We develop a method of non-perturbative optical control over adiabatic remagnetisation of the nuclear spin system in semiconductors and apply it to study nuclear spin thermodynamics in GaAs microcavities. The nuclear spin system is found to exactly follow the predictions of the spin-temperature theory, despite the quadrupole interactionthat was earlier reported to disrupt nuclear spin thermalisation [2]. These findings open a way to deep cooling of nuclear spins in semiconductor structures, with a prospect of realisation of nuclear spin-ordered states for high fidelity spin-photon interfaces.References[1] A. S. Oja, O. V. Lounasmaa, Rev. Mod. Phys 69, 1 (1997).[2] P. Maletinsky, M. Kroner, A. Imamoglu, Nat. Phys 5, 407 (2009).

The original goal of our study is to synthesize by co-evaporation the phase that could be formed at the interface between polycrystalline p-Cu(In,Ga)Se2 treated with KF and n-CdS. Hence, a new buffer layer, CdIn2S4 (C24), deposited by co-evaporation is presented for the use in thin film solar cells, exhibiting device efficiencies as high as 16.2%, comparable to that obtained on a reference standard CdS-buffered device. The physico-chemical and optical properties of close to stoichiometry 400 nm-thick films of C24 show similar properties to what has been reported in the literature for single crystals. The layer stack used for solar cells is investigated by transmission electron microscopy, showing the formation of an ultrathin Cd-deficient C24 layer at the CIGSe/C24 interface, while a clear lattice match is observed at the C24/ZnO interface. Advanced electrical characterizations of the devices suggest that the output voltage and fill factor of the solar cells based on Cu(In,Ga)Se2/(PVD)C24 are limited by tunneling-enhanced recombination through extended band tail states. These results open new routes to explain the superiority of wet processes used for the junction formation compared to vacuum-based approaches.

$Cu_{2}O{\backslash}ZnO$ nanowires (NWs) heterojunctions were successfully prepared by combining Atomic layer Deposition (ALD) and Electrochemical Deposition (ECD) processes. The crystallinity, morphology and photoconductivity properties of the$Cu_{2}O{\backslash}ZnO$ nanostructures have been investigated. The properties of the $Cu_{2}O$ absorber layer and the nanostructured heterojunction were studied in order to understand the mechanisms lying behind the low photoconductivity measured. It has been found that the interface state defects and the high resistivity of $Cu_{2}O$ film were limiting the photovoltaic properties of the prepared devices. The understanding presented in this work is expected to enable the optimization of solar cell devices based on $Cu_{2}O{\backslash}ZnO$ nanomaterials and improve their overall performance.

Nous discutons les signatures Raman de nanotubes de carbone monofeuillets (single-wall carbon nanotubes,SWNT) et de feuillets de graphène monofeuillets (single layer graphene, SLG) dispersés dans l’eau (fig. 1) et leurorigine physique. Les encres de SWNT sont stabilisées avec des tensio-actifs. Les études optiques dans le procheinfrarouge permettent de mesurer simultanément le signal Raman et le signal de photoluminescence caractéristiquedes nanotubes dispersés à l’échelle individuelle (fig. 2, gauche). Le signal de PL est sensible à l’environnementdiélectrique des nanotubes et permet d’étudier les interactions avec le tensio-actif [1]. A fortes concentrations, lesSWNT forment des phases cristal liquide et l’étude de la polarisation des signaux Raman/PL conduit à la mesure du paramètre d’ordre orientationnel [2]. Les encres de SWNT peuvent être déposées par jet d’encre, les textures des dépôts et leur conductivité électrique dépendent de la concentration des encres [3].
Des encres de graphène SLG, baptisées ‘‘eau de graphène’’ peuvent être préparées sans tensioactif en dispersant despolyélectrolytes de SLG dans de l’eau dégazée [4]. Les signatures Raman des SLG dispersées dans l’eau sontvoisines de celles des SLG suspendues dans l’air (fig. 2), avec des décalages modérés des bandes principales quisont discutées en terme de dopage et de contraintes mécaniques [5]. Les défauts ponctuels observés sur les SLG dispersées dans l’eau peuvent être facilement éliminés par un recuit des dépôts à 800°C.
References
[1] F. Torres-Cañas et al, J. Phys. Chem. C 119 (2015), pp. 703-709
[2] C. Zamora-Ledezma et al, J. Phys. Chem. C 115 (2011), pp. 3272-3278
[3] F. Torres-Cañas et al, Mat. Res. Exp. 4 (2016)
[4] G. Bepete et al, Nature Chem. 9 (2016), pp. 347-352
[5] G. Bepete et al, J. Phys. Chem. C 120 (2016), pp. 28204-28214