In situ STM study of zinc electrodeposition on Au(111) from the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate

The electrodeposition of Zn on Au(111) was investigated with cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) in the air and water stable ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) with a Zn(TfO)₂ concentration of 0.2 M. It has been found that the structure [EMIm]TfO/Au(111) is very complex. Furthermore, the addition of Zn(TfO)₂ changes the interfacial structure significantly. The first STM-probed Zn islands appear at +0.3 V, and their growth leads to the formation of a thin zinc layer. A bulk deposition of Zn is obtained with in situ STM at ?0.1 V. Furthermore, in situ STM reveals that the deposition of Zn is accompanied by the formation of Au-Zn surface alloys.     

Decorated Ru/Au(111) and Os/Au(111) surfaces: An in situ STM and electrochemistry study

The structure and reactivity of bimetallic electrodes obtained by spontaneous deposition of Ru and Os on Au(111) single-crystal surfaces are studied. In situ electrochemical STM and cyclic voltammetry are used to characterize a wide range of surface morphologies thus produced. The STM results on Ru/Au(111) demonstrate a pronounced step decoration, while a random distribution of Ru nuclei, quite uniform in size, occurs on terraces. Osmium deposits show a slight preference for deposition on steps, but it also occurs readily on terraces. However, many of the Os islands grow into multilayer heights. The coverage of the Au(111) by the deposited Ru or Os islands for a particular solution concentration depends on the deposition time. Nanostructures of Ru and Os are tested for catalytic behavior and correlated to CO oxidation activity as measured by CO stripping voltammetry. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1385–1392. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

In situ STM study of Au(111)/Os bimetallic surfaces: spontaneous deposition and electrochemical dissolution

We provide an electrochemical and structural characterization by in situ STM of Au(111)/Os electrodes prepared by spontaneous deposition of Os on Au(111). Surfaces with Os coverage values up to the saturation coverage were examined, from 10%. Using comparisons to previous work on Au(111)/Ru, Pt(111)/Ru, and Pt(111)/Os, we find that we may now generalize that Os deposits spontaneously faster than Ru and has a greater tendency to form 3-D structures. Additionally, the Au(111) substrate shows preferential step and near-step decoration in both cases, although it is less pronounced for Os than Ru. We also investigated the incremental dissolution of the Os from Au(111), to better understand electrochemical dissolution processes in general and to better control the Os deposit structure. The application of controlled electrochemical treatments (cyclic voltammetry up to increasingly positive values) significantly increased the dispersion of the Os deposit by generating smaller, more widely spaced islands. Upon voltammetry up to 0.75 V, the Au(111)/Os surface showed evidence of alloying and the formation of 3-D structures suggestive of strong Os-Os (oxidized) species interactions. The CO stripping results show the Au(111)/Os is not particularly effective for this reaction, but such results help to complete the overall picture of NM-NM catalytic combinations. Although the Au(111)/Os system itself is not catalytically active, the electrochemical manipulation of the deposit structure demonstrated here may be applied to other noble metal/noble metal (NM/NM) catalytic substrates to find optimal deposit morphologies.     

Ordered arrays of semi-crown ligands on an Au(111) electrode surface: in situ STM study

Self-organized systems have attracted much at-tention due to their potential applications in nano- technology as a bottom-up?approach for the con-struction of molecule-scale devices and nanostruc-tures[1—4]. Beyond the self-assembly of small molecu-lar building blocks, Schnherr et al. recently suc-ceeded in arranging the rosette supramolecular nanos-tructures in two dimensions on HOPG[5,6]. Moreover, interest has tremendously increased in the su-pramolecular structures via coordination-dr…     

In situ STM investigation of spinodal decomposition and surface alloying during underpotential deposition of Cd on Au(111) from an ionic liquid

The electrodeposition and anodic dissolution of Cd on Au(111) in an acidic chloroaluminate ionic liquid (MBIC-AlCl(3), 42 : 58 mol%) have been investigated by cyclic voltammetry and in situ STM. In the Cd underpotential deposition region, various nanostructures can be distinguished. At a potential of 0.95 V vs. Al/Al(iii), a transformation from a well ordered AlCl(4)(-) adlayer to a ( radical3 x radical19) superstructure, presumably due to Cd-AlCl(4)(-) coadsorption, is observed. Reducing the potential to 0.45 V, surface alloying of Cd and Au occurs, which is evidenced for the first time by typical spinodal structures occurring both during deposition and dissolution of the surface alloy layer having a hexagonal structure. At still lower potentials below 0.21 V, a layer-by-layer growth of bulk Cd sets in.     

