Surface morphology of amorphous SiO2 substrates bombarded with 1.0 MeV Si+ ions.

Surface pattern formation on amorphous SiO2 substrates by implantation of 1.0 MeV Si+ ions at a current of 1.3 µA at 70° angle is reported. Surface micrometer sized ripples perpendicular to the ion beam direction are formed, observed by scanning electron microscopy and atomic force microscopy. The morphological features are more or less similar for different fluences. The formation of surface ripples at this energy is discussed in terms of ion stopping mechanisms and patterns obtained within the low- and medium-energy ranges.

Surface morphology of molybdenum silicide films upon low-energy ion beam sputtering.

The surface morphology of molybdenum silicide (Mo x Si1-x ) films has been studied after low-energy Ar+ ion beam sputtering (IBS) to explore eventual pattern formation on compound targets and, simultaneously, gather information about the mechanisms behind silicide-assisted nanopatterning of silicon surfaces by IBS. For this purpose, Mo x Si1-x films with compositions below, equal and above the MoSi2 stoichiometry (x = 0.33) have been produced by magnetron sputtering, as assessed by Rutherford backscattering spectrometry (RBS). The surface morphology of silicon and silicide films before and after IBS has been imaged by atomic force microscopy (AFM), comprising conditions where typical nanodot or ripple patterns emerge on the former. In the case of irradiated Mo x Si1-x surfaces, AFM shows a marked surface smoothing at normal incidence with and without additional Mo incorporation (the former results in nanodot patterns on Si). The morphological analysis also provides no evidence of ion-induced phase separation in irradiated Mo x Si1-x . Contrary to silicon, Mo x Si1-x surfaces also do not display ripple formation for (impurity free) oblique irradiations, except at grazing incidence conditions where parallel ripples emerge in a more evident fashion than in the Si counterpart. By means of RBS, irradiated Mo x Si1-x films with 1 keV Ar+ at normal incidence have also been used to measure experimentally the (absolute) sputtering yield and rate of Si and Mo x Si1-x materials. The analysis reveals that, under the present working conditions, the erosion rate of silicides is larger than for silicon, supporting simulations from the TRIDYN code. This finding questions the shielding effect from silicide regions as roughening mechanism in metal-assisted nanopatterning of silicon. On the contrary, the results highlight the relevance of in situ silicide formation. Ripple formation on Mo x Si1-x under grazing incidence is also attributed to the dominance of sputtering effects under this geometry. In conclusion, our work provides some insights into the complex morphological evolution of compound surfaces and solid experimental evidences regarding the mechanisms behind silicide-assisted nanopatterning.

Features of electronic and lattice mechanisms of transboundary heat transfer in multilayer nanolaminate TiAlN/Ag coatings.

Plasmon resonance heterogeneities were identified and studied along Ag and TiAlN layers within a multilayer stack in nanolaminate TiAlN/Ag coatings. For this purpose, a high-resolution plasmon microscopy was used. The plasmons intensity, energy, and depth of interface plasmon-polariton penetration were studied by scanning reflected electron energy loss spectroscopy. The heat conductivity of such metal-insulator-metal (MIM) nanolaminate coatings was measured by laser reflectometry. Dependencies of thermal conductivity coefficient of coatings, MIM interfaces, and resistivity of Ag layers as a function of the Ag-TiAlN bilayer thickness were calculated on the basis of experimental data. The contribution of plasmon resonance confinement to the abnormal lower thermal conductivity in the MIM metamaterial with Ag layer thickness below 25 nm is discussed. In particular, the results highlight the relevant role of different heat transfer mechanisms between MI and IM interfaces: asymmetry of plasmon-polariton interactions on upper and lower boundaries of Ag layer and asymmetry of LA and TA phonons propagation through interfaces.

Influence of metal co-deposition on silicon nanodot patterning dynamics during ion-beam sputtering.

