扫描隧道显微镜诱导单分子发光热荧光现象的全量子理论

使用量子主方程方法从理论上研究了STM诱导分子电致发光现象,并特别考虑了分子和量子化等离激元相互作用对于单分子光学性质的影响. 分子-等离激元相互作用大大增加了分子的自发辐射速率和分子发光的的强度,而且当分子自发辐射速率和振动弛豫速率可比拟的时候,将会出现热荧光现象.     

衬底上原子级凸起对隧道结中分子发光的影响

扫描隧道显微镜诱导发光可以用于研究单分子的各种光电现象,理解所涉及的基本光物理机制. 为了清楚地观察具有分子特征的发光,提高分子在金属纳腔中的量子效率非常重要. 本文采用电磁学模拟的方法,从理论上研究了在银纳腔中衬底上原子级凸起对平行于衬底的点偶极发射特性的影响. 这种衬底凸起结构可以大幅提高水平偶极发光体的量子效率,具有跟针尖尖端带有原子级凸起的情况类似的增强效应. 本文还考察了在针尖和衬底都具有原子级凸起的双凸起隧道结结构,并发现这种结构与没有凸起情况相比,确实提供了显著增强的发光,但与单凸起的情况相比,似乎没能进一步提高量子效率. 这些结果对今后的单分子扫描隧道显微镜诱导电致和光致发光研究具有指导意义.     

自组装双硫醇分子膜阻抗谱的研究

对交流电场下双巯基烷烃硫醇自组装分子膜的阻抗谱进行了研究.利用汞金属作为衬底,制备出双巯基烷烃硫醇自组装分子膜,并通过交流频谱仪对其进行频谱的扫描．明确了膜的作用范围为阻抗谱中频部分为了解释该阻抗谱,提出了一种串联的等效电路来进行了拟合,并与其他的模型进行比较.同时,观察到在损耗谱中损耗峰随硫醇碳链原子数的增加而向低频方向移动并得出双巯基硫醇(C6-C10)在交流电场下的激活能为23～39 meV．     

烷基硫醇/金自组装单分子膜表面上金属沉积特性研究进展

本文介绍了金属原子在烷基硫醇自组装单分子膜表面的再沉积行为,从理论上分析了其作用机理,归纳出了金属在自组装单层膜表面的再沉积规律。     

烷基硫醇/金自组装单分子膜表面上金属沉积特性研究进展

本文介绍了金属原子在烷基硫醇自组装单分子膜表面的再沉积行为,从理论上分析了其作用机理,归纳出了金属在自组装单层膜表面的再沉积规律。     

Ag(100)表面α-6T分子的自组装和STM诱导发光

利用扫描隧道显微镜诱导发光技术, 对有机分子α-6T在Ag(100)表面的自组装和光子发射特性进行了研究. 发现在极低的覆盖率下,α-6T分子以四个分子形成一种独特的风车形状的异构体. 随着覆盖率的增加,α-6T分子倾向于肩并肩紧密排列形成条纹状结构. 进一步增加覆盖率时,分子以低层分子的条纹结构作为模板,一层一层往上生长. 在五层分子厚度的样品上,利用光致方法可以获得分子荧光,这说明顶层分子已经被有效脱耦合. 然而在同样的样品上,STM诱导发光光谱却只展现出类似等离激元的发射特性. 在这种情况下,分子荧     

自组装双硫醇分子膜在交流电场下的介电特性

研究了交流电场下双巯基烷烃硫醇自组装分子膜的阻抗谱.利用汞金属作为衬底,制备出双巯基烷烃硫醇自组装分子膜,并通过交流频谱仪对其进行频谱的扫描.通过实验明确了膜的作用范围为阻抗谱中频部分,并给出相应的等效电路对阻抗谱进行了拟合.同时,根据损耗谱中损耗峰随硫醇碳链原子数的增加而向低频方向移动的现象得出双巯基硫醇Cn(n=3～10)在交流电场下的动能为14～48 meV.     

