Sub-mm Scale Research Articles

Dynamic Properties of Heart Fragments from Different Regions and Their Synchronization.

The dynamic properties of the heart differ based on the regions that effectively circulate blood throughout the body with each heartbeat. These properties, including the inter-beat interval (IBI) of autonomous beat activity, are retained even in in vitro tissue fragments. However, details of beat dynamics have not been well analyzed, particularly at the sub-mm scale, although such dynamics of size are important for regenerative medicine and computational studies of the heart. We analyzed the beat dynamics in sub-mm tissue fragments from atria and ventricles of hearts obtained from chick embryos over a period of 40 h. The IBI and contraction speed differed by region and atrial fragments retained their values for a longer time. The major finding of this study is synchronization of these fragment pairs physically attached to each other. The probability of achieving this and the time required differ for regional pairs: atrium–atrium, ventricle–ventricle, or atrium–ventricle. Furthermore, the time required to achieve 1:1 synchronization does not depend on the proximity of initial IBI of paired fragments. Various interesting phenomena, such as 1:n synchronization and a reentrant-like beat sequence, are revealed during synchronization. Finally, our observation of fragment dynamics indicates that mechanical motion itself contributes to the synchronization of atria.

Arsenic redox transformations and cycling in the rhizosphere of Pteris vittata and Pteris quadriaurita

Pteris vittata (PV) and Pteris quadriaurita (PQ) are reported to hyperaccumulate arsenic (As) when grown in As-rich soil. Yet, little is known about the impact of their unique As accumulation mechanisms on As transformations and cycling at the soil-root interface. Using a combined approach of two-dimensional (2D), sub-mm scale solute imaging of arsenite (AsIII), arsenate (AsV), phosphorus (P), manganese (Mn), iron (Fe) and oxygen (O2), we found localized patterns of AsIII/AsV redox transformations in the PV rhizosphere (AsIII/AsV ratio of 0.57) compared to bulk soil (AsIII/AsV ratio of ≤0.04). Our data indicate that the high As root uptake, translocation and accumulation from the As-rich experimental soil (2080 mg kg−1) to PV fronds (6986 mg kg−1) induced As detoxification via AsV reduction and AsIII root efflux, leading to AsIII accumulation and re-oxidation to AsV in the rhizosphere porewater. This As cycling mechanism is linked to the reduction of O2 and MnIII/IV (oxyhydr)oxides resulting in decreased O2 levels and increased Mn solubilization along roots. Compared to PV, we found 4-fold lower As translocation to PQ fronds (1611 mg kg−1), 2-fold lower AsV depletion in the PQ rhizosphere, and no AsIII efflux from PQ roots, suggesting that PQ efficiently controls As uptake to avoid toxic As levels in roots. Analysis of root exudates obtained from soil-grown PV showed that As acquisition by PV roots was not associated with phytic acid release. Our study demonstrates that two closely-related As-accumulating ferns have distinct mechanisms for As uptake modulating As cycling in As-rich environments.

Automatic Data Reduction and Quantification of X-Ray Computed Tomography Images of Sedimentary Cores: Method and Illustration

This paper presents a procedure from which information contained in 3-Dimensional single energy X-ray computed tomography (XR-CT) images of sedimentary rocks is converted into sub-mm scale resolution core scalar and core image logs. This new data provide a quantitative and compact (data volume reduction of ~90%) description of the XR-CT images. Density-related outputs are calibrated through automatic integration with continuous digital visual core description (VCD) and discrete moisture and density (MAD) property index measurements of selected samples. After lithology-based calibration of the X-ray attenuation coefficients into density values, quantitative displays include: 1) histogram of the distribution of density values and its related statistical parameters, 2) radial and angular distributions of core density values, 3) volume, average density and mass contributions of three core fractions defined by density thresholds corresponding to voids or vugs (VV, density ≤ ~1 g•cm−3), and a break in the histogram of distribution of the density values showing the limit between the damaged (DM) and non-damaged (ND) fractions of the core material, and so, 4) providing a sub-mm scale bulk density core log free of any drilling disturbance. The procedure is illustrated on data from the 365 m deep Hole C9001C drilled off-shore Shimokita (northeast coast of Honshu, Japan). Usage of the outputs include: 1) derivation of sub-mm scale porosity core log, 2) correction of volume sensitive measurements in case of poor core quality and partially filled core liner, and 3) seismic modeling and well ties.

