Lecture-9 SIMS

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Lecture-9 SIMS NDT

• SIMS
• Basic Principles
• Instrumentation
• Mass Resolution
• Modes of Analysis
• Applications
• Non-Destructive Analysis (NDA)
• or Non-Destructive Testing (NDT)

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Instrumentation
Bombardment of a sample surface with a primary
ion beam followed by mass spectrometry of the
emitted secondary ions constitutes secondary ion
mass spectrometry (SIMS).

• Ion Sources
• Ion sources with electron impact ionization -
  Duoplasmatron Ar, O2, O-
• Ion sources with surface ionization - Cs ion
  sources
• Ion sources with field emission - Ga liquid
  metal ion sources
• Mass Analyzers
• Magnetic sector analyzer
• Quadrupole mass analyzer
• Time of flight analyzer
• Ion Detectors
• Faraday cup
• Dynode electron multiplier

Vacuum lt 10-6 torr
Ion detectors Mass Analyzers
Ip
Is
Ion sources
SIMS CAMECA 6F
Mass analyzers
http//www.youtube.com/watch?vIO-KCjxznLs
to150
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Cameca SIMS
Accelerating voltage Secondary ions have low
kinetic energies from zero to a few hundred eV.
L1, L2 and L3 - electromagnetic lens
http//www.eaglabs.com/mc/sims-instrumentation.htm
l
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Energy Analyzer and Mass Spectrometer
ESA bends lower energy ions more strongly than
higher energy ions. The sputtering process
produces a range of ion energies. An energy slit
can be set to intercept the high energy ions.
Sweeping the magnetic field in MA provides the
separation of ions according to mass-to-charge
ratios in time sequence.
E
Mass Analyzer (MA)
Degree (r) of deflection of ions by the magnetic
filed depends on m/q ratio. V - ion acceleration
voltage
Magnet Sector
Electrostatic Sector
r - radius of curvature of an ion
Energy Focal plane
https//www.youtube.com/watch?vNuIH9-6Fm6U
at340-516
https//www.youtube.com/watch?vEzvQzImBuq8
to206
http//www.youtube.com/watch?vlxAfw1rftIA
at100-412
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Basic Equations of Mass Spectrometry
Ions kinetic E function of accelerating voltage
(V) and charge (z).
r
Centrifugal force
Applied magnetic field Lorentz force
Balance as ion goes through flight tube
r
Combine equations to obtain
r
Fundamental equation of mass spectrometry
Change mass-to-charge (m/z) ratio by changing V
or changing B. NOTE if B, V, z constant,
then
m/z m/e for singly charged ions
r - radius of circular ion path
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MA
ESA
MA
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Ion Detectors
http//www.eaglabs.com/mc/sims-secondary-ion-detec
tors.htmlnext
A Faraday cup measures the ion current hitting a
metal cup, and is sometimes used for high current
secondary ion signals. With an electron
multiplier an impact of a single ion starts off
an electron cascade, resulting in a pulse of 108
electrons which is recorded directly. Usually
it is combined with a fluorescent screen, and
signals are recorded either with a CCD-camera or
with a fluorescence detector.
Faraday Cup
Secondary electron Multiplier 20 dynodes Current
gain 107
https//www.youtube.com/watch?vNuIH9-6Fm6U
at518-650 and to925
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M/z
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Time of Flight (TOF) SIMS - Reflectron
http//www.youtube.com/watch?vZoAUxsEBUnk
TOF-SIMS http//www.youtube.com/watch?vKAWu6SmvHj
c
TOF SIMS is based on the fact that ions with the
same energy but different masses travel with
different velocities. Basically, ions formed by a
short ionization event are accelerated by an
electrostatic field to a common energy and travel
over a drift path to the detector. The lighter
ones arrive before the heavier ones and a mass
spectrum is recorded. Measuring the flight time
for each ion allows the determination of its mass.

• (TOF) SIMS enables the analysis of an unlimited
  mass range with high sensitivity and
  quasi-simultaneous detection of all secondary
  ions collected by the mass spectrometer.

