十七烷基苯酰胺的STM图像分析

通过两种扫描技术,得到不同尺寸下清晰的十七烷基苯酰胺分子图像,这些吸附在高度定向排列石墨基质(HOPG)上的十七烷基苯酰胺分子长轴与石墨表面平行,分子呈首尾一致的定向排列。图中不仅能清楚地识别分子骨架上的甲基或亚甲基,而且较大的苯酰胺基团也能与烷基链清晰地区别开来。     

Chirality in supramolecular self-assembled monolayers of achiral molecules on graphite: formation of enantiomorphous domains from arachidic anhydride

The molecular arrangement and chirality of the self-assembled arachidic anhydride monolayer on graphite were investigated using scanning tunneling microscopy (STM). This molecule has two identical alkyl chains, linked by an anhydride group in the middle. In its extended form, one alkyl chain is shifted, with respect to the other, along the molecular backbone. Upon adsorption on graphite, this achiral anhydride spontaneously forms two types of homogeneous domains (denoted as m and m') with mirror symmetry. The angle from the molecular chain to the row-packing direction is 98.0 degrees +/- 0.5 degrees and 82.0 degrees +/- 0.5 degrees for domains m and m', respectively. Domain m is the mirror image of m'. The molecular arrangement of this self-assembled monolayer shows that domains m and m' are two-dimensional enantiomers with opposite chiralities. This new molecular packing motif is confirmed by line-profile analyses along the molecule-chain and the row-packing directions. This finding demonstrates the spontaneous formation of highly ordered homogeneous enantiomorphous domains on graphite resulting only from weak van der Waals forces between the achiral arachidic anhydride molecules.     

Self-assembly of long chain alkanes and their derivatives on graphite

We combine scanning tunneling microscopy (STM) measurements with ab initio calculations to study the self-assembly of long chain alkanes and related alcohol and carboxylic acid molecules on graphite. For each system, we identify the optimum adsorption geometry and explain the energetic origin of the domain formation observed in the STM images. Our results for the hierarchy of adsorbate-adsorbate and adsorbate-substrate interactions provide a quantitative basis to understand the ordering of long chain alkanes in self-assembled monolayers and ways to modify it using alcohol and acid functional groups.     

STM imaging of a heptanuclear ruthenium(II) dendrimer, mono-add layer on graphite

Scanning tunneling microscopy (STM) and molecular mechanics calculations were used to investigate the long-range packing and the structure of an heptanuclear ruthenium (II) dendritic species, as a PF6- salt. STM imaging was carried out on a mono-add layer of the ruthenium dendrimer formed by physisorption from a 1,2,4-trichlorobenzene solution at the liquid-graphite interface. The packing of the molecules on the surface was visualised by the formation of ordered patterns and a distance of 27 +/- 2 A was measured between two adjacent lamellae. The comparison of this dimension with the molecular-modelling data indicates that the lamellae were formed by rows of dendrimer molecules in which the counterions (PF6-) were strongly associated with the Ru atoms. The images acquired with higher spatial resolution revealed the presence of repeating units within the lamellae. The comparison of the STM images with the modelling results allowed the attribution of the repeating units observed in the imaged pattern to the STM signature of single dendrimer molecules.     

Sum frequency generation vibrational spectroscopic and high-pressure scanning tunneling microscopic studies of benzene hydrogenation on Pt(111)

Sum frequency generation (SFG) vibrational spectroscopy and high-pressure scanning tunneling microscopy (HP-STM) have been used in combination for the first time to study a catalytic reaction. These techniques have been able to identify surface intermediates in situ during benzene hydrogenation on a Pt(111) single-crystal surface at Torr pressures. In a background of 10 Torr of benzene, STM is able to image small ordered regions corresponding to the c(2 radical3 x 3)rect structure in which each molecule is chemisorbed at a bridge site. In addition, individual benzene molecules are also observed between the ordered regions. These individual molecules are assumed to be physisorbed benzene on the basis of the SFG results showing both chemisorbed and physisorbed molecules. The surface becomes too mobile to image upon addition of hydrogen but is determined to have physisorbed and chemisorbed benzene present by SFG. It was spectroscopically determined that heating the platinum surface after poisoning with CO displaces benzene molecules. The high-coverage pure CO structure of (radical19 x radical19)R23.4 degrees imaged with STM is a verification of spectroscopic measurements.     

取代烷基侧链长度对二维纳米结构的影响

合成了一系列烷基取代的间苯三酚衍生物,并在大气条件下用扫描隧道显微镜研究了它们在高定向裂解石墨表面的吸附和组装行为.实验结果表明,这些自组装分子具有条状结构特征.在链长较短的分子图像中,两条平行的烷氧基链肩并肩地排列在苯环的一侧,另一条烷氧基链则排列在苯环的另一侧,链与链之间彼此相互交错排列形成均一的烷基条带.当链长增加时,这种高稳定性和密排结构遭到破坏,出现单个分子和分子对共存的组装结构.这是由于烷基链与烷基链之间以及烷基链与基底之间的作用力共同决定的.通过调控分子烷基链的长度可以得到不同的表面二维纳米结构.     

