structural, electrical and optical properties of cula...

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].


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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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.


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


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.


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


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.


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.


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,


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


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].


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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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


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


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].


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.


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]


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].


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)


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


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


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).


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


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


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


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


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.


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


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


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


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


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.


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


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


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


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


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)


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


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


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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54

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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

structural, electrical and optical properties of cula...

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