In Situ Experiments in the Scanning Electron Microscope Chamber

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In Situ Experiments in the
Scanning Electron Microscope Chamber
Renaud Podor, Johann Ravaux and Henri-Pierre Brau
Institut de Chimie Séparative de Marcoule, UMR 5257 CEA-CNRS-UM2-ENSCM
Site de Marcoule, Bagnols sur Cèze cedex,
France
1. Introduction
Since the first scanning electron microscope by Knoll (1935) and theoretical developments
by von Ardenne (1938a, b) in the 30’s, this imaging technique has been widely used by
generations of searchers from all the scientific domains to characterize the inner structure of
matter. Even if the obtained information is essential for matter description or
comprehension of matter transformation, the main constraints associated with classical
electron microscopy, i.e. the necessity to work under vacuum and the necessity to prepare
the sample before imaging, have always limited the possibilities to “post mortem”
characterisation of samples and avoided observation of biological samples.
Electron microscopists early identified the necessity to undergo these limits. The development
of a SEM chamber that is capable of maintaining a relatively high pressure and that allows
imaging uncoated insulating samples began in the 70’s and has been “achieved” in the late 90’s
– early 00’s (Stokes, 2008) with the commercialisation of the low-vacuum and environmental
SEM. The availability of new generations of electron guns (and more particularly the field
effect electron gun characterized by a very intense brightness), as well as the new generation of
electronic columns that are now commonly associated with the environmental scanning
electron microscopes opens new possibilities for material characterisation up to the nanometer
scale. The development of this generation of microscopes have opened the door for
performing real time experiments, using the electron microscope chamber as a microlab
allowing direct observation of reactions at the micrometer scale. Many SEM providers or
researchers have developed specific stages that can be used for the in situ experimentation in
the scanning electron microscope chamber. This field is one of the most interesting uses of the
ESEM that offers fantastic opportunities for matter properties characterisation. Even if
numerous recent articles and reviews are dedicated to in situ experimentation in the VP/ESEM
(Donald, 2003 ; Mendez-Vilas et al., 2008 ; Stokes, 2008 ; Stabentheiner et al., 2010 ; Gianola et
al., 2011 ; Torres & Ramirez, 2011), no one describes all the possibilities of this technique. The
present chapter will provide a large – and as exhaustive as possible – overview of the
possibilities offered by the new SEM and ESEM generation in terms of “in situ experiments”
focussing specifically on the more recent results (2000-2011).
This chapter will be split into five parts. We will first discuss the goals of in situ
experimentation. Then, specific parts will be devoted to in situ mechanical tests, experiments

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under wet conditions, and a forth part dedicated to high temperature experiments in the
SEM. Last, a specific part will be devoted to the “future” of in-SEM experiments. In each
part, the main limits of the technique as well as the detection modes will be reported. Each
part will be focussed on examples of the use of the technique for performing in situ
experiments.
2. Goals and implementation requirements of in situ experimentation
The main goal of in situ experimentation in the SEM (or ESEM) chamber is to determine
properties of matter through the study of its behaviour under constraint. This requires the
combination of data collection over a given duration (on a unique sample) and image
treatment for information extraction. The studied properties are generally related to
microscopic phenomena and hardly assessable by other techniques. In situ experiment in the
SEM chamber corresponds to both imaging systems in evolution under a constraint and
imaging systems stabilized under controlled conditions.
To achieve this goal, several requirements are necessary:
•
The duration of the phenomenon to be observed must be suitable with the image
recording time. If the system evolution is too fast, it will be impossible to record several
images and observe this evolution. At the contrary, if the reaction kinetic is low, the
time necessary for image recording will be too long and incompatible with
experimentation. The high and low limits can be estimated ranging between 2 minutes
and 48 hours.
The system must remain stable under the environmental conditions and/or irradiation
by the electron beam during the time necessary for image recording. In the case of
easily degradable samples, it is necessary to adjust the imaging conditions (high
voltage, beam current, aperture, working distance, detector bias…) constantly, as the
sample environmental conditions are modified during the experiment. Thus, the effect
of the electron beam on the sample morphology modifications must be verified. Some
authors report that it can act as an accelerator (Popma, 2002) or inhibitor (Courtois et al.,
2011) of the observed reactions.
The image resolution must fit well with the size of details to be observed.
Improvements in the image resolution have been achieved in the last decade thanks to
the field effect emission guns. However, the presence of gas in the VP-SEM/ESEM
chamber contributes to the incident electron beam scattering and subsequent
degradation of the image resolution. Thus, the acquisition conditions must be adapted
to the sample to be studied depending on the higher magnification to be reached.
The gaseous environmental conditions in which the studied system evolutes (or can be
stabilized) must be reproduced in the SEM/LV-SEM/ESEM chamber. The development
of the ESEM offers real new opportunities in term of composition of the atmosphere
surrounding the sample. The large field detector and the gaseous secondary electron
detector (Stokes, 2008) have been developed specifically for imaging under “high
pressure” conditions (up to 300Pa and 3000Pa respectively) whatever the gas
composition (air, water, He, He+H2 mixtures, O2). Other detectors have been developed
for very specific applications (high temperature under vacuum (Nakamura et al., 2002),
EBSD at high temperature (Fielden, 2005)).
•
•
•

