HARAMAYA UNIVERSITY
POSTGRADUATE PROGRAM DIRCTORATE
GROWING AND CHARACTERIZATION OF ZINC OXIDE
NANORODS
M.SC. PROJECT WORK
BY
TOLASA KUMSA
COLLEGE:
NATURAL AND COMPUTATIONAL SCIENCES
DEPARTMENT:
PHYSICS
PROGRAM:
NANOSCALE PHYSICS
ADVISOR:
PROF US TANDON
AUGUST 2015
HARMAYA UNIVERSITY, HARAMAYA
Growing And Characterization Of Zinc Oxide Nanorods
M.Sc. Project Work
A Project Submitted to College of Natural and Computational Sciences,
Department of Physics, School of Graduate Studies
HARAMAYA UNIVERSITY
In Partial Fulfillment of the Requirements for the Degree of
MASTER OF SCIENCE IN PHYSICS (NANOSCALE PHYSICS)
Tolasa Kumsa
August 2015
Haramaya University, Haramaya
HARAMAYA UNIVERSITY
ii
POSTGRADUATE PROGRAM DIRCTORATE
I hereby certify that I have read and evaluated this Project entitled “Growing And
Characterization Zinc Oxide nanords, ” prepared under my guidance by Tolasa Kumsa. I
recommend that it be submitted as fulfilling the project requirement.
_______________
Major Advisor
______________
_______________
Signature
Date
As members of the Board of Examiners of the M.Sc. project Open Defense Examination, I
certify that I have read and evaluated the project prepared by Tolasa Kumsa and examined the
candidate. I recommend that the project be accepted as fulfilling the project requirements for the
degree of Master of Science in Physics (nanoscale physics).
______________________
Chairperson
______________________
Internal Examiner
______________________
External Examiner
_________________
Signature
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Date
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Signature
Date
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Signature
Date
Final approval and acceptance of the Graduate Project is contingent up on the submission of its
final copy to the council of Graduate Studies (CGS) through the candidate’s department or
school of graduate committee (DGC or SGS).
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STATEMENT OF THE AUTHOR
By my signature below, I declare that this project is my own work and that all sources of
materials used for this project have been dully acknowledged. This project has been submitted
in partial fulfillment of the requirement for M. Sc degree at Haramaya University and is
deposited at the university library to be made available and borrow under rules of library. I
solemnly declare that this project is not submitted to any other institution for the award of any
academic degree, diploma, or certificate.
Brief quotation from this Graduate project may be made without special permission provided that
accurate and complete acknowledgment of the source is made. Requests for permission for extended
quotations from or reproduction of this Graduate project in whole or in part may be granted by the Head
of the School or Department when in his or her judgment the proposed use of material is in the interest
of scholarship. In all other instance, however, permission must be obtained from the author of the
Graduate project.
Name: Tolasa Kumsa Birmachu
Date: ___________
Signature: ___________
School/Department_________________
iv
BIOGRAPHICAL SKETCH
The author was born in April 1982 at Mudi Baro Kebele, west Shoa zone, Oromia Region,
Ethiopia. He attended his primary education in Kachse Primary School and Secondary
education in Gendeberet, Ambo and Adola. After completion of secondary school education,
he joined Adama Teacher’s training college in September 2000 and graduated with Diploma in
2002. Then he got employed in Limu Woreda high School. Then joined Haramaya University
in 2003 B.Ed. degree in Physics and graduated with degree in September 2007. Then he has
been working in Ambo Preparatory school as a teacher until he joined the School of Graduate
Studies of Haramaya University in 2011 to pursue his M.Sc. in Physics.
v
ACKNOWLEDGEMENTS
I would like to take this opportunity to gratefully thank the almighty God for letting me to
finish this project work. Next I would like to thank my advisor Prof. US Tandon for his
patience and meticulous guidance. I gratefully acknowledge Haramaya University Chemistry
Research Laboratory. My genuine thanks also to Dr. Gemechu Deresa for his support for
characterizing the as-synthesized samples using EDX, XRD and SEM at Pukyong National
University of South Korea.
This work would not have been possible without considerable support provided to me by my
wife Jifare terefa, my parents and my colleagues. My sincere thank goes to Fituma Diriba for
his technical support.
vi
ABBREVIATIONS AND ACRONYMS
1D
One-dimension
NRS
Nanorods
SEM
Scanning Electron Microscope
UV
Ultra Violet
ZAH
Zinc acetate hydrate
VLS
Vapor–liquid–solid
ZnO
Zinc oxide
MOCVD
Metalo organic chemical vapor deposition
PVT
Physical vapor transport
HMTA
Hexamethylenetetramine
PL
Photoluminescence
TMAH
Tetraethyl ammonium hydroxide
ZEH
Zinc 2ethylhexanoate
XRD
X-ray diffraction
SEM
Scanning electron microscopy
EDX
Energy dissipative X-ray
THG
Third harmonic generation
SHG
Second harmonic generation
vii
TABLE OF CONTENTS
BIOGRAPHICAL SKETCH
v
ACKNOWLEDGEMENTS
vi
ABBREVIATIONS AND ACRONYMS
vii
TABLE OF CONTENT
viii
LIST OF FIGURES
x
List of Tables in the Appendix
xi
ABSTRACT
xii
1.INTRODUCTION
1
2. LITERATURE REVIEW
4
2.1 Synthesis of ZnO nanorods
4
2.1.1. Chemical method
4
2.1.2. Hydrothermal method
5
2.1.3. Synthesis of ZnO nanorods by vapor- liquid- solid method
6
.2.1.4 Synthesis of zinc oxide nanorods by controlled precipitation method
8
8
2.2. Optical properties of Zinc Oxide nanorods
2.2.1 Photoluminescence
9
2.3. Characterization Tools
13
13
2.3.1. Structural characterization tools
3. MATERIALS AND METHODS
16
3.1. Experimental Site
16
3.2. Materials and Apparatus
16
3.3. Chemicals and Reagents
16
3.4 Experimental Procedure
16
16
3.4.1. Synthesis of zinc oxide nanorods
viii
Continued
4. RESULT AND DISCUSSION
18
4.1. UV-visible absorption measurement
18
4.2. SEM analysis
20
4.3. EDS (Energy dispersive X-ray spectroscopy) analysis
22
4.4 .XRD Analysis
24
5. SUMMARY ANDCONCLUSION
29
6. REFERENCES
30
7. APPENDICES
33
ix
LIST OF FIGURES
Figure
Page
1: a) ZnO nanorods grown using gold as catalst
showing
b, An enlarged image of nanorods as catalyst
Au particles at the tips (Courtesy DR Kong).
7
2: PL spectrum of ZnO nanorods from the sample grown on a1.7nm thick Au-layer deposited
(001) Si substrate at 8900𝑐 measured at room temperature with excitation power of 5mW, the
excitation wavelength is 350nm (Yang, 2008).
12
3 : SEM (JEOL-JSM 5800)
15
4: Absorption spectrum of zinc oxide nanorods at 400oc
18
5: Absorption spectrum of zinc oxide nanorods at 600oc
19
6: Absorption spectra of zinc oxide nanorods at 800o c.
20
7: Scanning electron microscopy images of at (400oc) and b(600oc) respectively.
21
8: Scanning electron microscopy image at 800oc
21
9: EDS image as synthesize zinc oxide nanorods at 400oc.
23
10: EDS image of as synthesis zinc oxide nanorods at 600 °c.
23
11: EDS image of as synthesis zinc oxide nanorods at 800°c.
