Honeycomb Network Research Articles

Graphene: A Comprehensive Review

Graphene, a one-atom thick, two-dimensional sheets of sp2hybridized carbon atoms packed in a hexagonal lattice with a Caron-Carbon distance of about 0.142 nm. Its extended honeycomb network forms the basic building block of other important allotropes; it can be stacked to form 3-Dgraphite, rolled to form 1-D-nanotubes and wrapped to form 0-D-fullerenes. Long-range π conjugation in graphene results in its extraordinary thermal, mechanical and electrical properties, which have been the interest of many theoretical studies and recently became an exciting area for scientists. Graphene is impermeable to gas and liquids, has excellent thermal conductivity and higher current density in comparison to other most effective materials. All of its exceptional properties have opened up new avenues for the use of graphene in nano-devices and nano-systems, which initiated its prominent use as a material for drug targeting. In addition, several fabrication techniques are outlined, starting from the mechanical exfoliation of high-quality graphene to the direct growth on silicon carbide or metal substrates and from the chemical routes utilizing graphene oxide to the newly developed approach at the molecular level. By this article reviewers intend to emphasize on unique properties, fabrication techniques and updated applications of graphene. In addition, we discuss about the potential of graphene in drug targeting in fields of nanotechnology, biomedical engineering and technology and its use for innovations in various fields such as electronics and photonics.

Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice

The nature of Na ion distribution, diffusion path, and the spin structure of $P2$-type Na$_2$Ni$_2$TeO$_6$ with a Ni honeycomb network has been explored. The nuclear density distribution of Na ions reveals a 2D chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron diffraction technique. The Na diffusion pathway described by the calculated iso-surface of Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni$^{2+}$ spin ordering were examined in detail with the electron density mapping, neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single crystal sample through the $k$-scan in the momentum space corresponding to the AFM peak of ($\frac{1}{2}$, 0, 1).

Model Microvascular Networks Can Have Many Equilibria.

We show that large microvascular networks with realistic topologies, geometries, boundary conditions, and constitutive laws can exhibit many steady-state flow configurations. This is in direct contrast to most previous studies which have assumed, implicitly or explicitly, that a given network can only possess one equilibrium state. While our techniques are general and can be applied to any network, we focus on two distinct network types that model human tissues: perturbed honeycomb networks and random networks generated from Voronoi diagrams. We demonstrate that the disparity between observed and predicted flow directions reported in previous studies might be attributable to the presence of multiple equilibria. We show that the pathway effect, in which hematocrit is steadily increased along a series of diverging junctions, has important implications for equilibrium discovery, and that our estimates of the number of equilibria supported by these networks are conservative. If a more complete description of the plasma skimming effect that captures red blood cell allocation at junctions with high feed hematocrit were to be obtained empirically, then the number of equilibria found by our approach would at worst remain the same and would in all likelihood increase significantly.

More results on computation of topological indices of certain networks

There are certain types of topological indices such as degree-based topological indices, distance-based topological indices and counting-related topological indices. Among degree-based topological indices, the so-called atom-bond connectivity (ABC), geometric-arithmetic (GA) are of vital importance. These topological indices correlate certain physico-chemical properties of chemical compounds such as boiling point, stability, strain energy and others. In this paper, the augmented Zagreb, first reformulated Zagreb and sum connectivity indices for certain networks like silicate, chain silicate, hexagonal, oxide and honeycomb networks are computed.

More results on computation of topological indices of certain networks

There are certain types of topological indices such as degree-based topological indices, distance-based topological indices and counting-related topological indices. Among degree-based topological indices, the so-called atom-bond connectivity (ABC), geometric-arithmetic (GA) are of vital importance. These topological indices correlate certain physico-chemical properties of chemical compounds such as boiling point, stability, strain energy and others. In this paper, the augmented Zagreb, first reformulated Zagreb and sum connectivity indices for certain networks like silicate, chain silicate, hexagonal, oxide and honeycomb networks are computed.