Schematic of time of flight (TOF) spectrometer -
reflectron
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Time of Flight (TOF) Spectrometer
TOF operates in a pulse mode.
During a short pulse of E, ions are accelerated
and acquire a constant kinetic energy kinetic
energy mv2/2 but have different m/q and
Vs. Thus they arrive to the detector in time
sequence after travel the same distance. Time
required to travel distance l from the ion origin
to the detector is The light ions with
higher Vs arrive to the detector first.
pulse width
Schematic of TOF spectrometer with a spectrum
In order to provide higher resolution the pulse
should be as narrow as 1-10 ns. The pulse
repetition frequency is usually in a kHz range.
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SIMS can do trace element analysis
WDS 100ppm EDS 1000ppm
Detection limit is affected by
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1 and 2 Static SIMS
3 Dynamic SIMS
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Dynamic Secondary Ion Mass Spectrometry
Dynamic SIMS involves the use of a much higher
energy primary beam (larger amp beam current). It
is used to generate sample depth profiles. The
higher ion flux eats away at the surface of the
sample, burying the beam steadily deeper into the
sample and generating secondary ions that
characterize the composition at varying depths.
The beam typically consists of O2 or Cs ions
and has a diameter of less than 10 µm. The
experiment time is typically less than a second.
Ion yield changes with time as primary particles
build up on the material effecting the ejection
and path of secondary ions.
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Dynamic SIMS Depth Profiling
Factors affecting depth resolution
http//www.youtube.com/watch?v-7gSbaslRCUfeature
related
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Crater Effect
(a) (b)
(a) Ions sputtered from a selected central area
(using a physical aperture or electronic gating)
of the crater are passed into the mass
spectrometer. (b) The beam is usually swept over
a large area of the sample and signal detected
from the central portion of the sweep. This
avoids crater edge effects.
The analyzed area is usually required to be at
least a factor of 3 ? 3 smaller than the scanned
area.
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Sample Rotation Effect
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Gate Oxide Breakdown
http//www.youtube.com/watch?vIO-KCjxznLsNR1fe
atureendscreen 208-240
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Dynamic SIMS vs Static SIMS
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http//www.youtube.com/watch?vIO-KCjxznLs at245
-318
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Mapping Chemical Elements

• Some instruments simultaneously produce high mass
  resolution and high lateral resolution. However,
  the SIMS analyst must trade high sensitivity for
  high lateral resolution because focusing the
  primary beam to smaller diameters also reduces
  beam intensity. High lateral resolution is
  required for mapping chemical elements.

34 S
197 AU

• The example (microbeam) images show a pyrite
  (FeS2) grain from a sample of gold ore with gold
  located in the rims of the pyrite grains. The
  image numerical scales and associated colors
  represent different ranges of secondary ion
  intensities per pixel.

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Summary

• SIMS can be used to determine the composition of
  organic and inorganic solids at the outer 5 nm of
  a sample.
• To determine the composition of the sample at
  varying spatial and depth resolutions depending
  on the method used. This can generate spatial or
  depth profiles of elemental or molecular
  concentrations.
• These profiles can be used to generate element
  specific images of the sample that display the
  varying concentrations over the area of the
  sample.
• To detect impurities or trace elements,
  especially in semi-conductors and thin filaments.
• Secondary ion images have resolution on the order
  of 0.5 to 5 µm.
• Detection limits for trace elements range between
  1012 to 1016 atoms/cc.
• Spatial resolution is determined by primary ion
  beam widths, which can be as small as 100 nm.

SIMS is the most sensitive elemental and isotopic
surface microanalysis technique (bulk
concentrations of impurities of around 1
part-per-billion). However, very expensive.
http//www.youtube.com/watch?vQTjZutbLRu0
at138-214 advantages and disadvantages of SIMS
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Review Questions for SIMS

• What are matrix effects?
• What is the difference between ion yield and
  sputtering yield?
• When are oxygen and cesium ions used as primary
  ions?
• What is mass resolution?
• How can depth resolution be improved?
• Applications of SIMS
• Advantages and disadvantages of SIMS

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Non-destructive Analysis (NDA)Non-destructive
Testing (NDT)
https//www.nde-ed.org/index_flash.php

• Introduction to NDT
• Overview of Six Most Common NDT Methods
• Selected Applications

https//www.youtube.com/watch?vtlE3eK0g6vU
NDT very good
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Definition of NDT
The use of noninvasive techniques to determine
the integrity of a material, component or
structure or quantitatively measure some
characteristic of an object.
i.e. Inspect or measure without doing harm.
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What are Some Uses of NDT Methods?

