Formation of silicon nanocrystals in sapphire by ion implantation and the origin of visible photoluminescence

Cataloged from PDF version of article.Silicon nanocrystals, average sizes ranging between 3 and 7 nm, were formed in sapphire matrix by ion implantation and subsequent annealing. Evolution of the nanocrystals was detected by Raman spectroscopy and x-ray diffraction (XRD). Raman spectra display that clusters in the matrix start to form nanocrystalline structures at annealing temperatures as low as 800 degrees C in samples with high dose Si implantation. The onset temperature of crystallization increases with decreasing dose. Raman spectroscopy and XRD reveal gradual transformation of Si clusters into crystalline form. Visible photoluminescence band appears following implantation and its intensity increases with subsequent annealing process. While the center of the peak does not shift, the intensity of the peak decreases with increasing dose. The origin of the observed photoluminescence is discussed in terms of radiation induced defects in the sapphire matrix. (c) 2006 American Institute of Physics

Effects of salicylic acid on wheat salt sensitivity

Salicylic acid (SA), a plant phenolic compound, is now considered as a hormone-like endogenous regulator, and there is a great interest to clarify its role in the defence mechanisms against biotic and abiotic stressors. In this study, investigations on the effects of foliar-applied SA on salt sensitivity, hydrogen peroxide (H2O2) generation and activities of antioxidant enzymes like peroxidase (POX) and catalase (CAT) in plant tissues under salt stress was performed. SA treatment significantly increased the fresh and dry weights in both root and shoots of wheat plants under salt stress. Similarly, POX and CAT activities were also augmented by SA treatment. While the highest POX activity was recorded at SA+120 mM NaCl, CAT activity also exhibited an increase compared to salt treatment without SA. In parallel to increasing antioxidative activity, SA treatment decreased H2O2 content when compared to plants growing under salt stress without SA. The results revealed that salt-induced deleterious effect in wheat seedlings were significantly alleviated by the SA treatment. SA can be used as a signal molecule to investigate plant defense to abiotic stress. After the application of SA, increasing tolerance of wheat seedlings to salt stress may be related to increases in antioxidative enzyme activitiy.Key words: Wheat, salicylic acid, antioxidative enzyme activities, peroxidase (POX), catalase (CAT), hydrogen peroxide (H2O2) content

HESEB The Helmholtz state of the art Soft X Ray Undulator beamline at SESAME

SESAME and a consortium of five Helmholtz Centers are designing and installing a state of the art soft X Ray undulator beamline at the SESAME light source in Amman, Jordan. Funding is provided by the Helmholtz Association over a four year project cycle that started in January 2019. This is an interim report covering the first 36 months of the project where the construction and installation has been almost completed and commissioning and characterization of the beamline is about to start. Additionally, seminars, workshops, and a training program are part of the project aimed at establishing a broad user communit

HESEB Soft X ray Beamline ID11 L at SESAME Performance and First User Experiments

The ID11 L HESEB Soft X ray beamline and end station significantly enhance soft X ray research capabilities. Operating in an energy range of 90 1800 eV, extendable to 70 2000 eV, the beamline achieves high performance with an energy resolution of E amp; 916;E gt; 8000 and a photon flux of 1010 to 3.4 1012 photons s. Its 500 250 amp; 956;m lt; beam spot size allows for precise measurements, including studies on magnetic materials using variable circular polarization. This paper presents the end station s design, including the receptacle, magnetic sample holder, and ambient pressure capabilities, along with experimental results that demonstrate the beamline s potential for diverse scientific application

Theoretical and spectroscopic investigations on the structure and bonding in B-C-N thin films

Cataloged from PDF version of article.In this study, we have synthesized boron, carbon, and nitrogen containing films using RF sputter deposition. We investigated the effects of deposition parameters on the chemical environment of boron, carbon, and nitrogen atoms inside the films. Techniques used for this purpose were grazing incidence reflectance-Fourier-transform infrared spectroscopy (GIR-FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). GIR-FTIR experiments on the B-C-N films deposited indicated presence of multiple features in the 600 to 1700 cm(-1) range for the infrared (IR) spectra. Analysis of the IR spectra, XPS and the corresponding EELS data from the films has been done in a collective manner. The results from this study suggested even under nitrogen rich synthesis conditions carbon atoms in the B-C-N films prefer to be surrounded by other carbon atoms rather than boron and/or nitrogen. Furthermore, we have observed a similar behavior in the chemistry of B-C-N films deposited with increasing substrate bias conditions. In order to better understand these results, we have compared and evaluated the relative stability of various nearest-neighbor and structural configurations of carbon atoms in a single BN sheet using DFT calculations. These calculations also indicated that structures and configurations that increase the relative amount of C-C bonding with respect to B-C and/or C-N were energetically favorable than otherwise. As a conclusion, carbon tends to phase-segregate in to carbon clusters rather than displaying a homogeneous distribution for the films deposited in this study under the deposition conditions studied. (C) 2009 Elsevier B.V. All rights reserved

CHANGES IN INORGANIC COMPOSITION AND ACCUMULATION OF HEAVY METALS IN AQUATIC PLANTS GROWING IN THE AREAS CONTAMINATED BY CEMENT FACTORY

