This work reports on the electrodeposition
of zinc on nanoporous
metal oxide titania nanotube arrays (TiO2 NTAs) using a
zinc-containing deep eutectic solvent (Zn2+–DES).
The effects of substrate morphology and crystallinity, deposition
temperature, zinc concentration, and deposition time on the morphology
and electrochemical properties of the Zn/TiO2 NTAs were
investigated. Two-dimensional zinc nanohexagons (NHexs) with a mean
diameter of ∼300 nm and a thickness of 10–20 nm were
decorated onto the TiO2 NTAs (with a pore diameter of ∼80
nm and a tube length of ∼5 μm) via electrodeposition
at −1.6 V using Zn2+–DES. Cyclic voltammetry
tests on the Zn2+–DES electrolyte revealed an electrochemical
window of ∼3.5 V, and the diffusion coefficient of Zn2+ was found to be 4.29 × 10–10 cm2 s–1 at room temperature and 7.10 × 10–10 cm2 s–1 at 40 °C.
Zinc nucleation on TiO2 NTA substrates followed an instantaneous
model. Using a higher electrodeposition temperature increased the
nucleation and growth rate of zinc NHexs, while annealing TiO2 NTAs was found to improve their uniformity and morphology.
During the initial stage of deposition, hexagonal close-packed zinc
NHexs were found to preferentially grow on tetragonal anatase TiO2 NTAs. The electrodeposition of zinc resulted in lowering
the impedance and improving the overall electrochemical properties
of TiO2 NTAs. The Zn/TiO2 NTAs developed in
this study offer a promising electrocatalyst material system for implantable
electrochemical sensors.
Work function (WF) of radio-frequency (RF) sputtered Gallium-Doped Zinc Oxide (GZO) thin films has been estimated using the electrical characteristics of an n-metal oxide semiconductor field-effect transistor (n-MOSFET) device. Two identical sets of MOSFETs were fabricated in this work using a four-level mask. These MOSFETs have two different types of gate contact materials (Al and GZO, respectively). GZO was deposited by using RF magnetron sputtering technique while Al was deposited using thermal evaporation technique. By comparison of the work function of the two MOSFETs, the work function of RF sputtered GZO thin films was identified to be around 4.58 eV.
For the first time in the literature, the material properties of gallium-doped zinc oxide, grown from a high impulse magnetron sputtering system (HiPIMS), are reported. These material properties are compared to those of a typical radio frequency (RF) sputtering deposition. The films were grown without thermal assistance and were compared across multiple average deposition powers. The films’ resistivity, crystallinity, absorption coefficient, band gap, and refractive index were measured for each of the samples. It was observed that very similar results could be obtained between the HiPIMS and RF sputtering processes under the same average power conditions. It was found that the RF depositions demonstrated a slightly higher band gap and deposition rate as well as lower resistivity and optical absorption coefficient. Band gaps and grain size were found to increase with the power of the deposition for both HiPIMS and RF. These values ranged between 3.45 eV and 3.79 eV and 9 nm and 23 nm in this study, respectively. The absorption coefficient and resistivity were both found to decline with increasing power in both methods but reached minimums of 2800 cm−1 and 0.94 mOhm-cm, respectively, when sputtered using an RF power supply.
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