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1.
2.
Electrochemical deposition of metals (platinum or gold) only on top of an organothiolate, 1,4-benzenedimethanethiol (BDMT) or hexanedithiol (HDT), self-assembled monolayer (SAM) on a Au(111) substrate was achieved by electrochemical reduction of PtCl(4)(2-) or AuCl(4)(-) ion, which was preadsorbed on one free thiol end group of the dithiol SAM formed on a Au surface, in a metal-ion-free sulfuric acid solution at potentials more negative than the reduction potential of the metal ion. Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) measurement after the reduction of preadsorbed PtCl(4)(2-) ion on BDMT/Au(111) electrode showed the presence of Pt not underneath but on top of the BDMT SAM. After a negative potential scan of the Pt/BDMT/Au(111) electrode to -1.30 V in 0.1 M KOH solution, a typical cyclic voltammogram of a clean Au(111) electrode was obtained, showing that the BDMT SAM with a Pt layer was reductively desorbed. These results proved that a Pt-BDMT SAM-Au substrate sandwich structure without a short circuit between the two metals was successfully constructed by this technique. Furthermore, a decanethiol (DT) monolayer was constructed on a Au layer, which was formed by the reduction of preadsorbed AuCl(4)(-) ion on HDT/Au(111) electrode. The formation of DT/Au/HDT/Au(111) structure was confirmed as two cathodic peaks corresponding to reductive desorption of DT from Au on top of the HDT/Au(111) at -0.97 V and that of Au/ HDT from Au(111) at -1.12 V were observed when potential was scanned negatively to -1.35 V. 相似文献
3.
Sek S Chen M Brosseau CL Lipkowski J 《Langmuir : the ACS journal of surfaces and colloids》2007,23(25):12529-12534
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. 相似文献
4.
The kinetics of phase transitions of cytidine adsorbed on mercury are studied by chronoamperometry and capacitance measurements. Cytidine forms highly ordered two-dimensional adlayers in a broad range of pH. In acid solvent, only one kind of condensed layer is formed. In the alkaline solution, cytidine forms two different two-dimensional (2D) adlayers. The minimum capacitance value in adlayer II at pH 5 is 7.0 microF cm(-2) and, at pH 8.3, it is 5.1 microF cm(-2); in adlayer III, the minimum capacitance is 10.6 microF cm(-2). The formation of a physisorbed film of cytidine molecules adsorbed at the mercury surface proceeds by complex mechanisms. From j-t transients, it can be seen that the phase transformations from dilute adlayer Ia to condensed physisorbed film II is accompanied by the reorientation of cytidine molecules at the mercury surface (inverted current transient). The interfacial transformations of the cytidine film yield a sigmoidal C-t transient. This experimentally measured C-t transient were analysed by Avrami theorem. The rate of the transformations from dilute adlayer Ia to condensed film II of cytidine at pH 5 depends strongly on temperature but is only slightly affected by temperature at pH 8.3. The effect of pH and ionic composition of the supporting electrolyte on the rate of transformation of cytidine films was studied as well. 相似文献
5.
In order to study the adsorption mechanism of Hg on Au and Ag substrates, thin film Au(111) and Ag(111) substrates were exposed
to gaseous metallic mercury, while the mercury concentration, substrate temperature, and exposure length were varied. The
resulting changes in the surface morphology of the substrates were studied with scanning tunneling microscopy (STM). The amount
of adsorbed Hg required to cause saturation, i.e. a decrease in the adsorption rate was found to be dependent on the mercury
concentration and substrate temperature. The observations lead to the conclusion that the adsorption includes place exchange
processes and concerted adsorption of more than one Hg atom in one process. The results show that the collection efficiency
of single-crystalline surfaces is a function of both mercury concentration and temperature. Therefore, results from measurements
performed at different conditions using single-crystalline surfaces may not be comparable.
Received: 3 February 1999 / Revised: 7 June 1999 / Accepted: 9 June 1999 相似文献
6.