24
12:XRD patterns of ZnO Nano rods calcined at different temperature (a) 800 ℃ (b) 600 ℃
and (c) 400 ℃.
25
13: XRD data of zinc oxide nanorods calcined at 800°.
26
14:XRD data of zinc oxide nanorods calcined at 600°𝑐.
27
15: XRD data that calcined at 400°c.
28
x
List of Tables in the Appendix
Table
1. UV-Vis absorbance spectra at 400o c.
2. Maximum wavelength and energy bandgap of the as – synthesize zinc oxide nanorods.
3. Crystal size of as-synthesized zinc oxide nanorods.
xi
Page
39
43
43
ABSTRACT
Zinc oxide nanorods have been prepared by controlled precipitation method. The prepared
zinc oxide nanorods were characterized by UV-Vis to estimate optical absorption and energy
band gaps and X-ray diffraction to determine particle size. Morphology of the selected
nanorods was characterized by Scanning electronic microscopy and energy-dispersive x-ray
for elemental analysis. The temperature dependence of the size of the prepared nanorods has
also been studied. The energy band gap of zinc oxide was observed from UV-vis that showed
the band gap energy decrease with increase of temperature and particles size increase from
17.42 to 34.65 nm as temperature increase from 400oC to 800oC. The size of as synthesize zinc
oxide increase with increasing temperature.
Key words: synthesis, characterization, XRD and UV-Vis
xii
1. INTRODUCTION
Nanotechnology involves the manipulation of matter at the atomic level where conventional
physics breaks down impart new materials or devices with performance characteristics that far
exceed those predicted for more orthodox approaches. In nanotechnology, nanorods are
morphology of nanoscale objects, whose dimension ranges from 1-100nm (Orhan et al., 2012).
A nanorod is a particle with nanoscale dimension in which the length of particle can vary from
10nm up to a few micrometers but the width is of the order of nanometers (10 to100 nm).
Nanotechnology can be useful in diagnostic techniques, drug delivery, sunscreens,
antimicrobial bandages, disinfectant, and a friendly manufacturing process that reduce waste
products. Nanorods and nanowires have recently attracted considerable attention towards
scientific community because of their novel properties and potential technological applications;
it is widely used in the field of catalyst, gas sensor, solar cell materials, antimicrobial materials,
optoelectronics devices ( Prason, 2012).
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is
insoluble in water, and it is widely used as an additive in numerous materials and products
including rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives,
sealants, pigments, foods (source of Zn nutrient), batteries, ferrites, fire retardants, and first-aid
tapes. It occurs naturally as the mineral zincite, but most zinc oxide is produced synthetically
(Riba et al., 2008).
ZnO is one of the most intensively studied metal-oxide semiconductor materials having direct
wide band gap of 3.37eV, high excitonic binding energy of 60 meV at room temperature and
high optical gain, which makes it a significant material of catalytic, electronic, optoelectronic
and piezoelectric properties( Bacaksiz et al., 2008). One of the obstacles in its applications is
that there is current misunderstanding regarding the biological effects and cytotoxicity profiles
of ZnO nanoparticles. The discrepancies in the literature are likely attributable to the lack of
common understanding between life scientists and materials scientists regarding the other’s
limitations and capabilities. Nanoparticles are not necessarily identical from batch-to-batch
2
and may display alterations in surface chemistry or size distribution. Life scientists might not
appreciate the difficulty in controlling the synthesis process, while nanotechnologists might not
sensitivity of mammalian cells to these variations. There is also concern that researchers may
treat ZnO nanopartiles made by different synthesis methods as a single entity with insufficient
regard to their potential to exert different biological responses. Other confounding factors
include differences in handling, pH variations of the dispersion media, long term stability
versus freshly prepared such as nanorods, nanowires, nanobelts, nanotubes, nanorings, and
nanonails. These ZnO nanostructures are easily formed even on cheap substrates such as glass,
paper and plastic ( Wadeasa et al., 2009). Several reviews on bulk, thin film, and onedimensional materials of ZnO are reported in the literature. A comprehensive review on various
aspects of ZnO bulk material, thin films, and nanostructure is reported (Jagadish and Pearton,
2006). Recently, one-dimensional ZnO nanostructure has been widely studied for their easy
synthesis and application in nanoscle devices. ZnO nanorods (NRs) have attracted considerable
attention owing to their large surface area, good crystal quality, and unique photonic properties.
Intensive research has been focused on the fabrication of one dimensional ZnO nanostructures
and to correlate their morphologies with their size-related optical and electrical properties.
Although various kinds of ZnO nanostructures such as nanorods, nanowires, nanobelts,
nanonalls, nanohelixs, nanorings, mesoporous single-crystal nanowires, and polyhedral cages
have been realized, ZnO nanorods (NRs) continue to be the most widely studied because of
their easy formation and device applications. Different approaches have been adopted for ZnO
growth such as vapor-liquid-solid (VLS), metal- organic chemical vapor deposition (MOCVD),
sol-gel, and hydrothermal synthesis, controlled precipitation ( Chunran and Huina , 2010).
Although metal oxide nanomaterials hold potential for improving human health, there are still
multiple challenges regarding their assay and morphology during the synthesis, and variations
in their aspect ratio or agglomeration potential. A lack of careful surface and physiochemical
characterizations of ZnO nanoparticles has confusion regarding the biological responses
elicited from these materials. To avoid these problems an understanding of the intersecting
areas of science between nanomaterial scientists and biologists, is necessary. The use of metal
oxide nanomaterials represents an expanding domain for the diagnosis and treatment of cancer.
3
Currently insufficient in vivo data is available to know the biological effects of these materials
with respect to inflammation and functional alterations at the cellular or whole body level.
Although ZnO nanoparticles are widely used in the cosmetic industry and evidence against skin
penetration is encouraging, there remains some debate regarding epidermal penetration and
lingering questions regarding the safety of these materials. Most studies have been performed
with limited longitudinal studies to assess long-term effects to kidneys, liver, and spleen, and
whether the particles are cleared from the body, dissolve, or remain indefinitely. As drug
carriers, ZnO nanomaterials have an advantage over dissolvable polymers in that they can exist
in the body for considerable periods of time. Industries are looking for the next breakthrough
for a better management of diseases and medicine and drug deliveries (Muhammad, 2009).
.
General Objective
The objective of this project is to synthesize and characterize zinc oxide nanorods.
Specific Objectives
 To synthesize zinc oxide nanorods by controlled precipitation method.
 To characterize zinc oxide nanorods with respect to modern spectroscopic
instruments such as XRD, UV-Vis , SEM and EDS
4
2. LITERATURE REVIEW
2.1 Synthesis of ZnO nanorods
Zinc oxide (ZnO) is not stranger to scientific community. In the past 100 years, it has featured
as subject of thousands of research papers, dating back as early as 1993 valued for its
ultraviolet absorbance, wide chemistry, piezoelectricity and luminescence at high temperatures.
ZnO has penetrated far into industry, and is one of the critical building blocks in today’s
modern society. It can be found in paints, cosmetics, plastic and rubber manufacturing,
electronics and pharmaceuticals, to name just a few. More recently however, ZnO has again
entered the scientific spotlight, this time for its semiconducting properties.
One of the most important and dominating parameters to reduce the cost is to fabricate basic
electronic devices on cheap substrates like glass, plastic and paper. The low temperature
growth of ZnO nanorods on large area cheap and disposable substrates would open up man
photonic and electronic applications. The combination of ZnO NRs with low temperature
growth process and the large area low cost substrates may pave the way for the large-area
disposable electronic devices and flexible electronics that can be folded (Willander et al.,
2011). Up to now, many approaches have been developed to synthesize 1D-ZnO nanorods,
such as vapor- liquid-solid (VLS), controlled precipitation, hydrothermal, chemical vapor
deposition (CVD) and many other methods.
