INVESTIGATION ON THE STRUCTURAL AND OPTICAL …monografias.poli.ufrj.br/monografias/monopoli10026499.pdf · Projeto de Graduação apresentado ao Curso ... Kumar and their family,

INVESTIGATION ON THE STRUCTURAL AND

OPTICAL PROPERTIES OF Alq3/METAL/Alq3 HYBRID

SANDWICH STRUCTURE FOR OLED APPLICATIONS

Thaiana Vale Smilgevicius

Projeto de Graduação apresentado ao

Curso de Engenharia de Materiais da

Escola Politécnica, Universidade Federal

do Rio de Janeiro, como parte dos

requisitos necessários à obtenção do

título de Engenheira de Materiais.

Orientadores: Prof. Renata Antoun Simão, DSc.

Prof. Vidhya Chavan, DSc.

Ing. Mohan Amalraj, MSc.

Rio de Janeiro

Julho de 201

iii

Smilgevicius, Thaiana Vale

Investigation on the Structural and Optical

Properties of Alq3/Metal/Alq3 Hybrid Sandwich

Structure for OLED Applications / Thaiana Vale

Smilgevicius. – Rio de Janeiro: UFRJ / Escola

Politécnica, 2018.

xiii, 50 p.: II; 29,7 cm.

Orientadores: Prof. Renata Antoun Simão, DSc., Prof.

Vidhya Bhavan, DSC., Ing. Mohan Amalraj. MSc.

Projeto de Graduação – UFRJ / Escola

Politécnica / Engenharia de Materiais, 2018.

Referências Bibliográficas: p. 45-50.

1. Sandwich Structure. 2. OLED 3. Physical Vapor

Deposition. I. Simão, Renata Autoun. II.

Universidade Federal do Rio de Janeiro, Escola

Politécnica, Curso de Engenharia de Materiais. III.

Investigation on the Structural and Optical

Properties of Alq3/Metal/Alq3 Hybrid Sandwich

Structure for OLED Applications.

iv

Acknowledgements

First and foremost, I thank my parents Vera Lúcia da S. V. Smilgevicius and

Otávio Luís Smilgevicius, my sister Vanessa Vale Smilgevicius and her

daughter Ana Clara, my uncles and my grandmothers for their unconditional

love and support throughout my life.

Even with cultural diversity, I chose to seek a differential for my academic

life and to acquire new knowledge. I found out about the IAEST program and I

have decided to register. In 2017 I was selected to participate in the program, in

Tamil Nadu, India. I would like to express my gratitude to the Karunya

University for providing necessary infrastructure and resources to accomplish

my research work. I thank the IAEST members for the internship opportunity.

This experience has made me a different person.

Thanks Federal University of Rio de Janeiro for renowned quality and

technology. It was a pleasure to study at one of the best university in Brasil.

I am thankful to my supervisor Renata Antoun Simão, in Federal University

of Rio de Janeiro, who has proved to be a great coordinator and an enabler

teacher. She always ready to help and teach all her students.

I pay homage to my supervisor Dr. B. Vidhya, in Karunya University. This

work would not have possible without her important guidance, innovative ideas,

comments and suggestions which made the project more interesting. I also

thank A. Mohan for the constant support, valuable explications and patience

throughout the project.

I would like to thank all professors in Federal University of Rio de Janeiro,

who were help to improve my studies. I can not forget the Vinay and Pranay

Kumar and their family, Sr. Alex, Isaac Nelson. P, S. Rajesh, Sheeba, Ashwini,

Judy, Vani, Amal, Adebisi and all my laboratory friends for make my internship

more agreeable.

Thank you Larissa Gôuvea and Olga Veridiano for being the best friends and

Jules Guépratte for joining me in these years.

To all my friends and for everyone, who directly or indirectly, contributed to

my formation as an engineer.

v

“Persistence is the

smallest phat to success.”

Charles Chaplin

vi

Resumo do Projeto de Graduação apresentado à Escola Politécnica/UFRJ como

parte dos requisitos necessários para a obtenção do grau de Engenheira de

Materiais.

INVESTIGATION ON THE STRUCTURAL AND OPTICAL

PROPERTIES OF Alq3/METAL/Alq3 HYBRID SANDWICH

STRUCTURE FOR OLED APPLICATIONS

Thaiana Vale Smilgevicius

Orientadores: Prof. Renata Antoun Simão, DSc., Prof. Vidhya Bhavan, DSC.,

Ing. Mohan Amalraj. MSc

Curso: Engenharia de Materiais

O Tris(8-hidroxiquinolinato) de alumínio (Alq3) é utilizado tanto na

camada de emissão como na camada de transporte de elétrons em diodos

orgânicos emissores de luz. (OLED).

Este trabalho contém resultados de investigação das propriedades

estruturais e ópticas de filmes finos de Alq3 comparados com a estrutura em

forma de sanduíche (Alq3 / Metal /Alq3), sendo os metais: Índio (In), Gálio (Ga),

Cobre (Cu) e Estanho (Sn); e depois comparado com o processo recozido da

estrutura (Alq3 / In /Alq3) a 150° C, 250° C e 350° C.

Esta estrutura em sanduíche foi preparada utilizando a técnica de

deposição física de vapor à temperatura ambiente. As espessuras das camadas

são de 50 nm e 30 nm respectivamente, para Alq3 e Metal.

As propriedades ópticas foram caracterizadas por emissão via

Fotoluminescência (PL) e Espectroscopia UV-Visível. As propriedades

estruturais foram analisadas por difração de raios X, Microscopia Eletrônica de

Varredura (MEV).

Os estudos de difração de raios X revelam a formação de compósitos.

Novas emissões de cores foram observadas na estrutura de sanduíche aquecida

e suas propriedades estruturais e ópticas foram melhoradas. Essas estruturas

multicamadas possuem amplas aplicações em dispositivos optoeletrônicos,

particularmente em OLEDs.

Palavras-chave: Alq3, Estrutura sanduíche, OLED, Deposição Física de Vapor

vii

Abstract of Undergraduate Project presented to POLI/UFRJ as a partial

fulfillment or the requirements for the degree of Materials Engineer.

INVESTIGATION ON THE STRUCTURAL AND OPTICAL

PROPERTIES OF Alq3/METAL/Alq3 HYBRID SANDWICH

STRUCTURE FOR OLED APPLICATIONS

Advisors: Prof. Renata Antoun Simão, DSc., Prof. Vidhya Bhavan, DSC., Ing.

Mohan Amalraj. MSc

Course :MaterialsEngineering

Tris- (8-hydroxyquinolinate) Aluminum (Alq3) is used both as the

emission and electron transport layer in organic light emitting diodes

(OLED).

This work contains results of investigation of the structural and optical

properties of Alq3thin films compared to sandwich (Alq3/ Metal Alq3)

structure being the metal Indium (In) (after compared with the its annealed

process (150o C, 250o C and 350o)), Gallium (Ga), Cooper (Cu) or Tin (Sn).

This sandwich structure was prepared using physical vapor deposition

technique at room temperature. The layers thickness is 50 nm and 30 nm

respectively for Alq3 and Metal. The photophysical properties were

characterized by emission via Photoluminescence (PL) and UV-Visible

Spectroscopy.

The structural properties were analyzed through X-ray diffraction,

Scanning Electron Microscopy (SEM). The X-ray diffraction studies reveal the

formation of composites. News colors emission was observed in the annealed

sandwich structure. The structural and optical properties were improved in

annealed hybrid sandwich structure. These type multilayer structures find ample

applications in optoelectronics devices particularly in OLEDs.

Keywords: Alq3, Sandwich Structure, OLED, Physical Vapor Deposition

viii

Summary of Contents

1. Introduction............................................................................................1

1.1. Aims..............................................................................................2

1.1.1. Specific Aims and Objective................................................2

2. Literature Review...................................................................................3

2.1. Tris (8-hydroxyquinoline) Aluminium (Alq3)..............................3

2.1.1. Structure of Alq3...................................................................3

2.1.2. Optical Properties of Alq3.....................................................4

2.1.3. Application of Alq3...............................................................5

2.2. Organic Light-Emitting Diodes (OLEDs)………………………5

2.3. Materials and Methods………………………………………….7

2.3.1. Importance of Alq3…………………………………………7

2.3.2. Properties and Application of Metals…………...…………8

2.3.2.1. Indium (In)…………………………………………8

2.3.2.2. Copper (Cu)……………..…………………………8

2.3.2.3. Gallium (Ga)…………………………………...…..9

2.3.2.4. Tin (Sn)………………………………………….....9

2.3.3. The Film Deposition…………………...…………………10

2.3.4. Physical Vapor Deposition (PVD)……………………..…11

2.3.4.1. PVD Working Principle………………………..…12

2.3.5. Selection of Materials…………………………………….13

2.3.6. Substrate Cleaning Process……………………………….14

2.3.7. Preparation of Alq3/Metal/Alq3 Hybrid Sandwich

Structure.…………………………………………...……….14

2.3.8. X-ray Diffraction Pattern…………………………………15

ix

2.3.8.1. Braggs Diffraction Law…………………………..15

2.3.8.2. Determination of Structural Parameters…………..16

2.3.9. Scanning Electron Microscopy………………...…………17

2.3.10. UV-Visible Spectroscopy……………………………...…18

2.3.11. Photoluminescence Spectroscopy………………………...20

3. Results and Discussion……………………………………………22

3.1. Enhancement of PL Emission Through Alq3 / Metal / Alq3

Hybrid Sandwich Structure With Different Metal Layers…………22

3.1.1. Experimental Details………………………………….....22

3.1.2. X-ray Diffraction…………………………………..…….23

3.1.3. Surface Morphological Analysis………………………....24

3.1.4. Optical Studies…………………………..………………..25

3.1.5. Partial Conclusion….……………………………………..29

3.2. Investigation on Structural and Optical Properties of Hybrid

Alq3/In/Alq3 Composite Thin Films…………………….........30

3.2.1. Experimental Details……………………………………...30

3.2.2. Structural Studies………………………………………....31

3.2.3. Surface Morphological Studies……...………………....…31

3.2.4. Optical Studies……………………………………………32

3.2.5. Partial Conclusion………………….……………………..36

3.3. Impact of Annealing on Hybrid Alq3 / In / Alq3

Composite Thin Films…………..…...……………………………36

3.3.1. Experimental Details……………………………………...36

3.3.2. Structural Studies…………………………………………37

3.3.3. Surface Morphological Studies…………………………...38

3.3.4. Optical Studies………………………………..…………..40

3.3.5. Partial Conclusion….……………………………………..43

x

4. Final Conclusion.……………………………………………………43

5. Suggestions for Future Studies……………………………………...44

6. Bibliographic References……………………………………………44

List of Figures

Figure 1 - Structure of Tris (8-hydroxyquinoline) aluminium (Alq3)[1]

