Electron Energy Loss Spectroscopy (EELS)

Electron Energy Loss Spectroscopy (EELS) is a technique that provides elemental information on the nanometer scale when coupled with Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM). The energy of the incident electrons is altered (reduced) as they pass through the sample. This energy loss can be characterized using EELS to provide elemental identification. Compared to Energy Dispersive X-ray Spectroscopy (EDS), EELS provides improved signal to noise, better spatial resolution (down to 1nm), higher energy resolution (<1 eV for EELS) and increased sensitivity to the lower atomic number elements. For some elements, chemical bonding information can be obtained.

Ideal Uses of EELS

Elemental identification and mapping
Elemental identification (spot analysis, linescans, 2D chemical maps)
Chemical fingerprinting (limited cases)

Strengths

More signal collection than EDS
Especially useful in the Si/C/O/N system
1 nm probe size (EDS ~1-3 nm)
Higher energy resolution, can sometimes provide chemical information
Higher sensitivity to Low Z elements

Limitations

Longer to set up
Multi element detection sometimes requires multiple set ups
Backgrounds and peak shapes are complicated
Good detection of High Z elements can be problematic

EELS Technical Specifications

Elements Detected: B-U
Detection Limits: 0.5%
Lateral Resolution/Probe Size: 1 nm