Optical microscopic pattern structure

The resolution of a resist can be determined either optically or electrically by using special line-width-measuring equipment or by examining the resist with a scanning electron microscope (17). Correct feature size must be maintained within a wafer and from wafer to wafer, because device performance depends on the absolute size of the patterned structures. The term critical dimension (CD) refers to a specific feature size and is a measure of the resolution of a lithographic process. 

Fig. 4.11. Left (a) Optical microscope image of an OLED working at a luminance of 100 cd/m2 under water vapor atmosphere. Non-emitting dark spots can be seen clearly, (b) SEM image of the bubbles formed on the aluminum cathode in the dark spot area, (c) Correlation between dark spot growths (taken from the increase in diameter) and total current density [110]. Right (a) Shown here is the random pattern of carbonized areas on the surface of the cathode after operation, shown in wide field, (b) At higher resolution, the structure of one of these areas becomes more apparent, (c) and (d) show nanoscale views of carbonized areas with the extrusion of the polymer through the cathode and the resulting void underneath [111].

The major feature of polymers that have been bulk crystallized under quiescent conditions are polycrystalline structures called sphemlites. These are roughly spherical supercrystalline structures which exhibit Maltese cross-extinction patterns when examined under polarized light in an optical microscope. Spheruliies are characteristic of semicrystalline polymers and are also observed in low-molecular-weight materials that have been crystallized from viscous media. Sphemlites are aggregates of lamellar crystallites. They are not single crystals and include some... 

Sanidine is monoclinic (space group C2/m), and there is complete disorder in the occupation of the tetrahedral (T) sites by the A1 and Si atoms. Over geological time, ordering takes place. In low (or maximum) micro-cline, the ordering is complete (all A1 in TiO sites), and the symmetry is reduced to triclinic (CT). There are four main orientational variants in this structure two orientations related by the albite twin law (rotation of 180° about b ) and two orientations related by the pericline twin law (rotation of 180° about b). The composition planes of these two twins are, respectively, (010) and the rhombic section which is parallel to b and approximately normal to (001). Thus, the characteristic cross-hatched pattern observed in (001) sections between crossed-polarizers in the optical microscope has, for many years, been simply interpreted as intersecting sets of albite and pericline twin lamellae formed at the monoclinic-to-triclinic transformation. However, TEM observations indicate that this model is too simple. Because these observations, collectively, also constitute an excellent example of the application of the principal modes of operation of TEM to a specific mineralogical problem, we discuss them in some detail. 

Fig. lla and b. Cholesteric liquid crystalline structure of PBLG in m-cresol a, striation patterns observed under a polarizing microscope b, optical diffraction pattern with a beam from the He—Ne gas laser. Concentration is 17% volume fraction of polymer, and cell thickness is 2 mm... 

The structure of modified surface layer was investigated using powerful optical microscope Neophot-21 (resolution up to 0.4 pm). Furthermore, TEM images and selected area electron diffraction (SAED) patterns were obtained to study structural evolution caused by simultaneous friction treatment and nitriding. 

Some polymers, when they are suitably prepared in thin slices or as thin films, exhibit circular features when they are viewed in the optical microscope (fig. 3.13), whereas others show less regular patterns, depending on the polymer and the method of preparation of the sample. In order to see these features the polarising microscope with crossed polarisers (see section 2.8.1) is used. The circular features shown in fig. 3.13 are caused by spherical structures called spherulites which are a very important feature of polymer morphology, the subject of much of chapter 5, where the Maltese cross appearance seen in fig. 3.13 is explained. Each spherulite consists of an aggregate of crystallites arranged in a quite complicated but regular way. 

There is yet a larger scale of organization in many crystalline polymers, known as spherulites. These spherical structures are composed of many crystalline lamellae, which have grown radially in three dimensions and which are connected by amorphous molecular segments (Keith, 1969). Spherulites are easily seen with an optical microscope between crossed polarizers, and under these conditions they exhibit a characteristic pattern with circular birefringent areas possessing a Maltese cross pattern, as shown in Figure 1.11. 

With respect to evenness and plane parallelism, the attainable accuracies are comparable to those of lapped parts. Ground parts, however, exhibit a surface structure with curved grinding traces superimposing in all directions. Lapped surfaces on the other hand are characterized by a microscopic crater structure that does not reveal any directional dependencies. If surface isotropy is a necessary quality criterion as, e.g., in optical applications, then surface grinding with lapping kinematics cannot be used. The various removal mechanisms and resulting surface patterns are shown in Figure 16.2 for the example of a silicon nitride sample. 

A droplet of the latex suspension in water (solid content 0.1-1 %) was placed onto the patterned substrate, covered to prevent evaporation, and incubated for >3 h (preferably over night) at 4 °C (refridgerator). Excessive liquid was then slowly removed with a pipet and some patterns (when stable enough, e.g. carboxylated latex spheres on NR4 ) were carefully rinsed with water and ethanol. We refer to this procedure as drop coating . The assembly structures were investigated immediately after preparation with the optical microscope (Axioskop, Zeiss) in reflection mode. 

After preparation of honeycomb-patterned films, the surface layer of the film was removed by peehng with an adhesive tape (Scotch Tape). The surface structures of the films were also observed using an optical microscope and an SEM. 

In many cases unique optical textures are observed for the various orientations and structures of the three classes of liquid crystals. Thin films of nematic crystals, for example, can be identified by the pattern of dark tlueads (isogyres) which can appear in the optical microscope in transmission with crossed polarizers. Hot stage polarizing optical nucroscopy is often used to identify the phases and the transition temperatures. In some cases, the optical texture is not uniquely identifiable and x-ray diffraction and thermal analysis by DSC are used to complement the microscopy. 

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