共查询到10条相似文献,搜索用时 15 毫秒
1.
The local deposition of Ag nanoparticles (NPs) on ω-mercaptoalkanoic acid, HS(CH2)nCO2H, (n = 2, 10) self-assembled monolayers (SAMs) by scanning electrochemical microscopy (SECM) is reported. We found that the presence of a SAM had a pronounced effect on Ag deposition. Experiments were conducted by applying different potentials to an Au(1 1 1) substrate either in the presence of a constant concentration of Ag+ ions in solution (bulk deposition) or by generating a flux of Ag+ from an Ag microelectrode that was positioned close to the Au(1 1 1) substrate (SECM deposition). SECM was used for generating a controlled flux of silver ions by anodic dissolution of an Ag microelectrode close to the SAMs modified Au(1 1 1). We found that the shape of the NPs was affected by the length of the carbon-chain of the SAM. Tetrahedral NPs were obtained on bare Au(1 1 1) surfaces while rod like and cubic Ag NPs were deposited onto 3-mercaptopropanoic acid (MPA) and 11-mercaptoundecanoic acid (MUA) SAMs, respectively. The size and shape of the deposited NPs were influenced by the deposition potential.We conclude that the shape and distribution of locally deposited Ag NPs on Au(1 1 1) can be controlled by modification of the substrate with a SAM and through controlling the Ag+ flux generated by SECM. 相似文献
2.
Seyed Ehsan Salamifar Sayed Habib Kazemi Mir Fazllollah Mousavi 《Electrochimica acta》2010,56(2):896-904
Electron transfer (ET) kinetics through n-dodecanethiol (C12SH) self-assembled monolayer on gold electrode was studied using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). An SECM model for compensating pinhole contribution, was used to measure the ET kinetics of solution-phase probes of ferrocyanide/ferricyanide (Fe(CN)64−/3−) and ferrocenemethanol/ferrociniummethanol (FMC0/+) through the C12SH monolayer yielding standard tunneling rate constant () of (4 ± 1) × 10−11 and (3 ± 1) × 10−10 cm s−1 for Fe(CN)64−/3− and FMC0/+ respectively. Decay tunneling constants (β) of 0.97 and 0.96 Å−1 for saturated alkane thiol chains were obtained using Fe(CN)64− and FMC respectively. Also, it was found that methylene blue (MB) molecules are effectively immobilized on the C12SH monolayer and can mediate the ET between the solution-phase probes and underlying gold substrate. SECM-mediated model was used to simultaneously measure the bimolecular ET between the solution-phase probes and the monolayer-immobilized MB molecules, as well as tunneling ET between the monolayer-immobilized MB molecules and the underlying gold electrode, allowing the measurement of kBI = (5 ± 1) × 106 and (4 ± 2) × 107 cm3 mol−1 s−1 for the bimolecular ET and and (7 ± 3) × 10−2 s−1 for the standard tunneling rate constant of ET using Fe(CN)64−/3− and FMC0/+ probes respectively. 相似文献
3.
Yan Shen Ushula Mengesha Tefashe Thomas Loewenstein Gunther Wittstock 《Electrochimica acta》2009,55(2):458-21212
The overall efficiency of the light-induced charge separation in dye-sensitized solar cells depends on the kinetic competition between back electron transfer and dye regeneration processes by a redox electrolyte. In a previous study, the reduction of the intermittently formed photo-oxidized dye molecules by iodide ions in the electrolyte phase was investigated using the feedback mode of a scanning electrochemical microscope (SECM) and a quantitative model had been derived. Here we provide a more thorough experimental verification of this model by variation of the excitation wavelength, light intensities and mediator concentrations. Nanoporous ZnO/Eosin Y films prepared by self-assembly were used as model electrodes and were used with an iodide/triiodide electrolyte. The experimentally found effective rate constants could be related to the rate constant for the reaction of the dissolved donor with photo-oxidized Eosin Y bound to ZnO and the absorption spectrum of the dye and confirmed the assumption made in the derivation of the model. For the regeneration process of Eosin Y, a rate constant of kox with different light emitting diodes and light intensities is determined. 相似文献
4.
