Structural and Mechanical Study of CeO2/TiO2

Mixed Metal Oxide Thin Films

A thesis submitted for the degree of Honours in Physics and

Nanotechnology

at

Murdoch University 2018

Student Name: Shyam Bharatkumar Patel

Student Number (ID): 32483978

Supervisor: Dr Zhong-Tao Jiang

1

Declaration

I, Shyam Bharatkumar Patel hereby declare that this thesis represents my own

research work undertaken by myself and is accurate of my own account. No part of

this thesis has been concurrently submitted for a degree at any other tertiary

education institution

Shyam Patel

Shyam Bharatkumar Patel

2

Abstract

Thin films are well researched in the field of materials science and engineering.

Modern thin films have proven to be versatile as they have been developed and

modified to attain films with special properties such as high hardness values,

improved photovoltaic and photocatalytic properties to name a few. Thin films that

exhibit a wide range of exceptional properties are sought after as they could be the

solution to a wide range of global challenges.

CeO2/TiO2 mixed metal oxide (MMO) films are capable of showing a wide range of

excellent properties and relevant applications such as photovoltaic and

photocatalytic capabilities. However, the mechanical properties of these films are

not well researched. This study intends to link the Ce-Ti percentage to the mechanical

and structural properties of MMO films by studying them at the fundamental atomic

level.

The Magnetron sputtered CeO2/TiO2 MMO films were studied using advanced

characterization techniques. High temperature in-situ X-ray diffraction (XRD) was

conducted to identify and investigate the stability of the oxides present in the films

whilst X-ray photoelectron spectroscopy (XPS) was used to find the bonding states

within the film. The surface morphology was investigated using a field emission

scanning electron microscope (FESEM). The mechanical properties such as hardness

and Young’s modulus were determined using nanoindentation tests, whilst the

stresses within the film were visualized with the aid of finite element modeling (FEM).

The material characterization indicates the presence of a primary α-Ce2O3 phase in

samples containing cerium, whilst a rutile form of TiO2 was found for samples

containing TiO2. The mechanical test results of the pure CeOx film show a hardness

value as high as 20.1 GPa. The FEM results indicate the stress distribution and is

implemented to obtain models of several thin film and substrate combinations.

3

Acknowledgements

This project would not have been possible without the support of various mentors at

different universities and would like to thank them for their unconditional support. I

would like to start by acknowledging my supervisor, Dr Zhong-Tao Jiang (Physics and

Nanotechnology, school of engineering and IT), for giving me the opportunity to be a

part of Murdoch University’s Surface Analysis and Materials Engineering Research

Group (SAMERG), and for the constant technical and logistical support through the

entire project.

I would also like to acknowledge A/Prof Kevin Jack and his team for providing the

facilities, and the scientific and technical assistance, of the Australian Microscopy &

Microanalysis Research Facility at the Centre for Microscopy and Microanalysis, at

The University of Queensland. Dr Zhao Xiaoli (Edith Cowan University - Joondalup) is

acknowledged for his assistance in conducting and analyzing the nanoindentation

and FEM results. Dr Jean-Pierre Veder and Dr Elaine Miller from the John de Laeter

Centre (Curtin University) for their time and effort in obtaining the XPS and FESEM

results. Dr Zhi-feng Zhou (City University of Hong Kong) for helping manufacture the

thin film coatings. I would also like to acknowledge the support from Ph.D. candidates

Ehsan Mohammadpour and Nicholas Mondinos from the SAMERG.

And lastly, my parents, guru and close family for the sacrifices they made to give me

a chance to chase my dreams. Your support and positivity kept me going and I thank

you for your patience. A special thanks to my Australian family that I have had the

privilege of sharing cheerful moments with over the last few years.

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Contents

Declaration .............................................................................................................. 1

Abstract ................................................................................................................... 2

Acknowledgements ................................................................................................. 3

Contents .................................................................................................................. 4

List of Abbreviations ................................................................................................ 5

List of Equations ...................................................................................................... 6

List of Figures ........................................................................................................... 7

List of Tables ............................................................................................................ 9

Chapter 1. Introduction ......................................................................................... 10

1.1 Cerium Oxide (CeO2) .................................................................................... 12

1.2 Titanium Dioxide (TiO2) ................................................................................ 14

1.3 CeO2/TiO2 Mixed Metal Oxides ................................................................... 17

1.4 Thesis Outline and Objectives ..................................................................... 18

Chapter 2. Methodology ....................................................................................... 19

2.1 Overview of procedures .............................................................................. 19

2.2 Thin Film Preparation .................................................................................. 19

2.3 XPS Characterization .................................................................................... 22

2.4 XRD Characterization ................................................................................... 24

2.5 FESEM Imaging............................................................................................. 26

2.6 Nanoindentation and Finite Element Modeling (FEM) ............................... 28

Chapter 3. Results and Discussion ......................................................................... 31

3.1 Bonding State Identification - XPS ............................................................... 31

3.2 Phase and Crystalline Structure Determination – XRD ............................... 33

3.3 FESEM Imaging............................................................................................. 40

3.4 Mechanical Properties ................................................................................. 47

Chapter 4. Conclusion and Scope for Future Work ............................................... 54

4.1 Overall result Interpretation method .......................................................... 54

4.2 Future work ................................................................................................. 55

References ............................................................................................................. 55

Appendices ............................................................................................................ 65

5

List of Abbreviations

BCC - Body centered cubic

BH – Shear modulus

E - Young’s modulus

EDI - Elastic deformation index

EDX - Energy-dispersive X-ray spectroscopy

FEM - Finite element modeling

FESEM – Field emission scanning electron microscope

H - Hardness

HCP - Hexagonal closed pack

MMO – Mixed metal oxide

PDF – Powder diffraction file

PDI - Plastic deformation index

sccm – Standard cubic centimeter per minute

SG – Space group

SOFC – Solid oxide fuel cells

UHV – Ultra high vacuum

UV - Ultra-violet

XPS – X-ray photoelectron spectroscopy

XRD – X-ray diffraction

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List of Equations

Eq 2.6.1 𝑃𝐷𝐼 (𝐺𝑃𝑎) = 𝐻3 𝐸2⁄

Eq 2.6.2 𝐸𝐷𝐼 = 𝐻 𝐸⁄

Eq 2.6.3 𝜎𝑒𝑞𝑢𝑖𝑣 = {0.5 [(𝜎𝑥𝑥 − 𝜎𝑦𝑦)2

+ (𝜎𝑦𝑦 − 𝜎𝑧𝑧)2

+ (𝜎𝑧𝑧 − 𝜎𝑥𝑥)2

+ (𝜎𝑥𝑦 + 𝜎𝑦𝑧 + 𝜎𝑧𝑥)2

]}1/2

Eq 3.1.1 %𝐶𝑒4+ =

𝑆𝑎𝑡𝑒𝑙𝑙𝑖𝑡𝑒 𝑃𝑒𝑎𝑘 %

14 × 100%

7

List of Figures

Figure 1.0.1. A graphical representation by Eustis et al. of the surface plasmon

resonance effect of two differently shaped nanoparticles [7]

Figure 2.2.1. A picture of the UDP650 magnetron sputtering system used to produce

the films for this study (City University of Hong Kong)

Figure 2.3.1. The Kratos AXIS Ultra DLD (2013) XPS system at the John de Laeter

Center (Curtin University) which was used to collect the XPS data

Figure 2.4.1. The Rigaku smartlab X-ray diffraction machine used to carry out in-situ

XRD experiments in this study (University of Queensland)

Figure 2.5.1. The Cressington 208HR High Resolution Sputter Coater used to apply a

platinum coating for better conduction on the surface of the samples

Figure 2.5.2. An image of the Zeiss Neon 40EsB CROSS-BEAM FESEM system used to

obtain FESEM images of the samples

Figure 2.6.1. The Ultra-Micro Indentation 2000 workstation (CSIRO, Sydney,

Australia) system used in this study

Figure 3.2.1. XRD data collected for the T1 film at the temperatures given in the

legend

Figure 3.2.2. XRD data collected for the T2 film at the temperatures given in the

legend

Figure 3.2.3. XRD data collected for the T3 film at the temperatures given in the

legend

Figure 3.2.4. XRD data collected for the T4 film at the temperatures given in the

legend

Figure 3.3.1. FESEM images of the top surface of T1 at a magnification of (A) X5000

and (B) X50 000

Figure 3.3.2. FESEM images of the top surface of T2 at a magnification of (A) X5000

and (B) X50 000

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Figure 3.3.3. FESEM images of the top surface of T3 at a magnification of (A) X5000

and (B) X50 000

Figure 3.3.4. FESEM images of the top surface of T4 at a magnification of (A) X5000

and (B) X50 000

Figure 3.3.5. The grain size distribution as found using FESEM results for each of the

4 samples

Figure 3.4.1. Averaged hardness values [H (GPa)] for each of the samples as found by

the nanoindentation test

Figure 3.4.2. Young’s modulus [E (GPa)] as found using the loading and unloading

curve during nanoindentation of each sample

Figure 3.4.3. FEM modelling results of equivalent stress distribution within the films

(a) T1 (b) T2 (c) T3 and (d) T4 on a Si (111) substrate

Figure 3.4.4. FEM results of equivalent stress distribution within the T1 film,

deposited on (a) Silica, (b) Si (111), (c) low strength steel, and (d) high strength steel

substrates

Figure 3.4.5. FEM results of all 4 films (see legend) modelled on a (a) Silica substrate,

(b) Si (111) substrate, (c) low strength steel substrate and (d) high strength steel

substrate

Figure 3.4.6. FEM results of equivalent stress from the top of the film to the film-

substrate interface of T1, with different loading conditions (depth) on (a) Silica, (b) Si

(111), (c) low strength steel and (d) high strength steel substrates

Figure 3.4.7. FEM results of the equivalent stress distribution within T1 modelled on

a Si (111) substrate with thicknesses of (a) 1.2 m, (b) 1.6 m, (c) 2.0 m, (d) 2.4 m.

