n÷¾ó> ]± 6 1 Èjµs ±¿uÿ9Ï¿shodhganga.inflibnet.ac.in/bitstream/10603/37018/9/09_chapter 2.pdfPropanol at 100 C for 15 min. and this was repeated four times. Then, the substrates

Chapter 2

Experimental details

Chapter 2 Experimental details

25

Chapter 2

Experimental details

In this Chapter, the method adopted and the procedure followed to synthesize

Lithium doped Zinc Oxide (LZO) thin films, particulars of irradiation experiment and

the characterization techniques used to investigate LZO thin films are discussed.

Irradiation was carried out on the prepared thin films by electrons and γ- rays. The

particulars of electron and γ- irradiation experiments are briefly explained. Lastly, the

techniques used to investigate both pristine and irradiated films are discussed. The

structural investigations were done using X-ray Diffractometer, Scanning Electron

Microscope, Atomic Force Microscope; optical investigations by UV-Visible

Spectrophotometer, Photoluminescence and Raman setup. The ferroelectric

measurements using RADIANT P-E hysteresis loop tracer, dielectric studies, AC

conductivity measurements and I-V studies were performed.

2.1. Sol-Gel technique

The technique mainly involves the transition of the system from a colloidal

liquid, named sol, into the solid gel phase [1]. It can be widely used to synthesize

ceramic or glassy materials in a wide variety of forms: thin film coatings, ceramic

fibers, micro porous inorganic membranes, monolithic or extremely porous aerogels

[2]. Schematic picture of the sol-gel process is shown in Fig.2.1. In this technique, the

processing temperature is low, the composition is on molecular scale and the porosity

to obtain high surface area materials can be controlled easily. In addition, the

complex composition materials can also be prepared to form higher purity products


26

through the use of high pure reagents and to provide coatings over complex

geometries [3].

Fig. 2.1 Overview of the sol-gel process.

Generally, inorganic metal salts or metal organic compounds are the starting materials

of sol-gel technique. The sol will be formed by hydrolysis and poly condensation

reactions. The thin films can be prepared by spin-coating or dip-coating. Further,

ceramic materials in different forms can be obtained by processing the sol; when the

sol is cast into a mould, a wet gel will form. By drying and heat-treatment, the gel

gets converted into dense ceramic or glass. Aerogel, a highly porous and extremely

low density material can be obtained by removing the liquid from wet gel under a

supercritical condition. Ceramic fibers can be drawn from the sol by adjusting the


27

viscosity of the sol in the suitable viscosity range. Ultra-fine and uniform ceramic

powders are formed by precipitation, spray pyrolysis or emulsion techniques.

2.2 Synthesis

Synthesis of LZO thin films was carried out by sol-gel technique (Fig.2.2).

The sol was prepared by selecting the precursors: Zinc acetate (Zn (CH3COO)2,

99.99%, Aldrich), Lithium acetate dihydrate ((CH3COO)2Li.2H2O, 99.99%, Aldrich).

Methanol was used as a solvent to dissolve the precursors. For stability,

Diethanolamine (HN (CH2CH2OH)2, Ranbaxy) was added. The precursors were

dissolved in Methanol to form a clear solution with a designed doping ion

concentration. Platinized Silica (Pt-Si) served as the substrate / bottom electrode for

electrical measurements. Prior to the coating, substrates were cleaned in Acetone, 2-

Propanol at 100 C for 15 min. and this was repeated four times. Then, the substrates

were dried by flushing with Nitrogen gas. Spin coater (Laurell WS-650MZ-

23NPP/LITE) was used to coat the thin films on the substrates. To get the thin film in

micron thickness and free from the cracks, the optimization was done by choosing the

different speed and time. Optimized values of RPM and time were 2000 rpm and time

30 s. To remove the organic solvents after each coating, thin films were dried at 200

C for 15 min. Coating was done four times to get the desired thickness. To get high

crystallinity of thin films, annealing was done at 450 C for 30 min. Top Al contacts

were made by thermal evaporation technique using a mask on it. Hence, a device

with Metal-Ferroelectric-Metal (Al/LZO/Pt-Si) configuration (Fig.2.3) was made.


28

Fig. 2.2 Synthesis of LZO thin films by sol-gel technique.

Fig. 2.3 Metal-Ferroelectric-Metal configuration.

