Nanocarbon Phase Research Articles

Laser Engineering Nanocarbon Phases within Diamond for Science and Electronics.

Diamond, as the densest allotrope of carbon, displays a range of exemplary material properties that are attractive from a device perspective. Despite diamond displaying high carbon-carbon bond strength, ultrashort (femtosecond) pulse laser radiation can provide sufficient energy for highly localized internal breakdown of the diamond lattice. The less-dense carbon structures generated on lattice breakdown are subject to significant pressure from the surrounding diamond matrix, leading to highly unusual formation conditions. By tailoring the laser dose delivered to the diamond, it is shown that it is possible to create continuously modified internal tracks with varying electrical conduction properties. In addition to the widely reported conducting tracks, conditions leading to semiconducting and insulating written tracks have been identified. High-resolution transmission electron microscopy (HRTEM) is used to visualize the structural transformations taking place and provide insight into the different conduction regimes. The HRTEM reveals a highly diverse range of nanocarbon structures are generated by the laser irradiation, including many signatures for different so-called diaphite complexes, which have been seen in meteorite samples and seem to mediate the laser-induced breakdown of the diamond. This work offers insight into possible formation methods for the diamond and related nanocarbon phases found in meteorites.

Mixed sp2-sp3 Nanocarbon Materials: A Status Quo Review.

Carbon nanomaterials with a different character of the chemical bond—graphene (sp2) and nanodiamond (sp3)—are the building bricks for a new class of all-carbon hybrid nanomaterials, where the two different carbon networks with sp3 and sp2 hybridization coexist, interacting and even transforming into one another. The extraordinary physiochemical properties defined by the unique electronic band structure of the two border nanoallotropes ensure the immense application potential and versatility of these all-carbon nanomaterials. The review summarizes the status quo of sp2 – sp3 nanomaterials, including graphene/graphene-oxide—nanodiamond composites and hybrids, graphene/graphene-oxide—diamond heterojunctions, and other sp2–sp3 nanocarbon hybrids for sensing, electronic, and other emergent applications. Novel sp2–sp3 transitional nanocarbon phases and architectures are also discussed. Furthermore, the two-way sp2 (graphene) to sp3 (diamond surface and nanodiamond) transformations at the nanoscale, essential for innovative fabrication, and stability and chemical reactivity assessment are discussed based on extensive theoretical, computational and experimental studies.

Electrical and structural characterization of nano-carbon–aluminum composites fabricated by electro-charging-assisted process

Incorporating nano-carbon phases into metal-matrix composites is a promising strategy for simultaneously enhancing electrical conductivity and mechanical properties of metals. Here, we describe the manufacture of novel nano-carbon-aluminum composites by an electro-charging-assisted process (EAP) that show 5.6% ± 1.7% increase in electrical conductivity compared to the base metal alloy. The source of nano-carbon that was used in this study is activated carbon with particle size less than 100 nm. The enhancement is attributed to nano-graphitic structures that extend through the lattice of the metal. Through electron transfer from the metal to the nano-structures the electron density at the interface of nano-crystalline graphite and the metal lattice increases thereby enhancing the bulk electrical conductivity. We identify the important fabrication parameters of the EAP for a reaction system employing a tapered graphite cathode. A high current density of 100 A/cm2 causes ionization and crystallization of the carbon in the liquid metal. The increase in electrical conductivity of the composite is directly related to the incorporation of the nanocrystalline carbon in the metal lattice. The superior performance of these nano-carbon aluminum composites makes them promising candidates for power transmission lines and other applications.

Development of NiO-Nanocarbon and MnO2-Nanocarbon Energetic Catalytic Electrode Materials to Synthesize Electrical Energy through Electrochemical Oxidation of Glucose

