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OPTICAL CHARACTERIZATION OF GRAPHENE AND GRAPHENE OXIDE
A Mini Project Report Submitted in Partial Fulfillment of the Requirement of the Degree of
BACHELOR OF TECHNOLOGY
In
ELECTRONICS AND COMMUNICATION ENGINEERING
by
PRADUMN KUMAR - 20130442
SAMA KAVYA SHREE REDDY - 20130432
Under the guidance of
Mr.Himangshu Pal
Assistant Professor
SMIT
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
SIKKIM MANIPAL INSTITUTE OF TECHNOLOGYMAJITAR, EAST SIKKIM-737136, DECEMBER 2016.
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CERTIFICATE
This is to certify that the project report entitled “Optical characterization of graphene and graphene
oxide” submitted by Pradumn Kumar(20130442) and Sama Kavyashree Reddy (20130432) to Sikkim
Manipal Institute Of Technology, Sikkim in partial fulfillment for the award of degree of Bachelor of
Technology in Electronics And Communication Engineering, is a bonafide record of the project work
carried out by him under my guidance and supervision during the academic session August–
December, 2016.
Himangshu Pal Prof. (Dr.) R. Bera
Assistant Professor H.O.D
Dept. Of Electronics & Communication Dept. Of Electronics & Communication
Sikkim Manipal Institute of Technology Sikkim Manipal Institute of Technology
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ABSTRACT
Recently, much attention has turned to the structural and optical properties of carbon based materials.
At present, especially, graphene is the hottest topics in condensed-matter physics and materials science.
The aim of this research is to develop optical properties of Graphene oxide. A simple analysis is
performed for the optical properties of graphene.
UV-VIS is used for the measurement of the optical properties of graphene powder, graphene oxide,
reduced graphene oxide and thermally exfoliated graphene. The optical properties include the
transmittance, absorption and band gap energy.
The Optical properties are studied and depending upon the characterization their possible applications
are then stated.
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ACKNOWLEDGEMENTWe would like to express our sincere gratitude and appreciation to our supervisor Prof. (Dr.)
R. Bera, Head, Department of Electronics & Communication Engineering, Sikkim Manipal
Institute of Technology, for guiding us throughout our research technically and
methodologically.
We would like to express our sincere gratitude to Brig (Dr) S.N. Mishra, Vice Chancellor,
Sikkim Manipal University, Col. (Dr.) Sadasivan Thekkey Veetil (Retd.), Director, Sikkim
Manipal Institute of Technology, Prof. (Dr.) M.K. Ghosh, Dean (Academics), Sikkim Manipal
Institute of Technology and Prof. (DR.) AJOY Kumar Ray, Dean (R&D), Sikkim Manipal
Institute of Technology for constant encouragement and motivation.
We would like to thank our project guide Mr. Himangshu Pal Sir (Asst. prof.) for his constant
support throughout the project work. We would also like to thank all the scientists, teaching
and non-teaching staffs of E&C Engg. Department, Sikkim Manipal Institute of Technology,
for providing enormous support to carry out our research works. We would also like to thank
all our colleagues of Sikkim Manipal Institute of Technology, for providing their support in
various manners during this research work.
Last but not the least, we would like to thank our family for supporting us constantly during
our research work.
Sama Kavyashree Reddy (20130432) Pradumn kumar (20130442)Department of E&C Engineering, SMIT. Department of E&C Engineering, SMIT.
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List of Figures
1. UV-Vis 1800 10
2. Cuvette 11
3. Ultrasonic Bath 13
4. Analytical Balance 15
5. Digital Hotplate 16
6. Table 1 25
7. Table 2 26
8. Table 3 29
9. Graph of Graphite powder(absorption,transmittance,energy) 30
10. Graph of Graphene Oxide(absorption,transmittance,energy) 31
11. Graph of Reduced Graphene Oxide(absorption,transmittance,energy) 32
12. Graph of Thermally Exfoliated Graphene(absorption,transmittance,
energy) 33
13. UV Spectrum 36
14. Comparative graph of Absorption 38
15. Comparative graph of Transmittance 39
16. Comparative graph of Energy 40
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List of Abbreviations
1. UV VIS - Ultraviolet visible
2. FET - Field effect transistor
3. OLED - Organic light emitting diode
4. HOMO - Highest occupied molecular orbital
5. LUMO - Lowest unoccupied molecular orbital
6. GO - Graphene Oxide
7. RGO - Reduced Graphene Oxide
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Motivation
The world today needs a revolutionary material that has the capability of handling the
demands of the future generation. But, the evolution towards such futuristic devices seems to
have come to a stand-still waiting for that ‘amazing all-round material’. Graphene, as of now,
seems to be leading in the race for hunt of such material. The graphene is breaking so many
records in terms of strength, electricity and heat conduction (as well as many others). But, we
currently know just the tip of the iceberg. Before graphene is heavily integrated into the areas
in which we believe it will excel at, we need to spend a lot more time understanding just what
makes it such an amazing material. So, let us explore just what makes graphene so special.
What are its optical properties that separate it from other forms of carbon, and other 2D
crystalline compounds?
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Table of Contents
Certificate 2
Abstract 3
Acknowledgement 4
List of figures 5
List of Abbreviations 6
Motivation 7
Chapter 1
Introduction and Basic aspects 10
1.1 UV-VIS Spectrometer 12
1.2 Cuvette 14
1.3 Ultrasonic bath 15
1.4 Analytical balance 16
1.5 Digital hotplate 17
1.6 De-ionized water 19
Chapter 2
Literature Review 20
2.1 Reviews on Graphene Oxide and Reduced Graphene Oxide 20
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2.2 Review on Properties of Graphene 22
Chapter 3
Optical properties 23
3.1 Absorption 24
3.2 Transmittance 28
3.3 Energy 29
Chapter 4
UV- Spectrum 36
Chapter 5
Results and Discussion 39
5.1 Future scope and applications 43
Chapter 6
Conclusion 45
References 46
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1. INTRODUCTION AND BASIC ASPECTS
Nowadays, in the development of new and efficient and optically active
materials, research is focused towards the synthesis of graphene and its composites.
