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Republic of Iraq Ministry of Higher Education And Scientific Research University of Baghdad College of Science
Structural, Electrical and Optical Properties of CuLayFe2-y
Ferrite System
A Thesis Submitted to the College of Science University of Baghdad
In Partial Fulfillment of the Requirements for the Degree of Master of Science in Physics
By
Douaa Basil Fahad
Supervisors
Assist. Prof. Dr. Assist. Prof. Dr. Muthafar F.Jamil FarahT.MohammadNoori
2014 A.D. 1435 A.H.
Certification
We the examining committee certify that we read this thesis, entitled “ Structural, Electrical and Optical Properties of CuLayFe2-y Ferrite System” and have examined the student (Douaa Basil Fahad). In its contents and that in our opinion it is adequate as a thesis for degree of Master of Science in Physics.
Signature Name: Dr.Izzat.M.AL-Essa Title: Professor
Date: / / 2014 (Chairman)
Signature: Signature: Name : Dr. Shihab Ahmed Zaidan Name: Dr. Salma M. Shaban Title: Assistant Professor Title: Assistant Professor Data: / / 2014 Data: / / 2014 (Member) (Member)
Signature: Signature: Name: Dr. Muthafar F. Jamil Name: Dr. Farah T.MohammadNoori Title: Assistant Professor Title: Assistant Professor Data: / / 2014 Data: / / 2014 (Supervisor) ( supervisor)
Signature: Name: Mohammed A. Atiya Title: Assistant Professor Address: Dean of College of Science/ University of Baghdad. Data: / / 2014
Supervisors Certification
We certify that this thesis was prepared by :
“ Douaa Basil Fahad ”
under our supervision at the University of Baghdad, college of science as partial fulfillment of the requirement for the degree of Master of Science in Physics.
Signature: Signature:
Supervisor: Dr. Muthafar F. Jamil Supervisor: Dr. Farah T.Mohammad
Title: Assit. Prof. Title: Assit. Prof.
Address: college of Science Address: college of Science University of Baghdad University of Baghdad
Data: / / 2014 Data: / / 2014
In view of the available recommendations, I for warded this thesis for debate by the examining committee.
Signature:
Name: Dr. Raad M.S.AL-Haddad
Title: professor
Address: Chairman of the Department of Physics, College of Science, University of Baghdad
Data: / / 2014
Dedication
To ......
My Father
My mother
My family
And My Friends
For their Kindness,
Attention and
encouragement
Douaa
Acknowledgments
First, I should like to express my deep thanks to the Almighty God,
ALLAH JALA JALALAH, for what I have been.
I would like to express my deep thanks and gratitude to my supervisor
Dr. Muthafar F. Jamil and Dr. Farah T. Mohammad Noori for suggesting
the topic of the thesis, continuous advice and their guidance throughout
this work.
I am very grateful to my supervisor Dr. Issam M. Ibrahim for providing
necessary facilities and help.
I am grateful to the chairman of physics department Prof. Dr.Raad
M.S.AL-Haddad for providing the necessary facilities and help.
Special thanks are due to Assist. Prof. Dr.Mahdi Hasan Suhail for
encouragement and help.
I am grateful to the staff of thin film laboratory and my colleagues,
especially Dr. Kadhim Abdul wahid Aadim, Assist Mohammed Ridah.
Great thanks to my beloved family for their patience and support and
also to all my friends and to all lovely people who helped me, directly or
indirectly to complete this work.
Finally I ask Allah to give my family good health and happiness and
may He bless our people and country.
Abstract
Ferrite with the general formula CuLayFe2-yO4 (where y=0.02, 0.04,
0.06, 0.08 and 0.1), were prepared by standard ceramic technique for bulk
and deposited (using pulsed laser deposition (PLD) technique) thin films.
The main cubic spinel structure phase for bulk samples was confirmed by
x-ray diffraction patterns with the appearance of small amount of
secondary phases. For thin films, the main phase was pure cubic structure
for all samples. The lattice parameter (a) results were 8.285-8.348Å for
bulk and 8.298-8.311 Å for thin films. X-ray density increased with La
addition and showed values between 5.5826–5.7461g/cm3for bulk and
5.5762-5.7575 g/cm3for thin films. The atomic force microscope (AFM)
micrographs showed that the average grain size was decreasing with the
increase in La concentration. The optical measurements showed that the
CuLayFe2-yO4 ferrite thin films have direct energy gap of values ranging
between (3.25-2.28) eV. The transmittance decreased with increasing La
content. The absorption coefficient increased with increasing La content.
The resistivity was found to decrease with La content due to the increase
in charge mobility. The results of Hall coefficient showed a p-type
semiconductor behavior. The activation energy Ea decreased with the
frequency increase. The conductivity was found to increase with the
frequency. The imaginary part of dielectric constant ε2 revealed the same
behavior as the real part ε1 with the variation of La content. Both of ε1&
ε2 decreased with the increase of frequency.
List of Contents
Subject Page
Chapter (1): Introduc on
Introduction 1
1.1 Types of Ferrites 2
1.2 Spinel Ferrites 2
1.3 Types of Spinel Ferrites 4
1.3.1 Normal Spinel Ferrites 4
1.3.2 Inverse Spinel Ferrites 4
1.3.3 Intermediate Spinel Ferrites 5
1.4 Application of Ferrites 6
1.5 Copper Ferrite 7
1.6 Survey of Previous Literatures 8
1.7 Aim of the Present Work 12
Chapter (2): Theore cal Aspects
2.1 Ferrite Thin Films 13
2.2 Pulsed Laser Deposi on (PLD) 13
2.2.1 Advantage of PLD 14
2.2.2 Laser ‐Target Interaction 15
2.3 Op cal Proper es 17
2.3.1 Op cal Absorp on and Absorp on Edge 18
2.4 Electrical Properties of Spinel Ferrites 19
2.4.1 A.C Conductivity 20
2.4.2 Dielectric Properties 21
2.4.3 Hall‐Effect 22
Subject Page
Chapter (3): Experimental Work
3.1 Introduction 24
3.2 Substrate Prepara on 24
3.2.1Glass Slides 24
3.2.2 Silicon Wafer Substrate 24
3.3 Prepara on of Pellet 24
3.4 Preparation of Thin Films 25
3.5 Structural and Morphological Measurements 27
3.5.1 X‐Ray Diffraction Patterns 27
3.5.2 Atomic Force Microscopy (AFM) 27
3‐6 Thickness Measurement 28
3.7 Op cal Measurement 28
3.8 Electrical Properties 28
3.8.1 AC Measurements 28
3.8.2 Hall Measurements 29
Chapter (4): Results & Discussion
Introduction 30
4.1 X‐Ray Diffraction 30
4.1.1 X‐Ray Diffraction for Bulk 30
4.1.2 X‐Ray Diffraction for Thin Films 33
Subject Page
4.2 Atomic Force Microscopy Analysis (AFM) 36
4.2.1 Atomic Force Microscopy for Bulk 36
4.2.2 Atomic Force Microscopy for Thin Film 38
4.3 Op cal Proper es of Thin Film 40
4.3.1 The Transmission Spectrum 40
4.3.2 Absorp on Coefficient 41
4.3.3 Optical Energy Gap 42
4.4 Electrical Properties 44
4.4.1 Hall Effect Measurements 44
4.4.2 AC Conductivity 47
4.4.3 Dielectric Properties 49
Chapter (5): Conclusion & Sugges ons
5.1 Conclusion 52
5.2 Sugges on for Future Work 53
References 54
Symbol Description Unit δ Inversion parameter - h Plank’s constant J.sec
ν Incident photon frequency Hz
λ Wave length nm c Velocity of light m/s α Absorption coefficient cm-1
t Thickness nm G.S Grain size Å Eg Energy gap eV I Current A
hkl Miller indices - Ea Activation energy eV KB Boltzmann constant J/K ω Angular frequency Hz R Resistance Ω ρ Resistivity Ω.cm C Capacitance Farad
Egopt Optical energy gap eV
a Lattice constant Å dx X-ray density g/ cm3
N Avogadro’s number mole-1 Z Number of molecules per unit cell - M Molecular weight g/mole T Absolute temperature Kelvin T Transmission % σ Conductivity (cm.Ω)-1
σο Minimum electrical conductivity at 0K
(cm.Ω)-1
RH Hall coefficient m2/C μH Hall mobility cm2/V.s μe Mobility of the electrons Cm2/V.s p Carrier concentration of holes cm-3
n Carrier concentration of electrons cm-3 μh Mobility of holes cm2/V.s q Electronic charge coulomb ε1 Real part of dielectric constant F/m ε2 Imaginary part of dielectric
constant F/m
B Magnetic field Tesla VH Hall voltage volt
List of Symbols and Acronyms
((Introduction and Literature Survey))
Chapter One Introduction
1
Chapter One
Introduction and Literature Survey
Introduction
Ferrites are electrically ferrimagnetic ceramic compound materials,
consisting of various mixtures of iron oxides such as Hematite (Fe2O3) or
Magnetite (Fe3O4) and oxides of other metals like NiO, CuO, ZnO, MnO,
CoO. The prime property of ferrites is that, in the magnetized state, all spin
magnetic moments are not oriented in the same direction. Few of them are in
the opposite direction. But as the spin magnetic moments are of two types
with different values, the net magnetic moment will have some finite value
[1].
