Surface and Materials Analysis Techniques

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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

				
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