HW 1
1. Seat preference – None
2. Name of supervisor – Dr. Yuxin Wang
Email address - Yuxin Wang <yuxin.wang1@mail.wvu.edu>
3. no, this is first.
4. no, this is first.
5. My project is of microwave assisted pyrolysis
6. metal oxide catalyst powders
7. I don’t think so!
HW 2
1. Wavelength 0.037 A, yes in principle it can resolve it. The spatial resolution of retinal
image determines how small an object can be distinguished depending on 3 factors size
of receptor cells ,2. Imperfection of focusing, 3. Diffraction of light at the entrance of pupil
of eye.
Solution for this limitation: - Cs-corrector for STEM
2. The vacuum level needed for conventional TEM with thermionic electron source is 10 -4
Pa. Vacuum level is achieved using the following pumps includes Ion pump,
Turbomolecular pump and diffusion pumps high/Ultra high vacuum.
3. Ordinary contamination that can be induced easily into the high vacuum TEM column is
majorly ourselves and includes:-Touching anything that will get in the high vacuum TEM,
Breathing on the specimen and not using latex gloves when loading specimen, Not pre
pump fresh vacuum in film dissector.
The working principle of ACD is that two things happen at the same time the cool trap is
heated so the dirt condensed on it desorbs and the pumping is rerouted so this dirt can
be pumped out.
HW 3
1. The two types of electron sources used in TEM are Thermionic and Field-emission sources.
In thermionic sources, Tungsten (W) filaments or Lanthanum hexaboride (LaB6) crystals
are used to produces electrons when heated. Wehnelt cylinder is used to controlling and
focusing electron beam for thermionic emissions.
In field emissions, fine tungsten needles are used. In this method, the electron is produced
when a large electric potential is applied between it and an anode. Field emission can only
take place if the surface is free of contaminants and oxide, in ultra-high vacuum
conditions.
2. The two thermionic sources which are used in TEMs are Tungsten (W) and Lanthanum
hexaboride (LaB6).
Properties: - yield smallest source size for best coherency and images
3.
Thermionic emission
Field emission
uses Tungsten filaments or LaB6 crystals. uses Tungsten needles.
Electrons are produce using heat
electrons are produced with large
electric potential difference
Produces less monochromatic and more Produces
more
monochromatic
white electrons.
electrons and less white electron
4. Brightness can be measured by current density which is electrons per unit area per unit
time. Brightness is the current density per unit solid angle of the source. Brightness
increases linearly with increasing accelerating voltage for thermionic sources.
5. FEG must be operated under high vacuum condition to keep the contaminants and oxide
free surface.
6. Yes, the tungsten source will get brighter if we sharpen the tip of the hairpin because of
spatial coherency or brightness. As the radius is reduced the electric field emission will
increases.
HW 4
1. Electron is negatively charged particle. In TEM the emitted electron work on the principle
of electron scattering, wave particle duality of electron beam is also accounted while
interpreting TEM.
2. Forward scattering takes place when the sample is thin. It happens at a very low angle, 110°. When the specimen gets thick, few electrons are forward scattered whereas most
electrons are backscattered. Forward scattering is coherent while backward scattering is
incoherent.
3. Forward scattering occurs in thin sample, at a very low angle, it is coherent. In thick
samples backscattering occurs, it is incoherent.
4.
Elastic scattering
Occurs in angles of 1-10° and higher angle
it has more coherency
When the angle is low, the scattering is
forward.
coherent
Inelastic scattering
occurs at very low angles (<1°).
As the sample is thick few electrons are
forward scattered
incoherent
5. Coherent Scattering –
When wavelength is identical and have same wavelength it results in coherent scattering.
Scattered electron in coherent scattering remain instep.
Incoherent Scattering- If the wavelengths does not propagate with the same wavelength
it is incoherent scattering. Incoherent scattering has no phase relationship.
HW 5
1. Secondary Electrons -. It is very small in energy and therefore it reflects the surface
topography. Secondary electrons are often used to measure the operating voltage of
a circuit in a semiconductor device.
Backscattered Electrons –. The number of backscattered electrons reaching the
detector is proportional to their atomic number. This phenomenon helps to
differentiate between different phases, providing images for the sample composition.
