Desempenho do inhame (taro) em plantio direto e no consórcio com crotalária, sob manejo orgânico.

Estudaram-se os efeitos do plantio direto em cobertura morta de aveia-preta e do consórcio com Crotalaria juncea, em sistema orgânico de produção de inhame, em ensaio na EE de Nova Friburgo(Pesagro-Rio), região serrana do estado do Rio de Janeiro. Utilizouse o delineamento de blocos ao acaso com quatro repetições, em esquema fatorial 2 x 2, onde os tratamentos corresponderam ao: modo de plantio (direto ou convencional) e modo de cultivo (monocultivo ou consórcio com crotalária). O cultivo consorciado com a leguminosa promoveu maior altura nas plantas do inhame, assim como reduziu a queima de folhas pelos raios solares. A população infestante de ervas espontâneas foi mais efetivamente controlada com a combinação entre consórcio e plantio direto. Nenhum dos tratamentos influenciou a produtividade do inhame, que foi considerada satisfatória, indicando o potencial do manejo orgânico adotado

Rapid thermal annealing of rare earth implanted ZnO epitaxial layers

Zinc oxide epilayers grown by metal organic vapour phase epitaxy on (0 0 0 1) sapphire substrates were doped with Praseodymium and Europium by ion implantation. The as-implanted samples were either annealed in air for 20 min in a tube furnace or rapid thermal annealing (RTA) was performed, for 2 min, in a nitrogen atmosphere. The samples were characterized by Rutherford Backscattering Spectrometry/Channelling and photoluminescence. The presented results indicate that in the as-implanted samples the majority of the rare earth (RE) ions are incorporated into substitutional Zn-sites. Furnace annealing at 1000 °C recovers the crystal quality of the samples but leads to an out-diffusion of the RE. RTA suppresses diffusion but lattice damage is not fully recovered at 1000 °C. More importantly, during RTA the RE ions are driven from the substitutional site and are now found mainly on random interstitial sites and no optical activation could be achievedCiência 2007SFRH/BD/45774/2008PTDC/CTM/100756/200

Enhanced dynamic annealing and optical activation of Eu implanted a-plane GaN

The implantation damage build-up and optical activation of a-plane and c-plane GaN epitaxial films were compared upon 300 keV Eu implantation at room temperature. The implantation defects cause an expansion of the lattice normal to the surface, i.e. along the a-direction in a-plane and along the c-direction in c-plane GaN. The defect profile is bimodal with a pronounced surface damage peak and a second damage peak deeper in the bulk of the samples in both cases. For both surface orientations, the bulk damage saturates for high fluences. Interestingly, the saturation level for a-plane GaN is nearly three times lower than that for c-plane material suggesting very efficient dynamic annealing and strong resistance to radiation. a-plane GaN also shows superior damage recovery during post-implant annealing compared to c-plane GaN. For the lowest fluence, damage in a-plane GaN was fully removed and strong Eu-related red luminescence is observed. Although some residual damage remained after annealing for higher fluences as well as in all c-plane samples, optical activation was achieved in all samples revealing the red emission lines due to the ^5Do -> ^7F_2transition in the Eu_3+ ion. The presented results demonstrate a great promise for the use of ion beam processing for a-plane GaN based electronic devices as well as for the development of radiation tolerant electronics

Radiation damage formation and annealing in GaN and ZnO

The radiation damage formation upon low temperature ion implantation and neutron irradiation has been compared for GaN and ZnO. Both materials exhibit strong dynamic annealing effects during implantation, even at 15 K, leading to high amorphisation thresholds. The damage build-up with fluence was found to proceed in a similar way for GaN and ZnO, both showing two saturation regimes below the amorphisation level where, over wide fluence regions, the damage level increases only very slowly. For low fluences the damage accumulation rate is similar for both materials. For higher fluences, on the other hand, GaN shows considerably higher damage levels and finally collapses into an amorphous structure while ZnO remains single crystalline up to the highest fluence of 7×1016 Ar/cm2. Neutron irradiation produces similar defects as ion implantation but within the entire sample while the defect density is much lower. The main effect of irradiation on the structural properties of GaN is an expansion of the c-lattice parameter. Optical properties are significantly deteriorated after irradiation and only recover partially after annealing. ZnO does not suffer such a pronounced change of the lattice parameters but reveals a strong deterioration of the surface, possibly due to blistering and exfoliation. At the same time the optical properties are less affected than for GaN. The near band edge emission is partly quenched but recovers to a large extend after annealing while broad defect bands are observed below the bandgap for irradiated samples, before and after annealing.FCT - PTDC/CTM/100756/2008Ciência 2007bilateral collaboration program Acções Integradas Luso-Alemãs/DAAD-FCTSFRH/BD/45774/2008SFRH/BD/44635/200

Towards the understanding of the intentionally induced yellow luminescence in GaN nanowires

Gallium nitride (GaN) has gained a lot of attention due to its high range of applications as solid state light emitters and detectors. However, the nitride samples often evidence deep level optically active defects affecting their performance on the high energy spectral region. This is the case for the commonly observed yellow luminescence (YL) band detected in bulk samples and thin films. Despite the large amount of literature reports on the processes that rule this emission in GaN films, there is still some controversy regarding the origin of the defects from where the YL originates. Furthermore, decreasing the dimensionality by analysing GaN nanowires provides new information on the luminescence behaviour when compared with epilayers. By using room temperature optical analysis, we aim to contribute to a deeper insight into the understanding of the YL detected in GaN NW, where YL was induced/enhanced by ion implantation and annealing treatments. YL was seen to be strongly dependent on different surface modifications, the analysis environment and illumination/irradiation excitation time. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

High pressure annealing of Europium implanted GaN

GaN epilayers were implanted with Eu to fluences of 1×1013 Eu/cm2 and 1×1015 Eu/cm2. Post-implant thermal annealing was performed in ultra-high nitrogen pressures at temperatures up to 1450 ºC. For the lower fluence effective structural recovery of the crystal was observed for annealing at 1000 ºC while optical activation could be further improved at higher annealing temperatures. The higher fluence samples also reveal good optical activation; however, some residual implantation damage remains even for annealing at 1450 ºC which leads to a reduced incorporation of Eu on substitutional sites, a broadening of the Eu luminescence lines and to a strongly reduced fraction of optically active Eu ions. Possibilities for further optimization of implantation and annealing conditions are discussed