31 | P a g e

Thin Film Deposition Technique

Physical Chemical

1. Resistive Heating 2. Flash Evaporation 3. Electron Beam

Evaporation 4. Laser

Evaporation 5. Arc Evaporation 6. Radio Frequency

(RF)Heationg

1. Glow Discharge Sputtering

2. Triode Sputtering 3. RF Sputtering 4. Magnetron

Sputtering 5. Face Target

Sputtering 6. Ion Beam

Sputtering 7. A.C. Sputtering

1. Chemical Vapour Deposition (CVD)

2. Laser CVD 3. Photo CVD 4. Plasma Enhanced

CVD 5. Metal Organo

CVD (MOCVD) 6. Atmospheric

Pressure CVD

1. Electro Deposition 2. Electroless

Deposition 3. Spray Pyrolysis 4. Sol Gel Process 5. SILAR 6. Solution Growth

Technique 7. Anodization 8. Liquid Phase

Epitaxy

2.1 FILM FORMATION TECHNIQUE:

The Physical properties of polymer film basically depend on the film

preparation/formation technique. There are several methods that can be used for

formation of polymer thin film. The formation of synthetic polymer is a process

which occurs via chemical connection of many hundred to thousand of monomer

molecules. As a result, macromolecule is formed [1,2]. The important thin film

formation processes are based on liquid phase chemical techniques, gas phase

chemical processes, glow discharge processes and evaporation methods [3]. The

methods employed for thin film deposition can be divided into two groups based on

the nature of deposition process, namely physical or chemical as shown in Fig. 2.1.

Fig.2.1 Classification of Thin Film Deposition Technique

The details of all physical methods are beyond the scope of this dissertation.

Chemical deposition techniques are the most important methods for growth of the

films owing to their versatility for depositing large number of elements and

compounds at low temperature [4]. The chemical deposition process is economically

Vacuum Sputtering Gas Phase Liquid Phase

32 | P a g e

effective and has been industrially exploited to large scale. Brief ideas about some

important physical and chemical methods of thin film formation are mentioned here

for general understanding.

2.1.1 Physical Vapor Deposition (PVD) Processes

Physical vapor deposition is a technique whereby physical process, such as

evaporation, sublimation or ionic impingement on a target, facilitates the transfer of

atoms from a solid or molten source onto a substrate. Evaporation and sputtering are

the most widely used PVD methods for depositing films [5]. Typically, PVD

processes are used to deposit films with thicknesses in the range of a few nanometers

to thousand of nanometers; however, they can also be used to form multilayer

coatings graded composition deposits, very thick deposits and freestanding structures.

The substrates can range in size from very small to very large such as the 10' × 12'

glass panels used for architectural glass. The substrates can range in shape from flat to

complex geometries such as watchbands and tool bits. Typical PVD deposition rates

are 10-100Å (1-10 nanometers) per second.

PVD processes can be used to deposit films of elements and alloys as well as

compounds using reactive deposition processes. In reactive deposition processes,

compounds are formed by the reaction of depositing material with the ambient gas

environment such as nitrogen (e.g. titanium nitride, TiN) or with a co-depositing

material (e.g. titanium carbide, TiC). Quasi-reactive deposition is the deposition of

films of a compound material from a compound source where loss of the more

volatile species or less reactive species during the transport and condensation process,

is compensated for by having a partial pressure of reactive gas in the deposition

environment. For example, the quasi-reactive sputter deposition of ITO (indium-tin-

oxide) from an ITO sputtering target using a partial pressure of oxygen in the plasma.

The main categories of PVD processing are vacuum evaporation, sputter deposition,

arc deposition and ion plating as depicted in Fig. 2.2.

33

Fig

22

PV

Dte

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:(1

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(1b

and

1c)

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| P a g e

Fig

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P

VD

tec

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vapo

urat

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(1b

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1c)

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(1d)

sp

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ith

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apou

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ourc

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on b

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6]

34 | P a g e

A. Vacuum deposition

Vacuum deposition which is sometimes called vacuum evaporation is a PVD

process in which material from a thermal vaporization source reaches the substrate

with title or no collision with gas molecules in the space between the source and

substrate. The trajectory of the vaporized material is “line-of-sight”. The vacuum

environment also provides the ability to reduce gaseous contamination in the

deposition system to a low level. Typically, vacuum deposition takes place in the gas

pressure range of 10-5 to 10-9 Torr depending on the level of gaseous contamination

that can be tolerated in the deposition system. The thermal vapourization rate can be

very high compared to other vapourization methods. The material vapourized from

the source has a composition which is in proportion to the relative vapour pressure of

the material in the molten source material. Thermal evaporation is generally done

using thermally heated sources such as tungsten wire coils or by high energy electron

beam heating of the source material itself. Generally the substrates are mounted at an

appreciable distance away from the vapourization source to reduce radiant heating of

the substrate by the vapourization source.

Vacuum deposition is used to form optical interference coating, mirror

coating, decorative coatings, permeation barrier film on flexible packaging materials,

electrically conducting films, wear resistant coatings, and corrosion protective

coatings.

B. Sputter deposition

Sputter deposition is the deposition of particles vapourized from a surface

(“target”), by the physical sputtering process. Physical sputtering is a non-thermal

vapourization process where surface atoms are physically ejected from a solid surface

by momentum transfer from an atomic sized energetic bombarding particles which is

usually a gaseous ion accelerated from a plasma. This PVD process is sometimes just

called sputtering i.e. “Sputtered films of –” which is an improper term in that the film

is not being sputtered. Generally the source-to-substrate distance is short compared to

vacuum deposition. Sputter deposition can be performed by energetic ion

bombardment of a solid surface (sputtering target) in vacuum using an ion gun or low

pressure plasma (<5 m Torr) where the sputtered particles suffer few or no gas phase

35 | P a g e

collisions in the space between the target and the substrate. Sputtering can also be

done in a higher plasma pressure (5-30 m Torr) where energetic particles sputtered or

reflected from the sputtering target are “thermalized” by gas phase collisions before

they reach the substrate surface. The plasma used in sputtering can be confined near

the sputtering surface or may fill the region between the source and the substrate. The

sputtering source can be an element, alloy mixture, or a compound and the material is

vapourized with the bulk composition of the target. The sputtering target provides a

long lived vapourization source that can be mounted so as to vapourize in any

direction. Compound materials such as titanium nitride (TiN) and zirconium nitride

(ZrN) are commonly reactively sputter deposited by using a reactive gas in the

plasma. The presence of the plasma “activities” the reactive gas (“plasma activation”)

making it more chemically reactive.

