Electron Injection to Unoccupied Electronic States in Organic Semiconductor Thin Films Studied by Inverse Photoemission Spectroscopy (INTERFACE SCIENCE-Molecular Aggregates)

Inverse photoemission spectroscopy (IPES) in the vacuum ultraviolet region was applied to directly observe behaviors of electron injection into unoccupied electronic states in perylene-3,4,9,10- tetracarboxylic dianhydride (PTCDA) thin films due to alkali metal. By the analysis of the observed results the amount of injected electrons per PTCDA molecule was evaluated with relation to the dopant concentration. The derived relationship has been explained with the aid of DV-X calculations of energy levels concerned

Development and underground test of radiopure ZnMoO4 scintillating bolometers for the LUMINEU 0 nu 2 beta project

The LUMINEU (Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature) project envisages a high-sensitivity search for neutrinoless double beta (0 nu 2 beta) decay of Mo-100 with the help of scintillating bolometers based on zinc molybdate (ZnMoO4) crystals. One of the crucial points for the successful performance of this experiment is the development of a protocol for producing high quality large mass ZnMoO4 crystal scintillators with extremely high internal radiopurity. Here we report a significant progress in the development of large volume ZnMoO4 crystalline boules (with mass up to 1 kg) from deeply purified materials. We present and discuss the results achieved with two ZnMoO4 samples (with mass of about 0.3 kg each): one is a precursor of the LUMINEU project, while the other one was produced in the framework of LUMINEU with an improved purification / crystallization procedure. The two crystals were measured deep underground as scintillating bolometers in the EDELWEISS dilution refrigerator at the Laboratoire Souterrain de Modane (France) protected by a rock overburden corresponding to 4800 m w.e. The results indicate that both tested crystals are highly radiopure. However, the advanced LUMINEU sample shows a clear improvement with respect to the precursor, exhibiting only a trace internal contamination related with Po-210 at the level of 1 mBq/kg, while the activity of Ra-226 and Th-228 is below 0.005 mBq/kg. This demonstrates that the LUMINEU purification and crystal-growth procedures are very efficient and leads to radiopurity levels which exceedingly satisfy not only the LUMINEU goals but also the requirements of a next-generation 0 nu 2 beta experiment.Expérience souterraine avec détecteurs luminescents de molybdate de zinc pour l'étude de la masse et la nature des neutrino

Radiopure ZnMoO4 scintillating bolometers for the LUMINEU double-beta experiment

The results of R&D of radiopure zinc molybdate (ZnMoO4) based scintillating bolometers for the LUMINEU (Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature) double-beta decay experiment are presented. A dedicated two-stage molybdenum purification technique (sublimation in vacuum and recrystallization from aqueous solutions) and an advanced directional solidification method (the low-thermal-gradient Czochralski technique) were utilized to produce high optical quality large mass (∼1 kg) ZnMoO4 crystal boules and first 100Mo (99.5%) enriched Zn100MoO4 crystal scintillator (mass of ∼0.2 kg). Scintillating bolometers based on ZnMoO4 (≈ 0.33 kg) and Zn100MoO4 (≈ 0.06 kg) scintillation elements and high purity Ge wafers were tested in the EDELWEISS set-up at the Modane Underground Laboratory (France). Long term low temperature tests demonstrate excellent detectors’ performance and effectiveness of the purification and solidification procedures for the achievement of high radiopurity of the material, in particular with a bulk activity of 228Th and 226Ra below 4 µBq/kg. The adopted protocol was used to produce for the first time a large volume Zn100MoO4 crystal scintillator (mass of ∼1.4 kg, 100Mo enrichment is 99.5%) to search for neutrinoless double-beta decay of 100Mo in the framework of the LUMINEU project.Expérience souterraine avec détecteurs luminescents de molybdate de zinc pour l'étude de la masse et la nature des neutrino