Formation Of Carbon Nanostructures Research Articles

Time-dependent quantum dynamical simulations of C2condensation under extreme conditions

We report theoretical studies of the initial phase of bulk C(2) condensation into carbon nano-structures by means of Born-Oppenheimer and time-dependent quantum mechanical Liouville-von Neumann molecular dynamics based on the density-functional tight-binding (DFTB) framework for electrons. We observe that the time-dependent quantum mechanical approach leads to faster formation of carbon nanostructures than analogous Born-Oppenheimer simulations. Our results suggest that the condensation of bulk carbon is nonadiabatic in nature, with the critical role of electronic stopping as in ion-irradiation of materials. Contrary to time-dependent quantum mechanical simulations, Born-Oppenheimer dynamics incorrectly predict that the short carbon chains obtained from initial reactive collisions between C(2) quickly evaporate, leading to much lower probability of secondary collisions and condensation. We also discuss some deficiencies in Born-Oppenheimer dynamics that lead to unphysical charge polarization and electron transfer.

Electron-beam-induced Reduction of a Graphene-oxide Film and In-situ Formation of Various Carbon Nanostructures

Electron-beam irradiation (EBI) on a graphene oxide (GO) film resulted in a stepwise growth of carbon nanostructures from a few-layered graphitic- and stripe-like nucleation to embedded onions; the formation mechanism of these embedded onions is dierent from that of free onions. Further, EBI-induced reduction and size-dependent onion and nanodiamond formations were observed. The detailed in-situ observations reveal that the formation of unique carbon nanostructures results from a GO film’s intrinsic properties related to slow reactivity with heat generation, thermodynamic stability, and a physically well-bound flat reaction surface.

Low-temperature process of the formation of tubular and graphene carbon structures

The formation of carbon nanostructures by chemical vapor deposition enhanced by glow-discharge plasma is considered. The studies are conducted in the temperature range 300 to 700°C. Dependences of the structure of the carbon deposit on the thickness of the Ni catalyst film and on the concentration of the carbon-containing component in the vapor phase are analyzed. The reproducible growth of arrays of homogeneous vertical nanotubes or graphene flakes is observed at a low temperature (∼350°C). The electrical properties of the structures are studied.

Growth of carbon nanocoils using Fe–Sn–O catalyst film prepared by a spin-coating method

Abstract

ChemInform Abstract: Formation and Conversion of Carbon Nanostructures under Radiation

AbstractReview: 158 refs.

Evaluation of the Role of Au in Improving Catalytic Activity of Ni Nanoparticles for the Formation of One-Dimensional Carbon Nanostructures

In situ dynamic imaging, using an environmental transmission electron microscope, was employed to evaluate the catalytic activity of Au/SiO(2), Ni/SiO(2), and Au-Ni/SiO(2) nanoparticles for the formation of one-dimensional (1-D) carbon nanostructures such as carbon nanofibers (CNFs) and nanotubes (CNTs). While pure-Au thin-film samples were inactive for carbon deposition at 520 °C in 0.4 Pa of C(2)H(2), multiwalled CNTs formed from Ni thin films samples under these conditions. The number of nanoparticles active for CNF and CNT formation increased for thin films containing 0.1 mol fraction and 0.2 mol fraction of Au but decreased as the overall Au content in thin films was increased above 0.5 mol fraction. Multiwalled CNTs formed with a root growth mechanism for pure Ni samples, while with the addition of 0.1 mol fraction or 0.2 mol fraction of Au, CNFs were formed via a tip growth mechanism at 520 °C. Single-walled CNTs formed at temperatures above 600 °C in samples doped with less than 0.2 mol fraction of Au. Ex situ analysis via high-resolution scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) revealed that catalytically active particles exhibit a heterogeneous distribution of Au and Ni, where only a small fraction of the overall Au content was found in the portion of each particle actively involved in the nucleation of graphitic layers. Instead, the majority of the Au was found to be segregated to an inactive capping structure at one the end of the particles. Using density-functional theory calculations, we show that the activation energy for bulk diffusion of carbon in Ni reduces from ≈1.62 eV for pure Ni to 0.07 eV with the addition of small amounts (≈0.06 mol fraction) of Au. This suggests that the enhancement of C diffusion through the bulk of the particles may be responsible for improving the number of particles active for nucleating the 1-D carbon nanostructures and thereby the yield.

On the conditions of formation of carbon nanostructures on the steel reactor surface from the products of hydrocarbon decomposition in a low-temperature plasma. 3. depth analysis of the material, hypothesis of the growth mechanism

The results of experimental investigations of the process of growth of carbon nanostructures on a metallic surface have been presented. A depth analysis of the formed material has been made for different reagent–oxidant ratios. The probable mechanism of growth of carbon nanostructures has been proposed.