The simplest among the ferrites are spinel type. Simple spinel ferrite have
the general chemical formula (M2+ Fe23+O4
2-) or (MO.Fe2O3), where (M) is a
divalent metal ion and the crystal structure is that possessed by the mineral
spinel. Mixed ferrites spinel have the general composition (M1-x2+ Bx
3+ Fe23+
O42-). Mixed ferrites occur when the divalent metal (M) in the formula (M
Fe2 O4)is a mixture of two divalent ions or ( monovalent + trivalent) ions,
while still retaining the spinel structure [2].
Chapter One Introduction
2
1.1 Types of Ferrites
Ferrites can be classified into three different types [3].
(1) Spinel ferrites (Cubic ferrites)
(2) Hexagonal ferrites
(3) Garnets
The present work is focused on spinel ferrites, therefore it shall be discussed
here in some details.
1.2 Spinel Ferrites
Spinel ferrites is the most widely used family of ferrites which are called
cubic ferrites. Its high electrical resistivity and low eddy current losses make
them ideal for their use at microwave frequencies. The spinel structure of
ferrites as possessed by mineral spinel MgAl2O4 was first determined by
Bragg and Nishikawa in 1915 [3].The chemical composition of a spinel
ferrite can be written in general as MFe2O4 where M is a divalent metal ion
such as Co2+ , Zn2+ , Fe2+ , Mg2+ , Ni2+ , Cd2+, Cu2+ or a combination of these
ions such as ( Ni0.52+ Zn0.5
2+ or Cu0.52+ Zn0.5
2+) etc.
The unit cell of spinel ferrite belongs to the cubic structure (space group
Oh7F3dm) and presents itself as a cube formed by 8 MeOFe2O3 molecules
and consisting of 32 of O2- anions. The oxygen anions form the close face-
centered cube (fcc) packing consisting in 64 tetrahedral (A) and 32
octahedral (B) empty spaces partly populated by Fe3+ and Me2+cations[4].
Fig.1-1 (a) shows spinel unit cell structure, (b) represents octahedral
interstice (B-site: 32 per unit cell, 16 occupied), and (c) tetrahedral interstice
(A-site: 64 per unit cell, 8 occupied). The ionic positions are the same in
octants sharing only one edge and different in octants sharing a face. Each
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Chapter One Introduction
4
1.3 Types of Spinel Ferrites
The spinel ferrites have been classified into three categories due to the
distribution of cations on tetrahedral A- and octahedral B- sites.
1. Normal spinel ferrites
2. Inverse spinel ferrites
3. Intermediate spinel ferrites
1.3.1 Normal Spinel Ferrites
If there is only one kind of cations on octahedral B-site, the spinel is
normal. In these ferrites, the divalent cations occupy tetrahedral A-sites
while the trivalent cations are on octahedral B-site. Square brackets are used
to indicate the ionic distribution of the octahedral B-sites. Normal spinel are
represented by the formula (M2+)A[Me3+]B O4. Where M represents divalent
ions and Me trivalent ions as shown in Fig.1-2. A typical example of normal
spinel ferrite is bulk ZnFe2O4.
↓ ↓↓↓↓↓↓↓ δ=1 A
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ B
Fig. 1-2 Normal Ferrites
1.3.2 Inverse Spinel Ferrites
In this structure half of the trivalent ions occupy tetrahedral A-site and half
octahedral B-site, the remaining cations being randomly distributed among
the octahedral B-sites. These ferrites are represented by the formula
(Me3+)A[M2+Me3+]BO4.
Chapter One Introduction
5
A typical example of inverse spinel ferrite is Fe2O4 in which divalent cations
of Fe occupy the octahedral B-site [6], as shown in Fig.1-3.
↓↓↓↓↓↓↓↓δ =0 A
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ B
Fig. 1-3 Inverse Ferrites
1.3.3 Intermediate Spinel Ferrites
Spinel with ionic distribution that are intermediate between normal and
inverse are known as mixed spinel e.g. (Mδ2+Me1-δ
3+)A[M1-δ2+Me1+ δ
3+]BO4,
where δ is called inversion parameter. Quantity δ depends on the method of
preparation and nature of the constituents of the ferrites. For complete
normal spinel ferrites δ = 1, for complete inverse spinel ferrites δ =0, for
mixed spinel ferrite, δ ranges between these two extreme values. For
completelymixed ferrites δ = 1/3. If there is unequal number of each kind of
cations on octahedralsites, the spinel is called mixed as shown in Fig.1-4.
Typical example of mixed spinel ferrites are MgFe2O4and MnFe2O4[7].
↓↓↓↓↓↓↓↓δ = 0.25 A
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ B1
Fig.1-4 Intermediate Ferrites
Néel [8] suggested that magnetic moments in ferrites are sum of magnetic
moments of individual sub lattices. In spinel structure, exchange interaction
between electrons of ions in A-and B-sites have different values. Usually
Chapter One Introduction
6
interaction between magnetic ions of A- and B-sites (AB-sites interaction) is
the strongest. The interaction between AA-sites is almost ten times weaker
than that of AB-sites interaction whereas the BB-sites interaction is the
weakest. The dominant AB-sites interaction results into complete or partial
(non-compensated) antiferromagnetic known as ferrimagnetism. The
dominant AB-sites interaction having the greatest exchange energy,
produces antiparallel arrangement of cations between the magnetic moments
in the two types of sublattices and also parallel arrangement of the cations
within each sublattice, despite of AA-sites or BB-sites antiferromagnetic
interaction [9].
1.4 Applications of Ferrites
Ferrites are very important magnetic materials because of their high electric
resistivity; they have wide applications in technology, particularly at high
frequencies. Ferrites are widely used due to the following properties.
1. Ferrites are part of low power and high flux transformers which are
used in television.
2. Soft ferrites were used for the manufacture of inductor core in
combination with capacitor circuits in telephone system, at present,
solid state devices have replaced them. The soft Ni-Zn and Mn-Zn
ferrites are used for core manufacture.
3. Small antennas are made by winding a coil on ferrite rod used in
transistor radio receiver.
4. Ferrites are used in microwave devices like circulators, isolators,
switches phase shiftersand in radar circuits.
Chapter One Introduction
7
5. Ferrites are used in high frequency transformer core and computer
memories i.e computer hard disk, floppy disks, credit cards, audio
cassettes, video cassettes and recorder heads.
6. Ferrites used in magnetic tapes and disks are made of very small
needle like particles of Fe2O3 or CrO2 which are coated on polymeric
disk. Each particle is a single domain of size 10-100 nm.
7. Ferrites are used to produce low frequency ultrasonic waves by
magnetostriction.
8. They are used as electromagnetic wave absorbers at low dielectric
values.
9. Ferro fluids, as cooling materials, in speakers. They cool the coils
with vibrations.
1.5 Copper ferrite
The Cu-Fe-O system is of long standing interest in solid state physics,
mineralogy, ceramics and metallurgy. By virtue of its magnetic and
semiconducting properties, copper ferrite (CuFe2O4) and its solid solutions
with other ferrites are widely used in the electronic industry [10]. Copper
ferrite is one of the important spinel ferrites MFe2O4 because it exhibits
phase transitions, changes semiconducting properties, shows electrical
switching and tetragonality variation when treated under different conditions
in addition to interesting magnetic and electrical properties with chemical
and thermal stabilities [11]. It is used in wide range of applications in gas
sensing [12], catalytic applications [13], Li ion batteries [14] high density
magneto-optic recording devices, color imaging, bioprocessing, magnetic
refrigeration and Ferro fluids[15]. Moreover, CuFe2O4 assumes great
Chapter One Introduction
8
significance because of its high electric conductivity, high thermal stability
and high catalytic activity for O2 evolution from alumina–cryolite system
used for aluminum production [16]. CuFe2O4 is known to exist in tetragonal
and cubic structures. Under slow cooling Cu-ferrite crystallizes in a
tetragonal structure with lattice parameter ratio c/a of about 1.06. Tetragonal
phase of Cu-ferrite has inverse spinel structure with almost all Cu2+ ions
occupying octahedral sublattice, whereas Fe3+ ions divide equally between
the tetrahedral and octahedral sublattices [17]. The tetragonal structure is
stable at room temperature and transforms to cubic phase only at a
temperature of 360°C and above due to Jahn–Teller distortion. The
distortion is directly related to the magnetic properties. The cubic structure
possesses a larger magnetic moment than that of the tetragonal one, because
there are more cupric ions (Cu2+) at tetrahedral sites in cubic structure as
compared to that in the case of tetragonal structure [18].
1.6 Survey of Previous Literatures
1. N.Rezlescu and E.Rezlescu (1974) [19] reported the abnormal dielectric
behavior of copper ferrite. Abnormal behavior of the dielectric constant
is found and also the loss factor as a function of frequency and
temperature in comparison with the normal behavior of spinel ferrite. The
origin of this abnormal behavior is attributed to the presence of Cu1+ ions
which determine the appearance of p-carriers in these ferrites.