But, at the same time, there is much less focus on the complex optical properties of
graphene . Graphene, a monolayer of carbon atoms packed into a dense, honeycomb
crystal structure, has shown attractive electronic and optical properties that could make
them useful in a variety of applications. These electrical and optical properties of
graphene show much promise for commercial applications in Nano electronic and
optoelectronic devices such as organic photovoltaic devices, ultrasensitive sensors and
ultra-capacitors, but perfect graphene itself does not exist. One of the most important
ways of studying graphene is through its optical properties in the UV-Vis region by
decorating its surface.
The bandgap within a graphene sheet could be opened by
reducing the dimensions of graphene to the Nano level or by introducing dopants . The
deposition of inorganic nanoparticles, such as metals or semiconductors, onto
graphene sheets would confer special features in new hybrids and be useful in optical
and electronic devices, catalysis, sensors, and so on. Optical properties exhibited by
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single materials are quite different from those of their composites and those of
graphene-based nanoparticles, which are able to absorb UV-Vis light .
Tuning the optical properties of various materials has been of
great interest due to their potential applications in optoelectronic devices . Among many
optical materials, graphene oxide (GO) has gained intense interest due to its versatility
in various devices such as flexible electronics , solar cells and chemical sensors. In recent
past, intense research has been carried out to understand the properties of GO and
transform it as reduced GO (RGO) in order to utilize in aforesaid applications.
Essentially, GO is a single layer of the graphite oxide and consists of several
oxygenated functional groups on its basal plane and at the edges. Graphite Oxide and
GO are chemically identical and the latter consists of many oxygenated functional groups such
as hydroxyl, epoxide, carbonyl and carboxyl groups. Among them, carbonyl and carboxyl
groups are arranged on the edges of GO and hydroxyl, epoxy groups exist on the basal plane .
As a result of many functional groups, GO structure is still ambiguous. The stoichiometry and
the conductance of GO change due to the fact that the oxygenated-type functional groups
change with different synthesis conditions. This would allow one to tune the electronic
structure of GO from insulator to semiconductor and hence to metal in nature. Various
methods like chemical, thermal and mechanical methods have been used to control the band
gap by controlling the electronic structure of GO.
In terms of how far along we are to understanding the true properties of graphene, this is just
the tip of the iceberg. Before graphene is heavily integrated into the areas in which we believe
it will excel at, we need to spend a lot more time understanding just what makes it such an
amazing material. Unfortunately, while we have a lot of imagination in coming up with new
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ideas for potential applications and uses for graphene, it takes time to fully appreciate how and
what graphene really is in order to develop these ideas into reality. This is not necessarily a
bad thing, however, as it gives us opportunities to stumble over other previously under-
researched or overlooked super-materials, such as the family of 2D crystalline structures that
graphene has born.
1.1 UV-VIZ SPECTROMETERUltraviolet/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 photodetector, and the intensity of a beam of light is measured
before and after passing through the sample. 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.
Nanoparticles have optical properties that are sensitive to size, shape, concentration,
agglomeration state, and refractive index near the nanoparticle surface, which makes
UV/Vis/IR spectroscopy a valuable tool for identifying, characterizing, and studying these
materials. Nanoparticles made from certain metals, such as gold and silver, strongly interact
with specific wavelengths of light and the unique optical properties of these materials is the
foundation for the field of plasmonics. A various numerical modeling algorithms that can be
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used to predict the optical properties of various nanoparticles allowing for comparison
between theoretical and measured properties.
FIG 1: UV VIS 1800-spectrophotometer
Our standard UV-Vis analysis is performed with an UV VIS 1800- spectrometer, which
collects spectra from 200-1100 nm using a slit width of 1 nm. Deuterium and tungsten lamps
are used to provide illumination across the ultraviolet, visible, and near infrared
electromagnetic spectrum. Spectra are typically collected from 1 ml of a sample dispersion,
but we can test volumes as small as 100 µL using a microcell with a path length of 1 cm.
Additionally, we have assembled a variety of light source/spectrometer custom setups for
measuring optical properties of materials from the ultraviolet to the deep-infrared (200 nm to
20 m), and can customize analytical systems to measure scattering or absorption from both
liquid and solid samples. We also have a highly instrumented chamber for aerosolizing
nanoparticles and measuring the optical properties of the suspended particles.
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1.2 CUVETTEA straight-sided clear container for holding liquid samples in a spectrophotometer or
other instrument.
A cuvette (from French cuvette = "little vessel") is a small tube of circular or square cross
section, sealed at one end, made of plastic, glass, or fused quartz(for UV light) and designed
to hold samples for spectroscopic experiments. Disposable plastic cuvettes are often used in
fast spectroscopic analysis, where speed is more important than high accuracy. Glass cuvettes
are typically for use in the wavelength range of visible light and fused quartz tends to be used
in the UV through NIR ranges.
