Critical Strain Region Evaluation of Self-Assembled Semiconductor Quantum Dots

A novel peak finding method to map the strain from high resolution transmission electron micrographs, known as the Peak Pairs method, has been applied to In(Ga) As/AlGaAs quantum dot (QD) samples, which present stacking faults emerging from the QD edges. Moreover, strain distribution has been simulated by the finite element method applying the elastic theory on a 3D QD model. The agreement existing between determined and simulated strain values reveals that these techniques are consistent enough to qualitatively characterize the strain distribution of nanostructured materials. The correct application of both methods allows the localization of critical strain zones in semiconductor QDs, predicting the nucleation of defects, and being a very useful tool for the design of semiconductor device

Influence of hydrogen on the structural stability of annealed ultrathin Si/Ge amorphous layers

Semiconductor structures based on Si and Ge are generally submitted to hydrogenation because H passivates the dangling bonds of Si and Ge. By this way the devices prepared from those semiconductors, e.g., solar cells, have much better electrical properties. However, H stability is still a critical issue. In fact, there is wide evidence that H is very unstable against illumination as well as heat treatment. It has been seen that H out effuses from the samples under such treatments. As this causes unsaturation of the dangling bonds the electrical properties worsen significantly. In this work we will show that in the case of ultrathin Si/Ge amorphous layers the H thermal instability also affects the structural stability even up to the micrometric scale depending on the H content. Such type of structure can also be used to prepare SiGe alloys by mixing the layers with heat treatments. The samples were amorphous multilayers (MLs) of alternating ultrathin (3 nm) layers of Si and Ge deposited by sputtering on (100) oriented Si substrate. The total thickness of the MLs was 300 nm. The samples were hydrogenated by introducing H in the sputter chamber with flow rates varying from 0.8 to 6 ml/min. The MLs underwent different heat treatments, from the one at 350 ?C for 1 h up to the one at 250 ?C for 0.5 h + 450 ?C for 5 h. The samples were analysed by AFM, TEM, energy filtering TEM and Small-Angle X-Ray Diffraction (SAXRD). AFM showed that upon annealing the structure of the samples degrades with formation of surface bumps whose size increases by increasing the annealing temperature and/or time, for the same H content, or by increasing the H content for the same annealing conditions. For high H content and/or annealing conditions AFM showed that the bumps have blown up giving rise to craters. This suggests that H was released from its dangling bonds to Si and Ge and formed H bubbles in the MLs because of the energy supplied by the annealing. Additional energy for the break of the Si-H and Ge-H bonds could be the one supplied by the recombination of thermally generated carriers associated with the band gap fluctuations caused by the not uniform distribution of H in the MLs. The first sites of H accumulation are very likely nanocavities certainly present in the amorphous MLs. By TEM it has been seen that layer intermixing occurred which could be the first step of H bubbles formation. SAXRD measurements as well as TEM energy filtering maps for Si and Ge showed that Si and Ge interdiffusion took place in an asymmetric way as Si was seen to diffuse to the Ge layers whereas Ge did not diffuse to the Si layers. This might be due to the higher density of free dangling bonds in the Ge layers created by annealing because the binding energy of the Ge-H bond is smaller than the one of the Si-H bond

Tungsten oxide nanowires grown on amorphous-like tungsten films

Tungsten oxide nanowires have been synthesized by vacuum annealing in the range 500-710 °C from amorphous-like tungsten films, deposited on a Si(100) substrate by pulsed laser deposition (PLD) in the presence of a He background pressure. The oxygen required for the nanowires formation is already adsorbed in the W matrix before annealing, its amount depending on deposition parameters. Nanowire crystalline phase and stoichiometry depend on annealing temperature, ranging from W18O49-Magneli phase to monoclinic WO3. Sufficiently long annealing induces the formation of micrometer-long nanowires, up to 3.6 μm with an aspect ratio up to 90. Oxide nanowire growth appears to be triggered by the crystallization of the underlying amorphous W film, promoting their synthesis at low temperatures

Dendritic Cells Cause Bone Lesions in a New Mouse Model of Histiocytosis.

