MODELING OF EARLY STAGES OF ISLAND GROWTH DURING PULSED DEPOSITION: ROLE OF CLOSED COMPACT ISLANDS M. Maˇ s´ ın and M. Kotrla Institute of Physics AS CR, Praha, Czech Republic e-mail: kotrla@fzu.cz, masin@fzu.cz 1 Introduction ❒ molecular beam epitaxy (MBE) was extensively studied in the past, there is increased interest in pulsed–laser deposition (PLD) recently PLD t MBE F PLD t θ MBE ❒ reasons: decreased surface roughness, new type of scal- ing behavior ❒ submonolayer island MBE growth is well understood [1], but PLD is not ❒ this study: limited to sub–monolayer PLD growth, mo- tivated by PLD experiment on Fe/Mo(110) [2] 2 Model • solid-on-solid model in sub–monolayer regime • kinetic Monte Carlo (KMC) simulations with reversible growth [3] for both PLD & MBE • PLD: modulation of incident flux F with the chopping frequency f =1/(∆t dep +∆t diff ), ∆t dep = 10 μs, and f = 10 Hz as in experiment • thermally activated diffusion, probability of a jump P i ∼ exp  - E A(i) k B T  ,E A (i)= E d + lE b • interaction with the lateral neighbors (the second term). is controlled by bond counting • two cases are investigated (i) interaction only with n.n. and E b1 = 330 meV (ii) interaction up to third neighbors E b1 = 330 meV, E b2 = 72 meV, E b3 = 79 meV, results for E b1 = 600 meV were published in [4] • other parameters: - activation diffusion energy E d =0.4 eV - temperature 200 K – 800 K - deposition flux F AV = F =0.005 ML/s - system size 250000-1000000 occup. sites 3 Examples of surface configurations a) b) c) d) e) f) g) h) i) Figs. a)–c) development of MBE system at coverage θ =0.010, 0.025 and 0.040. Figs. d)–f) development of PLD at same coverage as in Figs. a)–c). In the case of PLD, details of selected small clusters in particle resolu- tion are displayed in Figs. g)–i). 4 Arrhenius plot of total island density 1 2 3 4 5 6 1000/T [1/K] 10 -5 10 -4 10 -3 10 -2 N tot PLD, E b = 600 meV PLD, E b1 = 330 meV, E b2 = 72 meV, E b3 = 79 meV PLD, E b = 330 meV MBE, E b = 600 meV MBE, E b1 = 330 meV, E b2 = 72 meV, E b3 = 79 meV Jubert et al. 200 300 400 600 T [K] 400 500 650 Comparison of temperature dependence of island densities for PLD and MBE mode and for different interactions 5 Concentration of small clusters at dif- ferent temperatures 200 300 400 500 600 700 800 T [K} 5.0×10 -5 1.0×10 -4 1.5×10 -4 2.0×10 -4 2.5×10 -4 3.0×10 -4 N x monomer 2 3 4 5 6 7 8 9 10 500 600 700 800 1e-05 2e-05 200 250 300 350 400 450 500 550 T 5.0×10 -5 1.0×10 -4 1.5×10 -4 2.0×10 -4 2.5×10 -4 3.0×10 -4 N x monomer 2 3 4 5 6 7 8 9 10 400 500 1×10 -5 2×10 -5 3×10 -5 4×10 -5 5×10 -5 Concentration of monomers and small cluster up to cluster with 10 atoms in the PLD mode after 1 s of deposition (10 pulses) as function of the temperature, Concentrations are shown at the end of diffusion period, i.e. nearly to new pulse is approaching the surface. Inset: Detail for intermediate and high temperatures. The data are for E b1 = 330 meV (above panel) and for E b1 = 330 meV, E b2 = 72 meV, E b3 = 79 meV (lower panel). 6 Time development of cluster sizes 0 5 10 15 20 25 30 35 40 t [s] 0.0 1.0×10 -5 2.0×10 -5 N x 1 2 3 4 5 6 7 8 9 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 00000000000000000 0 5 10 15 20 25 30 35 40 t [s] 0 2×10 -4 4×10 -4 6×10 -4 N TOT N TOT 0 0 1 1.05 1.1 0 1×10 -5 2×10 -5 1 2 3 4 5 6 7 8 9 10 Time development of the cluster size distribution at T = 400 K. Total island density N tot is plotted with black solid line, other curves in the main window represent densities of small clusters measured just before pulse of particles approaching the surface. 7 Island size distribution 0 100 200 300 400 500 N 0.0 5.0×10 -6 1.0×10 -5 N x t = 1 s t = 5 s t = 40 s 0 5 10 15 20 25 0 1×10 -5 2×10 -5 t = 1 s t = 5 s t = 40 s Island density as a function of island size for three different times at temperature T = 400 K. 8 Conclusions ✱ island density in PLD mode is higher than MBE mode ✱ PLD island density exhibits anomalous behavior at intermediate temperatures ☛ small compact islands play crucial role ☛ compact islands are more stable than other island ✱ same features are present for interaction to first n.n. as well as up to third n.n. only temperature interval is shifted Acknowledgments The research was carried out within the project AV0Z1-010-0520 of the Academy of Sciences of the Czech Republic. Financial support was provided by the Grant Agency of the Czech Republic (Projects 202/07/0775). References [1] J.A. Venables, G.D.T. Spiller and M. Hanb¨ ucken, Rep. Prog. Phys., 47, 399 (1984). [2] P. O. Jubert, O. Fruchart and C. Mayer, Surf. Sci. 522, 8 (2003). [3] M. Kotrla, Comp. Phys. Comm., 97, 82-100 (1996). [4] M. Maˇ s´ ın, and M. Kotrla, Europhys. Lett., 90 18006 (2010) View publication stats View publication stats