Effect of growth conditions on optical properties of CdSe/ZnSe single quantum dots

In this work, we have investigated the optical properties of two samples of CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect of vicinal-surface GaAs substrates on their properties has been also assessed. The thinner sample, grown on a substrate with vicinal surface, includes only dots with a diameter of less than 10 nm (type A islands). Islands of an average diameter of about 16 nm (type B islands) that are related to a phase transition via a Stranski-Krastanow growth process are also distributed in the thicker sample grown on an oriented substrate. We have studied the evolution of lineshapes of PL spectra for these two samples by improving spatial resolution that was achieved using nanoapertures or mesa structures. It was found that the use of a substrate with the vicinal surface leads to the suppression of excitonic PL emitted from a wetting layer.Comment: 2pages, 2 figures, Proceedings of International Conference On Superlattices Nano-Structures And Nano-Devices, July, Toulouse, France, to appear in the special issue of Physica

All-optical memory based on the injection locking bistability of a two-color laser diode

We study the injection locking bistability of a specially engineered two-color semiconductor Fabry-Perot laser. Oscillation in the uninjected primary mode leads to a bistability of single mode and two-color equilibria. With pulsed modulation of the injected power we demonstrate an all-optical memory element based on this bistability, where the uninjected primary mode is switched with 35 dB intensity contrast. Using experimental and theoretical analysis, we describe the associated bifurcation structure, which is not found in single mode systems with optical injection.Comment: 5 pages, 5 figure

An image classification approach to analyze the suppression of plant immunity by the human pathogen <it>Salmonella</it> Typhimurium

<p>Abstract</p> <p>Background</p> <p>The enteric pathogen <it>Salmonella</it> is the causative agent of the majority of food-borne bacterial poisonings. Resent research revealed that colonization of plants by <it>Salmonella</it> is an active infection process. <it>Salmonella</it> changes the metabolism and adjust the plant host by suppressing the defense mechanisms. In this report we developed an automatic algorithm to quantify the symptoms caused by <it>Salmonella</it> infection on <it>Arabidopsis</it>.</p> <p>Results</p> <p>The algorithm is designed to attribute image pixels into one of the two classes: healthy and unhealthy. The task is solved in three steps. First, we perform segmentation to divide the image into foreground and background. In the second step, a support vector machine (SVM) is applied to predict the class of each pixel belonging to the foreground. And finally, we do refinement by a neighborhood-check in order to omit all falsely classified pixels from the second step. The developed algorithm was tested on infection with the non-pathogenic <it>E. coli</it> and the plant pathogen <it>Pseudomonas syringae</it> and used to study the interaction between plants and <it>Salmonella</it> wild type and T3SS mutants. We proved that T3SS mutants of <it>Salmonella</it> are unable to suppress the plant defenses. Results obtained through the automatic analyses were further verified on biochemical and transcriptome levels.</p> <p>Conclusion</p> <p>This report presents an automatic pixel-based classification method for detecting “unhealthy” regions in leaf images. The proposed method was compared to existing method and showed a higher accuracy. We used this algorithm to study the impact of the human pathogenic bacterium <it>Salmonella</it> Typhimurium on plants immune system. The comparison between wild type bacteria and T3SS mutants showed similarity in the infection process in animals and in plants. Plant epidemiology is only one possible application of the proposed algorithm, it can be easily extended to other detection tasks, which also rely on color information, or even extended to other features.</p

Raman phonon modes of zinc blende InxGa1-xN alloy epitaxial layers

Transverse-optical (TO) and longitudinal-optical (LO) phonons of zinc blende InxGa1-xN (0 less than or equal to x less than or equal to 0.31) layers are observed through first-order micro-Raman scattering experiments. The samples are grown by molecular-beam epitaxy on GaAs (001) substrates, and x-ray diffraction measurements are performed to determine the epilayer alloy composition. Both the TO and LO phonons exhibit a one-mode-type behavior, and their frequencies display a linear dependence on the composition. The Raman data reported here are used to predict the A(1) (TO) and E-1 (TO) phonon frequencies of the hexagonal InxGa1-xN alloy. (C) 1999 American Institute of Physics. [S0003-6951(99)01234-6].7581095109

