Kiran Shankar Hazra

Thinning of multilayer graphene to monolayer graphene in a plasma environment.

We present a facile approach to transform multilayer graphene to single-layer graphene in a gradual thinning process. Our technique is based upon gradual etching of multilayer graphene in a hydrogen and nitrogen plasma environment. High resolution transmission microscopy, selected area electron diffraction and Raman spectroscopy confirm the transformation of multilayer graphene to monolayer graphene at a substrate temperature of ∼ 400 °C. The shift in the position of the G-band peak shows a perfect linear dependence with substrate temperature, which indicates a controlled gradual etching process. Selected area electron diffraction also confirmed the removal of functional groups from the graphene surface due to the plasma treatment. We also show that plasma treatment can be used to engineer graphene nanomesh structures.

Dramatic enhancement of the emission current density from carbon nanotube based nanosize tips with extremely low onset fields.

Nanostructures based on multiwalled carbon nanotubes (MWNTs) are fabricated using plasma of the mixture of hydrogen and nitrogen gases. The plasma-sharpened tips of nanotubes contain only a few tubes at the apex of the structure and lead to the dramatic enhancement in the emission current density by a factor >10(6) with the onset field as low as 0.16 V/microm. We propose that the nature of the tunneling barrier changes significantly for a nanosize tip at very high local electric field and may lead to the saturation in the emission current density.

Enhanced Field Emission and Improved Supercapacitor Obtained from Plasma‐Modified Bucky Paper

The surface morphology of bucky papers (BPs) made from single-walled carbon nanotubes (CNTs) is modified by plasma treatment resulting in the formation of vertical microstructures on the surface. The shapes of these structures are either pillarlike or conelike depending on whether the gas used during plasma treatment is Ar or CH(4) . A complex interplay between different factors, such as the electric field within the plasma sheath, polarization of the CNT, intertubular cohesive forces, and ion bombardment, result in the formation of these structures. The roles played by these factors are quantitatively and qualitatively analyzed. The final material is flexible, substrate-free, composite-free, made only of CNTs, and has discrete vertically aligned structures on its surface. It shows enhanced field emission and electrochemical charge-storage capabilities. The field enhancement factor is increased by 6.8 times, and the turn-on field drops by 3.5 times from an initial value of 0.35 to 0.1 V μm(-1) as a result of the treatment. The increase in Brunauer-Emmett-Teller surface area results in about a fourfold improvement in the specific capacitance of the BP electrodes. Capacitance values before and after the treatments are 75 and 290 F g(-1) , respectively. It is predicted that this controlled surface modification technique could be put to good use in several applications based on macroscopic CNT films.

Nanotip formation on a carbon nanotube pillar array for field emission application

The field emission of a carbon nanotube (CNT) pillar array has been improved significantly by plasma treatment in a mixture of hydrogen and nitrogen gases. The plasma treatment for 30s on a pillar array decreased the turn-on electric field from 0.48to0.37V∕μm and increased the field enhancement factor from 6200 to 6900. The emission current density increased by a factor of ≈40. We report in this letter the technique of generating nanotips on CNT pillars with an enormous potential to become a tool for the control and manipulation of CNTs and nanostructures.

Facile one-step transfer process of graphene

Chemical vapour deposition (CVD) is emerging as a popular method for growing large-area graphene on metal substrates. For transferring graphene to other substrates the technique generally used involves deposition of a polymer support with subsequent etching of the metal substrate. Here we report a simpler one-step transfer process. Few-layer graphene (FLG) grown on a Cu substrate were transferred to a silanized wafer by just pressing them together. Hydrogen bonding between the hydroxyl group on FLG and the amine group on silane molecules facilitate the transfer.

Tailoring the electrostatic screening effect during field emission from hollow multiwalled carbon nanotube pillars

Field emission from hollow pillars of multi wall carbon nanotubes show lower screening effect and their turn on field can be tailored by tuning the annular width of the pillars. Simulations show that the energy variation in the extracted electrons can be decreased by lowering the annular width of the hollow pillars; for the hollow pillars of 10 μm annular width the energy width is ∼0.5 eV, fourfold lower than the solid pillars. This can reduce further by reducing the annular width of the pillars paving the way forward for the monochromatic electron emission.

Effect of top metal contact on electrical transport through individual multiwalled carbon nanotubes

The effect of position of top metal contact on the electrical transport through individual multiwalled carbon nanotubes (MWNTs) has been investigated using gas injection system in situ in scanning electron microscope to deposit the top platinum metal contacts at different desired sites on the side contacted MWNTs in bridging structure. Current-voltage measurements reveal a significant improvement in electrical properties of the tubes after the top contact is made. This improvement has been found to be independent of position of top contact, i.e., whether the top contact is made on the ends or at any other site of the tube.

Healing of Broken Multiwalled Carbon Nanotubes Using Very Low Energy Electrons in SEM: A Route Toward Complete Recovery

We report the healing of electrically broken multiwalled carbon nanotubes (MWNTs) using very low energy electrons (3-10 keV) in scanning electron microscopy (SEM). Current-induced breakdown caused by Joule heating has been achieved by applying suitably high voltages. The broken tubes were examined and exposed to electrons of 3-10 keV in situ in SEM with careful maneuvering of the electron beam at the broken site, which results in the mechanical joining of the tube. Electrical recovery of the same tube has been confirmed by performing the current-voltage measurements after joining. This easy approach is directly applicable for the repairing of carbon nanotubes incorporated in ready devices, such as in on-chip horizontal interconnects or on-tip probing applications, such as in scanning tunneling microscopy.

Graphene Oxide Demonstrates Experimental Confirmation of Abraham Pressure on Solid Surface

The century-old controversy over two contradicting theories on radiation pressure of light proposed by Abraham and Minkowski can come to an end if there is a direct method to measure the surface deformation of the target material due to momentum transfer of photons. Here we have investigated the effect of radiation pressure on the surface morphology of Graphene Oxide (GO) film, experienced due to low power focused laser irradiation. In-depth investigation has been carried out to probe the bending of the GO surface due to radiation pressure by Atomic Force Microscopy (AFM) and subsequently the uniaxial strain induced on the GO film has been probed by Raman Spectroscopy. Our results show GO film experience an inward pressure due to laser radiation resulting in inward bending of the surface, which is consistent with the Abraham theory. The bending diameter and depth of the irradiated spot show linear dependence with the laser power while an abrupt change in depth and diameter of the irradiated spot is observed at the breaking point. Such abrupt change in depth is attributed to the thinning of the GO film by laser irradiation.

Controlled formation of nanostructures on MoS2 layers by focused laser irradiation

MoS2 nanostructures, i.e., nanoribbons, nano-mesh, etc., may open different prospect of applications in nano-electronic and opto-electronic devices and sensors. However, the fabrication of these complicated nanostructures can be executed by using standard nano-patterning techniques such as lithography, printing, etc. Nevertheless, these standard techniques involve affluent multistep processes to optimize scalability, form factors and accuracy in the feature size. Herein, we demonstrate the fabrication of unique nano-structures on MoS2, such as nano-ribbons and nano-mesh, by a simple one-step process of direct laser writing using 532 nm low power focused laser. The minimum power required to etch a MoS2 layer for a 532 nm laser is found to be ∼6.95 mW and the minimum void size observed is ∼300 nm, which is very close to the diffraction limit of the laser used. Both the experimental and computational results have shown that the voids induced by laser etching always take a hexagonal or triangular shape, which...