Low-loss SiGe waveguides for mid-infrared photonics fabricated on 200 mm wafers.

This article presents low-loss mid-infrared waveguides fabricated on a Ge-rich SiGe strain-relaxed buffer grown on an industrial-scale 200 mm wafer, with propagation losses below 0.5 dB/cm for 5-7 µm wavelengths and below 5 dB/cm up to 11 µm. Investigation reveals free-carrier absorption as the primary loss factor for 5-6.5 µm and silicon multiphonon absorption beyond 7 µm wavelength. This result establishes a foundation for a scalable, silicon-compatible mid-infrared platform, enabling the realisation of photonic integrated circuits for various applications in the mid-infrared spectral region, from hazard detection to spectroscopy and military imaging.

Land-derived litter load to the Indian Ocean: a case study in the Cimandiri River, southern West Java, Indonesia.

The first study related to the characteristics of the riverine litter was carried out at the mouth of the Cimandiri River in the southern West Java to provide a national database, as mandated in the Indonesian Presidential Regulation 83/2018 concerning the handling of marine debris. We examined floating riverine litter entering the South Java Sea at Cimandiri River outlets four times between December 2020 and October 2021 using a Thomsea 1 T trawl-net. The amount of litter collected tended to rise throughout the sampling period. Daily floating riverine litter released into the South Java Sea was estimated to be 285,931 ± 133.70 items or 307 ± 192.69 kg. Our monitoring data revealed no sampling period differences in litter release into the South Java Sea with no correlation with rainfall. Our data indicate that plastics are the most single abundant type of floating riverine litter entering the South Java Sea from the Cimandiri River, accounting for 99.92% of abundance (285,701 ± 133,464.75 items per day) or 97.78% in terms of weight (300 ± 181.99 kg per day) of the total litter collected. As the Cimandiri River is one of the major rivers with an outlet in the south of Java, this land-derived litter information could be an archetype for riverine ecosystems in the nation and region.

Host perspective on academic supervision, health care provision and institutional partnership during short-term electives in global health.

CONTEXT: Studies about the impact of global health electives on host institutions are scarce and often made from the perspective of institutions that send students. The present research examined the impact of short-term electives in global health (STEGHs) from the under-represented perspective of host institutions in Benin. METHODS: The authors conducted 30 semi-structured interviews from a convenience sample of Beninese health care professionals who had hosted Canadian medical students. Interviewees had previously supervised STEGHs in one of the five different institutions. A subsequent qualitative thematic analysis methodology was used to compilate codes and generate themes. RESULTS: Hosting STEGH students motivated respondents to increase their medical knowledge through self-driven learning. They perceived an improvement in the quality of their care and felt a negligible impact on patient safety. They negatively commented on the lack of clear pedagogic objectives that they could rely on. Interviewees think current STEGH partnerships do not advantage them because institutions that send students offer little support during the electives. Furthermore, sending institutions do not offer the same opportunity for local medical students or professionals to take part in such electives outside of Benin. CONCLUSIONS: Although host health care professionals evaluated global health electives positively overall, specific improvements could mitigate their negative impacts and help create a more balanced partnership between sending and host institutions. Sending institutions could involve host institutions in curriculum planning. They could invest in building reciprocal elective programmes to receive students from elsewhere. Meanwhile they can maximise the transfer of relevant medical knowledge, and provide expertise, resources and support during the electives.

Impact of Stoichiometry on the Structure of van der Waals Layered GeTe/Sb2 Te3 Superlattices Used in Interfacial Phase-Change Memory (iPCM) Devices.

