Electronic state and bonding state analysis on the surface
Band gap measurement of semiconductors
Compare the relative hydrogen content of materials
Observe evidence for conjugation/aromaticity in materials
Discrimination of sp2/sp3 bonds of carbon
Band gap measurement by REELS
REELS spectrum of SiO2 thermal oxide film (25 nm) on Si wafer. A peak rises at an energy 8.8 eV lower than the reflected incident electron, allowing the band gap of the SiO2 film to be measured (*1).
Figure 1. REELS spectrum of SiO2 (incident electron: 1.5 keV)
Evaluation of hydrogen and aromatic content in organic films by REELS
Due to the rebound effect of hydrogen atoms, hydrogen-derived energy loss peaks appear. You can compare the relative hydrogen content from the intensities of these peaks. Additional peaks (π –π*), located about 7 eV from the reflected incident peak, also provide information about the relative degree of conjugation/aromaticity in the samples.
Figure 2. REELS spectra of various polymer films (incident electron: 1.5 keV, 100 pA)
Evaluation of Diamond-Like Carbon (DLC) Film by REELS
Using diamond (sp3 bonding) and graphite (sp2 bonding) as references, the bonding states of various DLC films can be determined (*2,3). Using the Gas Cluster Ion Beam (GCIB) to remove surface contamination without damage to the sample surface, it is possible to analyze the carbon material more precisely.
Figure 3. REELS spectra (incident electron: 1 keV) of DLC films on a PET bottle and on a hard disc media, compared to spectra obtained from diamond (sp3) and graphite (sp2) reference materials.
Principle of REELS
REELS is a surface analysis technique in which a specimen is bombarded with an electron beam (typically ≤ 1500 eV) and the energy distribution of the reflected electrons is measured. This energy distribution contains features corresponding to discrete losses of energy of the reflected electrons due to excited atomic states, core level and valence band transitions, material bandgaps, etc. It also provides information on H content and the type and geometric structure of compounds at the surface of the specimen.
Structure of REELS
REELS measurement can be made by selecting one of the two electron gun options on the VersaProbe III. Both electron guns can perform REELS measurements with high energy resolution of 0.5 eV or less when using the Fixed Analyzer Transmission (FAT) mode.
Electron guns for REELS
This option uses a newly developed tungsten filament electron gun with excellent cost performance for REELS measurements. The gun generates stable electron energies from hundreds of eV up to 2 kV.
Scanning electron gun for Auger and REELS analysis
When the Auger option is selected, REELS measurements are also possible using the scanning electron gun for Auger analysis. Similar to Auger points or areas of interest for REELS analysis can simply be selected from the SEM image.