FIG 2: Cuvette
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The other types of cuvettes are more expensive than the plastic cuvette. It is disposable and
will be eliminated once complete the spectrometric experiment to prevent risk from reusing
cuvettes and damaging expensive quartz. Colour and UV range can be analysed by this type of
cuvette. Some cuvettes will be clear only on opposite sides, so that they pass a single beam of
light through that pair of sides; often the unclear sides have ridges or are rough to allow easy
handling. Typically, cuvettes are 10 mm (0.39 in) across, to allow for easy calculations
of coefficients of absorption. To measure the sample, the transparent side must be placed
toward the light in spectrophotometer. For accurate measurement, these testing tubes should
be cleaned and without any scratches.
1.3 ULTRA SONIC BATHS
The Ultra Sonic Bath is used for the rapid and complete removal of contaminants from
objects by immersing them in a tank of liquid flooded with high frequency sounds waves.
Sonication is the act of applying sound energy to agitate particles in a sample, for various
purposes. Ultrasonic frequencies (>20 kHz) are usually used, leading to the process also being
known as ultra-sonication or ultra-sonication.
FUNCTION PRINCIPLE
A high-frequency generator in the ultrasonic bath produces about 35000 oscillations per
second, which are transferred into the cleaning solution and cause it to resonate. The energy
density of the sound field is so high that a cavitation effect sets in. Innumerable extremely
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small vacuum bubbles develop in the ultrasonic bath and collapse in microseconds due to
pressure and suction. The pulses triggered by this remove dirt particles even at the deepest,
least accessible places or they result in homogenisation, dispersion and degassing.
FIG 3: ULTRA SONIC BATH
1.4 ANALYTICAL BALANCE
An analytical balance is so sensitive that it can detect the mass of a single grain of a
chemical substance. Thus, if a method of direct weighing is used, the substance ought to be
added to the tared container which will hold it, never directly to the pan or even to weighing
paper placed on the pan. The container used should be completely dry and at room
temperature, never at an elevated or reduced temperature. Even slight temperature differences
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can produce apparent changes in mass of the container. Finally, the container ought to be
completely dry, inside and out.
TARING
First, before weighing anything on this analytical balance, it needs to be "tared," or
recalibrated to read 0.0000 g. When first turned on, or when left by the previous user, the
balance may indicate something other than 0.0000 g. The Tare button needs to be pressed and
released to effect this recalibration.
FIG 4: Analytical balance
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1.5 DIGITAL HOTPLATE
The Digital Hotplate provides powerful heating and stirring with LED digital display
of the set temperature and real-time temperature display. LED heating and analog stirring are
simply controlled turning the respective control knobs.
FIG 5: Digital Hotplate
FEATURES OF TARSON SPINOT DIGITAL
Easy-to-read LED display for heat, analog control for stirring.
Heat only, stir only or heat and stir together functions.
Low temperature stability.
PT-1000 Sensor for medium temperature control.
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Electronic speed control for constant speed even during changes in load.
High magnetic adhesion.
Hot warning above 50°C.
1.6 DE-IONISED WATER
Deionized water is deeply demineralized, ultrapure water with the resistivity close to
18 mega ohm-cm. It is used in microelectronics, printed circuit boards, instrument
manufacture, pharmacy, washing liquids etc.
In order to obtain the high quality pure deionised water a multi-stage water purification
process can be used. After pre-cleaning, the water is supplied to the reverse osmosis
membrane, and then the water is filtered through a special deionization medium, which
removes the rest of the ions in the water. The purity of deionized water can exceed the purity
of distilled water
DIFFERENCE BETWEEN DE IONISED WATER AND DISTILLED WATER
The basis of the process is the transfer of water in the vapor phase with its subsequent
condensation. The main drawback of this method is the very high maintenance costs of the
electricity needed to convert the water into the steam. In addition, in the process of steam
formation along with water molecules other solutes can enter the steam according to their
volatility. Evaporation is achieved in various ways: the vacuum above the water, heating, etc.
The water molecules have the boiling point of 100°C or 212° F. Other substances have
different boiling points. The substance that boils at a lower temperature evaporates first. The
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boiling point of various impurities is higher, and, theoretically, they will begin to evaporate,
when the water has already boiled out. The substance that boils at a lower temperature
evaporates first. Due to this difference the water is separated. The absolute advantage of the
distilled water is the complete absence of harmful substances.
2. LITERATURE REVIEW
1.7 Reviews on Graphene Oxide, Reduced Graphene Oxide and Graphite powder
Graphene is a carbon based material that can be viewed as a one atom thick sheet of
graphite and has been investigated intensely in recent years following a report by
Konstantin Novoselov on its isolation and measurement of its unique electronic
properties. Quickly after its initial discovery, graphene was used to make electronic
devices for a variety of applications. Because high quality sheets of graphene is often
prepared by chemical vapor deposition (CVD), which requires expensive equipment,
many groups have looked at using graphene oxide as a solution process able
alternative for the preparation of graphene like materials. Indeed, graphene oxide can
be reduced in solution and as a thin film using a variety of reducing conditions, and
reduction converts the graphene oxide into a material that has a large enhancement in
electrical conductivity. In addition to its use in making reduced graphene oxide for
electronic devices, graphene oxide has been used in catalytic oxidation
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biotechnology and as a surfactant. Graphene is also related to carbon nanomaterials
such as carbon nanotubes and fullerene.
Graphite oxide, formerly called graphitic oxide or graphitic acid, is a
compound of carbon, oxygen, and hydrogen in variable ratios, obtained by
treating graphite with strong oxidizers. The bulk material disperses in basic solutions
to yield monomolecular sheets, known as graphene oxide by analogy to graphene, the
single-layer form of graphite. Graphene oxide sheets have been used to prepare a
strong paper-like materials, membranes, thin films, composite materials. Initially
Graphene oxide attracted substantial interest as a possible intermediate for the
manufacture of graphene. The graphene obtained by reduction of graphene oxide still
has many chemical and structural defects which is a problem for some applications but
an advantage for some others.
