O. S. Panwar

Superior nano-mechanical properties of reduced graphene oxide reinforced polyurethane composites

Polyurethane (PU) based composites were prepared by solvent casting techniques using different wt% (0–5 wt%) of reduced graphene oxide (RGO) as reinforcement. A nanoindentation study has been carried out on these composite sheets in order to investigate their nano-mechanical properties. Incorporation of different wt% RGO into the PU matrix led to a significant increase in the hardness and elastic modulus of the composites. The maximum nanoindentation hardness of 140 MPa for 5.0 wt% RGO loading was observed as compared to 58.5 MPa for pure PU (an overall improvement of 139%). The nanoindentation elastic modulus for the 5.0 wt% RGO loaded sample was 881.7 MPa as compared to 385.7 MPa for pure PU (an overall improvement of 129%). The enhancement in the nano-mechanical properties was correlated with spectroscopic and microscopic investigations using Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Due to their excellent nano-mechanical properties, these composites find usefulness in structural applications such as the automobile and wind mill blade industries. These composites can also be used in hard and scratch-less coatings on automotive vehicles. The experimental results were in good agreement with theoretical predictions.

Diamond‐like carbon films grown using a saddle field source

This article reports the measurement of deposition rate, dark conductivity versus temperature, optical band gap, refractive index, extinction coefficient, hardness, adhesion, and internal stress of diamond‐like carbon (DLC) films grown by aspirating hydrocarbon gases (CH4 and C2H2) and C6H6 vapors into a saddle field source. The source operates at 0.7–1.0 kV in the pressure range of 1.0×10−4–7.0×10−4 Torr and is of a modular design to cover increasingly larger areas. DLC films have been grown for the first time using CH4 by this technique. The effect of source to substrate distance on the deposition rate and uniformity of the films has been studied at varying power to the source using C2H2 gas. The films are found to be hard and they adhere well to 7059 glass, quartz, silicon, Mo, and Mylar substrates. Though the deposition rate increases with increasing power and with increasing carbon to hydrogen ratio of the hydrocarbon feedstock, the material properties are relatively independent of the type of hydroc...

Characterization studies of diamond-like carbon films grown using a saddle-field fast-atom-beam source

In this article, we report results of an extensive characterization study involving scanning electron microscopy, spectroscopic ellipsometry (SE), photothermal deflection spectroscopy (PDS), x-ray photoelectron spectroscopy, x-ray Auger electron spectroscopy (XAES), current–voltage (I–V) measurements, hydrogen content evaluated from Fourier transform infrared spectroscopy and elastic recoil detection analysis, and also measurement of stress and hardness of diamond-like carbon (DLC) films. These films were grown using methane (CH4), acetylene (C2H2) gases, and benzene (C6H6) vapors into a saddle-field fast-atom-beam (FAB) source. DLC films formed by the saddle-field FAB source technique exhibit extremely low residual stress (0.12–0.26 GPa) and high Knoop hardness (9–22 GPa) measured at 50 g load. The values of optical constants (n, k, e1,u2002e2) evaluated from SE, characteristic energy of band tail (Urbach energy, E0) evaluated from PDS studies, sp2 percentage evaluated from XAES data, the density of states [N(EF)] derived from space-charge-limited conduction, and the hydrogen content are found to decrease, and the sp3/sp2 ratio evaluated are found to increase with the increase of carbon-to-hydrogen ratio in the hydrocarbon gases/vapors used for growing DLC films by this technique. The values of E0,u2002N(EF), hydrogen content, and sp3/sp2 ratio of these DLC films are found to be in the range of 180–280 meV, 1–6×1017u200aeV−1u200acm−3, 3–8 at.u200a% and 5.2–12.3, respectively, which are lower than the values of E0 (300–500 meV), N(EF)u2002(∼1018u200aeV−1u200acm−3), and hydrogen content (15–40 at.u200a%) and higher than sp3/sp2 ratio (1.3–2.5) of DLC films grown by the more conventional rf self-bias technique reported in the literature.In this article, we report results of an extensive characterization study involving scanning electron microscopy, spectroscopic ellipsometry (SE), photothermal deflection spectroscopy (PDS), x-ray photoelectron spectroscopy, x-ray Auger electron spectroscopy (XAES), current–voltage (I–V) measurements, hydrogen content evaluated from Fourier transform infrared spectroscopy and elastic recoil detection analysis, and also measurement of stress and hardness of diamond-like carbon (DLC) films. These films were grown using methane (CH4), acetylene (C2H2) gases, and benzene (C6H6) vapors into a saddle-field fast-atom-beam (FAB) source. DLC films formed by the saddle-field FAB source technique exhibit extremely low residual stress (0.12–0.26 GPa) and high Knoop hardness (9–22 GPa) measured at 50 g load. The values of optical constants (n, k, e1,u2002e2) evaluated from SE, characteristic energy of band tail (Urbach energy, E0) evaluated from PDS studies, sp2 percentage evaluated from XAES data, the density of states [...

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 10u2009nm to 38u2009nm 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 850u2009°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 10u2009nm and 18u2009nm thicknesses. The optimum temperature of annealing was observed to be 750u2009°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.

