Surface characterization of thin film induced by He+ ion-beam irradiation into PLLA

Ion beams were irradiated into biodegradable polymer sheets to develop thin film, self-assembled cellular sheets that exfoliated spontaneously from the substrates in a water solution. We previously reported that thin film and self-assembled cellular sheet were obtained by irradiating He+ ion beams into biodegradable polymer sheets. However, the mechanisms of exfoliation from the substrates have not been clarified. Poly-l-lactic acid (PLLA) sheets were used as substrates. He+ ion-beams were irradiated at an energy of 150 keV with a fluence of 1×1015 ions/cm2. We investigated surface characteristics of He+ ion-beam-irradiated PLLA by means of SAICAS, SIMS, FT-IR-ATR and Raman scattering measurements. Ion-beam-irradiated exfoliated thin films had two layers, a harder layer than the original and a softer one. He+ ion-beam-irradiated exfoliated thin film included a disordered graphite structure produced by ion-beam irradiation. We concluded that thin film and self-assembled cellular sheets could be obtained by He+ ion-beam irradiation into PLLA using localized energy deposition.