Ion Scattering Spectroscopy (ISS)

Ion scattering spectroscopy (ISS) provides quantitative elemental composition information from the very outermost atomic layer of a surface.

Strengths

• Maximally surface-selective: signal isolated from outermost atomic monolayer
• Highly sensitive, quantitative elemental composition
• No calibration standards required for quantification
• Nondestructive analysis
• Can measure buried interfaces via depth profiling

Limitations

• Difficult to accurately measure light-element films over heavy-element substrates
• Surfaces must be clean to get good results

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Example Outputs Instruments Used How ISS Works

• Solid phase
• Must be stable under high vacuum
• Maximum Thickness: 20 mm
• Maximum Lateral Dimensions: 60 mm x 60 mm

In ISS measurements, a low-energy probe beam of noble gas ions is applied to the sample surface. These ions undergo elastic back-scattering interactions with the outermost surface atoms, during which energy – in the form of momentum – is transferred. The magnitude of momentum transfer is dependent on the elemental species of the sample atom: lighter elements (with closer relative mass to the probe ions) will cause greater reduction in the noble ion’s kinetic energy.

The ISS detector measures the amount of back-scattered noble ions with particular kinetic energies, and scans over a range of energy values up to the incident beam energy.

By taking the difference between the original and final kinetic energies of the back-scattered ions, the system produces a spectrum of peaks with energy indicative of elemental species, and intensity indicative of quantitative concentration.