Crystals transmission electron microscopy

The morphologies of both ABA and ANA homopolymers and 73/27 ABA/ANA copol5nner prepared by thin-film polymerization show that crystallization occurs in the homopolymerization systems and the liquid crystal state remains stable in the copolymerization system (39-44), clearly indicating that the random copolymerization is an effective way to retard the crystallization. Transmission electron microscopy revealed that the microstructures of homopol5nners of ABA and ANA had more obvious lamellar texture (41-44). 

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

A progressive etching technique (39,40), combined with x-ray diffraction analysis, revealed the presence of a number of a polytypes within a single crystal of sihcon carbide. Work using lattice imaging techniques via transmission electron microscopy has shown that a-siUcon carbide formed by transformation from the P-phase (cubic) can consist of a number of the a polytypes in a syntactic array (41). 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Small needle-shaped single crystals were examined by transmission electron microscopy (TEM) and electron diffraction (ED) (see Fig. 16-17). The results show that the crystals are elongated along the b-axis, which is the direction of weak intermolecular n-n interactions, and have a well-developed (ab) top surface. It corresponds to the surface of aliphatic tails (direction of weak intermolecular interactions). There are indications of displacement of successive ( / )-laycrs along the fl-axis, in line with the other signs of disorder in the aliphatic layer. 

A T = 5.5-13 K under high pressure, P = 0.4 GPa. I was estimated by transmission electron microscopy (TEM). As schematically shown in Fig. 4, ECSCs or FCCs once melted were kept at Tmax = 160 °C for 5 min at atmospheric pressure. After that, samples were isothermally crystallized at various Tcs. Hereafter, we abbreviate these processes as ECSCs-melt-FCSC or FCCs-melt-FCSC, respectively, where FCSC means folded chain single crystal. The range of AT was about 10-14 K. 

Crystallization of ECSCs was isothermally carried out under high pressure using a piston cylinder high pressure cell with diamond window (PCDW) originally made by us. The formation of isolated ECSCs was confirmed by means of transmission electron microscopy (TEM). 

In the case of extended chain crystals, we showed that a single crystal is easily formed even for Mn higher than 105. An ECSC shows a cigar-like and tapered shape morphology, observed by polarizing optical microscopy [22] and by transmission electron microscopy [48]. 

With such a definition, it was found that vfc at 445 K did not change within experimental error as the average Pd particle size, determined by transmission electron microscopy (TEM), was varied between 1.5 and 8.0 nm (Figure 1). Besides, this value of v was also the same as that reported for the ill face of a single crystal of Pd (2), the latter value being itself very much the same on other planes of Pd or on a polycrystalline wire (3). 

The 11 nm-sized Ti02 were crystallized using either hydrothermal or thermal methods from 100 nm, amorphous gel spheres. The Ti02 crystal and agglomerate sizes were determined by X-ray diffraction (Philip 1080) and transmission electron microscopy (JEOL JEM 2010), respectively. The surface area and chemistry of the nanostructured Ti02 were analyzed by nitrogen physisorption (Coulter SA 3100) and Fourier transform infrared spectroscopy (FTIR, Perkin-Elmer GX 2000). Metal catalyst was deposited by incipient... 

The main techniques employed for the characterization of clusters include UV/vis optical absorption, luminescence, mass spectrometry, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR). Single crystal X-ray diffraction (XRD) has been used to determine the structures of a few clusters [17-19]. 

In chemistry, we are often interested in the bulk of the material, and for this purpose we must view the structures with a probe that penetrates through the object. Transmission electron microscopy is ideal for this. The 3D structure of a transparent object is much more complex than the surface, which can be considered as a 2D object, although it often is not at all flat. In the case of a crystal, the object may be hundreds of atoms thick, resulting in a massive overlap of atoms in any direction we chose to look at the crystal from. It is easily realized that even three orthogonal views are not sufficient for resolving all overlapping reflections, unless the structure is very simple. The larger the unit cell is, the more projections are needed in order to obtain a structure with all atoms resolved. 

Transmission electron microscopy (TEM) can provide detailed stmcture of zeolites. I use the word characterize or characterization for stmctural study on a unit cell scale, such as various kind of stmctural defects and basic stmctural units, and determine or determination for obtaining atomic coordinates within the unit cell for all the atoms of a crystal. A simple text or reviews for stmctural characterization of porous materials can be found in a book or review articles [1-6]. Now, we are in a new era, that is, we can determine new stmctures of micro- and mesoporous materials only by electron microscopy(EM), an area called electron crystallography (EC) [7-11]. 

Transition metal oxides attract great interests mainly due to their redox nature, which is thought to be related with their flexible stmcture modiflcation under reductive and oxidative conditions. Such stmcture modiflcation takes place by forming so called crystallographic shear (CS) stmctures to accommodate anion vacancies in speciflc crystallographic planes by simultaneous shear displacement and crystal stmctural collapse [30-32]. High-resolution transmission electron microscopy (HRTEM) is a... 

---