Microscale trace-element distribution across the Cretaceous/Palaeogene ejecta layer at the Agost section: Constraining the recovery of pre-impact conditions

A high-resolution, sub-mm scale analysis of the distribution of major and trace elements across the ejecta layer marking the Cretaceous/Palaeogene boundary (KPgB) at the Agost section (SE Spain) was performed using Laser Ablation-Inductivity Coupled Plasma-Mass Spectrometry (LA-ICP-MS). A KPgB interval ≈17 mm thick, has been selected for this study. It includes gray calcareous marl from the uppermost Maastrichtian (Cretaceous), 2.02-mm-thick red clay (the ejecta layer), and blackish-gray clay (boundary clay layer) from the lowermost Danian (Palaeogene). The unconsolidated sediments were resin-embedded under O2-free conditions and analyzed by LA-ICP-MS line continuous scan measurements at 20 μm increments and a laser-beam of 120 μm. These micron-scale analyses show that the anomalous contents of trace and major elements in this boundary are restricted to the ejecta layer, which displays a relatively uniform distribution over its ≈2 mm thickness. Trace and major elemental ratios, such as Ca/Al, Ti/Al, Cr/Al, Fe/Al, Ni/Al, Cu/Al, Zn/Al, As/Al, Sb/Al and Pb/Al have similar values below and above the ejecta layer, consistent with similar palaeoenvironmental conditions prior to and after the impact event. Such element distribution points to anomalies exclusively restricted to the ejecta, thus a nearly instantaneous re-establishment of pre-impact conditions right after the impact event is observed.

Integration of silver nanowires into SU-8 hollow cantilevers for piezoresistive-based sensing

We established a process for the microfabrication of SU-8 AFM cantilevers with an embedded microchannel and an integrated layer of silver nanowires as piezoresistive element. The self-sensing detection is based on the electrical resistance increase of the silver nanowire network associated with the strain applied upon deflection of the cantilever. We observed a sensitivity of 1.4 × 10−6 nm−1 at large strains of 4 % (gauge factor of 10) and a sensitivity of 0.1 × 10−6 nm−1 at small strains of 0.6 % (gauge factor of 1). We obtained a still higher sensitivity (gauge factor of 28) by coating the silver nanowires network with a thin (∼10 nm) aluminum oxide layer acting as an insulating barrier. As application, we studied the cantilever deformation as a function of the overpressure applied in the microchannel while the cantilever was kept in contact with a glass surface confirming their large deflection detection capabilities. The results were qualitatively rationalized in the percolation framework. The presented self-sensing micropipettes could be used for experiments that require remarkably important bending, such as localized single cell deposition by squeezing the micropipette against the substrate, as well as force-controlled electrochemical additive manufacturing at the sub-mm scale.

Instrument for Measuring Local Ionic Conductivity of Porous Electrodes

Due to the nature of how porous battery electrodes are fabricated, their microstructure is not uniform. For instance, there are variations in composition, effective electronic transport, and effective ionic transport. Such heterogeneity has been associated with several battery application issues. For example, variability in transport of ions can lead to a tendency for localized plating of lithium on anodes during fast charging [1-2]. Studying the heterogeneity of electrodes is a growing research topic. Our research group has previously developed a micro-four-line probe that successfully measured the variation of electronic conductivity of electrodes [3]. Another method to study the microstructure of electrodes is by means of SEM and X-ray tomography, and the variation of tortuosity (effective ionic resistance) in electrodes was computed by analyzing the tomographic data of microstructure [4]. We report here on a new technique to measure the local ionic resistance on a sub-mm length scale. A probe was made to detect the local transport of ions through a small aperture. The probe is scanned across the surface of a porous thin-film electrode in order to create maps of tortuosity or MacMullin number. The measurement was performed using electrochemical impedance spectroscopy, and an associated model is needed to invert the experimental results. [1] Harris et al., The Journal of Physical Chemistry C 117, 6481 (2013). [2] Vogel et al., Electrochimica Acta 297, 820 (2019). [3] Lanterman et al., Journal of the Electrochemical Society 162, A2145 (2015). [4] Kehrwald et al. Journal of The Electrochemical Society 158, A1393 (2011). Figure 1

Motion of Heavy Particles on a Submerged Chladni Plate.

