Invited Paper SE+TF-TuA1
Evolution of Crystal Orientation during Oblique Angle Deposition

Tuesday, November 1, 2011, 2:00 pm, Room 104

The oblique angle deposition (OAD) has attracted attention due to the shadowing effect that results in interesting morphology of isolated nanostructures. These artificial nanostructures have rich textures depending on the growth conditions such as the angle of incidence, substrate temperature, deposition rate, and substrate rotation speed or mode. These OAD films often have biaxial textures even on amorphous substrates because the in-plane symmetry is broken under the off-normal incidence of the deposited atoms on the substrate. The most frequently used characterization technique for biaxial texture films is x-ray pole figure analysis. However, the texture obtained by x-ray is an average texture from the entire thickness of the film due to the x-ray’s few micron penetration depth. As the texture of a film often changes during growth, information on the basic mechanisms that control the final texture is often lost. In this talk we will show how we can use our newly developed reflection high energy electron diffraction (RHEED) surface pole figure technique to probe the surface texture evolution of the growth front from the initial stage (a few nm thick) to the later stage of thick films [1] either in situ or ex situ. Examples of biaxial texture evolution of CaF₂ [2], Mg, W [3] and Mo nanostructures as a function of thickness, incident angle, and rotation schemes, will be presented. The surface sensitive RHEED pole figure technique reveals that biaxial texture can be formed at thickness as small as 20 nm. In some cases, surface texture at the growth front is seen to be quite different from the bulk texture measured by x-ray pole figures. We also show that these biaxial textured films can be used as buffer layers to grow near-single crystal semiconductor films which may find important applications in energy conversion devices.

Work was supported by NSF-0506738.

[1] F. Tang, T. Parker, G.-C. Wang, and T.-M. Lu, "Surface texture evolution of polycrystalline and nanostructured films: RHEED surface pole figure analysis", Journal of Physics D: Applied Physics 40, R427 (2007).

[2] C. Gaire, P. Snow, T.-L. Chan, W. Yuan, M. Riley, Y. Liu, S.B. Zhang, G.-C.Wang and T.-M. Lu, “Morphology and texture evolution of nanostructured CaF₂ films on amorphous substrates under oblique incidence flux”, Nanotechnology 21, 445701 (2010).

[3] R. Krishnan, Y. Liu, C. Gaire, L. Chen, G.-C. Wang and T.-M. Lu, Texture evolution of vertically aligned biaxial tungsten nanorods using RHEED surface pole figure technique, Nanotechnology 21, 325704 (2010).