Tham khảo tài liệu 'ferroelectrics material aspects part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 375 Epitaxial Integration of Ferroelectric BaTiO3 with Semiconductor Si From a Structure-Property Correlation Point of View contribution of the temperature dependent lattice strain Sm Tg and the thermal strain Stherm T 59 which can be approximated by the linear relation Sm T Sm Tg Stherm T 1 Stherm T a - af T - Tg 2 where Tg 873 K is the growth temperature Stherm T is the thermal strain as and Xf are linear thermal expansion coefficients TECs of the substrate and prototypic cubic phase of the film. Sm Tg as Tg - Tg as Tg is the effective misfit strain of the film and substrate at Tg as as 1 - p is the effective lattice parameter of the substrate 60 and p is the dislocation density 61 which reflects the effect of strain relaxation induced by the appearance of misfit dislocations at the film substrate interface at Tg. For the convenience of understanding we define an original misfit lattice strain Sm0 Tg which means the actual original misfit strain between the as-grown film and the supporting substrate if the film does not relax at all at the growth conditions as follows S m Tg as Tg - af Tg as Tg 3 Taking into account the thermal expansion the lattice constant of the film and substrate at Tg can be approximated by af Tg af RT 1 af Tg - RT and as Tg as RT 1 as Tg - RT respectively. As a matter of fact the Sm0 Tg does not really exist because the film growth and relaxation occur simultaneously. However we assume the film growth process and the strain relaxation process can occur in the following two successive steps. First the film doesn t relax during the whole growth procedure holding a Sm0 Tg and then when growth is done the relaxation process dominates and the as-grown film begins to relax only when the accumulated Sm0 Tg exceeds the critical relaxation requirements. In this picture the Sm Tg in equation 1 can be thus equivalently and much more schematically divided into the combination of an original lattice strain Sm0 Tg at Tg and a strain variation due to
