Atomic structure of thin dysprosium-silicide layers on Si(1 1 1)

doi:10.1016/j.susc.2005.11.029

Surface Science

Volume 600, Issue 3, 1 February 2006, Pages 755-761

https://doi.org/10.1016/j.susc.2005.11.029 Get rights and content

Abstract

We report on scanning tunneling microscopy results of thin dysprosium-silicide layers formed on Si(1 1 1). In the submonolayer regime, both a $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ and a 5 × 2 superstructure were found. Based on images taken at different tunneling conditions, a structure model could be developed for the $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ superstructure. For one monolayer, a 1 × 1 superstructure based on hexagonal DySi₂ was observed, while several monolayers thick films are characterized by a $\sqrt{3} \times \sqrt{3} R 30 °$ superstructure from Dy₃Si₅.

Introduction

Silicides of the trivalent rare earth metals grown as thin films on silicon surfaces are currently of high interest because of their low Schottky-barrier heights on n-type substrates [1], [2], [3], [4], [5], their epitaxial growth on Si(1 1 1) [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18] and the self-organized formation of nanowires on Si(0 0 1) [19], [20], [21], [22], [23]. These silicide films can be prepared by rare-earth deposition and subsequent annealing. In several publications, the atomic structure of films on Si(1 1 1) has been studied using scanning tunneling microscopy (STM), showing a variety of structures mainly depending on the rare-earth element and its coverage. Most of these studies were related to erbium silicides. The detailed atomic structure of the different structures occurring for dysprosium-silicide films on Si(1 1 1), however, is not completely understood up to now.

Here we present detailed scanning tunneling microscopy results on the growth of dysprosium-silicide films in the range from submonolayer coverages up to a few monolayers. Submonolayer silicide layers are characterized by domains of $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ and 5 × 2 superstructures. At one monolayer, a 1 × 1 structure is found, and several monolayers thick films form a $\sqrt{3} \times \sqrt{3} R 30 °$ superstructure. Using a variety of tunneling conditions, we were able to derive the atomic structure of the $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ submonolayer and the $\sqrt{3} \times \sqrt{3} R 30 °$ multilayer films.

Section snippets

Experimental

Si(1 1 1)7 × 7 substrates were prepared by repeated flashing of n-type Si(1 1 1) wafers followed by slow cooling down in order to enable the formation of a defect-free reconstruction. The silicide films were grown in situ by depositing dysprosium on the clean Si(1 1 1)7 × 7 surface held at room temperature, and afterwards annealing at 500 °C for 1 min to form the silicide. The base pressure was lower than 5 × 10⁻¹¹ mbar and did not exceed 2 × 10⁻¹⁰ mbar during preparation. Such vacuum conditions are prerequisite

The general growth behavior

Representative overview images of the typical silicide structures are presented in Fig. 1. At submonolayer coverages (Fig. 1(a)), the surface is covered by domains of the bare Si(1 1 1)7 × 7 and occasionally also the Si(1 1 1)5 × 5 surface [25] as well as by thin silicide films with $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ and 5 × 2 superstructures. The $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ superstructure is characterized by triangular domains separated by linear dislocations. At sufficiently high coverages, also the rather flat monolayer structure becomes

Summary

Using high-resolution scanning tunneling microscopy, we were able to observe different atomic structures during growth of dysprosium silicides on Si(1 1 1). At submonolayer coverages, structures with $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ and 5 × 2 periodicity were found. A detailed structure model could be derived for the $2 \sqrt{3} \times 2 \sqrt{3} R 30 °$ superstructure as well as for the dislocation network separating the single-crystalline domains. The monolayer is formed from hexagonal DySi₂ with a 1 × 1 periodicity, and both silicon layers in the

Acknowledgements

The authors would like to thank the Deutsche Forschungsgemeinschaft, Projects Da408/5 and Da408/11 for financial support.

References (25)

T.P. Roge et al.
Surf. Sci.
(1996)
P. Wetzel et al.
Surf. Sci.
(1996)
T.P. Roge et al.
Surf. Sci.
(1997)
J.A. Martín-Gago et al.
Surf. Sci.
(1996)
M. Lohmeier et al.
Surf. Sci.
(1996)
K.N. Tu et al.
Appl. Phys. Lett.
(1981)
S. Vandré et al.
Phys. Rev. Lett.
(1999)
S. Vandré et al.
Appl. Phys. Lett.
(2001)
S. Vandré et al.
J. Vac. Sci. Technol. B
(1999)
M. Dähne et al.
Adv. Solid State Phys.
(2001)

J.A. Knapp et al.

Appl. Phys. Lett.

(1986)

F. Arnaud d’Avitaya et al.

Appl. Phys. Lett.

(1989)

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Atomic structure of thin dysprosium-silicide layers on Si(1 1 1)

Abstract

Introduction

Section snippets

Experimental

The general growth behavior

Summary

Acknowledgements

Surf. Sci.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Surf. Sci.

Appl. Phys. Lett.

Phys. Rev. Lett.

Appl. Phys. Lett.

J. Vac. Sci. Technol. B

Adv. Solid State Phys.

Appl. Phys. Lett.

Appl. Phys. Lett.