Micromorfologia foliar na análise da fitotoxidez por glyphosate em Eucalyptus grandis

Foram avaliados os efeitos da deriva de formulações comerciais de glyphosate sobre a superfície foliar e o crescimento de clones de eucalipto. Mudas de seis clones foram submetidas a 129,6 g ha-1 de glyphosate das formulações comerciais Scout®, Roundup NA®, Roundup transorb® e Zapp QI®. Entre os clones não foram identificadas diferenças quanto à tolerância ao glyphosate. Plantas expostas à deriva simulada de Roundup transorb® e Zapp QI® apresentaram, respectivamente, a maior e menor porcentagem de intoxicação. Observou-se menor massa seca em plantas expostas ao glyphosate, independentemente da formulação, e menor altura naquelas expostas ao Scout® e ao Roundup transorb®. As características quantitativas da superfície foliar não foram afetadas pelo glyphosate. As alterações micromorfológicas ocorreram na ausência de danos visíveis e foram observadas em ambas as faces da epiderme, em todos os clones avaliados. Danos como erosão e aspecto amorfo das ceras epicuticulares e infestação por hifas fúngicas ocorreram, independentemente da formulação utilizada. A avaliação anatômica da superfície foliar foi relevante para descrição e interpretação dos danos causados pelo glyphosate. Os dados de crescimento e de intoxicação indicam o Zapp QI® como a formulação de menor risco para a cultura do eucalipto quanto aos efeitos indesejáveis da deriva.The effects of commercial glyphosate drift on the leaf surface and growth of eucalypt clones were evaluated. Seedlings of six clones were submitted to 129.6 g ha-1 sub-rate of commercial glyphosate formulations Scout®, Roundup NA®, Roundup transorb® and Zapp QI®. No differences in tolerance to glyphosate were observed among the clones. Plants exposed to simulated drift of Roundup transorb® and Zapp QI® presented the highest and lowest intoxication percentages, respectively. Plants exposed to glyphosate reduced dry biomass, regardless of the formulation, and also reduced height of the plants exposed to Scout® and Roundup transorb®. Leaf surface characteristics were not affected by glyphosate application. However, the micromorphological damages occurred prior to the appearance of visible symptoms, and were observed on both faces of the epidermis, in all clones tested. Damages such as erosion and amorphous aspect of epicuticular waxes and infestation of fungal hyphae occurred, independently of the formulation used. The anatomical evaluation of the leaf surface effectively described the damages caused by glyphosate. The growth and intoxication data indicate Zapp QI® formulation as presenting the lowest risk to eucalypt culture, in relation to the undesirable herbicide drift effects

Indirect optical transitions from carriers trapped on the delta doping and on the parabolic quantum well

AbstractIn this work, doped AlGaAs/GaAs parabolic quantum wells (PQW) with different well widths (from 1000Å up to 3000Å) were investigated by means of photoluminescence (PL) measurements. In order to achieve the 2DEG inside the PQW Si delta doping is placed at both side of the well. We have observed that the thickness of this space layer plays a major rule on the characteristics of the 2DEG. It has to be thicker enough to prevent any diffusions of Si to the well and thin enough to allow electrons migration inside the well. From PL measurement, we have observed beside the intra well transitions, indirect transitions involving still trapped electron on the delta doping and holes inside the PQW. For the thinness sample, we have measured a well defined PL peak at low energy side of the GaAs bulk emission. With the increasing of the well thickness this peak intensity decreases and for the thickest sample it almost disappears. Our theoretical calculation indicated that carriers (electron and holes) are more placed at the center of the PQW. In this way, when the well thickness increases the distance between electrons on the delta doping and holes on the well also increases, it decreases the probability of occurrence of these indirect optical transitions

New Results On Bound Excitons In Quantum Wells

The formation of bound excitons (BE) is investigated for a GaAs/GaAlAs multiple quantum well (QW) system. The photoluminescence (PL) spectra are analysed as a function of the excitation energy. It was found that the carriers photogeneration, either in the barrier or directly in the well, do not play an important role on the BE formation. We conclude that defects localized at interfaces are ionized by of capture charges which in turn bound the free exciton (FE).274194197Bacher, G., Hartmann, C., Scheweizer, H., Held, T., Mahler, G., Nickel, H., (1993) Phys. Rev. B, 47, p. 9545Fujiwara, K., Kanamoto, H., Tsukada, N., (1989) Phys. Rev. B, 40, p. 9698Christen, J., Bimberg, D., (1990) Phys. Rev. B, 42, p. 7213Srinivas, V., Chen, Y.J., Wood, C.E.C., (1994) Solid State Commun., 89, p. 611De Oliveira, J.B.B., Meneses, E.A., Silva, E.C.F., (1996) Proceedings of the 12th International Conference High Magnetic Fields in Semiconductor Physics, , accepted for publication Wurzbur

Influence Of Illumination On The Quantum Mobility Of A Two-dimensional Electron Gas In Si δ-doped Gaas/in0.15ga0.85as Quantum Wells

