Surface morphology characterisation : magnetron sputtering of nanostructured titanium carbide thin films on titanium and its alloys
- Authors: Abegunde, Olayinka Oluwatosin
- Date: 2020
- Subjects: Titanium , Titanium alloys , Sputtering (Physics)
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/480476 , uj:43497
- Description: Abstract: The selection process for functionally engineered materials cannot only rely on the physical appearance of the materials, texture, aesthetic and bulk properties but also on the surface characteristics composition especially in the area of applications where surface contact is of high priority. The behaviour of a material is greatly dependent on the surface properties of the material. Functionally engineered materials must be able to satisfactorily perform desired functions completely and effectively, under various conditions in aggressive environments without failing or yielding into a disastrous catastrophe when in service. Savaging, protecting and optimizing scarce natural materials like Titanium from surface defects and deformation like corrosion and wear is a major problem around the world. Titanium alloys are reactive materials and have a high affinity for oxygen, resulting in the formation of protective oxide film spontaneously in the presence of oxygen. However, it can give rise to disruption in the mechanical properties when the system is suffering from starvation of oxygen to form the protective layer. Also, titanium exhibits low wear and abrasion resistance, which can result in reduced service life... , Ph.D. (Mechanical Engineering Science)
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Optimization of process parameters for sputtering of hydroxyapatite target on stainless steel
- Authors: Oladijo, Segun Stephen
- Date: 2021
- Subjects: Biomedical materials , Hydroxyapatite coating , Thin films , Steel, Stainless , Sputtering (Physics)
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/481892 , uj:43679
- Description: Abstract: Biomaterials are natural or synthetic in origin materials ‘other than drug’ or the combination of two or more materials that can be used for some period for the replacement or treatment of any organs, tissue, or body. Metallic biomaterials like titanium, stainless steel, and cobalt alloys are notable materials that are adapted and used for medical applications purpose due to their favorable properties such as toughness, relatively low rate of corrosion, and excellent strength. Biomaterials are essential for the replacement of human joints and requires a long period of time such as 15 years to 20 years for older ages and more than 25 years above for younger age patients to serve as implant in their body and therefore, it is necessary to prolong the service life of biomaterials. In this study, the surface modification process was used for the enhancement of existing materials to improve the surface properties of the samples. For this research work, radio-frequency magnetron sputtering was considered for the deposition of the Hydroxyapatite (HAP) thin-film coating on stainless steel. This is due to its potential surface modification capability of high deposition rate, strong bond affinity, low cost of production, and capability to deposit insulating materials since Hydroxyapatite is known to be a good reinforcement for surface modification due to its favorable properties such as excellent bioactive and biocompatibility. Therefore, RF- magnetron sputtering was used for the deposition of a nanostructured thin film of Hydroxyapatite ceramic on the surface of stainless steel AISI 304. The RF sputtering process parameters (such as the RF-power and the deposition time in the deposition process) were characterized/optimized by Taguchi analysis, and evaluating the thin film phases and wear resistance, and the corrosion resistance was determined by electrochemical techniques. The scanning electron microscope (SEM) equipped with electron discharge microscopy, the atomic force microscope (AFM), X-ray diffraction, and optical microscopy were used to characterize the properties of the HAP thin-film coatings. The mechanical property and the tribological properties of the HAP coating were measured using Vickers hardness and, micro scratch tester. The electrochemical corrosion technique was used to analyze the corrosion behavior of the thin film. Whilst optimization of the process parameter was carried out using L9 Taguchi orthogonal array... , M.Ing. (Mechanical Engineering)
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Formation of CuIn(Se,S)₂ and Cu(In,Ga)(Se,S)₂ thin films by chalcogenization of sputtered metallic alloys
- Authors: Sheppard, Charles Johannes
- Date: 2009-04-23T08:17:38Z
- Subjects: Thin films , Sputtering (Physics) , Alloys , Solar cells , Chalcopyrite , Photovoltaic cells
- Type: Thesis
- Identifier: uj:8306 , http://hdl.handle.net/10210/2435
- Description: Ph.D. , The reaction of direct current (DC) magnetron sputtered metallic CuIn and CuInGa alloys to a reactive H2Se/Ar/H2S gaseous atmosphere is an attractive industrial production process to produce Cu-based chalcopyrite absorber films for applications in high efficiency photovoltaic modules. This deposition process is generally referred to as a two-step deposition technology. However, the obvious technological advantages of this deposition technology are overshadowed by growth-related anomalies, such as the separation or at least partial separation of the ternary phases (i.e. CuInSe2, CuGaSe2 and CuInS2) during the high temperature chalcogenization. This in turn prevents the effective band-gap widening of the semiconductor alloys in order to achieve open-circuit voltages in excess of 600mV, which is a critical prerequisite for the optimal performance of thin film solar modules. Against this background, a detailed study was undertaken in order to understand the formation kinetics of quaternary CuIn(Se,S)2 and pentenary Cu(In,Ga)(Se,S)2 alloys deposited with a reproducible two-step growth technology. The main objective of this study was to optimize a complex set of experimental parameters in order to deposit homogenous alloys in which the band-gap value of the resulting semiconductor film could be modified in order to maximize the operating parameters of photovoltaic devices. This was achieved by the homogenous incorporation of S and/or Ga into the chalcopyrite lattice, resulting in shrinkage of the lattice parameters and hence increase in band-gap value Eg. However, the substitution of In with Ga and Se with S proved to be a complex process. It was, for example, observed that separation or at least partial separation of the ternary phases already occurs during the chemical reaction between the hydrogen selenides (H2Se) gas and the metallic precursors. Detailed studies indicated that this phenomenon was strongly related to the selenization parameters (e.g. reactive gas concentration, and reaction temperature and time) as well as the Cu/(In + Ga) atomic ratio. In optimized processes, the metallic precursor films were partially selenized in order to produce at least one partially reacted Cu-III-VI2 ternary alloy and group Cu-VI and III-VI binary phases. The partially selenized alloys were subsequently sulphurized under optimal thermal conditions in a H2S:Ar gas mixture to produce homogeneous single-phase quaternary and pentenary chalcopyrite alloys. X-ray diffraction (XRD) studies revealed that the lattice parameters of the chalcopyrite lattice decreased linearly with the incorporation of S and/or Ga, according to the predictions of Vegard’s law. Gracing incidence x-ray diffraction (GIXRD) studies on the compound semiconductors revealed that the lattice parameters remained virtually constant through the entire depth of the layer. Optical studies revealed a shift in the band-gap value of the absorber films as function of the S concentration. The band-gap of the absorber films could be varied between 0.99 and 1.35eV by controlling the S/Se anion ratio during the diffusion process, while maintaining the Ga/III atomic ratio constant at 0.25. Solar cells were completed by chemical bath deposition (CBD) of CdS and radio frequency (RF) sputtered intrinsic and highly conductive ZnO films onto the absorber films. The cells were evaluated under standard A.M. 1.5 conditions. Devices manufactured from CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 based alloys demonstrated average open-circuit voltages (Voc) and short-circuit current densities (Jsc) values of 470 and 650 mV and 20 and 33 mA.cm-2, respectively. A plot of the open-circuit voltage as function of the band-gap revealed an experimental relationship of: Voc = (Eg/q – 0.6) mV for Eg < 1.3 eV. The fill factor (FF) values varied between 35 and 56% and device efficiencies () between 4 and 13%, depending on the S/Se anion ratio and Ga incorporation. The findings from the studies clearly indicated that a better understanding of the CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 formation process led to absorber material with improved material properties. It was also demonstrated that it is possible to produce a homogenous CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 absorber films with the scalable two-step deposition process.
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