CHAPTER 3 EXPERIMENTAL PROCEDURE AND SAMPLE CHARACTERIZATIONS

CHAPTER 3
EXPERIMENTAL PROCEDURE AND SAMPLE
CHARACTERIZATIONS
All experimental procedure that had been done in this thesis will be
summarized in this chapter. The experimental detail is focused on the synthesis of
CNTs
and
CuO
NSs
whereas
fabrication
of
nanocomposite
films
of
MWNTs/CuO/Cu2O were investigated in the film resistance and the angle sensor
application. The sample characterizations such as morphological, structural and
optical properties are described.
3.1 Chemical substances
3.1.1 Iron wire (Fe,  0.25 mm, 99.97% purity, Advance Research Material
LTD)
3.1.2 Cobalt wire (Co,  0.25 mm, 99.97% purity, Advance Research Material
LTD)
3.1.3 Nickel wire (Ni,  0.25 mm, 99.97% purity, Advance Research Material
LTD)
3.1.4 Copper plate
3.1.5 Argon gas (Ar, High purity, 99.9%)
3.1.6 Acetylene gas (C2H2)
3.1.7 Ethanol (C2H5OH, 99.9% Merk)
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3.1.8 Acetone (99.9% Merk)
3.1.4 Stainless steel plate
3.1.5 Cover glass slide (thickness 160 µM, Deckglaser)
3.1.6 Polyethylene terephthalate (PET, thickness 100 µM, 3M)
3.1.7 Deionized water (RCI Labscan)
3.1.8 MWNTs powder
3.1.9 Silver paint (SPI Supplies)
3.1.10 Copper wire ( 0.25 mm)
3.2 Instruments
3.2.1 High voltage power supply (PHYWE, 0-25 kV)
3.2.2 Capacitor 25 nF
3.2.3 Ultrasonic cleaner (Mettler Electronics)
3.2.4 Mullite tube furnace (2.5×46 cm2)
3.2.5 Glass tube furnace (2.5×46 cm2)
3.2.6 Temperature controller (J&D, DB5090)
3.2.7 Flow meter (Cole Pamer)
3.2.8 DC power supply (Kenji, 30V, 3mA)
3.2.9 Venire Caliper
3.2.10 Glass bath
3.2.11 Multi-meter (Uni-T)
3.2.12 Computer
3.2.13 Stepping motor
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3.1.14 Angle measurement apparatus
3.1.15 Polyvinyl chloride sheet
3.3 Synthesis of CNTs by CVD method
3.3.1 Experimental setup and experimental procedure
Copper substrates with sizes of 10×10×0.4 mm3 were mirror-like polished,
sonically cleaned in acetone, distilled water and ethanol and dried in air. The Ni, Fe
and Co wires ( 0.25 mm) were sharpened by cutting with pliers and connected to a
circuit of the sparking process, as shown in Figure 3.1 and 3.2 [67]. The two sharp
tips were placed horizontally at 1 mm spacing and 1 mm above the center of the
substrate. The NPs preparation of Ni, Fe and Co using as single and co-catalysts were
deposited on the copper substrates by sparking in air for 5 times at 12 kV. The
catalyst-coated copper substrate was placed at the center of a tube furnace, as shown
in Figure 3.3 and 3.4 [68]. After the sample was heated to 750ºC under constant
flowing of argon gas at the rate of 100 ml/min, C2 H2 at the rates of 3, 5 and 10 ml/min
was introduced to the tube furnace for 5 min which step of conditions are shown in
Figure 3.5
49
Figure 3.1 Schematic diagrams of the sparking apparatus for depositing the catalysts
on copper substrates.
Figure 3.2 Sparking setup contains: copper plate as substrate, wire as anode and
cathode, capacitor, switch and high voltage power supply.
50
Figure 3.3 Schematic diagrams of the CVD reactor.
Figure 3.4 CVD reactor setup contains: mullite tube furnace, temperature controller,
flow meter, Ar gas and C2H2 gas.
51
Figure 3.5 Schematic diagrams of the conditions for synthesizing CNTs from C2H2.
3.3.2 Sample characterization
Surface morphologies of the NP-deposited substrates were observed by the
tapping mode of atomic force microscopy (AFM). Element ratios of the co-catalysts
were measured by x-ray fluorescence (XRF). The morphology and structures of the
as-grown products were characterized by scanning electron microscopy (SEM),
transmission electron microscopy (TEM) and Raman spectroscopy.