Reduced Graphene Oxide (RGO) is obtained by reducing Graphene Oxide
(GO). It can be done chemically, thermally or via irradiation (UV or IR) to get a powder
form. Graphite powder can be used as a dry lubricant in its original form or as a
lubrication additive in greases, oils or colloidal solutions. Graphite contains high levels
of carbon and therefore offers good electrical conductivity.
.
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2.2 Review on Properties of Graphene oxide and Reduced Graphene oxide
Reduced Graphene oxide properties
· Form: Powder
· Reduction method: Chemically reduced
· Sheet dimension: Variable
· Colour: Black
· Odour: Odourless
· Solubility: Insoluble
· Dispersability: It can be dispersed at low concentrations
· Humidity : 3.7 - 4.2%
· Electrical conductivity: 666,7 S/m
· BET surface area: 422.69 – 499.85 m2/g
· Density: 1.91 g/cm3
Graphene oxide properties
· Form: layer structure with larger irregularities
· Sheet dimension:1.1 ± 0.2 nm thick
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· Colour: Black
· Odour: Odourless
· Solubility: Insoluble
· Charge mobility: 0.1 to 10 cm2/Vs
· Electrical conductivity: 1 and 5×10−3 S/cm
3. OPTICAL PROPERTIES
GRAPHENE is, basically, a single atomic layer of graphite; an abundant mineral
which is an allotrope of carbon that is made up of very tightly bonded carbon atoms organised
into a hexagonal lattice. What makes graphene so special is its sp2 hybridisation and very thin
atomic thickness (of 0.345Nm). These properties are what enable graphene to break so many
records in terms of strength, electricity and heat conduction (as well as many others).
FUNDAMENTAL CHARACTERISTICS
Before monolayer graphene was isolated in 2004, it was theoretically believed that two
dimensional compounds could not exist due to thermal instability when separated. However,
once graphene was isolated, it was clear that it was actually possible, and it took scientists
some time to find out exactly how. After suspended graphene sheets were studied by
transmission electron microscopy, scientists believed that they found the reason to be due to
slight rippling in the graphene, modifying the structure of the material. However, later
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research suggests that it is actually due to the fact that the carbon to carbon bonds in graphene
are so small and strong that they prevent thermal fluctuations from destabilizing it.
Graphene’s ability to absorb a rather large 2.3% of white light is also a unique and
interesting property, especially considering that it is only 1 atom thick. This is due to the
electrons acting like massless charge carriers with very high mobility. A few years ago, it was
proved that the amount of white light absorbed is based on the Fine Structure Constant, rather
than being dictated by material specifics. Adding another layer of graphene increases the
amount of white light absorbed by approximately the same value (2.3%). Graphene’s opacity
of 2.3% equates to a universal dynamic conductivity value of over the visible frequency range.
Due to these impressive characteristics, it has been observed that once optical intensity
reaches a certain threshold satiable absorption takes place (very high intensity light causes a
reduction in absorption). This is an important characteristic with regards to the mode-locking
of fibre lasers. Due to graphene’s properties of wavelength-insensitive ultrafast satiable
absorption, full-band mode locking has been achieved using an erbium-doped dissipative
soliton fibre laser capable of obtaining wavelength tuning as large as 30 nm.
3.1 ABSORPTION
When a light beam in impinged on a material surface, portion of the incident beam that
is not reflected by the material is either absorbed or transmitted through the material. Light
absorption in thin films has always been a relevant topic in optics, especially from the
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application point of view. Graphene is in many ways the ultimate thin film, only one atomic
layer thick, and has photonic properties of high interest for optoelectronic applications.
Noteworthy is that for pristine, unbiased graphene an impressive 2.3% (απ, where e c α 4/ πε
is the fine structure constant) of incident visible light is absorbed.
Crucial for the optical performance of small particles and ultra-thin structures is often that
relevant (surface) plasmon excitations are available. Recently, an optical switching
mechanism using gated graphene, coupling to external radiation through surface plasmon-
polaritons rather than directly to incoming photons, has been described. Graphene based
sensors are another area of importance, where it has been suggested that graphene ribbons can
be used to convert molecular signatures to electrical signals based on graphene plasmons
being very sensitive to the molecular analytes one is monitoring. Since for graphene we have
the possibility of controlling its “optical” properties with a proper gate voltage and/or doping,
which through the chemical potential governs the optical conductivity and thus its spectral
signature, a multitude of possible mechanisms for sensing and tuneable optics are available
over a broad frequency range .
If we were to freely tune the optical properties of a film with the thickness of a single
layer of graphene, the maximum attainable light absorption would be dictated by the contrast
of the surrounding media. This general limit for light absorption in ultrathin films may under
favourable conditions (that is for high damping materials with nearly imaginary dielectric
constant) be approached by tuning of the film thickness alone. However a more widely
applicable approach to realize these optimal conditions is to exploit Plasmon resonances in
nanostructures where metallic elements and other materials adding functionality are combined
into nanocomposites. By tuning the geometrical properties and thereby the effective dielectric
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function of the nanocomposite structure in relation to the dielectric properties of the
surrounding media, the impedance of the system can be matched to maximize the absorption .
Related contrast effects are exploited when making graphene “visible” by placing it on top of
silicon wafers or using holes in a metallic screen. Here we investigate another line of
approach, not invoking surface Plasmon or other collective excitations, to realize optimal
conditions for light absorption, namely the possibility to tune the optical properties of a single
layer of graphene by means of realistic bias voltages and doping levels, and by appropriate
choice of the dielectric environment.