Automobile and transportation on land and in air are the major causes of global environment pollution through the chemical combustion of petroleum fuels. The need of the hour is to run the transportation units by fuel cells which convert fuels to energy through electrochemical oxidation, straight to pure electrical energy with no polluting substances. Development of fuel cell lies on exhaustive research on development of high energetic electrocatalytic electrodes over which the fuels break to produce free electron and ions, delivering electrical energy. The present work aims at developing two electrocatalytic materials: NiO-nanocarbon and MnO2-nanocarbon by electrosynthesis method. The performance of the materials was investigated by electrochemical characterization: cyclic voltammetry, chronoammetry, polarization tests and impedance spectroscopy. The materials were found to deliver a high current on electro-oxidation of glucose. The effect of nanocarbon on NiO and MnO2 has enhanced the current to a level of over 100 mA/cm2. XRD study showed the presence of metal oxides and carbon. The electron microscopy images revealed fine grain oxides with entrapped nanocarbon. The carbon seems to be in the form of graphene, produced during electrochemical exfoliation at anode. The SEM morphology of enhanced 3D surface area with high energetic nanocarbon phase entrapped with fine structure metal oxides accounts for the high current obtained by electro-oxidation of the fuel. The materials developed are found to be very good energetic electrodes for future fuel cell in automotive industry.

A comparative outlook of corrosion behaviour and chlorophyll assisted growth kinetics of various carbon nano-structure reinforced hydroxyapatite-calcium orthophosphate coating synthesized in-situ through pulsed electrochemical deposition

Chlorophyll functionalised carbon nanostructures namely exfoliated graphene, reduced graphene oxide (RGO) and multi-walled carbon nanotube (MWCNT) have been successfully co-deposited from aqueous media along with in-situ formed hydroxyapatite-calcium orthophosphate phases to develop a biocompatible coating, which eventually can increase the overall coating strength as reinforcement. Chlorophyll disperses and functionalised carbon nanostructure in aqueous media excluding the need of surfactant during pulsed electrochemical deposition, which was earlier not possible for defect-free graphene as well as carbon nanotubes. It also controls the growth kinetics of these coatings which eventually responsible for the overall characteristics of the composite material.The lattice parameter of calcium phosphate phase remain unchanged in all the composite coating whereas, the lattice parameter and weight percentage (35–73%) of hydroxyapatite crystal are found changing with the type of reinforcement on account of difference in growth kinetics controlled via chlorophyll amphiphilicity along with defect state over nano-graphene. The osteoconduction performance is mostly related with the surface characteristics along with corrosion properties which lead to the formation of different shapes and size of porous apatite scaffold starting from sub-micron spherical shape to lamellar structure with varying Ca/P ratio. The gradual evolution of lamellar structure in RGO and exfoliated graphene, and increased surface porosity in exfoliated graphene compare to other reinforcements, predicts their increased probability of successful adaption over implant surfaces by surrounding tissues. RGO reinforcement forms higher amount of stable hydroxyapatite phase over the surface leading to a better corrosion protection which is on account of faster reactions kinetics associated with a quantitative increase of carbon within the given deposition parameter. These results suggest that chlorophyll functionalized carbon reinforcements can be exploited to craft a range of strategies for the development of functional biocompatible layer over metallic implant surfaces where chlorophyll plays a significant role in controlling overall nano carbon phases reinforcement.

Synergistic icephobic behaviour of swollen nitrile butadiene rubber graphene and/or carbon nanotube composites

Spontaneous change of adhesion of solidifying liquid on surfaces is of significant importance in materials technology where it finds applications such as anti-icing components operating in extreme environments like those of seals. In this work, nitrile butadiene rubber (NBR) composites reinforced with graphene, carbon nanotubes, and a mix of them after immersion in several fluids, experienced both a swelling and a reduction of the cross-link density that reduces ice adhesion, being this effect more evident for graphene containing samples. These results have been rationalized via a first principles atomistic modellization of interfaces formed by ice water of increasing thickness and graphene and scaling laws from fracture mechanics, revealing a clear synergy between swelling and nanocarbon phase in the icephobic nature of the composite, dictated by a competition between elastic modulus and adsorption energy. These findings could find an upscale in component validation readily applied to different areas where de-icing demands handling of large amount of environmental harmful agents.

Enhancing the electrical and mechanical properties of copper by introducing nanocarbon derived from polydopamine coating

Introduction of nanocarbon into metal matrices has shown promising improvement over the base metals. In this study, we examine the effect of a new nanocarbon phase – carbonized polydopamine (cPDA) – on the electrical, thermal, and mechanical properties of sintered copper. The composite samples exhibited better electrical conductivity, thermal diffusivity, hardness and wear resistance. Composites with a low cPDA concentration (0.4 vol%) possessed the best electrical conductivity and mechanical properties, while composite samples with higher cPDA concentrations (3.5 vol %) showed significantly enhanced thermal diffusivity as high as 104.5 mm2/s that is 63.5% higher than the sintered Cu sample.