(e) stress distribution along the symmetry axis for respective substrate thickness

Figure A1. Peak fitting in the high-resolution Ce 3d, O 1s and Ti 2p regions

Figure A2. XRD data plot for T1 in the 2θ range of 20° ≤ 2θ ≤ 80°

Figure A3. XRD data plot of the bare Si (1 0 0) substrate in the 2θ range of 20° ≤ 2θ ≤

80°

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List of Tables

Table 2.2.1. Magnetron sputtering deposition conditions for 4 samples prepared for

this study.

Table 2.6.1. Modeling parameters of substrate, indenter and interlayer. LS and HS

represent low strength and high strength respectively [79]–[81].

Table 3.1.1. Atomic percentages of each thin film coating by XPS analysis after

etching.

Table 3.1.2. Percentages and ratios of Ce and Ti for each film as calculated using the

XPS results.

Table 3.4.1. Compilation of hardness and Young’s modulus and other derived values

using Eq 2.6.1 and Eq 2.6.2.

Table A1. Fitted peak details for the T2 sample at specified high-resolution XPS

regions.

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Chapter 1. Introduction

Thin film research is driven by the need to develop more efficient and functional

coatings that are capable of solving various challenges and problems faced in the

modern era. Research on thin films with special properties are highly sought after.

Recent developments in thin films have made them applicable in multiple fields and

industries ranging from the medical industry through to the manufacturing industry.

Current thin film technologies are helping tackle global problems such as climate

change when used as photocatalytic films by removing greenhouse gases like NO2 [1]

and photovoltaic thin films when used as a source of clean energy [2]–[4]. The

scientific community has also found thin films to be useful in other fields by exploring

chemical and physical properties of these thin films at the fundamental atomic level.

The possibility of altering these properties by combining materials and treating them

under specific conditions has created opportunities to make films more versatile and

efficient.

A lot of these properties change when thin films are manufactured with features in

the nanoscale. Bulk materials tend to have a consistent set of properties which are

independent of their size. At the nanoscale however, the properties tend to change

mainly due to the size effect [5][6]. Some examples of size dependent properties

include surface plasmon resonance observed in some metals and quantum

confinement effects in semiconductor materials (Figure 1.0.1) [7]. This figure (Figure

1.0.1) shows how the wavelength of the emitted light varies with a change in shape

and size of the particle. However, these special properties are only observed on

materials that have one or more dimensions in the nanoscale (1-100nm) and are

known as nanomaterials. Nanomaterials are also well known for having a very high

surface area to volume ratio in comparison to their bulk counterparts [8]. This

property makes nanomaterials ideal for surface area dependent applications.

Chemical reactions times and surface catalysis efficiency can be improved with an

increase in surface area due to the presence of more reaction sites and dangling

bonds as the atoms on the surface have a lower number of neighboring atoms.

Fundamental properties of compounds can also be changed by introducing impurities

or dopants into the lattice structure. This method can be used to enhance certain

11

properties as adding dopants can change properties such as the material’s band gaps,

surface hardness and other mechanical properties. For instance, a ductile material

may be incorporated in a ceramic bulk material to overcome its brittleness [9].

Figure 1.0.1. A graphical representation by Eustis et al. of the surface plasmon

resonance effect of two differently shaped nanoparticles [7]

Thin film deposition techniques are being constantly developed with a view of

allowing greater control on deposition parameters in order to attain special coatings

with desired compositions. Thin films can be deposited using several methods

including chemical vapor deposition (CVD), physical vapor deposition (PVD) and other

liquid phase chemical techniques such as spray pyrolysis, liquid phase epitaxy

amongst many others [10]–[15]. Each of these techniques allows the user to control

the growth of the film in terms of deposition rates and even allows for deposition of

films with certain surface morphologies. Coatings that are intended to produce

superior mechanical properties are generally coated using PVD methods as it results

in a more consistent and smooth film surface[16]. CVD does have an advantage over

PVD methods as it has a higher deposition rate [17]. CVDs however require the

substrate to be heated, making the substrate material choices restricted. Due to the

necessity of high temperatures, it can be difficult to avoid substrate distortion. The

precursor gases used in CVD systems can also be flammable, thereby making the

entire process hazardous [18].

Inte

nsi

ty (

a.u

.)

12

Magnetron sputtering is one of the common PVD techniques used in the research

industry to produce thin films by sputtering material onto a desired substrate. The

basic layout of a magnetron sputtering system includes a target material being placed

above the substrate, which is kept at a negative bias. The deposition chamber is

maintained at ∽0.1mbar in the presence of Ar+ ions. Due to the bias, the Ar+ atoms

naturally hit the target with a certain kinetic energy (controlled by bias voltage). The

bias voltage is set to a value for which the Ar+ atom has enough energy to etch into

the target material. The dislodged particles then fall onto the substrate under the

force of gravity and form a thin film. Magnets are used to control the carrier gas

within the chamber. Some of the advantages of such a system include low working

temperatures whist maintaining a high purity, little porosity, good substrate

adhesion and uniformity of the coating to mention a few [19][20]. Magnetron

sputtering systems can also be easily upscaled, making it a viable option for industrial

applications.

As researchers explore new materials, each of them can bring its own unique

challenge. Conventionally, a magnetron sputtering system requires a target bias. This

means that is can be difficult to get the sputtering process working if the target is not

a good conductor. However, researchers have found other means of combating such

challenges. A radio-frequency bias may be used if the target material is non-

conductive. These types of innovations have led to a lot of modern techniques that

can be implemented to attain specific films. Metal oxide thin films can be deposited

if a reactive gas is passed along with the inert carrier gas (Ar+) [21].

1.1 Cerium Oxide (CeO2)

Cerium is the most abundant (64ppm) naturally occurring rare earth metal in the

upper crust of earth and is found in its ores of bastnaesite and monazite. It is

generally extracted from its ore by introducing an oxidant, which reacts with the

cerium to form CeO2 (also known as ceria). The low solubility of ceria is then exploited

to isolate it from other minerals in the ore [22]

Cerium is a tetravalent metal with its two most common oxidation states being Ce3+

and Ce4+ and readily oxidizes in the presence of air to form ceria. Ceria has a fluorite-

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structure and can be produced synthetically using various methods which can be

chosen depending on the desired properties.

Ceria has a wide range of uses in several fields. Research conducted on ceria have

found it to have good oxygen storage capabilities due to its ability to react with

oxygen in a reversible reaction to form Ce2O3 [23][24]. Optical studies have shown

that ceria has the ability to block radiation in the UV region [25][26]. Its catalytic

properties due to it being a redox agent are also well studied and have played a key

role in the modern development of catalytic converters in the automobile industry

[27][28].

Cerium oxide is used in the medical industry due to its ability to absorb oxygen. This

property has been exploited to make oxygen detectors [29]. Ceria has also been

studied by cancer researchers due to its selective radiation protection capabilities

[30]. Another potential application in the medical field for ceria was found by a recent

study conducted in 2017 which showed that it could be used as a glucose detector

[31]. An exploration study in 2011 by Khan et al. showed the possibility of using ceria

nanoparticles for sensing ethanol as well [32]. Their research found ceria

nanoparticles to have good sensitivity to ethanol with linearity in short response

times.

With countries across the globe pushing for cleaner and more sustainable energy

sources in the midst of global warming, the search and development for energy

generating and storing devices and technologies will continue. Solid oxide fuel cells

(SOFCs) is one such technology that can positively contribute to a cleaner and

sustainable future. SOFCs are known for being the most efficient electrochemical

storage devices with the capability of converting chemical energy from fuels such as

hydrogen into electrical energy with minimal pollutants being generated as

byproducts [33]–[36]. However, this technology is currently not viable due to its high

operating temperatures which can be as high as 1000 °C, resulting in additional costs.

Researchers have shown that the use of ceria as an interlayer can help by reducing

the working temperature [33]. Other investigations have found that cerium oxide

containing compounds such as perovskite Sr1-xCexCoO3-δ (0.05 ≤ x ≤ 0.15) can also be

14

used as a cathode in a SOFC, thereby reducing its working temperature to 700 °C

with the power density being as high as 1.01 W cm-2 [37].

The mechanical properties of ceria are well studied. Several methods have been used

to make ceria films. The method of film production has been shown to have a direct

impact on its properties. A study in 1992 by Maschio et al. showed ceria to have a

hardness value of 3.9 GPa [38]. However, the method of synthesis they used was a

simple ball milling technique by which the size of the particles was reduced, and then

recompressed to obtain a film of ceria. The hardness of such a film is expected to be

low due to the porosity/vacancies left after manual compression of the particles.

Another widely used technique for synthesis of thin films for enhanced mechanical

capabilities is the PVD technique. Zhen Shi et al. studied the mechanical properties

of magnetron sputtered ceria with varying oxygen (reactive gas) flow rates and

variance in bias voltage [39]. Their research on the effect of oxygen flow rate found

the hardness to vary from 4.1 GPa (with no oxygen flow) to a potential maximum

hardness of 18.1 GPa with the flow percentage being at 7% of O2. A reduction of

hardness was noted upon an increase of % O2 flow rate [39]. Their other study which

investigates the variation of hardness in relation to the bias voltage revealed an

increase in hardness from 13.5 GPa (-20V bias) to 18 GPa (-80V bias) [40]. A further

increase in bias voltage resulted in the film losing its hardness. This result was

attributed to the re-sputtering phenomenon as the energy of the impinging atoms

increases to an extent that they etched the sample due to it having excessive energy.

