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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volume 190, Issues 1-4, May 2002, Pages 840-845

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DOI: 10.1016/S0168-583X(01)01208-3
PII: S0168-583X(01)01208-3
Copyright © 2002 Elsevier Science B.V. All rights reserved.

Hyperfine interaction studies with monolayer depth resolution using ultra-low energy radioactive ion beams

A. Vantomme ^,, B. Degroote, S. Degroote, K. Vanormelingen, J. Meersschaut, B. Croonenborghs, S. M. Van Eek, H. Pattyn, M. Rots and G. Langouche

Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium

Available online 4 January 2002.

Abstract

A variety of nuclear techniques rely on the incorporation of radioactive atoms to investigate the microscopic structural, electronic and magnetic properties of a material. In the past, ion implantation has been utilized to introduce these radioactive probes, resulting in a depth distribution of typically several hundreds of Å, and damaging the sample. Both implantation-related deficiencies are incompatible with the ever shrinking sizes relevant in nanostructures. This problem can be circumvented by using ultra-low energy ion beams _¯ of the order of 5 eV, i.e. below the displacement energy of the substrate atoms. Consequently, the radioactive probes are "deposited" on top of the sample, without generating damage to the substrate. Since the implantation chamber is in vacuo connected with the molecular beam epitaxy deposition chamber, the probe layer can be introduced at any stage during the sample growth (from surface to interface) _¯ with monolayer depth resolution. As an example, we discuss the ultra-low energy ion deposition of ¹¹¹In in Cr, followed by analysis with perturbed angular correlation spectroscopy. The aim of the study is to explore the magnetic ordering of Cr thin films.

Author Keywords: Low energy ion deposition; Nuclear solid state physics; Soft landing; Nanotechnology; Cr spin density wave

PACS classification codes: 75.70.Ak; 68.35.-p; 31.30.G; 61.18.F

Article Outline

1. Introduction
2. LEID: the technique and the setup
3. Low energy ion deposition of In on Cr 3.1. Deposition of stable ¹¹⁵In ions 3.2. Deposition of radioactive ¹¹¹In ions 3.3. Perturbed angular correlation experiment
4. Conclusion
Acknowledgements
References

(5K)
Fig. 1. Schematic diagram of the LEID set-up. The deposition energy is selected by adjusting the output voltage of the power supply V₂.

(3K)
Fig. 2. Ion current through the grid as a function of output voltage V₂. The zero-point energy is set at approximately 50 V using power supply V₁.

(10K)
Fig. 3. Schematic configuration of a transversal SDW with its wave vector in the plane (a,c) or out of the plane (b,d) of the Cr layer. The confinement of the radioactive probes in case of soft landing (c,d) results in monolayer depth sensitivity, which cannot be obtained when using conventional ion implantation (a,b).

(10K)
Fig. 4. PAC time spectrum of a 200 Å thick Cr layer, which was halfway decorated with ¹¹¹In probes, using ion beam deposition at 5 eV. The solid line is a fit assuming a longitudinal SDW.

References

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2. G. Langouche, Editor, Hyperfine Interaction of Defects in Semiconductors, Elsevier, Amsterdam (1992).

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6. J. Dekoster, B. Degroote, H. Pattyn, G. Langouche, A. Vantomme and S. Degroote Appl. Phys. Lett. 75 (1999), p. 938. Abstract-INSPEC | $Order Document | OJPS full text | Full Text via CrossRef

7. B. Degroote, Ph.D. Thesis, Katholieke Universiteit Leuven, 2001, available at www.fys.kuleuven.ac.be/iks/nvsf/nvsf.htm.

8. C.R. Laurens, L. Venema, G.J. Kemerink and L. Niesen Nucl. Instr. and Meth. B 129 (1997), p. 429. Abstract | PDF (440 K)

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10. B. Degroote, A. Vantomme, H. Pattyn, K. Vanormelingen, submitted to Phys. Rev. B.

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Corresponding author. Tel.: +32-16-32-75-14; fax: +32-16-32-79-85; email: andre.vantomme@fys.kuleuven.ac.be

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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volume 190, Issues 1-4, May 2002, Pages 840-845

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