Sputter deposition is widely used to deposit thin film metallization on

semiconductor material, coatings on architectural glass, reflective coatings on

compact discs, magnetic films, dry film lubricants and decorative coatings.

C. ARC vapour deposition

Arc vapour deposition uses a high current, low-voltage arc to vapourize a

cathodic electrode (cathodic arc) on anodic electrode (anodic arc) and deposit the

vapourized material on a substrate. The vapourized material is highly ionized and

usually the substrate is biased so as to accelerate the ions (“film ions”) to the substrate

surface.

D. Ion plating

Ion plating which is sometimes called Ion Assisted Deposition (IAD) or Ion

Vapour Deposition (IVD) utilizes concurrent or periodic bombardment of the

depositing film by atomic-sized energetic particles, to modify and control the

properties of the depositing film. In ion plating the energy, flux and mass of the

bombarding species along with the ratio of bombarding particles are important

processing variables. The deposition material may be vapourized either by

evaporation, sputtering, arc erosion or by decomposition of a chemical vapour

precursor. The energetic particles used for bombardment are usually ions of an inert

36 | P a g e

or reactive gas, or, in some cases, ions of the condensing film material (“film ions”).

Ion plating can be done in a plasma environment where ions for bombardment are

extracted from the plasma or it may be done in a vacuum environment where ions for

bombardment are formed in a separate “ion gun”. The latter ion plating configuration

is often called Ion Beam Assisted Deposition (IBAD). By using a reactive gas in the

plasma, films of compound materials can be deposited. Ion plating can provide dense

coatings at relatively high gas pressures where gas scattering can enhance surface

coverage. Ion plating is used to deposit hard coating of compound materials, adherent

metal coatings, optical coating with high densities, and conformal coatings on

complex surfaces.

2.1.2 Chemical Vapour Deposition

Chemical vapour deposition (CVD) processes are widely used in industry due

to their versatility for depositing a very large variety of elements and compounds

covering a wide range from amorphous deposits to epitaxial layers having high degree

of perfection and purity.

CVD can be defined as a process in which the gaseous chemical reactants are

transported to the reaction chamber, activated thermally (conventional CVD) or by

other than thermal means (plasma assisted CVD or laser induced CVD), in the

vicinity of the substrate, and made to react to form a solid deposit on the substrate

surface. It is possible to deposit films of uniform thickness and low porosity even on

substrates of complicated shape in this process.

A major area for utility of CVD is in microelectronics applications, such as

gate insulating layers, passivation layers, oxidation barrier, polycrystalline silicon, etc.

CVD techniques are also extensively employed for protective coating for a variety of

operating environments where, for example, protection is required against wear,

erosion, and high temperature oxidation [7]. CVD has numerous other names and

adjectives associated with it such as Vapour Phase Epitaxy (VPE) when CVD is used

to deposit single crystal films, Metal-organic CVD (MOCVD) when the precursor gas

is a metal-organic species, Plasma Enhanced CVD (PECVD) when a plasma is used

to induce or enhance decomposition and reaction, and Low Pressure CVD (LPCVD)

when the pressure is less than ambient.

37 | P a g e

Plasmas can be used in CVD reactors to activate and partially decompose the

precursor species. This allows deposition at a temperature lower than thermal CVD

and the process is called plasma-enhanced CVD (PECVD) or plasma-assisted CVD

(PACVD) [8,9]. The plasmas are typically generated by radio-frequency techniques.

At low pressures, concurrent energetic particle bombardment during deposition can

affect the properties of films deposited by PECVD [10].

Plasma based CVD are also used to deposit polymer film (Plasma

polymerization) [11]. In this case the precursor vapour is a monomer that becomes

cross linked in the plasma and on the surface to form an organic or inorganic polymer

film. These films have very low porosity and excellent surface coverage. When

plasma depositing films from organo-silane precursors, oxygen can be added to the

plasma to oxidize more or less of the silicon in the film [12].

2.1.3 Electroplating, Electroless Plating and Displacement Plating

Electroplating is the deposition on the cathode of metallic ions from the

electrolyte of an electrolysis cell [13, 14]. Only about 10 elements (Cr, Ni, Zn, Sn, In,

Ag, Cd, Au, Pb, and Rh) are commercially deposited from aqueous solutions. Some

alloy composition such as Cu-Zn, Cu-Sn, Pb-Sn, Au-Co, Sn-Ni, Ni-Fe, Ni-P and Co-P

are commercially deposited, Conductive oxides such as PbO2 and Cr2O3 can also be

deposited by electroplating. A thin film of material deposited by electroplating is

often called a “flash” and is on the order of 40 thousandths of an inch thick. Typically,

the anode of the electrolytic cell is of the material to be deposited and is consumed in

the deposition process. In some cases, the anode material is not consumed and the

material to be deposited comes only from solution. For example, lead oxide, PbO2 can

be electrodeposited from a lead nitrate plating bath using carbon anodes. Stainless

steel and platinum are also often used as non consumable anode materials.

In electroless or autocatalytic plating no external voltage/current source is

required. The voltage/current is supplied by the chemical reduction of an agent at the

deposit surface. The reduction reaction is catalyzed by a material, which is often

boron or phosphorous. Materials that are commonly deposited by electroless

deposition are Ni, Cu, Au, Pd, Pt, Ag, Co and Ni-Fe alloys. Displacement plating is

the deposition of ions in solution on a surface and results from the difference in

38 | P a g e

electro negativity of the surface and the ions. Electrophoresis is the migration of

charged particles in an electric field. Electrophoretic deposition, or electrocoating, is

the electro deposition of large charged particles from a solution [15,16]. The particles

may be charged dielectric particles (glass particles, organic molecules, paint globules,

etc.) which are non soluble in the aqueous electrolyte. Alternatively some of the

components can be treated so that they are soluble in water but will chemically react

in the vicinity of an electrode and their solubility is decreased. Particles are usually

deposited on the anode but sometimes on the cathode.

