Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Physics

Supervisor

Lyudmila Goncharova

Abstract

Physical vapor deposition was used to grow good quality crystalline stoichiometric SrTiO3 thin films on Si(001) substrate using a systematic approach starting from understanding of kinetics and thermodynamics of the system and finishing with the development of procedure for high quality SrTiO3/Si interface. Growth of optimized SrTiO3 perovskite structure on Si requires careful transformation of a thin interfacial SrSix layer into the initial SrTiO3 lattice cells. The critical aspects of the growth, such as low temperature and low oxidant partial pressure, are explained in details. Crystallinity and stoichiometry of SrTiO3 were verified using powder x-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). SrTiO3/Si(001) interface was examined with X-ray photoemission spectroscopy (XPS) and RBS and optimum composition can be represented with low concentration (thickness) of strontium silicate phases at the interface (SrxSiyOy) as well as strong signal from strontium titanate peaks. Thicker samples were grown with the developed procedure and were implanted with iron at 2´1016 ions/cm2 for future magnetic characterization.

In parallel to the thin film growth, (001) SrTiO3 single crystals were implanted with iron at doses ranging from 2x1014 to 2x1016 ions/cm2 ­and their magnetic measurements were carried out with superconducting quantum interference device (SQUID). The results show negative susceptibility, predominately diamagnetic behavior which is characteristic of SrTiO3 and small paramagnetic response at low magnetic fields, indicating the possible presence of oxygen/titanium vacancies. Temperature dependence of magnetization measurements did not reveal phase changes. We note that it was difficult to identify any trends between implanted samples most likely due to oxygen contamination of the measurement system. Future experiments are proposed to develop a quantitative and consistent agreement between Fe phases in SrTiO3, SrTiO3 defect concentrations and magnetic responses.

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