2.1.1. Chemical method
Chemistry has played a major role in developing new materials with novel and technologically
important properties. The main advantage of chemical synthesis is its versatility in designing
and synthesizing new materials that can be refined into a final product. The superiority of
chemical processes over other methods is good chemical homogeneity, as chemical synthesis
offers mixing at the molecular level. A basic understanding of the principles of crystal
chemistry, thermodynamics, phase equilibrium, and reaction kinetics is important to take
5
advantage of the many benefits that chemical processing has to offer Solution chemistry is
sometimes used to prepare the precursor, which is subsequently converted to the nano phase
particles by chemical reactions (Li.et.al, 2009). Precipitation of a solid from a solution is a
common technique for the synthesis of fine particles. The general procedure involves reactions
in the aqueous or non-aqueous solutions containing the soluble or suspended salts. Once the
solution becomes supersaturated with the product, the precipitate is formed by either
homogeneous or heterogeneous nucleation. The formation of a stable material with or without
the presence of a foreign species is referred to as heterogeneous or homogeneous nucleation.
The growth of the nuclei after formation usually proceeds by diffusion, in which case
concentration gradients and reaction temperatures are very important in determining the growth
rate of particles, to form the mono dispersed particles. For the formation of un agglomerated
particles with a very narrow size distribution, all the nuclei must be formed at nearly the same
time and the subsequent growth must occur without further nucleation or agglomeration of
particles. Nano structured materials can also be prepared by other chemical methods such as
chemical vapour deposition, (CVD), hydrothermal method, sol-gel method ( Hassan, and
Elham, .2011), co-precipitation method etc.
.
2.1.2. Hydrothermal method
Hydrothermal synthesis uses a solvent under pressures and temperature above its critical point
to increase the solubility of a solid and to speed up reactions. In a typical procedure, a
precursor and a reagent capable of regulating the crystal growth are added into a solvent with
appropriate ratios. This mixture is then placed in an autoclave to allow the reaction and to grow
1-D nano -strurtured materials at elevated temperatures and pressures. The major advantage of
this process that most materials can be made soluble in a proper solvent by heating and
pressurizing the system to its critical point. Basically, hydrothermal process is complex and a
systematical study of the growth mechanism has not been reported yet. Thus, a comprehensive
understanding of the reaction and growth mechanism under hydrothermal conditions in 1-D
nano materials (Choi, 2004). As defined; hydrothermal synthesis is a subset of solvo-thermal
synthesis and it involves water at elevated conditions. The basic principle is that small crystals
will homogeneously nucleate and growth from the solution when subjected high temperatures
and pressure. During the nucleation and growth process, water is both a catalyst and
6
occasionally a solid-state phase component. Under the extreme condition of the synthesis
vessel (autoclave) water often becomes supercritical; thus increase in the pressure of the vessel
provides an avenue to tailor the density of the final product (Hughes, 2006).
Recently, high quality zinc oxide nanorod has been fabricated by hydrothermal method on the
ITO glass substrate. It was achieved by suspending ZnO seed-coated ITO substrate upside
down in an aqueous solution of equal mole zinc nitrate (Zn(NO3)2 and hexamethylenetetramine
(HMTA) at low temperature.. The structure and optical properties of the nanorods prepared by
hydrothermal process shows strong dependence on conditions such as seed layer crystallinity,
choice and concentration of surfactant used and reaction time for growth (Shakti et al., .2011).
Materials that are made hydrothermally are generally high-quality, single crystal with diversity
of shape and sizes (Wei et al., 2011).
2.1.3. Synthesis of ZnO nanorods by vapor- liquid- solid method
The vapor–liquid-solid growth method is a highly versatile approach; various elementary and
compound semiconductor nanorods have been synthesized using this method. This process
involves the reduction of ZnO powder by carbon to form zinc and co2/co vapor in the high
temperature zone. The zinc vapor is transported and reacted with the Au solvent on substrate
located at lower temperature to form liquid alloy droplet (Bhakat, 2012 ). As the droplets
become supersaturated, crystalline ZnO nanorods are formed, possibly by the reaction between
Zn and CO / CO2 in the low temperature zone. In most of the reports on ZnO nanorods or
nanowires growth, the vapor- liquid-solid process has been used. In this case gold (Au)
nanoparticles are used as catalyst to grow ZnO nanorods. The other intrinsic feature of the
VLS growth mechanism is that on the tips of the ZnO nanorods there are always impurity
particles that could be undesirable for device fabrication. Even though, the as grown ZnO
nanorods are of n-type, intentional n-type doping is necessary to increase the carrier
concentration required for practical applications in electronic devices. With the use of In metal
acting simultaneously as the catalyst as well as the doping source, VLS growth of order and
vertically aligned n-type doped ZnO nanorods arrays has been achieved on p-Ga\Al2O3
substrates (Zhou et al ., 2008). Figure 1 shows the SEM image of the well-ordered n-type
7
ZnO nanorods arrays. The ordering was accomplished by using a 15nm thick film evaporated
onto a self–organized polystyrene nanosphere.
(a) 300nm
(b)
200nm
Figure 1: a) ZnO nanorods grown using gold as catalyst and b, An enlarged image of
nanorods as catalyst showing
Au particles at the tips (Zhou et al ., 2008).
The ability to grow high ZnO nanorods is expected to greatly increase the versatility and power
of these building blocks for nanoscale photonic and electronic device applications. Although
there are several methods of fabricating zinc oxide nanorods, p-type ZnO has not been
achieved. The main issue currently limiting production of ZnO based devices is that of the
achievement of p-type ZnO. ZnO is predicted to be an intrinsic semiconductor. Recent
improvement in the as grown quality of ZnO material as well as successes with dopant atoms
indicate that p-type doping of zinc oxide is an achievable goal.
.
8
.2.1.4 Synthesis of zinc oxide nanorods by controlled precipitation method
Controlled precipitation is a widely used method of obtaining zinc oxide, since it makes it
possible to obtain a product with repeatable properties. The method involves fast and
spontaneous reduction of a solution of zinc salt using a reducing agent, to limit the growth of
particles with specified dimensions, followed by precipitation of a precursor of ZnO from the
solution. At the next stage this precursor undergoes thermal treatment, followed by milling to
remove impurities. It is very difficult to break down the agglomerates that form, so the
calcined powders have a high level of agglomeration of particles. The process of precipitation
is controlled by parameters such as pH, temperature and time of precipitation (Agnieszka and
Teofil, .2014)
Zinc oxide has also been precipitated from aqueous solutions of zinc chloride and zinc acetate
(Kołodziejczak.et al., 2010). Controlled parameters in this process included the concentration
of the reagents, the rate of addition of substrates, and the reaction temperature. Zinc oxide
nanorods were produced with a monomodal particle size distribution and high surface area. A
controlled precipitation method was also used by (Hong et al., 2006). An increase in the
temperature caused an increase in the size of the ZnO particles. A controlled precipitation
method was also used by (Hong et al., 2006). The process of precipitating zinc oxide was
carried out using zinc acetate (Zn (CH3COO)2·H2O) and ammonium carbonate (NH4)2CO3.
.