2.3 Irradiation

The prepared thin films were irradiated with electrons and γ- rays. The details

of the experimental part are explained below:

Step -1:

Stirred till the

clear solution

is formed

Step -2:

RPM – 2000 Time: 30sec

Step -3: Dried at 200C

Annealed at 450C

for 30 min


29

2.3.1 Electron irradiation

Electron irradiation was carried out using Microtron Accelerator available at

Mangalore University, Mangalore. The beam extraction system and principle of

operation of the Microtron is as shown in Figs. 2.4 and 2.5, respectively. The

Microtron set up is shown in Fig. 2.6. The thin films were put in a plastic sachet and

kept in front of the beam, in air, at room temperature. The energy of electron beam

was fixed to 8 MeV, while the fluence was varied: 3 x 1012

, 3 x 1013

and 3 x 1014

electrons/cm2.

2.3.1.1 Microtron – an electron Accelerator

The Microtron, an electron Accelerator is a powerful tool for research, medical

and industrial applications which need electron beam in energy range of few tens of

MeV. In research, these machines are used for photon and neutron activation analysis,

study of interaction of radiation with matter, study of kinetics of chemical reactions,

construction of free electron laser and injection of beam into larger circular

Accelerators. The beam energy is raised in steps by recirculating the electron through

the same radio frequency accelerating sections. A magnetic guide field produces

stable orbits in which the electron flows as they are accelerated. The number of orbits

required to reach a given energy is determined by the magnet geometry and is usually

in the range of 10-100. Only moderate R.F. power is required because of beam

recirculation.

The basic principle of operation for all Microtrons is embedded in the coherence

condition which requires that the geometry of the electron orbits be adjusted to ensure

that the transit time, from exit to R.F. accelerating section to entrance on the next


30

traversal of R.F. section, be an integral multiple of the R.F. period. Under these

conditions the electron beam will be uniformly accelerated from injection to

extraction energy. For particles travelling at close to the speed of light, successive

orbits increase in length by an integral number ν of R.F. wavelengths. The principle

of synchronism is applicable only for relativistic particles having almost constant

velocity independent of their energy. Therefore, Microtron is useful for accelerating

light particles like electrons, which become relativistic during first orbit itself.

Fig.2.4 Beam Extraction System


31

Fig.2.5 The principle of Microtron


32

Fig. 2.6 Microtron Accelerator at Mangalore University.

[Courtesy: Microtron Centre, Mangalore University, Mangalore]

2.3.2 Gamma irradiation

ZnO:Li thin films were exposed to γ-irradiation, to see the kind of

modification it induces in their properties. The synthesis of the films is explained

earlier, in Section 2.2. Gamma irradiation was carried out using a Gamma Chamber

5000 (GC-5000) available at CARRT, Mangalore University, Mangalore (Fig.2.7).

The activity and effective dose rate were 13.46 x 103 Curie and 6.89 kGy/hour,

respectively. 60

Co gamma irradiation was carried out by varying the delivered dosage:

2, 6 and 10 kGy.

Gamma Chamber 5000 is a compact self-shielded Cobalt-60 gamma irradiator

providing an irradiation volume of approximately 5000cc. The material for irradiation


33

is placed in an irradiation chamber located in the vertical drawer inside the Lead

flask. This drawer can be moved up and down with the help of a system of motorized

drive which enables precise positioning of the irradiation chamber at the centre of the

radiation field. Radiation field is provided by a set of stationary 60

Co sources placed

in a cylindrical cage. The sources are doubly encapsulated in corrosion resistant

stainless steel pencil and are tested in accordance with international standards. Two

access holes of 8 mm diameter are provided in the vertical drawer for introduction of

service sleeve for gases, thermocouple etc. A mechanism for rotating/stirring samples

during irradiation is also incorporated. The Lead shield provided around the source is

adequate to keep the external radiation field well within the permissible limits.

Fig. 2.7 Gamma Chamber 5000 at Mangalore University.

[Courtesy: CARRT, Mangalore University, Mangalore]


34

2.4 Characterization techniques

The following characterizations were carried out employing different

techniques and the details are presented below:

2.4.1 Structural studies

In this Section, the techniques that were employed to investigate the structural

characterizations of the thin films are discussed in detail. The techniques were X-ray

diffraction, Scanning Electron Microscopy, Atomic Force Microscopy. The thickness

measurement was carried out by a Profilometer.

