knowledgecontextknowledgecontext.org/cosmos/surface_and_materials... · • surface analysis •...

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NanotechnologyFoothill DeAnza Colleges

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• 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

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

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

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

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

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

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• 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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• 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)

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

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The Machine

The Man

Auger (as in ‘Pierre’)

1923:Pierre Auger

discovers

the Auger process

Electron Spectroscopy

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• 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.

Why is Auger so surface sensitive?

Ref: Charles Evans & Assoc. web page tutorial by Ron Flleming http://www.cea.com

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Raw Data Differentiated Data

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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

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

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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.

#'����$������������������������Small Area Detection

XX--ray Beamray Beam

XX--ray penetration ray penetration depth ~1depth ~1µµµµµµµµm.m.Electrons can be Electrons can be excited in this excited in this entire volume.entire volume.

XX--ray excitation area ~1x1 cmray 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=KE=hvhv--BEBE--ΦΦ�� 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

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FermiFermiLevelLevel

Free Free Electron Electron LevelLevel

Incident XIncident X--rayrayEjected PhotoelectronEjected Photoelectron

1s1s

2s2s

2p2p

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�� 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)KE=E(K)--E(L2)E(L2)--E(L3).E(L3).

Conduction BandConduction Band

Valence BandValence Band

L2,L3L2,L3

L1L1

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FermiFermiLevelLevel

Free Free Electron Electron LevelLevel

Emitted Auger ElectronEmitted Auger Electron

1s1s

2s2s

2p2p

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SSX-100 ESCA on the left, Auger Spectrometer on the right

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• 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

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• 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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Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

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• 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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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

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• 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.

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A schematic of SAM (n-alkanethiol CH3(CH2)nSHmolecules) formation on a Au(111) sample.

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• 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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• 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

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http://sibener-group.uchicago.edu/has/sam2.html

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• 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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• AFM– Atomic Force Microscopy

• SEM - EDX– Scanning Electron Microscopy– Energy Dispersive Wavelength X-Ray

• TEM– Transmission Electron Microscope

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

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PNI Nano-R AFM Instrumentation as used at Foothill College

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• 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)

STMTopographySpectroscopyLithographyEChem.BEEM

SNOM(NSOM)ApertureAperaturelessReflectionTransmission

Contact ModesTopographyLFM, SThMLithography

AC ModesTopographyMFM, EFMSKPMOthers

EChem

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AC – Close Contact Mode- Soft Samples- Sharp Probe <20nm

DC – Contact Mode- Hard Samples- Probes > 20 nm

Material Sensing ModesLateral ForceVibrating Phase

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Point and Scan™Crystal SensorStage AutomationSoftware

Z Motion Control

xyz scanner

XY Motion Control

AFM Force Sensor

Optic

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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

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High Resolution Video Microscope

Scanner

Sample Puck

X-Y Stage(in granite block)

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Cutting edge of razor blade

4 X 4 µ

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100 X 100µ

AFM is used to understand the glossing characteristics of paper surfaces

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• AFM can be used to understand surface morphology.

• This material was prepared using a spray / cast technique.

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

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• 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

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• Electron beam• Electron gun• Anode• Magnetic lens• Scanning coils• Secondary electron

detector• Stage and specimen

http://mse.iastate.edu/microscopy/beaminteractions.html

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Imaging of microscopic scale objects in high resolution

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SEM AFMWide range of sample roughness True 3D imageOperated in low to high vacuum Vacuum, Air or Liquid

http://mse.iastate.edu/microscopy/proimage.html

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

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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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• 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 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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• Surface techniques– AES– ESCA / XPS

• Deeper techniques– RBS and PIXE

• Ion techniques– SIMS

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

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

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• Evans Analytical Group• Center for Microanalysis of Materials• Stanford Nanofabrication Facility• Text• Text

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• 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