Micrometric Domains Research Articles

Exact analytical solutions for micrometer structured vortex beams with applications to optical tweezers

Bessel beams are widely known by their non-diffracting properties, i.e. beams that sustain their transverse profile along the propagation. It is also well known that by a suitable superposition of Bessel beams of the same frequency, but different longitudinal wave numbers, amplitudes and phases, it is possible to obtain a resulting beam whose longitudinal intensity pattern can be shaped along the propagation z-axis. Such approach, named Frozen Wave method, can be implemented through discrete or continuous superposition, the latter being more appropriate for obtaining spatially structured beams in micrometer domains. In previous studies, authors constructed analytical solutions for micrometer zero-order (i.e., null topological charge) Frozen Wave and, thereafter, of order one and two, by making use of a topological charge raising operator. In this paper, we present an analytical closed solution for the general case where the topological charge raising operator is applied an arbitrary number of times to a micrometer zero-order Frozen Wave beam, thus generating one of arbitrary topological charge. We also apply the new solutions to model optical tweezers (in Rayleigh regime) considering different light polarizations.

The microstructure and He+ ion irradiation behavior of novel low-activation W-Ta-Cr-V refractory high entropy alloy for nuclear applications

Microstructure and nanohardness of a nearly equimolar W-Ta-Cr-V high entropy alloy (HEA), as well as its irradiation response under He+ irradiation, were investigated. The single-phase body-centered cubic nanostructured alloy with a 1 µm thick layer was fabricated on a silicon substrate using a magnetron sputtering method. The HEA film has a complex microstructure consisting of micrometric domains that exhibit internal nanostructure controlled by their crystal orientation. The measured nanohardness of the W-Ta-Cr-V alloy is 13 ± 2 GPa, which significantly exceeds the hardness of nanocrystalline tungsten as a result of the high solid-solution strengthening effect. In order to evaluate the irradiation resistance of the HEA film, the material was irradiated with 200 keV He+ ions at room temperature, with two different ion fluences: 1 × 1016 and 5 × 1016 ions/cm2. Using transmission electron microscopy, a high density of extremely fine He bubbles is observed that were uniformly distributed in the matrix. The increase of He+ ion fluence increased the density of bubbles, whereas their size remained at a similar level, which indicates that the damage proceeds by the nucleation of additional He bubbles, not by their growth.

Optical response of plasmonic silver nanoparticles after treatment by a warm microwave plasma jet

This work investigates the effect of plasma treatment on the morphology and composition of 15 × 15 mm2 silver nanoparticle (70–80 nm) thin films. The silver nanoparticles are deposited onto thermal silica (SiO2/Si) substrates by spin-coating, then they are treated by an open-to-air microwave argon plasma jet characterized by a neutral gas temperature of 2200 ± 200 K. Scanning electron microscopy analysis reveals that the number of isolated nanoparticles in the film sample decreases after exposure to multiple jet passes, and that polygonal structures with sharp corners and edges are produced. Similar structures with much rounder edges are obtained after conventional thermal annealing at temperatures up to 1300 K. Based on localized surface plasmon resonance analysis in the range of 350–800 nm, the main extinction band of silver nanoparticles experiences a redshift after treatment with the plasma jet or with thermal annealing. Moreover, both treatments induce surface oxidation of the nanoparticles, as evidenced by x-ray photoelectron spectroscopy. However, only the plasma-exposed samples exhibit a significant rise in the surface-enhanced Raman scattering (SERS) signal of oxidized silver at 960 cm−1. 29 29 μm2 mappings of hyperspectral Raman IMAging (RIMA) and multivariate curve resolution analysis by log-likelihood maximization demonstrate that the SERS signal is controlled by large-scale micrometer domains that exhibit sharp corners and edges.

The intracrystalline microstructure of Monte Fico lizardite, by optics, <i>μ</i>-Raman spectroscopy and TEM

Abstract. The Monte Fico lizardite crystals have an internal skeletal spongy microstructure, formed by two micrometric domains having different optical reliefs. This intracrystalline microstructure parallels the previously reported intercrystalline arrangement, consisting of lizardite prisms within a chrysotile plus polygonal serpentine matrix. In the high-wavenumber region, the larger and more abundant domains (that represent approximately 87 % of the total field view) produce μ-Raman spectra characterized by two major peaks at 3686 and 3705 cm−1. The smaller, less abundant domains present a wide band confined between these wavenumbers. These features are interpreted as lizardite and chrysotile, respectively. Raman results are confirmed by TEM, which emphasizes the presence of well-recognizable polygonal serpentine too. Tight crystallographic control exists between lizardite and this first serpentine generation. A second serpentine generation occurs perpendicularly to the first one. The lizardite crystals grew up with a skeletal habit, whereas chrysotile fibres and polygonal serpentine filled the voids, growing epitactically on the lizardite crystals, with fast crystal growth in a fluid-rich environment.

