Synergistic erosion process of hydrocarbon films: a molecular dynamics study

P N Maya,C Hopf,U Von Toussaint

doi:10.1088/1367-2630/10/2/023002

P N Maya, C Hopf + Show 1 more

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https://doi.org/10.1088/1367-2630/10/2/023002

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Abstract

Fundamental processes leading to the erosion of hydrocarbon films due to energetic argon ions and hydrogen atoms have been investigated using molecular dynamics simulations. A generic mechanism has been identified for carbon erosion due to energetic (150 eV) argon ions in the presence of sub-eV hydrogen atoms. This surface erosion process, which we call hydrogen enhanced physical sputtering (HEPS), is primarily a physical sputtering mechanism, enhanced due to the screening effect of hydrogen atoms. The energetic argon ions create open bonds within their penetration range. The hydrogen atoms passivate the open bonds created within the first few atomic layers. Subsequent ion bombardment causes the breaking of C–C bonds within and beyond the H penetration range. The steric effect of H atoms bound to the top layer of carbon atoms prevents the re-attachment of the broken bonds, and this leads to unsaturated molecule emission from the surface. The kinetic energy of the emitted molecules is above thermal energy and the emission takes place within 5 ps after the ion impact.

Highlights

The number of hydrogen atoms (50) was determined in such a way that an increase in the number of hydrogen atoms had no detectable impact on the simulation with the present argon energy of 150 eV, since the total amount of near-surface hydrogen was in saturation; incident H atoms were either reflected from the sample or replaced hydrogen atoms already present on the surface
The mechanism which leads to the yield enhancement in the simulations, hydrogen enhanced physical sputtering (HEPS), can be described by the following steps: first, the energetic argon ions create dangling bonds within the penetration range
The abundant hydrogen atoms saturate most of the broken bonds in the first few atomic layers

Summary

Introduction

There exists an energy threshold for this process and the energy distribution of the sputtered species is well above thermal energies Another recently described erosion mechanism, termed swift chemical sputtering, has been identified by Salonen et al [22] using molecular dynamics simulations. In this process, incident ions with energies down to about 2 eV cause the kinetic emission of hydrocarbon radicals from a-C:H films. Chemical sputtering by two individual beams of energetic noble gas ions and thermal hydrogen atoms was studied in particle beam experiments [13]–[16] for different Ar energies and a varying hydrogen to argon flux ratio of between 0 and ≈ 500.

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