2.1.4 Films from Polymer Solution

The techniques of film formation described above are not expected to give

useful films for research purposes. Further, the polymer films formed by these

techniques may have different degree of polymerisation and may contain undesired

impurities." Polymer films formed by vacuum deposition technique are also not quite

useful as these have pin holes. Films of doped polymer cannot be obtained by above

mentioned methods since it is difficult to control the quality of dopant both during

evaporation as well as during polymerisation. Film with uniform degree of

polymerisation and high purity can be prepared from polymer solution using highly

pure polymer as solute and inert solvents of AR grade. The doping percentage can be

controlled easily by dissolving known amount of dopant in the solution.

There are two main methods available for preparing thin films from polymer

solution:

A. Isothermal immersion technique

Solution of suitable concentration is kept at a desired temperature and

substrate is immersed into it vertically for a given period of time depending upon the

required film thickness. When the film is deposited, the substrate is slowly taken out

and dried by hot air. The deposited film is then gently detached using a sharp knife

edge [17]. Doped films can also be prepared using desired quantity of dopant in

solution. Rastogi and Chopra [18] found that the thickness of film depends upon

concentration of the solution, its temperature, nature of the substrate, and the time for

which the substrate is kept immersed in the solution. This method requires a great

39 | P a g e

care in selecting the temperature and concentration of the solution. Also, sophisticated

mechanical instrumentation is required for taking out the substrate from the solution

and keeping them exactly vertical to the solution surface. Lack of proper

instrumentation and precautions may result into the films containing air bubbles and

nonuniform thickness.

B. Casting from the solution

Polymer solution of known concentration and quantity is spread over plane

clear glass plate of known surface area which is made to float in a mercury pool.

Solvent is allowed to evaporate at a suitable constant temperature and the resulting

film is gently detached from the substrate. Films of different thickness may be

obtained using solution of different concentrations [19]. The films obtained by this

technique are of uniform thickness and perfectly plane. Also, an elaborate cleaning

procedure must be adopted for substrate in order to eliminate any possible impurity

and deformation.

In the present investigation, plane glass plates were used as substrate for

deposition of polymer films. The glass plates were cleaned carefully by acid, water

and finally in soap water. Subsequently, these were rinsed in the distilled water. The

cleaned substrates were then dried up in hot air.

2.2 PREPARATION OF PURE PVA, PALM LEAF POWDER AND THEIR

POLYMER BIOCOMPOSITE FILM SAMPLES

The 98% acetalized Poly vinyl alcohol (PVA) with molecular weight of 1400

was procured from M/S Chemical Industries, Mumbai, India and used without further

purification. The Alexander Palm leaf has been obtained from Jawaharlal Nehru

Agriculture University, Jabalpur, M.P., India. The obtained green leaves were made to

dry at room temperature, after that these were grinded and fine powder of palm leaves

was obtained for further use. This powder was stored in to desiccators to avoid the

effect of moisture and other environmental fluctuations/conditions.

The PVA-Palm leaf films of following weight percentage were prepared for the

present investigation:

40 | P a g e

(i) Pure PVA (0.0 wt%PL+PVA)

(ii) 5 wt% Palm Leaf Powder+PVA (5%PL+PVA)

(iii) 10 wt% Palm Leaf Powder+PVA (10%PL+PVA)

(iv) 15 wt% Palm Leaf Powder+PVA (15%PL+PVA)

(v) 20 wt% Palm Leaf Powder+PVA (20%PL+PVA)

For this pure PVA and Palm leaf powder were weighed for their desired ratio.

These were then mixed and dissolved in deionized water. This solution was stirred at

40°C in a magnetic stirrer for a minimum time of four hours. Thereafter, the

homogeneous solution thus obtained was poured over the glass plates floating in the

mercury pools kept inside the oven. The oven temperature was maintained between

40-50 oC. Great care was taken to avoid air bubbles during the settling of polymer

solution over the plates. After the film was formed the glass plates were taken out

carefully. Pure PVA polymer film and Palm leaf powder reinforced biocomposite

films of about 50 to 250 µm in thickness were prepared by this solvent cast technique

for various characterizations. The films were preserved in desicator so that these are

not damaged.

2.3 MEASUREMENT OF FILM THICKNESS

The thickness of a thin film is its most important characteristic feature and

thickness measurements are therefore of primary importance in any thin film

investigation. Various film thickness measurement techniques have been developed

over the years. Out of which some are listed below. Each method has its limitations

and may not be suitable for routine measurements. A qualitative description and

associated limitations of the following class of techniques is given here:

(i) Mechanical methods

(ii) Optical methods

(iii) Electrical methods

2.3.1 Mechanical Methods

This includes three important methods namely stylus method, weighing

method and micrometer gauge method.

41 | P a g e

A. Stylus method

A diamond tip is moved along the film surface while its vertical displacement

is electronically enlarged by a factor of 106 and recorded. From the film edge the

thickness is found directly as the step height detected by the stylus [20, 21].

B. Weighing method

This method depends on the increase of the weight of a film due to its mass

increase and from the knowledge of its density and the deposited area; film thickness

(d or t) can be evaluated form the relation

2.1

where W is the weight difference of the film, is its density and A is the

deposited area. The increase in the film weight can be measured by a suitable

microbalance [22, 23]

C. Micrometer gauge method

This technique allows a direct thickness measurement. The film surfaces are

never ideally flat; the thickness is usually specified as a mean thickness. This concept

allows one to define an average thickness for even a discontinuous film. In this

method of measurement of the film thickness a micrometer is used. Generally, a

number of observations are taken and they are averaged to find out the exact

thickness. During the present investigation, the author has used this method for

determining the thickness of the film. A highly accurate micrometer screw gauge with

the least count 0.001mm, manufactured by M/S Mitutoys Mfg. Co. Ltd., Japan, was

used.

2.3.2 Optical Methods

Optical techniques for film thickness determinations are widely used for a

number of reasons. They are applicable to both opaque and transparent films, yielding

thickness values of generally high accuracy. In addition, measurements are quickly

performed, frequently nondestructive, and utilize inexpensive equipment.

42 | P a g e

A. Photometric method

This method depends on the change in the transmittance of light at normal

incidence with the increase of film thickness as given by the Lambert law

2.2

where is the absorption coefficient and t is the film thickness. I and Io are

respectively, the intensity of transmittance and incident monochromatic light. A

transmittance (T = I/Io) versus film thickness graph on a semi-log scale will be a

straight line. Thus it is possible to correlate film thickness with transmittance. This

technique can be used for absorbing as well as semi-absorbing films provided the

deposition parameters have no effect on the transmittance of the films. However, in

many cases it is not so and hence this technique is not suitable except for a few cases.