52
3.4 Fabrication of CuO NRs and their bundles by an electrochemical dissolution
and deposition process
3.4.1 Experimental setup and experimental procedure
Synthesis of CuO NRs and their bundles by an electrochemical dissolution and
deposition process was operated by using copper and stainless steel plates with sizes
of 1.5 × 5.0 × 0.04 cm3 as an anode and a cathode, respectively. A glass substrate with
a size of 0.5 × 2.2 × 0.016 cm3 was attached on the cathode for deposition of the NSs,
as shown in Figure 3.6. The experimental set-up was as shown in Figure 3.7. The two
electrodes were immersed in 100 ml of deionized water and a voltage of 10-30 V DC
was applied [19,69]. The electrochemical dissolution and deposition were performed
by varying the electrode separations from 2 to 10 mm and the deposition time from 1
to 8 h. The as-deposited samples were dried for 1 h and annealed in the furnace tube.
Figure 3.6 Schematic diagrams of electrochemical dissolution and deposition
processes.
53
Figure 3.7 Electrochemical dissolution and deposition setup contains: copper plate as
anode, stainless steel plate as cathode and solution of deionized water.
3.4.2 Annealing treatment
The as-deposited samples were annealed in tube furnace which placed on the
alumina boat at the center of furnace. The annealing temperature was operated at 300500oC for 0.5 to 3 h in an air atmosphere (Figure 3.8) [14].
Figure 3.8 Furnace for annealing setup contains: glass tube furnace, temperature
controller.
54
3.4.3 Sample characterization
Morphology of the as-deposited and annealed samples was characterized by
scanning electron microscopy (SEM, JEOL JSM-6335F). Crystal structures were
analyzed by transmission electron microscopy (TEM, JEOL JEM-2010), operated at
200 kV, Raman spectroscopy (Ar ion laser excitation 514.5 nm, power laser 0.5 mW,
HORIBA JOBIN YVON T64000) and x-ray diffraction (XRD, Bruker D8 Advance).
Optical properties were measured using a photoluminescence (PL) spectrometer
(Perkin–Elmer LS50B) with a 290 nm excitation wavelength at room temperature.
3.5 Fabrication of MWNTs/CuOCu2O nanocomposite films by an electrophoretic
co-deposition process
3.5.1 Experimental setup and experimental procedure
As-synthesized MWNTs were prepared at a temperature of 700 °C by the
chemical vapor deposition method, using nickel oxide as the catalyst and liquid
ethanol as the carbon source [68]. The electrophoretic co-deposition process was
carried out in MWNT samples in deionized water, with MWNT concentrations of
0.05 mg/ml to 0.5 mg/ml. The samples were sonicated for 1 h before the deposition
process. Electrode separations between the copper anode and stainless steel cathode of
6 mm, 8 mm and 10 mm, direct-current (DC) voltages of 10 V to 30 V and deposition
times of 1 h to 4 h were used, with a polyethylene terephthalate (PET) sheet (5 × 20 ×
0.1 mm) attached to the cathode as shown in Figure 3.9 and 3.10.
55
Figure 3.9 Schematic diagrams of electrophoretic co-deposition process.
Figure 3.10 Electrophoretic co-deposition setup contains: copper plate as anode,
stainless steel plate as cathode and solution of MWNTs and deionized water.
56
3.5.2 Sample characterization
The as-deposited samples were then dried in air at room temperature.
Characterizations were performed using scanning electron microscopy (SEM, JEOL
JSM-6335F), transmission electron microscopy (TEM, JEOL JEM-2010) at an
operating voltage of 200 kV and x-ray diffraction (XRD, Rigaku Miniflex II) at 30 kV
and 15 mA with a Cu Kα target. The as-deposited samples were measured the film
resistance and tested the angle sensor at room temperature.
Film resistance measurements of the as-deposited samples were performed
between two silver electrodes 5 mm in length, with a 10 mm separation (Figure 3.11),
using an ohm meter at room temperature. The set-up for the angle sensor
measurement is shown in the schematic diagram in Figure 3.12a. This setup measured
the resistance and bending angle of the as-deposited samples. The resistance signals
were recorded via a connection between the serial port (RS 232) of the digital multimeter and the computer. The bending angle was controlled using the rotation of a
stepping motor (2 degree/second) which started at angles from 100 to 260 degrees and
returned to the original angle, as shown in Figure 3.12b. The angle sensor was shown
the set-up of equipment in Figure 3.13.
