【作者】 冯卫；

【导师】 侯建国； 王兵；

【作者基本信息】 中国科学技术大学 ， 单分子科学， 2012， 博士

【摘要】 扫描隧道显微镜（scanning tunneling microscope，STM）不仅能够获得表面和表面吸附体系的高分辨图像，还能探测表面的局域扫描隧道谱（scanningtunneling spectroscopy，STS），甚至能够对表面吸附体系进行操纵。近三十年来，STM作为一种非常重要的科学分析仪器，在物理、化学、材料和生物等诸多学科领域得到了广泛的应用。在本论文中，我们利用超高真空低温扫描隧道显微镜对单层石墨/Ru(0001)、石墨和Ru(0001)表面的吸附物电子学性质进行了研究。第一章是本论文的基础，简单介绍了STM的发明、发展以及基本工作原理，另外还特别介绍了实验中所使用的超高真空低温扫描隧道显微镜的结构以及实验中所用到的一些工作模式。在第二章中，我们利用STM/STS主要对比研究了Ru (0001)表面外延生长的单层、双层石墨。研究发现在一个很宽的能量范围内，单层石墨表面摩尔纹较高区域的电子态密度和双层石墨表面的局域电子态密度相同。和双层石墨表面一样，单层石墨较高区域在费米面以下0.5 V处也有一个狄拉克点。另外，研究发现单层石墨的局域功函数远低于HOPG的功函数，并且呈周期性分布，其中摩尔纹的较高区域和较低区域的功函数差别约为200 meV；而双层石墨的功函数比单层石墨大，向HOPG恢复。分析后我们认为单层石墨表面的局域势垒高度值偏小以及呈周期分布是因为表面存在着周期分布的正的表面电偶极矩。在第三章中，我们主要研究了在MG/Ru(0001)表面吸附的钴酞菁（CoPc）分子，发现只有CoPc分子在MG/Ru(0001)表面上出现了很明显的整流效应，并且该整流效应只存在于中心Co上。通过CoPc直接吸附在Ru(0001)表面的对比实验，以及对这两个体系的理论计算分析，我们发现，由于MG的脱耦合作用，大大减弱了分子与衬底间的相互作用，而中心Co上的d轨道相对于费米面的不对称分布使CoPc的中心Co在MG/Ru(0001)表面表现出了整流效应。在第四章中，我们选用高定向热解石墨（HOPG）作为衬底继续研究CoPc分子与衬底的相互作用。结合STM形貌、STS的谱学和第一性原理计算的方法，我们发现CoPc分子与衬底之间的相互作用很弱，因此在针尖—CoPc分子—HOPG之间形成双势垒隧穿结。通过分析CoPc分子上通过LUMO轨道的双势垒隧穿引起的双峰位置与针尖高度关系，我们还发现需要在3d金属酞菁分子与HOPG之间引入电容的量子修正。在第五章中，我们主要阐述单个钴（Co）原子及其团簇在Ru(0001)表面的近藤效应。结合STM的横向操纵技术，我们发现，在Ru(0001)表面的单个Co原子、Co二聚体和线状三聚体的近藤共振具有峰宽不变、而峰型变化的特点；而一旦Co原子形成三角形密排三聚体或者更大的密排团簇时，近藤共振就消失不见了。另外，利用STM的纵向操纵技术，针尖变成具有近藤效应的近藤针尖，用这样的针尖来探测样品表面具有近藤效应的单个Co原子时，新得到的近藤共振主要由针尖上的近藤共振决定。更多还原

【Abstract】 Scanning tunneling microscope (STM) can not only obtain high-resolutionimages of the surface and surface adsorption system in real space, but also probethe scanning tunneling spectroscopy (STS) of them, and can manipulate thesurface-adsorbate. In the nearly three decades, as an important scientific analyticalinstrument, STM has been widely utilized in physical science, chemical and materialscience, biology. In this thesis, we use ultra-high vacuum low temperature scanningtunneling microscopy (UHV LT-STM) to study the electronics properties of theadsorbate on monolayer graphene/Ru(0001), Highly Oriented Pyrolytic Graphite(HOPG) and Ru(0001) surface.The ChapterⅠis the basis of this thesis, we briefly introduced the invention,development and simple fundamental principle of STM, in addition, and theinstrument structure and work mode of the UHV LT-STM used in our experiment.In ChapterⅡ, the epitaxial monolayer and bilayer graphene (MG and BG) onRu(0001) surface was studied comparatively. We found that the local density of states(LDOS) of the high sites of MG is the same with that of the BG in a wide energyrange, and there is a Dirac point on the high regions of MG as BG at about 0.5 Vbelow Fermi energy. In addition, it is found that the local work function (LWF) ofMG is around 3.5 eV, and the LWF difference between the high and low sites of MGis about 100 to 200 meV. But LWF of BG is larger than that of MG. We concludedthat the LWF of MG surface is too small value and periodic distribution is due to theexistence of periodic surface dipole moment.In ChapterⅢ, we mainly studied the cobalt phthalocyanine (CoPc) adsorbed onMG/Ru(0001) surface. We found that there is an obvious rectification effect inthe central Co ion of the CoPc molecules. Through the comparative studies ofthe CoPc molecules adsorbed on Ru(0001) surface, and combined with the theoreticalcalculations of these two systems, we found that the interaction between the CoPcmolecules and Ru(0001) surface become much weaker due to the decoupling effect ofthe MG. And the asymmetry of the d orbital of the central Co ion relative tothe Fermi energy results in the rectification effect on the central Co ion.In ChapterⅣ, highly oriented pyrolytic graphite (HOPG) was chosen asthe substrate to study the interaction between CoPc molecules and the substrate further. Combined with the STM/STS and the first principles calculation, we foundthat the interaction between the CoPc molecules and the substrate is very weak, soa double barrier tunneling junction (DBTJ) is formed, the two tunnel barriers in thejunction are the vacuum gap between the STM tip and the molecule, and the vacuumgap between the molecule and HOPG. By analyzing the double barrier tunnelingthrough the LUMO orbital of CoPc molecules, we find that the quantum correctionsshould be introduced to the capacitance of this two tunnel barriers.In ChapterⅤ,we mainly studied the Kondo effect of single cobalt (Co) atomsand clusters in Ru(0001) surface. Combined with the lateral manipulation andSTM/STS, we found that the width of Kondo peaks is almost unchanged fromsingle Co atoms to dimer then linear trimer, only their line shape is little changed. Butwhen the Co atoms form a triangle compact trimer or larger compact clusters,the Kondo peak disappear. We can obtained tips with Kondo resonance by the use ofvertical manipulation, use these tips to detect the Kondo resonance of the single Coatoms on Ru(0001) surface, the new Kondo resonance is mainly contributed bythe Kondo resonance on the tip.更多还原