离子液体中Au(111)和Pt(111)表面Ge欠电位沉积的现场STM研究

本文研究BMIPF₆离子液体中Au(111)和Pt(111)表面Ge的电沉积行为. 循环伏安法测试结果表明,在含0.1 mol·L^-1 GeCl₄的BMIPF₆溶液Au(111)和Pt(111)表面均有两个与Ge沉积过程相关的还原峰. 第一个还原峰包含了Ge⁴⁺还原成Ge²⁺及Ge的欠电位沉积,第二个还原峰对应Ge的本体沉积. 现场扫描隧道显微镜研究结果表明,Ge在Au(111)和Pt(111)表面均有两层欠电位沉积. 第一层欠电位沉积厚度约为0.25 nm、形貌平整、带有缝隙的亚单层结构. 第二层欠电位沉积形貌相对粗糙的点状团簇结构. 该欠电位沉积过程伴随表面合金化.     

Characterization of self-assembled monolayers of thiols on Au(111)

Self-assembled monolayers (SAMs) of n-butanethiol, n-dodecanethiol and their equimolar mixture on Au(111) were prepared and characterized by ellipsometry, contact angle measurement, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results revealed that these SAMs are oriented ultrathin films with the thickness of nanometer scale, and the SAMs were influenced by the molecular chain length, the lattice orientation and cleanliness of the substrates. The surface of the longer chain SAM is hydrophobic. The thicknesses of three SAMs of n-butanethiol, n-dodecanethiol and their mixture revealed by ellipsometry and XPS are about 0.59 - 0.67nm, 1.60- 1.69 nm and 1.23 - 1.32nm, respectively. AFM images further demonstrated that the SAM formed by the mixture has some microdomains with two different thicknesses.     

Synthesis of TiO2 nanoparticles on the Au(111) surface

The growth of titanium oxide nanoparticles on reconstructed Au(111) was investigated by scanning tunneling microscopy and x-ray photoelectron spectroscopy. Ti was deposited by physical-vapor deposition at 300 K. Regular arrays of titanium nanoparticles form by preferential nucleation of Ti at the elbow sites of the herringbone reconstruction. The titanium oxide nanoclusters were synthesized by subsequent exposure to O(2) at 300 K. Two-and three-dimensional titanium oxide nanocrystallites form during annealing in the temperature range from 600 to 900 K. At the same time, the Au(111) surface assumes a serrated 110-oriented step-edge morphology suggesting step-edge pinning by titanium oxide nanoparticles. The oxidation state of the titanium oxide nanoparticles varies with annealing temperature. Specifically, annealing to 900 K results in the formation of stoichiometric TiO(2) nanocrystals as judged by the Ti(2p) binding energies measured in the x-ray photoelectron data. The nanodispersed TiO(2) on Au(111) is an ideal system to test the various models proposed for the enhanced catalytic reactivity of supported Au nanoparticles.     

Dispersion and STM Characterization of Au-CdSe Nanohybrids on Au(111)

We report the dispersion and scanning tunneling microscopy (STM) characterization of iso-lated Au-CdSe nanohybrids on atomically flat Au(111) through surface modifications. The top terminal groups of spacer molecules self-assembled on the surface are found critical for locking the nanohybrids into a well-separated state. The STM results indicate that both thiol and carboxylic terminals are effective in this aspect by making strong interaction with the Au portions of the nanohybrids. An argon ion sputtering technique is also proposed to clean up organic contaminants on the surface for improved STM imaging of individual Au-CdSe nanohybrids. These observations help to enrich technical approaches to dispersing individual nanostructures on the surface and provide opportunities to explore their local electroluminescent and energy transfer properties at the nanoscale.     

