Matt Dawber's group in the Department of Physics and Astronomy at Stony Brook University is focused on the growth, characterization and understanding of ferroelectric materials and other oxides. Besides a general interest in ferroelectric materials the focus in this lab is on producing superlattice materials where interfacial coupling gives rise to either enhanced or totally new behaviour. Ferroelectric materials possess high degrees of functionality making them extremely useful in a broad variety of applications. Find out more on our research overview page.
In-situ x-ray diffraction and the evolution of polarization during the growth of ferroelectric superlattices
Benjamin Bein, Hsiang-Chun Hsing, Sara J. Callori, John Sinsheimer, Priya V. Chinta, Randall L. Headrick, Matthew Dawber
In epitaxially strained ferroelectric thin films and superlattices, the ferroelectric transition temperature can lie above the growth temperature. Ferroelectric polarization and domains should then evolve during the growth of a sample, and electrostatic boundary conditions may play an important role. In this work, ferroelectric domains, surface termination, average lattice parameter and bilayer thickness are simultaneously monitored using in-situ synchrotron x-ray diffraction during the growth of BaTiO3/SrTiO3 superlattices on SrTiO3 substrates by off-axis RF magnetron sputtering. The technique used allows for scan times substantially faster than the growth of a single layer of material. Effects of electric boundary conditions are investigated by growing the same superlattice alternatively on SrTiO3 substrates and 20nm SrRuO3 thin films on SrTiO3 substrates. These experiments provide important insights into the formation and evolution of ferroelectric domains when the sample is ferroelectric during the growth process.
This manuscript is also available on the arxiv: http://arxiv.org/abs/1502.07632
In this video Benjamin Bein explains this work for a general audience
Extrinsic and Intrinsic Charge Trapping at the Graphene/Ferroelectric Interface
M.H. Yusuf, B. Nielsen, M. Dawber, and X. Du
The interface between graphene and the ferroelectric superlattice PbTiO3/SrTiO3 (PTO/STO) is studied. Tuning the transition temperature through the PTO/STO volume fraction minimizes the adorbates at the graphene/ferroelectric interface, allowing robust ferroelectric hysteresis to be demonstrated. “Intrinsic” charge traps from the ferroelectric surface defects can adversely affect the graphene channel hysteresis and can be controlled by careful sample processing, enabling systematic study of the charge trapping mechanism.
This paper is also available on the arXiv at: http://arxiv.org/abs/1408.6169
In-situ x-ray diffraction study of the growth of highly strained epitaxial BaTiO3 thin films
J. Sinsheimer, S. J. Callori, B. Ziegler, B. Bein, P. V. Chinta, A. Ashrafi, R. L. Headrick and M. Dawber
In-situ synchrotron x-ray diffraction was performed during the growth of BaTiO3 thin films on SrTiO3 substrates using both off-axis RF magnetron sputtering and pulsed laser deposition techniques. It was found that the films were ferroelectric during the growth process, and the presence or absence of a bottom SrRuO3 electrode played an important role in the growth of the films. Pulsed laser deposited films on SrRuO3 displayed an anomalously high tetragonality and unit volume, which may be connected to the previously predicted negative pressure phase of BaTiO3.
Engineering polarization rotation in a ferroelectric superlattice
J. Sinsheimer, S.J. Callori, B. Bein, Y. Benkara, J. Daley, J. Coraor, D. Su, P.W. Stephens, and M. Dawber
A key property that drives research in ferroelectric perovskite oxides is their strong piezoelectric response in which an electric field is induced by an applied strain, and vice-versa for the converse piezoelectric effect. We have achieved an experimental enhancement of the piezoelectric response and dielectric tunability in artificially layered epitaxial PbTiO3/CaTiO3 superlattices through an engineered rotation of the polarization direction. As the relative layer thicknesses within the superlattice were changed from sample to sample we found evidence for polarization rotation in multiple x-ray diffraction measurements. Associated changes in functional properties were seen in electrical measurements and piezoforce microscopy. The results demonstrate a new approach to inducing polarization rotation under ambient conditions in an artificially layered thin film.
This paper is also available on the arXiv at http://arxiv.org/abs/1209.3227.
Ferroelectric PbTiO3/SrRuO3 superlattices with broken inversion symmetry
S.J. Callori, J. Gabel, D. Su, J. Sinsheimer, M.V. Fernandez-Serra, M. Dawber
We have fabricated PbTiO3/SrRuO3 superlattices with ultra-thin SrRuO3 layers. Due to the superlattice geometry, the samples show a large anisotropy in their electrical resistivity, which can be controlled by changing the thickness of the PbTiO3 layers. Therefore, along the ferroelectric direction, SrRuO3 layers can act as dielectric, rather than metallic, elements. We show that, by reducing the concentration of PbTiO3, an increasingly important effect of polarization asymmetry due to compositional inversion symmetry breaking occurs. The results are significant as they represent a new class of ferroelectric superlattices, with a rich and complex phase diagram. By expanding our set of materials we are able to introduce new behaviors that can only occur when one of the materials is not a perovskite titanate. Here, compositional inversion symmetry breaking in bi-color superlattices, due to the combined variation of A and B site ions within the superlattice, is demonstrated using a combination of experimental measurements and first principles density functional theory.
This paper is also available on the arXiv at http://arxiv.org/abs/1201.2893
Research in our lab is supported by the National Science Foundation under: