Growth of CNTs - Mihir Dass

Growthof Carbon Nanotubes
Mihir Dass, Amity University Page 1
GROWTH OF CARBON NANOTUBES ON VARIOUS SUBSTRATES WITH AND
WITHOUT CATALYST FOR FIELD EMISSION APPLICATION
A SUMMER INTERN PROJECT REPORT
at
SOLID STATE PHYSICS LABORATORY
Submitted by
MIHIR DASS
A1223312027
In fulfillment of Summer Internship
Amity Institute of Nanotechnology
AMITY UNIVERSITY
Sector – 125,
Noida, Uttar Pradesh.
Guide Name :
Dr P.K. Chaudhary Dr Preeti Shah
(Scientist G) (Scientist D)

ACKNOWLEDGEMENT
Firstly I would like to thank the Director of SSPL, Dr. R.Muralidharan, for giving me the
opportunity to do an internship within the organization. I would also like to thank Dr. P. K.
Chaudhary for providing me with the unique experience to be at SSPL and to study an
interesting material specie. It also helped to build my interest in research in nanotechnology and
to have new plans for my future career.
I also would like all the people working in the office of Nanotechnology Group in SSPL. With
their patience and openness they created an enjoyable working environment.
I would also like to thank Dr. J.S.B.S. Rawat for showing me the scope of my branch by giving
me interesting problems to solve that proved to be really tricky and utilized the scope beyond
that of nanotechnology to be solved.
I would specially like to thank Dr. Preeti V. Shah for being an excellent supervisor, and being
patient enough to clear all my doubts that arose during my internship at SSPL. Her knowledge in
the subject was always an inspiration for me. I would also like to thank Mr. Prashant for
familiarizing me with the equipment and its intricacies. Last but not the least; I would like to
thank Mr. U. S. Ojha for enlightening me with new facts regarding various technologies,
especially sputtering.
Furthermore I want to thank all the scientists and trainees, with whom I did the experimental
work. I have experienced great things during my term at SSPL in the shadow of the intelligence
of such wise scientists.

Table of Contents
ACKNOWLEDGEMENT.........................................................................................................................2
AN INTRODUCTION.............................................................................................................................4
CHAPTER 1. AN INTRODUCTION TO CARBON NANOTUBES ..................................................................5
1.1 Structure of Carbon Nanotubes .................................................................................................5
1.1.1 Single Wall Carbon Nanotubes (SWNT)...............................................................................5
1.1.2 Multi Wall Carbon Nanotubes(MWNT)..............................................................................6
1.2 SYNTHESIS TECHNIQUES...........................................................................................................7
1.2.1 Growth mechanism using thermal chemical vapour deposition ............................................7
CHAPTER 2. GROWTH OF CARBON NANOTUBES ..............................................................................11
2.1 GROWTH OF CNTS..................................................................................................................11
2.1.1 Cleaning..........................................................................................................................11
2.1.2 Sputtering......................................................................................................................12
2.1.3 Lift Off ............................................................................................................................12
2.1.4 Growth of Carbon Nanotubes...........................................................................................13
2.1.4.1 APCVD Set-up...............................................................................................................13
2.1.4.2 Result and Discussion...................................................................................................16
1. CNT growthon Fe-sputtered (4 nm) patterned Si .................................................................16
2. CNT growthon Continuous Ni (40 Å) over SiO2 grown Si........................................................17
3. CNT growthon Cu film without catalyst...............................................................................18
2.2 ETCHING................................................................................................................................18
2.2.1 Materials Used................................................................................................................19
2.2.2 Gold etchant...................................................................................................................20
2.2.3 Silicon Oxide etchant.......................................................................................................20
2.2.4 Silicon etchant.................................................................................................................20
2.3 BONDING METALS USING PREFORM.......................................................................................21
Result.......................................................................................................................................21
CONCLUSION....................................................................................................................................22
REFERENCES.....................................................................................................................................23