An in situ STM study on the long-range surface restructuring of Au(1 1 1) in a non-chloroaluminumated ionic liquid

We report an in situ STM study of a potential-dependent long-range surface restructuring of Au(1 1 1) electrode in neat 1-butyl-3-methylimidazolium tetrafluoroborates (BMIBF₄) ionic liquid. Au(1 1 1) undergoes a significant long-range surface restructuring upon cathodic excursion to −1.0 V vs. Pt quasi-reference. The restructuring involves the formation of tiny pits, which then develops into a stable worm-like network with an average width of the network grids 2 nm. Electrochemical annealing occurs at the cathodic limit with the presence of a reduction product of cation BMI⁺. A smooth surface is recovered with the appearance of the typical (√3 × 22) reconstruction of Au(1 1 1). The surface restructuring is reestablished upon anodic excursion to −1.3 V after the adsorbed reduction product is oxidized. The long-range surface restructuring phenomenon is tentatively explained as a result of partial charge transfer to the weakly adsorbed BMI⁺, which reduces the metal–metal cohesive energy. In addition, the synergetic effect of the counter anion BF₄⁻ may also be involved. The results provide a knowledge of Au(1 1 1) electrode behavior in the neat ionic liquid and are beneficial to understanding in situ STM results involving surface morphological changes in such a media.     

Structure of thiocyanate adlayers on Rh(111): an in situ STM study

In situ scanning tunneling microscopy (STM) was used to examine the structure of thiocyanate adlayers specifically adsorbed on Rh(111) in solutions of potassium hydroxide and perchloric acid, both containing potassium thiocyanate (KSCN). An atomically flat terrace-step structure was consistently observed on Rh(111) surfaces prepared by the flame-annealing-quenching method. The Rh(111)-(1 × 1) atomic structure was discerned on the atomically flat terrace even in the alkaline solution. High-resolution STM images disclosed two different structures of the SCN⁻ adlayers, () and (2 × 2), in the alkaline and the acidic media, respectively. In each structure, an individual adsorbed SCN⁻ ion appeared as a single spot with a constant corrugation height in STM images, suggesting that SCN⁻ ions adsorbed predominantly with their S-ends at particular bonding sites on Rh(111). The difference in the adlayer structure in the two solutions can be attributed to the interaction between adsorbed SCN⁻ and coadsorbed K⁺ in the alkaline solution, and is different from that between adsorbed SCN⁻ and H⁺ in the acidic solution. Received: 26 February 1997 / Accepted: 3 March 1997     

Probing double layer structures of Au (111)-BMIPF6 ionic liquid interfaces from potential-dependent AFM force curves

High quality AFM force curves are presented with detailed potential dependent layering behaviors of the ionic liquid molecules, from which charged interior and neutral exterior layers are distinguished. The electric double layer is confined within the interior layers of one to two molecular size within the potential range of up to 1 V negative of the PZC.     

In situ STM investigation of gold reconstruction and of silicon electrodeposition on Au(111) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

The electrodeposition of silicon on Au(111) was investigated by cyclic voltammety (CV) and by in situ scanning tunneling microscopy (STM) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with a SiCl(4) concentration of 0.1 mol/L. A main reduction process begins in the cyclic voltammogram at about -1800 mV versus ferrocene/ferrocinium, which is correlated to the electrodeposition of elemental semiconducting silicon. It has been found that at an electrode potential more negative than the open circuit potential (OCP), the Au(111) surface is subject to a restructuring/reconstruction both in the case of the pure ionic liquid and in the presence of SiCl(4). The first STM-probed silicon islands with 150-450 pm in height appear at about -1700 mV versus ferrocene/ferrocinium. Their lateral and vertical growth leads to the formation of a rough layer with silicon islands of up to 1 nm in height. At about -1800 mV the islands merge and form silicon agglomerates. In situ I/U tunneling spectroscopy reveals a band gap of 1.1 +/- 0.2 eV for layers of about 5 nm in height, a value that has to be expected for semiconducting silicon.     

In situ STM imaging of polyethylene glycol adsorbed on an Au(111) electrode in pH 3

In situ scanning tunneling microscopy (STM) is used to examine the electrified interface of Au(111) immersed in a pH 3 sulfate medium containing polyethylene glycol (PEG) with an average molecular weight of 6000. The cyclic voltammograms thus obtained show two sharp peaks at − 0.35 and − 0.38 V (vs. reversible hydrogen electrode), which correlates with the STM observation of a highly ordered (2 × 2 √ 3)rect structure and the adsorption of PEGs. X-ray photoelectron spectroscopy is used to examine the film formed at − 0.4 V, revealing prominent C–C and C–O–C structures, thereby supporting the view of adsorption and reduction PEGs on the Au(111) electrode. STM imaging at the initial stage of PEG's adsorption reveals winding linear segments 0.6 nm wide and 20–40 nm long, implying helical conformations of PEGs. The PEG film dissolves and yields a high density of nanoclusters, as the potential is switched stepwise from − 0.4 to 0.9 V.     