Figure 2 - Light Emission [2]

Figure 3 - Organic light emitting diode [3]

Figure 4 - Schematic diagram of OLED device structure [4]

Figure 5 - Thermal evaporation unit

Figure 6 - HINDHIVAC Vacuum Chamber model 12A4D,

Figure 7 - Schematic diagram of Alq3/metal/Alq3 hybrid structure

Figure 8 - Schematic representation of Briggs’s Law [5]

Figure 9 - Ultraviolet-visible (UV-vis) spectroscopy working process [6]

Figure 11 - PL Spectrometer working setup [7]

Figure 10 - PL absorption and emission process [8]

Figure 12- Schematic diagram of Alq3/metal/Alq3 hybrid structure (a)

Alq3/Cu/Alq3 , (b) Alq3/Ga/Alq3, (c) Alq3/In/Alq3 and (d) Alq3/Sn/Alq3

Figure 13 - X-ray diffraction pattern of hybrids structures

Figure 14 - SEM image of Alq3/metal/Alq3 hybrid structure (a)

Alq3/Cu/Alq3, (b) Alq3/Ga/Alq3, (c) Alq3/In/Alq3 and

xi

(d) Alq3/Sn/Alq3

Figure 15 - Optical spectra of (a) as deposited Alq3and Alq3/metal/Alq3

hybrid structure (b) Alq3/Cu/Alq3 , (c) Alq3/Ga/Alq3, (d) Alq3/In/Alq3 and

(e) Alq3/Sn/Alq3

Figure 16 - Optical energy band gap of (a) as deposited Alq3and

Alq3/metal/Alq3 hybrid structure (b) Alq3/Cu/Alq3 ,

(c) Alq3/Ga/Alq3, (d) Alq3/In/Alq3 and (e) Alq3/Sn/Alq3

Figure 17 - PL emission spectra of (a) as deposited Alq3and Alq3/metal/Alq3

hybrid structure (b) Alq3/Cu/Alq3 (c) Alq3/Ga/Alq3, (d) Alq3/In/Alq3 and (e)

Alq3/Sn/Alq3

Figure 18 - Structure of hybrid sandwich (Alq3/In/Alq3)

Figure 19 - X-ray diffraction pattern, (a) Alq3 and (b) Alq3/In/ Alq3 hybrid

structure

Figure 20 - SEM images (a) Alq3and (b) Alq3/In/Alq3 hybrid structure

Figure 21 - Optical spectra of as deposited Alq3 and Alq3/In/Alq3 hybrid

structure (a) transmission and (b) absorption spectra

Figure 22 - Optical energy band gap (a) Alq3 and (b) Alq3/In/Alq3 hybrid

structure

Figure 23 - PL emission spectra (a) Alq3 and (b). Alq3/In/Alq3 hybrid

structure

Figure 24 - Alq3/In/Alq3 hybrid sandwich structure

Figure 25 - X-ray diffraction pattern of hybrid sandwich structure (a) as

deposited, (b)150°C, (c) 250°C and (d) 350°C

Figure 26 - SEM image of Alq3/In/ Alq3 hybrid structure with different

annealing temperatures

Figure 27 - Optical absorption spectra of of Alq3/In/ Alq3 hybrid structure

with different annealing temperatures

xii

Figure 28 - Optical energy band gap of Alq3/In/ Alq3 hybrid structure with

different annealing temperatures

Figure 29 - PL emission spectra of Alq3/In/Alq3 hybrid structure with


List of Tables

Table 1 - Fundamental properties of different metals [9]

Table 2 - Physical vapor deposition unit specification (HHV – 12A4D)

Table 3 - XRD characteristic of hybrid structure


List of Symbols and Abbreviations

D Grain size

Wavelength

β Full width at half maximum

δ Density

Micro strain

θ Bragg’s angle

k Excitation coefficient

T Transmission of film

Absorption coefficient

hυ Incident photon energy

Eg Optical energy band gap

B Constant

xiii

n Direct or indirect allowed transition coefficient

g Grams

Alq3 Tris (8-hydroxyquinoline) aluminium

In Indium

Cu Copper

Ga Gallium

Sn Tin

N Nitrogen

O Oxygen

mer Meridional

fac Facial

OLED Organic light-emitting diode

ETM Electron-transport material

ELM Emitting layer material

PVD Physical vapor deposition

XRD X-ray diffraction

SEM Scanning electron microscopy

UV Ultraviolet

PL Photoluminescence

1

1 Introduction

An organic light-emitting diode (OLED) is a light emitting diode (LED) with

an organic semiconductor layer located between two electrodes

(electroluminescent emission layer) and are composed of thin films which can

create light with the application of electricity and use less power and it can have

a brighter display than the LEDs or liquid crystal displays (LCDs). [10]

Conducting polymers has a great interest in research focus due to their

potential application such as optoelectronics, OLED displays, flexible solar

cells, etc. The OLEDs are used on digital displays of devices such as televisions,

computer monitors, cell phones, etc and it can be deposited on flexible surfaces.

Tris-(8-hydroxyquinoline) aluminum (Alq3) is an organometallic, compound

containing at least one bond between a carbon atom of an organic compound

and a metal and it has an important property of emitting light over different

wavelengths in the visible spectra.

The Alq3 is one of the materials which is the most commonly used in

molecular organic light emitting diodes (OLEDs), specifically used as electron

transport layer or emissive layer. Considerable works have been done to

improve the device performance and stability and each research is a step

towards the advancement of material science.[11, 12]

In the present study, a sandwich layer was produced by physical vapor

deposition technique (PVD) at room temperature and was investigate the

structural and optical properties of Alq3 thin films compared to sandwich

(Alq3/Metal/Alq3) structure being the metal Indium, Gallium (Ga), Cooper (Cu)

and Tin (Sn). The Indium deserved a better attention and because that, annealed

sandwich Alq3/In/Alq3 structures were studies.

Metals peaks were revealed through X-ray diffraction and the grain size was

calculated. The sandwich structure was analyzed by SEM image showing the

thin films surfaces and their morphological studies. The transmission and

absorption optical was produce by Ultraviolet-visible (UV-Vis) spectroscopy

and the optical energy band was calculated. Finally, a Photoluminescence (PL)

emission spectra was studied the optical properties. The results were analyzed

and discussed to come a descriptive conclusion.

2

1.1 Aims

The main goal of this work was to produce, obtain and characterize

the structural, optical and morphologically properties of a composite

Structure formed by the Tris (8-hydroxyquinoline) aluminium (Alq3) in form

of powder and a metal. Metals were chosen as Indium (In), Copper (Cu),

Gallium (Ga) or Tin (Sn) and they were deposited by Physical Vapor

Deposition (PVD) over the glass substrate. The samples Alq3/In/Alq3 were

annealed at different temperatures (150o C, 250o C and 350o) and their

properties compared.

The purpose of the study is the investigation these sandwich structures

and find applications in optoelectronics devices particularly in OLEDs.

1.1.1 Specific Aims and Objectives

In order to achieve the objective, the following work elements have been

set.

• Preparation of Alq3/Metal/Alq3 hybrid sandwich structure with different

metal layers such as Cu, In, Ga and Sn.

• Preparation of Alq3/In/Alq3 hybrid sandwich structure and to investigate

structural and optical properties.

• Preparation of Alq3/In/Alq3 hybrid sandwich structure and to investigate

the impact of annealing with different temperatures.

• The research findings are analysed through the characterizations of the

samples using XRD, SEM, optical absorption spectra and

photoluminescence.

3

2 Literature Review

2.1 Tris (8-hydroxyquinoline) Aluminium(Alq3)

2.1.1 Structure of Alq3

The tris (8-hydroxyquinoline) aluminium (Alq3) has the formula

Al(C9H6NO)3 , and it is an organometallic, compound containing at least one

bond between a carbon atom of an organic compound and a metal. The Alq3

density is 459.43 g/mol. A binder arrangement may give rise to optical isomers.

The octahedral complexes of the type MN3O

3, where M is a trivalent metal and

N and O stand for the nitrogen and oxygen atoms in the quinolone ligands, can

exhibit two different geometric isomers: meridional and facial.[13,14]

The figure 1 shows the different isomers of Alq3 which are related to the

crystalline phases, α-, β-, γ-, δ- and ε-. It is known that the isomeric state of α-

and β- have two mer-Alq3 molecules in a unit cell, while δ- have four fac-Alq3

per unit cell. Between the both forms, the meridional isomers are the dominant

form both in amorphous films and crystals of Alq3.[15,16]

Figure 1- Structure of Tris (8-hydroxyquinoline) aluminium (Alq3)

The different HOMO and LUMO levels predicted for the two isomers

influences the injection barrier and could act as traps for charge carriers. The

energy separation between the both is determined by the material bonding

structure. After external excitation, the electrons of atoms gain enough energy

4

and jump from HOMO level, the highest occupied molecular orbit to the LUMO

level, the lowest unoccupied molecular orbit.[17]

2.1.2 Optical Properties of Alq3

Theoretically, linear and nonlinear optical properties of the organometallic

compounds are similar to organic materials though the intensity of the nonlinear

response is higher. The Alq3 has an important property: The organic material

can emit light. It can be observed over different wavelengths in the visible

spectra. Green, blue and red colors are obtained from Alq3 and thereby the white

is acquired. The relationship between structures and light emission is decisive

to control the spectral yield of electro-luminescent devices. The Alq3 isomeric

states are an important parameter to relate the colors. For example, the green

emission is caused by a mer-isomer, while the blue emission is caused by a fac-

isomer.

The value of band gap Eg defines the fundamental light absorption edge

and because of that, this optical parameter is also important to be considered.

The light with enough energy can stimulate electrons from the highest occupied

molecular orbital (HOMO) to the lowest unoccupied molecular orbital

(LUMO). A small band gap is desire for the electron can walk a short way.