AN INTRODUCTION
Carbon nanotubes (CNTs) have been extensively investigated in the last decade because their
superior properties can benefit many applications. However, CNTs have not yet made a major
leap into industries, especially for electronic devices, because of challenges faced in their
fabrication.
The aim of this experiment was to synthesize multi-wall carbon nanotubes (MWCNTs), in the
presence and absence of a transition metal catalyst, for applications in field emission.
Atmospheric Pressure Chemical Vapour Deposition was used for the synthesis of the CNTs.
The CVD technique was used since it allows CNTs to be grown in predefined locations,
provides a certain degree of control of the types of CNTs grown, and may have the highest
chance to succeed commercially.
Understanding the primary growth mechanisms at play during CVD is critical for controlling the
properties of the CNTs grown and remains the major hurdle to overcome. Various factors that
influence CNT growth receive a special focus: choice of catalyst and substrate materials, source
gases, and process parameters.

CHAPTER 1. AN INTRODUCTION TO CARBON NANOTUBES
1.1 Structure of Carbon Nanotubes
Since their discovery in 1991 by Iijima, carbon nanotubes have been of great interest, both from
a fundamental point of view and for future applications. A carbon nanotube (CNT) is a tubular
structure made of carbon atoms, having diameter of nanometer order but length in
micrometers.[1]
Figure 1.1 : Basic Structure of an unrolled CNT[2]
1.1.1 Single Wall Carbon Nanotubes (SWNT)
The structure of a SWNT can be visualized as a layer of graphite, a single atom thick, called
graphene, which is rolled into a seamless cylinder.
Depending on how the sheet is wrapped, the resulting structure can be described similar to a
vector (n,m), where n and m are unit vectors in two directions along the honeycomb structure of
the sheet. [3]

Figure 1.2 : Vector representation of an unrolled CNT[4]
SWNTs can be divided into three classes based on the values of these unit vectors.
Figure 1.3 : Classes of SWCNT[5]
A SWNT consists of two separate regions with different physical and chemical properties. The
first is the sidewall of the tube and the second is the end cap of the tube. The end cap structure is
similar to or derived from a smaller fullerene, such as C60.SWNTs with different chiral vectors have
dissimilar properties such as optical activity, mechanical strength and electrical conductivity. [6]
1.1.2 Multi Wall Carbon Nanotubes (MWNT)
Multi-wall nanotubes can appear either in the form of a coaxial assembly consisting of
concentric SWNTs, or as a single sheet of graphite rolled into the shape of a scroll.
The diameters of MWNT are typically in the range of 5 nm to 50 nm. The interlayer distance in
MWNT is close to the distance between graphene layers in graphite.[7]

Figure 1.4 : Comparison between A) a Single Wall and B) a Multi Wall CNT[8]
MWNTs exhibit advantages over SWNTs, such as ease of mass production, low product cost per
unit, and enhanced thermal and chemical stability. In general, the electrical and mechanical
properties of SWNTs can change when functionalized, due to the structural defects occurred by
C=C bond breakages during chemical processes. However, intrinsic properties of carbon
nanotubes can be preserved by the surface modification of MWNTs, where the outer wall of
MWNTs is exposed to chemical modifiers.
1.2 SYNTHESIS TECHNIQUES
There exist many methods by which CNTs can be produced, including but not limited to
chemical vapor deposition, arc discharge and laser ablation, though scientists are researching
more economic ways to produce these structures.
Some of the major challenges facing the CNT industrial and research communities are to find a
synthesis technique that :
 minimizes amorphous carbon content in the sample,
 yields CNTs of a specified or uniform chirality,
 and is suitable for economically feasible mass production of CNTs.
1.2.1 Growth mechanism using thermal chemical vapour deposition
The Chemical Vapour Deposition (CVD) technique provides an answer to these challenges,
while simultaneously providing good control over the properties of the CNTs synthesized. It
allows us to directly grow CNTs usable for field emission. Thus, this report focuses on the
growth mechanism of CNTs by this process.
The most widely accepted general mechanism for CNT growth using CVD can be outlined as
follows:
1) Pretreatment under suitable temperature for nucleation of metal and formation of metal
nanoparticles