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•
The constraint in which the studied system evolutes (or can be stabilized) must also be
reproduced in the microscope chamber. Some devices are commercialized by official
sellers. Among them, we must report the Peltier stage for temperature control in the -10
to 60°C range, hot stages for temperature control up to 1500°C, stages for mechanical
tests (Figure 1). Some authors have developed their own specific stages adapted to the
problem to be treated (Fielden, 2005; Bogner et al., 2007). However, the development of
miniaturized stages that can be positioned in the SEM chamber without creating
perturbations on the incident electron beam can be really challenging. This will
probably be a key in the development of in situ experimentation in the next years
(Torres & Ramirez, 2011).

a
b

Fig. 1. a) hot stage (FEI) b) Hot tension/compression stage integrated into an SEM
(Kammrath & Weiss Co.) (After Biallas & Maier, 2007 ; Gorkaya et al., 2010).
The basis of in situ experimentation in the SEM is the study of the morphological
modifications of the sample under constraint. Thus, this requires recording of numerous
high quality images for image post treatment and data extraction in order to characterize the
reaction or matter properties. The sample size can vary from 1µm to 50mm, and the image
resolution is in the 1-10nm range, depending on recording conditions. The images are SEM
images, i.e. with a large depth of field and with grey level contrasts. In-SEM
experimentation can be extended to a wide range of applications, corresponding to very
different materials (plants (Stabentheiner et al., 2010), food (Thiel et al., 2002 ; James, 2009),
paper (Manero et al., 1998), soft matter, polymers, metals, ceramics, solids, liquids…) or
problems (plant behaviour, chemical reactivity, properties characterization, sintering, grain
growth, corrosion…). In the literature, the main part of the data reported has been acquired
using an environmental scanning electron microscope.
3. In situ mechanical tests
Boehlert (2011) have recently underlined the interest of performing in situ mechanical tests
in the SEM and summarized it as follows. “In situ scanning electron microscopy is now
being routinely performed around the world to characterize the surface deformation
behavior of a wide variety of materials. The types of loading conditions include simple
tension, compression, bending, and creep as well as dynamic conditions including cyclic
fatigue with dwell times. These experiments can be performed at ambient and elevated

