GROWTH OF GRAPHENE ON COPPER SUBSTRATE A DISSERTATION REPORT SUBMITTED TO DEPARTMENT OF MATERIALS SCIENCE SARDAR PATEL UNIVERSITY VALLABH VIDYANAGAR-388120 VIDYANAGAR-388120 FOR FULFILLMENT OF THE DEGREE OF MASTER OF SCIENCE IN MATERIAL MATERIALSS SCIENCE SCIENCE BY MALAY MAJI (ROLL NO:09) TARAKNATH MAITY (ROLL NO: 15) M.Sc MATERIALS SCIENCE 4th SEMESTER APRIL, 2012 1
CERTIFICATE
It is to certify that the project report entitled “ GROWTH OF GRAPHENE ON COPPER SUBSTRATE” contains the work carried
out by Mr. Malay Maji and Mr. Taraknath Maity Maity during the 4th semester of M.Sc (Materials Science) course at the department of Materials Science , Sardar Patel University and is being submitted as part of the course work. This work has not been presented anywhere for the award of any other degree.
MALAY MAJI TARAKNATH MAITY Countersigned by, PROF. L.M.MANOCHA
PROF. S.M. MANOCHA
2
CERTIFICATE
It is to certify that the project report entitled “ GROWTH OF GRAPHENE ON COPPER SUBSTRATE” contains the work carried
out by Mr. Malay Maji and Mr. Taraknath Maity Maity during the 4th semester of M.Sc (Materials Science) course at the department of Materials Science , Sardar Patel University and is being submitted as part of the course work. This work has not been presented anywhere for the award of any other degree.
MALAY MAJI TARAKNATH MAITY Countersigned by, PROF. L.M.MANOCHA
PROF. S.M. MANOCHA
2
ACKNOWLEDGEMENT We most respectfully express our thanks and gratitude to our respected teachers and guide Dr. L.M MANOCHA, professor of G.H. PATEL Institute of Materials Science ,Sardar Patel University , Vallabh Vidyanagar , for the inspiring guidance ,time to time suggestions and encouragement during the course of our study. It gives us immense pleasure in expressing sincere thanks to Dr. S.Manocha, head of G.H. Patel institute of Materials Science , Sardar Patel University, Vallabh Vidyanagar, for the valuable guidance, time to time suggestions and encouragement during the course of our project work. We are also thankful to research students Miss Arpana Basak , Mr. Hasmukh Gajera for their kind co-operations and discussions during the project work. We sincerely thank our friends and collegues for their help and kind support during and towards the successful completion of our project work. We are also thankful to non teaching stuff members Mrs. Parul Sheth, Mr.Sanjay. Date:
Malay Maji (09)
Place: Vallabh Vidyanagar
Taraknath Maity (15)
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ABSTRACT
In its monolayer form, graphene is an one-atom-thick two-dimensional layer of carbon with excellent electrical, mechanical, and thermal properties. Large-scale production of high-quality graphene is attracting an increasing amount of attention. Chemical Vapor Deposition(CVD) methods have been developed to grow graphene from organic gases on metal substrate like Ni , Cu etc. In this work, we have tried to grow
graphene directly on the backside of a Cu foil at 1000 °C under H2 /Ar gas flow using a solid carbon precursor (Pitch). The graphene layer grown as the solid carbon source decomposed and diffused to the backside of the Cu foil, leaving the other elemental residues on the original side . Analysis by Raman spectroscopy indicates that the monolayer of graphene derived from these carbon sources is of good quality.