Pan Y Gao Y Kong D Wang G Hou J Hu S Pan H Zhu J 《Langmuir : the ACS journal of surfaces and colloids》2012,28(14):6045-6051
The model catalysts of ZrO(2)-supported Au nanoparticles have been prepared by deposition of Au atoms onto the surfaces of thin ZrO(2) films with different morphologies. The adsorption and thermal stability of Au nanoparticles on thin ZrO(2) films have been investigated using synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS). The thin ZrO(2) films were prepared by two different methods, giving rise to different morphologies. The first method utilized wet chemical impregnation to synthesize the thin ZrO(2) film through the procedure of first spin-coating a zirconium ethoxide (Zr(OC(2)H(5))(4)) precursor onto a SiO(2)/Si(100) substrate at room temperature followed by calcination at 773 K for 12 h. Scanning electron microscopy (SEM) investigations indicate that highly porous "sponge-like nanostructures" were obtained in this case. The second method was epitaxial growth of a ZrO(2)(111) film through vacuum evaporation of Zr metal onto Pt(111) in 1 × 10(-6) Torr of oxygen at 550 K followed by annealing at 1000 K. The structural analysis with low energy electron diffraction (LEED) of this film exhibits good long-range ordering. It has been found that Au forms smaller particles on the porous ZrO(2) film as compared to those on the ordered ZrO(2)(111) film at a given coverage. Thermal annealing experiments demonstrate that Au particles are more thermally stable on the porous ZrO(2) surface than on the ZrO(2)(111) surface, although on both surfaces, Au particles experience significant sintering at elevated temperatures. In addition, by annealing the surfaces to 1100 K, Au particles desorb completely from ZrO(2)(111) but not from porous ZrO(2). The enhanced thermal stability for Au on porous ZrO(2) can be attributed to the stronger interaction of the adsorbed Au with the defects and the hindered migration or coalescence resulting from the porous structures. 相似文献
7.
Li M Chen M Sheepwash E Brosseau CL Li H Pettinger B Gruler H Lipkowski J 《Langmuir : the ACS journal of surfaces and colloids》2008,24(18):10313-10323
Atomic force microscopy (AFM) has been used to characterize the formation of a phospholipid bilayer composed of 1,2-dimyristyl-sn-glycero-3-phosphocholine (DMPC) at a Au(111) electrode surface. The bilayer was formed by one of two methods: fusion of lamellar vesicles or by the combination of Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) deposition. Results indicate that phospholipid vesicles rapidly adsorb and fuse to form a film at the electrode surface. The resulting film undergoes a very slow structural transformation until a characteristic corrugated phase is formed. Force-distance curve measurements reveal that the thickness of the corrugated phase is consistent with the thickness of a bilayer lipid membrane. The formation of the corrugated phase may be explained by considering the elastic properties of the film and taking into account spontaneous curvature induced by the asymmetric environment of the bilayer, in which one side faces the gold substrate and the other side faces the solution. The effect of temperature and electrode potential on the stability of the corrugated phase has also been described. 相似文献
8.
Leitch JJ Collins J Friedrich AK Stimming U Dutcher JR Lipkowski J 《Langmuir : the ACS journal of surfaces and colloids》2012,28(5):2455-2464
Quantitative subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was used to determine the conformation and orientation of sodium dodecyl sulfate (SDS) molecules adsorbed at the single crystal Au(111) surface. The SDS molecules form a hemimicellar/hemicylindrical (phase I) structure for the range of potentials between -200 ≤ E < 450 mV and condensed (phase II) film for electrode potentials ≥500 mV vs Ag/AgCl. The SNIFTIRS measurements indicate that the alkyl chains within the two adsorbed states of SDS film are in the liquid-crystalline state rather than the gel state. However, the sulfate headgroup is in an oriented state in phase I and is disordered in phase II. The newly acquired SNIFTIR spectroscopy measurements were coupled with previous electrochemical, atomic force microscopy, and neutron reflectivity data to improve the current existing models of the SDS film adsorbed on the Au(111) surface. The IR data support the existence of a hemicylindrical film for SDS molecules adsorbed at the Au(111) surface in phase I and suggest that the structure of the condensed film in phase II can be more accurately modeled by a disordered bilayer. 相似文献
9.
