Etude de l'implantation d'atomes de fer dans le carbure de silicium 6H- en vue de l'élaboration d'un nouveau semi-conducteur magnétique dilué

L'objectif de ce travail était de réaliser une étude microstructurale détaillée du système Fe :SiC candidat pour devenir un semi-conducteur magnétique dilué. Des monocristaux de 6H-SiC (0001)Si de type n(2.5x10+18/cm3) et de type p (5.7x10+18/cm3) ont été multi-implantés en 56Fe et 57Fe à différentes énergies et différentes fluences conduisant à une concentration atomique constante (de 0, 5% à 7%) de 20 à 100 nm de la surface. Les implantations se sont déroulées depuis la température ambiante jusqu'à 550C. L'influence de la dose et de la température d'implantation de fer sur l'état microstructural de la matrice 6H-SiC a été étudiée. Les effets de différents traitements post-implantation (recuit thermique classique/rapide, recuit par laser à excimères en phase solide, irradiations aux ions lourds) ont été étudiés et comparés. Dans le cadre de ce travail, nous avons établi de nouveaux résultats : une substitution importante dans les échantillons tel-qu'implantés ; nature et dimensions des amas dans les échantillons traités ; évaluation du nombre d'atomes de fer ferromagnétiques. Dans l'état tel-qu'implanté nous avons réussi à nous mettre dans les conditions favorables pour l'introduction d'un ordre ferromagnétique dans le SiC (atomes de fer en substitution des atomes de silicium) mais les échantillons n'ont pas montré de propriétés magnétiques, le faible dopage initial des substrats utilisés dans cette étude pouvant expliquer ce constat. Nous avons montré qu'il était nécessaire de coupler de nombreuses techniques de caractérisation microstructurales et magnétiques afin de donner une description détaillée des différents échantillons étudiés et expliquer les résultats observés.In this work, we report results on Fe-implanted 6H-SiC which is a good candidate for Diluted Magnetic Semiconductor (DMS). Commercial (CREE) single crystalline 6H-SiC near (0001)-oriented samples were submitted to multi-step implantations with 56Fe+ and 57Fe+ ions at different energies and fluences leading to an iron concentration reaching a plateau of a few at.% (from 0.5% up to 7%) at a depth between 20 nm and 100 nm from the sample surface. The samples temperature was kept from RT up to 550C during implantation. First results obtained in samples implanted with CFe 6% at 380C and then furnace-annealed (from 900C upto 1300C) show interesting magnetic behaviour : Hysteresis cycle at 10 K and saturation magnetization MS up to 1.8 B/Fe at RT. Nevertheless, microstructural results from SR-XRD, TEM (HR and STEM-HAADF) and GISAXS reveal the presence of small (a few nm) iron-rich clusters (Fe3Si) into a light matrix SiC damaged but still crystallized rather than purely diluted iron atoms in the SiC matrix. These small clusters could contribute to the observed magnetic properties, in accordance with the conclusions of a recent work on the same kind of samples. From these first results, in order to limit the formation of parasitic magnetic secondary phases, we decided to limit the iron concentration around 2% and to explore other ways of treatments for implantation-induced damage recovery and iron incorporation and activation in the SiC matrix : the effects of furnace annealing on microstructure and magnetic properties of Fe-implanted 6H-SiC are compared to those of Rapid Thermal Annealing (RTA), laser processing in the solid phase and swift heavy ion irradiation.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Blindages électromagnétiques à forte transparence optique à l'aide de dépôts de films minces sur substrats diélectriques

National audienc

Ensemble de blindage électromagnétique transparent optiquement

The presence of HPV-specific antibodies in patients with head and neck cancer at enrolment has prognostic significance. In cervical carcinoma patients, the decrease of HPV E6/E7-specific antibodies appears to be associated with a better prognosis. In this study, we analysed sera of 93 patients taken a year after the end of treatment and sera from 58 of these patients taken up to 14 years after treatment. HPV-specific antibodies in patients with oropharyngeal cancer reflect the tumour removal and their level declines with time from the treatment. The decline of HPV16 E7-specific antibodies is statistically steeper in non-recurrent in comparison to recurrent patients. However, since the decline occurs both in recurrent and non-recurrent patients these antibodies cannot be used as a marker for stratification of patients to the risk groups. While the presence of HPV-specific antibodies at enrolment is predictive of better survival, their level at enrolment is not. However, the changes in the level of HPV16 E6 antibodies on the one-year follow-up after the treatment predict better overall as well as disease-specific survival

Dépôt en couche mince de blindage électromagnétique préservant la transparence optique de substrats de verre : ajustement des performances par modélisation

International audienc

Shielding effectiveness adjustment of planar mesh screen by fine-tuning metal thickness

International audienceThe study presents the thickness effect of mesh metal films printed onto glass substrate on the shielding effectiveness (SE) of such transparent screens. Currently, standards in microelectronic technology use a metal film thickness of between ∼100 nm and few micrometres, depending on the available deposition and implementation techniques. This study demonstrates that the thickness of mesh metal films is a key parameter which needs to be adjusted precisely. A theoretical model based on SE, complex impedance and optical transparency has been developed for this purpose. At microwaves, a relevant selection of the metal thickness values from 0.1 to 2 µm changes the SE at low frequency (from 36 to 40 dB at 2 GHz, respectively) while maintaining it constantly at a higher frequency (close to 20 dB at 18 GHz). The optical transparency of such mesh screens is kept constant over the entire visible light spectrum (78%). Experimental data are in complete agreement with the theoretical values

Adjustment of shielding effectiveness, optical transmission and sheet resistance of conducting films deposited on glass substrates

International audienc

On the importance of light scattering for high performances nanostructured antireflective surfaces

An antireflective coating presenting a continuous refractive index gradient is theoretically better than its discrete counterpart because it can give rise to a perfect broadband transparency. This kind of surface treatment can be obtained with nanostructures like moth-eye. Despite the light scattering behavior must be accounted as it can lead to a significant transmittance drop, no methods are actually available to anticipate scattering losses in such nanostructured antireflective coatings. To overcome this current limitation, we present here an original way to simulate the scattering losses in these systems and routes to optimize the transparency. This method, which was validated by a comparative study of coatings presenting refractive indices with either discrete or continuous gradient, shows that a discrete antireflective coating bilayer made by oblique angle deposition allows reaching ultra-high mean transmittance of 98.97% over the broadband [400-1800] nm. Such simple surface treatment outperforms moth-eye architectures thanks to both interference effect and small dimensions nanostructures that minimize the scattering losses as confirmed by finite-difference time domain simulations performed on reconstructed volumes obtained from electron tomography experiments