Electron Paramagnetic Resonance (EPR) or Electron Spin Resonance (ESR) spectroscopy is a technique that allows the detection and study of transient and stable paramagnetic species over a wide range of temperatures and sample states.
The basic concepts of EPR are analogous to those of Nuclear Magnetic Resonance (NMR), but it is electron spins that are excited instead of the spins of atomic nuclei.
This technique can give us information about characterization of organic and/or inorganic materials, radical-radical interactions or spin-trapping process. In particular, in molecular materials based on organic radicals the EPR spectra can provide us information about the chemical structure of such molecules with the simulation of the spectra, because the electron can couple with atoms with nuclear spin I ≠ 0 such as 1H, 14N, 13C, etc., located in the molecule.
The samples to be analyzed can be in solution, powder or single crystals and they can be studied in a range of temperatures: from 4.2 K (Aarhus), 100 K (CSIC-ICMAB) to 400 K.
Microwave frequencies: X-band (continuous wave and pulse), Q-band (continuous wave).
A. Continuous wave Electron Paramagnetic Resonance at X- and Q-band
B. Pulsed Electron Paramagnetic Resonance. 2-pulse and 3-pulse ESEEM, 2D-HYSCORE, Davies and Mims-type ENDOR
A. CW-EPR
X-band: BRUKER ESP 380E, ER220D. Temperature range: 4.2 - 300 K. Electromagnet 1.0 T
Q-band Home assembled. Temperature range: 4.2 - 300 K. Electromagnet 1.4 T
B. Pulsed EPR
X-band BRUKER ESP 380E. Temperature range: 4.2 - 300 K. Electromagnet 1.0 T
In SEM a beam is scanned over a sample surface while a signal from secondary or back-scattered electrons is recorded. SEM is used to image an area of the sample with nanometric resolution, and also to measure its composition, crystallographic phase distribution and local texture.
In TEM/Scanning TEM (STEM) high energy electrons incident on ultra-thin samples, allow imaging, diffraction, electron energy loss spectroscopy and chemical analysis of solid materials with a spatial resolution on the order of 1-2 Å. Samples must have a thickness of a few tens of nanometres and are prepared in sample preparation laboratory.
XPS is a surface spectroscopic technique for quantitative measurements of the elemental composition or stoichiometry and the chemical state of the present elements, like their oxidation state and chemical bonds. XPS is highly surface sensitive, giving chemical and binding energy information from the a narrow region close to the surface.
AFM is a surface sensitive technique permitting to obtain a microscopic image of the topography of a material surface and certain properties (like friction force, magnetization properties…). Typical lateral image sizes are within a range of only a few Nanometers to several Micrometers, and height changes of less than a Nanometer.
XAS is sensitive to the local bonding environment of the atom absorbing the X-rays, providing information on oxidation states, local orbital symmetry, molecular orientation and chemically selective density of states. It is widely used in molecular and condensed matter physics, material science, engineering, chemistry, earth science and biology.
