Solid flow drives surface nanopatterning by ion-beam irradiation

Ion Beam Sputtering (IBS) is known to produce surface nanopatterns over macroscopic areas on a wide range of materials. However, in spite of the technological potential of this route to nanostructuring, the physical process by which these surfaces self-organize remains poorly under- stood. We have performed detailed experiments of IBS on Si substrates that validate dynamical and morphological predictions from a hydrodynamic description of the phenomenon. Our results elucidate flow of a nanoscopically thin and highly viscous surface layer, driven by the stress created by the ion-beam, as a description of the system. This type of slow relaxation is akin to flow of macroscopic solids like glaciers or lead pipes, that is driven by defect dynamics.Comment: 12 pages, 4 figure

A study of the antioxidant capacity of oak wood used in wine ageing and the correlation with polyphenol composition

The antioxidant capacity of oak wood used in the ageing of wine was studied by four different methods: measurement of scavenging capacity against a given radical (ABTS, DPPH), oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP). Although, the four methods tested gave comparable results for the antioxidant capacity measured in oak wood extracts, the ORAC method gave results with some differences from the other methods. Non-toasted oak wood samples displayed more antioxidant power than toasted ones due to differences in the polyphenol compositon. A correlation analysis revealed that ellagitannins were the compounds mainly responsible for the antioxidant capacity of oak wood. Some phenolic acids, mainly gallic acid, also showed a significant correlation with antioxidant capacity

Infinite-time concentration in aggregation-diffusion equations with a given potential

Typically, aggregation-diffusion is modeled by parabolic equations that combine linear or nonlinear diffusion with a Fokker-Planck convection term. Under very general suitable assumptions, we prove that radial solutions of the evolution process converge asymptotically in time towards a stationary state representing the balance between the two effects. Our parabolic system is the gradient how of an energy functional, and in fact we show that the stationary states are minimizers of a relaxed energy. Here, we study radial solutions of an aggregation-diffusion model that combines nonlinear fast diffusion with a convection term driven by the gradient of a potential, both in balls and the whole space. We show that, depending on the exponent of fast diffusion and the potential, the steady state is given by the sum of an explicit integrable function, plus a Dirac delta at the origin containing the rest of the mass of the initial datum. Furthermore, it is a global minimizer of the relaxed energy. This splitting phenomenon is an uncommon example of blow-up in inffinite time.Depto. de Análisis Matemático y Matemática AplicadaFac. de Ciencias MatemáticasFALSEUnión Europea. Horizonte 2020Ministerio de Ciencia e Innovación (MICINN)pu

Self-Organized Ordering of Nanostructures Produced by Ion-Beam Sputtering

We study the self-organized ordering of nanostructures produced by ion-beam sputtering (IBS) of targets amorphizing under irradiation. By introducing a model akin to models of pattern formation in aeolian sand dunes, we extend consistently the current continuum theory of erosion by IBS. We obtain new non-linear effects responsible for the in-plane ordering of the structures, whose strength correlates with the degree of ordering found in experiments. Our results highlight the importance of redeposition and surface viscous flow to this nanopattern formation process.Comment: 4 pages, 2 figure

Dynamical Renormalization Group Study for a Class of Non-local Interface Equations

We provide a detailed Dynamic Renormalization Group study for a class of stochastic equations that describe non-conserved interface growth mediated by non-local interactions. We consider explicitly both the morphologically stable case, and the less studied case in which pattern formation occurs, for which flat surfaces are linearly unstable to periodic perturbations. We show that the latter leads to non-trivial scaling behavior in an appropriate parameter range when combined with the Kardar-Parisi-Zhang (KPZ) non-linearity, that nevertheless does not correspond to the KPZ universality class. This novel asymptotic behavior is characterized by two scaling laws that fix the critical exponents to dimension-independent values, that agree with previous reports from numerical simulations and experimental systems. We show that the precise form of the linear stabilizing terms does not modify the hydrodynamic behavior of these equations. One of the scaling laws, usually associated with Galilean invariance, is shown to derive from a vertex cancellation that occurs (at least to one loop order) for any choice of linear terms in the equation of motion and is independent on the morphological stability of the surface, hence generalizing this well-known property of the KPZ equation. Moreover, the argument carries over to other systems like the Lai-Das Sarma-Villain equation, in which vertex cancellation is known {\em not to} imply an associated symmetry of the equation.Comment: 34 pages, 9 figures. Journal of Statistical Mechanics: Theory and Experiments (in press

