Search query: Theoretical two-atom thick semiconducting carbon sheet

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abstract: A two dimensional carbon allotrope, H net, is proposed using first principle calculations. H net incorporates C4 distorted squares, C6 hexagons, and C8 octagons. Unlike previously reported planar graphene and other theoretical carbon sheets, H net is a two atom thick polymorph with identical C6 C4 C6 components cross facing and covalently buckled to feature a handshake like model. The feasibility of H net is evident from its dynamic stability as confirmed by phonon mode analysis and its lower total energy. H net is energetically more favorable than synthesized graphdiyne and theoretical graphyne, BPC, S graphene, polycyclic net, a squarographite, and lithographite. We explored a possible route for the synthesis of H net from graphene nanoribbons. Electronic band structure calculations indicated that H net is a semiconductor with an indirect band gap of 2.11 eV, whereas graphene and many other two dimensional carbon sheets are metallic. We also explored the electronic structure of one dimensional nanoribbons derived from H net. The narrowest H net nanoribbon showed metallic behavior, whereas the other nanoribbons are semiconductors with band gaps that increase as the nanoribbons widen. H net and its tailored nanoribbons are expected to possess more electronic properties than graphene because of their exceptional crystal structure and different energy band gaps.
author_names: Meng Hu

Yu Shu

Lin Cui

Bo Xu

Dongli Yu

Julong He
title: Theoretical two atom thick semiconducting carbon sheet.
venue: Physical chemistry chemical physics PCCP
year: 2014

abstract: Abstract Hydrogen adsorption on a single Si and SiO2 molecule, doped within C(6,6) and C(10,0) carbon nanotubes (CNTs) is studied using first principles calculations based on density functional theory. Two orientations of the H2 molecule, inside the nanotubes, are compared. Our calculations revealed a rather weak hydrogen binding energy inside both types of pristine CNTs namely, 0.51 eV/H2 and 0.38 eV/H2 for C(6,6) and C(10,0) nanotubes, respectively. When a single Si atom is doped in the interior surface of either type of CNTs, it tends to decouple from the wall and to drift towards the nanotube's axis. A Si atom can bind two hydrogen atoms more strongly 1.4 eV/H2 and 1.13 eV/H2 on Si within metallic and semiconducting CNTs, respectively) than just a pristine CNT would do. A SiO2 molecule binds the hydrogen atoms even stronger, along with formation of water molecule within the metallic CNT. The corresponding binding energy of 1.73 eV/H2 for the C(6,6) is found to be the highest one among the configurations considered. Based on our resuls, we believe that intrinsically Si and SiO2 doped CNTs can be considered as plausible candidates for enhancing the hydrogen adsorption properties.
author_names: Seyed Vahid Hosseini

Hadi Arabi

Ahmad Kompany
title: Silicon atom and silicon oxide molecule, within the metallic and semiconducting carbon nanotubes as promising centers candidates for hydrogen adsorption: A DFT theoretical study
year: 2018

abstract: Abstract Mechanical, electronic and magnetic properties of a single boron atom doped C 6 N 6 sheet B 1 C 6 N 6 and two boron atoms doped C 6 N 6 B 2 C 6 N 6 sheet are studied using first principles calculations based on density functional theory. The in plane stiffness, E for B 2 C 6 N 6 (100.75 N/m) and bulk modulus, G for both B 1 C 6 N 6 (73.61 N/m) and B 2 C 6 N 6 (67.8 N/m) sheets are found to be less than that of pure s triazine C 6 N 6 E 134.41 N/m and G 82.80 N/m) sheet. Interestingly, the substitution of C atom with a B atom in C 6 N 6 sheet induced a total magnetic moment of 1 m B and 2 m B for B 1 C 6 N 6 and B 2 C 6 N 6 cases respectively. This shows that some of the bonding electron in the sheet is freed up as a result of an added hole. This gives rise to the spin polarized 2p orbitals of the nitrogen and neighbouring B or C atoms. After B doping, the semiconducting property is well preserved. These interesting properties make the B 1 C 6 N 6 and B 2 C 6 N 6 sheet as suitable candidates for applications in spin related device.
author_names: Yusuf Zuntu Abdullahi

Tiem Leong Yoon

A A Kassimu
title: Metal free ferromagnetic semiconductor: Mechanical, electronic and magnetic properties of boron doped graphitic carbon nitride (g C6N6) sheet
year: 2020

abstract: We investigate the structural, electronic and magnetic properties of three configurations of buckled heptazine supercell with adsorbed hydrogen, namely, and using DFT approach. The calculated adsorption energy for the three structures is very disparate. The structure is energetically more stable than structures. The less stable structures which contain H atoms adsorbed in vertical direction induced a total magnetic moment of whereas for the case, the adsorbed H atom formed a dangling bond (in the horizontal direction) with N having or like hybridized structure that leaves no unpaired electrons. A different electronic character is found for the three configurations. Specifically, appears to be semiconducting with a narrow band gap whereas the other two configurations, and are half metallic and metallic respectively. In general, our findings present theoretical insights of the most stable buckled heptazine with adsorbed H atom structure for the applications in hydrogen gas storage.
author_names: Yusuf Zuntu Abdullahi

