Showing papers by "Albert-László Barabási published in 1998"

Irregularities and power law distributions in the breathing pattern in preterm and term infants.

Abstract: Unlike older children, young infants are prone to develop unstable respiratory patterns, suggesting important differences in their control of breathing. We examined the irregular breathing pattern ...

Dynamics of ripening of self-assembled II-VI semiconductor quantum dots

Abstract: We report the systematic investigation of ripening of CdSe self-assembled quantum dots (QDs) on ZnSe. We investigate the size and density of the QDs as a function of time after deposition of CdSe has stopped. The dynamics of the ripening process is interpreted in terms of the theory of Ostwald ripening. Furthermore, the experimental results allow us to identify the growth mode of the QD formation process. [S0031-9007(98)07378-5]

Ratchet Effect in Surface Electromigration: Smoothing Surfaces by an ac Field

Abstract: We demonstrate that for surfaces that have a nonzero Schwoebel barrier the application of an ac field parallel to the surface induces a net electromigration current that points in the descending step direction. The magnitude of the current is calculated analytically and compared with Monte Carlo simulations. Since a downhill current smoothes the surface, our results imply that the application of ac fields can aid the smoothing process during annealing and can slow or eliminate the Schwoebel-barrier-induced mound formation during growth. [S0031-9007(97)05220-4]

Equilibrium phase diagrams for dislocation free self-assembled quantum dots

Abstract: The equilibrium theory of self-assembled quantum dot (SAQD) formation can account for many of the experimentally observed growth modes. Here, we show that despite the large number of material constants entering the free energy of strained islands, there are only four topologically different phase diagrams describing the SAQD formation process. We derive each of these phase diagrams and discuss the physical properties of the predicted growth modes.

Spatial ordering of islands grown on patterned surfaces

Abstract: We demonstrate that growth on a sample patterned with an ordered defect array can lead to islands with rather narrow size distribution. However, improvement in the size distribution is achieved only if the growth conditions (flux and temperature) have optimal values, determined by the patterning length scale. Since the scanning tunelling and the atomic force microscopes are capable of inducing surface perturbations that act as potential preferential nucleation sites, our work demonstrates that nanoscale surface patterning can improve the ordering of platelets and self-assembled quantum dots.

Driven Interfaces in Disordered Media: Determination of Universality Classes from Experimental Data

Abstract: Interface motion in a random medium presents us with an archetype problem, with direct impact on various phenomena in condensed matter physics, including fluid flow in porous media [1], domain growth in disordered magnets [2], and flux lines in disordered superconductors [3]. In particular, much attention has been focused on understanding the morphological evolution of an interface driven through a disordered medium. Twophase fluid flow experiments have provided evidence that the morphology of the interface can be either selfsimilar or self-affine [4]. The self-similar morphology has been successfully described by various percolation based models, such as invasion percolation [1]. The motion and roughening of self-affine interface morphologies can be quantified by the global interface width wsL, td, where L is the system size. The study of discrete models and continuum growth equations leads to the observation that the width follows [5,6]

Secondary ion yield changes on rippled interfaces

Abstract: Sputter erosion often leads to the development of surface ripples. Here we investigate the effect of the ripples on the secondary ion yield, by calculating the yield as a function of the microscopic parameters characterizing the ion cascade (such as penetration depth, widths of the deposited energy distribution) and the ripples (ripple amplitude, wavelength). We find that ripples can strongly enhance the yield, with the magnitude of the effect depending on the interplay between the ion and ripple characteristics. Furthermore, we compare our predictions with existing experimental results.

Effect of surface roughness on the secondary ion yield in ion sputtering

Abstract: There is extensive experimental evidence that, at low temperatures, surface erosion by ion bombardment roughens the sputtered substrate, leading to a self-affine surface. These changes in the surface morphology also modify the secondary ion yield. Here, we calculate analytically the secondary ion yield in terms of parameters characterizing the sputtering process and the interface roughness.

Low Temperature Ripple Formation: Ion-Induced Effective Surface Diffusion in Ion Sputtering

Abstract: Surfaces bombarded with energetic ions may develop a rough or a ripple surface morphology. The ripple formation has been successfully described by the instability caused by preferential erosion, the ripple wavelength being determined by the competition between surface erosion and thermally activated diffusion. However, as recent experiments and computer simulations have shown, ripple formation takes place even at the low temperatures, when thermally activated processes are suppressed. In this paper we propose a theory to explain low-temperature ripple formation based on the ion-induced effective surface diffusion.