2.2. Optical Properties of Zinc Oxide Nanorods
Optical properties of any materials are the result of photon interaction with the constituents of
material that leads to effects, which are the base for many technologies, such as detectors,
emitters, optical communications, display panels, and optical oscillations. Optical properties of
the solids are generally defined by the processes refraction, absorption, luminescence, and the
scattering. In bulk material, these optical properties normally do not depend on the size but as
we move towards low dimensional structures, size dependence of optical properties becomes
significant. The size dependence of optical properties in very small crystals is the consequence
of quantum confinement effect. The optical property of Zinc oxide is heavily influenced by the
9
energy band structure lattice dynamics. Optical transitions in zinc oxide have been studied by a
variety of experimental techniques like optical absorption, transmission, reflection, photoreflection,
spectroscope,
ellipsometery,
photoluminescence,
cathodoluminescence
and
calorimetric spectroscopy. Many body effect such as band gap renormalization, enhancement
of optical gain due to the attractive electron-hole interaction(coulomb or exaction
enhancement) and so considered important in the description of optical properties of
semiconductors (Yeo and Woo, 2001). However, compared to the linear optical properties,
there is less understanding of the nonlinear optical response, such as second-harmonic
generation (SHG) and third-harmonic generation (THG) , have been reported (Han et. al.
2009).
Semiconductor nanomaterials exhibit a change in their electronic properties relative to that of
the bulk material; as the size of solid becomes smaller, the band gap becomes larger. According
to the quantum confinement theory, electrons in the conduction band and holes in the valence
band are confined spatially by the potential barrier of the surface or trapped by the potential
well of the quantum box. The smallest energy needed for making optical transition from the
valance to the conduction band increases, effectively increasing the energy gap (Eg). The sum
of potential and kinetic energy of the freely moving carriers is responsible for the E g expansion
Therefore; the width of the confined Eg grows as the characteristic dimensions of the crystallite
decreases. This allows materials scientists the unique opportunity to change the properties of a
material simply by controlling its particle size which leads to the fabrication of a number of
devices. The size- dependence of the optical properties of quantum dots has been one of the
main subjects of research work during the last decade (Piprek, 2003).
2.2.1 Photoluminescence
Photoluminescence spectroscopy is a contact-less, non-destructive method of probing the
electronic structure of materials. Light is directed onto a sample, where it is absorbed and
imparts excess energy into the material in a process called photo-excitation. One of the ways
through which this excess energy can be dissipated by the sample is through the emission of
light, or luminescence. In the case of photo-excitation, this luminescence is called
10
photoluminescence. Photo-excitation causes electrons within the material to move into
permissible excited states. When these electrons return to their equilibrium states, the excess
energy is released and may include the emission of light (a radiative process) or may not (a non
radiative process). The energy of the emitted light (photoluminescence) relates to the difference
in energy levels between the two electron states involved in the transition between the excited
state and the equilibrium state. The quantity of the emitted light is related to the relative
contribution of the radiative process. The intensity and spectral content of this
photoluminescence is a direct measure of various important material properties. The excitation
energy and intensity are chosen to probe different regions and excitation concentrations in the
sample. PL investigations can be used to characterize a variety of material parameters. Features
of the emission spectrum can be used to identify surface, interface, uniformity and impurity
levels and to gauge alloy disorder and interface roughness. The intensity of the PL signal
provides information on the quality of surfaces and interfaces
Luminescence is a process, which involves at least two steps: the excitation of the electronic
system of the material and the subsequent emission of photons... These steps may or may not
be separated by intermediate processes. Excitation may be achieved by bombardment with
photons (photoluminescence), with electrons (cathodoluminescence), or with other particles.
Luminescence can also be induced as the result of a chemical reaction (chemiluminescence) or
by the application of an electric field (electroluminescence). When light of sufficient energy is
incident on a material, photons are absorbed and electronic excitations are created. Eventually,
these excitations relax and the electrons return to the ground state. If radiative relaxation
occurs, the emitted light is called PL. This light can be collected and analyzed to yield a wealth
of information about the photo-excited material ( Jeeju ,2012)
Following are some of the important uses of photoluminescence studies
1) Band gap determination
The most common radiative transition in semiconductors is between states in the valence band
and conduction band, with the energy difference being known as the band gap. Band gap
determination is particularly useful when working with new compound semiconductors.
i)
Impurity levels and defect detection
11
Radiative transitions in semiconductors involve localized defect levels. The PL energy
associated with these levels can be used to identify specific defects and the intensity of PL
emission can be used to determine the concentration.
ii) Recombination mechanism
The return to the equilibrium also known as the “recombination” can involve both radiative and
non-radiative processes. The intensity of PL emission and its dependence on the level of photo
excitation and temperature are directly related to the dominant recombination processes.
Analysis of PL spectrum helps to understand the underlying physics of recombination
mechanism
iii) Material quality
In general, non-radiative processes are associated with localized defect levels, whose presence
is detrimental to material quality and subsequent device performance. Material quality can be
assessed by a qualitative analysis of radiative recombination.
Photoluminescence (pL) is the spontaneous of light from a material under optical excitation.
The excitation energy and intensity are chosen to probe different regions and excitation
concentration in the sample. PL depends on the nature of the optical excitation. Because PL
often originates near the surface of a material, PL analysis is an important tool in the
characterization of surface (Patra, 2012). Photon spectrum in sensitive to factors such as
temperature, pressure, and excitation intensity and wavelength. In general, PL spectrum is
narrower and appears to have higher energy at lower temperature.
It is well known that at room temperature the PL spectrum from ZnO typically consists of a UV
emission band and a broad emission band in the visible region shown in figure2. The UV
emission band is dominated by the free excitation (FE) emission .The UV emission band is
related to a near band –edge transition of ZnO namely the recombination of the free excitations.
The excitation may have activities like they can be free and able to move through the crystal or
they can be bound to donors and accepters with neutral or charged emission. The stronger the
intensity of the green luminescence, the more single ionized oxygen vacancies there are (Wang
et al., 2010). Due to the radiative defects different wavelength emission from ZnO NRs have
been observed. The deep broad band emission from ZnO exhibited violet, blue, green, yellow
and orange-red color emissions (Willander et al., 2011), that is, it covers the whole visible
12
region. Quantum confinement shifts the energy levels of the conduction and valance bands
apart, giving rise to a blue shift in the PL exciton emission as the particle size decreases.
Figure 2: PL spectrum of ZnO nanorods grown on a1.7nm thick Au-layer deposited on (001) Si
substrate at 𝟖𝟗𝟎𝟎 𝒄 measured at room temperature with excitation power of 5mW, the
excitation wavelength is 350nm (Yang, 2008).
.
13
2.3. Characterization Tools
2.3.1. Structural characterization tools
I. Ultraviolet/Visible/Infrared (UV/Vis/IR) spectroscopy is a technique used to quantify the
light that is absorbed and scattered by a sample (a quantity known as the extinction, which is
defined as the sum of absorbed and scattered light). In its simplest form, a sample is placed
between a light source and a photo detector, and the intensity of a beam of light is measured
before and after passing through the sample (Ives et al., 2001). These measurements are
compared at each wavelength to quantify the sample’s wavelength dependent extinction
spectrum. The data is typically plotted as extinction as a function of wavelength. Each
spectrum is background corrected using a “blank” – a cuvette filled with only the dispersing
medium – to guarantee that spectral features from the solvent are not included in the sample
extinction spectrum.