2. Kolekar et al.(1994) [20] studied polycrystalline ferrite of composition
CdxCu1-xFe2-yGdyO4 (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0; y=0.0 and 0.1). The
infrared absorption of the powder samples showed two strong absorption
bands in the frequency range (400-600) cm-1 and the analysis showed that
Gd occupied B- sites.
Chapter One Introduction
9
3. Elhiti et al.(1995) [21] studied dielectric behavior of Cu-Cr ferrites.
Samples of the system CuFe2-xCrx O4 where x= 0, 0.2, 0.4, 0.6 and 0.8
were prepared. The dielectric constant and dielectric loss were studied.
The results showed that the dielectric loss decreases with increasing
frequency and Cr substitution. The dielectric constant decreases with
both frequency and Cr substitution at room temperature.
4. Goya and Rechenberg (1998) [22] studied structural and magnetic
properties of ball milled copper ferrites. The structural and magnetic
evolution in copper ferrite (CuFe2O4) caused by high-energy ball milling
were investigated by X-ray diffraction, Mossbauer spectroscopy, and
magnetization measurements. The milling process reduced the average
grain size of CuFe2O4 to about 6 nm and induced cations redistribution
between A- and B- sites.
5. Sattar et al. (1999) [23] investigated Cu-Zn ferrite doped with rare earth
ions like La, Sm, Nd, Gd, and Dy. They found that all samples were of
high relative density and low porosity. The magnetization of the samples
with Sm and La were higher than that of undoped. On the other hand,
samples with Gd and Dy had lower values than that of the undoped ones.
The magnetization values of the sample with Nd may be higher or lower
than that of the undoped ones depending on the applied magnetizing
field. Sample with La, Sm and Nd had higher values of µr than that of the
undoped ones. Those with Gd and Dy had lower values of µr.The
important result in this work was that the relative permeability has
increased by about 60%, 35.5% and 25%, in case of Sm, La and Nd,
respectively.
6. Mahajan et al. (2000) [24] studied the Conductivity, dielectric behaviour
and magnetoelectric effect in copper ferrite–barium titanate composites.
Chapter One Introduction
10
The variation of resistivity and thermo emf with temperature in these
samples were studied. All the composites showed n-type behaviour. The
variation of dielectric constant in the frequency range 100Hz to 1 MHz
and with temperature at constant frequency were studied.
7. Ravinder (2000) [25] examined the electrical transport properties such as
electrical conductivity (σ) and thermoelectric power (S) of cadmium
substituted copper ferrites.The chemical formula Cu1−xCdxFe2O4, where
x=0.2, 0.4, 0.6, 0.8 and 1.0 was investigated with temperature ranging
from room temperature to those well beyond the Curie temperature.
Based on the Seebeck coefficient (S), the ferrites under investigation
were classified as n-type semiconductors. The values of charge carrier
concentration and mobility were computed from experimental values of
Seebeck coefficient and electrical conductivity. The activation energy in
the ferrimagnetic region was in general less than that in the paramagnetic
region. An attempt was made to explain the conduction mechanism in
these ferrites. The properties of cadmium substituted copper ferrites were
correlated with those of zinc substituted copper ferrites, cadmium and
zinc being two non-magnetic divalent ions occupying essentially
tetrahedral A-sites when substituted in ferrites.
8. Jingjing Sun et al. (2002) [26] investigated the effect of Fe substitution
by La2O3 and Gd2O3 (Ni0.5Zn0.5Fe2-xRxO4 R=La or Gd, x= 0-0.04) on the
structure, magnetic and dielectric properties of Ni-Zn ferrite. With
increasing R2O3, the relative density of sintered bodies decreased, while
the lattice parameter increased.La2O3 and Gd2O3 both tend to increase the
cut-off frequency. The addition of R decreased the initial permeability in
the range 300 MHz. Rare earth addition flattened the ε1-f curves,
Chapter One Introduction
11
increased ε1 values and decreased dielectric loss tangent in the range of
1M-40 MHz .
9. Ahmed et al. (2005) [27] investigated the spinel ferrite system Ni1-
xZnxLayFe2-yO4; 0.0 ≤ x ≤ 1.0 and y = 0.0, 0.05 which was prepared by
standard ceramic method. X-ray diffraction was used to obtain the
structural characterization of Ni, Zn, Ni–Zn and Ni–Zn–La ferrite. The
influence of zinc ion substitution on the electrical properties of samples
was investigated. The ac conductivity (ln σ) as well as dielectric constant
(ɛ′) were nearly constant for small Zn ion concentration, while they
increased at high Zn content (x = 0.6).
10. Rao (2005) [28] studied the copper ferrite and found that tetravalent
substitution was more capable of development of high resistivity ferrites
while the pentavalent (+5) cation is useful for high conductivity ferrite
development. The tetravalent cations are capable of forming stable bonds
hindering the electron hopping process for high resistivity.
11. Roy and Bera (2009) [29] reported the impact of La3+ and
Sm3+substitution.They also found that relative density and grain size of
the ferrites increased with increasing Sm3+ substitution. Increased
densification may be due to the appearance of excess Ni, Cu and Zn
compared with Fe in the composition. Rare earth ions can improve
densification and increase the permeability and resistivity in (Ni1-x-
yZnxCuy)RzFe2-zO4 ferrites where, R enters into the B-sites by displacing
a proportionate number of Fe3+ from B- to A-sites. Previous studies
suggest that the in homogeneous magnetic spin structure can be
effectively suppressed by La doping .
12. G. Ravikumar et al. (2012) [30] studied electrical conductivity and
dielectric properties of copper doped nickel ferrites prepared by double
Chapter One Introduction
12
sintering method. The activation energies in the ferromagnetic region and
paramagnetic region are calculated from the slops of log (σT) versus
(103/T). The values of activation energy decrease with increase of copper
content. The variation of dielectric constant as a function of frequency for
mixed Ni-Cu ferrites for different compositions. The value of dielectric
constant decrease with increase frequency.
1.7 Aim of the Present Work:
The aim of this work is prepared spinel ferrite materials of CuLayFe2-yO4 to
see the comparison between the structural, electrical and optical properties
of bulk and thin film of ferrites are examined and discussed in details.
((Theoretical Part))
Chapter Two Theoretical
13
Chapter Two
Theoretical Part
2.1 Ferrite Thin Films
Thin films technology is one of the most accelerating fields in research.
The film is said to be thin, if its thickness is less than 1 µm [31]. Thin film
plays an important role in many technological application including storage
devices, microelectronics and surface coating etc. [32].
Thin films of magnetic materials can be a replacement of bulk material.
These materials play a vital role in the development of advanced technology.
These are being fabricated for the development of integrated circuit industry.
In order to meet the demand for the progress of the miniaturization in
electronic devices with more capacity and higher speed, it requires new
techniques and new materials. Thin film cost is cheap compared to its
corresponding bulk material [33].
2.2 Pulsed Laser Deposition (PLD)
Pulsed laser deposition (PLD) is a thin-film deposition method, which uses
short and intensive laser pulses to evaporate target material. The ablated
particles escape from the target and condense on the substrate. The
deposition process is done in a vacuum chamber to minimize the scattering
of the particles. Reactive gases are used to vary the stoichiometry of the
deposit[34]. The PLD process depends on laser wavelength, pulse width,
repetition rate, energy density (fluence), background gas pressure, substrate
temperature and target-to-substrate distance[35].
Chapter Two Theoretical
14
2.2.1 Advantage of PLD
PLD technique is proved to be a very effective method to deposit
high‐quality films. That is because of the following reasons:
1- Films grown by PLD can be realized at room temperature. The most
import characteristics in PLD is the ability to implement stoichiometric
transfer of ablated material from targets to substrate for many materials. The
benefit of pulsed laser ablation are flexibility, fast response, energetic
evaporates, and congruent evaporation.
2- The main PLD parameters are: substrate temperature, laser fluence, target
substrate distance, type of gas atmosphere (active or passive) and deposition
pressure. Since the parameters are very few, it makes the PLD technique a
very attractive research tool. Industrialization of the PLD technique is still
held back by the surface coverage since it is hard to apply to larger surfaces
without affecting the homogeneity of the thin film[36].
3- Complex material films can be deposited by PLD.
4- The decoupling of the vacuum hardware and the evaporation power
source makes this technique so flexible that it is easily adaptable to different
operational modes without the constraints imposed by the use of internally
powered evaporation sources.
5- Pure and uniform thin films can be produced by PLD.
6- Because of the high heating rate of ablated materials, laser deposition of
crystalline film demands a much lower substrate temperature than other film
growth techniques. For this reason the semiconductor and the underlying
integrated circuit can refrain from thermal degradation.
