Defect induced electronic states and magnetism in ball-milled graphite

Abstract

The electronic structure and magnetism of nanocrystalline graphite prepared by ball milling of graphite in an inert atmosphere have been investigated using valence band spectroscopy (VB), core level near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and magnetic measurements as a function of the milling time. The NEXAFS spectroscopy of graphite milled for 30 hours shows simultaneous evolution of new states at ~284.0 eV and at ~290.5 eV superimposed upon the characteristic transitions at 285.4 eV and 291.6 eV, respectively. The modulation of the density of states is explained by evolution of discontinuities within the sheets and along the fracture lines in the milled graphite. The magnetic measurements in the temperature interval 2-300-2 K at constant magnetic field strength show a correlation between magnetic properties and evolution of the new electronic states. With the reduction of the crystallite sizes of the graphite fragments, the milled material progressively changes its magnetic properties from diamagnetic to paramagnetic with contributions from both Pauli and Curie paramagnetism due to the evolution of new states at ~284 and ~290.5 eV, respectively. These results indicate that the magnetic behaviour of ball-milled graphite can be manipulated by changing the milling conditions.

Favorable Carbon Conductive Additives in Li3PS4Composite Positive Electrode Prepared by Ball-Milling for All-Solid-State Lithium Batteries

“…In previous reports, electronic state and structure changes of ball-milled carbons were investigated for the fundamental research. [46][47][48][49][50][51][52] Morphology changes, electronic state changes, and z E-mail: tatsu@chem.osakafu-u.ac.jp structure defects of the ball-milled carbon were characterized by using X-ray diffraction, 47,51 Raman spectroscopy, 46,49,51 scanning electron microscope (SEM), 49,50 transmission electron microscope, [47][48][49][50][51] X-ray absorption near edge structure, 50,52 and electron probe micro analyzer. 46 In the positive electrode of all-solid-state Li/S batteries, the pulverization of the carbons has not been discussed in detail.…”

Oxygen Plasma Treatment of Rear Multilayered Graphene: A Potential Top Electrode for Transparent Organic Light-Emitting Diodes

“…The resonance peaks at photon energies of 285.6 and 292.1 eV are formed by the electron transitions from carbon 1s to sp 2 π* orbital or σ* of the C-C bond, respectively [26]. The peak at a photon energy of 287.8 eV originates from σ* bonds of hydrocarbon functional groups such as -CH, -OH, and -CO x , which favor the formation of defective graphene sites [27,28]. The broad curves above a photon energy of 300 eV are formed by the σ* resonances of the C=C bond [24].…”

Molten Salt Electrosynthesis of Cr2AlC-Derived Porous Carbon for Supercapacitors

“…In-plane crystallite sizes ( L a ) for carbon materials are related to I D / I G and usually can be estimated through a general formula, i.e. L a (nm) = (2.4 × 10 –10 ) λ 4 ( I D / I G ) –1 , , where λ represents Raman excitation wavelength in nanometer. The L a values for Cr 2 AlC-CDC obtained at 600, 700, 800, and 900 °C are 16.3, 17.0, 17.2, and 27.9 nm, respectively, suggesting that the CDC sample obtained at 900 °C has a larger crystalline size.…”