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Results for “CARBYNES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Oxidation of carbynes: Signatures in infrared spectra

We report and solidly interpret the infrared spectrum of both pristine and oxidized carbynes embedded in a pure-carbon matrix. The spectra probe separately the effects of oxidation on sp- and on sp{sup 2}-hybridized carbon, and provide information on the stability of the different structures in an oxidizing atmosphere. The final products are mostly short end-oxidized carbynes anchored with a double bond to sp{sup 2} fragments, plus an oxidized sp{sup 2} amorphous matrix. Our results have important implications for the realization of carbyne-based nano-electronics devices and highlight the active participation of carbynes in astrochemical reactions where they act as carbon source for the promotion of more complex organic species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Epitaxial Carbyne: Analytical Results

The Green’s function method in the tight-binding approximation is used to obtain analytical expressions for the electronic spectra and densities of states for two carbyne structural modifications (cumulene and polyyne). Metal and semiconductor substrates are considered and charge-transfer estimates are deduced. Criteria for the occurrence of a charge-density wave in free-standing and epitaxial carbynes are proposed taking into account the intra- and interatomic Coulomb repulsion. Analytical expressions for the phonon spectrum of free-standing carbyne are presented. The data obtained are compared with the results of numerical calculations performed by other researchers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Terminal Iron Carbyne Complexes Derived from Arrested CO 2 Reductive Disproportionation

The encumbered tetraisocyanide dianion Na 2 [Fe-(CNAr Mes 2 ) 4 ] reacts with two molecules of CO 2 to effect reductive disproportionation to CO and carbonate ([CO 3 ] 2– ). When the reaction is performed in the presence of silyl triflates, reductive disproportionation is arrested by silylative esterification of a mono-CO 2 adduct. This results in the formation of four-coordinate terminal iron carbynes possessing an aryl carbamate substituent owing to the direct attachment of an C(O)OSiR 3 group to an isocyanide nitrogen atom. In this work, crystallographic, spectroscopic, and computational analyses of these iron–carbon multiply bonded species reveal electronic structure properties indicative of a conformationally locked iron carbyne unit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Photosensitive free-standing ultra-thin carbyne–gold films

In the article we introduce the experiment of the photostimulation effect in the tunneling conductivity of free-standing thin carbyne-gold films. We observe a sharp increase of the conductivity of hybrid film due to the electromagnetic exciting at the frequencies which are close to the plasmon resonance of gold nanoparticles. The use of carbyne threads as a stabilizing matrix makes it possible to obtain free-standing thin films that demonstrate a good structural stability. The tunnel current–voltage measurements demonstrate a strong dependence of the current value on the intensity of green laser radiation used to photostimulate thin C–Au in area of the measuring experiment.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Selective Permeability of Carbyne Membranes

The paper considers carbyne nanostructures as filtering members for separation of gas mixtures based on selective adsorption of its components, in particular, hydrogen, helium and methane. The size of a highlyselective cell is determined in this paper. It is found that the number of layers in carbyne membrane has no effect on the selective separation of gas mixtures.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Estimations of the Fermi Velocity and Effective Mass in Epitaxial Graphene and Carbyne

It is shown that the Fermi velocity of electrons is a natural characteristic of gapless graphene and cumulene modification of carbyne weakly coupled with the substrate. At the same time, in the presence of gap (graphene with a gap and polyyne modification of carbyne), the corresponding characteristic is the effective electron mass. The corresponding analytical estimations have been performed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Carbyne fiber synthesis within evaporating metallic liquid carbon

Carbyne (e.g., linear chains of sp-bonded carbon) has been the subject of intense research focus due to its presence in astrophysical bodies, as well as its potential for use as a nanoelectronic device and superhard material. In this work, we discuss the formation of carbyne fiber bundles over a nanosecond time scale in laser pulse melting studies, using a previously determined density functional tight binding model for carbon coupled with a new correction for the dispersion energy. We determine our dispersion energy model by optimizing a modified Lennard-Jones potential to an experimentally determined equation of state for graphite, yielding excellent results for the bulk modulus and density under ambient conditions. We then simulate previous experiments by heating graphite to high temperature, followed by expanding the ensuing liquid phase to low density. Our results indicate that the initial, hot liquid phase mainly consists of sp2-bonded carbon atoms, which form a system of sp-bonded strands bound together via dispersion interactions upon achieving low density and temperature. Lastly, the high computational efficiency of our approach allows for direct comparison with experiments that span a wide range of thermodynamic conditions and can help determine parameters for synthesis of carbon-based materials with potentially exotic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

O -Functionalization of a cobalt carbonyl generates a terminal cobalt carbyne

Despite efforts toward extending multiple bonding motifs to late metal systems, examples of late transition metal carbynes remain scarce. Herein, we describe the synthesis of a series of L 3 Co(CO) complexes supported by a trisphosphine ligand framework, with the most reduced of these complexes being amenable to O-functionalization. Furthermore, this transformation provides access to the second reported example of a terminal Co-carbyne complex, in this case stabilized in a pseudotetrahedral geometry (i.e., L 3 Co≡C-OSiR 3 ). Its geometry makes its electronic structure suitable for comparison to structurally-related examples of terminal Co-imido and oxo species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Cohesion energetics of carbon allotropes: Quantum Monte Carlo study

