C. He

Tunable electronic and magnetic properties of monolayer MoS2 on decorated AlN nanosheets: a van der Waals density functional study

In this study, structural, electronic, and magnetic properties of monolayer MoS2 on decorated AlN nanosheets have been systematically investigated using density functional theory with van der Waals corrections. The results indicate that the surface microstructure of the AlN substrate and stacking patterns significantly affect the electronic and magnetic properties of heterostructures. Moreover, the n type semiconductor to p type semiconductor to metal transition accompanied with the nonmagnetic to magnetic transfer can be achieved for monolayer MoS2. The diverse electronic and magnetic properties highlight the potential of MoS2 nanosheets for applications in electronics and spintronics.

A tunable and sizable bandgap of a g-C3N4/graphene/g-C3N4 sandwich heterostructure: a van der Waals density functional study

The structural and electronic properties of a g-C3N4/graphene/g-C3N4 (g-C3N4/SLG/g-C3N4) sandwich heterostructure have been systematically investigated using density functional theory with van der Waals corrections. The results indicate that the band gap of the g-C3N4/SLG/g-C3N4 sandwich heterostructure can be opened to 106 meV without strain. Applying strain is a promising way to tune the electronic properties of a sandwich heterostructure. After applying uniaxial strain, the heterostructure can withstand larger tensile strain than compression strain without damaging the structure and the band gap is more easily increased by the X-direction strain. When the 5% X-direction strain is applied, the band gap could be opened to 525 meV and meanwhile maintain a high carrier mobility. These electronic properties may provide a potential application in nanodevices.

Tuning electronic and magnetic properties of zigzag graphene nanoribbons with a Stone–Wales line defect by position and axis tensile strain

In this study, the electronic and magnetic properties of zigzag graphene nanoribbons (ZGNR) with a Stone–Wales line defect (SW LD) under axis tensile strain have been investigated by density functional theory. The calculation results reveal that the axis tensile strain and the position of the SW LD significantly affect the electronic and magnetic properties of the ZGNRs. In the unstrained systems, the SW LD is more stable near the edge, and the antiferromagnetic (AFM) semiconductors have indirect band gaps (Eg). With the increasing tensile strain, e, the Eg values of all the AFM semiconducting systems gradually decrease. Moreover, by shifting the SW LD from the center to the edge or increasing the tensile strain, e, semiconductor → half-metal → metal transition with antiferromagnetic → ferromagnetic transfer can be achieved for the systems. The diverse and tunable electronic and magnetic properties enlarge the defective ZGNRs potential applications in electronics and spintronics.

Tuning the structures and electron transport properties of ultrathin Cu nanowires by size and bending stress using DFT and DFTB methods

The electron transport properties of ultrathin Cu nanowires (NWs) with diameters of 0.2–1.0 nm under different bending stresses are reported for potential future application in flexible displays and flexible solar cells. Density functional theory (DFT) and density-functional-based tight-binding (DFTB) approaches have been combined to systematically discover the ballistic transport and diffusive transport of ultrathin Cu NWs at the nanoscale. Our DFT calculations show that with an increase of bending stress (f), the structures of both nonhelical and helical wires become disordered, then exhibit a phase transition and eventually collapse. Therefore, the quantum conduction (G) values are reduced. In addition, as the size of the nanowires increases, the maximum bearable bending stress (fc) reduces. fc of a helical atomic strand is decided by its diameter, while fc of a nonhelical atomic strand is decided by the area of the cross section. Our DFTB calculations reveal that the intermediary atoms are the most important for forming the loop between two electrodes and implementing diffusion transport. Among the seven structures, 6-1b exhibits the best properties, after comprehensively considering the results of quantum transport, diffusive transport and collapse-resistance.

Synthesis, crystal structure and photoluminescence of novel blue-emitting Eu2+-doped (SiC)x–(AlN)1−x phosphors by a nitriding combustion reaction

