Wide-angle reflection mode

The structural anisotropy in crystalline or structurally ordered BPDA-PFMB films was studied in this laboratory with wide-angle X-ray diffraction (WAXD) methods. In brief, WAXD experiments were designed to examine both the reflection and transmission modes of thin-fihn samples. In addition, uniaxially oriented polyimide fiber WAXD patterns were obtained to aid in the identification of the film structure. The film WAXD pattern obtained from the reflection mode corresponded well to the fiber pattern scanned along the equatorial direction (Figure 16.3), " which indicates that the reflection mode pattern represents the (hkQ) diffractions. On the other hand, as shown in Figure 16.4, the (001) diffractions were predominant in the film WAXD pattern obtained via the transmission mode. This pattern corresponded to the fiber pattern scanned along the meridian direction. These experimental observations clearly indicate that the c-axes of the crystals are preferentially oriented parallel to the film surface however, within the film, they are randomly oriented. 4.2 5 j( should be pointed out that the WAXD experiments are only sensitive to crystalline or ordered structures in polyimide films. They do not provide any information on the amorphous regions. 

Several experiments have been customarily utilized to characterize the structural anisotropy in films. One of the most widely used methods is wide angle X-ray diffraction WAXD) experiments (1-4). Figure 2 shows a set of WAXD patterns under both the reflection and transmission modes on a crystalline aromatic polyimide films synthesized from 3,3, 4,4 -biphenyltetracarboxylic dianhydride (BPDA) and 2,2-... 

The twisted nematic field effect is probably the most important of the field effects because of its combined properties of very low voltage threshold, low resistive power dissipation, and relatively wide viewing angle in the reflective mode. 

A Bruker AXS wide-angle X-ray diffractometer with a Cu Ka average source (k = 1.5418 A) was utilized to look at the crystalline structure of the overall composite sample and to calculate the Herman orientation factor. The samples were run in transmission and reflection modes. In the reflection mode, the... 

Wide-angle X-ray scattering experiments were performed in transmission mode with an HZG diffractometer. For these purposes, specimens with dimension of 100x20x2 mm were prepared from extmdates. Radial scans of intensity vs. diffraction angle 20 were recorded in the range of 10-30 ° by steps of 0.05 ° and step scan interval of 5 s at ambient temperature. The degree of orientation of PP phase (O) was evaluated as a ratio between the intensities of (110) reflection (/no) and (040) reflection (/040), O =/ o/(/no + /o4o). 

Figure Bl.25.12. Excitation mechanisms in electron energy loss spectroscopy for a simple adsorbate system Dipole scattering excites only the vibration perpendicular to the surface (v ) in which a dipole moment nonnal to the surface changes the electron wave is reflected by the surface into the specular direction. Impact scattering excites also the bending mode v- in which the atom moves parallel to the surface electrons are scattered over a wide range of angles. The EELS spectra show the higlily intense elastic peak and the relatively weak loss peaks. Off-specular loss peaks are in general one to two orders of magnitude weaker than specular loss peaks.

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