Heavy particles are traditionally believed to gather at the nodes of a resonating plate, forming standard Chladni patterns. Here, for the first time, we experimentally show that heavy particles, i.e., sub-mm particles, can move towards the antinodes of a resonating plate. By submerging the resonating plate inside a fluidic medium, the acoustic radiation force and the lateral effective weight become dominant at the sub-mm scale. Those forces, averaged over a vibration cycle, move the particles towards the antinodes and generate sophisticated patterns. We create a statistical model that relates the complex motion of particles to their locations and plate vibration frequencies in a wide spectrum of both resonant and nonresonant frequencies. Additionally, we employ our model to control the motion of single particles and a swarm of particles on the submerged plate. Our device can move particles with sufficient power at an exceptionally wide frequency range, potentially opening a path to new particle manipulation techniques at sub-mm scale in fluidic media.

Magnetic Field Surveys of Thin Sections

Scanning magnetic microscopy (SMM) maps the magnetic field generated by petrologic thin sections or polished rock surfaces at the sub-mm scale, creating the possibility to resolve the contribution of individual grains and mineral phases to bulk magnetic signal. The instrument developed at NTNU has the capability to measure both remanence properties and, uniquely, the magnetic response in a field of known magnitude and direction. A series of case studies are presented to examine the capabilities of the microscope and to describe applications to the study of crustal magnetism. The use of well-characterized samples allows signals in magnetic scans to be attributed to grains of known composition, including the discrimination of signal associated with discrete oxides and assemblages of exsolved oxides in silicates, which can be observed to have differing directions of magnetisation. The ability of this instrument to image in fields mimicking those experienced in the crust allows the observation of the induced magnetic response, both qualitatively in the form of changes in magnetization direction, and quantitatively by varying experimental conditions. This capability gives SMM the ability to map both remanent response and generate a map of susceptibility, and provides a powerful new tool for the examination of bulk magnetic response in the Earth’s crust.

Characterization of phosphorus availability in response to radial oxygen losses in the rhizosphere of Vallisneria spiralis

The viewpoint that radial oxygen loss (ROL) of submerged macrophytes induces changes in redox conditions and the associated phosphorus (P) availability has been indirectly confirmed at larger spatial scales using conventional, destructive techniques. However, critical information about microniches has largely been overlooked due to the lack of satisfactory in situ mapping technologies. In this study, we deployed a recently developed hybrid sensor in the rhizosphere of Vallisneria spiralis (V. spiralis) during two vegetation periods to provide 2-D imaging of the spatiotemporal co-distribution of oxygen (O2) and P from a fixed observation point. Overall, the images of O2 and P showed a high degree of spatiotemporal heterogeneity throughout the rhizosphere at the sub-mm scale. A clear decrease in the P mobilization corresponded well to the steep O2 enhancement within a 2-mm-thick zone around younger V. spiralis root, indicating a significant coupling relationship between ROL and P availability. Surprisingly, despite significant diurnal shifts in ROL along the older V. spiralis roots, P availability did not fluctuate in a substantial part of the rhizosphere throughout the day; however, ROL increased the P immobilization significantly by changing the redox gradients at the outer rhizosphere. This study clearly demonstrates how continuous ROL of V. spiralis can play a major role in regulating P availability within the rhizosphere. The premise behind this statement is the discovery of how this continuous ROL can lead to the formation of three distinctive redox landscapes in the rooting sediment (oxic, suboxic, or anaerobic layers).

In situ observation of localized, sub-mm scale changes of phosphorus biogeochemistry in the rhizosphere

AimsWe imaged the sub-mm distribution of labile P and pH in the rhizosphere of three plant species to localize zones and hot spots of P depletion and accumulation along individual root axes and to relate our findings to nutrient acquisition / root exudation strategies in P-limited conditions at different soil pH, and to mobilization pattern of other elements (Al, Fe, Ca, Mg, Mn) in the rhizosphere.MethodsSub-mm distributions of labile elemental patterns were sampled using diffusive gradients in thin films and analysed using laser ablation inductively coupled plasma mass spectrometry. pH images were taken using planar optodes.ResultsWe found distinct patterns of highly localized labile P depletion and accumulation reflecting the complex interaction of plant P acquisition strategies with soil pH, fertilizer treatment, root age, and elements (Al, Fe, Ca) that are involved in P biogeochemistry in soil. We show that the plants respond to P deficiency either by acidification or alkalization, depending on initial bulk soil pH and other factors of P solubility.ConclusionsP solubilization activities of roots are highly localized, typically around root apices, but may also extend towards the extension / root hair zone.