It is used for determining the crystallography, topography and magnetic field of the
sample.
To understand the chemistry of the sample, BSE should be used.
Secondary Electrons
Backscattered Electrons
Produced by the emissions of valence Produced by the elastic collision of
electrons of the atoms in the specimen electrons with atoms
It reflects the surface topography
Helps to differentiate between different
phases, providing images for the sample
composition
Used to measure the operating voltage Used
for
determining
the
of a circuit in a semiconductor device
crystallography,
topography,
and
magnetic field of the sample
2.
Elastic scattering
Occurs in angles of 1-10° and higher angle
it has more coherency
When the angle is low, the scattering is
forward.
coherent
Inelastic scattering
occurs at very low angles (<1°).
As the sample is thick few electrons are
forward scattered
incoherent
3. Coherent Scattering – When wavelength is identical and have same wavelength it
results in coherent scattering. Scattered electron in coherent scattering remain instep.
Incoherent Scattering- If the wavelengths does not propagate with the same
wavelength it is incoherent scattering. Incoherent scattering has no phase
relationship.
4.
5.Kikuchi pattern is the occurs due to electron scattering. It occurs in case of samples that are not
too thick. Ideal specimen thickness is that in which both the spot pattern and the Kikuchi lines
can be seen.
HW 6
1 Electron backscattered diffraction (EBSD) is a technique used to determine the crystallographic
orientation and microstructure of materials at the sub-micron scale. EBSD involves directing an
electron beam onto a polished surface of a sample and detecting the backscattered electrons
using a detector. The interaction between the incident electrons and the sample's crystalline
lattice generates a diffraction pattern, which can be used to determine the crystallographic
orientation of the sample.
In scanning electron microscopy (SEM), the electron backscattered diffraction (EBSD) signal is
generated when the incident electron beam interacts with the crystal structure of the sample.
When the incident electron beam strikes the sample, it interacts with the atoms in the crystal
lattice, generating both forward scattered and backscattered electrons.
Backscattered electrons have energies that are near the incident electron energy and are
deflected in the opposite direction of the incident beam. These backscattered electrons can be
detected using a solid-state detector placed in the SEM chamber. The detector collects the
backscattered electrons, generating a signal that can be used to determine the crystallographic
orientation of the sample.
To collect EBSD data in SEM, a specialized detector, known as an EBSD detector, is used. The EBSD
detector is typically placed at an angle to the incident electron beam, allowing it to collect the
backscattered electrons at a specific angle relative to the surface of the sample. The detector
consists of a phosphor screen that emits light when struck by electrons, which is then detected
by a charge-coupled device (CCD) camera.
As the electron beam scans across the surface of the sample, the EBSD detector records the
backscattered electrons and generates a diffraction pattern. This diffraction pattern is then
analyzed using specialized software to determine the crystallographic orientation of the sample.
The software compares the diffraction pattern with known crystallographic databases to identify
the crystal structure and orientation of the material.
unique applications of Electron Backscattered Diffraction (EBSD) in different materials:
1. Materials characterization in metallurgy: EBSD is commonly used to analyze the
microstructure and crystallographic texture of metals and alloys. It can be used to study
grain size and orientation, phase identification, and texture analysis.
2. Geological studies: EBSD is used in the field of geology to study the crystallographic
orientation and microstructure of rocks and minerals. It can be used to identify mineral
phases and to study the deformation and recrystallization of rocks.
3. Semiconductor analysis: EBSD is used in the semiconductor industry to study the
crystallographic orientation and defect structure of materials used in electronic devices.
It can be used to study the microstructure of thin films, the interface between different
materials, and to identify defects such as dislocations and grain boundaries.
2. Pole figures are graphical representations of the distribution of crystallographic orientations
in a polycrystalline material. They are commonly used to analyze the preferred orientation or
texture of a material. The procedure for establishing pole figures typically involves the following
steps:

Preparation of the sample: The first step is to prepare a polished and flat surface of the
material. The surface needs to be free from any surface deformations or scratches that
can affect the diffraction pattern.
 Orientation determination: The sample is mounted on a goniometer and rotated in
different directions relative to the incident X-ray or electron beam. The diffraction pattern
is recorded for each orientation using a detector. The orientation of each diffracted spot
is determined using software that compares the pattern with a reference database of
known diffraction angles.
