Hamburg 2001 – wissenschaftliches Programm
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O: Oberflächenphysik
O 22: Epitaxie und Wachstum (I)
O 22.7: Vortrag
Dienstag, 27. März 2001, 17:45–18:00, C
Concentration dependent two-dimensional “glass” formation in the system Dy/Mo(112) — •H. Pfnür2, A. Fedorus1, V. Koval1, A. Naumovets1, G. Godzik2 und D. Krügel2 — 1Inst. of Physics, Natl. Academy of Sciences of Ukraine, Kiev — 2Inst. f. Festkörperphysik, Uni Hannover
Annealing-driven irreversible structural transitions are studied by LEED in submonolayer Dy films adsorbed on the Mo(112) surface. In a wide coverage range, Dy overlayers deposited at low temperature (T ≈ 100 K) are ordered and keep their structure upon annealing up to 350–600 K. Within these temperature limits, the following succession of film structures is observed with the increase of coverage θ: a chain-like (6 × 1), c(1.56 × 2), a rectangular but non-centred (1/θ × 2), and an oblique (1/θ × 1). The former two phases grow via a first order transition, whereas the latter two structures show a continuous uniaxial compression with increasing θ up to the close-packed monolayer (θ = 0.78). Most of these structures are metastable. Only near the coverage θ = 0.68, the overlayers are stable up to the temperature of film evaporation. The denser films are metastable and transform to more stable ordered structures (4 × 1), (5 × 1) and (2 × 1).
An unusual annealing effect is found for θ < 0.6: the initially ordered metastable phases are replaced by phases having no extended order, which are assumed to be two-dimensional glasses, without removing adsorbate atoms from the surface. As mechanisms annealing driven hindering of adatom mobility and activated adsorption-induced reconstruction to a more rough structure are discussed.