Scaaning electron microscope

VISVESVARAYA TECHNOLOGICAL UNIVERSITY
Jnana Sangama, Belagavi – 590 018.
TECHNICAL SEMINAR REPORT
on
“SCANNING ELECTRON MICROSCOPE”
Bachelor of Engineering
In
Mechanical Engineering
by
Girish H V
1VI16ME013
Under the guidance of
Mr. TIPPESWAMY M S
Asst. professor
Department of Mechanical Engineering
DEPARTMENT OF MECHANICAL ENGINEERING
VEMANA INSTITUTE OF TECHNOLOGY
BENGALURU – 560034
2019 - 20

Karnataka ReddyJana Sangha®
VEMANA INSTITUTE OF TECHNOLOGY
Koramangala, Bengaluru-34.
(Affiliated to Visvesvaraya Technological University, Belagavi)
Department of Mechanical Engineering
Certificate
This is to certify that the technical seminar report entitled “SCANNING ELECTRON
MICROSCOPE” presented by Girish H V bearing USN 1VI16ME013 during the
academic year 2019-20 in partial fulfillment of the requirement for the 8th
Semester course
for the Bachelor of Engineering in Mechanical Engineering of the Visvesvaraya
Technological University, Belagavi. It is certified that all corrections/suggestions indicated
for internal assessment have been incorporated in the report. The seminar report has been
approved as it satisfies the academic requirements in respect of the technical seminar
prescribed for the said degree.
________________ __________________ _____________________
Guide HOD Principal
Mr. Tippeswamy M S Dr. Lokesh G Reddy Dr. Vijayasimha Reddy. B. G

ACKNOWLEDGEMENT
At the outset, I thank the lord almighty for the grace, strength and blessing that have been
bestowed upon me and have made this endeavor a success.
I consider it as a privilege to express my gratitude to all those who guided me in the completion of
this seminar.
I am deeply grateful to Dr. Vijayasimha Reddy B G, Principal, Vemana Institute of Technology,
and Dr. Lokesh G Reddy, Head of the Department for providing me with adequate facilities and
means by which I was able to undertake this seminar. Their constant motivation and valuable
suggestions have been instrumental to the successful completion of this seminar.
I would like to thank my guide Mr. Tippeswamy M S, Assistant Professor of Mechanical
Engineering for helping me to adhere through the seminar.
I thank Mr. Kiran Kumar, Assistant Professor and Mr. S Puneeth, Assistant Professor our
seminar coordinators for their boundless cooperation and all the help extended for this seminar. I
express my immense pleasure and thankfulness to all the teachers and staff of the department of
Mechanical Engineering for their cooperation and support.
Girish H V
(1VI16ME013)

i
ABSTRACT
In the present study, definition of scanning electron microscopy (SEM) was presented in terms
of the main component of the instrument and step-by-step the process of SEM system.
Schematic drawings with SEM components pictures were provided for understanding the
procedure of work in easy and true way. Also, types of SEM were presented and discussed.
The capability of energy-dispersive spectrometer (EDS) was also presented; this included
historical background of EDS and how it works in accordance with SEM. The existence of
EDS capability with SEM instrument is very essential for qualitative and quantitative analysis
for any specimen. In the absence of EDS only information on surface topography of the
specimen can be produced through SEM. The two most powerful features of SEM image are
introduced and discussed namely secondary electron imaging and backscattered electron
imaging. Understanding principle of work of both features is very important to have a complete
knowledge on how SEM instrument works. SEM is characterized by its easy operation. Having
that knowledge one can manage to perform the analysis and imaging very smoothly.
Keywords: Backscattered electron imaging, Energy-dispersive spectrometer, Scanning
electron microscopy, Secondary electron imaging.

CONTENTS
Sl no. Topic Pg no.
1 Introduction 1
2 Principle of Scanning Electron Microscope (SEM) 2-3
3 Components of SEM 4-7
4 Working Scanning electron microscope 8-9
5 Characteristics that can be viewed on SEM 10
6 Comparison of LM V/S SEM 11
7 Sem Sample Preparation 12-13
8 Applications & limitations of SEM 14
9 REFERENCES 15

LIST OF FIGURES
Fig no. Topic Pg no.
2.1
The interaction of electron beam with specimen and the signal
emitted from the sample
3
3.1 Sectional view of SEM 4
4.1 schematic representation of the basic SEM components 8
6.1 Light microscope 11
6.2 Scanning electron microscope 11
7.1 SEM Sample 12

