An-Najah National University 

 

Faculty of Graduate Studies 
 

 

 

 

 

 

 

 

CHARACTERIZATION OF DAMAGE IN 

ALUMINUM NITRIDE SINGLE CRYSTALS BY 

RBS-C, AN ION BEAM ANALYSIS TECHNIQUE 
 

 

 

 

 

 

 

 

By 

Sarab Awwad Hussein 
 

 

 

 

Supervisors 

Prof. Ismail Warad  

Dr. Ahmed Bassalat  

 

 

 

 

This Thesis is Submitted in Partial Fulfillment of the Requirements for the Degree 

of Master of Chemistry, Faculty of Graduate Studies, An-Najah National 

University, Nablus – Palestine. 

2024 



 

ii 

 

 

 

 

 

 

 

 

 

 
CHARACTERIZATION OF DAMAGE IN 

ALUMINUM NITRIDE SINGLE CRYSTALS BY 

RBS-C, AN ION BEAM ANALYSIS TECHNIQUE 
 

By 

Sarab Awwad Hussein 

 
 

This Thesis was defended successfully on 20/10/2024 and approved by: 

 

 



 

iii 

Dedication 

Praise be to God Almighty, Lord of the worlds before and after, I dedicate this thesis to 

my beloved parents, my siblings, especially my brother Mohammed, and to the memory 

of my sister Hanan. I also dedicate this work to my wonderful husband Omar. 

Especially dedicated to my amazing supervisor Aurélie, and to all the professors and 

doctors who taught me; to everyone who provided opportunities and believed in me; to 

my friends and everyone who left a mark on my educational journey. 

 

 

 

 

  



 

iv 

Acknowledgments 

First, I praise and thank Allah for guiding me on the right path.  

I am grateful to An-Najah National University for the opportunity to participate in the 

Erasmus+ program, allowing me to conduct my thesis research at Paris-Saclay 

University. Special thanks to IJCLab for welcoming me into their team.  

I deeply appreciate my supervisor, Dr. Aurélie Gentils, Scientific Leader of the JANNuS-

SCALP facility, and my co-supervisor, Prof. Frédéric Garrido from Université Paris-

Saclay, for their exceptional guidance and support. Their mentorship has been crucial to 

my research's direction and success.  

The experimental work for this research took place at IJCLab from May 9 to July 29, 

2023. Dr. Gentils and Prof. Garrido's mentorship, insightful feedback, and support were 

vital to my work during this time. I am also grateful to my supervisor, Prof. Ismail Warad, 

and to Dr. Ahmed Bassalat and Dr. Hadil Abualrob for offering me the chance to be part 

of their team in France.  

I would like to thank my group at IJCLab, especially Gabriel and Mohammed, for their 

help and encouragement, and Florian Pallier and the technical staff at the SCALP facility.  

I am profoundly grateful to my family, especially my parents, brother Mohammed, and 

sister Dr. Shaima, for their constant love and support. Special thanks to my friends Shaima 

and Attaa for their encouragement.  

Finally, my deepest gratitude goes to my husband, Omar, for his unwavering love and 

support throughout this journey.  

Sarab A. Hussein  

 

  



 

v 

Declaration 

I, the undersigned, declare that I submitted the thesis entitled: 

CHARACTERIZATION OF DAMAGE IN 

ALUMINUM NITRIDE SINGLE CRYSTALS BY 

RBS-C, AN ION BEAM ANALYSIS TECHNIQUE 
 

 

I declare that the work provided in this thesis, unless otherwise referenced, is the 

researcher’s own work, and has not been submitted elsewhere for any other degree or 

qualification. 

Student's Name Sarab Awwad Hussein 

Signature:  

Date: 20/10/2024 

 

 

 

 

 

 

 

 

 

 



 

vi 

List of Contents 

[ 

Dedication ........................................................................................................................ iii 

Acknowledgments ........................................................................................................... iv 

Declaration ........................................................................................................................ v 

List of Contents ................................................................................................................ vi 

List of Tables ................................................................................................................. viii 

List of Figures .................................................................................................................. ix 

Chapter One: Introduction ................................................................................................ 1 

1.1 Nuclear Reactors for Electricity Production ............................................................... 1 

1.2 Nuclear materials ........................................................................................................ 4 

1.2.1 Damages (defects) in nuclear materials produced by ion irradiation and implantation

 ................................................................................................................................. 6 

1.2.2 Ceramics .................................................................................................................. 7 

1.2.2.1 Aluminum nitride (AlN) ....................................................................................... 8 

1.3 Principles of Microstructure Characterization Techniques ...................................... 10 

1.3.1 Ion Beam Analysis ................................................................................................. 10 

1.3.1.1 Rutherford Backscattering Spectrometry in Channeling Geometry (RBS-C) .... 11 

1.3.1.2 XRD Technique .................................................................................................. 16 

1.3.1.3 TEM Technique .................................................................................................. 17 

1.4 Crystallography of AlN ............................................................................................ 18 

1.4.1 VESTA, CaRIne crystallography programs .......................................................... 19 

1.5 Simulation software for irradiation and ion beam analysis ...................................... 20 

1.5.1 SRIM simulation .................................................................................................... 20 

1.5.2 RUMP .................................................................................................................... 22 

1.5.3 Monte-Carlo (McChasy) ........................................................................................ 22 

1.6 Objectives of the Study ............................................................................................. 24 

Chapter Two: Experimental Work: Materials and methods ........................................... 25 

2.1 Sample preparation and Ion implantation irradiation (as-received condition) ......... 25 

2.2 SRIM simulation ....................................................................................................... 28 

2.3 Crystallography of AlN ............................................................................................ 30 

2.4 Carbon layer deposition ............................................................................................ 32 

2.5 Rutherford Backscattering Spectrometry (RBS-C) experiment ............................... 33 

2.6 Analysis of the RBS-C experimental spectra ........................................................... 35 

2.6.1 RUMP simulation .................................................................................................. 35 

2.6.2 McChasy simulation .............................................................................................. 37 

Chapter Three: Results and Discussion .......................................................................... 41 



 

vii 

3.1 SRIM simulation results: depth profiles, impurity fraction (at%), and damage (dpa)

 ............................................................................................................................... 41 

3.2 Data analysis of the RBS-C spectra .......................................................................... 44 

3.3 Extraction of the damage-depth experimental profile of the crystals ....................... 47 

3.4 XRD and TEM results .............................................................................................. 49 

3.5 Conclusions ............................................................................................................... 53 

3.6 Future perspectives ................................................................................................... 54 

List of Abbreviations ...................................................................................................... 55 

References ....................................................................................................................... 56 

 .................................................................................................................................. الملخص 

 ب ................................................................................................................................ 

 

 

 

 

 

  



 

viii 

List of Tables 

[ 

Table 2.1: Implantation fluences were used to implant the crystals with 6MeV Au+ ions 

at room temperature ............................................................................................... 28 

Table 2.2: Example of an input file from McChasy code for different RDAs that were 

used ........................................................................................................................ 40 

Table 3.1: The number of displacements per atom (dpa), which were calculated using 

Equation 4 by using different fluence of Au+ ions ............................................... 43 

Table 3.2: The impurity fraction at 100%, which was calculated using Equation 5 by using 

different fluence of Au+ ions ................................................................................ 44 

Table 3.3: Elastic strains for the near-surface region and at maximum are reported for all 

fluences .................................................................................................................. 51 

 

 

 

 

 

 

  



 

ix 

List of Figures 

[ 

Figure 1.1: Different penetration levels for different types of radiation, with alpha 

showing the lowest penetrating level and gamma being one of the most highly 

penetrating ............................................................................................................... 4 

Figure 1.2: Types of implantation-induced defects inside a crystal, including Frenkel pairs 

(vacancy, interstitial), dislocation loops, precipitates, and atomic clusters............. 7 

Figure 1.3: Aluminum nitride (AlN) ................................................................................. 9 

Figure 1.4: The binary collision model describes a collision between a projectile and 

target atom, resulting in a scattered ion or recoil atom ......................................... 12 

Figure 2.1: S ample preparation and Ion implantation irradiation (as-received condition)

 ............................................................................................................................... 27 

Figure 2.2: Depth profiles of implanted ions with different energies in the AlN target at a 

7° angle using the SRIM simulation program ....................................................... 29 

Figure 2.3: Carbon layer deposition ............................................................................... 33 

Figure 2.4: RUMP simulation ......................................................................................... 36 

Figure 3.1: C ross-sectional TEM micrographs of an AlN layer after 6 MeV Au 

implantation at RT (7.4x10¹⁴ cm⁻²) ....................................................................... 50 

Figure 3.2: X- ray intensity distribution around the (0001) reflection of AlN templates 

implanted with 6 MeV Au ions at room temperature, with fluences from 3×10¹⁴ to 

5.4×10¹⁵ cm⁻² ......................................................................................................... 52 

 

 

 

 

 

 

 

  



 

x 

List of Schemes  

[ 

Scheme 1.1: Sketch of the channeling phenomenon ...................................................... 13 

Scheme 1.2: Typical channeling spectrum of a crystal with defects (red), random 

spectrum (blue), and channeling spectrum of the perfect crystal (green ............... 15 

Scheme 2.1: Crystallography of AlN .............................................................................. 31 

Scheme 3.1: The damage distributions (at the maximum fluence) for each of (a) 6MeV 

Au+, (b) 50 keV He+ ion, and (c) 280 keV Al ion, were calculated according to the 

SRIM code ............................................................................................................. 42 

Scheme 3.2: T he Ion range (at the maximum fluence (4x1015)) for 6MeV Au+ ......... 43 

Scheme 3.3: RBS/C aligned (A) and random (R) spectra were recorded for implanted AlN 

crystals at room temperature with the 6MeV Au+ ion at various ion influences .. 45 

Scheme 3.4: Monte Carlo simulation of RBS/C spectra of AlN crystals irradiated with 

1.5 keV He ions at room temperature .................................................................... 46 

Scheme 3.5: Extraction of the damage-depth experimental profile of the crystals ........ 48 

Scheme 3.6: Elastic strain values were estimated from XRD curves vs. fluence for Au 

implantation at room temperature in AlN samples, with εS (near-surface) and εM 

(maximum) reported .............................................................................................. 52 

 

 

 

 

 

 

  



 

xi 

CHARACTERIZATION OF DAMAGE IN ALUMINUM NITRIDE 

SINGLE CRYSTALS BY RBS-C, AN ION BEAM ANALYSIS 

TECHNIQUE 
By 

Sarab Awwad Hussein 

Supervisors 

Prof. Prof. Ismail Warad 

Dr. Ahmed Bassalat 

Abstract 

Insulating optical materials such as aluminum nitride (AlN) will play a crucial role in 

future fusion reactors, particularly in diagnostic systems. AlN is being considered as an 

insulating coating in some reactor designs due to it is high resistance to chemical 

corrosion and also exhibits a high thermal conductivity up to 321 W/(m·K). 

