Quantitative Investigation of the Factors Affecting the Hydrothermal Growth of Zinc Oxide Nanowires

Abstract

Zinc oxide (ZnO) nanowires (NWs) are receiving significant industrial and academic attention for a variety of novel electronic, optoelectronic and MEMS device applications due to their unusual combination of physical properties, including being optically transparent, semiconducting and piezoelectric. Hydrothermal growth is possible at significantly lower temperatures (and hence lower thermal budgets) compared with other NW growth methods, such as chemical vapour deposition. In this context, the hydrothermal growth of ZnO NWs on seeded substrates immersed in equimolar zinc nitrate/HMTA aqueous solution was investigated. NWs were grown on polished silicon (001) substrates, and the solution concentrations, temperatures and growth times were varied. Importantly, the NW diameter was found to depend only on concentration during hydrothermal growth for times up to 4 hours. The average diameter was 14 nm in 0.005 M solution and increased up to a maximum 150 nm at 0.07 M, when the NWs formed a continuous polycrystalline film. Concentration and temperature were all found to affect the axial growth rate of NWs in the [0001] direction. The growth rate was constant up to 4 hours (200 nm hr -1 ) for constant conditions (81 o C, 0.025 M). The growth rate was found to increase approximately linearly with concentration at a rate of 7840 nm M -1 hr -1 up to 0.06 M (81 o C solution). The growth rate also increased linearly with temperature at a rate of 4.9 nm hr -1 K -1 (0.025 M solution). This indicates that growth takes place close to the equilibrium point, found by linear regression to be 36 o C for 0.025 M solution.

In Situ Monitoring of Laser‐Assisted Hydrothermal Growth of ZnO Nanowires: Thermally Deactivating Growth Kinetics

“…The growth rates can increase further with higher laser power, but the laser power is limited below the level of bubble generation. As shown in Figure b, the apparent growth rate (or growth yield) of our laser‐assisted hydrothermal growth is remarkably fast: tens of micrometers for an hour, which is approximately two orders of magnitude higher than other conventional hydrothermal growth rates obtained under similar conditions . The growth parameters of the compared studies are listed in Table S1 of Supporting Information.…”

“…Figure b also indicates that the nanowire height (obtained by 1 h growth) increases linearly with higher laser power. Nanowires could not be grown below a specific level of laser power, which should be related to the equilibrium temperature of the growth reactions …”