Development of Crystallinity in Turbostratic Boron Nitride Derived from Polymeric Precursors

Boron nitride derived from polymer precursors is of great interest for applications such as fibers, coatings and novel forms such as aerogels. The BN is prepared by the polymerization of functionalized borazine and thermal treatment in nitrogen at 1200°C. The BN powders obtained by this route are invariably trubostratic wherein the sheets of hexagonal BN are randomly oriented to yield the so-called turbostratic modification. Fib 1a and 1b show images of BN powder with the corresponding diffraction pattern in fig. 1c. The (0002) reflection from BN is seen as a diffuse ring with occational spots that come from crystals of BN such as those shown in fig. 1b. The (0002) lattice fringes of BN seen in these powders are the most characteristic indication of the crystallinity of the BN.

TEM Analysis of Psuedo-Amorphous and Polycrystalline Silicon Thin Films

Thin polycrystalline Si films are used in certain aspects of the fabrication of integrated circuits in the electronics industry. To date, analysis of Si films has been confined to thick films (10-50μ) deposited and/or heat-treated at temperatures over 800°C. The pyrolytic decomposition of silane gas in nitrogen or hydrogen carriers is the most common deposition technique in the industry. In the present work, thin Si films, e-beam evaporated at 300°C onto SiO2 and Si3N4 substrates and subsequently heat-treated at temperatures from 450°C to 1040°C are compared to films deposited onto SiO2, Si3N4 and Al2O3 by the pyrolytic decomposition of silane gas at temperatures from 500°C to 900°C with no further heat-treatment.The evaporated films are psuedo-amorphous as-deposited and remain so after subsequent heat-treatments up to 600°C for one hour. A psuedo-amorphous diffraction pattern is seen in Fig.1; the first diffuse ring occurs at the Si (111) radius and the second broad diffuse ring spans the radii of the Si (220) and (311) reflections.