Electronic and optical features of silicon carbide nanoparticles and nanocomposites
Electron paramagnetic resonance (EPR) investigations were carried out on hybrid Core-Shell nanomaterials associating silicon carbide nanoparticles and conducting polyaniline. The performed experiments compare the paramagnetic centres, the electronic transport features and the interface effects in two classes of materials, bare polymers and core-shell nanocomposites. By EPR, large doping rates were demonstrated in the bare doped polymers through important saturation phenomena which alter significantly the EPR spectrum features. Furthermore, memory effects were involved in the bare doped polymer with regard to the EPR spectrum features depending on the conditions of its thermal treatments. In the hybrid core-shell nanocomposites nor such saturation and nor memory effects were found on the EPR signals even if similar paramagnetic centres exist in both classes of samples. These behaviors were discussed taking into account the thermal stability and the doping efficiency in the considered classes of materials. Optimal doping levels were then realized and their effects on the polymers and the nanocomposites were clarified by using EPR and DRS (dielectric relaxation spectroscopy) measurements. Also, it is demonstrated that the charge carriers consist in polarons in the nanocomposites while bipolarons contributions dominate the electrical conductivity in the bare doped polymers.
Stoichiometry and interface effects on the electronic and optical properties of SiC nanoparticles
The physical properties of nanosized SiC particles are investigated as a function of the C/Si ratios. The synthesis by the laser pyrolysis process monitors the particle stoichiometry by the initial fluxes of the reactants (SiH4 and C2H2) and leads to Si- or C-rich batches. Spectroscopic methods such as EPR and Raman are used to probe the paramagnetic active electronic centres as well as the role played by the external surface composition on the effective vibrational and optical properties of the nanoparticles. Numerical methods are undertaken in order to point out the role played by the carbon or silicon excess on the interface properties. In particular, simulations by quantum chemistry codes within the configuration interaction and the parametric method (PM3) evidence the relevant features of the Raman spectra induced by a suitable distribution of C or Si excess within the SiC nanoparticles.
Positive Rights and State Constitutions: The Limits of Federal Rationality Review
INTRODUCTION ............................................................................................................................. 1132 I. STATE CONSTITUTIONAL WELFARE PRACTICE ............................................................. 1144 A. A Mandatory Obligation: The New York Example .................................................. 1144 B. A Typology of Current State Court Decisions .......................................................... 1145 IT. RECONSIDERING FEDERAL RATIONALITY REVIEW IN STATE CONSTITUTIONAL WELFARE CASES ................................................................................ 1153 A. Rationality Review and Positive Rights .................................................................. 1155 B. Rationality Review and Democratic Legitimacy .................................................... 1157 C. Rationality Review and Judicial Finality ............................................................. xi61 D. Rationality Review and Federalism ......................................................................... i166 E. Rationality Review Revisited .................................................................................... 1169 III. TOWARD A NEW STANDARD OF REVIEW ......................................................................... 1169 A. The Need for Judicial Review .................................................................................. 1170 B. Institutional Competence and Welfare Litigation ................................................... 1175 I. State Courts as Fact Gatherers ......................................................................... 1175 2. State Courts as Policymakers ......................................................................... " 179 3. State Courts as Rights Enforcers ..................................................................... 1182 C. A Jurisprudence of Consequences .............................................................................. 1183 D. Why Education and Not Welfare? ........................................................................... i86 E. Implications for Welfare Litigation ........................................................................... i9i IV. CONCLUSION ........................................................................................................................ 1194