Shansheng Yu

Effect of N/B doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons

Carbon nanotubes, carbon nanocones, and graphene nanoribbons are carbon-based nanomaterials, and their electronic and field emission properties can be altered by either electron donors or electron acceptors. Among both donors and accepters, nitrogen and boron atoms are typical substitutional dopants for carbon materials. The contribution of this paper mainly provides a comprehensive overview of the theoretical topics. The effect of nitrogen/boron doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons is reviewed. It is also suggested that nitrogen is more an n-type donor. The discussion about the mechanism of field emission for N-doped carbon nanotubes and electronic structures of N-doped graphene nanoribbons is interesting and timely.

Growth, structural, and magnetic properties of iron nitride thin films deposited by dc magnetron sputtering

Abstract FeN thin films were deposited on glass substrates by dc magnetron sputtering at different Ar/N 2 discharges. The composition, structure and the surface morphology of the films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). Films deposited at different nitrogen pressures exhibited different structures with different nitrogen contents, and the surface roughness depended on the mechanism of the film growth. Saturation magnetization and coercivity of all films were determined using superconducting quantum interference device, which showed that if N 2 /(Ar+N 2 ) flow ratio was equal to or larger than 30% the nonmagnetic single-phase γ″-FeN appeared. If N 2 /(Ar+N 2 ) flow ratio was less than 10%, the films consisted of the mixed phases of FeN 0.056 and γ′-Fe 16 N 2 , whose saturation magnetizations were larger than that of α-Fe. If N 2 /(Ar+N 2 ) flow ratio was 10%, the phases of γ′-Fe 4 N and e-Fe 3 N appeared, whose saturation magnetizations were lower than that of α-Fe.

Nitrogen/Boron Doping Position Dependence of the Electronic Properties of a Triangular Graphene

We investigate the effect of N/B doping on the electronic properties for a zero-dimensional zigzag-edged triangular graphene, wherein two sets of sublattices are unbalanced, using density functional theory (DFT). We find that the substitutional N/B atom energetically prefers to distribute in the major sublattice. After the N/B doping, the net spin for triangular graphene is reduced and full or partial depolarization occurs depending on doping sites. Our DFT calculations show that the triangular graphene with N/B doped in the major sublattice has a larger energy gap, and the electronic properties depend on the doping position. There is an impurity state below or above the Fermi level for the N/B-doped triangular graphene, depending on the sublattice at which the dopant locates. The dependence of the electronic properties on doping position is attributed to the competition between the Coulomb attraction of N(+) (B(-)) and the correlation with nonbonding states for the extra charge introduced by the N/B atom.

Effects of doping nitrogen atoms on the structure and electronic properties of zigzag single-walled carbon nanotubes through first-principles calculations

Calculations have been made for single-walled zigzag (n, 0) carbon nanotubes containing substitutional nitrogen impurity atoms using ab initio density functional theory. It is found that the formation energies of these nanotubes depend on the tube diameter, as do the electronic properties, and that they show periodic features which result from their different π bonding structures compared to those of perfect zigzag carbon nanotubes. When two nitrogen atoms are doped in the same hexagon per five tube units, the semiconducting tubes exhibit some special electronic structures, in which the impurity level is occupied fully by two excess electrons from doped nitrogen atoms. The electronic structures for the tubes depend on the sites that two nitrogen atoms occupy in the hexagon, by which the impurity states can be near the bottom of the conduction band or can be far apart from the bottom of the conduction band.

Electronic Properties of Nitrogen-Atom-Adsorbed Graphene Nanoribbons With Armchair Edges

Using first-principles calculations based on density functional theory, we systematically study adsorption of nitrogen atom on graphene nanoribbons with armchair edges (AGNRs). It is found that the N atom prefers to be adsorbed at the edge. The adsorption mechanism is discussed from the strong hybridization between the electron states in both N adatom and AGNR. It is also exhibited that the ¿p-d molecular bands appear in the electronic structures. For some AGNRs, the electronic structures are spin-polarized, in which the ¿p-d molecular bands are split off. However, other AGNRs are spin-unpolarized, which can be turned into p-type AGNRs. These results indicate that the properties of AGNRs can be strongly modified through the adsorption of N atom.

