meso-四(对甲氧基苯基)卟啉钴在货币金属单晶表面的吸附与自组装研究

利用超高真空低温扫描隧道显微镜系统研究了meso-四对甲氧基苯基卟啉钴分子在Au（111）、Ag（111）和Cu（111）表面的吸附与自组装.该分子在金属表面可以形成两种组装结构A和B.在结构A中,分子间的相互作用主要为π-π堆叠,仅在Au（111）和Ag（111）表面被实验观察到;在结构B中,分子间的相互作用为氢键,仅在Ag（111）和Cu（111）表面被实验观察到.分子-衬底相互作用的差异所引起的分子吸附构象变化被认为是导致不同衬底上的分子形成不同组装结构的原因.研究发现在不同衬底上,分子形成自组装结构的行为存在明显差异.在相近覆盖度下,未参与组装的分子的比例在Cu（111）表面最高,Au（111）次之,Ag（111）最低.表面上参与形成两种组装结构的分子与未参与组装的分子的比例还可通过覆盖度和退火来进行调控.     

非手性的棒状分子在非手性表面形成的风车团簇

利用低温STM研究了非手性的棒状并五苯分子在Bi（111）表面形成的手性风车团簇.在团簇内部,并五苯分子分别沿Bi（111）的3个对称轴方向平行排列,形成6个不同的分子带.在每个分子带中,相邻分子之间有一个滑移错位.当平行排列的分子数多于4时,滑移错位发生反向,形成弯曲的风车扇叶.我们认为,分子的滑移错位来自于分子之间的π-π相互作用;而滑移错位的反向是团簇内部的吸引力导致的密堆积的结果.这两种作用的竞争是形成手性风车团簇的微观机制.     

表面分子手性识别与组装结构的STM研究

表面手性现象是物理化学科学研究的重要内容之一,研究表面手性现象,将有助于对分子吸附,分子间相互作用,多相手性催化,手性分离与拆分等科学和实际应用问题的深入理解.在表面手性现象和手性结构的研究中,扫描隧道显微技术（STM）发挥着重要作用,成为研究表面手性现象的重要手段.该综述文章以本课题组近年已发表的研究工作为主,重点介绍利用STM研究固体表面分子吸附组装体系中关于手性问题的部分结果,包括固有手性分子在固体表面的吸附,非手性分子组装形成手性结构,以及表面手性结构的转化和调控.还结合实验结果分析探讨了表面手性的结构形成、放大和传递等,展望了该研究领域的发展趋势.     

基于全氟酞菁铜和碗烯双分子体系在银和石墨表面自组装行为的低温扫描隧道显微镜研究（英文）

由于其独特的分子构型和电子结构,碗烯被认为是组成有机分子电子器件的一种重要的结构单元。在不同金属表面上单一组分的碗烯或其衍生物进行自组装的行为,及其所形成自组装薄膜的电子结构已经被广泛研究。这里我们利用低温扫描隧道显微镜(LT-STM),对全氟酞菁铜和碗烯两种组分在高定向热解石墨和银(111)两种不同衬底上的自组装结构进行了报道。在石墨衬底上,全氟酞菁铜和碗烯分子间形成的氢键成为双分子网络结构能够形成的关键;同时,由于这种分子间氢键的存在,碗烯分子大多采取"开口朝下"的空间构型,以保证分子间氢键最大限度的形成。但在银衬底上观察到的碗烯分子则随机采取"开口向上"或"开口向下"两种构型,并没有一种优势构型的存在。我们认为此时银(111)衬底和有机分子间强烈的相互作用限制了碗烯两种构型之间的翻转,使得碗烯分子一旦被吸附就只能保持其原本的构型,从而导致了在结果上两种构型的随机分布。     

在半金属表面上应力诱导的红荧烯晶态薄膜

报道了在Bi（001）衬底上从第一层开始形成的红荧烯晶体薄膜.随着覆盖度的增加,红荧烯薄膜的结构会发生从自组装到混合相的转变.在混合相中存在着红荧烯的晶体畴和分子自组装形成的畴壁.特别是,我们在这种晶体畴中发现了Kurdjunov-Sachs（KS）转动外延和巨大的压缩应力.随着覆盖度的增加,红荧烯薄膜会按照逐层生长的模式进行,直至第四个分子单层.我们认为,转动外延过程中所产生的巨大压缩应力是导致晶态红荧烯薄膜的形成原因.     

BIC和HA体系的氢键驱动的HOPG表面手性自组装分子动力学模拟

5-（苄氧基）-间苯二甲酸衍生物（BIC）与庚醇（HA）分子在高定向热解石墨（HOPG）表面吸附,通过氢键等弱相互作用会形成具有手性特征的二维网络结构。对该过程进行分子动力学模拟,通过几何结构、能量、氢键数目、氢键键长、氢键键角等特征性参数的定量分析,并与实验结果比照,进行氢键与手性自组装结构的形成趋势和稳定性的相关性研究。     

水分子在Bi(111)表面上的吸附和自组装

利用低温扫描隧道显微镜(STM)研究了水分子在半金属Bi(111)表面的吸附和自组装.当沉积速率比较低时,水分子主要以单体和二聚体的形式吸附在衬底表面.高分辨STM图表明,水单体平躺在衬底表面且占据on-top位.水二聚体表现为平行于衬底晶轴方向的两个亮点.当沉积速率比较高时,水分子自组装为单分散的六聚体阵列.每个六聚体表现为由3个亮点组成的三角形,其3个边分别平行于衬底晶轴方向.进一步分析表明,六聚体的3个亮点来自处于高位的3个水分子,一个H原子指向衬底上方,另一个H原子用于分子间氢键.处于低位的另外3个水分子,两个H原子参与分子间的氢键作用,因而在STM图中不易被观察到.我们认为,在半金属Bi(111)表面上水分子的自组装是一个动力学控制的生长过程.     