Figure 2 - Light Emission

5

The absorption and emission in Alq3 may happen due to electron transitions

between the both orbitals[18-21].

The first report on blue luminescent Alq3 obtained by a simple annealing

process from yellowish-green Alq3 (𝛂-phase), above the phase transition at

about 380 °C as the 𝛅-phase[31]. The figure 2 exemplify the organic material

light emission.

2.1.3 Applications of Alq3

The low molecular weight and conjugated organic materials constitute a big

field for the flat panel display technology. Hybrid organic-inorganic

nanocomposite materials can change the properties as the chemical resistance,

thermal stability, electrical and optical properties. These materials offer a wide

range of possibilities for preparing tailor-made materials and several advantages

for new optical applications. Tris(8-hydroxyquinoline)aluminum has become

the most widely used electroluminescent materials in organic light-emitting

diodes (OLED), solar cells and organic field- effect transistors (OFET)[22]. The

most important is the OLED, because the Alq3 can be used as electron-transport

material (ETM) for the ability to have good electron injection a high electron

mobility. The ETMs are utilized to accept electrons from cathode efficiently.

The other application, inside the OLED is emitting layer material (ELM) that

consists of light-emitting dyes or dopants dispersed in a suitable host material.

Other Alq3 advantages include the high thermal stability, high quantum

yield, even in the solid state and the formation of stable and pinhole-free thin

films. Alq3 serves as host material for various dyes to tune the emission color

from green to red[23,24].

2.2 Organic Light-Emitting Diodes (OLEDs)

Organic materials have previously been considered for the fabrication of

practical electroluminescent (EL) devices. There is a large number of organic

materials known to have extremely high fluorescence quantum efficiencies in

6

the visible spectrum[25,26].

Figure 3 - Organic light emitting diode

Organic electronics were study as an educational object in 50’ decades. In

1987, OLEDs were studied by C. Tang and VanSlyke. They invented an OLED

device using the resistive thermal deposition technique of thin films, controlling

the work voltage (~10V) being able to control, with precision, the thicknesses

of the layers. The film can be deposited on several flexible substrates and,

furthermore, it can produce a wide range of colors emission. Those properties

enable the OLEDs technologies to be used in computer screens, cell phones,

panels, optical sensors, etc[27].

The OLED structure can be formed by a basic layer, composed by a cathode,

an anode and an emitting layer and can be more complex, with different types

of layers with a very specific transport property. The figure 3 shows an organic

light emitting diode.

The figure 4 demonstrate the OLED structure and the layers are observed

between the metal cathode and the anode. Organic layers in OLEDs with

efficient light emission, good electron- and hole-injection and transport

properties significantly improve the device performance.

The electron-transport material (ETM) is a good electron injection, high

electron mobility and can be used to accept electrons from cathode efficiently.

The emitting layer material (ELM) consists of light-emitting dyes or dopants

disperses in a suitable host material.

Some advantages can be cited like a high thermal stability, electron-transport

ability and light emitting, formation of stable thin films, etc[28-30].

7

Figure 4 - Schematic diagram of OLED device structure

2.3 Materials and Methods

2.3.1 Importance of Alq3

Recently, conducting polymers and polymer-based devices has a greater

interest in research focus due to their potential application such as

optoelectronics, organic light emitting diode (OLED) displays, flexible solar

cells, etc. [32-34] It is well-known that inorganic semiconductors when reduced

to the nanometer regime possess characteristics between the classic bulk and

molecular descriptions, exhibiting properties of quantum confinement. Thus,

adding metallic, semiconducting and dielectric nanocrystals into polymer

matrices enables the enhancement of efficiency and service duration of the

devices[35,36].

The inorganic additives usually were nanoparticles. The influence of

nanocrystalline oxides on the properties of semiconducting polymers has been

largely investigated by many groups [37,38]. It has been found that

nanostructured composites and nanohybrid layers or heterojunctions can be

applied to a variety of practical purposes.

Among these applications, two main directions have been set: one is focused

on the interaction between electrons and photons in devices such as OLEDs,

where the electricity generates light and the other aim at the generation of

8

electricity as in organic solar cells (OSCs). Tris-(8-hydroxyquinolinate)

aluminum (Alq3) is used both as the emission and electron transport layer in

organic light emitting diodes (OLED).

2.3.2 Properties and Application of Metals

2.3.2.1 Indium (In)

It was discovered by German chemists Ferdinand Reich and Hieronymus

Theodor Richter while they were examining zinc ore samples om 1863. A soft,

silvery metal that is stable in air and water. Most indium is used to make indium

tin oxide (ITO), which is an important part of touch screens, flat screen TVs and

solar panels. This is because it conducts electricity, bonds strongly to glass and

is transparent. Traditionally it has been one of the metals used to make coins,

along with silver and gold. However, it is the most common of the three and

therefore the least valued.[39]

2.3.2.2 Copper (Cu)

Copper was discovered by the ancients. The reddish-gold metal is easily

worked and drawn into wires. Most copper is used in electrical equipment such

as wiring and motors. This is because it conducts both heat and electricity very

well and can be drawn into wires. It also has uses in construction (for example

roofing and plumbing), and industrial machinery (such as heat exchangers).

Copper sulfate is used widely as an agricultural poison and as an algicide in

water purification. Copper compounds, such as Fehling’s solution, are used in

chemical tests for sugar detection[40].

2.3.2.3 Gallium (Ga)

Gallium was discovered by Paul-Émile Lecoq de Boisbaudran in 1875. It is

9

very soft, silvery-white metal, similar to aluminum. Solid gallium is a blue-gray

metal with orthorhombic crystalline structure; very pure gallium has a stunning

silvery color. Gallium is solid at normal room temperatures, but similar to

mercury, cesium, and rubidium it becomes liquid when heated slightly. Solid

gallium is soft enough to be cut with a knife. It is stable in air and water; but it

reacts with and dissolves in acids and alkalis.

Gallium arsenide has a similar structure to silicon and is a useful silicon

substitute for the electronics industry. It is an important component of many

semiconductors. It is also used in red LEDs (light emitting diodes) because of

its ability to convert electricity to light. Solar panels on the Mars Exploration

Rover contained gallium arsenide. Gallium nitride is also a semiconductor. It

has properties that make it very versatile. It has important uses in Blu-ray

technology, mobile phones, blue and green LEDs and pressure sensors for touch

switches. Gallium readily alloys with most metals. It is particularly used in low-

melting alloys[41].

2.3.2.4 Tin (Sn)

Tin is soft, pliable metal. Below 13°C it slowly changes to a powder form

and it has many uses. It takes a high polish and is used to coat other metals to

prevent corrosion, such as in tin cans, which are made of tin-coated steel. Alloys

of tin are important, such as soft solder, pewter, bronze and phosphor bronze. A

niobium-tin alloy is used for superconducting magnets. Most window glass is

made by floating molten glass on molten tin to produce a flat surface. Tin salts

sprayed onto glass are used to produce electrically conductive coatings. The

most important tin salt used is tin(II) chloride, which is used as a reducing agent

and as a mordant for dyeing calico and silk. Tin oxide is used for ceramics and

gas sensors. Zinc stannate (Zn2SnO4) is a fire-retardant used in plastics. Some

tin compounds have been used as anti-fouling paint for ships and boats, to

prevent barnacles. However, even at low levels these compounds are deadly to

marine life, especially oysters [42].

10

The table 1 organizes some important properties of each metal mentioned

above.

Properties Indium (In) Copper (Cu) Gallium (Ga) Tin (Sn)

Group 13 11 13 14

Period 5 4 4 5

Block p d p P

Atomic

number 49 29 31 50

State at 20°C Solid Solid Solid Solid

Electron

configuration [Kr] 4d105s25p1 [Ar] 3d104s1 [Ar] 3d104s24p1 [Kr] 4d105s25p2

Melting point 156.60°C 1084.62°C 29.76°C 231.93°C

Boiling point 2027°C 2560°C 2229°C 2586°C

Density (g

cm−3) 7.31 8.96 5.91 7.29

Atomic mass 114.82 63.55 69.72 118.71

Appearance

Table 1 - Fundamental properties of different metals

2.3.3 Thin Film Deposition

The deposition techniques can be classified under two main categories: The

vapor deposition and chemical deposition. Each process has its parameters

which determines the deposition atmosphere, deposition rate and the substrate

temperature. These parameters ensure thin films with specific and high quality

properties for the microstructure and the morphology of a given material[43].

The chemical vapor deposition (CVD) is used to produce high quality and

11

high performance solid materials generally in the semiconductor industry. The

technique consists of a deposition coating on a substrate previously cleaned.

One or more volatile fluid precursors produces a chemical change, reacting

or/and decomposing on the substrate surface leaving a chemically deposited

coating.

The physical vapor deposition (PVD) is fundamentally used to produce thin

films coatings. The two most common techniques of PVD are Thermal

Evaporation and Sputtering. In the present work the samples were prepared by

thermal evaporation due to its versatility to prepare quality thin films. The

thermal evaporation technique has been described below. [44,45].

2.3.4 Physical Vapor Deposition (PVD)

One of the promising methods of PVD technique is thermal evaporation

approach. It is vacuum based technology. It can deposit thin film, which are

usually in the thickness range of angstroms to microns. Also, it is possible to

deposit a single material, or multiple materials in a layered structure. The

materials to be deposited can be pure atomic elements including both metals and

non-metals or can be molecules such as oxides and nitrides. The object to be

coated is referred to as the substrate and can be any of a wide variety of materials

such as: semiconductor wafers, solar cells, glass, metallic surface or many other

possibilities[46].

Thermal evaporation involves heating a solid material inside a high vacuum

chamber, taking it to a temperature which produces some vapor pressure. Under

the vacuum condition, even a relatively low vapor pressure is sufficient to raise

a vapor cloud inside the chamber. This evaporated material now constitutes a

vapor stream, which traverses the chamber and hits the substrate, sticking to it

as a coating or film. Since, in most cases, the material is heated to its melting

point and is liquid, it is usually located in the bottom of the chamber, often in

some sort of upright crucible. The vapor then rises above this bottom source,

and the substrates are held inverted in appropriate fixtures at the top of the

chamber. The surfaces intended to be coated are thus facing down toward the

12

heated source material to receive their vapor. Steps may have to be taken to

assure film adhesion, as well as control various film properties as desired.

