摘要:

The past few years have witnessed tremendous advances in experimental and theoretical techniques for probing both the static and dynamic properties of surfaces at the ångstrom level. Here we review how these advances have furthered our fundamental understanding of adhesion−particularly those processes that contribute to energy dissipation during adhesion and separation (loading–unloading cycles), and friction−particularly how the dynamic (e.g., viscous and rheological) properties of liquids in ultrathin films differ from the bulk liquid properties, and how this affects the friction forces of lubricated contacts. The emphasis will be on ‘‘ideal’’ surfaces and interfaces, i.e., surfaces that are molecularly smooth, and interfacial films that are no more than a few molecular layers thick.

ISSN:0734-2101    

DOI:10.1116/1.577894

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The utilization of infrared reflection–absorption spectroscopy (IRAS) and scanning tunneling microscopy (STM) for extracting atomic‐resolution information for ordered metal–solution interfaces in a related (and relatable) fashion to metal‐ultrahigh vacuum (UHV) surfaces is illustrated by means of some recent results from our laboratory. Two specific topics are addressed. The first involves the potential‐dependent properties of saturated CO adlayers on low‐index platinum and rhodium electrodes in aqueous and nonaqueous media. The central role of the surface potential in controlling the CO adlayer structure is discussed on the basis ofinsituIRAS data, especially in comparison with the properties of corresponding metal‐UHV interfaces. The application ofinsituatomic‐resolution STM in tandem with IRAS for elucidating real‐space adsorbate structures is noted for saturated CO adlayers on Rh(111) and Rh(110) electrodes. The second topic concerns the application ofinsituSTM to probe potential‐induced reconstruction at gold‐aqueous interfaces. All three low‐index gold surfaces are seen to undergo reconstruction at potentials corresponding to small (∼10–15 μC cm−2) negative electrode charges. The subtle surface relaxation observed for Au(111) is essentially identical to that observed recently by atomic‐resolution STM in UHV. The (5×27) and (1×n) (n=2,3) symmetries observed for reconstructed Au(100) and (110) electrodes, respectively, are compatible with the structures deduced for the UHV systems by diffraction methods, although the STM data afford greater real‐space detail.

ISSN:0734-2101    

DOI:10.1116/1.577895

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Light emission from metal, induced by electron injection from solvated electrons, was observed in an electrochemical system. The efficiency of emitted light increases drastically as electrode potential becomes positive. The high energy threshold of the spectrum increases as the electrode potential becomes positive by 1 eV/V. The peak energy also shifts positively as the electrode potential becomes positive, although the degree of the shift is much smaller. Various processes are considered as a possible mechanism for a photon emission. From the qualitative comparison of the results at platinum and gold electrode, the contribution of the inverse photoemission process to the bulk band states at the light emission process in the electrochemical system is suggested. The feasibility of applying this phenomenon to a novel spectroscopy is discussed.

ISSN:0734-2101    

DOI:10.1116/1.577896

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The rotational anisotropy of the second harmonic intensity has been used to provide information about the structural and electronic properties of a Cu(111) electrode surface in 0.01 M NaClO4. The experiments have involved measurement of the changes in the second harmonic (SH) intensity and relative phase of the SH response as the surface is biased at various potentials. Complementary measurements of the SH response from Cu(111) examined in ultrahigh vacuum (UHV) have also been performed and indicate that when this surface is in solution, it has very different optical (electronic) properties from the native surface at all applied potentials studied. Dosing of the sample in UHV with oxygen provides evidence for the existence of oxygen containing species on the surface in the electrochemical environment despite rigorous exclusion of molecular oxygen during both the surface preparation and the optical measurements. These studies demonstrate the utility of making comparative measurements of the surface in different environments, for which the SH technique is ideally suited.

ISSN:0734-2101    

DOI:10.1116/1.577897

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Upon oxidation of a clean Al surface, an electrical double layer (EDL) is formed at the Al–Al2O3interface. This EDL is investigated using x‐ray photoelectron spectroscopy data available in the literature. The EDL strength, measured as a potential difference across the EDL, depends on the Al surface and the oxidation process. The polarity of the EDL is however invariably the same: the Al2O3side of the Al–Al2O3interface is always positively charged. The reduction of the Al work function upon oxidation is attributed to this EDL. The asymmetry in the potential barrier shape formed in Al–Al2O3–Al sandwiches is also attributed to a strong EDL at the electrode‐film interface and a weaker EDL at the interface between the counter electrode and the film.