2.4.1.1 X-ray diffraction

X-ray diffraction (XRD) technique is used to determine the crystal structure of

the powder as well of the thin film forms of crystalline samples. It gives information

on phase purity, crystal structure, lattice constant, preferred orientation, defects,

stress. The Bragg peaks correspond to the basic Bragg reflection, belonging to a

particular family of atomic planes. The Bragg equation relates the lattice spacing and

the observed 2 [4, 5].

2 dhkl sin = n (2.1)

where dhkl is the lattice spacing of a particular (h k l) plane, , the diffraction angle, n,

order of diffraction, , wavelength of the X-ray (CuK, λ= 1.5418 Å) and β being the

Full Width at Half Maximum. The pictorial representation of constructive

interference is shown in Fig.2.8.


35

Fig. 2.8 X-ray diffraction from Bragg planes.

Fig. 2.9 PANalytical XRD at Materials Research Centre.

[Courtesy: MRC, I. I. Sc., Bengaluru]


36

Pristine and irradiated thin films were characterized using PANalytical (Fig.

2.9), X-ray diffractometer with CuK radiation. The spectra were collected in the 2

range 20–80 . Crystallite size and lattice parameters were determined using,

(2.2)

2.4.1.2 Scanning Electron Microscopy

The Scanning Electron Microscopy is the most useful technique to examine

external morphology (texture), chemical composition and crystalline structure and

orientation of materials making up the sample. The principle involved in imaging is to

make use of the scattered secondary electrons and backscattered electrons; to show

morphology and topography of samples, secondary electrons are utmost vital and

backscattered electrons are most appreciated for elucidation contrasts in composition

in multiphase samples. High energy electron accelerated onto material results into a

number of interactions with the atoms of the target sample. Elastic scattering may

occur, if the electrons come out without any interactions and can also be inelastically

scattered which is depicted below in Fig.2.10 and the setup used is shown in Fig.

2.11. Quantitative and semi-quantitative analysis of compounds could be done by the

secondary electrons, backscattered electrons, cathode-luminescence, Auger electrons

and characteristic X-rays which could be useful in covering the signals that are used

for imaging. Heated Tungsten filament or field emission cathode ray tube present in

the SEM produces the electrons [6, 7].


37

Fig. 2.10 Electron-Specimen interactions.

Fig. 2.11 SEM set up at I. I. Sc., Bengaluru.

[Courtesy: CENSE, I. I. Sc., Bengaluru]

2.4.1.3 Atomic Force Microscope

An Atomic Force Microscope (AFM) scans the surface of a sample using a

sharp tip that is ~ 2mm long, ˂ 1 Å in diameter, which is located at the free end of


38

a Cantilever 100-200 mm long. The Cantilever has a spring constant which is less

than the effective spring constant holding the atoms of the sample together. As the

scanner starts moving gently, the tip across the contact force causes the Cantilever to

bend or deflect to accommodate the changes in the topography. A Position Sensitive

Photo Detector (PSPD) will then measure the deflection of Cantilever as the sample

is scanned under the tip. The deflection sensor works by reflecting a laser beam off

the back of the Cantilever onto a PSPD. This technique would be called as “beam

bounce detection” technique. As the Cantilever bends, the position of the laser spot

on the PSPD shifts. This shift gives the amount deflection of Cantilever and these

deflections allow the software to generate a map of surface topography.

The schematics of the hardware components of a basic AFM are shown in

Fig.2.12. The extensively used modes of operation of an AFM are contact mode and

non-contact mode. In a contact mode AFM, the distance between the tip of the

Cantilever and surface of the sample would be less than a few Angstrom while in the

non-contact mode, it ranges between 10-100 A. In terms of inter atomic force

between the tip and the sample, the contact mode is in the repulsive regime and the

non-contact mode is in the attractive regime.


39

Fig. 2.12 Schematics of AFM hardware.

2.4.1.4 Thickness measurement

The geometrical thickness at the edge of the films was measured by a

DEKTAK thickness Profilometer. This instrument is a highly sensitive, computer

aided surface profiler, which measures surface roughness, step height and other

surface characteristics in a variety of applications. A step was created between the

film and the substrate. During the measurement, a diamond tipped stylus directly

contacts the surface and follows the height variations as the tip scans the surface.

These height variations were converted into electric signals and thus produce a

profile. Film thickness was directly read out as the height of the resulting step-contour

trace. In order to minimize the measuring error, series of measurements at different

regions were taken and they were averaged out to derive the effective film thickness.


