Reaction of the butadiynyl complex (η5-C5Me5)Re(NO)(PPh3)(C⋮CC⋮CH) (ReC 4 H) with Cu(OAc)2 (pyridine, 80 °C) gives the μ-octatetraynediyl complex ReC 8 Re (70%). Analogous cross-coupling of ReC 4 H and ReC 2 H gives (after chromatography) ReC 4 Re (14%), ReC 6 Re (44%), and ReC 8 Re (15%). Longer sp carbon chains are accessed by reactions of ReC 4 H with n-BuLi and CuI, which give ReC 4 Cu. This isolable species is treated in situ with BrC⋮CSiEt3 or BrC⋮CC⋮CSiMe3 (excess EtNH2, THF) to give ReC 6 SiEt 3 or ReC 8 SiMe 3 (84−77%). Desilylations (wet n-Bu4N+F-) yield ReC 6 H or ReC 8 H (88−73%). Then Cu(OAc)2 (pyridine, 50 °C) gives ReC 12 Re or ReC 16 Re (71−67%). The former is also available from ReC 4 Cu and BrC⋮CC⋮CBr (45%), and ReC 10 Re can be accessed by cross-coupling. ReC 6 H and ReC 8 H are similarly converted to ReC 10 SiR 3 (R = Me, Et; 51−26%) and ReC 12 SiMe 3 (43%). Desilylation of ReC 10 SiR 3 gives labile ReC 10 H, but only black powder is obtained from ReC 12 SiMe 3 . In situ coupling of ReC 10 H gives ReC 20 Re (52−34%), which unlike lower homologues is not obtained in analytically pure form. The effects of chain length upon visible spectra (progressively red-shifted and more intense bands; ε >190 000 M-1 cm-1), IR/Raman νC ⋮ C patterns (progressively more bands), 13C NMR chemical shifts (asymptotic limit of 64−67 ppm for ReC⋮C( C ⋮ C ) n ), cyclic voltammetry (decreased reversibility of two oxidations; a gradual shift of the first to thermodynamically less favorable potentials, so that only a single oxidation is observed for ReC 20 Re), and thermal stabilities (solid-state decompositions at 155 °C, ReC 20 Re, and 178−217 °C, lower homologues) are studied in detail.

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Degradation mechanism beyond device self-heating in high power light-emitting diodes J. Appl. Phys. 109, 094509 (2011); 10.1063/1.3580264Optical studies of degradation of AlGaN quantum well based deep ultraviolet light emitting diodes

The nonlinear magnetoresistance of the two-dimensional electron gas measured in GaAs/ Al~aaq As heterostructures is attributed to the breakdown of edge-state electrons into the partly filled Landau level at the bulk part of the sample. Based on a simplified model, the transition between edge and bulk states is described with use of the electron mean free path at the edge channels. It was found that the mean free path scales exponentially with the product of the Hall voltage and the number of edge channels.High-mobility samples of GaAs/Al Gaq As heterostructures generally exhibit the strongly asymmetric line shapes of Shubnikovde Haas (SdH) oscillations in p(B) at high magnetic fields. Published data on this effect show a reduced resistivity (or conductivity) on the low-energy (i.e., high-magnetic-field) side of the peaks.~S uch an asymmetry can be suppressed or even reversed by several factors, including an increase of the width of the conducting channel in very narrow samples, enhancement of the measuring current and/or temperature, and the application of a backgate voltage to the structure. 2 It seems to be evident from the published data that there are two distinct types of asymmetry observed. The first of them concerns the form of individual subpeaks corresponding to one particular orientation of the spin within a Landau level. In extreme conditions (very narrow samples, low current density and temperature) these spin-resolved peaks take a sawtooth form. Several alternative explanations of this asymmetry have been suggested s depending on the particular conditions of the experiment and we will not deal with this effect here.The second type of asyrrimetry concerns the line shape of the double peak connected with one Landau level that consists of two more-or-less overlapping spin-resolved subpeaks. It has been observed that the relative heights of the two subpeaks depend strongly on the measuring current density j (Ref. 2) due to their widely different current dependence. This is the effect we want to address in this paper.In Fig. 1 we present the p(B) dependence for three different values of the measuring current I. The data have been taken at T = 1.3 K on a GaAs/Al Gaq As heterostructure in the form of a common Hall bar with the overall width of' the conducting channel n = 400 pm and the distance between voltage contacts along the sample I, = 1100 pm. The basic parameters of the 1.2 0. 8-C: 4g 0. 6-0. 4-2T l t I s IJ& 1«& iliad(I 10 12 B (T) FIG. 1. Dependence of the Shubnikovde Haas oscillations at T = 1.3 K on the measuring dc current I: I=0.7 pA (full line), I= 7 pA (dashed line), and I= 70 pA (dotted line), respectively.two-dimensional electron gas (2DEG) in the samplethe carrier density and mobilityhave been found to be n, = 5.5 x 10t~c m~and p = 3.04 x 10s cm2/V s, respectively. The most striking effect is a remarkable increase with I of the peak value for the spin-up subpeak (as compared to the spin-down one) for all Landau levels where the spin splitting has been observed. It is worth noting that with...