Reflection Surface-enhanced Infrared Absorption Spectroscopy Research Articles

Spectroelectrochemical behavior of 4-aminobenzenethiol on nanostructured platinum and silver electrodes

The adsorption of 4-aminobenzenethiol (4-ABT) on Ag and Pt nanoparticles is studied by spectroelectrochemical means (cyclic voltammetry, Surface-Enhanced Raman Spectroscopy (SERS) and Surface-Enhanced Infrared Reflection Absorption Spectroscopy (SEIRAS)). Similar SERS spectra are obtained when 4-ABT is adsorbed on platinum and silver nanostructured substrates. In addition, unless a low power density of the laser is used, these spectra show, both under open circuit conditions and when applying electrode potentials above −0.50V vs AgCl/Ag, bands not observed in the normal Raman spectrum of 4-ABT. These bands disappear when the electrode potential is shifted to more negative values. Conversely, the SEIRA spectra of 4-ABT adsorbed on Ag do not show any significant change with the electrode potential, which indicates that there are no new species electrochemically formed in the range of potentials considered, which include some anodic and cathodic processes as shown in the corresponding cyclic voltammograms. In this regard, SERS measurements put in evidence the time dependence of the spectra obtained at potentials above −0.50V just after switching on the laser suggesting the formation of new species, probably dimercaptoazobenzene (4-4′-DMAB), formed by a photochemical process of the adsorbed 4-ABT.

Infrared Spectroscopy of Thin Organic Films Adsorbed at a Gold Electrode Surface

This lecture will review our research involving IR spectroscopy at the solid –liquid interface. After a brief review of basic principles of IR spectroscopy and the laws of reflection of light at interfaces, three methods of Infrared Reflection Absorption Spectroscopy (IRRAS) will be described. The first is subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) or in short potential difference IR spectroscopy. This technique finds application to study reversible adsorption of soluble molecules at electrode surfaces. The methods of optimisation of the SNIFTIRS experiment will be discussed. Its application will be illustrated by the case of adsorption of a soluble surfactant such as sodium dodecyl sulphate (SDS) at a gold electrode surface.1 The second technique to measure IR spectra at interfaces is the photon polarization modulation infrared reflection absorption spectroscopy (PM IRRAS). This technique is used to study films of insoluble molecules a various interfaces. I will discuss application of this technique to study model biological membranes supported at a gold electrode surface.2 The third technique is the surface enhanced infrared reflection absorption spectroscopy (SEIRAS). It is performed using attenuated total internal reflection (ATR) element covered by nanoparticles of gold. The intensity of the IR signal is then enhanced by a factor of 100. In addition, since the film of metal nanoparticles is conductive it is used to study phenomena at electrified interfaces. I will describe application of this technique to study structure of water in model biological membrane supported at a gold electrode surface.3 I will emphasize complementarity of SEIRAS and PMIRRAS in application to bio-electrochemical research.Literature1.Jay Leitch, John Collins, K. Andreas Friedrich, Ulrich Stimming, John R. Dutcher, Jacek Lipkowski “Infrared Studies of the Potential Controlled Adsorption of Sodium Dodecyl Sulfate at the Au(111) Electrode Surface”, Langmuir, 2012,28,2455-2464.2. Jacek Lipkowski, “Building model biomimetic membrane at a gold electrode surface”, Phys. Chem. Chem. Phys., 2010,12,13874-13887.3. Taro Uchida, Masatoshi Osawa and Jacek Lipkowski, “SEIRAS studies of water structure at the gold electrode surface in the presence of supported lipid bilayer”, J.Electroanal.Chem. DOI:10.1016/j.jelechem.2013.10.015

Electrocatalysis of Ethanol on a Pd Electrode in Alkaline Media: An in Situ Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy Study

In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy in conjunction with H–D isotope replacement is used to investigate the dissociation and oxidation of CH3CH2OH on a Pd electrode in 0.1 M NaOH, with a focus on identifying the chemical nature of the pivotal intermediate in the so-called dual-pathway (C1 and C2) reaction mechanism. Real-time spectroelectrochemical measurements reveal a band at ∼1625 cm–1 showing up prior to the multiply bonded COad band. CH3CD2OH and D2O are used to exclude the spectral interference with this band from interfacial acetaldehyde and H2O, respectively, confirming for the first time that the ∼1625 cm–1 band is due to the adsorbed acetyl on the Pd electrode in alkaline media. The spectral results suggest that the as-adsorbed acetyl (CH3COad) is oxidized to acetate from approximately −0.4 V as the potential moves positively to conclude the C2 pathway. Alternatively, in the C1 pathway, the CH3COad is decomposed to α-COad and β-CHx species on the ...

