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Surface and Materials
Analysis Techniques
Nanotechnology
Foothill DeAnza Colleges
Your Instructor
• Robert Cormia
• Associate Professor, Foothill College
• Informatics and Nanotechnology
• Background in surface chemistry and
surface modification, materials analysis,
• Contact info
– rdcormia@earthlink.net ph. 650.747.1588
Overview
• Why characterize?
• Techniques
• Approaches
• Examples
• Where to learn more
Why Characterize?
• Nanostructures are unknown
• QA/QC of fabrication process
• Failure analysis of products
• Materials characterization
• Process development / optimization
Characterization Techniques
• Surface analysis
• Image analysis
• Organic analysis
• Structural analysis
• Physical properties
Types of Approaches
• Failure analysis
• Problem solving
• Materials characterization
• Process development
• QA/QC
Industry Examples
• Semiconductors and MEMS
• Bionanotechnology
• Self Assembled Monolayers (SAMs)
• Thin film coatings
• Plasma deposited films
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
Surface Analysis
• Electron • Ion Spectroscopies
Spectroscopies – SIMS: Secondary Ion
– XPS: X-ray Mass Spectrometry
Photoelectron
– SNMS: Sputtered
Spectroscopy
Neutral Mass
– AES: Auger
Spectrometry
Electron
Spectroscopy – ISS: Ion Scattering
– EELS: Electron Spectroscopy
Energy Loss – RBS: Rutherford
Spectroscopy Back Scattering
The Study of the Outer-Most Layers of Materials (<100A)
XPS/AES Analysis Volume
AES - Auger
• Surface sensitivity
• Microbeam
• Depth profiling
• Elemental composition
• Some chemical bonding
Why the Odd Name?
Auger (as in ‘Pierre’)
Electron Spectroscopy
The Machine
The Man
1923:
Pierre Auger discovers
the Auger process
Surface Sensitivity
Why is Auger so surface sensitive?
• 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.
R va
ef: Charles E ns & Assoc. web pa ge tutoria l by Ron Fllem ing
http://www.c ea.c om
Auger Data Formats
Raw Data Differentiated Data
Auger Instrumentation
PHI Model 660 Scanning Auger Microprobe
Sputtering (Ion Etching) of Samples
Al/Pd/GaN Thin Film Example
(cross section)
Al/Pd/GaN Profile Data
Al/Pd/GaN Atomic Concentration Data
XPS / ESCA
• Surface sensitivity
• Microbeam resolution
• Depth profiling
• Elemental composition
• Some chemical bonding
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.
X-ray Photoelectron Spectroscopy
Small Area Detection
Electrons are extracted
only from a narrow solid
X-ray Beam angle.
X-ray penetration
depth ~1mm.
Electrons can be 10 nm
excited in this
entire volume. 1 mm2
X-ray excitation area ~1x1 cm2. Electrons
are emitted from this entire area
The Photoelectric Process
Ejected Photoelectron
Incident X-ray
Free XPS spectral lines are
Electron
identified by the shell
Conduction Band Level
Fermi
from which the electron
Level was ejected (1s, 2s, 2p,
Valence Band etc.).
The ejected
2p L2,L3
photoelectron has
2s L1 kinetic energy:
KE=hv-BE-
1s K Following this process,
the atom will release
energy by the emission
of an Auger Electron.
Auger Relation of Core Hole
Emitted Auger Electron
Free
Electron
Conduction Band Level L electron falls to fill core
Fermi level vacancy (step 1).
Level
Valence Band
KLL Auger electron
emitted to conserve
2p L2,L3 energy released in step
2s L1
1.
The kinetic energy of the
emitted Auger electron is:
1s K
KE=E(K)-E(L2)-E(L3).
Surface Analysis Tools
SSX-100 ESCA on the left, Auger Spectrometer on the right
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-C=O
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)
Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
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
Molecular Self Assembly
Figure1: 3D diagram of a lipid bilayer membrane - water molecules not represented for clarity
Figure 2: Different lipid model
-top : multi-particles lipid molecule
http://www.shu.ac.uk/schools/research/mri/model/micelles/micelles.htm -bottom: single-particle lipid molecule
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
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.