Epitaxial supramolecular assembly of fullerenes formed by using a coronene template on a Au(111) surface in solution

Characteristic properties of the coronene layer formed on Au(111) for the epitaxial growth of various fullerenes are described. The electrochemical behavior of the coronene adlayer prepared by immersing a Au(111) substrate into a benzene solution containing coronene was investigated in 0.1 M HClO4. The as-prepared coronene adlayer on Au(111) revealed a well-defined (4 x 4) structure. Structural changes of the array of coronene molecules induced by potential manipulation were clearly observed by in situ scanning tunneling microscopy (STM). Supramolecularly assembled layers of fullerenes such as C60, C70, C60-C60 dumbbell dimer (C120), C60-C70 cross-dimer (C130), and C60 triangle trimer (C180) were formed on the well-defined coronene adlayer on the Au(111) surface by immersing the coronene-adsorbed Au(111) substrate into benzene solutions containing those molecules. The adlayers thus prepared were characterized by comparison with those which were directly attached to the Au(111) surface. The C60 molecules formed a honeycomb array with an internal structure in each C60 cage on the coronene adlayer, whereas C70 molecules were one-dimensionally arranged with the same orientations. The dimers, C120 and C130 molecules, formed an identical structure with c(11 x 4 radical3)rect symmetry. For the C130 cross-dimer molecule, C60 and C70 cages were clearly recognized at the molecular level. It was difficult to identify the adlayer of the C180 molecule directly attached to Au(111); however, individual C180 molecules could be recognized on the coronene-modified Au(111) surface. Thus, the adlayer structures of those fullerenes were strongly influenced by the underlying coronene adlayer, suggesting that the insertion of a coronene adlayer plays an important role in the formation of supramolecular assemblies of fullerenes.     

Characterization of mixed alcohol monolayers adsorbed onto a Au(111) electrode using electro-fluorescence microscopy

A single-crystal Au(111) electrode modified with an adsorbed layer of 1-octadecanol (C18OH) or oleyl alcohol (OLA) in pure or mixed composition was characterized using electrochemical and in situ fluorescence microscopy. Cyclic voltammetry and differential capacitance measurements revealed a repeatable, potential-induced adsorption/desorption process of the surfactant to/from the electrode surface while charge density and film pressure measurements indicated quasi-ideal mixing of the two adsorbed alcohols. A layer less defective than pure C18OH was created with incorporated OLA. Optical characterization was accomplished using epi-fluorescence microscopy combined with electrochemistry (electro-fluorescence microscopy) through the incorporation of two fluorescent probes into the adsorbed surfactant layer. Since molecular luminescence is quenched by a nearby metal, fluorescence was only observed when the fluorescent dye/alcohol layers were desorbed and therefore separated from the metal surface. When desorbed, the structure of the alcohol layers were similar in character, revealing aggregated features which did not change in morphology over numerous desorption/re-adsorption cycles. We have also used the electro-fluorescence technique to estimate the distance separating the metal and desorbed surfactant and believe that the molecules are displaced from the electrode surface by a distance not more than 40 nm.     

Scanning tunneling microscopy studies of pulse deposition of dinuclear organometallic molecules on Au(111)

Ultrahigh-vacuum scanning tunneling microscopy (STM) was used to study trans-[Cl(dppe)2Ru(C Triple Bond C)6Ru(dppe)2Cl] [abbreviated as Ru2, diphenylphosphinoethane (dppe)] on Au(111). This large organometallic molecule was pulse deposited onto the Au(111) surface under ultrahigh-vacuum (UHV) conditions. UHV STM studies on the prepared sample were carried out at room temperature and 77 K in order to probe molecular adsorption and to characterize the surface produced by the pulse deposition process. Isolated Ru2 molecules were successfully imaged by STM at room temperature; however, STM images were degraded by mobile toluene solvent molecules that remain on the surface after the deposition. Cooling the sample to 77 K allows the solvent molecules to be observed directly using STM, and under these conditions, toluene forms organized striped domains with regular domain boundaries and a lattice characterized by 5.3 and 2.7 A intermolecular distances. When methylene chloride is used as the solvent, it forms analogous domains on the surface at 77 K. Mild annealing under vacuum causes most toluene molecules to desorb from the surface; however, this annealing process may lead to thermal degradation of Ru2 molecules. Although pulse deposition is an effective way to deposit molecules on surfaces, the presence of solvent on the surface after pulse deposition is unavoidable without thermal annealing, and this annealing may cause undesired chemical changes in the adsorbates under study. Preparation of samples using pulse deposition must take into account the characteristics of sample molecules, solvent, and surfaces.     

