Dual Beam Irradiation and Channeled Rutherford Backscattering
Dual Beam Irradiation and Channeled Rutherford Backscattering (RBS) spectroscopy at the Ruđer Bošković Institute in Zagreb
Accelerated ions can interact with the nucleus of atoms in a sample through elastic collisions. The ion is often repelled at angles close to 180 degrees, called Rutherford backscattering. By measuring the energy and intensity of the backscattered beam of high energy protons, it is possible to determine the composition and depth profile of elements on the sample surface and below. In addition to elemental compositional information, RBS can also be used to study the structure of single crystal samples. When a sample is channeled, the rows of atoms in the lattice are aligned parallel to the incident ion beam. The bombarding high energy beam will backscatter from the first few monolayers of material at the same rate as a non-aligned sample but backscattering from buried atoms in the lattice will be drastically reduced, since these atoms are shielded from the incident ions by the atoms in the surface layers. By measuring the reduction in backscattering when a sample is channeled, it is possible quantitatively to measure and profile the crystal perfection of a sample and to determine its crystal orientation.
The dual beam irradiation chamber is installed at -30 degree beam line of the Tandem van de Graaff accelerator and +10 degree line of the Tandetron accelerator. This allows experiments and applications that require simultaneous irradiation by two beams. Further positioning the beam into the channeling direction, while exposing the sample to the beam from the second accelerator, allows radiation damage to be observed and quantified on-line.
Contact: Milko Jakšić
Tel: +385 1 468 0942
For irradiation purposes, the beam from the 6.0 MV tandem is collimated to a rectangular area by adjustable slits having a maximum opening of 5 mm. The ion beam from the 1.0 MV tandem is collimated by circular interchangeable apertures of 1, 3 and 5 mm. The scattering chamber is also equipped with an RBS detector and also has the possibility of mounting an x-ray detector for PIXE.
Samples are positioned by motorized xyz stage and three-axis goniometer. The sample holder is circular, with a diameter of 2.5 cm. All samples have to be positioned within this holder and their maximum number therefore depends on the size of individual samples. Detailed information can be found on the instrument’s webpage.