Optical control of spin coherence in singly charged (In,Ga)As/GaAs quantum dots

Electron spin coherence has been generated optically in n-type modulation doped (In,Ga)As/GaAs quantum dots (QDs) which contain on average a single electron per dot. The coherence arises from resonant excitation of the QDs by circularly-polarized laser pulses, creating a coherent superposition of an electron and a trion state. Time dependent Faraday rotation is used to probe the spin precession of the optically oriented electrons about a transverse magnetic field. Spin coherence generation can be controlled by pulse intensity, being most efficient for (2n+1)pi-pulses.Comment: 5 pages, 4 figure

Tailored quantum dots for entangled photon pair creation

We compare the asymmetry-induced exchange splitting delta_1 of the bright-exciton ground-state doublet in self-assembled (In,Ga)As/GaAs quantum dots, determined by Faraday rotation, with its homogeneous linewidth gamma, obtained from the radiative decay in time-resolved photoluminescence. Post-growth thermal annealing of the dot structures leads to a considerable increase of the homogeneous linewidth, while a strong reduction of the exchange splitting is simultaneously observed. The annealing can be tailored such that delta_1 and gamma become comparable, whereupon the carriers are still well confined. This opens the possibility to observe polarization entangled photon pairs through the biexciton decay cascade.Comment: 4 pages, 4 figure

Temperature dependence of capture coefficients in trapping phenomena

The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian type and is in a good agreement with the experimental results. © 2010 IEEE

Exciton dephasing via phonon interactions in InAs quantum dots: dependence on quantum confinement

We report systematic measurements of the dephasing of the excitonic ground-state transition in a series of InGaAs?GaAs quantum dots having different quantum confinement potentials. Using a highly sensitive four-wave mixing technique, we measure the polarization decay in the temperature range from 5 to 120 K on nine samples having the energy distance from the dot ground-state transition to the wetting layer continuum (confinement energy) tuned from 332 to 69 meV by thermal annealing. The width and the weight of the zero-phonon line in the homogeneous line shape are inferred from the measured polarization decay and are discussed within the framework of recent theoretical models of the exciton-acoustic phonon interaction in quantum dots. The weight of the zero-phonon line is found to decrease with increasing lattice temperature and confinement energy, consistently with theoretical predictions by the independent Boson model. The temperature-dependent width of the zero-phonon line is well reproduced by a thermally activated behavior having two constant activation energies of 6 and 28 meV, independent of confinement energy. Only the coefficient to the 6-meV activation energy shows a systematic increase with increasing confinement energy. These findings rule out that the process of one-phonon absorption from the excitonic ground state into higher energy states is the underlying dephasing mechanism

Stress-induced traps in multilayered structures

The trap parameters of defects in Si/CaF 2 multilayered structures were determined from the analysis of optical charging spectroscopy measurements. Two kinds of maxima were observed. Some of them were rather broad, corresponding to "normal" traps, while the others, very sharp, were attributed to stress-induced traps. A procedure of optimal linear smoothing the noisy experimental data has been developed and applied. This procedure is based on finding the minimal value of the relative error with respect to the value of the smoothing window. In order to obtain a better accuracy for the description of the trapping-detrapping process, a Gaussian temperature dependence of the capture cross-sections characterizing the stress-induced traps was introduced. Both the normal and the stress-induced traps have been characterized, including some previously considered as only noise features. ©2011 American Institute of Physics

Flexible heterostructures based on metal phthalocyanines thin films obtained by MAPLE

Heterostructures based on zinc phthalocyanine (ZnPc), magnesium phthalocyanine (MgPc) and 5,10,15,20-tetra(4-pyrydil)21H,23H-porphine (TPyP) were deposited on ITO flexible substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Organic heterostructures containing (TPyP/ZnPc(MgPc)) stacked or (ZnPc(MgPc):TPyP) mixed layers were characterized by X-ray diffraction-XRD, photoluminescence-PL, UV–vis and FTIR spectroscopy. No chemical decomposition of the initial materials was observed. The investigated structures present a large spectral absorption in the visible range making them suitable for organic photovoltaics applications (OPV). Scanning electron microscopy-SEM and atomic force microscopy-AFM revealed morphologies typical for the films prepared by MAPLE. The current–voltage characteristics of the investigated structures, measured in dark and under light, present an improvement in the current value (∼3 order of magnitude larger) for the structure based on the mixed layer (Al/MgPc:TPyP/ITO) in comparison with the stacked layer (Al/MgPc//TPyP/ITO). A photogeneration process was evidenced in the case of structures Al/ZnPc:TPyP/ITO with mixed layers

PINK1 Defect Causes Mitochondrial Dysfunction, Proteasomal Deficit and α-Synuclein Aggregation in Cell Culture Models of Parkinson's Disease

Mutations in PTEN induced kinase 1 (PINK1), a mitochondrial Ser/Thr kinase, cause an autosomal recessive form of Parkinson's disease (PD), PARK6. Here, we report that PINK1 exists as a dimer in mitochondrial protein complexes that co-migrate with respiratory chain complexes in sucrose gradients. PARK6 related mutations do not affect this dimerization and its associated complexes. Using in vitro cell culture systems, we found that mutant PINK1 or PINK1 knock-down caused deficits in mitochondrial respiration and ATP synthesis. Furthermore, proteasome function is impaired with a loss of PINK1. Importantly, these deficits are accompanied by increased α-synclein aggregation. Our results indicate that it will be important to delineate the relationship between mitochondrial functional deficits, proteasome dysfunction and α-synclein aggregation

Studies regarding the performance of some bluegrass and ryegrass varieties used in lawns under the climatic conditions in the forrest steppe of North - East Romania

The turf varieties sold in Romania are breeded in foreign countries that are different in terms of climatic conditions, and may not always perform as well in conditions of extreme drought and heat that often occurs in the summers of eastern Romania. From this point of view, trial testing of imported turf varieties in this part of the country or another, throughout the country, would be a necessary and positive research especially if it would be achieved before selling these varieties on the romanian market, thus pleasing the quality demands of the public and also helping the breeders to optimize the range of varieties for specific areas. In this research we had the chance to test by trial, for a period of two consecutive years, seven varieties of kentucky bluegrass (KB) and three of perennial ryegrass (PR) breeded in the USA, the world market leader in turfgrass varieties. Field trials were started at a farm located nearby the city of Iasi, in 2005, consisting in randomized plots replicated three times for statistical interpretation of the data. The soil was a chernozem soil type. Each plot had an area of 4 m2. Seeding rate was 15g m-1 for bluegrass varieties and 30g m-1 as recommended by the breeding companies. The weather conditions in the area are quite rough for turfgrasses, with 520 mm of rain annualy and an annual mean temperature of 9.60C. The evaluation of turgrass overall quality was done using the visual rating scale used by the National Turfgrass Evaluation Program from USA. This organization is well accepted in more than 30 countries around the world, and the rating scale is used by most of the turfgrass breeders. Following results we learned that ryegrass quality is affected by the prolonged lack of water in a higher percentage than bluegrass, by comparing the quality ratings of these two varieties over a period of two years, correlated with the climatic conditions from the same time period. The monthly ratings were used to calculate the annual mean quality rating for each individual variety, and the best quality was observed in the year 2006, for varieties: Nudestiny rated 6.5, Liberator rated 6.2 and Impact rated 6.1, all three belonging to Poa pratensis species. This study proves the importance of trial testing of imported turf varities because of the following reasons: there are large differences between turfgrass species in terms of turf quality influenced by climatic conditions but also there are differences betwen varieties that belong to the same botanical species, as we have seen in the seven bluegrass varieties studied