Philippe Bugnon

Sublimation Not an Innocent Technique : A Case of Bis-Cyclometalated Iridium Emitter for OLED

Isomerization of a neutral bis-cyclometalated iridium(III) complex has been observed for the first time during the preparation of vacuum-processed organic light-emitting devices (OLEDs) and reproduced in solution. Isolation of the isomer revealed a cis organization of the two pyridine rings of the cyclometalating ligands. Photophysical studies show very similar emission properties of the two isomers. However, due to in situ isomerization, it is only possible to prepare vacuum-processed OLED devices having a mixture of isomers.

Transgenic Mice Reveal Novel Activities of Growth Hormone in Wound Repair, Angiogenesis, and Myofibroblast Differentiation

An increasing number of patients are being treated with growth hormone (GH) for the enhancement of body growth but also as an anti-aging strategy. However, the side effects of GH have been poorly defined. In this study we determined the effect of GH on wound repair and its mechanisms of action at the wound site. For this purpose, we performed wound healing studies in transgenic mice overexpressing GH. Full thickness incisional and excisional wounds of transgenic animals developed extensive, highly vascularized granulation tissue. However, wound bursting strength was not increased. Wound closure was strongly delayed as a result of enhanced granulation tissue formation and impaired wound contraction. The latter effect is most likely due to a significantly reduced number of myofibroblasts at the wound site. By using in vitro studies with stressed collagen lattices, we identified GH as an inhibitor of transforming growth factor β-induced myofibroblast differentiation, resulting in a reduction in fibroblast contractile activity. These results revealed novel roles of GH in angiogenesis and myofibroblast differentiation, which are most likely not mediated via insulin-like growth factors at the wound site. Furthermore, our data suggested that systemic GH treatment is detrimental for wound healing in healthy individuals.

An ester-substituted iridium complex for efficient vacuum-processed organic light-emitting diodes

An orange-red-emitting iridium complex (N958) was prepared, and its photophysical and device-based characteristics were investigated. Despite N958 displaying quite poor photophysical properties in solution (acetonitrile), organic light-emitting diode (OLED) devices based on the complex exhibit an efficiency close to 10%.

Optical properties of BiTeBr and BiTeCl

We present a comparative study of the optical properties-reflectance, transmission, and optical conductivity- and Raman spectra of two layered bismuth-tellurohalides BiTeBr and BiTeCl at 300 and 5 K, for light polarized in the a-b planes. Despite different space groups, the optical properties of the two compounds are very similar. Both materials are doped semiconductors, with the absorption edge above the optical gap which is lower in BiTeBr (0.62 eV) than in BiTeCl (0.77 eV). The same Rashba splitting is observed in the two materials. A non-Drude free carrier contribution in the optical conductivity, as well as three Raman and two infrared phonon modes, are observed in each compound. There is a dramatic difference in the highest infrared phonon intensity for the two compounds, and a difference in the doping levels. Aspects of the strong electron-phonon interaction are identified. Several interband transitions are assigned, among them the low-lying absorption beta which has the same value 0.25 eV in both compounds, and is caused by the Rashba spin splitting of the conduction band. An additional weak transition is found in BiTeCl, caused by the lower crystal symmetry.

Unusual Shubnikov-de Haas oscillations in BiTeCl

We report measurements of Shubnikov-de Haas oscillations in single crystals of BiTeCl at magnetic fields up to 31 T and at temperatures as low as 0.4 K. Two oscillation frequencies were resolved at the lowest temperatures, F-1 = 65 +/- 4 T and F-2 = 156 +/- 5 T. We also measured the infrared optical reflectance [R(omega)] and Hall effect; we propose that the two frequencies correspond respectively to the inner and outer Fermi sheets of the Rashba spin-split bulk conduction band. The bulk carrier concentration was n(e) approximate to 1 x 10(19) cm(-3) and the effective masses m(1)* = 0.20m(0) for the inner and m(2)* = 0.27m(0) for the outer sheet. Surprisingly, despite its low effective mass, we found that the amplitude of F-2 is very rapidly suppressed with increasing temperature, being almost undetectable above T approximate to 4 K.

Experimental determination of the bulk Rashba parameters in BiTeBr

Shubnikov-de Haas (SdH) oscillations, Hall effect, and optical reflectance

Universal scattering response across the type-II Weyl semimetal phase diagram

(\cal R(\omega))

Time-resolved ARPES at LACUS: Band Structure and Ultrafast Electron Dynamics of Solids

measurements have been performed on single crystals of BiTeBr. Under magnetic fields up to 32 tesla and at temperatures as low as 0.4 K, the SdH data shows a single oscillation frequency

Structural and electronic implications for carrier injection into organic semiconductors

F = 102 \pm 5\ \text{tesla}

Thermal diffusivity measurements of templated nanocomposite using infrared thermography

. The combined transport and optical studies establish that the SdH effect originates from the Rashba spin-split bulk conduction band, with the chemical potential situated about 13 meV below the crossing (Dirac) point. The bulk carrier concentration was