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CONTENTS Chapter 1 INTRODUCTION 1.1 ALLOTROPES OF CARBON
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1.11 AMORPHOUS CARBON 1.12CRYSTALLINE CARBON 1.12A GRAPHITE 1.12B DIAMOND 1.12C FULLERENES
1.2 GRAPHENE 1.3 HISTORY OF GRAPHENE 1.4 METHODS OF FABRICATION OF GARAPHENE
1.4A MECHANICAL CLEAVAGE METHOD. 1.4B CHEMICAL METHOD. 1.4C CHEMICAL VAPOUR DEPOSITION (CVD). 1.4D EPITAXIAL GROWTH OF GRAPHENE ON SILICON SUBSTRATE. 5
13 15 15
1.4E GROWTH OF GRAPHENE FROM SOLID CARBON SOURCES
1.5 MECHANISM OF GRAPHENE GROWTH ON METAL SUBSTRATE (COPPER) 1.6 CHALLENGES OF GRAPHENE GROWTH ON COPPER SUBSTRATE
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1.7 AIMS AND OBJECTIVES
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Chapter 2 EXPERIMENTAL 2.1 MATERIALS USED
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2.11 Cu SUBSTRATE 2.12 PRECURSOR- PITCH. 2.13 HYDROGEN GAS 2.14 INERT GAS (ARGON)
2.2 EXPERIMENTAL SET UP
6
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2.3 EXPERIMENTAL
PROCESS
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2.4 PARAMETERS
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2.5 CHARACTERIZATION
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Chapter 3 RESULT AND DISCUSSION 3.1 RAMAN SPECTRUM OF SAMPLE NO.1
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3.2 RAMAN SPECTRUM OF SAMPLE NO.2
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3.3 RAMAN SPECTRUM OF SAMPLE NO.3
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3.4 RAMAN SPECTRUM OF SAMPLE NO.4
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CONCLUSIONS
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BIBLIOGRAPHY
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APPENDIX
7
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Chapter 1 INTRODUCTION
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1.1 ALLOTROPES OF CARBON:
Carbon is a unique solid substance of great interest to mankind and scientific community in particular. It is considered the most versatile and widely researched element on the earth. It is the 15th most abundant element in the Earth crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is considered unique because it possesses an electronic configuration (1s22s22p2) which allows single, double and triple bonds to be formed. It has the ability to combine with itself , other chemical elements in different ways giving rise to different structural forms of solid carbon . This lead to the development of different types of carbon having different applications especially to high performance materials such as carbon fibres ,fullerenes, composites, carbon nanotubes. Carbon is found in amorphous and crystalline forms. The four major allotropes of carbon are : 1. Amorphous Carbon 2. Crystalline Carbon A. Graphite B. Diamond C. Fullerenes
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1.11 AMORPHOUS CARBON Amorphous carbon does not possess any long range order or crystallinity . It has got somewhat definite order in one plane but in other planes the arrangement is random . It is present as a powder. Charcoal, lampblack (soot) and activated carbon are the examples of amorphous carbon.
Fig 1.1 Amorphous carbon
1.12CRYSTALLINE CARBON:
1.12A GRAPHITE The structure of graphite consists of succession of layers arranged two dimensionally having connected six member rings formed by carbon atom. An individual sheet of carbon within the lamellar structure is called a graphene layer which can either be stacked in a hexagonal or rhombohedral fashion. In the graphite structure , each carbon atom is covalently bonded to three other surrounding carbon atoms. The ideal crystal structure consists of layers in which the carbon atoms are arranged in an open honeycomb network with two atoms per unit cell. 10
The interlayer distance can be determined to c =3.35 A0 ,each carbon atom possesses sp2 hybridized orbital.
Fig1.2 Structure of Graphite
Conductivity of graphite is thus determined by the π orbital electrons delocalised across the hexagonal atomic sheets of carbon. The conductivity parallel to the sheets is greater than perpendicular to the sheets. Because of this delocalised π orbitals the forces acting between two layers of graphite are very weak , whereas the bonds between atoms within a layer are very strong. Because of this, graphite layers can easily be shifted against each other.
1.12B DIAMOND Diamond is one of the hardest materials known to man. The electrons also bound very tightly and therefore diamond exhibits a low electrical conductivity . It also possesses an unusually high thermal conductivity . Diamond consists of a three dimensional network of carbon atoms arranged in a tetrahedral form. 11
Each carbon atom is bonded covalently to four neighbouring carbon atoms in a sp3 configuration.
Fig1.3 unit cell of diamond crystal.
1.12C FULLERENES: The fullerenes family represents molecular form of carbon having interesting chemical and physical properties. Fullerenes are zero dimensional form of carbon . There are many types of fullerenes such as C60,C72,C82 etc .The C60 molecule contains 12 pentagons(five carbon atoms ring) and 20 hexagons(six carbon atom ring).
Fig 1.4 Fullerene(C60) C60 is highly stable molecule in the family and is consider as third allotropes of carbon. All fullerenes molecule have an even number of 12
carbon atoms arranged over the surface of a hollow closed cage, each carbon atom is trigonally linked to three neighbouring carbon atoms with three of the four valence electrons are sp2 ϭ bonding ,the remaining one free electron is delocalised in π molecular orbital covering outside and inside surface of the molecule resulting cloud of π electron density
is similar to that a sheet of graphite . Fullerenes exhibits feature of both organic and inorganic materials. Their electronic properties play an important role as conducting and semiconducting materials for batteries, transistors and sensors.
