Hierarchical Field Emission Devices - Hierarchical Nanostructures for Energy Devices - page 239

d n 3 r 4 n g | 0

Figure 10.3 Metal oxide HFE cathodes: ZnO nanosleeve-fishes (a) - reproduced with
permission from ref. 17; ZnO nanorod arrays with abruptly sharpened
tips (b) - reproduced with permission from ref. 18; hierarchical Zn/ZnO
micro/nano tip arrays (c) - reproduced with permission from ref. 22;
cauliflower, rutile TiO 2 hierarchical nanostructures (d) - reproduced
with permission from ref. 24; MoO 2 nanowires decorated with nano-
protrusions (e) - reproduced with permission from ref. 26; WO 3 NWs
onto carbon fibers (f) - reproduced with permission from ref. 28; J-E
plots of the field emission from four types of hierarchical ZnO nanos-
tructures (the transparent anode image of the electron emission from
radial nanowire arrays at a field strength of 4.4 V mm 1 is shown in the
inset (g) - reproduced with permission from ref. 17; J-E plots of the
field emission from the two hierarchical SnO 2 structures (the corres-
ponding F-N plots and the transparent anode image of the electron
emission from sallow-like structures at field strength of 3.98 V mm 1 are
shown in the two insets respectively), (h) - reproduced with permission
from ref. 27.

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fabricated by a direct annealing process. 22 Transmission electron micro-
scopy analysis revealed that the oxide layer grows epitaxially from the Zn
microtips and then the branches grow epitaxially from the oxide layer
(Figure 10.3c). Finally, Nayeri et al. synthesized single-crystalline ZnO
nanowires on vertically aligned MWCNT arrays. ZnO nanowires are grown on