Beam energy overlapping

Minimum detection limit 1-100 ppm depending on beam energy, sample matrix, elemental overlaps, etc. Limited by court rate 100 ppm-1 % depending on beam energy, sample matrix, elemental overlaps, etc. Limited by background... 

The double-focusing mass spectrometer consists of both magnetic sector and electrostatic analysers (ESAs), the latter being a device which focuses ions with the same m jz values but differing energies. The extent to which the beams of ions of closely similar m jz ratios overlap is thus reduced so that in many cases they may be separated. This then allows their mjz ratios to be determined with more accuracy and precision and the atomic composition of the ion to be determined. 

In resonant Raman spectroscopy, the frequency of the incident beam is resonant with the energy difference between two real electronic levels and so the efficiency can be enhanced by a factor of 10 . However, to observe resonant Raman scattering it is necessary to prevent the possible overlap with the more efficient emission spectra. Thus, Raman experiments are usually realized under nonresonant illumination, so that the Raman spectrum cannot be masked by fluorescence. 

The nautre of the He-surface interaction potential determines the major characteristics of the He beam as surface analytical tool. At larger distances the He atom is weakly attracted due to dispersion forces. At a closer approach, the electronic densities of the He atom and of the surface atoms overlap, giving rise to a steep repulsion. The classical turning point for thermal He is a few angstroms in front of the outermost surface layer. This makes the He atom sensitive exclusively to the outermost layer. The low energy of the He atoms and their inert nature ensures that He scattering is a completely nondestructive surface probe. This is particularly important when delicate phases, like physisorbed layers, are investigated. 

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