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Epitaxial Growth and Atomic Scale Imaging of Bismuth, Manganese Nitride, and Manganese Gallium Thin Films /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Epitaxial Growth and Atomic Scale Imaging of Bismuth, Manganese Nitride, and Manganese Gallium Thin Films // Ashok Shrestha.
Author:	Shrestha, Ashok,
Description:	1 electronic resource (121 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 87-01, Section: B.
Contained By:	Dissertations Abstracts International87-01B.
Subject:	Physics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=32184359
ISBN:	9798286450473

Epitaxial Growth and Atomic Scale Imaging of Bismuth, Manganese Nitride, and Manganese Gallium Thin Films /
Shrestha, Ashok,

Epitaxial Growth and Atomic Scale Imaging of Bismuth, Manganese Nitride, and Manganese Gallium Thin Films /Ashok Shrestha. - 1 electronic resource (121 pages)

Source: Dissertations Abstracts International, Volume: 87-01, Section: B.

This study investigates the growth and surface characterization of bismuth-nitrogen alloy on MgO (001), transition metal nitride Mn2N on MgO (001), and Kagome Mn3Ga on GaN (0001) substrates. Molecular beam epitaxy was used to grow thin films and various in-situ and ex-situ techniques were used for the surface and structural investigation of the grown samples under ultra-high vacuum condition.The first project begins with the aim of growing an alloy of a topological material. We attempted to grow a thin film of BiN by co-deposition of bismuth and nitrogen on rock-salt structure MgO (001) substrates. Furthermore, we studied the effect of variation of the growth temperature and the nitrogen to bismuth flux ratios on sample growth. For the samples grown and conditions used, we do not find strong evidence for the formation of a bulk Bi-N alloy. Even for very high nitrogen to bismuth flux ratio, we observed only bismuth and no nitrogen using bulk Rutherford back-scattering spectroscopy measurements, and only 1-2% nitrogen was seen through surface Auger electron spectroscopy measurements. The in-plane lattice measurements show that the resulting Bi (110) samples are strained, which is presumably caused by lattice mismatch between the sample and the substrate when grown without any buffer layer. The use of a high-temperature buffer layer helps to release strain in the sample but only along one axis. Measurements of the atomic layer spacing using X-ray diffraction and also scanning tunneling microscopy confirm the Bi (110) thin film sample structure.The growth mechanism and strain induced surface structures of thin film due to the lattice mismatch and symmetry mismatch between samples and substrates were studied in the next project. One example of such a system is the growth of hexagonal material on top of a cubic substrate. The thin films of c-plane dominated hexagonal ζ- phase Mn2N were successfully grown on a cubic MgO (001) substrate directly using plasma-assisted molecular beam epitaxy. The surface was comprehensively studied through experimental and theoretical approaches. Reflection high energy electron diffraction revealed two pseudo-cubic domains along [100]MgO and [110]MgO, and one hexagonal domain, which is 30 degree apart from the [100]MgO direction. Scanning tunneling microscopy was used to image and resolve the high quality surface, revealing a distorted hexagonal surface structure. Furthermore, atomic resolution of the hexagonal domain with a 2 x 2 reconstructed surface is presented. For c-plane surface, theoretical investigations were carried out using first-principle studies to determine the surface formation energy for various reconstructed surfaces. The theoretical study shows the nitrogen terminated 2 x 2 structure with a manganese adatom on the surface as the most stable reconstruction that reproduces the experimental results. A corresponding simulated scanning tunneling microscopy model is also presented, providing strong support for the experimentally observed in-plane lattice structures. The manganese:nitrogen stoichiometry within the bulk and surface is in good agreement with the expected ratio of 2:1.As a final project, the hexagonal phase of antiferromagnetic Mn3Ga (0001) was grown on the Ga polar GaN (0001) substrate, and its structural and surface properties were investigated down to atomic scale. This material has garnered significant attention due to their exotic properties and possible applications in next generation spintronic memory and computing devices. The sample quality, lattice constants and crystal structure of the grown films were determined by in-situ reflection high energy electron diffraction, scanning tunneling microscopy and ex-situ X-ray diffraction. Upon examination with scanning tunneling microscopy, the surface revealed multiple terraces and row-like structures. Notably, the edges of the terraces form nearly 120 degree angles with each other, consistent with the hexagonal crystal structure of Mn3Ga. Additionally, several stacking of just a monolayer or bilayer, with their heights matching the c/2 or c value of Mn3Ga were observed. These measurements are further confirmed by X-ray diffraction. At atomic resolution, hexagonally arranged atoms with a 1 x 1 crystal structure were observed. The measured average in-plane atomic spacing was 5.45 +/- 0.10 Angstrom, deviating only 0.93 % from theoretical predictions. Various reconstructions and surface features are observed on the surface. Chemical analysis via Rutherford backscattering confirmed the sample's Mn:Ga ratio as 3.2:1.0. Our investigations indicate that the concentration of Mn atoms in the sample is significantly affected by the growth temperature.