Other tested methods of improving mechanical properties include the addition of

dopants to the ceria lattice. Research groups have examined the change in

mechanical properties when ceria is combined with other materials such as cobalt

oxide, titanium dioxide, aluminum nitride, gadolinium, Praseodymium and yttria

stabilized zirconia coatings to name a few [41]–[46].

1.2 Titanium Dioxide (TiO2)

Titanium dioxide is one of the stable, naturally occurring oxides of titanium. Since its

commercial production in the twentieth century, it has been used in various

industries due to its favorable optical properties amongst others. TiO2 is polymorphic

and is commonly found in three forms; rutile, anatase and brookite. Both rutile and

15

anatase have a tetragonal crystal structure [47]. Brookite on the other hand has an

orthorhombic crystal structure [47].

The crystal structure of commercially pure titanium (CP titanium) is a hexagonal close

packed structure (HCP). Titanium undergoes an allotropic phase change at 882 °C

transforming from HCP to the body center cubic (BCC) structure [48]. Literature

suggests that titanium is in the beta phase from 882 °C to the melting point, and is in

the alpha phase below 882 °C [48]. The transition from alpha to beta phase is highly

dependent on the purity of the titanium. With the addition of alpha and beta

stabilizing elements, the transition temperature can be shifted to a higher or lower

value. The addition of beta stabilizers lowers the transition temperature while the

addition of alpha stabilizers increases the transition temperature.

TiO2 can play a major role in the industry due to its optical, photovoltaic and

photocatalytic properties. TiO2 already has good industrial value as it is used in

various industries for different purposes. A report published by Grand View Research

expects the market value for TiO2 to reach USD 28.5 billion by 2025 from an

estimated USD 13.21 billion in 2016 [49]. The same report predicts the growth to be

as a result of the increase in demand in the construction industry and its use in paints

and coatings. Another recent market analysis of TiO2 conducted by Ceresana showed

that up to 56% of the world’s TiO2 Is used as pigments in paints [50]. Due to its UV-

protecting properties, TiO2 is widely used in the automobile industry to preserve the

gloss and colour of the paint coating.

The mechanism of UV-protection of rutile TiO2 are well documented. Many research

groups consider rutile to be UV reflective whilst other research groups have claimed

rutile to be UV absorbent in its mechanism in protecting against UV [51]–[55].

Research conducted in 2004 by Yang et al. concluded that rutile TiO2 protects against

UV by absorbing it, regardless of the size of the particle [56]. The reflection of the UV

rays was found to be in the region where rutile TiO2 had little to no UV absorption.

For this reason, they are also widely used in sunscreen products.

In recent times, a lot of research has been conducted to further the development of

TiO2 materials at the nanoscale. Different synthesis methods of TiO2 nanomaterials

have been studied and have proven to play a major role in dictating the final

16

properties of the material. Titanium dioxide’s ability to act as a reducing and oxidizing

agent in the presence of photons is a property that makes it a great candidate for

photocatalysis. This property can be enhanced by tweaking the synthesis method as

it is interlinked with the particle size of the powder used [57][58]. These types of

properties can also be varied by introducing dopants into the TiO2 lattice. Various

metallic and non-metallic doped forms of TiO2 have been researched. Some of the

dopants studied include the addition of Zn, Cu, Fe and Co amongst others [59]–[62].

These dopants have resulted in changes in properties such as optical (Zn-Doped TiO2),

electrical (Co-Doped TiO2) and Photocatalytic (Fe, Cu and Zn-Doped TiO2) properties.

Qu et al. showed that yttrium doped TiO2 porous films can be used as photoanodes

for dye-sensitized solar cells and exhibits an enhanced photovoltaic performance.

This improvement may be due to the increased visible light harvesting due to the

change in band gap of the material [4].

The mechanical properties of TiO2 are also of great interest to the manufacturing

industry. Researchers have been looking for a cheaper material that has similar

mechanical properties to diamond, which is a naturally occurring allotrope of carbon.

Diamond has the highest bulk modulus value known today of 444 GPa with its single

crystal hardness being as high as 48 GPa [63]. Research in the area in the early 21st

century found a specific polymorph of TiO2 with a cotunnite structure to have one of

the highest observed hardness for any oxide [64]. This polymorph was synthesized at

high temperatures (1600 – 1800 K) and pressures (60 GPa). The microhardness tests

found the hardness of that phase to be 38 GPa with a bulk modulus of 431 GPa.

However, the authors mentioned that the cotunnite phase could only be maintained

at low temperatures (170 K), at atmospheric pressure. However, this hardness value

is considerably larger than those found for TiO2 by other groups, thereby making it

special. Some groups have found rutile to have a hardness of 6.73 GPa, whilst others

found it to be around 16.5 GPa[65][66]. Literature suggests that the hardness of

anatase is around 8.5 GPa, which is lower than the average value of the rutile form

of TiO2 [66]. Rodrigues et al. determined the hardness to be 11 GPa, but could not

use their XRD results to determine the crystal structure of the TiO2 present in the film

due to it being in an amorphous phase [67]. The influence of dopants on mechanical

properties are also well researched. The same article by Rodrigues et al. tested the

17

addition of silver and gold atoms as dopants in the TiO2 system. Addition of silver

reduced the hardness of TiO2, regardless of the amount added. On the other hand,

the introduction of gold as dopants increased the hardness from 11 GPa (TiO2) to 13.1

GPa (14% Au – TiO2). However, a reduction in hardness was found upon addition of

Au above 14% with the hardness reducing to values as low as 6.1 GPa for the sample

containing 73% Au [67].

1.3 CeO2/TiO2 Mixed Metal Oxides

CeO2/TiO2 MMOs exhibit properties similar to those when analyzed as individual

metal oxides. Research has shown CeO2/TiO2 MMOs to have good photovoltaic

capabilities to go with its ability to act as electrochemical sensors.

Uzunoglu et al. managed to create an enzyme-based electrochemical sensor. They

used CeO2 - TiO2 nanoparticles as modifiers on the surface of a Pt electrode enabling

it to be used as an electrochemical lactate sensor with high sensitivity. The

performance of these sensors was analyzed using cyclic voltammetry and

chronoamperometry methods [68].

The photovoltaic capabilities of TiO2 films have been shown to improve upon

introducing Ce into the devices. Results show that this addition results in a shift of

the absorption region significantly into the visible range of the electromagnetic

spectrum. Dye-sensitized high-performance Mo-Ce doped TiO2 nanotubes

photoelectrodes have also been tested and have been found to absorb

electromagnetic radiation in a broader region of the visible spectrum. A reduction in

ion recombination was also noted [69].

CeO2 - TiO2 MMOs have shown excellent electro-optical behaviors, making them an

ideal candidate for transparent counter electrode material for electrochromic

devices. It’s ion storage capabilities when used as a counter electrode in an

electrochromic device have been tested and have been found to be effective [70].

CeO2 - TiO2 MMOs could potentially play a role in the process of reducing human

induced harms to the environment. They have been used in the cleanup process of

nuclear waste. Fe2O3 particles were added to the MMOs to form CeO2- TiO2- Fe2O3

and were successfully used in the removal of uranium ions from industrial waste [71].

18

The photocatalytic property of these MMOs has shown the capability of reducing CO2

into methane at a better rate than that shown by TiO2 itself [72]. These technologies

need to be further developed to enable them to be implemented on a larger scale.

The mechanical properties of these MMOs are still ill defined. Wang et al. studied the

hardness of these MMOs and found the hardness to be around 7 GPa [73]. However,

they used a different method of thin film fabrication which involved ball milling. This

means that their film is expected to have a lower hardness value in comparison to

that found of a magnetron sputtered film simply due to the porosity of the film [73].

1.4 Thesis Outline and Objectives

Previous studies on TiO2, CeO2 and CeO2/TiO2 mixed metals were compiled and their

basic characteristics were reviewed. An experimental analysis was then carried out

on magnetron sputtered CeO2/TiO2 thin films on Si (100) substrates. Chapter 2

outlines the procedures undertaken to synthesize the thin films, and the parameters

chosen in order to find the structure of each film, at varying temperatures. Four thin

film coated samples were chosen with two samples intentionally being made to be

pure TiO2 and CeO2 coated samples. The other two chosen samples were prepared

with the bias voltage being controlled to form mixed metal oxide thin films with

varying Ce-Ti percentages. The latter half of this thesis discusses the research findings

and interlinks the results of different characterization techniques to develop a unique

insight into the mechanical and structural properties of CeO2/TiO2 mixed metal oxide

films.

The objective of this thesis is to characterize and analyze the structural and

mechanical properties of CeO2/TiO2 MMOs with different Ce:Ti ratios. The relation

between this ratio and their respective properties will be drawn and verified by

several advanced characterization techniques, to help understand the changes within

the film that occur as a result of the addition of one metal oxide to another.

19

Chapter 2. Methodology

2.1 Overview of procedures

To test the hypothesis of the study, the following test were conducted on specially

designed thin films. The thin films were first prepared with an objective of attaining

coated samples with varying amounts of CeO2 and TiO2. Each film was then subjected

to specific characterization techniques with an aim of attaining clear details of the

films, which could then be analyzed in relation to one another to determine and

explain the final properties of each of the films. The chemical compounds/phases and

their lattice structure were analyzed with the aid of the results obtained using the X-

ray photoelectron spectroscopy (XPS) and in-situ X-ray diffraction (XRD) technique.

The mechanical properties of the film were determined using nanoindentation tests.

The load induced stresses were studied in relation to the film thickness and

substrates using finite element modeling (FEM).

The coated samples were split into smaller pieces to avoid cross-contamination as

some of the techniques required sample preparation which may result in the

sample’s other properties being changed. For instance, for FESEM imaging, the

samples needed to be coated with a conductive platinum coat. This may alter the

film’s other true properties such as its hardness.