1.2 GRAPHENE Graphene is a basic building block of graphite . Single basal plane of graphite is called Graphene. It is 2D crystal made up of single atomic layer of carbon arranged in honeycomb structure making bond with three neighbouring carbon atoms by sigma bond involved in sp2 hybridization . It has got bond length of ~ 1.42 A0 . Since a 2D crystal structure may have impact of thermal vibration it is assumed that in graphene this migration and fluctuation are passed by anharmonic bending and stretching of membrane type structure . Graphene is also the basic building block of some carbon allotropes including graphite, carbon nanotubes and fullerenes . When wrapped in spherical from it make 0D carbon Fullerene, When rolled into 1D it makes carbon nanotube ,when stacked in 3D it makes graphite.
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Fig 1.5 Schematic Graphene Sheet Graphene has very high Young‟s modulus of ~1TPa. Researchers have also estimated a very high thermal conductivity of ~5000 Watt m -1 K-1 for monolayer graphene. Single layer graphene absorbs 2.3% of incident light which is very high considering only one layer thickness. Due to the above mentioned properties, graphene finds a variety of applications. Most important application in field effect transistor(FET) because of its very high electrical mobility ( 10,000-1,40,000 cm2 V−1s1 ), having band gap 0 eV. Graphene based composite materials show high electrical conductivity and have found potential applications in biosensors as well as Li ion batteries . Due to very low electrical resistance and high electron mobility graphene nanoribbons also have the potential to replace copper as interconnects in microelectronics. Chemically derived graphene has been used to fabricate ultracapacitors with very high energy density. Graphene based sensors are also very promising because a sharp dependence of electrical conductivity of graphene on concentration of adsorbates. Transparent conducting graphene films can be used as transparent electrodes in photovoltaic applications, Liquid Crystal Displays (LCDs) as well as Organic Light Emitting Diodes (OLEDs). Potentially replace ITO glass films since graphene‟s mechanical strength and flexibility are superior compared to Indium Tin Oxide (ITO). 14
1.3 HISTORY OF GRAPHENE The term graphene first appeared in 1987 to describe single sheets of graphite as one of the constituents of graphite intercalation compounds (GICs). Studies on few layer graphene had begun long ago in late 1970‟s. These studies were primarily based on epitaxial growth of few layer graphene films on transition metal surfaces by decomposing organic gases. In 2004 Geim and co-workers at the University of Manchester were successful in isolating single layer graphite on an insulating substrate (SiO2) by mechanical exfoliation. Geim and Novoselov were jointly awarded the Nobel Prize in Physics, 2010 In 2008, graphene produced by exfoliation method was one of the most expensive materials on Earth. Since then hundreds of researchers have entered into the area.
1.4 METHODS OF FABRICATION OF GARAPHENE: Various techniques have been found for producing graphene. These will be discussed in details below. 1.4a Mechanical cleavage method. 1.4b.Chemical method. 1.4c Chemical Vapour Deposition. 1.4c Epitaxial growth of graphene on silicon substrate. 1.4e Growth of graphene from solid carbon sources. 1.4f Miscellaneous methods.
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1.4a Mechanical cleavage method : In
the late 90‟s Ruoff and co workers tried isolating thin
graphitic flakes on SiO2 substrates by mechanical rubbing of patterned islands on HOPG. Using a similar method this was later achieved in 2005 by Kim and co workers . Since then various other techniques were developed to produce thin graphitic films and few layer graphene from bulk graphite or HOPG. Mechanical exfoliation is perhaps one of the most unusual and famous method for obtaining single layer graphene flakes on desired substrates. This method produces graphene flakes from HOPG by repeated peeling/exfoliation . This peeling/exfoliation can be done using a variety of agents like scotch tape, ultrasonication, electric field and even by transfer printing technique etc.
(a) HOPG mounted in epoxy and trimmed to pyramid shape. (b) Setup showing wedge alignment with HOPG layers. (c) Actual experimental setup.