Tiem Leong Yoon

Rania Edrees Adam Mohammad
title: Selective hydrogen adsorption on a buckled carbon nitride sheet: first principles calculation
year: 2018

abstract: The semimetallic bandstructure of graphene and silicene limit their use in functional devices. Mixing silicon and carbon offers a rather unexplored pathway to build semiconducting sheets compatible with current Si based electronics. We present here a complete theoretical study of the phase diagram of two dimensional silicon carbon binaries. To scan the composition range, we employ an ab initio global structural prediction method, complemented by exhaustive enumeration of two dimensional structure prototypes. We find a wealth of two dimensional low energy structures, from standard honeycomb single and double layers, passing by dumbbell geometries, to carbon nanosheets bridged by Si atoms. Many of these phases depart from planarity, either through buckling, or by germinating three dimensional networks with a mixture of sp2 and sp3 bonds. We further characterize the most interesting crystal structures, unveiling a large variety of electronic properties, that could be exploited to develop high performance electronic devices at the nanoscale.
author_names: Pedro Borlido

Ahmad W Huran

Miguel A L Marques

Silvana Botti
title: Novel two dimensional silicon carbon binaries by crystal structure prediction.
venue: Physical chemistry chemical physics PCCP
year: 2020

abstract: Metamaterials and transformation optics have received considerable attention in the recent years, as they have found an immense role in many areas of optical science and engineering by offering schemes to control electromagnetic fields. Another area of science that has been under the spotlight for the last few years relates to exploration of graphene, which is formed of carbon atoms densely packed into a honey comb lattice. This material exhibits unconventional electronic and optical properties, intriguing many research groups across the world including us. But our interest is mostly in studying interaction of electromagnetic waves with graphene and applications that might follow. Our group as well as few others pioneered investigating prospect of graphene for plasmonic devices and in particular plasmonic metamaterial structures and transformation optical devices. In this thesis, relying on theoretical models and numerical simulations, we show that by designing and manipulating spatially inhomogeneous, nonuniform conductivity patterns across a flake of graphene, one can have this material as a one atom thick platform for infrared metamaterials and transformation optical devices. Varying the graphene chemical potential by using static electric field allows for tuning the graphene conductivity in the terahertz and infrared frequencies. Such design flexibility can be exploited to create "patches" with differing conductivities within a single flake of graphene. Numerous photonic functions and metamaterial concepts are expected to follow from such platform. This work presents several numerical examples demonstrating these functions. Our findings show that it is possible to design one atom thick variant of several optical elements analogous to those in classic optics. Here we theoretically study one atom thick metamaterials, one atom thick waveguide elements, cavities, mirrors, lenses, Fourier optics and finally a few case studies illustrating transformation optics on a single sheet of graphene in mid infrared wavelengths. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Electrical Systems Engineering First Advisor Nader Engheta This dissertation is available at ScholarlyCommons: http:/repository.upenn.edu/edissertations/715
author_names: Ashka Vakil
title: Transformation optics using graphene: One atom thick optical devices based on graphene
year: 2012

abstract: Atomically thick two dimensional materials have been increasingly attracting research interest not only due to their promising applications in a range of functional devices but also to their theoretical value to unraveling the catalytic electron transfer process within a simplified scenario. In this work, the monoatomic thick dot sized graphitic carbon nitride (g C3N4) has been synthesized and intimately contacted to the basal plane of the graphene sheet to form the monolayer g C3N4 dots@graphene (MTCG) The electrocatalytic activity of the MTCG in the oxygen reduction reaction is found to rival that of the commercial Pt/C catalyst in terms of the catalytic current density and half wave potential. The density functional theory calculations confirm the catalytic improvement of the MTCG originates from a higher efficiency for the reduction of OOH( than that of the g C3N4 alone; therefore, the current work is expected to provide new insights in developing next generation, highly efficient catalysts for the oxygen reduction reaction.
author_names: Xiaopeng Wang

