共查询到20条相似文献,搜索用时 31 毫秒
1.
We have developed the mechanically controllable break junction setup with an electrochemical cell (EC-MCBJ) to measure the electric conductance of metal nanowires under electrochemical potential control. The electric conductance of Au nanowires was investigated in 0.1 M Na2SO4 solution using EC-MCBJ. The conductance of the Au nanowires was quantized in units of G0 (=2e2/h), showing clear features in the conductance histogram. The atomic contact with a specific conductance value was kept for >5 s, indicating the relatively high stability of the present EC-MCBJ system. 相似文献
2.
Manabu Kiguchi Tatsuya Konishi Shinichi Miura Kei Murakoshi 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):530
We have mechanically fabricated Ni and Cu nano-constrictions in solution to study their quantized conductance behavior under electrochemical potential control. Conductance quantization was observed at both metals in solution at room temperature for the first time. The conductance of Cu nano-constriction was quantized in units of G0(=2e2/h). A sharp 1G0 peak was observed in the conductance histogram. For Ni, a rather broad peak at 1–1.5G0 was observed in the histogram. The conductance quantization behavior was discussed by comparing previously documented results of nano-constrictions fabricated in air or ultra-high vacuum conditions, with those fabricated in solution. 相似文献
3.
We study the electrical conductance of gold nanoconstrictions by controlling the electrochemical potential. At positive potentials, the conductance is quantized near integer multiples of G0(2e(2)/h) as shown by well-defined peaks in the conductance histogram. Below a certain potential, however, additional peaks near 0.5G(0) and 1. 5G(0) appear in the histogram. The fractional conductance steps are as stable and well defined as the integer steps. The experimental data are discussed in terms of electrochemical-potential-induced defect scattering and Fermi energy shift, but a complete theory of the phenomenon is yet to be developed. 相似文献
4.
Daniel Friebel Christian Schlaup Peter Broekmann Klaus Wandelt 《Surface science》2006,600(13):2800-2809
We describe the electrochemical preparation of an ultrathin copper sulfide film on Au(1 1 1) and its structural characterization by in situ STM. The first step, underpotential deposition of a Cu submonolayer from CuSO4/H2SO4 solution, is followed by two electrolyte exchanges for (i) Cu-free (blank) H2SO4 solution and (ii) NaOH/Na2S solution. The well-known (√3 × √3)R30° structure of the upd Cu layer is stable in the blank electrolyte for at least 2 h. After exposure to bisulfide, the Cu layer contracts and forms two-dimensional islands of two distinct ordered surface phases, i.e. a rectangular and, at higher potentials, a hexagonal phase, with Cu-free Au(1 1 1) regions between them, the latter exhibiting the characteristic (√3 × √3)R30°-S adlayer structure. Potential changes lead to a complex phase behaviour including HS− ? Sx oxidation/reduction and, at strongly anodic potentials, dissolution of the Cu adlayer. 相似文献
5.
Wang Geun Shim 《Applied Surface Science》2010,256(17):5566-865
The heterogeneous adsorption and catalytic oxidation of benzene, toluene and o-xylene (BTX) over the spent platinum catalyst supported on activated carbon (Pt/AC) as well as the chemically treated spent catalysts were studied to understand their catalytic and adsorption activities. Sulfuric aqueous acid solution (0.1N, H2SO4) was used to regenerate the spent Pt/AC catalyst. The physico-chemical properties of the catalysts in the spent and chemically treated states were analyzed by using nitrogen adsorption-desorption isotherm and elemental analysis (EDX). The gravimetric adsorption and the light-off curve analysis were employed to study the BTX adsorption and oxidation on the spent catalyst and its modified Pt/AC catalysts. The experimental results indicate that the spent Pt/AC catalyst treated with the H2SO4 aqueous solution has a higher toluene adsorption and conversion ability than that of the spent Pt/AC catalyst. A further studies of H2SO4 treated Pt/AC catalyst on their catalytic and heterogeneous adsorption behaviours for BTX revealed that the activity of the H2SO4 treated Pt/AC catalyst follows the sequence of benzene > toluene > o-xylene. The adsorption equilibrium isotherms of BTX on the H2SO4 treated Pt/AC were measured at different temperatures ranging from 120 to 180 °C. To correlate the equilibrium data and evaluate their adsorption affinity for BTX, the two sites localized Langmuir (L2m) isotherm model was employed. The heterogeneous surface feature of the H2SO4 treated Pt/AC was described in detail with the information obtained from the results of isosteric enthalpy of adsorption and adsorption energy distributions. Furthermore, the activity of H2SO4 treated Pt/AC about BTX was found to be directly related to the Henry's constant, isosteric enthalpy of adsorption and adsorption energy distribution functions. 相似文献
6.