2) Introducing a carbon feedstock such as acetylene
3) Maintaining growth conditions for CNT growth.
The process involves passing a hydrocarbon vapor (typically 15–60 min) through a tubular
reactor in which a catalyst material is present at sufficiently high temperature (600–1200 C) to
decompose the hydrocarbon. CNTs grow on the catalyst in the reactor, which are then collected
upon cooling the system to room temperature.
Figure 1.5 shows a schematic diagram of the experimental set-up used for CNT growth by CVD
method in its simplest form.[9]
Figure 1.5 : Schematic diagram of a CVD setup in its simplest form.[10]
 Hydrocarbon vapor when comes in contact with the “hot” metal nanoparticles, first
decomposes into carbon and hydrogen species; hydrogen flies away and carbon gets
dissolved into the metal.
 After reaching the carbon-solubility limit in the metal at that temperature, dissolved
carbon precipitates out and crystallizes in the form of a cylindrical network having no
dangling bonds and hence energetically stable.
Hydrocarbon decomposition (being an exothermic process) releases some heat to the metal’s
exposed zone, while carbon crystallization (being an endothermic process) absorbs some heat
from the metal’s precipitation zone. This precise thermal gradient inside the metal particle keeps
the process going.
Now there are two general cases.
 (Fig. 1.6(a)) When the catalyst–substrate interaction is weak (metal has an acute contact
angle with the substrate), hydrocarbon decomposes on the top surface of the metal,
carbon diffuses down through the metal, and CNT precipitates out across the metal
bottom, pushing the whole metal particle off the substrate (as depicted in step (i)). As
long as the metal’s top is open for fresh hydrocarbon decomposition (concentration
gradient exists in the metal allowing carbon diffusion), CNT continues to grow longer
and longer (ii). Once the metal is fully covered with excess carbon, its catalytic activity
ceases and the CNT growth is stopped (iii). This is known as “tip-growth model.”
 In the other case, (Fig. 1.6(b)) when the catalyst–substrate interaction is strong (metal has
an obtuse contact angle with the substrate), initial hydrocarbon decomposition and carbon

diffusion take place similar to that in the tip-growth case, but the CNT precipitation fails
to push the metal particle up; so the precipitation is compelled to emerge out from the
metal’s apex (farthest from the substrate, having minimum interaction with the substrate).
First, carbon crystallizes out as a hemispherical dome which then extends up in the form
of seamless graphitic cylinder. Subsequent hydrocarbon deposition takes place on the
lower peripheral surface of the metal, and the dissolved carbon diffuses upward. Thus
CNT grows up with the catalyst particle rooted on its base; hence, this is known as “base-
growth model.”
a)
b)
Fig. 1.6 . Widely-accepted growth mechanisms for CNTs: (a) tip-growth model, (b) base-
growth model.[11]
Formation of single- or multi-wall CNT (SWCNT or MWCNT, respectively) is governed by the
size of the catalyst particle. Broadly speaking, when the particle size is a few nm, SWCNT
forms; whereas particles—a few tens nm wide—favor MWCNT formation. [12]
Chemical vapor deposition (CVD) is the most popular method of producing CNTs nowadays. If
in this process, thermal decomposition of a hydrocarbon vapor is achieved in the presence of a
metal catalyst, it is known as thermal CVD or catalytic CVD (to distinguish it from many other
kinds of CVD used for various purposes).[13]
Chemical Vapor Deposition technique is of various types:
a) Thermal CVD: reaction promoted by heat

b) Photo assisted CVD: reaction promoted by light
c) Plasma Enhanced CVD: reaction promoted by plasma
d) Metal Oxide CVD: uses organometallic compounds for deposition
e) Metal Organic Vapor Phase Epitaxy: used for depositing single crystal films on single
crystal substrates using metal oxides.
f) Atomic Layer Deposition: it uses sequential introduction of gaseous precursors and
evacuation between precursor pulses.

