Removal Of Amorphous Carbon Research Articles

Tabular Two-Dimensional Correlation Analysis for Multifaceted Characterization Data.

We propose tabular two-dimensional correlation spectroscopy analysis for extracting features from multifaceted characterization data, essential for understanding material properties. This method visualizes similarities and phase lags in structural parameter changes through heatmaps, combining hierarchical clustering and asynchronous correlations. We applied the proposed method to data sets of carbon nanotube (CNT) films annealed at various temperatures and revealed the complexity of their hierarchical structures, which include elements such as voids, bundles, and amorphous carbon. Our analysis addresses the challenge of attempting to understand the sequence of structural changes, especially in multifaceted characterization data where 11 structural parameters derived from eight characterization methods interact with complex behavior. The results show how phase lags (asynchronous changes from stimuli), and parameter similarities can illuminate the sequence of structural changes in materials, providing insights into phenomena such as the removal of amorphous carbon and graphitization in annealed CNTs. This approach is beneficial even with limited data and holds promise for a wide range of material analyses, demonstrating its potential in elucidating complex material behaviors and properties.

Plasma Functionalized CNT/Cyanate Ester Nanocomposites for Aerospace Structural Applications

AbstractAtmospheric pressure (AP) plasma treatment, a proven direct and dry means of surface modification, was deployed for the functionalization of carbon nanotube (CNT). AP plasma treatment successfully incorporated the functional groups such as −COOH and ‐NH2 onto the surface of CNT without affecting its crystallinity. Reduction in tube diameter and increased purity through the removal of amorphous carbon were confirmed by transmission electron microscopy (TEM) and Raman analysis. As a result of these surface chemistry and morphological changes induced by AP plasma treatment, the modified CNT‐cyanate ester nanocomposite exhibited enhanced dispersion via reduced van‐der Walls interaction. At optimum concentration of 0.1 wt% loading, the functionalized CNT with its high aspect ratio showed a well wetting behavior with cyanate ester (BADCy) matrix leading to remarkable increase in the mechanical properties like tensile, impact and flexural strengths and thus rendering them for potential aerospace structural applications.

Coral-like prussian blue analogues-derived bimetallic phosphide with enhanced electrocatalytic performance for hydrogen evolution reaction

Tailoring the architecture is of great significance for developing and designing highly active non-noble metal-based electrocatalysts for hydrogen evolution reaction (HER). Here, the architecture of the precursor was improved by alkali etching after the introduction of Prussian blue analogue (PBA). The coral-like precursor was transformed into bimetallic phosphide via phosphating. Detailed investigation disclares that the introduction of PBA could dramatically improves the electrochemical surface area of the material, and the abundant active site could be obtained via alkali etching. In addition, the removal of amorphous carbon may be the main reason for the enhanced conductivity.

Purification, structural evolutions, and electrical properties of carbon nanotube yarns processed via incandescent annealing

Incandescent annealing in high vacuum is investigated for the purification of carbon nanotube (CNT) yarns produced via the floating catalyst chemical vapor deposition (CVD) method. The existing chemical purification routes damage CNTs and often require CNT dispersion. As an alternative, thermal annealing in inert or vacuum atmospheres has proved to remove impurities alongside improving CNT graphitization. Current-induced incandescent annealing process (IAP) in high vacuum provides a scalable and efficient route for the purification of CNT structures in a matter of seconds compared to hours of thermal annealing, reducing time and energy by orders of magnitude. In this study, electrical properties of CNT yarns are correlated with the morphological changes of their structure resulted from the IAP. Three distinct resistivity ranges based on the IAP current were identified and the detailed chemical composition, structure, and temperature-dependent resistivity of their corresponding yarns were investigated. It is concluded that the transport mechanism in the CNT yarns changes dynamically and drastically with the removal of amorphous carbon, iron, sulfur, and reduction in chlorine content. The correlations between the chemical composition, structure, and resistivity of samples provide new insight into CNT doping mechanisms and can be utilized to improve the conductivity of commercially available CNT yarns.

