View
3.611
Download
1
Category
Tags:
Preview:
DESCRIPTION
surface and materials analysis techniques for nanoeducation
Citation preview
Surface and Materials Analysis Techniques
Nanotechnology
Foothill College
Your Instructor
• Robert Cormia
• Associate Professor, Foothill College
• Engineering 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 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 (<100A)
XPS/AES Analysis Volume
AES - Auger
• Surface sensitivity
• Microbeam
• Depth profiling
• Elemental composition
• Some chemical bonding
Why the Odd Name?
The M ach ine
The M an
Auger (as in ‘Pierre’)
1923:Pierre Auger
d iscovers
the A uger process
Electron Spectroscopy
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.
W hy is A uger so surface sensitive?
Re f: C ha rle s Eva ns & Asso c . we b p a g e tuto ria l b y Ro n Flle m ing http ://www.c e a .c o m
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 SpectroscopySmall Area Detection
X-ray BeamX-ray Beam
X-ray penetration X-ray penetration depth ~1depth ~1m.m.Electrons can be Electrons can be excited in this excited in this entire volume.entire volume.
X-ray excitation area ~1x1 cmX-ray excitation area ~1x1 cm22. Electrons . Electrons are emitted from this entire areaare emitted from this entire area
Electrons are extracted Electrons are extracted only from a narrow solid only from a narrow solid angle.angle.
1 mm1 mm22
10 nm10 nm
XPS spectral lines are XPS spectral lines are identified by the shell identified by the shell from which the electron from which the electron was ejected (1s, 2s, 2p, was ejected (1s, 2s, 2p, etc.).etc.).
The ejected The ejected photoelectron has photoelectron has kinetic energy:kinetic energy:
KE=hv-BE-KE=hv-BE- Following this process, Following this process,
the atom will release the atom will release energy by the emission energy by the emission of an Auger Electron.of an Auger Electron.
Conduction BandConduction Band
Valence BandValence Band
L2,L3L2,L3
L1L1
KK
FermiFermiLevelLevel
Free Free Electron Electron LevelLevel
Incident X-rayIncident X-rayEjected PhotoelectronEjected Photoelectron
1s1s
2s2s
2p2p
The Photoelectric Process
L electron falls to fill core L electron falls to fill core level vacancy (step 1).level vacancy (step 1).
KLL Auger electron KLL Auger electron emitted to conserve emitted to conserve energy released in step energy released in step 1.1.
The kinetic energy of the The kinetic energy of the emitted Auger electron is: emitted Auger electron is:
KE=E(K)-E(L2)-KE=E(K)-E(L2)-E(L3).E(L3).
Conduction BandConduction Band
Valence BandValence Band
L2,L3L2,L3
L1L1
KK
FermiFermiLevelLevel
Free Free Electron Electron LevelLevel
Emitted Auger ElectronEmitted Auger Electron
1s1s
2s2s
2p2p
Auger Relation of Core Hole
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
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
Surface Treatment of NiTi
Molecular Self Assembly
Figure1: 3D diagram of a lipid bilayer membrane - water molecules not represented for clarity
http://www.shu.ac.uk/schools/research/mri/model/micelles/micelles.htm
Figure 2: Different lipid model -top : multi-particles lipid molecule
-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. 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.
The Self-Assembly Process
A schematic of SAM (n-alkanethiol CH3(CH2)nSH
molecules) formation on
a Au(111) sample.
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
AFM
SPM (air, liquid, vacuum)
STM Topography Spectroscopy Lithography EChem. BEEM
SNOM(NSOM) Aperture Aperatureless Reflection Transmission
Contact Modes Topography LFM, SThM Lithography
AC Modes Topography MFM, EFM SKPM Others
EChem
A Family of Microscopes
Many Imaging Modes
AC – Close Contact Mode- Soft Samples- Sharp Probe
<20nm
DC – Contact Mode- Hard Samples- Probes > 20 nm
Material Sensing Modes Lateral Force Vibrating Phase
Crystal ScannerPoint and Scan™
Crystal SensorStage AutomationSoftware
Z Motion Control
xyz scanner
XY Motion Control
AFM Force Sensor
Optic
AFM Stage Assembly
AFM Stage for sample orientation, with scanner and optics
Signal out
Sample
When the cantilever moves up and down, the position of the laser on the photo detector moves up and down.
Differential Amplifier
AFM Light Lever – Force Sensor
High Resolution Video Microscope
Scanner
Sample Puck
X-Y Stage(in granite block)
Light LeverCrystal
Nano-R™ Stage
Software control of videomicroscope functions
Optical Microscope
High ResolutionVideo Microscope
Easy Sample Load
Load and Unload Sample Positions
Sample Puck
Video Optical Microscope
Laser AlignmentFeature Location
Information Technology – DVD
Consumer – Razor Blade
Cutting edge of razor blade
4 X 4 µ
Consumer Applications
100 X 100µ
AFM is used to understand the glossing characteristics of paper surfaces
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
http://mse.iastate.edu/microscopy/path2.html
SEM Principles of Operation
• Electron beam• Electron gun• Anode• Magnetic lens• Scanning coils• Secondary electron
detector• Stage and specimen
http://mse.iastate.edu/microscopy/beaminteractions.html
SEM Principles of Operation
http://mse.iastate.edu/microscopy/proimage.html
SEM Principles of Operation
SEM Imaging
Imaging of microscopic scale objects in high resolution
SEM Instrument
SEM – AFM Comparison
SEM AFMWide 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
• Nanolab Technologies
• Center for Microanalysis of Materials
• Stanford Nanofabrication Facility
• Exponent
• 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
Recommended