ISSN:0734-2101    

DOI:10.1116/1.577898

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The detailed frequency dependence of second‐harmonic generation (SHG) from Ag(111) is remarkably similar for the metal/electrolyte and metal/vacuum interface. In both environments, resonant enhancement of the SHG is observed which is attributed to optical transitions at the metal surface consistent with the surface electronic band structure.

ISSN:0734-2101    

DOI:10.1116/1.577899

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The growth of an oxide film and the dissolution of the metal were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) for titanium electrodes which had been pretreated by a chemical polishing procedure. Images were obtained with a gas–solid interface and under an aqueous solution containing 0.1 M oxalic acid. The electrochemical polarization of titanium in 0.1 M oxalic acid is qualitatively the same as observed in chloride or sulfate medium, and the dissolution reaction in oxalic acid appears to follow the same monolayer coverage mechanism as in the other media. The titanium specimen is polycrystalline and the presence of grain boundaries between individual crystallites is observed by AFM.Insitumicroscopy indicates that both the rate of growth of oxide and the dissolution of the metal are dependent on the crystallographic face of the titanium. AFM and STM show that the growth of titanium (IV) oxide or hydrous oxide has the appearance of hemispherical domes which grow together to form peaks on the surface. Dissolution of the metal in the active region occurs first in areas between the peaks where the oxide is thin, and later the oxide coverage of the small peaks appears to coalesce to a smaller number of large peaks.

ISSN:0734-2101    

DOI:10.1116/1.577856

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The influence of S on the anodic corrosion of Fe in a 55 wt % Ca(NO3)2solution at 60 °C has been examined using both electrochemical and surface analysis methods. Pure Fe, S‐implanted Fe, and Fe with S adsorbed on the surface have been studied. The presence of S, in sufficient amounts, was found to accelerate the corrosion of Fe at 750 mV. For S layers adsorbed on the Fe surface this threshold amount was approximately 1 monolayer. The effect of S was to thicken the oxide layer that formed on the metal and the S remained within the film in a nonoxidized form. These results are consistent with an observed rapid stress corrosion crack growth in the nitrate solution for Fe with S at grain boundaries.  

ISSN:0734-2101    

DOI:10.1116/1.577857

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We have usedinsituscanning tunneling microscopy to examine submonolayer Cu deposition from a sulfuric acid electrolyte on Au(111), sampling over large areas of the surface. We describe the growth of three distinct superlattice phases of Cu on the Au(111) surface before the onset of bulk deposition of Cu. In the earliest stages of deposition, during an electrochemical current peak, we observe the rapid growth of a low height phase, with an apparent height of 0.46±0.10 Å. During this time, a second, monolayer‐height phase forms as small islands. We identify these phases as the (√3×√3)R30° and (1×1) Cu superlattices, respectively. A third phase appears at about 175 mV (versus Cu/Cu+2), and grows from nucleation points at the top edges of atomic steps and around the small (1×1) Cu islands. This phase, which we believe is a (5×5) Cu adlayer, slowly supplants the (√3×√3)R30° layer.

ISSN:0734-2101    

DOI:10.1116/1.577858

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The structure of the Au(111) electrode surface in a 0.01 M NaCl electrolyte has been investigated using grazing incident angle x‐ray diffraction. The top layer of gold atoms undergoes a reversible phase transition between the (1×1) bulk termination and a (p×√3) uniaxial discommensuration (striped) phase on changing the electrode potential. Below a critical potential the stripe separation,p=23, is identical to vacuum measurements. At sufficiently positive potentials the surface forms an ideally terminated, (1×1), Au(111) surface. Cycling the potential in the reconstructed region improves the reconstructed surface order.

ISSN:0734-2101    

DOI:10.1116/1.577859

出版商:American Vacuum Society    

年代:1992

数据来源: AIP