Staff directory Jeremy David

Jeremy David

Postdoctoral Researcher
Advanced Electron Nanoscopy



  • Ab Initio Structure Determination of Cu2- xTe Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging

    Mugnaioli E., Gemmi M., Tu R., David J., Bertoni G., Gaspari R., De Trizio L., Manna L. Inorganic Chemistry; 57 (16): 10241 - 10248. 2018. 10.1021/acs.inorgchem.8b01445.

    We investigated pseudo-cubic Cu2-xTe nanosheets using electron diffraction tomography and high-resolution HAADF-STEM imaging. The structure of this metastable nanomaterial, which has a strong localized surface plasmon resonance in the near-infrared region, was determined ab initio by 3D electron diffraction data recorded in low-dose nanobeam precession mode, using a new generation background-free single-electron detector. The presence of two different, crystallographically defined modulations creates a 3D connected vacancy channel system, which may account for the strong plasmonic response of this material. Moreover, a pervasive rotational twinning is observed for nanosheets as thin as 40 nm, resulting in a tetragonal pseudo-symmetry. Copyright © 2018 American Chemical Society.

  • Colloidal Ni2-: XCoxP nanocrystals for the hydrogen evolution reaction

    Liu J., Wang Z., David J., Llorca J., Li J., Yu X., Shavel A., Arbiol J., Meyns M., Cabot A. Journal of Materials Chemistry A; 6 (24): 11453 - 11462. 2018. 10.1039/c8ta03485k.

    A cost-effective and scalable approach was developed to produce monodisperse Ni2-xCoxP nanocrystals (NCs) with composition tuned over the entire range (0 ≤ x ≤ 2). Ni2-xCoxP NCs were synthesized using low-cost, stable and low-toxicity triphenyl phosphite (TPP) as a phosphorus source, metal chlorides as metal precursors and hexadecylamine (HDA) as a ligand. The synthesis involved the nucleation of amorphous Ni-P and its posterior crystallization and simultaneous incorporation of Co. The composition, size and morphology of the Ni2-xCoxP NCs could be controlled simply by varying the ratio of Ni and Co precursors and the amounts of TPP and HDA. Ternary Ni2-xCoxP-based electrocatalysts exhibited enhanced electrocatalytic activity toward the hydrogen evolution reaction (HER) compared to binary phosphides. In particular, NiCoP electrocatalysts displayed the lowest overpotential of 97 mV at J = 10 mA cm-2 and an excellent long-term stability. DFT calculations of the Gibbs free energy for hydrogen adsorption at the surface of Ni2-xCoxP NCs showed NiCoP to have the most appropriate composition to optimize this parameter within the whole Ni2-xCoxP series. However, the hydrogen adsorption energy was demonstrated not to be the only parameter controlling the HER activity in Ni2-xCoxP. © The Royal Society of Chemistry 2018.

  • High Thermoelectric Performance in Crystallographically Textured n-Type Bi2Te3- xSex Produced from Asymmetric Colloidal Nanocrystals

    Liu Y., Zhang Y., Lim K.H., Ibáñez M., Ortega S., Li M., David J., Martí-Sánchez S., Ng K.M., Arbiol J., Kovalenko M.V., Cadavid D., Cabot A. ACS Nano; 12 (7): 7174 - 7184. 2018. 10.1021/acsnano.8b03099.

    In the present work, we demonstrate crystallographically textured n-type Bi2Te3-xSex nanomaterials with exceptional thermoelectric figures of merit produced by consolidating disk-shaped Bi2Te3-xSex colloidal nanocrystals (NCs). Crystallographic texture was achieved by hot pressing the asymmetric NCs in the presence of an excess of tellurium. During the hot press, tellurium acted both as lubricant to facilitate the rotation of NCs lying close to normal to the pressure axis and as solvent to dissolve the NCs approximately aligned with the pressing direction, which afterward recrystallize with a preferential orientation. NC-based Bi2Te3-xSex nanomaterials showed very high electrical conductivities associated with large charge carrier concentrations, n. We hypothesize that such large n resulted from the presence of an excess of tellurium during processing, which introduced a high density of donor TeBi antisites. Additionally, the presence in between grains of traces of elemental Te, a narrow band gap semiconductor with a work function well below Bi2Te3-xSex, might further contribute to increase n through spillover of electrons, while at the same time blocking phonon propagation and hole transport through the nanomaterial. NC-based Bi2Te3-xSex nanomaterials were characterized by very low thermal conductivities in the pressing direction, which resulted in ZT values up to 1.31 at 438 K in this direction. This corresponds to a ca. 40% ZT enhancement from commercial ingots. Additionally, high ZT values were extended over wider temperature ranges due to reduced bipolar contribution to the Seebeck coefficient and the thermal conductivity. Average ZT values up to 1.15 over a wide temperature range, 320 to 500 K, were measured, which corresponds to a ca. 50% increase over commercial materials in the same temperature range. Contrary to most previous works, highest ZT values were obtained in the pressing direction, corresponding to the c crystallographic axis, due to the predominance of the thermal conductivity reduction over the electrical conductivity difference when comparing the two crystal directions. © 2018 American Chemical Society.