WASHINGTON: Researchers have created the world's thinnest light bulb using graphene , an atomically thin and perfectly crystalline form of carbon , as a filament.Led by Young Duck Kim, a postdoctoral research scientist in James Hone's group at Columbia University School of Engineering, a team of scientists from Columbia, Seoul National University, and Korea Research Institute of Standards and Science said that they have demonstrated - for the first time - an on-chip visible light source using graphene as a filament.They attached small strips of graphene to metal electrodes, suspended the strips above the substrate, and passed a current through the filaments to cause them to heat up."We've created what is essentially the world's thinnest light bulb," said Hone, Wang Fon-Jen Professor of Mechanical Engineering at Columbia Engineering and co-author of the study."This new type of 'broadband' light emitter can be integrated into chips and will pave the way towards the realisation of atomically thin, flexible, and transparent displays, and graphene-based on-chip optical communications," said Hone.Creating light in small structures on the surface of a chip is crucial for developing fully integrated 'photonic' circuits that do with light what is now done with electric currents in semiconductor integrated circuits.Researchers have developed many approaches to do this, but have not yet been able to put the oldest and simplest artificial light source - the incandescent light bulb - onto a chip.This is primarily because light bulb filaments must be extremely hot - thousands of degrees Celsius - in order to glow in the visible range and micro-scale metal wires cannot withstand such temperatures.In addition, heat transfer from the hot filament to its surroundings is extremely efficient at the microscale, making such structures impractical and leading to damage of the surrounding chip.By measuring the spectrum of the light emitted from the graphene, the team was able to show that the graphene was reaching temperatures of above 2500 degrees Celsius, hot enough to glow brightly."The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification," said Kim.The team also demonstrated the scalability of their technique by realising large-scale of arrays of chemical-vapour-deposited (CVD) graphene light emitters The team is currently working to further characterise the performance of these devices - for example, how fast they can be turned on and off to create 'bits' for optical communications - and to develop techniques for integrating them into flexible substrates.