Μm Side Research Articles

Stochastic reconstruction and a scaling method to determine effective transport coefficients of a proton exchange membrane fuel cell catalyst layer

This work uses a method for the stochastic reconstruction of catalyst layers (CLs) proposing a scaling method to determine effective transport properties in proton exchange membrane fuel cell (PEMFC). The algorithm that generates the numerical grid makes use of available information before and after manufacturing the CL. The structures so generated are characterized statistically by two-point correlation functions and by the resultant pore size distribution. As an example of this method, the continuity equation for charge transport is solved directly on the three-dimensional grid of finite control volumes (FCVs), to determine effective electrical and proton conductivities of different structures. The stochastic reconstruction and the electrical and proton conductivity of a 45 μm side size cubic sample of a CL, represented by more than 3.3 × 10 12 FVCs were realized in a much shorter time compared with non-scaling methods. Variables studied in an example of CL structure were: (i) volume fraction of dispersed electrolyte, (ii) total CL porosity and (iii) pore size distribution. Results for the conduction efficiency for this example are also presented.

The Morin transition in nanostructured pseudocubic hematite: Effect of the intercrystallite magnetic exchange

The Morin transition in α-Fe 2O 3 particles with homogeneous pseudocubic morphology of about 1.8 μm side has been studied by different techniques. The particles are made up of nanometric crystallites with a narrow size distribution. Samples annealed at 673, 773 and 873 K, yielded Morin transition temperatures, T M, of about 230, 241, and 245 K, respectively, which are lower than the bulk value, T M ≈ 263 K. In addition, the temperature range Δ T M through which these samples undergo the transition is very narrow with respect to the values reported in the literature. Ranges of 20, 10 and 8 K, were obtained for the samples annealed at 673, 773 and 873 K. In this work, through the estimation of the exchange magnetic energy, we demonstrate that the existence of the Morin transition, and its shift and breadth are related to the presence of intercrystallite interactions within the pseudocubic particles. These intercrystallite interactions are modified by the annealing treatments, which help to remove non-stoichiometric hydroxyl groups and incorporated water molecules.

3D simulation of the effects of sphericity on char entrainment in fluidised beds

The paper presents a 3-dimensional simulation of the effect of particle shape on char entrainment in a bubbling fluidised bed reactor. Three char particles of 350 μm side length but of different shapes (cube, sphere, and tetrahedron) are injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. Due to the fluidising conditions, reactor design and particle shape the char particles will either be entrained from the reactor or remain inside the bubbling bed. The sphericity of the particles is the factor that differentiates the particle motion inside the reactor and their efficient entrainment out of it. The simulation has been performed with a completely revised momentum transport model for bubble three-phase flow, taking into account the sphericity factors, and has been applied as an extension to the commercial finite volume code FLUENT 6.3.

Microstructures and improved wear resistance of 3D needled C/SiC composites with graphite filler

Three-dimensional (3D) needled carbon/carbon (C/C) composites with a lowest porosity of 15.6% were achieved after 1 cycle of impregnation by phenolic resin slurry containing graphite filler, hot-pressing curing and pyrolysis. Carbon/silicon carbide (C/SiC) composites were obtained by liquid silicon infiltrating C/C composites. The aim was to incorporate cost effectiveness and excellent performance of C/SiC braking material. Using filler content not exceeding 30 wt% in the slurry promised undamaged C/C segments in C/SiC composites. The linear wear rate of C/SiC using 30 wt% filler was 0.33 μm side −1 cycle −1 and displayed a fourfold decrease; its weight wear rate was 2.46 mg side −1 cycle −1 and minus 171%, compared with the previously reported values of C/SiC without filler, at a braking velocity of 28 m/s. Its friction coefficients and friction stability coefficients appeared relative insensitive to changes in braking velocities and displayed higher values at high braking velocities compared with the previous values.

