Thomas Dobbelaere

Independent tuning of size and coverage of supported Pt nanoparticles using atomic layer deposition

Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl)platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance.The performance of supported nanoparticle catalysts is closely related to their size, shape and interparticle distance. Here, the authors introduce an atomic layer deposition-based strategy to independently tune the size and coverage of platinum nanoparticles with atomic-level precision.

Plasma enhanced atomic layer deposition of zinc sulfide thin films

Zinc sulfide thin films were deposited by plasma enhanced atomic layer deposition (PE-ALD) using diethylzinc and H2S/Ar plasma. The growth characteristics were studied in situ with spectroscopic ellipsometry and ex situ with x-ray reflectometry. The growth was linear and self-limited. Furthermore, it was demonstrated that the growth per cycle was less temperature dependent for the PE-ALD process compared to the thermal process. ZnS thin film properties were investigated ex situ using x-ray photoelectron spectroscopy, x-ray diffraction, ultraviolet/visible optical spectroscopy, and atomic force microscopy. The as-deposited films were crystalline with a transmittance of >90% and a band gap of 3.49 eV. ZnS films deposited by PE-ALD were smoother than films deposited by thermal ALD. The plasma enhanced ALD process may have an advantage for ALD of ternary compounds where different temperature windows have to be matched or for applications where a smooth interface is required.

Plasma-enhanced atomic layer deposition of vanadium phosphate as a lithium-ion battery electrode material

Vanadium phosphate films were deposited by a new process consisting of sequential exposures to trimethyl phosphate (TMP) plasma, O2 plasma, and either vanadium oxytriisopropoxide [VTIP, OV(O-i-Pr)3] or tetrakisethylmethylamido vanadium [TEMAV, V(NEtMe)4] as the vanadium precursor. At a substrate temperature of 300 °C, the decomposition behavior of these precursors could not be neglected; while VTIP decomposed and thus yielded a plasma-enhanced chemical vapor deposition process, the author found that the decomposition of the TEMAV precursor was inhibited by the preceding TMP plasma/O2 plasma exposures. The TEMAV process showed linear growth, saturating behavior, and yielded uniform and smooth films; as such, it was regarded as a plasma-enhanced atomic layer deposition process. The resulting films had an elastic recoil detection-measured stoichiometry of V1.1PO4.3 with 3% hydrogen and no detectable carbon contamination. They could be electrochemically lithiated and showed desirable properties as lithium-ion...

Atomic layer deposition of vanadium oxides for thin-film lithium-ion battery applications

Amorphous VO2 thin films are deposited by atomic layer deposition (ALD) using tetrakis[ethylmethylamino]vanadium (TEMAV) as vanadium precursor and water or ozone as the oxygen source. The crystallisation and oxidation behaviour is investigated for different oxygen partial pressures between ambient air and 3.7 Pa, resulting in phase formation diagrams on SiO2, TiN and Pt substrates, demonstrating a series of stable vanadium oxide phases in the VO2–V2O5 series. Most of the obtained phases exhibit lithium intercalation behaviour in the 1.5–4.5 V vs. Li+/Li potential range, and demonstrate high volumetric capacities in the order of V2O5 < VO2 (B) < V6O13 < V3O7 < V4O9, with the latter at more than twice the capacity of the best commercial cathode materials.