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temperatures and in different environments and pressures. Most modern SEMs allow for
the adaptation of heating and mechanical testing assemblies to the SEM stage, which allows
for tilting and rotation to optimal imaging conditions as well as energy dispersive
spectroscopy X-ray capture. Perhaps some of the most useful techniques involve acquisition
of electron backscatter diffraction (EBSD) Kikuchi patterns for the identification of
crystallographic orientations. Such information allows for the identification of phase
transformations and plastic deformation as they relate to the local and global textures and
other microstructural features. Understanding the microscale deformation mechanisms is
useful for modeling and simulations used to link the microscale to the mesoscale behavior.
In turn, simulations require verification through in situ microscale observations. Together
simulations and in situ experimental verification studies are setting the stage for the future
of material science, which undoubtedly involves accurate prediction of local and global
mechanical properties and deformation behavior given only the processed microstructural
condition”.
As a direct consequence of the great interest of the collected information, many different
works from several scientific domains have been published for long. Thiel & Donald (1998)
and Stabentheiner et al. (2010) describe the deformation of plants (carrots and leaves
respectively) during room temperature tensile tests performed in the ESEM chamber.
Similar tests are also reported with food (Stokes & Donald, 2000) and they are regularly
performed on polymers (Poelt et al., 2010; Lin et al., 2011), composites (Schoßig et al., 2011)
and metals (Boehlert et al., 2006; Gorkaya et al., 2007). Mechanical tests on metals, alloys and
ceramics can also be performed at high temperature (Biallas & Maier, 2007; Chen & Boehlert,
2010). High temperature EDSB, developed by Seward et al. (2002), offers the possibility to
observe phase transformations in materials as a function of temperature, as well as the direct
visualization of the associated microstructural modifications (Seward et al., 2004).

c
Fig. 2. (a) & (b) Single cell surgery without cell bursting using Si-Ti nanoneedle , (c) Force-
cell deformation curve using Ti-Si and W2 nanoneedles at three different stages, i.e. (a)
before penetration, (b) after penetration and (c) touching the substrate. (Ahmad et al., 2010).

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Several recently developed techniques allow characterizing materials at the nanometer scale
through both technological miniaturization and advancements in imaging and small-scale
mechanical testing. Ahmad et al. (2010) have developed a coupled ESEM-atomic force
microscope to characterize single cells mechanical properties (Figure 2). This ESEM-
nanomanipulation system allowed determining effects of internal influences (cell size and
growth phases) and external influence (environmental conditions) on the cell strength.
Gianola et al. (2011) reports the development of a quantitative in situ nanomechanical testing
approach adapted to a dualbeam focused ion beam and scanning electron microscope. In
situ tensile tests on 75 nm diameter Cu nanowhiskers as well as compression tests on
nanoporous Au micropillars fabricated using FIB annular milling are reported, the scientific
question being the mechanical behaviour of nanosize materials. Both examples probably
represent what will be the future of in situ mechanical tests using scanning electron
microscopes.
4. In situ experimentation under wet conditions
4.1 Conditions for experimentation
Combination of the use of the ESEM and a Peltier stage with the development of specific
detectors allows the possibility to control both specimen temperature and water pressure
around the sample (Leary & Brydson, 2010). Water can be condensed or evaporated on the
demand from the sample (Figure 3). This allows performing in situ experiments in a
temperature-pressure domain that is reported on Figure 3a (dot zone). An easy to perform
experiment, illustrated by a 6 images series, corresponding to the NaCl dissolution (during
the increasing of the water pressure in the ESEM chamber and consecutive water
condensation, at constant temperature) in water followed by the crystallization of NaCl
(decrease of the water pressure) is reported on Figure 3b. This example corresponds to an
“isothermal experiment”. Another ways to work are to perform isobar experiments or to
heat or cool a sample using a constant relative humidity (iso-RH experiments). These
techniques allow the characterization of structural transitions of hydrated samples as a
function of temperature (Bonnefond, 2011).
4.2 Biology and soft matter applications
This technique is particularly well adapted for the observation or experimentation on
biological samples (Muscariello et al., 2005). Images of small and highly hydrated samples
such as liposomes have been obtained by several authors (Perrie et al., 2007 ; Ruozi et al;,
2011) without any particular sample preparation. Perrie et al. (2007) have also been able to
dynamically follow the hydration of lipid films and changes in liposome suspensions as
water condenses onto, or evaporates from, the sample in real-time. The data obtained
provides an insight into the resistance of liposomes to coalescence during dehydration,
thereby providing an alternative assay for liposome formulation and stability (Perrie et al.,
2010). However, Kirk et al. (2009) report that ESEM imaging of biological samples must
remain combined with the classical techniques for sample preparation. Several works are
specifically dedicated to in situ experimentation. Stabentheiner et al. (2010) state that “one
unrivaled possibility of ESEM is the in situ investigation of dynamic processes that are
impossible to access with CSEM where samples have to be fixed and processed”. These
authors have studied the anther opening that is a highly dynamic process involving several

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tissue layers and controlled tissue desiccation. This phenomenon can be observed because
the sample is very stable under the ESEM conditions (Figure 4). Another recent study is
relative to the closure of stomatal pores by Mc Gregor & Donald (2010). Even if the
possibility for experimentation on biological samples is clearly demonstrated, the authors
outline the fact that the electron beam damages are important even at low accelerating
voltage (Zheng et al., 2009). Another surprising example that can be reported is the direct
observation of living acarids available online: in the movie, colonies of acarids are directly
observed in the ESEM chamber under several conditions (FEI movie).