Photocatalytic oxygen evolution from low-bandgap conjugated microporous polymer nanosheets: a combined first-principles calculation and experimental study.

Nanostructured semiconducting polymers have emerged as a very promising class of metal-free photocatalytic materials for solar water splitting. However, they generally exhibit low efficiency and lack the ability to utilize long-wavelength photons in a photocatalytic oxygen evolution reaction (OER). Here, based on first-principles calculations, we reveal that the two-dimensional (2D) aza-fused conjugated microporous polymer (aza-CMP) with a honeycomb network is a semiconductor with novel layer-dependent electronic properties. The bandgap of the as-synthesized aza-CMP nanosheets is measured to be 1.22 eV, suggesting that they can effectively boost light absorption in the visible and near infrared (NIR) region. More importantly, aza-CMP also possesses a valence band margin suitable for a photocatalytic OER. Taking advantage of the 2D layered nanostructure, we further show that the exfoliated ultrathin aza-CMP nanosheets can exhibit a three-fold enhancement in the photocatalytic OER. After deposition of a Co(OH)2 cocatalyst, the hybrid Co(OH)2/aza-CMP photocatalyst exhibits a markedly improved performance for photocatalytic O2 evolution. Furthermore, first-principles calculations reveal that the photocatalytic O2 evolution reaction is energetically feasible for aza-CMP nanosheets under visible light irradiation. Our findings reveal that nanostructured polymers hold great potential for photocatalytic applications with efficient solar energy utilization.

Two unusual 3D honeycomb networks based on Wells-Dawson arsenomolybdates with d10 transition-metal-pyrazole connectors.

Herein, two Wells -Dawson-type arsenomolybdates, formulated as [Cu(pyr)2]6[As2Mo18O62] (1) and [Ag(pyr)2]6[As2Mo18O62] (2) (pyr = pyrazole), were hydrothermally synthesized and structurally characterized via single-crystal X-ray diffraction, elemental analysis, IR and UV-vis-NIR spectroscopies, XPS, XRD, and TG analysis. The structural analysis indicated that compounds 1 and 2 were isomorphic. They are the first reported 3D honeycomb structures of Wells-Dawson-type arsenomolybdates. The [M(pyr)2] (M = Cu and Ag) connected with [As2Mo18O62]6- polyoxoanions to form the {812·123}{8}3 topological structure. The contributions of organic ligands, pH value, reaction temperature, and transition-metal (TM) to the construction of 3D networks were elucidated. Furthermore, compounds 1 and 2 exhibited fluorescence properties in the solid state at room temperature, highly efficient catalytic ability for the degradation of five organic dyes (MB, RhB, MO, AP, and CR) under UV irradiation, and obvious electrocatalytic activities for the reduction of H2O2. The mechanisms of photocatalysis and electrocatalysis have also been discussed in detail.

Tailor-made copper(ii) coordination polymers based on the C3symmetric methanetriacetate as a ligand

The construction of coordination polymers based on flexible ligands in a pre-designed manner is a difficult task which needs deep knowledge of the ligands involved. With this objective in mind, we have investigated the complex formation between methanetriacetic acid (H3mta) and copper(II) in the presence of 2,2′-bipyridine (bpy) as a blocking coligand to limit the number of coordination sites available at the metal ion. In this primary target, five complexes of formulae [Cu3(bpy)6(mta)](ClO4)3·2H2O (1), [Cu4(bpy)6(mta)2(H2O)2](ClO4)2·20H2O (2), [Cu(bpy)(Hmta)]n (3), {[Cu4(bpy)4(mta)2](ClO4)2·3H2O}n (4) and {[Cu3(mta)2(bpy)3(H2O)]3·3dmf·13H2O}n (5) were synthesized and their crystal structures were solved by single crystal X-ray diffraction. Compounds 1 and 2 are tri- and tetranuclear species, respectively, whereas 3 and 4 are one-dimensional compounds and 5 is a three-dimensional coordination polymer. This series of complexes reveals that methanetriacetate behaves as a tritopic ligand which keeps its C3 symmetry despite its flexibility. On the basis of the structural knowledge of 1–5, a (6,3)-honeycomb network of formula {[Cu12(tppz)6(mta)4(H2O)24](NO3)12·66H2O}n (6) [tppz = tetrakis(2-pyridyl)pyrazine] was prepared by design where each methanetriacetate ligand acts as a three-connected node. Magnetic susceptibility measurements in the temperature range 2.0–300 K for 1–6 show the occurrence of very weak antiferro- (1 and 2) and ferromagnetic (3–5) interactions, whereas an intermediate antiferromagnetic coupling (J = −43 cm−1, the spin Hamiltonian being defined as H = −JS1·S2) is observed for 6. The different size and nature of the magnetic interactions in 1–6 are analyzed and discussed in the light of the respective exchange pathways involved.

