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Jing Lia, Bryan D. Gaunttb and Elizabeth C. Dickeya, b, 
, 
Abstract
Both pulsed-DC biased and commercial ion-beam sputtered VOx thin films maintain a face-centered-cubic nanocrystalline phase, even for stoichiometries of x > 1.5, which is well outside the bulk equilibrium solubility range for cubic VOx. Many of these highly nonstoichiometric films exhibit a high density of microtwins, which give rise to unusual fine structure in the selected-area electron diffraction patterns, namely: an additional defect ring; a significant broadening of the {2 0 0} ring; pairs of parallel rod features which are tangent to the additional defect ring; and additional fine-structure features between the {2 0 0} and {2 2 0} rings. The formation of the microtwins is correlated with the coalescence of vanadium vacancies along the {1 1 1} twin planes in the crystalline lattice.
Keywords: Bolometer materials; Transmission electron microscopy (TEM); Thin films; Nanocrystalline microstructure; Twinning
Article Outline
Fig. 1. Complementary TEM bright-field (a) and dark-field (b) images of a pulsed-DC sputtered VOx thin film showing planar defect contrast with periodic dark and light fringes on the order of
0.5 nm in spacing. SAED pattern containing the area in (a) and (b) is shown in (c). Long, parallel rod features marked by two inclined white arrows are perpendicular to the planar defect contrast shown in (a) and (b), and touch with the circumference of the “defect ring”.Fig. 2. (a) HRTEM image showing typical (1 1 1) microtwin platelets structure in
0 1 1
projection. The inset shows schematically (1 1 1) microtwins platelets. (b) The SAED pattern from the HRTEM image area in (a) showing parallel long-rod features marked by a pair of inclined white arrows. The long rods touch with the defect ring. The vertical arrow marks a “cross-like” feature on 200 ring. The 200 ring (marked by horizontal arrow) shows significant broadening.Fig. 3. Another representative SAED pattern of the pulsed-DC sputtered VOx thin film. The 111 reflection ring is split and the 200 ring is broadened. The inclined white arrows mark cross-like features on the 200 ring and between the 200 and 220 rings.
Fig. 4. (a) A schematic
Fig. 5. A schematic illustration of a polycrystalline microtwin SAED pattern produced by rotating of the pattern in Fig. 4b around the
Fig. 6. (a) Cross-sectional TEM dark-field image of the ion-beam sputtered VOx film, showing columnar structure and periodic dark and light fringes. (b) SAED pattern of the area in (a); the long-rod features marked by five white arrows show preferred orientation with around ±15° to the normal direction of the film surface. The split of the 111 ring is marked by a horizontal black arrow and the broadening of the 200 ring is marked by a horizontal white arrow.
Corresponding author at: Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA. Tel.: +1 814 865 9067; fax: +1 814 865 2326.
