Au(111)表面吸附单个八乙基钴卟啉分子的电子态和输运性质调控  

Controlling the electronic states and transport properties of single cobalt(II)octaethylporphyrin molecule adsorbed on Au(111) surface

作　　者：李竟成[1,2] 赵爱迪[1] 王兵[1] 

机构地区：[1]中国科学技术大学,合肥微尺度物质科学国家实验室,合肥230026 [2]中国科学院物理研究所,北京100190

出　　处：《物理学报》2015年第7期11-20,共10页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2011CB921400);国家自然科学基金(批准号:11074236,21473174,51132007);中国科学院战略性先导科技专项(B类)(批准号:KJCX2-EW-J02,XDB01020100)资助的课题~~

摘　　要：通过低温超高真空扫描隧道显微镜及其谱学方法研究并展示了分子配体在调控表面吸附的单个八乙基钴卟啉(Co OEP)分子的电子态和输运性质中的重要作用.通过单分子剪裁可以脱去该分子外围的甲基,并在中心钴原子的微分电导谱中观察测到d轨道共振到近藤共振的演变.实验结果结合第一性原理的理论计算研究表明,在脱去甲基前后中心钴原子的化学环境和磁矩均未发生显著变化,这一演变可以通过一个简化模型来阐释并被归结为脱去甲基后分子配体与衬底成键改变了体系隧穿参数所导致.此外,实验结果表明Co OEP分子配体的输运性质可受到分子间距离和范德华相互作用的显著调控.在Co OEP低聚体中位于分子之间的乙基被抬高,同时在其微分电导谱谱中0—0.8 V区域内新出现一个强的共振峰.这一新的共振峰表现出等间距的多峰细节,其峰间距与卟啉环和乙基之间的C—C键伸缩模式能量符合.这一新共振峰的出现被归结为由于分子局部与衬底耦合减弱形成双结隧穿体系所导致的振子态隧穿峰.We demonstrate that the molecular ligands play important roles in controlling the electronic states and electron transport properties of single cobalt（II） octaethylporphyrin（Co OEP） molecule adsorbed on Au（111） surface by using low-temperature scanning tunneling microscopy and spectroscopy. Single Co OEP molecule adsorbed on Au（111） surface has eight methyl groups pointing out of the surface plane. A peak located at-50 mV in d I/d V spectrum measured on the Co atom of Co OEP is identified as a d-orbital mediated resonance. We find that the methyl groups in Co OEP can be removed in a stepwise manner, and finally lead to a fully-demethylized Co OEP. The d-orbital mediated resonance gradually evolves into a sharp Kondo resonance located right at Fermi level in the demethylization process. Both experimental and theoretical results indicate that the chemical environment and magnetic moment of the central Co atom change slightly in the fully-demethylized Co OEP： the Co atom is slightly lifted by 0.15 ？ and the magnetic moment increases from 0.5 μB to 0.6 μB. The emergence of Kondo effect is qualitatively explained with a simple model by consideringthe change in the tunneling parameters of the ligands upon demethylization. We also show that the transport properties of the Co OEP can be dramatically controlled by weak intramolecular van der Waals interaction. In Co OEP closely-packed dimers and trimers where Co OEP molecules are introduced close enough to each other, the ethyl groups in the neighboring area are found to be strongly lifted by 0.4 A. More surprisingly, a pronounced resonance shows up at 0—0.8 V in the d I/d V spectra of the lifted ethyl groups. High resolution spectra show that the new resonance consists of multiple peaks with equal spacing of 137 ± 8 mV. The spacing energy coincides with the vibrational energy of stretching mode of C—C bond between ethyl group and the brim carbon atom of the porphyrin ring. Therefore the newly-emerged resonance is attributed to the vibronic stat

关 键 词：扫描隧道显微学 单分子 近藤效应 振子态 

分 类 号：O647.3[理学—物理化学]