Selective breaking of carbon-hydrogen bond using low-energy hydrogen ion beam for the formation of ultrathin polymer films

Ultra-thin polymer films are applied specially in modern industries. In this study, a new novel method has been developed to form ultra-thin polymer films from small molecules by using mass-separated low energy hydrogen ion beam treatment. Different kinds of small organic molecules were treated by hydrogen ions at different bombardment energies of 5, 10 and 100 eV, and with the dose ranging from 1 × 105 to 5 × 10 16 ions/cm2. The chemical interactions between the bombardment ions and the small molecules were investigated in-situ by x-ray photoelectron spectroscopy (XPS), and characterized ex-situ by using atomic force microscopy (AFM). Surface properties were also evaluated and compared. Results revealed that precise control of 10 eV H+ ion beam treatment could break C-H bonds selectively while leaving C-C bonds intact. C-H bond breakage created activated carbon centers. Cross-links between the activated molecules resulted in the formation of uniform, dense, and both physically and chemically stable network films. The thickness of the films could be controlled, in an atomic layer scale, by the H+ ion dosage. It was found that four kinds simple organic molecules, dotriacontane (CH₃(CH₂)₃₀CH ₃), docosane (CH₃(CH₂)₂₀CH₃), 1-bromodocosane (CH₃(CH₂)₂₀CH₂Br) and docosanoic acid (CH₃(CH₂)₂₀COOH), could form different ultra-thin (4–7 nm) polymer films by using the same surface treatment. And the ultra-thin polymer films could be prepared on both Si and SiO₂ surfaces.{09}This method opens a new route in using simple organic molecules to prepare nanometer-thick network polymer films.