This document provides information about SEM (scanning electron microscope) and FTIR (Fourier transform infrared spectroscopy). It describes the key components and workings of an SEM, including the electron gun, vacuum chamber, lenses, sample chamber, and detectors. It also outlines sample preparation steps and advantages/disadvantages of SEM. For FTIR, the document discusses the interferometer component, types of detectors, advantages of higher signal-to-noise ratio and resolution, and limitations of its small sampling chamber size.

1. SEM & FTIR
PRESENTED TO
MAM SIDRA SAQIB

2. PRESENTED BY
Hafiz Muhammad Shehroz Saleem 19013123-070
Muhammad Hanzla Tahir 19013123-078
Muhammad Hasaan 19013123-018
Muhammad Suffyan Nadeem 19013123-040

3. SCANNING ELECTRON MICROSCOPE
A Scanning Electron Microscope (SEM) is a powerful magnification
tool that utilizes focused beams of electrons to obtain information. The high-
resolution, three-dimensional images produced by SEMs provide
topographical, morphological and compositional information makes them
vital in science and industry.
Designed for directly studying the surfaces of solid objects, that utilizes a
beam of focused electrons of relatively low energy as a probe that is scanned
in a regular manner over the specimen.

4. PARTS OF SEM
• Electron gun – produces the steady stream of electrons necessary for SEMs
to operate. Electron guns are typically one of two types.
• Thermionic guns – the most common type, apply thermal energy to a filament
to coax electrons away from the gun and toward the specimen.
• Field emission guns – create a strong electrical field to pull electrons away
from the atoms they're associated with.
• Vacuum chamber – required for the microscope to operate. Without a
vacuum, the electron beam generated by the electron gun would encounter
constant interference from air particles in the atmosphere.

5. PARTS OF SEM
• Lenses – used to produce clear and detailed images. The lenses aren't made
of glass but instead are made of magnets capable of bending the path of
electrons.
• Sample chamber – where researchers place the specimen that they are
examining. It must be sturdy and insulated from vibration.
• Detectors – devices detect the various ways that the electron beam
interacts with the sample object.
• Everhart-Thornley detectors – register secondary electrons dislodged from the
outer surface of a specimen. These detectors are capable of producing the most
detailed images of an object's surface.
• Backscattered electron and X-ray detectors – can tell researchers about the
composition of a substance.

6. SCANNING ELECTRON MICROSCOPE
Metals require no preparation, as they already conduct electricity and will
respond favorably when bombarded with electrons.
Non-metals need to be coated by a conductive material like gold or platinum
through a process called sputter coating. Sputter coating allows a sample to
be grounded, preventing it from being damaged by the electron beam.
In addition, preparation traditionally includes the removal of all
water. Water molecules will vaporize in a vacuum, creating obstacles for the
electron beams and obscuring the clarity of the image.

7. ADVANTAGES
• Has a wide array of applications, detailed three-dimensional imaging and
versatile information.
• Easy to operate with the proper training.
• Advances in computer technology and associated software make operation
user-friendly.
• This instrument works fast, often completing analyses in less than five
minutes.
• It allows the generation of data in digital form.
• Most samples require minimal preparation actions.

8. DISADVANTAGES
• Expensive, large and must be housed in an area free of any possible electric, magnetic or
vibration interference.
• Maintenance involves keeping a steady voltage, currents to electromagnetic coils and
circulation of cool water.
• Special training is required to operate.
• The preparation of samples can result in artifacts.
• Limited to solid, inorganic samples small enough to fit inside the vacuum chamber that
can handle moderate vacuum pressure.
• Carries a small risk of radiation exposure associated with the electrons that scatter from
beneath the sample surface.

9. FOURIER TRANSFORM INFRARED
SPECTROSCOPY
• Fourier Transform Infrared (FT-IR) spectrometry was developed in order to
overcome the limitations encountered with dispersive instruments.
• The main difficulty was the slow scanning process.
• As it was necessary for a method for measuring all of the infrared frequencies
simultaneously, rather than individually, a very simple optical device called an
interferometer was developed.
• Thus, the time element per sample is reduced to a matter of a few seconds
rather than several minutes.

10. INSTRUMENTATION
The common FTIR spectrometer consists of the following components. The
major difference between dispersive IR and FTIR is the inclusion of
interferometer. All other components are almost same as like that of a
dispersive IR spectrometer. • An interferometer requires an IR light source,
mirrors, beam splitter and detector. However the components are as follows:
• Source of light
• Interferometer
• Sample compartment
• Detector
• Read out device.

11. DETECTORS
Detectors are used to measure the intensity of unabsorbed infrared radiation.
1. Thermocouples Detectors: Thermocouple consists of a pair of junction of
different metals, for e.g. Two pieces of bismuth fused together to either
end of a piece of antimony. The potential difference (voltage) between the
junctions changes according to the difference in temperature between the
junction.
2. Pyroelectric Detectors:
• These are made from a single crystalline wafer of a pyroelectric material, such as
triglyceride sulphate.
• The properties of a pyroelectric material are such that when an electric field is applied
across it, electric polarization occurs ( usually happens in any dielectric material). In a
pyroelectric material, when the field is removed, the polarization persists.

12. ADVANTAGES
• The signal-to-noise ratio of spectrum is significantly higher than to
previous generation infrared spectrometers.
• The accuracy of wave number is high. The error is within the range of =
0.01.
• The scan time of all frequencies is short (approximately 1s).
• The resolution is extremely high(0.1-0.005).
• The scan range is wide (1000-10 cm−1 ).
• The interference from stray light is reduced. Due the these advantages,
FTIR Spectrometers have replaced dispersive IR spectrometers.

13. DISADVANTAGES
1. The sampling chamber of an FTIR can present some limitations due to its
relatively small size.
2. Mounted pieces can obstruct the IR beam.
3. Usually, only small items as rings can be tested.
4. Several materials completely absorb Infrared radiation; consequently, it
may be impossible to get a reliable result