Neutron reflectometry : a probe for materials surfaces : proceedings of a technical meeting

208 Pages·2006·5.752 MB·English

by  International Atomic Energy Agency

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NEUTRON REFLECTOMETRY:
A PROBE FOR MATERIALS
SURFACES
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PROCEEDINGS SERIES
NEUTRON REFLECTOMETRY:
A PROBE FOR MATERIALS
SURFACES
PROCEEDINGS OF A TECHNICAL MEETING
ORGANIZED BY THE
INTERNATIONAL ATOMIC ENERGY AGENCY
AND HELD IN VIENNA, 16–20 AUGUST 2004
INTERNATIONAL ATOMIC ENERGY AGENCY
VIENNA, 2006
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STI/PUB/1246
IAEA Library Cataloguing in Publication Data
Neutron reflectometry : a probe for materials surfaces : proceedings of a
technical meeting / organized by the International Atomic Energy
Agency and held in Vienna, 16-20 August 2004. — Vienna : The
Agency, 2006.
p. ; 24 cm. — (Proceedings series, ISSN 0074–1884)
STI/PUB/1246
ISBN 92–0–103906–9
Includes bibliographical references.
1. Reflectometer — Congresses. 2. Neutrons — Congress.
I. International Atomic Energy Agency. II. Series: Proceedings series
(International Atomic Energy Agency).
IAEAL 05–00447
FOREWORD
Research reactors play an important role in delivering the benefits of
nuclear science and technology. The IAEA, through its project on the effective
utilization of research reactors, has been providing technical support to
Member States and promotes activities related to specific applications.
Neutron beam research is one of the main components in materials science
studies.
Neutron reflectometry is extremely useful for characterizing thin films
and layered structures, polymers, oxide coatings on metals and biological
membranes. The neutron has been a major probe for investigating magnetic
materials. Development of magnetic multilayers is important for diverse
applications in sensors, memory devices, etc. The special nature of the
interaction of the neutron with matter makes it an important tool to locate low
z elements in the presence of high z elements, which is useful in biology and
polymer science.
The role of neutron reflectometry in research and development in
materials science and technology was discussed in a consultants meeting held in
2003. Following this, a technical meeting was organized from 16 to 20 August
2004 in Vienna to discuss the current status of neutron reflectometry, including
the instrumentation, data acquisition, data analysis and applications. Experts in
the field of neutron reflectometry presented their contributions, after which
there was a brainstorming session on various aspects of the technique and its
applications. This publication is the outcome of deliberations during the
meeting and the presentations by the participants.
This publication will be of use to scientists planning to develop a neutron
reflectometer at research reactors. It will also help disseminate knowledge and
information to material scientists, biologists and chemists working towards
characterizing and developing new materials. The IAEA thanks all the experts
for their active participation in the meeting, for the manuscripts of their
presentations and for their contribution in preparing the summary. Thanks are
also due to A.R.Wildes from the Institut Laue-Langevin, Grenoble, France, for
his paper on polarized neutron reflectometry.
The IAEA officer responsible for this publication was S.K. Paranjpe of
the Division of Physical and Chemical Sciences.
EDITORIAL NOTE
These Proceedings have been edited by the editorial staff of the IAEA to the extent
considered necessary for the reader’s assistance. The views expressed remain, however, the
responsibility of the named authors or participants. In addition, the views are not
necessarily those of the IAEA, the governments of the nominating Member States or the
nominating organizations.
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or omissions on the part of any person.
The use of particular designations of countries or territories does not imply any
judgement by the publisher, the IAEA, as to the legal status of such countries or territories,
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The mention of names of specific companies or products (whether or not indicated
as registered) does not imply any intention to infringe proprietary rights, nor should it be
construed as an endorsement or recommendation on the part of the IAEA.
The authors are responsible for having obtained the necessary permission for the
IAEA to reproduce, translate or use material from sources already protected by
copyrights.
CONTENTS
SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Principles of reflectometry with reactors and pulsed sources . . . . . . . . . . . 29
J. Penfold
Specular neutron reflectivity: Applications to soft matter. . . . . . . . . . . . . . 45
J. Penfold
Design of a neutron reflectometry at a research reactor . . . . . . . . . . . . . . . 59
Z. Tun
Polarized neutron reflectivity on D17 at the Institut Laue-Langevin. . . . . 69
R. Cubitt
Oxide films and corrosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
J.J. Noël
Neutron reflection studies of solid–liquid interfaces. . . . . . . . . . . . . . . . . . . 85
A.R. Rennie
Neutron reflectometry in Australia: Present and future. . . . . . . . . . . . . . . . 95
A. Nelson, M. James, J.C. Schulz, A. Brule
Development of a TOF reflectometer at the Greek Research Reactor. . . 103
K. Mergia, G. Apostolopoulos
Neutron reflectometer at the Budapest research reactor with
polarization option. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
L. Cser
Neutron reflectometry at Dhruva reactor: Specular and off-specular
neutron reflectivity studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
S. Basu, S. Singh
Application of polarized neutron reflectometry . . . . . . . . . . . . . . . . . . . . . . 145
A.R. Wildes
n/X materials science reflectometer at FRM-II in Garching . . . . . . . . . . . . 161
A. Rühm, U. Wildgruber, J. Franke, J. Major, H. Dosch
Neutron specular reflectometry: Some aspects of theory. . . . . . . . . . . . . . . 177
H. Leeb
List of Participants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
SUMMARY
1. REVIEW OF NEUTRON REFLECTOMETRY
1.1. Introduction
Neutron reflectometry (NREF) is a relatively new technique that has
widespread applications as a powerful analytical tool to analyse interfacial
structure and composition. The recent upsurge in phenomena occurring over
the nanometre scale and the unusual properties of low dimensional materials,
compared with their bulk counterparts, are expected to yield a range of new
products for electronics, photonics, etc. NREF is poised to help address the
questions that will arise in the development of advanced thin film devices and
functional interfaces of active materials with large surface areas.
In its simplest form this technique measures the intensity of a specularly
(angle of incidence = angle of reflection) reflected neutron beam as a function
of wavelength and/or angle. If the thin film surface constitutes the (x, y) plane
and the z axis is normal to the surface, then for specular reflectivity, momentum
transfer Q and Q are zero and Q is given by:
x y z
Q =(4p l)sin(q) (1)
Z
where λ is the wavelength of the incident neutron beam and θ the angle of
incidence (or reflection). A neutron beam of very low divergence (~1–5 arc/
min) is made to impinge on a thin film surface at a grazing incidence. For most
of the materials the refractive index ‘n’ for neutrons is given by: n = 1 – δ, where
δ ~ 10–6. Up to a critical angle of incidence the neutron beam undergoes total
external reflection and beyond that the beam penetrates the stratification and
gets reflected at the interfaces. The reflected neutron beam bears the signature
of the thickness of the layers, their densities, interface roughness, etc., of the
thin film sample. Specular reflectivity is usually measured as a function of Q ,
z
which can easily be obtained with knowledge of the wavelength and the sample
reflection angle from the above relation.
If one measures reflectivity outside the specular condition, i.e. angle of
reflection ≠ angle of incidence, then the reflected beam will also have non-zero
Q and Q components. Such measurements constitute the class of experiments
x y
under diffuse neutron scattering and provide information on the in-plane
height–height correlation function at various interfaces in the thin film.
Although various techniques are available (Table 1) for studying surface
properties, the special features of neutron interaction with matter make NREF
1