It is very important to determine the size, structure and surface morphology of the different
types of ‘samples synthesized in the present work. A variety of techniques can be used for this
purpose, and the details are given in the following section
II. X-ray diffraction
X-ray diffraction (XRD) yields the atomic structure of materials and is based on the elastic
scattering of X-rays from the electron clouds of the individual atoms in the system. Diffraction
occurs as X—rays interact with a regular structure whose repeat distance is about the same as
the X-ray wavelength
Powder diffraction is a technique used to characterize the crystallographic structure, crystallite
size (grain size), and preferred orientation in polycrystalline or powdered solid samples. This
technique commonly used to identify unknown substances, by comparing diffraction data
against a database maintained by the Imitational Centre for Diffraction Data. It may also be
used to characterize heterogeneous solid mixtures to determine relative abundance of
crystalline compounds and, can provide structural information on unknown materials. Powder
14
diffraction is also a common method for determining strains in crystalline materials. The effect
of the finite crystallite sizes is seen as a broadening of the peaks in the X-ray diffraction pattern
and is explained by the Debye Scherrer Equation ( Cullity and Stock, 2001).
n𝝀 =2d sin𝜽, ----------------------------------------------- --
(2.4.1)
where n is the order of diffraction, 𝜆 is the wavelength of the X-rays, d is the spacing between
consecutive parallel planes and 𝜃 is the glancing angle (or the complement of the angle of
incidence. The average crystal size of the sample can be calculated using the Scherrer’s
formula ( Cullity and Stock, 2001).
𝟎.𝟗𝝀
D=𝜷𝒄𝒐𝒔𝜽
[2.4.2]
Where, 𝜆 is the wavelength of the X-rays and 𝛽 is the full width at half maximum intensity in
radians
III. Scanning electron microscope (SEM)
The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to
generate a variety of signals at the surface of solid specimens. The signals that derive from
interactions between the electron and the sample reveal information about the sample including
external morphology (Texture), chemical composition, and crystalline structure and orientation
of materials making up the sample. In most applications, the data are collected over a selected
area of the surface of the sample, and a 2-dimensional image is generated that displays spatial
variations in these properties. Areas ranging from approximately 5 microns to 1 cm in width
can be imaged in scanning mode using conventional SEM techniques (magnification ranging
from 20X to approximately 30,000X, spatial resolution of 50 to 100 nm). The SEM is also
capable of performing analyses of selected point locations on the sample; this approach is
especially useful in qualitatively or semi-quantitatively determining chemical compositions
(Dieter, 2005) (using EDS), crystalline structure, and crystal orientations (using EBSD). The
design and function of the SEM is very similar to the EPMA, and considerable overlap in
capabilities exists between the two instruments.
15
Fig. 3 SEM (JEOL-JSM 5800) (Dieter, 2005)
IV. Energy dispersive X-ray (EDX)
The elemental analysis or chemical composition of the synthesized powder done by using
energy dispersive x-ray at the Electron Microscope Unit. To prepare the sample for this
purpose a small amount of the synthesized powder is scooped and placed in the pellet maker.
The prepared pellet is then coated with carbon before mounting in the machine. The powder is
compressed with a high pressure. The operation is done at excitation energy of 20 keV with
scan or acquisition time of 600sec.
16
3. MATERIALS AND METHODS
3.1. Experimental Site
Apparatus and reagents were collected from Haramaya University. Synthesis of zinc oxide
nanorods and UV-vis measurements were carried out at Chemistry Department research
laboratory, Haramaya University. XRD, SEM and EDS characterization of the synthesized
ZnO nanorods were conducted at Pukyong National University of South Korea.
3.2. Materials and apparatus
Beakers, magnetic stirs, panels, filter paper, hot air oven, furnace(temperature controller)
,measuring cylinder ,UV-Vis, X-ray diffractometer , SEM and EDS were used.
3.3. Chemicals and reagents
Zn(NO3 )2 , ethanol, deionized water and Na2CO3 were used
.
3.4 Experimental Procedure
In the preparation of zinc oxide nanorods the procedure followed was: 80g of Zn(NO3)2 was
dissolved in deionized 100ml water and agitated for 1h by magnetic strirrer.
3.4.1. Synthesis of zinc oxide nanorods
Pure zinc oxide was prepared by reaction of Zn (NO3)2 and Na2CO3 through controlled precipitation.
3.4.2. Synthesis procedures
The zinc oxide (ZnO) nanorods were prepared by controlled precipitation method using zinc
nitrate and sodium carbonate precursors. Different concentrations 80g (0.54mol) of Zn(NO3)2
was dissolved in 100ml of distilled water. Then the solution was kept under constant stirring using
magnetic stirrer to completely dissolve the zinc nitrate for one hour. After complete dissolution
of zinc nitrate, 0.44 mol of sodium carbonate solution was added under constant stirring, drop by
17
1
drop touching the walls of the vessel. The reaction was allowed to proceed for 2 2 h (two and
half hours) after complete addition of sodium carbonate, the solution was allowed to settle for
overnight and the supernatant solution was then discarded carefully. Thus obtained nanorods
were washed three times using distilled water and two times using ethanol. Washing was
carried out to remove the by products. After washing, the nanoparticles were dried at 80°C for
12h. During drying, conversion of Zn (CO3) into ZnO takes place.
Then Zn (CO3)→ZnO +CO2 by the calcinations at different temperature ( 400oC, 600oC and
800oC) for 3h.
.
3.4.3. Characterization
In order to investigate various properties of the prepared zinc oxide, a number of
characterization techniques were used. UV-visible absorption measurement, XRD, SEM and
EDX were the tools used for characterization.
18
4. RESULTS AND DISCUSSION
4.1. UV-visible absorption measurement
The UV–vis absorption spectra of zinc oxide were investigated. The solution of each precursor
was prepared according to the procedure described in the experimental section. Figure 5: shows
the UV–vis absorption spectra of the zinc oxide which was calcined at 400oC. The result
obtained showed peak at wavelength 366nm. The term “band gap” refers to the energy
difference between the top of the valence band (electrons orbits which electrons are not free to
move) to the bottom of the conduction band (which electrons are relatively free to move). The
electrons are able to jump from one band to another. In order for an electron to jump from a
valence band to a conduction band, it requires a specific minimum amount of energy for the
transition, which is equal to the band gap energy. The band gap energy of zinc oxide nanorods
that calcined at temperature of 400oc is 3.39eV. No absorption measured for water. Water is
not absorbed in visible region spectrum.
Figure 4: Absorption spectrum of zinc oxide nanorods at 400oC.
The band gap enrgy of ZnO nanorods that was calcined at 400oC can be obtained as (Ives et al,
2001).
𝐸𝑔 =
ℎ𝑐
𝜆𝑚𝑎𝑥
Where: h= Planks constant = 6.626 x 10-34 Joules sec
19
C = Speed of light = 3.0 x 108 meter/sec,
λ = wavelength = 366 x 10-9 m, 1eV = 1.6 X 10-19 J
𝐸=
Then
6.63 x 10−34 J.sec x3.0 x 108 m./sec
366 x 10−9 m
=
19.89𝑥10−26 𝐽.𝑚
366𝑥10−9 𝑚
=0.0516x10-17J (in Joule) Using
conversion factor 1ev =1.6x10-19J, we have E=3.39ev (Ives et al., 2000).
Eg=
1240
𝜆
1240
eV= 366 eV=3.39eV This result agree with the Ives et al ( 20000).
The band gape energy of ZnO nanorods at 400oC agrees with the wide band gap value in the
literature.
abs
vs
wavelength
y vs .
fit 1
2
x
1.9
absorbance(au(
1.8
X: 366.9
Y : 1.73
1.7
1.6
1.5
1.4
1.3
300
400
wavelength (nm)
Figure 5: Absorption spectrum of zinc oxide nanorods at 600oC( UV/VIS).
