Assignment# 02
Name: Tahreem Tahir
Reg. No: 2019-ag-2242
Degree: M. Phil Chemistry (E)
Course Title: Methods & Techniques of
Experimental Physics
Course Code: PY-706
Submitted To: Dr. HAFEEZ ANWAR
Session: 2019-2021
Date: 03-01-2021
DEPARTMENT of CHEMISTRY
UNIVERSITY OF AGRICULTURE
FAISALABAD
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Transmission Electron Microscope
What is TEM ?
Transmission electron microscopy (TEM) is the original form of electron microscopy and
analogues to the optical microscope. It can achieve a resolution of ~0.1 nm, thousand times
better resolution, cannot be reached by the light microscope. The beam of electrons passes
through the specimen and analyzes the internal structure of the specimen in the form of images.
The electron has the poor penetrating capability and gets absorbed in the thick specimen.
Therefore, the thickness of the specimen should not be more than few hundred Angstroms (one
angstrom = 10-10 m) However sometimes, slightly thickens samples are used in High Voltage
Electron Microscope. (Nixon 1971)
Fig. 1. Transmission electron microscope (TEM)
(Williams and Carter 1996)
Principle of TEM
The TEM operates on the same basic principles as the light microscope but uses electrons instead
of light. Because the wavelength of electrons is much smaller than that of light, the optimal
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resolution attainable for TEM images is many orders of magnitude better than that from a light
microscope.(Williams and Carter 1996)
Fig. 2. a) General layout of a TEM describing the path of electron beam in a TEM. b) A ray diagram for the diffraction mechanism
in TEM
Imaging
The beam of electrons from the electron gun is focused into a small, thin, coherent beam using
the condenser lens. This beam is restricted by the condenser aperture, which excludes high angle
electrons. The beam then strikes the specimen and parts of it are transmitted depending upon the
thickness and electron transparency of the specimen. This transmitted portion is focused by the
objective lens into an image on phosphor screen or charge coupled device (CCD) camera. The
image then passed down the column through the intermediate and projector lenses, is enlarged all
the way. The image strikes the phosphor screen and light is generated, allowing the user to see
the image.(Inkson 2016)
Diffraction
As the electrons pass through the sample, they are scattered by the electrostatic potential set up
by the constituent elements in the specimen. After passing through the specimen, they pass
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through the electromagnetic objective lens which focuses all the electrons scattered from one
point of the specimen into one point in the image plane. Also, shown in fig 2 is a dotted line
where the electrons scattered in the same direction by the sample are collected into a single
point. This is the back focal plane of the objective lens and is where the diffraction pattern is
formed.(Inkson 2016)
Components of TEM
Transmission electron microscope has three essential components.
1. The Electron Gun And Condenser System.
2. The Image-Producing System.
3. Image Recording
Electron gun:
The source of electrons, the cathode, is a heated a sharply pointed rod shaped lanthanum hexaboride. The
filament is surrounded by a control grid called as Wehnelt cylinder, with a central aperture arranged on
the axis of the column; the apex of the cathode is arranged to lie at or just above or below this aperture.
The cathode and control grid are at a negative potential equal to the desired accelerating voltage and are
insulated from the rest of the instrument. The final electrode of the electron gun is the anode, which takes
the form of a disk with an axial hole. Electrons leave the cathode and accelerate toward the anode. The
control and alignment of the electron gun are critical in ensuring satisfactory operation. (Williams and
Carter 1996)
Condenser lenses system:
The intensity and angular aperture of the beam are controlled by the condenser lens system between the
gun and the specimen. A single lens may be used to converge the beam onto the object, but, more
commonly, a double condenser is employed. In this the first lens is strong and produces a reduced image
of the source, which is then imaged by the second lens onto the object. The use of a small spot size
minimizes disturbances in the specimen due to heating and irradiation.(Nixon 1971)
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The image-producing system
Objective lenses and projector lenses
The specimen grid is carried in a small holder in a movable specimen stage. The objective lens is usually
of short focal length (1–5 mm) and produces a real intermediate image that is further magnified by the
projector lens or lenses. A single projector lens may provide a range of magnification of 5:1 and using
interchangeable pole pieces in the projector a wider range of magnifications may be obtained. Modern
instruments employ two projector lenses (one called the intermediate lens) to permit a greater range of
magnification and to provide a greater overall magnification without a commensurate increase in the
physical length of the column of the microscope.(Nixon 1971)
Image Recording:
The electron image is monochromatic and must be made visible either by allowing the electrons
to fall on a fluorescent screen fitted at the base of the microscope column or by capturing the
image digitally for display on a computer monitor. Computerized images are stored in a format
such as TIFF or JPEG and can be analyzed or image-processed prior to publication. The
identification of specific areas of an image, or pixels with specified characteristics, allows
spurious colours to be added to a monochrome image. This can be an aid to visual interpretation
and teaching and can create a visually attractive picture from the raw image.(Williams and Carter
1996)
How can we calculate the particle size from TEM?