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gh amplitud
then start
Fig.
nitial abso
vaporizatio
ate motion
LD are sm
que. It is q
sequential
Interactio
ion in PLD
beam with
material fr
et by laser
ntense hea
es results in
s energy d
lse induce
et materia
de stress w
to boil of
2-1: Shows
orption of
on begin (
n of solid–
15
all compa
quite easy
ablation o
n
D techniqu
h bulk targ
from the ta
r irradiatio
ating of th
n melting
density[37
es extreme
al. This m
waves in th
ff and expa
the stages o
f laser radi
(shaded ar
–liquid int
red with th
y to produc
of assorted
ue can be
get, and (i
arget. The
on depend
he surface
and / or ev
].
ely rapid
may cause
he solid ta
and into th
of a PLD ev
iation (ind
rea indicat
terface). (b
he large si
ce multi-la
d targets.
divided in
ii) interact
removal o
ds on the c
e layer by
vaporation
heating o
e phase t
arget.
he gas pha
vent [38]
dicated by
tes melted
b) Melt fr
Theor
ize require
ayered film
nto two pa
tion of the
or sputteri
coupling o
high- pow
n of the su
of a signif
transitions
ase.
y long arr
material,
ront propa
retical
ed for
ms of
art: (i)
e laser
ing of
of the
wered
urface
ficant
s and
ows),
short
agates
Chapter Two Theoretical
16
into the solid, vaporization continues and laser-plume interactions start to
become important. (c) Absorption of incident laser radiation by the plume,
and plasma formation. Finally, (d) Melt front recedes leading to eventual re-
solidification[38]. In general, the interaction between the laser radiation and
the solid material takes place through the absorption of photons by electrons
of the atomic system, electromagnetic energy is immediately converted into
electronic excitations in the form of Plasmon’s and unbound electrons. The
excited electrons then transfer their energy to the lattice via electron–
phonon (e–p) coupling[39]. In a high vacuum chamber, elementary or alloy
targets are struck at an angle of 45o by pulsed and focused laser beam.
The atoms and ions ablated from the target are deposited on substrate, which
is mostly attached with the surface parallel to the target surface at a target-
to-substrate distance of typically 2-10 cm[40], Fig. 2-2 shows a schematic
diagram for an ideal PLD system.
The subsequent melting and evaporation of the surface would essentially be
thermal i.e the difference between the melting points and vapor pressures of
the target constituents would cause them to evaporate at different rates so
that the composition of the evaporated material would change with time and
would not represent that of the target. This incongruent evaporation
sometimes leads to a film with very different stoichiometry from the
target[36].High heating rate of the target surface (108 K/s) due to pulsed
laser irradiation, may lead to the congruent evaporation of the target
irrespective of the evaporating point of the constituent elements or
compounds of the target[41]. At low intensity laser, the quantity of the
evaporated substance mostly depends on the material heat conductivity
rather than from its latent evaporation warmth. When the laser power density
Cha
is in
no t
Las
(e.g
Nd-
and
2.3
Op
sem
usu
infl
apter Two
ncreased u
time to be
ser used in
g. a CO2 l
-YAG lase
d 532) and
F
Optical
ptical mea
miconducto
ually creat
uence both
up to a cri
taken awa
n PLD stud
aser, 10.6
er, with fu
down into
Fig. 2-2: Sch
l Propert
asurements
ors. Extrin
te discrete
h optical a
itical value
ay any mo
dies range
6 mm), thr
undamenta
o the ultrav
hematic of th
ties
s provide
nsic prope
e electron
absorption
17
e, the heat
ore becaus
e in output
rough the
al and seco
violet (UV
he pulsed la
a good w
erties are r
nic states
n and emis
t is allocat
e of heat c
t waveleng
near infra
ond harmo
V)[38].
aser depositi
way of exa
related to
in the b
ssion proce
ted so qui
conductivi
gth from th
ared and v
onic outpu
ion system[
amining th
dopant or
band gap,
esses[43].
Theor
ickly that
ity.
he mid inf
visible (e.g
uts at (106
42]
he properti
r defects w
and ther
retical
it has
frared
g. the
64 nm
ies of
which
refore
Chapter Two Theoretical
18
2.3.1 Optical Absorption and Absorption Edge
The fundamental absorption is the most important absorption process
which involves the transition of electrons from the valence band (V.B) to the
conduction band (C.B). The process manifests itself by a rapid rise in
absorption and this can be used to determine the energy gap of the
semiconductor [44].The semiconductor absorbs photons from the incident
beam. The absorption depends on the photon energy (hν); where h is Plank's
constant, ν is the incident photon frequency. The absorption associated with
the electronic transition between the V.B and the C.B in the material starts at
the absorption edge which corresponds to a minimum energy difference (Eg)
between the lowest minimum of the C.B. and the highest maximum of the
V.B [45]. If the photon energy (hν) is equal or higher than energy gap (Eg),
the photon can interact with a valence electron, elevates the electron into the
C.B and creates an electron–hole pair [46].The maximum wavelength (c) of
the incident photon which creates the electron–hole pair is defined as [46].
. ……………..(2-1)
Where c is the velocity of light.
The intensity of the photon flux decreases exponentially with distance
through the semiconductor according to the following equation.
exp ………………..(2-2)
Where I, I are the incident and the transmitted photon intensity
respectively, is the absorption coefficient, which is defined as the relative
number of the photons absorbed per unit distance of semiconductor, and t is
the thickness of the material [47].
Chapter Two Theoretical
19
2.4 Electrical Properties of Spinel Ferrites
Spinel ferrites are more important over conventional magnetic materials
because of their wide variety of applications. These materials have low
electrical conductivity when compared to other magnetic materials and
hence they find wide use at microwave frequencies. Spinel ferrites, in
general are semiconductors with their conductivity lying in between 102and
10-11 Ohm-1 cm-1. The conductivity is due to the presence of Fe2+ and the
metal ions (Me3+). The presence of Fe2+ results in n-type behavior and that
of Me3+ in p -type behavior. The conductivity arises due to the mobility of
the extra electron or the positive hole through the crystal lattice. The
movement is described by a hopping mechanism, in which the charge
carriers jump from one ionic site to the other. In short, one can say that the
electrostatic interaction between conduction electron(or hole) and nearby
ions may result in a displacement of the latter and polarization of the
surrounding region, so that the career is situated at the center of a
polarization potential well. The career is trapped at a lattice site, if this
potential well is deep enough. Its transition to a neighboring site is
determined by thermal activation. This has been described as the hopping
mechanism. In such a process the mobility of the jumping electrons or holes
are found to be proportional to exp (-Ea/ KBT), where Ea is the activation
energy, kB Boltzmann’s constant and T the temperature in degree absolute.
Chapter Two Theoretical
20
2.4.1 A.C Conductivity
Alternative current response as a function of frequency offers valuable
additional information about the dynamic response of the system. However
the principle strength of ac-studies lies their ability to provide information
on the polarization response under the study, from which many deductions
may be regarding the physical process involved the ac-conductivity for
many materials such as amorphous semiconductor, chalcogenide and
crystals increases linearly with frequency and to obey the empirical
formula[48].
sAww )( ……… (2-3)
Where A is multiplicity factor, (s) is exponent factor w is the angular
frequency.
The value of s less than one if A and s are independent on temperature, but
if they are temperature dependent, s will equal unity at low temperature.
The ac-conductivity is constant at low frequencies and increases rapidly at
higher frequencies this behavior is observed in all amorphous
semiconductors, so the total conductivity σtot(w) at particular frequency is
given by [49]
σtot( w) = σdc+Aws……… (2-4)
Where cd . is the dc conductivity at zero frequency.
The conductivity is frequency and temperature dependent entity. The
electrical conduction is a thermally activated process and follows the
Arrhenious law [50]
Chapter Two Theoretical
21
exp ⁄ ………(2-5)
Where σο: is the minimum electrical conductivity at 0K.
σ : is the electrical conductivity at T°K.
kB: is Boltzmann’s constant.
T: is absolute temperature in Kelvin.
The activation energy (Ea) could be calculated using the equation (2-6):
Ea / 1.6 10 . …….(2-6)
The conductivity may be determined by using the equation:-
= .
………………(2-7)
Where R is the resistance, t is the thickness of the pellet sample, A is the
cross-sectional area of the flat surface of the pellet.
2.4.2 Dielectric Properties
The real and imaginary parts of the dielectric constant and or dielectric
loss factor may be determined as follows:
⁄ …………(2-8)
……………(2-9)
Where εo is the constant of permittivity for free space= 8.854 × 10−12 F/m, f
is the frequency, tanδ is the loss tangent [51].
Chapter Two Theoretical
22
2.4.3 Hall-Effect
Hall measurements are widely used in the initial characterization of
semiconductors to measure carrier concentration and mobility. It is used to
distinguish whether a semiconductor is n- or p – type. When a constant
current (I) flows along the x-axis from left to right in the presence of a z-
directional magnetic field (B) (0.55T), electrons are subjected to Lorentz
force initially and they drift toward the negative y-axis, resulting in an
excess surface electrical charge on the side of the sample and causing a
transverse voltage. This transverse voltage is known as the Hall voltage (VH)
as shown in Fig.2-3. The Hall coefficient (RH) is determined by measuring
the Hall voltage that generates the Hall field across the sample thickness (t),
and is given by the following equation which is known as the Hall
coefficient equation [52]:
. ⁄⁄ …………..(2-10)
According to this equations, the carrier’s concentration of the
semiconductor can be determined as well as the carrier type, since RH is
negative or positive for n- or p- type, respectively:
.For n-type …………(2-11)
.For p-type ………….(2-12)
Where (e) is the electron charge. If the conduction is due to one carriers
type e.g. electrons the conductivity due to electrons is:
For n-type ..………(2-13)
Chapter Two Theoretical
23
The conductivity due to holes is:
For p-type …………(2-14)
Hall mobility can be calculated as:
.……………….. (2-15)
l l…………… (2-16)
i.e., by knowing σ, the mobility can be determined [52].