Understanding the degradation mechanisms of AlN under implantation and irradiation is 

of utmost importance. 

This study investigated the effect of helium ions on the structure of aluminum nitride 

(AlN) single crystals using 6 MeV Au+ ions. The crystals were implanted with Au+ ions 

and analyzed using the Rutherford Backscattering in Channeling (RBS/C) technique 

across various ion fluences to mimic damage from heavy recoil nuclei. Results showed a 

gradual increase in damage, measured as a percentage of defects, with increasing ion 

fluences, reaching saturation at a depth of around 1.3 µm. Monte Carlo McChasy 

simulations validated the experimental Rutherford Backscattering in Channeling RBS/C 

data, demonstrating excellent agreement. 

Transmission electron microscopy (TEM) observations of AlN samples pre-implanted 

with 6 MeV Au+ ions at room temperature revealed a gradient of defect concentration, 

with higher densities at the rear of the damaged layer and notably high defect density at 

the surface. Discrepancies between observed defect sizes and the Stopping and Range of 

Ions in Matter (SRIM) predictions highlighted SRIM's limitations for high-energy, high-

mass projectiles on light targets. X-ray diffraction (XRD) analysis provided insights into 

strain values influenced by implantation fluence and flux. Despite a slight temperature 

increase in the highest fluence sample, strain values remained consistent with lower 

fluences, indicating robust behavior. Elastic strains increased with fluence, reaching 

saturation at approximately 1.7% and 2.5% for near-surface and peak damage regions, 



 

xii 

respectively. Challenges in determining near-surface strain due to complex XRD curve 

shapes were noted, but an overall trend was observed 

This study offers valuable insights into the structural changes induced by helium in AlN 

crystals, enhancing our understanding of material responses to irradiation and aiding in 

the development of predictive models for radiation-induced damage in materials. 

Keywords: aluminum nitride crystals; Ion implantation; Rutherford backscattering 

spectroscopy-channeling (RBS/C), Monte Carlo simulation McChasy code; Defects; 

Strain; He+; Au+ ions. 



 

1 

Chapter One 

Introduction  

1.1 Nuclear Reactors for Electricity Production 

For decades modern societies have been developing and searching for various 

technologies to cover energy demands, and among those, is one of the most important 

technologies is nuclear reactors. Nuclear reactor technology, which started for research 

applications in the 1940s, and electricity was generated for the first time from nuclear 

energy in 1951, stands out as an exceptional source of power. These complicated systems 

operate through controlled nuclear reactions, primarily involving fusion and fission 

processes; nuclear reactions are initiated, managed, and directed to take advantage of the 

enormous energy stored within the atomic nuclei [1].  

The nuclear reactor produces and controls the release of energy from splitting atoms of 

certain elements. The core of a nuclear reactor consists of fuel rods, each containing fissile 

material mostly uranium-235 or plutonium-239. The reactor operates on the principles of 

chain reactions [1][2]. In nuclear fission, the nucleus of a heavy atom is bombarded with 

a neutron, and the nucleus splits into smaller fragments, releasing large amounts of 

energy, for example, the approximate energy released from the uranium-235 fission 

reaction is 200 MeV in terms of kinetic energy (heat). The released energy is computed 

by Einstein's equation.  

E = mc2                                    (1) 

Where E, m, and c represent the total energy of a nucleus, its mass, and the speed of light, 

respectively. This process also releases additional neutrons, these released neutrons in 

another step collide with other fissile nuclei, perpetuating the chain reaction [3]. 

Fission is the process behind the operation of the existing nuclear power plants, where 

controlled chain reactions occur in the reactor core, generating heat that is used to produce 

steam which drives turbines to generate electricity for various applications [2]. 

In contrast to fission reaction, nuclear fusion reaction involves combining light atomic 

nuclei, mostly isotopes of hydrogen, to form a heavier nucleus, for example, the reaction 



 

2 

between deuterium (2H) and tritium (3H) that yields helium (4He) and a neutron (1n), this 

process releases an enormous amount of energy. 

The fusion reaction is the process that powers the sun and other stars [2]. On Earth, 

achieving controlled fusion has proven to be challenging due to the extreme conditions 

required, such as high temperatures and pressures. Successful fusion could offer a nearly 

limitless and clean source of energy due to its lack of greenhouse gas emissions, minimal 

long-lived radioactive waste, it produces no air pollution, has a high energy yield, and 

poses no meltdown risks, as reactions stop automatically if containment fails, but as of 

now, sustained and controlled fusion reactions are still being researched and developed 

[4]. 

Although fusion's challenges are enormous, including achieving and maintaining the 

extreme conditions required for fusion reactions, many projects are investing in this field. 

The International Thermonuclear Experimental Reactor (ITER) project is an international 

scientific project funded and operated by seven member parties. These members are 

China, the European Union, India, Japan, Russia, South Korea, and the United States. The 

project is based in France and aims to demonstrate the feasibility of controlled fusion on 

a global scale [5]. 

As a comparison between nuclear fission and fusion, fission is one of the most important 

technologies for power generation. It offers practical applications, but it generates long-

lived radioactive waste and increases the risk of nuclear waste increase. On the other 

hand, fusion promises a nearly boundless and clean energy source, generating less 

radioactive waste than fission. However, achieving fusion reactions remains an ongoing 

scientific and engineering challenge [4][6]. 

The usage of nuclear fission to generate energy is very common in many countries, for 

instance, the United States of America has 92 commercial reactors that produce a 

substantial portion of its electricity from nuclear sources, contributing to its energy 

security and low-carbon energy. France stands out as a pioneer in nuclear energy, with 

70% of its electricity generated by nuclear fission energy, emphasizing its commitment 

to clean energy. Russia too is a major player in nuclear power generation [7]. 



 

3 

Nuclear reactions including fission and fusion, release various types of ionizing radiation 

including alpha particles (α), beta particles (β), and gamma rays (γ).  

Alpha particles consist of two protons and two neutrons and when they're produced it's 

called alpha decay. Due to their relatively large mass, they have limited penetration 

capability, these particles can be stopped by a sheet of paper or even human skin. 

However, particles could carry high kinetic energy, upon colliding with a material, which 

can disrupt atomic bonds and create defects in the material's structure. Yet, the limited 

range of alpha particles typically borders their damage to the surface layer of the material. 

Furthermore, it is also the most ionizing form of radiation compared to others [8]. 

Beta radiation consists of high-energy electrons or positrons (the antiparticle of an 

electron), and it has a greater penetration capacity compared to alpha particles. The 

damage they cause is similar to that of alpha but on a broader scale, as beta particles break 

through further, they interact with more atoms, leading to a wider range of atomic 

displacements and defects. Beta particles can cause ionization in both living tissues and 

materials. Although beta radiation can be blocked by materials like clothing or plastic, it 

still can break through the skin, potentially causing burns or cellular damage [8]. 

Gamma Rays are photons with no mass and no charge that carries electromagnetic energy 

propagating with a velocity equal to the speed of light. Since gamma rays are a form of 

electromagnetic waves, it is capable of substantial breakthroughs through most materials, 

including human tissue. As gamma rays pass through, they ionize atoms and molecules 

along their path, creating cascades of secondary radiation, this secondary radiation can 

cause widespread damage within the material, leading to the creation of defects, changes 

in a crystalline structure, and overall degradation of mechanical properties. They can also 

cause ionization and cellular damage, posing significant health risks, especially for long 

exposure duration [8]. 

These reactions emit various types of ionizing radiation, each possessing unique 

breakthrough capabilities and biological effects, the impact of radiation on nuclear 

materials depends on the type of radiation and nuclear material. Types of radiation with 

different penetration levels shown in Figure 1.1.  

  



 

4 

Figure 1.1 

Different penetration levels for different types of radiation, with alpha showing the lowest 

penetrating level and gamma being one of the most highly penetrating 

 
Note: Energy Education. (2022). 

Due to the high penetration capability of these radiations within materials and their 

potential to induce significant structural damage in materials used in reactors, including 

atoms being displaced from their regular positions, leading to the formation of vacancies 

in the material's structure, these defects can change the mechanical, and the thermal 

properties of the materials, potentially making it more brittle, less flexible, and less 

thermally conductive [10]. 

This research project will concentrate on the materials used in fusion reactors, with a 

particular emphasis on exploring the impacts caused by neutrons and the buildup of 

gasses, like helium and hydrogen. These factors can have significant consequences on the 

properties and structural soundness of materials in the demanding environment of fusion 

reactors. The study will explore the intricate relationship between gas accumulation and 

irradiation damage to enhance the durability and efficiency of these materials. 

1.2 Nuclear materials 

The development of high-performance materials for energy generation, containment, and 

storage has become a key factor for more sustainable management of the ever-growing 

demand for electrical power. Depending on the applicability, certain material's physical 



 

5 

properties will have to be analyzed and enhanced to boost safety, long-term use, or energy 

conversion efficiency on specific applications. In nuclear technology, other materials are 

needed to moderate the reaction and prevent radiation leakage besides fissile materials 

like uranium and plutonium pellets that sustain chain reactions that generate energy. 

These latter materials need to be radiation tolerant while maintaining good mechanical 

and corrosion resistance [11]. 

In the case of thermoelectric technology, the materials that will be used to convert heat 

into electricity need to have good electric transport properties and poor thermal 

conductivity. In the case of combined nuclear-thermopower applications, they also 

maintain their integrity in a harsh radiation environment. Nuclear materials are a 

characteristic class of solid substances that steadily face an extremely hard environment 

of radiation sources and potential additional thermodynamic conditions, including 

temperature, pressure, and chemical agents. The complex interaction of these factors 

creates a challenge in understanding and estimating material behavior under radiation [9]. 

Examples of nuclear materials: the nuclear fuel (uranium dioxide in fission PWR), 

structural materials (often steels, zirconium-based alloys, tungsten in fusion), ceramics 

and glasses for nuclear waste management, and polymers. 

