Nanostructure of Fluorocarbon Films Deposited on Polystyrene from Hyperthermal C₃F₅⁺ Ions

Abstract

Fluorocarbon films were grown on polystyrene in vacuum from 25- to 100-eV mass-selected C3F5 + ion beams. The films were analyzed by X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray reflectivity after exposure to the atmosphere for 4−8 weeks. The X-ray reflectivity indicates films that range from ∼30 to 60-Å thick. The thinner films form at lower ion energies, where the ion penetration depth and efficiency of film formation are lowest. X-ray reflectivity estimates air−fluorocarbon film roughness values of ∼6 Å for 25- and 50-eV films but ∼20 Å for the 100-eV films. The fluorocarbon−polystyrene-buried interface displays similar roughness and trends with ion energy. The AFM roughness trends are similar, but the absolute AFM roughnesses are only ∼/4 of the X-ray reflectivity values. This discrepancy is attributed to tip effects and the method of determining roughness by AFM. The AFM images and power spectral densities of the 100-eV films displayed quasi-periodic cones spaced 300−700 Å apart. Such features are either absent or of much lower amplitude in the 25- and 50-eV films. Classical molecular dynamics simulations of C3F5 + deposition on polystyrene at energies of 50 and 100 eV/ion reveal that etching at the higher energy is largely responsible for the dissimilar film structures obtained experimentally. These results demonstrate that deposition of the fluorocarbon polyatomic ion C3F5 + allows control of film nanostructure at the surface and buried interface.

Polyatomicity and kinetic energy effects on surface polymerization by ion-assisted deposition

“…FTIR spectra of 200 eV SPIAD films display much lower vibrational band intensities compared to those of the 100 eV SPIAD films, a trend which agrees with the lower PL observed at higher ion kinetic energy. This data collectively indicate that high ion kinetic energy destroys more of the film structure upon ballistic ion impact, a phenomenon previously observed for direct polyatomic ion deposition on polymer surfaces [5,18,19].…”

“…XRD of the 3T evaporated film show the strong first-, second-, and thirdorder reflections at 2θ angles of 6.72 • , 13.63 • , and 20.5 • , respectively. XRD of the 100 eV Ar + SPIAD film displays all these 3T peaks (marked "*" when labels are adjacent to multiple peaks) and several new diffraction peaks at 19 19.80 • peak. The peak at 32.90 • seen in the XRD of all three films is from the silicon substrate.…”

Determining the Conformation of an Adsorbed Br−PEG−Peptide by Long Period X-Ray Standing Wave Fluorescence

“…16,31 The thickness of the polystyrene layer was previously determined by x-ray reflectivity to be ~250 Å. 16 The surface cleanliness and uniformity of the polystyrene film are examined via survey and valence band x-ray photoelectron spectra, as described previously. 32…”

“…A polystyrene layer is then spin coated onto the Si wafer under conditions previously shown by x-ray reflectivity and AFM to produce a film of thickness of ~250 Å and roughness of 2 Å RMS. 16 Next, the surface of the polystyrene film is functionalized with a mixture of primary and secondary amine groups by non-mass selected ion deposition of gaseous allylamine ions at either 50 or 200 eV kinetic energy. Table 1 summarizes the elemental percentages that are obtained via XPS for the clean oxidized Si wafer, spin coated polystyrene layer, and aminefunctionalized polystyrene.…”

“…The effects of ion kinetic energy on polystyrene morphology have been previously discussed for the deposition of gaseous fluorocarbon ions. 16 Briefly, a rougher surface is produced in vacuum (prior to the aqueous adsorption step) by higher kinetic energy ions that simultaneously deposit onto and sputter away the polystyrene layer. This leads to a thinner and rougher polystyrene substrate that nevertheless presents similar polar amine and oxygenated moieties for the subsequent aqueous adsorption of Br-PEG-peptide.…”