Therefore, a better control of the reaction process and the imaging experiments is achieved. An additional advantage is that the sealed-cell approach only modifies a small device on the tip of a TEM sample holder, thus can be used in any normal TEM without modifications to any other parts of a TEM. The cost of performing ETEM studies using the sealed-cell approach is typically a tiny fraction of the cost of a dedicated ETEM using open-type approach, because the latter requires modifications to the whole column.
Thereby the sealed-cell approach allows in situ ETEM studies to be easily extended to many laboratories in the field. Last but not least, the sealed-cell platforms enable in situ ETEM characterization with the introduction of any types of volatile carbon-based electrolytes, which is impossible for open-type approach due to the high vacuum requirement inside TEM chamber.
Due to the various advantages over the open-type approach, sealed-cell approach has become the dominant way to perform ETEM studies under ambient conditions. A fast-growing number of research groups worldwide are conducting researches using this technology. Different designs and applications of the sealed cells for in situ TEM observations are summarized.
TEM is one of the most powerful techniques to characterize structure and chemistry of solids at the atomic scale. For materials such as catalysts, fuel cells, and biological molecules, in situ investigation under real-world conditions other than vacuum is essential to obtain practical information [ 2 ]. Therefore, the ability to study gas-solid interactions with atomic resolution at ambient pressures in TEM promises new insights into the growth, properties, and functionality of nanomaterials.
The original designs for ETEM observations under gaseous conditions have been around for over 70 years [ 14 ] and are made available by two main kinds of methods [ 15 ]: one is the opened type, which confines the gas near the sample by means of pressure-limiting apertures and maintain the vacuum in the remaining column by a differential pumping scheme [ 16 — 19 ] e. For the opened type, the pressure-limiting apertures with small holes are positioned in the objective lens in close proximity to the sample, and the differential pumping system is equipped to avoid diffusion of the gas molecules from the chamber toward other parts of TEM, especially the electron gun.
Any type of specimen holder can be accepted by the opened-type ETEM. On the other hand, the sealed-type ETEM using a sealed gas cell has various advantages over the differential pumping approach. The resulting gas path length is on the order of a few microns [ 6 , 7 ], much thinner than the opened-type approach and allowing much better resolution to observe lattice images. Consequently, the acceptable reaction pressures within the gas cell can equal or exceed a full atmosphere [ 6 , 8 — 10 ] while maintaining the ability to record atomic resolution images [ 8 — 11 ].
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Furthermore, much more rapid thermal response than standard heating holders and more rapid stabilization of specimen drift are realized by integrating miniaturized, low mass heating devices [ 12 ] or laser heating [ 1 ] into the sealed gas cell. An additional advantage is that the sealed-gas-cell approach only modifies a small device on the tip of a TEM sample holder, thus can be used in any normal TEM without modifications to any other parts of a TEM. The cost of performing ETEM studies using the gas-cell approach is typically a tiny fraction of the cost of a dedicated ETEM using differential-pumping approach, because the latter requires modifications to the whole column.
Thereby, the sealed-gas-cell approach allows in situ ETEM studies to be easily extended to many laboratories in the field. Due to the various advantages, sealed-gas-cell approach has become the dominant way to perform ETEM studies under gaseous environment. Advances in 0D [ 26 ], 1D [ 27 ], and 2D [ 28 — 43 ] material fabrication technologies have enabled various forms of nanoscale materials, which increased the needs of in situ ETEM studies through the closed-type approach, i.
Sealed gas cells enabled in situ TEM observations, thus allowing the evaluation of the effect of external stimuli including mechanical, electrical, and magnetic force on nanomaterials. Some advantages of in situ TEM observations with sealed gas cells are listed as follows [ 44 ]: 1. Concurrent observations of structural, morphological, and chemical changes in ambient atmosphere are enabled. The same area is observed during the whole reaction process in ambient atmosphere, when sample is subjected to external stimuli.
Both thermodynamic and kinetic data leading to nanomaterials synthesis or functioning in ambient atmosphere can be obtained. Considerable time saving as the synthesis and characterization are performed concurrently in ambient atmosphere. Some groups just used their newly developed sealed cells to demonstrate their properties and improved technical limits for in situ TEM observations [ 1 , 9 , 10 , 48 , 49 ].