ℎ℧
1240
Eg = 𝜆𝑚𝑎𝑥=366.9 𝑒𝑉=3.38eV. Compared to the band gap energy of the
500
20
absorbance vs wavelength
1.3
abobance(au)
1.25
1.2
X: 444
Y: 1.142
1.15
1.1
1.05
250
300
350
400
wavelength (nm)
450
500
Figure 6: Absorption spectra of zinc oxide nanorods at 800o C.
Eg =1240eV/444=2.79eV at temperature of 800o C.
From the above figure the relationship between, band gap energy and temperature is inverse, as
the temperature of the as synthesized zinc oxide increases the band gap decreases. Zinc oxide
is a color less white oxide that shows peaks at different temperatures that used to predict band
gap energy. From as-synthesis zinc oxide nanorods the energy band gap determined at wave
length of 366nm, 366.9.nm and 444nm respectively. As temperature increases from 400oC to
800°C, the band gap energy decreases from 3.39 to 2.79eV. The result of UV-Vis shows that
the relation between temperature and the band gap energy.
4.2. SEM analysis
Field emission gun scanning electron microscopy (SEM) was used to investigate surface
topography and particle morphology of the materials. The SEM images of selected assynthesized zinc oxide nanords with selected magnification are shown in Figure 7 (a and b) and
Figure 8 a. The as-synthesized ZnO particles (Figure:8a) shows irregular shape and non-
21
uniform size, with morphology of aggregated status due to low temperature calcinations at
400oC for three hours. In case of the two temperatures the surface area of the oxide becomes
more visible than the lower temperature calcinations.
(a)
(b)
Figure 7: Scanning electron microscopy images of at (400oC) and (600oC) respectively.
(a)
Figure 8: Scanning electron microscopy image at 800oC
.
22
From the SEM image zinc oxide nanorods a hexagonal structure was investigated. The mean
particle size of the as-synthesized zinc oxide nanorods from the SEM image was in 200nm
which is the space between particle size. An increament in partle size of printed thick film form
of as-synthesized nanorods was due to the firing at high temperature, resulting particle binding
agglomeration.
4.3. EDS (Energy dispersive X-ray spectroscopy) analysis
Energy dispersive X-ray spectroscopy (EDS, EDX or EDXRF) is an analytical technique used
for the elemental analysis or chemical characterization of a sample. It is one of the variants of
XRF. As a type of spectroscopy, it relies on the investigation of a sample through interactions
between electromagnetic radiation and matter, analyzing x-rays emitted by the matter in
response to being hit with charged particles. Its characterization capabilities are due in large
part to the fundamental principle that each element has a unique atomic structure allowing xrays that are characteristic of an element's atomic structure to be identified uniquely from each
other.
Spectrum processing : Peak possibly omitted : 0.273 keV
Processing option : All elements analyzed (Normalised)
Number of iterations = 2
Standard :
O
SiO2 1-Jun-1999 12:00 AM
Zn
Zn 1-Jun-1999 12:00 AM
Element Weight%
Atomic
%
OK
30.30
63.98
Zn K
69.70
31.02
Totals
100.00
23
Figure 9: EDS image as synthesize zinc oxide nanorods at 400oc.
Spectrum processing: Peaks possibly omitted : 0.277, 2.790 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 2
Standard :
O
SiO2 1-Jun-1999 12:00 AM
Zn
Zn 1-Jun-1999 12:00 AM
Element Weight%
Atomic
%
OK
25.77
58.65
Zn K
74.23
41.35
Totals
100.00
10: EDS image of as synthesis zinc oxide nanorods at 600 °C.
Processing option : All elements analyzed (Normalised)
Number of iterations = 3
Standard :
O
SiO2 1-Jun-1999 12:00 AM
Zn
Zn 1-Jun-1999 12:00 AM
Element Weight%
Atomic
%
OK
20.78
51.73
Zn K
79.22
48.27
Totals
100.00
24
Figure 11: EDS image of as synthesis zinc oxide nanorods at 800°c.
The number and energy of the X-rays emitted from a specimen can be measured by an energy
dispersive spectrometer. As the energy of the X-rays is characteristics of the difference in
energy between the two shells, and of the atomic structure of the element from which they were
emitted, this allows the elemental composition of the specimen to be measured. The EDS
reveals that the required phase is obtained. Both Zinc (Zn) and Oxygen (O) are present in the
sample. From the elemental analysis the weight of zinc increases at high temperature and
oxygen decreases with increase of temperature as carbon dioxide given out from the
compound. The elemental compositions of ZnO at the three temperatures had different values.
This show when the calcinations temperatures increase the elimination of carbon dioxide
increases this results in decreasing the elemental weight of oxygen.
4.4 .XRD Analysis
As a primary characterization tool for obtaining critical features such as crystal structure,
crystallite size, and strain, x-ray diffraction patterns have been widely used in nanoparticle
research. However, this method is only available for crystalline and polycrystalline materials
due to the regular long range arrangement of atoms. For these study the X-ray diffracto meter
(XRD) operating with monochromatic high intensity Cu Kα (λ= 0.15406 nm) radiation was
used. The x-ray diffraction pattern of the as-synthesized nanrods of S1, S2 and S3 samples
were shown in Figure 13. The results showed distinct peaks with their corresponding 2θ and β
values (given in units’ degree and radians, respectively) which accounts for the crystalline
nature of all the as-synthesized nanorods. The average crystallite sizes of the as synthesized
semiconductors were calculated and given below. The 2θ recorded ranging from 100–700. The
particle size (D) of the powders was calculated by Scherer’s Formula (Cullity and Stock, 2001).
25
Figure 12:XRD patterns of ZnO Nano rods calcined at different temperature (a) 800 ℃ (b) 600
℃ and (c) 400 ℃.
Among the peaks, the ZnO NRs that were calcined at 800oc resulted in the narrowest peak of
full width at half maximum (FWHM). By contrast, the ZnO NRs that were prepared at 400o c
showed the widest peak of ( FWHM). Simultaneously, the ZnO nanorods also showed the
highest peak intensities on the (101) plane.
Compared with the standard diffraction peaks of ZnO, the clear and sharp peaks indicated that
the ZnO NRs possessed an excellent crystal quality, with no other diffraction peaks and
characteristic peaks of impurities in the ZnO NRs. Therefore, all of the diffraction peaks
were similar to those of the bulk ZnO. figure 13 shows the ZnO XRD from the data card
compared with the measured ZnO XRD results.
26
Figure 13: XRD data of zinc oxide nanorods calcined at 800°𝑪.
𝑇ℎ𝑒 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑔𝑟𝑎𝑖𝑛 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑎𝑚𝑝𝑙𝑒 𝑐𝑎𝑛 𝑏𝑒 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑢𝑠𝑖𝑛𝑔 𝑡ℎ𝑒 𝑆𝑐ℎ𝑒𝑟𝑟𝑒𝑟’𝑠 𝑓𝑜𝑟𝑚𝑢𝑙𝑎
𝑫=
𝟎. 𝟗𝝀
𝜷𝒄𝒐𝒔𝜽
[𝟐. 𝟒. 𝟐]
𝛽(𝐹𝑊𝐻𝑀) 𝑖𝑠 𝑓𝑜𝑢𝑛𝑑 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 36.54° 𝑎𝑛𝑑 35.98°. 𝛽 = 0.0049 𝑟𝑎𝑑𝑖𝑎𝑛.