CHAPTER 2. GROWTH OF CARBON NANOTUBES
The following tasks were undertaken for the making of this report :
1) Growth of MWCNTs on different substrates (Fe-sputtered Si, Ni-coated Si and Cu foil)
via CVD at Nanotechnology Group, SSPL
2) Etching of substrates to attain pits on the surface. These pits can then be used as sites for
CNT growth in device processing. Successive etching of Au, Si and SiO2 was done to
create pits on the wafer. Catalyst can then be deposited in these pits for preferential
growth of CNTs in these pits.
3) Using Au-Sn preform for bonding Si with metals for field emission measurements. Si was
bonded with Au wafer using an Au-Sn preform at elevated temperatures. This method of
bonding can be used to bond CNT growth samples to Cu metal for field emission
measurements.
2.1 GROWTH OF CNTS
Growth of CNTs involved the following processes to ensure the sample gave best results :
1) Cleaning of substrate for growth of Carbon Nanotubes
2) Deposition of suitable Catalyst along with catalyst supports if necessary using Sputtering
3) Lifting off the catalyst from areas where growth is not desired (Lift-off)
4) Placing the substrate in the reactor and maintaining growth conditions.
2.1.1 Cleaning
The purpose of substrate cleaning is to remove organic contaminants (such as dust particles,
grease or silica gel) from the substrate surface; then remove any oxide layer that may have built
up; and finally remove any ionic or heavy metal contaminants.
The RCA clean is a standard set of wafer cleaning steps which need to be performed before
high-temperature processing steps (CVD) of silicon wafers can be performed.[14] It involves the
following chemical processes performed in sequence:
1) Removal of the organic contaminants (organic clean + particle clean)
2) Removal of thin oxide layer (oxide strip, optional)
3) Removal of ionic contamination (ionic clean)
4) Drying the substrate.

2.1.2 Sputtering
In this experiment, the sputtering system was used to deposit a 2nm thin layer of Fe on patterned
Si and Cu tape. Since Fe can act as a catalyst for CNT growth, we can get CNTs in any desired
pattern.
Sputtering is a process whereby atoms are ejected from a solid target material due to
bombardment of the target by energetic particles. It is commonly utilized for catalyst thin-
film deposition, etching and analytical techniques.[15]
For an efficient CNT growth, the catalyst–substrate interaction should be investigated with
utmost attention. Metal–substrate reaction (chemical bond formation) would cease the catalytic
behavior of the metal. .
Generally Fe, Ni or Co is used as a catalyst for growth of CNTs. Each catalyst incorporates a
different growth mechanism thus a different growth rate and different properties of the CNTs
hence formed. The sputtered catalyst film is broken into nanoparticles at high temperatures in
presence of an etchant such as ammonia.
Figure 2.1 : A basic sputtering system[16]
Gas used for plasma: Argon
Gas flow: 50 SCCM
RF Power: 150 W
Deposition Pressure: 8.2e-002 mbar
Table 1: Table of conditions of sputtering during experiments
2.1.3 Lift Off
Lift-off process is a method of creating structures (patterning) of a target material on the surface
of a substrate (e.g. wafer) using a sacrificial material (e.g. Photoresist). It is an additive technique
as opposed to more traditional subtracting technique like etching.[17]Lift-off is applied in cases
where a direct etching of structural material would have undesirable effects on the layer below.

Lift off of the sputtered sample was done using acetone for removing the photoresist along with
the sputtered films to allow patterned growth in certain areas. Sample was then dipped in de-
ionized water and dried using nitrogen gun.
2.1.4 Growth of Carbon Nanotubes
2.1.4.1 APCVD Set-up
Figure 2.2 : Schematic of APCVD system
The APCVD set-up consists of the following parts:
1) Quartz Tube : Quartz tube used in the experiment is a GE 214 tube of diameter 40mm is
placed along the axis of reactor. It can withstand temperature up to 1200°C. Quartz tube
is used due to its high softening point and its better purity at high temperatures compared
to other materials.
2) Reactor : It is a cylindrical muffle type horizontal furnace. The heater wire is Kanthal
APM wire. It is made of iron-chromium-aluminum alloy which is suitable for furnace
temperature up to 1250°C. This reactor is powered by a variac which is an
autotransformer with only one winding. The portions of same winding act as both
primary and secondary coils.
3) Thermocouple: An alumel (95% nickel, 2% manganese, 2% aluminium and 1% silicon)
is used to measure the temperature inside the reactor which is a k type thermo couple. It
has thermal conductivity of 30 W/m/K.