 Pole figure calculation: The orientation data is then used to calculate the pole figure. The
pole figure is a 2D map of the crystallographic orientation of the material, where each
point on the map represents a specific orientation.
 Interpretation: The pole figure is interpreted to determine the preferred orientation or
texture of the material. This information can be used to understand the anisotropic
properties of the material.
The inverse pole figure is a graphical representation of the same information as the pole figure,
but with the axes of the coordinate system reversed. In the inverse pole figure, the
crystallographic axes of the material are represented on the surface of a unit sphere, and the
orientation of each crystal is represented by a point within the sphere. The inverse pole figure is
useful for understanding the crystallographic relationships between different grains in the
material. The main difference between the pole figure and inverse pole figure is the way the data
is represented graphically.
3. In an EBSD map, the orientation of each crystal in the material is represented by a unique color.
The color coding is based on the crystallographic orientation of the material, which is determined
by the pattern of backscattered electrons. In general, grains that have similar orientations will be
represented by similar colors, while grains with different orientations will be represented by
different colors.
The color coding is usually represented using a color wheel, where each color represents a
particular crystallographic orientation. The orientation information is typically presented as an
RGB (red-green-blue) color code, where each color channel represents a particular
crystallographic direction. For example, in a cubic crystal system, the (100) direction is
represented by red, the (010) direction by green, and the (001) direction by blue. By combining
these three colors in different proportions, a unique color can be assigned to each crystal
orientation.
In addition to color coding, EBSD maps may also include other types of information, such as grain
boundaries, phase boundaries, and deformation patterns. These additional features can help to
provide a more complete picture of the material's microstructure and properties.
HW 7 / Quiz 2
1 . One key difference between electron and ion illumination sources is the energy of the particles
they generate. Electrons typically have much lower mass and higher energy than ions, which
means that they can penetrate deeper into a sample and provide higher resolution images.
However, ions can be used to probe the chemical composition of a sample with greater sensitivity
than electrons.
Another difference is the type of information that can be obtained. Electron illumination sources
are better suited for imaging and analysis of the internal structure of a sample, while ion
illumination sources are better suited for analyzing the chemical composition of the sample's
surface.
2. Scanning electron microscopy (SEM) and focused ion beam (FIB) are both imaging and analysis
techniques that use a focused beam to probe the surface of a sample. However, there are several
differences between these two techniques in terms of the instrumentation and signals utilized
for imaging and analysis.
Instrumentation:
SEM uses an electron beam, which is focused onto the surface of the sample using a series of
electromagnetic lenses. The electrons interact with the atoms in the sample, producing signals
such as secondary electrons, backscattered electrons, and X-rays, which are detected by
detectors and used to create an image of the sample.
FIB, on the other hand, uses a beam of charged ions, typically gallium ions, which are focused
onto the sample using a series of electromagnetic lenses. The ions interact with the atoms in the
sample, sputtering away material and producing signals such as secondary electrons,
backscattered ions, and ions emitted from the sample, which are detected by detectors and used
to create an image of the sample.
Signals:
SEM and FIB both utilize several signals to create images of the sample. These signals include:
Secondary electrons: Electrons that are ejected from the surface of the sample when it is
bombarded with an electron or ion beam. These electrons are detected by a detector and used
to create an image of the surface topography.
Backscattered electrons/ions: Electrons or ions that are reflected back from the sample surface
due to interactions with the sample's atoms. These signals are detected by a detector and used
to create an image of the sample's composition.
3. Some examples of FIB applications in materials science are:
Sample preparation: FIB can be used to prepare cross-sections and thin sections of materials for
examination using other techniques, such as transmission electron microscopy (TEM) and
scanning transmission electron microscopy (STEM).
Nanofabrication: FIB can be used to create nanoscale structures, such as patterns and cavities,
on a variety of materials, including metals, semiconductors, and polymers.
Failure analysis: FIB can be used to investigate the cause of material failures, such as corrosion,
cracking, and wear.
Surface modification: FIB can be used to modify the surface of materials, such as introducing
defects, doping, or creating nanostructures, to enhance their properties.