Controlling Electronic States of Few-walled Carbon Nanotube Yarn via Joule-annealing and p-type Doping Towards Large Thermoelectric Power Factor

Flexible, light-weight and robust thermoelectric (TE) materials have attracted much attention to convert waste heat from low-grade heat sources, such as human body, to electricity. Carbon nanotube (CNT) yarn is one of the potential TE materials owing to its narrow band-gap energy, high charge carrier mobility, and excellent mechanical property, which is conducive for flexible and wearable devices. Herein, we propose a way to improve the power factor of CNT yarns fabricated from few-walled carbon nanotubes (FWCNTs) by two-step method; Joule-annealing in the vacuum followed by doping with p-type dopants, 2,3,5,6-tetrafluo-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Numerical calculations and experimental results explain that Joule-annealing and doping modulate the electronic states (Fermi energy level) of FWCNTs, resulting in extremely large thermoelectric power factor of 2250 µW m−1 K−2 at a measurement temperature of 423 K. Joule-annealing removes amorphous carbon on the surface of the CNT yarn, which facilitates doping in the subsequent step, and leads to higher Seebeck coefficient due to the transformation from (semi) metallic to semiconductor behavior. Doping also significantly increases the electrical conductivity due to the effective charge transfers between CNT yarn and F4TCNQ upon the removal of amorphous carbon after Joule-annealing.

High speed and low roughness micromachining of silicon carbide by plasma etching aided femtosecond laser processing

Silicon carbide has a high hardness and corrosion resistance. Accordingly, high rate machining of this material is a big challenge to obtain good surface quality. In this work, plasma etching aided femtosecond laser micromachining was proposed to address this issue. A series of square and circular blind holes for forming SiC pressure sensor diaphragms were obtained by using a 50fs, 800 nm, 1000Hz Ti:Sapphire laser. Using the control variable method, the effects of laser machining power, scan line spacing and scanning rate on surface topography of the structure were investigated. As demonstrated by experimental results, surface roughness of the structure increases with the laser machining power within a certain range. While the scanning rate has negligible effects on surface quality of the structure. The maximum surface roughness after femtosecond laser micromachining is 2.867 μm measured by laser scanning confocal microscope, and this value is reduced to 2.143 μm after inductively coupled plasma etching. In addition, a Raman spectroscopy shows that this composite micromachining method can eliminate accumulation of amorphous carbon on SiC surface caused by the femtosecond laser processing. The reduction of surface roughness and removal of amorphous carbon can effectively decrease probability of crack failure of the sensor diaphragm and increase its deformation capability, thereby ensuring sensitivity of the sensor. The composite micromachining method fully combines the advantages of high efficiency of femtosecond laser machining and high surface quality of plasma etching, making it has high potential to be applied in precision machining of silicon carbide and fabrication of SiC sensors.

Thermal induced order fluctuations in carbon nanosystem with carbon nanotubes

The allotropes of carbon nanomaterials such as carbon nanotubes (CNTs) and nanoparticles (CNPs) have emerged as a thrust area of research during the last decade because of their unique properties. CNTs are widely used in microelectronic, sensor, bio-imaging, supercapacitors, fuel cell, and etc. applications. In the present work, we report the thermal induced order fluctuations in the CNPs with CNTs synthesized from camphor. The samples annealed to different temperatures are characterized by various spectroscopic techniques such as UV–Visible, Raman, Fourier Transform Infrared, and X-ray Photoelectron Spectroscopy. Samples’ structure and morphology are analyzed by scanning and transmission electron microscopes, and X-ray diffraction. The thermogravimetric analysis indicates not only the mass variation upon annealing but the thermal stability also. The spectroscopic and thermal analyses reveal the thermal induced oscillations in the carbon system which can be assigned to the dynamics in CNTs through desorption of hydrogen/ thinning or shortening of multi-walled CNTs/sp2 - sp3 conversions and the removal of amorphous carbon (AC). Since the amount of CNTs in the sample decides the electrical behavior, the sample can be tuned to a desired electrical conductivity by annealing and thus making it a tunable material for electronic applications.

Effects of oxidation on silicon vacancy photoluminescence and microstructure of separated domain formed nanodiamond films

In order to increase the oxidation sites for enhancing the Si-V photoluminescence intensity of nanocrytalline diamond films, we prepare nanocrystalline diamond films; these films each are comprised of separated domains and oxidized for different times. Each single domain consists of nanodiamond grains with a size of larger than 100 nm and amorphous carbon. In the gaps between domains of separated domain there is formed a film that allows more sites to contact air to ensure the efficient oxidation of the film. As a result, silicon vacancy photoluminescence intensity of the separated domain forming the film is largely enhanced by about 22.7 times after oxidation. The SEM images and Raman spectra of oxidized samples show that the film contains flower-shaped diamond aggregates, each of which is comprised of radially arranged diamond grains. The mixture of nanodiamond grains and amorphous carbon fills the gaps between diamond petals. These fillers disappear after long-term oxidation, but the diamond petals stay stable. Raman spectra show that the amount of amorphous carbon largely decreases after oxidation, while diamond content apparently rises. Hydrogen is desorbed from the film after short-time oxidation according to Raman spectra, thus the quenching effect on silicon vacancy photoluminescence caused by hydrogen termination of diamond surface state is removed. Diamond petals of large size and nanodiamond grains in the fillers are both silicon vacancy photoluminescence sources of the film; the exposed diamond flats on the surface of unoxidized domains provide limited silicon vacancy photoluminescence for the film. The sufficient exposure of diamond grains after the removal of amorphous carbon leads to the significant enhancement of film’s silicon vacancy photoluminescence. With longer-time oxidation, the photoluminescence of film will slightly decrease due to the disappearance of small-sized nanodiamond grains, but the film photoluminescence almost remains stable in both intensity and property due to the stability of large-sized diamond grains. The film after 140-min oxidation remains photoluminescence enhancement, 8.3 times the photoluminescence of the unoxidized sample. The full width at half maximum of photoluminescence peak declines to merely 5.6－6.0 nm because of diamond petals’ high degree of order, which is advantageous for diamond silicon vacancy photoluminescence.