Figure 5 - Thermal evaporation unit

Fortunately, evaporation system design can allow adjustability of a number

of parameters in order to give process engineers the ability to achieve desired

results for such variables as thickness, uniformity, adhesion strength, stress,

grain structure, optical or electrical properties, etc.[47]

The thermal evaporation unit utilized at work is shown in figure 5.

2.3.4.1 PVD Working Principle and Instrument Specifications

The thermal evaporation technique can be used to produce thin films

involving transfer of material on an atomic level. The model used is

HINDHIVAC Vacuum Chamber model 12A4D and it is shown in figure 6. The

instrument specifications are in the table 2

13

Figure 6 - HINDHIVAC Vacuum Chamber model 12A4D

Table 2 -Physical vapor deposition unit specification (HHV – 12A4D)

2.3.5 Selection of Materials

Source materials with good trace metal basis are essential one to prepare

high quality thin films by thermal evaporation technique. A high purity Cu, Sn

Electrical Supply 230 volt AC

Pirani Gauge Range 0.05 to 0.001 m.bar

Penning Gauge Range 10-4 – 10-6m.bar

Number of boat used in a time 2 boats

Deposition pressure range 10-5 – 10-6m.bar

Radiant heater 275°C (maximum) about 30 min

Substrate heater 500°C (maximum) about 30 min

Deposition rate (uniform coating ) 1-3 Å /Sec

14

in the form as an ingot, In, Ga and Tris(8-hydroxyquinoline) aluminium (Alq3)

the form metal powder were purchased from Alfa Aesar and Sigma Aldrich,

respectively, with 99.99% trace metal basis. These metals are used to prepare

Alq3/metal/Alq3 hybrid sandwich structures. Two individual molybdenum

boats (200 amp) were used to place the source materials as an evaporator to

prepare the sandwich structures. One of the main reasons for choosing thermal

evaporation is less expensive and does not require any kind of substrates like

sapphire. In this work, glass substrates were used to prepare both reference and

multilayer composite structures.

2.3.6 Substrate Cleaning Process

When the substrate is exposed to atmosphere its gets contaminated by

dispersant particles in the air and even gases. The very important and first step

in thin film deposition is the substrate cleaning. Clean glass substrates are

important to assure the removal all the residual impurities. Firstly, the

substrates are cleaned thoroughly with soup solution and subsequently with

acetone. After that, the substrates were ultrasonically treated for ten minutes and

kept in a hot air oven to evaporate the residues. The cleaned glass substrates

were as substrates in the PVD technique.

2.3.7 Preparation of Alq3/metal/Alq3 hybrid Sandwich

Structure

The hybrid Alq3/ metal/Alq3 composite structure were deposited over the

glass substrate using thermal evaporation technique as shown figure 7. The high

purity base materials were placed in molybdenum boat (Alq3) and tungsten

basket (Cu, In, Ga and Sn) separately. The distance between the source

materials to substrate is fixed (28 cm). Initially Alq3 was deposited on the

substrate with a thickness of 50 nm and then metals (Cu, In, Ga and Sn) were

deposited with 30 nm thickness. Again, 50 nm of Alq3 was deposited followed

by metal layer without breaking the vacuum. The final structure seems like

15

sandwich and is known as hybrid structure. The thicknesses of each layer were

controlled and rate of evaporation was maintained 1-3 Å/sec using an in-situ

quartz crystal monitor throughout experiments. The figure 7 below the

schematic diagram Alq3/metal/Alq3 hybrid structure is represented.

Figure 7- Schematic diagram of Alq3/metal/Alq3 hybrid structure

2.3.8 X-ray Diffraction Pattern

X-ray diffraction is a fundamental and powerful tool to study the structure of

materials. It is non-destructive and common method for uses in all fields of

science and technology especially in material science. It can provide clear

information about the phase, crystallographic unit cell and crystal structure,

crystallographic texture, crystalline size, macro-stress and micro strain. Also, it

is widely used to determine materials in the atomic scale. In this work, Cu Kα

source was used to study the structural properties with the help X-ray

Diffractometer (Shimadzu XRD-6000) and diffraction angle (2θ) ranging

between 0-90◦. [48, 49]

2.3.8.1 Braggs Diffraction Law

An X-ray which reflects from the surface of a substance has travelled less

distance than an X-ray which reflects from a plane of atoms inside the crystal.

16

The penetrating X-ray travels down to the internal layer, reflects and travels

back over the same distance before being back at the surface. The distance

travelled depends on the separation of the layers and the angle at which the X-

ray entered the material. For this wave to be in phase with the wave which

reflected from the surface it needs to have travelled a whole number of

wavelengths while inside the material. Bragg expressed this in an equation now

known as Bragg's Law, in the figure 8: [50]

Figure 8 - Schematic Representation of Braggs’s Law

When X-rays are scattered from a crystal lattice, peaks of scattered intensity

are observed which correspond to the following conditions:

1. The angle of incidence = angle of scattering.

2. The path length difference is equal to an integer number of wavelengths.

The condition for maximum intensity contained in Bragg's law above allow

us to calculate details about the crystal structure, or if the crystal structure is

known, to determine the wavelength of the x-rays incident upon the crystal.

2.3.8.2 Determination of Structural Parameters

The x-ray diffraction patterns data can be used to calculate the structural

parameters like average grain size, macrostrain, dislocation density and lattice

http://hyperphysics.phy-astr.gsu.edu/hbase/ems3.html#c4

17

parameter. The average grain size (D) of sandwich films was calculated using

Scherer’s equation

D =0.94

βcosθ ……………………… (1)

Where is the wavelength of the X-ray beam used (Cu k = 1.54Å), 2θ is

the angle between the incident and scattered X-ray beam and β is the full width

at half maximum. The dislocation density (δ) and micro strain () developed in

multilayer film are calculated from the relations[51-53].

=1

D2…………………….…… (2)

= βcosθ/4 ………………….. (3)

2.3.9 Scanning Electron Microscopy (SEM)

The electrons are emitted from the cathode and are accelerated by an electric

field up to required energy. Then the electrons are focused and scanned by

magnetic lenses which works based on the Lorentz force. The beam scans each

point in the sample surface and the detectors above the sample collect the

information, usually generated by the secondary beam electrons. Focal length

can be modified by using magnetic lenses and the size of the beam spot.

The scan generator controls the electron beam scanning and the succession

of pixels on the screen. The main factors determining resolution are the size of

the beam on the sample surface, the energy escaped of the sample surface and

excited by the beam sample volume.

The scanning electron microscopy is perhaps the most routinely utilized

instrument for the characterization of nanomaterials. It is possible to obtain

secondary electron images of organic and inorganic materials with nano scale

resolution. It can be used for studying the surface topography, microstructure

and chemistry of metallic and non-metallic specimens at magnification from 50

up to ~ 100, 000 X, with a resolution limit < 10nm (down to ~ 1nm) and a depth

of focus up to several μm (at magnifications ~ 10, 000 X). The surface

18

morphological properties, size, shape was studied by using scanning electron

microscopy (SEM - Jeol). The elemental analysis of films was obtained by

energy-dispersive X-ray spectroscopy (EDXS - Oxford)[54].

2.3.10 UV-Visible Spectroscopy

The UV-Visible absorption experiment for samples as shown in figure 9 for

film samples, the mechanism is the same. A light is emitted from the lamp and

then it passes through a filter. A beam of monochromatic light is split into two

beams; one of them passes through the sample and the other passes through a

reference.

Figure 9 – UV-Visible Spectroscopy Working Process

After the light is transmitted over the sample and reference the two beams

are directed back to the detectors where they are compared. The difference

between the signals is then measured. The result of the measurement is shown

by a graph. [55]

Ultraviolet-visible (UV-vis) spectroscopy is widely utilized to quantitatively

characterize organic, inorganic, nanomaterials and thin films. A sample is

irradiated with electromagnetic waves in the ultraviolet and visible ranges and

the absorbed light is analyzed through the resulting spectrum. It is not only used

for characterization, but also for sensing applications. The samples can be either

19

organic or inorganic, and may exist in gaseous, liquid or solid form. Different

sized materials can be characterized, ranging from transition metal ions and

small molecular weight organic molecules, whose diameters can be several, to

nano-particles and bulk materials. Size dependent properties can also be

observed Ångstroms in a UV-visible spectrum, particularly in the nano and

atomic scales. These include peak broadening and shifts in the absorption

wavelength.

Many electronic properties, such as the band gap of a material, can also be

determined by this technique. Optical absorption and transmission spectra was

recorded using UV-VIS-NIR spectrophotometer (Jasco-570 UV/VIS/ NIR

Spectrophotometer) in the range of 200 to 2500 nm. The absorption and

excitation coefficient were calculated from the following the relations:

k = ln(

1

T)

4t…………………. (4)

= 4k

…………………… (5)

Here k is an excitation coefficient, λ is an incident wavelength and T is

transmission of film, t is thickness of film and α is an absorption coefficient.

Most of the semiconductors especially chalcogenide follows an exponential law

and the absorption coefficient could be obeying the given equation

(αhυ)1

n = B (hυ − Eg) …………….. (6)

Where α is absorption coefficient, hυ is incident photon energy, B is a

constant, Eg is the optical energy band gap and n is an exponent constant. For,

the band gap of semiconductor follows the Fermi golden rule of direct (n = ½)

and indirect (n = 2) allowed transition for fundamental band-to-band electronic

transitions. Therefore, the optical energy band gap (Eg) can be expressed

following relation: [56,57]

(αhυ)2 = B (hυ − Eg) …………….. (7)

20

2.3.11 Photoluminescence Spectroscopy

PL spectroscopy concerns monitoring the light emitted from atoms or

molecules after they have absorbed photons. PL spectroscopy is suitable for the

characterization of both organic and inorganic materials of virtually any size,

and the samples can be in solid, liquid, or gaseous forms. Electromagnetic

radiation in the UV and visible ranges is utilized in PL spectroscopy. The figure

10 a simple scheme to exemplify the Spectrometer working setup.

The sample’s PL emission properties are characterized by four parameters:

intensity, emission wavelength, bandwidth of the emission peak and the

emission stability. The PL properties of a material can change in different

ambient environments, or in the presence of other molecules[58,59].

Many nanotechnology-enabled sensors are based on monitoring such

changes. Furthermore, as dimensions are reduced to the nanoscale, PL emission

properties can change, in particular a size dependent shift in the emission

wavelength can be observed. Additionally, because the released photon

corresponds to the energy difference between the states, PL spectroscopy can

be utilized to study material properties such as band gap, recombination

mechanisms and impurity levels.