These applications are discussed in details as follows. Hydrogen storage materials are needed for hydrogen fuel, particularly in the automotive industry. The electron beam was found to have no disturbing influence on the determination of the de hydrogenation temperatures in the case of Pd, under normal working conditions and at pressures of and Torr.
The relationship between de hydrogenation and pressure fitted well with bulk experiments in which the pressure was varied. Fast determination of the hydrogenation and dehydrogenation temperatures was allowed by realizing a very fast change in temperature. In , Hiroshi Fujita et. Reaction between wet H2 gas and an iron foil. The same sealed gas cell by Hiroshi Fujita et al. Making use of the heating element and the enclosed gases, in situ observations of oxidation and reduction processes can be performed with sealed gas cells.
Komatsu et al.
Oxygen was then introduced into the cell to 9. The film was gradually reheated in 9. In situ observation of the growth process of CuO whiskers was carried out in the same sealed gas cell by M. The enhanced electron flux could increase the concentrations of both reducing electrons and oxygen ions. Below a certain threshold, oxidization dominated the system response and resulted in accelerated interaction between silver and oxygen ions.
At current densities of 0. At current densities greater than 0. Due to the increased oxygen fugacity associated with higher concentrations of ionized and atomic oxygen, all Ag 2 O phase was further oxidized to AgO at current densities greater than 0. Above 0. Once the electron current density increased beyond 0. The reaction between the nanoparticles NPs and gas produced a concentration gradient around the particles that was observed as a bright ring around each silver grain.
The silver oxide depletion width in the gas phase indicated a strong chemical interaction between the solid and vapor phases. The competition between oxidation and electron-beam-induced reduction also provided excess heat. For significantly high fluxes of ionized oxygen, a thermal effect could induce local vaporization at the surface, and sequentially an in situ nanoscale reaction ion sputtering. This investigation revealed a variety of microstructural processes associated with the oxidation of Ag by atomic and ionized gas species. The electron beam was demonstrated to be an important source of both oxidation and reduction.
The sealed cell approach provided an opportunity to make early observations of real-time nanoscale dynamics associated with oxidation in ionized and atomic gas, the movement of a partial pressure of a gas phase, and interactions between the condensed and vapor phases of a material. The results provided new insights into manipulating nanostructure and chemistry through ionized gas treatment and offered unique access to simulate reactions with atomic and ionized gas.
Microstructure of the observation area in an air-filled cell after exposure of a 0 s with 0. One of the earliest attempts to observe a catalyst in a sealed gas cell was reported by Parkinson et al. Using a narrow-gap, sealed gas cell and a kV TEM, images of the crystal lattice of ceria 0. Seventeen years later, the atomic-scale in situ observations of catalysts were performed by S. Giorgio et al. For the first time, Au and Pd clusters supported on Ti0 2 and amorphous carbon were observed with a sealed gas cell with the resolution of lattice fringes.
Initially, an Au cluster in vacuum was strongly contaminated, but the contamination disappeared while the faceting and the crystalline lattice were visible in the cluster after circulation of H 2 at a pressure of 3 Torr at room temperature. The resolution of in situ observation of catalysts was improved by a novel MEMS-type nanoreactor in [ 8 ]. The in situ TEM images showed atomic lattice fringes in the Cu nanocrystals with spacing of 0.
The system of Cu nanocrystals on a ZnO support is commonly used as catalyst for methanol synthesis and for conversion of hydrocarbons in fuel cells. Also, it is a prototype example of the industrially important group of 3d transition metal catalysts. The CuO appeared as smaller patches of more irregular shapes at the edges of ZnO.
Lattice fringes with spacings of 0. Image sequences of the Cu nanocrystal growth and mobility on ZnO. After growth, nanocrystals can exhibit transient mobility white square. Crystallites on the opposite window are seen out of focus black arrows in a and c.
A Transmission Electron Microscopy Investigation of Reaustenitized-and-Cooled HSLA-100 Steel
All frames are averaged over four consecutive images. The exposure time for each image is 0. The bright dots represent sets of lattice fringes. Their lattice spacing corresponds to the distance to the origin and reveals the crystallographic identity. The large, red circle corresponds a spacing of 0. The smallest, resolved lattice spacing is 0.