纳腔等离激元对分子上和分子旁边的隧穿电子诱导发光的作用研究

本文使用含时量子主方程,从理论上计算了当分子或者等离激元分别被激发的情形下等离激元-分子耦合体系发光特性的时间和光谱演化,并在此基础上讨论了纳腔等离激元在扫描隧道显微镜（STM）诱导发光中发挥的不同作用.当STM针尖在分子上方,隧穿电子可以直接激发分子时,纳腔等离激元的主要作用是通过提高分子的辐射速率来增强其发光,此时耦合体系表现出具有分子特征的尖锐发光峰.另一方面,当STM针尖非常靠近分子边缘但没有载流子注入直接激发分子时,等离激元-分子之间的相干耦合会在这两个量子客体之间产生相消干涉,导致在分子激子能量附近出现法诺共振,使我们观察到具有法诺凹谷特征的等离激元发光光谱.     

自组装硫醇分子膜电输运特性的导电原子力显微镜研究

在Au(111)表面自组装制备了不同链长的烷烃硫醇分子膜,并利用导电原子力显微镜研究了 自组装分子膜的输运特性随外加压力的变化.结果发现分子膜的电流随压力的增加而增大, 其变化特征可以较好地用Hertz模型描述.在相同压力和电压下,通过分子膜的电流随分子链 长的增加呈指数衰减,其衰减因子先随压力的增加而减小,后逐渐趋于稳定.此外,长链分 子自组装膜的电流随压力的变化比短链分子膜更为明显.分析表明,自组装硫醇分子膜输运 特征的压力依赖性主要源于电荷在分子膜中的链间隧穿过程. 关键词：分子自组装输运特性原子力显微镜     

硫醇自组装分子膜末端基团对其电荷输运特性的影响

在金(111)表面组装了具有不同末端基团的硫醇单层分子膜,并利用导电原子力显微镜研究了分子膜的电输运性质,发现不同末端基团的分子自组装膜的导电能力有明显差别.结合X射线光电子能谱,研究了末端基团中碳原子的结合能与相应硫醇分子电导的关系.结果表明不同末端基团分子膜导电能力的差别可归结为末端基团碳原子电子结合能的差异.结合能越高,末端基团电子的局域化程度越强,导致电子有效注入分子主链的势垒越高,从而减弱了分子膜对电子的输运能力.此外,实验还发现不同末端基团的硫醇单层分子膜有不同的表面电势,导致分子膜电流电压特性曲线的零点产生偏离.关键词：分子自组装膜输运特性末端基团导电原子力显微镜     

STM tip-enhanced photoluminescence from porphyrin film

Tunneling electrons-induced molecular fluorescence in organic film is enhanced by the surface plasmons. The plasmon enhancement can be expected not only by the plasmons of the substrate but also by the noble metal tip of scanning tunneling microscope (STM). In this report we investigate the tip effect in photoluminescence of meso-tetrakis(3,5-di-tertiarybutyl-phenyl)porphyrin (H₂TBPP) film on indium tin oxide (ITO) combined with a STM. The experimental result shows the PL of molecules is enhanced by an Ag tip. This enhancement factor is evaluated larger than 2000.     

Current flow through different phases of dodecanethiol self-assembled monolayer

A self-assembled monolayer of dodecanethiol grown on Au(1 1 1) substrate has been annealed to form different structural phases: a higher density phase, a lower density stripe phase, and a disordered mixed phase. The electrical properties of each phases have been studied by using scanning tunneling spectroscopy. The current-voltage curves measured on the disordered phase were less reproducible than those measured on the two well-ordered phases. Molecular resolution STM image obtained on the stripe phase shows that the structural instability of the alkyl chain of the stripe phase affect the current flow through the molecule. Our study shows that the ordering and structural stability of the molecules are very important in stable measurement of the electrical properties of the molecular films.     

单个铂酞菁分子在正负偏压激发下的电致发光特性研究

本文利用扫描隧道显微镜诱导发光技术,系统地研究了铂酞菁分子在正负偏压激发下的电致发光行为及其相关的电子激发机制. 铂酞菁分子在正负偏压激发下均可以发光,但发光特征有所不同. 在负偏压激发下,观察到了源于中性PtPc分子LUMO→HOMO跃迁的峰位在637 nm处的荧光峰. 荧光强度在三个不同的激发区域呈阶梯状增加. 当激发偏压处于区域(I)时,可以产生较强的荧光,其主导激发机制是载流子注入激发机制;当激发偏压处于区域(II)时,可以产生中等发光强度的荧光,其主导激发机制是非弹性电子散射激发机制;当激发偏压处于区域(III)时,激发电子能量小于荧光光子能量,存在上转换现象,荧光峰非常弱,其激发过程需要自旋三重态作为中继态,并由载流子注入和非弹性电子散射两种机制共同作用产生. 在正偏压激发下,分子的电致发光光谱特征变得更加复杂,具有多个发光峰. 911 nm处的尖锐发光峰起源于PtPc^-阴离子的LUMO+1→LUMO跃迁,其激发主要是由载流子注入激发机制主导.     

