Expulsion d'un électron lié dûe au choc de deux atomes d'un métal

Abstract

Dans cet article, nous poursuivons l'étude de l'émission cinétique d'ions secondaires dont le mécanisme se résume ainsi. Au cours d'un choc violent, un électron lié peut être arraché à un atome qui, s'il parvient à la surface du métal assez rapidement pour conserver son excitation, donnera un ion secondaire. Nous présentons ici le calcul de la probabilité de formation du trou profond. Lors du rapprochement de deux noyaux, un niveau moléculaire issu de deux niveaux atomiques liés voit son énergie croître jusqu'à atteindre le continuum des états libres. Un état lié virtuel prend alors naissance sur lequel un électron a un temps de vie fini. Si l'état lié virtuel interagit suffisamment longtemps avec les états non occupés de la bande de conduction, un trou peut s'y former et les atomes se séparer en emportant un trou profond

Formation of excited Ag atoms in sputtering of silver

“…͑1͒ are expected at higher Ag kinetic energies, however, when promotion of electrons from deeper levels can take place during a close collision. 24,25 If the 4d level of a Ag atom is promoted to an energy above the Fermi level, the electron may escape, leading to a semilocalized d hole. 25 According to a calculated ab initio correlation diagram for the Ag-Ag interaction, 10 such a promotion of semilocalized 4d levels can occur when the internuclear separation is below a critical distance of R c ϭ1.2 Å, which is attained during a collision in which the center-of-mass energy is above 135 eV.…”

“…24,25 If the 4d level of a Ag atom is promoted to an energy above the Fermi level, the electron may escape, leading to a semilocalized d hole. 25 According to a calculated ab initio correlation diagram for the Ag-Ag interaction, 10 such a promotion of semilocalized 4d levels can occur when the internuclear separation is below a critical distance of R c ϭ1.2 Å, which is attained during a collision in which the center-of-mass energy is above 135 eV. Thus, if a Ag atom in the cascade hits a surface Ag atom originally at rest from below with a kinetic energy of 270 eV or higher, the surface atom can be sputtered into the 4d 9 5s…”

Bombardment induced electron-capture processes at sodium halide surfaces

“…10 , both Sequences A.1 and A.4 describe a single-collision event in which both excitation and capture of a projectile electron take place simultaneously. Since the free-atom binding energies (ionization potentials) for an Ar 0 (15.8 eV) or Ne 0 (21.6 eV) projectile are not very high, electron capture, as well as excitation, during a collision is certainly possible and can be described in terms of quasi-molecular correlation diagrams and electron-promotion, curve-crossing mechanisms [ 2 – 4 ]. In Sequence A.1 the collision results in an excited, neutral Na 0 * atom that can decay by emitting a characteristic electron.…”

“…Inner-shell atomic excitation which takes place at ion-bombarded surfaces, as well as in heavy-particle gas-phase collisions, is known to result from orbital interactions and electron promotion processes that occur during energetic binary encounters. Collisional excitation mechanisms as originally proposed by Weizel and Beeck [ 1 ], Fano and Lichten [ 2 ], Barat and Lichten [ 3 ], and Joyes [ 4 ], involve atomic orbital perturbation, level crossing, and quasi-molecular orbital formation which, after the inelastic collision is over, result in an excited-state atom with an inner-shell vacancy. These excitation processes are now well established [ 5 ] and have recently been discussed by Kuik et al [ 6 ].…”

Émission Auger de l'argon lors du bombardement de divers métaux par des ions A+

“…Dans le cas où la collision a lieu au sein d'un métal, il peut y avoir interaction avec les électrons de la bande de conduction, pendant ou après la collision. L'interaction, qui peut être décrite par l'intermédiaire d'un état lié virtuel [44], ne remet pas en cause, au moins qualitativement, le mécanisme de formation du trou par promotion électronique et croisement d'orbitales.…”