Publications (6)1.34 Total impact
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Article: Equilibrium morphology of Au(111) vicinal surfaces revealed by scanning tunneling microscopy
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ABSTRACT: We have investigated the thermal instability of Au(111) vicinal surfaces by scanning tunneling microscopy in ultrahigh vacuum. Above an annealing temperature of 700 K, both the Au(11,9,9) and the Au(4,3,3) surfaces undergo a phase separation into (111) facets and portions of (7,5,5). In addition, the faceted surfaces present a long‐range order: the superperiod is 70 Å for Au(11,9,9) and 110 Å for Au(4,3,3). Large scale images show that this structure extends everywhere on the samples. It is demonstrated that the novel periodic morphology is an equilibrium state. Comparison is made with preliminary results of the Au(4,5,5) surface that belongs to the opposite zone. Observations suggest a dramatically different behavior: The surface phase separates into large (2,3,3) portions and a more complicated vicinal surface. The superperiod seems to be greater than 2000 Å. © 1996 American Vacuum SocietyJournal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 04/1996; · 1.34 Impact Factor -
Article: LEED study of Pt25Co75(111)
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ABSTRACT: A quantitative LEED study of the Pt25Co75(111) surface (in the substitutionally disordered state) shows weak relaxations of interlayer spacings (Δd12/dbulk, Δd23/dbulk, Δd34/dbulk) = (000-1.9, −1.4, 3.6)%, no st but a significant oscillatory composition profile (C1, C2, C3) = (46, 3, 37) at% Pt. This behaviour is very close to the ge observed for PtNi(111) surfaces as a function of the bulk concentration Cb and in good agreement with the predictions of the tight binding Ising model of Treglia, Legrand and Ducastelle and of the embedded atom method results of Lundberg.Surface Science. -
Article: LEED study of activated nitrogen adsorption on (100) and (h11) faces of copper
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ABSTRACT: LEED observations on nitrogen adsorbed on (h11) stepped and (100) copper faces have shown the existence of two surface phases with a first order transition. The first one corresponds, on the (100) face, to the formation of an ordered stepped overlayer composed of alternating square c(2 × 2)N island and bare copper of 〈100〉 atomic rows and on the (h11) stepped faces, to an unusual nitrogen induced faceting into (100) and (h′11) facets: the terrace width of these (h′11) facets decreases with coverages and a (h11) stepped face (h = 65 ± 4) with large (100) terrace widths is observed. The second phase, in the ultimate state of adsorption might correspond to the formation of a copper nitride surface layer in epitaxy on all the copper faces under investigation.Surface Science. -
Article: Self-ordering on crystal surfaces: fundamentals and applications
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ABSTRACT: Self-ordering on crystal surfaces has been the subject of intense efforts during the last ten years. It has been recognized as a promising way for growing uniform nanostructures with regular sizes and spacings. Continuum models have been proposed where long-range elastic repulsive interactions are responsible for the periodic domain spontaneous formation. Vicinal surfaces unstable towards faceting lead to a one dimensional (1D) periodic morphology. Au(111) vicinals self-ordering provides a unique opportunity to point out the interplay between atomic and mesoscopic order. 2D ordering has been investigated in the complex case of atomic nitrogen adsorbed on Cu(100). Using scanning tunneling microscopy (STM) at elevated temperature, we have followed the ordered arrays of N square-shaped domains spontaneous formation. Observations are discussed in the light of previous continuum models for self-ordering. The question of understanding self-ordering is not only of fundamental but also of technological interest since it is a fruitful way of growing regularly spaced nanostructures in the 1–100 nm range. This will be illustrated by two examples: (i) self-ordered substrates can serve as templates for growing 2D square lattice of regular nanostructures; (ii) magnetic domains of an ultra-thin film can be tailored by using self-ordered substrates.Materials Science and Engineering: B. -
Article: Self-ordering in two dimensions: nitrogen adsorption on copper (100) followed by STM at elevated temperature
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ABSTRACT: We have followed the adsorption and the desorption of nitrogen on the copper (1 0 0) surface in real time using scanning tunneling microscopy at elevated temperatures. This gives an unprecedented view, especially of the adsorption behavior at very low coverage. Growth proceeds by splitting of square-shaped islands of critical size without loss of C4 symmetry. The equilibrium structures are analyzed in terms of their dimensionality and shape showing that the phase diagram comprises two periodic domain morphologies as a function of nitrogen coverage: two-dimensional (2D) array of compact nitrogen islands at low and high coverage and a quasi 1D arrangement of striped domains (rows of squares) at intermediate coverages. Furthermore, we investigated the sensitivity of the system to small changes in the elastic properties of the substrate by pre-deposition of gold on the bare copper surface. Finally, the comparison all our observations in the light of existing model predictions for long-range interactions in 2D systems reveals crucial differences and, therefore, these models have to be extended to include short range relaxation and interactions in order to reproduce the fundamental aspects of this system.Surface Science. -
Article: Superperiodicity in the thermal faceting of Au(111) vicinal surfaces
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ABSTRACT: Using scanning tunneling microscopy and low energy electron diffraction, the thermal faceting of two Au(111) vicinal surfaces belonging to the [01] zone is investigated. Above 700 K, a final stable state is found: it consists of a periodic succession of (111) and (755) facets. The superperiod is 70 Å for Au(1199) and 110 Å for Au(433). The quantitative agreement between our results and the observations of macroscopic gold crystals strongly suggests that the novel periodic morphology is an equilibrium state. Possible origins to account for this morphology are discussed.Surface Science. 324(1).