We developed a new method for fabrication of nanometer-sized carbon fiber disk electrodes and applied them to micropattern active horseradish peroxidase (HRP) with a high-resolution by scanning electrochemical microscopy (SECM). In order to pattern active HRP, except for active HRP micropatterns predesigned other regions on a HRP-immobilized substrate was deactivated by a reactive species generated at the electrode as the tip of SECM held at 1.7 V through oxidation of Br− in 0.20 mol/L phosphate buffer (PB) containing 2.5 × 10−2 mol/L KBr and 2.0 × 10−3 mol/L BQ (pH 7.0). The micropatterns of active HRP were characterized using the feedback mode of SECM in PB containing 2.0 × 10−3 mol/L BQ and 2.0 × 10−3 mol/L H2O2, when the tip potential was held at −0.2 V. 相似文献
5.
Scanning electrochemical microscopy (SECM) was used to study the film formation of benzotriazole towards corrosion of copper. SECM was operated in the feedback mode by using ferrocene-methanol as redox mediator, and the sample was left unbiased at all times to freely attain its open circuit potential in the test environment. Following exposure to aggressive electrolytes the anticorrosion abilities of the layers were characterized by image analysis and by an electrochemical method derived from the experimental approach curves. Changes in the shape of the approach curves were clearly observed during the inhibitor film formation process. They showed the transition from an active conducting behaviour towards ferrocinium reoxidation typical of unprotected copper, to a surface exhibiting insulating characteristics when the metal was covered by a surface film containing the inhibitor. This supports that SECM is a practical technique in the investigation of corrosion inhibitor performance. However, a consistent tendency for the characterization of inhibitor film formation using SECM measurements in the positive feedback mode for the copper-benzotriazole system was only found if the experiments were conducted when the inhibitor molecule was not present in the test solution. That is, inhibitor molecules were found to interact not only with the copper surface during the monitoring process, but with the SECM tip as well, this effect being significantly enhanced when chloride ions were present in the electrolyte. Finally, a procedure to image the chemical activity of copper surfaces partially covered with the inhibitor film with SECM is proposed. 相似文献
6.
Bernardo Ballesteros Katemann Pablo A Castro Ernesto J Calvo 《Electrochimica acta》2003,48(9):1115-1121
In solutions of low conductivity and at high frequencies the impedance of a SECM tip-auxiliary electrode cell is dominated by the solution resistance between the tip and counter electrode. Alternating current scanning electrochemical microscopy (AC-SECM) utilises the effect of an increasing (decreasing) solution resistance as the SECM tip approaches an insulator (conductor) for mapping domains of different conductivity/electrochemical activity on surfaces immersed into electrolytes. In the present study, we employed AC-SECM in aqueous solutions to evaluate the integrity of the solid/liquid interface of lacquered tinplates as commonly used in industry to manufacture, i.e. food cans. Significant differences were determined between the AC response and the phase shift measured with the SECM tip above the intact coating and above defects where the surface of the steel base is exposed. This allowed with high lateral resolution to detect and to visualise artificial micro cavities which we consider as an experimental model of microscopically small precursor sites for localised corrosion. 相似文献
7.
Zhihui Dai 《Electrochimica acta》2004,49(13):2139-2144
The immobilization and electrochemical behaviors of cytochrome c on a NaY zeolite modified electrode were studied. The interaction between cytochrome c and NaY zeolite particles was examined by using UV-Vis spectroscopy and electrochemical methods. The direct electron transfer of the immobilized cytochrome c exhibited a pair of redox peaks with the E1/2 of (versus SCE) in 0.1 M pH 7.0 PBS. The electrode reaction showed a surface-controlled process with a single proton transfer at the scan rate range from 20 to 500 mV s−1. Based on the immobilization of cytochrome c on NaY zeolite a high performance biosensor was constructed, which displayed an excellent response to the reduction of hydrogen peroxide (H2O2) without the aid of an electron mediator and could be used for H2O2 detection. NaY zeolite provided a good matrix for protein immobilization and biosensor preparation. 相似文献
8.
