PDMS residues-free micro/macrostructures on flexible substrates

Transfer printing has been reported recently as a viable route for electronics on flexible substrates. The method involves transferring micro-/macrostructures such as wires or ultra-thin chips from Si (silicon) wafers to the flexible substrates by using elastomeric transfer substrates such as poly(dimethylsiloxane) (PDMS). A major challenge in this process is posed by the residues of PDMS, which are left over on Si surface after the nanostructures have been transferred. As insulator, PDMS residues make it difficult to realize metal connections and hence pose challenge in the way of using nanostructures as the building blocks for active electronics. This paper presents a method for PDMS residues-free transfer of Si micro-/macrostructures to flexible substrates such as polyimide (PI). The PDMS residues are removed from Si surface by immersing the transferred structures in a solution of quaternary ammonium fluoride such as TBAF (Tetrabutylammonium Fluoride) and non-hydroxylic aprotic solvent such as PMA (propylene glycol methyl ether acetate). The residues are removed at a rate (∼1.5 μm/min) which is about five times faster than the traditional dry etch methods. Unlike traditional alternatives, the presented method removes PDMS without attacking the flexible PI substrates

Une arme miracle contre le chômage ?:Une nouvelle évaluation des effets des allègements de charges sociales sur les bas salaires

La revue Économie et Statistique vient de faire paraître un article de Bruno Crépon et Rozenn Desplatz qui propose une nouvelle évaluation des effets des allègements de charges sociales sur les bas salaires. Selon cette étude, ceux-ci auraient provoqué, de 1994 à 1997, une augmentation de 460 000 du nombre d’emplois dans l’économie française. Ce chiffre est nettement supérieur aux estimations antérieures 1. Il est maintenant évoqué dans le débat public pour justifier la poursuite de la politique de baisse des charges sociales, comme axe central de la politique de l’emploi. Compte tenu de la complexité de l’article, la plupart des commentateurs se contentent de citer le chiffre tel quel : « Les experts ont parlé ». Mais quelle est la fiabilité de ce résultat ? Par quels mécanismes, ces emplois ont-ils été créés ? La réduction des cotisations sociales est-elle une arme miracle contre le chômage ? [Premier paragraphe]Bruno Crépon et Rozenn Deslpatz, Une nouvelle évaluation des effets des allègements de charges sociales sur les bas salaires, Economie et Statistique, n°348, 2001, 0336-145

critical relative indentation depth in carbon based thin films

Abstract The thin film hardness estimation by nanoindentation is influenced by substrate beyond a critical relative indentation depth (CRID). In this study we developed a methodology to identify the CRID in amorphous carbon film. Three types of amorphous carbon film deposited on silicon have been studied. The nanoindentation tests were carried out applying a 0.1–10 mN load range on a Berkovich diamond tip, leading to penetration depth-to-film thickness ratios of 8–100%. The work regained during unloading ( W e ) and the work performed during loading ( W t ) was estimated for each indentation. The trend of unload-to-load ratio ( W e / W t ) data as a function of depth has been studied. W e / W t depth profiles showed a sigmoid trend and the data were fitted by means of a Hill sigmoid equation. Using Hill sigmoid fit and a simple analytical method it is possible to estimate CRID of carbon based films

Development of W–SiO2 and Nb–TiO2 solar absorber coatings for combined heat and power systems at intermediate operation temperatures

Two new absorber coatings for mid-temperature operation (300–350 1C) in collectors for solar thermal electricity plants are presented in this study. The absorbers consist of two cermet layers of either W–SiO2 or Nb–TiO2, deposited on a molybdenum infrared reflector and coated with an antireflection layer of silicon oxide. The optimization of the optical performance was made in two steps. First, the layer structure was optimized in model calculations. The optical constants used in this modelling were derived directly from sputtered films of the cermet constituents using reflectance and transmittance measure- ments. The absorber coatings were then sputter-deposited using parameters from the modelling. The results show good agreement between modelled and sputtered optical performance evaluated as solar absorptance and thermal emittance at 350 1C. The optimal values reached for W–SiO2 was 0.91 in combination with 0.08 and 0.93 in combination with 0.09 for Nb–TiO2. The materials characterization from XRD, AES and TEM shows that the composite coatings contain nano-metal inclusions, meaning that they are cermet coatings. Scratch tests show that the coatings adhere well to the substrate of stainless steel. Temperature testing at 350 1C in vacuum for up to 1500 h shows that both coatings are stable under such conditions. Only a slight change occurs during the first 72 h that decreases the emittance but does not change the solar absorptance. ERDA confirms that there is no detectable level of ion migration between layers, only a small decrease in hydrogen content was observed, which indicates outgassing.Digespo projec