SCANNIG ELECTRON MICROSCOPE
Dept Of Mechanical Engineering, Vemana IT 1
1. Introduction
The scanning electron microscope (SEM) is one of the most widely used instruments in materials
research laboratories and is common in various forms in fabrication plants. Scanning electron
microscopy is central to microstructural analysis and therefore important to any investigation relating to
the processing, properties, and behaviour of materials that involves their microstructure. The SEM
provides information relating to topographical features, morphology, phase distribution, compositional
differences, crystal structure, crystal orientation, and the presence and location of electrical defects. The
SEM is also capable of determining elemental composition of microvolumes with the addition of an x-
ray or electron spectrometer and phase identification through analysis of electron diffraction
patterns. The strength of the SEM lies in its inherent versatility due to the multiple signals generated,
simple image formation process, wide magnification range, and excellent depth of field.
Lenses in the SEM are not a part of the image formation system but are used to demagnify and focus
the electron beam onto the sample surface. This gives rise to two of the major benefits of the SEM: range
of magnification and depth of field in the image. Depth of field is that property of SEM images where
surfaces at different distances from the lens appear in focus, giving the image three-dimensional
information. The SEM has more than 300 times the depth of field of the light microscope. Another
important advantage of the SEM over the optical microscope is its high resolution. Subnanometer
resolution at low beam energies (e.g., 1 kV) is now achievable from an SEM with a field emission (FE)
electron gun. Magnification is a function of the scanning system rather than the lenses, and therefore a
surface in focus can be imaged at a wide range of magnifications. The higher magnification of the SEM
is rivaled only by the transmission electron microscope (TEM), which requires the electrons to penetrate
through the entire thickness of the sample. As a consequence, TEM sample preparation of bulk materials
is tedious and time-consuming, compared to the ease of SEM sample preparation, and may damage the
microstructure. The information content of the SEM and TEM images is different, with the TEM image
showing the internal structure of the material.
Due to these unique features, SEM images frequently appear not only in the scientific literature but also
in the daily newspapers and popular magazines. The SEM is relatively easy to operate and affordable
and allows for multiple operation modes, corresponding to the collection of different signals. The
following sections review the SEM instrumentation and principles, its capabilities and applications, and
recent trends and developments.

2. Principle of Scanning Electron Microscope (SEM)
The SEM instrument is based on the principle that the primary electrons released from the source provide
energy to the atomic electrons of the specimen which can then release as the secondary electrons (SEs)
and an image can be formed by collecting these secondary electrons from each point of the specimen,
the basic requirement for SEM to operate under a vacuum to avoid interactions of electrons with gas
molecules in order to obtain high resolution. In addition, the primary electrons produced and emitted
from the electron gun are accelerated by heating or applying high energy in the range of 1−40 keV These
emitted electrons are focused and confined to a monochromatic beam (to a diameter of 100 nm or less)
by magnetic field lenses and metal slits within a vacuumed column. The confined primary electrons are
scanned across the sample surface by scanning coils in a raster pattern. Once the primary electron beam
hits the sample surface, it will interact with the near-surface area of the sample to a certain depth in
many different ways The impinging electrons accelerated towards the specimens have substantial
quantities of kinetic energy, which lose their energy inside the sample by generating several signals from
the interactions of electrons with specimen. It scattered both elastically and inelastically in the sample.
The scattering of electrons and interaction volume depends on the atomic number, concentration of
atoms of the analysed sample and the incoming electron energy (accelerating voltage). Increasing the
electron energy (accelerating voltage) will increase the interaction volume and scattering process, and
if the concentration of atoms and atomic number of the element is high, then the interaction volume and
scattering will be low. Similarly, angle of incidence of the electron beam also play an important role in
the interaction volume and scattering process. Thus, the angle of incidence of the electron beam, atomic
number of the material under examination and accelerating voltage are the main factors for the volume
inside the specimen in which interactions occur. The materials having higher atomic number absorb or
stop more electrons and will thus generate smaller interaction volume. Similarly, if high voltages are
applied, it will generate electrons with high energy and will thus penetrate farther into the sample and
generate a larger interaction volume. Similarly, the greater the angle of incidence (further from normal),
the smaller will be the interaction volume.