Fig. 3. (a) Simplified phase diagram for water indicating the ESEM domain (dot zone) and
schemes to understand how isothermal or isobar experiments are performed.
(b) Solubilisation and crystallization of NaCl directly observed in the ESEM chamber.

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Fig. 4. In situ anther opening of C. angustifolia observed in LV-ESEM. 1) At the beginning,
the valves of the anther are closed; 2) opening starts at the end of the stomium; 3) polyads
are already seen; 4) opening proceeds till the valves are completely bent back and all eight
polyads are presented (scale bar = 100µm). Time span from 1) to 3) was 25 min; 4) imaged 1
h after the start of the opening process (after Stabentheiner et al., 2010)
4.3 Applications on cements
Several works have been performed in order to study the reactivity of cement materials
versus humidity. Hydration or dehydration (Sorgi & De Gennaro, 2007; Fonseca & Jennings,
2010; Camacho-Bragado et al., 2011) of phases have been followed and used to extract
kinetic parameters (Montes-Hernandez, 2002 ; Montes & Swelling, 2005 ; Maison et al.,
2009), as reported on Figure 5. In this work, the author uses ESEM image series to determine
a three-step mechanism for bentonite aggregates evolution with relative humidity
corresponding to an arrangement of particles followed by a particle swelling and a full
destructuration. In SEM experiments are also used to characterize chemical reactivity
(Camacho-Bragado et al., 2011). It has been recently used to characterize reaction of fly ash
activated by sodium silicate by Duchene et al. (2010). These authors have determined very
accurately the different steps of the reaction determining that the sodium silicate activator
dissolves rapidly and begins to bond fly ash particles. Open porosity was observed and it
was rapidly filled with gel as soon as the liquid phase is able to reach the ash particle. The
importance of the liquid phase is underlined as a fluid transport medium permitting the
activator to reach and react with the fly ash particles. The reaction products had a gel like
morphology and no crystallized phase was observed.
4.4 Hydration and dehydration experiments
As previously reported for liposomes, new opportunities for the study of polyelectrolyte
microcapsules versus their resistance to relative humidity and temperature modifications
are opened and under consideration. The image series reported on Figure 6 clearly illustrate
the possibility to image the native soft capsule at high relative humidity without any
deformation. When decreasing the water pressure near the capsule, the object is deformed
and do not shrink as observed when it is heated in water at temperature higher than 25°C
(Basset et al., 2010). Thus, the walls of the object do not rearrange but collapse when
submitted to a relative humidity decrease.
Similar tests have been performed on self-organized metal-organic framework compounds
(Bonnefond, 2011). According to the image series reported on Figure 7, when the water
pressure decreases, the size of sample remains constant up to a given water pressure (i.e.
relative humidity) and for a transition pressure, the sample size decreases regularly. This

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can be associated to a local reorganisation in the sample that corresponds to a water loss
associated to the sample collapsing The enthalpy of water ordering in the sample can be
derived from the recorded image series as reported by Sievers et al.

Fig. 5. Swelling kinetics of raw bentonite aggregates scale using ESEM-digital image
analyses coupling (after Montes & Swelling, 2005).


