Multilayer electron diffraction

Figure 4 is an optical absorption spectrum from a multilayer assembly and shows the sharp absorption in the visible characteristic of the polydiacetylenes. Electron diffraction reveals a crystalline layered structure. However, registry between layers is less than perfect. Electron diffraction from a few layers indicates a strong possibility for growing well-oriented structures, and this is being pursued in our laboratory. 

No direct method exists by which monolayer film structures on water can be studied. Therefore, the LB method has been used to study molecular structures in past decades. The most useful method for investigating the detailed LB-deposited film structure is the well-known electron diffraction technique (or the scanning probe microscope [Birdi, 2002a]). The molecular arrangements of deposited mono-and multilayer films of fatty acids and their salts, using this technique, have been reported. The analyses showed that the molecules were almost perpendicular to the solid surface in the first monolayer. It was also reported that Ba-stearate molecules have a more precise normal alignment compared to stearic-acid monolayers. In some investigations, the thermal stability of these films has been found to be remarkably stable up to 90°C. 

Based on structural analyses obtained by the electron diffraction technique, the deposited films are known to be monocrystalline in nature, and thus, can be regarded as a special case of a layer-bilayer mechanical growth forming almost two-dimensional crystals. However, there is evidence that Ba-behenate multilayers do in fact show absence of crystallization, as demonstrated by electron micrographic studies. 

Whereas the disclination picture provides a convincing explanation of the properties of multilayers of fatty acids, being consistent with both the electron diffraction and optical evidence, it is not yet proven that, at room temperature, such systems are really in the hexatic state. It is equally probable that the existence of an initial hexatic monolayer on which subsequent layers are grown by epitaxy produces a material which is far from thermal equilibrium and has more of the nature of a glass state rather than of a mesophase. Indeed, the relative hardness of multilayers and their resemblance to true three-dimensional crystals of fatty acids tends to support this view. 

Finally we only mention that, for example, calorimetric investigations [72, 395], LEED [91], high-energy electron diffraction [313], neutron diffraction [45, 371], high-resolution electron energy loss spectroscopy [304], and ellipsometric studies [111, 147, 366] were extended much beyond the fully compressed N2 monolayer into multilayer and film regimes. 

More recently, the analysis of pristine PPV has been supplemented by x-ray data obtained by Chen et al. [273] on a four-circle diffractometer, thus avoiding some of the complications inherent in the use of electron diffraction data, such as dynamical effects and the lack of absolute intensities. The samples consist of multilayers of stretched (///o = 10) film stacked to a thickness not exceeding 200 pm a c-axis mosaic spread of less than 7° is determined from equatorial reflections. Since crystallographic results have been found to vary somewhat among the investigations... 

The complex instrumentations include LEED, low energy electron diffraction, which is revealing a complex model for surface structure when apparent multilayer adsorption of oxygen proceeds on clean metal surfaces. 

A Millipore Milll-Q purification system was used for subphase preparation, and a constant temperature bath was used to control the subphase temperature. The mixed spreading solutions were dispersed at the air-water Interface and then slowly compressed at speeds of about 5 A2 mol min-" to surface pressures of 10-15 mN/m prior to deposition. Monolayers were transferred onto electron microscope grids for transmission electron microscopy and electron diffraction, using both the horizontal and vertical dipping techniques. Multilayer assemblies were prepared onto platinum-coated substrates using the vertical dipping technique for Near Edge X-Ray Absorption Fine Structure Spectroscopy (NEXAFS). 

Weiss W, Baibieri A, Vanhove MA, Somorjai GA (1993) Surface stmcture determination of an oxide film grown on a foreign substrate Fc304 multilayer on Pt(lll) identified by low energy electron diffraction. Phys Rev Lett 71 1848-1851... 

Seyller Th, Diehl RD, Jona F (1999) Low-energy electron diffraction study of the multilayer relaxation of Cu(211). J Vacuum SciTechnA 17 1635-1638... 

The occurance of the lattice controlled diyne polymerization in lipid layers provoked the question for the state of order of these structures. Several studies therefore dealt with the investigation of structure and morphology mainly of multilayer samples using X-ray 0,79,90) electron diffraction 3.74,79.90,95) electron 3,64, and polarizing mica oscopy , infrared spertroscopyand infrared dichroism measurements... 

Further informations on texture and mutual orientation of the molecules in multilayer were obtained from electron diffraction studies. These studies indicstte a unique orientation of the molecules in crystallites (domains) with a lateral extension of the order of 10 to 10 micrometers in diameter. In adjacent domains the orientation of the molecules is different. From the diffraction patterns regular subcells of the paraffin chain packing have been determined. ... 

Fig. 14a and b. Electron micrographs of polymerized multilayers of (a) ia, and (b) Ua (thickness 20 layers), showing different morphologies as also indicated by the electron diffraction patterns... 

Phase separation on one hand, and formation of a superstructure of the diyne compound on the other hand, have been explained by assuming strong interactions between the parafBn chains of the otherwise immiscible compounds. Such interactions could originate from similarities in the packing geometry of the paraffinic portions of the hydrophobic chains, as it was indicated by electron diffraction studies of the mixed multilayers... 

The morphology most likely originates from the ability of the two isomers to form a 1 1 complex. Complex formation was evidenced by UV/VIS-spectroscopy, X-ray and electron diffraction studies of the multilayers It is most likely caused by the similar chemical structures of the two isomers. 

By changing the parameters of the ICB system, crystalline C o-TCNQ thin films can be obtained. As shown in Fig. 17a, the electron diffraction pattern corresponding to the TEM image indicates that the ICB-deposited thin film can be single crystalline with a multilayered structure. The crystal structure was determined to be monoclinic [14] with lattice parameters a = 1.753 nm, b = 0.569 nm, c = 0.515 nm, and (3 = 81.6°. 

Multilayer adsorption of Xe, Ar, and Ne films on graphite has been studied by high-energy electron diffraction techniques [70 and references therein], finding clear disagreement with the previous theories based on statistical models. 

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