Computer modelling of the plasma chemistry and plasma-based growth mechanisms for nanostructured materials

In this review paper, an overview is given of different modelling efforts for plasmas used for the formation and growth of nanostructured materials. This includes both the plasma chemistry, providing information on the precursors for nanostructure formation, as well as the growth processes itself. We limit ourselves to carbon (and silicon) nanostructures. Examples of the plasma modelling comprise nanoparticle formation in silane and hydrocarbon plasmas, as well as the plasma chemistry giving rise to carbon nanostructure formation, such as (ultra)nanocrystalline diamond ((U)NCD) and carbon nanotubes (CNTs). The second part of the paper deals with the simulation of the (plasma-based) growth mechanisms of the same carbon nanostructures, i.e. (U)NCD and CNTs, both by mechanistic modelling and detailed atomistic simulations.

On the carbo-thermal reduction of silica for carbon nano-fibre formation via CVD

ABSTRACTThe formation of carbon nanostructures using silica nanoparticles from quartz substrates as a catalyst in an aerosol assisted chemical vapor deposition process was examined. The silica particles are reduced to silicon carbide via a carbothermal reduction process. The recyclability of the explored quartz substrates is also presented. The addition of triethyl borate improves the efficiency of the carbothermal reduction process and carbon nanotubes formation. Moreover, the addition of hydrogen during the chemical vapor deposition leads to the helical carbon nanostructures formation.

Characterization of condensed phase beryllium species in the presence of aluminium and silicon matrices during electrothermal heating on graphite and tungsten platforms

Condensed phase beryllium species occurring on graphite and tungsten platforms in the presence of aluminium and silicon matrices were characterised over a wide temperature range. The solid residue was viewed by scanning electron microscopy (SEM), while the chemical composition was probed by energy dispersive (ED) X-ray spectrometry (XRS), Fourier transform-infrared (FT-IR) spectrometry and Raman microanalysis. Beryllium oxide phases were found to be the predominant species over a wide temperature range, persisting up to about 1800 °C on the graphite platform. Beryllium metal species were also identified at high temperatures (1500 °C), but the transformation of beryllium oxide to beryllium was influenced by the amount and localised behaviour of concomitant species on the platform surface. For graphite platform atomisation, aluminium and silicon concomitants are present as metal oxides. Other silicon species, such as silicon carbide, were found mainly at temperatures above 900 °C. Little or no beryllium oxide was found on tungsten platforms up to 1800 °C, although there was evidence of some beryllium alloyed to tungsten. Tungsten from the platform supports some hydration forming different tungsten oxidation states (W6+, W5+, W4+). Also, at 900 °C, silicon was present as an oxide, but also as elemental silicon, silicon carbide, and silicon alloyed to tungsten forming tungsten disilicide at the surface interface. When tungsten platform atomisation was used for samples containing silicon, evidence of degradation of the graphite tube through formation of carbon clusters and nanostructures was more easily noticeable and evaluated by Raman spectrometry.

Effect of Organometallic Compounds on the Formation of Carbon Nanostructures by Pulsed Electric Discharge of Fluorine-Containing Organic Liquid between Metal Electrodes

The carbon nanotube and carbon nanoparticle that contain fluorine on their surfaces were prepared by a pulsed electric discharge in a fluorine-containing organic liquid. The dominant product was nanoparticles with the diameters of ca. 5–100 nm in all experiments, however, the intensity ratio of G-band (1580 cm-1) to D-band (1350 cm-1) of the Raman spectrum of the products increased by addition of a catalyst indicating the formation of crystalline particles. The product formation rate also increased to 39.3 mg/A•s with ferrocene and 79.4 mg/A•s with nickelocene while with no catalyst it resulted in 12.5 mg/A•s.

Formation of carbon nanostructures containing single-crystalline cobalt carbides by ion irradiation method

Carbon nanofibers (CNFs) with a diameter of 17nm, and carbon nanoneedles (CNNs) with sharp tips have been synthesized on graphite substrates by ion irradiation of argon ions with the Co supplies rate of 1 and 3.4nm/min, respectively. Energy dispersive X-ray spectrometry, combined with selected area electron diffraction patterns has been used to identify the chemical composition and crystallinity of these carbon nanostructures. The CNFs were found to be amorphous in nature, while the structures of the CNNs consisted of cubic CoCx, orthorhombic Co2C and Co3C depending on the cobalt content in the CNNs. The diameter of the carbide crystals was almost as large as the diameter of the CNN. Compared to the ion-induced nickel carbides and iron carbides, the formation of single-crystalline cobalt carbides might be due to the high temperature produced by the irradiation.

Synthesis of biocompatible surfaces by nanotechnology methods

The modification of the surface of low-density polyethylene (LDPE) and polyurethane (PU) by means of the pulsed ion-plasma deposition of nanostructural carbon coatings at 20–60°C has been studied. The effect of this low-temperature treatment on the biocompatibility of the LDPE and PU has been assessed. Optimum technological parameters for the formation of mosaic carbon nanostructures with a thickness of 0.3–15 nm and a cluster lateral size of 10–500 nm are determined. These structures give the polymer surface increased hemocompatible properties. The surface of samples was studied by methods of scanning electron microscopy, scanning probe microscopy, and Raman spectroscopy. The effect of the UV light of a krypton lamp (λ = 123.6 nm) and white synchrotron radiation on the surface of poly(methyl methacrylate) (PMMA) preliminarily treated in an oxygen-containing RF discharge plasma has been investigated by varying the duration of exposure (from several minutes to several dozen minutes) and the residual gas pressure (2 and 100 Pa). This processing ensures the smoothing of the surface relief on micro- and nanoscale levels, which can improve the biocompatibility of the modified PMMA film surface. The principles of a two-stage technology for rendering the titanium (implant) surface biocompatible are developed. This technology consists of the chemical pretreatment of the surface for creating a microrelief (2–3 μm roughness), followed by the deposition of a titanium oxide film with controlled composition (TiO2) and thickness (10–60 nm). The influence of the mechanisms and technological parameters of the oxide film deposition on its composition, structure, uniformity (conformal coating of involved shapes), and biocompatibility of the modified surface have been studied.