For transparent films is 0 or negligible and hence this method is not applicable.

B. Ellipsometric method

Ellipsometry is a commonly used non-destructive technique to characterize

thin films [24, 25] Ellipsometry is a very powerful and accurate optical method to

measure the thickness of thin films. This technique involves the use of a polarized

light for reflection from a film on a substrate at a non-normal incidence but preferably

at an angle of incidence of 45o. A reflection from an absorbing film will cause a

change both in the relative amplitude of the two perpendicular components of the

reflection viz. parallel to the plane of incidence and perpendicular to the plane of

incidence, leading to an elliptically polarized light. An ellipsometer is an instrument

by the different parameters of the elliptically polarized reflected beam can be

measured and from these data film thickness can be evaluated. In this method a

complicated mathematical analysis is required and therefore is not generally used

[26].

C. Interferometry

Film thickness can be measured using interferometry [27]. It can also be

measured accurately from interference fringes using multiple beam interferometry

[28] and also from the fringes of equal chromatic order (FECO) techniques. In the

43 | P a g e

former case two reflecting surfaces are brought in close proximity such that a small

wedge with a small air gap in between them is formed. If a monochromatic light is

now incident on them at normal incidence, then an interference of light due to

interactions of multiple reflected beams in air gap will take place resulting in a series

of fringes which can be observed in the back reflected light. The distance between the

fringes or lines depends on the air gap as well as one the wave length of the

monochromatic light. This principle is adopted and suitably modified for the multiple

beam interferometric method of the measurement of film thickness [29]. After

obtaining a set of sharp fringes, the thickness (t) can be determined uing the relation

/2 2.3

Where b is the displacement of the fringes at the step and a is the distance between

consecutive fringes. The fringe displacements which are in the form of parallel lines,

however, occur at the film edge.

D. Light sectioning method

A device known as a light-section microscope (Carl Zeiss, Oberkochen,

Germany) is available which non-destructively measure the thickness of transparent

films allowing the determination of film thickness at selected regions on substrate

surfaces. It allows analysis of the variation in film thickness and an estimate of

surface roughness without physical contact with the surface [30].

An incandescent lamp of variable brightness illuminates a slit which projects a

narrow band of light through an objective at an angle of 45o to the plane of the surface

being measured. Some of the light is reflected from the surface of film; the remainder

penetrates the film and is reflected from the surface of substrate or core. In the

eyepiece of the microscope at the opposite 45o angle, the profiles of the film and

substrate or core can be seen coincidently as a series of peaks and troughs after the

band of light has been reflected/refracted at the sample. A cross-line graticule in the

eyepiece can be moved within the field of view by means of a graduated measuring

drum. The required distance values can then be read off with the drum with a

sensitivity of 0.1 µm over longitudinal or transversal movements of upto 25mm. For

44 | P a g e

measurement of film thickness, this technique is restricted therefore to transparent

films.

E. Other methods

There are several other methods which are less universal and can be used for

some specific cases and some of them are eminently suitable for mass or routine

productions. In some of them the basic assumption is that the film properties such as

resistance, capacitance, hall voltage, etc. are dependent only on the film thickness, but

not on deposition conditions. Such a criterion may be satisfied only in routine of mass

production cases where a standard procedure is adopted. Since film properties are

dependent also on the deposition parameters the methods depending on the above

properties are used in specific cases only and for restricted thickness range.

Film thickness can also be estimated from its absorption property of radiation

such as light, X-rays, -ray, -rays, electron beam etc. and the absorption is generally

an exponential function of the film thickness. Absorption of X-rays, and -rays by a

material takes place when these are allowed to pass through it. This property is then

used for the determination of the thickness of the material and can be used say

between about 100 Å to about 1 mm of thickness. High velocity electron beam say

between 50 kV to 100 kV can be used for measuring film thickness of about a few

thousand Å. In the later method electron absorption is measured when the Bragg

reflection is absent. The back scattering of and -rays by a material, X-rays

fluorescence, electron microprobe methods etc. are also used for measuring film

thickness, though some of these are not straight forward and involve the measurement

of the mass of the material.

2.3.3 Electrical Method

In this method vacuum evaporated electrodes are deposited on both the

surfaces of the film specimen and the capacitance of the film condenser so formed is

measured using a sensitive LCR bridge [31]. If the high frequency dielectric constant,

area of the metallic electrodes, etc. are known then the thickness of the sample can be

very accurately known provided the film is of uniform thickness with no pin holes.

This method, therefore, is the most suitable for solution grown samples.

45 | P a g e

2.4 ELECTRODES (Types of Contacts)

The polymer electrode contact plays an important role in all electrical

measurements [31, 32]. The shape of energy band near dielectric electrode interface

decides which one of the three categories of contacts is at work. When energy band is

completely horizontal, it is called a neutral contact; if a band bends downwards

helping in injection of carriers of the opposite sign then the electrode is an ohmic

electrode; when the energy band bends upwards hindering the injection and

neutralisation of charges, the contact made is called a blocking contact.

Following four types of electrodes can be used for making electrical contacts

with polymer films for the purpose of studying the charging and discharging

phenomena:

(a) Painted electrodes,

(b) Liquid contact electrodes,

(c) Vacuum deposited electrodes, and

(d) Pressed metal foil electrodes.

2.4.1 Painted Electrodes

Conducting material paste can be used for painting the polymer film and can

be used as the electrodes. Such materials are graphite, silver and epoxy paints.

However, such paints may react with the polymer and can damage it also. Therefore,

use of such painted electrodes is restricted to only those polymers which do not react

with these.

2.4.2 Liquid Contact Electrodes

In this, non-metallised surface of a unilaterally metallised film specimen is

kept in contact with a liquid, such as water or ethyl alcohol so that a thin uniform

layer of liquid rests over the film surface. A potential is applied between the metallic

electrode and rear unmetallised surface of the film. A double charge layer is formed at

the solid-liquid interface and as a result of interaction between electrostatic and

molecular forces; charge transfer to polymer film takes place. Electrode should be

withdrawn and liquid evaporated before removal of the voltage to ensure charge

46 | P a g e

retention on the specimen surfaces.

