Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.

Surface and interface morphology of polystyrene/poly(methyl methacrylate) thin-film blends and bilayers

The surface and interface morphologies of polystyrene (PS)/poly(methyl methacrylate) (PMMA) thin-film blends and bilayers were investigated by means of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy. Spin-coating a drop of a PS solution directly onto a PMMA bottom layer from a common solvent for both polymers yielded lateral domains that exhibited a well-defined topographical structure. Two common solvents were used in this study. The structure of the films changed progressively as the concentration of the PS solution was varied. The formation of the blend morphology could be explained by the difference in the solubility of the two polymers in the solvent and the dewetting of PS-rich domains from the PMMA-rich phase. Films of the PS/PMMA blend and bilayer were annealed at temperatures above their glass-transition temperatures for up to 70 h. All samples investigated with AFM were covered with PS droplets of various size distributions. Moreover, we investigated the evolution of the annealed PS/PMMA thin-film blend and bilayer and gave a proper explanation for the formation of a relatively complicated interface inside a larger PS droplet.

Interface morphology snapshots of vertically segregated thin films of semiconducting polymer/polystyrene blends

We present atomic force microscopic images of the interphase morphology of vertically segregated thin films spin coated from two-component mixtures of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and polystyrene (PS). We investigate the mechanism leading to the formation of wetting layers and lateral structures during spin coating using different PS molecular weights, solvents and blend compositions. Spinodal decomposition competes with the formation of surface enrichment layers. The spinodal wavelength as a function of PS molecular weight follows a power-law similar to bulk-like spinodal decomposition. Our experimental results indicate that length scales of interface topographical features can be adjusted from the nanometer to micrometer range. The importance of controlled arrangement of semiconducting polymers in thin film geometries for organic optoelectronic device applications is discussed. (c) 2007 Elsevier Ltd. All rights reserved.

Role of interface curvature on stress distribution under indentation for ZrN/Zr multilayer coating

Contact damage in curved interface nano-layeredmetal/nitride (150 (ZrN)/10 (Zr) nm) multilayer is investigated in order to understand the role of interface morphology on contact damage under indentation. A finite element method (FEM) model was formulated with different wavelengths of 1000 nm, 500 nm, 250 nm and common height of 50 nm, which gives insight on the effect of different curvature on stress field generated under indentation. Elastic-plastic properties were assigned to the metal layer and substrate while the nitride layer was assigned perfectly elastic properties. Curved interface multilayers show delamination along the metal/nitride interface and vertical cracks emanating from the ends of the delamination. FEM revealed the presence of tensile stress normal to the interface even under the contact, along with tensile radial stresses, both present at the valley part of the curve, which leads to vertical cracks associated with interfacial delamination. Stress enhancement was seen to be relatively insensitive to curvature. (C) 2014 Elsevier B.V. All rights reserved.

Temperature Dependence of Surface Composition and Morphology in Polymer Blend Film

Thin films of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) blend can phase separate upon heating to above its critical temperature. Temperature dependence of the surface composition and morphology in the blend thin film upon thermal treatment was studied using in situ X-ray photoelectron spectroscopy (XPS) and in situ atomic force microscopy (AFM). It was found that in addition to phase separation, the blend component preferentially diffused to and aggregated at the surface of the blend film, leading to the variation of surface composition with temperature. At 185 degrees C, above the critical temperature, the amounts of PMMA and SAN phases were comparable.

Gold nanoparticles as fine tuners of electrochemical properties of the electrode/solution interface

Recently, a novel approach for preparing SERS and SPR substrates was developed, which indicates a potential application in tailoring the interfacial structure of an electrode surface. In this study, (3-mercaptopropyl)trimethoxysilane (MPTMS) was selected as a polymeric adhesive layer, and a low concentration of colloid Au solution was used to achieve a more accurate control over interface morphology at nanoscale dimensions due to slow self-assembling kinetics of gold nanoparticle's. Subsequent seeding growth of these MPTMS-supported submonolayers of gold nanoparticles in Au3+/NH2OH aqueous solution enlarges particle size and eventually results in the generation of conductive gold films (similar to previous (3-aminopropyl)trimethoxysilane-supported gold films). Such tunable interface structure was evaluated by atomic force microscopy (AFM). Also, ac impedance spectroscopy (ACIS) and cyclic voltammograms were performed to evaluate electrochemical properties of the as-prepared interfaces by using Fe(CN)(6) (3-/4-) couples as a probe. Furthermore, relevant theories of microarray electrodes were introduced into this study to explain the highly tunable electrochemical properties of the as-prepared interfaces. As a result, it is concluded that the electrochemical properties toward Fe(CN)(6) (3-/4-) couples are highly dependent on the active nanoelectrode (nanoparticles) area fraction and nanoparticles are fine-tuners of interfacial properties because the number density. (numbers/unit area) and size of nanoparticles are highly tunable by self-assembling and seeding growth time scale control. This is in agreement with the theoretical expectations for a microarray electrode if a single nanoparticle tethered to a blocking SAM is taken as a nanoelectrode and 2-D nanoparticle assemblies are taken as nanoelectrode arrays.

