Hydrostatic strain enhancement in laterally confined SiGe nanostripes

Strain-engineering in SiGe nanostructures is fundamental for the design of optoelectronic devices at the nanoscale. Here we explore a new strategy, where SiGe structures are laterally confined by the Si substrate, to obtain high tensile strain avoiding the use of external stressors, and thus improving the scalability. Spectro-microscopy techniques, finite element method simulations and ab initio calculations are used to investigate the strain state of laterally confined Ge-rich SiGe nano-stripes. Strain information is obtained by tip enhanced Raman spectroscopy with an unprecedented lateral resolution of ~ 30 nm. The nano-stripes exhibit a large tensile hydrostatic strain component, which is maximum at the center of the top free surface, and becomes very small at the edges. The maximum lattice deformation is larger than the typical values of thermally relaxed Ge/Si(001) layers. This strain enhancement originates from a frustrated relaxation in the out-of-plane direction, resulting from the combination of the lateral confinement induced by the substrate side walls and the plastic relaxation of the misfit strain in the (001) plane at the SiGe/Si interface. The effect of this tensile lattice deformation at the stripe surface is probed by work function mapping, performed with a spatial resolution better than 100 nm using X-ray photoelectron emission microscopy. The nano-stripes exhibit a positive work function shift with respect to a bulk SiGe alloy, quantitatively confirmed by electronic structure calculations of tensile strained configurations. The present results have a potential impact on the design of optoelectronic devices at a nanometer length scale.Comment: 40 pages, 11 figures, submitted to Physical Review

Multiscale modelling for fusion and fission materials: the M4F project

The M4F project brings together the fusion and fission materials communities working on the prediction of radiation damage production and evolution and its effects on the mechanical behaviour of irradiated ferritic/martensitic (F/M) steels. It is a multidisciplinary project in which several different experimental and computational materials science tools are integrated to understand and model the complex phenomena associated with the formation and evolution of irradiation induced defects and their effects on the macroscopic behaviour of the target materials. In particular the project focuses on two specific aspects: (1) To develop physical understanding and predictive models of the origin and consequences of localised deformation under irradiation in F/M steels; (2) To develop good practices and possibly advance towards the definition of protocols for the use of ion irradiation as a tool to evaluate radiation effects on materials. Nineteen modelling codes across different scales are being used and developed and an experimental validation programme based on the examination of materials irradiated with neutrons and ions is being carried out. The project enters now its 4th year and is close to delivering high-quality results. This paper overviews the work performed so far within the project, highlighting its impact for fission and fusion materials science.This work has received funding from the Euratom research and training programme 2014-2018 under grant agreement No. 755039 (M4F project)

Tomografia computerizzata e radiografia tradizionale nella diagnosi della spondiloartropatia destruente. Nostra esperienza in 30 pazienti sottoposti a emodialisi periodica

Thirty patients of both sexes (15 males and 15 females) with chronic renal failure who had under gone hemodialysis for 2-184 months (mean 45.1 months) were examined with conventional radiographs of the cervical spine and thin-layer CT of C4-C5-C6 to evaluate the radiographic patterns of destructive spondyloarthropathy. The radiographic patterns obtained with conventional and CT exams were compared with one another and with clinical (carpal tunnel syndrome) and biochemical data (alkaline phosphatase, parathormon, Ca, P, Ca/P, Al, beta 2-microglobulin). DSA (erosion and narrowing of the intervertebral space, collapse of the vertebral body and erosion of the vertebral plates) was recognized in 7 patients with conventional radiographs and in 11 patients with CT thanks to greater CT capabilities to recognize minimal osteolytic lesions of the vertebral body. All the patients with destructive spondyloarthropathy had personal and hemodialysis age higher than those without destructive spondyloarthropathy: 59.3 vs 57.7 years; 49 vs 39 months. Parathormon and alkaline phosphatase were increased while beta 2-microglobulin was normal. Only 2 patients with DSA had carpal tunnel syndrome. In conclusion, CT is a valuable technique for the diagnosis of destructive spondyloarthropathy but it must be performed only after conventional radiographs of the cervical spine or in the presence of clinical signs of destructive spondyloarthropathy (parathormon and beta 2-microglobulin increased, long-term hemodialysis)

Valutazione del carcinoma epatocellulare mediante tomografia computerizzata dopo iniezione di lipiodol ultrafluido in arteria epatica

Fifteen patients with nodular HCC, focal or multifocal, were submitted to CT 15-20 days after injection of Lipiodol in the hepatic artery. CT-Lipiodol showed all lesions recognized before by ultrasound and visualized further lesions in 7 patients (46.6%) for a total number of 32 lesions. In 16/32 lesions (50%) enhancement was homogeneous, in 14/32 (43.8%) unhomogeneous while in 2/32 (6.2%) Lipiodol wasn't retained. Retention of Lipiodol depended on the size of the lesions: if the size was 1-2 cm retention was homogeneous but if the lesion was larger accumulation was unhomogeneous. Lesions larger than 4 cm didn't retain Lipiodol and showed necrosis. 7/15 patients were operated (46.6%). Lipiodol-CT is a good technique in the pre-operative screening of HCC, particularly in the recognition of additional lesions: in our work these were recognized in 46.6% of the cases

Il ruolo della tomografia computerizzata nei traumi chiusi della milza

The CT scans of 18 patients (12 males and 6 females; mean age: 43.6 years) with splenic blunt trauma were reviewed. CT examinations had been made at different times after trauma. The CT images were grouped according to the time of examination and both structure and densitometry were evaluated in all lesions. In all cases CT findings were correlated with surgical and pathologic data. The patients were divided into two groups: group I included 11 subjects in whom CT had been performed within 48 hours following trauma and group II included 7 patients who had undergone CT at different times after trauma (3-13 days; mean: 6.5 days). All the lesions in group I exhibited blurred outlines, while the lesions in group II had clear-cut margins. The lesions in group I were always hyperdense while those in group II were hypodense. CT diagnosis was always in agreement with surgical findings. In conclusion, we confirm the value of CT in the examination of splenic lesions by blunt abdominal trauma. The evolution of splenic lesions is usually typical: CT yields useful information for injury evaluation and is therefore very important to plan treatment. We believe that CT should be performed as soon as possible, even on the basis of minor clinical and laboratory data

Analisi della casistica di 342 pazienti con bassa statura esaminati con il metodo Tanner-Whitehouse 2 (TW2)

342 short-stature patients were examined to assess the agreement between anagraphic and bone ages. 190 men and 152 women (age range: 0 to 17.5 years) underwent conventional radiographs of the left wrist. The radiographs were studied with the TW2 method which provides an index of the skeletal maturity of short and long bones and a global index of the hand. The bone ages thus obtained were compared with anagraphic ages. Patients' statures were compared with their parents' ones. Finally, radiation exposures were evaluated. Anagraphic and bone ages were in agreement in 199 patients and in disagreement in 220. Three patients were adult. The short stature in 78 patients was in agreement with their parents' one, while 253 patients had at least one parent with normal stature. No comparison could be made in 11 patients. In conclusion, TW2 is a simple method to calculate bone age (in months and years) and to select the patients to submit to further examinations and to hormone therapy

Investigation of small-scale plasticity/fatigue mechanisms and size effects using advanced transmission electron microscopy

In the present work, the fundamental plasticity/fatigue mechanisms operating at interfaces in micro/nano-scale Ni samples have been investigated. in-situ SEM fatigue tests have been performed on FIB prepared single and bi-crystal micropillars with well-known orientations as revealed by electron backscatter diffraction (EBSD). Careful characterizations of the nature and the distribution of deformation dislocations, the character and the local structure of the interface as well as the mechanisms controlling the interaction between these defects under cyclic loads were performed using ex-situ TEM techniques including diffraction contrast imaging, automated crystallographic orientation and nanostrain mapping in TEM (ACOM-TEM) as well as electron diffraction tomography. Furthermore, quantified in-situ TEM nanotensile tests were performed on both single and bi-crystal samples in order to directly observe the plasticity mechanisms. Recently, an original method combining the measurement of dislocation mobility using commercial in-situ TEM nanomechanical testing and dislocation dynamic (DD) simulations has been used to revisit the plasticity of olivine single crystals at low temperature [1]. Cyclic deformation was applied in the load control mode. Load was increased to a given value, which is maintained constant for several minutes before unloading. During the plateau, dislocation motion is observed and characterized (hence, under a known and constant applied stress). Using this method, we found that the intrinsic ductility of olivine at low temperature is significantly lower than previously reported values which were obtained under strain-hardened laboratory conditions. More generally, we demonstrated the possibility of characterizing the mechanical properties of specimens which could be available in the form of sub-millimetre sized particles only. References [1] H. Idrissi, C. Bollinger, F. Boioli, D. Schryvers, P. Cordier, Low-temperature plasticity of olivine revisited with in situ TEM nanomechanical testing. Science Advances. 2 (2016) e1501671