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Investigating the Interface of Cobalt Ferrite and Hafnia.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Investigating the Interface of Cobalt Ferrite and Hafnia./
作者:	Cruz, Alexandria.
面頁冊數:	1 online resource (139 pages)
附註:	Source: Dissertations Abstracts International, Volume: 83-04, Section: B.
Contained By:	Dissertations Abstracts International83-04B.
標題:	Silicon. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28445113click for full text (PQDT)
ISBN:	9798728295747

Investigating the Interface of Cobalt Ferrite and Hafnia.
Cruz, Alexandria.

Investigating the Interface of Cobalt Ferrite and Hafnia. - 1 online resource (139 pages)

Source: Dissertations Abstracts International, Volume: 83-04, Section: B.

Thesis (Ph.D.)--North Carolina State University, 2021.

Includes bibliographical references

Magnetoelectric composites have potential to be electric current sensors, attenuators, circulators and signal filters in wireless technology. Magnetoelectric composites are made of two parts: a magnetostrictive component and a piezoelectric component. Magnetostrictive materials generate a magnetic field when they are stretched or compressed. Piezoelectric materials polarize upon application of a force and deform when in an electric field. Magnetoelectric composites depend heavily on the interface between the piezoelectric and magnetostrictive layers. If strain cannot transfer between the piezoelectric and magnetostrictive layers, then the magnetoelectric composite will not work. Cobalt ferrite (CoFe2O4) is the magnetostrictive material in our magnetoelectric composite because it is magnetostrictive without any expensive rare-earth metals. Hafnia (HfO2) is the piezoelectric material because it can be ferroelectric at less than 10nm while other ferroelectric materials lose their ferroelectric properties around 100nm. Hafnia is also leadfree, unlike PZT, which would allow it to be in products in the European Union. The combination of CoFe2O4 and HfO2 is a novel composite that can make smaller magnetoelectric devices. A deeper understanding of the CoFe2O4/HfO2 interface is required for future magnetoelectric devices that are smaller, lead-free, and commercially viable. In order to test our hypothesis that the CoFe2O4/HfO2 interface is stable, we needed to characterize the evolution of crystallographic phases, the roughness of the interface, and the diffusion of chemical elements across the interface.Samples of CoFe2O4/HfO2 were made on silicon (Si) wafers and annealed at different temperatures to examine how the interfaces changed with temperature. Diffusion, formation of secondary phases, and the connectivity of CoFe2O4 and HfO2 phases were studied. The 4 types of samples studied were: 1) unannealed [referred to as Unannealed], 2) annealed at 500°C for 60 seconds [referred to as 500°C], 3) annealed at 800°C for 60 seconds [referred to as 800°C], and 4) annealed at 800°C for 1 hr [referred to as Extreme Conditions].We deployed a variety of relevant characterization tools including x-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and time of flight secondary ion mass spectrometry. These tools provided useful information about the stability of the interface, increasing our fundamental knowledge of the CoFe2O4/HfO2 interfacial science. X-ray diffraction confirmed the crystalline CoFe2O4 and HfO2 phases for 500°C, 800°C, and Extreme Conditions. Transmission electron microscopy revealed that voids/partial voids formed at the CoFe2O4/HfO2 interface when the sample was annealed at 500°C.Unannealed has no voids and 500°C showed little to no voids. 800°C showed numerous partial voids and Extreme Conditions had larger partial voids than 800°C. Energy dispersive spectroscopy showed that there was strong Co diffusion at the CoFe2O4/SiO2 interface while Unannealed and 500°C showed less Co diffusion. Surprisingly, Extreme Conditions showed no Co diffusion. TOF-SIMS showed that Unannealed and 500°C have nearly identical elemental profiles. TOF-SIMS's sensitivity also showed that Fe and Si start to diffuse into other layers at 800°C. In contrast, this diffusion was not detectable by energy dispersive spectroscopy. With this data, CoFe2O4 and HfO2 de-adhere from each other, because the CoFe2O4/HfO2 interfacial energy is greater than the surface energy of both CoFe2O4 and HfO2 combined.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798728295747Subjects--Topical Terms:

669429
Silicon.
Index Terms--Genre/Form:

542853
Electronic books.

Investigating the Interface of Cobalt Ferrite and Hafnia.
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500 $a Source: Dissertations Abstracts International, Volume: 83-04, Section: B.
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502 $a Thesis (Ph.D.)--North Carolina State University, 2021.
504 $a Includes bibliographical references
520 $a Magnetoelectric composites have potential to be electric current sensors, attenuators, circulators and signal filters in wireless technology. Magnetoelectric composites are made of two parts: a magnetostrictive component and a piezoelectric component. Magnetostrictive materials generate a magnetic field when they are stretched or compressed. Piezoelectric materials polarize upon application of a force and deform when in an electric field. Magnetoelectric composites depend heavily on the interface between the piezoelectric and magnetostrictive layers. If strain cannot transfer between the piezoelectric and magnetostrictive layers, then the magnetoelectric composite will not work. Cobalt ferrite (CoFe2O4) is the magnetostrictive material in our magnetoelectric composite because it is magnetostrictive without any expensive rare-earth metals. Hafnia (HfO2) is the piezoelectric material because it can be ferroelectric at less than 10nm while other ferroelectric materials lose their ferroelectric properties around 100nm. Hafnia is also leadfree, unlike PZT, which would allow it to be in products in the European Union. The combination of CoFe2O4 and HfO2 is a novel composite that can make smaller magnetoelectric devices. A deeper understanding of the CoFe2O4/HfO2 interface is required for future magnetoelectric devices that are smaller, lead-free, and commercially viable. In order to test our hypothesis that the CoFe2O4/HfO2 interface is stable, we needed to characterize the evolution of crystallographic phases, the roughness of the interface, and the diffusion of chemical elements across the interface.Samples of CoFe2O4/HfO2 were made on silicon (Si) wafers and annealed at different temperatures to examine how the interfaces changed with temperature. Diffusion, formation of secondary phases, and the connectivity of CoFe2O4 and HfO2 phases were studied. The 4 types of samples studied were: 1) unannealed [referred to as Unannealed], 2) annealed at 500°C for 60 seconds [referred to as 500°C], 3) annealed at 800°C for 60 seconds [referred to as 800°C], and 4) annealed at 800°C for 1 hr [referred to as Extreme Conditions].We deployed a variety of relevant characterization tools including x-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and time of flight secondary ion mass spectrometry. These tools provided useful information about the stability of the interface, increasing our fundamental knowledge of the CoFe2O4/HfO2 interfacial science. X-ray diffraction confirmed the crystalline CoFe2O4 and HfO2 phases for 500°C, 800°C, and Extreme Conditions. Transmission electron microscopy revealed that voids/partial voids formed at the CoFe2O4/HfO2 interface when the sample was annealed at 500°C.Unannealed has no voids and 500°C showed little to no voids. 800°C showed numerous partial voids and Extreme Conditions had larger partial voids than 800°C. Energy dispersive spectroscopy showed that there was strong Co diffusion at the CoFe2O4/SiO2 interface while Unannealed and 500°C showed less Co diffusion. Surprisingly, Extreme Conditions showed no Co diffusion. TOF-SIMS showed that Unannealed and 500°C have nearly identical elemental profiles. TOF-SIMS's sensitivity also showed that Fe and Si start to diffuse into other layers at 800°C. In contrast, this diffusion was not detectable by energy dispersive spectroscopy. With this data, CoFe2O4 and HfO2 de-adhere from each other, because the CoFe2O4/HfO2 interfacial energy is greater than the surface energy of both CoFe2O4 and HfO2 combined.
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538 $a Mode of access: World Wide Web
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650 4 $a Energy. $3 876794
650 4 $a Lead content. $3 3687496
650 4 $a Cobalt. $3 3682549
650 4 $a Magnetism. $3 524508
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650 4 $a Morphology. $3 591167
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