Enhanced surface evolution induced by the molecular desorption in dodecanethiol self-assembled monolayer on Au(1 1 1)

The evolution of the surface structure in dodecanethiol self-assembled monolayer on Au(1 1 1) substrate has been studied with ultra high vacuum scanning tunneling microscopy at several temperatures. The structure of substrate Au(1 1 1) surface changed suddenly at a temperature of 110 °C. The enhanced mobility of the substrate gold atoms at this temperature is attributed to the desorption of the dodecanethiol molecules.     

A novel method for elimination of the gold-islands formed in the self-assembled monolayers of benzeneselenol on Au(1 1 1) surface

Molecular ordering of benzeneselenol (BSe) self-assembled monolayers (SAMs) on Au(1 1 1) substrates have been investigated by scanning tunnelling microscopy (STM) [1]. After short immersion time (10 min), elevated islands with height of 2.4 Å were found to cover the entire gold surface. On and among the islands, the STM results exhibited the formation of a highly ordered phase (α-phase) by BSe species. In the present study, a novel method is presented to completely eradicate the elevated gold-islands. The method depends on a repetitive STM scanning over the same part of the SAM at restricted tunnelling conditions. After almost 6 h of successive scanning, the surface becomes clean and free of the elevated islands. Moreover, this method was found to induce phase transformation into β-phase. The size of the ordered domains of the β-phase was found to exceed five times that of α-phase. Such a long-range ordering of the β-phase at room temperature has not been previously observed for any system on Au(1 1 1). After detailed analyses, the β-phase was found to have a 33.5% of lower packing density than that of α-phase.     

Insight into STM image contrast of n-tetradecane and n-hexadecane molecules on highly oriented pyrolytic graphite

Two-dimensional ordered patterns of n-tetradecane (n-C₁₄H₃₀) and n-hexadecane (n-C₁₆H₃₄) molecules at liquid/graphite interface have been directly imaged using scanning tunneling microscope (STM) under ambient conditions. STM images reveal that the two different kinds of molecules self-organize into ordered lamellar structures in which alkane chains of the molecules extend along one of three equivalent lattice axes of highly oriented pyrolytic graphite (HOPG) basal plane. For n-C₁₄H₃₀ molecules, the molecular axes are observed to tilt by 60° with respect to inter-lamellar trough lines and the carbon backbones of the alkane chains are perpendicular to the HOPG basal plane in an all-trans conformation. However, for n-C₁₆H₃₄ molecules, the molecular axes are perpendicular to lamellar borders (90°) and the planes of the all-trans carbon skeletons are parallel to the graphite basal plane. The results clearly indicate that outmost hydrogen atoms of the alkane chains dominate atom-scaled features of the STM images. That is, in the case of long-chain alkane molecules, topographic effects dominantly determine STM image contrast of the methylene regions of the alkane chains that are adsorbed on HOPG.     

Scanning tunneling microscope with long range lateral motion

We present our work on a recently built scanning tunneling microscope (STM), with coarse motion in two-dimensions. The tip of this STM can be translated a few millimeters in directions both parallel and perpendicular to the tip. This feature allows sampling of a larger area for experiments such as the study of how the electrical properties of charge density waves evolve between contacts, the proximity effect near a normal metal–superconducting interface, charge transport near the contact of a semiconductor interface, and for finding microscopically small samples like graphene. This STM is based on one of our previous one-dimensional designs. It utilizes orchestrated motion of six piezoelectric tubes in a slip–stick configuration in order to produce long range motion for the walker. This device is a single unit with a compact design making it very stable. It is stable enough to obtain atomic resolution on HOPG. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures. It was designed entirely from non-magnetic materials for potential work in a magnetic field.