Kinked silicon nanowires: Superstructures by metal assisted chemical etching

We report on metal assisted chemical etching of Si for the synthesis of mechanically-stable, hybrid crystallographic orientation Si superstructures with high aspect ratio, above 200. This one-pot-type method sustains high etching rates and facilitates reproducible results. The protocol enables the control of the number, angle and location of kinks via successive etch-quench sequences. We analysed relevant Au mask catalyst features to systematically assess their impact on a wide spectrum of etched morphologies that can be easily attained and customized by fine tuning of the critical etching parameters. For instance, the designed kinked Si nanowires can be internalized in biological cells, without affecting their viability. An accessible numerical model is provided to explain the etch profiles and the physico-chemical events at the Si-Au-electrolyte interface and offers guidelines for the development of finite-element modeling of metal assisted Si chemical etching

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Summary Background Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. Methods We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung’s disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. Findings We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung’s disease) from 264 hospitals (89 in high-income countries, 166 in middleincome countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in lowincome countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. Interpretation Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between lowincome, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

Injection d'un courant polarisé en spin dans un dispositif en Germanium : étude théorique des apsects géométriques

We present a two-dimensional (2D) model of spin injection/extraction from a ferromagnetic (FM) germanide Mn5Ge3 into Ge in a geometry similar to real devices. Our model addresses the challenges of describing current line distributions, barrier interface nonlinearity (thermionic emission and tunnel effect), the formation of a depletion region and the influence of the detection method (spin valves, Hanle precession). Results show the impact of confinement effects due to a scaling-down of injector electrode width, channel thickness and channel length. We highlight the importance of current crowding and depletion area on the spin injection ratio and spin lifetime and we determine the existence of an optimal current density for efficient spin-injection. Finally, we demonstrate that the spin diffusion length is impacted by current lines distribution and intensity, limiting the coherence of spin transport.Quantum magnetic tweezers for manipulating charge and spi

Injection of spin-polarized current in a Ge- based magnetic device with coplanar contacts

Electron spin injection and spin detection in magnetic materials are key features to the functionalization of electron spin polarization as a degree of freedom for both information processing and storage. Currently, spin-dependent tunneling in magnetic junction devices is the most common approach to achieve efficient spin injection. However, many recent studies highlighted the interesting possibility to create spin-polarized currents in structures which combine a magnetic semiconductor, e.g. magnetic alloys based on group-IV semiconductors or diluted magnetic semiconductor compounds, forming a Schottky-like rectifying junction with a metallic ferromagnet. Although theoretical works have already addressed the performance of this structure by numerical simulations of the spin drift and spin diffusion equations, taking into account various characteristics of the ferromagnet (FM) / semiconductor (SC) interface such as barrier height and boundary roughness in 1D models, correlations with experimental results are scarce. This work aims at achieving spin injection with Ge-based magnetic structures using a rectifying junction in a coplanar architecture. We performed 2D numerical calculations of the spin drift and diffusion process in the direct neighborhood of a junction consisting of a Mn5Ge3 half-metallic ferromagnet acting as the injecting contact and an n-type Ge film, forming 3- and 4-terminal devices (Fig. 1). Our results show that geometrical effects play a major role on the spin injection efficiency. Moreover, the simulations emphasize the asymmetry of spin accumulation at the FM/SC interface as well as a strong effect of the depletion layer caused by the Schottky contact junction. We report values of spin polarization related potential differences higher than 5 μV for a bias of 1 mV, in agreement with previous experimental results.Quantum magnetic tweezers for manipulating charge and spi

Influence of the inhomogeneous properties of a superconducting film on the penetration of the magnetic flux

We consider the penetration of magnetic flux perpendicular to a Nb superconducting film containing edge indentations and/or defects. The presence of such defects and indented edges forces the induced currents to change direction abruptly, which gives rise to discontinuity lines (d-lines). It has been recently shown, by magneto-optical means, that the shape of the d-lines contain information about the size and the shape of the indentations [1]. Moreover, in contrast with what is commonly assumed, thermomagnetic instabilities are not preferentially triggered near the manufactured indentations, but rather along smooth edges [1]. Such phenomena can lead to unexpected quenching of superconducting samples and considerably damage them, which must be avoided in applications. In this poster, we investigate whether inhomogeneous superconducting properties can be responsible for triggering magnetic flux avalanches. To this aim, we numerically model the flux penetration and determine the distribution of current lines and electric fields for a situation where the superconducting properties vary locally over a small region of the film. We consider the variation of the thickness of the film, the critical current density and the size of the discontinuity. The resulting shapes of the d-lines are deduced and compared to analytical critical state approximations. We also determine the location and the amplitude of the maximal electric field in the film and compare it to typical values which must be reached in order to trigger magnetic flux avalanches. We conclude that the investigated variations lead to levels of electric field which are of the same order of magnitude as those generated by artificial indentations.ARC 13/18-0

