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