Centre for Carbon Materials (CCM)
Over the last one decade the competing technologies of vacuum electronics devices and solid state devices have synergized to give rise to the new area of vacuum microelectronic devices. These devices exploit the motion of electronics in vacuum to get the advantages of vacuum electronics and micro fabrication technology. The basic elements of vacuum microelectronic devices are cold emission source. The present day solid state devices limited in their capabilities and the vacuum microelectronic devices appear to be promising. Extending the frequency of TWTs to millimeter range requires high current densities. Because the required beam current density is proportional to the square of operating frequency, the use of field-emission cathodes is an alternative method for delivering a high current density and direct modulation of the emitted beam is possible in FEAs.It can improve the efficiency and reduce the size of the microwave source. As they exploit the best of the both worlds of vacuum electronics and solid state fabrication technology. Carbon Nanotubes field emitter arrays are preferred for use in vacuum microelectronic devices.
- Large aspect ratio (>1000) and Atomically sharp tips
- Low work function.
- High electrical and thermal conductivity.
- High temperature and chemical stability.
- Very high current carrying capacity – 1010 A/cm2
- Excellent mechanical properties
- Flat Panel Display
- Electron Source
- Emission Triode
- Cathode Source X-Rays
- Vertically aligned carbon nanotubes (CNTs) were developed by CVD Process
- Controlling the microstructures i.e. bamboo type & the Nitrogen content
- Patterning the Aligned CNT through micromachining by Laser
Major Patents / Publications
- Influence of N doping concentration on morphology & microstructure of N-doped super aligned CNTs arrays J. Advanced Microscopy Research, 8, 300-304, 2013.
- Nitrogen incorporated highly aligned carbon nanotube arrays thin film grown from single feed stock for field emission Journal of Nanoelectronics and Optoelectronics, Vol. 8, 1-5, 2013
- Self Organized growth of bamboo like carbon nanotubes arrays for field emission properties Applied Nanoscience (2012) 2:253-259
- Synthesis of Vertically aligned CNTs Arrays by Injection method in CVD Journal of Nanoscience and Nanotechnology, Vol. 10, pp 4960- 4966 (2010)
The stacked parallel layers in natural graphite flakes (NGF) are separated by 0.34 nm and the layers in a stack are attached or bonded with a weak Van der waal forces. For successful exfoliation, overcoming the van der Waal attraction between the adjacent layers is crucial. The best feasible method is to decrease the attractions by increasing the distance between the adjacent layers via oxidation and chemical intercalating reactions. During oxidation of graphite, the functional groups like hydroxyl, epoxide and hydroxide etc are inserted between the layers leads to increase in d-spacing from 0.34 to 0.70 nm. Due to thermal shock, the functional moieties try to escape and create porous structure is termed as exfoliated graphite (EG). EG can be moulded into various desired shapes (sheets, tapes, seals, and boards) by mechanical compaction without adding any sort of binders. Self-binding capability of the porous-structured material is a unique characteristic of this technology. Our technology demonstrates the production of EG in bulk quantity by chemical intercalation and thermal exfoliation of NGF. It is a cost-effective and continuous process for bulk production.
- Binder-free compaction of material
- Shape-tailored material
- Very light weight
- Density-controlled compaction
- Sandwich or reinforced material with better mechanical properties
- Efficient and cost-effective
- Flexible sheets
- Flexible tapes
- Bipolar plates
- Reinforced seals, sheets and tapes etc
- Ultra light weight boards
- Scale-up and pilot plant is established
- Demonstration of bulk quantity through thermal reactor is done
- Various types of prototype module has been established
Major Patents / Publications
For last few decades, the rapid growth in the manufacturing sector for sustainable global economy has increased the demand for energy consumption. The energy generation is mainly relying on conventional energy sources. The depletion of fossil fuels, global warming and environmental-friendly energy sources prompted the development of efficient energy storage and conversion technologies. Now a day, ultracapacitors, a category of energy storage appliance which can bridge the gap between conventional capacitor and electrochemical batteries are widely studied to serve as one of the promising candidate for next generation energy storage devices owing to their exceptional characteristics like high power density, fast charge/discharge process and long cycle life. Among all, nanocarbon materials (carbon nanotubes, graphene, carbon sphere etc) are extremely explored as electrode material due to their intriguing thermal, electrical, mechanical and chemical properties. Our technology demonstrates the development of high performance nanoelectrode for hybrid supercapcitor based on nanoscaled-carbon integrated with electroactive oxide/sulphide and conducting polymers.
- Facile synthesis of nanoscaled-carbon with surface modification
- Activated porous graphene with tailored pore size distribution
- Shape-tailored metal oxide/sulphide with controllable surface area
- Hybridizing nanocarbon with oxide/sulphide or conducting polymer
- High power density with moderate energy density and multifunctionality
- All-solid-state supercapacitor
- Scalable preparation process
- Power grid system
- Consumer electronics
- Nanocomposites for electrode preparation are fabricated
- A prototype all-solid-state supercapacitor is developed
- Development of multifunctional supercapacitor is underway
Research activities in area of chemiresistors used in gas sensing is rising due to the demand for cost effective, fast response and sensitive sensors which are vital in detecting hazardous and harmful gases such as greenhouse gases, organic vapor and other gases produced by combustion of fossil fuels, power plants and automobiles etc. In such needs, nanoparticles serve as building blocks as they have very high aspect ratio combined with large surface area which is favourable for adsorption of gaseous analytes over them. Particularly, the advent of nanoscaled-carbon fuelled the invention of gas sensors that exploit unique geometry (tubular, spherical and sheet-like) and material properties. The electrical conductivity of nanocarbon (carbon nanotubes, carbon onion and graphene) is much higher in comparison with metal oxides and sulphides. The formation of heterojunctions (p-n) in nanocarbon-metal oxide/sulfide or conducting polymer hybrid lead to enhanced gas sensitivity of such hybridized gas sensor as the decrease in work function of the metal oxide/sulphide sensitive layer lead to improvement in performance of chemiresistor at low operating temperatures.
- n-type metal oxide-anchored nanocarbon hybrids
- Surface modified carbon nanomaterials for gas selectivity
- Various kinds of metal oxides with tuneable bandgap
- Facile route to coat metal oxide on carbon nanomaterials
- Fast sensing characteristics
- Gas sensing
- Organic vapor detection
- Automobile exhaust analysis
- Environment diagnosis
- Coal mine area monitoring
- Drainage lines monitoring
- Preparation metal oxide anchored carbon nanomaterials
- Organic vapor sensing characteristics evaluated
- Development of sensor to detect organic vapor is underway
Electrical energy storage is one of the most critical needs of 21st century. At present, among various energy storage technologies, Lithium (Li)-ion batteries have conquered the portable electronic market. They have also proven suitable for next generation large scale energy storage (electric vehicle) due to their high energy density and remarkable cyclic life at higher currents. However, Li-ion batteries are expensive due to the heavy capital investment needed in mining and extraction of Li. Li is unevenly distributed in earth crust which is a critical barrier to the scale-up of Li production and thus Li battery energy storage for large-scale applications such as electrical vehicles remains limited. In this perspective, replacing expensive Li based electrodes with a sustainable battery electrode material is a major challenge to meet the increasing demand for portable electronics and zero emission vehicles. Li based active material electrodes and electrolytes may be replaced with the abundant alkaline element in earth’s crust with similar characteristics. In this direction, sodium (Na) based rechargeable batteries have been demonstrated with similar energy storage mechanism in 1980. However, Na-ion cells will always fall short of energy density compared to Li-ion batteries due to large atomic size compared to Li. This large atomic size not only results in lower energy density, it also limits the intercalation of Na into layers of graphite. Increasing surface area and electronic conductivity for improved specific capacity with good cyclic performance is a key challenge for commercialization of Na-ion batteries.
- Na helps in making rechargeable batteries cheaper due to the relatively abundant sodium sources, ease of recovery and usage of water-based electrolytes instead of the organic ones.
- Expensive copper (Cu) current collector can be replaced by lightweight aluminium (Al) current collector for the anode in Na-ion battery, which is electrochemically inactive and does not form an alloy with Na.
- Supports high voltage cathodes.
- Packing technology is similar to Lithium ion battery.
- Powering up portable electronics to electric vehicle
- Grid storage
- Various electrolyte compositions for better ionic conductivity are being investigated.
- Engineered carbon Nanomaterials such as carbon nanoparticles and high surface area carbons are being investigated as anode material for Na-ion battery.
Lubrication has been an area of extensive research in search to achieve the conditions of a super lubricant i.e. zero friction. Among all approaches, engine friction reduction is a key and relatively cost-effective approach, which has been receiving significant attention from tribologists. However, a large amount of fuel energy is still lost in overcoming friction even after many revolutions in this sector. Carbon nano-additives have the potential to be the replacement to present day additives and give improved results. The quantity of additives in the dispersion is less than the commercial additives by a magnitude of 25-27%. Tribological studies with few layered graphene in an engine oil suspension showed comparable results with the commercial oil. Significant reduction in wear rate and friction was observed for lubricant with graphene nanoplatelets additives. Tests at elevated temperatures at 75°C, with high load and speed of rotation showed similar results of reduction in wear and friction coefficient. The Few-layer graphene nanosheets loaded in a base oil forms thin films over a mating surfaces to minimize the friction-induced effects and can act as thermal conductivity enhancer to transfer heat effectively.
- Various kinds of nanostructured carbon materials
- Microwave irradiation for rapid synthesis
- Surfactant-free dispersion in oil
- Minimum quantity lubrication is focused in terms of additive concentration
- Scalable manufacturing process
- Homogeneous dispersion
- Stability for long duration
- Engine oils for automobiles
- Regenerative braking system
- As grease additives in high load bearing joints
- Thermal property enhancer in radiator coolants
- Non-corrosive coatings for bottle neck joints
- Rheological properties with better stability achieved
- Wear and friction characteristics are validated at laboratory scale
- Application oriented tests on related materials is to be followed up using raw base oil
Every year with new events of oil spills has increased the need of finding a solution for this worldwide issue. This causes excess amounts of loss of oil, aquatic habitats, loss of gallons of water, and economic resources too. With daily achievement of new materials for oil remediation dispersants, absorbents, solidifiers, booms and skimmers in the market, exfoliated graphite has been found to be the best oil absorbent in oil spill absorption and recovery. This kind of materials shows porosity and ability to absorb oil in the presence of water selectively. Heavy oils sorption into the exfoliated graphite could be recovered either by a simple compression or suction filtration with a recovery ratio of 60–80 %. The bulk density of exfoliated graphite (EG) and viscosity of oil are the major influencing factors on absorption kinetic characteristics. The EG with the bulk density of 10 kg/m3 has a little less sorption capacity (about 70 g/g). Various types of oils (Hydraulic, Engine, Diesel, Shell SAE 90, Shell SAE 140, and Transformer Oil) with different viscosity were tested in order to know the amount of sorption happening over exfoliated graphite.
- Highly porous with very less density
- Nearly 300 % expansion
- Selectively absorb oil in oil-water mixture
- Hydrophobic in nature
- Binder-free compaction
- Continuous bulk production
- Oil remediation
- Nano grease
- Oil based thermally conductive ink
- Oil absorption is validated at laboratory scale
- Continuous production of exfoliated graphite
- Oil absorption unit is established for demonstration
2-D graphene nanosheets, which is composed of one atom thick sp2 carbon network, shows great potential for industrial applications owing to their excellent electrical, thermal mechanical, electronic, chemical properties and high surface area. Preparation of graphene through exfoliation and fragmentation is one of the most effective methods to produce graphene-based conductive materials in a large quantity. The exfoliation through microwave irradiation is much more cost-effective than all other methods as it heats the materials uniformly and effectively. The graphite structures consist of layers of hexagonal carbon structures within which a chemical compound can be intercalated and is escaped due to thermal shock by creating large number of pores in worm-like structured exfoliated graphite. This unique process exhibited volume expansion of 300 % with extremely porous structure. Graphene nanoplatelets (GNP) shown specific surface area of 117 m2/g. As produced GNP are highly crystalline in nature with very limited defects. GNP preparation by microwave irradiation and shear mixing is a unique novel process for bulk production.
- Very high aspect (width to thickness) ratio
- Majority of platelets are less than 10 nm thickness
- Compatible with almost all polymers
- Thermally and electrically conductive
- Contains naturally occurring functional groups like carboxyl and hydroxyl
- Scalable production process
- Electrode for Supercapacitor
- Thermally conductive additive
- Electrically conductive additive
- Wear and friction modifier
- Additive for composite materials (polymer, metal and ceramic matrix)
- Anode material for metal-ion batteries (Li, Na and K)
- Scalable quantity with tailored sizes
- Scale-up and prototype module has been established
- Demonstration of heavy-duty mixer-driven bulk production is underway
Field electron emission (FE) is a phenomenon where emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into vacuum. However, field emission can arise from solid or liquid surfaces, into vacuum, air, a fluid, or any non-conducting or weakly conducting dielectric. Carbon nanotubes (CNT) have attracted much attention owing to their mechanical, electrical and thermal properties etc. CNTs are promising candidates for use in FE devices and nanoelectronics as they possess sharp tips with unusual characteristics. These types of application will require a fabrication method capable of producing CNTs with well-defined and controllable properties such as the orientation, spatial distribution, diameters and lengths of the CNT. In addition, FE devices would need island-like structured high density and well-ordered nanotube arrays to alleviate screening effect. Our technology demonstrates the production of CNT arrays and producing microislands through ultrafast laser-assisted micromachining to improve FE characteristics.
- Self-assembled arrays of macroscopic carbon nanotube forest
- Easy to control height and spatial distribution of carbon nanotubes
- Nitrogen-content modulated arrays of carbon nanotubes
- Microstructure-tuned edge-density controlled carbon nanotube arrays
- Laser-assisted patterned arrays of microislands with assorted size
- Optimized-growth of carbon nanotube forest on silicon wafer
- Scalable process in batch-mode
- For electron gun
- For microwave amplifiers
- For X-ray tubes
- For flat panel display
- FE performance and stability are validated at laboratory scale
- Cathode material is integrated to an electron gun and field emission properties were evaluated.
Major Patents / Publications
- Nanotech Insights Vol. (3-4), 94-97 (2014)
- J. nanoelectronic and optoelectronics 8 (2),177-181 (2013)
- AIP Conf.Proc. 1538, 196-199 (2013)