Effect of molecule-substrate interaction on thin-film structures and molecular orientation of pentacene on silver and gold

Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates have been studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-film structures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurements revealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which is attributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74+/-5 degrees and 46+/-5 degrees molecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene molecules stand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domains with molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to an average tilt angle of 46 degrees for the whole film and the change in valence band structures. STM and distance-voltage (z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties. z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase".     

液晶CPBOB吸附的STM研究

利用STM对吸附在导电基底上的液晶进行研究，能提供近原子分辨的液晶分子图象，这一创新不仅拓宽了STM的研究领域，也使STM成为研究液晶吸附的重要手段之一．根据液晶相变特征不同，样品的制备方法大致分四种情况：直接法，加热法，气相沉积法和溶剂法．无论采用以上哪种方法，     

STM study of morphology and electron transport features in cytochrome c and nanocluster molecule monolayers.

The morphology and electron tunneling through single cytochrome c and nanocluster Pt(5)(CO)(7)[P(C(6)H(5))](4) molecules organized as monolayer Langmuir-Blodgett (LB) films on graphite substrate have been studied experimentally using scanning tunneling microscopy (STM) and spectroscopy techniques with sub-nanometer spatial resolution in a double barrier tunnel junction configuration STM tip-monomolecular film-conducting substrate at ambient conditions. STM images of the films revealed globular structures with characteristic diameters (approximately 3.5 nm for the protein molecule and approximately 1.2 nm for the nanocluster). The spectroscopic study by recording the tunneling current-bias voltage (I-V) curves revealed tunneling I-V characteristics with features as steps of different width and heights that are dependent on the STM tip position over the molecule in the monolayer, giving evidence for sequential discrete electron-tunneling effects with the combination of the single electron Coulomb-charging energy and the electronic energy level separation (molecular spectrum) in such immobilized metalloprotein and nanocluster structures that can be of interest for the development of bioelectronic and hybrid functional nanosystems.     

Formation of one-dimensional C60 rows on TiO2(110)-1 x 2-cross-link structure and their local polymerization

Adsorption and growth of a C(60) monolayer on a TiO(2)(110)-1 x 2-cross-link structure were investigated by scanning tunneling microscopy (STM). Single C(60) molecules were preferentially anchored at the cross-link site due to interaction with undercoordinated Ti cations, and C(60) rows grew along the troughs between the 1 x 2-added rows. The C(60) monolayer structure is characterized by closely packed (r(C(60)-C(60)) = 1.0 nm) C(60) rows that are paired with every second added row (separation of paired rows is 1.1 nm). By applying a high negative bias voltage (-3.5 V) to an STM tip on the C(60) monolayer, C(60) oligomers were formed accompanied with the contraction of C(60)-C(60) distance along the C(60) row and bright contrast in the STM image.     

Edge-on bonding of benzene molecules in the second adsorbed layer on Cu(110)

The bilayer of benzene on Cu(110) was studied with temperature-programmed desorption (TPD), time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), and scanning tunneling microscopy (STM). TPD spectra show that three well-defined adsorption states exist. The alpha layer corresponds to the first layer containing flat-lying benzene molecules. As coverage increases, the beta layer forms on top of the alpha layer, and eventually, a multilayer, gamma, forms. TPD measurements show that the number of benzene molecules in the beta layer is equal to the number of benzene molecules in the alpha layer. ESDIAD measurements establish that the orientation of the benzene molecules in the beta layer is edge-on, with two C-H bonds directed toward the surface. STM images of the beta layer reveal closely spaced edge-on benzene molecules arranged in repeating hexagons, as well as loosely spaced benzene molecules with greater apparent height, which are also edge-on species. Correlation between the different measurements suggests a structural model for the benzene bilayer.     

STM studies on adsorbed liquid crystal on HOPG

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Low-temperature STM images of methyl-terminated Si(111) surfaces

Low-temperature scanning tunneling microscopy (STM) has been used to image CH(3)-terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a well-ordered structure commensurate with the atop sites of an unreconstructed 1 x 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 +/- 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 +/- 3 degrees away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident.     