Figure 10- PL Spectrometer working setup

21

Figure 10 - PL absorption and emission process

In a typical PL spectroscopy setup for liquid samples a solution containing

the sample is placed in a quartz cuvette with a known path length. Double beam

optics are generally employed. The first beam passes through an excitation filter

or monochromator, then through the sample and onto a detector. This impinging

light causes photoluminescence, which is emitted in all directions. A small

portion of the emitted light arrives at the detector after passing through an

22

optional emission filter or monochromator. A second reference beam is

attenuated and compared with the beam from the sample. Solid samples can also

be analyzed, with the incident beam impinging on the material (thin film,

powder etc.). the figure 10 shows the PL absorption and emission process.

Generally, an emission spectrum is recorded, where the sample is irradiated

with a single wavelength and the intensity of the luminescence emission is

recorded as a function of wavelength. The fluorescence of a sample can also be

monitored as a function of time, after excitation by a flash of light. This

technique is called time resolved fluorescence spectroscopy.

3 Results and Discussion

3.1 Enhancement of PL Emission Through Alq3 / Metal /

Alq3 Hybrid Sandwich Structure With Different Metal Layers

3.1.1 Experimental Details

The hybrid Alq3/Metal/Alq3 composite structure were deposited over the

glass substrate using thermal evaporation technique at ambient temperature as

shown in Figure 12. The thicknesses of each layer were controlled and rate of

evaporation was maintained at 1-3 Å/sec using an in-situ quartz crystal monitor.

After that all the films were taken for structural, optical and morphological

studies.

Figure 12 - Schematic diagram of Alq3/metal/Alq3 hybrid structure (a) Alq3/Cu/Alq3 ,

(b) Alq3/Ga/Alq3, (c) Alq3/In/Alq3 and (d) Alq3/Sn/Alq3

23

3.1.2 X-Ray Diffraction

Figure 13 shows the XRD pattern of as deposited Alq3/metal/Alq3 hybrid

structure with different metal layers. There is no significant peak found for as

deposited Alq3 [60]. All the samples have single diffraction peak at different 2θ

value and which indicates the presence of metal layers. The diffraction peaks

observed at 32.77, 42.88, 30.10 and 23.67° corresponds to (111), (020), (200)

and (101) planes respectively. Which is characteristic peak of Cu, Ga, In and

Sn.

10 20 30 40 50 60

(101)

(200)

(020)

(e).Alq3/Sn/Alq

3

(d).Alq3/In/Alq

3

(c).Alq3/Ga/Alq

3

(b).Alq3/Cu/Alq

3

(a). Alq3

Inte

ns

ity

(a

.u)

2 (deg)

(111)

Figure 13 - X-ray diffraction pattern of hybrids structures

Table 3 shows the XRD characteristic of hybrid sandwich structure for its d-

spacing, grain size and dislocation density. The grain size (D) was calculated

using Scherer’s equation [61,62].

24

Sample /

parameter

2θ

(deg)

FWHM

(deg)

D

(nm)

( )

X 10-22 (nm-2)

X 10-3

AIA 32.77 0.76 11 0.83 3.20

ACA 42.88 0.84 10.5 9.90 7. 30

AGA 30.10 3.00 3 10.40 11.21

ASA 23.67 1.30 6.5 2.35 5.08


3.1.3 Surface Morphological Analysis

Figure 14 -SEM image of Alq3/metal/Alq3 hybrid structure (a) Alq3/Cu/Alq3 ,

(b) Alq3/Ga/Alq3, (c) Alq3/In/Alq3 and (d) Alq3/Sn/Alq3

a) b)

c) d)

25

Figure 14 shows the surface morphology of Alq3/metal/Alq3 hybrid structure.

The non- homogenous surface with rod like structure was observed for

Alq3/Cu/Alq3 as shown in figure 14.a. The mixed surface of rod and

nanocrystals was observed for Alq3/Ga/Alq3. Uniform spherical grains was

spread over the entire surface on which rod like structure appreared for

Alq3/In/Alq3 .

The non-homogenous hollow like shape was observed for Alq3/Sn/Alq3.

From the SEM images, it is clear that metal layer play vital role in surface

morphology due to variation in grain size.

It is important to observe the image shows only the deposition of Alq3 on the

metal and. The metal covers all the bottom layer. When the indium metal is

deposited over the polymeric surface, distinct grains were evident and definite

particles were seen on the surface.

3.1.4 Optical Studies

Figure 15 shows the optical absorption spectra of the Alq3/metal/Alq3 hybrid

structure with different metal layers. Strong absorption was observed in UV-

Visible region and higher transmission in infrared region.

There are two absorption peaks almost near 300 nm and 390 nm for all the

samples. The absorption edge was found at 393 nm and red-shift was observed

for Alq3/In/Alq3 hybrid structure compared to other structures. This is mainly

due to large grains size which is evident in XRD pattern.

Figure 15.a shows the optical transmission spectra of the Alq3/metal/ Alq3

hybrid structure with different metal layers. As deposited Alq3 films has higher

transmission than hybrid structures. The transmission was reducing due to

sandwiching metal layers. It is very interesting to state that metal layers play

very important role in sandwich structure.

Figure 16 shows the optical band energy for Alq3/metal/Alq3 hybrid structure

with different metal layers. A couple of energy band was observed for almost

all samples. The estimated values were found to be between 1.92 and 3.36 eV.

A single band gap value found at 2.48 eV for Alq3/In/Alq3 hybrid structure

because only the π-π* electronic excitation is evident while in Alq3 UV-Vis

26

shows two electronic transitions [63]. The Alq3/Cu/Alq3 hybrid structure have

two band gaps at 2.59 and 3.15 eV as shown in figure 16.

500 1000 1500 2000 2500

Tra

ns

mis

sio

n (

a.u

)

Wavelength (nm)

(a). Alq3

(b). ACA

(c). AGA

(d). AIA

(e). ASA

300 400 500 600 700 800 900 1000

Ab

so

rpti

on

(a

.u)

Wavelength (nm)

(a). Alq3

(b). ACA

(c). AGA

(d). AIA

(e). ASA

Figure 15 -Optical spectra (Transmission a) and Absorption b)) of (a) as

deposited Alq3and Alq3/metal/Alq3 hybrid structure (b) Alq3/Cu/Alq3 ,

(c) Alq3/Ga/Alq3, (d) Alq3/In/Alq3 and (e) Alq3/Sn/Alq3

a)

b)

27

Figure 16 -Optical energy band gap of (a) as deposited Alq3and Alq3/metal/Alq3

hybrid structure (b) Alq3/Cu/Alq3 , (c) Alq3/Ga/Alq3, (d) Alq3/In/Alq3 and

(e) Alq3/Sn/Alq3

28

The band gap values were found to 2.72 and 3.36 eV for Alq3/Ga/Alq3, which

is wider than another hybrid structure. This increase in the optical band gap can

be related to formation of nanocrystal and rod like shapes for Alq3/Ga/Alq3

hybrid structure.

Three band values were found at 1.89, 2.48, 2.94 eV due to hollow shapes,

which leads to optical splitting for Alq3/Sn/Alq3 hybrid structure. The band gap

splitting due to nanocrystal formation and there can be possiblilty for more than

one band-to-band electronic transitions. The phenomena is mainly due to spin-

orbit split of the valence band. The blue shift, optical splitting and increasing in

band gap is evident for confinement effect or quantum size effect.

450 500 550 600 650 700 750

PL

em

issi

on

(a.u

)

Wavelength (nm)

(a). Alq3

(b). ACA

(c). AGA

(d). AIA

(e). ASA

Figure 17 - PL emission spectra of (a) as deposited Alq3and Alq3/metal/Alq3 hybrid

structure (b) Alq3/Cu/Alq3 , (c) Alq3/Ga/Alq3, (d) Alq3/In/Alq3 and (e) Alq3/Sn/Alq3

Figure 17 shows the PL spectra of Alq3 and Alq3/Metal/Alq3 hybrid film

structure. All the films were excited at 400 nm at ambient temperature. There

are three emission bands in the visible region, which are centered at 451 513,

and 638 nm for as deposited Alq3 film. Similar emission peak was reported in

previous couple of new emission bands were observed at blue and green for

29

Alq3/In/Alq3 hybrid structure as shown in figure 17.b. The Alq3/Ga/Alq3 hybrid

structure having two emission, one is belonging to blue region and almost in red

region as seen in figure 17.c. Two emission bands were obtained at blue and

orange region for Alq3/Sn/Alq3 and Alq3/Cu/Alq3 hybrid structure.

The Cu and Sn sandwich has similar emission properties compared to other

sandwich structures. This is mainly due to the new composite formation and

impact of metal layer [60]. From the emission spectra, unique emission

properties were observed based on metal layers. It can provide information

about emission properties in all regions and it almost covers UV-Visible

spectrum.

3.1.5 Partial Conclusion

Alq3/metal/Alq3 hybrid sandwich structure were successfully deposited using

different metal layers. The structural, optical and morphological properties were

studied through different analytical techniques. The XRD pattern reveals that

diffraction peaks confirmed different metal layers. The calculated crystalline

size varied from 3 to 11 nm depending on metal layers. The hybrid structure

shows unique morphology such as spherical grains and rod like shape. The

change in band gap values and crystalline size are reflects quantum size effect

and quantum confinement properties.

The Alq3/In/Alq3 hybrid structure was the most different of the analyzed

sandwiches layers and because that here was a curiosity to study it more.

The PL emission almost covers UV-Visible ranges. This is mainly due to the

new composite formation and impact of metal layer [23]. From the emission

spectra, different emission properties were observed with the different metal

layers. It can provide information about emission properties in all regions and it

almost covers UV-Visible spectrum. These hybrid structures show unique

surface, optical band and emission band properties. It is very interesting to

develop optoelectronic devices in particularly OLED application and solar cells.