Fig 1.6: Fabrication of graphene by Mechanical cleavage method
Another novel method to synthesize few layer graphene from bulk graphite is mechanical cleavage . In this method an ultra sharp single crystal diamond wedge is used to cleave a highly ordered pyrolytic graphite sample to generate the graphene layers. Cleaving is aided by the use of ultrasonic oscillations along the wedge. Characterization of the obtained layers are shown that the process is able to synthesize graphene layers with an area of a few micrometers. 16
1.4b.Chemical method : Graphene had been mainly produced through chemical route from graphite oxide. Graphite oxide was produced long ago in 1860 and since then it was being mainly produced by Brodie, Hummers and Staudenmaier methods. Each of these methods involves oxidation of graphite on presence of strong acids and oxidants. In this method Ist graphite oxide was produced from natural graphite flakes. Graphite oxide had been mainly produced by the Brodie, Staudenmaier and Hummers methods. All three methods involve oxidation of graphite in the presence of strong acids and oxidants Graphite oxide. The level of the oxidation can be varied on the basis of the method, the reaction conditions and the graphite precursors . Graphite oxide consists of a layered structure of „graphene oxide‟ sheets that are strongly hydrophilic such that intercalation of water molecules between the layers readily occur.
Fig 1.7: Synthesis of graphene by chemical method
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The interlayer distance between the graphene oxide sheets increases reversibly from 6 to 12 Å with increasing relative humidity. Graphite oxide can be dispersed directly in several polar solvents such as ethylene glycol, DMF, and THF at about 0.5 mg ml−1 . A homogeneous colloidal suspensions of graphene oxide in aqueous and various organic solvents can be achieved by simple sonication of graphite oxide .Graphene oxide is reduced by chemical methods (using reductants such as hydrazine, dimethylhydrazine , hydroquinone and NaBH4) to produce graphene.
1.4c Chemical Vapour Deposition In CVD growth the metallic substrates are in the form of thin foils or films. Nickel was the first substrate on which CVD growth of large area graphene was attempted . These efforts had begun right from 2007. However better control of the growth procedure was not achieved and thus the works largely remained unnoticed. First concrete reports of controlled synthesis of large area graphene on nickel substrates appeared around late 2008 and early 2009.
Fig1.8 : Graphene by Chemical Vapour Deposition
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Few-layer graphene was synthesized by the CVD method. A 300 nm thick Ni film was positioned at the center of a quartz tube and heated to 1000 °C at a 40 deg C/min heating rate, under a flow of argon and hydrogen (Ar/H2=1, 1000 sccm)gas. The substrate remained at 1000 °C in a Ar/H2 flow for 20 min to anneal the Ni film. The CVD growth of FLG was conducted at 960 ~ 970 °C, using a mixture of gases with a composition (CH4 : Ar : H2 = 250 : 1000 : 4000 sccm). The reaction time was varied from 30 sec to 7 min. After the CVD reaction, the sample in the quartz tube was cooled down to 400 °C at the rate 8.5 oC/min, under a flow of argon and hydrogen gas. Then the gas valve for hydrogen was closed and the sample was cooled to room temperature under Argon atmosphere.
1.4c Epitaxial growth of graphene on silicon substrate Epitaxial graphene growth on metal carbides has been practiced since long . But none of the earlier reports have used Silicon carbide as substrate for epitaxial growth. In 2004 a report on epitaxial graphene grown on SiC first appeared .
Fig1.9:Epitaxial graphene growth on silicon substrate 19
The idea of Epitaxial growth of graphene on silicon substrate( GOS) is to form epitaxial graphene (EG) on a SiC thin film preformed on a Si substrate, instead of using a bulk SiC crystal. In this method a thin SiC film was grown on the Silicon substrate by gas-source molecular-beam epitaxy(GSMBE) using mono methyl silane as source. The film thickness is typically 80nm . After the growth of SiC film on Si substrate , the sample was annealed uniformly by resistive heating at 1473K to epitaxially graphitize the SiC film into graphene. The GOS method has a potential to form graphene on large scale Si wafers , if realized , makes GOS technology compatible with Silicon technology . 1.4e Growth of graphene from solid carbon sources, on metal substrate(Cu)
Large area, high-quality graphene with controllable thickness can be grown from different solid carbon sources — such as polymer films or small molecules — deposited on a metal catalyst substrate such as Cu, Ni etc at a temperatures as low as 800°C. Both pristine graphene and doped graphene were grown with this one-step process using the same experimental set-up.
Fig. 1.10 Schematic illustrating graphene growth on copper foil. 20
The first solid carbon source was a spin-coated poly methyl methacrylate (PMMA) thin film (~100nm) and the metal catalyst substrate was a Cu foil. At a temperature as low as 800°C or as high as 1000°C (tested limit) for 10 min, with a reductive gas flow (H2 /Ar) and under low pressure conditions, a single uniform layer of graphene was formed on the substrate.
