2,263 research outputs found
Effects of extrinsic point defects in phosphorene: B, C, N, O and F Adatoms
Phosphorene is emerging as a promising 2D semiconducting material with a
direct band gap and high carrier mobility. In this paper, we examine the role
of the extrinsic point defects including surface adatoms in modifying the
electronic properties of phosphorene using density functional theory. The
surface adatoms considered are B, C, N, O and F with a [He] core electronic
configuration. Our calculations show that B and C, with electronegativity close
to P, prefer to break the sp3 bonds of phosphorene, and reside at the
interstitial sites in the 2D lattice by forming sp2 bonds with the native
atoms. On the other hand, N, O and F, which are more electronegative than P,
prefer the surface sites by attracting the lone pairs of phosphorene. B, N and
F adsorption will also introduce local magnetic moment to the lattice.
Moreover, B, C, N and F adatoms will modify the band gap of phosphorene
yielding metallic transverse tunneling characters. Oxygen does not modify the
band gap of phosphorene, and a diode like tunneling behavior is observed. Our
results therefore offer a possible route to tailor the electronic and magnetic
properties of phosphorene by the adatom functionalization, and provide the
physical insights of the environmental sensitivity of phosphorene, which will
be helpful to experimentalists in evaluating the performance and aging effects
of phosphorene-based electronic devices
Atomically thin group-V elemental films: theoretical investigations of antimonene allotropes
Group-V elemental monolayers including phosphorene are emerging as promising
2D materials with semiconducting electronic properties. Here, we present the
results of first principles calculations on stability, mechanical and
electronic properties of 2D antimony (Sb), antimonene. Our calculations show
that free-standing {\alpha} and \b{eta} allotropes of antimonene are stable and
semiconducting. The {\alpha}-Sb has a puckered structure with two atomic
sub-layers and \b{eta}-Sb has a buckled hexagonal lattice. The calculated Raman
spectra and STM images have distinct features thus facilitating
characterization of both allotropes. The \b{eta}-Sb has nearly isotropic
mechanical properties while {\alpha}-Sb shows strongly anisotropic
characteristics. An indirect-direct band gap transition is expected with
moderate tensile strains applied to the monolayers, which opens up the
possibility of their applications in optoelectronics
Electronic and quantum transport properties of a graphene-BN dot-ring hetero-nanostructure
Quantum dots, quantum rings, and, most recently, quantum dot-ring nanostructures have been studied for their interesting potential applications in nanoelectronic applications. Here, the electronic properties of a dot-ring hetero-nanostructure consisting of a graphene ring and graphene dot with a hexagonal boron nitride (h-BN) ring serving as barrier between ring and dot are investigated using density functional theory. Analysis of the character of the wave functions near the Fermi level and of the charge distribution of this dot-ring structure and calculations of the quantum transport properties ļ¬nd asymmetry in the conductance resonances leading to asymmetric IāV characteristics which can be modiļ¬ed by applying a negative voltage potential to the central graphene dot
Degradation of Phosphorene in Air: Understanding at Atomic Level
Phosphorene is a promising two dimensional (2D) material with a direct band
gap, high carrier mobility, and anisotropic electronic properties.
Phosphorene-based electronic devices, however, are found to degrade upon
exposure to air. In this paper, we provide an atomic level understanding of
stability of phosphorene in terms of its interaction with O2 and H2O. The
results based on density functional theory together with first principles
molecular dynamics calculations show that O2 could spontaneously dissociate on
phosphorene at room temperature. H2O will not strongly interact with pristine
phosphorene, however, an exothermic reaction could occur if phosphorene is
first oxidized. The pathway of oxidation first followed by exothermic reaction
with water is the most likely route for the chemical degradation of the
phosphorene-based devices in air
Tunnelling Characteristics of Stone-Wales Defects in Monolayers of Sn and Group-V Elements
Topological defects in ultrathin layers are often formed during synthesis and
processing, thereby, strongly influencing their electronic properties . In this
paper, we investigate the role of Stone-Wales (SW) defects in modifying the
electronic properties of the monolayers of Sn and group-V elements. The
calculated results find the electronic properties of stanene (monolayer of Sn
atoms) to be strongly dependent on the concentration of SW-defects e.g.,
defective stanene has nearly zero band gap (~ 0.03 eV) for the defect
concentration of 2.2 x 10^13 cm^-2 which opens up to 0.2 eV for the defect
concentration of 3.7 x 10^13 cm^-2. In contrast, SW-defects appear to induce
conduction states in the semiconducting monolayers of group-V elements. These
conduction states act as channels for electron tunnelling, and the calculated
tunnelling characteristics show the highest differential conductance for the
negative bias with the asymmetric current-voltage characteristics. On the other
hand, the highest differential conductance was found for the positive bias in
stanene. Simulated STM topographical images of stanene and group-V monolayers
show distinctly different features in terms of their cross-sectional views and
distance-height profiles which can serve as fingerprints to identify the
topological defects in the monolayers of group-IV and group-V elements in
experiments.Comment: 18 pages, 5 figures, 1 tabl
Phosphorene Oxide: Stability and electronic properties of a novel 2D material
Phosphorene, the monolayer form of the (black) phosphorus, was recently
exfoliated from its bulk counterpart. Phosphorene oxide, by analogy to graphene
oxide, is expected to have novel chemical and electronic properties, and may
provide an alternative route to synthesis of phosphorene. In this letter, we
investigate physical and chemical properties of the phosphorene oxide including
its formation by the oxygen adsorption on the bare phosphorene. Analysis of the
phonon dispersion curves finds stoichiometric and non-stoichiometric oxide
configurations to be stable at ambient conditions, thus suggesting that the
oxygen absorption may not degrade the phosphorene. The nature of the band gap
of the oxides depends on the degree of the functionalization of phosphorene;
indirect gap is predicted for the non-stoichiometric configurations whereas a
direct gap is predicted for the stoichiometric oxide. Application of the
mechanical strain and external electric field leads to tunability of the band
gap of the phosphorene oxide. In contrast to the case of the bare phosphorene,
dependence of the diode-like asymmetric current-voltage response on the degree
of stoichiometry is predicted for the phosphorene oxide
Theoretical study of electron transport in boron nanotubes
The electron transport in single-walled boron nanotube (BNT) is studied using the Landauer-BĆ¼ttiker [R. Landauer, J. Phys.: Condens: Matter 1, 8099 (1989); M. BĆ¼ttiker, Phys. Rev. Lett. 57, 1761 (1986)] multichannel approach in conjunction with the tight-binding method. In the range of the calculated length (1-5.0 nm) of the tubes, the calculations predict a ballistic transport in BNT and find a relatively low resistance for BNTs as compared to that of the single-walled carbon nanotubes (CNTs) of comparable length. A lower resistance in the case of BNT than the CNT may be attributed to electron-deficient nature of boron characterized by the presence of two-center, and multicenter bonds in the former
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