Nuclear materials have a wide range of applications. They are used in medical treatments 

and imaging to monitor and treat metabolic processes or tissues in humans. Similarly, 

they are also used in veterinary treatments to cure animals. In industries, nuclear materials 

are used in different devices such as irradiators, gauging devices, well-logging devices, 

and industrial radiography systems. Additionally, academic institutions such as 

universities and colleges use nuclear materials for coursework, laboratory 

demonstrations, and research purposes [12]. 

Silicon (Si) and Gallium (Ga) elements both hold significance in this field due to their 

unique properties and high-potential applications. Indeed, the importance of silicon as a 

semiconductor in nuclear technology cannot be overstated, as it plays a critical role in 

detecting and responding to ionizing radiation, making it an essential component of 

radiation detection equipment, and in nuclear environments, accurate monitoring, and 

evaluation of radiation levels hinge on the reliable performance of this indispensable 

material. Additionally, silicon's stability at elevated temperatures and corrosion resistance 



 

6 

makes it suitable for use in cladding materials for nuclear fuel rods, contributing to the 

structural integrity of reactor systems [13]. 

Gallium, on the other hand, with its unique characteristics makes (Ga) a good material 

for use in the nuclear industry, with its low melting point and liquid-state properties, 

gallium is ideal for applications involving liquid metal coolants in advanced reactor 

designs [11]. 

Also, Aluminum Nitride ( ) is one of the most promising materials in nuclear 

applications, especially for fusion applications due to its excellent mechanical properties, 

chemical inertness, and high melting point. The AlN is suitable to operate in high 

temperatures and harsh environmental conditions and therefore is very promising to be 

employed in industrial applications [14]. 

1.2.1 Damages (defects) in nuclear materials produced by ion irradiation and 

implantation 

Irradiations in reactors induce damage to materials. At the nanoscale, a crystallographic 

defect refers to the disruption of the typical arrangement of atoms or molecules in 

crystalline solids. The interaction of accelerated particles with the target’s atoms leads to 

the target’s microstructure modification, and thus to a modification of their physical and 

chemical properties. In nuclear materials, for example, exposure to energetic particles can 

cause nuclear materials to weaken, leading to a decrease in their lifespan. Similarly, when 

semiconductor materials undergo ion implantation or irradiation, The defects that form 

can significantly alter the material's electrical and thermal properties [15]. 

The interactions of energetic particles with a target generate collision cascades that will 

give rise to atomic displacements and defects. Heavier particles, such as neutrons and 

heavy ions produce denser collision cascades when compared to particles and/or light 

ions, facilitating the accumulation of point defects. Moreover, the material will have 

temperature effects depending on the cascade density.  

Ion implantation can produce defects such as dislocation loops, precipitates, atomic 

clusters, and Frenkel pairs. This defect forms when an atom or smaller ion (usually a 

cation) leaves its place in the lattice, creating a vacancy (an empty lattice site ), and 

becomes an interstitial by lodging in a nearby location, which interstitial is atoms were 



 

7 

knocked out of their original site, and come to stop in the solid. In some special cases, the 

vacancy may be re-occupied with new atoms identical to their original atom and this is 

called Replacement Collision. Although this may sound complicated, this mechanism 

may reduce the total vacancies by up to 30%. [16]. 

However, the damage and transformation of a material's structure can lead to various 

changes in its properties, such as swelling, local amorphization, and modification of 

chemical, electronic, thermal, and mechanical characteristics. Some examples of 

implantation-induced defects are presented in Figure 1.2. 

Figure 1.2  

Types of implantation-induced defects inside a crystal, including Frenkel pairs (vacancy, 

interstitial), dislocation loops, precipitates, and atomic clusters 

 
Note: Each circle is an atom. Meissner, & Medjdoub, (2024). 

1.2.2 Ceramics  

Ceramics have gained significant attention in the realm of nuclear materials due to their 

exceptional combination of properties that make them well-suited for challenging nuclear 

environments. These inorganic, non-metallic materials exhibit excellent thermal stability, 

corrosion resistance, and remarkable radiation tolerance, making them ideal candidates 

for various nuclear applications [18]. 



 

8 

In nuclear reactors, ceramics are essential structural materials that can withstand high 

temperatures and harsh radiation conditions while retaining their mechanical integrity.  

Zirconium dioxide ( ), and silicon carbide ( ) are exceptional examples of 

ceramics used in nuclear reactor components. Their unique ability to endure extreme 

conditions, coupled with their low neutron absorption characteristics, significantly 

enhances the safety and longevity of nuclear reactors. 

Furthermore, ceramics play a crucial role in the production and containment of nuclear 

fuel, contributing significantly to the overall efficiency and reliability of the nuclear 

energy generation process. Their remarkable versatility and flexibility make them 

indispensable materials in the field of nuclear science and technology [18]. 

A promising category of ceramics for use as structural radiation-resistant materials 

includes nitride ceramics such as AlN, Si3N4, TiN, and ZrN, with AlN being particularly 

noteworthy. The interest in these materials arises from their distinctive properties. 

1.2.2.1 Aluminum nitride (AlN) 

In the quest for technological advancements, aluminum nitride (AlN) has become a 

transformative component with a profound impact across various sectors.  

AlN, a covalently-bonded ceramic, is synthesized from the abundant elements aluminum 

and nitrogen by the carbothermal reduction of aluminum oxide in the presence of gaseous 

nitrogen or ammonia or by direct nitridation of aluminum. AlN has a hexagonal structure 

with strong covalent bonding for crystal and lattice systems; the space group symmetry 

of AlN is P6_3mc and its point group symmetry is C6v, with the dimensions: {a = b = 

3.13A°, c = 5.02A°}, and angles alpha = 90°, beta = 90°, and gamma = 120° [19]. See 

figure 1.3. 

AlN is an extremely hard ceramic material with a molar mass of 20.495g/mol, and it has 

high stability in inert atmospheres at temperatures over 2000°C. Aluminum nitride melts 

at about 2200 °C, and in a vacuum, AlN decomposes at ~1800 °C. [19] [20] 

  



 

9 

Figure 1.3  

Aluminum nitride (AlN) 

Note: (A) AlN synthesized crystal (B) 3-D AlN crystal construction (C) a typical design of AlN. (Jublot-

Leclerc, Bouhali, Pallier, & Declémy, 2021; Hexatech Inc., 2024).  

Aluminum nitride (AlN) was chosen as the focus of study over other nitride materials 

such as Si₃N₄, TiN, and BN due to its exceptional tolerance and resistance to radiation 

damage. Initial experiments demonstrated that AlN could retain its structural integrity 

under neutron fluence levels as high as 5.8 × 10¹⁸ n·cm⁻². Additionally, AlN exhibits 

remarkable resistance to chemical corrosion and boasts a high thermal conductivity of up 

to 321 W/(m·K), surpassing that of GaN. Despite these advantages, AlN is recognized as 

a strong dielectric [21]. 

The versatility of AlN makes it widely used in various industries. AlN distinguishes itself 

as a unique material within the semiconductor realm, as it possesses both an exceptionally 

wide and direct bandgap (Egap = 6.0–6.2 eV), thus its optical absorption/emission in the 

deep ultraviolet (UV) at ~ 200 nm wavelengths, The bandgap value for SiC and GaN is 

almost twice that of AlN, while concurrently exhibiting substantial thermal conductivity 

[23]. 

AlN serves as a substrate for high-power radio-frequency components and power 

modules in the electronics industry. Its high thermal conductivity significantly enhances 

device performance. 

AlN is also used in the field of photonics, where it is used in UV light-emitting diodes 

(LEDs) and photodetectors, leading to advancements in communication and sensing 

technologies. Furthermore, AlN is a stable in the field of acoustic resonators, sensors, and 

actuators due to its unique piezoelectric properties. This unusual combination of 

properties makes AlN a critical advanced material for many future applications in optics, 



 

10 

lighting, electronics, renewable energy, and in the nuclear field as nuclear materials and 

high-power applications [23]. 

The present work aims to investigate the influence of helium on the microstructure of 

aluminum nitride (AlN) single crystals and to test its damage resistance. The effect of 

helium presence in AlN will be investigated by using helium ion implantation in single 

crystalline layers of AlN deposited on a substrate. Then it will be characterized by using 

ion beam analysis techniques to extract the depth distribution of displaced solid atoms as 

a function of fluence and to monitor possible structural transformations, such as the 

amorphization of the material at large fluence. 

1.3 Principles of Microstructure Characterization Techniques  

When a material is exposed to irradiation, either internally or through incident particles 

like ions, electrons, or neutrons, it can undergo various microstructural changes. The 

accumulation of defects during sustained radiation drives microstructural evolution. 

These changes can range from simple point defect formation to complex extended defects 

such as dislocation loops and cavities, and may even result in phase transformations like 

amorphization in crystalline materials. The choice of techniques to determine the extent 

of irradiation damage depends on several factors, including the nature and level of the 

damage, the type of material, and others [24]. 

There are many techniques used for studying the microstructure of nuclear materials 

damaged by irradiation that can characterize point defects as vacancies, interstitials, and 

their associations as Frenkel pairs, but in this study, the focus will be on ion beam analysis 

techniques, in particular Rutherford Backscattering Spectrometry in the Channelling 

mode (RBS-C). 

1.3.1 Ion Beam Analysis 

Ion Beam Analysis (IBA) constitutes a crucial class of modern analytical techniques that 

employ MeV ion beams for investigating the material composition and acquiring 

elemental depth profiles within the near-surface layers of solids. All IBA methodologies 

exhibit remarkable sensitivity, detecting elements down to sub-monolayer levels. 

Typically, the depth resolution falls within the range of a few nanometers to several tens 



 

11 

of nanometers, with the potential for achieving atomic depth resolution when employing 

specialized equipment [25]. 

The analyzed depth spans from a few tens of nanometers to a few tens of micrometers. 

By using channeling, we can accurately determine the depth profile of damage present in 

single crystals. Ion beam analysis is based on the principle of bombarding probing ions 

to a test sample. The interactions between the ions and atoms within the sample lead to 

the emission of various products. This emission provides valuable data about the quantity, 

types, distribution, and structural organization of atoms within the sample. To utilize 

these interactions effectively for determining sample composition, one must carefully 

select a suitable technique, specify irradiation conditions, and choose an optimal detection 

system that can isolate the desired radiation while achieving the desired levels of 

sensitivity and detection limits [26]. 