Pb deposition on I-coated Au(111). UHV-EC and EC-STM studies

This article concerns the growth of an atomic layer of Pb on the Au(111)( radical3 x radical3)R30 degrees -I structure. The importance of this study lies in the use of Pb underpotential deposition (UPD) as a sacrificial layer in surface-limited redox replacement (SLRR). SLRR reactions are being applied in the formation of metal nanofilms via electrochemical atomic layer deposition (ALD). Pb UPD is a surface-limited reaction, and if it is placed in a solution of ions of a more noble metal, redox replacement can occur, but limited by the amount of Pb present. Pb UPD is a candidate for use as a sacrificial layer for replacement by any more noble element. It has been used by this group for both Cu and Pt nanofilm formation using electrochemical ALD. The I atom layer was intended to facilitate electrochemical annealing during nanofilm growth. Two distinctly different Pb atomic layer structures are reported, studied using in situ scanning tunneling microscopy (STM) with an electrochemical flow cell and ultrahigh vacuum surface analysis combined directly with electrochemical reactions (UHV-EC). Starting with the initial Au(111)( radical3 x radical3)R30 degrees -I, 1/3 monolayer of I on the Au(111) surface, Pb deposition began at approximately 0.1 V. The first Pb UPD structure was observed just below -0.2 V and displayed a (2 x radical3)-rect unit cell, for a structure composed of 1/4 monolayer each of Pb and I. The I atoms fit in Pb 4-fold sites, on the Au(111) surface. The structure was present in domains rotated by 120 degrees. Deposition to -0.4 V resulted in complete loss of the I atoms and formation of a Pb monolayer on the Au(111), which produced a Moiré pattern, due to the Pb and Au lattice mismatch. These structures represent two well-defined starting points for the growth of nanofilms of other more noble elements. It is apparent from these studies that the adsorption of I- on Pb is weak, and it will rinse away. If Pb is used as a sacrificial metal in an electrochemical ALD cycle and adsorbed I atoms are employed for electrochemical annealing, I atoms will need to be applied each cycle.     

Mechanism for nucleation and growth of electrochemical palladium deposition on an Au(111) electrode

The initial kinetics of electrochemical deposition of palladium on an Au(111) electrode in 0.1 M H₂SO₄ solution containing K₂PdCl₄ have been investigated quantitatively by cyclic voltammetry (CV) and potentiostatic current transient measurements. A cathodic current maximum was observed in the initial stage of Pd deposition process in 0.1 mM K₂PdCl₄ solution. The analysis shows that the deposition of palladium in this solution proceeds by an instantaneous nucleation and two-dimensional (2D) growth mode. When the concentration of K₂PdCl₄ became higher, a potential-dependent cathodic current ‘plateau’ after the current maximum was observed. Simple nucleation-growth models cannot fit the transients in the region of the ‘current plateau’. The present current transient results were discussed in comparison with the results obtained by in situ scanning tunneling microscopy (STM).     

In situ friction study of Ag Underpotential deposition (UPD) on Au(111) in aqueous electrolyte

The electrodeposition of silver on Au(111) was investigated using lateral force microscopy (LFM) in Ag⁺ containing sulfuric acid. Friction force images show that adsorbed sulfate forms structure ( on Au(111) prior to Ag underpotential deposition (UPD) and structure ( ) on a complete monolayer or bilayer of Ag. Variation of friction with normal load shows a non-monotonous dependence, which is caused by increasing penetration of the tip into the sulfate adlayer. In addition, the friction force is influenced by the varying coverage and mobility of Ag atoms on the surface. Before Ag coverage reaches the critical value, the deposited silver atoms may be mobile enough to be dragged by the movement of AFM tip. Possible penetration of the tip into the UPD layer at very high loads is discussed as a model for self-healing wear. However, when the coverage of Ag is close to 1, the deposited Ag atoms are tight enough to resist the influence of the AFM tip and the tip penetrates only into the sulfate adlayer.     