2.4.3 Vacuum Deposited Electrodes

This is probably one of the best and most convenient methods of depositing

metallic electrodes of desired sizes and shapes. Metal can be evaporated in vacuum on

any metallic or nonmetallic substrate of the film specimen under study. No air gap

exists between the evaporated electrodes and the substrate. The electrodes so obtained

can be very conveniently used for measurements at low as well as high temperatures

provided the melting point of electrode metal is higher than the temperature of

measurements.

2.4.4 Pressed Metal Foil Electrodes

In this, polymer film is sandwiched between two plane metallic foil electrodes

of the desired shape and area. Springs are used to ensure uniform pressure throughout

the film for proper contacts. However, in case of polymers, following precautions

need to be taken:

(a) Measurements at high temperatures should not be carried out. At high

temperatures, the polymer is softened. Due to the pressure of the spring loaded

electrodes on the film, its thickness is reduced and sometimes it results in the

breakdown of the film.

(b) Metallic surface of the foil needs to be cleaned or else the foil electrode should

be changed.

2.5 CHARACTERIZATION METHODS FOR BIOCOMPOSITE POLYMER

FILMS

The operation and use of principal experimental equipments and techniques

used for investigation of biocomposite polymer films have been discussed in this

chapter. This has been detailed out under the following sections:

1. Microhardness Measurements.

2. Tensile Characterization

3. Fourier Transform Infrared Spectroscopy

47 | P a g e

4. Differential Scanning Calorimetry

5. X-ray Diffraction Analys

6. Atomic Force Microscopy

7. Thermally Stimulated Discharge Current

2.6 DIFFERENTIAL SCANNING CALORIMETRY

Differential scanning calorimetry measures the amount of energy (heat)

absorbed or released by a specimen as it is heated, cooled or held at a constant

temperature. It is a thermal technique that measures the energy absorbed or emitted by

a specimen as a function of temperature or time. When thermal transition occurs in

the specimen, DSC provides a direct calorimetric measurement of the transition

energy at the temperature of transition. It is often used to characterize the thermal

transitions in polymers such as glass transition temperature and melting point.

Organic liquids or solids, and inorganics can also be analyzed. Thus it can be

successfully applied to transformations both physical and chemical in polymers. It can

be used for a wide variety of applications, including biocomposite polymer, organic

and inorganic analysis to measure.

Glass transition temperature

Heat of crystallization and fusion

Degree of cure of thermoset

Heat of curing reactions

Oxidative stability

Heat of decomposition (dehydration)

Identification of phase transformation

Experimentally, in DSC, the thermal properties of a specimen are compared

against a standard reference material which has no transition in the temperature range.

A plot of the difference in energy supplied to the specimen against the temperature, as

the latter is slowly increased, through one or more thermal transitions of the specimen

yields important information about the transition, such as latent heat or a relatively

abrupt change in heat capacity.

In p

were recor

temperature

100C/min a

F

2.7 X-RA

X-ra

crystallite

crystalline

and electro

properties

analytical c

probe have

quantitative

played a lea

The

from the cr

present stud

rded on DS

e range of

at Consortiu

Fig. 2.3 DS

AY DIFFRA

ay diffracti

size, orien

polymers [3

onic structu

of thin film

characteriza

e dominated

e and nond

ading role, a

e phenomen

rystallograph

dy the DSC

SC 2910 In

550C – 22

um for Scien

SC 2910 Ins

ACTION A

ion data fo

ntation of

33]. The str

ure of thin

m materials

ation techni

d the field m

destructive

as a fundam

na of X-ray

hic planes o

C thermogr

nstrument

200C under

ntific Resea

strument fr

ANALYSIS

or polymer

the crystal

rong relation

n film micr

has led to

iques for th

mainly bec

nature. Of

mental tool f

diffraction

of the mater

ams of pre

from TA I

N2 atmosp

arch, Indore

rom TA In

provide in

llites, and

nship of phy

ro and nan

o developme

hin films. Th

ause of the

these tech

for material

can be con

rial and is g

epared bioco

Instrument

phere and a

.

strument I

nformation

phase com

ysical, chem

nomaterials

ent of large

he techniqu

eir simplicit

hniques, X-r

characteriz

nsidered as

overned by

48

omposite p

Inc., USA

at a heating

Inc., USA

about cryst

mposition in

mical, meta

with the p

e number o

ues based o

ty, more rel

ray diffract

zation.

reflection o

y Bragg’s eq

| P a g e

polymers

, in the

g rate of

tallinity,

n semi-

llurgical

physical

of micro

on X-ray

liability,

tion has

of X-ray

quation,

where is

diffraction

Fig. 2.4.

The

and mecha

biocomposi

intense diff

where, K v

wavelength

of the peak

In th

Advanced

minute. The

the wavele

angle and n

e grain size

anical prop

ite is estima

fraction line

varies from

h of X-ray u

k, and is th

he present s

X-ray Diff

e Bruker D8

2

ength of inc

n is the orde

Fig. 2.4

of the film

perties of

ated from th

e by Scherre

0.89 to 1.3

used ( = 1.5

he Bragg’s a

study the X

fractometer

8 Advanced

cident X-ra

er of diffrac

4 Schemati

m co-relates

materials.

he full widt

er’s equatio

39, in prese

54056Å),

angle of the

X-ray diffrac

for 2=10

d X-ray Diff

ay, d is the

tion. Schem

ic view of X

s the depen

The crys

th at half m

n as follow

ent case we

is full wid

e X-ray diffr

ction has be

00 to 500 w

ffractometer

inter-plana

matic view o

XRD.

ndence of s

stallite size

maximum (FW

s [34]:

have taken

th in radian

raction peak

een carried o

with scannin

r is shown in

49

ar distance,

of XRD is s

structural, e

e of the p

WHM) of t

n K as 0.9.

ns at half m

k.

out with Br

ng rate of

n Fig. 2.5.

| P a g e

2.4

is the

shown in

electrical

polymer

the most

2.5

is the

maximum

ruker D8

0.20 per

2.8 FOUR

Infr

study of th

sensitive w

inexpensive

The

develop an

spectra is

mode, of p

samples wa

recorded o

Fig. 2.5

RIER TRA

rared spectr

he polymer

with samplin

e and opera

e FTIR spec

n understan

dependent

pure poly v

as taken in

on Perkin-E

5 Bruker D

ANSFORM

oscopy is o

, composite

ng technique

ation of the e

ctrograph o

nding of co

on sample

inyl alcoho

the frequen

Elmer Spect

D8 Advance

INFRARE

one of the m

e, and bioc

es that are

equipment i

of biocompo

omposition

preparation

ol (PVA), p

ncy range 4

trum BX I

ed X-ray D

ED SPECTR

most often u

composites.

easy to use

is simple[35

osite sampl

of the bioc

n. The FTI

palm leaf po

4400-400 cm

R spectrop

Diffractome

ROSCOPY

used spectro

The IR m

e. Also, the

5].

les has been

composite.