Surface-Enhanced Infrared Absorption Spectroscopy Study of Anticorrosion Behavior of 2-Mercaptobenzothiazole on Copper

2-Mercaptobenzothiazole (MBT) is a highly efficient inhibitor of Cu. However, the inhibition mechanism is still unclear. In this paper, the anticorrosive effect of MBT on a Cu surface at the macroscopic level was evaluated using a polarization curve technique. The potential-dependent adsorption geometries of MBT at the molecular level were investigated using electrochemical surface-enhanced infrared reflection absorption spectroscopy in attenuated total reflection mode, together with theoretical calculations. The results indicated that the MBT molecules were adsorbed on the Cu surface vertically, in a thiolate form, through exocyclic S atoms at a potential negative of 0 V (vs saturated calomel electrode (SCE)). At a potential positive of 0 V (vs SCE), electrons were transferred between MBT and the Cu substrate, meaning that MBT molecules can interact with the Cu surface via exocyclic S and endocyclic N atoms to form a polymer film, resulting in the formation of a compact protecting layer to prevent Cu dissolution.

In Situ Molecular Level Measurements of Ion Dynamics in an Electrochemical Capacitor

Improving the energy storage capability of batteries and capacitors is inherently dependent on clarifying our understanding of ion dynamics of advanced electrolytes in a variety of materials. Herein we report a new attenuated total reflectance–surface-enhanced infrared absorption spectroscopy technique that can selectively and simultaneously measure both cation and anion transport of an ionic liquid (1-ethyl-3-methylimidazolium triflate (EMIm-Tf)) in a functioning electrochemical pseudocapacitor (actuator). This new capacitor–spectroscopy technique was utilized to probe the gold current collector/RuO2 electrode interface during both square wave and cyclic voltammetry experiments. Results show that the cations and anions transport as aggregates and the cation dominates and dictates the direction of ion transport in these devices. Results also show that ion dynamics in pseudocapacitors is a diffusion-limited process.

A comparative study of the adsorption and oxidation of L-alanine and L-serine on Au(1 0 0), Au(1 1 1) and gold thin film electrodes in acid media

The adsorption and oxidation of l-alanine and l-serine at Au(111) and Au(100) single crystal and evaporated thin-film electrodes with preferential (111) orientation was studied in perchloric acid solutions. For this purpose, cyclic voltammetry experiments were combined with external reflection infrared spectroscopy (gold single crystals) and surface-enhanced infrared reflection–absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) (gold thin films). In addition, theoretical harmonic vibrational frequencies, obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations for the zwitterionic species adsorbed on Au clusters with (111) orientation, were used to interpret the experimental spectra. The optimized geometry obtained from DFT calculations for the corresponding zwitterion plus a water molecule, under the application of an external electric field of 0.01a.u. corresponds to a bidentate asymmetrical bridge adsorption configuration. The absence of an adsorbate band for the asymmetric OCO stretching in the experimental infrared spectra confirms the bidentate bonding of the adsorbed zwitterion through the oxygen atoms of the carboxylate group irrespective of the crystallographic orientation of the electrode surface, the adsorbate coverage and the electrode potential. In addition to typical interfacial water bands associated to perchlorate anions, which are co-adsorbed in order to compensate the positive charge of the ammonium group, the ATR-SEIRA spectra also show bands around 2950cm−1 that can be related to the formation of hydrogen bonds between interfacial water and the ammonium group of the adsorbed zwitterion. The voltammetric experiments have shown that, as in the case of platinum electrodes, l-serine oxidizes at lower potentials than l-alanine. Under these conditions, the in situ infrared experiments show the formation of carbon dioxide and adsorbed cyanide as oxidation products of l-serine. In the case of l-alanine, only carbon dioxide was detected.

