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Effects of the atomic level shift in the Auger neutralization rates of noble metal surfaces.

Monreal RC, Goebl D, Primetzhofer D, Bauer P - Nucl Instrum Methods Phys Res B (2013)

Bottom Line: In this work we compare characteristics of Auger neutralization of [Formula: see text] ions at noble metal and free-electron metal surfaces.For noble metals, we find that the position of the energy level of He with respect to the Fermi level has a non-negligible influence on the values of the calculated Auger rates through the evaluation of the surface dielectric susceptibility.We conclude that even though our calculated rates are accurate, further theoretical effort is needed to obtain realistic values of the energy level of He in front of these surfaces.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Centre (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain.

ABSTRACT

In this work we compare characteristics of Auger neutralization of [Formula: see text] ions at noble metal and free-electron metal surfaces. For noble metals, we find that the position of the energy level of He with respect to the Fermi level has a non-negligible influence on the values of the calculated Auger rates through the evaluation of the surface dielectric susceptibility. We conclude that even though our calculated rates are accurate, further theoretical effort is needed to obtain realistic values of the energy level of He in front of these surfaces.

No MeSH data available.


The Auger neutralization rate of He on Au (1 1 1) (a) and Al (1 1 1) (b) as a function of the distance to the surface for different lateral positions of He on the lattice unit cell.
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f0020: The Auger neutralization rate of He on Au (1 1 1) (a) and Al (1 1 1) (b) as a function of the distance to the surface for different lateral positions of He on the lattice unit cell.

Mentions: Calculations of the Auger transition rates for interacting with Ag (1 1 1) and (1 1 0) surfaces were presented in Refs. [42–44]. Here we will first compare the AN rates for He on Al (1 1 1) and Au (1 1 1) to appreciate the differences found between a noble metal and the prototype of a free-electron-metal. This is done in Fig. 3 which shows the rates as a function of the distance to the surface, for He on top of a metal atom. The main contribution to the rate of Al, which dominates at all distances, is made by the 3 orbitals of the on-top atom and its neighbors. The z direction is pointing towards the He atom. In contrast, the AN rate of Au is dominated by different orbitals depending on the distance between He and Au. At large distances, AN due to s electrons of many atoms of Au is the main contribution to the AN rate, while the prominent maximum found at 1 a.u. is due to the contribution of the d-electrons of the Au atom on top of He. Notice that the rate of Au can be 3× larger than that of Al at distances of ca. 1 a.u. but the opposite happens at 4 a.u. Another difference between Al and the other noble metals is that the latter show much more corrugation than Al with respect to Auger neutralization. Fig. 4(a) and (b) shows the AN rates of Au (1 1 1) and Al (1 1 1), respectively, assuming the He atom to be at the following lateral positions within the (1 1 1) unit cell: on-top, the two non-equivalent center positions and in the mid point between two neighbor atoms (Pos 1). We can appreciate that the rate of Al shows a weak dependence on lateral position compared to Au. The reason is, again, that the electrons contributing to the rate of Al are the extended 3sp electrons while the localized d electrons are the important ones in the Au case and for the other noble metals as well. It is also interesting to note that in the case of Au, the on-top rate is the smallest one close enough to the surface due to the strong decrease in overlap between the 1s electron of He and the 5d electrons of Au. In Figs. 3 and 4 the He level has been shifted up in energies by 2 eV, which is the typical value for small incident energies. We stress here that these rates yielded excellent agreement between calculated ion fractions and experiments for He on Ag (1 1 1) and (1 1 0) at grazing incidence in [42,43] and the azimuthal dependence of the ion fractions was very well reproduced. We also found a good agreement in the He/Al system investigated in Ref. [41]. This means that our calculated rates are accurate enough since they differ by a large factor in Ag and Al.


Effects of the atomic level shift in the Auger neutralization rates of noble metal surfaces.

Monreal RC, Goebl D, Primetzhofer D, Bauer P - Nucl Instrum Methods Phys Res B (2013)

The Auger neutralization rate of He on Au (1 1 1) (a) and Al (1 1 1) (b) as a function of the distance to the surface for different lateral positions of He on the lattice unit cell.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4376069&req=5

f0020: The Auger neutralization rate of He on Au (1 1 1) (a) and Al (1 1 1) (b) as a function of the distance to the surface for different lateral positions of He on the lattice unit cell.
Mentions: Calculations of the Auger transition rates for interacting with Ag (1 1 1) and (1 1 0) surfaces were presented in Refs. [42–44]. Here we will first compare the AN rates for He on Al (1 1 1) and Au (1 1 1) to appreciate the differences found between a noble metal and the prototype of a free-electron-metal. This is done in Fig. 3 which shows the rates as a function of the distance to the surface, for He on top of a metal atom. The main contribution to the rate of Al, which dominates at all distances, is made by the 3 orbitals of the on-top atom and its neighbors. The z direction is pointing towards the He atom. In contrast, the AN rate of Au is dominated by different orbitals depending on the distance between He and Au. At large distances, AN due to s electrons of many atoms of Au is the main contribution to the AN rate, while the prominent maximum found at 1 a.u. is due to the contribution of the d-electrons of the Au atom on top of He. Notice that the rate of Au can be 3× larger than that of Al at distances of ca. 1 a.u. but the opposite happens at 4 a.u. Another difference between Al and the other noble metals is that the latter show much more corrugation than Al with respect to Auger neutralization. Fig. 4(a) and (b) shows the AN rates of Au (1 1 1) and Al (1 1 1), respectively, assuming the He atom to be at the following lateral positions within the (1 1 1) unit cell: on-top, the two non-equivalent center positions and in the mid point between two neighbor atoms (Pos 1). We can appreciate that the rate of Al shows a weak dependence on lateral position compared to Au. The reason is, again, that the electrons contributing to the rate of Al are the extended 3sp electrons while the localized d electrons are the important ones in the Au case and for the other noble metals as well. It is also interesting to note that in the case of Au, the on-top rate is the smallest one close enough to the surface due to the strong decrease in overlap between the 1s electron of He and the 5d electrons of Au. In Figs. 3 and 4 the He level has been shifted up in energies by 2 eV, which is the typical value for small incident energies. We stress here that these rates yielded excellent agreement between calculated ion fractions and experiments for He on Ag (1 1 1) and (1 1 0) at grazing incidence in [42,43] and the azimuthal dependence of the ion fractions was very well reproduced. We also found a good agreement in the He/Al system investigated in Ref. [41]. This means that our calculated rates are accurate enough since they differ by a large factor in Ag and Al.

Bottom Line: In this work we compare characteristics of Auger neutralization of [Formula: see text] ions at noble metal and free-electron metal surfaces.For noble metals, we find that the position of the energy level of He with respect to the Fermi level has a non-negligible influence on the values of the calculated Auger rates through the evaluation of the surface dielectric susceptibility.We conclude that even though our calculated rates are accurate, further theoretical effort is needed to obtain realistic values of the energy level of He in front of these surfaces.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Centre (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain.

ABSTRACT

In this work we compare characteristics of Auger neutralization of [Formula: see text] ions at noble metal and free-electron metal surfaces. For noble metals, we find that the position of the energy level of He with respect to the Fermi level has a non-negligible influence on the values of the calculated Auger rates through the evaluation of the surface dielectric susceptibility. We conclude that even though our calculated rates are accurate, further theoretical effort is needed to obtain realistic values of the energy level of He in front of these surfaces.

No MeSH data available.