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Spin dependent recombination in GaAsN offers many interesting possibilities in the design of spintronic devices mostly due to its astounding capability to reach conduction band electron spin polarizations close to 100% at room temperature. The mechanism behind the spin selective capture of electrons in Ga$^{2+}$ paramagnetic centers is revisited in this paper to address inconsistencies common to most previously presented models. Primarily, these errors manifest themselves as major disagreements with the experimental observations of two key characteristics of this phenomenon: the effective Overhauser-like magnetic field and the width of the photoluminescence Lorentzian-like curves as a function of the illumination power. These features are not only essential to understand the spin dependent recombination in GaAsN, but are also key to the design of novel spintronic devices. Here we demonstrate that the particular structure of the electron capture expressions introduces spurious electron-nucleus correlations that artificially alter the balance between the hyperfine and the Zeeman contributions. This imbalance strongly distorts the effective magnetic field and width characteristics. In this work we propose an alternative recombination mechanism that preserves the electron-nucleus correlations and, at the same time, keeps the essential properties of the spin selective capture of electrons. This mechanism yields a significant improvement to the agreement between experimental and theoretical results. In particular, our model gives results in very good accord with the experimental effective Overhauser-like magnetic field and width data, and with the degree of circular polarization under oblique magnetic fields., Comment: 13 pages, 6 figures

Similar to nitrogen-vacancy centers in diamond and impurity atoms in silicon, interstitial gallium deep paramagnetic centers in GaAsN have been proven to have useful characteristics for the development of spintronic devices. Among other interesting properties, under circularly polarized light, gallium centers in GaAsN act as spin filters that dynamically polarize free and bound electrons reaching record spin polarizations (100\%). Furthermore, the recent observation of the amplification of the spin filtering effect under a Faraday configuration magnetic field has suggested that the hyperfine interaction that couples bound electrons and nuclei permits the optical manipulation of its nuclear spin polarization. Even though the mechanisms behind the nuclear spin polarization in gallium centers are fairly well understood, the origin of nuclear spin relaxation and the formation of an Overhauser-like magnetic field remain elusive. In this work we develop a model based on the master equation approach to describe the evolution of electronic and nuclear spin polarizations of gallium centers interacting with free electrons and holes. Our results are in good agreement with existing experimental observations. In regard to the nuclear spin relaxation, the roles of nuclear dipolar and quadrupolar interactions are discussed. Our findings show that, besides the hyperfine interaction, the spin relaxation mechanisms are key to understand the amplification of the spin filtering effect and the appearance of the Overhauser-like magnetic field. Based on our model's results we propose an experimental protocol based on time resolved spectroscopy. It consists of a pump-probe photoluminescence scheme that would allow the detection and the tracing of the electron-nucleus flip-flops through time resolved PL measurements., Comment: 14 pages, 9 figures

By combining optical spin injection techniques with transport spectroscopy tools, we demonstrate a spin-photodetector allowing for the electrical measurement and active filtering of conduction band electron spin at room temperature in a non-magnetic GaAsN semiconductor structure. By switching the polarization of the incident light from linear to circular, we observe a Giant Spin-dependent Photoconductivity (GSP) reaching up to 40 % without the need of an external magnetic field. We show that the GSP is due to a very efficient spin filtering effect of conduction band electrons on Nitrogen-induced Ga self-interstitial deep paramagnetic centers., Comment: 4 pages, 3 figures

International audience; The organic solvent pretreatment promotes the bioconversion of the organic solid waste. A low acid concentration increases the hydrogen production. Lactate production is favoured by high acid concentration and temperature of the pretreatment.

International audience; Organic solid waste is one of the most promising feedstocks for the implementation of the circular economy principles in waste management. Its anaerobic treatment can indeed promote organic matter conversion into a number of value-added products as well as energy carriers. However, the identification of sustainable strategies to handle organic solid waste in a biorefinery framework still poses technological as well as economic challenges. The aim of this study was in enhancing the potential of the organic fraction of municipal solid waste (OFMSW) to produce bioenergy and biochemicals by combining dark fermentation with a formic acid pretreatment. Hydrogen yields up to 31.6 ml/g VS were obtained pre-treating the OFMSW with 5% formic acid, at 80 � C for 70 min. Concomitantly, a wide range of metabolites of market significance, including acetic acid, butyric acid and ethanol, accumulated. The concentration of these metabolites further enhanced after the dark fermentation of the pretreated substrates. Experimental tests highlighted the influence of the different pretreatment operating conditions on the relative production of hydrogen and main metabolites as well as the related pathways. It was found that the acid concentration plays a key role in promoting the biological conversion of OFMSW and that the adjustment of the operating temperature and treatment time can be targeted towards the production of either building blocks or energy carriers, so as to ensure the viability of the process for its scale up.