Preferential antiferromagnetic coupling of vacancies in graphene on SiO2: Electron spin resonance and scanning tunneling spectroscopy

Article

关键词: ROOM-TEMPERATURE FERROMAGNETISM;    EPITAXIAL GRAPHENE;    GRAPHITE SURFACES;    POINT-DEFECTS;    MICROSCOPY;    CARBON;    OXIDE;    NANORIBBONS;    MAGNETISM;    ORIGIN;   

DOI  :  10.1103/PhysRevB.90.125449

来源: SCIE

【 摘 要 】

Monolayer graphene grown by chemical vapor deposition and transferred to SiO2 is used to introduce vacancies by Ar+ ion bombardment at a kinetic energy of 50 eV. The density of defects visible in scanning tunneling microscopy is considerably lower than the ion fluence, implying that most of the defects are single vacancies as expected from the low ion energy. The vacancies are characterized by scanning tunneling spectroscopy on graphene and highly oriented pyrolytic graphite (HOPG). A peak close to the Dirac point is found within the local density of states of the vacancies similar to the peak found previously for vacancies on HOPG. The peak persists after air exposure up to 180 min, such that electron spin resonance (ESR) at 9.6 GHz can probe the vacancies exhibiting such a peak. After an ion flux of 10/nm(2), we find an ESR signal corresponding to a g factor of 2.001-2.003 and a spin density of 1-2 spins/nm(2). The peak width is as small as 0.17 mT indicating exchange narrowing. Consistently, the temperature-dependent measurements reveal antiferromagnetic correlations with a Curie-Weiss temperature of -10 K. Thus, the vacancies preferentially couple antiferromagnetically, ruling out a ferromagnetic graphene monolayer at ion induced spin densities of 1-2 nm(2).

【 授权许可】

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