CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

One‐Electron Oxidation of [M(PtBu3)2] (M=Pd,Pt): Isolation of Monomeric [Pd(PtBu3)2]+ and Redox‐Promoted C−H Bond Cyclometalation

Oxidation of zero‐valent phosphine complexes [M(P^tBu₃)₂] (M=Pd, Pt) has been investigated in 1,2‐difluorobenzene solution using cyclic voltammetry and subsequently using the ferrocenium cation as a chemical redox agent. In the case of palladium, a mononuclear paramagnetic Pd^I derivative was readily isolated from solution and fully characterized (EPR, X‐ray crystallography). While in situ electrochemical measurements are consistent with initial one‐electron oxidation, the heavier congener undergoes C−H bond cyclometalation and ultimately affords the 14 valence‐electron Pt^II complex [Pt(κ²_PC‐P^tBu₂CMe₂CH₂)(P^tBu₃)]⁺ with concomitant formation of [Pt(P^tBu₃)₂H]⁺.     

Possible transition from space-charge-limited to injection-limited conduction in poly(3-hexylthiophene) thin films

Two-terminal thin films of poly(3-hexylthiophene) (P3HT) with a wide electrode separation (150 m) has been studied using current-voltage characteristics at different temperatures. Space-charge-limited conduction (SCLC) with high injection barriers (1.3 eV) has been observed at all temperatures in the low electric field regime. A possible transition from SCLC to injection-limited conduction (ILC) is reported. The experimental results have been compared with the disorder-controlled injection model proposed by Arkhipov et al. [V.I. Arkhipov, H. von Seggern, E.V. Emilianova, Appl. Phys. Lett. 83 (2003) 5074; V.I. Arkhipov, E.V. Emilianova, Y.-H. Tak, H. Bässler, J. Appl. Phys. 84 (1998) 848; V.I. Arkhipov, U. Wolf, H. Bässler, Phys. Rev. B 59 (1999) 7514].     

Hepcidin in iron metabolism

Hepcidin, which has been recently identified both by biochemical and genomic approaches, is a 25 amino acid polypeptide synthesized mainly by hepatocytes and secreted into the plasma. Besides its potential activity in antimicrobial defense, hepcidin plays a major role in iron metabolism. It controls two key steps of iron bioavailability, likely through a hormonal action: digestive iron absorption by enterocytes and iron recycling by macrophages. In humans, this could explain that low levels of hepcidin found during juvenile haemochromatosis and HFE-1 genetic haemochromatosis are associated with an iron overload phenotype. Conversely, an increase of hepcidin expression is suspected to play a major role in the development of anemia of chronic inflammatory diseases. However, the regulatory mechanisms of hepcidin expression are multiple, including iron-related parameters, anemia, hypoxia, inflammation and hepatocyte function. Therefore, many physiological and pathological situations may modulate hepcidin expression and subsequently iron metabolism. A better knowledge of the biological effects of hepcidin and of its expression regulatory mechanisms will clarify the place of hepcidin in the diagnosis and treatment of iron-related diseases.     

Propriétés magnétiques et électriques de thiospinelles quaternaires

Quaternary thiospinels CuBB′S₄ (B = Ti, V, Cr, Co; B′ = Ti, Zr, Sn) containing monovalent copper in tetrahedral sites, have been prepared. The magnetic and electrical studies reveal two types of compounds: the former of formula CuB³⁺B′⁴⁺S₄ exhibit a semiconducting and paramagnetic behavior, the latter of formula CuB⁴⁺B′⁴⁺S₄ are metallic conducting and temperature-independent paramagnetic. The semiconductor and paramagnetic thiospinel CuCo_0.5Sn_1.5S₄ contains Co²⁺ and Sn⁴⁺.     

Switching in organic devices caused by nanoscale Schottky barrier patches

We have identified a possible electronic origin of metal filaments, invoked to explain the switching behavior of organic devices. Interfaces of two representative organics polyparaphenylene (PPP) and poly(2-methoxy-5-2-ethyl-hexyloxy-1,4-phenylenevinylene) with Ag are investigated using ballistic emission microscopy. Nanometer scale spatial nonuniformity of carrier injection is observed in ballistic electron emission microscopy images of both interfaces. The measured Schottky barrier (SB) appears to be consistent with metal states tailing into the gap of the PPP. We find that the SB values exhibit a distribution, even for the diodes with low ideality factors. The implications of this distribution on the measured physical properties of the diode are discussed, in light of work on devices of similar geometry, published in the literature. We also demonstrate that patches of low SB are likely to nucleate current filaments which can cause local ionization and are reported to be responsible for the switching behavior observed in metal-organic, metal-CuS and Ag-AgSe structures.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.