Synthesis of silver nanoclusters on zeolite substrates

Silver nanoclusters were synthesized by reducing silver nitrate with ethylene glycol at 160 °C in the presence of zeolite. A one-pot procedure has rendered uniform size distributions of quasispherical silver clusters of average sizes of 100–200 nm synthesized on the surfaces of cubiclike zeolite substrates of ∼1 μm side. Bulk material microanalysis measurements showed samples with silver mass percentages of 20%–38%. Surface atomic composition analysis found silver concentrations of 3.1%–5.7%, zeolite compounds and nontraces of nitrogen were measured. The binding energy for the Ag 3d5/2 core electrons was shifted to higher energies at 368.6 eV compared to that of metallic silver. Herein, is presented a cost-effective technique for producing a narrow size distribution of silver nanocomposites with great potential for optoelectronics, catalysis, and nanobiotechnological applications.

Optical bistability in InP/GaInAsP equilateral-triangle-resonator microlasers

Optical bistability is reported in InP/GaInAsP equilateral-triangle-resonator (ETR) microlasers, which are fabricated by planar technology. For a 30 mum side ETR microlaser with a 2-mum-wide output waveguide connected to one of the vertices of the ETR, hysteresis loops are observed for the output power versus the injection current from 215 to 235 K. The laser output spectra are measured in the upper and lower states of the hysteresis loop, which show strong mode competition among transverse modes. The hysteresis loops are demonstrated by two-mode rate equations with asymmetric cross gain saturation and different output efficiencies.

Synthesis and characterization of Cu 2Se prepared by hydrothermal co-reduction

Cu 2Se compounds were synthesized by hydrothermal co-reduction at 150–200 °C from CuSO 4·5H 2O and SeO 2 in deionized water. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM). Experimental results show that, the product powders with Cu 2Se phase obtained at 180 and 200 °C almost consist of regular hexagonal flakes which grow along (1 1 1) crystal plane. The side lengths between 100 and 200 nm of hexagonal flakes synthesized at 180 °C are much smaller than those of the product with 1.3–2 μm side length at 200 °C.

Top surface and side roughness of Inconel 625 parts processed using selective laser melting

PurposeObtaining the required part top surface roughness and side roughness is critical in some applications. Each of these part properties can often be improved to the detriment of the other during selective laser melting (SLM). The purpose of this paper is to investigate the selective laser melting of Inconel 625 using an Nd:YAG pulsed laser to produce thin wall parts with an emphasis on attaining parts with minimum top surface and side surface roughness.Design/methodology/approachA full factorial approach was used to vary process parameters and identify a usable Inconel 625 processing region. The effects laser process parameters had on the formation of part surface roughness for multi‐layer parts were examined. Processing parameters that specifically affected top surface and side roughness were identified.FindingsHigher peak powers tended to reduce top surface roughness and reduce side roughness as recoil pressures flatten out the melt pool and reduce balling formation by increasing wettability of the melt. Increased repetition rate and reduced scan speed reduced top surface roughness but increased side roughness. A compromise between attaining a relatively low surface roughness and side roughness can be attained by comparing part surface roughness values and understanding the factors that affect them. A sample with 9 μm top surface roughness and 10 μm side roughness was produced.Originality/valueThe research is the first of its kind directly processing Inconel 625 using SLM and investigating processing parameters that affect top surface and side roughness simultaneously. It is a useful aid in unveiling a relationship between process parameters and top/side roughness of thin walled parts.

In situ determination of precise stable Si isotope ratios by UV-femtosecond laser ablation high-resolution multi-collector ICP-MS