Particle size can be determined by using Image J software.
ZnO Image Analysis
Procedure:
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After installation, I used the drag and drop feature in ImageJ software to open the SEM
image of ZnO nanoparticles.
Figure. 3 ZnO Nanoparticles captured by SEM
I selected the line tool on the toolbar of ImageJ then I hold down the shift key and draw a
straight line along the length of the scale bar of the ZnO image as accurate as possible.
This gives me the “distance in pixels” of 77 pixels.
I set the scale by choosing the option analyze and then set scale. In the options “known
distance” and “unit of length”, I entered the distance and units of ZnO image scale bar
that was 3μm. This is the distance that is used as a standard to set the measurements.
Then, I selected the region of interest by choosing the box tool and drawn a box around
the area of interest. Then I cropped that part.
Then, I adjusted the ZnO image to threshold.
Figure. 4 Threshold Image of ZnO nanoparticles
When these particles were analyzed by Image J software, the following Figure 4 was obtained.
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Figure. 5 Analyzed ZnO nanoparticles by Image J package
Then, I set the measurements that I wanted to take like area, min & max gray value, mean gray
value etc. by selecting the option “Set measurements” under the analyze tab.
I analyzed the particles by selecting the option “analyze particles” and check the display results
under analyze tab.
I saved those results and opened in excel sheet.
From the values of area, I determined the values of diameter by applying these formulas in excel
sheet.
The following table 1 give the output results of ZnO nanoparticles obtained by Image J.
Table 1. Calculated results of ZnO nanoparticles
Sr. No Area r2 r d
1 4.71 1.49924 1.224434 2.448869
2 4.71 1.49924 1.224434 2.448869
3 4.71 1.49924 1.224434 2.448869
4 9.42 2.998479 1.731612 3.463223
5 28.26 8.995437 2.999239 5.998479
6 4.71 1.49924 1.224434 2.448869
7 9.42 2.998479 1.731612 3.463223
8 9.42 2.998479 1.731612 3.463223
9 14.13 4.497719 2.120783 4.241565
10 4.71 1.49924 1.224434 2.448869
11 4.71 1.49924 1.224434 2.448869
12 18.84 5.996958 2.448869 4.897738
13 211.953 67.46674 8.213814 16.42763
14 9.42 2.998479 1.731612 3.463223
15 4.71 1.49924 1.224434 2.448869
16 4.71 1.49924 1.224434 2.448869
17 4.71 1.49924 1.224434 2.448869
18 108.332 34.48315 5.872235 11.74447
19 18.84 5.996958 2.448869 4.897738
20 4.71 1.49924 1.224434 2.448869
21 4.71 1.49924 1.224434 2.448869
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22 1177.517 374.8153 19.36015 38.72029
23 4.71 1.49924 1.224434 2.448869
24 4.71 1.49924 1.224434 2.448869
25 18.84 5.996958 2.448869 4.897738
26 4.71 1.49924 1.224434 2.448869
27 14.13 4.497719 2.120783 4.241565
28 4.71 1.49924 1.224434 2.448869
29 4.71 1.49924 1.224434 2.448869
30 4.71 1.49924 1.224434 2.448869
31 4.71 1.49924 1.224434 2.448869
32 14.13 4.497719 2.120783 4.241565
33 4.71 1.49924 1.224434 2.448869
34 18.84 5.996958 2.448869 4.897738
35 18.84 5.996958 2.448869 4.897738
36 23.55 7.496198 2.737919 5.475837
37 4.71 1.49924 1.224434 2.448869
38 14.13 4.497719 2.120783 4.241565
39 32.97 10.49468 3.239549 6.479098
40 4.71 1.49924 1.224434 2.448869
41 4.71 1.49924 1.224434 2.448869
42 23.55 7.496198 2.737919 5.475837
43 23.55 7.496198 2.737919 5.475837
44 4.71 1.49924 1.224434 2.448869
45 9.42 2.998479 1.731612 3.463223
46 14.13 4.497719 2.120783 4.241565
47 4.71 1.49924 1.224434 2.448869
48 4.71 1.49924 1.224434 2.448869
