Sreekumar Chockalingam

Few layer graphene synthesized by filtered cathodic vacuum arc technique

Filtered cathodic vacuum arc technique has been used to deposit amorphous carbon (a-C) films of varying thicknesses from 10 nm to 38 nm on catalytic nickel thin film grown on SiO2/Si substrates. Subsequently, a-C films were annealed in vacuum in the temperature range from 650 to 850 °C. Micro-Raman spectroscopic study in combination with optical microscopy and scanning electron microscopy has revealed few layer graphene formations with optical transmittance in the range 85%–88% with a-C films deposited with 10 nm and 18 nm thicknesses. The optimum temperature of annealing was observed to be 750 °C.

Structural, nanomechanical, field emission and ammonia gas sensing properties of nitrogenated amorphous carbon films deposited by filtered anodic jet carbon arc technique

This paper reports the effect of substrate bias on the structural, nanomechanical, field emission and ammonia gas sensing properties of nitrogenated amorphous carbon films embedded with nanocrystallites (a-C: N: nc) deposited by a filtered anodic jet carbon arc (FAJCA) technique. The films are characterized by X-ray diffraction, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopic analysis, Raman spectroscopy, nanoindentation, field emission and ammonia gas sensing measurements. The properties of the films obtained are found to depend on the substrate bias. The maximum hardness (H)=42.7 GPa, elastic modulus (E)=330.4 GPa, plastic index parameter (H/E)=0.129 and elastic recovery (% ER)=74.4% have been obtained in a-C: N: nc films deposited at -60 V substrate bias which show the lowest ID/IG=0.43, emission threshold (ET)=4.9 V/µm accompanied with the largest emission current density (Jmax)=1 mA/cm(2) and field enhancement factor (β)=1805.6. The gas sensing behavior of the a-C: N: nc film has been tested by measuring the change in electrical resistance of the sample in ammonia environment at room temperature with the fast response and recovery time as 29 and 66.9s, respectively.

Structural, Nanomechanical, and Field Emission Properties of Amorphous Carbon Films Having Embedded Nanocrystallites Deposited by Filtered Anodic Jet Carbon Arc Technique

This paper reports the effect of substrate bias on the structural, nanomechanical, and field emission properties of amorphous carbon films having embedded nanocrystallites (a-C:nc films) deposited by filtered anodic jet carbon arc technique. X-ray diffraction results exhibit predominantly an amorphous nature of the films. High-resolution transmission electron microscope images showed the amorphous nature of the films with nanocrystallites embedded in the amorphous matrix. Ultrafine nanograined microstructures with average grain size between 20 and 30 nm are observed throughout the film with a majority of the grains of single crystallites. A strong influence of substrate bias has been observed on the structural, nanomechanical, and field emission properties. Maximum nanohardness (H) of 58.3 GPa, elastic modulus (E) of 426.2 GPa, and H/E of 0.136 have been observed in a-C:nc films deposited at −60 V substrate bias which showed 82.6% sp3 content.

Investigations on phosphorous doped hydrogenated amorphous silicon carbide thin films deposited by a filtered cathodic vacuum arc technique for photo detecting applications

This paper reports the growth and properties of phosphorous doped hydrogenated amorphous silicon carbide (P doped a-SiC:H) thin films deposited at room temperature by a filtered cathodic vacuum arc (FCVA) technique using a phosphorous doped solid silicon target as a cathode in the presence of acetylene gas. These films have been characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray analysis, dark conductivity, activation energy, optical band gap, secondary ion mass spectroscopy, Raman spectroscopy, current–voltage, capacitance–voltage and photoconductive measurements. XRD results exhibit predominantly an amorphous phase for the films. The effect of the arc current on the properties of P doped a-SiC:H films have been studied. A P doped a-SiC:H/c-Si heterojunction diode was fabricated which showed a diode ideality factor between 1.5 to 1.7 and the density of states were 9.6 × 1016 to 4.8 × 1017 cm−3 eV−1. The photo response behaviors of the P doped a-SiC:H films have been tested by measuring the change in the electrical resistance on light illumination with the fast response and recovery time as 7.8 to 9.5 and 6.2 to 12.8 s, respectively. The P doped a-SiC:H film deposited at a 30 A arc current has shown a photo response of ∼1.6% at an illumination intensity of ∼100 mW cm−2.

