Investigation of proton damage in III-V semiconductors by optical spectroscopy

We studied the damage produced by 2 MeV proton radiation on epitaxially grown InGaP/GaAs structure by means of spatially resolved Raman and photoluminescence (PL) spectroscopy. The irradiation was performed parallel to the sample surface in order to determine the proton penetration range in both compounds. An increase in the intensity of longitudinal optical phonons and a decrease in the luminescence were observed. We associate these changes with the creation of defects in the damaged region, also responsible for the observed change of the carrier concentration in the GaAs layer, determined by the shift of the phonon-plasmon coupled mode frequency. From the spatially resolved profile of the PL and phonon intensities, we obtained the proton range in both materials and we compared them with stopping and range of ions in matter simulations. The comparison between the experimentally obtained proton range and simulations shows a very good agreement for GaAs but a discrepancy of 20% for InGaP. This discrepancy can be explained in terms of limitations of the model to simulate the electronic orbitals and bonding structure of the simulated compound. In order to overcome this limitation, we propose an increase in 40% in the electronic stopping power for InGaP.Fil: Yaccuzzi, Exequiel Eliseo. Comision Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones no Nucleares. Gerencia Física (CAC). Grupo Energía Solar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sevak Khachadorian. Technishe Universitat Berlin; AlemaniaFil: Suarez, Sergio Gabriel. Comisión Nacional de Energí­a Atómica. Gerencia del Area Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Balseiro). División Colisiones Atómicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Reinoso, Maria Elba. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Goñi, A. R.. Consejo Superior de Investigaciones Científicas. Instituto de Ciencia de los Materiales de Barcelona; EspañaFil: Strittmatter, A.. Technishe Universitat Berlin; AlemaniaFil: Hoffmann, A.. Technishe Universitat Berlin; AlemaniaFil: Giudici, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones no Nucleares. Gerencia Física (CAC). Grupo Energía Solar; Argentin

Neuroprotective Effect of the AMPA Receptor Antagonist LY-293558 in Focal Cerebral Ischemia in the Cat

The effects of the glutamate α-amino-3-hydroxy 5-methyl-4-isoxazole propionate (AMPA) receptor antagonist LY-293558 in reducing ischemic brain damage have been assessed in halothane-anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of one middle cerebral artery, and the animals were killed 6 h later. The amount of early irreversible ischemic damage was assessed at 16 predetermined stereotactic planes by an observer blinded to treatment paradigm employed. Treatment with LY-293558 (15 mg/kg i.v., plus infusion of 7 mg/kg/h) initiated 30 min prior to middle cerebral artery occlusion reduced significantly (p < 0.02) the volume of ischemic damage (from 3,423 ± 212 mm3 of the cerebral hemisphere in vehicle-treated cats to 2,822 ± 569 mm3 in LY-293558-treated cats). The present data demonstrate that an AMPA receptor antagonist can reduce focal ischemic damage in a gyrencephalic species in which key physiological variables have been controlled and monitored throughout the postischemic period. These data provide additional support for the clinical evaluation of AMPA receptor antagonists in focal cerebral ischemia in humans