Fig. 6. ESEM micrographs of polyelectrolyte microcapsules suspended in double distilled
water. Microcapsules were subjected to controlled dehydration in the ESEM sample
chamber at T=5°C. At an operating pressure of 800Pa, vesicles appeared as spherical
structures. (a) Gradual decrease of the operating pressure to 350 Pa showed regular
deformation of the microcaspsules (b to h)

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82
84
86
88
90
92
94
96
98
100
102
0 200400600 800100012001400
Pressure(Pa)
Normalized length (%)

Fig. 7. Dehydration experiments performed on self-assembled organo-metallic compounds
at T=22°C and corresponding size modification versus water vapour pressure (Bonnefond,
2011).
The effect of dehydration on lamellar bones was also studied by in situ ESEM experiments
(Utku et al., 2008). The obtained results indicate that dehydration affects the dimensions of
lamellar bone in an anisotropic manner in longitudinal sections, whereas in transverse
sections the extent of contraction is almost the same in both the radial and tangential
directions.
An original work on the heterogeneous ice nucleation on synthetic silver iodide, natural
kaolinite and montmorillonite particles has been performed using the “increasing water
pressure at constant temperature” (Zimmermann et al., 2007) in the temperature range of
250–270 K. Ice formation was related to the chemical composition of the particles. The
obtained data are in very good agreement with previous ones obtained by diffusion
chamber measurements (Figure 8).
4.5 Characterization of surface wetting properties
Characterization of the wetting properties of surfaces through the formation of
microdroplets or nanodroplets is another important investigation field that can be explored
using the ESEM. A recent review by Mendez-Vilas et al. (2009) has highlighted the main
fundamental and applied results. Several strategies for the contact angle between water and
the surface determination are reported (Stelmashenko et al., 2001; Stokes, 2001; Lau et al.,
2003; Wei, 2004; Yu et al., 2006; Jung & Bhushan, 2008; Rykaczewski & Scott, 2011). The
investigation of the hydrophobicity and/or hydrophilicity of a catalyst layer have been
performed using ESEM for the first time by Yu et al. (2006). These authors have determined
the micro-contact angle distribution as a function of the catalyst microstructure.
Microdroplets growing and merging process was observed directly in the ESEM chamber by
Lau et al. (2003).

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Fig. 8. Supersaturation versus temperature diagram for silver iodide (After Zimmermann et
al., 2007).

Fig. 9. Microdroplets growing and merging process under ESEM during increasing
condensation by decreasing temperature. (After Jung & Bhushan, 2008)
4.6 Using the Wet-STEM mode
The development of the Wet-STEM by Bogner et al. (2005, 2007) allows observing samples in
the transmission mode in the ESEM chamber, and more particularly, it offers the possibility
to image directly nanoparticles dispersed in a few micrometer thin water film (Bogner et al.,
2008), emulsions or vesicles (Maraloiu et al., 2010), without removing the liquid
surrounding the objects of interest. One must keep in mind that images with soft matter,
and more generally sample sensitive to the electron beam are very hard to obtain.
Nevertheless, this technique also opens new research fields using in situ experimentation
that only begin to be explored for wettability or deliquescence studies. By combining Wet-
STEM imaging with Monte-Carlo simulation (Figure 10), Barkay (2010) have studied the
initial stages of water nanodroplet condensation over a nonhomogeneous holey thin film.
This study has shown a preferred water droplet condensation over the residual water film

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areas in the holes and has provided corresponding droplet shape and contact angle. On a
similar way, Wise et al. (2008) have studied water uptake by NaCl particles prior to
deliquescence by varying the relative humidity in the Wet-STEM environment (Figure 11).

Fig. 10. Bright field image of 100 nm polystyrene latex spheres. Insert is the calibrated
intensity corresponding to the dark line in the image (After Barkay (2010))

Fig. 11. ~40 nm NaCl particles as the RH was increased past the deliquescence point. Water
uptake [(a)  (b)] prior to full deliquescence (c) is clearly observed. (After Wise et al., 2008)
4.7 Development of specific materials for experimentation
Several specific devices have been developed to characterize specific properties or reactions.
Two of them will be shortly described below.
Chen et al. (2011) have developed an experimental platform that can be used to investigate
chemical reaction pathways, to monitor phase changes in electrodes or to investigate
degradation effects in batteries. They have performed in situ experiment runs inside a
scanning electron microscope (SEM) and tracked the morphology of an electrode including
active and passive materials in real time. This work has been used to observe SnO2 during
lithium uptake and release inside a working battery electrode.

