Surface and Materials Analysis Techniques

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Surface and Materials Analysis Techniques

• Nanotechnology
• Foothill DeAnza Colleges

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Your Instructor

• Robert Cormia
• Associate Professor, Foothill College
• Informatics and Nanotechnology
• Background in surface chemistry and surface
  modification, materials analysis,
• Contact info
• rdcormia_at_earthlink.net ph. 650.747.1588

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Overview

• Why characterize?
• Techniques
• Approaches
• Examples
• Where to learn more

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Why Characterize?

• Nanostructures are unknown
• QA/QC of fabrication process
• Failure analysis of products
• Materials characterization
• Process development / optimization

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Characterization Techniques

• Surface analysis
• Image analysis
• Organic analysis
• Structural analysis
• Physical properties

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Types of Approaches

• Failure analysis
• Problem solving
• Materials characterization
• Process development
• QA/QC

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Industry Examples

• Semiconductors and MEMS
• Bionanotechnology
• Self Assembled Monolayers (SAMs)
• Thin film coatings
• Plasma deposited films

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Surface Techniques

• AES Auger Electron Spectroscopy
• XPS X-ray Photoelectron Spectroscopy
• SSIMS Static Secondary Ion Spectroscopy
• TOF-SIMS Time-Of-Flight SIMS
• LEEDS Low Energy Electron Diffraction

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Surface Analysis

• Electron Spectroscopies
• XPS X-ray Photoelectron Spectroscopy
• AES Auger Electron Spectroscopy
• EELS Electron Energy Loss Spectroscopy

• Ion Spectroscopies
• SIMS Secondary Ion Mass Spectrometry
• SNMS Sputtered Neutral Mass Spectrometry
• ISS Ion Scattering Spectroscopy
• RBS Rutherford Back Scattering

The Study of the Outer-Most Layers of Materials
(lt100A)
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XPS/AES Analysis Volume
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AES - Auger

• Surface sensitivity
• Microbeam
• Depth profiling
• Elemental composition
• Some chemical bonding

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Why the Odd Name?
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Surface Sensitivity

• Escape depth of electrons limits the sample
  information volume.
• For AES and XPS, this is 40 Angstroms.
• Angle of sample to detector can be varied to
  change the surface sensitivity.

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Auger Data Formats
Raw Data
Differentiated Data
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Auger Instrumentation
PHI Model 660 Scanning Auger Microprobe
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Sputtering (Ion Etching) of Samples
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Al/Pd/GaN Thin Film Example
(cross section)
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Al/Pd/GaN Profile Data
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Al/Pd/GaN Atomic Concentration Data
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XPS / ESCA

• Surface sensitivity
• Microbeam resolution
• Depth profiling
• Elemental composition
• Some chemical bonding

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What is XPS / ESCA?
X-ray Photoelectron Spectroscopy (XPS), also
known as Electron Spectroscopy for Chemical
Analysis (ESCA) is a widely used technique to
investigate the chemical composition of surfaces.
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X-ray Photoelectron SpectroscopySmall Area
Detection
Electrons are extracted only from a narrow solid
angle.
X-ray Beam
X-ray penetration depth 1mm. Electrons can be
excited in this entire volume.
10 nm
1 mm2
X-ray excitation area 1x1 cm2. Electrons are
emitted from this entire area
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The Photoelectric Process
Ejected Photoelectron
Incident X-ray

• XPS spectral lines are identified by the shell
  from which the electron was ejected (1s, 2s, 2p,
  etc.).
• The ejected photoelectron has kinetic energy
• KEhv-BE-?
• Following this process, the atom will release
  energy by the emission of an Auger Electron.

Free Electron Level
Conduction Band
Fermi Level
Valence Band
L2,L3
2p
L1
2s
K
1s
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Auger Relation of Core Hole
Emitted Auger Electron
Free Electron Level

• L electron falls to fill core level vacancy (step
  1).
• KLL Auger electron emitted to conserve energy
  released in step 1.
• The kinetic energy of the emitted Auger electron
  is
• KEE(K)-E(L2)-E(L3).