Infrared Energy Harvesting in Millimeter-Scale GaAs Photovoltaics.

The design and characterization of mm-scale GaAs photovoltaic cells are presented and demonstrate highly efficient energy harvesting in the near infrared. Device performance is improved dramatically by optimization of the device structure for the near-infrared spectral region and improving surface and sidewall passivation with ammonium sulfide treatment and subsequent silicon nitride deposition. The power conversion efficiency of a 6.4 mm2 cell under 660 nW/mm2 NIR illumination at 850 nm is greater than 30 %, which is higher than commercial crystalline silicon solar cells under similar illumination conditions. Critical performance limiting factors of sub-mm scale GaAs photovoltaic cells are addressed and compared to theoretical calculations.

Textural diversity of hierarchical macroscopic structures of colloidal liquid crystalline nanosheets organized under electric fields

Inorganic nanosheets prepared by exfoliation of layered crystals of niobate form colloidal liquid crystals, and liquid crystalline niobate nanosheets are hierarchically organized to develop macroscopic textures. They are obtained through a two-stage process, which is growth of the liquid crystalline domains called tactoids induced by incubation and subsequent alignment of the tactoids with an electric field. Diverse macroscopic textures with sub-mm scale characteristic size are organized from niobate nanosheet liquid crystals by varying both of the tactoid growth and electric alignment processes. The tactoid growth is regulated by the nanosheet concentration and elapsed time for the incubation. Application of an AC electric field to the incubated samples turns the nanosheet alignment to the direction parallel to the field, resulting in developing various macroscopic textures. The texture depends on the nanosheet concentration; dendritic, net-like, and interdigitated textures are evolved at low, middle, and high nanosheet concentrations, respectively. Thickness of sample cell for the electric field application also influences the texture. The tactoid size is comparable to the characteristic length of the textures under the electric field even though the tactoid size exceeds the cell thickness. Continuous application of the electric field indicates temporal nature of the texture organization as the textures are gradually collapsed; larger electric voltages tend to generate and collapse the textures faster.

Examining Inhomogeneous Degradation of Graphite/Carbon Black Composite Electrodes in Li-Ion Batteries by Lock-In Thermography

Understanding the degradation of graphite anodes plays a major role in the improvement of Li-ion batteries. Herein, we used the nondestructive character of lock-in thermography (LIT) to investigate the aging of graphite anodes in pouch cells. The aged cells show a typical ring pattern in lock-in thermography images, which can be explained by the help of Raman spectroscopy. We attribute this pattern to the different contact due to the formation of a gas during operation, which also leads to inhomogeneous degradation of the graphite electrode. Finally, we demonstrate the detection of two-dimensional variances on the sub-mm scale in the composition of the graphite anodes in pouch cells by LIT. For this purpose, we combined LIT measurements with Raman spectroscopy mapping to link differences in the heat emission to those in the structure of the graphite.