4) Mass Flow Controller : Mass flow controllers are used to measure and control the flow
rate of gases entering the reactor. The mass flow controllers are attached onto the gas
flow tubes and are used as a switch for the gases as well as to maintain the required flow
of the gases for growth.
5) Hydrogen Purifier : A Palladium filament based purifier is used to purify the hydrogen
gas coming from the cylinder. This Hydrogen purifier is capable of providing 99.99999%
pure hydrogen for the experiment. It works at temperature of 350˚C to 400˚C.
6) Bubbler : A bubbler is attached to the reactor to prevent backflow of water from the
exhaust to the reactor.
Following samples were considered for the growth of CNTs :
1) Fe-sputtered (4 nm) on patterned Si
2) Continuous Ni (40 Å) over SiO2 grown Si through e-beam.
3) Cu foil
Steps followed for growth of the CNTs :
1) Bypass: The reactor was bypassed in order to remove any residual gases from the gas
lines and also to check proper flow of gases in the lines through the system.
2) Purging: Along with precursors inert gases are also used during the chemical vapor
deposition process. The use of inert gas ensures removal of any precursors in the chamber
as well as removal of any volatile by products. Purging of the gas reactor as discussed
above was done using an inert gas to remove any residual gases or volatile residues in the
chamber to create a pure ambient in the reactor. Hydrogen gas was used as it provides a
reducing environment inside the reactor and also acts as a good carrier for residual gases.
3) Heating: After purging, the samples were heated in presence of hydrogen. Heating was
done till a high temperature suitable for breaking the thin film into nanoparticles as well
as a temperature suitable for growth was obtained. The temperature was measured
continuously during the complete growth process using a thermocouple.
4) Pretreatment: Ammonia was passed through the reactor at high temperature, which
caused the nucleation of the deposited thin film into nanoparticles which then acted as
catalysts for nanotube growth. Pretreatment exploits the property of ammonia as a very
good etchant and thus its use for breaking thin films into nanoparticles of sizes depending
upon film thickness.
5) Growth: Carbon feedstock such as methane, ethylene, ethanol etc. have been used for
growth of CNTs. The choice of the feedstock depends majorly on the reactivity of the
hydrocarbon. Due to this reason, growth in acetylene is observed at lower temperatures as
compared to methane due to high reactivity of acetylene. Virtually all growth methods
dilute the active carbon species in argon, hydrogen, nitrogen, helium, or some mixture of
these four, which provides yet another degree of freedom.[18]
In our experiment, after pretreatment, ammonia, hydrogen and carbon feedstock
in the form of acetylene were passed through the reaction chamber for the growth of

carbon nanotubes. The growth is seen to be dependent mainly upon the flow of gases,
temperature and time of flow. Also, ammonia was used as at temperatures between 800-
950˚C, it removes the amorphous carbon that starts depositing on the catalyst and thus
promotes growth of vertically aligned CNTs. [19]
6) Cooling: After growth the samples are left to cool inside the furnace. A supply of
hydrogen is maintained for carrying away the gases inside the chamber and also to
maintain a pressure inside the reactor to prevent creation of vacuum inside the reactor due
to dissolution of ammonia in water inside bubbler.
After cooling the samples were unloaded and prepared for characterization.
S.No. Step Name Gas used Flow Rate Temperature Duration
1. Purging H2 500 SCCM ~ 25°C 15-20 min
2. Heating H2 500 SCCM ~ 850C 40-45 min
3. Pretreatment H2
NH3
200 SCCM
250 SCCM
~ 850C 15-20 min
4. Growth C2H2
H2
NH3
40 SCCM
400 SCCM
240 SCCM
~ 850C 10-12 min
5. Cooling H2 500 SCCM Till ~ 200C 2-3 hours
Table 2 : Conditions during growth

2.1.4.2 Result and Discussion
CNT growth on a particular catalyst depends on the carbon-solubility of that catalyst. Only after
reaching the carbon-solubility limit in the metal at that temperature, does the dissolved carbon
precipitate out and crystallize in the form of a cylindrical network having no dangling bonds and
hence energetically stable.
Fe and Ni have much higher carbon-solubility than Cu.
1. CNT growth on Fe-sputtered (4 nm) patterned Si
Fe was used as a catalyst because of two main reasons:
(i) High solubility of carbon in Fe at high temperatures. The Fe catalyst was deposited in
a circular pattern, the deposited Fe reaching a height of 4 nm; and
(ii) High carbon diffusion rate in Fe. C atoms diffuse in Fe lattice by interstitial diffusion,
since C atoms are much smaller in size (~0.071nm) than Fe (~0.14 nm).
.
RESULT : Vertically aligned CNTs obtained which were 8µm in length.
Figure 2.3 : Vertically aligned CNTs on Fe-sputtered Si