Fig. 2.3: Geometry of the Hall effect.
B
-YJ
t
EH
W+X
(( Experimental Procedure))
Chapter Three Experimental Procedure
24
Chapter Three
Experimental Procedure
3.1 Introduction
This chapter describes the preparation conditions of the CuLayFe2-yO4thin
films were deposited by pulsed laser deposition technique on glass and
silicon (Si-n-type wafers) substrates of concentrations (y=0.02, 0.04, 0.06,
0.08 and 0.1) wt%.
3.2 Substrate Preparation
3.2.1Glass Slides
The glass substrates (10×10 mm) used in the deposition were sodium glass.
They were cleaned using chromic acid for 10 min and ethanol for 10 min,
with ultrasonic agitation.
3.2.2 Silicon Wafer Substrate
Circular- shaped n-type silicon (111) with diameter 76.2(mm), thickness
508+-15(µm) and resistivity 1.5-4(Ωcm) were used after they were cleaned
in acetone with ultrasonic agitation for 30 minutes, rinsed with deionized
distilled water, and dried using air blower.
3.3 Preparation of Pellet
Ferrites with the general formula CuLayFe2-yO4 (where y=0.02, 0.04, 0.06,
0.08 and 0.1) were prepared by standard ceramic technique. High purity
powders of CuO, Fe2O3 and La2O3 were weighted and mixed according to
the general composition formula by moles ratio. The powders were mixed
Chapter Three Experimental Procedure
25
and blended homogenously through dry mixing using a ball mill. Then the
powders were pressed using a pressure of 17MPa to produce a pellet
specimen of diameter 1.5 cm. The specimen were finally sintered at 900˚C
for (2 hr) and left to cool down naturally to room temperature.
3.4Preparation of Thin Films
Ferrite thin films were prepared by pulse laser deposition. An incident
beam of Nd:YAG SHG Q-switched laser was focused on the target surface
to make an angle of 45° with it. The films were deposited on silicon wafers
[111] and glass substrates at room temperature. The laser source
characteristics are λ=1064nm, energy=900mJ, frequency 6Hz, distance
between substrate and target 1cm with chamber pressure of 6х10-2mbar, and
number of pulses= 1500. The films were annealed in an oven at a
temperature of 600˚C for 2 hr. The specimen preparation and experimental
measurements can be summarized in the following block diagram.
Cha
apter Threee
Fig. 3.1
1: A block d
26
diagram of t
the experime
Experim
ent work.
mental Proccedure
Chapter Three Experimental Procedure
27
3.5 Structural and Morphological Measurements
3.5.1 X-Ray Diffraction Patterns
The phase identification of the prepared specimen was performed with a
SHIMADZU 6000 X-ray diffractometer with Cu(kα) radiation of wavelength
of ( λ=1.5405Å ) at scanning speed of 5 deg/min.
The X-ray patterns were used to calculate the lattice parameter (a) from the
d-spacing using equation (3-1), for cubic structure
……….(3-1)
where (h, k and l) are the Miller’s indices.
The x-ray density for the prepared specimen was calculated from
dx ⁄ ……………….(3-2)
Where (Z) is the number of molecules per unit cell (Z= 8) for cubic spinel
ferrites, (M) is the molecular weight and (N= 6.022х 1023 /mol) is
Avagadro’s number[53].
3.5.2 Atomic Force Microscopy (AFM)
The morphological surface analysis was carried out with an atomic force
microscope (AA3000 Scanning Probe Microscope SPM, tip NSC35/AIBS
from Angstrom Ad-Vance Inc).
Chapter Three Experimental Procedure
28
3-6 Thickness Measurement
Film thickness measurements were done using optical interferometer
method. This method is based on interference of a light beam reflected from
a thin film surface and substrate bottom, with error rate at 3%. He-Ne laser
(0.632µm) as the light source was used and the thickness is determined
using the formula:
t =∆
……………(3-3)
Where x is the fringe width, ∆x is the distance between two fringes and λ
wavelength of laser light [54].
3.7 Optical Measurement
A double –beam UV-VIS SP-8001 Spectrophotometer was used to measure
the absorption of copper ferrite films deposited at different conditions in the
range of (300-1100) nm.
The optical energy gap Eg of the CuLayFe2-yO4 prepared with different La
content and thickness 100nm was calculated using Tauc formula by plotting
(αhѵ)n versus (h ѵ). The energy gap is obtained from the intercept of the
extrapolated linear part of the curve with the energy axis.
3.8 Electrical Properties
3.8.1 AC Measurements
The dielectric properties, i.e dielectric constant and dielectric loss factor
were determined using LCR meter bridge. For this purpose, silver paste was
Chapter Three Experimental Procedure
29
applied on both sides of the specimen to make good ohmic contacts. The ac-
measurements were performed using Agilent impedence analyzer (4294 A)
with frequency range between (25049.75-5000000)Hz used to measure the
dielectric properties were calculated from equations (2-8) and (2-9). For ac-
measurement, an HP-R2C unit model (4275 A) multi frequency LCR meter
used to measure the capacitance (C) and resistance (R) with frequency range
between 100Hz-100KHz.
3.8.2 Hall Measurements
Hall Effect measurements were done by Van der Pauw (Ecopia HMS-
3000) which were carried out at room temperature using the four probe
technique. The principle Hall effect refers to potential difference (Hall
voltage) on opposite sides of a thin sheet of conducting or semi-conducting
material through which an electric current is flowing, created by a magnetic
field (B=0.55 Tesla)were determined using LCR meter bridge. For this
purpose silver paste was applied on both sides of the sample to make good
ohmic contacts.
The Hall effect measurements involved measuring the Hall coefficient (RH),
Hall mobility (µH), sheet carrier concentration (nsheet).
((Results and Discussion))
Chapter Four Results and Discussion
30
Chapter Four
Results and Discussion
4- Introduction
In this chapter, the results of the structural, electrical and optical properties
of CuLayFe2-yO4 ferrites for bulk and thin film samples are presented and
discussed in details. The discussion is divided into two parts for bulk and
thin films for the sake of comparison and better understanding. Hence the
differences of properties between bulk and thin film samples are discussed.
4.1 X-Ray Diffraction
4.1.1 X-Ray Diffraction for Bulk
The x-ray diffraction patterns for samples of Lanthanum doped copper
ferrite CuLayFe2-yO4 with (y=0.02, 0.04, 0.06, 0.08 and 0.1) of Lanthanum
additions fired at 900 °C for (2 h) are shown in Fig.4-1.
All the XRD patterns shown indicate the formation of crystalline cubic
spinel phase ferrite with space group (Fd3m).In some cases, there exists very
limited amount of second phases with extremely small peaks induced by the
presence of rare earth oxides; this results is in agreement with the results
given by Ahmed et al. [55]. The peaks showed different amounts of
crystallinity depending upon the doping level of La3+.It can be noticed from
the x-ray patterns that the peaks at (2θ=35.85°, 36.25°, 38.97°, 40.00°,
45.29°, 46.52°, 49.05°, 50.38°, 57.78° and 58.35°) referred to (131), (211),
(111), (012), (330), (-112), (20-2), (214), (151) and (321) plane directions,
respectively. With that the strongest peak occurs for the (131) plane at
Cha
2θ=
dire
Inte
valu
d₀ is
Fig.
cont
apter Four
=35.85°. A
ection. Tab
ernational
ues is due
s the stand
4-1: X-ray
tent.
A point of
ble 4-1pre
Centre fo
to the stra
dard value
diffraction
interest is
esents the
or Diffract
ain in crys
e of the dhk
n patterns f
31
s that the p
experime
tion Data)
stal lattice
kl - spacing
for bulk C
preferentia
ental and t
). The diff
which is d
g .
CuLayFe2-yO
Results
al orientati
the standa
ference be
defined as
4 ferrites w
s and Discu
ion is the
ard values(
etween the
s (∆d/d₀), w
with differe
ussion
(131)
(from
e two
where
ent La
Chapter Four Results and Discussion
32
Table 4-1: X-ray diffraction pattern data for bulk CuLayFe2-yO4 ferrites with different La
content.
y 2θ exp.
(Deg.)
dExp.
(Å)
dStd.
(Å) Chemical Phase (hkl) Card No.
FWHM
(Deg.)