R
Figure 3.11 Schematic diagram of the setup for the film resistance measurements.
57
Figure 3.12 Schematic diagrams of (a) the set-up of the angle sensor measurements
and (b) the bending angles of the sample from 100 to 260 degrees.
58
Figure 3.13 Photograph of the angle sensor set-up.
3.6 Sample characterization
3.6.1 Atomic force microscopy (AFM)
The morphology of the nanoparticles which prepared by the sparking process
was characterized by Atomic Force Microscope (AFM, Digital Instruments, Inc.,
Santa Barbara, CA) using the tapping mode with the Nanoscope IIIa 5.12r3 software,
as shown in Figure 3.14.
Figure 3.14 Atomic force microscope.
59
3.6.2 Scanning electron microscopy (SEM) and energy dispersive X-ray
(EDX) spectroscopy
The morphology and sizes of as-obtained samples were determined by a field
emission scanning electron microscope (FE-SEM, JEOL JSM-6335F) operated at
accelerating voltage of 15 kV with an energy dispersive X-ray analyzer (EDX), as
shown in Figure 3.15. The samples were pasted on the brass sample holder and coated
with gold coating by sputtering techniques. The EDX analysis controlled by Inca
program used to determine the chemical composition which identified peaks at
energies characteristic of the elements and calculated the concentrations of the
elements in the samples by the weight and the atomic percents.
Figure 3.15 Scanning electron microscope
60
3.6.3 Transmission electron microscopy (TEM) and the selected area
electron diffraction (SAED) patterns
The morphology of the samples was observed by transmission electron
microscopy (TEM, JEOL JEM 2010), as shown in Figure 3.16. The samples for TEM
analysis were prepared by dispersing small amount of the powder in absolute ethanol
and placing a drop of the solution onto a copper grid coated with holey carbon film
and letting the ethanol evaporate slowly in air. After then, the samples were
characterized by TEM operating at voltage of 200 kV which could be analyzed the
selected area electron diffraction (SAED) patterns and energy dispersive X-ray
analyzer (EDX).
Figure 3.16 Transmission electron microscope.
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3.6.4 X-Ray Fluorescence Spectrometry (XRF)
Element ratios of the co-catalysts were measured by x-ray fluorescence (XRF,
Philips Magix Pro) as shown in Figure 3.17. X-ray Fluorescence (XRF) analysis is a
non-destructive technique that is used to quantify the elemental composition of an
unknown sample or mixture. XRF can accurately quantify the elemental composition
of both solid and liquid samples. The resulting X-ray spectrum reveals a number of
characteristic peaks. In the XRF analysis
the intensity and energy of these x-rays
are being recorded. The energy of the peaks provides information on the elements
present in the sample (qualitative analysis) and the peaks intensity provides the
relevant or absolute elemental concentration (semi-quantitative or quantitative
analysis).
Figure 3.17 X-ray fluorescence spectrometer.
62
3.6.5 X-ray diffractometry (XRD)
XRD is very useful in determining the detailed crystallographic structures of
nanostructured materials because they are normally in the form of single crystal
phase. In addition to the crystallographic structure information, the grain size effect
can be revealed by XRD in the explanation of relevant phenomena.
XRD is a versatile, non-destructive analytical technique that is widely used to
identify and characterize the chemical composition, crystallographic structure and the
relevant interplanar spacings of unknown materials. The atoms in a regular crystal are
3-dimensionally distributed in space and can be simulated by a series of lattice
structure (i.e. cubic, hexagonal, rhombic, etc.), in which the crystallographic planes
are separated from one another by a distance d. The d-spacing varies in accord to the
geometric nature of materials. As a result, any plane present in a crystal with different
orientations can be characterized with its own specific d-spacing.
Figure 3.18 schematically illustrates the scattering process used in the XRD
measurement. When an incoming monochromatic x-ray beam with a wavelength λ
passes the crystalline planes in a crystal at angle θ diffraction can occur under the
constructive interference conditions. It is known as Bragg’s Law, which is that the
distance difference traveled by the x-ray beam reflected from two successive planes
differs by a complete number n (i.e. 1, 2, 3 etc.) of wavelengths as given.
nλ =2dsinθ
(3.1)
63
By varying the incident angle θ, Bragg’s Law conditions are satisfied by different d
spacing in a crystalline material. On the one hand, the Bragg’s Law determines the
position of a diffraction peak in diffraction experiment.