The aim of the study was to evaluate the changes in contents of some essential elements and heavy metals in the aquatic plants as a reflection of the impact of chemical nature pollution in a cement factory region (CFR). For this purpose, P, S, K, Ca, Fe, Cl, Mn, Cu, Zn, Mo, Ni, Si, Al and Cd concentrations were measured in the aquatic plants, Lemna minor, Potamogeton natans and Ceratophyllum submersum, taken from a CFR. As a control, aquatic plants were collected at a distance of 2000 m from the outer zone of the cement factory. Inorganic element compositions were measured by energy dispersive X-ray fluorescence spectrometry (EDXRF). Three aquatic plants exhibited similar changes in contents of microelements and macroelements in their leaves. P, S, K, Cl, Ca and Mo contents in plants grown in the CFR were reduced significantly compared to control plants, whereas their contents of Al, Mn, Fe, Ni, Cu, Zn and Cd were very high. According to these findings, it is possible that aquatic plants inhabiting in the vicinity of cement factory sustain the deficiency of important essential elements like P, S, K, Ca and Mo and greatly accumulate heavy metals like Al, Mn, Fe, Ni, Cu, Zn and Cd. In addition, results of water analysis showed that heavy metal content such as Cu, Pb, Zn, Co and Al of water taken from CFR was remarkably high than that of outer zone of CFR. These findings with relation to changes in inorganic composition can contribute to be elucidated of effect mechanism on growth and development of aquatic plants of pollution resulted from cement factories

Effects of Progesterone, β-Estradiol, and Androsterone on the Changes of Inorganic Element Content in Barley Leaves

The present study was performed to determine the changes in inorganic element content in barley leaves of mammalian sex hormones (MSH). Barley leaves were sprayed with 10(-4), 10(-6), 10(-9), 10(-12), 10(-15) M concentrations of progesterone, beta-estradiol, and androsterone at 7th day after sowing. The plants were harvested at the end of 18 days after treatment with MSH solutions. The inorganic element concentrations were determined using wavelength dispersive X-ray fluorescence spectroscopy technique. Although the all MSH concentrations significantly (p < 0.05) increased the concentrations of calcium, magnesium, phosphorus, sulfur, copper, manganese, aluminum, zinc, iron, potassium, and chlorine, it decreased those of sodium concentration in barley leaves. The maximum changes in the element concentrations were obtained at 10(-9) M for plant leaves treated with progesterone, 10(-6) M for plant leaves treated with beta-estradiol and androsterone. The present study elucidated that MSH significantly (p < 0.05) affected the inorganic element concentrations in barley leaves

Formation of silicon nanocrystals in sapphire by ion implantation and the origin of visible photoluminescence

Silicon nanocrystals, average sizes ranging between 3 and 7 nm, were formed in sapphire matrix by ion implantation and subsequent annealing. Evolution of the nanocrystals was detected by Raman spectroscopy and x-ray diffraction ͑XRD͒. Raman spectra display that clusters in the matrix start to form nanocrystalline structures at annealing temperatures as low as 800°C in samples with high dose Si implantation. The onset temperature of crystallization increases with decreasing dose. Raman spectroscopy and XRD reveal gradual transformation of Si clusters into crystalline form. Visible photoluminescence band appears following implantation and its intensity increases with subsequent annealing process. While the center of the peak does not shift, the intensity of the peak decreases with increasing dose. The origin of the observed photoluminescence is discussed in terms of radiation induced defects in the sapphire matrix

Effects of salicylic acid on wheat salt sensitivity

Salicylic acid (SA), a plant phenolic compound, is now considered as a hormone-like endogenous regulator, and there is a great interest to clarify its role in the defence mechanisms against biotic and abiotic stressors. In this study, investigations on the effects of foliar-applied SA on salt sensitivity, hydrogen peroxide (H2O2) generation and activities of antioxidant enzymes like peroxidase (POX) and catalase (CAT) in plant tissues under salt stress was performed. SA treatment significantly increased the fresh and dry weights in both root and shoots of wheat plants under salt stress. Similarly, POX and CAT activities were also augmented by SA treatment. While the highest POX activity was recorded at SA+120 mM NaCl, CAT activity also exhibited an increase compared to salt treatment without SA. In parallel to increasing antioxidative activity, SA treatment decreased H2O2 content when compared to plants growing under salt stress without SA. The results revealed that salt-induced deleterious effect in wheat seedlings were significantly alleviated by the SA treatment. SA can be used as a signal molecule to investigate plant defense to abiotic stress. After the application of SA, increasing tolerance of wheat seedlings to salt stress may be related to increases in antioxidative enzyme activitiy

EFFECT OF LEAD STRESS ON ANTIOXIDANT MECHANISM AND DNA PROFILE IN DIFFERENT WHEAT CULTIVARS

Lead (Pb) is known to cause highly toxic direct and indirect effects on plants, animals and humans. This research was an attempt to study relationship between oxidative damage and DNA structure in two wheat genotypes exposed to heavy metal lead stress. For this reason, changes in root and shoot growth, the modulation of enzymatic antioxidant system, production of reactive oxygen species (ROS) and the extent of oxidative damage (membranes and DNA structure) in a drought-tolerant (cv. Bezostaya) and drought-sensitive (cv. Alpu) cultivars of wheat under 1, 1.5 and 2 mM lead concentrations (Pb(NO3)(2)) were determined. At the 5th day of germination stage under lead stress, root and shoot lengths decreased when compared with the control for both genotypes. While the activities of superoxide dismutase (SOD), peroxidase (PDX) and ascorbate peroxidase (APX) enzymes in both of wheat varieties increased markedly, catalase (CAT) activity decreased under the stress. Lead induced oxidative stress, causing membrane injury, measured by changes in malondialdehyde (MDA) contents, superoxide anion (O-2(-)) productions and hydrogen peroxide (H2O2) level in two wheat cultivars. The increment degree of MDA in Alpu was higher than those in B ezostaya. Effects of lead stress on genetic material were determined by comparing Random Amplified Polymorphic DNA (RAPD) profiles of normal and treated-wheat seedlings. Lead treatments caused to marked DNA mutations, however, the deterioration in genetic material of sensitive species was higher than in resistant one. As a result, this study showed that Alpu cultivar was negatively affected more than the Bezostaya variety from lead-induced oxidative stress