IR spectrum

owder and

m-1. The inf

photometer,

50

eter.

Y

oscopic too

method is ra

e instrumen

n taken in

The qualit

m, in transm

their bioco

frared spect

USA. The

| P a g e

l for the

apid and

ntation is

order to

ty of IR

mittance

omposite

tra were

e Perkin

Elmer Instr

2.9 ELEC

The

more than

morphology

images, ma

million tim

Some instru

but prepara

modern mic

adding to th

Apa

generally d

multiphase

study at hig

to see fine

rument is sh

Fig. 2.6 T

CTRON MI

e structure a

60 years

y of object

agnified fro

mes in a mic

uments giv

ation metho

croscopes a

he structura

art from thi

determines w

polymer m

gher resolut

e details on

hown in Fig

The Perkin-

ICROSCO

and morpho

[36]. Mi

s with the

om a few tim

croscopes th

e informati

ods can cre

are integrate

al image.

is, the size

which instru

may require

tion using e

n the fract

g. 2.6.

-Elmer FT

OPY

ology of po

icroscopy i

use of a m

mes in an o

hat can reso

ion about th

ate an inter

ed with syst

e and visibi

uments are t

a light-opt

electron mic

ture surface

IR Spectro

lymers hav

is the stud

microscope.

optical stere

olve individ

he surface a

rnal surface

tems that gi

ility of the

to be used.

tical techniq

croscopy an

e. Combina

oscopy Instr

e been und

dy of the

Microscop

eo microsco

dual atoms i

and not the

e that may

ve local che

structure t

For examp

que for the

nd scanning

ations of v

51

rument

der investiga

fine struct

pes form m

ope to mor

in suitable s

e specimen

be imaged

emical infor

to be chara

ple, the fract

"big pictur

g probe micr

various mic

| P a g e

ation for

ure and

magnified

e than a

samples.

interior,

. Many

rmation,

acterized

ture of a

re" but a

roscopy,

croscopy

52 | P a g e

techniques generally provide the best insight into the morphology of polymer

materials [37].

In the present study the Scanning electron microscopy and atomic force

microscopy have been utilized to develop the understanding of surface structure of

biocomposite polymer. The brief descriptions of above microscopies are given in

following paragraphs.

2.9.1 Atomic Force Microscopy

Atomic force microscopy, also referred to as scanning force microscopy, is

obviously not a technique based on electron microscopy. However, it has been

widespread practiced in the last few years to supplement electron microscopy with

atomic force microscopy, as the latter enables the straightforward surface

characterization of polymers and provides supplementary insight into the structure

and properties of homopolymers, blends and composites [38]. The surface

topography of prepared biocomposite polymer samples was determined using an

Atomic Force Microscope (AFM) Nanoscope II from the Digital Instrument; in the

contact mode and analysis was carried out using software (Version 2.2) available with

the AFM at consortium for scientific research, Indore.

2.10 MICROHARDNESS MEASUREMENTS

The search for quantitative structure-property relationships for the control and

prediction of the mechanical behaviour of polymers and biocomposite has occupied a

central role in the development of polymer science and engineering. Mechanical

performance factors such as creep resistance, fatigue life, toughness and the stability

of properties with time, stress and temperature have become subjects of major

activity. Within this context microhardness emerges as a property which is sensitive

to structural changes.The most important hardness test has two variants: (i) the nature

of indenter, and (ii) the load applied.

The methods most widely used in determining the hardness of metals are the

static indentation methods. These involve the formation of a permanent indentation on

the surface of the material under examination, the hardness being determined by the

load and the size of the indentation formed.In the Brinell test [39] the indenter

53 | P a g e

consists of a hard steel ball, though in examining very hard metals the spherical

indenter may be made of tungsten carbide or even of diamond.Another type of

indenter which has been widely used is the conical or pyramidal indenter as used in

the Ludwik [40] and Vickers [41] hardness tests, respectively. These indenters are

now usually made of diamond. The hardness behaviour is different from that observed

with spherical indenters. In the present investigation, Vickers Diamond Pyramid

Indenter has been used for the determination of hardness. This method is, therefore,

discussed in detail in the following section.

2.10.1 Vicker's Test

Vicker's tester was introduced by Smith and Sandland in 1925. The test given

by them is an ideal method which can be used for research and laboratory work [41].

The advantage of the method is that it can be used for thin and superficially hardened

materials for which other methods are not suitable in comparison to this method.

Diamond in the form of square based pyramid, makes the Vickers indenter.

Like the Brinell test the (Fig. 2.9) hardness number is derived from the relationship

between the applied load and the surface area of the indentation. A pyramid has the

advantage that similar geometrical impressions are obtained at different applied loads.

As the ideal and most desirable ratio of indentation diameter to the ball

diameter in Brinell test was 0.375. Smith and Sandland chose 136° for the included

angle between diamond pyramid faces. Fig. 2.7 illustrates the most desirable ball

impression of 0.375 D. If the tangents are drawn at the point of contacts at the ends of

such an impression diameter, the included angle comes out to be 136°. Fig. 2.8 shows

the shape of such a diamond pyramid indenter.

In Vicker's test the indenter is pressed into the material under observation for a

specific period. The applied load may be 5 g to 160 g, which is selected according to

the thickness and the hardness of the specimen. When the applied load is removed the

impression produced is of the form as shown in Fig 2.8.

By

the resultin

often design

whe

means of m

ng impressi

nated as Hv

ere,

L = loa

d = Me

Fig. 2.7 B

Fig. 2.8 V

micrometer e

ion is meas

v which is gi

d in kilogra

an diagonal

(Ve

Ball Impress

Vicker’s Pyr

eye piece, t

sured. The

iven by

am.

l of the imp

ertical + Hor

sion for ide

ramidal In

the average

Diamond

ression in m

rizontal dia

eal ball

denter

length of th

Pyramid H

mm

gonal) / 2.

