Electrons are generated and focused into a beam with magnetic confinement.
Electron beam is shot at the sample, all of which is kept under vauum
The backscattered electrons (pass through) and secondary (resulting from sample ionization) are used to generate the image.
Allows for surface level morphology and rough 3D approximations. Resolution down to 1nm
TEM requires samples being sliced (like Cryo-TEM) thin, and solely using backscattered electrons.
(P)XRD
Powder xray diffraction is better for inorganic (because crystals)
Xrays are shot at atom, electrons adsorb and remit (elastic scattering)
Use Braggs law to find spacing between crystal lattice
By varying incident angle the rays are shot at, changes the distance and angle the reflect ray comes back at.
If the the diagonal distance between crystal units is an integer multiple of the wavelength, it will interfere constructively
If not an integer, it will be destructive. So no return signal at the detector. By varying the angle and measuring for the return, you can determine the lattice spacing in a sample
This has obvious importance to MOFS
EDS (aka EDX)
Built in to SEM or TEM methods. The same electron beam will sometimes ejected a core-shell electron.
This is then filled by a higher orbital, which drops down and releases an X-ray which is unique to the atom or origin.
The peak position therefore identifies the element, and the intensity correlates with concentration.
NMR
Only works on elements/isotopes which have unequal numbers of protons and neutrons (not many)
This allows the spin to be non-zero, and therefore have a magnetic moment
You see sharp spiky peaks in terms of PPM for a specific element
These peaks are often split into smaller neighbors, because of something called coupling which is complicated
Put stuff in a strong magnetic field and detect the radiowave emissions
Can be used for structural determination and stuff
ICP-MS
Ionize samples into plasma then shoot the ions through an MS
Based on how the moving charge interacts with a curved magnetic tube, the scattering locations can identify what kind of ion is present,
Very good for measuring trace amounts of metal ions
UV-Vis
Type of absorbance spectroscopy
Shine monochromatic light on liquid sample with known path length, measure intensity before and after passing through sample
Absorbance = Log(Light in) / Log(Light out)
Beer-lambert law says A = (e)(L)(c) where each is the adsobtivity, path length, and concentration.
Most useful for chromophore organics, some metal complexes too
FTIR
Best for organics
Type of absorbance spectroscopy
Mechanism revolved around Michelson Interferometer
Broadband beam goes through intereferometer. By splitting the light (half intensities, same wavelengths), shifting the frequency of one using a moving mirror, then recombining them to interefere constructive/destructive
This is done over the full range of phase shift, shining beam on the sample.
This can then be deconvoluted to the wavelength using a Fourier transform, final plot is % transmittance / wavenumber.
generates a chemical fingerprint spectrum
ATR tip lets you do surface measurements rather than powdered material’
FIB
Similar working principles to a SEM but launches a beam of ions (positive) instead
At low currents, the ions deflected can be detected to generate image resolutions down to 5 nm
At high currents, the ions cause ablation of the material, allowing for precision milling
Raman
Mainly organic, some inorganic
Monochromatic radiation is emitted to a sample and instantly transforms its rotational or vibrational state
The incoming photon is scattered to a new energy (Stokes = lower and Anti-stokes = higher)
but there is NO excited or transitional state, and no electronic changes. It happens immediately. It indicates the change in polarizability. This is what makes it difference from Fluorescence
Indicates what kinds of bonds are present in the sample (C=0, O-H, etc.)
Fluorescence
Molecules actually absorb radiation and transition electronic states.
When the electrons fall back down to baseline, photons are emitted with typically a lower energy and higher wavelength
Cleanroom
When entering, gown from top to bottom. Start with gloves first.
When leaving, go in reverse.
You operated in an ISO6 cleanroom.
Gamma
Plot of count over energy (proxy for wavelength) gives unique fingerprint for every isotope