R.G. Wilks E. Santos Jr E.Z. Kurmaev M.V. Yablonskikh A. Moewes N.K. Kuromoto G.A. Soares 《Journal of Electron Spectroscopy and Related Phenomena》2009
The oxide layers of electrolytic oxidized titanium (Ti) were characterized using Ti L2,3 and O K edge X-ray absorption. The spectra show that the structure of the oxide layers that are formed during a 1 min treatment are dependent on the concentration of the electrolyte (H2SO4 or Na2SO4) with which the Ti surface was treated, and also on the magnitude of the potential that was applied during the anodic oxidation process (100 V or 150 V). It is found that a potential of 150 V and an electrolyte concentration of 0.5 M or 1.0 M produces a layer of TiO2 having rutile crystal structure. 相似文献
7.
G. Mészáros S. Kronholz S. Karthäuser D. Mayer T. Wandlowski 《Applied Physics A: Materials Science & Processing》2007,87(3):569-575
Copper nanocontacts and molecular-sized nanogaps were prepared and characterized at electrified solid/liquid interfaces employing
lithographic and electrochemical techniques. A dedicated four-electrode potentiostat was developed for controlling the electrochemical
fabrication process and for monitoring the electrical characteristics of the nanostructures created. The formation and breaking
of Cu nanocontacts exhibits conductance quantization characteristics. The statistical analysis of conductance histograms revealed
a preferential stability of nanocontacts with integer values of G0, with a clear preference for 1 G0, 2 G0 and 3 G0. The growth of molecular-sized gaps shows quantized tunneling current, which is attributed to the discrete nature of Cu atoms,
water molecules, and specifically adsorbed ions.
PACS 73.23Ad; 73.63.Rt; 82.45.Yz; 85.35.-p 相似文献
8.
Haibo Zhao 《Surface science》2009,603(23):3355-12149
The influence of hydrogen coadsorption on hydrocarbon chemistry on transition metal surfaces is a key aspect to an improved understanding of catalytic selective hydrogenation. We have investigated the effects of H preadsorption on adsorption and reaction of 1,3-butadiene (H2CCHCHCH2, C4H6) on Pt(1 1 1) surfaces by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Preadsorbed hydrogen adatoms decrease the amount of 1,3-butadiene chemisorbed on the surface and chemisorption is completely blocked by the hydrogen monolayer (saturation) coverage (θH = 0.92 ML). No hydrogenation products of reactions between coadsorbed H adatoms and 1,3-butadiene were observed to desorb in TPD experiments over the range of θH investigated (θH = 0.6-0.9 ML). This is in strong contrast to the copious evolution of ethane (CH3CH3, C2H6) from coadsorbed hydrogen and ethylene (CH2CH2, C2H4) on Pt(1 1 1). Hydrogen adatoms effectively (in a 1:1 stoichiometry) remove sites from interaction with chemisorbed 1,3-butadiene, but do not affect adjacent sites. The adsorption energy of coadsorbed 1,3-butadiene is not affected by the presence of hydrogen on Pt(1 1 1). The chemisorbed 1,3-butadiene on hydrogen preadsorbed Pt(1 1 1) completely dehydrogenates to H2 and surface carbon upon heating without any molecular desorption detected, which is identical to that observed on clean Pt(1 1 1). In addition to revealing aspects of site blocking that should have broad implications for hydrogen coadsorption with hydrocarbon molecules on transition metal surfaces in general, these results also provide additional basic information on the surface science of selective catalytic hydrogenation of butadiene in butadiene-butene mixtures. 相似文献
9.