Abstract A new method for the in situ measurement of stable Si isotope ratio using UV-femtosecond laser ablation connected to a multiple-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) has been established. The use of medium mass resolution mode (with a resolving power m /Δ m = 8000) permits to resolve spectral interferences on 28 Si, 29 Si and 30 Si allowing for determination of the 29 Si/ 28 Si and 30 Si/ 28 Si ratios with high accuracy and precision on wide, interference-free plateaus. A three-isotope plot demonstrated that interferences, if existing, are negligible for Si isotope ratios. The laser spot size is 35 μm and measurements are made using square rasters of 150 μm side length. Different types of elemental Si, Si-oxide and silicate matrices have been analysed by laser ablation using the international standard NBS28 as the bracketing standard. Thus δ 29 Si and δ 30 Si have been determined for the silicon isotope standard IRMM-017 ( δ 30 Si ± 2 S.D. = − 1.26 ± 0.24‰; n = 89) and BigBatch ( δ 30 Si = − 10.55 ± 0.42‰; n = 15), as well as San Carlos Olivine ( δ 30 Si = − 0.81 ± 0.19‰; n = 14), Caltech Rose Quartz ( δ 30 Si = 0.10 ± 0.13‰; n = 14) sponge needles ( Stylocordyla borealis ; δ 30 Si = − 2.19 ± 0.32‰; n = 14) and JER-diopside glass ( δ 30 Si = 0 ± 0.09‰; n = 14) samples. The overall repeatability achievable is 0.15‰ (2 S.D.) on δ 29 Si and 0.24‰ (2 S.D.) on δ 30 Si. The silicon isotope standard IRMM-018 has also been measured and was confirmed to be heterogeneous. The two isotope ratios follow an equilibrium mass-dependent fractionation law which can be represented as δ 30 Si = 1.93 × δ 29 Si. Published extractions methods have been used to wet-chemically purify Si from the JER-diopside glass. The Si extracted was presented as Si-gel and ablated like a solid. The results show excellent agreement with in situ measurements of this glass that confirms that this technique can be employed to a wide variety of matrices, including Si purified from solution. The new technique presents a viable alternative to solution MC-ICP-MS for bulk measurements and the most precise technique so far for in situ measurement of Si isotope ratios.

Printing of Patterned Copper on Pliable, Microtextured PDMS/Ceramic Composites

AbstractIn this work, we present a novel printing technique that enables the usage of PDMS and ceramic powder mixed PDMS composites (we refer as “PDMS-ceramic composites” in this context), as a substrate for printing of copper conduction layers. This technique is based on microtransfer molding (μTM) and lift-off for pattern formation [4]. Another key feature is the usage of microtextured PDMS and PDMS-ceramic composites before any copper film deposition. Our microtextured surface is composed of pyramid shaped wells (100 μm depth and 150 μm sides on PDMS surface). The poor adhesion between PDMS and copper is overcome by oxygen plasma application and titanium deposition before copper layer.In order to demonstrate the convenience of this technique in RF applications, copper conduction lines (5 mm wide, different lengths) were printed on microtextured PDMS substrates. These transmission lines successfully maintained a low resistance during large strain. The printed lines have the DC resistance of 0.5 Ω and conductivity of 1.3e6 S/m, and the transmission analysis of these lines show good results especially in the MHz range when compared to copper tape measurements.Apart from the conduction lines, the substrates can have ranging dielectric constants from 3 (no powder) to 23 (50% D270 powder, provided by TransTech) by volume mixing rule. Dielectric constant is important for RF applications, especially antenna designs. Therefore, provided with a range of dielectric constants, these composite substrates are a great promise in RF field for pliable antenna fabrication [5]. For experiment purposes, some of the transmission lines are printed on these composite substrates as well as pure PDMS.In this study, apart from the fabrication of transmission lines, this novel technique will be applied in a GPS antenna design for demonstration purposes. This antenna design is a single-fed circularly-polarized stacked antenna for tri-band GPS (L1, L2 and L5) applications [6]. For the fabrication of the antenna, polymer-ceramic materials of ε1=16 and ε2=30 will be utilized as the substrates [6].