30

3.2 Investigation on Structural and Optical Properties of

Hybrid Alq3/In/Alq3 Composite Thin Films


The hybrid Alq3/In/Alq3 composite structure as shown in figure 12. It was

deposited over the glass substrate using thermal evaporation technique. Initially

Alq3 was deposited on the substrate with a thickness of 50 nm and then indium

was deposited with 30 nm thickness. Again, 50nm of Alq3 was deposited

followed by In layer without breaking the vacuum. The final structure seems

like sandwich which is known as hybrid structure. The thicknesses of each layer

were controlled and rate of evaporation was maintained 1-3 Å/sec using an in-

situ quartz crystal monitor. For the best comparison, single layer Alq3 was

prepared and studied.

Figure 18 - Structure of hybrid sandwich (Alq3/In/Alq3)

Finally, the single layer and hybrid sandwich films were taken for structural,

optical and morphological studies. The structural properties were studied using

Shimadzu XRD-6000 X-ray Diffractometer and LabRAM HR 800 micro

Raman Spectrometer with 514.12 nm laser source. The surface morphology was

captured using Jeol scanning electron microscopy. The elemental composition

was analyzed using Energy Dispersive X-ray analysis. The optical properties

were studied y Jasco-570UV/VIS/NI Spectrophotometer in the range of 200 -

2500 nm. Photoluminescence (PL) emission were studied by Spectro

Fluorometer (JASCO FP-8200) recorded in the range between 200 to 900 nm.

31

3.2.2 Structural Studies

Figure 19 - X-ray diffraction pattern, (a) Alq3 and (b) Alq3/In/ Alq3 hybrid structure

Figure 19 shows the as deposited reference Alq3 and hybrid sandwich

structured film. There is no significant peak found and the broad hump indicates

amorphous nature at high vacuum condition for as deposited Alq3 as shown in

figure 19.a [23].

A single diffraction peak was observed at 32.77˚ in the hybrid sandwich

structure as shown figure 19.b. The grain size (D) of hybrid structure was

calculated using Scherer’s equation [40,41] and grain size is 11 nm for hybrid

structure.

3.2.3 Surface Morphological Studies

Figure 20 shows the surface morphology of reference Alq3 and Alq3/In/Alq3

hybrid structure films. The non-homogenos surface was observed due to

polymeric nature of Alq3 as shown in figure 20.a The hybird structure shows a

mixed surface of spherical grains androd like shape as seen in figure 20.b. The

32

spherical grains may be Indium (In) atom and rod like a structure corresponds

to Alq3.

Figure 20 - SEM images (a) Alq3 and (b) Alq3/In/Alq3 hybrid structure

It clear that rod like structures are grown over the spherical grains due to

sandwiching layers of Alq3, not forming a continous layer. From the SEM

images, the hybrid structure shows unique surface morphological properties.


Figure 21 shows the optical spectra of as deposited Alq3 and Alq3/In/Alq3

a)

b)

33

hybrid structure. A strong absorption was observed in near ultra violet region

and highest transmission in UV-visible as well as infrared region. There are two

absorption peaks observed for the deposited Alq3 and located at 298 nm and 393

nm, respectively as shown in Figure 21.a.

Figure 21 - Optical spectra of as deposited Alq3 and Alq3/In/Alq3 hybrid structure

(a) transmission and (b) absorption spectra

34

A single strong absorption was found at 393 nm and red-shift was observed

for Alq3/In/ Alq3 hybrid structure. The strong absorption and red shift is mainly

due to Indium (In) sandwiching in the hybrid structure as seen Figure 21.b.

Figure 22 shows the optical band energy for as deposited Alq3 and hybrid

structure film. The direct band gap value was calculated using standard relation

[64]. The couple of band gap values are found to be 2.87eV and 3.34 eV for as

deposited Alq3 as shown in figure 22.a.

2.0 2.5 3.0 3.5 4.0

(h

)

(a.u

)

Photon Energy (eV)

(a). Alq3

2.87 eV 3.34 eV

1.0 1.5 2.0 2.5 3.0

(h

)

(a.u

)

Photon Energy (eV)

(b). Alq3/In/Alq

3

2.49 eV

Figure 22 - Optical energy band gap (a) Alq3 and (b) Alq3/In/Alq3 hybrid structure

35

The theoretical optical band gap value of value Alq3 is obtained at 2.80 eV

and experiment values is 2.87 eV. The calculated band gap value is a good

agreement with previous reports [63]. In this case, two optical band gaps were

observed, and it owns unique optical properties due to preparation method. A

single band gap was found, and the value is 2.49 eV for hybrid structure as seen

in figure 16.b. The decrease in the optical band gap can be related to mixed

surface morphological in SEM images.

Figure 23 shows the PL spectra of Alq3 and Alq3/In/Alq3 hybrid structure

film. All the films were excited at 400 nm at room temperature. Three emission

bands were observed in the visible region, which is centered at 451, 513 and

638 nm for as deposited Alq3 film as seen figure 23.a.A couple of new emission

bands were observed at 479 and 562 nm for Alq3/In/Alq3 hybrid structure. This

is mainly due to the new composite formation and impact of In layer [23].

Spherical grain with rod shapes and Indium plays important role in the new

emission band in the hybrid structure. This kind of emission properties are much

need to design and fabricate optoelectronic devices.

400 450 500 550 600 650 700 750

PL

em

iss

ion

(a

.u)

Wavelength (nm)

(a). Alq3

(b). Alq3/In/Alq

3

451 nm 479 nm 562 nm

513 nm

638 nm

Figure 23- PL emission spectra (a) Alq3 and (b). Alq3/In/Alq3 hybrid structure

36


The hybrid Alq3/ In/Alq3 composite structure were successfully deposited

over the glass substrate using thermal evaporation technique. The structural,

optical and morphological properties were studied through several analytical

techniques. The XRD pattern reveals that single diffraction peak is found at

31.77° and belongs to Indium (In) in the hybrid sandwich structure and the

calculated grain size is found to be 11 nm for hybrid structure. The hybird

structure shows the mixed surface of spherical grains with rod like shape.

A single band gap was found to be 2.49 eV for hybrid structure. A couple of

new emission bands were observed at 479 and 562 nm for hybrid structure. The

hybrid structure shows unique surface, optical band and emission band

properties. Further studies on the effect of annealing and different metal layers

other than In could result in better understanding of the properties of this

composite material.

3.3 Impact of Annealing on Hybrid Alq3 / In / Alq3

Composite Thin Films


The hybrid Alq3/ In/Alq3 composite structure were deposited over the glass

substrate using thermal evaporation technique at ambient temperature as shown in

Figure 24. The thicknesses of each layer were controlled, and rate of evaporation

was maintained as 1-3 Å/sec using an in-situ quartz crystal monitor. The hybrid

sandwich structure was taken for annealing process and placed in the substrate heater

setup. The annealing was done under the vacuum in the chamber. The temperatures

were varied in between 150°C and 350°C for about 30 min and the pressure range

was maintained as 10-5 – 10-6m.bar. After that all the films were taken for structural,

optical and morphological studies.

37

Figure 24 -Alq3/In/Alq3 hybrid sandwich structure

3.3.2 Structural Studies

Figure 25 shows the Alq3/In/Alq3 hybrid sandwich structure film annealed at

different temperatures. A single diffraction peak was observed at 32.77˚

corresponding to (1 0 1) for as deposited films as shown figure 19.a. It is

noteworthy to mention that alternate layers of indium and Alq3, leads to form

the Alq3/In/Alq3 composite.

10 20 30 40 50 60 70 80 90

(10

0)

(10

1)

Inte

ns

ity

(a

.u)

2 (deg)

(d). 350oC

(c). 250oC

(b). 150oC

(a). As deposited

Figure 25 - X-ray diffraction pattern of hybrid sandwich structure (a) as deposited,

(b)150°C, (c) 250°C and (d) 350°C

38

A couple of peaks were observed for annealed films. The major peaks were

found at 32.56°- 30.30° and additional peaks was found at 27° corresponds

to (100) plane. This main peak was shifted towards lower diffraction angle.

This is mainly due to strain induced mechanism in hybrid sandwich structure.

This can lead to form the new composites and structural change due to annealing

process.

Table 4 - The XRD characteristic of hybrid sandwich structure

Table 4 shows the XRD characteristic of hybrid sandwich structure for

grain size (D), micro strain () and dislocation density (). The grain size (D)

was calculated using Debye Scherer’s equation [40, 41]. It is clear that 2θ value

decrease shifts the lower angle due to annealing. The calculated grain size was

found to be between 5 to 11 nm. As deposited film has large grain size than

annealed films. Commonly grain size should increase during annealing, but in

our case, the grain size is reduced during annealing process due probably to the

formation of composite in 150°C annealed hybrid structure.

Upon annealing, the grain size was decreased for 250°C and further

annealing improves the grain size for 350°C films. The change in grain size is

linked with structural change in hybrid structure, which can be confirmed

through further studies such SEM and PL emission.

3.3.3 Surface Morphological Analysis

Figure 26 shows the SEM image of Alq3/In/Alq3 hybrid structure with

Sample /

parameter

2θ

(deg)

FWHM

(deg)

D

(nm)

( )

X 10-22 (nm-2)

X 10-3

As deposited 32.77 0.76 11 0.83 3.20

150°C 32.56 1.32 7 2.04 4.95

250°C 30.51 1.63 5 3.70 6.92

350°C 30.30 0.98 9 1.23 4.10

39

different annealing temperatures. The hybird structure shows the mixed surface

of spherical grains with rod like shape as seen in figure 26.a.

The spherical grains may be Indium (In) atom and rod like a structure

corresponds to Alq3. Upon annealing, the non-uniform surface with random

orientaion of smaller grains was observed for at 150°C as shown in figure 26.b.

Figure 26 -SEM image of Alq3/In/ Alq3 hybrid structure with different annealing

temperatures

Upon further annealing, the spherical grains was spread over the surface for

250°C films as displayed in figure 26.c.Where as mixed spherical grains and

nanorod was observed for 350°C films as seen figure 26.d. It is clearlyseen that

the rods were grown over the spherical grains and spherical grains may be

Indium atom. Different kind of morphology was observed for different

annealing temperatures.

40


Figure 27 shows the optical spectra of Alq3/In/ Alq3 hybrid structure for

different annealing temperature. Strong absorption was observed in near ultra

violet region and highest transmission in infrared region for higher annealing

temperature. The absorption shoulder was observed at around 400 nm for all the

samples.