(Invited) Thin Porous Silicon Produced By Metal-Assisted Etching

Metal-assisted etching of silicon can produce porous silicon and silicon nanowires by simply immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias (1). Such etching proceeds by a local galvanic cell mechanism consisting of local anodic dissolution of silicon and local cathodic reduction of an oxidizing agent on metal. The structure of porous silicon is widely controlled from nm to sub-mm scale in pore size and from straight to an ants’ nest like in pore morphology by changing etching conditions (1-3). We have been studying the metal-assisted etching of silicon to produce porous structures for antireflection of solar cells (2), and for autocatalytic electroless formation of metal-nanorods and metal films on Si surfaces (4). In this paper, we present size-controlled thin porous silicon layers consisting of straight pores and those applications. Noble metal nanoparticles were deposited on crystalline silicon wafers by electroless displacement deposition immersing the wafers into a metal salt solution containing hydrofluoric acid. The metal-particle-deposited silicon wafers were immersed in a hydrofluoric acid solution including hydrogen peroxide as an oxidizing agent. Under suitable etching conditions, uniform porous silicon thin layers consisting of straight pores were formed on silicon wafers. The diameter of pores was consistent with the size of metal nanoparticles remained at the bottom of each pore. Thus, the diameter of pores, that is, the porosity of porous layers is easily controlled in the nm scale with the deposition time of nanoparticles. The thickness of porous layers, that is, the length of the straight pores is also easily controlled by the etching time. Optical properties of the porous layers thinner than 1 μm depends on those porosity and thickness (5). This is applicable for antireflection of solar cells. The strength of metal nanorods, which were produced by electrolessly filling the pores, increased with the diameter of pores from 10 to 25 nm. These nanorods work as nanoanchors of metal films on silicon wafers. Acknowledgements The present work was partly supported by JSPS KAKENHI (26289276). References 1) Z. Huang, N. Geyer, P. Werner, J. de Boor, U. Gösele, Adv. Mater., 23, 285 (2011). 2) S. Yae, H. Tanaka, T. Kobayashi, N. Fukumuro, H. Matsuda, Phys. Stat. Sol. (c), 2(9), 3476 (2005). 3) S. Yae, M. Tashiro, M. Abe, N. Fukumuro, H. Matsuda, J. Electrochem. Soc., 157, D90 (2010). 4) S. Yae, K. Sakabe, N. Fukumuro, S. Sakamoto, and H. Matsuda, J. Electrochem. Soc., 158, D573 (2011). 5) K. Yamakawa, S. Sakamoto, N. Fukumuro, S. Yae, ECS Trans., 69(2), 185 (2015).

Indicators and Methods to Understand Past Environments from ExoMars Rover Drills.

Great advances are expected during the analysis of drilled material acquired from 2m depth by ExoMars rover, supported by the comparison to local context, and the joint use of different instruments. Textural information might be less detailed relatively to what is usually obtained at outcrops during classical geological field work on the Earth, partly because of the lack of optical imaging of the borehole wall and also because the collected samples are crushed. However sub-mm scale layering and some other sedimentary features might be identified in the borehole wall observations, or in the collected sample prior to crushing, and also at nearby outcrops. The candidate landing sites provide different targets and focus for research: Oxia Planum requires analysis of phyllosilicates and OH content, at Mawrth Vallis the layering of various phyllosilicates and the role of shallow-subsurface leaching should be emphasized. At Aram Dorsum the particle size and fluvial sedimentary features will be interesting. Hydrated perchlorates and sulphates are ideal targets possibly at every landing sites because of OH retention, especially if they are mixed with smectites, thus could point to even ancient wet periods. Extensive use of information from the infrared wall scanning will be complemented for geological context by orbital and rover imaging of nearby outcrops. Information from the context is especially useful to infer the possible action of past H2O. Separation of the ice and liquid water effects will be supported by cation abundance and sedimentary context. Shape of grains also helps here, and composition of transported grains points to the weathering potential of the environment in general. The work on Mars during the drilling and sample analysis will provide brand new experience and knowledge for future missions.

Strontium isotope systematics of scheelite and apatite from the Felbertal tungsten deposit, Austria – results of in-situ LA-MC-ICP-MS analysis

