STM imaging of electrically floating islands (original) (raw)
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The Journal of Physical Chemistry B, 2001
The dynamics of nanoscale island growth, stability, and dissolution, accompanying the potential-induced phase transitions between the (22 × 3) and (1 × 1) structures of the Au(111) surface in 0.1 M HClO 4 solution, have been investigated by potential pulse perturbation time-resolved scanning tunneling microscopy (P 3 TR-STM). Starting from a potential at which the reconstructed (22 × 3) phase is stable, a short positive potential pulse briefly brings the electrode to a potential at which the (1 × 1) phase is stable. This pulse induces a perturbation that lifts the Au(111)-(22 × 3) reconstruction completely, resulting in nanoscale island formation on the surface. The nanoscale islands are metastable and dissolve with time. The initial average island area and the island decay rate are related to the pulse amplitude and duration. The higher and longer the pulse, the smaller the average size of the islands produced and the more slowly the islands decay. This result reveals a "voltammetric annealing" process that may be important in stable island formation at electrochemical interfaces. The dynamics of individual islands are quite heterogeneous and nonmonotonic. Small islands decay faster than large islands. Even under metastable conditions, large islands frequently grow before ultimately decaying, providing evidence for electrochemical Ostwald ripening in this system. A simple model, based on perimeter detachment as the rate-limiting step, provides a qualitative explanation for the observed decay dynamics.
Island dynamics on charged silver electrodes: Kinetic Monte-Carlo simulations
Electrochimica Acta, 2009
The fluctuations of steps and the shapes of islands on metal surfaces generally depend strongly on the electrode potential, an effect that has been attributed to the interaction of local surface dipole moments with the double-layer field. In order to understand the details of this effect, we have calculated the relevant energies and dipole moments for the diffusion processes that govern the fluctuations of steps and island shapes on Ag(1 0 0). The corresponding rates have been used in kinetic Monte-Carlo simulations to explore the dynamics of these structures. Due to the field-dipole interactions the mobility of the surface becomes larger with increasing electrode potential. Fourier analysis allows us to determine the step stiffness and the kink energy, and from the shape of the islands we have obtained the line tension. All three quantities decrease with increasing double-layer field.
Applied Physics Letters, 1994
Scanning tunneling microscopy has been applied to observe hydrogen-terminated Si(111) surfaces at room temperature. A clear image was easily observed for a Si surface prepared by rinsing in pure water with very low dissolved oxygen after removal of native oxide by 1% HF solution dipping. A smooth surface in an atomic scale was exhibited in a 50×50 nm area. Completely triangular-shaped holes were observed on the surface. The holes were surrounded by steps which were very likely directed toward 〈112̄〉. The treatment of the surface was remarkably stable even after a 3 h air exposure. Furthermore, nm size pits were found at the bottom part of the triangular-shaped holes. The results imply that the nm size pits appeared to be due to microdefects and that the pits might be the origin of surface etching at the Si surface.
The Journal of Chemical Physics, 2015
Past scanning tunneling microscopy (STM) experiments of H manipulation on Pd(111), at low temperature, have shown that it is possible to induce diffusion of surface species as well as of those deeply buried under the surface. Several questions remain open regarding the role of subsurface site occupancies. In the present work, the interaction potential of H atoms with Pd(111) under various H coverage conditions is determined by means of density functional theory calculations in order to provide an answer to two of these questions: (i) whether subsurface sites are the final locations for the H impurities that attempt to emerge from bulk regions, and (ii) whether penetration of the surface is a competing route of on-surface diffusion during depletion of surface H on densely covered Pd . We find that a high H coverage has the effect of blocking resurfacing of H atoms travelling from below, which would otherwise reach the surface f cc sites, but it hardly alters deeper diffusion energy barriers. Penetration is unlikely and restricted to high occupancies of hcp hollows. In agreement with experiments, the Pd lattice expands vertically as a consequence of H atoms being blocked at subsurface sites, and surface H enhances this expansion. STM tip effects are included in the calculations self-consistently as an external static electric field. The main contribution to the induced surface electric dipoles originates from the Pd substrate polarisability. We find that the electric field has a non-negligible effect on the H-Pd potential in the vicinity of the topmost Pd atomic layer, yet typical STM intensities of 1-2 VÅ −1 are insufficient to invert the stabilities of the surface and subsurface equilibrium sites. C 2015 AIP Publishing LLC. [http://dx.
Surface Science, 1998
We propose to use low work function substrates to extend the possibilities of STM in the visualization of weakly-conducting overlayers. One such substrate, the (100) surface of LaB 6 , has the work function Q=2.5 eV, is easily obtainable by cleaving LaB 6 crystals and has sufficiently large atomically perfect areas. This surface is stable enough to allow STM investigations for reasonable times even in air. In addition, the polar character of chemical bonds on LaB 6 (100) favors adhesion and the orientational ordering in molecular overlayers deposited on it. We suggest that the utilization of such substrates may be particularly attractive in STM studies of large organic molecules.
Electronic mechanism of STM-induced diffusion of hydrogen on Si(100)
Faraday Discussions, 2000
We have observed a scanning tunneling microscopy (STM) induced lateral transfer of a single hydrogen atom on the Si(100) surface. The transfer rate of the hydrogen atom is proportional to the electron dose, indicating an electron-assisted transfer mechanism. Measurements of the relations between the transfer rate and the sample bias and temperature give further support for an electronic mechanism. The bias dependence of the transfer rate shows a peak, and from a Ðrst principles electronic structure calculation we show that the position of the peak is related to the energy of a localized surface resonance. We propose that the hydrogen transfer is related to inelastic hole scattering with this surface resonance. We develop a microscopic model for the hydrogen transfer, and using the experimental data we extract information on the resonance lifetime and the transfer yield per resonant electron. The transfer takes place by tunneling through a small excited state transfer barrier. The transfer rate is increased if the hydrogen atom before the resonant excitation is vibrationally excited, and this gives rise to an increasing transfer rate with increasing sample temperature. ¤ Present address : VirTech A/S,
STM-theory: Image potential, chemistry and surface relaxation
Progress in Surface Science, 2006
A critical review of the different methods used nowadays for calculating tunneling currents and STMimages is presented with a special emphasis on the role played by the interface image potential and the interaction between the tip and the sample at short distances. After presenting the most commonly used approaches to this problem, we discuss in full detail how the image potential modifies critically the interface tip-sample barrier and how neglecting this effect underestimates the tunneling currents by several orders of magnitude. Although interface non-local image potential effects are difficult to introduce in a plane-wave Density Functional approach, we show how a Green's function Density Functional formalism based on a local-orbital basis set allows us to introduce those image effects with a good accuracy. The effect of the interaction between the tip and the sample is illustrated for an Al-tip approaching an Al surface; and the role of the electronegative atoms adsorbed on the tip is discussed considering the O/Pd(1 1 1) interface and the effect of having an O-atom adsorbed on the tip apex. Finally, by analyzing the Si(1 1 2)-Ga interface we also show how the Green's function Density Functional approach based on a local orbital basis can also be reliably used to analyze surface steochiometries.