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Thermal exfoliation Reduced GO.SPC Graphene oxide Graphite powderWL/nm Abs WL/nm Abs WL/nm Abs WL/nm Abs
1100 0.902 1100 0.103 1100 0.561 1100 0.331099 0.902 1099 0.103 1099 0.561 1099 0.331098 0.902 1098 0.103 1098 0.56 1098 0.331097 0.902 1097 0.104 1097 0.559 1097 0.331096 0.902 1096 0.104 1096 0.559 1096 0.3291095 0.902 1095 0.104 1095 0.56 1095 0.3291094 0.901 1094 0.105 1094 0.56 1094 0.3291093 0.901 1093 0.106 1093 0.56 1093 0.3291092 0.901 1092 0.107 1092 0.561 1092 0.3291091 0.901 1091 0.107 1091 0.562 1091 0.3291090 0.901 1090 0.107 1090 0.562 1090 0.3291089 0.901 1089 0.108 1089 0.562 1089 0.3291088 0.901 1088 0.108 1088 0.563 1088 0.3291087 0.901 1087 0.109 1087 0.563 1087 0.3291086 0.9 1086 0.109 1086 0.563 1086 0.3281085 0.9 1085 0.108 1085 0.563 1085 0.328
k1084 0.9 1084 0.108 1084 0.563 1084 0.3281083 0.9 1083 0.108 1083 0.563 1083 0.3281082 0.9 1082 0.109 1082 0.563 1082 0.3281081 0.9 1081 0.109 1081 0.564 1081 0.3281080 0.9 1080 0.11 1080 0.565 1080 0.3281079 0.899 1079 0.111 1079 0.566 1079 0.3281078 0.899 1078 0.112 1078 0.566 1078 0.3281077 0.899 1077 0.112 1077 0.566 1077 0.3281076 0.898 1076 0.113 1076 0.567 1076 0.3281075 0.898 1075 0.114 1075 0.567 1075 0.3281074 0.898 1074 0.114 1074 0.567 1074 0.3281073 0.897 1073 0.115 1073 0.567 1073 0.328
Table 1: ABSORPTION READINGS (Graphene powder, Reduced Graphene Oxide, Graphene Oxide and Thermally Exfoliated Graphene)
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3.2 TRANSMITTANCE
Graphene may outperform existing transparent conductive materials, and a graphene based
flexible touch screen. Multilayer graphene is a graphene thin film with weak van der Waals
interaction between the layers, and its electronic and optical properties are sensitive to the
number of layers as well as the stacking sequence. Multilayer graphene, the optical
transmission through a graphene films is directly dependent on the optical conductance of the
graphene stack, and the optical transmittance
In order to verify the dependence of the optical transmittance of multilayer graphene layers,
two sets of multilayer CVD graphene films were grown on a nickel coated wafer. The
multilayer graphene films are polycrystalline with an irregular number of layers, however with
uniform optical transparency on a macroscopic scale. The transmittance curves of each of
these stacks with λ ranging from 400 nm to 800 nm.
Thermal exfoliation RGO
graphene oxide Graphite powder
WL/nm %T WL/nm %T WL/nm %T WL/nm %T1100 33.1 1100 66.5 1100 71.6 1100 58.61099 33.1 1099 66.4 1099 71.6 1099 58.61098 33.1 1098 66.3 1098 71.6 1098 58.71097 33.1 1097 66.1 1097 71.6 1097 58.71096 33.1 1096 65.9 1096 71.5 1096 58.71095 33.1 1095 65.8 1095 71.5 1095 58.81094 33.1 1094 65.6 1094 71.5 1094 58.91093 33.1 1093 65.4 1093 71.5 1093 591092 33.1 1092 65.2 1092 71.4 1092 59.11091 33.1 1091 65.1 1091 71.4 1091 59.21090 33.1 1090 65 1090 71.4 1090 59.3
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1089 33.1 1089 64.8 1089 71.3 1089 59.31088 33.1 1088 64.7 1088 71.3 1088 59.41087 33.1 1087 64.6 1087 71.3 1087 59.51086 33.1 1086 64.6 1086 71.3 1086 59.61085 33.1 1085 64.5 1085 71.2 1085 59.61084 33.1 1084 64.4 1084 71.2 1084 59.71083 33.1 1083 64.2 1083 71.2 1083 59.71082 33.1 1082 64.1 1082 71.1 1082 59.81081 33.1 1081 64 1081 71.1 1081 59.81080 33.1 1080 63.9 1080 71.1 1080 59.91079 33.1 1079 63.8 1079 71.1 1079 601078 33.1 1078 63.6 1078 71 1078 601077 33.2 1077 63.5 1077 71 1077 601076 33.2 1076 63.3 1076 71 1076 601075 33.1 1075 63.3 1075 70.9 1075 601074 33.1 1074 63.2 1074 70.9 1074 601073 33.2 1073 63.1 1073 70.9 1073 60.11072 33.2 1072 63 1072 70.8 1072 60.21071 33.2 1071 63 1071 70.8 1071 60.21070 33.2 1070 62.9 1070 70.8 1070 60.21069 33.2 1069 62.8 1069 70.8 1069 60.21068 33.2 1068 62.8 1068 70.7 1068 60.21067 33.2 1067 62.7 1067 70.7 1067 60.21066 33.2 1066 62.7 1066 70.7 1066 60.21065 33.2 1065 62.7 1065 70.6 1065 60.31064 33.2 1064 62.6 1064 70.6 1064 60.31063 33.2 1063 62.4 1063 70.6 1063 60.4
Table 2: Wavelength and transmittance of GO, RGO, thermally Exfoliated Graphene and Graphite powder.