Water-assisted growth of graphene-carbon nanotube hybrids in plasma

The enhanced growth of graphene-carbon nanotube (CNT) hybrids in a hydrocarbon and hydrogen plasma assisted by water is numerically formulated. The catalyst activity and agglomeration of catalyst particles are the rate determining factors in the growth of hybrids and their constituents, i.e., the CNT and graphene. The water vapor concentration is varied to investigate its effect on the growth process. The enhanced catalyst activity on account of oxidation by hydroxyl ions of water to impede the agglomeration of catalyst particles and the removal of amorphous carbon through etching by hydrogen ions of water are seen to be the main driving forces behind the many fold increase in the dimensions of constituent nanostructures and the hybrids with water vapor concentration. Importantly, beyond a certain specific water vapor concentration, the growth rates dropped due to active oxidation of the catalyst particle.

Theoretical modeling to study the impact of different oxidizers (etchants) on the plasma-assisted catalytic carbon nanofiber growth

An analytical model based on the various surface deposition processes and plasma sheath kinetics of the plasma species (electrons, positively charged ions, radicals, and neutrals) has been developed to investigate the effects of different plasmas (different etchants) on the catalyzed plasma aided growth of carbon nanofibers (CNFs). In particular, the model accounts the poisoning of the catalyst nanoparticle, i.e., the formation of the amorphous carbon layer on the catalyst active surface due to the continuous dissociation of incoming hydrocarbon species from the plasma. It is observed that oxidizers (H2O and O2) in the typical hydrocarbon/hydrogen (C2H2 + H2) plasma act as the dominant etchants and remove the amorphous carbon layer from the catalyst surface and, thus, preserve and enhance the catalyst activity. However, the growth rate of CNFs is much higher when O2 is added as an etchant in the reactive plasma as compared to H2O. This is due to the dual role played by the oxygen, i.e., (i) removal of amorphous carbon from the catalyst active surface, (ii) removal of hydrogen radicals that interact with the carbon species generated on the catalyst surface and suppress their diffusion through the catalyst nanoparticles. The CNF grows much longer in the presence of O2, therefore, etching of CNF tip and deformation of catalyst nanoparticle is the maximum, and hence, the CNF tip diameter is least. Moreover, in the present investigation, we also found that the relative concentrations of H2O or O2 species in the reactive plasma have significant effects on the CNF growth. Our theoretical results are in good agreement with the experimental observations.

Phototransformation-Induced Aggregation of Functionalized Single-Walled Carbon Nanotubes: The Importance of Amorphous Carbon.

Single-walled carbon nanotubes (SWCNTs) with proper functionalization are desirable for applications that require dispersion in aqueous and biological environments, and functionalized SWCNTs also serve as building blocks for conjugation with specific molecules in these applications. In this study, we examined the phototransformation of carboxylated SWCNTs and associated amorphous carbon impurities in the presence or absence of H2O2 under simulated sunlight conditions. We found that while carboxylated SWCNTs were rather unreactive with respect to direct solar photolysis, they photoreacted in the presence of H2O2, forming CO2 and strongly aggregated SWCNT products that precipitated. Photoreaction caused SWCNTs to lose oxygen-containing functionalities, and interestingly, the resulting photoproducts had spectral characteristics similar to those of parent carboxylated SWCNTs whose amorphous carbon was removed by base washing. These results indicated that photoreaction of the amorphous carbon was likely involved. The removal of amorphous carbon after indirect photoreaction was confirmed with thermogravimetric analysis (TGA). Further studies using carboxylated SWCNTs with and without base washing indicate that amorphous carbon reduced the extent of aggregation caused by photoreaction. The second-order rate constant for carboxylated SWCNTs reacting with (•)OH was estimated to be in the range of 1.7-3.8 × 10(9) MC(-1) s(-1). The modeled phototransformation half-lives fall in the range of 2.8-280 days in typical sunlit freshwaters. Our study indicates that photosensitized reactions involving (•)OH may be a transformation and removal pathway of functionalized SWCNTs in the aquatic environment, and that the residual amorphous carbon associated with SWCNTs plays a role in SWCNT stabilization.