A series of GaAs/InGaAs quantum wells with a silicon δ-doped layer in the top barrier was investigated by Shubnikov-de Haas measurements as a function of the illumination time of the samples. During the illumination process strong modifications of the electronic density and the quantum mobility of each occupied subband were observed. Based on self-consistent calculations, the dominant mechanism which caused the changes in the subband quantum mobilities with illumination was elucidated.152121132Ferry, D.K., Goodnick, S.M., (1997) Transport in Nanostructures, , (Cambridge: Cambridge University Press)Nguyen, L.D., Radulescu, D.C., Foisy, M.C., Tasker, P.J., Eastman, L.F., (1989) IEEE Trans. Electron Devices, 36, p. 833Schubert, E.F., (1996) Delta Doping of Semiconductors, p. 498. , ed E F Schubert (Cambridge: Cambridge University Press)Ando, T., Fowler, A.B., Stern, F., (1982) Rev. Mod. Phys., 54, p. 437Pfeiffer, L., West, K.W., Stormer, H.L., Baldwin, K.W., (1989) Appl. Phys. Lett., 55, p. 1888Van Der Burgt, M., Karavolas, V.C., Peeters, F.M., Singleton, J., Nicholas, R.J., Herlach, F., Harris, J.J., Borghs, G., (1995) Phys. Rev. B, 52, p. 12218Lo, I., Kao, M.J., Hsu, W.C., Kuo, K.K., Chang, Y.C., Weng, H.M., Chiang, J.C., Tsay, S.F., (1996) Phys. Rev. B, 54, p. 4774Babinski, A., Li, G., Jagadish, C., (1997) Appl. Phys. Lett., 71, p. 1664Zervos, M., Elliott, M., Westwood, D.I., (1999) Appl. Phys. Lett., 74, p. 2026Cavalheiro, A., Da Silva, E.C.F., Takahashi, E.K., Quivy, A.A., Leite, J.R., Meneses, E.A., (2002) Phys. Rev. B, 65, p. 111Yamada, S., Makimoto, T., (1990) Appl. Phys. Lett., 57, p. 1022Henriques, A.B., (1994) Phys. Rev. B, 50, p. 8658Henriques, A.B., (1996) Phys. Rev. B, 53, p. 16365Ke, M.-L., Westwood, D., Williams, R.H., Godfrey, M.J., (1995) Phys. Rev. B, 51, p. 5038Reddy, U.K., Ji, G., Henderson, T., Huang, D., Houdre, R., Morkoc, H., Litton, C.W., (1989) J. Vac. Sci. Technol. B, 7, p. 1106Skuras, E., Kumar, R., Williams, R.L., Stradling, R.A., Dmochowski, J.E., Johnson, E.A., Mackinnon, A., Wisniewski, P., (1991) Semicond. Sci. Technol., 6, p. 535Koenraad, P.M., Van Hest, B.F.A., Blom, F.A.P., Van Dalen, R., Leys, M., Perenboom, J.A.A.J., Wolter, J.H., (1992) Physica B, 177, p. 485Harris, J.J., Murray, R., Foxon, C.T., (1993) Semicond. Sci. Technol., 8, p. 31Gobsch, G., Schulze, D., Paasch, G., (1988) Phys. Rev. B, 38, p. 10943Van Houten, H., Williamson, J.G., Broekart, M.E.I., Foxon, C.T., Harris, J.J., (1988) Phys. Rev. B, 37, p. 2756Stormer, H.L., Gossard, A.C., Wiegmann, W., (1982) Solid State Commun., 41, p. 70

Band-edge Modifications Due To Photogenerated Carriers In Single P-type δ-doped Gaas Layers

The photogenerated carrier-induced band-edge modifications of beryllium single δ-doped GaAs layers comprising a two-dimensional hole gas (2DHG) were investigated by means of photoluminescence, selective photoluminescence, and photoluminescence excitation spectroscopies. The results show direct evidence for a photoinduced electron confinement effect, which strongly enhances the radiative-recombination probability between electrons and holes of the 2DHG at low temperatures. © 1999 The American Physical Society.59746344637Schubert, E.F., (1994) Epitaxial Microstructures, 40, p. 1. , edited by A. C. Gossard, Semiconductors and Semimetals Academic, New YorkEnderlein, R., Sipahi, G.M., Scolfaro, L.M.R., Leite, J.R., Diaz, I.F.L., (1994) Mater. Sci. Eng., B, 35, p. 396Sipahi, G.M., Enderlein, R., Scolfaro, L.M.R., Leite, J.R., (1996) Phys. Rev. B, 53, p. 9930Buyanova, I.A., Chen, W.M., Henry, A., Ni, W.-X., Hansson, G.V., Monemar, B., (1996) Phys. Rev. B, 53, p. 9587Sipahi, G.M., Enderlein, R., Scolfaro, L.M.R., Leite, J.R., Da Silva, E.C.F., Levine, A., (1998) Phys. Rev. B, 57, p. 9168Gilinsky, A.M., Zhuravlev, K.S., Lubyshev, D.I., Migal, V.P., Preobrashenskii, V.V., Semiagin, B.R., (1991) Superlattices Microstruct., 10, p. 399Estimated from Hall measurements on molecular beam epitaxy grown bulk GaAsAshen, D.J., Dean, P.J., Hurle, D.T.J., Mullin, J.B., White, A.M., Greene, P.D., (1975) J. Phys. Chem. Solids, 36, p. 1041Richards, D., Wagner, J., Schneider, H., Hendorfer, G., Maier, M., Fischer, A., Ploog, K., (1993) Phys. Rev. B, 47, p. 962