500 1000 1500 2000 2500

Tra

ns

mis

sio

n (

a.u

)

Wavelength (nm)

(a). Asdeposited

(b). 150oC

(c). 250oC

(d). 350oC

(b)

500 1000 1500 2000 2500

Ab

so

rpti

on

(a

.u)

Wavelength (nm)

(a). Asdeposited

(b). 150oC

(c). 250oC

(d). 350oC

Figure 27 -Optical absorption spectra of of Alq3/In/ Alq3 hybrid structure with different


b)

a)

41

The absorption edge was shifted towards higher wavelength region for higher

annealing temperature. Broad absorption was observed in UV-Visible region

for 350°C films.

Figure 28 shows the optical band energy for Alq3/In/ Alq3 hybrid structure

with different annealing temperatures. The calculated direct band gap values are

found to vary between 1.90 to 2.67 eV with the function of annealing

temperature and are lower than the Alq3 films.

Figure 28 -Optical energy band gap of Alq3/In/ Alq3 hybrid structure with


42

The film annealed at 250°C shows a wider band gap than other films due to

uniform spherical grains over the surface. It is also directly linked with quantum

size effect during annealing process. The changes in band gap values reflect

structural changes upon annealing at different temperatures. The increase in

band gap gives information about quantum confinement in hybrid structure. The

blue shift, optical splitting and increase in band gap are evident for templating

confinement effect. Different energy bands are need for optoelectronic device

in particularly LEDs and OLED applications.

Figure 29 shows the PL spectra of Alq3/In/Alq3 hybrid structure for different

annealing temperatures. All the films were excited at 400 nm at room

temperature. A couple of emission was observed in the UV-Visible region. One

emission in blue region (479 nm) and another emission occur in green region

(564 nm). Upon annealing, single emission was observed at 517 nm due to

mixed rod and spherical grains surface. The emission bands were observed at

455 and 593 nm for 250°C as seen in figure 29.c. This is mainly due to the new

composite formation and impact of In layer [60].

450 500 550 600 650 700

PL

em

iss

ion

in

ten

sit

y (

a.u

)

Wavelength (nm)

(a). AD

(b). 150oC

(c). 250oC

(d). 350oC

455 nm 479 nm

517 nm564 nm 593 nm

501 nm

Figure 29 -PL emission spectra of Alq3/In/Alq3 hybrid structure with different


43


Post deposition annealing is appreciable in thin films for a better nucleation

process which could result in better morphology. Because that the annealed

Alq3/In/Alq3 hybrid investigation. However in this work, at 150º and 250º the

grain size decreased and at 350º the grain size increase. An investigation is

necessary to understand if that event was due to the insufficient time or the

temperature was inadequate or if there was a structural change.

Structural, optical and morphological properties were studied with the

function of annealing temperatures. XRD pattern reveals the single diffraction

peak of Indium (In) and calculated grain is varied from 5 to11 nm with different

annealing temperatures. The hybird structure shows unique morphology such as

spherical grains and rod like shape. The calculate band gap was found to be 1.90

and 2.67 eV with function of annealing.

The change in band gap values and grains reflects quantum size effect and

quantum confinement properties. The PL emission almost covers UV-Visible

ranges, which can be useful to fabricate OLED devices. The hybrid structure

shows unique surface, optical band and emission band properties.

4 Final Conclusion

Analyzing the results obtained, it can be observed that the metals were not

modified significantly the optical properties of the film, except the Indium. The

morphological analysis shows the different structures and it can be observed

due the variation of the grain size and the energy surface. It clear that the choice

of the metal has a vital importance on morphology of the formed film.

A very large structural and optical changes were observed when the Indium

was added in the sandwich structure. When the PL spectra is analyzed, the

Alq3/In/Alq3 showed a new emission, with another wavelength and because that

great attention to study the impact of Indium layer in the sandwich structure.

A great attention can be given to the annealed Alq3/In/Alq3 sandwich grain

size. Its common the grain size increase with the temperature, but in this case,

44

until the 250º C, the grain size decrease. The appearance of a new plan was

observed. Meanwhile, the morphological studies showed the Alq3 in different

depositions shapes. At 250º, apparently, the Alq3 is not observed in the surface

and at 350º C, the Alq3 is showed in rods form and it were grown over the

spherical grains.

Understanding the properties changes, it possible be able to apply each thin

film analyzed in OLED structures for the purpose of moving forward the

Material Science.

5 Suggestions for Future Studies

A suggestion for future works may be an in-depth analysis of the morphology of

the Alq3/In/Alq3 and understand more why the structure is so different.

A multi-layer analysis is too important to study how the Indium is organized with

more than one layer, and it is interesting study a possible property change.

The discussed topic of this work is in increasing research for the advancement of

materials science, a deepening of this study is relevant.

45

6 Bibliographic References

1. W. Brütting, M. Cölle, C. Gärditz, “The Isomerism of the

Alq3 Molecule: Evidence from Structural, Thermal and Photophysical

Investigations”, Journal of Molecular Structure, v. 36, n. 2, pp. 669-680,

2002.

2. Sumitomo Chemical , “Global Organic Light-emitting Diode (OLED) Materials

Market 2017”, Available in: https://www.openpr.com/news/583660/Global-

Organic-Light-emitting-Diode-OLED-Materials-Market-2017-DuPont-Merck-

Sumitomo-Chemical-Universal-Display.html, accessed in 06 May, 2018.

3. Agency for Science, Technology and Research, “True blue light emission could

make OLED displays the next big thing in consumer electronics”, available in:

https://phys.org/news/2011-06-true-blue-emission-oled-big.html, accessed in:

06 May, 2018

4. Kyushu University, “Fundamental Structure of OLEDs”, available in:

http://www.cstf.kyushu-u.ac.jp, accessed in: 06 May, 2018.

5. Hyper Physics, “Bragg”, available in : http://hyperphysics.phy-astr.gsu.edu

/hbase/quantum/bragg.html, accessed in : 06 May, 2018.

6. Sobarwiki2013, “Schematic of UV-Visible Spectrophotometer”, available in:

https://commons.wikimedia.org/wiki/File:Schematic_of_UV_visible_spectrop

hotometer.html, accessed in 07 May, 2018.

7. Chemical Libre Texts, “Photoluminescence Spectroscopy”, available in:

https://chem.libretexts.org/Textbook_Maps/Analytical_Chemistry/Book%3A_

Analytical_Chemistry_2.0_(Harvey)/10_Spectroscopic_Methods/10.6%3A_P

hotoluminescence_Spectroscopy.html, accessed in: 07 May, 2018.

8. Renishaw plc., “Photoluminescence Spectroscopy”, available in :

http://www.renishaw.de/de/photoluminescence-explained—25809101.html,

accessed in: 07 May, 2018.

9. Education in Chemistry, “Elements Information”, available in:

https://eic.rsc.org/elements/indium/2020012.article.html, accessed in: 07 May,

2018.

10. E. Fred. Schubert, “Light-Emitting Diodes”, 3 ed., New York, Cambridge

University Press, 2018.

https://www.openpr.com/news/583660/Global-Organic-Light-emitting-Diode-OLED-Materials-Market-2017-DuPont-Merck-Sumitomo-Chemical-Universal-Display.html



https://phys.org/news/2011-06-true-blue-emission-oled-big.html

http://hyperphysics.phy-astr.gsu.edu/

https://commons.wikimedia.org/wiki/File:Schematic_of_UV_visible_spectrophotometer.html

https://commons.wikimedia.org/wiki/File:Schematic_of_UV_visible_spectrophotometer.html

https://chem.libretexts.org/Textbook_Maps/Analytical_Chemistry/Book%3A_Analytical_Chemistry_2.0_(Harvey)/10_Spectroscopic_Methods/10.6%3A_Photoluminescence_Spectroscopy



http://www.renishaw.de/de/photoluminescence-explained—25809101.html

https://eic.rsc.org/elements/indium/2020012.article.html

46

11. J. Dittmer, R. Lazzaroni, P. Leclere, P. Moretti, M. Granstrom, K. Petritsch, E.

A. Marseglia, R. H. Friend, J. L. Bredas, H. Rost and A. B. Holmes, “Crystal

Network Formation in Organic Solar Cells,” Solar Energy Materials and

Solar Cells, v. 61, pp. 53-61, 2000.

12. M. Cuba, G. Muralidharan, “Effect of Thermal Annealing on the Structural and

Optical Properties of Tris‐(8‐hydroxyquinoline)Aluminum(III) (Alq3) Films”,

Luminescence, v. 30, n. 3, pp. 352-357, 2015.

13. D.J. Williams, “Organic Electroluminescent Diodes”, Photonics Spectra,

2003, pp. 116-120.

14. J. Majer, M. Reade, “Isomerism in the Metal Derivatives of 8-

hydroxyquinoline”, Chemical Communications, v. 1, pp. 58-59, 1970.

15. A. Curioni, W. Andreoni, “Atom-resolved electronic spectra for

Alq₃ from theory and experiment”, Applied Physics Letters, v.72, n.13,

pp.1575-1577, 1998.

16. B. C. Lin, C. P. Cheng, Z. Q. You, C. P. Hsu, “Charge Transport Properties of

Tris(8-hydroxyquinolinato)aluminum(III): Why It Is an Electron Transporter”,

Journal of the American Chemical Society, v. 127, n. 1, pp. 66–67, 2005.

17. L. S. Hung, C. W. Tang, M. G. Mason, “ Enhanced Electron Injection in Organic

Electroluminescence Devices Using an Al/LiF Electrode”, Application

Physics Letters, v.70, pp. 152-154, 1997.

18. M. Cölle, J. Gmeiner, W. Milius, H. Hillebrecht, and W. Brütting, “Preparation

and Characterization of Blue‐Luminescent Tris(8‐hydroxyquinoline)‐

aluminum (Alq3)”, Advanced Functional Materials, v. 13, pp. 108-112, 2003.

19. G. Baldacchini, S. Gagliardi, R.M. Montereali, A. Pace, R.B. Pode, “Optical

Spectroscopy of Tris(8- Hydroxyquinoline)Aluminium Thin Films”,

Phylosophical Magazine, v. 82, n 6, pp. 669-680, 2002.

20. C.W. Tang, S.A. Van Slyke, “Organic Electroluminescent Diodes”,

Application Physics Letters, v. 51, pp. 913-915, 1987.

21. B. R. Kanchibotla, K. Garre, D. Aurongze, “Correlated Growth of Organic

Material Tris (8-hydroxyquinoline) Aluminum (Alq3) and its Relation to

Optical Properties”, Journal of Applied Physics, v. 106, pp. 096101-1 -

096101-3, 2009.

