Atomic layer deposition of aluminum phosphate based on the plasma polymerization of trimethyl phosphate

Aluminum phosphate thin films were deposited by plasma-assisted atomic layer deposition (ALD) using a sequence of trimethyl phosphate (TMP, Me3PO4) plasma, O-2 plasma, and trimethylaluminum (TMA, Me3Al) exposures. In situ characterization was performed, including spectroscopic ellipsometry, optical emission spectroscopy, mass spectrometry and FTIR. In the investigated temperature region between 50 and 320 degrees C, nucleation delays were absent and linear growth was observed, with the growth per cycle (GPC) being strongly dependent on temperature. The plasma polymerization of TMP was found to play an important role in this process, resulting in CVD-like behavior at low temperatures and ALD-like behavior at high temperatures. Films grown at 320 degrees C had a GPC value of 0.37 nm/cycle and consisted of amorphous aluminum pyrophosphate (Al4P6O21). They could be crystallized to triclinic AlPO4 (tridymite) by annealing to 900 degrees C, as evidenced by high-temperature XRD measurements. The use of a TMP plasma might open up the possibility of depositing many other metal phosphates by combining it with appropriate organometallic precursors

Bifunctional earth-abundant phosphate/phosphide catalysts prepared via atomic layer deposition for electrocatalytic water splitting

The development of active and stable earth-abundant catalysts for hydrogen and oxygen evolution is one of the requirements for successful production of solar fuels. Atomic Layer Deposition (ALD) is a proven technique for conformal coating of structured (photo)electrode surfaces with such electrocatalyst materials. Here, we show that ALD can be used for the deposition of iron and cobalt phosphate electrocatalysts. A PE-ALD process was developed to obtain cobalt phosphate films without the need for a phosphidation step. The cobalt phosphate material acts as a bifunctional catalyst, able to also perform hydrogen evolution after either a thermal or electrochemical reduction step

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

In situ study of the thermal stability of supported Pt nanoparticles and their stabilization via atomic layer deposition overcoating

Downscaling of supported Pt structures to the nanoscale is motivated by the augmentation of the catalytic activity and selectivity, which depend on the particle size, shape and coverage. Harsh thermal and chemical conditions generally required for catalytic applications entail an undesirable particle coarsening, and consequently limit the catalyst lifetime. Herein we report an in situ synchrotron study on the stability of supported Pt nanoparticles and their stabilization using atomic layer deposition (ALD) as the stabilizing methodology against particle coarsening. Pt nanoparticles were thermally annealed up to 850 degrees C in an oxidizing environment while recording in situ synchrotron grazing incidence small angle X-ray scattering (GISAXS) 2D patterns, thereby obtaining continuous information about the particle radius evolution. Al2O3 overcoat as a protective capping layer against coarsening via ALD was investigated. In situ data proved that only 1 cycle of Al2O3 ALD caused an augmentation of the onset temperature for particle coarsening. Moreover, the results showed a dependence of the required overcoat thickness on the initial particle size and distribution, being more efficient (i.e. requiring lower thicknesses) when isolated particles are present on the sample surface. The Pt surface accessibility, which is decisive in catalytic applications, was analyzed using the low energy ion scattering (LEIS) technique, revealing a larger Pt surface accessibility for a sample with Al2O3 overcoat than for a sample without a protective layer after a long-term isothermal annealing

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