• Flaw Detection and Evaluation
• Leak Detection
• Location Determination
• Dimensional Measurements
• Structure and Microstructure Characterization
• Estimation of Mechanical and Physical Properties
• Material Sorting and Chemical Composition
  Determination

Fluorescent penetrant indication
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Why Nondestructive?

• Test piece too precious to be destroyed
• Test piece to be reused after inspection
• Test piece is in service
• For quality control purpose
• Something you simply cannot do harm to, e.g.
  fetus in mothers uterus

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When are NDE Methods Used?
There are NDE applications at almost any stage in
the production or life cycle of a component.

• To assist in product development
• To screen or sort incoming materials
• To monitor, improve or control manufacturing
  processes
• To verify proper processing such as heat treating
• To verify proper assembly
• To inspect for in-service damage

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Six Most Common NDT Methods
Detection of surface flaws

• Visual
• Liquid Penetrant
• Magnetic
• Ultrasonic
• Eddy Current
• Radiography

Detection of internal flaws
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1. Visual Inspection
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https//www.youtube.com/watch?vxEK-c1pkTUI
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Liquid Penetrant Inspection
Low surface wetting

• A liquid with high surface wetting
  characteristics is applied to the surface of the
  part and allowed time to seep into surface
  breaking defects.

• The excess liquid is removed from the surface of
  the part.

High surface wetting
https//www.youtube.com/watch?vtlE3eK0g6vU
at248-333 https//www.youtube.com/watch?vbHTRm
TQDZzg
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Magnetic Particle Inspection (MPI)

• A NDT method used for defect detection. Fast and
  relatively easy to apply and part surface
  preparation is not as critical as for some other
  NDT methods. MPI one of the most widely
  utilized nondestructive testing methods.
• MPI uses magnetic fields and small magnetic
  particles, such as iron filings to detect flaws
  in components. The only requirement from an
  inspectability standpoint is that the component
  being inspected must be made of a ferromagnetic
  material such as iron, nickel, cobalt, or some of
  their alloys. Ferromagnetic materials are
  materials that can be magnetized to a level that
  will allow the inspection to be effective.
• The method is used to inspect a variety of
  product forms such as castings, forgings, and
  weldments. Many different industries use MPI for
  determining a component's fitness-for-use. Some
  examples of industries that use magnetic particle
  inspection are the structural steel, automotive,
  petrochemical, power generation, and aerospace
  industries. Underwater inspection is another area
  where magnetic particle inspection may be used to
  test such things as offshore structures and
  underwater pipelines.

https//www.youtube.com/watch?vtlE3eK0g6vU
at110-248 MPI https//www.nde-ed.org/EducationR
esources/CommunityCollege/MagParticle/cc_mpi_index
.php
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Magnetic Particle Inspection
https//www.youtube.com/watch?vqpgcD5k1494
to303

• The part is magnetized. Finely milled iron
  particles coated with a dye pigment are then
  applied to the specimen. These particles are
  attracted to magnetic flux leakage fields and
  will cluster to form an indication directly over
  the discontinuity. This indication can be
  visually detected under proper lighting
  conditions.

