescence (SPL) and photoluminescence excitation. Acceptor spectroscopy in such a biaxially strained material is shown to be possible and a good agreement between the experimental observation and a theoretical approach based on effective mass calculations is obtained for the ground state. Ground-to-excited-state 1S32-2S32 transitions of C, Si and Ge were observed for the first time. A noticeable binding energy reduction of these excited states is evidenced.

We report first-order Raman spectroscopy and low-temperature photoluminescence (PL) studies of GaAs layers grown by metalorganic vapor phase epitaxy (MOVPE) on InP (100) substrates. From both the shift of the longitudinal-optical phonons in the Raman spectra and the splitting and shift of band-edge exciton lines in PL, the epilayers are found to be under (100) coplanar tensile stress, which is consistent with the difference between the thermoelastic properties of the two materials. The PL analysis shows that carbon is the main residual acceptor impurity in MOVPE-grown GaAs/InP.

The crystallographic structure of crater-containing oriented overgrowths on GaAs epitaxial layers grown by metalorganic vapor phase epitaxy (MOVPE) has been studied by transmission electron microscopy and diffraction. The craters are the visible outward sign of polycrystalline constructions of 6 grains or more having low order twin relations with the matrix. Anisotropic development of the facets of the grains is proposed to be the growth mechanism of the hillock. Stacking fault pyramids are present but their correlation with craters and overgrowths is not systematic.

Preferential diffusion channels of silicon are evidenced in GaAs grown by metalorganic vapor phase epitaxy on Si(100). The density of these diffusion channels is found to be consistent with the measured dislocation density. In addition, combining scanning electron microscopy and x-ray fluorescence it is shown that a large amount of Si emerges at the surface inside small 〈011〉 overgrowth oriented defects (≊1 μm) present at the GaAs/Si surface.