Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

Singamaneni, Srinivasa Rao; Stesmans, André; Tol, Johan van; Kosynkin, Dmitry V.; Tour, James M.

doi:10.1063/1.4870942

Cited by 10 publications

(4 citation statements)

References 44 publications

(54 reference statements)

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“…These are higher than the g-factor of free electrons (2.002) and fall in the region of the oxygen-centered radicals. [48] Added to this, the discharged state spectrum has a markedly higher intensity, suggesting a larger number of unpaired electrons. Hence, there is an increased density of electronic charge transfer events occurring at the oxygen atoms of the rGO functional groups during discharge.…”

Section: Role Of Al 3+ In the Charge Storage Mechanismmentioning

confidence: 90%

Aqueous Aluminum‐Carbon Rechargeable Batteries

Smajic

Hasanov

Alazmi

et al. 2021

Adv Materials Inter

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Carbon cathodes have shown excellent electrochemical behavior in aluminum batteries based on non‐aqueous electrolytes. By contrast, their use in Al systems operating in a salt‐water medium is plagued by poor and unstable performance. Herein, it is sustained that a successful C cathode for rechargeable aqueous Al batteries requires surface customization to enable hydrophilicity and grafting of charged Al molecules. Employing a freeze‐dried reduced graphene oxide (rGO) as the active electrode material, an aqueous Al‐C battery is assembled with a high energy density (136 Wh kg−1 per cathode mass) and one of the best capacity retentions reported (≈60% across a range of current densities and constant Coulombic efficiencies close to unit). Furthermore, the rGO cathode more than doubles the benchmark for life cycles (to ≈200 cycles) and can be charged rapidly (<5 min). To explain this response, a charge storage mechanism is proposed wherein the [Al(H2O)6]3+ ions do not get desolvated when inserted into the cathode. The guest Al ions (surface adsorbed or intercalated) act as proton donors and may get anchored on the oxygen moieties of the rGO, further promoting the formation of an electrochemical double layer. A mixed charge‐storage regime follows that stabilizes the carbon cathode and enables an unprecedented response.

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Section: Role Of Al 3+ In the Charge Storage Mechanismmentioning

confidence: 90%

Aqueous Aluminum‐Carbon Rechargeable Batteries

Smajic

Hasanov

Alazmi

et al. 2021

Adv Materials Inter

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show abstract

“…Often g = 2 is assumed for the analysis of spin precession measurements. For pristine or moderately modified graphene flakes this assumption is confirmed by electron spin resonance (ESR) measurements [42,44,128]. It remains to be seen if this value also holds for functionalized graphene.…”

Section: Determination Of Spin Lifetimesmentioning

confidence: 76%

Spin and charge transport in graphene-based spin transport devices with Co/MgO spin injection and spin detection electrodes

et al. 2015

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In this review we discuss spin and charge transport properties in graphene-based single-layer and few-layer spin-valve devices. We give an overview of challenges and recent advances in the field of device fabrication and discuss two of our fabrication methods in more detail which result in distinctly different device performances. In the first class of devices, Co/MgO electrodes are directly deposited onto graphene which results in rough MgO-to-Co interfaces and favor the formation of conducting pinholes throughout the MgO layer. We show that the contact resistance area product (R c A) is a benchmark for spin transport properties as it scales with the measured spin lifetime in these devices indicating that contact-induced spin dephasing is the bottleneck for spin transport even in devices with large R c A values. In a second class of devices, Co/MgO electrodes are first patterned onto a silicon substrate. Subsequently, a graphene-hBN heterostructure is directly transferred onto these prepatterned electrodes which provides improved interface properties. This is seen by a strong enhancement of both charge and spin transport properties yielding charge carrier mobilities exceeding 20000 cm 2 /(Vs) and spin lifetimes up to 3.7 ns at room temperature. We discuss several shortcomings in the determination of both quantities which complicates the analysis of both extrinsic and intrinsic spin scattering mechanisms. Furthermore, we show that contacts can be the origin of a second charge neutrality point in gate dependent resistance measurements which is influenced by the quantum capacitance of the underlying graphene layer.

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“…The pulsed EPR techniques are useful for studying the isolated PCs in graphene-related materials. ,,,,− PCs with long spin–lattice, T 1 , and phase memory, T m , times in GO were revealed and identified as covering defects, , similar to those observed in other highly functionalized graphene materials. , …”

Section: Introductionmentioning

confidence: 79%

Electron Spin Echo Studies of Hydrothermally Reduced Graphene Oxide

et al. 2021

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Ecofriendly hydrothermal reduction of graphene oxide is widely used for producing hydrogels and aerogels, but it yields partly reduced graphene oxide (prGO) containing oxygen groups and some number of paramagnetic centers (PCs). In order to identify structural changes introduced by the reduction process, these PCs are studied by electron spin echo spectroscopy in the temperature range of 5–160 K. Two types of PCs with different spin–lattice (T 1) and phase memory (T m) relaxation times observed below 20 K result from a nonuniform distribution of magnetic defects. Above 20 K, only the PCs with the shorter T 1 and T m persist. Temperature dependences of T 1 and the distribution of T 1 for each type of the PCs reveal lattice distortions around the PCs and structural disorder in prGO. The unusually strong temperature dependence of the spin echo intensity is explained by the localization of conduction electrons. The localization is destroyed at high temperature, and exchange interactions decrease the number of the observed PCs. Every such PC is created by the sp 3 defect induced by hydrogen covalently bonded to graphene. The obtained results indicate that the hydrothermal reduction is accompanied by partial hydrogenation of graphene. The presence of such hydrogen atoms is confirmed by infrared spectroscopy.

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Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

Cited by 10 publications

References 44 publications

Aqueous Aluminum‐Carbon Rechargeable Batteries

Aqueous Aluminum‐Carbon Rechargeable Batteries

Spin and charge transport in graphene-based spin transport devices with Co/MgO spin injection and spin detection electrodes

Electron Spin Echo Studies of Hydrothermally Reduced Graphene Oxide

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