Control of layer stacking in CVD graphene under quasi-static condition

The type of layer stacking in bilayer graphene has a significant influence on its electronic properties because of the contrast nature of layer coupling. Herein, different geometries of the reaction site for the growth of bilayer graphene by the chemical vapor deposition (CVD) technique and their effects on the nature of layer stacking are investigated. Micro-Raman mapping and curve fitting analysis confirmed the type of layer stacking for the CVD grown bilayer graphene. The samples grown with sandwiched structure such as quartz/Cu foil/quartz along with a spacer, between the two quartz plates to create a sealed space, resulted in Bernal or AB stacked bilayer graphene while the sample sandwiched without a spacer produced the twisted bilayer graphene. The contrast difference in the layer stacking is a consequence of the difference in the growth mechanism associated with different geometries of the reaction site. The diffusion dominated process under quasi-static control is responsible for the growth of twisted bilayer graphene in sandwiched geometry while surface controlled growth with ample and continual supply of carbon in sandwiched geometry along with a spacer, leads to AB stacked bilayer graphene. Through this new approach, an efficient technique is presented to control the nature of layer stacking

Mechanical, electrical and thermal properties of graphene oxide-carbon nanotube/ ABS hybrid polymer nanocomposites

Multiwalled carbon nanotubes (MWCNTs), functionalized carbon nanotubes (FCNTs) and graphene oxide-carbon nanotube (GCNTs) hybrid Bucky paper (BP) reinforced acrylonitrile-butadiene-styrene (ABS) composites are prepared via vacuum filtration followed by hot compression molding. The nanomechanical, electrical and thermal properties of these BP reinforced ABS composites are studied. The nanoindentation hardness and elastic modulus of GCNTs-ABS hybrid composites reached to 389.98 +/- 91.79 MPa and 7669.6 +/- 1179.12 MPa respectively. Other nanomechanical parameters such as plastic index parameter, elastic recovery, the ratio of residual displacement after load removal and displacement at maximum load are also investigated. The improved nanomechanical properties are correlated with Raman spectroscopy and scanning electron microscopy (SEM). It is found that GCNTs and their composites showed the higher value of defect density. The maximum value of defect density range for GCNTs and GCNTs-ABS is (297.4 to 159.6) and (16.0 to11.6), respectively. The higher defect density of GCNTs indicates that the interfacial interaction between the ABS, which was further correlated with electrical and thermal properties. Additionally, the through-plane electrical conductivities of MWCNTs, FCNTs and GCNTs based ABS composites were 6.5 +/- 0.6, 4.5 +/- 0.7 and 6.97 +/- 1.2 S/cm respectively and thermal conductivities of MWCNTs, FCNTs and GCNTs reinforced ABS composites; 1.80, 1.70 and 1.98 W/mK respectively. These GCNTs-ABS composites with this value of thermal conductivity can be used in various applications of efficient heat dissipative materials for electronic devices

One-pot synthesis of multifunctional ZnO nanomaterials: study of superhydrophobicity and UV photosensing property

ZnO nanomaterials are synthesized using one-pot synthesis method. Equimolar solution of Zinc Nitrate hexahydrate (Zn(NO3)(2).6H(2)O) and Hexamethylenetetramine (C6H12N4) is used as a precursor for ZnO formation. Different nanostructures of ZnO are achieved by controlling the pH of the growth solution in the range 2-12 (acidic to alkali). ZnO nanostructures are evaluated for hydrophobic property using static contact angle measurement setup and UV photosensing activity. Surface morphology, structural properties and compositional analysis of ZnO nanostructures are examined by field emission scanning electron microscope (FE-SEM), energy dispersive X-ray analysis (EDX), high-resolution transmission electron microscope (FEG-TEM) and X-ray diffraction (XRD) measurements. Existence of ZnO wurtzite structure is confirmed from XRD study and is analyzed by Rietveld refinement method. Nanomaterials are characterized using Raman spectroscopy which confirms highest oxygen deficiency in ZnO nanorods. The material shows remarkable superhydrophobic and UV photosensing property and hence the name multifunctional. Among all morphologies grown at different pH values, ZnO nanorods show superhydrophobic nature with contact angle more than 170 degrees. Total surface energy value of ZnO nanostructures is calculated using Wendt two-component theory. Different ZnO nanostructures (with variation of pH value) are used to study UV photosensing property. Responsivity and photocurrent show a strong dependence on the morphology of ZnO

Facile and Nondestructive Transformation of Intrinsic Hydrophobic Behavior of a Carbon Nanotubes Sheet to Hydrophilic

It is imperative to induce hydrophilicity in intrinsically hydrophobic carbon nanotubes (CNTs) without losing their superior properties for applications that specifically deal with aqueous media. A method for transforming a CNTs sheet from hydrophobic to hydrophilic by treatment with N-methyl-2-pyrrolidone (NMP) is explored. The NMP-treated CNT sheets are assessed based on complementing characterization, and it is concluded that the binding of NMP to a CNTs surface is through noncovalent interaction without the incorporation of defects in CNTs. The induced hydrophilicity in the CNTs sheet is stable for water exposure over a longer duration while it displays a semireversible nature upon heat treatment. The mechanical and electrical properties of the NMP-treated CNTs sheet revealed enhancement in the tensile strength from 221 to 421 MPa while maintaining a good electrical conductivity of ∼1.22 × 104 S/m because of the improved interfacial properties. The hydrophilic CNTs exhibited excellent adsorption capacity for methylene blue dye. The NMP-treated CNTs sheets demonstrated their suitability in flexible hybrid supercapacitor (FHSC) devices with improved electrochemical performance with enhancement in the capacitance from 5.4 to 7.6 F/g and a decrease in the equivalent series resistance from 53 to 34 Ω compared to pristine CNTs-based devices. These solid-state FHSC devices displayed excellent cyclic charge–discharge performance along with robust behavior over thousands of bending cycles without significant performance degradation. The excellent dye removal capability and superior electrochemical performance of the NMP-treated CNTs sheet is a consequence of their improved interface with aqueous media, which is governed by the hydrophilic nature of the CNTs sheet

