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The Materials Science of Thin Films 2011 Part 6

Tham khảo tài liệu 'the materials science of thin films 2011 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 228 Film Formation and Structure is limited and therefore their occurrence is ubiquitous. For example columnar grains have been observed in high-melting-point materials Cr Be Si and Ge in compounds of high binding energy Tic TiN CaF2 and PbS and in non-noble metals evaporated in the presence of oxygen Fe and Fe-Ni . Amorphous films of Si Ge SiO and rare earth-transition metal alloys e.g. Gd-Co whose very existence depends on limited adatom mobility are frequently columnar when deposited at sufficiently low temperature. Inasmuch as grain boundaries are axiomatically absent in amorphous films it is more correct to speak of columnar morphology in this case. This columnar morphology is frequently made visible by transverse fracture of the film because of crack propagation along the weak low-density intercolumnar regions. Magnetic optical electrical mechanical and surface properties of films are affected sometimes strongly by columnar structures. In particular the magnetic anisotropy of seemingly isotropic amorphous Gd-Co films is apparently due to its columnar structure and interspersed voids. A collection of assorted electron micrographs of film and coating columnar structures is shown in Fig. 5-14. Particularly noteworthy are the structural similarities among varied materials deposited by different processes suggesting common nucleation and growth mechanisms. An interesting observation Ref. 20 on the geometry of columnar grains has been formulated into the so-called tangent rule expressed by Eq. 5-43. Careful measurements on obliquely evaporated Al films reveal that the columns are oriented toward the vapor source as shown in the microfractograph of Fig. 5-15. The angle 3 between the columns and substrate normal is universally observed to be somewhat less than the angle a formed by the source direction and substrate normal. An experimental relation connecting values of and 3 obtained by varying the incident vapor angle over a broad range 0 a 90 was found to closely .