Flux leakage
Cracks just below the surface can also be
revealed. Relative direction between the
magnetic field and the defect line is important.
The magnetic particles form a ridge many times
wider than the crack itself, thus making the
otherwise invisible crack visible.
https//www.youtube.com/watch?vdQoB7jpxSe8
MPI testing procedure
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Magnetic particles

• Pulverized iron oxide (Fe3O4) or carbonyl iron
  powder can be used
• Colored or even fluorescent magnetic powder can
  be used to increase visibility
• Powder can either be used dry or suspended in
  liquid

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Advantages of MPI

• One of the most dependable and sensitive methods
  for surface defects
• fast, simple and inexpensive
• direct, visible indication on surface
• unaffected by possible deposits, e.g. oil, grease
  or other metals chips, in the cracks
• can be used on painted objects
• results readily documented with photo or tape
  impression

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Limitations of MPI

• Only good for ferromagnetic materials
• sub-surface defects will not always be indicated
• relative direction between the magnetic field and
  the defect line is important
• objects must be demagnetized before and after the
  examination
• the current magnetization may cause burn scars on
  the item examined

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https//www.youtube.com/watch?vgqJN8tyosDw
to042
Ultrasonic Inspection (Pulse-Echo)
In ultrasonic testing, high-frequency sound waves
are transmitted into a material to detect
imperfections or to locate changes in material
properties.
The most commonly used ultrasonic testing
technique is pulse echo, whereby sound is
introduced into a test object and reflections
(echoes) from internal imperfections or the
part's geometrical surfaces are returned to a
receiver.   The time interval between the
transmission and reception of pulses give clues
to the internal structure of the material.
https//www.youtube.com/watch?vtlE3eK0g6vU
at645-800 or to 1135
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Ultrasonic Inspection (Pulse-Echo)
High frequency sound waves are introduced into a
material and they are reflected back from
surfaces or flaws. Reflected sound energy is
displayed versus time, and inspector can
visualize a cross section of the specimen showing
the depth of features that reflect sound.
Principle of ultrasonic testing LEFT A probe
sends a sound wave into a test material. There
are two indications, one from the initial pulse
of the probe, and the second due to the back wall
echo. RIGHT A defect creates a third indication
and simultaneously reduces the amplitude of the
back wall indication. The depth of the defect is
determined by the ratio D/Ep
Ultrasonic Probe
f
Oscilloscope, or flaw detector screen
Ultrasonic probe is made of piezoelectric
transducers.
https//www.youtube.com/watch?vUM6XKvXWVFA
at118-308 http//www.doitpoms.ac.uk/tlplib/piez
oelectrics/applications.php
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How It Works?
At a construction site, a technician tests
a pipeline weld for defects using an
ultrasonic instrument. The scanner, which
consists of a frame with magnetic wheels, holds
the probe in contact with the pipe by a spring.
The wet area is the ultrasonic couplant (medium,
such as water and oil) that allows the sound to
pass into the pipe wall.
Spline cracking
Non-destructive testing of a swing shaft
showing spline cracking.
Backwall
Spline any of a series of projections on a
shaft that fit into slots on a corresponding
shaft, enabling both to rotate together.
Lower end
Upper end
https//www.youtube.com/watch?vUM6XKvXWVFA
at308-410
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Images obtained by C-Scan
High resolution scan can produce very detailed
images. Both images were produced using a
pulse-echo techniques with the transducer scanned
over the head side in an immersion scanning
system.
Gray scale image produced using the sound
reflected from the back surface of the coin
(inspected from heads side)
Gray scale image produced using the sound
reflected from the front surface of the coin
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Applications of Ultrasonic Inspection
Ultrasonic inspection is often performed on steel
and other metals and alloys, though it can also
be used on concrete, wood and composites, albeit
with less resolution. It is used in many
industries including steel and aluminium
construction, metallurgy, manufacturing,
aerospace, automotive and other transportation sec
tors.
Limitations of Ultrasonic Inspection
1. Manual operation requires careful attention by
experienced technicians. 2. Extensive technical
knowledge is required for the development of
inspection procedures. 3. Parts that are rough,
irregular in shape, very small or thin, or not
homogeneous are difficult to inspect. 4. Surface
must be prepared by cleaning and removing loose
scale, paint, etc. 5. Couplants are needed to
provide effective transfer of ultrasonic wave
energy between transducers and parts being
inspected unless a non-contact technique is
used.  6. Inspected items must be water
resistant, when using water based couplants that
do not contain rust inhibitors.
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Eddy Current Testing (ECT)
Electrical currents are generated in a conductive
material by an induced alternating magnetic
field. The electrical currents are called eddy
currents because they flow in circles at and just
below the surface of the material. Interruptions
in the flow of eddy currents, caused by
imperfections, dimensional changes, or changes in
the material's conductive and permeability
properties, can be detected with the proper
equipment.

