Direct observation of molecular orbitals in an individual single-molecule magnet Mn12 on Bi(111).
Direct observation of molecular orbitals in an individual single-molecule magnet Mn12 on Bi(111).
复制标题
DOI：
10.1021/nn401827h
复制
发表时间：
2013-07
期刊：
影响因子：
17.1
通讯作者：
K. Sun;Kyungwha Park;Jia-Le Xie;Jiyong Luo;Hongkuan Yuan;Zuhong Xiong;Junzhong Wang;Q. Xue
中科院分区：
文献类型：
--
作者：
K. Sun;Kyungwha Park;Jia-Le Xie;Jiyong Luo;Hongkuan Yuan;Zuhong Xiong;Junzhong Wang;Q. Xue
单分子纳米磁体具有独特的量子性质，其潜在的应用需要对不同衬底上的单个单分子磁体进行表征和访问。我们开发了一种温和的针尖沉积方法，利用低温扫描隧道显微镜将单个原型单分子磁体--醋酸锰(Mn12)分子，在没有连接物分子的半金属Bi(111)表面上沉积。在4.5K下，我们能够分辨出Mn12分子的几乎平卧和侧卧取向。能量分辨光谱图谱使我们能够首次观察到单个Mn12分子在真实空间中的几个分子轨道，这与密度泛函理论的计算是一致的。实验和理论结果都表明，几乎平坦的Mn12分子的最高占据分子轨道(HOMO)和最低空分子轨道(LUMO)之间的能隙仅为孤立的(自由)Mn12分子的40%，这是由于从铋的金属表面态向Mn12分子的电荷转移造成的。尽管这一能隙减小，但STM图像显示被Mn12覆盖的Bi(111)的局域晶格基本保持不变，表明Mn12-Bi相互作用不强。我们的发现开辟了一条直接解决固体衬底上单个单分子磁体的局部结构和电子性质的途径。
Single-molecule nanomagnets have unique quantum properties, and their potential applications require characterization and accessibility of individual single-molecule magnets on various substrates. We develop a gentle tip-deposition method to bring individual prototype single-molecule magnets, manganese-12-acetate (Mn12) molecules, onto the semimetallic Bi(111) surface without linker molecules, using low-temperature scanning tunneling microscopy. We are able to identify both the almost flat-lying and side-lying orientations of Mn12 molecules at 4.5 K. Energy-resolved spectroscopic mapping enables the first observation of several molecular orbitals of individual Mn12 molecules in real space, which is consistent with density functional theory calculations. Both experimental and theoretical results suggest that an energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the almost flat-lying Mn12 is only 40% of such a gap for an isolated (free) Mn12 molecule, which is caused by charge transfer from the metallic surface states of Bi to the Mn12. Despite the reduction of this gap, STM images show that the local lattices of Bi(111) covered with Mn12 remain essentially intact, indicating that Mn12-Bi interactions are not strong. Our findings open an avenue to address directly the local structural and electronic properties of individual single-molecule magnets on solid substrates.