Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA.
Nanoscale. 2013 Aug 21;5(16):7512-9. doi: 10.1039/c3nr01971c. Epub 2013 Jul 8.
CoO and Co nanocrystals with cubic crystal structures were prepared by thermal decomposition of cobalt(II) acetate tetrahydrate in a mixture of oleylamine and oleic acid under the protection of nitrogen gas at 300 °C for 2 h. The products of CoO or Co nanocrystals are determined by the relative amount of oleylamine due to its reducibility. The sizes and shapes of CoO or Co can be controlled by the ratio of cobalt : oleylamine : oleic acid due to different binding capabilities of the two capping ligands (oleylamine and oleic acid). A modification of the surface state by surface passivation arising from the capping ligands for CoO nanocrystals leads to the blue shift of the ligand-metal charge transfer (LMCT) absorption. Room temperature ferromagnetism originating from uncompensated surface spins, as well as magnetic moments weakly exchange coupled to the CoO lattice due to defects inside CoO nanoparticles, are observed. The magnetic behaviors of CoO and Co nanoparticles also shed light on the synthesis and the magnetic properties of the antiferromagnetic and ferromagnetic nanomaterials.
通过在氮气保护下于 300°C 下将四水合乙酸钴在油胺和油酸的混合物中热分解 2 小时，制备具有立方晶体结构的 CoO 和 Co 纳米晶。由于油胺的还原性，CoO 或 Co 纳米晶的产物取决于油胺的相对量。由于两种封端配体（油胺和油酸）的结合能力不同，CoO 或 Co 的尺寸和形状可以通过钴：油胺：油酸的比例来控制。表面封端配体导致 CoO 纳米晶表面状态的修饰，从而导致配体-金属电荷转移（LMCT）吸收的蓝移。观察到室温铁磁性源于未补偿的表面自旋，以及由于 CoO 纳米颗粒内部的缺陷而与 CoO 晶格弱交换耦合的磁矩。CoO 和 Co 纳米颗粒的磁行为也揭示了反铁磁和铁磁纳米材料的合成和磁性质。
