With expanding interest in graphene-based electronics, it is crucial that high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001) (Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce epitaxial graphene sheets on a semiconductor. In this paper we show that graphene grown from the SiC(0001) (C-terminated) surface are of higher quality than those previously grown on SiC(0001). Graphene grown on the C-face can have structural domain sizes more than three times larger than those grown on the Si-face while at the same time reducing SiC substrate disorder from sublimation by an order of magnitude.

Electrochemical measurements, atomic force microscopy, and scanning tunneling microscopy have been combined to present the first direct images of the potential-controlled phase transition between the hemimicellar and condensed states of a dodecyl sulfate (SDS) film at the Au(111) electrode surface. The adsorbed SDS forms stripe-shaped hemimicellar aggregates at small or moderate charge densities at the electrode. High-resolution STM images of these aggregates revealed that adsorbed SDS molecules are ordered and form a long-range two-dimensional lattice. A unit cell of this lattice consists of two vectors that are 4.4 and 0.5 nm long and are oriented at an angle of 70°. We propose that each unit cell contains two flat-laying SDS molecules stretched out along the longer axis of the cell with the hydrocarbon tails directed toward the interior of the cell. The remaining SDS molecules in the hemimicelle assume a tilted orientation. This long-range structure is stabilized by the interactions of sulfate groups belonging to the adjacent cells. The sulfate groups of the flat-laying SDS molecules are arranged into a characteristic (√3 × √7) structure in which the sulfate groups along the √7 direction are bridged by hydrogen-bonded water molecules. When the positive charge on the metal either becomes equal to or exceeds the charge of adsorbed surfactant, the surface aggregates melt to form a condensed film. The transition between the hemimicellar and condensed states of the film is reversible. The hemimicellar aggregates may be re-formed by decreasing the charge density at the electrode surface. The charging and discharging of the gold electrode can be easily controlled by a proper variation of the electrode potential.

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Surface x-ray scattering and scanning-tunneling microscopy experiments reveal novel coarsening behavior of Pb nanocrystals grown on Si 111 -7 7 . It is found that quantum size effects lead to the breakdown of the classical Gibbs-Thomson analysis. This is manifested by the lack of scaling of the island densities. In addition, island decay times are orders of magnitude faster than expected from the classical analysis and have an unusual dependence on the growth flux F (i.e., 1=F). As a result, a highly monodispersed 7-layer island height distribution is found after coarsening if the islands are grown at high rather than low flux rates. These results have important implications, especially at low temperatures, for the controlled growth and self-organization of nanostructures. DOI: 10.1103/PhysRevLett.96.106105 PACS numbers: 68.55.Ac, 81.16.Dn, 61.14.Hg, 68.35.Fx Electron confinement in nanostructures gives rise to new quantized energy levels that are strongly dependent on the nanostructure's dimensions. This means that an object's size or shape is coupled to its total energy. This coupling is referred to as the quantum size effect (QSE) [1]. An example is the growth of Pb nanocrystalline islands on Si(111) [2 -6]. In this system, the height distribution of the grown islands is found to peak in increments of two Pb layers. This bilayer stability is understood in terms of oscillations in the electronic energy as the discrete quantum states fall below the Fermi level approximately every two Pb layers [7][8][9]. While this energetic reason is the driving force for the observed height preference, it is unclear how the preferred islands are assembled and what role kinetic barriers play. The formation of the preferred islands is not exclusively controlled by thermodynamics, since these QSE islands are not in equilibrium.The nucleation, growth, and coarsening of islands have been extensively described by a classical analysis [10]. In this scenario, the initial island nucleation is established by a steady state concentration of adatoms on the surface, which yields stable islands if they exceed a critical size of i atoms. The island density n is predicted and found to scale as the ratio F=D , where i= i 2 , D is the surface diffusion constant, and F is the deposition rate [11]. Once the deposition flux is turned off, the island density slowly begins to decrease due to coarsening (Ostwald ripening), whereby a critical island radius r C is established such that islands having radii larger than r C will slowly grow at the expense of islands having smaller radii. This process, and its inherent dependence on island radius r, is controlled by the chemical potential difference between islands r and a 2D gas of adatoms Free , which is given by the Gibbs-Thomson relation: r ÿ Free 2 =!r (where is the surface tension of an island and ! is the atomic density of Pb) [12]. In particular, the GibbsThomson relation was shown to accurately describe the situation for 2D islands on metal surfaces [10,13]. Such systems have been extensivel...

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