Etude des mecanismes de nitruration du titane massif et des films minces de titane, dans un reacteur plasma basse pression hors equilibre, en atmosphere d'ammoniac

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Anti-adhesion of thin polymer films as cells/biofilm repellent for biomedical devices

Surface with abilities for anti-adhesion of living tissue is vital for biomedical applications such as in sensors and medical implants. Cellular (MG-63 osteo-blast cells) anti-adhesion properties of plasma de- posited thin polymer films using CH 4 gas as a precursor were investigated. Thinner coatings reduce the risk of swelling or delamination in wet environment considerably. X-ray photoelectron spectroscopy and contact angle measurements were used to provide molecular and surface energy information, respec- tively, to assist in forming properties-structure relationships. SEM was used to provide information re- garding surface topography and morphology. All plasma deposited surfaces showed an increase in con- tact angle measurements while SEM images showed a visible thin coating that masked the surface fea- tures, and chemistry, of PEEK. The osteoblast cells responded to all surface attributes. Chemistry wise, the percentage of living cells on the plasma treated PEEK substrates reduced with the reduction of relative oxygen concentration on the surface especially with C-O functional groups. Hence the relative concen- tration of C-functional groups could be used as a controlled variable to regulate anti adhesion properties for medical devices. Cells also showed a clear positive trend with the sp3/sp2 ratio. Positive trends were noticed between cells spreading and proliferation and C-O functional group and the increase of contact angle measurements

Etude électrochimique et photo-électrochimique des modes de conduction dans les films de TiO2 nanostructurés

Two types of TiO2 nano-tubular arrays with nanotubes (NT) aligned perpendicular to the titanium substrate were obtained by anodization of a titanium foil, in two different solutions (TiO2-NT(TB), TiO2-NT(EG)). In the dark, in the Na2SO4 solution, the EIS study of TiO2-NT (TB) anatase showed that a presence of a localized energy state in the gap which is the signature of the adsorption of molecular water. After UV exposure, the quasi irreversible disappearance of the localized energy states is related to photo-induced adsorbed water dissociation. Furthermore, the increase by a factor 112 of the capacity of the space charge layer was observed after UV exposure. This increase can be explained by the photo activation of the surface of NT, which was inactive before UV exposure. This activation is related to the dissociation of adsorbed molecular water and the insertion of hydrogen into the walls of NT. With a geometric model proposed, a carrier density of about 1018 cm-3 and 1020 cm-3 respectively before and after UV illumination were determined, confirming that the photo-induced activation of the wall of NT is linked to the phenomenon of doping due to hydrogen insertion. In the case of TiO2 NT(EG), the contribution of adsorption of molecular water was not observed. The carrier density is about 1020cm-3 before and after illumination. In other words, these tubes of TiO2 NT(EG), are already activated before illumination. For a better identification of the chemical nature of the surface state in the case of TiO2 NT(TB), EIS measurements were performed in the same manner, but in acidic and basic media, in order to compare the behaviour to that observed in the Na2SO4 solutionDeux types de nanotubes de TiO2 (NT) alignés perpendiculairement ont été obtenus par anodisation d'une feuille de titane et ce, dans deux différents électrolytes (TiO2-NT (TB), TiO2-NT (EG)). Les deux types de nanotubes ont été caractérisés par SIE. A l'obscurité et en solution neutre de Na2SO4, l'étude par SIE de TiO2-NT (TB) anatase a montré que la présence d'un état d'énergie localisé qui est la signature de l'adsorption de molécules d eau. Après une exposition, la disparition des états d énergie localisée est liée à la photodissociation irréversible de l'eau adsorbée. Une augmentation, de la capacité de la zone de charge d'espace cause de la photo-activation de la surface des NT qui était inactive à l obscurité est observé. Cette activation est liée à la dissociation des molécules d eau adsorbées et à l'insertion d hydrogène dans les parois des NT. Un modèle géométrique proposé permet de estimer une densité de porteurs d'environ 1018 cm-3 et 1020 cm-3, respectivement avant et après éclairement sous UV. Dans le cas du TiO2-NT (EG), la contribution de l'adsorption des molécules d eau n'a pas été observée. Les analyses par SIE avant et après exposition aux UV n'ont pas montré un changement significatif. La simulation avec le modèle proposé montre que la densité des porteurs est d'environ 1020 cm-3 avant et après éclairement. En d'autres termes, ces tubes de TiO2-NT (EG) sont déjà activés à l obscurité et les effets photo-induits sont moins importants par rapport aux tubes de TiO2-NT (TB). Pour une meilleure identification de la nature chimique de l'état de surface dans le cas de tubes bruts de TiO2-NT (TB), des mesures de SIE ont été réalisées en milieu acide et en milieu basiquePARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Croissance par sputtering en radio-fréquence et caractérisation d'oxydes à large bande interdite dopés par de la terre rare