Van der Waals layered GeTe/Sb2 Te3 superlattices (SLs) have demonstrated outstanding performances for use in resistive memories in so-called interfacial phase-change memory (iPCM) devices. GeTe/Sb2 Te3 SLs are made by periodically stacking ultrathin GeTe and Sb2 Te3 crystalline layers. The mechanism of the resistance change in iPCM devices is still highly debated. Recent experimental studies on SLs grown by molecular beam epitaxy or pulsed laser deposition indicate that the local structure does not correspond to any of the previously proposed structural models. Here, a new insight is given into the complex structure of prototypical GeTe/Sb2 Te3 SLs deposited by magnetron sputtering, which is the used industrial technique for SL growth in iPCM devices. X-ray diffraction analysis shows that the structural quality of the SL depends critically on its stoichiometry. Moreover, high-angle annular dark-field-scanning transmission electron microscopy analysis of the local atomic order in a perfectly stoichiometric SL reveals the absence of GeTe layers, and that Ge atoms intermix with Sb atoms in, for instance, Ge2 Sb2 Te5 blocks. This result shows that an alternative structural model is required to explain the origin of the electrical contrast and the nature of the resistive switching mechanism observed in iPCM devices.

Non-rigid alignment in electron tomography in materials science.

Electron tomography is a key technique that enables the visualization of an object in three dimensions with a resolution of about a nanometre. High-quality 3D reconstruction is possible thanks to the latest compressed sensing algorithms and/or better alignment and preprocessing of the 2D projections. Rigid alignment of 2D projections is routine in electron tomography. However, it cannot correct misalignments induced by (i) deformations of the sample due to radiation damage or (ii) drifting of the sample during the acquisition of an image in scanning transmission electron microscope mode. In both cases, those misalignments can give rise to artefacts in the reconstruction. We propose a simple-to-implement non-rigid alignment technique to correct those artefacts. This technique is particularly suited for needle-shaped samples in materials science. It is initiated by a rigid alignment of the projections and it is then followed by several rigid alignments of different parts of the projections. Piecewise linear deformations are applied to each projection to force them to simultaneously satisfy the rigid alignments of the different parts. The efficiency of this technique is demonstrated on three samples, an intermetallic sample with deformation misalignments due to a high electron dose typical to spectroscopic electron tomography, a porous silicon sample with an extremely thin end particularly sensitive to electron beam and another porous silicon sample that was drifting during image acquisitions.

Combining 2 nm Spatial Resolution and 0.02% Precision for Deformation Mapping of Semiconductor Specimens in a Transmission Electron Microscope by Precession Electron Diffraction.

Precession electron diffraction has been used to provide accurate deformation maps of a device structure showing that this technique can provide a spatial resolution of better than 2 nm and a precision of better than 0.02%. The deformation maps have been fitted to simulations that account for thin specimen relaxation. By combining the experimental deformation maps and simulations, we have been able to separate the effects of the stressor and recessed sources and drains and show that the Si3N4 stressor increases the in-plane deformation in the silicon channel from 0.92 to 1.52 ± 0.02%. In addition, the stress in the deposited Si3N4 film has been calculated from the simulations, which is an important parameter for device design.

Guest-triggered Zn(II) translocation and supramolecular nuclearity control in calix[6]arene-based complexes.

Two new polytopic ligands based on a calix[6]arene scaffold were synthesized. The truncated cone-shaped calixarene was functionalized at its small rim by a tris-imidazole site, aimed at generating a tetrahedral Zn(II) complex, where a fourth labile site inside the cavity is accessible through the funnel provided by its large rim. Tridentate aza ligands (either two or three) were then grafted at this large rim (the entrance of the cavity). Zn(II) coordination studies, monitored by (1)H NMR spectroscopy, showed unprecedented behavior in this family of heteropolytopic ligands. Indeed, it gives access to complexes of various nuclearities in acetonitrile, where zinc binding is under the supramolecular control of the guest. It is first shown that, in the absence of a good guest donor (a primary amine), Zn(II) binding is favored at the large rim where two tridentate nitrogenous groups can form an octahedral complex. The addition of a long guest such as heptylamine induces the quantitative translocation of the Zn(II) ion from the large rim octahedral (O(h)) site to the small rim tetrahedral (T(d)) site provided by the trisimidazole core and the guest ligand. With 2 equiv of Zn(II), well-defined dinuclear complexes were obtained and isolated, with one Zn(II) ion bound at each rim. Interestingly, it is shown that the binding mode at the large rim is under the supramolecular control of the guest bound at the small rim (with short guests, the O(h) environment is obtained at the large rim, whereas long guests disrupt this core through an induced-fit process); the partially included and dangling alkyl chain opens the large rim (entrance of the cavity) and pushes apart the tridentate moieties. As a result, a guest-induced switch of Zn(II) binding mode occurs and frees one of the tridentate groups from coordination, allowing further extension of the complex nuclearity.

Laser Generation of Sub-Micrometer Wrinkles in a Chalcogenide Glass Film as Physical Unclonable Functions.

Laser interaction with solids is routinely used for functionalizing materials' surfaces. In most cases, the generation of patterns/structures is the key feature to endow materials with specific properties like hardening, superhydrophobicity, plasmonic color-enhancement, or dedicated functions like anti-counterfeiting tags. A way to generate random patterns, by means of generation of wrinkles on surfaces resulting from laser melting of amorphous Ge-based chalcogenide thin films, is presented. These patterns, similar to fingerprints, are modulations of the surface height by a few tens of nanometers with a sub-micrometer periodicity. It is shown that the patterns' spatial frequency depends on the melted layer thickness, which can be tuned by varying the impinging laser fluence. The randomness of these patterns makes them an excellent candidate for the generation of physical unclonable function tags (PUF-tags) for anti-counterfeiting applications. Two specific ways are tested to identify the obtained PUF-tag: cross-correlation procedure or using a neural network. In both cases, it is demonstrated that the PUF-tag can be compared to a reference image (PUF-key) and identified with a high recognition ratio on most real application conditions. This paves the way to straightforward non-deterministic PUF-tag generation dedicated to small sensitive parts such as, for example, electronic devices/components, jewelry, or watchmak.

Elastic distortion determining conduction in BiFeO3 phase boundaries.

It is now well-established that boundaries separating tetragonal-like (T) and rhombohedral-like (R) phases in BiFeO3 thin films can show enhanced electrical conductivity. However, the origin of this conductivity remains elusive. Here, we study mixed-phase BiFeO3 thin films, where local populations of T and R can be readily altered using stress and electric fields. We observe that phase boundary electrical conductivity in regions which have undergone stress-writing is significantly greater than in the virgin microstructure. We use high-end electron microscopy techniques to identify key differences between the R-T boundaries present in stress-written and as-grown microstructures, to gain a better understanding of the mechanism responsible for electrical conduction. We find that point defects (and associated mixed valence states) are present in both electrically conducting and non-conducting regions; crucially, in both cases, the spatial distribution of defects is relatively homogeneous: there is no evidence of phase boundary defect aggregation. Atomic resolution imaging reveals that the only significant difference between non-conducting and conducting boundaries is the elastic distortion evident - detailed analysis of localised crystallography shows that the strain accommodation across the R-T boundaries is much more extensive in stress-written than in as-grown microstructures; this has a substantial effect on the straightening of local bonds within regions seen to electrically conduct. This work therefore offers distinct evidence that the elastic distortion is more important than point defect accumulation in determining the phase boundary conduction properties in mixed-phase BiFeO3.

Combined forest and soil management after a catastrophic event.

At the end of October 2018, a storm of unprecedented strength severely damaged the forests of the eastern sector of the Italian Alps. The affected forest area covers 42,500 ha. The president of one of the damaged regions asked for help from the University of Padua. After eight months of discussion, the authors of this article wrote a consensus text. The sometimes asper debate brought to light some crucial aspects: 1) even experienced specialists may have various opinions based on scientific knowledge that lead to conflicting proposals for action. For some of them there is evidence that to restore a destroyed natural environment it is more judicious to do nothing; 2) the soil corresponds to a living structure and every ecosystem's management should be based on it; 3) faced with a catastrophe, people and politicians find themselves unarmed, also because they rarely have the scientific background to understand natural processes. Yet politicians are the only persons who make the key decisions that drive the economy in play and therefore determine the near future of our planet. This article is an attempt to respond directly to a governor with a degree in animal production science, who formally and prudently asked a university department called "Land, Environment, Agriculture and Forestry" for help before taking decisions; 4) the authors also propose an artistic interpretation of facts (uncontrolled storm) and conclusions (listen to the soil). Briefly, the authors identify the soil as an indispensable source for the renewal of the destroyed forest, give indications on how to prepare a map of the soils of the damaged region, and suggest to anchor on this soil map a series of silvicultural and soil management actions that will promote the soil conservation and the faster recovery of the natural dynamic stability and resilience. ELECTRONIC SUPPLEMENTARY MATERIAL: Supplementary material is available for this article at 10.1007/s11629-019-5890-0 and is accessible for authorized users.