Conduction Band
Fermi Level
Valence Band
L2,L3
2p
L1
2s
K
1s
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Surface Analysis Tools
SSX-100 ESCA on the left, Auger Spectrometer on
the right
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XPS Spectrum of Carbon

• XPS can determine the types of carbon present by
  shifts in the binding energy of the C(1s) peak.
  These data show three primary types of carbon
  present in PET. These are C-C, C-O, and O-CO

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Surface Treatments

• Control friction, lubrication, and wear
• Improve corrosion resistance (passivation)
• Change physical property, e.g., conductivity,
  resistivity, and reflection
• Alter dimension (flatten, smooth, etc.)
• Vary appearance, e.g., color and roughness
• Reduce cost (replace bulk material)

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Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants SJSU
Guna Selvaduray
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Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants SJSU
Guna Selvaduray
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Surface Treatment of NiTi

• XPS spectra of the Ni(2p) and Ti(2p) signals from
  Nitinol undergoing surface treatments show
  removal of surface Ni from electropolish, and
  oxidation of Ni from chemical and plasma etch.
  Mechanical etch enhances surface Ni.

Biomedical Devices and Biomedical Implants SJSU
Guna Selvaduray
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Molecular Self Assembly
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Self Assembled Monolayers

• SAMS Self Assembled Monolayers
• Cast a film onto a surface from a liquid
• You can also use a spray technique
• Films spontaneously order / reorder
• Modifying surface properties yields materials
  with a bulk strength but modified surface
  interaction phase

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The Self-Assembly Process
A schematic of SAM (n-alkanethiol CH3(CH2)nSH
molecules) formation on a Au(111) sample.
The self-assembly process. An n-alkane thiol is
added to an ethanol solution (0.001 M). A gold
(111) surface is immersed in the solution and the
self-assembled structure rapidly evolves. A
properly assembled monolayer on gold (111)
typically exhibits a lattice.
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SAM Technology Platform

• SAM reagents are used for electrochemical,
  optical and other detection systems.
  Self-Assembled Monolayers (SAMs) are
  unidirectional layers formed on a solid surface
  by spontaneous organization of molecules.
• Using functionally derivatized C10 monolayer,
  surfaces can be prepared with active chemistry
  for binding analytes.

http//www.dojindo.com/sam/SAM.html
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SAM Surface Derivatization

• Biomolecules (green) functionalized with biotin
  groups (red) can be selectively immobilized onto
  a gold surface using a streptavidin linker (blue)
  bound to a mixed biotinylated thiol / ethylene
  glycol thiol self-assembled monolayer.

http//www.chm.ulaval.ca/chm10139/peter/figures4.d
oc
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SAMs C10 Imaging with AFM
http//sibener-group.uchicago.edu/has/sam2.html
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AES vs. XPS?

• AES needs an electrically conductive substrate
  metals and semiconductors
• XPS can analyze polymers and metals
• AES very small area imaging
• XPS somewhat small area imaging
• Depth profiling of thin films, faster by AES, but
  only for conductive materials

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Image Analysis

• AFM
• Atomic Force Microscopy
• SEM - EDX
• Scanning Electron Microscopy
• Energy Dispersive Wavelength X-Ray
• TEM
• Transmission Electron Microscope

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Seeing the Nano World

• Because visible light has wavelengths that are
  hundreds of nanometers long we can not use
  optical microscopes to see into the nano world.
  Atoms are like boats on a sea compared to light
  waves.

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AFM

• Atomic Force Microscope (AFM)
• Scanning Tunneling Microscope (STM)
• Scanning Probe Microscopy (SPM)
• Magnetic Force Microscopy (MFM)
• Lateral Force Microscopy (LFM)

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AFM Instrumentation
PNI Nano-R AFM Instrumentation as used at
Foothill College
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What is an SPM?