G.S
(Å)
0.02
35.85 2.505 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.678 116
36.25 2.478 2.486 Tet. CuFe2O4 (211) 96-901-1013 0.678 116
37.50 2.398 2.415 Tet. CuFe2O4 (222) 96-901-1013 0.388 204
38.97 2.311 2.311 CuO (111) 96-101-1149 0.265 300
49.05 1.857 1.855 CuO (20-2) 96-101-1149 0.389 211
53.92 1.700 1.708 Cub. CuFe2O4 (242) 96-901-2439 0.882 95
57.78 1.595 1.610 Cub. CuFe2O4 (151) 96-901-2439 0.910 94
0.04
35.85 2.504 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.511 154
36.25 2.478 2.486 Tet. CuFe2O4 (211) 96-901-1013 0.422 187
37.49 2.399 2.415 Tet. CuFe2O4 (222) 96-901-1013 0.456 173
38.97 2.311 2.311 CuO (111) 96-101-1149 0.262 303
40.00 2.254 2.279 La2O3 (012) 96-101-0279 0.621 131
46.52 1.952 1.951 CuO (-112) 96-101-1149 0.600 136
48.98 1.859 1.855 CuO (20-2) 96-101-1149 0.800 103
50.38 1.811 1.816 Fe2O3 (214) 96-901-2693 0.771 107
57.78 1.595 1.582 Tet. CuFe2O4 (321) 96-901-1013 0.773 111
0.06
35.85 2.505 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.421 187
36.33 2.473 2.486 Tet. CuFe2O4 (211) 96-901-1013 0.321 245
37.53 2.396 2.415 Tet. CuFe2O4 (222) 96-901-1013 0.621 127
39.05 2.306 2.311 CuO (111) 96-101-1149 0.182 436
40.00 2.254 2.279 La2O3 (012) 96-101-0279 0.151 527
45.29 2.002 1.955 Fe2O3 (330) 96-101-1268 0.425 191
46.51 1.952 1.951 CuO (-112) 96-101-1149 0.716 114
49.05 1.857 1.855 CuO (20-2) 96-101-1149 0.487 169
50.40 1.810 1.816 Fe2O3 (214) 96-901-2693 0.345 240
57.75 1.596 1.610 Cub. CuFe2O4 (151) 96-901-2439 0.589 145
58.45 1.579 1.582 Tet. CuFe2O4 (321) 96-901-1013 0.911 94
0.08
35.95 2.498 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.450 175
36.27 2.477 2.486 Tet. CuFe2O4 (211) 96-901-1013 0.400 197
39.11 2.303 2.311 CuO (111) 96-101-1149 0.216 368
40.06 2.250 2.279 La2O3 (012) 96-101-0279 0.336 237
45.38 1.998 1.955 Fe2O3 (330) 96-101-1268 0.343 236
46.58 1.949 1.951 CuO (-112) 96-101-1149 0.196 416
49.07 1.856 1.855 CuO (20-2) 96-101-1149 0.242 340
50.50 1.807 1.816 Fe2O3 (214) 96-901-2693 0.474 175
57.85 1.594 1.582 Tet. CuFe2O4 (321) 96-901-1013 0.520 164
0.1
35.66 2.517 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.521 151
36.09 2.488 2.486 Tet. CuFe2O4 (211) 96-901-1013 0.305 258
37.26 2.413 2.415 Tet. CuFe2O4 (222) 96-901-1013 0.523 151
38.85 2.318 2.311 CuO (111) 96-101-1149 0.197 403
39.78 2.265 2.279 La2O3 (012) 96-101-0279 0.223 357
45.12 2.009 1.955 Fe2O3 (330) 96-101-1268 0.321 252
46.38 1.957 1.951 CuO (-112) 96-101-1149 0.256 318
47.73 1.905 1.911 Fe2O3 (313) 96-901-2693 0.334 245
48.90 1.862 1.855 CuO (20-2) 96-101-1149 0.309 266
50.20 1.817 1.816 Fe2O3 (214) 96-901-2693 0.336 246
53.55 1.711 1.708 Cub. CuFe2O4 (242) 96-901-2439 0.321 261
57.58 1.600 1.610 Cub. CuFe2O4 (151) 96-901-2439 0.262 326
58.35 1.581 1.582 Tet. CuFe2O4 (321) 96-901-1013 0.521 164
Chapter Four Results and Discussion
33
The lattice parameter a (Å) and x-ray density was calculated by using
equations (3-1) and (3-2) respectively. The lattice parameter value were
between 8.285-8.348 Å. X-ray density increases with La addition between
5.5826 – 5.7461 gm/cm3as shown in Table 4-2.
Table 4-2: Effect of La addition on Lattice parameter (a), x-ray density of unit cell
(dx)and Molecular weight (M).
y dhkl (Å) hkl M (g/mol) a (Å) V (cm3) dx (g/cm3)
0.02 2.505 (131) 240.911 8.308 5.735*10-22 5.5826
0.04 2.504 (131) 242.572 8.305 5.728*10-22 5.6278
0.06 2.505 (131) 244.233 8.308 5.735*10-22 5.6596
0.08 2.498 (131) 245.894 8.285 5.687*10-22 5.7461
4.1.2 X-Ray Diffraction for Thin Films
Fig.4-2 shows the X-ray diffraction pattern of CuLayFe2-yO4 ferrites thin
films prepared by pulsed laser deposition (PLD) technique on Si (111)
substrate at room temperature. The samples were annealed at temperature of
600˚C for 2 hr. The main phase was cubic spinel structure for all samples.
The x-ray diffraction patterns showed peaks at (2θ=35.80°, 38.99°and
49.16°) referred to the (131), (111) and (20-2) plane directions, respectively.
It can be noticed from the x-ray patterns that the strongest peak occurs at the
(131) plane at 2θ=35.80°. The characteristic peaks belongs to the (Fd3m)
cubic spinel space group. Table 4-3 presents the x-ray diffraction pattern
data for CuLayFe2-yO4 ferrites thin films with different La content.
Cha
Fig
apter Four
g.4-2: X-ray
y diffraction
n patterns for
34
r CuLayFe2-
content.
-yO4 ferrites
Results
s thin films w
s and Discu
with differen
ussion
nt La
Chapter Four Results and Discussion
35
Table 4-3: X-ray diffraction pattern data for CuLayFe2-yO4 ferrites thin films with
different La content.
Y 2θ exp.
(Deg.)
dExp.
(Å)
dStd.
(Å)
Chemical
Phase
(hkl) Card No. FWHM
(Deg.)
G.S
(Å)
0.02 35.80 2.506 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.613 128
38.99 2.308 2.311 CuO (111) 96-101-1149 0.551 144
0.04 35.80 2.506 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.490 160
38.99 2.308 2.311 CuO (111) 96-101-1149 0.674 118
49.16 1.852 1.855 CuO (20-2) 96-101-1149 0.306 269
0.06 35.80 2.506 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.490 160
38.99 2.308 2.311 CuO (111) 96-101-1149 0.674 118
49.10 1.854 1.855 CuO (20-2) 96-101-1149 0.306 269
0.08 35.87 2.502 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.490 161
39.17 2.298 2.311 CuO (111) 96-101-1149 0.796 100
49.22 1.850 1.855 CuO (20-2) 96-101-1149 0.613 134
0.1 35.87 2.502 2.523 Cub. CuFe2O4 (131) 96-901-2439 0.490 161
39.11 2.301 2.311 CuO (111) 96-101-1149 0.674 118
49.28 1.848 1.855 CuO (20-2) 96-101-1149 0.429 192
The lattice parameter (a) was calculated using Bragg's law and these values
are given in Table 4-4. It is noticed that the lattice parameter for all samples
seems to be independent of the type of doped rare earth ions. This means
that the rare earth ions occupy either the iron positions or go to the grain
boundaries. The probability that the rare earth ions occupy the A-sites of
Fe3+ ions must be excluded, since the tetrahedral sites too small to be
occupied by the large rare earth ions which have large ionic radius.
Chapter Four Results and Discussion
36
However, the probability of occupancy of the octahedral B- sites by the rare
earth ions increases with decreasing of the R ionic radius [56].
X-ray density was calculated by using equation (3-2). It were generally
found to increase with La addition and showed values between 5.5762 –
5.7575 g/cm3 as shown in Table 4-4.
Table 4-4: Effect of La addition on the Lattice parameter (a), x-ray density of unit cell
(dx) and Molecular weight (M).
y dhkl (Å) hkl M (g/mol) a (Å) V (cm3)*10-22 dx (g/cm3)
0.02 2.506 (131) 240.911 8.311 5.7416 5.5762
0.04 2.506 (131) 242.572 8.311 5.7416 5.6146
0.06 2.506 (131) 244.233 8.311 5.7416 5.6531
0.08 2.502 (131) 245.894 8.298 5.7141 5.7189
0.1 2.502 (131) 247.555 8.298 5.7141 5.7575
4.2 Atomic Force Microscopy Analysis (AFM)
4.2.1 Atomic Force Microscopy for Bulk
The atomic force microscopy of bulk CuLayFe2-yO4 ferrites showed that the
average grain size decreased from 125.75nm to 88.25nm for y=0.04 and 0.1,
respectively (i.e the average grain size decreased with the increase in La
substitution) as shown in Figs.4-3 and 4-4. On the other hand the average
roughness increases from 2.83 to 2.96 nm for y= 0.04 and 0.1, respectively
(i.e the average roughness increased with La substitution) as shown in Table
(4-5).
Cha
apter Four
Fig.4-3:
Fig.4-4
AFM micro
: AFM micr
ographs for
rographs for
37
the compos
r the compo
sition (CuLa
osition (CuL
Results
a0.04Fe1.96O4
La0.1Fe1.9O4)
s and Discu
4) for bulk.