1.4f Miscellaneous methods: Besides the above mentioned methods a few alternative methods have also emerged for synthesis of graphene. Primary among them is the arc discharge method. Analogous to carbon nanotubes graphene can be synthesized by arc discharge of graphite electrodes. The synthesized graphene is in the form of nanosheets or nanoflakes which appears as black powder. Typically arc discharge is carried out under high pressure of hydrogen + helium for pure graphene. Even there is a report on graphene synthesis by arc discharge of graphite electrodes in air. This process does not require any substrate or catalyst unlike other methods. It has been found that graphene formation occurs at very high gas pressures and at comparatively lower pressures, carbon nanotubes, nanohorns and other products is favoured. Arc discharge method is also very suitable for producing doped graphenes by introducing of nitrogen and boron containing gases in discharge atmospheres along with hydrogen or even using ammonia or boron stuffed graphite electrodes.
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1.5
MECHANISM OF GRAPHENE GROWTH ON METAL
SUBSTRATE(Cu) 1.5a: Dissolution and precipitation process:
During the growth at elevated temperature dissociated carbon atoms on the catalyst surface may dissolve into the bulk due to the finite solubility. Dissolved carbon atoms precipitate back onto the metal surface as temperature drops and form graphene. Different cooling rate suggest the different thickness of graphene.
Fig 1.6:Mechanism of graphene growth on metal substrate
1.5b:Diffusion process: During the growth at elevated temperature dissociated carbon atoms on the catalyst surface may diffuse to the opposite side of metal substrate and result into formation of graphene. 22
1.6 CHALLENGES OF GRAPHENE GROWTH ON Cu SUBSTRATE Cu substrate should not oxidize during growth. Cooling rate play a key role in growth mechanism. Therefore cooling rate is to be controlled very carefully. It requires much lower base pressure and temperature at which the sample could be unloaded . In the subsequent graphene transfer step stronger etchants should be used to remove Cu, therefore higher possibility to be damaged by etchant. As a result the properties of graphene might be poorer .
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1.7 AIMS AND OBJECTIVES To grow continuous layers of high-quality graphene over large areas from solid carbon source on metal substrate(Cu) at 1000 °C and under flow of H2 /Ar gas . To study the growth
Mechanism and to characterize the as grown
graphene.
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Chapter 2 EXPERIMENTAL 25
2.1 MATERIALS USED 2.11 Cu substrate (99.8% purity).
Fig 2.1 :Cu substrate on Quartz boat
2.12 Precursor-Pitch/Chocolate.. 2.13 Hydrogen Gas The assay of Hydrogen gas is as follows: TABLE 2.1 impurities in hydrogen gas(flow gas)
Impurities
Oxygen Moisture Carbon monoxide Carbon-di- oxide Nitrogen Oxide of nitrogen Hydrocarbon
Maximum Content(ppm) 4 4 1 0.5 40 0.5 1 26
2.14 Inert Gas (Argon) Argon gas obtained from Vadilal used as a inert gas. The assay of Argon gas is as follows:
TABLE 2.2 Impurities in argon gas(flow gas)
Impurities Oxygen Moisture Hydrocarbon Carbon monoxide Carbon- di- oxide
Maximum content(ppm) 2 2 0.5 N.D N.D
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2.2 EXPERIMENTAL SET UP
Fig 2.2 : experimental set up for Graphene Growth.
The experimental set up for Graphene Growth is shown in Figure 2.2. It consists of a furnace ,a quartz tube, Mass Flow Controllers (MFCs) that control the flow rates of the gases(argon gas and hydrogen gas) passing through the reactor and carbon precursor (pitch). A thermocouple was used to measure the temperature of the furnace at the heating zone. The set up is connected to the programmer to set the parameters like temperature and time. In this set up Hydrogen gas was used as a reducing agent (reduce oxide scale developed on the cooper foil or prepared substrate before reaction started ), argon gas maintain the inert atmosphere during reaction.
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2.3 EXPERIMENTAL
PROCESS
For the growth of graphene , 10 mg of a carbon precursor was placed atop the Cu foil (99.8% purity). The foil was then placed on quartz boat, as shown in the Figure 2.1 . The sample is heated to a temperature of 1000 °C at a heating rate of 200 °C/min. The sample was annealed at 1000 °C for 25 min with Ar flow at 250 sccm and H2 flow at 50 sccm. The system was then fast cooled (moved to the cool zone by moving the quartz tube ) to room temperature under the H2 /Ar gas flow.