Weiping Zhou 《Surface science》2004,573(2):176-182
We present a study of the influence of an electrostatic potential across the Au(1 1 1)/4,4′-dithiodipyridine (PySSPy)-SAM/0.01 M NaOH interface on the electron binding energies of the N 1s and S 2p orbitals of the adsorbate, as probed by X-ray photoelectron spectroscopy (XPS). The observed systematic binding energy shift for N(1s) with electrode potential of −0.9 eV/V has been assigned to a so-called electrochemical shift, i.e., an apparent shift of the binding energy due to the potential drop in the electric double layer. No systematical shift was observed for the S(2p) core level of the thiol with electrode potential. The results are contrasted by measurements in 0.1 M H2SO4, where no electrochemical shift was found for the protonated nitrogen. 相似文献
10.
Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H2SO4 was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy disperse spectrometer (EDS). The weight loss results showed that berberine is an excellent corrosion inhibitor for mild steel immersed in 1 M H2SO4. Potentiodynamic curves suggested that berberine suppressed both cathodic and anodic processes for its concentrations higher than 1.0 × 10−4 M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H2SO4 containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increased with the inhibitor concentration rising. A good fit to Flory-Huggins isotherm was obtained between surface coverage degree and inhibitor concentration. The surface morphology and EDS analysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by the weight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study. 相似文献
11.
The bias-dependence of the quantized conductance in Au nanocontacts has been measured at liquid He temperature. A well-defined 1G0 peak (G0=2e2/h is the conductance quantum unit) appears in the conductance histogram. With increasing the bias, the 1G0 peak decreases in height, while its position remains unshifted. This behavior of the 1G0 peak is just the same as that observed at room temperature [H. Yasuda, A. Sakai, Phys. Rev. B 56 (1997) 1069]. The critical bias Vbc at which the 1G0 peak disappears is ∼2.2 V, which is not much different from Vbc at 300 and 77 K. This weak temperature dependence of Vbc is compatible with high-current contact instability due to electromigration of contact atoms. 相似文献
12.
T. Mangen 《Journal of magnetism and magnetic materials》2010,322(13):1863-23808
The formation of Co films on polycrystalline copper in diluted sulphuric acid was investigated by employing cyclic voltammetry (CV), atomic force microscopy, and in-situ magneto-optic Kerr effect (MOKE) techniques. By comparing CV measurements in the pure supporting electrolyte (11 mM K2SO4/1 mM H2SO4) and the cobalt sulphate solution (10 mM K2SO4/1 mM H2SO4/1 mM CoSO4), peaks from voltammetric cycling for copper dissolution, readsorption of dissolved copper ions, cobalt bulk dissolution and oxidation of hydrogen could be resolved. As the electroplating time increases, the size of the Co clusters increases and the deposition of Co corresponds to island growth. The first hysteresis loop occurs at a Co thickness of 0.33 nm in the longitudinal configuration. For films thinner than 7 nm, the Kerr intensity increases linearly because the Curie temperature of the film is well above 300 K. 相似文献
13.
It is well established from experiments in premixed, laminar flames, jet-stirred reactors, flow reactors, and batch reactors that SO2 acts to catalyze hydrogen atom removal at stoichiometric and reducing conditions. However, the commonly accepted mechanism for radical removal, SO2 + H(+M) ? HOSO(+M), HOSO + H/OH ? SO2 + H2/H2O, has been challenged by recent theoretical and experimental results. Based on ab initio calculations for key reactions, we update the kinetic model for this chemistry and re-examine the mechanism of fuel/SO2 interactions. We find that the interaction of SO2 with the radical pool is more complex than previously assumed, involving HOSO and SO, as well as, at high temperatures also HSO, SH, and S. The revised mechanism with a high rate constant for H + SO2 recombination and with SO + H2O, rather than SO2 + H2, as major products of the HOSO + H reaction is in agreement with a range of experimental results from batch and flow reactors, as well as laminar flames. 相似文献
14.