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The time shown in the lower right-hand corners of d — f correspond to intervals measured from the time at which c was recorded color online . The shape of the gold particle changed markedly over a short period of time, such as the 0. However, the lattice fringes of the gold could not be observed due to electron scattering by the high-pressure gas. Vendelbo et al. TEM image series of the Pt NPs were acquired at windows both at the entrance and exit of the reaction zone, at a rate 1—2 frames per second faster than the rate of the reaction oscillations, to directly visualize the NPs on this timescale.
Near the reaction zone entrance, the NPs had a stationary and more spherical morphology during the oscillating reaction. As the CO conversion increased rapidly, Pt NPs started a gradual transformation from the more spherical shape towards a more facetted shape. Thus, the individual NPs near the exit from the reaction zone underwent oscillatory and reversible shape changes with a temporal frequency matching the oscillations in reaction power, indicating that the oscillatory CO conversion and the dynamic shape change of the Pt NPs were coupled.
The spacing of crystalline lattice planes and the uniform contrast across the projected image of the NPs were consistent with metallic Pt. The combined high-resolution TEM and DFT analyses indicated that the Pt surfaces remained in the metallic state under the present conditions. The gas entering the reaction zone is 1.
Fast Fourier transforms included as insets in c — e reveal a lattice spacing corresponding to the Pt lattice planes. The orientation of the observed Pt lattice fringes is consistent with the superimposed crystal lattice vectors and zone axis color online . Apart from the homemade sealed gas cells above, commercial MEMS-type sealed gas cells have also been applied to in situ studies of catalysts.
The membrane-type heating chip manufactured by Hummingbird Scientific Lacey, WA, USA provided a temperature controllable reaction platform for oxidation reactions of cobalt NPs with flowing oxygen 0.
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The metallic core was finally eliminated, but at an even slower volume shrinking rate. The particle's oxide shell was in contact with other particles with upper and lower right boundaries open. In situ heating of cobalt NPs in flowing oxygen. Scale bar is 10 nm  color online. The sealed gas cells encapsulated specimens in a thin gas layer, preventing specimens from destruction as in vacuum.
Therefore, the sealed gas cells have also been widely applied into biological studies. This section will discuss the biological applications of the sealed gas cells for in situ TEM observation. The first application of sealed gas cells in biology was reported by H. Heide in [ 4 ]. For organic specimens, it is necessary to prevent carbon removal from increasing to a rate higher than the rate of contamination, which would destruct the specimen. A rapid dehydration of the specimen can be prevented if unnecessary heating is avoided even at pressures of — Torr, which was proved by TEM pictures of small water droplets in air at Torr.
In , an in situ sealed gas cell was used to study the reduction of Cr VI by bacterium Shewanella oneidensis by T.
In Situ Transmission Electron Microscopy Studies in Gas/Liquid Environment
Daulton et al. Bacteria from rinsed cultures were placed directly in the gas cell and examined under However, damage to the cells was observed within minutes of electron-beam exposure, arising from the primary destruction of weak Van der Waals biomolecular bonds. Direct in situ TEM imaging revealed two distinct populations of S. The cell envelopes of non-encrusted cells produced very low image contrast as compared to encrusted bacteria. The increase in contrast indicated that the cell envelope was saturated with absorbed elements of heavy mass, such as Cr.
The binding of heavy elements in the cell envelope was associated with Cr reduction. The arrowhead in panel d points to a low contrast bacterium in the same field of view as a bacterium with electron dense particulates, illustrating the dramatic contrast difference. The low-contrast, diffuse background, best seen in panel a , represents the extracellular polymeric substances that surround the cells .
Cladding is the outer layer of the fuel rods, preventing radioactive fission fragments from escaping the fuel into the coolant and contaminating it. Exposures to irradiation, temperature changes, and stresses may induce microstructural changes, and ultimately result in failure of the cladding. It is thus essential to use in situ TEM to observe microstructural changes at the nanoscale dynamically, for predicting the performance of cladding in-service and during storage, understanding the dominant processes related to these changes and their consequences. In , a sealed gas cell developed by K.
Hattar et al. Despite loss in resolution, prominent features of the foil that were previously observed under vacuum still remained visible. Images of Zircaloy lamella at nominally atmospheric pressure. The same device was applied to study hydride formation in Zirlo TM cladding material [ 12 ] recently. In some regions they are more of less parallel and needle-shaped with a cross section of the order of 1 xm2 Figure la and b. These grains are dislocation free and are typical of the so-called fibrolitic texture. In some other regions the grains are much bigger typically 10 to im size and contain isolated dislocations mostly dissociated c's with dominantly screw character and a density 1 to 5 x cm-2 , as well as subgrain boundaries composed of one or two dislocation families.
