One challenge of investigating ferroelectrics at the nanoscale has been controlling the stoichiometry during growth. Historically, the growth of barium titanate (BaTiO3) by molecular beam epitaxy has relied on a growth technique called shuttered RHEED. Shuttered RHEED controls the stoichiometry of barium titanate through the precise deposition of alternating layers of BaO and TiO2. While this approach has achieved 1% control of stoichiometry, finding self-limiting mechanisms to lock-in stoichiometry has been the focus of the growth community. The Goldschmidt tolerance factor predicts an unstable perovskite when barium sits in the titanium lattice site. The BaO-TiO2 phase diagram predicts a low-solubility (<100 ppm) of excess barium oxide at molecular beam epitaxy (MBE) growth temperatures of 600-800 °C. We show that excess barium provided during MBE growth is a self-limiting mechanism to grow stoichiometric barium titanate thin films.
Features in RHEED oscillations were identified for both shuttered RHEED and co-deposition that confirm barium rich growth condition. Barium-rich growth condition was confirmed to lead to bulk BTO values for out-of-plane lattice constant, Ti/Ba ratio, and piezoelectric coefficient for 40 nm thick BTO thin films. Angle-resolved x-ray photoelectron spectroscopy studies show that excess barium accumulates at the surface in the form of a barium-rich surface layer referred to here as BaO. For titanium-rich growth condition, the layer assumed stoichiometric bulk BTO values. The excess barium accumulated at the surface was removed with methanol sonication.
Barium titanate thin films were shown to self-assemble when excess barium was provided during co-deposition. A systematic comparison of 5 nm thick BTO films grown comparing the shuttered RHEED and co-deposition growth approaches was performed to prove that excess barium doesn’t incorporate into the film but only as BaO at the surface. Both growth approaches produce identical out-of-plane lattice parameter, Ti/Ba ratio, and piezoelectric coefficients. An enhancement in the d33 for the 5 nm thin films compared to the 40 nm thin films was also observed. The compressive strain on 5 nm thin films enhanced the polarization over fully relaxed 40 nm thin films.
","abstract_html":"<p>One challenge of investigating ferroelectrics at the nanoscale has been controlling the stoichiometry during growth. Historically, the growth of barium titanate (BaTiO3) by molecular beam epitaxy has relied on a growth technique called shuttered RHEED. Shuttered RHEED controls the stoichiometry of barium titanate through the precise deposition of alternating layers of BaO and TiO2. While this approach has achieved 1% control of stoichiometry, finding self-limiting mechanisms to lock-in stoichiometry has been the focus of the growth community. The Goldschmidt tolerance factor predicts an unstable perovskite when barium sits in the titanium lattice site. The BaO-TiO2 phase diagram predicts a low-solubility (<100 ppm) of excess barium oxide at molecular beam epitaxy (MBE) growth temperatures of 600-800 °C. We show that excess barium provided during MBE growth is a self-limiting mechanism to grow stoichiometric barium titanate thin films. </p> <p>Features in RHEED oscillations were identified for both shuttered RHEED and co-deposition that confirm barium rich growth condition. Barium-rich growth condition was confirmed to lead to bulk BTO values for out-of-plane lattice constant, Ti/Ba ratio, and piezoelectric coefficient for 40 nm thick BTO thin films. Angle-resolved x-ray photoelectron spectroscopy studies show that excess barium accumulates at the surface in the form of a barium-rich surface layer referred to here as BaO. For titanium-rich growth condition, the layer assumed stoichiometric bulk BTO values. The excess barium accumulated at the surface was removed with methanol sonication. </p> <p>Barium titanate thin films were shown to self-assemble when excess barium was provided during co-deposition. A systematic comparison of 5 nm thick BTO films grown comparing the shuttered RHEED and co-deposition growth approaches was performed to prove that excess barium doesn’t incorporate into the film but only as BaO at the surface. Both growth approaches produce identical out-of-plane lattice parameter, Ti/Ba ratio, and piezoelectric coefficients. An enhancement in the d33 for the 5 nm thin films compared to the 40 nm thin films was also observed. The compressive strain on 5 nm thin films enhanced the polarization over fully relaxed 40 nm thin films. </p>","abstract_has_math":false,"creators":["Morgan, Timothy Allen"],"institution":null,"degree_name":"Doctor of Philosophy in Microelectronics-Photonics (PhD)","degree_level":"Dissertation","degree_discipline":null,"degree_department":null,"school":null,"contributors":["Bellaiche, Laurent","Churchill, Hugh O.H."],"advisors":["Salamo, Gregory J."],"committee_chairs":[],"committee_members":[],"year":2018,"date_issued":"2018-05-01T07:00:00Z","date_published":"2018-05-01T07:00:00Z","updated_at":"2026-07-24T00:59:32Z","subjects":["Ferroelectrics","Molecular Beam Epitaxy","Piezoforce Microscopy","X-ray Photoelectron Spectroscopy","Metallurgy","Nanoscience and Nanotechnology","Polymer and Organic Materials"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://scholarworks.uark.edu/etd/2817","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Bellaiche, Laurent","Churchill, Hugh O.H."]},{"key":"dc:contributor.advisor","label":"Advisor","values":["Salamo, Gregory J."]},{"key":"dc:creator","label":"Author","values":["Morgan, Timothy Allen"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2018"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2021-11-04T07:00:00Z"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy in Microelectronics-Photonics (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Ferroelectrics","Molecular Beam Epitaxy","Piezoforce Microscopy","X-ray Photoelectron Spectroscopy","Metallurgy","Nanoscience and Nanotechnology","Polymer and Organic Materials"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://scholarworks.uark.edu/etd/2817"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["One challenge of investigating ferroelectrics at the nanoscale has been controlling the stoichiometry during growth. Historically, the growth of barium titanate (BaTiO3) by molecular beam epitaxy has relied on a growth technique called shuttered RHEED. Shuttered RHEED controls the stoichiometry of barium titanate through the precise deposition of alternating layers of BaO and TiO2. While this approach has achieved 1% control of stoichiometry, finding self-limiting mechanisms to lock-in stoichiometry has been the focus of the growth community. The Goldschmidt tolerance factor predicts an unstable perovskite when barium sits in the titanium lattice site. The BaO-TiO2 phase diagram predicts a low-solubility (<100 ppm) of excess barium oxide at molecular beam epitaxy (MBE) growth temperatures of 600-800 °C. We show that excess barium provided during MBE growth is a self-limiting mechanism to grow stoichiometric barium titanate thin films.
