Stopping of 0.3 - 1.2 MeV/u protons and alpha particles in Si

TL;DR

This study measures the stopping cross sections of silicon for protons and alpha particles in the 0.3-1.2 MeV/u range using Rutherford Backscattering Spectrometry, providing data that align with existing models and highlighting charge exchange effects.

Contribution

It introduces a precise experimental method with minimized uncertainties for measuring ion stopping in silicon and compares results with established computational models, including charge exchange parameters.

Findings

Measured S(E) data agree with existing compilations and SRIM 06 calculations.

Experimental gamma-effective charge parameters for alpha particles were derived.

Charge exchange effects cause deviations in gamma-parameters near the stopping maximum.

Abstract

The stopping cross sections S (E) of silicon for protons and alpha particles have been measured over the velocity range 0.3-1.2 MeV/u from a SIMOX target using the Rutherford Backscattering Spectrometry (RBS) with special emphasis put on experimental aspects. A detection geometry coupling simultaneously two solid-state Si detectors placed at 165 degrees and 150 degrees relative to each side of the incident beam direction was used to measure the energies of the scattered ions and determine their energy losses within the stopping medium. In this way, the basic energy parameter, Ex, at the Si-SiO2 interface for a given incident energy E0 is the same for ions backscattered in the two directions off both the Si and O target elements, and systematic uncertainties in the S (E) data mainly originating from the target thickness are significantly minimized. A powerful computer code has been elaborated for extracting the relevant S (E) experimental data and the associated overall uncertainty that amounts to less than 3%. The measured S (E) data sets were found to be in fair agreement with H. Paul compilation and with values calculated by the SRIM 06 computer code. In the case of 4He+ ions, experimental data for the gamma-effective charge parameter have been deduced via scaling the measured stopping cross sections to those for protons crossing the same target at the same velocity and compared to the predictions of the SRIM 06 code. It is found that the gamma-parameter values generated by the latter code slightly deviate from experiment over the velocity region around the stopping cross section maximum where strong charge exchanges usually occur.