5 Mössbauer Spectroscopy with High Spatial Resolution …
255
to noise ratio that provide a meaningful answer to the research questions being investigated. This chapter demonstrates how experiments can be optimised with regard
to spectrometer geometry and choice of radioactive source for lab-based measurements, choice of time or energy domain for synchrotron measurements, and how to
prepare samples (form and thickness) for both types of measurements. Calculations
of thickness and geometry are straightforward, and free software is available that
enables simulation of potential spectra to facilitate the best decisions. High spatial
resolution is therefore not a barrier to obtaining high quality spectra.
Applications of high spatial resolution Mössbauer spectroscopy in geoscience
cover a wide range of research questions, but also show a number of trends. In situ
high-pressure investigations using a radioactive source focus mainly on transitions
and material properties, while synchrotron studies address a broader scope of research
questions and focus deeper within Earth. This trend may reflect the predominance
of physics and chemistry laboratories carrying out high-pressure studies in the early
days of radioactive source experiments, while synchrotron facilities allowed the user
base to expand to include those without in house facilities. Post mortem investigations
involve predominantly samples quenched from large-volume apparatus, where large
and homogeneous samples offer the convenience of in house (radioactive source)
studies. All high-pressure studies, both in situ and ex situ, focus nearly exclusively
on single phase samples due to constraints on beam size. This constraint also restricts
the size of diamond inclusions that can be studied, as well as the spatial resolution
that can be achieved in studies of inhomogeneous samples.
The dominant role of iron in myriads of processes that take place on and within
Earth as well as the diversity of iron species means that many important research
questions are still waiting to be addressed with current capabilities. Furthermore,
recent developments have expanded possibilities, for example the focussed ion beam
(FIB) technique combined with SMS enables the collection of Mössbauer spectra on
single-phase samples quenched from diamond anvil cell experiments.
Future developments will expand possibilities further and allow entirely new areas
of science to be explored. For example the upgrade at ESRF [298, 299] is expected
to offer users a sub-micron beam size for SMS measurements, opening many new
possibilities, including studies of multiphase samples at high pressure. Such experiments include the study of chemical reactions, the motor of most Earth processes,
not to mention life itself. Further applications of sub-micron beam size are presented
in Chap. 1 of this volume. In the same way that reducing the beam size of Mössbauer
measurements by two orders of magnitude (radioactive point source) or three orders
of magnitude (synchrotron source) brought incomparable new insights described in
the more than 250 studies reported in Sect. 5.6, the further reduction in beam size by
one to two orders of magnitude will surely bring new surprises and understanding
of how our planet works.
255
to noise ratio that provide a meaningful answer to the research questions being investigated. This chapter demonstrates how experiments can be optimised with regard
to spectrometer geometry and choice of radioactive source for lab-based measurements, choice of time or energy domain for synchrotron measurements, and how to
prepare samples (form and thickness) for both types of measurements. Calculations
of thickness and geometry are straightforward, and free software is available that
enables simulation of potential spectra to facilitate the best decisions. High spatial
resolution is therefore not a barrier to obtaining high quality spectra.
Applications of high spatial resolution Mössbauer spectroscopy in geoscience
cover a wide range of research questions, but also show a number of trends. In situ
high-pressure investigations using a radioactive source focus mainly on transitions
and material properties, while synchrotron studies address a broader scope of research
questions and focus deeper within Earth. This trend may reflect the predominance
of physics and chemistry laboratories carrying out high-pressure studies in the early
days of radioactive source experiments, while synchrotron facilities allowed the user
base to expand to include those without in house facilities. Post mortem investigations
involve predominantly samples quenched from large-volume apparatus, where large
and homogeneous samples offer the convenience of in house (radioactive source)
studies. All high-pressure studies, both in situ and ex situ, focus nearly exclusively
on single phase samples due to constraints on beam size. This constraint also restricts
the size of diamond inclusions that can be studied, as well as the spatial resolution
that can be achieved in studies of inhomogeneous samples.
The dominant role of iron in myriads of processes that take place on and within
Earth as well as the diversity of iron species means that many important research
questions are still waiting to be addressed with current capabilities. Furthermore,
recent developments have expanded possibilities, for example the focussed ion beam
(FIB) technique combined with SMS enables the collection of Mössbauer spectra on
single-phase samples quenched from diamond anvil cell experiments.
Future developments will expand possibilities further and allow entirely new areas
of science to be explored. For example the upgrade at ESRF [298, 299] is expected
to offer users a sub-micron beam size for SMS measurements, opening many new
possibilities, including studies of multiphase samples at high pressure. Such experiments include the study of chemical reactions, the motor of most Earth processes,
not to mention life itself. Further applications of sub-micron beam size are presented
in Chap. 1 of this volume. In the same way that reducing the beam size of Mössbauer
measurements by two orders of magnitude (radioactive point source) or three orders
of magnitude (synchrotron source) brought incomparable new insights described in
the more than 250 studies reported in Sect. 5.6, the further reduction in beam size by
one to two orders of magnitude will surely bring new surprises and understanding
of how our planet works.