We address the impact of metal co-deposition in the nanodot patterning dynamics of Si(100) surfaces under normal-incidence 1 keV Ar(+) ion-beam sputtering (IBS). In particular, the effect of both the metal nature (Fe or Mo) and flux has been studied. Morphological and compositional evolution were followed by atomic force microscopy (AFM) and Rutherford backscattering spectrometry, respectively. For the same type of impurity, the dynamics is faster for a higher co-deposition flux, which also drives to larger asymptotic roughness and wavelength. Mo co-deposition yields rougher surfaces for a lower metal coverage than Fe and, remarkably, higher ordered patterns. X-ray photoelectron spectroscopy reveals the formation of silicide bonds even before pattern onset, stressing the relevant role of the affinity of the co-deposited metals for silicon. Further, current-sensing AFM performed at the initial and asymptotic stages indicates that the nanodot structures are metal-rich, resulting in coupled compositional and morphological patterns. These results are discussed in terms of phase segregation, morphology-driven local flux variations of impurities and silicide formation. This analysis reveals that the underlying (concurrent) mechanisms of pattern formation are complex since many processes can come into play with a different relative weight depending on the specific patterning conditions. From a practical point of view, it is shown that, by proper selection of the process parameters, IBS with metal co-deposition can be used to tune the dynamics and pattern properties and, interestingly, to produce highly ordered arrays.

Independence of interrupted coarsening on initial system order: ion-beam nanopatterning of amorphous versus crystalline silicon targets.

Interrupted coarsening (IC) has recently been identified as an important feature for the dynamics of the typical length-scale in pattern-forming systems on surfaces. In practice, it can be beneficial to improve pattern ordering since it combines a certain degree of defect suppression with a limited increase in the typical pattern wavelength. However, little is known about its robustness with respect to changes in the preparation of the initial system for cases with potential applications. Working in the context of nano-scale pattern formation by ion-beam sputtering (IBS), we prove that IC properties do not depend on sample preparation. Specifically, interface dynamics under IBS is quantitatively compared on virgin amorphous and crystalline silicon surfaces, using 1 keV Ar(+) ions at normal incidence where nanodot pattern formation is triggered by concurrent co-deposition of Fe atoms during processing. Atomic force microscopy shows that dot patterns with similar spatial order and dynamics are obtained in both cases, underscoring the key dynamical role of the amorphous surface layer produced by irradiation. Both systems have been quantitatively described by an effective interface equation. We employ a new procedure based on the linear growth of the initial surface correlations to accurately estimate the equation coefficients. Such a method improves the predictive power of the interface equation with respect to previous studies and leads to a better description of the experimental pattern and its dynamical features.

Production of nanohole/nanodot patterns on Si(001) by ion beam sputtering with simultaneous metal incorporation.

We have established the conditions for which nanohole and nanodot patterns are produced on Si(001) surfaces by 1 keV Ar(+) ion beam sputtering (IBS) at normal incidence with an alternating cold cathode ion source (ACC-IS). Nanohole patterns are produced within a narrow IBS window for low ion fluxes (<100 µA cm(-2)) and relatively low ion fluences (<10(18) ions cm(-2)) whereas nanodot morphologies are produced above this window. The nanohole pattern is not stable after prolonged irradiation since it evolves to a nanodot morphology. Rutherford backscattering spectrometry (RBS) measurements show that nanohole patterns are produced when the metal content on the irradiated surfaces is higher (within (2.5-3.5 × 10(15)) atoms cm(-2)) than in the case of nanodots (<2.5 × 10(15) atoms cm(-2)). The different metal content is related to the ACC-IS operation, since the set-up provides simultaneous incorporation of Fe and Mo on the target surface from the erosion of the cathodes and sample holder, respectively. The role of metal incorporation on pattern selectivity has been corroborated qualitatively by extending the results obtained with the ACC-IS to a standard Kaufman-type source. In order to gain further information on the metal effects, chemical analysis of the surface has been performed to complement the compositional RBS results, showing for the first time the relevant participation of metal silicides. Further outlook and a discussion regarding the role of metal incorporation are also given.

Early stage of ripple formation on Ge(001) surfaces under near-normal ion beam sputtering.

We present a study of the early stage of ripple formation on Ge(001) surfaces irradiated by a 1 keV Xe(+) ion beam at room temperature and near-normal incidence. A combination of a grazing incidence x-ray scattering technique and atomic force microscopy allowed us to observe a variation of the symmetry of the surface nanopattern upon increase of the ion fluence. The isotropic dot pattern formed during the first minutes of sputtering evolves into an anisotropic ripple pattern for longer sputtering time. These results provide a new basis for further steps in the theoretical description of the morphology evolution during ion beam sputtering.

Tuning the surface morphology in self-organized ion beam nanopatterning of Si(001) via metal incorporation: from holes to dots.