Decoration of the inert basal plane of defect-rich MoS2 with Pd atoms for achieving Pt-similar HER activity

Outstanding hydrogen evolution reaction (HER) activity and stability are highly desired for transition metal dichalcogenide (TMD)-based catalysts as Pt substitutes. Here, we theoretically calculated and experimentally showed that adsorbing Pd atoms on the basal plane of defect-rich (DR) MoS2 will effectively modulate the surface electronic state of MoS2 while retaining its active sites, which greatly enhanced the HER activity. Three decoration strategies were used to implement this design: direct epitaxial growth, assembling spherical nanoparticles and assembling Pd nanodisks (NDs). The results showed that only Pd NDs are able to be site-specifically decorated on the basal plane of DR-MoS2 through lamellar-counterpart-induced van der Waals pre-combination and covalent bonding. This Pd ND/DR-MoS2 heterostructure exhibits exceptional Pt-similar HER properties with a low onset-overpotential (40 mV), small Tafel slope (41 mV dec−1), extremely high exchange current density (426.58 μA cm−2) and robust HER durability. These results demonstrate a novel modification strategy by a lamellar metallic nanostructure for designing excellent layered TMD-based HER catalysts.

Nature of substitutional impurity atom B/N in zigzag single-wall carbon nanotubes revealed by first principle calculations

We present systematic calculations for the single-walled zigzag (n,0) carbon nanotubes containing the substitutional impurity atom B/N using the ab initio density- functional theory. It is found that the formation energies of the single-walled zigzag carbon nanotubes with substitutional impurity atom B/N depend on the tube diameters as well as the electric properties, and show periodic features. The nature of these periodic features has been revealed, which results from the different bonding structures of the perfect zigzag carbon tubes with different diameters, rather than the defects (substitutional impurity atom B/N) in the zigzag tubes

Engineering Pt/Pd Interfacial Electronic Structures for Highly Efficient Hydrogen Evolution and Alcohol Oxidation

Tailoring the interfacial structure of Pt-based catalysts has emerged as an effective strategy to improve catalytic activity. However, little attention has been focused on investigating the relationship between the interfacial facets and their catalytic activity. Here, we design and implement Pd-Pt interfaces with controlled heterostructure features by epitaxially growing Pt nanoparticles on Pd nanosheets. On the basis of both density functional theory calculation and experimental results, we demonstrate that charge transfer from Pd to Pt is highly dependent on the interfacial facets of Pd substrates. Therefore, the Pd-Pt heterostructure with Pd(100)-Pt interface exhibits excellent activity and long-term stability for hydrogen evolution and methanol/ethanol oxidation reactions in alkaline medium, much better than that with Pd (111)-Pt interface or commercial Pt/C. Interfacial crystal facet-dependent electronic structural modulation sheds a light on the design and investigation of new heterostructures for high-activity catalysts.

Oxidation of Graphene Nanoribbon by Molecular Oxygen

Density-functional theory based on first principles is used to investigate oxidation of a semiconducting graphene nanoribbon with armchair edges (9-AGNR) by oxygen. The calculated results demonstrate that the oxygen is favorably physisorbed on the inner of 9-AGNR, while the oxygen is chemisorbed at the edge of 9-AGNR. Compared to the oxygen chemisorbed (cyclo- addition) 9-AGNR, two epoxy groups formed from cyclo-additions at the edge of 9-AGNR is energetically preferred. It is also found that the uniaxial strain generated by the cooperative alignment of two epoxy groups can significantly change the band gaps of 9-AGNR, leading to a change in the band gap for 9-AGNR as the concentration of epoxy groups varies. The pronounced change in the electronic properties, in particular, the band gaps, of 9-AGNR, as oxygen is adsorbed on 9-AGNR, may indicate that a semiconducting AGNR could have a potential application as a chemical (oxygen) sensor.

Preparation of c-BN films by RF sputtering and the relation of BN phase formation to the substrate bias and temperature

Abstract This paper deals with the deposition of cubic boron nitride (c-BN) films by radio frequency(RF)magnetron sputtering. The nearly pure c-BN films have been prepared on Si(100)substrates using hexagonal boron nitride(h-BN)targets. Argon gas mixed with nitrogen gas was used as sputtering gas. The deposited films were characterized by Fourier transform infrared (FTIR) spectroscopy and transmission electron diffraction (TED). A ‘temperature-bias’ phase diagram has been worked out. It indicates that the c-BN phase prefers the relative high temperature and negative bias. An opinion was presented that the c-BN nuclei grow discontinuously with every time the ‘thermal spike’ coming.