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
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.doc
SAMs C10 Imaging with AFM
http://sibener-group.uchicago.edu/has/sam2.html
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
Image Analysis
• AFM
– Atomic Force Microscopy
• SEM - EDX
– Scanning Electron Microscopy
– Energy Dispersive Wavelength X-Ray
• TEM
– Transmission Electron Microscope
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.
AFM
• Atomic Force Microscope (AFM)
• Scanning Tunneling Microscope (STM)
• Scanning Probe Microscopy (SPM)
• Magnetic Force Microscopy (MFM)
• Lateral Force Microscopy (LFM)
AFM Instrumentation
PNI Nano-R AFM Instrumentation as used at Foothill College
What is an SPM?
• An SPM is a mechanical imaging instrument in which a small, <
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
A Family of Microscopes
SPM (air, liquid, vacuum)
AFM STM
Contact Modes Topography
Topography Spectroscopy
LFM, SThM Lithography
Lithography EChem.
BEEM
AC Modes
Topography
MFM, EFM SNOM(NSOM)
SKPM Aperture
Others Aperatureless
Reflection
EChem Transmission
Many Imaging Modes
DC – Contact Mode
- Hard Samples
- Probes > 20 nm
AC – Close Contact Mode
- Soft Samples
- Sharp Probe <20nm
Material Sensing Modes
Lateral Force
Vibrating Phase
Crystal Scanner
Point and Scan™
Crystal Sensor
Stage Automation
Software
AFM Stage Assembly
Z Motion Control
Optic
xyz scanner
AFM Force Sensor
XY Motion Control
AFM Stage for sample orientation, with scanner and optics
AFM Light Lever – Force Sensor
Signal out
Differential
Amplifier
Sample
When the cantilever moves up and down, the position of the
laser on the photo detector moves up and down.
Nano-R™ Stage
High Resolution Video
Microscope
Scanner
Light Lever
Crystal
Sample Puck
X-Y Stage
(in granite block)
High Resolution
Video Microscope
Optical Microscope
Software control of video
microscope functions
Easy Sample Load
Load and Unload Sample
Positions
Sample Puck
Video Optical Microscope
Laser Alignment
Feature Location
Information Technology – DVD
Consumer – Razor Blade
Cutting edge of razor blade
4X4µ
Consumer Applications
AFM is used to understand
the glossing characteristics
of paper surfaces
100 X 100µ
Metrology of Metals
• AFM can be used
to understand
surface
morphology.
• This material was
prepared using a
spray / cast
technique.
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.
NanoMechanics- MEMS
SEM Techniques
• Scanning Electron Microscopy (SEM)
• Wavelength Dispersive X-Ray (WDX)
• Primary electron imaging
• Secondary electron imaging
• X-ray (WDX) elemental mapping
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
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
SEM Principles of Operation
http://mse.iastate.edu/microscopy/beaminteractions.html
SEM Principles of Operation
http://mse.iastate.edu/microscopy/proimage.html
SEM Imaging
Imaging of microscopic scale objects in high resolution
SEM Instrument
SEM – AFM Comparison
SEM AFM
Wide range of sample roughness True 3D image
Operated in low to high vacuum Vacuum, Air or Liquid
Imaging Applications
• Imaging individual atoms.
• Imaging of surface materials.
• Imaging of nanotubes.
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.
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.
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.
Summary of Techniques
• Surface techniques
– AES
– ESCA / XPS
• Deeper techniques
– RBS and PIXE
• Ion techniques
– SIMS
Materials Analysis Review
• What is it you need to know?
• What volume of material?
• Elemental information?
• Chemical information?
• Molecular information?
• Structural information?
Analyst Skills
• Instrument skills
• Analytical reasoning ability
• Materials science
• Process knowledge
• Industry knowledge
Commercial Laboratories
• Evans Analytical Group
• Center for Microanalysis of Materials
• Stanford Nanofabrication Facility
• Failure Analysis Associates
• Balaz Analytical Laboratories
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