54

he two diag

Hardness nu

| P a g e

gonals of

umber is

2.6

55 | P a g e

= angle between the opposite faces of the diamond (136°).

Hence, the Vicker's hardness number,

H2LSin68

d

H.

2.7

In the present investigation specimens of biocomposite polymer, 1cm x 1 cm

in size prepared from the films were characterized with Carl-Zeiss Universal Research

Microscope NU-2. The universal research microscope NU–2 is a reflection type

microscope. It can also be used as a reflection phase contrast microscope, multiple

beam interference equipment and mhp – 160 microhardness tester. The same surface

can be observed in transmitted, incident and polarized light. The field of view can be

dark as well as in phase contrast. The important specification of the microhardness

tester is as below:

Model - Carl Zeiss NU-2 universal research microscope

Microhardness - mhp – 160 microhardness tester

Load Range - 5-160g

Light Source - Xenon lamp

Indenter - Vicker’s diamond pyramid indenter

Fig. 2.9 C

16

2.11 TENS

The

load carried

Universal T

data can be

The

specificatio

Carl Zeiss N

60 microha

SILE CHAR

e tensile tes

d by the spe

Testing Ma

e translated i

e tensile test

ons:

NU-2 univer

ardness test

RACTERI

ting is perf

ecimen. Thi

achine. Usin

into a stress

t was carrie

rsal resear

ter

IZATION

formed by e

is is done u

ng the spec

s strain curv

ed out with

rch microsc

elongating a

using a test

cimen dimen

ve [42].

Instron 336

cope attach

a specimen

machine kn

nsion, the l

69 (UTM). I

56

hed with mh

and measu

nown as the

load and de

It has the fo

| P a g e

hp –

uring the

e Instron

eflection

ollowing

Instron 33

Load cell c

Maximum

Speed rang

Height

Width

Depth

Fi

2.12 TH

In t

necessary e

current me

accurate m

voltage uni

were used a

69

apacity

force

ge

g. 2.10 Ins

ERMALLY

this section

equipments

easurement.

measuremen

it, Keithley

at various p

stron 3369-

Y STIMUL

we describ

used for ele

Sample ho

nt with eas

y electrome

laces depen

S

5

2

0

7

7

- Instrumen

LATED DI

be the detai

ectrical mea

older has b

se. Other i

eter (Type-6

nding upon

Specificatio

50 kN (112

25 kn (at m

0.005 to 500

1582 mm

756 mm

707 mm

nt for Tens

SCHARGE

ils of circui

asurements

been specia

instrument,

610C) and

the experim

on

50 lb)

aximum spe

0 mm/min

ile Charact

E CURREN

try, instrum

. Fig. 2.11 s

ally designe

e.g. electr

temperatur

mental requir

57

eed)

terisation.

NT

mentation an

shows the s

ed for carry

ric amplifie

re programm

irements.

| P a g e

nd other

setup for

ying out

er, high

mer etc.

58 | P a g e

2.12.1 Sample Holder Arrangement

To obtain reliable result in accurate measurement of current, the specimen

must be kept in the sample holder, which is dry, rigid and well shielded from spurious

current. A good sample holder has high insulation resistance, possesses freedom from

spurious voltage, induced charges, microphonics, and has no leakage of current.

Rigidity is required to avoid picking up of undesired induction.

In the present investigation, the insulators of high resistivity were used as test

specimen. In almost all the studies, high values of voltage and low values of currents

were involved. During the measurement of very low current produced due to high

voltage drop across a high resistance, insulation of the leads, fixture and voltmeter

must be several orders of magnitude greater than the resistance of the specimen. In the

absence of such insulation the current will start flowing through leads and other less

insulating parts. Keeping this in mind, best insulating material Teflon – FEP was used

wherever the insulation was required. Teflon-FEP has a very high volume resistivity

and a surface on which water/moisture film is not readily formed. Its insulation

properties remain unaffected by humidity of the air, perspiration and finger oil due to

normal manual handling. It is chemically inert to various organic solvents and can be

cleaned by many liquids and also can be machined in the desired shape. This is

possible because of its excellent mechanical and thermal properties. However, to

avoid surface conduction through the deposited dust, solid flux and oil or water film

on the surface, attention was constantly paid for keeping the insulation clean and dry.

Methyl alcohol or benzene was used for cleaning purpose.

Spurious voltage is always expected to affect the system performance in high

resistance circuits. This may be caused either due to internal electrical disturbances or

due to the internal induced signals. Line disturbances were avoided using highly

stabilized voltage to drive electrical instruments and the induced signals were avoided

using electrostatic shielding. To achieve this, all leads were surrounded by grounded

conducting surfaces and the high resistance circuit was enclosed in a shielded

aluminum enclosure inside the oven.

In any high resistance circuitry, physical motion of the system, may distort the

result in the following ways:

59 | P a g e

(a) If the coaxial cables are moved during the measurements, friction between the

braid and the insulator surrounding the central conductor or piezoelectric effect

in insulator may develop voltage across the electrometer input, thus distorting

the result. This can greatly be minimized by using “low noise cables” type RC

58 A/u. In these cables the surface under the shielded braid is coated with

graphite powder to provide a conducting equi-potential cylinder around the

insulator and conducting path for any charge that is generated.

(b) The movements of coaxial cables may also change the capacitance between the

shield and input lead, as a small charge is always present in this capacitance.

This change in capacitance ΔC may produce a voltage change ΔV, where,

ΔV = Q/ΔC 2.8

which should be seen by the electrometer. Rigid connection and firm

mechanical support to the flexible cables were found to be necessary to

minimise these effects.

2.12.2 Other Equipments Used

Important specifications of other equipments used during the electrical

investigations are given as:

(a) Electric amplifier

Model EA – 815

Manufacturer Electronic Corporation of India Limited Hyderabad.

Current range 10-5 to 10-14 amperes (full scale for both polarities )

Accuracy 3%

Voltage range 10 m V to 10 V (full scale for both polarities)

Input impedance More than 1014 ohms in open position of input impedance switch (voltage measurements)

60 | P a g e

(b) High voltage unit

Model Type 4800B

Manufacturer Electronic corporation of India Limited, Hyderabad.

Output voltage 50 to 3000 Volt (On both polarities).

(c) Keithley electrometer

Model Type 610C

Manufacturer Keithley Instruments, Inc. Cleveland. Ohio, USA

Range Current 10-14 to 0.3 amperes.

