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Register a new userPentagonal Monolayer Crystals of Carbon, Boron Nitride, and Silver Azide
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Added by
Mehmet Yagmurcukardes
Publication date
2015
fields
Physics
and research's language is
English
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In this study we present a theoretical investigation of structural, electronic and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$) and silver azide (p-AgN$_{3}$) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN$_{3}$ are semiconductors with indirect bandgaps, p-BN structures display metallic behavior. We also investigate the mechanical properties (in-plane stiffness and the Poissons ratio) of four different pentagonal structures under uniaxial strain. p-graphene is found to have the highest stiffness value and the corresponding Poissons ratio is found to be negative. Similarly, p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$ have negative Poissons ratio values. On the other hand, the p-AgN$_{3}$ has a large and positive Poissons ratio. In dynamical stability tests based on calculated phonon spectra of these pentagonal monolayers, we find that only p-graphene and p-B$_{2}$N$_{4}$ are stable, but p-AgN$_{3}$ and p-B$_{4}$N$_{2}$ are vulnerable against vibrational excitations.
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Hexagonal boron nitride (h-BN) is unique among two-dimensional materials, with a large band gap (~6 eV) and high thermal conductivity (>400 W/m/K), second only to diamond among electrical insulators. Most electronic studies to date have relied on h-BN exfoliated from bulk crystals; however, for scalable applications the material must be synthesized by methods such as chemical vapor deposition (CVD). Here, we demonstrate single- and few-layer h-BN synthesized by CVD on single crystal platinum and on carbon nanotube (CNT) substrates, also comparing these films with h-BN deposited on the more commonly used polycrystalline Pt and Cu growth substrates. The h-BN film grown on single crystal Pt has a lower surface roughness and is more spatially homogeneous than the film from a polycrystalline Pt foil, and our electrochemical transfer process allows for these expensive foils to be reused with no measurable degradation. In addition, we demonstrate monolayer h-BN as an ultrathin, 3.33 $unicode{x212B}$ barrier protecting MoS2 from damage at high temperatures and discuss other applications that take advantage of the conformal h-BN deposition on various substrates demonstrated in this work.
Very recently, it was demonstrated that the carrier mobility of a molecular monolayer dioctylbenzothienobenzothiophene (C8-BTBT) on boron nitride can reach 10 cm2/Vs, the highest among the previously reported monolayer molecular field-effect transistors. Here we show that the high-quality single crystal of the C8-BTBT monolayer may be the key origin of the record-high carrier mobility. We discover that the C8-BTBT molecules prefer layer-by-layer growth on both hexagonal boron nitride and graphene. The flatness of these substrates substantially decreases the C8-BTBT nucleation density and enables repeatable growth of large-area single crystal of the C8-BTBT monolayer. Our experimental result indicates that only out-of-plane roughness greater than 0.6 nm of the substrates could induce disturbance in the crystal growth and consequently affect the charge transport. This information would be important in guiding the growth of high-quality epitaxy molecular film.
Recently hybridized monolayers consisting of hexagonal boron nitride (h-BN) phases inside graphene layer have been synthesized and shown to be an effective way of opening band gap in graphene monolayers [1]. In this letter, we report an ab initio density functional theory (DFT)- based study of h-BN domain size effect on the elastic properties of graphene/boron nitride hybrid monolayers (h-BNC). We found both inplane stiffness and longitudinal sound velocity of h-BNC linearly decrease with h-BN concentration.
We demonstrate single crystal growth of wafer-scale hexagonal boron nitride (hBN), an insulating atomic thin monolayer, on high-symmetry index surface plane Cu(111). The unidirectional epitaxial growth is guaranteed by large binding energy difference, ~0.23 eV, between A- and B-steps edges on Cu(111) docking with B6N7 clusters, confirmed by density functional theory calculations.
We study the effect of boron (B) and Phosphorous (P) co-doping on electronic and optical properties of graphitic carbon nitride (g-C$_3$N$_4$ or GCN) monolayer using density functional simulations. The energy band structure indicates that the incorporation of B and P into a hexagonal lattice of GCN reduces the energy band gap from $3.1$ for pristine GCN to $1.9$ eV, thus extending light absorption toward the visible region. Moreover, on the basis of calculating absorption spectra and dielectric function, the co-doped system exhibits an improved absorption intensity in the visible region and more electronic transitions, which named $pi^*$ electronic transitions that occurred and were prohibited in the pristine GCN. These transitions can be attributed to charge redistribution upon doping, caused by distorted configurable B/P co-doped GCN confirmed by both electron density and Mulliken charge population. Therefore, B/P co-doped GCN is expected to be an auspicious candidate to be used as a promising photoelectrode in Photoelectrochemical water splitting reactions leading to efficient solar H$_2$ production.
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