Atomic Kinks Research Articles

Adsorption of CO on kinked surface areas of Pt and Rh: the relation between work function change upon saturated adsorption and the work function of the corresponding clean adsorbent area

Using FEM, work function measurements were carried out on kinked surface areas of Pt and Rh ({210}, {531}Rh, {321}, {520}, {310}, {320}, {430} and {741}Pt). The work function change after saturated CO adsorption at room temperature, Δø CO, increases with decreasing work function of the corresponding clean adsorbent area, ø k. The dependence appears to be linear. The slope was identified as the ratio of two surface dipole moments, μ CO μ Me . (μ CO dipole moment (per molecule) of the CO adlayer adsorbed on kink atoms; μ Me dipole moment of the metal kink atom.) The experimental values of the ratio are close to unity.

Dependence of interface state density on the atomic roughness at the Si — SiO 2 interface

Quasi static Capacitance Voltage (CV) measurements have been performed on Si(111) metal-oxide-semiconductor (MOS) structures with different and well known atomic roughness. The atomic roughness was determined on an atomic scale quantitatively with spot profile analysis of low energy electron diffraction pattern (SPA-LEED). The results demonstrate a strong correlation between atomic roughness and interface state density. Even after an additional post-metallization-annealing (PMA) treatment when surface states should be minimized, the remaining interface state density is strongly correlated to the atomic roughness. A simple model which is associated with each kind of step atom, i.e. edge or kink atoms, suggests the creation of a dangling bond and therefore a surface state can explain the results. The correlation of the fixed charge Q fix to the atomic roughness can be determined in the same way. Assuming that ionized atoms which are responsible for Q fix are located preferentially at those steps or kinks which are also correlated to the dangling bonds at the interface, we confirm the general opinion that Q fix and surface states have at least one common physical origin: the atomic roughness.

The Si–SiO2 interface: Correlation of atomic structure and electrical properties

The roughness at the Si–SiO2 interface has been determined quantitatively on an atomic scale by SPA-LEED (spot profile analysis of low energy electron diffraction) in ultrahigh vacuum after removal of the oxide. At the Si–SiO2 interface the steps are randomly distributed. With the help of model calculations the measured spot broadening provides the step atom density and therefore the roughness on an atomic scale. The roughness will be decreased by low oxidation rates (thick oxides, dry atmosphere) and appropriate annealing in N2 and will be increased by high oxidation rates (thin oxides and wet atmosphere). Furthermore metal oxide semiconductor (MOS) structures were built on chips which were also suited for LEED measurements. Hall mobilities for Si(111) p-channel inversion layers MOS-FETs with varying roughness at the Si–SiO2 interface have been measured at temperatures between 4.2 K and room temperature. It was found that there exists a strong correlation between Hall mobility and atomic roughness at high inversion, nearly a proportionality. Even at room temperature the transistors with the lower interface roughness exhibit the higher mobility. Further quasistatic capacitance–voltage (C–V) measurements have been performed on Si(111) MOS structures with different but well-known atomic roughness. The results demonstrate a strong correlation between atomic roughness and interface state density too, even after an additional postmetallization-annealing (PMA) treatment. A simple model which is associated with each kind of step atom, i.e., edge or kink atoms, suggests the creation of a dangling bond and therefore, a surface state can explain the result. Assuming that ionized atoms which are responsible for Qfix are located preferentially at those steps or kinks which are also correlated to the dangling bonds at the interface, we confirm the general opinion that Qfix and surface states have at least one common physical origin: the atomic roughness.

An atomistic model of kinetic crack growth in brittle solids

A general theory of kinetic crack growth in ideally brittle solids is developed from first principles. In setting up a basic model, emphasis is placed on the essential need to provide for the existence of an energy barrier to activated, non-linear crack motions at the atomic level. The picture is presented of an ideally brittle fracture crack in which sequential bond rupture occurs via the lateral motion of atomic kinks along the crack front. Approximate solutions to the equations of kink motion are then obtained from the discrete, “lattice trapping” theory of Thomson and co-workers. Assuming a classical distribution of kink sites, an expression for the steady-state crack velocity follows. A feature of the present theory is the formulation in terms of the fundamental energy-balance concept of Griffith, with two major advantages: in the first place, standard fracture-mechanics parameters, such as the mechanical-energy-release rate and the fracture-surface energy, enter into the description in a natural manner; in the second, the effect of extrinsic agents on activated kink motion is readily accountable, through a simple modification of the total energy function for the crack system. To illustrate the model, the case of a slowly growing brittle crack in the presence of an interacting ideal gas environment is treated in some detail.

Decoration of facets on silver

Abstract The facets produced on silver by thermal etching have been investigated in detail by examining decorated replicas of them in an electron microscope. Gold, condensed on the surface in vacuum, forms perfectly oriented sheets on the complex facets which contain many kink atoms. By contrast, the gold condenses on {100} and {111} planes as separated, randomly distributed, crystals with some preferred orientations. Atomic steps on these planes are decorated by preferential nucleation.