氧化锌有序结构在Au(111)和Cu(111)上的生长

利用NO₂或O₂作为氧化剂,研究了氧化锌在Au(111)和Cu(111)上的生长和结构。NO₂表现了更好的氧化性能,有利于有序氧化锌纳米结构或薄膜的生长。在Au(111)和Cu(111)这两个表面上,化学计量比氧化锌都形成非极性的平面化ZnO(0001)的表面结构。在Au(111)上,NO₂气氛下室温沉积锌倾向于形成双层氧化锌纳米结构;而在更高的沉积温度下,在NO₂气氛中沉积锌则可同时观测到单层和双层氧化锌纳米结构。O₂作为氧化剂时可导致形成亚化学计量比的ZnO_x结构。由于铜和锌之间的强相互作用会促进锌的体相扩散,并且铜表面可以被氧化形成表面氧化物,整层氧化锌在Cu(111)上的生长相当困难。我们通过使用NO₂作为氧化剂解决了这个问题,生长出了覆盖Cu(111)表面的满层有序氧化锌薄膜。这些有序氧化锌薄膜表面显示出莫尔条纹,表明存在一个ZnO和Cu(111)之间的莫尔超晶格。实验上观察到的超晶格结构与最近理论计算提出的Cu(111)上的氧化锌薄膜结构相符,具有最小应力。我们的研究表明,氧化锌薄膜的表界面结构可能会随氧化程度或氧化剂的不同而变化,而Cu(111)的表面氧化也可能影响氧化锌的生长。当Cu(111)表面被预氧化成铜表面氧化物时,ZnO_x的生长模式会发生变化,锌原子会受到铜氧化物晶格的限域形成单位点锌。我们的研究表明了氧化锌的生长需要抑制锌向金属基底的扩散,并阻止亚化学计量比ZnO_x的形成。因此,使用原子氧源有利于在Au(111)和Cu(111)表面上生长有序氧化锌薄膜。     

The electrochemical characterisation of benzyl mercaptan-modified Au(111): structure and copper deposition

The behaviour of benzyl mercaptan self-assembled monolayers on Au(111) in sulfuric acid solution was studied using cyclic voltammetry and in situ scanning tunnelling microscopy. Modification of the Au(111) surface in an ethanolic solution of benzyl mercaptan leads to a disordered monolayer. However, by partial reductive desorption a striped c (15 x sqrt [3]) and a (2 x sqrt [3]) structure were obtained. The disordered benzyl mercaptan film was also used for the study of copper deposition. At -0.02 V versus SCE, that is in the underpotential deposition region, monoatomic high islands appear on the surface. Bulk deposition of copper starts at -0.08 V versus SCE with the growth of dendrites underneath the thiol film. At higher overpotentials, the growth of three-dimensional copper clusters commences.     

Adsorptive behavior of dimethylglyoxime on Au(111)

Dimethylglyoxime (DMG) adsorbed on Au(111) was investigated using electrochemical scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM experiments revealed three different structures of adsorbed DMG at open circuit potential (~0.07 V versus Ag/AgCl): (2√3×2√3)R30°-α, (2√3×4√3)R30°-β, and (2√3×4√3)R30°-γ. The coverage of adsorbed DMG obtained using XPS was 0.33. A combination of structural and quantitative information identified the adsorbed DMG as an anionic tetramer, held together by intermolecular hydrogen bonding and arrayed in three ordered patterns. Domains of adsorbed DMG underwent phase transitions between the observed structures, most likely due to the influence of the STM tip. However, a significant correlation between the observed structures and the imaging conditions was not found. The ordered layers existed only at open circuit potential as evidenced by their disappearance when the potential was shifted to 0.2 or -0.15 V. The ordered layers were also removed by immersion in a solution of Ni(2+), implying that the adsorbed DMG was converted to a soluble dimer complex with the Ni(2+) ion. This particular observation is discussed in terms of the rigidity of the organic network.     

In situ stress and nanogravimetric measurements during underpotential deposition of bismuth on (111)-textured Au

The surface stress associated with the underpotential deposition (upd) of bismuth on (111)-textured Au is examined, using the wafer curvature method, in acidic perchlorate and nitrate supporting electrolyte. The surface stress is correlated to Bi coverage by independent nanogravimetric measurements using an electrochemical quartz crystal nanobalance. The mass increase measured in the presence of perchlorate is consistent with the (2 x 2) and (p x square root 3)-2Bi adlayers reported in the literature. ClO(4)(-) does not play a significant role in the upd process. The complete Bi monolayer causes an overall surface stress change of about -1.4 N m(-1). We attribute this compressive stress to the formation of Bi-Au bonds which partially satisfy the bonding requirements of the Au surface atoms, thereby reducing the tensile surface stress inherent to the clean Au surface. At higher Bi coverage, an additional contribution to the compressive stress is due to the electrocompression of the (p x square root 3)-2Bi adlayer. In nitric acid electrolyte, NO(3)(-) coadsorbs with Bi over the entire upd region but has little fundamental impact on adlayer structure and stress.     