Anticorrosive Behavior of AMT on Cobalt Electrode: From Electrochemical Methods to Surface-Enhanced Vibrational Spectroscopy Study

Anticorrosive behaviors of 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) on a cobalt film electrode surface were comparatively studied by means of electrochemical techniques such as cyclic voltammetry, polarization curves, and electrochemical impedance spectroscopy. The anticorrosion ability of AMT on a Co electrode in a neutral solution was confirmed at the macroscopic level. The adsorption geometry of AMT and the inhibition mechanism were further investigated by in situ electrochemical surface-enhanced infrared reflection absorption spectroscopy and surface-enhanced Raman scattering techniques. Free and adsorbed AMT information by theoretical calculations provided the powerful supports for the assignments of the bands and the establishment of the adsorption configurations. The results implied that the adsorbed AMT molecules were bonded to the Co electrode surface via the S1, S6, and N7 atoms at a small angle, with their ring planes tilted to the local surface at the potential negative of −0.4 V (vs SCE). A...

In Situ Monitoring of Protein Adsorption on a Nanoparticulated Gold Film by Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy

In situ surface enhanced infrared absorption spectroscopy (SEIRAS) with an attenuated total reflection (ATR) configuration has been used to monitor the adsorption kinetics of bovine hemoglobin (BHb) on a Au nanoparticle (NP) film. The IR absorbance for BHb molecules on a gold nanoparticle film deposited on a Si hemispherical optical window is about 58 times higher than that on a bare Si optical window and the detection sensitivity has been improved by 3 orders of magnitude. From the IR signal as a function of adsorption time, the adsorption kinetics and thermodynamics can be explored in situ. It is found that both the electrostatic interaction and the coordination bonds between BHb residues and Au NP film surface affect the adsorption kinetics. The maximum adsorption can be obtained in solution pH 7.0 (close to the isoelectric point of the protein) due to the electrostatic interaction among proteins. In addition, the isotherm of BHb adsorption follows well the Freundlich adsorption model.

Depression and heart failure

[1] Wu YP, Stella PR, Chen SF, et al. Beta-radiation reduces the reactivity of extra cellular matrix proteins in intravascular brachytherapy (IVBT), resulting in decreased platelet adhesion. Int J Cardiol 2012;156:283–8. [2] Xu JY, Jin B, Zhao Y, Wang K, Xia XH. In situ monitoring of the DNA hybridization by attenuated total reflection surface-enhanced infrared absorption spectroscopy. Chem Commun (Camb) 2012;48:3052–4. [3] Raizner AE, Kaluza GL, Ali NM. Clinical experience with a spiral balloon centering catheter for the delivery of intracoronary radiation therapy. Cardiovasc Radiat Med 1999;1:214–9. [4] Goodfellow M, Hayes A, Murphy S, et al. A retrospective study of (90)Strontium plesiotherapy for feline squamous cell carcinoma of the nasal planum. J FelineMed Surg 2006;8:169–76. [5] Hammond GM, Gordon IK, Theon AP, et al. Evaluation of strontium Sr 90 for the treatment of superficial squamous cell carcinoma of the nasal planum in cats: 49 cases (1990–2006). J Am Vet Med Assoc 2007;231:736–41. [6] Belbachir Karima, Noreen Razia, Gouspillou Gilles, Petibois Cyril. Collagen types analysis and differentiation by FTIR spectroscopy. Anal Bioanal Chem 2009;395:829–37.

In situ infrared study of adenine adsorption on gold electrodes in acid media

In situ external reflection infrared reflection spectroscopy (IRRAS) and surface-enhanced infrared reflection absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) have been used to study the adsorption of adenine at Au(111) and gold thin-film electrodes in 0.1M HClO4 solutions in deuterium oxide and in water. The existence of protonated and deprotonated adenine molecules at the electrode surface has been proved from the comparison of the spectra for adsorbed adenine with those obtained for dissolved adenine. In all cases, characteristic band frequencies are observed for the enhanced ring stretching band in D2O and also the bending band of the amino group in H2O. Both signals appear at higher wavenumbers for the protonated species. In acid media, deprotonation of adsorbed adenine is induced by increasing positive potentials and/or adenine coverage leading to the same adsorbed species as previously reported in basic media, namely chemically adsorbed adenine with a tilted orientation of the molecular plane on the electrode. Co-adsorption of water and perchlorate anions is detected in the case of the acid media, indicating the involvement of these species in the stabilization of the organic film. Time-resolved experiments at negative potentials and low adenine concentrations have shown also the physical adsorption of protonated adenine and have allowed the monitoring of the adsorption of the protonated and unprotonated forms as a function of time. Adsorption of unprotonated adenine is slower but is favored at the equilibrium at the electrode surface even if the pH of the media is three units lower than the pKa of adenine in solution.