Microanalysis: FIB can be used for microanalysis of materials, such as determining the elemental
composition and crystal structure of materials and mapping the distribution of impurities.
Device fabrication: FIB can be used to fabricate micro and nano-electronic devices, such as
transistors, nanowires, and sensors.
Ion implantation: FIB can be used for ion implantation to introduce dopants into materials to
modify their electrical and optical properties.
4. Focused ion beam (FIB) technology is particularly suitable for making transmission electron
microscopy (TEM) samples due to its unique features, including:
High resolution: FIB systems can produce a focused ion beam with a spot size as small as a few
nanometers, allowing for precise milling of TEM samples with high resolution.
Precise material removal: FIB can precisely remove material from the sample, allowing for the
creation of thin lamellae with thicknesses as low as a few tens of nanometers, which are ideal for
TEM imaging.
Three-dimensional imaging: FIB can be used to create a thin lamella from a bulk material,
allowing for 3D imaging of the material using TEM.
In situ sample preparation: FIB can perform sample preparation directly in the TEM chamber,
enabling real-time imaging of the sample during preparation.
Versatility: FIB can be used to prepare TEM samples from a wide range of materials, including
metals, semiconductors, ceramics, and polymers.
5. The major steps for making transmission electron microscopy (TEM) samples are:
Sample selection: The first step is to select an appropriate sample for TEM analysis. Samples
should be flat and thin enough to be electron transparent, typically less than 200 nanometers
thick.
Sample preparation: There are several methods for preparing TEM samples, including mechanical
polishing, ion milling, and focused ion beam (FIB) milling. Each method has its own advantages
and disadvantages, and the choice of method depends on the nature of the sample and the
desired outcome.
Mounting the sample: The prepared sample is mounted on a TEM grid, which is typically a thin
metal grid with a diameter of 3-5 millimeters. The grid is coated with a thin film of carbon or
other materials to support the sample and prevent electron beam damage.
Imaging: The sample is placed in the TEM column, and an electron beam is focused onto the
sample. The electrons interact with the sample, and the resulting image is magnified and
projected onto a screen or detector. Different imaging modes, such as bright field, dark field, and
high-resolution TEM, can provide different types of information about the sample.
Analysis: TEM analysis can provide information about the microstructure, crystal structure, and
chemistry of materials at the nanoscale level. Various techniques, such as diffraction, imaging,
and spectroscopy, can be used to analyze the sample and obtain information about its properties.
HW 8
1. Field ion microscopy (FIM) is a type of microscopy that utilizes the principles of field emission
to obtain extremely high-resolution images of the surfaces of metals and other conductive
materials.
In FIM, a sample is placed in a vacuum chamber and subjected to a high electric field, typically on
the order of several volts per nanometer. At this high electric field, electrons are emitted from
the surface of the sample and are attracted to an electrode, called a "field ionizer", positioned a
short distance away.
As the emitted electrons approach the field ionizer, they undergo a process called "field
ionization", in which they are ionized and then accelerated back towards the surface of the
sample. As the ionized electrons approach the surface, they cause the emission of additional
electrons, creating a cascade of ionization events that produces a strong electrical signal. This
signal can be detected and used to create an image of the surface of the sample, with subnanometer resolution. The image is formed by scanning a sharp needle-like probe over the
surface of the sample and measuring the electrical signal generated by the ionization events.
The high resolution of FIM is because the emitted electrons are localized to atomic-scale regions
on the surface of the sample, which allows for the imaging of individual atoms and the
determination of their positions in three-dimensional space. FIM has been used to study a wide
range of materials, including metals, semiconductors, and insulators, and has played an
important role in the development of nanotechnology and materials science.
2. One of the biggest challenges for imaging and identifying individual atoms using Field Ion
Microscopy (FIM) is that the signal-to-noise ratio is low, which can make it difficult to distinguish
individual atoms. In addition, the field evaporation process that leads to ionization of the atoms
on the surface can be highly stochastic, resulting in a non-uniform evaporation and thus
introducing distortions in the resulting image.