We have performed quantum Monte Carlo calculations to study the cohesion energetics of carbon allotropes, including sp{sup 3}-bonded diamond, sp{sup 2}-bonded graphene, sp–sp{sup 2} hybridized graphynes, and sp-bonded carbyne. The computed cohesive energies of diamond and graphene are found to be in excellent agreement with the corresponding values determined experimentally for diamond and graphite, respectively, when the zero-point energies, along with the interlayer binding in the case of graphite, are included. We have also found that the cohesive energy of graphyne decreases systematically as the ratio of sp-bonded carbon atoms increases. The cohesive energy of γ-graphyne, the most energetically stable graphyne, turns out to be 6.766(6) eV/atom, which is smaller than that of graphene by 0.698(12) eV/atom. Experimental difficulty in synthesizing graphynes could be explained by their significantly smaller cohesive energies. Finally, we conclude that the cohesive energy of a newly proposed graphyne can be accurately estimated with the carbon–carbon bond energies determined from the cohesive energies of graphene and three different graphynes considered here.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Carbon Nanostructures on a Semiconductor Substrate

The analytical expressions for the density of states and the occupation numbers are obtained for simple models of carbon nanostructures (graphene–boron nitride lateral heterostructure, decorated zigzag edges of semi-infinity graphene and graphene nanoribbons, and decorated carbyne). The main attention is placed to the strong-coupling regime of the nanostructures with a semiconducting substrate. The numerical estimations are given for the SiC substrate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tungsten Catalyst Incorporating a Well‐Defined Tetracoordinated Aluminum Surface Ligand for Selective Metathesis of Propane, [(≡Si−O−Si≡)(≡Si−O−) 2 Al−O−W(≡C t Bu) (H) 2 ]

Abstract A well‐defined aluminium‐bound hydroxyl group on the surface of mesoporous SBA‐15, [(≡Si−O−Si≡) (≡Si−O) 2 Al−OH], 3 was obtained by reacting di‐isopropyl aluminium hydride with SBA‐15 treated at 700 °C. The resulting surface [(≡Si−O−Si≡) (≡Si−O) 2 Al (isobutyl) fragment undergoes β‐H elimination at 400 °C leading to [(≡Si−O−Si≡)(≡Si−O−) 2 Al−O) Al−H]. Further oxidation of this Al‐hydride with N 2 O leads to 3 . This acidic support was used to create a well‐defined surface organo‐tungsten fragment [(≡Si−O−Si≡)(≡Si−O−) 2 Al−O−W(≡C t Bu)(CH 2 tBu) 2 ] by reacting 3 with W(≡C‐ t Bu)(CH 2 ‐ t Bu) 3 . A further reaction with hydrogen under mild conditions afforded the tungsten carbyne bis‐hydride [(≡Si−O−Si≡)(≡Si−O−) 2 Al−O−W(H) 2 (≡C‐ t Bu)]. The performance of each of the W‐supported catalysts was assessed for propane metathesis in a flow reactor at 150 °C. [(≡Si−O−Si≡)(≡Si−O−) 2 Al−O−W(≡C t Bu)(H) 2 ] was found to be a single‐site catalyst, giving the highest turnover number (TON=800) and the highest reported selectivity for butane (45 %) vs . ethane (32 %) known for oxide‐supported tungsten complex catalysts (with the supports being silica, silica‐alumina, and alumina). The results demonstrate that modification of the oxide ligands on silica via the creation of Al Lewis acid center as an anchoring site for organometallic complexes opens up new catalytic properties, markedly enhancing the catalytic performance of supported organo‐tungsten species.

Werghi, Baraa↗
DOE OSTI2015

Molecular models of site-isolated cobalt, rhodium, and iridium catalysts supported on zeolites: Ligand bond dissociation energies

The chemistry of zeolite-supported site-isolated cobalt, rhodium, and iridium complexes that are essentially molecular was investigated with density functional theory (DFT) and the results compared with experimentally determined spectra characterizing rhodium and iridium species formed by the reactions of Rh(C 2 H 4 ) 2 (acac) and Ir(C 2 H 4 ) 2 (acac) (acac = acetylacetonate) with acidic zeolites such as dealuminated HY zeolite. The experimental results characterize ligand exchange reactions and catalytic reactions of adsorbed ligands, including olefin hydrogenation and dimerization. Two molecular models were used to characterize various binding sites of the metal complexes in the zeolites, and the agreement between experimental and calculated infrared frequencies and metal-ligand distances determined by extended X-ray absorption fine structure spectroscopy was generally very good. The calculated structures and energies indicate a metal-support-oxygen (M(I)-O) coordination number of two for most of the supported complexes and a value of three when the ligands include the radicals C 2 H 5 or H. The results characterizing various isomers of the supported metal complexes incorporating hydrocarbon ligands indicate that some carbene and carbyne ligands could form. Ligand bond dissociation energies (LDEs) are reported to explain the observed reactivity trends. The experimental observations of a stronger M-CO bond than M-(C 2 H 4 ) bond for both Ir and Rh match the calculated LDEs, which show that the single-ligand LDEs of the mono and dual-ligand complexes for CO are similar to 12 and similar to 15 kcal/mol higher in energy (when the metal is Rh) and similar to 17 and similar to 20 kcal/mol higher (when the metal is Ir) than the single-ligand LDEs of the mono and dual ligand complexes for C 2 H 4 , respectively. The results provide a foundation for the prediction of the catalytic properties of numerous supported metal complexes, as summarized in detail here.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The transformation of diamond to graphite: Experiments reveal the presence of an intermediate linear carbon phase

