First-principles Studies On Structure And Properties' Regulation Of Several Novel Low-dimensional Materials

The discovery of varieties of two-dimensional?2D?materials has attracted lots of attentions,owing to their novel electronic,optical properties and the great potential applications in nanodevices and nanotechnology.It has become a research hotspot to predicte new two-dimensional materials with novel structures and explore their electronic and optical properties using theoretical design technology.In this paper,the electronic properties as well as the modulation of one-dimensional nanoribbons,novel two-dimensional materials and three-dimensional heterstructures are investigated by using first principles calculations based on density functional theory.The main results are summarized as follows:?1?Using ab inito calculations within Density Functional Theory,,we investigate the effects of electric field and strain on electronic structures of armchair and zigzag arsenene nanoribbons with different widths.The results show that the band gap values for each considered arsenene nanoribbons can be decreased when the size is increased.Moreover,electric field can reduce effectively the band gap of arsenene nanoribbons and can induce the indirect-direct?direct-indirect?band transition for armchair?zigzag?nanoribbons with narrow size.The band gap decrease more rapidly and the threshold electric field induced metal becomes smaller in the wider arsenene nanoribbons.These results demonstrate the effects of electric field have more obvious influences on the larger size nanoribbons.The results also show that the strain can tune the electric structure of arsenene nanoribbons effectively.Interestingly,for armchair arsenene nanoribbons,the indirect to direct band transition can be obtained under the tensile strain for considered wideths.In comparision,the direct-indirect transition only occurs under some strain range for zigzag arsenene nanoribbons.We expect that these results can provide a reference on understanding the underlying physical mechanism of arsenene nanoribbons and related device applications.?2?Using ab inito calculations within Density Functional Theory,,we investigate the structure and electric properties of layer material SnP₃ from bulk to monolayer.The results show that the bulk-to-monolayer transition is accompanied by an abrupt switch in the electronic properties from metallic to semiconducting.Based on structure optimization and phonon-mode calculations,we determine that the monolayer SnP₃ have buckled honeycomb stable structures similar to the arsenene layers and blue phosphorene.The cleavage energy for monolayer and double layer are 0.49 and 0.38 Jm^-2,which are comparable in magnitude to that of black phosphorene of 0.339 Jm^-2 and graphene of 0.344 Jm^-2,suggesting it is easily to separate from the corresponding layer bulk.Furthermore,the monolayer and bilayer are both semiconductors with small indirect band gaps of 0.43 and 0.53 eV,respectively.Interestingly,the monolayer undergoes an indirect-to-direct band-gap transition under a narrow range of compression strain and then change to a metallic nature from semiconductor.It implies that aside from promising electronic and optoelectronic properties,these novel 2D semiconductors can also be anticipated to function as mechanical sensor devices.?3?Using ab inito calculations within Density Functional Theory,we explored the possible structures and the various properties of porous AlN monolayer materials.Two kinds of porous AlN?H-and T-?monolayer are identified,and the phonon dispersion spectrum together with the ab inito molecular dynamics simulations demonstrated that their structures are stable and can be maintained even at high temperatures??1300K?.We further show that these porous AlN monolayers have a well-defined porous nanostructures and even higher specific surface areas,namely,2863 m²/g and 2615 m²/g,which can be comparable with graphene?2630 m²/g?.Furthermore,both porous monolayers exhibit the semiconductor properties with 2.89eV and 2.86 eV indirect band gap,respectively.More interestingly,the electronic structures of such porous monolayers can be modulated by applying strains,i.e.,the T-AlN will change from an indirect to a direct gap when the compressive strain is up to-9%,and to indirect gap again up to-15%.These results indicate that the porous AlN sheets may be potential for optoelectronic applications,as well as for underlying catalysts in the future.?4?The electronic properties of Phosphorene/h-BN heterostructure modulated by different interlayer distances are investigated in this work by using first-principles calculations.The results show that the electronic states in the vicinity of the Fermi level are dominated by the phosphorene layer,and the system exhibits type-I band alignment.It is also found that the h-BN could be suitable substrate to stabilize the phosphorene from being degraded and to protect the electronic properties.Furthermore,it is concluded that the transition between the direct and the indirect band gap with tunable values is dependent on the interlayer distances.The related mechanism is mainly attributed to the opposite behaviors of the P_pz and P_px,p_y bonding states on the conduction band of the heterostructure,along with the enhancement of the interlayer interaction.These findings are expected to play a guiding role in the future design of phosphorene based nano-electronics.