Nanocarbon phase transformations controlled by solubility of carbon species in gold nanoparticles

The hybrid structures of carbon nanomaterials reveal the excellent properties and open new windows for the applications of carbon-based nanomaterials. However, the structural transformation of carbon nanomaterials should be better understood to design the new hybrid carbon nanomaterials. For this reason, we explore the growth of carbon nanorods composed of nanocrystalline graphite sheets and amorphous carbon nanoparticles by plasma enhanced hot filament chemical vapor deposition using Au film as the catalyst. The results indicate that the carbon nanorods are a hybrid structure of nanocrystalline graphite sheets and amorphous carbon nanoparticles formed via the large Au nanoparticles. The studies of transformation mechanism indicate that the solubility of C2 and C3 carbon species in the Au nanoparticles plays an important role in the conversion between graphite carbon and amorphous carbon. Moreover, the solubility of C, C2 and C3 carbon species in the Au nanoparticles can control the graphitic nanostructure and morphology. Furthermore, the study on the photoluminescence of carbon nanorods indicates the synthesized carbon nanorods emit the ultraviolet and green light at room temperature, which originates from the hydrocarbon radicals on the carbon nanorods and the transition between π* and π bands of sp2 carbon clusters in the carbon nanorods, respectively. The results enable us not only to control the structure of carbon nanomaterials but also develop the next-generation optoelectronic devices based on carbon nanomaterials.

Copper-polydopamine composite derived from bioinspired polymer coating

Metal matrix composites with nanocarbon phases, such carbon nanotube (CNT) and graphene, have shown potentials to achieve improved mechanical, thermal, and electrical properties. However, incorporation of these nanocarbons into the metal matrix usually involves complicated processes. This study explored a new processing method to fabricate copper (Cu) matrix composite by coating Cu powder particles with nanometer-thick polydopamine (PDA) thin films and sintering of the powder compacts. For sintering temperatures between 300 °C and 750 °C, the Cu-PDA composite samples showed higher electrical conductivity and thermal conductivity than the uncoated Cu samples, which is likely related to the higher mass densities of the composite samples. After being sintered at 950 °C, the thermal conductivity of the Cu-PDA sample was approximately 12% higher than the Cu sample, while the electrical conductivity did not show significant difference. On the other hand, Knoop micro-hardness values were comparable between the Cu-PDA and Cu samples sintered at the same temperatures.

Carbon Covetic Nanomaterials Show Promise

Abstract A recently discovered nanocarbon phase, first imaged to atomic resolution in 2012, is being exploited to increase the electrical and thermal conductivity of metals and alloys. These unique materials, known as carbon covetic nanomaterials or covetics for short, represent an opportunity to improve energy efficiency over a wide range of applications using low-cost raw materials and scalable processes. This article briefly describes the structure, properties, and potential applications for covetics.

Detonation Nanodiamond Seeding Technique for Nucleation Enhancement of CVD Diamond – Some Experimental Insights

Detonation nanodiamond (DND) seeding recently emerged as an effective method for enhancing nucleation of chemical vapor deposited (CVD) diamond on non-diamond substrates. This work attempts to provide insight on this effect. For this purpose, polycrystalline diamond coatings were deposited on DND-treated silicon substrates. The exposed nucleation surface side was examined with x-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM); it was found to contain micron-sized granular features, composed of 25-40 nm diamond nanocrystals, similar in size to the DND seeds. HRTEM images further confirm this similarity. A detailed analysis of the nanocarbon phase diagram suggests that nanodiamond crystals can form under CVD environments.

High‐temperature Transitions of C60 at Moderate Pressures

We have prepared new nanocarbon phases using high‐temperature (1000–1600 K) treatment of C60 at moderate (0.1–1.5 GPa) pressures attainable for large‐volume high‐pressure apparatus. The structure of the phases has been studied by x‐ray diffraction and high resolution transmission electron microscopy (HRTEM). The Raman spectra and electron energy loss spectroscopy (EELS) provide evidence of the sp 2 bonding in the new materials. Mechanical and elastic properties are also presented. Whereas the values of density for the new nanocarbon phases are lower than that of graphite, they are still quite hard materials (H≈10–15 GPa) and have a high (∼90%) elastic recovery and record high values of the hardness‐to‐Young modulus ratio H/E≈0.17–0.22.