Figure 3.18 Principle of x-ray diffraction as indicated by Bragg’s law.
In this work, X-ray diffraction (XRD) was used to identify phases on the
surfaces of CuO NSs. The X-ray Diffraction (XRD) was performed on sample using a
Bruker D8 Advance diffractrometer equipped with a copper anode was shown in
Figure 3.19. The diffractrometer was operated at 40 kV with 30 mA current.
Monochromatic Cu K radiation of wavelength 1.54 Å was used throughout. Each
sample was scanned for a 2 range from 10-90 degree and used with a step size of
0.02 degree/second. The identification samples were assisted by Philips X’Pert
Highscore Computer Software (search-match program) on the database of JCPDS
software.
64
Figure 3.19 X-ray diffractrometer
3.6.6 Raman spectroscopy
In Raman spectroscopy, vibrations and rotations of molecules are studied. In
practice, the sample is irradiated by a monochromatic incident beam, the radiation and
scattered by sample enables measured. The scattered light most consists of phonons
with the same frequency as the incident radiation. In molecular systems, these
frequencies are principally in the ranges associated with rotational, vibrational and
electronic level transitions. Light scattered from a molecule has several components;
the Rayleigh scatter and the Stokes and Anti-Stokes Raman scatter (Figure 3.20). The
scattering process without a change of frequency is called Rayleigh scattering, and is
the same process described by Lord Rayleigh and which accounts for the blue color of
the sky. A change in the frequency (wavelength) of the light is called Raman
65
scattering. Raman shifted photons of light can be either of higher or lower energy,
depending upon the vibrational state of the molecule. By far the stronger of the two
processes is the Stokes scattering, whereby the photon is scattered at lower energy.
Since at room temperature the population state of a molecule is principally in its
ground vibrational state this is the larger Raman scattering effect [47].
In this study, micro-Raman spectroscopy was used for characterization of
structural properties of the samples. In this work, we were performed using a Horiba;
Jobin Yuon-T 64000 with an Ar ion laser (514.5 nm, 50mW), as shown in Figure
3.21.
Figure 3.20 Rayleigh and Raman scattering
66
Figure 3.21 Raman spectroscope
3.6.7 Photoluminescence (PL) spectroscopy
The principle of the photoluminescence of a semiconductor is simple. When
the light of sufficient energy incidents on a material in a process called
photoexcitation, photons are absorbed and electronic excitations are created, usually
in the near surface region. These photo generated electrons and holes diffuse into the
bulk. At the same time, they relax and recombine via various channels, such as free-to
bound recombination or bound excitation recombination. These recombination
processes typically result in characteristic photoluminescence emission from the
sample as shown in Figure 3.22.
Photo-excitation causes electrons within the material to move into permissible
excited states. When these electrons return to their equilibrium states, the excess
67
energy is released and may emit light (a radiative process) or may not (a nonradiative
process). The energy of the emitted light (photoluminescence) relates to the difference
in energy levels between the two electron states involved in the transition between the
excited state and the equilibrium state. The quantity of the emitted light is related to
the relative contribution of the radiation process.
The most common radiative transition in semiconductors is between states in
the conduction and valence bands with band gap, an energy difference. The band gap
determination
is
particularly
useful
when
working
with
new
compound
semiconductors. Radiative transitions in semiconductors also involve localized defect
levels. The photoluminescence energy associated with these levels can be used to
identify specific defects, and the amount of photoluminescence can be used to
determine their concentration.
The PL signal can easily be detected by a suitable detector through a
monochromator or filter. By scanning the monochromator, a PL spectrum is obtained.
Photoluminescence processes are very sensitive to the sample temperature; therefore,
the most PL processes are experimented at a low temperature.
In this study, the luminescence emission spectra of the CuO nanostructures
were investigated using Perkin Elmer Luminescence spectrometer LS50B with a 290
nm excitation wavelength at room temperature, as shown in Figure 3.23.
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Figure 3.22 The simple diagram of electron emitted from valence band to conduction
band by excitation.
Figure 3.23 Luminescence spectrometer