Scanning electron microscopy operation

In contrast to many other surface analytical techniques, like e. g. scanning electron microscopy, AFM does not require vacuum. Therefore, it can be operated under ambient conditions which enables direct observation of processes at solid-gas and solid-liquid interfaces. The latter can be accomplished by means of a liquid cell which is schematically shown in Fig. 5.6. The cell is formed by the sample at the bottom, a glass cover - holding the cantilever - at the top, and a silicone o-ring seal between. Studies with such a liquid cell can also be performed under potential control which opens up valuable opportunities for electrochemistry [5.11, 5.12]. Moreover, imaging under liquids opens up the possibility to protect sensitive surfaces by in-situ preparation and imaging under an inert fluid [5.13]. 

Scanning electron microscopy (SEM) utilizes a highly focused electron beam which is scanned over the surface of the specimen. Since penetration through the specimen is not essential for this instrument, thicker samples (cm range) and lower accelerating potentials (low kV range) are commonly used. The most popular mode of operation is the emissive mode which utilizes those electrons that have either been emitted by the... 

The sizing methods involve both classical and modem instrumentations, based on a broad spectrum of physical principles. The typical measuring systems may be classified according to their operation mechanisms, which include mechanical (sieving), optical and electronic (microscopy, laser Doppler phase shift, Fraunhofer diffraction, transmission electron miscroscopy [TEM], and scanning electron microscopy [SEM]), dynamic (sedimentation), and physical and chemical (gas adsorption) principles. The methods to be introduced later are briefly summarized in Table 1.2. A more complete list of particle sizing methods is given by Svarovsky (1990). 

The next stage of characterization focuses upon the different phases present within the catalyst particle and their nature. Bulk, component structural information is determined principally by x-ray powder diffraction (XRD). In FCC catalysts, for example, XRD is used to determine the unit cell size of the zeolite component within the catalyst particle. The zeolite unit cell size is a function of the number of aluminum atoms in the framework and has been related to the coke selectivity and octane performance of the catalyst in commercial operations. Scanning electron microscopy (SEM) can provide information about the distribution of crystalline and chemical phases greater than lOOnm within the catalyst particle. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) can be used to obtain information on crystal transformations, decomposition, or chemical reactions within the particles. Cotterman, et al describe how the generation of this information can be used to understand an FCC catalyst system. 

The transmission electron microscopy (TEM) images were acquired using a Phillips CM200FEG microscope operated at lOOkV. The scanning electron microscopy (SEM) photograph was obtained on a JEOL, JSM-35C microscope operated at 25kV. 

Characterization Powder X-ray diffraction patterns (XRD) were recorded with a Rigaku D/Max-llA diffractometer with Cu Ka radiation. TEM images were taken on a JEM-2010 microscope (JEOL), operated at 200 kV. Scanning electron microscopy (SEM) was obtained with a Philip XL30. Nitrogen adsorption measurements were performed at 77 K using a Micromeritics Tristar 3000 analyzer. The samples were pretreated at 473 K under the blow of the N2 for at least 3 h. 

Figure 28 Schematic representation and operating principles of Li batteries, (a) Rechargeable Li-metal battery (the picture of the dendrite growth at the Li surface was obtained directly from in situ scanning electron microscopy measurements), (b) Rechargeable Li-ion battery. (Ref 47. Reproduced by permission of Nature Publishing Group (www.nature.com))...

Microscopic measurements were performed by using a Quanta 200 ESEM (environmental scanning electron microscopy) instrument (EEY Company), operating in low-vacuum mode, with an electron beam emitted at 25 or 30 kV under 1 Torr (133 Pa) pressiue. Solid-state backscatter detector (SSB) allowed collecting backscattered electrons emitted from the samples. 

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