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Characterization (Microscopy), image, image, image, image, image, image,…
Characterization (Microscopy)
Energy Dispersive X-Ray Spectrometry (EDX/EDS)
For elemental composition determination
Commonly coupled with SEM/TEM
Inelastic collisions between X-ray photons and electrons cause charge carriers, counted as pulses and converted to voltage (energy)
All atoms will have unique values of energy due to varying size and electronic configuration
Dynamic Light Scattering (DLS)
Measures size of particles in suspension via speed of their Brownian motion
Diffusion speed measured by intensity of scattered light fluctuation
Smaller particles, increased fluctuation
Hydrodynamic diameter is measured, which is the diameter of a hard sphere that diffuses at the same speed as the particle being measured
Advantages
Fast measurements
Small sample volume
Any suitable suspending liquid can be used
0.001 to several microns
Disadvantages
Low-resolution size distribution histogram
Difficult to get shape information, only hydrodynamic size
Affected by multiple scattering
Tedious sample preparation
Electron Microscopes
Scanning Electron Microscopy (SEM)
For surface visualization of materials
Operation modes
Secondary: Characteristic X-rays (EDX technique)
Tertiary: Back-scattered electron imaging
Primary: Secondary electron imaging
Advantages
Detailed 3D topography
Data can be generated digitally
Fast measurements
Minimal sample preparation
Disadvantages
Sample preparation can result in artifacts
Only solid samples
Need special training
Small risk of radiation
Expensive & large
Transmission Electron Microscopy (TEM)
For inner structure visualization of materials
Operation modes
Imaging mode: Topography
Scattering mode: Morphology and composition
Focused mode: Thermal and mechanical properties
Crystalline sample interacts with electron beam by diffraction, leading to formation of a high contrast image depending on the intensity of the diffraction
Advantages
Wide range of applications
Provide information on element and compound structure
Powerful magnification and resolution
High-quality and detailed 2D images
Disadvantages
Tedious sample preparation
Need special training
Expensive
Electron-transparent samples
Need special housing & maintenance
Only black & white images
Atomic Field Microscopy (AFM)
Provides 3D profile of surface by measuring forces between probe and surface
Forces measured by Hooke's law, F = -kx
Modes
Non-contact mode
Hovers above surface, measures attraction
Tapping mode
Intermittent tip contact, variable force measured
Contact mode
Close contact with surface, measures repulsion
Advantages
Minimal sample preparation
Does not require conductive sample
Provides 3D surface profile
Functions in ambient air/liquid environment
Can study biological macromolecules/living organisms
Inexpensive
Small size, easy to couple with other instruments
Disadvantages
Limited scanning speed
Images affected by nonlinearity, hysteresis and creep of piezoelectric material
Area smaller than 100 microns
Possibility of image artifacts
Only represents interaction between surface and probe