40

2.4.2 Optical studies

In this Section, the techniques that were employed to investigate the optical

properties of the thin films are discussed.

2.4.2.1 UV- Visible

Largely, a study that involves the interaction of light and matter is termed as

Spectroscopy. UV-Visible spectroscopy involves the measurement of the absorption

of light by molecules. It can be used for both qualitative and quantitative

investigations. The mechanism depends on the potential of a molecule to absorb

ultraviolet and visible light which leads to an excitation of outer electrons from the

Highest Occupied Molecular Orbital (HOMO) to the Lowest Unoccupied Molecular

Orbital (LUMO). The σ orbitals are termed as the occupied molecular orbitals with

lowest energy, π orbitals are termed as higher energy non – bonding orbitals

(unshared pair electrons). π* and σ* are termed as the highest energy states. Fig.2.13

shows electronic energy levels and transitions [8, 9].

Fig. 2.13 Energy levels and transitions.


41

Fig. 2.14 UV-Visible spectrophotometer assembly.

System consists of a source that emits a beam of light (visible and/or UV

light) and it is divided into its component wavelengths by a prism or diffraction

grating (Fig. 2.14). A monochromatic beam splits into two equal intensity beams with

same wavelength by a half-mirrored device. The first beam (colored magenta) passes

through the sample and other beam passes through the reference sample. The

intensity of these two beams is then studied by electronic detectors and is related. The

intensity of the reference beam is generally referred to as I0, which has a little or no

light absorption and the intensity of sample beam is referred to as I. The spectrometer

starts scanning the sample at all the wavelengths automatically (200 to 3000 nm).

Initially, it starts with ultraviolet region. Once it scans entirely in this region, then it

moves for higher wavelengths, in the visible range from 400 to 800 nm and so on. If

the light doesn’t get absorbed while passing through the sample, then I = I0 and if


42

some amount of light gets absorbed while passing through the sample, then I > I0. The

difference in the intensity of these two will be plotted against the wavelength and that

gives the spectrum. Absorption may be presented as a) Transmittance (T = I/I0), b)

Absorbance (A= log I0/I) [10]. The equipment used is shown in Fig. 2.15.

Fig. 2.15 UV-Visible (SPECORD) Spectrometer.

[Courtesy: SID, I. I. Sc., Bengaluru]

2.4.2.2 Photoluminescence

Photoluminescence is the emission of light which is caused by the irradiation

of a substance with other light. The term embraces both fluorescence and

phosphorescence, which differ in the time after irradiation over which the

luminescence occurs. Different parts of sample could be investigated by varying the

excitation energy and intensity. Emission spectrum could be used to recognize

surface, interface and impurity levels. In pulsed excitation state, PL intensity

transients yield lifetimes of excited states. Basically, PL is a non-destructive and

contact less technique for obtaining information about the impurity and defect levels


43

in semiconductors [11, 12]. It also provides important information about the

sample quality, band gap and excitonic properties of the material. Thus, it is an

excellent technique to characterize different semiconductors in bulk and thin film

forms.

The mechanism could be explained by excitation of a material, atomic

electrons using a relatively high frequency (hν > Eg) light [13]. The excited electrons

will relax by emission of photons that are characteristic of the crystal or defect site

that emits the light. The emitted photons could result from the band to band

recombination, intrinsic crystalline defects (growth defects), dopant impurities

(introduced during growth or ion implantation), or other extrinsic defect levels (as a

result of radiation or thermal effects). The bombardment of photons with energy

higher than the band gap of the material emits characteristic photons via several

different types of radiative and non-radiative recombination events. The resultant

spectrum allows determining the specific type of semiconductor defects. The highly

sensitive, qualitative measurement of native and extrinsic impurity levels formed

within the material bandgap can be found by the interaction between incident light

and defect levels. The photoluminescence process (Fig. 2.16) includes mainly three

types of mechanisms; excitation, thermalization and recombination. In excitation,

electrons absorb the energy from lasers and excite to a higher energy level. During

this process electron-hole pairs are created [14]. In thermalization, excited pairs

acquire quasi-thermal equilibrium level while relaxing down [15]. In recombination,

while falling down, the electron releases a lower energy photon. This process can

occur radiatively or non-radiatively [16].


44

Fig. 2.16 Photoluminescence process.

