•At a temperature of 700 °C the vacancies in SiC are mobile enough to form cavities.•Small Solid xenon bubbles form in implanted/annealed SiC.•The stacking faults are related to the formation of ...bubbles.•SiC confines xenon.
Xenon ions were implanted in 4H-SiC at 400 and 700 °C with fluences of 1 × 1016 and 3 × 1016 cm−2, respectively. Transmission Electron Microscopy (TEM) experiments were carried out to study the resulting microstructure and its evolution after a 1400 °C annealing. Observations show that the temperature of implantation plays an active role in the formation of as-generated defects. The implantation temperature of 400 °C is too low to allow the formation of visible defects and only a strongly damaged band is observed in the ion stopping range. The post-implantation annealing results in the formation of nanometric cavities along the ion path. In the buried ion stopping region, xenon solid cavities or nano-precipitates of about 10 nm in diameter are present. Other types of defects were also formed during annealing, a high density of stacking faults is observed among the solid cavities and black spot defects are observed beyond the implanted area. At a temperature of 700 °C, the vacancies become mobile enough to cause the formation of nanocavities all along the ions path, i.e. voids in the near surface region and full-gas cavities in the xenon stopping range. At this temperature stacking faults were also formed as well as the defect band at the back. The annealing only causes a slight growth of the solid cavities.
Eutectic solders AuIn19 and AuGe12 and nanosilver paste were investigated for SiC die attach in high-temperature (300°C) applications. The soldering or sintering conditions were optimized through die ...shear tests performed at room temperature. In particular, application of static pressure (3.5 MPa) during sintering resulted in greatly improved mechanical behavior of the nanosilver-based joint. Microstructural study of the eutectic solders showed formation of Au-rich grains in AuGe die attach and significant diffusion of Au and In through the Ni layer in AuIn19 die attach, which could lead to formation of intermetallic compounds. Die shear tests versus temperature showed that the behaviors of the studied die attaches are different; nevertheless they present suitable shear strengths required for high-temperature applications. The mechanical behavior of joints under various levels of thermal and mechanical stress was also studied. Creep experiments were carried out on the eutectic solders to describe the thermomechanical behavior of the complete module; only one creep mechanism was observed in the working range.
Damage formation in implanted 4H-SiC was studied as a function of dose and temperature of implantation. At RT the maximal strain as well as the surface swelling linearly increases suggesting a point ...defects swelling. With increasing temperature the slope decreases due to irradiation-induced dynamic recovery with activation energy of 0.13±0.02eV. From 300°C the amorphisation is avoided and the strain build-up can be fitted according to a direct impact model. At 300°C the as-induced strain profile consists of three different zones of damage with depth, resulting from the damage accumulation in the near surface region, the formation of Xe-vacancy complexes in the ion distribution and beyond a zone of end-of-range strain associated with interstitial accumulation.
The master biological clock situated in the suprachiasmatic nuclei of the anterior hypothalamus plays a vital role in orchestrating the circadian rhythms of multiple biological processes. Increasing ...evidence points to a role of the biological clock in the development of depression. In seasonal depression and in bipolar disorders it seems likely that the circadian system plays a vital role in the genesis of the disorder. For major unipolar depressive disorder (MDD) available data suggest a primary involvement of the circadian system but further and larger studies are necessary to conclude. Melatonin and melatonin agonists have chronobiotic effects, which mean that they can readjust the circadian system. Seasonal affective disorders and mood disturbances caused by circadian malfunction are theoretically treatable by manipulating the circadian system using chronobiotic drugs, chronotherapy or bright light therapy. In MDD, melatonin alone has no antidepressant action but novel melatoninergic compounds demonstrate antidepressant properties. Of these, the most advanced is the novel melatonin agonist agomelatine, which combines joint MT1 and MT2 agonism with 5-HT(2C) receptor antagonism. Adding a chronobiotic effect to the inhibition of 5-HT(2C) receptors may explain the rapid impact of agomelatine on depression, since studies showed that agomelatine had an early impact on sleep quality and alertness at awakening. Further studies are necessary in order to better characterize the effect of agomelatine and other novel melatoninergic drugs on the circadian system of MDD patients. In summary, antidepressants with intrinsic chronobiotic properties offer a novel approach to treatment of depression.
Implantation damage in heavy gas implanted 4H-SiC Jiang, C.; Nicolaï, J.; Declémy, A. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
05/2016, Letnik:
374
Journal Article
Recenzirano
Single crystals of SiC were implanted with heavy inert gases (Xe, Ar) at elevated temperatures (300–800°C) and for a large range of fluence (1×1012–1×1015ions cm−2). Thermodesorption measurements ...suggest that gas is trapped by implantation-induced vacancy-type defects impeding any gas diffusion. The damage accumulation versus dose was studied through the tensile elastic strain determined by using X-ray diffraction. Results show that at low dose the strain is predictable via a thermally activated direct impact model. The low thermal activation energy at saturation suggests a dynamic recovery process dominated by the migration of interstitial-type defects as its relaxation during post thermal annealing. As compared with light-gas implantation the heavy-gas to defect ratio is low enhancing the formation of strongly perturbed zones rather than the formation of bubble precursors.