3D Printing Microactuators for Soft Microrobots.

Current additive manufacturing, including three-dimensional (3D) and so-called four-dimensional printing, of soft robotic devices is limited to millimeter sizes. In this study, we present additive manufacturing of soft microactuators and microrobots to fabricate even smaller structures in the micrometer domain. Using a custom-built extrusion 3D printer, microactuators are scaled down to a size of 300 × 1000 μm2, with minimum thickness of 20 μm. Microactuators combined with printed body and electroactive polymers to drive the actuators are fabricated from computer-aided design model of the device structure. To demonstrate the ease and versatility of 3D printing process, microactuators with varying lengths ranging from 1000 to 5000 μm are fabricated and operated. Likewise, microrobotic devices consisting of a rigid body and individually controlled free-moving arms or legs are 3D printed to explore the microfabrication of soft grippers, manipulators, or microrobots through simple additive manufacturing technique.

Micro and nanodomains on structured silica/titania photocatalysts surface evaluated in RhB degradation: Effect of structural properties on catalytic efficiency

Mesoporous nanoparticles and mixed-structure silica with existing nanometric and micrometric domains on their surface were prepared using SiCl4. TiCl4 was used as precursor to obtain nano- and mixed heterogeneous supported titania photocatalysts. The systems and, for comparative reasons, commercial (P25) were evaluated for Rhodamine B (RhB) photodegradation in deionized and lake water solution. The structural differences between nano- and mixed photocatalysts were observed and are due to the degree of particles structural organization, according to small-angle X-ray scattering (SAXS) profiles. The structural analysis obtained by fractal dimension (pL) showed that photocatalysts which were organized as mass fractal structures presented higher catalytic activity than the photocatalysts of rough surface fractal or non-fractal. A compressive discussion on surface topology, size, band gap, surface area, surface charge density, and catalysts amount was done to explain the effect of these features on the photocatalysts performance. The distribution of Ti-O-Si species on the support surface was determined by X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). The higher photocatalytic activity for the degradation of RhB dye was achieved by SNCl5Ti sample. This catalyst achieved high efficiency factor, EF = mg of RhB degraded/ mg of catalyst, equal to 0.020 and 0.0132, under UV and Vis radiation, respectively, which is lower catalyst amount than the similar TiO2-SiO2 based systems reported in the literature. These findings broaden the opportunities to degrade other harmful pollutants in wastewater. This work also provides an insight on how structural properties are correlated to the efficiency of titania supported nano/micrometric catalysts.

Heterogeneous Random Laser with Switching Activity Visualized by Replica Symmetry Breaking Maps

In the past decade, complex networks of light emitters are proposed as novel platforms for photonic circuits and lab-on-chip active devices. Lasing networks made by connected multiple gain components and graphs of nanoscale random lasers (RLs) obtained from complex meshes of polymeric nanofibers are successful prototypes. However, in the reported research, mainly collective emission from a whole network of resonators is investigated, and only in a few cases, the emission from single points showing, although homogeneous and broad, spatial emission. In all cases, simultaneous activation of the miniaturized lasers is observed. Here, differently, we realize heterogeneous random lasers made of ribbon-like and highly porous fibers with evident RL action from separated micrometric domains that alternatively switch on and off by tuning the pumping light intensity. We visualize this novel effect by building for the first time replica symmetry breaking (RSB) maps of the emitting fibers with 2 {\mu}m spatial resolution. In addition, we calculate the spatial correlations of the laser regions showing clearly an average extension of 50 {\mu}m. The observed blinking effect is due to mode interaction along light guiding fibers and opens new avenues in the fabrication of flexible photonic networks with specific and adaptable activity.

Lipid Rafts, Sphingolipids, and Ergosterol in Yeast Vacuole Fusion and Maturation.

The Saccharomyces cerevisiae lysosome-like vacuole is a useful model for studying membrane fusion events and organelle maturation processes utilized by all eukaryotes. The vacuolar membrane is capable of forming micrometer and nanometer scale domains that can be visualized using microscopic techniques and segregate into regions with surprisingly distinct lipid and protein compositions. These lipid raft domains are liquid-ordered (Lo) like regions that are rich in sphingolipids, phospholipids with saturated acyl chains, and ergosterol. Recent studies have shown that these lipid rafts contain an enrichment of many different proteins that function in essential activities such as nutrient transport, organelle contact, membrane trafficking, and homotypic fusion, suggesting that they are biologically relevant regions within the vacuole membrane. Here, we discuss recent developments and the current understanding of sphingolipid and ergosterol function at the vacuole, the composition and function of lipid rafts at this organelle and how the distinct lipid and protein composition of these regions facilitates the biological processes outlined above.

Hybrid starch/silica films with improved mechanical properties

Environmental concern has increased the research in development of biodegradable packaging. Although there are many reports about starch films, their physicochemical properties need to be improved, and the introduction of an inorganic compound is an alternative to be applied. However, there are few reports about the development of biodegradable hybrid organic–inorganic films for food packaging. Therefore, the preparation of biodegradable films was proposed by using sol–gel and casting techniques, based on starch and glycerol as plasticizers, with the incorporation of an alkoxide precursor containing silicon, TEOS (tetraethyl orthosilicate) in different concentrations. Morphological, thermal, optical, and mechanical properties, water solubility, swelling, and water vapor permeability were evaluated. The addition of TEOS was more efficient when it underwent pre-hydrolysis before incorporation into the film-forming solution, significantly interfering with the results of mechanical, optical, and barrier properties. The silica phase was uniformly incorporated into the polymer, presenting micrometric domains. The hybrid films produced have satisfactory properties for application as biodegradable packaging.

Dry Sliding Tribological Properties of a Hard Anodized AA6082 Aluminum Alloy

The applications of aluminum and its alloys are still limited by low hardness and low wear resistance properties. Surface modifications, such anodizing and plasma electrolytic oxidation, represent a feasible way to overcome these drawbacks. In this study, discs of AA6082 were subjected to the so-called G.H.A. hard anodizing process leading to an anodized layer having a honeycomb-like structure. Samples having alumina layer thicknesses of 10, 50 and 100 μm were subjected to unidirectional dry sliding wear tests, using bearing steel and silicon nitride as counterbody materials. Surface and structure characterization of the samples were performed before and after the tribological tests, using a wide range of techniques; atomic force microscopy and scanning electron microscopy techniques were used before the wear tests. The wear scars were characterized by scanning electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy techniques. Results show that the different thickness of the anodized layer does not affect the pores dimensions but has an influence on the micrometric domains in which the pores are divided. These features coupled with the wear test conditions, show to have a strong influence on the wear behavior. The thinnest sample showed also the best performance against the ceramic counterbody.

Numerical Simulation of Melt Hydrodynamics in Laser Micro Processing of Metals

Laser material processing at micro-meter domain can be used for a plethora of applications such as micro drilling, micro welding, micro cutting, micro-texturing as well as micro polishing. In laser micro-cutting, welding and drilling, a high power laser (Intensity ~1010 W/m2) is used to melt and vaporize the material to produce high penetration welds, kerf cuts, and high aspect ratio micro holes. Whereas, in the case of laser texturing, conduction mode welding and polishing, the laser power density is sufficiently low to allow only melting of the material. With the irradiance of high-intensity laser, generation of highly dynamic melt pool occurs due to the presence of vaporization induced recoil pressure, Young Laplace surface tension force, and thermo-capillary shear stress. The melt pool convection results in geometrical defects such as recast layer, porosity, spatter formation, humping, protuberances and melt ripples. These defects pose a severe challenge towards industry utilization of laser micro processing, where precision and repeatability is of utmost importance. Therefore, a competent numerical model considering three co-existing phases (solid-liquid-gas) is developed to predict defects and characterize different regimes through insights on micro-scale melt hydrodynamics. This paper gives an overview of characteristic melt pool hydrodynamics and associated defects in laser micro-processing operations. The developed model has been validated using experiments obtained with 1.07 μm SPI fiber laser.