English

ISBN: 9798286450473Subjects--Topical Terms:

516296
Physics.
Subjects--Index Terms:

Thin films

Epitaxial Growth and Atomic Scale Imaging of Bismuth, Manganese Nitride, and Manganese Gallium Thin Films /
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520 $a This study investigates the growth and surface characterization of bismuth-nitrogen alloy on MgO (001), transition metal nitride Mn2N on MgO (001), and Kagome Mn3Ga on GaN (0001) substrates. Molecular beam epitaxy was used to grow thin films and various in-situ and ex-situ techniques were used for the surface and structural investigation of the grown samples under ultra-high vacuum condition.The first project begins with the aim of growing an alloy of a topological material. We attempted to grow a thin film of BiN by co-deposition of bismuth and nitrogen on rock-salt structure MgO (001) substrates. Furthermore, we studied the effect of variation of the growth temperature and the nitrogen to bismuth flux ratios on sample growth. For the samples grown and conditions used, we do not find strong evidence for the formation of a bulk Bi-N alloy. Even for very high nitrogen to bismuth flux ratio, we observed only bismuth and no nitrogen using bulk Rutherford back-scattering spectroscopy measurements, and only 1-2% nitrogen was seen through surface Auger electron spectroscopy measurements. The in-plane lattice measurements show that the resulting Bi (110) samples are strained, which is presumably caused by lattice mismatch between the sample and the substrate when grown without any buffer layer. The use of a high-temperature buffer layer helps to release strain in the sample but only along one axis. Measurements of the atomic layer spacing using X-ray diffraction and also scanning tunneling microscopy confirm the Bi (110) thin film sample structure.The growth mechanism and strain induced surface structures of thin film due to the lattice mismatch and symmetry mismatch between samples and substrates were studied in the next project. One example of such a system is the growth of hexagonal material on top of a cubic substrate. The thin films of c-plane dominated hexagonal ζ- phase Mn2N were successfully grown on a cubic MgO (001) substrate directly using plasma-assisted molecular beam epitaxy. The surface was comprehensively studied through experimental and theoretical approaches. Reflection high energy electron diffraction revealed two pseudo-cubic domains along [100]MgO and [110]MgO, and one hexagonal domain, which is 30 degree apart from the [100]MgO direction. Scanning tunneling microscopy was used to image and resolve the high quality surface, revealing a distorted hexagonal surface structure. Furthermore, atomic resolution of the hexagonal domain with a 2 x 2 reconstructed surface is presented. For c-plane surface, theoretical investigations were carried out using first-principle studies to determine the surface formation energy for various reconstructed surfaces. The theoretical study shows the nitrogen terminated 2 x 2 structure with a manganese adatom on the surface as the most stable reconstruction that reproduces the experimental results. A corresponding simulated scanning tunneling microscopy model is also presented, providing strong support for the experimentally observed in-plane lattice structures. The manganese:nitrogen stoichiometry within the bulk and surface is in good agreement with the expected ratio of 2:1.As a final project, the hexagonal phase of antiferromagnetic Mn3Ga (0001) was grown on the Ga polar GaN (0001) substrate, and its structural and surface properties were investigated down to atomic scale. This material has garnered significant attention due to their exotic properties and possible applications in next generation spintronic memory and computing devices. The sample quality, lattice constants and crystal structure of the grown films were determined by in-situ reflection high energy electron diffraction, scanning tunneling microscopy and ex-situ X-ray diffraction. Upon examination with scanning tunneling microscopy, the surface revealed multiple terraces and row-like structures. Notably, the edges of the terraces form nearly 120 degree angles with each other, consistent with the hexagonal crystal structure of Mn3Ga. Additionally, several stacking of just a monolayer or bilayer, with their heights matching the c/2 or c value of Mn3Ga were observed. These measurements are further confirmed by X-ray diffraction. At atomic resolution, hexagonally arranged atoms with a 1 x 1 crystal structure were observed. The measured average in-plane atomic spacing was 5.45 +/- 0.10 Angstrom, deviating only 0.93 % from theoretical predictions. Various reconstructions and surface features are observed on the surface. Chemical analysis via Rutherford backscattering confirmed the sample's Mn:Ga ratio as 3.2:1.0. Our investigations indicate that the concentration of Mn atoms in the sample is significantly affected by the growth temperature.
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653 $a Thin films
653 $a Molecular beam epitaxy
653 $a Scanning tunneling microscopy
653 $a Antiferromagnetic
653 $a Bismuth
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