49 14.13 4.497719 2.120783 4.241565
50 4.71 1.49924 1.224434 2.448869
51 4.71 1.49924 1.224434 2.448869
52 14.13 4.497719 2.120783 4.241565
53 4.71 1.49924 1.224434 2.448869
54 28.26 8.995437 2.999239 5.998479
55 18.84 5.996958 2.448869 4.897738
56 18.84 5.996958 2.448869 4.897738
57 4.71 1.49924 1.224434 2.448869
58 324.995 103.4491 10.17099 20.34199
59 4.71 1.49924 1.224434 2.448869
60 4.71 1.49924 1.224434 2.448869
61 9.42 2.998479 1.731612 3.463223
62 226.083 71.96445 8.483187 16.96637
63 4.71 1.49924 1.224434 2.448869
64 178.983 56.97206 7.547984 15.09597
65 4.71 1.49924 1.224434 2.448869
66 4.71 1.49924 1.224434 2.448869
67 4.71 1.49924 1.224434 2.448869
68 9.42 2.998479 1.731612 3.463223
69 4.71 1.49924 1.224434 2.448869
70 9.42 2.998479 1.731612 3.463223
71 4.71 1.49924 1.224434 2.448869
72 9.42 2.998479 1.731612 3.463223
73 150.722 47.9763 6.926493 13.85299
74 4.71 1.49924 1.224434 2.448869
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75 4.71 1.49924 1.224434 2.448869
76 9.42 2.998479 1.731612 3.463223
77 14.13 4.497719 2.120783 4.241565
78 18.84 5.996958 2.448869 4.897738
79 23.55 7.496198 2.737919 5.475837
80 4.71 1.49924 1.224434 2.448869
81 4.71 1.49924 1.224434 2.448869
82 9.42 2.998479 1.731612 3.463223
83 4.71 1.49924 1.224434 2.448869
84 4.71 1.49924 1.224434 2.448869
85 4.71 1.49924 1.224434 2.448869
86 4.71 1.49924 1.224434 2.448869
87 4.71 1.49924 1.224434 2.448869
88 4.71 1.49924 1.224434 2.448869
89 4.71 1.49924 1.224434 2.448869
90 9.42 2.998479 1.731612 3.463223
91 14.13 4.497719 2.120783 4.241565
92 4.71 1.49924 1.224434 2.448869
93 4.71 1.49924 1.224434 2.448869
94 14.13 4.497719 2.120783 4.241565
95 23.55 7.496198 2.737919 5.475837
96 4.71 1.49924 1.224434 2.448869
97 18.84 5.996958 2.448869 4.897738
98 4.71 1.49924 1.224434 2.448869
99 4.71 1.49924 1.224434 2.448869
100 4.71 1.49924 1.224434 2.448869
From these values their Histogram is plotted that has shown in Figure 6.
Line graph
Figure. 6 Histogram of ZnO nanoparticles via Origin Figure. 7 ZnO nanoparticles with different particles size
frequency
The following calculations were performed for the determination of average particle size.
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Area (A) = πr2
A
Radius (r) =
√ π
;
Diameter (d) = 2r
Average
particle
References
1. Aal, N. A., et al. (2015). "Novel rapid synthesis of zinc oxide nanotubes via hydrothermal
technique and antibacterial properties." Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy 135: 871-877.
2. Inkson, B. (2016). Scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) for materials characterization. Materials characterization using
nondestructive evaluation (NDE) methods, Elsevier: 17-43.
3. Nixon, W. (1971). "The general principles of scanning electron microscopy."
Philosophical Transactions of the Royal Society of London. B, Biological Sciences
261(837): 45-50.
4. Ullah, K., et al. (2015). "Degradation of organic dyes by cdse decorated graphene
nanocomposite in dark ambiance." Fullerenes, Nanotubes and Carbon Nanostructures
23(5): 437-448.
5. Wang, M.-H., et al. (2015). "Synthesis of Pr-doped ZnO nanoparticles by sol–gel method
and varistor properties study." Journal of Alloys and Compounds 621: 220-224.
6. Williams, D. B. and C. B. Carter (1996). The transmission electron microscope.
Transmission electron microscopy, Springer: 3-17.
7. Williams, D. B. and C. B. Carter (1996). Transmission Electron Microscopy:
Spectrometry. IV, Plenum Press.
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