Formation of pyrene crystalline thin films assisted by helium ion bombardment

Abstract

This paper reports on the effect of low energy He+ ion-beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Films are prepared by vacuum evaporation during ion bombardment at room temperature. The structure of the film is controlled by the kinetic energy and current density of the ions. The colorless and transparent crystalline films preferentially oriented with their {001} plane parallel to the substrates are obtained by bombardment of 350 to 500 eV, 60 nA/cm2 He+ ions. Ion-beam irradiation of the higher ion current density enhances intermolecular chemical reactions and, as a result, a crystalline polymer with its {001} plane parallel to the substrate is produced.

Thickness-Varied Carbon Nanomembranes from Polycyclic Aromatic Hydrocarbons

“…29,30 Yet, pyrene films can persist vacuum conditions down to the 10 −7 mbar range, and their cross-linking into planar sheets was accomplished by low-energy He + ions back in 1985. 31 In this study, we take advantage of the thermodynamic characteristics of PAHs and prepare CNMs from pyrene films deposited onto gold, copper, and aluminum supports. The deposition is done through a simple drop-casting from toluene solutions, and following the solvent evaporation, the substrates are placed in an HV irradiation chamber.…”

“…Ordered thin films of anthracene (C 14 H 10 ), pyrene (C 16 H 10 ), and other ubiquitous PAHs have been extensively investigated in light of their photophysical properties and environmental impact. − The deposition of PAHs onto solid substrates is readily done by thermal evaporation as well as upon casting dilute solutions in ordinary organic solvents. The sublimation rate of the molecular layers formed varies much depending on the surrounding pressure, and for example, pyrene adsorbates on gold and silver surfaces were found to survive even under ultrahigh vacuum (UHV). , At room temperature, pyrene multilayers were not observed in UHV consistent with its saturation vapor pressure that is known to be below 10 –5 mbar. , Yet, pyrene films can persist vacuum conditions down to the 10 –7 mbar range, and their cross-linking into planar sheets was accomplished by low-energy He + ions back in 1985 …”