Radiation Chemistry Provides Nanoscopic Insights into the Role of Intermediate Phases in CeO2 Mesocrystal Formation.

The role of intermediate phases in CeO2 mesocrystal formation from aqueous CeIII solutions subjected to γ-radiation was studied. Radiolytically formed hydroxyl radicals convert soluble CeIII into less soluble CeIV . Transmission electron microscopy (TEM) and X-ray diffraction studies of samples from different stages of the process allowed the identification of several stages in CeO2 mesocrystal evolution following the oxidation to CeIV : (1) formation of hydrated CeIV hydroxides, serving as intermediates in the liquid-to-solid phase transformation; (2) CeO2 primary particle growth inside the intermediate phase; (3) alignment of the primary particles into "pre-mesocrystals" and subsequently to mesocrystals, guided by confinement of the amorphous intermediate phase and accompanied by the formation of "mineral bridges". Further alignment of the obtained mesocrystals into supracrystals occurs upon slow drying, making it possible to form complex hierarchical architectures.

Tuning morphology, composition and oxygen reduction reaction (ORR) catalytic performance of manganese oxide particles fabricated by γ-radiation induced synthesis.

A γ-radiation induced synthesis method is used to fabricate manganese oxide catalysts through both reduction and oxidation routes. It is shown that the morphology, composition and electrochemical performance of the produced manganese oxide particles can be tuned by altering the redox conditions. The catalysts prepared via radiolytic oxidation have a hollow spherical morphology, possess γ-MnO2 structure and show high catalytic activity for the complete four-electron reaction pathway of the oxygen reduction reaction (ORR) in alkaline electrolyte. Meanwhile, the catalysts synthesized via radiolytic reduction possess a rod-like morphology with a Mn3O4 bulk structure and favour the incomplete two-electron reaction pathway for ORR. The high catalytic activity of the manganese oxide synthesized via the oxidation route can be attributed to high electrochemical surface area and increased amount of Mn3+ on the surface as compared to those in the sample obtained via the reduction route.

Single crystal structure and opto-electronic properties of oxidized Spiro-OMeTAD.

Single crystals of Spiro(TFSI)2 were grown, the optical and electronic properties were characterized and compared with neutral Spiro-OMeTAD. Density-functional theory was used to get insights into binding and band structure properties. The flat valence bands indicate a rather limited orbital overlap in Spiro(TFSI)2.

Contactless, nondestructive determination of dopant profiles of localized boron-diffused regions in silicon wafers at room temperature.

We develop a photoluminescence-based technique to determine dopant profiles of localized boron-diffused regions in silicon wafers and solar cell precursors employing two excitation wavelengths. The technique utilizes a strong dependence of room-temperature photoluminescence spectra on dopant profiles of diffused layers, courtesy of bandgap narrowing effects in heavily-doped silicon, and different penetration depths of the two excitation wavelengths in silicon. It is fast, contactless, and nondestructive. The measurements are performed at room temperature with micron-scale spatial resolution. We apply the technique to reconstruct dopant profiles of a large-area (1 cm × 1 cm) boron-diffused sample and heavily-doped regions (30 µm in diameter) of passivated-emitter rear localized-diffused solar cell precursors. The reconstructed profiles are confirmed with the well-established electrochemical capacitance voltage technique. The developed technique could be useful for determining boron dopant profiles in small doped features employed in both photovoltaic and microelectronic applications.

pH-Control as a way to fine-tune the Cu/Cu2O ratio in radiation induced synthesis of Cu2O particles.

In this work we have optimized the γ-radiation induced synthesis of Cu-Cu2O particles from aqueous CuSO4 solution by investigating the effect of pH. The obtained precipitate was analyzed by XRD and SEM techniques. The results indicated that at solution pH lower than 3.75, quasi-spherical Cu agglomerates can be formed while at pH higher than 4.40 only octahedron-shaped Cu2O particles are produced. At solution pH in the range from 3.75 to 4.40, a Cu-Cu2O mixture is produced. It was found that the relative amount of Cu2O in the Cu-Cu2O precipitate increases with pH in the studied range. The influence of solution pH on the Cu/Cu2O ratios in the product can be explained on the basis of pH-dependent competition kinetics between the reactions leading to either Cu or Cu2O formation. As a consequence, the composition and morphology of the Cu-Cu2O precipitate can be tuned by controlling pH of the aqueous CuSO4 solution during the γ-radiation induced synthesis.