Novel blue-emitting phosphors with the chemical composition of (SiC)x–(AlN)1−x:yEu2+ (x = 0.06–0.50, y = 0.001–0.01) were synthesized by a nitriding combustion reaction route, and the crystal structure, luminescence properties and thermal stability of the (SiC)x–(AlN)1−x:yEu2+ phosphors were investigated by theoretical and experimental approaches. First-principles calculation results prove that the solid solution of SiC with AlN promotes the doping of Eu2+ ions into the (SiC)x–(AlN)1−x host lattice, and Eu2+ ions tend to occupy Al sites of the host. The synthesized (SiC)x–(AlN)1−x:yEu2+ phosphors absorb light in the region of 250–425 nm and show a single and symmetric broadband emission centered at about 470 nm due to the 4f65d–4f7 transitions of Eu2+. The luminescence intensity increases with the SiC content and reaches its maximum at x = 0.20. The critical quenching concentration of Eu2+ in the (SiC)0.20–(AlN)0.80:yEu2+ phosphor is about y = 0.006. The composition-optimized (SiC)0.20–(AlN)0.80:0.006Eu2+ phosphor shows a small thermal quenching, retaining the luminance of 91.1% at 150 °C. The CIE coordinates were measured as (0.135, 0.167) with high color purity. The above results indicate that (SiC)x–(AlN)1−x:yEu2+ is a promising candidate as a blue-emitting ultraviolet convertible phosphor for white LEDs, and the combustion reaction route is expected to be applicable to the synthesis of other kinds of nitride phosphors.

Coupling of electric field and bending modulated ballistic transport properties of copper nanowires

Abstract Coupling effect of electric field and bending on ballistic transport properties of copper nanowires (NWs) has been studied for the future application in solar cells and flexible displays. Our density function calculations show that when electric field strength V is equal to 0·5 V Å−1, both structures (non-helical strand and helical strand) of CuNW are more stable and exhibit excellent quantum conductivity. Moreover, the helical structures have better stability than the non-helical ones since it owns higher collapse resistant f when V = 1 V Å−1. These results suggested that coupling of electric field and bending can be used to tune transport properties of CuNWs, which may be of help in the design of flexible nanodevices.

Electronic structure and magnetic properties of N monodoping and (Ag,N) codoped graphene-like ZnO sheet

Abstract We perform first principles density functional theory calculations to investigate the atomic structures, electronic structures and magnetic properties of dopant complexes involving Ag and N in graphene-like ZnO sheet (Gr–ZnO). The results indicate that monodoping of N in Gr–ZnO favours a spin polarised state. Ag substituted on the cation site (AgZn) acts as a single acceptor and exhibits a strong attractive interaction with a nitrogen acceptor located at the nearest neighbour oxygen site, forming passive Ag–N complex. By introducing a higher concentration of nitrogen, Ag–2N complex forms. The ferromagnetism is decreased, but the formation energy can be evidently reduced for the defective system. Our findings suggest that (Ag,N) codoping of Gr–ZnO could turn the ferromagnetic stability and is likely to yield better p-type conductivity.

Tuning the electronic and magnetic properties of graphene-like SiGe hybrid nanosheets by surface functionalization

In this paper, the structural, electronic and magnetic properties of fully and partially surface modified SiGe nanosheets (NSs) have been investigated using first-principles calculations based on density functional theory. The results demonstrate that the electronic and magnetic properties of SiGe NSs can be tuned by decorating H, Cl and F atoms on Si sites in SiGe NSs. It is shown that by decorating their surface with H, F, and Cl atoms, H-SiGe, F-SiGe, and Cl-SiGe NSs in FM states are predicted to behave as a semiconductor, half-metal, and metal, respectively. The diverse electronic and magnetic properties define the potential applications of SiGe nanosheets in electronics and spintronics.

First-principle study on the effect of high Ag–2N co-doping on the conductivity of ZnO

The geometric structure, band structure (BS) and density of state (DOS) of pure and p-type co-doping wurtzite ZnO have been investigated by the first-principle ultrasoft pseudopotential method with the generalized gradient approximation. These structures induce fully occupied defect states above the valence-band maximum of doped ZnO. The calculation results show that in the range of high doping concentration, when the co-doping concentration is more than a certain value, the conductivity decreased with the increase of co-doping concentration of Ag–2N in ZnO. Our findings suggest that co-doping of Ag–2N could efficiently enhance the N dopant solubility and is likely to yield better p-type conductivity.

First-Principles Investigation on Ag, N Codoped in p-Type ZnO

The geometric structure, band structure and density of state of pure and Ag-N, Ag-2N codoped wurtzite ZnO have been investigated by first-principles ultrasoft pseudopotential method in the generalized gradient approximation. These structures induce fully occupied defect states above the valence-band maximum of bulk ZnO. The calculation results show that the codoped structure Ag-N has better stability. Meanwhile, the carrier concentration is increased in the Ag-2N codoped configuration where the delocalized features are obvious. Our findings suggest that codoping of Ag-2N could efficiently enhance the N dopant solubility and is likely to yield better p-type conductivity.