2.4 PARAMETERS TABLE 2.3 Experimental details Experiment number
Sample used
Growth time (in minute)
H2 /Ar gas flow rate(sccm)
Temperature in 0 ( C)
Copper foil thickness in µm
1. 2. 3 4. 5.
Chocolate(10mg) Pitch(10mg) Pitch(6mg) Pitch Blank
25 40 40 40 40
50/250 50/250 50/250 50/250 50/250
1000 1000 1000 1000 1000
140 80 65 80 75
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2.5 CHARACTERIZATION
Raman spectroscopy : After graphene was grown on copper foil using the method described above to ensure that graphene does exist on the copper foil ,Raman Spectroscopy data was collected from opposite side of the copper foil which is the most important confirmity test for Graphene . Raman spectroscopy is not only a versatile tool to determine the number of graphene layers, doping level, and edge chirality of graphene , but is a rapid and nondestructive method to study graphene. Raman spectroscopy is widely used to characterize electronic properties and microstructure of graphene. Raman spectrum was taken by the “ RENISHAW RAMAN SPECTROMETER” using a 514.5 nm laser.
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MICRO
Chapter 3 RESULT AND DISCUSSION
31
3.1 Raman spectrum of sample no.1:
After the Graphene grown on Cu foil (of thickness 140µm) by CVD technique, it was analysed using using a 514.5 nm laser in a Renishaw Raman Spectrometer .
Fig 3.1: Raman spectrum of sample no.1 The Raman spectrum ( Fig 3.1) of sample no. 1 shows a single peak at 1600 cm-1. The ID band is missing. The I2D band is also not visible in this case. It is difficult to conclude whether graphene like structure did get deposited on the Cu Foil. 32
3.2 Raman spectrum of sample no. 2 :
Fig 3.2: Raman spectrum of sample no.2 The Raman spectrum (Fig 3.2 ) of sample no. 2 (of thickness 80µm) shows a peak at 1359 cm-1 which is due to the disordered carbon, also known as the D band and the second prominent peak appearing at 1594 cm-1 is due to the graphitic nature of the carbon deposited, also known as the G band.
The fig 3.2 also indicates the presence of 2D band at ~2700cm-1 but the exact intensity of the peak could not be determined since it is overlapped by the „hump‟ appearing due to the Cu base. The ratio of intensity of D
band to G band i.e. I2D /IG is indicative of the ordered nature of the 33
carbon deposited on the Cu foil. But we can not determined the exact I2D /IG value because of presence of hump . So from the position of the signal we can say that the spectrum indicate ordered carbon layer has developed on the opposite side of the copper foil , it may be graphene. 3.3 Raman spectrum of sample no. 3 :
Fig 3.3: Raman spectrum of sample no.3 The Raman spectrum (Fig 3.3 ) of sample no. 3 (of thickness 65µm) shows the two separate peaks clearly. The ID band in this case is missing and The large I2D /IG ( i.e. 1.7 ) ratio might suggest the formation of monolayer graphene.
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3.4 Raman spectrum of sample no. 4 (blank):
Fig 3.4: Raman spectrum of sample no.4 The spectrum of sample no.4 (blank sample ) does not show any distinguisable peak but hump is obtained that was also obtained in the case of the sample no.1,2 and 3 . So from the raman spectrum shown above we can conclude that the hump has appeared because of copper background.
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CONCLUSIONS We have tried to grow continuous layers of high-quality graphene over large areas from solid carbon source (Pitch) at 1000 °C and under H2 /Ar flow on metal substrate(Cu). The mechanism is surface related due to the peculiar interactions between Cu and C and therefore self-limited to a single layer of graphene because of very low carbon solubility in Cu. Growth of graphene utilizing copper as the catalyst is one of the most promising method for producing continuous layers of high quality graphene over large areas. Scalable synthesis will require a better understanding and optimization of the growth process.In addition, direct deposition of graphene with controllable number of layers will be a key breakthrough.
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BIBLIOGRAPHY
37
1.“ Growth of Graphene from Food, Insects, and Waste ” by Gedeng Ruan†, Zhengzong Sun, Zhiwei Peng, and James M. Smalley Institute for Nanoscale Science and Technology, Rice University,DOI: 1021/nn202625c Publication Date (Web): July 29, 2011 .ACS Nano, 2011 ,
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15.“Graphenes Converted from Polymers ”Sun-Jung Byun,Hyunseob Lim, Ga-Young Shin, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyungbuk 790-784, Republic of Korea ,The Journal of Physical Chemistry Letters
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APPENDIX 40