Heat of explosion of commercial and brisant high explosives

Methods for determining the heat of explosion of high explosives (HEs) with ideal and nonideal processes of explosive decomposition are considered. It is shown that the heat of explosion is of significance for estimating the efficiency of commercial HEs and is used in the energetic characterization of the working capacity. The heat of explosion of brisant HEs is only part of the blast heat of explosion and is the heat content of gaseous detonation products during their isentropic expansion from the initial state to a certain expansion ratio (determined by experimental conditions). The heat of explosion can be obtained by thermodynamic calculations based on physically justified equations of state for fluids (gaseous detonation products in the chemical-reaction zone of the detonation wave in the supercritical state) and condensed nanocarbon phases (nanographite, nanodiamond, and liquid carbon). Experimental and calculated values of the heat of explosion are given. The thermodynamic calculation is inapplicable to commercial HEs because of the nonideal nature of their detonation. The heat of explosion of commercial HEs can be calculated using the Hess law. The heat of explosion of brisant HEs is not a measure of power. The power of HEs is characterized by the propellant performance. It is shown that even detonation velocity cannot be a measure of the power of HEs. The power and detonation parameters of brisant HEs are determined by the energy release density in unit volume of the chemical-reaction zone of the detonation wave and by the rate of energy release from the shock front rather than by the heat of explosion, which cannot be considered a universal characteristic.

Theory and modeling of nanocarbon phase stability

The transformation of nanodiamonds into carbon-onions (and vice versa) has been observed experimentally and has been modeled computationally at various levels of sophistication. Also, several analytical theories have been derived to describe the size, temperature and pressure dependence of this phase transition. However, in most cases a pure carbon-onion or nanodiamond is not the final product. More often than not an intermediary is formed, known as a bucky-diamond, with a diamond-like core encased in an onion-like shell. This has prompted a number of studies investigating the relative stability of nanodiamonds, bucky-diamonds, carbon-onions and fullerenes, in various size regimes. Presented here is a review outlining results of numerous theoretical studies examining the phase diagrams and phase stability of carbon nanoparticles, to clarify the complicated relationship between fullerenic and diamond structures at the nanoscale.

Optical characterization of nanocarbon phases in detonation soot and shocked graphite

Raman spectroscopy, photoluminescence and FTIR absorption were used to characterize the carbon phases in detonation soot and shocked graphite samples. Detonation synthesized diamond and shock synthesized diamond, which were separated from the detonation soot and shocked graphite respectively, were also collected for further examination. The detonation soot was obtained under different charge conditions and environmental conditions including gas and water, and the diamond was separated from the detonation soot by different purification methods. Size-induced transformation in the Raman and photoluminescence spectra was observed. Sp 2 carbon is a dominant defect in both detonation synthesized diamond and shock synthesized diamond. The two dynamically synthesized diamonds have similar structure and surface properties. The properties of detonation soot and detonation synthesized diamond are influenced by charge conditions and environmental conditions. The diamond and graphite crystallites in detonation soot and shocked graphite are both in nanometer sizes. The diamond and graphite crystallites in detonation soot have a smaller size and are more disordered than those in shocked graphite.

Raman investigation of amorphous carbon in diamond film treated by laser

Micro-Raman spectroscopy was employed to investigate the structural changes of diamond films prepared by hot filament chemical vapor deposition and treated by femtosecond (fs) laser and nanosecond (ns) lasers. Breit–Wigner–Fano and Lorentzian line shape simulations were used to fit the spectra. For 266 nm ns laser treated samples, increasing laser power density results in the transformation of amorphous carbons in diamond films into nanocarbon clusters whose size increases and saturates rapidly at around 5.1 nm. At the same time, the Raman G peak position considerably shifts upwardly with increasing laser power density. The different change behavior of the nanocarbons and G peak is interpreted in light of the charge transfer from the graphite π bands to the localized edge states. As the 266 nm laser power density is high enough, a Raman peak in the range of 1150–1200 cm−1 appears, which is attributed to the presence of amorphous diamond. In the case of fs laser treated samples, much more power density (>15 TW/cm2) is needed to transform the amorphous carbon into nanocarbon phases. With increasing fs laser power density, the diamond peak is broadened and downshifted due to the presence of nanocrystalline diamond produced by the high laser power density.