TTF、TCNQ及电荷转移复合物TTF-TCNQ在Au（111）表面吸附的ECSTM研究

研究发现当电极电位处于双层区时,三种分子在Au（111）电极表面均可形成高度有序的吸附结构.TTF与TCNQ分子有序吸附层的单胞结构分别为（6×3）和（4×7）,如图1中的模型所示,分子均是以平躺的方式吸附在Au（111）电极表面.而当电极电位向负方向移至0.08V（RHE）时,TCNQ分子的吸附结构发生了相转变,形成了一种单胞为（3√3×12）的新型结构.这是由于在较负的电位下,TCNQ分子与金电极之间的作用减弱,而相邻分子之间的排斥作用占据主导地位,使得相邻分子间的角度由原来的60°增大至90°,单胞结构发生了相应的改变.电荷转移复合物TTF-TCNQ在Au（111）表面则构筑了层状吸附结构,而且分子不再以平躺形式进行吸附,而是采取肩并肩站立的方式堆积成有序结构,与单纯两种分子在吸附结构和吸附方式上均不相同,如图2所示.此时π-π堆积作用在分子的组装过程中占据主导地位,该堆积方式与TTF-TCNQ单晶和薄膜的结构具有一定的相似性.     

D-，L-苯丙氨酸诱导非手性菁染料的手性组装

超分子手性与分子自组装是生命体中非常重要和有趣的现象．报道了D,L-苯丙氨酸等氨基酸在氯化钠溶液中通过非共价键相互作用诱导非手性菁染料（Pseudoisocyanine,PIC）J-聚集体超分子手性的形成．实验结果表明,诱导的手性菁染料PIC聚集体发色团在π-π^＊跃迁区域产生了特征的镜像圆二色性,其圆二色信号和强度强烈地依赖于氨基酸的绝对构型、浓度、侧链基团和溶液温度．原子力显微镜照片清楚地表明,^聚集体由相互交联的纳米纤维组成,诱导的圆二色性可能来源于纤维状聚集体的宏观螺旋排列．     

谷胱甘肽在汞表面吸附与自组装行为的原子力显微镜研究

用原子力显微镜研究谷胱甘肽（GSH）在汞表面的吸附与自组装状态。谷胱甘肽在汞表面首先形成非均匀地堡状吸附体,大部分单个吸附体高约10-13mn,半高直径约20nm。约每6个单吸附体以近似等边三角形形态自组装成一簇。随着吸附时间的延长,GSH可在汞表面自组装成约15nm的多分子层紧密层。与此同时,在紧密吸附层上可自组装成高约90—170nm、半高直径约130nm的特大吸附簇。     

Chirality transfer from a single chiral molecule to 2D superstructures in alaninol on the Cu(100) surface

The formation of 2D chiral monolayers obtained by self-assembly of chiral molecules on surfaces has been widely reported in the literature. Control of chirality transfer from a single molecule to surface superstructures is a challenging and important aspect for tailoring the properties of 2D nanostructures. However, despite the wealth of investigations performed in recent years, how chiral transfer takes place on a large scale still remains an open question. In this paper we report a coupling of scanning tunneling microscopy and low energy electron diffraction measurements with an original theoretical approach, combining molecular dynamics and essential dynamics with density functional theory, to investigate self-assembled chiral structures formed when alaninol adsorbs on Cu(100). The peculiarity of this system is related to the formation of tetrameric molecular structures which constitute the building blocks of the self-assembled chiral monolayer. Such characteristics make alaninol/Cu(100) a good candidate to reveal chiral expression changes. We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage or when geometrical confinement prevents long-range order. Conversely, a rotation of 14° with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. An insight to the process leading to a 2D globally chiral surface has been obtained by monitoring molecular assemblies as they grow from the early stages of adsorption, suggesting that the distinctive orientation of the self-assembled monolayer originates from a balance of cooperating forces which start acting only when tetramers pack together to form small clusters.     

Adsorption and assembly of copper phthalocyanine on cross-linked TiO2(110)-(1 x 2) and TiO2(210)

Copper phthalocyanine (CuPc) on reconstructed rutile TiO(2) was studied with ultrahigh vacuum variable temperature scanning tunneling microscopy. On cross-linked TiO(2)(110)-(1 x 2), the CuPc molecules at low coverages sparsely lay flat at the link sites and tilted in troughs between [001] rows. Increase of the CuPc coverage led to the trapping of the CuPc molecules by the rectangular surface cells fenced by the oxygen columns along the [001] direction and the cross-link rows. Each cell could trap one CuPc molecule at intermediate coverages and two CuPc molecules at higher coverages. On TiO(2)(210), the CuPc molecules tilted in defect-free areas and lay at defect sites with their molecular planes parallel to the substrate surface. Further increase of the CuPc coverage induced the formation of one- and two-dimensional assemblies on TiO(2)(210).     