Fig. 2.1 The interaction of electron beam with specimen and the signal emitted from the sample
In consequence, it will emit a variety of signals due to Coulomb (electric charge) field interaction of
incoming electrons with specimen nucleus and electrons, such as secondary electrons (SEs),
backscattered electrons (BSEs), photons (X-rays used for elemental analysis) and visible light
(cathodoluminescence – CL). The signals are gathered by electron collectors (detectors), which are then
manipulated by the computer to form the required image. According to the detected signal (secondary
electrons, backscattered electrons or X-rays), different information about the sample could be observed.
The two routinely used electrons for sample image creation are the backscattered and secondary
electrons. However, secondary electrons are considered the most important electrons, indicating sample
morphology and topography, while backscattered electrons are used for demonstrating the contrasts
in multiphase samples composition (i.e. for prompt phase judgement). Similarly, X-rays are generated
by the inflexible impacts of the incident electrons with the electrons available in the orbitals of sample
atoms. After this the electrons are excited to the higher energy levels; when it comes back to the lower
energy levels, it emits X-rays, having a specified wavelength, depending on the difference in energy
level of various elements. In this way each element generated a characteristic X-ray after the impinging
of electrons beam. SEM is non-destructive, as the generation of X-rays does not lead to any loss in the
volume of the specimen; therefore, one can repeatedly analyse the same material (Fig. 2).

3. Components of SEM
Fig. 3.1 Sectional view of SEM
3.1. Electron optical column consists:
The electron column is where the electron beam is generated under vacuum, focused to a small diameter,
and scanned across the surface of a specimen by electromagnetic deflection coils. The lower portion of
the column is called the specimen chamber. The secondary electron detector is located above the sample
stage inside the specimen chamber. Specimens are mounted and secured onto the stage which is
controlled by a goniometer. The manual stage controls are found on the front side of the specimen
chamber and allow for x-y-z movement, 360 rotation and 90 tilt however only the tilt cannot be
controlled through the computer system thus there is no need to use all of the manual controls manipulate
the orientation of the sample inside the sample chamber. Below is a diagram of the electron column and
a description of each of the components of the electron column.
 Electron gun: Located at the top of the column where free electrons are generated by thermionic
emission from a tungsten filament at ~2700K. The filament is inside the Wehnelt which controls
the number of electrons leaving the gun. Electrons are primarily accelerated toward an anode that
is adjustable from 200V to 30 kV (1kV=1000V).

 Condenser Lenses: After the beam passes the anode it is influenced by two condenser lenses that
cause the beam to converge and pass through a focal point. What occurs is that the electron beam
is essentially focused down to 1000 times its original size. In conjunction with the selected
accelerating voltage the condenser lenses are primarily responsible for determining the intensity
of the electron beam when it strikes the specimen.
 Apertures: Depending on the microscope one or more apertures may be found in the electron
column. The function of these apertures is to reduce and exclude extraneous electrons in the
lenses. The final lens aperture located below the scanning coils determines the diameter or spot
size of the beam at the specimen. The spot size on the specimen will in part determine the
resolution and depth of field. Decreasing the spot size will allow for an increase in resolution and
depth of field with a loss of brightness.
 Scanning System: Images are formed by rastering the electron beam across the specimen using
deflection coils inside the objective lens. The stigmator or astigmatism corrector is located in the
objective lens and uses a magnetic field in order to reduce aberrations of the electron beam. The
electron beam should have a circular cross section when it strikes the specimen however it is
usually elliptical thus the stigmator acts to control this problem.
 Specimen Chamber: At the lower portion of the column the specimen stage and controls are
located. The secondary electrons from the specimen are attracted to the detector by a positive
charge.
3.2. Vacuum System
The ability for a SEM to provide a controlled electron beam requires that the electronic column be under
vacuum at a pressure of at least 5x10-5 Torr. A high vacuum pressure is required for a variety of reasons.
First, the current that passes through the filament causes the filament to reach temperatures around
2700K. A hot tungsten filament will oxidize and burn out in the presence of air at atmospheric pressure.
Secondly, the ability of the column optics to operate properly requires a fairly clean, dust-free
environment. Third, air particles and dust inside the column can interfere and block the electrons before
the ever reach the specimen in the sample chamber. In order to provide adequate vacuum pressure inside
the column, a vacuum system consisting of two or more pumps is typically present.
Separate pumps are required because one pump isn’t really capable of doing all the work but, in
conjunction they can provide a good vacuum pressure relatively quickly and efficiently. A majority of
the initial pumping is done by the action of a mechanical pump often called a roughing pump. The