Limmer SJ Kulp EA Switzer JA 《Langmuir : the ACS journal of surfaces and colloids》2006,22(25):10535-10539
The amphoteric nature of ZnO is used to produce the material from strongly alkaline solution. The solution pH is lowered globally to produce ZnO powder, and it is lowered locally at a Au(111) surface to produce epitaxial films. ZnO powder is precipitated from a solution of 10 mM Zn(II) in 0.25 M NaOH by simply adding 1 M HNO3 to the solution. For the film electrodeposition, the local pH at the electrode surface is decreased by electrochemically oxidizing the ascorbate dianion. The chemically precipitated ZnO powder grows with a sea urchin-like nanostructure, whereas the electrodeposited films have a columnar structure. ZnO electrodeposited onto a Au(111) single crystal has a ZnO(0001)[1011]//Au(111)[110] orientation relationship. 相似文献
10.
Hernandez F Baltruschat H 《Langmuir : the ACS journal of surfaces and colloids》2006,22(10):4877-4884
Three different single crystals, Au(111), Au(332), and Au(331), were used as the substrate for palladium deposition in the underpotential deposition (UPD) regime. The Au(111) single crystal was used for control experiments to compare the behavior of the vicinal surfaces. Cyclic voltammetry in 0.1 M sulfuric acid solution, as well as electrochemical impedance spectroscopy (EIS) were used to study the hydrogen adsorption on the Pd thin films. Our results suggest that the voltammetric peaks at approximately 0.3 V versus the reversible hydrogen electrode (RHE) are related to the adsorption of hydrogen at large palladium terraces, and that at least two adjacent Pd rows are needed in order for the adsorption to take place. Further cycling to more positive potentials leads to the oxidation and slow dissolution of the Pd film. The behavior of the oxidation cycles is explained in terms of a higher stability of Pd at the steps. 相似文献
11.
We described the first scanning tunneling microscopy study of spreading unilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) at a Au(111) electrode surface. At the initial stage of the film formation, the molecular resolution images revealed that DMPC molecules are adsorbed flat with the acyl chains oriented parallel to the surface. The molecules assemble into double rows by aligning the acyl chains in the nearest neighbor direction of the reconstructed Au(111) surface and assuming a 90 +/- 10 degrees angle with respect to line of the molecular row. After approximately 30 min, this film is transformed into a hemimicellar state with long rows characteristic for the formation of hemicylindrical surface micelles. At hydrophilic surfaces such as glass, spreading of vesicles involves adsorption, rupture, and sliding of a single bilayer on a lubricating film of the solvent. We have provided the first evidence that a different mechanism is involved in spreading the vesicles at gold. The molecules released by rupture of vesicles self-assemble into an ordered film, and the assembly is controlled by the chain-substrate interaction. 相似文献
12.
The coadsorption of the anionic and cationic components of a model quaternary ammonium bromide surfactant on Au(111) has been measured using the thermodynamics of an ideally polarized electrode. The results indicate that both bromide and trimethyloctylammonium (OTA(+)) ions are coadsorbed over a broad range of the electrical state of the gold surface. At negative polarizations, the Gibbs surface excess of the cationic surfactant is largely unperturbed by the presence of bromide ions in solution. However, when the Au(111) surface is weakly charged the existence of a low-coverage, gaslike phase of adsorbed halide induces an appreciable (~25%) enhancement of the interfacial concentration of the cationic surfactant ion. At more positive polarizations, the coadsorbed OTA(+)/Br(-) layer undergoes at least one phase transition which appears to be concomitant with the lifting of the Au(111) reconstruction and the formation of a densely packed bromide adlayer. In the absence of coadsorbed halide, the OTA(+) ions are completely desorbed from the Au(111) surface at the most positive electrode polarizations studied. However, with NaBr present in the electrolyte, a high surface excess of bromide species leads to the stabilization of adsorbed OTA(+) at such positive potentials (or equivalent charge densities). 相似文献
13.