Highly Reactive TiO2 Anatase Single Crystal Domains Grown by Atomic Layer Deposition

Anatase TiO2 films with unusual domains-like morphology were obtained by postdeposition annealing of amorphous TiO2 films deposited by atomic layer deposition (ALD). Such particular morphology was observed only for TiO2 films deposited using TiCl4 precursor in a nonconventional ALD regime where the reaction byproducts or nonreacted precursors are incorporated into the film and induce an explosive recrystallization upon annealing. This recrystallization leads to the formation of micrometric single crystal domains. The investigation of domains by electron backscatter diffraction shows the formation of a significant amount of highly reactive anatase crystalline facets such as (111) that contradicts fundamental crystal growth rules. The stabilization of (111) facets in films without additional seed layers has a strong interest for photocatalysis-based applications for environmental remediation or hydrogen production.

Fractal Dimension of Erythrocyte Membranes: A Highly Useful Precursor for Rapid Morphological Assay.

Morphology of erythrocyte membrane has been recognized as an alternative biomarker of several patho-physiological states. Numerous attempts have been made to upgrade the existing method of primitive manual counting, particularly exploring the light scattering properties of erythrocyte. All the techniques are at best semi-empirical and heavily rely on the effectiveness of the statistical correlations. Precisely, this is due to the lack of a non-empirical scale of the so-called "morphological scores". In this article, fractal dimension of erythrocyte membrane has been used to formulate a suitable scoring scale. Subsequently, the rapid experimental output of flow-cytometry has been functionally related to the mean morphological quantifier of the whole cell population via an optimum neural network model (R2 = 0.98). Moreover, the fractal dimension has been further demonstrated to be an important parameter in early detection of an abnormal patho-physiological state, even without any noticeable poikilocytic transformation in micrometric domain.

Structuring light under different polarization states within micrometer domains: exact analysis from the Maxwell equations.

We show the possibility of arbitrary longitudinal spatial modeling of non-diffracting light beams over micrometric regions. The resulting beams, which are highly non-paraxial, possess subwavelength spots and can acquire multiple intensity peaks at predefined locations over regions that are few times larger than the wavelength. The formulation we present here provides exact solutions to the Maxwell's equations where the linear, radial, and azimuthal beam polarizations are all considered. Modeling the longitudinal intensity pattern at small scale can address many challenges in three-dimensional optical trapping and micromanipulation.

Hyperbranched PDLA-polyglicerol: A novel additive for tuning PLLA electrospun fiber degradation and properties

In this paper, it was developed the synthesis of a novel polymer additive potentially capable of modifying the features of electrospun fibers based on poly(l-lactide) (PLLA). Indeed, the above molecule, which was designed by taking into account both the features of the polymer matrix and the specific applications of the final material, was made up of a high-molecular-mass hyperbranched polyglicerol (HBPG) core and poly(d-lactide) (PDLA) arms (HBPG-PDLA). 1H NMR characterization allowed to assess the successful preparation of the dendritic HBPG-PDLA, synthesized by means of ring opening polymerization (ROP) of d-lactide, as well as the number average molecular weight per arm, that is about 1100g/mol. Moreover, by combining 1H NMR and TGA results, it was determined an average number of polylactide arms of about 300. Electrospun fibers based on PLLA and HBPG-PDLA were prepared by directly adding the as-synthesized dendritic additive into the electrospinning solution to a final concentration of ca. 25wt.%. FE-SEM analysis of the system, prepared by applying the optimized electrospinning conditions, demonstrated the formation of defect-free fibers without separated, micrometric domains of the additive. The thermal properties of both neat PLLA and composite fibers were studied by DSC analysis. The partial stereocomplexation of the systems containing HBPG-PDLA, resulting from the combination of the PDLA arms of the dendritic polymer with the chains of PLLA, was confirmed by calorimetric measurements as well as by X-ray diffraction analysis. The dendritic additive, featuring the hyperbranched polyglycerol core, was found to enhance the hydrophilicity of the fibers and consequently their enzymatic degradation rate, which turned out to be much higher than that of the neat PLLA fibers. Unlike the organic additives usually applied to modify the properties of PLLA, the addition of HBPG-PDLA to the fibers was also found to lead to an increase of the mechanical properties of the composite systems, that is an increment of their Young’s modulus.

Perspective: 4D ultrafast electron microscopy--Evolutions and revolutions.

