Laurent Cario

Simple and Reproducible Procedure to Prepare Self-Nanostructured NiO Films for the Fabrication of P-Type Dye-Sensitized Solar Cells

Porous and nanostructured thin films of NiO (3.5 microm thick) were prepared on FTO coated glass by annealing nickel acetate films obtained by recrystallization under hydrothermal conditions in the presence of hexamethylenetetramine. The photovoltaic performances of the NiO films were optimized with coumarin C343 as sensitizer and iodide/triodide as redox mediator and led to the following values of V(OC), J(SC), ff, and eta: 117 mV, 0.88 mA/cm(2), 0.28, and 0.036% respectively, under AM 1.5. With the improved PMI-NDI dyad as sensitizer and the tris(4,4-bis(tertbutyl)bipyridine) cobalt(II/III) couple as redox mediator, the overall photoconversion efficiency reached 0.16%. An essential advantage of this procedure lies in its good reproducibility offering a reliable strategy to test new dyes and other parameters to improve the photoconversion efficiency of this new type of DSSC.

Pressure dependence of superconducting critical temperature and upper critical field of 2H-NbS2

This work was supported by Spanish MINECO (Consolider-Ingenio CSD2007-00010 and nCSD2009-00013 programs, SAB2009-0057, FIS2011-23488, and MAT2011-27470-C02-02), by the Comunidad de Madrid through program Nanobiomagnet, and by NanoSc-COST program

Rational design of new inorganic compounds with the ZrSiCuAs structure type using 2D building blocks

We have used the concept of 2D building blocks and optimization methods to design (i.e., predict) the composition and the structure of four hypothetical compounds: BaFZnP, BaFZnSb, BaFMnP and SrFZnP. With a high temperature ceramic method and/or a metathesis reaction we have then succeeded to synthesize these compounds. The structure refinement from X-ray powder diffraction patterns have confirmed the structure predictions and showed their good accuracy. The structure of the four compounds (ZrSiCuAs type) results from the alternated stacking of fluorite [AeF] (Ae = Sr, Ba) and anti-fluorite [MPn] (M = Zn, Mn; Pn = P, Sb) 2D building blocks. As shown by band structure calculations these 2D blocks behave as a charge reservoir [AeF]+ and a charge acceptor [MPn]−. The charge transfer between these blocks insures the cohesion of the structure.

P-type transparent conductors Sr1−xNaxFCuS and SrF1−xOxCuS: design, synthesis and physical properties

SrFCuS was synthesized via the ceramic route at 600 °C and characterized by means of EDX analysis, X-ray powder diffraction, optical and electrical measurements. This transparent semi-conducting compound crystallizes in the P4/nmm space group and adopts the ZrSiCuAs structure type. Preliminary DFT band structure calculations revealed that the partial substitution of Na for Sr should create positive charge carriers in the material. The solid solutions Sr1−xNaxFCuS and SrF1−xOxCuS (x = 0.05, 0.1) were then explored. Their optical and electrical characterization confirms the p-type transparent character of these inorganic solids.

Modulation of Defects in Semiconductors by Facile and Controllable Reduction: The Case of p-type CuCrO2 Nanoparticles

Optical and electrical characteristics of solid materials are well-known to be intimately related to the presence of intrinsic or extrinsic defects. Hence, the control of defects in semiconductors is of great importance to achieve specific properties, for example, transparency and conductivity. Herein, a facile and controllable reduction method for modulating the defects is proposed and used for the case of p-type delafossite CuCrO2 nanoparticles. The optical absorption in the infrared region of the CuCrO2 material can then be fine-tuned via the continuous reduction of nonstoichiometric Cu(II), naturally stabilized in small amounts. This reduction modifies the concentration of positive charge carriers in the material, and thus the conductive and reflective properties, as well as the flat band potential. Indeed, this controllable reduction methodology provides a novel strategy to modulate the (opto-) electronic characteristics of semiconductors.

Unravelling the origin of the giant Zn deficiency in wurtzite type ZnO nanoparticles.