Low-temperature mobility and structure formation of a prochiral aromatic thiol (2,5-dichlorothiophenol) on Cu(111)

We present a low-temperature scanning tunneling microscopy study of increasing coverages of 2,5-dichlorothiophenol, an asymmetrically halo-substituted aromatic thiol, on Cu(111). At low coverage, deprotonation of the thiol occurs spontaneously upon adsorption at 80 K. Albeit the low deposition temperature, we find the formation of adsorbate islands at low coverage, which coalesce into a well-ordered film of horizontally adsorbed molecules at increasing coverage. This behavior indicates (i) significant mobility of the thiols on Cu(111) even at low temperatures and (ii) attractive adsorbate-adsorbate interactions. At higher coverages intermolecular interactions prevent long-range diffusion of adsorbates and thermal activation of the S-H bond becomes necessary. A close analysis of the molecular films reveals chiral recognition between neighboring molecules, which leads to the formation of enantiopure areas on the surface. Upright orientation of individual molecules starts at the boundaries between such phases and can be induced by scanning tunneling microscopy.     

Rastertunnelmikroskopie an chiralen Molekülen: Nanochemie

The imaging and manipulation capabilities of the scanning tunnelling microscope (STM) render possible a novel nanoscale chemistry based on experiments with single molecules. Herein, we address several aspects of a nanoscale stereochemistry using the STM. As an example, we investigate 1‐nitronaphthalene on Au(111). 1‐Nitronaphthalene becomes chiral upon planar adsorption on the metal surface. High‐resolution STM images reflect the asymmetric electronic structure of the molecules and allow for the determination of the absolute configuration of any individual molecule within complex molecular structures. At medium coverage, spontaneous breaking of the chiral symmetry results in the formation of homochiral conglomerates, while at high coverage racemic structures prevail. Finally, the tip of the STM is used to separate “supramolecule‐by‐supramolecule” a racemic mixture of chiral 1‐nitronaphthalene aggregates into the enantiopure compounds.     

Investigation of the scanning tunneling microscopy image, the stacking pattern, and the bias-voltage-dependent structural instability of 1,10'-phenanthroline molecules adsorbed on Au(111) in terms of electronic structure calculations

A self-assembled monolayer of 1,10'-phenanthroline (phen) molecules on Au(111) was found to undergo a structural phase transition when the bias voltage is switched in scanning tunneling microscopy (STM) experiments (Phys. Rev. Lett. 1995, 75, 2376; Surf. Sci. 1997, 389, 19). The nature of two bright spots representing each phen molecule in the high-resolution STM images of phen molecules on Au(111) was identified by calculating the partial density plots for a monolayer of phen molecules adsorbed on Au(111) with tight-binding electronic structure calculations. The stacking pattern of chains of phen molecules on Au(111) was explained by studying the intermolecular interactions between phen molecules on the basis of first-principles electronic structure calculations for a phen dimer, (phen)(2). The structural instability of phen molecule arrangement caused by the bias-voltage switch was probed by estimating the adsorbate-surface interaction energy with the point-charge approximation for Au(111).     

Self-assembly of l-tryptophan on Cu(111) studied by low-temperature scanning tunneling microscopy

The self-assembly of l-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope (STM) at 4.4 K. When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer, molecular trimers, tetramers, hexamers, and chains coexist on Cu(111). Then almost all molecules self-assemble into chiral hexamers after being annealed at room temperature. When increasing molecular coverage to the full layer, a new type of chain is observed on the surface. Based on the high-resolution STM images at sub-molecular level, we suggest that the l-tryptophan molecules are present in neutral, zwitterionic or anionic states in these structures.     

Self-assembly of L-tryptophan on Cu(111) studied by low-temperature scanning tunneling microscopy

The self-assembly of L-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope (STM) at 4.4 K. A series of novel supramolecular structures have been prepared with different annealing temperatures.     

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces

Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface.     

Alkanethiol/Au(111) self-assembled monolayers contain gold adatoms: scanning tunneling microscopy before and after reaction with atomic hydrogen

Alkanethiol self-assembled monolayers on Au(111) are widely studied, yet the exact nature of the sulfur-gold bond is still debated. Recent studies suggest that Au(111) is significantly reconstructed, with alkanethiol molecules binding to gold adatoms on the surface. These adatoms are observed using scanning tunneling microscopy before and after removing the organic monolayer with an atomic hydrogen beam. Upon monolayer removal, changes in the gold substrate are seen in the formation of bright, triangularly shaped islands, decreasing size of surface vacancy islands, and faceting of terrace edges. A 0.143 +/- 0.033 increase in gold coverage after monolayer removal shows that there is one additional gold adatom for every two octanethiol molecules on the surface.