Accuracy +2% of full scale on 0.3 to 10-14 ampere ranges. + 4% of full scale on 10-12 to 10-4 ampere range.

Input impedance

More than 1014 ohms shunted by Pico farads (input impedance selectable in steps from 10 to 1011 ohms)

(d) Temperature programmer

Model Cole Parmer Model No.5C 6010 S.

Manufacturer Valley Forge Instruments Co.Inc. Phoenixville Pa.U.S.A.

Temperature range

0º to 400ºC

Rate of temperature rise

1º to 10º C/min. (adjustable).

61

Fig

2.1

1

Inst

rum

ent

for

Cu

rren

t M

easu

rem

ent

| P a g e

g

62 | P a g e

2.13 References:

[1] Braun Dietrich, CherdronHarald, Rehahn Matthias, Ritter H., Polymer

synthesis: theory and practice : fundamentals, methods, experiments, Springer

Berlin Heidelberg New York, 2005.

[2] KorotcenkovGhenadii, Chemical Sensors: Volume 1 General Approaches,

Momentum Press, New York, 2010.

[3] Glocker, D. A. and Shah, S. I. (Eds.), Handbook of Thin Film Process

Technology, Institute of Physics Publishing, Bristol and Philadelphia, 1998.

[4] L.P.Deshmukh, A.B.Palwe and V.S.Sawant, Sol. Energy Mater., 20, 337, 1990.

[5] Freund L. B., Suresh Subra, Thin Film Materials: Stress, Defect Formation, and

Surface Evolution, Cambridge University Press, U.K., 2003

[6] Mattox Donald M., Handbook of Physical Vapor Deposition (PVD) Processing,

Second Edition, Elsevier Inc, 2010.

[7] BunshahRointanFramroze, Handbook of Hard Coatings: Deposition

Technologies, Properties and Applications, Noyes Publication, Norwich, New

York, USA, 2001

[8] Popov, O. A., Physics of Thin Film Series, (Eds. M. H. Francombe and J.

Vossen), Vol. 18, pp. 122, Academic Press, 1991.

[9] Reif, R. and Kern, W., Thin Film Processes II, (Eds. J. L. Vossen and W. Kern),

Academic Press, 1991.

[10] Hey, H. P. W., Sluijk, B. G. and Hemmes, D. G., Solid State Tech., 33, 139,

1990.

[11] d’Agnostino, R. (Ed.), Plasma Deposition, Treatment and Etching of Polymers,

Academic Press, 1991.

[12] Felts, J. T. and Grubb, A. D., J. Vac. Sci. Tech, A10, 1675, 1992.

[13] Schwartz, M., Deposition from Aqueous Solutions: An overview. In: Handbook

of Deposition Technologies for Film and Coatings (Ed. R. F. Bunshah,), Noyes

Publications, 1994.

63 | P a g e

[14] Dinni, J. W., Electrodeposition: The Material Science of Coatings and

Substrates, Noyes Publications, 1993.

[15] Brewer, G. E. F. (Ed.), Electrodeposition of Coatings. In: Advances in

Chemistry, Series No. 119, American Chemical Society, 1973.

[16] Jonothan, J. and Berger, R., Plat. Surf. Finish, 80, 8, 1993.

[17] Koutsky, J. A. et al., J. Polym. Sci., 4, 661, 1966.

[18] Rastogi, A. C. and Chopra, K. L., Thin Solid Films, 18, 187, 1973.

[19] Khare, P. K. and Pal, A., J. Electrostat., 68, 328, 2010.

[20] Wagner, M. F., Thermochemic. Acta, 23, 93, 1978.

[21] Jain, K., Rastogi, A. C. and Chopra K. L., Phys. Stat. Sol. (a), 20, 167, 1973.

[22] Nakagawa, K. and Ishida, Y., J. Polym. Sci. Polym., Phys., 11, 1503, 1973.

[23] Gasso, J., Thin Solid Films, 21, 43, 1974.

[24] Benes, N. E., Spijksma, G., Verweij, H., Wormesster, H. and Poelsema, B.,

Materials, Interfaces, and Electrochemical Phenomena, 47, 1212, 2001.

[25] Wormeester, H., Benes, N. E., Spijksma, G. I., Verweij,H. and Poelsema, Thin

Solid Films, 455, 747, 2004.

[26] Campbell, D. S., Handbook of Thin Film Technology, (Eds. L. I. Maissel and R.

Galang), McGraw Hill, New York, 1970.

[27] Lakatos, A. I., J. Appl. Phys., 46, 1744, 1970.

[28] Tolansky, S., Multiple Beam Interferometry of Surface and Films, Oxford

University Press, UK, 1948.

[29] Kondratenko, M. L. and Malik, A. I., Instrumet. and Expt. Tech., 17, 855, 1974.

[30] Reucroff, P. J. and Takahasi, K., J. Non-Cryst. Solids, 1, 71, 1975.

[31] Lupu, A. and Baltog, J., J. Polym. Sci. Polym. Phys., 12, 2399, 1974.

[32] Davis, D. K., J. Appl. Phys. D, 2, 1533, 1969.

[33] Sibilia John P., A Guide to Materials Characterization and Chemical Analysis,

John Wiley & Sons, Inc., New York, USA, 1996.

64 | P a g e

[34] Cullity B.D., Elements of X-raf Diffraction, Second Edition, Addition Wesely,

London, 1978.

[35] Koenig, Jack L. Spectroscopy of polymers, Elsevier Science Inc., New York,

1999.

[36] MichlerGoerg H. Electron Microscopy of Polymers, Springer Berlin

Heidelberg, Germany, 2008.

[37] Sawyer Linda C., Grubb David T., Meyers Gregory F., Polymer Microscopy,

Third Edition, Spring, New York, USA, 2008.

[38] MichlerGoerg H., Electron Microscopy of Polymers, Springer-Verlag Berlin

Heidelberg, 2008

[39] Meyer, E., Z d. Vereines Deutsch. Ingenieure 52, 645, 1908.

[40] Ludwik, P., Die Kegelprobe, J. Springer, Berlin, 1908.

[41] Smith, R. &Sandland, G., J. Iron & Steel Inst. 1, 285, 1925.

[42] McKeen Laurence W., The effect of temperature and other factors on plastics

and elastomers,William Andrew, USA, 2007.