Effective Exfoliation\nof Violet Phosphorus by Gas\nIntercalation on Thermal-Cold Cycling

The\nexfoliation of violet phosphorus into violet phosphorene\nnanosheets\n(VPNS) is crucial for various applications. Large quantities of VPNS\nare typically prepared through solution exfoliation, but prolonged\nsonication often introduces extra functional groups, influencing their\npristine properties. Herein, gas intercalation with thermal-cold cycles\nhas been introduced to enhance VPNS exfoliation and minimize functionalization.\nThe exfoliation of VPNS on the thermal-cold cycle was found to be\nenhanced by about 50% with helium intercalation. Excellent yield was\nachieved through thermal (60 °C)-cold cycle treatment in a helium\natmosphere. Less functionalized or oxidized VPNS with a larger lateral\nsize (4–7 μm) were obtained compared with those from\ntraditional liquid exfoliation. The optical band gap of the exfoliated\nVPNS on thermal-cold cycling with helium intercalation was measured\nby optical transmission spectroscopy to be 2.15 eV, similar to that\nfrom mechanically exfoliated ones and slightly smaller than that (2.16\neV) from prolonged sonication. The assistance of gas intercalation\nfor exfoliation was found to be consistent with theoretical prediction\nby density functional theory, where the penetration barrier of He\n(pore: 0.54 eV; interlayer: 0.14 eV) was calculated to be much lower\nthan that of Ar (pore: 1.77 eV; interlayer: 10 eV).