Tesis Doctorado
Exploring multiferroic thin films towards molecular adsorptive properties.
Autor
Cabrera, Alejandro
Pontificia Universidad Católica de Chile
Institución
Resumen
Of particular interest is thai anomalies in catalysis have been observed in ferromagnetic and
ferroelectric substrates around the phase transition temperatures. On the other hand, the
research activity of multiferroic materials, which exhibit a coupling between ferroelectric
and ferromagnetic orders, have increased exponentially since ten years ago due lo their
significant technological promise in multifunctional novel devices such as transducers,
electronic phase fihters, fleid effect transistors, and bio-compatible devices. The study of
molecular adsorption and catalysis on multiferroic substrates is an unexplored area iii both
surface and condensed matter sciences. The aim of this thesis is to highlight the correlation
hetween the multiferroic properties of thin films, and ihe molecular adsorption process, in
order lo inquire the physical basis of the sequestration of toxic gases such as CO 2 , CO and
NO.
In this thesis, 1 have summarized relevani experimental procedures and results regarding
thc fabrication and characterization of the promising rnultiferroic material YMnO 1
grown on the semiconductor GaN by molecular beam epitaxy. Several characterization
techniques such as energy dispersive spectroscopy, atomic force microscopy, Auger electron
spectroscopy, x-ray diffraction, local Raman spectroscopy, and x-rays photoelectron
spectroscopy, were performed in order to study the physical properties of the ihin films. It
was found that a fine control of thc growth conditions Icad lo thc formation of intcrcsting
nanostructures, which exhibit an enhancement in the structural, ferroelectric and adsorptive
performance, when cornparing with thin films.
Thermal desorption experimenis were carried out in high vacuurn conditions, by dosing
CO, onto PbNb0Zr0 19Ti077 O3thin films. The CO2adsorption was successfully detected
by measuring the ferroelectric properties, which might lead Lo the development of highly
sensitive gas sensors. Different adsorptive and catalytic behaviors were found when varying
thc ferroelectric state of the substrate. In particular, the inhluence of the electric dipoledipole
interaction between the gas molecule and the substrate was demonstrated, and
different sticking strength and reactivity were found between acid and basic substrates.
The discovery of Ihese intcresting properties aliows the control of selective adsorption and
catalysis of polar molecules on multiferroic substrates.