2. CNT growth on Continuous Ni (40 Å) over SiO2 grown Si
A continuous film of Ni was used as catalyst. Ni, being a transition metal, has high carbon-
solubility making it a suitable catalyst for CNT growth.
The reason the CNTs obtained are inferior to those obtained on Fe may be that both the samples
were loaded together in the APCVD reactor and growth conditions could not be altered
according to the different samples.
RESULT : A bed of CNTs 3-4 µm in length were obtained.
Figure 2.4 : Bed of CNTs on continuous Ni

3. CNT growth onCu film withoutcatalyst
Although copper is a transition metal, it shows insignificant catalytic effect on CNT growth due
to its lower carbon-solubility as compared to other transition metals such as Fe and Ni.
No catalyst was deposited on the Cu foil used for growth.
RESULT : CNT growth was not observed.
Figure 2.5 : Cu-film surface after being subjected to growth conditions
2.2 ETCHING
Successive etching of substrates (Au, Si and SiO2) was done to attain pits on the surface. These
pits can then be used as sites for CNT growth in device processing. Catalyst can then be
deposited in these pits for preferential growth of CNTs in these pits. The following etching
solutions were made :
1) Gold etchant comprising of KI, I2 and H2O
2) SiO2 etchant comprising of NH4Fand HF ; and
3) Si etchant comprising of HNO3, HF, CH3COOH andNaClO2.
Etching is the process of chemically removing layers from the surface of a wafer. It is a
critically important process, and every wafer undergoes many etching steps before it is
complete.[20]
The purpose of etching is to create pits on the substrate wafer which can act as sites for CNT
growth.
The Etching process can be divided into two categories:-

 Isotropic etching
 Anisotropic etching
Isotropic etching is defined by having the same etch rate in all directions. It is not direction
sensitive. Anisotropic etching on the other hand, is defined by its direction sensitivity. For
example, KOH is highly selective to {100} and {110} crystallographic planes of Si over
{111} planes.
Figure 2.6 : Types of etching[21]
Different etchants are better at selectively etching certain materials. Etchants were prepared for
etching Au, Si and SiO2.
2.2.1 Materials Used
 Substrates :
1) Si wafer
2) Au-coated SiO2/Si
 Reagents :
1) HF (49%)
2) NH4F
3) DI water
4) KI
5) I2
6) HNO3
7) CH3COOH
8) NaClO2

2.2.2 Gold etchant
Wet chemical etching of gold requires a strong oxidizer for separation of its unpaired electrons,
as well as a complexing agent which suppresses reassembly of oxidized gold atoms back into the
crystal.[22]
The gold etchant prepared consisted of KI, I2 and H2O in the ratio of 4 : 1 : 40.
2Au + I2  2AuI
KI can dissolve AuI, which keeps the reaction moving in the forward direction. The substrate
was agitated while soaking in the etchants, to increase the etch rate.
Result
A solution of KI, I2 and H2O in the ratio of 4 : 1 : 40 gave an etch rate of 75 Å/min.
2.2.3 Silicon Oxide etchant
Buffered HF (also called Buffered Oxide Etch) was used for more controllable etching of the
SiO2 layer, since concentrated HF (typically 49% HF in water) etches silicon dioxide too quickly
for good process control and also peels photoresist used in lithographic patterning.
A Buffered HF solution comprising 6:1 volume ratio of 40% NH4F in water to 49% HF in water
was prepared in order to etch the SiO2 layer.
SiO2 + 4HF + 2NH4F  2NH4
+ + SiF6
2- + 2H2O
Result
A solution comprising 6:1 volume ratio of 40% NH4F in water to 49% HF in water gave an etch
rate of 20 Å/s.
2.2.4 Silicon etchant
1 litre silicon etchant can be prepared by mixing 900mL HNO3, 95 mL HF, 5mL CH3COOH and
14g NaClO2.[23]
The chemical reaction summarizing the basic etch mechanism for isotropic etching of silicon
using a HF/HNO3 etching mixture:
Si + 2OH- + 2H2O  SiO2(OH)2-
2 + 2H2
In conclusion, HNO3 oxidizes Si, and HF etches the SiO2 hereby formed.
Result
The prepared solution for etching Si gave an etch rate of 150 nm/min.

