Ex situ TEM

V0)2P207 retains the morphology of the precursor VOHPO4 O.5H2O. Detailed in situ Raman spectroscopy (87) and ex situ TEM studies have shown the nature of the structural transformations that occur. 

A detailed ex situ TEM study on the formation of mesoscopic silica thin films was carried out by Yao et al. (2000). Films grown at the air/water interface from dilute acidic TEOS/C16TACI solutions were harvested at intervals. Under the conditions used, a visible continuous film about 20 nm thick developed after 5 h. The solution turned cloudy after... 

Figure 14 Ex situ TEM micrographs of the indium nanoparticies generated in the deposition experiments of the (a) 0.4-nm-, (b) 0.6-nm-, and (c) 0.8-nm-thickfilms, (d) Corresponding caiorimetric curves, with the vertical dashed lines indicating the position in the temperature of each maximum, (e) Radius difference corresponding to the separation between adjacent maxima, as calculated using eqn [2]. The horizontai dashed iines represent the thickness of a monolayer for the two bulk lattice parameters of indium. Reproduced with permission from Efremov, M. Y. Schiettekatte, F. Zhang, M. etal. Phys. Rev. Lett. 2000, 85,3560-3563. ...

The acidic conditions of standard SBA-15 synthesis [35] cause the precipitation of metal nanoparticles without silica encapsulation, or the formation of amorphous silica due to the presence of the polymer used for nanoparticle synthesis. Therefore, the SBA-15 framework was synthesized under neutral condition using sodium fluoride as a hydrolysis catalyst and tetramethylorthosilicate (TMOS) as the silica precursor. Pt particles with different sizes were dispersed in the aqueous template polymer solution sodium fluoride and TMOS were added to the reaction mixture. The slurry aged at 313 K for a day, followed by an additional day at 373 K. Pt(X)/SBA-15-NE (X = 1.7, 2.9, 3.6, and 7.1nm) catalysts were obtained by ex-situ calcination (see Section 3.2). TEM images of the ordered... 

The gas reaction chamber and the objective aperture assembly occupied the gap between the upper and lower objective pole pieces, leading to a gas reservoir around the sample. Such ECELL systems were a major step forward in scientific capability, being used by Gai et al. (3,73-78), Doole et al. (79), Crozier et al. (80), and Goringe et al. (81) to characterize catalysis. Other developments for catalytic studies include an ex situ reaction chamber attached externally to the column of a TEM, for example, by Parkinson and White (82) and Colloso-Davila et al. (83). Reactions were carried out in the ex situ chamber (and not in situ), and the sample was cooled to room temperature and inserted into the column of the TEM (without exposure to the atmosphere) under vacuum. Baker et al. (84) used ETEM at gas pressures of a few mbar with limited resolution, and, in these experiments, representative higher gas pressures were not employed. 

The primary methods for analysis were usually gravimetric, thermal, and spectroscopic in nature but not necessarily correlated with in situ analysis (XPS, AFM, TEM, etc.) or ex situ analysis of surface-bound polymers by de-grafting (NMR, MW, polydispersity, etc.). Colloidal stability and homogeneity of the grafting process is a primary concern. A range of these systems were analogous to what has been done in solution and in bulk and should be thoroughly examined in terms of chemistry on flat substrate surfaces. Several examples follow. 

Various in situ and ex situ tip sharpening procedures were demonstrated. These procedures might provides atomic resolution, but often makes the tip end looks even worse under SEM or TEM. 

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are recognized as powerful and versatile tools for the characterization of supported metal catalysts, because real-space images of catalysts with spatial resolution down to 0.1 nm can be recorded and combined with high-spatially resolved spectroscopic information. However, TEM has been used mainly for ex situ characterization, for example, of catalysts after gas treatments. 

This so-called ex situ or quasi in situ TEM approach has allowed researchers to determine important structural information about catalysts containing, for... 

Thin epitaxial films (less than 3 nm) of CrAs and CrSb with zinc-blende structure can be grown on GaAs substrates by MBE. Their 7c exceeds 400 K (Akinaga et al. 2000c Zhao et al. 2001b). A zinc-blende structure is confirmed by in-situ RHEED collected during the growth and ex-situ cross-sectional transmission electron microscopy (TEM). The... 

In the past TEM has been extensively used to study the nucleation and growth kinetics (see the review by Poppa [66]). These studies are in general made sequentially and ex situ because the sample has to be thinned to be transparent to the electron beam. For clusters larger than 1 nm and that are not reactive with air, TEM gives reliable results but these studies are very time consuming. Some studies of nucleation and growth have been made in situ in an UHV-TEM mainly by Poppa [66, 82]. 

The results obtained ex situ provide a valuable supplementary information that is not available in in situ studies. For instance, the surface precipitate can be directly seen on images of the adsorbent particles obtained by means of high resolution transmission electron microcopy (TEM),... 

The structure of CdSe nanoparticles segregated to the fluid interface as shown by confocal microscopy (Fig. 4a) has been investigated ex situ with scanning force microscopy (SFM) and transmission electron microscopy (TEM) methods. All results point to a monolayer of nanoparticles with liquidlike ordering at the interface (Fig. 4b,c) [46],... 

Samples are crushed into pieces (< 0.1pm thick), dusted onto standard holey-carbon coated TEM grids, and examined in a bright field TEM imaging mode of a Philips CM200F instrument. The same Ru crystals were examined following different ex-situ reduction treatments using a special cell that allows inert transfer to the microscope and viewing of same area of the sample. ... 

Various approaches have been described in the literature for the characterization of carbon-supported metal catalysts. The catalysts are usually analyzed before and after (postmortem) their electrochemical operation with conventional ex situ techniques such as x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive x-ray analysis (EDX), x-ray photoelectron spectroscopy (XPS), and x-ray absorption spectroscopy (XAS). Although ex situ analysis provides an important starting point in catalyst characterization, one must keep in mind that significant morphological changes may occur under the operational conditions. It is thus vitally important... 

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