The thesis reports the results of an experimental research on rare earth ion-doping effects on the structural, chemical, optical and near-infra-red photoluminescence properties of wide band gap oxide films. The aim of the work was to develop materials with good photoluminescence properties, which can be applied to increase the photovoltaic conversion efficiency of crystalline Si-based solar cells, through the increase of the most efficient and useful fraction of the solar spectrum which hits the cells, thanks to a photon frequency down-shifting process. Neodymium trivalent ion (Nd3+) was used as dopant of TiO2 and ZnO thin films. The films, with different Nd concentrations were grown onto quartz by RF plasma co-sputtering and annealed at different temperatures (400-800). Different film architectures were investigated for their photoluminescence properties. Structural changes such as phase transformation from anatase to rutile, internal strain building and lattice distortion due to Nd3+ incorporation in titania, correlated with optical changes, were evidenced. Exciting titania and zinc oxide matrices with optimal Nd concentrations, with ultra-violet (UV) light energies equal to or above their gap values resulted in an efficient frequency down-shifting from UV to near-infra-red emission. The joint study of the vibrational, chemical and structural properties of the doped films allows the understanding of the excitation energy transfer process between the matrix to the ion, where self-trapped excitons can be involved. To conclude this study, the doped films were tested as down-shifter layers onto a Si-solar cell where they gave promising results. They were also tested for their photoactivity with methylene blue, showing their inhibitor effect on the photo-degradation of this organic dye molecule.Le travail de thèse a porté sur l étude des effets de dopage de couches minces d oxydes à large bande interdite par des ions de terre rare sur leur propriétés chimiques, structurelles, morphologiques, optiques et de photoluminescence dans le proche infra-rouge. Les couches dopées ont été produites par co-sputtering en radio-fréquence. Le travail a eu pour but de déveloper un matériau fonctionnel photon downshifter , susceptible d être appliqué dans le domaine de conversion photovoltaique sur des cellules solaires à base de silicium, pour en augmenter le rendement. Par ses proprietés de photoluminescence et de downshifting, ce materiau intervient dans ce processus en augmentant la fraction utile du spectre solaire incident sur la cellule. L ion trivalent du neodyme (Nd3+) a été utilisé comme dopant de couches minces de TiO2 et de ZnO, deposées avec différentes concentrations de Nd sur des substrats de quartz et recuits à différentes temperatures, entre 400C et 800C. L étude a mis en evidence des modifications structurelles, des transformation de phase, la creation de tensions mécaniques internes resultant en des distortions importantes du réseau crystallin et corrélées avec des modifications des propriétés optiques et de photoluminescence. L'excitation des matrices de TiO2 et de ZnO dopées avec des concentrations de Nd optimales, avec la radiation UV correspondant à la valeur de la bande interdite, a donné lieu à d intenses emissions dans le proche infra-rouge, grâce à un processus de transfert d energie entre la matrice et l ion Nd3+. L accés à de nombreuses techniques d analyse a permis d accéder à la compréhension du processus de transfert d énergie entre la matrice et l ion, dans lequel des excitons auto-piégés peuvent avoir un rôle. Pour conclure cette étude, les couches de TiO2 dopées ont été testées pour leur function de downshifter sur des cellules solaires à base de silicium, donnant des résultats prometteurs. En testant leur photo-activité en presence de methylène bleu, ces couches ont montré leur caractère inhibiteur de dégradation de cette molecule organique.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF