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New dynamic scaling in increasing systems

100%
Pastor J., Galeano J.
Open Physics
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2007
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vol. 5
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issue 4
539-548
EN
We report a new dynamic scaling ansatz for systems whose system size is increasing with time. We apply this new hypothesis in the Eden model in two geometries. In strip geometry, we impose the system to increase with a power law, L ∼ h a. In increasing linear clusters, if a < 1/z, where z is the dynamic exponent, the correlation length reaches the whole system, and we find two regimes: the first, where the interface fluctuations initially grow with an exponent β = 0.3, and the second, where a crossover comes out and fluctuations evolve as h aα. If a = 1/z, there is not a crossover and fluctuations keep on growing in a unique regimen with the same exponent β. In particular, in circular geometry, a = 1, we find this kind of regime and in consequence, a unique regime holds.
2
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Wetting of Nanostructurized Sapphire and Gold Surfaces

100%
Kempiński M., Jenczyk J., Jurga S., Śliwińska-Bartkowiak M.
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EN
We present the results of preliminary experiments regarding research on the contact angle measurements of various liquids on solid surfaces with different morphology. The aim was to get insight into the dependence of wetting phenomena on the nanoscale surface roughness. Flat and nanostructurized surfaces of gold and sapphire were used in the experiments. Four liquids - bromobenzene, water, mercury, and gallium - covering a broad range of surface tension values were used to check how varying roughness influences wetting in the systems with different adhesion/cohesion ratio. Structurization was anisotropic, which resulted in the very interesting behaviour of the examined liquids on the selected surfaces. Significant change of the wetting properties was observed as well as a strong dependence on the surface morphology.
3
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Can Ising model and/or QKPZ equation properly describe reactive-wetting interface dynamics?

84%
Efraim Y., Taitelbaum H.
Open Physics
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2009
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vol. 7
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issue 3
503-508
EN
The reactive-wetting process, e.g. spreading of a liquid droplet on a reactive substrate is known as a complex, non-linear process with high sensitivity to minor fluctuations. The dynamics and geometry of the interface (triple line) between the materials is supposed to shed light on the main mechanisms of the process. We recently studied a room temperature reactive-wetting system of a small (∼ 150 μm) Hg droplet that spreads on a thin (∼ 4000 Å) Ag substrate. We calculated the kinetic roughening exponents (growth and roughness), as well as the persistence exponent of points on the advancing interface. In this paper we address the question whether there exists a well-defined model to describe the interface dynamics of this system, by performing two sets of numerical simulations. The first one is a simulation of an interface propagating according to the QKPZ equation, and the second one is a landscape of an Ising chain with ferromagnetic interactions in zero temperature. We show that none of these models gives a full description of the dynamics of the experimental reactivewetting system, but each one of them has certain common growth properties with it. We conjecture that this results from a microscopic behavior different from the macroscopic one. The microscopic mechanism, reflected by the persistence exponent, resembles the Ising behavior, while in the macroscopic scale, exemplified by the growth exponent, the dynamics looks more like the QKPZ dynamics.
4
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High-quality MBE growth of AlχGa1-χ As-based THz quantum cascade lasers

68%
Roch T., Andrews A., Fasching G., Benz A., Schrenk W., Unterrainer K., Strasser G.
Open Physics
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2007
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vol. 5
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issue 2
244-251
EN
High-quality GaAs-based quantum cascade laser (QCL) structures for the terahertz (THz) emission have been grown by solid source molecular-beam epitaxy. Ex-situ high-resolution x-ray diffraction shows that layer thickness and its control is the most critical growth aspect and that the lasing potential of the structure can be determined by the thickness accuracy of the layers. For our samples, the thickness tolerance for working lasing structures emitting approximately 100 μm was determined to be minimally above 1% for a 15 μm active region which was composed of 54.6 nm cascade cells. Increasing interface roughness adversely affects the lasing threshold and power.
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