1.3.1.1 Rutherford Backscattering Spectrometry in Channeling Geometry (RBS-C) 

Rutherford backscattering spectrometry/channeling is a well-established technique based 

on collisions between atomic nuclei and took its name from Ernest Rutherford’s famous 

explanation of alpha particle scattering from thin gold foil in 1911. This method primarily 

relies on the measurement of both the quantity and energy of ions that have been 

backscattered after an elastic collision at a given incident energy and deflection angle 

with the nuclei located close to the surface of the target material [27]. 

The energy exhibited by these backscattered ions hinges on several factors:  

- Their initial energy upon impact. 

- The mass of the target atom they collide with. 

- The depth at which this collision interaction occurs. 

Backscattering may occur only when the projectile is lighter than the nucleus of an atom. 

Therefore, RBS experiments are often conducted using helium ions (or protons, 

deuterons). 

In elastic scattering, total kinetic energy is conserved but the projectile loses part of its 

energy that is given to the target atom. See Figure 1.4. 



 

12 

On the other hand, in an inelastic binary elastic collision, two particles collide and 

perform a single collision where the projectile transfers energy to the particle. The amount 

of energy lost depends on the masses of the particles involved [28]. 

Figure 1.4 

The binary collision model describes a collision between a projectile and target atom, resulting 

in a scattered ion or recoil atom 

 
Note: with masses mp and mt, velocities v0, vt, and VP, and angles θ (scattering) and φ (recoil). Salih, 

(2020). 

In the case of a single crystal, the direction of the incident ion beam (helium ion beam) 

can be chosen to coincide with the direction of the <100> crystal axis. A large number of 

incident ions then enter the target without encountering any atoms, traveling between the 

atomic planes, and the elastic backscattering efficiency is therefore very low in this case: 

this phenomenon is called channeling. 

The channeling technique is a valuable tool that utilizes the principles of Rutherford 

Backscattering (RBS) on a single crystal. Its primary purpose is to investigate crystal 

damage, defect concentration, and epitaxial crystal alignment. By directing an ion beam 

along a major crystal axis or plane, the likelihood of ion-atom interaction is significantly 

reduced. This leads to fewer scattering events and deeper penetration of ions into the 

crystal. Additionally, the ion flux within the channel undergoes redistribution, which 

causes a phenomenon referred to as flux-peaking. This results in a higher ion flux at the 

center of the channel compared to the crystal axis or plane [30]. As a result, when defects 

are not perfectly located in the crystal lattice, there is a greater chance of backscattering 

for incoming ions. 



 

13 

The channeling technique is crucial because it enables the observation of well-aligned 

crystalline lattice site target atoms in the material as rows or planes of periodically 

repeated atoms between ion channels (see Scheme 1.1). Channeling results in a much 

lower number of detections of backscattered ions since the majority of ions channel 

through the crystal with a low probability of being backscattered. This is in contrast to 

the situation where the ion beam is randomly oriented towards the crystal, where only a 

small fraction (approximately 1%) of a backscattered event is recorded. 

To assess the degree of lattice disorder in a sample, it is possible to record a spectrum 

with ions channeling the sample and compare the resulting spectrum with that of a crystal 

exhibiting perfect order or a random spectrum. By doing so, one can obtain a precise 

measure of the level of disorder present. The RBS/C method is especially valuable for 

monitoring a sample’s depth and degree of lattice disorder [31]. 

Scheme 1.1 

Sketch of the channeling phenomenon 

 

Scheme 1.2 illustrates a typical spectrum obtained by RBS and the channeling technique. 

The graph shows three different backscattering spectra recorded under distinct conditions. 

The blue line represents the random spectrum that is obtained when the incident beam is 

randomly oriented towards the crystal. This configuration yields a relatively high 

backscattering signal as the probability of the backscattering of incident ions is high. The 

random spectrum is usually recorded by rotating the crystal around the incident beam at 

a certain open angle. When an ion beam is directed along the crystallographic orientation 



 

14 

of a flawless crystal (perfect crystal without any defects), the number of backscattering 

events decreases significantly as most of the ions pass through the crystal without 

scattering. In this case, only a small fraction of ions may scatter on the lattice atoms, 

resulting in a low signal in the backscattering spectrum compared to a random 

spectrum[32]. 

The green curves in Scheme 1.2 demonstrate this channeling spectrum produced by a 

non-defective crystal. The ratio of the backscattering yield of the axial channeling 

spectrum to that of the random spectrum integrated into a specific energy range is called 

the minimum axial yield (χmin). The theoretical value of χmin for a perfect crystal 

generally ranges from 1% to 2%, depending on the type of crystal. 

If the ion beam is oriented along the crystallographic orientation of a crystal containing 

defects, the backscattering will be improved as compared to the perfect crystal. As the 

defects are present in random positions within the crystalline structure, they function as 

both direct and indirect obstructions to the channeling of the incident beam. The 

obstruction to the incident ion beam at a given depth from the surface of the crystal is 

proportional to the local concentration of defect. The crystal-containing defect will result 

in a higher channeling spectrum compared to the virgin crystal [32]. 

The red curve in Scheme 1.2 represents the channeling spectrum recorded on a crystal 

that has defects. The spectrum consists of three main parts: (i) a surface peak caused by 

ions bouncing back from atoms on the crystal's surface, (ii) a damage peak resulting from 

ions bouncing back from atoms randomly distributed within the crystal's lattice structure 

(the level of this peak indicates the concentration of disordered atoms at a specific depth), 

and (iii) a de-channeling signal due to the small angle. 

  



 

15 

Scheme 1.2 

Typical channeling spectrum of a crystal with defects (red), random spectrum (blue), and 

channeling spectrum of the perfect crystal (green) 

 

Consequently, the RBS-C technique allows for determining the atomic mass and the 

concentrations of various elements present in a solid material concerning its depth. 

Assuming the conservation of momentum and kinetic energy, the scattered projectile 

energy, E1 can be expressed as: 

                                     (2) 

                    (3) 

Where: 

K: the ratio of the projectile energies called the Kinematic factor.  

Eo: the energy of the incident particle 

m1: the mass of the incoming particle 

m2: the mass of the target particle 

θ1: the scattering angle in the laboratory, respectively. 



 

16 

For a given θ1, m1, and Eo, the mass of the target atom determines the energy of the 

backscattered particles. So, in the case of a thin target, the energy spectrum shows several 

peaks corresponding to the mass of each element that constitutes the target [33]. 

In addition to the impact of a charged particle on a material, there is also a loss of energy 

of the projectile ion through electronic excitation when the ion enters and exits the 

material after backscattering. This additional energy dissipation provides valuable 

information about the depth at which the collision event takes place. When the 

backscattering angle is fixed, the analysis of the energies of the ions collected can provide 

information about the elemental composition of the material and the variations in their 

concentration beneath the surface [33]. 

In the energy spectrum, each element is linked to a noticeable peak, whose exact location 

is determined by the principles of energy and momentum conservation. This is also 

known as the kinematic factor. Typically, heavier elements are visible at higher energy 

fronts, while lighter elements are identifiable at lower energy fronts. 

RBS/C measurements presented in this experiment were made using helium ions 

delivered by the ARAMIS accelerator in the JANNuS-Orsay experimental hall of the 

MOSAIC facility, IJCLab [https://mosaic.ijclab.in2p3.fr]. The characterization beam 

uses He+ 1.5 MeV as kinetic energy. The He beam was incident along the [0001] direction 

(c-axis), and the backscattered beam was collected by a detector. RBS/C was conducted 

at RT. 

In addition to the RBS-C technique, there are many characterization techniques as X-ray 

diffraction (XRD) and transmission electron microscopy (TEM) that are complementary 

to each other and allow us to better understand the evolution of the microstructure of a 

material submitted to ion implantation. 

1.3.1.2 XRD Technique 

X-ray diffraction is an essential technique in the characterization of crystalline materials, 

providing insight into the lattice parameters and arrangement of individual atoms within 

a single crystal. It is also useful for analyzing the phase of polycrystalline materials and 

compounds. Understanding XRD and crystallography enables one to determine the 

crystal structure and molecular formula of a crystalline compound. 



 

17 

XRD is a valuable non-destructive technique that can work together with other commonly 

utilized methods such as Rutherford backscattering spectrometry in channeling geometry 

and transmission electron microscopy to identify and analyze irradiation damage in 

crystalline samples [34]. 

XRD operation involves directing an X-ray beam onto the material, resulting in some X-

rays interacting with the atoms in the crystal. In various directions, the X-rays will 

counteract destructively and negate each other. However, in particular directions, the X-

rays encourage constructive interference, creating reinforced diffracted X-rays that 

produce a distinct diffraction pattern. It is these reinforced diffracted X-rays that produce 

the characteristic X-ray diffraction pattern that is used for crystal structure determination. 

While RBS-C provides information on the disorder (fraction of atoms displaced from 

their site), X-ray diffraction is capable of determining the elastic strains and eventual 

changes in lattice parameters caused by irradiation-induced defects in single-crystal 

layers. Point defects, especially interstitial defects, can generate significant elastic strains, 

thus making the technique highly sensitive to even low levels of damage that may not be 

detectable by RBS-C or TEM. As a result, X-ray diffraction can detect damage at an 

earlier stage than other methods [35]. 

1.3.1.3 TEM Technique 

Transmission electron microscopy (TEM) is a popular method for characterizing cavities 

and extended defects such as dislocations, dislocation loops, and stacking faults. By 

bypassing an electron beam through the foil of the material of interest, it's possible to 

obtain local structural and chemical information on a few nanometers or even atomic 

scale with the latest generation of microscopes. This technique is suitable for 

characterizing various materials, whether they are metallic or insulating [36]. 

As an electron beam travels through a sample, it interacts with the material in various 

ways, such as elastic and inelastic interactions. While some parts of the beam pass through 

without any deviation, others are deflected by the crystal planes of the material, which is 

referred to as elastic scattering. Observing the cavities induced by radiation is an essential 

aspect of characterizing nuclear materials. In TEM, these cavities can be viewed by 



 

18 

defocusing the electron beam. If under-focused, the cavities appear bright with a dark 

fringe, while if over-focused, they appear dark with a bright fringe [36]. 

Although transmission electron microscopy (TEM) is a formidable technique, it does 

have its limitations. Specifically, it can only offer information at a highly localized level. 

Furthermore, TEM is not proficient in identifying the global disorder. This stands in 

contrast to the statistical information that can be garnered through methods such as 

Rutherford backscattering spectroscopy in channeling geometry (RBS-C) or X-ray 

diffraction (XRD). 

1.4 Crystallography of AlN  

Crystallography is a scientific field that focuses on understanding the arrangement and 

bonding of atoms in crystalline solids, as well as the geometric structure of crystal lattices. 

