Reminders for this week Homework #4 Due Wednesday (5/20) Lithography Lab Due Thursday (5/21) Quiz #3 on Thursday (5/21) – In Classroom –Covers Lithography, Special Nanostructures, Characterization of Nanostructures –Format similar to Quiz #2

Characterization of Nanomaterials NANO 101 Introduction to Nanotechnology 2

3 Observations and Measurement: Studying physical properties related to nanometer size Needs: –Extreme sensitivity –Extreme accuracy –Atomic-level resolution documents/webpages/nanocrystals.html

4 Characterization Techniques Structural Characterization Scanning electron microscopy Transmission electron microscopy Scanning probe microscopy Chemical Characterization Optical spectroscopy Electron spectroscopy

Characterization Techniques Individual Measurements –Electron Microscopy –Scanning Probe Microscopy –Electron Spectroscopy Ensemble Measurements –Optical Spectroscopy –Crystallography 5

6 Structural Characterization Techniques already used for crystal structures X-Ray Diffraction Many techniques already used for studying the surfaces of bulk material Scanning Probe Microscopy (AFM & STM) Electron Microscopes Provide topographical images

Crystallography Arrangement of atoms Crystals have atoms in ordered lattices Amorphous: no ordering of atoms 7 Source: Wikipedia Source: Encyclopedia of Alternative Energy and Sustainable Living.

Bragg’s Law/Scherrer Equation Constructrive interference of X-rays leads to peaks Less planes for diffraction -> broadened peaks 8

XRD 9

Crystallography Controls Properties BiVO 4 (Monoclinic is photocatalytic, Tetragonal is not) 10 Chem. Soc. Rev.Chem. Soc. Rev., 2013, 42,

Electron Microscopes Used to count individual atoms What can electron microscopes tell us? Morphology –Size and shape Topography –Surface features (roughness, texture, hardness) Crystallography –Organization of atoms in a lattice

Microscopes: History Light microscopes –500 X to 1500 X magnification –Resolution of 0.2 µm –Limits reached by early 1930s Electron Microscopes –Use focused beam of electrons instead of light Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM) 12 Source: Wikipedia

Electron Microscopy Steps to form an image 1.Stream of electrons formed by an electron source and accelerated toward the specimen 2.Electrons confined and focused into thin beam 3.Electron beam focused onto sample 4.Electron beam affected as interacts with sample 5.Interactions / effects are detected 6.Image is formed from the detected signals

Electron Beam –Accelerated and focused using deflection coils –Energy: ,000,000 eV Sample –TEM: conductive, very thin! –SEM: conductive Electron Microscopes Detection ◦ TEM: transmitted e- ◦ SEM: emitted e- 14 Source: Virtual Classroom Biology

EM Resolution Resolution dependent on: wavelength of electrons ( ) NA of lens system Wavelength dependent on: Electron mass (m) Electron charge (q) Potential difference to accelerate electrons (V) 15 NA = n sin θ

Transmission EM Magnification: ~50X to 1,000,000X 1.E-beam strikes sample and is transmitted through film 2.Scattering occurs 3.Unscattered electrons pass through sample and are detected 16 Source: Wikipedia

TEM 17

TEM Samples Must be ultra thin More difficult for biological samples 18 Nature Protocols 7, 1716– 1727 (2012)

TEM Information 19 alian_lung_-_TEM_(2).jpg s-fundamental-research/silicide-nanowires- from-coordination-compound-precursors

Scanning EM Magnification: ~10X to 300,000X 1.E-beam strikes sample and electron penetrate surface 2.Interactions occur between electrons and sample 3.Electrons and photons emitted from sample 4.Emitted e- or photons detected 20 Source: Wikipedia

Valence electrons Inelastic scattering Can be emitted from sample “secondary electron” Atomic nuclei Elastic scattering Bounce back - “backscattered electrons” Core electrons Core electron ejected from sample; atom excited To return to ground state, x-ray photon or Auger electron emitted SEM: Electron Beam Interactions valence e- core e- nucleus 21

Secondary versus Backscattered Top – Secondary electron image –Shallow escape depth -> better resolution Bottom – Backscattered electron image –More sensitive to elements of different masses 22

SEM Samples Must have conductive surface –Electrons must go around surface not stay on surface 23 SEM/Imaging.html

STEM Still requires thin sample E-beam is scanned as in SEM and secondary or backscattered electrons can be detected

1.e- or photon strikes atom; ejects core e- 2.e- from outer shell fills inner shell hole 3.Energy is released as X-ray or Auger electron EDS: Energy Dispersive X-ray Spectroscopy AES: Auger Electron Spectroscopy EELS: Electron Energy Loss Spectroscopy 25 Electron Spectroscopy Energy Ground state e- emitted; excited state Relaxes to ground state X-ray Auger e-

26 Electron Spectroscopy Emitted energy is characteristic of a specific type of atom Each atom has its own unique electronic structure and energy levels AES is a surface analytical technique <1.5 nm deep AES can detect almost all elements EDS only detects elements Z > 11 EDS can perform quantitative chemical analysis EELS is sensitive to lighter elements (Carbon – Transition Metals) EELs is sensitive to chemical environment

EDS Chemical Composition Mapping 27 Pb paint chip, SEM, pment/scanning_electron_microscopy.html Metal-Polymer Core Shell and-developments/ecologically-friendly-polymer-metal-and- polymer-metal-oxide-nanocomposites-for-complex-water-treatme

AES AES -> Surface chemical mapping, depth profile 28 Battery Electrode Surface J. Mater. Chem.J. Mater. Chem., 2010, 20,

EELS 29

SEM and TEM Comparison SEM makes clearer images than TEM SEM has easier sample preparation than TEM TEM has greater magnification than SEM SEM has large depth of field SEM is often paired with detectors for elemental analysis (chemical characterization)