Sputtering behavior of P3HT under low-energy monoatomic projectile bombardment : insights from molecular dynamics simulations

Molecular dynamic computer simulations have been employed to investigate the sputtering process of multilayer poly(3-hexylthiophene) (P3HT) with a layered structure arranged in the Z-direction deposited on a silicon substrate. The sputtering process was induced by low-energy He, Ar, and Xe projectiles. The sputtering yield volume, mass spectra, and structural and chemical damages induced in the bombarded systems are probed depending on the type of projectile and the thickness of the organic overlayer. While most studies are performed with a 500 eV primary kinetic energy and an impact angle of 45°, the effect of these two parameters on the sputtering yield is investigated for the Ar projectile. The main goal is to elucidate the influence of various primary beam properties on the sputtering process and structural and chemical damages occurring in P3HT. The implications of the present results for the chemical analysis of P3HT by secondary ion mass spectrometry (SIMS) or secondary neutral mass spectrometry (SNMS) and low-energy atomic projectiles are discussed. It has been found that the sputtering yield volume is the largest for Ar and the smallest for He. The yield does not depend on the organic overlayer thickness within the computational uncertainty. The number of ejected atoms scaled to the sample atomic density decreases monotonically with depth. Interestingly, the shape of this distribution, known as the information depth distribution, is the same for all investigated projectiles, regardless of their penetration range, which indicates that this quantity is determined by the properties of the sample. Additionally, the projectiles are not deposited equally in the sample volume but are trapped at organic/substrate and interlayer interfaces. The vertical extent of damage is directly related to the projectile range, which is the largest for He and the smallest for Xe. The shape of vertical damage distribution depends in an oscillatory manner on depth. It is shown that the alkyl side chains are mostly damaged. Our results indicate that among all tested projectiles, Ar, followed by Xe, are the best candidates for the chemical analysis of P3HT by SIMS/SNMS techniques.