2.2 Thin Film Preparation

The mixed metal thin films were deposited onto a 0.5 mm thick Si (100) wafer using

a closed field unbalanced reactive magnetron sputtering system (UDP650, Teer

Coating Limited, Droitwich, Worcestershire, UK) (Figure 2.2.1). The sputtering system

was configured with two targets with one of them being a pure Ti target whilst the

other target being a pure Ce target. The substrate was rotated at a constant 10rpm

for the duration of the coating process, for each of the films, with an aim of ensuring

a homogenous distribution of synthesized phases on the substrate. The carrier gas

for the sputtering process was chosen to be Ar, whilst the reactive gas was selected

to be O2 gas with an intention of it reacting to form the desired metal oxides, which

would then be deposited onto the substrate. Sputtering was conducted in this Ar/O2

mixed gas environment throughout the deposition of the films. The substrate bias

20

was set to -60V during the deposition process for all coatings as literature has shown

that variations in the substrate bias can affect the properties of the films [40]. The

substrates were not intentionally heated during the deposition phase and were

hence assumed to be at room temperature during the sputtering process. The

substrates were cleaned using an ultrasound bath in a methanol and acetone mixture

before being dried using highly pure nitrogen gas. Both target materials were also

cleaned adequately prior to sputtering the thin films. The substrate was protected

from contamination during this process by a shutter between the target and

substrate. The base pressure in the chamber (pressure before introducing the carrier

and reactive gases) was in the order of magnitude of 10-6 torr for all films. Four

samples were chosen from a total of seven prepared samples due to the time

constraints of this project, being an honours thesis. Given below is a table compiling

the deposition conditions for the samples chosen for this study (Table 2.2.1).

Table 2.2.1 Magnetron sputtering deposition conditions for samples prepared for

this study.

Sample ID

T1 T2 T3 T4

Ce target Bias (V) 227 233 234 -

Current (A) 4 4 4 -

Ti target Bias (V) - 372 393 400

Current (A) - 4 6 6

Argon gas flow rate (sccm) 20 20 50 20

Oxygen gas flow rate (sccm) 15 15 15 15

Working chamber pressure (torr) 2.5 X 10-3 2.7 X 10-3 2.5 X 10-3 2.5 X 10-3

Deposition time (h) 4 4 3.5 6

The pure CeO2 film (T1) was deposited with the target bias of the Ce target being set

to 227V and 4A. The argon carrier gas flow rate for this film was set to 20 sccm whilst

being mixed with 15 sccm of O2 gas. The sputtering chamber was held at a pressure

21

of 2.5 X 10-3 torr for the duration of the sputtering process (also known as the working

chamber pressure), which took 4 hours.

The second film (T2) was synthesized by setting the Ti target bias to 372V and 4A,

with the Ce target bias (233V and 4A) being similar to that of T1. The Ar and O2 flow

rate was set to 20 and 15 sccm, respectively. The chamber pressure was maintained

at 2.5 X 10-3 torr and the deposition of the film took 4 hours.

T3 was synthesized with a higher Ti target bias (in comparison to T2) at 393V and 6A

whilst the Ce target was held at 234V and 4A. The deposition of this film took 3.5h,

and the pressure in the chamber was recorded to be 2.7 X 10-3 torr. The Ar flow rate

was kept at 50 sccm with the O2 flow rate being 15 sccm.

The fourth film for this study (T4) was synthesized with the aim of obtaining a pure

TiO2 film. The Ti target bias for this film was set to a higher voltage of 400V in

comparison to T3, with the current being maintained at 6A and the chamber pressure

being 2.8 X 10-3 torr for the duration of the 6-hour deposition time. The carrier Ar gas

had a flow rate of 20 sccm whilst the reactive gas was pumped into the sputtering

chamber at 15 sccm.

Figure 2.2.1 A picture of the UDP650 magnetron sputtering system used to produce

the films for this study (City University of Hong Kong)

22

2.3 XPS Characterization

X-ray photoemission spectroscopy (XPS), also known as electron spectroscopy for

chemical analysis (ESCA), is a technique widely used in modern research of samples

containing nanomaterials and thin films. It is useful for identifying or verifying the

presence of species and their bonding states in the sample’s top surface (2nm – 5nm).

Atomic percentages can be quantitatively analyzed by peak fitting the XPS intensity

(a.u.) vs binding energy (eV) graph.

For this research, a Kratos AXIS Ultra DLD (2013) XPS system (Figure 2.3.1) was used

to identify the species present in each of the samples using an overall survey scan.

For more in-depth information regarding the bonding state of each of the elements

identified, high resolution XPS data was collected in selected photo electron energy

regions related to the MMOs. The XPS system used high intensity Al-Kα

monochromatic radiation with a photon energy of 1486.6 eV.

Figure 2.3.1. The Kratos AXIS Ultra DLD (2013) XPS system at the John de Laeter

Center (Curtin University) which was used to collect the XPS data

23

The instrument used offered several working modes in order to facilitate desirable

data collection conditions for specific samples. The machine had a neutralizing device

which purged low energy electrons onto the surface of the sample to compensate

for a positive charge build up for semi conductive or insulating samples during data

collection. This device could be turned on or off to control the charging of the sample

which could lead to the data being shifted due to some photoelectrons being

trapped. The analysis chamber also had a magnet which created a field around the

sample to guide the negatively charged photoelectrons towards the detector for a

better signal. The argon ion sputtering gun’s power could be controlled to match the

needs of the operator. It also had two working modes, namely the cluster mode and

a mono atomic mode. When the cluster mode is used, the ions are used to cleanse

the surface of the sample being analyzed. This technique is useful for softer materials

or layer sensitive studies as it does minimal damage to the top layer, whist removing

surface contaminants. The mono atomic mode on the other hand uses a stream of

argon ions to etch into the sample. This mode can help clear out surface

contaminants which may have embedded/attached themselves onto the top layer.

This mode can also be useful for depth sensitive studies, as the sample can be etched

to a desired depth to analyze specific layers at certain sample depths.

For this study, the X-ray source power was set to 225W for the duration of the data

collection for all samples. An even UHV of ∽3x10-9 Torr was maintained in the analysis

chamber during the experiment. The field of view was set to 1, with an aperture of

110 µm. The magnet in the analysis chamber was kept on in order to promote higher

signals from the sample.

The neutralizer was turned off to avoid overcompensating for charge build up on the

surface of the sample.

The samples were placed on a steel beam sample holder, with carbon tape being

applied under the sample to ensure conductivity from the sample through to the

steel stage. A thin piece of carbon tape was also applied on the top of the sample to

reduce charge build up during the experiment. The sample stage was then placed in

the machine and a vacuum was generated in the sample loading chamber. Once the

pressures were low enough, the samples were moved into the analysis chamber

24

where the argon ion sputtering gun was present. The sample heights were manually

entered to receive a higher signal from the sample. A survey scan was taken with the

neutralizer being turned on to compensate for the charge build up due to the oxides

on the surface due to the film being exposed to air during storage, prior to etching

the surface. A binding energy step of 1.0 eV was used in the range of 1.2 keV – 1.0

keV to attain an overall scan for analysis of the surface before etching.

An argon ion gun was then used to etch the top layer of atoms away to get rid of

surface oxides and contaminants. A 2mm X 2mm window was etched onto the

surface of the sample using the gun in monoatomic mode to ensure that the top layer

was taken away. The size of the etching zone was kept relatively large to ensure that

the crater created was significantly larger than the scanning area. The argon ion gun

was set to 5 keV and the samples were etched for 10 minutes under UHV conditions.

Upon etching, a survey scan was conducted on each of the samples for analysis of

the overall composition, with the neutralizer being turned off, whilst keeping the

magnet on. These scans were conducted with the step size being 1eV. The pass

energy for the survey scans was set to 160 eV. A higher resolution scan was

conducted in specific regions of the spectrum for better bonding state analysis of

individual elements. A step size of 100meV was used to scan for binding energies in

the Ce 3d, Ti 2p and O 1s regions to attain a higher resolution scan for peak fitting

analysis later. The pass energy for the high-resolution scans was set to 20eV.

2.4 XRD Characterization

The XRD results were found using a Rigaku smartlab X-ray diffraction machine (Figure

2.4.1), equipped with an Anton Paar DHS110 furnace. The furnace was used to raise

the temperature of the sample as in-situ measurements were taken.

A rotating copper anode was used as the source of X-rays. The wavelength of the

monochromatic X-rays used was 1.5406 Å, with the X-ray tube voltage and current

set to 45 kV and 200 mA, respectively, for all scans.

25

Figure 2.4.1 The Rigaku smartlab X-ray diffraction machine used to carry out in-situ

XRD experiments in this study (University of Queensland)

The results were collected over a range of 2θ values of 20° to 80°. The temperatures

at which in-situ XRD measurements were taken were at 30 °C, 200 °C, 500 °C, 600 °C,

700 °C, 800 °C, 900 °C and 1000 °C.

The XRD machine was first calibrated using a silicon powder sample. A scan was also

taken to ensure that the graphite dome which was used as an attachment to the

furnace did not add peaks to the XRD data of the film to be studied.

For analysis, the samples were placed in the furnace, with the graphite dome

covering the sample. A vacuum was generated inside the furnace dome to avoid

oxidation of the sample at high temperatures. The X-ray beam was set to the Bragg-

Brentano geometry to take the measurements. The sample was initially aligned, and

its height calibrated to ensure minimal interference with the data collected. This was

done autonomously using the manufacturer provided guidance software. XRD

readings for each sample were taken with a step size of 0.01°.

The first scan at 30 °C was conducted after aligning and calibrating the height of the

sample. The temperature was attained using the temperature-controlled furnace.

