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Title: Intrinsic and extrinsic defects in a family of coal-derived graphene quantum dots

In this letter, we report on the high frequency (239.2 and 336 GHz) electron spin resonance (ESR) studies performed on graphene quantum dots (GQDs), prepared through a wet chemistry route from three types of coal: (a) bituminous, (b) anthracite, and (c) coke; and from non-coal derived GQDs. The microwave frequency-, power-, and temperature-dependent ESR spectra coupled with computer-aided simulations reveal four distinct magnetic defect centers. In bituminous- and anthracite-derived GQDs, we have identified two of them as intrinsic carbon-centered magnetic defect centers (a broad signal of peak to peak width = 697 (10{sup −4} T), g = 2.0023; and a narrow signal of peak to peak width = 60 (10{sup −4} T), g = 2.003). The third defect center is Mn{sup 2+} ({sup 6}S{sub 5/2}, 3d{sup 5}) (signal width = 61 (10{sup −4} T), g = 2.0023, A{sub iso} = 93(10{sup −4} T)), and the fourth defect is identified as Cu{sup 2+} ({sup 2}D{sub 5/2}, 3d{sup 9}) (g{sub ⊥} = 2.048 and g{sub ‖} = 2.279), previously undetected. Coke-derived and non-coal derived GQDs show Mn{sup 2+} and two-carbon related signals, and no Cu{sup 2+} signal. The extrinsic impurities most likely originate from the starting coal. Furthermore, Raman, photoluminescence, and ESR measurements detected no noticeable changes in the properties of the bituminous GQDs after one year. This study highlights the importance of employingmore » high frequency ESR spectroscopy in identifying the (magnetic) defects, which are roadblocks for spin relaxation times of graphene-based materials. These defects would not have been possible to probe by other spin transport measurements.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [2] ;  [2]
  1. Materials Science Division, Army Research Office, Research Triangle Park, North Carolina 27709 (United States)
  2. (United States)
  3. National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310 (United States)
  4. Department of Chemistry, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005 (United States)
Publication Date:
OSTI Identifier:
22486126
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 107; Journal Issue: 21; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANTHRACITE; COKE; COPPER IONS; ELECTRON SPIN RESONANCE; GHZ RANGE; GRAPHENE; MANGANESE IONS; MICROWAVE RADIATION; PEAKS; PHOTOLUMINESCENCE; QUANTUM DOTS; SIGNALS; SPIN; TEMPERATURE DEPENDENCE