In this Perspective, the evolutionary and revolutionary developments of ultrafast electron imaging are overviewed with focus on the "single-electron concept" for probing methodology. From the first electron microscope of Knoll and Ruska [Z. Phys. 78, 318 (1932)], constructed in the 1930s, to aberration-corrected instruments and on, to four-dimensional ultrafast electron microscopy (4D UEM), the developments over eight decades have transformed humans' scope of visualization. The changes in the length and time scales involved are unimaginable, beginning with the micrometer and second domains, and now reaching the space and time dimensions of atoms in matter. With these advances, it has become possible to follow the elementary structural dynamics as it unfolds in real time and to provide the means for visualizing materials behavior and biological functions. The aim is to understand emergent phenomena in complex systems, and 4D UEM is now central for the visualization of elementary processes involved, as illustrated here with examples from past achievements and future outlook.

Mesoscopic crystallographic textures on shells of a hyaline radial foraminifer Ammonia beccarii

Most foraminifera, simple unicellular protists, create calcareous shells with precisely controlled architectures. We investigated the crystal fabric of porous shells of a hyaline radial foraminifer, Ammonia beccarii. The complex structures of the calcitic shell include micrometric single-crystalline domains around a straight pore ∼2 μm in diameter which are divided by strained intermediate regions. The c axes of calcite in the domains were almost perpendicular to the shell surface. The mesoscopic textures, such as periodic lateral lines with a ∼200–450 nm interval and vertical cracks with a ∼150 nm interval, were observed throughout the single-crystalline domains in the shell wall. Specific mechanical properties, such as a lower Young's modulus and a higher hardness of the shells than those of Iceland spar, are ascribed to the presence of the specific mesoscopic textures.

Study on micro-patterning process of vertically aligned carbon nanotubes (VACNTs)

ABSTRACTVertically aligned carbon nanotubes (VACNTs) have drawn significant attention by the researchers because of their nanometric size and favorable material properties. Patterning of CNT forests in the micrometric domain is very important for their application in the area of microelectromechanical system (MEMS). For the first time this paper reports, detailed experimental investigation on a post growth μ-patterning process of VACNT forests. The micromechanical bending (M2B) process was locally applied at the targeted area in order to change the alignment of VACNT forests. Interestingly, the VACNT forest was transformed from typical black body absorber to reflective mirror as the M2B process was applied. Several parameters were identified that govern the resultant patterns such as rotational spindle speed, lateral bending speed, step size, tool morphology, and total depth of bend. Optimization of the parameters was carried out experimentally to obtain the best surface roughness and integrity of the microstructure. A minimum average surface roughness of Ra = 15 nm was achieved with 2000 rpm spindle speed, 1 mm/min bending speed and 1 µm step size.

Kinetic selection of polymeric guanosine architectures from dynamic supramolecular libraries

We report the constitutional resolution and selection of the dynamic supramolecular guanosine systems by using a kinetically irreversible polymerization process. We report an original strategy to transcribe and to fix supramolecular guanosine architectures in self-organized polymers. In the first resolution step, the G-quartet and G-quadruplex architectures are pre-amplified in solution in the presence of K + cations from a dynamic pool of ribbon-type or cyclic supramolecular architectures. Then in a second selection polymerization step, the G-quadruplex is kinetically fixed in a covalent polymethacrylate network via an irreversible amplification step. Both supramolecular and polymeric components mutually (synergistically) adapt their spatial constitution during simultaneous (collective) formation of micrometric self-organized hybrid domains. This contributes to the high level of adaptability and correlativity of the self-organization of the supramolecular G-quadruplexes and of the polymeric systems. Biomimetic-type hybrid systems can be generated by using this strategy.

Adaptive lipid packing and bioactivity in membrane domains.

Lateral compositional and physicochemical heterogeneity is a ubiquitous feature of cellular membranes on various length scales, from molecular assemblies to micrometric domains. Segregated lipid domains of increased local order, referred to as rafts, are believed to be prominent features in eukaryotic plasma membranes; however, their exact nature (i.e. size, lifetime, composition, homogeneity) in live cells remains difficult to define. Here we present evidence that both synthetic and natural plasma membranes assume a wide range of lipid packing states with varying levels of molecular order. These states may be adapted and specifically tuned by cells during active cellular processes, as we show for stimulated insulin secretion. Most importantly, these states regulate both the partitioning of molecules between coexisting domains and the bioactivity of their constituent molecules, which we demonstrate for the ligand binding activity of the glycosphingolipid receptor GM1. These results confirm the complexity and flexibility of lipid-mediated membrane organization and reveal mechanisms by which this flexibility could be functionalized by cells.