TEM bend-contour technique for direct lattice orientation analysis [1, 2] developed earlier gave the chance to discover unusual micro crystals growing in thin (20-100 nm) amorphous films with strong (dislocation independent) internal bending of the crystal lattice planes [3]. Initially we observed the new phenomenon for Se (primarily in situ ) and Te. Later on it has been revealed for many other substances and materials of different chemical bonding and various preparation conditions (Se-C, Se-Te, Sb2Se3, Sb2S3, Ge-Sb2Se3, Ge-Te, Tl-Se, Cu-Te, a‑Fe2O3, Cr2O3, Co-Pd, Re, W, carbides, amorphous metals, ferroelectrics, phase change materials for memory devices). HREM, correlative AFM-TEM were used in due cases.
The main feature of novel micro-, nanostructure is the permanent regular bending/curving of the lattice planes (about axes primarily lying in the film plane) in thin growing crystal. Different geometries are revealed, Fig.1. Thus one can detect in a perfect crystal (“single crystal”) usual translation complicated by relatively small rotation of the unit cell. Anyway more or less significant rotations, up to 300 degrees per 1 micrometer of the crystal length can be attained. Therefore the new term “transrotation” [4] was introduced for such novel crystals/structures. The geometry and gradient of lattice orientations depend upon crystallography of the substance, crystal growth rate (e.g., upon heating), film thickness (the thinner is the film, the stronger is the transrotation) and composition (for binary films with composition gradients).
Earlier hypothetical mechanism of unusual phenomenon based on surface nucleation has been improved and supported by atomistic model of transrotational microcrystals. The last is based on mathematic instruments of conformal transformations. Generally transrotational crystals/structures revealed by TEM can be considered as a new state intermediate between glassy and crystalline ones (similarly to the structure of liquid crystals intermediate between crystalline and liquid). Alternatively transrotation can be regarded as an example of new kind of extended defect in condensed matter. In this sense transrotations (in thin crystals) supplement dislocations (in crystals) and disclinations (in liquid crystals). Microcrystals and nanostructures with “transrotation” during last years have been eventually recognized/studied in various thin films by different authors (e.g. [5-7]).
Fig.1 Schemes of lattice transrotation geometries with corresponding crystal TEM images placed below for thin-film materials: Se, Fe2O3, Ta2O5, C+Se+C, Cu-Te (from left to right). Bar = 1 µm (where not specified).
[1] I.E. Bolotov, V.Yu. Kolosov, Phys. Stat. sol., 69a, 85-96 (1982).
[2] V.Yu. Kolosov, Electron Microscopy, Proc. XII ICEM, 1, 574-575 (1990).
[3] I.E. Bolotov, V.Yu. Kolosov, A.V. Kozhyn, Phys. Stat. sol. 72a, 645-654 (1982)
[4] V.Yu.Kolosov, A.R. Thölén, Acta Mater. 48, 1829-1840 (2000).
[5] B. J. Kooi, and J. Th. M. De Hosson, J. of App. Phys., 95, 4714 (2004).
[6] E. Rimini, et. al., J. Applied Physics 105, p.123502 (2009).
[7] V. Longo, M.A. Verheijen, F. Roozeboom, W.M.M. Kessels ECS J. Sol. St. Sci. & Tech., 2 (5) N120-N124 (2013)
* Partially supported by RF Ministry Education & Sci. and RF Government (Program 211, N02.A03.21.0006).
