New Kind of Microstructure Essential for Amorphous-Crystalline Transitions in Chalcogenide-Based Films.

Apr 13, 2007 - 9:30 AM -  I11.4
Room 3006 (Moscone West)
Vladimir Kolosov 1 , Lev Veretennikov 1
1 , Ural State Economic University, Ekaterinburg Russian Federation
Chalcogenide-based films are widely used as the active media for rewritable information storage and are prospective for further developments. Anyway detailed microstructure characterisation of the crystallised spots seems lacking. Using some initially amorphous vacuum condensates (Se-Te, Sb2Se3 and bilayers Ge-Sb2Se3) we study the crystals growing under the influence of local electron beam annealing in transmission electron microscope (TEM). Primarily we focus on the specific feature inherent to amorphous-crystalline transformation in thin films - "transrotational" structure [1], most prominent between micro- and nanoscale [2]. Extinction bend contours indicating such regular imperfections on the TEM images of crystallised spots of chalcogenide thin films (e.g., phase change materials for optical recording) are widespread and can be found in corresponding publications (e.g., [3-4]). We used bend contour technique preferentially for measurements of local and integral magnitudes of lattice bending and for estimates of geometry and general character of lattice disorientations in the crystallized areas.To study the effect of thickness (10-100 nm) and composition the films with strong gradient either of composition (Se-Te) or thickness (Sb2Se3, bilayers Ge-Sb2Se3) were prepared and placed on the TEM grids. Samples were irradiated by the electron beam inside TEM thus making possible a broad choice of various intensities, different irradiated spots (~ 1 μm and above) and also in situ studies.Strong internal lattice bending around axes lying in the film plane are observed for the materials studied. In Se-Te films the relative concentration strongly affects the magnitude of internal lattice bending. In Sb2Se3 films the internal lattice bending strongly increases as the film gets thinner, while growth rate decreases. In Ge-Sb2Se3 bilayers (with variable thicknesses of the layers) the influence of Ge layer on the crystal growth and microstructure can be more or less pronounced but depends upon the layer position (sublayer or overlayer). The intensity of the electron beam strongly influences the crystallization and the structure of crystallized spot in the case of Ge sublayer. Above microstructure parameters (primarily magnitude of internal lattice bending) that may be revealed by TEM (but usually missed in the papers) can strongly influence the time, energy an other features essential for writing/rewriting in chalcogenide films used as phase change materials.[1] V.Yu. Kolosov and A.R. Tholen, Acta Mater. v. 48 (2000), p. 1829 [2] V. Yu. Kolosov, Proc. 13th EMC, Antwerp, v. 2, 255 (2004).[3] S. J. Price; A. L. Greer; C. E. Davies, Optical Data Storage 2000 (2000).[4] B. J. Kooi, and J. Th. M. De Hosson, J. of App. Phys., 95, 4714 (2004).This work was supported by INTAS (00-100), pending support from RFBR.