Filtered saddle field fast atom beam deposition of diamondlike carbon films

An innovation to separate out ionic and neutral radicals from the beam coming out of a saddle field fast atom beam (FAB) source is reported. Diamondlike carbon (DLC) films were grown simultaneously by these ionic and filtered neutral radicals using methane (CH4) as the source gas in the FAB source, on to the substrates placed at different positions inside the deposition chamber. Faraday cup measurements carried out on the two beams confirm the separation of ionic and neutral radicals. It was found that the DLC films deposited by neutral radicals have higher hardness values (980–1070u2009kg/mm2) than those deposited by ionic radicals (810–970u2009kg/mm2), whereas, the values of optical band gap and refractive index are found to be higher in DLC films deposited by ionic radicals than those deposited by neutral radicals. It is emphasized that during normal operation of a saddle field source, to grow DLC films, one essentially has a mixed deposition with contributions both from neutral and ionized radicals. Higher ha...

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 30u2009nm 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 58.3u2009GPa, elastic modulus (E) of 426.2u2009GPa, and H/E of 0.136 have been observed in a-C:nc films deposited at −60u2009V substrate bias which showed 82.6% sp3 content.

Easy synthesis of organic–inorganic hybrid nanomaterials: study of DC conduction mechanism for light dependent resistors

A surfactant assisted chemical oxidation method has been employed for facial synthesis of polypyrrole/tin oxide (PPy/SnO2) hybrid nanoneedles. The charge transport properties of the prepared hybrid nanomaterials have been analyzed under different conduction mechanisms for their possible application for light dependent resistors (LDRs). The scanning electron microscopy studies revealed that the increased concentration of additive SnO2 quantum dots alters the surface morphology from nanowall-like to nanoneedle-like and the formation of PPy/SnO2 nanocomposites is confirmed X-ray diffraction studies. The strong coupling between the PPy and SnO2 results in the transformation of PPy from highly oxidized states to oxidized states and is confirmed through Raman analysis. The simple band conduction model and Kivelsons power law based conduction mechanism could not be applied to explain the conduction mechanism due to different reasons. The logu2006σdc curves for all samples were well fitted for γ = 1/4, suggesting the applicability of Motts three dimensional variable range hopping VRH model for charge transport. The room temperature dark conductivity of the samples was found to decrease with an increase in SnO2 concentration. The formation of p–n junctions between p-type PPy and n-type SnO2 changes the bandgap of PPy and the work function. This modifies the electronic structure of PPy which brings a synergistic effect in the photosensitivity of the PPy/SnO2 nanocomposites. The room temperature photoresponse of the PPy/SnO2 samples was found to increase from 2.85 to 6.25% at 100 mW cm−2 illumination intensity with an increase in the SnO2 doping concentration from 0 to 20%.

Growth of single and bilayer graphene by filtered cathodic vacuum arc technique

The authors present a viable process to grow the high quality graphene films with control over number of layers by the filtered cathodic vacuum arc (FCVA) technique. In the FCVA process, the different carbon concentrations can be controlled by precisely tuning the arc time (1–4u2009s). The arc generated carbon was deposited on the nickel catalyst at 800u2009°C, annealed for 10u2009min, and cooled down to room temperature in the presence of hydrogen gas, resulting in the graphene films with control over number of layers. Prior to arcing, hydrogen etching of nickel was carried out to clean the surface of the substrate. A growth model to prepare the high quality graphene has also been proposed. The as-grown graphene films were transferred to different substrates and are characterized by Raman spectroscopy, optical microscopy, high resolution transmission electron microscopy, and atomic force microscopy to determine the number of layers present in these films. Raman spectra of the prepared graphene films exhibit change i...

Organic–inorganic hybrid cathodes: facile synthesis of polypyrrole/zinc oxide nanofibers for low turn-on electron field emitters

The identification of new materials capable of sustaining a high electron emission current is a key requirement in the development of the next generation of cold cathode devices and technology. Compatibility with large volume material production methods is a further important practical consideration with solution chemistry-based methods providing for routes to industrial scale-up. Here we demonstrate a new class of organic–inorganic hybrid material based on polypyrrole and zinc oxide (PPy/ZnO) nanofibers for use as a low-cost large-area cathode material. Solution chemistry based surfactant chemical oxidation polymerisation is used to synthesise the nanofibers and the macroscopic turn-on electric field for emission has been measured to be as low as 1.8 V μm−1, with an emission current density of 1 mA cm−2 possible for an applied electric field of less than 4 V μm−1. Specific surface area measurements reveal a linear increase in the nanofiber surface area with ZnO incorporation, which when coupled with electron microscopy and X-ray diffraction analysis reveals that the wurtzite ZnO nanoparticles (around 45 nm in size) act as nucleation sites for the growth of PPy nanofibers. Our study demonstrates for the first time how an inorganic nanocrystal acting as a nucleation site allows the tailored growth of the organic component without diminishing the overall electrical properties and opens the potential for a new type of organic–inorganic hybrid large-area cathode material. The broader impacts and advantages of using hybrid materials, when compared to other composite nanomaterial systems, as large area cathode materials are also discussed.