) for bulk.
ussion
Chapter Four Results and Discussion
38
Table (4-5): Average grain size and average roughness for bulk CuLayFe2-yO4
ferrites
La content ( y ) Ave. grain size (nm) Ave. Roughness (nm)
0.04 125.75 2.83
0.1 88.25 2.96
4.2.2 Atomic Force Microscopy for Thin Film
The atomic force microscopy of CuLayFe2-yO4 ferrites thin films deposited
on glass substrate at room temperature are shown in Fig.4-5 and Fig.4-6. It
can be noticed from the images that the average grain size decreased from
92.99nm to 86.85nm for y=0.04 and 0.1, respectively (i.e the average grain
size decreased with the increase in La substitution). On the other hand the
average roughness increases from 0.798 to 0.973 nm for y= 0.04 and 0.1,
respectively (i.e the average roughness increased with La substitution) as
shown in Table (4-6).
Table (4-6): Average grain size and average roughness for CuLayFe2-yO4 ferrites thin film
La content ( y ) Ave. grain size (nm) Ave. Roughness (nm)
0.04 92.99 0.798
0.1 86.85 0.973
Cha
Fig.
Fig.
apter Four
4-5:AFM m
(4-6) AFM
micrographs
micrograph
for the com
hs for the co
39
mposition (C
omposition (
CuLa0.04Fe1.9
(CuLa0.1Fe1
Results
96O4)for thin
.9O4) for thi
s and Discu
n film.
n film.
ussion
Chapter Four Results and Discussion
40
4.3 Optical Properties of Thin Film
The optical properties of CuLayFe2-yO4 ferrites thin films prepared by
pulsed laser deposition (PLD) technique on glass at room substrate
temperature with thickness of (100)nm and which were annealed at
600˚C,were determined using UV-VIS in the region 300-1100 nm. The
properties include the UV-VIS absorption and the transmission spectrum.
The energy gap of the prepared samples was determined.
4.3.1 The Transmission Spectrum
Fig.4-7 shows the optical transmission as a function of wavelength in the
range 300-1100 nm of CuLayFe2-yO4 ferrites thin films prepared on glass
substrate at room temperature with thickness of (100)nm, and annealed at
600˚C under air for 2h. The maximum transmission was observed for
CuLayFe2-yO4 was almost (78.65%), (57.31%), (52.85%) and (42.84%)up to
1100nm of (y=0.02, 0.06, 0.08 and 0.1) respectively. In general, It may be
observed that transmittance decreases with increasing of La content which
means increase in the absorption. The decrease in transmittance with most of
the radiation absorbed for incident photons in the wavelength range 500-
700nm is associated with the fundamental absorption. It is evident from the
spectra that the fundamental absorption edge shows a positive shift in the
wavelength with decreasing grain size ( see table 4-6), which indicates a
shift in optical band gap to lower energy ( table 4-7). However, the relative
high spectral transmission above the fundamental edge reveals that these
ferrites films, in general are weakly absorbing in the spectral range of
investigation. The transmission spectrum reveals that the Cu-La ferrite thin
Chapter Four Results and Discussion
41
films has low absorbance in the visible region and close to the IR region,
however absorbance in the UV region is high.
Fig.4-7: The transmittance versus the wavelength for CuLayFe2-yO4 films with different
La content.
4.3.2 Absorption Coefficient
The variation of absorption coefficient with wave length for CuLayFe2-yO4
ferrites thin films prepared on glass substrate at room temperature with
thickness of (100)nm, and annealed at 600˚C under air for 2h are shown in
Fig.(4-8). It is observed that the absorption coefficient increases with
increasing wavelength due to decrease in transmittance. The linear variation
of absorption coefficient of the ferrite thin films at high frequencies indicates
that these thin films have direct transition across the energy band gap. The
0
20
40
60
80
100
300 400 500 600 700 800 900 1000 1100
Tra
nsm
issi
on%
λ (nm)
y=0.02
y=0.06
y=0.08
y=0.10
Chapter Four Results and Discussion
42
absorption coefficient increased with La content may be due to the increase
in lattice strain caused by the larger ionic radius of La ions.
Fig.(4-8): Shows the absorption coefficient α (cm-1) versus wavelength (nm)
forCuLayFe2-yO4 ferrites thin films.
4.3.3 Optical Energy Gap
The optical energy gap values (Egopt) for CuLayFe2-yO4 films with different
La content was determined by using Tauc formula by plotting the relations
of (αhν)2 vs (hν) in (eV) for direct energy gap. The energy gap is obtained
from intercept of the extrapolated linear part of the curve with the energy
axis.
The direct energy gap values for CuLayFe2-yO4 films with different La
content (y=0.02, 0.06, 0.08 and 0.10) in the range of 3.25-2.28 eV, as shown
in the Fig.4-9. It is also observed that the direct energy gap decrease with La
0.00
100000.00
200000.00
300000.00
400000.00
500000.00
600000.00
700000.00
800000.00
900000.00
300.00 500.00 700.00 900.00 1100.00
α(cm
‐1)
λ (nm)
0.10
0.08
0.06
0.02
Cha
con
fact
con
the
may
F
apter Four
ntent as sh
tors such
ncentration
film and l
y be attrib
Fig.4-9: Ene
own in Ta
as film th
ns, presenc
lattice stra
uted to the
ergy band g
able 4-7. T
hickness, c
ce of imp
ain [57]. T
e decrease
gap at R.T fo
43
The band g
crystallite
urities and
The decrea
e in lattice
or CuLayFe2
gap value
size, stru
d deviatio
ase in band
parameter
2-yO4 films w
Results
is influen
uctural par
on from st
d gap in th
r with La c
with differe
s and Discu
nced by va
rameter, c
toichoimet
he present
concentrat
ent La conten
ussion
arious
arrier
try of
t case
tion.
nt.
Chapter Four Results and Discussion
44
Table 4-7: Effect of La content on energy gap of CuLayFe2-yO4.
La concentration (y) Energy gap (eV)
0.02 3.25
0.06 2.7
0.08 2.65
0.10 2.28
4.4Electrical Properties
The electrical properties of Lanthanum doped copper ferrite CuLayFe2-yO4
with (y=0.02, 0.04, 0.06, 0.08 and 0.1) of Lanthanum additions include the
d.c conductivity, dielectric properties and Hall effect.
4.4.1 Hall Effect Measurements
The Hall effect measurements involved the Hall mobility, Hall coefficient,
resistivity, conductivity and charge carrier concentration as shown in Tables
4-8 and 4-9.
Figs.4-10 and 4-11 show the resistivity (ρ) versus Lanthanum content for
bulk and thin film samples. The resistivity of bulk samples reveals the same
behavior for thin films with the variation of La content. The resistivity was
found to decrease with La content due to the increase in charge mobility.
The results of Hall coefficient listed in Tables 4-8 and 4-9 showed a p-type
semiconductor behavior. Therefore the conduction mechanism in this ferrite
is hopping of electrons between Fe3+and Fe2+ions and hopping of holes
between Cu+2and Cu+3which is the dominant one. The number of hopping of
holes between Cu+2and Cu+3 ions increases with La+3doping. This is because
Chapter Four Results and Discussion
45
of Fe3+ ions migration from the octahedral to the tetrahedral sites [59]. The
decrease in Hall mobility with La addition can be attributed to the
restrictions in the lattice by the large La3+ doping ions.
Table 4-8: Lanthanum ion content effect on Hall mobility, sheet charge concentration,
Resistivity, conductivity and Hall coefficient for CuLayFe2-yO4 bulk.
La content
(y)
Sheet concentration
[ /cm3]
Mobility [cm2/Vs]
Sheet Resistivity
[Ω cm]
Sheet Conductivity
[1/Ω cm]
Average hall coefficient
[m2/C] 0.02 2.383E+6 2.254E+2 3.486E+9 2.869E-10 7.857 E+11
0.04 2.356E+6 7.417E+2 1.072E+9 9.331E-10 7.948 E+11
0.06 5.888E+6 4.015E+2 7.922E+8 1.262E-9 3.181E+11
Table 4-9: Lanthanum ion content effect on Hall mobility, sheet charge concentration,
Resistivity, conductivity and Hall coefficient for CuLayFe2-yO4 thin film .
La content (y)
Sheet concentration [ /cm2]
Mobility [cm2/Vs]
Sheet Resistivity [Ω cm]
Sheet Conductivity [1/Ω cm]
Average hall coefficient [m2/c]
0.04 2.495E+6 2.507E+3 9.981E+3 1.002E-4 2.502E+7
0.06 5.084E+5 1.459E+2 8.414E+3 1.189E-4 1.228E+6
0.08 1.159E+7 3.879E+3 1.388E+3 7.203E-4 5.386E+6
Chapter Four Results and Discussion
46
Fig.4-10: Effect of La concentration as a function of resistivity for CuLayFe2-yO4 bulk .
Fig.4-11: Effect of La concentration as a function of resistivity for CuLayFe2-yO4 thin film.
