Group3

Hexagonal-boron nitride (h-BN) or "white graphene" has many outstanding properties including high thermal conductivity, high mechanical strength, chemical inertness, and high electrical resistance, which open up a wide range of applications such as thermal interface material, protective coatings, and dielectric in nanoelectronics that easily exceed the current advertised benefits pertaining to the graphene-based applications. The development of h-BN films using chemical vapor deposition (CVD) has thus far led into nucleation of triangular or asymmetric diamond shapes on different metallic surfaces. Additionally, the average size of the triangular domains has remained relatively small (∼ 0.5 μm(2)) leading to a large number of grain boundaries and defects. While the morphology of Cu surfaces for CVD-grown graphene may have impacts on the nucleation density, domain sizes, thickness, and uniformity, the effects of the decreased roughness of Cu surface to develop h-BN films are unknown. Here, we report the growth and characterization of novel large area h-BN hexagons using highly electropolished Cu substrate under atmospheric pressure CVD conditions. We found that the nucleation density of h-BN is significantly reduced while domain sizes increase. In this study, the largest hexagonal-shape h-BN domain observed is 35 μm(2), which is an order of magnitude larger than a typical triangular domain. As the domains coalesce to form a continuous film, the larger grain size offers a more pristine and smoother film with lesser grain boundaries induced defects.

We report the results of our first-principles investigation on the interaction of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) with graphene, carried out within the density functional theory framework, with additional calculations utilizing Hartree-Fock plus second-order Møller-Plesset perturbation theory. The calculated binding energy of the nucleobases shows the following hierarchy: G > T ≈ C ≈ A > U, with the equilibrium configuration being very similar for all five of them. Our results clearly demonstrate that the nucleobases exhibit significantly different interaction strengths when physisorbed on graphene. The stabilizing factor in the interaction between the base molecule and graphene sheet is dominated by the molecular polarizability that allows a weakly attractive dispersion force to be induced between them. The present study represents a significant step towards a first-principles understanding of how the base sequence of DNA can affect its interaction with carbon nanotubes, as observed experimentally. PACS numbers: 68.43.-h, 81.07.De, 82.37.RsDNA-coated carbon nanotubes represent a hybrid system which unites the biological regime and the nanomaterials world. They possess features which make them attractive for a broad range of applications, e.g., as an efficient method to separate carbon nanotubes (CNTs) according to their electronic properties [1, 2, 3], as highly specific nanosensors, or as an in vivo optical detector for ions. Potential applications of single-stranded DNA (ss-DNA) covered CNTs range from electron sensing of various odors [4], to probing conformational changes in DNA triggered by shifts in the surrounding ionic concentration [5], and detection of hybridization between complementary strands of DNA [6,7]. The interaction of DNA with CNT is not limited to the outer surface of the tube; it has also been experimentally demonstrated that ssDNA can be inserted into a CNT [8], further enhancing the potential applications of this nano-bio system.The details of the interaction of DNA with CNTs have not yet been fully understood, though it is generally assumed to be mediated by the π-electron networks of the base parts of DNA and the graphene-like surface of CNTs. One would like to obtain a better understanding of the binding mechanism, and the relative strength of base-CNT binding as it is indicated experimentally from sequence-dependent interactions of DNA with CNTs [3,4]. In this Letter, we present the results of our first-principles study of the interaction of nucleobases with a graphene sheet as a significant step towards a deeper understanding of the interaction of ssDNA with * Corresponding authors. CNTs.Previous theoretical studies focused on the adsorption of the nucleobase adenine on graphite [9]. In the present study, we have considered all five nucleobases of DNA and RNA, namely the two purine bases adenine (A) and guanine (G), and the three pyrimidine bases cytosine (C), thymine (T), and uracil (U). Our specific interest is to assess the subtl...

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 O 2 and H 2 O. The results based on density functional theory together with first principles molecular dynamics calculations show that O 2 could spontaneously dissociate on phosphorene at room temperature. H 2 O 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.

This article summarizes the detailed equations for the time-dependent Hartree-Fock treatment of nonlinear properties for perturbations made up of a static electric field and an oscillating field. Explicit expressions for all nonlinear processes up to third order are obtained in terms of the density matrices at the same order.For processes at second and third order in perturbation, expressions in terms of lower order quantities are also obtained by applying the (Zn + 1) theorem of perturbation theory. The corresponding computer implementation in the HONDO program is described.

The field of nonlinear optics in molecules and polymers offers challenging opportunities for theorists on both molecular modeling of new structures with enhanced microscopic response and manifestations of bulk effect in nonlinearity. This article presents an experimental point of view in assessing the current status of various theoretical approaches. Experimental results are presented for two model compounds together with predictions by various theoretical models to discuss issues and future opportunities. Three different types of nonlinear optical processes are discussed (i) second order, (ii) third order, and (iii) photorefractivity.

Phosphorene, the monolayer form of (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 the synthesis of phosphorene. In this research, the physical and chemical properties of phosphorene oxide including its formation by oxygen adsorption on the bare phosphorene was investigated. Analysis of the phonon dispersion curves finds stoichiometric and non-stoichiometric oxide configurations to be stable at ambient conditions, thus suggesting that the oxygen adsorption may not degrade the phosphorene. The nature of the band gap of the oxides depends on the degree of functionalization of phosphorene; an indirect gap is predicted for the non-stoichiometric configurations, whereas a direct gap is predicted for the stoichiometric oxide. Application of mechanical strain or an 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.

Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of carbon phosphide (CP) monolayer consisted of sp 2 hybridized C atoms and sp 3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered and buckled surfaces, respectively are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest the binary CP monolayer to be yet unexplored 2D materials holding great promises for applications in high-performance electronics and optoelectronics.