Anion recognition by a macrobicycle based on a tetraoxadiaza macrocycle and an isophthalamide head unit.

A macrobicycle formed by a tetraoxadiaza macrocycle containing a dibenzofuran (DBF) spacer and an isophthalamide head unit, named DBF-bz, was used as receptor for anion recognition. The molecular structure of DBF-bz was established in solution by NMR and ESI-MS spectroscopies and in single crystal by X-ray diffraction analysis. The X-ray structure showed a water molecule encapsulated into the macrobicyclic cavity by four hydrogen bonds, two of them involving the two N-H amide binding sites and the oxygen of the water molecule (N-H...O hydrogen bonds) and the other two (O-H...N) involving the amine groups as hydrogen bonding acceptors. (1)H NMR temperature dependence studies demonstrated that the same structure exists in solution. The ability of this ditopic receptor to recognize alkali halide salts was evaluated by extraction studies followed by (1)H NMR and ESI-MS spectroscopies. The macrobicycle showed a capacity to extract halide salts from aqueous solutions into organic phases. The binding ability of this macrobicycle for halides was also quantitatively investigated using (1)H NMR titrations in CDCl(3) (and DMSO-d(6)) solution, and in acidic D(2)O solution. The largest binding association constant was found for the chloride anion and the completely protonated receptor. The results suggest that the diammonium-diamide unit of the receptor strongly bind the anionic substrate via multiple N-H...Cl(-) hydrogen bonds and electrostatic interactions. The binding trend follows the order Cl(-) > Br(-) > I(-) approximately F(-) established from the best fit between the size of the anion and the cavity size of the protonated macrobicycle. Molecular dynamics (MD) simulations of the DBF-bz in CHCl(3) solution allowed a detailed insight into the structural and binding properties of the receptor.

Evidence of a strong perpendicular magnetic anisotropy in Au/Co/MgO/GaN heterostructures.

We report a strong perpendicular magnetic anisotropy (PMA) in Au/Co/MgO/GaN heterostructures from both experiments and first-principles calculations. The Au/Co/MgO heterostructures have been grown by molecular beam epitaxy (MBE) on GaN/sapphire substrates. By carefully optimizing the growth conditions, we obtained a fully epitaxial structure with a crystalline orientation relationship Au(111)[1̄10]//Co(0001)[112̄0]//MgO(111)[101̄]//GaN(0002)[112̄0]. More interestingly, we demonstrate that a 4.6 nm thick Co film grown on MgO/GaN still exhibits a large perpendicular magnetic anisotropy. First-principles calculations performed on the Co (4ML)/MgO(111) structure showed that the MgO(111) surface can strongly enhance the magnetic anisotropy energy by 40% compared to a reference 4ML thick Co hcp film. Our layer-resolved and orbital-hybridization resolved anisotropy analyses helped to clarify that the origin of the PMA enhancement is due to the interfacial hybridization of O 2p and Co 3d orbitals at the Co/MgO interface. The perpendicularly magnetized Au/Co/MgO/GaN heterostructures are promising for efficient spin injection and detection in GaN based opto-electronics without any external magnetic field.

High-precision deformation mapping in finFET transistors with two nanometre spatial resolution by precession electron diffraction.

Precession electron diffraction has been used to systematically measure the deformation in Si/SiGe blanket films and patterned finFET test structures grown on silicon-on-insulator type wafers. Deformation maps have been obtained with a spatial resolution of 2.0 nm and a precision of ±0.025%. The measured deformation by precession diffraction for the blanket films has been validated by comparison to energy dispersive x-ray spectrometry, X-Ray diffraction, and finite element simulations. We show that although the blanket films remain biaxially strained, the patterned fin structures are fully relaxed in the crystallographic planes that have been investigated. We demonstrate that precession diffraction is a viable deformation mapping technique that can be used to provide useful studies of state-of-the-art electronic devices.