The in-situ Sr isotopic systematics of scheelite and apatite from the Felbertal W deposit and a few regional Variscan orthogneisses (“Zentralgneise”) have been determined by LA-MC-ICP-MS. The 87Sr/86Sr ratios of scheelite and apatite from the deposit are highly radiogenic and remarkably scattering. In the early magmatic-hydrothermal scheelite generations (Scheelite 1 and 2) the 87Sr/86Sr ratios range from 0.72078 to 0.76417 and from 0.70724 to 0.76832, respectively. Metamorphic Scheelite 3, formed by recrystallisation and local mobilisation of older scheelite, is characterised by even higher 87Sr/86Sr values between 0.74331 and 0.80689. Statistics allows discriminating the three scheelite generations although there is considerable overlap between Scheelite 1 and 2; they could be mixtures of the same isotopic reservoirs. The heterogeneous and scattering 87Sr/86Sr ratios of the two primary scheelite generations suggest modification of the Sr isotope system due to fluid-rock interaction and isotopic disequilibrium. Incongruent release of 87Sr from micas in the Early Palaeozoic host rocks of the Habach Complex contributed to the solute budget of the hydrothermal fluids and may explain the radiogenic Sr isotope signature of scheelite. Spatially resolved analyses revealed isotopic disequilibrium even on a sub-mm scale within zoned Scheelite 2 crystals indicating scheelite growth in an isotopic dynamical hydrothermal system. Zoned apatite from the W mineralised Early Carboniferous K1-K3 orthogneiss in the western ore field yielded 87Sr/86Sr of 0.72044–0.74514 for the cores and 0.74535–0.77937 for the rims. Values of magmatic apatite cores from the K1-K3 orthogneiss are comparable to those of primary Scheelite 1; they are too radiogenic to be magmatic. The Sr isotopic composition of apatite cores was therefore equally modified during the hydrothermal mineralisation processes, therefore supporting the single-stage genetic model in which W mineralisation is associated with the intrusion of the K1-K3 metagranitoid at Felbertal. The subsequent regional metamorphic overprint of the deposit caused redistribution of 87Sr as a consequence of metamorphic reactions involving Rb and Sr-bearing minerals. Metamorphic Scheelite 3 and apatite rims (e.g., in the K1-K3 orthogneiss) generally became more radiogenic during this process. However, local recrystallisation of primary scheelite under closed conditions (without addition of 87Sr by the metamorphic fluid) is also documented. The latter process resulted in a homogenisation of the isotope composition of Scheelite 3. Further increase in 87Sr/86Sr ratios in Scheelite 3 and apatite rims is attributed to Late Alpine (?) metamorphic recrystallisation and redistribution of 87Sr by metamorphic fluids.

A 4D Filtering and Calibration Technique for Small-Scale Point Cloud Change Detection with a Terrestrial Laser Scanner

This study presents a point cloud de-noising and calibration approach that takes advantage of point redundancy in both space and time (4D). The purpose is to detect displacements using terrestrial laser scanner data at the sub-mm scale or smaller, similar to radar systems, for the study of very small natural changes, i.e., pre-failure deformation in rock slopes, small-scale failures or talus flux. The algorithm calculates distances using a multi-scale normal distance approach and uses a set of calibration point clouds to remove systematic errors. The median is used to filter distance values for a neighbourhood in space and time to reduce random type errors. The use of space and time neighbours does need to be optimized to the signal being studied, in order to avoid smoothing in either spatial or temporal domains. This is demonstrated in the application of the algorithm to synthetic and experimental case examples. Optimum combinations of space and time neighbours in practical applications can lead to an improvement of an order or two of magnitude in the level of detection for change, which will greatly improve our ability to detect small changes in many disciplines, such as rock slope pre-failure deformation, deformation in civil infrastructure and small-scale geomorphological change.

Optical power transfer and communication methods for wireless implantable sensing platforms.

Ultrasmall scale implants have recently attracted focus as valuable tools for monitoring both acute and chronic diseases. Semiconductor optical technologies are the key to miniaturizing these devices to the long-sought sub-mm scale, which will enable long-term use of these devices for medical applications. This can also enable the use of multiple implantable devices concurrently to form a true body area network of sensors. We demonstrate optical power transfer techniques and methods to effectively harness this power for implantable devices. Furthermore, we also present methods for optical data transfer from such implants. Simultaneous use of these technologies can result in miniaturized sensing platforms that can allow for large-scale use of such systems in real world applications.

Aerosol based direct-write micro-additive fabrication method for sub-mm 3D metal-dielectric structures

The fabrication of 3D metal-dielectric structures at sub-mm length scale is highly important in order to realize low-loss passives and GHz wavelength antennas with applications in wearable and Internet-of-Things (IoT) devices. The inherent 2D nature of lithographic processes severely limits the available manufacturing routes to fabricate 3D structures. Further, the lithographic processes are subtractive and require the use of environmentally harmful chemicals. In this letter, we demonstrate an additive manufacturing method to fabricate 3D metal-dielectric structures at sub-mm length scale. A UV curable dielectric is dispensed from an Aerosol Jet system at 10–100 µm length scale and instantaneously cured to build complex 3D shapes at a length scale <1 mm. A metal nanoparticle ink is then dispensed over the 3D dielectric using a combination of jetting action and tilted dispense head, also using the Aerosol Jet technique and at a length scale 10–100 µm, followed by the nanoparticle sintering. Simulation studies are carried out to demonstrate the feasibility of using such structures as mm-wave antennas. The manufacturing method described in this letter opens up the possibility of fabricating an entirely new class of custom-shaped 3D structures at a sub-mm length scale with potential applications in 3D antennas and passives.