Crystallography groups are composed of 32 classes of symmetry derived from 

observations of the external crystal form. From these 32 classes, 230 space groups are 

distinguishable using x-ray analysis. As mentioned in section 1.2.2.1 AlN has a hexagonal 

structure with strong covalent bonding for crystal and lattice system; the space group 

symmetry of AlN is P6_3mc and its point group symmetry is C6v, with the dimensions: 

{a = b = 3.13A°, c = 5.02A°}, and angles (alpha = beta = 90°, and gamma = 120°). 

Materials scientists use crystallography to analyze and characterize different materials. In 

single crystals, the arrangement of atoms is often visible to the naked eye because the 

natural shapes of crystals reflect the atomic structure. Additionally, physical properties 

can be influenced by defects in the crystal structure, making it important to understand 

crystal structures and their defects to know the properties of a material [37]. 

Crystallography helps predict the crystal's behavior under different conditions, enabling 

us to explain experimental results accurately. This information is vital for understanding 

crystal stability, chemical bonding, and the overall crystal structure. Modern software 

programs have become a vital asset for researchers and materials scientists across 

multiple disciplines. Using these software programs has proven to be crucial in advancing 

the understanding of materials and their properties [38]. 



 

19 

This study employed two highly specialized and efficient crystallography software: Vesta 

and CaRIne. Vesta is known for its versatility in crystal structure visualization and 

analysis, while CaRIne specializes in the analysis of diffuse scattering in crystallography. 

1.4.1 VESTA, CaRIne crystallography programs  

VESTA and CaRIne Crystallography programs are 3D visualization programs for 

structural, crystal morphologies models, and volumetric data like (nuclear\electron) 

densities. They also can deal with multiple structural models, crystal morphologies 

models, and volumetric data at the same window, and they give all information as output 

files. 

VESTA Crystallography Software, which stands for Visualization of Electron/Nuclear 

and Structures Analysis, is a versatile program mainly used for visualizing and analyzing 

crystal structures. The software was developed by Professor Koichi Momma and has 

gained popularity due to its user-friendly interface and robust capabilities. VESTA 

enables researchers to create, view, and manipulate crystal structures easily. It supports a 

wide range of crystallographic file formats, making it a versatile tool for 

crystallographers. In addition to visualization, Vesta provides powerful tools for 

analyzing crystal structures, including symmetry operations, coordination polyhedral, and 

electron density maps [39]. 

CaRIne Crystallography Software is a specialized program designed to analyze diffuse 

scattering in crystallography. It meets the intricate demands of crystallographers and 

materials scientists, particularly when it comes to analyzing diffuse scattering in crystal 

structures. With its specialized capabilities, CaRIne allows researchers to explore and 

measure structural defects, vacancies, and other irregularities in crystalline materials [40]. 

It excels in revealing insights into the complexity of disordered materials, making it an 

invaluable tool for studying glasses, complex oxides, biomaterials, and other substances 

with non-ideal crystal structures. CaRIne's advanced data fitting algorithms and 

comprehensive analysis tools give scientists the power to delve deep into the structural 

intricacies of materials, improving our understanding of their properties and behavior, 

and facilitating breakthroughs in materials science. To fully understand how materials 

like AlN respond to irradiation, it's crucial to have a comprehensive understanding of 



 

20 

crystallography. This understanding hinges on the capacity to discern the arrangement of 

atoms or molecules within the crystal lattice [41]. 

Crystallography also plays a vital role in identifying the principal axis in AlN crystals. 

This information is crucial in aligning the ion beam with the crystal axis during RBS/C 

analysis, which in turn determines the trajectory of the ion beam during experiments. 

1.5 Simulation software for irradiation and ion beam analysis  

Simulation software plays a crucial role in the field of irradiation and ion beam analysis 

(IBA), as it enables researchers to replicate complex atomic and molecular processes. 

Simulation software in irradiation and ion beam analysis before and after conducting 

experiments is preferred due to its ease of use, efficiency, and flexibility. 

These techniques simplify complex models into basic events and interactions, making it 

possible to encode model behavior through a set of rules that can be implemented on a 

computer with ease. This, in turn, enables researchers to develop and study much more 

general models on a computer than they could by using analytical methods [42]. 

Moreover, simulation software algorithms can be highly scalable, which means that the 

complexity of a simulation program would typically not depend on the number of 

processes involved. Additionally, many algorithms employed in simulation software can 

be parallelized, making it possible to run different parts of the program on different 

computers and processors, thereby reducing the computation time significantly [43]. 

Through these simulation programs, researchers can obtain a clear initial picture of the 

results that can be expected after practical experimentation, which saves them a great deal 

of time, effort, and money. 

1.5.1 SRIM simulation  

In simulations of a beam of ions hitting a target, variations in the impact parameters of 

each ion are made to produce different outcomes. The impact parameter is defined as the 

distance at which particles would pass each other if no forces acted between them. The 

simulations have an average error of 2%, except for heavy ions in light targets where the 

error is 5% due to a lack of experimental data to correct the calculations [44]. 



 

21 

The Stopping and Range of Ions in Matter (SRIM) software uses the binary collision 

approximation in its Monte Carlo method, which assumes that the ion moves through the 

target by experiencing a series of elastic collisions with the atoms in the material. The ion 

always moves in a straight line and loses its energy to the target electrons through 

electronic stopping power. The target is assumed to be fully amorphous, and the distance 

between each collision is equal to N−1/3, where N is the atomic density of the material.  

A collision integral is evaluated to calculate the scattering angle and energy loss of a 

binary collision. This collision integral is a complex mathematically constructed equation 

based on interatomic potentials between the ion and the atom. In a solid target, ions get 

implanted, and the surface changes during the collision experiment. However, SRIM 

assumes a target with a fixed composition and does not track such changes.  

It is important to note that after multiple approximations, the computation time of SRIM 

is significantly reduced. However, for accurate analysis, the approximation methods used 

must be considered [45]. In simulations of a beam of ions hitting a target, variations in 

the impact parameters of each ion are made to produce different outcomes.  

In conclusion, the SRIM package is used for a variety of applications, such as: 

1. Calculate the energy loss of ions in matter, which produces tables of stopping powers, 

range, and range straggling distributions for any ion at any energy in any elemental 

target. This tool is also used in more complex calculations involving targets with 

multi-layer configurations.  

2. Ion implantation uses ion beams to modify samples by injecting atoms to change the 

target's chemical and electronic properties. This process also causes damage to solid 

targets through atom displacement, and the SRIM package contains part of the kinetic 

effects associated with this kind of interaction. 

3. Calculate sputtering, which occurs when the ion beam knocks out target atoms. Any 

ion can perform this process at any energy. Ion transmission is another application 

of SRIM, which allows ion beams to be followed through mixed gas/solid target 

layers, as is the case in ionization chambers or in energy degrader blocks used to 

reduce ion beam energies [46]. 

  



 

22 

1.5.2 RUMP 

In 1976, Ziegler and colleagues published the first code capable of performing full 

Rutherford backscattering (RBS) spectrum simulations, called IBA. In the following 

decade, several codes emerged, the most popular of which was RUMP. RUMP 

(Rutherford Universal Manipulation Program) is a software tool designed for RBS 

(Rutherford Backscattering Spectrometry) plotting, analysis, and simulation. [47] 

The RUMP software enables users to plot real RBS random and aligned spectra, as well 

as user-provided simulation spectra, based on various factors such as energy calibration, 

composition, and experimental parameters. 

These experimental data include the geometry of the detector and the energy of the 

incident ions. The simulation spectrum depends on the user's entry of the chemical 

composition, as each chemical element contributes differently to the yield. [48] 

This method allows for the identification of the composition that matches the actual 

spectrum or the chemical composition of the crystal. RUMP helps extract valuable 

information regarding the elemental composition, depth profiles, and structural 

characteristics of materials, thus significantly enhancing the efficiency and precision of 

RBS analysis. This software plays a crucial role in advancing our understanding of 

atomic-scale properties and contributing significantly to the field of materials 

characterization [49]. 

1.5.3 Monte-Carlo (McChasy)  

The McChasy simulation code, developed at NCBJ Warsaw, is a Monte Carlo code used 

to simulate the trajectories of ions in a crystal. This helps to calculate the expected ion 

channeling spectra, assuming a given (defective) structure. McChasy stands for "Monte 

Carlo Channeling Simulation code". [50] 

McChasy is a simulation tool that helps researchers in materials science gain a better 

understanding of the complex phenomena of ion channeling into crystals. The tool uses 

the Monte Carlo simulation technique which is specifically tailored for investigating how 

ion beams interact with crystalline structures. With McChasy, researchers can predict and 

analyze various outcomes of processes such as radiation damage and structural 

alterations. The tool can also calculate the backscattering energy spectra obtained at 



 

23 

channeling, random, or any specific angle between the projectile and the normal to the 

target's surface [50]. 

McChasy's Monte Carlo method involves the random sampling of probabilistic events 

such as ion collisions and energy transfers to simulate the behavior of particles over time. 

Additionally, McChasy is versatile enough to simulate complex depth distribution of 

defects and their nature, making it an indispensable tool for researchers who seek a deep 

and nuanced understanding of material behavior through computational modeling. The 

provided code presupposes a specified crystal structure and permits the incorporation of 

various structural defects. These defects include the amorphization of a fraction of matrix 

atoms within a designated sublattice, termed randomly displaced atoms, and dislocations 

characterized by size and density. The concentrations of structural defects can be 

specified at any depth. Comparing the calculated spectra with experimental data allows 

the extraction of pertinent information regarding the distribution of defects in the actual 

crystal [51]. 

Defining several parameters in the initial stage is crucial for accurate results. These 

parameters encompass crystallographic structure, composition, experimental geometry 

input/output angles, characteristics or parameters of the incident beam, and detector 

parameters. In Monte Carlo simulations, the crystal is divided into several layers with 

increasing depth. A random initial impact parameter (p0) is selected from a uniform 

distribution, and changes to it are then calculated. The simulation uses a Coulomb-

screened potential to model interactions between ions and atoms, which determines the 

path of the incoming particle. It is important to mention that McChasy consistently 

employs a single crystal cell, apart from an initial random selection of the impact 

parameter [52]. 

The Monte Carlo simulation method offers a significant advantage as it enables a 

quantitative examination of crystals with a range of authentic defects, unlike traditional 

dechanneling studies that rely on simplified defect models and analytical analysis of 

experimental spectra. 

