Micromagnetic Simulation of Non Uniform Nanodots with Perpendicular Anisotropy

Multilayered Pt/[Co/Pt]/sub 5/ films were fabricated into patterned dots with diameters of 120 and 200 nm by laser interference lithography. Anomalous Hall effect (AHE) measurements were used on an array of dots to measure the switching field and the effects of reversal of an area with reduced anisotropy in the dot were also investigated by micromagnetic simulation. It was shown that a reduction in switching field is caused by an area of reduced anisotropy. The effect of various combinations of a reduction in anisotropy and/or exchange constant, and the size and shape of the area were also discussed in this paper

Elastocapillary folding using stop-programmable hinges fabricated by 3D micro-machining

We show elasto-capillary folding of silicon nitride objects with accurate folding angles between flaps of 70.6$\pm$0.1{\deg} and demonstrate the feasibility of such accurate micro-assembly with a final folding angle of 90{\deg}. The folding angle is defined by stop-programmable hinges that are fabricated starting from silicon molds employing accurate three-dimensional corner lithography. This nano-patterning method exploits the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as an inversion mask in subsequent steps. Hinges designed to stop the folding at 70.6{\deg} were fabricated batchwise by machining the V-grooves obtained by KOH etching in (110) silicon wafers; 90{\deg} stop-programmable hinges were obtained starting from silicon molds obtained by dry etching on (100) wafers. The presented technique is applicable to any folding angle and opens a new route towards creating structures with increased complexity, which will ultimately lead to a novel method for device fabrication.Comment: Submitted to a peer reviewed journa

Capillary origami of micro-machined micro-objects: Bi-layer conductive hinges

Recently, we demonstrated controllable 3D self-folding by means of capillary forces of silicon-nitride micro-objects made of rigid plates connected to each other by flexible hinges [1]. In this paper, we introduce platinum electrodes running from the substrate to the plates over these bendable hinges. The fabrication yield is as high as (77 +/- 2) % for hinges with a length less than 75 {\mu}m. The yield reduces to (18 +/- 2) % when the length increases above 100 {\mu}m. Most of the failures in conductivity are due to degradation of the platinum/chromium layer stack during the final plasma cleaning step. The bi-layer hinges survive the capillary folding process, even for extremely small bending radii of 5 {\mu}m, nor does the bending have any impact on the conductivity. Stress in the different layers deforms the hinges, which does not affect the conductivity. Once assembled, the conductive hinges can withstand a current density of (1.6 +/- 0.4) $10^6$ A/cm$^2$ . This introduction of conductive electrodes to elastocapillary self-folded silicon-based micro-objects extends the range of their possible applications by allowing an electronic functionality of the folded parts.Comment: Currently on a peer review process. 13 page

Drug-Loaded IRONSperm clusters: modeling, wireless actuation, and ultrasound imaging

Individual biohybrid microrobots have the potential to perform biomedical in vivo tasks such as remote-controlled drug and cell delivery and minimally invasive surgery. This work demonstrates the formation of biohybrid sperm-templated clusters under the influence of an external magnetic field and essential functionalities for wireless actuation and drug delivery. Ferromagnetic nanoparticles are electrostatically assembled around dead sperm cells, and the resulting nanoparticle-coated cells are magnetically assembled into three-dimensional biohybrid clusters. The aim of this clustering is threefold: First, to enable rolling locomotion on a nearby solid boundary using a rotating magnetic field; second, to allow for noninvasive localization; third, to load the cells inside the cluster with drugs for targeted therapy. A magneto-hydrodynamic model captures the rotational response of the clusters in a viscous fluid, and predicts an upper bound for their step-out frequency, which is independent of their volume or aspect ratio. Below the step-out frequency, the rolling velocity of the clusters increases nonlinearly with their perimeter and actuation frequency. During rolling locomotion, the clusters are localized using ultrasound images at a relatively large distance, which makes these biohybrid clusters promising for deep-tissue applications. Finally, we show that the estimated drug load scales with the number of cells in the cluster and can be retained for more than 10 h. The aggregation of microrobots enables them to collectively roll in a predictable way in response to an external rotating magnetic field, and enhances ultrasound detectability and drug loading capacity compared to the individual microrobots. The favorable features of biohybrid microrobot clusters place emphasis on the importance of the investigation and development of collective microrobots and their potential for in vivo applications

History of oceanic front development in the New Zealand sector of the Southern Ocean during the Cenozoic--a synthesis

