Micrometer Dimensions Research Articles

A fiberized highly birefringent glass micrometer-size ridge waveguide

We report the fabrication of a fiberized micrometer-size ridge waveguide using a sheet-stacking method. The fabrication conditions for maintaining the ridge geometry with micrometer dimensions were investigated and discussed. A loss of 3.9dB/m was measured at 1.55μm in the fiber ridge waveguide, showing no extra loss above the bulk loss of the glass. A high birefringence of 9.5×10−3 was measured in the waveguide at 1.55μm which is close to the reported highest birefringence (1.1×10−2) in optical fibers. Fusion splicing was successfully employed to splice the fabricated waveguide to a conventional silica fiber with reasonable loss.

Interplay of Different Reaction Pathways in the Pulsed Galvanostatic Deposition of Zinc Oxide

The electrochemical deposition of crystalline zinc oxide (ZnO) out of aqueous Zn(NO3)2 solutions under pulses of controlled current were studied on gold substrates in micrometer dimensions. Three significant stages were observed for the potential established during depositions in all potential-time curves. Scanning electron and confocal laser microscopy analysis revealed a correlation between a successively completed coverage of the gold electrode by ZnO and an abrupt transition of the deposition and rest potential to less negative values. The deposition time at which such a transition was detected depended not only on the amount of deposited ZnO but also on the current density during electrodeposition, pointing at a different growth mode of ZnO, and on the electrode geometry, pointing at the influence of different diffusion profiles of the reacting ions. In order to elucidate the role of different participating redox reactions in the course of electrodepositions of ZnO, measurements were also carried out in various reference electrolytes. Additionally, pulsating times were varied which revealed that the three stages in the potential were only seen for pauses which were equal or longer in time than the current pulse. The significance of each stage and the corresponding reaction is discussed for the preparation of ZnO films completely covering an electrode surface to optimize the deposition for future applications in electronic devices.

Colossal Permittivity Observed in Yttrium Doped BaTiO<sub>3</sub>

Colossal permittivity (CP) in BaTiO3(BT)-based polycrystalline ceramics with normal grain sizes has been successfully obtained in yttrium (Y) doped BT ceramics (BYT) via a simple and effective method. Considering the necessary factors for CP formation mechanism, well designed doping condition and sintering procedure were carried out in the sample preparation. Characterizations show that BYT is with a pure tetragonal perovskite structure and the grain growth is depressed under the action of Y donor doping. The frequency independence of permittivity and Debye-like relaxation related to Maxwell-Wagner relaxation which occurred at the interfaces between semiconducting grains and insulating grain boundaries can be detected. These are induced by an internal barrier layer capacitance (IBLC)-type structure which formed under an overall and carefully designed synthesis procedure. But the temperature independence of permittivity does not arise because of the particular tetragonal structure and micron dimension grain sizes of BYT.

Formation of self-organized nano-surfaces on III–V semiconductors by low energy oxygen ion bombardment

Pattern formation on surfaces of III–V compound semiconductors GaAs, GaSb, and InSb by O2+ ion sputtering was studied. For GaAs, a ripple pattern was observed under a 2-keV primary beam energy for two ion fluences, i.e., 3.1×1018 ions/cm2 and 5.4×1018 ions/cm2. The pattern wavelengths were 175nm and 200.2nm. A bubble-like structure was observed on the GaSb surface bombarded with 1-keV and 2-keV oxygen ions. In the case of InSb, several pyramidal structures with sub-micrometer dimensions were observed when the ion energy was 1keV. When the ion energy was increased to 2keV, the pyramidal structures acquired micrometer dimensions and a ripple pattern with a wavelength of 246nm was observed in the surrounding area.

The effect of B4C particle size on the reaction process and product in the Cu–Zr–B4C system

ZrC and ZrB2 were prepared by self-propagating high-temperature synthesis in a Cu–Zr–B4C system. We explored the influence of B4C particle size on the reaction process, phase composition and microstructure of the products. The results show that the production of ZrC and ZrB2 is mainly controlled by the dissolution of B4C in Cu–Zr liquid. Increasing the size of B4C will not affect the reaction path, but will retard the formation of the Cu–Zr–B–C liquid. This leads to the incomplete conversion of ZrC and ZrB2 once the B4C exceeds 28 μm. In addition, ZrC and ZrB2 particle sizes greatly decrease from the micrometer dimension with a polyhedral morphology to the nanometer scale with a nearly spherical shape.

Infrared Photothermal Therapy with Water Soluble Reduced Graphene Oxide: Shape, Size and Reduction Degree Effects

In this work, we investigate the effects of lateral size and reduction level of polyethylene glycol (PEG)-modified graphene oxide (GO) nanosheets on the photothermal properties. PEG-modified GO (GO–PEG) and reduced graphene oxide (rGO–PEG) matrices were synthesized through amide bond formation between the carboxyl groups of carboxylated GO and rGO and the amine groups of a PEG linker. We found that the reaction temperature has an important influence on the morphology and size of the pegylated nanostructures. While rGO–PEG formed at 80°C is of nanometer size, the GO–PEG, prepared at room temperature, has needle-like shape with micrometric dimensions. The rGO–PEG matrix was found to be highly soluble under physiological conditions with no aggregation observed even after 6 months of storage. The cytotoxicity of both matrices as well as their photothermal properties to ablate cervical HeLa cancer cells and MDA-MB-231 human breast carcinoma cells were studied. There was no sign of acute toxicity of rGO–PEG for HeLa and MDA-MB-31 cancer cells over a wide concentration range. A complete destruction of the tumor cells could be achieved with a laser power of 6 W cm-2 and a concentration of 60 μg mL-1 of rGO–PEG.

Effects of pretreatment for micron glass on its nano-Fe3O4 coating layer

To prepare pearlyescent pigment of micron glass/nano-Fe3O4 by co-precipitation method, the micron dimension glass as substrate must be eroded by sodium hydroxide solution and hydrofluoric acid for appropriate time so as to obtain more “growing points” for “crystal seed point” of Fe3O4. The effects of eroding time of sodium hydroxide solution, eroding time of hydrofluoric acid and the reaction temperature on coating layer of micron glass/nano-Fe3O4 were investigated. The results showed when the micro glass as a substrate would be eroded by 0.5 mol/L sodium hydroxide solution for 20 min and then by 0.1 mol/L hydrofluoric acid for 8 min, the Fe3O4 coated layer displays uniform tightly packed nano-scales granular shape, the particle size can be estimated ≈30 nm. The samples were characterized by XRD, HRSEM, XPS, VSM, FT-IR and color measurement.

High conductivity micro-wires in diamond following arbitrary paths

High quality graphitic wires embedded beneath the surface of single crystal diamond are fabricated using a combination of adaptive ultrashort pulsed laser fabrication, high numerical aperture focusing, and an axial multi-fabrication scheme. Wires are created with micrometer and sub-micrometer dimensions that can follow any three dimensional path within the diamond. The measured conductivities are over an order of magnitude greater than previously reported wires fabricated by ultra-short pulsed lasers. The increased level of graphitization control in this scheme appears particularly important for fabrication of wires parallel to the diamond surface.

Profiling of oxygen in biofilms using individually addressable disk microelectrodes on a microfabricated needle

A novel microelectrode array sensor was fabricated using MEMS technology on a needle, and then applied to real-time measurement of dissolved oxygen (DO) inside biofilms. The sensor consists of eleven gold disk microelectrodes, a rectangular auxiliary electrode along them, and an external and internal reference electrode. Three kinds of sensors were designed and their responses were characterized and evaluated under various conditions. The arrays exhibit a linear response to DO in the 0–8 mg·L−1 concentration range in water, high sensitivity, repeatability, and low limits of detection (<0.11 mg·L−1 of DO) and quantification (0.38 mg·L−1 DO). The sensors were validated against a commercial Clark-type microelectrode and applied to profiling of DO in a heterotrophic biofilm cultivated in a flat-plate bioreactor. It is shown that the sensor array can provide a multipoint, simultaneous snapshot profile of DO inside a biofilm with high spatial resolution due to its micrometric dimensions. We conclude that this new sensor array represents a powerful tool for sensing of DO biofilms and in numerous bioprocesses.

High Temperature Oxidation Stability of Aerodynamically Optimised Riblets for Blades of Aero-engine Applications

The mechanism of nature’s way of friction reduction and aerodynamical optimisation is applied worldwide. There is ample literature on investigations and measurement of skin friction reduction in the boundary layer over flat plates and on turbo machinery type blades. When using a surface with riblet structures, the turbulent momentum transfer at the wall which is responsible for the skin friction is hampered. This paper deals with the oxidation and characterisation of riblets with micrometer dimensions for aerodynamically optimised high temperature turbine applications. Riblets were fabricated on EB-PVD NiCoCrAlY coatings by using a pico-second laser. The high temperature oxidation stability of the riblets was tested by conducting cyclic oxidation tests. The temperatures were selected as 900 and 1100 °C and the time of oxidation was varied between 1 and 1,000 cycles. The thermocyclic tests at 900 °C proved that the riblets are stable even after 1,000 cycles and at 1,100 °C the stability is permitted to until only 100 cycles. With few modifications in the structuring process this stability can be further improved.

Effects of crevice size on the establishment of macroalgae in subtropical streams.

Considering that in previous studies, the surface roughness (micrometric dimension) showed a weak effect on the colonization of stream macroalgae, we investigated the effects of different crevice sizes (milimetric dimension, a scale slightly higher than previous investigations) on the macroalgal abundance in three streams exposed to full sunlight in southern Brazil. We used smooth sterile glass plates with different shapes: P - plane surface without crevices; S - sinuous surface (depth of crevices with 0.159 mm ± 0.03); N - non-unifom surface (0.498 mm ± 0.09); C - surfaces with convex structures (1.190 mm ± 0.12); and three additional surface types with different patterns of heterogeneity with combinations of glass pieces: P + S (H1); P + S + N (H2) and P + S + N + C (H3). The plates were placed into the streams and after 105 days the percent cover of macroalgal community was measured. No significant differences among treatments were recorded. However, we observed a trend of macroalgae occurs within the crevices in all treatments and this suggests that, for stream macroalgae, the crevice sizes used in this study was still not enough to provide an expressive algal growth, even in the treatment with bigger crevices.

Protein-resistant cross-linked poly(vinyl alcohol) micropatterns via photolithography using removable polyoxometalate photocatalyst.

In the last years, there has been an increasing interest in controlling the protein adsorption properties of surfaces because this control is crucial for the design of biomaterials. On the other hand, controlled immobilization of proteins is also important for their application as solid surfaces in immunodiagnostics and biosensors. Herein we report a new protein patterning method where regions of the substrate are covered by a hydrophilic film that minimizes protein adsorption. Particularly, poly(vinyl alcohol) (PVA) cross-linked structures created by an especially developed photolithographic process are proved to prevent protein physisorption and they are used as a guide for selective protein adsorption on the uncovered areas of a protein adsorbing substrate such as polystyrene. The PVA cross-linking is induced by photo-oxidation using, as a catalyst, polyoxometalate (H3PW12O40 or α-(NH4)6P2W18O62), which is removed using a methyl alcohol/water mixed solvent as the developer. We demonstrate that the polystyrene and the cross-linked PVA exhibit dramatically different performances in terms of protein physisorption. In particular, the polystyrene areas presented up to 130 times higher protein binding capacity than the PVA ones, whereas the patterning resolution could easily reach dimensions of a few micrometers. The proposed approach can be applied on any substrate where PVA films can be coated for controlling protein adsorption onto surface areas custom defined by the user.

Patterning of Epitaxial Perovskites from Micro and Nano Molded Stencil Masks

A process is developed that combines soft lithographic molding with pulsed laser deposition (PLD) to make heteroepitaxial patterns of functional perovskite oxide materials. Micro‐ and nanostructures of sacrificial ZnO are made by micro molding in capillaries (MiMiC) and nano transfer molding, respectively, and used to screen the single crystalline substrates during subsequent PLD. ZnO is used because of its compatibility with the high temperatures reached during PLD and because of the ease of its removal after use by benefiting from its amphoteric nature. Sub‐micrometer sized lines of La0.67Sr0.33MnO3 are made by the transfer molding approach, preserving the anisotropic features expected for a fully oriented thin film and taking account for the magnetostatic contribution from the line shapes. Different patterns of SrRuO3 are made with lateral dimensions of a few micrometers having individual features for which electrical isolation is illustrated. The bottom‐up soft lithographic methods can be compliantly utilized for making epitaxial structures of various shapes and sizes in the μm down to the nm range, and offer unique opportunities for fundamental studies as well as for realizing technological applications.

Role of oxygen content on micro-whiskers in mercury based superconductors

In this study, the formation of micro-whiskers at the mercury based cuprate superconductors, synthesized by solid state reaction technique has been investigated for both oxygen and argon annealed samples. In this context, the superconducting samples have been annealed by the oxygen or argon gases in same rate (pressure) of 150 bar. Moreover, the over doped sample has been subjected to oxygen annealing twice at the same oxygen rate. Hence, micro-whiskers in the mercury cuprates have spontaneously grown for the over oxygen annealed sample, so we have not intended to have whisker grown. The whiskers grown in the mercury based cuprate superconductor has been investigated by Scanning Electron Microscopy, X-Ray Diffraction analysis and Superconducting Quantum Interference Devices measurements for the first time. It has been determined that whiskers grown on the over doped sample, which are in micrometer dimensions, have been observed only surfaces of the bulk sample. Moreover, the formation of whiskers has been examined for the optimally oxygen and argon doped samples. It has been shown that neither the optimally oxygen doped nor argon doped samples with the same gas rate have displayed any whisker structures. Hence, it has been decided that that the type of gas, the density of gas flowing and the bulk properties of the superconductor play a crucial role on formation of whisker structure in the system. Moreover, it has been revealed that in order to get rich whisker content, the oxygen process should be applied to the powder form of the superconductor in such a way to get the over oxygen doping rate for the superconducting system investigated. For further works, the magnetic and transport properties of the mercury based whiskers grown are planned to be determined. • Effect of gas type on whiskers has been investigated for Hg-based superconductor. • Concentration of the gas have a crucial role for whisker formation. • Shape of the superconducting sample is important for formation of whisker. • Argon or optimum oxygen doping procedures do not affect formation of whiskers. • Whiskers have been observed on the surface of the over oxygen doped sample.

Synthesis of Microcrystals of the [Fe(L)(bipy)] Spin Crossover Coordination Polymer in a Poly‐4‐vinylpyridine Matrix

Microcrystals of the spin-crossover coordination polymer [FeL(bipy)] (L=[3,3']-[1,2-phenylenebis(iminoethylidyne)]bis-(2,4-pentanedionato)(2-), bipy=4,4'-bipyridine) have been prepared in a poly(4-vinylpyridine) (P4VP) matrix. This was done by sequential addition of the iron(II) precursor complex and the bridging ligand bipy to a P4VP matrix, and by repetition of this cycle. The obtained composite material was characterized using TEM, SEM, XRPD, and SQUID measurements, and Mössbauer spectroscopy. With repeating cycles, the size of the [FeL(bipy)] crystals in the P4VP matrix increases from submicrometer to micrometer dimensions. A strong dependence on the number of cycles is observed. Above a critical size and concentration, the microcrystals show the same cooperative spin transition as the bulk material. No indication for a gradual spin transition is observed, but the remaining iron centers are either high-spin or low-spin depending on the coordination environment.

Chemical precipitation of sulfur nanoparticles from aqueous solutions

Process of formation and coarsening of sulfur nanoparticles deposited from aqueous solutions of calcium and sodium polysulfides and sodium thiosulfate and from solutions of elementary sulfur in a mixture of hydrazine hydrate and monoethanolamine was considered. The sulfur nanoparticles were characterized with a laser analyzer of particle sizes, X-ray diffraction analysis, and electron probe microscopy. It was shown that the sizes of primary particles strongly depend on the concentration of an acid and on the molar ratio between the sulfur-containing solutions and the acid. The antifungal effects of sulfur with nano- and micrometer dimensions were compared. The experimental results demonstrated a strong antifungal effect of sulfur nanoparticles on various kinds of fungi.