The typical experimental setup is shown in Fig. 2.17. The PL intensity was

measured using a Jobin Yvon LabRAM HR 800 UV system with a Helium-

Cadmium laser source with 325 nm excitation wavelength (Fig. 2.18). The

films were scanned in the range 300 to 800 nm to obtain a PL emission peak.


45

Fig. 2.17 Typical experimental set-up for PL measurements.

Fig. 2.18 Photoluminescence setup.

[Courtesy: SENSE, I. I. Sc., Bengaluru]

2.4.2.3 Raman

It is a spectroscopic technique used to observe the vibrational, rotational and

other low frequency modes in the system. The principle of this technique relies on


46

Raman scattering or inelastic scattering of monochromatic light generally from a

source in the visible, near infrared or near ultraviolet range [17]. When a light from

the source impinges on a sample or a substance, most of its energy scatters elastically.

In elastic scattering the molecules of the substance gets excited to a higher electronic

state and fall back immediately to the lower state or original state by releasing a

photon. If the energy of the scattered light is equal to that of the incident light, then

the process is called Rayleigh scattering. A molecule can fall back to either a higher

energy state (Stokes type scattering) or lower energy state (Anti stokes type scattering)

instead of its original state. The difference in the incoming and scattered photon

energy (Raman shift) resembles the energy difference between vibrational levels of a

molecule. The different modes of a molecule can hence be recognized by identifying

Raman shifts in the inelastically scattered light spectrum (Fig. 2.19).

Fig. 2.19 Schematics of Raman scattering.

Generally, Raman shift is represented by w or v and expressed in wave

numbers. However, in general, these symbols are used for angular and linear

frequency, but in Raman spectroscopy these are defined as


47

Raman shift =

7 7

1 1

0

10 10( ) ( )

( ) ( )cm cm

nm nm

(2.3)

where Raman shift is measured in wave numbers (cm-1

), o being the wavelength of

the laser light and , the wavelength of the scattered light. Positive Raman shift (o >

) corresponds to stokes lines in the spectrum, where the emission of photons takes

place while negative Raman shift ( < o) corresponds to the antistokes lines in the

spectrum, where the absorption of photons takes place.

The general set-up of Raman scattering consists of; (i) Laser source for

excitation; monochromatic light, ii) an optical equipment that is used for bringing up

the laser beam on the sample and to collect the scattered light, iii) Spectrometer to

analyze the scattered light and iv) a Detector for collecting the signal. The

information of the sample can be derived by manipulating the exciting and analyzing

lights with optical filters, polarizers.

2.4.3 Electrical characterization

In this Section, the techniques that were employed to investigate the electrical

properties of the thin films (M-F-M; Metal-Ferroelectric-Metal configuration) are

discussed in detail. To make M-F-M structure, Al dots were deposited using the

thermal evaporation technique and Platinized-Si substrate was used as the bottom

electrode. To accomplish all the electrical measurements such as dielectric, P-E

hysteresis and current-voltage measurements, a probe station consisting of two XYZ

micro positioners and an inbuilt furnace was used. Fig. 2.20 shows the setup used for

electrical characterization of the sample at wide range of temperatures. The chamber

can be evacuated and the liquid Nitrogen would be poured through an inlet for


48

making low temperature measurements. The temperature of the sample can be

monitored by a single Chromel-Alumel thermocouple connected to a Eurotherm (247)

temperature controller. The sample was mounted on a stainless steel heater block,

which was welded on a stainless steel cavity. Using the micro positioners, the top and

bottom contacts were made onto the thin film. The leads of the micro positioners

were connected to the respective instruments such as Radiant Technologies RT66A

ferroelectric test system for P-E measurement, Impedance analyzer (HP 4294A) for

dielectric measurement and KEITHLEY 2611A for I-V characteristics.

Fig. 2.20 Probe station set up.

2.4.3.1 Frequency domain measurements

The low field dielectric properties were measured using an Impedance

Analyzer (HP 4294A) and by an LCR meter (Fig. 2.21). The dielectric measurements

were carried out in the frequency range 100 Hz to 1 MHz at different temperatures

(300-350 K). Initially, the capacitance and loss of the thin films were measured.

Capacitance values were converted into dielectric constant using:

0

'Cd

A

where A,


49

is the area of the dot and d, the thickness of the thin film, 0 - permittivity of free

space and C is the measured capacitance. In the same manner, by measuring the

impedance (Z) and the phase angle (θ), at various frequencies and temperature, the

AC conductivity was calculated using0

' tanac

where, - angular

frequency and tan is the tangent loss.