In situ monitoring of the DNA hybridization by attenuated total reflection surface-enhanced infrared absorption spectroscopy

In situ monitoring of DNA hybridization kinetics is achieved via an attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) technique using a sandwich assay structure. The synergistic enhancement effect gives this ATR-SEIRAS-based detection strategy promise to be a convenient and unique platform for bioanalysis.

Interfacial Water at a CO-Predosed Platinum Electrode: A Surface Enhanced Infrared Study with Strong Hydrogen Evolution Reaction Control

Attenuated total reflection surface-enhanced infrared absorption spectroscopy, in conjunction with Gram−Schmidt intensity response and 2-dimensional correlation IR analyses, has been extended to study the structure and interaction of interfacial H2O at a CO-predosed platinum electrode in 0.1 M HClO4 with its potential navigated from the double-layer region to the strong hydrogen evolution reaction (HER) region. The strong HER enables at least part of the outer interfacial H2O layers to be effectively expelled by tremendous amounts of H2 bubbles dynamically formed on the Pt surface. The H2 bubbles could effectively survive during a fairly fast potential excursion to a positive limit for CO stripping at which a single-beam spectrum was then acquired and used as the reference, facilitating the analysis of “quasi-absolute” spectra of the initial interfacial H2O and CO at the Pt electrode prior to the significant HER. As a result, the broad νOH band may be deconvoluted into four peaks at ca. 3630, 3550, 3250, ...

Recent Progress in Electrochemical Surface Science with Atomic and Molecular Levels

Until the mid 1980’s, there had been only few in situ methods available for structural determination of an electrode surface in solution at atomic and monolayer levels. Nowadays, many powerful in situ techniques, such as electrochemical scanning tunneling microscopy (EC-STM), infrared reflection absorption spectroscopy (IRAS), surface-enhanced Raman scattering (SERS), and surface-enhanced infrared reflection absorption spectroscopy (SEIRAS), second harmonic generation (SHG), sum frequency generation (SFG), and surface X-ray scattering (SXS) have been widely employed to characterize the electrode surfaces under potential control with atomic and/or molecular resolution. The object of this review is to highlight some of the progress on in situ methods at solid-liquid interface with atomic and molecular levels. Several selected topics are focused on, specifically adsorbed anions on metal surface, electrocatalysis of the carbon oxide oxidation and xygen reduction, and direct observation of single crystal electrode surfaces.

Recent Progress in Electrochemical Surface Science with Atomic and Molecular Levels

Until the mid 1980’s, there had been only few in situ methods available for structural determination of an electrode surface in solution at atomic and monolayer levels. Nowadays, many powerful in situ techniques, such as electrochemical scanning tunneling microscopy (EC-STM), infrared reflection absorption spectroscopy (IRAS), surface-enhanced Raman scattering (SERS), and surface-enhanced infrared reflection absorption spectroscopy (SEIRAS), second harmonic generation (SHG), sum frequency generation (SFG), and surface X-ray scattering (SXS) have been widely employed to characterize the electrode surfaces under potential control with atomic and/or molecular resolution. The object of this review is to highlight some of the progress on in situ methods at solid-liquid interface with atomic and molecular levels. Several selected topics are focused on, specifically adsorbed anions on metal surface, electrocatalysis of the carbon oxide oxidation and dioxygen reduction, and direct observation of single crystal electrode surfaces.

Activity of Membrane Proteins Immobilized on Surfaces as a Function of Packing Density

A systematic study of the influence of the packing density of proteins on their activity is performed with cytochrome c oxidase (CcO) from R. sphaeroides as an example. The protein was incorporated into a protein-tethered bilayer lipid membrane and CcO was genetically engineered with a histidine-tag, attached to Subunit II, and then tethered by an interaction with functionalized thiol compounds bound to a gold electrode. The packing density was varied by diluting the functionalized thiol with a nonfunctionalized thiol that does not bind to the enzyme. After attaching the CcO to the gold surface, a lipid bilayer was formed to incorporate the tethered proteins. The reconstituted protein-lipid bilayer was characterized by surface enhanced infrared reflection absorption spectroscopy (SEIRAS), electrochemical impedance spectroscopy, surface plasmon resonance, and atomic force microscopy. The activity of the proteins within the reconstituted bilayer was probed by direct electrochemical electron injection and was shown to be very sensitive to the packing density of protein molecules. At low surface density of CcO, the bilayer did not effectively form, and protein aggregates were observed, whereas at very high surface density, very little lipid is able to intrude between the closely packed proteins. In both of these cases, redox activity, measured by the efficiency to accept electrons, is low. Redox activity of the enzyme is preserved in the biomimetic structure but only at a moderate surface coverage in which a continuous lipid bilayer is present and the proteins are not forced to aggregate. Electrostatic and other interaction forces between protein molecules are held responsible for these effects.

