Morphology and texture evolution of nanostructured CaF2 films on amorphous substrates under oblique incidence flux.

The morphology and biaxial texture of vacuum evaporated CaF(2) films on amorphous substrates as a function of vapour incident angle, substrate temperature and film thickness were investigated by scanning electron microscopy, x-ray pole figure and reflection high energy electron diffraction surface pole figure analyses. Results show that an anomalous [220] out-of-plane texture was preferred in CaF(2) films deposited on Si substrates at < 200 °C with normal vapour incidence. With an increase of the vapour incident angle, the out-of-plane orientation changed from [220] to [111] at a substrate temperature of 100 °C. In films deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at 100 °C to [111] at 400 °C. In films deposited with an oblique vapour incidence at 100 °C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness (20 nm or more). Using first principles density functional theory calculation, it was shown that [220] texture formation is a consequence of energetically favourable adsorption of CaF(2) molecules onto the CaF(2)(110) facet.

Texture evolution of vertically aligned biaxial tungsten nanorods using RHEED surface pole figure technique.

Vertically aligned biaxial tungsten nanorods with cubic A15 crystal structure were deposited by DC magnetron sputtering on native oxide covered Si(100) substrates with glancing angle flux incidence (theta approximately 85 degrees) and a two-step substrate rotation mode at room temperature. These vertical nanorods were grown to different thicknesses (10, 25, 50 and 100 nm) and analyzed for biaxial texture evolution using a highly surface sensitive reflection high-energy electron diffraction (RHEED) pole figure technique. The initial polycrystalline film begins to show the inception of biaxial texture with a fiber background between 10 and 25 nm. Biaxial texture development is eventually completed between 50 and 100 nm thicknesses of the film. The out-of-plane crystallographic direction is [002] and the in-plane texture is selected so as to obtain maximum capture area. In a comparison with 100 nm thick inclined tungsten nanorods deposited at 85 degrees without substrate rotation, it is found that the selection of in-plane texture does not maintain maximum in-plane capture area. This anomalous behavior is observed when the [002] texture axis is tilted approximately 17 degrees from the substrate normal in the direction towards the glancing incident flux.

Mechanical testing of isolated amorphous silicon slanted nanorods.

Mechanical testing was performed on a new class of nanostructures-amorphous Si slanted nanorods of rectangular cross section, fixed at one end to the substrate. These nanorods were grown spatially well separated on nano-pillars under the oblique angle physical vapor deposition technique. Various samples with different dimensions and inclination angles were tested in bending using an atomic force microscope. The material response was elastic up to large stresses/deflections. The Young's modulus was calculated from the slope of the experimentally observed stiffness versus the geometrical factor common to all the samples and was found to be (94.14 +/- 10.21) GPa. No size effect of this parameter was observed within the accuracy of the present measurement.