Fig. 2.21 LCR meter.

2.4.3.2 Polarization hysteresis

It is one of the powerful techniques to confirm that the material is a

ferroelectric material. The equivalent circuits of these two test modes are shown in

Figs. 2.22 and 2.23. P-E hysteresis measurement of thin films was carried out using a

Radiant Technologies RT66A ferroelectric test system (Fig. 2.24). The available

modes of the ferroelectric test system are Virtual Ground and Sawyer Tower modes.

In the Sawyer-Tower technique, the capacitive voltage of the thin films would be used

and it comprises the test sample and a sensing capacitor (C-sense). The voltage


50

generated across the sense capacitor is proportional to the charge stored in the sample.

In the virtual ground mode, the stored charge of the ferroelectric sample would be

measured by integrating the current required to maintain one terminal of the sample at

zero volts - hence called as virtual ground. By eliminating the external sense

capacitor, this circuit drastically reduces the effects of parasitic elements. The

precision capacitor used as the feedback element in the current integrator is now a key

element in obtaining high accuracy with this technique.

Fig. 2.22 Equivalent circuit in Sawyer Tower Mode.


51

Fig. 2.23 Equivalent circuit in Virtual Ground Mode.

Fig. 2.24 P-E loop measurement set up.


52

Fig. 2.25 SMU-2611A set-up for I-V measurements.

2.4.3.3 Leakage current

I-V characteristics of the thin films were carried out using a KEITHLEY

Source Measure Unit (Model SMU 236) (Fig. 2.25.), which could simultaneously act

as a constant voltage source and measure the current flowing through the circuit. The

I-V characterizations were done at different temperatures. From the obtained I-V

data, the parameters such as barrier height, ideality factor were calculated.


53

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Silicates and Borates, Am. Chem. Soc., part II, (1988).

[2] Jones R W, Fundamental Principles of Sol-Gel Technology, IOM

Communications Ltd (1989).

[3] Brinker C J, Scherer S W, Sol–Gel science: the physics and chemistry of sol–gel

processing, Academic Press, New York, (1990).

[4] Azaroff LV, Elements of X-ray crystallography, McGraw Hill, New York, (1968).

[5] Cullity B D, Elements of X Elements of X-ray Diffraction, 2nd Ed, Addison-

Wesley (1978).

[6] McMullan, D. Von Ardenne and the scanning electron microscope. Proc. Roy

Microsc. Soc., 23 (1988).

[7] Zworykin V A, Hillier J and Snyder R L, A Scanning Electron Microscope,

ASTM Bull., 117 (1942).

[8] Douglas Skoog A, James Holler F and Stanley Crouch R, Principles of

Instrumental Analysis, 6th Ed., Belmont, CA: Thomson Brooks/Cole (2007).

[9] Misra Prabhakar and Dubinskii Mark, Ultraviolet Spectroscopy and UV Lasers.

New York: Marcel Dekker (2002).

[10] Sooväli L, Rõõm E.I, Kütt A, Kaljurand I, Leito I.. Uncertainty sources in UV-Vis

spectrophotometric measurement. Accred. Qual. Assur. 11 (2006) p.246

[11] Kira Jahnke M, Koch F, S W, “Quantum Theory of secondary emissions in

optically excited semiconductor wells”, Phy. Rev. Lett., 82(17) (1999) p.3544.

[12] Kimble H J, Dagenais M and Mandel L, “Photon Antibunching in Resonance

Fluorescence". Physical Review Letters 39(11) (1977) p.691.

[13] Klingshim and Claus F, Semiconductor Optics, Springer (2012).

[14] Balkan, Naci. Hot Electrons in Semiconductors: Physics and Devices. Oxford

University Press (1998).

[15] Polland H, Ruhle W, Kuhl J, Ploog K, Fujiwara K and Nakayama T, Physical

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[16] Wang Hailin, Ferrio Kyle, Dunacan, Hu Y, Blinder R and Koch S W, Phy. Rev.

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54

[17] Gardiner D J, Practical Raman spectroscopy, Springer- Verlag (1989).

Documents

n÷¾ó> ]± 6 1 Èjµs ±¿uÿ9Ï¿shodhganga.inflibnet.ac.in/bitstream/10603/37018/9/09_chapter 2.pdfPropanol at 100 C for 15 min. and this was repeated four times. Then, the substrates