  



 

24 

1.6 Objectives of the Study  

The aim of this thesis is to investigate the influence of helium on the microstructure of 

aluminum nitride (AlN) single crystals, focusing on the helium concentration and ion 

implantation temperature. The damage will be characterized using Rutherford 

Backscattering Spectrometry in Channelling geometry (RBS\C) technique.  

The effect of helium presence in AlN will be explored using single crystalline layers of 

AlN deposited on a substrate as a model system. These crystals will be bombarded with 

energetic He ions at the JANNuS-Orsay experimental hall located at the MOSAIC 

facility, IJCLab, to simulate helium presence. 

The He-implanted single crystals will be characterized using ion channeling of light ions 

and Rutherford backscattering spectrometry to extract the depth distribution of displaced 

solid atoms and monitor structural transformations, such as material amorphization at 

large fluence. Monte Carlo simulation code will be utilized for a full analysis of 

experimental spectra to quantify radiation effects as a function of bombarding particle 

fluence. 

Various models of radiation-induced defects will be tested to simulate experimental ion 

channeling spectra and achieve a comprehensive description of crystal evolution from 

lightly damaged to the highest envisaged irradiation fluences expected in a fusion system. 

These steps will be taken to propose a model of crystalline defects creation in AlN and 

its healing rates based on sample chemistry, temperature, and to determine the viability 

of AlN as a nuclear material in a nuclear reactor. 

The results obtained in this internship will be used to complete those obtained during 

Gabriel Bouhali's Ph.D. thesis (ED PHENIICS, IJCLab, defense on 21st December 2023). 

  



 

25 

Chapter Two 

Experimental Work: Materials and methods 

All of the experimental work in this master thesis was performed within the CHIMèNE 

team (Chemistry, Irradiation, Materials, Modeling, and Electrochemistry for Nuclear 

Energy), and in particular the Material and irradiation theme, at the Energy & 

Environment pole at IJCLab, the Laboratory of the 2 Infinities Irène Joliot-Curie, located 

on the Orsay campus, France. Some of the equipment of the MOSAIC ion beam facility 

was used, in particular the ARAMIS ion accelerator located in the JANNuS-Orsay 

experimental hall [53]. 

AlN crystals were prepared, implanted, and irradiated with ions to make the crystals ready 

before the first characterization by Rutherford Backscattering Spectrometry in 

Channelling Geometry (RBS/C) and other analysis methods. 

2.1 Sample preparation and Ion implantation irradiation (as-received condition) 

The aluminum nitride (AlN) sample preparation process consists of many steps including: 

- Starting with synthesizing the crystal. An AlN epitaxial film with a thickness of 4μm 

was deposited on a substrate with a thickness of 300μm, composed of Al2O3 Ceramic 

Substrate (ADS-996) and grown by MTi, which was previously purchased [54]. 

(MTi: name of the substrate company which used to grow the samples on it). 

- The second step was crystal cutting, as the as-received wafer was typically a 10 cm 

diameter circle, while only a roughly 1 cm² specimen was required for damage 

characterization under a single irradiation condition. Since AlN was a tough crystal, 

the machine used for this step featured a diamond edge.  

- The next step was cleaning: after cutting, it was necessary to remove all dust and any 

material layers adsorbed on the surface of the sample by cleaning the pieces in an 

acetone and ethanol bath (as described in 2.4). 

- The final step was the deposition of a thin carbon layer on the surface, mandatory for 

ion beam analysis of insulating materials (see details in paragraph 2.4), to avoid 

charge effects due to the insulating material. 



 

26 

The as-received samples are then ready for as-received characterization using ion beam 

analysis (and more specifically RBS/C, see its principle in paragraph 2.5), and for ion 

irradiation. 

The ion implantation in this experiment has been performed using a 190 kV IRMA ion 

implanter and/or the 2MV ARAMIS ion accelerator. IRMA and ARAMIS are two of the 

4 ion beam accelerators of the MOSAIC facility, located in the JANNuS-Orsay 

experimental hall, the other ones are SIDONIE and Andromède.  

ARAMIS is an ion accelerator with a nominal voltage of 2 MV, which was developed in 

the laboratory in the 80s. Equipped with various sample holders, the ARAMIS ion 

accelerator allows a wide range of ion irradiation and material synthesis analysis studies 

to be carried out. 

Thirty five chemical elements are available from one of the two ARAMIS ion sources (a 

positive source (Penning type) and a negative source (Middleton)) and make it possible 

to carry out ion beam analysis and ion implantation and “self-irradiation” damage studies 

(including “self-irradiation”, without adding chemical pollution, i.e. choosing an element 

already present in the specimen to be irradiated), with fluxes between 1×109 and 1×1012 

at/(s.cm2) [53]. The irradiation temperature can vary from -170°C to 1000°C, as seen in 

Figure 2.1. 

The IRMA ion implanter can deliver ion beams of 65 different chemical elements, with 

energies ranging from 5 to 570 keV, allowing materials to be modified up to 500 nm in 

depth.  

The three ion beam accelerators have different features (for example ARAMIS has both 

a positive source (Penning type) and a negative source (Middleton). In contrast, the two 

others have only a positive source), different ranges of energy, and different usages and 

operating temperatures of -170 - 1000o C. 

 

 

  



 

27 

Figure 2.1 

Sample preparation and Ion implantation irradiation (as-received condition) 

 
Note: (a) Operating energy range and elements available to accelerate as an ion beam in ARAMIS, IRMA, 

and SIDONIE accelerators. (b) Overview of the JANNuS-Orsay experimental hall/MOSAIC platform. 

Ishikawa, et al. (2000). 

The accelerators ARAMIS and IRMA are connected, and there are 5 beamlines in the 

hall. One of these lines is for Ion Beam Analysis (IBA), which is used for the structural 

and chemical characterization of materials using Rutherford Backscattering Spectrometry 

(RBS, RBS/C), Particle-Induced X-ray Emission (PIXE), and Elastic Recoil Detection 

Analysis (ERDA). Two beamlines are custom to the ion implantation/irradiation process, 

and the last two lines are employed for connecting the accelerators IRMA and ARAMIS 

to a Transmission Electron Microscope (TEM), allowing in situ observation at the 

(a) 

(b) 



 

28 

nanoscale of modifications induced in a material by ion irradiation with one or two ion 

beams.  

6 samples of AlN were irradiated with different fluences (number of ions/cm2) with a 

beam of Au+ ions at an energy of 6 MeV. 

Irradiations were performed at room temperature (RT) to fluences between (3.1*1014 cm-

2, and 4*1015 cm2), One sample was kept virgin (without ion irradiation, in the as-received 

state), as shown in Table 2.1. Ion irradiations were performed at 7o off the (0001) surface.  

Table 2.1 

Implantation fluences were used to implant the crystals with 6MeV Au+ ions at room temperature 

Sample Fluence (cm-2) 

φ0 (virgin) 0 

φ 1 3.1x1014 

φ 2 7x1014 

φ 3 1.5x1015 

φ 4 2.2x1015 

φ 5 3.0x1015 

φ 6 4.0x1015 
 

2.2 SRIM simulation  

Before the experiment, the SRIM simulation program was utilized to gain a more accurate 

understanding of the ion implantation/irradiation process (the deposition of ions into a 

target material). SRIM simulations provide predictions of ion behavior as they penetrate 

the material, calculating ion ranges (depth), energy distributions, and damage profiles. 

These predictions are essential for understanding and controlling the ion implantation 

process prior to conducting RBS-C analysis. 

For this study, SRIM simulations were performed on the AlN crystal under the same 

conditions used in the irradiation process. This included a 7° angle offset relative to the 

ion beam, nearly perpendicular to the specimen surface. The simulations were conducted 

for Au⁺ ions with an energy of 6 MeV, as well as other ions (He ions at 50 keV and Al 

ions at 280 keV) to compare the damage profiles in AlN crystals resulting from different 

ion types and energies. See Figure 2.2 for details. 



 

29 

Figure 2.2 

Depth profiles of implanted ions with different energies in the AlN target at a 7° angle using the 

SRIM simulation program  

 

Note: (a) 6MeV Au+ ion beam (b) He (50keV) ion beam (c) Al (280 keV) ion beam. 

After the simulation was done, the number of displacements per atom (dpa), and the 

concentration of implanted ions in the target crystal were calculated by using equations 2 

and 3 based on the simulation results. 

The number of displacements per atom (dpa) (used to measure the damage in an irradiated 

material), was calculated by using equation 4: 

 dpa= N displaced atoms/N total atoms = (N displ. atom/V)/ (N total. atom/V)                       (4) 

where (N displ. atom/V) = (N displ. atom/ɸ)/ Δx  

=  
[
Ndispl.stom

∆x ]
SRIM

[
Nions

S ]

[
N
V]

atom

 

so dpa =  
[

Ndispl.stom

∆x
]

SRIM

 Φ𝑖𝑜𝑛𝑠

[
N

V
]
atom

  

With: 

N displaced atoms: number of displaced atoms 

N total atoms: number of total atoms 

V: volume (cm3) 

ɸ: the fluence (at.cm-2) 

Δx: target depth (Ang.) 

S: irradiated area of the layer  



 

30 

The impurity fraction that was incorporated into the material during the ion 

implantation/irradiation process was calculated by using Equation 5: 

                         (5) 

This can also be expressed as: 

                       (6) 

Where: 

N/V: represents the number density per unit volume. 

N/S: represents the number density per unit surface area. 

ϕ: is the related factor for impurities.(at.cm-2) 

All results of these simulations will be discussed in Chapter 3.  

2.3 Crystallography of AlN  

As mentioned in the introduction, defects are a common occurrence in both natural and 

industrial crystals, as perfect crystals don't exist. When crystals are exposed to ion beam 

irradiation, there is an increase in displaced crystal atoms, resulting in the formation of 

Frenkel pairs defect. This displacement can alter the positions of atoms, causing damage 

to the crystallographic lattice, affecting specific orientations, or even leading to 

amorphization. Understanding the crystallography of a material, such as AlN in this 

study, is crucial for predicting its response to irradiation. It allows us to determine the 

arrangement of atoms or molecules within the crystal lattice, providing insights into its 

behavior under irradiation. 

Crystallography also helps to know what the main axis in the AlN crystal is, which is 

important for aligning this main axis with the ion beam used during RBS/C analysis, thus 

choosing the path that the ion beam will follow during RBS-C ion beam analysis 

experiments. There are two different paths used by the ion beam in our RBS-C analysis 

of AlN single crystals: one is aligned along the c-axis of the crystal, and the other one is 

random. In an aligned ion beam, the line axis's orientation or the beam's channels will be 

known. In the random path, the orientation of the crystal keeps changing randomly so it 



 

31 

can get the maximum yield of backscattered atoms because the ion beam will collide with 

a high number of displaced atoms in the crystal. 

