Bromine-adsorption-induced change in the electronic and magnetic properties of nanographite network systems
Bromine-adsorption-induced change in the electronic and magnetic properties of nanographite network systems
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DOI：
10.1103/physrevb.73.035435
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发表时间：
2006-01-01
影响因子：
3.7
通讯作者：
Enoki, T
中科院分区：
文献类型：
--
作者：
Takai, K;Kumagai, H;Enoki, T
具有开放边缘的纳米石墨具有边缘起源的非键合π电子状态（边缘状态），这导致非常规的电子和磁性特征。以活性炭纤维（ACFs）为主体材料，研究了溴吸附对由柔性三维无规纳米石墨网络系统组成的纳米多孔炭的电磁性能的影响。在室温下溴不可逆吸附到活性炭纤维得到的组成为Br/C=0.43。纳米石墨和吸附的溴之间的相互作用被分为三组：电荷转移，共价键合，和物理吸附相互作用，其中后两个是大多数。虽然从碳到溴的电荷转移速率相当小（最大为0.0004/C原子），但与体相石墨-溴插层化合物相比，费米能级的下移导致边缘态的局域自旋浓度和轨道抗磁性的大幅度降低.这证明了边缘态在电荷转移过程中的重要作用。电子自旋共振结果表明，溴的轨道特性的贡献，通过轨道混合的边缘状态在纳米石墨。物理吸附的溴被容纳到纳米孔中，引起纳米石墨的介电和结构效应。前者由于电荷效应导致载流子传导过程的改变，而后者由于物理吸附溴物种对边态自旋的有效压力导致磁开关现象。
Nanographite having open edges has a nonbonding pi-electron state of edge origin (edge state), which causes unconventional electronic and magnetic features. Bromine-adsorption effect on the electronic and magnetic properties of nanoporus carbon consisting of a flexible three-dimensional random nanographite network system is investigated by using activated carbon fibers (ACFs) as host material. The irreversible adsorption of bromine into ACFs at room temperature gives compositions up to Br/C=0.43. The interaction between nanographite and the adsorbed bromine is classified into three groups; charge transfer, covalent bonding, and physisorption interactions, where the latter two are the majorities. Although the charge transfer rate from carbon to bromine is considerably small (0.0004 per C atom at maximum), in comparison with that in bulk graphite-bromine intercalation compounds, the downshift of the Fermi energy results in the large reduction of the localized spin concentration of edge state and the orbital diamagnetism. This proves the important role of the edge state in the charge transfer process. The electron spin resonance results demonstrate the contribution of the orbital character of bromine to the edge state in nanographite through orbital mixing. The physisorbed bromine accommodated into the nanopores induces the dielectric and structural effects on the nanographite. The former causes the modification of the carrier conduction process due to the charging effect, while the latter results in the magnetic switching phenomenon induced by the effective pressure of physisorbed bromine species to the edge-state spins.