Implementacja zewnętrznych czynników - pola magnetycznego i elektrycznego oraz odkształcenia – w technologii epitaksji z wiązek molekularnych: realizacja i przykłady zastosowań
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Adam Dziwoki PhD thesis.pdf (12.23 MB)
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0000-0002-8196-8085 Date
2026
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Instytut Katalizy i Fizykochemii Powierzchni im. Jerzego Habera Polskiej Akademii Nauk
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Abstract
The aim of the doctoral dissertation was to develop a new technology for the growth of epitaxial layers and nanostructures using molecular beam epitaxy (MBE) with the application of external electromagnetic and mechanical factors: electric field, magnetic field and deformation. The MBE method is a powerful tool in modern technologies covering electronic, optoelectronic, spintronic and sensory applications. However, despite its advantages, MBE has certain limitations related to: (i) the demanding ultra-high vacuum (UHV) environment, (ii) complicated sample preparation, and (iii) restrictions on the use of special conditions during the growth of epitaxial heterostructures and their post-growth processing. In the standard MBE method, the layer growth process is controlled by substrate temperature, deposition rate and gas partial pressure in the case of reactive deposition. Other factors, including external ones such as electric and magnetic fields, are increasingly being used in material synthesis. For example, high-temperature annealing in a magnetic field (MF) is a routine procedure for shaping the magnetic anisotropy of materials. However, external factors are virtually absent in MBE processes under UHV conditions and during in situ processing after deposition, mainly due to the lack of suitable technological solutions.
The dissertation describes UHV technology, the types of components used, and the reconstruction of the experimental system, which was then used for technological testing. The system was adapted by modifying the manipulators and the transfer system. The current solution allows research to be conducted using two commonly used types of holders: PTS – a universal functional base, and FLAG – a simple plate for mounting the substrate. The key idea behind the solution is the interchangeability of PTS and FLAG holders, so that each standard can be used independently. The most important part of the work describes sample holders. Magnetic, electrical and mechanical stimuli are transferred to the sample using a combination of magnets, coils, electrodes and actuators integrated into dedicated PTS holders. Several PTS holders act as adapters for FLAG holders, and the FLAG plate with the substrate can be transferred between different PTS adapters for subsequent sample preparation steps (substrate cleaning, deposition, annealing) performed with or without various external stimuli. In addition, external fields can be used during in situ sample characterization: electrical transport measurements and MOKE (magneto-optical Kerr effect) magnetometry. Two types of PTS adapters with magnetic fields have been developed. The concept of permanent magnet holders focused on epitaxial growth and annealing after deposition in two magnetic field (MF) geometries: in the plane and perpendicular to the sample plane. Two versions of the solutions were optimized: (i) for maximum MF and (ii) for a combination of MF and high temperatures. PTS adapters with variable MF were implemented using a small electromagnet with a soft iron core. The electromagnets were optimized for maximum MF enabling MOKE measurements. The developed units provided field geometries for MOKE measurements: polar (P-MOKE), longitudinal (L-MOKE) and transversal (T-MOKE). For the use of electric field (EF) in the plane or transport measurements, four additional contacts were provided in the PTS station of the manipulator in the preparation/analysis chamber. They enable the transmission of electrical signals to the sample mounted on the PTS holder via spring connections to the appropriate contacts. The PTS manipulator station has a cooling function by pressing a cold finger against the PTS holder. This function has been used to bend the substrate. A movable piston, pushed by a cold finger, presses against the flexible substrate, causing a change in its curvature. The substrate can be bent both during sample preparation and growth processes, as well as after growth. By using different methods of fixing the substrate, bending with compressive or tensile stress can be achieved.
The effectiveness of the proposed technological solutions was verified in a series of experiments. In order to verify the role of MF applied during growth, reactive growth of Fe₃O₄(111) layers on MgO(111) was selected. A significant influence of MF on magnetic properties was demonstrated. Using in situ scanning tunneling microscopy and conversion electron Mössbauer spectroscopy (CEMS) as well as ex situ MOKE, it was shown that a moderate MF of 0.1 T applied in the plane during the reactive deposition of a 10 nm Fe₃O₄(111) layer induces a distinct perpendicular magnetic anisotropy. PTS adapters with electromagnets can generate the magnetic fields required for all MOKE geometries, but their use is limited to samples with moderate saturation fields not exceeding 100 mT. As an example of application, the results of MOKE measurements for a Pt/Co/Pt/MgO(111) heterostructure are presented, in which the thickness of the Co layer gradually changes from 0 to 2 nm. Magnetic loops showed that cobalt layers exhibit perpendicular magnetization below 0.6 nm, at which thickness the spin reorientation transition (SRT) begins. As an example of in situ electrical transport measurement, studies of the resistivity of ultra-thin Fe₃O₄(111) magnetite layers deposited on MgO(111) are presented. To investigate the effect of bending stresses on magnetic properties, epitaxial cobalt layers on Au(111)/mica were selected. This system is known for the self-organization of cobalt induced by a specific reconstruction of the gold surface, known as ‘herringbone’, occurring in three domains at an angle of 120°, which results in a threefold symmetry of the magnetic properties of the cobalt layers. The dissertation shows that the application of stress during preparation resulted in the elimination of the triaxial symmetry of the magnetic anisotropy of the cobalt layer. The last chapter of the thesis summarizes the main results and presents possible directions for further research.
Description
The research was carried out as part of the 5th edition of the program of the Ministry of Education and Science (currently the Ministry of Science and Higher Education) ‘Implementation Doctorate’ program at the Jerzy Haber Institute of Catalysis and Surface Chemistry of the Polish Academy of Sciences in cooperation with an industrial partner, Prevac Sp. z o.o., and as part of the OPUS project of the National Science Centre No. 2020/39/B/ST5/01838 entitled: ‘Functional layers and nanostructures obtained by molecular beam epitaxy assisted by external factors’.
Citation
Dziwoki, Adam., "Implementacja zewnętrznych czynników - pola magnetycznego i elektrycznego oraz odkształcenia – w technologii epitaksji z wiązek molekularnych: realizacja i przykłady zastosowań." Praca doktorska, Instytut Katalizy i Fizykochemii Powierzchni im. Jerzego Habera Polskiej Akademii Nauk, 2026.
https://open.icm.edu.pl/handle/123456789/27040