《Bioelectrochemistry and bioenergetics (Lausanne, Switzerland)》1980,7(3):517-526
The alternating current polarograms of cytosine, cytidine and deoxycytidine at pH 5 and cytidine at pH 9 were measured. With increasing concentration of the cytosine derivatives a sort of a pit appears on the a.c. polarograms indicating the region of potentials at which the bases and/or nucleosides are reoriented at the electrode surface from the planar position to the perpendicular one, associate and form a compact surface film. Cytidine at pH 5 begins to form a pit starting at a concentration of about 15 mM. At pH 9 cytidine begins associate already at a concentration of 7 mM. Deoxycytidine at pH 5 associate on the electrode surface at still lower concentrations than cytidine.The potential Upit of the centre of the pit of the investigated derivatives shifts to more negative values in the order deoxycytidine pH 5 (−0.45) - cytidine pH 5 (−0.70) - cytidine pH 9 (−0.85) cytosine pH 5 (−1.20 V). This order seems to correlate with the increasing value of the electrostatic attraction of the cytosine derivatives on the negatively charged electrode via their positive charge on N-3 and/or dipole moment. According to this conception the greatest electrostatic adsorption on the negatively charged electrode should be exhibited by cytosine at pH 5, which is attracted to the electrode via the protonated N-3, the next in the series being cytidine at pH 9, which is attracted to the electrode via the dipole moment. The smallest electrostatic adsorption exhibits deoxycytidine at pH 5, by which the effective value of the dipole moment is reduced due to the positive charge on N-3.The more negative is the potential Upit of the pit of nucleosides, the lower is the capacitance of the minimum of the pit indicating the changes in the orientation of the adsorbed nucleosides and/or changes of the compactness of the surface film. The possible orientations of the cytosine derivatives in the compact layer on the electrode surface are presented. At more negative electrode potentials the positive charge (cytosine at pH 5) or positive end of dipole moment (cytidine at pH 9) points to the electrode surface.With cytidine at pH 9 the pit disappears at concentrations higher than about 100 mM, probably due to the self-association of the neutral cytidine molecules in the bulk of solution. At pH 5 the pit is observed with all of the investigated derivatives up to the highest concentrations. The self-association is at pH 5 possibly prevented due to the repulsion of charges at N-3. 相似文献
14.
The adsorption of a model quaternary ammonium surfactant, octyltrimethylammonium triflate, on Au(111) has been studied using capacity and chronoculometry methods. The surfactant adsorbs on the metal surface as a non‐dissociated ion pair at moderate potentials but can be desorbed by either positive or negative polarization. Within the adsorption region, two states are observed which correspond to a horizontal monolayer and a higher coverage vertically oriented film. Measurements of capacity transients upon potential steps reveal a slow organization of the molecular film. Although it is possible to equate the transients to known surfactant film aggregate geometries, the results are in disagreement with thermodynamic results. In comparison with other studies, the results indicate that the states of surfactant adsorption depend on surfactant chain length and electrode crystallography. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
Multibranched gold (Au) nanocomposite materials encapsulated by poly(o-phenylenediamine) (PoPD) (Au@PoPD) were synthesized in a Nafion polymer film through the electroless synthetic route. The micro-heterogeneous structured Nafion film acted as a reaction vessel and as the template for the formation of Au@PoPD nanocomposite materials leading to the formation of highly uniform distribution of high density of the polymer-gold nanocomposite material. The formation of Au@PoPD nanomaterials at the GP/Nf surface was scrutinized by recording in situ absorption spectra and was characterized. The formation of the (111) plane of gold was dominant at the Au@PoPD nanocomposite. The ratio of the benzenoid and quinoid units of the PoPD (ca. 1.65) observed for the Au@PoPD confirmed that the micro-heterogeneous structure of Nf film acted as a reaction vessel and as template for the formation of Au@PoPD nanocomposite material. Both PoPD and Au at the Au@PoPD nanocomposite showed electrochemical activities at the GC/Nf-Au@PoPD modified electrode. The electrocatalytic activity of the GC/Nf-Au@PoPD modified electrode was studied for oxygen reduction reaction (ORR). 相似文献
16.
Horswell SL Zamlynny V Li HQ Merrill AR Lipkowski J 《Faraday discussions》2002,(121):405-22;discussion 441-62
Chronocoulometry and photon polarisation modulation infrared reflection absorption spectroscopy (PM-IRRAS) have been employed to study the fusion of dimyristoylphosphatidylcholine (DMPC) vesicles onto a Au(111) electrode surface. The results show that fusion of the vesicles is controlled by the electrode potential or charge at the electrode surface (sigmaM). At charge densities of -15 microC cm(-2) < sigmaM < 0 microC cm(-2), DMPC vesicles fuse to form a condensed film. When sigmaM < -15 microC cm(-2), de-wetting of the film from the electrode surface occurs. The film is detached from the electrode surface; however, phospholipid molecules remain in its close proximity in an ad-vesicle state. The state of the film can be conveniently changed by adjustment of the potential applied to the gold electrode. PM-IRRAS experiments demonstrated that the potential-controlled transitions between various DMPC states proceed without conformational changes and changes in the packing of the acyl chains of DMPC molecules. However, a remarkable change in the tilt angle of the acyl chains with respect to the surface normal occurs when ad-vesicles spread to form a film at the gold surface. When the bilayer is formed at the gold surface, the acyl chains of DMPC molecules are significantly tilted. The IR spectra have also demonstrated a pronounced change in the hydration of the polar head region that accompanies the spreading of ad-vesicles into the film. For the film deposited at the electrode surface, the infrared results showed that the temperature-controlled phase transition from the gel state to the liquid crystalline state occurs within the same temperature range as that observed for aqueous solutions of vesicles. The results presented in this work show that PM-FTIR spectroscopy, in combination with electrochemical techniques, is an extremely powerful tool for the study of the structure of model membrane systems at electrode surfaces. 相似文献
17.