3.3 BAND GAP ENERGY
The electronic structure of an isolated C atom is (1s) 2 (2s) 2 (2p) 4; in a solid-state
environment the 1s electrons remain more or less inert, but the 2s and 2p electrons hybridize.
One possible result is four sp3 orbitals, which naturally tend to establish a tetrahedral bonding
pattern that soaks up all the valence electrons: this is precisely what happens in the best
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known solid form of C, namely diamond, which is a very good insulator (band gap ∼ 5 eV).
However, an alternative possibility is to form three sp2 orbitals, leaving over a more or less
pure p-orbital. In that case the natural tendency is for the sp2 orbitals to arrange themselves in
a plane at 120◦ angles, and the lattice thus formed is the honeycomb lattice.
The band structure of graphene can be approximated using tight-binding model considering
only the nearest neighbour hopping energy a hexagon with a unit cell of two atoms. For an
intrinsic or lightly doped graphene, the Fermi level is around the Dirac point, where charge
carriers only experience a linear dispersion. This linear dispersion is called the Dirac cone
since it is described by the relativistic Dirac equation. To calculate optical properties of
graphene in the visible range, one can consider only the Dirac cone if the photon frequency is
low compared to the resonance frequency and the Fermi energy is near the Dirac point. Since
the resonance energy is larger than the photon energy in the visible range, for intrinsic
graphene we can therefore approximate the optical properties within visible range assuming
linear energy dispersion. One can anticipate the approximation will fail if the Fermi level is
well above γ by electric gating or impurity doping. The assumption is also not valid if photon
energies are beyond the visible range.
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Graphene oxide
Reduced GO
Thermal exfoliation
WL/nm E WL/nm E WL/nm E1100 6.6 1100 3.3 1100 1.91099 6.8 1099 3.4 1099 21098 6.9 1098 3.5 1098 21097 7.1 1097 3.6 1097 2.11096 7.3 1096 3.7 1096 2.11095 7.4 1095 3.8 1095 2.21094 7.6 1094 3.9 1094 2.21093 7.8 1093 4 1093 2.31092 8 1092 4.1 1092 2.31091 8.2 1091 4.2 1091 2.41090 8.4 1090 4.3 1090 2.51089 8.6 1089 4.3 1089 2.51088 8.8 1088 4.4 1088 2.61087 9 1087 4.5 1087 2.61086 9.1 1086 4.6 1086 2.71085 9.4 1085 4.7 1085 2.81084 9.5 1084 4.8 1084 2.81083 9.7 1083 4.9 1083 2.91082 9.9 1082 5 1082 2.91081 10.2 1081 5.1 1081 31080 10.4 1080 5.2 1080 31079 10.6 1079 5.3 1079 3.11078 10.8 1078 5.4 1078 3.21077 11 1077 5.5 1077 3.21076 11.2 1076 5.6 1076 3.31075 11.4 1075 5.7 1075 3.31074 11.6 1074 5.8 1074 3.4
Table 3: Wavelength and energy of GO, RGO. Thermally Exfoliated Graphene.
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0 200 400 600 800 1000 12000
0.1
0.2
0.3
0.4
0.5
Graphite powder Absorption
Wavelength(nm)
Abso
rban
ce
0 200 400 600 800 1000 12000
5
10
15
20
25Graphne powder Energy
Wavelength(nm)
Ener
gy
0 200 400 600 800 1000 120054
56
58
60
62
64
66
68Graphene powder transmittance
Wavelength(nm)
Tran
smitt
ance
FIG 9: ABSORPTION, TRANSMITTANCE, ENERGY OF GRAPHITE
POWDER
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0 200 400 600 800 1000 12000
0.2
0.4
0.6
0.8
1
1.2
GO ABSORPTION.SPC
Wavelength(nm)
Abso
rban
ce
0 200 400 600 800 1000 12000
10
20
30
40
50
60
70GO Transmittance.SPC
Wavelength(nm)
Tran
smitt
ance
0 200 400 600 800 1000 120005
1015202530354045
GO ENERGY.SPC
Wavelength(nm)
Ener
gy
FIG 10: ABSORPTION, TRANSMITTANCE, ENERGY OF GRAPHENE
OXIDE
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0 200 400 600 800 1000 12000
0.05
0.1
0.15
0.2
0.25
RGO Absorption.SPC
Wavelength(nm)
Abso
rban
ce
0 200 400 600 800 1000 12000
10203040506070
RGO transmittance
Wavelength(nm)
Tran
smitt
ance
0 200 400 600 800 1000 12000
10
20
30
40
50
RGO Energy
Wavelength(nm)
Ener
gy
FIG 11: ABSORPTION, TRANSMITTANCE, ENERGY OF REDUCED GRAPHENE OXIDE
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0 200 400 600 800 1000 12000.65
0.70.75
0.80.85
0.90.95
Thermal exfoliation Abs.SPC
Wavelength(nm)
Abso
rban
ce
0 200 400 600 800 1000 12000
10203040506070
RGO transmittance
Wavelength(nm)
Tran
smitt
ance
0 200 400 600 800 1000 120002468
101214
TE energy.SPC
Wavelength(nm)
Ener
gy
FIG 12: ABSORPTION, TRANSMITTANCE, ENERGY OF THERMALLY EXFOLIATED GRAPHENE
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4. ELECTROMAGNETIC SPECTRUM
Electromagnetic radiation is the means for many of our interactions with the world:
light allows us to see; radio waves give us TV and radio; microwaves are used in radar
communications; X-rays allow glimpses of our internal organs; and gamma rays let us
eavesdrop on exploding stars thousands of light-years away. Electromagnetic radiation is the
messenger, or the signal from sender to receiver. The sender could be a TV station, a star, or
the burner on a stove. The receiver could be a TV set, an eye, or an X-ray film. In each case,
the sender gives off or reflects some kind of electromagnetic radiation. All these different
kinds of electromagnetic radiation actually differ only in a single property — their
wavelength. When electromagnetic radiation is spread out according to its wavelength, the
result is a spectrum. The visible spectrum, as seen in a rainbow, is only a small part of the
whole electromagnetic spectrum. The electromagnetic spectrum is divided into five major
types of radiation. These include radio waves (including microwaves), light (including
ultraviolet, visible, and infrared), heat radiation, X-rays, gamma rays, and cosmic rays.