Atom Probe Tomography (APT) is an alternative technique that overcomes many of the
challenges associated with FIM. APT uses a pulsed electric field to evaporate atoms from the
sample surface one-by-one, in a highly controlled manner. The evaporated ions are then analyzed
using a mass spectrometer, providing highly accurate information about the elemental
composition and three-dimensional position of individual atoms within the sample.
Some of the specific advantages of APT over FIM include:




Higher spatial resolution: APT can achieve sub-nanometer spatial resolution, allowing for
imaging and identification of individual atoms with higher precision.
Better signal-to-noise ratio: APT has a higher signal-to-noise ratio than FIM, making it
easier to distinguish individual atoms.
Better control of ionization: APT uses a pulsed electric field to ionize atoms one-by-one,
allowing for better control of the ionization process and reducing the stochastic nature of
the field evaporation process in FIM.
Wider range of materials: APT can be used to study a wider range of materials than FIM,
including insulators and semiconductors.
3. Atom Probe Tomography (APT) is a powerful technique for imaging and analyzing the atomic
structure of materials at sub-nanometer scales. However, there are some specific requirements
for samples that are suitable for APT imaging and analysis. These requirements include:





Sample size and geometry: APT typically requires samples that are needle-shaped or have
a pointed tip, with a length of 100-500 micrometers and a diameter of 50-200
nanometers. The sample needs to be mounted on a suitable substrate that is conductive
and stable under high vacuum conditions.
Material composition: APT is primarily used for imaging and analyzing metallic materials,
although it can also be used for some semiconductors and insulators. The sample should
be free of contaminants that may interfere with the analysis, and it should have a uniform
composition throughout the volume of interest.
Chemical stability: The sample should be chemically stable under high vacuum conditions
and should not react with the ions or electrons used in the analysis. Some materials may
require special preparation or coating to protect them from oxidation or other chemical
reactions during analysis.
Homogeneity and purity: The sample should have a high degree of homogeneity and
purity to ensure accurate analysis. Any impurities or variations in the sample composition
can interfere with the accuracy of the measurements.
Electrical conductivity: The sample should be electrically conductive to allow for the
detection of the evaporated ions. For non-conductive samples, a conductive coating may
be required.
4. Atom Probe Tomography (APT) is a powerful technique for imaging and analyzing the atomic
structure of materials at sub-nanometer scales. Some of the key advantages of APT include:







High spatial resolution: APT can achieve sub-nanometer spatial resolution, allowing for
imaging and identifying individual atoms and their positions within a material.
Three-dimensional imaging: APT provides 3D imaging of the atomic structure of a
material, allowing for the visualization of complex nanostructures and interfaces.
Elemental composition analysis: APT provides highly accurate information about the
elemental composition of a material at the atomic scale.
Isotopic analysis: APT can also be used to analyze the isotopic composition of a material,
providing information about the distribution of isotopes within the sample.
Chemical bonding information: APT can provide information about the chemical bonding
and coordination of atoms within a material, allowing for a better understanding of
chemical reactions and processes.
Wide range of materials: APT can be used to study a wide range of materials, including
metals, semiconductors, and insulators.
Quantitative analysis: APT provides quantitative analysis of the atomic structure and
composition of a material, allowing for accurate characterization and comparison of
different samples.
5. Some of the current limitations of APT imaging and analysis include:






Sample preparation: APT requires samples that are carefully prepared, mounted, and
prepared under high vacuum conditions, which can be time-consuming and challenging.
Limited sample size: APT requires small sample sizes, typically in the range of 100-500
micrometers in length and 50-200 nanometers in diameter. This can limit the amount of
material that can be analyzed, particularly for materials that are difficult to obtain or are
rare.
Limited depth of analysis: The analysis depth of APT is typically limited to 50-100
nanometers, which can make it challenging to study the bulk properties of a material. It
may also miss important features that are located deeper within the material.
Detection efficiency: The efficiency of detecting the evaporated ions can be limited,
particularly for low-mass ions, which can lead to lower sensitivity and reduced spatial
resolution.
Data analysis: APT data analysis requires specialized software and expertise to analyze
the large amounts of data generated during the analysis, which can be time-consuming
and challenging.
Cost: APT equipment is expensive, and the analysis process can be time-consuming and
require specialized expertise, which can limit its accessibility to researchers.