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Optimizing the growth of Ca2RuO4 for piezotransistors and artificial synapses

Available immediately (October 2019) to ambitious students in applied physics, nanotechnology, and chemical engineering.

Project motivation:

Dicalcium ruthenate (Ca2RuO4) is a Mott insulating oxide material which shows a very strong metal to insulator transition with a resistance change of several orders of magnitude under influence of a small applied pressure at room temperature [1].

This material is highly interesting for use in piezoelectric transistors, where pressure instead is used as the driving force for on/off switching instead of high electric fields that are used in conventional integrated circuits. Piezotransistors could be used to build artificial synapses in neuromorphic computing devices for applications such as  hardware-based machine learning.

Project goal:

We want to epitaxially-grow, single-crystalline Ca2RuO4 thin films by pulsed laser deposition and monitor their electrical and chemical properties under various conditions [2]. Ideally, we will find a set of optimized deposition parameters at which high quality films can be grown on several substrates and a water-dissolvable buffer layer such that we can release the films from the growth substrates and study single-crystalline millimeter sized freestanding membranes under influence of externally applied stimuli such as uniaxial strain [3].

Possible tasks of a MSc student:

  • Grow thin films by pulsed laser deposition (PLD).
  • Perform high resolution X-ray diffraction (XRD) at variable temperatures.
  • Verify the thin film stoichiometry by XPS, EDX, RBS, XRF.
  • Measure electrical properties over a large temperature range (PPMS).
  • If interested, the electronic band structure can be investigated by spectroscopic and optical measurements.
  • If interested, students can get a professional cleanroom training and independently perform photolithography, metal electrode sputtering, and ion etching to fabricate demonstrator devices.

Successful candidates can likely become co-author of a peer-reviewed publication. For more information about background literature, please contact:


Ir. Yorick Birkhölzer, CR 3219,

Prof. dr. ir. Gertjan Koster, CR 3247,

Inorganic Materials Science Group


[1] Nakamura et al., PRB 65, 220402 (2002), “From Mott insulator to ferromagnetic metal: A pressure study of Ca2RuO4”, DOI: 10.1103/PhysRevB.65.220402

[2] Dietl et al., APL 112, 031902 (2018), “Tailoring the electronic properties of Ca2RuO4 via epitaxial strain”, DOI: 10.1063/1.5007680

[3] Birkhölzer and Koster, Nature 570, 39-40 (2019),   “How to make the thinnest possible free-standing sheets of perovskite materials”, DOI: 10.1038/d41586-019-01710-9