Scientists 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. This was achieved by James Hone’s group at Columbia Engineering, a team of scientists from Columbia University, Seoul National University (SNU), and Korea Research Institute of Standards and Science (KRISS), led by Young Duck Kim, a postdoctoral research scientist.
Wang Fon-Jen professor of mechanical engineering at Columbia Engineering and co-author of the study said that “We’ve created what is essentially the world’s thinnest light bulb,”.“This new type of ‘broadband’ light emitter can be integrated into chips and will pave the way towards the realization of atomically thin, flexible, and transparent displays, and graphene-based on-chip optical communications" he added.
For developing fully integrated “photonic” circuits, creating light in small structures on the surface of a chip is crucial. In spite of huge amount of efforts from researchers, they still haven't developed, a way to put the oldest and simplest artificial light source the incandescent light bulb onto a chip. This is because of the reason that light bulb filaments must be extremely hot nearly thousands of degrees Celsius in order to glow in the visible range but micro-scale metal wires cannot withstand such temperatures, in addition to that heat transfer from the hot filament to its surroundings is extremely efficient at the microscale, which makes such structures impractical and leads 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 2,500 C, hot enough to glow brightly. Kim, first and co-lead author on the paper said “The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification,”.
Interestingly, the spectrum of the emitted light showed peaks at specific wavelengths, which the team discovered was due to interference between the light emitted directly from the graphene and light reflecting off the silicon substrate and passing back through the graphene. Kim notes, “This is only possible because graphene is transparent, unlike any conventional filament, and allows us to tune the emission spectrum by changing the distance to the substrate.”
As graphene heats up, it becomes a much poorer conductor of heat. This means that the high temperatures stay confined to a small “hot spot” in the center, due to this property graphene is able to achieve high temperatures without melting the substrate or the metal electrodes. Myung-Ho Bae, a senior researcher at KRISS and co-lead author said " At the highest temperatures, the electron temperature is much higher than that of acoustic vibrational modes of the graphene lattice, so that less energy is needed to attain temperatures needed for visible light emission,”.“These unique thermal properties allow us to heat the suspended graphene up to half of the temperature of the sun, and improve efficiency 1000 times, as compared to graphene on a solid substrate," he added.
Yun Daniel Park, professor in the Department of Physics and Astronomy at Seoul National Univ. and co-lead author, notes that they are working with the same material that Thomas Edison used when he invented the incandescent light bulb: “Edison originally used carbon as a filament for his light bulb and here we are going back to the same element, but using it in its pure form—graphene—and at its ultimate size limit—one atom thick.”
The group is currently working to further characterize 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.
Hone adds, “We are just starting to dream about other uses for these structures—for example, as micro-hotplates that can be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.”
Source: R&D Magzine
Wang Fon-Jen professor of mechanical engineering at Columbia Engineering and co-author of the study said that “We’ve created what is essentially the world’s thinnest light bulb,”.“This new type of ‘broadband’ light emitter can be integrated into chips and will pave the way towards the realization of atomically thin, flexible, and transparent displays, and graphene-based on-chip optical communications" he added.
For developing fully integrated “photonic” circuits, creating light in small structures on the surface of a chip is crucial. In spite of huge amount of efforts from researchers, they still haven't developed, a way to put the oldest and simplest artificial light source the incandescent light bulb onto a chip. This is because of the reason that light bulb filaments must be extremely hot nearly thousands of degrees Celsius in order to glow in the visible range but micro-scale metal wires cannot withstand such temperatures, in addition to that heat transfer from the hot filament to its surroundings is extremely efficient at the microscale, which makes such structures impractical and leads 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 2,500 C, hot enough to glow brightly. Kim, first and co-lead author on the paper said “The visible light from atomically thin graphene is so intense that it is visible even to the naked eye, without any additional magnification,”.
Interestingly, the spectrum of the emitted light showed peaks at specific wavelengths, which the team discovered was due to interference between the light emitted directly from the graphene and light reflecting off the silicon substrate and passing back through the graphene. Kim notes, “This is only possible because graphene is transparent, unlike any conventional filament, and allows us to tune the emission spectrum by changing the distance to the substrate.”
As graphene heats up, it becomes a much poorer conductor of heat. This means that the high temperatures stay confined to a small “hot spot” in the center, due to this property graphene is able to achieve high temperatures without melting the substrate or the metal electrodes. Myung-Ho Bae, a senior researcher at KRISS and co-lead author said " At the highest temperatures, the electron temperature is much higher than that of acoustic vibrational modes of the graphene lattice, so that less energy is needed to attain temperatures needed for visible light emission,”.“These unique thermal properties allow us to heat the suspended graphene up to half of the temperature of the sun, and improve efficiency 1000 times, as compared to graphene on a solid substrate," he added.
Yun Daniel Park, professor in the Department of Physics and Astronomy at Seoul National Univ. and co-lead author, notes that they are working with the same material that Thomas Edison used when he invented the incandescent light bulb: “Edison originally used carbon as a filament for his light bulb and here we are going back to the same element, but using it in its pure form—graphene—and at its ultimate size limit—one atom thick.”
The group is currently working to further characterize 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.
Hone adds, “We are just starting to dream about other uses for these structures—for example, as micro-hotplates that can be heated to thousands of degrees in a fraction of a second to study high-temperature chemical reactions or catalysis.”
Source: R&D Magzine