Humans cannot sense any other part of the electromagnetic spectrum without the aid of
special equipment. Other animals (such as bees) can see the ultraviolet while some (snakes)
can see the infrared. In each case, the eye (or other sense organ) translates radiation (light)
into information that we (or the bee looking for pollen or the snake looking for prey) can use.
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VISIBLE LIGHT SPECTRUM
The visible spectrum is the portion of the electromagnetic spectrum that is visible to
the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or
simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm. In
terms of frequency, this corresponds to a band in the vicinity of 430–770 THz.
The spectrum does not, however, contain all the colours that the human eyes and brain can
distinguish. Unsaturated colours such as pink, or purple variations such as magenta, are
absent, for example, because they can be made only by a mix of multiple wavelengths.
Colours containing only one wavelength are also called pure colours or spectral colours.
Visible wavelengths pass through the "optical window", the region of the electromagnetic
spectrum that allows wavelengths to pass largely un-attenuated through the Earth’s
atmosphere. An example of this phenomenon is that clean air scatters blue light more than red
wavelengths, and so the midday sky appears blue. The optical window is also referred to as
the "visible window" because it overlaps the human visible response spectrum. The near
infrared (NIR) window lies just out of the human vision, as well as the Medium Wavelength
IR (MWIR) window, and the Long Wavelength or Far Infrared (LWIR or FIR) window,
although other animals may experience them.
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FIG 13 : UV SPECTRUM(courtesy: Wikipedia)
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5. RESULTS AND DISCUSSION
The UV VIS Spectrophotometer is used for characterization of compounds by showing
information about the electron transitions in d-orbitals. The two light sources used in the
spectrometer are the tungsten lamp and deuterium lamp. The tungsten lamp is used for
producing visible light while the deuterium lamp is used for UV light. The approximate range
visible spectrum is from 400 to 800nm while that for UV light is from 200 to 400nm. The
shorter is the wavelength, higher will be the frequency. A high frequency wave corresponds to
higher energy. Here, solution of various samples are used instead of powder form (solids)
because the solids won’t let light pass through.
As the light of various wavelengths incident on the sample solution, the
electrons in the highest occupied molecular orbital (HOMO) jump to the lowest unoccupied
molecular orbital (LUMO) by absorbing energy equal to the band gap between the two energy
levels. The HOMO comes under the bonding molecular orbital section which is at lower
energy while the LUMO falls in the section of anti-bonding molecular orbital. There are quite
a few types of electron transitions that take place when light of sufficient energy is incident on
the material under observation. These include the transition from sigma to sigma star state,
non-bonding MO state to the pie star state, pie to pie star state and the transition from n to pie
star transition.
For Absorption: The electrons move from the HOMO to the LUMO by absorbing energy
equal to the band gap between the two from the incident light. The UV VIS spectrometer used
is of high resolution (1nm). Light of various wavelengths in a step of 1nm is incident on the
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sample solution and the corresponding graph of the absorbance is obtained using the UV VIS.
The peak of the graph at a particular wavelength indicates that a large amount of electrons
have absorbed energy from the light of that particular wavelength. From the comparative
graph of absorbance, it is evident that the graphene powder has high absorbance in UV region
(from 200 to 300nm). The absorbance of graphene oxide is again high in the UV region and is
decreasing as we go towards the visible region. The Graphite powder behaves just the
opposite while that of reduced graphene oxide is almost constantly low throughout.
110010581016 974 932 890 848 806 764 722 680 638 596 554 512 470 428 386 344 302 260 2180
0.2
0.4
0.6
0.8
1
1.2
Absorption Comparison
Thermal exfoliation Abs Reduced GO.SPC AbsGraphene oxide Abs Graphite powder Abs
Wavelength(nm)Abso
rban
ce
FIG 14: ABSORPTION COMPARISION
For Transmittance: The concept of transmittance is just the opposite of absorbance. The
amount of absorption is inversely proportional to the amount of transmittance. The
wavelengths at which absorption is low shows good transmittance. The electrons remain in the
HOMO if it does not get enough energy to jump to the LUMO. So, the light of that particular
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wavelength is not absorbed and is hence said to be ‘transmitted’. Light of various wavelengths
in a step of 1nm is incident on the sample solution and the corresponding graph of the
transmittance is obtained using the UV VIS spectrophotometer. The peak of the graph at a
particular wavelength indicates that that particular wavelength does not supply enough energy
to the material. From the comparative graph of transmittance, it is observed that the optical
response is almost reverse of the respective absorbance characteristics.
110010541008 962 916 870 824 778 732 686 640 594 548 502 456 410 364 318 272 2260
10
20
30
40
50
60
70
80
Transmittance Comparison
Thermal exfoliation %T RGO %Tgraphene oxide %T Graphite powder %T
Wavelength(nm)
Tran
smitt
ance
FIG 15: TRANSMITTANCE COMPARISON
For Energy: The concept again remains the same. The electrons move from the HOMO to
the LUMO by absorbing energy equal to the band gap between the two from the incident light.