47

22. M.M. Nahass, A. M. Farid, A. A. Atta, “Structural and Optical Properties of

Tris(8-hydroxyquinoline) Aluminum (III) (Alq3) Thermal Evaporated Thin

Films”, Journal of Alloys and Compounds, v. 507, n. 1, pp. 112-119, 2010.

23. R. H. Friend, Gymer, R. W.,A. B. Holmes, J.H. Burroughes, R. N. Marks,

C. Taliani, D. D. C. Bradley, A. Brédas, J. L. Lögdlund, W. R. Salaneck,

“Electroluminescence in Conjugated Polymers”, Nature, v. 397, n. 6715, pp.

121-128, 1999.

24. G. E. Jabbour, B. Kippelen, N. R. Armstrong, N. Peyghambarian, “Aluminum

Based Cathode Structure for Enhanced Electron Injection in Electroluminescent

Organic Devices”, Application Physic Letters, v.73, n.9, pp. 1185-1187, 1998.

25. C. W. Tang, S. A. VanSlyke, “Organic Electroluminescent Diodes” Application

Physics Letters, v. 51, pp. 913-915, 1987.

26. G. Destriau, J. Saddy, “Preparation of Luminescent Substances. Electrical Field

Effect”, Journal Physic Radium, v.6, n.1, pp. 12-16, 1945.

27. Z. Yin, B. Wang, G. Chen, “One-dimensional 8-hydroxyquinoline Metal

Complex Nanomaterials: Synthesis, Optoelectronic Properties,

and Applications”, Journal of Materials Science, v.46, n. 8, pp. 2397-2410,

2011.

28. H. Uoyama, K. Goushi, K. Shizu,H. Nomura, C. Adachi,

“Highly Efficient Organic Light-emitting Diodes from Delayed Fluorescence”,

Nature, v.492, n. 7428, pp.234, 2012.

29. T. A. Hopkins, K. Meerholz, S. Shaheen, M. L. Anderson, A. Schmidt, B.

Kippelen, A. B. Padias, H. K. Hall, N. Peyghambarian, N. R. Armstrong,

“Substituted Aluminum and Zinc Quinolates with Blue-Shifted

Absorbance/Luminescence Bands: Synthesis and Spectroscopic,

Photoluminescence, and Electroluminescence Characterization”, Chemical

Materials, v.8, n.2 pp. 344–351, 1996

30. C. H. Cheung, A. B. Djurišić, C. Y. Kwong, H. L. Tam, K. W. Cheah, Z. T. Liu,

W. K. Chan, A. D. Rakić, “Change of the Emission Spectra in Organic Light

Emitting Diodes by Layer Thickness Modification”, Applied Physics Letters,

v. 5, n.14, pp. 2944-2946, 2004.

31. J. S. Salafsky, “Exciton Dissociation, Charge Transport, and Recombination in

Ultrathin, Conjugated Polymer, TiO2 Nanocrystal Intermixed Composites,”

Physical Review, v. 59, n. 16, pp. 10885-10894, 1999.

48

32. W. U. Huynh, J. J. Dittmer and A. P. Alivisatos, “Hybrid Nanorod, Polymer

Solar Cells”, Science, v. 295, n. 5564, pp. 2425-2427, 2002.

33. J. Dittmer, R. Lazzaroni, P. Leclere, P. Moretti, M. Granstrom, K. Petritsch, E.

A. Marseglia, R. H. Friend, J. L. Bredas, H. Rost and A. B. Holmes, “Crystal

Network Formation in Organic Solar Cells,” Solar Energy Materials and

Solar Cells, v. 61, pp. 53-61, 2000.

34. V. M. Burlakov, K. Kawata, H. E. Assender, G. A. D. Briggs, A. Ruseckas and

I. D. W. Samuel, “Discrete Hopping Model of Exciton Transport in Disordered

Media,” Physical Review, v. 72, n. 7, 2005.

35. S. A. Choulis, M. K. Mathai and V.-E. Choong, “Influence of Metallic

Nanoparticles on the Performance of Organic Electrophosphorescence

Devices,” Applied Physics Letters, v. 88, n 21, 2006.

36. S. A. Carter, J. C. Scott and J. Brock, “Enhanced Luminance in Polymer

Composite Light Emitting Diodes,” Applied Physics Letters, v. 71, n. 9, pp.

1145-1147, 1997.

37. A. Petrella, M. Tamborra, P. D. Cozzoli, M. L. Curri, M. Striccoli, P. Cosma,

G. M. Farinola, F. Babudri, F. Naso and A. Agostiano, “TiO2 Nanocrystals—

MEH-PPV Composite Thin Films as Photoactive Material,” Thin Solid Films,

v. 451-452, pp. 64-68, 2014.

38. A. A. Madhavan, G. G. Kumar, S. Kalluri, J. Joseph, S. Nagarajan, S. Nair, K.

R. V. Subramanian and A. Balakrishnan, “Effect of Embedded Plasmonic Au

Nanoparticles on Photocatalysis of Electro Spun TiO2 Nanofibers,” Journal of

Nanoscience and Nanotechnology, v. 12, n. 10, pp. 7963-7967, 2012.

39. R. Schlaf, H. Murata and Z. H. Kafafi, “Work Function Measurements on

Indium Tin Oxide Films,” Journal of Electron Spectroscopy and Related

Phenomena, v. 120, n. 1-3, pp. 149-154, 2011.

40. K. Kompoliti, “Copper”, Journal of the Neurological Sciences, v. 357, pp.478-

478, 2015.

41. L. M. Dennis, J. A. Bridgman, “Gallium”, Journal of the American Chemical

Society, v. 40, n. 10 pp.1531-1561, 1918.

42. K. Haris, A. Kramida, A. Tauheed, “Extended and Revised Analysis of Singly

Ionized Tin: Sn”, PhysicaScripta, v. 89, n.11 pp.115403-115424, 2014.

43. S. E. Harrison, B. Zhou, Y. Huo, A. Pushp, A. J. Kellock, S. S. P. Parkin, J. S.

Harris,Y. Chen, T. Hesjedal, “Preparation of Layered Thin Film Samples for

49

Angle-Resolved Photoemission Spectroscopy”, Applied Physics Letters, v.

105, n. 12, 2014.




v. 451-452, pp. 64-68, 2004.

45. A. Moarrefzadeh, “Simulation and Modeling of Physical Vapor Deposition

(PVD)”, WSEAS Transactions on Applied and Theoretical Mechanics, v.7,

v.2, pp. 106-111, 2012.

46. D. M. Mattox, “Physical vapor deposition (PVD)”, Metal Finishing, v. 100, n.

1, pp. 394-408, 2002

47. Donald M. Mattox, “Handbook of Physical Vapor Deposition (PVD) Process”,

2 ed., William Andrew, 2010.

48. D. Dorset, “X-ray Diffraction: A Practical Approach”, Microscopy and

Microanalysis, v. 4, n. 5, pp. 513-515, 1998.

49. B. D. Cullity, “Elements of X-Ray Diffraction,” 2nd Edition, Addison-Wesley

Publishing Company, Boston, 1978.

50. B.E. Warren, “X-Ray Diffraction”, 1 ed., Dover Publications, New York, 1990.

51. T. Mahalingan “Electrosynthesis and characterization of lead oxide thin films”,

Materials Characterization, v.58, pp. 8-9, 2007.

52. D. JunLee, E. YooYoon, , B. HoPark, Hyo WookPark, L JuPark, YuriEstrin, H.

SeopKim, “Dislocation Density-based Finite Element Analysis of Large Strain

Deformation Behavior of Copper Under High-Pressure Torsion”, Acta

Materialia, v.76, pp. 281-293.

53. Y. Zhao, J. Zhang, “Microstrain and grain-size analysis from diffraction peak

width and graphical derivation of highpressure thermomechanics”, Journal of

Applied Crystallography, v. 41, pp. 1095-1108, 2008.

54. N. J. Unakar, J. Y. Tsui, C. V. Harding, “Scanning Electron Microscopy”,

Ophthalmic, v. 13, pp.20-35, 1981.

55. H. H. Perkampus, “UV-Visible Spectroscopy and Its Applications”, 1 ed.

Springer-Verlag, Berlin, 1992.

56. C.Ghosh, B.P.Varma, “Some Optical properties of Amorphous and Crystalline

Antimony Trisulphide Thin Films”, Solid State Communications, v. 31, n. 9,

pp. 683-686, 1979.

https://www.sciencedirect.com/science/article/pii/S1359645414003759#!









https://www.sciencedirect.com/science/article/pii/0038109879903235#!

https://www.sciencedirect.com/science/article/pii/0038109879903235#!

https://www.sciencedirect.com/science/journal/00381098

50

57. J. Tauc, “Optical Properties of Solids”, Physics Review, v.25, pp. 749, 1970.

58. T. T. Chung-Thuy, L. H. Chi and N. N. Dinh, “Study of Photoluminescent and

Electrical Properties of Nanostructured MEH-PPV/TiO2 Hybrid Films,”

Journal of the Korean Physical Society, v. 54, 2009, pp. 291-295.

59. Challa S.S.R. Kumar , “UV-VIS and Photoluminescence Spectroscopy for

Nanomaterials Characterization”, 1 ed., Springer, New York, 2013.

60. GUO Yao, WANG Zhi-Bing, CUI Yi-Ping, ZHANG Jia-Yu, YE Yong-Hong,

“Tris (8-Hydroxyquinoline) Aluminum Nanostructure Film and Its

Fluorescence Properties”, Chinese Physic Letters, v. 25, pp. 4428, 2008.

61. S. A. Carter, J. C. Scott and J. Brock, “Enhanced Luminance in Polymer

Composite Light Emitting Diodes,” Applied Physics Letters, v. 71, n. 9, pp.

1145-1147, 1997.




v. 451-452, pp. 64-68, 2004.

63. R. L. Zhigang, “Organic Light-Emitting Materials and Devices”, 2 ed., CRC

Press, 2015.

64. M. Duvenhage, M.Ntwaeaborwa, H. G. Visser, P. J. Swarts, J. C. Swarts,

“Determination of the Optical Band Gap of Alq3 and its Derivatives for the Use

in Two-Layer OLEDs, Optical Materials”, v. 42, pp. 193-198, 2015.

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