Metal oxide nanoelectrodes for environmental sensors - ZnO rods and particulate films

ZnO structures were fabricated on substrates for electrodes of dye-sensitized molecular sensors. They were crystallized in the aqueous solutions at 60°C. Precise control of crystallization allowed us to form unique structures. ZnO rods were formed on fluorine doped tin oxide substrates without seed layers. They were 100-120 nm in diameter and 300-400 nm in length. They stood perpendicular to the substrates. Lengthwise direction of hexagonal prism was parallel to c-axis of ZnO crystal structure. They grew along long c-axis to form anisotropic shape. The ZnO rod arrays covered with dye using 1 μM and 100 nM solution and without dye showed photocurrent of 1.12x10 ^-7 A, 5.75x10^-9 A and 2.19x10^-9 A, respectively, under irradiation using 0.7 mW lasers. A high signal-to-noise ratio (S/N) of about 50 (=1.12x10^-7 A / 2.19x10^-9 A) was obtained under the irradiation. Moreover, ZnO particulate films were prepared on glass substrates in the solutions. The films consisted of multi-needle ZnO particles and thin sheets. The particles were firstly prepared at 60°C. The thin sheets were then formed in the solutions at 25°C. Thin sheets had a thickness of 10 - 50 nm and width of 1 - 10 μ and were connected to particles closely with no clearance. The particulate films had continuous open pores ranging from several nm to 10 μm in diameter.