arXiv subjects

Soumen Karmakar

Publications and source records attributed to Soumen Karmakar.

8 recordsLinked to original sources

arXiv2024

LaB6 aided spontaneous conversion of bulk graphite into carbon nanotubes at normal atmospheric conditions

Herein, we report a case study in which we saw the spontaneous conversion of commercial bulk graphite into LaB6 decorated carbon nanotubes (CNTs) under normal atmospheric conditions. The feedstock graphite was used as a hollow cylindrical anode filled with LaB6 powder and partially eroded in a DC electric-arc plasma reactor in pure nitrogen atmosphere. An unusual and spontaneous deformation of the plasma-treated residual anode into a fluffy powder was seen to continue for months when left to ambient atmospheric conditions. The existence of LaB6 decorated multi-walled CNTs at large quantity was confirmed in the as-generated powder by using electron microscopy, Raman spectroscopy and x-ray diffraction. The as-synthesized CNT-based large-area field emitter showed promising field-emitting properties with a low turn-on electric field of ~1.5 V per micrometer, and a current density of ~1.17 mA per square cm at an applied electric field of 3.24 V per micrometer.

cond-mat.mtrl-sci↗

arXiv2019

Unveiling the mystery of nucleation and growth of carbon nanotube and layered graphene inside carbon arc-discharge

A model for the formation of carbon nanotubes (CNTs) and layered graphene in an arc discharge method is developed on the basis of observed erosion of graphite anode under various experimental conditions and analyses of the morphology of the eroded anode-surface, concerned cathode deposits and their constituents. It is predicted that, cold thermal shock, triggered by the rapid movement of the anode-spot, leads to crack microbranching at some selected locations on the anode-surface. These crack-microbranches cleave and fragment the basal planes of pairs of adjacent crystallites into curved graphitic nanoribbons with minimum two basal planes. These nanoribbons further react chemically with the C2 and C3 precursors present in the dusty carbon plasma and evolve either in the form of CNT or layered-graphene, depending on the viscosity and composition of the gaseous environment they are exposed to, just after getting detached from the anode.

cond-mat.mtrl-sci↗

arXiv2013

Tailored conversion of synthetic graphite into rotationally misoriented few-layer graphene by a cold thermal shock

Following the discovery of graphene, keen attentions have been paid in comprehending the noticeably superior electromagnetic, optical and absorptive properties of few layer graphene (FLG) with rotational-stacking-faults. With achieving intense fundamental interests, the demands to synthesize such FLG are rapidly increasing. However, the potential applications of such FLG, especially in composite science and energy storage devices, are practically hindered because of non-fulfillment of required production rate. Additionally, synthesis of such FLG with controlled layer-numbers still remains an unsolved challenge. Further breakthroughs in this direction are thus highly desirable. The present article is a step ahead in this direction and is possibly the first of its kind. Here we show how such FLG, with precisely controlled number of layers, can readily be obtained from an isostatically compacted synthetic graphite, by controlled dynamic fracture, with microbranching instability, induced by cold-thermal-shock and discovered the mechanism behind such transformation by a theoretical modeling.

cond-mat.mtrl-sci↗

arXiv2012

Gas phase condensation of few-layer graphene with rotational stacking faults in an electric-arc

We report the synthesis efficiency of few-layer graphene (FLG) in an external magnetic field modulated DC carbon arc in different non-reactive buffer gases. The effects of buffer gases on the anode erosion rate and the cathode deposit (CD) formation rate have been investigated during the synthesis of FLG. The constituents of the as-synthesized CDs were investigated using transmission electron microscopy, selected area electron diffraction, Raman spectroscopy and X-ray diffraction analysis. A plausible growth mechanism of such FLG is predicted. The results indicate that, under a parametrically optimized condition, an electric-arc of this kind can efficiently generate FLG with rotational stacking faults at a production-rate of few g/min. A guideline for controlling the number of layers of such FLG has also been suggested.

cond-mat.mtrl-sci↗

arXiv2008

A novel approach towards selective bulk synthesis of delaminated graphenes in an electric arc

Here we demonstrate the selective bulk scale synthesis of delaminated graphene sheets by a proper choice of magnetic field modulating an electric-arc. An ultra-high purity glassy graphite anode was sublimated in an argon atmosphere. Carbon nanotubes, as well as graphene sheets were found inside the deposit formed on the cathode. Both the high purity carbon nanotubes as well as graphene sheets, with minimal structural defects, were synthesized separately by varying the strength and orientation of the external magnetic field generated by arrays of permanent magnets. The as-synthesized carbonaceous samples were characterized with the help of transmission electron microscopy, selected area electron diffraction, Raman spectroscopy and thermogravimetry for optimizing the highest selective production of delaminated graphenes. This optimization was done by varying the strength and orientation of the external magnetic field. The as-synthesized graphene sheets exhibited relatively high degree of graphitization and low structural defect density as confirmed by RS. They were found to exhibit higher oxidation temperature than that of the carbon nanocrystalline particles as inferred from the thermogravimatric analysis. Moreover, they were found to form scroll-like carbon nanotubes at their edges on account of their surface energy minimization. This was confirmed by the selected area electron diffraction analysis. With this new technique, we could successfully synthesize delaminated graphenes at a rate of few grams per hour.

cond-mat.mtrl-sci↗

arXiv2008

DC transferred arc thermal plasma assisted growth of nanoparticles with different crystalline phases

The control of the crystalline phases of the nanoparticles grown in a direct-current transferred-arc plasma-assisted reactor is reported. The crystalline phases of the as synthesized nanoparticles are shown to critically depend on the operating gas pressure. The paper reports about the change in the crystalline phases of three distinct compounds namely aluminium oxide (Al2O3), aluminium nitride (AlN) and iron oxide (FexOy). The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressure. The variations in the crystalline structures are discussed on the basis of the equilibrium defect density formed during the homogeneous nucleation. The as synthesized nanoparticles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis for the crystalline phases of the as synthesized iron oxides was carried out with the help of Mossbauer spectroscopy.

cond-mat.mtrl-sci↗

arXiv2007

AC conductivity of polymer composites: an efficient confirmatory tool for qualifying crude multi-walled carbon nanotube-samples

The present communication highlights that ac conductivity measurement of the multi-walled carbon nanotubes (MWNTs)-polymer composites is a very promising characterizing tool for qualifying any crude MWNT-sample synthesized by electric arc. It distinguishes graphite structures from that of the MWNTs and reflects the relative amount of nearly one-dimensional structures and disorders present within the samples. This new protocol would help in evolving more direct and quantitative criteria for qualification of MWNTs synthesized through diverse techniques and will definitely add up to the conceptual understanding in visualizing the exact roles of different controlling parameters affecting the growth of MWNTs.

cond-mat.mtrl-sci↗

arXiv2007

High yield production of defect less carbon nanotubes in an arc process

An efficient modified arc plasma method, where a focusing electric field is superimposed on the arc electric field, is optimized for the bulk generation of highly pure multi-walled carbon nanotubes. Raman spectroscopy and thermogravimetric measurements have been used to optimize the process.

cond-mat.stat-mech↗