Self-assembly of alkanols on Au(111) surfaces

Self-assembled monolayers (SAMs) of alkanols (1-C(N)H(2N+1)OH) with varying carbon-chain lengths (N = 10-30) have been systematically studied by means of scanning tunneling microscopy (STM) at the interfaces between alkanol solutions (or liquids) and Au(111) surfaces. The carbon skeletons were found to lie flat on the surfaces. This orientation is consistent with SAMs of alkanols on highly oriented pyrolytic graphite (HOPG) and MoS2 surfaces, and also with alkanes on reconstructed Au(111) surfaces. This result differs from a prior report, which claimed that 1-decanol molecules (N = 10) stood on their ends with the OH polar groups facing the gold substrate. Compared to alkanes, the replacement of one terminal CH3 group with an OH group introduces new bonding features for alkanols owing to the feasibility of forming hydrogen bonds. While SAMs of long-chain alkanols (N > 18) resemble those of alkanes, in which the aliphatic chains make a greater contribution, hydrogen bonding plays a more important role in the formation of SAMs of short-chain alkanols. Thus, in addition to the titled lamellar structure, a herringbone-like structure, seldom seen in SAMs of alkanes, is dominant in alkanol SAMs for values of N < 18. The odd-even effect present in alkane SAMs is also present in alkanol SAMs. Thus, the odd N alkanols (alkanols with an odd number of carbon atoms) adopt perpendicular lamellar structures owing to the favorable interactions of the CH3 terminal groups, similar to the result observed for odd alkanes. In contrast to alkanes on Au(111) surfaces, for which no SAMs on an unreconstructed gold substrate were observed, alkanols are capable of forming SAMs on either the reconstructed or the unreconstructed gold surfaces. Structural models for the packing of alkanol molecules on Au(111) surfaces have been proposed, which successfully explain these experimental observations.     

Reconstruction-Dependant Self-Assembly of n-Alkanes on Au(111)

Highly ordered molecular monolayers at the solid/liquid interfaces play a critical role in many technologically important areas, such as lubrication, adhesion, molecular recognition and chemical reactions. Although there are a number of results on the monolayers of organic molecules physisorbed on the solid surfaces being reported, the role of the substrate lattice parameters, the substrate structures and the defects in the formation of the highly ordered monolayers has not yet well explored. In this paper, we reported the scanning tunneling microscopy (STM) studies of the self-assembling phenomenon of n-alkanes in the interfaces between n-alkane solutions and the Au(111) surfaces.     

Multiple two-dimensional structures formed at monolayer and submonolayer coverages of p-sexiphenyl on the Au(111) surface

The two-dimensional structures formed by monolayers and submonolayers of p-sexiphenyl (p-6P) molecules evaporated onto the Au(111) surface are investigated using ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Five different 2D structures corresponding to different surface coverages are discovered and their 2D structures solved. The trends in the molecular alignment with respect to the underlying gold lattice are discussed. An unusual structure that consists of paired rows of p-6P molecules was discovered. A surface structure with alternating domains of slightly differently packed p-6P molecules was also found. The boundary between these two domains contains systematic molecular vacancies.     

Chiral structures of 6,12-dibromochrysene on Au(111) and Cu(111) surfaces

Nanoscale low-dimensional chiral architectures are increasingly receiving scientific interest, because of their potential applications in many fields such as chiral recognition, separation and transformation. Using 6,12-dibromochrysene (DBCh), we successfully constructed and characterized the large-area two-dimensional chiral networks on Au(111) and one-dimensional metal-liganded chiral chains on Cu(111) respectively. The reasons and processes of chiral transformation of chiral networks on Au(111) were analyzed. We used scanning tunneling spectroscopy (STS) to analyze the electronic state information of this chiral structure. This work combines scanning tunneling microscopy (STM) with non-contact atomic force microscopy (nc-AFM) techniques to achieve ultra-high-resolution characterization of chiral structures on low-dimensional surfaces, which may be applied to the bond analysis of functional nanofilms. Density functional theory (DFT) was used to simulate the adsorption behavior of the molecular and energy analysis in order to verify the experimental results.