The New Zealand sector of the Southern Ocean (NZSSO) has opened about the Indian-Pacific spreading ridge throughout the Cenozoic. Today the NZSSO is characterised by broad zonal belts of antarctic (cold), subantarctic (cool), and subtropical (warm) surface-water masses separated by prominent oceanic fronts: the Subtropical Front (STF) c. 43deg.S, Subantarctic Front (SAF) c. 50deg.S, and Antarctic Polar Front (AAPF) c. 60deg.S. Despite a meagre database, the broad pattern of Cenozoic evolution of these fronts is reviewed from the results of Deep Sea Drilling Project-based studies of sediment facies, microfossil assemblages and diversity, and stable isotope records, as well as from evidence in onland New Zealand Cenozoic sequences. Results are depicted schematically on seven paleogeographic maps covering the NZSSO at 10 m.y. intervals through the Cenozoic. During the Paleocene and most of the Eocene (65-35 Ma), the entire NZSSO was under the influence of warm to cool subtropical waters, with no detectable oceanic fronts. In the latest Eocene (c. 35 Ma), a proto-STF is shown separating subantarctic and subtropical waters offshore from Antarctica, near 65deg.S paleolatitude. During the earliest Oligocene, this front was displaced northwards by development of an AAPF following major global cooling and biotic turnover associated with ice sheet expansion to sea level on East Antarctica. Early Oligocene full opening (c. 31 Ma) of the Tasmanian gateway initiated vigorous proto-circum-Antarctic flow of cold/cool waters, possibly through a West Antarctic seaway linking the southern Pacific and Atlantic Oceans, including detached northwards "jetting" onto the New Zealand plateau where condensation and unconformity development was widespread in cool-water carbonate facies. Since this time, a broad tripartite division of antarctic, subantarctic, and subtropical waters has existed in the NZSSO, including possible development of a proto-SAF within the subantarctic belt. In the Early-early Middle Miocene (25-15 Ma), warm subtropical waters expanded southwards into the northern NZSSO, possibly associated with reduced ice volume on East Antarctica but particularly with restriction of the Indonesian gateway and redirection of intensified warm surface flows southwards into the Tasman Sea, as well as complete opening of the Drake gateway by 23 Ma allowing more complete decoupling of cool circum-Antarctic flow from the subtropical waters. During the late Middle-Late Miocene (15-5 Ma), both the STF and SAF proper were established in their present relative positions across and about the Campbell Plateau, respectively, accompanying renewed ice buildup on East Antarctica and formation of a permanent ice sheet on West Antarctica, as well as generally more expansive and intensified circum-Antarctic flow. The ultimate control on the history of oceanic front development in the NZSSO has been plate tectonics through its influence on the paleogeographic changes of the Australian-New Zealand-Antarctic continents and their intervening oceanic basins, the timing of opening and closing of critical seaways, the potential for submarine ridges and plateaus to exert some bathymetric control on the location of fronts, and the evolving ice budget on the Antarctic continent. The broad trends of the Cenozoic climate curve for New Zealand deduced from fossil evidence in the uplifted marine sedimentary record correspond well to the principal paleoceanographic events controlling the evolution and migration of the oceanic fronts in the NZSSO

Carbon Nanotubes Based 3-D Matrix for Enabling Three-Dimensional Nano-Magneto-Electronics

This letter describes the use of vertically aligned carbon nanotubes (CNT)-based arrays with estimated 2-nm thick cobalt (Co) nanoparticles deposited inside individual tubes to unravel the possibility of using the unique templates for ultra-high-density low-energy 3-D nano-magneto-electronic devices. The presence of oriented 2-nm thick Co layers within individual nanotubes in the CNT-based 3-D matrix is confirmed through VSM measurements as well as an energy-dispersive X-ray spectroscopy (EDS)

Scanning magneto-resistance microscopy with FIB trimmed yoke-type magneto-resistive tape heads

Scanning magneto-resistance microscopy has been performed with thin film yoke-type magneto-resistive tape heads possessing eight channels. The read flux guides of these channels have been trimmed down from 24 μm to widths varying between 5.5 μm and 148 nm by focused ion beam milling with Ga+ ions. Tracks written on ME tape with an untrimmed write channel have been successfully imaged with all the trimmed channels. A significant attenuation (>5%) of read-back voltage across the MR sensor is only observed for channels possessing flux guides trimmed by 77% to 5.5 μm. A 52% (6 dB) drop in read-back voltage is observed for a channel possessing a flux guide trimmed by 99.4% to 148 nm