Dynamics and Energetics of Ge(001) Dimers

The dynamic behavior of surface dimers on Ge(001) has been studied by positioning the tip of a scanning tunneling microscope over single flip-flopping dimers and measuring the tunneling current as a function of time. We observe that not just symmetric, but also asymmetric appearing dimers exhibit flip-flop motion. The dynamics of flip-flopping dimers can be used to sensitively gauge the local potential landscape of the surface. Through a spatial and time-resolved measurement of the flip-flop frequency of the dimers, local strain fields near surface defects can be accurately probed

Influence of dimer buckling on dimer diffusion: A scanning tunneling microscopy study

The diffusion of Ge dimers along the substrate dimer rows of Ge(001) has been investigated with scanning tunneling microscopy. The jump frequency of on-top Ge dimers along symmetric dimer rows at room temperature is found to be eight times higher than the diffusion along asymmetric dimer rows (0.36 s–1 versus 0.044 s–1). We ascribe this difference to limitations associated with the rocking motion that a dimer has to perform while diffusing along asymmetric dimer rows

Atomic manipulation on semiconductor surfaces at room temperature by Scanning Tunneling Microscopy

The scanning tunnelling microscope (STM) can be used as a tool for assembling nanostructures at the atomic level. In this article we briefly review several pathways for controlled manipulation of atoms and molecules on semiconductor surfaces at room temperature. As an illustrative example we discuss the controlled manipulation of atomic platinum chains. We were able to carry the constituting dimers of the atomic Pt chains from point to point with atomic precision at room temperature. Besides the ultimate control of the surface structure we also show that the manipulated Pt dimer can be attached to the apex of the STM tip in various stable configurations

Atomic seesaws

The dynamics of two types of atomic seesaws are studied by open feedback loop scanning tunneling microscopy. The first type of atomic seesaw is a regular Ge dimer of the dimer reconstructed Ge(001) surface and the second type of atomic seesaw is a dimer located on the ridges of Au induced nanowires on a Ge(001) surface. On the bare Ge(001) surface the flip-flop motion of the dimers is induced by phasons, which perform a one-dimensional random walk along the substrate dimer rows. The phasons on the Au induced nanowires ridges are pinned and therefore only a limited number of dimers exhibit flip-flop behavior for the Au/Ge(001) system

Microscopic Study of the Spinodal Decomposition of Supported Eutectic Droplets during Cooling:PtGe/Ge{110}

[Image: see text] We embarked on an in situ low-energy electron microscopy, photo-electron emission microscopy, and selected area low-energy electron diffraction study during the cooling of huge eutectic droplets through the critical stages of the eutectic transition. On this journey through uncharted waters, we revealed an expected initial shrinking of the exposed area of the droplet, followed by an unanticipated expansion. We attribute this behavior to an initial fast amorphization of the interface between the droplet and surface, followed by the recrystallization of Ge expelled from the droplet at the interface. As a major surprise, we discovered the emergence of extensive “spaghetti”-like patterns, which are rationalized in terms of parallel Ge ripples oriented along, mainly, [−554] and [−55–4] directions. They emerge during spinodal decomposition when passing the eutectic temperature of the system. Their sides are defined by Ge{111} and Ge{11–1} vicinals covered with Pt-modified (√3 × √3) superstructures. The distance between adjacent ripples is about 18 nm

Leidenfrost temperature increase for impacting droplets on carbon-nanofiber surfaces

Droplets impacting on a superheated surface can either exhibit a contact boiling regime, in which they make direct contact with the surface and boil violently, or a film boiling regime, in which they remain separated from the surface by their own vapor. The transition from the contact to the film boiling regime depends not only on the temperature of the surface and kinetic energy of the droplet, but also on the size of the structures fabricated on the surface. Here we experimentally show that surfaces covered with carbon-nanofibers delay the transition to film boiling to much higher temperature compared to smooth surfaces. We present physical arguments showing that, because of the small scale of the carbon fibers, they are cooled by the vapor flow just before the liquid impact, thus permitting contact boiling up to much higher temperatures than on smooth surfaces. We also show that, as long as the impact is in the film boiling regime, the spreading factor of impacting droplets follows the same \We^{3/10} scaling (with \We the Weber number) found for smooth surfaces, which is caused by the vapor flow underneath the droplet.Comment: 10 pages, 6 figure

Building micro-soccer-balls with evaporating colloidal fakir drops

Evaporation-driven particle self-assembly can be used to generate three-dimensional microstructures. We present a new method to create these colloidal microstructures, in which we can control the amount of particles and their packing fraction. To this end, we evaporate colloidal dispersion droplets on a special type of superhydrophobic micro-structured surface, on which the droplet re- mains in Cassie-Baxter state during the entire evaporative process. The remainders of the droplet consist of a massive spherical cluster of the microspheres, with diameters ranging from a few tens up to several hundreds of microns. We present scaling arguments to show how the final particle packing fraction of these balls depends on the dynamics of the droplet evaporation.Comment: Manuscript Submitted to Physical Review Letters, 29th February 201

Controlled damaging and repair of self-organized nanostructures by atom manipulation at room temperature

The possibility of controlled local demolition and repair of the recently discovered self-organized Pt nanowires on Ge(001) surfaces has been explored. These nanowires are composed of Pt dimers, which are found to be rather weakly bound to the underlying substrate. Using this property, we demonstrate the possibility of carrying the constituting dimers of the Pt nanowires from point to point with atomic precision at room temperature. Pt dimers can be picked-up in two configurations: (i) a horizontal configuration at the tip apex, resulting in double tip images and (ii) a configuration where the Pt dimer is attached to the side of the tip apex, resulting in well-defined atomically resolved images