Lixia Wang

Fei Zhao

Chuangang Hu

Yang Zhao

Zhipan Zhang

Shi-Lu Chen

Gaoquan Shi

Liangti Qu
title: Monoatomic thick graphitic carbon nitride dots on graphene sheets as an efficient catalyst in the oxygen reduction reaction.
venue: Nanoscale
year: 2015

abstract: Abstract Metallic Sn exhibits high theoretical capacity and low operating voltage for Na+ storage, but it suffers from huge volume changes during Na+ insertion/extraction and from big experimental difficulties to achieve high areal capacities with mass loadings larger than 10 mg cm 2. Here we propose a facile and novel synthesis strategy towards hierarchically porous foams of Sn nanodots (3.2 nm) uniformly distributed in a three dimensional sheet like nitrogen doped carbon (SNC) framework derived from a low cost SnO2/polyacrylamide composite hydrogel. The resulting Sn@SNC foams effectively integrate the intriguing merits of the two building blocks, namely both Sn nanodots and SNC framework as active materials providing capacity and the SNC framework as a flexible buffer for the volume change, as an excellent conductor for electrons and as a spacer for the Sn nanodots suppressing aggregation. Moreover, the hierarchically porous structure of the Sn@SNC foam enables fast Na+ diffusion in thick electrodes, finally offering high performance Na+ storage at high mass loadings of up to 20 mg cm 2 with a reversible areal capacity of 1.0 mA h cm 2 at 3 mA cm 2 over 700 cycles.
author_names: Long Pan

Haijian Huang

Mingdong Zhong

Markus Niederberger
title: Hydrogel derived foams of nitrogen doped carbon loaded with Sn nanodots for high mass loading Na ion storage
year: 2019

abstract: Silicon, the most commonly used semiconducting material, is intrinsically 3D. Although the element silicon lies directly beneath carbon in the periodic table, it does not easily form the crystalline bonding present in graphite because the arrangement is energetically unfavorable.1 However, if this bonding were to be realized in crystals made of silicon atoms, the resulting material could prove to be as exciting as the ultimately thin Nobel Prize winning 2D form of graphite: graphene. It has been predicted2 that with only three strong directional bonds for each atom, instead of the four formed in the diamond structure of silicon, silicene (the silicon analogue of graphene) could possess highly mobile charge carriers with exotic properties. Despite being predicted to be unstable in ambient conditions,1 we have succeeded in creating silicene on the surface of zirconium diboride (ZrB2/ a metallic ceramic material.3 Silicene has also been created by a number of researchers on silver surfaces.4 6 To prove the presence of silicene, a comprehensive characterization of the structural, electronic, and chemical properties is essential. However, the properties of these samples differ from those of the (currently hypothetical) freestanding silicene because the silicene is in close contact with the substrate surface. The silicene that we produced rests on thin, singlecrystalline ZrB2 films with silicon wafers as substrates (see Figure 1) Silicene is formed by surface segregation at elevated temperatures, under ultra high vacuum (UHV) conditions.3 In this process, silicon atoms diffuse from the silicon wafer to the diboride surface and segregate to spontaneously form silicene. Although the silicene is oxidized on exposure to air, it can be formed again at the same time as the oxide is removed by an annealing procedure in UHV. In this way, we were able to study silicene in different complementary experimental set ups, using Figure 1. Illustration of a silicene sheet (gray) on a zirconium diboride (ZrB2) substrate. Red: Zirconium atoms. Blue: Boron atoms.
author_names: Rainer Friedlein

Antoine Fleurence

Yukiko Yamada-Takamura

Taisuke Ozaki
title: Silicene: atom thick silicon with tunable properties
year: 2013

abstract: The present study is in sequel to the previous research (Phys. Chem. Chem. Phys. 16 (2014) p. 19122) where a solution based nucleation and growth approach that involved direct epitaxial nucleation of nanofibres of poly(3 hexylthiophene) (P3HT) on carbon nanotubes (CNTs) for potential use as next generation building blocks for applications including field effect transistors and photovoltaic devices, was described. Also presented was a theoretical analysis of epitaxial mechanism of nucleation and growth of semiconducting conjugated polymers notably, P3HT on CNTs. In the present study, we elucidate the impact of molecular weight of P3HT on structural morphology and photophysical properties. The change in average molecular weight of P3HT from ~14 to ~60 kDa resulted in several structural changes, even though the mechanism of nucleation and growth continued to be epitaxial process. In the case of high molecular weight P3HT, the crystallized fibrils were ~200 400 nm in length and ~2 3 nm thick. In contrast, for the low molecular weight, the fibrils were significantly longer >5 mm) in length and ~800 1000 nm thick, which are envisaged to involve chain folding in relation to shorter fibrils. Furthermore, the graft density of fibrils crystallized on CNTs was remarkably higher for the high molecular weight P3HT such that the connectivity between successive fibrils is anticipated to be through very small tie molecules. On the other hand, the graft density of low molecular weight P3HT crystallized on CNTs was low. Thus, the interconnectivity between successive fibrils is anticipated to involve large tie molecules. The differences in connectivity between successive fibrils (besides the structural morphology) for low and high molecular weight P3HT, would at least, in part, impact the charge carrier mobility.
author_names: V S A Challa

Krishna Chaitanya Nune

Raja Devesh Kumar Misra
title: The impact of molecular weight on nanoscale supramolecular structure of semiconducting poly(3 hexylthiophene) on carbon nanotubes and photophysical properties
year: 2016