Coulomb explosion sputtering of selectively oxidized Si

We have studied multiply charged Arq+ ion induced potential sputtering of a unique system comprising of coexisting Silicon and Silicon oxide surfaces. Such surfaces are produced by oblique angle oxygen ion bombardment on Si(100), where ripple structures are formed and one side of each ripple gets more oxidized. It is observed that higher the potential energy of Arq+ ion, higher the sputtering yield of the non conducting (oxide) side of the ripple as compared to the semiconducting side. The results are explained in terms of Coulomb explosion model where potential sputtering depends on the conductivity of the ion impact sites.Comment: 9 pages and 3 figure

Order enhancement and coarsening of self-organized silicon nanodot patterns induced by ion-beam sputtering

3 pages, 3 figures.-- PACS nrs.: 81.05.Cy, 81.07.-b, 68.47.Fg, 81.16.Rf, 79.20.Rf, 68.35.Bs.The temporal evolution of the characteristic wavelength (λ) and ordering range (ξ) of self-organized nanodot patterns induced during Ar+ ion beam sputtering on Si(001) and Si(111) surfaces is studied by atomic force microscopy and grazing incidence x-ray diffraction. The patterns exhibit initial coarsening of λ (up to 54–60 nm) and increase in ξ (up to 400–500 nm) after which both features stabilize. The pattern formation is only weakly controlled by the crystallographic surface orientation, Si(111) surfaces showing a faster evolution into a proper stationary state. This trend is attributed to a higher sputtering rate at this orientation, as confirmed by theoretical simulations.This work has been supported by grants BFM2003- 07749-C05-01, BFM2003-07749-C05-02, and BFM2003- 07749-C05-05 from the Spanish Ministerio de Educación y Ciencia (MEC). Two of the authors (R.G. and J.M.-G.) acknowledge financial support from MEC through the “Ramón y Cajal” and FPU programs, respectively.Publicad

Antitumor activity of copper(II) complexes with Schiff bases derived from N′-tosylbenzene-1,2-diamine

The electrochemical oxidation of anodic metal copper in a solution of the ligands N-[(5-tert-butyl-2-hydroxyphenyl)methylidine]-N′-tosylbenzene-1,2-diamine [H2L1] and N-[(3,5-di-tert-butyl-2-hydroxyphenyl)methylidine]-N′-tosylbenzene-1,2-diamine, [H2L2] afforded homoleptic [CuL] compounds or solvate [CuLS] complexes. The addition to the electrochemical cell of coligands (L') such as 2,2′-bipyridine (2-bpy), 4,4′-bipyridine(4-bpy) or 1,10-phenanthroline (phen) allowed the synthesis, in one step, of heteroleptic [CuLL'] compounds, namely [CuL1(H2O)] (1), [CuL1(2,2′-bpy)]⋅CH3CN (2), [CuL1(phen)]·H2O (3), [Cu2L12(4,4′-bpy)] (4), [CuL2(CH3OH)] (5), [CuL2(2,2′-bpy)] (6), [CuL2(phen)] (7) and [Cu2L22(4,4′-bpy)] (8). The crystal structures of both ligands, H2L1, H2L2, and those of the complexes (2), (4), (5), (6) and (7) have been determined by X-ray diffraction techniques. Coordination polyhedron around metal atom is square planar for [CuL2(CH3OH)] (5) and [Cu2L12(4,4′-bpy)] (4) and square pyramid for the other complexes with additional chelating ligands. The cytotoxic activity of this new series of copper(II) complexes against the SH-SY5Y neuroblastoma cell line and U87-MG and U373-MG glioblastoma cell lines has been investigated. Most of the test compounds showed higher activity than cisplatin in the three cell lines. Among this series, compound [CuL1(phen)] (3) displayed the highest activity with IC50 equal to 1.77 μM on SH-SY5Y whereas compound [Cu2L12(4.4′-bpy)] (4) resulted the most potent compounds on U87 MG and U373 MG glioblastoma cell lines. Studies on the cytotoxic activity of these derivatives suggest that these compounds induce cell death by a mechanism other than apoptosis.Xunta de GaliciaFinanciado para publicación en acceso aberto: Universidade de Vigo/CISU

