The Controllable Synthesises And Photoelectric Properties Of Group-VA Two-Dimensional Materials:Arsenene And Bismuthene

Due to the unique electrical structure and quantum confinement effect,two-dimensional layered materials exhibit excellent electrical,optical and mechanical properties,and are widely applied in optoelectronic semiconductor devices,flexible electronic devices,energy storage,and photoelectrocatalysis.The group-VA family of two-dimensional materials,including black phosphorus,arsenene,antimonene,and bismuthene,have attracted great attention in recent years due to their high carrier mobilities and tunable band gap.However,except for black phosphorus,the studies of other elemental two-dimensional materials of the group-VA is mainly focused on theoretical research.The actual experimental researches,including synthesis,studies of optical and electrical properties,is still insufficient.Therefore,we firstly review the background of two-dimensional materials,and then introduces the researches on the preparation and properties studies of group-VA two-dimensional materials:arsenene and bismuthene.The details are as follows:1.Van der Waals epitaxial growth two-dimensional single-crystalline gray arsenene nanoflakes.Hexagonal and half-hexagonal gray arsenene nanoflakes were synthesized on mica substrate via van der Waals epitaxy.The as-prepared arsenene nanoflakes depict oxygen-free feature with diagonal length up to 20 ?m and thickness as low as 4 nm,and can be easily transferred to other substrates,such as SiO2/Si substrates and Cu grids free from chemical degradation.Detailed morphology,composition and structure characterizations confirm the single-crystalline feature of synthesized arsenene nanoflakes with rhombohedral phase.Subsequently,the electrical characterizations of arsenene nanoflakes were performed,suggesting that the metallicity to semiconductivity transformation during exposed to air with different periods.2.Amorphization of arsenene nanoflakes:metal to semiconductor transition.The direct transformation of gray arsenene nanoflakes into amorphous arsenene nanoflakes with high purity can be realized through a hydrion aqueous induced decrystallization process.The amorphous arsenene nanoflakes shows superior photoluminescence centered at 609.5 nm,confirming the semiconductive characters of amorphous arsenene nanoflakes.The two terminal devices based on gray and amorphous arsenene nanoflakes confirm the metal to semiconductive transition after amorphization process.The amorphization of arsenene nanflakes offers a feasible way to manipulate the electrical properties of arsenene nanoflakes,which complement the semimetallic feature of gray arsenene nanofakes.3.Theoretical calculation and experimental verification of the interaction between arsenene and organic solvent small molecules and polymer coating.Firstly,the binding energy and charge transfer of arsenene absorbed with molecules(including polymers and solvent molecules)were theoretically calculated via first principles calculations.Then,the experiments were performed to verify the calculation results.In the case of polymer absorbed arsenene,the stronger interaction leads to the lower the protection efficiency of arsenene nanoflakes.In terms of arsenic and solvent molecules,a higher interacted energy results in a higher yield of arsenene nanosheet in liquid exfoliation.4.2D hexagonal bismuthene nanoflakes realized via BN encapsulation.Based on first principle calculations,the structure transformations of bismuthene are succefully suppressed by introducing BN as top layer to compensate the charge transfer from bismuthene to Cu(111)surface.Consistent with theoretical calculations,single-crystalline hexagonal Bi nanoflakes are realized via a BN encapsulated strategy.The sandwiched structure is further identified by cross-sectional SEM and EDS characterizations,manifesting that the Bi nanoflakes are developed between BN films and copper foils.Moreover,the BN-encapsulated structure endows Bi nanoflakes excellent thermal stability in air after 500 ? anneal.At last,we summarize the thesis,and list the current problems in the researches of group-VA two-dimensional materials.