Surface Of ZnO Thin Films Research Articles

Correlation of ZnO thin film surface properties with conductivity

Technological demands for the fabrication of nanostructured active coatings provide renewed motivation for understanding the properties that control the morphology of the thin film surface. With decreasing structure size, the issues of finite size and shape effects become non-negligible including issues of stability against decay and structural rearrangement. The surface of the wide band gap semiconductor ZnO is known to be very active, with a wide variety of absorption and chemisorptions phenomena taking place. These processes can alter the charge carrier distribution in the sub-surface region and locally change the doping levels. There is a limited amount of literature dedicated to systematic and detailed studies on the surface evolution with growth parameters and their effect on the ZnO surface conductivity under reduction/oxidation. Therefore, this work focuses on the analysis of the thin ZnO film surface properties by studying specific surface parameters such as amplitude related parameters (average roughness, the root mean square), mixed parameters (surface area ratio), functional parameters for characterizing bearing and fluid retention (skewness), and spatial parameters (the fractal dimensions) as they correlate with the film conductivity changes under subsequent exposure to UV light (as reductor factor) and ozone (as surface oxidant agent). All ZnO thin films of different thicknesses were grown by the dc planar magnetron sputtering technique under the same sputtering conditions.

ADSORPTION, DIFFUSION AND GROWTH MODE OF ZnO THIN FILM FROM FIRST PRINCIPLES

A heteroepitaxial growth model of the ZnO film on sapphire (0001) is calculated by using a plane wave ultrasoft pseudo-potential method based on density functional theory. It is found that interfacial atoms have different diffusivity at 400°C, 600°C and 800°C. The temperature has a decisive effect on the surface and interface structures of ZnO /α- Al 2 O 3 (0001) and on the growth mode of ZnO thin films. In the whole process of the adsorption and growth of ZnO , the diffusivity of O atoms is higher than that of Zn , and the interlayer diffusion has an important impact on the homogeneous growth of thin films. There are two growth modes of ZnO on sapphire (0001), which is further demonstrated by theoretical calculation. The growth mode at about 400°C has a character of mainly spiral-twisted growth with Zn -hexagonal symmetry structure, and it is favorable for forming the Zn -terminated surface. But in the case of 600°C, a regular in-plane growth is observed, which facilitates the O -terminated surface of the ZnO thin film. It can be observed from the calculation that the vacancies of Zn where the atomic layer is near to the α- Al 2 O 3 (0001) surface is more than that of O atoms.

Au cluster growth on ZnO thin films by pulsed laser deposition

Abstract Nanostructures formed by Au nanoparticles on ZnO thin film surface are of interest for applications which include medical implants, gas-sensors, and catalytic systems. A frequency tripled Nd:YAG laser ( λ = 355 nm, τ FWHM ∼ 10 ns) was used for the successive irradiation of the Zn and Au targets. The ZnO films were synthesized in 20 Pa oxygen pressure while the subsequent Au coverage was grown in vacuum. The obtained structures surface morphology, crystalline quality, and chemical composition depth profile were investigated by acoustic (dynamic) mode atomic force microscopy, X-ray diffraction, and wavelength dispersive X-ray spectroscopy. The surface is characterized by a granular morphology, with average grain diameters of a few tens of nanometers. The surface roughness decreases with the increase of the number of laser pulses applied for the irradiation of the Au target. The Au coverage reveals a predominant (1 1 1) texture, whereas the underlying ZnO films are c -axis oriented. A linear dependence was established between the thickness of the Au coverage and the number of laser pulses applied for the irradiation of the Au target.

Influence of pulsed laser deposition (PLD) parameters on the H 2 sensing properties of zinc oxide thin films

Thin films of n-type ZnO were produced by a novel two-target, two-pulsed laser deposition technique. This method allows on-line control of the film properties by just changing the laser parameters. A number of deposition parameters, as well as the dopants (Al, Au) and the substrate type (Si, SiO 2, glass), were changed. The sensing properties of the films were tested upon exposure to a H 2 flow in air ambient at working temperatures between 150 and 210 ∘C. Undoped ZnO thin films, deposited on SiO 2 substrates at 200 ∘C, in ambient O 2 at 20 Pa and with a laser fluence of 9.6 J/cm 3, exhibited a maximum sensitivity ( Δ R / R 0 ) higher than 97% and a response time lower than 3 min at the working temperature 180 ∘C. Decrease of the working temperature to 150 ∘C was achieved by means of surface sensitization of films after deposition of Au nanoclusters on the surface of the above-mentioned ZnO thin films.

The Polishing Effect of ZnO Thin Films on SAW Filters

SAW filters in a structure of ZnO/IDT/glass, have periodic convex and concave roughness on the surface of ZnO thin films which is caused by IDT electrodes. This investigation reports that the convex and concave roughness affects the SAW velocity, and mechanical polishing of the ZnO thin films has great effect on SAW filter frequency characteristics.

Crystallographic Character of ZnO Thin Film Formed at Low Sputtering Gas Pressure

The crystallographic character of ZnO thin films formed by the rf sputtering technique were investigated using X-ray diffraction and RHEED. When the sputtering gas pressure is 5×10-3 Torr, there is no preferred orientation of the crystal axis near the surface of ZnO thin film, but below its surface, the c-axis is oriented normal to the substrate within a certain distribution angle. The crystallites reorient so that the c-axes are normal to the substrate as new surface layers are formed.