Crystallization thin-film stage

Electroless crystallization proceeds in two basic stages (1) the thin-film stage (up to 3 p.m) and (2) the bulk stage. 

Thin-Film Stage. The mechanism of thin-film formation is characterized by three simultaneous crystal building processes nucleation (formation), growth, and coalescence of three-dimensional crystallites (TDCs). 

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. 

X-ray measurements also indicate photocrystallization at exposure values E > Typical results, i.e., X-ray diffraction patterns of photocrystallized samples (this stage refers to curve 5 of Fig. 7.11), show four crystalline peaks located at 29 = 24°, 30°, 41°, and 45°. These can be indexed as 100, 101, 110, and 111 of the hexagonal Se crystal, respectively. Similar X-ray diffraction patterns were obtained by Ishida and Tanaka [26] examining photoinduced birefringence in a-Se thin films. 

Soon after the discovery of the RNi2B2C compounds (see Section 1.1) high-quality polycrystalline samples and even single crystals could be prepared, thus enabling significant studies at an early stage. Some properties, however, sensitively depend on small stoichiometric variations or on atomic disorder in the samples. In this section, we focus on this problem including a short overview on preparation techniques. Studies on the deposition and on basic properties of thin films will also be reported. 

Fig. 31 AFM deflection images of P[(S)-LA] thin film with a thickness of about 30 nm, taken during isothermal crystallization at 165 °C on the AFM heating stage. In this sequence, the first frame (a) was taken at 7.5 min after the temperature reached 165 °C, and the following frames were taken at 15 (b), 22.5 (c), 30 (d), 50 (e), and 120 min (f), after reaching 165 °C [93]...

Dehydrated calcium pimelate is added (between 0.01 and 0.5 wt %) as the nucleating agent to isotactic polypropylene to produce the (3 modification of iPP [63]. Following molding between two glass plates at 220°C thin films of the polymer are isothermally crystallized at 140°C-143°C in a microscopy hot stage. After the hedritic structures develop, the samples are quenched to room temperature. Prior to AFM examination, the specimens are etched with a 1% solution of potassium permanganate in a mixture of sulfuric and orthophosphoric acid [64, 65]. This procedure is described in detail in the literature Caution consult the literature for safety precautions ) and helps to remove preferentially amorphous phase of PP [64]. Thus, unlike in the many other examples discussed in Sect. 3.2, here the interior of a specimen is analyzed after its exposure. 

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