Surface and Materials Analysis Techniques

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)

AES - Auger Surface sensitivity Microbeam Depth profiling Elemental composition Some chemical bonding

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.

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 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 X-ray Beam X-ray penetration depth ~1  m. Electrons can be excited in this entire volume. X-ray excitation area ~1x1 cm 2 . Electrons are emitted from this entire area Electrons are extracted only from a narrow solid angle. 1 mm 2 10 nm

The Photoelectric Process XPS spectral lines are identified by the shell from which the electron was ejected (1s, 2s, 2p, etc.). The ejected photoelectron has kinetic energy: KE=hv-BE-  Following this process, the atom will release energy by the emission of an Auger Electron. Conduction Band Valence Band L2,L3 L1 K Fermi Level Free Electron Level Incident X-ray Ejected Photoelectron 1s 2s 2p

Auger Relation of Core Hole L electron falls to fill core level vacancy (step 1). KLL Auger electron emitted to conserve energy released in step 1. The kinetic energy of the emitted Auger electron is: KE=E(K)-E(L2)-E(L3). Conduction Band Valence Band L2,L3 L1 K Fermi Level Free Electron Level Emitted Auger Electron 1s 2s 2p

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

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. Surface Treatment of NiTi 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 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 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. A schematic of SAM ( n -alkanethiol CH 3 (CH 2 ) n SH 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

A Family of Microscopes 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

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 Scanner Point and Scan™ Crystal Sensor Stage Automation Software

AFM Stage Assembly AFM Stage for sample orientation, with scanner and optics Z Motion Control xyz scanner XY Motion Control AFM Force Sensor Optic

AFM Light Lever – Force Sensor 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

High Resolution Video Microscope Scanner Sample Puck X-Y Stage (in granite block) Light Lever Crystal Nano-R™ Stage

High Resolution Video Microscope Software control of video microscope functions Optical Microscope

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 4 X 4 µ

Consumer Applications 100 X 100 µ 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.

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

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

SEM Principles of Operation http://mse.iastate.edu/microscopy/beaminteractions.html

http://mse.iastate.edu/microscopy/proimage.html SEM Principles of Operation

SEM Imaging Imaging of microscopic scale objects in high resolution

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 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

Surface and Materials Analysis Techniques

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