On topological indices of honeycomb networks and Graphene networks

In QSAR/QSPR study, topological indices such as the Shultz index, generalized Randic index,Zagreb index, general sum-connectivity index, atom-bond connectivity ($ABC$) index and geometric-arithmetic ($GA$) index exploited to estimate the bioactivity of chemical compounds. In this paper, we compute first general Zagreb index, general Randic connectivity index, general sum-connectivity index, $ABC$, $GA$, $ABC_4$ and $GA_5$ indices of the line graphs of subdivision graphs of honeycomb networks and graphene.

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H3LiIr2O6.

A powder sample of pure H3LiIr2O6 was synthesized from α-Li2IrO3 powder by a soft chemical replacement of Li+ with H+. The crystal structure of H3LiIr2O6 consists of sheets of edge sharing LiO6- and IrO6-octahedra forming a honeycomb network with layers stacked in a monoclinic distorted HCrO2 type pattern. Heavy stacking faulting of the sheets is indicated by anisotropic peak broadening in the X-ray powder diffraction (XRPD) pattern. The ideal, faultless crystal structure was obtained by a Rietveld refinement of the laboratory XRPD pattern while using the LiIr2O63--layers of α-Li2IrO3 as a starting model. The low radial distances of the PDF function, derived from synchrotron XRPD data, as constraints to stabilize the structural refinement. DIFFaX-simulations, structural considerations, high radial distances of the PDF function and a Rietveld compatible global optimization of a supercell were employed to derive a suitable faulting model and to refine the microstructure using the experimental data. We assumed that the overall stacking pattern of the layers in the structure of H3LiIr2O6 is governed by interlayer O-HO contacts. From the constitution of the layers, different stacking patterns with similar amounts of strong O-HO contacts are considered. Random transitions among these stacking patterns can occur as faults in the crystal structure of H3LiIr2O6, which quantitatively describe the observed XRPD.

Synthesis and self-assembly of a D3h symmetric polycyclic aromatic hydrocarbon into a rigid 2D honeycomb network

C 3 symmetric hexa-peri-hexabenzocoronene carboxylic acid assembles into a rigid 2D honeycomb network at a solid–liquid interface.

Design and Tailoring of the 3D Macroporous Hydrous RuO2 Hierarchical Architectures with a Hard-Template Method for High-Performance Supercapacitors.

In this work, RuO2 honeycomb networks (RHCs) and hollow spherical structures (RHSs) were rationally designed and synthesized with modified-SiO2 as a sacrificial template via two hydrothermal approaches. At a high current density of 20 A g-1, the two hierarchical porous RuO2·xH2O frameworks showed the specific capacitance as high as 628 and 597 F g-1; this is about 80% and 75% of the capacitance retention of 0.5 A g-1 for RHCs and RHSs, respectively. Even after 4000 cycles at 5 A g-1, the RHCs and RHSs can still remain at 86% and 91% of their initial specific capacitances, respectively. These two hierarchical frameworks have a well-defined pathway that benefits for the transmission/diffusion of electrolyte and surface redox reactions. As a result, they exhibit good supercapacitor performance in both acid (H2SO4) and alkaline (KOH) electrolytes. As compared to RuO2 bulk structure and similar RuO2 counterpart reported in pseudocapacitors, the two hierarchical porous RuO2·xH2O frameworks have better energy storage capabilities, high-rate performance, and excellent cycling stability.

