Effective Exfoliation of Violet Phosphorus by Gas Intercalation on Thermal-Cold Cycling

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