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Applications and Mechanisms of Epitaxy on Graphene-Terminated Surfaces.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Applications and Mechanisms of Epitaxy on Graphene-Terminated Surfaces./
Author:	Manzo, Sebastian O.
Description:	1 online resource (178 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-03, Section: B.
Contained By:	Dissertations Abstracts International85-03B.
Subject:	Condensed matter physics. -
Online resource:	click for full text (PQDT)
ISBN:	9798380307284

Applications and Mechanisms of Epitaxy on Graphene-Terminated Surfaces.
Manzo, Sebastian O.

Applications and Mechanisms of Epitaxy on Graphene-Terminated Surfaces. - 1 online resource (178 pages)

Source: Dissertations Abstracts International, Volume: 85-03, Section: B.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2023.

Includes bibliographical references

Remote epitaxy is a method for growing single-crystalline films on a graphene-terminated single-crystalline substrate, in which the epitaxial registry occurs between film and substrate rather than film and graphene. In an idealized picture, it has been argued that epitaxial registry between film and substrate originates from potential fluctuations of polar substrates that penetrate the graphene and template the overlayer. The main advantage of this approach is the absence of direct bonding between the underlying substrate and the film, making it attractive for various applications like highly mismatched heteroepitaxy, graphene-diffusion barriers and the production of single crystalline, flexible membranes. However, the atomic scale mechanisms for remote epitaxy remain unclear because most experiments have relied on post growth analysis of very thick films (several microns), making it difficult to distinguish a remote epitaxy mechanism from alternative mechanisms. In this dissertation, I focus on elucidating the atomistic mechanisms of remote epitaxy through ex-situ and in-situ tools and comment on some of the applications enabled by growth on graphene-terminated surfaces. First, I focus on the most commonly used system for remote epitaxy: transferred graphene on III-V semiconductor substrates. Using the standard cleaning and transfer procedures, we find that pinholes are created in the graphene immediately prior to growth, due to desorption of trapped interfacial oxides at the graphene/III-V interfaces. Crucially, our AFM and SEM studies show that these pinholes are the preferred sites for direct nucleation on the substrate, and that subsequent growth proceeds laterally until full coalescence of GaSb films on graphene/GaSb. Pinhole-seeded epitaxy can produce single-crystalline, exfoliateable membranes, thereby replicating the features of remote epitaxy via an alternate mechanism.Understanding the possible intrinsic mechanism for remote epitaxy requires very clean graphene/substrate interfaces with a low concentration of pinholes. Model calculations of idealized graphene/substrate interfaces suggest that lattice potential fluctuations through graphene are very weak (Δφ = 0-40 meV), smaller than the thermal energy kBT (~ 70 meV) at a typical growth temperature of 500 °C. It is unclear how such a low potential could template the growth. As a result, we hypothesize that step-edges provide larger potential fluctuations, which may be transmitted through draped graphene to seed epitaxy to the substrate. I grow GaAs on gr/Ge (111), a system which has a much lower defect-density than transferred graphene and perform ex-situ microscopy measurements to see where GaAs is nucleating. I find that nucleation on clean graphene occurs at defective wrinkles and at step-edges. These results suggest that epitaxy on graphene might not require a polar substrate if sites with enhanced lattice potential fluctuations, like step-edges, are available on the surface. Epitaxial lateral overgrowth using graphene masks is another promising growth approach that enables exfoliateable films with reduced defect densities. However, a clear understanding of the related kinetic factors that control nucleation selectivity and lateral coalescence is missing. I investigate the influence of various growth conditions such as temperature, atomic flux ratio and growth rate on the molecular beam epitaxial (MBE) growth of GaAs on partial coverage graphene masks on Ge (111). Microscopy, in-situ electron diffraction and photoemission demonstrate that elevated growth temperatures, low As/Ga flux ratios and moderate growth rates improve surface diffusion and desorption rates, promoting excellent selective nucleation and full coalescence of films within 400 nm.Lastly, I comment on some of the unique advantages of growing films on graphene-terminated substrates. We show that graphene successfully blocks metal interdiffusion into semiconductor substrates, which paves the way for growing lattice-matched Heusler alloys on graphene-terminated semiconductors for spintronic applications. Furthermore, films grown on graphene can be readily exfoliated to produce flexible single-crystalline membranes. We find that rippling GdPtSb and GdAuGe membranes allows us to access extreme strain states that give rise to magnetic and superconducting phases.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798380307284Subjects--Topical Terms:

1148471
Condensed matter physics.
Subjects--Index Terms:

2D materialsIndex Terms--Genre/Form:

554714
Electronic books.

Applications and Mechanisms of Epitaxy on Graphene-Terminated Surfaces.
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500 $a Advisor: Kawasaki, Jason K.
502 $a Thesis (Ph.D.)--The University of Wisconsin - Madison, 2023.
504 $a Includes bibliographical references
520 $a Remote epitaxy is a method for growing single-crystalline films on a graphene-terminated single-crystalline substrate, in which the epitaxial registry occurs between film and substrate rather than film and graphene. In an idealized picture, it has been argued that epitaxial registry between film and substrate originates from potential fluctuations of polar substrates that penetrate the graphene and template the overlayer. The main advantage of this approach is the absence of direct bonding between the underlying substrate and the film, making it attractive for various applications like highly mismatched heteroepitaxy, graphene-diffusion barriers and the production of single crystalline, flexible membranes. However, the atomic scale mechanisms for remote epitaxy remain unclear because most experiments have relied on post growth analysis of very thick films (several microns), making it difficult to distinguish a remote epitaxy mechanism from alternative mechanisms. In this dissertation, I focus on elucidating the atomistic mechanisms of remote epitaxy through ex-situ and in-situ tools and comment on some of the applications enabled by growth on graphene-terminated surfaces. First, I focus on the most commonly used system for remote epitaxy: transferred graphene on III-V semiconductor substrates. Using the standard cleaning and transfer procedures, we find that pinholes are created in the graphene immediately prior to growth, due to desorption of trapped interfacial oxides at the graphene/III-V interfaces. Crucially, our AFM and SEM studies show that these pinholes are the preferred sites for direct nucleation on the substrate, and that subsequent growth proceeds laterally until full coalescence of GaSb films on graphene/GaSb. Pinhole-seeded epitaxy can produce single-crystalline, exfoliateable membranes, thereby replicating the features of remote epitaxy via an alternate mechanism.Understanding the possible intrinsic mechanism for remote epitaxy requires very clean graphene/substrate interfaces with a low concentration of pinholes. Model calculations of idealized graphene/substrate interfaces suggest that lattice potential fluctuations through graphene are very weak (Δφ = 0-40 meV), smaller than the thermal energy kBT (~ 70 meV) at a typical growth temperature of 500 °C. It is unclear how such a low potential could template the growth. As a result, we hypothesize that step-edges provide larger potential fluctuations, which may be transmitted through draped graphene to seed epitaxy to the substrate. I grow GaAs on gr/Ge (111), a system which has a much lower defect-density than transferred graphene and perform ex-situ microscopy measurements to see where GaAs is nucleating. I find that nucleation on clean graphene occurs at defective wrinkles and at step-edges. These results suggest that epitaxy on graphene might not require a polar substrate if sites with enhanced lattice potential fluctuations, like step-edges, are available on the surface. Epitaxial lateral overgrowth using graphene masks is another promising growth approach that enables exfoliateable films with reduced defect densities. However, a clear understanding of the related kinetic factors that control nucleation selectivity and lateral coalescence is missing. I investigate the influence of various growth conditions such as temperature, atomic flux ratio and growth rate on the molecular beam epitaxial (MBE) growth of GaAs on partial coverage graphene masks on Ge (111). Microscopy, in-situ electron diffraction and photoemission demonstrate that elevated growth temperatures, low As/Ga flux ratios and moderate growth rates improve surface diffusion and desorption rates, promoting excellent selective nucleation and full coalescence of films within 400 nm.Lastly, I comment on some of the unique advantages of growing films on graphene-terminated substrates. We show that graphene successfully blocks metal interdiffusion into semiconductor substrates, which paves the way for growing lattice-matched Heusler alloys on graphene-terminated semiconductors for spintronic applications. Furthermore, films grown on graphene can be readily exfoliated to produce flexible single-crystalline membranes. We find that rippling GdPtSb and GdAuGe membranes allows us to access extreme strain states that give rise to magnetic and superconducting phases.
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653 $a Heterostructures
653 $a Remote epitaxy
653 $a Van der waals epitaxy
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690 $a 0611
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710 2 $a The University of Wisconsin - Madison. $b Materials Science and Engineering. $3 1478683
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