Procesos Auger en colisiones ion-superficie
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Universidad Nacional de Cuyo (Argentina). Instituto de Física "Dr. J. A. Balseiro
Comisión Nacional de Energía Atómica (Argentina). Centro Atómico Bariloche.
Comisión Nacional de Energía Atómica (Argentina). Centro Atómico Bariloche.
Resumen
Durante el bombardeo de un blanco sólido con iones de gases nobles de baja energia se puede observar emisión de electrones Auger de átomos del blanco y/o del proyectil. Ambos tipos de emisión presentan caracteristicas particulares; tanto los mecanismos de excitación como las formas de desexcitación pueden ser totalmente di-ferentes. En el presente trabaja hemos estudiado los siguientes casos: (i) emisión Auger del proyectil Hemos observada emisión Auger del Ne durante el bombardeo de superficies de Na, Mg, Al, y Si con iones Ne*. Hemos estudiado dicha emisión en función de la energía, ángulo de incidencia, y estada de carga del proyectil. Del análisis de estos experimentas se concluye que la emisión proviene de átomos de Ne que se han excitada y reflejado en su colisión con la superficie, y decaen en el vacio. No hemos observado emisión Auger caracteristica del proyectil durante el bombardeo de: superficies de K, V, y Ni con iones Ar+; superficies de Zr y Cs con iones Kr+ y Xe+, respectivamente; y superficies de Li y Be con iones He+. (i i) emisión Auger del blanco Hemos analizado los espectros de emisión de electrones Auger de superficies de Na, Mg, y Al bombardeadas con iones de gases nobles. En particular hemos estudiado el comportamiento de dichos espectros al variar la energia de los proyectiles y la función trabajo de la superficie. Los resultados obtenidos nos permiten identificar dos componentes en la linea Auger, correspondí entes a dos tipos de transiciones Auger: (a) parte de los átomos excitadas en el nivel 2p durante la cascada de colisiones, decaen en el interior del sólido con la participación de dos electrones de la banda de valencia, originando una estructura Auger ancha ( ~ 10 eV); (b) los átomos excitados en el nivel 2p que escapan del sólido durante la cascada de colisiones, decaen en el vacio en una transición Auger de tipo "atómico", originando picos angostos (ancho ~ 1 eV). El espectro total resulta de la superposición de ambos tipos de emisión. También hemos analizado espectros Auger de K, obtenidos durante el bombardeo con iones Ar* y K* de superficies de Be, Mg, Al, y Cu implantadas con K. Al igual que en las espectros Auger de Na, Mg, y Al , la linea Auger se compone de un pico angosto superpuesta sobre una estructura ancha. Ambas componentes corresponden a transiciones Auger en átomos de K con una vacancia 3p, que acurren en el vacío y en el interior del sólido, respectivamente.
Bombardment o-f solids targets with low-energy noble-gas ions can produce Auger electrón emission from the target atoms and/or from the projectiles. Both kinds o-f emission have particular features; both the excitation mechanisms and the deexcitatíon channels can be quite di-f-ferent. In this work we have studied the following cases: (i) Auger emission from the projectile We have observed Auger emission of Ne during the bombardment of Na, Mg, Al, and Si surfaces with Ne+ ions. We studied this emission as a function of the energy, incidence angle, and charge state of the projectile. From the analysis of these results we have concluded that the emission originates in the decay of excited Ne atoms moving outside the surface. The whole process involves reflection and excitation of the projectile in its collision with the salid, and the subsequent deexcitation while it escapes from the surface. We have not observed Auger emission from the projectile during the bombardment of K, V, and Ni surfaces with Ar+ ions; Zr and Cs surfaces with Kr"4" and Xe* ions, respectively; and Li and Be surfaces with He* ions. (ii) Auger emission from the target. We have analyzed the Na, Mg, and Al Auger electrón emission spectra abtained ' during "the bombardment of these surfaces -with noble-gas ions. In particular, we have studied the dependence af the Auger -feature on the projectile energy and the work -function of the surface. These results allow us to identify two components in the Auger feature, correspondíng to two kinds of Auger transitions: (a) part of the target atoms excited in the 2p level during the collision cascade, decay inside the salid in an Auger transitian invalving two electrans -fram the valence band; this originates a bandlike structure; (b) target atoms with a 2p vacancy which escape -from the sol id during the collision cascade decay in vacuum originating atomiclike peaks. The total Auger -feature is the superposi t i on of both kinds of decays. We have al so analyzed Auger spectra from K obtaíned during Ar+ and K+ bombardment of K— implanted Be, Mg, Al, and Cu surfaces. Similar to the Na, Mg, and Al Auger spectra, the K Auger feature is compased of an atomiclike peak superimposed on a bandlike structure. Both components carrespond to Auger transitions in K atoms with a 3p vacancy, occurring in vacuum and inside the salid, respectively.
Bombardment o-f solids targets with low-energy noble-gas ions can produce Auger electrón emission from the target atoms and/or from the projectiles. Both kinds o-f emission have particular features; both the excitation mechanisms and the deexcitatíon channels can be quite di-f-ferent. In this work we have studied the following cases: (i) Auger emission from the projectile We have observed Auger emission of Ne during the bombardment of Na, Mg, Al, and Si surfaces with Ne+ ions. We studied this emission as a function of the energy, incidence angle, and charge state of the projectile. From the analysis of these results we have concluded that the emission originates in the decay of excited Ne atoms moving outside the surface. The whole process involves reflection and excitation of the projectile in its collision with the salid, and the subsequent deexcitation while it escapes from the surface. We have not observed Auger emission from the projectile during the bombardment of K, V, and Ni surfaces with Ar+ ions; Zr and Cs surfaces with Kr"4" and Xe* ions, respectively; and Li and Be surfaces with He* ions. (ii) Auger emission from the target. We have analyzed the Na, Mg, and Al Auger electrón emission spectra abtained ' during "the bombardment of these surfaces -with noble-gas ions. In particular, we have studied the dependence af the Auger -feature on the projectile energy and the work -function of the surface. These results allow us to identify two components in the Auger feature, correspondíng to two kinds of Auger transitions: (a) part of the target atoms excited in the 2p level during the collision cascade, decay inside the salid in an Auger transitian invalving two electrans -fram the valence band; this originates a bandlike structure; (b) target atoms with a 2p vacancy which escape -from the sol id during the collision cascade decay in vacuum originating atomiclike peaks. The total Auger -feature is the superposi t i on of both kinds of decays. We have al so analyzed Auger spectra from K obtaíned during Ar+ and K+ bombardment of K— implanted Be, Mg, Al, and Cu surfaces. Similar to the Na, Mg, and Al Auger spectra, the K Auger feature is compased of an atomiclike peak superimposed on a bandlike structure. Both components carrespond to Auger transitions in K atoms with a 3p vacancy, occurring in vacuum and inside the salid, respectively.