Enhancement of Field Emission Properties of Carbon Nanotubes by ECR-Plasma Treatment

We report a significant improvement in electron field emission property of carbon nanotubes film by using an electron cyclotron resonance plasma treatment. Our research results reveal that plasma treatment can modify the surface morphology and enhance the field emission characteristics of carbon nanotubes. Raman spectra indicate that plasma treated CNTs sample has lesser defects. Before plasma treatment, low current density of 6.5 mA/cm2 at 3.0 V/μm and at a high turn-on field Eto of 2.4 V/μm was observed. ECR plasma treated CNTs showed a high current density of 20.0 mA/cm2 at 3.0 V/μm and at a low Eto of 1.6 V/μm. The calculated enhancement factors are 694 and 8721 for ECR-plasma untreated and treated carbon nanotubes, respectively. We found an increase in the enhancement factor and emission current after the ECR-plasma treatment. This may be attributed to creation of geometrical features through the removal of amorphous carbon and catalyst particles.

Multi-Walled Carbon Nanotubes (MWCNTs) modified electrodes: Effect of purification and functionalization on the electroanalytical performances

Different modified electrodes were prepared using multi-walled carbon nanotubes (MWCNTs) prepared and purified according to different procedures. Since MWCNTs purification and functionalization is a key point for the electroanalytical performance of the final devices, MWCNTs were previously characterized from the morphological, surface and electrochemical point of view. Different parameters, such as surface area, pore volume, mesoporosity (responsible of thin layer diffusion mechanism), covalent acidity, charge transfer resistance, amorphous impurities contribute to the final performances in terms of higher currents and more reversible behaviour. The best purification method consists in a treatment in sulphonitric mixture for 24 h with the removal of amorphous carbon. The new modified electrodes were successfully employed in the detection of o-toluidine, a hazardous and toxic water pollutant, reaching a sensitivity of 9.2 μA cm−2 ppm−1, a limit of detection of 0.16 ppm and apparent recovery factors very close to 100%. Their application in a complex matrix to monitor o-toluidine, during its photocatalytic removal by ZnO nanopowders, was also investigated.

Removal of Amorphous Carbon from SiC Powder using Flotation

Impurities in SiC powders affect their properties greatly. This paper reports a method to remove amorphous carbon from SiC powders using dispersion and flotation. SiC and amorphous carbon particles were successfully separated using polyacrylamide (PEI) as dispersant in the SiC powders suspension. Then oleic acid was added as a flotation agent to gather the amorphous carbon which was finally removed. A new way to determine the amount of amorphous carbon content was put forward. In this way, 82wt% of the amorphous carbon particles were wiped out in 20wt% suspension when added to 1 wt% PEI and 0.3 wt% oleic acid.

Effect of Magnetic Field on the Growth of Aligned Carbon Nanotubes Using a Metal Free Arc Discharge Method and their Purification

Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized using a low cost arc discharge method without using metal catalyst and vacuum devices. Effect of magnetic field on the synthesis of MWCNTs and their purity has been scrutinized. A magnetic field of 310 gauss has been found to give better purity of carbon nanotubes as confirmed by Raman spectroscopy. However, the removal of amorphous carbon from the surface of so prepared multiwalled carbon nanotubes has been achieved by different oxidizing conditions. It has been observed that the maximum removal of amorphous carbon found by using the strong oxidizing agent HNO3/H2O2. This strong oxidizing agent HNO3/H2O2removes most of the carbonaceous impurities leading to thermal stability of carbon nanotubes suggested by thermo gravimetric analysis. X-ray diffraction show the formation of carbon nanotubes having a peak indexed at (002) as the fingerprint for multiwalled carbon nanotubes. Fourier Transform Infrared (FTIR) spectra confirmed the formation of the multiwalled carbon nanotubes showing a characteristic stretching band at 1615 cm-1corresponding to the C=C bonds of tubular carbon. Raman spectroscopy revealed invaluable insights into the purification of nanotubes. G-band (1577 cm-1) corresponds to the confirmation of MWCNTs. Defect induced D-band (1355 cm-1) has been minimized after purifying CNTs with HNO3/H2O2for 24 hrs. Transmission Electron microscopic (TEM) studies indicate the formation of CNTs with controlled alignment having diameter in the range 2-8 nm.