2.3 BONDING METALS USING PREFORM
A brazing preform is a high quality, precision metal stamping used for a variety of joining
applications in manufacturing electronic devices and systems.
Previously, epoxy resin was used to bind metals. However, using a preform to bond metals is
more beneficial and efficient method for device processing.
For this purpose, two stainless steel discs, 20 mm in diameter were fabricated. One disc was used
to provide a base for the substrates and the other to put pressure on top of the substrates in order
to facilitate bonding. This assembly was loaded into the APCVD reactor and heated to 350C for
5 minutes.
a) b)
c)
Figure 2.7 : Photographs depicting a) Bonding assembly and preforms, b) a loaded bonding
assembly; and c) a Si wafer
Result
We were successful in bonding Si substrate to Au using the Au-Sn preform. This method can
now be used to bond Si substrates to Cu-plate for use in field emission measurements.

CONCLUSION
I was able to accomplish the following tasks during my Summer Internship at Nanotechnology
Group, SSPL, DRDO.
 The necessary processes required before CNTs can be grown were performed, such as
cleaning of substrates, sputtering to deposit catalyst thin film on substrates, and lift-off.
 Synthesis of Multi-walled carbon nanotubes was done using Atmospheric Pressure
Chemical Vapour Deposition on Fe-sputtered (4 nm) patterned Si and Continuous Ni (40
Å) over SiO2 grown Si, which can then be used for field emission applications. No growth
was observed on the Cu foil sample.
 Etchants were prepared for etching Au, SiO2 and Si, which after having been etched, can
then be used as substrates for CNT growth.
 An assembly which, under suitable temperature ( ~350C) was able to bond Si to Au
using an Au-Sn perform was fabricated. This assembly can be used to bond metals for
field emission measurements.

REFERENCES
1. Chemical Vapor Deposition of Carbon Nanotubes: A Review on Growth Mechanism and
Mass Production by Mukul Kumar and Yoshinori Ando.
2. http://en.wikipedia.org/wiki/Graphene
3. http://ffden-2.phys.uaf.edu
4. http://en.wikipedia.org/wiki/Carbon_nanotube
5. http://www.ks.uiuc.edu/Research/vmd/plugins/nanotube/
6. The Wondrous World of Carbon Nanotubes : M. Daenen, R.D. de Fouw, B. Hamers,P.G.A.
Janssen,K. Schouteden and M.A.J. Veld .
7. www.nanocyl.com
8. http://lifesun.info/tag/nanotube/
9. The Wondrous World of Carbon Nanotubes : M. Daenen, R.D. de Fouw, B. Hamers,P.G.A.
Janssen,K. Schouteden and M.A.J. Veld .
10. http://www.intechopen.com/books/carbon-nanotubes-synthesis-characterization-
applications/carbon-nanotube-synthesis-and-growth-mechanism
11. Chemical Vapor Deposition of Carbon Nanotubes : A Review on Growth Mechanism and
14. http://en.wikipedia.org/wiki/RCA_clean
15. http://en.wikipedia.org/wiki/Sputtering

16. Thin Film Growth Through Sputtering Technique and Its Applications - Edgar Alfonso, Jairo Olaya
and Gloria Cubillos
17. http://en.wikipedia.org/wiki/Lift-off_(microtechnology)
18. Carbon Nanotubes : Properties and Applications by Michael J. O’Connell
20. http://en.wikipedia.org/wiki/Etching_(microfabrication)
21. http://www.el-cat.com/silicon-properties.htm
22. http://www.microchemicals.eu/technical_information/gold_etching.pdf
23. http://www.cleanroom.byu.edu/wet_etch.phtml

Growth of CNTs - Mihir Dass

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