Matthias Filez

Bio: Matthias Filez is an academic researcher from Ghent University. The author has contributed to research in topics: Atomic layer deposition & Bimetallic strip. The author has an hindex of 9, co-authored 13 publications receiving 258 citations.

Low-Temperature Atomic Layer Deposition of Platinum Using (Methylcyclopentadienyl)trimethylplatinum and Ozone

Abstract: Thermal atomic layer deposition (ALD) of platinum is usually achieved using molecular oxygen as the reactant gas and deposition temperatures in the 250–300 °C range. In this work, crystalline thin films of metallic Pt have been grown by ALD at temperatures as low as 100 °C using (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) as the Pt precursor and ozone as the reactant gas. The novel process is characterized by a constant growth rate of 0.45 A per cycle within the 100–300 °C temperature window. The Pt films are uniform with low impurity levels and close-to-bulk resistivities even at the lowest deposition temperature. We show that the initial growth on SiO2 surfaces is nucleation-controlled and islandlike and demonstrate the good conformality of the low-temperature ALD process by Pt deposition on anodic alumina nanopores and mesoporous silica thin films.

Atomic Layer Deposition Route to Tailor Nanoalloys of Noble and Non-Noble Metals.

Abstract: Since their early discovery, bimetallic nanoparticles have revolutionized various fields, including nanomagnetism and optics as well as heterogeneous catalysis. Knowledge buildup in the past decades has witnessed that the nanoparticle size and composition strongly impact the nanoparticle’s properties and performance. Yet, conventional synthesis strategies lack proper control over the nanoparticle morphology and composition. Recently, atomically precise synthesis of bimetallic nanoparticles has been achieved by atomic layer deposition (ALD), alleviating particle size and compositional nonuniformities. However, this bimetal ALD strategy applies to noble metals only, a small niche within the extensive class of bimetallic alloys. We report an ALD-based approach for the tailored synthesis of bimetallic nanoparticles containing both noble and non-noble metals, here exemplified for Pt–In. First, a Pt/In2O3 bilayer is deposited by ALD, yielding precisely defined Pt–In nanoparticles after high-temperature H2 reduc...

The Role of Different Types of CuO in CuO–CeO2/Al2O3 for Total Oxidation

Abstract: Different types of copper oxide in CuO–CeO2/Al2O3 were investigated structurally and catalytically. Standard preparation lead to the presence of CuO monocrystals and Ce1−xCuxO2−x as evidenced by XRD, HRTEM and EDX. Washing with nitric acid removed the monocrystals, while leaving the Ce1−xCuxO2−x solid solution. The Fourier transformed Cu K patterns for the HNO3-washed catalyst showed a diminished second Cu shell, characteristic for Ce1−xCuxO2−x as well as for X-ray amorphous nano-sized CuAl2O4 spinel phase. XANES analysis and first shell Cu fitting confirmed this CuAl2O4 like structure outside Ce1−xCuxO2−x. By modeling the Ce K EXAFS signal in the washed sample, the amount of Cu in Ce1−xCuxO2−x was determined to be 18 ± 6 %. Total oxidation of CO and C3H8 as model reactions showed little difference in activity between non-washed and washed CuO–CeO2/Al2O3, indicating that CuO monocrystals were hardly active at temperatures below 450 °C. XRD performed in situ during TPR and TPO showed that CeO2 in Ce1−xCuxO2−x added to the redox capacity of both CuO–CeO2/Al2O3 samples as it was partially reduced at 300 °C. At higher temperatures, the CuO monocrystals also participated in reaction, leading to a higher activity for the oxidation of CH4.

Unravelling the Formation of Pt–Ga Alloyed Nanoparticles on Calcined Ga-Modified Hydrotalcites by in Situ XAS

Abstract: The chemical transformations taking place during the formation of catalytic Pt–Ga alloyed nanoparticles supported on calcined Ga-modified hydrotalcite Mg(Ga)(Al)Ox are investigated. The starting point is a Pt(acac)2 precursor impregnated onto a Mg(Ga)(Al)Ox support. An oxidative treatment first yields Pt nanoparticles, while subsequent reduction efficiently delivers Ga from the support framework to Pt, forming Pt–Ga alloyed clusters. Different steps are discerned in this process based on in situ XAS analysis. During oxidative heating to 350 °C, the initially adsorbed Pt(acac)2 precursor molecules decompose and form atomically dispersed Pt4+ species with 5-/6-fold oxygen coordination. A fraction of the formed Pt–O bonds consists of strong anchoring points between Pt4+ species and support oxygen, decreasing the Pt mobility induced by the basic support. Further calcination to 650 °C leads to scission of these Pt–O support bonds, allowing more mobile Pt species to form 3–11 atom Pt fcc nanoparticles with an o...

Molecular Interactions Driving the Layer-by-Layer Assembly of Multilayers

Abstract: This work received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. REGPOT-CT2012-316331-POLARIS. The work was also funded by FEDER through the Competitive Factors Operational Program (COMPETE) and by National funds through the Portuguese Foundation for Science and Technology (FCT) in the scope of the projects PTDC/FIS/115048/2009 and PTDC/CTM-BIO/1814/2012. The authors gratefully acknowledge Dr. Luca Gasperini (3B's Research Group, University of Minho, Portugal) for his help with the figures.

Direct and continuous strain control of catalysts with tunable battery electrode materials

Abstract: We report a method for using battery electrode materials to directly and continuously control the lattice strain of platinum (Pt) catalyst and thus tune its catalytic activity for the oxygen reduction reaction (ORR). Whereas the common approach of using metal overlayers introduces ligand effects in addition to strain, by electrochemically switching between the charging and discharging status of battery electrodes the change in volume can be precisely controlled to induce either compressive or tensile strain on supported catalysts. Lattice compression and tension induced by the lithium cobalt oxide substrate of ~5% were directly observed in individual Pt nanoparticles with aberration-corrected transmission electron microscopy. We observed 90% enhancement or 40% suppression in Pt ORR activity under compression or tension, respectively, which is consistent with theoretical predictions.

Conformality in atomic layer deposition : current status overview of analysis and modelling

Abstract: Atomic layer deposition (ALD) relies on alternated, self-limiting reactions between gaseous reactants and an exposed solid surface to deposit highly conformal coatings with a thickness controlled at the submonolayer level. These advantages have rendered ALD a mainstream technique in microelectronics and have triggered growing interest in ALD for a variety of nanotechnology applications, including energy technologies. Often, the choice for ALD is related to the need for a conformal coating on a 3D nanostructured surface, making the conformality of ALD processes a key factor in actual applications. In this work, we aim to review the current status of knowledge about the conformality of ALD processes. We describe the basic concepts related to the conformality of ALD, including an overview of relevant gas transport regimes, definitions of exposure and sticking probability, and a distinction between different ALD growth types observed in high aspect ratio structures. In addition, aiming for a more standardized and direct comparison of reported results concerning the conformality of ALD processes, we propose a new concept, Equivalent Aspect Ratio (EAR), to describe 3D substrates and introduce standard ways to express thin film conformality. Other than the conventional aspect ratio, the EAR provides a measure for the ease of coatability by referring to a cylindrical hole as the reference structure. The different types of high aspect ratio structures and characterization approaches that have been used for quantifying the conformality of ALD processes are reviewed. The published experimental data on the conformality of thermal, plasma-enhanced, and ozone-based ALD processes are tabulated and discussed. Besides discussing the experimental results of conformality of ALD, we will also give an overview of the reported models for simulating the conformality of ALD. The different classes of models are discussed with special attention for the key assumptions typically used in the different modelling approaches. The influence of certain assumptions on simulated deposition thickness profiles is illustrated and discussed with the aim of shedding light on how deposition thickness profiles can provide insights into factors governing the surface chemistry of ALD processes. We hope that this review can serve as a starting point and reference work for new and expert researchers interested in the conformality of ALD and, at the same time, will trigger new research to further improve our understanding of this famous characteristic of ALD processes.