We report on the selective production of self-organized nanohole and nanodot patterns on Si(001) surfaces by ion beam sputtering (IBS) under normal-incidence of 1 keV Ar(+) ions extracted with a cold cathode ion source. For a fixed ion fluence, nanohole patterns are induced for relatively low ion current densities (50-110 µA cm(-2)), evolving towards nanodot patterns for current densities above 190 µA cm(-2). Both patterns display similar characteristics in terms of wavelength, short-range hexagonal order and roughness. Rutherford backscattering spectrometry measurements show that the surface morphology is tuned by the incorporation of metals coming from the ion source and sample surroundings during the IBS process. The metal content measured in nanohole patterns is almost twice that found in nanodot morphologies. Thus, the pattern morphology results from the balance between the dependences of the erosion rate on the ion flux, the local surface topography and composition. These nanostructures have promising applications as growth templates for preferential growth on either hillocks or cavities.

Hybrid titania-aminosilane platforms evaluated with human mesenchymal stem cells.

The properties of hybrid aminopropyltriethoxysilane-tetraisopropylorthotitanate (APTS-TIPT) platforms prepared by a sol-gel route have been explored, and their biocompatibility was assayed after culture of human mesenchymal stem cells (hMSCs). The organic content of this material was observed to be preferably surface-oriented as indicated by microanalytical techniques. Furthermore, the surface showed characteristic amino-silane bands when explored by Raman spectroscopy as well as indications of silane and titanate condensation. Surface activity of the amino groups was probed by ultraviolet-visible spectroscopy imine derivatization and chemical force spectroscopy, showing a pH-dependent surface charge-induced potential. hMSCs cultured onto these surfaces showed relevant differences with respect to their behavior on gelatin-coated glass plates. Even if with a lower proliferative rate than controls, the cells develop long cytosolic prolongations in osteogenic differentiation medium, thus, supporting the idea of an APTS-TIPT stimulated process.

Hemocompatibility of low-friction boron-carbon-nitrogen containing coatings.

Mechanical heart valves are exposed to extreme mechanical demands, which require a surface showing not only nonhaemostatic properties, but also wear resistance and low friction. As alternative to different forms of amorphous carbon (a-C), so-called diamond-like carbon (DLC), the suitability of boron carbonitride (BCN) coatings is tested here for hemocompatible coatings. They have similar mechanical properties like a-C surfaces, but superior chemical stability at ferrous substrates or counterparts. BCN films with different nitrogen content were compared with hydrogenated a-C films regarding their mechanical properties, surface energy, adsorption of albumin and fibrinogen, blood platelet adherence, and activation of the contact system of the clotting cascade and kinin system. Similar mechanical properties and biological response have been found in the BCN films with respect to a-C, indicating the potential of these coatings for biomedical applications. The increase in the crystallinity and tribological properties of the BCN samples with a higher incorporation of N was also followed by a lower protein adsorption and low activation of the contact system, but an increased adherence of thrombocytes.

[Intergenerational study of the mutation that causes Myotonic Dystrophy Type 1 in Costa Rica]. / Estudio intergeneracional de la mutación que causa la distrofia miotónica tipo 1 en Costa Rica.

INTRODUCTION: Myotonic dystrophy type 1 is a neuromuscular, degenerative and progressive disease, with an autosomal dominant pattern of inheritance, variable expressivity and incomplete penetrance. The genetic defect is an unstable mutation due to the expansion of the triplet CTG in the 3 unstranslated region at the DMPK gene on chromosome 19q13.3. OBJECTIVE: The main objective was to study the intergenerational behavior of the DM1 mutation in order to evaluate the importance of this disease as a neurological problem that could be manageable by genetic counseling. PATIENTS AND METHODS: The study involved 84 patients with clinical diagnosis of DM1 and their relatives, which were confirmed through molecular diagnosis using Southern blot and PCR. RESULTS: Data analysis reveals the size of the mutation presents a positive correlation with the severity of the symptoms and a negative correlation with the age of onset. Transmission of the DM1 mutation is sex and size dependent among the Costa Rican patients. There is an important increment in the size of the mutation between generations and there are no differences in mutation size respect to the transmitting sex. CONCLUSION: The worldwide intergenerational behavior of the DM1 mutation is similar in Costa Rica