"Surface and Materials Analysis Techniques"
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 – firstname.lastname@example.org 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