Effect of Er:YAG laser and diamond drill on hybrid layer morphology obtained with self-etch adhesive: analysis by SEM and confocal laser scanning microscopy (CLSM)

This study aimed to evaluate the effect of Er:YAG (L) and diamond drills (DD) on: 1) the microshear bond strength (MPa); 2) the adhesive interface of two-step (TS) – Adper Scotchbond Multipurpose and one-step (OS) adhesives – Adper EasyOne, both from 3M ESPE. Material and methods: According to the preparation condition and adhesives, the samples were divided into four groups: DD_TS (control); DD_OS; L_TS and L_OS. 60 bovine incisors were randomly divided into experimental and groups: 40 for microshear bond strength (n = 10) and 20 for the adhesive interface morphology [6 to measure the thickness of the hybrid layer (HL) and length of tags (t) by CLSM (n = 3); 12 to the adhesive interface morphology by SEM (n = 3) and 2 to illustrate the effect of the instruments on dentine by SEM (n = 1)]. To conduct the microshear bond strength test, four cylinders (0.7 mm in diameter and 1 mm in height with area of adhesion of 0.38 mm) were constructed with resin composite (Filtek Z350 XT – 3M ESPE) on each dentin surface treated by either L or DD and after adhesives application. Microshear bond strength was performed in universal testing machine (EMIC 2000) with load cell of 500 kgf and a crosshead speed of 0.5 mm / min. Adhesive interface was characterized by thickness of hybrid layer (HL) and length of tags (t) in nm, with the aid of UTHSCSA ImageTool software. Results: Microshear bond strength values were: L_TS 34.10 ± 19.07, DD_TS 24.26 ± 9.35, L_OS 33.18 ± 12.46, DD_OS 21.24 ± 13.96. Two-way ANOVA resulted in statistically significant differences only for instruments (p = 0.047). Mann-Whitney identified the instruments which determined significant differences for HL thickness and tag length (t). Concerning to the adhesive types, these differences were only observed for (t). Conclusion: It can be concluded that 1) laser Er:YAG results in higher microshear bond strength values regardless of the adhesive system (TS and OS); 2) the tags did not significant affect the microshear bond strength; 3) the adhesive interface was affected by both the instruments for cavity preparation and the type of adhesive system used.

P-n junction organic photovoltaics fabricated by all solution processing

We have prepared p-n junction organic photovoltaic cells using an all solution processing method with poly(3-hexylthiophene) (P3HT) as the donor and phenyl-C 61-butyric acid methyl ester (PCBM) as the acceptor. Interdigitated donor/acceptor interface morphology was observed in the device processed with the lowest boiling point solvent for PCBM used in this study. The influences of different solvents on donor/acceptor morphology and respective device performance were investigated simultaneously. The best device obtained had characteristically rough interface morphology with a peak to valley value ∼15 nm. The device displayed a power conversion efficiency of 1.78%, an open circuit voltage (V oc) 0.44 V, a short circuit current density (J sc) 9.4 mA/cm 2 and a fill factor 43%.

Effect of nanoparticle dispersion on glass transition in thin films of polymer nanocomposites

We present spectroscopic ellipsometry measurements on thin films of polymer nanocomposites consisting of gold nanoparticles embedded in poly(styrene). The temperature dependence of thickness variation is used to estimate the glass transition temperature, T(g). In these thin films we find a significant dependence of T(g) on the nature of dispersion of the embedded nanoparticles. Our work thus highlights the crucial role played by the particle polymer interface morphology in determining the glass transition in particular and thermo-mechanical properties of such nanocomposite films.