Cost Effective Fabrication and Characterization of in-Membrane Micro-Fuel Cell

Micro fuel cells (μFCs) have been attracting much attention as a leading candidate for prospective portable power sources and battery replacements [1-3]. Their ability to create an efficient and clean source of energy combined with the ease of portability makes μFCs available to meet the needs of various portable electronic applications in the future [3, 4]. To this purpose, making more efficient devices with cost effective processes and materials is crucial. Many efforts on fuel cell miniaturization are focused on silicon-based techniques as silicon is the most common substrate in MEMS technology [5, 6]. However, combining silicon devices with polymeric fuel cells at mm or sub-mm scale presents many challenges, none of which have been solved in a completely satisfactory manner [7]. Distinct from previous attempts at fabricating in-plane μFCs by other studies, in this work we present a novel IMμFC (In-Membrane Micro Fuel Cell) design where the micro-flow channels for fuel and oxidant input and the MEA are fabricated using a Nafion membrane as the starting substrate. The fabrication procedure of IMμFCs has been illustrated in Fig. 1. In preparation for the microfabrication process, 100 μm thick SU-8 photoresist was spin coated, baked and developed to produce a micro stamp. The developed SU-8 on Si wafer was hard baked at 200°C for an hour to enhance the rigidity of the stamps. Fabricated stamps were cut and pressed onto Nafion 1110 membrane at 140°C and 300 psi by a NX2000- Nanoimprinter (Nanonex Corp., NJ, USA). Catalyst loading of conventional Pt/C dispersion on a selected area of microchannels was made by screen printing. Silver wire connections were secured in the designed electrical channels by Kapton tape and carbon black paste. In the sealing step, a laser patterned acrylic sheet was pressed onto the Nafion substrate by the nanoimprinter machine. The fabrication process was completed by mounting the gas inlet tubes on the acrylic sheet side of IMμFCs. The micro device performance was characterized by I-V polarization curves and impedance spectroscopy under dry and humidified conditions. Comparing to other studies on μFCs, the presented fabrication approach consists of cost effective processes with a great potential for scale-up production. This new architecture may lead to the deployment of an ultra-low weight, high energy density power source for flat-board-oriented electronic structures. Refrences: 1. Sundarrajan, S., Allakhverdiev, S. I., & Ramakrishna, S. (2012). Progress and perspectives in micro direct methanol fuel cell. International Journal of Hydrogen Energy, 37(10), 8765-8786. 2. Taylor, A. D., Lucas, B. D., Guo, L. J., & Thompson, L. T. (2007). Nanoimprinted electrodes for micro-fuel cell applications. Journal of Power Sources, 171(1), 218-223. 3. Kamarudin, S. K., Daud, W. R. W., Ho, S. L., & Hasran, U. A. (2007). Overview on the challenges and developments of micro-direct methanol fuel cells (DMFC).Journal of Power Sources, 163(2), 743-754. 4. Cao, J., Xu, J., Chen, Z., Wang, W., Huang, Q., & Zou, Z. (2013). A silicon‐based micro direct methanol fuel cell stack with a serial flow path design.International Journal of Energy Research, 37(4), 370-376. 5. Shah, K., Shin, W. C., & Besser, R. S. (2004). A PDMS micro proton exchange membrane fuel cell by conventional and non-conventional microfabrication techniques. Sensors and Actuators B: Chemical, 97(2), 157-167. 6. Lu, G. Q., Wang, C. Y., Yen, T. J., & Zhang, X. (2004). Development and characterization of a silicon-based micro direct methanol fuel cell.Electrochimica Acta, 49(5), 821-828. 7. Omosebi, A., & Besser, R. S. (2013). Fabrication and performance evaluation of an in membrane micro-fuel cell. Journal of Power Sources, 242, 672-676. Figure1. (a) Top-view illustration of μFC design imprinted on Nafion and (b) schematic fabrication steps of the μFC production Figure 1