Adsorption and self-assembly of aromatic carboxylic acids on Au/electrolyte interfaces

The adsorption and self-assembly of benzoic acid (BA), isophthalic acid (IA), and trimesic acid (TMA) on Au(111) single crystals and on Au(111-25 nm) quasi-single crystalline film electrodes have been investigated in 0.1 M HClO4 by combining in situ surface-enhanced infrared reflection absorption spectroscopy (SEIRAS) and scanning tunneling microscopy (STM) with cyclic voltammetry. All three acids are physisorbed on the electrode surface in a planar orientation at negative charge densities. Excursion to positive charge densities (or more positive potentials) causes an orientation change from planar to perpendicular. Chemisorbed structures are formed through the coordination of a deprotonated carboxyl group to the positively charged electrode surface. The three acid molecules assemble in different ordered patterns, which are controlled by pi-stacking (BA) or intermolecular hydrogen bonds between COOH groups (IA, TMA). A detailed analysis of the potential and time dependencies of the nu(C=O), nus(OCO), and nu(C-OH) vibration modes shows that the strength of lateral interactions increases upon chemisorption with an increasing number of COOH groups in the sequence of BA<IA<TMA. The vibration bands shift to higher wavenumbers due to dipole-dipole coupling, Stark tuning, and electron back donation from the electrode to COO-. In addition, an "indirect" electron donation to the COOH groups takes place via the conjugated molecular skeleton superimposed on the intermolecular hydrogen bonding.

Supramolecular Nanostructures of 1,3,5-Benzene-tricarboxylic Acid at Electrified Au(111)/0.05 M H2SO4 Interfaces: An in Situ Scanning Tunneling Microscopy Study

The potential-induced adsorption and self-assembly of 1,3,5-benzene-tricarboxylic acid (TMA) was investigated at the electrified Au(111)/0.05 M H2SO4 interface by in-situ scanning tunneling microscopy (STM) and surface enhanced infrared reflection absorption spectroscopy (SEIRAS) in combination with electrochemical techniques. Depending on the applied electric field, TMA forms five distinctly different, highly ordered supramolecular adlayers on Au(111) surfaces. We have elucidated their real-space structures at the molecular scale. In the potential range -0.25 V < E < 0.20 V, planar-oriented TMA molecules form a hexagonal open-ring honeycomb structure, Ia, a hydrogen-bonded ribbon-type phase, Ib, and a herringbone-type phase, Ic, stabilized by directional hydrogen bonding and weak substrate-adsorbate interactions. Interfacial water molecules are being replaced. In 0.20 V < or = E < 0.40 V, e.g., around the potential of zero charge, and at slightly higher coverages, a close-packed physisorbed adlayer of hydrogen-bonded TMA dimers, II, was observed. Further increase of the electrode potential to positive charge densities causes an orientation change from planar to upright. An initially disordered phase, IIIa, transforms into an ordered, stripelike chemisorbed adlayer, IIIb, of perpendicularly oriented TMA molecules. One carboxylate group per molecule is bound to the electrode surface, while the two other protonated carboxyl groups are directed toward the electrolyte and act as structure-determining components of a hydrogen-bonded two-dimensional ladder-type network. Structural transitions between the various types of ordered molecular adlayers are attributed to (hole) nucleation and growth processes.

Reflection and Absorption Techniques for Optical Characterization of Chemically Assembled Nanomaterials

AbstractThis review discusses recent developments in the areas of fabrication, certain types of optical characterization, and applications of a selected class of chemically assembled nanomaterials, namely i) gold and silver nanoparticles deposited onto optically transparent glass substrates; ii) thiol‐functionalized self‐assembled monolayers (SAMs); iii) chemically stabilized gold and silver nanoparticles (monolayer protected clusters, MPCs); and iv) MPCs linked to metallic substrates and adsorbates. Six linear optical techniques for the characterization of these materials are discussed: transmission localized surface plasmon resonance spectroscopy, T‐LSPR; propagating surface plasmon resonance spectroscopy, P‐SPR; polarization‐selective Fourier transform infrared reflection absorption spectroscopy, PS‐FTIRRAS; polarization‐modulation Fourier transform infrared reflection absorption spectroscopy, PM‐FTIRRAS; surface‐enhanced infrared reflection absorption spectroscopy, SEIRRAS; and infrared ellipsometry. The review focuses particularly on providing a unified treatment of these six optical techniques by using a relatively simple stratified multilayer model.