A SU-8 dish for cell irradiation

The objective of the CELLION project is radiation research at low doses. The main cell responses to low dose irradiation are bystander effects, genomic instability and adaptive responses. In order to study these effects it is convenient to make the cells addressable in space and time through locking the cell position. A new alternative dish has been developed for irradiation procedures at the Lund Nuclear Probe. The versatile dish can be used both to cultivate and to hold the cells during the irradiation procedure. The irradiation dish is made of an epoxy-based photopolymer named SU-8 chosen by its flexibility, non-toxicity and biological compatibility to cell attachment. It has been fabricated using a UV lithographic technique. The irradiation dish forms a 2 × 2 mm 2 grid which contains 400 squares. Each square has 80 μm side and is separated from neighbouring ones by 20 μm wide walls. The location of each square is marked by a row letter and column number patterned outside the grid. The Cell Irradiation Facility at the Lund Nuclear Probe utilizes protons to irradiate living cells. A post-cell detection set up is used to control the applied dose, detecting the number of protons after passing through the targeted cell. The transmission requirement is fulfilled by our new irradiation dish. So far, the dish has been used to perform non-targeted irradiation of Hepatoma cells. The cells attach and grow easily on the SU-8 surface. In addition, the irradiation procedure can be performed routinely and faster since the cells are incubated and irradiated in the same surface.

Development of an MeV ion beam lithography system in Jyväskylä

A lithographic facility for writing patterns with ion beams from cyclotron beams is under development for the Jyväskylä cyclotron. Instead of focusing and deflecting the beam with electrostatic and magnetic fields a different approach is used. Here a small rectangular beam spot is defined by the shadow of a computer-controlled variable aperture in close proximity to the sample. This allows parallel exposure of rectangular pattern elements of 5–500 μm side with protons up to 6 MeV and heavy ions ( 20Ne, 85Kr) up to few 100 MeV. Here we present a short overview of the system under construction and development of the aperture design, which is a critical aspect for all ion beam lithography systems.

Microstructure and properties of 3D needle-punched carbon/silicon carbide brake materials

The carbon/silicon carbide brake materials were prepared by chemical vapor infiltration (CVI) combined with liquid melt infiltration (LMI). The carbon fiber preform was fabricated with the three dimension needling method. The microstructure, mechanical, thermophysical, and frictional properties of C/SiC composites were investigated. The results indicated that the composites were composed of 65 wt%C, 27 wt%SiC, and 8 wt%Si. The density and porosity were 2.1 g cm −3 and 4.4%, respectively. The C/SiC brake materials exhibited excellent toughness. The average dynamic friction coefficient and static friction coefficient of the materials were about 0.34 and 0.41, respectively. The friction coefficient was stable. The fade ratio of the friction coefficient under moist conditions was about 2.9%. The linear wear rate was less than 1.9 μm side −1 cycle −1. These results show that C/SiC composites have excellent properties for use as brake materials for aircraft.

Polymer investment molding: Method for fabricating hollow, microscale parts

Polymer investment molding combines traditional injection molding with investment casting to create hollow parts on the microscale. Silicon mold inserts are manufactured using reactive ion etching or anisotropic wet etching. Then, a sacrificial element is placed in the mold. Plastic is injected into the mold and around the sacrificial element using an injection molding press. After removing the plastic part from the mold, liquid etchant dissolves the sacrificial element leaving a hollow plastic part. To demonstrate the process microneedles were formed by injection molding Cyclic Olefin Copolymer (Ticona Topas ®) around 32 μm diameter aluminum bond wire. Hollow, in-plane, microneedles were then achieved by dissolving the bond wire away in liquid aluminum etchant. Rectangular cross-section needles were created with dimensions of 130 μm × 100 μm, overall lengths of 280 μm, and approximate inner diameter of 35 μm. Tapered needles were also created having an approximately triangular cross-section with two 105 μm sides and one 150 μm side. These needles had a base-to-tip length of 300 μm and approximate inner diameter of 35 μm.