0
500000000
1E+09
1.5E+09
2E+09
2.5E+09
3E+09
3.5E+09
4E+09
0.02 0.03 0.04 0.05 0.06
Resistivity [Ω
cm]
La content
0
2000
4000
6000
8000
10000
12000
0.04 0.05 0.06 0.07 0.08
Resistivity [Ω
cm]
La content
Chapter Four Results and Discussion
47
4.4.2 A.C Conductivity:
In order to study conductivity mechanisms, it is convenient to plot
logarithm of the conductivity (Ln σ) as a function of 1000/T for CuLayFe2-
yO4 bulk in the range (298 – 473) K with fired at 900 °C for (2 h) as shown
in Fig.(4-13). The activation energy Eav decreased with the frequency
increase as shown in Fig.(4-14). Conductivity σ increases with the increase
in frequency as shown in Fig.(4-12). The frequency dependent σ can be
explained on the basis of Maxwell- Wagner two layers model. At lower
frequency, the grain boundaries are more active, hence the hopping
frequency of electrons between Fe3+ and Fe2+ ions is less. At higher
frequencies, the conductive grains boundaries become more active by
promoting the hopping of electrons between Fe3+ and Fe2+ ions therefore
increasing the hopping frequency [58]. So we observe the increase in
conductivity with the increase in frequency.
Fig. (4-12): Effect of conductivity as a function of frequency.
‐18
‐17.5
‐17
‐16.5
‐16
‐15.5
‐15
‐14.5
‐14
11 12 13 14 15 16 17 18
Ln
(σ)
Ln (ω)
y=0.1
y=0.08
y=0.06
y=0.04
y=0.02
Chapter Four Results and Discussion
48
Fig.(4-13): Plot of Ln (σ) versus 1000/T (K-1) for CuLayFe2-yO4 bulk.
Fig.(4-14): Effect of activation energy as a function of frequency of bulk CuLayFe2-yO4 .
-24
-23
-22
-21
-20
-19
-18
2 2.5 3 3.5
Ln
(σ)
1000/T (K-1)
f=100 kHz
f=40 kHz
f=20 kHz
f=4 kHz
f=1 kHz
f=200 Hz
0
0.01
0.02
0.03
0.04
0.05
100 1000 10000 100000
Ea
(eV
)
f (Hz)
Chapter Four Results and Discussion
49
4.4.3 Dielectric Properties
The variation of the real and imaginary parts of the dielectric constant
values versus frequency are drown in Figs. (4-15) and (4-16) for bulk
Lanthanum doped copper ferrite.
Fig.(4-15) shows the dependence of the real part of dielectric constant ε1
on the frequency ω, for different La doping contents. The dielectric constant
is found to decrease more rapidly at low frequencies than at higher
frequencies, showing the usual dielectric dispersion. The dispersion of
dielectric constant with frequency is due to Maxwell-Wagner type interfacial
polarization and is in agreement with koop’s phenomenological theory [59].
The polarization in ferrite is through a mechanism similar to the conduction
process. The presence of Fe3+ and Fe2+ ions has rendered ferrite materials
dipolar. Rotational displacement of dipoles results in orientational
polarization. In ferrites, the rotation of Fe2+↔Fe3+ dipoles may be visualized
as the exchange of electrons between the ions so that the dipoles align
themselves in response to the alternating field. The existence of inertia to the
charge movement would cause relaxation of the polarization. In general the
dielectric constant increase with La content may be due to the various
contributions to the polarization.
The imaginary part of dielectric constant (ε2 ) versus frequency ω is shown
in Fig.(4-16). The decrease in (ε2) with increasing frequency agrees well
with Deby’s type relaxation process [59]. The imaginary part of dielectric
constant was noticed to decrease with La content because rare earths are
known as low dielectric loss materials. The Conduction in ferrite is
attributed to hopping of electrons from Fe3+ to Fe2+ions. The number of such
Chapter Four Results and Discussion
50
ion pairs depends upon the sintering conditions and amount of reduction of
Fe3+ to Fe2+ at elevated temperatures. The resistivity of ferrite is controlled
by the Fe2+ concentration on the B-site.
The hole exchange between Cu2+and Cu1+ ions for responsible for p-type
charge carriers. The coupling mechanism for hole exchange can be
represented as
Cu2+↔Cu1++e+(hole)…….. (4-1)
The La3+ ion occupies an octahedral site (B-site), which leads to the
replacement of some Fe3+ ions from B-sites.
Fig.4-15: Effect of real part of dielectric constant with frequency and La addition.
0
5
10
15
20
25
30
11 12 13 14 15 16 17 18
ε 1
Ln(ω)
y=0.02
y=0.04
y=0.06
y=0.08
y=0.1
Chapter Four Results and Discussion
51
Fig.4-16: Effect of imaginary part of dielectric constant with frequency and La addition.
0
5
10
15
20
25
11 12 13 14 15 16 17 18
ε 2
Ln(ω)
y=0.02
y=0.04
y=0.06
y=0.08
y=0.1
((Conclusions and Suggestions for Future Work))
Chapter Five Conclusion and Suggestion
52
Chapter Five
Conclusion and Suggestion
5.1 Conclusion:
To summarize the main ideas obtained, the following conclusions can be
drawn from this work:
1. The main cubic spinel structure phase for bulk samples was confirmed
by the x-ray diffraction patterns with the appearance of small amount
of secondary phases. But for thin films the main phase was pure cubic
structure for all samples.
2. The atomic force microscope (AFM) micrographs showed that the
average grain size for thin films is less than the average grain size for
bulk.
3. The optical measurements showed that the CuLayFe2-yO4 ferrite thin
films have direct energy gap. It is also observed that the direct energy
gap decrease with La content.
4. The results of Hall coefficient showed a p-type semiconductor
behavior. The conduction mechanism in this ferrite is due to hopping
of holes between Cu2+ and Cu1+.
5. The conductivity was found to increase with the frequency.
6. The imaginary part of dielectric constant ε2 reveals the same behavior
of the real part ε1 with the variation of La content both decreased with
increased frequency. The decrease in ε1&ε2 with increased frequency
agrees well with Deby’s type relaxation process.
Chapter Five Conclusion and Suggestion
53
7. Comparison of bulk and thin film properties show that the properties
of the thin films in many aspects similar to those of the bulk, which
makes the PLD deposited ferrite films prime candidates for thin film
high-frequency microwave device applications.
5.2 Suggestions for Future Work:
The following studies for a future work are suggested:
1. Studying the effects of other kinds of rare earth substitutions (e.g. Eu,
Sm, Nd, Ce etc) with different doping levels on the properties of
copper ferrites.
2. Studying the magnetic permeability and magnetic susceptibility of La
doped copper.
3. Preparing copper ferrite thin films using different techniques e.g
chemical vapor deposition, to study the structural, electrical and
optical properties at various substrate temperature.
4. Studying the application of copper ferrite thin film as magnetic
sensors, magnetic recording media and microwave devices.
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الخالصةحيث أن CuLayFe2-yO4أحد أنواع الفيرايت ذو الصيغة التركيبية العامة حضرت
y=0.02,0.04,0.06,0.08 and 0.1) أستخدمت بالتحضير الطريقة القياسية في معالجة ،(
المساحيق لتحضير عينه بشكل قرص كما استخدمت تقنية الترسيب بالليزر النبضي لتحضير
راسة العينات المحضرة بأستخدام األشعه السينيه أظھرت النتائج تكون األغشية الرقيقة. عند د
ة جدا من االطوار الثانوية للعينه طور السبينل المكعب التركيب مع وجود كميات صغير
القرصيه. لألغشية الرقيقة من الفيرايت كان الطور االساسي بتركيب المكعب البسيط لجميع
-8.298للعينه القرصيه و Å 8.348-8.285العينات. قيمة ثابت الشبيكة كانت تتراوح بين
8.311 Å راكيزلالغشية الرقيقة. كثافة االشعة السينية تزداد مع زيادة تLa حيث تتراوح قيمھا
لألغشية الرقيقة. g/cm3 5.7575-5.5762 للعينه القرصيه،g/cm3 5.7461–5.5826بين
أظھرت . Laعند أستعمال مجھر القوة الذري كان معدل الحجم الحبيبي يقل مع زيادة تراكيز
قه مباشرة بأنه يمتلك فجوة طا CuLayFe2-yO4القياسات البصرية لألغشية الرقيقة للفيرايت
أما نفاذية االغشية الرقيقة لفيرايت النحاس المطعم eV 3.25-2.28تتراوح قيمتھا بين
معامل االمتصاص يزداد مع زيادة تراكيز مع زيادة تركيز الالنثينيوم. قلبالالنثينيوم فكانت ت
لتحركية. نتائج في ا الزيادةوذلك بسبب Laمع زيادة تراكيز ال تقلالمقاومة النوعية .الالنثينيوم
. طاقة التنشيط تقل كلما زاد pمعامالت ھول تبين لنا بأن حامالت الشحنة االغلبية تكون من نوع
التردد أما التوصيلية الكھربائية تزداد بزيادة التردد. الجزء الخيالي لثابت العزل الكھربائي يسلك
ا بزيادة التردد. نفس سلوك الجزء الحقيقي لثابت العزل الكھربائي حيث يقل كالھم
العراقجمھورية
وزارة التعليم العالي والبحث العلمي جامعة بغداد كلية العلوم
قسم الفيزياء
الخصائص فيرايت نظامالتركيبية و الكھربائية والبصرية ل
CuLayFe2-y
أطروحة مقدمة الى جامعة بغداد -كلية العلوم
وھي جزء من متطلبات نيل درجة الماجستير في الفيزياء
من قبل دعاء باسل فھد
بأشراف
نوري دمحم أ.م.د. فرح طارق أ.م.د. مظفر فؤاد جميل
ھ 1435 م 2014
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