Anomalous Resistance Hysteresis in Oxide ReRAM: Oxygen Evolution and Reincorporation Revealed by In Situ TEM.

The control and rational design of redox-based memristive devices, which are highly attractive candidates for next-generation nonvolatile memory and logic applications, is complicated by competing and poorly understood switching mechanisms, which can result in two coexisting resistance hystereses that have opposite voltage polarity. These competing processes can be defined as regular and anomalous resistive switching. Despite significant characterization efforts, the complex nanoscale redox processes that drive anomalous resistive switching and their implications for current transport remain poorly understood. Here, lateral and vertical mapping of O vacancy concentrations is used during the operation of such devices in situ in an aberration corrected transmission electron microscope to explain the anomalous switching mechanism. It is found that an increase (decrease) in the overall O vacancy concentration within the device after positive (negative) biasing of the Schottky-type electrode is associated with the electrocatalytic release and reincorporation of oxygen at the electrode/oxide interface and is responsible for the resistance change. This fundamental insight presents a novel perspective on resistive switching processes and opens up new technological opportunities for the implementation of memristive devices, as anomalous switching can now be suppressed selectively or used deliberately to achieve the desirable so-called deep Reset.

Strain mapping of semiconductor specimens with nm-scale resolution in a transmission electron microscope.

The last few years have seen a great deal of progress in the development of transmission electron microscopy based techniques for strain mapping. New techniques have appeared such as dark field electron holography and nanobeam diffraction and better known ones such as geometrical phase analysis have been improved by using aberration corrected ultra-stable modern electron microscopes. In this paper we apply dark field electron holography, the geometrical phase analysis of high angle annular dark field scanning transmission electron microscopy images, nanobeam diffraction and precession diffraction, all performed at the state-of-the-art to five different types of semiconductor samples. These include a simple calibration structure comprising 10-nm-thick SiGe layers to benchmark the techniques. A SiGe recessed source and drain device has been examined in order to test their capabilities on 2D structures. Devices that have been strained using a nitride stressor have been examined to test the sensitivity of the different techniques when applied to systems containing low values of deformation. To test the techniques on modern semiconductors, an electrically tested device grown on a SOI wafer has been examined. Finally a GaN/AlN superlattice was tested in order to assess the different methods of measuring deformation on specimens that do not have a perfect crystalline structure. The different deformation mapping techniques have been compared to one another and the strengths and weaknesses of each are discussed.

Self-adapting denoising, alignment and reconstruction in electron tomography in materials science.

An automatic procedure for electron tomography is presented. This procedure is adapted for specimens that can be fashioned into a needle-shaped sample and has been evaluated on inorganic samples. It consists of self-adapting denoising, automatic and accurate alignment including detection and correction of tilt axis, and 3D reconstruction. We propose the exploitation of a large amount of information of an electron tomography acquisition to achieve robust and automatic mixed Poisson-Gaussian noise parameter estimation and denoising using undecimated wavelet transforms. The alignment is made by mixing three techniques, namely (i) cross-correlations between neighboring projections, (ii) common line algorithm to get a precise shift correction in the direction of the tilt axis and (iii) intermediate reconstructions to precisely determine the tilt axis and shift correction in the direction perpendicular to that axis. Mixing alignment techniques turns out to be very efficient and fast. Significant improvements are highlighted in both simulations and real data reconstructions of porous silicon in high angle annular dark field mode and agglomerated silver nanoparticles in incoherent bright field mode. 3D reconstructions obtained with minimal user-intervention present fewer artefacts and less noise, which permits easier and more reliable segmentation and quantitative analysis. After careful sample preparation and data acquisition, the denoising procedure, alignment and reconstruction can be achieved within an hour for a 3D volume of about a hundred million voxels, which is a step toward a more routine use of electron tomography.

EBSD study of angular deviations from the Goss component in grain-oriented electrical steels.