Formation and conversion of carbon nanostructures under radiation

Consideration has been given to the current status of research on the use of radiation techniques for synthesizing new carbon nanomaterials based on fullerenes, carbon nanotubes, and graphene sheets and their derivatives, which are promising for practical application due to their unique properties. An analysis has been made of the existing experimental and theoretical works on studying different processes induced by the action of radiation on carbon nanostructures (melting of cross-linking carbon nanotubes and formation of molecular junctions between them, polymerization of fullerene layers, formation of new structures, radiation chemistry of fullerenes, and others).

Nanopatterning of carbonaceous structures by field-induced carbon dioxide splitting with a force microscope

We report a tip-based nanofabrication method to generate carbon nanopatterns. The process uses the field-induced transformation of carbon dioxide gas into a solid material. It requires the application of low-to-moderate voltages ∼10–40 V. The method allow us to fabricated sub-25 nm dots and it can be up scaled to pattern square centimeter areas. Photoemission spectroscopy shows that the carbon is the dominating atomic species of the fabricated structures. The formation of carbon nanostructures and oxides by atomic force microscope nanolithography expands its potential by providing patterns on the same sample with different chemical composition.

Graphitic carbon nanostructures from cellulose

Graphitic carbon nanostructures have been synthesized from cellulose via a simple methodology that essentially consists of the steps: (i) hydrothermal treatment of cellulose at 250 °C and (ii) impregnation of the carbonaceous product with a nickel salt followed by thermal treatment at 900 °C. The formation of graphitic carbon nanostructures seems to occur by a dissolution–precipitation mechanism in which amorphous carbon is dissolved in the catalyst nanoparticles and then precipitated as graphitic carbon around the catalyst particles. The subsequent removal of the nickel nanoparticles and amorphous carbon by oxidative treatment leads to graphitic nanostructures with a coil morphology. This material exhibits a high degree of crystallinity and large and accessible surface area.

Obtaining carbon nanomaterials in a plant with a plasma generator and a working zone of rectangular cross section

Results of experimental investigations of the conditions of formation of carbon nanostructures in a plasmachemical reactor of rectangular cross-section from the products of decomposition of hydrocarbons in a low-temperature plasma are presented. The influence of the additional flow region on the process was determined. Data on the content of structurized carbon in the material obtained and on the yield of the process are presented.

Nanobubble-assisted formation of carbon nanostructures on basal plane highly orderedpyrolytic graphite exposed to aqueous media

Ambient gas nanobubbles of size ∼ 101–102 nm occupying the hydrophobic surface of basal plane highly ordered pyrolyticgraphite (HOPG) immersed in aqueous media at room temperature cause exfoliation of thetop graphene layers, as revealed by both in situ and ex situ atomic force microscope (AFM)imaging. The formation of nanoparticles composed mostly from graphene-basednanoscrolls, nanohorn-like and onion-like nanostructures was resolved by high resolutiontransmission electron microscopy (TEM) and examined by diffraction and x-rayphotoelectron spectroscopy (XPS) analyses. The diameter of nanostructures varied fromabout 5 nm for single-layered scrolls to tens of nanometres for multishells. Ramanspectroscopy confirmed the structural rearrangement of the HOPG basal plane after theabove-mentioned treatment. The implications for nanobubble interfacial forces arediscussed.

Carbonization of wood and nanostructures formed from the cell wall

In this paper, formation of unique carbon nanostructures via carbonization of wood in a step-wise process is reviewed. The mechanism described for the production of carbon nanotubes improves our understanding of a historic mystery related to the production of Damascus steel.

The formation of carbon nanostructures by in situ TEM mechanical nanoscale fatigue andfracture of carbon thin films

A technique to quantify in real time the microstructural changes occurring duringmechanical nanoscale fatigue of ultrathin surface coatings has been developed. Cyclicnanoscale loading, with amplitudes less than 100 nm, is achieved with a mechanical probeminiaturized to fit inside a transmission electron microscope (TEM). The TEM tribologicalprobe can be used for nanofriction and nanofatigue testing, with 3D control ofthe loading direction and simultaneous TEM imaging of the nano-objects. It isdemonstrated that fracture of 10–20 nm thick amorphous carbon films on sharpgold asperities, by a single nanoscale shear impact, results in the formation of<10 nm diameter amorphous carbon filaments. Failure of the same carbon films after cyclicnanofatigue, however, results in the formation of carbon nanostructures with a significantdegree of graphitic ordering, including a carbon onion.