A new compound, K4(SO4)(HSO4)2(H3AsO4) was synthesized from water solution of KHSO4/K3H(SO4)2/H3AsO4. This compound crystallizes in the triclinic system with space group P1¯ and cell parameters: a=8.9076(2) Å, b=10.1258(2) Å, c=10.6785(3) Å; α=72.5250(14)°, β=66.3990(13)°, γ=65.5159(13)°, V=792.74(3) Å3, Z=2 and ρcal=2.466 g cm−3. The refinement of 3760 observed reflections (I>2σ(I)) leads to R1=0.0394 and wR2=0.0755. The structure is characterized by SO42−, HSO4− and H3AsO4 tetrahedra connected by hydrogen bridge to form two types of dimer (H(16)S(3)O4−?S(1)O42− and H(12)S(2)O4−?H3AsO4). These dimers are interconnected along the [1¯ 1 0] direction by the hydrogen bonds O(3)-H(3)?O(6). They are also linked by the hydrogen bridge assured by the hydrogen atoms H(2), H(3) and H(4) of the H3AsO4 group to build the chain S(1)O4?H3AsO4 which are parallel to the “a” direction. The potassium cations are coordinated by eight oxygen atoms with K-O distance ranging from 2.678(2) to 3.354(2) Å.Crystals of K4(SO4)(HSO4)2(H3AsO4) undergo one endothermic peak at 436 K. This transition detected by differential scanning calorimetry (DSC) is also analyzed by dielectric and conductivity measurements using the impedance spectroscopy techniques. The obtained results show that this transition is protonic by nature. 相似文献
15.
S. Frappart X. Feaugas F. Thebault H. Marchebois 《Journal of Physics and Chemistry of Solids》2010,71(10):1467-1479
Diffusion and trapping mechanisms are studied in order to improve Hydrogen embrittlement (HE) resistance of high yield strength steels. Investigations were carried on Fe-C-Mo model steel with a quenched and tempered martensitic microstructure. Hydrogen diffusion was studied by using the electrochemical permeation technique. The influence of the charging current densities in 1 M H2SO4 at ambient temperature shows a relation between the apparent diffusion coefficient Dapp and the apparent subsurface concentration of hydrogen C0app. Two domains can be separated and are mainly associated with a competition between two distinct processes: hydrogen trapping and hydrogen diffusion. These results are correlated to the quantities of reversible and irreversible traps into the membrane. Moreover, the experimental results revealed that the apparent diffusion coefficient increases and the total amount of trapped hydrogen decreases with temperature. The activation energy of the diffusion process (0.26 eV) and the trapping process (0.58 eV) are supposed to be, respectively, affiliated with lattice diffusion and with trapping on incidental dislocations and/or on martensitic lath interfaces due to misorientations (geometric necessary dislocations). 相似文献
16.
The electrodeposition of Au on Pt(1 1 1) from electrolytes containing μM concentrations of was studied by in situ scanning tunneling microscopy. Under these conditions the Au flux is limited by diffusion in the electrolyte over a wide potential range, which allows to assess the effect of the electrochemical environment on the growth kinetics. Similar to gas phase metal deposition Au film growth proceeds via nucleation and lateral growth of Au monolayer islands, with the saturation island density strongly depending on the deposition potential and on the anion species in the electrolyte. For deposition in H2SO4 solution the saturation island density continuously increases with increasing potential between −0.2 and 0.5 V (SCE), whereas in Cl-containing H2SO4 it first decreases and then increases again. Following nucleation and growth theories this behavior can be attributed to potential-induced changes of the Au surface mobility, caused by changes in the density and structure of coadsorbed sulfate/bisulfate and chloride adlayers. Under conditions of high Au surface mobility multilayer growth proceeds via a typical Stranski-Krastanov growth mode, with layer-by-layer growth of a pseudomorphic Au film up to 2 ML and 3D growth of structurally relaxed islands at higher coverage, indicating thermodynamic control under these conditions. 相似文献
17.
A.A. Gapud A.P. Weber J.A. Alexander L. Pham A. Khan R.I. Leatherbury A.P. Reyes L.L. Lumata P.L. Kuhns E.J. Valente R.E. Sykora 《Journal of Physics and Chemistry of Solids》2014
The synthesis and some physical properties of a new quasi-one-dimensional tetracyanidoplatinate, Cs4[Pt(CN)4](CF3SO3)2 (CsCP(OTf)) are reported and described in comparison to the well-known K2[Pt(CN)4]Br0.30·3.2H2O (KCP). Single-crystal X-ray diffraction reveals Pt–Pt spacings to be greater than those of KCP by 5% longitudinal and 38% transverse, but much shorter than comparable spacings in other non-partially oxidized platinates. Anomalies are observed between temperatures 100 K and 200 K: (1) Longitudinal DC conductivity is two orders of magnitude higher and is non-monotonic with temperature, showing a minimum at around 170 K. (2) Nuclear magnetic resonance (NMR) longitudinal relaxation time T1 is at least three orders of magnitude higher than that of KCP, and is also non-monotonic with temperature, showing a sharp peak at around 120 K. Since X-ray diffraction reveals no structural transition at 120 K, these suggest a possible lattice freezing or stiffening at around 120 K. 相似文献
18.