The magnetic properties of grain-oriented (GO) electrical steels strongly depend on the distribution of the α and ß angles, i.e., the deviations of the easy magnetisation <100> from the rolling direction (RD) in the rolling plane and out of the rolling plane, respectively. However, most Electron Backscatter Diffraction (EBSD) studies consider the standard Goss deviation angle, which includes the rotation of the (110) plane about the RD. Therefore, in the present work, a new procedure is demonstrated for deriving the α and ß angles from EBSD mappings to obtain a quantitative texture characterisation in line with the magnetic properties. This procedure is later applied to 37 GO steels after secondary recrystallisation that exhibit a wide range of permeability levels. The relation between the texture and the polarisation at 800A/m (J800) that is measured in the present study by EBSD is compared to the one that has been determined in previous papers with optical goniometers and X-ray diffraction techniques, and this relation is subsequently used to define a relevant parameter to describe the orientation quality of the grains. The results indicate that the average angle of the α and ß deviations is a relevant deviation parameter for the characterisation of grain orientations. Finally, it is demonstrated that the combination of the quantitative correlation between polarisation and texture with the orientation imaging of EBSD offers the possibilities of both studying the crystallographic environment of highly oriented grains in the primary recrystallised matrix for the production of high-permeability steels and evaluating the spatial distribution of the angular deviations in GO steels after secondary recrystallisation.

trans-Methylpyridine cyclen versus cross-bridged trans-methylpyridine cyclen. Synthesis, acid-base and metal complexation studies (metal = Co2+, Cu2+, and Zn2+).

The synthesis of the cross-bridged cyclen CRpy(2) {4,10-bis((pyridin-2-yl)methyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane}, a constrained analogue of the previously described trans-methylpyridine cyclen Cpy(2) is reported. The additional ethylene bridge confers to CRpy(2) proton-sponge type behaviour which was explored by NMR and potentiometric studies. Transition metal complexes have been synthesized (by complexation of both ligands with Co(2+), Cu(2+) and Zn(2+)) and characterized in solution and in the solid state. The single crystal X-ray structures of [CoCpy(2)](2+), [CuCpy(2)](2+) and [ZnCpy(2)](2+) complexes were determined. Stability constants of the complexes, including those of the cross-bridged derivative, were determined using potentiometric titration data and the kinetic inertness of the [CuCRpy(2)](2+) complex in an acidic medium (half-life values) was evaluated by spectrophotometry. The pre-organized structure of the cross-bridged ligand imposes an additional strain for the complexation leading to complexes with smaller thermodynamic stability in comparison with the related non-bridged ligand. The electrochemical study involving cyclic voltammetry underlines the importance of the ethylene cross-bridge on the redox properties of the transition metal complexes.

Electrochemically-driven conformational shift in mono- and di-copper constrained macrotricyclic cyclen receptors.

An electrochemical study of mono- and di-copper constrained cyclen macrotricycles is presented. Electrochemical data in DMF solution indicate that the reduction of dinuclear complexes occurs in two steps in the -0.4 to -0.8 V vs.AgCl/Ag potential range yielding CuII CuI and CuI CuI species further reduced to Cu metal at highly negative potentials. Mononuclear complexes are reduced in two steps to CuI and Cu metal. Electrochemical data suggest that reduction of both mononuclear and dinuclear complexes approach a square scheme involving electrochemically-driven conformational shifts for metal ions. The presence of endo- and exo-forms of the complexes are revealed by changes in the electrochemical response of the complexes in the presence of tetraethylammonium chloride, 1-azabicyclo[2.2.2]octane and diazabicyclo[2.2.2]octane competing ligands.

Complexation of the triphosphate anion: tuning the structure of cyclen based macrotricycles with 1,3-dimethylbenzene and 2,6-dimethylpyridine linkers. A potentiometric and NMR study.

The host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen-based macrotricyclic ligands was investigated by potentiometric measurements and NMR spectroscopy. The ligands differ from one another by the nature of their spacers, which are 1,3-dimethylbenzene (TMC), 2,6-dimethylpyridine (TPyC) or a combination of the two (TMPyC). In aqueous solution, each ligand gave protonated species that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The equilibrium constants found for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed that the ligand possessing a single supplementary anchoring site (the pyridinyl spacer) exhibited the greatest affinity for the phosphate species in a large p[H] range.