by 11(e) E−11 and (f) E−∗11 emission from a tube (9.7) where the intensity is integrated in a window of 37.4, 32.5 and 28.5 meV centered on each emission peak, respectively. Color scales are normalized to the maximum intensities in the respective maps. The faint features to the right of the tube are caused by reflection of the excitation laser from the bottom of the trench. The white broken lines show the trench edges. g A reflection image in the same area, where brighter and darker areas correspond to the surface of the substrate and the bottom of the trench, respectively. Scale bars in panels (b, d–g) are 1.0 μm. Special offer: Nature Communications (2022). DOI: 10.1038/s41467-022-30508-z” width=”800″ height=”445″/> Introduction of organic color centers into air-suspended nanotubes using a vapor phase reaction. a A schematic illustration of a functionalized SWCNT suspended in a trench on a Si substrate. b A scanning electron micrograph of a tube after functionalization and series of PL measurements. The particles at the top are patterned catalysts for growing SWCNTs, and the nanotube is indicated by an arrow. c Representative PL spectra of an identical air-suspended SWCNT (10.5) before and after functionalization obtained with 10 μW laser power and 1.59 eV excitation energy. PL intensity maps of (d) E11(EU−11and (f) E−∗11 emission from a tube (9.7) where the intensity is integrated in a window of 37.4, 32.5 and 28.5 meV centered on each emission peak, respectively. Color scales are normalized to the maximum intensities in the respective maps. The faint features to the right of the tube are caused by reflection of the excitation laser from the bottom of the trench. The white broken lines show the trench edges. g A reflection image in the same area, where brighter and darker areas correspond to the surface of the substrate and the bottom of the trench, respectively. Scale bars in panels (b, d–g) are 1.0 μm. Credit: Nature communications (2022). DOI: 10.1038/s41467-022-30508-z
RIKEN researchers have created an efficient source of single photons for emerging quantum technologies by adding molecules to carbon nanotubes using a reaction that occurs in the vapor phase.
Quantum technologies are on the verge of revolutionizing computing and communications, promising benefits such as secure communication, ultra-sensitive detection and parallel computing. Many of these applications require light sources that can produce single photons—the smallest possible packets of light—on demand.
A promising source of single photons in the infrared wavelength range used in telecommunications is carbon nanotubes—cylinders of graphene sheets about one nanometer in diameter—that have been endowed with new functions or functionalized by the addition of an organic molecule.
The cleanest way to do this would be to use carbon nanotubes suspended in an air gap, but unfortunately this is not compatible with the usual approach to carbon nanotube functionalization, which takes place in solutions. “Carbon nanotubes that work in solution tend to be really short and have defects everywhere,” notes Yuichiro Kato of the RIKEN Center for Advanced Photonics (RAP).
Now, Kato and Daichi Kozawa, also of RAP, and their colleagues have developed a method to functionalize carbon nanotubes that can be done in the vapor phase, and thus nanotubes suspended in a trench on a silicon substrate.
A carbon nanotube suspended in a trench on a silicon substrate. By developing a method that allows such suspended nanotubes to function with organic molecules, RIKEN researchers have enhanced their utility for single photon sources. Credit: Reproduced from Ref 1 and licensed under CC BY 4.0 © 2022 D. Kozawa et al.
“We grew quite large nanotubes and operated them in the vapor phase, so they were not in contact with solutions, which contain a lot of impurities,” says Kato. “This method allowed us to introduce organic molecules without also incorporating unwanted defects.”
The study was a collaboration born out of a pre-pandemic interaction at an international conference. Kato and Kozawa’s team at RAP produced the suspended nanotubes and then sent them to chemists at the University of Maryland in the United States for functionalization, who then sent them back for analysis. “YuHuang Wang at the University of Maryland is a great chemist, and he’s the one who explored the possibility of doing these reactions in the vapor phase,” says Kato. “It took us a few rounds, but we were able to see good emission from the organic molecules in the nanotubes.”
The team verified the optical performance of the carbon nanotubes by performing spectroscopic measurements on more than 2,000 of them. They found that the number of organic molecules introduced per nanotube increased with smaller diameter nanotubes, and were able to model this phenomenon in terms of the greater reactivity of narrower nanotubes.
The study is published in Nature communicationsand the team now intends to optimize the functionalization process so that only one organic molecule per nanotube is introduced.
More information:
Daichi Kozawa et al, Formation of organic color centers in carbon nanotubes suspended in air using vapor phase reaction, Nature communications (2022). DOI: 10.1038/s41467-022-30508-z
Reference: A cleaner, better way to produce single-photon emitters (2022, November 2) Retrieved November 3, 2022, from https://phys.org/news/2022-11-cleaner-single-photon-emitters.html
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