Metallographic Sample Prepared by Ion Beam Etching

Ion beam etching technique was used to reveal the metallograhpic microstructure and interface morphology of electroplating chromium coating, in particular, whose substrate surface layer was treated in advance by laser quenching. Chemical etchings were, also conducted for comparison. The reveal microstructures were observed and analyzed by scanning electron microscopy. The results show that ion beam etching can reveal well the whole microstructures of composite coating-substrate materials.

Tailoring of dendritic microstructure in solidification processing by crucible vibration

We analyzed the effects of both natural convection and forced flows on solid–liquid interface morphology during upward Bridgman solidification of metallic alloys. Experiments were carried out on Al–3.5wt% Ni alloy, for a cylindrical sample. The influence of natural convection induced by radial thermal gradient on solidified microstructure was first analyzed as a function of the pulling rate. Then, the influence of axial vibration on solidification microstructure was experimentally investigated by varying vibration parameters (frequency and amplitude). Experimental results demonstrated that vibrations could be used to either attenuate fluid flow in the melt and obtain a uniform dendritic pattern or to promote a fragmented dendritic microstructure. However, no marked effect was observed for cellular growth. This pointed out the critical role of the mushy zone in the interaction between fluid flow and solidification microstructure.

Influence of Forced Convection on Columnar Microstructure During Directional Solidification of Al-Ni Alloys

This paper presents a summary of cellular and dendritic morphologies resulting from the upward directional solidification of Al - Ni alloys in a cylindrical crucible. We analysed the coupling of solid-liquid interface morphology with natural and forced convection. The influence of natural convection was first analyzed as a function of growth parameters (solute concentration, growth rate and thermal gradient). In a second step, the influence of axial vibrations on solidification microstructure was investigated by varying vibration parameters (amplitude and frequency). Experimental results were compared to preliminary numerical simulations and a good agreement is found for natural convection. In this study, the critical role of the mushy zone in the interaction between fluid flow and solidification microstructure is pointed out.

Efeito do laser ER:YAG e ponta diamantada na morfologia da camada híbrida obtida com um adesivo autocondicionante: resistência de união ao microcisalhamento análise por MEV e MLCF

Pós-graduação em Ciências Odontológicas - FOAR

Cell mixing induced by myc is required for competitive tissue invasion and destruction

Cell-cell intercalation is used in several developmental processes to shape the normal body plan. There is no clear evidence that intercalation is involved in pathologies. Here we use the proto-oncogene myc to study a process analogous to early phase of tumour expansion: myc-induced cell competition. Cell competition is a conserved mechanism driving the elimination of slow-proliferating cells (so-called 'losers') by faster-proliferating neighbours (so-called 'winners') through apoptosis and is important in preventing developmental malformations and maintain tissue fitness. Here we show, using long-term live imaging of myc-driven competition in the Drosophila pupal notum and in the wing imaginal disc, that the probability of elimination of loser cells correlates with the surface of contact shared with winners. As such, modifying loser-winner interface morphology can modulate the strength of competition. We further show that elimination of loser clones requires winner-loser cell mixing through cell-cell intercalation. Cell mixing is driven by differential growth and the high tension at winner-winner interfaces relative to winner-loser and loser-loser interfaces, which leads to a preferential stabilization of winner-loser contacts and reduction of clone compactness over time. Differences in tension are generated by a relative difference in F-actin levels between loser and winner junctions, induced by differential levels of the membrane lipid phosphatidylinositol (3,4,5)-trisphosphate. Our results establish the first link between cell-cell intercalation induced by a proto-oncogene and how it promotes invasiveness and destruction of healthy tissues.

Lattice pulling effect and strain relaxation in axial (In, Ga)N/GaN nanowire heterostructures grown on GaN-buffered Si(111) substrate

Transmission electron microscopy and spatially resolved electron energy-loss spectroscopy have been applied to investigate the indium distribution and the interface morphology in axial (In,Ga)N/GaN nanowire heterostructures. The ordered axial (In,Ga)N/GaN nanowire heterostructures with an indium concentration up to 80% are grown by molecular beam epitaxy on GaN-buffered Si(111) substrates. We observed a pronounced lattice pulling effect in all the nanowire samples given in a broad transition region at the interface. The lattice pulling effect becomes smaller and the (In,Ga)N/GaN interface width is reduced as the indium concentration is increased in the (In,Ga)N section. The result can be interpreted in terms of the increased plastic strain relaxation via the generation of the misfit dislocations at the interface.