Rutherford Backscattering Spectrometry (RBS) is a powerful, non-destructive analytical technique for precise determination of elemental composition and depth distribution in materials. By analyzing the energy and intensity of ions elastically scattered from a sample, RBS delivers direct insight into layer structure, thickness, and composition.
When a material is irradiated with a high-energy ion beam, most ions penetrate deep into the sample, while a small fraction undergo elastic collisions with atomic nuclei near the surface. These interactions—governed by well-understood physical principles—allow accurate reconstruction of the sample’s compositional profile without altering or damaging it.
When a sample is irradiated with a high-energy ion beam, most ions penetrate into the material. This is due to the extremely small size of atomic nuclei (~10⁻¹⁵ m) compared with the interatomic spacing (~10⁻¹⁰ m). Only a small fraction of the incident ions undergo close encounters with nuclei in the top few micrometers of the sample. Such interactions do not involve physical contact; instead, energy transfer occurs through Coulomb forces between neighboring nuclei. These interactions can be accurately described as elastic collisions within the framework of classical physics.
The energy of ions backscattered at a given angle is governed by two main processes: energy loss due to electronic stopping as the ions traverse the sample before and after the collision, and energy loss during the collision itself. The former depends on the stopping power of the material, while the latter is determined by the mass ratio of the incident ion and the target atom. This makes RBS especially effective for depth-resolved analysis, enabling clear distinction between thin layers and interfaces: thin films produce sharp spectral features, while thicker layers result in broader signals. RBS is particularly well suited for detecting and quantifying heavier elements in lighter matrices, making it an ideal tool for thin-film analysis and impurity profiling, but it sensitivity to light elements and to features located deep beneath the surface is limited.
Applications of RBS include:
- Multi-element depth profiling
- Characterization of surface and near-surface structures
- Determination of stoichiometry in oxide and other thin-film layers
Advantages
- Rapid, non-destructive analysis
- Quantitative without standards
- Depth profiling up to ~20 µm (for 2 MeV proton beams)
- High depth resolution:
I. ~10–50 nm for light elements
II. Down to ~2 nm for heavy elements (depending on the matrix and projectile mass)
- Direct measurement of atomic density, largely independent of chemical state
Limitations
- Very limited sensitivity to elements lighter than the incident ion beam
- Reduced detectability of light elements in heavy matrices, despite simultaneous detection of elements from Be to U
- Does not provide information on chemical bonding
Example
- Depth profiling of optical coatings:
DOI: 10.3952/physics.v54i4.3015
DOI: 10.1016/j.tsf.2015.04.075
DOI: 10.3952/lithjphys.54205
2. Examples of photovoltaic and other samples:
DOI: 10.1016/j.cpc.2021.108187