Patterned copper sulfide (CuxS) microstructures on Si (1 1 1) wafers were successfully fabricated by a relatively simple solution growth method using copper sulfate, ethylenediaminetetraacetate and sodium thiosulfate aqueous solutions as precursors. The CuxS particles were selectively deposited on a patterned self-assembled monolayer of 3-aminopropyltriethoxysilane regions created by photolithography. To obtain high quality CuxS films, preparative conditions such as concentration, proportion, pH and temperature of the precursor solutions were optimized. Various techniques such as optical microscopy, atomic force microscopy (AFM), X-ray diffraction, optical absorption and scanning electrochemical microscopy (SECM) were employed to examine the topography and properties of the micro-patterned CuxS films. Optical microscopy and AFM results indicated that the CuxS micro-pattern possessed high selectivity and clear edge resolution. From combined X-ray diffraction analysis and optical band gap calculations we conclude that Cu9S5 (digenite) was the main phase within the resultant CuxS film. Both SECM image and cyclic voltammograms confirmed that the CuxS film had good electrical conductivity. Moreover, from SECM approach curve analysis, the apparent electron-transfer rate constant (k) in the micro-pattern of CuxS dominated surface was estimated as 0.04 cm/s. The SECM current map showed high edge acuity of the micro-patterned CuxS. 相似文献
9.
Scanning electrochemical microscopy (SECM) in the feedback mode was utilized for monitoring the surface reactivity and the localized corrosion processes occurring on the Nd13.5Fe79.5Si1B6 permanent magnet (intrinsically comprising iron inclusions). SECM imaging experiments, performed with the application of ferrocenecarboxylic acid as the mediator, revealed distinctly reactive areas at the magnet surface during early stages of its immersion in 0.1 mol dm−3 phosphate buffer (pH = 7). It was demonstrated that the iron inclusions were responsible for the existence of these reactive areas whereas the bulk material surface was practically unreactive (insulating). It was observed that the surface reactivity of the iron inclusions gradually decreased with time and after 7 h immersion the whole magnet surface became uniformly unreactive (insulating). The results were explained in terms of differences in the dynamics of the passive film formation on the iron inclusions and on the bulk material. Another factor that might be responsible for the observed non-uniform surface reactivity was also considered, namely, the differences in abilities to charge propagation through passive films existing on the iron inclusions and on the bulk material. The role of the iron inclusions as pitting precursor sites in the presence of chlorides in the phosphate buffer solution was also examined. 相似文献
10.
Seongpil Hwang Bang Sook Lee Young Shik Chi Insung S. Choi 《Electrochimica acta》2008,53(5):2630-2636
In this work, we studied interfacial proton transfer of the self-assembled monolayer (SAM) of 1-(12-mercaptododecyl)imidazole on a gold electrode by faradaic impedance titration method with Fe(CN)63− as an anionic redox probe molecule. The surface pK1/2 was found to be 7.3, which was nearly the same as that of 1-alkylimidazole in solution. We also investigated the electrochemical properties of the SAM-modified electrode by cyclic voltammetry. Cyclic voltammetry was performed (1) in the solution containing Fe(CN)63− with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN)63− and (2) in the acidic or basic electrolyte containing Ru(NH3)63+ as a cationic redox probe to verify the effect of the polarity of a redox probe. We observed the reversible adsorption/desorption of Fe(CN)63− and concluded that the adsorbed Fe(CN)63− catalyzed the electron transfer of both Fe(CN)63− itself and cationic Ru(NH3)63+. 相似文献