石墨烯基面上sp3畴分布的调控与磁性研究

Introducing sp3-type adatoms (such as H or F) on the basal plane of graphene is an effective way to tune its magnetic property, thus promising its application in spintronics. However, arising from the low migration barrier on the flat plane of graphene, sp3-type adatoms tend to self-assemble into large sp3-domains which inefficiently contribute magnetic moments, and hence, the spin density is quite low. In this project, we propose to prepare large-sized graphene which is fit for sp3-functionalization by electrolyzing graphite, then lightly oxidize it through thermal treatment in nitric acid to introduce dispersive ripples and oxygen groups which could serve as migration barrier. Thereafter, with the existence of migration barrier on the basal plane of graphene, by controllable hydrogenation or fluorination we would obtain a certain mount of dispersed small sp3-domains which could efficiently contribute magnetic moments to increase the spin density. By varying the experimental conditions of lightly oxidation, hydrogenation or fluorination to tune the distribution of sp3-domains, we could tune the coupling among the magnetic moments inside and / or outside the sp3-domains, and thus realize ferromagnetism with high magnetization in graphene. The combination of theory and experiment will be adopted to construct a reasonable distribution model of the sp3-domains, and which will help to provide theoretical suggestions for our experimental results by exploring the exchange coupling mechanism of intra- and inter-domain.

在石墨烯基面上引入H，F等sp3型掺杂原子能够有效调控其磁学性质，有利于推进石墨烯在自旋电子学领域的应用。然而，这些sp3型掺杂原子在平整的石墨烯基面上移动势垒很小，因而会自聚集形成大面积的sp3畴，非常低效地贡献磁矩，造成自旋浓度的降低。本申请拟采用电解石墨的方法制备适合sp3功能化的大片状石墨烯，通过硝酸热处理进行轻氧化，引入分散的褶皱和氧基团充当阻碍sp3型掺杂原子移动的壁垒；再通过H，F的掺杂在石墨烯基面上引入sp3型缺陷，形成数量众多、间距适中的sp3小畴，高效贡献磁矩以达到提升自旋浓度的目的。通过调控轻氧化、氢化或氟化的实验条件调控sp3畴的分布，调控畴内磁矩、畴间磁矩团之间的耦合作用，以期得到具有较强铁磁性的石墨烯材料。此外，结合实验结果，拟建立sp3畴分布的合理模型，通过理论计算探索sp3畴内、畴间微观交换耦合机制，为实验提供理论依据。

在石墨烯中引入磁矩在其自旋电子学领域的应用具有重要意义。石墨烯基面上的碳原子以sp3型成键方式结合如H、F、OH、NH2等原子或基团，从而引入sp3型磁矩，在理论上被认为是一种通用的方法。以石墨烯的各种sp3型功能化作为技术手段，本课题主要做了以下一些研究：.(1)通过采用电解石墨的方法，获得了大批量、纯净的石墨烯，通过热硝酸处理调控其羟基型sp3基团、通过在氨气中光照调控其氨基型sp3基团的分布，实验上证实了sp3型基团引入磁矩的通用有效性。氨基引入磁矩的效率约为1μB/100NH2。.(2)以基于Hummers方法制备的高浓度羟基型sp3功能化的石墨烯为基础，在NaOH溶液中通过水热法进一步调控羟基sp3畴分布，达到调控石墨烯磁性的目的。另外，通过在石墨烯基面上引入平面型氮原子，以调控羟基sp3畴产生的磁矩团之间的耦合。.(3)将sp3型功能化的石墨烯和碳纳米管应用到能源领域，有一定的应用前景。氨基sp3功能化的石墨烯/碳纳米管的结合体比电容达到368 F/g, 经过5000次循环其电容保持率为90.7%。以氟掺杂sp3功能化的石墨烯为基础而获得的超氮掺杂的石墨烯纤维/石墨烯泡沫，其比电容达到320 F/g, 经过1000次循环其电容保持率为92.8%。