The hexagonal AlN crystal, belonging to the P6₃mc space group, with dimensions {a = b 

= 313 pm, c = 502 pm} and angles {α = β = 90°, γ = 120°}, was modeled using the Vesta 

crystallography software program [32]. This process included determining the four 

principal axes: a₁ [2-10], a₂ [-120], a₃ [-1-10], and c [001]. The results of this analysis are 

presented in Scheme 2.1. 

Scheme 2.1 

Crystallography of AlN 

 

Note: (a) Example of an input file from Vesta crystallography software program to draw the hexagonal AlN 

crystal (b) The main four axes in the crystallographic structure of AlN crystal (1) a1 [2 -1 0] (2) a2 [ -1 2 0] 

(3) a3 [-1 -1 0] (4) c [0 0 1]. 

(a) 

(b) 



 

32 

2.4 Carbon layer deposition 

The final step in preparing the AlN crystal for RBS-C analysis involved depositing a 

graphite layer onto the polished surface of the samples. This step, which adds a 

conductive carbon layer, was crucial to prevent surface charge effects (charge 

accumulation) during the RBS characterization, ensuring accurate and reliable analysis. 

Without the carbon layer, the He ions used in RBS analysis would accumulate on the 

crystal's surface due to the insulating nature of AlN. This charge buildup would distort 

the RBS spectrum, rendering it unanalyzable. 

Prior to depositing the carbon layer, all samples were thoroughly cleaned using acetone 

(CH₃COCH₃) followed by ethanol (C₂H₅OH) to ensure the removal of any surface 

impurities. The AlN crystal features two distinct sides: the polished (shiny) side, 

corresponding to the AlN layer, and the substrate side. The carbon deposition was 

specifically carried out on the polished AlN side. The carbon deposition process was 

carried out in multiple steps. In each step, by using carbon rods a very thin carbon layer 

was deposited sequentially onto the surfaces of six samples in the following thicknesses: 

0.4 nm, 0.8 nm, 0.4 nm, 0.4 nm, 0.8 nm, 0.4 nm, 0.8 nm, 0.4 nm, 0.4 nm, 0.4 nm, and 1.2 

nm. This process resulted in a total carbon layer thickness of 6.4 nm. 

The deposit process was done using a carbon coater machine (Cressington carbon coater), 

see Figure 2.3 (a). The carbon coater machine was coupled to a pump responsible for 

providing a vacuum inside the system. Electric current was then passed through a thin 

graphite wire resulting in its evaporation and deposition to the samples located below it. 

With the carbon conductivity, no electric charge accumulates at the crystal surface and 

He+ ions used during the RBS/C analysis can then penetrate inside the crystal and be 

backscattered to the detector providing reliable elastic backscattering spectra. After 

finishing the previous process, all samples were fixed on a metallic holder one by one in 

a specific order using carbon tape in a specific order (see Figure 2.3 (b)). 

  



 

33 

Figure 2.3 

Carbon layer deposition 

 
Note: (a) A carbon coater machine (Cressington carbon coater) is used to deposit a graphite layer on the 

face-polished crystals (b) The aluminum holder containing the samples is fixed by using carbon tape.  

2.5 Rutherford Backscattering Spectrometry (RBS-C) experiment 

Rutherford Backscattering Spectrometry in Channeling geometry (RBS-C) is a highly 

effective tool for analyzing the damage caused by He+ ion irradiation in AlN crystals. 

When energetic ions such as He+ collide with a crystal lattice, they can displace atoms 

from their regular positions, create vacancies, and induce structural defects. 

RBS-C can precisely determine the extent and nature of this damage by measuring the 

backscattered incident helium ion’s energy and angles. By comparing the spectra before 

and after 6 MeV Au+ ion bombardment, the information about the density of defects, such 

as vacancies or interstitials, as well as their distribution within the crystal lattice, can be 

determined. RBS-C analysis is crucial for understanding the response of materials to 

radiation or ion implantation, aiding in the development of radiation-resistant materials, 

and advancing applications in semiconductor manufacturing and nuclear materials 

research. 

In this experiment, RBS-C was performed using helium ions delivered by the ARAMIS 

accelerator in the JANNuS-Orsay. The beamline used to experiment is equipped with a 

suitable sample holder (made of aluminum) to hold the samples at a correct angle and a 

holder to fix the detector at a suitable angle as well. The scattering angle was constant at 

15°. 



 

34 

The sample holder is remotely movable for the beam to cover all the samples. The 

characterization beam uses He+ 1.5 MeV as kinetic energy, this value of the energy was 

selected since it allows a good separation of the various chemical elements of the AlN 

crystal while keeping a good depth resolution that allows the depth distribution of defects 

to be extracted by channeling with good precision. 

Before starting the analysis, an alignment procedure of the goniometer was made to align 

the ion beam direction with the main axis [c axis 0001] for all of the AlN samples. 

Furthermore, adjustments were carried out in both the horizontal (x) and vertical (y) 

directions to ensure that the beam fully struck the crystal without any portion of it hitting 

the holder, this confirmation was achieved by capturing RBS yield spectra while 

operating the goniometer in random mode, involving continuous rotation (within a 4-

degree cone) relative to the major crystal axis. If the spectrum presents a characteristic 

front for the various atoms that constitute AlN and does not present the aluminum signal 

of the holder, then the beam is said to be impinging on the sample, this can be confirmed 

by recording spectra at multiple positions along the crystal, spanning from one end to the 

other. 

The primary c-axis for ion channeling was determined by carrying out angular 

displacements in the rotation angle (α) around the y-axis, and rotation angle (β) around 

the x-axis of the goniometer. This process aimed to identify specific (α, β) coordinates to 

exhibit the lowest backscattering yields. The dose (charge) was systematically varied at 

regular intervals to enhance the statistical data collection for the AlN crystal. The current 

was adjusted automatically to maintain a constant ion beam fluence.  

The first RBS-C spectra showed that there is a charge effect in the AlN samples, this 

charging effect appeared because the carbon layer was not thick enough to prevent it. 

An extra 7 nm of carbon was deposited on each AlN sample, and the total carbon layer 

thickness for the 6 samples was 13.4nm, as a precaution all carbon tape used to fix the 

sample was removed by dissolving it with alcohol (acetone\ methanol), and instead of 

carbon tape, metallic pieces were used to fix the samples. The final RBS-C spectra were 

collected with no charge effect in the AlN samples.  



 

35 

All recorded RBS-C spectra (random and aligned) which show the various fronts 

corresponding to the various chemical elements, will be discussed in section 3.2 in 

Chapter Three.  

2.6 Analysis of the RBS-C experimental spectra 

The interpretation of experimental spectra generated by the RBS-C experiment is a 

crucial and intricate process that enables us to gain insights into the composition and 

structure of materials, as well as the damage sustained by the AlN crystal. To extract 

useful information from the data collected, by using McChasy code and RUMP 

software.  

2.6.1 RUMP simulation 

The Rutherford Universal Manipulation Program (RUMP) is a sophisticated tool that 

streamlines RBS plotting, analysis, and simulation. It empowers users to create authentic 

RBS random and aligned spectra and simulate spectra by adjusting factors like energy 

calibration, composition, and experimental parameters that are needed for subsequent 

McChasy simulations. The simulated spectrum is influenced by the chemical composition 

the user provides, as each element uniquely impacts the yield.  

The first step in this analysis is writing a code that will be run by RUMP software to graph 

the experimental data obtained through (RBS) for all of the AlN samples, as shown in 

Figure 2.4. This process involves considering a range of parameters, including the energy 

of the incident particles, the composition of the target material, and the scattering angles, 

to construct a model that accurately represents the interaction between the incident 

particles and the target material.  

The composition and thickness of the layers formed were determined by simulating the 

experimental spectra RBS obtained by the RUMP software with standard experimental 

conditions, particle beam He+, 1.5 MeV energy, at an angle of detection of 165°.  

All results of these simulations are shown and discussed in Chapter 3.  

 

 



 

36 

Figure 2.4 

RUMP simulation 

  

Note: Figure (a) (b) describes the codes employed by RUMP software to graph the experimental data 

obtained through the (RBS) technique for all samples of (AlN). 

  

(a) 

(b) 



 

37 

2.6.2 McChasy simulation  

McChasy (abbreviation for Monte-Carlo CHAnnelling SImulation) is a technique that 

uses computational methods to replicate the movement of ions in crystals. This enables 

the creation of simulated Rutherford Backscattering Spectroscopy (RBS) spectra that can 

be compared with experimental data. The development of this method was based on the 

groundbreaking work of Barrett. 

The simulations involve computing ion trajectories through a series of iterations. At each 

iteration, the deflection of ions is determined, taking into account factors such as the 

screened Coulomb potential (the Coulomb potential describes the electrostatic interaction 

between ions and atomic nuclei or electrons. The screened Coulomb potential accounts 

for electron cloud effects, reducing the force at longer distances and enabling accurate 

modeling of ion deflection in the crystal lattice), thermal vibrations of atoms, and energy 

loss within a specific depth interval in the crystal. The normalized nuclear encounter 

probability (NEP) is then determined and used in the simulation process. The McChasy 

code was used to analyze the experimental RBS/C spectra in this study. The McChasy 

code simulates the trajectory of light ions (He+) traveling through AlN crystals; the code 

performs efficiently when dealing with heterostructures, superlattices, and materials that 

contain complex defects. The software also employs independent depth profiles of 

various defect types, such as interstitials, edge dislocations, substitutions, stacking faults, 

and grain boundaries to provide a fitting procedure for RBS/C spectra. The fitting 

procedure generates calculated channeling spectra as output that can be used to facilitate 

further analysis of the sample's structural properties [51]. 

The McChasy code's simulation outputs were observed to be in excellent alignment with 

the recorded spectra. The McChasy program follows a three-step process to conduct its 

analysis. The initial step in the McChasy simulation process involves the creation of an 

input file and this input file continues all experimental data, including ion beam 

characteristics, target characteristics, experiment geometry, crystal structure, chemical 

composition, thermal vibration, the solid angle of detector, incident and backscattering 

angle, nature of analyzing ion, energy, beam divergence, and energy resolution were 

inputted as a file into the code. For each Au+ fluence, which corresponds to a different 

RBS/C spectrum, the fraction of radiation-induced defects at a given depth (RDA) was 

set as input in the MC simulation. Next, the crystal is divided into thin layers and the 



 

38 

McChasy simulation provides an estimate of the concentration of the defects for each 

layer. The McChasy code employs a formula based on Monte Carlo ion trajectory 

simulation methods, emphasizing interaction probabilities between ions and the crystal 

lattice. 