roughing pump operates first during the pump-down process and has excellent efficiency above 10-2
Torr. Although many mechanical pumps used in SEMs are capable of producing pressures better than
5x10-5 Torr, a very long pump down time would mostly be required. Pressures lower than 10-2 Torr are
more easily acquired by the action of a turbo-molecular pump. Turbo-molecular pumps make use of a
turbine that rotates at 20,000 to 50,000 rotations per minute to evacuate gas molecules and particulates
found inside the column. Turbo-molecular pumps are expensive and sensitive to vibrations thus it is
important to remember that sudden jolts to the instrument can not only affect the beam but, the severely
damage turbo pumps.
3.3. Signal detection & display
 Electron Beam-Specimen Interactions
Originally microscopy was based on the use of the light microscope and could provide specimen
resolutions on the order of 0.2 microns. To achieve higher resolutions, an electron source is
required instead of light as the illumination source, which allows for resolutions of about 25
Angstroms. The use of electrons not only gives better resolution but, due to the nature electron
beam specimen interactions there are a variety of signals that can be used to provide information
regarding characteristics at and near the surface of a specimen.
In scanning electron microscopy visual inspection of the surface of a material utilizes signals of
two types, secondary and backscattered electrons. Secondary and backscattered electrons are
constantly being produced from the surface of the specimen while under the electron beam
however they are a result of two separate types of interaction. Secondary electrons are a result
of the inelastic collision and scattering of incident electrons with specimen electrons. They are
generally characterized by possessing energies of less than 50 eV. They are used to reveal the
surface structure of a material with a resolution of ~10 nm or better.
Backscattered electrons are a result of an elastic collision and scattering event between incident
electrons and specimen nuclei or electrons. Backscattered electrons can be generated further
from the surface of the material and help to resolve topographical contrast and atomic number
contrast with a resolution of >1 micron. While there are several types of signals that are generated
from a specimen under an electron beam the x-ray signal is typically the only other signal that is
used for scanning electron microscopy. The x-ray signal is a result of recombination interactions
between free electrons and positive electron holes that are generated within the material. The x-
ray signal can originate from further down into the surface of the specimen surface and allows
for determination of elemental composition through EDS (energy dispersive x-ray spectroscopy)

analysis of characteristic x-ray signals. is a diagram which displays a cross section of the volume
of primary excitation illustrating zones from which signals may be detected.
 Observation Techniques
Scanning microscopes are becoming much easier to use these days with the advancement of
electronics and introduction of new techniques. After just a short amount of training nearly
anybody can acquire relatively good images. As users begin to investigate a broader range of
materials and encounter more complex analysis scenarios, satisfactory images become more
difficult for the inexperienced user to obtain. When the image is not clear enough or an image of
a particular feature is seemingly impossible to obtain, it requires further problem solving to
determine what the cause really is. This section will focus on the techniques for successful
imaging.

4. Working Scanning electron microscope
Fig. 4.1 schematic representation of the basic SEM components
 A scanning electron microscope provides details surface information by tracing a sample in a
raster pattern with an electron beam.
 The process begins with an electron gun generating a beam of energetic electrons down the
column and onto a series of electromagnetic lenses. These lenses are tubes, wrapped in coil and
referred to as solenoids.
 The coils are adjusted to focus the incident electron beam onto the sample; these adjustments
cause fluctuations in the voltage, increasing/decreasing the speed in which the electrons come in
contact with the specimen surface.
 Controlled via computer, the SEM operator can adjust the beam to control magnification as well
as determine the surface area to be scanned.
 The beam is focused onto the stage, where a solid sample is placed. Most samples require some
preparation before being placed in the vacuum chamber. Of the variety of different preparation
processes, the two most commonly used prior to SEM analysis are sputter coating for non-
conductive samples and dehydration of most biological specimens.
 In addition, all samples need to be able to handle the low pressure inside the vacuum chamber.