Model for the penetration of magnetic flux in Nb superconducting films with lithographically defined indentations and defects due to inhomogeneities

We consider the penetration of magnetic flux perpendicularly to a Nb superconducting film containing edge indentations and/or defects. The induced currents undergo an abrupt change of direction around the indentations and the defects, giving rise to discontinuity lines (d-lines). It has recently been shown, by means of magneto-optical imaging and numerical models, that the detailed structure of the d-lines generated with lithographically-defined micro-indentations carry information about their size and shape, and vary with temperature [1]. In this talk, we describe the models which can be used to describe the d-lines and discuss the effects of temperature, demagnetization, and flux creep, as well as the influence of a field-dependent critical current density on the distribution of the magnetic field. We extend the model to discontinuities produced by defects arising from inhomogeneous properties of the film and discuss the information contained in the resulting d-line structure. Last, in contrast to what has been repeatedly predicted in the literature, artificial indentations were not observed to act as preferred nucleation spots for flux avalanches [1]. To investigate this result, we estimate the levels of electric field strengthening arising near indentations and defects, and compare with the levels necessary for triggering thermomagnetic instabilities.ARC 13/18-0

Magnetic flux penetration in superconducting films with border defects

Defects can have a large impact on the magnetic response of superconducting thin films by forcing changes in the path of the induced electrical currents. When the magnetic flux creep exponent is high, the associated perturbation is typically damped over a distance that can largely exceed the size of the defects. The current flow is then reorganized in large domains with different orientations of the electrical current density, separated by narrow domain walls. In the critical state limit with an infinite creep exponent, the domain walls degenerate into discontinuity lines, or d-lines. In this talk, I consider the penetration of magnetic flux perpendicularly to a Nb superconducting film containing edge indentations and/or defects. It has recently been shown, by means of magneto-optical imaging and numerical simulations, that the detailed shape of the d-lines generated by lithographically-defined micro-indentations carry information about their size and shape, and vary with temperature [1]. In this talk, I examine macroscopic models, constructed over length scales of many vortices, which can be used to describe the d-lines. I discuss the effects of temperature, demagnetization, and flux creep, as well as the influence of a field-dependent critical current density on the distribution of the magnetic field. The models are applied to both indentations and defects arising from inhomogeneous properties of the film. A comparison between the model predictions and the experimental data points to the importance of a lowered surface barrier in the presence of the defects. It is argued that indentations and defects help in releasing the magnetic flux pressure, and, thereby, help in avoiding thermomagnetic instabilities.ARC 13/18-0

Impedance sensing of polystyrene microspheres in a microfluidic channel: An integrated electrooptic method

Electrical impedance measurements through microfluidic channels have been extensively studied over the last years, because electrical impedance is a simple and essentially a noninvasive technique that allows characterization of nano- and microparticles or other inorganic nano- and microstructuresin a dielectric medium. Electrical impedance sensing has successfully been used in flow cell cytometry, allowing the classification of different cell types. Here are presented results for polystyrene microspheres in a custom electrical impedance system composed of a modified commercial microfluidic channel along with optical micro-imaging characterization in an inverted microscope, quantifying the relationship between microspheres density, wavelength illumination range and magnitude of the electrical impedance signal for carboxyl and amino functionalized-microspheres in different fluid media. These observations are sustained by numerical modeling and discussed within a general theoretical framework. The obtained results might have potential application to classify novel nano- and micro-objects and further develop artificial intelligence-enabled drug delivery platforms

Magnetic flux penetration in Nb superconducting films with lithographically defined micro-indentations

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d-lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n. In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities

Tailoring zigzag and kinked silicon nanowires with metal assisted chemical etching

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