Sonochemical Approach for Rapid Growth of Zinc Oxide Nanowalls Avinash P. Nayak 1,* , Aaron M. Katzenmeyer 2,† , Yasuhiro Gosho 3,¥ , M. Saif Islam 2, ‡ . * [email protected], † [email protected], ¥ [email protected], ‡ [email protected]. Department of Electrical Engineering, University of California - Davis, Davis, 95616, USA Abstract: In this report, we propose a new approach to synthesize ZnO (zinc oxide) nanowalls (NWall)on aluminum and alumina coated substrates at room ambient conditions. The synthesized ZnO NWalls are uniform and highly dense in areas where Al or Al 2 O 3 (Alumina) is present. The height and thickness of these ZnO NWalls average at 0.8μm-1.5μm to 20nm respectively. Photoluminescence (PL) measurements, transmission electron microscopy (TEM) images, UV Vis spectroscopy, SEM-EDS results indicate NWalls composed of ZnO. The sonochemical synthesis was tried on Si, SiO 2 , Cr, and Ag but did not result in NWalls. We find that the growth of ZnO NWalls only form on Al or alumina. We attribute the formation of Al assisted ZnO nanowall growth to the phase transformations that occur under high-pressure, high-temperature, and chemical growth kinetics. The deposition method reported is applicable to Al coated non- metallic surfaces such as glass and we show the as-formed NWalls function as UV photoconductors. Keywords: Zinc Oxide, Nanowalls, Sonochemistry, Solution Growth, Ultrasound, Self- Organization, Selective Deposition.
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Sonochemical Approach for Rapid Growth of Zinc Oxide Nanowalls
As shown in figure 11, Raman peak was characterized for each time interval. Raman peak for
ZnO is 1157 cm-1
, 1105 cm-1
, 1005 cm-1
, 98 cm-1
, 659 cm-1
, 580 cm-1
, 540 cm-1
,438 cm-1
, 412
cm-1
, 384 cm-1
, 331 cm-1
, 202 cm-1
. Of these, the strongest peak is seen at 438cm-1
which
corresponds to the E2
High nonpolar phonon mode, associated with oxygen. Raman for ZnAl2O4 is
660cm-1
, 419cm-1
. A faint peak at 419cm-1
is observed at 15 minutes. Al2O3 has no detectable
Raman peak.[23]
The 1053cm-1
peak which increases over time is associated with dioxygen.[24]
The Raman peak at 520cm-1
is associated to Si.[25]
The 937cm-1
Raman peak is attributed to
Zn2SiO4 [26]
Conclusion:
In summary, we have successfully fabricated ZnO nanowalls via a novel and simple
sonochemical route at room ambient conditions in the absence of an Au catalyst in less than
thirty minutes. The average thickness of the ZnO nanowalls is 20nm and the length varies from
0.8µm-1.5µm. We find that to grow ZnO nanowalls, an Al layer is essential. We attribute this
growth on Al to the formation of ZnAl2O4 at high temperatures which leads to vertical growth of
ZnO nanowalls. The same growth process was tried on different substrates but resulted in ZnO
nanowires. This substrate selective process allows us to selectively grow ZnO nanowalls in
regions where Al is present. We also find that Al is consumed in the growth process of these
ZnO nanowalls and that transmission increases by ~10% after growth.
Figure 11. Raman peak intensity for 3 minute time intervals and at 60 minutes.
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