 The interactions between the incident electrons and the surface of the sample is determined by
acceleration rate of incident electrons, which carry significant amounts of kinetic energy before
focused onto the sample.
 When the incident electrons come in contact with the sample, energetic electrons are released
from the surface of the sample. The scatter patterns made by the interaction yields information on
size, shape, texture and composition of the sample.
 A variety of detectors are used to attract different types of scattered electrons, including secondary
and backscattered electrons as well as X-rays.
 Backscatter electrons are incidental electrons reflected backwards; image provide composition
data related to element and compound detection.
 Diffracted backscatter electrons determine crystalline structures as well as the orientation of
minerals and micro fabrics. X-rays, emitted from beneath the sample surface, can provide element
and mineral information.
 SEM produces black and white, 3D images. Image magnification can be up to 10 nanometers and
although its not powerful as it TEM.

5. Characteristics that can be viewed on SEM
Topography
 The surface feature of an object or “how it looks”, its texture; direct relation between these
features and materials properties.
Morphology
 The shape and size of the particles making up the object; direct relation between these structures
and materials properties.
Composition
 The elements and compounds that the object is composed of and the relative amounts of them;
direct relationship between composition and materials properties
Crystallographic Information
 How the atoms are arranged in the object; direct relation between these arrangements and
material properties

6. Comparison of LM V/S SEM
Fig. 6.1 Light microscope Fig. 6.2 Scanning electron microscope
Light Microscope Scanning Electron Microscope
Uses light (approx 400-700 nm) as an
illuminating source
Uses electron beams (approx 1 nm) as an
illuminating source.
Lower magnification than an electron
microscope
Higher magnification
No risk of radiation leakage Risk of radiation leakage
Both live and dead specimen can be seen Only dead and the dried specimen can be seen
The image formation depends upon the light
absorption from the different zones of the
specimen
The image formation depends upon the electron
scattering
The image is seen through the ocular lens. No
screen needed
The image is received on a zinc sulphate
fluorescent screen
Useful magnification of 500x to 1500x photographic magnification as high as 10000 x
Low resolution High resolution

7. Sem Sample Preparation
Fig. 7.1 SEM Sample
Step by step Specimen preparation for scanning electron microscopy
1. Cleaning the surface of the specimen
In this process, specimen is cut to make it with an appropriate size so that it can be preserved
until the drying process. In order to prevent deformation of the specimen of the specimen,
sufficient care is needed. Cleaning of its surface may also may be necessary.
2. Stabilizing the specimen
In order to prevent the structural change in specimen. It is chemically fixed by chemicals such
as glutaraldehyde, formaldehyde. To stabilize the specimen.
3. Rinsing the specimen
In this process, specimen is dipped into isopropyl bath to remove contaminants present on the
specimen
4. Dehydrating the specimen
In dehydration process to prevent the deformation, the specimen is immersed in an ethanol or
acetone solution a certain period of time while the concentration of the solution is changed in
several steps
5. Drying the specimen
Ethanol or acetone in the specimen is removed and then, then the specimen is dried. If natural
drying is applied, a surface-tension effect deforms the specimen. Thus, a special drying method,
critical point drying or freeze drying for example, is used
6. Mounting the specimen
The specimen must be stably fixed to the specimen mount. In addition, the specimen must
electrically connect to this specimen mount

7. Coating the specimen
If the specimen is nonconductive, its surface to be coated with a thin metal film so that the surface
has a conductivity. This technique is called coating and ion sputtering and vacuum evaporation
typical methods.

8. Applications & limitations of SEM
Applications
1. Thickness of films and thin coatings
2. Surface morphology and appearance
3. Size and size distribution
4. Shape and dispersion of particles, fibers, nanomaterials or any other additives in composites and
blends
5. Height and lateral dimensions of nanometer-sized materials
6. Cell size and size distribution in foam materials
7. Chemical composition and elemental analysis of nano- and micro-materials
8. Fracture and structural defects analysis
Limitations
1. The microscope works in vacuum - so working with liquids is very challenging.
2. The microscope chamber and load lock have relatively small size - so the maximal specimen
size is tens of centimeters.
3. Electron beam can damage and even destroy organic and biological samples. So those samples
might require special sample preparation (freezing or coating).

9. REFERENCES
1. SCANNING ELECTRON MICROSCOPY DONOVAN N. LEONARD, 1 GARY W.
CHANDLER, 2 AND SUPAPAN SERAPHIN2 1 Oak Ridge National Laboratory, Oak Ridge,
TN, USA 2 University of Arizona, Tucson, AZ, USA
2. Scanning Electron Microscopy: Principle and Applications in Nanomaterials Characterization
Kalsoom Akhtar, Shahid Ali Khan, Sher Bahadar Khan, and Abdullah M. Asiri

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