Assembly dynamics and detailed structure of 1-propanethiol monolayers on Au(111) surfaces observed real time by in situ STM

1-Propanethiol is chosen as a model alkanethiol to probe detailed mechanisms of the self-assembled monolayer (SAM) formation at aqueous/Au(111) interfaces. The assembly processes, including initial physi- and chemisorption, pit formation, and domain growth, were recorded into movies in real-time with high resolution by in situ scanning tunneling microscopy (STM) under potential control. Two major adsorption steps were disclosed in the propanethiol SAM formation. The first step involves weak interactions accompanied by the lift of the Au(111) surface reconstruction, which depends reversibly on the electrochemical potentials. The second step is chemisorption to form a dense monolayer, accompanied by formation of pits as well as structural changes in the terrace edges. Pits emerged at the stage of the reconstruction lift and increased to a maximum surface coverage of 4.0 +/- 0.4% at the completion of the SAM formation. Well-defined triangular pits in the SAM were found on the large terraces (more than 300 nm wide), whereas few and small pinholes appeared at the terrace edge areas. Smooth edges were converted into saw-like structural features during the SAM formation, primarily along the Au(111) atomic rows. These observations suggest that shrinking and rearrangement of gold atoms are responsible for both formation of the pits and the shape changes of the terrace edges. STM images disclose a (2 square root 3 x 3)R30 degrees periodic lattice within the ordered domains. Along with electrochemical measurements, each lattice unit is assigned to contain four propanethiol molecules exhibiting different electronic contrasts, which might originate in different surface orientations of the adsorbed molecules.     

Incorporation and manipulation of coronene in an organic template structure

A two-dimensional molecular template structure of 1,3,5-benzenetricarboxylic acid (trimesic acid, TMA) was formed on a highly oriented pyrolytic graphite surface (HOPG) by self-assembly at the liquid-solid interface. Scanning tunneling microscopy (STM) investigations show high-resolution images of the porous structure on the surface. After the host structure was created, coronene molecules were inserted as guest molecules into the pores. STM results indicate that some of the guest molecules rotate inside their molecular bearing. Further investigations show that single coronene molecules can be directly kicked out of their pores by means of STM.     

Coexistence of multiple conformations in cysteamine monolayers on Au(111)

The structural organization, catalytic function, and electronic properties of cysteamine monolayers on Au(111) have been addressed comprehensively by voltammetry, in situ scanning tunneling microscopy (STM) in anaerobic environment, and a priori molecular dynamics (MD) simulation and STM image simulation. Two sets of voltammetric signals are observed. One peak at -(0.65-0.70) V (SCE) is caused by reductive desorption of cysteamine. The other signal, at -(0.25-0.40) V consists of a peak doublet. The pH dependence of the latter suggests that the origin is catalytic dihydrogen evolution. The doublet feature is indicative of two distinct cysteamine configurations. Cysteamine monolayer formation from initial nucleation to a highly ordered phase has been successfully observed in real time using oxygen-free in situ STM. Random cellular patterns, disordered adlayer formation accompanied by high step edge mobility, and ultimately a highly ordered (square root 3 x 4) R30 degrees lattice are observed sequentially. Pits are formed due to enclosure of the mobile edges during the adsorption process. In the highly ordered cysteamine layer, each unit has two spots with apparent 0.6 A height difference in STM images. The coverage 5.7 +/- 0.1 x 10(-10) mol cm(-2) determined by voltammetry supports that the spots represent two individual cysteamine molecules. A priori MD and density functional simulations hold other clues to the image interpretation and indicate that the NH(3)(+) groups dominate the tunneling contrast. A wide range of interface structures, showing variations in the sulfur binding site and orientation, gauche and trans conformers, and especially hydrogen-bonding interactions, are examined, from which it is concluded that the adsorbate structure is controlled by interactions with the solvent rather than with the substrate.     

Topography Structure and Scanning Tunneling Spectrum of Nickel（Ⅱ）-tetraphenylporphyrin Molecules on Au（111）

1 INTRODUCTION Metalloporphyrins are intensively studied for many reasons. They have been comprehensively used in biochemistry, analytical chemistry and so on. They play an important role in biological processes such as oxygen transport photosynthesis and enzyme catalysis. They can act as catalysts[1], and can undergo reversible redox reactions in which the site of electron transfer may be localized on the por- phyrin ring or on the central metal ion. Both reaction types are important in…     

Topography Structure and Scanning Tunneling Spectrum of Nickel(Ⅱ)-tetraphenylporphyrin Molecules on Au(111)

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.     

Nanometer-scale ordering in cast films of columnar metallomesogen as revealed by STM observations

STM observations were performed on a cast film of a columnar metallomesogen ([Cr(5C8)3]; 5C8 = 1-(3,4,5-trioctyloxyphenyl)-3-(3,4-dioctyloxyphenyl)propane-1,3-dionate anion) on a graphite surface, revealing the nanometer-scale surface ordering into an oblique lattice (a = 10.5 nm, b = 11.5 nm, alpha = 55 degrees) possibly due to the DeltaLambda-chiral interactions.     

Self-assembly of (perfluoroalkyl)alkanes on a substrate surface from solutions in supercritical carbon dioxide

Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly.