Prof. Dr. Matjaž Spreitzer

2008/3: Doctor of Chemical Technology, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Slovenia and Advanced Materials Department, Jožef Stefan Institute, Slovenia

Doctoral Thesis: “Influence of synthesis and structural characteristics on electrical properties of Na0.5Bi0.5TiO3-based voltage-tunable materials”

2003/8: Bachelor of Chemical Engineering, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Slovenia

2018/4 - present: Head of Department, Advanced Materials Department, Jožef Stefan Institute

2024/3 - present: Research Counsellor, Advanced Materials Department, Jožef Stefan Institute

2018/1 - 2024/3: Senior research associate, Advanced Materials Department, Jožef Stefan Institute

2017/8 - 2018/3: Assistant head, Advanced Materials Department, Jožef Stefan Institute

2016/10 - present: Assistant Professor of Materials Science and Engineering at University of Ljubljana, Faculty of Chemistry and Chemical Technology

2012/12 - 2018/1: Research associate, Advanced Materials Department, Jožef Stefan Institute

2008/3 - 2012/12: Postdoctoral researcher, Advanced Materials Department, Jožef Stefan Institute

2010/4 - 2011/4: Postdoctoral researcher, Inorganic Materials Science Group, group of prof. Guus Rijnders, Faculty of Science & Technology, University of Twente, The Netherlands

2017 - 2021: Member of Jožef Stefan Institute Investment Committee

Review of JSI investment strategy, investment analysis and monitoring.

Slovenian Smart Specialization Strategy (S4)

Preparation of strategic documents, related to Advanced Manufacturing Systems and New Materials within in the Factories of the Future domain. 

Silicon-oxide integration

For silicon-oxide interfaces we determined a new PLD-based pathway for components integration. For the first time we experimentally demonstrated a sub-monolayer control of Sr coverage using PLD and successful preparation of a reconstructed Si surface passivated with 1/2ML of Sr. Alternatively, we managed to reconstruct silicon also using SrO, which is chemically more stable compared to metallic Sr and thus outlines the importance of our achievement. For preparation of the STO layer on passivated Si we determined a complete protocol for epitaxial integration, taking into account the peculiarities of the PLD process. We observed that parameters for deposition and oxidation periods play a crucial role on the quality of the STO layer and the interface and have to be separated in time, while the reaction between STO and Si has to be kinetically trapped to minimize the thickness of the interface layer. These results present a milestone in the silicon-oxide integration and open a new technological route for oxide electronics, which demonstrate rich functionalities beyond the state-of-the-art silicon platform. Results have been published in several high-ranking journals (J. Mater. Chem. C, ACS Appl. Mater. Interfaces, Appl. Phys. Lett., etc.). 

Dielectric ceramics

In the field of dielectric materials we focused on research of ceramics for voltage-tunable microwave applications. For Ag(NbxTa1-x)O3 system we determined solid-state reaction mechanism and protocol for preparation of single-phase ceramics. We also described the relation between voltage tunability and material`s polar order, which normally combines ferroelectric and antiferroelectric response. These results enabled us to complete Ag(NbxTa1-x)O3 phase diagram. For similar applications we also investigated Na0.5Bi0.5TiO3–SrTiO3 system, especially high-temperature reactions and the effect of oxygen overpressure on matrix`s stoichiometry. Cubic symmetry of these relaxor-like materials was explained in details using high-resolution XRD studies. For Na0.5Bi0.5TiO3–SrTiO3 system we also formed layered heterostructures with temperature stable dielectric characteristics.

Nanoparticles

Part of my research was also directed on the hydrothermal and solvothermal synthesis of cobalt ferrite nanoparticles (CFO), which were further integrated with piezoelectric materials into magnetoelectric composites. We investigated the effect of oleic acid concentration on the physicochemical properties of derived nanoparticles. Conditions for preparation of well-dispersed, non-agglomerated spherical particles of about 6 nm were determined, as a result of bridging bidentate interactions between the oleic acid molecules and the metal atoms on the surface of the nanoparticles. We also observed that these interactions affect the surface strain of nanoparticles considerably, as well as their magnetic properties, which become superparamagnetic at a critical concentration with decreased surface anisotropy. In addition to CFO we also investigated formation of SrTiO3 single-crystalline nanoparticles in relation to their structural defects.