Surface enhanced infrared spectroscopy—Au(1 1 1-20 nm)/sulphuric acid—new aspects and challenges

The structure and orientation of water molecules on Au(1 1 1-20 nm) film electrodes in contact with aqueous sulphuric acid solution was studied by surface enhanced infrared reflection–absorption spectroscopy (SEIRAS) employing an attenuated total reflection (ATR) configuration (ATR-SEIRAS) with a vertical spectroelectrochemical cell. The spectrum of interfacial water is strongly dependent on electrode potential, ionic strength and pH. Coadsorption of hydronium ions with weakly hydrogen-bonded water molecules was found at E< E pzc. At E> E pzc strong hydrogen-bonding among water molecules and to coadsorbed sulphate species exists. Based on pH-dependent electrochemical, spectroscopic and in situ STM investigations, a new model is suggested to represent the ordered ( 3 × 7 ) adlayer at maximum sulphate coverage θ=0.2: a Zundel or hydrated hydronium ion H 5O 2 +, in which one proton is shared between two water molecules, bridges adjacent sulphate species via hydrogen-bonds along the main diagonal of the ( 3 × 7 ) unit cell. This alternating arrangement gives rise to a long-range ordered, 2D network of sulphate and water species interconnected by hydrogen-bonds, and capable to form hydrogen-bonds with second-layer water species. The suggested model is consistent with all experimental observations as well as predictions from quantum-chemical and molecular dynamic simulations.

Structural transitions in 4,4′-bipyridine adlayers on Au(111)—an electrochemical and in-situ STM-study

The adsorption and phase formation of 4,4′-bipyridine (4,4′-BP) on the Au(111)–(1×1) ∣ aqueous electrolyte interface has been studied using capacitance measurements, cyclic voltammetry (CV), surface enhanced infrared reflection/absorption spectroscopy (SEIRAS) and in-situ scanning tunneling microscopy (STM). The organic molecules form, dependent on the electrode potential applied and in the absence of Faradaic reactions, three highly ordered monolayers. The high coverage adlayer I is composed of 4,4′-BP co-ordinated with one nitrogen atom to the underlying, positively charged electrode surface, arranged in interdigitated, densely packed molecular stacks and stabilized by co-adsorbed interfacial water molecules. The corresponding unit cell ( a=1.15 nm, b=1.3 nm, α=74°) contains six molecules, which gives rise to a coverage Γ=6.9×10 −10 mol cm −2. Excursions of the electrode potential towards more negative values triggers two first-order phase transitions, characterized by the loss of parallel stacking rows, accompanied by an orientational change of 4,4′-BP from perpendicular towards an inclined position and a rearrangement of co-adsorbed interfacial water molecules. The adlayer coverage decreases from 6.8×10 −10 mol cm −2 (phase I) via 5.7×10 −10 mol cm −2 (phase II, striped structure) to 3.4×10 −10 mol cm −2 (phase III, rhombohedral structure). The vectors which determine the unit cells of the adlayers I and III are basically identical. II and III exhibit strict registry with the substrate surface geometry, the substrate–adsorbate corrugation potential in phase I appears to be somewhat smaller. The unperturbed imaging of the steady-state 4,4′-BP adlayers II and III was possible only with tunneling currents lower then 30 pA, often down to 6 pA. The STM contrast patterns of all three steady-state structures depend significantly on the applied tunneling conditions indicating that the electron transfer between tip and substrate is most probably mediated by the conjugated π-system of the molecule, e.g. ‘through bond’ tunneling occurs. On the other hand, current distance curves yielded barrier heights of 1.00±0.05 eV, rather independent of the type of adlayer. Chronoamperometric potential step- and dynamic in-situ STM—experiments revealed that the first order phase transitions I→II, II→III and III→II proceed preferentially by two-dimensional (hole) nucleation with surface-diffusion controlled growth processes. These phase transitions are quasi-reversible provided that all perturbations are limited to the potential range of an ideal polarizable organic adlayer.