While the exact formula is not detailed in the paragraph, the process relies on key 

principles such as: 

- Screened Coulomb potential for ion-atom interactions. A typical formula for the 

interaction might be: 

Here: 

                                        (7) 

Z1 and Z2: Atomic numbers of the ion and target atom. 

e: Elementary charge. 

ϵ0: Vacuum permittivity. 

r: Distance between the interacting particles. 

ϕ(r/a)): Screening function, with aa being the screening length. 

- Nuclear and electronic stopping powers, which describe energy loss by the ions: 

                                            (8) 

Where: 

Sn: Nuclear stopping power (collisions with nuclei). 

Se: Electronic stopping power (energy loss to electrons). 

- Radiation Defect Accumulation (RDA): The input fraction of radiation-induced 

defects is likely modeled using depth-dependent probability distributions to estimate 

defect concentrations in each crystal layer. This is often linked to nuclear stopping 

interactions. 

  



 

39 

The simulation is then run, producing a channeling spectrum that details the 

backscattering events at each acquisition channel, and the calculated and experimental 

spectra are compared. If necessary, the defect concentration can be adjusted to improve 

the fit. This updated input file is used to rerun the simulation code, and the process repeats 

until an optimal fit is achieved. Finally, the acquired spectra are normalized to enable 

comparison with experimental data. 

The simulation is a time-consuming and labor-intensive process demanding proficiency 

and self-assessment. It involves numerous runs of systematically adjusting the depth 

distribution of defects to achieve a resemblance to the experimental spectrum. 

The progression of the damage-depth distribution with ion fluence is obtained and 

scrutinized. Table 2.2 illustrates an example of a typical input file used in the study, where 

the data helps determine the optimal depth distribution of RDA defects that closely 

replicates the experimentally captured aligned spectra. 

 

  



 

40 

Table 2.2 

Example of an input file from McChasy code for different RDAs that were used 

 

Note: The first column at left is a command to the code corresponding to a parameter to be fixed followed 

by its name or by its value (in this example PRO helium is the He probing ion and ENE 1496 its energy in 

keV)  



 

41 

Chapter Three 

Results and Discussion 

3.1 SRIM simulation results: depth profiles, impurity fraction (at%), and damage 

(dpa) 

A calculation using SRIM was performed to estimate the stopping and range of various 

projectiles in an AlN crystal. The SRIM data was also used to determine the damage 

distribution in the crystal after simulated implantation with 6MeV Au+ ion, by drawing a 

graph showing the total number of vacancies in the crystal as a function of depth 

(measured in nanometers), depth profiles refer to the distribution of implanted ions, 

impurities, or damage as a function of depth within the target material. 

These profiles provide insight into how ions penetrate and interact with the material, 

showing how far the ions travel, their concentration at various depths, and where they 

primarily accumulate or cause structural modifications. 

Scheme 3.1 shows that at the maximum fluence for 6MeV Au at a depth of 860.001nm, 

the maximum number of total vacancies (maximum damage) is 2.08 . As a result, it can 

be observed that there are different interactions between ions and AlN crystals depending 

on ion mass and energy, for example, the point of using 6MeV Au is to create a large 

cascade of damage by using heavy elements, as observed from Scheme 3.1 

When ions are implanted into materials, they create damage by transferring energy to the 

orbital electrons and nuclei that make up the material. As the ions travel through the 

material, they lose energy, which causes changes and damage to the material. The amount 

of energy transferred is not constant and depends on collisions. This transfer of energy 

depends on factors such as the nature and initial energy of the ion, as well as the 

constituents of the material it passes through. [42][54] 

 

 

 

  



 

42 

Scheme 3.1 

The damage distributions (at the maximum fluence) for each of (a) 6MeV Au+, (b) 50 keV He+ 

ion, and (c) 280 keV Al ion, were calculated according to the SRIM code 

 

The results obtained from Figure 3.1 were used to calculate the number of displacements 

per atom (dpa) for Au+ ions induced during the irradiation using Equation 4, as shown in 

Table 3.1.  

Theoretically, the material damage is directly related to the displacements per atom (dpa) 

via the residual defects from induced displacements. However, in practice, the material 

damage is based on a correlation to the high-energy (E > 1.0 MeV) neutron fluence.  

Where dpa as mentioned before, stands for Displacements Per Atom, is a standard 

parameter used to determine the amount of radiation damage in materials. It is an 

important measure that takes into account both the material response (displaced atoms) 

and the magnitude and spectrum of the neutron fluence to which the material was 

exposed. dpa is a useful metric for comparing the radiation effects of low-energy ions 

under different conditions. The dpa can vary depending on the ion's mass and energy. 

As seen in Table 3.1 the relationship between fluence and the dpa is a direct correlation 

and a proportional relationship. 

  



 

43 

Table 3.1  

The number of displacements per atom (dpa), which were calculated using Equation 4 by using 

different fluence of Au+ ions. 

Fluence (cm-2) dpa 

3.1x1014 0.7 

7x1014 1.5 

1.5x1015 3.3 

2.2x1015 4.8 

3x1015 6.5 

4x1015 8.7 
 

Also, the ion range for Au+ ion was determined by using SRIM simulation data as seen 

in Scheme 3.2 

Scheme 3.2 

The Ion range (at the maximum fluence (4x1015)) for 6MeV Au+ 

 

By using data from Scheme 3.2 the impurity fraction that was incorporated into the 

material during the ion implantation/irradiation process was calculated using Equation 5 

  



 

44 

Table 3.2 

The impurity fraction at 100%, which was calculated using Equation 5 by using different 

fluence of Au+ ions 

Fluence (cm-2) impurity fraction at 100% 

3.1x1014 0.01 

7x1014 0.02 

1.5x1015 0.05 

2.2x1015 0.07 

3x1015 0.09 

4x1015 0.13 
 

Table 3.1 shows a direct and proportional correlation between fluence and impurity 

fraction. 

3.2 Data analysis of the RBS-C spectra  

To thoroughly examine the elemental composition, depth profile, and defect formation 

within AlN crystals implanted with Au+, RBS-C spectra analysis is required. As 

mentioned before, when Au+ ions are implanted into AlN crystals, they can cause defects 

like vacancies, interstitials, and lattice distortions due to differences in atomic size and 

lattice parameters between Au and AlN [55]. 

To analyze the implanted AlN crystal's RBS-C spectra data, RAMP and Monte Carlo 

simulation techniques and ion range calculations were used. By comparing the RBS 

spectra of the AlN crystal with a simulated one of Au+ implanted crystals, characteristic 

peaks or shifts that indicate the presence of Au+ ions and the induced defects can be 

identified. 

At room temperature and by using (1.5 MeV) He+ as a characterization beam, AlN 

crystals underwent RBS/C experiments. Scheme 3.3 shows the RBS-C aligned and 

random spectra recorded for all implanted AlN samples were extracted and plotted from 

the data collected with RBS-C. The comparison of the various random spectra recorded 

for the different samples shows that there is a difference observed pre- and post-



 

45 

implantation. Such a result was predictable because Au+ is a heavy element so it can 

substantially impact RBS signals in random and aligned directions [56]. 

The spectrum recorded on the virgin sample displays a favorable channeling behavior, 

with minimal axial yield and a low number of native defects in the crystal. However, as 

the ion fluence increases, we observe the emergence of a growing peak indicating damage 

in all sublattices. 

Scheme 3.3 

RBS/C aligned (A) and random (R) spectra were recorded for implanted AlN crystals at room 

temperature with the 6MeV Au+ ion at various ion influences 

 

The various elements present in the AlN crystal concerning its depth were determined by 

using kinematic factor {equations (2) and (3)}, so by using the previous equations the 

peak for aluminum is located at (834 KeV), nitrogen (478 KeV), carbon (389 KeV) from 

carbon layer deposition, oxygen (550 KeV) appears because amount of oxygen 

accumulated in the surface of AlN crystals during carbon deposition process, as shown in 

Scheme 3.3. 

To compare experimental and simulated data, all simulations were conducted at room 

temperature using the McChasy code. The code was applied to simulate the number of 



 

46 

defects caused by He+ irradiation by modeling the disorder using RBS spectra recorded. 

Scheme 3.4 displays the MC fits of the experimental RBS spectra at increasing fluences: 

φ 0 = 0, φ 1 = 3.1x1014, φ 2 =7x1014, φ 3 = 1.5x1015, φ 4 = 2.2x1015, φ 5 = 3x1015, φ 6 = 4x1015 

Scheme 3.4  

Monte Carlo simulation of RBS/C spectra of AlN crystals irradiated with 1.5 keV He ions at room 

temperature 

 

Note: Colored lines show experimental spectra, and orange lines represent the best fit from McChasy 

simulations. 

As shown in Scheme 3.4, ion irradiation causes a peak at an energy of approximately 820 

to 853 keV, also known as the "damage peak" This peak results from the direct 

backscattering of He ions on AlN atoms, which were randomly displaced by implantation 

with Au+ ions through elastic nuclear interaction. 

As shown in Scheme 3.4 the RBS/C yield exhibited a notable acceleration, and a 

qualitative analysis indicates a probability of amorphization occurring at the higher 

fluences. This is attributed to the displacement damage cascades resulting from the 

implantation of heavy ions into the AlN crystals, which can lead to amorphization in 

certain materials. The evolution of the RBS/C spectra at this stage strongly suggests the 

potential for amorphization to occur. [58] Based on multiple simulation runs, the 

McChasy code simulations (as depicted in Figure 3.2) show a strong alignment with the 

RBS experimental data collected. Notably, the disorder resulting from irradiation on AlN 

samples is consistent across all fluences. 



 

47 

3.3 Extraction of the damage-depth experimental profile of the crystals 

Scheme 3.5 (a) illustrates the progression of the damage-depth profile, represented as the 

percentage of defects, corresponding to varying ion fluence levels as derived from Monte 

Carlo simulations. As depicted in Scheme 3.5 (a), negligible damage is observable in the 

pristine AlN crystal, with a discernibly small amount becoming apparent at an ion fluence 

of φ 1 = (3.1x1014 cm- 2)