26

The sample was held at the desired temperature for a minute before starting data

collection to ensure even heat distribution within the sample. Once the data was

collected at 40 °C, the furnace was then turned on again to raise the temperature at

a rate of 10 °C/min to the next desired higher temperature for analysis. Once the

thermostat on the stage detected that the desired temperature was reached, the

sample was held again for a minute before the new sample height was found using

the software. The new sample height was used as the new benchmark for sample

height to reduce peak shifting due to thermal expansion of the sample. After the

sample height was re-measured, a new scan was conducted in the 2θ range of 20-80,

with the same step size.

The process of raising the temperature, holding for a minute, recalibrating the height

followed by collecting data was repeated until data was collected at all the desired

temperatures mentioned above.

2.5 FESEM Imaging

The samples were loaded on aluminum stubs to imaging. Carbon tape was first

applied on the stub before laying the sample flat on top of it for better conduction.

Carbon paint was then applied in the edges of the samples to ensure proper

conductivity from the top of the sample through to the stub. To ensure that there

was little charge build up for higher resolution imaging, the samples were coated with

a layer of platinum using a Cressington 208HR High Resolution Sputter Coater (Figure

2.5.1). The coated samples were then mounted onto a sample holder and loaded into

the FESEM machine.

27

Figure 2.5.1. The Cressington 208HR Sputter Coater used to apply a platinum

coating for better conduction on the surface of the samples.

FESEM scans were conducted using a Zeiss Neon 40EsB CROSS-BEAM FESEM system

(Figure 2.5.2). All imaged was taken with the accelerating voltage being set to 5kV.

The aperture size was also fixed at 30.00µm for all images taken.

Figure 2.5.2. An image of the Zeiss Neon 40EsB CROSS-BEAM FESEM system used to

obtain FESEM images of the samples.

28

Two images were captured for each sample with the first being at a relatively low

magnification of X5000. This image was taken using a 50:50 signal mixing mode with

the in-lens detector and the secondary electron detector being used at 50% each.

The second image was taken at a higher magnification of X50 000. This image was

captured using the in-lens detector by itself for better edge detection.

The average grain size for each of the samples were calculated using the higher

magnification image, whilst the low magnification image was used for qualitative

analysis.

2.6 Nanoindentation and Finite Element Modeling (FEM)

Mechanical properties such as hardness (H) and Young’s modulus (E) of the sputtered

thin films were found by experimental nanoindentation. An Ultra-Micro Indentation

System 2000 workstation (CSIRO, Sydney, Australia) system (Figure 2.6.1) equipped

with a diamond Berkovich indenter was used for the experiment. The indentation

system was calibrated using a standard fused silica specimen to ensure accurate

results. All experiments were carried out with a load-controlled method with the

maximum loading being set to 5mN. The 5mN load was set with a view of restricting

the indenter penetration depth to less than 10% of the film thickness, given that the

film was determined to have a minimum thickness of 1 micron based on deposition

conditions. This was done to prevent the surface from forming micro cracks under

loading conditions. The number of data collection points were set to 15 during the

loading phase, whilst 20 data points were set for the unloading phase of the

indentation process. This cycle of loading and unloading was repeated 20 times to

obtain an average and improve the reliability of the data. Other properties such as

the plastic deformation index (PDI) (Eq 2.6.1) and the elastic deformation index (EDI)

(Eq 2.6.2) for each film were derived from the values of hardness (H) and Young’s

modulus (E) as measured by nanoindentation experiments.

𝑃𝐷𝐼 (𝐺𝑃𝑎) = 𝐻3 𝐸2⁄ (Eq 2.6.1)

𝐸𝐷𝐼 = 𝐻 𝐸⁄ (Eq 2.6.2)

29

Figure 2.6.1. The Ultra-Micro Indentation 2000 workstation (CSIRO, Sydney,

Australia) system used in this study

Finite element modeling (FEM) was then carried out on the thin films to help envision

the load induced stress in the film. The commercially available Comsol Multiphysics

software was used in this work to simulate the intensity and distribution of load

induced stress within the thin film, for different thicknesses and substrates. Here,

“load induced stress” refers to the stress as a result of artificial loading during the

modelling process to evaluate the load carrying capability of the coating layer. This is

carried out in order to aid in differentiating this type of stress from “residual stress”,

which is the residual stress within the film, which is a result of the sputtering process.

A 2D axial symmetry model was incorporated in a similar manner to that used in

previous work [74][75], with a spherical indenter with a radius of 5 µm applying a

load at the top of film layer with different compositions and thickness. The load

induced stress of the thin film was modelled on four different types of substrate,

which are typically used in real industrial applications. The substrates that were

tested were silica, Si (111), low strength steel, and high strength steel. Further details

30

of FEM modeling, such as geometry, boundary conditions, and mesh generation,

have been given in previous work [76]–[78].

The load carrying capability of the films is frequently assessed by the equivalent

stress, or von Mises stress, labelled as σequiv. This is a measure of the potential

damage the level of stress could induce and can be expressed by Eq 2.6.3.

𝜎𝑒𝑞𝑢𝑖𝑣 = {0.5 [(𝜎𝑥𝑥 − 𝜎𝑦𝑦)2

+ (𝜎𝑦𝑦 − 𝜎𝑧𝑧)2

+ (𝜎𝑧𝑧 − 𝜎𝑥𝑥)2 + (𝜎𝑥𝑦 + 𝜎𝑦𝑧 +

𝜎𝑧𝑥)2

]}1/2

Eq 2.6.3

where σxx, σyy, σzz, σxy, σyz, σzx are the corresponding stress tensor components in

respective directions.

The parameters used for the FEM, in conjunction with the Young’s modulus of the

thin films (Table 3.4.1) are compiled in Table 2.6.1. Parameters of the substrate and

the indenter are also given in Table 2.6.1 [79]–[81]. This study also presents the

modelling results of CeO2/TiO2 films on steel substrates with different yield strength

from ∽250 MPa (low strength) to ∽750 MPa (high strength) [79][80] in order to

assess the substrate’s impact on the integrity of various film-substrate combinations.

The load-displacement curve is simulated using the bilinear model [82].

Table 2.6.1. Modeling parameters of substrate, indenter and interlayer [79]–[81]. LS

and HS represent low strength and high strength respectively.

Samples name

Young’s

modulus, E

(GPa)

Poisson’s

ratio

Yield

strength

(MPa)

Bulk modulus

BH (GPa)

Steel(LS) 200 0.30 250 1.7

Steel(HS) 200 0.30 750 1.7

Si (111) 168.9 0.25 - -

Silica 80 0.25 - -

Indenter (DM) 1141 0.07 - -

31

Chapter 3. Results and Discussion

3.1 Bonding State Identification - XPS

The XPS data was analyzed using CASA XPS software version 2.3.18PR1.0. The overall

spectrum was quantified, and the atomic percentages for Ce, Ti and O found were

compiled in Table 3.1.1. Peak fitting for scans in each photoelectron line region can

be performed and analyzed, however, this is beyond the scope of this thesis as the

chemical states are complex. An example of the possible peak fittings that could be

done for further analysis of the high-resolution scans in the Ce, Ti and O regions for

bonding state analysis are given in Figure A1. The peaks identified for the T2 film have

been compiled in Table A1.

XPS results were used to attain the composition and identify the phases present in

all chosen films. The XPS results obtained before and after 10 minutes of sputtering

showed that the amount of surface carbon had been reduced to a bare minimum.

This showed that the surface contaminants had been etched out of the scanning

surface. A compilation of the atomic composition of each of the films after etching

has been summarized in Table 3.1.1.

Table 3.1.1 Atomic percentages of each thin film coating by XPS analysis after

etching.

Atomic Percentage (%)

Ce O Ti

T1 34.36 65.64 0.00

T2 30.01 60.14 9.85

T3 27.94 58.63 13.43

T4 0.00 67.84 32.16

Data calibration was done by aligning the C 1s peak to a set value of 284.8 eV for all

samples. The XPS results showed that film T1 was a pure CexOy film upon analysis of

the overall scan conducted on the film after 10 minutes of etching. The Ce:O ratio

was found to be 1:2. Based on this, the stoichiometry of the film can be postulated

32

to be CeO2. However, the high-resolution scans revealed complex chemical bonding

states within the film (Figure A1), whose analysis is beyond the scope of this thesis.

The complexity is as a result of the mixing of several types of oxides that could have

been formed during the thin film deposition process. There are two possible

oxidation states of cerium, with one being Ce4+ and the other being Ce3+. The Ce4+

species can be hypothesized to be CeO2 whist the Ce3+ species being Ce2O3 due to

oxygen being the only other chemical species present in the film as confirmed by the

overall spectrum results. The percentage of Ce2O3 can be calculated using a formula

provided by Yu and Li [83]. This formula (Eq 3.1.1) uses the area of the satellite peak

at higher energies to calculate the percentage of Ce4+ species as this peak is

characteristic of the presence of the Ce4+ species. The % peak area of the satellite is

with respect to the entire Ce 3d region area and was found by peak fitting.

%𝐶𝑒4+ =𝑆𝑎𝑡𝑒𝑙𝑙𝑖𝑡𝑒 𝑃𝑒𝑎𝑘 %

14 × 100% (Eq 3.1.1)

A compilation of the %Ce4+ species for each sample is presented in Table 3.1.2

Table 3.1.2 Percentages and ratios of Ce and Ti for each film as calculated using the

XPS results.