Strain-induced ordering in InxGa1-xN alloys

The energetics and thermodynamic properties of cubic (c-)InxGa1-xN alloys are investigated by combining first-principles total energy calculations, a concentration-dependent cluster-based model, and Monte Carlo simulations. The search for the ground-state energies leads to the conclusion that biaxial strain suppresses phase separation, and acts as a driving force for chemical ordering in c-InxGa1-xN alloys. Ordered superlattice structures, with composition xcongruent to0.5 and stable up to T=1000 K, arises as the relevant thermodynamic property of the strained alloy. We suggest that the In-rich phases recently observed by us in c-GaN/InxGa1-xN/GaN double heterostructures are ordered domains formed in the alloy layers due to biaxial strain. (C) 2003 American Institute of Physics.82244274427

Raman Phonon Modes Of Zinc Blende Inxga1 - Xn Alloy Epitaxial Layers

Transverse-optical (TO) and longitudinal-optical (LO) phonons of zinc blende InxGa1 - xN (0≤x ≤0.31) layers are observed through first-order micro-Raman scattering experiments. The samples are grown by molecular-beam epitaxy on GaAs (001) substrates, and x-ray diffraction measurements are performed to determine the epilayer alloy composition. Both the TO and LO phonons exhibit a one-mode-type behavior, and their frequencies display a linear dependence on the composition. The Raman data reported here are used to predict the A1 (TO) and E1 (TO) phonon frequencies of the hexagonal InxGa1 - xN alloy. © 1999 American Institute of Physics.75810951097Pankove, J.I., Moustakas, T., Gallium nitrides I (1998) Semiconductors and Semimetals, 50. , Academic, San Diego, CAShan, W., Walukiewicz, W., Haller, E.E., Little, B.D., Song, J.J., McCluskey, M.D., Johnson, N.M., Stall, R.A., (1998) J. Appl. Phys., 84, p. 4452Chichibu, S., Azuhata, T., Sota, T., Nakamura, S., (1997) Appl. Phys. Lett., 70, p. 2822Shan, W., Perlin, P., Ager J.W. III, Walukiewicz, W., Haller, E.E., McCluskey, M.D., Johnson, N.M., Bour, D.P., (1998) Appl. Phys. Lett., 73, p. 1613Chichibu, S., Azuhata, T., Sota, T., Nakamura, S., (1996) Appl. Phys. Lett., 69, p. 4188Narukawa, Y., Kawakami, Y., Funato, M., Fujita, S., Nakamura, S., (1997) Appl. Phys. Lett., 70, p. 981Orton, J.W., Foxon, C.T., (1998) Rep. Prog. Phys., 61, p. 1Abernathy, C.R., MacKenzie, J.D., Bharatan, S.R., Jones, K.S., Pearton, S.J., (1995) Appl. Phys. Lett., 66, p. 1632(1995) J. Vac. Sci. Technol. A, 13, p. 716Müllhäuser, J.R., Jenichen, B., Wassermeier, M., Brandt, O., Ploog, K.H., (1997) Appl. Phys. Lett., 71, p. 909Müllhäuser, J.R., Brandt, O., Trompert, A., Jenichen, B., Ploog, K.H., (1998) Appl. Phys. Lett., 73, p. 1230Holst, J., Hoffmann, A., Broser, I., Frey, T., Schöttker, B., As, D.J., Schikora, D., Lischka, K., (1999) MRS Internet J. Nitride Semicond. Res., 4 S1, pp. G23Feng, Z.C., Schurman, M., Tran, C.A., Salagaj, T., Karlicek, B., Ferguson, I., Stall, R.A., Pitt, G.D., (1998) Mater. Sci. Forum, 264-268, p. 1359Behr, D., Niebuhr, R., Obloh, H., Wagner, J., Bachem, K.H., Kaufmann, U., (1997) Mater. Res. Soc. Symp. Proc., 468, p. 213Osamura, K., Naka, S., Murakami, Y., (1975) J. Appl. Phys., 46, p. 3432Tabata, A., Lima, A.P., Teles, L.K., Scolfaro, L.M.R., Leite, J.R., Lemos, V., Schöttker, B., Lischka, K., (1999) Appl. Phys. Lett., 74, p. 362Tabata, A., Enderlein, R., Leite, J.R., Da Silva, S.W., Galzerani, J.C., Schikora, D., Kloidt, M., Lischka, K., (1996) J. Appl. Phys., 79, p. 4137Strite, S., Chandrasekhar, D., Smith, D.J., Sariel, J., Chen, H., Teraguchi, N., Morkoç, H., (1993) J. Cryst. Growth, 127, p. 204Ho, I., Stringfellow, G.B., (1996) Appl. Phys. Lett., 69, p. 2701Inushima, T., Yaguchi, T., Nagase, A., Iso, A., Shiraishi, T., (1996) Proceedings of the 6th Conference on Silicon Carbide and Related Materials, , Bristol(1996) Inst. Phys. Conf. Ser., 142, p. 971Dyck, J.S., Kash, K., Kim, K., Lambrecht, W.R.L., Hayman, C.C., Argoitia, A., Grossner, M.T., Angus, J.C., (1998) Mater. Res. Soc. Symp. Proc., 482, p. 549Yu, S., Kim, K.W., Bergman, L., Dutta, M., Stroscio, M.A., Zavada, J.M., (1998) Phys. Rev. B, 58, p. 15283Kwon, H.-J., Lee, Y.-H., Miki, O., Yamano, H., Yoshida, A., (1996) Appl. Phys. Lett., 69, p. 937Lee, M.-C., Lin, H.-C., Pan, Y.-C., Shu, C.-K., Ou, J., Chen, W.-H., Chen, W.-K., (1998) Appl. Phys. Lett., 73, p. 260