• Eddy current testing can be used on all
  electrically conducting materials with a
  reasonably smooth surface.
• The test equipment consists of a generator (AC
  power supply), a test coil and recording
  equipment, e.g. a galvanometer or an oscilloscope
• Used for crack detection, material thickness
  measurement (corrosion detection), sorting
  materials, coating thickness measurement, metal
  detection, etc.

https//www.youtube.com/watch?vtlE3eK0g6vU
at1136-1238
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Eddy Current Instruments
Voltmeter
Coil
Conductive material
https//www.youtube.com/watch?vzJ23gmS3KHY
to124 what is Eddy current
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https//www.youtube.com/watch?v9A5fQtOwnzw
Applications of ECT

• Crack Detection
• Material Thickness Measurements
• Coating Thickness Measurements
• Conductivity Measurements for
• Material Identification
• Heat Damage Detection
• Case Depth Determination
• Heat Treatment Monitoring

Here a small surface probe is scanned over the
part surface in an attempt to detect a crack.
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Advantages of ECT

• Sensitive to small cracks and other defects
• Detects surface and near surface defects
• Inspection gives immediate results
• Equipment is very portable
• Method can be used for much more than flaw
  detection
• Minimum part preparation is required
• Test probe does not need to contact the part
• Inspects complex shapes and sizes of conductive
  materials

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Limitations of ECT

• Only conductive materials can be inspected
• Surface must be accessible to the probe
• Skill and training required is more extensive
  than other techniques
• Surface finish and roughness may interfere
• Reference standards needed for setup
• Depth of penetration is limited
• Flaws such as delaminations that lie parallel to
  the probe coil winding and probe scan direction
  are undetectable

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Radiography

• Radiography involves the use of penetrating
  gamma- or X-radiation to examine material's and
  product's defects and internal features. An X-ray
  machine or radioactive isotope is used as a
  source of radiation. Radiation is directed
  through a part and onto film or other media. The
  resulting shadowgraph shows the internal features
  and soundness of the part. Material thickness and
  density changes are indicated as lighter or
  darker areas on the film.

https//www.youtube.com/watch?vVscasN8jgfo
Introduction to radiography
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Film Radiography

• The film darkness (density) will vary with the
  amount of radiation reaching the film through the
  test object.
• Defects, such as voids, cracks, inclusions,
  etc., can be detected.

X-ray film
Top view of developed film
https//www.youtube.com/watch?vtlE3eK0g6vU
at335-645
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Applications of Radiography

• Can be used in any situation when one wishes to
  view the interior of an object
• To check for internal faults and construction
  defects, e.g. faulty welding
• To see through what is inside an object
• To perform measurements of size, e.g. thickness
  measurements of pipes

Limitations of Radiography

• There is an upper limit of thickness through
  which the radiation can penetrate, e.g. ?-ray
  from Co-60 can penetrate up to 150mm of steel
• The operator must have access to both sides of an
  object
• Highly skilled operator is required because of
  the potential health hazard of the energetic
  radiations
• Relative expensive equipment

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Radiographic Images
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Examples of radiograph
Burn through (icicles) results when too much heat
causes excessive weld metal to penetrate the weld
zone. Lumps of metal sag through the weld
creating a thick globular condition on the back
of the weld. On a radiograph, burn through
appears as dark spots surrounded by light
globular areas.
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For More Information on NDT
The Collaboration for NDT Education
www.ndt-ed.org
The American Society for Nondestructive Testing
www.asnt.org
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Review Questions for NDT

• Applications of NDT
• What are six most common NDT methods?
• Can liquid penetrant inspection be used to detect
  internal flaws? Why?
• Why relative direction between the magnetic field
  and the defect line is important in magnetic
  particle inspection?
• Why are couplants needed for ultrasonic
  inspection (UI)? Limitations of UI?
• Advantages and disadvantages of eddy current
  testing.
• What is rediography? Limitations of radiography.