Strategy to synthesise nano-engineered polymer nanocomposite with a mechanically strong interface: a highly flexible ammonia gas sensor

The work reported herein describes a facile strategy for synthesize of a highly flexible and free standing novel polymethyl methacrylate/nanographite platelets nanocomposite (P-NC) film through click chemistry. The unique concept involves the formation of P-NCs which not only imparts the strong covalent interaction between the azide functionalized polymethyl methacrylate (Az-f-PMMA) and alkyne functionalized nanographite platelets (Alk-f-NGPs) at the interface through triazole linkages but also enhances the exfoliation of NGPs within the polymer matrix. Thus, the synergy between the polymer and the NGPs through the high density of interfaces results in remarkable electrical, mechanical and sensing properties. The structure and micromorphology of the prepared P-NCs were confirmed by FTIR, NMR, XPS, UV spectroscopy, Raman spectroscopy, XRD, TGA, SEM, TEM and AFM techniques. A maximum indentation elastic modulus (E) of 4.1 GPa and hardness (H) of 0.23 GPa were obtained for P-NC with an ultralow loading of 0.1% NGPs, as compared to 3.3 GPa and 0.17 GPa, respectively, for pure PMMA. The flexible, robust P-NC films demonstrated excellent sensing properties towards ammonia vapor with fast response and recovery, both at room temperature (response = ∼2 s, recovery = ∼32 s) as well as at 0 °C (response = ∼1 s, recovery = ∼13 s). The work reported opens up new opportunities for the development of robust and portable P-NC sensors which can detect ammonia vapor in refrigeration plants where leakage should be indicated both at low temperature near the valves, as well as room temperature in the surrounding atmosphere, having flexibility to be fabricated in any shape as per the positioning of the sensor in the refrigeration plant.

Growth of dense CNT on the multilayer graphene film by the microwave plasma enhanced chemical vapor deposition technique and their field emission properties

Catalyst assisted carbon nanotubes (CNTs) were grown on multilayer graphene (MLG) on copper and silicon substrates by the microwave plasma enhanced chemical vapor deposition technique. The transmission of the MLG was found to vary between 82 to 91.8% with the increase of deposition time. Scanning electron microscopy depicted that the MLG film survived at the deposition condition of CNTs with the appearance of the damaged structure due to the plasma. Growth of CNTs was controlled by adjusting the flow rates of methane gas. The density of carbon nanotubes was observed to increase with a higher supply of methane gas. It was observed that the field emission properties were improved with the increased density of CNTs on MLG. The lowest turn-on field was found to be 1.6 V μm−1 accompanied with the highest current density of 2.8 mA cm−2 for the CNTs with the highest density. The findings suggested that the field emission properties can be tuned by changing the density of CNTs.

Synthesis of Nanostructure Carbon Films Deposited by Microwave Plasma-Enhanced Chemical Vapor Deposition Technique at Room Temperature

This paper reports the synthesis of nanostructure carbon (ns-carbon) films deposited by microwave plasma-enhanced chemical vapor deposition (MW PECVD) technique at low pressure and room temperature. ns-carbon films have been characterized by scanning electron microscopy, electron dispersive x-ray spectroscopic analysis, atomic force microscopy, Raman spectroscopy, X-ray diffraction, UV-visible spectroscopy and high-resolution transmission electron microscopy. The shape of nanostructure is changing from granular to sheet-like structure when the pressure increased from 55 to 110 mTorr.

Synthesis of Multilayer Graphene by Filtered Cathodic Vacuum Arc Technique

Filtered cathodic vacuum arc technique has been used to deposit amorphous carbon films of varying thickness on catalytic nickel thin film grown on SiO2/Si substrates. Subsequently these a-C films were annealed in vacuum at 650 °C. Raman spectroscopy together with optical microscopy and scanning electron microscopy has revealed multilayer graphene formation.

Synthesis of vertical graphene by microwave plasma enhanced chemical vapor deposition technique

Vertical graphene was synthesized on nickel substrate using microwave plasma enhanced chemical vapor deposition technique by varying gas pressure from 5 to 30 Torr under various mixing ratios of argon, hydrogen and methane. The Raman spectra show two major fingerprints of graphene, 2D peak at 2,700 cm−1 and G peak 1,580 cm−1. Scanning electron microscopy microstructure revealed flower like graphene structure which could find applications in gas sensing and field emission due to high surface-to-volume ratio.

Synthesis and Characterization of Phosphorus Doped Hydrogenated Silicon Films by Filtered Cathodic Vacuum Arc Technique

Phosphorous doped hydrogenated silicon thin film has been deposited by filtered cathodic vacuum arc technique at different substrate temperatures at a fixed hydrogen gas pressure. X-ray diffraction, electrical conductivity and optical band gap and scanning electron microscopy have been used to characterize the properties of films.