Reduced Graphene Oxide/α-Cyclodextrin-Based Electrochemical Sensor: Characterization and Simultaneous Detection of Adenine, Guanine and Thymine

Graphene, the rising star of carbon nanomaterials, is a single layer of sp 2 -bonded carbon atoms patterned in a 2D honeycomb network. Thanks to its unique features, graphene has attracted enormous attention and it has arisen various applications in the fields of optical and electrochemical sensors. In the present work, reduced graphene oxide/alpha cyclodextrin ( rGO/α-CD ) is proposed as a nanocomposite for individual and simultaneous detection of adenine, guanine and thymine. rGO/α-CD has been characterized by FT-IR, Raman spectroscopy, AFM, HR-TEM and SEM techniques. Cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques were utilized for detection of adenine, guanine and thymine. The limit of detection (LOD) values for adenine, guanine and thymine were calculated to be 145.5, 38.9 and 52.9 nmol L -1 , respectively. The results show that the developed sensor can be utilized for the determination of adenine, guanine and thymine in human serum, indicating its promising application in the analysis of real samples.

2D Tl–Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure

Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl–Pb compounds on Ge(1 1 1), -(Tl, Pb) and -(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1) compound is almost identical to the alike (Tl, Pb)/Si(1 1 1) system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1) compound contains six Tl atoms and seven Pb atoms per unit cell (i.e. ∼0.67 ML Tl and ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1) and (Tl, Pb)/Ge(1 1 1) compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1), these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

Numerical device simulation of carbon nanotube contacted CZTS solar cells

Nanolayers of graphene and nanotubes have become the attractive materials as the front or back electrodes in thin film solar cells. We propose a novel thin-film solar cell structure in which the traditional transparent conductive oxide electrode, ZnO:Al, is replaced by a thin layer of single-wall carbon nanotubes bundle with a honeycomb network. SCAPS simulation is used to investigate the band diagram, current–voltage characteristics and quantum efficiency of this hybrid device. The advantage of embedding metallic nanotubes is the superior electrical and optical properties such as wide and controllable work function and transparency to wider range of wavelengths as well as high charge transport conductivity. These excellent optical and electrical properties led to a better short-circuit current density and quantum efficiency in hybrid CZTS devices. In addition, we observed an improvement in open-circuit voltage of the Au:Cu doped nanotube bundles compared to undoped nanolayer network. Nanolayers do reduce the device degradation by covering the grain boundaries and surpassing the ion migration under aging conditions.

Coexistence of Dirac cones and Kagome flat bands in a porous graphene

We investigate the geometric and electronic structures of porous graphene networks consisting of phenalenyl and phenyl groups, which are connected alternately with C3 symmetry via single bonds to form a honeycomb network with an internal degree of freedom. The networks possess both Dirac cones and Kagome flat bands near the Fermi level (EF) because the phenalenyl and phenyl form hexagonal and Kagome lattices, respectively. Because of the large spacing between phenalenyl units, the networks possess very slow massless electrons/holes at EF, the Fermi velocity of which is a hundred times lower than that of graphene, leading to spin polarization on the networks with antiferromagnetic (AF) and ferromagnetic (F) ordering as their stable states. Our calculations show the AF state is the ground state whose energy is lower by 14 meV than that of the F state. We also demonstrate that the electronic structure of the 2D networks is sensitive to the rotation of the phenyl unit connecting phenalenyl units by changing the π electron network.

