Near-surface modification of polystyrene by Ar+: Molecular dynamics simulations and experimental validation

Abstract

Results are presented from molecular dynamics (MD) simulations of 100eV Ar+ bombardment of a model polystyrene (PS) surface. The simulations show that the system transitions from an initially high sputter yield (SY) for the virgin polymer to a drastically lower SY as steady state is approached. This is consistent with corresponding ion beam experiments. The MD indicates that this drop in SY is due to the formation of a heavily cross-linked, dehydrogenated damaged layer. The thickness and structure of this layer are also consistent with ellipsometry and x-ray photoelectron spectroscopy measurements of Ar plasma-exposed PS samples.

Relationship between nanoscale roughness and ion-damaged layer in argon plasma exposed polystyrene films

“…However, as material was removed from the top of the cell by sputtering, additional layers were added to the bottom of the cell during the simulation such that the modified layer was significantly far away from the bottom of the cell. 4 For the XPS analysis, it was assumed that the modified layer was homogeneous in chemical composition and density and that the aromatic ring structure of PS was lost inside the modified layer due to ion damage. 34 Therefore, h can be calculated by measuring the intensity of the − ‫ء‬ shake-up peak at 291.3 eV, which is unique to the aromatic ring structure of PS, 35 for damaged and undamaged PS.…”

“…The method of MD simulation and h measurement has been explained in detail in previous publications. 4,11,17 The complex index of refraction ͑n-ik͒ of the modified layer formed on PS samples was measured in situ by a single wavelength ͑HeNe laser͒ ellipsometer. The ellipsometer is an automated rotating compensator ellipsometer working in the polarizer-compensator-sample-analyzer configuration and with an angle of incidence of 71.3°.…”

“…In this paper, we report a quantitative relationship between modified layer properties and surface roughness morphology in the well-characterized 4,11,17 and elementary case of polystyrene under Ar plasma exposure that suggests a buckling mechanism for nanoscale roughness formation. In this condition, it has been shown that the formation of an Ar + ion-induced modified layer at the surface of PS is the dominant effect, while little modification by other plasma species ͑e.g., VUV, neutrals͒ is observed.…”

“…poly͑methyl methacrylate͒ ͑PMMA͒, 8 193 and 248 nm photoresists 5,6,9,10 ͔ and has been described as a thin, highly crosslinked and graphitized layer. [4][5][6][11][12][13][14][15][16] We have previously shown that under energetic Ar + ion bombardment during plasma etching, a dense, amorphous carbonlike modified layer is formed at the surface of a wide range of polymers ͓polystyrene ͑PS͒, poly͑␣-methylstyrene͒, poly͑4-methylstyrene͒, PMMA, poly͑hydroxyadamantyl acrylate͒, and poly͑hydroxyadaman-tyl methacrylate͔͒ with a thickness of a few nanometers. 17 This modified layer forms within the first few seconds of plasma exposure ͑corresponding to an ion fluence ϳ4 ϫ 10 16 cm −2 ͒, concurrent with a period of rapid surface roughening.…”

Gas-Phase Surface Engineering of Polystyrene Beads Used to Challenge Automated Particle Inspection Systems

“…Traditional CVD uses heat as the energy source required for functionalization, although CVD variants using plasma or UV light are preferred to functionalize substrates sensitive to heat 22 such as polystyrene. Radio frequency 23 and microwave [24][25] plasma CVD efficiently functionalize polystyrene both at low pressure 3 or atmospheric pressure, 26 using either oxygen (O 2 ), 25,27 argon (Ar), 23,25,[28][29] air 30 or helium/nitrogen mixtures (He/N 2 ) 31 as gas precursors. In order to maximize functional groups retention, keep a better control on the process and save costs, one would prefer to replace plasma CVD by luminous CVD, since the latter employs a lower energy source such as light.…”