Ce-Ti (%) %Ce4+ Ce:O Ti:O

T1 100-0 49.4 0.52 0.00

T2 75-25 22.5 0.50 0.16

T3 68-32 18.7 0.48 0.23

T4 0-100 0.00 0.00 0.47

The overall spectrum scan of the sample labelled T2 showed the presence of Ce, Ti

and O as expected due to the film deposition conditions. The overall scans revealed

that the film was composed of 9.85% Ti, 30.01% Ce and the remaining 60.14% O

(Table 3.1.1). The percentage drop of Ce can be attributed to the redistribution of the

total area with Ti taking a share of this total area. The Ce-Ti (%) was calculated to be

75-25 (Table 3.1.2). A characteristic Ce4+ satellite peak at 914.6 eV was also fitted

[84]. The percentage area of this satellite peak was less than that found in T1,

showing a smaller percentage of Ce4+ in comparison to Ce3+. The value of %Ce4+

33

reduced from 49.43 % for T1 to 22.50 % in T2 (Table 3.1.2). This characteristic Ce4+

satellite was also detected at 914.2 eV in T3. This peak however had an even smaller

area as compared to T1 and T2. This resulted in the %Ce4+ being less than T1 and T2

(Table 3.1.2).

The overall survey scan conducted on T4 showed that the film deposited was a pure

TixOy Film with the Ti:O ratio being 0.47.

The %Ce4+ reduced constantly with an increase in amount of Ti in the film. This shows

that the Ce4+ phase was being reduced to Ce3+. These results show that the TixOy

phases act as a reducing agent upon being mixed with CexOy. Other research groups

have attributed this reduction to be due to a photochemical process due to the X-ray

beam itself (used to attain XPS results) amongst other reasons such as natural light

exposure whilst storing the samples, which possibly led to the composition being

impacted within the film [85]. However, this explanation cannot be used to justify

the changes observed in this work. The major reason for this is that the reduction

was observed despite treating the samples in the same way. The method of sample

storage was also the same for all the samples. The samples were all subjected to the

same amount of X-ray exposure due to the experiments being carried out with the

same parameters resulting in extremely similar exposure times. Therefore, the

reason why the reduction could be observed in the XPS spectrum is said to be due to

intrinsic activities within the films.

The atomic percentage of T1 shows that the mole ratio is predominantly CeO2 as

evident by the 1:2 ratio of Ce: O (Table 3.1.1). Sample T2 can be said to have a Ce3O6Ti

mole ratio of Ce:O:Ti whilst T3 being Ce2O4.5Ti and T4 showing TiO2.

3.2 Phase and Crystalline Structure Determination – XRD

The data collected for each of the samples over the temperature range described in

Section 2.4 were plotted into a 3D graph using the Plotly extension under RStudio

Version 1.0.153.

The peaks found were then matched with powder diffraction files (PDF) from the PDF

database software. Some of the peaks were also matched for phase ID purposes

using a software called QualX by the Institute of Crystallography (IC)-CNR - Bari, Italy.

34

Figure 3.2.1. XRD data collected for the T1 film at the temperatures given in the

legend.

Phase analysis of T1 between 2θ values 20 ≤ 2θ ≤ 60 showed the presence of a Ce,

Ce2O3 and a SiO2 phase at 30 °C. The Ce phase found had a hexagonal crystal system

with one of its expected major peaks for the Ce (100) orientation appearing at 2θ =

28.01° (PDF – 00-900-8491) (Space group (SG) – P63/ mmc). This peak was not

prominent as it was in the lower 2θ angles where the amorphous nature of the

coating was apparent (Figure 3.2.1). The coating was responsible for the amorphous

behavior observed at lower 2θ angles because the substrate showed excellent

crystallinity. The substrate peaks showed high intensities, were sharp, indicating

crystallinity. The substrate had a main peak at 69.13° (Figure A2). Literature has

shown this peak to be related to Si (400) [86]–[88], which is characteristic of a Si (100)

substrate. A tetragonal SiO2 stishovite phase was detected in the same film (JCPDS-

ICDD - 04-008-7708) (SG – P42/mnm (136)) with its major sharp peak at 2θ = 30.44°

35

(110) being detected. The presence of this phase is a result of the initial stages of the

thin film deposition. It is very likely that the SiO2 phase was produced in the early

stages of deposition when the O2 reactive gas was allowed to flow into the deposition

chamber whilst the plasma was generated. Initially, due to a lower concentration of

deposited CeO2 and TiO2, the substrate would have been partially exposed (areas

that were not deposited yet) to the reactive gas in the presence of the plasma,

resulting in the formation of the stishovite phase. The detection of the Si substrate

and the SiO2 phase indicate that the X-rays penetrated deep into the sample and the

entire film was characterized, unlike the XPS results obtained, which only showed

phases present in the top layer of the film. The third phase detected in the film was

a trigonal α- Ce2O3 phase (PDF – 00-101-0279) (SG – P321). A sharp peak at 30.3° (10-

1) gave a strong indication of the presence of this phase alongside other peaks at

26.5° (100). This value of 2θ for the (10-1) orientation was however found to be 0.09°

lower than that reported in the PDF file (30.39°). This shift to a lower angle shows a

change in lattice parameters. This could be as a result of oxygen vacancies in the

Ce2O3 lattice. Similar variations in peak positions have been observed by Reddy et al.

[89]. A new phase was also found to be present at temperatures above 600 °C. The

new phase found was a cubic CeO2 phase (JCPDS-ICDD - 04-005-9595) (SG – Fm-3m

(225)). This phase was detected due to the appearance of a new broad and minor

peak at 2θ = 55.4°. The presence of this peak is obscured due to the presence of a

substrate peak at a similar angle. The presence of this new phase is more prominent

as a skew to the right can be observed in the peak at 55.4°. The skew is indicative of

the data peak being a sum of two different peaks, which can be independently

quantified by conducting peak fits. The peak skew is more prominent with an increase

in temperature indicating an increase in concentration of the new phase with an

increase in temperature. The other peaks found at 2θ = 30.5°, 33.0°, 33.6°, 44.4°,

46.0°, 46.3°, 47.7°, 54.6°, 55.4°, 56.3°, 57.3° and 59.3° were all related to the

substrates as they were detected on the scan conducted on the bare substrate

(Figure A3).

36

Figure 3.2.2. XRD data collected for the T2 film at the temperatures given in the

legend.

The T2 film which was shown to contain 9.8% Ti (Table 3.1.1) showed the presence

of various phases. Similar to film T1, an α-Ce2O3 phase (PDF – 00-101-0279) (SG –

P321) phase was found with peaks appearing at 2θ = 30.3° (10-1) and 26.5° (100)

(Figure 3.2.2). A different cubic form of CeO2 (JCPDS-ICDD - 00-034-0394) (SG – Fm-

3m (225)) was found with its peaks being visible at 28.4° (111) and another peak at

56.3° (311). The (311) peak however was also identified in the substrate XRD results,

indicating that this peak at 56.3° could be because of a combination of species being

present in the film. The other peak at 28.4° was also noticeably broader. This could

be due to the phase having a crystallite size in the nanoscale. This peak could also be

broad as a result of two peaks appearing at similar angles. A hexagonal SiO2 phase

(JCPDS-ICDD - 04-005-4723) (SG – P3121 (152)) was found to have a diffraction peak

at 28.5° from its (011) plane. The presence of this phase may have contributed to the

37

broadening of the peak. A rutile TiO2 phase (JCPDS-ICDD - 04-001-8956) (SG –

P42/mnm (136)) was also found to be part of the film with a high intensity sharp peak

appearing at 26.9°. The high intensity peak showed that (110) was the preferred

orientation of the rutile phase in this film. These results support the findings of the

XPS section as the same phases were detected in both the characterization

techniques. Some of the oxides detected in the XPS section were not matched with

the XRD results, but this is unavoidable due to the working mechanisms of the two

different techniques. XPS is more sensitive to chemical bonding states in the top

surface whilst XRD technique can be used to analyze the entire film, thereby missing

the finer details.

Figure 3.2.3. XRD data collected for the T3 film at the temperatures given in the

legend

Out of the 4 films analyzed, the crystallinity of T3 improved upon heating the samples

to a higher temperature. As Figure 3.2.3 clearly shows, XRD results of T3 showed the

reduction of the amorphous nature of the film upon heating. Two factors could have

38

played a major role in this change with the first being the Ce:Ti ratio and the second

being the amount of energy absorbed by the film during the heating process. It is

plausible that the phases in the film were in a metastable state and that the heat

provided was enough for the film to start crystalizing. The phases identified during

the phase analysis of this film were 2 variants of TiO2 with the other phases being an

α-Ce2O3 and SiO2 phase. The phase analysis revealed similar phases to those found in

the film labeled T2. An α-Ce2O3 phase (PDF – 00-101-0279) (SG – P321) was found

with peaks at 2θ = 26.4° (100) and 30.3° (10-1). Likewise, a tetragonal rutile TiO2

phase (JCPDS-ICDD - 04-001-8956) (SG – P42/mnm (136)) was found with peaks at

26.86° (110). This peak was however found to be shifted to a higher angle of 26.92°.

This shift indicates a change in lattice parameters which could have been varied due

to various reasons. One of the reasons for the shift could be due to the release of

stresses in the film during analysis. This however seems unlikely as the film was

analyzed at near room temperature (30 °C). External parameters such as

temperature rise or a change in pressure can result in these changes. Another reason

for this shift may be attributed to the contribution of dopants in the rutile structure.

As Ce is a larger atom than Ti, If Ce was to act as a dopant, then it would most likely

displace the smaller Ti atom, resulting in changed lattice parameters. Another faint

peak at 35.93 (101) was detected for the data collected at 30 °C. This peak was more

prominent as the crystallinity of the film increased upon increasing the temperature

to 200 °C. A monoclinic structured TiO2 phase (akaogiite) (JCPDS-ICDD - 00-048-1278)

(SG – P21/a (14)) was found to be present at 30 °C only with a peak at 26.42° being

recognized as a result of the diffraction due to the (0 1 1) plane. A high intensity peak

as a result of stishovite SiO2 (JCPDS-ICDD - 04-015-7198) (SG – P42/mnm (136)) was

detected at 30.44° (110). A subsequent peak at 46.00° (111) was also attributed to

this phase. A new cubic form of CeO2 was found at temperatures exceeding 800 °C.