《Journal of Electroanalytical Chemistry》1983,143(1-2):375-396
In this paper quantitative studies of the adsorption of diethylether on the three low-index faces (111), (100) and (110) of the gold electrode are presented. The equilibrium charge densities at the gold electrode were determined from combined chronocoulometric and admittance measurements. The adsorption parameters such as free energy of adsorption ΔGA, limiting Gibbs excess Γmax, lateral interaction constant a, etc. were calculated and compared with earlier results relative to the mercury electrode surface. These adsorption parameters were next discussed in terms of the properties characteristic for the nature (liquid, solid) and the structure (crystallographic orientation) of the surfaces investigated. Under the assumption that: (1) diethylether adsorption is a water-substitution process, and (2) the ether-metal interactions are weak and change slightly with the nature and the structure of the surface, the free energies of adsorption ΔGA0 were used as a probe of the surface hydrophilicity. The following series of increasing hydrophilicity was proposed:Au(111)≦Hg≦Au(100)<Au(110) and the earlier literature estimations of gold hydrophilicity were critically discussed. 相似文献
18.
Sorenson TA Morton SA Waddill GD Switzer JA 《Journal of the American Chemical Society》2002,124(25):7604-7609
Half-metallic ferrimagnetic materials such as Fe(3)O(4) are of interest for use in spintronic devices. These devices exploit both the spin and charge of an electron in spin-dependent charge transport. Epitaxial thin films of Fe(3)O(4) have been grown on the three low-index planes of gold by electrodeposition. On Au(110), a [110] Fe(3)O(4) orientation that is aligned with the underlying Au(110) substrate is observed. Thin films on Au(100) grow with three different orientations: [100], [111], and [511]. On Au(111), both [111] and [511] orientations of Fe(3)O(4) are observed. The [511] orientations are the result of twinning on [111] planes. A polarization value of approximately -40% at the Fermi level was measured by spin-polarized photoemission at room temperature for a thin film on Au(111). 相似文献
19.
The adsorption and adlayer structures of tetrathiofulvalene (TTF), tetracyanoquinodimethane (TCNQ) and TTF-TCNQ on Au(111)
have been systematically investigated by in situ electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry in 0.1 mol L−1 HClO4. All the three molecules were found to form well-ordered adlayers in the double-layer potential region of Au(111). For TTF
and TCNQ adlayers, (6×3) and (4×7) structures have been observed, respectively. A structural transition was observed on TCNQ
adlayer at potential negative of 0.08 V vs. the reversible hydrogen electrode (RHE), and induced a new phase with (3 × 12) structure. On the other hand, the charge transfer complex, TTF-TCNQ, self-organized into ordered domains with a lamellar
structure different from those of the pure TTF and TCNQ adlayers on Au(111). Its packing arrangement was comparable to surface
structures of either single crystal or thin film of TTF-TCNQ.
Supported by the National Natural Science Foundation of China (Grant Nos. 20673121, 20733004 & 20821003), the National Key
Project for Basic Research (Grant Nos. 2006CB806101 & 2006CB932100) and Chinese Academy of Sciences 相似文献
20.
Sagara T Nagata K Tsuruta H Nakashima N 《Chemical communications (Cambridge, England)》2002,(18):2116-2117
Potential-dependent dynamic adsorption-desorption and reorientation of a 4-pyridyl modified PAMAM G2 dendrimer at a Au(111) electrode has been demonstrated. 相似文献