Abstract
Electronic spin transport properties of graphene nanoribbons (GNRs) are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element) spin-sensitive techniques such as electron spin resonance (ESR) spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW), pulse and hyperfine sublevel correlation (HYSCORE) ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs), which were subsequently chemically converted (CCGNRs) with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH3 adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns) and fast (39 ns) components. HYSCORE ESR data demonstrate the explicit presence of protons and 13C atoms. With the provided identification of intrinsic point magnetic defects such as proton and 13C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic)-based transport properties of CCGNRs.
Highlights
Graphene-derived materials show remarkable spin transport properties originating from a very low intrinsic spin-orbit coupling [ SO ≈ 1 μeV] and small hyperfine interaction (due to a2158-3226/2014/4(4)/047104/13 C Author(s) 2014047104-2 Singamaneni et al.AIP Advances 4, 047104 (2014)low abundance of the C13 isotope).[1,2,3] Among all, graphene nano ribbons (GNRs) are expected to show superior semiconducting properties over pristine graphene due to a tunable band gap.[4,5] graphene nanoribbons (GNRs) have been shown to exhibit novel properties upon functionalization
In our previous X-band electron spin resonance (ESR) work[20] on chemically converted GNRs (CCGNRs), we have shown the presence of a specific carbon defect-related paramagnetic center (GC) at g = 2.0032
In our recent work[20] on CCGNRs, we found that molecular oxygen does not broaden the ESR signal width
Summary
As indicated above, owing to their novel physical properties, graphene-based materials have been thought to be excellent candidates envisaging them for applications ranging from information storage to catalysis, which are controlled by native and foreign defects. It is of fundamental scientific and technological interest to identify and understand the nature of such defects. This study has identified both localized and extended defects from the ribbons In another systematic work,[12] Su and co-authors have employed ESR spectroscopy in exploring the catalytic properties of graphene oxide and illustrated the role of defects, concluded that localized spins are created at the edge of pi-electron system.
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