A noticeable peak at 28.58° (100) was found and matched with the values found In

the PDF file JCPDS-ICDD - 04-003-1755 (SG – Fm-3m (225)). The appearance of this

new phase resulted in the crystallinity of the film being disturbed as shown by the

increase in background noise at 900 °C and 1000 °C.

39

Figure 3.2.4. XRD data collected for the T4 film at the temperatures given in the

legend

The fourth film - T4 showed the presence of various forms of TiO2 with another two

SiO2 phases being found to be present in the film. Two TiO2 phases were found at 30

°C, namely, a monoclinic akaogiite TiO2 (JCPDS-ICDD - 00-048-1278) (SG – P21/a (14))

and a tetragonal rutile phase (JCPDS-ICDD - 04-001-8956) (SG – P42/mnm (136)) with

its major peak being at 26.42° (011) and 26.86° (110) respectively. Both of the SiO2

phases found had a tetragonal crystal structure with major high intensity peaks at

30.36° (110) and 30.44° (110). These phases were matched with PDF files - JCPDS-

ICDD - 04-008-8697 (SG – P42/mnm (136)) and JCPDS-ICDD - 04-015-7198 (SG –

P42/mnm (136)). A new tetragonal anatase form of TiO2 (JCPDS-ICDD - 01-075-2553)

(SG - I41/amd (141)) was detected at higher temperatures of 900 °C and 1000 °C. Its

peaks appeared at 25.23° as a result of the (101) plane and were relatively broad and

of low intensity.

40

Overall, the results showed that the primary phase in all samples containing Ce (T1,

T2 and T3) was an α-Ce2O3 of cerium oxide, whilst the samples containing Ti (T2, T3

and T4) had a primary phase of the rutile form of TiO2. Heating the samples which

contained pure CexOy and TiOx resulted in a phase transition resulting in new CeO2

and anatase forms of TiO2 being detected respectively at higher temperatures.

Mixing the two compounds resulted in a variation of crystallinity of the films,

resulting in the disruption of phase transitions at the temperatures mentioned above

for the T2 film. The T1 film showed a new CeO2 phase at temperatures above 600 °C,

a CeO2 phase was found in T3 at temperatures above 800 °C whilst T4 showed a new

anatase phase at temperatures above 800 °C. T2 can be said to be the most thermally

stable film amongst the 4 films tested as no new phase was found upon increasing

the temperatures to a 1000 °C.

3.3 FESEM Imaging

FESEM imaging of the 4 films revealed interesting results. Two images were captured

at magnifications of X5000 and X50 000 for each of the samples. The first image was

taken at a lower magnification to allow for an overall long-range order analysis, whilst

the high magnification (X50 000) image was captured to find the average grain size

and to identify finer features of the film.

Low magnification images of the pure CexOy film T1 showed a smooth and consistent

morphology (Figure 3.3.1 (A)). The uniformity of the features across the image

indicates that the film was deposited consistently across the sample. Mountain and

valley like features were visible under low magnification and this effect was enhanced

upon looking at the high magnification images. Small crystals were visible which

appeared to be protruding from the film. These crystals looked like mountains (Figure

3.3.1 (B)) as described in the analogy previously mentioned. There was no obvious

preferred direction of growth as the objects protruding pointed in random directions

(Figure 3.3.1 (B)). The grain size was found to be 130 ± 20 nm.

Images of the top surface of the second film T2 revealed the presence of very fine

grains. The low magnification scan showed a smooth surface with possible impurities

on the surface (Figure 3.3.2 (A)). The film’s features were found to be consistent in a

similar way to that found for T1, showing an even deposition of the film. High

41

resolution scans revealed smaller grains. However, these grains did not appear to be

protruding from the film as observed in Figure 3.3.1 (B). The considerably smaller

grain size (17 ± 5 nm) in comparison to T1 shows that the Ti atoms which were added

to the film may have disrupted the crystallization process in the film.

The top surface of the T3 film looked fairly similar to that of T2. The X5000

magnification image showed a similarly consistent film with no surface features

visible apart from globular ones found on the sample surface. EDX (Energy-dispersive

X-ray spectroscopy) of these globules indicated a high concentration of cerium, which

means that they were part of the film and were not impurities. The high-resolution

scans showed an increase in grain size (23 ± 4 nm) in comparison to that found in T2.

This film however appeared to have wave like features across the film (Figure 3.3.3

(B)). These types of features could be an accurate representation of the film itself but

could also be because of the platinum coating on the top surface which was done for

better conduction. Due to the length of the waves and the small size of the grain, it

can be hypothesized that these wave like features are a result of the platinum

conductive coating rather than it being a characteristic feature of the film.

The pure TixOy film (T4) showed prominent features unlike those seen on any of the

other three films. The low magnification scans showed evenly distributed grains

across the sample (Figure 3.3.4 (A)). The second image which was taken at a higher

magnification (Figure 3.3.4 (B)) showed large globular crystals. Their shapes were not

well defined, and the growth did not appear to be promoted in any particular

direction. The grains themselves had dislocations which mostly ran from edge to edge

of the grain. The grains were also significantly larger (170 ± 40 nm) in comparison to

those found in T2 and T3. They were also found to be larger than those found in T1

(Figure 3.3.1 (B)). The image showed that the grains protruded from the film and

pictures of the initial stage of the formation of these grains can also be seen in

between the larger grains observed (Figure 3.3.4 (B)).

42

Figure 3.3.1. FESEM images of the top surface of T1 at a magnification of (A) X5000

and (B) X50 000

43

Figure 3.3.2. FESEM images of the top surface of T2 at a magnification of (A) X5000

and (B) X50 000

44

Figure 3.3.3. FESEM images of the top surface of T3 at a magnification of (A) X5000

and (B) X50 000

45

Figure 3.3.4. FESEM images of the top surface of T4 at a magnification of (A) X5000

and (B) X50 000

46

The grain sizes for each of the samples are presented graphically for better

comparison (Figure 3.3.5)

Figure 3.3.5 The grain size distribution on the surface as determined using FESEM

results for each of the 4 samples

Overall, it was clear that the pure TiOx T4 film had the largest grain size (Figure 3.3.4

(B) and Figure 3.3.5) of 170 ± 40 nm. The second largest grains were observed on the

pure CexOy film (T1) (130 ± 20 nm). When the two metal oxides were mixed to form

T2 and T3, the grain size was drastically reduced (T2 - 17 ± 5 nm and T3 - 23 ± 4 nm).

This showed that the mixing of the two compounds may have resulted in the

disruption of the crystallization process during deposition. T3 had a slightly larger

grain size in comparison to T2. This can be hypothesized to be as a result of the added

Ti in the film, which would have resulted in more TiOx being present in the film for

better crystallization after overcoming the hinderance caused by the Ce phase

present in the film.

47

3.4 Mechanical Properties

The hardness and Young’s modulus results are compiled in Table 3.4.1 along with

other derived values such as the plastic deformation index and the elastic

deformation index PDI and EDI.

Table 3.4.1 Compilation of hardness and Young’s modulus and other derived values

using Eq 2.6.1 and Eq 2.6.2.

H (GPa) E (GPa) PDI (GPa) EDI

T1 20.1 ± 1.0 245 ± 10 0.14 ± 0.01 0.082 ± 0.007

T2 19.2 ± 1.0 195 ± 4 0.19 ± 0.01 0.099 ± 0.007

T3 9.9 ± 0.3 169 ± 6 0.034 ± 0.002 0.059 ± 0.004

T4 14.1 ± 0.9 171 ± 10 0.09 ± 0.01 0.08 ± 0.01

The highest value of hardness attained was that of the pure CexOy film (T1) with a

value of 20.1 GPa. The pure TiOx film (T4) on the other hand was found to have a

hardness of 14.1 GPa, which is lower than that of T1. The value of the hardness of T4

matches to values found in literature (14.3 GPa) [90]. Upon adding TiOx to form T2,

the hardness reduced by 0.9 GPa. However, the absolute uncertainty of the hardness

was 1.0 GPa for both T1 and T2, meaning that the hardness of T1 can be considered

to be only marginally larger than that of T2 (Figure 3.4.1). Experimental

nanoindentation results did however show a 49% drop in hardness when more TiOx

was added (T3) to obtain a film with Ce-Ti (%) = 68-32. These results add to the

justification of the crystallinity in the CexOy film being disturbed upon addition of TiOx

as explained in section 3.3 of this study.

In general, the hardness results of the films found T1 (pure CexOy film) to have the

highest hardness values, with the hardness of the T4 (pure TiOx film) sample being

70% of T1. Films with the mixture of the two compounds (T2 and T3) showed that the

addition of a significant amount of the CexOy phase helped increase the hardness of

the TiOx film (T2). On the other hand, adding smaller amounts of the CexOy phase (T3)

resulted in a reduction in hardness of the film containing the TiOx phase (from 14.1

GPa for Ce-Ti (%) = 0-100 to 9.9 GPa for Ce-Ti (%) = 68-32).

48

The Young’s modulus values of the films showed T1 to have the highest value at 245

GPa, with the lowest being of T3 at 169 GPa. A steady reduction in the Young’s

modulus was observed upon adding TiOx to the samples containing the CexOy phase.

The variation in Young’s modulus however became marginal as the %Ti increased. T3

(32% Ti – 169 GPa) was found to have similar values as T4 (100% Ti – 171 GPa). This

shows that the Ce based phase in the film played a larger role in dictating the film’s

Young’s modulus property. This was further evident as a 25% reduction in %Ce

resulted in the Young’s modulus reducing by 20%. The T1 film is expected to be stiffer

than the others due to its higher Young’s modulus value. This was confirmed by FEM

results (Figure 3.4.5) which showed T1 to have a higher load induced stress in

comparison to the other films, regardless of the substrate used.

