Examination Paper for Foreign Graduates

Principle & Applications of TEM & HRTEM

Student Number: LS1401202

Submitted by: Mr.Gulfam Raza

Submitted to: Prof. Lilly Dong

Abstract: Transmission Electron Microscope (TEM) is a very powerful tool for

material science. A high energy beam of electrons is shone through a very thin

sample, and the interactions between the electrons and the atoms can be used to

observe features such as the crystal structure and features in the structure like

dislocations and grain boundaries. TEM can be used to study the growth of layers,

their composition and defects in semiconductors. High Resolution Transmission

Electron Microscope (HRTEM) can be used to analyze the quality, shape, size and

density of quantum wells, wires and dots.

2

TABLE of CONTENTS

Topic Number

Topic Name

Page Number

1 BRIEF INTRODUCTION TO MICROSCOPY 1.1 What is Microscopy?

1.2 What is Microscope?

1.3 Microscopic Terms

3-4

2 TRANSMISSION ELECTRON MICROSCOPE

(TEM) 2.1 What is TEM?

2.2 Working Principle of TEM

2.2.1 Imaging

2.2.2 Diffraction

4-6

3 APPLICATIONS OF TEM 3.1CoFe2O4:BaTiO3 Core Shell Nanocomposite

3.2 g-C3N4/TiO2 Photo Catalyst

3.3 Characterization of ZnO Nanotubes

3.4 CdSe-graphene Composites

3.5 Pr-doped ZnO Nanoparticles

6-7

4 HIGH RESOLUTION TRANSMISSION

ELECTRON MICROSCOPE

(HRTEM) 4.1 What is HRTEM?

4.2 Working Principle of HRTEM

7-9

5 APPLICATIONS OF HRTEM 5.1 CoFe2O4:BaTiO3 Core Shell Nanocomposite

5.2 Characterization of ZnO Nanotubes

9

3

TOPIC No. 01

BRIEF INTRODUCTION to MICROSCOPY

1.1What is Microscopy?

The science of investigating small objects using instruments like microscope is

called microscopy.Microscopy is the technical field of using microscopes to

viewing objects and areas of objects that are not within the resolution range of the

normal eye. There are three well-known branches of microscopy;

Optical Microscopy

Electron Microscopy

Scanning Probe Microscopy

On October 8, 2014, the Nobel Prize in Chemistry was awarded to Eric

Betzig, William Moerner and Stefan Hell for "the development of super-

resolved fluorescence microscopy," which brings "optical microscopy into

the nanodimension". [1]

1.2What is Microscope?

An optical instrument that uses a lens or combination of lenses to produce

magnified images of small objects especially which are too small to be seen by

naked or unaided eye.There are many types of microscopes. The most common

and the first to be invented is the optical microscope, which uses light to image the

sample. [2]

Other major types of microscopes are following;

Electron Microscope (TEM and SEM)

Ultra-microscope

Scanning Probe Microscopes

1.3Microscopic Terms

Resolution

The resolution of an optical microscope is defined as the shortest distance between

two points on a specimen that can still be distinguished by the observer or camera

system as separate entities.[3]

4

Magnification

Magnification in physical terms is defined as "a measure of the ability of a lens or

other optical instruments to magnify, expressed as the ratio of the size of the image

to that of the object". This means, that an object of any size is magnified to form an

enlarged image.

The magnification required to produce the visible image can be calculated using

the formula:[4]

Magnification = Image ÷ Object

Lenses

A lens is a transparent curved device that is used to refract light. A lens is usually made

from glass. There are two different shapes for lenses. They are called convex and concave.[5]

Aperture of Lense

In optics, an aperture is a hole or an opening through which light is admitted. More

specifically, the aperture of an optical system is the opening that determines the

cone angle of a bundle of rays that come to a focus in the image plane.It is crucial

in determining the resolving power of an optical devicebecause the aperture

determines the amount of diffraction and hence resolution.[6]

TOPIC No. 02

TRANSMISSION ELECTRON MICROSCOPY

2.1 What is TEM?

Transmission electron microscopy uses high energy electrons (up to 300 kV

accelerating voltage) which are accelerated to nearly the speed of light. The

electron beam behaves like a wavefront with wavelength about a million times

shorter than lightwaves.

5

2.2 Working Principle

of TEM

The TEM operates on the

same basic principles as

the light microscope but

uses electrons instead of

light. When an electron

beam passes through a

thin-section specimen of

a material, electrons are

scattered. A sophisticated

system of electromagnetic

lenses focuses the

scattered electrons into an

image or a diffraction

pattern, or a nano-

analytical spectrum,

depending on the mode of

operation.

Fig 1 - General layout of a TEM describing the path of electron beam in a TEM

Fig 2 - A ray diagram for the diffraction mechanism in TEM

2.2.1Imaging

The beam of electrons from the electron gun is focused into a small, thin, coherent

beam by the use of 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.

6

The image strikes the phosphor screen and light is generated, allowing the user to

see the image.