• An SPM is a mechanical imaging instrument in
  which a small, lt 1 µm, probe is scanned over a
  surface. By monitoring the motion of the probe,
  the surface topography and/or images of surface
  physical properties are measured with an SPM.

z
y
z
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A Family of Microscopes
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Many Imaging Modes
DC Contact Mode - Hard Samples - Probes gt 20
nm

• AC Close Contact Mode - Soft Samples - Sharp
  Probe lt20nm

Material Sensing Modes Lateral
Force Vibrating Phase
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Crystal Scanner
Point and Scan Crystal Sensor Stage
Automation Software
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AFM Stage Assembly
AFM Stage for sample orientation, with scanner
and optics
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AFM Light Lever Force Sensor
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Nano-R Stage
High Resolution Video Microscope
Scanner
Light LeverCrystal
Sample Puck
X-Y Stage(in granite block)
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High ResolutionVideo Microscope
Optical Microscope
Software control of videomicroscope functions
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Easy Sample Load
Load and Unload Sample Positions
Sample Puck
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Video Optical Microscope
Laser AlignmentFeature Location
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Information Technology DVD
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Consumer Razor Blade
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Consumer Applications
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Metrology of Metals

• AFM can be used to understand surface morphology.
• This material was prepared using a spray / cast
  technique.

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Metrology of Structures

• The pattern and depth of this micro lens can be
  determined using an AFM.
• This helps in both development and process
  control.

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NanoMechanics- MEMS
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SEM Techniques

• Scanning Electron Microscopy (SEM)
• Wavelength Dispersive X-Ray (WDX)
• Primary electron imaging
• Secondary electron imaging
• X-ray (WDX) elemental mapping

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SEM Principles of Operation

• In an electron microscope, electrons are
  accelerated in a vacuum until their wavelength is
  extremely short. The higher the voltage the
  shorter the wavelengths.
• Beams of these fast-moving electrons are focused
  on an object and are absorbed or scattered by the
  object so as to form an image on an
  electron-sensitive photographic plate

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SEM Principles of Operation

• Electron beam
• Electron gun
• Anode
• Magnetic lens
• Scanning coils
• Secondary electron detector
• Stage and specimen

http//mse.iastate.edu/microscopy/path2.html
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SEM Principles of Operation
http//mse.iastate.edu/microscopy/beaminteractions
.html
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SEM Principles of Operation
http//mse.iastate.edu/microscopy/proimage.html
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SEM Imaging

• Imaging of microscopic scale objects in high
  resolution

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SEM Instrument
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SEM AFM Comparison
SEM AFM Wide range of sample
roughness True 3D image Operated in low to high
vacuum Vacuum, Air or
Liquid
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Imaging Applications

• Imaging individual atoms.
• Imaging of surface materials.
• Imaging of nanotubes.

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TEM Diagram

• The TEM works like a slide projector. A beam of
  electron is shined though the surface with the
  transmitted electrons projector on a screen.

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TEM in Use

• The drawback is the sample must be very thin for
  the electrons to pass through and the sample has
  to be able to withstand the high energy electrons
  and a strong vacuum.

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X-Ray Diffraction

• X-Ray diffraction is an important tool in the
  characterization of nanostructures.
• It is the principle means by which the atomic
  structure of materials can be determined.

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Summary of Techniques

• Surface techniques
• AES
• ESCA / XPS
• Deeper techniques
• RBS and PIXE
• Ion techniques
• SIMS

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Materials Analysis Review

• What is it you need to know?
• What volume of material?
• Elemental information?
• Chemical information?
• Molecular information?
• Structural information?

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Analyst Skills

• Instrument skills
• Analytical reasoning ability
• Materials science
• Process knowledge
• Industry knowledge

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Commercial Laboratories

• Evans Analytical Group
• Center for Microanalysis of Materials
• Stanford Nanofabrication Facility
• Failure Analysis Associates
• Balaz Analytical Laboratories

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Summary

• Nanostructures are very small
• You need tools that characterize atoms and the
  world (neighborhood) of an atom
• Composition and chemistry
• Molecular bonding information
• Structural information
• Film thickness especially