Role of the metal supply pathway on silicon patterning by oblique ion beam sputtering

The dynamics of the pattern induced on a silicon surface by oblique incidence of a 40 keV Fe ion beam is studied. The results are compared with those obtained for two reference systems, namely a noble gas ion beam either without or with Fe co-deposition. The techniques employed include Atomic Force Microscopy, Rutherford Backscattering Spectrometry, Transmission Electron Microscopy, X-ray Photoelectron and hard X-ray photoelectron spectroscopies, as well as Superconducting Quantum Interference Device measurements. The Fe-induced pattern differs from those of both reference systems since a pattern displaying short hexagonal ordering develops, although it shares some features with them. In both Fe systems a chemical pattern, with iron silicide-rich and -poor regions, is formed upon prolonged irradiation. The metal pathway has a marked influence on the patterns’ morphological properties and on the spatial correlation between the chemical and morphological patterns. It also determines the iron silicide stoichiometry and the surface pattern magnetic properties that are better for the Fe-implanted system. These results show that in ion-beam-induced silicon surface patterning with reactive metals, the metal supply pathway is critical to determine not only the morphological pattern properties, but also the chemical and magnetic one

Growth dynamics of reactive-sputtering-deposited AlN films

8 pages, 7 figures.-- PACS nrs.: 81.05.Ea, 68.47.Fg, 81.15.Cd, 68.55.Ac, 68.55.Jk, 68.35.Bs.-- Issue title: "Structural, mechanical, thermodynamical and optical properties of condensed matter".We have studied the surface kinetic roughening of AlN films grown on Si(100) substrates by dc reactive sputtering within the framework of the dynamic scaling theory. Films deposited under the same experimental conditions for different growth times were analyzed by atomic force microscopy and x-ray diffraction. The AlN films display a (002) preferred orientation. We have found two growth regimes with a crossover time of 36 min. In the first regime, the growth dynamics is unstable and the films present two types of textured domains, well textured and randomly oriented, respectively. In contrast, in the second regime the films are homogeneous and well textured, leading to a relative stabilization of the surface roughness characterized by a growth exponent β=0.37±0.03. In this regime a superrough scaling behavior is found with the following exponents: (i) Global exponents: roughness exponent α=1.2±0.2 and β=0.37±0.03 and coarsening exponent 1/z=0.32±0.05; (ii) local exponents: α(loc)=1, β(loc)=0.32±0.01. The differences between the growth modes are found to be related to the different main growth mechanisms dominating their growth dynamics: sticking anisotropy and shadowing, respectively.Financial support from Spanish MCyT: Projects No. MAT 2002-04037-C03-03 and BFM 2003-07749-C05-01, BFM 2003-07749-C05-02, and BFM 2003-07749-C05-05, European Community: Project No. G5RD-CT-2000-00333, Slovak governmental Project No. 2003-SO 51/03R0600/01, and Slovak Grant Agency for Science VEGA, Project No. 2/3149/23, are acknowledged.Publicad