Langerhans cell histiocytosis (LCH) is a rare disease caused by the clonal accumulation of dendritic Langerhans cells, which is often accompanied by osteolytic lesions. It has been reported that osteoclast-like cells play a major role in the pathogenic bone destruction seen in patients with LCH and these cells are postulated to originate from the fusion of DCs. However, due to the lack of reliable animal models the pathogenesis of LCH is still poorly understood. In this study, we have established a mouse model of histiocytosis- recapitulating human disease for osteolytic lesions seen in LCH patients. At 12 weeks after birth, severe bone lesions were observed in our multisystem histiocytosis (Mushi) model, when CD8α conventional dendritic cells (DCs) are transformed (MuTuDC) and accumulate. Most importantly, our study demonstrates that bone loss in LCH can be accounted for the transdifferentiation of MuTuDCs into functional osteoclasts both in vivo and in vitro. Moreover, we have shown that injected MuTuDCs reverse the osteopetrotic phenotype of oc/oc mice in vivo. In conclusion, our results support a crucial role of DCs in bone lesions in histiocytosis patients. Furthermore, our new model of LCH based on adoptive transfer of MuTuDC lines, leading to bone lesions within 1-2 weeks, will be an important tool for investigating the pathophysiology of this disease and ultimately for evaluating the potential of anti-resorptive drugs for the treatment of bone lesions

Role of B diffusion in the interfacial Dzyaloshinskii-Moriya interaction in Ta / Co₂₀ Fe₆₀B₂₀/MgO nanowires

We report on current-induced domain wall motion in Ta/Co20Fe60B20/MgO nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient D=+0.06mJ/m2. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta buffer layer during annealing, which was observed by chemical depth profiling measurements. The experimental results are compared to one-dimensional model simulations including the effects of pinning. This modeling allows us to reproduce the experimental outcomes and reliably extract a spin-Hall angle θSH=-0.11 for Ta in the nanowires, showing the importance of an analysis that goes beyond the model for perfect nanowires

The Human Ecology and Geography of Burning in an Unstable Savanna Environment

According to new ecological theories, many savannas are inherently in disequilibrium and can flip from tree-dominated to grass-dominated landscapes depending upon the disturbance regime. In particular, a shift in a fire regime to a more frequent and intensive one can radically alter the tree-to-grass ratio in a given savanna. Drawing upon the ecological buffering model we argue that savanna persistence requires a relatively stable fire regime. We hypothesize that anthropogenic burning practices perform this function by producing a regular annual spatiotemporal pattern of fire that is linked to vegetation type. We test this hypothesis using a study of two areas, one in Mali and the other Burkina Faso. We use two sources of satellite data to produce an 11-year time series of the spatiotemporal pattern of fires and an example of the annual burned area pattern these fires produce. We combine the analysis of satellite imagery with interviews of rural inhabitants who set fires to understand the logic underlying the patterns of fire. Analysis of a time series of imagery reveals a strikingly regular annual spatiotemporal pattern of burning for both study areas, which cannot be explained by the regional climatic pattern alone. We conclude that the regularity of the annual fire regime in West Africa is a human-ecological phenomenon closely linked to vegetation type and controlled by people\u27s burning practices. We argue that the anthropogenic burning regime serves to buffer the savanna and maintain its ecological stability

A user-centred approach to developing bWell, a mobile app for arm and shoulder exercises after breast cancer treatment

Purpose: The study aim was to develop a mobile application (app) supported by user preferences to optimise self-management of arm and shoulder exercises for upper-limb dysfunction (ULD) after breast cancer treatment. Methods: Focus groups with breast cancer patients were held to identify user needs and requirements. Behaviour change techniques were explored by researchers and discussed during the focus groups. Concepts for content were identified by thematic analysis. A rapid review was conducted to inform the exercise programme. Preliminary testing was carried out to obtain user feedback from breast cancer patients who used the app for 8 weeks post-surgery. Results: Breast cancer patients’ experiences with ULD and exercise advice and routines varied widely. They identified and prioritised several app features: tailored information, video demonstrations of the exercises, push notifications, and tracking and progress features. An evidence-based programme was developed with a physiotherapist with progressive exercises for passive and active mobilisation, stretching and strengthening. The exercise demonstration videos were filmed with a breast cancer patient. Early user testing demonstrated ease of use, and clear and motivating app content. Conclusions: bWell, a novel app for arm and shoulder exercises was developed by breast cancer patients, health care professionals and academics. Further research is warranted to confirm its clinical effectiveness. Implications for Cancer Survivors: Mobile health has great potential to provide patients with information specific to their needs. bWell is a promising way to support breast cancer patients with exercise routines after treatment and may improve future self-management of clinical care