2.2.2Diffraction

Fig 2 shows a simple sketch of the path of a beam of electrons in a TEM from just

above the specimen and down the column to the phosphor screen. 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 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.[7]

TOPIC No. 03

APPLICATIONS of TEM

3.1CoFe2O4:BaTiO3Core Shell Nanocomposite

The TEM image of as-synthesized CFO nanoparticles is

given as;

Figure shows nearly spherical CFO nanoparticles with

diameter 20 nm.[8]

3.2 g-C3N4/TiO2Photo Catalyst

Morphology and microstructure of samples were investigated by TEM as shown;[9]

TEM images of g-C3N4 (a), TB1 (b), TB0.5 (c), TB0.2 (d), TB0.05 (e), and TB0 (f), respectively. Redand white

arrows in image (b) showing the presence of hollowstructured TiO2 nanobox and film-like g-C3N4, respectively.

7

3.3Characterization of ZnO Nanotubes

TEM micrograph indicates that the ZnO possesses uniform

nanotubes and are grown in large scale.[10]

3.4CdSe-graphene Composites

TEM images of CdSe-graphene

composite materials. From the

images, it can be observed that the

CdSe were the dark imaged

compounds almost spherical

nanoparticles attached to the surface

of the graphene sheets, whereas the

graphene components were found to

be relatively lighter than CdSe with

irregular edges, flat sheet-like

structure, having occasional distribution of CdSe on the surface.[11]

3.5Pr-doped ZnO Nanoparticles

The particles are agglomerated and the

shape of samples is turnover from

spheroid-like into the mixer of spheroid-

like and rod-like with the increase of

Prcontent, in which spheroid-like particles

are dominant.[12]

TOPIC No. 04

HIGH RESOLUTION TRANSMISSION ELECTRON

MICROSCOPE

4.1 What is HRTEM?

High-Resolution TEM (HRTEM) is the ultimate tool in imaging defects. In

favorable cases it shows directly a two dimensional projection of the crystal with

defects and all.

8

Of course, this only makes sense if the two-dimensional projection is down some

low-index direction, so atoms are exactly on top of each other.[13-14-15]

4.2 Working Principle of HRTEM

The basic principle involved in the image formation in both the microscopes (TEM

& HRTEM) is similar. However, HRTEM provides high resolution images at

atomic scale level.

Most precisely, HRTEM is a type of TEM.

The high-resolution transmission electron microscopy (HRTEM) uses both the

transmitted and the scattered

beams to create an interference

image. It is a phase contrast

image and can be as small as the

unit cell of crystal. In this case,

the outgoing modulated electron

waves at very low angles

interfere with itself during

propagation through the objective

lens. All electrons emerging from

the specimen are combined at a

point in the image plane.

In short, following are the salient

features to describe working

principle of HRTEM;

Consider a very thin slice of crystal that has been tilted so that a low-index

direction is exactly perpendicular to the electron beam. All lattice planes

about parallel to the electron beam will be close enough to the Bragg

position and will diffract the primary beam.

The diffraction pattern is the Fourier Transform of the periodic potential for

the electrons in two dimensions. In the objective lens all diffracted beams

and the primary beam are brought together again; their interference provides

a back-transformation and leads to an enlarged picture of the periodic

potential.

9

This picture is magnified by the following electron-optical system and

finally seen on the screen at magnifications of typically 106.[13-14-15]

TOPIC No. 05

APPLICATIONS of HRTEM

5.1CoFe2O4:BaTiO3Core Shell Nanocomposite

High Resolution Transmission Electron Microscope images confirm the core shell

structure.The CFO: BTO core shell nanoparticles are shown as;

Figure shows the core shell nanoparticles of CFO: BTO. Two crystallographic

phases are evident and were identified by measuring the interplanar spacings, d, of

an enlarged image.[8]

5.2Characterization of ZnO Nanotubes

Structural properties of the as-synthesized ZnO nanotubes were done by HRTEM.[10]

10

References

1: http://en.wikipedia.org/wiki/Microscope

2: http://www.thefreedictionary.com/microscope

3: http://www.microscopyu.com/articles/formulas/formulasresolution.html

4: http://www.wikilectures.eu/index.php/Magnification_of_optical_microscope

5: http://www.gcsescience.com/pwav24.htm

6: https://answers.yahoo.com/question/index?qid=20080516234223AA7QV11

7:http://www2.warwick.ac.uk/fac/sci/physics/current/postgraduate/regs/mpags/ex5/techniques/structural/tem/ ,

http://portal.tugraz.at/portal/page/portal/felmi/research/TEM%20and%20Nanoanalysis/Principles%20of%20TEM

8: http://www.sciencedirect.com/science/article/pii/S0304885314010658#(Paper had been accepted at

October 27, 2014)

9: http://www.sciencedirect.com/science/article/pii/S0926337314005773#(Paper had been accepted at

September 21, 2014)

10:http://www.sciencedirect.com/science/article/pii/S1386142514011809# (Paper had been accepted at

July 29, 2014)

11:http://www.tandfonline.com/doi/abs/10.1080/1536383X.2014.885954#.VKjpr8lYi-U (Paper had been

accepted at January 17, 2014)

12:http://www.sciencedirect.com/science/article/pii/S0925838814023913# (Paper had been accepted at

September 26, 2014)

13-14-15:http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_6/backbone/r6_3_4.pdf

http://www.researchgate.net/post/What_is_the_difference_between_TEM_and_HRTEM

https://www.google.nl/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&ved=0CE

kQFjAI&url=http%3A%2F%2Fcaur.uga.edu%2FHRTEM_Fan.ppt&ei=SaGmVLKHFcG0UbeGgMg

L&usg=AFQjCNGdiWkvYd6ZTGZX7DckCxKS9fvoEA