Evidence for phase-separated quantum dots in cubic InGaN layers from resonant Raman scattering

The emission of light in the blue-green region from cubic InxGa1-xN alloys grown by molecular beam epitaxy is observed at room temperature and 30 K. By using selective resonant Raman spectroscopy (RRS) we demonstrate that the emission;is due to quantum confinement effects taking place in phase-separated In-rich quantum dots formed in the layers. RRS data show that the In content of the dots fluctuates across the volume of the layers. We find that dot size and alloy fluctuation determine the emission wavelengths.84163666366

Structural properties and Raman modes of zinc blende InN epitaxial layers

We report on x-ray diffraction and micro-Raman scattering studies on zinc blende InN epitaxial films. The samples were grown by molecular beam epitaxy on GaAs(001) substrates using a InAs layer as a buffer. The transverse-optical (TO) and longitudinal-optical phonon frequencies at Gamma of c-InN are determined and compared to the corresponding values for c-GaN. Ab initio self-consistent calculations are carried out for the c-InN c-GaN lattice parameters and TO phonon frequencies. A good agreement between theory and experiment is found. (C) 1999 American Institute of Physics. [S0005-6951(99)00503-3].74336236

Conservation of Salmonella Infection Mechanisms in Plants and Animals

Salmonella virulence in animals depends on effectors injected by Type III Secretion Systems (T3SSs). In this report we demonstrate that Salmonella mutants that are unable to deliver effectors are also compromised in infection of Arabidopsis thaliana plants. Transcriptome analysis revealed that in contrast to wild type bacteria, T3SS mutants of Salmonella are compromised in suppressing highly conserved Arabidopsis genes that play a prominent role during Salmonella infection of animals. We also found that Salmonella originating from infected plants are equally virulent for human cells and mice. These results indicate a high degree of conservation in the defense and infection mechanism of animal and plant hosts during Salmonella infection

The Dark Side of the Salad: Salmonella typhimurium Overcomes the Innate Immune Response of Arabidopsis thaliana and Shows an Endopathogenic Lifestyle

Salmonella enterica serovar typhimurium contaminated vegetables and fruits are considerable sources of human infections. Bacteria present in raw plant-derived nutrients cause salmonellosis, the world wide most spread food poisoning. This facultative endopathogen enters and replicates in host cells and actively suppresses host immune responses. Although Salmonella survives on plants, the underlying bacterial infection mechanisms are only poorly understood. In this report we investigated the possibility to use Arabidopsis thaliana as a genetically tractable host system to study Salmonella-plant interactions. Using green fluorescent protein (GFP) marked bacteria, we show here that Salmonella can infect various Arabidopsis tissues and proliferate in intracelullar cellular compartments. Salmonella infection of Arabidopsis cells can occur via intact shoot or root tissues resulting in wilting, chlorosis and eventually death of the infected organs. Arabidopsis reacts to Salmonella by inducing the activation of mitogen-activated protein kinase (MAPK) cascades and enhanced expression of pathogenesis related (PR) genes. The induction of defense responses fails in plants that are compromised in ethylene or jasmonic acid signaling or in the MKK3-MPK6 MAPK pathway. These findings demonstrate that Arabidopsis represents a true host system for Salmonella, offering unique possibilities to study the interaction of this human pathogen with plants at the molecular level for developing novel drug targets and addressing current safety issues in human nutrition