𝐹𝑟𝑜𝑚 𝑆𝑐ℎ𝑒𝑟𝑟𝑒𝑟’𝑠 𝑓𝑜𝑟𝑚𝑢𝑙𝑎 𝐷 = 0.138456/0.00395440158 =
34.65𝑛𝑚. 𝑇ℎ𝑒 𝑋𝑅𝐷 𝑑𝑎𝑡𝑒 𝑖𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑛𝑎𝑛𝑜 𝑟𝑎𝑛𝑔𝑒 𝑎𝑡 8000𝐶.
27
Figure 14:XRD data of zinc oxide nanorods calcined at 600°𝒄.
The value of (FWHM) is found between 35.82° and 36.82°, 𝛽 = 0.0075𝑟𝑎𝑑.
From Schreer’s formula
quality nanorange.
D=0.138456/0.0060474525=22.89nm.This data also has good
28
figure 15: XRD data that calcined at 400°C.
2𝜃 for full width half maxima(FWHM) was between 35.66° and 36.8°.
The value of (FWHM) =𝛽=0.0099radian and the average crystal size D is
D =0.138456/0.0079478388=17.42nm
The above result showed that the direct dependence of the particle size on temperature, as the
temperature of the as-synthesized zinc oxide nanorods increased the particle size also increased
but band gap of the zinc oxide nano rods decreased with increasing temperature. The size of the
as-synthesized nanorods ranges from 17.42 to 34.65nm these results indicate the synthesized
nanorods were in nano range. As temperature changes from 400 oC to 800oC the
average crystal size increased.
29
5. SUMMARY AND CONCLUSION
In this study, ZnO NRs with a highly crystalline structure were synthesized by co precipitation
technique. The SEM images of the samples demonstrated that the diameters of the synthesized
ZnO NRs were 200 nm. The XRD patterns exhibited that all of the ZnO NRs have remarkably
crystal qualities. The EDS reveals that the required phase presents in. both Zinc (Zn) and
Oxygen (O) is present in the sample and the total weight of the oxide ZnO was 100.
.
The calculated band gap values of the synthesized ZnO NRs were decreased with the
increasing of temperature. The crystal qualities, grain size, diameter, and optical band gap of
the ZnO NRs were affected by calcinations temperature in the ZnO preparation. The ZnO NRs
that were synthesized with the use of water and ethanol, a solvent, the values exhibited the
most improved results, in terms of structural and optical properties; these ZnO NRs showed the
smallest grain size, smallest crystallite size, and highest band gap values. For the synthesized
zinc oxide nanorods the optical absorption was measured using UV-vis range for the
determination of band gap energy at the three stage temperature values. 400 oC, 600 oC and.
800 oC.
The obtained results can be summarized as follows:
XRD confirm the formation of nanosized semiconductors of ZnO. As-synthesized nanorods
samples were selected at three different temperatures for further characterization because of
their smallest size. The zinc oxide results in small size at 400oC temperature. The result showed
that the dependence of particle size and energy gap on temperature. The result shows that the
band gap energy decrease with increasing temperature. As temperatures increases from 400oC to
800o C the crystal size increases from 17.42nm to 34.65nm respectively.
30
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33
7. APPENDICES
Absorbance at 400oC
Wavelength Scan 1
Scan Wavelength: 200.0 nm - 600.0 nm Test Mode: Abs Mode
Peak/Valley Data Record
No.
Wavelength(nm)
Abs
Trans(%T)
Energy Energy(100%T)
Energy(0%T)
No Peak/Valley Data.
Wavelength Scan Data Record
No.
Wavelength(nm)
Abs
Trans(%T)
Energy Energy(100%T)
Energy(0%T)
1
600.0
0.000 100.0
1175
30517
75
2
598.0
1.450 3.5
1071
28003
75
3
596.0
1.453 3.5
977
25703
75
34
4
594.0
1.455 3.5
1783
47345
113
5
592.0
1.460 3.5
1621
43991
113
6
590.0
1.462 3.4
1555
41939
113
7
588.0
1.461 3.5
1501
40641
113
8
586.0
1.457 3.5
1505
40775
113
9
584.0
1.446 3.6
1247
31219
113
10
582.0
1.439 3.6
1331
33595
113
11
580.0
1.431 3.7
1425
35579
113
12
578.0
1.425 3.8
1509
37241
113
13
576.0
1.416 3.8
1597
38783
113
14
574.0
1.408 3.9
1663
40109
113
15
572.0
1.399 4.0
1773
41547
113
16
570.0
1.390 4.1
1861
42855
113
17
568.0
1.383 4.1
1937
44145
113
18
566.0
1.376 4.2
2017
45377
113
19
564.0
1.369 4.3
2093
46703
113
20
562.0
1.362 4.3
2197
47825
113
21
560.0
1.355 4.4
2269
48915
113
22
558.0
1.349 4.5
2339
49819
113
23
556.0
1.343 4.5
1223
25357
75
24
554.0
1.337 4.6
1249
25645
75
25
552.0
1.331 4.7
1269
25745
75
35
26
550.0
1.324 4.7
1293
25625
75
27
548.0
1.319 4.8
1291
25187
75
28
546.0
1.316 4.8
2471
48959
113
29
544.0
1.314 4.8
2353
46513
113
30
542.0
1.312 4.9
2245
43713
113
31
540.0
1.311 4.9
2095
40587
113
32
538.0
1.309 4.9
1953
37609
113
33
536.0
1.309 4.9
1827
35021
113
34
534.0
1.310 4.9
1731
32983
113
35
532.0
1.311 4.9
1641
31493
113
36
530.0
1.312 4.9
1589
30421
113
37
528.0
1.313 4.9
1567
29997
113
38
526.0
1.313 4.9
1567
30013
113
39
524.0
1.313 4.9
1579
30143
113
40
522.0
1.314 4.9
1569
30055
113
41
520.0
1.315 4.8
1547
29815
113
42
518.0
1.315 4.8
1531
29483
113
43
516.0
1.315 4.8
1515
29095
113
44
514.0
1.313 4.9
1505
28719
113
45
512.0
1.311 4.9
1489
28315
113
46
510.0
1.308 4.9
1485
27879
113
47
508.0
1.306 4.9
1461
27453
113
36
48
506.0
1.304 5.0
1453
27021
113
49
504.0
1.304 5.0
1429
26595
113
50
502.0
1.303 5.0
1411
26187
113
51
500.0
1.303 5.0
1387
25781
113
52
498.0
1.302 5.0
1375
25357
113
53
496.0
1.302 5.0
2663
49929
187
54
494.0
1.301 5.0
2629
49057
187
55
492.0
1.300 5.0
2577
48139
187
56
490.0
1.298 5.0
2561
47283
187
57
488.0
1.296 5.1
2539
46477
187
58
486.0
1.295 5.1
2485
45617
187
59
484.0
1.294 5.1
2445
44747
187
