TY - JOUR AB - Near-resonant Raman scattering measurements of zinc sulfide nanoparticles and thin films have been made and correlated to grain and particle size, respectively, using a 325 nm wavelength excitation source. The area ratios between the first, second, and third order peaks of ZnS identified as the T 2(LO) mode decrease with increasing ZnS grain size. This is an effect attributed to changes in the bandgap energy from quantum confinement due to the varying grain size between the films/particles, as noted by a shift in the room temperature photoluminescence emission corresponding to the free exciton emission energy. While Raman scattering spectroscopy is typically limited to identification of phases and their crystalline properties, it is possible to attain more than such straightforward information by calibrating the spectral features to variations between sets of samples. These results open the possibility of making a quantitative grain size estimation in ZnS thin films and nanostructures, as well as in other material systems where ZnS may be expected as a secondary phase, such as Cu2ZnSnS4. Additionally, more commonly used excitation wavelengths for Raman scattering, such as 514 and 532 nm, are shown to be of limited use in characterizing ZnS thin films due to the extremely low Raman scattering efficiency of ZnS in films with sub-micron thicknesses. AU - Fairbrother, Andrew AU - Izquierdo Roca, Victor AU - Fontané, Xavier AU - Ibáñez, Maria AU - Cabot, Andreu AU - Saucedo, Edgardo AU - Pérez Rodríguez, Alejandro ID - 357 IS - 20 JF - CrystEngComm TI - ZnS grain size effects on near-resonant Raman scattering: Optical non-destructive grain size estimation VL - 16 ER - TY - JOUR AB - An appropriate way of realizing property nanoengineering in complex quaternary chalcogenide nanocrystals is presented for Cu2Cd xSnSey(CCTSe) polypods. The pivotal role of the polarity in determining morphology, growth, and the polytypic branching mechanism is demonstrated. Polarity is considered to be responsible for the formation of an initial seed that takes the form of a tetrahedron with four cation-polar facets. Size and shape confinement of the intermediate pentatetrahedral seed is also attributed to polarity, as their external facets are anion-polar. The final polypod extensions also branch out as a result of a cation-polarity-driven mechanism. Aberration-corrected scanning transmission electron microscopy is used to identify stannite cation ordering, while ab initio studies are used to show the influence of cation ordering/distortion, stoichiometry, and polytypic structural change on the electronic band structure. AU - Zamani, Reza AU - Ibáñez, Maria AU - Luysberg, Martina AU - García Castelló, Nuria AU - Houben, Lothar AU - Prades, Joan AU - Grillo, Vincenzo AU - Dunin Borkowski, Rafal AU - Morante, Joan AU - Cabot, Andreu AU - Arbiol, Jordi ID - 359 IS - 3 JF - ACS Nano TI - Polarity-driven polytypic branching in Cu-based quaternary chalcogenide nanostructures VL - 8 ER - TY - JOUR AB - A robust combiner for hash functions takes two candidate implementations and constructs a hash function which is secure as long as at least one of the candidates is secure. So far, hash function combiners only aim at preserving a single property such as collision-resistance or pseudorandomness. However, when hash functions are used in protocols like TLS they are often required to provide several properties simultaneously. We therefore put forward the notion of robust multi-property combiners and elaborate on different definitions for such combiners. We then propose a combiner that provably preserves (target) collision-resistance, pseudorandomness, and being a secure message authentication code. This combiner satisfies the strongest notion we propose, which requires that the combined function satisfies every security property which is satisfied by at least one of the underlying hash function. If the underlying hash functions have output length n, the combiner has output length 2 n. This basically matches a known lower bound for black-box combiners for collision-resistance only, thus the other properties can be achieved without penalizing the length of the hash values. We then propose a combiner which also preserves the property of being indifferentiable from a random oracle, slightly increasing the output length to 2 n+ω(log n). Moreover, we show how to augment our constructions in order to make them also robust for the one-wayness property, but in this case require an a priory upper bound on the input length. AU - Fischlin, Marc AU - Lehmann, Anja AU - Pietrzak, Krzysztof Z ID - 2852 IS - 3 JF - Journal of Cryptology TI - Robust multi-property combiners for hash functions VL - 27 ER - TY - JOUR AB - Bi2S3-xTex bulk nanocomposites with crystal domain sizes in the range from 50 nm to 100 nm were obtained from the reaction of Bi2S3 nanorods with Te powder. The thermoelectric properties of the obtained nanocomposites were analysed in the temperature range from 0°C to 300°C. We observed how the thermoelectric properties of the material improved with the annealing temperature, being a spark plasma sintering process needed to maintain the material nanostructuration while maximising its electrical properties. Finally thermoelectric dimensionless figures of merit ZT up to 0.42 were obtained before any charge carrier concentration optimisation. Copyright © 2014 Inderscience Enterprises Ltd. AU - Cadavid, Doris AU - Ibáñez, Maria AU - Anselmi Tamburini, Umberto AU - Durá, Oscar AU - De La Torre, Marco AU - Cabot, Andreu ID - 348 IS - 9-11 JF - International Journal of Nanotechnology TI - Thermoelectric properties of bottom up assembled Bi2S 3-xTex nanocomposites VL - 11 ER - TY - JOUR AB - Herein, a colloidal synthetic route to produce highly monodisperse Cu2HgGeSe4 (CHGSe) nanoparticles (NPs) is presented in detail. The high yield of the developed procedure allowed the production of CHGSe NPs at the gram scale. A thorough analysis of their structural and optical properties is shown. CHGSe NPs displayed poly-tetrahedral morphology and narrow size distributions with average size in the range of 10–40 nm and size dispersions below 10 %. A 1.6 eV optical band gap was measured by mean of UV–Vis. By adjusting the cation ratio, an effective control of their electrical conductivity is achieved. The prepared NPs are used as building blocks for the production of CHGSe bulk nanostructured materials. The thermoelectric properties of CHGSe nanomaterials are studied in the temperature range from 300 to 730 K. CHGSe nanomaterials reached electrical conductivities up to 5 × 104 S m−1, Seebeck coefficients above 100 μV K−1, and thermal conductivities below 1.0 W m−1 K−1 which translated into thermoelectric figures of merit up to 0.34 at 730 K. AU - Li, Wenhua AU - Ibáñez, Maria AU - Cadavid, Doris AU - Zamani, Reza AU - Rubio Garcia, Javier AU - Gorsse, Stéphane AU - Morante, Joan AU - Arbiol, Jordi AU - Cabot, Andreu ID - 350 IS - 3 JF - Journal of Nanoparticle Research TI - Colloidal synthesis and functional properties of quaternary Cu based semiconductors: Cu2HgGeSe4 VL - 16 ER -