Image acceleration of highly charged xenon ions in front of a metal surface

Abstract

Xe^"*" ions with charge up to ^ =33 and energies 3.7^ keV are scattered under a grazing angle of incidence from a clean and flat Al(l 11) surface. Because of the image charge interaction the ions are accelerated on the incident path towards the surface plane which results in increased effective angles of incidence for the scattered projectiles. From the angular distributions for reflected neutralized projectiles we deduce the image charge interaction energies gained by the incident ions in front of the surface. Our data are in fair agreement with a q ^^^ dependence for the image energies as predicted from a simple classical overbarrier model. PACS numbers: 79.20.Nc, 34.70.+e, In recent years the study of the interactions of slow multiply charged ions with surfaces has developed into a very active field of research in particle solid interactions.Investigations of x rays and in particular electron emission have provided important data for elucidating the relevant interaction mechanisms. There is convincing evidence that the multielectron capture and loss processes in front of a metal surface result in the population of multiply and highly excited levels in the projectile and that most of the sparsely populated inner shells of those "hollow atoms" survive the approach to the surface [1-5]. As a consequence most of the high initial potential energy of the projectile is available close to the surface plane and is liberated there or in the bulk in close encounters with target atoms and conduction electrons.In all these studies the kinetic energy of the projectiles with respect to the approach to the surface is an important parameter, since this energy is related directly to the interaction times with the surface. Already at an early stage in the study of the scattering of multicharged ions from surfaces it was pointed out that the acceleration of ions due to their image charge interaction sets a lower bound with respect to the interaction energies and interaction times with the surface [6]. Experimental studies on electron emission phenomena at low effective projectile energies (eV domain) have revealed clear indications for such effects [7-9]. Recently we have demonstrated a method to measure directly those image interaction energies [10].Aside from the relevance of image interaction energies for a reliable knowledge of the effective interaction energies/times in scattering experiments, their magnitude also provides important information on the interaction mechanisms. Since the image charge interaction is strongly dependent on the charge state of the particle, image interaction energies reflect the dynamics of neutralization of the multicharged ions in front of the surface plane [6][7][8][9][10][11][12]. Based on the demonstration of the feasibility of our method with ions in low charge states [10], we present here first consequent studies of image charge interaction energies for incident ions ranging from low to relatively high charges.In our experiments we scatter Xe^"*" ions under a grazing angle of incidence ^in^=...

Population dynamics of the ions SVI, ClVII and ArVIII interacting with solid surfaces

“…The corresponding neutralization distances R N c ¼ R N c ðn c ; ZÞ could be compared (for Ar Zþ and Xe Zþ ions) with the data deduced on the base of experimentally obtained kinetic energy gain due to the image acceleration of the ions [23,24].…”

“…We point out that, up to now, direct observation of the electron exchange ''localization'' was experimentally performed only for the ionization of neutral Rydberg atoms (Z ¼ 1) [20,21] and H 2 molecules [22] slowly approaching solid surfaces. Also, the ''localization'' of the electron capture into the particular (critical) Rydberg state n A ¼ n c of multiply charged ions can be deduced, under some plausible physical assumptions [31], from the measured projectile kinetic energy gains [23,24]. This paper is organized as follows.…”

“…The electron exchange during the interaction of ions with solid surfaces has been intensively studied in the last decade both theoretically [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and experimentally [20][21][22][23][24]; for more details about some of the relevant theoretical models and experiments, see reviews [25] and [26]. However, the quantum description of the events in the time interval between the initial and final ''measurements'' is still uncompleted.…”

Slow multicharged ions hitting a solid surface: From hollow atoms to novel applications

“…On the one hand, the slow electron emission proceeds until close surface impact and the corresponding electron yield increases with decreasing perpendicular impact energy, for which DEq.im is setting the lower limit [6]. On the other hand, for grazing incident MCI on a very flat (monocrystalline) target surface the outgoing trajectory of the neutralized projectile becomes steeper than its incoming one due to image charge acceleration which acts until the close surface contact and subsequent specular reflection [7].…”

Collisions of Slow Highly Charged Ions With Surfaces

“…(7) was first indirectly tested ( Fig. 2) by measurements [27,28] of the energy gain due to the image acceleration (Eq. (3)).…”