60
482.0
1.292 5.1
2421
43959
187
61
480.0
1.290 5.1
2401
43031
187
62
478.0
1.291 5.1
2337
42257
187
63
476.0
1.290 5.1
2291
41463
187
64
474.0
1.289 5.1
2267
40649
187
65
472.0
1.287 5.2
2235
39761
187
66
470.0
1.285 5.2
2181
38831
187
67
468.0
1.283 5.2
2153
37927
187
68
466.0
1.280 5.2
2117
36883
187
69
464.0
1.277 5.3
2063
35783
187
37
70
462.0
1.274 5.3
2023
34653
187
71
460.0
1.272 5.3
1973
33571
187
72
458.0
1.270 5.4
1921
32459
187
73
456.0
1.269 5.4
1865
31341
187
74
454.0
1.269 5.4
1801
30085
187
75
452.0
1.269 5.4
1731
28863
187
76
450.0
1.270 5.4
1669
27803
187
77
448.0
1.271 5.4
2071
35347
187
78
446.0
1.271 5.4
2129
36615
187
79
444.0
1.271 5.4
2215
37875
187
80
442.0
1.270 5.4
2267
38833
187
81
440.0
1.270 5.4
2289
39541
187
82
438.0
1.269 5.4
2331
40047
187
83
436.0
1.267 5.4
2361
40449
187
84
434.0
1.264 5.4
2399
40713
187
85
432.0
1.262 5.5
2417
40881
187
86
430.0
1.260 5.5
2431
40885
187
87
428.0
1.258 5.5
2425
40777
187
88
426.0
1.257 5.5
2415
40553
187
89
424.0
1.254 5.6
2417
40229
187
90
422.0
1.252 5.6
2407
39783
187
91
420.0
1.250 5.6
2387
39253
187
38
92
418.0
1.248 5.6
2347
38465
187
93
416.0
1.247 5.7
2313
37661
187
94
414.0
1.246 5.7
2265
36763
187
95
412.0
1.246 5.7
2207
35791
187
96
410.0
1.245 5.7
2151
34789
187
97
408.0
1.243 5.7
2105
33737
187
98
406.0
1.241 5.7
2043
32607
187
99
404.0
1.239 5.8
1995
31479
187
100
402.0
1.237 5.8
1931
30331
187
101
400.0
1.235 5.8
1867
29087
187
102
398.0
1.234 5.8
1811
27935
187
103
396.0
1.232 5.9
1737
26613
187
104
394.0
1.232 5.9
1667
25417
187
105
392.0
1.232 5.9
3173
48137
369
106
390.0
1.232 5.9
3015
45559
369
107
388.0
1.231 5.9
2857
42737
369
108
386.0
1.231 5.9
2711
40167
369
109
384.0
1.230 5.9
2551
37477
369
110
382.0
1.228 5.9
2417
35069
369
111
380.0
1.225 6.0
2279
32551
369
112
378.0
1.220 6.0
2175
30373
369
113
376.0
1.214 6.1
2067
28255
369
39
114
374.0
1.205 6.2
1987
26445
369
115
372.0
1.195 6.4
3809
49053
727
116
370.0
1.184 6.6
3673
45905
727
117
368.0
1.172 6.7
2813
31373
727
118
366.0
1.163 6.9
2901
32351
727
119
364.0
1.156 7.0
2979
32979
727
120
362.0
1.151 7.1
3023
33183
727
121
360.0
1.146 7.1
3041
33057
727
122
358.0
1.142 7.2
3027
32671
727
123
356.0
1.138 7.3
3005
32009
727
124
354.0
1.135 7.3
2961
31221
727
125
352.0
1.131 7.4
2901
30197
727
126
350.0
1.127 7.5
2865
29185
727
127
348.0
1.124 7.5
2779
27983
727
128
346.0
1.121 7.6
2691
26767
727
129
344.0
1.117 7.6
2605
25353
727
130
342.0
1.114 7.7
4969
47335
1431
131
340.0
1.110 7.8
4779
44503
1431
132
338.0
1.107 7.8
3921
41479
727
133
336.0
1.104 7.9
3983
42187
727
134
334.0
1.102 7.9
4063
42899
727
135
332.0
1.101 7.9
4145
43743
727
40
136
330.0
1.100 7.9
4207
44543
727
137
328.0
1.101 7.9
4277
45455
727
138
326.0
1.102 7.9
4345
46353
727
139
324.0
1.104 7.9
4395
47401
727
140
322.0
1.107 7.8
2235
24229
369
141
320.0
1.111 7.7
2263
24753
369
142
318.0
1.115 7.7
2281
25255
369
143
316.0
1.121 7.6
2291
25773
369
144
314.0
1.126 7.5
2303
26311
369
145
312.0
1.131 7.4
2323
26797
369
146
310.0
1.135 7.3
2337
27273
369
147
308.0
1.139 7.3
2353
27727
369
148
306.0
1.140 7.2
2371
28151
369
149
304.0
1.140 7.2
2399
28511
369
150
302.0
1.137 7.3
2447
28821
369
151
300.0
1.134 7.3
2475
29065
369
152
298.0
1.130 7.4
2505
29239
369
153
296.0
1.126 7.5
2531
29311
369
154
294.0
1.120 7.6
2559
29291
369
155
292.0
1.113 7.7
2589
29191
369
156
290.0
1.105 7.8
2621
29025
369
157
288.0
1.098 8.0
2641
28869
369
41
158
286.0
1.091 8.1
2665
28761
369
159
284.0
1.084 8.2
2703
28701
369
160
282.0
1.077 8.4
2739
28647
369
161
280.0
1.070 8.5
2767
28615
369
162
278.0
1.063 8.6
2813
28623
369
163
276.0
1.057 8.8
2859
28735
369
164
274.0
1.051 8.9
2911
28971
369
165
272.0
1.046 9.0
2981
29401
369
166
270.0
1.042 9.1
3061
29983
369
167
268.0
1.037 9.2
3153
30713
369
168
266.0
1.033 9.3
3265
31575
369
169
264.0
1.030 9.3
3375
32475
369
170
262.0
1.028 9.4
3479
33371
369
171
260.0
1.029 9.4
3557
34295
369
172
258.0
1.034 9.2
3603
35069
369
173
256.0
1.044 9.0
3611
35837
369
174
254.0
1.063 8.7
3541
36431
369
175
252.0
1.093 8.1
3389
36883
369
176
250.0
1.141 7.2
3117
37255
369
177
248.0
1.214 6.1
2705
37527
369
178
246.0
1.322 4.8
2169
37651
369
179
244.0
1.470 3.4
1589
37609
369
42
180
242.0
1.669 2.1
1061
37361
369
181
240.0
1.919 1.2
713
36911
369
182
238.0
2.222 0.6
499
36055
369
183
236.0
2.524 0.3
433
34931
369
184
234.0
2.749 0.2
819
65535
727
185
232.0
2.792 0.2
813
63001
727
186
230.0
2.750 0.2
815
59125
727
187
228.0
2.601 0.3
1593
65535
1431
188
226.0
2.495 0.3
1587
65535
1431
189
224.0
2.370 0.4
3123
65535
2798
190
222.0
2.326 0.5
3127
65535
2798
191
220.0
2.308 0.5
3083
65535
2798
192
218.0
2.305 0.5
3111
65535
2798
193
216.0
2.305 0.5
3127
65535
2798
194
214.0
2.311 0.5
3097
65535
2798
195
212.0
2.318 0.5
3093
65535
2798
196
210.0
2.326 0.5
3103
65535
2798
197
208.0
2.327 0.5
3089
65535
2798
198
206.0
2.306 0.5
3073
65535
2798
199
204.0
2.250 0.6
3081
56951
2798
200
202.0
2.198 0.6
3097
47445
2798
201
200.0
2.144 0.7
3089
38849
2798
43
Table 2: Energy gap at three temperatures.
Temperature( o C)
wavelength(nm)
Energy gap(eV)
400
366
3.39
600
370
3.35
800
378
3.28
Table.3 Crystal size of as-synthesized zincoxide nanorods.
2θ (degree)
β (radians)
D
(nm)
400
36.26
0.0099
17.42
600
36.28
0.0075
22.89
800
36.22
0.0049
34.65
Temperature (oC)