Owing to its high technological importance for optoelectronics, zinc oxide received much attention. In particular, the role of defects on its physical properties has been extensively studied as well as their thermodynamical stability. In particular, a large concentration of Zn vacancies in ZnO bulk materials is so far considered highly unstable. Here we report that the thermal decomposition of zinc peroxide produces wurtzite-type ZnO nanoparticles with an extraordinary large amount of zinc vacancies (>15%). These Zn vacancies segregate at the surface of the nanoparticles, as confirmed by ab initio calculations, to form a pseudo core-shell structure made of a dense ZnO sphere coated by a Zn free oxo-hydroxide mono layer. In others terms, oxygen terminated surfaces are privileged over zinc-terminated surfaces for passivation reasons what accounts for the Zn off-stoichiometry observed in ultra-fine powdered samples. Such Zn-deficient Zn1-xO nanoparticles exhibit an unprecedented photoluminescence signature suggesting that the core-shell-like edifice drastically influences the electronic structure of ZnO. This nanostructuration could be at the origin of the recent stabilisation of p-type charge carriers in nitrogen-doped ZnO nanoparticles.

Scanning tunneling measurements of layers of superconducting 2H-TaSe2: Evidence for a zero-bias anomaly in single layers

This work was supported by the EU (ERC Advanced Grant SPINMOL and COST MP-1201), the Spanish MINECO (Consolider-Ingenio in Molecular Nanoscience, CSD2007-00010 and projects FIS2011-23488, MAT2011-25046, MAT2011-22785 nand ACI-2009-0905, co-financed by FEDER), by the Comunidad de Madrid (program Nanobiomagnet) and the Generalitat Valenciana (Programs Prometeo and ISIC-NANO)

Synthesis, structure and magnetic properties of the ternary nitride La3V2N6

Abstract Using gallium as a flux we were able to synthesize the rare earth – transition metal ternary nitride La 3 V 2 N 6 . This compound crystallizes in the tetragonal space group I 4/ mmm (No. 139) with a = b =3.9050(3) A and c =20.215(2) A. It is isostructural with the recently discovered ternary nitrides Ln 3 T 2 N 6 (Ln=La, Ce or Pr; T=Nb or Ta) and with the high T c superconducting copper oxide La 2− x Sr x CaCu 2 O 6 . LAPW band structure calculations show that Ln 3 V 2 N 6 contains VN 2 conducting layers. However, magnetic measurements show that La 3 V 2 N 6 is not a high T c superconductor. A comparison between Ln 3 V 2 N 6 and the cuprates is attempted to understand the discrepancy in their electronic behavior.

Deposition of GaV4S8 thin films by H2S/Ar reactive sputtering for ReRAM applications

The chalcogenide compound GaV4S8 is promising for applications as active materials in non-volatile memory applications. We report here a comprehensive study on the thin-film deposition of this compound using a stoichiometric GaV4S8 target and H2S/Ar reactive sputtering. We show that a fraction of 0.5% to 1% of H2S in the reactive plasma is sufficient to compensate the sulfur deficiency that appears in films deposited in pure Ar plasma. This reactive plasma method allows avoiding the addition of elemental sulfur during the annealing treatment required to obtain a crystallized and stoichiometric GaV4S8 layer. A simple Au/GaV4S8/Au structure presents a resistive switching behaviour well suited for non-volatile memory applications.

A p-Type Zinc-Based Metal–Organic Framework

An original concept for the property tuning of semiconductors is demonstrated by the synthesis of a p-type zinc oxide (ZnO)-like metal-organic framework (MOF), (ZnC2O3H2)n, which can be regarded as a possible alternative for ZnO, a natural n-type semiconductor. When small oxygen-rich organic linkers are introduced to the Zn-O system, oxygen vacancies and a deep valence-band maximum, the two obstacles for generating p-type behavior in ZnO, are restrained and raised, respectively. Further studies of this material on the doping and photoluminescence behaviors confirm its resemblance to metal oxides (MOs). This result answers the challenges of generating p-type behavior in an n-type-like system. This concept reveals that a new category of hybrid materials, with an embedded continuous metal-oxygen network, lies between the MOs and MOFs. It provides concrete support for the development of p-type hybrid semiconductors in the near future and, more importantly, the enrichment of tuning possibilities in inorganic semiconductors.