Figure 3.4.1. Averaged hardness values [H (GPa)] for each of the samples as found

by the nanoindentation test

The PDI value derived from the hardness and Young’s modulus value of each of the

films is a good representation of the material’s ability to dissipate energy during the

loading phase. Film T2’s PDI value is 5.6 times the value of that found of T3, showing

that it would dissipate energy better. Results also showed T1 to have a higher PDI

(36% higher) in comparison to T4. The EDI on the other hand can be used to relate

the film to its brittleness. A higher EDI can be interpreted as the film having a higher

hardness value for the same Young’s modulus, meaning that a film with a higher EDI

49

shows the film’s ability to avoid deformation upon manual loading. Therefore, if

enough force is applied, a film with a higher EDI would be expected to succumb to

the load and shatter earlier in comparison to a film with a lower EDI. Based on this

premise, T2 is expected to be more brittle in comparison to all the other films.

Figure 3.4.2. Young’s modulus [E (GPa)] as found using the loading and unloading

curve during nanoindentation of each sample

The finite element modelling (FEM) results are given in Figure 3.4.3 for the different

films (T1, T2, T3 and T4) with the same thickness of 1.2 m, when deposited on a Si

(111) substrate. The indentation depth modelled here is 0.16 m. As expected, for

films with smaller Young’s modulus (T3 and T4), the induced von Mises stress is

lower, whilst the distribution for all the four films presents similar shape. The stress

maximum is located around the symmetry axis and close to the surface of the film.

Modelling results on the same set of films deposited on silica and Si (111) substrate

(Figure 3.4.4 (a-b)) show that the distribution of the stress is similar in shape but

smaller in magnitude, due to the fact that the Young’s modulus of silica is lower than

that of Si (111).

50

Figure 3.4.3. FEM modelling results of equivalent stress distribution within the films

(a) T1 (b) T2 (c) T3 and (d) T4 on a Si (111) substrate

Figure 3.4.4. FEM results of equivalent stress distribution within the T1 film,

deposited on (a) Silica, (b) Si (111), (c) low strength steel, and (d) high strength steel

substrates.

51

However, a very different distribution is observed in the films modeled on steel

substrate (Figure 3.4.4 (c-d)). Steel, like many of other metals, has a yield point above

which a small loading will results in much larger displacement in the substrate than

that under the same loading when there is no yielding. As such larger displacement

occurs in the substrate below the coating, resulting in a higher level of shear stress

within the film along the film-substrate interface. Hence two separate locations of

von Mises stress concentration are clearly observed, with one being along the film-

substrate interface, and the other being close to the top surface of the film.

For a more detailed comparison, a vertical line is draw along the symmetry axis across

the film, from the top to the film-substrate interface. The stress distribution along

this line is show in Figure 3.4.5, for different films, and on different types of

substrates. General trends may be summarized as follows:

1. When deposited on the same type of substrate, the shape of the curves is

similar for all the four different films being studied,

2. Higher stress level will be induced within films with higher Young’s modulus.

Figure 3.4.5. FEM results of all 4 films (see legend) modelled on a (a) Silica

substrate, (b) Si (111) substrate, (c) low strength steel substrate and (d) high

strength steel substrate.

52

FEM results of different loading conditions are compiled in Figure 3.4.6. Here again,

the shapes of the curves are different for various type of substrate. For different

loading levels, a higher stress is induced upon increasing the indentation depth,

which is a direct result of increased loading conditions. Furthermore, a higher load

tends to push the maximum stress in the downwards direction, towards the film-

substrate interface. The legend used in figure 3.4.6 indicates the indentation depth

(nm), which is directly proportional to the applied load. An increased load would

result in a deeper indentation.

Figure 3.4.6. FEM results of equivalent stress from the top of the film to the film-

substrate interface of T1, with different loading conditions (depth) on (a) Silica, (b)

Si (111), (c) low strength steel and (d) high strength steel substrates

The influence of the substrate thickness on the stress level and distributions are

shown in Figure 3.4.7 and 3.4.8. For the Si (111) substrate, the stress concentration

is close to the film surface and away from film-substrate interface (Figure 3.4.7 (a-d).

When the indentation depth increased from 1.2 m to 1.6 m, a large increase

(about 30%) in the maximum stress level is observed (Figure 3.4.7 (e)). However, a

further increase in the film thickness does not result in significant change in the

maximum stress level (Figure 3.4.7 (e)).

53

Figure 3.4.7. FEM results of the equivalent stress distribution within T1 modelled on

a Si (111) substrate with thicknesses of (a) 1.2 m, (b) 1.6 m, (c) 2.0 m, (d) 2.4

m. (e) stress distribution along the symmetry axis for respective substrate

thickness

54

Chapter 4. Conclusion and Scope for Future

Work

This study successfully found the structural and mechanical characteristics in relation

to the preparation conditions and compositions of the CeO2/TiO2 MMO thin films.

The in-situ XRD experiments found all samples containing Ce (T1, T2 and T3) to have

a primary α-Ce2O3 cerium oxide phase, whilst the samples containing Ti (T2, T3 and

T4) had a primary phase of the rutile form of TiO2. Higher temperature XRD results

showed a phase transition to a new CeO2 and anatase forms of TiO2 for the samples

which contained pure CexOy and TiOx respectively. The crystallinity of the MMO films

T2 and T3 was found to vary as the two oxides were mixed. This was noted to be the

potential cause of the disruption in phase transition in T2. New phases were detected

at temperatures above 600 °C for T1 and above 800 °C for T3 and T4. Deposition

conditions of the T2 film resulted in the most thermally stable film out of the films

tested.

The XPS results were used to find the atomic percentages within each of the films.

The results also found that adding TiO2 to the CeO2 lattice resulted in the reduction

of this species. This was confirmed by the constant reduction of %Ce4+ as it was being

converted into Ce3+. The stoichiometry of each of the films was determined. The

Atomic percentage of T1 shows that the mole ratio was predominantly CeO2. Sample

T2 can be said to have a stoichiometry of Ce3O6Ti, T3 being Ce2O4.5Ti, whilst T4

showed TiO2 stoichiometry. The surface morphology studies found the pure films (T1

and T4) to have larger grains in comparison to the other two films (T2 and T3).

The mechanical tests yielded interesting results with T1 showing hardness values of

up to 20.1 GPa. The addition of Ti did not improve the value of the hardness and it

was determined that Ce phase played a larger role in the MMO film’s Young’s

modulus. FEM models showed that the substrate did make a difference to the

amount of loaded stress the film can take.

4.1 Overall result Interpretation method

The XPS results were used to find the chemical bonding states and composition

within the film. The XRD results confirmed the presence of the mixed phases of the

55

MMO. The FESEM images showed different morphologies for the samples studied

and hinted to the crystallinity of the film. The grain sizes were deduced from the

FESEM results. The mechanical properties were tested using nanoindentation tests

and the results were interpreted in relation to the phases and film compositions

found by the XPS results. Various other configurations of film thickness and

substrates were tested for load induced stresses by modelling them using the FEM

technique.

4.2 Future work

The mechanical properties of the MMO films studied showed great promise with high

hardness values (20.1 GPa). Further work can be done in this area by examining the

addition of other metal oxides (apart from TiO2) to the Ce lattice to investigate its

mechanical strength. From an industrial application point of view, other mechanical

tests can be implemented to find other characteristics such as the friction coefficient

and wear resistance. The results from the mechanical tests show that these films can

indeed be applied to tools and machines that require a high hardness value in order

to withstand the physical nature of certain tasks such as cutting, drilling and grinding

to name a few.

The films studied did not fully crystallize when deposited at room temperature.

Research still needs to be done in order to optimize the film for maximum hardness

and higher crystallinity. The film adhesion to the substrate is another area that can

be looked into as this information may be vital if this material was to ever be used in

the industry. The film-substrate adhesion can also be examined and perhaps

improved using a SiO2 interlayer. The effect of this interlayer on the overall

mechanical strength of the film can also be investigated.

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Appendices

Table A1 Fitted peak details for the T2 sample at specified high-resolution XPS

regions.

Region Position

(eV)

FWHM Raw

Area

%At Conc

T2 Ce 3d 5/2 880.4 2.75 56595 15.71

Ce 3d 5/2 882.4 2.07 13276 3.69

Ce 3d 5/2 885.1 3.96 120779 33.59

Ce 3d 5/2 888.0 2.26 3814 1.06

Ce 3d 3/2 894.7 2.82 6951 1.94

Ce 3d 3/2 899.1 3.30 49005 13.69

Ce 3d 3/2 903.6 4.77 95657 26.77

Ce 3d 3/2 907.2 1.35 1391 0.39

Ce 3d sat 914.6 6.94 11230 3.15

O 1s 528.5 1.24 2977 13.03

O 1s 529.3 1.51 11784 51.56

O 1s 530.6 2.22 6134 26.85

O 1s 532.3 1.76 1956 8.57

Ti 2p 3/2 455.4 1.71 402 3.76

Ti 2p 3/2 457.6 1.87 6289 58.72

Ti 2p 1/2 460.4 2.20 1232 11.50

Ti 2p 1/2 463.4 2.74 2790 26.03

66

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Figure A1. Peak fitting in the high-resolution Ce 3d, O 1s and Ti 2p regions

Figure A2. XRD data plot for T1 in the 2θ range of 20° ≤ 2θ ≤ 80°

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Figure A3. XRD data plot of the bare Si (1 0 0) substrate in the 2θ range of 20° ≤ 2θ

≤ 80°

The following attachment is a manuscript currently submitted for publication. This

was a study of metal nitride coatings and was completed as part of an independent

study contract completed at Murdoch University. This manuscript was completed

during the first semester of the Honours degree at Murdoch.

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