Rutherford back Scattering

Rutherford backscattering spectrometry (RBS) is a 100 year old technology that is still a powerful tool for determining the structure and elemental composition of thin samples. In RBS, a high energy beam of helium or hydrogen ions is directed at a sample. Ions which scatter elastically from the nuclei of atoms in the sample are detected using a silicon particle detector. Since the energy of the scattered ion depends on the mass and depth of the target atom, the composition and layering of the sample can be determined very precisely.

    The Rutgers General Iondex tandem accelerator is capable of producing He++ ions up to 5.1 MeV and H+ ions up to 3.4 MeV via a multi-stage acceleration process described here. The figure below shows a 2 MeV He++ RBS spectrum acquired from an Al2O3 sample with Au and Ni thin films deposited on the surface. The data has been fitted using SIMNRA in order to determine the thickness of the films and the order in which they were deposited on the surface. He++ ions that scatter from Au retain most of their kinetic energy due to the relatively high mass of the Au nucleus. He++ ions that scatter from Ni, Al, and O nuclei lose more energy and hence reach the detector with a lower percentage of their initial kinetic energy. The intensity of each peak is proportional to the number of atoms and the square of the atomic mass of the target atom.

    The Al and O signals in this spectrum appear as plateaus rather than peaks due to the fact that He++ beam continuously loses energy as it passes through the thick Al2O3 substrate. Consequently, scattering events that happen below the surface result in a lower recoil energy than those that happen near the surface. At 2 MeV, He++ ions can travel about 1 micron in most materials, which makes RBS more bulk sensitive than most electron spectroscopies.

    For monocrystalline solids, the ion beam can be aligned with high-symmetry directions of the lattice in a process called channeling. This effectively blocks the ion beam from reaching the sub-surface atoms of the crystal. Channeling can be used to quantify the crystallinity of a solid, determine the location of dopants, or minimize the substrate background signal in order to quantify light elements in a sample.

     In some cases, the incident ion beam can undergo nuclear reactions with the target atoms to produce high energy alpha particles or protons. This is known as Nuclear Reaction Analysis or NRA. By carefully selecting the incident ion energy and the geometry of the detector, these reactions can be used to profile light elements which might otherwise not be possible to detect using conventional RBS. One example is the 2H(3He,p)α reaction, wherein incident 3He++ ions fuse with deuterium atoms in the sample to produce an alpha particle and a proton. This is a powerful technique for depth profiling deuterium in a sample.

     Hydrogen cannot be detected by conventional RBS since no nucleon can backscatter from a hydrogen target. However Elastic Recoil Detection Analysis (ERDA), also known as Hydrogen Forward Scattering (HFS), can be used to quantify the hydrogen content of samples. In this technique, a detector is placed behind the sample, and forward scattered hydrogen atoms from the sample are detected. ERDA has a detection limit better than 0.1% and a depth resolution of about 30-60 nm.

RBS at Rutgers is avalable to measure your sample
RBS Data Analysis
Research Contract within University
Outside Company non-affiliated with Rutgers

RBS Data Interpretation
Research Contract within University
Outside Company non-affiliated with Rutgers

$50 + $180/hr
$100 + $360/hr


Contact Ryan Thorpe

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(848) 445-7937