Light of various wavelengths in a step of 1nm is incident on the sample solution and the
corresponding graph of the absorbance is obtained using the UV VIS spectrophotometer. The
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peak of the graph at a particular wavelength indicates the maximum energy gap. With the
reference from the base of the energy response, the relative peak indicates that energy of that
particular wavelength has given the electrons enough energy to cross even higher energy gap
states. From the comparative graph of absorbance, it is evident that the wavelength of 650 nm
supplies the maximum required energy to jump to certain higher energy state.
110010581016 974 932 890 848 806 764 722 680 638 596 554 512 470 428 386 344 302 260 2180
5
10
15
20
25
30
35
40
45
Energy Comparison
Graphene oxide E Reduced GO E Thermal exfoliation E Graphite powder E
Wavelength(nm)
Ener
gy
FIG 16: ENERGY COMPARISON
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5.1 FUTURE SCOPE AND APPLICATIONS
Optical Electronics
Graphene’s high electrical conductivity and high optical transparency make it a
candidate for transparent conducting electrodes. Its mechanical strength and
flexibility are advantageous compared to indium tin oxide, which is brittle. It
can be used in touchscreens, liquid crystal displays, organic photovoltaic cells,
OLEDs.
The bandgap—mobility tradeoff inevitably constrains the application of
graphene for the conventional field-effect transistor (FET) devices in digital
applications.
Light-emitting devices: Organic light-emitting diodes (OLEDs) have an
electroluminescent layer between two charge-injecting electrodes, at least one
of which is transparent. In these diodes, holes are injected into the highest
occupied molecular orbital (HOMO) of the polymer from the anode, and
electrons are injected into the lowest unoccupied molecular orbital (LUMO)
from the cathode.
Photodetectors: Photodetectors measure photon flux or optical power by
converting the absorbed photon energy into electrical current. They are widely
used in a range of common devices, such as remote controls, televisions and
DVD players. Most exploit the internal photo effect, in which the absorption of
photons results in carriers excited from the valence to the conduction band,
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outputting an electric current. The spectral bandwidth is typically limited by
the material's absorption.
Touch screens::Touch screens are visual outputs that can detect the presence
and location of a touch within the display area, permitting physical interaction
with what is shown on the display itself. Touch panels are currently used in a
wide range of applications such as cellular phones and digital cameras because
they allow quick, intuitive and accurate interaction by the user with the display
content.
Saturable absorbers and ultrafast lasers: Materials with nonlinear optical and
electro-optical properties are needed in most photonic applications. Laser
sources producing Nano- to sub picosecond pulses are a key component in the
portfolio of leading laser manufacturers.
Solar Cells
Graphene turned out to be a promising material for photo electrochemical energy
conversion in dye sensitized solar cells. The transparent, conductive, and ultrathin
graphene films are fabricated from exfoliated graphene oxide, followed by thermal
reduction.
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6.CONCLUSION
The optical properties of graphene was studied and it was noticed that Graphene is a good
candidate for optical sensor implementation. It is also a good candidate for transparent
conducting oxide. Light of various wavelengths in a step of 1nm was incident on the sample
solution and the corresponding graph of the transmittance, absorbance and energy was
obtained using the UV VIS spectrophotometer. The peak of the graphs at a particular
wavelength indicates that at that particular wavelength, the material shows maximum of that
optical property. From the comparative graph of transmittance, it is observed that the optical
response is almost opposite of the respective absorbance characteristics. The energy was
maximum at around 650nm for all the samples.
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REFERENCES
[1] Zhibo Liu, Yan Wang, Xiaoliang Zhang, Yanfei Xu, Yongsheng Chen , “Nonlinear optical properties of graphene oxide in nanosecond and picosecond regimes “ Appl. Phys. Lett. , 12 January 2009.
[2]V Xiaorui Zheng, Baohua Jia*,Xi Chen and Min Gu ,” In Situ Third-Order Non-linear Responses During Laser Reduction of Graphene Oxide Thin Films Towards On-Chip Non-linear Photonic Devices “ 17 MAR 2014.
[3] [Online] “Graphene,” in http://www.graphenea.com/pages/graphene
[4] Chang-Hua Liu1†, You-Chia Chang2†, Theodore B. Norris1,2* and Zhaohui Zhong1,“ Graphene photodetectors with ultra-broadband and high responsivity at room temperature” Nature Nanotechnology letters ,16 MARCH 2014
[5] F. Bonaccorso, Z. Sun, T. Hasan and A.C. Ferrari, "Graphene photonics and optoelectronics", Nature Photonics 4, 611-622 (2010).
[6] S. Thongrattanasiri, F. H.L. Koppens and F.J. García de Abajo, “Total light absorption in graphene”, arXiv:1106.4460v1 (2011).
[7] S.A. Mikhailov and K. Ziegler, “New electromagnetic mode in graphene”, Phys. Rev. Lett. 99, 016803 (2007).
[8] Stauber, T., N.M.R. Peres, and A.K. Geim, “Optical conductivity of graphene in the visible region of the spectrum”, Physical Review B, 2008. 78(8): p. 085432.
[9] Gray, A., et al., “Optical detection and characterization of graphene by broadband spectrophotometry”, Journal of Applied Physics, 2008. 104(5): p. 053109-8.
[10] Taft, E.A. and H.R. Philipp, “Optical Properties of Graphite”, Physical Review, 1965. 138(1A): p. A197-A202.
[11] Gusynin, V.P., S.G. Sharapov, and J.P. Carbotte, “On the universal ac optical background in graphene”, New Journal of Physics, 2009. 11(9): p. 095013.
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