Removal of amorphous C and Sn on Mo:Si multilayer mirror surface in Hydrogen plasma and afterglow

Removal of amorphous carbon and tin films from a Mo:Si multilayer mirror surface in a hydrogen plasma and its afterglow is investigated. In the afterglow, the mechanism of Sn and C films removal is solely driven by hydrogen atoms (radicals). Probabilities of Sn and C atoms removal by H atoms were measured. It was shown that the radical mechanism is also dominant for Sn atoms removal in the hydrogen plasma because of the low ion energy and flux. Unlike for Sn, the removal mechanism for C atoms in the plasma is ion-stimulated and provides a much higher removal rate.

Purification of Single-Wall Carbon Nanotubes by Controlling the Adsorbability onto Agarose Gels Using Deoxycholate

One of the key challenges to the industrialization of single-wall carbon nanotubes (SWCNTs) is the commercial-scale production of highly purified SWCNTs separated into metallic and semiconducting species. In the present study, the purification of SWCNTs, i.e., the removal of amorphous carbon or bundled SWCNTs, was performed by quantifying and controlling their adsorbability onto agarose gel. The quantification of the adsorbability was achieved by assuming the Langmuir isotherm, and control over the adsorbability was exerted using 0.05–1% sodium deoxycholate (DOC). The results show that the adsorbability depends on the concentration of DOC. At a low DOC concentration (approximately 0.05%), impurities such as amorphous carbon or bundled SWCNTs were preferentially adsorbed onto the gels, whereas, at an intermediate DOC concentration (ca. 0.25%), high-purity SWCNTs were mainly adsorbed onto the gels. Thus, the impurities, which are difficult to remove by conventional methods, could be separated from unpurified SWCNTs by controlling the adsorbability, leading to the extraction of high-purity SWCNTs. In the purification, diameter-selective separation of SWCNTs was also observed. The purification method using a gel column can be conducted simply and continuously, so that it can be applied for the high-throughput production of high-purity SWCNTs.

Improvement of Electron Field Emission in Patterned Carbon Nanotubes by High Temperature Hydrogen Plasma Treatment

In this paper, we report a significant improvement of electron field emission property in patterned carbon nanotubes films by using a high temperature (650 °C) hydrogen plasma treatment. This treatment was found to greatly increase the emission current, emission uniformity and stability. The mechanism study showed that these enhanced properties are attributed to the lowering of the potential barrier and the creation of geometrical features through the removal of amorphous carbon, catalyst particles and the saturation of dangling bonds after such a hydrogen plasma treatment.

The Adsorption Properties of Bacillus atrophaeus Spores on Single‐Wall Carbon Nanotubes

An adsorption equilibrium and a kinetic study of Bacillus atrophaeus on Single‐Wall Carbon Nanotubes (SWCNTs) were here performed to provide the basis for developing biosensor devices for detecting threatening micro‐organisms in water supply systems. B. atrophaeus spores and carbon nanotubes were subjected to a batch adsorption process to document their equilibria and kinetics. Here, commercial nanotubes were either studied as received or were acid‐purified before adsorption experiments. The Bacillus spores appear to show higher affinity towards the purified nanotubes than to the as‐received nanomaterial. The effective diffusivity of the spores onto the purified nanotubes was found to be approximately 30 percent higher than onto the as‐received nanotubes. It seems that the removal of amorphous carbon from the as‐received nanotubes through a purification process yielded an intimate nantoubes‐spore interaction as revealed by transmission electron microscopy. Freundlich model successfully correlated the adsorption equilibrium data for the nanotubes‐spore interaction. Transmission electron micrographs showed extensive contact between the Bacillus and the purified nanotubes, but the association appeared less intimate between the spores and the as‐received nanotubes.

Effect of surface cleaning and functionalization of nanotubes on gas adsorption

We present adsorption isotherm results for methane at $77\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ on multiwalled carbon nanotubes exposed to oxygen plasma for varying periods of time. We found a sharpening of the adsorption steps in the high pressure region of isotherms measured on nanotubes exposed to oxygen plasma for $24\phantom{\rule{0.3em}{0ex}}\mathrm{h}$. Transmission electron microscopy characterization and Raman spectroscopic measurements performed on the nanotube samples provide evidence that the appearance of the step is a consequence of surface modification of the nanotubes resulting from the removal of amorphous carbon, generation of defects, and surface functionalization of the nanotubes due to prolonged plasma exposure. Our results suggest that application of this procedure could lead to tunable nanotube surfaces with controllable adsorption properties.