The surface structure of flame-annealed Au(100) in aqueous solution: An STM study

The initial structure of flame-annealed Au(100) surfaces has been studied in air and in 0.1 M H₂SO₄ by scanning tunnelling microscopy (STM). It is shown that before, during and after contact with the electrolyte, at potentials sufficiently negative to prevent specific adsorption of anions, the flame-annealed Au(100) surface is reconstructed into exactly the same “hex” form as a surface which has been prepared by annealing in ultrahigh vacuum (UHV). However, the quality of the reconstructed surface depends sensitively on the sample preparation and on the experimental conditions of the flame-annealing procedure. The influence of the cooling procedure after flame annealing on the initial surface structure of the Au(100) electrode is demonstrated and briefly discussed in the light of results published previously.     

Oriented organic islands and one-dimensional chains on a Au(111) surface fabricated by electrodeposition: an STM study

Organic islands and oriented one-dimensional (1D) chains are fabricated on a Au(111) surface by electrodeposition. The cyclic voltammograms (CVs) of Au(111) in solutions containing nitrobenzene and picric acid show an electrochemical reaction in a negative potential region, which results in irreversible reductive deposition. The deposition process is monitored by in situ electrochemical scanning tunneling microscopy (ECSTM). At the double layer potential region, for example, nitrobenzene molecules form a well-defined adlayer in a (square root(3) x square root(3)) structure. With potential shifting negative to the reductive region, nitrobenzene is reduced to hydroxyaminobenzene. Organic islands were formed first and then aggregated into ordered 1D chains. The formation of these organic islands and 1D chains is completely potential-dependent. Intriguingly, the so-prepared islands and 1D chains are well-oriented along the reconstructed lines of the underlying Au(111) substrate and stable under ambient conditions even if the sample was removed from electrolyte solution. The results reported here provide a simple and effective method to fabricate oriented organic nanodots and nanowires on a solid surface by an electrochemical technique.     

Comparative electrochemical scanning tunneling microscopy study of nonionic fluorosurfactant zonyl FSN self-assembled monolayers on Au(111) and Au(100): a potential-induced structural transition

We investigate the structure of nonionic fluorosurfactant zonyl FSN self-assembled monolayers on Au(111) and Au(100) in 0.05 M H(2)SO(4) as a function of the electrode potential by electrochemical scanning tunneling microscopy (ECSTM). On Au(111), a (3(1/2) × 3(1/2))R30° arrangement of the FSN SAMs is observed, which remains unchanged in the potential range where the redox reaction of FSN molecules does not occur. On Au(100), some parallel corrugations of the FSN SAMs are observed, which originate from the smaller distance and the repulsive interaction between FSN molecules to make the FSN molecules deviate from the bridging sites, and ECSTM reveals a potential-induced structural transition of the FSN SAMs. The experimental observations are rationalized by the effect of the intermolecular interaction. The smaller distance between molecules on Au(100) results in the repulsive force, which increases the probability of structural change induced by external factors (i.e., the electrode potential). The appropriate distance and interactions of FSN molecules account for the stable structure of FSN SAMs on Au(111). Surface crystallography may influence the intermolecular interaction through changing the molecular arrangements of the SAMs. The results benefit the molecular-scale understanding of the behavior of the FSN SAMs under electrochemical potential control.     

In situ STM study of potential-dependent height change of a tetrathiafulvalene derivative embedded in alkanethiol self-assembled monolayers on Au(111)

Electroactive tetrathiafulvalene thiol islands embedded in an n-alkanethiol SAM matrix were studied under potential control using in situ scanning tunneling microscopy. Unlike previously studied stochastic switching, the apparent height of the island could be intentionally controlled in the present system by choosing the appropriate potential and the island size. The dependence of the height change on the potential and the size is explained as structural change of the island induced by the charging effect of the electroactive moiety.     

In situ STM study of potential-driven transitions in the film of a cationic surfactant adsorbed on a Au(111) electrode surface

Electrochemical scanning tunneling microscopy (EC-STM) has been employed to study the structure of a film formed by cationic surfactant N-decyl-N,N,N-trimethylammonium triflate (DeTATf) adsorbed on the Au(111) electrode surface. The film is disordered at potentials corresponding to either large negative charge densities or to positive charge densities. At small negative charge densities, an ordered adlayer of flat-lying DeTATf molecules is formed. High-resolution images of this adlayer reveal that the triflate anion is coadsorbed with the N-decyl-N,N,N-trimethylammonium cation, effectively forming an ion pair at the electrode surface. This is a significant result because it explains why this surfactant behaves like a zwitterionic surfactant at the metal/solution interface.     

