Background In many decades ago
In many decades ago, Titanium Dioxide (TiO?) has been widely used in various application since it is considered a safe material. TiO? which known as the transition metal comes with three main different polymorphs which rutile, anatase, and brookite. Each of this polymorphs has its own properties such as rutile where it has a thermodynamically stable phase of TiO? in the room temperature but it is a metastable phase for anatase and brookite. Commonly for the rutile TiO?, it is quite low in the applications usage since the specific surface area of this material is higher (Bourikas et al., 2014). However, based on Ghosh et al. (2003), the efficiency of the anatase is slightly higher compared to the brookite but only in some applications.
According to Hardy (2013), sputtering is one of the techniques that commonly for Physical Vapor Deposition and it a highlighted method to produce a new advanced product. For the standard sputtering, an inert gas such as argon is used and a target of any pure materials is compulsory but sometimes, the usage of non-inert gas like nitrogen and oxygen are possible to use in this process. Besides, non-inert gas is added to the inert gas and this mixture will react with the target of material vapor cloud which produced a molecular compound to form thin films. Figure 1 shows the set-up of DC magnetron that used in an experimental work.
Figure 1: DC magnetron sputtering system. (a) Overall system in 2-D view. (b) 3-D view of the main structure of the system
Source: Liu et al., 2014
In this era, the use of reactive sputtering deposition is well-known and established to the world especially in the coating’s industries. This reactive sputtering able to produce a very thin product with a high range value, for instance, thin films, optical components and flat panel display (Martynas, 2013). It is one of the complex processes of an exhibiting a non-linear behavior that respected to the main parameters process like the discharged powers and its partial pressure (Dalgleish et al., 2007).
The reactive sputtering becomes a very familiar method that used to produce TiO? films. This is because, by using this method it will create a dense and uniform film with a well-controlled stoichiometry, excellent adhesion and higher in purity. Nevertheless, based on Martin et al., (1997) state that to obtain a well-crystallized TiO? film which does not has any limits on its applications, the substrate must be heating and/or post-annealing at the high temperature.
Moreover, the characterized method of higher particle energies which is sputtering and ion beam able to form crystalline and amorphous TiO? films at the temperature lower than 200°C. But, some of the results that have been published from the previous experimental studies which using this deposition method are different and some of it shows an opposite result (Witit-anun et al., 2009).
As a problem that needs to be a concern, does the operating sputtering pressure will affect the surface morphology, structure, and optical properties of the TiO? films.
The sputtering pressure will affect the surface morphology, optical properties, and structures of TiO? thin films. However, the difference between pressures would produce a different phase of polymorphs such as anatase and rutile.
To identify the sputtering pressure on unheated DC reactive magnetron sputtering
To observe the effect of different pressure on the surface morphology, structure, and optical properties of TiO? Thin Films.
The scope of the study
In this experimental work, the TiO? thin films will be used to observe the effect on its surface morphology, structures, and optical properties when different sputtering pressure is applied to it. For this research, TiO? thin films need to deposit onto the glass slides which has been cleaned very well and silicon wafer substrate. The usage of DC magnetron sputtering for this experiment will give the further effect to the TiO? thin films since this systems use high purity of Ar and O? as a sputtering and reactive gas.
As the characterization of this sample, XRD will be chosen to observe its crystallography phase that forms during the reaction occur in DC unbalanced magnetron sputtering. Besides, AFM (Nanoscope IV, Veeco Instrument Inc.) used to investigate the development of surface morphology and thickness of that simple which undergoes three different sputtering pressure. The measurement of UV-VIS transmission spectroscopy will involve the UV-VIS-NIR spectrophotometer systems (Shimadzu MPC-31000) with the range in 200 mm to 2000 mm.
MATERIALS AND METHOD
TiO? thin films will be used along with the clean glass slide and silicon wafer substrate. The purity of metallic titanium which needed to act as a target is 99.97% and a high purity of Ar (99.999%) and O? (99.999%) also needed for this experimental work.
3.2.1 Preparation of sample
The TiO? thin films will be deposited on the glass slide which that has been cleaned well and silicon wafer substrate by the DC unbalanced magnetron sputter deposition systems as shown in figure 2. The diameter and height of cylindrical vacuum chamber which made up from stainless steel are 310 mm and 370 mm.