Features in RHEED oscillations were identified for both shuttered RHEED and co-deposition that confirm barium rich growth condition. Barium-rich growth condition was confirmed to lead to bulk BTO values for out-of-plane lattice constant, Ti/Ba ratio, and piezoelectric coefficient for 40 nm thick BTO thin films. Angle-resolved x-ray photoelectron spectroscopy studies show that excess barium accumulates at the surface in the form of a barium-rich surface layer referred to here as BaO. For titanium-rich growth condition, the layer assumed stoichiometric bulk BTO values. The excess barium accumulated at the surface was removed with methanol sonication.
Barium titanate thin films were shown to self-assemble when excess barium was provided during co-deposition. A systematic comparison of 5 nm thick BTO films grown comparing the shuttered RHEED and co-deposition growth approaches was performed to prove that excess barium doesn’t incorporate into the film but only as BaO at the surface. Both growth approaches produce identical out-of-plane lattice parameter, Ti/Ba ratio, and piezoelectric coefficients. An enhancement in the d33 for the 5 nm thin films compared to the 40 nm thin films was also observed. The compressive strain on 5 nm thin films enhanced the polarization over fully relaxed 40 nm thin films.
"]},{"key":"dc:title","label":"Title","values":["Self-Assembled Barium Titanate Nanoscale Films by Molecular Beam Epitaxy"]}]}],"canonical_facts":{"dc:contributor":["Bellaiche, Laurent","Churchill, Hugh O.H."],"dc:contributor.advisor":["Salamo, Gregory J."],"dc:creator":["Morgan, Timothy Allen"],"dc:date":["2018"],"dc:date.available":["2021-11-04T07:00:00Z"],"dc:description.abstract":["One challenge of investigating ferroelectrics at the nanoscale has been controlling the stoichiometry during growth. Historically, the growth of barium titanate (BaTiO3) by molecular beam epitaxy has relied on a growth technique called shuttered RHEED. Shuttered RHEED controls the stoichiometry of barium titanate through the precise deposition of alternating layers of BaO and TiO2. While this approach has achieved 1% control of stoichiometry, finding self-limiting mechanisms to lock-in stoichiometry has been the focus of the growth community. The Goldschmidt tolerance factor predicts an unstable perovskite when barium sits in the titanium lattice site. The BaO-TiO2 phase diagram predicts a low-solubility (<100 ppm) of excess barium oxide at molecular beam epitaxy (MBE) growth temperatures of 600-800 °C. We show that excess barium provided during MBE growth is a self-limiting mechanism to grow stoichiometric barium titanate thin films.
Features in RHEED oscillations were identified for both shuttered RHEED and co-deposition that confirm barium rich growth condition. Barium-rich growth condition was confirmed to lead to bulk BTO values for out-of-plane lattice constant, Ti/Ba ratio, and piezoelectric coefficient for 40 nm thick BTO thin films. Angle-resolved x-ray photoelectron spectroscopy studies show that excess barium accumulates at the surface in the form of a barium-rich surface layer referred to here as BaO. For titanium-rich growth condition, the layer assumed stoichiometric bulk BTO values. The excess barium accumulated at the surface was removed with methanol sonication.
Barium titanate thin films were shown to self-assemble when excess barium was provided during co-deposition. A systematic comparison of 5 nm thick BTO films grown comparing the shuttered RHEED and co-deposition growth approaches was performed to prove that excess barium doesn’t incorporate into the film but only as BaO at the surface. Both growth approaches produce identical out-of-plane lattice parameter, Ti/Ba ratio, and piezoelectric coefficients. An enhancement in the d33 for the 5 nm thin films compared to the 40 nm thin films was also observed. The compressive strain on 5 nm thin films enhanced the polarization over fully relaxed 40 nm thin films.
"],"dc:identifier":["https://scholarworks.uark.edu/etd/2817"],"dc:subject":["Ferroelectrics","Molecular Beam Epitaxy","Piezoforce Microscopy","X-ray Photoelectron Spectroscopy","Metallurgy","Nanoscience and Nanotechnology","Polymer and Organic Materials"],"dc:title":["Self-Assembled Barium Titanate Nanoscale Films by Molecular Beam Epitaxy"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy in Microelectronics-Photonics (PhD)"]},"updated_at":"2026-07-24T00:59:32Z"}