An in situ STM and DTS study of the extremely pure [EMIM]FAP/Au(111) interface

Herein the structure of the interfacial layer between the air- and water-stable ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM]FAP) and Au(111) is investigated using in situ scanning tunneling microscopy (STM), distance tunneling spectroscopy (DTS) and cyclic voltammetry (CV) measurements. The in situ STM measurements reveal that structured interfacial layers can be probed in both cathodic and anodic regimes at the IL/Au(111) interface. The structure of these layers is dependent on the applied electrode potential, the number of subsequent STM scans and the scan rate. Furthermore, first DTS results show that the tunneling barrier during the 1st STM scan does not seem to change significantly in the cathodic potential regime between the ocp (-0.2 V) and -2.0 V.     

Structural comparison of self-organized adlayers of ligands and their metal-coordinated complexes on a Au(111) surface: an STM study

Scanning tunneling microscopy (STM) was employed to investigate the adsorption of the linear-spacer-bridged ligands bis(pyrrol-2-yl-methyleneamine) (BPMB and BPMmB), and their Zn(II)-coordinated complexes, BPMB/Zn(II) and BPMmB/Zn(II), onto a Au(111) surface in 0.1 M HClO(4) solution. Both the ligands, with different spacer bridges, and their Zn(II) complexes adsorb onto the Au(111) surface and self-organize into highly ordered two-dimensional arrays. The complexes BPMB/Zn(II) and BPMmB/Zn(II) appear in helical and triangular conformations, respectively, consistent with their chemical structures. Although the metal complexes include ligands, the assembled structures and adlayer symmetries of the ligands and complexes are totally different. The structures and intramolecular features obtained by high-resolution STM imaging are discussed. The results should be important in fabricating surface supramolecular structures.     

STM study of mixed alkanethiol/biphenylthiol self-assembled monolayers on Au(111)

A method is presented for depositing mixed self-assembled monolayers (SAMs) of dodecanethiol (C12) and 4'-methyl-1,1'-biphenyl-4-butane (H3C-C6H4-C6H4-(CH2)4-SH, BP4) by insertion of BP4 into a closely packed SAM of dodecanethiol on Au(111). Insertion takes place at defect sites such as domain boundaries or etch pits in the gold surface that are characteristic of C12 monolayers on gold. With a lower probability, insertion also occurs beside defect sites inside dodecanethiol domains. Insertion at defect sites results in domains of BP4, whereas insertion into C12 domains leads to isolated BP4 molecules. The isolated BP4 molecules are shown not to move at room temperature. By comparing the apparent height of the isolated BP4 molecules and BP4 domains, it is proposed that the isolated molecules have the same conformation as in the full-coverage phase. A simple two-layer model is proposed to characterize the current transport through BP4. The decay constant beta for the phenylene groups is deduced from the apparent STM heights of the inserted BP4 islands compared to the STM heights of the C12 closely packed monolayers.     

In situ STM evidence for the adsorption geometry of three N-heteroaromatic thiols on Au(111)

The electrochemical behavior of three heteroaromatic thiols (MBs) (2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzoxazole (MBO)) on a Au(111) surface has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV) in 0.1 M HClO(4) solution. All three thiols form oriented molecular cluster lines along the reconstruction line direction at 0.55 V. With the electrode potential shifting negatively, the molecules undergo a disordered-ordered structural transition. Molecularly resolved STM images show that all three molecules form striped adlayers in the desorption region on the Au(111) surface. The different heteroatoms in the heteroaromatic rings result in different electrochemical behavior of the MB self-assembled monolayers (SAMs). MBI, MBT, and MBO are proposed to interact with the substrate via the S-Au bonds from thiol group and the coordination interaction of N, S, and O with the substrate from the heteroaromatic ring, respectively. These results provide direct evidence of the electrochemical behavior and the adlayer structures of MB SAMs on the Au electrode.     

In-situ STM observation of the phase transition of two-dimensional 2,5-distyrylpyrazine nanostructure adsorbed on Au(111) in an electrochemical environment

The phase transition of 2,5-distyrylpyrazine (DSP) adsorbed on Au(111) substrate was studied as a function of the substrate potential in 0.1 M HClO 4 , using an in situ scanning tunneling microscope (STM). Depending on the applied electric field, DSP formed three distinctly different, two-dimensionally (2D) ordered, supramolecular nanostructures on the Au(111) surface. In the potential range of 0.55 V < E < 0.75 V, the DSP molecules formed a close-packed stripe pattern with the adlayer structure 1 3 . 8 6 When the potential was reduced to 0.45 V < E < 0.55 V, a ridge-like pattern built from dimer subunits was observed, with the adlayer structure 4 5 . 12 4 Further decreasing in the electrode potential to 0.2 V < E < 0.45 V caused the appearance of a herringbone-like pattern consisting of dimer subunits, with the adlayer structure 9 0 . 3 9 The potential-induced phase transitions revealed the structure-determining role of substrate-adsorbate coordination and intermolecular interaction in forming the distinct 2D adlayer motifs.