A new phosphor in the Cl-F system doped with Dy, Ce and Eu has been reported. Characterization of this phosphor using XRD, PL and TL techniques is described. Polycrystalline Na6(SO4)2FCl:Dy; Na6(SO4)2FCl:Ce and Na6(SO4)2FCl:Eu phosphors prepared by a solid state diffusion method have been studied for their X-ray diffraction, photoluminescence (PL) and thermoluminescence (TL)characteristics. The PL excitation and emission spectra of phosphors were obtained. Dy3+ emission in the host at 475 and 570 nm is observed due to 4F9/2→6H15/2 and 4F9/2→6H13/2 transition, respectively, whereas the PL emission spectra of Na6(SO4)2FCl:Ce phosphor shows the Ce3+ emission at 322 nm due to 5d→4f transition of Ce3+ ion. In Na6(SO4)2FCl:Eu lattice, Eu2+ as well as Eu3+ emissions are observed. The emission of europium ion in this compound exhibits the blue as well as red emission. The TL glow curves of the same compounds have the simple structure with a prominent peak at 150, 175 and 200 °C. TL response, fading, reusability and trapping parameters of the phosphors are also studied. The TL glow curves of γ-irradiated Na6(SO4)2FCl sample show one glow peak indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The trapping parameters associated with the prominent glow peak are calculated using Chen’s half width method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. The intensity of the TL glow peaks increases with increase of the added γ-ray dose to the samples. 相似文献
19.
Ping He Xiaofang Yi Yongjun Ma Wei Wang Faqin Dong Licheng Du Hongtao Liu 《Journal of Physics and Chemistry of Solids》2011,72(11):1261-1264
The effect of rare earth compound, Gd2O3, on the microstructure and the hydrogen evolution property of Ni–Co alloy electrode was studied. The morphology and microstructure were characterized by SEM and XRD, respectively, and the electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from steady-state polarization curves, Tafel curves and electrochemical impedance spectroscopy measurements carried out in 0.50 M Na2SO4+0.10 M H2SO4 solution. It was found that the embedded Gd2O3 particles largely enhanced the electrocatalytic activity of Ni–Co alloy electrode to hydrogen evolution reaction. 相似文献
20.
Krzysztof Miecznikowski Pawel J. KuleszaSebastian Fiechter 《Applied Surface Science》2011,257(19):8215-8222
RuSex electrocatalytic nanoparticles were deposited onto hybrid carriers composed of Black Pearl carbon-supported tungsten oxide; and the resulting system's electrochemical activity was investigated during oxygen reduction reaction. The tungsten oxide-utilizing and RuSex nanoparticle-containing materials were characterized using transmission electron microscopy, X-ray diffraction and electrochemical diagnostic techniques such as cyclic voltammetry and rotating ring-disk voltammetry. Application of Black Pearl carbon carriers modified with ultra-thin films of WO3 as matrices (supports) for RuSex catalytic centers results during electroreduction of oxygen in 0.5 mol dm−3 H2SO4 (under rotating disk voltammetric conditions) in the potential shift of ca. 70 mV towards more positive values relative to the behavior of the analogous WO3-free system. Also the percent formation (at ring in the rotating ring-disk voltammetry) of the undesirable hydrogen peroxide has been decreased approximately twice by utilizing WO3-modified carbon carriers. The results are consistent with the bifunctional mechanism in which oxygen reduction is initiated at RuSex centers and the hydrogen peroxide intermediate is reductively decomposed at reactive WO3-modified Black Pearl supports. The electrocatalytic activity of the system utilizing WO3-modified Black Pearl supports has been basically unchanged upon addition of acetic acid, formic acid or methyl formate to the sulfuric acid supporting electrolyte. 相似文献