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Direct imaging of micro ink jets inside the ESEM chamber has been achieved using a specific
device developed by Deponte et al. (2009), using a two-fluid stream consisting of a water
inner core and a co-flowing outer gas sheath. ESEM images of water jets down to 700 nm
diameter have been recorded. Details of the jet structure (the point of jet breakup, size and
shape of the jet cone) can be measured. The authors conclude that ESEM imaging of liquid
jets offers a valuable research tool for the study of aerosol production, combustion
processes, ink-jet generation, and many other attributes of micro- and nanojet systems.
5. High temperature in the SEM
5.1 Application domains of HT-(E)SEM
Specific stages (and associated detectors) have been developed to heat samples up to 1500°C
directly in the microscope chamber (Knowles & Evans, 1997; Gregori et al., 2001). The
environmental scanning electron microscope (ESEM) equipped with this heating stage is an
excellent tool for the in situ and continuous observation of system modifications involved by
temperature. It allows recording image series of the morphological changes of a sample
during a heat treatment with both high magnification and high depth of focus. The
experiments can be carried out to observe the influence of all these parameters on the
studied phenomenon under various conditions (heating rates, atmosphere compositions,
variable pressure, final temperature and heating time). Images have been recorded up to
1400°C, with a decrease of the image resolution when the sample temperature increases
(Podor et al., 2012). It is possible to work under vacuum (classical SEM) or under controlled
atmosphere (H2O, O2, He+H2, N2, air...). Different types of studies have been reported,
relative to corrosion of metals (Jonsson et al., 2011), oxidation of metals (Schmid et al., 2001a,
2001b ; Oquab & Monceau, 2001 ; Schmid et al., 2002 ; Abolhassani et al., 2003 ; Reichmann
et al., 2008 ; Jonsson et al., 2009 ; Mège-Revil et al., 2009 ; Quémarda et al., 2009 ; Delehouzé
et al., 2011), reactivity at high temperature (Maroni et al., 1999 ; Boucetta et al., 2010), phase
changes (Fischer et al., 2004 ; Hung et al., 2007 ; Beattie & McGrady, 2009), hydrogen
desorption (Beattie et al., 2009, 2011), redox reactions (Klemensø et al., 2006), microstructural
modifications (Bestmann et al., 2005 ; Fielden, 2005 ; Yang, 2010), magnetic properties
(Reichmann et al., 2011), sintering (Sample et al., 1996 ; Srinivasan, 2002 ; Marzagui &
Cutard, 2004 ; Smith et al., 2006 ; Subramaniam, 2006 ; Courtois et al., 2011 ; Joly-Pottuz et
al., 2011 ; Podor et al., 2012), thermal decomposition (Gualtieri et al., 2008 ; Claparède et al.,
2011 ; Goodrich & Lattimer, 2011 ; Hingant et al., 2011), crystallisation (Gomez et al., 2009) in
melts (Imaizumi et al., 2003 ; Hillers et al., 2007) and study of self-repairing – self-healing –
properties of materials (Wilson & Case, 1997 ; Coillot et al., 2010a, 2010b, 2011) …
Even if numerous researchers are invested in HT-ESEM, only few of them have been
successful in pursuing dynamic experiments at temperatures higher than 1100°C. Two
recent studies report experiments performed at T=1350°C (Subramaniam, 2005) and 1450°C
(Gregori et al., 2002). However, the resolution of the images remains poor (more than 1µm)
mainly due to water cooling induced vibrations. Furthermore, the precision on the measure
of the sample temperature remains poor (temperature differences up to 150°C with the
expected temperature are sometimes measured). A recent device has been proposed by
Podor et al. (2011) to overcome this difficulty.
A complete review specifically dedicated to in situ high temperature experimentation in the
ESEM will be available soon. Several examples of in situ studies performed at high

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temperature in the ESEM chamber will be reported below, on the basis of original data
acquired in our laboratory.
5.2 Investigation of the crystallization behaviour in silicate melts
The crystal growth and morphology during isothermal heating of glass melts can be directly
observed using the hot stage associated with the ESEM. The image series reported on Figure
12 have been recorded during 10 minutes while heating the borosilicate melt sample
isothermally at T=740°C. The development of large crystals in the melt rapidly yields to the
complete crystallization of the melt. The crystal morphology presents cells filled with a
second phase and the crystal formation yields to the deformation of the sample surface.
Hillers et al. (2007) have used such data to quantify the variation of crystal length with time.
They have established that the growth is only linear during the first minutes; afterward the
growth rate decreases progressively with time.
This technique can also be used to determine the temperature of formation of the first
crystals at the melt surface and to observe their formation. In the case of glass-ceramics, the
density of nuclei as well as their size and shape development can be directly observed and
used for crystallization kinetic determination (Vigouroux et al., 2011, in prep).



Fig. 12. Growth of crystals in a borosilicate melt during 10 minutes isothermal heat
treatment at 740°C observed using the hot stage associated with the ESEM.
5.3 Decomposition of compounds
In situ thermal decomposition of composites, oxalates, oxides have been reported by several
authors. Images of the heat treatment of a mixed uranium-cerium oxalate grain from 25°C to
1235°C are gathered on Figure 13. Morphological changes with temperature are directly
linked with the oxalate decomposition as stated by Hingant et al. (2011) in the temperature
range 25-500°C. The sample shrinkage observed when T>500°C is probably related with the
first stage of the sintering process – i.e. beginning of bond formation between the
nanograins and with the oxide grain growth (that can not be directly observed at this stage
by HT-ESEM, but that is confirmed by X-Ray diffraction). Such a process has also been
recently reported by Claparede et al. (2011) and Joly-Pottuz et al. (2011).

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Fig. 13. Decomposition of a uranium-cerium mixed oxalate observed during in situ heating
in the ESEM chamber and relative size and shrinkage modifications.
5.4 Study of sintering and grain growth
Several studies are relative to the sintering and grain growth processes in metals and
ceramics. Depending on the system, the experiments have been performed in the
temperature range 300-1450°C. The main interest of these studies is the possibility of direct
observation of the individual grain behaviour during heat treatment. The example that is
reported on Figure 14a corresponds to the heat treatment of the grain decomposed in situ
(Figure 13). The image resolution is high enough to observe the nanograins growth inside
the square plate agglomerate. Consequently, relative shrinkage and average grain diameter
are extracted by image processing (Figure 14b). Assuming that the final density of the
agglomerate is 99%, the sintering map is directly derived from these experimental data
(Figure 14c). Thus, in situ sintering experiments can allow the establishment of the
trajectories of theoretical sintering. Such data have never been already reported in previous
studies, mainly due to the poor resolution of the recorded images.
The effect of the electron beam on sintering is controversy. Indeed, Popma (2002) noted that
a local sintering stop was achieved by focusing the electron beam at a certain position
during the in situ sintering experiments in the ESEM (performed on ZrO2 nanolayers). On
the contrary, Courtois et al (2011) performed experiments on the sintering of a lead
phosphovanadate and concluded that the electric current induced by the electron beam was
found to reduce the effective temperature of sintering by 50 to 150°C as well as to accelerate
the kinetics of shrinkage of a cluster composed of sub-micrometric grains of material. Such
effects were not evidenced in our study: the local sintering on sample surface zones that
were not observed (i.e. exposed to the electron beam) was identical to the local sintering
determined on the observed zone.

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a

b
c
Fig. 14. (a) Sintering and grain growth of a uranium-cerium mixed oxide observed in situ in
the ESEM chamber at T=1235°C, after 55’, 70’, 90’, 95’, 130’, 140’ (a). Corresponding Relative
(b) Shrinkage and Average grain diameter versus duration and (c) derived sintering map -
Grain growth versus densification rate –
6. Conclusions and perspectives
In situ scanning electron microscopy experimentation, that is generally associated with the
use of the ESEM, allows the study of very different problems, the main limit being the
availability of specific devices. Torres & Ramirez (2011) have written the best conclusion
indicating that “the new generation of SEMs shows innovative hardware and software
solutions that result in improved performance. This progress has turned the SEM into an
extraordinary tool to develop more complex and realistic in situ experiments, achieving even
at the subnanometer scale”. In the near future, new SEM imaging modes, nanomanipulation