This corresponds to a zero Schmid factor for c glide and to a maximum one for  and  glides a and b glides in planes. On voit ici leur section. The elongated sillimanite nucleii seem to grow at the expense of the feldspar matrix. At experimental conditions, it is comparable to that of dry quartz Heard and Carter, which is known to originate in the necessity for the mobile dislocations to break the strong Si-O bonds. The stress-strain curves are reported on figure 9. TEM investigations on deformed samples show contrasting dislocation structures shown on figure 10 Doukhan and Christie, :.
In some miso-riented regions c glide in and has been activated. Of course one also observes  glide which has a maximum Schmid factor in these experiments. The dissociation width reaches 0. The dissociation widths i. The dissociation width of the a dislocations also varies with the deformation conditions from — 0 to — 20 J,m but there is an important difference between the stacking faults. Figure 1 1 is a tentative representation of this transformation.
Compression axis parallel to . Between successive tests, a stress relaxation broken line allows recovery of the dislocation structure. The flow stress does not decrease as the temperature increases. Each test consists of two successive parts at constant T but at different P such that the T, P conditions move from the sillimanite field first part to the kyanite field second part. In sample C the deformation is followed by a stress relaxation at the final T, P conditions which results in a very slight deformation 0. In TEM, one observes very widely dissociated a dislocations up to 10 J,m, figure 10c.
Furthermore some thin lamellae of kyanite are nucleated on the faults Figure lOd. In TEM one. They are imaged with the K diffracted beam dark field. The a dislocations are not disso-only in the case of glide deformation at T, P. Comparison of samples C and D thus values near the sillimanite-kyanite boundary and. The chains of A edge sharing octahedra are shadowed and the cross-linking Si04 and A tetrahedra are outlined, b The fault runs in the middle of the cell.
It breaks no Si04 tetrahedron but the central chain is destroyed. This latter operation allows fitting to the other kyanite lattice parameters, d Idealized kyanite structure. These features are ones generally associated with martensitic transformations Rao and Rao, We believe that both phenomena are related to a core effect. Indeed, as the a dislocations become dissociated they are subjected to much higher Peierls friction because they have to cut the strong Si-O bonds.
A great decrease in their mobility results. At a given stress level, the strain rate which governs the transformation rate also decreases. Furthermore, since there is no easy mechanism for generating periodic shearing by partial dislocations in adjacent planes, the growth of the new phase is very slow. The self energy of a small glissile dislocation loop is Hirth and Lothe, :.
The work done by the applied stress is. This equation is represented on figure 12a for various B values.
This corresponds to B — 3. As a rough approximation, one can neglect the variations with T and P of the S and V's and use their values at normal conditions, which are Robie et al. The mechanism proposed here for single crystals probably does not operate in natural tectonic processes. However, aluminium silicates do not. At the moment, because of the lack of suitable diffusion data, it is not possible to compute these transformation rates. Until now all our TEM investigations on rocks containing at least two Al2Si05 polymorphs in contact have not provided any clear evidence that such-strain induced polymorphic transformations occur in nature.
The most remarkable feature of strain-induced lattice defects in Al2Si05 polymorphs is the influence of the T, P deformation conditions on the dissociation widths of mobile dislocations. Such a change in their core structures strongly affects the plastic properties of these minerals. In andalusite the flow stress for c glide increases with temperature. The authors thank B. Semelin, University of Strasbourg, and Dr. Grew, U. They also thank Prof. Lipshie, U. Los Angeles, for technical assistance in some experiments. Boland, J. Burnham, C.
Refinement of the crystal structure of sillimanite. Christian, J. Physique C, Coe, R. Day, H. Science, , Doukhan, J. Greenwood, G. Royal Soc. London, A , Grew, E. Heard, H. Hirth, J. Hold away, H. Kirby, S. Larsen, E. Science, 36, Lefebvre, A. Acta Crvst. Menard, D. Physique, 39, LL Menard, D.. Mc Graw Hill New York , p. Vaughan, M. An Box , Houston, Tx , U. Transmission electron microscopy investigation of lattice defects in Al 2 SiO 5 polymorphs and plasticity induced polymorphic transformations [article] Jean-Claude Doukhan Nicole Doukhan Philip S.