Magnetron-sputtered Ta3_3N5_5 thin films for water photoelectrolysis

International audienceTa$_3$N$_5$ has aroused interest in the scientific community as a small-band gap semiconductor able to split H 2 O molecules under sunlight illumination. Although its band gap of 2.1eV is highly suited, its synthesis is difficult. In this work, DC magnetron sputtering is used to successfully deposited thin films of Ta$_3$N$_5$ : the influence of the working gas composition Ar/N$_2$ /O$_2$ on the film properties is studied, notably the role of oxygen as a crucial ingredient for the structure. Previous attempts using magnetrons employed RF sputtering and investigated primarily temperature effects. The films were characterized structurally, optically (transmission/reflection spectrophotometry), electrically, chemically and subjected to photocatalytic measurements in 0.1M K$_2$ SO$_4$ aqueous solution adjusted to ph=11 by KOH. We show that variations scale with the O$_2$ flowrate: from amorphous at high O$_2$ flowrates, to Ta$_3$N$_5$ crystallization at reduced O$_2$ flowrate. Photo-spectrometry analyzed with a Tauc-Lorentz oscillator model shows that the band gap scales with the oxygen flowrate, from a metallic behavior to a maximum gap of 2.5 eV. Photocurrent measurements corrected by the conductivity in darkness show an insulating character for all films. Nevertheless the photo-conductivity drops by 9 orders of magnitude with increasing O$_2$ flowrate to reach minimum values around 10$^{-9}$ S/m.

Oxygen incorporated during deposition determines the crystallinity of magnetron-sputtered Ta3N5 films

International audienceTa3N5 belongs to the group of transition metal nitrides with the cation in a high oxidation state. These are typically challenging to synthesize owing to the low reactivity of nitrogen. This applies similarly to Ta3N5 that crystallizes only in the presence of oxygen during synthesis. Typical preparation methods are ammonolysis of oxidized Ta or magnetron sputtering of a Ta target in an atmosphere of Ar, N2 and O2. However, the material typically obtained by either synthesis method is of varying degrees of crystallinity and the key parameter affecting the crystallinity remains elusive. In this study, we examine the role of oxygen for the crystallinity of Ta3N5 samples by studying. Thin film samples prepared by magnetron sputtering reveal that oxygen is indeed the central driver for Ta3N5 crystallinity. While little oxygen in the films yields the metallic δ-TaN phase, excess oxygen results in low crystallinity Ta3N5 or Ta-O-N films. Ta3N5 samples with a high degree of crystallinity are obtained by limiting the oxygen supply to the sample during the deposition. A comparison with other studies suggests a fundamental oxygen incorporation limit above which the crystallinity of Ta3N5 is compromised. The most crystalline sample from this study contains 4.4 at.% of oxygen. It is grown onto a Si(100) substrate, covered with a 30 nm-thick metallic diffusion layer. For this sample, we observe Ta3N5 grains between 80 and 120 nm in size

Do Consonant Sonority and Status Influence Syllable-Based Segmentation Strategies in a Visual Letter Detection Task? Developmental Evidence in French Children

International audienceThis article queries whether consonant sonority (sonorant vs. obstruent) and status (coda vs. onset) within intervocalic clusters influence syllable-based segmentation strategies. We used a modified version of the illusory conjunction paradigm to test whether French beginning, intermediate, and advanced readers were sensitive to an optimal “sonorant coda–obstruent onset” sonority profile within the syllable boundaries as a cue for a syllable-based segmentation. Data showed that children used a syllable-based segmentation that improved with reading skills and age. The results are discussed to support that the visual letter detection within pseudowords primarily and early relies on acoustic-phonetic cues within the syllable boundaries, whereas the syllable effect seems to be developmentally constrained by reading skills and age

The socio-legal implications of the new biotechnologies

This review explores a number of legal-theoretical studies of the encounter between law and biotechnology. Rather than attempt an extensive compilation of scholarship, the review focuses on those studies that have addressed the effects that biotechnologies (understood in the broadest sense) have had on the composition of legal form. Although the relation between law and biotechnology is often seen as being one in which law is applied to biotechnology as a kind of prohibitory limit or regulatory force, this review explores some of the ways in which biotechnological programs have challenged and eroded the conceptual form of law. The hypothesis is that there is an antagonistic relation between law and biotechnology and that this antagonism is brought out in scholarship relating to the key areas in which the encounter between law and biotechnology is played out: intellectual property, governance and regulation, and those domains of law that have incorporated technologies of DNA fingerprinting