•Growth of Ti3SiC2 thin films onto 4H-SiC (0001) 8° and 4°-off substrates.•High temperature application for SiC ohmic contact.•Thermal annealing of Ti-Al layers.•Influence of the composition in the ...TixAl1−x alloy was investigated.•Influence of the annealing temperature (900–1200°C) after deposition was investigated.•The structural investigations were mainly performed by using X-ray diffraction (XRD), and transmission electron microscopy (TEM).•Elementary and profile characterization were performed using X-Ray photoelectron spectroscopy (XPS).
The growth of Ti3SiC2 thin films was studied onto 4H-SiC (0001) 8° and 4°-off substrates by thermal annealing of TixAl1−x (0.5≤x≤1) layers. The annealing time was fixed at 10min under Argon atmosphere. The synthesis conditions were also investigated according to the annealing temperature (900–1200°C) after deposition. X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM) show that the layer of Ti3SiC2 is epitaxially grown on the 4H-SiC substrate. In addition the interface looks sharp and smooth with evidence of interfacial ordering. Moreover, during the annealing procedure, the formation of unwanted aluminum oxide was detected by using X-Ray Photoelectron Spectroscopy (XPS); this layer can be removed by using a specific annealing procedure.
Effects of annealing on surface swelling in helium implanted 4H–SiC were studied for different implant conditions. The significant increase of surface swelling observed upon high temperature ...annealing of samples implanted under severe implant conditions (high temperature and fluence) is observed to be concomitant with the growth of cavities and the formation of other extended defects in the highly damaged zone. Frank loops resulting from the drift of interstitials only form in the highly damaged zone. These loops promote the formation of Shockley partial dislocations leading to stacking fault pile-up. For less severe conditions of implantation, low temperature and fluence, the formation of dislocations is avoided upon post-annealing, and the recovery of swelling progressively occurs. Under intermediate conditions of implantation, the compensation between elastic recovery of the implantation-induced strain and the limited formation of cavities and interstitial-type clusters result in a constant swelling.
ObjectiveTo investigate the evolution over 15 years of sleep schedules, sleepiness at the wheel and driving risk among highway drivers.MethodsComparative survey including questions on usual sleep ...schedules and before the trip, sleepiness at the wheel, the Epworth sleepiness scale, Basic Nordic Sleep Questionnaire (BNSQ) and a travel questionnaire.Results80% of drivers stopped by the highway patrol agreed to participate in both studies with a total of 3545 drivers in 2011 and 2196 drivers in 1996 interviewed. After standardisation based on sex, age and mean annual driving distance, drivers in 2011 reported shorter sleep time on week days (p<0.0001), and week-ends (p<0.0001) and shorter optimal sleep time (p<0.0001) compared to 1996 drivers. There were more drivers sleepy at the wheel in 2011 than in 1996 (p<0.0001) and 2.5 times more drivers in 2011 than in 1996 had an Epworth sleepiness score >15 indicating severe sleepiness.ConclusionsEven if drivers in 2011 reported good sleep hygiene prior to a highway journey, drivers have reduced their mean weekly sleep duration over 15 years and have a higher risk of sleepiness at the wheel. Sleep hygiene for automobile drivers remains an important concept to address.
Strain build-up in SiC implanted at different temperatures Barbot, J.-F.; Beaufort, M.-F.; Declémy, A.
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
05/2014, Letnik:
327
Journal Article
Recenzirano
Single crystals of 4H-SiC were implanted with helium ions at temperatures of 400 and 700°C in a large range of fluences. The damage accumulation versus fluence was studied through the tensile elastic ...strain determined by using X-ray diffraction measurements. Results were analyzed via the multi-step damage accumulation model. At low dose (step 1) the strain can be described assuming a thermally activated process with low activation energy. Damage cross-sections, independent of implantation temperature, for interstitial-type defects were determined. With increasing dose, the contribution of other defects arises leading to an accelerated strain build-up namely the second step of the disordering process. However, in this regime, the strain cannot be fully described due to others operative mechanisms such as the formation of tiny bubbles under severe conditions of implantation. The formation of bubbles accelerates the development of the elastic strain. The values of damage cross-sections show that only small clusters contribute to the tensile elastic strain.
The effects of temperature on helium implanted SiC were investigated through X-ray diffraction measurements. At low fluence and elevated temperature, dynamic annealing occurs resulting from point ...defect recombination. At high fluence, the dynamic annealing taking place in the near surface region is concomitant with the formation of a thin and deep highly strained region resulting from the accumulation of interstitial atoms drifted to the deep damaged region under the actions of strain gradient and temperature.
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