Photon counting X-ray imaging with CdTe pixel detectors based on XPAD2 circuit

Abstract A semiconductor hybrid pixel detector for photon counting X-ray imaging has been developed and tested under radiation. The sensor is based on recent uniform CdTe single crystal associated with XPAD 2 counting chip via innovative processes of interconnection. The building detector is 1 mm thick, with an area of 1 cm 2 and consists of 600 square pixels cells 330 μm side. The readout chip working in electron collection mode is capable of setting homogeneous threshold with only a dispersion of 730 e − . Maximum noise level has been evaluated around 15 keV. First experiments under X-rays demonstrate a very good efficiency of detection. Moreover, imaging system allows excellent linearity over a large-scale achieving count rate of 3×10 6 photons/s/mm 2 . Spectrometric measurements point up the system potential in multi-energies applications by locating and resolving X-rays lines of 241 Am and 57 Co sources.

Results on a prototype of a large-area X-ray imaging device using CMOS hybrid detectors

This paper presents the first results on a prototype of a large-area X-ray imaging device made out of hybrid CMOS pixel detectors. The challenges of manufacturing and implementing imaging devices on an area larger than the single component size, with a seamless sensitive area, are addressed via a preliminary evaluation of the images. A sensitive area of approximately 6×3 cm 2 was built with eight single ASIC chips performing photon counting and bump-bonded to two high-resistivity p–n silicon sensors working in a reverse bias mode. Each chip consists of 256×256 identical square pixels of 55 μm side. The image delivered is a 1024×512-pixel matrix. Dedicated read-out electronics, software and mechanical supports have been developed. We report and discuss the challenges of the system in terms of the resulting quality of static images obtained with a 70 kV X-ray tube.

Fabrication of a ZnO piezoelectric micro cantilever with a high-aspect-ratio nano tip

This paper reports on a ZnO piezoelectric micro cantilever with a high-aspect-ratio (HAR) nano tip, which is proposed for a ferroelectric material based nano storage system. The system uses the interaction between the nano tip and a storage medium, and the HAR nano tip is needed to suppress undesirable effects caused by the small gap between the cantilever and the storage medium. The fabrication process for the cantilever with the HAR nano tip consists of three parts: the HAR nano tip formation, the cantilever fabrication, and the bonding/releasing process. The HAR nano tip is formed by the Si deep reactive ion etching for a long shaft and the anisotropic wet etching for a nano tip end. The cantilever is made up of 1 μm-thick LPCVD poly-Si layer and 0.2 μm-thick Si nitride layer, and has 0.5 μm-thick ZnO actuation layer. A final releasing process is followed by an anodic bonding process. The fabricated HAR nano tip has 6 μm side length, over 18 μm height, and less than 15 nm tip radius, which is built on the 85 μm-wide, 300 μm-long, and 1.2 μm-thick cantilever. The experimental results show a linear behavior with respect to input voltage of 1 to 5 V and the first resonance frequency at 17.9 kHz.

Ti and TiO x seeding influence on the orientation and ferroelectric properties of sputtered PZT thin films

The integration of PZT thin films in MEMS requires a thorough control of nucleation and growth of the Metal/Ferroelectric/Metal multilayer. In this paper, the Ti seeding technology has been used to optimise the nucleation of Pb(Zr 0.52, Ti 0.48)O 3 thin films (PZT) on a stabilized Pt/TiO x /Si bottom electrode. TiO x (20 nm) and Pt (100 nm) films have been deposited on Si substrates by reactive sputtering in Ar+O 2 (90/10) and in pure Ar, respectively. The bottom electrode crystallisation rapid thermal annealing (RTA, 400 °C, 30 s) has been performed in N 2 or (N 2+O 2) atmospheres. A few nanometers thick Ti or TiO x seeding layer has been sputtered in Ar or Ar+O 2. Finally, 0.25 μm thick PZT films have been sputtered in pure Ar plasma and crystallised by RTA (700 °C, 30 s, in air). The PZT XRD measurements have shown the highest (1 1 1) orientation for the samples prepared with the Ti seeding layer deposited on the bottom electrode. Moreover, best ferroelectrics values have been measured for the sample with the air annealed bottom electrode and the Ti seeding layer ( P r=13.8 μC cm −2, E c=153 kV cm −1). These values have been recorded on 400 and 450 μm side length square top electrodes dispatched on a 1.5 cm 2 area. We have found a yield up to 80% with a 450 μm×450 μm top electrode surface. The comparison of these results with PZT/Pt/Ti basic structures point out the influence of the Ti seeding ultra-thin layer and the bottom electrode annealing conditions on the PZT crystallization in the perovskite phase.

