Indranil Lahiri

Synthesis of Graphene and Its Applications: A Review

Graphene, one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has grabbed appreciable attention due to its exceptional electronic and optoelectronic properties. The reported properties and applications of this two-dimensional form of carbon structure have opened up new opportunities for the future devices and systems. Although graphene is known as one of the best electronic materials, synthesizing single sheet of graphene has been less explored. This review article aims to present an overview of the advancement of research in graphene, in the area of synthesis, properties and applications, such as field emission, sensors, electronics, and energy. Wherever applicable, the limitations of present knowledgebase and future research directions have also been highlighted.

Large-area graphene on polymer film for flexible and transparent anode in field emission device

We present the fabrication and electrical characterization of large graphene structure on polyethylene terephthalate (PET) flexible substrate. Graphene film was grown on Cu foil by thermal chemical vapor deposition and transferred to PET by using hot press lamination. The graphene/PET film shows high quality, flexible transparent conductive structure with unique electrical-mechanical properties; ∼88.80% light transmittance and ∼1.1742 kΩ/sq sheet resistance. We demonstrate application of graphene/PET film as flexible and transparent electrode for field emission displays. Our proposed techniques can be tailored for any flexible substrate and large scale production, which could open up exciting device applications in foldable electronics.

Three-Dimensional Metal–Graphene–Nanotube Multifunctional Hybrid Materials

Graphene was grown directly on porous nickel films, followed by the growth of controlled lengths of vertical carbon nanotube (CNT) forests that seamlessly emanate from the graphene surface. The metal-graphene-CNT structure is used to directly fabricate field-emitter devices and double-layer capacitors. The three-dimensional nanostructured hybrid materials, with better interfacial contacts and volume utilization, can stimulate the development of several energy-efficient technologies.

High Capacity and Excellent Stability of Lithium Ion Battery Anode Using Interface-Controlled Binder-Free Multiwall Carbon Nanotubes Grown on Copper

We present a novel binder-free multiwall carbon nanotube (MWCNT) structure as an anode in Li ion batteries. The interface-controlled MWCNT structure, synthesized through a two-step process of catalyst deposition and chemical vapor deposition (CVD) and directly grown on a copper current collector, showed very high specific capacity, almost three times as that of graphite, excellent rate capability even at a charging/discharging rate of 3 C, and no capacity degradation up to 50 cycles. Significantly enhanced properties of this anode could be related to high Li ion intercalation on the carbon nanotube walls, strong bonding with the substrate, and excellent conductivity.

Ultrathin alumina-coated carbon nanotubes as an anode for high capacity Li-ion batteries

Alumina-coated carbon nanotubes (CNTs) were synthesized on a copper substrate and have been used as an anode in Li-ion batteries. CNTs were grown directly on the copper current collector by chemical vapor deposition and an ultrathin layer of alumina was deposited on the CNTs by atomic layer deposition, thus forming the binder-free electrode for the Li-ion battery. While CNTs, which form the core of the structure, provide excellent conductivity, structural integrity and Li-ion intercalation ability, the aluminium oxide coating provides additional stability to the electrode, with further enhancement of capacity. The anode showed very high specific capacity, good capacity retention ability and excellent rate capability. This novel anode may be considered as an advanced anode for future Li-ion batteries.

Carbon Nanotubes: How Strong Is Their Bond with the Substrate?

A reliable quantification technique for interpreting nanomaterial-substrate bond strength is highly desired to predict efficient, long-term performance of nanomaterial-based devices. Adopting a novel nanoscratch-based technique, here we demonstrate quantification of carbon nanotube (CNT)-substrate adhesion strength for dense CNT structure and for patterned carbon nanocone (CNC) structures. Debonding energy for a single CNT is illustrated to range between 1 and 10 pJ, and the variation is strongly dependent on the nature of the interface between CNTs, catalysts, and substrates. Our proposed technique could be adopted for characterization of bonding strength between a wide variety of nanotubes, nanowires, and other one-dimensional nanostructured materials and their underlying substrates.

Recent progress in nanostructured next-generation field emission devices

Field emission has been known to mankind for more than a century, and extensive research in this field for the last 40–50 years has led to development of exciting applications such as electron sources, miniature x-ray devices, display materials, etc. In the last decade, large-area field emitters were projected as an important material to revolutionize healthcare and medical devices, and space research. With the advent of nanotechnology and advancements related to carbon nanotubes, field emitters are demonstrating highly enhanced performance and novel applications. Next-generation emitters need ultra-high emission current density, high brightness, excellent stability and reproducible performance. Novel design considerations and application of new materials can lead to achievement of these capabilities. This article presents an overview of recent developments in this field and their effects on improved performance of field emitters. These advancements are demonstrated to hold great potential for application in next-generation field emission devices.

Carbon Nanostructures in Lithium Ion Batteries: Past, Present, and Future

Advent of nanotechnology has generated huge interest in application of carbon-based nanomaterials as a possible replacement for conventionally used graphite as anode of Li-ion batteries. Future Li-ion batteries demand high capacity, energy, power, and better safety, while graphite falls short of fulfilling all these necessities. Inspired by high conductivity, flexibility, surface area, and Li-ion insertion ability, a number of nano carbon materials, individually or as a composite, have been studied in detail to identify the best suitable material for next-generation energy storage devices. Many of these nano-C-based structures hold good promise, although issues like density of nanomaterials and scalability are yet to be addressed with confidence. This article aims to summarize the major research directions of nano-C materials in anodic application of Li-ion batteries and proposes possible future research directions in this widely studied field.

Synthesis and characterization of self-organized multilayered graphene–carbon nanotube hybrid films

We report the synthesis and characterization of a self-organized graphene–carbon nanotube (CNT) hybrid film consisting of multilayer graphene (MLG) supported by vertical CNTs on a Si substrate. The hybrid film shows an interesting structure of graphene in connecting to vertical CNTs while maintaining ohmic contact at its junction. The in situ formation of a CNT–graphene heterojunction is confirmed by high resolution transmission electron microscopy (HRTEM). The as-obtained film shows a linear relationship for electrical conductance with significantly low resistance varying from 100–400 Ω on Si substrate. This hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating an observable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current were found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8–3.1 V μm−1 and 4.2–0.4 mA, respectively.

Ultra-high current density carbon nanotube field emitter structure on three-dimensional micro-channeled copper

High-current field emitter with extended stability has been focus of many researchers, which can be fulfilled by application of engineered nanomaterials and beneficial design. In the present research, such a field emitter is designed and fabricated, involving growth of interface controlled carbon nanotubes along micro-channels of 3-dimensional copper template. The emitter offers very high emission current density (270 mA/cm2, peak), low turn-on field (1.1 V/μm), moderate threshold field (1.69 V/μm), emission stability for extended operation, and excellent resistance to structural damage. Higher conductivity of Cu, lower interfacial resistance, strong interfacial bonding, and unique 3-dimensional design leads to such 23-27 times higher current density, providing a potential approach to field emission devices.