Polar properties of a hexagonally bonded GaN sheet under biaxial compression

Using the density functional theory, we study the geometric and electronic structures of a GaN sheet possessing a honeycomb network. The sheet preserves the planar conformation under an equilibrium lattice constant of 3.2 Å, and has a semiconducting electronic structure with an indirect band gap of 2.28 eV. The biaxial compressive strain causes structural buckling, leading to polarization normal to the atomic layer. An external electric field normal to the layer also induces structural buckling with a height proportional to the field strength. The polarity of the buckled GaN sheet is tunable by attaching H atoms on Ga and N atoms.

Highly Tunable Complementary Micro/Submicro-Nanopatterned Surfaces Combining Block Copolymer Self-Assembly and Colloidal Lithography.

Two kinds of large-area ordered and highly tunable micro/submicro-nanopatterned surfaces in a complementary manner were successfully fabricated by elaborately combining block copolymer self-assembly and colloidal lithography. Employing a monolayer of polystyrene (PS) colloidal spheres assembled on top as etching mask, polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) or polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micelle films were patterned into micro/submicro patches by plasma etching, which could be further transferred into micropatterned metal nanoarrays by subsequent metal precursor loading and a second plasma etching. On the other hand, micro/submicro-nanopatterns in a complementary manner were generated via preloading a metal precursor in initial micelle films before the assembly of PS colloidal spheres on top. Both kinds of micro/submicro-nanopatterns showed good fidelity at the micro/submicroscale and nanoscale; meanwhile, they could be flexibly tuned by the sample and processing parameters. Significantly, when the PS colloidal sphere size was reduced to 250 nm, a high-resolution submicro-nanostructured surface with 3-5 metal nanoparticles in each patch or a single-nanoparticle interconnected honeycomb network was achieved. Moreover, by applying gold (Au) nanoparticles as anchoring points, micronanopatterned Au arrays can serve as a flexible template to pattern bovine serum albumin (BSA) molecules. This facile and cost-effective approach may provide a novel platform for fabrication of micropatterned nanoarrays with high tunability and controllability, which are promising in the applications of biological and microelectronic fields.

Formation of Coronene Clusters in Concentration and Temperature Controlled Two-Dimensional Porous Network.

In this research, with the assistance of scanning tunneling microscopy (STM), we observed the two-dimensional (2D) self-assembly transition of a star-shaped oligofluorene derivative (StOF) from disordered structure to honeycomb network by adjusting StOF concentration in solution. By introducing guest molecules coronene (COR), we for the first time achieved novel triangle-shaped COR trimers on liquid/highly oriented pyrolytic graphite (HOPG) interface in both honeycomb network and the disordered structure. In thermal tests, the COR/StOF-disorder system underwent a structural conformation to form well-ordered ladder structures, while the COR/StOF-honeycomb system remained the perfect hexagonal network with COR trimers included in the cavities. Density functional theory (DFT) calculations have been employed to investigate the forming mechanism of the molecular nanoarrays. These studies are expected to enhance controlling on 2D self-assembly and provide a facial approach toward constructing on-surface molecular clusters.

Modeling the PbI2 formation in perovskite solar cells using XRD/XPS patterns

The impact of prolonged irradiation and air humidity on the stability of perovskite solar cells is modeled using X-ray diffraction and X-ray photoelectron spectroscopy patterns reported in the literature. Light or air-moisture causes the formation of a thin PbI2 or oxide defective layers (in nanoscale) at the interface of perovskite/hole-transport-layer or at the junction with metallic back contact. This thin layer blocks the carrier transport/passivation at the interfaces and cause degradation of device parameters. Variation in thickness of defective layers, changes the XRD and XPS peaks. This allows detection and estimation of the type, crystallinity and thickness of the defective layer. A simple model is developed here to extract the thickness of such thin defective layers formed in nanometer scale at the back region of several perovskite devices. Based on this information, corrected energy band diagram of every device before and after degradation/aging is drawn and discussed in order to obtain insight into the carrier transport and charge collection at the barrier region. In addition, graphene contacted perovskite devices are investigated showing that honey-comb network of graphene contact reduces the effect of aging leading to formation of a thinner defective layer at the perovskite surface compared to perovskite devices with conventional inorganic contacts i.e. Au, Al.