Phase structure and photoluminescence properties of Er3+-doped Al2O3 powders prepared by the sol–gel method

The Er 3+ -doped Al 2 O 3 powders have been prepared by the sol–gel method, using the aluminium isopropoxide [Al(OC 3 H 7 ) 3 ]-derived Al 2 O 3 sols with addition of the erbium nitrate [Er(NO 3 ) 3 · 5H 2 O]. The different phase structure, including three crystalline types of (Al,Er) 2 O 3 phases, γ, θ, α, and two Er–Al–O phases, ErAlO 3 and Al 10 Er 6 O 24 , was obtained with the 0–5 mol% Er 3+ -doped Al 2 O 3 powders at the different sintering temperature of 600–1200 °C. The phase structure has an evident influence on the photoluminescence (PL) properties for the Er 3+ -doped Al 2 O 3 powders. For the phase mixture of γ-(Al,Er) 2 O 3 and θ-(Al,Er) 2 O 3 in minor amounts with the different Er 3+ doping concentration sintered at 900 °C, the PL spectra of the full widths at half maximum (FWHM) of about 55 nm were observed with a main peak at λ =1.533 μm and a side peak at λ =1.549 μm. The stronger PL intensity was detected with the 0.5 and 1 mol% Er 3+ doping concentration, and decreased with further increasing the Er 3+ doping concentration. The dramatic concentration quenching effect took place above the 1.5 mol% Er 3+ doping concentration. At the 1 mol% Er 3+ doping concentration, the PL intensity of the Er 3+ -doped Al 2 O 3 powders increased with the phase structure changed from γ-(Al,Er) 2 O 3 → θ-(Al,Er) 2 O 3 → α-(Al,Er) 2 O 3 , corresponding to the increase of sintering temperature from 600 to 1200 °C. The PL spectrum was observed with the main sharp peak at λ =1.533 μm and many sharp side peaks at the different wavelengths for the α-(Al,Er) 2 O 3 , ErAlO 3 and Al 10 Er 6 O 24 phases prepared at 1200 °C.

Optical ferromagnetic resonance studies of thin film magnetic structures

We have used a magneto-optical pump-probe technique to stimulate and characterize small amplitude precession of the magnetization in a variety of thin film magnetic structures. The sample is stimulated by an optically triggered magnetic field pulse and its response probed by means of a stroboscopic measurement of the magneto-optical Kerr effect. We demonstrate that the experimental technique is sensitive to small amplitude deflections of the magnetization and present formulae that describe the frequency of precession in continuous films containing either one or two magnetic layers. We show how the dependence of the precession frequency upon the orientation and magnitude of the static field may be used to characterize a 100 Å Co thin film, a Ni81Fe19(50 Å)/Cu(20 Å)/Co(50 Å)/IrMn(100 Å) spin-valve structure, and a square Ni81Fe19 element of 10 µm side and 150 nm thickness. Information may be obtained about the g factor, demagnetizing field, exchange bias effect and magnetic anisotropy within an individual ferromagnetic layer, and about the coupling between layers. We deduce the presence of a four-fold anisotropy in the square element that is associated with non-uniformity of the magnetization. Time resolved images show that the dynamic magnetization is generally non-uniform. A stripe pattern is observed when the static field is significantly larger than the anisotropy field. Measurements at low field show that the dynamic magnetization initially has a regular pattern associated with the underlying domain structure, but then evolves into a highly disordered state. Finally we discuss the outlook for further development and application of the experimental technique.