Natural diamonds that have been partially replaced by graphite have been observed to occur in natural rocks. While the graphite-to-diamond phase transition has been extensively studied the opposite of this (diamond to graphite) remains poorly understood. We performed high-pressure and temperature hydrous and anhydrous experiments up to 1.0 GPa and 1300 °C using Amplex premium virgin synthetic diamonds (20–40 μm size) as the starting material mixed with Mg(OH) 2 as a source of H 2 O for the hydrous experiments. The experiments revealed that the diamond-to-graphite transformation at P = 1.0 GPa and T = 1300 °C was triggered by the presence of H 2 O and was accomplished through a three-stage process. Stage 1: diamond reacts with a supercritical H 2 O producing an intermediate 200–500 nm size “globular carbon” phase. This phase is a linear carbon chain; i.e. a polyyne or carbyne. Stage 2: the linear carbon chains are unstable and highly reactive, and they decompose by zigzagging and cross-linking to form sp 2 -hybridized structures. Stage 3: normal, disordered, and onion-like graphite is produced by the decomposition of the sp-hybridized carbon chains which are re-organized into sp 2 bonds. Our experiments show that there is no direct transformation from sp 3 C-bonds into sp 2 C-bonds. Our hydrous high-pressure and high-temperature experiments show that the diamond-to-graphite transformation requires an intermediate metastable phase of a linear hydrocarbon. This process also provides a simple mechanism for the substitution of other elements into the graphite structure (e.g. H, S, O).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Neural network representation of electronic structure from ab initio molecular dynamics

Despite their rich information content, electronic structure data amassed at high volumes in ab initio molecular dynamics simulations are generally under-utilized. Here we introduce a transferable high-fidelity neural network representation of such data in the form of tight-binding Hamiltonians for crystalline materials. This predictive representation of ab initio electronic structure, combined with machine-learning boosted molecular dynamics, enables efficient and accurate electronic evolution and sampling. When it is applied to a one-dimension charge-density wave material, carbyne, we are able to compute the spectral function and optical conductivity in the canonical ensemble. The spectral functions evaluated during soliton-antisoliton pair annihilation process reveal significant renormalization of low-energy edge modes due to retarded electron-lattice coupling beyond the Born–Oppenheimer limit. The availability of an efficient and reusable surrogate model for the electronic structure dynamical system will enable calculating many interesting physical properties, paving the way to previously inaccessible or challenging avenues in materials modeling.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

From Linear Molecular Chains to Extended Polycyclic Networks: Polymerization of Dicyanoacetylene

Dicyanoacetylene (C 4 N 2 ) is an unusual energetic molecule with alternating triple and single bonds (think miniature, nitrogen-capped carbyne), which represents an interesting starting point for the transformation into extended carbon–nitrogen solids. While pressure-induced polymerization has been documented for a wide variety of related molecular solids, precise mechanistic details of reaction pathways are often poorly understood and the characterization of recovered products is typically incomplete. In this work, we study the high-pressure behavior of C 4 N 2 and demonstrate polymerization into a disordered carbon–nitrogen network that is recoverable to ambient conditions. The reaction proceeds via activation of linear molecules into buckled molecular chains, which spontaneously assemble into a polycyclic network that lacks long-range order. The recovered product was characterized using a variety of optical spectroscopies, X-ray methods, and theoretical simulations and is described as a predominately sp 2 network comprising “pyrrolic” and “pyridinic” rings with an overall tendency toward a two-dimensional structure. This understanding offers valuable mechanistic insights into design guidelines for next-generation carbon nitride materials with unique structures and compositions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Cumulene Wires Display Increasing Conductance with Increasing Length

One-dimensional sp-hybridized carbon wires, including cumulenes and polyynes, can be regarded as finite versions of carbynes. They are likely to be good candidates for molecular-scale conducting wires as they are predicted to have a high-conductance. In this study, we first characterize the single-molecule conductance of a series of cumulenes and polyynes with a backbone ranging in length from 4 to 8 carbon atoms, including [7]cumulene, the longest cumulenic carbon wire studied to date for molecular electronics. We observe different length dependence of conductance when comparing these two forms of carbon wires. Polyynes exhibit conductance decays with increasing molecular length, while cumulenes show a conductance increase with increasing molecular length. Their distinct conducting behaviors are attributed to their different bond length alternation, which is supported by theoretical calculations. Furthermore, this study confirms the long-standing theoretical predictions on sp-hybridized carbon wires and demonstrates that cumulenes can form highly conducting molecular wires.

36 MATERIALS SCIENCE↗