Characterization Flashcards
What is the symbol (like parenthesis) for crystallographic planes, plan families, directions, and direction families?
( Plane )
{ Plane Family }
[ Direction ]
< Direction Family >
What is Bragg’s law, and how can you prove it?
n(lambda)=2dsin(theta)
Draw two layers of atoms in a crystal and calculate the angle to form a coherent diffracted beam
SEM
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
SEM bombards a sample with a beam of high energy electrons, which cause the emission of secondary electrons and backscattered electrons which are detected to form an image
SEM provides high resolution images, elemental composition (when combined with energy dispersive x-ray spectroscopy), and topography
This technique analyzes the surface of a sample, or right below the surface
Advantages include high resolution imaging, ability to combine with EDS to get composition, and microstructure information
Disadvantages include that it needs to be under vacuum, potential damage to the sample by the electron beam, and involved sample preparation
TEM
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
TEM passes a high energy electron beam through a thin sample (50-200 nm) and uses transmitted and scattered electrons to form an image
TEM produces an image, and composition, conductivity, crystal structure (defects, grain boundaries, and phases)
Advantages include being able to study defects and extremely small sampling area
Disadvantages include high vacuum, damaging the sample, and intense sample prep
XRD
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
X-rays experience constructive interference as they diffract off of layers in a crystal. Can be performed on a single crystal or on a powdered sample.
Light intensity data is given, which gives information about crystal structure, coherency of epitaxial layers, and composition (indirectly)
This measures several mm into a sample, so bulk
XRD gives very precise information about the structure, usually giving unit cell dimensions with accuracy of below an Angstrom
It is destructive, limited to crystalline samples, single crystal XRD is likely to fail without precise sample loading, does not work well on alloys
AFM
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Atomic Force Microscopy is an imaging technique that drags a tiny tip across the surface of a sample, and a laser reflected off the cantilever that holds the tip creates an image
This technique is mostly used to give topographical data but can also give electrical and magnetic properties, even mechanical properties if used in the tapping mode
AFM is almost entirely limited to the surface of a sample
AFM is non-destructive and can be used in vacuum, air, or liquid environments
It has a relatively low scan speed, it is sensitive to noise, needs careful calibration, and some samples are too soft or fragile to be analyzed without being damaged by the tip
XRF
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
X-Ray fluorescence measures the characteristic radiation emitted by a sample that has been exposed to high energy x-rays
XRF produces a spectra of x-rays that can be used to find composition of the sample and works well on high z elements
XRF analyzes around 50 um into the sample, including the surface
XRF is non-destructive, useful for many kinds of samples, does not require lots of sample prep
It is not good at picking up trace elements or analyzing really small samples
FTIR
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Fourier-Transform Infrared Spectroscopy measures infrared interactions within the sample by transmitted and reflected light
FTIR gives and absorbance curve, and the x axis is wavenumber (cm^-1); it is used to find molecular compounds by identifying functional groups; fingerprint frequencies are usually below 1500/cm and functional groups are typically above
This analyzes the bulk of the sample with a penetration depth of 5mm
FTIR is non-destructive, viable on different types of samples, is very quick with little sample prep, and can be used in air or liquid
It does not provide information about the structure of a molecule, and is not good at detecting impurities or contaminants
TGA
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Thermogravimetric Analysis studies the thermal stability of materials by tracking mass loss over increasing temperature as well as exothermic or endothermic reactions
TGA analyzes the entirety of the sample
TGA is excellent for analyzing organic or biological samples, it is (mostly) non destructive, and requires minimal set up
It does not provide details about what happens upon heating like which gasses are released during thermal decomposition
NMR
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Nuclear Magnetic Resonance studies the properties of atomic nuclei in a sample; this is done by using a strong magnetic field to cause atoms with an odd number of protons or neutrons to align parallel or antiparallel to the field
NMR data gives information on present isotopes, spin-spin coupling (molecular connectivity), and relaxation time (molecular motion and interaction)
NMR analyzes the nuclei of all the atoms in the sample, but cannot affect atoms with both an even number of protons and neutrons
It is non-destructive, and provides quantitative structural information, but it is extremely expensive and struggles with trace isotopes
BET Adsorption and Desorption
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Brunauer-Emmet Teller Isothermal Adsorption is used to determine the surface area and porosity of a sample by tracking how much of a gas (usually nitrogen) it adsorbs
The constructed graph shows adsorbed volume over relative pressure and shows the level of porosity of a sample
BET Adsorption analyzes all of the sample that is available through open pores, but only the surface
It provides quantitative data on surface area and porosity, and is non-destructive
Only applicable for adsorbing materials with high surface areas
STM
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Scanning Transmission Microscopy produces topographical images of a sample with atomic resolution by scanning a tip with applied voltage across the sample surface; when the tip is close enough to the sample, electrons begin to tunnel between the tip and sample, and that tunneling current is measured to create an image
STM gives an image and also gives insight into the electrical properties of the surface
STM has the best resolution of current imaging techniques (atomic resolution), is non-destructive, and can be performed without vacuum
It is extremely sensitive to vibrations and thermal drift, and works best on conductive materials
Raman
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Raman Spectroscopy illuminates a sample with a monochromatic laser (usually near IR, visible, or near UV, but occasionally x-ray); the scattered photons are then collected after being filtered (the laser wavelength is filtered out)
The collected spectra gives information about the vibrational modes of the sample which is used to identify composition via functional groups and compounds
It analyzes up to a couple mm, depending on what laser is used (lower frequency has longer penetration depth)
Raman is non-destructive, highly sensitive, and can be used on solids, liquids, and gasses
It is susceptible to fluorescence interference, and does not have good spatial resolution
Gas Chromatography
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
Gas Chromatography is a method of analyzing gasses by passing them though a long capillary tube where there is both a mobile phase and a stationary phase
The data comes in the form of retention time, and is used to find relative composition of a sample (like in the boiling of a binary solution)
It analyzes the whole sample
GC has high sensitivity and selectivity, and is applicable for a wide range of compounds
It can only analyze volatiles, and is not good for complex mixtures
UV Vis
How does this analysis technique work?
What kind of data does it give you?
What part of the sample does it analyze?
What are the advantages of this technique, and the drawbacks?
UV-Vis Spectroscopy measures the absorbance and transmission of light through a sample
The data is given as relative intensity, and can give information on absorbing species, bacterial growth, bleaching, or purity
Is is simple. cheap, and fast, but provides limited information