Theory of spin-wave instability thresholds for ultrathin ferromagnetic films under parallel pumping

A microscopic, or Hamiltonian-based, theory is developed to study the spin-wave instability thresholds for the parametric processes occurring in ultrathin ferromagnetic films under conditions of parallel pumping with a microwave field. Most previous work has focused on spheres or films with dimensions of order several microns or more, and the theoretical interpretation has been in terms of macroscopic (continuum) methods. At smaller size scales, as in ultrathin films with thickness less than about 100 nm, the discreteness of the quantized spin waves and their spatial distributions become modified, making it more appropriate (particularly for the nonlinear dynamics) to employ a microscopic or Hamiltonian-based approach with a lattice of effective spins interacting with one another through the magnetic dipole-dipole and exchange interactions. This work utilizes a similar microscopic approach, but with the effects of microwave pumping included, to calculate the spin-wave instability thresholds for the bands of quantized spin waves in ultrathin films with the saturation magnetization parallel to their surface. Magnetic materials with different ratios of the exchange to dipole-dipole strengths are considered, taking examples for relatively strong, intermediate, and weak exchange. In the case of parallel pumping it is found that the shape of the typical ``butterfly curve,'' as conventionally obtained with macroscopic samples of YIG, becomes modified in these ultrathin films due to the occurrence of several quantized spin-wave bands and their spatial properties.

A piezoelectric micro-electromechanical microphone for implantable hearing aid applications

The human ear receives the sound signals from the ambient and converts those signals to the electrical domain and transmits them to the brain. According to the prevalence of human hearing impairments and necessity of using the hearing aid, this paper has been concentrated on the design of microphones to be implanted inside the ear. The intended design for this application is using microelectromechanical technology and piezoelectric material. Based on the important role of the diaphragm in the microphones structure and in order to achieve maximum displacement in diaphragm, variety of accurate studies in terms of shape and dimension have been done and will be presented in this paper. The examined shapes for selecting the optimum diaphragm's form are circle, square and hexagonal. In the performed simulations and analysis, four dimensions in micrometer have been considered for each selected shape. According to the contemplated the efficiency parameters (diaphragm's center displacement, first resonant frequency) and results of the simulations, the circular diaphragm's performance with dimension of 350 µm compared to the other cases is desirable for medical application of the microphone. The analysis and simulations have been performed in COMSOL software. The fabrication process of the proposed diaphragm has been done using bulk and surface micromachining. In addition, AlN was utilized as the piezoelectric material in this structure.

Scale-up and purification of graphite oxide as intermediate for functionalized graphene

High purity graphite oxide (GO) and scale-up of GO synthesis is in high demand for enabling GO applications in catalysis and the synthesis of functionalized carbon nanomaterials. Although Hummers method, which involves oxidizing graphite with KMnO4 in sulfuric acid, is highly attractive with respect to its cost-effective raw materials and low energy demand, still purification, scale-up and safety problems prompt numerous challenges in large scale production. Conventional dead-end-filtration (DE) is difficult, owing to the severe plugging of the filters by water-swollen GO, whereas dialysis requires massive amounts of water. Plugging problems are solved when using membrane separation with average membrane pores smaller than the lateral micrometer dimensions of GO nanoplatelets. In contrast to DE and dialysis, a short DE prefiltration of acidified GO dispersions, combined with subsequent cross-flow filtration (CF) enables easy GO scale-up and production of high purity GO. Equipped with on-line monitoring of waste-water, this CF process is automated and enables concentration of GO dispersions in the final stage. In GO purification, pH switching represents the key to removing Mn and S impurities.

Negative Poisson’s ratio for cubic crystals and nano/microtubes

The paper systemizes numerous cubic crystals which can have both positive and negative Poisson’s ratios (the so-called partial auxetics) depending on the specimen orientation in tension. Several complete cubic auxetics whose Poisson’s ratio is always negative are indicated. The partial cubic auxetics are classified with the use of two dimensionless elastic parameters. For one of the parameters, a critical value is found at which the orientation behavior of the crystals changes qualitatively. The behavior of mesotubes obtained by rolling up plates of cubic crystals (crystals with rectilinear anisotropy) is considered in detail. Such mesotubes with curvilinear cubic anisotropy can have micron and nanometer lateral dimensions. It is shown that uniform tension of nano/microtubes of cubic crystals is possible only in the particular case of zero chirality angle (the angle between the crystallographic axis and the axis of a stretched tube). It is demonstrated by the semi-inverse Saint-Venant method that solution of the axial tension problem for cylindrically anisotropic nano/microtubes of cubic crystals with a non-zero chirality angle is possible with radially inhomogeneous fields of three normal stresses and one shear stress. In the examples considered, the cylindrically anisotropic nano/microtubes of cubic crystals are auxetics even if they are initially non-auxetics with rectilinear anisotropy.