Facile and Nondestructive Transformation of Intrinsic Hydrophobic Behavior of a Carbon Nanotubes Sheet to Hydrophilic

It is imperative to induce hydrophilicity in intrinsically hydrophobic carbon nanotubes (CNTs) without losing their superior properties for applications that specifically deal with aqueous media. A method for transforming a CNTs sheet from hydrophobic to hydrophilic by treatment with N-methyl-2-pyrrolidone (NMP) is explored. The NMP-treated CNT sheets are assessed based on complementing characterization, and it is concluded that the binding of NMP to a CNTs surface is through noncovalent interaction without the incorporation of defects in CNTs. The induced hydrophilicity in the CNTs sheet is stable for water exposure over a longer duration while it displays a semireversible nature upon heat treatment. The mechanical and electrical properties of the NMP-treated CNTs sheet revealed enhancement in the tensile strength from 221 to 421 MPa while maintaining a good electrical conductivity of ∼1.22 × 104 S/m because of the improved interfacial properties. The hydrophilic CNTs exhibited excellent adsorption capacity for methylene blue dye. The NMP-treated CNTs sheets demonstrated their suitability in flexible hybrid supercapacitor (FHSC) devices with improved electrochemical performance with enhancement in the capacitance from 5.4 to 7.6 F/g and a decrease in the equivalent series resistance from 53 to 34 Ω compared to pristine CNTs-based devices. These solid-state FHSC devices displayed excellent cyclic charge–discharge performance along with robust behavior over thousands of bending cycles without significant performance degradation. The excellent dye removal capability and superior electrochemical performance of the NMP-treated CNTs sheet is a consequence of their improved interface with aqueous media, which is governed by the hydrophilic nature of the CNTs sheet

Polymer nanocomposite foam filled with carbon nanomaterials as an efficient electromagnetic interference shielding material

Increasing use of the latest electronic gadgets in modern society causes rapid growth in electromagnetic pollution, which leads to detrimental effects on the function of highly sensitive precision electronic equipment as well as on human life. Mitigating this effect requires efficient electromagnetic radiation shielding materials, which should be lightweight, corrosion resistant and cost-effective. In this review article, we have presented lightweight polymer composite foams filled with carbon nanofibers, carbon nanotubes and graphene as efficient electromagnetic radiation shielding materials. It is seen that the low loading of multiwalled carbon nanotubes with uniform dispersion in polymer, uniform cell size of pore and controlled dielectric constant results in the attenuation of electromagnetic radiation by absorption phenomena. Flexible graphene-polymer composite foam derived using the chemical vapor deposition technique demonstrates a specific shielding effectiveness of similar to 333 dB cm(3) g(-1), which is the highest value among those reported in literature. The SE is mostly dominated by the absorption of electromagnetic radiation, which is due to the multiple reflection of radiation inside the cells of the composite foam. Moreover, different carbon nanomaterial, such as carbon nanofibers and few layer graphene-filled polymer composite foams, with varying content of conducting filler are reported in this review. Their use in different applications, their future prospective and the challenges ahead are discussed in this review

The role of substrate purity and its crystallographic orientation in the defect density of chemical vapor deposition grown monolayer graphene

Defect free mono-layer graphene sheet growth has remained a challenge towards its huge potential applications in electronic and photonic devices. Here, we are reporting about the role of the copper substrate purity and its crystallographic orientation in the quality of the graphene grown using a low pressure chemical vapor deposition technique. Graphene is grown on three different (Cu-I, Cu-II and Cu-III) substrates of different purity under analogous conditions of optimized pre-growth annealing and cleaning processes. Irrespective of the purity level of all the substrates, it is demonstrated that monolayer graphene (I-G'/I-G similar to 4) with different defect density is observed. The amount of defects and the defect density in the three samples is correlated with the different lattice planes of Cu, which are participating during the growth process. The size of the lattice grain advance upon annealing is observed and it is substrate purity dependent. This reveals that graphene growth is favored by either the (111) or the (100) plane or both. It is demonstrated that the substrate purity is extremely accountable for the growth of defect free monolayer graphene for device applications which require ballistic transport properties

Monolayer graphene electrodes as alignment layer for ferroelectric liquid crystal devices

Transparent electrodes and alignment layers are two essential parts of the liquid crystal (LC) cell fabrication. Conventionally, indium tin oxide (ITO) acts as transparent electrode and a polyimide film is used as alignment layer. In present study, both of these are replaced by using a monolayer graphene film deposited on glass substrate. The graphene film used to fabricate LC cell show excellent optical transmittance (similar to 95%) over 450-800 nm range and electrical resistance of 328.77 Omega/square. Moreover, the alignment of FLC mesogens over graphene monolayer is achieved owing to the pi-pi electron stacking between benzene rings of FLC and honeycomb structure of graphene. Polarizing optical microscopy (POM) shows homogeneous planar alignment of filled FLC over graphene under crossed polarizers. The cell is switched between bright and dark states under the application of electric field to demonstrate the working of LC cell. Further, dielectric relaxation spectroscopy is used to measure the dielectric constant and absorption of FLC. This application of graphene would lead to thin and defect-free devices based on LC